T

National A

chapter focuses attention on a key episode in the history of

American aeronautics, stories in which breakthrough

developments in the field of aerodynamics shaped—or reshaped—the form and function of the airplane.

Providing drama along the way are the major aerodynamic problems identified by the America’s aeronautical

research establishment—notably by the National

Aeronautics and Space Administration’s (NASA) research

laboratories and those of its predecessor agency, the

National Advisory Committee for Aeronautics (NACA)—as

it worked to provide information and solve problems that

proved basic to the progress of the airplane. Volume I relates the story of the invention of the airplane by the Wright brothers and the creation of the original aeronautical research establishment in the United

States. Subsequent volumes cover the design revolution of

the 1920s and 1930s and the quest for improved airfoils

(Vol. 2); the aerodynamics of airships, flying boats, and rotary-wing aircraft (Vol. 3); breaking the sound barrier

and the supersonic design revolution (Vol. 4); the progressive refinement of the jetliner and the dream of a U.S.

commercial supersonic transport (Vol. 5); the development

in the latter part of the century of bold new aerodynamic research facilities, such as NASA’s National Transonic Facility, plus the development of hypersonic flight. The

series concludes with past and present aerodynamic experts speculating on what the form and function of the

airplane might be like in the future.

About the editors: James R. Hansen, Professor of History

at Auburn University, has written about aerospace history

for the past twenty-three years. His two-volume study of

NASA Langley Research Center—Engineer in Charge

(NASA SP-4305, 1987) and Spaceflight Revolution (NASA

SP-4308, 1995) earned significant critical acclaim. His

newest book, The Bird Is on the Wing (Texas A&M

University Press, 2003), explores the role of aerodynamics

in the progress of the airplane in America from before the Wright brothers to the present. Currently, Hansen is at

work on the authorized biography of Neil A. Armstrong. 

D. Bryan Taylor is Instructional Technology (IT)

Coordinator for the College of Liberal Arts at Auburn

University and is working on his Ph.D. in the history of

technology at Auburn. 

Jeremy R. Kinney is a curator in the Aeronautics Division,

National Air and Space Museum, Smithsonian Institution,

and holds a Ph.D. in the history of technology from Auburn

University, with a specialization in aerospace history. 

J. Lawrence Lee holds B.M.E., M.A., and Ph.D.

degrees from Auburn University. 
The Wind and Beyond
NASA SP-2003-4409

The Wind and Beyond: A Documentary

Journey into the History of Aerodynamics

in America

Volume 1: The Ascent of the Airplane

James R. Hansen, Editor

with D. Bryan Taylor, Jeremy Kinney, and J. Lawrence Lee

The NASA History Series

National Aeronautics and Space Administration

NASA History Office

Office of External Relations

Washington, D.C. 2003
Library of Congress Cataloging-in-Publication Data

The Wind and Beyond: A Documentary Journey into the History of Aerodynamics

in America/ James R. Hansen, editor; with D. Bryan Taylor, Jeremy Kinney, and J.

Lawrence Lee.

p. cm.— (The NASA history series) (NASA SP: 4409)

Includes bibliographical references and index.

Contents: v. 1. The ascent of the airplane

1. Aerodynamics—Research—United States—History. 2. Aeronautical

engineers—United States. I. Hansen, James R. II. Series III. Series: NASA SP: 4409

TL570.W64 2003

2002035774
v

Table of Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xi

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xv

Series Introduction: Talking with the Wind, Collaborating with Genius . . .xvii

Significant Aircraft List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xxxi

Series Bibliographic Essay: Days on the Wing . . . . . . . . . . . . . . . . . . . . . . .xxxv

Biographies of Volume 1 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . .lxxi

CHAPTER ONE: THE ACHIEVEMENT OF FLIGHT . . . . . . . . . . . . . . . . . .1

Essay: From Cayley’s Triple Paper to Orville Wright’s Telegram . . . . . . . . . . .1

The Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

1-1(a) George Cayley, “On Aerial Navigation,” Part One, 1809 . . . . . . .34

1-1(b) George Cayley, “On Aerial Navigation,” Part Two, 1810 . . . . . . .42

1-1(c) George Cayley, “On Aerial Navigation,” Part Three, 1810 . . . . . .47

1-2 Thomas Jefferson, letter to William D. B. Lee, 1822 . . . . . . . . . .57

1-3(a) Francis H. Wenham, “On Aerial Locomotion,” 1866 . . . . . . . . . .59

1-3(b) Report of the first wind tunnel built by Francis H. 

Wenham, 1871 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80

1-3(c) Minutes of the Royal Aeronautical Society, 1872 . . . . . . . . . . . . . .84

1-4 Samuel P. Langley, “Langley’s Law,” 1891 . . . . . . . . . . . . . . . . . . .89

1-5(a) Otto Lilienthal, “The Problem of Flying,” 1893 . . . . . . . . . . . . . .92

1-5(b) Otto Lilienthal, “Practical Experiments in Soaring,” 1893 . . . . . .95

1-5(c) Otto Lilienthal, “The Best Shapes for Wings,” 189 . . . . . . . . . . . 99

1-5(d) Vernon, “The Flying Man,” 1894 . . . . . . . . . . . . . . . . . . . . . . . .101

1-6 Hiram Maxim, “Natural and Artificial Flight,” 1896 . . . . . . . . .107

1-7 B. Baden-Powell, “Present State of Aeronautics,” 1896 . . . . . . . .126

1-8(a) Samuel P. Langley, “Story of Experiments 

in Mechanical Flight,” 1897 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131

1-8(b) Samuel P. Langley, “The New Flying Machine,” 1897 . . . . . . . .141

1-8(c) Alexander Graham Bell, “The Aerodromes in Flight,” 1897. . . .145

1-9(a) Octave Chanute, “Conditions of Success in the Design of 

Flying Machines,” 1898 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149

1-9(b) Augustus M. Herring, “A Solution to the Problem 

of the Century,” 1897 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156

1-9(c) Octave Chanute, “Experiments in Flying,” 1900 . . . . . . . . . . . .171

1-9(d) Octave Chanute, “Aerial Navigation,” 1901 . . . . . . . . . . . . . . . .179

1-10(a) Orville Wright on their interest in flight, 1920 . . . . . . . . . . . . . .188

1-10(b) Wilbur Wright, letter to the Smithsonian Institution, 1899 . . . .188

1-10(c) Wilbur Wright, letter to Octave Chanute, 1900 . . . . . . . . . . . . . .189

1-11(a) Wilbur Wright, letter to Milton Wright, 1900 . . . . . . . . . . . . . . .193

1-11(b) Wilbur Wright, “Some Aeronautical Experiments,” 1901 . . . . . .193

1-12(a) Octave Chanute, remarks at a meeting 

of the Aéro-Club,1903 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .208
vi

1-12(b) Wilbur Wright, “Experiments and Observations 

in Soaring Flight,” 1903 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .218

1-13(a) Orville Wright, diary entry for 17 December 1903 . . . . . . . . . . .222

1-13(b) Wilbur and Orville Wright, statement 

to the Associated Press, 5 January 1904 . . . . . . . . . . . . . . . . . . .223

1-14(a) Wilbur and Orville Wright, letter to the Secretary 

of War, 1905 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226

1-14(b) U.S. Army specifications for heavier-than-air flying 

machine, 1907 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .226

1-14(c) Wilbur and Orville Wright, letter to 

General James Allen, 1908 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .229

1-14(d) Octave Chanute, “Recent Aeronautical Progress in the United

States,” 1908 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .229

1-15 Simon Newcomb, “Aviation Declared a Failure,” 1908 . . . . . . . .233

CHAPTER TWO: BUILDING A RESEARCH ESTABLISHMENT . . . . . . .237

Essay: From the Wright Bicycle Shop to the Langley Full-Scale Tunnel . . . .237

The Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .273

2-1(a) Wilbur Wright, letter to George A. Sprat, 15 December 1901 . .274

2-1(b) Wilbur Wright, letter to Octave Chanute, 15 December 1901 . .275

2-1(c) Wilbur Wright, letter to Octave Chanute, 23 December 1901 . .282

2-1(d) Wilbur Wright, letter to Octave Chanute, 19 January 1902 . . . .284

2-2(a) W. I. Chambers, “Report on Aviation,” 1912 . . . . . . . . . . . . . . . .288

2-2(b) Jerome C. Hunsaker, Report on Facilities for Aeronautical 

Research in England, France, and Germany, Part III, 1913 . . . . . . .296

2-2(c) Albert F. Zahm, Report on European Aerodynamical 

Laboratories, 1914 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .301

2-3(a) U.S. Congress, Act Establishing an Advisory Committee for

Aeronautics, 3 March 1915 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .306

2-3(b) George P. Scriven, Chairman’s Letter for the first Annual 

Report of the National Advisory Committee 

for Aeronautics, 1915 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .307

2-3(c) George P. Scriven, “Existing Facilities for Aeronautic 

Investigation in Government Departments,” 1915 . . . . . . . . . . .309

2-4 Jerome C. Hunsaker, “The Wind Tunnel of the Massachusetts

Institute of Technology,” 1916 . . . . . . . . . . . . . . . . . . . . . . . . . . .311

2-5 G. I. Taylor, “Pressure Distribution Over the Wing of an 

Aeroplane in Flight,” 1916 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .318

2-6 Henry. T. Tizard, “Methods of Measuring Aircraft 

Performances,” 1917 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .340

2-7(a) Jerome C. Hunsaker, letter to H. M. Williams, 1918 . . . . . . . . .359

2-7(b) “Education in Advanced Aeronautical Engineering,” 

NACA Annual Report for 1920 . . . . . . . . . . . . . . . . . . . . . . . . . . . .360

2-8(a) U.S. Army, “Full Flight Performance Testing,” 1918 . . . . . . . . . .362

2-8(b) “Special Aerodynamic Investigations,” NACA Annual Report 

for 1919 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .373
vii

2-9(a) “Office of Aeronautical Intelligence,” NACA Annual Report 

for 1918 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .376

2-9(b) John J. Ide, “Report on Visit to England,” 1921 . . . . . . . . . . . . .377

2-9(c) John J. Ide, “Wind Tunnel at Issy-les-Moulineaux,” 1921 . . . . .380

2-10(a) D. W. Taylor, letter to Frederick C. Hicks, 1919 . . . . . . . . . . . . .384

2-10(b) Edward P. Warner, “Report on German Wind Tunnels and

Apparatus,” 1920 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .386

2-11 “Free Flight Tests,” NACA Annual Report for 1918 . . . . . . . . . . . .397

2-12(a) Edward P. Warner, F. H. Norton, and C. M. Hebbert, 

“Design of Wind Tunnels and Wind Tunnel Propellers,” 1919 . .398

2-12(b) F. H. Norton and Edward P. Warner, The Design of Wind Tunnels 

and Wind Tunnel Propellers, II, 1920 . . . . . . . . . . . . . . . . . . . . . . .426

2-13(a) “Report of Committee on Aerodynamics,” NACA Annual Report 

for 1919 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .440

2-13(b) “Report of Committee on Aerodynamics,” NACA Annual Report 

for 1920 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .444

2-13(c) “Report of Committee on Aerodynamics,” NACA Annual Report 

for 1921 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .454

2-14 Jerome C. Hunsaker, “Recommendations for Research 

Program—Comparison of Wing Characteristics in Models

and Free Flight,” 1920 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .463

2-15(a) Joseph S. Ames, letter to A. H. [sic] Zahm, L. J. Briggs, 

E. B. Wilson, W. F. Durand, E. N. Fales, J. G. Coffin, 

H. Bateman, and F. H. Norton, 23 August 1920 . . . . . . . . . . . .468

2-15(b) F. H. Norton, letter to Joseph S. Ames, 23 August 1920 . . . . . .468

2-15(c) A. F. Zahm, letter to Joseph S. Ames, 14 September 1920 . . . . .469

2-15(d) Joseph G. Coffin, letter to Joseph S. Ames, 

18 September 1920 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .470

2-15(e) W. F. Durand, letter to Joseph S. Ames, 24 September 1920 . . .472

2-15(f) Ludwig Prandtl, letter to William Knight, 1920 . . . . . . . . . . . . .474

2-15(g) “International Standardization of Wind-Tunnel Results,” 

NACA Annual Report for 1922 . . . . . . . . . . . . . . . . . . . . . . . . . . . .475

2-15(h) G.W. Lewis, memorandum to Langley Memorial Aeronautical

Laboratory, 1925 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .476

2-15(i) Aerodynamics Department, The National Physical 

Laboratory, “A Comparison between Results for R.A.F. 15 

in the N.P.L. Duplex Tunnel and in the N.A.C.A Compressed 

Air Tunnel,” [1925] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .476

2-16 “Summary of General Recommendations,” NACA Annual Report 

for 1921 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .478

2-17 F. H. Norton, “The National Advisory Committee’s 5-Ft. Wind

Tunnel,” 1921 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .481

2-18(a) Max M. Munk, letter to J. C. Hunsaker, 1920 . . . . . . . . . . . . . . .500

2-18(b) J. C. Hunsaker, letter to Lester D. Gardner, 1921 . . . . . . . . . . . .501

2-18(c) F. H. Norton, memorandum to NACA Executive Officer 

[G.W. Lewis], 1921 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .502
viii

2-18(d) W. Margoulis, “A New Method of Testing Models in Wind 

Tunnels,” 1920 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .502

2-18(e) Edward P. Warner, letter, to G. W. Lewis, 1921 . . . . . . . . . . . . . .506

2-18(f) W. Margoulis, “A New Method of Testing Models in Wind 

Tunnels,” [1921] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .507

2-18(g) Max M. Munk, “On a New Type of Wind Tunnel,” 1921 . . . . . .511

2-18(h) F. H. Norton, memorandum to G. W. Lewis,

“Design of Compressed Air Wind Tunnel,” 1921 . . . . . . . . . . . .521

2-18(i) “Compressed Air Wind Tunnel,” 

NACA Annual Report for 1921 . . . . . . . . . . . . . . . . . . . . . . . . . . . .522

2-18(j) Max M. Munk and Elton W. Miller, 

The Variable Density Wind Tunnel of the National Advisory

Committee for Aeronautics, 1925 . . . . . . . . . . . . . . . . . . . . . . . . . . .523

2-19(a) Ludwig Prandtl, letter to Jerome C. Hunsaker, 1916 . . . . . . . . .537

2-19(b) Joseph S. Ames, letter to Jerome C. Hunsaker, 1920 . . . . . . . . .537

2-19(c) Ludwig Prandtl, Applications of Modern Hydrodynamics to 

Aeronautics, 1921 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .538

2-20(a) Max M. Munk, memorandum to G. W. Lewis, 1925 . . . . . . . . . .557

2-20(b) Fred E. Weick and Donald H. Wood, The Twenty-Foot 

Propeller Research Tunnel of the National Advisory Committee 

for Aeronautics, 1928 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .560

2-20(c) Fred E. Weick, From the Ground Up, 1988 . . . . . . . . . . . . . . . . . . .576

2-21(a) Elliot G. Reid, “Memorandum on Proposed Giant Wind 

Tunnel,” 1925 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .585

2-21(b) Arthur W. Gardiner, “Memorandum on Proposed Giant 

Wind Tunnel,” 1925 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .588

2-21(c) Smith J. DeFrance, The NACA Full-Scale Wind Tunnel, 1933 . . . .591

2-22 Max M. Munk, memorandum on “Recommendations for 

New Research,” 1926 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .602

2-23(a) Daniel Guggenheim, letter to Herbert Hoover, 1926 . . . . . . . . .605

2-23(b) California Institute of Technology, “Development of 

Aeronautics,” 1926 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .608

2-24(a) C. G. Grey, “On Research,” 1928 . . . . . . . . . . . . . . . . . . . . . . . . .611

2-24(b) C. G. Grey, “On Research” continued, 1928 . . . . . . . . . . . . . . . .614

2-25(a) Frank A. Tichenor, “Air—Hot and Otherwise: Why the 

N.A.C.A.?” 1930 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .617

2-25(b) Frank A. Tichenor, “Air—Hot and Otherwise: The N.A.C.A.

Counters,” 1931 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .624

2-25(c) Edward P. Warner, “Speaking of Research,” 1931 . . . . . . . . . . . .628

2-26 Joseph S. Ames and Smith J. DeFrance, “Report of 

Proceedings of the Sixth Annual Aircraft Engineering 

Research Conference,” 1931 . . . . . . . . . . . . . . . . . . . . . . . . . . . .631

2-27 Minutes of the Second Technical Committee Meeting, 

United Aircraft and Transport Corporation, 1929 . . . . . . . . . . .636

2-28(a) A. L. Klein, “The Wind Tunnel as an Engineering 

Instrument,” 1930 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .643
ix

2-28(b) A. L. Klein, letter to V. E. Clark, 1934 . . . . . . . . . . . . . . . . . . . . .650

2-29 Starr Truscott, memorandum to [Henry J. E. Reid], 

“Work in connection with special aerodynamic tests 

for Bureau of Aeronautics which has been requested 

by Mr. Lougheed,” 1932 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .652

2-30(a) Edward P. Warner, “Research to the Fore,” 1934 . . . . . . . . . . . . .657

2-30(b) “Research Symphony,” 1935 . . . . . . . . . . . . . . . . . . . . . . . . . . . .659

NASA History Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .667

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .677
x
Foreword

Airplane travel is surely one of the most significant technological achievements of the last century. The impact of the airplane goes far beyond the realm

of the history of technology and touches upon virtually every aspect of society,

from economics to politics to engineering and science. While space exploration

often claims more public glory than aeronautics research, many more individuals

have been able to fly within the Earth’s atmosphere than above it. Thus, aeronautics and air travel have had an enormous practical impact on many more individuals. For this reason, if no other, it is certainly an appropriate time to document the rich legacy of aeronautical achievements that has permeated our society. It is especially timely to do so during the centennial anniversary of the Wright

brothers’ historic flight of 1903.

Dr. James R. Hansen and his collaborators do more than just document the

last century of flight. They go back and expertly trace the historical origins of

what made the first heavier-than-air, controlled, powered airplane flight possible

on 17 December 1903. Some names covered in this volume, such as Isaac Newton

and Leonardo da Vinci, are familiar to even the most casual reader. Other heralded, but less well-known, early pioneers of flight such as George Cayley, Otto

Lilienthal, Theodore von Kármán, and Theodore Theodorsen will come alive to

readers through their original letters, memos, and other primary documents as

they conjoin with the authors’ insightful and elegantly written essays.

This first volume, plus the succeeding five now in preparation, covers the

impact of aerodynamic development on the evolution of the airplane in America.

As the six-volume series will ultimately demonstrate, just as the airplane is a

defining technology of the twentieth century, aerodynamics has been the defining element of the airplane. Volumes two through six will proceed in roughly

chronological order, covering such developments as the biplane, the advent of

commercial airliners, flying boats, rotary aircraft, supersonic flight, and hypersonic flight.

This series is designed as an aeronautics companion to the Exploring the Unknown:

Selected Documents in the History of the U.S. Civil Space Program (NASA SP-4407) series of

books. As with Exploring the Unknown, the documents collected during this research project were assembled from a diverse number of public and private sources. A major repository of primary source materials relative to the history of the civil space program is the

NASA Historical Reference Collection in the NASA Headquarters History Office.

Historical materials housed at NASA field centers, academic institutions, and

Presidential libraries were other sources of documents considered for inclusion, as were

papers in the archives of private individuals and corporations.

xi
xii The Wind and Beyond: Volume 1

The format of this volume also is very similar to that of the Exploring the

Unknown volumes. Each section in the present volume is introduced by an

overview essay that is intended to introduce and complement the documents in

the section and to place them in a chronological and substantive context. Each

essay contains references to the documents in the section it introduces, and many

also contain references to documents in other sections of the collection. These

introductory essays are the responsibility of Dr. Hansen, the series’ author and

chief editor, and the views and conclusions contained therein do not necessarily

represent the opinions of either Auburn University or NASA.

The documents included in each section were chosen by Dr. Hansen’s project

team from a much longer list initially assembled by the research staff. The contents of this volume emphasize primary documents, including long-out-of-print

essays and articles as well as material from the private recollections of important

actors in shaping aerodynamic thinking in the United States and abroad. Some

key legislation and policy statements are also included. As much as possible, the

contents of this volume (and the five volumes to come) in themselves comprise an

integrated historical narrative, though Dr. Hansen’s team encourages readers to

supplement the account found herein with other sources that have already or will

come available. 

For the most part, the documents included in each section are arranged

chronologically. Each document is assigned its own number in terms of the section in which it is placed. As a result, for example, the fifteenth document in the

second chapter of this volume is designated “Document 2-l5.” Each document is

accompanied by a headnote setting out its context and providing a background

narrative. These headnotes also provide specific information and explanatory

notes about people and events discussed. Many of the documents, as is the case

with Document 2-15, involve document “strings,” i.e., Document 2-15(a–e). Such

strings involve multiple documents—in this case, five of them (a through e) that

have been grouped together because they relate to one another in a significant

way. Together, they work to tell one documentary “story.” 

The editorial method that has been adopted seeks to preserve, as much as

possible, the spelling, grammar, and language usage as they appear in the original documents. We have sometimes changed punctuation to enhance readability.

We have used the designation [ . . . ] to note where sections of a document have

not been included in this publication, and we have avoided including words and

phrases that had been deleted in the original document unless they contributed

to an understanding of the writer’s thought process in making the record.

Marginal notations on the original documents are inserted into the text of the

documents in brackets, each clearly marked as a marginal comment. Page numbers in the original document are noted in brackets internal to the document text.
Copies of all documents in their original form are available for research by any

interested person at the NASA History Office or Auburn University.

While the Exploring the Unknown series has been a good model in many ways,

this volume indeed represents the beginning of a yet another new undertaking

into uncharted waters. I am confident that Dr. Hansen and his team have crafted

a landmark work that will not only be an important reference work in the history

of aeronautics, but will be interesting and informative reading as well. We hope

you enjoy this useful book and the forthcoming volumes. 

Stephen Garber

NASA History Office

October 2003

xiii
xiv
ACKNOWLEDGMENTS

This volume represents the collected efforts of many members of an outstanding

team. At Auburn University, a number of individuals provided generous assistance to Dr. James R. Hansen’s project team. Dr. Paul F. Parks, former University

Provost, strongly encouraged and supported the project from its inception, as did

Dr. Michael C. Moriarty, Vice President for Research. To undertake his leadership

of the project, Dr. Hansen gave up his job as Chair of the Department of History,

something he would not have felt comfortable doing without being certain that

the administration of his department would be in the capable hands of worthy

successors—first, Dr. Larry Gerber, and then Dr. William F. Trimble. Both Gerber

and Trimble gave hearty and vocal support to Auburn’s NASA history project. A

number of colleagues in aerospace history gave help to the project, including

Distinguished University Professor Dr. W. David Lewis and Dr. Stephen L.

McFarland. Dr. Roy V. Houchin, who earned a Ph.D. under Hansen, lent aid and

comfort to the project team from his vantage point inside the U.S. Air Force. A

number of Hansen’s current graduate students helped the project in various ways,

notably Andrew Baird, Amy E. Foster, and Kristen Starr, as did Dr. David Arnold,

also of the USAF, who earned a Ph.D. in aerospace history during the time period

when this project was being conducted. 

Historians and archivists at a number of other facilities also aided the project.

Most of these are acknowledged in the “Series Bibliographic Essay,” which

appears early in this volume.

At NASA Headquarters, a number of people in the NASA History Office

deserve credit. M. Louise Alstork painstakingly edited the essays and proofread

all the documents. Jane Odom, Colin Fries, and John Hargenrader helped track

down documents from our Historical Reference Collection. Nadine Andreassen

provided much valuable general assistance and helped with the distribution. In

the Office of Aerospace Technology, Tony Springer served as an invaluable sounding

board on technical aeronautics issues. We also owe a special debt to Roger D. Launius,

the former NASA Chief Historian, who provided the initial impetus and guidance

for this worthy project.

At Headquarters Printing and Design Office, several individuals deserve

praise for their roles in turning a manuscript into a finished book. Anne Marson

did a careful job in copyediting a lengthy and detailed manuscript. Melissa Kennedy,

a graphic designer, performed her craft in an exemplary manner. Jeffrey McLean

and David Dixon expertly handled the physical printing of this book. Thanks are

due to all these devoted professionals.

xv
xvi The Wind and Beyond: Volume 1
The Wind and Beyond

Series Introduction

Talking with the Wind, Collaborating with Genius

Aerodynamics is not, strictly speaking, about the wind. Rather, it concerns the

motion of the air (or other gaseous fluid) plus the forces acting on a body in motion

relative to the airflow.1 Still, in choosing a title for this multivolume documentary

history of aerodynamics development in the United States, we ultimately concluded that no title would be more suggestive than The Wind and Beyond. 

Historically, the most basic instrument of aerodynamic research, by far, has

proved to be the wind tunnel. Many of the scientists and engineers who achieved

vital discoveries in aerodynamics described their breakthroughs in terms of a special

capacity to “talk with the wind.” By this, they meant visualizing what the air was

doing—using the mind’s eye as part of a creative process by which the air virtually

told them what needed to be done in order to make an airplane fly effectively.

“Beyond the wind” suggests many salient themes: the profound human curiosity

that gave birth to the science of aerodynamics and, before that, to the dream of

flight itself; the countless puzzles and mysteries hidden deep within all natural

phenomena, both in macrocosm and microcosm, plus the myriad theories and

concepts devised to fathom the forces at work; the countless technological forms

resulting from inventiveness as human ingenuity moved toward mastering those

natural forces, enabling humanity to leave the ground and soar above the clouds;

and the potential for flight above the atmosphere and into space, where the ambitions

of humankind may someday result in colonization of other worlds and perhaps

contact with extraterrestrial—mythically speaking, even a sort of divine—intelligence.

All this, and much more, is evoked by the title The Wind and Beyond. 

The poetry in the title is not original to this publication. In 1967, writer Lee Edson

selected it for the autobiography of Theodore von Kármán, one of the most brilliant

thinkers to make the sojourn into aerodynamics during the twentieth century.

(Von Kármán had just died, in 1963, at age eighty-two; Edson became his co-author.)

Recounting in the first person the amazing life story of the colorful Hungarian-born

xvii

1 Webster’s Third New International Dictionary defines “aerodynamics” as “the branch of dynamics

that deals with the motion of air and other gaseous fluids and with the forces acting on bodies in

motion relative to such fluids.”
xviii The Wind and Beyond: Volume 1

2 John D. Anderson, A History of Aerodynamics and Its Impact on Flying Machines (Cambridge, MA:

Cambridge University Press, 1997), p. 420.

3 See Paul Hanle, Bringing Aerodynamics to America (Cambridge, MA: MIT Press, 1982) and Michael

H. Gorn, The Universal Man: Theodore von Kármán’s Life in Aeronautics (Washington, DC:

Smithsonian Institution Press, 1992).

scientist who moved to the United States in 1930, only to tower over much of its

aeronautical science for the next four decades, The Wind and Beyond: Theodore von

Kármán, Pioneer in Aviation and Pathfinder in Space (Boston and Toronto: Little, Brown

and Company) quickly became a classic. Behind its popularity, which lasts to this day,

was von Kármán’s restless intellectual dynamism; his humor and eccentricities

(which were at least as awesome as his intellect); and his ability to express himself with

extreme cogency (even amid his thick accent), whether mathematically or verbally.

He made a number of fundamental breakthroughs in aerodynamic theory and, from

his post at the Guggenheim Aeronautical Laboratory at the California Institute of

Technology (GALCIT), he exerted massive influence over American aeronautical and

early space research and development (R&D), especially during the adolescence of the

United States Air Force. These facts encouraged readers to care about his remarkably

storied career. As American aerodynamicist and aerospace historian John Anderson

has written, “The name von Kármán has been accorded almost godlike importance

in the history of aerodynamics in the United States, and that aura existed well before

his death in 1963 and continues today because of the magnitude of his contributions

to, and advocacy for, aerodynamic research and development. Also, his influence

is seen today in the contributions of his students, many of whom have gone on to

leadership roles in the field.”2 Besides his autobiography, two biographies of von

Kármán have been written.3 This coverage reveals his powerful place in the field,

because certainly no other aerodynamicist has enjoyed such a spotlight. Most are

still in the figurative dark, not yet having been chosen by a single biographer.

What audacity, then, we have in redeploying the title The Wind and Beyond!

When we first suggested to colleagues in aerospace history and to the NASA

History Office that we wanted to use it for our documentary study of aerodynamic

development in the United States, thoughtful people raised eyebrows and asked

serious questions about the propriety of using a title so closely identified with

another book, especially one as adored as von Kármán’s autobiography. Even

though nearly forty years had passed since its original publication, reverence for

the book was too great, some said, to adopt its title. 

In the end, however, we decided that we could pay no greater respect to von

Kármán’s memory and to the vibrant intellectual passions of his extraordinary life

than by using his title once again. In this way, we hope to refresh the memories

of those already aware of his book and his other legacies—for some individuals
Series Introduction: Talking with the Wind, Collaborating with Genius xix

now in their golden years, memories of a teacher that are quite personal. But

even more importantly, we thought it desirable to bring The Wind and Beyond to

the attention of a new generation of students now that we find ourselves in the

twenty-first century—some forty years since von Kármán’s death. We feel that the

great aerodynamicist, a very generous spirit, would approve. 

✤ ✤ ✤ ✤

Anyone with the curiosity, and the fortitude, to venture into a serious study

of aerodynamics—or, as in this publication, into its marvelously intricate historical

development—will certainly keep wonderful company. For somewhere deep in

the heart of the adventure moves the spirit not just of von Kármán but also of

many of the greatest geniuses of all time. Roughly 500 years ago, during the period

of great intellectual and cultural growth in Europe known as the Renaissance, the

prototypical “universal man,” Leonardo da Vinci, became obsessed with the problems of

Dr. Theodore von Kármán (1881–1963), shown here at his blackboard at the California Institute of Technology,

personified the restless intellectual dynamism that turned the study of aerodynamics into one of the classic

expressions of 20th century science and technology. NASA Image #P30570B (JPL)
xx The Wind and Beyond: Volume 1

4 On Leonardo’s fascination for flight see Serge Bramley’s biography Discovering the Life of Leonardo

da Vinci (New York, NY: Harper Collins, 1991) as well as Irma Richter, ed., The Notebooks of

Leonardo da Vinci (Oxford: Oxford University Press, 1952; “World Classics Edition,” 1980). Readers

interested in a psychological treatment of Leonardo’s dreams of flight, see Sigmund Freud,

Leonardo da Vinci: A Study in Psychosexuality (New York, NY: Vintage Books, 1961). Perhaps surprisingly, Freud’s analysis does not try to reduce Leonardo’s genius to any sort of pathology; rather, it

provides a sensitive and respectful inquiry into da Vinci’s creative greatness. 

5 Theodore von Kármán with Lee Edson, The Wind and Beyond: Theodore von Kármán, Pioneer in

Aviation and Pathfinder in Space (Boston and Toronto: Little, Brown and Company, 1967), p. 58. 

flight. No subject fascinated him more. Not his study of the circulation of the blood

and the action of the eye; not his discoveries in meteorology and geology; not his

insights into the effects of the moon on tides; not his conceptions of continent

formation; not his schemes for the canalization of rivers; not any of his other myriad

inventive ideas; not even the brilliant artistic compositions for which people most

remember him today—Mona Lisa, The Adoration of the Magi, The Last Supper. Art

historian Kenneth Clark once called Leonardo “undoubtedly the most curious man

who ever lived.” And his greatest curiosity—and the curiosity left most unfulfilled—

centered on the preconditions of flight.4

As we shall see in Chapter 1 of this work, what da Vinci, the quintessential

artist-engineer, lacked was hardly imagination or ingenuity. He made amazing

sketches of birds in flight and, on paper, designed remarkable flying machines,

including a flapping-wing “ornithopter,” a parachute, and a helicopter. What the

great maestro and all other aeronautical conjurers of the next four centuries

lacked was a science of flight that could turn fantasy into reality. As von Kármán

would explain in his autobiography: “For advances in aviation in any real sense it

was necessary for science to catch up with the dreamers and experimenters and

set a basis for further development in a rational manner.”5

In critical ways the Scientific Revolution of the seventeenth and eighteenth

centuries primed the pump for the emergence of the science of flight; but in at

least one key respect, that great intellectual fermentation, one of the greatest in

all human history, also retarded it. With his monumental writings of the late

1600s, Isaac Newton, the culminating figure of the Scientific Revolution, gave

birth to the science of mechanics. But in doing so he made calculations and

expressed ideas about “upward forces” (what later scientists would call “lift”) and

“forces preventing motion” (later called “drag”) that many would read to mean

that human flight by means of a supporting wing was impossible. And, of course,

everyone took Sir Isaac’s conclusions very seriously, almost as divine guidance.

No real breakthrough occurred until fellow Englishman George Cayley, more

than a hundred years later, showed that the amount of lift attained by a forwardmoving plate was directly proportional not to the square of the angle, as Newton
Series Introduction: Talking with the Wind, Collaborating with Genius xxi

6 von Kármán, The Wind and Beyond, p. 58.

reasoned, but to the angle made by

the plate. An airplane wing need not

be impossibly large and heavy as

Newton had posited; its weight could

be sustained by the force of lift, and its

drag compensated for by a propulsion

device actuated by a powerful enough

engine. Although it would be several

decades before Cayley’s principle of the

modern airplane achieved the status

of a paradigm, one can argue, as von

Kármán himself did, that it was at this

point, during the first half of the nineteenth century, that science moved “off

the sharp horns of the dilemma created

by Newton.”6 In this sense, Cayley’s

notions were truly revolutionary.

Cayley built and flew a few gliders

of his own design, some of them

manned, and so did several other

intrepid experimenters during the

1800s. The Industrial Revolution was

sweeping across Europe, America, and

other parts of the globe, bringing with it greater and greater fascination for

machines of all kinds. The special interest in new forms of faster transportation

spurred all kinds of efforts to develop aviation into a practical technology. Piloted

balloons like those originally built by the Montgolfier brothers in France had

been aloft since the 1780s, and even military establishments were finding ways of

deploying them. Another form of lighter-than-air craft, the steerable airship or

“dirigible,” proved even more practical. The impetus for learning more about

what it took to fly grew ever stronger. 

What brought experimenters, finally in the late nineteenth century, to the

birth of a formal study of “aerodynamics” was the matter of lift—specifically the

question, “Why do curved surfaces, in particular, perform so well in flight?”

Cayley had shown that the curved shape of trout enjoyed low drag in water. This

prompted applications of the shape to airplanes. In the 1880s and early 1890s,

the great “Bird Man,” German engineer Otto Lilienthal, built and flew a number

If anyone can be known as the “father of modern aeronautics,” it is Sir George Cayley (1773–1857). Not only

did he set down the fundamental concepts that defined

the airplane in its present-day form, but he was also the

first to link a scientific study of aerodynamic principles

with the actual design and operation of flying

machines. SI Negative No. 75-16335
xxii The Wind and Beyond: Volume 1

7 von Kármán, The Wind and Beyond, pp. 58–59.

8 von Kármán, The Wind and Beyond, p. 59.

9 von Kármán, The Wind and Beyond, p. 59.

of effective hang gliders with wings having large curvatures. His flight experiments

showed that, compared to a flat plate of the same size, a large curved surface provided significantly greater lift for the same speed. But Lilienthal could not show

why. As von Kármán himself noted, the search for this why “led to the study of

what we now call aerodynamics, the science of flight.”7

It is the birth of this science and, even more, the unfolding of the century of rapid

development in flight technology that followed it that form the storyline of the

volumes to come.

Quickly, and quite necessarily, aerodynamics became highly mathematical.

But, as readers of our volumes will perceive, the story involves much more than

abstruse theories and differential equations. Unlike other modern technological

developments, in which theory mostly preceded practice (often by several

decades), aeronautical practice moved largely in parallel with theory, and even

occurred before the discovery of many fundamental laws and theories. It had not

happened this way in other science-based fields like thermodynamics, electricity,

or atomic power, but, for some reason, it did with aerodynamics. Von Kármán recognized this as “an extraordinary thing,” the fact that “scientific knowledge and

its technological application proceeded almost in parallel.”8 He did not begin to

try to explain the phenomenon historically—nor has anyone else. Perhaps it can

be explained simply by an age-old quest: we were too anxious to fly. We had

dreamed about it for too long, from time immemorial, to wait around for detailed

explanations. We were plunging ahead, into the wind and beyond, even if we did

not yet understand in detail how it worked. 

But that excited energy took us only a little way up. Not until aerodynamicists

existed as professional scientists and discovered the why behind lift—and a small

but growing community of aeronautical practitioners could truly benefit from “its

first real understanding of what makes flight possible”—did conditions become

ripe for the “amazingly swift progress” to come.9 We are fully aware of this synergy,

and a leitmotif of our study will be the critical relationship between theory and

experiment. Without a fruitful interplay between the two, progress in virtually all

science is spotty and can grind to a halt. That certainly proved to be true over and

over again with flight technology. In aerodynamics, specifically, we will see this

most clearly in the matter of wing design where designers often, especially early

in the century, shaped their airfoils independent of theory, sometimes with fortunate

results but often with extremely poor—even fatal—ones. As one of the documents
Series Introduction: Talking with the Wind, Collaborating with Genius xxiii

(from 1933) in a later volume suggests, “A large number of investigations are carried

out with little regard for the theory, and much testing of airfoils is done with insufficient knowledge of ultimate possibilities.”10 How theory came to inform experiment

in constructive ways over the course of the twentieth century should become apparent

in our study. But the back-and-forth between theory and experiment remains a

central concern today; to discern the most helpful balance between the two

approaches to gathering knowledge will perhaps forever be an issue for scientists

and engineers to resolve.

In conceiving the nature of our study, we determined very early on that our

documentary history of aerodynamics should not, and could not, dwell only in the

realm of ideas, concepts, equations, principles, and the like. As absolutely critical

as they were to the development of a science of flight, their historical evolution—

apart from the social drive to turn them into the physical realities of actual flight

hardware, e.g., airplanes, airships, helicopters, autogiros, missiles, and spacecraft—

made no sense. Our study would then only concern “the wind,” but not what lay

“beyond” it in terms of technological forms or their socio-economic, political, military,

and cultural contexts.

In adopting a broader approach, we felt secure knowing that John D. Anderson

in his 1997 History of Aerodynamics . . . took exactly the same tact, as can be seen

in the rest of his title . . . and Its Impact on Flying Machines. In the preface to his

book, Anderson wrote: “In addition to examining the history of aerodynamics per se

and assessing the state of the art of aerodynamics during various historical periods,

the book seeks to answer an important question: How much of the contemporary

state of the art in aerodynamics at any given time was incorporated into the actual

design of flying machines at that time? That is, what was the impact of aerodynamic

knowledge on contemporary designs of flying machines?”11

From the start we determined that we wanted to show through our flow of

documents not a linear development of technology but rather a matrix of dynamic

relationships involving not just ideas, but also organizations, social and economic

forces, political influences, and more. With this in mind, and recognizing that the

general perception of aviation history is focused on the evolution of aircraft, we

began work, ironically, on a list of aerodynamically significant American aircraft.

We consulted numerous sources, notably Milestones of the Air: Jane’s 100 Significant

Aircraft (1969), a compilation that included thirty-two American aircraft; Progress

10 Theodore Theodorsen, “Theory of Wing Sections of Arbitrary Shape,” NACA Technical Report

No. 411, printed in Eighteenth Annual Report of the National Advisory Committee for Aeronautics, 1932

(Washington, DC: the NACA, 1933), p. 29. 

11 Anderson, A History of Aerodynamics and Its Impact on Flying Machines (Cambridge, MA: Cambridge

University Press, 1997), p. xi.
xxiv The Wind and Beyond: Volume 1

12 See Richard K. Smith’s review of James Sinclair’s Wings of Gold: How the Aeroplane Developed in

New Guinea (Sydney, Australia, 1980) in Technology and Culture 22 (1981): 641–643. Smith praises

Sinclair’s book for working in economic, engineering, and social history, and for not being just

“another wearisome airplane book.”

13 See James R. Hansen, “Aviation History in the Wider View,” Technology and Culture 30 (1989):

643–656. 

14 See Joseph Corn’s review of Roger Bilstein, Flight in America 1900–1983: From the Wrights to the

Astronauts (Baltimore, MD, 1984) in Technology and Culture 26 (1985): 872.

in Aircraft Design Since 1903 (1973), prepared by the NASA Langley Research

Center, which covered ninety aircraft, seventy-six of which were American designs;

and Quest for Performance: The Evolution of Modern Aircraft (1985), which evaluated

ninety-three American aircraft in addition to a large number of foreign designs.

The list of fifty-two aerodynamically significant U.S. aircraft we came up with early

in our project is appended to this introduction. We used the list not as a definitive

categorization that defined the contents and structure of our narrative, but as a flexible

working outline that helped us organize and focus our research effort as we moved

out into aerospace archives and records centers across the United States in search of

significant documents. Our objective in highlighting certain aircraft was to use them

as subjects in a “pedigree chart,” to use a genealogical analogy, illustrating the vital

interactions between people, institutions, and ideas in the historical unfolding of

American aviation technology. The fifty-two aircraft we chose represented different

developmental stages of particular technologies in this “family history” of the evolution of aerodynamics. Some highlighted the primogeniture of certain technological

concepts, while others illustrated developments in maturity. Many of the aircraft were

significant because of the knowledge and techniques engendered through their use

in research, rather than simply because of their specific performance capabilities. We

treated some closely related sequences of aircraft (such as the DC-1/2/3, or Convair

XF92/F102/F106) as one subject because they represented a continuum of technological developments. We hoped that the research lines emanating from each identified

aircraft would provide links to an equal number of nonaircraft highlights, such as

identification of the key people involved, the development of testing facilities and

programs, and the broader social impact and meaning of the machine’s operation. 

Throughout our research and document-collecting phase, we kept this list of

aerodynamically significant American aircraft close by our side. But it never

defined or handcuffed our approach to the subject. We did not want our work to

become just “another wearisome airplane book.”12 We hoped to contribute to an

emerging historiography committed to fostering “Aviation History in the Wider

View.”13 This approach moved the scholarship beyond narrow “gee-whiz” fascination

with aircraft types to the “people, ideologies, and organizations” as well as the

deeper social and intellectual roots of the technology of flight.14 This became our
Series Introduction: Talking with the Wind, Collaborating with Genius xxv

goal—to the extent we could accomplish a significant historical treatment in a

documentary study involving something as technical as aerodynamics. A careful

study of aircraft themselves was, without question, critically important to a serious understanding of aerodynamic development, but aircraft, as complex and

dynamic as they are, are not alive. They never, once, have made history on their

own. In our study, the primary roles are played by the people who provided the

aerodynamic concepts; those who designed, built, and then used the airplane;

and all the institutions fundamental to those activities. 

We apologize up front, especially to our international readers, for our focus

on American topics. But the magnitude of the task of adequately covering aerodynamic development in the United States alone was so profound that we simply

could not hope to relate the global saga that aerodynamic development actually

experienced. The American story was epic enough. And one certainly does not

need to apologize for the American record. From the Wright brothers to the present-day

pioneers, no national community has contributed more to aerodynamics and to

resulting flight technology than the United States. 

Still, the American experience has always connected to a larger world, and

has been influenced in many critical and formative ways, especially in the early

decades of the century, by foreign—particularly European—developments. We

do our best in this study to relate the most essential connections, and to give all

the credit that is due to the scientists, engineers, and institutions of the many

other countries that have participated in the study of flight. In our volumes, readers

will find numerous references to international events and developments, relating

not only to countries whose aeronautical achievements are well known, such as

Great Britain, France, Germany, Italy, Russia (and the former Soviet Union), and

Japan, but also to the People’s Republic of China, Sweden, the Netherlands,

Poland, Israel, Brazil, and several others. Certainly, the cast of featured characters

in American aerodynamics will itself be international: von Kármán from

Hungary; Igor Sikorsky, Wladimir Margoulis, and Alexandre Seversky from

Russia; Max Munk and Adolf Busemann from Germany; Alexander Lippisch

from Switzerland; Theodore Theodorsen from Norway; Antonio Ferri from Italy;

Hsue-tsen Tsien from China; among others. In embarking on their new lives and

careers in America, many of them brought ideas, values, and techniques learned

while studying or otherwise associating with some of the world’s greatest aerodynamic thinkers: Germany’s Ludwig Prandtl, Switzerland’s Jakob Ackeret,

England’s Frederick William Lanchester, Russia’s Dimitri Riabouchinsky and

Nicolai Joukowski, and many more. In addition to coming into contact with the work

of these foreign thinkers—either directly or indirectly—native-born American

aerodynamicists engaged in a professional discipline that was, like most scientific

fields, increasingly international in character. They encountered books, articles,
xxvi The Wind and Beyond: Volume 1

and certainly hundreds and hundreds of foreign technical reports, both translated

into English and in their foreign tongues. Many of them also traveled to international meetings and symposia where they met the world’s leading lights face to

face. Some of these forums, such as the Volta Congress on High-Speed Aeronautics,

held in Italy in 1935, proved historic in their significance for future technological

developments in America and elsewhere.

Our focus had one other major limiting factor. Because the project had been

sponsored by the history program of the National Aeronautics and Space

Administration (NASA), we set out to highlight as much as possible the role of

NASA—and its predecessor organization, the National Advisory Committee for

Aeronautics (NACA)—in the development of aerodynamic theory and practice. In

exploring this, we hoped to contribute additional insights into the issue of

NACA/NASA’s overall significance in America’s “progress” into air and space. In

league with a growing body of historical scholarship that has mostly affirmed the

positive significance of these two related organizations, our study confirms that

the NACA and NASA were a vital part of the broader spectrum of aerodynamic

research activities involving both civilian and military aviation and aerospace

organizations in the United States. Without direct government involvement in the

form of well-equipped and rather expansive research laboratories dedicated to

“the scientific study of the problems of flight with a view to their practical solution”

(Law establishing the NACA: Public Law 271, 63d Congress, approved 3 March

1915), many fundamental aspects of aerospace science and technology, most

involving aerodynamics, would not have been addressed as quickly or as comprehensively. In the early decades of the century, the U.S. aircraft industry was simply

too fledgling to deal with a wide range of fundamental questions. Even after that

industry had exploded in size and capability, the short-term financial interests of

modern corporate capitalism would not engender the kind of long-term investment

in research and development that NACA/NASA laboratories provided. The proper

and most effective role of government in aerodynamic R&D remains a vital issue

today, and we hope the historical insights provided by our study will inform contemporary discussion of it. 

Within the framework of our contract with the NASA History Office, we tried

to branch out from the NACA/NASA focus to include sufficient information about

aerodynamic developments related to the U.S. military, universities, the aircraft

manufacturing industry, the airlines, and other pertinent government agencies

such as the U.S. Bureau of Standards, the U.S. Department of Transportation, and

the Federal Aviation Administration (and its precursor, the Civil Aeronautics Authority).

But we concede that the attention we paid to these entities is too limited. Nonetheless,

we hope that, overall, readers will come away with a feel for the whole scope of

aerodynamic history—NACA/NASA and otherwise, American and otherwise.
Series Introduction: Talking with the Wind, Collaborating with Genius xxvii

We would like to explain how even the admittedly confined scope of our study

ramified beyond anything anyone had originally intended. 

In 1997, the NASA History Office contracted with us (through the Science

Technology Corporation) to produce a documentary history of American aerodynamic development with a focus on NACA/NASA contributions. There were at

least two major reasons for the request. First, the History Office’s publication of

the first two volumes of Exploring the Unknown: Selected Documents in the History of

the U.S. Civil Space Program (NASA SP-4407; Vol. 1, 1995; Vol. 2, 1996), edited by

John M. Logsdon, et al., were well received both inside and outside of NASA.

These extensive documentary volumes (three more volumes have since been published) quickly became an essential reference for anyone interested in the history of

the U.S. space program. Given that NASA’s space activities had been covered

much more extensively in NASA history books than had its aeronautical activities,

Dr. Roger Launius, then the NASA chief historian, wisely felt that a complementary series of documentary histories devoted to aeronautics would prove valuable.

Launius chose to start with aerodynamics, the central component of all aeronautical technology. Other volumes, dedicated to propulsion, stability and control,

structures and materials, supersonics, and hypersonics, will follow.

Another inspiration for what became our project was the upcoming Wright centennial. In 2003, the United States and the rest of the world will be celebrating the 100th

anniversary of the historic first powered flight by the Wright brothers at Kitty Hawk,

North Carolina, on 17 December 1903. Although perhaps not comparable in magnitude to the United States Bicentennial in 1976 or the fifty-year commemoration

of the end of World War II celebrated in 1995, the Wright centennial will certainly

be a major national and international event. All over the world scholars and aviation

experts will be discussing the significance of flight, assessing the course of its historical

development, and projecting aviation’s future. Major conferences will undoubtedly

take place on the centennial of powered flight. In October 1998 Wright State University

in Dayton, Ohio, the Wright’s hometown, launched the anniversary events with a

National Aerospace Conference. Its theme, “The Meaning of Flight in the 20th

Century,” attracted some 400 historians, policy planners, aerospace professionals, and

just plain interested people.15 The following month, on 13 November 1998, President

William J. Clinton signed into law the Centennial of Flight Commemoration Act

(PL 105-389). This act established a commission responsible for planning all

national events involved with the Wright centennial celebration. 

From the start of our project, we kept the Wright centennial in mind—and not

just as a deadline for publication. We believed, as NASA did, that a documentary history

15 National Aerospace Conference Proceedings, Wright State University, April 1999.
xxviii The Wind and Beyond: Volume 1

of aerodynamics, one which started with “The Achievement of Flight” and that

took the reader through the entire twentieth century, to the present, and then

beyond to our future in flight, would be a worthy contribution to the national celebration of the Wright centennial. 

Originally, our contract called for a single volume incorporating between 150

and 250 documents. Initially, we planned eight chapters. Early into the project,

however, we knew that this framework was too confining. In producing rough

drafts of our first three chapters, we were forced to address two facts: that our

resulting book would grow to become extremely large, much larger than first

anticipated, and that some important topics in the overall history of aerodynamics

could not be well covered in a single volume structure. For the first three chapters

alone, it seemed we would need to publish in the neighborhood of 150 documents.

However, the latter point became the key issue for us. Expanding the work into

two volumes with a total of twelve or more chapters would result in a significantly

better history of aerodynamics—as well as two volumes that were much handier

for the reader.

No celebration of the Wright centennial would be complete without fully documenting the epic story of how aerodynamics progressed with such incredible speed and import, not just to the drama at Kitty Hawk on 17 December

1903, but also for the 100 years of systematic development following the historic first achievement of powered

flight. NASA Image #65-H-611 
Series Introduction: Talking with the Wind, Collaborating with Genius xxix

At this point, a key concept emerged to guide our organization of the two volumes.

The volumes would cover, respectively, “The Aerodynamics of Propeller Aircraft,”

and “The Aerodynamics of Jets and Rockets.” In the first volume we would then

have room not only to cover the mainline stories but also give adequate coverage

to important aerodynamic developments in lighter-than-air research, flying boats,

and rotorcraft, among others. It was evident to us, as we were sure it would be to

any informed student of aviation history, that each of these areas possessed

tremendous historical value and interest, and were vital components of technological

developments related to propeller-driven aircraft.

The second volume would begin with the dramatic story of the high-speed

research that led to the development of dedicated research aircraft and the breaking

of the sound barrier. It would include chapters on transonic research facilities and

supersonic flight, plus chapters covering the first generations of military and civil

jet aircraft, the quest for a commercial supersonic transport, hypersonics, and the

development of today’s most advanced wind tunnels and other aerodynamic

research tools. It would conclude with a special chapter looking ahead to the future

of flight. 

As bundles of photocopied documents continued to grow (and fill up our file

cabinets) as a result of our research trips into archives and depositories around the

country, a truly radical idea for our publication surfaced. What we were producing,

whether we liked it or not (and whether or not the NASA History Office could find

the funding to publish it in such an expansive format) were two multi-volume

boxed sets: one, with the general introduction, series reference material, and

chapters devoted to propeller aircraft; and the other, with chapters covering the

aerodynamics of jets and rockets. All told, the various chapters included over 350

document strings (groups of related documents) comprising almost 1,000 individual documents—or nearly eight times as many as anticipated in the initial concept. In keeping what was in fact the original format for the one-volume concept,

each volume would be introduced by a full-length analytical essay and substantial

introductory headers for each document string.

At this point, the practical demands and costs of publishing intervened, and

our view of the project’s organization evolved into an outline of six separately

bound volumes, each containing two chapters. The plan became for the first three volumes to cover the aerodynamics of propeller-driven aircraft, while volumes four

through six covered the aerodynamics of jets and rockets. Also planned was a general introduction with bibliographic information included as a third section in the first

volume and an epilogue included as a third section in the sixth volume.

The more we thought about this revised and greatly expanded format, the

more we liked it, and came to consider it absolutely vital to the success of our publication. Besides offering much more historical content, it seemed to us most
xxx The Wind and Beyond: Volume 1

“user-friendly.” We wanted the students of aerodynamics history to know by looking just at the physical makeup of our work that its authors intended for it to be read,

that each volume in the series tells a story that can be appreciated independently

of the others. A reader can start with the first volume to follow the document narrative we put together in “Chapter 1: The Achievement of Flight,” or turn to the

fourth volume to read “Chapter 8: The Supersonic Design Revolution.” In sum,

though we offer a reference work to those who want it, we also offer an integrated series of independent volumes. Each tells a story worth reading. (We were flattered beyond description when one of our referees, after reading our draft of

Chapter 1, told us “it was the best single shorthand telling of the invention of the

airplane” that he had ever read.) We chose the documents for every chapter to serve

as critical stepping-stones through an important, often complex, narrative that

would be compelling to the reader every step of the way.

Because, in the end, we wished for our readers, too, to “talk with the wind,”

as we felt we had been doing these past few years while engaging the history of

aerodynamics. As suggested earlier in this introduction, it is our dearest hope that

Dr. von Kármán himself would heartily endorse our use of his title, The Wind and

Beyond, as a token of our great affection, and that he would warmly welcome this

collection of books into his library. There, cigar in hand and with a wryly quizzical look on his face, he would spend evening after evening reading through our

volumes word for word, realizing that each tells a great story full of remarkable

ideas and people—and that together our volumes represent an epic intellectual

journey, a crucial episode in humankind’s quest to conquer nature and fly. We

flatter ourselves to imagine him nodding frequently in tacit recognition and

approval, perhaps even learning a few things here and there that he himself never

knew—though this seems hardly possible, knowing the universal experience of

the man. Optimistically, we believe he would excuse our minor errors and mistakes as instructively as he did the scientific and technical papers written by the

prized pupils at Caltech who came to love him so much. 

Writer Lee Edson began von Kármán’s autobiography with a tribute entitled,

“Collaboration with a Genius.” In sum, that is what we see ourselves doing in this

documentary history: collaborating not only with the genius of von Kármán but

with all the other tremendously inventive minds that played a part in the development of aerodynamic theory and practice from before the Wright brothers up

to the present. May there be many more in the new century at hand.
xxxi

Significant Aircraft List

The list of Aerodynamically Significant American Aircraft was compiled to aid

the development of a research plan for the AU/NASA History Project. As such, the

list is not intended to be a definitive categorization, but rather a flexible working

document to aid in organizing and focusing our research effort. The objective of

highlighting certain aircraft in this way is to use them as subjects in a “pedigree

chart” illustrating the dynamic relationship of people, institutions, and ideas in

the history of technology. 

The aircraft themselves represent different developmental stages of particular

technologies in this “family history” of aerodynamics. Some highlight the primogeniture of certain technological concepts, while others illustrate developments

in maturity. Many of the aircraft are more significant because of the knowledge

and techniques engendered through their use in research rather than their specific

performance capabilities. Along these development lines there may be other aircraft

that will serve just as well, if not better, than the ones listed. Some closely related

sequences of aircraft, like the Douglas DC-1/2/3, or the Convair XF92/F102/F106,

are treated as one subject on the list because they represent a continuum of technological developments. 

The listings on the accompanying page were prepared from a number of different

sources, each representing slightly different perspectives. The different sources

were compared to each other both to develop and to filter the list. Over 155 aircraft

“candidates” were considered in drawing up the list, fifty-two of which appear on

the following page. One of the considerations during this initial filtering was to

reduce the list to a more manageable proportion. 

The first source used is Milestones of the Air: Jane’s 100 Significant Aircraft (1969).

This compilation includes thiry-two American aircraft and, of this number, twentyfour are included on our list. The eight aircraft not included were deleted because

there were no collaborating entries from the other sources. Two of the aircraft not

listed, however, should perhaps still be considered for their aerodynamic significance:

the Sikorsky VS-300 and the Lockheed U-2.

The next two sources are NASA publications: Quest for Performance: The Evolution

of Modern Aircraft, by Laurence K. Loftin, Jr. (1985); and Progress in Aircraft Design

Since 1903, prepared by the Langley Research Center (1974). Loftin’s study of the

period from 1914 to 1980 covers ninety-three American aircraft, in addition to a

large number of foreign designs. One category of aircraft accorded considerable

attention by Loftin, but not well represented in the other sources, is that of flying

boats and amphibians. Few of these types appear on the following list, but they

deserve, and will get, more attention in a later volume. The Langley publication covers
xxxii

The Wind and Beyond: Volume 1

ninety aircraft, seventy-six of which are American designs. Of interest is the fact

that the Langley listing does not duplicate Loftin’s, and includes a number of aircraft not considered in Quest for Performance. The aircraft from these two sources that

appear on the following list are those that were also included in other lists.

The final listing of twenty-four aircraft is based on the previous lists and represents

an attempt to identify flight vehicles associated with specific NACA/NASA aerodynamic research programs. The intent of this filter was to focus further recognition of the aircraft as technological representatives of a dynamic interrelated train

of research and ideas. A second consideration was to help direct initial research

efforts to document trails that are most likely accessible in NASA collections.

Significant Aircraft List

Aircraft Year Jane's Loftin LRC NACA/NASA Aerodynamics

Wright Flyer 1903 ✓ ✓

Curtiss JN-4 1916 ✓ ✓ Flight tests

Curtiss NC-4 1919 ✓✓✓

Dayton-Wright RB-1 1920 ✓ ✓

Curtis R2C-1 1923 ✓ ✓

Sperry Messenger 1923 Airfoils, Full-scale wind tunnel

Ford Tri-Motor/5-AT 1926 ✓✓✓

Ryan NYP 1927 ✓✓✓

Lockheed Vega 1927 ✓✓✓

Curtiss AT-5 1927 NACA Cowling

Lockheed Air Express 1927

Pitcairn PCA (*Cierva) 1931 ✓ ✓ Rotary-wing tests

Taylor/Piper Cub 1931 ✓✓✓

Boeing 247 1933 ✓ ✓

Douglas DC-2/3 1933 ✓✓✓

Sikorsky S-42 1934 ✓ ✓

Boeing B-17 1935 ✓✓✓ Flaps, Cowls, Airfoil
Significant Aircraft List xxxiii

Aircraft Year Jane's Loftin LRC NACA/NASA Aerodynamics

Brewster XF2A 1938 ✓ Drag clean-up

Consolidated B-24 1939 ✓ ✓

Lockheed P-38 1939 ✓ ✓ Compressibility

North American P-51 1940 ✓✓✓ Laminar flow

Republic P-47 1941 ✓

Hughes H-1 1941

Boeing B-29 1942 ✓ ✓ Scale model testing, etc.

Lockheed L 1049/C-69 1943 ✓ ✓

Lockheed P-80 1944 ✓ ✓

Bell X-1 1946 ✓ ✓ Supersonic flight

North American F-86 1947 ✓ ✓ Swept wings

Boeing B-47 1947 ✓

Convair XF-92/102/106 1948 ✓✓✓ Delta wing/area rule

Northrup N-1M 1950

Bell X-5 1951 ✓ Variable geometry wing

North American F-100 1953 ✓ ✓

Lockheed F-104 1954 ✓ ✓ High-speed tests

Boeing 707 1954 ✓✓✓

Vought F-8 1955 ✓ ✓ Supercritical wing

Convair B-58 1956 ✓ ✓

Bell Model 204/UH-1 1956 ✓ Ogee tip

McDonnell F-4 1958 ✓✓✓

North American X-15A 1959 ✓ ✓ Hypersonic upper atmosphere

Sikorsky S-60/64 1959 ✓ ✓

Lockheed YF-12/SR-71 1963 ✓ Hypersonic flight

General Dynamics F-111 1964 ✓ ✓ TACT, Transonic research

North American XB-70 1964 ✓ Supersonic cruise
xxxiv The Wind and Beyond: Volume 1

Aircraft Year Jane's Loftin LRC NACA/NASA Aerodynamics

Northrup HL-10 1966 ✓ Lifting body

General Dynamics F-16 1974 ✓

Rockwell B-1 1974 ✓

Rockwell STS 1977 Space Shuttle

Bell XV-15 1978 Tilt-rotor

Gates Learjet 55 1980 Whitcomb winglet

Grumman X-29 1984 HiMAT, High maneuverability

Lockheed F-117 1988
xxxv

16 This section’s title has been inspired by the title of the World War I memoirs of Belgian fighter ace

Willy Coppens de Houthulst, Days on the Wing (London: J. Hamilton, 1934).

Series Bibliographic Essay:

Days on the Wing

Journeys to America’s Aviation Archives

Many historians and other scholars would admit that, next to seeing their

work finally appear in print, research is the most enjoyable experience of their

enterprise. That was the case for all of us with this project. The comprehensive

nature and scope of our documentary project required the members of the project team to travel to and spend extended periods of time in those archives and

libraries across the United States that held significant materials on the development of aerodynamics. These repositories included public institutions such the

National Archives and Records Administration (NARA) and the National Air and

Space Museum (NASM) as well as private facilities such as the Boeing Company’s

Historical Archives. The “days on the wing” that members of the project team

spent at these places resulted in our accumulating the bulk of the material readers will see in the following volumes. Those days of research and photocopying

also provided us with some unprecedented impressions not only of the state of

aerodynamics archives in the United States, but also of aeronautics archives in

general.16

Represented in the volumes of our documentary history is a cornucopia of

historical materials, of various types and in various formats. In the archives we

found diverse manuscript material in the form of correspondence, journal and

diary entries, meeting minutes, personal scrapbooks, and pilot reports. We also

found many relevant published primary sources such as periodical and newspaper

articles, autobiographies, and transcripts of oral histories. Our primary criterion

in the research phase was to find documents that, either alone or in combination,

could illuminate some significant point or historical moment that contributed to

the development of aerodynamics in the United States. Project researchers,

which included three Ph.D. students in the history of technology at Auburn

University working under the supervision of project director Professor James R.

Hansen, also sought related materials to support the documents—photographs,

negatives, blueprints, technical manuals, motion pictures, video records, sound

recordings, electronic data, etc. Though very few of these ancillary materials
xxxvi The Wind and Beyond: Volume 1

17 Cloyd Dake Gull, ed., A Guide to Sources for Air and Space History; Primary Historical Collections in

United States Repositories (Washington, DC: National Air and Space Museum, Smithsonian

Institution, 1994), and at http://www.nasm.edu/nasm/arch/ARCH_REPOS/gtsash1.html

could be included in the documentary volumes to follow, given the medium of

textual presentation, everything we collected helped us to see the historical development of aerodynamics in a fuller context. 

We went about identifying and locating significant documents in the history

of aerodynamics through several methods. First, we looked to the previous historical

record by searching through the footnotes and endnotes of notable works in the

field of aeronautical history. (An annotated list of significant secondary works

related specifically to the history of aerodynamics is at the end of this essay.) Such

a process allowed us to build a foundation for the evaluation of key documents as

well as improve the research team’s general knowledge of the subject. We went

one step further and asked leading historians to suggest archives and document

collections that they felt had been important to their research as well as to exploration of the subject in general. In recognition of their vital contribution, we have

listed these individuals in our acknowledgements. 

In a clear indication of the growing importance of digital information, we

found the Internet to be a highly valuable resource and general research tool.

The readily accessible technology in the form of our desktop PCs facilitated the

search and acquisition of information pertinent to the project. This ranged from

locating specific documents, to inventory listings for specific archives, to e-published articles related to aeronautical history and aerodynamic developments of

the present and very recent past. The use of mainstream search engines and of

keywords such as “aerodynamics,” “wind tunnels,” “laminar flow,” “helicopters”

brought us into a global matrix of information concerning the past, present, and

future of aerodynamics and its social, economic, political, and military contexts.

Much of this was in an electronic format that was instantaneously available. The

project’s specific use of Internet and other types of digital resources is mentioned

at appropriate points through this essay as well as at various points in the text. E-mail

also facilitated correspondence with archivists and librarians and kept us in our

offices at home working at a pace that greatly helped the progress of the project. 

Another valuable research tool for our process of document identification,

location, and acquisition were two published descriptions of American aerospace

archives. One of these was A Guide to Sources for Air and Space History; Primary

Historical Collections in United States Repositories (1994 edition, sponsored by the

National Air and Space Museum and edited by Cloyd Dake Gull), an extensive

listing available in both published and digital form.17 This guide highlights

approximately 2,250 collections in over 370 repositories across the United States,
Series Bibliographic Essay: Days on the Wing xxxvii

18 Catherine D. Scott, ed., Aeronautics and Space Flight Collections (New York, NY: Haworth Press, 1985).

which span from the flight experiments of the nineteenth century to the space

flight missions of the 1980s. First appearing in 1976, the last major edition of this

bibliography, from 1994, was available to us on the Internet. Gull’s listings are organized alphabetically, meaning that it takes some time for users of the bibliography

to search and read through the descriptions. Also, we found that the descriptions

were in no way comprehensive. Too often, Gull details a particular collection of

papers thoroughly but neglects to describe other potentially significant collections

found at the very same repository. Perspective researchers need to contact target

archives for more specific information about their collections.

The second major bibliographical work, Catherine Scott’s edition of

Aeronautics and Space Flight Collections (1985) details the state of aerospace archives

into the 1980s.18 Scott opens the volume with a guide to regional aerospace

archives across the United States; the guide is organized by subject (e.g., Wright

Brothers, Charles A. Lindbergh) and by region (e.g., Northeast, Southeast). The

volume includes specific essays describing the aeronautics collections in the

Library of Congress, New York Public Library, United States Air Force Historical

Collection, Gimble Collection at the United States Air Force Academy, National

Air and Space Museum Library, and the History of Aviation Collection at The

University of Texas at Dallas. Most of these essays are written by the archivists

responsible for them. 

There were limitations to using both Gull’s and Scott’s work. Neither one

mentions aerodynamics specifically, meaning that further inquiry by the project

team was necessary. In neither work is there a specific listing of aerodynamics

archives per se. The closest thing we found to an aerodynamics archive cited in

Scott’s bibliography involved the volumes of wind tunnel test reports housed in

the GALCIT Aero Library of the California Institute of Technology in Pasadena.

But this facility was closed in the early 1990s and most of its holdings turned over

to the Caltech Archives (although some went to aerospace corporations). As a

result of such institutional transitions, along with corporate downsizing and loss

of funding for records keeping, the archival landscape surveyed by Gull and by

Scott had changed significantly by the time we started our project in 1997. Not

just for our purposes but also generally speaking, by the mid-1990s both guides

were woefully out-of-date and in need of revision and updating. Despite their limitations, however, these guides still qualify as points of departure for any individual

starting a research project in aerospace history in the United States.

The research methodology of utilizing the previous historical record, suggestions

from leading historians, and published guides to American aerospace archives
xxxviii The Wind and Beyond: Volume 1

provided the preliminary foundation for building what would become a vast documentary collection related to the development of aerodynamics in America. From

it we successfully moved forward to collecting many documents of known value and

significance and many others that were forgotten or completely unknown. Our

objective was not only to make the most important of them available to historians

and present them to readers in an accessible form, but also to make sense of them,

to contextualize them, to interpret them, and to place them within a meaningful

narrative—telling the story of the development of aerodynamics in America, from

before the Wright brothers up to the present.

Members of the project team visited private, corporate, and both civilian and

military government archives to amass the documents that made the completed

volumes possible. Virtually all of the repositories we visited employed enthusiastic

caretakers dedicated to the preservation of aviation history, even though they all

represent different interests, outlooks, and agendas in their records keeping. We

found that the governmental, military, and corporate memory of American aerodynamics was principally alive and well. No one in the project experienced the

typical horror stories about tyrannical and paranoid archivists hindering historical research. All of the archivists and specialists we met were open to the promise

of our project. At each archive, the project team not only found many important

documents but we also benefited from conversations with archivists and, in the

process, learned considerably more about the aviation history we were researching. 

Many of these repositories are located near historic places related to U.S.

aeronautics. This enhanced our overall research experience greatly. We visited

Huffman Prairie where the Wright brothers developed their aircraft after going

back to Dayton from Kitty Hawk. We toured the dry lakebeds of Edwards Air Force

Base in the Mojave Desert, where the Bell X-1 and so many other important

experimental aircraft had test flown. We explored Boeing Field in Seattle, and we

stood in the vast test section of the thirty- by sixty-foot Full-Scale Tunnel at

Langley Research Center in Virginia. All of these first-hand experiences made the

importance of the project all the more apparent and committed us anew to documenting the history of aerodynamics in America. 

Although we specify the bibliographic origin of the many hundreds of documents reproduced and analyzed in our study, we have included a general exposition on the state of those American archives containing collections pertinent to the

development of aerodynamics. We believe this would be helpful to scholars wishing to expand upon the themes and topics presented in our volumes. The following descriptive essay therefore discusses the primary institutions holding significant collections of these records. It begins by taking a look at the NACA/NASA

materials we examined and is followed by summary inventories of what we found

in military, corporate, and academic libraries and repositories. 
Series Bibliographic Essay: Days on the Wing xxxix

19 NASA History Office, Code IQ, NASA Headquarters, 300 E Street SW, Washington, DC 20546-0001,

http://history.nasa.gov/

20 Research in NASA History: A Guide to the NASA History Program (Washington, DC: NASA History

Office, NASA HHR-64, June 1997), and at http://www.hq.nasa.gov/office/pao/History/hhrhist.pdf

NASA

NACA/NASA collections predominate in this documentary history. The very

nature of our work’s overarching theme—the development of aerodynamics in

the United States—meant that considerable time would be spent in archival repositories maintained by the National Aeronautics and Space Administration

(NASA). Throughout the twentieth century, NASA and its predecessor agency, the

National Advisory Committee for Aeronautics (NACA), founded in 1915, have

been the constant in aerodynamics research in the United States.

The NASA History Office at NASA Headquarters in Washington, D.C., directs

an extensive history and archival program dedicated to the preservation of both NACA

and NASA involvement in the development of flight.19 NASA created its history office

in 1959 and assigned it the duty of widely disseminating information about the

agency’s activities and about aerospace developments generally, under the mandate

of the 1958 National Air and Space Act. A commitment to serving both governmental and public interests has ensured that NACA/NASA involvement in the development of aerodynamics has been preserved. The Headquarters History Office

perpetuates this mission through its direction of history offices at all of NASA’s field

installations. This includes offices at Langley Research Center in Hampton, Virginia;

Ames Research Center at Moffett Field, California; Glenn Research Center at Lewis

Field in Cleveland, Ohio; and Dryden Flight Research Center at Edwards Air Force

Base in California. These are the NASA facilities that have been most directly involved

in aeronautics research. For a detailed synopsis of the NASA History Program and its

archival holdings across the United States, see Research in NASA History: A Guide

to the NASA History Program (1997), which is also accessible via the Internet.20

As an archival repository, the NASA History Office itself maintains extensive

biographical and subject files. The biography files cover approximately 5,000

individuals from the 1800s to the present and comprise 180 linear feet of archival

space. Arranged alphabetically, these files contain speeches, correspondence,

articles, clippings, press releases, and photographs. The aeronautics collection is

thirty-two linear feet and focuses on NACA/NASA activities from 1945 to the present.

These records contain photographs, newspaper and Congressional Record clippings,

articles, speeches, news releases, reports, studies, pamphlets, and brochures on

specific topics such as SST, V/STOL, X-aircraft, aerodynamics, wind tunnels, and

NACA contributions to historic aircraft.
xl The Wind and Beyond: Volume 1

21 Historical Program Manager, Mail Stop 446, Langley Research Center, Hampton, VA 23681-0001.

The archival core of our documentary project, however, proved to be the substantial collections housed in the Historical Archives at Langley, the original and the

oldest NACA/NASA laboratory.21 The collections housed at Langley are immensely

valuable to the study of the development of aerodynamics and are the closest

thing to a dedicated “aerodynamics archive” in the United States. The collections

possess materials dating back to the creation of the laboratory in 1917 and

include technical reports and data logs, internal correspondence and memoranda, personal papers of leading engineers, programs and minutes of technical conferences, transcripts of oral histories, and numerous special files, such as the one

compiled on the flight testing of the North American XP-51 Mustang. Members of

our project team concentrated most of their efforts in four important collections:

the NACA research authorization (RA) files; the Milton Ames collection; and the

papers of research engineers John Stack and Fred E. Weick. Detailed finding aids

for these and other collections at Langley are available in the archives and also

appear in bibliographies at the end of James R. Hansen’s two works on the history

of NACA/NASA Langley, both of which are referenced later in the “Secondary

Sources” portion of this essay.

In our view, the over 2,000 research authorization (RA) files housed in Langley’s

Historical Archives compose the single most valuable collection for the study of

the NACA’s involvement in the development of aerodynamics—and one of the

most important intact collections in all of American aeronautics history. Through

the voluminous materials in these RA files, historians are able to trace the evolution

of a research program from the original idea to the completed project featured in

a NACA publication. A clerk began an RA file whenever a research authorization was

signed by the NACA chairman in Washington, D.C., authorizing one of the laboratories to pursue a specific research project. An RA file thus should exist for each

and every authorized research program the NACA ever conducted. A typical RA

file consisted of the RA sheet itself, which officially authorized the research, specified its title and sequential number, and delivered a statement indicating the reason and method of research. Following this cover sheet in every RA file one finds

copies of all correspondence, memoranda, blueprints, drawings, and reports that

NACA file clerks designated as related to the RA. Copies of a large number of

original items such as this would also be placed in other related RA or correspondence files. This records-keeping scheme, invented by the NACA in the early

1920s, resulted in a truly historic and extremely extensive documentary collection.

Researching the NACA RA files allows the historian to gain both a broad perspective

and a very detailed picture of the NACA’s process of selecting research problems
Series Bibliographic Essay: Days on the Wing xli

22 For more information about the holdings of the Langley Research Center Historical Archives,

specifically the RA files, see James R. Hansen’s Engineer in Charge: A History of the Langley

Aeronautical Laboratory, 1917–1958 (Washington, DC: NASA SP-4305, 1987), pp. 567–588.

and then exploring ways to solve them. The RA files also illuminate the interaction

between the NACA committee structure and the NACA executive office in

Washington, D.C., and between those bodies and the field centers such as Langley.

They also provide an almost day-to-day picture of the research life of the laboratory and of the social, intellectual, and professional dynamics taking place within it. Typically, there are also indications in the RA files of which RA contributed

to a particular NACA publication. Still, quite a bit of time needs to be spent in

the RA files before a historical researcher can become adept at following the

many intricacies involved in the administration and contents of the RA files.

Many documents that follow in our volumes come from the RA files at Langley.

Many more, which we approximate to be in the neighborhood of some two million,22

might have been included had we time to examine them all. 

Another critical assembly of documents we fully utilized in the Historical

Archives at NASA Langley was the Milton Ames Collection. These files resulted

from an attempt made in the 1970s by the former Langley research engineer

(1936–1941) and staff member in the NACA’s Washington Office (1949–1958) to

write a technical history of NACA Langley laboratory, from its establishment in

1917 to the birth of NASA in 1958. By this time Ames was serving as the NACA’s

chief of aerodynamics. What made this collection so important to us was that it

embodied dozens of documents that Ames, a veteran researcher and aerodynamics

specialist, had personally identified as historically significant. Organized into

seven boxes, the Ames Collection spans from the Wright-brother era to Langley

laboratory’s involvement in the Apollo program and includes hundreds of significant

aerodynamics documents. Specific themes that the Ames Collection highlights

include the establishment of government aeronautical research establishments in

Europe and North America; the construction of the Variable Density Wind

Tunnel (VDT); the contributions of significant individuals to NACA research;

NACA research programs related to low-drag engine cowlings, the design and

operation of wind tunnels and other aerodynamic research facilities, airfoils and

propellers, boundary-layer control, and the potential of laminar flow; the design

of airships, flying boats, and rotary wing aircraft; NACA research contributions to

the aircraft that fought in World War II; the establishment of other NACA laboratories and field stations, notably what became NACA/NASA Ames, Lewis,

Wallops Island, and Dryden installations; post–World War II developments in

high-speed flight, including the breaking of the mythical sound barrier; and

Langley researcher Richard T. Whitcomb’s conception of the so-called “area
xlii The Wind and Beyond: Volume 1

rule.” Virtually all of the papers in the Ames Collection deserved our attention as

potential items for publication in our documentary history.

A third major collection we reviewed systematically in the Historical Archives

at NASA Langley involved the business papers of Langley research engineer and

supersonics pioneer John Stack. Divided into six major sections, the Stack

Collection documents Stack’s deep and diverse involvement in major aerodynamic

research projects from the 1930s to the 1970s. A pioneering specialist in high-speed

aerodynamics, Stack is considered by all aeronautical historians to be one of the

world’s most significant aerodynamic researchers. Many of his activities proved

crucial to the achievement of flight at transonic and supersonic speeds. He was

one of the driving forces behind the Bell X-1 and North American X-15 research

airplanes; the slotted-throat transonic wind tunnel; the national SST program;

and the General Dynamics F-111 (TFX) variable-sweep wing program. Stack

received both the prestigious Collier Trophy (twice) and the Wright Brothers

Memorial Trophy. Topics in the Stack papers cover wind tunnel design, operation,

and test techniques; research problems related to airfoils, compressible flow, and

the boundary layer; reports of important meetings such as NACA-sponsored conferences on aerodynamics in the late 1940s; memoranda and correspondence

related to high-speed aerodynamics during World War II and the immediate postwar

period; and aircraft development projects such as the North American P-51,

Republic P-47B, SST, V/STOL, and the TFX (F-111). Regrettably, no biography of

Stack has ever been attempted. When it is, the papers in the Stack Collection will

be an important starting place. Unfortunately, the collection includes almost no

papers of a personal nature. 

Another collection we reviewed at NASA Langley held the papers of American

aeronautics pioneer Fred E. Weick, a prolific NACA Langley researcher well

known for his work at the laboratory in the 1920s and 1930s. After leaving government employment permanently in 1936, Weick went on to a highly successful

career in academia and industry. The thousands of items in this collection (donated

by the Weick family to the Langley archives after Weick’s death in 1994) include

extensive correspondence, reports, memos, articles, newspaper clippings, speeches,

and oral histories. These papers document his work with the navy’s Bureau of

Aeronautics, the NACA, the United Aircraft and Transport Corporation, the

Engineering Research Corporation (ERCO), Texas A&M University, and the Piper

Aircraft Corporation. In searching through the Weick papers, we gained numerous

critical insights into major aeronautical developments from the 1920s to the

1970s, including propeller design; the drag-reduction experiments that resulted

in the NACA’s famous Collier Trophy–winning program of the late 1920s; the

design of pioneering general aviation aircraft such as the Weick W-1A and the

Ercoupe; and the refinement of agricultural aerial application (i.e., crop-dusting)
Series Bibliographic Essay: Days on the Wing xliii

23 Old Dominion University, Department of Aeronautical Engineering, The Langley Full-Scale

Tunnel, P.O. Box 65309, Langley Air Force Base, VA 23665-5309, and at http://www.lfst.com/

24 Office of External Affairs, Mail Stop TR-42, NASA Dryden Flight Research Center, Edwards, CA

93523, and at http://www.dfrc.nasa.gov/History/

aircraft such as the Piper Pawnee. Occasionally in the volumes to follow, we have

also reproduced excerpts from Weick’s published autobiography, From the Ground

Up: The Autobiography of an Aeronautical Engineer (Washington, DC, and London:

Smithsonian Institution Press, 1988), which was coauthored by project director

James R. Hansen.

On the grounds of the Langley Research Center we also reviewed the contents

of the Old Dominion University Experimental Aerodynamics Library. Housed

within Langley’s Full-Scale Wind Tunnel building, this library is the repository for

the bound volumes on the history of wind tunnels compiled by Langley aerospace

engineer and cryogenic wind tunnel pioneer Robert Kilgore, an individual whose

work is much discussed in our study.23 Kilgore’s volumes contain countless manuscripts and published primary documents, arranged chronologically and devoted

to specific subjects related both to his own career and to the development of wind

tunnels in general. The titles of these volumes are Development of Cryogenic Wind

Tunnels (Black Volumes 1969–1989) and the ETB Weekly Briefs (1980s–1990s). The

latter documents Langley’s Experimental Techniques Branch, the organization

that Kilgore directed while working to develop the cryogenic wind tunnel concept.

Kilgore also compiled a similar multivolume general history of wind tunnels that

he donated to Langley’s Floyd L. Thompson Technical Library.

Without question, we have included more documents from Langley than from

any other archives, repository, or library. This is due both to the integrity of the

collections at this particular NASA center, and to the extraordinary historical significance of the aerodynamics research activities that have taken place at this, the

oldest of the NACA/NASA facilities, over ten decades of operation.

But documents from many other major facilities also play a critical role in our

research story. One of the most important of these was the NASA Dryden Flight

Research Facility History Office located on Edwards Air Force Base in the Mojave

Desert of California, northeast of Los Angeles, which serves as the central repository

documenting NACA/NASA’s involvement in high-speed flight research.24 Since fall

1946, the NACA and NASA have maintained a collaborative presence at Edwards

with the Air Force and the Navy in the experimental testing of research aircraft.

NACA/NASA pilots, engineers, and managers played leading roles in the success

of state-of-the-art R&D projects that extended humankind’s presence into both

the air and space. Dryden’s history office maintains thirty linear feet of materials
xliv The Wind and Beyond: Volume 1

25 Research Information Resources, Library, Mail Stop 202-3, NASA Ames Research Center, CA

94035-1000, and at http://mainlib.arc.nasa.gov/

26 Elizabeth A. Muenger, Searching the Horizon A History of Ames Research Center, 1940–1976

(Washington, DC: NASA SP-4304, 1985).

27 Sources for Researchers of Ames History at http://history.arc.nasa.gov/research.htm

28 National Archives and Records Administration, 700 Pennsylvania Avenue NW, Washington, DC

20408, and at http://www.nara.gov/research/

concerning the X-series aircraft (X-1 through X-43) and D-558 program; Century

series fighters (F-100, F-101, F-102, F-104, F-105, F-106, F-107); lifting bodies;

the North American XB-70 supersonic research platform; the supercritical wing

on the modified F-8; and the Highly Maneuverable Aircraft Technology (HiMAT)

research vehicle. The office also sponsors an extensive oral history program covering important pilots and engineers in the history of flight research at Dryden.

To the north of Dryden at the mouth of the San Francisco Bay is NASA Ames

Research Center. Founded in 1939, the Ames laboratory established the NACA’s

presence on the West Coast, which contributed greatly to the success of the aircraft manufacturing industry during World War II and the Cold War era. The

Ames Research Center Library maintains a history collection documenting the

activities of the center from December 1939 through August 1998, when the collection was formally created.25 The collection measures twenty-eight linear feet

and consists chiefly of published primary materials, including promotional

brochures, newspaper clippings, and programs from official ceremonies. Other

components of the collection are the manuscript and research materials used in

the writing of Elizabeth A. Muenger’s Searching the Horizon: A History of Ames

Research Center, 1940–1976.

26 The library also maintains extensive Web-based

resources describing the location, scope, and content of other archival collections

concerning the history of Ames.27 The majority of the Ames records are held by

the National Archives and Records Administration, specifically at the Pacific

Region Office at San Bruno, California. There are also materials about Ames

housed at the NASA Headquarters History Office in Washington, D.C.

National Archives and Records Administration

A major part of our research necessarily involved the National Archives and

Records Administration (NARA), which at its various facilities around the country

maintains and preserves the largest collection of aerospace history archival

records in the United States.28 The federal government’s extensive civilian and

military involvement in aeronautical research and development since the late
Series Bibliographic Essay: Days on the Wing xlv

29 Guide to Federal Records in the National Archives of the United States—Record Group 255,

http://www.nara.gov/guide/rg255.html#255.2

30 NARA Mid Atlantic Region (Center City Philadelphia), 900 Market Street, Philadelphia, PA 19107-4292,

and at http://www.nara.gov/regional/philacc.html. This facility contains a total of 347 cubic feet of NACA

records, and finding aids are available. A portion of the collection is indexed by subject.

31 NARA Pacific Region, 1000 Commodore Drive, San Bruno, CA 94066-2350, and at

http://www.nara.gov/regional/sanfranc.html

nineteenth century has ensured the survival of significant collections. Organized into

record groups (RG), these collections document the activities of particular federal

agencies and departments involved in the development of American aeronautics. For

our purposes, the most important record group was RG 255, which holds documents of the NACA and NASA from 1915 to 1988. RG 255 measures a gargantuan

5,182 cubic feet; however, the files are not located in one place but are distributed

among various NARA facilities across the United States.29 RG 255 consists of correspondence, technical and administrative reports, blueprints and drawings, photographs, meeting minutes, and memoranda from NACA and NASA committees,

subcommittees, research units and facilities, and national and international

offices. The primary NARA facilities holding files of interest to our project were

the NARA Mid-Atlantic Region Office (City Center Philadelphia) in Philadelphia,

and the NARA Pacific Region (San Francisco) Office at San Bruno, California.

An effort to integrate portions of the archival collections of NACA/NASA into

the National Archives in the early 1990s resulted in, among other things, the

move of NASA Langley’s correspondence files (dating from 1917 to 1958) to the

NARA facility in Philadelphia.30 These files are also very significant historically.

The NACA’s manner of “correspondence control”—wherein all memoranda, letters,

and notices went through Langley’s engineer-in-charge before being sent out to

NACA Headquarters or to any outside addresses—led to a very effective historical

archive, one that enables historians to follow the business of the laboratory as it

routinely unfolded, virtually day by day. In our view, however, it was a mistake for

NARA to remove these correspondence files from Langley, where they not only

were being well preserved but also fit into a complete network of archival materials

involving the NACA research authorization (RA) files and a vast collection of library

holdings. Documents in RA files, for example, routinely include cross-references to

items in Langley’s correspondence files. Previous to NARA’s acquisition of the

correspondence files, researchers could simply move from one part of the Langley

historical archives to another to check the cross reference; now, unfortunately,

they must travel from Hampton, Virginia, to Philadelphia, Pennsylvania.

The other NARA facility that contributed to our research was the NARA

Pacific Region (San Francisco) Office at San Bruno, California, the central repository for the records of the Ames Research Center from 1939 to 1988.31 Finding
xlvi The Wind and Beyond: Volume 1

32 Air Force History Support Office, AFHSO/HOS, Reference and Analysis Division, 200 McChord Street,

Box 94, Bolling Air Force Base, Washington, DC 20332-1111, and at http://www.airforcehistory.hq.af.mil/

33 United States Air Force Aeronautical Systems Center History Office, 2275 D Street, Suite 2,

Wright-Patterson Air Force Base, OH 45433-7219.

aids are available for most of the 1,025-cubic-foot collection. Interspersed in the

center’s central files are correspondence, data sheets, meeting minutes, memoranda,

and technical reports pertaining to aerodynamics, high-performance aircraft

technology, and wind-tunnel tests of such notable World War II aircraft as the P-51

Mustang and P-38 Lightning. The materials from 1939 to the early 1960s are

processed, well organized, and readily accessible while those from 1970 have not

been fully integrated into the collection.

United States Air Force

The inextricable link between the technical development of flight and the

military’s participation in that quest has been a persistent theme throughout the

twentieth century—and through our documentary history as well. The Air Force

History Support Office (AFHSO), at Bolling Air Force Base, Washington, D.C.,

oversees the writing and publication of books, monographs, and professional

studies and reports that document Air Force history.32 These efforts are primarily for the benefit of Air Force leadership, but the program also exists for scholars

of the military’s role in aerospace. The History Support Office also directs the history of the various facilities of the Air Force as well as an extensive museum program across the nation. We reviewed several of these works in our research and

they helped provide an important context for the development of aerodynamics. 

Wright-Patterson Air Force Base (1948–present)—and its predecessors,

McCook Field (1917–1927) and Wright Field (1927–1948), near Dayton, Ohio—

has been a major center for the technical development of American military aviation. In addition to its importance as a research facility, Wright-Patterson Air

Force Base is also the home of two important archival repositories. Since 1917,

the successive incarnations of the Air Force Aeronautical Systems Center (ASC),

have worked to enhance the performance of military aircraft and their abilities to

achieve successful completion of military missions. The ASC History Office maintains and preserves not only the records of that organization, but also the individual papers of important Wright Field engineers who worked at the Air Force

Flight Dynamics Laboratory.33 Of particular importance to aerodynamics

researchers are the William Lamar Files, which include many documents regarding

the development of supersonic and hypersonic research aircraft and spacecraft

between 1949 and 1978. Some finding aids are available. We reviewed the contents
Series Bibliographic Essay: Days on the Wing xlvii

34 United States Air Force Museum/MUA, Research Division, 2601 E Street, Wright-Patterson Air

Force Base, OH 45433-7609, and at http://www.wpafb.af.mil/museum/mua.htm

35 United States Air Force Air Force Flight Test Center History Office, 305 E. Popson Avenue,

Edwards Air Force Base, CA 93524-6595, and at http://www.edwards.af.mil/history/index.html

36 Air Force Historical Research Agency, 600 Chennault Circle, Bldg 1405, Maxwell Air Force Base,

AL 36112-6424, and at http://www.maxwell.af.mil/au/afhra/

of these collections, though admittedly we could have done much more with

them. Two of the primary problems of working in military archives, of course, are

document classification and security clearance.

The Research Division of the United States Air Force Museum in Dayton

maintains an extensive collection of archival materials supporting the exhibition

of Air Force history.34 The museum’s collection approximates 200,000 documents.

It is comprised of photographs, technical manuals, drawings, reports, and other

materials, most of them dealing with specific artifacts in the museum’s collection.

Many of the documents are organized by subject airplanes, which facilitates a

researcher’s study of milestone aircraft such as the Martin B-10 of the 1930s and

the Century series fighters of the 1950s and 1960s.

While Wright-Patterson AFB has served the Army, and later the Air Force, as

its major center for aircraft research and development, Edwards AFB in the

Mojave Desert of California has, since the early years of the Cold War, been the

more broadly based center of high-performance flight research and testing. The

Air Force, Navy, and NACA/NASA have used this remote location to perform the

stunning aerospace trials related primarily to high-speed flight. The Air Force,

through its Flight Test Center, has also used the facility to evaluate experimental

and prototype military aircraft. The United States Air Force Air Force Flight Test

Center History Office (AFFTC/HO) is responsible for documenting the activities

of this organization.35 The history office preserves important material on the X-series

aircraft, with a particularly strong collection documenting the Bell X-1, fighter

aircraft from the air force inventory, biographical files on leading test pilots and

military officers, and general documents on high-speed flight research.

Because it is located so close to Auburn University and holds such a major collection of aerospace archives and library materials, Maxwell Air Force Base in

Montgomery, Alabama, the home of the Air Force’s Air University (which trains

the service’s officers for higher command and staff duties), was a mainstay of our

research project. On base at Maxwell is the Air Force Historical Research Agency

(AFHRA), which is the central repository for Air Force historical documents.36 Unit

histories, command and theater of operations records, and personal papers of

leading military engineers and personnel document the air force’s continued

involvement in the aerodynamic development of the airplane.
xlviii The Wind and Beyond: Volume 1

37 Smithsonian Institution, National Air and Space Museum, National Air and Space Archives, MRC 322,

Seventh Street and Independence Avenue SW, Washington, DC 20560, and at

http://www.nasm.edu/nasm/arch/archdiv.htm or http://www.nasm.edu/nasm/arch/ARCH_REPOS/

GUIDE.PT7.html#NASM

38 Paul E. Silbermann and Susan E. Ewing, Guide to the Collections of the National Air and Space Archives

(Washington, DC: National Air and Space Museum, April 1991).

National Air and Space Museum

Of course, no research project related to aeronautical development in the

United States would be complete without examination of the collection at the

National Air and Space Museum (NASM) in Washington, D.C., one of the premiere

aerospace archives and libraries in the world.37 NASM collections represent government, military, corporate, and academic involvement in humankind’s journey through

air and space. Overall, NASM possesses over 1,400 archival collections amounting

to some 10,000 cubic feet of material. The different types of collections include

personal and professional papers, corporate and institutional records, and “artificial” collections created from published sources to serve as reference files for a

particular subject. A good point of departure before embarking upon any

research at the museum is Paul E. Silbermann and Susan E. Ewing’s Guide to the

Collections of the National Air and Space Archives,

38 which describes 250 of the individual,

corporate, government, military, and artificial collections acquired by the museum

through 1989. Readers should be aware that this guide is not exhaustive, however,

as NASM holds more than the 250 collections described therein.

One of the more useful collections consulted by the project team was the

NASM Technical Files, which consists of 1,300 cubic feet of aviation and spacerelated materials arranged as a vertical file. Initially organized for the use of the

museum’s curatorial staff, these records are organized by subject, aircraft, individuals, organizations, events, and objects to include correspondence, reports,

brochures, press releases, clippings, and photographs. A particularly helpful document was the original 1934 Douglas Aircraft Company report on the development

of the DC-1 and DC-2, the first truly modern aircraft to emerge from the airplane

design revolution of the 1920s and 1930s. In addition to its huge collection of

manuscript material, the NASM archives also maintains an estimated 1.5 million

photographs; 700,000 feet of motion picture film; and 2 million technical drawings.

United States Navy

Members of the project team also visited the Naval Historical Center at the

Washington Navy Yard in Washington, D.C. Here, for example, we researched the
Series Bibliographic Essay: Days on the Wing xlix

39 Naval Historical Center, Naval Aviation History Branch, Washington Navy Yard, 805 Kidder

Breese, SE, Washington, DC 20374-5060, and at http://www.history.navy.mil/index.html or

http://www.history.navy.mil/branches/nhcorg4.htm

40 The following aerospace manufacturers that had no archival program or did not open their doors

to this scholarly study included Lockheed-Martin, Northrop-Grumman, members of the United

Technologies conglomerate (Sikorsky, Vought), Piper, and Cessna.

41 Historical Archives, The Boeing Company, MS4H-0Z, P.O. Box 3707, Seattle, WA 98124, and at

http://www.boeing.com/history/

Navy’s participation in the development of early wind tunnels.39 Records of U.S.

Navy aviation are located in two buildings within the Navy Yard. The main

History Center, located in Building 57, contains Navy organizational archives and

transcripts of interviews with several captains and admirals before their retirements, including individuals prominent in naval aviation. The Aviation History

Office in Building 157 maintains other naval aviation records. These include documents, published and unpublished manuscripts, and photographs concerning

Navy aircraft programs and facilities. Finding aids are available.

Industrial and Corporate

A primary objective of our documentary research was to visit archival centers

based in the aircraft industry and to fully integrate the industry’s contribution to

aerodynamics development into our larger study. Unfortunately, records-keeping

realities within the private sector made it very difficult for us to reach this goal.

Economic and financial transitions within the aerospace industry have doomed

some important collections to be closed forever. Fortunately, some of the succeeding corporate entities have been able to secure the integrity of some vital archival

collections.40 Most notably, through a series of mergers in the 1990s, the Boeing

Company of Seattle, Washington, has been able to integrate into its own historical memory the archives of North American Rockwell, Inc., as well as that of the

McDonnell-Douglas Corporation. As a result, Boeing now maintains the preeminent aerospace corporate archives in the United States.

The Boeing Company’s Historical Archives represents an unprecedented

commitment at the corporate level to preserve aviation history.41 The program

maintains archival facilities in Seattle; Long Beach, California; and St. Louis,

Missouri. These facilities are principally organized and maintained to serve the

company’s needs rather than those of the general historian—and the company

must give its permission for access to and use of its materials. Boeing’s Historical

Archives are not actually equipped to handle and provide service to general

researchers, though its directors will do their best to respond to outside inquiries
l The Wind and Beyond: Volume 1

and research objectives. Overall, the Boeing Company was very generous in its

assistance to our conduct of research, and we are happy to have the company’s

permission to reproduce some of the historically significant documents we found

in its collection. If our documentary history does nothing more than inspire the

aerospace industry to provide a greater commitment to archival collection and to

scholarly research, we shall have provided a critically important service to the history

of aeronautics and space in America. 

Because Boeing’s materials were so helpful to us, more about its archival collections should be said here. Seattle lumber magnate William E. Boeing started

manufacturing aircraft in 1916. By the 1920s, his company produced passenger

and mail airplanes as well as military fighters and bombers. Boeing’s enterprise

was one of the first manufacturing concerns to benefit from the innovations

brought forth by the airplane design revolution when the company moved toward

specialization in multi-engine aircraft. The Boeing Company pioneered the all-metal

“modern” airplane, the Model 247, as well as the Boeing B-17 Flying Fortress and

B-29 Superfortress of World War II. At the dawn of the jet age, the company produced

the first successful jet bombers, the B-47 Stratojet and B-52 Stratofortress plus the

prototype Model 367-80, the ancestor of the long running 707 series of modern

commercial jetliners. In the 1950s and 1960s, Boeing won the contract for the ill-fated

SST and introduced the “jumbo-jet” 747. In the 1990s, Boeing innovated the

“paper-less” 777 airliner, the first aircraft to be designed entirely with digital

imaging technology. All of these aircraft developments are detailed in our study.

Boeing made important business acquisitions over the course of the twentieth

century that greatly enhanced its prominence as an aircraft manufacturer. In the

1920s, Boeing’s control of the Stearman Company ensured a strong position in

the general aviation segment of the aviation industry. In 1960, Boeing acquired

the Vertol Aircraft Company of Philadelphia, Pennsylvania, manufacturers of the

CH-46 Sea Knight and CH-47 Chinook military helicopters. This made Boeing a

power in the manufacture of rotary-wing aircraft. These company developments,

too, make the Boeing archives critically important to any research into the history

of American aeronautics.

The Boeing Company Historical Archives facility in Seattle is the main repository for the company’s archival collections. Ninety percent of the archival and

microform material held there is organized around specific aircraft designated by

the Boeing model number; all of these numbers are indexed on computer.

Researchers need to be aware of the Boeing model number in order to access the

records successfully. For example, if a researcher wants to find records on the

famous B-17 Flying Fortress, one must know that Boeing’s designation for the

aircraft was Model 299. Materials that the project team consulted at Boeing

included its extensive collection of aircraft engineering reports; personal and
Series Bibliographic Essay: Days on the Wing li

company correspondence from the 1920s to the present; subject and biography

files; aircraft project files; personal and professional papers; and oral history

interviews of leading engineers and managers such as Claire Egtvedt, Maynard

Pennell, Ed Wells, and William Cook.

From 1929 to 1934, Boeing Aircraft was part of United Aircraft and Transport

Corporation, which included America’s leading airlines and manufacturers and

was one of the three major aviation conglomerates to emerge.42 The corporation

sponsored a technical advisory committee that included many leading aeronautical

engineers such as Igor Sikorsky, Jack Northrop, and Fred E. Weick. In the papers

of Claire Egtvedt, one of Boeing’s leading managers and engineers, survives the

only available transcriptions of the immensely valuable meeting minutes from

1929 to 1934. Nowhere else can a historian have the opportunity to see the verbatim

discussion of the technical development of the products from America’s most

powerful aviation corporation. Readers will find an outstanding example of the

importance of these meeting transcripts in Volume 1.

The Seattle location also maintains the records of North American Rockwell

Corporation. In 1934, North American Aviation, Inc., emerged from the nucleus

of the General Aviation Manufacturing Corporation of Dundalk, Maryland. The

resulting company specialized initially in the design of small, single-engine trainers—

notably the NA-16, BT-9, and AT-6 airplanes. By the early 1940s, North American

had set its sights higher and manufactured its highly successful P-51 Mustang

fighter and B-25 Mitchell medium bomber. The corporation’s highly profitable

transition into the design, production, and manufacture of high-performance

military jet aircraft included the F-86 Sabre, FJ-1 Fury (the navy’s first swept-wing

jet), and the F-100 Super Sabre. North American became the corporate partner

with the air force and NACA/NASA in the hypersonic X-15 research airplane and

the experimental supersonic, delta-wing XB-70 Valkyrie. In 1966, North American

Aviation merged with the Rockwell Standard Corporation and became North

American Rockwell Corporation. In 1973, North American Rockwell became

Rockwell International to reflect the company’s widening range of businesses. It

introduced the B-1 Bomber with variable-geometry wings. Rockwell’s pioneering

work on flight research and experimental design continued with its work on the

tail-less X-31 enhanced-fighter maneuverability demonstrator. In December

42 Member companies of the United Aircraft and Transport Corporation included airframe manufacturers Avion (Northrop), Boeing, Sikorsky, Chance Vought, and Stearman; engine and propeller makers Pratt and Whitney and Hamilton Standard; and the commercial operators United

Airlines and Boeing Air Transport. The airline component of the corporation included United

Airlines, Boeing Air Transport, National Air Transport, Pacific Air Transport, and Varney Air

Lines. The corporation also controlled the Boeing School of Aeronautics, United Aircraft Exports,

and the United Airports Company.
lii The Wind and Beyond: Volume 1

41 It is unfortunate that the documentary project was unable to access the archival records of

McDonnell Aircraft, due to its important position in aerospace history. After working for various

aircraft manufacturers, such as the Aviation Division of the Ford Motor Company and the Glenn

L. Martin Company, McDonnell established his own company in St. Louis, Missouri, in 1939. An

early project McDonnell pursued was his Doodlebug of 1927, which the NACA latter used as a

research vehicle for STOL experiments. Primarily a component manufacturer during World War

II, the company submitted pioneering designs such as the twin-engine, long-range XP-67 fighter.

The postwar period and the emergence of jet aircraft, specifically fighters, would catapult

McDonnell to a prominent position within the world aerospace industry. The FH-1 Phantom was

the first military jet aircraft to operate from an American aircraft carrier and was quickly followed

by the F2H Banshee. The highly versatile F-101 Voodoo and F-4 Phantom II of the 1950s and

1960s led to the even more adaptable F-15 Eagle and F/A-18 Hornet. Hughes Helicopters became

part of McDonnell Douglas in January 1984 and produced the important OH-6A Cayuse light

observation helicopter and the AH-64 Apache advanced attack helicopter.

1996, the space and defense divisions of the Boeing Company and Rockwell

International merged and the Rockwell contingents operated as a subsidiary

under the name Boeing North American.

The overwhelming majority of North America’s archival collection is not catalogued and remains unprocessed due to the relatively recent acquisition of the

materials. As in the case of the Boeing files, effective evaluation of this collection

requires extensive knowledge of North American’s model number system, which

can be acquired from secondary sources. The largest component of the collection

is project correspondence recorded on microfilm—especially of late 1930s and

1940s projects such as the first trainer, the NA-16; Model NA-73 (P-51 Mustang);

and the prototype XFJ-1 Fury. The collection also includes photographs, blueprints, and a small number of promotional materials from North American’s earliest ancestor, General Aviation.

The Boeing Company, along with its North American component, merged

with the McDonnell Douglas Corporation in August 1997. Itself the product of a

1967 merger of two eminent aerospace companies, McDonnell Douglas was a

world leader in the design and production of high-performance jet fighter aircraft and commercial airliners. Due to the proprietary and military nature of its

products, the records documenting the aerodynamic development of McDonnellDouglas’s fighter aircraft could not be made accessible to our project, and their

size and importance is thus unknown.43 As a result, we were able to research only

the former Douglas Company’s involvement in the aerodynamic development of

its products.

Donald W. Douglas founded the company that bore his name in 1920, and

the small enterprise quickly rose to prominence when it helped initiate the onset

of the airplane design revolution with its introduction of the pioneering DC series

of transports in 1933. Douglas employed such leading aeronautical engineers as

James H. “Dutch” Kindelberger, John K. Northrop, and Edward H. Heinemann.
Series Bibliographic Essay: Days on the Wing liii

During World War II, the company produced the A-20 Havoc and A-26 Invader

light bombers, the C-47 Skytrain and C-54 Skymaster transports, and the TBD

Devastator and SBD Dauntless naval aircraft. The Cold War era saw it manufacture

the military aircraft A4D Skyhawk and C-17 Globemaster III, the experimental

high-speed research aircraft of the D-558 series and the X-3 Stiletto, and the commercial airliners MD-90 and MD-11.

The Boeing Company’s Historical Archives at Long Beach, California, maintain

primarily the corporate memory of the Douglas Aircraft Company.44 Archival

materials housed there include internal correspondence, engineering data, photographs, press releases, GALCIT wind tunnel reports, personal papers, the company

newspaper Airview, and files organized by model number and subject. A collection

that proved crucial to the success of the documentary history was the group of

nine boxes containing the professional papers of Richard T. Cathers, who served

as chief of the Advanced Design Group at McDonnell Douglas from the 1970s to

the 1980s. Cathers’s materials included documents related to developmental

work on commercial airliners such as the DC-10, proposed SST and HSCT aircraft,

and STOL transports.

The N. Paul Whittier Aviation Library and Archives of the San Diego Aerospace

Museum preserves the history of the various incarnations of two other significant

West Coast aircraft manufacturers, Convair and Teledyne Ryan.45 The museum

holds the surviving papers of Consolidated-Vultee and Convair from the 1930s to

the 1960s and Ryan Aircraft and Teledyne Ryan from 1925 to 1960. These records

are organized by aircraft project and are in the form of scrapbooks, technical reports,

project correspondence, letters, memoranda, and GALCIT tests. The Convair

files were especially helpful in illuminating the aerodynamic development of highlift devices and big aircraft, primarily the B-24 and the B-36. There were also

records related to the development of the jet-powered XF2Y Sea Dart seaplane

interceptor; the VTOL XFY-1 Pogostick; and the Convair 240, 340, 440, 880, and

990 series airliners. The Ryan scrapbooks cover the development of the NYP

Spirit of St. Louis, the Fireball FR-1 hybrid jet-piston engine aircraft, the Dragonfly

YO-51 STOL observation plane, the X-13 Vertijet and Vertiplane V/STOL projects,

and the ducted-fan SV-5A and SV-5B. The museum also maintains extensive subject

files, which include entries on “aerodynamics” and “wings.”

Another useful collection found at the San Diego Aerospace Museum was of

the papers of Edward H. Heinemann (1908–1991), a prolific aircraft designer

44 Historical Archives, The Boeing Company, 3855 Lakewood Boulevard, Mail Code D036-0038,

Long Beach, CA 90846.

45 San Diego Aerospace Museum Archives, 2001 Pan American Plaza, Balboa Park, San Diego, CA

92101-1636, and at http://www.aerospacemuseum.org/library.htm
liv The Wind and Beyond: Volume 1

46 Henry Ford Museum, Archives and Research Library, Dearborn, MI 48121, and at http://www.hfmgv.org/

research/index.html

47 Missouri Historical Society Archives, Jefferson Memorial Building/Forest Park, St. Louis, MO

63112-1099, and at http://www.mohistory.org/

who primarily worked for the Douglas Aircraft Company. Heinemann was personally

responsible for the design of over twenty aircraft, which included the SBD

Dauntless, A-20 and A-26 bombers, A-1 Skyraider, F4D Skyray, A4 Skyhawk, and

D-558 Skystreak. Twelve boxes, ranging from 1926 to 1986, include correspondence;

biographical articles; and materials related to Heinemann’s designs, patents,

speeches, and involvement in specific aircraft projects.

Back in the country’s heartland, the Henry Ford Museum and Greenfield Village

Archives in Dearborn, Michigan, also contributed to our project. There, we found

records documenting Henry Ford’s and the Ford Motor Company’s involvement

in aeronautics from 1925 to 1936.46 Interested in doing for aviation what he had

already succeeded in doing for the automobile industry, Henry Ford bought the

Stout Metal Airplane Company and its idea for an all-metal airplane; he hoped

this would be the foundation for his new aviation enterprise. The Stout Metal

Airplane Company Collection, with some ninety linear feet of records in 169 boxes,

documents Ford’s earliest activities and their precursors. The internal correspondence,

technical reports, and photographs pertaining to the highly successful Tri-Motor

transport proved the most illustrative from the standpoint of aerodynamic development during the airplane design revolution. Another valuable resource found

at the Henry Ford Museum and Greenfield Village Archives was the oral history

of Harold Hicks, the engineer behind the development of the Ford Tri-Motor.

We also visited the Missouri Historical Society Archives in St. Louis, Missouri.

It maintains records pertaining to regional involvement in aviation, some of

which relates to aerodynamic development.47 Under the Graeco-Byzantine dome

of the renovated Historic United Hebrew Temple at Forest Park, researchers can

evaluate the papers of Lloyd Engelhardt (1905–1973), who served from 1924 to

1970 as an aeronautical engineer for the Curtiss-Wright Corporation, McDonnell

Aircraft Corporation, and McDonnell Douglas Corporation. The approximately

seven linear feet of materials include Engelhardt’s engineering papers for specific airplanes; inter-office memoranda; and published primary articles on V/STOL,

supersonic and hypersonic design, and commercial airliners.

Academic Sources

Along with the governmental, military, and industrial archives we visited in

the course of our project, we also sought to identify significant materials located
Series Bibliographic Essay: Days on the Wing lv

in the libraries and archives of America’s universities. We soon realized that one

of the most important academic collections to examine was at the California

Institute of Technology (Caltech) in Pasadena, California. 

The philanthropic Guggenheim Fund for the Promotion of Aeronautics catapulted the Caltech to a preeminent position within the aeronautical community

in the late 1920s, a position the institution retains today. The institute’s archives

maintain materials related to key individuals associated with the university’s aeronautical engineering program and the operation of the GALCIT.48 Organized by

individual collection, these papers include fifteen linear feet of the personal and

professional correspondence, government files, manuscripts, technical papers,

and personal diaries of Dr. Clark B. Millikan; a twenty-page oral history along

with the papers for the 1928–1934 period of Dr. Arthur E. Raymond, equaling

approximately one linear foot; and the two linear feet of oral history and papers

from 1928–1974 of Dr. Arthur L. Klein. Perhaps the most meaningful collection

at Caltech is the eighty-one linear feet of Theodore von Kármán’s 145,000 pages

of letters, scientific manuscripts, reports, unpublished speeches, and lecture notes

that span from the 1880s to 1960. GALCIT and its aeronautical library closed in

the early 1990s. The library’s voluminous collection of wind tunnel test reports of

specific aircraft was distributed among members of the aerospace industry in lieu

of complete disposal. 

Our research also took us to The University of Texas at Dallas History of

Aviation Collection at The University of Texas at Dallas Eugene McDermott

Library. There we found an archive containing over 200 private collection items

and 2.5 million items pertaining to aviation history.49 Of particular interest to

aeronautical researchers is the library’s Lighter-Than-Air Collection. Included in

this are the Rosendahl Collection, with almost 350 boxes of dirigible and blimp

materials, and the Robinson Collection, which contains forty-five boxes of materials dealing with dirigible operations and, surprisingly, also with B-58 bomber

development. The General Aviation Collection includes two boxes of personal

papers and documents regarding Edwin A. Link and Link flight trainers, as well

as other documents dealing with general aviation, but few of these are directly

related to aerodynamics. Good finding aids are available.

48 California Institute of Technology, Institute Archives, Mail Code 015A-74, Pasadena, CA 91125,

and at http://broccoli.caltech.edu/~archives/

49 University of Texas at Dallas, History of Aviation Collection, Eugene McDermott Library, Special

Collections, P.O. Box 830643, Richardson, TX 75083-0643, and at http://www.utdallas.edu/

library/special/aviation/
lvi The Wind and Beyond: Volume 1

50 The Floyd L. Thompson Technical Library, Langley Research Center, Hampton, VA 23681-0001.

51 NASA Center for Aerospace Information Technical Report Server, http://www.sti.nasa.gov/RECONselect.html

52 NACA Report Server, http://naca.larc.nasa.gov/

53 NASA Technical Report Server, http://techreports.larc.nasa.gov/cgi-bin/NTRS

54 Air University Library, 600 Chennault Circle, Building 1405, Maxwell Air Force Base, AL 36112-6424,

and at http://www.au.af.mil/au/aul/aulv2.htm

55 Auburn University Libraries, 231 Mell Street, Auburn University, AL 36849-5606, and at

http://www.lib.auburn.edu/

Primary Sources—Published

In addition to the primary archival and manuscript material that was central

to our documentary history, our project team also consulted a large number of

published primary sources in the form of articles, reports, and memoranda from

national and international agencies, trade groups, and the popular aviation

media. The team found these materials at three major libraries. The Floyd L.

Thompson Technical Library at NASA Langley Research Center holds complete

series of the major NACA and NASA publications—Technical Report (TR),

Technical Note (TN), Technical Memorandum (TM), Advanced Confidential

Report (ACR), and the Wartime Confidential Report (WCR).50 Several of these

publications, or selections from them, are reproduced in the documentary collection to follow. The Thompson library also maintains a comprehensive card-file

index to all types of aeronautical literature that dates back to the early days of the

NACA; much of this has not been computerized and is therefore not available

online. Most of these publications, such as professional papers generated by the

American Institute of Aeronautics and Astronautics (AIAA) and the North

Atlantic Treaty Organization’s (NATO’s) Advisory Group for Aircraft Research

and Development (AGARD), are accessible through the library system. 

An enormous amount of NACA/NASA information has become increasingly

available via the Internet. The NASA Center for Aerospace Information (CASI)

Technical Report Server,51 the NACA Report Server,52 and the NASA Technical

Report Server53 provide full-text FTP reproductions of major technical documents. At a certain point, all NACA/NASA publications should be available online

and will be an extraordinary resource of research into the history of aeronautics

and space exploration.

The Air University Library (AUL) at Maxwell Air Force Base, Alabama,54 and

the Auburn University Library, Auburn, Alabama,55 are both outstanding repositories for primary aeronautical periodicals and secondary works. These libraries

possess full or partial series of the various incarnations of Aviation Week and Space
Series Bibliographic Essay: Days on the Wing lvii

Technology, Journal of the Royal Aeronautical Society, Aero Digest, Flight, and The

Aeroplane as well as publications from professional societies such as the Society of

Automotive Engineers, the American Society of Mechanical Engineers, and the

AIAA. The Auburn University Interlibrary Loan Office provided access to materials that were not otherwise available in a timely and efficient manner.

Naturally, our project benefited from considerable documentation pertaining to the achievement of the Wright Brothers. In much the same spirit of this

documentary history, Marvin W. McFarland edited The Papers of Wilbur and Orville

Wright, Including the Chanute-Wright Letters and Other Papers of Octave Chanute. This

work from 1953 reproduced seminal documents from the development of the

first practical heavier-than-air aircraft.56

An individual who was intimately connected with several of the successful

aerodynamics programs at Langley was Fred E. Weick. His memoirs, From the

Ground Up: The Autobiography of an Aeronautical Engineer, co-written by James R.

Hansen, provide remarkable insights into the story of early aeronautical development in the United States that are not just associated with the NACA or Langley,

but with the navy and the aircraft industry as well.57 Weick went on to successful

careers in academia and industry and his autobiography illuminates those

aspects of his career as well.

One of the most prolific and important aerodynamicists of the twentieth century was Theodore von Kármán. As noted in our introduction, von Kármán’s

autobiography, The Wind and Beyond: Theodore von Kármán, Pioneer in Aviation and

Pathfinder in Space (co-written with Lee Edson) inspired our study in many ways,

including our choice of an overall title.58

Because our project focused on the history of aerodynamics in America and

not the world—and because our budget would not have allowed it anyway—we

did very little research outside of the United States. Wanting to place American

developments in global context, we did review a significant amount of secondary

literature related to the worldwide story and also located a number of nonAmerican (mostly European) reports and articles, some of which are reproduced

in this study. We did take the opportunity to explore the contents of one

European library, however. The library of the Royal Aeronautical Society (RAeS)

in London provided valuable information on the development of the early wind

56 Marvin W. McFarland, ed., The Papers of Wilbur and Orville Wright,Including the Chanute-Wright

Letters and Other Papers of Octave Chanute (New York, NY: McGraw-Hill, 1953).

57 Fred E. Weick and James R. Hansen, From the Ground Up: The Autobiography of an Aeronautical

Engineer (Washington, DC: Smithsonian Institution Press, 1988).

58 Theodore von Kármán with Lee Edson, The Wind and Beyond: Theodore von Kármán, Pioneer in

Aviation and Pathfinder in Space (Boston and Toronto: Little, Brown and Company, 1967).
lviii The Wind and Beyond: Volume 1

59 The Royal Aeronautical Society, 4, Hamilton Place, London, W1V 0BQ, United Kingdom, and at

http://www.raes.org.uk/

60 NASA Histories Online, http://www.hq.nasa.gov/office/pao/History/online.html

61 John D. Anderson, Jr., A History of Aerodynamics and Its Impact on Flying Machines (Cambridge, MA:

Cambridge University Press, 1997).

tunnel, primarily the activities of society members Francis Wenham and Horatio

Phillips in the late nineteenth century. The RAeS is one of the oldest institutions

devoted to aeronautical and aerospace engineering, and it maintains the oldest

library in the world dedicated to the study of aeronautics and astronautics. Its

collection includes all of the society’s earliest records, dating back to its first

meeting in 1866. The early Annual Reports are a goldmine of papers containing

the thoughts and ideas of prominent European researchers in the field. Finding

aids and excellent assistance are available, but access for non-RAeS members is

expensive, 10£ per day.59

Secondary Sources

The project team looked to the work of other historians and scholars not

only to formulate our research plan but also to inform our overall perspective.

The topics, themes, and interpretations offered in these volumes represent our

collective reflection upon what has become a vigorous field of aerospace history.

As a result, a growing body of substantial research into the history of flight and

its technical development has guided us through our deliberations. Much of this

work has been produced with the help of the NASA History Office. Since establishment in 1959, this office has sponsored a steady stream of important historical works discussing NACA/NASA’s involvement in the development of aeronautics and space. Many of these works are now out of print, but are available

online.60 Information on how to access them and other resources created by the

NASA History Office records are provided in footnotes at appropriate points

within this bibliographical essay.

But many fine works in aerospace history have come from places other than

NASA. Products of rigorous independent scholarship, these works have appeared in

books and articles published by academic and commercial presses. One of the most

fundamental studies that we utilized in our project was John D. Anderson, Jr.’s A History

of Aerodynamics and Its Impact on Flying Machines, published by Cambridge

University Press in 1997. Anderson’s was the first work of its kind to directly address

the emerging practice of aerodynamics from the nineteenth century to the present.61 Heavily footnoted and written in a context that benefits both aerodynamic
Series Bibliographic Essay: Days on the Wing lix

practitioners and historians, we viewed this work as our main point of departure. It

was our goal that our volumes would read profitably side-by-side with Anderson’s.

Lawrence K. Loftin, Jr.’s Quest for Performance: The Evolution of Modern Aircraft62

helped us enormously to understand some of the arcane aspects of aircraft engineering and aerodynamic design. His book also aided us in identifying, classifying, and describing the major eras in heaver-than-air powered flight. Similarly,

The Technical Development of Modern Aviation,

63 by Ronald Miller and David Sawers,

assisted us by addressing aerodynamic issues within the overall system of the airplane. The essays by John D. Anderson, Jr., James R. Hansen, Richard K. Smith,

and Terry Gwynn-Jones that appeared in John T. Greenwood’s edition of

Milestones of Aviation elaborated on different technological trends in aeronautics

crucial to aerodynamic development.64 Walter G. Vincenti’s What Engineers Know

and How They Know It: Analytical Studies from Aeronautical History,

65 challenged us to

apply epistemological and sociological notions to what we were discovering in the

empirical evidence. A general work that was immensely valuable to the less technically literate in our group (and thus to any nonspecialist’s understanding of the

mechanics of flight) was Theodore A. Talay’s Introduction to the Aerodynamics of Flight.

66

In our study of the Wrights, we placed tremendous value on the work of the

National Air and Space Museum’s Dr. Tom D. Crouch, the world’s leading scholar

of the early flight period. In A Dream of Wings: Americans and the Airplane,

1875–1905 and The Bishop’s Boys: A Life of Wilbur and Orville Wright, Crouch has

brilliantly recreated the international and personal environment in which the

Wrights developed their aircraft.67 Another major work that deserves special consideration is NASM’s Peter L. Jakab’s book, Visions of a Flying Machine: The Wright

Brothers and the Process of Invention, which successfully tackles the Wrights’ creative

engineering approach to solving the design challenges they faced.68

62 Lawrence K. Loftin, Jr., Quest for Performance: the Evolution of Modern Aircraft (Washington, DC:

NASA SP-468, 1985), http://www.hq.nasa.gov/office/pao/History/SP-468/cover.htm

63 Ronald Miller and David Sawers, The Technical Development of Modern Aviation, (New York, NY:

Praeger, 1970).

64 John T. Greenwood, ed., Milestones of Aviation (New York, NY: Macmillan, 1989).

65 Walter G. Vincenti, What Engineers Know and How They Know It: Analytical Studies from Aeronautical

History (Baltimore, MD: Johns Hopkins University Press, 1990).

66 Theodore A. Talay, Introduction to the Aerodynamics of Flight (Washington, DC: NASA SP-367, 1975),

http://history.nasa.gov/SP-367/cover367.htm

67 Tom D. Crouch, A Dream of Wings: Americans and the Airplane, 1875–1905 (Washington, DC:

Smithsonian Institution Press, 1989) and The Bishop’s Boys: A Life of Wilbur and Orville Wright (New

York, NY: W.W. Norton and Co., 1989).

68 Peter L. Jakab, Visions of a Flying Machine: The Wright Brothers and the Process of Invention

(Shrewsbury, England: Airlife, 1990).
lx The Wind and Beyond: Volume 1

69 Roger E. Bilstein, Orders of Magnitude: A History of the NACA and NASA, 1915–1990 (Washington,

DC: NASA SP-4406, 1989), http://www.hq.nasa.gov/office/pao/History/SP-4406/cover.html

70 Alex Roland, Model Research: The National Advisory Committee for Aeronautics, 1915–1958, 2 vols.

(Washington, DC: NASA SP-4103, 1985).

71 George W. Gray, Frontiers of Flight: The Story of NACA Research (New York, NY: Alfred A. Knopf,

1948).

72 James R. Hansen, Engineer in Charge: A History of the Langley Aeronautical Laboratory, 1917–1958

(Washington, DC: NASA SP-4305, 1987) and Spaceflight Revolution: NASA Langley Research Center

from Sputnik to Apollo (Washington, DC: NASA SP-4308, 1995).

General histories of the NACA and NASA proved valuable to the conceptualization of our documentary project. A fine overall survey of the two organizations, including coverage of their research commitment to aeronautics, is Roger

E. Bilstein’s Orders of Magnitude: A History of the NACA and NASA, 1915–1990.

69

There are two important histories that focus on the NACA specifically as well.

Alex Roland’s history, Model Research: The National Advisory Committee for

Aeronautics, 1915–1958, provides a useful and provocative critique of the NACA

style of research.70 The fact that our work questions the validity of many of

Roland’s interpretations does not detract from the overall esteem we have for his

insightful, shrewdly argued book. 

A work that we include here as a secondary source but in truth serves more

usefully as a primary document is George W. Gray’s 1948 book, Frontiers of Flight:

The Story of NACA Research. Readers will find that we have used it primarily as the

latter, reproducing selections from it as actual documents. The book does celebrate the NACA’s achievements, especially in regard to the Committee’s contributions to the outcome of World War II.71 But Gray’s technical discussions are so

exceptional in communicating difficult engineering concepts and activities to a

lay readership that we have incorporated them as a referenceænot as propaganda in the service of the NACA’s historical reputation. 

No single body of work underpins our entire study more than the histories

of NACA/NASA Langley Research Center provided by James R. Hansen. Langley

has been one of the epicenters—some might even argue the epicenter—of

American aerodynamics research since the 1920s, and thus its history informed

our study throughout. Hansen’s two books, Engineer in Charge: A History of the

Langley Aeronautical Laboratory, 1917–1958 and Spaceflight Revolution: NASA

Langley Research Center from Sputnik to Apollo,

72 examine the nature of aerodynamics research activities at Langley. The books cover the laboratory’s establishment

in 1917 through the transition to space and into the 1960s—with thoughts on

what has happened beyond and into the 1990s. Hansen’s goal was to present

more than just an institutional history of an important aeronautics research facility.
Series Bibliographic Essay: Days on the Wing lxi

In these books, he more broadly interprets the events within a government

research laboratory devoted to a technological development. As director of our

documentary project, he worked to expand—and to correct—some of the coverage

he provided in his two-volume study. For example, he delved into the history of NACA/

NASA research on helicopters and rotary-wing aircraft, mainly to correct his previous neglect of that topic. An excellent illustrated history of Langley based largely

on Hansen’s books is James Schultz’s Winds of Change: Expanding the Frontiers of

Flight, Langley Research Center’s Seventy-Five Years of Accomplishment, 1917–1992.

73

After establishment in 1940, NACA Ames Aeronautical Laboratory (later

renamed NASA Ames Research Center) became an important center for aerodynamics research, one that directly benefited from the high concentration of aviation manufacturers on the West Coast. Over the past thirty years, considerable

effort has been made to document the Ames contribution to aeronautics. Edwin

P. Hartman, a NACA/NASA official and leading aeronautical engineer and educator, contributed the first appraisal of the center’s activities in Adventures in

Research: A History of Ames Research Center, 1940–1965.

74 Elizabeth A. Muenger

provided another detailed account in Searching the Horizon: A History of Ames

Research Center, 1940–1976.

75 The latest update, Atmosphere of Freedom: Sixty Years

at the NASA Ames Research Center, by Glenn E. Bugos, focuses on the history of the

center during the last quarter of the twentieth century.76

One of the more important research programs conducted at the Ames

Research Center has concerned Vertical and Short Takeoff and Landing

(V/STOL) aircraft. In the last section of Volume 3 of our documentary history, we

study the history of V/STOL research as it has related to helicopter and other

rotary-wing aircraft development, as well as the NACA/NASA role in that history.

Readers will find that one type of modern rotary-wing aircraft, the tilt rotor, has

been a pet subject for NASA research, especially at Ames laboratory. We will make

significant use of a 2000 NASA publication on tilt rotor development entitled The

History of the XV-15 Tilt Rotor Research Aircraft: From Concept to Flight, authored by

three Ames researchers who have worked prominently in this field.77 Selections

from this book will also be used as part of our documentary story. A recent book

73 James Schultz, Winds of Change: Expanding the Frontiers of Flight, Langley Research Center’s SeventyFive Years of Accomplishment, 1917–1992 (Washington, DC: NASA, 1992).

74 Edwin P. Hartman, Adventures in Research: A History of Ames Research Center, 1940–1965

(Washington, DC: NASA SP-4302, 1970).

75 Elizabeth A. Muenger, Searching the Horizon: A History of Ames Research Center, 1940–1976

(Washington, DC: NASA SP-4304, 1985).

76 Glenn E. Bugos, Atmosphere of Freedom: Sixty Years at the NASA Ames Research Center (Washington,

DC: NASA SP-2000-4314). 
lxii The Wind and Beyond: Volume 1

77 Martin D. Maisel, Demo J. Giulianetti, and Daniel C. Dugan, The History of the XV-15 Tilt Rotor

Research Aircraft: From Concept to Flight (Washington, DC: NASA SP-2000-4517, NASA Monographs

in Aerospace History, No. 17, 2000).

78 E. K. Liberatore, Helicopters Before Helicopters (Malabar, FL: Krieger Publishing Co., 1998). 

79 Richard P. Hallion, On the Frontier: Flight Research at Dryden, 1946–1981 (Washington, DC: NASA

SP-4303, 1984), http://www.dfrc.nasa.gov/History/Publications/SP-4303/

80 Lane E. Wallace, Flights of Discovery: An Illustrated History of the Dryden Flight Research Center

(Washington, DC: NASA SP-4309, 1996).

81 Michael H. Gorn, Hugh L. Dryden’s Career in Aviation and Space (Washington, DC: NASA, NASA

Monographs in Aerospace History, No. 5, 1996), http://www.dfrc.nasa.gov/History/Publications/

Monograph_5/

82 J.D. Hunley, ed., Toward Mach 2: The Douglas D-558 Program (Washington, DC: NASA SP-4222,

1999), http://www.dfrc.nasa.gov/History/Publications/D-558/

83 R. Dale Reed, Wingless Flight: The Lifting Body Story (Washington, DC: NASA SP-4220, 1998),

http://www.dfrc.nasa.gov/History/Publications/WinglessFlight/; Milton O. Thompson and Curtis Peebles,

Flying Without Wings: NASA Lifting Bodies and the Birth of the Space Shuttle (Washington, DC:

Smithsonian Institution Press, 1999).

that proved tremendously useful for our discussion of helicopter development

was Eugene K. Liberatore’s Helicopters Before Helicopters.

78 So taken were we with

the conceptually stimulating epilogue to this book that we reproduced it as the

final document in that section. 

The highly successful flight research programs at the NACA’s High-Speed

Flight Research Station at Muroc, California, (later renamed NASA Dryden

Flight Research Center) have produced many of the most memorable moments

in aviation history, including the flight of the Bell XS-1, which broke the mythical

“sound barrier” in October 1947. Historian Richard P. Hallion provides an

exhaustive survey of the high-flying, high-speed activities over the Mojave Desert

in On the Frontier: Flight Research at Dryden, 1946–1981.

79 A helpful companion to

Hallion’s work is Lane E. Wallace’s Flights of Discovery: An Illustrated History of the

Dryden Flight Research Center.

80 Michael H. Gorn documents the career of a former

director of the center and the man for whom the center is now named in Hugh L.

Dryden’s Career in Aviation and Space.

81 An important part of Gorn’s biography is

the inclusion of facsimile reproductions of key documents from Dryden’s career.

Some of the flight research programs conducted at Dryden have garnered

their own histories. J. D. Hunley’s edition of Toward Mach 2: The Douglas D-558

Program documents the joint NACA–navy quest to break the sound barrier in the

late 1940s.82 Two notable histories of lifting bodies come from former NASA

employees. R. Dale Reed, a former Dryden engineer, and Milton O. Thompson

recount their involvement in Wingless Flight: The Lifting Body Story and Flying

Without Wings: NASA Lifting Bodies and the Birth of the Space Shuttle, respectively.83
Series Bibliographic Essay: Days on the Wing lxiii

Computers Take Flight: A History of NASA’s Pioneering Digital Fly-by-Wire Project documents an important episode in the refinement of aircraft control systems.84

Albert L. Braslow’s A History of Suction-Type Laminar-Flow Control with Emphasis on

Flight Research addresses an ongoing effort at Dryden to further refine aerodynamic efficiency through the application of new technology.85 We found Braslow’s

insights extremely useful as we endeavored to accept the esoteric nature of the

subtle aerodynamic conditions in the so-called “boundary layer.” 

Often overlooked is the fact that women played (and continue to play) a part

in the success of aerodynamics in the United States. Sheryll Goecke Powers, in

Women in Flight Research, tells the story of the unnamed women who in the early

days of Dryden—and at other NACA laboratories before them—worked as

“human computers” and were responsible for processing and analyzing wind tunnel and flight research data.86

Several important works addressing the development of hypersonic aerodynamics in the United States informed our study. In Hypersonics Before the Shuttle: A

Concise History of the X-15 Research Airplane, Dennis R. Jenkins analyzes the highly

successful flight research program of the late 1950s and 1960s that, in key

respects, led technologically to the Space Shuttle program of the 1970s and

beyond.87 Wendell H. Stillwell’s X-15 Research Results with a Selected Bibliography

provides an analysis and exhaustive listing of reports and other “lessons learned”

materials drawn from the X-15 program.88 In “Transiting from Air to Space: The

North American X-15,” which appeared in The Hypersonic Revolution: Case Studies

in the History of Hypersonic Technology, Robert S. Houston, Richard P. Hallion, and

Ronald G. Bostonis detail many crucial aspects of our country’s prototype transatmospheric vehicle or “spaceplane.”89 A definitive source listing for the Space Shuttle

appears in Roger D. Launius and Aaron K. Gillette’s Toward a History of the Space

84 Computers Take Flight: A History of NASA’a Pioneering Digital Fly-by-Wire Project (Washington, DC:

NASA SP-2000-4224), http://www.dfrc.nasa.gov/History/Publications/f8ctf/

85 Albert L. Braslow, A History of Suction-Type Laminar-Flow Control with Emphasis on Flight Research

(Washington, DC: NASA, NASA Monographs in Aerospace History, No. 13, 1999).

86 Sheryll Goecke Powers, Women in Flight Research (Washington, DC: NASA, NASA Monographs in

Aerospace History, No. 6, 1997), http://www.dfrc.nasa.gov/History/Publications/WIFR/contents.html

87 Dennis R. Jenkins, Hypersonics Before the Shuttle: A Concise History of the X-15 Research Airplane

(Washington, DC: NASA SP-2000-4518, NASA Monographs in Aerospace History, No. 18). 

88 Wendell H. Stillwell, X-15 Research Results with a Selected Bibliography (Washington, DC: NASA SP-60,

1965), http://www.hq.nasa.gov/office/pao/History/SP-60/cover.html

89 Bolling Air Force Base, The Hypersonic Revolution: Case Studies in the History of Hypersonic Technology,

3 vols. (Washington, DC: Air Force History and Museums Program, 1998), http://www.hq.nasa.gov/

office/pao/History/hyperrev-x15/cover.html
lxiv The Wind and Beyond: Volume 1

90 Roger D. Launius and Aaron K. Gillette, Toward a History of the Space Shuttle: An Annotated

Bibliography (Washington, DC: NASA, NASA Monographs in Aerospace History, No. 1, 1992),

http://www.hq.nasa.gov/office/pao/History/Shuttlebib/cover.html

91 Donald D. Baals and William R. Corliss, The Wind Tunnels of NASA (Washington, DC: NASA SP440, 1981), http://www.hq.nasa.gov/office/pao/History/SP-440/cover.htm

92 Alan Pope, Wind-Tunnel Testing, 2d ed. (New York, NY: John Wiley & Sons, 1954).

93 Jewel B. Barlow, William H. Rae, Jr., and Alan Pope, Low-Speed Wind Tunnel Testing, 3d ed. (New

York, NY: John Wiley & Sons, 1999).

94 Eugene E. Bauer, Boeing in Peace and War (Enumclaw, WA: TABA Publishing, 1991).

95 John V. Becker, The High Speed Frontier: Case Histories of Four NACA Programs, 1920–1950

(Washington, DC: NASA SP-445, 1980), http://www.hq.nasa.gov/office/pao/History/SP-445/cover.htm

96 Pamela Mack, ed., From Engineering Science to Big Science: The NACA and NASA Collier Trophy

Research Project Winners (Washington, DC: NASA SP-4219, 1998).

Shuttle: An Annotated Bibliography.

90 All of these works gave us a framework for our

profile of development in hypersonic aerodynamics.

One of the keys to the success of NASA, and the NACA before it, has been

the ability to design and construct world-class facilities in support of pioneering

research programs. In The Wind Tunnels of NASA, veteran NACA/NASA wind tunnel

engineer Donald D. Baals and technical writer William R. Corliss provide the

standard reference for NASA’s preeminent research tools.91 Those looking for

detailed technical information on the operation and use of wind tunnels may find

Alan Pope’s Wind-Tunnel Testing useful.92 Pope later collaborated with Jewel B.

Barlow and William H. Rae, Jr., on Low-Speed Wind Tunnel Testing,

93 and he coauthored High-Speed Wind Tunnel Testing with Kennith L. Goin.94 These books contain a wealth of information on the ways engineers have used wind tunnels to

develop aircraft designs over several decades.

Two other histories highlight the correlation between advanced research

tools and successful research programs. The High Speed Frontier: Case Histories of

Four NACA Programs, 1920–1950, was written by NACA/NASA engineer John V.

Becker, one of John Stack’s chief associates and the man who many regard as the

“father of the X-15.” In his book, Becker offers both first-hand and historical

insights into the story of the NACA’s work in the 1930s, 1940s, and 1950s on

high-speed airfoils, propellers, cowlings, internal-flow systems, and transonic

wind tunnels.95 An anthology of scholarly articles entitled From Engineering Science

to Big Science: The NACA and NASA Collier Trophy Research Project Winners, edited

by Clemson University historian of technology Pamela Mack, cover the processes

by which NACA and NASA scientists and engineers successfully employed wind

tunnels, aerodynamics, and other types of experimental tools and theoretical

methods to generate successful research programs.96
Series Bibliographic Essay: Days on the Wing lxv

Two biographical studies explore von Kármán’s role in the American academic

and scientific community. The first of these, Paul A. Hanle’s Bringing Aerodynamics

to America, examines the dramatic steps taken by proponents of American aeronautics to transfer European knowledge of aerodynamics from Ludwig Prandtl

and his talented group of students at the University of Göttingen to the United

States. This initiative led to the importation of two of Prandtl’s prize students: von

Kármán to Caltech, and Max M. Munk to the NACA.97 The work of both of these

individuals is covered in our text and documents to come. The second of the biographies, The Universal Man: Theodore von Kármán’s Life in Aeronautics, by Michael

H. Gorn, provides another important picture of von Kármán’s career as an aerodynamicist and aeronautical research leader.98 Whereas Hanle’s book concentrates

on the era of the 1920s and 1930s, Gorn’s study spends more time looking at von

Kármán’s career during and after World War II to his death in the early 1960s.

No single definitive history of the U.S. Air Force’s commitment to aeronautical research exists; one is badly needed. Works featuring research from the bountiful Sarah Clark collection in the National Archives have started to appear, but

none of them discuss the American military’s involvement in aerodynamic development. In From Huffman Prairie to the Moon: The History of Wright-Patterson Air

Force Base, Lois E. Walker and Shelby E. Wickam provide a valuable introduction

to the aeronautical research activities that have taken place at the army and—

later—air force installations near Dayton, Ohio.99

Project members found value in several secondary works on the history of the

Boeing Company. Boeing Historical Services, the unit that manages the firm’s

historical archives, published A Brief History of the Boeing Company, which provides

a useful and condensed introduction to the individuals, aircraft, and programs of

Boeing, North American Rockwell, and McDonnell Douglas.100 In Boeing’s Ed

Wells, Mary Wells Geer presents insightful biographical reminiscences of her engineer father, which highlight Boeing’s important activities in aircraft design and

manufacture during the 1940s.101 Two popular histories, Robert J. Serling’s Legend

and Legacy: The Story of Boeing and Its People and Harold Mansfield’s Vision: The

Story of Boeing, present the company in a very favorable light while providing a

97 Paul A. Hanle, Bringing Aerodynamics to America (Cambridge, MA: MIT Press, 1982).

98 Michael H. Gorn, The Universal Man: Theodore von Kármán’s Life in Aeronautics (Washington, DC:

Smithsonian Institution Press, 1992).

99 Lois E. Walker and Shelby E. Wickam, From Huffman Prairie to the Moon: The History of WrightPatterson Air Force Base (Washington, DC: General Printing Office, 1986).

100 A Brief History of the Boeing Company (Seattle, WA: Boeing Historical Services, 1998).

101 Mary Wells Geer, Boeing’s Ed Wells (Seattle, WA: University of Washington Press, 1992).
lxvi The Wind and Beyond: Volume 1

102 Robert J. Serling, Legend and Legacy: The Story of Boeing and Its People (New York, NY: St. Martin’s

Press, 1992); Harold Mansfield, Vision: The Story of Boeing (New York, NY: Popular Press, 1966).

103 Peter M. Bowers, Boeing Aircraft Since 1916 (Annapolis, MD: Naval Institute Press, 1989; reprint,

New York, NY: Funk and Wagnalls, 1966).

104 Eugene E. Bauer, Boeing in Peace and War (Enumclaw, WA: TABA Publishing, 1991).

105 Norm Avery, North American Aircraft 1934–1998, 2 vols. (Santa Ana, CA: Narkiewisc/Thompson, 1998).

106 Ray Wagner, Mustang Designer: Edgar Schmued and the P-51 (Washington, DC: Smithsonian

Institution Press, 2000).

107 Douglas J. Ingells, The McDonnell Douglas Story (Fallbrook, CA: Aero Publishers, Inc., 1979).

108 Rene Francillon, McDonnell Douglas Aircraft Since 1920, 2 vols. (London: Putnam Aeronautical

Books, 1990).

109 Henry M. Holden, The Legacy of the DC-3 (Niceville, FL: Wind Canyon Publishing, 1997).

110 Joseph J. Corn, The Winged Gospel: America’s Romance with Aviation, 1900–1950 (New York, NY:

Oxford University Press, 1983).

basic survey of the company’s history.102 The standard reference for Boeing aircraft over the decades is Boeing Aircraft Since 1916 by Peter M. Bowers.103 Another

work we consulted was Eugene E. Bauer’s Boeing in Peace and War.104

North American Aviation and Rockwell have yet to find their historians.

Norm Avery’s two-volume North American Aircraft 1934–1998 assists readers mostly

in determining the model numbers of individual aircraft and exciting them with

stunning photographs.105 Wagner’s Mustang Designer: Edgar Schmued and the P-51

focuses on the design environment at North American in which the famous World

War II fighter gestated. Wagner also highlights the careers of contemporary fellow

designers, such as Don Berlin of Curtiss-Wright, to illustrate the existence of an

American design community.106

Two works were especially helpful in studying the history of the Douglas

Company. Douglas J. Ingells, a prolific historian of the aviation industry, in The

McDonnell Douglas Story, traces the development of two separate companies and

the path they followed after their historic merger in 1967.107 In the same format

as Bowers’s book on Boeing, Rene Francillon’s McDonnell Douglas Aircraft Since

1920 rates as the major point of departure for any serious study of the corporation’s aircraft.108 Fully half of Henry M. Holden’s The Legacy of the DC-3 delves into

the early history of Douglas and the development of the DC-1/2/3 airplanes.109

For our epilogue on thoughts about the future of flight, Joseph J. Corn’s The

Winged Gospel: America’s Romance with Aviation, 1900–1950 offered critical social

and cultural insights.110 Corn’s classic little book focuses on America’s popular

infatuation with the airplane rather than on technological enthusiasm and concepts

within the aircraft industry and the aeronautical engineering community.
Series Bibliographic Essay: Days on the Wing lxvii

Nonetheless, it provides an overarching thesis illuminating the dynamics between

American culture and ideology and American technological belief and outlook. 

Points of Departure

Despite what we feel was a rather comprehensive examination of aeronautics

libraries and archives countrywide, without question we left many stones

unturned in our endeavor to document the history of aerodynamic development

in the United States, in terms of both topics and archival facilities. There was simply

no way to visit every potentially interesting repository or engage every related

topic. For example, we recognize that more needs to be done to cover general aviation

aircraft’s aerodynamic design and to explore aerodynamics in university research.

It is our hope that our documentary collection will provoke others to add to our

research and to create collections of their own. Readers should remember, however,

that the NASA History Office contracted with Auburn University to document

the history of aerodynamics in America as it related most specifically to the contributions made by the NACA and NASA. Such a focus demanded that we emphasize

certain archives and topics, and minimize others. 

As mentioned above, one area we regret to have neglected involves general—

or private—aviation. A leading general aviation manufacturer during the period

of the airplane design revolution of the 1920s and 1930s, well known for its

“Mystery Ship” and Model R air racers, was The Travel Air Company. We had

hoped to visit the special collections and archives of Wichita State University

Library, where the papers of Walter E. Burnham and Herb Rawdon are stored.

These materials document the engineering development of Travel Air general

aviation and racing aircraft during the 1920s and 1930s.111

Given the enormous scope of our project we were not even able to cover relevant NACA/NASA materials as exhaustively as we had hoped. One set of records

we regret to have minimized involves the activities of NASA John H. Glenn

Research Center at Lewis Field in Cleveland, Ohio, and the original NACA

Aircraft Engine Research Laboratory (AERL), which later became NASA Lewis

Research Center. While primarily concerned with problems pertaining to propulsion systems, the Glenn center has sponsored numerous projects pertinent to the

relationship between aerodynamics and propulsions systems. Work in this facility’s historic icing tunnel plus many other issues certainly relate to compromised

aerodynamic integrity, a problem that has had an important impact on the study

111 Special Collections and University Archives, Wichita State University, 1845 Fairmount, Wichita,

KS, 67260-0068, and at http://www.twsu.edu/library/specialcollections/sc.html
lxviii The Wind and Beyond: Volume 1

112 History Office, Mail Stop 21-8, Glenn Research Center, 21000 Brookpark Road, Cleveland, Ohio,

44135, and at http://www.grc.nasa.gov/WWW/PAO/html/history.htm

113 Virginia P. Dawson, Engines and Innovation: Lewis Laboratory and American Propulsion Technology

(Washington, DC: NASA SP-4306, 1991), and at http://history.nasa.gov/SP-4306/sp4306.htm

114 National Archives at College Park, 8601 Adelphi Road, College Park, MD 20740-6001, and at

http://www.nara.gov/nara/dc/Archives2_directions.html

115 NARA’s National Personnel Records Center, Military Personnel Records, 9700 Page Avenue, St.

Louis, Missouri 63132-5100, and at http://www.nara.gov/regional/mpr.html

of aerodynamics for both commercial and military aircraft.112 Given our focus on

NACA/NASA contributions, we could have done more to illuminate the importance of the work done at this installation, whose work dates back to 1941. Many

of NASA Glenn’s retired administrative files rest within six boxes at NARA’s facility at Suitland, Maryland, or are still in storage at the center’s Plum Brook

Station, located on Lake Erie near Sandusky. There were also nineteen boxes of

documents (mostly speeches, talks, and papers by center authors) accessioned

from NASA Glenn to the NARA center in Dayton, Ohio, plus four additional

boxes of center records stored at the federal records center in Chicago, Illinois.

For more description of NASA Lewis’s records situation, readers should consult

Virginia P. Dawson’s Engines and Innovation: Lewis Laboratory and American

Propulsion Technology.

113

Even within NARA, the project team concentrated on documenting NACA

and NASA involvement in the development of aerodynamics as it related to

Langley, Ames, and Dryden centers. This brought us to the NARA facilities at

Philadelphia and San Bruno but not to the other NARA facilities where the Glenn

center records are kept. Our focus also took us to the NARA facility at College

Park, Maryland, where a significant, if not the largest, portion of the previously

mentioned NACA Record Group 255 exists.114

Another important collection that NARA College Park maintains is RG 342,

the Records of the United States Air Force Commands, Activities, and

Organizations. Within that organization rests the well-known Sarah Clark

Collection, named after the clerk who processed the documents in preparation

for their transfer from the air force to NARA. Officially known as the research and

development project files of the Engineering Division, Material Command of

Wright-Patterson Air Force Base in Ohio, this collection features an extensive

record of the military’s pursuit of aeronautical excellence from 1917 to 1945. The

post-1945 version of the Sarah Clark collection is located at NARA’s National

Personnel Records Center in St. Louis.115

Other facilities where our project could have profitably spent more time include

the NASA Marshall History Office in Huntsville, Alabama;116 the NARA Southeast
Series Bibliographic Essay: Days on the Wing lxix

Regional Office at East Point, Georgia, near Atlanta;117 and the Arnold Engineering

Development Center (AEDC) History Office at Tullahoma, Tennessee.118 At each

of these facilities, we are sure we could have found additional materials related to

the development of hypersonic aircraft and high-speed wind tunnels. 

✤ ✤ ✤ ✤

The preceding bibliographic essay includes references from archives,

libraries, printed materials, primary sources, and secondary literature that proved

most influential to our study. We apologize to authors of other major works in

aerospace history if we have neglected to include references to them in this essay.

Not mentioning them does not mean that we were not aware of them, or failed to

take them into account in preparation of our study. We have, in fact, cited many

other works in our footnotes. But in a project of this magnitude, there was simply

not enough time and energy on our part to locate, read, and completely digest

every last document, every last article, and every last book that may have been relevant to the development of aerodynamics in America. As detailed and voluminous as this overall study became, just in terms of documents, it still only scratches the surface of what is available out there. Somewhere, on some dusty shelf, in

someone’s file drawer, hidden in some crumpled box, or some garage container,

there are works waiting for other curious historians and scholars to discover, analyze, and interpret them. 

What we offer, in the end, is not the final or penultimate “documentary journey through the history of aerodynamics in America,” but our own unique journey along the rivers and streams running through our massive country. We invite

you to retrace our steps and see what we found, what we mapped, the detours we

took, and the locales we found most engaging. We hope you enjoy the adventure

as much as we did, and that you are equally stimulated and informed by it, even

though you may have chosen to follow a different route. We are sure to revisit this

one incredible trip over and over again as we look back through these volumes,

like a family browsing over the photo albums of their memorable cross-country

vacation to the Grand Canyon. We are relieved the journey is over, and we feel

116 George C. Marshall Space Flight Center History Office, CN22, Marshall Space Flight Center,

Alabama 35812, and at http://history.msfc.nasa.gov/

117 NARA Southeast Region (Atlanta), 1557 St. Joseph Avenue, East Point, Georgia 30344-2593, and

at http://www.nara.gov/regional/atlanta.html

118 Arnold Engineering Development Center History Office, 100 Kindel Drive, Suite B-330, Arnold

Air Force Base, Tennessee 37389-2330, and at http://candice.arnold.af.mil/aedc/history.htm; E-mail:

history@hap.arnold.af.mil
lxx The Wind and Beyond: Volume 1

thankful that our own “family,” the Auburn University project team, made it

home in one piece. We are immensely proud of the contributions we made individually and collectively to what we hope will serve, for many years to come, as a

standard reference work in the history of aeronautics.
lxxi

Biographies of Volume 1 Contributors

James R. Hansen, Professor of History at Auburn University, has written

about aerospace history for the past twenty-three years. His two-volume study of

NASA Langley Research Center—Engineer in Charge (NASA SP-4305, 1987) and

Spaceflight Revolution (NASA SP-4308, 1995)—earned critical acclaim, as did his

From the Ground Up (Smithsonian Institution Press, 1988), the life story of aviation

pioneer Fred E. Weick. His newest book, The Bird Is on the Wing (Texas A&M

University Press, 2003), explores the role of aerodynamics in the American

progress of the airplane from before the Wright brothers to the present.

Currently, Hansen is at work on the authorized biography of Neil A. Armstrong. 

D. Bryan Taylor is Instructional Technology (IT) Coordinator for the

College of Liberal Arts at Auburn University. He holds an M.A. in history from

Brigham Young University and is working on his Ph.D. in the history of technology at Auburn. 

Jeremy R. Kinney is a curator in the Aeronautics Division, National Air and

Space Museum, Smithsonian Institution. He holds a Ph.D. in the history of technology from Auburn University, with a specialization in aerospace history. Prior

to joining NASM, he served as the American Historical Association NASA Fellow

in Aerospace History. 

J. Lawrence Lee holds B.M.E., M.A., and Ph.D. degrees from Auburn

University. Following a lengthy career in mechanical engineering, Lee changed

his focus to the history of technology, where his primary interests are transportation technology and engineering issues.
lxxii The Wind and Beyond: Volume 1
1

Chapter 1

The Achievement of Flight

Success four flights Thursday morning all against twenty-one mile wind

started from level with engine power alone average speed through air

thirty-one miles longest 57 seconds inform press home Christmas.

Orville Wright telegram sent on 17 December 1903 from the lifesaving station in

Kitty Hawk, North Carolina, to his father, Bishop Milton Wright, in Dayton,

Ohio. This document announced humankind’s first successful powered flight of

a heavier-than-air flying machine. 

From Cayley’s Triple Paper to Orville Wright’s Telegram

Even in a study of NASA’s—and its predecessor agency, the NACA’s—contributions to aerodynamic development, one must begin by looking at a fruitful

pairing, not of two government agencies but of two remarkable individuals, the

Wright brothers. It was the inventive genius of Wilbur and Orville Wright, rather

than an institutional imperative, that set the stage for aviation’s astonishing technological progress in the United States and abroad during the twentieth century.

Without retracing the path from the earliest concept of the airplane to the pioneering achievement of the Wrights, readers of this volume will not be able to

truly appreciate the formative ideas from which research and development in the

field of modern aerodynamics blossomed. 

The Wrights accomplished what no one before them had the insight to recognize and tackle—they worked out a means of controlling an aircraft aerodynamically by deflecting the wing and tail surfaces themselves, as Wilbur had seen

birds do. In this respect, they were far ahead of their predecessors and contemporaries, including some of the world’s top scientists. The secret of their success

was that they learned to fly: before they ever attempted to put an engine on their

glider, and thus complete the “invention” of the airplane, they learned how to

control a flying machine in the dynamic element of the air. They learned about

the use of aerodynamic surfaces to control the airplane in a satisfactory manner

and, together with the experience they developed as pilots of their kites and gliders,

were able to fly their “powered” plane without difficulty. They were marvelously

clear and pioneering thinkers, a rare combination. As such, they deserve a place

of distinction at the beginning of any history of modern aerodynamics, especially

one published during the centennial of their great achievement.
2 Chapter 1: The Achievement of Flight

1 Charles H. Gibbs-Smith covers the pre-history of flight in Aviation: An Historical Survey (London:

HMSO, 1970).

For this first chapter in the first volume of this series, then, there is no more fitting destination than the wind-blown sands of Kitty Hawk, North Carolina, where

on 17 December 1903, the Wrights made the world’s first successful powered flight

of a heavier-than-air craft. The flight of the Wright airplane in 1903 culminated a

long, faltering search for basic aerodynamic knowledge, a winding and irregular

path that runs far back into the dawn of human experience, back even to our

ancestors’ prehistoric fascination with the flight of birds. No doubt, humankind

dreamed about flying as soon as humans began dreaming. When civilizations

arose, men and women imagined gods in the sky and gave them wings—no matter what ancient civilization one looks at, its gods could fly. The power of flight,

denied to mortals, was envisioned as an ability of immortal deities. They lived in

the heavens above; they moved across the sky in golden chariots; they soared

majestically in and above the clouds. 

While the materials needed to fabricate a craft resembling a modern hang

glider were available thousands of years ago, unquestionably one of the major

reasons that mechanical flight did not happen for millennia rested in the basic

intuitive misconception that, in order for humans to fly, we needed to imitate

birds. But exactly how did birds accomplish flight? Before modern scientific

observations with high-speed cameras and, more importantly, before the dawn of

a mathematically derived and rational theory of aerodynamics in the early nineteenth century, naked-eye observation of bird flight fostered a wrongheaded

belief in flapping wings. From the wings crafted in ancient Greek mythology by

Daedalus and Icarus to the ornithopter designed by Leonardo da Vinci during

the Renaissance, the best idea anyone could come up with was to mimic a flapping wing structure and adapt it for human use. This path to heavier-than-air

flight proved not only ignominiously unsuccessful but also often fatal. Donning

makeshift wings of wood, feathers, and cloth, a handful of foolish men in the

Middle Ages, flapping away without a whit of aerodynamic understanding,

jumped to their deaths from the tops of cathedral towers and castle walls. 

Not just popular imagination but also esoteric intellectual conceptions of the

age mystified flight rather than rationalized it. Various medieval and Renaissance

thinkers ascribed the ability of the wing to produce lift to psychic and occult

forces possessed by the birds. This view held that for humans to fly required not

some understanding and application of natural laws but rather their circumvention

through the invocation of magical powers.1

This is not to say that, from ancient times to da Vinci, there was no one who

expressed sound aerodynamic ideas. In certain basic respects, aerodynamics
From Cayley’s Triple Paper to Orville Wright’s Telegram 3

2 Aristotle expressed most of the major tenets of his natural philosophy in his Treatise on the Heavens

(De Caelo), Book I. An excellent English translation of this entire treatise (in two books) was done

by Stuart Leggat in 1995. His translation and commentary help the reader to appraise Aristotle’s

ideas in relation to the cosmologies of his predecessors. Leggat makes it clear that, while tied 

to the thinking of his day, Aristotle placed natural philosophy on a new footing, with his use of

mathematics-style demonstration and his appeal to observation rather than reliance on what were

then more standard forms of argument. John D. Anderson does a good job of interpreting

Aristotle’s significance in aerodynamics in A History of Aerodynamics and Its Impact on Flying Machines

(Cambridge, England, and New York, NY: Cambridge University Press/Cambridge Aerospace

Series, 1997), pp. 14-17. 

began in classical Greece during the fourth century B.C. with the first “scientific” observer of nature, the philosopher Aristotle. He developed a theory of motion that a

projectile such as an arrow stayed in motion because the air separated in front of the

arrow and then rapidly filled in the region behind it. According to this concept,

the arrow kept flying because of the constant application of the medium’s force in

its wake. Despite being fundamentally wrong (though it was a widely accepted theory until Galileo’s time), Aristotle’s “medium theory” represented an attempt to

explain the phenomena of flight in rational terms with the help of mental pictures of physical operations. This type of visual thinking was a crucial first pathway in the maze leading to mature understanding. 

With other aerodynamic concepts, Aristotle proved even more insightful. He

was the first thinker to elaborate on the notion of a “continuum.” In a radically

altered form, this became a basic concept of modern science, the foundation of

aerodynamic flow applications today. In his writings, one can also find physical

reasoning consistent with a concept of aerodynamic “resistance,” inversely

expressed through the appreciation that a body in motion, in Aristotle’s words,

“will move indefinitely unless some obstacle comes into collision with it.”2

None of Aristotle’s ideas prompted anyone to consider designing an airplane,

however, nor did any of the concepts developed by Archimedes, the greatest engineering mind of the Hellenistic world. Archimedes, who developed the mechanical

lever, built ingenious catapults, and created a screw device for raising water, is also

recognized as founder of the science of fluid statics. But not even Archimedes, the

author of the world’s first “Eureka” experience, ever came close to the idea of

mechanical flight. It is one thing to say that the brilliant minds of antiquity produced

concepts in the raw, like the continuum or hydrostatic pressure that contributed

to the development of aerodynamics, but quite another to say that any of them

had technological import. 

If science did not stimulate technology, maybe technology stimulated science?

One might think that something like the invention of the kite, which took place

in China around 1000 A.D., and which appeared in Europe three centuries later

in the form of the windsock, would have provoked aerodynamic thinking. Or that
4 Chapter 1: The Achievement of Flight

the understanding of basic aerodynamics improved with the design of windmills,

a powerful new machine that migrated into Western Europe from the Near East

around the late thirteenth century. But neither seems to have been the case.

History records no serious attempt to bridge the gap between the dream of flight,

the actual world of invention, and basic scientific understanding of aerodynamic

forces until the work of Leonardo da Vinci in the late fifteenth and early sixteenth

centuries. Even then nothing came of da Vinci’s thoughts. Leonardo’s precious

notebooks, encoded with his curious “mirror-like” reverse handwriting, stayed

locked up and unknown in the hands of different private collectors for 300 years. 

One wonders what might have germinated if da Vinci’s ideas had been published and widely discussed during the Scientific Revolution of the sixteenth

through eighteenth centuries. Certainly no one before da Vinci, or for three centuries after him, offered anything close to his astonishing vision of flying

machines or considered so many of the principles affecting flight. In the same era

that Christopher Columbus sailed across the Atlantic Ocean and Vasco da Gama

circumnavigated Africa, Leonardo explored his own New World: diagramming

the wing structures of birds and bats, developing streamlined shapes and aerodynamically more efficient artillery projectiles, and studying complex flow patterns in streams of water. He drew plans for an ornithopter, a parachute, and a

vague sort of helicopter. He meticulously studied the mechanics of bird flight,

and shortly before his death in 1519 he was apparently close to the breakthrough

concept that a flying machine could be made with fixed instead of flapping wings.

Perhaps most significantly, da Vinci realized that “a bird is an instrument

working according to mathematical law, an instrument which is within the capacity

of man to reproduce with all its movements.” In other words, he realized that

applied mathematics was the key not only to understanding basic problems in

nature but also to designing advanced technology. “Let no man who is not a

mathematician read the elements of my work,” he wrote. Immersed in Euclid’s

geometry and other mathematical texts, and coupling this knowledge with his

meticulous observation of natural phenomena, Leonardo came up with the first

quantitative expressions for fluid flow conditions, and then applied the same analytical

thinking about flow conditions to aerodynamic phenomena. In 1513, he wrote:

What quality of air surrounds birds in flight? The air surrounding

birds is above thinner than the usual thinness of the other air, as below

it is thicker than the same, and it is thinner behind than above in proportion to the velocity of the bird in its motion forwards, in comparison with the motion of its wings towards the ground; and in the same

way the thickness of the air is thicker in front of the bird than below,

in proportion to the said thinness of the two said airs.3
From Cayley’s Triple Paper to Orville Wright’s Telegram 5

3 Leonardo da Vinci, Codex Atlanticus Volume E, translated by R. Giacomelli, “The Aerodynamics

of Leonardo da Vinci,” Journal of the Royal Aeronautical Society 34 (1930): 1016–1038, cited in John

D. Anderson, Jr., A History of Aerodynamics (New York, NY: Cambridge University Press, 1997), p. 24.

4 On Galileo, Torricelli, Pascal, and Newton as well, see Richard S. Westfall, The Construction of

Modern Science: Mechanisms and Mechanics (New York and London: John Wiley & Sons, Inc., 1971).

5 Anderson, A History of Aerodynamics, pp. 32–37.

Considering this passage, modern aerodynamic engineer and historian John

D. Anderson concluded that Leonardo was “three centuries ahead of his time.” In

his book A History of Aerodynamics and Its Impact on Flying Machines (1997),

Anderson notes that what Leonardo contributed was “a valid description,

expressed in the technical language of the early sixteenth century, of the sources

of lift as well as pressure drag (form drag) on an aerodynamic body.” Da Vinci’s

ideas about lift and drag, however, were not disseminated until the late 1790s

when the Italian physicist Giovanni Battista Venturi discovered twelve volumes of

Leonardo’s notes in the Institute of Paris, where they had been moved by

Napoleon’s troops after the looting of the Ambrosian Library in Milan.

By that time Leonardo’s undeniable genius was no longer critical, for other

scientists between his life and Venturi’s had advanced the understanding of fluid

dynamic phenomena beyond da Vinci’s own thinking. This started with the work

of Galileo Galilei (1564–1642), who developed concepts of inertia and momentum, offered insights into the parabolic trajectory and aerodynamics of ballistic

projectiles, and deduced that aerodynamic resistance was proportional not just to

velocity, as da Vinci had understood, but also to the air density. Along with

Galileo’s work there were the pioneering hydrodynamic theories and experiments

of the Italian physicist and mathematician Evangelista Torricelli (1608–1647), the

inventor of the barometer and the first to measure air pressure, as well as the work

of Frenchman Blaise Pascal (1625–1662), who advanced new fundamental principles

about the actions of atmospheric pressure on fluid behavior.4

Later in the seventeenth century came what is referred to as “the first major

breakthrough in the evolution of aerodynamics.” This was the formulation of the

“velocity-squared law,” which states that the force on an object varies as the square

of the flow velocity; or in other words, if velocity doubles, then the force acting on

it goes up by a factor of four, not of two as Galileo and others had believed.

Derived experimentally by Edme Mariotte (1620–1684) in France and Christian

Huygens (1625–1695) in Holland, and confirmed theoretically by Isaac Newton

(1642–1727) in his Principia of 1687, the velocity-squared law lifted scientific

understanding of aerodynamics to a new level by adding a crucial, quantifiably

exact variable to the mechanical relationships defining aerodynamic force.5
6 Chapter 1: The Achievement of Flight

6 A number of fine new books and translations have added considerably to our historical and technical understanding of Isaac Newton’s contributions, notably The Principia: Mathematical Principles

of Natural Philosophy, a translation of Newton’s great work of 1687 by Julia Budenz, Anne Whitman,

and I. Bernard Cohen (Berkeley, CA: University of California Press, 1999). Other important studies that have recently appeared include Francois De Gandt and Curtis Wilson, Force and Geometry in

Newton’s Principia (Princeton, NJ: Princeton University Press, 1995); Gale E. Christianson, Isaac

Newton and the Scientific Revolution (Oxford, England: Oxford University Press, 1996); A. Rupert

Hall, Isaac Newton: Adventurer in Thought (Cambridge, MA, and New York, NY: Cambridge

University Press/Cambridge Science Biographies, 1996); Jed. Z. Buchwald and I. Bernard Cohen,

Isaac Newton and Natural Philosophy (Cambridge, MA: MIT Press/Dibner Institute Studies in the

History of Science and Technology, 2000); and David Berlinski, Newton’s Gift: How Sir Isaac Newton

Unlocked the System of the World (New York, NY: Free Press, 2000).

On the heels of the velocity-squared law came Newton’s own “sine-squared

law.” Though later shown to be flawed, this suggested a means by which to calculate the pressure distribution over a body in motion and make predictions about

its lift and drag. Newton’s three laws of motion were another major contribution

to aerodynamic understanding, especially his second law, which stated that the

time rate of change for a moving body (momentum being the product of velocity

and mass) was proportional to the force. Applied to fluid flow, this Newtonian law

provided a basic equation on which to build further aerodynamic understanding.

Other major blocks in the foundation were laid by the great Swiss mathematicians

Daniel Bernouilli (1700–1782) and Leonhard Euler (1707–1783), who provided

differential equations that, once their solutions could be worked out in the mid1800s, provided accurate pressure distributions over aerodynamic bodies and,

thus, a way of eventually analyzing low-speed flows and reliably calculating lift.6 

But all this simply provided analytical tools for future use, for none of these scientists and mathematicians of the seventeenth and eighteenth centuries had any interest whatsoever in applying them to the design of a flying machine. Bernouilli and Euler

may have developed the mathematics that would be used to show how the pressure differential on the upper and lower surfaces of a wing developed the phenomena

of lift, but they themselves never attempted to design an effective shape to achieve this.

This, the problem of designing an effective wing or “airfoil,” was a fundamental

problem that needed a solution if heavier-than-air flight was ever to be achieved. 

All that came before the early 1800s served only as prologue to the story leading

to the invention of heavier-than-air flight by the Wright brothers. The genuine

narrative begins in 1804 when Sir George Cayley (1773–1857), a twenty-one-year-old

scientifically educated English country squire, designed and hand-launched a

small glider. Not more than a meter long, Cayley’s innocent-looking glider of

1804 represented a revolutionary breakthrough, as it essentially incorporated all

the elements of the modern airplane. This simple yet profound design effectively

combined the three essential features recognized today in the configuration of a

modern airplane: a fixed wing, a body or fuselage, and a tail with both horizontal
From Cayley’s Triple Paper to Orville Wright’s Telegram 7

7 Anderson does a very complete job of analyzing Sir George Cayley’s seminal contributions in A

History of Aerodynamics, pp. 64–80. There is no monographic treatment of Cayley, though one is

much needed. In 1968, the Science Museum of London published a “Science Museum Booklet”

entitled Sir George Cayley, 1773–1857, authored by C. H. Gibbs-Smith.

8 Anderson, A History of Aerodynamics, p. 79.

and vertical surfaces. While producing such a glider may seem like child’s play

today, at the time it was totally at variance with existing flapping wing, or

ornithopter, concepts of how to achieve heavier-than-air flight. 

Cayley’s configuration was the product of some bold new thinking about what

it was going to take to fly. For example, Cayley understood how to produce the lift

necessary for flight, because he recognized that curved surfaces produced more

lift and less drag than flat surfaces. He also understood that the airplane was

going to have to be stabilized and controlled, thus the need for tail surfaces. And

he understood mathematically what kind of power it was going to take to achieve

flight—and this was well in advance of the invention of practical lightweight

engines themselves. While he benefited from his knowledge of existing scientific

theory, such as Newton’s sine-squared law, Cayley’s 1804 glider design was essentially “his own.” On his own he performed laboratory experiments; conducted

flight testing, and analyzed his results. What was so remarkably new about Cayley

was the way he broke the elements necessary for flight into what would later be

called “systems,” i.e., a system to produce lift, a system for control of the craft in

the air, and a system to produce propulsion. Before Cayley, people had thought

not in terms of separate systems that could be effectively integrated, but of one

organic system, like that of a bird, that somehow could do everything.7

Though Cayley first arrived at his concept of the airplane in 1799 and integrated it into his 1804 glider, his radically new approach to understanding the

airplane is best exemplified in a three-part paper “On Aerial Navigation,” written

in 1809 and published in three parts in Nicholson’s Journal of Natural Philosophy,

Chemistry, and the Arts.

Without question, this paper, reproduced in its entirety as the inaugural document of this volume, represents “the highlight in the history of aerodynamics”—

not just for the beginning of the nineteenth century, but for all human history up

to that time. (See Document 1-1.) As John Anderson writes in his history, “the work

of all previous investigators pale” compared to Cayley’s treatise.8 For its relationship

to the subsequent development of the airplane, this document by George Cayley

compares to such seminal publications as Copernicus’ 1543 On the Revolution of

Heavenly Bodies, Darwin’s 1859 Origin of Species, and Watson and Crick’s 1953

paper on their discovery of the structure of DNA. Cayley himself kept working on

flying machines up to his death in 1857. 
8 Chapter 1: The Achievement of Flight

9 Pénaud is discussed in most surveys of the development of flight, but there is no single exhaustive

study devoted to his work. Anderson covers Pénaud adequately in A History of Aerodynamics, pp.

193–194. See also Tom D. Crouch, A Dream of Wings: Americans and the Airplane, 1875–1905

(Washington, DC, and London: Smithsonian Institution Press, 1981), pp. 36, 46, 57–59, 64, and

192; as well as Crouch’s The Bishop’s Boys: A Life of Wilbur and Orville Wright (New York and

London: W. W. Norton & Co., 1989), pp. 56–57, 161, 164, 168–169, 249, and 342.

Curiously, after the publication of the “Triple Paper,” Cayley shifted his attention

for four decades to the development of balloons and airships. Most likely he did

this because of the vexations of developing an engine for airplane applications.

Steam engines with huge boilers simply weighed too much, and innovative new

engines, such as gas-fueled, internal combustion engines, were still very experimental

and quite limited in their power output. But even without the right engine, in

1843 he refocused again on the airplane and began designing full-scale gliders

anew. One of them carried a ten-year-old boy without incident a few yards down

a hill in 1849. Four years later another carried his reluctant coachman across a

small valley, possibly flying as far as 500 yards. (Unaware of the historic auspices

of this 1853 flight, the coachman on landing allegedly remarked, “Please, Sir

George, I wish to give notice. I was hired to drive and not to fly.”)

With its roots in the scientific revolution, Cayley’s work provided the trunk for

a growing tree of aerodynamic knowledge and invention that in half a century led

to the Wright brothers’ achievement in December 1903. From that solid trunk,

however, at least three major branches of experimental heavier-than-air flight

technology grew in the nineteenth century, and no one at the time could be certain

which branch would ultimately bear the most fruit.

The first branch involved trying to learn about flight by experimenting with smallscale models. This proved to be a very useful approach for testing aerodynamic

concepts, one that cost little money and did not risk life or limb. The most important

individual taking this approach was the young French marine engineer, Alphonse

Pénaud (1850–1880), who in the 1860s and 1870s experimented with a number of

little flying models powered by twisted rubber bands, much like the toys children still

play with today. His most successful model flew 131 feet across the Tuileries Gardens

in Paris in August 1871. Pénaud based his model on Cayley’s 1804 glider design, but

improved it in key respects. He set its horizontal tail to a negative angle of eight

degrees relative to the chord line of the wing, which gave his airplane greater longitudinal (or pitching) stability. He also bent its wing tips up in a dihedral angle,

thereby providing lateral (or roll) stability. Changes like this, which would have

been difficult, expensive, and potentially dangerous if made with a full-scale, manned

aircraft, were relatively simple to make and flight test with a small-scale model.9

What Pénaud sought was a mechanism that would guarantee absolute inherent

stability, so he ignored the possibility of active pilot control. In this he shared the
From Cayley’s Triple Paper to Orville Wright’s Telegram 9

mindset of many aeronautical thinkers at that time, who believed that their first

task was to demonstrate how to fly in a simple straight line with a passenger on

board and that the issue of control could be dealt with later. Pénaud’s emphasis

on automatic stability was also a limitation of the scale-model approach. Working

with models powered by twisted rubber bands, and without any means of piloting

them once launched, Pénaud had little choice but to go after inherent stability.

With their inefficient power source, his best flights lasted only thirteen to fourteen

seconds, and were characterized by Professor Langley of the Smithsonian

Institution as being, “so erratic, and so short, that it was possible to learn very little

from them.” 

At the end of the nineteenth century many people regarded Samuel Pierpont

Langley (1834–1906) as the unofficial chief scientist of the United States, which

makes it even more significant that Langley, though aware of the limitations of

Pénaud’s experiments, also focused his own work on scale models. In fact,

Langley subscribed to the erroneous and ultimately tragic assumption that results

from scale models could be directly scaled up to design a full-scale airplane. In

Although he ultimately failed in his effort to build a successful man-carrying airplane, one should not minimize

Professor Samuel P. Langley’s many contributions to aerodynamic understanding, especially those embodied in the

flights of his large steam-powered models in 1896. In this photograph from December 1895, Langley’s Aerodrome

No. 6 (which evolved from No. 4) had not yet matured into its final configuration. SI Negative No. A-2854-J
10 Chapter 1: The Achievement of Flight

1887, Langley left his work in astronomy and solar science, for which he was very

distinguished, to take the prestigious position of Assistant Secretary of the

Smithsonian Institution (a few years later he became Secretary). There he

embarked on a new course of remarkable aeronautical experiments. He followed

the approach of Pénaud but with models that quickly grew much larger, more

complicated, and were powered by small steam and gasoline engines rather than

rubber bands. His research paid off, up to a point. On 6 May 1896, his Aerodrome

No. 5, a steam-powered model weighing thirty pounds and with tandem wings

spanning over thirteen feet, made two long flights from a launching platform

atop a houseboat in the Potomac River south of Washington, D.C. The best of the

flights that day covered 4,200 feet in forty-five seconds. Celebrated inventor

Alexander Graham Bell, a close friend of Langley’s, observed these flights firsthand and published ecstatic accounts of what Langley had achieved as a major

step on the way toward powered flight.10 (See Document 1-8.)

In terms of the history of aerodynamics, Langley made other major contributions.

His work in the late 1880s and 1890s has been called “the first meaningful aerodynamic research” in America, a systematic program of tests involving whirling

arms and other sophisticated experimental instruments of his own design, the purpose of which was to measure the various aerodynamic forces at work on different

surfaces, including propeller shapes. Interestingly, however, this program of basic

research “contributed little of practical value” to the design of either his or any

other flying machine of the day. Moreover, contemporary scientists, including

British giants Lord Kelvin and Lord Rayleigh, condemned his most provocative

aerodynamic conclusion, the so-called “Langley’s law,” which stated that the

power required for a vehicle to fly through the air decreased as the velocity

increased.11 (See Document 1-4.) Lilienthal, the Wrights, and others trying to fly

believed that this counterintuitive idea had to be wrong—which it was, except for

in the narrow range of Langley’s test velocities (20 meters per second or less). 

A difficult personality at best, Langley today is chiefly remembered as the one

who failed where the Wrights succeeded. Yet perhaps the best commentary on his

role and achievements came from the Wrights themselves. Writing to a friend

shortly after Langley’s death, Wilbur Wright said of him:

10 No comprehensive biography has yet been written of Dr. Samuel P. Langley. The books by Tom

Crouch cover Langley’s importance in some significant detail, as does Anderson’s A History of

Aerodynamics. But as much as any other figure in the early history of aviation that has not yet

received one, Langley deserves an exhaustive, singular treatment.

11 For an analysis of “Langley’s law” and how it erred, see Anderson, A History of Aerodynamics, pp.

179–181.
From Cayley’s Triple Paper to Orville Wright’s Telegram 11

The knowledge that the head of the most prominent scientific institution

of America believed in the possibility of human flight was one of the

influences that led us to undertake the preliminary investigation that

preceded our active work. He recommended to us the books which

enabled us to form sane ideas at the outset. It was a helping hand at a

critical time and we shall always be grateful. . . . When scientists in general

considered it discreditable to work in the field of aeronautics he possessed

both the discernment to discover possibilities there and the moral courage

to subject himself to the ridicule of the public and the apologies of his

friends. He deserves more credit for this than he has yet received. . . .

Though we have rarely followed his lead, we have always found a study

of his writings very profitable, especially at the time when we were trying

to find out what the real sticking points of flying were.12

The successful launch of Langley’s Aerodrome No. 5 from atop a houseboat in the Potomac River, on 6 May 1896.

SI Negative No. A-18870

12 Wilbur Wright, letter to Octave Chanute from Dayton, Ohio, 8 November 1906, found in The

Papers of Wilbur and Orville Wright, ed. Marvin W. McFarland, Vol. 2 (New York, NY: McGraw-Hill

Book Company, Inc., 1953), pp. 736–738.
12 Chapter 1: The Achievement of Flight

13 On the aerodynamics involved with the “aerial steam carriage” conceived by Henson and

Stringfellow in the 1840s, see Anderson, A History of Aerodynamics, p. 194. See also Crouch, A

Dream of Wings, pp. 28 and 89.

Langley’s contemporary impact on the development of aerodynamics extended

beyond his influence on the Wrights; as the culmination of the nineteenth century

scale-model approach to aeronautical knowledge, Langley’s experiments also had

a much broader significance. First, his publications, beginning with his 1891 book

Experiments in Aerodynamics, inspired others to step up their experimental efforts

and to be systematic in carrying them out. Second, and perhaps even more

importantly, the fact that one of the greatest scientists in the country had decided

to devote his efforts to the problems of flight convinced a great number of people

that “aeronautics was no longer the past-time of fools.” 

The notion that only fools tried to fly was certainly exacerbated by the second major branch of technological experimentation in heavier-than-air flight

during the nineteenth century. This method involved venturesome attempts to

build the real thing, full size, and then try to fly it with a person on board. This

approach offered the advantage of more meaningful, immediate, and sensational results—not to mention the possibility of great notoriety for the successful

inventor. But full-scale flying machines also meant considerably greater cost in

construction, dramatically increased danger in testing, and the inability to experimentally vary design parameters quickly and easily. 

Given the general impatience of human nature, though, it is not surprising that

a number of individuals pursued this course anyway. In the 1840s, two Englishmen,

William Henson and John Stringfellow, designed an “aerial steam carriage” with

a huge 150-foot wingspan, powered by a thirty-horsepower steam engine they

themselves planned to build. Their objective was to develop an “Aerial Transport

Company” to haul goods commercially worldwide, an idea far ahead of its time.

Their ambitious machine, however, never flew—in fact, it was never built, and all

they constructed was a twenty-foot model that never made it into the air. Yet so

many fanciful pictures of their proposed machine appeared in contemporary

newspapers and magazines that many people believed the Henson-Stringfellow

airplane flew over the Tower of London, the Pyramids, and even the Taj Mahal.

These drawings cemented in the public consciousness the image of what an airplane should look like, with rectilinear wings, an enclosed cabin fuselage directly

under the wing, twin screw propellers, and pilot-controlled tail surfaces. Thanks

to the publicity surrounding this “machine that never flew,” George Cayley’s basic

formula for configuring an airplane became the firmly established technological

norm. After about 1845, when anyone thought of an airplane, they pictured it in

terms resembling the Henson-Stringfellow vision of the basic Cayley design.13
From Cayley’s Triple Paper to Orville Wright’s Telegram 13

In the second half of the nineteenth century there were other full-scale

attempts at flying machines. Two naval officers, Felix du Temple in France in

1874 and Alexander Mozhaiski in Russia ten years later, sent subordinates in

steam-engined machines down inclined planes to achieve short powered hops,

but neither of these attempts did much to advance either aerodynamics or the

practical development of the airplane. The most elaborate full-scale attempt was

made by Hiram Maxim (1840–1916), the American engineer in London famous

for his invention of the machine gun. In the early 1890s Maxim spent a good part

of his new fortune on the three-year development of a large biplane called the

Leviathan, with a wingspan of 104 feet, powered by two 180 horsepower steam

engines driving eighteen-foot propellers, and weighing nearly four tons. The

design, however, was structurally weak, aerodynamically unsound, and lacked

Maxim’s huge four-ton biplane, with its eighteen-foot propeller, sits on its track ready for flight testing (unsuccessful)

in 1894. Ultimately the monster rose slightly from its guardrails, but only after traveling some 600 feet down the

track. It possessed no truly redeemable features and represented, in its two very efficient steam engines, a brute

force approach to getting an airplane aloft. SI Negative A-212-A

14 See Iain McCallum, Blood Brothers: Hiram and Hudson Maxim—Pioneers of Modern Warfare (Chatham

Publishers, 1999). Though this book focuses on weapons development, notably the “Maxim gun,”

it also covers Hiram S. Maxim’s unsuccessful attempts to fly. For first-hand accounts of his experiments in flight, see Hiram S. Maxim, “Natural and Artificial Flight,” Aeronautical Annual (1896);

and “Aerial Navigation by Bodies Heavier Than Air,” The Aeronautical Journal 6 (January 1902):

2–7. On Maxim’s views of the early work of the Wright brothers, see “The Recent Experiments

Conducted by the Wright Brothers,” The Aeronautical Journal 10 (January 1906): 37–39.
14 Chapter 1: The Achievement of Flight

effective controls. In 1894 the Leviathan crashed into a guide rail after briefly rising mere inches from the ground.14 (See Document 1-6.)

Perhaps the closest thing to a successful powered flight of a full-scale heavier-thanair machine took place in France four years prior to Maxim’s debacle, when Clement

Ader’s bat-winged L’Eole rose twelve inches off the ground in a “flight” of possibly

165 feet. But Ader’s achievement was not in the same league as the historic Wright

flight of 1903, no matter what French enthusiasts, then and now, may claim about

it. All L’Eole really managed was a short, uncontrolled, powered hop and nothing

more, which was fortunate given that the craft could not have sustained itself, as

it had no tail and no method of lateral control, a formula for disaster. 

A second Ader machine, the Avion II, was never completed, and a third in 1897,

the Avion III, refused to leave the ground. Neither Du Temple, Mozhaiski, Maxim,

nor Ader gave serious thought to how to control their aircraft in flight or what sort

of skill the pilot would need to have. All they wanted to do was simply get a machine

carrying a person into the air—and they did not truly accomplish even that.15

This is Ader’s own perspective sketch of the Éole. The craft’s wing spanned fourteen meters, with the length of

the fuselage only 6.5 meters. The airframe weighed just over 175 kilograms. The bat-shaped wings could be folded for storage. Notice that at this point in time Ader considered fitting his plane with narrow caterpillar-like tracks

rather than wheels. NASM File AA-006502-01

15 One can divide the works on Clement Ader into those that support the claim that his L’Eole successfully flew and those who refute or seriously qualify it. Among the works favorable to Ader are:

Jacques May, Ader (Librairie Aeronautique, 1910); Georges de Manthe, Clement Ader, sa vie, son oeuvre (Edition Privat, 1936); Louis Castex, L’homme qui donna des ailes au monde (Editions Plon, 1947);

Louis Castex, Clément Ader, ou l’homme qui voulait se faire oiseau (Presse de la cite, 1967); Raymond

Cahisa, L’aviation d’Ader et des temps héroiques (Albin Michel, 1950); and Pierre Lissaargue, Clément

Ader, Inventeur d’avions (Edition Privat, collection Bibliotheque Historique, 1990). For a more critical analysis, see Charles H. Gibbs-Smith, Clément Ader, his claims and his place in history

(London/Science Museum, Her Majesty’s Stationery Office, 1968). There are a number of Web

sites that are devoted to Ader, notably that administered by Le musée Clement Ader at http://le-village.

ifrance.com/eole/squeletteader.html There is information about the Avion III at www.cham.fr/museum/

revue/ref/r13a04_a.html, which is maintained by the Musée des arts et métiers in Paris. Restored in

the 1980s, the Avion III serves as one of the centerpieces of this museum.
From Cayley’s Triple Paper to Orville Wright’s Telegram 15

Fortunately, there existed a third approach, one pursued earlier by Cayley

himself, which investigated the problems of flight with full-scale manned gliders. This

approach may have seemed the most foolhardy to some, involving jumping off hills

and crashing nose first into the dirt; or the least sophisticated to others, because

it did not involve steam engines or other kinds of power plants. But learning what

type of wing shape and aerodynamic configuration best lifted a man into the air,

and what sort of system and piloting maneuvers then allowed that man to control

his flight in three dimensions, proved absolutely essential to solving what came to

be recognized in the late 1800s, not just by aeronautical enthusiasts but by the

engineering community as a whole, as “The Problem of the Century.”16

Certainly, if there was one secret to the Wrights’ success, it was that they learned

to fly and control their airplane in glider form before they ever put power into it. But

these brothers from Dayton, Ohio, were not the first to understand the fundamental

importance of this human/machine interface as part of the invention of powered,

heavier-than-air flight. Before the Wrights, there were two key individuals who

provided technological breakthroughs in this regard that built significantly on the

work started by Cayley and laid out a clear path to the future. They were two professional engineers: Otto Lilienthal (1848–1896) and Octave Chanute (1832–1910). 

German mechanical engineer Otto Lilienthal made his living manufacturing

small steam engines and marine foghorns in a little factory he operated on the

outskirts of Berlin. With an unbridled passion for flying machines, Lilienthal conducted laboratory experiments and gathered data throughout the 1880s, trying

to grasp and measure the way wings generated lift and generally searching for

some real understanding of aerodynamic principles. Feeling that he had learned

all he could from unmanned gliders, in 1891 he built and flew his first full-scale

manned hang glider. From then until his death, the result of a gliding accident in

October 1896, Lilienthal made about 2,000 glides.17 (See Document 1-5.)

Lilienthal was not the first human being to fly. At least five other individuals had

flown in gliders, beginning with Cayley’s two hapless “test pilots.” In France in the

16 This phrase was used by Augustus M. Herring as the title of a 1897 paper about his flying experiments with Octave Chanute.

17 There is no satisfactory biography of Lilienthal in English, nor have any of the monographic

treatments written in German ever been translated. In German, one should start with the works

by Gerhard Halle: Otto Lilienthal und seine Flugzeug-Konstructionen (Dusseldorf: VDI-Verlag, 1962)

and Otto Lilienthal: die erste Flieger (Dusseldorf: VDI-Verlag, 1976). Other studies of Lilienthal have

been done in German by Werner Schwipps, Jutta Wegener, Karl-Dieter Seifert, and Stephan

Nitsch. Anyone interested in Lilienthal’s life who does not read German should start with the

British translation of his autobiographical Birdflight As the Basis of Aviation: A Contribution Towards a

System of Aviation (London, 1911). Tom Crouch’s A Dream of Wing also offers an excellent chapter

on Lilienthal’s legacy in America, and the Smithsonian Institution Press/National Air and Space

Museum published a booklet on Otto Lilienthal and Octave Chanute: Pioneers of Gliding, 1980.
16 Chapter 1: The Achievement of Flight

18 See Crouch, A Dream of Wings, p. 90 on Le Bris; pp. 20–21, 65–72, 83, 90, 176–178, and 228 on

Mouillard; and pp. 87–100 and 307–309 on Montgomery.

19 For a more detailed technical analysis of Lilienthal’s aerodynamics and the reasons behind his

fatal crash in 1896, see Anderson, A History of Aerodynamics, pp. 138–164.

1860s Jean Marie le Bris and Louis Mouillard both flew in gliders, while American

John Joseph Montgomery flew three different hang gliders of his own design off a hill

near San Diego harbor in the 1880s.18 Universally, however, these predecessors became

so frightened after making a few flights that they either refused to go up again or went

back to the drawing board. Lilienthal was the first to persist. He continued making

gliding flights, incorporating what he learned in his flights into the design of subsequent gliders. He even arranged for a cone-shaped hill to be built for him so he

could fly his gliders no matter which direction the wind came from. He became

the first man to really know how to fly, earning the nickname “The Flying Man”

in accounts of his exploits. His machines were very well made and included both

monoplane and biplane configurations. Some of his flights covered over 1,000

feet and lasted as long as fifteen seconds. Stories about his wonderful flights and

piloting abilities appeared in newspapers and magazines around the world, and

Lilienthal himself wrote a book and published a number of articles explaining his

techniques and understanding of aerodynamic principles. These publications

educated people about flight and motivated countless people, including the

Wright brothers, to consider taking on the problem of flight for themselves. 

On 8 October 1896, Lilienthal was gliding about fifty feet in the air when a strong

gust of air caused his craft to nose up and stall. He was unable to regain control and

his hang glider entered a terminal spin and crashed to the ground. Lilienthal suffered a broken back in the crash and died the next day in a Berlin hospital. The

tragedy came as a terrible blow to all would-be aviators, for if not even the great

“Flying Man” could avoid a fatal accident, how could anyone else expect to do it?

As much as Lilienthal had worked to address the matter of aerodynamic control

in his gliders, what killed him was nonetheless insufficient control. In essence,

Lilienthal’s method for control depended solely on the pilot shifting his weight

under his glider in a type of “negative guidance” whereby he countered any

unwanted aircraft movement by using his own body to shift the center of gravity

of the whole machine. If the craft started to stall, all Lilienthal could do was throw

his legs forward to try to pull the nose down and regain flying speed. Such a control

system was fatally flawed because if the pilot did not shift his weight in just the

right way and at just the right time his movements could actually make things

worse. Furthermore, this system held little promise for purposes of subsequent

development, because the ability of a pilot to control an airplane by shifting his

own weight diminished rapidly as the size of the airplane increased.19
From Cayley’s Triple Paper to Orville Wright’s Telegram 17

20 See Crouch, A Dream of Wings, pp. 175–202, and Anderson, A History of Aerodynamics, pp. 192–197.

At the time of his death at age forty-eight, Lilienthal was thinking about

propulsion systems and the problems that needed to be solved if he was to move

forward to a powered airplane. There was no telling what he might have accomplished if he had survived. 

Aviation’s first martyrdom proved catalytic. Although pessimists took it as proof

that humankind was not meant to fly, more optimistic individuals reacted to news of

Lilienthal’s demise with even greater determination to get up into the air. In America,

Octave Chanute had just finished a successful summer season test flying a series of

different gliders at the Indiana Dunes on the south shore of Lake Michigan, east

of Chicago. By the time he heard the horrible news of Lilienthal’s death, Chanute

and a small group of young colleagues had evolved an advanced biplane glider

incorporating a new approach to the problem of airplane stability. This glider

proved to be “the most significant and influential aircraft of the pre-Wright era.”20

Given the depth of Chanute’s talents as an engineer and his encylopedic

awareness of what was being tried aeronautically in America and around the

world, it is not surprising that his 1896

glider represented the most advanced

state of the art of that time. He emigrated to the United States with his

family from France in 1838 when he

was six, by the mid-1870s Chanute was

one of the best known and most

respected civil engineers in the country, renowned for his bridges and railway structures. At the peak of his

career, Chanute was chief engineer of

the Erie Railroad and president of the

American Society of Civil Engineers

and the engineering section of the

American Association for the

Advancement of Science. Interested in

flight since his childhood, in the 1880s

Chanute entered a period of semiretirement that allowed him to devote his

energies to the problems of “aeronautical

navigation.” He initiated a regular

correspondence with dozens of people

An accomplished railroad engineer, when Octave

Chanute (1832–1910) turned his attention to the

design of flying machines in the 1880s and 1890s and

began corresponding with others with similar interests,

he inadvertently created the first international aviation

community, a creation essential to the successful

invention of the airplane. SI Negative A-21147-B
18 Chapter 1: The Achievement of Flight

21 It is truly amazing that there is yet no published biography of Chanute, considering how important he was to not only the development of flight technology but also of American engineering

generally. The seminal figure in Crouch’s A Dream of Wings is unquestionably Chanute rather than

Langley or the Wrights. The main collection of Chanute Papers rests in the Manuscript Division

of the Library of Congress. The Denver (CO) Public Library holds a large collection of Chanute

materials assembled by Ms. Pearl I. Young, who for many years, starting in the early 1920s,

worked for the National Advisory Committee for Aeronautics (NACA) at Langley Field, Virginia.

Young grew fascinated with the early history of flight, particularly Chanute’s contributions. At the

Denver Public Library, one will find Young’s Bibliography of Items About Octave Chanute, Complete

Writings of Octave Chanute, the Chanute-Mouillard Corespondence, and two essays by Young: “Octave

Chanute and New England Aeronautics” and on “The Contributions of Octave Chanute,

1832–1910.” Anyone reconstructing Chanute’s story would also want to see Marvin McFarland,

ed., The Papers of Wilbur and Orville Wright, Including the Chanute-Wright Letters and Other Papers of

Octave Chanute, recently reissued by McGraw Hill, in January 2001.

all over the world who were interested in flying machines, including prominent

members of the Aeronautical Society of Great Britain, the most important of the

early organizations devoted to the study of flight. He also published what he

learned, starting with a series of critically important essays on “Progress in Flying

Machines,” that appeared in twenty-seven installments in the Railroad and

Engineering Journal, beginning in October 1891, and was reprinted three years later

as a single volume.21

Not satisfied with the important role he filled in the aeronautics community,

by serving as an active clearinghouse for aeronautical information and by making

aeronautics a respectable concern for engineers, Chanute also wanted to test his

own ideas about flying. In 1888, he laid out an idea for the design of a flying

machine combining features of an airship and an airplane. Abandoning this

hybrid, he quickly turned to manned gliders, unveiling a bold new design in late

1894 that was to serve as a test bed for his own novel concepts. Chanute’s original glider design featured an approach to control problems that was significantly

different from Lilienthal’s negative or reactive stability, in which the pilot shifted

his body weight. The veteran engineer envisioned instead a system of automatic

stability that did not require much from a pilot—in essence, he wanted the structure itself to stabilize the airplane. To do this he proposed an arrangement of

multiple wings set in tandem, suggesting as many as four pairs of tandem biplane

wings, or sixteen in all. Such a redundant structure, he calculated, would reduce

the movement of the center of pressure on each surface by adjusting automatically

to shifts in the airplane’s center of gravity. The “operator,” using Chanute’s term,

“need only intervene when he wants to change direction, either up or down, or

sideways.” Furthermore, Chanute added yet another element of automatic stability

by designing each one of his tandem wings so that they could rotate slightly.

When hit by a strong gust of wind, explained Chanute, “the wings are blown backward . . . the aeroplane tips slightly to the front, thus decreasing the angle of incidence,
From Cayley’s Triple Paper to Orville Wright’s Telegram 19

so that the aggregate ‘lift’ is diminished.” When the wind subsided, a coil spring

pulled the wings forward to return to “their normal adjusted position.”

Flight trials with different gliders at the Indiana Dunes in the summer of 1896

showed Chanute the error of at least some of his concepts and stimulated a major rerigging of the multiplane glider, dubbed the Katydid for its insect-like appearance. The

redundant wings caused far too much lift, and with some surfaces creating more lift

than others this caused dangerous imbalances. No one, including the sixty-four-yearold Chanute, wanted to risk flying it at first, so the glider was initially flown tethered

like a kite. After numerous design changes, a young fellow engineer named Augustus

M. Herring made a series of flights in the glider, the longest a glide of eighty-two feet.

Word of the flights spread to neighboring Chicago and reporters from a number

of newspapers and the national wire services trekked to the southeast shore of

Lake Michigan to observe the action. Not wanting the attention, Chanute and his

men packed up and went back to a workshop in Chicago. There they applied what

they had learned to the design of a brand-new glider. 

One should view the work of Chanute and Herring as collaborative. In the truss bracing used on the gliding

machines, one detects Chanute’s engineering skills; in the cruciform tail and overall design schemes lay Herring’s

major contributions. In terms of the fundamental aerodynamics, it is unclear whose understanding was superior.

Chanute knew much more mathematics, but Herring’s physical intuition was in many ways sharper. Here, Herring

stands ready to take off in his two-surface gliding machine in 1896. SI Negative A-30907-H2
20 Chapter 1: The Achievement of Flight

22 On Herring, see Crouch, A Dream of Wings, pp. 203–223. His ancestors to this day continue to

believe that Augustus Herring made a powered flight in an airplane before the Wrights; see, for

example, Lou Mumford, “Family claim historical accounts of first flight aren’t ‘Wright,’” South

Bend Tribune, 11 October 1998. This story can be accessed at http://www.southbendtribune.com/98/

oct/101l98/local_ar/117176.htm 

The result was a simple, dramatic improvement: a far simpler, triplane glider

made with a single rigid box frame. Much less cumbersome than the Katydid, it

flew at the Indiana Dunes in 1896 as the first modern aeronautical structure, of

which Chanute’s team had evaluated the forces, figured the strengths, and precisely calculated the performance. Looking at its external bracing of crossed diagonal wires and upright struts, one could see the face of airplane structures to

come, beyond the World War I era. The new glider also featured an effective combination of horizontal and vertical tail surfaces put into a cruciform (or cross)

shape. That such a tail, appropriately positioned, enhanced the pitch stability of

an airplane was understood as far back as Cayley. But Chanute and his men were

not satisfied with just the advantages of a fixed tail. Under young Herring’s direction,

they made their tail moveable (or “regulating”) so that it could react positively to

gusts, keeping the airplane straight and level. At the suggestion of one of

Chanute’s men, carpenter and electrician William Avery, the triplane soon metamorphosed into a biplane simply by removing the bottom wings. The resulting

performance of this “two-surface” machine was phenomenal—the equal of anything flown by Lilienthal and, in its design features, significantly more progressive.

(See Document 1-9.)

One would think that Chanute and his men would have followed up immediately on their sensational success; after all, it was the season-after-season

buildup of knowledge and know-how that proved so essential to the Wright brothers’ eventual achievement at Kitty Hawk. But it did not happen this way with

Chanute. When the summer of 1896 ended, so did his experimental flying. The

following summer he and his men did not return to the Indiana Dunes. Herring

went to explore the possibility of powered hang gliders in the vicinity of St.

Joseph, Michigan.22 Chanute kept collecting aeronautical information, writing

articles for publication and corresponding with dozens of others in pursuit of the

dream. Perhaps due to his age, he did not persist with flight trials. It was certainly clear from his 1897 article, “Recent Experiments in Gliding Flight,” that he

was not sure that powered flight was imminent. In fact, without Herring around

to push him in bold new technological directions and describe what it was like to

pilot a plane, Chanute reverted to old ideas, notably the absolute priority of automatic stability. He set aside the world’s most advanced glider and reverted to the

design of yet another monstrously complex multiplane.
From Cayley’s Triple Paper to Orville Wright’s Telegram 21

The year 1896 was thus a pivotal time in the history of aeronautics, and in

that year two brothers in Ohio, self-trained designers without high-school diplomas,

turned their attention away from their print shop and bicycle business in order to

take a crack at inventing the airplane. These two unique individuals, Wilbur

Wright (1867–1912) and Orville Wright (1871–1948), brought not only fresh perspectives and new energy to the fledgling field of flight research, but also one of

the most remarkable collaborations of genuine talent in the history of invention.

Writing shortly before his death, Wilbur Wright offered the following insight into

the fruitful relationship that sustained them in their work and jointly magnified

their respective abilities:

From the time we were little children my brother Orville and myself

lived together, played together, worked together and, in fact, thought

together. We usually owned all of our toys in common, talked over our

thoughts and aspirations so that nearly everything that was done in

our lives has been the result of conversations, suggestions and discussions between us.23

Views of Herring’s three-surface glider from 1896. Smithsonian Institution

23 Wilbur Wright, Papers of Wilbur and Orville Wright, 3 April 1912.
22 Chapter 1: The Achievement of Flight

Without this creative synergism between them, it is impossible to imagine them

inventing the airplane.

Another thing that is very important to understand about the Wright brothers is

how they followed their own path in pursuit of the invention of the airplane. Not that

they ignored all the work of others. In fact, one of the first things they did after

deciding to address the problems of flight in 1896 was collect all the aeronautical

information that was available. First, they exhausted the collections at the Dayton

Public Library, then they wrote to Chanute, who was kind enough to write back

and advise them to learn how to glide before they tried a powered flight. Aware

of Langley’s work, they also wrote to the Smithsonian Institution, which replied

by sending them a number of articles, including works by both Langley and

Lilienthal. (See Document 1-8.) But once they had digested this knowledge, they

were not to be boxed in by it. Instead they approached technical problems from

their own unique perspective and came up with equally unique solutions. 

The most significant example of this crucial characteristic of the Wrights concerned the decisive matter of control. They did something that no airplane pioneer

up to that time had done: they isolated the control of an airplane as the main

problem that needed attention. Lilienthal, Chanute, and Langley had obviously

designed wings that were able to lift machines into the air, and while there were

many aerodynamic improvements yet to come regarding lift, the invention of the

airplane did not have to wait for them. Neither did the problem of propulsion

overly concern the Wrights, because all over the country mechanics were developing

small, lightweight internal combustion engines for automobiles and motorcycles.

When they needed an engine, the Wrights thought, the technology would be

there. That left the issue of pilot control, the very problem that had killed

Lilienthal and the aspect on which nobody else had placed such clear priority.24

The Wrights’ thought process about control ran against the grain of current

thinking, and in hindsight it appears that this was precisely why they eventually

succeeded where others failed. Because Lilienthal, the great “Flying Man,” had

died because not even he was able to control his aircraft, conventional wisdom

reasoned that what was needed was an inherently stable machine—for example,

the line of thinking followed by both Chanute and Langley. The Wrights turned

this logic on its head. They cared little about a flying machine’s stability, but

focused from the start on the critical aspect of making it controllable. No doubt,

24 For an extremely insightful analysis of how the Wrights defined their problems and solved them,

see Peter L. Jakab, Visions of a Flying Machine: The Wright Brothers and the Process of Invention

(Washington, DC: Smithsonian History of Aviation Series, 1990). Jakab takes his reader step by

step through the thought processes that led the Wright brothers to their successful invention of

the airplane.
From Cayley’s Triple Paper to Orville Wright’s Telegram 23

25 The analysis presented in this chapter of the evolutionary technological development from the

Wrights’s kites to their historic 1903 Flyer is based largely on the narrative and interpretations of

Tom Crouch, the world’s preeminent Wright brothers’ scholar and author of the prizewinning The

Bishop’s Boys. As with other sections of this chapter, a more detailed analysis of the Wright’s aerodynamics relied on Anderson’s A History of Aerodynamics, pp. 201–243. Of course, there are many

more works on the Wrights, some of which were consulted in preparation of this chapter.

their intimacy with bicycle technology influenced them greatly in this matter, for

a bicycle is an inherently unstable machine. The Wrights felt that the airplane

would need to be the same sort of dynamically interactive device as a bicycle:

unstable on its own but completely controllable and virtually automatic in the

hands of an experienced operator. The key was designing control features into

the airplane that a pilot could easily and effectively manage.

In 1899, they took their first important step toward that goal by experimenting

in Dayton with what came to be known as their “wing-warping kite.” The basic

idea was a mechanism that allowed the operator to control the kite in its roll axis,

considered the most challenging axis of motion to master in a flying machine.

The Wrights developed a set of controls that enabled them to induce a helical

twist across the wing surface that increased the lift on one side and decreased it

on the other, thereby changing the aerodynamic balance of the machine. They

did not realize at the time that others, like Yale physics instructor Edson

Fessendon Gallaudet, had flown large wing-warping kites already. Instead they

came up with the idea on their own, based on their observations of buzzards

employing a similar technique, regaining “their balance, when partly overturned

by a gust of wind, by a torsion of the tips of the wings.” Starting with the wingwarping kite of 1899, one can follow the links in an evolutionary chain of ever

more sophisticated flying machines, right up to the historic Wright Flyer of 1903.25 

In 1900, the brothers built their first full-scale machine, a biplane glider large

enough to carry a person. Though it resembled the Chanute-Herring glider of

1896 in many of its structural features, the Wright glider of 1900 differed in that

it had a large elevator (or canard) set directly in front of the lower wing. This horizontal surface moved up and down and was the Wrights’ way of managing pitch

control and preventing nose dives in case of stalls. They built this machine in

accordance with the tables of aerodynamic coefficients compiled by Otto

Lilienthal, and estimated the amount of wing surface needed to lift the weight of

their fifty-pound machine plus a pilot into the air. It was this machine that first

flew at Kitty Hawk, on the windy Outer Banks of North Carolina, for two weeks

in the early autumn of 1900, during what was to the Wrights a short “scientific

vacation.” (See Document 1-10.)

What concerned the Wright brothers most about their first season of flight

tests at Kitty Hawk was the fact that their glider simply did not generate the lift
24 Chapter 1: The Achievement of Flight

that their calculations indicated it should. Something was obviously wrong with

their calculations. While they did manage to fly their machine as a kite, and finally

on the last day to make a few very short free glides, overall, the results were deflating. They tried the glider “with tail in front, behind, and every other way,” but

with no real success. After their return to Dayton, Orville Wright noted of his

brother’s mood that, “When we got through Will was so mixed up he couldn’t

even theorize. It has been with considerable effort that I have succeeded in keeping him in the flying business at all.”

The flying season in the next year proved equally frustrating. The machine they

took to Kitty Hawk in the summer of 1901 was a good deal larger than their previous

glider—in fact, with a twenty-two-foot wingspan, it was the largest glider anyone

had ever tried to fly. Basically, they hoped to solve the problem of insufficient lift by

creating more wing surface and by increasing the curvature or camber of the wings,

but none of these changes worked. The glider produced much less lift than predicted,

and was plagued with serious control problems. The disappointment of this season was a critical point for the Wrights, for they recognized that if they failed to

solve these lift problems, sooner or later one of them was going to be killed.

Rather than giving up, though, the two brothers reevaluated their basic

assumptions and realized that something was seriously wrong with the scientific

tables on which they were basing their calculations. Back in Dayton they

The Wrights experienced frustration after frustration in their 1901 glider flying season at Kitty Hawk. But in battling

through their many problems and failures they learned lessons extremely valuable to their successful invention of the

airplane two years later. Assistants Dan Tate and Edward Huffaker launch Wilbur in his 1901 glider. SI Negative 84-12143
From Cayley’s Triple Paper to Orville Wright’s Telegram 25

embarked on a new course to conduct their own basic research and find out what

was wrong with the Lilienthal data. They constructed a small six-foot-long wind

tunnel in the back room of their bicycle shop and tested a whole new range of airfoil shapes, about two hundred in all. They also experimented with changes in

aspect ratio, with different wing tip shapes, and with varying gaps between the

wings of a biplane. At the conclusion of this intense period of original investigation they sat on a wealth of new aerodynamic information that would quickly

enable them to solve the problems that had hitherto blocked their progress. (For

material related to the invention of the wind tunnel by British engineer Francis H.

Wenham in the early 1870s, see Document 1-3.)

The resulting 1902 Wright glider flew beautifully. Besides incorporating new wing

shapes that gave them the lift they wanted, the airplane also featured the Wright’s most

recent significant discovery, the benefits of a moveable tail rudder linked directly to

the wing-warping mechanism, enabling the pilot to manage both controls easily and

in concert. With this machine the Wrights really learned to fly. They experienced a

magnificent season of soaring and making banks, turns, and recoveries in every

direction. Appropriately, it was this machine that these intrepid aviation pioneers

patented, not their powered airplane of 1903. They had set out to invent an airplane

that was controllable in the air, and by the end of 1902 they had done it. (See

Document 1-11.) All that was left was to add a propulsion system to the airplane. 

They did encounter one other aerodynamic problem related to propulsion in

the design of an effective propeller. In the beginning this was a problem that the

Wrights had not anticipated, since they believed it would be sufficient to find a

good marine propeller and simply adapt it for use in the air. After the surprises

of 1900 and 1901, however, they did not want to take any chances, and determined

to calculate precisely the performance requirements of an aviation propeller. In

what proved to be another case of their marvelous talent for applying clear engineering logic to a problem that others had either overlooked or ignored, they reasoned

that the propeller was no more than a rotating wing—and as a result of their wind

tunnel tests they knew a lot about wings. For a propeller, therefore, they selected

an appropriate airfoil shape from their own aerodynamic tables, with the camber

best suited for the speed at which their machine would be flying through the air,

and carved their own propeller blades. “The result,” according to aviation historian

and Wright biographer Tom Crouch, “was the world’s first true aircraft propeller,

a device whose performance could be precisely calculated.”26

The story of the design of the homemade engine for their airplane, although

interesting, does not concern aerodynamic development, save perhaps in one

26 Crouch, A Dream of Wings, p. 294.
26 Chapter 1: The Achievement of Flight

respect. The Wrights wanted an engine that provided just enough power to meet

their calculated requirements, with no extraneous weight or extra resources

devoted to redundant capability. They knew exactly from their calculations how

much power it would take to get them into the air, and once they had an engine

that could deliver that precise amount of power—a mere 12 1⁄2 horsepower from

a 200-pound motor—they concluded engine development right there. This efficient approach contrasted sharply with the design overkill of Professor Langley,

who had no practical idea how much power it was going to take to get his aerodrome up into the air, and wasted inordinate time, money, and energy on the

development of an overly powerful fifty-two horsepower engine while neglecting

the more critical areas of aerodynamic structure and control. 

The Wrights spent nearly three months at Kitty Hawk in late 1903 before they

were ready to try their first powered flight. Besides assembling, testing, and rigging their new machine, they also practiced extensively with the 1902 glider.

After a false start on 14 December using a downhill launch rail that produced a

take-off speed too high for effective control, Orville and Wilbur were ready to take

This photo from 24 October 1902 shows Wilbur maneuvering the glider (fitted with a single moveable vertical rudder)

through a gentle right turn. By the end of the 1902 season the brothers had taken their machine through a remarkable series of banks, turns, and recoveries. SI Negative A-43395-A
From Cayley’s Triple Paper to Orville Wright’s Telegram 27

to the air with their airplane from a level launch rail on 17 December 1903. The

brothers made a total of four flights that day. The first flight, made by Orville,

covered only 120 feet in a little over twelve seconds. The last, piloted by Wilbur,

covered 850 feet and lasted nearly a full minute. The telegram sent by Orville to

his father telling the story of this historic achievement is appropriately the destination document for this chapter, marking the realization of humankind’s longsought goal of sustained powered flight. (See Document 1-13.)

The Wrights went home to Ohio and in 1904 and 1905 built two new airplanes and tested them as they flew over a cow pasture known as Huffman Prairie,

today a part of Wright-Patterson Air Force Base. Their airplanes got better, as did

their piloting skills, and by the end of 1905 they were making flights of forty-five

minutes, flying repeated circles and other maneuvers over their “air field.” The

world surprisingly took little notice of these truly revolutionary achievements.

News of their initial flights produced only a scattering of stories, and those at

The secret of the Wrights’ success was that they learned to fly and control the airplane in glider form before they

put power into it. They learned a great deal about the use of aerodynamic surfaces to control the airplane in a satisfactory manner, and together with the experience they had as pilots, they were able to fly the plane without too

much difficulty when they did put power into it. That did not preclude a false start or two, however. In attempting

to fly on 14 December 1903, pictured here, Wilbur nosed up too rapidly and spun back into the ground, damaging the front horizontal rudder, lower rear wing spar, and skid. SI Negative A-38618-A
28 Chapter 1: The Achievement of Flight

Huffman Prairie a brief flurry of interest. The press soon forgot about the Wrights

and allowed them to continue their refinement of the airplane undisturbed. 

Part of the explanation for the

lack of greater publicity was due to

the ignominious public failure of

Professor Langley’s full-size manned

Great Aerodrome in 1903. Using the

familiar launch platform atop the

houseboat on the Potomac River, in

October Langley tried to fly his craft

with an assistant aboard, but the

machine crashed in the attempt. A

second climactic public attempt to

fly the machine on 8 December, a

mere nine days before the Wright’s

epochal achievement in isolated

Kitty Hawk, also resulted in utter

failure. These tests were covered by a

corps of newspapermen and photographers who scathingly reported

the failure of a government program

that had spent $75,000 (the equivalent of about $1.5 million today) to

produce an aircraft whose flying characteristics were compared to “a handful of mortar” or “a block of cement.”

The nation’s leading scientist was humiliated and became the target of public

scorn and ridicule. With Langley’s disgrace capturing the headlines, the press took

little notice of the work of two obscure inventors from Dayton. 

The coincidence of the Wrights’ success and Langley’s failure in the month of

December 1903 highlights a factor that proved to be critically important, not just to

the invention of the airplane, but for the entire course of aerodynamic research and

development in the twentieth century. The Wrights were engineers, not scientists—practical-minded and realistic men, who time and time again found simple

solutions to what turned out to be key problems. Langley, the scientist, on the

other hand, proved an inept technologist because he could not turn what he knew

into an accomplishment of his goal. The Wrights had clear vision and demonstrated their genius as creative technologists par excellence.

What they also did, once the world and particularly the different fields of

engineering became aware of what the Wrights achieved through their systematic

The Wright brothers were masters at thinking visually,

using what is sometimes called “the mind’s eye,” and translating abstractions into hardware. Their flying machine had

to “look right,” in both an aesthetic and a practical sense,

before they were convinced that they had everything right

in their invention of the airplane. Certainly everything

looks right in this picture of the 1905 Flyer in flight above

Huffman Prairie near Dayton. SI Negative No. A-317-B
From Cayley’s Triple Paper to Orville Wright’s Telegram 29

engineering approach, was help prepare the ways and means for the future evolution of the airplane. The form of the airplane as the Wrights conceived it in 1903

was only the beginning—a fact they themselves perhaps did not appreciate enough.

In all respects, save the decisive one of control, the performance of their 1903 airplane was highly marginal. As one analyst has observed, it really amounted to “the

first aeronautical ‘proof of concept’ design, and could not be used for anything else,

including repeated flying.”27 (The historic 1903 Flyer was never flown again after the

17 December flights.) If the airplane was to ever become truly practicable, its

technology had to improve dramatically and become much more capable and versatile.

Over the course of the next decades, the airplane would experience a number of

“reinventions” in many ways as remarkable as the original Wright invention. And in all

of them, a systematic engineering approach similar to that of the Wrights proved critical.

As much as the invention of the original airplane itself, this was the Wrights’ legacy.

Ironically, the country’s first civilian aeronautical research facility, under the auspices of the National Advisory Committee for Aeronautics (NACA), was named after

Langley, not the Wrights. The NACA Langley Memorial Aeronautical Laboratory

What the public acknowledged about powered flight after December 1903 was the ignominious, highly publicized

failure of Samuel P. Langley’s Great Aerodrome, not the successful flights of the Wrights, which few knew about

and even fewer believed had actually happened. Here, Langley’s Great Aerodrome rests on its catapult atop a

houseboat, ready for flight, on 8 December 1903. SI Negative No. A-18789

27 E. K. Liberatore, Helicopters before Helicopters (Malabar, FL: Krieger Publishing Co., 1998), pp. 158–159.
30 Chapter 1: The Achievement of Flight

Observers compared the aerodynamic qualities of Langley’s Great Aerodrome, seen here crashing into the

Potomac an instant after launch, to “a sackful of mortar.” SI Negative No. A-18853
From Cayley’s Triple Paper to Orville Wright’s Telegram 31

was founded near Hampton, Virginia, in 1917, eleven years after the death of the

discredited Smithsonian scientist. Fortunately, for the sake of the aeronautical

research investigations that took place at the NACA and for the positive impact that

NACA research would have on the nascent U.S. aircraft industry, the influence of

Langley’s devoted colleagues and friends in the Smithsonian Institution (enough to

get the first NACA laboratory named after him) was not compelling enough to stamp

the character of the once-fledgling organization with Langley’s unsuccessful

approach. The researchers at Langley followed the technological lead and the model

of the Wrights. For the study of aerodynamics to affect flying machines, and for flying

machines to indeed change the world, the ways of the Wrights ruled the day.

European skeptics watched in awe as Wilbur Wright unveiled what his airplane could do during his trip to France

in 1908. In one sensational flight made on 13 August 1908 above the Les Hanaudières race track near Le Mans,

France, Wilbur made seven circles of the track in 8 minutes, 13 2⁄5 seconds. Four months later, in December, he

made two stunning nonstop flights across France—one a distance of 99 kilometers in 1 hour, 54 minutes, 22 seconds, and the other of 124.7 kilometers in 2 hours, 20 minutes. SI Negative No. A-42962-A
32 Chapter 1: The Achievement of Flight
Document 1-1(a–c) 33

The Documents

Document 1-1(a–c)

(a) George Cayley, “On Aerial Navigation,” Part One,

Nicholson’s Journal, November 1809.

(b) George Cayley, “On Aerial Navigation,” Part Two,

Nicholson’s Journal, February 1810.

(c) George Cayley, “On Aerial Navigation,” Part Three,

Nicholson’s Journal, March 1810.

Note: All three parts were republished in James Mead, ed., The Aeronautical Annual 1,

(Boston: W.B. Clarke & Co., 1895): 16–48.

There is perhaps no more important individual paper in the entire history of

aeronautics than Sir George Cayley’s famous three-part treatise “On Aerial

Navigation,” written in 1809. In this paper, reproduced here in its entirety, Cayley

reported all his findings on airplane aerodynamics and provided a thorough

explanation of the potential of a fixed-wing flying machine. In addition to outlining a systems approach to solving the problems of lift, control, and power, he

demonstrated a clear understanding of the advantages of wing camber, the first

person ever to appreciate the subtleties of the effects of curvature on lift. He did

not fail to address the matter of drag, and in various passages of his treatise he

even expressed a modern concept of aerodynamic “streamlining,” before the term

was invented. The total effect of his presentation was momentous, although it may

not come across as such to the modern reader who takes for granted the basic

operating principles of the airplane. Cayley’s delineation of the form and function of the airplane, based on his intuitive genius and solid experimental

approach, is classic.

Cayley’s document was written in three parts for Nicholson’s Journal, and is

often referred to as the “Triple Paper.”
34 Chapter 1: The Achievement of Flight

Document 1-1(a), George Cayley, “On Aerial Navigation,” Part One, 1809.

BROMPTON, Sept. 6, 1809.

SIR, I observed in your Journal for last month, that a watchmaker at Vienna, of

the name of Degen, has succeeded in raising himself in the air by mechanical means.

I waited to receive your present number, in expectation of seeing some farther account

of this experiment, before I commenced transcribing the following essay upon aerial

navigation, from a number of memoranda which I have made at various times upon

this subject. I am induced to request your publication of this essay, because I conceive,

that, in stating the fundamental principles of this art, together with a considerable

number of facts and practical observations, that have arisen in the course of much

attention to this subject, I may be expediting the attainment of an object, that will

in time be found of great importance to mankind; so much so, that a new era in society will commence, from the moment that aerial navigation is familiarly realized.

It appears to me, and I am more confirmed by the success of the ingenious

Mr. Degen, that nothing more is necessary, in order to bring the following principles into common practical use, than the endeavours of skilful artificers, who

may vary the means of execution, till those most convenient are attained.

Since the days of Bishop Wilkins the scheme of flying by artificial wings has

been much ridiculed; and indeed the idea of attaching wings to the arms of a man

is ridiculous enough, as the pectoral muscles of a bird occupy more than twothirds of its whole muscular strength, whereas in man the muscles, that could

operate upon wings thus attached, would probably not exceed one-tenth of his

whole mass. There is no proof that, weight for weight, a man is comparatively

weaker than a bird; it is therefore probable, if he can be made to exert his whole

strength advantageously upon a light surface similarly proportioned to his weight

as that of the wing to the bird, that he would fly like the bird, and the ascent of

Mr. Degen is a sufficient proof of the truth of this statement.

The flight of a strong man by great muscular exertion, though a curious and

interesting circumstance, in as much as it will probably be the first means of ascertaining this power and supplying the basis whereon to improve it, would be of little use. I feel perfectly confident, however, that this noble art will soon be brought

home to man’s general convenience, and that we shall be able to transport ourselves and families, and their goods and chattels, more securely by air than by

water, and with a velocity of from 20 to 100 miles per hour.

To produce this effect, it is only necessary to have a first mover, which will

generate more power in a given time, in proportion to its weight, than the animal

system of muscles.

The consumption of coal in a Boulton and Watt’s steam engine is only about

5 1

⁄2 lbs. per hour for the power of one horse[power]. The heat produced by the
Document 1-1(a–c) 35

combustion of this portion of inflammable matter is the sole cause of the power

generated; but it is applied through the intervention of a weight of water expanded

into steam, and a still greater weight of cold water to condense it again. The

engine itself likewise must be massy enough to resist the whole external pressure

of the atmosphere, and therefore is not applicable to the purpose proposed.

Steam engines have lately been made to operate by expansion only, and those

might be constructed so as to be light enough for this purpose, provided the usual

plan of a large boiler be given up, and the principle of injecting a proper charge

of water into a mass of tubes, forming the cavity for the fire, be adopted in lieu of

it. The strength of vessels to resist internal pressure being inversely as their diameters, very slight metallic tubes would be abundantly strong, whereas a large boiler

must be of great substance to resist a strong pressure. The following estimate will

show the probable weight of such an engine with its charge for one hour.

lb.

The engine itself from 90 to 100 

Weight of inflamed cinders in a cavity presenting

about 4 feet surface of tube: 25 

Supply of coal for one hour: 6 

Water for ditto, allowing steam of one atmosphere 

to be 1/1800 the specific gravity of water: 32 

[Total weight in pounds:] 163 

I do not propose this statement in any other light than as a rude approximation to truth, for as the steam is operating under the disadvantage of atmospheric pressure, it must be raised to a higher temperature than in Messrs. Boulton and

Watt’s engine; and this will require more fuel; but if it take twice as much, still the

engine would be sufficiently light, for it would be exerting a force equal to raising

550 lb. one foot high per second, which is equivalent to the labour of six men,

whereas the whole weight does not much exceed that of one man.

It may seem superfluous to inquire farther relative to first movers for aerial

navigation; but lightness is of so much value in this instance, that it is proper to

notice the probability that exists of using the expansion of air by the sudden combustion of inflammable powders or fluids with great advantage. The French have

lately shown the great power produced by igniting inflammable powders in close

vessels; and several years ago an engine was made to work in this country in a similar manner, by the inflammation of spirit of tar. I am not acquainted with the

name of the person who invented and obtained a patent for this engine, but from

some minutes with which I was favoured by Mr. William Chapman, civil engineer

in Newcastle, I find that 80 drops of the oil of tar raised eight hundred weight to
36 Chapter 1: The Achievement of Flight

the height of 22 inches; hence a one horse power many consume from 10 to 12

pounds per hour, and the engine itself need not exceed 50 pounds weight. I am

informed by Mr. Chapman, that this engine was exhibited in a working state to

Mr. Rennie, Mr. Edmund Cartwright, and several other gentlemen, capable of

appreciating its powers; but that it was given up in consequence of the expense

attending its consumption being about eight times greater than that of a steam

engine of the same force.

Probably a much cheaper engine of this sort might be produced by a gas-light

apparatus, and by firing the inflammable air generated, with a due portion of

common air, under a piston. Upon some of these principles it is perfectly clear,

that force can be obtained by a much lighter apparatus than the muscles of animals or birds, and therefore in such proportion may aerial vehicles be loaded with

inactive matter. Even the expansion steam engine doing the work of six men, and

only weighing equal to one, will as readily raise five men into the air, as Mr. Degen

can elevate himself by his own exertions; but by increasing the magnitude of the

engine, 10, 50, or 500 men may equally well be conveyed; and convenience alone,

regulated by the strength and size of materials, will point out the limit for the size

of vessels in aerial navigation.

Having rendered the accomplishment of this object probable upon the general view of the subject, I shall proceed to point out the principles of the art itself.

For the sake of perspicuity I shall, in the first instance, analyze the most simple

action of the wing in birds, although it necessarily supposes many previous steps.

When large birds, that have a considerable extent of wing compared with their

weight, have acquired their full velocity, it may frequently be observed, that they

extend their wings, and without waving them, continue to skim for some time in

a horizontal path. Fig. 1, in the Plate, represents a bird in this act.

Let a b be a section of the plane of both wings opposing the horizontal current of the air (created by its own motion) which may be represented by the line

c d, and is the measure of the velocity of the bird. The angle b d c can be increased

at the will of the bird, and to preserve a perfectly horizontal path, without the

wing being waved, must continually be increased in a complete ratio, (useless at

present to enter into) till the motion is stopped altogether; but at one given time

the position of the wings may be truly represented by the angle b d c. Draw d e perpendicular to the plane of the wings, produce the line e d as far as required, and

from the point e, assumed at pleasure in the line d e, let fall e f perpendicular to

d f. Then d e will represent the whole force of the air under the wing; which being

resolved into the two forces e f and f d, the former represents the force that sustains the weight of the bird, the latter the retarding force by which the velocity of

the motion, producing the current c d, will continually be diminished. e f is always

a known quantity, being equal to the weight of the bird, and hence f d is also
Document 1-1(a–c) 37

known, as it will always bear the same proportion to the weight of the bird, as the

sine of the angle b d e bears to its cosine, the angles d e f, and b d c, being equal.

In addition to the retarding force thus received is the direct resistance, which the

bulk of the bird opposes to the current. This is a matter to be entered into separately from the principle now under consideration; and for the present may be

wholly neglected, under the supposition of its being balanced by a force precisely equal and opposite to itself.

Before it is possible to apply this basis of the principle of flying in birds to the

purposes of aerial navigation, it will be necessary to encumber it with a few practical observations. The whole problem is confined within these limits, viz. To make

a surface support a given weight by the application of power to the resistance of

air. Magnitude is the first question respecting the surface. Many experiments have

been made upon the direct resistance of air by Mr. Robins, Mr. Rouse, Mr.

Edgeworth, Mr. Smeaton, and others. The result of Mr. Smeaton’s experiments

and observations was, that a surface of a square foot met with a resistance of one

pound, when it travelled perpendicularly to itself through air at a velocity of 21

feet per second. I have tried many experiments upon a large scale to ascertain this

point. The instrument was similar to that used by Mr. Robins, but the surface used

was larger, being an exact square foot, moving round upon an arm about five feet

long, and turned by weights over a pulley. The time was measured by a stop watch,

and the distance travelled over in each experiment was 600 feet. I shall for the

present only give the result of many carefully repeated experiments, which is, that

a velocity of 11.538 feet per second generated a resistance of 4 ounces; and that

a velocity of 17.16 feet per second gave 8 ounces resistance. This delicate instrument would have been strained by the additional weight necessary to have tried

the velocity generating a pressure of one pound per square foot; but if the resistance be taken to vary as the square of the velocity, the former will give the velocity necessary for this purpose at 23.1 feet, the latter 24.28 per second. I shall

therefore take 23.6 feet as somewhat approaching the truth.

Having ascertained this point, had our tables of angular resistance been complete, the size of the surface necessary for any given weight would easily have been

determined. Theory, which gives the resistance of a surface opposed to the same

current in different angles, to be as the squares of the sine of the angle of incidence, is of no use in this case; as it appears from the experiments of the French

Academy, that in acute angles, the resistance varies much more nearly in the

direct ratio of the sines, than as the squares of the sines of the angles of incidence.

The flight of birds will prove to an attentive observer, that, with a concave wing

apparently parallel to the horizontal path of the bird, the same support, and of

course resistance, is obtained. And hence I am inclined to suspect, that, under

extremely acute angles, with concave surfaces, the resistance is nearly similar in
38 Chapter 1: The Achievement of Flight
Document 1-1(a–c) 39

them all. I conceive the operation may be of a different nature from what takes

place in larger angles, and may partake more of the principle of pressure exhibited in the instrument known by the name of the hydrostatic paradox, a slender

filament of the current is constantly received under the anterior edge of the surface, and directed upward into the cavity, by the filament above it, in being

obliged to mount along the convexity of the surface, having created a slight vacuity immediately behind the point of separation. The fluid accumulated thus within the cavity has to make its escape at the posterior edge of the surface, where it

is directed considerably downward; and therefore has to overcome and displace a

portion of the direct current passing with its full velocity immediately below it;

hence whatever elasticity this effort requires operates upon the whole concavity of

the surface, excepting a small portion of the anterior edge. This may or may not

be the true theory, but it appears to me to be the most probable account of a phenomenon, which the flight of birds proves to exist.

Six degrees was the most acute angle, the resistance of which was determined

by the valuable experiments of the French Academy; and it gave 4⁄10 of the resistance, which the same surface would have received from the same current when

perpendicular to itself. Hence then a superficial foot, forming an angle of six

degrees with the horizon, would, if carried forward horizontally (as a bird in the

act of skimming) with a velocity of 23.6 feet per second, receive a pressure of 4⁄10

of a pound perpendicular to itself. And, if we allow the resistance to increase as

the square of the velocity, at 27.3 feet per second it would receive a pressure of

one pound. I have weighed and measured the surface of a great many birds, but

at present shall select the common rook (corvus frugilegus) because its surface and

weight are as nearly as possible in the ratio of a superficial foot to a pound. The

flight of this bird, during any part of which they can skim at pleasure, is (from an

average of many observations) about 34.5 feet per second. The concavity of the

wing may account for the greater resistance here received, than the experiments

upon plain surfaces would indicate. I am convinced, that the angle made use of

in the crow’s wing is much more acute than six degrees; but in the observations,

that will be grounded upon these data, I may safely state, that every foot of such

curved surface, as will be used in aerial navigation, will receive a resistance of one

pound, perpendicular to itself, when carried through the air in an angle of six

degrees with the line of its path, at a velocity of about 34 or 35 feet per second.

Let a b, fig. 2, represent such a surface or sail made of thin cloth, and containing about 200 square feet (if of a square form the side will be a little more than I4

feet); and the whole of a firm texture. Let the weight of the man and the machine

be 200 pounds. Then if a current of wind blew in the direction c d, with a velocity of 35 feet per second, at the same time that a cord represented by c d would sustain a tension of 21 pounds, the machine would be suspended in the air, or at least
40 Chapter 1: The Achievement of Flight

be within a few ounces of it (falling short of such support only in the ratio of the

sine of the angle of 94 degrees compared with radius; to balance which defect,

suppose a little ballast to be thrown out) for the line d e represents a force of 200

pounds, which, as before, being resolved into d f and f e, the former will represent

the resistance in the direction of the current, and the latter that which sustains the

weight of the machine. It is perfectly indifferent whether the wind blow against

the plane, or the plane be driven with an equal velocity against the air. Hence, if

this machine were pulled alone by a cord c d, with a tension of about 21 pounds,

at a velocity of 35 feet per second, it would be suspended in a horizontal path;

and if in lieu of this cord any other propelling power were generated in this direction, with a like intensity, a similar effect would be produced. If therefore the waft

of surfaces advantageously moved, by any force generated within the machine,

took place to the extent required, aerial navigation would be accomplished. As

the acuteness of the angle between the plane and current increases, the propelling power required is less and less. The principle is similar to that of the

inclined plane, in which theoretically one pound may be made to sustain all but

an infinite quantity; for in this case, if the magnitude of the surface be increased

ad infinitum, the angle with the current may be diminished, and consequently the

propelling force, in the same ratio. In practice, the extra resistance of the car and

other parts of the machine, which consume a considerable portion of power, will

regulate the limits to which this principle, which is the true basis of aerial navigation, can be carried; and the perfect ease with which some birds are suspended in

long horizontal flights, without one waft of their wings, encourages the idea, that

a slight power only is necessary.

As there are many other considerations relative to the practical introduction

of this machine, which would occupy too much space for any one number of your

valuable Journal, I propose, with your approbation, to furnish these in your subsequent numbers; taking this opportunity to observe, that perfect steadiness, safety, and steerage, I have long since accomplished upon a considerable scale of

magnitude; and that I am engaged in making some farther experiments upon a

machine I constructed last summer, large enough for aerial navigation, but which

I have not had an opportunity to try the effect of, excepting as to its proper balance and security. It was very beautiful to see this noble white bird sail majestically from the top of a hill to any given point of the plane below it, according to the

set of its rudder, merely by its own weight, descending in an angle of about 18

degrees with the horizon. The exertions of an individual, with other avocations,

are extremely inadequate to the progress, which this valuable subject requires.

Every man acquainted with experiments upon a large scale well knows how

leisurely fact follows theory, if ever so well founded. I do therefore hope, that what

I have said, and have still to offer, will induce others to give their attention to this
Document 1-1(a–c) 41

subject; and that England may not be backward in rivalling the continent in a

more worthy contest than that of arms.

As it may be an amusement to some of your readers to see a machine rise in

the air by mechanical means, I will conclude my present communication by

describing an instrument of this kind, which any one can construct at the expense

of ten minutes labour.

a and b, fig. 3, are two corks, into each of which are inserted four wing feathers from any bird, so as to be slightly inclined like the sails of a windmill, but in

opposite directions in each set. A round shaft is fixed in the cork a, which ends in

a sharp point. At the upper part of the cork b is fixed a whalebone bow, having a

small pivot hole in its centre, to receive the point of the shaft. The bow is then to

be strung equally on each side to the upper portion of the shaft, and the little

machine is completed. Wind up the string by turning the flyers different ways, so

that the spring of the bow may unwind them with their anterior edges ascending;

then place the cork with the bow attached to it upon a table, and with a finger on

the upper cork press strong enough to prevent the string from unwinding, and

taking it away suddenly, the instrument will rise to the ceiling. This was the first

experiment I made upon this subject in the year 1796. If in lieu of these small

feathers large planes, containing together 200 square feet, were similarly placed,

or in any other more convenient position, and were turned by a man, or first

mover of adequate power, a similar effect would be the consequence, and for the

mere purpose of ascent this is perhaps the best apparatus; but speed is the great

object of this invention, and this requires a different structure.

P. S. In lieu of applying the continued action of the inclined plane by means

of the rotative motion of flyers, the same principle may be made use of by the

alternate motion of surfaces backward and forward; and although the scanty

description hitherto published of Mr. Degen’s apparatus will scarcely justify any

conclusion upon the subject; yet as the principle above described must be the

basis of every engine for aerial navigation by mechanical means, I conceive, that

the method adopted by him has been nearly as follows. Let A and B, fig. 4, be two

surfaces or parachutes, supported upon the long shafts C and D, which are fixed

to the ends of the connecting beam E, by hinges. At E, let there be a convenient

seat for the aeronaut, and before him a cross bar turning upon a pivot in its centre, which being connected with the shafts of the parachutes by the rods F and G,

will enable him to work them alternately backward and forward, as represented by

the dotted lines. If the upright shafts be elastic, or have a hinge to give way a little near their tops, the weight and resistance of the parachutes will incline them

so, as to make a small angle with the direction of their motion, and hence the

machine rises. A slight heeling of the parachutes toward one side, or an alteration

in the position of the weight, may enable the aeronaut to steer such an apparatus
42 Chapter 1: The Achievement of Flight

tolerably well; but many better constructions may be formed, for combining the

requisites of speed, convenience and steerage. It is a great point gained, when the

first experiments demonstrate the practicability of an art; and Mr. Degen, by

whatever means he has effected this purpose, deserves much credit for his ingenuity.

Document 1-1(b), George Cayley, “On Aerial Navigation,” Part Two, 1810.

HAVING, in my former communication, described the general principle of

support in aerial navigation, I shall proceed to show how this principle must be

applied, so as to be steady and manageable.

Several persons have ventured to descend from balloons in what is termed a

parachute, which exactly resembles a large umbrella, with a light car suspended

by cords underneath it.

Mr. Garnerin’s descent in one of these machines will be in the recollection of

many; and I make the remark for the purpose of alluding to the continued oscillation,

or want of steadiness, which is said to have endangered that bold aeronaut. It is

very remarkable, that the only machines of this sort, which have been constructed,

are nearly of the worst possible form for producing a steady descent, the purpose

for which they are intended. To render this subject more familiar, let us recollect,

that in a boat, swimming upon water, its stability or stiffness depends, in general

terms, upon the weight and distance from the centre of the section elevated above

the water, by any given heel of the boat, on one side; and on the bulk, and its distance from the centre, which is immersed below the water, on the other side; the

combined endeavour of the one to fall and of the other to swim, produces the

desired effect in a well-constructed boat. The centre of gravity of the boat being

more or less below the centre of suspension is an additional cause of its stability.

Let us now examine the effect of a parachute represented by A B, fig. 1, PI.

III. When it has heeled into the position a b, the side a is become perpendicular

to the current, created by the descent, and therefore resists with its greatest

power; whereas the side b is become more oblique, and of course its resistance is

much diminished. In the instance here represented, the angle of the parachute

itself is 144°, and it is supposed to heel 18°, the comparative resistance of the side

a to the side b, will be as the square of the line a, as radius, to the square of the sine

of the angle of b with the current; which, being 54 degrees, gives the resistances

nearly in the ratio of 1 to 0.67; and this will be reduced to only 0.544, when estimated in a direction perpendicular to the horizon. Hence, so far as this form of

the sail or plane is regarded, it operates directly in opposition to the principle of

stability; for the side that is required to fall resists much more in its new position,

and that which is required to rise resists much less; therefore complete inversion

would be the consequence, if it were not for the weight being suspended so very
Document 1-1(a–c) 43

much below the surface, which, counteracting this tendency, converts the effort

into a violent oscillation.

On the contrary, let the surface be applied in the inverted position, as represented at C D, fig. 2, and suppose it to be heeled to the same angle as before, represented by the dotted lines c d. Here the exact reverse of the former instance

takes place; for that side, which is required to rise, has gained resistance by its new

position, and that which is required to sink has lost it; so that as much power oper-
44 Chapter 1: The Achievement of Flight

ates to restore the equilibrium in this case, as tended to destroy it in the other:

the operation very much resembling what takes place in the common boat. (A

very simple experiment will show the truth of this theory. Take a circular piece of

writing paper, and folding up a small portion, in the line of two radii, it will be

formed into an obtuse cone. Place a small weight in the apex, and letting it fall

from any height, it will steadily preserve that position to the ground. Invert it,

and, if the weight be fixed, like the life boat, it rights itself instantly.)

This angular form, with the apex downward, is the chief basis of stability in

aerial navigation; but as the sheet which is to suspend the weight attached to it,

in its horizontal path through the air, must present a slightly concave surface in a

small angle with the current, this principle can only be used in the lateral extension of the sheet; and this most effectually prevents any rolling of the machine

from side to side. Hence the section of the inverted parachute, fig. 2, may equally well represent the cross section of a sheet for aerial navigation.

The principle of stability in the direction of the path of the machine, must be

derived from a different source. Let A B, fig. 3, be a longitudinal section of a sail,

and let C be its centre of resistance, which experiment shows to be considerably

more forward than the centre of the sail. Let C D be drawn perpendicular to A B,

and let the centre of gravity of the machine be at any point in that line, as at D.

Then, if it be projected in a horizontal path with velocity enough to support the

weight, the machine will retain its relative position, like a bird in the act of skimming;

for, drawing C E perpendicular to the horizon, and D E parallel to it, the line C

E will, at some particular moment, represent the supporting power, and likewise

its opponent the weight; and the line D E will represent the retarding power, and

its equivalent, that portion of the projectile force expended in overcoming it:

hence, these various powers being exactly balanced, there is no tendency in the

machine but to proceed in its path, with its remaining portion of projectile force.

The stability in this position, arising from the centre of gravity being below

the point of suspension, is aided by a remarkable circumstance that experiment

alone could point out. In very acute angles with the current it appears, that the

centre of resistance in the sail does not coincide with the centre of its surface, but

is considerably in front of it. As the obliquity of the current decreases, these centres

approach, and coincide when the current becomes perpendicular to the sail.

Hence any heel of the machine backward or forward removes the centre of support

behind or before the point of suspension; and operates to restore the original

position, by a power, equal to the whole weight of the machine, acting upon a

lever equal in length to the distance the centre has removed.

To render the machine perfectly steady, and likewise to enable it to ascend

and descend in its path, it becomes necessary to add a rudder in a similar position

to the tail in birds. Let F G be the section of such a surface, parallel to the current;
Document 1-1(a–c) 45

and let it be capable of moving up and down upon G, as a centre, and of being

fixed in any position. The powers of the machine being previously balanced, if the

least pressure be exerted by the current, either upon the upper or under surface

of the rudder, according to the will of the aeronaut, it will cause the machine to

rise or fall in its path, so long as the projectile or propelling force is continued

with sufficient energy. From a variety of experiments upon this subject I find, that,

when the machine is going forward with a superabundant velocity, or that which

would induce it to rise in its path, a very steady horizontal course is effected by a

considerable depression of the rudder, which has the advantage of making use of

this portion of sail in aiding the support of the weight. When the velocity is

becoming less, as in the act of alighting, then the rudder must gradually recede

from this position, and even become elevated, for the purpose of preventing the

machine from sinking too much in front, owing to the combined effect of the want

of projectile force sufficient to sustain the centre of gravity in its usual position,

and of the centre of support approaching the centre of the sail.

The elevation and depression of the machine are not the only purposes, for

which the rudder is designed. This appendage must be furnished with a vertical

sail and be capable of turning from side to side in addition to its other movements,

which effects the complete steerage of the vessel.

All these principles, upon which the support, steadiness, elevation, depression,

and steerage of vessels for aerial navigation, depend, have been abundantly verified

by experiments both upon a small and a large scale. Last year I made a machine,

having a surface of 300 square feet, which was accidentally broken before there

was an opportunity of trying the effect of the propelling apparatus; but its steerage

and steadiness were perfectly proved, and it would sail obliquely downward in any

direction, according to the set of the rudder. Even in this state, when any. person ran

forward in it, with his full speed, taking advantage of a gentle breeze in front, it

would bear upward so strongly as scarcely to allow him to touch the ground; and

would frequently lift him up, and convey him several yards together.

The best mode of producing the propelling power is the only thing, that

remains yet untried toward the completion of the invention. I am preparing to

resume my experiments upon this subject, and state the following observations, in

the hope that others may be induced to give their attention towards expediting

the attainment of this art.

The act of flying is continually exhibited to our view; and the principles upon which

it is effected are the same as those before stated. If an attentive observer examines

the waft of a wing, he will perceive, that about one third part, toward the extreme

point, is turned obliquely backward; this being the only portion, that has velocity

enough to overtake the current, passing so rapidly beneath it, when in this unfavourable

position. Hence this is the only portion that gives any propelling force.
46 Chapter 1: The Achievement of Flight

To make this more intelligible, let A B, fig. 4, be a section of this part of the

wing. Let C D represent the velocity of the bird’s path, or the current, and E D

that of the wing in its waft: then C E will represent the magnitude and direction

of the compound or actual current striking the under surface of the wing.

Suppose E F, perpendicular to A B, to represent the whole pressure; E G being

parallel to the horizon, will represent the propelling force; and G F, perpendicular to it, the supporting power. A bird is supported as effectually during the return

as during the beat of its wing; this is chiefly effected by receiving the resistance of

the current under that portion of the wing next the body where its receding

motion is so slow as to be of scarcely any effect. The extreme portion of the wing,

owing to its velocity, receives a pressure downward and obliquely forward, which

forms a part of the propelling force; and at the same time, by forcing the hinder

part of the middle portion of the wing downward, so increases its angle with the

current, as to enable it still to receive nearly its usual pressure from beneath.

As the common rook has its surface and weight in the ratio of a square foot

to a pound, it may be considered as a standard for calculations of this sort; and I

shall therefore state, from the average of many careful observations, the movements of that bird. Its velocity, represented by C D, fig. 4, is 34.5 feet per second.

It moves its wing up and down once in flying over a space of 12.9 feet. Hence, as

the centre of resistance of the extreme portion of the wing moves over a space of

0.75 of a foot each beat or return, its velocity is about 4 feet per second, represented by the line E D. As the wing certainly overtakes the current, it must be

inclined from it in an angle something less than 7°, for at this angle it would

scarcely be able to keep parallel with it, unless the waft downward were performed

with more velocity than the return; which may be and probably is the case, though

these movements appear to be of equal duration. The propelling power, represented by E G, under these circumstances, cannot be equal to an eighth part of

the supporting power G F, exerted upon this portion of the wing; yet this, together with the aid from the return of the wing, has to overcome all the retarding

power of the surface, and the direct resistance occasioned by the bulk of the body.

It has been before suggested, and I believe upon good grounds, that very

acute angles vary little in the degree of resistance they make under a similar

velocity of current. Hence it is probable, that this propelling part of the wing

receives little more than its common proportion of resistance, during the waft

downward. If it be taken at one-third of the whole surface, and one-eighth of this

be allowed as the propelling power, it will only amount to one twenty-fourth of

the weight of the bird; and even this is exerted only half the duration of the flight.

The power gained in the return of the wing must be added, to render this statement

correct, and it is difficult to estimate this; yet the following statement proves, that

a greater degree of propelling force is obtained, upon the whole, than the fore-
Document 1-1(a–c) 47

going observations will justify. Suppose the largest circle that can be described in

the breast of a crow, to be 12 inches in area. Such a surface, moving at the velocity of 34.5 feet per second, would meet a resistance of 0.216 of a pound, which,

reduced by the proportion of the resistance of a sphere to its great circle (given by 

Mr. Robins as 1 to 2.27) leaves a resistance of 0.095 of a pound, had the breast

been hemispherical. It is probable however, that the curve made use of by Nature

to avoid resistance, being so exquisitely adapted to its purpose, will reduce this

quantity to one half less than the resistance of the sphere, which would ultimately leave 0.0475 of a pound as somewhat approaching the true resistance. Unless

therefore the return of the wing gives a greater degree of propelling force than

the beat, which is improbable, no such resistance of the body could be sustained.

Hence, though the eye cannot perceive any distinction between the velocities of

the beat and return of the wing, it probably exists, and experiment alone can

determine the proper ratios between them.

From these observations we may, however, be justified in the remark—that the

act of flying, when properly adjusted by the Supreme Author of every power,

requires less exertions than, from the appearance, is supposed.

Document 1-1(c), George Cayley, “On Aerial Navigation,” Part Three, 1810.

BROMPTON, Dec. 6, 1809.

NOT having sufficient data to ascertain the exact degree of propelling power

exerted by birds in the act of flying, it is uncertain what degree of energy may be

required in this respect in vessels for aerial navigation: yet, when we consider the

many hundred miles of continued flight exerted by birds of passage, the idea of

its being only a small effort is greatly corroborated. To apply the power of the first

mover to the greatest advantage in producing this effect, is a very material point.

The mode universally adopted by nature is the oblique waft of the wing. We have

only to choose between the direct beat overtaking the velocity of the current, like

the oar of a boat; or one, applied like the wing, in some assigned degree of obliquity to it. Suppose 35 feet per second to be the velocity of an aerial vehicle, the

oar must be moved with this speed previous to its being able to receive any resistance; then, if it be only required to obtain a pressure of 1/10th of a pound upon

each square foot, it must exceed the velocity of the current 7.5 feet per second.

Hence its whole velocity must be 42.5 feet per second. Should the same surface

be wafted downward, like a wing, with the hinder edge inclined upward in an

angle of about 50° 40' to the current, it will overtake it at a velocity of 3.5 feet per

second; and as a slight unknown angle of resistance generates a pound pressure

per square foot at this velocity, probably a waft of little more than 4 feet per second would produce this effect; one tenth part of which would be the propelling
48 Chapter 1: The Achievement of Flight

power. The advantage in favour of this mode of application, compared with the

former, is rather more than ten to one.

In combining the general principles of aerial navigation for the practice of

the art many mechanical difficulties present themselves, which require a considerable course of skilfully applied experiments, before they can be overcome. But

to a certain extent the air has already been made navigable; and no one, who has

seen the steadiness with which weights to the amount of ten stone (including four

stone, the weight of the machine) hover in the air, can doubt of the ultimate

accomplishment of this object.

The first impediment I shall take notice of is the great proportion of power, that

must be exerted previous to the machine’s acquiring that velocity, which gives support

upon the principle of the inclined plane; together with the total want of all support

during the return of any surface used like a wing. Many birds, and particularly

water fowl, run and flap their wings for several yards before they can gain support

from the air. The swift (hirundo apus Lin.) is not able to elevate itself from level

ground. The inconvenience under consideration arises from very different causes

in these two instances. The supporting surface of most swimming birds does not

exceed the ratio of 4

⁄10ths of a square foot to every pound of their weight: the swift,

though it scarcely weighs an ounce, measures eighteen inches in extent of wing.

The want of surface in the one case, and the inconvenient length of wing in the other,

oblige these birds to aid the commencement of their flight by other expedients; yet

they can both fly with great power, when they have acquired their full velocity.

A second difficulty in aerial navigation arises from the great extent of lever,

which is constantly operating against the first mover, in consequence of the distance of the centre of support in large surfaces, if applied in the manner of wings.

A third and general obstacle is the mechanical skill required to unite great

extension of surface with strength and lightness of structure; at the same time

having a firm and steady movement in its working parts, without exposing unnecessary obstacles to the resistance of the air. The first of these obstacles, that have

been enumerated, operates much more powerfully against aerial navigation upon

a large scale, than against birds; because the small extent of their wings obliges

them to employ a very rapid succession of strokes, in order to acquire that velocity

which will give support; and during the small interval of the return of the wing,

their weight is still rising, as in a leap, by the impulse of one stroke, till it is again

aided by another. The large surfaces that aerial navigation will probably require,

though necessarily moved with the same velocity, will have a proportionably

longer duration both of the beat and return of the wing; and hence a greater

descent will take place during the latter action, than can be overcome by the former.

There appears to be several ways of obviating this difficulty. There may be two

surfaces, each capable of sustaining the weight, and placed one above the other,
49

having such a construction as to work up and down in opposition when they are

moved, so that one is always ready to descend, the moment the other ceases.

These surfaces may be so made, by a valvelike structure, as to give no opposition

in rising up, and only to resist in descent.

The action may be considered either oblique, as in rotative flyers; alternately

so, without any up and down waft, as in the engine I have ascribed to Mr. Degen;

by means of a number of small wings in lieu of large ones, upon the principle of

the flight of birds, with small intervals of time between each waft; and lastly by

making use of light wheels to preserve the propelling power both of the beat and

the return of the wings, till it accumulates sufficiently to elevate the machine,

upon the principle of those birds which run themselves up. This action might be

aided by making choice of a descending ground like the swift.

With regard to another part of the first obstacle I have mentioned, viz. the

absolute quantity of power demanded being so much greater at first than when

the full velocity has been acquired; it may be observed, that, in the case of human

muscular strength being made use of, a man can exert, for a few seconds, a surprising degree of force. He can run up stairs, for instance, with a velocity of from

6 to 8 feet perpendicular height per second, without any dangerous effort; here

the muscles of his legs only are in action; but, for the sake of making a moderate

statement, suppose that with the activity of his arms and body, in addition to that

of his legs, he is equal to raising his weight 8 feet per second; if in this case he

weighs 11 stone, or 154 pounds, he will be exerting, for the time, an energy equal

to more than the ordinary force of two of Messrs. Boulton and Watt’s steam horses;

and certainly more than twelve men can bestow upon their constant labour.

If expansive first movers be made use of, they may be so constructed, as to be

capable of doing more than their constant work; or their power may be made to

accumulate for a few moments by the formation of a vacuum, or the condensation

of air, so that these expedients may restore at one time, in addition to the working of the engine, that which they had previously absorbed from it.

With regard to the second obstacle in the way of aerial navigation, viz. the

length of leverage to which large wing-like surfaces are exposed, it may be

observed, that, being a constant and invariable quality, arising from the degree of

support such surfaces give, estimated at their centres of resistance, it may be balanced by any elastic agent, that is so placed as to oppose it. Let A and B, PI. IV,

fig. 1, be two wings of an aerial vehicle in the act of skimming; then half the

weight of the vessel is supported from the centre of resistance of each wing; as

represented by the arrows under them. If the shorter ends of these levers be connected by cords to the string of a bow C, of sufficient power to balance the weight

of the machine at the points A and B, then the moving power will be left at full

liberty to produce the waft necessary to bend up the hinder edge of the wing, and

Document 1-1(a–c)
50 Chapter 1: The Achievement of Flight

gain the propelling power. A bow is not in fact an equable spring, but may be

made so by using a spiral fusee. I have made use of it in this place merely as the

most simple mode of stating the principle I wished to exhibit. Should a counterbalancing spring of this kind be adopted in the practice of aerial navigation, a

small well polished cylinder, furnished with what may be termed a bag piston

(upon the principle made use of by nature in preventing the return of the blood

to the heart, when it has been driven into the aorta, by the intervention of the

semilunar valves) would, by a vacuum being excited each stroke of the wing, produce the desired effect, with scarcely any loss by friction. These elastic agents may

likewise be useful in gradually stopping the momentum of large surfaces when

used in any alternate motion, and in thus restoring it during their return.

(I have made use of several of these pistons, and have no scruple in asserting,

that for all blowing engines, where friction is an evil, and being very nearly airtight is sufficient, there is no other piston at all comparable with them. The most

irregular cylinder, with a piston of this kind, will act with surprising effect. To give

an instance; a cylinder of sheet tin, 8 inches long and 3 1⁄2 in diameter, required

4 pounds to force the piston down in 15 minutes; and in other trials became perfectly tight in some positions, and would proceed no farther. The friction, when

the cylinder was open at both ends, did not exceed 1⁄2 an ounce.)

Another principle, that may be applied to obviate this leverage of a wing, is

that of using such a construction as will make the supporting power of the air

counterbalance itself. It has been before observed, that only about one third of

the wing in birds is applied in producing the propelling power; the remainder,

not having velocity sufficient for this purpose, is employed in giving support,

both in the beat and return of the wing.

Let A and B, fig. 2, be two wings continued beyond the pole or hinge upon

which they turn at C. If the extreme parts at A and B be long and narrow, they

may be balanced, when in the act of skimming, by a broad extension of less length

on their opposite sides; this broad extension, like the lower part of the wing, will

always give nearly the same support, and the propelling part of the surface will

be at liberty to act unincumbered by the leverage of its supporting power. This

plan may be modified many different ways; but my intention, as in the former

case, is still the principle in its simplest form.

A third principle upon which the leverage of a surface may be prevented is by

giving it a motion parallel to itself, either directly up and down, or obliquely so.

The surface A 1, fig. 3, may be moved perpendicularly, by the shaft which supports it,

down to the position K C: or, if it be supported upon two shafts with hinges at D

and E, it may be moved obliquely parallel to itself into the position B L.

A fourth principle upon which the leverage may be greatly avoided, where

only one hinge is used, is by placing it considerably below the plane of the wing,
Document 1-1(a–c) 51

as at the point D, fig. 3, in respect to the surface A. It may be observed in the

heron, which is a weak bird with an extended surface, that its wings curve downward considerably from the hinge to the tip; hence the extreme portion, which

receives the chief part of the stroke, is applied obliquely to the current it creates;

and thus evades in a similar degree the leverage of that portion of the supporting

power, which is connected with the propelling power. These birds seldom carry

their waft much below the level of the hinge of the wing, where this principle, so

far as respects the supporting power, would vanish.
52 Chapter 1: The Achievement of Flight

By making use of two shafts of unequal length, the two last mentioned principles may be blended to any required extent. Suppose one hinge to be at F, and

the other at G, fig. 3, then the surface, at the extent of its beat, would be in the

position of the line H M. If the surface A 1, fig. 3, be supported only upon one

shaft, N E, be capable of being forced in some degree from its rectangular position in respect to the shaft, and be concave instead of flat as here represented;

then the waft may be used alternately backward and forward, according to the

principles of the machine I have ascribed to Mr. Degen. This construction combines the principles of counterpoising the supporting power of one part of the

surface, by that of an opposite part, when the machine is in the act of skimming;

and likewise the advantages of the low hinge, with the principle of leaving little

or no interval without support.

All that has hitherto appeared respecting Mr. Degen’s apparatus is, that it

consisted of two surfaces, which were worked by a person sitting between them.

This statement communicates no real information upon the subject; for scarcely

anyone would attempt to fly without two wings; without these being equally poised

by placing the weight between them; and also, without these surfaces being capable of receiving motion from his muscular action. I may be altogether mistaken in

my conjecture; my only reason for ascribing this structure of mine to Mr. Degen’s

machine is, that, if it were properly executed upon this principle, it would be

attended with success. The drawing, rather diagram, which is given of this

machine in the first part of my essay, is only for the purpose of exhibiting the

principle in a form capable of being understood. The necessary bracings, etc.,

required in the actual execution of such a plan, would have obscured the simple

nature of its action; and were therefore omitted. The plan of its movement is also

simply to exhibit, in a tangible form, the possibility of effecting the intended

alternate motion of the parachutes. The seat is fronted lengthwise for the purpose

of accommodating the mode of communicating the movement.

A fifth mode of avoiding leverage is by using the continued action of oblique

horizontal flyers, or an alternate action of the same kind, with surfaces so constructed as to accommodate their position to such alternate motion; the hinge or

joint being in these cases vertical. In the construction of large vessels for aerial

navigation, a considerable portion of fixed sail will probably be used; and no

more surface will be allotted, towards gaining the propelling power, than what is

barely necessary, with the extreme temporary exertion of the first mover, to elevate the machine and commence the flight. In this case the leverage of the fixed

surface is done away.

The general difficulties of structure in aerial vehicles, (arising from the extension, lightness, and strength required in them; together with great firmness in the

working parts, and at the same time such an arrangement as exposes no unnec-
Document 1-1(a–c) 53

essary obstacles to the current,) I cannot better explain than by describing a wing,

which has been constructed with a view to overcome them.

Fig. 4 represents the shape of the cloth, with a perspective view of the poles upon

which it is stretched with perfect tightness. Upon the point where the rods A and B

intersect is erected an oval shaft; embracing the two cross poles by a slender iron fork;

for the purpose of preserving their strength uninjured by boring. To this shaft are

braced the ends of the pole B, so as to give this pole any required degree of curvature.

The pole A is strung like a common bow to the same curve as the pole B; and is only

connected with the upright shaft by what may be called a check brace; which will allow

the hinder end of this pole to heel back to a certain extent, but not the fore end. The

short brace producing this effect is shown in fig. 4. Fig. 5 exhibits the fellow wing to

that represented in fig. 4, erected upon a beam, to which it is so braced, as to convert

the whole length of it into a hinge. The four braces coming from the ends of this beam

are shown: two of them terminate near the top of the centre of the other shaft; the

others are inserted into the point C, fig. 4, of the bending rod. A slight bow, not more

than three-eighths of an inch thick, properly curved by its string, and inserted

between the hinder end of the pole A, and the curved pole C, completes the wing.

This fabrick contained 54 square feet, and weighed only eleven pounds.

Although both these wings together did not compose more than half the surface

necessary for the support of a man in the air, yet during their waft they lifted the

weight of nine stone. The hinder edge, as is evident from the construction, being

capable of giving way to the resistance of the air, any degree of obliquity, for the

purpose of a propelling power, may be used.

I am the more particular in describing this wing, because it exemplifies

almost all the principles that can be resorted to in the construction of surfaces for

aerial navigation. Diagonal bracing is the great principle for producing strength

without accumulating weight; and, if performed by thin wires, looped at their

ends, so as to receive several laps of cordage, produces but a trifling resistance in

the air, and keeps tight in all weathers. When bracings are well applied, they make

the poles, to which are attached, bear endwise. The hollow form of the quill in

birds is a very admirable structure for lightness combined with strength, where

external bracings cannot be had; a tube being the best application of matter to

resist as a lever; but the principle of bracing is so effectual, that, if properly

applied, it will abundantly make up for the clumsiness of human invention in

other respects; and should we combine both these principles, and give diagonal

bracing to the tubular bamboo cane, surfaces might be constructed with a greater

degree of strength and lightness, than any made use of in the wings of birds.

The surface of a heron’s wing is in the ratio of 7 square feet to a pound. Hence,

according to this proportion, a wing of 54 square feet would weigh about 7 3

⁄4 pounds:

on the contrary the wings of water fowl are so much heavier, that a surface of 54 square
54 Chapter 1: The Achievement of Flight

feet, according to their structure, will weight 18 1⁄2 lb. I have in these instances quoted

nearly the extreme cases among British birds; the wing I have described may therefore

be considered as nearly of the same weight in proportion to its bulk as that of most birds.

Another principle exhibited in this wing is that of the poles being couched

within the cloth, so as to avoid resistance. This is accomplished by the convexity

of the frame, and the excessive lightness of the cloth. The poles are not allowed

to form the edge of the wing, excepting at the extreme point of the bow, where it

is very thin, and also oblique to the current. The thick part of this pole is purposely conveyed considerably within the edge. In birds, a membrane covered with

feathers is stretched before the thick part of the bone of the wing, in a similar

manner, and for the same purpose. The edge of the surface is thus reduced to the

thickness of a small cord, that is sown to the cloth, and gives out loops whenever

any fastening is required. The upright shaft is the only part that opposes much

direct resistance to the current, and this is obviated in a great degree by a flat oval

shape, having its longest axis parallel to the current.

The joint or hinge of this wing acts with great firmness, in consequence of its

being supported by bracings to the line of its axis, and at a considerable distance

from each other; in fact the bracings form the hinge.

The means of communicating motion to any surfaces must vary so much, according to the general structure of the whole machine, that I shall only observe at present,

that where human muscular action is employed, the movement should be similar to

the mode of pulling oars; from which any other required motion may be derived; the

foot-board in front enables a man to exert his full force in this position. The wings I

have described were wafted in this manner; and when they lifted with a power of 9

stone, not half of the blow, which a man’s strength could have given, was exerted, in

consequence of the velocity required being greater than convenient under the circumstances. Had these wings been intended for elevating the person who worked them,

they should have contained from 100 to 150 square feet each; but they were constructed for the purpose of an experiment relative to the propelling power only.

Avoiding direct resistance is the next general principle, that it is necessary to

discuss. Let it be remembered as a maxim in the art of aerial navigation, that

every pound of direct resistance, that is done away, will support 30 pounds of

additional weight without any additional power. The figure of a man seems but ill

calculated to pass with ease through the air, yet I hope to prove him to the full as

well made in this respect as the crow, which has hitherto been our standard of

comparison, paradoxical as it may appear.

The principle, that surfaces of similar bodies increase only as the squares of

their homologous lines, while their weights, or rather solid contents, increase as

the cubes of those lines, furnishes the solution. This principle is unanimously in

favour of large bodies. The largest circle that can be described in a crow’s breast
Document 1-1(a–c) 55

is about 12 square inches in area. If a man exposes a direct bulk of 6 square feet,

the ratio of their surfaces will be as 1 to 72; but the ratio of their weight is as 1 to

110; which is 1 1⁄2 to 1 in favour of the man, provided he were within a case as well

constructed for evading resistance, as the body of the crow; but even supposing

him to be exposed in his natural cylindric shape, in the foreshortened posture of

sitting to work his oars, he will probably receive less resistance than the crow.

It is of great importance to this art, to ascertain the real solid of least resistance,

when the length or breadth is limited. Sir Isaac Newton’s beautiful theorem upon

this subject is of no practical use, as it supposes each particle of the fluid, after

having struck the solid, to have free egress; making the angles of incidence and

reflection equal; particles of light seem to possess this power, and the theory will

be true in that case; but in air the action is more like an accumulation of particles,

rushing up against each other, in consequence of those in contact with the body

being retarded. The importance of this subject is not less than the difficulties it

presents; it affects the present interests of society in its relation to the time occupied in the voyages of ships; it will have still more effect when aerial navigation,

now in its cradle, is brought home to the uses of man. I shall state a few crude

hints upon this point, to which my subject has so unavoidably led, and on which

I am so much interested, and shall be glad if in so doing I may excite the attention of those, who are competent to an undertaking greatly beyond my grasp.

Perhaps some approach toward ascertaining the actual solid of least resistance

may be derived from treating the subject in a manner something similar to the

following. Admit that such a solid is already attained (the length and width being

necessarily taken at pleasure). Conceive the current intercepted or disturbed, by

the largest circle that can be drawn within the given spindle, to be divided into

concentric tubular laminae of equal thickness. At whatever distance from this

great circle the apex of the spindle commences, on all sides of this point the central

lamina will be reflected in diverging pencils, (or rather an expanding ring,) making their angles of incidence and reflection equal. After this reflection they rush

against the second lamina and displace it: this second lamina contains three times

more fluid than the first; consequently each pencil in the first meets three pencils

in the second; and their direction, after the union, will be one fourth of the angle,

with respect to the axis, which the first reflection created. In this direction these

two laminae proceed till they are themselves reflected, when they (considered as

one lamina of larger dimensions) rush against the third and fourth, which together

contain three times the fluid in the two former laminae, and thus reduce the

direction of the combined mass to one fourth of the angle between the axis and

the line of the second reflection. This process is constant, whatever be the angles

formed between the surface of the actual solid of least resistance at these points

of reflection, and the directions of the currents thus reflected.
56 Chapter 1: The Achievement of Flight

From this mode of reasoning, which must in some degree resemble what takes

place, and which I only propose as a resemblance, it appears, that the fluid keeps

creeping along the curved surface of such a solid, meeting it in very acute angles.

Hence, as the experiments of the French Academy show, that the difference of

resistance between the direct impulse, and that in an angle of six degrees, on the

same surface, is only in the ratio of 10 to 4, it is probable, that in the slight difference of angles that occur in this instance, the resistances may be taken as equal

upon every part, without any material deviation from truth. If this reasoning be

correct, it will reduce the question, so far as utility is concerned, within a strictly

abstract mathematical inquiry.

It has been found by experiment, that the shape of the hinder part of the spindle

is of as much importance as that of the front, in diminishing resistance. This arises

from the partial vacuity created behind the obstructing body. If there be no solid to

fill up this space, a deficiency of hydrostatic pressure exists within it, and is transferred to the spindle. This is seen distinctly near the rudder of a ship in full sail,

where the water is much below the level of the surrounding sea. The cause here,

being more evident, and uniform in its nature, may probably be obviated with better

success; in as much as this portion of the spindle may not differ essentially from

the simple cone. I fear however, that the whole of this subject is of so dark a

nature, as to be more usefully investigated by experiment, than by reasoning; and

in the absence of any conclusive evidence from either, the only way that presents

itself is to copy nature; accordingly I shall instance the spindles of the trout and

woodcock, which, lest the engravings should, in addition to the others, occupy too

much valuable space in your Journal, must be reserved to a future opportunity.
Document 1-2 57

Document 1-2

Thomas Jefferson, letter to William D. B. Lee, 27 April 1822.

The remarkable farsightedness of George Cayley’s understanding of aerodynamics can be gauged by the lack of confidence many of the leading intellectuals

and scientists of his day had in the future of “aerial navigation” with flying

machines. Responding to this issue just four years before his death, an elderly

Thomas Jefferson, principal author of the Declaration of Independence (1776)

and third President of the United States (from 1801 to 1809), took the following

cautiously pessimistic view about the possibility of mechanical flight. Jefferson

possessed a wide-ranging curiosity about all things, especially science and technology. But here in 1822, in his advanced years, he seems to be admitting that

they have progressed well beyond his capacity to understand them fully or to

assess the potential of such radically new concepts as mechanical flight. (The

spelling in this document is Jefferson’s.) 

Document 1-2, Thomas Jefferson, letter to William D. B. Lee, 27 April 1822.

Your letter of the 15th is received, but age has long since obliged me to withdraw my mind from speculations of the difficulty of those of your letter. That

there are means of artificial buoyancy by which man may be supported in the air,

the balloon has proved, and that means of directing it may be discovered is

against no law of nature and is therefore possible as in the case of birds. But to do

this by mechanical means alone in a medium so rare and unresisting as air must

have the aid of some principle not yet generally known. However I can really give

no opinion understandingly on the subject and with more goodwill than confidence wish you success.
58 Chapter 1: The Achievement of Flight

Document 1-3(a–c)

(a) Francis H. Wenham, “On Aerial Locomotion and the Laws

by Which Heavy Bodies Impelled Through Air are 

Sustained,” First Annual Report of the Aeronautical Society 

of Great Britain for the Year 1866, pp. 10–47.

(b) Report on the first wind tunnel built by 

Francis H. Wenham, Sixth Annual Report of the Aeronautical

Society of Great Britain, for the Year 1871, pp. 75–78.

(c) Minutes of Aeronautical Society, Seventh Annual Report 

of the Aeronautical Society of Great Britain, 

for the Year 1872, pp. 5–12.

A crucial step forward for aeronautics happened in January 1866 when a group

of serious aviation enthusiasts met for the first time, creating the Aeronautical

Society of Great Britain. Later this organization of gentleman amateurs and professional engineers interested in flight became the Royal Aeronautical Society.

Through its regular periodic meetings and publications, the study of human

flight received an important early measure of scholarly credence and viability. 

The first document below, from the year 1866, is one of the most interesting

of the very early papers presented at a meeting of the Aeronautical Society of

Great Britain. Its author, Francis H. Wenham (1824–1908), the son of an army

surgeon with no college education, rose to great prominence in the emerging

field of aeronautics; some even came to consider him “the father of aeronautics”

in Britain. In this 1866 paper, published in the society’s first annual report,

Wenham focused on a principle that its author called “sustainment,” by which he

meant principally aerodynamic lift. Although his paper contributed an important

idea in the form of his favorable analysis of what we would call a “high aspectratio” wing (with multiplane layout and propeller propulsion), most of Wenham’s

presentation suffered from a serious lack of clarity and depth regarding the basic

sources of aerodynamic force. One of the reasons for this was Wenham’s weakness

in higher mathematics. As readers will see, his 1866 paper contained no mathematical equations; his basic inclination was always to solve technical problems

through experimental means. 

This experimental approach can be clearly seen in the second document

below, from the Aeronautical Society of Great Britain’s report of 1871, which dis-
Document 1-3(a–c) 59

cusses Wenham’s design of what historians now recognize to be the world’s first

wind tunnel. Though Wenham used his primitive, steam-engine-driven wind tunnel (maximum velocity was forty miles per hour) solely to explore the lift and drag

characteristics of flat surfaces, the type of device he pioneered showed great

promise. In the following decade, in 1884, another member of the Aeronautical

Society of Great Britain, Horatio Phillips, built a second, improved tunnel to

demonstrate the improved lifting qualities of mildly cambered surfaces. Together,

these two tunnels paved the way for what, by the Wright brother era, became the

most basic and versatile tool in modern aeronautical experimentation.

Document 1-3(a), Francis H. Wenham, “On Aerial Locomotion,” 27 June 1866.

The resistance against a surface of a defined area, passing rapidly through

yielding media, may be divided into two opposing forces. One arising from the

cohesion of the separated particles; and the other from their weight and inertia,

which, according to well-known laws, will require a constant power to set them in

motion.

In plastic substances, the first condition, that of cohesion, will give rise to the

greatest resistance. In water this has very little retarding effect, but in air, from its

extreme fluidity, the cohesive force becomes inappreciable, and all resistances are

caused by its weight alone; therefore, a weight, suspended from a plane surface,

descending perpendicularly in air, is limited in its rate of fall by the weight of air

that can be set in motion in a given time.

If a weight of 150 lbs. is suspended from a surface of the same number of

square feet, the uniform descent will be 1,300 feet per minute, and the force given

out and expended on the, air, at this rate of fall, will be nearly six horse-power;

and, conversely, this same speed and power must be communicated to the surface

to keep the weight sustained at a fixed altitude. As the surface is increased, so does

the rate of descent and its accompanying power, expended in a given time,

decrease. It might, therefore, be inferred that, with a sufficient extent of surface

reproduced, or worked up to a higher altitude, a man might by his exertions raise

himself for a time, while the surface descends at a less speed.

A man, in raising his own body, can perform 4,250 units of work—that is, this

number of pounds raised one foot high per minute—and can raise his own

weight—say, 150 lbs.—twenty-two feet per minute. But at this speed the atmospheric resistance is so small that 120,000 square feet would be required to balance

his exertions, making no allowance for weight beyond his own body.

We have thus reasons for the failure of the many misdirected attempts that have,

from time to time, been made to raise weights perpendicularly in the air by wings or

descending surfaces. Though the flight of a bird is maintained by a constant reaction
60 Chapter 1: The Achievement of Flight

or abutment against an enormous weight of air in comparison with the weight of its

own body, yet, as will be subsequently shown, the support upon that weight is not necessarily commanded by great extent of wing-surface, but by the direction of motion.

One of the first birds in the scale of flying magnitude is the pelican. It is seen

in the streams and estuaries of warm climates, fish being its only food. On the

Nile, after the inundation, it arrives in flocks of many hundreds together, having

migrated from long distances. A specimen shot was found to weigh twenty-one

pounds, and measured ten feet across the wings, from end to end. The pelican

rises with much difficulty, but, once on the wing, appears to fly with very little

exertion, notwithstanding its great weight. Their mode of progress is peculiar and

graceful. They fly after a leader, in one single train. As he rises or descends, so his

followers do the same in succession, imitating his movements precisely. At a distance, this gives them the appearance of a long undulating ribbon, glistening

under the cloudless sun of an oriental sky. During their flight they make about

seventy strokes per minute with their wings. This uncouth-looking bird is somewhat whimsical in its habits. Groups of them may be seen far above the earth, at

a distance from the river-side, soaring, apparently for their own pleasure. With

outstretched and motionless wings, they float serenely, high in the atmosphere,

for more than an hour together, traversing the same locality in circling movements. With head thrown back, and enormous bills resting on their breasts, they

almost seem asleep. A few easy strokes of their wings each minute, as their

momentum or velocity diminishes, serves to keep them sustained at the same

level. The effort required is obviously slight, and not confirmatory of the excessive amount of power said to be requisite for maintaining the flight of a bird of

this weight and size. The pelican displays no symptom of being endowed with

great strength, for when only slightly wounded it is easily captured, not having

adequate power for effective resistance, but heavily flapping the huge wings, that

should, as some imagine, give a stroke equal in vigour to the kick of a horse.

During a calm evening, flocks of spoonbills take their flight directly up the river’s

course; as if linked together in unison, and moved by the same impulse, they alter

not their relative positions, but at less than fifteen inches above the water’s surface,

they speed swiftly by with ease and grace inimitable, a living sheet of spotless

white. Let one circumstance be remarked,—though they have fleeted past at a rate

of near thirty miles an hour, so little do they disturb the element in which they

move, that not a ripple of the placid bosom of the river, which they almost touch,

has marked their track. How wonderfully does their progress contrast with that of

creatures who are compelled to drag their slow and weary way against the fluid a

thousand fold more dense, flowing in strong and eddying current beneath them.

Our pennant droops listlessly, the wished-for north wind cometh not. According

to custom we step on shore, gun in hand. A flock of white herons, or “buffalo-birds,”
Document 1-3(a–c) 61

almost within our reach, run a short distance from the pathway as we approach

them. Others are seen perched in social groups upon the backs of the apathetic

and mud-begrimed animals whose name they bear. Beyond the ripening dhourra

crops which skirt the river-side, the land is covered with immense numbers of blue

pigeons, flying to and fro in shoals, and searching for food with restless diligence.

The musical whistle from the pinions of the wood-doves sounds cheerily, as they dart

past with the speed of an arrow. Ever and anon are seen a covey of the brilliant,

many-coloured partridges of the district, whose long and pointed wings give them a

strength and duration of flight that seems interminable, alighting at distances

beyond the possibility of marking them down, as we are accustomed to do with their

plumper brethren at home. But still more remarkable is the spectacle which the sky

presents. As far as the eye can reach it is dotted with birds of prey of every size and

description. Eagles, vultures, kites and hawks, of manifold species, down to the small,

swallow-like, insectivorous hawk common in the Delta, which skims the surface of the

ground in pursuit of its insect prey. None seem bent on going forward, but all are

soaring leisurely round over the same locality, as if the invisible element which

supports them were their medium of rest as well as motion. But mark that object

sitting in solitary state in the midst of yon plain: what a magnificent eagle! An

approach to within eighty yards arouses the king of birds from his apathy. He partly

opens his enormous wings, but stirs not yet from his station. On gaining a few feet

more he begins to walk away, with half-expanded, but motionless wings. Now for the

chance fire! A charge of No. 3 from 11 bore rattles audibly but ineffectively upon his

densely feathered body; his walk increases to a run, he gathers speed with his

slowly-waving wings, and eventually, leaves the ground. Rising at a gradual inclination

he mounts aloft and sails majestically away to his place of refuge in the Lybian range,

distant at least five miles from where he rose. Some fragments of feathers denote

the spot where the shot had struck him. The marks of his claws are traceable in

the sandy soil, as, at first with firm and decided digs, he forced his way, but as he

lightened his body and increased his speed with the aid of his wings, the imprints

of his talons gradually merged into long scratches. The measured distance from

the point where these vanished, to the place where he had stood, proved that with

all the stimulus that the shot must have given to his exertions, he had been compelled to run full twenty yards before he could raise himself from the earth.

Again the boat is under weigh, though the wind is but just sufficient to enable

us to stem the current. An immense kite is soaring overhead, scarcely higher than

the top of our lateen yard, affording a fine opportunity for contemplating his easy

and unlaboured movements. The cook has now thrown overboard some offal.

With a solemn swoop the bird descends and seizes it in his talons. How easily he

rises again with motionless expanded wings, the mere force and momentum of his

descent serving to raise him again to more than half-mast high. Observe him next,
62 Chapter 1: The Achievement of Flight

with lazy flapping wings, and head turned under his body; he is placidly devouring the pendant morsel from his foot, and calmly gliding onwards.

The Nile abounds with large aquatic birds of almost every variety. During a

residence upon its surface for nine months out of the year, immense numbers

have been seen to come and go, for the majority of them are migratory. Egypt

being merely a narrow strip of territory, passing through one of the most desert

parts of the earth, and rendered fertile only by the periodical rise of the waters of

the river, it is probable that these birds make it their grand thoroughfare into the

rich districts of Central Africa.

On nearing our own shores, steaming against a moderate head-wind, from a

station abaft the wheel the movements of some half-dozen gulls are observed, following in the wake of the ship, in patient expectation of any edibles that may be

thrown overboard. One that is more familiar than the rest comes so near at times

that the winnowing of his wings can be heard; he has just dropped astern, and

now comes on again. With the axis of his body exactly at the level of the eyesight,

his every movement can be distinctly marked. He approaches within ten yards,

and utters his wild plaintive note, as he turns his head from side to side, and

regards us with his jet black eye. But where is the angle or upward rise of his

wings, that should compensate for his descending tendency, in a yielding medium

like air? The incline cannot be detected, for, to all appearance, his wings are edgewise,

or parallel to his line of motion, and he appears to skim along a solid support. No

smooth-edged rails, or steel-tired wheels, with polished axles revolving in well oiled

brasses, are needed here for the purpose of diminishing friction, for Nature’s

machinery has surpassed them all. The retarding effects of gravity in the creature

under notice, are almost annulled, for he is gliding forward upon a frictionless

plane. There are various reasons for concluding that the direct flight of many

birds is maintained with a much less expenditure of power, for a high speed, than

by any mode of progression.

The first subject for consideration is the proportion of surface, to weight, and their

combined effect in descending perpendicularly through the atmosphere. The datum

is here based upon the consideration of safety, for it may sometimes be needful for

a living being to drop passively, without muscular effort. One square foot of sustaining surface, for every pound of the total weight, will be sufficient for security.

According to Smeaton’s table of atmospheric resistances, to produce a force

of one pound on a square foot, the wind must move against the plane (or, which is

the same thing, the plane against the wind), at the rate of twenty-two feet per second, or 1,320 feet per minute, equal to fifteen miles per hour. The resistance of

the air will now balance the weight on the descending surface, and, consequently,

it cannot exceed that speed. Now, twenty-two feet per second is the velocity acquired

at the end of a fall of eight feet—a height from which a well-knit man or animal
Document 1-3(a–c) 63

may leap down without much risk of injury. Therefore, if a man with parachute

weigh together 143 lbs., spreading the same number of square feet of surface contained in a circle fourteen and a half feet in diameter, he will descend at perhaps

an unpleasant velocity, but with safety to life and limb.

It is a remarkable fact how this proportion of wing-surface to weight extends

throughout a great variety of the flying portion of the animal kingdom, even

down to hornets, bees, and other insects. In some instances, however, as in the

gallinaceous tribe, including pheasants, this area is somewhat exceeded, but they

are known to be very poor flyers. Residing as they do chiefly on the ground, their

wings are only required for short distances, or for raising them or easing their

descent from their roosting-places in forest trees, the shortness of their wings preventing them from taking extended flights. The wing-surface of the common

swallow is rather more than in the ratio of two square feet per pound, but having

also great length of pinion, it is both swift and enduring in its flight. When on a

rapid course this bird is in the habit of furling its wings into a narrow compass.

The greater extent of surface is probably needful for the continual variations of

speed and instant stoppages requisite for obtaining its insect food.

On the other hand, there are some birds, particularly of the duck tribe, whose

wing-surface but little exceeds half a square foot, or seventy-two inches per pound,

yet they may be classed among the strongest and swiftest of flyers. A weight of one

pound, suspended from an area of this extent, would acquire a velocity due to a

fall of 16 feet—a height sufficient for the destruction or injury of most animals.

But when the plane is urged forward horizontally, in a manner analogous to the

wings of a bird during flight, the sustaining power is greatly influenced by the form

and arrangement of the surface.

In the case of perpendicular descent, as a parachute, the sustaining effect will be

much the same, whatever the figure of the outline of the superficies may be, and a

circle perhaps affords the best resistance of any. Take for example a circle of 20 square

feet (as possessed by the pelican) loaded with as many pounds. This, as just stated,

will limit the rate of perpendicular descent to 1,320 feet per minute. But instead of

a circle 61 inches in diameter, if the area is bounded by a parallelogram 10 feet long

by 2 feet broad, and whilst at perfect freedom to descend perpendicularly, let a force

be applied exactly in a horizontal direction, so as to carry it edgeways, with the long

side foremost, at a forward speed of 30 miles per hour—just double that of its passive

descent: the rate of fall under these conditions will be decreased most remarkably,

probably to less than one-fifteenth part, or 88 feet per minute, or one mile per hour.

The annexed line represents transversely the plane 2 feet wide and 10 feet

long, moving in the direction of the arrow with a forward speed of 30 miles per

hour, or 2,640 feet per minute, and descending at 88 feet per minute, the ratio

being as 1 to 30. Now, the particles of air, caught by the forward edge of the plane,
64 Chapter 1: The Achievement of Flight

must be carried down eight-tenths of an inch before they leave it. This stratum,

10 feet wide and 2,640 long, will weigh not less than 134 lbs.; therefore the weight

has continually to be moved downwards, 88 feet per minute, from a state of

absolute rest. If the plane, with this weight and an upward rise of eight-tenths of

an inch, be carried forward at a rate of 30 miles per hour, it will be maintained at

the same level without descending.

The following illustrations, though referring to the action of surfaces in a

denser fluid, are yet exactly analogous to the conditions set forth in air:— 

Take a stiff rod of wood, and nail to its end at right angles a thin lath or blade,

about two inches wide. Place the rod square across the thwarts of a rowing-boat in

motion, letting a foot or more of the blade hang perpendicularly over the side

into the water. The direct amount of resistance of the current against the flat side

of the blade may thus be felt. Next slide the rod to and fro thwart ship, keeping

all square; the resistance will now be found to have increased enormously; indeed,

the boat can be entirely stopped by such an appliance. Of course the same experiment may be tried in a running stream.

Another familiar example may be cited in the lee-boards and sliding keels used

in vessels of shadow draught, which act precisely on the same principle as the plane or

wing-surface of a bird when moving in air. These surfaces, though parallel to the line

of the vessel’s course, enable her to carry a heavy press of sail without giving way

under the side pressure, or making lee-way, so great is their resistance against the

rapidly passing body of water, which cannot be deflected sideways at a high speed.

The succeeding experiments will serve further to exemplify the action of the same

principle. Fix a thin blade, say one inch wide and one foot long, with its plane exactly

midway and at right angles, to the end of a spindle or rod. On thrusting this through

a body of water, or immersing it in a stream running in the direction of the axis of

the spindle, the resistance will be simply that caused by the water against the mere

superficies of the blade. Next put the spindle and blade in rapid rotation. The

retarding effect against direct motion will now be increased near tenfold, and is equal

to that due to the entire area of the circle of revolution. By trying the effect of blades of

various widths, it will be found that, for the purpose of effecting the maximum amount

of resistance, the more rapidly the spindle revolves the narrower may be the blade.

There is a specific ratio between the width of the blade and its velocity. It is of some

importance that this should be precisely defined, not only for its practical utility

in determining the best proportion of width to speed in the blades of screw-propellers,

but also for a correct demonstration of the principles involved in the subject now

under consideration; for it may be remarked that the swiftest-flying birds possess

extremely long and narrow wings, and the slow, heavy flyers short and wide ones.

In the early days of the screw-propeller, it was thought requisite, in order to

obtain the advantage of the utmost extent of surface, that the end view of the
Document 1-3(a–c) 65

screw should present no opening, but appear as a complete disc. Accordingly,

some were constructed with one or two threads, making an entire or two half-revolutions; but this was subsequently found to be a mistake. In the case of the two

blades, the length of the screw was shortened, and consequently the width of the

blades reduced, with increased effect, till each was brought down to considerably

less than one-sixth of the circumference or area of the entire circle; the maximum

speed was then obtained. Experiment has also shown that the effective propelling

area of the two-bladed screw is tantamount to its entire circle of revolution, and is

generally estimated as such.

Many experiments tried by the author, with various forms of screws, applied

to a small steam-boat, led to the same conclusion—that the two blades of onesixth of the circle gave the best result.

All screws reacting on a fluid such as water, must cause it to yield to some

extent; this is technically known as “slip,” and whatever the ratio or percentage

on the speed of the boat may be, it is tantamount to just so much loss of propelling

power—this being consumed in giving motion to the water instead of the boat.

On starting the engine of the steam-boat referred to, and grasping a mooring-rope at the stern, it was an easy matter to hold it back with one hand, though

the engine was equal in power to five horses, and the screw making more than 500

revolutions per minute. The whole force of the steam was absorbed in “slip,” or

in giving motion to the column of water; but let her go, and allow the screw to

find an abutment on a fresh body of water, not having received a gradual motion,

and with its inertia undisturbed when running under full way, the screw worked

almost as if in a solid nut, the “slip” amounting to only eleven per cent.

The laws which control the action of inclined surfaces, moving either in

straight lines or circles in air, are identical, and serve to show the inutility of

attempting to raise a heavy body in the atmosphere by means of rotating vanes or

a screw acting vertically; for unless the ratio of surface compared to weight is

exceedingly extensive, the whole power will be consumed in “slip,” or in giving a

downward motion to the column of air. Even if a sufficient force is obtained to

keep a body suspended by such means, yet, after the desired altitude is arrived at,

no further ascension is required; there the apparatus is to remain stationary as to

level, and its position on the constantly yielding support can only be maintained

at an enormous expenditure of power, for the screw cannot obtain a hold upon a

fresh and unmoved portion of air in the same manner as it does upon the body of

water when propelling the boat at full speed; its action under these conditions is

the same as when the boat is held fast, in which case, although the engine is working up to its usual rate, the tractive power is almost annulled.

Some experiments made with a screw, or pair of inclined vanes acting vertically in air, were tried, in the following manner. To an upright post was fixed a
66 Chapter 1: The Achievement of Flight

frame, containing a bevil wheel and pinion, multiplying in the ratio of three to

one. The axle of the wheel was horizontal, and turned by a handle of five-and-ahalf inches radius. The spindle of the pinion rotated vertically, and carried two

driving-pins at the end of a cross-piece, so that the top resembled the three

prongs of a trident. The upright shaft of the screw was bored hollow to receive the

middle prong, while the two outside ones took a bearing against a driving-bar, at

right angles to the lower end of the shaft, the top of which ended in a long iron

pivot, running in a socket fixed in a beam overhead; it could thus rise and fall

about two inches with very little friction. The top of the screw-shaft carried a crossarm, with a blade of equal size at each extremity, the distance from end to end

being six feet. The blades could be adjusted at any angle by clamping-screws.

Both their edges, and the arms that carried them, were bevilled away to a sharp

edge to diminish the effects of atmospheric resistance. A wire stay was taken from

the base of each blade to the bottom of the upright shaft, to give rigidity to the

arms, and to prevent them from springing upwards. With this apparatus experiments were made with weights attached to the upright screw-shaft, and the blades

set at different pitches, or angles of inclination. When the vanes were rotated rapidly, they rose and floated on the air, carrying the weights with them. Much difficulty was experienced in raising a heavy weight by a comparatively small extent

of surface, moving at a high velocity; the “slip” in these cases being so great as to

absorb all the power employed. The utmost effect obtained in this way was to raise

a weight of six pounds on one square foot of sustaining surface, the planes having been set at a coarse pitch. To keep up the rotation, required about half the

power a man could exert.

The ratio of weight to sustaining surface was next arranged in the proportion

approximating to that of birds. Two of the experiments are here quoted, which

gave the most satisfactory result. Weight of wings and shaft, 17 1⁄2 oz.; area of two

wings, 121 inches—equal to 110 square inches per pound. The annexed figures

are given approximately, in order to avoid decimal fractions:—

No. of Mean Feet per Pitch or Ratio of Slip per

revolutions sustaining minute. angle of pitch to cent.

per minute. speed. rise in one speed.

Miles per revolution.

hour. Inches.

1st 

experiment 210 38 3,360 26 1⁄8 nearly 12 1⁄2

2nd Do. 240 44 3,840 15 1⁄13 Do. 8

The power required to drive was nearly the same in both experiments—about

equal to one-sixteenth part of a horse-power, or the third part of the strength of
Document 1-3(a–c) 67

a man, as estimated by a constant force on the handle of twelve pounds in the first

experiment, and ten in the second, the radius of the handle being five-and-a-half

inches, and making seventy revolutions per minute in the first case, and eighty in

the other.

These experiments are so far satisfactory in showing the small pitch or angle

of rise required for sustaining the weight stated, and demonstrating the principle

before alluded to, of the slow descent of planes moving horizontally in the atmosphere at high velocities; but the question remains to be answered, concerning the

disposal of the excessive power consumed in raising a weight not exceeding that

of a carrier pigeon, for unless this can be satisfactorily accounted for, there is but

little prospect of finding an available power, of sufficient energy in its application

to the mechanism, for raising apparatus, either experimental or otherwise, in the

atmosphere. In the second experiment, the screw-shaft made 240 revolutions,

consequently, one vane (there being two) was constantly passing over the same spot

480 times each minute, or eight times in a second. This caused a descending current of air, moving at the rate of near four miles per hour, almost sufficient to blow

a candle out placed three feet underneath. This is the result of “slip,” and the giving both a downward and rotary motion to this column of air, will account for a

great part of the power employed, as the whole apparatus performed the work of

a blower. If the wings, instead of travelling in a circle, could have been urged continually forward in a straight line in a fresh and unmoved body of air the “slip”

would have been so inconsiderable, and the pitch consequently, reduced to such

a small angle, as to add but little to the direct forward atmospheric resistance of

the edge.

The small flying screws, sold as toys, are well known. It is an easy matter to

determine approximately the force expended in raising and maintaining them in

the atmosphere. The following is an example of one constructed of tin-plate with

three equidistant vanes. This was spun by means of a cord, wound round a wooden spindle, fitted into a forked handle as usual. The outer end of the coiled string

was attached to a small spring steelyard, which served as a handle to pull it out

by. The weight, or degree at which the index had been drawn, was afterwards ascertained by the mark left thereon by a pointed brass wire. It is not necessary to know

the time occupied in drawing out the string, as this item in the estimate may be

taken as the duration of the ascent; for it is evident that if the same force is reapplied at the descent, it would rise again, and a repeated series of these impulses will represent the power required to prolong the flight of the instrument. It is,

therefore, requisite to know the length of string, and the force applied in pulling

it out. The following are the data:

Diameter of screw 81 inches

Weight of ditto 396 grains
68 Chapter 1: The Achievement of Flight

Length of string drawn out 2 feet

Force employed 8 lbs.

Duration of flight 16 seconds

From this it may be computed that, in order to maintain the flight of the

instrument, a constant force is required of near sixty foot-pounds per minute—in

the ratio of about three horse-power for each hundred pounds raised by such means.

The force is perhaps over-estimated for a larger screw, for as the size and weight

is increased, the power required would be less than in this ratio. The result would be

more satisfactory if tried with a sheet-iron screw, impelled by a descending weight.

Methods analogous to this have been proposed for attempting aerial locomotion; but experiment has shown that a screw rotating in the air is an imperfect

principle for obtaining the means of flight, and supporting the needful weight,

for the power required is enormous. Suppose a machine to be constructed, having some adequate supply of force, the screw rotating vertically at a certain velocity will raise the whole. When the desired altitude is obtained, nearly the same

velocity of revolution, and the same excessive power, must be continued, and consumed entirely in “slip,” or in drawing down a rapid current of air.

If the axis of the screw is slightly inclined from the perpendicular, the whole

machine will travel forward. The “slip,” and consequently the power, is somewhat

reduced under these conditions; but a swift forward speed cannot be effected by

such means, for the resistance of the inclined disc of the screw will be very great,

far exceeding any form assimilating to the edge of the wing of a bird. But, arguing on the supposition that a forward speed of thirty miles an hour might thus be

obtained, even then nearly all the power would be expended in giving an unnecessary and rapid revolution to an immense screw, capable of raising a weight, say

of 200 pounds. The weight alone of such a machine must cause it to fail, and

every revolution of the screw is a subtraction from the much-desired direct forward speed. A simple narrow blade, or inclined plane, propelled in a direct course

at this speed—which is amply sufficient for sustaining heavy weights—is the best,

and, in fact, the only means of giving the maximum amount of supporting power

with the least possible degree of “slip,” and direct forward resistance. Thousands

of examples in Nature testify its success, and show the principle in perfection;—

apparently the only one, and therefore beyond the reach of amendment, the wing

of a bird, combining a propelling and supporting organ in one, each perfectly

efficient in its mechanical action.

This leads to the consideration of the amount of power requisite to maintain the

flight of a bird. Anatomists state that the pectoral muscles for giving motion to the

wings are excessively large and strong; but this furnishes no proof of the expenditure

of a great amount of force in the act of flying. The wings are hinged to the body like
Document 1-3(a–c) 69

two powerful levers, and some counteracting force of a passive nature, acting like a

spring under tension, must be requisite merely to balance the weight of the bird. It

cannot be shown that, while there is no active motion, there is any real exertion of

muscular force; for instance, during the time when a bird is soaring with motionless

wings. This must be considered as a state of equilibrium, the downward spring and

elasticity of the wings serving to support the body; the muscles, in such a case,

performing like stretched india-rubber springs would do. The motion or active

power required for the performance of flight must be considered exclusive of this.

It is difficult, if not impossible, by any form of dynamometer, to ascertain the

precise amount of force given out by the wings of birds; but this is perhaps not

requisite in proof of the principle involved, for when the laws governing their

movements in air are better understood, it is quite possible to demonstrate, by

isolated experiments, the amount of power required to sustain and propel a given

weight and surface at any speed.

If the pelican referred to as weighing twenty-one pounds, with near the same

amount of wing-area in square feet, were to descend perpendicularly, it would fall

at the rate of 1,320 feet per minute, being limited to this speed by the resistance

of the atmosphere.

The standard generally employed in estimating power is by the rate of

descent of a weight. Therefore, the weight of the bird being 21 pounds, which,

falling at the above speed will expend a force on the air set in motion nearly equal

to one horse (.84 HP.) or that of 5 men; and conversely, to raise this weight again

perpendicularly upon a yielding support like air, would require even more power

than this expression, which it is certain that a pelican does not possess; nor does

it appear that any large bird has the faculty of raising itself on the wing perpendicularly in a still atmosphere. A pigeon is able to accomplish this nearly, mounting

to the top of a house in a very narrow compass; but the exertion is evidently

severe, and can only be maintained for a short period. For its size, this bird has

great power of wing; but this is perhaps far exceeded in the humming-bird, which,

by the extremely rapid movements of its pinions, sustains itself for more than a

minute in still air in one position. The muscular force required for this feat is

much greater than for any other performance of flight. The body of the bird at

the time is nearly vertical. The wings uphold the weight, not by striking vertically downwards upon the air, but as inclined surfaces reciprocating horizontally like

a screw, but wanting in its continuous rotation in one direction, and, in consequence of the loss arising from rapid alternations of motion, the power required

for the flight will exceed that specified in the screw experiment before quoted,

viz.: three horse-power for every 100 pounds raised.

We have here an example of the exertion of enormous animal force expended in flight, necessary for the peculiar habits of the bird, and for obtaining its
70 Chapter 1: The Achievement of Flight

food; but in the other extreme, in large heavy birds, whose wings are merely

required for the purposes of migration or locomotion, flight is obtained with the

least possible degree of power, and this condition can only be commanded by a

rapid straightforward course through the air.

The sustaining power obtained in flight must depend upon certain laws of

action and reaction between relative weights; the weight of a bird, balanced, or

finding an abutment, against the fixed inertia of a far greater weight of air, continuously brought into action in a given time. This condition is secured, not by

extensive surface, but by great length of wing, which, in forward motion, takes a

support upon a wide stratum of air, extending transversely to the line of direction.

The pelican, for example, has wings extending out 10 feet. If the limits of

motion imparted to the substratum of air, acted upon by the incline of the wing,

be assumed as one foot in thickness, and the velocity of flight as 30 miles per

hour, or 2,640 feet per minute, the stratum of air passed over in this time will

weigh nearly one ton, or 100 times the weight of the body of the bird, thus giving such an enormous supporting power, that the comparatively small weight of

the bird has but little effect in deflecting the heavy length of stratum downwards,

and, therefore, the higher the velocity of flight the less the amount of “slip,” or

power wasted in compensation for descent.

As noticed at the commencement or this paper, large birds may be observed

to skim close above smooth water without ruffling the surface; showing that during

rapid flight the air does not give way beneath them, but approximates towards a

solid support.

In all inclined surfaces, moving rapidly through air, the whole sustaining

power approaches toward the front edge; and in order to exemplify the inutility

of surface alone, without proportionate length of wing, take a plane, ten feet long

by two broad, impelled with the narrow end forward, the first twelve or fifteen

inches will be as efficient at a high speed in supporting a weight as the entire following portion of the plane, which may be cut off, thus reducing the effective

wing-area of a pelican, arranged in this direction, to the totally inadequate equivalent of two-and-a-half square feet.

One of the most perfect natural examples of easy and long-sustained flight is

the wandering albatross. “A bird for endurance of flight probably unrivalled.

Found over all parts of the Southern Ocean, it seldom rests on the water. During

storms, even the most terrific, it is seen now dashing through the whirling clouds,

and now serenely floating, without the least observable motion of its outstretched

pinions.” The wings of this bird extend fourteen or fifteen feet from end to end, and

measure only eight-and-a-half inches across the broadest part. This conformation

gives the bird such an extraordinary sustaining power, that it is said to sleep on the

wing during stormy weather, when rest on the ocean is impossible. Rising high in
Document 1-3(a–c) 71

the air, it skims slowly down, with absolutely motionless wings, till a near approach

to the waves awakens it, when it rises again for another rest.

If the force expended in actually sustaining a long-winged bird upon a wide

and unyielding stratum of air, during rapid flight, is but a small fraction of its

strength, then nearly the whole is exerted in overcoming direct forward resistance. In the pelican referred to, the area of the body, at its greatest diameter, is

about 100 square inches; that of the pinions, eighty. But as the contour of many

birds during flight approximates nearly to Newton’s solid of least resistance, by

reason of this form, acting like the sharp bows of a ship, the opposing force

against the wind must be reduced down to one third or fourth part; this gives onetenth of a horse-power, or about half the strength of a man, expended during a

flight of thirty miles per hour. Judging from the action of the living bird when

captured, it does not appear to be more powerful than here stated.

The transverse area of a carrier pigeon during flight (including the outstretched wings) a little exceeds the ratio of twelve square inches for each pound,

and the wing-surface, or sustaining area, ninety square inches per pound.

Experiments have been made to test the resisting power of conical bodies of

various forms, in the following manner:—A thin lath was placed horizontally, so as

to move freely on a pivot set midway; at one end of the lath a circular card was attached,

at the other end a sliding clip traversed, for holding paper cones, having their bases

the exact size of the opposite disc. The instrument acted like a steelyard; and when

held against the wind, the paper cones were adjusted at different distances from

the centre, according to their forms and angles, in order to balance the resistance of

the air against the opposing flat surface. The resistance was found to be diminished

nearly in the ratio that the height of the cone exceeded the diameter of base.

It might be expected that the pull of the string of a flying kite should give

some indication of the force of inclined surfaces acting against a current of air; but

no correct data can be obtained in this way. The incline of the kite is far greater than

ever appears in the case of the advancing wing-surface of a bird. The tail is purposely

made to give steadiness by a strong pull backwards from the action of the wind, which

also exerts considerable force on the suspended cord, which for more than half its

length hangs nearly perpendicularly. But the kite, as a means of obtaining unlimited

lifting and tractive power, in certain cases where it might be usefully applied,

seems to have been somewhat neglected. For its power of raising weights, the following quotation is taken from Vol. XLI. of the Transactions of the Society of Arts,

relating to Captain Dansey’s mode of communicating with a lee-shore. The kite

was made of a sheet of holland exactly nine feet square, extended by two spars

placed diagonally, and as stretched spread a surface of fifty-five square feet. “The

kite, in a strong breeze, extended 1,100 yards of line five-eighths in circumference,

and would have extended more had it been at hand. It also extended 360 yards
72 Chapter 1: The Achievement of Flight

of line, one and three-quarters of an inch in circumference, weighing sixty pounds.

The holland weighed three and a half pounds; the spars, one of which was armed

at the head with iron spikes, for the purpose of mooring it, six and three-quarter

pounds; and the tail was five times its length, composed of eight pounds of rope

and fourteen of elm plank, weighing together twenty-two pounds.” 

We have here the remarkable fact of ninety-two and a quarter pounds carried

by a surface of only fifty-five square feet.

As all such experiments bear a very close relation to the subject of this paper,

it may be suggested that a form of kite should be employed for reconnoitring and

exploring purposes, in lieu of balloons held by ropes. These would be torn to

pieces in the very breeze that would render a kite most serviceable and safe. In

the arrangement there should be a smaller and upper kite, capable of sustaining

the weight of the apparatus. The lower kite should be as nearly as practicable in

the form of a circular flat plane, distended with ribs, with a car attached beneath

like a parachute. Four guy-ropes leading to the car would be required for altering

the angle of the plane—vertically with respect to the horizon, and laterally relative

to the direction of the wind. By these means the observer could regulate his altitude,

so as to command a view of a country in a radius of at least twenty miles; he could

veer to a great extent from side to side, from the wind’s course, or lower himself

gently, with the choice of a suitable spot for descent. Should the cord break, or

the wind fail, the kite would, in either case, act as a parachute, and as such might

be purposely detached from the cord, which then being sustained from the upper

kite, could be easily recovered. The direction of descent could be commanded by

the guy-ropes, these being hauled taut in the required direction for landing.

The author has good reasons for believing that there would be less risk associated with the employment of this apparatus, than the reconnoitring balloons

that have now frequently been made use of in warfare.

The wings of all flying creatures, whether of birds, bats, butterflies, or other

insects, have this one peculiarity of structure in common. The front, or leading

edge, is rendered rigid by bone, cartilage, or a thickening of the membrane; and

in most birds of perfect flight, even the individual feathers are formed upon the

same condition. In consequence of this, when the wing is waved in air, it gives a

persistent force in one direction, caused by the elastic reaction of the following

portion of the edge. The fins and tails of fishes act upon the same principle. In

most rapid swimmers these organs are termed “lobated and pointed.” The tail

extends out very wide transversely to the body, so that a powerful impulse is

obtained against a wide stratum of water, on the condition before explained. The

action is imitated in Macintosh’s screw-propeller, the blade of which his made of

thin steel, so as to be elastic. While the vessel is stationary, the blades are in a line

with the keel, but during rotation they bend on one side, more or less, according
Document 1-3(a–c) 73

to the speed and degree of propulsion required, and are thus self-compensating;

and could practical difficulties be overcome, would prove to be a form of propeller perfect in theory.

In the flying mechanism of beetles there is a difference of arrangement. When

the elytra, or wing-cases, are opened, they are checked by a stop, which sets them

at a fixed angle. It is probable that these serve as “aeroplanes,” for carrying the

weight of the insect, while the delicate membrane that folds beneath acts more as

a propelling than a supporting organ. A beetle cannot fly with the elytra removed.

The wing of a bird, or bat, is both a supporting and a propelling organ, and

flight is performed in a rapid course, as follows:—During the down-stroke it can

be easily imagined how the bird is sustained; but in the up-stroke, the weight is

also equally well supported, for in raising the wing, it is slightly inclined upwards

against the rapidly passing air, and as this angle is somewhat in excess of the

motion due to the raising of the wing, the bird is sustained as much during the

up as the down-stroke—in fact, though the wing may be rising, the bird is still

pressing against the air with a force equal to the weight of its body. The faculty of

turning up the wing may be easily seen when a large bird alights; for after gliding

down its aerial gradient, on its approach to the ground it turns up the plane of its

wing against the air; this checks its descent, and it lands gently.

It has before been shown how utterly inadequate the mere perpendicular

impulse of a plane is found to be in supporting a weight, when there is no horizontal motion at the time. There is no material weight of air to be acted upon,

and it yields to the slightest force, however great the velocity of impulse may be.

On the other hand, suppose that a large bird, in full flight, can make forty miles

per hour, or 3,520 feet per minute, and performs one stroke per second. Now,

during every fractional portion of that stroke, the wing is acting upon and obtaining an impulse from a fresh and undisturbed body of air; and if the vibration of

the wing is limited to an arc of two feet, this by no means represents the small

force of action that would be obtained when in a stationary position, for the

impulse is secured upon a stratum of fifty-eight feet in length of air at each stroke.

So that the conditions of weight of air for obtaining support equally well apply to

weight of air, and its reaction in producing forward impulse.

So necessary is the acquirement of this horizontal speed, even in commencing

flight, that most heavy birds, when possible, rise against the wind, and even run

at the top of their speed to make their wings available, as in the example of the

eagle, mentioned at the commencement of this paper. It is stated that the Arabs,

on horseback, can approach near enough to spear these birds, when on the plain,

before they are able to rise: their habit is to perch on an eminence, where possible.

The tail of a bird is not necessary for flight. A pigeon can fly perfectly with

this appendage cut short off: it probably performs an important function in steer-
74 Chapter 1: The Achievement of Flight

ing, for it is to be remarked, that most birds that have either to pursue or evade

pursuit are amply provided with this organ.

The foregoing reasoning is based upon facts, which tend to show that the

flight of the largest and heaviest of all birds is really performed with but a small

amount of force, and that man is endowed with sufficient muscular power to

enable him also to take individual and extended flights, and that success is probably

only involved in a question of suitable mechanical adaptations. But if the wings are

to be modelled in imitation of natural examples, but very little consideration will serve

to demonstrate its utter impracticability when applied in these forms. The annexed

diagram, fig. 1, would be about the proportions needed for a man of medium weight.

The wings, a a, must extend out sixty feet from end to end, and measure four feet

across the broadest part. The man, b, should be in a horizontal position, encased

in a strong framework, to which the wings are hinged at c c. The wings must be

stiffened by elastic ribs, extending back from the pinions. These must be trussed

by a thin band of steel, e e, fig. 2, for the purpose of diminishing the weight and

thickness of the spar. At the front, where the pinions are hinged, there are two

levers attached, and drawn together by a spiral spring, d, fig. 2, the tension of

which is sufficient to balance the weight of the body and machine, and cause the

wings to be easily vibrated by the movement of the feet acting on treadles. This

spring serves the purpose of the pectoral muscles in birds. But with all such

arrangements the apparatus must fail—length of wing is indispensable! and a spar

thirty feet long must be strong, heavy, and cumbrous; to propel this alone through

the air, at a high speed, would require more power than any man could command.

In repudiating all imitations of natural wings, it does not follow that the only

channel is closed in which flying mechanism may prove successful. Though birds

do fly upon definite mechanical principles, and with a moderate exertion of force,

yet the wing must necessarily be a vital organ and member of the living body. It

must have a marvellous self-acting principle of repair, in case the feathers are broken or torn; it must also fold up in a small compass, and form a covering for the

body. These considerations bear no relation to artificial wings; so in designing a

flying-machine, any deviations are admissible, provided the theoretical conditions involved in flight are borne in mind.

Having remarked how thin a stratum of air is displaced beneath the wings of

a bird in rapid flight, it follows that in order to obtain the necessary length of

plane of supporting heavy weights, the surfaces may be superposed, or placed in

parallel rows, with an interval between them. A dozen pelicans may fly one above

the other without mutual impediment, as if framed together; and it is thus shown how

two hundred weight may be supported in a transverse distance of only ten feet.

In order to test this idea, six bands of stiff paper, three feet long and three

inches wide, were stretched at a slight upward angle, in a light rectangular frame,
Document 1-3(a–c) 75

with an interval of three inches between them, the arrangement resembling an

open Venetian blind. When this was held against a breeze, the lifting power was

very great, and even by running with it in a calm it required much force to keep

it down. The success of this model led to the construction of one of a sufficient

size to carry the weight of a man. Fig. 3 represents the arrangement. a a is a thin

plank, tapered at the outer ends, and attached at the base to a triangle, b, made

of similar plank, for the insertion of the body. The boards, a a, were trussed with

thin bands of iron, c c, and at the ends were vertical rods, d d. Between these were

stretched five bands of holland, fifteen inches broad and sixteen feet long, the

total length of the web being eighty feet. This was taken out after dark into a wet

piece of meadow land, one November evening, during a strong breeze, wherein

it became quite unmanageable. The wind acting upon the already tightly

stretched webs, their united pull caused the central boards to bend considerably,

with a twisting, vibratory motion. During a lull, the head and shoulders were

inserted in the triangle, with the chest resting on the baseboard. A sudden gust

caught up the experimenter, who was carried some distance from the ground, and

the affair falling over sideways, broke up the right-hand set of webs.

In all new machines we gain experience by repeated failures, which frequently

form the stepping-stones to ultimate success. The rude contrivance just described

(which was but the work of a few hours) had taught, first, that the webs, or aeroplanes, must not be distended in a frame, as this must of necessity be strong and

heavy, to withstand their combined tension; second, that the planes must be made

so as either to furl or fold up, for the sake of portability.

In order to meet these conditions, the following arrangement was afterwards

tried:—a a, figs. 4 and 5, is the main spar, sixteen feet long, half an inch thick at

the base, and tapered, both in breadth and thickness, to the end; to this spar was

fastened the panels b b, having a base-board for the support of the body. Under

this, and fastened to the end of the main spar, is a thin steel tie-band, e e, with

struts starting from the spar. This served as the foundation of the superposed

aeroplanes, and, though very light, was found to be exceedingly strong; for when

the ends of the spar were placed upon supports, the middle bore the weight of

the body without any strain or deflection; and further, by a separation at the baseboard, the spars could be folded back, with a hinge, to half their length. Above

this were arranged the aeroplanes, consisting of six webs of thin holland, fifteen

inches broad; these were kept in parallel planes, by vertical divisions, two feet

wide, of the same fabric, so that when distended by a current of air, each two feet

of web pulled in opposition to its neighbour; and finally at the ends (which were

each sewn over laths), a pull due to only two feet had to be counteracted, instead

of the strain arising from the entire length, as in the former experiment. The endpull was sustained by vertical rods, sliding through loops on the transverse ones
76 Chapter 1: The Achievement of Flight

at the ends of the webs, the whole of which could fall flat on the spar, till raised

and distended by a breeze. The top was stretched by a lath, f and the system kept

vertical by staycords, taken from a bowsprit carried out in front, shown in fig. 6.

All the front edges of the aeroplanes were stiffened by bands of crinoline steel.

This series was for the supporting arrangement, being equivalent to a length of

wing of ninety-six feet. Exterior to this, two propellers were to be attached, turning on spindles just above the back. They are kept drawn up by a light spring, and

pulled down by cords or chains, running over pulleys in the panels b b, and fastened to the end of a swivelling cross-yoke, sliding on the base-board. By working

this cross-piece with the feet, motion will be communicated to the propellers, and

by giving a longer stroke with one foot than the other, a greater extent of motion

will be given to the corresponding propeller, thus enabling the machine to turn,

just as oars are worked in a rowing boat. The propellers act on the same principle as the wing of a bird or bat: their ends being made of fabric, stretched by elastic ribs, a simple waving motion up and down will give a strong forward impulse.

In order to start, the legs are lowered beneath the baseboard, and the experimenter must run against the wind.

An experiment recently made with this apparatus developed a cause of failure.

The angle required for producing the requisite supporting power was found to be

so small, that the crinoline steel would not keep the front edges in tension. Some

of them were borne downwards and more on one side than the other, by the operation of the wind, and this also produced a strong fluttering motion in the webs,

destroying the integrity of their plane surfaces, and fatal to their proper action.

Another arrangement has since been constructed, having laths sewn in both

edges of the webs, which are kept permanently distended by cross-stretchers. All

these planes are hinged to a vertical central board, so as to fold back when the

bottom ties are released, but the system is much heavier than the former one, and

no experiments of any consequence have as yet been tried with it.

It may be remarked that although a principle is here defined, yet considerable

difficulty is experienced in carrying the theory into practice. When the wind

approaches to fifteen or twenty miles per hour, the lifting power of these arrangements

is all that is requisite, and, by additional planes, can be increased to any extent;

but the capricious nature of the ground-currents is a perpetual source of trouble.

Great weight does not appear to be of much consequence, if carried in the body;

but the aeroplanes and their attachments seem as if they were required to be very

light, otherwise, they are awkward to carry, and impede the movements in running and making a start. In a dead calm, it is almost impracticable to get sufficient horizontal speed, by mere running alone, to raise the weight of the body. Once

off the ground, the speed must be an increasing one, if continued by suitable propellers. The small amount of experience as yet gained, appears to indicate that if
Document 1-3(a–c) 77

the aeroplanes could be raised in detail, like a superposed series of kites, they

would first carry the weight of the machine itself, and next relieve that of the body.

Until the last few months no substantial attempt has been made to construct

a flying-machine, in accordance with the principle involved in this paper, which

was written seven years ago. The author trusts that he has contributed something

towards the elucidation of a new theory, and shown that the flight of a bird in its

performance does not require that enormous amount of force usually supposed,

and that in fact birds do not exert more power in flying than quadrupeds in running, but considerably less; for the wing movements of a large bird, travelling at

a far higher speed in air, are very much slower; and, where weight is concerned,

great velocity of action in the locomotive organs is associated with great force.

It is to be hoped that further experiments will confirm the correctness of

these observations, and with a sound working theory upon which to base his operations, man may yet command the air with the same facility that birds now do.

The CHAIRMAN: “I think the paper just read is one of great interest and

importance, especially as it points out the true mechanical explanation of the

curious problem, as to how and why it is that birds of the most powerful flight

always have the longest and narrowest wings. I think it quite certain, that if the air

is ever to be navigated, it will not be by individual men flying by means of machinery; but that it is quite possible vessels may be invented, which will carry a number of men, and the motive force of which will not be muscular action. We must

first ascertain clearly the mechanical principles upon which flight is achieved; and

this is a subject which has scarcely ever been investigated in a scientific spirit. In

fact, you will see in our best works of science, by the most distinguished men, the

account given of the anatomy of birds is, that a bird flies by inflating itself with

warm air, by which it becomes buoyant, like a balloon. The fact is, however, that a

bird is never buoyant. A bird is immensely heavier than the air. We all know that

the moment a bird is shot it falls to the earth; and it must necessarily do so,

because one of the essential mechanical principles of flight is weight, without it

there can be no momentum, and no motive force capable of moving through

atmospheric currents.

“Until I read Mr. Wenham’s paper, a few weeks since, I was puzzled by the

fact, that birds with long and very narrow wings seem to be not only as efficient

fliers, but much more efficient fliers than birds with very large, broad wings. If you

observe the flight of the common heron—which is a bird with a very large wing,

disposed rather in breadth than in length—you will notice that it is exceedingly

slow, and that it has a very heavy, flapping motion. The common swallow, on the

other hand, is provided with a long and narrow wing, and I never understood how

it was that long-winged birds, such as these, achieved so rapid a flight, until I read

Mr. Wenham’s paper. Although I do not profess to be able to follow the elaborate
78 Chapter 1: The Achievement of Flight

calculations which he has laid before us, I think I now understand the explanation he has given. His explanation of the action of narrow wings upon the air is,

that it is precisely like the action of the narrow vanes of the ship’s screw in water,

and that the resisting power of the screw is the same, or nearly the same, whether

you have the total area of revolution covered by solid surface, or traversed by long

and narrow vanes in rotation.

“If Mr. Wenham’s explanation be nearly correct, that supposing this implement

(referring to a model) to be carried forward by some propelling power, the sustaining force of the whole area is simply the sustaining force of the narrow band

in front. This, however, is a matter which will have to be decided by experiment.

It certainly appears to explain the phenomena of the flight of birds. There are

one or two observations in the paper I do not quite agree with. Although I have

studied the subject for many years, I have not arrived at Mr. Wenbam’s conclusion

that the upward stroke of a bird’s wing has precisely the same effect as a downward stroke in sustaining. An upward stroke has a contrary effect to the downward

stroke; it has a propelling power certainly, but I believe that the sustaining power

of a bird’s flight is due entirely to the downward stroke. I should be glad to hear

what Mr. Wenham may have to say upon this. My belief is, that an upward stroke

must have, so far as sustaining is concerned, a reverse action to the downward stroke.

“Then with regard to another observation of Mr. Wenham’s, that the tails of

birds are used as rudders. I believe this to be an entire mistake; for if the tail of a

bird could have the slightest effect in guiding, the vane of it must be disposed perpendicularly, and not horizontally, or nearly so, as at present.

“If you cut off the tail of a pigeon, you will find that he can fly and turn perfectly

well without it. He may be a little awkward about it at first, but that is because he

has lost his balancing power. We all know that it is a common thing to see a sparrow without his tail, therefore, I do not in the least believe that tails have any

effect in guiding. They have an important effect in stopping progress, and,

undoubtedly, that is one of the necessary elements of turning. If a bird comes

close over your head, and is frightened, you will find his claws distended and his

tail spread out as a fan, to stop the momentum of his flight. These are the two

only observations with which I cannot agree; but as regards the explanation he

has given as to the resistance offered by long and narrow wings, he has made an

important discovery.”

Mr. WENHAM: “With regard to the wing not affording support to the bird

during the upward stroke, some of the largest birds move their wings slowly, that

is, with a less number than sixty strokes per minute. Now, as a body free to fall

must descend fifteen feet in one second, whether in horizontal motion or not, it

appears clear to me that there must be some counter-acting effect to prevent this

fall. When the wing has reached the limit of the down-stroke, it is inclined
Document 1-3(a–c) 79

upwards in the direction of motion, consequently the rush of air caused by the forward speed, weight, and momentum of the bird against the under surface of the

wing, supports the weight, even though the wing is rising in the up-stroke at the

time. In corroboration of my theory, I will read an extract from Sir George Cayley,

who made a large number of experiments. He says, in page 83, of Vol. xxv.,

‘Nicholson’s Journal’:—’The stability in this position, arising from the centre of

gravity, being below the point of suspension, is aided by a remarkable circumstance that experiment alone could point out. In very acute angles with the current,

it appears that the centre of resistance in the sail does not coincide with the centre

of its surface, but is considerably in front of it. As the obliquity of the current

decreases, these centres approach and coincide when the current becomes perpendicular to the plane, hence any heel of the machine backwards or forwards

removes the centre of support behind or before the point of suspension.’

“From this discovery, it seems remarkable that Sir George Cayley, finding that

at high speeds with very oblique incidences the supporting effect became transferred to the front edge, the idea should not have occurred to him that a narrow

plane, with its long edge in the direction of motion, would have been equally

effective. I may give another illustration. We all know, from our schoolboy experience, that ice which would not be safe to stand upon, is found to be quite strong

enough to bear heavy bodies passing over it, so long as rapid motion is kept up,

and then it will not even crack. We know, also, that in driving through a marshy

part of road, in which you expect the wheels to sink in up to the axles, you may

pass over much more easily by increasing the speed. In both these examples there

is a greater weight passed over in a given time, and consequently a better support

obtained. The ice will not become deflected; neither has the mud time to give way.

At a slow speed the same effect may be obtained by extending the breadth of the

wheel. Thus, suppose an ordinary wheel to sink ten inches, if you double this

width it will sink only five inches; and so on, until by extending the wheel into a

long roller you may pass over a quicksand with perfect safety. Now, Nature has

carried out this principle in the long wings of birds, and in the albatross it is seen

in perfection.”
80 Chapter 1: The Achievement of Flight

Document 1-3(b), Report on the first wind tunnel built by Francis H. Wenham, 1871.

By the aid of a special subscription the Society has been enabled to present

to its members some data with respect to the action of a current of air upon

inclined planes of necessarily limited area, but varying angles. When the instrument, designed for this object by Mr. Wenham, was completed, with the aid of Mr.

Browning, every facility was afforded for testing its capacities at Messrs. Penns’

Engineering Works at Greenwich.

By means of a fan-blower, a current of considerable force was directed

through a trunk ten feet long by eighteen inches square. The plane to be acted

upon was fixed to the long end of a horizontal arm, which vibrated like the beam

of a balance, and bore upon its shorter end a sliding counter weight, so as to balance the weight of any plane which might be fixed at the opposite extremity. The

horizontal or direct pressure was read off by a spring steelyard, which was connected to the end of a lever from a vertical spindle close to the base of the

machine. The vertical or sliding force due to the various inclinations was read off

by an upright spring steelyard.

ANGLES OF INCLINED PLANES.

Forces in lbs. 0° 15° 20° 45° 60° Force of wind 7⁄10 in water

Direct 3.24 0.33 0.52 2.4 3.05 Plane 1 square foot.

Vertical 0 1.5 1.8 2.4 1.7

Direct 3.1 0.43 0.62 2.45 3.05 " 1 circular foot

Vertical 0 1.6 1.75 2.45 1.8

Direct 2.2 0.23 0.38 1.25 1.62 " 41⁄2in. x 18in. =

81 square inches

Vertical 0 1.05 1.2 1.25 1

Direct 3.77 0.38 0.57 2.2 2.76 " 18in. x 9in. =

162 square inches.

Vertical 0 1.6 1.85 2.2 1.75

Force of wind 1 in water

Direct 4.29 0.62 0.95 3.74 4.75 Plane 1 square foot.

Vertical 0 2.35 2.7 3.47 2.45

Direct 4.26 0.62 1 3.5 3.24 " 1 circular foot

Vertical 0 2.25 2.85 3.5 1.8

Direct 2.8 0.3 0.57 1.6 1.52 " 41⁄2in. x 18in.

Vertical 0 1.5 1.8 1.6 1

Force of wind 6

⁄10 in water

Direct 3.24 0.43 0.76 2.7 2.7 Plane 1 square foot.
Document 1-3(a–c) 81

Vertical 0 1.6 2.05 2.7 1.6

Direct 3.24 0.43 1.24 2.45 2.96 " 1 circular foot

Vertical 0 1.75 2.5 2.45 1.8

Direct 2 0.29 0.38 1.3 1.57 " 41⁄2in. x 18in., 

long edge to wind

Vertical 0 1.25 1.3 1.3 1

Direct 2.57 0.24 0.43 1.65 2.1 " 41⁄2in. x 18in., 

end on to wind,

Vertical 0 0.8 1.3 1.65 1.3 8/10 in water

Direct *5 1.47 0.76 2.9 3.81 Plane 18in. square =

mean 21⁄4 square feet

Vertical 0 2 2.4 2.9 2.2

*Fluctuates 0.57 lbs.

MEAN OF THE ABOVE COLUMNS.

Direct 3.31 0.4 0.68 2.34 2.73 Mean height of water, say 0.73in.,

Vertical 0 1.6 1.96 2.34 1.26 which should represent 3.8lbs. per

foot; readings are 1⁄7th too 

high for actual force per foot.

These experiments, when all the angles are averaged for errors, seem to indicate

the law that the lifting force of inclined planes, carried horizontally through air, is

increased in the direct ratio that the sine bears to the length of the plane, or the

height to the incline to the base; thus, if instead of stating the angles in degrees,

we say “one in ten,” or “one in three or four,” as the case may be, this will at once

express the proportion in which the lifting force exceeds the resistance. The average of all results is very near to this, making a little allowance for the surface friction of the plane through the air. At 45° the two forces are equal; above this the

proportions are in the inverse ratio, as the lifting force is then less than the direct.

It has been stated that the resistance of wedges or cones through the air is

diminished directly in the ratio that the height or diameter of the base bears to

the length of the cone. The experiments do not confirm this, but show that the

resistance is less in proportion as the angle becomes more acute.

It will be seen on reference to these tables that as the angles become more

acute, the lifting force exceeds the horizontal or power required to propel planes

through air in an enormous ratio.

More acute angles than 15° were not experimented upon, but even at this the

lift is four times greater than the thrust, and alone serves to abate the mystery

relating to the support of weight in flight, which at least in the case of easy flying

birds, consists in the action of surfaces at acute angles with the line of motion.
82 Chapter 1: The Achievement of Flight

The experiments, though at present somewhat crude and incomplete, show

that very oblique incidences or angles, with a small rise, have a remarkably strong

lifting force compared with the power required to propel the plane, and that the

ratio of the lift to the thrust greatly increases as the angle or rise diminishes, in

all probability accounting for the long-sustained flight of birds with motionless

wings. It is desirable that these important experiments should be verified and

continued; the apparatus will be at the service of any member desirous of repeating them or trying others. For example, up to the present time only flat surfaces

have been experimented upon, and as all the sustaining surfaces in the wings of

birds are curved or hollow, it remains to be proved what is the relative advantage

of this form, for it is upon such data that plans of construction must be based, and

on which failure or success must depend, and to determine whether flight is practicable or not. The whole endeavour must be to find a support on the air in such

a way that it cannot yield, so that there shall be as little mechanical loss as possible from what is known as “slip.”

A most evident example of the enormous loss of power arising from “slip”

may be cited in the plans that appear, from time to time, for raising men or

machinery by means of vertical screws. Taking 200 lbs. as the lightest total weight

of the man and machine, the following result will show how utterly inadequate his

power is to raise any but the most trifling weight by such means. Assuming the

surface or area of revolution at any number of square feet, the fraction of this

weight of 200 lbs. is distributed over each foot of that surface. The force per

square foot must therefore represent the wind velocity to produce the reaction or

resistance necessary to support the weight. A surface of 25 square feet will then

stand thus:—for 200 lbs. there is a resistance of 8 lbs. per foot required. To get

this there must be a wind velocity of 3,600 ft. per minute, therefore 3,600 x 200

+ 33,000 = 22 horse power. The following table will show the comparative results

for four different diameters or areas of screw, making no allowance for the friction of the machine, thus demonstrating the hopelessness of any successful

arrangement on this system.

Diam of Area of Weight to be lbs. per ft. Velocity in Horse power

screw revolution raised ft. per minute

5ft.8in. = 25 feet 200 = 8 3,600 = 22

8 0 = 50 " 200 = 4 2,600 = 16

11 3 = 100 " 200 = 2 1,800 = 11

16 0 = 200 " 200 = 1 1,300 = 8

The difference of power required to produce the same effect in the last and first

case is nearly threefold; this arises from the increased slip of the smaller area screw.
Document 1-3(a–c) 83

The theory of the strong lifting power of planes at very oblique incidences, moving

rapidly through the air, having now to some extent been practically tested, a few words

may not be out of place concerning the position or arrangement of those planes.

Mr. Wenham, in a paper read at the first meeting of the Aëronautical Society, brought

forward a number of examples in evidence of this great lifting force, but without

defining any exact law, merely relying upon it as a fact for the reasons given.

Then came the question, how to obtain the large extent of surface in a compass

small enough to secure strength with lightness. In that essay he showed that an

apparatus intended to support a weight of even 200 lbs. on one long extended

plane, like the wings of a bird, would be an impracticable construction, requiring

long and heavy spars. He then proposed to cut the planes into lengths, and superpose them, like a Venetian blind. It has been objected that this is wrong in theory, and that the action of one plane will interfere with the other; but the fact is,

that there is no theory in the matter. It is simply a question of construction. The

planes are equally effective in detachments, and may evidently be so arranged as

not to interfere with each other. Thus, a series of planes made of thin silk, or tissuepaper, may be rigged, one above the other, like kites on a cord, and weighing not

more than half an ounce each, and yet have ample strength to sustain one pound.

Though another season has elapsed, the Society has no announcement to

make of the existence of a successful machine for aërial locomotion, or for travelling in any desired direction. Yet the retrospect of the past year shows a decided

improvement in the form of experiments made to elucidate and define a correct

law of action and propulsion of bodies sustained in air. We have no longer the

extravagant and impossible theories of gravity and the laws of motion to account

for this difficult phenomenon, so many of which were sent to the Society in the

early days of its existence, the publication of which would in no way have contributed to the end in view, but, on the contrary, being wholly unsupported by any

previous facts or experiments, would have brought discredit and ridicule upon

Aëronautics, as the science which it may fairly be considered.

Should the problem be solved, the Aëronautical Society will take a high rank

amongst its compeers, and cannot now be denounced as useless till flight for man

is proved to be impossible. There are some amongst, not the least earnest of our

members, who are quite willing to prove its impossibility, calmly regarding it as a

mere scientific question; but, in fact, there is more difficulty in proving an impossibility than in constructing a machine having partial or total success, and we are

far from being able to demonstrate the certainty of failure by any known laws,

either of principle or construction. However plausible a mere argument unsupported by facts may appear, we have only to raise our eyes to the machinery of

nature exemplified in large flying birds, and behold a reality yet incompletely

explained, and not scientifically accounted for.
84 Chapter 1: The Achievement of Flight

The Society may congratulate itself for having been the means of bringing

together and recording a number of facts not lost upon its members, which have

produced greater unanimity of purpose, and have, it is presumed, directed the

efforts of experimentalists in accordance with a more generally recognized and

practicable theory.

Document 1-3(c), Minutes of the Royal Aeronautical Society, 1872.

A General Meeting of the members of this Society was held in the Theatre of

the Society of Arts, John Street, Adelphi, on Tuesday evening, the 18th inst. Mr.

JAMES GLAISHER, F.R.S., presided.

A new machine, constructed under the direction of the Society, for measuring

the relation between the velocity and pressure of the wind, was exhibited.

At the request of the CHAIRMAN,

The minutes of the previous meeting were read by Mr. F. W. BREAREY, the

Hon. Secretary.

The Chairman: Ladies and Gentlemen,—the subject which will most naturally

attract our attention this evening is that of the experiments which have been made

by the apparatus now on the table before us. I had almost forgotten that at our last

meeting we spoke of this instrument having been designed. It was not completed so

soon as we expected; and, although much time has been occupied in making experiments, the results are not quite so conclusive as could be desired; but so far as

they go are important—not only in respect to the problem we now wish to solve, but,

as bearing upon the pressure of the wind on the surfaces of planes. I will not now

engage your time longer, but I will ask Mr. Wenham, under whose care, in conjunction with Mr. Browning, the experiments were carried out, to give a statement

respecting the results. It is an instrument of a kind which I have long desired, and it

seems calculated to achieve what we require in this direction with greater accuracy

than any other instrument I know. I call upon Mr. Wenham to explain the apparatus.

Mr. WENHAM expressed his regret at the absence of Mr. Browning, who had been

associated with them in these experiments. To make this instrument understood,

he would explain how it acted as an ordinary anemometer, for ascertaining the

direct force of the wind on a plane, when in a vertical direction to its surface. This

consists mainly of a vertical steel spindle, supported on a hardened steel centre.

Through an eye at the upper end of the spindle, a horizontal arm passes, and is

secured by a small cross-pin, which allows the arm to vibrate like the beam of a

balance. The long end of the arm carries the planes; and the opposite short one

has a sliding counter-weight, which is adjusted so as to exactly balance planes of

different sizes at the long end of the arm. Each plane is clamped at the end of a

tail rod, which is pivoted through the forked end of the arm, by a vertical steel
Document 1-3(a–c) 85

pin, as close to the plane as possible; the other end of the tail passes loosely

through a vertical slot, slightly curved as a radius, from the balance centre of the

arm. By this arrangement, the surface of the plane is always kept at right angles

to the current, throughout the extent of its horizontal motion. A wooden shield is

fixed close before the front of the arm, to protect this and the balance weight from

the wind, so that the planes only may be exposed to its force. The action of the

instrument, as a single anemometer only, or when the planes are set at right

angles to the current of air, is obvious. The direct pressure is read off by the spring

steel-yard, which is connected to the end of a lever from the vertical spindle, close

to the base of the machine. In order to measure the vertical forces, the planes are

set at the requisite angles from a divided sector, whose centre coincides with the

clamping screw at the back. The raising force due from the various inclines was

read off by the upright spring steel-yard. It was found almost impossible for one

observer to read off the horizontal and vertical forces simultaneously during fluctuations, therefore the readings were noted by two persons at a given signal—even

this was a matter of some difficulty. The arrangement would be far more useful and

perfect as a scientific machine, if fitted with a piece of clockwork, moving a paper

cylinder, on which the vertical and direct forces would be simultaneously registered by separate pencils, describing two undulating lines, showing at a glance the

relative forces; the experimenter would then have nothing else to attend to, but

to see that all other conditions were acting properly.

The CHAIRMAN: I think the remarks by Mr. Wenham are important, especially

with regard to the effects produced on the planes at different inclinations. When

the plane was placed vertical, the pressure of the blast of air was direct, and tended only to move the plane in a horizontal direction—being that of the direction

of the air itself—but when the plane was inclined, a part of the pressure was exerted

in raising the plate in a vertical direction, and a part only in exerting a horizontal

pressure; so that the latter was less than in the previous case. When the plane was

placed at an angle of 45°, the horizontal force and the vertical force were found

to be identical, as mentioned in the manner described by Mr. Wenham. It was also

found that whether the exposed surface was a circle, a square, or a parallelogram,

providing the area was the same, the results were identical to the degree of accuracy

to which the readings could be determined. Anyone who had not considered with

care the nature of the pressure produced by the flow or rush of a fluid, elastic or

incompressible, against a plane surface placed in its course, might imagine that

the system of parallel forces was merely equivalent to a single resultant force acting

at the centre of pressure, and capable of resolution according to the ordinary parallelogram law. But this of course is not the case, for the particles of the fluid

which come in contact with the plane have somehow or other to get out of the way,

by gliding along the surface of the plane (as they cannot get through it), and this
86 Chapter 1: The Achievement of Flight

produces a complication in the neighbourhood of the surface of such a kind as

cannot be theoretically predicted. One thing, however, is quite clear, and that is,

that the directions of all the small forces acting on the surface certainly are not

parallel, and that we must therefore have recourse to experiment. Even the fact

that when the inclination of the plane to the current (supposed moving horizontally) is 45°, the vertical and horizontal pressures are equal, is not by any means

evident; nor in fact can it be exactly true; for supposing (to fix the ideas) that the

upper part of the plane is bent over so as to point in a direction opposed to that

in which the current is moving, and making an angle of 45° with it, then most of

the particles of air in the vicinity of the plane will, in order to get out of the way,

be moving downwards along its surface; so that compounding this motion with

that of the current, we should expect the horizontal force to be greater than the

vertical. The experiments have shown that this difference is not appreciable to the

extent to which the instrument can measure it. The same qualification also must

be understood to apply to these results, from which it would appear that the pressure

was independent of the form of the surface. The velocity of the current in these

experiments was measured by a Lind’s anemometer, an instrument that has never

appeared to me to give very satisfactory results; but still the only one available for the

purpose. I regret that the apparatus is considered by Mr. Browning to be too delicate

to be used in the open air, but I hope that this will not be always found to be the case.

As I have said before, difficulties exist only to be overcome, and some day I trust,

we may obtain a series of experiments, in which ordinary wind will replace the use

of the artificial current. I see Mr. Brooke present, who helped us with the experiments, and he may be able to say something as to the results gained.

Mr. BROOKE said it was not exactly mentioned, but the fact was notorious to

everyone acquainted with mechanics, that in whatever position the plane was

placed, the horizontal pressure may be resolved into two—one perpendicular to the

plane, the other in the direction of the plane. It was clear that the resolved pressure

acting in the direction of the plane was wholly effective in raising the plane. The

resolution of the pressure into two was well known to everyone acquainted with the

principles of mechanics; but it was to be understood that there were many other facts

to be considered. The simple geometrical consideration of the action of the pressure

upon the plane, did not involve the necessity for the particles of air which had

impinged upon the plane, getting out of the way to enable other particles to

impinge upon it. This led, in this experiment, to a result which might have been

expected, but which it was important to ascertain. There were two rectangular

planes of the same shape and area, and one was capable of being inclined lengthwise, in relation to the wind, and the other crosswise. Supposing the wind to be

coming in a given direction (indicated as being towards the speaker) it was quite

clear, with the plane inclined lengthwise, there would be less surface of the plane
Document 1-3(a–c) 87

impinged upon than there would be in the transverse direction (indicated on the

instrument). The particles which impinged upon the former must move along the

plane and had much more difficulty in getting out of the way, than particles which

impinged on the plane in the latter position. This would show that the effective

pressure of the wind at the same velocity was greater upon the one plane than

upon the other. And, conversely, a revolving, or oscillating plane, moving in the

former direction (indicated), would move with less force than in the latter direction (indicated). And here was an illustration connected with the wings of birds,

particularly of those that had powerful flight—where the wing was exceedingly

long and narrow, it struck the wind in that direction (indicated). The experiment

showed that from the same amount of surface there would be greater effect upon

the air by a long narrow wing, than by a short and broad one of the same area.

That was one of the results that had been obtained by these experiments.

Mr. WENHAM: I partly neglected to show how this illustrates the flight of

birds. You will find that the lifting power of the smallest angle is nearly five times

that of the direct force. We were not able to try less angles. The smaller the angle

of inclination, in regard to the current, the less the direct force; and, comparatively, the lifting force is scarcely diminished. At 15 degrees, one force is nearly five

times that of the other.

Mr. HARTE asked if, in making those experiments, attempts were made to

ascertain any pressure of the wind downwards.

Mr. WENHAM: No! I omitted to mention that. A spirit level was laid across,

so as to level the instrument. We had a trunk twelve feet long and eighteen inches

square, to direct the current horizontally, and in a parallel course.

THE CHAIRMAN: Certain conditions of current were tried by Lind’s

Anemometer.

Mr. HARTE: Did you notice, in making these experiments, where the centre

of pressure came?

Mr. WENHAM: We were not able to ascertain very accurately. In all cases

there was a tendency to lift the front edge.

Mr. HARTE: Did you notice whether, according to the angle, the centre of

pressure came forward?

Mr. WENHAM: We found as the angle became more acute, the centre of pressure

came nearer to the front edge.

Mr. HALL (of Acton): Was the experiment made with a surface larger than

one foot?

The CHAIRMAN: We had one eighteen inches square.

Mr. HALL: A different result would, I think, be attained within two feet from

what was attained with one foot.

The CHAIRMAN: We have not spoken of two feet, because the shaft was
88 Chapter 1: The Achievement of Flight

scarcely large enough to give the even pressure required. We did not feel quite so

certain with respect to large planes; and, therefore, the experiments with them

are not included in these records; but I am ready to believe that the larger the

planes, the larger the results. With areas of six inches, twelve inches, or two feet, the

larger the area, the larger are the relative results. I have had three or four

anemometers together, and always found this to be the case.

Mr. BROOKE: I rise to make an explanation. The 0 in the return ought to be

90. It ought to be 15, 20, 45, and 90.

Mr. F. W. BREAREY (the Secretary): If there is any gentleman here who could

give us any advantage with regard to a fan-blower, we should be glad to avail ourselves of it. The area was so small that we could not expose much surface.

The CHAIRMAN: But we ought to give our thanks to Mr. Penn for the blower

he lent to us and for the use of his steam power. The entire work of the shop was

stopped during part of the time we occupied it. I should like to ask you to thank

Mr. Penn for the facilities he gave us on that occasion for making these experiments.

(Applause.)

Thanks were accorded to Mr. Penn by acclamation.
Document 1-4 89

Document 1-4

Samuel P. Langley, Experiments in Aerodynamics

(Washington, DC: Smithsonian Institution, 1891), 

excerpt “Langley’s Law” reprinted in 

The Aeronautical Annual 1, James Means, ed., 

(Boston: W.B. Clarke & Co., 1895): 127–128.

Professor Samuel Pierpont Langley’s paper, Experiments in Aerodynamics, published in 1891 by the Smithsonian Institution, has been called the “first substantive American contribution to aerodynamics.” The following passage taken from

this paper presents the theory that came to be known as “Langley’s Law.” This

“law” stated that the power required for a vehicle to fly through the air decreased

as the velocity increased—or, more simply, the higher the speed, the lower the

drag. While this optimistic theory was subsequently realized to be in error, at the

time it was published it represented an important new scientific approach to the

study of aerodynamics. The problem for aeronautical experimenters and designers during Langley’s time was that lift and drag forces were very difficult to measure with any precision, though Lilienthal, the Wrights, and other contemporaries

came to suspect that Langley’s law was badly mistaken. 

Document 1-4, Samuel P. Langley, “Langley’s Law,” 1891.28

“To prevent misapprehension, let me state at the outset that I do not undertake to explain any art of mechanical flight, but to demonstrate experimentally

certain propositions in aerodynamics which prove that such flight, under proper

direction, is practicable. This being understood, I may state that these researches

have led to the result that mechanical sustentation of heavy bodies in the air, combined with very great speeds, is not only possible, but within the reach of mechanical means we actually possess, and that while these researches are, as I have said,

not meant to demonstrate the art of guiding such heavy bodies in flight, they do

show that we now have the power to sustain and propel them.

Further than this, these new experiments (and theory, also, when reviewed in

their light) show that if in such aerial motion, there be given a plane of fixed size

and weight, inclined at such an angle, and moved forward at such a speed, that it

shall be sustained in horizontal flight, then the more rapid the motion is, the less

28 This document does not include six figures that appeared in the original. All six are photographs

of Otto Lilienthal making glider flights.
90 Chapter 1: The Achievement of Flight

will be the power required to support and advance it. This statement may, I am aware,

present an appearance so paradoxical that the reader may ask himself if he has

rightly understood it. To make the meaning quite indubitable, let me repeat it in

another form, and say that these experiments show that a definite amount of

power so expended at any constant rate, will attain more economical results at

high speeds than at low ones, e.g., one horse-power thus employed will transport

a larger weight at twenty miles an hour than at ten, a still larger at forty miles than

at twenty, and so on, with an increasing economy of power with each higher

speed, up to some remote limit not yet attained in experiment, but probably represented by higher speeds than have as yet been reached in any other mode of

transport—a statement which demands and will receive the amplest confirmation

later in these pages.”
Document 1-5(a–d) 91

Document 1-5(a–d)29

(a) Otto Lilienthal, “The Problem of Flying,” Annual Report of

the Board of Regents of the Smithsonian Institution, July 1893

(Washington, DC: Government Printing Office, 1894), pp.

189–194; translated from German article published in

Prometheus 4, No. 205 (1893): 769–744.

(b) Otto Lilienthal, “Practical Experiments in Soaring,” 

Annual Report of the Board of Regents of the Smithsonian

Institution, July 1893 (Washington, DC: Government Printing

Office, 1894), pp. 195–199; translated from German article 

published in Prometheus 5, No. 220 (1893).

(c) Otto Lilienthal, “The Best Shapes for Wings,” Aeronautical

Annual (Boston: W.B. Clarke & Co., 1897), pp. 35–37; 

abridged translation from Zeitschrift für Luftschiffahrt 14.

(d) Vernon, “The Flying Man: Otto Lilienthal’s Flying

Machine,” McClure’s Magazine 3 (September 1894): 323–31.

Otto Lilienthal was one of the most inspiring aviation pioneers of the late

nineteenth century. His gliding exploits were widely publicized and the articles

about him and photographs of his flights captured the imaginations of people in

Europe and America. His work galvanized others to action, and his martyrdom in a

flying accident in August 1896 motivated others to increase efforts to develop a flying

machine. Wilbur and Orville Wright were two men who were so influenced by him;

news of Lilienthal’s death sparked their initiation of active research into the problem

of flight, and their early work was guided by Lilienthal’s research and theories.

Representing Otto Lilienthal’s evangelical writings on aviation are the first

three documents below, translated from German and published in the United

States. “The Problem of Flying” and “Experiments in Soaring” are taken from

pieces included in 1893 in the German journal Prometheus, which subsequently

appeared in English in the Smithsonian Institution’s 1894 annual report. “The Best

29 All figures for this document are photographss and have been omitted here.
92 Chapter 1: The Achievement of Flight

Shapes for Wings” is an abridged translation from the 1897 edition of Aeronautical

Annual. The final piece, an article on “The Flying Man” that appeared in McClure’s

Magazine in September 1894, captures the technical genius inherent to Lilienthal’s

designs as well as the widespread popular enthusiasm for his intrepid flying.

Document 1-5(a), Otto Lilienthal, “The Problem of Flying,” 1893.

While theoretically no difficulty of any considerable importance precludes

flight, the problem can not be considered solved until the act of flying has been

accomplished by man. In its application, however, unforeseen difficulties arise of

which the theorist can have no conception.

The first obstacle to be overcome by the practical constructor is that of stability. It is an old adage that “Wasser hat keine Balken” [Water has no rafters]. What

then, shall be said of air?

Leaving out of the question propelling mechanisms which require more than ordinary refinements of construction, theory teaches that a properly constructed flying

apparatus may be brought to sail in a sufficiently strong wind; while in still air, such

a machine may be made to glide downward upon a slightly inclined path. In the practical application of these two methods, however, it is found that while the apparatus

is supported by moving air, it is also subjected to the whims of the wind, which often

places it in uncomfortable positions, overturns it, or carries it into higher regions and

then precipitates it, headforemost, to the ground. Lowering of the center of gravity

is of little avail, nor does the most ingenious change of the wings or the steering

surfaces alter the case. There is still no trace of the majestic soaring of the bird,

for the wind is a treacherous fellow, who follows his own inclinations and laughs

at our art. Therefore let us try the second method, the oblique descent in still air.

According to computation the apparatus should descend at a small angle,

reaching the ground at a considerable distance, but this experiment is a success

only in short flight. Beyond these the apparatus becomes unmanageable, darts

vertically up, turns about, comes to a full stop, stands on its head, and descends

with uncomfortable rapidity to the ground, the contact with which will probably

have demolished the machine, if it do not turn a lucky somersault and land upon

its back. Nor do repeated changes of the center of gravity alter the case beyond

making it turn over backward instead of forward, leaving the conditions as unstable as before. Fancy the fate of the man who confides in such an apparatus.

Shall we now give up all hopes of success or shall we try new means to deprive

the flying machine of its vicious propensities? This question has been answered in

various ways. On the one hand it is thought that it should be possible, by mechanical means, to produce stable flight automatically, and an association of engineers

of repute at Augsburg—an excellent proof that investigations of the art of flying
Document 1-5(a–d) 93

have begun to be taken up by willing and self-sacrificing men—has among other

things proposed mechanical contrivances for the regulation of soaring.

The apparatus is meant to descend from a captive balloon. By the application

of ingenious methods the sailing surfaces (wings) are forced to retain their inclination. According to the report of Engineer M. Von Siegsfeld on the subject, no

system has as yet been discovered that would promise sufficient security to any

one sailing at a considerable elevation.

As desirable as it is that these investigations should discover safe automatic

devices to give stability to soaring, it remains, on the other hand, doubtful

whether the dangers attending such flights could even then be obviated. I am of

the opinion that the evolution of the flying machine will be similar to that of the

bicycle, which was not made in a day, and that this will not be either. Although in

soaring the center of gravity may be placed below the center of pressure of the

supporting air, it appears that even in this case, on account of the elasticity of the

air itself, permanent stability could only be obtained by a constant and arbitrary

correction of the position of the center of gravity. This is performed by birds

incessantly and it is in virtue of a perfect adaptation of the form of their wings to

any aerial motion that their flight appears to us so sure, graceful, and beautiful.

In the same way, a man can move through the air and have the general ability to guide his apparatus by constant shifting of the center of gravity. Descent

should not be at first tried from great elevations, for such a feat requires practice.

In the beginning, the height should be moderate and the wings not too large, or

the wind will soon show that it is not to be trifled with. In fact, under some circumstances, one may be swept off toward still higher regions, the descent front

which might well be disastrous. It therefore seems best that the wings should not

exceed from 8 to 10 square meters (somewhat over 80 to 100 square feet), or that

the experiment should be conducted in any wind blowing more than 5 meters per

second (nearly 1,000 feet a minute), which represents a gentle breeze. A good run

against the wind, however, and a leap from a safe height of 2 or 3 meters may

secure a flight of 15 or 20 meters.

Constant practice will enable the experimenter to withstand a stronger

breeze, to increase the surface of the wings to 15 square meters (160 square feet),

and to start from a greater elevation, especially if there be a moderate slope

beneath him with a soft, yielding surface. After becoming sufficiently expert to

deviate from a straight line, the experimenter may enjoy the sensation of flying,

but it is always a necessary condition that he should face the wind while descending, as the birds do. If then flight is attempted with the wind, it must be more

rapid than the wind, or the result will be very apt to be a dangerous somersault at

the time of coming to the ground, so that it is, on the whole, most advisable to follow the lessons of the birds, who ascend and descend against the wind.
94 Chapter 1: The Achievement of Flight

I have been experimenting in this way for three years, and the constant

progress made in the perfection of my machine, and the increased security it gives

has convinced me of the correctness of the plan. At all events, I think it best to

perfect the soaring apparatus before attempting flight with moveable wings.

After numerous experiments from low elevations, I gradually ventured to increase

the height, and for this purpose I erected a tower-like shed, which, while it gave me

room to store my apparatus, enabled me to conduct my experiments from the roof.

The illustrations, taken from instantaneous photographs, show one of my securely

constructed machines for soaring and the various phases of a soaring experiment.

Figure 1 represents the first leap from the roof, the cut showing the front view of

the apparatus, which in some respects resembles the spread wings of a bat, and folds

up like those for convenience of storage and transportation. The frame is of willow,

covered with sheeting; the entire area contains nearly 150 square feet, and the entire

apparatus weighs about 45 pounds. The roof of the tower is rather over 30 feet above

the surrounding level, and from this elevation, after sufficient practice, one may glide

over a distance of over 50 yards at an angle of descent of from 10 to 15 degrees.

Figures 2, 3, 4 show the porgies of the experiment. While flying freely in the

air the proper angle of descent has to be regulated by shifting the center of gravity. Of course, the wind plays a very important part here, and it is only long and

constant practice that we can learn to make allowance for its irregularities and to

steer the apparatus properly. The capriciousness of the wind may exert unequal

pressure on the great expanse of wing, and then it may happen that one wing will

be elevated higher than the other. 

This is shown in fig. 5. In this case the equilibrium may be restored by a change

in the center of gravity, which may be effected by extending the legs as far to the left

as possible, and thus adding more weight to the wing on that side. The two steering

planes attached to the rear aid in enabling one to keep the face to the wind.

Figure 6 shows the simple manner of grasping the machine. There are no straps

or buckles, and yet the connection is perfect. Each arm rests on a cushion attached to

the framework, the hands seize a crossbar, and the remainder of the body hangs free.

My recent experiments have been made from hills having an elevation of

about 250 feet and sloping uniformly every way at an angle of 10 to 15°. From the

lower ridges I have already sailed a distance of over 250 yard. The great difficulty

to be encountered in the endeavor to soar comes in learning to guide the flight,

rather than in the difficulty of providing power to move the wings.

Progress in the mechanics of flying received at one time a severe check through

the utterances of a high authority in physics. Starting with an erroneous hypothesis

and putting too high a value on the amount of work required, he claimed that the maximum of possible flight had already been developed in the largest birds, and, as man

represented about four times the heaviest of them, human flight was to be discarded
Document 1-5(a–d) 95

as an utter impossibility. Now it must be admitted that the difficulties increase with

the size of the flying individual; but flying itself is not the difficulty, for the largest

flyers are at the same time the best flyers when once they get going in the air.

The object of this paper is to attempt to dispel old prejudices and to win new

adherents for the problem in question. Even considered only as a physical exercise, the sport of flying would create one of the healthiest of all enjoyments and

add one of the most effective remedies to the means now adopted for the conquest of those diseases which are now incident to our modern culture.

Document 1-5(b), Otto Lilienthal, “Practical Experiments in Soaring,” 1893.

My own experiments in flying were begun with great caution. The first

attempts were made from a grass plot in my own garden upon which, at a height

of 1 meter from the ground, I had erected a springboard, from which the leap with

my sailing apparatus gave me an oblique descent through the air. After several

hundred of these leaps I gradually increased the height of my board to 2 1/2 meters,

and from that elevation I could safely and without danger cross the entire grass

plot. I then went to a hilly section, where leaps from gradually increased elevations

added to my skill and suggested many improvements to my apparatus. The readers

of Prometheus have already been informed of the selection of a piece of ground

which enabled me to extend my flights over a distance of several hundred meters.

The remainder of the summer since my last publication (in Nos. 204 and 205 of this

journal) has sufficed to bring these experiments to a termination and to dispose

of some important questions as to the possible results.

Indulging in subtle inquiries and theorizing does not promote our knowledge

of flying, nor can the simple observation of natural flight, as useful as it may be,

transform men into flying beings, although it may give us hints pointing towards

the accomplishment of our purpose. We see buzzards rise skyward without any

motion of their wings; we observe how the storks intermingle in the flock with outspread wings and in beautiful spirals; we see, high up in the air, the piratical falcon in quest of booty remain stationary in the wind for minutes at a time. We recognize every spot on his brownish plumage, but we do not perceive the least exertion of his wings to maintain his stationary position, and this small bird of prey is

not in the least concerned at our presence. He reciprocates the protection secured

for him since Brehm and other naturalists have pointed out his usefulness by

undisturbedly precipitating himself to the grass before our eyes, and, seizing a

grasshopper, we again see him meters above our heads without having detected

the least flapping of his wings during the entire performance.

We notice that constant changes are going on in the force of the wind, but the

falcon does not alter his position by a single inch, although having already begun
96 Chapter 1: The Achievement of Flight

devouring his prey, he can give but divided attention to his flight. Now he bends

his head downward and backward, so that the world below must appear to him

inverted, and evidently enjoys eating the insect as his talons leisurely pluck it to

pieces. In the position in mid-air (which is maintained even during this

employment) he appears like an automaton rooted in the wind. Just the

faintest balancing motion, apparently serving to compensate for the irregularities

of the wind, is perceptible in the extreme points of his wings, which are slightly

inclined backwards.

The poise of the falcon in mid-air, which appears to us as a defiance to the

law of gravity, may be considered not only the most remarkable, but also the most

instructive example of flight.

In observing the majestic, circular soaring of other aërial travellers, one can

readily believe that these skillful wing artists understand how to profit by the periodic

currents of the air, and in describing spirals instinctively transform the force of

the opposing current of air into lifting or suspensive power; but when the bird,

without the least movement of his wings, remains stationary in one point of the

sky, we are led to infer the existence of a peculiar form of surface which may be

held suspended by the application of a uniformly moving wind.

While the existence of this possibility may be demonstrated by elementary

experiments, this does not discover the secret of soaring, and though nature conclusively demonstrates that it can not be the want of power that prevents our flying,

that knowledge alone does not provide us with wings. Furthermore, while nature

points out how it is done, that does not necessarily imply that there may not be

found other ways or means of doing it. However we may theorize on the subject,

without a practical application of the theory, things will remain unchanged and

our flight will only be in imagination or in dreams.

My experiments, then, should form the transition, the first step from theory

to practice. Like others, I too have, in the beginning, attempted using machines

with moveable wings, but this does not apparently aid in the development of an

art of flight. The mark is too high and not immediately attainable, and one’s

ambition should be fully satisfied by withstanding the wind with wings of the size

adapted to flying men. Each flight demands a rising from the ground and a landing;

the former is as difficult as the latter is dangerous, and regardless of the most

ingeniously constructed apparatus, the art of both will have to be acquired just as

the child learns to stand and walk. Anyone desirous of exposing himself unnecessarily to danger and of ruining in a few seconds the carefully constructed apparatus

need only expose his machine to the wind without having familiarized himself

with its management, and he will soon know what it means to control an apparatus

of from 10 to 15 square meters in area, where other people can but with difficulty

manage an open umbrella.
Document 1-5(a–d) 97

To all those who, by their own experience or otherwise, can form a correct

idea of the difficulties that present themselves, the instantaneous photographs by

Mr. Alexander Krajewsky, accompanying this paper, may be of interest.

In continuation of my formerly published experiments, I endeavor with every

new trial to gain more complete control over the wind, and without disregarding

any necessary precaution I have already succeeded in at least temporarily retaining

a uniform level and even in remaining stationary in the wind for a few seconds.

The simplicity of my flying machine, which is controlled by shifting the center of

gravity, has compelled me to avoid strong breezes, which however might presumably

have aided in securing a stationary position. During my continued flights, however,

I have been at times surprised by a sudden increase in the force of the wind which

either carried me upward almost perpendicularly or supported me in a stationary

position for a few seconds to the great delight of the spectators.

The freedom from accidents in these apparently daring attempts may be considered proof that the apparatus already described offers ample security in carrying

out my plan of investigation.

To those who, from a modest beginning and with gradually increased extent

and elevation of flight have gained full control over the apparatus, it is not in the

least dangerous to cross deep and broad ravines. 

It is a difficult task to convey to one who has never enjoyed aerial flight a clear

perception of the exhilarating pleasure of this elastic motion. The elevation above

the ground loses its terror, because we have learned by experience what sure

dependence may be placed upon the buoyancy of the air. Gradual increase of the

extent of these lofty leaps accustoms the eye to look unconcernedly upon the

landscape below. To the mountain climber the uncomfortable sensation experienced in thrusting his foot into the slippery notch cut in the ice or to a treacherous

rubble above deep abysses, with other dangers of the most terrifying nature, may

often tend to lessen the enjoyment of the magnificent scenery. The dizziness

caused by this, however, has nothing in common with the sensation experienced

by him who trusts himself to the air; for the air demonstrates its buoyancy in not

only separating him from the depth below, but also in keeping him suspended

over it. Resting upon the broad wings of a well-tested flying machine, which,

yielding to the least pressure of the body, obeys our directions; surrounded by air

and supported only by the wind, a feeling of absolute safety soon overcomes that

of danger.

One who has already practiced straight flights for some time will naturally

endeavor to next guide his apparatus in a lateral direction, and indeed there is

nothing easier than the guiding of the aerodrome, which is accomplished by shifting

the center of gravity. The steering blades have nothing to do with this, their function

being to keep the machine facing the wind.
98 Chapter 1: The Achievement of Flight

Plate XIII, fig. 1 illustrates such a serpentine flight. I started from a hill to the

right, the base of which is still visible in the figure, and soared toward the plain

below in a somewhat circuitous path. The photograph was taken at the moment

when I had almost turned my back to the plain. The view shown in Plate XIII, fig. 2,

was taken at a time when I was lifted and carried upward by a suddenly increasing

current which impeded progress and rendered me absolutely stationary.

In Plate XIV, flights are represented in geometric perspective. The lowest dotted

line, d, e, was described during a calm. Even the expert flyer must descend during

a calm at an angle of from 9° to 10°. The run began upon the top of the hill, near

a; at b I left firm ground and endeavored to glide along the mountain slope, placing the wings at c at such an angle that the pressure of the wind, L, would not only

support the machine, but also carry it forward. This increased the velocity sufficiently to enter at d into the line of stable flight. Such a maneuver is necessary,

because a velocity of 9 meters per second is required for a flight in a calm, while

but 6 meters were obtained by the run. At e the ground has almost been reached,

and by raising the wings slightly in front the momentum is diminished and a

landing effected without serious jar.

The second line, e f, shows a flight in a moderate breeze, in which the proper

position with a downward inclination of 6° had been assumed immediately upon

starting.

Flight against the wind is slower. The distance to be accomplished may be

extended by a carefully determined and properly maintained inclination of the

wings; in fact, by careful observation of this the soaring may be extended over a

distance equal to ten times the height of the starting point.

During a strong breeze a sinuous line of flight results from the temporary

support given by the wind at times. This is shown in the line b g, though such

experiments should be undertaken only by one fully familiar with the management of the apparatus. The indefinable pleasure however experienced in soaring

high up in the air, rocking above sunny slopes without jar or noise, accompanied

only by the æolian music issuing from the wires of the apparatus, is well worth the

labor given to the task of becoming and expert.

It does not seem at all impossible that the continuance of such flights may

lead to free, continuous sailing in agitated air.

The results of our present experiments already furnish an indication of the

degree of mechanical energy that must be added to that involved in oblique soaring

to enable us to gain independent horizontal flight.

The solution of this problem, however, would exceed the purposes of the

present article, and I content myself by stating that the conditions of a motor can

easily be met, supposing that the propelling mechanism has been properly chosen, and that extraordinary lightness is not even essential.
Document 1-5(a–d) 99

The interests of the professional flight-essayer demand further experiments

in practical flight and the gain of further efficiency. But even to those who only

desire to utilize, as a means of sport, the results already obtained, opportunities

are offered to promote the interest of the problem of flight and the way for a more

ready prosecution of the subject.

The time has passed when every person harboring thoughts of aerial flight can at

once be pronounced a charlatan. If we may hope that our aeronautic publications are

eventually to be taken seriously by the majority of those skilled in allied subjects, it is

important at the outside to awaken the interest of those whose natural concern this

great problem should be, but who now shrug their shoulders. We shall then at least be

able to show some practical results, and towards these ends we here take the first step.

Document 1-5(c), Otto Lilienthal, “The Best Shapes for Wings,” 1897.

The results which we reach by practical flying experiments will depend most

of all upon the shapes which we give to the wings used in experimenting.

Therefore there is probably no more important subject in the technics of flying

than that which refers to wing formation.

The primitive idea that the desired effects could be produced by means of flat

wings has now been abandoned, for we know that the curvature of birds’ wings

gives extraordinary advantages in flying.

The experiments on the resistance of air to curved surfaces have shown that

even very slight curvatures of the wing-profile increase considerably the sustaining

power, and thereby diminish the amount of power required in flight.

The wing of a bird is excellent not only because of the curvature of its crosssection, but the rest of its structure and formation also has influence upon the

flight. Therefore the outline of the wing is certainly of importance.

It is probable that the form of the cross-section of the wing and flight-feathers

(Schwungfedern) has a favorable influence upon the flight.

Experiments have not yet been made to show conclusively whether or not the

feather structure of a wing endows it with a special quality whereby the sustaining

power is increased. With investigators this has been a subject of conjecture.

Therefore it is questionable (auch fraglich) whether we are wrong if, in constructing

flying apparatus, we keep to the bat’s wing, which is easier to construct.

Bats fly much better than is generally thought. Two early bats, which I saw flying

this summer in broad sunshine and in somewhat windy weather, sailed along so

well without flapping their wings that I thought, at first, they were swallows. Of

course on evenings when there is no wind, the bat must flutter continually. The

early-flying bat is also called evening-sailer (Abendsegler) which indicates that its

sailing flight has been marked.
100 Chapter 1: The Achievement of Flight

The most important point as regards the form of the wing will always be the

curvature of its profile. If we examine any bird’s wing we find that the enclosed

bones cause a decided thickening at the forward edge. The question now is, What

part does this thickening play in the action of the curved surface? The thickening

is quite considerable, particularly in birds which have long, narrow wings. An

albatross in my possession has a breadth of wing 16 centimetres, the thickened

part of which measures 2 centimetres; the thickness is therefore 1/8 of the breadth

of the wing. As the albatross is one of the best sailers, we can scarcely assume that

the comparatively great thickness of the wing at its outer edge has a detrimental

effect upon the bird’s flight.

For a long time I have assumed that the thickening which all birds’ wings have

at the front edge produces a favorable effect in sailing flight. By means of freesailing models I have now learned that nature makes a virtue of necessity, that the

thickened front edge is not only harmless, but in sailing flight is helpful (sondern

den Schwebe-effect nicht unerheblich erhöht).

The experiments are easily tried. It is only necessary to make a number of

models of equal size and weight, each one having a different curve in its sustaining

surfaces. These models I make of strong drawing paper, the size of the surfaces

being about 4 inches in width by 20 inches in length.

The experimenter can let these models sail from any tower or roof in front of

which there is an open space. Each model must be made to glide through the air

many times until it reaches the ground. Experiments must be made in the stillest

possible air.

The lengths of flights are all noted down, and from a long series of experiments

the arithmetical mean for each design is computed. The models having the best

profiles will make the longest flights. In this way a reliable table can be made

which will show the relative merits of the profiles, and will also show quite plainly

in which direction the most useful form will have to be developed.

Until now I have endeavored to find out the best proportions for wings by constructing different kinds of sailing apparatus. In this way, of course, many important

facts have been ascertained. The construction of full-sized apparatus requires a

great deal of time and is expensive, therefore we must welcome a method which

permits inquiry into the forms of wings in models which fly automatically. Besides

that, it is not every one’s business to throw himself into space in a sailing apparatus,

although he who would succeed in practical flying can scarcely avoid this way.

Considering the fact that the most important thing is to ascertain what are

the best qualities of the natural wing, which is in every respect perfect,—these

steadily sailing models offer every one an opportunity of engaging in experiments

of this kind. Further, any one who takes up this kind of experiment will find great

pleasure in watching the manœuvers of his small flyers, which often vie with the
Document 1-5(a–d) 101

best sailers among birds. I can therefore recommend this occupation not only for

the furthering of the science of mechanical flight, but also because it affords a

most interesting pastime.

The few measurements made so far by this method are too incomplete to be

fit, as yet, for publication. I am preparing, however, a systematic series of experiments, the results of which will be stated when the experiments are finished.

Meanwhile, I cherish the hope that this paper may be an incentive to others

to make similar experiments, so that we may sooner reach the desired end.

Document 1-5(d), Vernon, “The Flying Man,” 1894.

Herr Otto Lilienthal, of Berlin, who has attained some celebrity as “The

Flying Man,” was born forty-six years ago in the antiquated little city of Anklarn,

near the Baltic coast of Pomerania, about sixty miles to the northwest of Stettin.

A residence so near the sea afforded him, in early life, many an opportunity of

prosecuting his favorite studies and observations. In later years he migrated with

his younger brother, Gustav, his enthusiastic coadjutor in all his researches in the

domain of aviatics, to Berlin, where he established, and is now conducting, a large

manufactory of small steam engines, whose mechanical appliances furnish him

with every facility for the construction of his flying apparatus. He is an accomplished mathematician, and a close observer of nature; and is, besides, endowed

in large measure with that poetic instinct which nearly always constitutes one side

of even the most practical German character.

THE BIRD’S WING ON LILIENTHAL’S MODEL. 

For more than twenty years Herr Lilienthal, with his brother’s aid, and in the

intervals of more serious occupations, has been studying the subject of aërial navigation. He has taken the flying bird as his teacher. After many experiments with

flat wings or plane surfaces, he became convinced that it was the gentle parabolic

curve of the wing which enables a bird to sustain itself without apparent effort in

the air, and even to soar, without a motion of the wings, against the wind. This he

has demonstrated not only by experiment, but by an application of the doctrine

of the resolution of forces to the action of the wind upon a concave surface. The

circling ascents of the carrier-pigeon, as he rises when released, to gain a general

view of the landscape, and to take his bearings before starting on his homeward

journey, depend upon this principle. He flies with the wind, but he sails or soars

against it. The fins of many fishes and. the web feet of aquatic birds, are strikingly

analogous in construction. The sails of a ship assume a similar form. It would be

impossible to sail so near the wind if the instrument of propulsion were a rigid flat

surface. It is the effort of the sail to get away from the wind, which it gathers in its

ample bosom and drives the boat forward, almost in the very teeth of the breeze.
102 Chapter 1: The Achievement of Flight

“There are still prominent investigators who will not see,” said Herr Lilienthal

to me, “that the arched or vaulted wing includes the secret of the art of flight. As

we came upon the track of this idea, my brother and I, who were then young and

wholly without means, used to spare from our breakfasts, penny by penny, the

money to prosecute our investigations; and often the ‘struggle for life’ compelled

us to interrupt them indefinitely. While we were devoting every moment of our

spare time to the solution of the problem, almost every one in Germany regarded

the man who would waste his energies in such unproductive labor as a fool. Years

ago the most distinguished professor of mathematics in the Berlin Industrial

Academy sent me word that of course it could do no harm to amuse myself with

such pastimes, but warned me earnestly against putting any money into them. A

special commission of experts, organized by the state, had, in fact, laid it down as

a fundamental principle, once for all, that it was impossible for a man to fly. German

societies for the promotion of aëronautics did not then exist, and those subsequently formed were devoted almost entirely to the interests of ballooning.

“I have always regarded the balloon, and the exclusive attention which it so

long attracted, as a hindrance rather than a help to the development of the art of

flight. If it had never been invented, it is probable that more serious investigations would have been prosecuted towards other solutions of the problem. Since

the time of Montgolfier nearly all practical efforts have been directed to the

improvement of the balloon. But it has nothing in common with the birds, and it

is these that we must take as our model and exemplar. What we are seeking is the

means of free motion in the air, in any direction. In this the balloon is of no aid;

there is no relation between the two systems.”

THE WING OF THE BIRD.

The wing of a bird is divided into three parts, corresponding to shoulderjoint, the forearm, and the hands and fingers of the human frame. The two former,

composed largely of bones and muscles and tendons, are comparatively heavy,

and their rapid movement demands the expenditure of considerable physical

force; the last consists almost entirely of “pen-feathers,” or pinions, which move

to a certain extent automatically. In the larger birds—the “sailers” or “soarers,”

which alone are to be considered here—the first two members, with their concave

under surfaces, furnish the sustaining power; and the last, being at the greatest

distance from the shoulder, or axis of motion, the chief propulsive force. The construction of each member is peculiarly adapted to its special purpose, and it is this

which Herr Lilienthal has endeavored to imitate.

An oarsman, on his forward stroke, opposes the blade of his oar almost perpendicularly to the resistance of the water. As he lifts it at the beginning of the

backward stroke he “feathers” it, or brings it into a nearly horizontal position, so

that its edge cuts the air. The pinions of birds act in precisely the same way. There
Document 1-5(a–d) 103

are other analogies between the wing and the oar. The backstroke of the oar occupies only about half the time of the “pull,” and the upstroke of the wing bears

about the same relation to the downward beat. Moreover, at certain inclinations

of the wing, the upward stroke, while detracting little or nothing from the sustaining power, contributes to the forward movement. As the pinions separate in consequence of the action of the air from above, they present their concave surface

obliquely to the resisting medium and act like an oar in “sculling,” which, whether

moved to the right or the left, impels the boat forward. It is evident that this must

greatly lighten the physical exertions of a bird in rapid flight, for in whichever

direction he moves his wings he gains propulsive force.

To the conviction that concave or vaulted wings were essential to success, Herr

Lilienthal was led not only by the examination of a great variety of natural wings,

and by theoretical deduction, but by actual experiment. The means adopted for

this purpose were ingenious and simple. He fitted up an apparatus in the form of

the fly-fans found above the dining tables of clubs and restaurants, with two long

arms revolving horizontally, to the ends of which surfaces of different kinds and

degrees of curvature could be affixed in any required position. The motive power

was furnished by a weight, and could be exactly measured. There was also an

adjustment which enabled the observer to measure the lifting force of various surfaces, moving at different angles of inclination through still air. By this means

Herr Lilienthal was enabled to reach conclusions which were of great value to him

in the construction of his flying machine; and the most important of them was

that the most effective form of wing was that whose convexity, as measured by the

versed sine of the arc, should be one-twelfth of the breadth of the wing, or of the

length of the chord connecting the opposite edges.

HERR LILIENTHAL’S WINGS.

The flying machine devised and now used by Herr Lilienthal is designed

rather for sailing than for flying, in the proper sense of the term; or, as he says,

“for being carried steadily and without danger, under the least possible angle of

descent, against a moderate wind, from an elevated point to the plain below.” It

is made almost entirely of closely woven muslin, washed with collodion to render

it impervious to air, and stretched upon a ribbed frame of split willow, which has

been found to be the lightest and strongest material for this purpose. Its main elements are the arched wings; a vertical rudder, shaped like a conventional palm-leaf,

which acts as a vane in keeping the head always towards the wind; and a flat, horizontal rudder, to prevent sudden changes in the equilibrium.

The operator so adjusts the apparatus to his person that, when in the air, he

will be either resting on his elbows or seated upon a narrow support near the

front. With the wings folded behind him he makes a short run from some elevated

point, always against the wind, and when he has attained sufficient velocity
104 Chapter 1: The Achievement of Flight

launches himself into the air by a spring or a jump, at the same time spreading

the wings which are at once extended to their full breath by atmospheric action;

whereupon he sails majestically along like a gigantic seagull. In this way Herr

Lilienthal has accomplished flights of nearly three hundred yards from the

starting point.

“No one,” said Herr Lilienthal to me, “can realize how substantial the air is,

until he feels its supporting power beneath him. It inspires confidence at once.

With flat wings it would be almost impossible to guard against a fall. With arched

wings it is possible to sail against a moderate breeze at an angle of not more than

six degrees to the horizon.”

The principle is recognized in the umbrella-form universally adopted for the

parachute. Try to run with an open umbrella held above the head and slightly

inclined backwards, and see what a lifting power it exerts. Mechanical birds have

been constructed with flat wings, which, so long as the machinery operated, were

able to sustain themselves moderately well and to fly rapidly; but no one has yet

succeeded in making any practical use of them. Their course has no intelligent

direction; when the motive power gives out, they fall heavily to the earth. Soaring,

in the sense of rising against the wind as the birds do, is possible only with domeshaped wings. The aeroplane, or flat wing, when inclined at a certain angle to the

breeze, may rise while its momentum continues, but once overcome its power is

gone and nothing can restore it.

PROPER DIMENSIONS FOR THE WINGS.

“The curve of a bird’s wing,” said Herr Lilienthal, “is parabolic ; but the simple parabola differs so little from the arc of a circle that I adopted the latter curve

as the more practicable, and the wings which I now use are in the main segments

of a spherical surface. They are so constructed that they can be folded together

like the wings of a bat, and require very little storage room when not in use.

“It was only gradually that I arrived at the proper dimensions. One does not

easily gain an adequate conception of the materiality of the air, and my apprehensions led me at first to make the wings too large. I found that the varying force of

the atmospheric currents, modified as they are by the undulations of the earth’s

surface, endangered my equilibrium in direct proportion to the spread of the

wings. Those which I now employ are never more than twenty-three feet from tip

to tip, and I am thus enabled, by a simple change of posture, so to alter the position

of the centre of gravity as to restore the equilibrium.

“There are limits also to the breadth of the wings, or their extension backwards.

The operator must be able in a moment to transfer the center gravity so far to the

rear as to overcome the action of the air, which might otherwise tend to throw him

forward, and precipitate him to the earth. When one feels himself falling, the natural

impulse is to stretch out the arms and legs in the direction of the fall; but it is one
Document 1-5(a–d) 105

of the peculiarities of this mode of navigation that the movement must be in the

contrary direction, or towards the upper side. The centre of gravity is thus shifted

to the one side or to the other, forward or backward, and the pressure of the air, acting

with greater force on the lighter and broader surface, soon restores the equilibrium.

It is not easy to realize in practice at first, but after a short experience the movement

becomes almost involuntary.

“When there is no wind, the apparatus acts simply as a parachute. The pressure

of the air is directly from beneath, and is equal on all parts of the under surface.

I have more than once found myself in this position, when I have utilized the

speed attained in a gradual descent, in rising to a greater height in order to soar

over some obstacle like a tree or a crowd of people. Under favorable circumstances it is easy to mount to a height even greater than that of the starting point,

but the forward motion is thereby partially or wholly neutralized, and it may happen

that one comes to a complete standstill in mid-air. In such cases it is only necessary

to throw the centre of gravity so far back that the air shall act more powerfully on

the forward surface, and the gradual gliding descent is resumed. So in landing I

bend backward, exactly as a crow does when alighting in a field, and reach the

ground without the slightest shock. The worst that is likely to happen in any case

is the breaking of the apparatus; there is little danger to life or limb.

“I am far from supposing that my wings, although they afford the means of

sailing, and even of soaring in the air, possess all the delicate and subtle qualities

necessary to the perfection of the art of flight. But my researches show that it is

well worthwhile to prosecute the investigations farther.”

THE LILIENTHAL MOTOR.

Having demonstrated the practicability of sailing and soaring, Herr Lilienthal

has sought, in his recent experiments, to reach a practical solution of the problems

of actual flight. The first difficulty to overcome was the discovery of a suitable

motor, without which all efforts to fly would be hopeless. If we estimate the ordinary

weight of a man at one hundred and sixty pounds, and add to that the weight of

the flying apparatus, we have a total burden of at least two hundred pounds to be

raised and supported simply by aerial resistance. It is calculated that to cover

come the attraction of gravity in such a case requires a force of one and one quarter

horse power, which no man is able to exert for more than a very short time.

With such an apparatus as Herr Lilienthal’s, steam engines and electric

motors are not readily available; but he conceived the ingenious idea of employing, as a motive force, the vapor of liquid carbonic acid, which, under ordinary

atmospheric pressure, boils at a temperature far below that at which mercury

freezes. His engine requires no fire, nor boiler, nor steam-chest; only a diminutive

cylinder with the requisite valve arrangements, which may be readily worked by

hand, and a small reservoir of the liquid acid lying close beside it.
106 Chapter 1: The Achievement of Flight

The one first constructed was of two horse-power, with a receiver to contain

enough carbonic acid to last for two hours, and was attached to the front of the

flying apparatus. The whole contrivance, with the necessary machinery to impart

motion to the wings, added less than twenty-five pounds to the weight, and this

will probably be reduced in the future by the use of some alloy of aluminum,

instead of iron, in the manufacture of the heavier portions. The wings were also

fitted with rotatory pinions, constructed on the principles already indicated, and

capable of automatic action under the pressure of the air.

The first experiments with this apparatus were rather too successful, at least in

demonstrating the power of the engine. Unfortunately, the inventor had underestimated the energy of his motor, which acted with such unexpected vigor that

the wings were broken, and the modifications thus shown to be necessary will

require some time for their completion. Herr Lilienthal confidently expects, however,

eventually to solve the problem in this way.
Document 1-6 107

Document 1-6

Hiram Maxim, excerpts from “Natural and 

Artificial Flight,” Aeronautical Annual 

(Boston: W.B. Clarke & Co., 1896), pp. 88–117. 

Hiram Maxim was an American engineer who went to Europe in the 1880s to

produce and sell small electrical appliances, but he instead gained fame and fortune

with his invention in 1884 of a weapon capable of firing bullets in a sustained fully

automatic mode, which he called a “machine gun.” Working in London in the

1890s he turned his attention to the problem of mechanical flight and designed

what was arguably the largest and most expensive attempt at a flying machine in

the nineteenth century. His airplane was a failure, and in terms of the advancing

science of aerodynamics he contributed little, but the association of his name and

the many articles he wrote for popular journals did much to stimulate an

increased interest in aerodynamic research. The document included here is one

of those articles, published in the Aeronautical Annual 1896 edition, and consists

of portions of a seven-part “thesis” outlining his own research. 

Document 1-6, Hiram Maxim, excerpts from “Natural and Artificial Flight,” 1896.

I. INTRODUCTORY.

At the time I commenced my experiments in aeronautics it was not generally

believed that it would ever be possible to make a large machine heavier than the air

that would lift itself from the earth by dynamic energy generated by the machine

itself. It is true that a great number of experiments had been made with balloons, but

these are in no sense true flying machines. Everyone who attempted a solution of

the question by machines heavier than the air, was looked upon in very much the

same light as the man is now who attempts to construct a perpetual motion

machine. Up to within a few years, nearly all experiments in aerial navigation by

flying machines have been made by men not versed in science, and who for the

most part have been ignorant of the most rudimentary laws of dynamics. It is only

quite recently that scientific engineers have taken up the question and removed it

from the hands of charlatans and mountebanks. A few years ago many engineers

would not have dared to face the ridicule which they would be liable to receive if

they had asserted that it would be possible to make a machine that would lift itself

by mechanical means into the air. However, thanks to the admirable work of

Professor Langley, Professor Thurston, Mr. Chanute and others, one may now

express his opinion freely on this subject and speculate as to the possibilities of

making flying machines, without being relegated to the realm of cranks and fanatics.
108 Chapter 1: The Achievement of Flight

During the last five years I have had occasion to write a large number of articles

for the public press on this subject, and I have always attempted, as far as it is in my

power, to discuss the subject in such a manner as to be easily understood by the

unscientific, and I believe that my efforts have done something in the direction of

popularizing the idea that it is possible to construct practical flying machines.

In preparing my present work, I have aimed as far as possible to discuss the

question in plain and simple language, and to abstain from the use of any formulæ

which may not be understood by every one. It has been my experience that if a

work abounds in formulæ and tables, even only a few of the scientific will take the

trouble to read or understand it. I have therefore confined myself to a plain statement of the actual facts, describing the character of my observations and experiments, and giving the results of the same. All experiments made by others in the

same direction have been on a very small scale, and, as a rule, the apparatus

employed has been made to travel around a circle, the size of which has not been

great enough to prevent the apparatus continually encountering air which had

been influenced in some way by the previous revolution.

The first experiments which I conducted were with an apparatus which travelled

around a circle 200 feet in circumference, and by mounting some delicate

anemometers directly under the path of the apparatus I ascertained that after it

had been travelling at a high velocity for a few seconds, there was a well-defined

air current blowing downward around the whole circle, so that my planes in passing

forward must have been influenced and their lifting effect reduced to some extent

by this downward current. My late experiments are the first which have ever been

made with an apparatus on a large scale moving in a straight line. In discussing

the question of aerial flight with Professor Langley before my large experiments

had been made, the Professor suggested that there might be some unknown factor

relating to size only which might defeat my experiments, and that none of our

experiments had at that time been on a sufficiently large scale to demonstrate

what the lifting effect of very large planes would be. A flying machine to be of any value

must of necessity be large enough to carry at least one man, and the larger the

machine the smaller the factor of the man’s weight. Moreover, it is possible to

make engines of say from 200 to 400 horse-power, lighter per unit of power than

very small engines of from one to two horse-power. On the other hand, it is not

advisable to construct a machine on too large a scale, because as the machine

becomes larger the relative strength of the material becomes less. In first designing my large machine I intended that it should weigh about 5,000 pounds without men, water, or fuel, that the screw thrust should be 1,500 pounds, and that

the total area of the planes should be 5,000 square feet. I expected to lift this

machine and drive it through the air at a velocity of 35 miles an hour with an

expenditure of about 250 horse-power. However, upon completing the machine I
Document 1-6 109

found that many parts were too weak, and these had to be supplanted by thicker

and stronger material. This increased the weight of the machine about 2,000

pounds. Upon trying my engines I found that if required they would develop 360

horse-power, and that a screw thrust of over 2,000 pounds could be easily

attained, but as an offset against this, the amount of power required for driving

the machine through the air was a good deal more than I had anticipated. 

II. NATURAL FLIGHT.

During the last 50 years a great deal has been said and written in regard to

the flight of birds. Perhaps no other natural phenomenon has excited so much

interest and has been so little understood. Learned treatises have been written to

prove that a bird is able to develop from 10 to 100 times as much power for its

weight as other animals, while other equally learned treatises have shown most

conclusively that no greater amount of energy is exerted by a bird in flying than

by land animals in running or jumping.

There is no question but what a bird has a higher physical development, as

far as the generation of power is concerned, than any other animal we know of.

Nevertheless, I think that every one who has made a study of the question will

agree that some animals, such as rabbits, exert quite as much power in running in

proportion to their weight as a sea-gull or an eagle exerts in flying.

The amount of power which a land animal has to exert is always a fixed and definite quantity. If an animal weighing 100 pounds has to ascend a hill 100 feet high,

it always means the development of 10,000 foot-pounds. With a bird, however, there

is no such thing as a fixed quantity, because the medium in which the bird is moving

is never stationary. If a bird weighing 100 pounds should raise itself into the air 100

feet during a perfect calm, the amount of energy developed would be 10,000 footpounds plus the slip of the wings. But, as a matter of fact, the air in which a bird flies

is never stationary, as I propose to show; it is always moving either up or down, and

soaring birds, by a very delicate sense of feeling, always take advantage of a rising

column of air. If a bird finds itself in a column of air which is descending, it is necessary for it to work its wings very rapidly in order to prevent a descent to the earth.

I have often observed the flight of hawks and eagles. They seem to glide

through the air with hardly any movement of their wings. Sometimes, however,

they stop and hold themselves in a stationary position directly over a certain spot,

carefully watching something on the earth immediately below. In such cases they

often work their wings with great rapidity, evidently expending an enormous

amount of energy. When, however, they cease to hover and commence to move

again through the air, they appear to keep themselves at the same height with an

almost imperceptible expenditure of force.

Many unscientific observers of the flight of birds have imagined that a wind

or a horizontal movement of the air is all that is necessary in order to sustain the
110 Chapter 1: The Achievement of Flight

weight of a bird in the air after the manner of a kite. If, however, the wind, which

is only air in motion, should be blowing everywhere at exactly the same speed and

in the same direction (horizontally), it would offer no more sustaining power to a

bird than a dead calm, because there is nothing to prevent the body of the bird

being blown along with the air, and whenever it had attained the same velocity as the

air, no possible arrangement of the wings would prevent it from falling to the earth.

The wind, however, seldom or never blows in a horizontal direction. Some

experimenters have lately asserted that if it were possible for us to ascend far enough,

we should find the temperature constantly falling until at about 20 or 25 miles above

the earth’s surface the absolute zero might be reached. Now, as the air near the earth

never falls in temperature to anything like the absolute zero, it follows that there is a

constant change going on, the relatively warm air near the surface of the earth always

ascending, and, in some cases, doing sufficient work in expanding to render a portion

of the water it contains visible, forming clouds, rain, or snow, while the very cold

air is constantly descending to take the place of the rising column of warm air.

On one occasion while crossing the Atlantic in fine weather, I noticed, some

miles directly ahead of the ship, a long line of glassy water. Small waves indicated

that the wind was blowing in the exact direction in which the ship was moving,

and I observed as we approached the glassy line that the waves became smaller

and smaller until they completely disappeared in a mirror-like surface which was

about 300 or 400 feet wide and extended both to the port and starboard in

approximately a straight line as far as the eye could reach. After passing the centre of this zone, I noticed that small waves began to show themselves, but in the

exact opposite direction to those through which we had already passed. I

observed that these waves became larger and larger for nearly an hour. Then they

began to get gradually smaller, when I observed another glassy line directly ahead

of the ship. As we approached it the waves completely disappeared, but after passing

through it I noticed that the wind was blowing in the opposite direction and that

the waves increased in size exactly in the same manner that they had diminished

on the opposite side of the glassy zone.

This would seem to indicate that directly over the centre of the first glassy

zone, the air was meeting from both sides and ascending, and that at the other

glassy zone the air was descending in practically a straight line to the surface of

the water where it spread out and set up a light wind in both directions.

I spent the winter of 1890–91 on the Riviera, between Hyères les Palmiers

and Monte Carlo. The weather for the most part was very fine, and I often had

opportunities of observing the peculiar phenomena which I had already noticed

in the Atlantic, only on a much smaller scale. Whereas, in the Atlantic, the glassy

zones were from 5 to 20 miles apart, I often found them not more than 500 feet

apart in the bays of the Mediterranean.
Document 1-6 111

At Nice and Monte Carlo this phenomenon was also very marked. On one occasion, while making observations from the highest part of the promontory of Monaco

on a perfectly calm day, I noticed that the whole of the sea presented this peculiar

effect as far as the eye could reach, and that the lines which marked the descending

air were never more than a thousand feet from those which marked the centre of the

ascending column. At about 3 o’clock in the afternoon, a large black steamer passed

along the coast in a perfectly straight line, and I noticed that its wake was at once

marked by a glassy line which indicated the centre of an ascending column. This line

remained almost straight for two hours, when finally it became crooked and broken.

The heat of the steamer had been sufficient to determine this upward current of air.

In 1893, I spent two weeks in the Mediterranean, going by a slow steamer

from Marseilles to Constantinople and returning, and I had many opportunities

of observing the peculiar phenomenon which I have before referred to. The

steamer passed over thousands of square miles of calm sea, the surface being only

disturbed by large batches of small ripples separated from each other by glassy

streaks, and I found that in no case was the wind blowing in the same direction

on both sides of these streaks, every one of them either indicating the centre of

an ascending or a descending column of air.

If we should investigate this phenomenon in what might be called a dead calm,

we should probably find that the air was rising straight up over the centres of some

of these streaks, and descending in a vertical line over the centres of the others. But,

as a matter of fact, there is no such thing as a dead calm. The movement of the air

is the resultant of more than one force. The air is not only rising in some places and

descending in others, but at the same time the whole mass is moving forward with

more or less rapidity from one part of the earth to another. So we might consider

that, instead of the air ascending directly from the relatively hot surface of the earth

and descending vertically in other places, in reality it is moving on an incline.

Suppose that the local influence which causes the up and down motion of the

air should be sufficiently great to cause it to rise at the rate of 2 miles an hour,

and that the wind at the same time should be blowing at the rate of 10 miles an

hour; the motion of the air would then be the resultant of these two velocities. In

other words, it would be blowing up an incline of 1 in 5. Suppose now, that a bird

should be able to so adjust its wings that it advanced 5 miles in falling 1 mile

through a perfectly calm atmosphere; it would be able to sustain itself in an

inclined wind, such as I have described, without any movement at all of its wings.

If it was able to adjust its wings in such a manner that it could advance 6 miles by

falling through 1 mile of air, it would then be able to rise as relates to the earth

while in reality falling as relates to the surrounding air.

In conducting a series of experiments with artillery and small guns in a very

large and level field just out of Madrid, I often observed the same phenomena as
112 Chapter 1: The Achievement of Flight

relates to the wind, that I have already spoken of as having observed at sea, except

that the lines marking the centre of an ascending or a descending column of air were

not so stationary as they were over the water. It was not an uncommon thing when

adjusting the sights of a gun to fire at a target at very long range, making due

allowances for the wind, to have the wind change and blow in the opposite direction

before the word of command was given to fire. While conducting these experiments,

I often noticed the flight of eagles. On one occasion a pair of eagles came into sight

on one side of the plain, passed directly over our heads and disappeared on the

opposite side. They were apparently always at the same height from the earth and

soared completely across the plain without once moving their wings. This phenomenon, I think, can only be accounted for on the hypothesis that they were able

to feel out with their wings an ascending column of air, that the centre of this column

of air was approximately a straight line running completely across the plain, that they

found the ascending column to be more than necessary to sustain their weight in

the air, and that whereas, as relates to the earth, they were not falling at all, they

were really falling some 2 or 3 miles an hour in the air which supported them.

Again, at Cadiz in Spain, when the wind was blowing in very strongly from the

sea, I noticed that the sea-gulls always took advantage of an ascending column of

air. As the wind blew in from the sea and rose to pass over the fortifications, the

seagulls selected a place where they could slide down on the ascending current of

air, keeping themselves always approximately in the same place without any

apparent exertion. When, however, they left this ascending column, I observed

that it was necessary for them to work their wings with great vigor until they again

found the proper place to encounter the favorable current.

I have often noticed sea-gulls following a ship. I have observed that they are

able to follow the ship without any apparent exertion; they simply balance themselves on an ascending column of air and seem to be quite as much at ease as they

would be if they were roosting on a solid support. If, however, they are driven out

of this position, I find that they generally have to commence at once to work their

passage. If anything is thrown overboard which is too heavy for them to lift, the

ship soon leaves them, and in order to catch up with it again, they move their

wings very much as other birds do; but when once established in the ascending

column of air, they manage to keep up with the ship by doing little or no work.

In a head wind we find them directly aft of the ship; if the wind is from the port

side, they may always be found on the starboard quarter, and vice versa.

Every one who has passed a winter on the northern shores of the

Mediterranean must have observed the cold wind which is generally called the

mistral. One may be out driving, the sun may be shining brightly, and the air be

warm and balmy, when, suddenly, without any apparent cause, one finds himself

in a cold descending wind. This is the much-dreaded mistral, and if at sea, it
Document 1-6 113

would be marked by a glassy line on the surface of the water. On land, however,

there is nothing to render its presence visible. I have found that the ascending column of air is always very much warmer than the descending column, and that this

action is constantly taking place in a greater or less degree.

From the foregoing deductions I think we may draw the following conclusions:

First, that there is a constant interchange of air taking place, the cold air

descending, spreading itself out over the surface of the earth, becoming warm,

and ascending in other places.

Second, that the centres of the two columns are generally separated from each

other by a distance which may be from 500 feet to 20 miles.

Third, that the centres of greatest action are not in spots, but in lines which

may be approximately straight but generally abound in many sinuosities.

Fourth, that this action is constantly taking place over both the sea and the

land, that the soaring of birds, a phenomenon which has heretofore been so little

understood, may be accounted for on the hypothesis that the bird seeks out an

ascending column of air, and that, while sustaining itself at the same height in the

air without any muscular exertion, it is in reality falling at a considerable speed

through the air that surrounds it.

It has been supposed by some scientists that the birds may take advantage of some

vibratory or rolling action of the air. I find, however, from careful observation and

experiment, that the motion of the wind is comparatively steady, and that the

short vibratory or rolling action is always very near to the earth and is produced by

the air flowing over the tops of hills, high buildings, or trees. If a kite is flown only a

few feet above the ground, it will be found that the current of air is very unsteady. If

it is allowed to mount to 500 feet, the unsteadiness nearly all disappears, while if it

is further allowed to mount to a height of 1,500 or 2,000 feet, the pull on the cord is

almost constant, and, if the kite is well made, it remains practically stationary in the air.

I have often noticed in high winds, that light and fleecy clouds come into view,

say, about 2,000 feet above the surface of the earth, and that they pass rapidly and

steadily by, preserving their shape completely. This would certainly indicate that

there is no rapid local disturbance in the air in their immediate vicinity, but that

the whole mass of air in which these clouds are formed is practically travelling in

the same direction and at the same velocity. Numerous aeronauts have also testified that, no matter how hard the wind may be blowing, the balloon is always practically in a dead calm, and if a piece of gold-leaf is thrown overboard even in a

gale, the gold-leaf and the balloon never part company in a horizontal direction,

though they may in a vertical direction.

Birds may be divided into two classes: first, the soaring birds, which practically

live upon the wing, and which, by some very delicate sense of touch, are able to

feel the exact condition of the air. Many fish which live near the top of the water
114 Chapter 1: The Achievement of Flight

are greatly distressed by sinking too deeply, while others which live at great depths

are almost instantly killed by being raised to the surface. The swim bladder of a

fish is in reality a delicate barometer provided with sensitive nerves which enable

the fish to feel whether it is sinking or rising in the water. With the surface fish, if

the pressure becomes too great, the fish involuntarily exerts itself to rise nearer

the surface and so diminish the pressure, and I have no doubt that the air-cells,

which are known to be very numerous and to abound throughout the bodies of

birds, are so sensitive as to enable soaring birds to know at once whether they are

in an ascending or a descending column of air.

The other class of birds consists of those which only employ their wings for

the purpose of taking them rapidly from one place to another. Such birds may be

considered not to expend their power so economically as the soaring birds. They

do not spend a very large portion of their time in the air, but what time they are

on the wing they exert an immense amount of power and fly very rapidly, generally in a straight line, taking no advantage of air currents. Partridges, pheasants,

wild ducks, geese, and some birds of passage may be taken as types of this kind.

This class of birds has relatively small wings, and carries about 21 times as much

weight per square foot of surface as soaring birds do.

[ . . . ]

IV. THE ADVANTAGES AND DISADVANTAGES OF VERY NARROW PLANES.

My experiments have demonstrated that relatively narrow aeroplanes lift more

per square foot than very wide ones, but as an aeroplane, now matter how narrow it

may be, must of necessity have some thickness, it is not advantageous to place them

too near together. Suppose that aeroplanes should be made 1

⁄4 in. thick and be superposed 3 inches apart, that is, at a pitch of 3 inches. One-twelfth part of the whole

space through which these planes would have to be driven would be occupied by the

planes themselves, and eleven-twelfths would be air space (Fig. 1). If a group of

planes thus mounted should be driven through the air at the rate of 36 miles an

hour, the air would have to be driven forward at the rate of 3 miles an hour, or else it

would have to be compressed, or spun out, and pass between the spaces at a speed

of 39 miles an hour. As a matter of fact, however, the difference in pressure is so very

small, that practically no atmospheric compression takes place. The air, therefore, is

driven forward at the rate of 3 miles an hour, and this consumes a great deal of

power, in fact, so much that there is a decided disadvantage in using narrow

planes thus arranged.

In regard to the curvature of narrow aeroplanes, I have found that if one only

desires to lift a large load in proportion to the area, the planes may be made very

hollow on the underneath side; but when one considers the lift in terms of screw

thrust, I find it advisable that the planes should be as thin as possible and the

underneath side nearly flat. I have also found that it is a great advantage to
Document 1-6 115

arrange the planes after the manner shown in fig. 2. In this manner, the sum of

all the spaces between the planes is equal to the whole area occupied by the planes;

consequently, the air neither has to be compressed, spun out, or driven forward.

I am therefore by this arrangement able to produce a large lifting effect per

square foot, and, at the same time, to keep the screw thrust within reasonable limits.

A large number of experiments with very narrow aeroplanes have been conducted by Mr. Horatio Phillips at Harrow, in England. . . . Mr. Phillips is of the

opinion that the air in striking the top side of the plane is thrown upward in the

manner shown and a partial vacuum is thereby formed over the central part of
116 Chapter 1: The Achievement of Flight

the plane, and that the lifting effect of planes made in this form is therefore very

much greater than with ordinary narrow planes. I have experimented with these

“sustainers” (as Mr. Phillips calls them) myself, and I find it is quite true that they

lift in some cases as much as 8 lb. per sq. ft., but the lifting effect is not produced

in the exact manner that Mr. Phillips seems to suppose. The air does not glance

off in the manner shown. As the “sustainer” strikes the air, two currents are

formed, one following the exact contour of the top and the other the bottom.

These two currents join and are thrown downward as relates to the “sustainer” at

an angle which is the resultant of the angles at which the two currents meet (Fig. 4).

These “sustainers” may be made to lift when the front edge is lower than the rear

edge because they encounter still air, and leave it with a downward motion.

In my experiments with narrow superposed planes, I have always found that

with strips of thin metal made sharp at both edges and only slightly curved, the

lifting effect, when considered in terms of screw thrust, was always greater than

with any arrangement of the wooden aeroplanes used in Phillips’ experiments. It

would therefore appear that there is no advantage in the peculiar form of “sustainer” employed by this inventor.

If an aeroplane be made perfectly flat on the bottom side and convex on the

top . . . and be mounted in the air so that the bottom-side is exactly horizontal, it pro-
Document 1-6 117

duces a lifting effect no matter in which direction it is run, because as it advances

it encounters stationary air which is divided into two streams. The top stream being

unable to fly off at a tangent when turning over the top curve, flows down the incline

and joins the current which is flowing over the lower horizontal surface. The angle at

which the combined stream of air leaves the plane is the resultant of these two

angles; consequently, as the plane finds the air in a stationary condition and

leaves it with a downward motion, the plane itself must be lifted. It is true that

small and narrow aeroplanes may be made to lift considerably more per square foot

of surface than very large ones, but they do not offer the same safeguard against a

rapid descent to the earth in case of a stoppage or breakdown of the machinery.

With a large aeroplane properly adjusted, a rapid and destructive fall to the earth

is quite impossible.

In the foregoing experiments with narrow aeroplanes, I employed an apparatus

(Fig. 6) [omitted] which enabled me to mount my planes at any angle in a powerful blast of air, and to weigh the exact lifting effect and also the tendency to drift

with the wind. This apparatus also enables me to determine with a great degree

of nicety the best form of an atmospheric condenser to employ.

V. THE EFFICIENCY OF SCREW PROPELLERS.—STEERING, STABILITY, ETC.

Before I commenced my experiments at Baldwyn’s Park, I attempted to

obtain some information in regard to the action of screw propellers working in the

air. I went to Paris and saw the apparatus which the French Government

employed for testing the efficiency of screw propellers, but the propellers were so

very badly made that the experiments were of no value. Upon consulting an

English experimenter who had made a “lifelong study” of the question, he

assured me that I should find the screw propeller very inefficient and very wasteful of power. He said that all screw propellers had a powerful fan-blower action,

drawing in air at the centre and discharging it with great force at the periphery. I

found that no two men were agreed as to the action of screw propellers. All the

data or formulæ available were so confusing and contradictory as to be of no value

whatsoever. Some experimenters were of the opinion that in computing the thrust

of a screw we should only consider the projected area of the blades, and that the

thrust would be equal to a wind blowing against a normal plane of equal area at

a velocity equal to the slip. Others were of the opinion that the whole screw disk

would have to be considered; that is, that the thrust would be equal to a wind

blowing against a normal plane equal to the area of the whole disk at the velocity of the slip. The projected area of the two screw blades of my machine is 94

square feet, and the area of the 2 screw disks is 500 square feet. According to the

first system of reasoning, therefore, the screw thrust of my large machine, when

running at 40 miles an hour with a slip of 18 miles per hour, would have been,

according to the well-known formula, V2 x .005 = P
118 Chapter 1: The Achievement of Flight

182 x .005 x 94 = 152.28 pounds.

If, however, we should have considered the whole screw disk, it would have been—

182 x .005 x 500 = 810 pounds.

However, when the machine was run over the track at this rate, the thrust was

found to be rather more than 2,000 lbs. When the machine was secured to the

track and the screws revolved until the pitch in feet multiplied by the turns per

minute was equal to 68 miles an hour, it was found that the screw thrust was 2,164

lbs. In this case it was of course all slip, and when the screws had been making a

few turns they had established a well-defined air-current, and the power exerted

by the engines was simply to maintain this air-current, and it is interesting to note

that if we compute the projected area of these blades by the foregoing formula,

the thrust would be—

682 x .005 x 94 = 2173.28 pounds,

which is almost exactly the observed screw thrust. From this, it would appear when

the machine is stationary, and all the power is consumed in slip, that only the projected area of the screw blades should be considered. But whenever the machine

is allowed to advance, and to encounter new air, the inertia of which has not been

disturbed, the efficiency increases in geometrical progression. The exact rate for

all speeds I have not yet ascertained. My experiments have, however, shown that

with a speed of 40 miles an hour and a screw slip of 18 miles an hour, a well-made

screw propeller is 13.1 times as efficient as early experimenters had supposed and

attempted to prove by elaborate formulæ.

When I first commenced my experiments with a large machine, I did not know

exactly what form of boiler, gas generator, or burner I should finally adopt; I did

not know the exact size that it would be necessary to make my engines; I did not

know the size, the pitch, or the diameter of the screws which would be the most

advantageous. Neither did I know the form of aeroplane which I should finally

adopt. It was therefore necessary for me to make the foundation or platform of

my machine of such a character that it would allow me to make the modifications

necessary to arrive at the best results. The platform of the machine is therefore

rather larger than is necessary, and I find if I were to design a completely new

machine, that it would be possible to greatly reduce the weight of the framework,

and, what is still more, to greatly reduce the force necessary to drive it through

the air. 

At the present time, the body of my machine is a large platform, about 8 ft.

wide and 40 ft. long. Each side is formed of very strong trusses of steel tubes,

braced in every direction by strong steel wires. The trusses which give stiffness to

this superstructure are all below the platform. In designing a new machine, I

should make the trusses much deeper and at the same time very much lighter,

and, instead of having them below the platform on which the boiler is situated, I
Document 1-6 119

should have them constructed in such a manner as to completely enclose the boiler and the greater part of the machinery. I should make the cross-section of the

framework rectangular, and pointed at each end. I should cover the outside very

carefully with balloon material, giving it a perfectly smooth and even surface

throughout, so that it might be easily driven through the air. 

In regard to the screws, I am at the present time able to mount screws 17 ft.

10 in. in diameter. I find, however, that my machine would be much more efficient

if the screws were 24 feet in diameter, and I believe with such very large screws,

four blades would be much more efficient than two.

My machine may be steered to the right or to the left by running one of the

propellers faster than the other. Very convenient throttle valves have been provided to facilitate this system of steering. An ordinary vertical rudder placed just

after the screws may, however, prove more convenient, if not more efficient.

The machine is provided with fore and aft horizontal rudders, both of which

are connected with the same windlass. If the forward rudder is placed at an angle

considerably greater than that of the main aeroplane, and the rear rudder placed

flat so as not to lift at all (Fig. 7) and the machine run over the track at a high

speed, the front wheels will be lifted from the steel rails, leaving the rear wheels

on the rails. If the rudders are placed in the reverse position so that the front rudder is thrown out of action, and the rear rudder lifts to its full extent (Fig. 8), the

hind wheels will be lifted from the steel rails, leaving only the forward wheels

touching. If both rudders are placed at such an angle that they both lift (Fig. 9),

and the machine is run at a very high velocity, all four of the wheels will be lifted

from the steel rails. This would seem to show that these rudders are efficient as

far as vertical steering is concerned. If the machine should break down in the air

it would be necessary to tilt the rudders in the position shown . . . when it would

fall to the ground without pitching or diving.

In regard to the stability of the machine, the centre of weight is much below

the centre of lifting effect; moreover, the upper wings are set at such an angle that
120 Chapter 1: The Achievement of Flight
Document 1-6 121

whenever the machine tilts to the right or to the left, the lifting effect is increased

on the lower side and diminished on the higher side (Fig. 11). This simple

arrangement makes the machine automatic as far as rolling is concerned. I am of

the opinion that whenever flying machines come into use it will be necessary to

steer them in a vertical direction by means of an automatic steering gear controlled by a gyroscope. It will certainly not be more difficult to manœuvre and

steer such machines than it is to control completely submerged torpedoes.

When the machine is once perfected, it will not require a railway track to

enable it to get the necessary velocity to rise. A short run over a moderately level

field will suffice. As far as landing is concerned, the aerial navigator will touch the

ground while moving forward, and the machine will be brought to a state of rest

by sliding on the ground for a short distance. In this manner very little shock will

result, whereas if the machine is stopped in the air and allowed to fall directly to

the earth without advancing, the shock, although not strong enough to be dangerous to life or limb, might be sufficient to disarrange or injure the machinery.

[ . . . ]

VII. CONCLUSION.

My large machine, which was injured in my late experiments, has now been

repaired and improved, and is quite ready to be used in any other experiments
122 Chapter 1: The Achievement of Flight

which I may wish to make on the limited area which I now have at my disposal.

The railway track on which my experiments have been made is 1,800 feet long

and the land on all sides is thickly studded with large trees. When making experiments about 500 feet of the track is used in getting up the necessary speed and 300

feet is utilized in bringing the machine again to a state of rest. My clear run is

therefore limited to 1,000 feet, and the time which the machine takes to pass over

this length of rail is at the most only a few seconds. It will therefore be seen that

it is not an easy matter to conduct experiments in a satisfactory manner. In addition to these experiments with a large machine, I am also conducting a series of

experiments in a blast of air issuing from a trunk 3 feet square. The air is set in

motion by the action of screw propellers driven by a steam engine of 60 horsepower, and I am able to obtain any atmospheric velocity that I require, from 5 to

90 miles an hour. This apparatus . . . is constructed in such a manner that it

enables me to mount in this current of air any object that I wish to experiment

with. For instance, a bar of wood 3 inches square is mounted in the blast of air so

that one of its sides forms a normal plane perpendicular to the direction of the

blast. The engine is then run until the air is passing through the trunk at a velocity of 50 miles an hour. The tendency of this bar of wood to travel in the direction of the air may then be accurately determined, and this is considered as unity.

A cylinder exactly 3 inches in diameter may then be mounted and tested in the

same manner. The cylinder will of course have less tendency to travel with the air

than the square bar of wood, and whatever this tendency is, will be the coefficient

of a cylinder. I have provided oval, elliptical, and various other shaped objects to

be experimented with, and when the experiments are finished I shall know the

exact coefficient of all shapes that it may be practical to use in the framework of

a flying machine, and also what effect is produced by placing two or more bodies

in close proximity to each other.

In addition to these experiments, I am also able with the same air blast to

ascertain the efficiency of various forms of aeroplanes, superposed or otherwise, and

placed at all angles, the apparatus being provided with a scale beam which not only

enables me to measure the drift, but also to accurately weigh the lifting effect. The

aeroplane, or grouping of aeroplanes, in which the drift will go the greatest number of times into the lift will be considered the most satisfactory for the purpose.

Experiments are also being made in the same air blast with a view of ascertaining

the condensing and lifting power of various forms of tubes, steam in the condition

of exhaust being passed through the tubes while the air is driven between them

at any velocity required. The experiments are being made with pure steam and

also with steam contaminated with oil, with a view of ascertaining to what extent

the efficiency of the condenser is reduced by a film of oil such as may be expected

from exhaust steam. These experiments will enable me to ascertain very exactly
Document 1-6 123

the weight and the efficiency of atmospheric condensers, the amount that their

tubes may be made to lift at various speeds and atmospheric conditions, and will

also enable me to select the form which I find most suitable for the purpose.

In navigating a boat, it is only necessary that one should be able to turn it to the

right or to the left (port or starboard), but with a flying machine it is not only necessary to steer it to the right or left (horizontally), but also in a vertical direction to prevent it from rearing up forward or pitching, and this, if it is accomplished by hand,

will require the constant vigilance of a man at the wheel who can make observations,

think, and act instantly. In order to prevent a too rapid up and down deviation of the

machine I have constructed it of great length, so that the man at the helm will have

more time to think and act. As before stated, however, I am of the opinion that the

steering in a vertical direction should be automatically controlled by a gyroscope,

and I have made an apparatus which consists of a steam piston acting directly

upon the fore and aft rudders, the steam valve being controlled by a gyroscope.

As the rudders are moved by the steam, their movement shuts the steam off in

exactly the same manner that the moving of a rudder shuts off the steam in the

well-known steam-steering apparatus now universally in use on all large steamers.

Now that it is definitely known that it is possible to construct a large machine

which is light enough and at the same time powerful enough to raise its own

weight and that of its engineers into the air, the next question which presents itself

for solution is to ascertain how to steer and control such a machine when actually free from the earth. When it is considered that the machine is of great size and

that it is necessary that it should move through the air at a velocity of at least 35

miles an hour in order to leave the ground, it will be obvious that manœuvring

experiments cannot be conducted in a circumscribed place such as I now have. It

is therefore necessary for me to obtain new and much larger premises where I

shall have a very large and level field at my disposal. It is not an easy matter to

obtain a field of this character in England, and it is almost impossible to find a

suitable place near London. Moreover, experiments of this character, which are of

little value unless conducted on a large scale, are exceedingly expensive, in fact,

too expensive to be conducted by private individuals. Nevertheless, as my experiments have shown most conclusively that flying machines are not only possible

but practicable, I think I am justified in continuing my experiments until a comparatively perfect flying machine has been evolved. When I have obtained possession of a suitable field, I propose to erect a large building which will contain the

machine with all its wings in position. The building which I have at present,

notwithstanding that it cost $15,000, is not large enough for the purpose, as the

wings all have to be taken off before the machine can be housed.

There are so many points that may be improved that I have determined to

build a new machine on a somewhat smaller scale, using about 200 or 250 horse-
124 Chapter 1: The Achievement of Flight

power. I shall make the engines of a longer stroke in proportion to their diameter

so as to get a greater piston speed. I shall construct my screw propellers with 4

long and narrow blades, very sharp and thin, and shall make them large enough

so that the pressure on the projected area of the blades will be about 10 lbs. per

square foot instead of over 20 lbs. as now. This will greatly reduce the waste of

power which is now lost in screw slip. As the present boiler has been found larger than is necessary, mv next boiler will be made lighter and smaller, and instead

carrying a pressure of 320 lbs. to the square inch, I shall only carry 275 lbs. But

the greatest improvement will be made in the framework of the machine, which

will be constructed with a view of enabling everything to be driven through the

air with the least possible resistance. The main aeroplane will be the same form

as now, but placed at an angle of 1 in 113 instead of 1 in 8, and will be used principally for preventing the machine from accidentally falling to the earth. The

principal lifting effect will be derived from a considerable number of relatively

narrow aeroplanes placed on each side of the machine and mounted in such a

position that the air can pass freely between them. The fore and aft rudders will

be the same form as those now employed. The condenser will consist of a large

number of small hollow aeroplanes about 2 inches wide, made of very thin and

light metal and placed immediately behind the screw propellers. They will be

placed at such an angle as to lift about 1,000 pounds in addition to their weight

and the weight of their contents. Instead of mounting my machine as now on 4

wheels, I propose to mount it on 3, the two hind wheels being about 40 feet apart

and the forward wheel placed about 60 feet in front of these. I propose to lay

down a track of 3 rails, the sleepers being embedded in the ground so as to produce a comparatively level surface. This railway track should be oval or circular

in form so that the machine may be heavily weighed to keep it on the track and

be run at a high speed. This will enable me to test the furnace draught, the burner, the steam, the boiler, the engines, the propelling effects of tile screws, and the

efficiency of the condenser while the machine is on the ground.

When all the machinery has been made to run smoothly I shall remove all the

weight except that directly over the front wheel, and shall place a device between

the wheel and the machine that will indicate the lift on the front end of the

machine. I shall then run the machine over the track at a velocity which will just

barely lift the hind wheels off the track, leaving the front wheel on the track. If

the rear end of the machine lifts into the air it will change the angle of the planes

and the lifting effect will be correspondingly diminished. This will prevent rising

too high. Special wheels with a wide face suitable for running on either the rails

or the earth will be provided for the purpose, and when I find that I can keep the

hind wheels in the air and produce a varying lifting effect above and below the

normal weight resting on the front wheel, I shall remove the weight from the for-
Document 1-6 125

ward wheel and attempt free flight by running the machine as near the ground as

possible, making the first attempt by running against the wind, and it will only be

after I find that I can steer my machine and manage it within a few feet of the

earth, ascend and descend again at will, that I shall attempt high flight.

My experiments have certainly demonstrated that a steam engine and boiler

may be made which will generate a horsepower for every six pounds of weight,

and that the whole motor, including the gas generator, the water supply, the condenser, and the pumps may be all made to come inside of 11 lbs. to the horsepower. They also show that well made screw propellers working in the air are fairly

efficient, and that they obtain a sufficient grip upon the air to drive the machine

forward at a high velocity; that very large aeroplanes, if well made and placed at

a proper angle, will lift as much as 2 1⁄2 lbs. per square foot at a velocity not greater

than 40 miles an hour; also that it is possible for a machine to be made so light

and at the same time so powerful that it will lift not only its own weight but a considerable amount besides, with no other energy except that derived from its own

engines. Therefore there can be no question but what a flying machine is now possible without the aid of a balloon in any form.

In order to obtain these results it has been necessary for me to make a great

number of expensive experiments and to carefully study many of the properties

of the air. Both Lord Kelvin and Lord Rayleigh, after witnessing a series of my

experiments, expressed themselves as of the opinion that all the mathematical

formulæ relating to planes driven through the air at an angle would have to be

completely modified. Lord Kelvin himself has written that in some cases my

experiments have proved that the conditions were from 20 to 50 times as favorable to the aerial navigator as had heretofore been shown by accepted formulæ,

and that the whole mathematical question would require revision.

Experiments of this character unless conducted with great care are exceedingly dangerous. No makeshift or imperfect apparatus should be employed, but the

experimenter should have the advantage of the most perfect appliances and

apparatus that modern civilization can afford. The necessary plant for conducting experiments in a proper and safe manner is unfortunately much more expensive than the machine itself. If I find that my experiments require more money

than I have at my disposal, I feel sure that some future experimenter more fortunate than myself will commence where I leave off, and with the advantages of the

knowledge which has been gained by recent experiments will be able to construct

a practical flying machine which cannot fail to be a great advantage to mankind.

The numerous and very expensive experiments, conducted on an unprecedented scale, which have made all this possible, and also brought to light new laws

relating to the atmosphere, cannot fail to be of the greatest value to mankind, and

it is on this basis that I submit the foregoing thesis.
126 Chapter 1: The Achievement of Flight

Document 1-7

B. Baden-Powell (Baden Fletcher Smyth), “Present State 

of Aeronautics,” interview in The Sunday Times [London], 

14 June 1896, reprinted in The Aeronautical Journal

(January 1897): 4–5.

Major Baden Fletcher Smyth Baden-Powell, a career officer in the British

army and brother of the founder of the Boy Scouts (Robert Stephenson Smyth

Baden-Powell, first baron Baden-Powell of Gilwell), joined the Aeronautical Society

of Great Britain in 1880, fourteen years after it was established. Although his

technical abilities were limited, his inventive spirit and enthusiasm for flight were perhaps unmatched. As secretary of the Aeronautical Society (elected in 1897), and

later its president (elected while absent on duty in South Africa), B. Baden-Powell

closely followed aviation developments internationally, corresponding regularly

with Octave Chanute, in America, and many others.

In this document from 1897, Baden-Powell told a reporter (in a 14 June 1896

interview) from the Sunday Times of London what he thought about the “present

state of aeronautics.” In his opinion, though there were many exaggerated reports

of aviation firsts, human flight “will come about, and very soon.” In the interview,

Baden-Powell reported on the work of Langley, Maxim, Lilienthal, as well as that

of fellow Englishman Percy Pilcher, and he also described his own work with mancarrying kites. He was also the first in England to call attention to the work of the

Wright brothers in his presidential address to the Aeronautical Society of Great

Britain in December 1902, one year before the Wright’s historic achievement of

powered flight. By 1904, Baden-Powell was corresponding with the Wrights. He

spent quite a bit of time with Wilbur during the Wright’s tour of France in the fall

of 1908 and published the article “A Trip with Wilbur Wright” in the December

1908 issue of Aeronautics magazine. 

Interestingly, in his 1896 interview Baden-Powell saw the predominant value of

flying machines resting in military applications: “It is, of course, in war that its great

importance will be apparent.” This runs contrary to the peace-bringing theme

emphasized by the Wrights in the early years after their invention of the airplane.

Document 1-7, B. Baden-Powell, “Present State of Aeronautics,” 1896.

The invention of a flying machine, or rather the announcement of a sanguine

inventor who believes he has accomplished this, must be to the editor of a paper

almost as valuable as the appearance, or reported appearance, of a sea serpent.
Document 1-7 127

Again and again we see paragraphs in the newspapers announcing some marvellous

advancement towards the solution of this intricate problem, but as often as not,

or a great deal oftener, the invention proves to be merely a design, or an idea,

formed by one who has but little real knowledge of the subject. During the last

few years, however, several men of undoubted scientific ability and inventive

genius have entered the arena, and have proved, both by figures and by experiment,

that a flying machine is a possibility, and has come within the range of practical

invention. The careful scientist is, however, just the man who does not, as a rule,

announce his device and publish full descriptions of it until he is fully convinced

that he is on the right track. It is, for this reason, rather difficult to get at the truth

as regards the present position of the subject. It will, therefore, be unnecessary for

me to refer to the many vague reports one has seen in the papers, except as

regards those I know something about. Some rumours have latterly come out

about a machine devised by Professor Langley, of the Smithsonian Institute, at

Washington. He is, I know, a most capable man, for he has written a book,

“Aerodynamics,” which, without doubt, is by far the most elaborate scientific study

of the question that has been written. He has for years made the most careful

experiments, and has deduced many facts with reference to the action of the air

on bodies moving through it of the greatest importance to inventors of aerial

machines. He seems now to have made some small machine which is reported to

be a great success, though I imagine it is nothing more than a model. No full

description of it has, I believe, been published, and in all probability the inventor

will not hurry to make common property that which has taken him so many years

of study and experiment to evolve, at any events, until he has progressed sufficiently to be sure of success.

Then there is the great Maxim machine. Here again we have a very capable

and very careful inventor devoting his attention and his money to the subject. The

result has been a truly marvellous machine. Doubtless the inventor himself

expected better results than it has proved capable of supplying, but nevertheless,

though the machine can scarcely be said to have left the earth, yet it has proved

a great success as regards the construction of very large and very light apparatus

provided with immensely powerful engines. No one, before this was constructed,

could have believed in the practicability of making a steam engine of 300 horse

power, and placing it in a flying machine presenting some thousands of square

feet of surface to the air, the whole apparatus only weighing some three tons.

However, the affair was altogether too large and unwieldy. A slight gust of

wind getting under this enormous awning would be apt to upset the whole thing,

and do hundreds of pounds’ worth of damage. Probably if the machine had really

been shot off into midair it would have gone all right, but there was an awkward

uncertainty as to how it might come down! I think myself it ought to have been
128 Chapter 1: The Achievement of Flight

supplied with air bladders, and sent over a cliff out to sea. Then when it fell in

the water it would have floated. Now, however, Mr. Maxim talks of constructing a

much smatter machine on the same lines, and I shall certainly look forward with

the greatest interest for the result, as I believe it will come very near the goal we

are searching for.

This machine, and probably Langley’s as well, is on what is known as the aeroplane principle; that is, a large fixed plane presenting a small angle to the air is

propelled horizontally at a great speed by means of screw propellers, and is forced

upwards by the pressure of the air on its under side. It is really simply a large kite,

which, instead of being held by a string for the wind to act on it, is driven through

the air, and raised much as a kite is when drawn along by its string. This principle has been proved theoretically to give the best results, that is to say, that with

a given amount of power a greater weight can be raised by this system of propelling a plane surface presenting a small upward angle to the horizontal. Lord

Kelvin and others have, however, pointed out that, notwithstanding this, a

machine with vertical screw propellers to lift it straight upwards might have better

practical results, even though more power might be required.

Then a good deal of talk is being made about two other inventors, Lilienthal,

in Germany, and Pilcher, in England. These machines are very similar in principle,

and though of great interest as experimental apparatus, cannot at present be considered as much more than parachutes. They partake of the nature of large wings

attached to the human body, and are, therefore, comparatively well under control,

but are only capable of “flying” if launched from some high place against, the

wind; both inventors however, propose to apply small engines to propel them

through the air, and success depends upon whether they can get sufficiently powerful engines without greatly increasing the size of the apparatus, and if they can

get sufficiently efficient propellers to drive them at the requisite speed.

You ask also about the Italian machines. All I know is that reports have

appeared of the Italian Government being in possession of a number of “air-ships”—

and all I can say is that until I hear more of the details I don’t believe a word of it.

Navigable balloons I look upon as a different subject. We know, of course, that

the French have some, and, as to other nations, my mouth is closed as regards all

I know in this line, but I may say at once that though on certain particular occasions, with favourable, i.e., calm weather, they may prove of the very greatest value

in war, yet they are so dependent on the absence of wind and other circumstances

that I cannot believe they will ever be very much used.

Then as for my own apparatus. Well, that again, is quite another matter. It is

not a flying machine in the ordinary acceptance of the term. It is simply a system

of large kites only for captive use. That is to say, it is held by a rope to the ground,

and is chiefly for use as a lofty observatory for looking over the enemy’s lines, and
Document 1-7 129

watching the country round about. I believe there are also other useful purposes

to which it may be applied, since the length of the tether line is practically unlimited,

but I need not speculate on future possibilities. My present object is to get an

apparatus to serve instead of a captive balloon without necessitating the transport

of cumbersome filling apparatus.

Kite-flying is not so simple a matter as some may suppose. To make an enormous

kite like a toy one would be no easy task. Remember, the tail should be as heavy

as the kite itself, which would, in my case, amount to some 60 lbs. or more. And

then the liability to dive must be done away with, else I am afraid there might be

a difficulty in providing observers. My present apparatus, which is now undergoing

its trials at Aldershot, folds up so compactly that it call be carried by one man. It

is capable of lifting a man to a height of 200 or 300 ft. One thing may be said

about it that, besides the balloon, it is the only means known by which a man has

been absolutely raised to any height in the air. And it is not entirely dependent

on wind, since in calms it may be made to ascend by towing it with horses.

As for the general question of the possibilities of human flight, I for one firmly

believe it will come about, and that very soon. It is, of course, in war that its great

importance will be apparent. And if it be found necessary to have a large, complicated, and costly machine to effect the purpose, doubtless it will be used for little

else. The first nation which can provide a secret flying-machine—and the secret

will probably be more in the smaller details of construction than in the general

principle—will undoubtedly possess an incalculable advantage in war. 
130 Chapter 1: The Achievement of Flight

Document 1-8(a–c)

(a) Samuel P. Langley, “Story of Experiments in Mechanical

Flight,” Aeronautical Annual (1897), reprinted in Researches

and Experiments in Aerial Navigation (Washington, DC:

Government Printing Office, 1908), pp. 169–179.

(b) Samuel P. Langley, excerpts from 

“The New Flying Machine.” McClure’s Magazine 9, 

No. 2 (June 1897): 647–660.

(c) Alexander Graham Bell, letter in McClure’s Magazine 9, 

No. 2, (June 1897): 659; published as “The Aerodromes in

Flight,” Aeronautical Annual (1897), pp. 140–141.

Dr. Samuel P. Langley’s work epitomized the nineteenth century “scale

model” development approach to solving the problems of flight. As a practical

exercise in applied aerodynamics, however, Langley’s experiments were plagued

with failure. Finally, in 1897, he achieved a signal success with the test flights of

his powered model Aerodrome No. 5. The following three documents present the

story of his experiments with flying scale models. The first is a selection from his

1896 interim report, which he referred to as a “narrative account of my work in

aerodromics.” A copy of this article was included in the documents sent to Wilbur

Wright in 1899 by the Smithsonian Institution. 

Regarding this and other reports by Langley, Wright later noted that, “his

accounts of the troubles he had encountered and overcome put us on our guard

and enabled us to entirely avoid some of the worst of them. He painted so vividly

the troubles resulting from excessive lightness that we have been as men vaccinated

against that disease.” 

Langley’s success in 1896 with Aerodrome No. 5 is recounted in an excerpt from

an article he published in 1897 on “The New Flying Machine,” along with the

report written by his good friend and supporter Alexander Graham Bell, who was

present to observe the experiments and took photographs of the model in flight.

Following his success with Aerodrome No. 5 Langley attempted to progress to a

full-scale manned model, his Great Aerodrome. The widely reported failure of this

flying machine in December 1903, mere days in advance of the Wrights success at

Kitty Hawk, led to Langley’s disgrace and public rejection. Langley died within

three years of this final crushing blow, but his few remaining partisans, including Bell,

continued for some time thereafter to tout the potential of Langley’s Aerodrome.
Document 1-8(a–c) 131

Document 1-8(a), Samuel P. Langley, 

“Story of Experiments in Mechanical Flight,” 1897. 

The subject of flight interested me as long ago as I can remember anything,

but it was a communication from Mr. Lancaster, read at the Buffalo meeting of the

American Association for the Advancement of Science, in 1886, which aroused my

then dormant attention to the subject. What he said contained some remarkable

but apparently mainly veracious observations on the soaring bird, and some more

or less paradoxical assertions, which caused his communication to be treated with

less consideration than it might otherwise have deserved. Among the latter was a

statement that a model, somewhat resembling a soaring bird, wholly inert, and

without any internal power, could, nevertheless, under some circumstances,

advance against the wind without falling; which seemed to me then, as it did to

members of the Association, an utter impossibility, but which I have since seen

reason to believe is, within limited conditions, theoretically possible.

I was then engaged in the study of astrophysics at the Observatory in

Allegheny, Pa. The subject of mechanical flight could not be said at that time to

possess any literature, unless it were the publications of the French and English

aeronautical societies, but in these, as in everything then accessible, fact had not

yet always been discriminated from fancy. Outside of these, almost everything was

even less trustworthy; but though, after I had experimentally demonstrated certain facts, anticipations of them were found by others on historical research, and

though we can now distinguish in retrospective examination what would have

been useful to the investigator if he had known it to be true, there was no test of

the kind to apply at the time. I went to work, then, to find out for myself, and in

my own way, what amount of mechanical power was requisite to sustain a given

weight in the air and make it advance at a given speed, for this seemed to be an

inquiry which must necessarily precede any attempt at mechanical flight, which

was the very remote aim of my efforts. 

The work was commenced in the beginning of 1887 by the construction, at

Allegheny, of a turntable of exceptional size, driven by a steam engine, and this

was used during three years in making the “Experiments in Aerodynamics,”

which were published by the Smithsonian Institution under that title in 1891.

Nearly all the conclusions reached were the result of direct experiment in an

investigation which aimed to take nothing on trust. Few of them were then familiar,

though they have since become so, and in this respect knowledge has advanced

so rapidly, that statements which were treated as paradoxical on my first enunciation of them are now admitted truisms.

It has taken me, indeed, but a few years to pass through the period when the

observer hears that his alleged observation was a mistake; the period when he is
132 Chapter 1: The Achievement of Flight

told that if it were true, it would be useless; and the period when he is told that it

is undoubtedly true, but that it has always been known.

May I quote from the introduction to this book what was said in 1891?

“I have now been engaged since the beginning of the year 1887 in experiments

on an extended scale for determining the possibilities of, and the conditions for,

transporting in the air a body whose specific gravity is greater than that of the air,

and I desire to repeat my conviction that the obstacles in its way are not such as

have been thought; that they lie more in such apparently secondary difficulties as

those of guiding the body so that it may move in the direction desired and ascend

or descend with safety, than in what may appear to be primary difficulties, due to

the air itself,” and, I added, that in this field of research I thought that we were,

at that time (only six years since), “in a relatively less advanced condition than the

study of steam was before the time of Newcomen.” It was also stated that the most

important inference from those experiments as a whole was that mechanical flight

was possible with engines we could then build, as one horsepower rightly applied

could sustain over 200 pounds in the air at a horizontal velocity of somewhat over

60 feet a second.

As this statement has been misconstrued, let me point out that it refers to surfaces,

used without guys, or other adjuncts, which would create friction; that the horsepower in question is that actually expended in the thrust, and that it is predicated

only on a rigorously horizontal flight. This implies a large deduction from the

power in the actual machine, where the brake horsepower of the engine, after a

requisite allowance for loss in transmission to the propellers, and for their slip on

the air, will probably be reduced to from one-half to one-quarter of its nominal

amount; where there is great friction from the enforced use of guys and other

adjuncts; but, above all, where there is no way to insure absolutely horizontal

flight in free air. All these things allowed for, however, since it seemed to me possible

to provide an engine which should give a horsepower for something like 10 pounds

of weight, there was still enough to justify the statement that we possessed in the

steam engine, as then constructed or in other heat engines, more than the indispensable power, though it was added that this was not asserting that a system of

supporting surfaces could be securely guided through the air or safely brought to

the ground, and that these and like considerations were of quite another order,

and belonged to some inchoate art which I might provisionally call aerdromics.

These important conclusions were reached before the actual publication of

the volume, and a little later others on the nature of the movements of air, which

were published under the title of “The Internal Work of the Wind” (Smithsonian

Contributions to Knowledge, Volume XXVII, 1893, No. 884). The latter were

founded on experiments independent of the former, and which led to certain theoretical conclusions unverified in practice. Among the most striking, and perhaps
Document 1-8(a–c) 133

paradoxical of these, was that a suitably disposed free body might, under certain

conditions, be sustained in an ordinary wind, and even advance against it without

the expenditure of any energy from within.

The first stage of the investigation was now over, so far as that I had satisfied

myself that mechanical flight was possible with the power we could hope to command, if only the art of directing that power could be acquired. 

The second stage (that of the acquisition of this art) I now decided to take up. It

may not be out of place to recall that at this time, only six years ago, a great many

scientific men treated the whole subject with entire indifference, as unworthy of

attention, or as outside of legitimate research, the proper field for the charlatan, and

one on which it was scarcely prudent for a man with a reputation to lose to enter.

The record of my attempts to acquire the art of flight may commence with the

year 1889, when I procured a stuffed frigate bird, a California condor, and an

albatross, and attempted to move them upon the whirling table at Allegheny. The

experiments were very imperfect and the records are unfortunately lost, but the

important conclusion to which they led was that a stuffed bird could not be made

to soar except at speeds which were unquestionably very much greater than what

served to sustain the living one, and the earliest experiments and all subsequent

ones with actually flying models have shown that thus far we cannot carry nearly

the weights which Nature does to a given sustaining surface without a power much

greater than she employs. At the time these experiments were begun, Pénaud[’s]

ingenious but toy-like model was the only thing which could sustain itself in the

air for even a few seconds, and calculations founded upon its performance sustained

the conclusion that the amount of power required in actual free flight was far

greater than that demanded by the theoretical enunciation. In order to learn

under what conditions the aerodrome should be balanced for horizontal flight, I

constructed over 30 modifications of the rubber-driven model, and spent many

months in endeavoring from these to ascertain the laws of “balancing”; that is, of

stability leading to horizontal flight. Most of these models had two propellers, and

it was extremely difficult to build them light and strong enough. Some of them

had superposed wings; some of them curved and some plane wings; in some the

propellers were side by side; in others one propeller was at the front and the other

at the rear, and so every variety of treatment was employed, but all were at first too

heavy, and only those flew successfully which had from 3 to 4 feet of sustaining

surface to a pound of weight, a proportion which is far greater than Nature employs

in the soaring bird, where in some cases less than half a foot of sustaining surface

is used to a pound. It had been shown in the “Experiments in Aerodynamics” that

the center of pressure on an inclined plane advancing was not at the center of the

figure, but much in front of it, and this knowledge was at first nearly all I possessed in balancing these early aerodromes. Even in the beginning, also, I met
134 Chapter 1: The Achievement of Flight

remarkable difficulty in throwing them into the air, and devised numerous forms

of launching apparatus which were all failures, and it was necessary to keep the

construction on so small a scale that they could be cast from the hand.

The earliest actual flights with these were extremely irregular and brief, lasting

only from three to four seconds. They were made at Allegheny in March, 1891, but

these and all subsequent ones were so erratic and so short that it was possible to learn

very little from them. Pénaud states that he once obtained a flight of 13 seconds. I

never got as much as this, but ordinarily little more than half as much, and came to

the conclusion that in order to learn the art of mechanical flight it was necessary to

have a model which would keep in the air for at any rate a longer period than these,

and move more steadily. Rubber twisted in the way that Pénaud used it will practically give about 300 foot-pounds to a pound of weight, and at least as much must be

allowed for the weight of the frame on which the rubber is strained. Twenty pounds

of rubber and frame, then, would give 3,000 foot-pounds, or 1 horsepower for less

than six seconds. A steam engine having apparatus for condensing its steam, weighing

in all 10 pounds, and carrying 10 pounds of fuel, would possess in this fuel, supposing that but one-tenth of its theoretical capacity is utilized, many thousand times

the power of an equal weight of rubber, or at least 1 horsepower for some hours.

Provided the steam could be condensed and the water reused, then the advantage

of the steam over the spring motor was enormous, even in a model constructed

only for the purpose of study. But the construction of a steam-driven aerodrome

was too formidable a task to be undertaken lightly, and I examined the capacities

of condensed air, carbonic-acid gas, of various applications of electricity, whether

in the primary or storage battery, of hot-water engines, of inertia motors, of the

gas engine, and of still other material. The gas engine promised best of all in theory, but it was not yet developed in a suitable form. The steam engine, as being

an apparently familiar construction, promised best in practice, but in taking it up,

I, to my cost, learned that in the special application to be made of it, little was

really familiar and everything had to be learned by experiment. I had myself no

previous knowledge of steam engineering, nor any assistants other than the very

capable workmen employed. I well remember my difficulties over the first aerodrome (No. 0), when everything, not only the engine, but the boilers which were

to supply it, the furnaces which were to heat it, the propellers which were to advance

it, the hull which was to hold all these—were all things to be originated, in a construction which, as far as I knew, had never yet been undertaken by anyone.

It was necessary to make a beginning, however, and a compound engine was

planned which, when completed, weighed about 4 pounds, and which could develop

rather over a horsepower with 60 pounds of steam, which it was expected could be

furnished by a series of tubular boilers arranged in “bee-hive” form and the whole was

to be contained in a hull about 5 feet in length and 10 inches in diameter. This hull
Document 1-8(a–c) 135

was, as in the construction of a ship, to carry all adjuncts. In front of it projected a steel

rod, or bowsprit, about its own length, and one still longer behind. The engines

rotated two propellers, each about 30 inches in diameter, which were on the end

of long shafts disposed at an acute angle to each other and actuated by a single gear

driven from the engine. A single pair of large wings contained about 50 square feet,

and a smaller one in the rear about half as much, or in all some 75 feet, of sustaining surface, for a weight which it was expected would not exceed 25 pounds.

Although this aerodrome was in every way a disappointment, its failure taught a

great many useful lessons. It had been built on the large scale described, with very little

knowledge of how it was to be launched into the air, but the construction developed

the fact that it was not likely to be launched at all, since there was a constant gain in

weight over the estimate at each step, and when the boilers were completed it was found

that they gave less than one-half the necessary steam, owing chiefly to the inability

to keep up a proper fire. The wings yielded so as to be entirely deformed under a

slight pressure of the air, and it was impossible to make them stronger without making

them heavier, where the weight was already prohibitory. The engines could not

transmit even what feeble power they furnished, without dangerous tremor in the

long shafts, and there were other difficulties. When the whole approached completion, it was found to weigh nearer 50 pounds than 25, to develop only about

one-half the estimated horsepower at the brake, to be radically weak in construction, owing to the yielding of the hull, and to be, in short, clearly a hopeless case.

The first steam-driven aerodrome had, then, proved a failure, and I reverted

during the remainder of the year to simpler plans, among them one of an elementary gasoline engine.

I may mention that I was favored with an invitation from Mr. Maxim to see

his great flying-machine at Bexley, in Kent, where I was greatly impressed with the

engineering skill shown in its construction, but I found the general design incompatible with the conclusions that I had reached by experiments with small models,

particularly as to what seemed to me advisable in the carrying of the center of

gravity as high as was possible with safety.

In 1892 another aerodrome (No. 1), which was to be used with carbonic acid gas,

or with compressed air, was commenced. The weight of this aerodrome was a little

over 4 1

⁄2 pounds, and the area of the supporting surfaces 6 1⁄2 square feet. The engines

developed but a small fraction of a horsepower, and they were able to give a dead

lift of only about one-tenth of the weight of the aerodrome, giving relatively less

power to weight than that obtained in the large aerodrome already condemned.

Toward the close of this year was taken up the more careful study of the position

of the center of gravity with reference to the line of thrust from the propellers,

and to the center of pressure. The center of gravity was carried as high as was consistent with safety, the propellers being placed so high, with reference to the sup-
136 Chapter 1: The Achievement of Flight

porting wings, that the intake of air was partly from above and partly from below

these latter. The lifting power (i.e., the dead lift) of the aerodromes was determined in the shop by a very useful contrivance which I have called the “pendulum,”

which consists of a large pendulum which rests on knife edges, but is prolonged

above the points of support, and counterbalanced so as to present a condition of

indifferent equilibrium. Near the lower end of this pendulum the aerodrome is

suspended, and when power is applied to it, the reaction of the propellers lifts the

pendulum through a certain angle. If the line of thrust passes through the center

of gravity, it will be seen that the sine of this angle will be the fraction of the

weight lifted, and thus the dead-lift power of the engines becomes known. Another

aerodrome was built, but both, however constructed, were shown by this pendulum

test to have insufficient power, and the year closed with disappointment.

Aerodrome No. 3 was of stronger and better construction, and the propellers,

which before this had been mounted on shafts inclined to each other in a V-Iike

form, were replaced by parallel ones. Boilers of the Serpolet type (that is, composed

of tubes of nearly capillary section) were experimented with at great cost of labor

and no results; and they were replaced with coil boilers. For these I introduced, in

April, 1893, a modification of the ælopile blast, which enormously increased the

heat-giving power of the fuel (which was then still alcohol), and with this blast for

the first time the boilers began to give steam enough for the engines. It had been

very difficult to introduce force pumps which would work effectively on the small

scale involved, and after many attempts to dispense with their use by other

devices, the acquisition of a sufficiently strong pump was found to be necessary in

spite of its weight, but was only secured after long experiment. It may be added

that all the aerodromes from the very nature of their construction were wasteful

of heat, the industrial efficiency little exceeding half of 1 per cent, or from one-tenth

to one-twentieth that of a stationary engine constructed under favorable conditions.

This last aerodrome lifted nearly 30 per cent of its weight upon the pendulum, which

implied that it could lift much more than its weight when running on a horizontal

track, and its engines were capable of running its 50-centimeter propellers at

something over 700 turns per minute. There was, however, so much that was

unsatisfactory about it, that it was deemed best to proceed to another construction

before an actual trial was made in the field, and a new aerodrome, designated as No. 4,

was begun. This last was an attempt, guided by the weary experience of preceding

failures, to construct one whose engines should run at a much higher pressure

than heretofore, and be much more economical in weight. The experiments with

the Serpolet boilers having been discontinued, the boiler was made with a continuous helix of copper tubing, which, as first employed, was about three milli-metres

internal diameter; and it may be here observed that a great deal of time was subsequently lost in attempts to construct a more advantageous form of boiler for the
Document 1-8(a–c) 137

actual purposes than this simple one, which, with a larger coil tube, eventually proved

to be the best; so that later constructions have gone back to this earlier type. A

great deal of time was lost in these experiments from my own unfamiliarity with

steam engineering, but it may also be said that there was little help either from

books or from counsel, for everything was here sui generis, and had to be worked

out from the beginning. In the construction which had been reached by the middle

of the third year of experiment, and which has not been greatly differed from since,

the boiler was composed of a coil of copper in the shape of a hollow helix,

through the center of which the blast from the ælopile was driven, the steam and

water passing into a vessel I called the “separator,” whence the steam was led into

the engines at a pressure of from 70 to 100 pounds (a pressure which has since

been considerably exceeded).

From the very commencement of this long investigation the great difficulty

was in keeping down the weight, for any of the aerodromes could probably have

flown had they been built light enough, and in every case before the construction

was completed the weight had so increased beyond the estimate, that the aerodrome

was too heavy to fly, and nothing but the most persistent resolution kept me in

continuing attempts to reduce it after further reduction seemed impossible.

Toward the close of the year (1893) I had, however, finally obtained an aerodrome

with mechanical power, as it seemed to me, to fly, and I procured, after much

thought as to where this flight should take place, a small house boat, to be moored

somewhere in the Potomac; but the vicinity of Washington was out of the question,

and no desirable place was found nearer than 30 miles below the city. It was

because it was known that the aerodrome might have to be set off in the face of a

wind, which might blow in any direction, and because it evidently was at first

desirable that it should light in the water rather than on the land, that the house

boat was selected as the place for the launch. The aerodrome (No. 4) weighed

between 9 and 10 pounds, and lifted 40 per cent of this on the pendulum with 60

pounds of steam pressure, a much more considerable amount than was theoretically necessary for horizontal flight. And now the construction of a launching apparatus, dismissed for some years, was resumed. Nearly every form seemed to have been

experimented with unsuccessfully in the smaller aerodromes. Most of the difficulties were

connected with the fact that it is necessary for an aerodrome, as it is for a soaring bird,

to have a certain considerable initial velocity before it can advantageously use its

own mechanism for flight, and the difficulties of imparting this initial velocity

with safety are surprisingly great, and in the open air are beyond all anticipation.

Here, then, commences another long story of delay and disappointment in

these efforts to obtain a successful launch. To convey to the reader an idea of its

difficulties, a few extracts from the diary of the period are given. (It will be

remembered that each attempt involved a journey of thirty miles each way.)
138 Chapter 1: The Achievement of Flight

November 18, 1893. Having gone down to the house boat, preparatory to the

first launch, in which the aerodrome was to be cast from a springing piece

beneath, it was found impossible to hold it in place on this before launching without its being prematurely torn from its support, although there was no wind

except a moderate breeze; and the party returned after a day’s fruitless effort.

Two days later a relative calm occurred in the afternoon of a second visit,

when the aerodrome was mounted again, but, though the wind was almost imperceptible, it was sufficient to wrench it about so that at first nothing could be done,

and when steam was gotten up the burning alcohol blew about so as to seriously

injure the inflammable parts. Finally, the engines being under full steam, the

launch was attempted, but, owing to the difficulties alluded to and to a failure in

the construction of the launching piece, the aerodrome was thrown down upon

the boat, fortunately with little damage.

Whatever form of launch was used, it became evident at this time that the

aerodrome must at any rate be firmly held up to the very instant of release, and

a device was arranged for clamping it to the launching apparatus.

On November 24 another attempt was made to launch, which was rendered

impossible by a very moderate wind indeed.

On November 27 a new apparatus was arranged, to merely drop the aerodrome

over the water, with the hope that it would get up sufficient speed before reaching

the surface to soar, but it was found that a very gentle intermittent breeze (probably

not more than 3 or 4 miles an hour) was sufficient to make it impossible even to

prepare to drop the aerodrome toward the water with safety. 

It is difficult to give an idea in few words of the nature of the trouble, but unless

one stands with the machine in the open air he can form no conception of what the

difficulties, are which are peculiar to practice in the open, and which do not present

themselves to the constructor in the shop, nor probably to the mind of the reader.

December 1, another failure; December 7, another; December 11, another;

December 20, another; December 21, another. These do not all involve a separate

journey, but five separate trips were made of a round distance of 60 miles each

before the close of the season. It may be remembered that these attempts were in

a site far from the conveniences of the workshop and under circumstances which

took up a great deal of time, for some hours were spent on mounting the aerodrome

on each occasion, and the year closed without a single cast of it into the air. It was

not known how it would have behaved there, for there had not been a launch

even in nine trials, each one representing an amount of trouble and difficulty

which this narrative gives no adequate idea of.

I pass over a long period of subsequent baffled effort, with the statement that

numerous devices for launching were tried in vain and that nearly a year passed

before one was effected.
Document 1-8(a–c) 139

Six trips and trials were made in the first six months of 1894 without securing

a launch. On the 24th of October a new launching piece was tried for the first

time, which embodied all the requisites whose necessity was taught by previous

experience, and, saving occasional accidents, the launching was from this time

forward accomplished with comparatively little difficulty.

The aerodromes were now for the first time put fairly in the air, and a new

class of difficulties arose, due to a cause which was at first obscure—for two successive launches of the same aerodrome, under conditions as near alike as possible,

would be followed by entirely different results. For example, in the first case it

might be found rushing, not falling, forward and downward into the water under

the impulse of its own engines; in the second case, with every condition from

observation apparently the same, it might be found soaring upward until its wings

made an angle of 60 degrees with the horizon, and, unable to sustain itself at such

a slope, sliding backward into the water.

After much embarrassment the trouble was discovered to be due to the fact

that the wings, though originally set at precisely the same angle in the two cases,

were irregularly deflected by the upward pressure of the air, so that they no longer

had the form which they appeared to possess but a moment before they were

upborne by it, and so that a very minute difference, too small to be certainly

noted, exaggerated by this pressure, might cause the wind of advance to strike either

below or above the wing and to produce the salient difference alluded to. When

this was noticed all aerodromes were inverted, and sand was dredged uniformly

over the wings until its weight represented that of the machine. The flexure of the

wings under these circumstances must be nearly that in free air, and it was found

to distort them beyond all anticipation. Here commences another series of trials in

which the wings were strengthened in various ways, but in none of which, without

incurring a prohibitive weight, was it possible to make them strong enough.

Various methods of guying them were tried, and they were rebuilt on different

designs—a slow and expensive process. Finally, it may be said, in anticipation (and

largely through the skill of Mr. Reed, the foreman of the work), the wings were

rendered strong enough without excessive weight, but a year or more passed in

these and other experiments.

In the latter part of 1894 two steel aerodromes had already been built, which

sustained from 40 to 50 per cent of their dead lift weight on the pendulum, and

each of which was apparently supplied with much more than sufficient power for

horizontal flight (the engine and all the moving parts furnishing over one horsepower at the brake weighed in one of these but 26 ounces); but it may be remarked

that the boilers and engines in lifting this per cent of the weight did so only at the

best performance in the shop, and that nothing like this could be counted upon

for regular performance in the open. Every experiment with the launch, when the
140 Chapter 1: The Achievement of Flight

aerodrome descended into the water, not gently, but impelled by the misdirected

power of its own engines, resulted at this stage in severe strains and local injury,

so that repairing, which was almost rebuilding, constantly went on, a hard but

necessary condition attendant on the necessity of trial in the free air. It was gradually found that it was indispensable to make the frame stronger than had hitherto

been done, though the absolute limit of strength consistent with weight seemed

to have been already reached, and the year 1895 was chiefly devoted to the labor

on the wings and what seemed at first the hopeless task of improving the construction

so that it might be stronger without additional weight, when every gram of weight

had already been scrupulously economized. With this went on attempts to carry

the effective power of the burners, boilers, and engines further, and modification

of the internal arrangement and a general disposition of the parts such that the

wings could be placed further forward or backward at pleasure, to more readily

meet the conditions necessary for bringing the center of gravity under the center

of pressure. So little had even now been learned about the system of balancing in

the open air, that at this late day recourse was again had to rubber models, of a

different character, however, from those previously used; for in the latter the rubber

was strained, not twisted. These experiments took up an inordinate time, though

the flight obtained from the models thus made was somewhat longer and much

steadier than that obtained with the Pénaud form, and from them a good deal of

valuable information was gained as to the number and position of the wings and

as to the effectiveness of different forms and dispositions of them. By the middle

of the year a launch took place with a brief flight, where the aerodrome shot down

into the water after a little over 50 yards. It was immediately followed by one in

which the same aerodrome rose at a considerable incline and fell backward with

scarcely any advance after sustaining itself rather less than ten seconds, and these

and subsequent attempts showed that the problem of disposing of the wings so

that they would not yield and of obtaining a proper “balance” was not yet solved.

Briefly it may be said that the year 1895 gave small results for the labor with which it

was filled, and that at its close the outlook for further substantial improvement

seemed to be almost hopeless, but it was at this time that final success was drawing

near. Shortly after its close I became convinced that substantial rigidity had been

secured for the wings; that the frame had been made stronger without prohibitive

weight, and that a degree of accuracy in the balance had been obtained which

had not been hoped for. Still there had been such a long succession of disasters

and accidents in the launching that hope was low when success finally came.

I have not spoken here of the aid which I received from others, and particularly

from Dr. Carl Barus and Mr. J. E. Watkins, who have been at different times associated

with me in the work. Mr. R. L. Reed’s mechanical skill has helped me everywhere, and

the lightness and efficiency of the engines are in a large part due to Mr. L. C. Maltby.
Document 1-8(a–c) 141

Document 1-8(b), Samuel P. Langley, excerpts 

from “The New Flying Machine,” 1897.

Has the reader had enough of this tale of disaster? If so, he may be spared

the account of what went the same way. Launch after launch was successively

made. The wings were finally, after infinite patience and labor, made at once light

enough and strong enough to do the work, and now in the long struggle the way

had been fought up to the face of the final difficulty, in which nearly a year more

passed, for the all-important difficulty of balancing the aerodrome was now

reached, where it could be discriminated from other preliminary ones, which

have been alluded to, and which at first obscured it. If the reader will look at the

hawk or any soaring bird, he will see that as it sails through the air without flapping the wing, there are hardly two consecutive seconds of its flight in which it is

not swaying a little from side to side, lifting one wing or the other, or turning in

a way that suggests an acrobat on a tight-rope, only that the bird uses its widely

outstretched wings in place of the pole.

There is something, then, which is difficult even for the bird, in this act of

balancing. In fact, he is sailing so close to the wind in order to fly at all, that if he

dips his head but the least he will catch the wind on the top of his wing and fall,

as I have seen gulls do, when they have literally tumbled toward the water before

they could recover themselves.

Beside this, there must be some provision for guarding against the incessant,

irregular currents of the wind, for the wind as a whole—and this is a point of

prime importance—is not a thing moving along all-of-a-piece, like water in the

Gulf Stream. Far from it. The wind, when we come to study it, as we have to do

here, is found to be made of innumerable currents and counter-currents which

exist altogether and simultaneously in the gentlest breeze, which is in reality

going fifty ways at once, although, as a whole, it may come from the east or the

west; and if we could see it, it would be something like seeing the rapids below

Niagara, where there is an infinite variety of motion in the parts, although there

is a common movement of the stream as a whole.

All this has to be provided for in our mechanical bird, which has neither

intelligence nor instinct, without which, although there be all the power of the

engines requisite, all the rigidity of wing, all the requisite initial velocity, it still

cannot fly. This is what is meant by balancing, or the disposal of the parts, so that

the airship will have a position of equilibrium into which it tends to fall when it

is disturbed, and which will enable it to move of its own volition, as it were, in a

horizontal course.

Now the reader may be prepared to look at the apparatus which finally has flown.

(See diagram above.) [Diagram on p. 143] In the completed form we see two pairs of
142 Chapter 1: The Achievement of Flight

wings, each slightly curved, each attached to a long steel rod which supports them

both, and from which depends the body of the machine, in which are the boilers, the

engines, the machinery, and the propeller wheels, these latter being not in the

position of those of an ocean steamer, but more nearly amidships. They are made

sometimes of wood, sometimes of steel and canvas, and are between three and

four feet in diameter.

The hull itself is formed of steel tubing; the front portion is closed by a

sheathing of metal which hides from view the fire-grate and apparatus for heating,

but allows us to see a little of the coils of the boiler and all of the relatively large

smokestack in which it ends. The conical vessel in front is an empty float, whose

use is to keep the whole from sinking if it should fall in the water.

This boiler supplies steam for an engine of between one and one and one-half

horsepower, and, with its fire-grate, weighs a little over five pounds. This weight

is exclusive of that of the engine, which weighs, with all its moving parts, but twentysix ounces. Its duty is to drive the propeller wheels, which it does at rates varying

from 800 to 1,200, or even more, turns a minute, the highest number being

reached when the whole is speeding freely ahead.

The rudder, it will be noticed, is of a shape very unlike that of a ship, for it is

adapted both for vertical and horizontal steering. It is impossible within the limits

of such an article as this, however, to give an intelligible account of the manner in

which it performs its automatic function. Sufficient it is to say that it does perform it.

The width of the wings from tip to tip is between twelve and thirteen feet, and

the length of the whole about sixteen feet. The weight is nearly thirty pounds, of

which about one-fourth is contained in the machinery. The engine and boilers are

constructed with an almost single eye to economy of weight, not of force, and are

very wasteful of steam, of which they spend their own weight in five minutes. This

steam might all be recondensed and the water re-used by proper condensing

apparatus, but this cannot be easily introduced in so small a scale of construction.

With it the time of flight might be hours instead of minutes, but without it the

flight (of the present aërodrome) is limited to about five minutes, though in that

time, as will be seen presently, it can go some miles; but owing to the danger of

its leaving the surface of the water for that of the land, and wrecking itself on

shore, the time of flight is limited designedly to less than two minutes.

I have spared the reader an account of numberless delays, from continuous

accidents and from failures in attempted flights, which prevented a single entirely

satisfactory one during nearly three years after a machine with power to fly had

been attained. It is true that the aërodrome maintained itself in the air at many

times, but some disaster had so often intervened to prevent a complete flight that

the most persistent hope must at some time have yielded. On the 6th of May of last

year I had journeyed, perhaps for the twentieth time, to the distant river station,
Document 1-8(a–c) 143

and recommenced the weary routine of another launch, with very moderate

expectation indeed; and when, on that, to me, memorable afternoon the signal

was given and the aërodrome sprang into the air, I watched it from the shore with

hardly a hope that the long series of accidents had come to a close. And yet it had,

and for the first time the aërodrome swept continuously through the air like a living

thing, and as second after second passed on the face of the stop-watch, until a

minute had gone by, and it still flew on, and as I heard the cheering of the few

spectators, I felt that something had been accomplished at last, for never in any part

of the world, or in any period, had any machine of man’s construction sustained

itself in the air before for even half of this brief time. Still the aërodrome went on

in a rising course until, at the end of a minute and a half (for which time only it

was provided with fuel and water), it had accomplished a little over half a mile,

and now it settled rather than fell into the river with a gentle descent. It was

immediately taken out and flown again with equal success, nor was there anything to

indicate that it might not have flown indefinitely except for the limit put upon it. . . .

On November 28th I witnessed, with another aërodrome of somewhat similar

construction, a rather longer flight, in which it traversed about three-quarters of

a mile, and descended with equal safety. In this the speed was greater, or about

thirty miles an hour. . . . We may live to see airships a common sight, but habit
144 Chapter 1: The Achievement of Flight

has not dulled the edge of wonder, and I wish that the reader could have witnessed the actual spectacle. “It looked like a miracle,” said one who saw it, and

the photograph, though taken from the original conveys but imperfectly the

impression given by the flight itself.

And now, it may be asked, what has been done? This has been done: a “flyingmachine,” so long a type for ridicule, has really flown; it has demonstrated its

practicability in the only satisfactory way—by actually flying, and by doing this

again and again, under conditions which leave no doubt.

There is no room here to enter on the consideration of the construction of

larger machines, or to offer the reasons for believing that they may be built to

remain for days in the air, or to travel at speeds higher than any with which we

are familiar; neither is there room to enter on a consideration of their commercial

value, or of those applications which will probably first come in the arts of war

rather than those of peace; but we may at least see that these may be such as to

change the whole conditions of warfare, when each of two opposing hosts will

have its every movement known to the other, when no lines of fortification will

keep out the foe, and when the difficulties of defending a country against an

attacking enemy in the air will be such that we may hope that this will hasten

rather than retard the coming of the day when war shall cease.

I have thus far had only a purely scientific interest in the results of these

labors. Perhaps if it could have been foreseen at the outset how much labor there

was to be, how much of life would be given to it, and how much care, I might have
Document 1-8(a–c) 145

hesitated to enter upon it at all. And now reward must be looked for, if reward

there be, in the knowledge that l have done the best I could in a difficult task, with

results which it may be hoped will be useful to others. I have brought to a close

the portion of the work which seemed to be specially mine—the demonstration of

the practicability of mechanical flight—and for the next stage, which is the commercial and practical development of the idea, it is probable that the world may

look to others. The world, indeed, will be supine if it do not realize that a new

possibility has come to it, and that the great universal highway overhead is now

soon to be opened.

Document 1-8(c), Alexander Graham Bell, “The Aerodromes in Flight,” 1897.

Through the courtesy of Dr. S. P. Langley, Secretary of the Smithsonian

Institution, I have had, on various occasions, the privilege of witnessing his experiments with aerodromes, and especially the remarkable success attained by him in

experiments made upon the Potomac river on Wednesday, May 6, 1896, which led

me to urge him to make public some of these results.

I had the pleasure of witnessing the successful flight of some of these aerodromes

more than a year ago, but Dr. Langley’s reluctance to make the results public at

that time prevented me from asking him, as I have done since, to let me give an

account of what I saw.

On the date named two ascensions were made by the aerodrome, or so-called

“flying-machine,” which I will not describe here further than to say that it

appeared to me to be built almost entirely of metal, and driven by a steam-engine

which I have understood was carrying fuel and a water supply for a very brief period, and which was of extraordinary lightness.

The absolute weight of the aerodrome, including that of the engine and all

appurtenances, was, as I was told, about 25 pounds, and the distance from tip to

tip of the supporting surfaces was, as I observed, about 12 or 14 feet. The method

of propulsion was by aerial screw-propellers, and there was no gas or other aid for

lifting it in the air except its own internal energy.

On the occasion referred to, the aerodrome, at a given signal, started from a

platform about 20 feet above the water, and rose at first directly in the face of the wind,

moving at all times with remarkable steadiness, and subsequently swinging

around in large curves of, perhaps, a hundred yards in diameter, and continually

ascending until its steam was exhausted, when, at a lapse of about a minute and a

half, and at a height which I judged to be between 80 and 100 feet in the air, the

wheels ceased turning, and the machine, deprived of the aid of its propellers, to

my surprise did not fall, but settled down so softly and gently that it touched the

water without the least shock, and was in fact immediately ready for another trial.
146 Chapter 1: The Achievement of Flight

In the second trial, which followed directly, it repeated in nearly every respect

the actions of the first, except that the direction of its course was different. It

ascended again in the face of the wind, afterwards moving steadily and continually

in large curves accompanied with a rising motion and a lateral advance. Its motion

was, in fact, so steady, that I think a glass of water on its surface would have

remained unspilled. When the steam gave out again, it repeated for a second time

the experience of the first trial when the steam had ceased, and settled gently and

easily down. What height it reached at this trial I cannot say, as I was not so favorably

placed as in the first; but I had occasion to notice that this time its course took it

over a wooded promontory, and I was relieved of some apprehension in seeing

that it was already so high as to pass the tree-tops by 20 or 30 feet. It reached the

water 1 minute and 31 seconds from the time it started, at a measured distance

of over 900 feet from the point at which it rose.

This, however, was by no means the length of its flight. I estimated from the

diameter of the curve described, from the number of turns of the propellers as

given by the automatic counter, after due allowance for slip, and from other measures,

that the actual length of flight on each occasion was slightly over 3,000 feet. It is

at least safe to say that each exceeded half an English mile.

From the time and distance it will be noticed that the velocity was between 20 and

25 miles an hour, in a course which was taking it constantly “up hill.” I may add

that on a previous occasion I have seen a far higher velocity attained by the same

aerodrome when its course was horizontal.

I have no desire to enter into detail further than I have done, but I cannot but add

that it seems to me that no one who was present on this interesting occasion could have

failed to recognize that the practicability of mechanical flight had been demonstrated.

ALEXANDER GRAHAM BELL.
Document 1-9(a–d) 147

Document 1-9(a–d)

(a) Octave Chanute, “Conditions of Success in the Design 

of Flying Machines,” (1898) Bulletin No. XXIII, appeared 

in American Magazine of Aeronautics 1 (July 1907).

(b) Augustus M. Herring, “A Solution to the Problem of 

the Century,” The Aeronautical Annual 3 (1897): 54–75.

(c) Octave Chanute, “Experiments in Flying: An Account 

of the Author’s Own Inventions and Adventures,” 

McClure’s Magazine 15 (June 1900): 127–133.

(d) Octave Chanute, excerpt from “Aerial Navigation,” 

Cassier’s Magazine 20 (May 1901): 111–123.

Octave Chanute was the central figure in the exchange of aeronautical information worldwide at the end of the nineteenth century, and, more than anyone

else, he brought the various pioneering researchers, experimenters, promoters,

and inventors together into a trans-Atlantic community of aviation enthusiasts.

He corresponded extensively and wrote widely in his efforts to advance the state

of aeronautics. 

Reflecting some of Chanute’s own experimental work to perfect a flying

machine, the documents presented here include his “Experiments in Flying”

from the June 1900 issue of McClure’s Magazine, and selections from Chanute’s

report “Aerial Navigation: Balloons and Flying Machines from an Engineering

Standpoint.” This latter article was printed in the May 1901 issue of Cassier’s

Magazine; Chanute read a revised and updated version with the same title before

the American Association for the Advancement of Science on 30 December 1903.

The Smithsonian Institution published this paper in its Annual Report of 1904.

Chanute’s associate, Augustus Moore Herring is, without doubt, one of the

more enigmatic actors in the drama associated with the invention of the airplane.

Besides serving as pilot for Chanute’s experimental glider flights in 1896, the

young Herring made important contributions to Chanute’s Katydid glider design.

Notably this involved Herring’s idea for a moveable—or “regulating”—tail that

reacted positively to gusts.

After Herring parted company with Chanute and then spent the summer gliding at the Indiana Dunes in 1896, he continued his own aeronautical experiments
148 Chapter 1: The Achievement of Flight

in southern Michigan. On 11 October 1898, Herring made a powered hop in a

machine of his own design. This took place at Silver Beach on Lake Michigan,

near the town of St. Joseph. On October 27, the Benton Harbor News reported on

the event: “During the flight, which lasted some 8 or 10 seconds, Prof. Herring’s

feet seemed almost to graze the ground while the machine skimmed along on a

level path over the beach. The landing was characterized by a slight turning to

the left and slowing of the engine, when the machine and operator came as gently to rest on the sand as a bird instinct with life.’’ Matthias Arnot, Herring’s financial backer, was present that day on Silver Beach, and he carried a camera.

Unfortunately, Arnot was allegedly so surprised by what he saw that he did not

take a picture until Herring was in the process of landing. The resulting photo

showed the propeller of Herring’s airplane revolving but the skids of his machine

were not airborne but plowing up the sand, clearly in contact with the ground.

Even if Herring’s eighty-eight-pound machine of 1898 did get slightly airborne, it lacked a control system and could only be controlled by the pilot shifting his weight. John Meiler, Herring’s great-grandson, who has researched his

ancestor’s aeronautical career, concedes that the 1898 machine lacked such a system, but he claims that his great-grandfather had equipped a different flying

machine with controls as early as 1894. “He realized the potential need for an

auxiliary kind of control,” Meiler has stated. “But he considered [his 1898 aircraft] an experimental flying machine,” one that represented “just one more step

in a lifetime of work,’’ not its definitive culmination.

To this day, there are Herring family members and others in the St. Joseph area

who believe that Augustus Herring made a powered flight in an airplane before the

Wrights and that he deserves far greater recognition. Unfortunately for his reputation,

there will always be the Arnot photograph as well as a negative report from his former

associate Octave Chanute. After his “successful experiment” at Silver Beach on 11

October, Herring invited Chanute to travel to St. Joseph to witness his next flight

attempt, on 16 October. Chanute came, but the air-compressed engine meant to

drive the airplane failed to cooperate. The next day, when Herring damaged his

plane trying to get it airborne, Chanute left town, thinking Herring a fraud. If he

had waited a few more days, his opinion might have changed. According to eyewitness reports, Herring flew his machine successfully on 22 October 1898. Sixtythree years after the event, in 1961, a Mr. Sam Lessing, a hot dog vender at the

time in 1898, told the St. Joseph Herald-Press that he had been among the witnesses to the event: “I saw it. . . . It couldn’t turn, just flew straight ahead.”

In his book A Dream of Wings: Americans and the Airplane (1981), historian Tom D.

Crouch reviews the fate of Herring’s aeronautical career: “Augustus Moore

Herring, badly shaken by the news of the Wright success, was unable to believe

that these two newcomers to the field had so quickly solved those problems he
Document 1-9(a–d) 149

had been unable to overcome. In 1908 he was a competitor with the Wrights for

the first U.S. Army airplane contract, but withdrew his bid without producing a

finished machine. The following year he entered a short-lived partnership with

Glenn H. Curtiss that ended in a long-running lawsuit with Curtiss and an out-of-court

settlement of $500,000 to Herring’s heirs. He died in 1926” (p. 307). 

Document 1-9(a), Octave Chanute, 

“Conditions of Success in the Design of Flying Machines,” 1898. 

After many centuries of failure, it is believed that we are at last within measurable

distance of success in Aerial Navigation; that there will be two solutions; one with

a dirigible balloon, which will chiefly be used in war, and the other with dynamic,

bird-like machines which will possess so much greater speed and usefulness that

they should preferably engage the attention of searchers.

I have, of late years, experimented with six full-sized gliding machines carrying a

man, comprising three different types, and having reached some definite opinions

as to the conditions of eventual success with power driven machines, it is ventured

to state them briefly for the benefit of other experimenters; for final success will

probably come through a process of evolution, and the last successful man will need

to add but little to the progress made by his predecessors.

It is true that the most important component of the future flying machine will

be the very light motor. It is the lack of this which has hitherto forbidden dynamic

flight and restricted dirigible balloons to inefficient speeds, but it is also true that

dynamic flight is impossible unless the stability is adequate. The progress made

in light motors within the last ten years has been very great; Maxim, Langley, and

Hargrave have produced steam engines weighing but about 5 kilogrammes to the

horsepower, and hundreds of ingenious men are now improving the gas engine

so rapidly that there is good hope that we shall soon be in possession of a prime

mover which shall approximate in lightness the motor muscles of birds, which are

believed to weigh but 3 to 9 kilogrammes per horsepower developed.

But even with a very light motor, success cannot be attained until we have

thoroughly mastered the problem of equilibrium in the air. This fluid is so evasive, the wind so constantly puts it into irregular motion, that it imposes great difficulties even upon a bird, endowed as he is both with an exquisite organization,

with life-instinct and with hereditary skill. It is to this one problem of equilibrium

that I have devoted all my attention, in the belief that an inanimate artificial

machine must be endowed with automatic stability in the air, and that experiments indicate that this can be achieved.

The wind is constantly in turmoil; it strikes the apparatus at different points

and angles, and this changes the position of the center of pressure, thus compro-
150 Chapter 1: The Achievement of Flight

mising the equilibrium. To re-establish the latter requires either that the center of

gravity, (or weight) shall be shifted to correspond, or that the supporting surfaces

themselves shall be shifted, thus bringing back the center of pressure over the

center of gravity. Birds employ both methods; they shift the weight of parts of

their bodies, or they shift either the position or angle of their wings. It is believed

that only the shifting of the wings is open for use for an artificial apparatus.

General Conditions.

It is inferred, therefore, that inventors who begin by working upon an artificial

motor, and who endeavor to evolve a complete flying machine at once, are beginning

at the wrong end, and are leaving behind them two very important prerequisites.

1st. That the apparatus shall possess automatic stability and safety under all

circumstances.

2nd. That the apparatus shall be so light and small as to be easily controlled

in the wind by the personal strength of the operator.

The general stability in the line of flight, the steering, can be obtained by a

rudder, but the automatic equilibrium must be secured in two directions; first

transversely to the apparatus, and secondly fore and aft. Very good results have

been automatically obtained to the transverse stability by imitating the attitude of

the soaring birds, the underlying principle of which consists in a slight dihedral

angle of the wings with each other, either upward or downward, but the very best

application of this principle is not yet evolved, and it requires more experimenting.

Experimenters have found but little difficulty in securing stability in this transverse

direction, but it must be worked out thoroughly.

The longitudinal equilibrium is, however, the most precarious and important.

I have tested three methods of securing it automatically.

First, by setting the tail at a slight upward angle with the supporting surfaces,

so as to change the angle of incidence of the latter through the action of the “relative

wind” on the upper or lower surface of the tail. This is known as the “Penaud”

tail; it is susceptible to great improvement in details of construction, as has been

abundantly proved, but it is not yet certain that it will counteract all movements

of the center of gravity in meeting sudden wind gusts.

Second, by pivoting the wings at their roots, so that they may swing backward

and forward horizontally, thus bringing back automatically the center of pressure

over the center of gravity, whenever a change occurs in the “relative wind.” The

so-called “multiple-wing” gliding machine was of this type, and it reduced the

movement of the aviator required to meet wind gusts to about 25 millimeters. It

cannot, however, be said its construction is perfected.

Third, by hinging vertically the supporting surfaces to the mainframe of the

apparatus, so that these surfaces shall change their angle of incidence automatically
Document 1-9(a–d) 151

when required. This last method has only been tested in models, other engagements having prevented experiments this year (1898). The other two methods

have been applied to full-sized machines carrying a man. They have given such

satisfactory results that not the slightest accident has occurred in two years of

experimenting, but their adjustment has not yet reached the consummation originally aimed at; i.e., that the aviator on the gliding machine shall not need to

move at all, and that the apparatus shall automatically take care of itself under all

circumstances except in landing.

I shall be glad to furnish more minute descriptions to those who may want to

repeat these experiments, or to apply the principles to machines of their own.

The stability of an apparatus is the very first thing to work out before it is attempted

to apply an artificial motor. This cannot be too strongly insisted upon, and the

best way of accomplishing this prerequisite is to experiment with a full-sized gliding

machine carrying a man. This utilizes the reliable force of gravity until such time

as the automatic equilibrium is fully attained. Then, and not until then, it becomes

safe to apply a motor.

When artificial power comes to be applied, it is probable that the best motor

to use at the beginning will be found in a compressed air engine, supplied from

a reservoir upon the apparatus. This is not a prime mover, but it is reliable and

easily applied. It will probably afford a flight for but a few seconds, but this will

enable the aviator to study the effects of the motor and propeller on the equilibrium

of his machine. When this is thoroughly ascertained another motor may be substituted, such as a steam or a gasoline engine, which will produce longer flights, but

this will require long and costly experimenting to obtain a light and reliable engine.

Another most important requisite is that the first apparatus with a motor shall be

of the smallest dimensions which it is possible to design, and shall therefore carry only

one man. This requisite is for four reasons: 1st. In order to keep down the relative

weight, which increases as the cube of the dimensions, while the supporting surfaces

increase approximately as the square; 2nd. In order to secure adequate control of

the apparatus in the wind; 3rd. To diminish the power required for the motor; and

4th . To have as little inertia as possible to overcome in landing. The whole apparatus

should be so light and small that the aviator shall carry it about on his shoulders

and control it in the wind. This can only be accomplished with a gliding machine.

My double-decked machine was of ample strength, with 12.5 square meters of

supporting surface, weighing 11 kilograms, and carried a man perfectly on a relative

wind of 10 meters per second. It showed an expenditure of 2 horsepower obtained

from gravity. It is believed that a power machine can be built with 16 square meters

of carrying surface, and a weight of 41 kilograms which will carry a man and a

motor of 5 horsepower, if the latter with its propellers and shafts does not weigh

more than 5 or 6 kilograms per horsepower. In fact, this has been done with a
152 Chapter 1: The Achievement of Flight

compressed air motor machine, but the apparatus thus far has produced doubtful

results, in consequence of the defects of the motor. It is firmly believed that it will be

a great mistake to experiment with a large and heavy machine, for it would probably

be smashed upon its first landing, before its possibilities could be ascertained.

The speed first aimed at should be about 10 meters per second, and to

achieve this the following are good proportions:

Sustaining surfaces 0.15 square meters per kilogram.

Sustaining surfaces 3.00 square meters per horsepower.

Equivalent head surface 0.25 square meters per horsepower.

Weight sustained 20.00 kilograms per horsepower.

Details of Construction.

The general arrangement and detail of the construction will conform, of

course, to the particular design to be tested by the experimenter, but some useful

hints may be given. There need be no hesitation as to the materials to employ.

The frame should be or wood, which although weaker than bamboo is more reliable and permits the shaping of the spars so as to diminish the head resistance.

It has been found by experiment that the best cross-section resembles that of a

fish, with the greatest thickness about one-third of the distance from the front

edge; this reduces the resistance to coefficients of one-sixth to one-tenth that of a

plane of equal area, while a round section, such as that of bamboo, gives a coefficient of about one-half. The spars of the frame can best be joined together with

lashing of glued twine or with very thin steel tubing, preferably silver or nickelplated. The stays or tension members should be of the best steel wire, also nickel-plated and oiled to prevent rust. A very important detail, not yet worked out,

consists in connecting the wires to the framework so that they shall pull alike. The

supporting surfaces should preferably be of balloon cloth or Japanese silk, varnished with two or three coats of Pyroxelene (collodion) varnish which possesses

the property of shrinking the fabric upon drying, so as to make it drum-like.

(A good recipe for this varnish is as follows:—Take 60 grams of gun cotton

no.1, dampen it with alcohol to make it safe to handle, and dissolve it in a bottle

containing a mixture of 1 liter of alcohol and 3 liters of sulphuric ether. When well

dissolved, add 20 grams of castor oil and 10 grams of Canadian Balsam. This is

to be kept in a corked can, and poured in small quantities into a saucer, whence

it is applied thinly with a flat brush. Two coats will generally be sufficient. It dries

very quickly, glues together all the laps in the fabric, and shrinks it in drying.)

An expeditious way of fastening the surfaces to the frame consists in stretching them as tight as possible and then doubling them back around the spar, the

flap so made to then fasten temporarily with pins; the first coat of varnish will

glue the surfaces together, and the pins may be withdrawn if desired.
Document 1-9(a–d) 153

Although it is preferable that some of the rear portions shall be flexible, the

supporting surfaces and the framework must be sufficiently stiff not to change

their general shape when under motion. This indicates bridge construction for

the framework and therefore the super-imposing of surfaces. Very little supporting or parachute action will be lost by this, for even when struck at right angles

by the wind, Thibaut found that a square plane placed behind another of equal

size, and spaced at a distance equal to the length of its side, still experienced a

pressure of 0.7 that on the front plane. The supporting surfaces will of course be

arched in the direction of flight in accordance with the practice inaugurated by

Lilienthal, who showed that they possessed angles of incidence of 3 degrees, five

times the lifting power of the planes. It is not probable that success will be

achieved in Aerial Navigation with flat sustaining surfaces.

Proportion of Parts.

In proportioning the parts, the factor of safety for static loads should generally

be 3, never less than 2, and preferably 5 for the parts subject to the more important

strains. These are computed in the same way as they are for bridges, with the difference, however, that the support (on the air), is to be considered as uniformly

distributed, and the load is to be assumed as concentrated at the center. It is not

believed that it is practicable to calculate the strains due to possible shocks upon

landing. They must be taken into consideration in a general way, but the utmost

efforts will be made to avoid them.

The sustaining power will be calculated in the manner given by Lilienthal in

Moedebeek’s “Taschenbuch für Flugtechniker und Luftschiffer.” He does not,

however, fully explain how to calculate the resistance; this consists of the “drift”

or horizontal component of normal pressure, plus or minus the tangential pressure, and of the “head resistance” of the framework, or the motor if any, and the

body of the operator. As an example how to compute this I give the calculations

for the “multiple wing” gliding machine of 1896, which was constructed before

experiments, that shows how the head resistance could be further reduced by

adopting better cross-sections for the framework.
154 Chapter 1: The Achievement of Flight

Area Head Resistance, Multiple Wing Machine. 

Description No. Dimensions Square Co-efficient Equivalent

Millimeters Meters Resistance sq. Meters

Front edge of wings 10 2225 x 12.70 .28257 – .14128

Main wing arms 10 1956 x 12.70 .24841 1⁄3 .08280

Ribs of top Aeroplane 3 1346 x 6.35 .02564 1 .02564

Posts of top Aeroplane 4 1829 x 12.70 .09291 1

⁄3 .03097

Posts connecting 

front wings 8 1280 x 12.70 .12995 1⁄3 .04332

Posts carrying pivots 2 823 x 19.05 .03135 1⁄3 .01045

Curved prow pieces 3 914 x 24.50 .06717 1 .06717

Front bow braces 2 731 x 12.70 .01857 1⁄3 .00619

Rear bow braces 2 841 x 12.70 .02136 1⁄3 .00712

Cross struts bow & frame 2 670 x 12.70 .01702 1⁄3 .03613

Rear wing braces 4 2134 x 12.70 .10840 1⁄3 .03613

Rudder braces 2 1219 x 12.70 .03096 1

⁄3 .01032

Rudder struts 2 548 x 12.70 .01392 1⁄3 .00464

Wire stays 61 meters 61000 x 1.27 .07747 1-1⁄2 .11620

Spring wire stays 8 meters 8000 x 1.27 .01016 1-1

⁄2 .01524

Rubber springs 6 1300 x 1.00 .00780 1 .00780

Sundry projecting parts Say .01198 1 .01198

Aviator’s body Say .46450 1 .46450

1.66014 1.08742

In order to calculate the resistance, we must first ascertain the requisite speed

for support and the consequent “drift.” The front wings measure 13.34 square

meters and carry all the weight, they are set at a positive angle of 3 degrees, for

which the Lilienthal normal co-efficient η is 0.546. Using the well known formula W = k s v2 η cos α in which W is the weight, k is the air co-efficient, s the surface, v the velocity, η the Lilienthal co-efficient (0.11) and α the angle of incidence, and calling W=86 kilos, we have for the support:

86 = 0.11 x 13.34 x v2 x 0.546 x cos 3°; 

and as cos 3° = 0.9986, we have for the speed: 

v = √ 86 / 0.11 x 13.34 x 0.546 x 0.9986 = 10.37 meters. 

Whence we have for the front wings: 

Rectangular pressure 0.11 x 10.372 = 11.829 kilos. per square meter. 

Normal pressure at 3° 11.829 x 13.34 x 0.546 = 86.16 kilograms.

Lift at 3° 86.16 x 0.9986 = 86 kilograms

Drift at 3° 86.16 x Sine 3° = 4.51 kilograms
Document 1-9(a–d) 155

The Tangential pressure upon the font wings is zero at 3°. The “drift” on the

rear wings, which measures 2.74 sq. meters, and were set at a negative angle of 3°,

consists in the product of their surface by the rectangular pressure, (Lilienthal’s θ)

which at this angle is positive, and the horizontal component of the normal

(Lilienthal’s η) which is negative at 3°, the latter being obtained by multiplying h

by the sine of 3°. We have therefore:

Drift rear wings = 11.829 x 2.74 (0.013 = 0.212 x 0.05233) = 0.98k.

The head resistance is the important factor, and depends upon the shapes

which are adopted for the framing to evade air resistance and to secure low coefficients. It has to be calculated in detail, and the table herewith given recapitulates the various elements of the area of head resistance of the multiple wing

machine, reduced by co-efficients to an equivalent area for further calculations.

The rectangular pressure of a speed of 10.37 meters per second being 11.829

kilos per square meter, we have therefore for the whole resistance:

Drift front wings 11.829 x 13.34 x 0.546 [x] 0.52333 = 4.51 kilos

Drift rear wings 11.829 x 2.74 (0.043 – 0.0126) = 0.98 "

Tangential component at 3° = 0.00 "

Head resistance 11.829 x 1.087 = 12.86 "

Total resistance = 18.35 "

As the speed is 10.37 meters per second, the power required to overcome this

total resistance is:

Power 18.35 x 10.37 = 190.28 kilogrammeters or 2.53 horsepower,

and as the weight is 86 kilos the angle of descent as a gliding machine ought to be:

Angle 18.35/86 = 0.2134 or tangent of 12°

In point of fact, the apparatus glides generally at this angle and frequently at

angles of descent of 10 or 11 degrees, this being probably due to an ascending wind

along the hillsides, and fully verifying this mode of calculating the resistance.

In the “double-decker” gliding machine, in which the framing was better

designed, the resistance was calculated at 14.46 kilos, and it absorbed a horsepower in

gliding in still air. By employing still better cross sections of framework, and especially

by placing the aviator in a horizontal position, the head resistance could be

reduced by at least one-third, but this particular attitude of the man would involve some

risk of accident in landing, and is considered to be too dangerous to be employed

in the preliminary experiments. It will be noticed in the table that the resistance

of the wire stays is given a co-efficient of 1-1

⁄2, while theoretically, being cylindrical,

their co-efficient should be about 1

⁄2. This allowance is based upon experience.

Wire stays produce undue resistance, and this is probably due to the fact that they

vibrate like violin strings when the apparatus is under rapid motion, and thus produce

a greater resistance than that due to their rounded cross-section.
156 Chapter 1: The Achievement of Flight

The power required will be seen to differ very materially from that indicated

by the formula recently proposed in France, which is based on the assumption

that the total wing surface, in square meters, multiplied by the co-efficient of air

resistance (i.e., the number of kilogrammes carried by a square meter, at a speed

of one meter per second) must at least be equal to the cube of the weight of the

apparatus in kilogrammes; divided by the square of the power exerted by the

motor in kilogrammes, or, K S T2 = P3 from which in our own case we would draw:

0.11 x 13.34 x T2 = 863 , or

T = √ 863 / 0.11 x 13.34 = 658.4 klgm

or 8.78 horsepower, which is more than three times the power calculated by the

method here given and tested by actual experiment and measuring.

It must be remembered, however, that the 2.53 and the 2 horsepower, which

have been found sufficient to sustain 86 kilogrammes in the air, are the net horsepower absorbed by the gliding machines. When a propeller and a motor are

added, it will be necessary to allow for the losses in efficiency incident to those

adjuncts, and so provide about twice the power to the engine which is indicated

by the resistance multiplied by the speed. A safe rule of approximation will be to

allow that each nominal horsepower at the engine will sustain 20 kilogrammes,

and that each kilogramme of the total weight of the apparatus will require 0.15

square meters of surface to sustain it at speeds of about 10 meters per second.

When greater speeds become practicable and safe, the surfaces may be reduced

below this so that at 20 meters per second they may be but about 0.05 square

meters per kilo, instead of 0.15 square meters per kilo indicated above, and this

would permit reducing the head area of the framing, but unless the co-efficient

for the aviator’s body was in some way reduced the resistance and power required

would be greater, because of the higher speed.

These are the conditions and considerations which experiments with fullsized gliding machines, carrying a man, have thus far indicated as necessary to

observe in order to achieve success with a dynamic flying machine provided with

a motor. The most important of them are:

FIRST, that the automatic equilibrium and safety shall first be secured before

an attempt is made to apply a motor, and SECOND, that the apparatus shall be

made as small and light as possible, so that the aviator may sustain its weight

before taking his flights.

Document 1-9(b), Augustus M. Herring, 

“A Solution to the Problem of the Century,” 1897.

Perhaps no subject offers more scope to the imagination than the benefits and

changes for mankind which would result from a practical solution of the problem
Document 1-9(a–d) 157

of manflight. At the same time there is probably no problem which the inventive

skill of man has ever attacked which apparently offers, at first sight, more numerous

and easy ways of unravelment, and yet which, on careful investigation, develops

greater or more unexpected difficulties. In beginning the experiments the methods

apparently open might be roughly divided into four classes.

The first of these would comprise all those machines in which the whole or

part of the weight was lifted by a balloon or gas-bag; the second, all those forms

of apparatus which were intended to sustain or lift their weight with screw propellers

revolving on vertical axes; the third, those machines which were intended to sustain

their weight (and that of the operator) on flapping or beating wings; the fourth,

and last, class would contain the aeroplane, or more properly the aerocurve

machines; for the aeroplane may now safely be said to have disappeared from

competition with the more efficient form of surface.

The limitations of the navigable balloon are now pretty well recognized. To

obtain a speed of even 20 miles per hour, a spindle-shaped envelope of very large

size is necessary, and the result at its best is an exceedingly frail and bulky

machine, whose ultimate speed capacity is insufficient for wind velocities which

frequently occur even near the ground. Its chief defects are great bulk and

extreme frailty; for the envelope, in proportion to its relative size, is not many

times stronger than a soap bubble. An instance may be cited in support of this in

the large navigable balloon built for the Antwerp exposition, which became tilted

up during a trial when the rush of gas to the higher end burst the balloon.

The future utility of the navigable balloon is still the subject of differences of

opinion; it is, however, certain that whatever may be its ultimate practical advantages

as a flying machine, the drawbacks of enormous size and frailty are sure to offer

a considerable offset to them.

The vertical screw machines have much to recommend them, but there are far

greater difficulties offered to their production than would be supposed. The ability

to rise directly into the air from any given spot would be an exceedingly desirable

quality. And hence we find that the great majority of experimenters who attack the

problem of dynamic flight begin here, starting with a plan of some modification of

this type of machine. The stumbling-blocks, however, are soon met. Not least

among them is the fact that when the surfaces which form the blades of the screws

are revolved over one spot (as they must be to rise directly into the air) they do

not give any considerable lifting effect in proportion to the power consumed; for

where one might from the theory even of the aeroplane expect a lift of possibly

100 pounds per horsepower, the best result the inventor can produce on a practical

scale is pretty sure to be less than one-seventh of that figure. In fact, the lift with

the lightest engines we can build is likely to be but little, if any, more than the

weight of the machine itself. With engines weighing much more than 4 or 5 pounds
158 Chapter 1: The Achievement of Flight

per horsepower (250 times as powerful weight for weight as a man), practical success

with this type of apparatus is not possible.

The third class, or the beating wing machines, are subject to the same disadvantages

in regard to the enormous power required as those of the vertical screw type. In addition

to this, the question of maintaining a stable equilibrium in windy weather still further

greatly complicates them, so much so, in fact, that there is but small hope of practical

machines operated on this principle ever being produced.

It is unnecessary to point out that any combination in a machine of the principles

involved in either of the above three classes would still subject it to the fundamental

objections of at least one of the classes. These objections are so formidable that,

to the great majority of the foremost workers in this field, there now appears but

one main principle left, and upon this there is an ever-increasing hope, if not certainty, that flight will be accomplished. This principle is the one which underlies

the aeroplane and aerocurve; namely, that when a thin surface is driven rapidly

through the air, and is slightly inclined to its path, the equivalent of a pressure is

developed on the side which is exposed to the air current—i.e., the under side—

which is much greater than the driving force necessary to produce it. If an arched

surface (arched in the line of motion) with the hollow side undermost be substituted for a plane, we have an aerocurve. Its chief advantage is that it possesses a

higher efficiency. Another, but minor, difference is that it is not necessary to

incline an aerocurve in order to develop a pressure on the hollow side when it is

moved through the air. 

The one advantage which the dynamic or power machine of the aerocurve

type has over the vertical screw is the fact that it can, through the agency of the

surfaces, convert the relatively small push of the screw propellers into a much

larger lifting effect.

It is interesting to note that the first approach to human flight of modern times

was attained only by the use of the aerocurve, when early in 1894 the late Otto

Lilienthal, of Berlin, Germany, built a huge bat-like machine, with curved rigid

wings, on which he was able to “slide” downhill on the air, 150 feet or so at a time.

Practice with this machine soon enabled him to start from very high places, and

his flights became correspondingly longer. Early in the beginning of these trials,

he became aware, as his writings show, of the enormous power and disturbing

effect which those ever-present irregularities in the wind produce, and which, in

a large measure, were the cause of his losing his life—a sad accident which has

taken from the field of aerodynamics one of, if not, the ablest of its workers; for

both the practical and theoretical work of Lilienthal in the new science is of the

greatest value, and will be so recognized when more generally understood.

In his first articles Lilienthal repeatedly cautioned others against attempting

to glide in winds which exceeded 7 meters a second (about 15 1

⁄2 miles an hour), as
Document 1-9(a–d) 159

being excessively dangerous. However, when he made the improvement on his

machine of superimposing two smaller surfaces and thereby reduced the “tip to tip”

measurement from about 24 feet to 18 feet, the diminished leverage upon which the

gusts could act enabled him to sail in stronger winds, so that he even experimented

in winds of 22 miles an hour. This, without further improvement in the automatic

stability of his machine, was an unwise thing to do, and the accident which occasioned

his death, on the 9th of last August, is, more or less correctly, attributed to it; nevertheless, the immediate cause was undoubtedly the result of defects in the machine

itself, which had been allowed to deteriorate and get out of repair. In his double-deck

machine the upper surface was joined to the lower one by two or three small vertical

posts and numerous wires. Probably some of these wires had become rusted or so

weakened that they broke when the machine was struck by a heavy puff, and so

allowed the upper surface to tilt back and suddenly stop the headway of the

machine, but not that of the unfortunate operator, who swung round and round

over the apparatus as it pitched to the ground. This tendency to revolve over

backward is frequently set up by a very strong sudden gust striking the machine

squarely in front; it can, however, be counteracted by a quick movement of the

operator’s body and legs toward the front. A serious defect in the design of the

Lilienthal apparatus is here seen, for on it the operator’s position is somewhat

strained, and his movement very limited, owing to the fact that he is obliged to

hold to a small bar with both hands while his weight is carried on his elbows, which

rest, a little farther back, on a portion of the main frame. (See Plate IX, Fig. 2.)

These defects suggested themselves to the writer when, in the summer of

1894, he built a machine similar in many respects to that of Lilienthal. It differed

from his in two important particulars: first, the upward movement of the horizontal

tail was limited; second, the range through which the operator could shift his

weight was nearly three feet instead of about eight inches. To obtain this range of

movement the weight of the body, when in flight, rested upon two horizontal bars

fitting under the armpits. (See Plate IX, Fig. 3.)

No very startling results, however, were obtained with this machine or with the

three subsequent ones, the longest flight attained being only 187 feet in length.

Experiment with these machines, nevertheless, furnished a great deal of valuable

information. No one who has not experimented with a machine of the Lilienthal type

can form any accurate conception of the tremendous power and lifting effect which

130 to 150 square feet of concave surface can exert. It is with an apparatus of this

kind that a novice first becomes fully aware that no wind is anything like constant,

and that the power of those much-talked-of “gusts” is real, and not imaginary.

Anyone wishing to begin experiment with a gliding machine cannot be too cautious in the selection of an experimental station. Nothing could be more dangerous

than to start from a flat roof or a precipitous cliff, or to begin experiment in a
160 Chapter 1: The Achievement of Flight

locality where surrounding objects, such as hills, buildings, or even large neighboring trees, are likely to break up the wind into swirls and eddies. What is most

desirable—in the beginning, at least—is a hill surrounded by country that is as

level as possible. Both the starting and landing points should be on comparatively

soft earth, free from stones, bushes, and snags. Perhaps the best station of all is to

be had where there are high, bare sandhills or dunes, facing a large body of water.

The slope of such a hill (to a beginner) is of as much importance as anything else;

it must be steep at the top and run off gradually as it nears the bottom so that

when he has gained proficiency enough he may start from near the top in calm

weather and yet have his flights always close to the hill-side. If this be so and the

soil be comparatively soft, the operator can easily save himself from a dangerous

fall which might result from a poor start or a breakage of the machine.

In the first experiment with a full-sized gliding machine, a man’s natural

instincts irresistibly impel him to move in the wrong direction when the balance

of the apparatus is disturbed. It is, therefore, at first, impossible to distinguish

between effects produced by one’s own errors and those produced by wind

changes, but in time three separate causes of unsteady flying become easily distinguishable from each other; namely, improper adjustment of the machine,

errors of the operator, and changes in the trend, velocity, or direction of the wind.

When the mastery of the machine becomes about as perfect as possible very

much of this unsteadiness disappears. Nevertheless, with a wind as steady as

winds ever are,—even after having blown for hundreds of miles over absolutely

level prairie, or, as in the case of our later experiments, having come in an unobstructed path for several hundred miles over the waters of Lake Michigan,—we

found that the effect was by no means a steady one, but was such as to indicate

that they were broken up into an inconceivable number of irregularities in pressure,

velocity, and direction, in spite of the fact that a light anemometer showed fluctuations in velocity of seldom more than 10 or 12 per cent in readings of 5 seconds

duration, taken 10 to 20 seconds apart.

In a wind of 9 to 10 miles per hour with a simple machine of the Lilienthal type

the disturbances of the wind are barely noticeable, but at 12 miles they are quite

apparent, at 14 miles they require considerable practice to combat, at 16 1

⁄2 miles,

even with best skill at command, a flight is more or less risky; and when the wind

blows above 18 miles per hour it is dangerous, even with a total load of 182 pounds

(machine, 27 pounds, operator, 155 pounds) on 130 square feet of surface.

Nothing, perhaps, is more surprising than the power which a gust in even a

14 or 15 mile wind will occasionally exhibit, such, for instance, as sometimes happens

to an inexperienced or careless operator, who, in facing the wind with the

machine preparatory to making a start, suddenly finds himself lifted anywhere

from 2 to 10 feet above his starting place. These flights are invariably backward,
Document 1-9(a–d) 161

and are due to mismanagement in allowing the wind to catch under the surface

of the machine while the operator is too far back on it to exert a proper control.

In the hands of a skilled person, the flights, in mild winds, generally appear to an

on-looker as remarkably smooth, and even in spite of the fact that the operator is

seen to frequently shift his position on the machine with considerable rapidity; yet

in slightly stronger winds—those of 15 to 16 1⁄2 miles per hour (mean velocity)—

the irregularities become very perceptible to the spectator, who may sometimes

see the apparatus rock and toss not unlike a ship in a rough sea.

To appreciate the causes which render a gliding machine, or in fact any

machine of the aerocurve type, unstable, it is necessary to understand, in a measure, both the peculiarities of the wind and the effect they have on the position of

the center of pressure of the surfaces.

In order for any apparatus in free air to be in equilibrium it is necessary, of course,

that the center of pressure should be in the same vertical line as the center of gravity.

It is not, as many believe, absolutely necessary that the center of weight should be

beneath the sustaining surfaces; this may be demonstrated by trying the small paper

model shown in Plate XII, Fig. 1, which, if not weighted too heavily, will always fly

with the “fin” side up, even if dropped with the weight and fin side undermost.

When a surface is inclined to the air through which it is moving, the lifting

pressure is not uniform, but is very much greater toward that edge which is first

struck by the current. On a square plane 100 inches on a side, the center of all the

lifting pressures may be anywhere between the center of the figure and as far forward (apparently) as 14 inches from the front edge, according to the angle and

speed at which the surface is presented to the air. The travel sidewise might be

even more, granting that gusts may come from either side. With an aerocurve the

travel is probably seldom more than 1

⁄5 as much as it would be with a plane. In

practice with any ordinary gliding machine of large surface it is found that the

gusts come from any quarter: in front of the apparatus, from the extreme left to

the extreme right, and in a wind of over 22 miles per hour they follow each other

with such suddenness and with such extreme changes that it is absolutely impossible to shift one’s weight in time to counteract them. These conditions, which had

to be met, made it imperative to seek for automatic stability along very different

lines from any that had heretofore been tried.

The changes or gusts which have the most influence in disturbing the

machine are seldom of more than half a second duration, and oftentimes they last

less than half that time; yet in so short an interval, it has frequently happened to

me, in my experiments with my first three gliding machines, that in less than half

a second the lateral equilibrium was so far disturbed that the lateral axis of the

machine would make an angle of 35 to 40 degrees with the horizontal. At other

times, the angle of advance (the angle at which the surfaces are presented to the
162 Chapter 1: The Achievement of Flight

air) was so much increased that nearly every bit of the headway was destroyed. On

two occasions, the change in direction, both vertically and to the side, was so violent and sudden as to shake my hold loose of the machine.

During my last flight on a Lilienthal type of machine, while experimenting in

a wind of about 18 miles an hour, the machine was struck twice in quick succession

by a gust from the right. The first impulse raised that side until the apparatus

stood at an angle of about 40 degrees; the second impulse, which came between

1

⁄4 and 3⁄4 of a second later, increased the inclination to nearly a vertical one, so

that one wing pointed to the ground and the other to the zenith. Anticipating a

complete overturning of the machine (as did happen) I let go my hold and

dropped to the sand below, a distance of not more than 12 or 14 feet, where I

landed on my feet, but on the left wing of the overturned machine, which had

drifted under me as I fell. This accident damaged the machine so much that it

was not rebuilt. We recognized from these experiments that the disturbances

increased much more rapidly than the mean velocity of the wind; also that in

winds of 18 miles or over, it was impossible for a man to shift his weight far

enough and rapidly enough on a single surface machine to keep it in proper equilibrium under all circumstances.

In addition, the conclusions were reached, first, that the angle of advance

must be automatically maintained, with almost absolute certainty, at a very small

angle; second, that the lateral equilibrium should also be largely, if not wholly,

automatic, and be maintained by some more effective method than a dihedral

angle between the surfaces, or by placing the operator far beneath the apparatus.

The first of these is considerably the most important, as disturbances of the angle

of advance generally entail disturbances of the lateral equilibrium as well.

In the beginning of experiment to obtain longitudinal stability, three clearly

defined methods (each with its own limitations developed by experiment)

appeared open.

The first and simplest method is to find such a surface, or grouping of surfaces, that the displacement of the center of pressure is very great for very small

changes of the angle of incidence; the second method is to find such a form of

surface that its center of pressure remains in one spot, no matter from what angle

the relative wind may come; the third method is to provide a separate mechanism

to either take up or counteract the disturbing effects of the wind changes.

The first method may be said to have been practically attained (as far as it is

attainable by such an arrangement) in the various modifications of the Hargrave

kite, and also in its predecessor, the Brown biplane, or, a little better still, in what

might be called a “bicurve,”—that is, a biplane machine on which slightly arched

surfaces have been substituted for planes. Such a model is shown in Plate IX, Fig. 4, B

being the front aerocurve. This model will maintain a very good equilibrium for
Document 1-9(a–d) 163

gliding flight so long as the center of gravity is anywhere between C and the rear

edge of B; but each change in the position of the center of gravity corresponds,

of course, to a different angle of flight, i.e., to an angle at which the center of pressure of the combined surfaces coincides with the vertical line through the center

of gravity of the whole apparatus.

The center of pressure travels toward B as the angle of flight is diminished, and

in the reverse direction when it is increased. This great range in the possible position

of the center of pressure is a measure of the corresponding change in efficiency

which the rear surface undergoes at various angles of flight. This efficiency diminishes very rapidly as the angle of flight is diminished; at very flat angles its useful

effect disappears altogether. Not only this, but at small angles of incidence, those

under .8 degrees, the longitudinal stability of the arrangement disappears as well.

From many experiments with gliding models of this type I found it impossible to

obtain glides which represented a travel of over 4 lineal feet for each foot of

height lost, unless the model was so weighted that no part of the weight rested on

the rear surface. Also, that the power required to support any given weight at an

angle of 15 degrees or less is about twice as much as would be needed on superimposed surfaces of the same size held at the same angles of inclination.

When the model shown in Plate IX, Fig. 4 (or any similar one) is so loaded

that each surface must carry about half the total weight, the apparatus will take up

an angle of about 26 degrees with the relative wind. Under this condition a dynamic

model would require between 40 and 46 per cent of its weight in thrust to keep it

“afloat,” or if liberated as a gliding model it will travel forward a little over twice

as far as it descends vertically. At the flattest angle, about 15 degrees, at which it

maintains a good equilibrium, it will glide only 3 to 3 1

⁄4 times as far as it falls.

As the rear surfaces in an apparatus with following surfaces come more and

more in the “wake” of the front elements, the relative supporting effect of the rear

becomes less and less as the angle of flight is diminished. Thus, through the phenomena of “interference,” the relative efficiency (as a lifting factor) of the rear

surfaces becomes greater or less (as the angle of flight is increased or diminished)—a corresponding travel of the center of pressure results which maintains

the longitudinal equilibrium, but at the expense of extra weight of the apparatus

and considerable additional power.

This fundamental principle—that of interference—underlies the stability of

the Malay, Eddy, Bazin, Lamson, Chanute, and Hargrave kites. It is still further

applied in the three last named, in which the vertical keels form pairs of Brown’s

“biplanes,” which maintain the lateral equilibrium as well.

It would seem that one might be able to avail of the wonderful stability which

a system of following surfaces exhibits, by so grouping the surfaces vertically as well

as horizontally that they could not interfere. It is comparatively easy to so space
164 Chapter 1: The Achievement of Flight

them that interference is practically avoided, but from several hundred experiments in this direction I have invariably found that the automatic equilibrium is

always impaired in direct proportion as the front and rear surfaces cease to interfere. The

further conclusion arrived at from these experiments was that in following surface

machines, a low efficiency is essential to insure safe equilibrium. Quantitively this

efficiency is so low that probably less than 30 pounds can be carried per horsepower when the surfaces are loaded to a greater extent than one pound per

square foot of area. Consequently, though dynamic models might be made that

would work satisfactorily on this plan, a full-sized machine to carry even one man

would offer no such encouragement to its projector, chiefly because the weight of

a machine increases much more rapidly than its surface or supporting power.

Following surfaces therefore are not available.

Just as experiment and careful measurement made this fact clear, a new

prospective method of obtaining automatic equilibrium began to open up. A study

of the peculiarities in the travel of the center of pressure of variously arched surfaces

indicated the possibility of evolving such a form that the center of the lifting pressures would remain in the same spot for all angles of inclination. The result of

much investigation in this line is shown in Plate XI, Fig. 1. Strictly speaking, this

piece of apparatus is a gliding model, and as such in a wind of 30 miles an hour

or less it possesses a perfect equilibrium, owing to the fact that the position of its

center of pressure is almost absolutely constant for all angles of incidence between

plus 90 degrees and minus 20 degrees; the same is also approximately true

whether the wind strikes from in front or “abeam.” It will also fly as a tailless kite,

but as such is somewhat inferior to the Hargrave, both in steadiness and in the

“angle of the string,” yet the lifting effect is probably four times as great per

square foot of surface. The projected area of the dome is not quite 6 square feet,

yet in some experiments it has registered a pull of over 40 pounds on a springbalance, and on one occasion repeatedly broke a cord tested to 69 pounds.

As a flying machine it would have the advantages of being able to sustain

great weight on a very small surface, and would require but a slow speed to do so.

A dome machine of only 9 1

⁄2 feet in diameter would be of sufficient size to carry

a man in gliding flight at a speed (relative to the air) of only 20 to 21 miles per

hour. But its drift is so great that it would not carry the operator horizontally

more than 2 1⁄4 to 2 3⁄4 times the height from which it started. As a great thrust of

the screw is far more costly in power than great speed, such a machine could hardly be a practical success. However, owing to the very low sailing speed, a dynamic machine to carry one man might be built which would fly. It would be of little

practical value, owing to the excessive power required, and its limited speed

capacity. This line of experiment was therefore laid aside in the spring of 1896.

By way of explanation I may here add that from a great number of previous
Document 1-9(a–d) 165

experiments with various devices—such as modifications of the drag rudder, gyrostat, and pendulum regulators—I had come to the belief (which all my more

recent experiments have only served to strengthen) that the action of any device to

maintain a machine in safe equilibrium must be such that it prepares the machine for each

impending wind change before that change actually occurs, and that any device which

tends to forcibly right the flying machine after it has departed from an even keel

more often produces (in the open air) greater unsteadiness than the reverse. The

reason for this is not far to seek. It lies chiefly in the fact that the most formidable,

as well as the most frequent, disturbances met within the natural wind are cycloid

gusts or rotating masses of air which frequently give a machine (or model) powerful double impulses. These impulses are generally opposite in their effect, and

succeed each other by irregular intervals varying from about one-fourth to one

second apart; and, therefore, a regulator, such as a pendulum or gyrostat mechanism, which begins to act on the machine after it is disturbed, and continues to

do so until it regains an even keel, is often the means of greatly augmenting the

second impulse of the pair, or the first of a new gust which may strike the apparatus from a different quarter. I do not mean to say that such devices will not work at

all; on the contrary, they can be made to give very good results in fairly mild weather,

but they all fail in winds of much less velocity than those which any practical

machine must be able to contend with. 

This conclusion reached, it would appear that the methods left would be

found only through a careful study of the wind changes themselves. As before stated,

I had become aware almost from the beginning of my gliding experiments of several distinct kinds of disturbances, the most formidable being very sharp, welldefined changes in the velocity and direction of the wind, which last but a fraction

of a second and appear to come in pairs. Their distinguishing characteristic

(besides their much greater suddenness and power) is, that in practically all cases they

are preceded by a perceptible warning which generally consists of a slight strengthening of the wind followed by a momentary calm, which in turn is followed immediately by the “gust” in its fullest force. During the momentary freshening, the

wind either comes from or veers in the direction from which the gust proper will

strike. These changes can easily be verified by an observer in a strong wind by noting

the effects as he feels them on his face.

There are many observations which might be given to corroborate the theory

that practically all the gusts which have any material effect in disturbing the angle

of advance or the lateral equilibrium of an apparatus are of a rotary character.

They are, in fact, nothing more or less than diminutive tornadoes which travel,

however, much more rarely on vertical axes than on diagonal or horizontal ones.

In a few cases the axis of a gust is found to be horizontal and parallel with the

wind. In the majority they are nearly horizontal, but across the direction of the
166 Chapter 1: The Achievement of Flight

mean wind. The direction of rotation is usually backward, i.e., in the reverse direction that a wheel would have in rolling over the ground. In what may be called

steady winds the swirls are of much greater diameter, and the out-flowing eddies,

or the momentary freshening of the wind, precede them by a longer interval.

The observations which led to a recognition of the rotary character of the wind

changes also were the means which furnished an explanation of the action of certain

simple devices, previously found to work with success as far back as 1890 on a small

dynamic model which has been illustrated in a previous issue of this Annual. I was,

therefore, not wholly in the dark in commencing experiments to produce a regulator

which should prepare the apparatus to meet each particular “gust” before it

arrived.

The horizontal regulator of the dynamic model was slightly modified to adapt it

more closely to the new theory, and in May, 1896, applied to the kite shown in

Plate XI, Fig. 2. This kite, which is here shown in a 28-mile wind, possessed such

perfect power in maintaining the surfaces at a small angle with the wind, through

changes which would otherwise prevent it from flying at all, that in momentary

freshening or changes, it would rise until the strings passed the zenith and made

an angle of 6 to 8 degrees beyond the vertical. The average angle maintained by the

surfaces with the horizontal varied between such narrow limits that it could not

be easily detected by the eye. From a number of observations it was found possible

to set the regulator to maintain an angle of between 2 and 3 degrees (above the

horizontal), and calculations from the weight and surface of the kite, the pull on the

string, and its angle above the horizontal show that the lift and drift of the kite correspond very closely indeed with the theoretical ones computed from the annexed tables.

Later in the summer this regulating device was improved and its use extended

so as to counteract the rotating columns whose axes were more or less vertical,

and thus preserve the lateral equilibrium of the apparatus. With this change it was

applied to the gliding machine shown in Plate XIII, Fig. 1. By its use the safe limit

of wind in which experiments could be carried on was raised from 16 1

⁄2 miles per

hour (with the simple Lilienthal, or 20 miles with the Lilienthal double deck) to

over 30 miles, and with it the maximum length of flight was increased from 187

feet to 359 feet; at the same time the rocking and tossing of the apparatus was

reduced to such an extent that an on-looker could not in any of the 150 to 200

flights detect that the apparatus in flight ever departed from an even keel, either

laterally or longitudinally,—i.e., the angle of advance was maintained perfectly at

the very flattest angle. It is evident from repeated measurements that this angle

never exceeded 4 degrees with the relative wind.

The difference in the amount of ascending trend of the wind at different

times and at various points in front of the hill made great differences in the

length of flights. The results of an average flight in calm air are here given:
Document 1-9(a–d) 167

Net projected area of 2 supporting surfaces, 134 square feet; size, 16 feet 2

inches x 4 feet 4 inches.

Net area of horizontal tail (which receives a pressure on its upper side), 19

square feet.

Weight of machine, 23 pounds.

Weight of operator, 155 pounds.

Press upper side of tail (acting as weight), about 7 pounds.

Total weight carried by 134 square feet, 185 pounds.

Total weight carried per square foot area, 1.37 pounds.

At the time of the following experiment the air was nearly calm, the only trace

of wind was from the northeast; the flight was made by running downhill toward

the north. Length of flight, 242 feet from last footprint to first at landing; time of

flight, 7.4 seconds (in the air); difference in level between points was 42 1⁄2 feet.

Speed of machine was therefore practically 22 miles an hour. The wind pressure

is 22 x 22 x .005 = 2.42 pounds per square foot. The proportion of this as a sustaining factor was 1.37/2.42, or 57 per cent. By referring to the tables hereto

appended it will appear that this amount of lift (57 per cent of the normal pressure) corresponds to a positive angle of the surfaces of between 3 and 4 degrees,

and by referring to the third column we find that the drift of the surfaces is (.0525

for 3 degrees and .0582 for 4 degrees) about .056 times the total weight of

machine and operator and negative pressure on the tail, or .056 x 185 = 10.36

pounds, which is drift of the surfaces alone; to it we must add the head resistance

offered by the framing of the machine and that offered by the operator’s body.

The framing consists of 64 lineal feet of timber which forms the main arms of the

wings; this has a thickness of an inch across the wind, and therefore exposes a

cross-section surface of about 3.3 square feet. The upright posts are 64 feet in collective length, being on an average 6

⁄10 of an inch in width (across the wind). Their

area is therefore practically 3.2 square feet. But as they are sharpened more or less

to lessen the resistance they offer to the wind, the total area offered by the woodwork, instead of being 3.3 + 3.2 = 6 1

⁄2 square feet, is equivalent to only 2 1⁄2

square feet. Besides this the framings of the tail and vertical rudder expose an

equivalent of half a square foot of surface. The regulator and its cords, bands, etc.

expose .52 of a square foot, and 160 lineal feet of wire .05 of an inch in diameter,

expose the equivalent of .5 square foot more, making the total equivalent area

exposed equal to 4.02 square feet. This at 22 miles an hour would offer a resistance of 4.02 x 2.42 = 9.73 pounds; to this must be added the resistance offered

by the 5 square feet of the operator’s body, arms, and legs. This brings the total

resistance to: Resistance of surfaces, or drift, 10.36 pounds; head resistance of

machine, 9.73 pounds; and resistance offered by operator, 12.1 pounds; total = 32.19

pounds. This moved over a distance of 242 feet would consume 242 x 32.19 = 7,790
168 Chapter 1: The Achievement of Flight

foot-pounds, which would be furnished by the weight of the machine and operator

(178 pounds), descending through a vertical distance of 7,790 ÷ 178 = 43 feet 9

inches, against an actual measured height of only 42 1⁄2 feet. The difference in

energy can easily be accounted for in either of three ways: First, a slight overestimate

of the resistance offered by the operator’s body; second, the presence of a slight

ascending current of air; or, lastly, that the speed gained in running down the hill

at the start was greater than 22 miles an hour. (It is possible to gain a speed of 26

miles if the weight is about half supported on the machine.) It may be interesting

to point out in passing that the energy (7,790 foot-pounds) absorbed in keeping the

machine and operator afloat during 7.4 seconds represents barely 2-horsepower,

but less than one-third of this is drift of the surfaces. It is, however, now pretty well

known that it would take at least 3-horsepower to produce a thrust of 32 pounds,

even with as large screws as could be conveniently carried on a machine of this size.

The details of the regulating mechanism of neither this nor the “three-deck”

machine have been here given, as they are now the subject of applications for

patents; nevertheless, to anyone wishing to repeat the experiments I shall be

pleased to give all the information necessary.

During October I constructed a new machine of the same general design as

the “double deck” but provided with three superimposed surfaces instead of two.

In this a considerable change was made in the mechanism which governed the

lateral equilibrium. Instead of depending upon the power in the small eddies

which precede a rotating gust to operate the machine, their power was used only

to work the valves of a mechanism operated by compressed air; in this way the

regulation (which is accomplished through a reflex action) became much more

powerful and prompt. The tests of the new gliding machine showed that a considerable advance had been made, in that the limit of wind velocity in which

flights were safe was raised from 31 1

⁄2 miles an hour to over 48, and the maximum

length of flight increased from 359 feet to 927 feet (best) and 893 feet (second

best); at the same time it was found quite safe to turn the apparatus and fly at a

considerable angle with the wind. It was by this means chiefly that the length of

flight was increased, as the longer flights were made while “quartering” on the

wind; that is, the apparatus after starting (the start must always be made dead

against the wind) was kept pointing at an angle from 15 to 35 degrees with the

wind, according to the strength of the latter, while the apparatus itself moved

along a course nearly, but not quite, at right angles to the wind. This enabled me

to keep close to the hillside and take advantage of the rising current of air flowing

over the slope. In a few of the flights it would have been possible to have landed

on a higher point than the starting one, owing to irregularity of the wind which

occasionally raised me, after having gone several hundred feet, to a level above

my starting place; these rises were only momentary, and all the flights as a whole
Document 1-9(a–d) 169

were on a descending grade. As the slope both to the right and left had several

clumps of small trees which it was necessary to steer over or around (according to

the height at which the machine happened to be while it passed near them), these

“quartering” flights were not made to any great extent.

With a machine on which the angle of advance is automatically controlled

with a fair degree of accuracy, the steering requires but little more effort than a

bicycle, and at the same speed, i.e., above 20 miles an hour, I have much doubt in

my mind whether a bicycle (on a level road) could be turned on a much shorter

radius than a flying machine. It is possible to land within less than 5 feet of any

predetermined spot if it be selected well within the range of flight of the starting place.

In a few of the glides with the last machine I attempted to carry an additional

weight, in the shape of a bag partially filled with sand. This bag was fastened

between the middle and bottom surfaces and, beginning with about 12 pounds,

the weight was gradually increased until 41 lbs. were carried without materially

shortening the length of flight. The heavier weight considerably increased the difficulty in landing in light wind, owing to the greater speed relative to the ground.

In high winds it was of very little hindrance either in starting or landing. The

object in view in experimenting with the weight was to ascertain the power

required on a dynamic machine and to test the manageability of the apparatus

with a weight equivalent to the necessary engines and supplies. The result was so

very encouraging that I have since then commenced constructing the engines.

One of the pair is shown in Plate XIII, Fig. 2. It develops (alone) about two-thirds

of the total thrust-power needed; its weight is only 12 pounds; its action is, however, a little irregular, and on that account is still the subject of experiment; it is a

gasolene engine of the Otto cycle type.

Not least among the interesting results brought out by these gliding experiments

is the fact, which becomes more and more evident from repeated experiment, that

there is a very great difference in the supporting power of the air, whether one

faces the natural wind or advances through still air; for while a natural wind of 18 to

19 miles per hour is sufficient (over level ground) to support the double-deck machine

and operator, and will even momentarily raise them directly in the air for a foot

or two, the same machine requires a minimum speed of 22 miles to support the

same weight at the same angle in still air.

On Plate XIV are given drawings of the three-deck machine; another drawing

will be found on Plate XII, Fig. 2, giving exact sizes of struts, etc., in cross-section.

If built to scale the machine will have 227 square feet (net) surface. This is, however,

40 per cent more than a man of average weight ever requires except in a calm or

in winds of less than 10 miles an hour. In winds over 12 miles an hour a beginner

will get along better with the upper surface removed. If this machine is built on

such a scale that the dimensions are only two-thirds of those given, it will be of
170 Chapter 1: The Achievement of Flight

ample size (103 square feet surface) for the average operator in any wind of over

25 miles an hour. It is better not to reduce the size of main spars and struts at all

from the sizes given for the larger machine when constructing the surfaces on a

smaller scale. The sizes given are for the best grade of black or silk spruce only;

this wood will stand at least 16,000 pounds to the square inch; it must be straight

grain and entirely free from flaws.

There is, perhaps, no better sport imaginable than coasting through the air,

especially so where the flights are comparatively long. In moderate winds, of 18

to 25 miles per hour, the path of the machine is often quite horizontal for a hundred

feet or so after leaving the hillside, until, in fact, the rising current which flows

over the hill has been cleared. If during the first part of the flight an operator

wishes to keep near the ground he may do so by moving an inch or two forward

on the machine; he will find, however, that in thus sailing downward through an

ascending wind the speed increases at a tremendous rate.

Perhaps the most trying ordeal is experienced when the machine unexpectedly

encounters a strongly ascending current of air which may raise the operator, in some

instances, 40 or 50 feet above his line of flight. Such occurrences are comparatively

frequent in a wind of 30 miles or over, but are not dangerous so long as the regulating

mechanism remains in working order, as the machine then retains an absolutely

level keel. I have twice been raised as much as 40 feet above my starting point without

either myself or those who were on the ground being able to detect any change

whatever in the inclination of either axis of the machine. Considering the fact that

the rise through even such a distance seldom takes more than 1 1

⁄4 to 1 1⁄2 seconds,

the automatic stability of the machine would seem to be well attained.

After having adjusted the regulators, and repeatedly tested them in a number

of short flights, and at the same time having found the correct position for his

weight, all the beginner need do, after starting, is to keep as still as possible and

he will make a very creditable flight. If it be necessary to steer to the right or left,

moving the body over to that side and a little forward will accomplish the result.

For ordinary steering it is seldom necessary to do more than stick out one leg

toward the side to which you wish to turn. If you meet a very strongly ascending

trend of wind it is manifested by an increase in the weight which appears to rest

on your arms; in such a case the vertical rise may be greatly diminished by moving

2 or 3 inches forward of the normal position as long as the rise continues; it is better,

though, to simply stick the legs out in front.

Descending currents of air diminish the weight on the arms and give one the

sensation experienced in a quick-starting elevator on a down trip. So far, out of,

possibly, over 300 trials with the regulated machines, a descending current has

never brought the machine quite down but once, but even then the dropping

speed was not too great to make a comparatively easy landing possible. On the
Document 1-9(a–d) 171

other hand, the machines have been momentarily raised above their line of flight

in probably 2 flights out of every 5. And in winds above 25 miles an hour the

machines have risen above the starting point in as many as 75 per cent. of the

flights. The highest rise was probably little short of 60 feet. The most difficult

thing a beginner has to learn is how to land, i.e., when to move back on the

machine in order to check its headway; this knowledge can only be gained by

actual experiment.

Document 1-9(c), Octave Chanute, “Experiments in Flying,” 1900.

It is considerably over forty years since I first became interested in the problem

of flight. This presented the attraction of an unsolved problem which did not

seem as visionary as that of perpetual motion. Birds gave daily proof that flying

could be done, and the reasons advanced by scientists why the performance was

inaccessible to man did not seem to be entirely conclusive, if sufficiently light

motors were eventually to be obtained. There was, to be sure, a record of several

thousand years of constant failures, often resulting in personal injuries; but it did

not seem useless for engineers to investigate the causes of such failures, with a

view to a remedy. I, therefore, gathered from time to time such information as was

to be found on the subject, and added thereto such speculations as suggested

themselves. After a while this grew absorbing, and interfered with regular duties,

so that in 1874 all the accumulated material was rolled up into a bundle and red

tape tied around it, a resolution being taken that it should not be undone until

the subject could be taken up again without detriment to any duty. It was fourteen

years before the knot was untied.

Meantime a considerable change had taken place in the public attitude on the

question. It was no longer considered proof of lunacy to investigate it, and great

progress had been made in producing artificial motors approximating those of the

birds in relative lightness. The problem was, therefore, taken up again under more

favorable circumstances. A study was begun of the history of past failures, and the

endeavor was made to account for them. In point of fact, this produced a series of

technical articles which swelled into a book, and also led to the conclusion that, when

a sufficiently light motor was evolved, the principal cause of failure would be that lack

of stability in the air which rendered all man-ridden flying machines most hazardous; but that, if this difficulty were overcome, further progress would be rapid.

Experiments were, therefore, begun to investigate this question of stability

and safety, and, if possible, to render the former automatic. These experiments

were hundreds in number, and were, at first, very modest. They consisted in liberating weighted paper models of various shapes, either ancient or new, with

gravity as a motive power, and observing their glides downward. This was done in
172 Chapter 1: The Achievement of Flight

still air. After a while, resort was had to larger models, with muslin wings and

wooden frameworks, carrying bricks as passengers; and these were dropped from

the house-top in the early morning when only the milkman was about. Very much

was learned as to the effect of the wind; and then tailless kites of all sorts of shapes

were flown, to the great admiration of small boys. During the seven or eight years

within which this work was carried on, some glimmerings were obtained of the

principles involved, and some definite conclusions were reached. But it was only

after Lilienthal had shown that such an adventure was feasible that courage was

gathered to experiment with full-sized machines carrying a man through the air. 

Otto Lilienthal was a very able German engineer and physicist. He demonstrated that concave wings afforded, at very acute angles, from three to seven

times as much support as flat wings in the air. He made, from 1891 to 1896, more

than 2,000 successful glides, the longest being about 1,200 feet, upon machines

of his own design, launching himself into the air from a hilltop and gliding down

against the wind. In 1895, he endeavored to add a motor, but found that this complicated the handling so much that he went back to his gliding-device. It was

while experimenting with a double-decked machine of this character, which probably was in bad order, that he fell and was killed, in August, 1896. Thus perished

the man who will probably be credited by posterity with having pointed out the

best way to preliminary experiments in human flight through the air.

Just before this dismal accident, I had been testing a full-sized Lilienthal

machine. I discarded it as hazardous, and then tested the value of an idea of my

own. This was to follow the same general method, but to reverse the principle

upon which Lilienthal had depended for maintaining his equilibrium in the air.

He shifted the weight of his body, under immovable wings, as fast and as far as

the sustaining pressure varied under his surfaces. This shifting was mainly done

by moving the feet, as the actions required were small except when alighting. My

notion was to have the operator remain seated in the machine in the air, and to

intervene only to steer or to alight; moving mechanism being provided to shift

the wings automatically, so as to restore the balance when endangered. There are

several ways in which this can be done. Two of them have been worked out to a

probable success in my experiments, and there is still a third which I intend to test

in due course.

To make such experiments truly instructive, they should be made with a full-sized

machine and with an operator riding therein. Models seldom fly twice alike in the

open air (where there is almost always some wind), and they cannot relate the

vicissitudes which they have encountered. A flying-machine would be of little

future use if it could not operate in a moderate wind; hence the necessity for an

operator to report upon what occurs in flight, and to acquire the art of the birds.

My own operations were conducted from that point of view, with the great disad-
Document 1-9(a–d) 173

vantage, however, that being over threescore years of age, I was no longer sufficiently young and active to perform any but short and insignificant glides in such

tentative experiments; the latter being directed solely to evolving the conditions of

stability, and without any expectation of advancing to the invention of a commercial

flying-machine. I simply tested various automatic devices to secure equilibrium,

and, with great anxiety, employed young and active assistants. The best way to

carry on such adventures is first to select a soft place on which to alight. This is

well secured on a dry and loose sand-hill, and there ought to be no bushes or trees

to run into. Our party found such sand-hills, almost a desert, in which we pitched

our tent, on the shore of Lake Michigan, about thirty miles east of Chicago. The

main hill selected was ninety-five feet high; but the highest point started from was

sixty-one feet above the beach, as the best instruction was to be obtained from

short glides at low speeds.

With parties of from four to six persons, five full-sized gliding-machines (one

rebuilt) were experimented with in 1896, and one in 1897. Out of these, two types

were evolved, the “Multiple-Wing” and the “Two-Surfaced,” which are believed to

be safer than any heretofore produced, and to work out fairly well the problem of

automatic equilibrium. The photographs herewith reproduced, many of them

heretofore unpublished, are from snapshots taken of these two types. In 1896,

very few photographs were taken, all the attention being devoted to studying the

action of the machines, and the one picture shown is the sixth permutation of the

“Multiple-Wing” machine, so-called. In 1897, there was more leisure to take snap-shots,

as the machine used was a duplication of the “Two-Surfaced” of 1896, supplied

with a regulating mechanism designed by Mr. A. M. Herring, my assistant. Each

photograph was taken from a different experiment (there were about 1,000

glides); but the point of view was varied, so as to exhibit the consecutive phases of

a single flight. The frog-like appearance of some of the legs is due to the speed.

The first thing which we discovered practically was that the wind flowing up

a hillside is not a steadily flowing current like that of a river. It comes as a rolling

mass, full of tumultuous whirls and eddies, like those issuing from a chimney; and

they strike the apparatus with constantly varying force and direction, sometimes

withdrawing support when most needed. It has long been known, through instrumental observations, that the wind is constantly changing in force and direction;

but it needed the experience of an operator afloat on a gliding-machine to realize

that this all proceeded from cyclonic action; so that more was learned in this

respect in a week than had previously been acquired by several years of experiments

with models. There was a pair of eagles, living in the top of a dead tree about two

miles from our tent, that came almost daily to show us how such wind effects are

overcome and utilized. The birds swept in circles overhead on pulseless wings, and

rose high up in air. Occasionally there was a side-rocking motion, as of a ship rolling
174 Chapter 1: The Achievement of Flight

at sea, and then the birds rocked back to an even keel; but although we thought

the action was clearly automatic, and were willing to learn, our teachers were too

far off to show us just how it was done, and we had to experiment for ourselves.

The operator stands on a hill-side. He raises up the apparatus, which is steadied

by a companion, and quickly slips under and within the machine. He faces the wind.

This wind buffets the wings from side to side, and up or down, so that he has much

difficulty in obtaining a poise. This is finally accomplished by bracing the crosspiece of the machine’s frame against his back, and depressing the front edge of

the wings so that they will be struck from above by the wind. His arm-pits rest on

a pair of horizontal bars, and he grasps a pair of vertical bars with his hands. He

is in no way attached to the machine, so that he may disengage himself instantly

should anything go wrong. Then, still facing dead into the wind, he takes one or

two, never more than four, running steps forward, raising up the front edge of the

apparatus at the last moment, and the air claims him. Then he sails forward into

the wind on a generally descending course. The “Multiple-Wing” machine was

provided with a seat, but, goodness ! there was no time to sit down, as each glide

of two to three hundred feet took but eight to twelve seconds, and then it was time

to alight. The latter phase of the problem had been the subject of meditation for

months, and the conclusion had been reached to imitate the sparrow. When the

latter approaches the street, he throws his body back, tilts his outspread wings

nearly square to the course, and on the cushion of air thus encountered he stops

his speed and drops lightly to the ground. So do all birds. We tried it with misgivings,

but found it perfectly effective. The soft sand was a great advantage, and even when

the experts were racing there was not a single sprained ankle.

The rebuilt “Multiple-wings” were pivoted at their roots, and vibrated backward

and forward on ball-bearings, restrained by rubber springs. As the wind varied,

they adjusted themselves thereto, and brought back the supporting air pressure over

the operator, thus reestablishing the threatened balance. This was done automatically.

But in consequence of various defects in construction and adjustment, the operator

still had to move one or two inches, as against the from seven to fifteen inches of

movement required by the Lilienthal apparatus. Some two or three hundred

glides were made with the “Multiple-wing” without any accident to man or

machine, and the action was deemed so effective, the principle so sound, that the

full plans were published in the Aëronautical Annual for l897, for the benefit of

experimenters desiring to improve on this apparatus.

There is no more delightful sensation than that of gliding through the air. All

the faculties are on the alert, and the motion is astonishingly smooth and elastic.

The machine responds instantly to the slightest movement of the operator; the

air rushes by one’s ears; the trees and bushes flit away underneath, and the landing comes all too quickly. Skating, sliding, and bicycling are not to be compared
Document 1-9(a–d) 175

for a moment to aërial conveyance, in which, perhaps, zest is added by the spice

of danger. For it must be distinctly understood that there is constant danger in

such preliminary experiments. When this hazard has been eliminated by further

evolution, gliding will become a most popular sport.

The “Two-surfaced” machine, so-called, produced longer and more numerous

glides. There were perhaps 700 or 800, at a rate of descent of about one foot in

six; so that while the longest distance traversed was 360 feet, we could have sailed

1,200 feet, had we started from a hill 200 feet high. In consequence of the speed

gained by running, the initial stage of the flight is nearly horizontal, and it is

thrilling to see the operator pass from thirty to forty feet overhead, steering his

machine, undulating his course, and struggling with the wind gusts which whistle

through the guy wires. The automatic mechanism restores the angle of advance

when compromised by variations of the breeze; but when these come from one

side and tilt the apparatus, the weight has to be shifted to right up the machine.

This is generally done by thrusting out the feet toward the side which has been

raised, a movement which is just the reverse of what would be instinctively made

on the ground, but which becomes second nature to an expert. These gusts sometimes

raise the machine from ten to twenty feet vertically, and sometimes they strike the

apparatus from above, causing it to descend suddenly. When sailing near the

ground, these vicissitudes can be counteracted by movements of the body of three

or four inches; but this has to be done instantly, for neither wind nor gravity will

wait on meditation. At a height of 300 or 400 feet the regulating mechanism

would probably take care of these wind gusts, as it does, in fact, for their minor

variations. The speed of the machine is generally about seventeen miles an hour

over the ground, and from twenty-two to thirty miles an hour relative to the air.

Constant effort was directed to keep down the velocity, which was at times fifty-two

miles an hour. This is the purpose of the starting and gliding against the wind,

which thus furnishes an initial velocity without there being undue speed at the

landing. The highest wind we dared to experiment in blew at thirty-one miles an

hour; when the wind was stronger, we waited and watched the birds.

There was a gull came fishing over the lake, and took up his station over its

very edge, about 100 feet high in air. The wind was blowing a steady gale from the

north at sixty-one measured miles an hour. The bird breasted it squarely, and

without beat of wing maintained for five minutes his position of observation.

Occasionally there was a short rocking motion fore and aft, or from side to side. At

times he was raised several feet and drifted backward; at others he drooped down;

but he never flapped once. It is evident that he derived from the wind alone all

the power required to remain afloat and to perforate the blast without drifting

back. Whether man will ever be able to perform this feat, which has been termed

“aspiration,” is perhaps doubtful, but there is no mistake about the observation.
176 Chapter 1: The Achievement of Flight

The only thing we could not ascertain was whether our practice hill, 350 feet to

his leeward, produced an ascending trend in the wind about the bird, who was

level with its summit.

Another day a curious thing occurred. We had taken one of the machines to the

top of the hill, and loaded its lower wings with sand to hold it while we went to lunch.

A gull came strolling inland, and flapped full-winged to inspect. He swept several

circles above the machine, stretched his neck, gave a squawk, and went off. Presently

he returned with eleven other gulls, and they seemed to hold a conclave, about 100

feet above the big new white bird which they had discovered on the sand. They circled

round after round, and once in a while there was a series of loud peeps, like those of

a rusty gate, as if in conference, with sudden flutterings, as if a terrifying suggestion had been made. The bolder birds occasionally swooped downward to inspect

the monster more closely; they twisted their heads around to bring first one eye

and then the other to bear, and then they rose again. After some seven or eight

minutes of this performance, they evidently concluded either that the stranger

was too formidable to tackle, if alive, or that he was not good to eat, if dead, and

they flew off to resume fishing, for the weak point about a bird is his stomach.

We did not have the slightest accident to lament during all our experiments.

These were chiefly performed by two young, active men, who took turns, and who

became expert in a week; but then, we attempted no feats and took no chances.

Toward the last, we gained such confidence in the machines that we allowed amateurs

to try them under guidance. Half a dozen performed fairly well, but awkwardly of

course. One of them was our cook, who was by profession a surgeon, and one was

a newspaper reporter who had succeeded in finding his way to the camp. Another

was a novice; he was picked up by a wind gust, raised forty feet vertically, and gently

set down again. Any young, quick, and handy man can master a gliding-machine

almost as soon as a bicycle, but the penalties for mistakes are much more severe.

After all, it will be by the cautious, observant man—the man who accepts no risks

which he can avoid, perhaps the ultra-timid man—that this hazardous investigation

of an art now known only to the birds will be most advanced. Not even the birds

could have operated more safely than we; but they would have made longer and

flatter glides, and they would have soared up into the blue.

In my judgment, neither of the machines above described is as yet perfected,

and I believe it is still premature to apply an artificial motor. This is sure to bring

about complications which it is preferable to avoid until the equilibrium has been

thoroughly evolved. I, therefore, advise that every plausible method of securing

stability and safety shall be tested, that many such experiments shall be made,

first with models, and then with full-sized machines, and that their designers shall

practice, practice, practice; to make sure of the action, to proportion and adjust

the parts, and to eliminate hidden defects. If any feat is attempted, it should be
Document 1-9(a–d) 177

over water, in order to break the fall, should any occur. All this once accomplished,

it will be time enough to apply a motor; and it seems not improbable that the glidingmachine will furnish the prototype. This step-by-step process is doubtless slow

and costly, but it greatly diminishes the chance of those accidents which bring a

whole line of investigation into contempt. We have no reason to believe that, contrary

to past experience, a practical flying-machine will be the result of the happy

thought of one or of two persons. It will come rather by a process of evolution:

one man accomplishing some promising results, but stopping short of success; the

next carrying the investigation somewhat further, and thus on, until a machine is

produced which will be as practical as the “safety” bicycle, which took some eighty

years for its development from the original despised velocipede.

Since the above described experiments were tried, another deplorable accident

has come to re-inculcate the necessity for extreme caution. Mr. Percy S. Pilcher, a

young, accomplished, and enthusiastic English engineer, lost his life September

30, 1899, while making experiments in soaring with a machine of his own design

upon Lilienthal principle. He had already formed hundreds of glides since 1894,

and had introduced a method of towing the machine with horses, by means of a

long cord with multiplying tackle, so that he could rise from level ground. On this

occasion, a first successful flight was made; but on the second trial, after a height

of some thirty feet had been gained, a snap was heard, the tail was seen to collapse,

and the apparatus dived forward, and fell to the ground, Mr. Pilcher receiving

injuries from which he died two days later. He doubtless was the victim of his own

amiability, for his apparatus had been wet by a shower, so that the canvass of the tail

had shrunk, thus producing undue strains upon the bamboo stretcher, the wind

was gusty, and the weather very unfavorable; but as many persons had come from

a distance to witness the experiments, Mr. Pilcher did not like to disappoint them,

and accepted the undue risks which cost him his life. He was less than thirty-four

years of age, a skilful and earnest mechanician, who had already built the oilengine and screw which he meant to apply to his machine.

Notably enough, he had written to me some eighteen months before for leave

to copy and test one of my machines, which leave, with instructions, had, of

course, been gladly given. The machine had been built, and was to have been

tried on the following day. It is a curious coincidence that Lilienthal is said to have

also built a machine, quite original with him, upon the same principle as that

above alluded to, and that this also was to have been tested within a day or two of

the owner’s death. It is idle to speculate on what would have been the result; but

then accidents might have happened in my own work, and I am profoundly

thankful that we were spared such anguish.

Having been compelled, for the last two years, to give all my time and attention to a practical business, I have been unable to experiment; but I have had an
178 Chapter 1: The Achievement of Flight

expert testing models of a third method of securing automatic stability, which I

hope to experiment full-sized.

Aside from the more imaginative and eccentric inventors, there are now a

number of scientific investigators who are working to bring about the solution of

this difficult problem; and it is not at all improbable that some experimenter will

succeed, within a year or so, in making a flight of something like a mile with a

motor. This is now fairly feasible, and there are several inventors who are preparing

to attempt it. But between this achievement and its extension to a journey, or even

to its indefinite repetition, there will intervene many accidents. Nor is there a fortune to be made by the first successful man. Experimenters who wish to advance

the final solution of the quest surely and safely must work without expectation of

other reward than that of being remembered hereafter; for, in the usual course of

such things, it will be the manufacturers who will reap the pecuniary benefits

when commercial flying-machines are finally evolved. There will probably be two

types of these, one of them a machine for sport, with a very light and simple

motor, if any, carrying but a single operator, and deriving most of its power from

wind and gravity, as do the soaring birds. This will be used in competitions of skill

and speed, and there will be no finer or more exciting sport. The other future

machine will probably be of a journeying type. It will be provided with a powerful,

but light, motor and with fuel for one or two days’ travel. It will preferably carry

but a single man, and will be utilized in exploration and in war. Its speed will be

from thirty to sixty miles an hour at the beginning, and eventually much greater,

for it is a singular fact that the higher speeds require less power in the air, within

certain limits, than low speeds. At high velocities, the surfaces may be smaller, lie at

flatter angles, and offer less resistance, but the pressure then increases on the framework, and the ultimate speed may not be more than 80 or 100 miles an hour. 

Neither of these machines seems likely to compete with existing modes of

transportation. But be this as it may, every improvement in transportation,

whether in cheapness, in comfort, or in speed, soon develops new and sometimes

unexpected uses of its own; so, even with sober anticipation of the benefits to be

realized, investigators and public spirited men may well afford to advance the

solution of a problem which has so warmly appealed to the imagination of men

for the past forty or fifty centuries.
Document 1-9(a–d) 179

Document 1-9(d), Octave Chanute, excerpt from “Aerial Navigation,” 1901.

FLYING MACHINES.

Some imaginative investigators have, therefore, resumed the search, antedating

by far the invention of the balloon, for the conditions to be observed in devising

a practical flying machine in imitation of the birds. Much of past work has been

fanciful and crude, but there are now aeronautical societies and technical publications in most countries which promote sound research for both balloons and flying

machines, and an international congress on these subjects was held at Paris in

September, 1900. This congress had an elaborate programme for papers and discussions. Only abstracts of the proceedings have been published at this time of

writing, but as no great advance or discovery was announced, this paper will not

be incomplete if it merely recapitulates what was already known.

Attempts at artificial flight date back to the very dawn of history, but such

attempts have been impeded by two main obstacles so prohibitive as at times to

cause the investigation to be classed with that into the possibility of perpetual

motion. These main obstacles are, first, the extreme danger in man’s attempts to

acquire the art of the birds, or to fly with an apparatus as yet imperfect; and second,

the lack of an artificial motor as light, in proportion the power developed, as bird

machinery. We know, approximately, that the motor muscles of birds develop such

an output of energy that a full horse-power, if such were produced, would weigh

but from six to twenty pounds, while our most powerful locomotives, with their

tenders, weigh about two hundred pounds to the horse-power. This great gap has

been partly closed within the last ten years, and investigators into flying devices

are no longer regarded as visionaries. 

It was about 1889 that a number of competent men simultaneously, but independently, took up the problem. Apparently the times were ripe, and already the

advance since then has been greater than during the preceding three centuries.

Langley, in the United States, and Maxim, in Great Britain, had become convinced

that the current coefficients used for oblique air reactions were incorrect, and

began experiments of their own to ascertain the facts. They both selected plane

surfaces for trial, and reached much the same results as to the lifting power and

resistance which are to be obtained from the air at various angles of inclination

and at various speeds. These proved to be many times greater than those given

by the ancient formulæ, and these experimenters determined upon building actual

flying apparatus which should be driven by power.

Aside from the general design and the form and arrangement of the supporting

surfaces, the important elements to consider are the ratio of those surfaces to the

weight and the comparative power and speed required. There has been considerable

range in these elements in the various experiments, and these will be described
180 Chapter 1: The Achievement of Flight

so as to bring out the important points. Langley began producing working models

of flying machines in 1891. He tested various arrangements of wings and of surfaces,

and successively applied steam, gasoline, and carbonic acid gas motors, and then

steam again, struggling also with various methods of launching the apparatus

into the air. At last, in May, 1896, one of his machines made two flights of about

half a mile each in about one minute and a half, and later, in November, another

machine flew once, more than three quarters of a mile. The whole apparatus

weighed 30 pounds and spread 70 square feet of supporting surface, or in the

ratio of 2 1

⁄3 square feet to the pound. The steam-engine was of 1 horse-power and

weighed 7 pounds, thus sustaining in flight 30 pounds per horse-power, but running down very soon because the water in the boiler was exhausted. 

Maxim began on a much larger scale. He undertook the construction of a

full-sized flying machine to carry three men, spreading 4000 square feet of supporting surface, and weighing 8000 pounds, thus affording only half a square foot

to the pound. It was provided with a compound steam-engine and a boiler of 363

H. P., a marvel of ingenuity and mechanical skill. This apparatus was provided

with wheels, and was placed upon a railway of 8 feet gauge, being restrained from

premature flight by a pair of outside wooden rails placed above the wheels. Many

experiments were made to test the speed required and the lifting effect, during

which various mishaps were encountered and repaired. After several years of this

study, the machine, in 1894, unexpectedly undertook free flight, by bursting

through the upper rails during one of the tests. It flew, perhaps, 300 feet, but

steam was at once shut off, and the apparatus alighted and was broken. The damage

was repaired, but as the machine sustained only about 28 pounds per horse

power, requiring a speed of 36 miles an hour, and as it had been very costly and

other business pressed, Mr. Maxim did not resume his experiments. He is understood

to be engrossed by his great manufacturing interests in gun and shipbuilding,

some of the profits from which may hereafter be invested in another flying

machine. This will probably be provided with a petroleum motor, now being

experimented with, from which he expects even better results than from the marvelous

steam-engine previously built by him, which latter weighed, with its boiler and a

condenser, less than 10 pounds per horse-power. 

About contemporaneously with Langley and Maxim, Hargrave, in Australia,

Phillips, in Great Britain, and Tatin and Ader, in France, besides many others,

experimented with flying devices. Hargrave began in 1885, and produced about

twenty working models, propelled by clockwork, by rubber, by compressed air, and

by steam. His last steam engine weighed about 10 pounds per H. P., but he hopes

to improve upon this with a gasoline engine. He employs for his models comparatively very large surfaces, as much as 5 square feet to the pound to be lifted, a

proportion which may not be realised in full-sized machines, and hence requires
Document 1-9(a–d) 181

speeds of only 10 miles per hour, with which he has succeeded sustaining 79 pounds

to the horse-power. He has invented the new form of kite which bears his name,

and designs to suspend a motor and propeller, as well as himself, below a team of

these novel cellular arrangements, and to fly through the air by towing the kites.

Phillips has been experimenting a long while, and has reached the conclusion

that very narrow wings, somewhat like slats, are the most effective. He produced,

in 1893, a machine looking like a Venetian blind on wheels, driven by a steamengine. With this he is said to have lifted about 72 pounds to the horse-power, at

speeds of 28 miles an hour, with surfaces in the proportion of one-third of a

square foot to the pound of weight. The stability was, however, so defective that

the apparatus, which weighed 402 pounds in all, could not be trusted in free

flight, and made only brief skims. Tatin is a veteran experimenter. In 1879 he produced a flying model, driven by compressed air, with which he made many flights

and had some breakages. In 1897 he produced, in connection with Dr. Richet, a

model weighing 72 pounds, driven by a steam-engine. He obtained a lift of 55

pounds to the horsepower, with speeds of about 40 miles an hour, and surfaces of

about 1 square foot to the pound; but the maximum flight was only 460 feet, much

inferior to Langley’s, and the equilibrium was defective. He says that he believes

that he can overcome this defect, which has hitherto brought to grief every powerdriven machine which has flown more than thrice, but this remains to be seen.

Ader is a French electrical engineer who has intermittently been engaged in

aerial investigations for thirty years. He has built three full-sized machines, one,

in 1872, to be driven by manpower, which, of course, was found inadequate, one

steam-driven in 1891, at the expense of a banker, which produced indifferent

results; and a third at the expense of the French Government, in 1897, which cost

half a million francs. This was tested on the Satory field of manœuvers, with the

most rigid precautions to guard the secrets of this war engine. The construction

reproduced almost servilely the anatomical structure of birds. The surfaces were

in the proportion of one-quarter of a square foot to the pound, and the whole

apparatus weighed 1100 pounds. It was driven by a steam-engine of 40 H. P.,

weighing about 7 pounds per H. P., and was provided with screw propellers. The

speed required for support was about 50 miles an hour, and the apparatus sustained

27 pounds per H. P., or somewhat less than Maxim’s or Langley’s.

No data have been published as to the tests, but it is said that wind squalls

produced a quick descent, and that further experiments were abandoned. The

equilibrium was probably so defective that it was deemed wise by the French

Government to spend no more money on the machine. It was shown at the Paris

Exhibition last year. All experts who have seen it agree that it is a wonderful piece

of mechanical workmanship, that the motor is adequate, and that the wings are

capable of sustaining all the weight, notwithstanding all their comparative exiguity.
182 Chapter 1: The Achievement of Flight

The men above mentioned are but a tithe, perhaps a hundredth, of those who

have been planning and experimenting with power-driven flying machines, but

they are here picked out as the men who have accomplished the more notable successes. We now come upon a small group of investigators who believed that it was

premature to apply artificial power to a flying machine until the proper arrangements

and shape of the supporting surfaces were evolved, and their management in the

air worked out by long practice.

First and chief among these was Lilienthal, a German engineer and physicist.

During ten or fifteen years he made a series of elaborate experiments upon the

best shapes for artificial wings, published a book on the subject, showing the superiority of arched forms, and, about 1891, brought out his first form of gliding

machine, with which, after careful training, he was enabled to make many personal

flights from hillsides, using gravity as a motive power. He gradually improved

upon this with different machines, the last being a double-decker, weighing about

50 pounds, and carrying his own weight of I70 pounds in addition. The surface

was 151 feet square, being thus in the proportion of about three-quarters of a

square foot to the pound, and with this he made many glides, at angles of descent

of about one in six, the maximum distance being 1200 feet, and depending, of course,

upon the height from which he started. The timing of the flights showed that

about 110 pounds were sustained per horse-power, at speeds of 23 miles an hour.

In 1895 Lilienthal applied to his apparatus a carbonic acid gas motor of 2 1

⁄2 H. P.;

which was found, however, to affect the equilibrium so seriously that it was given

up. He resumed gliding, and had, altogether, made about 2000 flights, with only

trifling accidents, when, in August, 1896, he was upset in the air by a wind gust,

fell, and was killed, to the great loss of aviation, which he would, doubtless, have

advanced further.

Lilienthal was imitated by Pilcher, an English engineer, who modified the

apparatus and made hundreds of glides between 1895 and 1899. His machine

spread eighty-five hundredths of a square foot to the pound, and showed 100

pounds to be supported to the horse-power, obtained from gravity, at speeds of

25 miles an hour. He provided himself with a gasoline motor, but did not get far

enough along to apply it. Towards the last he devised a method of starting up

from level ground by towing the apparatus with horses, and in one of these experiments, in September, 1899, taking undue risks in order not to disappoint visitors,

he was upset in the air and killed.

The writer of this has emulated Lilienthal and Pilcher, and thus far without

disaster. He has confined his endeavours wholly to the evolution of automatic stability, making the supporting surfaces movable instead of the man, an arrangement

the reverse of that of his predecessors. He has had about 1000 glides made by

assistants, with two different types (five machines) without the slightest accident.
Document 1-9(a–d) 183

The proportion of surfaces was three-quarters of a square foot to the pound, the

speed, 22 miles per hour, and the weight sustained, 89 pounds per horse-power.

He has been experimenting by proxy with a third type of movable surfaces, which

be intends to test full-sized, and he holds that it is entirely premature to introduce

an artificial motor.

Full particulars concerning the last three experimenters will be found in the

“Aeronautical Annual” for 1896 and 1897.

Since these experiments a further advance has been achieved by Messrs.

Wilbur and Orville Wright, who have produced a double decked gliding machine

in which the operator is placed in a horizontal position, thus opposing to forward

motion 1 square foot, instead of 5 square feet, when he is upright, and they have

further reduced the resistance of the framing by adopting improved shapes, so

that the aggregate head resistances are reduced to about one-half of those which

previously obtained. The experiments were made on the North Carolina coast, in

the United States, in October, 1900.

The above is the record of what has been accomplished within the last decade in

an investigation heretofore relegated to what had been termed “cranks.” While a journey of 1200 miles has been made with a globular balloon, at the will of the wind, trips

of only 5 or 6 miles have been made at the will of the operator, in calm weather, with

fusiform balloons. With flying machines a maximum flight of three-quarters of a mile

has been made by a model provided with a motor, and thousands of glides, up to 1200

feet, have been made by men-ridden machines with the aid of gravity, which latter

power imposes no extra weight upon the apparatus and is always in good order.

The maximum speed of the dirigible balloon thus far is about 18 miles an hour,

with eventual possibilities up to 44 miles per hour, while the speed of flying machines

has already been about 50 miles an hour, with possibilities to 60 or 100 miles an hour,

which speeds are attained by some swift birds. While fusiform balloons will, therefore,

constitute one solution, and while they will be gradually improved and will serve in

war, and perhaps in exploration, it now seems probable that future developments

will chiefly appertain to flying machines. To make these a success the two main

problems must be worked out; first, the motor, which must be very light, and, second,

the stability, which is even more important, and which should be automatic.

To appreciate the difficulties appertaining to the motor, we may consider the difference in amount of power required for land and for aerial transportation. An

American “Consolidation” locomotive will develop about 1000 H. P. and haul 2000

tons upon a level railway. Hence, it will haul 4000 pounds per horse-power. But this

1000 H. P., weighing, say, 100 tons with its tender, could impart a speed of only 57

miles an hour to Count Zeppelin’s air ship, were this vessel (a manifest absurdity) able

to lift the engine and to bear the resulting air pressure due to the speed. Neither could

the locomotive sustain itself in the air if attached to a weightless flying machine.
184 Chapter 1: The Achievement of Flight

We have seen that, with motor-driven apparatus, the best that has been positively done thus far has been to sustain from 27 to 55 pounds per horse-power by

impact upon the air. Gliding machines, it is true, using gravity as a motive power,

show 89 to 110 pounds sustained per horse-power, but these figures must be considerably reduced when an artificial motor is substituted, in order to cover the

inevitable mechanical losses in the machinery and in the propeller. Much has

been done within the past decade towards reducing the weight of motors. Steamengines have been produced weighing but 10 pounds per horse-power, and the

latest gasoline motor, that of Buchet, is said to weigh only 12 1

⁄2 per H. P.; but

much remains to be done to render machines working so nearly up to the limit

of endurance absolutely reliable and safe in the air. Numerous and costly experiments are required to accomplish this. It now seems probable that the successful

aerial motor will be some form of gasoline engine, using air instead of water as a

working fluid, and thus saving weight. But those who know how tedious and slow

has been the development of the steam-engine will have no very sanguine expectations of the early attaining of perfection in the gasoline motor.

It is still more imperative that the whole apparatus shall not fall by losing its

balance in the air. It must maintain its equilibrium and be reasonable safe under

all the vicissitudes of flight,—in starting, in sailing, in alighting, and in wind

gusts. The bare statement of this requirement meets with ready assent, and yet

how few of the investigators have the will or the patience to spend the time, and

to take the risk, to learn the art of the birds by personal experiments with gliding

machines. The writer has been advocating this method for some years, he has

confined his researches to its advance, and he sees no reason to change his views.

The underlying principle of maintaining equilibrium in the air is that the

centre of pressure upon the sustaining surfaces shall at all times be upon the same

vertical line as the centre of gravity due to the weight of the apparatus. In calm

air this is fairly secured, but in a wind the centre of pressure is constantly shifted

by the turmoils of the air, for it advances or recedes with the diminution or

increase of the angle of incidence. There are several ways of counteracting this

difficulty. The centre of gravity may be shifted back or forward to coincide again

with the vertical line passing through the new centre of pressure; this is the

method employed by Lilienthal and by Pilcher, which they applied by shifting the

position of their personal weight. Or the centre of pressure may be brought back

into a vertical line with a fixed centre of gravity, either by changing the angle of

incidence, or by shifting the surfaces themselves. These latter are the methods

which have been experimented upon by the writer in three different ways:— 

1st. Affixing a horizontal tail (the Pénaud tail) at an angle to the supporting

surfaces. This catches the air on its upper or lower surface, and shifts the angle of

incidence of the wings, and, consequently, the centre of pressure.
Document 1-9(a–d) 185

2d. Pivoting the wings at their roots, so as to move horizontally. These are

arranged so that the impact of the air shall bring them back into the proper position.

3d. Pivoting the surfaces so as to rock vertically. This is arranged so that the

impinging air shall automatically shift the angle of incidence, and, therefore, the

centre of pressure.

The third arrangement is believed to be the best, but one cannot be sure,

inasmuch as all the adjustments above indicated are most delicate. Simple as the

principles seem to be, it requires years of experiment to apply them properly. The

positions of the pivots, the strength and adjustments of restraining springs, and

the best position for the centre of gravity involve thousands of cut-and-try experiments, first with models, and then with full-sized gliding machines carrying a

man. The important feature is that the man shall remain stationary.

In regard to the shape of surfaces to be employed, Lilienthal demonstrated that

concavo-convex wings, like those of birds, are far superior in supporting power to

planes, and the latter have now been practically abandoned by aviation experts. The

amount of sustaining surfaces experimented with has varied, as above mentioned,

from 1/4 square foot to 5 square feet to the pound of weight, this corresponding to

speeds of from 50 miles down to 10 miles an hour, to obtain support. The amount

required evidently depends upon the speed, but the larger the surfaces the greater

is the weight. In the remote future it is probable that small surfaces will obtain, thus

reducing the amount of required framework and the consequent head resistance, but

until the problem of equilibrium has been fully solved it will be preferable to employ

surfaces of about 1 square foot to the pound, involving speeds of 20 to 25 miles an

hour in order to promote safety in alighting. With smaller surfaces we may hope

to sustain eventually as much as 80 pounds per indicated horse-power, but something

will depend upon the efficiency of the propeller.

The propeller is the next thing to be considered after the equilibrium has

been secured and a reliable motor worked out. Both Hargrave and Lilienthal gave

preference to flapping vanes over the screw propeller, but other experimenters

prefer screws. It is yet too soon to draw definite conclusions on this question, and

it opens a field for further experimenting.

We can, however, already calculate approximately the proportions, the strength

and weight, the supporting efficiency, the speed, and the power required for a

projected flying machine, so as to judge of the practicability of a design. Indeed, the

mathematics of the subject have been so far evolved that engineering computations

may eventually replace vague speculation in the domain of aerial navigation.

But after the problem has been worked out to a mechanical success, the commercial uses of aerial apparatus will be small. The limitations of the balloon have

already been mentioned; such craft will be slow, frail, and very costly. We are now

sufficiently advanced in the design of flying machines to perceive some of their
186 Chapter 1: The Achievement of Flight

limitations. They will be comparatively small and cranky, require much power,

carry little extra weight, and depend for their effective speed, on each journey,

whether they go against the wind or with it, so that they cannot compete with

existing modes of transportation in cheapness or in carrying capacity. It is true

that high speeds may be attained, and this may serve in war, in exploration, perhaps

in mail transportation, and in sport; but the loads will be very small, and the

expenses will be great. But flying machines will develop new uses of their own;

and as mankind has always been benefited by the introduction of new and faster

modes of transportation, we may hope that successful aerial navigation will

spread civilization, knit the nations closer together, make all regions accessible,

and perhaps so equalize the hazards of war as to abolish it altogether, thus bringing

about the predicted era of universal peace and good-will.
Document 1-10(a–c) 187

Document 1-10(a–c)

(a) Orville Wright, excerpt from deposition of 

13 January 1920, The Papers of Wilbur and Orville Wright, 

Marvin W. McFarland, ed. (New York, NY: 

McGraw-Hill Book Company, 1953), p. 3.

(b) Wilbur Wright, letter to the 

Smithsonian Institution, 30 May 1899, 

The Papers of Wilbur and Orville Wright, pp. 4–5.

(c) Wilbur Wright, letter to Octave Chanute, 13 May 1900, 

The Papers of Wilbur and Orville Wright, pp. 15–19.

The first document includes a response by Orville Wright, on 13 January 1920,

to the question, “When and under what circumstances did you and Wilbur Wright

first become interested in the problem of flight?” His brief statement sets up the

two letters that follow with comments on how the Wrights were interested in flight

even as children and how as young adults they began to tackle the problems of

heavier-than-air flight, by first writing to the Smithsonian Institution for information. 

The second and third documents are two letters written by Wilbur Wright that

express his and his brother’s early interest and commitment to flight research.

The first of these letters was written in 1899 to the Smithsonian Institution, where

Professor Langley was working, to request articles on aeronautics. In response to

it, Richard Rathbun, the Assistant Secretary of the Smithsonian Institute, sent the

Wrights four pamphlets: Empire of the Air (1893) by Louis-Pierre Mouillard; The

Problem of Flying and Practical Experiments in Soaring (1893) by Otto Lilienthal; Story

of Experiments in Mechanical Flight (1897) by Samuel P. Langley; and On Soaring

Flight (1897) by E.C. Huffaker. Rathbun’s letter of response also referred the

Wrights to a list of other works, including Progress in Flying Machines (1894) by

Octave Chanute and Experiments in Aerodynamics (1891) by Samuel P. Langley,

along with the 1895, 1896, and 1897 issues of The Aeronautical Annual. The second was a 1900 letter to Octave Chanute. The search for an appropriate location

to test their designs mentioned in the letter to Chanute led the Wrights to the

Outer Banks of North Carolina and the winds of Kitty Hawk. 
188 Chapter 1: The Achievement of Flight

Document 1-10(a), Orville Wright on the brothers’ interest in flight, 1920.

Our first interest began when we were children. Father brought home to us a

small toy actuated by a rubber spring which would lift itself into the air. We built a

number of copies of this toy, which flew successfully. By “we” I refer to my brother

Wilbur and myself. But when we undertook to build the toy on a much larger scale

it failed to work so well. The reason for this was not understood by us at the time, so

we finally abandoned the experiments. In 1896 we read in the daily papers, or in some

of the magazines, of the experiments of Otto Lilienthal, who was making some

gliding flights from the top of a small hill in Germany. His death a few months

later while making a glide off the hill increased our interest in the subject, and we

began looking for books pertaining to flight. We found a work written by

Professor Marey on animal mechanism which treated of the bird mechanism as

applied to flight, but other than this, so far as I can remember, we found little. 

In the spring of the year 1899 our interest in the subject was again aroused

through the reading of a book on ornithology. We could not understand that

there was anything about a bird that would enable it to fly that could not be built

on a larger scale and used by man. At this time our thought pertained more particularly to gliding flight and soaring. If the bird’s wings would sustain it in the

air without the use of any muscular effort, we did not see why man could not be

sustained by the same means. We knew that the Smithsonian Institution had been

interested in some work on the problem of flight, and, accordingly, on the 30th

of May 1899, my brother Wilbur wrote a letter to the Smithsonian inquiring about

publications on the subject. . . .

Document 1-10(b), letter by Wilbur Wright to the 

Smithsonian Institution from Dayton, Ohio, 30 May 1899.

I have been interested in the problem of mechanical and human flight ever

since as a boy I constructed a number of bats of various sizes after the style of

Cayley’s and Pénaud’s machines. My observations since have only convinced me

more firmly that human flight is possible and practicable. It is only a question of

knowledge and skill just as in all acrobatic feats. Birds are the most perfectly

trained gymnasts in the world and are specially well fitted for their work, and it

may be that man will never equal them, but no one who has watched a bird chasing an insect or another bird can doubt that feats are performed which require

three or four times the effort required in ordinary flight. I believe that simple

flight at least is possible to man and that the experiments and investigations of a

large number of independent workers will result in the accumulation of information and knowledge and skill which will finally lead to accomplished flight.
Document 1-10(a–c) 189

The works on the subject to which I have had access are Marey’s and

Jamieson’s books published by Appleton’s and various magazine and cyclopaedic

articles. I am about to begin a systematic study of the subject in preparation for

practical work to which I expect to devote what time I can spare from my regular

business. I wish to obtain such papers as the Smithsonian Institution has published on this subject, and if possible a list of other works in print in the English

language. I am an enthusiast, but not a crank in the sense that I have some pet

theories as to the proper construction of a flying machine. I wish to avail myself

of all that is already known and then if possible add my mite to help on the future

worker who will attain final success. I do not know the terms on which you send

out your publications but if you will inform me of the cost I will remit the price.

Document 1-10(c), letter from Wilbur Wright to Octave Chanute, 13 May 1900.

For some years I have been afflicted with the belief that flight is possible to

man. My disease has increased in severity and I feel that it will soon cost me an

increased amount of money if not my life. I have been trying to arrange my affairs

in such a way that I can devote my entire time for a few months to experiment in

this field.

My general ideas of the subject are similar to those held by most practical

experimenters, to wit: that what is chiefly needed is skill rather than machinery.

The flight of the buzzard and similar sailers is a convincing demonstration of the

value of skill, and the partial needlessness of motors. It is possible to fly without

motors, but not without knowledge & skill. This I conceive to be fortunate, for

man, by reason of his greater intellect, can more reasonably hope to equal birds

in knowledge, than to equal nature in the perfection of her machinery.

Assuming then that Lilienthal was correct in his ideas of the principles on

which man should proceed, I conceive that his failure was due chiefly to the inadequacy of his method, and of his apparatus. As to his method, the fact that in five

years time he spent only about five hours, altogether, in actual flight is sufficient

to show that his method was inadequate. Even the simplest intellectual or acrobatic feats could never be learned with so short practice, and even Methuselah

could never have become an expert stenographer with one hour per year for

practice. I also conceive Lilienthal’s apparatus to be inadequate not only from the

fact that he failed, but my observations of the flight of birds convince me that

birds use more positive and energetic methods of regaining equilibrium than that

of shifting the center of gravity.

With this general statement of my principles and belief I will proceed to

describe the plan and apparatus it is my intention to test. In explaining these, my

object is to learn to what extent similar plans have been tested and found to be
190 Chapter 1: The Achievement of Flight

failures, and also to obtain such suggestions as your great knowledge and experience might enable you to give me. I make no secret of my plans for the reason

that I believe no financial profit will accrue to the inventor of the first flying

machine, and that only those who are willing to give as well as to receive suggestions can hope to link their names with the honor of its discovery. The problem

is too great for one man alone and unaided to solve in secret.

My plan then is this. I shall in a suitable locality erect a light tower about one

hundred and fifty feet high. A rope passing over a pulley at the top will serve as

a sort of kite string. It will be so counterbalanced that when the rope is drawn out

one hundred & fifty feet it will sustain a pull equal to the weight of the operator

and apparatus or nearly so. The wind will blow the machine out from the base of

the tower and the weight will be sustained partly by the upward pull of the rope

and partly by the lift of the wind. The counterbalance will be so arranged that the

pull decreases as the line becomes shorter and ceases entirely when its length has

been decreased to one hundred feet. The aim will be to eventually practice in a

wind capable of sustaining the operator at a height equal to the top of the tower.

The pull of the rope will take the place of a motor in counteracting drift. I see, of

course, that the pull of the rope will introduce complications which are not met

in free flight, but if the plan will only enable me to remain in the air for practice

by the hour instead of by the second, I hope to acquire skill sufficient to overcome

both these difficulties and those inherent to flight. Knowledge and skill in handling the machine are absolute essentials to flight and it is impossible to obtain

them without extensive practice. The method employed by Mr. Pilcher of towing

with horses in many respects is better than that I propose to employ, but offers no

guarantee that the experimenter will escape accident long enough to acquire skill

sufficient to prevent accident. In my plan I rely on the rope and counterbalance

to at least break the force of a fall. My observation of the flight of buzzards leads

me to believe that they regain their lateral balance, when partly overturned by a

gust of wind, by a torsion of the tips of the wings. If the rear edge of the right

wing tip is twisted upward and the left downward the bird becomes an animated

windmill and instantly begins to turn, a line from its head to its tail being the axis.

It thus regains its level even if thrown on its beam ends, so to speak, as I have frequently seen them. I think the bird also in general retains its lateral equilibrium,

partly by presenting its two wings at different angles to the wind, and partly by

drawing in one wing, thus reducing its area. I incline to the belief that the first is

the more important and usual method. In the apparatus I intend to employ I

make use of the torsion principle. In appearance it is very similar to the “double-deck”

machine with which the experiments of yourself and Mr. Herring were conducted

in 1896-7. The point on which it differs in principle is that the cross-stays which

prevent the upper plane from moving forward and backward are removed, and
Document 1-10(a–c) 191

each end of the upper plane is independently moved forward or backward with

respect to the lower plane by a suitable lever or other arrangement. By this plan

the whole upper plane may be moved forward or backward, to attain longitudinal

equilibrium, by moving both hands forward or backward together. Lateral equilibrium is gained by moving one end more than the other or by moving them in

opposite directions. If you will make a square cardboard tube two inches in diameter

and eight or ten long and choose two sides for your planes you will at once see the

torsional effect of moving one end of the upper plane forward and the other backward,

and how this effect is attained without sacrificing lateral stiffness. My plan is to

attach the tail rigidly to the rear upright stays which connect the planes, the effect

of which will be that when the upper plane is thrown forward the end of the tail is

elevated, so that the tail assists gravity in restoring longitudinal balance. My

experiments hitherto with this apparatus have been confined to machines spreading

about fifteen square feet of surface, and have been sufficiently encouraging to

induce me to lay plans for a trial with [a] full-sized machine.

My business requires that my experimental work be confined to the months

between September and January and I would be particularly thankful for advice as

to a suitable locality where I could depend on winds of about fifteen miles per hour

without rain or too inclement weather. I am certain that such localities are rare.

I have your Progress in Flying Machines and your articles in the Annuals of ’95,

’96, & ’97, as also your recent articles in the Independent. If you can give me information as to where an account of Pilcher’s experiments can be obtained I would

greatly appreciate your kindness.
192 Chapter 1: The Achievement of Flight

Document 1-11(a–b)

(a) Wilbur Wright, letter to Bishop Milton Wright from 

Kitty Hawk, North Carolina, 23 September 1900, 

The Papers of Wilbur and Orville Wright, pp. 25–27.

(b) Wilbur Wright, “Some Aeronautical Experiments,” 

lecture delivered at the meeting of the Western Society 

of Engineers, Chicago, Illinois, 18 September 1901, 

The Papers of Wilbur and Orville Wright, pp. 99–118.

The following two documents by Wilbur Wright present different perspectives

on the Wright brothers’ first gliding experiments at Kitty Hawk, North Carolina.

The first is an excerpt from a letter written to his father at the beginning of their

first season of flight tests there in 1900. The second is a lecture given in Chicago

before the Western Society of Engineers after the conclusion of their second season

in 1901. Preceding Wilbur Wright’s lecture was an introduction by Octave

Chanute, who hosted Wilbur during his stay in Chicago. 

Chanute played a critical role in boosting the morale of the Wrights, especially

Wilbur’s declining confidence, after the many frustrations and disappointments

of their 1900 and 1901 gliding seasons at Kitty Hawk. While a guest in Chanute’s

home (which was “cluttered up” with “models of flying machines suspended from

the ceiling so thick that you could not see any ceiling at all”), Wilbur had long

talks with the veteran engineer, many of them about the merits of Lilienthal’s airfoil data. In his Chicago speech, Wilbur had not questioned the validity of any of

Lilienthal’s data, but he would start doing so soon thereafter, a change of mind

reflected in how he edited his speech for subsequent publication. When he

returned to Dayton, Wilbur poured over all available data with his brother Orville,

including the poor performance of their own wings. They determined that they

would need to start over from scratch, building from an experimental research

program of their own. This decision led them to construct a makeshift wind tunnel

in which they systematically tested a whole new range of airfoil shapes, some 200

of them. From this test program they attained the aerodynamic data they needed

to design their highly successful glider of 1902 and the historic 1903 Flyer that

resulted from it.
Document 1-11(a–b) 193

Document 1-11(a), letter from Wilbur Wright to Milton Wright, 23 September 1900.

I have my machine nearly finished. It is not to have a motor and is not expected to fly in any true sense of the word. My idea is merely to experiment and practice with a view to solving the problem of equilibrium. I have plans which I hope

to find much in advance of the methods tried by previous experimenters. When

once a machine is under proper control under all conditions, the motor problem

will be quickly solved. A failure of motor will then mean simply a slow descent &

safe landing instead of a disastrous fall. In my experiments I do not expect to rise

many feet from the ground, and in case I am upset there is nothing but soft sand

to strike on. I do not intend to take dangerous chances, both because I have no

wish to get hurt and because a fall would stop my experimenting, which I would

not like at all. The man who wishes to keep at the problem long enough to really

learn anything positively must not take dangerous risks. Carelessness and overconfidence are usually more dangerous than deliberately accepted risks. I am constructing my machine to sustain about five times my weight and am testing every

piece. I think there is no possible chance of its breaking while in the air. If it is

broken it will be by awkward landing. My machine will be trussed like a bridge and

will be much stronger than that of Lilienthal, which, by the way, was upset through

the failure of a movable tail and not by breakage of the machine. The tail of my

machine is fixed, and even if my steering arrangement should fail, it would still

leave me with the same control that Lilienthal had at the best. The safe and secure

construction & management are my main improvements. My machine is more

simple in construction and at the same time capable of greater adjustment and

control than previous machines.

I have not taken up the problem with the expectation of financial profit.

Neither do I have any strong expectation of achieving the solution at the present

time or possibly any time. My trip would be no great disappointment if I accomplish practically nothing. I look upon it as a pleasure trip pure and simple, and I

know of no trip from which I could expect greater pleasure at the same cost. I am

watching my health very closely and expect to return home heavier and stronger

than I left. I am taking every precaution about my drinking water.

Document 1-11(b), Wilbur Wright, “Some Aeronautical Experiments,”

Chicago, 18 September 1901.

The difficulties which obstruct the pathway to success in flying machine construction are of three general classes: (1) Those which relate to the construction

of the sustaining wings. (2) Those which relate to the generation and application

of the power required to drive the machine through the air. (3) Those relating to
194 Chapter 1: The Achievement of Flight

the balancing and steering of the machine after it is actually in flight. Of these

difficulties two are already to a certain extent solved. Men already know how to

construct wings or aeroplanes, which when driven through the air at sufficient

speed, will not only sustain the weight of the wings themselves, but also that of

the engine, and of the engineer as well. Men also know how to build engines and

screws of sufficient lightness and power to drive these planes at sustaining speed.

As long ago as 1893 a machine weighing 8,000 lbs. demonstrated its power both

to lift itself from the ground and to maintain a speed of from thirty to forty miles

per hour; but it came to grief in an accidental free flight, owing to the inability of

the operators to balance and steer it properly. This inability to balance and steer

still confronts students of the flying problem, although nearly ten years have

passed. When this one feature has been worked out the age of flying machines will

have arrived, for all other difficulties are of minor importance.

The person who merely watches the flight of a bird gathers the impression

that the bird has nothing to think of but the flapping of its wings. As a matter of

fact this is a very small part of its mental labor. To even mention all the things the

bird must constantly keep in mind in order to fly securely through the air would

take a considerable part of the evening. If I take this piece of paper, and after

placing it parallel with the ground, quickly let it fall, it will not settle steadily down

as a staid, sensible piece of paper ought to do, but it insists on contravening every

recognized rule of decorum, turning over and darting hither and thither in the

most erratic manner, much after the style of an untrained horse. Yet this is the

style of steed that men must learn to manage before flying can become an everyday sport. The bird has learned this art of equilibrium, and learned it so thoroughly that its skill is not apparent to our sight. We only learn to appreciate it

when we try to imitate it. Now, there are two ways of learning how to ride a fractious horse: one is to get on him and learn by actual practice how each motion

and trick may be best met; the other is to sit on a fence and watch the beast a

while, and then retire to the house and at leisure figure out the best way of overcoming his jumps and kicks. The latter system is the safest; but the former, on the

whole, turns out the larger proportion of good riders. It is very much the same in

learning to ride a flying machine; if you are looking for perfect safety, you will do

well to sit on a fence and watch the birds; but if you really wish to learn, you must

mount a machine and become acquainted with its tricks by actual trial.

Herr Otto Lilienthal seems to have been the first man who really comprehended that balancing was the first instead of the last of the great problems in connection with human flight. He began where others left off, and thus saved the

many thousands of dollars that it had theretofore been customary to spend in

building and fitting expensive engines to machines which were uncontrollable

when tried. He built a pair of wings of a size suitable to sustain his own weight,
Document 1-11(a–b) 195

and made use of gravity as his motor. This motor not only cost him nothing to

begin with, but it required no expensive fuel while in operation, and never had to

be sent to the shop for repairs. It had one serious drawback, however, in that it

always insisted on fixing the conditions under which it would work. These were

that the man should first betake himself and machine to the top of a hill and fly

with a downward as well as a forward motion. Unless these conditions were complied with, gravity served no better than a balky horse—it would not work at all.

Although Lilienthal must have thought the conditions were rather hard, he nevertheless accepted them till something better should turn up; and in this manner

he made some two thousand flights, in a few cases landing at a point more than

a thousand feet distant from his place of starting. Other men, no doubt, long

before had thought of trying such a plan. Lilienthal not only thought, but acted;

and in so doing probably made the greatest contribution to the solution of the flying

problem that has ever been made by any one man. He demonstrated the feasibility of actual practice in the air, without which success is impossible. Herr Lilienthal

was followed by Mr. Pilcher, a young English engineer, and by Mr. Chanute, a distinguished member of the society I now address. A few others have built

machines, but nearly all that is of real value is due to the experiments conducted

under the direction of the three men just mentioned.

The balancing of a gliding or flying machine is very simple in theory. It merely

consists in causing the center of pressure to coincide with the center of gravity. But

in actual practice there seems to be an almost boundless incompatibility of temper

which prevents their remaining peaceably together for a single instant, so that the

operator, who in this case acts as peacemaker, often suffers injury to himself while

attempting to bring them together. If a wind strikes a vertical plane, the pressure

on that part to one side of the center will exactly balance that on the other side,

and the part above the center will balance that below. This point we call the center

of pressure. But if the plane be slightly inclined, the pressure on the part nearest

the wind is increased, and the pressure on the other part decreased, so that the

center of pressure is now located, not in the center of the surface, but a little

toward the side which is in advance. If the plane be still further inclined the center

of pressure will move still farther forward. And if the wind blow a little to one side,

it will also move over as if to meet it. Now, since neither the wind nor the machine

for even an instant maintains exactly the same direction and velocity, it is evident

that the man who would trace the course of the center of pressure must be very

quick of mind; and he who would attempt to move his body to that spot at every

change must be very active indeed. Yet this is what Herr Lilienthal attempted to do,

and did do with most remarkable skill, as his two thousand glides sufficiently attest.

However he did not escape being overturned by wind gusts several times, and

finally lost his life through a breakage of his machine, due to defective construction.
196 Chapter 1: The Achievement of Flight

The Pilcher machine was similar to that of Lilienthal, and like it, seems to have

been structurally weak; for on one occasion, while exhibiting the flight of his

machine to several members of the Aeronautical Society of Great Britain, it suddenly collapsed and fell to the ground, causing injuries to the operator which

proved sadly fatal. The method of management of this machine differed in no

important respect from that of Lilienthal, the operator shifting his body to make

the centers of pressure and gravity coincide. Although the fatalities which befell

the designers of these machines were due to the lack of structural strength, rather

than to lack of control, nevertheless it had become clear to the students of the

problem that a more perfect method of control must be evolved. The Chanute

machines marked a great advance in both respects. In the multiple-wing machine,

the tips folded slightly backward under the pressure of wind gusts, so that the

travel of the center of pressure was thus largely counterbalanced. The guiding of

the machine was done by a slight movement of the operator’s body toward the

direction in which it was desired that the machine should go. The double-deck

machine built and tried at the same time marked a very great structural advance,

as it was the first in which the principles of the modern truss bridges were fully

applied to flying machine construction. This machine in addition to its greatly

improved construction and general design of parts also differed from the

machine of Lilienthal in the operation of its tail. In the Lilienthal machine the

tail, instead of being fixed in one position, was prevented by a stop from folding

downward beyond a certain point, but was free to fold upward without any hindrance. In the Chanute machine the tail was at first rigid, but afterward, at the

suggestion of Mr. Herring, it was held in place by a spring that allowed it to move

slightly either upward or downward with reference to its normal position, thus

modifying the action of the wind gusts upon it, very much to its advantage. The

guiding of the machine was effected by slight movements of the operator’s body,

as in the multiple-wing machines. Both these machines were much more manageable than the Lilienthal type, and their structural strength, notwithstanding their

extreme lightness, was such that no fatalities, or even accidents, marked the glides

made with them, although winds were successfully encountered much greater in

violence than any which previous experimenters had dared to attempt.

My own active interest in aeronautical problems dates back to the death of

Lilienthal in 1896. The brief notice of his death which appeared in the telegraphic

news at that time aroused a passive interest which had existed from my childhood,

and led me to take down from the shelves of our home library a book on Animal

Mechanism by Prof. Marey, which I had already read several times. From this I was

led to read more modern works, and as my brother soon became equally interested

with myself, we soon passed from the reading to the thinking, and finally to the

working stage. It seemed to us that the main reason why the problem had
Document 1-11(a–b) 197

remained so long unsolved was that no one had been able to obtain any adequate

practice. We figured that Lilienthal in five years of time had spent only about five

hours in actual gliding through the air. The wonder was not that he had done so

little, but that he had accomplished so much. It would not be considered at all safe

for a bicycle rider to attempt to ride through a crowded city street after only five

hours’ practice, spread out in bits of ten seconds each over a period of five years;

yet Lilienthal with this brief practice was remarkably successful in meeting the

fluctuations and eddies of wind gusts. We thought that if some method could be

found by which it would be possible to practice by the hour instead of by the second,

there would be hope of advancing the solution of a very difficult problem. It

seemed feasible to do this by building a machine which would be sustained at a

speed of 18 miles per hour, and then finding a locality where winds of this velocity

were common. With these conditions, a rope attached to the machine to keep it

from floating backward would answer very nearly the same purpose as a propeller

driven by a motor, and it would be possible to practice by the hour, and without

any serious danger, as it would not be necessary to rise far from the ground, and

the machine would not have any forward motion at all. We found, according to

the accepted tables of air pressures on curved surfaces that a machine spreading

200 square feet of wing surface would be sufficient for our purpose, and that

places could easily be found along the Atlantic coast where winds of 16 to 25 miles

were not at all uncommon. When the winds were low, it was our plan to glide from

the tops of sand hills, and when they were sufficiently strong, to use a rope for our

motor and fly over one spot. Our next work was to draw up the plans for a suitable machine. After much study we finally concluded that tails were a source of

trouble rather than of assistance; and therefore we decided to dispense with them

altogether. It seemed reasonable that if the body of the operator could be placed

in a horizontal position instead of the upright, as in the machines of Lilienthal,

Pilcher and Chanute, the wind resistance could be very materially reduced since

only one square foot instead of five would be exposed. As a full half horsepower

could be saved by this change, we arranged to try at least the horizontal position.

Then the method of control used by Lilienthal, which consisted in shifting the

body, did not seem quite as quick or effective as the case required; so, after long

study, we contrived a system consisting of two large surfaces on the Chanute doubledeck plan, and a smaller surface placed a short distance in front of the main surfaces in such a position that the action of the wind upon it would counterbalance

the effect of the travel of the center of pressure on the main surfaces. Thus

changes in the direction and velocity of the wind would have little disturbing

effect, and the operator would be required to attend only to the steering of the

machine, which was to be affected by curving the forward surface up or down. The

lateral equilibrium and the steering to right or left was to be attained by a pecu-
198 Chapter 1: The Achievement of Flight

liar torsion of the main surfaces, which was equivalent to presenting one end of

the wings at a greater angle than the other. In the main frame a few changes were

also made in the details of construction and trussing employed by Mr. Chanute.

The most important of these were: (1) the moving of the forward main cross-piece

of the frame to the extreme front edge; (2) the encasing in the cloth of all crosspieces and ribs of the surfaces; (3) a rearrangement of the wires used in trussing

the two surfaces together, which rendered it possible to tighten all the wires by

simply shortening two of them.

With these plans we proceeded in the summer of 1900 to Kitty Hawk, North

Carolina, a little settlement located on the strip of land that separates Albemarle

Sound from the Atlantic Ocean. Owing to the impossibility of obtaining suitable

material for a 200 square-foot machine, we were compelled to make it only 165

square feet in area, which, according to the Lilienthal tables, would be supported

at an angle of three degrees in a wind of about 21 miles per hour. On the very day

that the machine was completed the wind blew from 25 to 30 miles per hour, and

we took it out for trial as a kite. We found that while it was supported with a man

on it in a wind of about 25 miles, its angle was much nearer twenty degrees than

three degrees. Even in gusts of 30 miles the angles of incidence did not get as low

as three degrees, although the wind at this speed has more than twice the lifting

power of a 21-mile wind. As winds of 30 miles per hour are not plentiful on clear

days, it was at once evident that our plan of practicing by the hour, day after day,

would have to be postponed. Our system of twisting the surfaces to regulate the

lateral balance was tried and found to be much more effective than shifting the

operator’s body. On subsequent days, when the wind was too light to support the

machine with a man on it, we tested it as a kite, working the rudders by cords

reaching to the ground. The results were very satisfactory, yet we were well aware

that this method of testing is never wholly convincing until the results are confirmed by actual gliding experience.

We then turned our attention to making a series of actual measurements of

the lift and drift of the machine under various loads. So far as we were aware this

had never previously been done with any full-size machine. The results obtained

were most astonishing, for it appeared that the total horizontal pull of the

machine, while sustaining a weight of 52 pounds, was only 8.5 lbs., which was less

than had previously been estimated for head resistance of the framing alone.

Making allowance for the weight carried, it appeared that the head resistance of

the framing was but little more than 50 percent of the amount which Mr. Chanute

had estimated as the head resistance of the framing of his machine. On the other

hand it appeared sadly deficient in lifting power as compared with the calculated

lift of curved surfaces of its size. This deficiency we supposed might be due to one

or more of the following causes: (1) That the depth of the curvature of our sur-
Document 1-11(a–b) 199

faces was insufficient, being only about 1 in 22, instead of 1 in 12. (2) That the

cloth used in our wings was not sufficiently airtight. (3) That the Lilienthal tables

might themselves be somewhat in error. We decided to arrange our machine for

the following year so that the depth of curvature of its surfaces could be varied at

will, and its covering airproofed.

Our attention was next turned to gliding, but no hill suitable for the purpose

could be found near our camp at Kitty Hawk. This compelled us to take the

machine to a point 4 miles south, where the Kill Devil sand hill rises from the flat

sand to a height of more than 100 feet. Its main slope is toward the northeast, and

has an inclination of 10 degrees. On the day of our arrival the wind blew about

25 miles an hour, and as we had had no experience at all in gliding, we deemed

it unsafe to attempt to leave the ground. But on the day following, the wind having subsided to 14 miles per hour, we made about a dozen glides. It had been the

original intention that the operator should run with the machine to obtain initial

velocity, and assume the horizontal position only after the machine was in free

flight. When it came time to land he was to resume the upright position and light

on his feet, after the style of previous gliding experimenters. But on actual trial

we found it much better to employ the help of two assistants in starting, which the

peculiar form of our machine enabled us readily to do; and in landing we found

that it was entirely practicable to land while still reclining in a horizontal position

upon the machine. Although the landings were made while moving at speeds of

more than 20 miles an hour, neither machine nor operator suffered any injury.

The slope of the hill was 9.5 deg., or a drop of 1 foot in 6. We found that after

attaining a speed of about 25 or 30 miles with reference to the wind, or 10 to 15

miles over the ground, the machine not only glided parallel to the slope of the

hill, but greatly increased its speed, thus indicating its ability to glide on a somewhat less angle than 9.5 deg., when we should feel it safe to rise higher from the

surface. The control of the machine proved even better than we had dared to

expect, responding quickly to the slightest motion of the rudder. With these glides

our experiments for the year 1900 closed. Although the hours and hours of practice we had hoped to obtain finally dwindled down to about two minutes, we were

very much pleased with the general results of the trip, for setting out as we did,

with almost revolutionary theories on many points, and an entirely untried form

of machine, we considered it quite a point to be able to return without having our

pet theories completely knocked in the head by the hard logic of experience, and

our own brains dashed out in the bargain. Everything seemed to us to confirm the

correctness of our original opinions: (1) that practice is the key to the secret of flying; (2) that it is practicable to assume the horizontal position; (3) that a smaller

surface set at a negative angle in front of the main bearing surfaces, or wings, will

largely counteract the effect of the fore and aft travel of the center of pressure; (4)
200 Chapter 1: The Achievement of Flight

that steering up and down can be attained with a rudder, without moving the

position of the operator’s body; (5) that twisting the wings so as to present their

ends to the wind at different angles is a more prompt and efficient way of maintaining lateral equilibrium than shifting the body of the operator.

When the time came to design our new machine for 1901, we decided to

make it exactly like the previous machine in theory and method of operation. But

as the former machine was not able to support the weight of the operator when

flown as a kite, except in very high winds and at very large angles of incidence,

we decided to increase its lifting power. Accordingly, the curvature of the surfaces

was increased to 1 in 12, to conform to the shape on which Lilienthal’s table was

based, and to be on the safe side, we decided also to increase the area of the

machine from 165 square feet to 308 square feet, although so large a machine had

never before been deemed controllable. The Lilienthal machine had an area of

151 square feet; that of Pilcher, 165 square feet; and the Chanute double-decker,

134 square feet. As our system of control consisted in a manipulation of the surfaces themselves instead of shifting the operator’s body, we hoped that the new

machine would be controllable, notwithstanding its great size. According to calculations it would obtain support in a wind of 17 miles per hour with an angle of

incidence of only 3 degrees.

Our experience of the previous year having shown the necessity of a suitable

building for housing the machine, we erected a cheap frame building, 16 feet

wide, 25 feet long, and 7 feet high at the eaves. As our machine was 22 feet wide,

14 feet long (including the rudder) and about 6 feet high, it was not necessary to

take the machine apart in any way in order to house it. Both ends of the building,

except the gable parts, were made into doors which hinged above, so that when

opened they formed an awning at each end, and left an entrance the full width of

the building. We went into camp about the middle of July, and were soon joined

by Mr. E. C. Huffaker, of Tennessee, an experienced aeronautical investigator in the

employ of Mr. Chanute, by whom his services were kindly loaned, and by Dr. G. A.

Spratt, of Pennsylvania, a young man who has made some valuable investigations

of the properties of variously curved surfaces and the travel of the center of pressure thereon. Early in August, Mr. Chanute came down from Chicago to witness

our experiments, and spent a week in camp with us. These gentlemen, with my brother

and myself, formed our camping party, but in addition we had in many of our experiments the valuable assistance of Mr. W. J. Tate and Mr. Dan Tate, of Kitty Hawk.

The machine was completed and tried for the first time on the 27th of July

in a wind blowing about 13 miles an hour. The operator having taken a position

where the center of pressure was supposed to be, an attempt at gliding was made;

but the machine turned downward and landed after going only a few yards. This

indicated that the center of gravity was too far in front of the center of pressure.
Document 1-11(a–b) 201

In the second attempt the operator took a position several inches further back but

the result was much the same. He kept moving further and further back with each

trial, till finally he occupied a position nearly a foot back of that at which we had

expected to find the center of pressure. The machine then sailed off and made an

undulating flight of a little more than 300 feet. To the onlookers this flight

seemed very successful, but to the operator it was known that the full power of the

rudder had been required to keep the machine from either running into the

ground or rising so high as to lose all headway. In the 1900 machine one fourth

as much rudder action had been sufficient to give much better control. It was

apparent that something was radically wrong, though we were for some time

unable to locate the trouble. In one glide the machine rose higher and higher till

it lost all headway. This was the position from which Lilienthal had always found

difficulty to extricate himself, as his machine then, in spite of his greatest exertions, manifested a tendency to dive downward almost vertically and strike the

ground head on with frightful velocity. In this case a warning cry from the ground

caused the operator to turn the rudder to its full extent and also to move his body

slightly forward. The machine then settled slowly to the ground, maintaining its

horizontal position almost perfectly, and landed without any injury at all. This was

very encouraging, as it showed that one of the very greatest dangers in machines

with horizontal tails had been overcome by the use of a front rudder. Several

glides later the same experience was repeated with the same result. In the latter

case the machine had even commenced to move backward, but was nevertheless

brought safely to the ground in a horizontal position. On the whole, this day’s

experiments were encouraging, for while the action of the rudder did not seem at

all like that of our 1900 machine, yet we had escaped without difficulty from positions which had proved very dangerous to preceding experimenters, and after less

than one minute’s actual practice had made a glide of more than 300 feet, at an

angle of descent of 10 degrees, and with a machine nearly twice as large as had

previously been considered safe. The trouble with its control, which has been

mentioned, we believed could be corrected when we should have located its cause.

Several possible explanations occurred to us, but we finally concluded that the

trouble was due to a reversal of the direction of the travel of the center of pressure at small angles. In deeply curved surfaces the center of pressure at 90 degrees

is near the center of the surface, but moves forward as the angle becomes less, till

a certain point is reached, varying with the depth of curvature. After this point is

passed, the center of pressure, instead of continuing to move forward, with the

decreasing angle, turns and moves rapidly toward the rear. The phenomena are due

to the fact that at small angles the wind strikes the forward part of the surface on

the upper side instead of the lower, and thus this part altogether ceases to lift,

instead of being the most effective part of all, as in the case of the plane.
202 Chapter 1: The Achievement of Flight

Lilienthal had called attention to the danger of using surfaces with a curvature as

great as one in eight, on account of this action on the upper side; but he seems

never to have investigated the curvature and angle at which the phenomena

entirely cease. My brother and I had never made any original investigation of the

matter, but assumed that a curvature of one in twelve would be safe, as this was

the curvature on which Lilienthal based his tables. However, to be on the safe

side, instead of using the arc of a circle, we had made the curve of our machine

very abrupt at the front, so as to expose the least possible area to this downward

pressure. While the machine was building, Messrs. Huffaker and Spratt had suggested that we would find this reversal of the center of pressure, but we believed

it sufficiently guarded against. Accordingly, we were not at first disposed to believe

that this reversal actually existed in our machine, although it offered a perfect

explanation of the action we had noticed in gliding. Our peculiar plan of control

by forward surfaces, instead of tails, was based on the assumption that the center

of pressure would continue to move farther and farther forward, as the angle of

incidence became less, and it will be readily perceived that it would make quite a

difference if the front surface instead of counteracting this assumed forward travel,

should in reality be expediting an actual backward movement. For several days we

were in a state of indecision, but were finally convinced by observing the following

phenomena: (Figure 1) We had removed the upper surface from the machine and

were flying it in a wind to see at what angles it would be supported in winds of different strengths. We noticed that in light winds it flew in the upper position shown

in the figure, with a strong upward pull on the cord c. As the wind became stronger,

the angle of incidence became less, and the surface flew in the position shown in the

middle of the figure, with a slight horizontal pull. But when the wind became still

stronger, it took the lower position shown in the figure, with a strong downward pull.

It at once occurred to me that here was the answer to our problem, for it is evident

that in the first case the center of pressure was in front of the center of gravity and

thus pushed up the front edge; in the second case, they were in coincidence, and the

surface in equilibrium; while in the third case the center of pressure had reached

a point even behind the center of gravity, and there was therefore a downward pull

on the cord. This point having been definitely settled, we proceeded to truss down

the ribs of the whole machine, so as to reduce the depth of curvature. In Figure

2, line 1, shows the original curvature; line 2, the curvature when supporting the

operator’s weight; and line 3, the curvature after trussing.

On resuming our gliding, we found that the old conditions of the preceding

year had returned; and after a few trials, made a glide of 366 feet and soon after

one of 389 feet. The machine with its new curvature never failed to respond

promptly to even small movements of the rudder. The operator could cause it to

almost skim the ground, following the undulations of its surface, or he could
Document 1-11(a–b) 203

cause it to sail out almost on a level with the starting point, and passing high

above the foot of the hill, gradually settle down to the ground. The wind on this

day was blowing 11 to 14 miles per hour. The next day, the conditions being favorable, the machine was again taken out for trial. This time the velocity of the wind

was 18 to 22 miles per hour. At first we felt some doubt as to the safety of attempting free flight in so strong a wind, with a machine of over 300 square feet, and a

practice of less than five minutes spent in actual flight. But after several preliminary experiments we decided to try a glide. The control of the machine seemed

so good that we then felt no apprehension in sailing boldly forth. And thereafter

we made glide after glide, sometimes following the ground closely, and sometimes

sailing high in the air. Chanute had his camera with him, and took pictures of

some of these glides, several of which are among those shown.

We made glides on subsequent days, whenever the conditions were favorable.

The highest wind thus experimented in was a little over 12 meters per second—

nearly 27 miles per hour.

It had been our intention when building the machine to do the larger part of

the experimenting in the following manner: When the wind blew 17 miles an

hour, or more, we would attach a rope to the machine and let it rise as a kite with

the operator upon it. When it should reach a proper height the operator would

cast off the rope and glide down to the ground just as from the top of a hill. In

this way we would be saved the trouble of carrying the machine uphill after each

glide, and could make at least 10 glides in the time required for 1 in the other

way. But when we came to try it we found that a wind of 17 miles, as measured by

Richard’s anemometer, instead of sustaining the machine with its operator, a total

weight of 240 lbs., at an angle of incidence of 3 degrees, in reality would not sustain

the machine alone—100 pounds—at this angle. Its lifting capacity seemed scarcely

one third of the calculated amount. In order to make sure that this was not due to

the porosity of the cloth, we constructed two small experimental surfaces of equal size,

one of which was airproofed and the other left in its natural state; but we could

detect no difference in their lifting powers. For a time we were led to suspect that

the lift of curved surfaces little exceeded that of planes of the same size, but further

investigation and experiment led to the opinion that (1) the anemometer used by

us over recorded the true velocity of the wind by nearly 15 percent; (2) that the

well known Smeaton coefficient of .005V2 for the wind pressure at 90 degrees is

probably too great by at least 20 percent; (3) that Lilienthal’s estimate that the

pressure on a curved surface having an angle of incidence of 3 degrees equals .545

of the pressure at 90 degrees is too large, being nearly 50 percent greater than very

recent experiments of our own with a special pressure testing machine indicate;

(4) that the superposition of the surfaces somewhat reduced the lift per square

foot, as compared with a single surface of equal area. 
204 Chapter 1: The Achievement of Flight

In gliding experiments, however, the amount of lift is of less relative importance than the ratio of lift to drift, as this alone decides the angle of gliding

descent. In a plane the pressure is always perpendicular to the surface, and the

ratio of lift to drift is therefore the same as that of the cosine to the sine of the

angle of incidence. But in curved surfaces a very remarkable situation is found.

The pressure instead of being uniformly normal to the chord of the arc, is usually inclined considerably in front of the perpendicular. The result is that the lift is

greater and the drift less than if the pressure were normal. Lilienthal was the first

to discover this exceedingly important fact, which is fully set forth in his book,

Bird Flight the Basis of the Flying Art, but owing to some errors in the methods he

used in making measurements, question was raised by other investigators not

only as to the accuracy of his figures, but even as to the existence of any tangential force at all. Our experiments confirm the existence of this force, though our

measurements differ considerably from those of Lilienthal. While at Kitty Hawk

we spent much time in measuring the horizontal pressure on our unloaded

machine at various angles of incidence. We found that at 13 degrees the horizontal

pressure was about 23 lbs. This included not only the drift proper, or horizontal

component of the pressure on the side of the surface, but also the head resistance

of the framing as well. The weight of the machine at the time of this test was about

108 lbs. Now, if the pressure had been normal to the chord of the surface, the drift

proper would have been to the lift (108 lbs.) as the sine of 13 degrees is to the

cosine of 13 degrees, or .22 x 108 / .97 = 24+ lbs.; but this slightly exceeds the

total pull of 23 lbs. on our scales. Therefore, it is evident that the average pressure

on the surface instead of being normal to the chord was so far inclined toward the

front that all the head resistance of framing and wires used in the construction

was more than overcome. In a wind of 14 miles per hour, resistance is by no

means a negligible factor, so that tangential is evidently a force of considerable

value. In a higher wind which sustained the machine at an angle of 10 degrees,

the pull on the scales was 18 lbs. With the pressure normal to the chord, the drift

proper would have been .17 x 98 / .98 = 17 lbs., so that, although the higher wind

velocity must have caused an increase in the head resistance, the tangential force

still came within one pound of overcoming it. After our return from Kitty Hawk

we began a series of experiments to accurately determine the amount and direction of the pressure produced on curved surfaces when acted upon by winds at the

various angles from zero to 90 degrees. These experiments are not yet concluded,

but in general they support Lilienthal in the claim that the curves give pressures

more favorable in amount and direction than planes; but we find marked differences in the exact values, especially at angles below 10 degrees. We were unable

to obtain direct measurements of the horizontal pressures of the machine with the

operator on board, but by comparing the distance traveled in gliding with the
Document 1-11(a–b) 205

vertical fall, it was easily calculated that at a speed of 24 miles per hour the total

horizontal resistances of our machine, when bearing the operator, amounted to

40 pounds which is equivalent to about 2 1⁄2 horsepower. It must not be supposed,

however, that a motor developing this power would be sufficient to drive a manbearing machine. The extra weight of the motor would require either a larger

machine, higher speed, or a greater angle of incidence, in order to support it, and

therefore more power. It is probable, however, that an engine of 6 horsepower,

weighing 200 pounds, would answer the purpose. Such an engine is entirely practicable. Indeed, working motors of one half this weight per horsepower (9 pounds

per horsepower) have been constructed by several different builders. Increasing

the speed of our machine from 24 to 33 miles per hour reduced the total horizontal pressure from 40 to about 35 pounds. This was quite an advantage in gliding as it made it possible to sail about 15 percent further with a given drop.

However, it would be of little or no advantage in reducing the size of the motor

in a power-driven machine, because the lessened thrust would be counterbalanced by the increased speed per minute. Some years ago Prof. Langley called

attention to the great economy of thrust which might be obtained by using very

high speeds, and from this many were led to suppose that high speed was essential to success in a motor-driven machine. But the economy to which Prof. Langley

called attention was in foot pounds per mile of travel, not in foot pounds per

minute. It is the foot pounds per minute that fixes the size of a relatively low

speed, perhaps not much exceeding 20 miles per hour, but the problem of

increasing the speed will be much simpler in some respects than that of increasing the speed of a steamboat; for, whereas in the latter case the size of the engine

must increase as the cube of the speed, in the flying machine, until extremely high

speeds are reached, the capacity of the motor increases in less than simple ratio;

and there is even a decrease in the fuel consumption per mile of travel. In other

words to double the speed of a steamship (and the same is true of the balloon type

of airship) eight times the engine and boiler capacity would be required, and four

times the fuel consumption per mile of travel; while a flying machine would

require engines of less than double the size, and there would be an actual decrease

in the fuel consumption per mile of travel. But looking at the matter conversely,

the great disadvantage of the flying machine is apparent, for in the latter no flight

at all is possible unless the proportion of horsepower to flying capacity is very

high; but on the other hand a steamship is a mechanical success if its ratio of

horsepower to tonnage is insignificant. A flying machine that would fly at a speed

of 50 miles an hour with engines of 1,000 horsepower, would not be upheld by its

wings at all at a speed of less than 25 miles an hour, and nothing less than 500 horsepower could drive it at this speed. But a boat which could make 40 miles per hour

with engines of 1,000 horsepower, would still move 4 miles an hour even if the
206 Chapter 1: The Achievement of Flight

engines were reduced to 1 horsepower. The problems of land and water travel

were solved in the 19th century because it was possible to begin with small

achievements and gradually work up to our present success. The flying problem

was left over to the 20th century, because in this case the art must be highly developed before any flight of any considerable duration at all can be obtained.

However, there is another way of flying which requires no artificial motor, and

many workers believe that success will first come by this road. I refer to the soaring flight, by which the machine is permanently sustained in the air by the same

means that are employed by soaring birds. They spread their wings to the wind,

and sail by the hour, with no perceptible exertion beyond that required to balance

and steer themselves. What sustains them is not definitely known, though it is

almost certain that it is a rising current of air. But whether it be a rising current

or something else, it is as well able to support a flying machine as a bird, if man

once learns the art of utilizing it. In gliding experiments it has long been known

that the rate of vertical descent is very much retarded and the duration of the

flight greatly prolonged, if a strong wind blows up the face of the hill parallel to

its surface. Our machine, when gliding in still air, has a rate of vertical descent of

nearly 6 feet per second, while in a wind blowing 26 miles per hour up a steep

hill, we made glides in which the rate of descent was less than 2 feet per second.

And during the larger part of this time, while the machine remained exactly in

the rising current, there was no descent at all, but even a slight rise. If the operator

had had sufficient skill to keep himself from passing beyond the rising current,

he would have been sustained indefinitely at a higher point than that from which

he started. The illustration shows one of these very slow glides at a time when the

machine was practically at a standstill. The failure to advance more rapidly caused

the photographer some trouble in aiming, as you will perceive. In looking at this

picture you will readily understand that the excitement of gliding experiments

does not entirely cease with the breaking up of camp. In the photographic darkroom at home we pass moments of as thrilling interest as any in the field, when

the image begins to appear on the plate and it is yet an open question whether

we have a picture of a flying machine, or merely a patch of open sky. These slow

glides in rising currents probably hold out greater hope of extensive practice than

any other method within man’s reach, but they have the disadvantage of requiring rather strong winds or very large supporting surfaces. However, when gliding

operators have attained greater skill, they can, with comparative safety, maintain

themselves in the air for hours at a time in this way, and thus by constant practice

so increase their knowledge and skill that they can rise into the higher air and

search out the currents which enable the soaring birds to transport themselves to

any desired point by first rising in a circle and then sailing off at a descending

angle. This illustration shows the machine, alone, flying in a wind of 35 miles per
Document 1-11(a–b) 207

hour on the face of a steep hill, 100 feet high. It will be seen that the machine not

only pulls upward, but also pulls forward in the direction from which the wind

blows, thus overcoming both gravity and the speed of the wind. We tried the same

experiment with a man on it, but found danger that the forward pull would

become so strong that the men holding the ropes would be dragged from their

insecure foothold on the slope of the hill. So this form of experimenting was discontinued after four or five minute trials.

In looking over our experiments of the past two years, with models and fullsized machines, the following points stand out with clearness:

1. That the lifting power of a large machine, held stationary in a wind at a

small distance from the earth, is much less than the Lilienthal table and our own

laboratory experiments would lead us to expect. When the machine is moved

through the air, as in gliding, the discrepancy seems much less marked.

2. That the ratio of drift to lift in well-shaped surfaces is less at angles of incidence of five degrees to 12 degrees than at an angle of three degrees.

3. That in arched surfaces the center of pressure at 90 degrees is near the center of the surface, but moves slowly forward as the angle becomes less, till a critical angle varying with the shape and depth of the curve is reached, after which it

moves rapidly toward the rear till the angle of no lift is found.

4. That with similar conditions, large surfaces may be controlled with not

much greater difficulty than small ones, if the control is effected by manipulation

of the surfaces themselves, rather than by a movement of the body of the operator.

5. That the head resistances of the framing can be brought to a point much

below that usually estimated as necessary.

6. That tails, both vertical and horizontal, may with safety be eliminated in

gliding and other flying experiments.

7. That a horizontal position of the operator’s body may be assumed without

excessive danger, and thus the head resistance reduced to about one fifth that of

the upright position.

8. That a pair of superposed, or tandem surfaces, has less lift in proportion

to drift than either surface separately, even after making allowance for weight and

head resistance of the connections.
208 Chapter 1: The Achievement of Flight

Document 1-12(a–b)

(a) Octave Chanute, excerpt from remarks at a meeting of 

the Aéro-Club, Paris, 2 April 1903, translated from Ernest

Archdeacon, La Locomotion, 11 April 1903, pp. 225–227, 

in The Papers of Wilbur and Orville Wright, pp. 654–673.

(b) Wilbur Wright, excerpts from “Experiments and

Observations in Soaring Flight,” address at the meeting 

of the Western Society of Engineers, Chicago, 24 June 1903,

published in Journal of the Western Society of Engineers

(December 1903), in The Papers of Wilbur and 

Orville Wright, pp. 318–330.

One of the most influential reports on the glider experiments done in

America, and especially of the recent work of Wilbur and Orville Wright, was an

address given in Paris by Octave Chanute in the spring of 1903. At the time

Chanute made these remarks, the Wrights were applying what they had learned

from their gliding experiments to the design of a powered airplane.

The Wright brothers’ third season of flight tests at Kitty Hawk in 1902 crossed

a threshold in the development of flight. With their newly designed glider they

had, for the first time, a machine in which they could really learn how to fly. In

the following document, Wilbur Wright describes this breakthrough season of

flight experiments. This passage is taken from an address given at the 1903 meeting of the Western Society of Engineers, as a follow-up to his earlier address presented in September 1901. These remarks were made on the eve of the Wrights’

departure for a fourth season of tests at Kitty Hawk, where they planned to fly

their new powered airplane based on the glider described here. 

Document 1-12(a), Octave Chanute, excerpt from remarks 

at a meeting of the Aéro-Club, Paris, 2 April 1903.

The strains arise from the irregularities and turmoils of the wind. The current does not come as an evenly flowing stream, but as a series of swirling waves,

as shown in the smoke issuing from a chimney. These waves strike the apparatus

either on one side or on the other, from below or from above, and constantly tend

to upset it. The velocity and force with which the machine is struck by the wave

depend both upon the distance from the center of rotation of the latter and upon
Document 1-12(a–b) 209

the speed of the current, and this is probably the reason why anemometers show

such varying pressures. A flying machine must meet and overcome all these vicissitudes and this must be done instantly.

In 1896 and 1897, being impressed that the equilibrium of the bird was partly automatic, and that the problem of stability in the wind was the first which must

be solved, I undertook some experiments near Chicago, Illinois, with full-sized

gliding machines carrying a man, in order to study equilibrium, and that alone. I

caused to be built five machines of four different types. The first was a Lilienthal

apparatus, in order to start from the known before passing to the unknown, and

three of the other machines were based upon the reverse of the Lilienthal type,

that is to say that instead of re-establishing the equilibrium (when compromised

by the variations of the wind) by displacing the body of the operator, and therefore that of the center of gravity, as did Lilienthal and Pilcher, the new machines

were based upon the theory that it was possible so to arrange the carrying surfaces

that they should move automatically under the action of the wind and bring back

the center of pressure vertically over the center of gravity—a condition absolutely necessary in order to maintain equilibrium.

One of these machines, called the “multiple-wing,” is shown in figures 1 to 5.

The supporting wings are at the front and are superposed and braced together.

They turn upon ball bearings marked B, and are restrained in front by rubber

springs which allows a certain amount of horizontal movement. If the relative wind

increases, thus requiring a lesser angle of incidence to sustain the weight, the

wings are blown backward, the apparatus oscillates towards the front, and the

angle becomes smaller. Once the squall passed, the springs bring the wings back

to their normal position. The rear wings are flexible and merely aid in balancing,

and an aeroplane, which might be replaced by an additional pair of wings, surmounts the whole. The whole apparatus weighed 15.2 kilograms, the supporting

area of the front wings being 13.33 square meters and that of the rear wings 2.74

m2

. This machine proved very nearly automatic, the operator having to move but

25 millimeters, in ordinary glides, as against 127 mm. with the Lilienthal and 63

mm. with the “two-surface” machine, which is next to be described.

The “two-surface” machine gave the best results and the longest glides. It is

shown in figures 6 to 10. The supporting surfaces are of varnished silk and are

affixed to a framework similar to a bridge truss, and the operator is below in an

upright position, being sustained under the armpits by two horizontal bars.

Equilibrium is obtained through a horizontal tail, similar to that invented by

Pénaud, but with elastic fastenings devised by Mr. Herring. This tail generally

makes an angle of 7 to 8 degrees with the carrying surfaces, and by receiving the

relative wind below or above automatically changes the angle of attack according

to the exigencies of the moment. The frame was of wood and the weight was 11 kg.
210 Chapter 1: The Achievement of Flight

and the surface 12.45 square meters, which easily sustained an operator weighing

71 kg. More than one thousand glides were made with these machines in 1896

and 1897 without accident, the following tables giving an idea of the results with

each of the machines:

SOME GLIDES OF MULTIPLE-WING MACHINE—WEIGHT 86 KG.,

MOUNTED

Operator Length Time Speed Remarks

(meters) (Seconds) M. per sec.

Herring 45.11 7.0 6.45

Avery 53.04 7.6 7.00

Herring 50.60 7.5 6.72

Avery 55.77 7.9 7.00 Angle of descent not measured but about 10° to 11°

Herring 52.43 7.8 6.70

SOME GLIDES OF TWO-SURFACE—WEIGHT 82 KG., MOUNTED

Operator Length Time Angle Height Speed Rate of Kg. Remarks

(meters) (seconds) descent fallen M. per descent

(meters) sec

Avery 60.64 8 10o 10.5 7.62 1 in 5.75 106.

Herring 71.32 8.7 7 1

⁄2o 9.3 8.23 1 in 7.69 87.

Avery 77.11 .... 10 1

⁄2o 14 .... 1 in 5.50 Time not taken

Herring 72.84 .... 11o 14.1 .... 1 in 5.24 Time not taken

" 67.06 9 .... .... 7.42 .............. Angle not taken

" 71.62 10.3 .... .... 7. .............. Angle not taken

Avery 78.03 10.2 8o 10.8 7.6 1 in 7.18 86.

Herring 109.42 14. 10o 18.9 7.8 1 in 5.75 110.

The slope of the hill being steep and the wind ascending, it was estimated

that the resistance required 2 horsepower, instead of the 1 1⁄3 H.P. shown by the

work done as calculated. The drawings of these various machines were published

in the Aeronautical Annual for 1897, edited by Jas. Means, Boston, U.S.A., and

amateurs were invited to repeat and to improve upon the performances.

In 1902 I caused to be built an apparatus to obtain automatic stability by a

third method. This consists in pivoting the sustaining surfaces about 4/10 of their

width from the front, and restraining them by springs. If the relative wind increases,

the center of pressure moves backward and tends to give the surfaces a smaller
Document 1-12(a–b) 211

angle of attack. Only a few tests were made in 1902, but more are to be carried on

in 1903. The apparatus is shown in figures 11 to 15 for the benefit of amateurs

and a photograph of one of the glides is herewith reproduced.

All these experiments were made without accident. It is true that in the beginning all

possible precautions were taken. The practice ground selected was on the soft sand

hills which border the southern edge of Lake Michigan, some 50 kilometers from

Chicago, where there are but few trees or bushes. No glides were made in very gusty

winds, or those exceeding 50 kilometers to the hour, and Messrs. Herring and Avery,

my assistants, were alone allowed to experiment. Later on, more confidence was

gained and visitors were allowed to make short glides under instruction from the

experts. All succeeded well, and even the cook became almost an expert in a short

time. It must, however, be recognized that this sport is dangerous and that all who

would engage in it must take all possible precautions before venturing upon it.

The invitation to amateurs to repeat these experiments remained unacted

upon till 1900, when Messrs. Wilbur & Orville Wright of Dayton (Ohio), took up

the question. They have accomplished such advance upon all previous practice

that the rest of this paper will be devoted to giving an account thereof. The

improvements which they have introduced are the following:

lst. Placing the horizontal rudder or tail at the front, a position which proves

more efficient in acting upon the air.

2nd. Placing the operator prone on the machine, thus diminishing by 4

⁄5 the

resistance due to his body.
212 Chapter 1: The Achievement of Flight

3rd. Warping the wings to steer to right or left.

The practice ground chosen by the Wright brothers, after an inquiry made of the

National Signal Bureau of the United States, is far superior to the hills near Chicago.

It is situated at Kitty Hawk near the ocean in North Carolina, and consists of a soft

sand hill about 30 meters high, on a tongue of land, without a single tree, bush or

grass. At its foot a sand beach one kilometer wide extends to the sea, and regular sea

breezes blow daily from the ocean. Moreover the spot is a desert and quite inaccessible

to the curious, who are always in the way when one is seeking for unknown phenomena.

The Wright apparatus of 1900 measured 5.64 meters across by a width of 1.52 m.,

there being two surfaces aggregating 15.6 square meters, and weighing 21.8 kg.

It chiefly served to study the result of placing the horizontal rudder at the front,

the apparatus being loaded with sandbags or weights and flown as a kite. Having

ascertained that the machine worked well, the Wrights ventured to make a few

glides with good success, and postponed to the next season learning the difficult

art of the birds.

The method of conducting the experiments necessarily differed from those

adopted by Lilienthal and his imitators. In those machines the operator, being on

his feet, carries the apparatus, poises it in the wind, and runs forward until he

leaves the ground. With the two-surface machine, for instance, which weighed but

11 kg. (for 12.45 m. surface) the aviator could walk about with his wings on his

shoulders. The Wrights, desiring to build a larger and heavier machine and to

place the aviator horizontally, had to devise a new method of getting under way.
Document 1-12(a–b) 213

This consisted in employing two assistants each grasping one extremity of the

machine, and running forward against the wind. The aviator, placed in the center, first remains on his feet, runs a few steps and, as speed and supporting power

increase, tips forward prone on the framing, hooking his feet on the rear transverse bar, and as soon as he feels himself well carried by the air, he cries, “Let go.”

From this on gravity serves as a motor; he glides along down the slope of the hill,

keeping near the ground, meeting the irregularities of the wind by the action of

the front rudder and steering to the right or left, by the torsion of the wings,

which are framed loosely, and by the vertical rudder behind. When the foot of the

hill is reached, a vigorous action of the front rudder causes the machine to shoot

upward a little, thus increasing the resistance and diminishing the speed. The

machine then alights upon the sand and stops after a short slide upon its shoes.
214 Chapter 1: The Achievement of Flight

The 1901 machine was 6.7 meters across by a width of 2.13 m., the two surfaces

being spaced 1.42 m. vertically and giving a surface of 27.1 m2, with a weight of

45.4 kg. This apparatus performed several hundred glides without accident, but

although the head resistance was less, by reason of the horizontal position of the

aviator, the angles of descent were nearly the same (8° to 10°) as with the machines in

which the aviator stood upright. Now the important thing for a gliding apparatus is

that the fall through the air shall be the least possible. We can always lengthen the

glides by starting from a higher point, but the angle of descent shows at once the

ratio between the propelling force (the weight) and the horizontal resistance, and

the latter should be reduced to a minimum before proceeding to other details.

The horizontal resistance consists of three factors:

1st. The drift, depending upon the angle of incidence. 

2nd. The head resistance of the various thicknesses.

3rd. The tangential force, recognized by Lilienthal.

The drift is the horizontal resultant of the normal pressure and has been thoroughly written upon heretofore, so that it need not be here discussed. Recent

experiments seem to show, however, that the friction of the air upon the surfaces

is not negligible, and should be separately added.

The head resistance is the most important, and is the one in which improvements may be achieved, by shaping the framing so as to give the lowest possible

coefficients, by diminishing the number of parts, and by reducing all guy wires

and similar vibrating parts to a minimum.

The tangential force only applies to arched surfaces, and presents the curious

property that at certain angles of incidence it acts as a propulsive force. Those

who may wish to learn more about this are referred to Lilienthal’s book, Der

Vogelflug als Grundlage der Fliegekunst, and to his chapter in Moedebeck’s

Taschenbuch für Flugtechniker und Luftschiffer.

We arrive at the aggregate horizontal resistance by three different processes,

as follows:

1st. The speed required for support and the angle of incidence with the relative

wind, being first ascertained as accurately as possible, the normal pressure is computed

by the aid of Lilienthal’s table for arched surfaces, which will be found in Moedebeck’s

Taschenbuch, and this normal is multiplied by the sine of the angle of application

to obtain the drift. To this is added the head resistance due to the framing, the aviator

and adjuncts, which is obtained by measuring accurately all the thicknesses and

applying to each a coefficient due to its form. It is interesting in this connection

to know that beams fishlike in cross section offer but one sixth the resistance on

a plane of the same area as their “master section” while vibrating wires offer about

twice the resistance due to their “master section.” All this is best obtained by drawing

up a tabular schedule of all the parts and deducing there from the equivalent or
Document 1-12(a–b) 215

fictive area of resistance of the apparatus, which, when multiplied by the air pressure due to the speed, gives the aggregate head resistance; to the sum of the latter

with the drift is added or deducted the tangential force, as obtained from

Lilienthal’s table, according to whether it is positive or negative. In other words:

Resistance = drift + head resistance ± tangential. This process is tedious and

slow, but it is well worth the trouble, for it indicates those parts of the apparatus

in which resistance can be reduced.

2nd. The second process furnishes a check upon the first and consists in floating the mounted machine in a wind of sufficient intensity or towing it by a cord

at sufficient speed to obtain support and measuring the actual pull with a hand

scale. This cannot be done very often as it involves considerable preparation, but

it is a check not to be disputed.

3rd. The third process consists in simply multiplying the weight by the sine of

the angle of descent. In fact, as the speed of the glides is almost always uniform

it is evident that the forces balance, and the resistance along the path is to the

weight as the sine of the angle to the radius. It is found as the result of a great

many such computations that the three processes agree very closely.

The Messrs. Wright concluded from their experiments in 1901 that there

were a number of defects in the apparatus used that year. That the shape of the

surfaces was not the best possible and that they became deformed under the pressure of the relative wind. During the succeeding winter they made a whole series

of laboratory experiments upon various surfaces, and built a third machine for

experiment in 1902.

This last apparatus was 9.75 meters across, by a width of 1.52 m., the two surfaces being spaced 1.42 m. apart, and giving 28.4 m2. of supporting surface. The

front rudder was 1.4 m2. in area, and the weight was 53 kg. Fig. 16 to 20 show this

apparatus. The main pieces are shown full size. They were all of wood, the front

spar and the main arm were of an American wood for which pine would be a substitute; these parts were either imbedded in the cloth, or in a sheath or strip glued

on afterwards. The ribs were of ash, steamed and bent, with a curvature of 1/20

one third of the chord from the front. All fastenings were made by lashing the

sticks together, and it is well to dampen the twine with thin glue when wrapping

it around. The surfaces consisted of tightly woven cotton cloth such as that used

for balloons. It was not varnished but would have been the better for it. The

braces were of piano wire and it was generally aimed to have a factor of safety of

10 times the breaking weight. A light pair of shoes or skis was attached to the

framing and spar at the front.

The machine was tested on the practice ground already described, in September

and October, 1902, and it gave very superior results to those obtained with preceding machines. The angles of descent were flatter and the weight sustained per
216 Chapter 1: The Achievement of Flight

horsepower was greater. The two brothers glided alternately and they soon

attained almost complete mastery over the inconstancies of the wind. They met

the wind gusts and steered as they willed. They did not venture to sweep much

more than one quarter circle, so as not to lose the advantage of a head wind, but
Document 1-12(a–b) 217

they constantly improved in the control of the machine and in learning the art of

the birds. Some 800 glides were made of which the following are representative:

The variations mainly result from more or less skill in each glide and consequent slight swerving.

The last column in the table is that which best indicates the advance made over

previous practice. The machine of Mr. Maxim supported 12.7 kg., per horsepower,

that of Professor Langley 13.6 kg., while previous glides from Lilienthal down

showed 45 kg. per horsepower. It is quite true that when a motor is added the weight

sustained per horsepower is diminished about one half by reason of the inevitable

losses due to the motor, the transmission and the propeller, but Messrs. Wright

have so far diminished the resistances that they now sustain 62 kg. per horsepower,

and the time is evidently approaching when, the problems of equilibrium and

control having been solved, it will be safe to apply a motor and a propeller.

In point of fact the Messrs. Wright are now gliding very nearly as well as the

vulture, which generally descends one meter in ten (5°45') in calm air. It is therefore

not impossible that man shall eventually master sailing flight and learn, when once

well in the air and at speed, to imitate the soaring birds which circle and rise

through the force of the wind alone when circumstances are favorable; which conditions chiefly consist in an ascending trend of the wind, such as is frequently found

in hot countries, those being the regions which are frequented by sailing birds.

This does not mean that the future flying machine, if such is developed, can

entirely do without a motor. This adjunct will be indispensable, not only to fly in

those regions where the wind seldom has an ascending trend, but also to restore

the speed or the equilibrium very quickly under many circumstances, such as a

very sudden wind gust, or a descent too near to the ground. It is easily perceived,

however, that when the motor need only be used occasionally the length of possible

journeys of flying apparatus will be greatly increased in the countries where circumstances favor sailing flight.

It is thus seen that there has been a gradual evolution from Lilienthal onward. That

gliding machines have been made much safer and are now fairly under control. There

is doubtless a chance for further improvement, and this can only be accomplished by

experiment. The present indications are that such experiments will be extensively

undertaken, and a word of warning may well be given in concluding this article.

Let all exert the utmost possible prudence in conducting gliding experiments.

First select suitable ground, a soft sand hill is the best, so isolated from other hills

as to have no cross currents or whirling winds. Begin practice very gradually, starting

from a small elevation and learning by degrees the control of the machine and

the best way of alighting safely. Follow the slope of the hill closely, so as to have

but a short distance to fall if a false maneuver is made. Examine the apparatus

after each glide, and if anything has gotten out of order, repair it at once before
218 Chapter 1: The Achievement of Flight

making another glide. Try no feats which involve being high in air except over an

appropriate sheet of water, but do not resort to that method of experimenting

upon ordinary occasions. It involves too much loss of time in drying oneself and

the machine, and the latter is likely to become distorted.

More important than all, do not try to beat previous records. This leads to

taking risks and to producing accidents. It is well to have competitions at which

several amateurs practice together, because they learn from each other and

because they are then more disposed to have a surgeon present, a precaution which

I have always taken, but we must always remember that the important things to be

secured are control of the machine and safe landings, without regard to the distance glided over, the latter mainly depending upon the elevation started from.

Progress and safety will be greatly promoted by beginning with small

machines just as the Wrights have done. An apparatus 6 meters by 1.3 meters, giving

with two surfaces arched to 1⁄25 of their width some 15 square meters of supporting area, is ample to carry a man and will be found far more manageable than the

last machine of Messrs. Wright of which the drawings are here given. As the cost

is not great, being from 500 to 1500 francs, according to the amount of care

bestowed on the apparatus, it is feasible to build new machines from time to time

in order to introduce the improvements which constantly suggest themselves. It is

hoped that when many experimenters get at work such progress shall be made as

materially to advance the time when aviation shall become practical.

Document 1-12(b), Wilbur Wright, excerpts from 

“Experiments and Observations in Soaring Flight,” Chicago, 24 June 1903.

The prime object in these experiments was to obtain practice in the management

of a man-carrying machine, but an object of scarcely less importance was to obtain

data for the study of the scientific problems involved in flight. Observations were

almost constantly being made for the purpose of determining the amount and

direction of the pressures upon the sustaining wings; the minimum speed

required for support; the speed and angle of incidence at which the horizontal

resistance became least; and the minimum angle of descent at which it was possible

to glide. To determine any of these points with exactness was found to be very difficult indeed, but by careful observations under test conditions it was possible to

obtain reasonably close approximations. . . .

In addition to the work with the machine we also made many observations on

the flight of soaring birds, which were very abundant in the vicinity of our camp.

Bald eagles, ospreys, hawks, and buzzards gave us daily exhibitions of their powers.

The buzzards were the most numerous and were the most persistent soarers. They

apparently never flapped except when it was absolutely necessary, while the eagles
Document 1-12(a–b) 219

and hawks usually soared only when they were at leisure. Two methods of soaring

were employed. When the weather was cold and damp and the wind strong, the

buzzards would be seen soaring back and forth along the hills or at the edge of a

clump of trees. They were evidently taking advantage of the current of air flowing

upward over these obstructions. On such days they were often utterly unable to

soar except in these special places. But on warm clear days when the wind was

light they would be seen high in the air soaring in great circles. Usually however

it seemed to be necessary to reach a height of several hundred feet by flapping

before this style of soaring became possible. Frequently a great number of them

would begin circling in one spot, rising together higher and higher till finally they

would disperse, each gliding off in whatever direction it wished to go. At such times

other buzzards only a short distance away found it necessary to flap frequently in

order to maintain themselves. But when they reached a point beneath the circling

flock they too began to rise on motionless wings. This seemed to indicate that rising

columns of air do not exist everywhere, but that the birds must find them. They

evidently watch each other and when one finds a rising current the others quickly

make their way to it. One day when scarce a breath of wind was stirring on the ground,

we noticed two bald eagles sailing in circling sweeps at a height of probably 500 feet.

After a time our attention was attracted to the flashing of some object considerably

lower down. Examination with a field glass proved it to be a feather which one of

the birds had evidently cast. As it seemed apparent that it would come to earth

only a short distance away some of our party started to get it. But in a little while

it was noticed that the feather was no longer falling but on the contrary was rising

rapidly. It finally went out of sight upward. It apparently was drawn into the same

rising current in which the eagles were soaring, and was carried up like the birds.

The days when the wind blew horizontally gave us the most satisfactory observations, as then the birds were compelled to make use of the currents flowing up the

sides of the hills and it was possible for us to measure the velocity and trend of the wind

in which the soaring was performed. One day four buzzards began soaring on the

northeast slope of the Big Hill at a height of only ten or twelve feet from the surface.

We took a position to windward and about 1,200 feet distant. The clinometer

showed that they were 4 1

⁄2 to 5 1⁄2 degrees above our horizon. We could see them very

distinctly with a field glass. When facing us the under side of their wings made a

broad band on the sky, but when in circling they faced from us we could no longer

see the underside of their wings. Though the wings then made little more than a

line on the sky the glass showed clearly that it was not the under side that we saw.

It was evident that the buzzards were soaring with their wings constantly inclined

above five degrees above the horizon. They were attempting to gain sufficient altitude

to enable them to glide to the ocean beach three fourths of a mile distant, but after

reaching a height of about 75 feet above the top of the hill they seemed to be unable
220 Chapter 1: The Achievement of Flight

to rise higher, though they tried a long time. At last they started to glide toward the

ocean but were compelled to begin flapping almost immediately. We at once

measured the slope and the wind. The former was 12 1⁄2 degrees; the latter was six to

eight meters per second. Since the wings were inclined 5 degrees above the horizon and the wind had a rising trend of fully 12 degrees, the angle of incidence was

about 17 degrees. The wind did not average more than seven meters, 15 miles an

hour. For the most part the birds faced the wind steadily, but in the lulls they were

compelled to circle or glide back and forth in order to obtain speed sufficient to provide support. As the buzzard weighs about .8 pounds per square foot of wing area,

the lifting power of the wind at 17 degrees angle of incidence was apparently as

great as it would have been had it been blowing straight upward with equal velocity.

The pressure was inclined 5 degrees in front of the normal, and the angle descent

was 12 1

⁄2 degrees.

On another day I stood on top of the West Hill directly behind a buzzard which

was soaring on the steep southern slope. It was just on a level with my eye and not more

than 75 feet distant. For some time it remained almost motionless. Although the wings

were inclined about five degrees above the horizon, it was not driven backward by the

wind. This bird is specially adapted to soaring at large angles of incidence in strongly

rising currents. Its wings are deeply curved. Unless the upward trend amounts to at

least eight degrees it seems to be unable to maintain itself. One day we watched a flock

attempting to soar on the west slope of the Big Hill, which has a descent of nearly

nine degrees. The birds would start near the top and glide down along the slope very

much as we did with the machine but we noticed that whenever they glided parallel

with the slope their speed diminished, and when their speed was maintained the angle

of descent was greater than that of the hill. In every case they found it necessary to

flap before they had gone two hundred feet. They tried time and again but always with

the same results. Finally they resorted to hard flapping till a height of about 150 feet

above the top of the hill was reached, after which they were able to soar in circles

without difficulty. On another day they finally succeeded in rising on almost the same

slope, from which it was concluded that the buzzard’s best angle of descent could not

be far from eight degrees. There is no question in my mind that men can build wings

having as little or less relative resistance than that of the best soaring birds. The

bird’s wings are undoubtedly very well designed indeed, but it is not any extraordinary efficiency that strikes with astonishment but rather the marvelous skill with

which they are used. It is true that I have seen birds perform soaring feats of

almost incredible nature in positions where it was not possible to measure the

speed and trend of the wind, but whenever it was possible to determine by actual

measurement the conditions under which the soaring was performed, it was easy

to account for it on the basis of the results obtained with artificial wings. The soaring

problem is apparently not so much one of better wings as of better operators.
Document 1-13(a–b) 221

Document 1-13(a–b)

(a) Orville Wright, diary entry for 17 December 1903, 

published as “Diary of the First Flight,” 

Collier’s 25 (December 1948): 33.

(b) Wilbur and Orville Wright, statement to the 

Associated Press, Dayton, Ohio, 5 January 1904.

The following documents are companions to the Wright brothers’ telegram, sent

to their father in Dayton, announcing the historic achievement of powered flight

on 17 December 1903. The first is the diary entry for that historic day, composed

by Orville, and the second is the public statement of their achievement, subsequently

prepared by the Wrights for release to the press. The latter was given to the local

representative of the Associated Press in Dayton (a man by the name of Frank

Tunison), but he was not interested. Articles about the Wrights containing part of this

statement did appear in miscellaneous newspapers, beginning on 6 January 1904.

But only the Dayton Press carried the full statement contained here. Instead of the

carefully crafted, low-key statements deliberately thought out by the Wrights, what

appeared in newspapers about their flying—when anything appeared at all—were

imaginative, inaccurate accounts that disturbed the Wrights and misled the public

into thinking that this story was no different than all the others that came before—

that was, mostly fanciful and not worthy of serious attention.

It is truly astonishing how the press bungled the story of the Wright’s achievement.

Not only did the press botch the story in 1903, but it continued to neglect or completely distort it for the next five years, well into 1908. One aviation historian, the

distinguished Richard K. Smith, has gone so far as to say that “the relationship

between the Wrights and the news medium of their day is one of the most

grotesque stories of the 20th century and it was by no means the fault of the

Wrights” [“Not a Success—But a Triumph: 80 Years Since Kitty Hawk,” Naval War

College Review 36 (November–December 1983): 13]. As indicated in the historic

telegram itself, the Wrights chose to inform the press with carefully worded statements

and continued to do so for months, but the press paid no attention. December 1903

and early 1904 were not good times for the press to give much credence to anyone’s

claims of a successful flying machine. Just nine days before the alleged achievement

at Kitty Hawk, the press had seen, with its own eyes, the debacle in the Potomac River

involving Dr. Samuel P. Langley’s full-scale aerodrome. If the great Professor

Langley, one of America’s greatest scientists, could not solve the problems of flight,

then how could a couple of unknown bicycle mechanics from Dayton, Ohio?
222 Chapter 1: The Achievement of Flight

Document 1-13(a), Orville Wright, diary entry for 17 December 1903.

Thursday, December 17, 1903 

When we got up a wind of between 20 and 25 miles was blowing from the

north. We got the machine out early and put out the signal for the men at the station. Before we were quite ready, John T. Daniels, W. S. Dough, A. D. Etheridge,

W. C. Brinkley of Manteo, and Johnny Moore of Nags Head arrived. After running the engine and propellors a few minutes to get them in working order, I got

on the machine at 10:35 for the first trial. The wind, according to our anemometers at this time, was blowing a little over 20 miles (corrected) 27 miles according

to the Government anemometer at Kitty Hawk. On slipping the rope the machine

started off increasing in speed to probably 7 or 8 miles. The machine lifted from

the track just as it was entering on the fourth rail. 

Mr. Daniels took a picture just as it left the tracks. I found the control of the

front rudder quite difficult on account of its being balanced too near the center

and thus had a tendency to turn itself when started so that the rudder was turned

too far on one side and then too far on the other. As a result the machine would

rise suddenly to about 10 ft. and then as suddenly, on turning the rudder, dart for

the ground. A sudden dart when out about 100 feet from the end of the tracks

ended the flight. Time about 12 seconds (not known exactly as watch was not

promptly stopped). The lever for throwing off the engine was broken, and the

skid under the rudder cracked. After repairs, at 20 min. after 11 o’clock Will

made the second trial. The course was about like mine, up and down but a little

longer over the ground though about the same in time. Dist. not measured but

about 175 ft. Wind speed not quite so strong. With the aid of the station men present, we picked the machine up and carried it back to the starting ways. At about

20 minutes till 12 o’clock I made the third trial. When out about the same distance as Will’s, I met with a strong gust from the left which raised the left wing

and sidled the machine off to the right in a lively manner. I immediately turned

the rudder to bring the machine down and then worked the end control. Much

to our surprise, on reaching the ground the left wing struck first showing the lateral control of this machine much more effective than on any of our former ones.

At the time of its sidling it had raised to a height of probably 12 to 14 feet. At just

12 o’clock Will started on the fourth and last trip. The machine started off with

its ups and downs as it had before, but by the time he had gone three or four hundred feet he had it under much better control, and was traveling on a fairly even

course. It proceeded in this manner till it reached a small hummock out about

800 feet from the starting ways, when it began its pitching again and suddenly

darted into the ground. The front rudder frame was badly broken up, but the

main frame suffered none at all. The distance over the ground was 852 feet in 59
Document 1-13(a–b) 223

seconds. The engine turns was 1071, but this included several seconds while on

the starting ways and probably about a half second after landing. The jar of landing had set the watch on machine back so that we have no exact record for the

1071 turns. Will took a picture of my third flight just before the gust struck the

machine. The machine left the ways successfully at every trial, and the tail was

never caught by the truck as we had feared.

After removing the front rudder, we carried the machine back to camp. We set

the machine down a few feet west of the building, and while standing about discussing

the last flight, a sudden gust of wind struck the machine and started to turn it over.

All rushed to stop it. Will who was near the end ran to the front, but too late to do

any good. Mr. Daniels and myself seized spars at the rear, but to no purpose. The

machine gradually turned over on us. Mr. Daniels, having had no experience in

handling a machine of this kind, hung on to it from the inside, and as a result was

knocked down and turned over and over with it as it went. His escape was miraculous,

as he was in with the engine and chains. The engine legs were all broken off, the chain

guides badly bent, a number of uprights, and nearly all the rear ends of the ribs

were broken. One spar only was broken.

After dinner we went to Kitty Hawk to send off telegram to M. W. While there

we called on Capt. and Mrs. Hobbs, Dr. Cogswell and the station men.

Document 1-13(b), statement by the Wright brothers 

to the Associated Press, 5 January 1904.

It had not been our intention to make any detailed public statement concerning

the private trials of our power “Flyer” on the 17th of December last; but since the

contents of a private telegram, announcing to our folks at home the success of our

trials, was dishonestly communicated to the newspapermen at the Norfolk office,

and led to the imposition upon the public, by persons who never saw the “Flyer”

or its flights, of a fictitious story incorrect in almost every detail; and since this

story together with several pretended interviews or statements, which were fakes

pure and simple, have been very widely disseminated we feel impelled to make

correction. The real facts were as follows:

On the morning of December 17th, between the hours of 10:30 o’clock and

noon, four flights were made, two by Orville Wright and two by Wilbur Wright.

The starts were all made from a point on the level sand about two hundred feet

west of our camp, which is located a quarter of a mile north of the Kill Devil sand

hill, in Dare County, North Carolina. The wind at the time of the flights had a

velocity of 27 miles an hour at ten o’clock, and 24 miles an hour at noon, as

recorded by the anemometer at the Kitty Hawk Weather Bureau Station. This

anemometer is thirty feet from the ground. Our own measurements, made with a
224 Chapter 1: The Achievement of Flight

hand anemometer at a height of four feet from the ground, showed a velocity of

about 22 miles when the first flight was made, and 20 1/2 miles at the time of the

last one. The flights were directly against the wind. Each time the machine started

from the level ground by its own power alone no assistance from gravity, or any

other source whatever. After a run of about 40 feet along a monorail track, which

held the machine eight inches from the ground, it rose from the track and under

the direction of the operator climbed upward on an inclined course till a height

of eight or ten feet from the ground was reached, after which the course was kept

as near horizontal as the wind gusts and the limited skill of the operator would

permit. Into the teeth of a December gale the “Flyer” made its way forward with

a speed of ten miles an hour over the ground and thirty to thirty-five miles an hour

through the air. It had previously been decided that for reasons of personal safety

these first trials should be made as close to the ground as possible. The height chosen

was scarcely sufficient for maneuvering in so gusty a wind and with no previous

acquaintance with the conduct of the machine and its controlling mechanisms.

Consequently the first flight was short. The succeeding flights rapidly increased

in length and at the fourth trial a flight of fifty-nine seconds was made, in which

time the machine flew a little more than a half mile through the air, and a distance of 852 feet over the ground. The landing was due to a slight error of judgment on the part of the aviator. After passing over a little hummock of sand, in

attempting to bring the machine down to the desired height, the operator turned

the rudder too far; and the machine turned downward more quickly than had

been expected. The reverse movement of the rudder was a fraction of a second

too late to prevent the machine from touching the ground and thus ending the

flight. The whole occurrence occupied little, if any, more than one second of time.

Only those who are acquainted with practical aeronautics can appreciate the

difficulties of attempting the first trials of a flying machine in a twenty-five mile

gale. As winter was already well set in, we should have postponed our trials to a

more favorable season, but for the fact that we were determined, before returning

home, to know whether the machine possessed sufficient power to fly, sufficient

strength to withstand the shocks of landings, and sufficient capacity of control to

make flight safe in boisterous winds, as well as in calm air. When these points had

been definitely established, we at once packed our goods and returned home,

knowing that the age the flying machine had come at last.

From the beginning we have employed entirely new principles of control; and

as all the experiments have been conducted at our own expense without assistance from any individual or institution, we do not feel ready at present to give

out any pictures or detailed description of the machine.
Document 1-14(a–d) 225

Document 1-14(a–d)

(a) Wilbur and Orville Wright, letter to the Secretary of War,

Dayton, Ohio, 9 October 1905, The Papers of 

Wilbur and Orville Wright, pp. 514–515.

(b) U.S. Army Signal Corps, “Specification No. 486,

Advertisement and specification for a heavier-than-air 

flying machine,” issued 23 December 1907, copy in Milton

Ames Collection, Historical Archives, NASA Langley 

Research Center, Hampton, Virginia.

(c) Wilbur and Orville Wright, letter to General James Allen,

U.S. Army Signal Corps, 27 January 1908, The Papers of Wilbur

and Orville Wright, p. 856.

(d) Octave Chanute, excerpts from “Recent Aeronautical

Progress in the United States,” The Aeronautical Journal

[London] (12 July 1908): 52–55.

While the anniversary of the invention of the airplane is marked from the

Wright brothers’ successful test flights of 1903, the inaugural of the airplane’s

development into a practical, useable device was marked by a subsequent

improved Wright airplane’s successful completion of government trials, which led

to the Wright’s first sale of a flying machine on 2 August 1909. 

This significant step in the development of aviation is marked through the

following four documents, and conclude this chapter. In 1905, Wilbur and Orville

Wright initiated a correspondence with the Secretary of War offering their aircraft

for sale to the government after a public demonstration of its capabilities. After a

further bit of prodding, in 1907 the United States Army issued the second document, an official statement of specifications regarding the aerodynamic performance of a flying machine to be used by the Signal Corps as an observation aircraft.

The third document is the Wright brothers’ responding bid. Rounding out this

group of documents is a summary by Octave Chanute published in Great Britain

reviewing the “Recent Aeronautical Progress in the United States.” 

With Wilbur away in Europe demonstrating one of their airplanes to astonished crowds, Orville was left to pilot the airplane for the Army. The military tests
226 Chapter 1: The Achievement of Flight

were held at Fort Myer, Virginia, just outside of Washington, D.C., beginning on

3 September 1908. A week of impressive demonstrations, in which the aircraft

met or exceeded requirements, dramatically opened the eyes of America to the

amazing technological achievement of the Wright brothers and the promise of

aviation. Thereafter, not even the unfortunate crash on 17 September that injured

Orville and killed his official passenger, Lieutenant Thomas E. Selfridge, could

stifle the growing appreciation that the day of the airplane was finally at hand. 

Orville recovered from his injuries, and with Wilbur’s help the tests resumed

in July 1909. In the government contract awarded to the Wrights following the

acceptance of their flying machine by the U.S. Army, the brothers received

$30,000 for the delivery of one aircraft and the training of two pilots. The price

included a $5,000 bonus for exceeding the stipulated speed requirement by a

recorded average speed of 42.583 miles per hour over the 10-mile test course.

Document 1-14(a), letter from the Wright brothers 

to the Secretary of War, 9 October 1905.

Some months ago we made an informal offer to furnish to the War Department

practical flying machines suitable for scouting purposes. The matter was referred to

the Board of Ordnance and Fortification, which seems to have given it scant consideration. We do not wish to take this invention abroad, unless we find it necessary to do so, and therefore write again, renewing the offer.

We are prepared to furnish a machine on contract, to be accepted only after trial

trips in which the conditions of the contract have been fulfilled; the machine to carry

an operator and supplies of fuel, etc., sufficient for a flight of one hundred miles;

the price of the machine to be regulated according to a sliding scale based on the

performance of the machine in the trial trips; the minimum performance to be a

flight of at least twenty-five miles at a speed of not less than thirty miles an hour.

We are also willing to take contracts to build machines carrying more than

one man.

Document 1-14(b), U.S. Army Signal Corps, “Specification No. 486, Advertisement

and specification for a heavier-than-air flying machine,” 23 December 1907.

Signal Corps Specification, No. 486

Advertisement and specification for a heavier-than-air flying machine.

To the Public:

Sealed proposals, in duplicate, will be received at this office until 12 o’clock

noon on February 1, 1908, on behalf of the Board of Ordnance and Fortification

for furnishing the Signal Corps with a heavier-than-air flying machine. All proposals
Document 1-14(a–d) 227

received will be turned over to the Board of Ordnance and Fortification at its first

meeting after February 1 for its official action.

Persons wishing to submit proposals under this specification can obtain the

necessary forms and envelopes by application to the Chief Signal Officer, United

States Army, War Department, Washington, D.C. The United States reserves the

right to reject any and all proposals.

Unless the bidders are also the manufacturers of the flying machine they must

state the name and place of the maker.

Preliminary.—This specification covers the construction of a flying machine

supported entirely by the dynamic reaction of the atmosphere and having no gas bag.

Acceptance.—The flying machine will be accepted only after a successful trial

flight, during which it will comply with all requirements of this specification. No

payments on account will be made until after the trial flight and acceptance.

Inspection.—The Government reserves the right to inspect any and all

processes of manufacture.

General Requirements

The general requirements of the flying machine will be determined by the

manufacturer, subject to the following conditions:

1. Builders must submit with the proposals the following:

(a) Drawings to scale showing the general dimensions and shape of the flying

machine which they propose to build under this specification.

(b) Statement of the speed for which it is designed

(c) Statement of the total surface area of the supporting planes

(d) Statement of the total weight.

(e) Description of the engine which will be used for motive power.

(f) The material of which the frame, planes, and propellers will be constructed.

Plans received will not be shown to other bidders.

2. It is desirable that the flying machine should be designed so that it may be

quickly and easily assembled and taken apart and packed for transportation in

army wagons. It should be capable of being assembled and put in operation in

about one hour.

3. The flying machine must be designed to carry two persons having a combined weight of about 350 pounds, also sufficient fuel for a flight of 125 miles.

4. The flying machine should be designed to have a speed of at least forty

miles per hour in still air, but bidders must submit quotations in their proposals

for cost depending upon the speed attained during the trial flight, according to

the following scale:

40 miles per hour, 100 per cent.

39 miles per hour, 90 per cent.

38 miles per hour, 80 per cent.
228 Chapter 1: The Achievement of Flight

37 miles per hour, 70 per cent.

36 miles per hour, 60 per cent.

Less than 36 miles per hour rejected

41 miles per hour, 110 per cent.

42 miles per hour, 120 per cent.

43 miles per hour, 130 per cent.

44 miles per hour, 140 per cent.

5. The speed accomplished during the trial flight will be determined by taking

an average of the time over a measured course of more than five miles, against

and with the wind. The time will be taken by a flying start, passing the starting

point at full speed at both ends of the course. This test subject to such additional

details as the Chief Signal Officer of the Army may prescribe at the time.

6. Before acceptance a trial endurance flight will be required of at least one

hour during which time the flying machine must remain continuously in the air

without landing. It shall return to the starting point and land without any damage that would prevent it immediately starting upon another flight. During this

trial flight of one hour it must be steered in all directions without difficulty and

at all times under perfect control and equilibrium.

7. Three trials will be allowed for speed as provided for in paragraphs 4 and 5.

Three trials for endurance as provided for in paragraph 6, and both tests must be

completed within a period of thirty days from date of delivery. The expense of the

tests to be borne by the manufacturer. The place of delivery to the Government

and trial flights will be at Fort Myer, Virginia.

8. It should be so designed as to ascend in any country which may be encountered in field service. The starting device must be simple and transportable. It

should also land in a field without requiring a specially prepared spot and without damaging its structure.

9. It should be provided with some device to permit of a safe descent in case

of an accident to the propelling machinery.

10. It should be sufficiently simple in its construction and operation to permit

an intelligent man to become proficient in its use within a reasonable length of time.

11. Bidders must furnish evidence that the Government of the United States

has the lawful right to use all patented devices or appurtenances which may be a

part of the flying machine, and that the manufacturers of the flying machine are

authorized to convey the same to the Government. This refers to the exclusive

purchase of patent rights for duplicating the flying machine.

12. Bidders will be required to furnish with their proposal a certified check

amounting to ten per cent of the price stated for the 40-mile speed. Upon making

the award for this flying machine these certified checks will be returned to the bidders,

and the successful bidder will be required to furnish a bond, according to Army
Document 1-14(a–d) 229

Regulations, of the amount equal to the price stated for the 40-mile speed.

13. The price quoted in proposals must be understood to include the instruction of two men in the handling and operation of the flying machine. No extra

charge for this service will be allowed.

14. Bidders must state the time which will be required for delivery after

receipt of order.

James Allen

Brigadier General, Chief Signal Officer of the Army.

Signal Office,

Washington, D. C., December 23, 1907.

Document 1-14(c), letter from Wilbur and Orville Wright 

to General James Allen, 27 January 1908.

We herewith inclose a bid for furnishing the Signal Corps with a heavier-thanair flying machine, in accordance with Specification No. 486, of December 23,

1907, together with a certified check for two thousand five hundred dollars

($2,500.00).

The machine we propose to deliver is designed to weigh between 1,100 and

1,250 lbs. with two men on board, and for a speed of forty miles an hour. It will

have an area of 500 square feet in the supporting planes; and will be propelled by

a four-cycle, water-cooled gasoline motor. The frames of the planes will be constructed of spruce and ash covered with cotton muslin; the propellers of spruce

and linen.

We have made the date of delivery of the machine 200 days, in order to provide

sufficient time for increasing the speed of the machine now under construction,

in case Requirement No. 5 is to be interpreted literally. If, however, Requirement

No. 5 is interpreted to mean an average of the speeds with and against the wind

over a measured course, which is the correct method to give and average corresponding to flight made in still air, as specified in Requirement No. 4, we would

be able to make delivery at a much earlier date.

We inclose a photograph of our machine of 1905, which was similar to the one

we now propose to furnish. We would request that this, as well as the drawings, be

kept confidential.

Document 1-14(d), Octave Chanute, excerpts from 

“Recent Aeronautical Progress in the United States,” London, 1908.

The public attitude in the United States in 1906 and 1907 concerning aërial

navigation has been one of expectancy and apathy. The announcements of the
230 Chapter 1: The Achievement of Flight

marvellous success achieved by Wright Brothers, which every investigation

seemed to confirm, must have deterred many searchers from experimenting at

all, until they know how much remained to be accomplished in aviation. . . . 

Meanwhile Aëro Clubs have sprung up like mushrooms all over the country.

The leading one still is the Aëro Club of America in New York, which was organized in 1905. It has held several exhibitions, has promoted the publication of an

interesting book, “Navigating the Air,” the establishment of a correspondence

School of Aëronautics by Mr. Triaca, and an effort is now being made in connection with the Club to raise a fund of £5,000 to be offered in prizes for Aviation. 

In St. Louis and Chicago local aëro clubs propose to organize balloon races

to be held in 1908. In these and other cities, members are encouraged to engage

in the sport by owning and riding balloons themselves, and it remains to be seen

how long the enthusiasm will last.

Two monthly Aëronautical Magazines have been started, one in New York

and one in St. Louis, but it is yet to be ascertained how well they will be supported.

The Jamestown Exposition of 1907 organized an aëronautical exhibit which

amounted to but little, as well as an Aëronautical Congress which brought out few

papers, but searchers have been building apparatus to be experimented with in

the summer of 1908.

The most distinguished of these is Dr. Alexander Graham Bell, the inventor

of the Telephone, who has been experimenting with his tetrahedral kite. He tested

on December 6th, 1907, his gigantic man-lifting kite “Cygnet,” consisting of

3,393 wing cells, presenting 1,966 square feet of oblique surfaces, and weighing

with the floats and passenger an aggregate of 600 pounds. This was towed into

the middle of a lake and raised against a wind of 21 miles an hour by a tug-boat.

It exhibited that perfect stability which all previous experiments indicated, and

upon the wind’s dying away it descended gently from a height of 168 feet, but was

broken on striking the water. It is to be tested again during the summer of 1908

with a view to eventually apply a motor. There is no question as to the automatic

equilibrium of this form of apparatus, but it is possible that the inferior lifting

power of the oblique surfaces and the resistance of so many front edges will make

the design less favorable for a flying machine than other forms.

Dr. Bell then generously provided the means (he gives credit to his wife) and

organized the so-called “Aërial Experiment Association” with its headquarters at

Hammondsport, New York, to give his assistants a chance to experiment their

own ideas. The first result was the construction of the motor-driven aëroplane

“Red Wing,” chiefly designed by Lieutenant T. Selfridge, which made its trial trip on

sleigh runners on the ice of Lake Leuka on March 9th, 1908. It is a double-decked

apparatus 43 feet across, the surfaces being arched both fore and aft and from tip

to tip; the upper aëroplane being bowed downward somewhat in the attitude of
Document 1-14(a–d) 231

the gull and the lower aëroplane, which is 6 feet shorter, being bowed upward

somewhat to the attitude of the vulture when soaring. The total surface is 386

square feet and the total weight, including the aviator, is 570 pounds. It is driven

by a Curtiss motor of 40-horse power, actuating a screw propeller.

At the very first attempt the apparatus left the ice after travelling only 200 feet

and flew a total distance of 319 feet from the point where it left the ice to the point

of descending. It alighted somewhat clumsily and broke one strut, this being the

first public exhibition of the flight of a heavier-than-air machine in America. . . .

The main interest, however, attaches to the pending United States

Government tests of flying machines which are under contract for delivery next

August. On December 23rd, 1907, the United States Army Signal Corps issued

invitations to tenders, which produced much amazement. European and

American journals have said that these specifications assume that flying machines

are almost a usual method of transportation, and that the terms are so exacting as

to seem unreasonable. The Signal Services officers answer that the specifications

were drawn up after interviews with some of the inventors and merely cover what they

said they could perform, while some clauses were added to prevent the Government’s

being trifled with, and that the tests will be conducted with judicious reason and

liberality. More especially does this apply to the granting but three trials each for

the speed test and the endurance test of one hour, which might be defeated on

each occasion by some fortuitous and trifling circumstance. . . .

The performances of the Wright Brothers have been viewed with incredulity

because of the mystery with which they have been surrounded in the hope of a

rich money reward, yet it is now generally conceded that they have accomplished

all that they have claimed, i.e., to have made a first dynamic flight in 1903, to

have mastered circular courses in 1904, making 105 flights, the longest of which

was three miles, and to have obtained thorough control over their apparatus in

1905, making 49 flights, the longest of which was 24 miles, consisting of 30

sweeps over a circular course at an average speed of 38 miles an hour. Since then

they have made no flights, having been engaged in negotiations with a view to

marketing their invention.

Now they have made a contract with the United States Government to furnish a

flying machine under those formidable specifications. They set to work at once. They

have built parts of more than one machine, so as to guard against bad breakages, and

have returned to their old experimental grounds near Kitty Hawk, North Carolina.

This is situated on a long sand spit, two or three miles wide, between the waters of

Pamlico Sound and the Atlantic Ocean. It is about as inaccessible a spot near civilisation [sic] as can well be, being almost a desert, occupied by a few fishermen and a

Government lifesaving station. Near the camp is “Kill Devil Hill,” a cone of drifted

sand about 100 feet high, on which former gliding experiments were made.
232 Chapter 1: The Achievement of Flight

Here the Wrights have established themselves and begun their practice, for it

is only by strenuous practice that the mastery of the air is to be obtained. They

are said to be proceeding with great caution, testing every part and peculiarity of

the machine, the longest flight yet reported (May 14th, 1908) being eight miles,

followed, however, by a serious breakage on landing, said to be due to a false

maneuvre, in consequence of some change in the location of the levers which control the rudders. It is stated that the wreck was so complete that the parts will be

shipped back to Dayton, Ohio, where the craft will be rebuilt.

The Wrights are understood to have until August 27th to deliver their

machine to the Signal Corps for testing, so that there will be sufficient time to

resume practice after the machine is repaired. Whether this practice will take

place on the same ground or elsewhere is not known. The spot is very secluded,

but the ubiquitous reporter has found the camp and is sending “news” both true

and untrue, to the great annoyance of [the] Wright Brothers. . . . 

An amusing struggle has resulted. The reporters are frantic for information,

and the Wrights most determined that no description be given of their apparatus.

It is probable that many contradictory cablegrams will have been received in

Great Britain when the present paper reaches the Hon. Secretary.

The Wright brothers stand a fair chance of passing the tests and having their

machine accepted. They may be defeated by some accident during the preliminary

trials or the formal tests, but the present writer is sure that all the members of the

Aëronautical Society of Great Britain will join him in the hope that the best of luck

will attend the demonstration.
Document 1-15 233

Document 1-15

Simon Newcomb, “Aviation Declared a Failure,” 

Literary Digest 37, 17 October 1908, 549.

The press was not the only group to bungle the Wright brothers’ story and to

minimize the importance of what they had achieved and what the flying machine

signified for society. One of the most vocal “bah-humbugs” in the early 1900s happened to be one of the greatest scientists of his day, Professor Simon Newcomb

(1835–1909). 

Newcomb was a giant in the field of celestial mechanics. His work in the late

nineteenth century on the orbital motion of the planets of the Solar System provided the cornerstone of the nautical and astronomical almanacs of the United

States and Great Britain, not just in the early 1900s but as recently as 1984. Albert

Einstein acknowledged the importance of Newcomb’s work in the development of

his own theory of relativity. Born in England, he immigrated in 1854 at age 19 to

Maryland to join his father. Newcomb taught himself most of the mathematics

and astronomy he knew, taking a job in 1857 in the American Nautical Almanac

Office, which was located in Cambridge, Massachusetts. Admitted to Harvard, he

graduated in 1858, and three years later he took an appointment to the Naval

Observatory at Washington, D.C. The next ten years he spent determining the

positions of celestial objects using various telescopes, some of his own design. In

1877, at age forty-two, he became director of the American Nautical Almanac

Office, now located in Washington, D.C., and initiated the work on celestial

motion for which he would become most famous. In 1884, Newcomb became professor of mathematics and astronomy at The Johns Hopkins University, staying

there until 1893. He served as editor of the American Journal of Mathematics for

many years and was a founding member and the first president (1899–1905) of

the American Astronomical Society. He also served as president of the American

Mathematical Society from 1897 to 1898. By the time the Wright brothers made

their historic first flight in 1903, Newcomb had risen to the top of the astronomical

community in the United States, the recipient of many of the highest national and

international awards given to scientists, including Fellow of the British Royal Society. 

Newcomb loved to travel. He spoke French and German fluently and enough

Italian and Swedish to travel easily in those countries. An avid hiker, at age seventy

(in 1905) he climbed to the chalet high up the side of the Matterhorn in the Swiss

Alps, a feat almost unprecedented for a man of his age. One may not expect that

such a brilliant and adventurous man would be so pessimistic about the future of

aviation, but no one was more outspoken or pungent in his pessimism about the

usefulness of flying than Newcomb.
234 Chapter 1: The Achievement of Flight

What follows is an article published in the Literary Digest in October 1908

revealing Newcomb’s ongoing pessimism. Newcomb in fact had been writing

about aviation in condescending terms since the 1890s. In one article published

in McClure’s Magazine around the turn of the century, Newcomb had written:

“Man’s desire to fly like a bird is inborn in our race, and we can no more be

expected to abandon the idea than the ancient mathematician could have been

expected to give up the problems of squaring the circle.” In other words, he

believed the problems of flight could never be solved. In the article below,

Newcomb’s skepticism about the future of aviation is quoted at length. The caption under the picture of Newcomb that ran with the story read “The eminent

American astronomer. He doubts if aviation will ever be of much practical value.”

Newcomb’s was not the only voice still expressing such negativism. In 1910,

the New York Telegraph called a proposal from a Texas congressman for a study of

the possibility of U.S. airmail operations “ludicrous.” The paper mocked: “Love

letters will be carried in rose-pink aeroplane, steered with Cupid’s wings and

operated by perfumed gasoline” [quoted in Roger E. Bilstein, Flight in America:

From the Wrights to the Astronauts (Baltimore, MD: Johns Hopkins University Press,

1984), pp. 16–17]. 

Though Newcomb died in 1909, his attitudes and others like them did not

fade as quickly as one might think. But as aviation caught Americans’ attention in the

early 1910s, the public’s misgivings greatly diminished. When the airplane

proved a dynamic instrument in the Great War (1914–1918), most doubt about the

practicality of aviation disappeared. Still today, though, there are millions of people

who share the basis of Newcomb’s resistance to flying. As he is quoted as saying

in the article below: “Is it not evident, on careful consideration, that the ground

affords a much better bade than air ever can? Resting upon it we feel safe and we

know where we are. In the air we are carried about by every wind that blows.”

Though the world’s emerging aerodynamic specialists might surely have

argued with Newcomb’s point of view, not even they could undervalue the many

dangers, uncertainties, and inefficiencies of machines flying through the air. In

an important sense, aerodynamicists would be spending the next 100 years

answering Newcomb’s complaint.

Document 1-15, Simon Newcomb, “Aviation Declared a Failure,” 1908.

A pessimist has been defined as a man who, when offered the choice of two

evils, takes both. Prof. Simon Newcomb in his recent article on “The Problem of

Aerial Navigation” (The Nineteenth Century, London, September) varies the formula somewhat. When offered two perfectly good methods of navigating the air, he

rejects both. He concludes that the disadvantages of both dirigible balloons and
Document 1-15 235

aeroplanes outweigh all existing and possible advantages, and that the solid earth

is good enough for him, anyhow. We have not space for the professor’s extended

bill of particulars, but will proceed at once to his general statement of the case

against aviation. First summing up the advantages in one paragraph, only to overwhelm them in the next, be says:

“Let us . . . in fairness see what is to be placed on the credit side. First and

almost alone among these is the fact that steam transportation on land requires

the building of railways, which are so expensive that the capital involved in them

probably exceeds that invested in all other forms of transportation. Moreover,

there are large areas of the earth’s surface not yet accessible by rail, among which

are the poles and the higher mountains. All such regions, the mountains excepted,

we may suppose to be attainable by the perfected air-ship of the future. The more

carefully we analyze these possible advantages, the more we shall find them to

diminish in importance. Every part of the earth’s surface on which men now live

in large numbers, and in which important industries are prosecuted, can now be

reached by railways, or will be so reached in time. True, this will involve a constantly increasing investment of capital. But the interest on this investment will be

a trifle in comparison with the cost and drawbacks incident to the general introduction of the best system of aerial transportation that is even ideally possible in

the present state of our knowledge. . . . ”

“May we not say . . . that the efforts at aerial navigation now being made are

simply most ingenious attempts to substitute, as a support of moving bodies, the

thin air for the solid ground? And is it not evident, on careful consideration, that

the ground affords a much better base than air ever can? Resting upon it we feel

safe and know where we are. In the air we are carried about by every wind that

blows. Any use that we can make of the air for the purpose of transportation, even

when our machinery attains ideal perfection, will be uncertain, dangerous, expensive, and inefficient, as compared with transportation on the earth and ocean.

The glamour which surrounds the idea of flying through the air is the result of

ancestral notions, implanted in the minds of our race before steam transportation

had attained is present development. Exceptional cases there may be in which the

air-ship will serve a purpose, but they are few and unimportant.”

Professor Newcomb admits that in certain special cases flyers or balloons may

accomplish what could be done in no other way. For instance, he thinks it not

unlikely that the pole may be first reached by a dirigible balloon. The balloon as

an engine of war, however, he regards as an impossibility, and he reassures the

Englishmen who have been looking forward apprehensively to a vertical bombardment of British towns by a fleet of German dirigibles. He says in conclusion:

“In presenting the views set forth in the present article the writer is conscious

that they diverge from the general trend, not only of public opinion, but of the
236 Chapter 1: The Achievement of Flight

ideas of some able and distinguished authorities in technical science, who have

given encouragement to the idea of aerial navigation. Were it a simple question

of weight of opinion he would frankly admit the unwisdom of engaging in so

unequal a contest. But questions of what can be done through the application of

mechanical power to bodies in motion have no relation to opinion. They can be

determined only by calculations made by experts and based upon the data and

principles of mechanics.”

“If any calculations of the kind exist, the writer has never met with them, nor

has he ever seen them either quoted or used by any author engaged in discussing

the subject. So far as his observation has extended, the problem has been everywhere looked upon as merely one of experiments ingeniously conducted with all

the aid afforded by modern apparatus. He has seen no evidence that any writer

or projector has ever weighed the considerations here adduced, which seem to

him to bring out the insuperable difficulties of the system he has been discussing,

and the small utility to be expected from it even if the difficulties were surmounted.”

If he is wrong in any point—and he makes no claim to infallibility—it must

be easy to point out in what his error consists. He therefore concludes with the

hope that if his conclusions are ill-founded their fallacy will be shown, and that if

well-founded they may not be entirely useless in affording food for thought to

those interested in the subject.

Experts in aviation and the members of aero-clubs will not be apt to agree with

all this, but it will certainly be useful in counteracting the ardor of those enthusiasts

who think that we are all going to fly to Europe before the end of 1909.
237

Chapter 2

Building a Research Establishment

The American Way

The only people so far who have been able to get at something like accurate

results from wind-tunnel experiments are the workers at the Experimental

Station at Langley Field, which is run by the National Advisory

Committee for Aeronautics of the United States of America. Thanks to the

wealth of the United States and the high intelligence of those who are

charged with the task of aeronautical experiments, workers in the

American research establishments have acquired knowledge that is in

many ways far ahead of anything we have in this country. And they have

it very largely by what is called “ad hoc research,”—that is to say, going

and looking for the solution of one particular problem, instead of experimenting around blindly in the hope that something may turn up, after the

fashion which is known as “basic research.”

The above editorial comment by C. G. Grey, a prominent British aeronautical engineer

and editor of the aviation journal The Aeroplane, appeared in the 6 February 1929

issue of that journal.

From the Wright Bicycle Shop to the Langley Full-Scale Tunnel

For those who followed the ingenious Wright brothers into the air after 1903,

the maturation of the airplane depended on a growing and increasingly sophisticated

understanding of aerodynamics, for there was still much about flight that was

unknown. The route to greater aeronautical knowledge in the post-Wright era was

not a straight highway. To the extent a map even existed, it offered a maze of

twisting roads involving trial-and-error design of new flying machines; dogged

pragmatic testing; deeper scientific inquiry; and, perhaps most importantly, a

shrewd combination of the best that both theory and experiment had to offer. 

Yet for the aeronautical scientists and engineers in pursuit of aviation

progress in the early twentieth century, there was perhaps no surer course to

progress than the one laid out by the Wright brothers themselves. Unfortunately,

not everyone in the brave new world of aeronautics understood the Wrights’ path

to success. Many wrongly interpreted their invention of the airplane either as the

heroic act of ingenious mechanical tinkerers or as a basic scientific discovery,

rather than as a solid technological program of engineering research and development.
238 Chapter 2: Building a Research Establishment

In fact, the Wrights’ first successful flying machines, starting with their 1902 glider

and the 1903 airplane that followed, not only represented key breakthroughs in

their efforts to master heavier-than-air flight, but also bore testimony to the

irreplaceable value of combining careful laboratory experiments with actual

flight testing. 

In 1915, twelve long years after the epochal Wright flight, the U.S. Congress

established the National Advisory Committee for Aeronautics, the predecessor of

present-day NASA, with the mission “to supervise and direct the scientific study

of the problems of flight with a view to their practical solution.” Eventually this

agency recreated the Wrights’ formula for success in a series of federal research

laboratories.1 The NACA accomplished this, originally, by building an extraordinary community of aeronautical engineers, scientists, technicians, and test pilots

at the Langley Memorial Aeronautical Laboratory (LMAL) in Tidewater, Virginia—

the NACA’s first and, until 1941, only research facility.2 At NACA Langley, the laboratory staff faced, and eventually resolved, many fundamental questions about

how to plan and conduct institutional aerodynamic research. These questions

dealt with issues of how research should be focused, what sort of facilities should

be built, what type of experimental investigations should be carried out, and how

experimentalists and theoreticians could work together fruitfully. The early

NACA community also dealt with the issue of whether science or engineering

should be in control of the research program, and especially whether the German

academic laboratory model could be transferred successfully to America—or

whether an American lab would have to find its own way. Through the resolution

of these issues, in conjunction with a growing list of important achievements in

aeronautics, a sustainable organizational identity for Langley and for the subsequent NACA laboratories began to evolve. The result was a dynamic and highly

creative organization that, although its original facility was named after scientist

Samuel P. Langley, actually reflected more the systematic engineering approach

of Wilbur and Orville Wright, with an emphasis on a search for practical solutions.

Throughout this sometimes torturous process, the NACA helped a fledgling

American aircraft industry advance the airplane in a few short decades to an

astoundingly high level of technological performance and corresponding importance in modern society.

1 On the history of the National Advisory Committee for Aeronautics, the place to start is Alex Roland’s

Model Research: The National Advisory Committee for Aeronautics (Washington, DC: NASA SP-4103, 1985),

two volumes.

2 NACA Langley’s history is told in James R. Hansen’s Engineer in Charge: A History of the Langley

Aeronautical Laboratory (Washington, DC: NASA SP-4305, 1987).
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 239

Center stage in NACA research, from the beginning, was a unique device

designed for basic aerodynamic investigation: the “wind tunnel.” Following the

initial achievement of flight, wind tunnels quickly became the central research

facilities at aeronautical laboratories all over the world. This, too, was a legacy of

the Wright brothers’ approach, for the aerodynamic shape of their landmark aircraft had evolved directly out of testing conducted in a simple little wind tunnel

they built in their Dayton bicycle shop. From these wind tunnel experiments in

1901, they garnered the empirical insights needed to design the first truly effective flying machine, their breakthrough glider of 1902.

The Wright brothers did not invent the wind tunnel, and the basic concept behind

it predated their work by roughly 400 years. During the Renaissance, the brilliant

technological dreamer Leonardo da Vinci recognized that air blown past a stationary

object produced the same effect as the object itself moving at the same relative

In building a test device like the wind tunnel and then using it systematically to generate reliable data, the Wright brothers

forged a solid link between aeronautical research and the design of successful aircraft. SI Negative No. A-2708-G
240 Chapter 2: Building a Research Establishment

speed through the air, the fundamental concept upon which wind tunnels operate.

Da Vinci expressed this idea in his statement from the Codex Atlanticus, “As it is to

move the object against the motionless air so it is to move the air against the

motionless object.” Sir Isaac Newton later recognized this same principle. 

From these humble beginnings, the first person to apply the concept to practical

aerodynamic research seems to have been Benjamin Robbins (1707–1751), a brilliant

English mathematician who conducted a series of fundamental experiments on

the ballistic properties of artillery projectiles. To evaluate the air resistance of different

shapes, Robbins constructed a device known as a “whirling arm.” This apparatus

consisted of a four-foot horizontal arm attached to a vertical spindle that was

rotated by the force of a falling weight. Robbins mounted test shapes with similar

cross-section areas on the end of his whirling arm, and found that the speed of

the arm’s rotation varied considerably with objects of different profiles. From this

he concluded that different shapes produced different amounts of air resistance,

identifying the factor subsequently understood as aerodynamic “drag.”3

Following Robbins came John Smeaton (1724–1792), an English civil engineer

interested in sources of power for practical applications. Smeaton used a whirling

arm device of his own making to investigate the function of windmill sails. In

1759, he described his experiments and the elaborate apparatus used in his tests

in a seminal paper presented to the Royal Society of London. In this report, he

outlined the need for such equipment by noting a basic problem in aerodynamic

research: relying solely on natural wind. “In trying experiments on windmill sails,

the wind itself is too uncertain to answer the purpose; we must therefore have

recourse to an artificial wind,” wrote Smeaton, adding that tests “may be done two

ways: either by causing the air to move against the machine, or the machine to

move against the air.” This principle of relative motion, the same observed earlier

by da Vinci, proved to be the key to the future development of the wind tunnel.

However, at the time, and indeed for the next hundred years, relatively few of

Smeaton’s colleagues or successors either understood or accepted it.4

Nevertheless, there were some provident individuals intrigued with the investigation of flight in the nineteenth century who utilized Smeaton’s whirling arm

apparatus to understand aerodynamic principles. Sir George Cayley, for one,

whose work outlined the basic shape of the airplane (see Chapter 1 of this volume),

used a five-foot whirling arm that achieved tip speeds of up to twenty feet per second

3 John D. Anderson, Jr., provides a concise technical summary of the contributions of Leonardo da Vinci,

Benjamin Robins, and other pioneers to the genesis of early aerodynamic concepts in A History of

Aerodynamics and Its Impact on Flying Machines (Cambridge, England: Cambridge University Press,

1997), pp. 14–27 and 55–57.

4 On John Smeaton, see Anderson, A History of Aerodynamics, pp. 58–61 and 76–79.
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 241

to measure the lift and drag properties of different wing shapes.5 Later in the century, some of the most important whirling arm experiments of the pre-flight era

were conducted by Professor Samuel P. Langley, who built a large testing apparatus with a thirty-foot arm on the roof of Pittsburgh’s Allegheny Observatory in

1886. Powered by a ten-horsepower steam engine, this whirling arm produced tip

speeds of nearly 150 feet per second, the equivalent of about 100 miles per hour.

But while Langley’s research produced much valuable information, his frustrations with the whirling arm also epitomized the limitations of this type of aerodynamic testing machine. Because its sixty-foot diameter made the device too large

to be used indoors, Langley was forced to conduct his tests outside where the

results were influenced by the vagaries of natural wind and atmospheric conditions. Even worse, the rotation of the arm itself created currents that disrupted

the air and compromised the test results.6 Clearly, researchers needed a superior

apparatus if they were to obtain reliable results in a controlled laboratory setting.

A completely new type of device invented by Francis H. Wenham (1824–1908)

offered the solution. In 1867 Wenham, a British marine engineer, submitted a

proposal to the Aeronautical Society of Great Britain to build a novel machine

that applied the principles garnered from earlier studies of hydrodynamic water

channels to the new field of aerodynamic research. The Aeronautical Society

sponsored Wenham’s project, and in 1871 he completed an apparatus equipped

with a steam-powered fan that blew air through “a trunk 12 feet long and 18 inches

square, to direct the current horizontally, and in parallel course.” It was, in

essence, the world’s first “wind tunnel”—though this term would not be coined

until forty-two years later.7

From the very beginning, wind tunnels proved a boon to aerodynamic discovery,

and the technical data they generated established a new and much more viable basis

of knowledge about virtually all phenomena of flight. From Wenham’s inaugural

wind tunnel investigations came the realization that the aerodynamic lifting forces

working on wing surfaces were much greater than Newtonian theory predicted.

This early result bred real confidence that powered flight was possible, and it

bequeathed much-needed credibility to the serious scientific study of aeronautics.

Following Wenham’s lead, more students of flight adopted the wind tunnel, start5 Sir George Cayley’s significance in aerodynamic research is analyzed in Tom D. Crouch, A Dream of

Wings: Americans and the Airplane, 1875–1905 (Washington, DC: Smithsonian Institution Press,

1981, 1989), pp. 27–29, 33–35, 47–48, and 63–64. 

6 See Crouch, A Dream of Wings, pp. 48–52, for insights into Samuel P. Langley’s research equipment.

7 N. H. Randers-Pherson, “Pioneer Wind Tunnels,” Smithsonian Miscellaneous Collections 93 (19 January

1935): 1–2. See also F. H. Wenham, “On Forms of Surfaces Impelled Through the Air and Their

Effects on Sustaining Weights.” On Wenham’s contributions to aerodynamics, see Anderson, A

History of Aerodynamics, pp. 116–117 and 119–126.
242 Chapter 2: Building a Research Establishment

ing with fellow Englishman Horatio Phillips, who in 1884 used a wind tunnel of

his own design to establish that cambered airfoils developed significantly more lift

than flat planes. By 1896, when Hiram Maxim constructed a wind tunnel to

advance his aerodynamic research (outlined in the Maxim document in Chapter 1),

the use of wind tunnels had spread to France and other European nations. In that

year, wind tunnel technology also crossed the Atlantic to the Massachusetts

Institute of Technology (MIT), where an inventive graduate student in engineering by the name of A. J. Wells built the first American wind tunnel, a makeshift

arrangement that diverted air from a building ventilation duct for simple aerodynamic tests of flat planes.8

By the dawn of the twentieth century, though wind tunnel development was

still in its infancy, awareness of these valuable tools had spread through the small

community of aviation advocates working to achieve mechanical flight. What was

most significant for the subsequent history of aviation was that Wilbur and Orville

Wright knew enough about wind tunnels to turn to one when they were confronted with anomalous data about the lifting power of wings. As outlined in the previous chapter, the Wrights reached this point after the frustrating 1901 season of

flight tests, when they were forced to face the fact that their gliders, based on Otto

Lilienthal’s coefficients, simply did not achieve the predicted amount of lift. From

this they reasoned that Lilienthal’s tables might possibly contain errors, which led

them to conduct tests of previous assumptions and then move on to develop their

own experimental data. 

Before building a wind tunnel, the Wrights utilized a clever apparatus of their

own design, consisting of a freely rotating horizontal wheel mounted on the front

of a bicycle. An airfoil model and a control shape were mounted on opposite sides

of this wheel, and the forward movement of the bicycle was used to generate a

flow of air past these test surfaces. Results obtained from tests with this device

confirmed their suspicion that the Lilienthal tables were indeed faulty, but the

method was neither precise nor consistent enough to develop data for a new set

of tables. For this purpose, the Wrights required a wind tunnel. In their bicycle

workshop they constructed a six-foot-long square trough sixteen inches wide,

through which they channeled a twenty-seven-mile-per-hour airflow produced by

a two-blade fan driven by an electrical shop motor. As part of their tunnel they

also designed a set of balances to measure the relative lift and drag on test airfoil

sections. With their “laboratory” thus equipped, sometime around 22 November

8 Albert J. Wells describes his wind tunnel device in his bachelor’s thesis, “An Investigation of Wind

Pressure upon Surfaces,” (pp. 4–23), completed at MIT in 1896. For descriptions of the tunnels

devised by Horatio Phillips and Hiram Maxim, see Randers-Pherson, “Pioneer Wind Tunnels,”

pp. 3–4.
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 243

1901 they began a short but intensive two-week sequence of tests, through which

they systematically and precisely evaluated over 150 different airfoil shapes. By

the conclusion of these tests the Wrights had amassed the greatest body of aerodynamic data in the world, and from this pinnacle of understanding they were

armed with the knowledge to build a true working flying machine. Noted historian and Wright biographer Tom Crouch observed of this period of wind tunnel

testing that “[b]oth brothers would look back on these few weeks in November

and December 1901 as the psychological peak of their joint career in aeronautics.”9

In retrospect, this short stretch of time also proved to be a turning point in the

Reproduction of the 1901 Wright drag balance. Orville actually built two balances, one for lift measurements and

the other for drag. Model airfoils could be mounted on both balances and easily changed. Lift and drag forces calculated from these measurements clearly indicated that the previously accepted aerodynamic coefficients on which

the design of airfoils were being based were grossly in error. SI Negative No. A-41899-B

9 Tom D. Crouch, The Bishop’s Boys: A Life of Wilbur and Orville Wright (New York, NY: W.W. Norton &

Co., 1989), pp. 227–228. See also Crouch, A Dream of Wings, pp. 246–248.
244 Chapter 2: Building a Research Establishment

entire history of technology, because it prepared the way, only two years later, for

the successful flight of a powered airplane. 

On 7 December 1901 the Wright’s sister Katherine noted in a message to

their father that “[t]he boys have finished their tables of the action of the wind on

various surfaces, or rather they have finished their experiments.” The important

work of analyzing and applying the results lay ahead, and it is at this point that

the documentary trail of Chapter 2 begins, with a series of letters written by

Wilbur Wright to Octave Chanute and George Spratt, a Chanute disciple who,

with his mentor, would subsequently join the Wrights at Kitty Hawk for the

momentous 1902 flying season.

Like the airplane itself, the use of wind tunnels quickly advanced beyond the

work of the Wright brothers. In unrelated work in 1901, Professor Albert F. Zahm

(1862–1954) began operating an impressively sized forty-foot-long tunnel with a

six-foot-square cross section at Catholic University of America in Washington,

D.C. This large test apparatus was entirely enclosed in a building specifically

designed for its operation, making it the world’s first true wind tunnel laboratory.

Zahm used this facility to conduct pioneering tests on skin friction, and went on

to become an important figure in the institutional foundation of American aerodynamic research.10

Although the Wrights, Zahm, and other Americans continued to pursue aerodynamic discoveries, it was the Europeans who quickly came to dominate the field

in the first quarter of the twentieth century. Between 1903 and the start of World

War I in 1914, no less than ten wind tunnels began operation in Europe, as bellicose governments concerned with the military applications of aircraft invested in

new aeronautical laboratories. This government interest produced such important facilities as the British National Physical Laboratory outside London and the

influential German laboratory at the University of Göttingen. The latter facility

featured an innovative closed-circuit wind tunnel designed by Professor Ludwig

Prandtl, who was at the time perhaps the greatest scientific mind delving into

aerodynamic phenomena. Its signature design feature was the incorporation of a

return passage, which kept all the air moving through the tunnel instead of allowing the air to circulate uncontrolled through the building. Although Prandtl’s tunnel was simple, with a constant two- by two-meter cross section throughout, his

design was vastly more efficient and eventually spawned a whole new generation

of wind tunnels. With a lower volume of air in motion, the closed tunnel required

10 A. F. Zahm, “New Methods of Experimentation in Aerodynamics” [paper presented at the meeting of the American Association for the Advancement of Science, Pittsburgh, PA, 20 June 1902], in

Aeronautical Papers of Albert F. Zahm, Ph.D., 1885–1945 (Notre Dame, IN: University of Notre

Dame, 1950).
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 245

less power than comparably sized open tunnels; furthermore, the quality of the air

and its flow could be more precisely controlled. The majority of modern wind tunnels utilize this closed-circuit concept, and their lineage can be traced to the original tunnels of Ludwig Prandtl.11

In neighboring France, renowned structures engineer Gustav Alexandre Eiffel

(1832–1923) invested not only his legendary energy but also his considerable fortune in aeronautical research, establishing two wind tunnel facilities in and

around Paris. In 1909, he built a 1.5 meter diameter tunnel at Champs de Mars,

near the famous tower that bears his name. Two years later, after conducting over

4,000 tests in his first tunnel, Eiffel constructed a new and much larger wind tunnel

laboratory at Auteuil. (Eiffel published a book entitled La Resistance de l’Air to

report on his initial research, and a 1913 translation of this volume by American

naval observer Jerome C. Hunsaker was the first to use the term “wind tunnel” to

describe these facilities.) An important focus of Eiffel’s tests involved pressure distribution on airfoil surfaces, and he used his wind tunnels to reveal that the reduction

in surface pressure on the top surface of a wing was more significant in generating

aerodynamic lift than the pressure increase on its lower surface. Eiffel also conducted

important research on propeller aerodynamics, and he was the first to test models

of complete airplanes in a wind tunnel. This work helped to establish a clearer

understanding of the correlation between test results and the actual performance

of full-size aircraft. Eiffel was also able to establish empirically the validity of the

relative motion principle, providing scientific proof for the fundamental theory

underlying wind tunnel simulation that began back with da Vinci’s idea.12

While the epicenter of aerodynamic research and development shifted to

Europe by the start of the Great War, small pockets of aeronautical enthusiasts

existed in the United States, many of whom were not at all happy that the homeland

of the Wright brothers had given away its early advantage to the French, Germans,

and British. American research lacked a strong organizational backing, and a few

farsighted individuals who appreciated the long-term importance of aviation to

the United States lobbied for a governmental commitment to aeronautical

11 For the history of the aerodynamics research organized under Ludwig Prandtl’s leadership at the

University of Göttingen, see Paul A. Hanle, Bringing Aerodynamics to America (Cambridge, MA: MIT

Press, 1982). Those who read German should consult Julius C. Rotta, Die Aerodynamische

Versuchsanstalt in Göttingen (Göttingen, Germany: Vanderhoeck & Ruprecht, 1990), especially pp.

45–47. For a detailed analysis of Prandtl’s contribution to aerodynamics, see Anderson, A History of

Aerodynamics, pp. 251–260. 

12 For an English translation of Eiffel’s own description of his wind tunnels, see G. Eiffel, The

Resistance of Air and Aviation: Experiments Conducted at the Champs-de-Mars Laboratory, trans. Jerome

C. Hunsaker (London: Constable & Co.; and Boston: Houghton Mifflin & Co., 1913). For an

assessment of Eiffel’s tunnels and their contributions to aerodynamics, see Anderson, A History of

Aerodynamics, pp. 267–282. 
246 Chapter 2: Building a Research Establishment

research that could compete with the European establishments. Some of the most

dedicated enthusiasts were naval officers Jerome C. Hunsaker, David W. Taylor,

and Washington Irving Chambers. In 1912, Chambers produced a report on aviation for the U.S. Navy (part of which is included in this chapter), which included

a detailed proposal for a national aerodynamic laboratory. Following this, David

Taylor enlisted the technical assistance of Albert Zahm to design a closed-circuit

wind tunnel with an eight-foot-square test section, completed in 1913 at the

Washington Navy Yard. 

On the academic side, MIT, where wind tunnel pioneer A. J. Wells held a

position on the faculty, initiated efforts to develop a program in aeronautical

research. MIT president Richard Maclaurin personally investigated Britain’s

National Physical Laboratory in 1910, and shortly thereafter he approached the

U.S. Navy about a cooperative effort to establish a course of study in aeronautical engineering. When Jerome Hunsaker finished a master’s degree at MIT in

1912, Maclaurin asked the Navy to allow him to remain for three years as an

instructor. Before taking up this assignment, Hunsaker accompanied Zahm on

part of the latter’s six-month inspection of European aeronautical research facilities, sponsored by the Smithsonian Institution. An excerpt from Zahm’s report

of this trip is included in the following documents. After his return to the United

States, Hunsaker used plans of the British National Physical Laboratory’s (NPL)

four- by four-foot open-circuit wind tunnel to construct a duplicate facility on the

MIT campus.13 The Smithsonian published papers by Hunsaker and five other

MIT professors in 1916 as Reports on Wind Tunnel Experiments in Aerodynamics, one

of the earliest comprehensive reports on American aeronautical research.

Hunsaker’s description of wind tunnel testing at MIT is excerpted from these

papers and included in the document section of this chapter. 

Finally the United States government took action and, with a two-paragraph

rider attached to a 3 March 1915 naval appropriations bill, Congress established

a new agency, the National Advisory Committee for Aeronautics (NACA). This

charter—with its specific charge “to supervise and direct the scientific study of the

problems of flight with a view to their practical solution”—guided the NACA for

the next forty-three years, until on 1 October 1958 it became the nucleus of the

new National Aeronautics and Space Administration. In the beginning, however,

the NACA was just a single panel of advisers with a modest $5,000 annual budget

to tackle the ambitious task of coordinating both civilian and military aeronautical

research and development programs. Initially, the NACA sponsored research in

13 For an excellent treatment of Jerome C. Hunsaker’s role in the progress of American aeronautical

research, see William F. Trimble, Jerome C. Hunsaker and the Rise of American Aeronautics

(Washington, DC: Smithsonian Institution Press, 2002).
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 247

the Washington Navy Yard tunnel and at Stanford University, where Dr. William F.

Durand pursued a systematic delineation of the best propeller shapes.14 It was not

long, however, until the Committee realized that it needed a fully staffed laboratory

of its own that could investigate all aspects of aeronautical research. With two special

appropriations in 1916 and 1917 of nearly $190,000 to establish an aeronautical

laboratory, the NACA sought a site where they could share a flying field with the

military. After consideration they settled on a location near Hampton, Virginia, where

the U.S. Army was setting up an air base christened Langley Field. Construction

at Langley began in April 1917, just as the United States entered World War I.

America’s entry into the war injected a sense of urgency into the nation’s aviation research, but the timing could not have been worse for the concept of a joint

No organization would ever do more to foster the development of wind tunnel technology than the National

Advisory Committee for Aeronautics. This photograph shows a meeting of the NACA in January 1921. Around the

table, from left to right, sat Professor Charles F. Marvin, chief of the U.S. Weather Bureau; Dr. John F. Hayford of

Northwestern University; Orville Wright; Major Thurman H. Bane, chief of the engineering division of the U.S.

Army; Paul Henderson, second assistant to the postmaster general; Rear Adm. William A. Moffett, chief of the

Navy Bureau of Aeronautics; Dr. Michael I. Pupin of Columbia University; Rear Adm. D. W. Taylor, chief of the U.S.

Navy’s bureau of construction and repair; Dr. Charles D. Walcott, secretary of the Smithsonian Institution and

chairman of the NACA; and Dr. Joseph S. Ames of The Johns Hopkins University, chairman of the NACA’s executive committee. NASA Image #NACA-1921

14 On the Washington Navy Yard tunnel and its aeronautical research, see J. Norman Fresh, “The

Aerodynamics Laboratory—The First 50 Years,” Aero Report 1070 (Washington, DC: Department of

the Navy, 1964), pp. 7–14. 
248 Chapter 2: Building a Research Establishment

civilian-military laboratory. Both the army and the navy felt that the civilian laboratory at Langley Field could not be adequately equipped and staffed in time to

solve wartime problems. Thus, using the rationale of wartime expediency, both

services put their efforts into their own resources. The navy expanded its

Washington Navy Yard laboratory, while the army established a facility of its own

at McCook Field near Dayton. 

To handle the increasing work load at the Washington Navy Yard, David

Taylor persuaded Albert Zahm in 1917 to leave Catholic University and take a new

position as head of the navy aeronautical laboratory. There at the Navy Yard in 1918,

a second wind tunnel began operation. This was an unsophisticated copy of a

1912 British NPL open-circuit, forty-five-MPH design with a four- by four-foot

test section. The navy used the new wind tunnel mainly for tests on airfoils and

for instrument development and calibration, freeing the older but larger eight-foot

tunnel for studies involving scale models of complete aircraft. Zahm supervised

the navy’s aeronautical laboratory until 1930, and during his thirteen-year career

The U.S. Army’s first-ever wind tunnel, built at McCook Field in Ohio in 1918, could reach extremely high speeds

for its day. It had a twenty-four-blade fan that spanned five feet in diameter, which could push the airspeed (within its small fourteen-inch diameter closed-throat test area) to a little over 450 miles per hour. The tunnel is now

on display in the Air Force Museum in Dayton. SI Negative No. A-1855
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 249

at the Washington Navy Yard he conducted important research concerning skin friction, component drag, instrumentation, and wind tunnel design, with results presented in more than thirty-five published papers.

On the army side, the wartime Air Production Board established by Congress

authorized the establishment of a “temporary” aviation engineering and experimental facility at McCook Field in September 1917. To staff the facility, the army

pulled its research people from the still-incomplete Langley Field. Initially, work

at McCook Field focused on production matters, but the need for basic research

rapidly became apparent, resulting in the construction of a small wind tunnel in

1918. The army’s wartime research concentrated on the refinement of engines,

propellers, and a variety of aircraft-operation issues, but also saw the beginnings

of an aerodynamic research program utilizing both wind tunnels and in-flight

testing. An excerpt of a July 1918 report from the Airplane Engineering

Department at McCook, “Full Flight Performance Testing,” is included in this

chapter’s documents. 

By the end of the war, Langley Field was essentially out of the army’s aviation

research efforts, leaving the NACA alone in Virginia to develop its own independent

program. Although the NACA began its own flight testing at Langley Field in

1919, it was not until the following year that its first wind tunnel was ready for

operation. This “NACA Wind Tunnel No. 1,” an open-circuit design with a five-foot

test section, was nothing more than another American copy of an outdated British

NPL tunnel. While limited, this first tunnel did allow NACA engineers to practice

the application of airflow theory and the design of wind tunnel equipment.15 This

critical initial experience is reflected in early NACA technical reports on the

“Design of Wind Tunnels” from 1919 and 1920. Other documents provided in

this chapter also bear witness to the immature state of the American aeronautical

engineering community around 1920 and signal how far that community had to

advance to catch up with the Europeans. 

The formative nature of the entire field of aerodynamic research in the 1920s

is captured in an interesting sequence of documents beginning with a 23 August

1920 call from Dr. Joseph Ames, physics professor and then vice-chairman of the

NACA Committee on Aerodynamics (Ames would later serve as the chairman of

the NACA’s Main Committee, from 1927 to 1939), for the “standardization of

wind tunnels”—or as Ames described it, “information which would enable one to

connect the data published” from all the various wind tunnels around the world.

In answer to Ames’s appeal for standardization came letters from many of the

greatest names in aerodynamic research, including Dr. Prandtl at the University

15 The design of the NACA’s first wind tunnel is examined in Donald D. Baals and William R.

Corliss, Wind Tunnels of NASA (Washington, DC: NASA SP-440, 1981), pp. 2–3.
250 Chapter 2: Building a Research Establishment

of Göttingen, Dr. Zahm at the Washington Navy Yard, Dr. Durand at Stanford,

and many representatives of the nascent American aircraft industry. A selection

of these responses to Ames are included in the documentary collection, and they

provide a snapshot into what the leading aerodynamic researchers thought needed to be done in order to improve the reliability of wind tunnel data around the

world and to build an international network that would allow aerodynamic

experts to better learn from each other. The NACA eventually drew up specifications for comparative tests in wind tunnels followed by wind tunnel personnel at

Langley. While the overall objective of worldwide standardization was never fully

realized, this early attempt toward it brought the minds of international experts

together on basic issues of aerodynamic research, and it raised fundamental questions about the problems of testing scale models in wind tunnels.

A comparable call for more exactitude in aerodynamic testing came a few

months later in 1920 when Commander Jerome Hunsaker, at that time with the

U.S. Navy Bureau of Construction and Repair, recommended that the NACA

Two wind tunnel researchers pose near the entrance end of Langley’s five-foot Atmospheric Wind Tunnel (AWT),

where air was pulled into the test section through a honeycomb arrangement meant to smoothen the flow. NASA

Image #L-1990-04342 (LaRC)
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 251

pursue a systematic program comparing wing characteristics as ascertained in

wind tunnel tests with those learned in free flight. (Hunsaker became a committee member of the NACA in 1922 and later served as NACA chairman from 1941

to 1956.) The proposal, which the NACA embraced and carried out at Langley,

led to the establishment of new research methods that produced important

results. For the first flight tests the NACA obtained a Curtiss JN4H “Jenny”

biplane, and Langley model makers built two models of this aircraft for wind tunnel testing. The engineers used one model for tests measuring lift, drag, and

moments, while the other was outfitted for pressure-distribution tests. The wind

tunnel data from the models was then compared to measurements obtained during actual flight tests of the full-size Jenny. Such comparative tests were first tried

a decade earlier by Gustav Eiffel, but the Langley program sparked by Hunsaker’s

proposal proved far more extensive and was accomplished with considerably

greater precision. Learning a great deal from research programs that combined

wind tunnel experiments with free flight tests, the NACA began to stake out a crucial role

for itself as a research establishment. Unlike the Army and Navy programs, which

tended to be more development-oriented than research-oriented, the NACA focused

on basic aerodynamic problems that affected civilian and military aviation alike.

In a roundabout way that was nevertheless typical of the serendipitous path

of basic research, Langley’s JN4H comparison studies also helped lead the NACA

to an altogether unexpected destination, the design of a revolutionary new type

of wind tunnel. The test program resulting from Hunsaker’s proposal confirmed

that wind tunnel testing was a valid predictor of aircraft performance and behavior,

but it also pointed NACA researchers toward another well-known, but poorly

understood, problem concerning scale effects. Prior to 1920, no wind tunnel ever

built had been able to address scale effects with any success. Yet by that time people

working in aeronautical research realized that the forces generated by a scale

model were not, in fact, proportional to the model’s scale. A novice to the field

might assume that a 1

⁄20-scale model of a airplane placed into an air stream moving 1

⁄20 as fast as the actual airplane flew would generate roughly the same forces

of lift and drag as a full-scale machine in flight, but that was far from the truth;

the scale model actually generated considerably less. Early aerodynamicists had

developed empirical coefficients to “scale-up” the data, but the NACA comparison tests showed just how unreliable these coefficients were. The air itself could

not be “scaled-down” to model size, and air properties, such as density and temperature, manifested themselves the same way in the wind tunnel as they did around

a full-size airplane. To gain the maximum value from wind tunnel testing, an

answer to the scaling problem had to be found.

The conceptual tools needed were found in the hydrodynamic work of Osborne

Reynolds (1842–1912). Experimenting with the characteristics of fluid flows at the
252 Chapter 2: Building a Research Establishment

University of Manchester in England, in 1883 Reynolds established experimentally

that the transition from laminar or smooth flow to turbulent flow always occurred

when certain variables exceeded a critical value defined by a specified flow

parameter. The dimensionless number that resulted came to be known as the

“Reynolds number,” and it became the key to understanding scale factors. This

fundamental finding, acknowledged as “a stunning discovery,” eventually enabled

researchers to establish a direct quantitative link between experiments with scale

models used in wind tunnels and the airflow patterns of full-scale designs. In

essence, it meant that the testing of scale models in wind tunnels could lead not only

to meaningful theoretical results, but also to practical design applications.16 It took

nearly forty years for Reynolds’s breakthrough to make the transfer from scientific

esoterica into a practical factor for aircraft engineers, but the tremendous expansion

of wind tunnel work in the United States in the 1920s was in part driven by a growing

appreciation of the significance of Reynolds number effects.

In demonstrating that a fluid flow suddenly changed from laminar to turbulent

as speed increased, Reynolds showed that the forces a moving fluid exerted on a

body depended on the fluid’s velocity, density, and viscosity, and on key dimensions

of the body itself, such as length or diameter. To achieve the “Reynolds number,”

he combined these parameters into a mathematical expression where all of the dimensions cancelled one another out. Because it was dimensionless, the Reynolds number

could be used to compare fluid-flow forces around similarly shaped, but differently

sized, objects. One could achieve what came to be called “dynamical similarity”

by varying different parameters, such as decreasing the velocity or increasing the

density, to produce the same Reynolds number for different tests. 

In theory, then, it was possible for aerodynamicists to make an excellent correlation

between model tests and aircraft performance, but this was easier said than done.

When a 1

⁄20-scale model was tested in the NACA’s original atmospheric wind tunnel in 1920, the Reynolds number for the test represented no better than 1

⁄10 that of

the corresponding full-scale flight. In principle, larger models could have been

used, but wingspans greater than about 3 1

⁄2 feet could not be used in the fivefoot-diameter test section of the first NACA wind tunnel due to aerodynamic

interference from the tunnel walls. In addition this atmospheric wind tunnel also

lacked the power to run at the high speed necessary to generate the required

Reynolds number, as such a velocity was simply not practical in an open wind tunnel.

16 See Osborne Reynolds, “An Experimental Investigation of the Circumstances Which Determine

Whether the Motion of Water in Parallel Channels Shall Be Direct or Sinuous, and the Law of

Resistance in Parallel Channels,” Proceedings of the Royal Society (London, 1883), pp. 84–89. On

Reynolds’s contribution to fluid mechanics, particularly the concept of the “Reynolds number,” see

Anderson, A History of Aerodynamics, pp. 109–114.
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 253

Two possible solutions to the problem emerged almost simultaneously in the

year 1920. Both originated in Europe, and both were offered for “sale” to the

NACA in America. In each case, the technical solution was to increase the density/

viscosity factors in the Reynolds number calculation. The first concept came from

Wladimir Margoulis, a Russian-born aerodynamicist and protégé of Nikolai Joukowski

and Gustav Eiffel, who had just started work for the NACA’s Office of Aeronautical

Intelligence in Paris as technical consultant and translator. Margoulis’s proposal

was to replace air with carbon dioxide and completely seal this atmosphere in a

fully enclosed wind tunnel. Because carbon dioxide’s density was over 1 1

⁄2 times

greater than that of air, the Reynolds number of any test in such a chamber would

be correspondingly higher. 

The second concept (though it is impossible to resolve whose idea actually

developed first) came from Dr. Max Munk, a brilliant star student of Ludwig

Prandtl, whose laboratory at Göttingen was the leading aerodynamic research

facility in the world. In 1916, Prandtl had designed a major new wind tunnel, the

virtues of which American aeronautical observer and NACA consultant Edward P.

Warner extolled in his 1920 “Report on German Wind Tunnels and Apparatus.”

Unlike his earlier 1908 tunnel, which had a constant cross section, Prandtl’s secondgeneration apparatus merged the tapered diffuser of an open tunnel with a

Dr. Joseph S. Ames at his desk at NACA headquarters in the early 1920s. Ames was a founding member of the

NACA, appointed by President Woodrow Wilson in 1915. He served as chairman of the NACA’s Main Committee

from 1927 to 1939. NASA Image #LAL90-3738 (Ames)
254 Chapter 2: Building a Research Establishment

closed-circuit design, resulting in much-improved air management. Prandtl

based the design on the principle that the potential energy (static pressure) and

kinetic energy (velocity) of air could be interchanged in different parts of a wind

tunnel to enhance performance. The open test section of the new Göttingen wind

tunnel measured two meters in diameter, but by enlarging the return duct and

thereby reducing the velocity of the returning air, friction and the associated

power requirements were reduced—yet because slower-moving air exerted a higher static pressure than high-speed air, the air’s momentum was retained. The

return duct, cast in concrete (and in this particular tunnel uniquely placed in a vertical orientation underneath the floor) possessed guide vanes to turn the air flow

around the corners. Two other particularly significant features of this design were

the incorporation of a stilling chamber and a contraction cone ahead of the testing area that acted to reduce turbulence and then accelerate the air passing into

the test section. The design was so efficient that a 300-horsepower motor rotating a four-bladed fan was sufficient to produce test section wind velocities of 170

feet per second. While historians sometimes call Prandtl’s earlier 1908 design the

first “modern” wind tunnel, it is actually his second Göttingen tunnel that truly

The young NACA first built its reputation as an outstanding aeronautical research institution on the strength of its

Variable Density Tunnel (VDT). The tank for the VDT arrived at Langley by rail from its manufacturer, the Newport

News (Va.) Shipbuilding & Dry Dock Company in February 1922. It was an eighty-five-ton pressure shell with

walls made from steel plate lapped and riveted according to a practice standard in steam-boiler construction.

NASA Image #L-1990-04352 (LaRC)
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 255

deserves the accolade, for this revolutionary design established a new standard

and became the model for subsonic wind tunnels around the world.

It was the environment and technical culture of Prandtl’s laboratory that

structured the thinking and nurtured the remarkable talent of Max Munk, who in

1917 earned not one but two doctorates at Göttingen (in both engineering and

physics). With the exception of Prandtl, no one knew the Göttingen wind tunnels

better than Munk—and as subsequent achievements in wind tunnel design

proved, no one, not even Prandtl, better understood the principles and potential

of wind tunnel technology.

In early 1920, Munk proposed the idea of a wind tunnel built inside a pressure

vessel so that tests could be run under high pressure, thus increasing the density

of the air as much as twentyfold. The thirty-year-old temperamental genius

tempted the American research establishment with his concept in a personal letter

sent from Germany to the navy’s Hunsaker, who knew of Munk’s work at Göttingen

from his continuous review of German aeronautical activities. Hunsaker informed

NACA Chairman Dr. Joseph Ames of Munk’s idea, and Ames persuaded the rest

of the Committee, which was hard-pressed for talented aerodynamicists, to offer

Munk a position as a technical consultant. To employ the German aerodynamicist

in the United States required two special orders from President Woodrow Wilson,

one to allow a recent enemy into the country, and the other to authorize him to

hold a government job. When these were secured, Munk arrived in Washington, D.C.,

in late 1920 and began seven turbulent years of NACA employment, first as a

technical assistant in the NACA’s Washington office and later as chief of aerodynamics at Langley.17

The acceptance of Munk’s idea and the design of such a bold new type of

wind tunnel turned the NACA from a second-rate player into a world leader in

aerodynamic research. This tunnel, known as the Variable Density Tunnel, or

VDT, went into service at Langley as “NACA Wind Tunnel No. 2” in 1922, and its

results were vastly superior to those obtained with any previous tunnel design.

Two NACA technical papers by Munk excerpted as documents for this chapter

provide insights into the revolutionary nature of the VDT’s design. Externally, it

appeared to be little more than a large cylindrical tank with hemispherical ends.

But, in fact, a five-foot-diameter wind tunnel was mounted inside such that air

flowed through a central test section, then past a fan that blew the air back around

via an annular return passage. The entire tank could be pressurized to 300 pounds

per square inch (20 atmospheres), sufficient to produce Reynolds numbers for

tests of 1

⁄20-scale models that were equivalent to full-scale flight. An externally

17 On Munk’s coming to the NACA, see Hansen, Engineer in Charge, pp. 72–78 and 84–95 and

Roland, Model Research, pp. 87–98.
256 Chapter 2: Building a Research Establishment

mounted 250-horsepower synchronous motor turned a seven-foot-diameter propeller

to produce test speeds of seventy-five feet per second. Small windows in the tank

permitted technicians to view the test section during operation, and a hatch at one

end provided access for mounting test specimens and for tunnel maintenance. 

Langley engineers quickly ran a wide variety of tests in the VDT, including

studies of several model airplanes, to validate the high-pressure concept. But the

most long-lasting and significant investigations involved airfoils. Through extensive

use of the VDT, the NACA drew accurate performance curves for the commonly

used airfoils of the era, and then extended the investigation to develop entire

families of airfoils with similar characteristics. This iterative process eventually

led to the development of the highly refined airfoils prominent in both the aircraft

design revolution of the 1930s and the laminar flow developments of the 1940s,

areas that will be addressed in subsequent chapters. Even now, it is difficult to

overestimate the effect of these airfoil test programs on aeronautical development.

The unique capabilities of the VDT and the valuable library of airfoil data it generated greatly advanced the state of aerodynamics not only in the United States

but also around the world.

NACA Langley’s chief of aerodynamics, Elton W. Miller, inspects his researcher’s installation of a Sperry M-1

Messenger airplane into the lab’s new Propeller Research Tunnel (PRT) in early January 1927. This was the first

complete, full-scale airplane ever to be tested in a wind tunnel in the United States. NASA Image #L-01892 (LaRC)
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 257

As a civilian organization, the NACA was relatively unencumbered with military

security requirements during this period, and it made the airfoil information

readily available to airplane designers through a formal series of “Technical

Reports.” These “TRs” were carefully prepared publications that not only helped the

American aircraft industry select its wing shapes but also served as basic textbook

material for an entire generation of up-and-coming aeronautical engineers. A number of documents in this chapter and in the chapters that follow are excerpts from

classic NACA Technical Reports. 

The VDT provided for unprecedented airfoil research at high Reynolds numbers, but it was not well suited for certain other investigations, such as propeller

testing. Model propellers were unsuitable because they did not deflect during

operation the same way full-size propellers did, a source of such significant error as

to invalidate model tests. Testing of full-size propellers, on the other hand, required

an evaluation of actual performance on an airplane in expensive and often dangerous flight tests, and even then accurate measurements were difficult to obtain.

Though the NACA sponsored propeller research in Stanford University’s Eiffeltype tunnel started in 1917, until the mid-1920s no valid laboratory method of

studying the entire propulsion system and its relationship with the body of the

aircraft existed. The NACA’s response to this situation is shown in documents

starting with a series of memos from Dr. Munk and others at the NACA that trace

the genesis of the world’s first wind tunnel of considerable size, the Propeller

Research Tunnel (PRT) of 1926–1927.18 These contemporary documents are complemented by a retrospective account from the autobiography of Langley engineer Fred E. Weick, who built and first operated the NACA Propeller Research

Tunnel (PRT) at the Langley laboratory. 

The PRT featured a Prandtl-style tunnel with a huge twenty-foot open test section.

The enormous power required for a tunnel of this size was provided by two navy

surplus 1,000-horsepower submarine engines, which produced wind velocities of

over 160 feet per second, or the equivalent of 110 miles per hour. The balance supported a full-size airplane body or a substitute “test fuselage” equipped with an

onboard dynamometer to measure engine torque directly. Special methods were

devised to measure blade deflection optically during tests. When it went into operation in 1927, the PRT quickly proved its worth for propeller testing in conditions

that were close to those in actual flight, but because it was the first tunnel large

enough to accommodate full-size airplane fuselages its use soon expanded to

18 On the design, construction, and early operation of the NACA’s Propeller Research Tunnel, see

Fred E. Weick and James R. Hansen, From the Ground Up: The Autobiography of an Aeronautical

Engineer (Washington, DC: Smithsonian Institution Press, 1988), pp. 49–59, as well as Hansen,

Engineer in Charge, pp. 87–90. 
258 Chapter 2: Building a Research Establishment

include drag studies of other aircraft components, such as landing gears, tail planes,

and cooling systems. The latter tests in the PRT led to the development of the celebrated NACA cowling for radial aircraft engines and Langley’s first Collier

Trophy Award. (These events are detailed in the next chapter, found in the forthcoming Volume 2, which deals with the design revolution in aircraft aerodynamics.) These crucial results from the PRT, following closely on the heels of the contributions of the VDT, catapulted the NACA Langley research laboratory to a position of unparalleled importance in American aviation.19

The PRT also inspired the NACA to build an even larger wind tunnel. The

close connection that existed between the engineering design of the PRT and the

conception of Langley’s next mammoth facility, the historic thirty- by sixty-foot

Full-Scale Tunnel completed in 1931, has not been fully appreciated by historians.

But thanks to the discovery of a series of neglected NACA memos from 1925,

Four hundred thirty-four feet long, 222 feet wide, and ninety feet high, the building housing the thirty- by sixty-foot

Full-Scale Tunnel dominated the Langley scene. Its location along the Little Back River, a tidal river off the nearby Chesapeake Bay, occasionally caused flooding problems for the tunnel during hurricanes and nor’easters.

NASA Image #EL-1999-00405 (LaRC)

19 For a historical analysis of the NACA cowling program, see James R. Hansen, “Engineering

Science and the Development of the NACA Cowling,” in From Engineering Science to Big Science:

The NACA and NASA Collier Trophy Research Project Winners, ed. Pamela E. Mack (Washington, DC:

NASA SP-4219, 1998), pp. 1–28. The latter is an expanded version of Hansen’s chapter on the

cowling in Engineer in Charge.
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 259

reproduced in the document section of this chapter, one can now see how NACA

engineers actually anticipated the FST in the building of the PRT. On 7 April

1925, after reviewing a seven-page memo on a “Proposed Giant New Wind Tunnel”

from an enthusiastic assistant aeronautical engineer named Elliott G. Reid,

Langley engineer-in-charge Leigh M. Griffith asked the NACA Washington

office, Why not, after finishing the PRT, plunge ahead with an even larger tunnel

capable of testing a full-size aircraft? “If we could actually fly the same model that

we test in the tunnel,” Griffith wrote, “we would have the unquestioned means of

investigating airplane performance and characteristics in the most direct, accurate, convenient, and conclusive manner.” 

In other words, the NACA would have a means of eliminating the scale effect

factor altogether. The VDT showed that scale-model tests at high Reynolds numbers

produced accurate data about airfoils, but was not effective for testing fuselages.

The PRT, on the other hand, demonstrated the value of testing the synergistic

component characteristics of full-size aircraft, but were not large enough to include

The first tests of an aircraft in the FST involved a Vought O3U-1 “Corsair.” In the summer of 1931, the NACA used

the navy airplane for some preliminary tests to check out the FST and as the subject of the first publicity photographs taken of FST operations. NASA Image #EL-1999-00425 (LaRC)
260 Chapter 2: Building a Research Establishment

the full span of the wings. So while both tunnels produced valuable breakthroughs,

neither was capable of totally reproducing the conditions experienced by an

entire airplane in flight. It was the desire to cross this new threshold in aerodynamic research, prompted by the work of the VDT and PRT, that inspired NACA

engineers to design and build a wind tunnel large enough for full-scale testing.

The NACA Full-Scale Tunnel (FST), completed in 1931, proved gigantic in

every respect and loomed over every other structure at Langley. A closed-circuit

wind tunnel with an unprecedented thirty- by sixty-foot open test section, the FST

was large enough to handle airplanes or large-scale models with wingspans of up

to forty-five feet. Two monstrous thirty-five-foot-diameter propellers in the dual

return ducts, each driven by a 4,000 horsepower electric motor, circulated almost

160 tons of air through the 838-foot-long circuit and produced wind velocities of

nearly 120 miles per hour. These speeds were sufficient to enable measurements

that could be confidently extrapolated to cover the aircraft’s entire speed range

because scale factors were minimized or eliminated entirely. The remarkable FST

and the aerodynamic research it enabled was a crowning achievement for the

The cavernous test section of the FST also came in handy at NACA conferences. In this picture from May 1934,

attendees at the NACA’s annual aircraft engineering conference posed beneath a Boeing P-26A “Peashooter.”

Present in this photo, among other notables, were Orville Wright, Charles Lindbergh, and Howard Hughes. NASA

Image #EL-1996-00157 (LaRC)
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 261

NACA, and it marked how far American aeronautic research institutions had

come since the end of World War I.20

The NACA also built other wind tunnels along with the highlighted VDT,

PRT, and FST. The first pioneering high-speed research was begun in 1927 with

a small eleven-inch tunnel that used the exhaust air released when the VDT was

depressurized to produce brief flows approaching the speed of sound. The concept

proved successful and led to the construction of two improved high-speed tunnels

in the next decade. In 1929 Langley’s obsolete “Wind Tunnel No. 1” was dismantled

and replaced with two new tunnels, a seven- by ten-foot Atmospheric Wind

Tunnel (AWT) and a five-foot Vertical Wind Tunnel. Completed in 1930, the new

In 1928, the NACA replaced its original Atmospheric Wind Tunnel (“Wind Tunnel No. 1”) with two tunnels—a fivefoot vertical tunnel and a seven- by ten-foot Atmospheric Wind Tunnel. An NACA engineer sets up a test in

Langley’s seven- by ten-foot AWT. Though an all-purpose facility, its main purpose was to study stability and control problems. NASA Image #EL-1999-00418 (LaRC)

20 On the design and history of the NACA’s Full-Scale Tunnel, see Baals and Corliss, Wind Tunnels of

NASA, pp. 22–23, plus Hansen, Engineer in Charge, pp. 101–105, 194–202, and 447–449.
262 Chapter 2: Building a Research Establishment

Housed in the same building as the seven- by ten-foot AWT, Langley researchers used the five-foot Vertical Wind

Tunnel mainly for spin tests. An engineer kneels on a platform next to the test chamber. In the foreground is the

device’s (closed) return passage. Like the AWT, the tunnel had an open throat. The vertical tunnel stood thirty-one

feet tall and was twenty feet long and ten feet wide. It was not ready for operation until early 1931. NASA Image

#EL-1999-00410 (LaRC)
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 263

AWT was a marked improvement over the 1920 tunnel it replaced, and it remained

a workhorse facility at Langley for many years. The novel Vertical Tunnel, with its

upward flowing air stream, was an innovative concept that offered an unprecedented opportunity to investigate aircraft spins, a leading cause of disastrous

crashes. An excellent example of adapting an existing technology to a new use,

the Vertical Tunnel of 1930 was the prototype for additional spin tunnels at

Langley, as well as for the concept of free-flight wind tunnel testing, which the

NACA also pioneered.21

By the beginning of the 1930s, the NACA had assembled a collection of wind

tunnels at Langley whose collective capabilities surpassed those of any other

Another major center of U.S. aerodynamic research—this one sponsored by the U.S. Army—flourished at

McCook Field near Dayton, Ohio. During World War I, McCook engineers made significant contributions to airplane and engine development, but even greater contributions came in the decade after the war. Like NACA

Langley, the aircraft engineering division at McCook combined systematic wind tunnel testing with a full program

of flight research. But beyond that, the McCook operation also engaged more directly in the actual design, construction, and operational problems of aircraft, which were beyond the mandate of NACA research. In 1927, the

army closed McCook and moved its flying field and associated units to a major new parcel of land dubbed Wright

Field. Eventually the site became Wright-Patterson AFB. SI Negative No. A-1848

21 All of the early NACA tunnels are discussed in Baals and Corliss, Wind Tunnels of NASA. Appendix

D of Hansen’s Engineer in Charge provides a comprehensive catalog of all the facilities that were

developed at NACA Langley from 1917 to 1958.
264 Chapter 2: Building a Research Establishment

aeronautical laboratory in the world, an achievement highlighted in the C. G.

Grey editorial reproduced at the beginning of this chapter. That a European

authority acknowledged America’s leading position in aerodynamic research was

particularly significant, considering how far behind the United States had been

just fifteen years earlier. 

The NACA was not alone in the establishment of American aerodynamic

research institutions during this period. The United States Army Air Service

expanded its aerodynamic work at McCook Field after World War I and constructed

a five-foot-diameter open wind tunnel there in 1922. An important area of aerodynamic research in this facility became the search for solutions to aircraft “flutter,”

the often catastrophic uncontrolled oscillations of wings and control surfaces in

flight, a subject that NACA researchers also pursued vigorously beginning in the

Between 1926 and 1930, the Daniel Guggenheim Fund for the Promotion of Aeronautics disbursed over $3 million for the creation of aeronautical engineering programs at several American universities. In association with

these programs, a number of new wind tunnel facilities came to life. Trustees of the Guggenheim fund included,

left to right standing, J. W. Miller, secretary; F. Trubee Davison; Elihu Root, Jr.; Hutchinson Cone; Charles

Lindbergh; Harry Guggenheim, the fund’s president; Dr. Robert Millikan; and, left to right seated, John D. Ryan;

Daniel Guggenheim, the fund’s creator; Orville Wright; and Dr. William F. Durand. SI Negative No. A-3519
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 265

late 1920s. When McCook Field closed in 1927, the Army moved this tunnel to

the new Wright Field (now Wright-Patterson Air Force Base) near Dayton, where

the five-foot tunnel remained in service into the 1990s as an educational learning

tool for the Air Force Institute of Technology (AFIT). And as already noted in the

work of Albert Zahm, during this period the U.S. Navy also sponsored important

research in the wind tunnels of the Washington Navy Yard.

Along with the government investment, there was also a growing private

interest in advancing aerodynamic research in the 1920s. A leading figure in this

was multimillionaire philanthropist Daniel Guggenheim, who devoted part of his

mining fortune to foster the development of academic programs in aeronautics at

American universities. In 1925, when only the MIT and the University of

Michigan offered degrees in aeronautical engineering, Guggenheim donated half

a million dollars to New York University to establish a School of Aeronautics. The

next year he founded the Daniel Guggenheim Fund for the Promotion of

Aeronautics with an endowment of $2.5 million. Between 1926 and 1930, the

Guggenheim Fund awarded major grants to seven prestigious engineering

schools, expanding the programs at MIT and the University of Michigan and

starting new programs at Stanford, the California Institute of Technology

(Caltech), the University of Washington, the Georgia Institute of Technology

(Georgia Tech), and the University of Akron. A large portion of these grants went

into construction of wind tunnel laboratories, but, significantly, some funds were

earmarked for the hiring of exceptional professors and researchers. For example,

a Guggenheim grant allowed Clark and Robert Millikan to recruit Theodore von

Kármán, one of Europe’s most outstanding theoretical aerodynamicists, to come

to the United States as the new director of Caltech’s Guggenheim Aeronautical

Laboratory (GALCIT), where, for the next thirty years, he would play a dominant

role in shaping the growth of theoretical aeronautics in the United States. By midcentury, over 90 percent of the nation’s leading aeronautical engineers were graduates of Guggenheim-funded colleges.22

Another significant factor in the formation of the American aeronautical

engineering community in the 1920s and 1930s was the diaspora of experienced

research engineers from NACA Langley into the larger world of aeronautics. Dozens

of early NACA employees moved on to accept important positions in the aircraft

industry or at universities. For example, Montgomery Knight and Elliot G. Reid

22 On the Guggenheim connection with aviation, see Richard P. Hallion, Legacy of Flight: The

Guggenheim Contribution to American Aviation (Seattle, WA: University of Washington Press, 1977).

See also Hallion’s chapter, “Daniel and Harry Guggenheim and the Philanthropy of Aviation,” in

Aviation’s Golden Age: Portraits from the 1920s and 1930s, ed. William M. Leary (Iowa City:

University of Iowa Press, 1989), pp. 18–34.
266 Chapter 2: Building a Research Establishment

left Langley to help start the Guggenheim programs in aerodynamics at Georgia

Tech and Stanford, respectively. These programs in turn produced a new crop of

aeronautical engineers for the future expansion of the NACA and the civilian aircraft

manufacturing industry. This process of networking and cross-fertilization with the

broader American aeronautical community proved to be one of the NACA’s most

important contributions to aerodynamics and American aeronautics generally.

To be sure, it was people—primarily engineers and scientists—who perceived

the needs of aeronautics, envisioned the flying machines and wind tunnels,

brought them to life, and thought up and performed the aerodynamic test programs.

With such a complex and exciting technology as aviation, it should not be surprising

that the field attracted some of the finest minds available. But with brilliance frequently comes ego and a high degree of individualism, a combination that can

make it difficult to establish and maintain a sense of community among professionals

with different ideas and opposing modes of operation and cultural norms. 

Over time, in America as elsewhere, an international aeronautical research community formed as practitioners in various countries began to realize that significant

progress resulted at least as much from cooperation and the free exchange of ideas

as from secrecy and cut-throat competition. Indeed, corporate and national competitions remained intense in the inter-war period. Americans for their part wanted to

catch up with and surpass the Europeans in the field of aeronautics. Documents in

this chapter involving the NACA’s Office of Aeronautical Intelligence—primarily John

Jay Ide’s reports from Paris back to the NACA in Washington, D.C., on what was developing at Europe’s many aeronautical centers in the early 1920s—certainly need to

be evaluated with the American military and commercial goals of the early inter-war

period in mind. For the United States to be on the cutting edge of aeronautical

science and technology, its aeronautical specialists had to know what its European

rivals were up to in their laboratories, aircraft industries, and military installations. Although complete histories of NACA and U.S. military intelligence in the

field of aeronautics have not yet been written, it is clear from what is known, and

from the progressive evolution of the American propeller-driven airplane into the

World War II era, that the intelligence mission succeeded in major respects.

Unsavory manifestations of national loyalties surfaced from time to time just about

everywhere. Without dwelling on them, this chapter offers one arresting insight into

the chauvinism of an early NACA researcher, Frederick H. Norton, Langley’s chief

physicist from 1920 to 1923. In 1921 Norton wrote to NACA Headquarters complaining that Dr. Max Munk, only recently arrived to the NACA from Germany,

had the audacity to propose the use of a German airfoil section for a small helicopter he was considering. An MIT graduate, who one might think possessed a

less parochial view, Norton could not understand how NACA leadership would

allow Munk to use any foreign airfoil, especially one from Germany, the wartime
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 267

enemy, when there were plenty of good American airfoils from which to choose. 

Munk himself continued to be embroiled in conflict; it was not easy for anyone

to work with this temperamental genius, either during the early years at NACA

Langley or in subsequent jobs. Whether the problems with Munk at Langley

(which eventually resulted in Munk’s dismissal from the NACA in 1927) represented simply a clash of personalities or something deeper like a culture clash has

been a matter of some interesting historical analysis and interpretation.

One way to understand the Munk affair is to consider that two basic approaches to aerodynamic research exist: the empirical approach, where experimentation

and practical assumptions seek solutions to problems; and the theoretical

approach, where a mathematical analogy is created to foster an understanding

that can be used to solve problems. Such a dichotomy oversimplifies the research

process, unquestionably, but it serves to illustrate the mindsets of two emphases

in research that definitely exist—and that sometimes even break into camps. In

the era following the Wrights’ first flight covered by this chapter, both empiricists

and theorists contributed important elements to the overall picture, and what

began in many places as a mutual lack of understanding and distrust of each

other’s methods slowly merged into a mature discipline with room, and a need,

Dr. Max M. Munk, the Variable Density Tunnel’s creator, inspecting the machine not long after its installation. One

peered into the machine through two small portals on the side. NASA Image #EL-1999-00258 (LaRC)
268 Chapter 2: Building a Research Establishment

for both. Yet the maturing did not take place without occasional trouble. 

The roots of aeronautical empiricism penetrated deep, and dated at least as far

back as Cayley. Generally speaking, all of the aeronautical pioneers from Cayley to

the Wrights were experimenters who learned through careful observation of their successes and failures. By the 1920s, this long tradition had led not only to successful

flight and a proliferation of practical flying machines, but also to the establishment of aeronautical laboratories dedicated to expanding the knowledge of flight

through experimental means. The empirical investigations performed by several

of these researchers, including Francis Wenham, Horatio Phillips, Gustav Eiffel,

Albert Zahm, and the Wrights, created a firm base for later theoretical work.

Faced with a dearth of knowledge about aerodynamics, they built machines with

which reliable measurements could be made. In so doing, they not only learned

how various objects interacted with an airstream, but also furnished themselves

and others with the fundamental facts needed to construct theoretical models

Von Kármán (black coat and tie) sketches out a plan on the wing of an airplane as members of his Jet-Assisted

Takeoff (JATO) engineering team looks on. Clark Millikan stands to von Kármán’s far right with Martin

Summerfield in between. To von Kármán’s immediate right is Caltech rocket pioneer Frank J. Molina. The man in

uniform is Capt. Homer A. Boushey, who later that day (23 August 1941) became the first American to pilot an

airplane that used JATO solid propellant rockets. NASA Image #JATO-VONKARMAN (Ames)
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 269

that could describe and predict those interactions with increasing accuracy.

In the United States during the first decades of the twentieth century, empirical

methods and straightforward approaches to solving practical problems suited the

mood of the engineering culture and the abilities of its practitioners well; this certainly proved to be the case at the NACA laboratories, where the engineer—not

the scientist—gained the upper hand. Nonetheless, the contributions of science

and, perhaps even more importantly, the public perception of science greatly

influenced the course of NACA research. American scientists sought a fundamental

understanding of natural phenomena, as European scientists did, but science and

engineering were often seen as one and the same by the American public; typically,

what engineers did—at least what they did successfully—was credited as “science.”

Engineering accomplishments, solutions to practical problems built out of concrete

or steel rather than new knowledge for its own sake, were commonly celebrated

as “scientific” achievements. In America, “science” solved problems and built

things, and the field was largely open to anyone who could prove himself. Like

the rest of American society, a sense of democracy permeated the enterprise. This

is not to imply there was no management hierarchy in American technology—far

from it—but ideas could originate from lower strata and receive consideration.

Subordinates in many organizations, including the NACA, felt free to debate and

test notions coming to them from the top down. Even more often, ideas percolated

from the bottom up.

The European model, and especially the German, differed substantially. In

the physical sciences, mathematics was seen as the route to true understanding,

and the objective of an investigation was the development of a mathematical formula

that described the phenomenon.23 Although an admirable objective, this could

lead to formulae that were extremely difficult, if not impossible, to solve when

applied to practical engineering problems. At the very least, such a technical culture required its engineers and scientists to be good mathematicians and to think

abstractly. The national technical cultures of most European nations remained

hierarchical and, unless one had the benefits of aristocracy, scientists and engineers earned their positions in the upper echelons of a profession through many

years of formal study and subservient work. In such cultures, the leader of an

organization held a commanding position over the ideas and methods that the

entire organization would use.

Ludwig Prandtl, Max Munk, and Theodore von Kármán were outstanding

products of the German system and, not coincidentally, they proved to be among

23 See Paul A. Hanle, Bringing Aerodynamics to America (Cambridge, MA: MIT Press, 1982), for an

insightful analysis of the “Prandtl School” and the German technological culture of aerodynamic

research in the early 1900s. 
270 Chapter 2: Building a Research Establishment

the first and finest theoretical aerodynamicists. Prandtl led the way for his two

brilliant students. In demonstrating his ability to tackle practical problems in

innovative ways by building the first closed wind tunnels, he built, not successful

airplanes, but an edifice of fundamental aerodynamic understanding that was

unexcelled anywhere. Prandtl wanted not to observe and measure lift so much as

he wanted a mathematical explanation of it; this ambition underlay most of his

published papers, including his classic statement of 1921, “Applications of

Hydrodynamics to Aeronautics,” written expressly for NACA publication

(excerpts of which are published in this chapter’s documents). In this quest for

theoretical enrichment, Prandtl was not alone. Other contemporary Europeans,

notably Nikolai Joukowski in Russia and F. W. Lanchester in England, also devoted

most of their careers to a search for satisfying theoretical explanations of this complex phenomenon. None of them completely solved the problem, but all of them

contributed vital pieces to the puzzle. Munk and von Kármán acquired their

mentor’s appreciation of the value of theoretical aerodynamics, and they both

brought it, along with their considerable intelligence and talent, to the United

States in the 1920s. Both men were well known to prominent American aeronautical figures, notably to Hunsaker and Zahm, who recommended them highly.

Once in America, however, their careers took decidedly different directions.

Von Kármán, who arrived later (in 1929), came to the U.S. after being actively

recruited by Caltech’s Robert Millikan. He moved into a university research environment that shared characteristics with his former school, the Technische

Hochschule in Aachen, Germany. At Caltech, von Kármán directed GALCIT, but

he also continued to work with graduate students and pursue his own research.

He adapted well to academic life in America, and he quickly gained the respect

of the American aeronautical community.24

Munk’s American career started out perhaps even more meteorically but

later came crashing down. Munk started his NACA employment in the early

1920s, working almost exclusively by himself on theoretical problems in the

Washington, D.C., office. Besides refining and carrying out his idea for the VDT,

he explored a number of critical aerodynamic problems and published an important series of reports. (The NACA would eventually publish over forty of Munk’s

papers.) But Munk wanted to be in charge of aeronautical research at Langley. 

Only a few of the many documents that exist in the NACA archives related to

problems with Munk need to be seen to appreciate the clash of ideas and attitudes that ultimately led to a revolt against Munk at Langley—and to his forced

departure from the NACA. One of them published in this chapter involved Munk’s

24 Theodore von Kármán’s life is covered in fascinating detail in Michael H. Gorn’s The Universal Man:

Theodore von Kármán's Life in Aeronautics (Washington, DC: Smithsonian Institution Press, 1992).
From the Wright Bicycle Shop to the Langley Full-Scale Tunnel 271

supervision of the construction of the VDT. In a 6 October 1921 memo to

Washington, Langley Chief Physicist Frederick Norton expressed resentment at

Munk’s overbearing manner and vague directions during construction of the tunnel, complaining that “Dr. Munk does not seem to have any clear idea as to what

he wishes in the engineering design, excepting that he is sure that he does not want

anything that [I or my men] suggest.” The best story about the difficulties of working with Munk comes from Langley engineer Fred E. Weick’s autobiography From

the Ground Up (Washington, DC: Smithsonian Institution Press, 1999), an excerpt

from which is included in this chapter. Moving from the Navy Bureau of

Aeronautics, where he worked as a civilian engineer, to the NACA in 1925, Weick

took on the responsibility of actually building the Propeller Research Tunnel, which

was also a Munk concept. Unfortunately for Weick, Munk’s incredibly demanding

supervision of the PRT work nearly drove Weick crazy trying to find ways to please

the man and still do the job correctly. To Weick’s credit, he found a way of working

with—and mostly around—Munk, and the facility was successfully built.

Other documents in this chapter reveal different perspectives on the Munk

affair. A 16 November 1926 memo from Munk to George Lewis, the NACA’s

director for research in Washington, D.C., indicated that Langley was “at present

pretty well filled up with problems; we are really overstocked.” On the surface,

Munk’s memo simply expressed concern over the need to give “the fullest amount

of thought and interest” to the research problems his laboratory staff was already

busy exploring. Reading between the lines, however, one senses that Munk may

actually have been more concerned about his own personal control of the research

program at Langley and wanted to prevent new ideas from reaching NACA

Headquarters that he had not evaluated first. 

Relations with Munk were difficult from the start, even when he spent most of his

time in Washington; the problems definitely intensified when George Lewis sent him

to Langley for extended periods. The Langley engineers considered Munk an arrogant outsider, and Munk’s efforts to fit in, to the extent he made them, failed miserably. Perhaps it was because he saw himself as intellectually and technically superior

to those around him—and made that belief clear to others, insisting they conform to

his own ideas and conclusions. While they respected Munk’s abilities, the engineers

at Langley, many of them capable people in their own right, balked at his autocratic

rule. Resignations of key people, like Norton, began in 1923; the rate increased after

Munk was assigned to Langley as chief of aerodynamics in 1926, culminating with the

mass resignation of all the section heads less than a year later. Lewis still hoped to

retain Munk in Washington, but Munk, not yet grasping the “culture-shock” nature

of the problem, chose to leave the NACA. When he left, the section heads returned.

Even though Munk’s personality doomed him at Langley, he succeeded in

introducing theoretical aerodynamics to the laboratory, and he helped to usher in
272 Chapter 2: Building a Research Establishment

an important change in the way the LMAL worked. Munk, like Prandtl, saw the

connection between empirical and theoretical aeronautics and how each could

help advance the other. One of his seminal papers, “General Theory of Thin

Wing Sections,” published by the NACA as Technical Report 142 in 1922, resulted

from his conviction that theoretical aerodynamicists would not be able to generate

improved airfoils from scratch using only the mathematical methods suggested by

Kutta and Joukowski. Instead, Munk reversed the process. He decided to start

with an empirically proven airfoil and then fit an analysis to it. Starting from a

known design allowed him to validate the theory, something that had eluded

many theorists. His theory was not perfect, but it allowed for an easier and more

accurate prediction of wing performance. Over the next few years, a small group

of scientists and engineers with better analytical capabilities and backgrounds

joined the LMAL staff. Although conflicts between the empiricists and the theorists

never disappeared totally, empirical and theoretical results came increasingly into

agreement, as both the experimental tools and the analytical methods improved.

Inexorably, the two camps pulled together into a mature discipline.

By the early 1930s, aeronautical research and development had come of age in

the United States. Vigorous debates about the quality of the direction being followed

by the NACA still took place, notably the fiery public back and forth in 1930 and 1931

between Aero Digest’s opinionated editor Frank Tichenor, the NACA’s main detractor,

and Aviation’s Dr. Edward P. Warner, its principal defender. (Their exchange of editorials is included in this chapter’s documents.) But, in the opinion of most

observers and colleagues in the aeronautics community, the program of research

being pursued by the NACA by the 1930s, in cooperation with the military air

services, the aircraft industry, and the universities, seemed to be exactly what the

country needed not just for better airplanes but for global aeronautical hegemony. 

In two decades’ time, American aeronautical research had grown from having

virtually nothing in the way of laboratory facilities to a position of preeminence in

the world, with more than twenty major wind tunnels in operation for universities,

aircraft manufacturers, the military, and the NACA. Equally important were the

bright, trained, and experienced researchers who could effectively use these

experimental tools and increasingly powerful analytical methods—combined with

their own innate creativity and vision—to generate new knowledge and solve the

fundamental problems facing a rapidly growing technology. The stage was set for

an honest-to-goodness revolution in aerodynamics and aircraft design.
Document 2-1(a–d) 273

The Documents

Document 2-1(a–d)

(a) Wilbur Wright, letter to George A. Sprat, 15 December 1901. 

(b) Wilbur Wright, letter to Octave Chanute, 15 December 1901.

(c) Wilbur Wright, letter to Octave Chanute, 23 December 1901.

(d) Wilbur Wright, letter to Octave Chanute, 19 January 1902.

All of the above documents are found in 

The Papers of Wilbur and Orville Wright, 1899–1948, 

Marvin W. McFarland, ed. (New York, NY: McGraw-Hill), 1953. 

The originals are in the Library of Congress, Washington, D.C.

The successful flights of Wilbur and Orville Wright on 17 December 1903

were due in no small part to the brothers’ systematic pursuit of aeronautical

knowledge. Recognizing that tables developed by John Smeaton and Otto

Lilienthal—tables the brothers had used in designing their disappointing 1900

and 1901 gliders—included significant errors, the Wrights designed and built

novel research devices and used them systematically to generate reliable data that

pointed to a successful design. As he did throughout the project, Wilbur Wright

frequently communicated their progress and questions with several prominent

figures in early aviation. These letters, a sample of many written during the

Wrights’ wind tunnel, or “trough,” experiment period, discuss their test results,

how these results compared to Lilienthal’s data, and their efforts to obtain “a perfectly straight current of wind” for the tests. While the work was distinctly empirical

in nature, the details of measurement and experiment design, especially those

noted in Wright’s 15 December 1901 letter to Octave Chanute, clearly show the

brothers’ attention to accuracy and repeatability—vital elements of any empirical

program. Also of interest is Wilbur’s 23 December 1901 rejection of Chanute’s offer

to try and interest Andrew Carnegie in supporting the Wright’s work (in a 19 October

1901 letter not included herein) and his pragmatic analysis of an aviation competition

in a letter to Chanute dated 19 January 1902.
274 Chapter 2: Building a Research Establishment

Document 2-1(a), letter from Wilbur Wright to George A. Sprat, 15 December 1901.

We were pleased to receive your letter and the photograph of your new testing

machine. It seems quite ingeniously designed and I think should give good

results. As you say, the greatest trouble will probably be with the changeableness

of the wind. If I understand you properly, the machine is intended for locating

the center of pressure at any angle (or rather locating the angle for any center of

pressure), and for finding the direction of the resultant pressure as measured in

degrees from the wind direction, so that the ratio of lift to drift is easily obtained,

the lift being the cotangent and the drift being the tangent of the angle at which

the arm stands. Does the machine also measure the lift, in terms of per cent of

the pressure at 90°? so that you can make tables like that of Lilienthal?

I think I told you in my last that we had been experimenting with a lift measuring machine. We have carried our experiments further and have made a measurement of the lifts of about 30 surfaces at angles of 0°, 2 1

⁄2°, 5°, 7 1⁄2°, 10°, 12 1⁄2°,

15°, 17 1⁄2°, 20°, 25°, 30°, 35°, 40°, & 45°. The results have rather surprised us as

we find at angles of 7° to 15° with some surfaces a greater lift than Lilienthal gives

in his table. Our #7 surface, which is a rectangle 1:6 with a depth of curve of 1⁄12

the chord, has a lift of one hundred and nineteen per cent at l7 1⁄2 degrees.

Lilienthal only claims about 80 per cent. But at 3° our measurement is way below

him. I will try to send you a blueprint showing the lifts of some of the surfaces we

have tested. Some surfaces which lift big at very small angles are no good at large

angles & vice versa. We have not attempted to trace the travel of the center of

pressure except that by holding some of the surfaces between the tips of our fingers we were able to roughly determine which ones tended to reverse and which

did not. It seems that surfaces with rather flat upper sides and thickened front

edges lift more at small angles than plain curves and have little reversal of the travel of the center of pressure. Thickening the front edge does not seem to add near

as much to the drift as I expected though it adds some.

We have found less drift with surfaces 1

⁄20 deep than with curves 1⁄12 deep.

What is your experience?
Document 2-1(a–d) 275

Document 2-1(b), letter from Wilbur Wright to Octave Chanute, 15 December 1901.

I have your letter of 11th with enclosures and have read all with much interest.

Moedebeck evidently is a balloonist rather than an aviator. Mr. Lilienthal says that the

results obtained by his brother with the apparatus exactly coincided with their joint

measurements. My study of Otto Lilienthal’s writings leads me to question whether

this is not too strong a term. After Lilienthal began gliding I do not recall that he ever

recommended 3° as being a specially desirable angle of incidence. In his calculations

of glides he invariably uses angles of from 9° to 12° incidence. If he had found the

great advantage in the smaller angles which the tables pronounced best, he would

surely have mentioned it. From this I am led to think that Lilienthal himself had

noticed that there was a discrepancy between his glides and his tables, at small

angles especially. There is also some question whether a surface about 8 ft. x 20 ft.,

that is, 1:2.5, would give the exact result obtained with the surface of very different

aspect which was used in the experiments on which the tables were based.

Prof. Marvin’s article has evidently been prepared with some care and is well

worth close study. I quite agree with him that data of a glide in which the forces

are not in equilibrium throughout the glide or the portion of it on which the data

are based must be worthless for purposes of calculation. You will remember that

at Kitty Hawk we said that the #3 glide of Aug. 8th, A.M., was really the only one

of much value for purposes of calculation because in it, alone, the speed from the

instant of starting to the instant of landing was very nearly uniform. The angle of

incidence varied scarcely at all; the line of motion was exactly opposite to the

direction of the wind so that the conditions were equivalent to a glide of about

double the speed in still air. Owing to the practical impossibility of obtaining correct

data I have never considered glides of very great value for purposes of calculation.

I notice that Prof. Marvin holds about the same view on the tangential that I

held last July, viz., that the front edge must be lower than the rear edge or the bird

or machine can not go forward. But the sight of a buzzard which maintained its

speed with its wings constantly pointed above the horizon, and the fact that our

machine pulled less than the weight X tang. of the angle of incidence, in spite of

the head resistance of the framing, led me to suspect that Lilienthal might be

right about the tangential. Our recent experiments are so clear on this point that

I can no longer doubt that a suitably arched surface can glide forward in a

descending course of ten degrees with the front edge of the surface pointed as

much as five degrees above the horizon.

I send you blueprints of some of the preliminary charts of our recent measurements of lifts. They were made on common paper so that the blueprints from

them scarcely show the small squares, and this makes it hard to read the exact values,

but you can see the general result. The lines run exactly according to our observations
276 Chapter 2: Building a Research Establishment

at the points at which measurements were made, viz., 0°, 2 1⁄2°, 5°, 7 1⁄2°, 10°, 12 1⁄2°,

15°, 17 1

⁄2°, 20°, 25°, 30°, 35°, 40°, & 45°. In connecting these points we have used

our best judgment as to the course in the intervening spaces. I am not sure but

that there is room for some improvement as to this. I send three of our series

charts and one large one with a selection of surfaces of various types.

The aspects and curvatures are shown on the back of the large sheet. On the

whole the finished charts give me a better impression of the accuracy of the
Document 2-1(a–d) 277

results than I had after plotting the first few lines, as I find that many kinks in the

lines, which at first seemed to be due to errors of the observations or imperfections in the machine, are now seen to be due to the surfaces themselves. Thus

when #7 was plotted we found an uncalled-for depression at 10° and a hump at

12 1⁄2°, and though we verified the observations we were not entirely easy in our

minds till we plotted #8 and #9 and found that they had exactly corresponding

depressions and humps. The fact that the hump on #9 comes exactly at the

depression on #7 makes #9 the greater lifter at 10°. 
278 Chapter 2: Building a Research Establishment

You will also note that #4, #5, & #6 have corresponding depressions at

10°–12° and humps at 17°–20°. When we first measured #10 we struck a snag at

12 1⁄2°, for the machine, which at the lower angles had been recording a reasonably regular increase in lift with each successive observation, suddenly refused to

indicate any increase and, though we examined the machine carefully and verified the angle of incidence, we could not believe that the observation was correct

till we had remeasured 10° also. Afterward we found that this was a characteristic

of all surfaces having the curvature well to the front. Arcs rise in regular peaks

while parabolic surfaces show summits like volcanoes, the crater being more or

less marked according to the depth of curvature.
Document 2-1(a–d) 279

It has been a great advantage we think to make a systematic measurement of

several typical series of surfaces rather than to work blindly on all sorts of shapes,

as a study of the series plates quickly discloses the general principles which govern

lift and tangential and thus renders the search for the best shapes much easier. A

mere glance shows that while increasing the ratio of breadth to length does not

increase the maximum lift to any great extent it does cause the maximum to be

reached at a smaller angle; and the wider the spread from tip to tip the smaller

the angle at which large lifts can be obtained. 
280 Chapter 2: Building a Research Establishment

By comparing #1, #4, #5, & #6 it is seen that the effect of curving the surface is to give a steady increase in the lift of all angles without affecting the angle

of maximum pressure. Varying the depth of curvature has a less marked effect

than the experiments of Lilienthal would indicate in the matter of lift, but when

we come to consider tangential the difference is very marked. The great advantage of moving the maximum curvature well forward is in the matter of center of

pressure, though it seems also to cause an increase in lift at smaller angles, and

in general gives a slightly more favorable tangential at angles of 4°–10°.

Thickening the front edge has a marked tendency to give big lifts at small

angles—vide #20, #25, & #35; and is even better than moving the curvature forward in its effect on center of pressure. It somewhat increases the head resistance,

however, though not near so much as the great increase in thickness might be

expected to cause.
Document 2-1(a–d) 281

The charts showing the effect of superposing are not completed, but there

seems to be some indication that they will tend to establish a general law that

(eliminating connections) the lift and tangentials of a set of superposed or following surfaces spaced about their length apart [are] approximately equal to [those]

of a single surface of similar profile or curvature having a breadth equal to that

of one surface and a length equal to the sum of their lengths. That is, two 1:6 surfaces would give the same results as one 2:6 surface; and four of them that of a

4:6 surface. From this it would appear that superposing reduces the efficiency of

the individual surfaces. In considering a double-deck or triple-deck machine, as

compared with a single surface of equal area, it would seem the single surface can

be cut up as in Fig. 1 and the parts superposed without loss, but if cut as in Fig. 2

there is a loss. Superposing may be used to reduce the fore-and-aft dimension but

not the lateral.

A somewhat similar law seems to hold when comparing rectangles with segments

or triangles. Surface may be cut off at one point and added at another without

affecting the efficiency of the surface. Thus if the corners be cut off at aa and

added at a'a' thus forming a triangle, the effect remains about the same, so long

as the spread from tip to tip remains the same. It is at least roughly true that both

in superposing and in reshaping a single surface the efficiency depends on the

ratio of maximum breadth to area, rather than on the ratio of breadth to length.

I regret that we did not have time to carry some of these experiments further, but

having set a time for the experiments to cease, we stopped when the time was up. At

least two thirds of my time in the past six months has been devoted to aeronautical

matters. Unless I decide to devote myself to something other than a business
282 Chapter 2: Building a Research Establishment

career I must give closer attention to my regular work for a while. I hope at some

later time to resume these investigations and also to carry out a plan I have considered of obtaining an accurate measurement of the value of P90.

You will note that #7 reaches a lift of 119 per cent at 17 1⁄2°, a greater amount

than any preceding investigation has found, so far as I am aware. And that #4

reaches almost as high at 30°. By means of an entirely different instrument I have

confirmed the fact that the normal pressure of #4 at 20° (twenty) is slightly more

than equal size at 90°. At 30° the normal pressure of #4 is much greater than the

normal plane. At about 45° the normal pressure of #4 is equal to the normal

pressure of a plane at about 70°. If these high values of #7 and #4 at 17 1⁄2° and

30° are too high, then the lift of #1 at 17 1

⁄2° is also too high in the same ratio. In

fact all the measurements of all the surfaces were made under conditions which

make all the measurements true if any of them are true.

I will return the Marvin document in a few days.

[p.s.] #12 has the highest dynamic efficiency of all the surfaces shown.

Document 2-1(c), letter from Wilbur Wright to Octave Chanute, 23 December 1901.

I am returning the Marvin papers herewith. I should have sent them much

sooner but that I hoped to be able to complete some notes to send with them. I

find however that it is more difficult than I expected and though I have made several attempts I have not yet been able to get everything shaped up to suit my

ideas of the real operation of the forces which arise in glides. I think that the real

angle of incidence should be not the angle bounded by the chord of the surface

and the line of the path, but an angle bounded by the line which marks the negative angle at which lift begins and the line of the relative wind. The true normal

should be perpendicular to the line of no lift instead of to the chord, and the tangential is the deflection of the direction of the resultant pressure from this true normal. You will see that all this greatly increases the complication of calculations but

I see no other way of arriving at theoretically perfect results. For rough work

much of this refinement would be unnecessary, but in defining the meaning of terms
Document 2-1(a–d) 283

we should aim to get them exactly as they really are. I will send you my ideas on

some of these points as soon as I can get them properly straightened out. I get

lost now and then.

I return the Langley letter which I have read with regret. I was not unprepared for his decision as some remarks Mr. Huffaker made last summer gave the

impression that Lilienthal was not in high favor among the Washington group of

workers for some reason. Mr. Huffaker seemed to think that Lilienthal had been

overestimated. Since seeing his book I can not help thinking that he is underestimated, and that he will stand even higher when the doubts with which some of his

most important discoveries have been accepted are finally cleared away. It seemed

to me that the publication of his book in English would not only be of very great

value to all aeronautical workers but it would be a well deserved tribute to the

memory of a man who spent much money, an immense amount of his time, and

finally his life in carrying out investigations which he gave freely to the world.

Your offer to assist in figuring out the results of our recent experiments is

thankfully received. The labor itself is not so tremendously great, though there

are several days’ work required; but I have felt the need of a verification of our

calculations to guard against blunders. If you desire I will send you our data as

read from the machine, with directions for translating them into per cent of the

pressure on a square plane of equal area at 90°. I will also send you photographs

of our instruments and try to make it clear just how they operated. As to the accuracy

of the results I think I am very safe in saying that the possible error is less than

one twentieth. I think the average is much closer than this. We spent nearly a month

getting a straight wind, but finally were able to get a current whose direction did

not vary one eighth of one degree. A possible error of one twentieth, or 5%, is by

no means insignificant but it does not greatly reduce the practical value of the

tables. For purposes of comparing the lifts of different surfaces at the same angle

or different angles, or of comparing the relative lifts of the same surface at different

angles, the tables will be more accurate still, as some of the most serious sources

of error are eliminated when the exact value of the common resistance against

which the surfaces are weighed is not required to be fixed. I think about 2% would

easily cover the errors which could arise from errors in mounting the surface at

the exact angle desired, variations in wind direction, and errors in reading. This

of course does not include mere blunders.

Our measurements of the tangential include the edge resistance of the surfaces

and I can devise no way of eliminating this from the measurements. On the whole

I am inclined to think that it is possible with large surfaces to get rather more

favorable tangentials than the small surfaces show. The thickness of our regular

surfaces was about three per cent of the fore-and-aft dimension. This you will

notice is more than the relative thickness of the largest spars of our gliding
284 Chapter 2: Building a Research Establishment

machines. We did not use thinner material because it was deemed to be of the

utmost importance that the surface should be sufficiently strong and stiff to prevent

any twisting or warping under pressure of the wind. A distortion too small to be

noticed and almost too small to be measured might cause quite serious errors in

measurements where great exactness was desired. I am inclined to think that this

has been a more serious matter than most investigators have supposed.

It was with very great reluctance that we discontinued our experiments at the

time we did, but there were so many things yet to be investigated that it was very

evident that we would be unable to spare the time to carry them through at the

present. We got all that we originally set out for, so we thought it a favorable time

to take a recess. Then, too, we saw that any further time consumed now would

seriously impair our chance of a trip to Kitty Hawk next fall.

As to your suggestion in regard to Mr. Carnegie, of course nothing would give

me greater pleasure than to devote my entire time to scientific investigations; and

a salary of ten or twenty thousand a year would be no insuperable objection, but

I think it possible that Andrew is too hardheaded a Scotchman to become interested in such a visionary pursuit as flying. But to discuss the matter more seriously,

I will say that several times in the years that are past I have had thoughts of a scientific career, but the lack of a suitable opening, and the knowledge that I had no

special preparation in any particular line, kept me from entertaining the idea very

seriously. I do not think it would be wise for me to accept help in carrying our

present investigations further, unless it was with the intention of cutting loose

from business entirely and taking up a different line of lifework. There are limits

to the neglect that business will endure, and a little pay for the time spent in

neglecting it would only increase the neglect, without bringing in enough to offset

the damage resulting from a wrecked business. So, while I would give serious consideration to a chance to enter upon a new line of work, I would not think it wise

to make outside work too pronounced a feature of a business life. Pay for such outside

work would tend to increase the danger. The kindness of your offers to assist,

however, is very much appreciated by us.

Document 2-1(d), letter from Wilbur Wright to Octave Chanute, 19 January 1902.

I am sending you herewith photo and description of our pressure-testing

machine. It is our belief that the method and construction employed entirely avoid

errors from the following sources: (1) Variation in wind velocity; (2) Variation in temperature and density of the atmosphere; (3) Travel of center of pressure; (4) Variation

in angle of incidence owing to movements of the mounting arms. The first two causes

gave Mr. Langley trouble; while the 3rd & 4th vitiate somewhat the natural wind

experiments of Lilienthal. Gravity and centrifugal force are also rendered nugatory.
Document 2-1(a–d) 285

Our greatest trouble was in obtaining a perfectly straight current of wind, but

finally, by using a wind straightener, and changing the resistance plane to a position

where its ill influence was much reduced, and also by breaking it up into a number

of narrow vertical surfaces instead of a single square, we obtained a current very

nearly constant in direction. The instrument itself was mounted in a long square

tube or trough having a glass cover. After we began to make our record measurements

we allowed no large object in the room to be moved and no one except the observer

was allowed to come near the apparatus, and he occupied exactly the same position

beside the trough at each observation. We had found by previous experience that

these precautions were necessary, as very little is required to deflect a current a

tenth of a degree, which is enough to very seriously affect the results. I will send

another batch of data in a few days.

Your letter from St. Louis of course interested us very much. The newspapers

of yesterday announce that the fair will be held in 1903 as originally planned. If

this be final there will be little time for designing and building a power machine

which is, I suppose, the only kind that could hope to be awarded a prize of any

size. Whether we shall compete will depend much on the conditions tinder which

the prizes are offered. I have little of the gambling instinct, and unless there is

reasonable hope of getting at least the amount expended in competing I would

enter only after very careful consideration. Mathematically it would be foolish to

spend two or three thousand dollars competing for a hundred thousand dollar

prize if the chance of winning be only one in a hundred. However we shall see

about the matter later.

Meanwhile it will be just as well for me to postpone the paper on our late

experiments on pressures & tangentials till we have decided whether or not we

shall compete, as it would be hardly advisable to make public information which

might assist others to carry off the prize from us. If the exposition authorities

should deem it advisable to offer some preliminary prizes for papers on such subjects

with a view to getting into the hands of all the competitors the best possible information and thus rendering the final contest of machines more exciting, I would

place our tables in competition, but otherwise we ought to delay publication for a

short time at least. This injection of the mercenary idea into the flying problem is

really a nuisance in some respects.
286 Chapter 2: Building a Research Establishment

Document 2-2(a–c)

(a) Washington Irving Chambers, excerpt from 

“Report on Aviation,” 21 September 1912, Annual Report

of the Secretary of the Navy for 1912 (Washington, DC, 1912).

(b) Jerome C. Hunsaker, Assistant Naval Constructor, 

Report on Facilities for Aeronautical Research in England,

France, and Germany, Part III—Germany, undated 

(ca. November 1913), NASA Record Group 255, 

Hunsaker Biography File, Entry 3, Box 12, 

National Archives, Washington, D.C.

(c) Albert F. Zahm, excerpt from Report on 

European Aerodynamical Laboratories 

(Washington, DC: Smithsonian Institution, 1914).

A few months after the untimely death of Wilbur Wright in 1912, Captain

Washington Irving Chambers of the United States Navy submitted “Report on

Aviation” to the Navy Department’s Bureau of Navigation. Chambers began his report

by outlining possible uses of aircraft in naval warfare. Concerned about the lagging

state of aviation research in the United States, especially when compared to what was

being carried out in Europe, Chambers concluded his report with a detailed proposal

for the establishment of “a national aerodynamical laboratory” in the United

States. It is this part of the document that is reproduced here. While Chambers’s

specific recommendations were not acted on at the time, his report stands as a farsighted statement of the need for a national research establishment. 

Following the success of the Wright Brothers, European interest in aeronautical

research intensified, but, incredibly, it languished for a decade in the United States.

Between 1903 and the start of World War I, no less than ten wind tunnels began

operation in Europe, while only two were built in America. Much of the European

work was due to a realization, particularly after the Wrights’ 1908 demonstration

flights in France, that airplanes could provide a military advantage, something of

great value in an increasingly antagonistic Europe. In England, Italy, and Germany,

governments invested in both airplanes and new aeronautical laboratories, such

as the one at the National Physical Laboratory in London and a laboratory at

Göttingen, Germany, that featured an innovative, closed-circuit wind tunnel. Private
Document 2-2(a–c) 287

funds underwrote new facilities in Russia and France, including two laboratories

built by Gustav Eiffel in and near Paris. The United States, on the other hand,

cared little about the looming catastrophe in Europe, preferring to remain neutral

and, thus, seeing little need for an investment in military aviation. The long

Wright-Curtiss patent fight over ownership of rights to the airplane further

dampened America’s enthusiasm for airplanes and aeronautical development. 

Within the military, a few farsighted naval officers, including Washington

Irving Chambers, David W. Taylor, and Jerome C. Hunsaker, realized the long-term

importance of aviation to the military and lobbied for an aeronautical laboratory.

An investigative board chaired by Chambers recommended a national aerodynamic

laboratory in its 1912 “Report on Aviation.” This report includes considerable

detail about the nature of the work to be done in such a laboratory and the necessary facilities, and it goes so far as to suggest a joint military-civilian agency

“advisory committee” to direct the operation. Although Chambers’ recommendation for joint military-civilian management angered his superior officers—unlike

Taylor, Hunsaker, and other pioneers of naval aviation, Chambers was never promoted to rear admiral—his report described a research organization very close to the

one adopted for the National Advisory Committee on Aeronautics three years later.

The Chambers report also inspired the navy to take action on its own. Taylor,

assisted by two lieutenants and Zahm, was developing a design for a closed-circuit

wind tunnel. With encouragement from the Chambers Report, Taylor managed to

obtain the funds to build it, and the eight- by eight-foot Washington Navy Yard

tunnel, the first wind tunnel built by the United States Government, began operation in March 1914.

While America did not invest in aeronautical laboratories to the extent that

European nations did before World War I, a few interested parties stayed abreast

of the European developments and pressed for the establishment of such facilities in the United States. Supported by the Smithsonian Institution, Catholic

University Professor Albert F. Zahm and Assistant Naval Constructor Jerome C.

Hunsaker, two of the leading figures in American aviation, visited the major

European research facilities in 1913 to evaluate their capabilities and progress in

aeronautics. Hunsaker first submitted his findings to his superiors in the navy in

an extensive three-part report. Part III of his Report on Facilities for Aeronautical

Research in England, France, and Germany covers six facilities and gives a good picture of the state of the German aeronautical art. The work of Ludwig Prandtl at

the University of Göttingen particularly impressed the perceptive Hunsaker.

While he found the Göttingen work to be “characterized by poor equipment

made the most of by men of extraordinary ability,” he noted that the Kaiser

Foundation was underwriting a new wind tunnel there. Hunsaker’s report also

mentions Prandtl’s theoretical work in computing dirigible resistance using
288 Chapter 2: Building a Research Establishment

hydrodynamic theory, work that would be a major foundation for the development of theoretical aerodynamics. 

Zahm’s Report on European Aeronautical Laboratories, a public report of the same

inspection trip published by the Smithsonian Institution in 1914, described the

European research laboratories and apparatus in considerable detail, but this report

did not contain the kind of analysis and insightful evaluation of the facilities and work

that can be found in Hunsaker’s report. Nevertheless, Zahm’s report showed that

America was considerably behind the Europeans. This report, being a published document, was widely circulated in aviation and political circles, and it proved to be the

catalyst that spurred the creation of the National Advisory Committee for Aeronautics.

Document 2-2(a), Washington Irving Chambers, 

excerpt from “Report on Aviation,” 21 September 1912.

INFLUENCE OF FOREIGN LABORATORIES

Little more than a year ago our knowledge of the effect of air currents upon aeroplane surfaces was almost entirely a matter of theory. The exact information available

was so meager that aeroplanes were built either as copies, slightly modified, of other

machines, or else by way of haphazard experiment. This state of affairs pertains to

some extent in the United States today, although in Europe aeroplane construction

is now largely based on scientific data obtained at notable aerodynamic laboratories.

The intuitive, hasty, and crude methods of the pioneer can not succeed in

competition with the accurate and systematic methods of the scientific engineer,

and it is beginning to dawn upon our perceptions that through lack of preparation for the work of the scientific engineer, i.e., through delay in establishing an

aerodynamic laboratory, a waste of time and money, a decline of prestige, and an

unnecessary sacrifice of human life has already resulted.

Students of aviation do not need to be informed of the practical necessity for

aerodynamic laboratories. They have repeatedly pointed out, in aeronautical

publications, the immense commercial advantages to be anticipated from the

establishment of at least one in this country, and they have naturally expected that

some philanthropic patriot of wealth and scientific interest would come to the rescue

with a suitable endowment fund that would enable such work to be started in

short order without Government aid. The fact that no patriot has responded is

disappointing, in view of the large private donations that have done so much for

aviation in France, but in my opinion, it simply indicates something lacking in the

manner of disseminating information concerning the importance of the subject.

I am not willing to believe that our people will refuse to establish one when they

are fully acquainted with the advantages to humanity and to sane industrial progress,

and when a reasonable concrete proposition is advanced for their consideration.
Document 2-2(a–c) 289

It is now my purpose to submit such a proposition, and, in doing so, I will follow briefly,

in general outline, the ideas advanced in an address to the Fifth International

Aeronautic Congress by one of the greatest authorities in the world, the Commandant

Paul Renard, president of the International Aeronautic Commission.

A NATIONAL AERODYNAMIC LABORATORY

Before considering the character of the work to be done and some details of

the needed plant, it will facilitate matters to show what should not be done at such

a laboratory.

There are those who dream of supplying the laboratory with all the instruments known to mechanics, to physics, and even to chemistry, in order to have a

creditable and complete national institution. They would concentrate in one

locality all the scientific instruments and acumen available, with the false idea that

economy would result. This would be a grave error.

The financial resources, however great, are sure to be limited, and a too ambitious

or a superfluous installation would squander the sources of power and indirectly

menace the initiative of other industries. The character of the new work to be

done demands that everything should be rejected that can be dispensed with

readily in order that appliances specially needed in the new work may be provided

and that these appliances be of the latest and most efficient types.

For the sake of economy, not only of money but of time and intellectual energy,

tests and experiments that can be executed as well or better elsewhere by existing

establishments should be avoided. For example, it is unnecessary to install a complete

set of instruments and implements for testing the tensile strength of materials or

their bending and crushing strength. Many other establishments permit of such work.

If the laboratory is to be located in Washington, where certain advantages exist,

such work could be readily done at the navy yard, where other facilities exist such, for

instance, as the testing of models for hydroaeroplanes and flying boats. The Bureau

of Standards and Measures and other Government branches in Washington also

offer facilities which it would not be wise to duplicate in such a laboratory.

I do not think that such an institution should be burdened with measuring the

power of motors or preoccupied with the details of their performances. This may

be done at various other Government establishments, and it is understood that

the Automobile Club of America is also equipped for this work.

Nor is it necessary to have a complete chemical laboratory under the pretext

of studying questions relating to the chemistry of fuel or the permeability of balloon envelopes.

I do not wish to convey the idea that an aerodynamic laboratory should be deprived

entirely of such facilities and that it should be obliged to seek minor information from

other establishments when that information may be more economically obtained by

a duplicate plant on a small scale. Such duplicate conveniences, however, should
290 Chapter 2: Building a Research Establishment

be regarded as strictly accessory; but it should be well understood that whenever

important researches can be prosecuted as well or better elsewhere, dependence

should be placed on those other establishments where such work is a specialty.

TWO DISTINCT CLASSES OF WORK

An aerodynamic laboratory should be devoted to (1) experimental verification, (2)

experimental research. The first is concerned with testing the qualities of existing appliances, propellers, sustaining surfaces, control mechanism, etc. Usually these tests are

made at the request of interested parties (as is now the case with water models at the

navy-yard model basin). A constructor or a designer will bring, for example, a propeller

and will wish to know its power or thrust at a given speed on the block or on a moving

appliance under the conditions of flight, or he may bring several propellers to compare

their performances and to ascertain what power they absorb at different speeds.

One of the very successful appliances devoted to this work at St. Cyr is a movable

car, in which an aeroplane may be mounted and tested at speeds in perfect safety

as to its strength, its efficiency, and the suitability of its control mechanism. This

device is specially adapted to make actual service tests of sustaining surfaces, in

other words, to try out in perfect safety the relative efficiencies of finished aeroplanes.

It is a most important adjunct, as it supplements and rounds out the important

research work on models in the closed laboratory.

Tests of this character, i.e., verification tests, constitute, so to speak, standard

work. They are performed at the request of manufacturers, clubs, independent

investigators, and other interested parties on condition of payment for the actual

cost of the work. They therefore contribute to the support of the establishment.

The tests of verification, however, notwithstanding their great utility, do not

constitute either the most important or the most interesting work of the laboratory.

The research work, which prosecutes continuously and patiently systematic, thorough,

and precise investigation of new ideas, or of old ideas with new applications, with

the specific intention of discovering laws and formulas for advancing the progress of

aerial navigation, is of greater importance, because it is the short cut to substantial

efficiency, economy, improvement, and prestige.

This work is concerned with developing adequate methods of research in all

branches of aerial navigation and in furnishing reliable information to all students, engineers, inventors, manufacturers, pilots, navigators, strategists, and

statesmen. The knowledge thus gained should be disseminated regularly through

publications, lectures, open-air demonstrations, and by exhibitions of apparatus,

instruments, materials, and models—in fact, by all the facilities of the aerodrome,

the showroom, the library, and the lecture room.

An exact knowledge of aerodynamics can best be acquired in such a laboratory

by experimentation with standard scale models in air tunnels such as those used

by M. Eiffel and others. In this way reliable data is obtained of the air resistance
Document 2-2(a–c) 291

to be encountered and the efficiency at various velocities, the amount of lift, the

effect of varying impact at different angles of attack on the stability—in fact, all

the exact data which, reduced to curves and diagrams, enables the engineer to

design a machine in a scientific manner. From such data the performance of a new

machine can be closely predicted. The performance of the finished product can

be verified later as before described.

Much of the research work will be prosecuted at the request of technical men

outside of the institution, to whom the laboratory should offer, gratuitously as far

as possible, its material and personal resources.

THE COUNCIL AND ORGANIZATION

To obtain benefit from these researches it will be necessary to know that they

are worth the time and expense, and a body of men—a council or a board of governors—should be authorized to accept or reject requests for this work. This will

be a delicate task, but the principal duty of the council should be to establish and

to correct from time to time a program of the research work to be executed by the

director and his staff and to coordinate the work to the best advantages within the

limits of the money available. The disbursement of the Government funds, however,

and the responsibility therefore should be entirely under the director.

With the actual state of aerial navigation and its deficiencies as a guide it will

be the policy of the council to concentrate effort upon such points as seem most

important, promising, and interesting for the time being.

I do not think there would be any doubt, if we had the laboratory in working

order now, but that all questions relating to improvement in stability, automatic

control, and safety in general would have the right of way.

The council or board, which in England is called the “advisory committee,”

should be representative of other Government departments than that employing

the director, and should be independent of the director and his administrative

staff. It might be possible for the director to act as a member of the council and,

if so, it would conduce to harmony and expedition.

The council should not be a large body, but should be composed mostly of

specialists of unquestioned ability, men interested in the development of aerial

navigation in various branches of the Government and in its useful and safe adaptation to commerce and sport.

Whatever the ability of this council it should not be allowed to pretend that it

has a monopoly of aeronautic acumen. Many brilliant and worthy ideas may originate

outside of the establishment which it will be wise to investigate. And to avoid any

possibility of the council being charged with narrow prejudice, it is indispensable

that it be not composed entirely of specialists. In a few words, it should comprise

representative men who are also learned and technical men, with broad vision and

reputation, whose presence will guarantee to industrial investigators that their
292 Chapter 2: Building a Research Establishment

ideas will be treated in an unpartisan or unbiased spirit. I will not attempt to suggest the composition of this council or board, but it is evident that the Army and

Navy should each be adequately represented on it.

ENDOWMENTS, PRIZES, AND REWARDS

If the laboratory should obtain, in addition to the funds required for prosecuting

researches by its staff, any endowments of financial aid in excess of immediate

needs (and I am confident it will eventually), it would accomplish useful work by

offering prizes and granting rewards for important results achieved outside of the

institution. The division of rewards would be one of the functions of the council,

and it is possible that this would be one of the best uses of such resources, after

the success of the laboratory is assured.

The complete role of an ideal aerodynamic laboratory can be summed up now in

a few words in the natural order of establishment: (1) Execution of verification tests by

means of nominal fees; (2) facilities to technical men for prosecuting original research;

(3) execution of researches in accordance with a program arranged by the council,

and (4) reward of commendable results accomplished outside of the laboratory.

NATURE OF THE PLANT

Researches and tests can be made on either a large or a small scale, preferably

on both.

The use of small models can be made prolific in results because of the comparatively small cost, provided we understand the laws governing transformation

into the full sized products. For model work a large plant is unnecessary. M. Eiffel

has done very valuable work in a very small establishment.

Certain classes of tests with large models, such, for example, as the block test of

propellers, do not require much space. But the conditions are altered when such

tests are made on a machine in motion. These more difficult tests are absolutely

indispensable and very important to the usefulness of an official laboratory.

Experiments and tests with small models being comparatively inexpensive,

private establishments often undertake their execution, but when we attempt to draw

conclusions from their results we are obliged to admit that the laws of comparison

with full-sized machines are debatable the world over. Comparisons are sensibly true

between small surfaces and larger surfaces that have been extended proportionately to the square of the linear dimensions, even to surfaces five or ten times larger,

but when we pass to much larger surfaces, as we are obliged to, we are forced to

adopt formulas with empirical coefficients, about which there is indefinite dispute.

The difficulty can be overcome only by precise experiments upon large surfaces,

and such experiments, whatever the manner in which they are performed, will be

costly. If privately executed, the financial returns would not cover the cost.

The laboratory should comprise, therefore, two distinct parts, one devoted to

experiments on small-scale models and the other to experiments on surfaces of
Document 2-2(a–c) 293

large dimensions. But in both parts precise and thorough work is necessary.

When we have studied separately each element of an aeroplane, for example,

it will be necessary to test the complete apparatus. An aerodrome annex is therefore

necessary, or, at least, the laboratory should be located in proximity to an aerodrome

of which it can make use. In order that the observations may not only be qualitative

but quantitative, it will be necessary to follow all the movements of the complete

machine to know at each instant the speed, the inclination, the thrust of the propellers,

the effective horsepower, and, in fact, to conduct a true open-air laboratory for

aircraft after the manner of certain tests that have been prolific of results in France.

The English have established close relations between the royal aircraft factory

and their laboratory, the function of the former being the reconstruction and

repair of aeroplanes, the test of motors, and the instruction of mechanics.

LOCATION OF THE LABORATORY

The location of the model-testing plant, the headquarters of the administration

staff, requires comparatively small space, and there is no reason why it should be

remote from a city or from intellectual and material resources. It is advantageous

to have it easy of access to many interested people who are not attached to it.

The location of the open-air laboratory should obviously be at an aerodrome as

near as may be convenient to the model-testing plant or headquarters. Close proximity of the two parts is desirable, but not necessary. The high price of land near a large

city obliges the aerodrome annex of foreign plants to be located at a distance, but we

are fortunate in having here at Washington ideal conditions for the location of both

parts. The model laboratory should obviously be located on the site of Langley’s notable

work at the Smithsonian Institution, where the nucleus, an extensive library of records,

and a certain collection of instruments, are still available. The National Museum

is also an ideal location for the historical collection of models that will result.

No more ideal location for the annex, the open-air laboratory, or aerodrome

exists in all the world than that afforded by the as yet undeveloped extension of

Potomac Park. This is Government property which is of doubtful utility as a park

only, but which would be of immense utility and interest as a park combined with

a scientific plant of the character under consideration.

There is no reason why the public should be excluded from such a practice

field, but there is much to recommend that it be open to the public under proper

regulations as to the traffic, especially on occasion of certain tests or flights of an

educational value. It is of sufficient area, about 1 square mile. It is about 2 miles

long, is almost entirely surrounded by broad expanses of water, and, while convenient

of access, is so situated that the public may be readily excluded when tests of a

dangerous character are in process of execution. The fine driveways that will be

required as a park will offer excellent facilities for the practice work of the aerodrome

and for the moving test cars that should be supplied.
294 Chapter 2: Building a Research Establishment

One of the most attractive features of this location is the advantage it offers as an

ideal aerodrome for both the Army and the Navy, for both land and water flying and

the opportunity it affords for cooperation in all branches of the work of instruction

and experimentation. Furthermore, it is near to the shop facilities of the navy yard,

the accommodations of the Washington Barracks, the conveniences of various

Government hospitals, and it would doubtless add to the information and interest

of the near-by War College Staff and the General Board of the Navy. Its location would

enable our statesmen in Congress and a great number of officials in all departments to

keep in touch at first hand with the progress of aeronautics, with the quality of the work

done, and with the manner in which the money appropriated was being expended.

The educational facilities afforded by the work and by the lectures would be invaluable to the course of instruction for Army, Navy, and civil students of aeronautics.

As Washington is a mecca for business people of all parts of the country, a laboratory located here would be convenient in a commercial sense, especially in

view of its southerly location, which renders the open aerodrome available for use

throughout the greater part of the year. The only objection that I can see to the

Potomac Park extension is that the ground will require a considerable clearing, but

the trees on the harbor side of the location would not necessarily require removal.

THE APPARATUS NEEDED

It is useless to discuss here the various instruments and methods that have been

a source of some dispute abroad. All have some good feature, but time has shown

where some of the cumbersome and unnecessary installations may be eliminated

to advantage and where others may be improved. The new plant of M. Eiffel, at

Auteuil, may be regarded as a model for the wind tunnel and the aerodynamic

balance. A duplicate of that plant alone would be of inestimable value. The last

volume published by M. Eiffel is a forcible example of the value of his discoveries

by this method with respect to the angle of incidence and the displacements of

the center of pressure. It seems to merit the utmost confidence, although the

details of his installation differ from those at Chalais, at Koutchino, at the Italian

laboratory, and others. This method permits of testing the resistance of body

structures, the sustaining power of surfaces, the tractive power of propellers, and

the influence of transverse or oblique currents. If “free drop” apparatus at uniform

speed be regarded as indispensable to obtaining the coefficients of air resistance to

solid bodies of different shapes, it is possible that the interior of the Washington

Monument could be used to advantage, as was the Eiffel Tower, without disturbance

of the main function of that noble structure. This would be an excellent place from

which to observe the stability or action of falling models cast adrift at an altitude

of 500 feet under varying atmospheric conditions. The free drop of full-sized

models would of course require the use of kites or captive balloons.
Document 2-2(a–c) 295

The moving car previously referred to for tests of verification would be the

most useful open-air plant and would soon repay the outlay required by the value

of the information obtained from its use. A miniature duplicate of this method for

preliminary tests on models with a wire trolley would be of value in a hall of large

dimensions. It would be useful in winter work but not invaluable.

The track of the open-air vehicle at St. Cyr is too restricted to give the best results.

The car can not circulate continuously at high speed and maintain the speed for a

sufficient length of time. An ideal endless track may readily be arranged at the

Potomac Park extension, preferably of rectangular form with rounded corners. A

railway track would be preferable, but excellent results could be obtained from

auto trucks run on macadamized roadbeds. Good results could be obtained by the

use of suitable hydroaeroplanes or flying boats suitably equipped with instruments.

At the aerodrome annex ample facilities should be provided for measuring the

wind velocity at various heights and at different points. The convenient installation

of recording anemometers and the employment of kites or captive balloons

should be considered.

A branch of the United States Weather Bureau could readily be established at

the aerodrome here in connection with the investigation of meteorological phenomena affecting the movements of aeroplanes in flight and as an adjunct to the

national laboratory.

Exactly measured bases and posts of observation are also required, as well as

instruments of vision or photographic apparatus, to permit of following machines

in their flights and of preserving the records for study.

One of the most useful installations for recording advanced information is an

actual aeroplane itself equipped with instruments adapted to record, while in

flight, much of the information that is desired. Such machines are already in use

in France and in England.

It will be in perfect harmony and convenient to the laboratory to obtain all

the services of an aircraft factory from the Washington Navy Yard, where facilities

already exist for the reconstruction and repair of aeroplanes, the test of motors,

and the instruction of mechanics. But this should not be allowed to interfere with

our policy of relying upon private industry for the purchase of new machines, for

the sake of encouraging the art among private builders.

It will suffice to merely mention the hangars or sheds required of the local

accessories, such as drafting room, office, and minor repair shops. The character

and location of these present no difficulties, but they should not be made the

principal part of the institution as they are in several elaborately equipped foreign

laboratories. The power plant, however, is a subject for careful consideration and the

economy effected by M. Eiffel in his new installation at Auteuil is worthy of study.
296 Chapter 2: Building a Research Establishment

COST

I have seen estimates varying from $250,000 to $500,000 for such a plant, but

inasmuch as $100,000, with an annuity of $3,000 donated by M. Henry Deutsch

de la Meurthe to the University of Paris for the establishment of the aeronautical

laboratory at St. Cyr, seems to have been sufficient for a very creditable though

somewhat deficient plant, I will venture an opinion that $200,000 would be sufficient

in our case. Although the same plant would cost more in this country, I assume that

some of the buildings required are already available at the Smithsonian Institution.

If located elsewhere the cost would be considerably more than the sum named.

A COMMISSION RECOMMENDED

Inasmuch as more definite information regarding the actual cost of a dignified

and creditable but modest and sufficient installation should be obtained, and as the

details of the plan, the scope, the organization, and the location of such an important

undertaking should not be left to the recommendations of one man, I respectfully

recommend that a commission or board be appointed to consider and report to

the President, for recommendation to Congress, on the necessity or desirability

for the establishment of a national aerodynamic laboratory, and on its scope, its

organization, the most suitable location for it, and the cost of its installation.

W. Irving Chambers

Document 2-2(b), J. C. Hunsaker, Report on Facilities for Aeronautical

Research in England, France, and Germany, Part III—Germany, undated 

(ca. November 1913).

Part III—Germany 

(a) Modellversuchsoustalt fur Luftschiffart und Flugtechnik and der Universitat,

Göttingen,

Director: Dr. Prandtl.

In 1907, the Motorluftschiff-Studien-Gesellschaft was founded to promote

the German air craft industry. Various banks, commercial houses, and industrial

works contributed heavily. The parent society later floated stock companies to

build the German Wright aeroplane, and the Parseval air ship, and founded aero

clubs in the principal cities. Money was allotted to the University of Gottingen for

experimental research, and in 1908-9 a laboratory was built there. The director

of the laboratory was Dr. Prandtl, head of the department of applied mechanics,

at the University. He has given a great part of his time to aeronautical research

since that date while still holding his position at the University and delivering lectures

there on mathematics and mechanics. He has had only the assistance of his students

and a few mechanics. There have usually been two students in the laboratory working

for a doctorate. These men remained only a year or two and were replaced by new
Document 2-2(a–c) 297

men. In view of the changing personnel, the excellence and continuity of the research

is most remarkable. However, it is not likely that men of the ability of Fuhrmann,

Fokke, and others could have been hired as assistants for a reasonable sum.

The Gottingen work is characterized by poor equipment made the most of by

men of extraordinary ability.

In June, 1913, the Moroluftschiff-Studien-Gesellschaft had expended its capital and had accomplished its purpose.

In the first place, the German Wright Company has been distanced by its

competitors in the aeroplane field, which is proof that the society’s object of creating

the industry has been attained. In the second place, the Parseval air ship, made

by the Luftfahrzeug Gesellschaft, has been successfully developed and is financially

profitable. Germany leads the world in air ship building. Accordingly the M-S-G

has gone into liquidation and the Gottingen laboratory grant is stopped.

However, model research will be continued by a large grant from the Kaiser

Foundation. The old wind tunnel will be abandoned, and a new and more powerful one

built. It is expected that new buildings will be erected in Gottingen and that Dr. Prandtl

will leave the University to be the director. Dr. Prandtl is now inspecting the aeroplane

laboratories of Europe. I met him in Paris at the Eiffel laboratory, and in England at

the National Physical Laboratory. Both wind tunnels he considers good. He is not yet

ready to announce the type of his new tunnel, but he will not reproduce his old one.

It seems that with a closed circuit great difficulty is ahead in securing a uniform

stream of air if high speeds are used.

The closed circuit tunnel at Gottingen gives a uniform stream of air of velocity

10 meters per second but nearly two years have been spent adjusting baffles,

screens, and honey combs to attain a good result.

The tunnel and its work are well known to the readers of aeronautic literature.

Descriptions will be found in:—Jahrbuch der Motorluftschiff-Studien-Gesellschaft

for the years 1908-1910-1911-1912, published by Gustav Braunbeck, Berlin.

Also in—Jahrbuch der Luftfahrt by A. Vorreiter, 1910-11-12, published by J.F.

Schmanns, Munich.

Also in—Zeitschrift—fur Flugtechnik und Motorluftschaffahrt, a periodical

published by Oldenburg, Berlin.

The balance used by Dr. Prandtl is very delicate, and also very complicated.

The best description is given by Vorreiter. Its precision is less than 3/4%.

A special device is used for model propeller testing in connection with the

regular balance.

A great deal of work has been done on balloon shapes, aeroplane wings and

model propellers.

A most interesting piece of work has been the computation of the head of

resistance of a model dirigible by hydrodynamic theory and its verification by
298 Chapter 2: Building a Research Establishment

experiment. The discrepancy found is considered to be skin friction.

A research on propellers has been made to determine the distribution of pressure

over the blade in motion. A model in wax was covered with copper by electro

deposit and the wax melted out. The hollow copper model then had holes bored

at intervals over the blades. One hole at a time was opened and the internal pressure

transmitted through a hollow shaft and slip joint to a manometer.

The form of a Parseval air ship and the arrangement of fins and rudders is the

result of model research at Gottingen. As Count Zeppelin is an officer of the M-S-G,

considerable work has been done on Zeppelin models but none of it is published.

As the wind tunnel is not to be duplicated in the new laboratory no detail criticism

of it is given here. The general statement can be made that an irregular flow is

created which must be smoothed out by a multiplicity of obstructions in the channel.

That irregularity has been removed is more to the credit of the personnel of the

laboratory than to the design of the wind tunnel.

It appears that there is no relation between model research at Gottingen and

full scale experiment. The laboratory is devoted primarily to scientific research

and at odd times undertakes industrial testing for private firms.

(b) Zeppelin Versuchsanstalt, Friederichshafen.

The Zeppelin company’s works are not open to visitors, and I was unable to

secure admission. It is generally known that the company has a very complete

engine testing plant and is equipped with a complete meteorological station

including an outfit of pilot balloons for sounding the upper air levels.

In addition there is machinery for testing the strength of materials of construction.

A large and rough wind tunnel of rather blast of wind is reported to be used

to study the stability of route of air ship models.

(c) Technische Hochschule Aachen, Aachen.

Director of laboratory—Prof. Reisswer.

Under Prof. Reisswer at Aachen courses in aeronautics and aerodynamics have

been given to students who elected to attend. No design work was given. A large wind

tunnel of square section 2 m. by 2 m. has been built. The tunnel is open to the outdoor air at one end and at the other is a powerful exhauster. A velocity of 30 meters

per second can be maintained and provided there is no wind outside, the current is very

uniform. There are no baffles or honey combs in the channel. A 75 H.P. motor is used. 

It is noted that Eiffel obtains 30 meters per second in a 2 meter channel with

less than 50 H.P.

When there is any wind outside the air stream is not uniform. Much time is

lost waiting for a calm day and an advantage must be taken of still times at dawn

and evening.

No expensive balance has been designed, and work is largely confined to propeller
Document 2-2(a–c) 299

testing. The model propeller attached to the axis of a small electric motor is suspended by two wires in a canal. The torque is measured by the difference in pull

on the two wires. The thrust is measured by the pull on a third wire led up stream.

There is no permanent staff working with the tunnel and no great amount of work

is done at present. This winter one of the assistants from Gottingen will take charge.

(d) Versuchsanstalt für Flugwesen der Kgl. Technischen Hochschule zu Berlin,

Spandauer Weg, Reinickendorf-West, Berlin.

Director:—Major Von Parseval.

Asst. Dr. Quittner.

The laboratory is in process of construction under the direction of Maj. Von

Parseval, the inventor of the Parseval dirigible.

An office building of 4 rooms has been erected beside an old wooden air ship

shed of the Parseval Company.

This shed is 25 by 70 by 22 meters high.

Down the center is built a trestle 5m high and 70m long carrying a track on

which a dynamometer carriage runs.

The carriage is drawn by a cable leading over suitable blocks to two sets of

sand bags. The first set fall and accelerate the car in a few meters while the second

set continue to fall and maintain the car in uniform motion. The weight of sand

will be adjusted after trials. Automatic brakes are provided.

The car is some 2m high and is designed to measure lift, drift, and center of

pressure of aeroplane wings of span not greater than 10 meters. Forces are measured

against hydraulic pressure boxes and recorded graphically on ordinary steam

engine indicators from which the springs are removed.

Great precision of measurement is not attempted. It is hoped to study the

effect on aeroplane coefficients of change in area.

It is not likely that a high speed can be reached.

A small whirling arm, radius 5.5 meters, is completed. This arm is turned by falling

weights. The trouble from a following wind is avoided by giving only two complete

turns for a test. Only head resistance forces can be measured. A steam engine indicator drum records the force on the model. A velocity of 12 meters per second is used.

It is expected to study small surfaces to compare their coefficients with those

for large surfaces tested on the railway.

The staff consists of the director Major v. Parseval, and his assistant Dr. Quittner,

with 3 mechanics.

The courses in aeronautics at the Hochschule include lectures on aeroplane

and dirigible construction by Major v. Parseval, with the mathematics and

mechanics of flight given by other members of the faculty. No practical design is

attempted. Aeronautical studies are optional.
300 Chapter 2: Building a Research Establishment

(e) Prof. Dr. Fr. Ahlborn, 23 Ufer Strasse, Hamburg.

Prof. Ahlborn is well known to naval architects for his contributions to

“Schiffbau,” on stream line flow in water. He first called attention to the inherent

stability of the East Indian Zanonia leaf, and was the means of causing Igo Etricn

of Vienna to develop the Zanonia form aeroplane.

All of his investigations have been conducted in a tank of water some 3 x 3 x 15

feet long. Models at very low speed were drawn through the water by an electric

carriage running above the tank.

He found that fine beech sawdust boiled until it reached the density of water

could be used to show stream line phenomena. Various photographic methods

were developed which have been described in his papers. At the present time, the

Hamburg American Line and the City of Hamburg are to build him an experimental model tank for the further study of fluid motion.

All of Prof. Ahlborn’s results are qualitative and serve to illustrate fluid flow

at very low speeds. Their application to aeronautics is not apparent.

The Massachusetts Institute of Technology has purchased some 30 slides

from Prof. Ahlborn which represent his most important work. Permission is given

to copy them provided they are not published.

It seems that work such as Prof. Ahlborn has done should go hand in hand

with wind tunnel research. No one has yet been able to delineate the flow of air

in a high speed wind tunnel. At the National Physical Laboratory the whole

stream becomes cloudy if tobacco smoke is used and the camera only shows a fog.

Mr. Eiffel has tried salammoniac vapor without success. At Gottingen cork dust

has been tried and abandoned.

(f) Deutschen Versuchsanstalt für Flugwesen, Adlershof, bei Berlin.

Director:—Dr. Bendemann.

Dr. Bendemann conducted the test for the Kaiser Prize for the best German

aeroplane motor. This competition showed the necessity for having in Germany

a motor testing establishment when impartial comparisons could be made.

The German Society of Mechanical Engineers has now endowed a laboratory of which Dr. Bendemann is to be director.

Five motor testing beds in separate buildings are completed. Five motors can

thus be tested at the same time without interference due to noise and flying oil.

The main building contains offices and an aeroplane hanger. A tower 100 feet

high surmounts it. It is expected to suspend an aeroplane from cables reaching

up inside this tower to the top in such a manner that by the method of oscillations

the moment of inertia about the various axes may be measured. Work of this

nature is not yet commenced.

No wind tunnel will be built.

Experiments will be conducted on full-scale aeroplanes in flight, carrying
Document 2-2(a–c) 301

recording instruments. Work will be started as soon as the proper instruments are

completed.

The first experiments will be to send up aeroplanes with a form of recording

dynamometer attached to the controls. The force exerted by the pilot and the

rapidity of his movements will thus be studied.

Designs are being made for a dynamometer car to run on the railroad and to

carry a full size aeroplane. The car will be pushed by a locomotive and high

speeds are expected.

There seem to be unlimited funds.

The staff already consists of the Director and 10 assistants.

The laboratory is next to the Johannistahl flying grounds.

[signed] J. C. Hunsaker

Document 2-2(c), Albert F. Zahm, excerpt from 

Report on European Aerodynamical Laboratories, 1914.

GENERALITIES

Places visited.—During August and September, 1913, in company with Jerome C.

Hunsaker, Assistant Naval Constructor, U. S. N., I visited the principal aeronautical

laboratories near London, Paris, and Göttingen, to study, in the interest of the

Smithsonian Institution, the latest developments in instruments, methods, and

resources used and contemplated for the prosecution of scientific aeronautical

investigations. Incidentally we visited many of the best aerodromes (flying fields)

and air craft factories in the neighborhood of those cities, and took copious notes

of our observations. We also visited many aeronautical libraries, book stores, and

aero clubs, in order to prepare a comprehensive list of the best and latest publications

on aerial navigation and its immediately kindred subjects. In each of the countries,

England, France and Germany, we spent about two weeks. We were made welcome

at all the places visited, and thus established personal relations which should be

valuable in future negotiations with the aeronautical constructors and investigators

in those countries. But these incidental visits and studies, though they may prove

serviceable, do not seem germane to the present report. Neither does it seem

advisable to take more than passing notice of the aeronautical laboratories themselves in those manifold details which have been already published in large and

comprehensive reports now accessible in the Smithsonian Library.

Organization, resources, and scope of the laboratories.—The laboratories examined

by us are in particular (1) the aeronautical research and test establishments of the

British government near London; (2) the Institut Aerotechnique de St. Cyr, and

the Laboratoire Aerodynamique Eiffel, both near Paris; (3) the Göttingen

Modelversuchsanstalt at Göttingen; and (4) the newly organized laboratory
302 Chapter 2: Building a Research Establishment

adjoining the flying field at Johannisthal near Berlin, known as the “Deutsche

Versuchsanstalt für Luftfahrt zu Adlershof.”

These establishments resemble each other in some important features, but differ

in others. All are devoted to both academic and engineering investigations. All are

directed by highly trained scientific and technical men. The directors are not merely

executives; they are the technical heads—scientists or engineers specifically qualified

by superior training in aeronautical engineering and its immediately cognate

branches—who initiate the researches, and assist their technical staffs in devising

apparatus, interpreting results, and making systematic reports.

The establishments differ in their organization, resources, and equipments,

and, to a considerable extent, in the scope and character of their investigations.

Of the five institutions mentioned, the one in England and the one at Göttingen

are now supported largely by governmental appropriations; and the other three

are maintained by private capital, allotted as required, or accruing from fees or

endowment funds. Again, the laboratories near London, at St. Cyr, and at

Adlershof are practically unlimited in the scope of their researches, while Eiffel’s

and the Göttingen laboratory have confined their activities substantially to windtunnel experiments.

The aeronautical researches of the British Government are in charge of the British

Advisory Committee for Aeronautics, a self-governing civilian organization which was

appointed by the Prime Minister of England to work out theoretical and experimental

problems in aeronautics for the army and navy, and comprises twelve to fourteen expert

men, under the presidency of Lord Rayleigh. This committee initiates and directs investigations and tests at the Royal Air Craft Factory, at the National Physical Laboratory,

at the Meteorological Office, at Vickers Sons, and Maxim’s etc. It expends, in performing its regular functions, a sum exceeding the income of any private aeronautical laboratory and received directly from the government treasury.

The committee is primarily occupied with work for the government, but also

performs researches and tests for private individuals, for suitable fees, but without

guaranteeing secrecy as to the results. The work of the committee is manifold and

comprehensive. Whirling-table measurements, wind-tunnel measurements, testing

of engines, propellers, woods, metals, fabrics, varnishes, hydromechanic studies,

meteorological observations, mathematical investigations in fluid dynamics, the

theory of gyroscopes, aeroplane and dirigible design—whatever studies will promote

the art of aircraft construction and navigation may be prosecuted by this committee.

A detailed program and the results of actual investigations have been published

in the annual report of this committee.

M. Eiffel has paid from his personal fortune all the expenses of his plant and

elaborate researches, though it is understood that he may sometimes charge nominal fees for investigations made for private individuals who wish exclusive rights
Document 2-2(a–c) 303

to the data and results obtained. The general director of the laboratory is Eiffel

himself—who initiates the researches and publishes the results. He has in immediate charge two able engineers, MM. Rith and Lapresle, aided by three trained

observers who are skilled draughtsmen. Two mechanics and one janitor complete

the personnel. The work of the laboratory is all indoors, and is confined to

researches in aerodynamics alone, or more specifically to wind-tunnel measurements and reports thereon.

The institute at St. Cyr was founded by Deutsch de la Meurthe, who gave

$100,000 for the original plant and has provided $3000 per year, during his life,

for maintenance. It was presented by him to the University of Paris, and is now

under the general direction of the professor of physics, M. Maurain, aided by a

technical staff and a large advisory council of eminent engineers, scientists, and

officers of the university, officers of the French government, and members of various

clubs and aeronautical organizations. The staff comprises the director in charge

and his assistant, together with such students, two or three at a time, as may come

as temporary volunteers from the University of Paris.

The institute conducts large-scale experiments in the open field as well as

indoor researches, makes investigations for general publication or for private

interests, on payment of suitable fees, and permits private persons to conduct

researches in the laboratory. The work is practically unlimited, as is the case in the

English aeronautical laboratories. A special feature of the institute is its threequarter mile long track with electric cars for tests on large screws, large models,

and full-size aeroplanes.

The Göttingen aerodynamical laboratory was begun as a private enterprise, but is

now to be enlarged and maintained in part by financial aid of the Kaiser Foundation.

The original building, with its wind tunnel, was erected in 1908 after the plans of

its director, Prof. Prandtl of the University of Göttingen, at a cost of 20,000 marks

supplied by the Motorluftschiff-Studien-Gesellschaft. Its available income is said

to be $7,000 a year. The enterprise was inaugurated on a small scale because of

the uncertainty, at that date, as to the practical value of such an establishment.

The work of this laboratory, as in Eiffel’s, has been practically limited to wind-tunnel experiments, though Prof. Prandtl has written some valuable theoretical investigations, and is reported to be undertaking large-scale experiments in the open

air by use of a car on a level track, as at St. Cyr.

The Deutsche Versuchsanstalt für Lutftfahrt zu Adlershof has been recently founded

by the Verein Deutscher Ingeniure. The laboratory adjoins the great Flugplatz,

with its two square kilometer flying field surrounded by numerous air craft factories, scores of hangars, an aero club house, and a grand stand. Major Von Tschudi,

a retired German officer, is general manager of the organization which operates

the flying field in the interest of all aero manufacturers and experimentalists,
304 Chapter 2: Building a Research Establishment

whether civilian or governmental. Dr. Eng. F. Bendeman is director of the laboratory and has ten assistants, comprising, among others, Dr. Fuhrman, who was

former assistant in the Göttingen laboratory. I have not ascertained the financial

resources of the laboratory, but a prelude to its present operations was a competition involving some three score German aeronautical motors, for the Kaiser

Prize, and additional contributions from the country at large, aggregating in all

125,000 marks. It is understood that the laboratory is liberally supported, is

unlimited in the scope of its work, and will conduct both indoor researches and

field experiments similar to those at St. Cyr.

After this general view, a technical account of the foregoing aeronautical

establishments may be useful.
Document 2-3(a–c) 305

Document 2-3(a–c)

(a) U.S. Congress, “An Act Establishing an Advisory 

Committee for Aeronautics,” Public Law 271, 6

3rd Congress, 3rd Session, passed 3 March 1915.

(b) George P. Scriven, “Letter of Submittal” (Chairman’s 

Letter for the first Annual Report, 9 December 1915), 

NACA Annual Report for 1915 (Washington, DC). 

(c) George P. Scriven, “Existing Facilities for Aeronautic

Investigation in Government Departments,” 

NACA Annual Report for 1915 (Washington, DC).

Zahm’s Report on European Aeronautical Laboratories, published by the

Smithsonian Institution in 1914, revealed just how far the United States trailed

Europe in aeronautical research. Armed with this new information, the Smithsonian’s

regents recommended that Congress establish a national advisory committee for

aeronautics, based largely on the British Advisory Committee for Aeronautics

organization, in February 1915. The navy, content with its own aerodynamical laboratory at the Washington Navy Yard, did little to support the recommendation,

but it ended up in an ironic supporting role nevertheless. The text that established the National Advisory Committee for Aeronautics comprised only two

paragraphs, and Congress included them in a Naval Appropriations Act that it

passed on 3 March 1915. While only $5,000 per year for five years was appropriated, this brief rider set the tone for the organization, stating, “That it shall be the

duty of the Advisory Committee for Aeronautics to supervise and direct the scientific study of the problems of flight, with a view to their practical solution, and to

determine the problems which should be experimentally attacked, and to discuss

their solution and their application to practical questions.” Over the next two

decades, that small investment in the NACA would grow into several million dollars,

and the NACA would build a superb aeronautical laboratory and research program.

Congress defined the NACA to include members from the army, navy,

Smithsonian Institution, weather bureau, and bureau of standards, as well as

members from the broader aeronautical community. In so doing, it intended to

coordinate both military and civilian aeronautical research and development

through one agency that was charged with the authority to conduct research in

any laboratory that might be assigned to it. During its earliest years, the NACA
306 Chapter 2: Building a Research Establishment

sponsored research in the Washington Navy Yard tunnel and elsewhere, such as

William F. Durand’s propeller research at Stanford University, but the committee

members soon realized that they needed a comprehensive laboratory and staff

that could support all facets of aeronautical research. Indeed, one of the NACA’s

first tasks was to examine the available facilities in the United States. The 1915

annual report outlined the capabilities and work loads of five government agencies

in a section entitled “Existing Facilities for Aeronautic Investigation in Government

Departments,” and concluded “that utilizing all facilities at present available, the

progress that can be made will be fragmentary and at best lack the coordination

that is necessary to accomplish . . . the important work now in sight.” Armed with

this conclusion, the NACA’s first chairman, Army Brigadier General George P.

Scriven, proposed a joint military-civilian facility, but Navy Secretary Josephus

Daniels objected, fearing it could jeopardize the navy’s research plans. With its

Washington Navy Yard wind tunnel in operation and Jerome Hunsaker involved

in research at MIT, the navy was already actively engaged in aerodynamical

research in 1915, and Daniels saw no need to change course. Nevertheless, he

allowed an $82,516 NACA appropriation, which included $53,580 for construction of a new laboratory, to be attached to a 1916 Naval Appropriations Act. (The

following year’s Naval Appropriations Act provided the NACA with an additional

$107,000, but subsequent NACA funding came from civil appropriations acts.)

Given the navy’s reticence, the NACA worked with the army to find a site where

they could build and share a flying field, and where the NACA could build its laboratory. They settled on a location near Hampton, Virginia, and construction at

Langley Field began in April 1917, just as the United States entered World War I. 

Document 2-3(a), U.S. Congress, 

“An Act Establishing an Advisory Committee for Aeronautics,” 1915.

Public Law 271, 63d Cong., 3d sess., passed 3 March 1915 (38 Stat. 930).

An Act making appropriations for the naval service for the fiscal year ending

June thirtieth, nineteen hundred and sixteen, and for other purposes.

An Advisory Committee for Aeronautics is hereby established, and the

President is authorized to appoint not to exceed twelve members, to consist of two

members from the War Department, from the office in charge of military aeronautics; two members from the Navy Department, from the office in charge of

naval aeronautics; a representative each of the Smithsonian Institution, of the

United States Weather Bureau, and of the United States Bureau of Standards;

together with not more than five additional persons who shall be acquainted with

the needs of aeronautical science, either civil or military, or skilled in aeronautical

engineering or its allied sciences: Provided, That the members of the Advisory
Document 2-3(a–c) 307

Committee for Aeronautics, as such, shall serve without compensation: Provided

further, That it shall be the duty of the Advisory Committee for Aeronautics to

supervise and direct the scientific study of the problems of flight, with a view to their

practical solution, and to determine the problems which should be experimentally

attacked, and to discuss their solution and their application to practical questions.

In the event of a laboratory or laboratories, either in whole or in part, being placed

under the direction of the committee, the committee may direct and conduct

research and experiment in aeronautics in such laboratory or laboratories: And

provided further, That rules and regulations for the conduct of the work of the

committee shall be formulated by the committee and approved by the President.

That the sum of $5,000 a year, or so much thereof as may be necessary, for

five years is hereby appropriated, out of any money in the Treasury not otherwise

appropriated, to be immediately available, for experimental work and investigations

undertaken by the Committee, clerical expenses and supplies, and necessary

expenses of members of the committee in going to, returning from, and while

attending meetings of the committee: Provided, That an annual report to the

Congress shall be submitted through the President, including an itemized statement

of expenditures.

Document 2-3(b), George P. Scriven, Chairman’s 

Letter for the first NACA Annual Report, 1915.

LETTER OF SUBMITTAL.

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS,

STATE, WAR, AND NAVY BUILDING

Washington, D. C., December 9, 1915.

The PRESIDENT:

In compliance with the provisions of the act of Congress approved March 3, 1915

(naval appropriation act, Public, No. 273, 63d Cong.), the National Advisory

Committee for Aeronautics has the honor to submit herewith its annual report for

the period from March 3, 1915, to June 30, 1915, including certain recommendations

for future work and a statement of expenditures to June 30, 1915.

The committee was appointed by the President on April 2, 1915, and held its

first meeting for organization on April 23, 1915. On June 14 the President

approved rules and regulations which had been formulated by the committee for

the conduct of its operations.

By the act establishing the committee, an appropriation of $5,000 a year for

five years was made immediately available. Of the appropriation for the first year,

ending June 30, 1915, there was expended a total of $3,938.94, as shown by the

itemized statement in the accompanying report, and the unobligated balance of
308 Chapter 2: Building a Research Establishment

$1,061.06 was covered into the Treasury as required by law.

In order to carry out its purposes and objectives, as defined in the act of

March 3, 1915, the committee submits herewith certain recommendations and an

estimate of expenses for the fiscal year ending June 30, 1917. The estimates in

detail were submitted through the Secretary of the Navy.

Attention is invited to the appendixes of the committee’s report, and it is requested that they be published with the report of the committee as a public document.

It is apparent to the committee that there is a large amount of important work

to be done to place aeronautics on a satisfactory foundation in this country.

Competent engineers and limited facilities are already available and can be

employed by the committee to advantage, provided sufficient funds be placed at

its disposal, as estimated for the fiscal year 1917.

What has been already accomplished by the committee has shown that

although its members have devoted as much personal attention as practicable to

its operations, yet in order to do all that should be done, technical assistance

should be provided which can be continuously employed. There are many practical

problems in aeronautics now in too indefinite a form to enable their solution to

be undertaken. The committee is of the opinion that one of the first and most

important steps to be taken in connection with the committee’s work is the provision

and equipment of a flying field together with aeroplanes and suitable testing gear

for determining the forces acting on full-sized machines in constrained and in free

flight, and to this end the estimates submitted contemplate the development of

such a technical and operating staff, with the proper equipment for the conduct

of full-sized experiments.

It is evident that there will ultimately be required a well-equipped laboratory

specially suited to the solving of those problems which are sure to develop, but

since the equipment of such a laboratory as could be laid down at this time might well

prove unsuited to the needs of the early future, it is believed that such provision

should be the result of gradual development.

The investigations which the committee proposes in its program for the coming

year can only be carried out to a satisfactory degree, with the limited facilities

already existing, provided sufficient funds are made available. The estimates of the

committee are based on such line of action, and on the assumption that a flying

field can be placed at its disposal on Government land. If, however, such facilities

be not practicable at this time, some progress may still be made by the utilization of

the facilities of the Government aeronautic stations at Pensacola and San Diego.

The estimate of expenses for the fiscal year ending June 30, 1917, is as follows:

For carrying into effect the provisions of the act approved March third, nineteen

hundred and fifteen, establishing a National Advisory Committee for Aeronautics,

there is hereby appropriated, out of any money in the Treasury not otherwise
Document 2-3(a–c) 309

appropriated, for experimental work undertaken by the committee, assistants and

the necessary unskilled labor, equipment, supplies, office rent, and the necessary

traveling expenses of the members and employees of the committee, personal

services in the field, and in the District of Columbia: Provided, That an annual

report to the Congress shall be submitted through the President, including an

itemized statement of expenditures, $85,000.

The committee, therefore, submits its report, recommendations, and estimates

to your favorable consideration.

Very respectfully,

George P. Scriven,

Brigadier General, Chief Signal Officer of the Army,

Chairman.

Document 2-3(c), George P. Scriven, “Existing Facilities for Aeronautic 

Investigation in Government Departments,” NACA Annual Report for 1915.

For the conduct of the work outlined, limited facilities already exist in different

Government departments about as described in general terms in the following.

These facilities can be augmented by the facilities described as existing the different

technical institutions, etc., previously referred to:

A. The Bureau of Standards is well equipped for carrying on all investigations

involving the determination of the physical factors entering into aeronautic

design, and is prepared to take up such matters as are of sufficient general interest

to warrant same.

B. The Navy Department is equipped with a model basin and wind tunnel at

the Washington Navy Yard, with adequate shop facilities for carrying on the work

in a limited way, and is also constructing at the Washington Navy Yard a plant for

the testing of aeronautic motors and devices involved in their operation, which

will be in commission at an early date. Also, under the Navy Department steady

progress is being made in attacking practical problems involved in the development of the Navy aeronautic service at its station at Pensacola, and theoretical and

practical designs are in hand in the Bureaus of Construction and Repair and

Steam Engineering.

C. The War Department has limited facilities at the flying school at San

Diego, for investigations of interest to that branch of the service, and is able to

carry out in a limited way experiments of interest to the service on full-sized

machines, for which work it has the assistance of technical experts.

D. The Weather Bureau is well equipped for the determination of the problems

of the atmosphere in relation to aeronautics, and Prof. Marvin, a member of the

advisory committee, is the chairman of a subcommittee engaged on this problem.
310 Chapter 2: Building a Research Establishment

The work, however, will necessarily be limited until the necessary funds for more

extensive work become available. There is already available in the records of the

bureau much information of value which requires compilation in a form suited to

aeronautic requirements, and this work is the subject of a preliminary report

included in the annual report of the committee.

E. The Smithsonian Institution has been engaged for a number of years on

the compilation of the bibliography of aeronautics, and is prepared to continue

this work for at least two years more with the funds at its disposal. The institution has

also contributed funds toward the development of the work of the subcommittee

of the Weather Bureau in its investigation of the problem of the atmosphere in

relation to aeronautics.

CONCLUSIONS.

From the above, it will be apparent that utilizing all facilities at present available,

the progress that can be made will be fragmentary and at best lack that coordination

which is necessary to accomplish in a direct, continuous, and efficient manner,

and as rapidly as practicable, the important work now in sight. If the committee

is to be prepared to keep pace with the increasing needs of the very rapid development already under way, stimulated by the unusual conditions existing in

Europe, the facilities and technical assistance recommended are essential. While

the needs at present are principally those which have an important bearing on

military preparedness, the committee is of the opinion that aeronautics has made

such rapid strides that when the war is over there will be found available classes

of aircraft and a trained personnel for their operation, which will rapidly force

aeronautics into commercial fields, involving developments of which today we

barely dream.

Respectfully submitted.

George P. Scriven,

Brigadier General, Chief Signal Officer of the Army,

Chairman.
Document 2-4 311

Document 2-4

Jerome C. Hunsaker, excerpt from “The Wind Tunnel 

of the Massachusetts Institute of Technology,” 

Reports on Wind Tunnel Experiments in Aerodynamics 

(Washington, DC: Smithsonian Institution, 1916).

The Massachusetts Institute of Technology became interested in aeronautical

research and the idea of creating a course of study in aeronautical engineering in

1913—about the same time the navy began to pursue aeronautical research. MIT

President Richard Maclaurin approached the navy about a cooperative effort and

asked that Jerome Hunsaker, who had taken a masters degree at MIT in 1909, be

assigned to the school for three years. The navy agreed, and Hunsaker reported

to the school early in 1914, but only after his return from a previously scheduled

European inspection trip with Albert Zahm. 

While visiting the National Physical Laboratory in England during that trip,

Hunsaker obtained plans for the NPL’s four- by four-foot open tunnel and its latest balance instrument. Using the NPL plans, Hunsaker and MIT erected a duplicate tunnel on campus in 1914 and began experimental work. Two years later, the

Smithsonian Institution published Reports on Wind Tunnel Experiments in

Aerodynamics, written by Hunsaker and five other MIT professors. One of the earliest

comprehensive reports on organized American aeronautical research, it describes

the tunnel and some fundamental research being conducted. More importantly, it

shows a degree of cooperation on the working level between several government

agencies—cooperation that was not readily apparent at the executive level as the

debate over a national aeronautical laboratory peaked.

Document 2-4, Jerome C. Hunsaker, excerpt from 

“The Wind Tunnel of the Massachusetts Institute of Technology,” 1916.

An aeroplane or airship in flight has six degrees of freedom, three of translation and three of rotation, and any study of its behavior must be based on the

determination of three forces—vertical, transverse, and longitudinal—as well as

couples about the three axes in space. Full-scale experiments to investigate the

aerodynamical characteristics of a proposed design naturally become mechanically

difficult to arrange. The experimental work is much simplified if tests be made on

small models as in naval architecture, and a further simplication is made by holding

the model stationary in an artificial current of air instead of towing the model at

high speed through still air to simulate actual flying conditions.
312 Chapter 2: Building a Research Establishment

The use of a wind tunnel depends on the assumption that it is immaterial

whether the model be moved through still air or held stationary in a current of

air of the same velocity. The principle of relative velocity is fundamental, and the

experimental discrepancies between the results of tests conducted by the two

methods may be ascribed on the one hand to the effect of the moving carriage on

the flow of air about the model and to the effect of gusty air, and on the other

hand to unsteadiness of flow in some wind tunnels.

The wind tunnel method requires primarily a current of air which is steady in

velocity both in time and across a section of the tunnel. The production of a

steady flow of air at high velocity is a delicate problem, and can only be obtained by

a long process of experimentation. A study was made of the principal aerodynamical

laboratories of Europe from which these conclusions were reached: (1) That the

wind tunnel method permits a leisurely study of the forces and couples produced

by the wind on a model; (2) that the staff of the National Physical Laboratory,

Teddington, England, have developed a wind tunnel of remarkable steadiness of

flow and an aerodynamical balance well adapted to measure with precision the

forces and couples on a model in any position; and (3) that the results of model

tests made at the above laboratory are applicable to full scale aircraft.

Consequently it was decided to reproduce in Boston the four-foot wind tunnel

of the National Physical Laboratory, together with the aerodynamical balance and

instruments for velocity measurement. Dr. R. T. Glazebrook, F. R. S., director of

the National Physical Laboratory, most generously presented us with detail plans

of the complete installation, including the patterns from which the aerodynamical

balance was made. Due to this encouragement and assistance we have been able

to set up an aerodynamical laboratory with confidence in obtaining a steady flow

of air of known velocity. The time saved us by Dr. Glazebrook, which must have

been spent in original development, is difficult to estimate.

The staff of the National Physical Laboratory have developed several forms

of wind tunnel in the past few years. In 1912–13 Mr. Bairstow and his assistants

conducted an elaborate investigation into the steadiness of wind channels as

affected by the design both of the channel and the building by which it is

enclosed. The conclusions reached may be summarized as follows:

(1) The suction side of a fan is fairly free from turbulence.

(2) A fan made by a low pitch four-bladed propeller gives a steadier flow than

the ordinary propeller fan used in ventilation, and a much steadier flow than fans

of the Sirocco or centrifugal type. 

(3) A wind tunnel should be completely housed to avoid effect of outside wind

gusts.

(4) Air from the propeller should be discharged into a large perforated box or

diffuser to damp out the turbulent wake and return the air at low velocity to the room.
Document 2-4 313

(5) The room through which air is returned from the diffuser to the suction

end of the tunnel should be at least 20 times the sectional area of the tunnel.

(6) The room should be clear of large objects. 

The wind tunnel of the Institute of Technology was built in accordance with

the English plans, with the exception of several changes of an engineering nature

introduced with a view to a more economical use of power and an increase of the

maximum wind speed from 34 to 40 miles per hour. 

Upon completion of the tunnel an investigation of the steadiness of flow and

the precision of measurements was made in which it appeared that the equipment

had lost none of its excellence in reproduction in the United States.

As will be shown below, the current is steady both in time and across a crosssection within about 1 per cent in velocity. Measurements of velocity by means of

the calibrated Pitot tube presented by the National Physical Laboratory are precise

to one-half of 1 per cent. Force and couple measurements on the balance are precise

to one-half of 1 per cent for ordinary magnitudes. Calculated coefficients which

involve several measurements of force, moment, velocity, angle, area, and distance,

as well as one or more assumptions, can be considered as precise to within 2 per cent.

It is believed that it is not practicable to increase the precision of the observations

to such an extent that the possible cumulative error shall be materially less than

the above.

DESCRIPTION OF WIND TUNNEL

A shed 20 by 25 by 66 feet houses the wind tunnel proper, 16 square feet in

section, and some 53 feet in length (pl. 1). Air is drawn through an entrance nozzle

and through the square tunnel by a four-bladed propeller, driven by a 10 H. P.

motor. Models under test are mounted in the center of the square trunk on the

vertical arm of the balance to be described later.

The air entering the mouth passes through a honeycomb made up of a nest

of 3-inch metal conduit pipes 2 feet 6 inches in length. This honeycomb has an

important effect in straightening the flow and preventing swirl.

Passing through the square trunk and past the model, the air is drawn past a

star-shaped longitudinal baffle into an expanding cone. In this the plans of the

National Physical Laboratory were departed from by expanding in a length of 11

feet to a cylinder of 7 feet diameter. This cone expands to 6 feet in the English

tunnel. M. Eiffel affirms that the working of a fan is much improved by expanding the suction pipe in such a manner as to reduce the velocity and so raise the

static pressure of the air. Since the fan must discharge into the room, the pressure

difference that the fan must maintain is thus reduced. Also with a larger fan the

velocity of discharge is reduced, and the turbulence of the wake kept down.

The propeller works in a sheet metal cylinder 7 feet in diameter, and discharges into the large perforated diffuser. The panels of the latter are gratings
314 Chapter 2: Building a Research Establishment

and may be interchanged fore and aft. The gratings are made of 1 1⁄2-inch stock

with holes 1 1

⁄2 by 1 1⁄2 inches. Each hole is then a square nozzle one diameter

long. The end of the diffuser is formed by a blank wall. The race from the propeller is stopped by this wall and the air forced out through the holes of the diffuser. Its velocity is then turned through 90 degrees. The area of the diffuser

holes is several times the sectional area of the tunnel, and the holes are so distributed that the outflow of air is fairly uniform and of low velocity (pl. 2, fig. 1).

A four-bladed black walnut propeller (pl. 2, fig. 2) was designed on the

Drzwiecki system and has proved very satisfactory. In order to keep down turbulence a very low pitch with broad blades had to be used. To gain efficiency such

blades must be made thin. It then became of considerable difficulty to insure

proper strength for 900 R. P. M. as well as freedom from oscillation.

The blade sections were considered as model aeroplane wings and their

effect integrated graphically over the blade. The blade was given an angle of

incidence of 3 degrees to the relative wind at every point for 600 R. P. M. and 25

miles per hour. The pitch is thus variable radially. 

To prevent torsional oscillations, the blade sections were arranged so that the

centers of pressure all lie on a straight line, drawn radially on the face of the blade.
Document 2-4 315

This artifice seems to have prevented the howling at high speeds commonly found

with thin blades. The propeller has a clearance of 1⁄2 inch in the metal cylinder.

The propeller is driven by a “silent” chain from a 10 H. P. interpole motor

beneath it. The propeller and motor are mounted on a bracket fixed to a concrete

block and are independent of the alignment of the tunnel. Vibration of the motor

and propeller can not be transmitted to the tunnel as there is no connection.

The English plans for power contemplate a steady, direct current voltage. Such

is not available here. A 15 H. P. induction motor is connected to the mains of the

Cambridge Electric Light Company. This motor then turns at a speed proportional

to the frequency of the supply current for a given load. Fluctuations of voltage are

without sensible effect, and the frequency may be taken as practically constant.

The induction motor is directly connected to a 12 H. P. direct current generator, which is turned at constant speed and which generates, therefore, a constant

direct current voltage for given load.

By change of the generator field rheostat and motor field rheostat the propeller speed can be regulated to hold any wind velocity from 4 to 40 miles per
316 Chapter 2: Building a Research Establishment

hour. The control is very sensitive. Left to itself, the speed of the wind in the tunnel

will vary by 2 per cent in 2 or 3 minutes. This variation is so slow that by manipulation of the rheostats the flow can be kept constant within 1

⁄2 per cent. The cause

of the surging of the air is not understood, but is probably due to hunting of the

governor of the prime mover in the Cambridge power house causing changes in

frequency too small to be apparent. The gustiness of outdoor winds seems to have

no effect, although the building is not airtight.

AERODYNAMICAL BALANCE

The aerodynamical balance (pl. 3) was constructed by the Cambridge

Scientific Instrument Company, England, to the plans and patterns of the

National Physical Laboratory. The balance is described in detail by Mr. L. Bairstow

in the Technical Report of the Advisory Committee for Aeronautics, London,

1912–13. For details of operation and the precision of measurements reference

may be made to the original article.

In general, the balance consists of three arms mutually at right angles representing the axes of coordinates in space about and along which couples and forces

are to be measured. The model is mounted on the upper end of the vertical arm

which projects through an oil seal in the bottom of the tunnel.

The entire balance rests on a steel point, bearing in a steel cone. The point is

supported on a cast-iron standard secured to a concrete pillar, which in turn rests

on a large concrete slab. The balance is then quite free from vibration of the floor,

building, or tunnel.

The balance is normally free to rock about its pivot in any direction. When

wind blows against the model, the components of the force exerted are measured

by determining what weights must be hung on the two horizontal arms to hold

the model in position. Likewise the balance is free to rotate about a vertical axis

through the pivot. The moment producing this rotation is balanced by a calibrated

wire with graduated torsion head.

Force in the vertical axis is measured by means of a fourth arm. The model

for this measurement is mounted on a vertical rod which slides freely on rollers

inside the main vertical arm of the balance. The lower end of this rod rests on one

end of a horizontal arm having a knife edge and sliding weight.

For special work on moments, the interior vertical rod is replaced by another

having a small bell crank device on its head which converts a moment about the

center of the model into a vertical force to be measured as above (pl. 4).

In this way provision is made for the precise measurement of the three forces

and the three couples which the wind may impress on any model held in any

unsymmetrical position to the wind.

The balance is fitted with suitable oil dash pots to damp oscillations, and

devices for limiting the degrees of freedom to simplify tests in which only one or
Document 2-4 317

two quantities are to be measured. The balance can be adjusted to tilt for 1/10,000

pound force on the model. In general, the precision of measurements is not so

good as the sensitivity, and in the end is limited by the steadiness of the wind and

the skill of the observer.

The weights and dimensions of the balance were verified by the National

Physical Laboratory, where also the torsion wires were calibrated.

For ordinary forces, weighings may be considered correct to 0.5 per cent.

Naturally for very small forces, such as the rolling moment caused by a small

angle of yaw, the measurements can not be so precise.

[Not included here are the final sections of Hunsaker’s report, concerning the alignment

of the wind tunnel and the means by which tunnel instrumentation measured air velocity.]
318 Chapter 2: Building a Research Establishment

Document 2-5

G. I. Taylor, “Pressure Distribution Over the Wing of 

an Aeroplane in Flight,” British Advisory Committee 

for Aeronautics, Reports and Memoranda, 

No. 287 (London, 1916).

Early airplane designers found themselves confronting a paradox. They

could obtain repeatable data on new designs using models in wind tunnels—

something almost impossible to achieve in flight—but the forces and moments

measured on wind tunnel models did not agree with what an actual airplane experienced in flight. While many recognized the paradox, only a few researchers even

approached a possible solution to it prior to the introduction of dynamical similarity concepts in the 1920s. Gustav Eiffel grappled with this problem around

1910, using what he called “augments,” developed from his experiments, to adjust

model data and predict full-size performance. Although Eiffel concluded that

“the calculations are in each case in complete accord with the actual conditions

observed in flight,” his augments were not sufficiently accurate to be universally

applicable. With other wind tunnel work, however, Eiffel showed how measurements

of the air pressure distribution across the surface of a wing could be correlated to

the lift and drag generated by the wing. This work pointed the way toward a useful

design technique, but much more work was needed to correlate performance data

of models and full-size airplanes before the technique could be fully exploited.

A major problem in determining this correlation was obtaining useful data

from airplanes in flight. No one knew how to measure propeller performance and

efficiency accurately, so drag could not be directly determined from engine performance. G. I. Taylor reasoned that Eiffel’s pressure-distribution techniques

would work on an airplane in flight. He devised a rib with pressure taps that could

be mounted in a wing along with a clever means to measure and record pressuredistribution data in flight. Taylor still found that a correction, which he believed

was due to skin friction, was necessary, but his device worked, and it produced lift

and drag coefficient curves of a similar shape to those obtained from wind tunnel

models at all but the lowest lift coefficients. 

Document 2-5, G. I. Taylor, “Pressure Distribution Over the Wing of an Aeroplane

in Flight,” 1916.

SUMMARY.—The comparison of the results of experiments performed with

model aerofoils in wind channels with the actual performance of an aeroplane in
Document 2-5 319

flight has proved extremely difficult. It has been possible to find the relationship

between angle of incidence and lift coefficient for a full-scale machine, but when

attempts are made to find the resistance of the wing of an aeroplane in flight, various

causes combine to diminish the accuracy of the result. In the first place the thrust

of the airscrew is the subject of considerable uncertainty, for it depends on the

power of the engine and on the efficiency of the airscrew, neither of which are

known accurately. If the thrust of the airscrew were known, the total resistance of

the aeroplane would be known, but considerable uncertainty would still exist as to

what proportion of the total resistance is due to the wings.

In spite of these various sources of error, there is strong evidence to show that

the resistance of a full-scale aeroplane differs from the predictions made as a

result of model experiments.

The measurements here described were undertaken with a view to getting further

and more direct information as to the relationship between model and full-scale

aerofoils. Simultaneous measurements of the pressures at various points round a

certain section of the lower wing of a B.E.2C aeroplane were made by means of

an apparatus which registered photographically the heights of the liquid in a

number of manometer tubes. Observations were taken at various speeds ranging

from 50 to 95 miles per hour.

The pressures were integrated, and the normal and longitudinal forces and

moments, which act on the wing in the experimental section, were found.

The inclinometer measurements of the angle of incidence corresponding with

various lift coefficients were then used to find the drag coefficient of the section.

The results are shown in Fig. 12. For the purpose of comparison the drag

curves obtained from model experiments and also from the performance tests of

full-scale aeroplanes, are shown in the same figure. It will be seen that the present

measurements agree with the performance tests over the greater part of the

curves, but that for small lift coefficients the pressure-integration curve indicates

a higher drag than the performance tests. The drag curve for the model lies

below the pressure-integration curve over its whole range, but on the other hand,

the general shapes of the two curves are very similar.

It will be possible to say more about the relationship between the present

measurements and the model results when the pressure distribution around a

similar section of a model has been measured. This work is now being carried out

at the National Physical Laboratory.

The pressure distribution has also been used to obtain the moment coefficient.

A curve showing the moment coefficients for various lift coefficients is given. (Fig. 11)

1. The section chosen for these experiments was the old B.E.2C section with

a hollow undersurface. A brass rib was made to drawing, and eighteen small copper tubes were fixed to it in the positions shown in Fig. 1. These were filled at the
320 Chapter 2: Building a Research Establishment

ends with brass plugs, through which holes 1/32nd inch diameter were drilled.

These holes were flush with the surface of the wing.

2. The holes were numbered α, β, 1a, 2, 3, 4, 5, 6, 7, 8 on the upper surface,

and 9, 10, 11, 12, 13, 14, 15 and 1b on the lower surface. There was also a hole

numbered (1) in the leading edge of the wing. The positions of the holes are

given in terms of co-ordinates in Table (1), the axis of x being along the chord and

the axis of y the perpendicular through the leading edge. x and y are expressed

as fractions of the chord, so that x varies from 0 to 1.

3. The pressures at the holes were measured simultaneously by means of an

apparatus shown in Fig. 2, which consisted of twenty glass manometer tubes, connected at their lower ends to a reservoir which was full of alcohol. Their upper

ends were connected by means of rubber tubes with the pipes which led through

the interior of the wing to the pressure holes. When the aeroplane was at rest the

alcohol stood about half-way up the tubes.

4. When the aeroplane was in flight the height of the liquid in the tubes connected with the various holes registered the pressure at the holes. These heights

were recorded photographically. A small electric light, some ten inches from the

tubes, was used to cast shadows of the columns of liquid on to some bromide

paper, which could be wound between two light-tight boxes past the tubes. The

bromide paper was pressed up against the tubes by means of a back (shown leaning

up against the apparatus in Fig. 2), and the whole apparatus was shut in by a

hinged light-tight door (shown open in Fig. 2). To make an exposure, the small

electric light was switched on for half a second.

5. The shadow of the meniscus at the top of the alcohol was very sharp, and

it was possible to read the height of the liquid in the tube to 1

⁄10th of a mil1imetre. A

specimen of the records obtained is shown in Fig. 3.

6. On testing the apparatus, it was found that the maximum error in measuring

pressure by means of the photographic records was 0.4 mm. of alcohol, and the

probable error was a little more than 0.1 mm. It was found, however, that the

error for a given position of the liquid in a tube was always the same. A table of

errors was therefore constructed, and by using this table the pressures could be

obtained correct to 0.1 mm. of alcohol.

7. The whole apparatus was hung in the aeroplane by rubber suspensions, so

that it might not be affected by the vibration of the aeroplane.

8. As a further preventive to possible rapid movements of the alcohol in the

tubes the rubber pipes, which served to connect them with the alcohol reservoir,

were constricted by passing them through a series of holes in a brass rod. The

sizes of these holes were adjusted by means of screws, so that the time taken by

the alcohol to come to rest after a sudden change in speed of the aeroplane was

about fifteen seconds.
Document 2-5 321

9. In order to measure the height of the meniscus at the top of the fluid in

each tube, it was necessary to know what direction in the plane of the photograph

was horizontal. For this purpose the two outside tubes in the apparatus were both

connected with the static pressure side of the pitot tube. A straight line was drawn

on each photograph touching the two outside meniscuses, and this was used as a

base line from which the pressures in the other tubes were measured. This line is

shown in Fig. 3.

10. The aeroplane had a constant weight of 2,020 lbs. during the experiments; the lift coefficient and angle of incidence should therefore depend only on

the reading of the pitot tube. For a given angle of incidence the pressure at each

of the holes should be a given fraction of ρV2

, r being the density of the air and V

the velocity of the aeroplane.

11. Hence, to each reading of the pitot tube there should correspond a definite pressure at each hole, whatever the density of the air might be. This was specially convenient because observations could be taken at whatever height the air

happened to be calmest, without the necessity of considering its density.

12. One of the central tubes was connected with the high pressure side of the

pitot tube, and the reading of the liquid in this was used instead of an air speed

indicator to obtain an accurate measure of the airspeed of the machine.

13. In order to find what value of ρV2 corresponded with a given pitot reading, it was necessary to fly the machine at known speeds through air of known

density, and to take the corresponding readings of the liquid in the pitot tube.

This was done on a speed course of known length, and it was found that at 60 and

at 80 miles per hour the pressure difference between the static pressure tube and

the pitot tube was 0.475ρV2. When a pressure head is placed facing the wind in a

wind channel, this pressure difference is 1⁄2 ρV2 . The discrepancy between the two

seems to be due to the disturbing effect of the wings of the machine, which probably increases the pressure in the static pressure tube without affecting the pressure in the pitot head.

14. The pressure at each hole is expressed in all cases as a fraction of ρV2. This

fraction is found by multiplying the ratio of the head of liquid in the tube connected with the hole to the head in the tube connected with the pitot tube by

0.475. The readings for different air speeds of the aeroplane are shown graphically in Figs. 4, 5, and 6. In these diagrams each hole, as numbered on the righthand side of each curve, is represented by a special mark, and smooth curves have

been drawn through the points in order to eliminate accidental errors as far as

possible. The magnitude of the accidental errors can be estimated by noticing the

distances of the observed points from the smooth curves. In the case of hole 2, for

instance, the accidental error which may be expected is about 0.003ρV2

, while in

the case of holes 10, 1b, and 15 it is much greater, being about 0.01ρV2.
322 Chapter 2: Building a Research Establishment

15. In the case of hole 10 the source of error was detected. It was found that

the fabric was inclined to come away from the rib in the immediate neighbourhood

of this hole, so that the pressure recorded was probably intermediate between the

pressure outside and the pressure inside the wing. In the cases of holes lb and 15

it seems probable that the errors are due to the peculiar conditions of air flow,

which seem to exist immediately underneath a turned-down leading edge.

16. Pressure integration.—Having determined the pressure at each hole as

accurately as seems possible from present observations, it remains to estimate by

integration the forces which act on the aerofoil in the neighbourhood of the section chosen for the pressure distribution experiments.

17. The integrations were effected graphically by the method used by Jones

and Patterson in the case of a model aerofoil. Curves were plotted for various

speeds of the aeroplane, ranging from 50 to 95 miles per hour by intervals of 5

miles per hour, showing the pressure round the aerofoil as a function of x and as

a function of y. These curves, when integrated by means of a plantimeter give the

normal and longitudinal force coefficients.

18. Curves were also plotted showing the relationship between (pressure multiplied by x) and x. These curves give the part of the moment coefficient due to the

component of pressure perpendicular to the chord. The part of the moment coefficient due to the component parallel to the chord is so small as to be negligible.

19. The points on the pressure curves corresponding to the various holes are

taken from the curves of Figs. 4, 5, and 6. In drawing the pressure curves shown

in Figs. 7, 8, and 9, it will be seen that it is possible to vary their forms to a certain extent, while at the same time keeping them to the determined points. When

the first set of experiments was made there were no pressure holes between 1 and

1a. Under these circumstances it was found that very considerable variations in

the areas of the curves in Fig. 8 were possible; accordingly the holes a and b were

constructed. By making the curves pass through the points corresponding with

these two new holes, and bearing in mind certain geometrical limitations, which

the curves must comply with, it was found that the differences in their area, due to

various possible ways of drawing the curves were not large enough to affect the results.

20. The geometrical limitations alluded to above are obvious. In the case of

the normal force and moment curves of Figs. 7 and 9, the curves must lie between

x = 0 and x = 1, and the values of x must increase steadily in going along the

curve from the point corresponding with the nose to the point corresponding

with the trailing edge. In the case of the longitudinal force curves of Fig. 8, the

values of y must increase steadily along the curves from y = 0 to y = 0.0793.

21. Besides these geometrical limitations there is a hydro-dynamical one. The

pressure can not be greater, at any point on the wing, than 1

⁄2 ρV2 above the pressure

in the surrounding undisturbed air; and, moreover, it appears certain that, at
Document 2-5 323

some point near the nose of the wing, the pressure will attain this value. It seems

probable that the pressure in the pitot tube is 1⁄2 ρV2. In this case the pressure in

the static pressure tube would be 1⁄2 ρV2 – 0.475ρV2, or 0.025ρV2, above the pressure

in the surrounding air; and since the pressures measured by the instrument are

the differences between the pressures in the holes and the pressure in the static

pressure tube, the maximum possible pressure on the diagrams should be 0.475ρV2.

On looking at Figs. 4 and 6 it will be seen that the point of maximum pressure,

which presumably corresponds with the point where the air divides to pass over

and under the wing, crosses hole 1, in the nose, when the aeroplane is flying at

53 miles per hour, while at about 80 miles an hour it crosses hole a. At the highest

speed attained—95 miles per hour—it had not crossed the next hole, β.

22. The normal force, longitudinal force, and moment coefficients derived by

integrating the curves are given in the 6th, 7th and 8th columns of Table (2). They

are denoted by the, symbols [kz]s, [kx]s, and [km]s, the “s” being used to show that the

coefficients apply to the experimental section only. In order to get the lift and

drag coefficients of the section explored, it is necessary to find the angle of incidence of the section. The aeroplane was measured and it was found that the angle

of incidence of the wing in the neighbourhood of the experimental rib was 18 ́,

or 0.3° less than the mean angle of incidence. The mean angle of incidence has

been measured for different mean lift coefficients by means of an inclinometer,

and the relationship between them is shown graphically in Fig. 10.

23. The mean lift coefficients for various speeds were obtained by dividing

the weight of the aeroplane by ρV2 and by the area of the wings. The weight of the

aeroplane was 2,020 lbs. The area of its wings was 384 square feet. Hence if V be

expressed in miles per hour, the mean lift coefficient

The mean angle of incidence, θ, was found from the curve in Fig. 10. The angle

of incidence of the experimental rib was 0.3° less than this. These angles are tabulated for various speeds in column 5, Table (2).

24. The lift and drag coefficients of the section, [kl]s and [kd]s, are related to

[kz]s, and [kx]s by the relations

[kl]s = [kz]s cos (θ - 0.3°) - [kx]s sin (θ - 0.3°),

[kd]s = [kx]s cos (θ - 0.3°) - [kz]s sin (θ - 0.3°),

They are tabulated in columns 9 and 10 of Table (2).

25. In order to find the “scale effect” between the forces on the experimental section and those on the same section of a model, curves of the lift and drag coefficients

of the section should be drawn for various angles of incidence. On the other

hand, in order to compare the drag of the section with the drag of the whole wing,
324 Chapter 2: Building a Research Establishment

as calculated from the performance of an aeroplane, it is in some ways more convenient to draw curves representing the drag of the section for different values of

the lift coefficient of the whole machine. For this purpose it is necessary to correct

the lift coefficient of the whole machine to what it would be if the mean angle of

incidence were the same as that of the experimental section. This is done by taking

the lift coefficient corresponding with the angle of incidence of the experimental

section from the curve in Fig. 10 instead of the actual mean lift coefficient given

in column 2 of Table (2). These corrected lift coefficients are given in column 4.

26. Results.—The results have been plotted in the form of curves representing

the lift, drag, and moment coefficients of the experimental section for various values

of the lift coefficient of the whole aeroplane. These curves are shown in Figs. 11

and 12. In the case of the drag curve it must be remembered that the drag

obtained from pressure integration, shown as the full curve in Fig. 12, is less than

the actual drag because no account is of tangential forces (i.e., skin friction) in

pressure integration. The effect of skin friction may be allowed for roughly by

adding 0.0035 to the drag coefficient. After making this allowance the final drag

curve resulting from these experiments is shown as curve B, Mg. 12.

27. For the purpose of comparison the drag curves obtained from model

experiments (curve D) and also from the performance tests of full-scale aeroplanes

(curve C) are shown in the same figure. It will be seen that pressure distribution

experiments indicate a higher drag than that obtained by either of the other

methods, but it must be remembered that curve B represents the drag on a certain

section of the lower plane of a biplane, while curves C and D apply to the mean

drag of both wings. It is quite possible also that the drag at the ribs is greater than

the drag at the intermediate points of the wing where the fabric sags below the

true wing section; this is not probable, however, in view of the fact that model tests

show that the drag of a scalloped wing is the same as that of a smooth wing.

28. It is not possible to compare the moment coefficient of a model with [km]s

because no measurements of the forces acting on a biplane fitted with B.E.2C section

have been made. On the other hand it has been found that the moment curve for

a single B.E.2C section wing is practically identical with the moment curve for

R.A.F. 6. The moment coefficients of the lower wing of a biplane of R.A.F. 6 section

have been measured, and it seems probable that they will be nearly the same as

the moment coefficients we require.

29. The moment curve for the lower wing of a biplane of R.A.F. 6 section is

shown as a dotted curve in Fig. 11. It will be seen that it lies very near the moment

curve for the experimental section.
Document 2-5 325
326 Chapter 2: Building a Research Establishment
Document 2-5 327
328 Chapter 2: Building a Research Establishment
Document 2-5 329
330 Chapter 2: Building a Research Establishment
Document 2-5 331
332 Chapter 2: Building a Research Establishment
Document 2-5 333
334 Chapter 2: Building a Research Establishment
Document 2-5 335
336 Chapter 2: Building a Research Establishment
Document 2-5 337
338 Chapter 2: Building a Research Establishment
Document 2-6 339

Document 2-6

Henry T. Tizard, “Methods of Measuring Aircraft

Performances,” Aeronautical Society of Great Britain,

Aeronautical Journal, No. 82 (April–June 1917).

To be useful, aircraft flight testing demands accuracy, repeatability, and continuity

in two crucial areas: flight instruments and test flight methods. As World War I

progressed in Europe, the fledgling air forces and airplane manufacturers increasingly realized that no standards or consistency existed for such basic performance

parameters as rate of climb and altitude. Even the idea of “level flight” was an

uncertain concept due to the variations experienced with aneroid altimeters. If,

however, airplanes were to be thoroughly evaluated and their performance envelopes

determined for the pilots who would fly them, some standards were essential.

England’s Royal Aircraft Factory led the effort in establishing what H. T. Tizard

called “the general principles of . . . scientific testing of airplanes,” principles

quickly adopted by the Royal Flying Corps, in which Tizard served as a pilot with

the rank of captain.

Tizard’s “Methods of Measuring Aircraft Performances” was notable in two areas.

First, he explained the effects that normal variations in air temperature, pressure,

and density had on the accuracy of contemporary aircraft instruments, particularly

altimeters and airspeed indicators, and he discussed methods to recognize and

minimize errors. Perhaps of greater interest are his comments regarding the flyers—

those now known as test pilots. Here we see possibly the earliest published recognition

that test pilots play a unique role in aircraft development that requires special

training. Tizard mentioned this repeatedly in his paper, noting that, “it is . . . the

flyer on whom the accuracy of the tests depends. I feel that too great stress can

not be laid on this; he is the man who does most of the experiments, and . . . he

requires training and a great deal of practice.”

Tizard himself went on to a distinguished career in aeronautical research.

Knighted for his contributions, in 1935 Sir Henry Tizard was appointed the chair

of the RAF’s newly established Committee for the Scientific Survey of Air Defense.

In that role he sponsored R. A. Watson-Watt’s development of Radio Direction

Finding, or “radar,” and helped to develop the vital air defense system that

defeated the World War II German aerial assault in the strategically crucial 1940

Battle of Britain.
340 Chapter 2: Building a Research Establishment

Document 2-6, Henry T. Tizard, 

“Methods of Measuring Aircraft Performances,” 1916.

AEROPLANE TESTING.

The accurate testing of aeroplanes is one of the many branches of aeronautics

which have been greatly developed during the war, and especially during the last

year. For some months after the war began a climb to 3,000 to 5,000 feet by

aneroid and a run over a speed course was considered quite a sufficient test of a

new aeroplane; now we all realise that for military reasons certainly, and probably

for commercial reasons in the future, it is the performance of a machine at far

greater heights with which we are mainly concerned. In this paper I propose to

give a short general account of some of the methods of testing now in use at the

Testing Squadron of the Royal Flying Corps, and to indicate the way in which

results of actual tests may be reduced, so as to represent as accurately as possible

the performance of a machine independently of abnormal weather conditions,

and of the time of the year. For obvious reasons full details of the tests and methods

employed can not yet be given. So far as England is concerned, I believe that the

general principles of what may be called the scientific testing of aeroplanes were first

laid down at the Royal Aircraft Factory. Our methods of reduction were based on

theirs to a considerable extent, with modifications that were agreed upon between

us; they have been still further modified since, and recently a joint discussion of the

points at issue has led to the naval and military tests being coordinated, so that

all official tests are now reduced to the same standard. It should be emphasised

that once the methods are thought out scientific testing does not really demand

any high degree of scientific knowledge; in the end the accuracy of the results

really depends upon the flyer, who must be prepared to exercise a care and

patience unnecessary in ordinary flying. Get careful flyers whose judgment and

reliability you can trust and your task is comparatively easy; get careless flyers and

it is impossible.

At the outset it may be useful to point out by an example the nature of the

problems that arise in aeroplane testing. Suppose that it is desired to find out

which of two wing sections is most suitable for a given aeroplane. The aeroplane

is tested with one set of wings, which are then replaced by the other set, and the

tests repeated some days later. The results might be expressed thus:—

A Wings. B Wings.

Speed at 10,000 ft. 90 m.p.h. 93 m.p.h.

Rate of climb at 10,000 ft. 25ft. a minute. 300ft. a minute.
Document 2-6 341

Now the intelligent designer knows, or soon will know, that firstly an aneroid

may indicate extremely misleading “heights,” and secondly, that even if the actual

height above the ground is the same in the two tests the actual conditions of

atmospheric pressure and temperature may have been very different on the two

days. He will therefore say, what does that 10,000 mean? Do you mean that your

aneroid read 10,000 feet, or do you mean 10,000 feet above the spot you started

from, or 10,000 feet above sea level? If he proceeds to think a trifle further he will

say—what was the density of the atmosphere at your 10,000 feet; was it the same

in the two tests? If not, the results do not convey much. There he will touch the

keynote of the whole problem, for it is on the density of the atmosphere that the

whole performance of an aeroplane depends; the power of the engine and the

efficiency of the machine depend essentially on the density, the resistance to the

motion of the machine through the air is proportional to the density, and so finally

is the lift on the wings. None of these properties are proportional solely to the

pressure of the atmosphere, but to the density, that is the weight of air actually

present in unit volume. It follows that it is essential when comparing the performances of machines to compare them as far as possible under the same conditions

of atmospheric density, not as is loosely done at the same height above the earth,

since the density of the atmosphere at the same height above the earth may vary

considerably on different days, and on the same day at different places.

At the same time, in expressing the final results, this principle may be carried

too far. Thus, if the speed of a machine were expressed as 40 metres a second at

a density of 0.8 kilogrammes per cubic metre, the statement, though it may be strictly

and scientifically accurate, will convey nothing to 99 per cent of those directly

concerned with the results of the test. The result is rendered intelligible and

indeed useful by the form “90 m.p.h. at 10,000 feet,” or whatever it is. With this

form of statement, in order that all the statements of results may be consistent and

comparative, we must be careful to mean by “10,000 feet” a certain definite density,

in fact the average density of the atmosphere at a height of 10,000 feet above mean

sea level. This is what the problem of “reduction” of tests boils down to; what is

the relation between atmospheric density and height above sea level? This knowledge is obtained from meteorological observations. We have collected all the

available data—mostly unpublished—with results shown in the following table:—

Table I.

MEAN ATMOSPHERIC PRESSURE, TEMPERATURE AND DENSITY AT

VARIOUS HEIGHTS ABOVE SEA LEVEL.

Height Height in Mean pressure Mean temp. in Mean density

inkilometers equivalent feet. in millibars. absolute degrees in kgm. 

centigrades. per cubic meter.

0 0 1,014 282 1.253
342 Chapter 2: Building a Research Establishment

1 3,280 900 278 1.128

2 6,560 795 273 1.014

3 9,840 699 268 0.909

4 13,120 615 262 0.818

5 16,400 568 255 0.735

6 19,680 469 248 0.658

7 22,960 407 241 0.589

These are the mean results of a long series of actual observations made by Mr.

W.H. Dines, F.R.S. It is convenient to choose some density as standard, call it

unity, and refer all other densities as fractions or per centages of this “standard

density.” We have taken, in conformity with the R.A.F., the density of dry air at

76m.m. pressure and 16 degrees centigrade as our standard density; it is 1.221

kgm. per cubic metre. The reason this standard has been taken is that the air

speed indicators in use are so constructed as to read correctly at this density,

assuring the law: 

p=1⁄2ρV2

where V is the air speed, p the pressure obtained, ρ the standard density.

In some ways it would doubtless be more convenient to take the average density at sea level as the standard density, but it does not really matter what you take

so long as you make your units quite clear. Translated into feet, and fraction of

standard density, the above table becomes:—

Table II.

Height in feet. Per centage of standard density.

0 102.6

1,000 99.4

2,000 96.3

3,000 93.2

4,000 90.3

5,000 87.4

6,000 84.6

*6,500 83.3

7,000 81.9

8,000 79.2

9,000 76.5

*10,000 74.0

11,000 71.7

12,000 69.5

*13,000 67.3
Document 2-6 343

14,000 65.2

15,000 63.0

16,000 61.1

*16,500 60.1

17,000 59.1

18,000 57.1

19,000 55.2

20,000 53.3

*6,500 feet is introduced as corresponding roughly to the French test height of 2,000 metres. 10,000

feet similarly corresponds roughly to comparing aeroplane test performances to the French standard

of 3,000 metres, and similarly for 13,000 and 16,500 feet.

Let us briefly consider what these figures mean. For example, we say that the density at 10, 000 feet is 74 per cent of our standard density, but it is not meant that at

10, 000 feet above mean sea level the atmospheric density will always be 74 per cent

of the standard density. Unfortunately for aeroplane tests this is far from true. The

atmospheric density at any particular height may vary considerably from season to

season, from day to day, and even from hour to hour; what we do mean is that if the

density at 10,000 feet could be measured every day, then the average of the results

would be, as closely as we can tell at present, 74 per cent of the standard density.

The above table may therefore be taken to represent the conditions prevailing

in a “normal” or “standard” atmosphere, and we endeavour, in order to obtain a

strict basis of comparison, to reduce all observed aeroplane performances to this

standard atmosphere, i.e., to express the final results as the performance which

may be expected of the aeroplane on a day on which the atmospheric density at every

point is equal to the average density at the point. Some days the aeroplane may

put up a better performance, some days a worse, but on the average, if the engine

power and other characteristics of the aeroplane remain the same, its performance

will be that given.

It must be remembered that a standard atmosphere is a very abnormal occurrence; besides changes in density there may occur up and down air currents which

exaggerate or diminish the performance of an aeroplane, and which must be taken

carefully into account. They show themselves in an otherwise unaccountable increase

or decrease in rate of climb or in full speed flying level at a particular height.

We now pass to the actual tests, beginning with a description of the observations

which have to be made and thereafter to the instruments necessary. The tests

resolve themselves mainly into

(a) A climbing test at the maximum rate of climb for the machine.

(b) Speed tests at various heights from the “ground” or some other agreed low

level upwards.
344 Chapter 2: Building a Research Establishment

Experience agrees with theory in showing that the best climb is obtained by

keeping that which is frequently called the air speed of an aeroplane, namely, the

indications of the ordinary air speed indicator, nearly constant whatever the

height. [In other words ρV2 is kept constant.] We can look at this in this way. There

is a limiting height for every aeroplane above which it can not climb; at this limiting height, called the ceiling of the machine, there is only one speed at which

the aeroplane will fly level, at any other air speed higher or lower it will descend.

Suppose this speed is 55 m.p.h. on the air speed indicator. Then the best rate of

climb from the ground is obtained by keeping the speed of the machine to a

steady indicated 55 m.p.h. Fortunately a variation in the speed does not make

very much difference to the rate of climb; for instance, a B.E.2C with a maximum

rate of climb at 53 m.p.h. climbs just as fast up, say, to 5,000 feet at about 58 m.p.h.

This is fortunate as it requires considerable concentration to keep climbing at a

steady air speed, especially with a light scout machine; if the air is at all “bumpy”

it is impossible. At great heights the air is usually very steady, and it is much easier

to keep to one air speed. It is often difficult to judge the best climbing speed of a new

machine; flyers differ very much on this point, as on most. The Testing Squadron,

therefore, introduced some time ago a rate of climb indicator intended to show

the pilot when he is climbing at the maximum rate. It consists of a thermos flask,

communicating with the outer air through a thermometer tube leak. A liquid

pressure gauge of small bore indicates the difference of pressure between the

inside and outside of the vessel. Now, when climbing, the atmospheric pressure is

diminishing steadily; the pressure inside the thermos flask tends therefore to

become greater than the outside atmospheric pressure. It goes on increasing until

air is being forced out through the thermometer tubing at such a rate that the rate

of change of pressure inside the flask is equal to the rate of change of atmospheric

pressure due to climbing. When climbing at a maximum rate, therefore, the pressure

inside the thermos flask is a maximum. The pilot therefore varies his air speed

until the liquid in the gauge is as high as possible, and this is the best climbing

speed for the machine.

What observations during the test are necessary in order that the results may

be reduced to the standard atmosphere? Firstly, we want the time from the start

read at intervals, and the height reached noted at the same time. Here we

encounter a difficulty at once, for there is no instrument which records height

with accuracy. The aneroid is an old friend now of aeronauts as well as of mountaineers, but although it has often been tentatively exposed, it is doubtful whether

1 per cent of those who use it daily realise how extraordinarily rare it is that it ever

does what it is supposed to do, that is, indicate the correct height above the

ground, or starting place. The faults of the aeroplane aneroid are partly unavoidable

and partly due to those who first laid down the conditions of its manufacture. An
Document 2-6 345

aneroid is an instrument which in the first place measures only the pressure of the

surrounding air. Now if p1 and p2 are the pressures at two points in the atmosphere,

the difference of height between these points is given very closely by the relation, 

where θ is the average temperature, expressed in “absolute” degrees, of the air

between the two points and k is a constant. It is obvious that if we wish to graduate an aneroid in feet we must choose arbitrarily some value for θ. The temperature that was originally chosen for aeroplane aneroids was 50 degrees Fahrenheit,

or 10 degrees centigrade. An aneroid, as now graduated, will therefore only read

the correct height in feet if the atmosphere has a uniform temperature of 50

degrees Fahrenheit from the ground upwards, and it will be the more inaccurate

the greater the average temperature between the ground and the height reached

differs from 50 degrees Fahr. Unfortunately 50 degrees F. is much too high an

average temperature; to take an extreme example it is only on the hottest days in

summer, and even then very rarely, that the average temperature between the

ground and 20, 000 feet will be as high as 50 degrees F. On these very rare occasions an aneroid will read approximately correctly at high altitudes; otherwise it

will always read too high. In winter it may read on cold days 2,000 feet too high

at 16,000 feet, i.e., it will indicate a height of 18,000 feet when the real height is

only 16,000. It is always necessary therefore to “correct” the aneroid readings for

temperature. The equation

gives us the necessary correction. Here H is the true difference in height between

any two points, t the average temperature in degrees centigrade between the

points, and h the difference in height indicated by aneroid. It is convenient to

draw a curve showing the necessary factors at different temperatures, some of

which are given in the following table:—

Table III.

Aneroid Correction Factors

Temperature. Correction factor.

70° Fahr. 1.040

50° 1.000

30° 0.961

10° 0.922

-10° 0.883
346 Chapter 2: Building a Research Establishment

For example, if a climb is made through 1,000 feet by aneroid and the average

temperature is 10 degrees Fahr., the actual distance in feet is only 1,000 x 0.922 =

922 feet. The above equation is probably quite accurate enough for small differences

of height—up to 1,000 feet say—and approximately so for bigger differences.

The magnitude of the correction which may be necessary shows how important

it is that observations of temperature should be made during every test. For this

purpose a special thermometer is attached to a strut of the machine, well away

from the fuselage, and so clear of any warm air which may come from the engine.

The French, I believe, do not measure temperature, but note the ground temperature

at the start of a test, and assume a uniform fall of temperature with height. This,

undoubtedly, may lead to serious errors. The change of temperature with height

is usually very irregular, and only becomes fairly regular at heights well above

10,000. [Tizard illustrates this with a chart entitled “Variations of Temperature with Height,”

omitted here, which displays the data with a series of curves.]

The aneroid being what it is, one soon comes to the conclusion that the only

way to make use of it in aeroplane tests is to treat it purely as a pressure instrument.

For this reason it is best to do away with the zero adjustment for all test purposes

and lock the instrument so that the zero point on the height scale corresponds to

the standard atmospheric pressure of 29.9 inches or 760mm. of mercury. Every

other height then corresponds to a definite pressure; for instance, the locked

aneroid reads 5,000 feet when the atmospheric pressure is 24.8ins., and 10,000

feet when it is 20.7ins., and so on. If the temperature is noted at the same time as

the aneroid reading, we then know both the atmospheric pressure and temperature

at the point, and hence the density can be calculated, or, more conveniently, read

off curves drawn for the purpose. The observations necessary (after noting the gross

aeroplane weight, and nett or useful weight carried) are therefore, (i.) aneroid

height every 1,000 feet, (ii.) time which has elapsed from the start of the climb,

and (iii.) temperature; to these should be added also (iv.) the air speed, and (v.)

engine revolutions at frequent intervals. The observed times are then plotted on

squared paper against the aneroid heights and a curve drawn through them.

From this curve the rate of climb at any part (also in aneroid feet) can be obtained

by measuring the tangent to the curve at the point. This is done for every 1,000

feet by aneroid. The true rate of climb is then obtained by multiplying the

aneroid rate by the correction factor corresponding to the observed temperature.

These true rates are then plotted afresh against standard heights and from this

curve we can obtain the rates of climb corresponding to the standard heights

1,000, 2,000, 3,000, etc. Knowing the change of rate of climb with height, the

time to any required height is best obtained by graphical integration. The following table gives the results of an actual test:—
Document 2-6 347

Table IV.

Machine Engine

Date 27/12/16.

From Curve

Height in Observed Per Observed Rate of Real rate Standard % of Time Rate of

Aneroid ft. temp centage of time climb in of climb height standard climb

Fahr. standard Aneroid ft. (corrected density

density for temp.)

0 36° 0.00

1,000 37° 101.0 1.00 835 814 1,000 99.40 1.20 775

2,000 38° 97.2 2.10 735 718 2,000 96.30 2.56 685

3,000 36° 94.0 3.70 640 655 3,000 93.26 4.11 610

4,000 36° 90.7 5.40 560 544 4,000 90.25 5.85 545

5,000 36° 87.4 7.25 540 495 5,000 87.32 7.80 490

6,000 33° 84.7 9.40 450 435 6,000 84.50 9.96 435

7,000 30° 82.1 11.90 405 389 7,000 81.80 12.40 385

8,000 26° 79.9 14.25 365 347 8,000 79.16 15.14 345

9,000 22° 77.6 17.00 330 312 9,000 76.55 18.20 310

10,000 23° 74.7 20.25 310 294 10,000 74.00 21.61 280

11,000 21° 72.2 23.60 280 264 11,000 71.70 25.41 245

12,000 20° 69.8 27.40 230 216 12,000 69.50 29.81 210

13,000 17° 67.7 31.90 195 182 13,000 67.32 35.13 170

14,000 12° 65.9 37.90 150 139 14,000 65.17 41.33 130

15,000 8° 64.1 45.25 110 101 14,500 64.11 46.23 105

The corrections are often much greater than those necessary in the above case.

It will be noticed that the rate of climb of this machine is approximately

halved for a difference in height of 5,000 feet. Now it is possible to get a difference

in density near the ground of as much as 15 per cent between a hot day in summer

and a cold day in winter. This corresponds to a difference in height of 5,000 feet,

so that this machine would climb off the ground on a hot day at only half the rate

that it would on a very cold day. Variation in atmospheric density, combined with

the errors of an aneroid, fully account for the observed difference between a

“good climbing day” and a “bad climbing day.”

At least two climbing tests of every new machine are carried out up to 16,000

feet or over by aneroid. If time permits three or more tests are made. The final

results given are the average of the tests and represent as closely as possible the

performance on a standard day, with temperature effects, up and down currents,

and other errors eliminated.
348 Chapter 2: Building a Research Establishment

If we produce the rate of climb curve upwards it cuts the height axis at a point

at which the rate of climb would be zero, and therefore the limit of climb reached.

This is the “ceiling” of the machine.

SPEEDS.

His 16,000 feet, or whatever it is, reached, the flyer’s next duty is to measure

the speed flying level by air speed indicator at regular intervals of height (generally

every 2,000 feet) from the highest point downwards. To do this he requires a sensitive

instrument which will tell him when he is flying level. The aneroid is quite useless

for this purpose, and a “statoscope” is used. The principle of this instrument is

really the same as that of a climbmeter. It consists of a thermos flask connected to

a small glass gauge, slightly curved, but placed about horizontally. In this gauge

is a small drop of liquid, and at either end are two glass traps which prevent the

liquid from escaping either into the outside air or into the thermos flask. As the

machine ascends the atmospheric pressure becomes smaller, and the pressure in

the flask being then higher than the external pressure, the liquid is pushed up to

the right hand trap, where it breaks, allowing the air to escape. On descending

the reverse happens; the liquid travels to the left, breaks, and air enters the flask.

When flying truly level the drop remains stationary, moving neither up nor down.

The instrument is made by the British Wright Co.

The flyer or the observer notes the maximum speed by the air speed indicator,

i.e., the speed at full engine throttle. At one or more heights also, he observes the

speeds at various positions of the throttle down to the minimum speed which will

keep the machine flying at the height in question. The petrol consumption and

the engine revolutions are noted at the same time, as well, of course, as the

aneroid height and temperature. Accurate observation of speeds needs very careful

flying—in fact much more so than in climbing tests. If the air is at an all bumpy

observations are necessarily subject to much greater error, since the machine is

always accelerating and decelerating. The best way to carry out the test seems to

be as follows. The machine is flown first just down hill and then just up hill and

the air speeds noted. This will give a small range between which the real level

speed must lie. The flyer must then keep the speed as steadily as possible on a

reading midway between these limits, and watch the statoscope with his other eye.

If it shows steady movement, one way or the other, the air speed must be altered

accordingly by 1 m.p.h. In this way it is always possible at heights where the air is

steady to obtain the reading correct at any rate to 1 m.p.h., even with light

machines, provided always sufficient patience is exercised. The r.p.m. at this

speed are then noted.

One difficulty, however, can not be avoided. If at any height there is a steady

up or down air current, then though the air may appear calm, i.e., there may be no

“bumps,” the air speed indicator reading may be wrong, since to keep the
Document 2-6 349

machine level in an up current it is necessary to fly slightly down hill relatively to

the air. Such unavoidable errors are, however, eliminated to a large extent by the

method of taking speeds every 2,000 feet, and finally averaging the results.

We must now consider how the true speed of the aeroplane is deduced from

the reading of the air speed indicator. It is well known that an air speed indicator

reads too low at great heights—for example, if it reads 70 m.p.h. at 8,000 feet the

real speed of the machine through the air is nearer 80 m.p.h. The reason for this

is that the indicator, like the aneroid, is only a pressure gauge—a sensitive pressure gauge, in fact, which registers the difference of pressure between the air in a

tube with its open end pointing forward along the lines of flight of the machine,

and the real pressure (the static pressure) of the external air. This difference of

pressure is as nearly as we can judge by experiment = 1⁄2 pV2 (where p is the density of the air and V the speed of the machine), provided that the open end of the

tube is well clear of wings, struts, fuselage, etc., and so is not affected by eddies

and other disturbances. Now assuming this law, air speed indicators are graduated to read correctly, as I have said above, at a density of 1.221 kgm. per cubic

metre, which we have taken as our standard density and called “unity.” It corresponds on an average to a height of about 800 feet above sea level.

Then suppose the real air speed of an aeroplane at a height of “h” feet is V

m.p.h., and the indicated air speed is 70 m.p.h., this means that the excess pressure in the tube due to the speed is proportional to 1 x 702

, 

or ρ x V2 = 1 x 702,

where ρ is the density at the height in question, expressed as a fraction of the standard density. To correct the observed speed, we therefore divide the reading by

the square root of the density. Thus, observation of the maximum speed of an

aeroplane at a height of 8,000 feet by the locked aneroid gave 80 m.p.h. on the

indicator, the temperature being 31 degrees Fahr. From the curve we find that the

density corresponding to 8,000 feet and 31 degrees is 0.85 of standard density.

The corrected airspeed is therefore:— 

This “corrected” air speed will only be true if the above law holds, that is to

say, if there are no disturbances due to the pressure head being in close proximity

to struts or wings. It is always necessary to find out the magnitude of this possible

error, that is, to calibrate the air speed indicator, and the only way to do this is to

measure a real air speed of the aeroplane at some reasonable altitude for easy

observation by actual timed observations from the ground, and from these timed
350 Chapter 2: Building a Research Establishment

results check those deduced from the air speed indicator readings. This calibration

is the most important and difficult test of all, since on the accuracy of the results

depends the accuracy of all the other speed measurements. It can either be done

by speed trials over a speed course close to the ground, or when the aeroplane is

flying at a considerable height above the ground. In the Testing Squadron we

have till lately attached more importance to the latter method, mainly because

the conditions approximate more to the conditions of the ordinary air speed

measurements at different heights, and because the weather conditions are much

steadier and the flyer can devote more attention to flying the machine at a constant

air speed than he can when very close to the ground.

One method is to use two camera obscuras, one of which points vertically

upwards and the other is set up sloping towards the vertical camera. At one

important testing centre the cameras are about 3⁄4 mile apart, and the angle of the

sloping camera is 45°. By this arrangement, if an aeroplane is directly over the

vertical camera it will be seen in the field of the sloping camera if its height is anywhere between 1,000 and 16,000 feet, although at very great heights it would be

too indistinct for measurements except on a very clear day. The height the tests

are usually carried out is 4,000 feet to 6,000 feet.

The aeroplane is flown as nearly as possible directly over the vertical camera,

and in a direction approximately at right angles to the line joining the two cameras.

The pilot flies in as straight a line and at as constant an airspeed as he can.

Observers in the two cameras dot in the position of the aeroplane every second.

A line is drawn on the tables of each camera pointing directly towards the other

camera, so that if the image of the aeroplane is seen to cross the lines in the one

camera it crosses the line in the other simultaneously. From these observations it

is possible to calculate the height of the aeroplane with considerable accuracy; the

error can be brought down to less than 1 part in 1,000 with care. Knowing the

height, we can then calculate the speed over the ground of the aeroplane by

measuring the average distance on the paper passed over per second by the

image in the vertical camera. If x inches is this distance, and f the focal length of

the lens, the ground speed is x x h/f feet per second.

It is necessary to know also the speed and direction of the wind at the height

of the test. For this purpose the pilot or his observer fires a smoke puff slightly

upwards when over the cameras, and the observer in the vertical camera dots in

its trail every second. The height of the smoke puff is assumed to be the same as

that of the aeroplane—it probably does not differ from this enough to introduce

any appreciable error in the results. The true speed through the air is then found. 

[Tizard then shows this graphically in the form of a simple ABC triangle in which length

AB represents the ground speed of the aeroplane as measured in the camera, CB represents the

velocity and direction of the wind, and the length AC represents the true air speed of the machine.]
Document 2-6 351

The tests are done in any direction relative to the wind, and generally at three

air speeds, four runs being made at each air speed.

The advantages of this method are:—

(1) Being well above the earth the pilot can devote his whole attention

to the test.

(2) Within reasonable limits any height can be chosen, so that it is generally possible to find a height at which the wind is steady.

(3) It does not matter if the pilot does not fly along a level path so long

as he does so approximately. What is more important is that he

should fly at a constant air speed.

(4) It is not necessary that there should be any communication between

the two cameras, although it is convenient. The two tracks are

made quite independently, and synchronised afterwards from the

knowledge that the image must have passed over the centre line

simultaneously in the two cameras.

The main disadvantage is that somewhat elaborate apparatus is necessary, but

this is of not much importance in a permanent testing station.

There are often periods in war time, however, when an aeroplane has to be

tested quickly, and low cloud layers and other causes prevent the camera test from

being carried out. It is then necessary to rely on measurements of speeds near the

ground for the calibration of the air speed indicator. In this method the aeroplane

is flown about 50 feet off the ground, and is timed over a measured run. There

are two observers, one at each end of the course; when the aeroplane passes the

starting point the observer sends a signal and starts his stop-watch simultaneously;

the second observer starts his stop-watch when he hears the signal, and in his turn

sends a signal and stops his watch when the aeroplane passes the finishing point.

By this double timing, errors due to the so-called “reaction time” of the observers

are practically eliminated, for the observer at the end of the course tends to start

his watch late, while the first observer stops his late. The mean of the two observations

gives the real time. Four runs, two each up and down the course, are done at each

air speed, the pilot or his observer noting carefully the average air speed during

the run. Observations of the atmospheric pressure and temperature from which

the density can be obtained are also taken. The average strength and direction of

the wind during each trial are noted from a small direct reading (or recording)

anemometer and the speed corrected in the same way as in the camera tests. If there

is a strong cross wind the aeroplane may have to be pointed at a considerable

angle to the course, and this makes the test a very difficult one to carry out well.

Generally speaking, it is only reliable when the wind is quite light, not more, at

any rate, than 10 m.p.h. Even this is too strong if it is a cross wind.
352 Chapter 2: Building a Research Establishment

A further difficulty is that at high speeds, over 100 m.p.h., an aeroplane may

take quite a considerable time to accelerate up to a steady speed, and so it must

fly level for a long distance each end before reaching the actual course. At the

testing station previously alluded to the course is a mile long, and there is a clear

half mile or more at each end, but it is doubtful whether even this distance is

enough for the machine to attain steady speed before the starting point. Finally,

the flyer of a single-seater is generally too busy watching the ground to do more

than glance at his air speed indicator more than a few times during the run.

Doubtless it would be better in such a case to use some form of recording air

speed instrument, although then other difficulties would arise.

Having gotten the true air speed from camera or speed course tests, and knowing

the density at the height at which the test was carried out, we obtain what the air speed

indicator should have read by multiplying the measured air speed by the square

root of the density. By comparing this with the actual reading of the indicator we

obtain the necessary correction. The whole procedure may be shown best by a

table giving part of the results of a camera test made at the beginning of the year.

A summary of the complete speed tests may now be given. Firstly, the air speed

and engine revolutions are noted flying level at full throttle every 2,000 feet approximately, by aneroid. From the aneroid reading and the temperature observations at

each height the density is obtained. The reading of the air speed indicator is then first

corrected for instrumental errors by adding or subtracting the correction found by

calibration tests over the cameras or speed course. This number is then again corrected for height by dividing by the square root of the density. The result should

give the true air speed, subject, of course, to errors of observation. The numbers

so obtained are plotted against the “standard” heights, i.e., the average height in

feet corresponding to the density during the test. A smooth curve is then drawn

through the points and the air speeds at standard heights of 3,000, 6,500, 10,000,

13,000, and 16,500 read off the curve. These heights are chosen because they correspond closely with 1, 2, 3, etc., kilometres. The indicated engine revolutions are

also plotted against the standard heights, because these observations form a

check on the reliability of the results; also the ratio of speed to engine revolutions

at different heights may give valuable information with regard to the propeller.

[At this point Tizard includes a set of tables that present data from tests of air speed at height,

showing the need for the outlined adjustments in order to obtain reliable and accurate results.

Tizard also presents another set of figures showing curves drawn from the calculated data.

In it the air speeds lie very closely on a smooth curve except at one point—about 10,000

feet—where the author believes they were probably affected by a downward current of air.]

In a brief paper it is impossible to do more than explain the more important

of the “performance” tests of aeroplanes, considered solely as flying machines.

For military purposes a number of tests are necessary, some of which can not easily
Document 2-6 353

be reduced to figures. Nor can it be supposed for an instant that the methods outlined

here are final; aeroplane testing, like all other work connected with aeroplanes, is

only in its infancy; and as time goes on, and knowledge accumulates, better methods

and instruments will evolve. There are some who lay considerable emphasis on

the necessity of every test instrument being self-recording, and although this

scheme appears at first sight Utopian and would relieve the pilot of a single-seater

of considerable trouble, there are many objections to it when considered in detail,

not the least of which is the difficulty of getting new and elaborate instruments

made at a time when all manufacturers are fully engaged on other important

work. When an observer can be taken I would personally place much more

reliance on direct observations at the present time, and one great advantage of

direct observation is that the results are there, and no time is lost through the failure of a recording instrument to record, a circumstance which is not unknown in

practice. So far as we use recording instruments, we use them only as a check on

direct observations, although we may probably adopt recording air speed indicators

for the calibration tests of single seaters. But whether recording or direct reading

instruments are used, it is as I said before, the flyer on whom the accuracy of the

tests depends. I feel that too great stress can not be laid on this; he is the man who

does most of the experiments, and like all experimenters in every branch of science,

he requires training and a great deal of practice. Although the methods themselves

may be greatly changed, this much may perhaps be claimed, that the general

principles on which they are founded are sound, and will only be altered in detail.

The importance of the work can hardly be exaggerated; model experiments are

notoriously subject to scale and other corrections, which if not carefully scrutinised

may be very misleading, and it is only by accurate full-scale work in addition that

we can hope to maintain a steady improvement in the efficiency of aeroplanes.

[The published paper includes the following transcript of the discussion after its presentation by Captain Tizard.]

FIFTH MEETING, 52nd SESSION.

An ordinary general meeting of the Society was held in the Theatre of Royal

Society of Arts, London, on Wednesday, March 7th, 1917, at 8:00 p.m. There was

a large attendance of members and guests. The chair was to be the Right Hon.

Lord Sydenham, G.C.I.E., F.R.S.

Captain H. J. TIZARD, of the R.F.C., Associate Fellow, read a paper, illustrated

by slides, on “Methods of Measuring Aircraft Performances.”

On the conclusion of the lecture a discussion followed.

Squadron-Commander BUSTEED: I regret that the Naval Testing Department

is not as far advanced as one would like it to be. A good deal of useful work has

been done, but the R.N.A.S. and R.F.C. Department had adopted different density

standards, though these were now the same.
354 Chapter 2: Building a Research Establishment

I appreciate the necessity for instruments, but my experience goes to show that

the machine instruments were most required for single-seaters, and unfortunately,

after the pilot had managed to get in, there was very little room for them. They

were also a source of trouble in getting tests through quickly; readings taken by

pilots had proved very fair.

Lieutenant G. H. MILLAR, R.N.V.R., said that in his opinion it was a pity that the

standard atmosphere which had been adopted was a purely empirical one; he would

have preferred one based on a given temperature and pressure at sea-level and a uniform rate of fall of temperature. Some months previously he had calculated such a

standard atmosphere, taking as the condition at sea-level a pressure of 760mm. and

a temperature of 15 deg. C., with a fall of 1.5 deg. C. per 1,000 ft. rise, and the curve

of density against height thus obtained did not differ greatly from that given in this

paper, the difference varying between 400 and 700 ft. for height from 0 to 20,000 ft.

By reducing the assumed ground temperature the curves could be brought nearly

into coincidence. The advantage of such a standard over the empirical one was that

it could be calculated at any time by remembering two constants. He also thought that

the unit of density should cetainly be the density at zero height for the standard atmosphere adopted. No advantage was gained by using the density for which the speed

indicators were initially calibrated, since the instrument had to be calibrated in the

machine in any case, and in practice instruments were found to be anything up to

20 per cent out. With regard to calibration in the machine, calibration at height had

the disadvantage that the speed range of the machine was reduced, unless the

machine was flown slightly downhill for the higher speeds. He had found that it was

best to take four pairs of runs at different speeds over as wide a range of speed as possible, and even with quite rough methods of timing, the four spots usually came very

nearly on a straight line. He was inclined to doubt Captain Tizard’s statement that

the best climbing speed was the same at all heights, although probably little was

sacrificed by climbing throughout at the “ceiling” speed. He stated that terms

were badly needed for the quantities v

⁄√ρ and n⁄√ρ where “v” was the speed, “n” the

r.p.m., and “ρ” the density. These quantities were of great importance in considering the aerodynamic properties of the machine and propeller (apart from the

engine) and the relations between them, and the angle of incidence and angle of

ascent or descent were independent of the height or density. He wished to express

his admiration for the thoroughness with which the R.F.C. tests were carried out.

Captain GRINSTED: The principle of the methods of testing of aeroplanes and

of the reduction of the results to a standard basis as now established and improvements in accuracy of testing can now be made only by improving the instruments

by which measurements are made.

Captain Tizard objected to the use of an aneroid as a height-measuring

instrument, and preferred to use it simply as a pressure-measuring instrument.
Document 2-6 355

Even as such the aneroid is not perfect, and in saying that it measures pressure it

is given too good a character. Owing to its lag it does not give a correct measurement

of pressure when the rate of change of pressure is at all rapid. I should like to

know if Captain Tizard has found difficulty in obtaining instruments sufficiently

free from lag for the purpose of accurate aeroplane testing.

The measurement of performance is now confined to tests of speed and climb.

There are other things of importance, such as the rate at which the aeroplane can be

brought on to a given bank or its direction of flight turned through a given angle

which should be measured when comparing performances of aeroplanes. I should

like to know if Captain Tizard has considered methods of making such measurements.

Mr. BERTRAM COOPER: I should like to ask Captain Tizard if he could tell us

something about the lag of the climbmeter. We have had several “lags” mentioned

tonight, but not this “lag,” which seems to me to be a pretty serious one.

The action of the instrument depends on the accumulation of pressure in the

bottle, which is relieved by the leak. It will be clear, therefore, that the reading will

always lag behind the real state of affairs at the spot where it is made, the exact

amount depending on how fast the upward or downward journey to that spot was

made. For instance, a pilot could stall his machine when seeking his best “climb”

and the instrument would still tell him he was climbing when he was, in fact,

falling owing to stalling. Moreover, the error here would be aggravated by the

“gravity error” on the liquid. This liquid would be relatively lighter owing to the

falling, and would consequently tend to show a rate of climb in excess of that actually appropriate to the pressure difference that existed. And this leads me to ask

Captain Tizard what is the most serious error in practice, the “lag” error or the

“gravity” error? I notice he said that the instrument was not satisfactory near the

ground. I take it that is chiefly because of the gravity error and “bumpy” flying,

but is not the “lag” error serious at all heights?

Captain FARREN: The methods of measuring aeroplane performance

described by Captain Tizard are, as he said, only different in some minor points

from those in use at the R.A.F., where they serve both for the testing of new types and

for reducing the full-scale experiments on aeroplane resistance, etc., which have been

going on there for some time. The methods were, in fact, arrived at to a great

extent by discussion between the R.A.F. and the Testing Squadron. The same standards of density are used, and we agree with him generally on the superiority of

ordinary instruments and good observers over automatic recording instruments.

We have not had so much experience as he has had with single-seaters, which are

rather a different problem from two-seaters, demanding much more skill from the

pilot, but it seems that even here automatic recorders have disadvantages.

With regard to measuring speeds at heights, Captain Tizard is of the opinion

that it is not possible to fly level except by using a statoscope. My experience is
356 Chapter 2: Building a Research Establishment

that in the case of certain very expert pilots a flight taking as long as ten minutes can

sometimes be made, during which the aneroid shows no appreciable movement.

(The aneroids used are very high-class instruments, with 20 ft. divisions.) I realise

that this does not really mean that no height is gained or lost in the test, because

every aneroid is known to possess lag. But under these circumstances on the average

the height difference between the beginning and end of the run can not be more

than about 100 ft. in a length of about 12 miles—corresponding to a slope of 1

in 600 or so, which represents a correction to the speed of well under the error of

observation. But undoubtedly the statoscope gives generally much better results.

The instrument in use at the R.A.F. is similar in principle to the one shown, but

very much smaller, occupying a space 1 in. by 1 in by 6 ins, approximately. This

gives very satisfactory results in use.

With regard to the rate-of-climbmeter—which, it may be interesting to know,

was christened the “coffeeometer” by the pilots at the R.A.F., on account of the

thermos flask used on the first instrument!—this was first shown me by Captain

Dobson (then of the Testing Squadron) in July, 1916. A search in the Instrument

Stores at the R.A.F. brought to light an exactly similar instrument—made in

Germany! It is apparently a standard balloon instrument, but the credit of introducing it into aeroplane testing is due to the Testing Squadron. This instrument

again has been much reduced in size, and occupies about the same space as the

statoscope, referred to above. In use it suffers from one disadvantage—any vertical

acceleration, such as that which occurs as the result of a change in speed, causes

the indicating column to move on account of the change in effective gravity. As a

result only very gradual changes in speed must be made in searching for the best

climbing speed. An attempt has been made to develop a dial indicator (in which

the defect would not appear), but without success, on account of the large volume

of air enclosed in the diaphragm.

Captain Tizard laid stress on the necessity for very careful work on the part

of the pilot. I think too much emphasis can not be put on this point. We are now

emerging from the middle age of aeronautics—when flying was, to the ordinary

man, a kind of magic, practised by a sort of superman who daily carried his life

in his hands, but nevertheless continued to survive in spite of the apparently rash

things he habitually did. To some extent the fear of the passing generation of flyers

that flying would become cheapened and commonplace helped to keep alive this

idea. They saw their living vanishing. It must be admitted that their fears were

justified. It is difficult to estimate aright the value of their work. We are too near

to see it in its true place. I think we can be sure that history will not be unjust to

them or stinting in its acknowledgments. But it is evident that nowadays it is

becoming easier and easier to fly—also less risky. The “magic” has gone. In its

place we find a new branch of engineering—a new science. For accurate and useful
Document 2-6 357

work nowadays skill and nerve are still essential, but to these care, thoroughness,

and training in making accurate observations must be added. Everyone who has

had anything to do with aeroplane testing knows how it was common talk that A.

always got a better climb out of a machine than anyone else. Perhaps he did it by

willpower or some other occult practice; anyhow, it was beyond us. Naturally A.

gained in many ways, and it can not be reckoned against him that he did not make

any special efforts to dispel the idea. Pilots are human. But the real truth is that A.

was possessed of a power of accurate and thorough workmanship, which always,

in any kind of work, brings the best results.

Aeroplane testing, as a part of aeroplane designing, demands for satisfactory

results the highest training. It occupies no special place by virtue of this—it merely

comes into line with the rest of engineering. Now, one can learn to fly in a

month—even in England in war time—but an engineer’s training requires years.

It is evidently necessary, therefore, that engineers—men with scientific training

and trained to observe accurately, to criticise fairly, to think logically—should

become pilots, in order that the development of aeroplanes may proceed at the

rate at which it must proceed if we are to hold that place in the air to which we

lay claim—the highest.

I wish to add the following remarks:—

In the years immediately preceding the war aeronautics suffered very much

from a lack of full-scale experiments. Money was but grudgingly given, and the

foresight of the Government in this matter was not conspicuous. As a nation we

are remarkable for our inertia. After the outbreak of war for some time little

improvement was evident, but gradually the state of affairs became better. At the

present moment we are in a fairly good position, but it is necessary to make provision for “after the war.” At the moment experiments are not killed—as they used

to be—for lack of money. But after the war the inevitable reaction will almost certainly mean that a partial slump will occur. Money will be scarce and aeronautics

will suffer in company with other activities. It is here that the trade must help.

They must realise that if they are to build up aeronautics as a branch of engineering they must be prepared to experiment thoroughly. They must provide money

and manufacturing facilities for testing and for full-scale experiments. Men will

not be lacking. In no branch of engineering have we ever had to want for men—

aeronautics has special attractions which will ensure a steady supply of the best.

But only if the prospects are sufficiently attractive. A stinting policy here will only

result in other countries beating us. It has been our unhappy experience in the

past in more than one science to see our brains and our energies wasted owing to

lack of encouragement from those who could and should have given it. We have

seen other countries gifted with more foresight take our ideas—and our men—and

forge ahead. Eventually we have generally managed to regain some of our losses.
358 Chapter 2: Building a Research Establishment

But in the keener struggle which is to come in every trade we must not go back

to the old tactics, or we shall not find Fate so kind to us. It is to be hoped that

Captain Tizard’s lecture will cause aeroplane manufacturers to see that if they are

prepared to treat their productions as other engineers do, to provide for testing

and experiment on a liberal scale as is done in every other kind of profession,

then they will reap their reward.

Captain TIZARD replied.

Lord SYDENHAM expressed on behalf of those present their indebtedness to

Captain Tizard for his interesting and valuable paper.

A vote of thanks was then offered to Lord Sydenham for presiding, and the

meeting terminated.
Document 2-7(a–b) 359

Document 2-7(a–b)

(a) Jerome C. Hunsaker, Assistant Naval Constructor, letter 

to H. M. Williams, Managing Editor, Aviation and 

Aeronautical Engineering, 11 March 1918, Hunsaker

Collection, Box 1, Folder 1, File A.

(b) “Education in Advanced Aeronautical Engineering,” 

NACA Annual Report for 1920 (Washington, DC), p. 20.

The following two documents illustrate the nascent state of American aerodynamic education at the end of the second decade of the twentieth century. In the

spring of 1918, Jerome Hunsaker was busy overseeing the design of airplanes, airships, catapults, and aircraft engines for the U.S. Navy. At that time he wrote to

H. M. Williams, the managing editor of Aviation magazine, to praise their decision to publish a much-needed textbook on aerodynamics and aeronautical engineering. Two years later in its sixth annual report, the NACA published a resolution adopted in April 1920 calling for both the military services and American

universities to establish courses in “advanced aeronautical engineering.” 

Document 2-7(a), letter from Jerome C. Hunsaker to H. M. Williams, 1918.

March 11, 1918.

Dear Mr. Williams:

I am very glad indeed to learn that you are to bring out in book form the

“Course in Aerodynamics and Aeronautical Engineering” by Klemin and Huff, as

published serially in your paper.

I know there is a real need for a thorough treatment of the subject such as this

course presents. A large part of the work is fundamental and hence will not quickly

pass out of date as is unfortunately the case with a great deal of technical literature.

Let me add to my good wishes for the success of the book, my suggestion that

you expedite the printing.

Very truly yours,

Jerome C. Hunsaker

Asst. Naval Constructor, U.S.N.
360 Chapter 2: Building a Research Establishment

Document 2-7(b), “Education in Advanced Engineering,” 

NACA Annual Report for 1920.

At the semiannual meeting of the full committee in April, 1920, consideration was given to the question of education in advanced aeronautical engineering.

This meeting was attended by all the members of the committee connected with

universities: Drs. Ames, Durand, Hayford, and Pupin, and it is deemed worthy of

special notice that each of these members individually expressed his approval of

the resolution which was adopted at that meeting in the following terms:

Whereas it is deemed essential to the development of aviation in America for

military and naval purposes that advanced instruction in aeronautical engineering

be given to military and naval officers at a competent educational Institution; and

Whereas the public demand for such instruction will in all probability not be

sufficient to justify or permit the offering of such advanced courses in more than

one institution at the present time; and

Whereas such an advanced course is now being given at the Massachusetts

Institute of Technology; and 

Whereas it is deemed further essential that actual experience with aerodynamic research should form a part of such advanced Instruction: Therefore be it

Resolved, That the National Advisory Committee for Aeronautics hereby recommends to the Secretary of War and to the Secretary of the Navy the adoption of a

continuing policy for the instruction of officers in advanced aeronautical engineering,

and that for the next three years classes of 15 Army officers and 15 Navy officers

be detailed annually to take such instruction in advanced aeronautical engineering

at the Massachusetts Institute of Technology at the expense of the War and Navy

Departments, respectively.

Resolved further, That, in connection with the course in advanced aeronautical

engineering, the National Advisory Committee for Aeronautics cooperate in

every way with the Massachusetts Institute of Technology by offering to its faculty

and students the facilities for investigations in aerodynamics and experimental

work on actual airplanes at the committee’s research laboratory, Langley Field, Va.

Resolved further, That the National Advisory Committee for Aeronautics offer to

give at various engineering universities courses of lectures in advanced aeronautical

engineering by members of its engineering staff.

Resolved further, That the National Advisory Committee for Aeronautics recommend that educational institutions generally not consider the establishment of

courses in aeronautical engineering at the present time, as it is the opinion of the

committee that the demand for such instruction outside of the Government service

is not sufficient, and competent instructors for such courses are not available.

This resolution was transmitted to the Secretary of War and to the Secretary
Document 2-7(a–b) 361

of the Navy. The War Department, acting on the committee’s recommendation,

secured the necessary authority from Congress to detail 25 officers for special

instruction at the Massachusetts Institute of Technology. It is understood that the

Navy has not secured similar authority. The committee therefore strongly recommends

to Congress that similar authority be given for the detail of naval officers for such

special training. At the present time both services are weak in respect to the number

of officers sufficiently educated in aeronautical engineering. The committee considers

that the diligent prosecution of a continuing program of education will be of great

value within a few years in the development of military and naval aviation.
362 Chapter 2: Building a Research Establishment

Document 2-8(a–b)

(a) United States Army, excerpts from “Full Flight 

Performance Testing,” Bulletin of the Airplane Engineering

Department, U.S.A. 1, No. 2 (July 1918): 20–49.

(b) “Special Aerodynamic Investigations,” NACA Annual 

Report for 1919 (Washington, DC), pp. 27–28.

Early in World War I, military officials saw that the NACA’s Langley Laboratory

would not be ready in time to meet its research needs. Accordingly, the U.S. Army

built a temporary facility at McCook Field, in Dayton, Ohio, and moved its

Airplane Engineering Department personnel from Langley. Because the army

was interested in practical research to quickly identify and solve problems that

directly affected aircraft production, performance, and reliability, much of

McCook’s work involved flight testing. Recognizing that “the possibilities of error

in full flight testing are very great,” one of McCook’s first investigations examined

methods to standardize test methods and ascertain the accuracy of instruments

such as altimeters and airspeed indicators. 

“Full Flight Performance Testing” was one of McCook’s earliest publications,

and it shows the army’s practical approach to flight research. The following

excerpts include the report’s introduction and the second section that describes

the basic types of instruments recommended by the McCook Field engineers for

recording aerodynamic data from flight tests. 

Noting the success of McCook’s approach, as well as the slow progress of construction at Langley, the NACA sought to work with the army at McCook. The

committee, which included the commanding officer at McCook Field, Colonel

Thurman H. Bane, approved a broad program of “scientific work” at McCook.

Outlined under “Special Aerodynamic Investigations” in the NACA Annual Report

for 1919, this work marked the beginning of a fruitful cooperation between the

Army and the NACA. 

Document 2-8(a), United States Army, excerpts from 

“Full Flight Performance Testing,” 1918.

AERONAUTICAL RESEARCH DEPARTMENT REPORT

The possibilities of error in full flight testing are very great, both as regards

the use of instruments, the methods of observation, and the corrections applicable

for varying atmospheric conditions. This article has been written as a definite
Document 2-8(a–b) 363

summary of the subject to facilitate standardization of the methods of testing and

recording of results. It deals solely with standard performance tests and climb and

speeds at varying altitude, with no consideration of stability, controllability or

radiator and engine performance.

In Section I is included a review of such physical data as is required for a complete

understanding of the subject. The points considered in this section are: formulae

for density of air; density in grammes per cubic meter and pounds per cubic foot;

reduction to per centage of standard density; standard atmosphere; density values

at various relationship between pressure, temperature and altitude at constant

temperature; Halley’s formula for temperature, and corrections; Bureau of

Standards altitude pressure curve; calibration chart for altimeter, and an alignment

chart for altitude.

In Section 2 are described the commonest and most useful forms of instruments

employed in performance testing, with their principles and calibration. These

include air speed indicators whose utility is obvious; barographs and altimeters

for measuring pressures and allowing altitudes to be deduced therefrom; strut

thermometers so that necessary temperature corrections may be made; tachometers

whereby the r.p.m. of the motor may be obtained; statoscopes to enable the pilot

to fly level at altitudes; recording drums used on various types of measuring

instruments, and anemometers and wind vanes.

Finally, in Section 3 are described the methods employed in the calibration of

the air-speed meter, in measuring climb and speed at altitude, and the various

methods of correcting and recording results.

In the Appendix a standard form for recording results is submitted. This form

has been adopted for use at McCook Field.

Simplicity of presentation rather than an exhaustive, scientific treatment has

been sought.

[ . . . ]

Section 2

AIR SPEED INDICATORS

Several types of air speed indicators, based on a number of principles, have

been employed in the past, such as pressure instruments with a plate balanced by

a spring, rotating vane anemometers, and hot wire anemometers. For a number

of practical and theoretical reasons, instruments of this type have been discarded,

and attention is now concentrated on instruments measuring differences of pressure transmitted from two Pitot tubes or Pitot and Venturi tubes.

Pitot and Venturi Tubes

Since all air speed indicators based on pressure differences are of the Pitot, or Pitot

and Venturi type, a simple explanation of the principles involved will be included.
364 Chapter 2: Building a Research Establishment

(a) Pitot tube.—In Fig. 10 is shown a Pitot tube in diagrammatic form. It consists of two concentric tubes, the inner open to the wind, the outer closed and

communicating with the current of air only by a series of fine holes. The tubes

are connected to the two arms of a pressure gauge, which measures the difference

in pressure between them. The inner tube, open to the wind, brings the air

impinging on it to rest, and the pressure on it is, therefore, a measure of both the

static pressure in stream and of the kinetic energy head of the stream. If p is the

static pressure of the stream, V the velocity, the total pressure on the inner tube

will be given by

The outer tube, on the other hand, being closed to the wind, will, if the holes

are small enough, read the static pressure of the air flow p.

Hence the differences in pressures read on gauge will be

and the gauge reading will be a measure of the velocity.

Pitot tubes with suitable gauges are widely used in laboratory practice, but owing

to the small difference in head DV2

⁄2g, the forces acting on the gauge are very small

and hard to record.
Document 2-8(a–b) 365

(b) Combination of Pitot and Venturi.—To increase the pressure differences, and

thus get practicable forces on the gauges, the Venturi tube is coupled with the

pressure part of the Pitot. Such a combination is shown diagrammatically in Fig.

9. Here the velocity at the throat will be considerably greater than that acting on

the suction side of a Pitot, and therefore has a considerably greater effect. The

mathematical theory of the Venturi is a little more complicated than that of the

Pitot and the theoretical suction heads are not always in accord with practical

results. From the simple formula of Fig. 9 it can be seen that the gauge readings

will be proportional to DV2

⁄2g, hence are a measure of the velocity.

Correction for density and reduction to standard density in air speed meters.—From

the preceding considerations of the Venturi and Pitot tubes, it is seen that the

forces on the gauge are proportional to A D V2, where D is the density, V the velocity and A some constant depending on the instrument. The airspeed reading

equation is therefore

R = ADV2

Airspeed meters being calibrated at 16 deg. C. and 760 mm., they will only

be correct at the standard density D corresponding to this condition.

If the instrument gives a certain reading V1 at density D1 then true reading Vt

will be given by equation: AD1Vt

2 = AD0V12

and

Since
366 Chapter 2: Building a Research Establishment

The correction can be applied either by computation or from the curves of

Figs. 2 and 3 where densities for varying temperatures and pressures are given as

per centages of the standard density, as well as the values of the ratios ÷D0/D1.

On certain occasions it may be quicker to use table 3.

Approximate air speed correction at heights.—A very useful table furnished by the

Technical Department, British Aircraft Production, allows air speed corrections at

heights to be made with fair accuracy, on the assumption of certain standard conditions. Its use is not recommended for the computation of performance results,

but may be very handy as a check. The table employs mean value of the density

at various altimeter heights. Ground temperature of 16 deg. C. and pressure of

760 mm. are assumed, and a lapse rate of 1.75 deg. C. per 1000 ft. ascent.

Table 3

Multiplying Factors to Reduce Speed Readings at Varying Pressure and

Temperatures to Standard Density Pressure in Millimeters of Mercury

Temperature, 200 250 300 350 400 450 500 550

degrees 

centigrade

- 40∞ 1.750 1.566 1.429 1.324 1.236 1.168 1.109 1.057

-30 1.790 1.599 1.459 1.351 1.265 1.191 1.130 1.080

-20 1.830 1.631 1.492 1.380 1.290 1.218 1.155 1.100

-10 1.852 1.661 1.521 1.407 1.318 1.239 1.175 1.121

0 1.899 1.673 1.550 1.430 1.340 1.264 1.120 1.142

10 1.924 1.729 1.574 1.459 1.365 1.286 1.220 1.162

20 1.961 1.757 1.602 1.483 1.388 1.308 1.241 1.182

30 1.990 1.787 1.630 1.508 1.410 1.330 1.261 1.204

40 1.815 1.661 1.533 1.437 1.354 1.281 1.224

Temperature, 600 650 700 750 800 850 900 950

degrees 

centigrade

- 40∞ 1.010 .944 .936 .904

-30 1.031 .982 .956 .925 .894

-20 1.051 1.012 .975 .942 .911

-10 1.075 1.031 .995 .960 .930 .902

0 1.094 1.051 1.012 .978 .949 .920 .893

10 1.115 1.070 1.030 .996 .965 .937 .910

20 1.132 1.089 1.050 1.012 .982 .954 .926

30 1.151 1.098 1.068 1.030 .997 .979 .941

40 1.170 1.120 1.078 1.050 1.013 .984 .958
Document 2-8(a–b) 367

Typical Recording Air Speed Meter

In the Toussaint-Lepère air speed meter the dynamic pressure of the wind is

measured by a combination of Pitot tube and Venturi meter. This pressure is

transmitted to a clock work recording device by a gauge consisting of bellows and

a tension spring.

The Pitot tube and Venturi meter are combined in a small casting conveniently

called by the French antenna and similar to that of many other speed indicators.

This antenna is shown in Fig. 11. The Venturi is carefully proportioned to give the

maximum possible suction with a given air speed. The antenna is supported by a long,

slender, hollow arm of light wood which contains the tubes transmitting the pressure

to the recording device as shown in Fig. 12. It is fastened to this arm by a light,

adjustable clip, in order that the antenna may be turned directly into the wind.

The recording device is shown in Fig. 14 and diagrammatically in Fig. 13. It has

the ordinary clockwork drum and pen. These are described elsewhere. The gauge

consists of two movable circular plates S1 and S2, rigidly connected by a rod ab.

The plates form the tops of the bellows f1 and f2. The sides of these bellows are

made of thin rubber that is very flexible, the bottoms are formed by the fixed

plates m and n. The suction from the Venturi is led to the airtight chamber c-c,

and so acts on top of the plate S1. The pressure from the Pitot is led to the under

side of the plate S2. The top of S2 and the bottom of S1 are open to the air inside

of the box. Thus a variation of that pressure causes no motion of the rod ab which

is moved only by the difference of the pressure transmitted from the antenna.

The rod ab is constrained to move vertically by the form bar linkage a-d-c-b. The
368 Chapter 2: Building a Research Establishment

link bc carries on one end the marking pen g; on the other a counter weight for

the movable parts of the instrument. At the end of this link is fastened the spring

R, whose tension balances the pressure of the pen. This spring is so placed that

the displacement of the pen is nearly proportional to the wind speed. The recording

apparatus is enclosed in a box about 9 in. x 6 in. x 5 in., total weight about 4 1⁄4 lbs.

The apparatus slides out of this box to facilitate adjustment of paper on the drum.

The complete speed indicator must be calibrated and a chart or table made

for converting the readings on this drum into true wind speeds. This chart of

course is only correct for readings in air of standard density.

The recording apparatus is suspended in the air by elastic cords or may be

held by the passenger in a two-seater. The antenna must not be placed near any
Document 2-8(a–b) 369

obstructions or disturbance including the slip-stream, body, etc. The supporting

arm is fastened to any convenient part of the airplane such as a strut by tape or

a fitting (see Fig. 21). The antenna is then adjusted to point directly into the wind.

With this instrument as with all air speed meters, a test run in flight must be made

over a measured course to determine the effect of interference of the plane upon

the air flow to the antenna, and to find the correction due to this interference.

The Foxboro-Zahm Direct Reading Air Speed Meter

In Figs. 15 and 16 are shown views of a very widely used combination of the

Foxboro indicating box and the Zahm Pitot-Venturi tube (now adopted as standard

by the Signal Corps). The pressure lead of the Pitot enters the small cylinders

located in the indicating case which in itself is made air-tight by a gasket under

the cover. The, suction of the Venturi is transmitted to the case itself. When a difference of pressure exists between the inside and outside of the two cylinders, they

elongate or contract. The motion is transmitted to the pointer by means of links

to a circular rack which engages a pinion on the spindle.

It may be useful to include also the old type Foxboro head which is widely

used. This is shown in Fig. 17. The tube in front presents a large opening to the

wind. In this opening is fitted a conical guard pointing into the wind, behind
370 Chapter 2: Building a Research Establishment

which is located the opening to a small pipe. This pipe is the only outlet from the

cup-shaped opening, and it transmits the dynamic pressure to the gauge. The

wind passing the tube creates a suction in the space inclosed by the frustrum of

the cone. A small pipe, seen in the photograph at the base of the cone to the left,

transmits this suction to the gauge.

In airspeed meters, since the movement of the aneroid boxes is proportional

to the square of velocity, the scale on the dial is not uniformly graduated; and

were it not for a compensating device, the divisions of the scale for the higher

velocities would increase rapidly as the velocity increased. The small springs fastened to the aneroid boxes shown in Fig. 15 restrict the movement of the boxes

and shorten the scale divisions.

Table 4

Air Speed Corrections at Heights

Apparent speed Corrected Speeds at Heights (m.p.h.)

instrument 

reading m.p.h. 6500 ft. 10000 ft. 15000 ft. 20000 ft.

40 44 46 50 54

45 49 52 56 60

50 65 58 62 67

55 60 63 68 74

60 66 69 75 80

65 71 75 81 87

70 76 81 87 94

75 82 86 93 100

80 87 92 99 107

85 93 98 106 114

90 98 104 112 120

95 104 109 118 127

100 109 115 124 131

105 115 121 130 140

110 120 127 137 147

115 120 132 143 154

120 131 138 140 161

125 137 144 155 [170]

130 142 150 161 171

135 147 156 168 171

140 153 161 174 187

145 158 167 180 194

150 161 173 186 201

155 169 179 193 207
Document 2-8(a–b) 371

Miscellaneous Air Speed Meters

The British R.A.F. IV-A air speed indicator head is of the Pitot type modified

in construction. The dynamic pressure tube and the static pressure tube are

entirely separate, held parallel about 2 in. apart by a small fitting. The dynamic

tube is just a plain tube open to the wind, but the static pressure tube is closed by

a small streamlined cap. The holes are drilled well back along the cylindrical part

of the tube. The leads are separate and the head is very easy to make. The gauge,

shown diagrammatically in Fig. 18, is typical of most of those used for this type

of air speed indicator. The whole gauge is made airtight by rubber gaskets. Inside

there are two diaphragms A and B made of thin flexible metal. The top of B and

the bottom of A are fixed to the case. The movable ends push through small rods

to the cross-arm C on the spindle D. At the end of this spindle is an arm E which

engages a quadrant suitably geared to the pointer. The motion of the pointer is

opposed by a light hairspring. The dynamic pressure is led to the inside of the

diaphragms, the static merely inside of the case. The diaphragms therefore tend

to expand and so the gauge is sensibly independent of gravity and centrifugal

force, and entirely free of the pressure in the cockpit. Other makers of gauges

have different managements of diaphragms and different mechanism, but the

principle is the same.

Another British instrument, the Ogilvie indicator-head is merely a Pitot tube.

The gauge is different from the usual type. It has a single airtight chamber divided into two parts by a flexible rubber diaphragm. The static pressure is on one

side, the dynamic on the other. A light silk thread is attached to the center of this

diaphragm. The thread is kept taut at all times by a very light hairspring. The

whole mechanism is very delicate, almost too fragile for rugged work. Later types

of Ogilvie indicators have a gauge made similar to the R.A.F. IV.-A.

Badin Double Venturi Head

The Badin type of head is a double Venturi meter as in Fig. 19. The small

inner meter has its exit at the throat of the outer meter. This greatly increases the
372 Chapter 2: Building a Research Establishment

suction at a given wind speed; a very desirable quality, especially on slow speed

machines or dirigibles. The Badin system appears to have only the suction lead

from the head to the gauge. This is not good practice as the total pressure in the

cockpit may be quite different from the static pressure at the head.

The Sperry Venturi speed meter is also of the double Venturi type. There are

three leads for pressure difference. One, the suction, from the throat of the small

Venturi, one from an open tube pointing back along the outside of the outer

Venturi, and the third from the front edge of the case of the outer Venturi.

Readings may be taken between the first and either of the others. There seems to

be a distinct disadvantage in using the tube pointing back for this gives a reading

less than the static pressure and so reduces the available pressure difference. For

use on high speed airplanes there is a Sperry head of the Pitot tube type.
Document 2-8(a–b) 373

Important Practical Points

Attachment of Pitot tube heads.—A simple attachment as shown in Fig. 21 is customary, but this is open to the objection that the air stream is interfered with by

the strut. It is much better to offset the instrument from the strut.

Connecting up Venturi-Pitot tube with airspeed indicating instrument.—The VenturiPitot tube is connected with the airspeed indicator by flexible aluminum tubing.

In using the aluminum tubing sharp bends and kinks must be avoided. It is

absolutely necessary that the connections at all joints be airtight. For this reason

the following method is recommended for making connections between the aluminum tubing and the outlets of the Venturi, or the nipples of the indicators, or

between sections of the tubing. (See Fig. 20.)

(1) Slip a 4 in. length of standard rubber tubing, 1

⁄4 in. bore over the 2 in.

length of the 5⁄16 dia. aluminum sheath, so that the ends of the rubber tube extend

1 in. beyond the extremities of the sheath.

(2) Butt the ends of the aluminum tube and the connection, and slide the sheath

in the rubber tube over the joint so that the joint comes at the middle of the sheath.

(3) Bind the two ends of rubber tubing with wire. First tie the wire near the

sheath with a simple knot, leaving one short end free, which is pressed down

along the tube and bound under. The wire is wrapped around the tube and when

the wrapping is finished the two ends of the wire are twisted together and cut off,

leaving a 1

⁄4 in. stub to prevent slipping. In binding the rubber care should be

taken not to cut it.

Document 2-8(b), “Special Aerodynamical Investigations,” 

NACA Annual Report for 1919.

SPECIAL AERODYNAMIC INVESTIGATIONS.

In the summer of 1919 the executive committee approved a program of scientific work to be carried out at McCook Field, Dayton, Ohio, under the supervision

of its aerodynamical expert, Dr. George de Bothezat. This work involved: First,

the theoretical analysis of the full performance of an airplane in steady flight; second, the development of new instruments and methods in order to measure in a

single test flight the full performance characteristics of an airplane; third, the

analysis of the full performance record of an airplane and deductions there from

as to how the efficiency of an airplane can be increased by minor changes; fourth,

the making of such minor changes in a given type of airplane to be followed by a

second full performance test; fifth, the checking of the results against the original

theory and the necessary modifications of the theory to permit in the future the

determination of all the performance characteristics of an airplane in steady

flight by mathematical calculation.
374 Chapter 2: Building a Research Establishment

Dr. de Bothezat has been stationed at Dayton since August, 1919, and a small

staff has been selected from members of the engineering division of the Air

Service and assigned by the commanding officer at McCook Field to work with

him in the prosecution of this work. The present commanding officer at McCook

Field, Col. Thurman H. Bane, is also a member of the National Advisory

Committee for Aeronautics. This work has been successfully inaugurated with the

hearty cooperation of the officials and civilian engineers of the Air Service.
Document 2-9(a–c) 375

Document 2-9(a–c)

(a) “Office of Aeronautical Intelligence,” NACA Annual 

Report for 1918 (Washington, DC), pp. 24–25.

(b) John J. Ide, Technical Assistant in Europe, 

to the NACA, excerpts from “Report on Visit to England, 

July 1–22, 1921,” 4 August 1921, Ide Collection, Box 8,

National Air and Space Museum, Washington, D.C.

(c) John J. Ide, Technical Assistant in Europe, 

to the NACA, “Wind Tunnel at Issy-les-Moulineaux,” 

8 December 1921, Ide Collection, Box 8, National Air 

and Space Museum, Washington, D.C.

While the young NACA actively pursued the construction of a laboratory to

seek new aeronautical knowledge as America fought in a world war, the committee

recognized that considerable progress continued to be made in other countries

and that some means of managing the growing body of “scientific and technical

data relating to aeronautics” was essential. Thus, the committee established the

Office of Aeronautical Intelligence in 1918. As outlined in the NACA Annual

Report for 1918, the Office of Aeronautical Intelligence worked closely with the

military and naval intelligence offices, including “special committees stationed at

London, Paris, and Rome to collect information regarding all phases of the scientific

and technical study of war problems.”

In December 1918, a naval reserve ensign by the name of John J. Ide wrote

the chief of naval operations (aviation) requesting that he be assigned to the naval

attaché at the American Embassy in Paris to follow the progress of European aviation.

Although the navy originally denied his request, Ide persisted and ultimately

received a Paris posting in 1921 as the NACA’s technical assistant in Europe. In this

role, Ide repeatedly visited manufacturers and aeronautical laboratories throughout

Europe, and he submitted many detailed reports on airplanes, wind tunnels,

instruments, engines, and other aviation-related matters to the committee on a

regular basis. The two documents reproduced herein are typical of Ide’s reports. The

reader will note that Ide took great care not to judge the merits or applicability of

what he observed, but rather to report what he had learned as factually as possible.

The NACA treated these reports as confidential, but the information proved

useful to the American military, manufacturers, and the staff at Langley. For an
376 Chapter 2: Building a Research Establishment

example, note Ide’s description of an optical method to observe propeller blade

bending under the “Aerodynamical Department” section of his 4 August 1921 report.

While not totally successful in England, there can be little doubt that this idea

influenced the Langley researchers who developed a successful technique to optically measure blade bending in the Propeller Research Tunnel a few years later.

Document 2-9(a), “Office of Aeronautical Intelligence,” 

NACA Annual Report for 1918.

OFFICE OF AERONAUTICAL INTELLIGENCE.

In January, 1918, the need for a central governmental depository in Washington

for scientific and technical data relating to aeronautics was recognized, and the

Aircraft Board suggested that the National Advisory Committee for Aeronautics

was the logical governmental agency for the collection and classification of such

data to be made available to the military and naval air services in this country.

This committee, accordingly, established an Office of Aeronautical Intelligence

and adopted rules and regulations for the handling of its work.

The committee has made the necessary arrangements at home and abroad

for the collection of such data. There are many sources of obtaining such information,

the chief at the present time being the research information committee, organized

under the National Research Council in January 1918, by funds provided by the

Council of National Defense. It consists of the Director of Military Intelligence,

Director of Naval Intelligence, and Dr. S. W. Stratton as chairman.

The purpose of the research information committee is to serve as a collector

and distributor of scientific and technical information regarding all war problems.

Special committees stationed at London, Paris, and Rome collect information

regarding all phases of the scientific and technical study of war problems and

transmit the same to the central committee in Washington for distribution to the

interested services. Similarly, these special committees receive information from

Washington and transmit the same to the interested services abroad.

Since February, 1918, Dr. William F. Durand, chairman of the National

Advisory Committee for Aeronautics, has served as scientific attaché to the

American Embassy in Paris, representing the National Research Council on this

research information service, and has, in addition, acted as special representative

of the Aircraft Board at the International Aircraft Standardization Conferences in

London in February and in October, 1918, besides serving as a special liaison officer

in aeronautical matters between France and the United States.

In September, 1918, Dr. W.C. Sabine, head of the department of technical

information of the Bureau of Aircraft Production and a member of the National

Advisory Committee for Aeronautics, was placed in charge of the Office of
Document 2-9(a–c) 377

Aeronautical Intelligence of the National Advisory Committee for Aeronautics,

with the title of director of scientific and technical data.

Many valuable documents dealing with important research problems in aeronautics have been secured by the Office of Aeronautical Intelligence, and copies

have been distributed to those concerned with the problems involved.

The committee has established in connection with its Office of Aeronautical

Intelligence, and particularly for the use of its engineering staff, a small selected

library, containing the most useful and valuable aeronautical and technical books

and publications.

Document 2-9(b), John J. Ide, excerpts from 

“Report on Visit to England, July 1–22, 1921.”

American Embassy, 

7 Rue de Chaillot, Paris, XVIe 

August 4, 1921.

CONFIDENTIAL

From: Technical Assistant in Europe, U.S.N.A.C.A..

To: National Advisory Committee for Aeronautics, Washington, D.C.

Subject: Report on Visit to England, July 1–22, 1921.

On July 1st I went from Paris to London.

R.A.F. Pageant.

On July 2nd I witnessed the R.A.F. Pageant at Hendon. The Pageant was a

remarkable display of the proficiency attained by the Royal Air Force in formation

flying, fighting, stunting, and bombing. The airplanes used, with one exception,

were standard service types developed during or shortly after the war. The exception was the Siddeley “Siskin,” which replaced the Westland “Wagtail” in the mock

duel with the Nieuport “Nighthawk.”

Siddeley “Siskin”.

The Siddeley “Siskin” (Figs. 1 and 2) has been built by the ArmstrongSiddeley Company of Coventry. It is a single-seater fighter, originally designed to

take a 320 HP A.B.C. “Dragonfly” radial engine. After the failure of this engine

to fulfill expectations, the design of the “Siskin” was slightly changed to accommodate the Siddeley 300 HP 14 cylinder radial engine. This engine, although

considerably heavier than the “Dragonfly,” is very reliable and develops its rated

power. The “Siskin” clearly outmaneuvered the “Nighthawk” in the mock fight.

As seen from the illustrations, the “Siskin” has one pair of inclined struts on

each side of the fuselage. Ailerons are fitted only to the upper plane which has a

certain amount of overhang. Two sets of struts run from the fuselage to the upper

plane, forming two W’s.
378 Chapter 2: Building a Research Establishment

Tests have been discontinued for the present with a single cylinder watercooled engine of 8 x 11 in. bore and stroke. It has developed 120 HP and there

are rumors that Beardmore is going to construct a slow speed ungeared airship

engine of six of the cylinders, the total weight to be 1600 lbs. Tests are proceeding

with direct fuel injection with a monosoupape air-cooled cylinder. The fuel is forced

into the cylinder under pressure, mixing with air sucked in through the valve.

I saw a Siddeley 150 HP 7 cylinder radial engine being tested. The Siddeley

radials, designed by Capt. Green, are very highly considered at the R.A.E. While

fairly heavy, the 150 HP model weighing 400 lbs. complete, they are very reliable.

The R.A.E. is still occupied with redesigning the A.B.C. “Dragonfly” engine.

As redesigned, the aluminum heads overlap the steel cylinders by 1 inch. The

heads have fins to assist cooling. The crankshaft and master rod have been made

heavier, and the induction system is quite new. Six of these engines have been finished

to be fitted to Nieuport “Nighthawks.”

A universal engine test bench, similar to the standard type but lightened, has

been constructed for the purpose of being installed in a Handley Page, the fuselage

of which has been fitted with an aluminum lined chamber to take the bench. A

small propeller, placed in the nose of the fuselage, is to be connected with the

engine under test. Mr. Smith stated that it was possible that tests with this apparatus

might not be carried out as one of the engine testing rooms is to be converted

into an altitude chamber, Squadron Leader Norman having studied the installation

at the Bureau of Standards while in America.

Aerodynamical Department.

I was taken through the 7 x 7 ft. and the 4 x 4 ft. wind tunnels. The screen

fitted in the newer 7 x 7 ft. tunnel, which has an engine of 200 HP, effects a saving

of power in the order of 15% by smoothing out the air flow. This screen consists

merely of a brick wall in which there is an air space between each brick.

Considerable work has been done in propeller design for wind tunnels.

Contrary to expectations, a four-bladed propeller gave more even flow than one

with six blades.

Observations have been made of the bending of propeller blades. Small white

squares have been marked along the otherwise black blades

of a propeller. The bending effect at various speeds has

been observed by means of reflected light. These experiments have come to a standstill owing to inability to express

mathematically the curve of the blade.

A small propeller has been enclosed in a box suitably

shaped on the inside so that the propeller makes its own air.

The section of the box is shown in the sketch given herewith.
Document 2-9(a–c) 379

Through windows on the side of the box the behavior of the air stream is

observed by the movements of threads suspended from another thread.

The experiments in recording the pressures along propeller blades have been

interrupted by an accident, the plate holding the manometers having broken

loose and smashed them. Contrary to previous reports, no difficulty was experienced with fastening the tubes to the propeller blades.

[ . . . ]

National Physical Laboratory.

On July 19th I visited the National Physical Laboratory at Teddington, where

I was taken through the wind tunnels by Mr. Nayler.

The 7 x 14 ft. wind tunnel has been completed and is in operation. The

power is supplied by two 200 HP engines with a synchronized gear which has

been developed by Vickers. A perforated brick wall, similar to that used at the

R.A.E., divides the room into two sections. The principal advantage of this wall

according to Mr. Nayler, is the fact that the wind tunnel can be made very much

shorter with it than without it, thus saving a considerable amount of space. No

balance has yet been installed in this tunnel. At present the 7 x 14 ft. tunnel is

being used for the measurement of rotary derivatives, such as the rolling due to

rolling (Lp), the yawing due to rolling (Np). and the rolling due to yawing (Lr). A

model of an S.E.5 suspended on wires as shown in the accompanying sketch, is

used for these measurements.

The amplitude of yaw or roll is ascertained by measuring the movement of a

spot of light reflected from a lamp by a mirror on the side of the fuselage to a

strip of thin paper placed at the observer’s station at the side of the tunnel. The

model is placed in motion by moving the arm (E), to which one end of the wire

running thwartships above the model is secured, there being a spiral spring at the

other end of this wire.
380 Chapter 2: Building a Research Establishment

One of the 7 x 7 ft. wind tunnels is being used for pressure plotting over a

model rigid airship hull of the R 33 type. Mr. Nayler stated that this test is a result

of the fact that the bow girders of several Zeppelins collapsed when making turns

at high speeds. Although the British had as yet experienced no trouble from this

source, it was desired to ascertain the pressures to which the airship was subjected.

In another 7 x 7 ft. tunnel there is being conducted a series of tests for thrust

and torque of a family of air screws. There are six air screws in the family, all having

the same section but with various pitch diameter ratios. The diameter of all the

air screws is 3 ft. 6 in.

Mr. Nayler also conducted me through the material testing laboratory. A new

method of fatigue testing of metals has been developed by Mr. Gough of the

N.P.L. It is expected that a report of this method will shortly be published in “The

Engineer,” as the manuscript has been accepted.

By Mr. Gough’s method, the ultimate strength of the material under test can

be determined in about 15 minutes instead of the considerable number of hours

necessary by the present methods. The new method is based upon the principle

that a change in molecular construction resulting in an increase in the amplitude

of vibration occurs after a short period of test. Light is employed for the measurement of the vibrations.

On July 22d I returned to Paris from London.

Respectfully,

[signed] John Jay Ide.

Document 2-9(c), John J. Ide, 

“Report on Wind Tunnel at Issy-les-Moulineaux,” 1921.

December 8, 1921

From: Technical Assistant in Europe, U.S.N.A.C.A.

To: National Advisory Committee for Aeronautics, Washington, D.C.

Subject: Wind Tunnel at Issy-les-Moulineaux.

I recently visited the wind tunnel under construction at the headquarters of

the French Aeronautical Technical Service at Issly-les-Moulineaux outside the

gates of Paris. This tunnel is housed in a building of brick, steel and glass about

100 ft. wide and 210 ft. long which was almost completed at the time it was decided

to use it for a wind tunnel. The building is not particularly well adapted for the

purpose having numerous columns and trusses which project into the interior

and impede the smooth flow of air around the tunnel. Also, not much advantage

can be taken of good atmospheric conditions by admitting outside air as there is

only one large door which is at the entrance cone end.
Document 2-9(a–c) 381

The tunnel itself, of the Eiffel type, is constructed entirely of reinforced concrete

and it was made to the designs of the Aerodynamical Section of the Technical

Service by the company of which M. Caquot, formerly director of the Technical

Section, is the head. The tunnel is in a large cement pit about eight feed deep and

taking up the entire floor space of the building with the exception of gangways

along the sides and ends. The tunnel is supported by two concrete walls running

longitudinally and about eight feet high leaving a free air passage under the tunnel.

The entrance nozzle is set back very far from the front end of the building. The

section of the outer walls of the collector has been made square instead of circular

and of a width equal to the diameter of the front end of the collector. This permits

the outer walls of the collector to be parallel to the walls and floor of the room

and also eliminates any break in contour caused by the experimental chamber. Aft

of the latter, the outer walls are gradually faired into the diffuser.

The diameter of the tunnel at the experimental section is 3 meters (9.84 ft.)

and at the propeller end 7 meters (22.96 ft.). The propeller itself is to have 6

blades with square tips and each blade is to be an arc of a circle. The pitch of the

blades will be variable, though not while in motion. It was stated that the efficiency of the propeller was in the neighborhood of 75 per cent. The propeller will be

driven by an electric motor of 1000 H.P. which it is expected will enable a speed

of 80 meters (262 ft.) per second to be realized.

Behind the diffusor is the concrete stand for the motor. In order to change

the direction of the air leaving the diffusor the two forward faces of the stand are

curved thus in plan:
382 Chapter 2: Building a Research Establishment

It is proposed to continue these curves upward and outward by wooded partitions.

Entrance to the experimental chamber is by means of a passage with a staircase

arranged in the thickness of one of the supporting walls of the tunnel. There are

two doors to insure an air lock. The chamber itself is very large being roughly a

cube of about 20 ft., a side into which project the ends of the diffusor and collector.

The only natural light is that which comes through the latter. In the centre of the

floor is a square trap closed by a platform. When it is desired to have large models,

etc. brought into the experimental chamber, movement of a lever lowers the platform

sufficiently for it to be rolled clear of the opening on rails attached to the inner

faces of the two longitudinal walls below the tunnel.

Arrangements will be made so that the tunnel can be partially or completely

closed at the experimental section if desired. There are a number of hooks flush

with the concrete surface of the diffusor and collector cones near the experimental

section. These hooks can be pulled outward and to them can be attached the supports

of the cones of a small tunnel of 80 cm. (2.62 ft.) diameter placed concentrically

with the large tunnel. By using the same propeller and the power available for the

large tunnel it is expected that a speed of 400 meters (1312 ft.) per second will be

reached by the 80 cm. tunnel.

The model suspension will be by wires instead of by a spindle. It is understood

that the balance will be of a dynamometric type having various gauges to which

the wires supporting the models will be attached, according to the strength of the

forces to be measured.

It is hoped to have the wind tunnel completed by July 1922.

[signed] John Jay Ide.
Document 2-10(a–b) 383

Document 2-10(a–b)

(a) D. W. Taylor, letter to Frederick C. Hicks, 

9 December 1919, Hunsaker Collection, Box 3, File H.

(b) Edward P. Warner, excerpts from “Report on German 

Wind Tunnels and Apparatus,” October 1920, Box 18, 

Folder 24, McDermott Library Archives, University of

Texas–Dallas. [Also published, with the same title, in 

Aerial Age Weekly (15 November 1920): 275–277.]

While the NACA worked to gather information through its Office of

Aeronautical Intelligence, other Americans with a particular interest in foreign

developments did all they could to stay abreast of these activities as well. U.S.

Navy officer Jerome Hunsaker was among the first to cultivate friendships with

aeronautical experts outside the United States. After a tour of the primary

European laboratories in 1913, he maintained these relationships during and

after World War I. As the 9 December 1919 response—from his superior Rear

Admiral D.W. Taylor to an inquiry from Congressman Frederick C. Hicks—shows,

the expert intelligence provided by sources like Hunsaker proved useful to politicians

and policy makers as well as researchers. Of particular interest are the comments

on Japan’s purchase of French technology to aid its own fledgling aviation industry.

Although relative newcomers to aeronautics in 1919, Japanese progress over the

next two decades would provide the island nation with formidable aerial weapons

for World War II.

Edward P. Warner, an aviation consultant who had been the NACA’s first chief

scientist, prepared an independent report to the NACA covering his 1920 inspection

of German laboratories at Göttingen, Aachen, and Dessau that he also published

in Aerial Age Weekly later that year. Coverage of the Aachen and Dessau installations

was brief, but Warner went into considerable detail concerning Ludwig Prandtl’s

second wind tunnel at Göttingen. The detail was warranted, for this was the first

truly modern, closed-circuit wind tunnel, with efficient turning vanes in the corners

and a variable cross-sectional area for improved air management, lower power

consumption, and reduced turbulence. Prandtl’s balance apparatus for this tunnel

also impressed Warner with its accuracy and simplicity of operation.
384 Chapter 2: Building a Research Establishment

Document 2-10(a), letter from D. W. Taylor to Frederick C. Hicks, 1919.

December 9, 1919

My dear Mr. Hicks:

Referring to your letter of the 4th inst., relative to the Aviation Program of

Foreign Countries, my information in regard to Aviation in Japan is not very full,

but it is possible that Captain Craven can give you something additional. The last

we have heard about Japan was that they had a mission of some 24 officers of the

army and navy, together with civilian professors representing the engineering colleges in Japan, which has made an inspection of aviation in England, France,

Italy, and the United States and has now returned to Japan and, presumably, will

make definite recommendations.

There is a rumor that the Japanese have purchased the rights to manufacture

one or two French aviation engines developed during the War and are equipping

one of their arsenals to turn out this engine. I understand that French experts

have gone, or will go, to Japan to assist in this development. The Japanese are

also supposed to be purchasing in France planes left over as excess War material.

I have no information that they have purchased anything in the line of large flying

boats. I know that they made no attempt to do so while in the United States.

With regard to Italy, I don’t believe that the Government has under way any

military or naval program, but the Caproni Company is attempting to develop

their large bomber for passenger carrying with the idea of running a commercial

business for the expected tourists trade. The Italian Government is also rebuilding

one or more of their semi-rigid airships so as to fit them to carry a large number

of passengers. This appears to be an attempt to make some use of the excess

stocks of airships left over from the War.

In France such development as is proceeding appears to be entirely directed

toward commerce, and the French have arranged for a subsidy to concerns which

will maintain machines and aviators available for military purposes in time of war.

The French also are commencing the construction of rigid airships primarily for

commercial travel between France and Africa, but I understand the Government’s

connection is very close as the ships are being designed by the Technical Section

of the Army, but are to be operated for commercial purposes.

In England all seems to be in turmoil. As you know, General Seely under

Secretary of State for Air has resigned, giving as his reason the impossibility of the

existing arrangement which places the Royal Air Force under Mr. Churchill, the

War Minister. The opposition press intimates that Mr. Churchill having absorbed

the Royal Air Force is attempting by political maneuver to obtain the post of

Minister of Defense, and absorb the Admiralty in addition, thus carrying consolidation to the limit. The Royal Air Force started off the beginning of the year with
Document 2-10(a–b) 385

an ambitious program for the development of civil aviation, but due to the economic crisis their funds have been cut to about one half the original credit, which

appears to be no more than enough to wipe out outstanding war obligations and

close out their various contracts. The result is that building has stopped on practically all types, in particular the great program of rigid airships is suspended for

lack of funds. The only new airship building in England is R-38 which is being

completed for the United States Navy.

The Royal Air Force is under fire from three sides; from the public for gross

extravagance and bad administration and waste of public funds, because they did

not cancel war-time contracts with a firm hand, but have permitted certain

favored concerns to continue the production of aircraft contracted during the War

with a result that now the cut has come, the layoff of men is demoralizing, and the

amount of money already spent is wasted. The second attack comes from the

Aeronautical trade or industry, which objects to military control in the development

of commercial aviation and complains of the lack of results and positive action in

stimulating this development as promised. The third attack comes from those

interested in the efficiency of the Fleet with a charge that since the Air Ministry

has taken control no progress has been made in Naval Aviation, but on the contrary conditions have become progressively worse. The development of large flying boats has been allowed to come to a stop because of lack of sympathy with the

type in the Royal Air Force. The flying boat type and the construction of airships

of the Zeppelin type for use of the Fleet has been stopped for lack of funds

because the Air Ministry has frittered away its fund on other things which are of

no benefit to the Navy, so it is alleged.

The net result in England is a very pretty row and it is difficult to see exactly

what is going on because of the smoke. I enclose, herewith, extracts from the

British aeronautical press whose tone will give you an idea of conditions.

With regard to your request for reports of the National Committee for

Aeronautics, I forward, herewith, the reports mentioned. The correct title of this

Board is “National Advisory Committee for Aeronautics,” as given by the Sundry

Civil Act for 1920. This Committee was originally called “Advisory Committee for

Aeronautics” in the Naval Bill of 1916 which carried funds for the first year. This

title was changed because of confusion with a British Committee of identical title.

I am not in very close touch with the Helium Plant which comes under

Admiral Griffin, but I understand that a Helium Board which coordinates the

interests of the Army and the Navy in this matter is directing the development of

this project, and that things are going along in accordance with the agreed plan,

and so far as I know without any friction or difficulty. You know there have been

some difficulties in the past with the Bureau of Mines of the Interior Department

which was urging a technical process for the separation of Helium which other
386 Chapter 2: Building a Research Establishment

experts did not favor in war time as it was experimental. Possibly, what you have

heard is a result of this.

Very respectfully,

[signed] D. W. Taylor.

Document 2-10(b), Edward P. Warner, excerpts from 

“Report on German Wind Tunnels and Apparatus,” 1920.

REPORT ON GERMAN WIND TUNNELS AND APPARATUS

By

Edward P. Warner

The National Advisory Committee for Aeronautics, in view of the important

research work that has been conducted in the German wind tunnels at Göttingen,

Aachen, Dessau, and Friedrichshafen, requested Professor Edward P. Warner, the

Committee’s Acting Technical Assistant in Europe, to submit the following report,

descriptive of the above mentioned wind tunnels, together with methods of operation and details of the apparatus used.

It is appropriate that any discussion of aerodynamical work in Germany

should begin with Göttingen and with Prof. Prandtl, where the first serious work

of the kind was undertaken, before the war, and where the most extensive and

interesting results have been obtained both in respect of wind tunnel testing and

of purely mathematical investigations.

There are, at the present time, two wind tunnels at the Göttingen laboratory,

one being the original 1-meter tunnel of pre-war days, but moved into a new

building; the other a newer installation 2 meters in diameter. During the war both

tunnels were kept in service, but that is impossible with the present shortage of

funds and of employees, and the small tunnel is now seldom used. The small tunnel

was described by Dr. Zahm in his report to the Smithsonian Institution in 1913,

and need not here be gone into in detail. The newer and larger one is built on

essentially the same principle, but with substantial modification in detail. In the

first place, the plane of the closed circuit which the air follows has been turned

from the horizontal to the vertical, the return passage being underground. The

whole tunnel, except the portion immediately around and adjacent to the test section,

is made of concrete, so there is no question of air-tightness.

The section, 2 meters in diameter at the throat, expands in each direction to

a diameter of 4.5 meters before the first turns are reached, and this size is maintained all the way around the return, making an area ratio of 5 to 1. The air is still

guided around the turns by means of vanes, but these vanes are no longer

adjustable in position or inclination to secure regularity of flow, such adjustment

having been found unnecessary, nor are they now made in honey comb form.
Document 2-10(a–b) 387

They are cast in the concrete, are of crescent form with a maximum thickness of

about one-fifteenth of the chord, which is about 18 inches, and are spaced

approximately 8 inches apart. The vanes are not arranged to cause all the particles of air to swing about a common center, as might perhaps be expected, but are

all of the same size and all curved to the same radius, so that the outside boundary

of the tunnel comes to a corner and the section is increased at the turns.

The stream is not enclosed at its throat, although a tube is available which can

be put into place to partially restrain the flow if desired. The stream being

enclosed at every other point of its travel, the pressure at the throat is the atmospheric pressure in the free air, while that in the return passage is raised above

atmospheric, and no experimental chamber or air-lock is necessary.

The only means provided for regularizing the flow is a honeycomb placed in

the large section of the tunnel, before the contraction to the throat begins. This

honeycomb is made up of metal plates separated by corrugated strips, so that the

cells have a rather eccentric form, approximately semi-circular. The mean effective

radius of these cells is about 3⁄8", the length 8 inches. Prof. Prandtl lays great stress

on the value of placing the honeycomb where he has it, before the entrance cone,

in order to avoid turbulence and minute eddies which he believes are produced by a

honeycomb of the ordinary type. Admittedly there is some loss in regularity of

flow as ordinarily judged when the honeycomb is moved farther away from the

throat, yet the regularity at Göttingen seems to be very good. Incidentally, I found

Capt. Toussaint quite convinced of the merits of Prandtl’s placing of the honeycomb and preparing to adopt a similar disposition at St. Cyr, and the matter was

also receiving serious consideration at the N.P.L.

The current is produced by a four-bladed wooden propeller of ordinary type,

driven by a 300 H.P. electric motor. The maximum wind speed obtainable is 50 m.

per sec., which, if the motor is working at rated power without overload, corresponds

to an energy factor of 1.36 (a result not in any way remarkable). The motor is outside

the tunnel and drives the propeller by a shaft passing through the wall at the turn.

The forces and moments on the models are ultimately weighed on ordinary

platform balances, the only special apparatus being that which transmits the

forces from the roof of the tunnel, or, more properly, from the platform erected

above the airstream, down to the balances which are placed conveniently for the

observers standing on the floor. The apparatus is primarily of interest in that the

support in all cases is solely by wires, no spindles being used under any conditions.

Furthermore the measurements of lift and drag are direct and entirely separate,

no moments entering in until the balances are reached. 

In the case of an airship model or other similar streamline body, the support

is by five wires. Four of these are arranged in two pairs the two members of a pair

attaching to the model at the same point and then diverging, their plane being
388 Chapter 2: Building a Research Establishment

perpendicular to the direction of the wind. One pair is attached about a quarter

of the way back from the nose of the model, the other about three-fifths of the

way back. The fifth wire is attached at the same point as the forward pair, and runs

forward exactly parallel to the wind direction. At a point about two feet forward

of the nose of the airship this wire terminates in a small ring to which are also

fixed two other wires, one running vertically upwards and the other obliquely

downwards and forwards to the floor at the end of the entrance cone. This diagonal

wire is simply fixed to a screw-eye in the floor, while the vertical wire is attached

to a crank on a rocking beam, another offset crank on which bears against a vertical

rod running down to the pan of the platform balance. The pull in the vertical wire

can thus be weighed directly, and, knowing the directions of the other two wires

attached to the ring, the pull in the horizontal wire, which is equal to the drag of

the model, can be calculated. As a matter of fact, I believe, although I am not certain,

that the oblique wire runs off at just 45°, so that the balance reads the drag directly

with ordinary weights. The total pull in each pair of vertical wires is similarly

measured, the two members of a pair being attached to two cranks on a single

beam so that the total is obtained directly. The lift on the model is then equal to

the sum of the two readings (correction having been made for the tensions due to

the weight of the model), and the pitching moment can be directly calculated

from their difference. The angle of attack is adjusted by raising and lowering the

rear beam and wires. Of course, as the angle is changed the horizontal distance

between the points of attachment of the two sets of wires changes, and, if the rear

beam were raised or lowered vertically, it would be impossible for both pairs of

wires to remain truly vertical. The two beams are therefore connected together by

a link forming, with the two sets of wires and the line connecting their points of

attachment in the model, a parallelogram. The five wires suffice to restrain the

model from all motions except those in roll, and these are resisted by its own

weight. As an additional safeguard against rolling, a wire may be attached to the

lower surface of the model and run downwards and backwards over a pulley, a

heavy weight being hung at its free end, thus introducing a constant correction to

both lift and drag. Despite this precaution, the model of an airship which was

being tested while I was at the laboratory several times started oscillating badly

and it was necessary to reach into the current with a stick and steady the model

just before the final balance readings were taken.

In the case of wings, the same balances are used and the method is essentially

the same, but there are differences in details of attachment. The model is made

with four hooks cut from thin sheet metal mounted on it, three of these hooks

being distributed along the leading edge and the fourth carried by a rod which

projects about one and a half chord lengths to the rear of the trailing edge. The

two hooks mounted near the tips on the leading edge carry wires running vertically
Document 2-10(a–b) 389

to the forward lift beam, the center hook carries the wire which runs forward to

measure the drag, and the rear hook, on the rod, forms the point of attachment

for two wires running off in a V to the rear lift beam. The model is then definitely

fixed except in regard to yaw. Should any particular model show a tendency to

oscillate in that respect it can easily be checked by running two wires from each

corner of the leading edge to the forward lift beam, the whole set of four then

appearing from the front as a W. This is to be done as a regular practice at the

Zeppelin laboratory.

The spindle correction for wings is obtained by substituting for the model a

T made of two pieces of stream-line wire about 5

⁄8" x 3⁄16" in section. The cross-arm of

the T has a length equal to the span of the aerofoil, the shank a length equal to

the distance between the leading edge of the aerofoil and the rear point of attachment used for the determination of pitching moments. This T is hung up in

exactly the same manner as the model, and the drag measured. The resistance of

the stream-line wires being known with fair accuracy by computation and by previous experiment, the effect of the supporting wires can be determined at once by

subtraction. In the case of an airship model the method is the same, but a single

pointed rod is used in place of the T, the rod being held parallel to the wind direction.

The method is not absolutely satisfactory in this case, as no allowance is made for

the interference between the supporting wires and the model, which is quite different

from the interference between the supporting wires and the rod, but the per centage

error from this cause is undoubtedly very small.

The wing models in use at Göttingen are all made of plaster, scraped to form

while still soft. One or, more usually, two aluminum plates are used as the core.

The finish is excellent, as good as I have ever seen on plaster models, although I

think it is no better than on the best of the models made for the Garden City laboratory. The standard size of wing model at Göttingen is 1 m. by 20 cm., an aspect

ratio of 5.

The method of regulating the wind speed is of particular interest, as it is

entirely automatic and seems to work with absolute perfection. The speed is fundamentally measured, in accordance with the usual practice by measuring the

pressure difference between the large and the small sections of the tunnel. The

pressure difference is measured by leading the pressure which differs from atmospheric in under a cup the rim of which dips in oil, and by weighing the “lift” on

this cup with a balance, just as is done at the Leland Stanford tunnel. In this case,

since the pressure under the cup is greater than atmospheric, the weights have to

be hung on the same side of the balance axis with the cup. On the other arm of

the balance is an oil dash-pot, while a long pointer runs downwards from the balance axis and moves between two contacts. As the pointer makes contact on one

side or the other a servo motor is started in one direction or the other, steadily
390 Chapter 2: Building a Research Establishment

moving a rheostat and increasing or decreasing the motor speed, in such a way

as to bring the wind speed back to normal, until the contact is broken and the

pointer once more floats freely. In order to secure a greater range and a more

sensitive maintenance of speed, the pointer is made with a subsidiary contact in

the form of a light flat spring on each side of the main contact, and these subsidiary contacts actuate a fine rheostat. If the deviation from normal speed is really

large, the unbalancing of the beam overcomes the resistance of the light contact

spring and the beam moves, far enough to bring the main pointer into contact

with its stops and actuate the coarse rheostat. In order to prevent the fine rheostat

being brought up against its stops, a contact is automatically made when the handle

draws near to the limit of its travel and this moves the coarse rheostat one step.

The whole adjustment is now automatic. There is a push-button starter, and, the

motor once started, the operator has only to hang the proper weight on the balance

(the weights are marked directly in meters per sec.) and go away and 1eave it.

Although it appears that not much stability work has been done at Göttingen,

a balance for measuring all forces and moments simultaneously is now under

construction and is nearly completed. For this purpose, the model is hung from

a platform, the model being heavily enough ballasted to keep all the suspension

wires taut. These suspension wires are rigidly attached to the platform. The platform

is held in position by six wires, two running vertically, two parallel to the wind

stream, and the remaining pair horizontally and perpendicular to the tunnel
Document 2-10(a–b) 391

axis, and the simultaneous measurement of the tensions in all these wires permits

calculation of the six forces and moments acting. This is much the same in principle

as the roof balance which has long been used for certain special experiments at

the N.P.L. and to the all-wire-support roof balance which is now being designed

at the R.A.E. The most interesting and original feature of the Göttingen balance

is the automatic adjustment of the six balances, all of which are arranged in a row

before the operator.

[At this point the author goes into great detail about the design of the wind tunnel balance,

which is omitted here.]

No propeller testing has been done at Göttingen recently, but a propeller balance

of unique type has been designed and partially constructed. The propeller under

test will be driven through bevel gears and a vertical shaft from a motor outside

the wind-stream, and the whole apparatus, motor, transmission, and propeller,

will be carried on floats in a tank of water or oil. The thrust is to be measured by

the combined pull in two wires running parallel to the wind direction, the torque

by the pull which has to be applied to a vertical wire attached to one side of the

floating platform in order to keep that platform horizontal. The cross-wind force

and pitching and yawing moments can also be obtained with ease if desired by

running other wires in suitable directions. In order that the measurements of

torque may be sensitive, the inherent stability of flotation must be small, so that

the angle of tilt due to the torque would be large were it not for the restraining

wire. In order to accomplish this the metacentric height must be reduced or, since

metacentric height is equal to I/V and V is fixed by the weight of the apparatus,

the moment of inertia of the water-line section about a longitudinal axis must be

made as small as possible without actually bringing the metacenter below the center

of gravity. This is done in the Göttingen apparatus by making the floats proper of such

a size that they will be completely submerged and the surface of the water will only

be broken by the tubes which connect the floats to the platform. The propellers

tested are to be one meter in diameter.

Great confidence is felt at Göttingen that the Prandtl theory of wing action,

together with the work done along the same lines by Munk and Betz, now furnishes

a practical tool for the engineer. There is no question of the consistency of the

results obtained within a certain field, and notably in predicting the effect of

changes in aspect ratio. A series of tests on wings of the same section but of different aspect ratios was recently made, and when the results obtained were

reduced to aspect ratio 5 by Prandtl’s formulae all the points lay, well within the

experimental error, on a single curve. In view of this, Prandtl considers further

testing for aspect ratio effect on new sections as quite unnecessary.
392 Chapter 2: Building a Research Establishment

Aerodynamic Work at Aachen.

A regular course in aerodynamics is given by Prof. Karman at the Technische

Hochschule at Aachen, and there are a number of students undertaking investigations in that field. The laboratory equipment, however, is very limited. The

only wind tunnel available is on the roof of the building and takes its air from the

free atmosphere, with no protection from gusts. It is also very short, and the flow

is so irregular that it would be impossible to work with wings or, indeed, to do any

work at all with a balance. The tunnel is two meters in diameter and has a 100 H.P.

motor, realizing a speed of 33 meters per sec. There is no expansion in the exit cone,

the sirocco fan which produces the current being of the same diameter as the

throat of the tunnel. The experimental chamber is enclosed as in the Eiffel type,

and the irregularity of flow in the stream is attested by a pronounced circulation

of air all around the chamber. The honeycomb cells appear too large for best

results, being about eight inches in diameter and two feet long. The most interesting thing about the Aachen tunnel itself is its noise-making characteristic. Up

to about 25 meters per sec., while not by any means silent, the amount of noise is not

unusual for the corresponding size and speed. At that speed there is a sudden

change, and above 25 m. per sec. there is an ear-splitting shriek totally unlike

anything that I ever heard from a wind tunnel before. The most peculiar thing

about it, however, is that if one thrusts an arm into the stream until the hand is near

its middle the high-pitched noise instantly stops, recommencing as soon as the

arm is withdrawn. The question of noise in wind tunnels is at present considered

as a vital one all over Europe, having come up for discussion without any effort

on my part at Aachen, St. Cyr, Teddington, and Farnborough, and a multitude of

different causes are ascribed. The problem is a very interesting one allied to, but

more complex than, the general question of propeller noise, on which Bryan and

Lanchester have already done some work and on which the former presented a

paper to the British Association last year. Apparently no one has even attempted to

explain completely the strange behavior of the Karman tunnel, but it is evidently

due to the formation and dissipation of eddies with an accompanying strong

reduction of pressure and density. The sound is not unlike the whine of a highvelocity bullet as it passes overhead.

At the present time the Aachen tunnel is working chiefly on the heat dissipation

from and the flow of air through radiators. In carrying out these experiments a

section of the radiator is closed off from the remainder, so that no water can flow

through it, and minute holes are made in the sides of these isolated passages.

Connecting the holes thus made to a gauge, the static air pressure is found at several

points between those where the air enters and where it leaves the radiator, and

the resistance can be studied and computed from the pressure gradient thus

found, in the manner commonly employed in examining the flow of fluids through
Document 2-10(a–b) 393

pipes. Water is pumped through the radiator at variable speeds and variable inlet

temperatures and the heat dissipation is computed in the usual way.

Prof. Karman anticipates doing some work at very high velocities with the aid of

a l00 H.P. centrifugal compressor delivering air at a pressure of one-half atmosphere,

but no start has been made as yet.

Karman is now working on the theory of turning wings, or wings which rotate

simultaneously, but not necessarily with constant or equal angular velocities,

about an axis in the plane of the chords and about another axis parallel to the first

but at a considerable distance from the plane of the chords. If the two rotations

are properly adjusted to each other there is a lift and also a driving force, the

action being something similar to that of flapping flight and eliminating the need

for a propeller. The investigations now being made are directed towards finding the

most efficient type of rotation, and will be followed by actual experiments with such

wings. Another professor at Aachen is specializing in the study of the equations of

viscous flow and attempting to apply them to aircraft parts, apparently proceeding

somewhat along the lines on which Bairstow is now working.

A small water-channel is being used by one of Karman’s research students for

photographing the flow through diverging and converging passages of various sorts

with a view to analyzing the flow in the exit and entrance cones of wind tunnels.

Aluminum powder is used for making the flow visible. The most striking thing

about the results so far obtained is the abrupt change in type of flow which appears

about ten seconds after the motion has commenced, the flow initially “filling” a

diverging cone and then breaking away from the walls, passing straight down the center

as a stream of approximately constant cross-section with a region of dead-water on

each side. Unfortunately, no moving pictures have as yet been taken to show the exact

mechanism of the change. The alteration of the flow probably depends at least in

part on the cessation of acceleration and the establishment of steady conditions.

During the war Prof. Karman was in Austria and had there a very large wind

tunnel, which, however, does not appear to have been run for very long or in a very

scientific manner. The tunnel was 3.2 meters in diameter, and propellers up to a

diameter of 2.8 meters were tested, the ratio between these figures being far larger

than has ever been considered safe elsewhere. The speed attained was 40 meters

per second. The propeller thrust and torque were measured by the pendulum

method, the whole apparatus being carried by four parallel wires. The tunnel was

apparently rather short in proportion to its diameter, and the motor driving the

propeller under test and the supporting wires were placed outside the mouth, a

long shaft projecting along the entrance cone to drive the propeller. The whole

tunnel was on wheels so that it could be moved to one side when the pendulum

apparatus and driving motor were to be used for making static tests. The cost of

the tunnel was one million kroner, or $200,000 at normal rates of exchange.
394 Chapter 2: Building a Research Establishment

The Junkers Laboratory at Dessau.

This wind tunnel is hardly to be compared with Prandtl’s, as the aim in its

construction was entirely different. The Junkers laboratory is admittedly solely

commercial in its aims, its only object being to furnish data for improving the

Junkers airplanes. None of the work done there has been published, and there is no

intention of publishing any. The experiments at Dessau have been chiefly concerned

with the development of improved sections for cantilever wings, although a little

stability testing of an elementary sort has been undertaken, and the constant attempt

has been to speed up and systematize the making of routine tests with a moderate

degree of accuracy, rather than to seek increased refinement in measurement.

The Junkers tunnel is octagonal in section, but the octagon is not a regular

one, the breadth of the stream being 1.2 meters, the height only 0.9. A fan is used

instead of a propeller for producing the air current. The tunnel is of true Eiffel

type as regards the experimental chamber, and a couple of inches of water is left

standing on the floor at all times to minimize leakage and to suppress the dust.

The drive is by an electric motor of 100 H.P., and the maximum wind-speed is 39

meters per second, giving an energy ration of .497/. 

The steadiness of flow in the Dessau laboratory seems distinctly inferior to

that at Göttingen, and there is no question that there is more disturbance of the

air in the room and spreading of the stream. The honeycomb is similar to that

used by Prof. Prandtl as far as the form and arrangement of the cells are concerned, but it is placed at the beginning of the throat instead of at an enlarged

section. The cells are 1

⁄2" in mean diameter and 2" long.

The balance at the Junkers laboratory is of interest chiefly because it is completely autographic. The measurements depend entirely on springs, no weights

being used. The balance carriage slides longitudinally and is carried on two steel rods

running parallel to the wind direction. The weight of the carriage is considerable,

and the friction in sliding on fixed rods would be intolerably large, but this friction

is practically eliminated by rotating the rods at high speed through a belt drive—

a very ingenious and successful method. The longitudinal motion of the carriage is

proportional to the drag, and is transmitted through a linkage to a pencil which moves

vertically over a record-sheet. The lift is measured by the tilt of a beam which carries

the model and which is also restrained by springs, and is also transmitted through

a linkage to a pencil making its record on the same sheet as the first one. The angle

of attack is changed steadily and progressively by a motor which winds up a wire

attached to the trailing edge of the model, and which, at the same time, rotates

the drum carrying the record-sheet at a constant speed. The making of a complete

test requires only about twenty minutes. No attempt is made to keep the speed

constant automatically, the rheostats being set at a beginning of a run and then left

alone. It is assumed that the changes in speed due to voltage changes are negligible.
Document 2-10(a–b) 395

The wing models tested are made of wood, and painted so that I could not

examine the method of construction in detail. A very large number of thick wings

have been tested, at least a hundred models being stored in their cabinets at the

time of my visit, and work is still continuing in the effort to improve the present

Junkers wing. The best results obtained to date with thick wings at Dessau are:

max. 

L

⁄D 17.0, max. Lc .65, at 35 meters per second. The maximum lift coefficient is not in any way remarkable, and the high maximum L

⁄D is largely accounted for by the way in which the model was supported. All tests are made with the

aerofoil carried by a stream-line spindle about 3

⁄16" wide passing into the model at

the center of the span and near the leading edge, and it is well known that such

a support, when its resistance is corrected for in the usual approximate fashion,

leads to values of the drag which are far below the correct figures.

The Zeppelin Wind Tunnel at Friedrichshafen.

The only remaining wind tunnel of any importance is that which is under

construction, but not yet completed, for the Zeppelin Airship Company. To be

sure, there is a tunnel at Adlershof, but this is old and little used, and was fully

described in the report submitted by Dr. Zahm after his tour in 1913 and published by the Smithsonian Institution.

The Zeppelin tunnel has been designed by, and is being built under the

supervision of Dr. Max Munk, and is naturally similar in many respects to the

Göttingen installation, since it was at Göttingen that Dr. Munk received all his

aerodynamical training and much of the apparatus there was designed by him.

The Zeppelin tunnel, however, is considerably larger than either of those at

Göttingen, and will be the largest tunnel in the world from the time of its opening

until the new 7 x 14-foot channel at the N.P.L. goes into action. The diameter of

the wind-stream at Friedrichshafen is 3 meters. The drive will be by two Maybach

engines coupled together in tandem, delivering a total of 500 H.P., and a speed

of 30 meters per sec. is anticipated.

The most original feature of the tunnel design lies in the provision of air-tight

gangways, of much larger section than the tunnel itself or even than the large end

of the exit cone, for the return of the air. The principle is the same as a Göttingen,

but the mechanical execution is somewhat different, largely because of the great

size of the laboratory. There are two return passages, one on each side of the tunnel,

instead of a single one, and these passages take the form of gangways each about

three meters wide and six meters high, with air-tight windows and air-locks and

without any guide vanes at the corners. The passages are shaped at the ends so

that there will be as gradual a change of section and of direction as possible, the

whole, including the entrance cone, being made in concrete. The exit cone, however,

is of wood. Since the gangways are air-tight, the throat section can be open to the
396 Chapter 2: Building a Research Establishment

atmosphere, just as at Göttingen, and admission to the test room is perfectly free

at all times, no air-lock or other control being necessary. In order to permit access

to the test chamber there is a subway under each of the gangways.

The slope of the exit cone is small, the vertex angle being 7-1⁄2°, and the

length is not sufficient to give as large an area ratio as is the usual custom. The

length of the cone is to be 15 meters and the diameter of the propeller 5 meters,

the propeller being driven with the same gear reduction as is employed in the

Maybach engines on Zeppelin airships.

No honeycomb has been fitted as yet, and Dr. Munk hopes to avoid the use

of any straightening device, but his hopes apparently have no sound basis.

The measuring instruments will be of the same general type as those at

Göttingen, but naturally much stronger. The whole weighing apparatus is to be

installed on an overhead platform where the observers will work, the support

being by steel rails carried by concrete piers. The most striking feature about the

balance is its construction, which follows Zeppelin airship lines faithfully, the

cross-beams used for weighing the lift being built-up duralumin lattice girders.

The total weight of the moving parts will certainly be less than in any other balance ever built for so large a VL. Of the two bridges, the forward one will be fixed

rigidly to the rails, but the other will be mounted on wheels and will be allowed

to move longitudinally as the angle of attack is changed so that the horizontal distance between the two bridges will always remain equal to the horizontal distance

between the lower ends of the two sets of wires. The adjustment of the angle of

attack is by raising one of the bridges, the supports for which slide on vertical

rods. The bridge is raised with a cable which is wound up on a drum by turning

a graduated handwheel.

The speed is to be controlled automatically by the same method as that

employed at Göttingen, the servo motor operating the engine throttles instead of

a rheostat.

The Friedrichshafen laboratory will work for the parent airship company and

for all its subsidiaries, of which there are a considerable number, including the

airplane firm at Seemoos (formerly located at Lindau) where the Dornier flying

boats are built, and the aircraft company at Staaken, for which Rohrbach is the

chief engineer.

September, 1920.
Document 2-11 397

Document 2-11

“Free Flight Tests,” NACA Annual Report for 1918

(Washington, DC) pp. 20–21.

Like the British Royal Aircraft Factory, the NACA sought to develop “as complete

tests as possible of the performance, in all respects, of airplanes while in the air

under normal conditions,” and it established a subcommittee on free flight tests

to pursue that end. There was, however, a larger goal in the committee’s mind. As

this portion of the Annual Report for 1918 indicates, the committee specifically wanted to develop the means to correlate the “information gained from all sorts of

tests on the ground” with flight-test data to obtain not only a validation of

ground-based methods, but a synergy of laboratory and flight testing as well. 

Document 2-11, “Free Flight Tests,” NACA Annual Report for 1918.

Free Flight Tests

The general purpose of the work of the subcommittee on free flight tests is to

obtain as complete tests as possible of the performance, in all respects, of airplanes while in the air under normal conditions. The general purpose of these

tests is to supplement and make more valuable the information gained from all

sorts of tests on the ground, including tests of engines and tests of airplane parts

and airplane models in wind tunnels. It is obvious that the actual performance in

the air, when it becomes known, is the best possible basis for future progress. 

The committee now has, in a late stage of development, instruments for

recording in the air the torque and revolutions per minute of the engine, the

thrust of the propeller, the air speed, the angle of attack, and the inclination of

the wing chord to the true horizon. It is proposed to complete this development

as promptly as possible, and to get these instruments in action in the air, presumably

on a D.H.4 airplane, to determine the power-plant performance and the relations

in the air between the lift, drag, air speed, and angle of attack.

When such tests have been successfully demonstrated as possible, by making

them, the next steps on the program of the committee are to analyze the results

and show what conclusions can be drawn from them.

The committee then proposes, in due time, to extend the free-flight tests to such

quantities as will help to develop the stability characteristics of airplanes, possibly to

furnish some information as to the stresses in various parts of an airplane in operation.

To secure the necessary degree of accuracy and reliability in free-flight observations,

the new instruments have in each case been so designed as to give a continuous

autographic record.
398 Chapter 2: Building a Research Establishment

Document 2-12(a–b)

(a) Edward P. Warner, F. H. Norton, and C. M. Hebbert, 

The Design of Wind Tunnels and Wind Tunnel Propellers, NACA

Technical Report No. 73 (Washington, DC, 1919).

(b) F. H. Norton and Edward P. Warner, The Design of 

Wind Tunnels and Wind Tunnel Propellers, II, NACA Technical

Report No. 98 (Washington, DC, 1920).

Although American aeronautical researchers usually chose to pursue a more

empirically based path in designing wind tunnels than did their German counterparts, they were nevertheless interested in a thorough understanding of these

machines and the aerodynamic phenomena they could produce. During the

NACA’s early years, Frederick Norton and Edward Warner led an investigation at

Langley to determine the key aspects of wind tunnel design that engineers could

use with confidence. Their report, The Design of Wind Tunnels and Wind Tunnel

Propellers, published in two parts, clearly reveals the empirical approach to design

optimization employed by the Americans for many years, and it shows the limited

state of theoretical aerodynamics in the United States at the time. The publication

of these two technical reports also demonstrates the NACA’s commitment to making

useful information about experimental tools and methods as well as developments

in aircraft design available to the aviation community.

Document 2-12(a), Edward P. Warner, F. H. Norton, and C. M. Hebbert, The

Design of Wind Tunnels and Wind Tunnel Propellers, NACA Technical Report

No. 73, 1919.

THE ELEMENTARY THEORY OF THE FLOW OF AIR THROUGH

WIND TUNNELS.

If the air flowing through a wind tunnel and back through the room from the

exit to the entrance of the tunnel followed Bernouilli’s theorem with exactness,

there would be no change in the energy, possessed by a given particle of air,

except for the loss due to friction as the kinetic energy lost on issuing from the

tunnel would be restored in the form of pressure energy. The power required to

maintain the flow would then be

P=m x hf
Document 2-12(a–b) 399

where hf is the head (in feet of air) lost by friction and m is the mass of air flowing

per second. As the same mass of air must pass every point in the tunnel, the product

of mean air speed by cross-section area must be a constant for its whole length,

neglecting compressibility and changes in temperature during the passage. Since

the major part of the frictional losses occur in the reduced section of the tunnel

(provided that it is not very short and that the diffuser is not so constructed as

excessively to hamper the travel of the air from the tunnel back into the room), hf

would be practically independent of the size and angle of the exit cone, and the

power consumed would also be independent of these factors.

As a matter of fact, the conditions of flow are not simple enough to permit the

direct application of Bernouilli’s theorem. Borda has shown that the loss of energy

when fluid moving at high velocity in a pipe is discharged abruptly into a large

room or reservoir is equal to the kinetic energy initially possessed. The kinetic

energy is not converted into pressure energy as the theory indicates that it should

be, and it is therefore profitable to use an exit cone of considerable length, in order

that part of the kinetic energy may be saved by conversion into the potential form

before the sudden discharge into the room. The length to which it is desirable to

prolong the cone is limited by the growing loss by friction within the exit cone

itself. A more rapid conversion of the kinetic energy by increasing the vertex

angle of the exit cone is forbidden by the unwillingness of the air to change its

course suddenly and follow the walls of the exit cone. If the vertex angle be made

too large the effect is almost the same as that of an abrupt increase in cross section.

Eiffel, as the result of an elaborate theoretical and experimental research on tunnels

having exit cones generated by straight lines, has come to the conclusion that the

vertex angle of the exit cone should be not more than 7°, and that the diameter

at the large end of the exit cone should be three times that at the small end. It is

necessary to base the dimensions of a tunnel on a compromise, as the arrangement

which would give the absolute maximum of efficiency would have to be housed in

a building of prohibitive size. The overall length can be materially reduced at the

cost of a slight increase in power, and the first cost of the building, depending on

its dimensions, must be balanced against the cost of operation, which varies with

the power of the motor and so with the efficiency of the tunnel. The relations to

be observed among the various dimensions of the tunnel and the angles of the cones

will be discussed more fully elsewhere. Knowing the power consumed by a tunnel,

its diameter, and the speed of the air, the total losses can easily be computed for

that particular speed, and the magnitude of the figure thus obtained will serve as

a measure of the efficiency of operation of the tunnel. Since, however, the losses

vary with the speed, they can not be compared directly for two tunnels unless they

are run at the same speed. The factor most commonly used for comparisons

between tunnels is the ratio of the kinetic energy possessed by the air passing
400 Chapter 2: Building a Research Establishment

through the tunnel in unit time to the work done by the motor in unit time. This

is sometimes called the “over-all efficiency,” but is herein alluded to as the “energy

ratio.” The term efficiency in this connection is misleading, as the two quantities

introduced into the ratio are not directly connected, but merely happen to have the

same dimensions and so to be convenient for the purpose. Furthermore, the value

of the ratio is very commonly more than 1, and is sometimes very much more.

To determine the manner in which the power consumed varies with speed,

and so determine the validity or otherwise of the above relation, as well as to find

the relation which must be preserved among the various factors in order that geometrically similar tunnels may be strictly comparable, the Theory of Dimensions may

be used. The method pursued need not be gone into in detail, as it has been described

many times before, and it will suffice to summarize the results. It appears that, if

the compressibility of the air and the action of gravity on it be assumed to be of

negligible importance at the speeds employed, the power consumed is proportional, for geometrically similar tunnels, to the cross-section area and to the cube

of the speed, provided that VD⁄v, where V is the air speed, D the tunnel diameter,

and v the coefficient of kinematic viscosity, is maintained constant. Experiments

conducted with a model tunnel at Langley Field and fully described elsewhere in

this report, as well as those carried on by Durand, Castellazzi, and others, show

that the “energy ratio” varies but little with changes of VD⁄v and it is therefore safe

to apply the results of model experiments to full-sized tunnels, even though the

speeds may not be strictly in inverse ratio to the diameters. In general, the “energy

ratio” increases as VD⁄v increases, and it therefore requires less power to drive a tunnel

than would be predicted from a direct application of the results of tests on a

model of the tunnel and propeller.

The useful work done by a propeller is equal to the product of the thrust by

the speed of flow of the fluid through the propeller disk. The thrust of a wind tunnel

propeller is then

m x hf

V'

where V ' is the speed of the air past the propeller, and this equation holds good

whether Bernouilli’s theorem is followed or not, so long as hf is the total loss of

head from all causes.

m=ρ

⁄g x A'xV'

A' being the cross-section area at the propeller, and the propeller thrust is

therefore equal to the weight of a column of air having a height equal to the total

loss of head and a cross-sectional area equal to the disc area of the propeller. Since

the power is proportional to the cube of the speed, the thrust varies as its square.
Document 2-12(a–b) 401

If the factors causing departures from Bernouilli’s theorem are neglected, the

useful work done in moving the air against friction will be, as already mentioned,

independent of the degree of expansion of area in the exit cone, and so of the

diameter of the propeller. Under these conditions, in fact, the advantage in

respect of power consumed would rest with the short exit cone and small propeller, as the propeller efficiency is highest for a large value of the “slip function”

and this is obtained by making the speed of the air through the propeller high

and keeping down the diameter of the propeller. Assuming that the output of

work is the same in all cases, the thrust will be inversely proportional to the speed

of air through the propeller, or directly proportional to the disk area.

LAWS OF SIMILITUDE FOR WIND TUNNEL PROPELLERS.

It is obvious from a study of the Drzewiecki theory of propeller action that a

series of propellers of similar blade form and width-diameter ratio, all working at

the same true angle of attack, will give thrusts approximately proportional to

N2D4, where N is the engine speed in revolutions per unit time and D the propeller diameter. This proportion can be demonstrated by the Theory of

Dimensions to hold exactly true for geometrically similar propellers of perfect

rigidity, but it is very nearly correct even where propellers of different pitches are

concerned. It has been shown that the thrusts of a series of propellers designed

to drive the same wind tunnel or geometrically similar tunnels is proportional to

N2D4, and also to the cross-section area, which, in turn, varies as D2. It follows from

these two relations that N2D2 must be a constant, and the peripheral speed of the

propeller required to draw air through a wind tunnel at any particular speed will

therefore be quite independent of the diameter of the propeller if the power

required is independent of that diameter. It follows as an obvious corollary that, if

the power required is not independent of the degree of expansion in the exit

cone, the peripheral speed of the propeller will be least under the same conditions

as those for which the power required has its minimum value.

It is easily demonstrable that the stresses, both those due to centrifugal force

and those due to bending by the air pressure, in a series of geometrically similar

propellers depend only on the peripheral speed, and that they vary as the square

of that quantity. There is therefore a limiting peripheral speed which can not be

exceeded with safety. For wooden propellers, it is unsafe to run the peripheral

speed much beyond 60,000 feet per minute, or 305 meters per second, and it is

better to stay well inside this figure. In the case of an airplane or airship where

large power must be taken on a single propeller the peripheral speed can be

reduced by gearing down, as the engine speed decreases more rapidly than the

propeller diameter increases. In the wind tunnel, it has just been shown that this

is not the case, and that the peripheral speed, and so the stress, actually increases

if the propeller diameter is enlarged beyond a certain point. There is then a clearly
402 Chapter 2: Building a Research Establishment

defined upper limit to the power which it is safe to apply to driving the propeller

in any given wind tunnel, and therefore a limit to the maximum speed attainable.

This maximum can only be raised by reducing the losses and so improving the

over-all efficiency of the plant.

Since the power required to secure a given speed with a given “energy ratio”

is proportional to the cross-sectional area of the tunnel, and is also proportional

to VN2D4, the propellers in a series of tunnels of different diameters operating, at

the same speed and having the same “energy ratio,” all work at the same value of

N2

D2, and so of the peripheral speed. This leads to the rather astonishing conclusion

that the peripheral speed necessary to produce a given air speed depends only on

that air speed and on the energy ratio, and is not at all affected by the size of the

tunnel or of the propeller (except indirectly, in so far as these factors have an

effect on the energy ratio). For any value of the energy ratio, then, there is a limiting air speed which can not be exceeded without running the peripheral speed

up beyond the limits of safety, and this speed is the same for large tunnels as for

small, although the actual power consumed of course varies with the tunnel diameter. In order to realize the highest possible wind speed the power coefficient of the

propeller must be made as large as possible. This can be done by using many

blades and by making them of high sections set at relatively large angles of attack.

If the velocities desired are too high to be obtained in this way, it will be necessary to

use two or more propellers arranged in tandem, acting like a multi-stage compressor.

It has been shown that

P=K1D1

2

V1

3

and also that

P=K2V2N2D2

4

where the subscripts 1 and 2 denote, respectively, the conditions existing in the

experimental chamber and at the propeller, and K1 and K2 are experimental constants depending on the type of tunnel and propeller. Since D1

2

V1 = D2

2

V2, if the

velocity across the exit cone at the propeller is uniform, the first of these relations

may be written

P=K1D2

2

V2V1

2

Dividing this by the second of the relations above,

K2N2

D2

2

=K1V1

2

and

The ratio of the air speed to the peripheral speed is thus a constant for a given
Document 2-12(a–b) 403

tunnel and its value for any particular tunnel depends only on the type of installation—not at all on its size. Values of V1

⁄ND2 for a few tunnels are tabulated herewith:

Name. V1(m./sec.). N(r.p.s.). D2(m). V1/ND2.

Eiffel, Auteuil31.8 3.83 3.80 2.18

Leland Stanford, Jr. 24.0 6.77 3.35 1.06

Langley Field, model 41.5 68.3 0.610 1.00

N. P. L., 4-foot 15.24 22.5 1.6761 0.40

Curtiss, 4-foot 34.5 22.92 2.44 0.62

Curtiss, 7-foot 42.8 20.00 3.66 0.58

McCook Field 221.0 29.50 1.52 4.92 1

This tunnel was square and the ratio of V1 to V2 is therefore equal to the ratio of the cross-section

areas and not to that of the squares of diameters at the minimum section and at the propeller.

Castellazzi’s experiments.

Number of Blade width, V1(m./sec.). N (r. p. s.). D2(m). V1/ND2.

blades. diameter.

24 0.0435 25.0 17.25 0.600 2.41

24 .0300 25.0 19.17 .600 2.17

16 .0650 25.0 16.67 .600 2.50

12 .0435 25.0 20.50 .600 2.03

8 .0650 25.0 19.33 .600 2.15

6 .0650 25.0 22.17 .600 1.88

It will be noted that the highest value of V1⁄ND2 in this table, with one exception,

is 2.50, and this value was obtained in a tunnel of very efficient type in combination

with a propeller having a total blade width equal to one-third of its circumference.

Analysis by the Drzewiecki method leads to the belief that it will be possible to

raise V1⁄ND2 to 3, but that this figure can hardly be exceeded with propellers resembling those now in use. The exception mentioned above, the small tunnel at

McCook Field, has a fan of special type and will be discussed later.

If the allowable peripheral speed be taken as 285 meters per second, ND2 is

90.6 meters per second. If V1⁄ND2 be assumed to be 3, the limiting value for V is 271.8

meters per second, or 607 miles an hour. This is a considerably higher speed than

has yet been attained, or than is ever likely to be desired in connection with the

study of aircraft. If higher speeds should be needed they can be secured either by

the use of a multiplicity of propellers in series or, up to a certain point, by the use

of a fan with an abnormally large hub and short blades entirely filling the periphery

of the hub, as in the McCook Field tunnel, where the hub diameter is two-thirds

of the total diameter. If V1

⁄ND2 is raised to 5, a value only a little higher than that

in the McCook Field tunnel, the limiting air speed for the peripheral speed given
404 Chapter 2: Building a Research Establishment

above is increased to 453 meters per second, or 1,012 mile an hour. ([Footnote:] In

this analysis the change of density of the air, due to decrease of static pressure with

increasing speed, is neglected. This does not lead to a very large error, as both the

propeller thrust and the frictional resistance to the passage of the air increase

with the air density, the former varying more rapidly than the latter.)

The assumption has so far been made that the air has a free passage across

the whole area swept by the propeller. Of course the hub always blocks off a part

of this area, but it has usually been an insignificant fraction. If the propeller diameter is n times the hub diameter, the proportion of the area blocked off is 1

⁄n2, and

the speed of the air across the propeller blades, assuming a uniform distribution

everywhere outside the hub, is increased in the ratio 1 . 

1-1⁄n2

If the propeller be made, as is the common practice, with a constant blade

width, and if the lift coefficient be assumed constant all along the blade, the portion of the total thrust given by the part of the blade inside of any given point is

very nearly proportional to the cube of the radius at that point. For example, one

eighth of the thrust would be given by the inner half of the blades if they extended

clear to the center, with no hub at all. The use of a hub, or the covering up of part

of the blades with a “spinner,” therefore decreases the thrust in the ratio 1- 1⁄n2.

Since useful power is equal to this product of the thrust by the speed across the

propeller disk, the net change in power, due to hub or spinner, is

The increase in power coefficient by the use of a spinner, the propeller pitch

being adjusted to give the same angle of attack of the blades with or without the

spinner, is 5 per cent for a spinner of hub one-quarter the diameter of the propeller, 17 per cent when the ratio is one-half, and 27 per cent when, as in the

McCook Field tunnel, it is two-thirds. Furthermore, the use of a very large hub

makes it possible to use more blades and make their total width a larger fraction

of the circumference of the circle swept by the blades. In the McCook field fan

there are 24 blades, and their total width is approximately equal to the circumference of the hub.

Where very high speeds are desired, as in the calibration of air-speed meters,

a throttling insert has sometimes been used to reduce the section of a large tunnel. The effect is to increase the speed, but usually much less than is expected. If

the “energy ratio” remained constant, halving the diameter of the tunnel would

increase the speed available with a given expenditure of power by 59 per cent. A
Document 2-12(a–b) 405

change of this sort usually, however, diminishes the energy ratio unless the tunnel

is of the type combining a long straight portion with conical ends, and permitting

the extension of the cones back into the straight cylindrical part. The use of a

throttling insert in a tunnel with a short experimental chamber, like those used by

Eiffel and Crocco, is almost certain to lead to a large drop in energy ratio, and the

increase of speed by halving the diameter in such a laboratory would probably be

less [than] 50 per cent. Furthermore, it is necessary for best results that the propeller

ordinarily used be replaced by one especially designed for use in conjunction with

the throttling insert. If the diameter of the tunnel be halved the area at the smallest

section is divided by four, and, even with an increase of 59 per cent in speed at

the throat or in the experimental chamber, the speed of the air past the propeller

is reduced by 60 per cent. Since the propeller diameter and its normal rotational

speed to develop the rated power are unchanged, the propeller for use with the

throttling insert must have a much smaller effective pitch than that employed

with the full section, if the maximum of efficiency is to be obtained.

RELATIVE ADVANTAGE OF SMALL AND LARGE TUNNELS.

It has just been shown that the gain in speed by reducing the diameters by the

use of throttling insert is disappointingly small. This leads naturally to a study of

the best size of wind tunnel to be employed, and of the relation between speed

and size which should be sought.

In the construction of aerodynamical laboratories, as the attempt has been

made to approach ever more nearly to full-flight conditions, two divergent

schools of practice have grown up. The first, best represented by the National

Physical Laboratory in England, has constantly increased the diameter of the

wind stream, and so increased the size of model which may be tested, but has

remained content with relatively moderate wind speeds. The second, on the other

hand, has concentrated its efforts on the pumping of the air across a small section

at enormous velocity.

In comparing the merits of the high speed and the large diameter tunnels,

there are three points which must be borne in mind. In the first place, the highest

possible value of LV (LV being the criterion of dynamic similarity) is to be obtained

with a minimum expenditure of power. Secondly, the interference between the

model and its support is to be reduced to a minimum, and, finally, that disposition

should be favored which enables us to secure the greatest accuracy in the construction

of the models.

It has been shown that

P=KAV3

+K1D2V3

where D is the diameter of the tunnel and K1 is a constant.

In order to avoid interference between the model and the walls of the tunnel,
406 Chapter 2: Building a Research Establishment

the ratio of maximum span to tunnel diameter must not exceed a certain value

(usually about 0.4). Setting L, the span of the model, proportional to D, we can

then modify the above equation:

The power required to drive the fan will therefore be least, for any given value

of LV, in that tunnel where the diameter is largest and the speed is smallest.

The relative magnitude of the interference between the model and its support,

the so-called “spindle effect,” depends on the ratio of the spindle diameter to the

linear dimension of the model. Its reduction is a matter of very vital importance,

the spindle correction undoubtedly being the largest single source of error in

most wind-tunnel tests.

The bending moment in the spindle at any point (say one chord length from the

wing tip) is proportional to the product of the span by the force acting on the model.

M=C1LF=C2L(L2

V2)=C2L3V2

If d is the diameter of the spindle, the relations between the bending

moment, fiber stress, and deflection may be written:

if the material of the spindle be the same in all cases.

If the maximum fiber stress be limited to a definite value,

The ratio of spindle diameter to model size, and consequently the spindle

interference, will therefore be greatest in the high-speed, small diameter tunnel.

If, as is usually the case, it is stiffness and not strength which prescribes the

diameter of the spindle, and if the deflection be limited to a determined value,

the required spindle size is given by the equation:
Document 2-12(a–b) 407

For a given value of LV, then, d⁄L will be least when the speed is low and the

tunnel diameter large. The advantage of the large tunnel on this score is even

greater than appears at first, as a larger spindle deflection is permissible with a

large tunnel than with a small one. In fact, the permissible deflection increases

nearly as rapidly as does the tunnel diameter.

In respect of the third consideration, accuracy of construction of the model, the

superiority of the large tunnel, permitting the use of a large model, is so manifest

as hardly to call for discussion. A model of 3-foot span can include many parts,

such as fittings and wires, which it is quite hopeless to put on one of half that size.

So far, the advantage has rested with the large diameter in every particular. It

has one disadvantage in that the size and weight of the balance are much

increased, longer weighing arms, heavier counterweights, and a general strengthening up of the apparatus are necessitated. Furthermore, the initial cost of the

building to house a large tunnel is very high. In the writer’s opinion, however, the

advantages far outweigh the drawbacks, and any future development of wind tunnels

for model testing should proceed along the lines of increasing the diameter

rather than the speed.

All that has been said against high speeds applies, of course, only to tunnels

for the testing of models. Speeds equal to the speeds of flight of airplanes are

essential for the calibration of instruments.

DESIGN OF WIND TUNNEL PROPELLERS BY THE DRZEWIECKI THEORY.

It is possible, if the rate of flow of the air through a wind-tunnel propeller be

known, to predict the performance of the propeller by the Drzewiecki theory.

Indeed, the application of that theory to wind-tunnel propellers is rather simpler

than its application to the airplane, as there is no in-draught correction to contend

with. If the velocity at the minimum section of the tunnel is given, the velocity

through the propeller can be computed with absolute accuracy on the assumption

that the distribution across the exit cone is uniform. This assumption can only justify

itself in the results of the analysis derived from it as a basis.

The best way of checking the accuracy of the analytical method of design is to

apply it to a propeller already working satisfactorily. This has been done with the

propeller used in the model wind-tunnel experiments described in a later section

of the report. The angle of the relative wind to the plane of the propeller can be

computed from the wind speed, and it is then possible, knowing the angles of
408 Chapter 2: Building a Research Establishment

blade setting, to work and find the angle of attack of each blade element. Having

this, the power consumed by the propeller and its efficiency can be found in the

usual way. This was done for two cases. In the first case the tunnel was of the Eiffel

type, with an enlarged experimental chamber, and the calculated power checked

the actual consumption within the experimental error (about 2 per cent, owing to

uncertainty as to motor losses). In the second case the air stream was inclosed

throughout, a cylindrical tube being carried across the experimental chamber,

and the power consumed was about 15 per cent more than that calculated. It is

considered that both of these tests showed a very fair check and that the use of

the Drzewiecki theory for design is amply justified. The average error, both in

these and in other cases which have been tried, is in the direction of underestimation of the power consumption.

In designing a propeller for a new tunnel it is necessary to make an estimate

of the energy ratio, and so of the speed for a given power. If the estimate is too

low, the propeller pitch will be made too low, and the propeller will work at an

inefficiently small angle of attack. The speed will be higher than that estimated,

but still not so high as it would be with a proper propeller. If the propeller blades

are made too narrow, or if too few blades are used, the full power of the motor

will not be absorbed at the rated revolutions per minute. The speed will then fail

to reach the value expected for the rotational speed realized, the angle of the relative wind to the plane of the propeller will fall below the estimated value, and

the angle of attack of the blade elements will become inefficiently large. Any

change of this sort from the designed conditions of operation tends to correct

itself, as the larger angle of attack increases the power consumed and the thrust

given by the propeller. This in turn speeds up the air and brings the angle of

attack to a lower value. It is for this reason that fairly satisfactory results have so

frequently been secured with propellers chosen almost at random, but the best

efficiencies can only be obtained with a propeller designed especially for the conditions under which it is to operate. The commonest faults in the design of windtunnel propellers have been either to overestimate the energy ratio for a projected tunnel or to underestimate the total blade width required for the absorption

of the given power at the most efficient angle of attack. The result in both eases

is to cause the blades to work at too large an angle of attack.

There is some doubt as to the manner in which the angle of attack should

vary along the blades. Most wind-tunnel propellers in which the Drzewiecki sytem

was used at all have been designed for a constant angle of attack, but since, as was

just noted, the propellers have usually been made too small to absorb the full

power of the motor, they actually work at an angle of attack larger than that

desired and increasing from the tip to the root of the blade. In the design of a

propeller for the Langley Field wind tunnel, the opposite disposition has been
Document 2-12(a–b) 409
410 Chapter 2: Building a Research Establishment

deliberately chosen, the angle of attack being made largest near the tips and

decreased toward the hub in order that the air may be drawn out along the sides

of the exit cone and in order that the larger part of the thrust may come on the

most efficient portion of the blades. No experimental data on the effect of this

arrangement of the blade sections are available as yet.

In order to make it easy to estimate the number of blades and the blade width

required in a propeller for a tunnel, assuming that the wind speed, power consumption, and revolutions per minute are known, a number of propellers have

been computed for a variety of conditions and the results expressed by a formula

and a curve. The power is given by the formula

where P is the horsepower input of the motor, V the air-speed through the propeller in meters per second, b the blade width in centimeters, N the revolutions

per minute, n the number of blades, D the propeller diameter in meters, and C a

constant, the magnitude of which depends on the pitch of the propeller. C is plotted

against V2⁄ND2 in figure 1. If English units be used, V being given in miles an hour,

D in feet, and b in inches, a factor 109 replaces 108 in the denominator of the

power formula given above, and C is given by the dotted curve in figure 1. The

theoretical basis for the derivation of this formula is the same as that for a formula

derived by the writer, and previously published, for the power consumption of airplane and airship propellers.

The efficiency of wind-tunnel propellers is usually very low, and the maximum

attainable depends largely on the magnitude of the pitch ratio. In the propeller

designed for the Langley Field tunnel the calculated efficiency is 58 per cent. In

figure 2, probable propeller efficiencies have been plotted against V2

⁄ND2. The efficiencies there predicted may be exceeded when the peripheral speed is low, so

that thin sections can be used over the whole length of the blade, or when a very

large hub or spinner is used to cover up the less efficient parts. In order to give

an idea of the range of values of V2⁄ND2 employed in successful tunnels, a few are

tabulated below, the data being taken from the table under “Laws of Similitude

for Wind Tunnel Propellers”.
Document 2-12(a–b) 411

V2

⁄ND2

Leland Stanford, Jr. .0265

N. P. L., 4-foot .27

Curtiss, 4-foot .20

Curtiss, 7-foot .20

Langley Field model .25

McCook Field .48
412 Chapter 2: Building a Research Establishment

THE FORMS OF ENTRANCE AND EXIT CONES.

There has been a great deal of discussion and dispute as to the best form for

the cones in which the air acquires and loses its speed, and further experiment is

desirable. The effect which changes in the form of these cones have on the efficiency is, however, much less than has commonly been supposed, judging from

experiments recently performed at Langley Field and reported in another part of

this paper.

In the absence of data to indicate the best form, most of the wind tunnels

which have been constructed have used, at least on the exit side of the experimental

chamber, the frustrum of a right cone generated by a straight line. This was true

of the N.P.L. and all their imitators, and it has been true also of most of the tunnels

designed with an eye to the results of the experiments of Crocco and Castellazzi,

and using long exit cones of very gradual slope. A surface of this type has at least

the advantage of being easy to generate and to fabricate from wood or sheet

metal. There is, however, no particular reason to believe that it is the most efficient that can be constructed from an aerodynamical point of view. Eiffel and his

followers, on the other hand, have always used cones of curving form. It seems

fair to assume that the loss in diverging nozzle is partially dependent on the

deceleration of the fluid, and that the loss will usually be least where the deceleration is least. It is obvious, furthermore, that the flow through the exit cone will

be smoothest and least turbulent when the form of the cone is smooth, and that

any abrupt change of slope of the walls, such as that at the juncture of the parallel

portion of the tunnel with an exit cone generated by a straight line, is liable to

cause the lines of flow to break away from the contour of the tunnel wall, and to

establish a region of “dead-water” and turbulence around the periphery of the

exit cone. The smoothness of a curve can best be judged by taking differences, or,

if the equation of the curve is known, by plotting the derivative. This was done in

designing the cones for the Leland Stanford, Jr., tunnel. The plotting of the curve

of acceleration for a tunnel will then serve the double purpose of indicating the

smoothness of the curve and of giving the maximum rate at which the velocity of

the air is changing, and so the maximum force necessary for accelerating the

moving stream.

A curve of velocity against distance along the axis of the tunnel can be drawn

on the assumption that velocity is inversely proportional to the square of the

diameter of the tunnel. This, of course, is true only for velocity parallel to the axis,

and entirely neglects the radial component. In order to obtain the acceleration

from this curve, the derivative giving acceleration is written
Document 2-12(a–b) 413

The acceleration at any point along the tunnel is therefore equal to the product

of the ordinate of the curve just described by its slope at that point. These factors

can be found graphically or, in the case of a curve for which the equation is know,

analytically.

In the case of a straight cone, for example, the formula for diameter at any

point is

where D1 and D2 are the diameters at the small and large ends of the cone, respectively, l the length of the cone, and x the distance from the small end. Then

and 

The acceleration is equal to the product of these expressions, or

If the exit cone is generated by rotating about the axis of the tunnel a parabola having its vertex at the junction of the exit cone with the straight portion the

formula for diameter of the cone at any point becomes

The acceleration may then be obtained by the same steps just employed for

the straight cone.
414 Chapter 2: Building a Research Establishment

In figure 3, the velocity and acceleration, as well as the cone diameter, are

plotted against x for cones of these two forms. The units are meters and seconds,

and the curves relate to a tunnel having an exit cone tapering in diameter from

1.5 meters to 3 meters in a length of 6 meters, and a wind speed of 50 meters per

second. It appears that the straight cone is far inferior, judged by the criteria laid

down above, to that of parabolic form. The maximum acceleration for the first is

more than two and a half time that for the second, and there is a large discontinuity in the acceleration curve for the straight cone, as might be anticipated from

the discontinuity in the slope of the side of the tunnel. The parabolic form gives

zero acceleration at the point where the air emerges from the exit cone. There is

some question as to the desirability of using a reverse curve which will have tangents parallel to the axis of the tunnel at both its ends, and so securing zero acceleration at both ends of the exit cone. The air has to be slowed down some time,

and there would seem to be little advantage in bringing it to a constant velocity

as it leaves the retaining walls of the exit cone if it is to be decelerated again the

instant that it is free from those walls. Also, the current of air, since it is to be

turned through an angle of 180° and travel back through the room to the

entrance of the tunnel, must acquire a radial velocity either inside the exit cone

or immediately after it has left it. No gain is apparent from a construction which

permits the air to acquire a certain amount of radial velocity and then straightens

it out again, only to force it to turn outward once more a few feet father along its

path. The effect of a reversal in the curve of the walls near the large end of the

exit cone is certainly slight, as very good results have been obtained both with and

without such a reversal.

The form of the entrance cone appears to have but little effect on the “energy ration,” and this is in accord with the results of hydraulic experiments, where

it is always found that the loss in a converging nozzle is much less than that in a
Document 2-12(a–b) 415
416 Chapter 2: Building a Research Establishment

diverging one, and that the nozzle can converge very abruptly without seriously

increasing the loss. 

Most of the European experiments on model tunnels have been made with

straight entrance cones. While these are probably as efficient as any other type,

they must have avena contracta near the large end, causing turbulence which persists into the experimental chamber, and there is further eddying and disturbance

due to the turning of the air around a sharp corner at the small end of the cone.

To avoid these difficulties and to secure as steady a flow as possible in the experimental chamber it is the almost universal practice, in actual tunnels, to make the

entrance cone of curing form. It has been found at the National Physical

Laboratory that even if the entrance cone, or bell-mouth, as it is called there, is

curved around until a tangent to the wall at the large end is perpendicular to the

axis of the tunnel, there still are marked and persistent eddies in the neighbor-
Document 2-12(a–b) 417

hood of the sharp edge. To entirely eliminate this edge it is not the practice at the

N.P.L. to carry the bell-mouth around, as shown in figure 4, until it meets the

straight portion of the tunnel. This method has not been adopted at Langley

Field, as it is desired to make some experiments on the full-sized tunnel with the

normal entrance cone, but provision has been made for building a fairing to

extend clear around to the experimental chamber, as shown by the dotted lines in

figure 5, so giving the air a perfectly smooth passage.

THE THEORY OF LOSSES IN THE EXIT CONE.

The losses in the exit cone of a wind tunnel arise from three sources. The first

is the friction against the walls, and is best determined by Fritzsche’s formula for

fluid friction. The second is the diverging angle of the cone, which, as already

noted, always leads to a loss of energy as compared with the ideal conditions

expressed by Bernouilli’s theorem. The magnitude of this loss is determined with

satisfactory accuracy by a formula devised by Fliegner. Finally, there is a loss due

to the sudden release of the air from the exit cone and its passage into the room,

where its velocity drops almost to zero. This loss was shown by Borda to be equal

to the kinetic energy possessed by the air at the large end of the cone. These losses,

and their relation to the factors entering into wind tunnel design, together with

all the losses in other parts of the tunnel, have been fully addressed by Eiffel, and

it is not necessary to repeat his work here. For the benefit of those designing tunnels, however, a set of curves has been plotted which make it possible to read off

at once the loss in a straight conical exit cone of any type, and to determine, given

the limiting conditions, such as the size of a building to house the tunnel, the

characteristics of the best exit cone of that particular case. Since from 80 per cent

to 90 per cent of the total losses in a tunnel (not including those in the propeller)

occur in the exit cone, the problem of designing a tunnel with a high energy ratio

is essentially a problem of reducing the losses in the exit cone.

In figure 6 the ordinates are the vertex angles of exit cones, the abscissae, the

ratio of the cross-section area at the large end of the cone to the cross-section area

where models are tested, at the throat or in the experimental chamber. The family

of curves drawn in full lines are curves of equal loss, and the number which one

bears expresses the loss in the exit cone as a per centage of the kinetic energy possessed by the air at the smallest section of the tunnel. For example, if there were

no losses except those in the exit cone, a tunnel having an exit cone of form corresponding to any point on the curve marked 20 would have an energy ratio of 5.

The nearly straight dotted lines running across the sheet diagonally correspond

to various constant lengths of exit cone, and they are marked with the ratio of

length to diameter at the small end.

To illustrate the use of this chart in choosing an exit cone a few illustrative

examples will be given.
418 Chapter 2: Building a Research Establishment

1. A tunnel is to be 2 meters in diameter. In order to keep the size and cost

of the building within reasonable limits, it is desired that the length of the exit

cone shall not exceed 20 meters. Subject to this limitation, the cone is to be chosen

for maximum efficiency. 

The ratio of length to diameter here is 10. Passing along the dotted line bearing

that number, it is seen that it cuts the curve of 16 per cent loss at two points and

that it does not cut the 14 per cent curve at all, but that it approaches nearest to

the latter at the point (α = 6.8 degrees, n = 4.8). It is usually best to make n a little

smaller than the value for the minimum loss in the exit cone, as a reduction in n

in the diameter at the large end of the cone and so in the propeller diameter, and

it has already been shown that this is favorable to propeller efficiency. It would

probably be best, in this case, to take n = 4.3, α = 6.1 degrees, or some other

combination in that immediate neighborhood.

2. A very large wind tunnel is to be built, and, in order that the propeller

diameter may not be unreasonably large, as well as to keep down the height of the

building, the propeller diameter is limited to twice the diameter of the tunnel at

the minimum section.

If the ratio of diameters at the ends of the exit cone is 2, n = 4. Drawing a

vertical from the scale of abscissae at this point, it is seen that it approaches nearest to the 14 per cent curve at (α = 4.5 degrees). The length of the exit cone for

this angle is 13 times the minimum diameter. It would not be advisable, under

these conditions, to choose the cone for the absolute maximum efficiency, as the

length could be decreased 4 1

⁄2 diameters at a cost of only 5 per cent increase in

total power by increasing α to 6.7 degrees. Since the curvature of the constant

power curves is not abrupt, the conditions can be changed considerably from

those for minimum loss without very much affecting the efficiency, and it is almost

always worthwhile to make some concession of efficiency in order to reduce the

dimensions of the building and of the tunnel itself.

EXPERIMENTS ON MODEL WIND TUNNELS.

The first set of experiments conducted dealt with a model of the wind tunnel

for Langley Field, as it was originally planned. The tunnel was of the Eiffel type,

with a large experimental chamber, and this chamber was reproduced to the

proper scale in the model. All of the models used were one-fifth the size of the

large tunnel, the experimental chamber being 30.5 cm. in diameter in the models.

The entrance and exit cones were made of plaster over a base of wall board, and

were shellacked, so that a very smooth surface was secured. The plaster was

scraped to form, as soon as it is set, with a steel template rotated about a shaft

running along the axis of the tunnel. An exit cone is shown, with the template in

place and ready to apply the plaster, in figure 7. The drive was by belt from a 2-

horsepower induction motor, and the propeller was four-bladed. The blade had
Document 2-12(a–b) 419

a constant width of 4.5 cm. The speed

of the propeller was measured with a

Veeder liquid tachometer, and the

power consumption with a polyphase

watt-meter. The tunnel and instruments

ready for use are shown from two points

of view in figures 8 and 9, the propeller

in figure 10. Figure 11 illustrates the

Pitot tube used for measuring the

wind speed. A hole 1 mm. in diameter

is bored in the tapering end, and communicates with one of the two hypodermic tubes passing down the shank. The

static pressure is secured inside a hole 2.5 mm. in diameter drilled from the other

end of the tube, and this hole communicates with the other hypodermic tube. The

piece between the two hypodermic tubes is a solid rod to provide stiffness. Since the

static pressure points to the rear, the pressure in that side of the gauge is less than

the true static, and the readings are higher than they theoretically should be. The

tube was calibrated against a standard Pitot in the wind tunnel of the Bureau of

Standards, and was found to have a constant of 1.167 (i.e., the readings of the small

Pitot tube were 16.7 per cent higher than they theoretically should have been).

This Pitot tube was very insensitive to rotations in all planes, as it could be turned

20 degrees without affecting the reading more than 8 per cent. This is a great

advantage where, as in traversing the cones, the direction of flow of air is uncertain. The dynamic head on the Pitot tube was measured by an alcohol gauge, shown

in figure 12. Only one side of the gauge is ordinarily used. Since the glass tube is

raised and lowered by a micrometer screw so that the meniscus of the alcohol

stands opposite the same mark on the tube for each reading there are no corrections, such as are required in the ordinary Krell manometer, for varying diameter of

the glass tube or for changing level of the fluid in the reservoir.

The mode of procedure in each complete test was to make traverses of the

entrance and exit cones and the experimental chamber at several points, measuring

the wind speed at several radii, and then to make runs at a number of different

speeds, measuring the wind speed at the point where a model would be placed for

test and the power consumption. The energy ratio and the manner of its variation

with speed was determined from this set of runs.

The traverses for the original model are plotted in figure 13. The points A

and B were in the entrance cone, A being at the large end of the cone, B midway

between the ends. C was in the experimental chamber, 5 cm. from the entrance

cone side. D was 20 cm. downstream from the entrance cone and E was 46 cm.

from the entrance cone, 15 cm. from the exit. F, G, and H were in the exit cone,
420 Chapter 2: Building a Research Establishment

and were equally spaced along its length, H being in front of the propeller and as

close as it could be placed without danger of having the tube struck by the blades.

The exit cone in this model was parabolic in form. The location of the point D

corresponded to that at which the model is to be placed in the full-sized tunnel.

The speed in the entrance cone had a maximum at the center and one near

the wall, the one near the wall being higher than that in the center. The maximum

occurred with 2 cm. of the wall. On going still farther out the speed dropped rapidly,

due to friction. The velocity in the experimental chamber near the entrance cone

was constant, as nearly as could be detected, over 90 per cent of the diameter of

the stream. On going farther downstream the velocity distribution became more

irregular, the speed being a maximum at the center and dropping off steadily

toward the edges of the stream. The ratio of the velocity 75 per cent of the way

out to the edge of the stream to that at the center was 1.00 at C, 0.97 at D, and
Document 2-12(a–b) 421

0.96 at E. The edge of the stream was not sharply defined, even very near to the

point of issuance from the entrance cone, and at E, three-quarters of the way across

the chamber, the velocity dropped off in a smooth curve from very near the center of the stream out to far beyond its normal boundaries.

The velocity distribution in the exit cone was exceedingly strange. The velocity

dropped off rapidly from a maximum at the center, so that the stream appears

actually to contract rather than to expand in the exit cone. As in the entrance cone,

there was another maximum near the wall, but it was farther from the wall than

was that at the entrance, and the velocity was much lower than at the center. Directly

in front of the propeller the velocity at the center dropped sharply, due to the

hub, and varied in an irregular manner over the rest of the section. The flow at

this point was so turbulent and so varying in direction that the measurements of

velocity may contain considerable errors.

In order to make direct observations on the sharpness of definition of the

edge of the stream in the experimental chamber and to determine the general

nature of the flow in the chamber an observer got inside and sounded the flow

with a thread. It was evident that the air in the whole chamber was much stirred

up, and that the flow near the nominal edge of the stream was extremely turbulent,

except in the immediate neighborhood of the entrance. Even in the farthest corners

of the chamber, at a distance from the center of the stream equal to more than

three times its nominal diameter, there was still a distinct movement of the air.

The motion everywhere was very unsteady, the direction of flow at a given point

changing 60 degrees or more almost instantaneously. The best defined part of the

circulation was near the small end of the exit cone, where two strong vortices

rotating in opposite directions existed in the corners of the chamber. The examination of the flow was not extended to points above and below the stream in this

neighborhood, so it is not certain whether or not a complete vortex ring, surrounding the opening into the exit cone, existed. The results of this examination

of the flow in the experimental chamber made it clear that the balance would

have to be shielded in some way from the air currents if any accurate work was to

be done. In Eiffel’s tunnel, partial shielding of the balance is accomplished by

placing it on a platform which, however, extends across only a small proportion

of the width of the room, and can hardly act as a complete protection from aircurrents for the measuring instruments.

The power curve is plotted in figure 14 (curve No. 1) and the curve of speed

against revolutions per minute in figure 15 (curve No. 1). The energy ratio varied

too little and too irregularly to make it worthwhile to plot a curve. Its mean value

was 0.90, making no allowance for propeller losses. If the propeller efficiency be

assumed to be 57 per cent (the value calculated by the Drzewiecki method), the

energy ratio for the tunnel proper becomes 1.58.
422 Chapter 2: Building a Research Establishment

In view of the irregularities of flow found in the experimental chamber it was

decided to try next the effect of inclosing the stream in a cylindrical tube during its

passage across the experimental chamber. No attempt was made to make the tube

air-tight, the static pressure inside the tube being equal to that in the experimental

chamber, which was carefully made air-tight. Curve No. 2 in figure 14, and also in

figure 15, correspond to this case, and the traverse of the stream at points corresponding with those taken for the original model are plotted in figure 16.

Comparing these traverses with those in figure 13, it is seen that the nature

of the distribution in the entrance cone is practically unaffected. The velocity at

point C was a little less regular than for the case of the unconstrained stream,

showing an increase near the walls similar to that which characterized the

entrance cone. At D and E, however, the velocity was much more even with the

inclosing tube than without it, being constant within 1 per cent over 75 per cent

of the diameter. Evidently, from the standpoint of steadiness of flow, the inclosed

type of tunnel is superior to the Eiffel type.

In the exit cone the effect of surrounding the stream with a definite boundary

was still more apparent. At F the velocity three-quarters of the way from the center

to the walls was 94 per cent of that at the center, as against 67 per cent in the original

model. At G the corresponding figures were 82 per cent and 40 per cent. At H

there was, as in the first case, a minimum at the center and two maximums, the

distribution of velocity being reasonably uniform across the outer 70 per cent of

the blade, which is the most effective portion. 

It is reasonable to suppose, in view of the better filling of the exit cone and of

the generally improved velocity distribution, that the energy ratio would be

increased by inclosing the stream, and this supposition was fully justified by the

power measurements. For a given rate of rotation of the propeller the wind speed

was increased while the power consumption for a given wind speed was decreased

just about 50 percent. The energy ratio with the inclosing tube was 1.83 for the

whole installation, or, making due allowance for the propeller losses, 3.20 for the

tunnel alone.

It is evident that the enclosure of the stream improves the results in every way.

The experiments, so far as power consumption is concerned, check very well with

those obtained in some similar experiments on model tunnels, carried out by

Lieut. Castellazzi. Lieut. Castellazzi found that the efficiency was decreased 40

per cent by the use of an open experimental chamber. The experimental chamber

used in his experiments was round in cross section and was twice as large in diameter

as the entrance and exit cones where they entered the chamber, and the slightly

greater loss in efficiency found in the experiments conducted at Langley Field

may be accounted for by the larger size and more irregular form of the experimental chamber there employed.
Document 2-12(a–b) 423

EFFECTS OF VARIATION IN EXIT CONE FORM.

The next series of experiments dealt with the effect of alterations in exit cone

form. It was originally the intention to make a number of cones of different forms,

but this plan was abandoned after two had been tried, and the experiments cover

only the parabolic and straight forms of cone. These are as widely different from

each other in respect of their acceleration curves as are any two forms which

would be likely to be used.

The curves of power and revolutions per minute with the straight cone are

plotted as curve No. 3 in figures 14 and l5. The mean energy ratio is l.83 for the
424 Chapter 2: Building a Research Establishment

combination of tunnel and propeller, or 3.20 for the tunnel alone, values identical with those for the parabolic cone. It is evident from the curves that the effect

of changing the exit cone from a parabolic to a straight form was very slight. The

parabolic form seems to have a slight advantage at high values of VD and to be

inferior at low values, but the difference between the two curves is in no case in

excess of the possible experimental error. In view of these results it appears that

the efficiency of a tunnel is not affected appreciably by exit cone form or by the

nature of the acceleration in the cone, but only by its length, mean angle, and

total expansion ratio.

The large acceleration suddenly imposed on the air at the juncture between

the parallel-sided portion of the tunnel and a straight exit cone might be expected to cause turbulence, so that the flow would be less regular than with a parabolic or other smoothly curving form. No experimental data are available on this

point as yet, as the experiments were temporarily halted by an accident to the

propeller before traverses and investigations of the flow had been carried out with

the straight cone.

OBSERVATIONS OF THE NATURE OF THE FLOW 

THROUGH THE PROPELLER.

The most noticeable feature of the flow behind the propeller is the great

rapidity with which the slip stream spreads. Instead of contracting, as in the case

of an airplane propeller, where the direction of inflow is unrestricted, the stream

expands immediately on passing clear of the cone, the air changing its direction

so that there is a strong movement of the air, in a direction approximately at right

angles to the axis of the tunnel, at a distance of 30 cm. back and 50 cm. out radially

from the edge of the exit cone.

The flow in the throat and cones was very steady at all points except near the

edges of the stream. The velocity head varied with a total amplitude of oscillation

of about 2 per cent of the head and a period of from 20 to 40 seconds. On passing

the propeller the pulsations of velocity became much more marked. The period

of the pulsations close behind the propeller was about half a second, and the maximum velocity was estimated to be about 50 per cent greater than the minimum,

although no means of measuring and making a continuous record of a rapidly

varying velocity were available. On going farther away from the propeller along

the lines of flow of the air, the pulsations steadily increased in violence and the

period lengthened, until at a distance of about 80 cm. to the rear of the propeller,

the flow consisted of a violent gust about every second, the velocity in the intervals

between these gusts being so low as to be hardly perceptible. These observations

on the nature of the flow and its variations held in a general way for all the models

tried, but the pulsations of velocity were much more marked for the case where the

experimental chamber was left open than for that where it was inclosed in a tube.
Document 2-12(a–b) 425

EXPERIMENTS ON THE EFFECT OF DISKS AND SPINNERS 

ON THE PROPELLER.

In order to secure some idea of the effect of enlarging the hub of a propeller

or of attaching a spinner, some experiments were made with disks of wall board

attached in front of and behind the propeller, and also with a paper cone projecting

from the propeller into the exit cone. The results of these tests do not fairly represent what might be secured with a good spinner and a propeller especially

designed for it, as the propeller pitch should be increased when a spinner is incorporated or the hub is enlarged, but they will give some idea of the effect.

The effect of placing a disk in front of the central portion of the propeller, the

rear not being covered and the blades not being housed in any way, was to decrease

the wind speed and increase the power consumption. The inner parts of the

blades acted as a centrifugal blower, taking air in from the rear and throwing it

our radially. The increase in power, with a disk half the diameter of the propeller,

was 9 per cent, the decrease of speed with the same disk 19 per cent. With a disk

only one-fifth the diameter of the propeller the speed was decreased 5 per cent.

These measurements were made at a speed of 10 meters per second and with the

parabolic exit cone. The relative loss by the addition of a disk was greater with the

straight cone and at high speeds, the addition of a disk four-tenths the diameter

of the propeller causing an increase of 28 per cent in power and a decrease of 19

per cent in speed at a speed of 34 meters a second with the straight exit cone. The

energy ratio was decreased 59 per cent. All subsequent tests were made with the

straight cone, and the losses would probably be less with other forms.

The addition of another disk of equal size behind the propeller, so preventing

any flow in from the rear and out toward the tips, improved the performance as

compared with the single disk in front of the propeller, but remained inferior to

the original case with no shielding at all. The power was increased only 6 per cent

as compared with the original case without nay disks, but the speed was decreased

16 per cent and the energy ratio fell off 44 per cent. When the rear disk alone was

in place, so that any air thrown radially outward had to come from inside the exit

cone, the power was increased 6 per cent, the velocity decreased 5 per cent, and

the energy ratio decreased 19 per cent, using the model without disks as a standard

in all cases. The disk behind the propeller therefore gave better results than did

complete sheathing, either in the form of disks or faired by a cone in front.

The addition of a cone, having a diameter equal to two-fifths the diameter of the

exit cone at its large end and an altitude of one and a quarter times its own diameter,

in front of the propeller decreased the power about 2 per cent and increased the speed

7 per cent as compared with the values for the disks alone, but the energy ratio was

still 30 per cent lower than for the original case. It seems strange at first that the entire

blocking off of a considerable portion of the blades should increase the power
426 Chapter 2: Building a Research Establishment

consumption for a given number of revolutions per minute, but the phenomenon

can be accounted for by the higher air speed past the propeller when the area of

the exit cone is constricted by enlarging the hub. The theory of the effect of an

enlarged hub or spinner has been discussed in another section of this report.

It appears that the addition of a spinner or the enlargement of the hub

caused serious loss in every case where it was tried with the straight cone. The loss

with a parabolic cone is much less, and it is likely that, with a propeller properly

designed to allow for the increased velocity due to the blocking off of part of the

area of the exit cone by the spinner, results as good as those in the original case

could be obtained. It may even be that they could be materially improved on, but

this does not seem very probable in view of the uniformly poor results shown in

these experiments, where the presence of the spinner can hardly have decreased

the propeller efficiency more than 10 per cent (a loss which, as already noted,

could be prevented by the adoption of a propeller designed especially for the new

conditions). The loss in propeller efficiency, therefore, would not be sufficient

entirely to account for the decrease of energy ratio. The principal value of a very

large hub is to increase the power coefficient of the propeller and make possible

the reduction of the peripheral speed for a given wind speed. 

Document 2-12(b), F. H. Norton and Edward P. Warner, The Design of Wind 

Tunnels and Wind Tunnel Propellers, II, NACA Technical Report No. 98, 1920.

SUMMARY.

This report is a continuation of National Advisory Committee for Aeronautics

Report No. 73, and was undertaken at the Langley Memorial Aeronautical

Laboratory for the purpose of supplying further data to the designer of wind tunnels.

Particular emphasis was placed on the study of directional variation in the wind

stream. For this purpose a recording yawmeter, which could also be used as an air

speed meter, was developed, and gave very satisfactory results. It is regrettable

that the voltage supplied to the driving motor was not very constant, due to varying

loads on the line, but as this motor was of a lightly loaded induction type, the variation in speed was not as large as the variation in voltage. The work was carried

on both in a 1-foot model and the 5-foot full-sized tunnel, and wherever possible

a comparison was made between them. It was found that placing radial vanes

directly before the propeller actually increased the efficiency of the tunnel to a

considerable extent. The placing of a honeycomb at the mouth of the experimental

portion was of the greatest aid in improving the flow, but, of course, somewhat

reduced the efficiency. Several types of diffusers were tried in the return air, but

only slight improvement resulted in the steadiness of flow, they not being nearly

as effective as the honeycomb.
Document 2-12(a–b) 427

APPARATUS.

The efficiency of the tunnel and the slip of the propeller were determined by

the same method as described in Report No. 73, but to better record the fluctuations in velocity and direction a recording instrument was constructed. This

instrument, as shown in Figs. 1 and 2, consists of a thin mica diaphragm whose

movement rotates a very light spindle containing a small silvered mirror. Light

from an illuminated slit is transmitted by a lens to this mirror and the reflected

beam is then focused on a moving photographic film so that any movement of the

mica diaphragm is recorded as a continuous curve. By this method any small and

rapid variation in the air flow of the tunnel is indicated and recorded by means of

a Pitot-static tube which is connected to the two compartments separated by the

diaphragm, and any change in direction is recorded in the same way by connecting the sides of a yawhead to the compartments on opposite sides of the mica

diaphragm. The Pitot and the connecting tubes are made comparatively large so

that any rapid fluctuation in velocity can be immediately transmitted to the

diaphragm without damping or lag. Over 50 records were taken but only a few
428 Chapter 2: Building a Research Establishment

typical ones are reproduced here. Numerous experiments on the efficiency of tunnels and on speed fluctuation have previously been made in England.

EFFICIENCY AND SLIP WITH NEW PROPELLER.

In order to give a more even flow of air in the exit cone a new propeller was

designed for the model tunnel having a larger pitch at the tip so that the air in this

portion would be drawn through with a relatively greater velocity. In every other

respect this propeller is very similar to the propeller used in the test described in

Report No. 73, which, owing to a piece of wood being dropped in the running tunnel,

was completely destroyed. In Fig. 3 is shown the efficiency of this propeller when

working in a parabolic cone and in a straight cone. It will be noted that in the

same way as with the first propeller the straight cone is considerably more efficient

at high speed than the parabolic cone. In Fig. 4 is shown the slip of this propeller in

the parabolic cone and in the straight cone and it is noted that the slip is less at

high speed for the straight cone. It is then evident that the straight cone is aerodynamically superior to the parabolic cone, in addition to being easier to build.

EFFECT OF SIZE OF THE ROOM.

All the test runs described in Report No. 73 were conducted in a large room,

approximating to free-air conditions. In the tests described in this report a temporary

room was built around the tunnel, representing to scale the building provided for

the 5-foot N.A.C.A. wind tunnel; and all runs except those shown in Figs. 3 and

4 were made in this model room. The cross section of the model room and the
Document 2-12(a–b) 429

wind tunnel are shown in Fig. 5. For the same power this room decreased the air

speed from 69 to 59 miles per hour or a decrease of 14.5 per cent. In the small

room the maximum variation of speed was ±7 per cent and the maximum variation in direction was ±10°. The air speed records show that for the first 20 seconds after starting, in the large room, and for the first 10 seconds in the small

room, the air speed is very steady, and that the fluctuations suddenly appear at a

definite time and will be indicated on the record. This appearance of sudden fluctuations seems to indicate that the large part of the speed fluctuations are due to

the disturbed air from the propeller as it returns through the room to the

entrance cone.

EFFECT OF RADIAL VANES.

Eight radial vanes 3 mm. thick and 450 mm. deep were placed symmetrically

in the exit cone immediately before the propeller. These vanes joined in the center

in a stationery spinner which was of the same diameter as the propeller base. (Fig. 6.)

These vanes actually increased the speed of the air in the tunnel for the same

power by 5 per cent, but the fluctuations in direction and velocity remained

unchanged. In order to determine what part of the vane gave the increased efficiency, 25 mm. was cut off of the outer end of each vane and the run repeated

which gave a 3 per cent increase in speed for the same power over the tunnel with

no vanes. Again the vanes were cut off on the end 75 mm. and in this case the

same speed was obtained as with the tunnel without vanes. This seems to show

that it is the whole area of the vane which acts as a straightener for the air flow

and that no particular part is especially valuable in increasing the efficiency of the

tunnel. Eight additional vanes 3 mm. thick were then placed along the inner surface
430 Chapter 2: Building a Research Establishment

of exit cone, each vane being 75 mm. wide. This distribution of vanes decreased

the speed by 12 percent for the same power and the variation in speed was ±6 percent and the variation in direction was ±10°. The same vanes were then placed in

the entrance cone, as shown in Fig. 7, and in this case the speed was decreased by

8 percent and the variation in direction was ±8°. With this type of vane in both

the exit and entrance cone the speed was decreased by 20 percent for the same

power and the variation in direction was ±8°. It is evident from these tests that

the narrow vanes in either the exit or entrance cones are of little value in any way.

EFFECT OF PLACING SCREEN ACROSS THE TUNNEL.

A section of chicken wire of 25 mm. mesh was placed across the exit cone 45

centimeters ahead of the propeller. The use of the chicken wire decreased the

speed by only 3 per cent, so it does not seem that this distribution of screen would

be of any great harm to the efficiency of the tunnel and it is of great use in preventing small objects from being drawn into the propeller. A piece of window

screen placed at the beginning of the straight portion of the tunnel decreased the
Document 2-12(a–b) 431

speed by 14 per cent and the fluctuation in speed was -12 per cent and was -10

per cent in direction, showing that the screen in no way helps the steadiness of

flow for the particular condition of this test. Screens have been used to advantage

in other tunnels. With window screen at the mouth of the entrance cone the speed

was decreased by only 7 per cent.

EFFECT OF PLACING SPINNERS BEFORE THE PROPELLER.

A spinner 75 mm. in diameter and 450 mm. long was supported by steel wires

before the propeller, as shown in Fig. 8. The use of this spinner seemed to have

no material effect on the air flow.

THE EFFECT OF EXTENDING THE EXIT CONE BEYOND THE 

PROPELLER.

By extending the exit cone as shown in Fig. 9, there was no change of the air

flow inside the tunnel, but the tangential flow, which had been noticed before with

the propeller, was somewhat straightened out, and the air flow was more directly

to the rear through the extension of the cone. A cylinder was then attached to the

propeller end of the tunnel as shown in Fig. 10, which decreased the air speed
432 Chapter 2: Building a Research Establishment

about 5 per cent, the air issuing from the tunnel at a considerably higher velocity

and in a more compact stream, the borders of the stream still being sharply

defined at a distance of 20 feet. As extensions of this kind mean a larger and

longer building for the wind tunnel there would certainly be no advantage in

using them.

EFFECT OF HONEYCOMBS.

A honeycomb was constructed as shown in Fig. 11 and was placed at the

entrance to the straight portion of the tunnel. Owing to the difficulty in obtaining thin-walled metal tubing and to the expense of constructing honeycombs of

this type, only this one was tried. It is quite evident, however, even from this one

test that the honeycomb is of the greatest importance in straightening out the flow.

The speed is reduced 19 per cent and the energy ratio 45 per cent by this honeycomb, but the maximum speed variation was only ±2 per cent and the variation

in direction was reduced to ±0.5°. 

In order to show more clearly the great increase in steadiness of flow, a curve

taken with a recording yawmeter is shown for the open tunnel and for the tunnel
Document 2-12(a–b) 433

containing the honeycomb. (Figs.12 and 13.) It is evident from these how great is

the advantage of the honeycomb. As the length diameter ratio in the tubes of this

honeycomb are only 2 1⁄2 it is quite possible that by using longer tubes the flow

would be even better and the reduction in speed should not be appreciable. There

seems to be no doubt from these tests that the honeycomb is absolutely essential

in most wind tunnels.

EFFECT OF DIFFUSERS.

The first diffuser tried is shown in Fig. 14 and consists essentially of a cubical

box of which both sides are perforated with small holes, whose diameter is equal

to the thickness of the wall of the box and whose spacing between centers is about

twice that of the diameter of the hole. This box was connected rigidly to the rear
434 Chapter 2: Building a Research Establishment

of the exit cone so that all the air passing

through the propeller must escape

through these small holes. It was hoped in

this way to break up any pulsations which

would originate from the propeller. This

arrangement decreased the speed of the

tunnel by 7 per cent and the maximum

variation of speed was ±6 per cent and

the direction variation was ±5°, so that it

would seem that the flow is slightly

straightened, but nowhere near as much

as with the honeycomb. A second diffuser was tried as shown in Fig. 15, which consists of a latticework across the tunnel room at the experimental chamber consisting of 50 mm. square cells having a 6 mm. wall with a length 2 1/4 times their

diameter. This diffuser only reduced the speed of the tunnel by 2 per cent, and

the maximum variation was ±7 per cent, and the variation in direction was ±5°.

Although this diffuser has very little effect on the efficiency of the tunnel, at the

same time it does not much improve the steadiness of flow. A third diffuser was

constructed as shown in Fig. 16 and placed in the same position as the last. This

diffuser decreased the air speed for the same power about 5 per cent, the variation in velocity was ±5 per cent, and the variation in direction was ±4°, showing

only a slight improvement over the open room. It seems strange that these diffusers did not improve the air flow more, as the British have found that diffusers

greatly improve the flow in their tunnels. The results of these tests would not,

however, justify the use of a diffuser in a full-sized tunnel because of the rather

large expense of construction of such a piece of apparatus.

EFFECT OF PERFORATING THE STRAIGHT PORTION OF THE TUNNEL.

In order to determine the effect on air flow of opening the doors in the cylindrical portion of the tunnel and in using small holes for the introduction of apparatus, various tests were made on the model in order to see how this would effect

the efficiency and steadiness of flow. Also the velocity of the air in the experimental

chamber was determined by a small anemometer. A slot was first cut in the cylinder

parallel to its axis and one-fifteenth of the diameter wide, running the whole

length of the experimental chamber. The air flow extended out about the width

of the slot from the walls of the cylinder, and beyond this there was no flow in the

chamber and the efficiency of the tunnel was not appreciably affected. This slot

was then increased in width to one-sixth of the diameter of the tunnel, thus

decreasing the efficiency of the tunnel very slightly, and the flow of air extended

about one-sixth of the tunnel diameter into the experimental chamber nearest

the exit cone, but this air flow was less marked as the distance to the entrance
Document 2-12(a–b) 435

cone was decreased. When the width of the slot was increased to three-eighths of

the tunnel diameter the efficiency was decreased about 15 per cent and the air

flow extended two-thirds of the width of the slot into the experimental chamber,

near the exit cone, but there was no flow elsewhere in the experimental chamber.

TESTS IN FULL-SIZED TUNNEL.

A few tests were made in the large tunnel in order to afford a comparison with

the model. In Fig. 17 is shown the slip in the large tunnel. In comparing this with

a similar condition in the model tunnel (Fig. 4) it is seen that for the same air

speed the revolutions per minute is 5.7 times as large in the small tunnel as in the

large one. Theoretically, the ratio should be exactly 5, but the fact that the model

test was run in a proportionately larger room would account for this difference.

As the exact efficiency of the driving motor in the large tunnel is unknown, a

curve of horsepower supplied to the motor is plotted against air speed, but to give

some idea of the power supplied to the propeller a dotted curve is drawn from the

estimated motor efficiency. (Fig. 18.)

In comparing this curve with the one obtained in the model, it is seen that

the full-sized tunnel is slightly more efficient, so that results may be taken from

models to safely predict the performance of the full-sized tunnels. It is also interesting to notice that the power does not increase as rapidly as the cube of the

speed but more nearly as V2.5, although, as the efficiency of the motor is not exactly

known, the value of the exponent can not be determined very closely.

Records were taken in the full-sized tunnel of variations in velocity, and these

are reproduced in Figs. 19 and 20. In the first figure the wind-tunnel motor was

connected to a gasoline driven generator of 25 kilowatts and records taken at several
436 Chapter 2: Building a Research Establishment

speeds. In Fig. 20 the motor was connected to a 300-kilowatt generator driven by

a Liberty motor. The most important characteristic of these records is that the

magnitudes of the fluctuations do not increase as rapidly as the air speed, so that

at the higher speeds, quite contrary to expectations, the velocity is relatively

steadier. The maximum variation in air speed at 90 miles per hour was about

±1.5 per cent, whereas in the model it was about ±2 per cent, so that it would

seem that the steadiness was about the same in any size of tunnel.

Yawmeter records were also taken in the large tunnel, but were not reproduced, as they show practically a straight line, indicating that the honeycomb was

satisfactorily straightening out the flow.

NATURAL PERIODS OF TUNNEL.

A wind tunnel acts as an open organ pipe and its natural period will be given by:

where l is the length of the tunnel in feet,and V is the velocity of sound, or 1,040 ft./sec.
Document 2-12(a–b) 437
438 Chapter 2: Building a Research Establishment

The model tunnel would then have a period of 0.03 seconds and the large

tunnel a period of 0.15 seconds. Vibrations of this nature are very evident audibly

in the tunnels at certain speeds, but do not seem to be present on the records, as

the pitot tube is very nearly at the node of the vibration. The honeycomb has a

considerable influence in damping, these vibrations, which are more of a curiosity

than of any practical interest.

AUTOMATIC REGULATORS.

As it is not practical to supply a constant voltage to a wind tunnel, although

some tests have been made with storage batteries where an extremely constant

speed was required, it is either necessary to keep the voltage constant as nearly as

possible by hand regulations or use some type of automatic regulator. In small

tunnels it is quite easy to regulate the wind by hand, but in larger tunnels the inertia

of the moving parts is so great that there is considerable amount of lag between

the change in regulation and the response of the air speed, making hand regulation

very difficult. A very complicated regulator has been constructed at Göttingen

(N.A.C.A. File No. 5346-10) and seems to hold the velocity quite constant. There

are also numerous electrical devices for maintaining a constant motor speed, and

some of these regulators will hold the speed within 0.1 per cent. It seems probable,

however, that even if the revolutions per minute of the propeller is constant that

there will still be fluctuations in the air speed, so that a successful regulator must

be actuated by the air flow. There is a great deal of work to be done on such regulators, and the N.A.C.A. intends to carry on work of this kind in the near future.

CONCLUSIONS.

The qualities that should be aimed at in wind-tunnel design in order of their

importance are:

1. Constant direction of flow.

2. Constant velocity of flow.

3. Uniform velocity across section.

4. Efficiency.

5. Ease of working around tunnels.

6. Simplicity and cheapness of construction.

A good many of these qualities are contradictory, and the best compromise

must be made between them and the type of work that is to be undertaken. For

example, a tunnel for testing instruments should have a high efficiency, but need

not have a very steady flow. On the other hand, a tunnel for testing wings should

have its efficiency somewhat lowered in order to obtain a steady flow. It is quite

possible to so arrange the honeycomb and diffusers that they may be removed

when it is desired to obtain the highest speed. It would also be of value to make

it possible to open the ends of the building, as there are many days when the wind

would have little effect on the steadiness, and the efficiency would apparently thus
Document 2-12(a–b) 439

be considerably increased. This arrangement would also make it possible to cool

off the air in the building in a very short time, an advantage that would be greatly

appreciated in hot weather.

This work seems to show conclusively that a straight exit cone is more efficient

than a curved one, and it is certainly cheaper to construct. Diffusers affect the air flow

very little, and they do not seem to warrant the expense of construction. Honeycombs,

however, are of the greatest value and should be placed in every tunnel. 
440 Chapter 2: Building a Research Establishment

Document 2-13(a–c)

(a) “Report of Committee on Aerodynamics,” NACA Annual

Report for 1919 (Washington, DC), pp. 28–31.

(b) “Report of Committee on Aerodynamics,” NACA Annual

Report for 1920 (Washington, DC), pp. 22–28.

(c) “Report of Committee on Aerodynamics,” NACA Annual

Report for 1921 (Washington, DC), pp. 31–36.

In its annual reports, the NACA published reports on the activities of its committees (actually subcommittees, as the NACA itself was a committee). These reports

outlined the current state of the art and the investigations in progress. This series

of reports (1919 to 1921) by the committee on aerodynamics identifies the aerodynamic problems of greatest concern to the NACA during that formative era, as well

as the rudimentary state of aerodynamic knowledge. The reader will note how the

committee on aerodynamics defined its own role as it proceeded with its research

programs during these years, and how the NACA researchers developed cooperative working relationships with McCook Field and the Washington Navy Yard.

Document 2-13(a), “Report of Committee on Aerodynamics,” 

NACA Annual Report for 1919.

REPORT OF COMMITTEE ON AERODYNAMICS.

The committee on aerodynamics is a consolidation, made in April 1919, of

the three committees on aircraft design, navigation of aircraft and aeronautic

instruments, and free flight tests.

The committee on aerodynamics recommended that in the part of the work

at Langley Field within its domain the emphasis should be placed mainly on—

(a) Studies, in the laboratories, of propellers from the aerodynamic point of view;

(b) Studies, in the laboratories, of the flow of air around parts of airplanes and

airships, separately or assembled, and of the forces brought to bear on those parts

by the air;

(c) Free flight tests on fullsized machines; and

(d) The development of instruments, equipment, and methods for making

such studies and tests.

This policy has been followed during the year.
Document 2-13(a–c) 441

The work at Langley Field under these four heads, carried on under the general

direction of Edward P. Warner, has been largely one of development and design,

although some research work complete in itself has been carried on. The wind

tunnel has been under construction throughout most of the year and is now nearing

completion, and a number of experiments on model tunnels have been made to

determine the best form to adopt for the 5-foot tunnel now under construction.

The balance for this tunnel has also been designed and constructed at Langley

Field, and is ready for use. As an accessory to the design of the balance, a theoretical

investigation of the errors to which such balances are subject and the considerations

governing their design has been made and is published as a technical appendix

to this report. The most important experimental work complete in itself has dealt

with free flight tests, researches having been conducted throughout the summer

on two airplanes furnished by the Air Service. These researches have dealt chiefly

with the determination of the lift and drag coefficients and with the balance of the

airplanes, thus giving data for purposes of comparison with those obtained in

model tests. Several minor investigations on the performance of airplanes and on

stresses in the airplane have also been undertaken, and two of them are published

as appendixes to this report.

The development of autographic recording instruments for free flight tests

has continued at the Bureau of Standards under the general direction of John F.

Hayford and Lyman J. Briggs for the committee. Of the six new instruments

designed five are now complete, namely, the air-speed meter, the angle-of-attack

meter, the recording tachometer, the torque meter, and the thrust meter. The first

three named have passed through extensive laboratory tests and calibrations, and

are substantially ready for use in the air. The torque meter and thrust meter must

be subjected to extensive laboratory tests and possible modifications before they

will be ready for use. The stable zenith instrument, to be used for recording continuously the angle between the wing chord and the horizontal, has been

redesigned as a result of considerable experience with this type of instrument.

The redesigned instrument is being built and is nearly complete.

Special investigations have been made and are still in progress at the Bureau

of Standards, under the recommendation of the committee, on the Parker variable

camber wing for airplanes. This is a promising line of attack of the problem of

reducing the landing speeds of an airplane without reducing its flying speed.

Incidentally, some valuable information is being secured in regard to the possibility

of using a streamline wing and the ordinary type in a biplane combination.

Researches on airplane propellers are being continued at Stanford University

under the general direction of Prof. W. F. Durand.

The Bureau of Standards has undertaken four investigations for the aerodynamics committee:
442 Chapter 2: Building a Research Establishment

1. Development of open scale altimeter.

2. Diaphragms and elastic fatigue.

3. Altitude correction for air speed indicators.

4. General report on aeronautic instruments.

The first three of these are definite experimental problems while the fourth

consists not only of a summary of recent experimental investigations of instruments

carried out in cooperation with the committee at the Bureau of Standards, but will

go further and embrace a general survey of the state of this subject at the close of

the war both in the United States and abroad.

1. The work on the open scale altimeter has progressed to a point where a

working model of the essential parts of the altimeter, exclusive of the indicating

mechanism, has been assembled and tested. By proper theoretical design of the

spring and diaphragm elements an instrument has been made whose performance depends on the material of the steel spring almost entirely and only to a

slight degree on the material of the diaphragm. It has been possible to secure

steel nearly free from elastic fatigue effects, although such is not the case with the

alloys used for the thin flexible diaphragm. As a result this instrument has been

shown by test to have less than one-third of the fatigue effects (i.e., discrepancy

between increasing and decreasing readings) permitted by the Bureau of

Standards specifications for altimeters. The object of this work, which will be continued until completed, is to provide a precision altimeter suitable for altitude

determination in aircraft performance tests.

2. Thin metallic diaphragms, usually corrugated for flexibility, form a necessary

element in a great variety of engineering instruments, particularly in aneroid

barometers for altitude measurement, in air-speed indicators, certain forms of

statoscopes and rate-of-climb indicators, balloon manometers, and aviator’s oxygen

control apparatus. Such diaphragms are never perfectly elastic but show what are

known as fatigue effects, failing to recover instantly from the deformations undergone

in the normal operation of the instrument; hence, the importance of experiments

to select the most promising alloys, to determine the most effective thermal and

mechanical treatment in the process of manufacture, and to establish the most

efficient geometrical design for the diaphragms when used either singly or in

combinations. Up to the present, this investigation has resulted in the development

of measuring appliances for detecting the small changes in question by micrometric

methods, in the preparation and use of suitable shop equipment for spinning

sample diaphragms at the bureau in considerable numbers, in a preliminary

study of a variety of alloys, to select those which warrant more detailed study, and

in a special study of mechanical seasoning processes. This last phase of the work

has led to the conclusion that diaphragms can be seasoned mechanically; that is,

artificially aged and thus brought into a permanent state where they will repeat
Document 2-13(a–c) 443

their performance in successive tests under the same conditions. This is done by

repeated deformation of a suitable amount several thousand times, and is done

automatically by a mechanism designed for the purpose. Some such seasoning

process appears to be a necessary preliminary to the comparative measurement of

the effects of different processes of heat treatment, different compositions of the alloy,

and different mechanical design. The seasoning process, it will be understood, is

not intended to eliminate elastic fatigue, although it does always reduce it somewhat.

The object of the seasoning is to secure definite and uniform results, so that those

factors which will diminish the fatigue can be analyzed quantitatively.

3. It has hitherto been taken for granted that Venturi tubes, when used for airspeed indicators, will follow a familiar law which states that the suction produced

is directly proportional to the density of the air and to the square of the speed.

The object of this investigation is to determine by direct experiment whether this

law does apply to Venturi tubes or whether on the contrary, the compressibility and

viscosity of the atmosphere may cause some effects which will complicate the correction of these instruments for different altitudes. The experiments are conducted in

a so-called vacuum wind tunnel (that is, a very small air-tight wind tunnel in which

reduced pressures corresponding to high altitudes may be secured). The conclusion

has been reached that the instruments examined are free from the effect of compressibility but not entirely free from the effect of viscosity. These experiments are to

be completed and brought to a conclusion which can be expressed numerically for the

purpose of correcting such instruments when used in aircraft performance tests.

4. The general report on aeronautic instruments presents the results of investigations made during the war by the Bureau of Standards to determine the characteristic

sources of error of the various types of instruments. Tachometers, for example, for

measuring the revolutions per minute of the propeller shaft are built in a variety of

different types, operating on diverse physical principles. There are the chronometric,

centrifugal, magnetic, electric, air viscosity, air-pump, and liquid types, each of

which has its own characteristic sources of error. Aside from the ordinary errors

met in engineering instruments, such as incorrect calibration, parallax, looseness

of friction in the mechanism, elastic hysteresis, and secular changes, those used

on aircraft may be further influenced by the physical conditions peculiar to aviation,

viz, (1) extreme drop of pressure, (2) extreme change of temperature, (3) vibration,

(4) acceleration or inclination. Besides the above results, this report, which is

nearly completed, gives a description of the instruments collected by the Bureau

of Standards in cooperation with this committee during the war, including those

of British, French, Italian, Russian, Danish, and German construction.

In light of that report it will be evident that the objects toward which instrument

development work should chiefly be directed in the immediate future may be

summarized as follows:
444 Chapter 2: Building a Research Establishment

1. Open scale instruments for performance testing of aircraft. These need not

necessarily be so compact, light, or rugged as service instruments, and hence

offer freedom for such design as will insure the highest accuracy.

2. Instruments for long distance navigation, including an absolute or ground

speed indicator, and such a form of gyroscopic stabilizer as may be needed for

mounting the instruments.

3. Instruments to guide the pilot in flying through fog, such as more reliable

gyro turn indicators and compasses.

4. Better materials for springs and diaphragms and a more systematic determination of the thermal and elastic constants of the materials.

The Bureau of Standards has developed (primarily for the Air Mail Service)

a field-marking radio device which enables a pilot to steer directly to the center

of his landing field, although it may be obscured by clouds, rain, snow, or fog.

This apparatus utilizes the same transmitting equipment for the ordinary radio

direction finding signals and for the landing signals. The landing signals are projected vertically as an electromagnetic cone of great intensity, which can be heard

satisfactorily at an altitude of three to four thousand feet. The device enables the

pilot to first find the approximate vicinity of a landing field and then fly directly

to its center, thus making a safe landing in a fog or in the dark. As elevated aerial

systems are manifestly dangerous to air navigation, the Air Mail Service experimented extensively in radio transmission with antennas only 20 feet in height,

highly directional, and admitting of sharp tuning. The installation of high-powered

stations in the vicinity of flying fields is therefore made possible. Efforts are being

made to provide and perfect a practical visual signal to take the place of the present

audible signal requiring an audibility of 10,000 to overcome engine ignition

interference noises. Such a signal will greatly enlarge the field of operation. A new

type of gyroscopic nonmagnetic compass, intended to overcome the unreliability

of the magnetic compass caused by vibrations and other disturbing influences of

an airplane in motion, is now being developed by the Air Mail Service. This compass

is now in a usable form for operation on land or sea, and only requires such

changes as will adapt it to use on airplanes. It consists essentially of a solid metal

ball floating on a film of compressed air and rotating coordinately in fixed relation

to the earth’s rotation.

Document 2-13(b), “Report of Committee on Aerodynamics,” 

NACA Annual Report for 1920.

REPORT OF THE COMMITTEE ON AERODYNAMICS.

Following is a statement of the organization and functions of the committee

on aerodynamics:
Document 2-13(a–c) 445

ORGANIZATION.

Dr. John F. Hayford, Northwestern University, chairman. 

Dr. Joseph S. Ames, Johns Hopkins University, vice chairman. 

Maj. T. H. Bane, United States Army. 

Dr. L. J. Briggs, Bureau of Standards. 

Maj. V. E. Clark, United States Army. 

Commander J. C. Hunsaker, United States Navy. 

Franklin L. Hunt, Bureau of Standards. 

Prof. Charles F. Marvin, Chief Weather Bureau. 

Edward P. Warner, Massachusetts Institute of Technology, secretary. 

Dr. A. F. Zahm, United States Navy.

FUNCTIONS.

1. To aid in determining the problems relating to the theoretical and experimental study of aerodynamics to be experimentally attacked by governmental and

private agencies.

2. To endeavor to coordinate, by counsel and suggestion, the research and

experimental work involved in the investigation of such problems.

3. To act as a medium for the interchange of information regarding aerodynamic investigations, in progress or proposed.

4. The committee may direct and conduct research and experiment in aerodynamics in such laboratory or laboratories as may be placed (either in whole or

in part) under its direction.

5. The committee shall meet from time to time, on call of the chairman, and

report its actions and recommendations to the executive committee.

The committee on aerodynamics by reason of the representation of the

Bureau of Standards, the Army, the Navy, technical institutions, and the industry,

is in close contact with aerodynamical research and development work being carried

on in the United States. Its representation enables it, by counsel and suggestion,

to coordinate the experimental research work involved in the investigation of

aerodynamical problems, and to influence the direction of the proper expenditure

of energy toward those problems which seem of greatest importance.

The committee has direct control of aerodynamical research conducted at the

Langley Memorial Aeronautical Laboratory and also directs propeller research

conducted at Leland Stanford Junior University under the supervision of Dr. W.F.

Durand, and through its membership it keeps in close touch with the work being

carried on at the Bureau of Standards, at McCook Field by the engineering division of the Army Air Service, and at the Washington Navy Yard by the Bureau of

Construction and Repair, United States Navy.

Two new wind tunnels have been completed and put in operation in the

United States within the past year. A new 5-foot wind tunnel at the Langley
446 Chapter 2: Building a Research Establishment

Memorial Aeronautical Laboratory has gone into service and has already run at

speeds slightly in excess of 110 miles per hour. It is anticipated that speeds of 140

miles per hour will be attained with a new propeller which will be better suited to

the characteristics of the electric motor employed. The other new wind tunnel of

the year is that constructed by the Curtiss Engineering Corporation at Garden

City and is of the true Eiffel type.

The committee on aerodynamics, in directing the research work at the

Langley Memorial Aeronautical Laboratory, has adopted a definite policy with

reference to research work to be conducted at this laboratory. The policy adopted

confines the work to three general problems, and, in order to obtain results which

will be of general use, experiments are to be conducted in such a manner that

general conclusions and, if possible, general theories may result from them. The

following three general problems covering the work of the aerodynamical laboratory

for the coming year have been adopted:

(a) Comparison between the stability of airplanes, as determined from fullflight test and as determined from calculations based on wind tunnel

measurements.

The committee will endeavor to determine the characteristics and peculiarities of certain existing airplanes, and attempt to account for these by calculations based on wind tunnel work. The matter of control will also fall

under this heading. The first work conducted will probably be confined to the

explanation of the theory of small oscillations and its verification with full-scale

work. Later, a study of maneuverability and controllability will follow, as it is

felt that in the present state of the art there is not available to airplane designers a rational method of predicting the maneuverability of airplanes from the

drawings of the airplanes or from wind tunnel experiments with models.

(b) Similar comparison between the performance of airplanes full-scale and

the calculations based on wind tunnel experiments.

A great deal of attention has been given by the British to the prediction of performance based on aerodynamic data, but there is still a gap

between model and full-scale results which can not be bridged until we

have more information. The performance is intimately connected with

the propeller, and it is the intention of the committee to have all propeller research conducted at the Aerodynamical Laboratory of Leland

Stanford Junior University under the direction of Dr. Durand. An effort

will be made to tie in the results obtained at Leland Stanford with the

performance work being done at Langley Field. Experiments will also be

conducted on models of well-known airplanes to better understand the

landing and starting characteristics of airplanes and to determine exactly

what it is that makes certain airplanes require a long run.
Document 2-13(a–c) 447

(c) General aerofoil problem, including control surfaces, with particular reference to thick sections and combinations and modifications of such sections.

The committee is to undertake a systematic investigation of thick wing

sections, after a thorough analysis of what has been done in this matter,

and to duplicate some of the experiments already performed. After the

determination of what properties of thick wing sections are of interest,

work will then be carried along with a view to systematic variation of the

variables which determine the aerodynamic properties of a series.

Determination will also be made of the relation between aerodynamic

properties of such standard aerofoils and aerofoils of similar profile but of

different aspect ratio and taper. It is also desirable to know biplane and

other interference effects when the aerofoils are used in combination. A

careful study will also be made of recent work, by which it appears possible to predict from a knowledge of the lift coefficient the properties of

aerofoils in combination and of different aspect ratio, as well as the influence of a boundary.

Such problems arising in connection with the Army and Navy programs of

development as fit in logically with the above program will be referred to the committee on aerodynamics, and the research work covering the problems will be conducted at the Langley Memorial Aeronautical Laboratory.

At the Langley Memorial Aeronautical Laboratory a large number of experiments

have been carried on with model wind tunnels in the past year to determine the best

form for steadiness of flow and efficiency of operation. The effect of various shapes

of cones, experimental chambers, and types of propellers, honeycombs, and diffusers were thoroughly studied. A special recording air-speed meter and recording

yaw meter were designed in order to study the steadiness of flow, and it was found

that the tunnel with a continuous throat was superior to the open or Eiffel type of

tunnel both in efficiency and steadiness of flow. It was also demonstrated that a

honeycomb placed in the entrance cone is of the greatest value in straightening

the air flow, but a diffuser placed in the return circuit was apparently of little value.

The National Advisory Committee’s 5-foot wind tunnel was completed in the

spring of 1920 and has been in continuous operation since. This tunnel is designed

from the data obtained in the model experiments and is very satisfactory both in

efficiency and steadiness of flow. The 10-foot four-bladed propeller is driven by a 200-

horsepower variable-speed electric motor. The power for this motor is obtained

from gasoline-driven generating sets, and the control system is very convenient,

the motor being started and stopped simply by pushing a button in the experimental

chamber, and the speed being controlled by a rheostat from the same place.

The balance used in this tunnel is of the modified N.P.L. type, and was constructed in the shop of the National Advisory Committee at Langley Field. Unlike
448 Chapter 2: Building a Research Establishment

the usual balance, the weight is supported on a half bearing socket, rather than a

conical pivot, as this device considerably reduces the friction and will carry a

much larger load. It is also possible with this balance to simultaneously read the

lift, drag, and pitching moment. As the N.P.L. type of balance is not suited to

holding tapered wings, and as a large amount of work of this kind is planned for

the future, a simple wire type of balance is being constructed at the present time,

similar to that used in the wind tunnel at Göttingen.

It has been the practice in the past when setting up a model to align the chord of

the wing with the wind by placing a thin wooden batten on the wing and comparing

this batten with a straight line on the floor of the tunnel. But as this method is rather

laborious and inaccurate, a new type of aligning apparatus has been designed for this

tunnel, consisting essentially of a mechanism for reflecting a beam of light from a plain

mirror which is attached parallel to the chord of the wing, so that by rotating the wing

the reflected beam of light is brought to a cross line on a small target on the side of

the experimental chamber. In this way a wing can be lined up with an accuracy of 0.01°

in a very few seconds. As the air speeds used in this wind tunnel are considerably

higher than those usually encountered, a special type of manometer was constructed

to obviate the necessity of having an extremely long inclined tube. This gauge changes

the head of liquid and at the same time the inclination of the tube, so that the

fluctuations of the liquid are approximately equal at any speed. A multiple

manometer has also been constructed for pressure distribution work on models,

containing 20 glass tubes, the inclination of which can be adjusted to any desired angle.

A thorough investigation has been made of the problem of spindle interference

and the best manner of protecting the spindle by a fairwater. Different types and

lengths of fairwater were tested in order to determine which condition would give

the least total interference. An accurate determination of the effective resistance

of the spindle was made for various lengths of spindle and for various air speeds

so that a complete set of data is available for use on any model tests for the future.

In order to provide data for stability calculations a wing was tested through an

angle of 360 degrees, and a model of an airplane was tested in the same way. In

order to determine the scale corrections for model airplanes a model of the JN4H

was constructed with great accuracy, and all details of the airplane were reproduced

in the model, including the radiator and motor, but the wires were omitted as it

was thought that their resistance could be determined better from tests of the fullsized wires. This model was tested at speeds of 30, 60, and 90 miles per hour in

order to determine the corrections that must be applied to it in order to give the

full-flight performance which was carefully determined on the full-sized machine.

FREE FLIGHT.

The machines available for the committee’s use at the Langley Memorial

Aeronautical Laboratory consist of two JN4H training machines and one DH4.
Document 2-13(a–c) 449

During the summer the machines have been in the air about 60 hours. Numerous

small changes have been made on these machines during the different tests,

including changing the stagger, changing the angle of the tail plane, and changing

the position of the center of gravity by adding weight at the front or rear of the

fuselage. A large number of special instruments have been designed and constructed at Langley Field for research in full flight. An accelerometer has been

developed for obtaining the loads on an airplane during stunts and landings, and

satisfactory results have been obtained with it, which are of considerably greater

accuracy than those obtained by other types of instruments. Instruments were also

developed for recording the position of and the force on all three controls of the

airplane, and variable results have been obtained with these instruments. For

obtaining the pressure distribution on the tail of the full-sized machine a special

multiple manometer was constructed having 110 glass manometer tubes, all of

which could be photographed at one time by an automatic film camera placed in

the fuselage. As this instrument will only determine accurately the pressure distribution in steady flight, another manometer is now being constructed consisting

of a large number of small diaphragm gauges which will record continuously on

a moving film so that the rise and fall of the pressure at various points on the tail

surfaces can be recorded during any stunt maneuver.

An air-speed meter and yaw meter have been constructed, working on the

optical recording principle, having the actual period of the instrument high and

its friction small, so that air-speed records can be obtained of any small or high

period fluctuations in the wind velocity. To determine the angular rotation of the

airplane during flight, in order to study its stability properties, a kymograph was

constructed consisting of a narrow slit which focused the image of the sun on moving

bromide paper, and another instrument of the same type has been constructed

working on the gyroscopic principle. For obtaining the full-flight lift and drag

coefficient a special longitudinal inclinometer was constructed which would give

a large scale deflection and would be convenient and accurate to read.

The investigations undertaken consist of the determination of the lift and drag

coefficients of the JN4H in free flight, and it is found possible by careful piloting to flay

the machine at or slightly beyond the burble point. A thorough experimental investigation has been made of the static longitudinal stability of the airplane and a great

many factors have been altered on the full-sized machine, such as changing the angle

of the tail plane, changing the center of gravity of the machine, changing the section

of the tail plane, and inclining the angle of the propeller axis. A study was made of

the angle of attack and the air speed at the wing tips during spins and loops. This

was accomplished by placing vanes and air-speed meters at the wing tips and photographing them during the maneuver by means of a camera gun and then plotting

the curve of angle and speed against time from the photographs so obtained.
450 Chapter 2: Building a Research Establishment

A very extensive investigation of the pressure distribution over the tail of an

airplane in free flight has been undertaken. The pressure at 110 points on the left

and right hand sides of the tail have been taken independently and the total pressure

determined from these two curves. By means of photographic recording methods

the time taken for making this investigation in the air is brief, but the computation

and plotting of the results are laborious and require a long time for their completion.

Runs were made with three positions of the center of gravity and two angles of

setting of the stabilizer, as well as one run with celluloid over the crack between

the stabilizer and the elevator. In all cases the pressure found over the tail was

extremely low and in steady flight the load on the tail would be found very small

compared with the load resulting from accelerated flight. A large number of

records have been taken with the recording accelerometer designed by the

N.A.C.A., these records being taken in the JN4H and several other machines during

various stunts and landings. It was found that the maximum acceleration experienced

in any stunt was during a roll, where the acceleration reached a maximum of 4.2 g.

In order to determine the characteristics of an airplane during circling flight a

record of the forces on all three controls was made doing banks of various angles

up to 60 degrees and side slips up to 20 degrees of yaw.

The wind tunnel at Leland Stanford Junior University has again been occupied entirely with propeller tests. The results of the research work conducted this

year are contained in technical report No. 109. Preparations are being made for

tests on propellers at large angles of yaw, which will give data for the analysis of

helicopters traveling horizontally.

Dr. George de Bothezat, aerodynamical expert of the National Advisory

Committee for Aeronautics, has carried on at McCook Field, with the cooperation

of the Engineering Division of the Army Air Service, a special investigation for

the measurement of aerodynamic performance. The report on this investigation

has been completed and approved as technical report No. 97, entitled “General

Theory of the Steady Motion of an Airplane.” This investigation involved the

design and construction of a new type of barograph. Also in connection with his

investigation of airplane performance, Dr. de Bothezat has designed a torque

meter and a rate-of-climbmeter, which are under construction. The torque meter is

a very simple design, and present indications are that it will be a most serviceable

and efficient instrument. The rate-of-climbmeter is not based on a new principle;

it is simply a new construction and design embodying the experience obtained in

the use of other instruments.

The research work conducted by the Bureau of Construction and Repair of

the Navy Department is carried on at the aerodynamical laboratory of the

Washington Navy Yard and at the naval aircraft factory, Philadelphia Navy Yard.

At the Washington Navy Yard two wind tunnels are in operation, and during the
Document 2-13(a–c) 451

year a large number of airplanes and seaplane models have been given routine

tests, and tests on many new aerofoil sections have also been made. Special attention has been given to testing streamline forms and struts. Yawing tests were conducted on the EP and the IE envelopes, which are formed from mathematical

curves and have very low resistance. The tests indicate that the yawing moment

about the center of gravity of a bare streamlined form varies but little from one

shape to another. In connection with the tests on struts, it was shown that the Navy

I strut has approximately 15 per cent less resistance than that given for the “Best”

strut by the National Physical Laboratory. Wind tunnel tests were also conducted

on two airship cars, one of faired contour and the other with facets of the same

general contour, the results of which show the great value of fairing. The resistance

of the faired car was 15 per cent less than that of the unfaired.

In connection with the wind tunnel at the Washington Navy Yard, a new aerodynamic balance of great interest has been developed. The balance is so designed that

all adjustments of weights to bring the balance into equilibrium are automatic, and the

time required for testing and the number of skilled operators are thus much decreased.

The Bureau of Construction and Repair has also undertaken the development

and construction of the following instruments:

A precision recording barograph intended for use in airplane trials,

and especially for measuring the landing angle of airplanes, for

which no wind tunnel test is available. This instrument will have

a range of from 0 to 5,000 feet, and will incorporate the desirable

features of the present Bureau of Standards precision altimeter.

Two thermometer altimeters and density indicators. These instruments

will combine a thermometric element with a pressure element in

such a manner as to show at all times the altitude corrected for

temperature.

Two instruments intended to measure quantitatively the permeability

of gas cells of envelopes without the removal of samples. The

construction of these instruments has been suggested by the technical staff of the Bureau of Standards. This instrument is to take

the form of a cup of suitable area which is pressed against the

envelope at the point where the permeability is to be determined.

A current of air is either sucked or driven through the cup,

sweeping it out at a known rate. The mixture of gas and air from

the cup is then passed through a thermal conductivity cell, and

the proportion of hydrogen contained in the mixture is determined from the thermal conductivity of the mixture.

In the high-speed wind tunnel at McCook Field, which is operated under the

direction of the technical staff of the Army Air Service, work has been continued
452 Chapter 2: Building a Research Establishment

along the same general lines as those indicated in technical report No. 83. During

the year it is contemplated that tests will be conducted to determine the flow

around a sphere and around biplane combinations. It is hoped thus to determine

how nearly the action of the visible vapor particles indicate the true air flow about

a body, and to visualize the flow around combinations of more than one supporting

surface so as to determine the nature of the interference between the upper and

lower surfaces should be of the greatest interest. It is also hoped to photograph

the vapor action about a sphere over as large an air-speed range as possible. The

sphere is to be supported in a manner to produce a minimum disturbance due to the

support, and the photographs obtained are to be compared with existing photographs of flow about spheres and with the theoretical streamlines.

It is also hoped that tests will be conducted to determine the effect of rake

and tapered wing tips on air flow, as this information may make it possible to further

improve the airplane form and nature of taper in wings.

Performance tests are also conducted at McCook Field, and the committee on

aerodynamics has requested that special tests be made on longitudinal stability to

obtain an index of the dynamic longitudinal stability of the various airplanes used

by the Army. The work already done by the staff of the National Advisory

Committee for Aeronautics at Dayton with the cooperation of the Engineering

Division of the Air Service on five airplanes is but a beginning of longitudinal stability investigation. It is desirable to obtain readings of stick forces and elevator

angles on every type of machine in the Army’s possession, and to have curves

plotted in the same way as in National Advisory Committee’s report No. 96.

The investigations carried on at the two wind tunnels of the Bureau of

Standards under the direction of Dr. L.J. Briggs have consisted largely in instrument

calibration and testing. The principal research has been in connection with the

resistance of spheres and projectiles.

The work of the Aeronautic Instruments Section of the Bureau of Standards

comprises the investigation, experimental development, and testing of aircraft

instruments; also the development of methods of testing, fundamental researches

on the physical principles involved in such instruments, and the study of their

behavior in actual service.

The more important investigations which have been undertaken by the section

during the past year are as follows:

An investigation has been completed and prepared for publication through

the National Advisory Committee for Aeronautics on the effect on the performance

of Venturi tube air-speed indicators of changes in atmospheric pressure. The

results show that in certain instruments commonly used a correction should be

applied for the viscosity of the air, a factor which has not hitherto been taken into

account. This is of special interest in dirigible work where the air speeds may be
Document 2-13(a–c) 453

low, and also in aircraft performance tests where exceptional precision is required.

An altimeter of exceptional accuracy designed and made at the Bureau of

Standards has been completed and submitted to the Army. Another model with

additional improvements has recently been designed and is under construction.

At the request of the National Advisory Committee for Aeronautics a fundamental investigation of the factors determining the behavior of flexible

diaphragms as used in aeronautic instruments has been undertaken. The irreversible effects which cause the lag in diaphragm instruments has been formulated

mathematically. The relation between force and deflection for diaphragms of different

sizes, thickness, and materials has been studied graphically, practical methods for

spinning diaphragms and building up diaphragm boxes have been investigated,

and the possibilities of mechanical seasoning by repeated stress considered.

An improved rate of climb indicator, which indicates directly the rate of climb

of aircraft in hundreds of feet per minute, has been completed and tested, and

specifications have been prepared for the Army to use in the manufacture of a

number of these instruments.

Information regarding instruments available for aerial navigation in cloudy

weather or at night or for long-distance flights has been compiled at the request of

the National Advisory Committee for Aeronautics and the Air Mail Service by the

Aeronautic Instruments Section. This work will be continued and the development of new instruments undertaken.

Other investigations have been the development of a motion-picture apparatus

for recording instrument readings during the flight of an airplane; a study of the

errors in instruments used for determining the direction of aircraft, such as gyroscopic and liquid inclinometers and banking indicators, gyroscopic and magnetic

compasses and turn indicators, a systematic investigation of commercial sphygnomanometers; a paper on the results of investigations on German instruments; a

statistical study of the causes of failure in aeronautic instruments.

Assistance has been given the Air Service, the Aero Club of America, and others

interested, during the past year, in the world’s altitude competition for airplanes.

Instruments have been calibrated and the best procedure for determining the altitude

attained formulated.
454 Chapter 2: Building a Research Establishment

Document 2-13(c), “Report of Committee on Aerodynamics,” 

NACA Annual Report for 1921.

ORGANIZATION.

The Committee on aerodynamics is at present composed of the following members:

Dr. John F. Hayford, Northwestern University, chairman. 

Dr. Joseph S. Ames, Johns Hopkins University, vice chairman. 

Maj. T. H. Bane, United States Army. 

Dr. L. J. Briggs, Bureau of Standards. 

Commander J. C. Hunsaker, United States Navy. 

Dr. Franklin L. Hunt, Bureau of Standards. 

Maj. H. S. Martin, engineering division, McCook Field.

Prof. Charles F. Marvin, Chief Weather Bureau. 

C. I . Stanton, Air Mail Service.

Edward P. Warner, Massachusetts Institute of Technology, secretary. 

Dr. A. F. Zahm, United States Navy.

FUNCTIONS.

The functions of the committee on aerodynamics are as follows:

1. To determine what problems in theoretical and experimental aerodynamics

are most important for investigation by government and private agencies.

2. To coordinate by counsel and suggestion the research work involved in the

investigation of such problems.

3. To act as a medium for the interchange of information regarding aerodynamic investigations and developments in progress or proposed.

4. The committee may direct and conduct research in experimental aerodynamics in such laboratory or laboratories as may be placed either in whole or in

part under its direction.

5. The committee shall meet from time to time on the call of the chairman

and report its actions and recommendations to the executive committee.

The committee on aerodynamics by reason of the representation of various

organizations interested in aeronautics is in close contact with all aerodynamical

work being carried out in the United States. In this way the current work of each

organization is made known to all, thus preventing duplication of effort. Also all

research work is stimulated by the prompt distribution of new ideas and new

results which adds greatly to the efficient conduction of aerodynamic research.

The committee keeps the research workers in this country supplied with information

on all European progress in aerodynamics by means of a foreign representative

who is in close touch with all aeronautical activities in Europe. This direct information

is supplemented by the translation and circulation of copies of the more important

foreign reports and articles.
Document 2-13(a–c) 455

The Aerodynamic Committee has direct control of the aerodynamical

research conducted at Langley Field, the propeller research conducted at Leland

Stanford University under the supervision of Dr. W.F. Durand, and some special

investigations conducted at the Bureau of Standards and at a number of universities.

WIND TUNNEL.

The committee’s wind tunnel at Langley Field has recently had several

changes made in it which have considerably improved the steadiness of flow. The

most important of these is a new electrical system consisting of a synchronous

motor-generator set which furnishes power direct to the wind tunnel motor. The

speed of the wind tunnel motor is kept at a constant value within ±0.2 of a per cent

by means of automatic voltage regulators. The air flow has also been considerably

improved by placing a series of vanes around the end of the exit cone so that the

air escapes radially. A wire type of balance is now used in this tunnel for all speeds

between 30 and 60 meters per second.

It has long been felt that the tests made in the wind tunnel with a model varying

much from the usual type are unreliable because of the uncertainty of the scale

correction. For this reason the committee is now constructing at Langley Field a

compressed-air wind tunnel with a throat diameter of 1.6 meters, a maximum

speed of 25 meters per second, and a working pressure of 20 atmospheres. This

wind tunnel will give a Reynolds number which is the same as for a full-sized airplane,

and although the difficulties of supporting the model are great, the use of a comparatively low velocity and a high pressure have overcome the mechanical difficulties.

There are being constructed at the present time in the United States four

other wind tunnels. At the Massachusetts Institute of Technology there are being

erected a 1.25 meter and a 2.50 meter tunnel of the open-circuit type and with

continuous throats. At McCook Field there is being constructed a high-speed 1.6 meter

wind tunnel of the open-circuit type, which is designed for a velocity of 200 miles

per hour. The Bureau of Standards at Washington is constructing a wind tunnel

with a throat diameter of 3.25 meters. This wind tunnel is novel in that it is built

in the open without any housing. The wind tunnel is well surrounded by trees and

hills to prevent as far as possible the atmospheric conditions affecting the air flow.

The three-dimensional balance designed by Dr. A.F. Zahm for the Washington

Navy Yard wind tunnel has proved very satisfactory. The weights of this balance

are automatically actuated by electrically driven lead screws, and the time of making

a test is much shorter than with other types of balances.

FREE FLIGHT.

The committee now has in use for aerodynamic research at Langley Field five

airplanes; three JN4H’s, one VE-7, and one Thomas-Morse MB3. The JN4H has

been used by the committee extensively in experimental work, mainly because of

its strength and the economy of operation. During the past year the flying time
456 Chapter 2: Building a Research Establishment

of the airplane has been 110 hours, representing 260 flights. Fifty-two per cent of

the flying time has been used in actually making measurements in the air. No

accidents of any kind have occurred with the committee’s airplanes. One forced

landing was made due to the sticking of the carburetor float during violent stunting,

but the airplane was brought down without damage to itself or the instruments

which it contained. Although complete airplanes have not as yet been constructed

by the committee, a number of parts, such as wings, tail surfaces, etc., have been

designed and constructed at Langley Field for use in free flight research.

INSTRUMENTS.

A number of new pieces of apparatus have been constructed for the wind tunnel,

including a machine for forming plaster wings, a new micromanometer, a light

balance for measuring the moments of control surfaces, and an instrument for

measuring the rolling velocity of wings. It has become more and more evident, as

the discrepancies between free flight and model tests have been discovered, that

it is necessary to produce in the wind tunnel a slip stream comparable with that

on the full-sized airplanes. A very small flexible shaft has been developed which

is able to drive the model airplane propeller up to speeds of 30,000 revolutions

per minute, which corresponds to the normal speed of a full-sized propeller. The

flexible shaft is so small that it disturbs the air flow inappreciably and in this

respect is superior to an electric motor or a turbine.

It is realized that all free-flight data must be obtained by recording instruments,

first, because events happen so rapidly that observations are difficult to make, and

secondly, because the observer is under rather a nervous strain and can not take

observations as accurately as he could in the laboratory. For this reason the committee

has designed and constructed a considerable number of standardized recording

instruments, electrically driven and synchronized, for taking records on interchangeable film drums. With these instruments the only duty of the observer is to

change the drums at the end of the record, for the pilot can start and stop all of

the instruments with a single switch. The following instruments have been constructed and used during the year:

(1) A new accelerometer more compact and accurate than the previous model.

(2) A recording air speed meter with a high natural frequency and small friction.

(3) A new model of a kymograph.

(4) A multiple manometer which will record on a moving film 30 simultaneous

records of varying pressures. The natural frequency of this instrument is very high

and the volume does not change appreciably with changes in pressure, which is a

very important fact when recording pressures through long tubes.

(5) An instrument for recording annular velocities about a single axis.

(6) A control position recorder for three controls.

(7) A balance for measuring the forces on a trailing wing in flight.
Document 2-13(a–c) 457

The aeronautic instruments section of the Bureau of Standards has been

engaged in an extensive program of research and development work on aircraft

instruments in cooperation with the National Advisory Committee for Aeronautics,

the Army, the Navy, and to a more limited extent with other Government agencies

and private concerns. In addition to the experimental investigations and the

development of new instruments a considerable amount of work has been carried

out in connection with the routine testing of service instruments.

The investigation of the altitude effect on air speed indicators undertaken at

the request of the National Advisory Committee for Aeronautics has been continued

and extended. The experiments have been conducted in an improved wind tunnel

with a 16-inch throat and mounted in one of the Bureau of Standards altitude

chambers. With this apparatus valuable data have been obtained at speeds up to

100 miles per hour and under conditions of pressure and temperature corresponding

to altitudes up to 30,000 feet.

Research concerning the action of diaphragms and Bourdon tubes undertaken

at the request of the National Advisory Committee for Aeronautics has been continued with the purpose of determining the laws of deflection and of obtaining

essential information of value in the design of instruments involving the use of

diaphragms and Bourdon tubes.

A series of eight reports dealing with the various aeronautic instruments has

been prepared for the National Advisory Committee for Aeronautics and will be

found in the Seventh Annual Report.

At the request of the Army and the Navy, the development of the following

instruments has been undertaken:

An improved aircraft sextant. 

An improved compass.

An improved precision barometer.

A precision altimeter compensated for air temperature.

A precision barograph. 

An improved rate of climb indicator. 

An improved rate of climb recorder.

A combined statoscope and rate of climb indicator.

A synchronizing type ground speed indicator. 

An astronomical position finder. 

A horizontal angle indicator. 

An improved centrifugal tachometer. 

An air speed indicator for dirigibles. 

A ballonet volume indicator for dirigibles. 

Standard testing sets for field use.

Pursuant of the policy of following the latest developments in aeronautic
458 Chapter 2: Building a Research Establishment

instruments in foreign countries, a member of the aeronautic instruments section

was detailed to investigate the recent developments in England, France, Italy, and

Germany. This work was carried on in cooperation with the National Advisory

Committee for Aeronautics representative in Europe and our military, naval, and

commercial attachés, and much valuable information has been obtained.

A carbon pile tensiometer is being developed for the Navy which allows the

accurate recording of tensions at a distance. An instrument has been devised by

the Navy for the measurement of the ground speed of an airplane at frequent

intervals of time on taking off or landing.

AEROFOIL TESTS.

During the past year the committee has conducted a large number of aerofoil

tests in its 5-foot wind tunnel at Langley Field. The main object of these tests was

to study the properties of thick aerofoils suitable for internal bracing. The tests

were made at 35 meters per second, and in some cases as high as 60 meters per

second as it was found that thick wings improve in efficiency with the speed more

rapidly than thin wings. Some of the sections developed had at all angles a higher efficiency than the R.A.F. 15 section tested under the same conditions, and yet

were more than three times as thick as that section in the center, while the maximum lift coefficients were approximately the same. A number of wings were tested which tapered in plan form, and it was found, contrary to expectations, that

heavily tapered wings had the same center of pressure travel and practically the

same efficiency as wings of uniform section.

The distribution of pressure was studied over 12 thick aerofoils of various

types in order to determine the loading along the spars when the section varied

along the span. A new method was devised for constructing pressure distribution

models with comparatively little expense.

The effect of placing an aerofoil close to a flat surface representing the earth

was thoroughly investigated both at the Massachusetts Institute of Technology

and at the Washington Navy Yard. It was found that there was a remarkable

increase in efficiency of the wing when close to a flat surface, which accounts for

the fact that certain airplanes float for such long distances before landing.

Work has been continued in the McCook Field wind tunnel on various aerofoils

at very high speeds, and a further study of vortex motion has been made.

Perhaps the most interesting work which has been carried out on aerofoils is

that done by the committee in the testing of large aerofoils when suspended

beneath a flying airplane. The aerofoil, constructed in the same way as an ordinary

airplane wing of wood and fabric, is pulled up against the lower side of the fuselage

in taking off, and when in the air is lowered down by means of a windlass to a distance

of 20 or 30 feet or as far as is necessary to got out of the influence of the downwash.

The magnitude of the resultant force is measured by a balance in the fuselage and
Document 2-13(a–c) 459

the angle at which the wing trails back from the vertical measures the angle of the

resultant. From these figures the lift and drag can be easily computed. At present

only small wings of 6 feet span have been tested in this way, but it is evident from

the great steadiness with which they trail beneath the airplane that accuracies

probably as great as those obtained in the wind tunnel can be reached, although

it is necessary to fly in smooth air for this kind of work. The results from the present

apparatus although only of a preliminary character show such a good agreement

with high speed wind tunnel tests of the same section that it is proposed to use a

large bombing machine and trail wings of 30 feet span beneath it. Tests of this

nature have not only the same Reynolds number, but also the same velocity, the

same size, and the same amount of turbulence as the full-sized airplane, so that

the results can be used by designers with perfect confidence.

A number of aerofoil sections have been tested, among which were several of the

Göttingen series. The Washington Navy Yard tests check the Göttingen tests as closely

as could be expected, the general types of the characteristic curves being very similar

in every case. The Göttingen aerofoils tested were: Nos. 173, 255, 256, and 822.

Tests for scale effect have also been made on the R.A.F. 15 and R.A.F. 19 aerofoils.

STRUTS.

An interesting investigation has been made at the navy yard wind tunnel in

Washington in the distribution of pressure over a strut. It is concluded that the total

drag of the strut is the small difference between the upstream and downstream

drag, so that a small error in measuring these will cause a huge error in the total.

STABILITY.

A very complete investigation has been made of the oscillations in flight of

the VE-7 and JN4H, the latter airplane with a special tail plane to make it statically

stable. The results on the whole are in poor agreement with the theory, due mainly,

it is believed, to the fact that the oscillations are large, often over 60 degrees, and

that the slip stream has a considerable influence.

Considerable work has been done on static stability and it is becoming more

and more evident that the aspect ratio of the tail plane has by far the greatest

influence on the stability. It has also been found in actual flight that complete static

stability may be obtained when the load is positive upon tail surfaces at all times.

A study of the distribution of pressure over the tail surfaces of this surface in

steady flight has given valuable information as to the functions of this surface in

producing stability.

The lateral stability derivatives Yv, Lv, and Nv have been determined in free flight

for the JN4H and comparison has been made with the results from wind tunnel tests.

On the whole the agreement is good, the discrepancies being mainly due to the influence of the slip stream and to the fact that in the model the control surfaces were

assumed to be in a neutral position, whereas actually they were at a considerable angle.
460 Chapter 2: Building a Research Establishment

A mechanical device has been constructed which will illustrate in every particular

the dynamic and statical stability of an airplane. By the adjustment of weights the

effect of changing the mass, the moment of inertia, the damping, etc., can be produced at will. As yet it has not been possible to obtain any quantitative value for

stability with this instrument, but it is hoped that it may be used for quickly finding

the stability properties of a new airplane from its known characteristics.

Tests have been made by the Navy on a series of balanced control surfaces with

various types of balance. The characteristics of the type in which the axis is placed aft

of the leading edge of the movable surface have been investigated at some length.

STRESSES IN FLIGHT.

The distribution of pressure was determined over the horizontal tail surfaces

of a JN4H during all types of maneuver. In no case did the maximum loading on

the tail exceed 6 pounds per square foot, and contrary to the usual expectations

this load was in an upward direction. A theory has been devised which will give

the loading on the tail surfaces in close agreement with the actual measurements.

The distribution of pressure over the rudder and fin have also been investigated on the same airplane and it was found that the heaviest loads occur in a roll

where the loading may go as high as 10 pounds per square foot. It is interesting

to notice from the standpoint of fuselage design that the maximum load on the

horizontal tail surfaces, the maximum load on the rudder and fin, and the maximum load on the wings may all occur at the same time.

The recent development of very high speed airplanes has shown that very

large unexpected loads may occur on the wing surface, several instances causing

the stripping of the fabric or crippling of the trailing edge. A Thomas-Morse single

seater which has a speed of over 160 miles an hour has been fitted up for measuring

the distribution of pressure over the wing surfaces. It is hoped to determine the

pressures both in steady flight and during violent maneuvering, and for this purpose

the wings have been especially strengthened.

CONTROLLABILITY.

The measurement of and the design for controllability are very important

problems and ones which have received but scant attention. In fact, the very definition of controllability is at the present time stated vaguely. The committee is

now making an attempt to find some accurate quantitative means of measuring

the controllability of various airplanes and to find the effect on controllability of

various changes in control surfaces.

The desire for high speed has led many designers to eliminate the external

bracing on the horizontal tail surfaces and for this reason a number of airplanes have

been constructed with rather thick sections for the tail surfaces. Several airplanes

of this type have been found by pilots to be extremely sluggish in responding to the

controls; that is, for a certain range about the neutral position the controls have no
Document 2-13(a–c) 461

effect. This condition was investigated in the wind tunnel on a tail plane of this type,

and it was found that the elevator must be moved several degrees on either side of

its neutral position before the force on the tail is appreciably changed, due to the

fact that the elevator seemed to be in the shadow of the thicker portion of the tail

surfaces and could have no effect until it was turned out into the free air stream.

The angular velocity and angular accelerations have been measured on a

JN4H during all types of maneuver, in order to provide designers with data which

will be of use in construction of airplanes.

The subject of control, especially lateral control, at low flying speeds has

received some attention. It is evident, however, that different airplanes, although

varying only slightly in external characteristics, vary tremendously in the amount

of lateral control which they have at the stalling speed, and an explanation of this

would be of great value. The Navy has recently devised an entirely new type of lateral

control which in wind tunnel tests shows great promise.

AIRSHIPS.

Several types of external-pressure pads developed by the Navy have been tested

upon the wind of an airplane at Langley Field in order to assure that such opening

when cemented to the outside of the wing will give the same reading as a flush hole.

One type of pad has proved to be very successful. The possibilities have been considered of measuring the pressure over the surface of an airship during accelerated

flight, and as yet no satisfactory method has been devised for entirely eliminating

the rather large errors due to the forces acting upon the air column in the long

connecting tubes which are necessary in this experiment. The investigation, however, has not be abandoned, and it is believed that the difficulties will be overcome.

Extensive tests have been made on two models of the rigid airship ZR-1.

These tests were made on the hulls, bare and with six types of control surfaces.

Tests have been conducted at the navy yard wind tunnel in Washington on the

effect of fineness, ratio, and length of parallel middle body on airship forms.

PROPELLERS.

Experiments have been conducted in the wind tunnel to measure the drag of

various propellers under various degrees of yaw and with different amounts of

braking. The drags of propellers are rather small so that the possibility of the save

vertical descent of the helicopter without power does not look very probably if the

usual type of propeller is used. Test have also been conducted upon a helicopter

propeller having blades which are automatically set at a constant angle of attack

by means of individual tail planes.

An extensive investigation has been carried out at Leland Stanford University

on the properties of propellers at angles of yaw. The results look very promising

in connection with the horizontal travel of helicopters, as a considerable horizontal

thrust may be obtained with no more power than is required in ordinary flight.
462 Chapter 2: Building a Research Establishment

BOMBS.

The Bureau of Standards has been conducting a very extensive investigation

of bombs and projectiles not only in their 150-mile wind tunnel but also in a 12-

inch air stream from a high-power compressor where speed can be obtained

above the velocity of sound. Some very interesting conclusions have been reached

in connection with stream lining at very high speeds.
Document 2-14 463

Document 2-14

J. C. Hunsaker, memorandum to NACA, “Recommendations for

Research Program—Comparison of Wing Characteristics 

in Models and Free Flight,” 10 November 1920, RA file J,

Historical Archives, NASA, Langley.

One of the NACA’s most important early research programs began in 1920

after Jerome Hunsaker recommended that the committee pursue a systematic

program comparing the wing characteristics of wind tunnel models with those of

identical, but full-size, wings in free flight. This proposal, which the NACA

embraced and carried out at Langley, led to the establishment of new research

methods and produced some of the first reliable data comparing actual and

model airplanes. Interestingly, the agreement between model and actual wings

was generally good, but the fuselage comparisons revealed considerable discrepancies. Understanding why would require several more years of experiments and

analysis and would ultimately help justify larger wind tunnels at Langley. (Note:

The duplication of paragraphs numbered “5” in the report is from the original.)

Document 2-14, Jerome Hunsaker to NACA, 

“Recommendations for Research Program,” 1920.

November 10, 1920

From: J. C. Hunsaker, Commander (C.C.), U.S.N.

To: National Advisory Committee for Aeronautics, Room 2722, Navy Building.

Subject: Recommendations for Research Program—Comparison of Wing

Characteristics in Models and Free Flight.

1. It is recommended that the contemplated research on comparison between

model and full-scale airplanes be made as thorough as possible in order to furnish

accurate and complete data on which we may base performance estimates. A

research of this nature should include a study of at least three aerofoil sections

which are widely separated in their characteristics. The sections recommended by

Mr. Norton, i.e., Curtiss (JN-4), R.A.F.-15, Albatross, and U.S.A.T.S.-5 seem to

answer all requirements. The problem would be somewhat simplified if a Parasol

type of monoplane were available, but perhaps more information may be

obtained from a study of a biplane such as the JN4H now available.

2. It is suggested that very accurate scale models of the component parts of this

airplane be constructed and tested in the tunnel at various speeds, singly and in

combination, with a view to determine the probable scale effect and the interferences.
464 Chapter 2: Building a Research Establishment

The wing combinations should be tested carefully and investigated analytically by

means of the Gottingen equations (Prandtl and Munk). These equations give very

satisfactory results and it is thought that additional constants should be determined

for all cases in common use. The German tests have not undertaken a study of

tapered wings and, in view of the probable importance of this feature in internally

braced designs, it is suggested that a study be made of taper in monoplane and

biplane combination as a parallel work. Reference is made to Munk’s article in

Technische Berichte II-2, for the method of determining the constants.

3. The resistance derivatives should be determined for this machine by experiments on the model and also by calculations based on considerations of the

design. An attempt should be made to arrive at some conclusion in regard to the

best way to determine each derivative, it being well known that certain derivatives

can not be obtained with a necessary accuracy from a direct test. In this respect it

is recommend that the findings of Mr. O. Glauert as reported in “Aircraft Engineering”

during 1920, be given careful consideration.

4. Additional wind tunnel tests will be suggested by the results of these investigations and should be made in view of the specific requirements.

5. In the full-scale, or free-flight, tests there are several outstanding problems

such as:

(a) Determination of the variation of lift and drag coefficients with angle.

(b) Pressure distributions on wings and perhaps on tail surfaces (in addition

to the research now under way).

(c) Efficiencies of control surfaces.

(d) Forces on tail surfaces and effect of down wash from different wings on

balance and stability.

(e) Stability.

5. The variation of lift and drag with angle should be determined by the usual

method of timing a horizontal steady flight over a measured course and checked

by gliding flights with the propeller stopped (see Br. A.C.A. R&M Nos. 541 and

603). A method of analyzing the performance in a climb may be found in

Zeitschrift F.u.M. June 30, 1920, and it is suggested that a similar scheme be used

in this research.

6. It seems desirable to actually determine the effectiveness of the control surfaces

by introducing a known moment to be counteracted. This has been done in some

German tests reported in Zeitschrift F.u.M. for November 15, 1919, and

November 29, 1919. The results apparently justify further experimentation.

7. The study on efficiencies of and forces on control surfaces should determine

the variations due to thickness and plan forms of these surfaces. Some very good

work has been done in this field and the present research should be made with

the view of completing such work.
Document 2-14 465

8. Free flight stability testing has been limited to determinations of period,

damping, etc. The previous work of the Advisory Committee furnishes a very

good foundation for the present investigation.

9. A comparison of the various reports on free flight tests is sufficient to

emphasize the importance of accurate data. Special attention should be given to

the determinations of velocity, density, thrust, weight, and center of gravity location. This research will require an immense amount of work, but the results will

justify the efforts providing care is taken in planning and executing every test.

[signed] J. C. Hunsaker
466 Chapter 2: Building a Research Establishment

Document 2-15(a–i)

(a) Joseph S. Ames, vice chairman, committee on aerodynamics,

NACA, letter to A. [F.] Zahm, L. J. Briggs, E. B. Wilson, 

W. F. Durand, E. N. Fales, J. G. Coffin, H. Bateman, and 

F. H. Norton, 23 August 1920, RA file 70, 

Historical Archives, NASA, Langley.

(b) F. H. Norton, acting chief physicist, NACA Langley,

response to Joseph S. Ames, 26 August 1920, 

RA file 70, Historical Archives, NASA, Langley.

(c) A. F. Zahm, Washington Navy Yard, response to

Joseph S. Ames, 17 September 1920, RA file 70, 

Historical Archives, NASA, Langley.

(d) Joseph G. Coffin, Curtiss Aeroplane & Motor Corporation,

response to Joseph S. Ames, 18 September 1920, RA file 70,

Historical Archives, NASA, Langley. 

(e) W. F. Durand, Leland Stanford University, response to 

J. S. Ames, 24 September 1920, RA file 70, 

Historical Archives, NASA, Langley.

(f) Ludwig Prandtl, University of Göttingen, letter to 

William Knight, NACA Technical Assistant (translation), 

the NACA, 1 May 1920, RA file 70, 

Historical Archives, NASA, Langley.

(g) “International Standardization of Wind-Tunnel Results,”

NACA Annual Report for 1922 (Washington, DC), p. 36.

(h) G. W. Lewis, director of aeronautical research, NACA, 

memorandum to Langley Memorial Aeronautical Laboratory,

1 April 1925, RA file 70, Historical Archives, NASA, Langley. 
Document 2-15(a–i) 467

(i) Aerodynamics Department, The National Physical

Laboratory [Great Britain], “A Comparison between 

Results for R.A.F. 15 in N.P.L. Duplex Tunnel and in the

N.A.C.A. Compressed Air Tunnel,” (summary), n.d. [1925], 

RA file 70, Historical Archives, NASA, Langley.

As the number and variety of wind tunnels around the world increased,

researchers became more concerned that measurements taken in one tunnel

might not be reproducible in other tunnels. In 1920, the British Advisory

Committee for Aeronautics (ACA) spearheaded an effort to run a series of tests to

compare the performance of the world’s major wind tunnels. The NACA

Committee on Aerodynamics readily endorsed the concept, but it was not sure

just what should be measured or how the program should be structured. In an

effort to obtain broad input and achieve some consensus in the American aeronautical community, the aerodynamics committee’s vice chairman, Joseph S.

Ames (for whom the Ames Laboratory would later be named), wrote to eight leading aerodynamics figures, asking them “to outline a program of tests to be made

in the wind tunnels of this country and of Europe” that would enable researchers

to “connect” data from different tunnels. Responses from F. H. Norton, A. F.

Zahm, J. G. Coffin, and W. F. Durand, reproduced herein, uniformly expressed

interest in such an effort, but there are interesting differences in their suggestions

for the program. Ames received advice and comments from other noted wellknown aeronautics personages as well, including Ludwig Prandtl, who offered

Ames his suggestions earlier in the year.

The NACA prepared specifications for the American tests and, as the

“International Standardization of Wind-Tunnel Results” section from the NACA

Annual Report for 1922 shows, participated fully in the project. Although the standardization tests were initially expected to be a one-time, straightforward proposition,

the project rapidly grew in complexity, and the NACA was an active participant in

tests for many years. Research Authorization (RA) 70, the in-house authority for

the program and the source file for most of these documents, became one of the

longest-running projects on the committee’s books.

The NACA and ACA published numerous reports that described the various

tests and analyzed results. The final document in this section is the summary from

a British report by the Aerodynamics Department of the National Physical

Laboratory comparing results from the tests of a standard wing section in the

N.P.L. Duplex tunnel and the new Variable Density Tunnel (VDT) at Langley. The

British expression of confidence in the American VDT is of particular interest in

this document.
468 Chapter 2: Building a Research Establishment

In the final analysis, however, standardization remained a dream that was never

fully realized because of the widely varying capabilities of the world’s wind tunnels

and the complexities inherent in wind tunnel testing. In another sense, however, the

standardization project was a success in that it focused the greatest minds in aerodynamics around the world on the fundamental questions of wind tunnel testing and

stimulated an unprecedented degree of cooperation and information exchange.

Document 2-15(a), Joseph S. Ames,

letter regarding standardization of wind tunnels, 1920.

August 23, 1920

My dear Sir:

At the last meeting of the Subcommittee on Aerodynamics of the National

Advisory Committee for Aeronautics, I was requested to ask you if you would be

kind enough to outline a program of tests to be made in the wind tunnels of this

country and of Europe with a view to securing what one might call standardization,

that is, information which would enable one to connect the data published, as

obtained in these different wind tunnels.

This request is being sent to several others, and after replies are received from

all, which I trust will be at an early date, I will see that a comprehensive program

is prepared for submission at the next meeting of the committee.

Sincerely yours,

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

[signed] Joseph S. Ames

Vice-Chairman, Committee on Aerodynamics

Copies to A. H. Zahm, L. J. Briggs, E. B. Wilson, W. F. Durand, E. N. Fales, J. G.

Coffin, H. Bateman, and F. H. Norton.

Document 2-15(b), F. H. Norton, reply to Joseph S. Ames, 1920.

August 26, 1920.

From: Langley Memorial Aeronautical Laboratory. 

To: National Advisory Committee for Aeronautics. 

(Atten. Vice-Chairman, Com. on Aerodynamics) 

Subject: Comparison of wind tunnels.

Reference: (a) NACA Let. Aug. 23, 1920, and enclosures.

1. It is evident that for a given model, a given angle of incidence and a given

velocity there is only one correct value for Lc and Dc. Tests with the same model

in various wind tunnels will not necessarily give these correct values but they will

show any large error for any one particular tunnel.
Document 2-15(a–i) 469

2. The purpose of these tests should be to determine factors for converting

past, present and future results, at least approximately, to agree with similar

results obtained in any one tunnel. These tests should also determine the merits

of the various types of wind tunnel.

3. The main classes of errors which may arise in wind tunnel work are:—First,

errors in speed of wind; Second, errors in measuring the forces; and Third, errors

in determining the true resistance of the model exclusive of its supports.

4. It is advisable in tests of this nature to make the models as simple and as few

in number as possible, and it would seem to me that a standard type of aerofoil would

be best suited for this purpose, and I believe that a single test would show everything

that would be shown by a more extensive series of tests. In order that the aerofoil may

be used in the smaller tunnels it should be made with a span of 18", and a chord of

3" and should be run at a speed of 40 feet per second. It has been suggested that

it might be desirable to make tests on a complete model but I do not believe that

any more information would be obtained in this way than from the simple aerofoil and the model would have the disadvantage that even a very slight misalignment of the wings would introduce a considerable amount of error in the results.

5. It will be very desirable to determine the steadiness of flow both in direction

and velocity for various tunnels. A method for accomplishing this in a rough way

has been suggested by using a sphere or cylinder for the test but this method can

not give quantitative results. It is suggested that a very complete and valuable

record would be obtained by using a recording air speed meter and recording

yawmeter in order to obtain records of the actual variation in the flow of each tunnel.

Such an instrument has been used very successfully at Langley Field and it is suggested that the same instrument should be used in all tunnels.

[signed] F. H. Norton

F. H. Norton,

Acting Chief Physicist.

Document 2-15(c), Albert F. Zahm, reply to 

Joseph S. Ames from Washington Navy Yard, 1920.

September 14, 1920

Dear Prof. Ames:

Your letter of August 23 arrived while I was away on vacation.

One of the main objects of wind-tunnel research is to determine the action of

the air on and about a model in a stream of indefinite extent flowing uniformly

without a pressure gradient, except that caused by the model.

I would suggest first that a very few of the ablest theoretical aerodynamists,

such as Prof. Prandtl, be invited to discuss the mathematical theory of the flow in
470 Chapter 2: Building a Research Establishment

a wind tunnel—not too ideal for practical use—both when empty and when containing a model; and to indicate what corrections should be made to render the windtunnel data applicable to a model in a uniform infinite stream, or to a model

moving uniformly through an infinite still atmosphere. Prof. Prandtl has written

somewhat on this subject, and Dr. de Bothezat has expressed a wish to do so.

After that I would suggest that a few laboratories be invited to determine the action

of the air on and about a few very simple models in their tunnels, and thence, after

their own peculiar corrections, to derive the air action on the same models in a uniform

infinite stream. If the final results agree, the methods of standardization are provided.

The careful testing of a variety of identical models in a variety of tunnels differently manned would probably yield results a little more consistent than those

already available. But unless the tests were guided by adequate theory, furnished

before hand, it seems improbable that all the observations and precautions would

be taken that are necessary to make wind tunnel data strictly comparable.

In case the comparative tests are to begin at once, I would suggest as models

a sphere and a thin circular disc in normal presentation to the wind, preferably

with its edge champfered [sic] on the back; both to be of specified dimensions. In

each case I would have the velocity and pressure distributions, for various fixed

wind speeds, mapped throughout the working part of the tunnel both when

vacant and when containing the model. The resultant air force on the model, and

the pressure distribution all over its surface should be determined. It should be

required also to report the temperature and moisture of the air in the tunnel during

the test, so that the density and viscosity may be known. Finally, correction should be

made to derive the resultant air force on the model in a uniform infinite stream.

In both cases a number of spheres and discs, as nearly geometrically similar

as may be feasible, should be used as a check in finding the V1 or scale effect.

If these tests are to be made to establish trustworthy doctrine, rather than to

expose the defects of busy routine tunnels, I would suggest that they be limited to

research laboratories, with ample equipment, and supervised by high-grade men

with sufficient leisure.

Very truly yours,

[signed] A. F. Zahm.

Document 2-15(d), Joseph G. Coffin, reply to 

Joseph S. Ames from Curtiss Aeroplane Corporation, 1920.

September 18, 1920

Dr. Joseph S. Ames, 

National Advisory Committee for Aeronautics,

Washington, D.C.
Document 2-15(a–i) 471

Dear Sir:—

Your communication of August 23rd must have gone astray as I have received

but that of September 14th.

I am extremely interested in the question of standardization tests or rather

comparison of tests in various wind tunnels. The following suggestions show in a

general way the kind of tests that in my opinion would be useful.

1. Tunnels should show uniform air flow over experimental section as tested

by standard type of Pitot.

2. Tests on any standard rings should give identical curves (within experimental

area) when reversed.

3. Balance should be checked up for absolute forces.

If these three conditions are satisfactorily met, then:

1. Comparison of results should be made on a standard airfoil. This airfoil

should be a species of primary standard sent around from place to place somewhat

as an invariable pendulum is used in the determination of “g”. It should be of

metal to withstand high air speeds.

2. Tests should be made on similar airfoils of geometrical constructions such

as shown in sketch below, for example, which can be constructed mechanically

and checked up at the various laboratory shops.

3. Comparison tests of an airplane model of “invariable” all-metal type construction.

4. Resistance at zero yaw of streamline airship model which is of a fairly large size,

(volume). This brings in the pressure gradient correction, standard surface and shape.

5. No uniformity can be expected unless great and careful attention is paid to

spindle and attachment location corrections. These are extremely troublesome

and in my opinion deserve the greatest amount of attention at the present time.

6. Tests on a sphere and a cylinder.

7. Attention must be paid to nature of surface. Surface has a model characteristic.

I have had constructed a very carefully made aluminum wing with a RAF-6

upper camber and an absolutely flat under camber. It is provided with holes for

end spindle attachment at either end and also for crank spindle attachment at the

center. Comparison results with this wing have already been made by M.I.T. and

the Bureau of Standards. The results are very interesting.

By sending around an invariable standard wing we eliminate possible surface

differences, spindle attachment location differences, as well as differences due to
472 Chapter 2: Building a Research Establishment

the spindles themselves. Special spindles accompany the model. I believe the

Curtiss Company would be glad to cooperate by allowing the use of this standard.

8. Tests on pressure gradients along the tunnel should be made.

9. Tests should be repeated at various air speeds.

After all, what is desired is that any given tunnel, when properly used, should

give identical test results. This standardization would go a long way toward attaining this ideal.

I would like to say also that a new type of balance should be developed. I have

in mind such a balance which would eliminate to a great extant the difficulties

with spindle corrections.

Very truly yours,

[signed] Joseph G. Coffin

Document 2-15(e), W. F. Durand, reply to 

Joseph S. Ames from Stanford University, 1920.

24th September 1920.

Dr. J. S. Ames

Chairman, Aerodynamic Com.

N.A.C.A.

Washington, D.C.

My Dear Dr. Ames,

I have just returned from a summer trip to the Hawaiian Islands, and find

your letter in regard to experimental work in aerodynamical laboratories looking

toward a standardization of results. While in the Islands I was beyond reach of

mail, and this must be my excuse for the long delay in my reply.

The subject of your inquiry is one in which I have felt much interest and it

has seemed to me that the general program of standardization involves two principal features:

(1) The adoption of a system of standard dimensionless units and the expression

of results of laboratory research in terms of such units. Already a good start has

been made by the N.A.C.A. in this respect, in the work of the technical data division,

in reducing to standard terms and forms, results of miscellaneous laboratory

research work in this country and abroad.

(2) Some program of test or standardization which would, in effect operate as

a test on laboratories and laboratory equipment. Thus a test is made in laboratory

A on a series of airfoil sections specified in terms of a drawing or a series of ordinates.

Laboratory B desires to check up on Laboratory A and attempts to reproduce the

same section. It is very sure that the reproduction will not be exact and may even

differ to such a degree as to seriously compromise the comparison. Similarly with
Document 2-15(a–i) 473

propeller tests. In order to make our results strictly comparable with those made

in other laboratories, notable by Eiffel and at the N.P.L., there should in effect be

a standardization of laboratory equipment—balance, dynamometers, wind speed

measures, etc.

Just how to accomplish such a standardization or comparison in the most

effective manner is not entirely clear, but I believe that something could be

accomplished by carrying out a series of tests on a series of carefully selected type

models, made of metal and therefore invariable in form, and sent bodily from one

laboratory to another. Thus if a persistent difference develops as between two laboratories in measuring the same thing, it must obviously be inhere in the laboratory

equipment. Or again, if in a dozen laboratories all but one or two are in sensible

agreement regarding certain measurements, the presumption is that in the divergent

cases some error traceable to the equipment or mode of carrying on the measurements has been introduced. A search for this source of error should then serve to

definitely clear up the matter and establish all laboratories on a uniform basis at

least as regards this particular feature.

Of course in all laboratory equipment, time changes develop and certain

standard forms should be requested from time to time in order to make sure that

no secular change of importance is in progress.

The particular features regarding which such laboratory standardization

should be carried out are clearly the following:

(a) Air foil sections:

Lift Force.

Drift Force.

(b) Models of planes:

Forces as above.

Tipping movements.

(c) Propellers:

Torque.

Thrust.

R.P.S.

(d) Wind Speed:

This is fundamental in all tests.

Regarding (d), I have thought that a special form of wind speed measuring

device might be devised, which could be sent bodily from one laboratory to another,

and which, through it’s indications in comparison with the method or device used

at each laboratory, might serve to give a comparison or a comparative calibration

of one laboratory in terms of another.

Regarding (a), (b), and (c), standard metal forms and a standard program of

test might be devised, the carrying out of which in each laboratory would thus
474 Chapter 2: Building a Research Establishment

serve to check one against another and to develop cases which might be specially

divergent from the others.

There is much in the way of detail here which would have to be carefully studied,

but I believe that something might be done, especially through the agency of a

central body such as our Committee.

Hoping that something may develop along these or equivalent lines, and with

assurances of our desire to co-operate in all ways practical, I am,

Sincerely yours,

[signed] W. F. Durand

P.S. I have not attempted to discuss this matter in detail, in the thought that a

general understanding of the field to be covered and of the general grand strategy would first be desirable. 

W.F.D.

Document 2-15(f), Ludwig Prandtl, letter to William Knight 

from Göttingen, Germany (translation), 1920.

May 1st 1920.

To: Mr. William Knight, Technical Assistant, U.S. Commission for Aeronautics,

American Commission, Wilhelmsplatz 7, Berlin.

My Dear Mr. Knight:

I hope you reached Berlin safely. I want to make definite proposals at once

for the comparisons to tests made at various laboratories. The following five

experiments appear to be, in my opinion, the right ones to propose:

1) Measurement of resistance of a flat circular metal plate, set at right angles

to the air flow in order to test the measurement of velocity in the laboratory.

2) Measurement of resistance of a smooth sphere, diameter 20 cm., made as

exact as possible, to test the eddying of the air current.

3) Measurement of resistance of a metal wing of about 20 x 100 cm.,

equipped with the proper fastenings for all the laboratories, which will be sent

from one laboratory to another.

4) Measurement or resistance of a wing as constructed from the same drawing

by each laboratory, with its own manufacturing means. The drawing may be identical

with the one used in experiment 3.

5) Measurement of resistance of a dirigible balloon body model, which may be

made of polished wood, to test the uniformity of the air flow lengthwise. (If speed

increases down stream, the measurement of resistance will be too large, and vice-versa.)

I shall be obliged if you will negotiate with the various laboratories on the

basis of this program, if you agree to it, and collect the statements of the separate
Document 2-15(a–i) 475

laboratories as to the fastenings they require (hooks, screw sockets, etc.) for each

model. The models to be turned out in common can then be produced in accordance with those specifications.

I have looked over my old studies, and find that a reprint of only one of the

papers you are concerned with is missing; i.e., a paper given at the International

Congress of Mathematicians at Heidelberg, 1904. It was a particularly important

paper, at least from a historical point of view. If you attach importance to it, you

can still probably purchase the Proceedings of that Congress (1905) published by

Teubner, Leipzig.

Some other important studies done at my old laboratory deserve your attention.

They appeared in the Jahrbuch der Motorluftschiff-Studeingesellschaft 1910/11,

1911/12, and in the Jahrbuch der Luftfahrzeugegesellschaft 1912/13 (Springer,

Berline). Everything else of consequence is to be found in the Technische

Berichte, or you can get reprints of the papers in questions.

I send you my best regards and hope to hear from you.

[signed] L. PRANDTL.

Document 2-15(g), “International Standardization of 

Wind-Tunnel Results,” NACA Annual Report for 1922.

INTERNATIONAL STANDARDIZATION OF WIND-TUNNEL RESULTS.

During the past year, the committee has entered into an agreement with the

Aeronautical Research Committee of Great Britain, through the National Physical

Laboratory, to arrange for the conduct of certain definite tests in the wind tunnels

of the world. The tests are to be made on standard airfoil and airship models

which have been designed and constructed by the National Physical Laboratory.

The National Advisory Committee or Aeronautics undertook to arrange for the

test in the wind tunnels of the United States. In September 1922, the committee

received from the National Physical Laboratory two airship models for comparative

tests. These models have been tested under the direction of Dr. A. F. Zahm, at the

aeronautical laboratory of the Washington Navy Yard.

The National Advisory Committee has further authorized the testing of standard

models in the United States, the models consisting of three cylinders, having

length-diameter ratios of 5 to 1, and four models of the U.S.A. 16 wing section,

each having an aspect ratio of 6 and the length varying from 18 to 36 inches. The

tests on both cylinder models and wing models are to be made over as wide a

range of V/L as possible, and to include determinations of lift, drag, and pitching

moments every 4° from -4° to +20°. The streamline airship models to be tested

will have the proportions of the Navy “C” class airship described in a recent report

of the Washington Navy Yard wind tunnel. Four streamline airship models, of 4,
476 Chapter 2: Building a Research Establishment

6, 9, and 12 inches diameter, respectively, are to be tested, and are to be supported

by spindles of lenticular form, the least diameter of spindle being one-twentieth

the diameter of the model, and the fineness ratio of the spindle being 3. After

completion of the test in the wind tunnels of the United States, the models will be

sent to laboratories in European countries and to Canada for test.

Document 2-15(h), George W. Lewis, memorandum to 

Langley Memorial Aeronautical Laboratory, 1925.

From: National Advisory Committee for Aeronautics.

To: Langley Memorial Aeronautical Laboratory.

Subject: Results of tests of standard R.A.F. airfoil.

1. The Committee is in receipt of a letter from the Aeronautical Research

Committee of Great Britain suggesting that each country publish independently

the results of the wind tunnel tests on the standard N.P.L. models. It is further

suggested that the results of the tests on the standard R.A.F. airfoil be published

as soon as possible, as the Aeronautical Research Committee desires to issue at

some future date a complete memorandum comparing the results in the different

countries.

2. Before a meeting is called of the representatives of the various laboratories

in this country in which the airfoil was tested, it seems desirable that the reports

of these tests be circulated among those representatives. There is accordingly

enclosed herewith a copy of the report of the Massachusetts Institute of

Technology on the tests of the standard R.A.F. model. The report of the Bureau

of Standards has already been sent to you, and the report of the Engineering

Division of the Air Service will be forwarded as soon as received.

3. It is desired that a meeting of the representatives of the various laboratories

be held during the first week in May to consider the preparation of the joint

reports on the tests of this model.

G. W. Lewis,

Director of Aeronautical Research.

Document 2-15(i), Aerodynamics Department, National Physical Laboratory

[Great Britain], “A Comparison between Results for R.A.F. 15 in the N.P.L. Duplex

Tunnel and in the N.A.C.A. Compressed Air Tunnel” (summary), n.d. [1925].

It does not appear justifiable to use any full scale figures for further comparison,

since the above results refer to a square-ended monoplane of 6:1 aspect ratio. The

only important discrepancy revealed by the above comparison is that occurring at

maximum lift, and this difference, at the point where the flow is critical, can not
Document 2-15(a–i) 477

be considered surprising. The agreement, apart from this limited region is surprisingly good, when the extreme difference between the two types of tunnels is

taken into consideration, and tends to establish a considerable amount of confidence in the compressed air tunnel results. The marked difference in lift at the

stall needs further explanation, and future comparisons on other sections might

throw some light upon it. Further information on this point is very desirable if the

merits of the compressed air tunnel are to be fairly assessed, on account of the

importance of a correct prediction of maximum lift to the designer.
478 Chapter 2: Building a Research Establishment

Document 2-16

“Summary of General Recommendations,” 

NACA Annual Report for 1921 (Washington, DC) pp. 4–5.

By 1921, the NACA had the first portions of its Langley laboratory up and

running, and the committee began to take its advisory role as seriously as it had

its research role. The NACA Annual Report for 1921 contained a fascinating section

entitled “Summary of General Recommendations” wherein the committee made

a number of specific recommendations for federal legislation and policies in support

of aviation growth and safety. From what the committee termed “the most urgent

need”—that of federal legislation to regulate all facets of aviation—to policies

that would encourage and support the “aerological” (weather) service, air mail,

aircraft manufacturers, helium production for airships, and “greater provision for

the continuous prosecution of research on a larger scale,” these recommendations

became the nucleus of major federal legislation. The Air Commerce Act, enacted

during the decade, and the ensuing regulations played a role in shaping aviation that

was at least as important as the NACA’s scientific and technical research programs.

Document 2-16, “Summary of General Recommendations,” 

NACA Annual Report for 1921.

SUMMARY OF GENERAL RECOMMENDATIONS.

The more important general recommendations of the National Advisory

Committee for Aeronautics are summarized as follows:

LEGISLATION FOR THE DEVELOPMENT OF AVIATION.

The most urgent need for the successful development of aviation at the present

time, either for military or civil purposes, is the enactment of legislation providing

for the Federal regulation of air navigation, and the establishment of airways and

airdromes under Federal regulation. The Federal regulation should include the

licensing of aviators, aircraft, and airdromes; the airways should consist of chains

of landing fields providing supply and repair facilities and including the necessary

meteorological stations, observations, and reports. If the Federal Government will

establish and regulate transcontinental airways, as recommended, the committee

is confident that air lines for the transportation of passengers or goods will be

rapidly established by private enterprise in all parts of the country. The first

national airways, however, should be carefully planned to serve military as well as

civil needs. The committee reiterates its former recommendations as to the manner

of accomplishing the desired results, and urgently recommends the establishment

by law of a Bureau of Air Navigation in the Department of Commerce.
Document 2-16 479

EXTENSION OF AEROLOGICAL SERVICE.

The committee emphasizes the importance of extending aerological service

(under the Weather Bureau) along airways as established, and recommends that

adequate provision of law be made for this service, which is so indispensable to

the success and safety of air navigation.

POLICY TO SUSTAIN THE INDUSTRY.

Whatever may have been the faults or the shortcomings of the aircraft industry

during or since the war, the fact remains that there must be an aircraft industry,

and that it should be kept in such a condition as to be able to expand promptly

and properly to meet increased demand in case of emergency. The Government,

as the principal consumer, is directly concerned in the matter, and should formulate

a policy which would be effective to sustain and stabilize the aeronautical industry

and encourage the development of new and improved types of aircraft. In this respect

the committee invites attention to the recommendation contained in its special

report submitted to the President on April 9, 1921, published as House Document 17,

and again recommends the adoption of a policy which, while safeguarding the

interests of the Government, will tend to sustain and stabilize the industry.

IMPORTANCE OF MILITARY AVIATION.

Aviation is indispensable to the Army and to the Navy in warfare; and its relative

importance will continue to increase. Other branches of the military services are

comparatively well developed, whereas aviation is still in the early stages of its

development. The demand for greatly reduced expenditures in the military and

naval services should not apply to the air services. The committee recommends

that liberal provision be made for the Army and Navy Air Services, not only that

provision be made for the maintenance and training of personnel, but also that

the funds be adequate to insure the fullest development of aviation for military

and naval purposes.

SCIENTIFIC RESEARCH.

Substantial progress in aeronautical development, whether for military or

commercial purposes, must be based upon the application to the problems of

flight of scientific principles and the results of research. The exact prescribed

function of the National Advisory Committee for Aeronautics is the prosecution

and coordination of scientific research, and, while encouragement may be taken

from the progress made, greater provision for the continuous prosecution of

research on a larger scale is strongly recommended by the committee.

THE AIR MAIL SERVICE.

The Air Mail Service has demonstrated that airplanes can be utilized with certain

advantages in carrying the mail. And it has done more than this, despite the

handicap of using, military types of aircraft, poorly adapted to its work or to any

civil or commercial purpose, in demonstrating that commercial aviation for the
480 Chapter 2: Building a Research Establishment

transportation of passengers or goods is feasible. There are several causes which

are delaying the development of civil aviation, such as the lack of airways, landing

fields, aerological service, and aircraft properly designed for commercial uses.

The Air Mail Service stands out as a pioneer agency, overcoming these handicaps

and blazing the way, so to speak, for the practical development of commercial aviation.

As a permanent proposition, however, the Post Office Department, as its functions

are now conceived, should no more operate directly a special air mail service than

it should operate a special railroad mail service; but until such time as the necessary

aids to commercial aviation have been established it will be next to impossible for

any private corporation to operate under contract an air mail service in competition

with the railroads. The National Advisory Committee for Aeronautics therefore

recommends that provision be made for the continuation of the Air Mail Service

under the Post Office Department.

HELIUM AND AIRSHIPS.

The United States has a virtual monopoly of the known sources of supply of

helium, and these are limited. Experiments have been conducted by the Bureau

of Mines with a view to the development of methods of production and storage,

but as yet the problem of storage in large quantities has not been satisfactorily

solved. Because the known supply is limited, because it is escaping into the atmosphere at an estimated rate sufficient to fill four large airships weekly, and because

of the tremendously increased value and safety which the use of helium would

give to airships, particularly in warfare, it is, in the opinion of the National

Advisory Committee for Aeronautics, the very essence of wisdom and prudence to

provide for the conservation of large reserves through the acquisition and sealing

by the Government of the best helium-producing fields. Attention now being

given to the development of types of airships to realize fully the advantages which

the use of helium would afford should be continued. Such development would

give America advantages, for purposes either of war or commerce, with which no

other nation could successfully compete.
Document 2-17 481

Document 2-17

F. H. Norton, “The National Advisory Committee’s 

5-Ft. Wind Tunnel,” Journal of the Society of 

Automotive Engineers (May 1921): 1–7.

In spite of World War I and increasing discontent with its Langley Field landlord,

the NACA continued work on its first facilities, a five-foot open wind tunnel modeled

after Britain’s four-foot National Physical Laboratory tunnel and a dynamometer

laboratory for engine testing. The Atmospheric Wind Tunnel (AWT), which began

operation in 1920, was an obsolete design even before it was built, but it was a

proven commodity, and it allowed the NACA’s technicians to finally get to work

with their own equipment. During the dedication of the Langley Memorial

Aeronautical Laboratory (LMAL) on 20 June 1920, praise was lavish. None other

than former opponent David Taylor hailed the modest brick wind tunnel building

as a “shrine to which all visiting aeronautical engineers and scientists will be

drawn.” Taylor’s statement was a bit exaggerated for the time, but Langley soon

began to chart its course and produce significant results. The following year,

Frederick H. Norton, Langley’s chief physicist, reported on the work being done

in the AWT, noting that the work at Langley was “entirely research on the fundamental problems of aeronautics, such as the systematic design of airfoils, the scale

effect on models, and the relation of the stability on models to that in free flight.” 

For one of its most important early programs, the NACA obtained a Curtiss

JN4H Jenny for flight tests, and Langley model makers built two models of the

plane for wind tunnel testing. One was used for tests measuring lift, drag, and

moments, while the other was outfitted for pressure-distribution tests. The wind

tunnel data then were compared to measurements obtained during flight tests of

the JN4H. Gustav Eiffel had done the first such comparative tests a decade earlier in France, but the Langley program was more extensive and done with considerably greater precision. With such research programs, the NACA began to stake

out a crucial role for itself. 

Document 2-17, F. H. Norton,

“The National Advisory Committee’s 5-Ft. Wind Tunnel,” 1921.

In the spring of 1919 work was started on a 5-ft. wind tunnel for the National

Advisory Committee for Aeronautics at Langley Field, Va., and in the spring of

1920 the tunnel was completed and ready for calibration and for conducting tests.

This tunnel has now been in operation for about one year and during this time

new apparatus and equipment have constantly been added to increase efficiency
482 Chapter 2: Building a Research Establishment

and usefulness. While the tunnel is not as large as some that are now in use, it has,

it is believed, the highest useful speed of any wind tunnel in the world, that is, it

maintains a high velocity flow which is steady in speed and direction, and it possesses

satisfactory means for measuring the forces on models at the highest velocities. At

present, useful speeds up to 120 m.p.h. can be attained; but, as the propeller was

originally designed for other conditions, it is estimated that with a new and higherpitch propeller a maximum speed of 140 m.p.h. can be reached. Testing models

at such high velocities is not a simple matter and a number of new methods and

devices had to be developed to accomplish this successfully. For this reason a large

portion of the time that the tunnel has been in active operation has been occupied

in carefully studying the aerodynamic properties of the tunnel and in constructing

apparatus for holding models at the high velocities which can be reached so that

only in the last few months has the tunnel been devoted continuously to research

work. From now on, the work of the tunnel will be devoted almost exclusively to

tests on thick airfoils, including an investigation of their pressure distribution,

and to study the stability of model airplanes.

TUNNEL AND BUILDING.

The wind-tunnel building, which is constructed substantially of brick and

steel, is approximately 92 ft. long, 43 ft. wide, and 28 ft. high at the eaves. In Fig.

1 is shown a longitudinal section of the building and tunnel giving the principal

dimensions of the structure. A heavy concrete foundation runs the whole length

of the tunnel and a separate foundation is used for the power plant, so that any

vibrations which may be set up by the propeller or motor are not directly transmitted to the tunnel or balance. The interior of the building is smooth and free

from obstructions so that the return flow of air from the tunnel will be disturbed

as little as possible. Large doors at one end of the building allow the circulation

of outdoor air for cooling the building in summer, which is necessary because of

the rising temperature due to the power loss in the tunnel at the higher speeds,

although, of course, these doors can not be open while the actual tests are being

carried on, owing to possible disturbances from the wind. Besides the main room

for the tunnel there are several small rooms for offices in the building.

The tunnel itself is of the venturi type with a continuous throat of circular section,

and there is an air-tight experimental chamber built about the working section in

order that small holes may be opened into the tunnel while it is running, without

disturbing the airflow; and this chamber has proved of great convenience in much

of the work. The tunnel expands, as shown in Fig. 1, from the 5-ft. diameter working

section to a diameter of 10 ft. at the mouth of the entrance and exit cones. This

type of tunnel was selected after a considerable amount of investigation had been

made upon a model tunnel 1 ft. in diameter, by measuring its efficiency and

steadiness while varying many of its characteristics, especially the form of the
Document 2-17 483

cones, the type of the experimental chamber, the diffusers, and the honeycombs.

It will be noted that, contrary to usual practice, no diffuser is used in the return

flow, and this is because the gain in steadiness from its use was found to be very

slight on the model, while the cost of the full-sized diffuser would be considerable.

Taking into consideration the aerodynamic efficiency of the tunnel, the cost of

construction, and the steadiness of the air flow, this type of tunnel was considered

to be the best for the proposed investigations, although for some classes of work

a larger diameter and slower speed tunnel would be more advantageous.

The cones of the wind tunnel as shown in Fig. 2 are supported from a concrete foundation by heavy steelwork and the surface of the cones is planked with

cypress with the inside highly polished. This construction may first seem unduly

heavy but when it is realized how great are the vibrations set up by the higher

wind speeds and the necessity for having the cones remain perfectly true, it is evident that such a construction is quite justified.

The experimental chamber, which is about 10 ft. long, 14 ft. wide, and 23 ft. high,

is built around four concrete columns of very massive construction to withstand the

heavy pressures, in some cases as much as 80 lb. per sq. ft., that arise during the highspeed runs. The lower story of the experimental chamber contains the National

Physical Laboratory balance and the controlling devices for the air speed, while the

upper story contains the propeller dynamometer and wire type of balance. The chamber is entered either by a large door when the tunnel is not running, or, when it is

necessary to enter with a difference in pressure, an air lock is provided which consists

of two small doors with air valves. Adjustments are made on the model through large

doors which can be opened in the throat of the tunnel, these doors being curved to fit
484 Chapter 2: Building a Research Establishment

the section of the throat. In order

that the model may be inspected

during a test, there are three curved

glass windows set flush with the

inner surface of the tunnel, two in

the floor of the tunnel and one

in the top. Besides these inspection

windows there are also four illuminating windows with electric

bulbs, providing a powerful light

for photographic purposes. A general view of the lower story of the

experimental chamber is shown

in Fig. 3, with one of the curved

tunnel doors open, indicating

the ease with which the model

may be reached for adjustment.

POWERPLANT.

The driving motor consists

of a 200-hp. direct-current,

adjustable-speed motor, with a

speed range of from 1 to 1000

r.p.m. At present, power is supplied to this motor at 250 volts

from a dynamo driven by a

Liberty engine in an adjacent

building, but as this powerplant

is expensive and inconvenient it

is hoped that a more suitable

source of supply will soon be

available. The propeller is directly

connected to the motor by a 3-in.

shaft supported on a steel framework and mounted in three ball

bearings, while the propeller

itself is 10 ft. in diameter and has

four blades. As this propeller was

designed to be driven by a

Liberty engine at 1400 r.p.m. it does not at present absorb all the power which

the electric motor can deliver and a new propeller with a larger number of blades
Document 2-17 485

and a higher pitch is soon to be used which will increase the air speed obtainable

in the tunnel to a considerable extent. The main switchboard is at the entrance of

the building, and to obviate the necessity of running heavy wires down to the

experimental chamber, the control is by automatic push buttons, one for starting

and one for stopping, while a field rheostat is used for speed control above the

normal rate of 250 r.p.m. and a series rheostat or potentiometer for speeds below

this. The rheostats are placed outside of the experimental chamber to eliminate

the heat which would raise the temperature in the small chamber to an uncomfortable degree.

In Fig. 4 is shown a curve of power input to the driving motor plotted against the

air speed in the throat of the tunnel. It should be noted that the efficiency of the motor

with the very small field excitation which occurs at the higher speeds is exceedingly

low and the actual power supplied to the tunnel is much less than that supplied to

the motor. An approximate energy factor for the tunnel and propeller of 1.90 is

obtained, showing an efficiency considerably higher than that for either the National

Physical Laboratory or the straight Eiffel type of tunnel. The reason for the power

curve showing a sudden increase at the basic speed is because the potentiometer

rheostat is connected in at this speed and absorbs a constant amount of power

which is much more than the motor itself absorbs. In Fig. 4 is also shown a curve

of the propeller speed plotted against the air speed, that is, the effective propeller

slip; and, as would be expected, the slip is constant for all air speeds.

The steadiness of velocity in this wind tunnel compares favorably with that of

other tunnels, the maximum variation of the velocity from the mean at any air
486 Chapter 2: Building a Research Establishment

speed not being greater than 1 per cent at a given point in the tunnel. No manual operation of the controls is necessary during a test, except at long intervals,

to compensate for the changing resistance of the motor due to a temperature rise.

It was at first planned to construct a speed regulator similar to the one used at

Göttingen, but with the proper adjustment of the governor on the generating set,

such satisfactory results were obtained that the regulator was found unnecessary.

The maximum variation of wind direction in the throat as determined by a

recording yawmeter is ±0.5 deg., and this variation is of such a high period that

it does not appreciably affect the readings of the balance.

BALANCES.

The balance mainly used in this wind tunnel is of the modified National

Physical Laboratory type, designed and constructed at the Committee’s laboratory, a cross-section of which is shown in Fig. 5. The distance from the center of the

model to the pivot point on this balance is 54 in., while the distance from the

pivot to the end of the weighing arm is 27 in., so that the weights are actually

twice as heavy as they are marked. The balance was designed to measure forces

on the model up to 50 lb., while the weight of the moving parts was kept down to

46 lb. by the use of aluminum alloys and high-tensile steel. While the National

Physical Laboratory type of balance is convenient and satisfactory for small tunnels and low wind

speeds, it is felt that an entirely

different type of balance must be

designed if it is desired to measure forces any larger than 30 or

40 lb., as it is found when the

maximum forces are used on this

balance that a great amount of

trouble is introduced by deflection of the various members and

especially by the vibration which

is set up when a model is turned

to an angle near its burble point.

Another objection to the National

Physical Laboratory balance for

large forces is the heavy weights

that must be used; that is, for balancing a weight of 50 lb. on the

model, weights to the amount of

100 lb. must be lifted onto the
Document 2-17 487

arms, which is very inconvenient when rapid tests are being made. The principal

changes besides weights and dimensions which have been made in the original

National Physical Laboratory balance are as follows:

(1) A ball-bearing pivot is used in place of the usual conical pivot as the latter

gave considerable friction under large loads and also gave trouble

through a shifting of its position so that the zero reading was changed

during a run.

(2) A weighing arm is used for measuring moments instead of the former torsion

wire, and in this way lift, drag and pitching moments can be measured

simultaneously.

(3) The weighing arms are made of light steel tubing, and to prevent deflection

they are trussed up with tie-rods, thus greatly diminishing the weight of

the arm, while at the same time increasing its stiffness.

(4) A pinion is used for turning the head of the balance to make small adjustments more accurately and a prism is used for reflecting the horizontal

graduations in a convenient direction.

(5) An improved locking device is used on the lower balance tube.

(6) The lift is measured very satisfactorily and quickly by a Toledo weightless

scale, which allows direct readings to be made.

It was found necessary to use a mercury seal to prevent air from passing

around the balance spindle into the tunnel, even though the doors in the experimental chamber were closed. This is due to the fact that even with the tightest

possible construction there are a number of small leaks about the experimental

chamber, the air from which accumulating at the crack around the balance spindle

produces an air flow large enough to introduce a considerable error into the readings

of the balance. This seal is made of cast iron and allows a maximum head of mercury

of 2 in., the height of the mercury being at all times observable by a glass tube on

the outside of the seal. Models are usually supported from the top of the balance

by a tapered steel spindle, which is 1 in. in diameter at the base and tapers to 5/16 in.

at the top, and this is enclosed up to within 2 in. of the model with a thin brass

fair-water to reduce the spindle correction to a minimum. As the bending

moment in this spindle is very large at high speed and as there is considerable

trouble with the model vibrating, a method has been devised by D. L. Bacon for

supporting the top of the model rigidly and at the same time reading the forces

with accuracy and great rapidity on the balance.

This method is shown in Fig. 6 and consists of a set of small wires, one extending

from the top of the model, one from the lifting arm of the balance and a diagonal

to the top of the experimental chamber, the direction of this diagonal being such

that if it were projected downward it would pass exactly through the center of rotation of the moving parts of the balance. It is also necessary that the plane of these
488 Chapter 2: Building a Research Establishment

wires shall be exactly in the plane of the spindle and the lift arm so that there will

be no component of lift transferred to the drag arm; and this is done by carefully adjusting the top of the diagonal wire until a force on the model in the direction of the lift plane will have no effect upon the reading of the drag arm. The

same method could be used on the drag arm but as the forces are not so great it
Document 2-17 489
490 Chapter 2: Building a Research Establishment

was found sufficient to run a

diagonal wire directly down to

the end of the arm. These wires

pass through small holes in the

tunnel walls which are large

enough to allow the free play of

the tunnel wires and yet due to

the air-tight experimental

chamber there is very little air

passing through them. By this

method it has been possible to

test a 1⁄24 size model of the

Curtiss JN4 up to 100 m.p.h.

without excessive vibration or

deflection and this speed was

the limit only because the

model itself, even though made

of metal, was not sufficiently

rigid to stand a heavier load.

As it is believed that the important development in aeronautics of the future

centers about the internally braced wing, the Committee’s policy is to conduct

extensive researches on this type of airfoil. The National Physical Laboratory type

of balance is unfortunately unsuited to tests of this nature, especially where the

wings are tapered down to a thin section at the tip, as it is practically impossible

to support such a model by a spindle attached to the end of the wing. For this reason it has been necessary to design and construct another type of balance, which

supports the wing nearly at its center by wires, as shown in Fig. 7. The lift and

drag can be measured on this balance directly, the lift on a Toledo scale and the

drag on a small balance connected to the wing by a parallelogram of wires. The

center of pressure is determined directly by finding the point about which the

wing is in equilibrium when balanced on knife edges, as shown in Fig. 8. This

method is very convenient and accurate and eliminates the large amount of computation which was necessary in finding the center of pressure travel by the usual

methods. While this balance does not take the place of the National Physical

Laboratory balance for the majority of the tests, still it is a necessity when it is

required to support the model by its center and for wings of high aspect ratio

where it would be impossible to support them steadily by an end spindle.

SPECIAL APPARATUS.

The air speed in the tunnel is originally determined by a pitot tube and the

micro-manometer shown in Fig. 9. This manometer can measure a head of water
Document 2-17 491

to 0.001 in., which is sufficiently accurate for any

work required in the wind

tunnel, and is very much

more convenient than the

Chattock gage generally

used in wind tunnels, as its

sensitivity can be changed

by altering the slope of the

glass tube, and its range

can be extended to a head

of 18 in. without difficulty.

For usual running, the

air speed in the tunnel is

determined by the difference between the static

pressure in the side of the

tunnel and the outside air

in the building, this difference in pressure being

measured by the manometer shown in Fig. 10. This manometer is arranged so that its sensitivity will be

inversely proportional to the head measured so that at the higher speeds where

the fluctuations are naturally greater than at the lower speeds, the variations

shown by the liquid will be proportionately the same as at the low speed, which is

a necessity when running at the highest velocities. This gage also obviates the

necessity of having a very long inclined tube, which would mean that the meniscus must change its position by several feet, so that the operator would have to

stand in different positions for various velocities in the tunnel. This gage is, of

course, used as a secondary instrument and is calibrated from the readings of the

pitot tube, but actual heads can be easily read on it by measuring the angle of the

tube and knowing the distance from the center of the reservoir to the meniscus of

the liquid.

A multiple manometer is used to a large extent in determining the distribution

of pressure over models, and one containing 20 tubes is shown in Fig. 11. The two

outside tubes are connected directly to the top of the reservoir so that they will

read the height of the liquid at all times, while the other 18 tubes are connected to

the pressure holes on the model. The height of the liquid can be adjusted by raising or lowering the reservoir, while the sensitivity can be changed by varying the

inclination of the glass tubes.
492 Chapter 2: Building a Research Establishment

For the study of fluctuations in velocity and direction

in both the model and fullsized tunnel, a number of

high-period recording airspeed meters have been constructed, the most recent one

being shown in Fig. 12. This

instrument was designed to

be portable, requiring only

a small battery for the light

and the motor, and the film

is carried in light-tight

drums which are used like

plate holders. The sensitivity and position of the zero

of this gage can be

changed easily, making it

available for a large number of uses, while its natural period is so high and the friction is so small that it can easily record the highest period fluctuations that will occur in any wind-tunnel work.

Because of the inconvenience and inaccuracy of the old method of aligning

wings by attaching a batten to them and then aligning this batten with a parallel

line on the floor of the tunnel, a new method is used consisting essentially of a

projector which throws a parallel beam of light upon a small plane mirror temporarily attached parallel to the chord of the wing, and this beam of light is

reflected back to the cross line of a white target on the wall of the experimental

chamber, Fig. 13. To align the model all the operator has to do is turn the head

of the balance until the

light spot falls on this cross

line, which he can see from

any part of the experimental

chamber, so that one man

can line up a wing to within

0.02 deg. in a few seconds,

thus greatly reducing the

time and increasing the

accuracy compared with

the older methods. 
Document 2-17 493

This method is also

applicable for determining

the angular deflection of a

wing or model during actual test. The optical method

of aligning has been in use

for a considerable length of

time and has proved very

satisfactory, entirely eliminating those errors in

alignment which are bound

to creep in with the older

method, due to unskilled

operators or curvature in

the batten.

One of the chief causes of dissimilarity between a model test and a free-flight

test is the lack of a slipstream in the model, and to produce this effect in the wind

tunnel a small propeller is driven before the model by a belt from a high-speed

electric motor above the tunnel, the propeller being supported by steel wires from

the walls of the tunnel as shown in Fig. 14. The wires, the belt, and the propeller

mounting undoubtedly cause a somewhat different air flow from that occurring in

full flight, but this interference is probably very small and at least gives us a much

closer approximation of actual conditions than has been obtained before. While

it has not been possible as yet to drive a model propeller at a proportional speed

to the full-size propeller, it has been possible by using a model with a pitch slightly
494 Chapter 2: Building a Research Establishment
Document 2-17 495

larger than the full-scale propeller to get a slipstream of the same characteristics

as the slipstream in the full-sized machine, which should give identical results as

far as the interference of the model is concerned. Work is being carried out on the

design of a very small high-pressure turbine to drive the propeller at a higher

speed and so that a smaller mounting can be used through reducing the interference.

MODELS.

While the models tested in the wind tunnel are, strictly speaking, not a part

of the equipment, still those models of such standard form that they are used

repeatedly in tests can be considered as such. The Committee has constructed two

models of the JN4H airplane, one of them being the l

⁄24 scale model illustrated in

Fig. 15, which is constructed with the greatest accuracy to reproduce all parts that

might affect the air flow, that is, the engine, radiator, and wind shields, the only

omission being the wires and fittings which can be more accurately calculated than

tested. The other model of the same machine has been constructed to 1⁄15 model

size for pressure distribution tests on the tail surfaces.

All of the medium or thick wings that are tested in the tunnel are constructed

of maple, as this material can be worked with proper precautions to within an

error of 0.002 in. The wings are cut upon a special machine shown in Fig. 16,

which not only will cut the usual constant-section type, but will also cut wings

tapering in plan form and thickness, as, for example, a wing with a depth-tochord ratio falling off toward the tip as a parabolic function, and at the same time

with an elliptical plan form. A much heavier and more precise machine of the

same type has been designed for cutting and grinding aluminum or steel wings.

Without a machine of this type the Committee’s extensive program on thick

tapered wings would be impossible because of the great expense of making the

models by hand.
496 Chapter 2: Building a Research Establishment

The wind-tunnel work of the National Advisory Committee at Langley Field,

in contrast to the work of most of the tunnels in this country, is entirely research

on the fundamental problems of aeronautics, such as the systematic design of airfoils,

the scale effect on models and the relation of the stability on models to that in free

flight. Fortunately, it is possible to carry this work on most efficiently because of

the close cooperation that can be had with the free flight investigations which are

being conducted by the Committee at the same time. It is, however, realized that

with only one wind tunnel, the various model investigations can not be carried on

simultaneously, and so the work can not be conducted as rapidly as desired, but

it is expected that a second and larger tunnel will be constructed by the

Committee in the near future, which will greatly extend the range and amount of

investigation possible. 
Document 2-18(a–j) 497

Document 2-18(a–j)

(a) Max M. Munk, letter to J. C. Hunsaker, 

7 October 1920, Hunsaker Collection, Box 4, File M.

(b) J. C. Hunsaker, letter to Lester D. Gardner, 

3 May 1921, Hunsaker Collection, Box 2, Folder 4, File G.

(c) F. H. Norton, Chief Physicist, NACA Langley, 

memorandum to NACA Executive Officer (G. W. Lewis),

5 August 1921, RA file 44, Historical Archives, NASA Langley.

(d) W. Margoulis, excerpts from “A New Method of Testing

Models in Wind Tunnels,” Aeronautics [Britain] XIX, 

No. 373 (New Series), (9 December 1920): 412–413.

(e) Edward P. Warner, Massachusetts Institute of Technology,

letter to G. W. Lewis, Director of Aeronautical Research, 

NACA, 5 March 1921, NASA Record Group 255, General

Correspondence File, Box 12, National Archives, Washington.

(f) W. Margoulis, excerpts from “A New Method of 

Testing Models in Wind Tunnels,” NACA Technical 

Note No. 52, [1921].

(g) Max M. Munk, “On a New Type of Wind Tunnel,” 

NACA Technical Note No. 60, May 1921.

(h) F. H. Norton, memorandum to G. W. Lewis, 

“Design of compressed air wind tunnel,” 6 October 1921,

NASA Record Group 255, General Correspondence 

Numeric File 21-5, Box 80, National Archives, Washington.

(i) “Compressed Air Wind Tunnel,” NACA Annual Report 

for 1921 (Washington, DC), pp. 29–30.
498 Chapter 2: Building a Research Establishment

(j) Max M. Munk and Elton W. Miller, The Variable Density

Wind Tunnel of the National Advisory Committee for

Aeronautics, NACA Technical Report No. 227 

(Washington, DC, 1925).

Langley’s study comparing a Curtiss JN4H in flight to models of the same

airplane in the Atmospheric Wind Tunnel confirmed that wind tunnel testing was

a valid predictor of aircraft performance and behavior, but it also pointed the NACA

researchers toward another well-known, but poorly understood, problem: scale. It

had long been known that the forces generated by a model were not proportional

to the model’s scale. A 1

⁄20-scale model of a plane in an air stream 1⁄20 as fast as the

actual plane flies generated considerably less than 1⁄20 of the actual lift and drag

forces. Early aerodynamicists had developed empirical coefficients to “scale up”

the data, but the comparison tests showed just how unreliable these coefficients

were. The problem was that the air itself could not be “scaled-down” to model

size, and its properties, such as density and temperature, were almost the same in

the wind tunnel as they were around a full-size airplane. To gain the maximum

value from wind tunnel testing, an answer to the scaling problem had to be found.

The answer to the scaling problem had its roots in the work of a nineteenthcentury British scientist, Osborne Reynolds. Reynolds showed that the forces a

moving fluid exerts on a body, or vice versa, depended on the fluid’s velocity, density,

and viscosity, and on a key dimension of the body, such as length or diameter. He

combined these parameters into a mathematical expression where all of the

dimensions cancelled one another out. The dimensionless result, known as the

Reynolds number, was a key to understanding scale factor. Because it was dimensionless, the Reynolds number could be used to compare fluid-flow forces around

similarly shaped, but differently sized objects. By varying different parameters,

such as increasing the velocity or decreasing the density, to obtain the same

Reynolds number for different tests—a condition known as dynamical similarity—

an excellent correlation between model tests and aircraft performance was possible.

But this was easier said than done. When a 1

⁄20-scale model was tested in the AWT,

the Reynolds number was about 1⁄10 that of the corresponding actual flight. Larger

models could theoretically be used, but wingspans greater than about 3 1⁄2 feet

were not useful in the five-foot-diameter tunnel due to interference by tunnel

walls. The AWT lacked the power to run at the high speeds necessary to generate

the required Reynolds numbers; furthermore, such speeds were not practical in

open wind tunnels anyway.

Two possible solutions to the problem emerged almost simultaneously in the

early 1920s. In both cases, the intent was to increase the density/viscosity term in
Document 2-18(a–j) 499

the Reynolds number calculation. Wladimir Margoulis, a Russian-born aerodynamicist and former director of the Eiffel laboratory in France, proposed using

carbon dioxide instead of air in a sealed wind tunnel, because carbon dioxide’s

density was over one-and-one-half times that of air. Max Munk, a brilliant and

quixotic German student of Prandtl, suggested that a wind tunnel be built inside

a pressure vessel so that tests could be run under pressure, thus increasing the

density of the air as much as twentyfold. The NACA employed both experts,

bringing Munk to the United States and retaining Margoulis as an agent in Paris.

Debate continues over which man was first to suggest using higher densities, but

the NACA chose to pursue Munk’s concept. 

The result was the Variable Density Tunnel (VDT), Langley’s second wind tunnel, which went into service in 1922. Externally, it appeared to be little more than

a large cylindrical tank with spherical ends. A closed five-foot-diameter wind tunnel was mounted inside, such that air flowed through the central test section, past

the fan, and returned via an annular passage. The entire tank could be pressurized to 300 pounds per square inch (twenty atmospheres), sufficient to produce

Reynolds numbers for tests of 1

⁄20-scale models that were equivalent to full-scale

flight. A wide variety of tests were run in the VDT, including studies of several model

airplanes to validate the high-pressure concept, but the most significant investigations involved airfoils. Through extensive use of the VDT, Munk and other NACA

researchers drew accurate performance curves for the commonly used airfoils of

the era, and then extended the investigation to develop families of airfoils with

similar characteristics. The VDT provided unique capabilities, and the airfoil data

produced with it put the NACA and its Langley Laboratory “on the map” of first-class

aeronautical laboratories in the mid-1920s. (Document 2-15(i) in the preceding section

on international standardization of wind tunnels is a 1925 report from Britain’s

National Physical Laboratory comparing results from their Duplex wind tunnel

and the NACA VDT. It notes that the favorable comparison “tends to establish a

considerable amount of confidence in the compressed air tunnel results.”)

The documents included herein illustrate how Munk’s idea of a compressed

air wind tunnel moved from a concept to a reality. In a 7 October 1920 letter to

Jerome Hunsaker, Munk mentioned that he had “finally found a perfectly new

manner for increasing Reynold’s [sic] number,” but he declined to provide any

details prior to employment. Once on the NACA’s payroll, he readily furnished

the theoretical basis for his proposal, which the committee published as Technical

Note No. 60, “On a New Type of Wind Tunnel.” Once the VDT was in operation, the

NACA published a thorough description of the tunnel in Technical Report No. 227,

The Variable Density Wind Tunnel of the National Advisory Committee for Aeronautics. 

A secondary theme in this section concerns some of the problems surrounding

Max Munk himself. From the start he was embroiled in controversy, both national
500 Chapter 2: Building a Research Establishment

(because he was German), and personal (because he was unbearable to work with).

Documents in this section hint at the difficulties Langley personnel had with

Munk. As shown in the 1921 letter from Hunsaker regarding reactions to employing

German experts at the time, Munk faced an uphill battle from the start. Readers

should note that just to bring Munk into the United States and employ him in

federal service took no less than two special Presidential orders. 

Frederick Norton’s 5 August 1921 letter regarding the use of German airfoils

is another case in point; Norton was incensed that the NACA would even consider

allowing the use of a foreign—especially a German—airfoil when a number of good

American designs were available. While such national parochialism is perhaps

understandable so soon after the end of World War I, these documents suggest

that acceptance at Langley during this period would have been very difficult for any

German immigrant, not just Munk. 

Norton’s letter of 6 October 1921, dealing this time with VDT issues, shows that

the situation had continued to deteriorate. In his case, however, Munk managed to

retain George Lewis’s support, leading Norton to resign two years later. Max Munk’s

triumph was not long-lived, however. The recollections of Fred Weick, included as

Document 2-20(c) in the section on the success of the Propeller Wind Tunnel (PRT),

recount some of the continuing difficulties encountered in working with the brilliant but

temperamental German aerodynamicist. This challenge culminated in a 1927 “revolt”

by Langley personnel against Munk that resulted in his departure from the NACA.

Document 2-18(a), letter from Max M. Munk in Germany to Jerome Hunsaker, 1920.

Oct. 7th. 1920

To: Commander J. C. Hunsaker, U.S.N.

Assistant for Aeronautics to the Chief of the Bureau of Constr. and Repair of the

U.S. Navy Department

Washington, Navy-Building

Sir,

hoping [sic] to support my request of July 1920 at Göttingen, I beg leave to inform

you, that I made an important invention concerning wind-tunnel tests. You told me

then to be greatly discouraged by the present model-tests, on account of the small value

of their Reynold’s number and of the want of security in applying them on large bodies,

following from it. I quite agree with you in this matter: the law of the lift of wings

being found, there remain only investigations about details in the present wind-tunnels.

Meditating on these things, I finally found a perfectly new manner for

increasing Reynold’s number to about eightfold or even the elevenfold (but then

with a little complication surmountable however) without increasing the expenses
Document 2-18(a–j) 501

of the construction or the tests. The new method is important for such investigations

where Reynold’s number is to be considered. But then, you either get the eightfold value of this number or otherwise you can save seven eights of the costs.—

Not even knowing, whether your address is correct, I dont [sic] like to explain

the new method in this letter. Indeed I do not like to do this at all, as long as I

have not yet any answer to my request. I prefer reserving my idea to my next

employer. I shall however thank you very much for passing on the matter to the

Committee and for helping my next employer to be in the U.S.

Trusting you to excuse my once more troubling you in this matter, I shall be

very much obliged for the favor of an early reply.

Believe me Sir to be Yours most respectfully

[signed] M. Munk.

Document 2-18(b), letter from J. C. Hunsaker to Lester D. Gardner, 1921.

May 3, 1921.

Mr. Lester D. Gardner,

The Gardner, Moffat Co., Inc.

225 Fourth Avenue

New York, N.Y.

Dear Gardner:

I note with interest the row you appear to have got into over the report to the

President on the aeronautical situation, and so long as you are convinced you are

doing good I suppose your policy is correct from your point of view. However, you

ought to be more careful about using the term “minority report” since there wasn’t

any, and since the gentleman who wrote a special letter to the President had

already agreed in committee that [there] would be no minority report.

The information you wanted about Dr. Munk is that he was got from the University

of Göttingen by the National Advisory Committee for Aeronautics on my recommendation as knowing more about German aerodynamics and theoretical questions generally than [anybody] else they could get, and that the best way to bring ourselves up

to date with the research work at the Göttingen laboratory, and especially the unpublished portions of it, was to import the man who had done most of it himself. He

has not been turned over to the Navy or anybody else but is employed in Lewis’ office

in translating German data and preparing dope [intelligence information]. I don’t

think you can get anywhere by attacking the Committee for having employed a

German in order to make available in this country what the Germans know.

With kind regards,

Very truly yours,

[signed] J. C. Hunsaker
502 Chapter 2: Building a Research Establishment

Document 2-18(c), F. H. Norton, memorandum to George W. Lewis, 1921.

August 5, 1921.

From: Langley Memorial Aeronautical Laboratory

To: National Advisory Committee for Aeronautics

(Attention Executive Officer.)

Subject: Tests of Gottingen wing section.

Reference: (a) NACA Let. 54-6(44/21)—18648, Aug. 4, 1921.

1. Under no circumstances would I consider it advisable to use a German

wing section on a Committee helicopter as I am sure our own wing sections are

fully as good as Germany’s and if Dr. Munk can not find one which we have

already tested which has the properties he desires I will gladly undertake to

design and test one if he will furnish me with more particulars.

2. I think you will see that we should use every means to advertise the

Committee and the Committee’s work and the use of a German wing section in

its own helicopter should certainly not be advisable from this point of view.

F. H. Norton

Chief Physicist

Document 2-18(d), W. Margoulis, excerpts from 

“New Method of Testing Models in Wind Tunnels,” Aeronautics [Britain], 1921.

In forecasting the conditions of flight of aeroplanes by the results of model

tests made in existing laboratories, serious errors are inevitably made, owing to

the fact that in the laboratory it is impossible to observe the laws of similitude

requiring the equality of Reynolds numbers and the equality of the ratios of the

velocities to the velocity of sound (Law of Bairstow and Booth). The first of these

conditions is due to viscosity, and is of special importance at low speeds; the second

is due to the consideration of compressibility, and should be observed at high speeds.

Now, the Reynolds numbers attained in existing laboratories are from 15 to 25

less than those reached by machines in flight, whilst the velocities of the airstream

remain from two to three times lower than the speed in free flight. Thus, when a

model aeroplane is tested in the laboratory, the streamline wires resist relatively

twice as much, and the struts of the rigging and landing chassis five times as much,

whilst the wings carry up to 30 per cent less on the model than on the aeroplane.

It will be the same in the large laboratories (1,000 to 1,500 h.p.) now being

planned, which, though realizing higher velocities, will not attain the seventh part

of the true value of Reynolds number.

WE WILL SHOW, HOWEVER, THAT IT IS POSSIBLE TO HAVE WIND TUNNELS GIVING

HIGHER VALUES OF REYNOLDS’S NUMBER AND OF THE RATIO OF THE VELOCITY TO THE
Document 2-18(a–j) 503

VELOCITY OF SOUND THAN THOSE REACHED BY FULL SCALE MACHINES, AND THAT WITH

LESS OUTLAY FOR INSTALLATION AND UPKEEP THAN IS REQUIRED FOR THE LABORATORIES NOW BEING PLANNED. 

THIS RESULT WILL BE ATTAINED BY EMPLOYING SOME GAS OTHER THAN AIR, AND ESPECIALLY CARBONIC ACID, AT PRESSURES AND TEMPERATURES WHICH ARE SUITABLE AND

GENERALLY VERY DIFFERENT FROM THOSE OF THE SURROUNDING ATMOSPHERE.

Let v and d be respectively the velocity and diameter in the working section

of a wind tunnel; μ—the coefficient of viscosity; ρo

—the density at 1 kg.⁄cm2and

273°; p—the pressure, and T the absolute temperature of the fluid circulating in

the flue. The units employed are the kg., the metre, and the second.
504 Chapter 2: Building a Research Establishment

The motive power Pm required for working the fan of a closed circuit wind

tunnel of the Crocco type is:

Pm=0.47v2.75d1.75μ1.25ρ0

0.75p1.75T-0.75 (1) 

If the span of the model aeroplane is equal to 6/10 of the diameter of the flue

the Reynolds number will be:

N=0.6vd⁄ν=0.0164vdμ-1ρ0 pT-1 (2) 

Where ν is the kinematic coefficient of viscosity; ν = μ/ρ.

The velocity of sound in a fluid being equal to √γ p⁄ρ, γ being the ratio of the

specific heats, the condition of equality of the ratios of the velocity to the velocity

of sound requires that:

v=1.1086ρ0

-0.5γ0.5T0.5V (3)

V being the speed of the full scale machine.

We will examine three cases:

1st Case.—Tests of model aeroplanes and dirigibles; N is given.

From formulas (1) and (2) we deduce:

(4)

and

(5)

THE USE IN A WIND TUNNEL OF CARBONIC ACID AT 15 KG./CM2 AND 253° REDUCES

THE POWER REQUIRED FOR REALIZING A GIVEN REYNOLDS’ NUMBER WITH A GIVEN DIAMETER OF FLUE IN THE RATIO OF 1088 TO 1.

2nd Case.—Tests of model propellers; V is given.

We have:

(6)

the true speed (V) in the tunnel being determined by formula (3).

THE USE OF CO2 AT 0.5 KG./CM2 AND 253° REDUCES THE POWER REQUIRED BY 70

PER CENT. AND IF WE REDUCE THE PRESSURE TO 0.1 KG./CM2, THE POWER REQUIRED WILL

BE REDUCED BY 90 PER CENT.

3rd Case.—Any model whatever: V, N, and d are given.
Document 2-18(a–j) 505

We have:

(7)

and

(8)

the value of v being given by formula (3).

THE USE OF CO2 AT 253° AND AT A PRESSURE DETERMINED BY FORMULA (8),

REDUCES THE POWER REQUIRED BY 55 PER CENT.

We would point out that the terms characterizing the nature of the fluid and

the conditions of temperature and pressure in formulas (4) and (7) are independent

of the experimental value of n the expression giving the power drop in tunnels:

∆=a . μnρ0

1-n . p1-n

Tn-1 . v2-nd-1-n

It is the same for all the terms of formulas (3), (5), and (8).

As an application of the method, we will consider a closed circuit tunnel 2 m.

in diameter, 300 horse-power, utilizing carbonic acid. Model aeroplanes will be

tested at a pressure of 15 kg./cm2 and at 253°; we shall thus realize at 30 m./sec. a

Reynolds number of 81.106, corresponding to that of an aeroplane with a span of

26 m. at 150 km./h. or of a racing plane at 650 km./h.

If the propeller tests are made at 0.5 kg./cm2, the speed attained will be 76

m./sec., equivalent to a speed in free flight of 103 m./sec., that is 370 km./h, whilst

at 0.1 kg./cm2 the speed will be 570 km./h.

FOR REALIZING THESE CONDITIONS AN ORDINARY WIND TUNNEL 2 METRES IN DIAMETER

WOULD REQUIRE 326,000 H.P. IN THE FIST CASE, AND 3,000 H.P. IN THE SECOND CASE.

During the manipulations of the model, the working section can be isolated

by means of two doors, the carbonic acid contained in the working section having

been previously collected in a special tank. The measuring devices, registering the

stresses automatically, will be placed in an airtight cabin fixed on the wall of the

working section. . . .

[The author here discusses a graph and calculations, omitted here, that “represents the

functioning of a tunnel of our system (diameter 2 m, carbonic acid at 253°).”]

We thus see that for all aeroplanes, except giant planes (42 m. span), we realize the condition of equality of Reynolds’s number, that for dirigibles (24 m. in

diameter) we attain the half of Reynolds’s number which is sufficient to give a

good approximation, and that for all propellers we realize the conditions imposed

by the consideration of compressibility and viscosity. . . .
506 Chapter 2: Building a Research Establishment

Remark.—In the application just given of our system to a tunnel of 2m., we

assumed, in order to treat a general case, that the carbonic acid was cooled to –20°.

Practically this cooling leads to complications of installation and functioning which

are not justified by the slight gain of power (see formulas 4, 6 and 7) which results.

We therefore consider it preferable to work at the temperature of the surrounding atmosphere. If we assume a mean temperature of +10°, formulas (7)

and (8) show that for the same values of V and N the power is increased by 11 per

cent and the pressure by 6 per cent, with respect to those corresponding to a temperature of -20°.

Document 2-18(e), letter from Edward P. Warner, Massachusetts 

Institute of Technology, to George W. Lewis, 1921.

March 5, 1921.

Mr. G.W. Lewis,

National Advisory Committee for Aeronautics

Washington, D.C.

Dear Mr. Lewis:

I have recently received a letter from Mr. Margoulis relative to his new system

of high-pressure windtunnel employing carbon dioxide, and I am really quite

favorably impressed with such a tunnel for some classes of work. For determining

the speed and density effects on air speed meters, for example, such a tunnel

would be favorably used and also in connection with the test of streamlined bodies.

Margoulis is anxious to be retained as consulting engineer to construct such

a tunnel here, and while I do not see the necessity of this, as it would be easy to

secure the necessary talent for securing a high-pressure tunnel in America (incidentally I think that it would be best to use air at high pressure in preference to

carbon dioxide sacrificing some of the theoretical advantages but considerably

simplifying the construction and obviating the necessity of absolute leak-proofness),

I do recommend that Mr. Margoulis be retained by contract for not over 2500

francs to prepare a 12,000-work report on “European Windtunnel Practice” and

on suggestions for windtunnel design. He has shown himself possessed of many

excellent schemes and we would avail ourselves of his knowledge at least to that

extent. I further recommend that Margoulis be retained to prepare a general

report on the use of nomograms and alignment charts in aeronautics. It is a subject which we have too much neglected and which he is better qualified by experience to treat than any one else in the world, as he is the originator of almost all

the very ingenious nomograms used at the Eiffel laboratory.

Yours sincerely,

[signed] Edward P. Warner
Document 2-18(a–j) 507

Document 2-18(f), W. Margoulis, excerpts from “A New Method of Testing 

Models in Wind Tunnels,” NACA Technical Note No. 52, 1921.

We know that the two essential conditions of the application of the law of proportionality of pressure to the product of density, the square of the linear dimensions

and the square of the speed to the results of model tests are: 

1) THE EQUALITY OF REYNOLDS’ NUMBER.

v being the velocity of the airstream in the tunnel, 

V being the speed of the machine in free flight,

l and L respectively one of the principal linear dimensions of the model and of

the full-scale airplane.

ν and ν1 respectively the kinematic coefficients of viscosity of the fluid circulating in the tunnel and of the air in which the machine flies.

2) THE EQUALITY OF THE RATIOS OF THE SPEED TO THE VELOCITY

OF SOUND (Law of Bairstow and Booth).

w and W being respectively the velocities of sound in the tunnel and in the air.

The first of these conditions is due to viscosity and is important especially at low

speeds (tests of model airplanes); the second condition is due to the consideration

of compressibility and must be observed at high speeds (tests of model propellers).

Now, in existing laboratories utilizing a horsepower of 100 to 300, the models

are generally made to a 1

⁄10 scale and the speed is appreciably lower than the

speeds currently attained by airplanes; the Reynolds’ Number realized in the laboratories is thus from 15 to 25 times smaller than that reached by airplanes in free flight,

while the ratio M varies between the third and three-fourths of the true ratio.

Thus, when a model airplane, for instance, is tested in such a laboratory, the

streamline wires resist relatively twice as much, the struts of the rigging and

undercarriage five times as much, while the wings carry 30% less on the model

than on the airplane, so that RESULTS OBTAINED IN EXISTING LABORATORIES

CAN NOT BE PRACTICALLY UTILIZED.

We cannot appreciably increase Reynolds’ Number by increasing either the

diameter (d) of the tunnel, or the velocity (v) of the airstream, for the motive

power required for working the fan producing the airstream is proportional to

d1.75 v2.75 and such increase would therefore lead to installations much too costly

both as to establishment and upkeep.
508 Chapter 2: Building a Research Establishment

Thus wind tunnels are now being planned having a diameter of 3 to 5 m.,

speeds of 60 to 75 m/sec., and horsepower of 1000 to 1500; but the Reynolds’

Numbers attained in such tunnels will still be 8 times less than those of existing

large airplanes.

We will show, however, that it is possible to have wind tunnels in which the

Reynolds’ Number will be greater than that now attained by airplanes, and in which

the ratio of the velocity to the velocity of sound will also be greater than that realized

in practice, and we will show that this can be done with an outlay for installation

and upkeep much below that required by the laboratories now being planned.

In order to attain this result we have only to employ a gas other than air, at a

pressure and temperature different from those of the surrounding atmosphere.

[ . . . ]

2.—lst CASE—REYNOLDS’ NUMBER IS GIVEN; TESTS OF MODEL AIRPLANES AND AIRSHIPS.

Eliminating v from equations (1) and (2) [same as (1) and (2) in Document 2-18d]

we have:

(4)

and

(5)

Formula (4) shows that the power Pm is proportional to the term μ3

⁄ρ0

2 characterizing the fluid, and to the term T2

/p2 characterizing the conditions of temperature and pressure.

THE GAS WHICH IS PRACTICALLY MOST SUITABLE TO THE DIFFERENT CONDITIONS LAID DOWN BY THE ABOVE FORMULAS, AND BY

THOSE WHICH FOLLOW, IS CARBONIC ACID (CO2), AS A GAS HAVING A

LOW COEFFICIENT OF VISCOSITY, HIGH DENSITY, AND A LOW RATIO

OF SPECIFIC HEATS.

For air, μ3/ρ0

2 = 301/1018 for CO2, μ3

/ρ0

2 = 72.4/1018,

[Footnote:] (Other gases, such as chloride of methyl (CH3Cl) and Xenon would

give better results but could not be practically employed. Thus μ3

/ρ0

2 is equal to

571/1018 for water, to 15.6/1018 for CH3Cl and to 33/1018 for Xe. It is evident that

in the formulas we must always assume for water p = 1 kg/cm2 and T = 273°.) 
Document 2-18(a–j) 509

WE THUS SEE THAT FOR A GIVEN REYNOLDS’ NUMBER AND WITH

EQUAL DIAMETER OF FLUES, THE USE OF CARBONIC ACID AT 273° AND

1 KG/CM2 WILL ECONOMIZE 3/4 OF THE POWER REQUIRED WITH

ATMOSPHERIC AIR AND THAT COMPRESSION TO 15 KG/CM2 AND COOLING TO 253° WILL REDUCE THIS POWER IN THE RATIO OF 1088 TO 1,

WHICH CERTAINLY CONSTITUTES A REMARKABLE RESULT.

THE SPEED WILL BE REDUCED IN THE RATIO OF 1.85 TO 1 IN THE

FIRST CASE AND IN THE RATIO OF 30 TO 1 IN THE SECOND CASE.

[Margoulis here includes two additional cases that are essentially the same as the 2nd

and 3rd case in Document 2-18(d).]

WE THUS SEE THAT IF WE WISH TO ESTABLISH A LABORATORY FOR

WELL DETERMINED VALUES OF V AND N, THE USE OF CARBONIC ACID

AT 15 KG/CM2 AND 253° REDUCES THE POWER REQUIRED IN THE RATIO

OF 48.5 TO 1 AND REDUCES THE DIAMETER IN THE RATIO OF 22 TO 1.

IN A LABORATORY ALREADY BUILT, THE USE OF CARBONIC ACID

AT 253° REDUCES THE POWER REQUIRED IN TEE RATIO OF 2.2 TO 1;

THE PRESSURE SHOULD THEN BE EQUAL TO 68/100 OF THE PRESSURE

REQUIRED WITH AIR.

[ . . . ]

REMARK I.—When, in the formulas giving the value of the power in the

three cases considered, we compare the values of the terms characterizing the

nature of the fluid, we find that water forms the least advantageous fluid for use in

a laboratory, the more so as, being incompressible, its density can not be varied.

We may remark, however, that heating water to 100° reduces its coefficient of

viscosity in the ratio of 6 to 1; in the lst case it then becomes more advantageous

than air at atmospheric temperature and pressure. On this subject we may say that

we may consider the use in wind tunnels not only of gas (that is, of fluids for which

the temperature of saturation at 1 kg/cm2 is below 273° absolute) but also of

vapors, which must be heated so that their temperature is above the temperature

of saturation at the pressure at which they are utilized. Thus we may consider

using water vapor, although its characteristics (μ = 0.89 x 106

, ρ0 = 0.079) are not

favorable.

REMARK II.—In our theory of wind tunnels, we have called the coefficient of

utilization of a tunnel (rs) the ratio of the kinetic energy of the fluid stream in the

working section to the power of the engine running the fan.

For the closed circuit tunnels which we are studying, this coefficient takes the

very simple form:

Ns = vd/ν = N/0.6.
510 Chapter 2: Building a Research Establishment

5.—PRELIMINARY PROJECT OF A WIND TUNNEL.

As a practical application let us consider a closed circuit tunnel, 2 m. in diameter, utilizing carbonic acid.

For tests of MODEL AIRPLANES we use carbonic acid compressed to 15

kg/cm2 and cooled to 253° and we fix a speed of 30 m/sec. (corresponding, according to formula (3) to a speed in the air of 41 m/sec.).

The power required given by formula (1) will be 300 HP and the Reynolds’

number realized will be 81.106 and equal to that realized by the largest existing

airplanes (N is greater for large airplanes going slowly than for small planes flying at a high speed). This Reynolds’ number will correspond to that of a racing

plane flying at 650 km/hr.

The large laboratories now being planned will realize Reynolds numbers 8

times smaller with powers about 4 times greater. If in one of these laboratories

having a diameter of 3 m. we wished to attain N = 81.106, we should require a

power of 300 x 1088 x 2/3 = 217,000 HP. [Footnote:] (This figure must be considered rather as a proof of the impossibility of realizing this Reynolds’ number in

an ordinary tunnel than as an exact value of the required power. As a matter of

fact, the speed in this case should reach 900 m/sec. and we have not the right to

apply our formulas to such speeds, for which moreover the phenomena of compressibility would completely distort the results.)

For high speed tests, and especially for PROPELLER tests, the pressure must

be below 1 kg/cm2

. Thus formula (1) shows that with carbonic acid at 0.5 kg/cm2

and 253°, the speed realized with the same power of 300 h.p. would be:

equivalent to a speed in the air of 76/0.74 = 103 m/sec., that is 370 km/hr.

If the pressure is reduced to 0.1 kg/cm2, the equivalent speed in the air would

be 570 km/hr., with an economy in power of 90%; to attain such a speed an ordinary tunnel of 3 m. would thus require 

Lastly, we would say a few words on the realization of this wind tunnel.

There should be a closed circuit flue with continuous wall formed of thick
Document 2-18(a–j) 511

sheet metal and protected from over-heating. Two doors sliding perpendicularly

to the axis of the flue will isolate the working section while the model is being

handled. The measuring devices will be placed in an airtight cabin on the wall of

the working section, so that the rods of the model supports can traverse the wall

of the flue by joints which should not be airtight. The measurements will be registered automatically by apparatus installed either in the cabin and visible from

outside, or actually installed outside the cabin. In the latter case the apparatus will

consist of manometers connected with dynamometric capsules placed in the

cabin. The propeller-fan will have adjustable blades so that it can be adapted to

the density of the fluid used in the tunnel.

[ . . . ]

Document 2-18(g), Max M. Munk, 

“On a New Type of Wind Tunnel,” NACA Technical Note No. 60, 1921.

Introduction.

The difficulties involved in conducting tests on airplanes and airships in actual flight, difficulties greater in the early years of aviation than now, and the matter of expense also, induced investigators to seek information through tests upon

models. The first of such tests was made by moving the model through stationary

air either by means of a whirling arm or in a straight line. Later the method

adopted was to suspend the model in a current of air flowing in a large tube. Wind

tunnels of this type have become of increasingly great importance. At first the tunnels were only small pieces of physical apparatus in a laboratory, but at last they

require an entire building. The latest wind tunnel of the Zeppelin Company in

Germany provides a current of air ten feet in diameter, which has a velocity of 110

mi/hr. and absorbs 500 H.P.

The results obtained with this type of wind tunnel are of very great value and

at the present time they are the chief source of information for the aircraft designer.

However, there are certain critics who declare that the results of wind tunnel tests

are valueless for purposes of design. Indeed, justification for such opinions is not

wholly lacking. There is, in fact, no necessary and exact connection between the

motion of air around a small airplane model and that around the full-sized airplane. Sometimes the results of the tests on models agree well with those observed

with the airplane itself, but important cases are known where the two do not

agree. Further, there are questions the answers to which it is most important for

the designer to have, and yet the answer deduced from tests of models in wind

tunnels would be absolutely wrong. There is always an uncertainty connected with

such tests, because one is never quite sure whether or not the results thus obtained

may be applied to full-sized bodies.
512 Chapter 2: Building a Research Establishment

In spite of this uncertainty, wind tunnels have been of the greatest use in the

development of aeronautics. Tests upon models led to the construction of streamlined bodies having small resistance, and of aerofoils of good section.

Experiments in wind tunnels led to the discovery of the theorems referring to the

lift of aerofoils and to the effect of combining several aerofoils. A wind tunnel is

still the most important means available for scientific tests. It can not be denied,

however, that it is becoming more and more difficult to find a problem suitable

for study by a wind tunnel, which can be immediately applied in aeronautics.

Many tests of a theoretical character can be suggested, but it is difficult to interpret them. There are many important and urgent tests with respect to the design

of aircraft which should be performed, but the results would be worthless if they

were carried out in a wind tunnel of the present type. The theory of non-viscous

motion is almost complete, the tests referring to it have been made, and the field

of investigation lying between non-viscous motion and actual motion in the air is

cultivated so intensely that it is difficult to find a new problem.

For all these reasons, the author believes that his proposition to make use of

compressed air in a new type of wind tunnel comes at the right moment. Tests in

such a tunnel will give information concerning those questions which could not

be investigated with the present tunnels because of the exaggerated effect of viscosity.

The new type of tunnel is free of the uncertainty characteristic of the older type, and

will indicate clearly what problems may be undertaken with the latter. It will make

unnecessary many full-flight tests, and will mark a step in advance in aeronautics.

Let us then consider this new type of wind tunnel; its advantages, the difficulties

attendant upon its use, and the special methods required.

I. PRINCIPLE OF THE PROPOSED WIND TUNNEL.

The main difference between the new type of wind tunnel and the ones now

in operation is the use of a different fluid. The idea is to diminish the effect of

viscosity. It would not be surprising if any other fluid were better than air in this

respect. However, there does not seem to be such a fluid. Water, the liquid most

easily obtained, has, indeed, a comparatively small viscosity; that is, the ratio of

its viscosity to its density is only the 13th part of the similar ratio for air. The density

of water, however, is so great that it is hardly possible to afford the horsepower

required to force water through a large tunnel. But, even supposing that such a

current of water could be obtained, e.g. by using a natural waterfall, it would be

quite impossible to make tests in it. A model could not be made sufficiently strong

to withstand the enormous forces acting on it, nor would it be possible to hold the

model stationary. The same difficulty would be met in using any other liquid. As

for gases other than air, carbonic acid is the only one which has a ratio of viscosity

to density less than that of air, but the difference is so small that it would not pay

to use it. It is less expensive to build a larger wind tunnel than to construct one
Document 2-18(a–j) 513

for using carbonic acid gas, which has to be sealed and requires gasometers and

other contrivances for holding the gas; and, further, the difficulties of operation

would all be increased.

The fact that there is still another way of changing the fluid did not occur to

any one for many years. Air may be used, but, if it is compressed, it becomes a

fluid with new properties,—a fluid which is the best suited for reliable and exact

tests on models. When air is compressed, its density increases but its viscosity does

not. The increased pressure, it is true, requires strong walls for the tunnel to withstand the pressure and to prevent the air from expanding, but the increase of

effectiveness secured for the tests is so great that it will pay to make the necessary

changes and to replace the light walls of existing tunnels by heavy steel ones.

Before discussing this point we must first convince ourselves that the increase

of pressure greatly increases the range and value of wind tunnel tests.

II. THE REYNOLDS NUMBER.

We are inclined naturally to compare small objects with large ones, with the

assumption that all the qualities are independent of the size of the object, and

that therefore the effects will be correspondingly smaller or larger. Coming at

once to our problem, we are disposed to think that useful information for the

designer of a flying machine may be obtained by observing the shapes of a butterfly or of various insects. In fact, this is the idea underlying tests on models. The

absolute size of bodies is, it must be noted, a concept devoid of exact meaning.

There is no absolute length; the length of any object can only be compared with

that of another. Imagine all scales to have been destroyed, and let us not be conscious of the dimensions of our own bodies. Then we would not be able to decide

whether our physical world should be called a dwarf one or a giant one—we

would have no basis of comparison. We may therefore reasonably expect that a

world on a different scale than ours would not differ essentially from ours if the

same physical laws are valid in both.

This does not mean that all numerical ratios would be the same in both. It is

not necessary that the same physical laws produce the same motion of a fluid, i.e.

a geometrically similar motion, around two similar bodies. For the streamlines of

a fluid around an immersed solid are not related to its shape by geometrical relations

but by those derived from the laws of mechanics. It is possible, however, to derive the

condition for obtaining such similar motions by extending our general considerations, without using mathematical processes.

We picture two phenomena, independent of each other; in particular we presuppose that no scale is carried from the seat of one phenomenon to that of the

other. We consider separately two geometrically similar solids, each immersed in

its own fluid, and endeavor, under these conditions, to see if we can detect any

difference between them. If we can not, it would be absurd to expect two differ-
514 Chapter 2: Building a Research Establishment

ent motions, for one of the absolute truths, of which everyone is convinced, is that

equal causes have equal effects. Further, where we can not find a difference, we

believe, there is equality.

The two solids being supposed to be geometrically similar, no difference can be

found between them, since we do not have a scale. By selecting any particular

length of the body, its dimensions can provide us only with a standard length for the

investigation of the relation between the body and the space qualities of the fluid.

For the same reason we can not detect any difference between the densities of

the two fluids. Instead of considering density as the second standard unit—length

being the first—we will obtain a more useful one and one to which we are more

accustomed if we combine the concepts of volume and of density, and consider,

for instance, the mass of a cube of unit volume filled by the fluid as our standard

unit of mass.

The velocity of the fluid relative to the immersed body and at a great distance

from it may be considered as a third standard unit.

It is essential to realize that it is not possible to find any relation between

these three quantities. Neither do any two of them mean the same physical thing,

nor can any two of them be combined in such a way that the third appears. If,

therefore, the qualities mentioned were sufficient to determine all the features of

the phenomenon, the flow around similar bodies would always be similar also; we

would not be able to detect any difference. This is the actual case if the fluid is

non-viscous, and therefore motions around similar bodies immersed in perfect

fluids are similar.

The viscosity of a fluid is characterized as follows: consider a unit cube of the

fluid, so chosen that in any plane parallel to one of its faces the fluid has a constant velocity; let the velocity of the fluid increase uniformly as one passes from

this face across to the opposite one; then, if this change in velocity equals the unit

of velocity, the force of friction on the face of the cube is called the coefficient of

viscosity of the fluid. This appears to be a complicated concept, so we shall try to

combine it with the two standard units of length and of mass, so that we obtain a

velocity characteristic of the viscosity of the fluid, in combination with the other

two qualities. Let us imagine now a unit cube of the fluid and any difference of

velocity on the two opposite sides. There is a force of friction on each such face. If

this force were to act on a unit cube of the fluid, i.e., on a unit mass, it would produce

an acceleration, and in the course of being moved through a unit distance this

cube would have its velocity increased from 0 to a definite value.

We may imagine the conditions of velocity on the two opposite faces of the

unit cube varied until the force of friction is such that the resulting velocity of the

second cube equals the difference in velocity at the two faces of the first cube. Half

this velocity may be called the “Reynolds velocity.” It is characteristic of the vis-
Document 2-18(a–j) 515

cosity of a fluid whose density is known, the dimensions of a solid body immersed

in it being known, so as to furnish a unit of length. It can be determined for one

of the two phenomena considered without reference to the other.

Therefore the ratio of the velocity of a fluid to this Reynolds velocity can be

determined without reference to another phenomenon; it is an absolute number,

called the Reynolds number. It may be the same in the case of two phenomena,

or it may be different. If it is not the same, here is an essential difference between

the phenomena, which may be observed and stated; and it would be most remarkable if, in spite of this difference, the fluids should have the same motions; it

would in fact be impossible. But if, on the other hand, the two numbers are equal,

we describe the motions of the two fluids as identical, taking viscosity into

account, too. We may seek other differences; if there are none, it would be absurd

to expect different motions.

Before extending our general considerations, we shall express the Reynolds

number in terms of the quantities ordinarily used. Let r be the density of the fluid;

m be the coefficient of viscosity; B be the characteristic length of the immersed

solid. The mass of a cube of the fluid of length B on each edge is B3r; the force

of friction on a face of area B2 is mBV1, when V1 is the difference of velocity at

the two opposite faces; the work performed by this force if acting through a distance B is mB2V1, which equals the kinetic energy gained by the (second) cube of

mass rB3 —i.e. 1

⁄2 ρB3V1

2

. Hence, if V1 = V2

the Reynolds velocity is one-half of this, i.e.

Writing V for the velocity of the fluid at a great distance from the solid, we

have, by definition, the Reynolds number 

If this has the same value in two phenomena of flow, they are alike in all

respects. This may be called the Reynolds Law.

III. DEDUCTIONS FROM THE REYNOLDS LAW.

In the preceding section an attempt has been made to derive the expression

for the Reynolds Law in as elementary a manner as possible. Only by knowing the
516 Chapter 2: Building a Research Establishment

basis of the law can one grasp its complete meaning and obtain the absolute confidence in it which is required for one to apply it safely. A mathematical proof was

not given although it would have been shorter, for it would at the same time have

been poorer of content.

We considered only the viscosity of the air, and did not discuss the other differences which exist between the tests on models and those on full-sized objects.

The next stop is to investigate whether these differences do not introduce such

errors that it would not be worthwhile simply to get rid of a possible error due to

viscosity. Before doing this we must consider the deductions from the Reynolds

Law so far as wind tunnel tests are concerned.

Let the span of the wing of a model be 3 ft., and the air velocity be 60 mi/hr.

(= 88 ft./sec.). The kinematical viscosity of air at 0°C and normal pressure is

0.001433, i.e., about 1 ft.2⁄700 sec.. Hence the Reynolds number, regarding the span

as the characteristic length is

That is, the velocity of the air in the tunnel would be almost two hundred thousand times the velocity called the Reynolds velocity. The full-sized airplane may

have a span ten times as great, and the velocity of flight may be 1 1

⁄2 times as great;

so that its Reynolds number is

10 x 1.5 x 185,000 = 2,775,000.

The magnitude of these numbers is surprising. The viscosity of the air is so

small that in the neighborhood of the wings of an airplane the velocities produced by the forces of friction are only about three millionth of the velocity of

flight. Equation (1) shows that the kinetic energy is proportional to the square of

the velocity, while the work performed by the frictional force is proportional to

the velocity. Hence the work performed by the frictional force is a minute fraction

of the kinetic energy, 10⁄185,000 in the model test referred to and 10⁄2,775,000 in the

case of the airplane. It seems surprising that any effect of friction can be detected,

since it increases or decreases the kinetic energy by such a small fraction.

However, in the calculation of the Reynolds number one quantity is chosen

arbitrarily. An arbitrary length occurs in the formula, and the magnitude of the

number depends upon the choice of this length. Indeed, within a range of a

dimension like the span of wings, the viscosity has almost no influence, but the

smaller the range considered, the greater is the effect of viscosity, provided there

are in this range the same differences of velocities as in the other. It must be noted
Document 2-18(a–j) 517

that great differences of velocity occur within very small ranges. Near the surface

of the wing velocities almost zero occur close to velocities of the magnitude of the

velocity of flight. The character of the motion depends upon the stability of flow

near the surfaces, and therefore, upon phenomena within small ranges. Within

these the Reynolds number and the ratio of the acceleration to the viscosity is less

than the number commonly used for comparison.

In any case, tests show that there are considerable differences of motion at the

Reynolds numbers of the test and the flight. There is even instability, changing

the character of the motion near the largest airships, on increasing its velocity,

when flying at normal velocities.

These facts are not contradictions of the Reynolds Law, but, on the contrary,

are in agreement with it. The surprising fact that, even when the Reynolds number

is large, its influence is considerable, does not furnish the least reason-for doubting

the correctness of a law based upon such elementary considerations.

Doubts about the Reynolds Law are based upon a different fact. In spite of the

convincing proof, it happens that model tests at the same Reynolds number sometimes give quite different results. Now the Reynolds Law does not mean that at

the same Reynolds number only one particular motion of the air is possible. It

states that there is no difference between two phenomena with the same number.

It may be that two or more motions are possible, but then they are possible in any

case of the same Reynolds number.

There must be some reason, however, why the one or the other motion

occurs. The reasons may be different. Sometimes there is a kind of hysteresis, the

fluid remembered, as it were, what happened before this particular motion began;

and the motion is different, for instance, if the angle of attack was larger or smaller

immediately before. If such a phenomenon occurs with the full-sized body, it can

be investigated by a model test at the same Reynolds number. Sometimes there is

no such hysteresis, but the motion is very sensitive and is changed by the least

change of the shape of the body, or of the smoothness of its surface, or with a

change of the turbulence of the air. In such cases the motion around the full-sized

body will be sensitive at the same Reynolds number as in the model tests. In this

case it will be difficult to obtain the exact shape of the model and the right

smoothness of its surface in order to have the same motion. At the same time

other differences between the model test and the actual flight will produce differences

in the results; but in such cases it is very doubtful whether two airplanes which are

apparently identical have the same qualities. There does not exist a definite

motion around the body at that particular Reynolds number. The careful investigator

will observe this fact. Then the model test has shown all there is to be shown, and

the method is not to be blamed for revealing phenomena which are surprising to

the designer but true nevertheless.
518 Chapter 2: Building a Research Establishment

IV. ERRORS DUE TO OTHER CAUSES.

There are still other differences between the tests on models and in actual

flight, which will cause errors. It is necessary to realize that these, other than the

one due to viscosity, do not affect seriously the value of the results of the tests. The

new type of wind tunnel may, then, be expected to give reliable results.

The best evidence of the insignificance of these errors due to other causes is

obtained by comparing tests made in different wind tunnels. It may be stated that

there is found a certain agreement, but only with the same value of the Reynolds

number. Reynolds himself deduced the law called by his name from experiments

upon water flowing through pipes. In the two wind tunnels at Göttingen very

careful investigations were made on aerofoils, over a large range of Reynolds

numbers, and under very different conditions. Most results at the same Reynolds

number agree well; even the results which can not be plotted on a curve against

the Reynolds number appear much more regular when so plotted than when plotted in any other way. The results of these tests show that full-sized tests are much

better than model ones, and provide the designer with clear, reliable and useful

information. It is not sufficient, however, to compare the results of several tests in

a perfunctory manner; care must be taken.

The Göttingen tests were not made under conditions geometrically similar;

the two tunnels are not equally good. There are many tunnels which have more

turbulence than is necessary, the designer having only taken care to obtain a uniform velocity. The older wind tunnel at Göttingen was exceedingly turbulent. The

surfaces of the models were different purposely. Only the results obtained in good

wind tunnels should be compared, the model having a proper surface, and the

test being thoroughly laid out with reference to its influence. Then the differences

would be smaller, and the reliability and usefulness of tests at the full-sized

Reynolds number would appear more distinctly.

The matter may be considered also from another point of view. The tests

show that under particular conditions the results of different tests agree very well;

in certain cases only is good agreement lacking. Now it is not evident that the

results may be expected to agree. It may be and is very probable that the motions

which do not agree with each other are such sensitive motions as were described

in the previous section. Of course this sensitiveness appears exaggerated if the

differences in the test conditions are.

Theoretical reasons are not wanting, however, as to why the character of the

motion depends almost exclusively on the ratio of the velocity of air to the

Reynolds velocity, and not upon other ratios, e.g. the ratio of the Reynolds velocity to the velocity of sound in the medium, the latter being characteristic of its

compressibility. It is not at all sufficient to state that this ratio is small, the

Reynolds number (or its inverse) being small too. But the ratio of velocity to the
Document 2-18(a–j) 519

velocity of sound has only one meaning; there is no arbitrary quantity used in

forming it—such as B in the-Reynolds number. It does not matter whether this

ratio is calculated for a wide range or for a small one. There is no discontinuity if

the range or the compressibility passes to zero. In this case the fluid acts, with

respect to its compressibility, like a perfect fluid. If the ratio of the velocity of flight

to the velocity of sound is small, there is no physical reason for expecting a large

influence. So much the less is the influence of a difference of compressibility in

the tests on the model and in flight. Stated mathematically, any coefficient is a

function of the two ratios; but, when both are small, the function is continuous

with respect to the one and irregular with respect to the Reynolds number.

The same deduction is valid for the other errors; whether the cause be the

contrivance used for supporting the model, the turbulence of the air, the variation

of pressure or of velocity, or the finite distance of the walls of the tunnel or the

boundaries of the current of air, the error is small provided the cause is. Their

influence can be made as small as is necessary and customary in any technical test.

Not only is the error small, it is regular, it can be compensated for, and it does not

impair the comparison of different tests, as would the error due to viscosity.

V. THE DIMENSIONS OF A COMPRESSED AIR WIND TUNNEL.

In a tunnel filled with compressed air it is possible to obtain a Reynolds number

much larger than in the tunnels now in use. But the range is limited in several

respects, and its features must harmonize with each other in order to secure good

results and also a low cost of operation.

The size of the tunnel is limited by the size of the models. It is not possible to

make correctly shaped models if they are too small. The velocity of flow, on the

other hand, must not be too great, lest the contrivances for supporting the model

become so large that they disturb the motion. The stresses in the model must also

be considered. This condition is duly respected if the dynamical pressure of the

air does not exceed a particular value.

Hence the velocity must be the smaller the greater the density. This is desirable

also with respect to the power required, to the increase of temperature produced,

and to the dimensions of the fan and its shaft. The designer must also consider

the time required to fill the tunnel with a compressor of proper dimensions. The

pressure is limited only by questions of construction.

Let D be the diameter of the section where the model is placed, V be the

velocity of the air and P be the maximum pressure. Then

Reynolds number RαDVP

Power required PαD2

V3P

Heat produced per unit of surface αV3P

Dynamical pressure qαV2P

Weight of tunnel walls αD3P
520 Chapter 2: Building a Research Establishment

Energy required to fill tunnel αD3P1.25

Shaft diameter/diameter of tunnel αVP1⁄

3

(velocity of circumference of fan constant)

The designer, in the first place, must choose the dynamical pressure he can

permit without the supports of the model introducing too great an error. Then he

may calculate the pressure needed for the Reynolds number desired, and the

smallest diameter he considers proper. If he selects too high a pressure, the diameter

must be made greater. Generally this will increase both the cost of operation and

other difficulties. The Reynolds number and the dynamical pressure being given,

the diameter and the velocity may be expressed as functions of the pressure.

If R=aDVP and q=bV2

P then V=AP-1/2 [and] D=BP-1/2 where a, b, A and B are

constant coefficients. Substitutions may then be made in the expressions for the

different quantities. It appears:

Power absorbed α P-3/2

Heat produced per unit of surface α P-1/2

Weight of tunnel walls α P-1/2

Energy required to fill tunnel α P-1/4

Shaft diameter/diameter of tunnel α P-1/6

That is to say, all the quantities mentioned are more favorable the higher the

pressure. This advantage must be compared with the difficulty of construction in

consequence of high pressure, and the disadvantage of a smaller diameter. A theoretical limit for the pressure is the critical point where the air ceases to be a “perfect

gas.” In the neighborhood of this point the viscosity increases and therefore it is

of no advantage to increase the pressure; but reason of construction would prevent

this point being reached. The critical point of carbonic acid gas is, however, much

lower, especially if it is cooled.

We can not close this chapter without considering the most interesting question,

whether it would be possible to build a wind tunnel for tests of models of airships,

having a Reynolds number equal to flight conditions. Let the length of the actual

ship be 655 ft., and its velocity be 95 mi/hr. In a tunnel designed for tests of ship

models only, the dynamical pressure could be increased to 2000 lbs./ft.2 The pressure

could be 100 atmospheres (200,000 lb./ft.2). Then the velocity would have to be

just 95 mi/hr., and happens to be “full sized.” The scale would be 1:100; the diameter

could be 2 ft., and the power about 1000 HP. We think this tunnel could be made.

It would give the designer information long desired.

The results of tests in a compressed air wind tunnel would be applied in the

same way as is the practice with existing tunnels. The tunnel would give the ordinary

coefficients, and the right ones. The Reynolds number could be calculated from

the observed temperature and pressure.

The results would be, first of all, for the information of the designer of aircraft,
Document 2-18(a–j) 521

giving him the true values of the coefficient required for any problem. The tunnel

could also be used with advantage for scientific investigations. The differences in

the Reynolds numbers which could be realized in such a tunnel are much greater

than can be obtained in existing tunnels. At the same time, the pressures and the

forces on the model vary only as the Reynolds number, if the same model is used,

whereas in existing tunnels they vary as the square of this number.

Document 2-18(h), F. H. Norton, memorandum to G. W. Lewis, 1921.

October 6, 1921

From: Langley Memorial Aeronautical Laboratory

To: National Advisory Committee for Aeronautics

(Attention Executive Officer)

Subject: Design of compressed air wind tunnel

1. There are at present three Draftsmen spending almost all of their time on

this work as it takes most of Mr. Morgan’s time to supervise Mr. Pratt and Mr. McAvoy.

Mr. Morgan feels that they are working very inefficiently and are getting very few

results, as Dr. Munk does not seem to have any clear idea as to what he wishes in

the engineering design excepting that he is sure that he does not want anything

that Mr. Griffith or myself suggest. At the end of this week I must take Mr. Morgan

and Mr. Pratt entirely away from this work and let Mr. McAvoy struggle along as

best he can. For this reason it is requested that Mr. McAvoy be ordered to

Washington so that he can be directly under Dr. Munk’s supervision. I am getting

so disgusted with the way the whole thing is being carried out that I would like to

keep as much of it in Washington as possible.

[signed] F. H. Norton

F. H. Norton

Chief Physicist.
522 Chapter 2: Building a Research Establishment

Document 2-18(i), “Compressed Air Wind Tunnel,” NACA Annual Report for 1921.

THE LANGLEY MEMORIAL AERONAUTICAL LABORATORY.

In previous annual reports the committee described the progress made in the

development of its field station at Langley Field, Va., for the prosecution of scientific

research in aeronautics. The station now comprises three principal units, namely,

an aerodynamical laboratory or wind tunnel, an engine dynamometer laboratory,

and a research laboratory building, the latter including administrative and drafting

offices, machine and woodworking shops, and photographic and instrument laboratories. The research laboratory and the wind tunnel building are of permanent

brick construction; the engine dynamometer laboratory is housed in a temporary

four-section steel airplane hangar.

The committee has recently completed the construction of a factory type

building of brick and steel, designed to house the new compressed-air wind tunnel.

It is expected that the new wind tunnel will be in operation about July, 1922.

The Langley Memorial Aeronautical Laboratory occupies a plot of ground known

as plot 16, Langley Field, Va., the plot having been set aside for the committee’s

use by the Chief Signal Officer of the Army in 1916, at the time the site was selected

as a proposed joint experimental station and proving ground for the Army and

Navy air services and the advisory committee. The use of that plot of ground was

officially approved by the Acting Secretary of War on April 24, 1919. The four

buildings at present constituting the Langley Memorial Aeronautical Laboratory

have been erected by the committee pursuant to authority granted by Congress.

COMPRESSED AIR WIND TUNNEL.

On June 9, 1921, the executive committee of the National Advisory Committee

for Aeronautics authorized the construction at the Langley Memorial Aeronautical

Laboratory of a compressed air type of wind tunnel designed by Dr. Max Munk,

technical assistant of the committee.

The utility of the present type of wind tunnel is limited by the fact that owing

to a “scale effect” the results of tests on the small models, which are usually about

1

⁄20 scale, are not immediately applicable to the full-size machine. Obviously it is

very desirable to obtain, if possible, test results which are strictly proportional to

those obtained in free flight. This condition may be realized by the use of a wind

tunnel in which the air is compressed to about 20 atmospheres or more in order

to compensate for the difference in the “scale” or Reynolds number for the model

and for the full-size airplane.

The wind tunnel under construction has a diameter of 5 feet, the wind tunnel

proper being placed within a steel cylinder 15 feet in diameter and 34 feet long. The

steel cylinder has been tested for an internal pressure of 450 pounds per square inch

and is designed for an average working pressure of 300 pounds per square inch.
Document 2-18(a–j) 523

The design of the cylinder further provides for a large door at one end and

means for observing and operating the balance and setting wing angles from

without the cylinder. The design of the balance has been carefully considered and

due provision is made for the large forces to be measured.

The wind tunnel motor is 300 horsepower and the Reynolds number will be

controlled by changing the air density rather than by changing the air speed. The

air compressing units consist of two 300-horsepower compound compressors

which compress the air to 115 pounds per square inch. The air is compressed into

a receiving chamber and is then compressed by a 175-horsepower duplex booster compressor to the desired pressure in the test chamber. With the compressor

units selected it will require approximately one hour to fill the chamber with air

at a pressure at 300 pounds per square inch and every provision is being made in

the design to make it unnecessary to open the chamber until the model is completely tested. Provision is also being made to maintain constant density so as to

take care of temperature variations.

This tunnel when in operation will test models with a span of about 2 feet, but

the results will be strictly comparable to similar data for a full scale machine, with

a span of 30 feet, flying at 100 miles per hour. The construction of the models will

therefore require special study and care.

Document 2-18(j), Max M. Munk and Elton W. Miller, The Variable 

Density Wind Tunnel of the National Advisory Committee for Aeronautics, 

NACA Technical Report No. 227, 1925.

SUMMARY

This report contains a discussion of the novel features of this tunnel and a

general description thereof.

PART I

FUNDAMENTAL PRINCIPLES

By MAX M. MUNK

All the novel features of the new variable density wind tunnel of the National

Advisory Committee for Aeronautics were adopted in order to eliminate the scale

effect. The leading feature adopted was the use, as the working fluid, of highly

compressed air rather than air under normal conditions.

It is not at once obvious that the substitution of compressed air eliminates the

scale effect with aerodynamic model tests, although the necessary theoretical discussion has been available for some years. The idea of using compressed air must

have occurred, in all probability, to many. It was not, however, till early in 1920

that the thought came to the writer; and in what follows is given his own line of

reasoning, expressed in as simple language as possible.
524 Chapter 2: Building a Research Establishment

In a paper entitled “Similarity of Motion in Relation to the Surface Friction

of Fluids,” by T. E. Stanton and J. R. Pannell, Philosophical Transactions A, volume

214, pages 199–224, 1914, will be found an excellent treatment of the subject,

with references to the earlier discussions by Newton, Helmholtz, and Rayleigh.

Proceeding at once to the motion of a rigid body immersed in a fluid, the aim

of the investigation is to obtain information concerning the fluid forces on such a

body. Everything in connection with the problem has to be studied to that end,

and has to be included in the investigation, whether this latter be analytical or, as

we suppose now, experimental. There are the properties of the immersed body,

its shape, its direction of motion, eventually the character of its surface. Even

more important is the action of the fluid brought into play by these properties.

Every detail of the motion of the fluid, together with the physical properties of

the fluid, is immediately connected with the kind and magnitude of the forces created. We can only attain to a full knowledge of the forces created by regarding

their cause, the fluid motion. All velocity components at all points of the flow are

important and characteristic details of the cause of the forces on the body

immersed in the fluid.

Then, why do investigators think that they can learn about what will occur on

a large scale by observing what occurs on a small scale? Not from any intuitive

feeling, inexpressible in words because devoid of thought; not from any vague

metaphysical argument difficult to explain. There is a definite, extremely sound

and simple reason why we expect to obtain reliable information from model tests.

It is because we expect the two cases when compared with each other will perfectly,

at all points, conform to each other, point by point. We do not mentally confine

the geometrical similarity to the bodies immersed and to the dimensions of the

entire arrangement, leaving as an unsolved and uninteresting question what the

fluid does in the two cases. We do not expect that, for some mysterious reason,

the fluid forces will correspond to each other in accordance with some simple

rule. On the contrary, we include the flow patterns in our conception of “model.”

Any two corresponding portions of the flow, however small, are supposed to be

similar with respect to shape and direction of the streamlines and with respect to

the magnitude of velocities. The ratio of the lengths of a pair of corresponding

portions of a streamline is supposed to be constant throughout the flow, and so is

the ratio of two velocities corresponding to each other. We are under the impression

that with respect to every detail the entire small-scale experiment is an exact replica

of what occurs on a large scale, and we believe that the smallest quantity, whatever

it is, occurs in a numerically corresponding way with the same conversion factor

throughout the entire flow. In such a case, and only then, are we entitled to expect

a simple relation between the fluid forces of the model test and those on the

large-scale experiment. Such forces are the integrals of the elementary forces, and
Document 2-18(a–j) 525

hence they stand in a constant ratio if the elementary forces do. This constant

ratio can furthermore be expected to be a simple algebraic expression of the

ratios between the characteristic quantities of the two arrangements.

Not only the model but the entire flow is the replica. There is a good illustration.

It sometimes occurs in aerodynamics that the same body moved in the same way

in the same fluid gives rise to different configurations of flow. The air forces are

then also different.

The question, “Can we learn from aerodynamic model tests?” is thus reduced

to the equivalent question, “Can flow patterns be geometrically similar?” If so the

boundaries of the flow in general, and the immersed bodies in particular, have to

be similar, but this alone is no sufficient reason why the similarity should extend

to every streamline. The question whether a test is really a model test in the strict

meaning, the question whether the small-scale flow is similar to the large-scale

flow, requires a special examination. This examination will decide whether we can

obtain reliable information from the test. If the flows are not exactly similar, but

only approximately, the information also will only be approximately correct and

not wholly reliable. There will exist a “scale effect.”

Two configurations of aerodynamic flow are created in different fluids under

conditions geometrically similar. We wish to know whether the flow patterns are

geometrically similar. We imagine a small-scale flow to exist exactly similar to the

large-scale flow really existing, and we ask whether this imagined small-scale flow

is compatible with the general laws of mechanics and hence identical with the

actual small-scale flow. More particularly, we examine whether each particle of the

imagined small-scale flow is in equilibrium, remembering that the corresponding

particle of the large-scale flow is.

We assume first that no physical properties of the fluids, nor differences of

such properties, have any influence on the shape of the flow pattern or on the

fluid forces, except the density of the fluids. We dismiss also any external influence,

like that of gravity. Then the only type of force brought into action by the motion

of the fluid is the mass force of all the particles, and they are equalized by means

of a variable pressure. The pressure distribution is only the natural reaction

against changes of mutual positions of all the fluid particles, which changes must

be compatible with the continuity conditions of the fluid. Each particle has the

natural tendency to move straight ahead with constant velocity. This tendency is

in conflict with the other tendency of each fluid particle to claim its own space, not

to share its space with any other particle. These two conflicting tendencies lead to

a distribution of varying pressure and to mass forces on the particles due to their

motion along curved paths and with varying velocities. The pressure distribution

gives rise to an elementary force on each particle, and the flow arranges itself in

such a configuration that this pressure force is in equilibrium with the mass force.
526 Chapter 2: Building a Research Establishment

Let us consider now the case when the linear dimensions are diminished in

the ratio l2⁄l1 , all velocities diminished in the ratio V2⁄V1, and the density ρ2, bears

the ratio ρ2⁄ρ1 to the original density.

The mass forces are expressed mathematically by a type of term occurring in

Euler’s or Bernouilli’s equation. Per unit volume, they are of the type

Density x Velocity2

Length

and hence resultant mass forces of corresponding portions of the flow are of the type

(1) Density x Length2 x Velocity3

Such forces are in equilibrium with the pressure forces, and this determines

the latter. Hence a change of density, scale, and velocity gives rise to a change of

all elementary forces and hence of all resultant forces in the ratio

The equilibrium of the particles remains unimpaired by the change of scale, and

we conclude that corresponding flow patterns are necessarily similar. Hence, if

the density of the fluid were the only property influencing the fluid paths and

hence the fluid forces, all aerodynamic model tests would be interpreted correctly

by the application of the so-called “square law.” Corresponding fluid forces would

be proportional to the fluid density, to the square of the velocity, and to the square

of the linear scale. Accordingly, the absolute coefficients generally in use for

expressing the magnitude of fluid forces would not only be absolute, but also constant

for similar shapes and arrangements.

Experience has shown that the “square law” does not strictly hold, but that

the air-force coefficients vary, sometimes slightly and sometimes in a very pronounced way. This is due to the influence of other properties of fluid, neglected

before. There arises the question which other property of air is the principal cause

of variations of flow patterns under conditions otherwise geometrically similar. All

men who have devoted much thought to this problem agree that viscosity has

such an effect, greatly in excess of that of other properties. The point is that the

forces taken care of by the introduction of such properties of the fluid are very

small when compared with the mass forces, which latter alone are governed by the

“square law.” This holds true at all points of the flow and with respect to all fluid

properties, except with viscosity, where it only holds at most points. Viscous forces
Document 2-18(a–j) 527

are proportional to the rate of sliding of adjacent layers of fluid, and are

expressed by terms of the type,

Here the constant quantity m is called the modulus of viscosity. u, a velocity,

is at right angles to y, a Cartesian coordinate, together with x and z. Hence δu

⁄δy

has the physical dimension of an angular velocity, 1⁄Time. Now, this rate of sliding

is small throughout an aerodynamic flow except near the boundary. There it may

assume a very large magnitude. So, in spite of the small value of the modulus of

friction of air, μ, the friction μ

δu

⁄δy can assume a very large value and can become

dominating at certain points of the flow. It can then produce essential changes of

the entire flow pattern. Very little in detail is known about these things, and it

seems useless to carry the discussion on at this point. Experience has shown that

proper attention to the viscosity brings system and regularity into results of tests

otherwise obscure and contradictory. It is for this reason that the elimination of

the effect of viscosity for many years was thought desirable in the first place as a

fundamental improvement of aerodynamic model tests, resulting in the elimination of the scale effect.

There has been some controversy as to whether these arguments are sufficient for

the final decision that viscosity is the all-important fluid property. No arguments whatsoever will definitely decide that, but only final success. The separation of the physical effects to be taken into consideration for any practical purpose from those which

may be neglected is a mental step which can not be accomplished by mere logics.

Granted, now, that viscosity is of practical importance, the question arises, Are

similar flows possible in viscous fluids; and if so, under what conditions will the

flows be similar? It is understood now that the arrangements are geometrically

similar, that only the density r and viscosity m of the fluid have to be considered

in addition to the linear scales of the arrangement and the ratio of the velocities.

The answer to the last question depends again upon the result of the examination whether each particle of an imagined small-scale flow, similar to an actual

large-scale flow, is in equilibrium or not. Now, in viscous fluids the mass forces are

not in equilibrium with the pressure forces, but in equilibrium with the combination

of both the pressure forces and the viscosity forces. We have now three types of

forces in equilibrium with each other, and that gives rise to a variety of possibilities.

Two forces in equilibrium are, of necessity, numerically equal, hence if one of

them be changed in a given ratio the other will too. With three forces, all three

may be changed in a different ratio and still the equilibrium maintained.
528 Chapter 2: Building a Research Establishment

The criterion for the similarity of flows is, therefore, that two of the three

forces be changed in the same ratio. Then the third, in equilibrium with the two,

will be changed in this same ratio and needs no special examination.

We compare the ratio of chance of the mass forces and of the viscosity forces

with each other. We have seen already (1) that the mass forces are changed in the ratio 

The viscous forces being of the type 

are seen to be changed in the ratio 

Now, the two flow patterns will be similar and the test will be a strict model test

only if the mass forces and the viscosity forces are changed in the same ratio.

Hence we obtain, as the condition of an exact model test,

or, written in a different way,

The expressions on either side of equation (3) are generally called “Reynolds

numbers,” from Osborne Reynolds, who was the first to emphasize their importance.

Since V and l are certain velocities and lengths in the two flows, corresponding to

each other, but otherwise arbitrarily chosen as “characteristic” velocity or length,

the value of one special Reynolds number in one single case has as little meaning

as the scale of one single object. The equality of the Reynolds numbers of two

arrangements, different but geometrically similar, expresses the dynamic equivalence

of the two flows compared.

If the ratio of the two Reynolds numbers is different from unity the value of this

ratio can be considered as a kind of relative scale between these two tests, not of the

geometric scale but one which may be called dynamic scale. The ratio of the

Reynolds numbers indicates differences in the relative importance of the mass forces

and of the viscosity forces. A single Reynolds number, together with the definition

of the characteristic velocity and length, is only an identification number, not

much more than the street number of a house. Comparison of Reynolds numbers of

flows where the conditions are not geometrically similar have hardly any meaning.
Document 2-18(a–j) 529

The preceding discussion has led us to the condition under which a wind tunnel

will have no scale effect due to viscosity, and probably not any scale effect of practical

importance. This condition is not equal velocity in model test and in flight. Full

velocity is only of value for investigating certain original airplane parts and original

flight instruments. The test with a model of diminished scale but at the velocity

of flight is by no way distinguished from tests at other wind-tunnel velocities. On

the other hand, if there is no scale effect expected, the Reynolds number being

equal in both model test and free flight, the dynamic scale being 1, and if there

are still arguments raised doubting the validity of such tests, such arguments hold

with equal right or wrong against all other model tests, more particularly against

such tests in ordinary atmospheric wind tunnels. For the principal difference

between the variable density tunnel and atmospheric tunnels is the elimination of

one source of error, of the one moreover, which is believed by most experts to be

the most serious.

The fact is, then, that in general model tests in atmospheric wind tunnels are

made at a Reynolds number smaller than in free flight. The linear dimensions of

the model are largely diminished, and nothing is done to make up for this; the

velocity is at best the same as in flight and the ratio μ/ρ is the same, the same fluid

being used in test and in flight.

It is neither practical nor sound to make up for the diminution of the model by

correspondingly increasing the velocity so as to obtain the original value of the product V l as required in equation (3). It is not practical because such a wind tunnel would

consume an excessively high horsepower, and because the air forces on the model

would become excessive to such an extent as to make the test practically impossible.

Such a method would also be unsound. For the differences in air pressure, which

amount only to little more than 1 per cent in flight and in ordinary wind tunnels,

would increase rapidly with velocities approaching the velocity of sound. Thereby

the influence of the compressibility would be rapidly increased, and thus another

error, now negligible, would make the results unsuitable for the desired purpose.

There remains then only the diminution of the ratio μ/ρ often denoted by v,

in order to make up for the diminution of l in equation (3). This means the choice

of another fluid. The use of water instead of air has been seriously proposed. With

water v = μ/ρ is indeed seven times as small as with air. The problem of the large

power consumption could eventually be solved, either by using a natural stream

or by towing the model. However, water is about 800 times as dense as air, and

hence the forces produced at the same velocity are 800 times as large, giving rise

to stresses 800 times enlarged. It is practically impossible to make ordinary model

tests with forces on the model 800 times as large as they are now.

What we need is a fluid which may be denser than atmospheric air at sea level,

but only so to a moderate degree. Its dynamic viscosity modulus v = μ/ρ should
530 Chapter 2: Building a Research Establishment

be distinctly smaller than that of air, in order to make up for the scale of the

model and eventually for the diminished velocity necessary for bringing down the

pressure on the model and the absorbed horsepower. No such fluid is known

under ordinary atmospheric conditions. Further consideration showed that a

high pressure transforms air (or another gas) into a fluid suitable for wind-tunnel

work giving results without scale effect. This fact depends on the physical property of air of keeping the same viscosity modulus m under all variations of pressure. This has been confirmed by experiments and is mentioned in treatises on

physics. It is in keeping with the molecular theory, with denser air the average

free paths are proportionally shorter. The viscosity modulus μ remains the same,

but the density increases when the pressure increases. Hence the ratio v = μ/ρ

varies inversely with the pressure (the temperature remaining unchanged). Hence

we have

Kinematic viscosity ~ Pressure-1

Model pressure ~ Pressure x Velocity2

Absorbed horsepower ~ Pressure x Velocity3

Assuming a model scale of say 10, we want a kinematic viscosity at least 10

times as small as with air. With pressure of 20 atmospheres we could get

Test velocity = 1⁄2 flight velocity.

Resultant model pressure = 20(1⁄2)

2

, 5 times actual pressure.

Horsepower consumption of the tunnel = 20(1⁄2)

3

, 2.5 that of an atmospheric

tunnel of the same size and operating at full scale velocity.

Reynolds number = Reynolds number in free flight. These figures seemed

practical. On them the design of the variable density wind tunnel of the National

Advisory Committee for Aeronautics has been based.

More generally it can be seen that the principle of compressing the air allows

any Reynolds number, even with a small model, if only the pressure can be produced

and maintained. For keeping the Reynolds number constant and increasing the

pressure in the ratio A, decreases the resultant pressure on the model as A-1 and

the required horsepower as A-2.

The throat diameter of 5 feet was chosen in order to be able to use the same

models as in the atmospheric wind tunnel of the National Advisory Committee

for Aeronautics. A small diameter would require smaller models, and it becomes

increasingly difficult to construct such models accurate enough.

Furthermore, 5 feet is the smallest diameter for a closed tunnel where a man can

walk and work without exceeding discomfort. The choice of the smallest diameter

suitable was necessary in view of the large costs and difficulties for procuring a large

enough housing strong enough to withstand an internal pressure of 25 atmospheres.

The same restriction of space decided the choice of a closed (not free jet) type

of tunnel.
Document 2-18(a–j) 531

All other novel features can be traced back to the particular features of this

tunnel, the large inside pressure and the larger resultant force on the model. They

are described in the second part of this paper.

PART II

DESCRIPTION OF TUNNEL

By Elton W. Miller.

In the pages which follow a description is given in some detail of the tunnel

and the methods of operation. The purpose in preparing this report is to make

clear the testing methods employed, in order that the technical reports now in

preparation may be better understood. The building of this tunnel was first suggested by Dr. Max M. Munk in 1921 (Reference 1). The writer has assisted Doctor

Munk and Mr. David L. Bacon in the design and development of the mechanical

features of the tunnel.

The tunnel is shown in sectional elevation in Figure 1, and consists briefly in

an experiment section, E, 5 feet (1.52 meters) in diameter, with entrance and exit

cones housed within a steel tank 15 feet (4.57 meters) in diameter and 34 feet 6

inches (10.52 meters) long. The air is circulated by a two-blade propeller, returning

from the propeller to the entrance cone through the annular space between the

walls of the tank and an outer cone, Co. The balance, which is of novel construction,

is mounted in the dead, or noncirculating, air space between the walls of the

experiment section and the outer cone. The balance is operated electrically, and

readings are taken through peepholes in the shell of the tank. Figures 2 and 3 are

general views of the tunnel. Figure 4 is a plan of the building showing the tunnel

and compressors.

The tank, which was built by the Newport News Shipbuilding & Dry Dock

Co., of Newport News, Va., is capable of withstanding a working pressure of 21

atmospheres. It is built of steel plates lapped and riveted according to the usual

practice in steam boiler construction, although, because of the size of the tank

and the high working pressure, the construction is unusually heavy. There is a

cylindrical body portion of 2 1

⁄8-inch (53.98 millimeters) steel plate with hemispherical ends 1 1

⁄4 inches (31.75 millimeters) in thickness. Entrance to the tank

is gained by an elliptical door K 36 inches (914 millimeters) wide by 42 inches

(1,066 millimeters) high. The tank, which with its contents weighs about 100 tons

(90.7 metric tons), is supported by a foundation of reinforced concrete.

The walls of the experiment section and cones are of wood; those of the

experiment section consist of a series of doors which may be unbolted and

removed to gain access to the balance. The cross-sectional area at the large end

of the exit cone is substantially twice that of the experiment section, and the crosssectional area of the return passage at its largest part is about five times that of

the experiment section. Two honeycombs, Hp and Hs, are provided for straightening
532 Chapter 2: Building a Research Establishment

the air flow. Honeycomb Hp is of 2-inch (50.8 millimeters) round cells, while honeycomb Hs is of 1 1

⁄4-inch (31.75 millimeters) square cells. The latter honeycomb is

made removable to permit access to the experiment section; it is suspended from

a removable trolley track by which it may be rolled to one side of the entrance

cone. In order that the honeycomb may be returned to exactly the same place

each time, it is made to seat on three conical points where it may be securely

locked. Arrangements have also been made for adjusting the position of the honeycomb, as shown in Figure 5.

The propeller is driven directly by a synchronous motor of 250 horsepower

(253.5 metric horsepower), which runs at a speed of 900 revolutions per minute.

The synchronous motor has an advantage over the usual direct-current motor in

that no complicated devices are necessary for maintaining a constant speed of

revolution. Such variations in dynamic pressure as are made in the ordinary

atmospheric tunnel by changing the air velocity are here made by changing the

density of the air. It is therefore not necessary to vary the air velocity. Fluctuations

of a fraction of a per cent occur, due to variations in the frequency of the electric

current supplied to the motor; otherwise the velocity is constant for a given tank

pressure. There is a slight increase in air velocity with an increase in tank pressure,

as shown in Figure 16, but this is not objectionable.

The propeller, which is 7 feet (2.14 meters) in diameter, is mounted on a ballbearing shaft which passes through one end of the tank. The stuffing box through

which this shaft passes is only loosely packed, and air leakage is reduced to a minimum

by means of oil which is fed by gravity from a reservoir above. The oil which is carried

through the stuffing box is returned to the reservoir by a motor-driven pump.

Air compressors for filling the tank with air are shown in Figure 4. The air is

compressed in two or three stages, according to the terminal pressure in the tank.

A two-stage primary compressor is used up to a terminal pressure of about seven

atmospheres. For pressures above this a booster compressor is used in conjunction with the primary compressor. The booster compressor may be used also as

an exhauster when it is desired to operate the tunnel at pressures below that of

the atmosphere. The primary compressors are driven by 250-horsepower synchronous motors and the booster compressor by a 150-horsepower squirrel-cage

induction motor.

A diagrammatic drawing of the balance is shown in Figure 6. It consists essentially

in a structural aluminum ring (1) which encircles the experiment section, two lever

balances (2) and (3) for measuring lift, and a third lever balance (4) for measuring

drag. The ring as it looked before assembly in the tunnel is shown in Figure 7. An

assembly view in the tunnel is seen in Figure 8. The doors which surround the

experiment section have here been removed, exposing the balance to view. The model

is attached to the ring, by wires or other means, and all forces are transmitted to
Document 2-18(a–j) 533

the ring and thence to the lever balances. The ring is suspended from lever balances

(2) and (3), Figure 6, by the vertical members (9), of which there are four, two on each

side. Cross shafts and levers are employed in order to carry the full weight of the ring

to the two lever balances. The drag forces are transmitted by horizontal members (10)

to bell cranks and thence by vertical members (11) to lever balance (4). Hanging from

the ring are bridges which carry coarse weights (5) and (6). Any desired number

of coarse weights may be added or removed by means of motor-driven cam shafts.

A similar bridge carrying coarse weights (7) is hung from lever balance (4).

The sliding weights are moved by motor-driven screws to which are geared

revolution counters; these may be read through peepholes in the shell of the tank.

At the end of each beam is a pair of electrical contact points by which the beam

may be made to balance automatically. The sliding weights may also be controlled

by a manually operated switch. The lift balances are sensitive to plus or minus 10

grams and the drag balance to plus or minus 1 gram.

It is possible with this balance to measure any three components; for instance,

lift, drag, and pitching moments. The lift is first approximately counterbalanced

by increasing or decreasing the number of coarse weights hanging from the two

weight bridges. The remainder is then counterbalanced by moving the sliding

weights on the two lever balances. The drag is measured similarly. The total lift is

the sum of the readings of the two lift balances; the pitching moment is the algebraic sum of the three balance readings multiplied by their respective lever arms.

The model may be supported in the tunnel by wires only, or by a combination

of wires or struts and a spindle. In the latter case the spindle is attached to a vertical

bar (12) which may be raised or lowered by appropriate gearing thus changing

the angle of attack of the model. The angle of attack is indicated by an electrically

controlled dial on the outside of the tank. The vertical bar (12) is protected from

the air flow by a fairing (13).

Round wires of about 0.040 inch (1 millimeter) diameter have been used for

supporting models, this much larger diameter being necessary because of the

large forces, but streamlined wires of much larger section have been found preferable.

These wires are attached to the balance ring below and to the model above, thus

serving as struts or free columns to support the weight of the model when the air

stream is not on. The struts may be attached to the wheels of the model as shown

in Figure 9 or to threaded plugs screwed into the wings as in Figures 10 and 11.

The advantage of the streamline wires over the round wires is illustrated in Figure

12. The wire and spindle drag for two airfoils and one airplane model have been

reduced to a per centage of the gross minimum drag of the model with wires and

plotted against Reynolds number.

All the various operations required within the tunnel while running, such as

the shifting of balance weights and the setting of the manometers, are performed
534 Chapter 2: Building a Research Establishment

by small electric motors. It has been necessary, therefore, to carry a large number

of electric wires through the shell of the tank. These wires pass through a suitable

packing gland and are attached to terminal boards inside and out. The outside

terminal board may be seen in Figure 3.

The airspeed is measured by static plates, one of which is located in the wall

of the experiment section and the other in the wall of the other cone. The static

plates are calibrated against Pilot tubes placed in the experiment section. A

micromanometer designed especially for use in this tunnel is shown in Figure 13.

Alcohol is the liquid used, and a head up to 1 meter may be measured. This

manometer is similar in principle to that described in National Advisory

Committee for Aeronautics Technical Note No. 81, but is different in that the

index tube is stationary and the reservoir is raised or lowered by a motor-driven

screw. A revolution counter geared to the motor indicates the head to 0.1 millimeter.

It is possible to determine the dynamic pressure to an accuracy of plus or minus

0.2 per cent.

The dynamic-pressure distribution in the experiment section is represented

by contour lines in Figure 14. This survey was made by using a number of Pitot

tubes mounted on a bar which could be revolved in the tunnel. Observations were

thus made at a large number of points. The dynamic pressure will be seen to vary

in the region occupied by the model within a range of plus or minus 2 per cent.

This survey was made at one and two atmospheres only. We know from check runs

that the same flow condition holds for other pressures. The horizontal static pressure

gradient in the tunnel at various pressures is shown in Figure 15. Pressures are

given with reference to a static plate located in the wall of the experiment section.

It will be noted that the curves which are plotted on semilog paper are parallel,

indicating that the pressure gradient is proportional to the density. Operating

data of general interest, as the time required for raising pressure in the tank, the

time required to exhaust the tank, the power consumption of the compressors

and drive motor, are shown in Figure 16. The velocity change with change of tank

pressure is also shown. The energy ratio of the tunnel for various tank pressures

is shown in Figure 17.

The building of this tunnel and the development of its various mechanical

devices to a point where routine testing may be done has required the solution of

a number of mechanical problems. This development period has passed, and the

results now being obtained in the tunnel are believed to be as consistent and reliable

as those obtained in any other wind tunnel. Two airplane models and thirty-seven

airfoils have so far been tested. Tests of a Sperry Messenger airplane model provided

with eight different sets of wings are now in progress.

The variation of the aerodynamic characteristics of an airplane model with

change of scale is shown in Figure 18. This figure gives the polar curves of the
Document 2-18(a–j) 535

Fokker D-7 airplane model tested at various tank pressures. The minimum drag

and the lift/drag ratio for this model, and also for a Sperry Messenger model, are

plotted against the Reynolds number in Figure 19.

CONCLUSIONS

The underlying theory of the variable density tunnel has been discussed, the

mechanical construction of the tunnel has been described, and some typical

results obtained on an airplane model have been given. The tunnel is in continuous operation, and there is every reason to believe that the results obtained at

the higher densities are truly representative of full-scale conditions.

REFERENCES

Reference 1.—”On a New Type of Wind Tunnel,” by Dr. Max M. Munk. N. A.

C. A. Technical Note No. 60. 

“Abriss der Lehre von der Flüssigkeits und Gasbewegung,” by Dr. L. Prandtl.

Handwörterbuch der Naturwissenschaften, vol. 4.

“Experimental Investigations,” by O. Reynolds, Phil. Trans. 174 (1883), and

“On the Dynamic Theory of Viscous Fluids,” Phil. Trans. A. 186 (1894).

“Similarity of Motion in Relation to the Surface Friction of Fluids,” by T. E.

Stanton and J. R. Pannell, Phil. Trans. A, vol. 214, pp. 199-224, 1914.
536 Chapter 2: Building a Research Establishment

Document 2-19(a–c)

(a) Ludwig Prandtl, letter to J. C. Hunsaker (translation), 

30 March 1916, Hunsaker Collection, Box 4, File 4.

(b) Joseph S. Ames, NACA Headquarters, letter to

J. C. Hunsaker, Navy Department, 15 October 1920, 

Hunsaker Collection, Box 1, File A.

(c) Ludwig Prandtl, Applications of Modern Hydrodynamics

to Aeronautics, Part 1, NACA Technical Report No. 116

(Washington, DC, 1921).

It is difficult to overstate the degree of difference between the American and

German approaches to understanding aerodynamics. While the American researchers

opted for a practical, problem-solving approach, the Germans chose to pursue a

rigorous, mathematically based understanding of the supporting theory. Ludwig

Prandtl was the leader of the German school of thought, and he influenced many

of the leading aerodynamicists of the twentieth century, including Max Munk and

Theodore von Kármán. Most of Prandtl’s publications were in German, but the

NACA commissioned and published a seminal paper, Applications of Modern

Hydrodynamics to Aeronautics, in 1921. Much of this extensive paper involved mathematical derivations, but portions are included herein to illustrate what Prandtl

called “the leading ideas” and their experimental confirmation. 

Not all Americans disdained the theoretical approach, however. Jerome

Hunsaker and Joseph Ames, both of whom held graduate degrees in science or

engineering, understood what a sound theoretical footing could add to the experimental work of the NACA, and both men were well acquainted with the German

developments in this area. Hunsaker had known Ludwig Prandtl since his 1913

European inspection trip, and the latter’s 30 March 1916 letter to Hunsaker, noting

that “it has pleased me very much to see that you have agreed with my ideas

regarding the boundary lamina of viscous fluids,” indicates they shared a belief

that the complex nature of fluid flow could be understood and predicted. Ames,

too, realized the importance of the German theoretical work. Ames’s enthusiasm

for having obtained several copies of the “Technische Berichte,” a collection of

German wartime research reports, is readily apparent in his 15 October 1920 letter

to Hunsaker, where he states, “The importance of the information . . . can not be

over-estimated.” 
Document 2-19(a–c) 537

Such an attitude provides a stark contrast to the parochial views of Frederick

Norton noted elsewhere in this chapter, and the NACA was fortunate to have the

services of such strong and well-respected personalities to argue the merits of theoretical methods and press for the employment of Prandtl protégés. Through the

immigration of Prandtl’s students, especially von Kármán, theoretical aerodynamics came to the United States, and it gradually claimed a leading role in the

saga of aeronautical progress.

Document 2-19(a), letter from Ludwig Prandtl to J. C. Hunsaker (translation), 1916.

[Göttingen, Germany, 30 March 1916]

TRANSLATION

Mr. J.C. Hunsaker

Instructor in Aeronautics, Massachusetts Institute of Technology

Boston, Mass.

Dear Sir:

Please accept my heartiest thanks for the gift of your survey of the

Hydrodynamical Theory in its application to experimental aerodynamics as well as

for the interesting collection of the results of the experiments of the aerodynamical

laboratory at the Smithsonian Institute. I am forwarding under separate cover a small

acknowledgement and hope that you will receive it as well as I received yours.

(This may be translated, “hope that you will value it as highly as I valued yours”).

With reference to the survey of the “Hydronamical Theory” it has pleased me

very much to see that you have agreed with my ideas regarding the boundary lamina

of viscous fluids. This is the first publication in the English language which has

taken notice of it. The exceptional collection of original references has been a

great pleasure as it has also been of great value to me. It contains some things with

which I was not yet acquainted.

With greatest respect, I am, Yours very truly,

[Prof. Dr. L. Prandtl]

Document 2-19(b), letter from Joseph S. Ames 

to J. C. Hunsaker from NACA Headquarters, 1920.

[October 15, 1920]

Commander J. C. Hunsaker, U.S.N.

Navy Department

Washington, D.C.

Dear Commander Hunsaker:

It is with pleasure that I am informing you that the National Advisory
538 Chapter 2: Building a Research Establishment

Committee for Aeronautics has been successful in obtaining a number of sets of

the “Technische Berichte” and we are mailing you under separate cover volumes

No. 1, 2, and 3. The Committee is also forwarding a carefully prepared translation

of the index of the first three volumes together with a list of symbols used.

The “Technische Berichte” consists of separate memoranda issued as confidential

material during the course of the war by the Aeronautical Supply Department of

the German Air Force.

These reports contain practically all of the official German aeronautical information resulting from research conducted during the period of the war. The research

work carried on in German covers a wide range of subjects, including the study

of propellers, the pressure distribution on control surfaces, resistance of struts,

methods of calculating performances, analysis of the performance and design of

airplane engines, and systematic tests of approximately 350 wing sections.

The importance of the information contained in the “Technische Berichte” can

not be over-estimated and it is the desire of this Committee that all research laboratories and individuals interested in aeronautical research should become familiar

with the results of the aeronautical research carried on in Germany during the War.

Respectfully,

National Advisory Committee for Aeronautics

[signed] Joseph S. Ames

Chairman, Committee on Publications and Intelligence.

Document 2-19(c), Ludwig Prandtl, Applications of Modern Hydrodynamics 

to Aeronautics, Part 1, NACA Technical Report No. 116, 1921.

PREFACE.

I have been requested by the United States National Advisory Committee for

Aeronautics to prepare for the reports of the committee a detailed treatise on the

present condition of those applications of hydrodynamics which lead to the calculation of the forces acting on airplane wings and airship bodies. I have acceded

to the request of the National Advisory Committee all the more willingly because

the theories in question have at this time reached a certain conclusion where it is

worthwhile to show in a comprehensive manner the leading ideas and the results

of these theories and to indicate what confirmation the theoretical results have

received by tests.

The report will give, in a rather brief Part I, an introduction to hydrodynamics

which is designed to give those who have not yet been actively concerned with this

science such a grasp of the theoretical underlying principles that they can follow

the subsequent developments. In Part II follow then separate discussions of the

different questions to be considered, in which the theory of aerofoils claims the
Document 2-19(a–c) 539

greatest portion of the space. The last part is devoted to the application of the

aerofoil theory to screw propellers. [Note: Only Part I is included in this chapter.]

At the express wish of the National Advisory Committee for Aeronautics I have

used the same symbols in my formulae as in my papers written in German. These

are already for the most part known by readers of the Technische Berichte. A table

giving the most important quantities is at the end of the report. A short reference

list of the literature on the subject and also a table of contents are added.

PART I.

FUNDAMENTAL CONCEPTS AND THE MOST IMPORTANT THEOREMS.

1. All actual fluids show internal friction (viscosity), yet the forces due to viscosity,

with the dimensions and velocities ordinarily occurring in practice, are so very

small in comparison with the forces due to inertia, for water as well as for air, that

we seem justified, as a first approximation, in entirely neglecting viscosity. Since

the consideration of viscosity in the mathematical treatment of the problem introduces

difficulties which have so far been overcome only in a few specially simple cases,

we are forced to neglect entirely internal friction unless we wish to do without the

mathematical treatment.

We must now ask how far this is allowable for actual fluids, and how far not.

A closer examination shows us that for the interior of the fluid we can immediately

apply our knowledge of the motion of a nonviscous fluid, but that care must be

taken in considering the layers of the fluid in the immediate neighborhood of

solid bodies. Friction between fluid and solid body never comes into consideration

in the fields of application to be treated here, because it is established by reliable

experiments that fluids like water and air never slide on the surface of the body;

what happens is, the final fluid layer immediately in contact with the body is

attached to it (is at rest relative to it), and all the friction of fluids with solid bodies

is therefore an internal friction of the fluid. Theory and experiment agree in indicating that the transition from the velocity of the body to that of the stream in

such a case takes place in a thin layer of the fluid, which is so much the thinner,

the less the viscosity. In this layer, which we call the boundary layer, the forces due

to viscosity are of the same order of magnitude as the forces due to inertia, as may

be seen without difficulty. [Footnote] (From this consideration one can calculate the

approximate thickness of the boundary layer for each special case.) It is therefore

important to prove that, however small the viscosity is, there are always in a

boundary layer on the surface of the body forces due to viscosity (reckoned per

unit volume) which are of the same order of magnitude as those due to inertia.

Closer investigation concerning this shows that under certain conditions there

may occur a reversal of flow in the boundary layer, and as a consequence a stopping

of the fluid in the layer which is set in rotation by the viscous forces, so that, further

on, the whole flow is changed owing to the formation of vortices. The analysis of
540 Chapter 2: Building a Research Establishment

the phenomena which lead to the formation of vortices shows that it takes place

where the fluid experiences a retardation of flow along the body. The retardation

in some cases must reach a certain finite amount so that a reverse flow arises. Such

retardation of flow occurs regularly in the rear of blunt bodies; therefore vortices

are formed there very soon after the flow begins, and consequently the results

which are furnished by the theory of nonviscous flow can not be applied. On the

other hand, in the rear of very tapering bodies the retardations are often so small

that there is no noticeable formation of vortices. The principal successful results

of hydrodynamics apply to this case. Since it is these tapering bodies which offer

specially small resistance and which, therefore, have found special consideration

in aeronautics under similar applications, the theory can be made useful exactly

for those bodies which are of most technical interest.

For the considerations which follow we obtain from what has gone before the

result that in the interior of the fluid its viscosity, if it is small, has no essential

influence, but that for layers of the fluid in immediate contact with solid bodies

exceptions to the laws of a nonviscous fluid must be allowable. We shall try to formulate these exceptions so as to be, as far as possible, in agreement with the facts

of experiment.

2. A further remark must be made concerning the effect of the compressibility

of the fluid upon the character of the flow in the case of the motion of solid bodies

in the fluid. All actual fluids are compressible. In order to compress a volume of

air by 1 per cent, a pressure of about one one-hundredth of an atmosphere is

needed. In the case of water, to produce an equal change in volume, a pressure of

200 atmospheres is required; the difference therefore is very great. With water it

is nearly always allowable to neglect the changes in volume arising from the pressure

differences due to the motions, and therefore to treat it as absolutely incompressible.

But also in the case of motions in air we can ignore the compressibility so long as

the pressure differences caused by the motion are sufficiently small. Consideration

of compressibility in the mathematical treatment of flow phenomena introduces

such great difficulties that we will quietly neglect volume changes of several per

cent, and in the calculations air will be looked upon as incompressible. A compression of 3 per cent, for instance, occurs in front of a body which is being moved

with a velocity of about 80 m./sec. It is seen, then, that it appears allowable to neglect

the compressibility in the ordinary applications to technical aeronautics. Only with

the blades of the air screw do essentially greater velocities occur, and in this case the

influence of the compressibility is to be expected and has already been observed. The

motion of a body with great velocity has been investigated up to the present, only

along general lines. It appears that if the velocity of motion exceeds that of sound

for the fluid, the phenomena are changed entirely, but that up close to this velocity

the flow is approximately of the same character as in an incompressible fluid.
Document 2-19(a–c) 541

3. We shall concern ourselves in what follows only with a nonviscous and

incompressible fluid, about which we have learned that it will furnish an approximation sufficient for our applications, with the reservations made. Such a fluid is

also called “the ideal fluid.”

What are the properties of such an ideal fluid? I do not consider it here my

task to develop and to prove all of them, since the theorems of classical hydrodynamics are contained in all textbooks on the subject and may be studied there. I

propose to state in what follows, for the benefit of those readers who have not yet

studied hydrodynamics, the most important principles and theorems which will

be needed for further developments, in such a manner that these developments

may be grasped. I ask these readers, therefore, simply to believe the theorems

which I shall state until they have the time to study the subject in some textbook

on hydrodynamics.

The principal method of description of problems in hydrodynamics consists

in expressing in formulas as functions of space and time the velocity of flow, given

by its three rectangular components, u, v, w, and in addition the fluid pressure p.

The condition of flow is evidently completely known if u, v, w, and p are given as

functions of x, y, z, and t, since then u, v, w, and p can be calculated for any arbitrarily selected point and for every instant of time. The direction of flow is defined

by the ratios of u, v, and w; the magnitude of the velocity is √u2 + v2 + w2

. The

“streamlines” will be obtained if lines are drawn which coincide with the direction

of flow at all points where they touch, which can be accomplished mathematically

by an integration. If the flow described by the formulas is to be that caused by a

definite body, then at those points in space, which at any instant form the surface

of the body, the components of the fluid velocity normal to this surface must coincide with the corresponding components of the velocity of the body. In this way

the condition is expressed that neither does the fluid penetrate into the body nor

is there any gap between it and the fluid. If the body is at rest in a stream, the normal components of the velocity at its surface must be zero; that is, the flow must

be tangential to the surface, which in this case therefore is formed of stream lines.

4. In a stationary flow—that is, in a flow which does not change with the time,

in which then every new fluid particle, when it replaces another particle in front

of it, assumes its velocity, both in magnitude and in direction and also the same

pressure—there is, for the fluid particles lying on the same stream line, a very

remarkable relation between the magnitude of the velocity, designated here by V,

and the pressure, the so-called Bernouilli equation—

(1)
542 Chapter 2: Building a Research Establishment

(ρ is the density of the fluid, i.e.,

the mass of a unit volume). This

relation is at once applicable to

the case of a body moving uniformly and in a straight line in a

fluid at rest, for we are always at

liberty to use for our discussions

any reference system having a

uniform motion in a straight

line. If we make the velocity of

the reference system coincide

with that of the body, then the

body is at rest with reference to

it, and the flow around it is stationary. If now V is the velocity of the body relative

to the stationary air, the latter will have in the new reference system the velocity

V upon the body (a man on an airplane in flight makes observations in terms of

such a reference system, and feels the motion of flight as “wind”).

The flow of incident air is divided at a blunt body, as shown in figure 1. At the

point A the flow comes completely to rest, and then is again set in motion in

opposite directions, tangential to the surface of the body. We learn from equation (1)

that at such a point, which we shall call a “rest-point,” the pressure must be

greater by ρ

⁄2V2 than in the undisturbed fluid. We shall call the magnitude of this

pressure, of which we shall make frequent use, the “dynamical pressure,” and shall

designate it by q. An open end of a tube facing the stream produces a rest point of

a similar kind, and there arises in the interior of the tube, as very careful experiments

have shown, the exact dynamical pressure, so that this principle can be used for

the measurement of the velocity, and is in fact much used. The dynamical pressure

is also well suited to express the laws of air resistance. It is known that this resistance

is proportional to the square of the velocity and to the density of the medium; but

q=ρ

⁄2V2; so the law of air resistance may also be expressed by the formula

W = c . F . q (2)

where F is the area of the surface and c is a pure number. With this mode of

expression it appears very clearly that the force called the “drag” is equal to surface

times pressure difference (the formula has the same form as the one for the piston

force in a steam engine). This mode of stating the relation has been introduced

in Germany and Austria and has proved useful. The air-resistance coefficients

then become twice as large as the “absolute” coefficients previously used.

Since V2 can not become less than zero, an increase of pressure greater than

q can not, by equation (1), occur. For diminution of pressure, however, no definite

limit can be set. In the case of flow past convex surfaces marked increases of velocity
Document 2-19(a–c) 543

of flow occur and in connection with them diminutions of pressure which frequently

amount to 3q and more.

5. A series of typical properties of motion of nonviscous fluids may be

deduced in a useful manner from the following theorem, which is due to Lord

Kelvin. Before the theorem itself is stated, two concepts must be defined. 1. The

circulation: Consider the line integral of the velocity ∫ V cos (V, ds) ⋅ ds, which is

formed exactly like the line integral of a force, which is called “the work of the

force.” The amount of this line integral, taken over a path which returns on itself

is called the circulation of the flow. 2. The fluid line: By this is meant a line which

is always formed of the same fluid particles, which therefore shares in the motion

of the fluid. The theorem of Lord Kelvin is: In a nonviscous fluid the circulation

along every fluid line remains unchanged as time goes on. But the following must

be added:

(1) The case may arise that a fluid line is intersected by a solid body moving in the fluid. If this

occurs, the theorem ceases to apply. As an example I

mention the case in which one pushes a flat plate

into a fluid at rest, and then by means of the plate

exerts a pressure on the fluid. By this a circulation

arises which will remain if afterwards the plate is

quickly withdrawn in its own plane. See figure 2.

(2) In order that the theorem may apply, we must exclude mass forces of such

a character that work is furnished by them along a path which returns on itself.

Such forces do not ordinarily arise and need not be taken into account here,

where we are concerned regularly only with gravity.

(3) The fluid must be homogenous, i. e., of the same density at all points. We

can easily see that in the case of nonuniform density circulation can arise of itself

in the course of time if we think of the natural ascent of heated air in the midst

of cold air. The circulation increases continuously along a line which passes

upward in the warm air and returns downward in the cold air.

Frequently the case arises that the fluid at the beginning is at rest or in

absolutely uniform motion, so that the circulation for every imaginable closed line

in the fluid is zero. Our theorem then says that for every closed line that can arise

from one of the originally closed lines the circulation remains zero, in which we

must make exception, as mentioned above, of those lines which are cut by bodies.

If the line integral along every closed line is zero, the line integral for an open

curve from a definite point O to an arbitrary point P is independent of the selection

of the line along which the integral is taken (if this were not so, and if the integrals

along two lines from O to P were different, it is evident that the line integral along

the closed curve OPO would not be zero, which contradicts our premise). The line
544 Chapter 2: Building a Research Establishment

integral along the line OP depends, therefore, since we will consider once for all

the point O as a fixed one, only on the coordinates of the point P, or, expressed

differently, it is a function of these coordinates. From analogy with corresponding

considerations in the case of fields of force, this line integral is called the “velocity potential,” and the particular kind of motion in which such a potential exists

is called a “potential motion.” As follows immediately from the meaning of line

integrals, the component of the velocity in a definite direction is the derivative of

the potential in this direction. If the line-element is perpendicular to the resultant velocity, the increase of the potential equals zero, i. e., the surfaces of constant

potential are everywhere normal to the velocity of flow. The velocity itself is called

the gradient of the potential. The velocity components u, v, w are connected with

the potential Φ by the following equations:

(3)

The fact that the flow takes place without any change in volume is expressed

by stating that as much flows out of every element of volume as flows in. This

leads to the equation

(4)

In the case of potential flow we therefore have

(4a)

as the condition for flow without change in volume. All functions Φ (x, y, z, t),

which satisfy this last equation, represent possible forms of flow. This representation

of a flow is specially convenient for calculations, since by it the entire flow is given

by means of the one function Φ. The most valuable property of the representations

is, though, that the sum of two, or of as many as one desires, functions Φ, each of

which satisfies equation (4a), also satisfies this equation, and therefore represents

a possible type of flow (“superposition of flows”).

6. Another concept can be derived from the circulation, which is convenient

for many considerations, viz, that of rotation. The component of the rotation with
Document 2-19(a–c) 545

reference to any axis is obtained if the circulation is taken around an elementary

surface of unit area in a plane perpendicular to the axis. Expressed more exactly,

such a rotation component is the ratio of the circulation around the edge of any

such infinitesimal surface to the area of the surface. The total rotation is a vector

and is obtained from the rotation components for three mutually perpendicular

axes. In the case that the fluid rotates like a rigid body, the rotation thus defined

comes out as twice the angular velocity of the rigid body. If we take a rectangular

system of axes and consider the rotations with reference to the separate axes, we

find that the rotation can also be expressed as the geometrical sum of the angular velocities with reference to the three axes.

The statement that in the case of a potential motion the circulation is zero for

every closed fluid line can now be expressed by saying the rotation in it is always zero.

The theorem that the circulation, if it is zero, remains zero under the conditions

mentioned, can also now be expressed by saying that, if these conditions are satisfied

in a fluid in which there is no rotation, rotation can never arise. An irrotational

fluid motion, therefore, always remains irrotational. In this, however, the following

exceptions are to be noted: If the fluid is divided owing to bodies being present

in it, the theorem under consideration does not apply to the fluid layer in which

the divided flow reunites, not only in the case of figure 2 but also in the case of

stationary phenomena as in figure 3, since in this case a closed fluid line drawn

in front of the body can not be transformed into a fluid line that intersects the

region where the fluid streams come together. Figure 3 shows four successive

shapes of such a fluid line. This region is, besides, filled with fluid particles which

have come very close to the body. We are therefore led to the conclusion from the
546 Chapter 2: Building a Research Establishment

standpoint of a fluid with very small but not entirely vanishing viscosity that the

appearance of vortices at the points of reunion of the flow in the rear of the body

does not contradict the laws of hydrodynamics. The three components of the rotation ξ, η, ζ are expressed as follows by means of the velocity components u, v, w.

(5)

If the velocity components are derived from a potential, as shown in equation

(2), the rotation components, according to equation (5) vanish identically, since 

7. Very remarkable theorems hold for the rotation, which were discovered by

V. Helmholtz and stated in his famous work on vortex motions. Concerning the

geometrical properties of the rotation the following must be said:

At all points of the fluid where rotation exists the direction of the resultant

rotation axes can be indicated, and lines can also be drawn whose directions coincide

everywhere with these axes, just as the stream lines are drawn so as to coincide

with the directions of the velocity. These lines will be called, following Helmholtz,

“vortex lines.” The vortex lines through the points of a small closed curve form a

tube called a “vortex tube.” It is an immediate consequence of the geometrical

idea of rotation as deduced above that through the entire extent of a vortex tube

its strength—i. e., the circulation around the boundary of the tube—is constant.

It is seen, in fact, that on geometrical grounds the space distribution of rotation

quite independently of the special properties of the velocity field from which it is

deduced is of the same nature as the space distribution of the velocities in an

incompressible fluid. Consequently a vortex tube, just like a stream line in an

incompressible fluid, can not end anywhere in the interior of the fluid and the

strength of the vortex, exactly like the quantity of fluid passing per second

through the tube of stream lines, has at one and the same instant the same value

throughout the vortex tube. If Lord Kelvin’s theorem is now applied to the closed

fluid line which forms the edge of a small element of the surface of a vortex tube,

the circulation along it is zero, since the surface inclosed is parallel to the rotation

axis at that point. Since the circulation can not change with the time, it follows

that the element of surface at all later times will also be part of the surface of a

vortex tube. If we picture the entire bounding surface of a vortex tube as made up

of such elementary surfaces, it is evident that, since as the motion continues this

relation remains unchanged, the particles of the fluid which at any one time have

formed the boundary of a vortex tube will continue to form its boundary. From
Document 2-19(a–c) 547

the consideration of the circulation along a closed line enclosing the vortex tube,

we see that this circulation—i.e., the strength of our vortex tube—has the same

value at all times. Thus we have obtained the theorems of Helmholtz, which now

can be expressed as follows, calling the contents of a vortex tube a “vortex filament”: “The particles of a fluid which at any instant belong to a vortex filament

always remain in it; the strength of a vortex filament throughout its extent and for

all time has the same value.” From this follows, among other things, that if a portion

of the filament is stretched, say, to double its length, and thereby its cross section

made one-half as great, then the rotation is doubled, because the strength of the

vortex, the product of the rotation and the cross section, must remain the same. We

arrive, therefore, at the result that the vector expressing the rotation is changed in

magnitude and direction exactly as the distance between two neighboring particles

on the axis of the filament is changed.

8. From the way the strengths of vortices have been defined it follows for a

space filled with any arbitrary vortex filaments, as a consequence of a known theorem of Stokes, that the circulation around any closed line is equal to the algebraic sum of the vortex strengths of all the filaments which cross a surface having the

closed line as its boundary. If this closed line is in any way continuously changed

so that filaments are thereby cut, then evidently the circulation is changed according to the extent of the strengths of the vortices which are cut. Conversely we may

conclude from the circumstance that the circulation around a closed line (which

naturally can not be a fluid line) is changed by a definite amount by a certain displacement, that by the displacement vortex strength of this amount will be cut, or

expressed differently, that the surface passed over by the closed line in its displacement is traversed by vortex filaments whose strengths add up algebraically

to the amount of the change in the circulation.

The theorems concerning vortex motion are specially important because in

many cases it is easier to make a statement as to the shape of the vortex filaments

than as to the shape of the stream lines, and because there is a mode of calculation by means of which the velocity at any point of the space may be determined

from a knowledge of the distribution of the rotation. This formula, so important

for us, must now be discussed. If Γ is the strength of a thin vortex filament and ds

an element of its medial line, and if, further, r is the distance from the vortex element to a point P at which the velocity is to be calculated, finally if α is the angle

between ds and r, then the amount of the velocity due to the vortex element is

(6)
548 Chapter 2: Building a Research Establishment

the direction of this contribution to the velocity is perpendicular to the plane of

ds and r. The total velocity at the point P is obtained if the contributions of all the

vortex elements present in the space are added. The law for this calculation

agrees then exactly with that of Biot-Savart, by the help of which the magnetic

field due to an electric current is calculated. Vortex filaments correspond in it to

the electric currents, and the vector of the velocity to the vector of the magnetic field.

As an example we may take an infinitely long straight vortex filament. The

contributions to the velocity at a point P are all in the same direction, and the

total velocity can be determined by a simple integration of equation (6).

Therefore this velocity is

As seen by figure 4, s = h ctg α, and by differentiation, 

(6a)

This result could be deduced in a

simpler manner from the concept of circulation if we were to use the theorem,

already proved, that the circulation for

any closed line coincides with the vortex

strength of the filaments which are

inclosed by it. The circulation for every

closed line which goes once around a single filament must therefore coincide with

its strength. If the velocity at a point of a

circle of radius h around our straight filament equals v then this circulation equals

“path times velocity” = 2 πh ⋅ v, whence immediately follows v=Γ

⁄2πh. The more

exact investigation of this velocity field shows that for every point outside the filament (and the formula applies only to such points) the rotation is zero, so that
Document 2-19(a–c) 549

in fact we are treating the case of a velocity distribution in which only along the

axis does rotation prevail, at all other points rotation is not present.

For a finite portion of a straight vortex filament the preceding calculation

gives the value

. (6b)

This formula may be applied only for a series of portions of vortices which together

give an infinite or a closed line. The velocity field of a single portion of a filament

would require rotation also outside the filament, in the sense that from the end of

the portion of the filament vortex lines spread out in all the space and then all

return together at the beginning of the portion. In the case of a line that has no

ends this external rotation is removed, since one end always coincides with the

beginning of another portion of equal strength, and rotation is present only

where it is predicated in the calculation.

9. If one wishes to represent the flow around solid bodies in a fluid, one can

in many cases proceed by imagining the place of the solid bodies taken by the

fluid, in the interior of which disturbances of flow (singularities) are introduced,

by which the flow is so altered that the boundaries of the bodies become streamline

surfaces. For such hypothetical constructions in the interior of the space actually

occupied by the body, one can assume, for instance, any suitably selected vortices,

which, however, since they are only imaginary, need not obey the laws of Helmholtz.

As we shall see later, such imaginary vortices can be the seat of lifting forces. Sources

and sinks also, i.e., points where fluid continuously appears, or disappears, offer

a useful method for constructions of this kind. While vortex filaments can actually

occur in the fluid, such sources and sinks may be assumed only in that part of the

space which actually is occupied by the body, since they represent a phenomenon

which can not be realized. A contradiction of the law of the conservation of matter

is avoided, however, if there are assumed to be inside the body both sources and

sinks, of equal strengths, so that the fluid produced by the sources is taken back

again by the sinks.

The method of sources and sinks will be described in greater detail when certain

practical problems are discussed; but at this point, to make the matter clearer, the

distribution of velocities in the case of a source may be described. It is very simple,

the flow takes place out from the source uniformly on all sides in the direction of

the radii. Let us describe around the point source a concentric spherical surface,

then, if the fluid output per second is Q, the velocity at the surface is

(7)
550 Chapter 2: Building a Research Establishment

the velocity therefore decreases inversely proportional to the square of the distance. The flow is a potential one, the potential comes out (as line-integral along

the radius)

(7a)

If a uniform velocity toward the right of the whole fluid mass is superimposed

on this velocity distribution while the point source remains stationary—then a

flow is obtained which, at a considerable distance from the source, is in straight

lines from left to right. The fluid coming out of the source is therefore pressed

toward the right (see fig. 5); it fills, at some distance from the source, a cylinder

whose diameter may be determined easily. If V is the velocity of the uniform flow,

the radius r of the cylinder is given by the condition Q = πr2 ⋅ V. All that is necessary

now is to assume on the axis of the source further to the right a sink of the same

strength as the source for the whole mass of fluid from the source to vanish in this,

and the flow closes up behind the sink again exactly as it opened out in front of the

source. In this way we obtain the flow around an elongated body with blunt ends.

10. The special case when in a fluid flow the phenomena in all planes which

are parallel to a given plane coincide absolutely plays an important role both

practically and theoretically. If the lines which connect the corresponding points

of the different planes are perpendicular to the planes, and all the streamlines are

plane curves which lie entirely in one of those planes, we speak of a uniplanar
Document 2-19(a–c) 551

flow. The flow around a strut whose axis is perpendicular to the direction of the

wind is an example of such a motion.

The mathematical treatment of plane potential flow of the ideal fluid has

been worked out specially completely more than any other problem in hydrodynamics. This is due to the fact that with the help of the complex quantities (x + iy,

where i=√-1, is called the imaginary unit) there can be deduced from every analytic

function a case of flow of this type which is incompressible and irrotational. Every

real function, Φ (x, y) and Ψ (x, y), which satisfies the relation

Φ + i Ψ = f ( x + iy ), (8)

where f is any analytic function, is the potential of such a flow. This can be seen

from these considerations: Let x + iy be put = z, where z is now a “complex number.”

Differentiate equation (8) first with reference to x and then with reference to y,

thus giving

In these the real parts on the two sides of the equations must be equal and

the imaginary parts also. If Φ is selected as the potential, the velocity components

u and v are given by

(9)

If now we write the expressions δΦ⁄δx + δv

⁄δy (continuity) and δΦ⁄δx −

δv

⁄δy (rotation)

first in terms of Φ and then of Ψ, they become

(10)
552 Chapter 2: Building a Research Establishment

It is seen therefore that not only is the motion irrotational (as is self-evident

since there is a potential), but it is also continuous. The relation δ2

Φ

⁄δx2 + δ2

Φ

⁄δy2=o

besides corresponds exactly to our equation (4a). Since it is satisfied also by Ψ,

this can also be used as potential.

The function Ψ, however, has, with reference to the flow deduced by using Φ,

as potential, a special individual meaning. From equation (8) we can easily deduce

that the lines Ψ = const. are parallel to the velocity; therefore, in other words,

they are streamlines. In fact if we put

which expresses the fact of parallelism. The lines Ψ = const. are therefore perpendicular to the lines Φ = const. If we draw families of lines, Φ = const. and Ψ = const.

for values of Φ and Ψ which differ from each other by the same small amount, it

follows from the easily derived equation dΦ + idΨ = df⁄dz (dx + idy) that the two

bundles form a square network; from which follows that the diagonal curves of the

network again form an orthogonal and in fact a square network. This fact can be

used practically in drawing such families of curves, because an error in the drawing

can be recognized by the eye in the wrong shape of the network of diagonal

curves and so can be improved. With a little practice fairly good accuracy may be

obtained by simply using the eye. Naturally there are also mathematical methods

for further improvement of such networks of curves. The function Ψ, which is

called the “stream function,” has another special meaning. If we consider two

streamlines Ψ = Ψ1 and Ψ = Ψ2, the quantity of fluid which flows between the two

streamlines in a unit of time in a region of uniplanar flow of thickness 1 equals

Ψ2-Ψ1. In fact if we consider the flow through a plane perpendicular to the X-axis,

this quantity is

The numerical value of the stream function coincides therefore with the quantity

of fluid which flows between the point x, y and the streamline Ψ = o.

As an example let the function

Φ + iΨ = A (x + iy)

n

be discussed briefly. It is simplest in general to ask first about the streamline Ψ =o.

As is well known, if a transformation is made from rectangular coordinates to
Document 2-19(a–c) 553

polar ones r, φ, (x + iy)

n = rn (cos nφ + i sin nφ). The imaginary part of this expression is irn sin nφ. This is to be put equal to iΨ. Ψ = o therefore gives sin nφ = o,

i.e., nφ = o, π, 2π, etc. The streamlines Ψ = o are therefore straight lines through

the origin of coordinates, which make an angle α = π/n with each other, the flow

is therefore the potential flow between two plane walls making the angle α with

each other. The other streamlines satisfy the equation rn sin nφ = const. The

velocities can be obtained by differentiation, e.g., with reference to x:

δΦ⁄δx = i δΨ⁄δx = u − iv = An (x + iy)

n−1 = Anrn−1 {cos (n−1) φ + i sin (n−1) φ}.

For r = o this expression becomes zero or

infinite, according as n is greater or less than

11, i.e., according as the angle α is less or

greater than π (= 180°). Figures 6 and 7 give

the streamlines for = π⁄4 = 45° and 3⁄2π = 270°,

corresponding to n = 4 and 2⁄3. In the case of

figure 7, the velocity, as just explained,

becomes infinite at the corner. It would be

expected that in the case of the actual flow

some effect due to friction would enter. In fact

there are observed at such corners, at the

beginning of the motion, great velocities, and

immediately thereafter the formation of vortices, by which the motion is so

changed that the velocity at the comer becomes finite.

It must also be noted that with an equation

p + iq = φ (x + iy) (11)

the x-y plane can be mapped upon the p-q plane, since to every pair of values x,y

a pair of values p,q corresponds, to every point of the x-y plane corresponds a

point of the p-q plane, and therefore also to every element of a line or to every

curve in the former plane a linear element and a curve in the latter plane. The

transformation keeps all angles unchanged, i. e., corresponding lines intersect in

both figures at the same angle.

By inverting the function φ of equation (11) we can write

x+iy = x(p+iq)
554 Chapter 2: Building a Research Establishment

and therefore deduce from equation (8) that

Φ+iΨ = f [x(p+iq)] = Φ(p+iq) (12)

Φ and Ψ are connected therefore with π and θ by an equation of the type of equation

(8), and hence, in the p-q plane, are potential and stream functions of a flow, and

further of that flow which arises from the transformation of the Φ, Ψ network in

the x-y plane into the p-q plane.

This is a powerful method used to obtain by transformation from a known

simple flow new types of flow for other given boundaries. Applications of this will

be given in section 14.

11. The discussion of the principles of the hydrodynamics of nonviscous fluids

to be applied by us may be stopped here. I add but one consideration, which has

reference to a very useful theorem for obtaining the forces in fluid motion, namely

the so-called “momentum theorem for stationary motions.”

We have to apply to fluid motion the theorem of general mechanics, which

states that the rate of change with the

time of the linear momentum is equal to

the resultant of all the external forces. To

do this, consider a definite portion of

the fluid separated from the rest of the

fluid by a closed surface. This surface may,

in accordance with the spirit of the theorem, be considered as a “fluid surface,” i. e.,

made up always of the same fluid particles.

We must now state in a formula the

change of the momentum of the fluid

within the surface. If, as we shall assume,

the flow is stationary, then after a time dt

every fluid particle in the interior will be

replaced by another, which has the same velocity as had the former. On the

boundary, however, owing to its displacement, mass will pass out at the side where

the fluid is approaching and a corresponding mass will enter on the side away

from which the flow takes place. If dS is the area of an element of surface, and vn

the component of the velocity in the direction of the outward drawn normal at

this element, then at this point dm = ρdS ⋅ vn dt. If we wish to derive the component of the “impulse”—defined as the time rate of the change of momentum—for

any direction s, the contribution to it of the element of surface is

dJs = vs (dm / dt) = ρdS ⋅ vnvs. (13)
Document 2-19(a–c) 555

With this formula we have made the transition from the fluid surface to a corresponding solid “control surface.”

The external forces are compounded of the fluid pressures on the control surface

and the forces which are exercised on the fluid by any solid bodies which may be

inside of the control surface. If we call the latter P, we obtain the equation

∑Ps = ∫ ∫ p ⋅ cos(n,s) ⋅ dS + ρ∫ ∫ vnvsdS (14)

for the s component of the momentum theorem. The surface integrals are to be

taken over the entire closed control surface. The impulse integral can be limited

to the exit side, if for every velocity vs on that side the velocity vs' is known with

which the same particle arrives at the approach side. Then in equation (13) dJ is

to be replaced by

dJ − dJ' = (vs - vs') (dm / dt) = ρdS vn (vs - vs'). (13a)

The applications given in Part II will furnish illustrations of the theorem.
556 Chapter 2: Building a Research Establishment

Document 2-20(a–c)

(a) Max M. Munk, memorandum to George W. Lewis, 

10 March 1925, RA file 44, Historical Archives, NASA Langley.

(b) Fred E. Weick and Donald H. Wood, The Twenty-Foot

Propeller Research Tunnel of the National Advisory 

Committee for Aeronautics, NACA Technical 

Report No. 300 (Washington, DC, 1928).

(c) Fred E. Weick, excerpts from From the Ground Up

(Washington, DC: Smithsonian Institution Press, 1988), 

pp. 46–67.

While the VDT provided unprecedented capabilities for airfoil research at

high Reynolds numbers, it was not well suited for certain other investigations,

such as propeller testing. No practical means to utilize model propellers existed,

because they did not deflect during operation the same way full-size ones did; this

introduced significant error. After a promising propeller design had been tested

for structural integrity and to determine its basic characteristics, an evaluation of its

actual performance on an airplane required expensive and sometimes dangerous

flight tests. However, accurate measurements in flight were difficult at best.

Langley had a dynamometer to get reliable data on engine performance, and the

NACA had sponsored propeller research in Stanford University’s Eiffel-type tunnel

since 1917, but no valid laboratory method of studying the entire propulsion system

and its interaction with the aircraft fuselage existed in the mid-1920s. 

The NACA’s response was to construct the first very-large wind tunnel, the

Propeller Research Tunnel (PRT). The PRT, completed in 1927, was a closed tunnel

with an open test section, often referred to as an open-jet type. The nozzle supplied

a twenty-foot-diameter air stream with velocities up to 110 miles per hour. A tunnel this size required more electrical power than was available at LMAL, so the

PRT used two 1,000 horsepower diesel engines that had been removed from a

navy submarine. The balance could support an airplane or a substitute “test fuselage” that featured an onboard dynamometer to directly measure engine torque.

Technicians developed optical methods to measure blade deflection during operation.

The PRT quickly proved its worth for propeller testing in conditions that were

very close to those in actual flight, but since it was the first tunnel large enough

to accommodate full-size airplanes (except for their full wing spans), its role soon
Document 2-20(a–c) 557

expanded to include drag studies of aircraft components such as landing gears,

radiators, tail planes, and—perhaps most significantly—radial engine cowlings.

The PRT also served as the model for even larger wind tunnels that the NACA

would build over the next two decades.

As the 10 March 1925 letter from Max Munk to George Lewis shows, it was

Munk who conceived this large tunnel, and it was he who convinced Lewis that

such a tunnel would be not only feasible, but also tremendously valuable to the

NACA. As he had with the VDT, Munk correctly assessed a current research problem—propeller performance tests that were not possible in the VDT—and

devised a solution that was at once bold and theoretically sound. Unfortunately,

he ran into serious non-technical problems when Lewis put him in charge of the

PRT’s construction.

While Max Munk brought a keen theoretical mind to America in 1920, he also

brought a large ego and an unremitting belief in the German organizational

model, in which a leader’s ideas were unquestioningly accepted and practiced.

Munk was clearly brilliant, but he did not—perhaps could not—adapt to the more

egalitarian mode of operation at Langley. The other Langley researchers and

engineers considered his style overbearing and excessively autocratic, and they

finally revolted against him. No single document fully portrays the situation, but

Fred Weick recalled several incidents in his autobiography, From the Ground Up,

which gives a good picture of the mismatch between Munk and other Langley

personnel. In addition, a letter from Fred Norton to NACA Director of

Aeronautical Research George Lewis, one of many written by Langley managers

between 1921 and 1927, illustrates his frustration with the situation. However,

these letters met blind eyes, as Lewis was Munk’s biggest supporter. Even after the

mass resignation of LMAL section heads in 1927, Lewis tried, unsuccessfully, to

find some way to retain Munk in the Washington office. Munk, however, would

not accept this loss of “his” laboratory and chose to resign from the NACA.

Although Munk maintained some visibility in aeronautics for a while, notably as

the author of a series of articles on basic aerodynamics in Aero Digest during the

1930s, his resignation from the NACA effectively marked the end of his serious

contributions to the field.

Document 2-20(a), Max M. Munk, memorandum to George W. Lewis, 1925.

March 10, 1925.

MEMORANDUM for Mr. Lewis. 

Subject:Laboratory for Testing Full Size Propellers.

1. At the present, our aerodynamic free flight research has not yet been

brought forward enough to separate the performance of an airplane into that of
558 Chapter 2: Building a Research Establishment

the engine, that of the propeller, and that of the remaining airplane. Nor has it

been possible to obtain any definite comparisons between the results of model

tests and free flight tests.

The first step taken to logically and systematically adapt our research work to

the requirements of the practice was the construction of the variable density tunnel

in order to get rid of the scale effect. This step was successful as far as could be

expected. The model results in the new tunnel agree better with free flight experiments than with results from ordinary tunnels. The influence of the propeller

slipstream will be included in the variable density tunnel tests by providing apparatus for driving and observing a model propeller.

The model propeller in the variable density tunnel will be free from the scale

effect proper. It will, however, experience pressures and hence elastic (and permanent)

deformation different from those of the full size propeller. Further, the influence

of the compressibility of the air will not properly be taken care of. It will be very

difficult and expensive to make an exact model of the propeller and of the portion

of the airplane in its vicinity. At last, the variable density tunnel is fully occupied

for the next years by tests not directly referring to the propeller.

2. I wish, therefore, to recommend that the tests referring to propeller performance and to the influence of the other portions of the airplane on the performance of the propellers be excluded from the research assigned to the variable

density tunnel. I wish further, to recommend that the mentioned part of our

research program be turned over and assigned to a special laboratory to be constructed for this purpose.

A similar laboratory was built during the last war at Fishamend (near Vienna,

Austria) by Prof. Th. v. Karman. No published description has ever come to my

attention. As far as I know, this laboratory was destroyed under the terms of the

Peace Treaty of Versailles. It may be possible to obtain some information about it

from Dr. v. Karman, now at Aachen.

3. The tests to be made in the laboratory would comprise:

(a) Determination of Torque and Thrust of actual propellers (up to 10 ft.

diameter, say) at different ratios U/V of the propeller tip velocity U to

the velocity of motion and at actual speeds.

The tests would be run in air of sea level pressure and would be correct as to deformation of the propeller, compressibility of the air, and would not involve any scale effect.

(b) The same tests with the propeller in front of any airplane fuselage,

and in the presence of the wings and of other parts of the airplane.

The results will then include the forces on the several parts of the airplane

and will give the actual merits of the propeller under these conditions,

(c) Propeller tests with the axis of the propeller slightly tilted. This will

correspond to the use of propellers under different angles of attack.
Document 2-20(a–c) 559

(d) Determination of the engine performance. The propeller can be driven by any airplane engine and the tests can then be made to include

a test of that engine. In particular, the merits of the cooling system

can be examined.

(e) The tests will further give information of the merits of different shapes

of fuselages or engine cars taking into account the slipstream produced by the propeller under different conditions.

(f) In special cases, the laboratory would be available as the largest wind

tunnel in the world.

4. The laboratory is contemplated to consist of a 20-ft. wind tunnel with open

jet test chamber and with the return channels being under compression. At first

glance, the cost of a 20-ft. tunnel would seem to be prohibitive, but a closer examination will show that such is not the case. Our present atmospheric 5-ft. tunnel

could be built much cheaper and must not be taken as a basis for the costs of the

new laboratory. Our variable density tunnel is costly on account of the high compression of the air used. This new 20-ft. tunnel is supposed to be built especially

for the purpose indicated and will be comparatively cheap on account of the following items:

1. The power plant will consist of [two] 400 H.P. combustion engines, say

Liberties, and not of electric motors. A third engine will be required to

drive the propeller.

2. The building will be made chiefly of wood frame construction, and

internal steel rod bracing used where required.

3. No high priced special balances will be built but only ordinary balances

will be used as can be purchased on the market.

No estimate of the costs has been made yet, but I believe that the entire cost

will not be in excess of the cost of an ordinary good wind tunnel. The results will

be of much greater value, being free from any important error and giving plenty

of information needed and wanted by the practice for many years. The research

program will not be exhausted for many years, but on the contrary will probably

grow larger and larger as the development of aeronautics goes on.

5. The need for a laboratory as the one in question is demonstrated by the many

unsuccessful attempts to require the information to be obtained in other ways.

There have been constructed giant whirling arms, towers on railroad cars,

dynamometer hubs on airplanes, airplanes gliding along cables in an airship

shed, and the Fishamend Laboratory mentioned above. (The latter was possible

with open return.)

[signed] Max M. Munk.
560 Chapter 2: Building a Research Establishment

Document 2-20(b), Fred E. Weick and Donald H. Wood, The Twenty-Foot 

Propeller Research Tunnel of the National Advisory Committee for 

Aeronautics, NACA Technical Report No. 300, 1928.

SUMMARY

This report describes in detail the new propeller research tunnel of the National

Advisory Committee for Aeronautics at Langley Field, Va. This tunnel has an open jet air

stream 20 feet in diameter in which velocities up to 110 M.P.H. are obtained. Although the

tunnel was built primarily to make possible accurate full-scale tests on aircraft propellers, it may

also be used for making aerodynamic tests on full-size fuselages, landing gears, tail surfaces,

and other aircraft parts, and on model wings of large size. [Italics appeared in original.]

INTRODUCTION

The need of an accurate means for making aerodynamic measurements on

full-size aircraft propellers has been realized for some time. Tests on model propellers in wind tunnels are not entirely satisfactory because the deflection of the

model is different from that of a similar full-scale propeller, which introduces a

rather large error in some cases. The difference in scale and tip speed between

the model and full-scale propeller is also a cause of error. Full-scale flight tests on

propellers are made, of course, under the correct conditions, but at the present

time they can not be made with sufficient accuracy.

In the spring of 1925 the design and construction of a propeller research

wind tunnel to fill this need for full-scale tests was started by the National

Advisory Committee for Aeronautics. It was completed during the summer of

1927 and testing has been carried on since that time. The tunnel is of the open-jet

type with an air stream 20 feet in diameter. This is large enough to permit the

mounting of a full-sized airplane fuselage with its engine and propeller. The

open-jet type is particularly suitable for testing propellers because no corrections

are required for tunnel-wall interference. (References 4 and 5.) Also, since with

the open-jet type the inside of the experiment chamber is free from restricting

walls, the installation of the objects to be tested is relatively simple.

This wind tunnel makes it possible for the first time to make aerodynamic

tests with laboratory accuracy on full-scale aircraft propellers and also on full-scale

fuselages, engine cowlings, cooling systems, landing gears, tail surfaces and other

airplane parts. Full-scale tests of wings are not, of course, possible in a 20-foot air

stream, but large model wings (12 feet in span) can be tested at comparatively

high values of the Reynolds number.

Dr. Max M. Munk is responsible for the general arrangement of the propeller

research tunnel, and the detail design and construction were carried out under

the direction of Mr. E. W. Miller of the laboratory staff.
Document 2-20(a–c) 561

DESCRIPTION OF THE TUNNEL

GENERAL

The propeller research tunnel of the National Advisory Committee for

Aeronautics is located at Langley Field, Va., on a plot adjacent to the committee’s

other research equipment. Figure 1 is a diagrammatic sketch indicating the general arrangement of the tunnel and Figure 2 illustrates the exterior appearance.
562 Chapter 2: Building a Research Establishment

The tunnel proper is a wood walled steel-framed structure 166 feet long and 89

feet wide, having a maximum height of 56 feet. The walls are of 2 inch by 6 inch

tongued and grooved pine sheathing attached to steel columns with wooden nailers.

Except for the fact that the walls are on the inside of the framing only and that

the heights vary from point to point, standard structural practice is followed.

The tunnel (fig. 1) is of the open-throat, closed test chamber, return passage

type. The direction of the air flow is indicated by arrows. The air is drawn across

the test chamber into the exit cone by a propeller fan. After passing through the

fan the air column divides, passes through successive sets of guide vanes at the

corners, and returns through the side passages to the entrance cone. The areas of

the passages are varied in the case of the exit cone by varying the diameter, and

of the return passages by sloping the roof and floor, so that the velocity of the

moving air is gradually decreased at the large end of the entrance cone to about

one-eighth that through the test chamber. It is then rapidly accelerated in passing

through the entrance cone.

TEST CHAMBER

The test chamber is about 50 by 60 by 55 ft., located, as shown in Figure 1,

near the center of the tunnel structure. Large windows in the east and west walls

afford ample light. Doors open out of the west wall to permit the movement of

material to and from the test chamber. An electric crane traveling along a roof

truss is useful in lifting loads about the chamber and onto the balance. Electrical

outlets for light and power are provided at convenient points.

ENTRANCE CONE

The entrance cone (fig. 3) is of 50 ft. square section at the large end, changing

to 20 ft. diameter in its length of 36 ft. It is constructed of a double layer of 3

⁄4 in.
Document 2-20(a–c) 563

by 2 in. sheathing bent, fitted, and nailed to wood forming rings. These, in turn,

are bolted to angle clips riveted to I-beams bent to proper shape. A built-up wood

ring forms the end of the cone. At the large end the cone runs into the return passage

on a gradual curve.

EXIT CONE

The exit cone (fig. 4) is similar in construction to the entrance cone. It is circular in section from the mouth of the bell in the test chamber to the fan. The

cone has a diameter of 33 ft. at the mouth of the bell, reducing to 25 ft. at the test

chamber wall and then increasing with a 7∞ included angle to 28 ft. in diameter

at the fan. From the fan a gradual change is made to 30 ft. square at the return

passage. The total length of the exit cone is 52 ft.

GUIDE VANES

Guide vanes (fig. 5) are located, as shown in Figure 1, at each point of change

of direction of the air stream. These consist of metal covered wood framed curved
564 Chapter 2: Building a Research Establishment
Document 2-20(a–c) 565

shapes built up in sections 5 ft. long. Rounded leading edges and pointed trailing edges are of wood. The vanes are so proportioned that the free area between

them is about a mean of the passage areas before and behind them. Streamlined

wood separators run diagonally across the corners and act as stiffeners and supports for each tier of vane sections. It may also be noted in Figure 5 that cross

bracing in the return passages is streamlined in the direction of flow.

FAN

Circulation of air is accomplished with a 28 ft. diameter propeller type fan.

(Fig. 6 and fig. 1.) It consists of eight cast, heat-treated, aluminum-alloy blades

screwed into a cast steel hub and locked in place by means of wedge rings which

are forced between the blade shanks and the hub. This makes it possible to

change the pitch to adapt the fan to the driving engine characteristics or to secure

different air speeds with the same engine speed. At present 100 M. P. H. is
566 Chapter 2: Building a Research Establishment

obtained with 330 R. P. M. of the engines and fan. The weight of each blade is

600 pounds and the total weight of the fan is about 3 1⁄2 tons.

A steel framed sheet aluminum spinner 7 ft. in diameter is attached to the

hub. This fairs into the cylindrical propeller shaft housing.

DRIVE SHAFT

The fan hub is keyed on to the tapered end of an 8-in. solid steel shaft running

back through the exit cone and return passage. This shaft is supported on four

plain, collar oiled, bearings and one combination plain radial bearing and deep

groove ball thrust bearing. The latter is located at the end of the shaft opposite

the propeller. The bearings are supported, in turn, on steel I-beam A frames resting

on spread footings in the ground below the exit cone.

The shaft and bearing bracing are surrounded by a cylindrical sheet steel fairing

on wood formers of the same diameter as the fan spinner. The legs of the A

frames are also suitably faired.

POWER PLANT AND TRANSMISSION

Because of local conditions it was found advisable to use Diesel engines rather
Document 2-20(a–c) 567

than electric motors to furnish power for circulating the air through the tunnel.

Two Diesel engines, which had been removed from a submarine, were furnished

by the Navy Department.

These engines are full Diesel M.A.N. type, 6 cylinder, 4 cycle, single acting,

rated at 1,000 HP. each at 375 R.P.M. After due consideration, it was decided to

install these end to end as they had been in the submarine, using the existing flywheels and clutches, spacing them far enough apart to allow the installation of a

driving sheave between. The location of the engine room is shown in Figure 1,

with the engine and sheave position indicated. The auxiliary machinery is

arranged on the opposite side of the room from the engines. Figure 7 is a general

view of the engine room.

Power is transmitted from the driving sheave to a similar sheave located forward

of the thrust bearing on a part of the fan shaft extending through the main tunnel

wall. Forty-four “Texrope” V-belts are used with two adjustable grooved idler pulleys

located as shown in the end view, Figure 1. The transmission ratio is 1 to 1. The

belt pull is carried on a suitable steel structure and the whole framing, is roofed

over and sided with a protected corrugated metal. This same material is a covering

for the engine room proper, rendering this part of the installation practically fireproof.
568 Chapter 2: Building a Research Establishment

BALANCE

The testing of full size airplane fuselages necessitated the design of a new

type balance. This, as shown in Figures 8 and 9, consists essentially of a triangular frame A of steel channels and gussets resting on tubular steel posts B, which

in turn bear on the platforms of ordinary beam scales C. Double knife edges are

provided at both ends of these posts. The rear post of the frame is on the longitudinal center line of the balance and the forward posts are at equal distances (5

ft.) on either side. The sum of the net readings on all three balances is the lift.

The pitching moment is computed from the sum of the front balance readings

and from the rear balance reading. Since the rear balance is on the longitudinal

axis, the rolling moment is computed from the net readings on the front balances.
Document 2-20(a–c) 569

At D are located knife edges connected to tie rods E running forward to a bell

crank G and a counterweight H, and aft to a bell crank F and a post I resting on the

scale T. A forward pull or thrust on the frame produces a down force on the post or

an increase in load on the scale T. The counterweight H produces an initial load on the

scale T and consequently a drag or backward force is measured as a diminution

of load on the scale. The counterweight consists of several 50-lb. units and can be

easily adapted to the range of thrusts and drags expected during any one test.
570 Chapter 2: Building a Research Establishment

The fixed knife edges on the bell cranks are seated on blocks bolted to a rectangular steel frame rigidly fastened to the floor, as shown in Figure 9. In addition,

this frame is provided with knife edges, links, and counterweights which hold the

triangular frame in a fixed lateral position. Screws are also provided for raising

the triangular frame from the knife edges while working on the attached apparatus. A stairway at the rear and a grating floor facilitate work on the supports and

apparatus mounted on the balance.

At each corner of the triangular frame are ball ended steel tubes, adjustable

in length and angle, which support the body under test. The forward tubes, in the

case of a fuselage with landing gear, have a fitting at the upper end which clamps

the axle of the landing gear. The rear post has a ball-and-socket attachment to the

fuselage. The drag of these supports is reduced by streamline fairings which also

serve to cover wires and fuel and water lines running to the fuselage.

TORQUE DYNAMOMETER

As the engine power is one of the major variables determining the propeller

characteristics, a test fuselage has been developed which allows the engine driving the propeller to be mounted on a dynamometer and the torque to be measured directly.

As shown in Figure 10, this is a heavy angle and strap steel frame so shaped

that it can be slipped inside a standard airplane fuselage and supported by suitable
Document 2-20(a–c) 571

blocking. At its forward end a steel casting is fixed carrying two large ball bearings

and an extension shaft and plate. An airplane engine can be mounted on this

plate. Its torque, which is carried through the plate and shaft and a special linkage,

is read on a dial scale mounted farther back in the fuselage. This dial reads directly

in lb. ft. up to 2,000 lb. ft. and a total of 4,000 lb. ft. may be obtained with a counterweight. A double link system renders the operation independent of the direction

of engine rotation.

Figure 11 shows a VE-7 airplane mounted on the test fuselage with an E-2

engine on the plate. The radiator is mounted independently of the engine and is

not used for cooling. Cooling water is supplied and returned through rubber hose

running back through the fuselage and down the rear post to the floor. Figure 12

shows the dial in the rear cockpit.

To reduce the fire hazard and to simplify installation, fuel is supplied from a

small tank located on the outer wall of the tunnel, feeding by gravity to the engine

carburetor. The gravity tank is filled from a large storage tank by an electric gear

pump which is started and stopped by an automatic float switch in the gravity tank.

PROPELLER BLADE DEFLECTION

Propeller blade deflections are measured as follows. A telescope with cross hairs,

in conjunction with a prism, is mounted on a lathe bed beneath the propeller
572 Chapter 2: Building a Research Establishment

being tested. One blade of the

propeller at a time is painted

black and a black background is

painted on the ceiling. Two lights

are arranged so that their beams

strike the propeller blade. On

sighting through the telescope

no image will be seen when the

black blade passes the black

background; but when the white

or bright metal blade passes, a

line of the leading or trailing

edge will appear. By locating, the

cross hairs successively on these

lines and reading, the distance

moved it is possible to compute

the angular deflection of the propeller blade at any given radius.

Further development of this

apparatus is in process.

MANOMETER

For routine testing, velocities are calculated from the readings of an N.A.C.A.

micro-manometer, one side of which is connected to plates set in the walls of the return

passage and entrance cone, and the other side open to the air in the test chamber.

SPEED REGULATOR

An air-speed regulator has been developed to insure a uniform dynamic pressure, but to date its use has not been found necessary.

ENGINE STARTER

For starting an airplane engine mounted on the balance, an electric starter is

secured to the entrance cone shown in Figures 12 and 13. A hollow shaft with a

pin meshing with a dog on the propeller shaft is driven by means of a chain from

an electric motor. The whole unit is arranged to swing down clear of the air

stream during a test.

CALIBRATIONS

A velocity survey has been made over the entire cross section of the air stream

at a point about 6 ft. back of the entrance cone edge. Seventy-nine points were

taken at 2 ft. intervals. The velocity without a honeycomb or air straightener was

found to be constant within 1 per cent over the test area. This is attributed to the

large reduction of area in the entrance cone. Large variations of velocity at the
Document 2-20(a–c) 573

entrance to the cone are greatly reduced by the rapid acceleration through it. In

consequence, while provision was made in the structure for the installation of a

honeycomb, none has been deemed necessary.

The wall plates and manometer are calibrated from time to time against a

group of Pitot tubes set in the air stream. These are attached to a movable frame

to which one or more Pitot tubes may be attached and the velocity at any point in

the air stream determined without a special installation. In particular, this apparatus is used to measure the velocities in the plane of the airplane propeller.

The tunnel was designed to give a velocity of 100 M.P.H. with an energy ratio

of 1.2 based on the power input to the fan. A velocity of 110 M.P.H. has been

obtained indicating an energy ratio higher than that assumed.

Figure 13 is a view in the test chamber during a standard propeller test.

Balances, manometer and deflection apparatus are shown in operation. An

observer stationed in the fuselage to control the engine and read the torque scale

does not appear in this view.

SOME RESULTS

A considerable amount of testing has already been accomplished since operation

began in July, 1927. Figure 14, taken from Technical Note No. 271 (Reference 1),

indicates the proportional drag of various parts of the Sperry Messenger airplane

fuselage. The propeller research tunnel is particularly adapted to full-scale tests

of this nature. Figure 15 shows the characteristics of Propeller I, previously tested

in model form at Stanford University, and in two separate flight tests. (References
574 Chapter 2: Building a Research Establishment

2 and 3.) Curves from these tests are given for comparison. Attention is called to

the inaccuracy of flight data mentioned in the introduction to this paper. Tests of

wings of 12 ft. span have also been made at speeds up to 100 M. P. H. A comparatively high Reynolds number is thus attained. Figure 16 is a view of a wing set up

for test. A comprehensive program of tests to determine the effect of propellers

on air-cooled engines operating in front of various types of fuselages with several shapes of cowling is now in progress. The effect of these bodies on the propeller

is also being determined.

ACCURACY

Dynamic pressure, thrust, torque, and R.P.M. are measured with an accuracy

of from 1 to 2 per cent. Computed data are, therefore, correct to approximately plus

or minus 2 per cent and final faired curves through computed points to about

plus or minus 1 per cent. This compares favorably with other engineering measurements. The beam thrust balance is to be replaced with a dial scale which will

increase the accuracy and will enable the observers to read more quickly and more

nearly simultaneously. A change in the linkage of the torque scale is contemplated which will increase the accuracy of that reading. When these changes are in

effect it is hoped that computed points will be correct to plus or minus 1 per cent.

CONCLUSION

The propeller research tunnel fulfills a long-felt want in aerodynamic

research. Propellers can be tested full scale, and with actual engines and bodies in

place, with an accuracy not attained in flight tests. The components of the airplane,

fuselage, landing gear, and tail surfaces can be tested full scale. While full size
Document 2-20(a–c) 575

wings can not be accommodated, a stub wing can be installed which is sufficient

to study the effects of all parts of the airplane on the propulsive system, and vice

versa. Tests thus far made are consistent and reliable and it is increasingly evident

that the propeller research tunnel is a useful addition to the extensive research

facilities of the National Advisory Committee for Aeronautics.

LANGLEY MEMORIAL AERONAUTICAL LABORATORY,

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS,

LANGLEY FIELD, VA., June 2, 1928.

REFERENCES

Reference 1. Weick, Fred E.: Full Scale Drag on Various Parts of Sperry

Messenger Airplane. N.A.C.A. Technical Note No. 271, 1928.

Reference 2. Durand, W. F., and Lesley, E. P.: Comparison of Tests on Air

Propellers in Flight with Wind Tunnel Model Tests on Similar Forms. N.A.C.A.

Technical Report No. 220, 1926.

Reference 3. Crowley, J. W., Jr., and Mixson, R. E.: Characteristics of Five

Propellers in Flight. N.A.C.A. Technical Report No. 292, 1928.

Reference 4. Glauert, H., and Locke, C. N. H.: On the Advantages of an Open

Jet Wind Tunnel for Airscrew Tests. B.A.C.A. R.& M. 1033, 1926.

Reference 5. Durand, W. F.: Experimental Research on Air Propellers.

N.A.C.A. Technical Report No. 14, 1917.
576 Chapter 2: Building a Research Establishment

Document 2-20(c), Fred E. Weick, excerpts from From the Ground Up, 1988.

In response to the requests of Dr. Lewis about how NACA might help the Bureau

of Aeronautics, I kept mentioning the need for fullscale propeller tests at high tip

speed, where compressibility losses became evident. Compressibility is the physical

property by which the volume of matter decreases to some extent as pressure is

brought to bear on it. The British had made high-tip-speed tests on two-foot models

in a wind tunnel, but the Reynolds number was so low that the results were questionable when applied to full scale. Their compressibility losses were much greater than

those indicated by our meager flight tests in this country. At that time, however, I

could not see any practical way of making full-scale tests other than in flight.

One day in early 1925 Dr. Lewis called me into his office and asked me how

I would like to see a wind tunnel capable of making the full-scale propeller tests.

But, I said, in order to make full-scale tests on a 10-foot propeller, the diameter

of the tunnel’s throat would have to be at least 20 feet, or four times the size of

NACA’s largest wind tunnel at Langley up to that time. “Yes, you’re right,” Dr.

Lewis said. “But,” I said, “in order for it to be practical, the tunnel’s airflow would

have to reach at least 100 miles an hour, and to achieve that, you’d have to have

an immense amount of power—probably a couple of thousand horsepower.”

“Yes,” Dr. Lewis said again. “I’ve been talking it over with Dr. Munk and we think

that such an arrangement might be practical.” I was astonished: a 20-foot tunnel

would require a structure of 43 or sixty-four times the volume! Neither the

Hampton nor Newport News power plant was large enough to supply electric

power, but NACA, Dr. Lewis informed me, had arranged to get two navy surplus

diesel engines of 1,000 horsepower each, taken from a T-2 submarine. “If we can

get this tunnel built,” Dr. Lewis asked me, “would you like to come down to

Langley Field and run it for us?” Without hesitation, I said that I would indeed.

When Dr. Lewis made the suggestion that I be transferred from the navy to

NACA, the assistant chief of the Bureau of Aeronautics, Capt. Emory S. Land,

absolutely refused. The captain could not see losing me to another government

organization when I had just become useful in his propeller department. Some

time passed without approval for my transfer, until the line officer in charge of

the propeller department, Lt. Stanton Wooster, who had replaced my old boss

Lieutenant Shoemaker, advised Captain Land that I would probably do the Navy

Department at least as much good doing research in NACA’s new propeller tunnel

at Langley. Moreover, Wooster told him he didn’t exactly like standing in the way

of a possible improvement for me. So after this polite badgering, Captain Land

finally said, “All right, all right,” and the transfer was made.

NACA at that time had an annual appropriation of roughly $250,000 with

which to pay a staff of one hundred twenty-five, buy buildings and equipment,
Document 2-20(a–c) 577

and take care of operating expenses. As I remember it, the total cost of the bare

structure for the propeller research tunnel was about $70,000. In order to get it

started as soon as possible, NACA had skimped and saved $35,000 out of its FY

appropriation, which ended on June 30, until the early 1970s the end of the government’s fiscal year. On June 30 NACA had entered into a contract with the

Austin Company to construct the tunnel’s outer shell for $35,000. Then on the

next day, July 1, it had entered into another contract to construct the internal

structure, entrance and exit cones, and return passages. Construction started at

once. This all happened before my transfer and was the main reason I was itching

to move from Washington down to Langley.

[ . . . ]

The distance by air from Washington, D.C., to Hampton, Virginia, the town

nearest Langley Field, is only about 120 miles, but by road through Richmond it

is about 175 miles. In the 1920s these roads were surfaced with gravel and often

badly rutted; smooth ribbons of concrete were not to be found in rural Virginia.

In our Model T roadster, packed to overflowing, it took us all day to make the trip.

The engineer in charge of the Langley Memorial Aeronautical Laboratory at

that time, a Californian by the name of Leigh M. Griffith, appeared unhappy with

the idea that I had been placed under him from above; in fact, Griffith must have

been generally unhappy with his situation at Langley, for he left within the

month. He was replaced by Henry J.E. Reid, an electrical engineer who had been

in charge of the laboratory’s instrumentation. Reid remained the engineer-in-charge

until he retired from the National Aeronautics and Space Administration (NASA)

in 1960. The lab had a flight research division headed by test pilot Thomas

Carroll, a power plant division headed by Carlton Kemper, and two wind tunnel

sections, one, the 5-foot or atmospheric wind tunnel (AWT) section headed by

Elliott G. Reid, and, the other, the variable-density tunnel (VDT) section headed

by George J. Higgins. There was also an instrument shop, model shop, technical

service department, and a clerical and property office headed by Edward R.

(“Ray”) Sharp. The new 20-foot propeller research tunnel (PRT) was being constructed under the supervision of Elton W. Miller, a mechanical engineer who had

previously been in charge of the construction of the variable-density tunnel. I was

placed under Miller until the tunnel was ready for operation.

By the time I started at Langley, the outer shell of the new tunnel had been

completed but work on the entrance and exit cones and guide vanes was still

going on. The tunnel, which had been laid out by Dr. Max Munk in Washington,

was of the open-throat type then most suitable for testing propellers. My first job

was to design and get constructed a balance arrangement that measured the aerodynamic forces on the model and the model’s reaction to them. This balance had

to support an airplane fuselage, complete with engine and propeller, 25 feet
578 Chapter 2: Building a Research Establishment

above the floor in the center of the tunnel’s 20-foot-in-diameter airstream. All of

the pertinent forces, such as drag, thrust, and moments, were to be measured

down below by four small and simple beam scales.

Since 1921 Dr. Munk had been holed up in a little office at NACA headquarters in Washington, where he had been turning out excellent theoretical work.

Munk had studied under Ludwig Prandtl at the University of Göttingen in

Germany and had been brought to this country by the NACA in 1921. His entry

into this country required two presidential orders: one to get a former enemy into

the country, and another to get him a job in the government. And I guessed this

helped him to appreciate his importance.

Without question, Munk was a genius, and, without question, he was a difficult

person to work with. In early 1926 he decided on his own that, since Langley laboratory was where all the real action was taking place, that was where he should

be. NACA headquarters must have agreed, because it made him the lab’s chief of

aerodynamics; this put him in charge of the flight research division and the two

wind tunnel sections. My boss, Elton Miller, now reported to Munk, and all of my

work ultimately had to be approved by him. I had known Munk in Washington

and had great respect for his abilities. On the other hand, I did not want my balance

design turned down at the last minute; so I had taken the pain to take each detail

of design, mostly on cross-section paper, up to Munk to get his approval, and I

got his initials on every single one of them. This, I thought, would certainly assure

his final approval.

The movable parts of the balance supporting the airplane were supported by

a structural steel framework about 12-feet high, 12-feet wide, and 16-feet long. In

place of adjustable cables, steel angles 1

⁄4 by 2 1⁄2 by 2 1⁄2 inches provided the diagonal bracing.

A couple of days before we expected to try out the balance using a little

Sperry Messenger airplane with its 60-horsepower engine running, Munk made

an unannounced visit to the PRT building. Just as he walked into the bare-walled

50-foot cubicle that housed the test section, a loud horn squawked, calling someone

to the telephone. This sent Dr. Munk into a tantrum, and I immediately had one

of my mechanics disconnect the horn. Before he had entirely calmed down, he

walked over toward the balance structure and put his hands on the long diagonal

braces. These were fairly flexible, and he found he could move them back and

forth a bit. Visualizing the entire structure vibrating to the point of failure and the

whole airplane and balance crashing to the ground, the perturbed Munk ordered

me to tear down the balance entirely and to design a new foundation and framework for it. He then turned and went back to his office a couple of blocks away.

Naturally I, too, was perturbed. Munk, after all, had approved every detail of

my balance design. Not knowing what to do, I waited for some time to give him
Document 2-20(a–c) 579

an opportunity to cool down. Then I went to his office and, as calmly as I could

manage, mentioned that I thought the natural frequencies of the long diagonal

members would be so low that vibrations would not be incited by the more rapid

impulses from the engine and propeller. But mainly I suggested that, inasmuch

as all the parts were made and ready to be put up, why not wait a couple of days

before tearing it down and make a careful trial using the Sperry Messenger, starting

at low speed, gradually increasing it, before dismantling the apparatus. Munk

finally agreed, but demanded to be present when the test was made.

I did not like the idea of his presence one iota. To start the engine, the

Messenger’s propeller had to be cranked by hand from a balloon ladder that was

put up in front of the propeller 25-feet above the floor. (A balloon ladder was like a

fireman’s ladder but its base was attached to a pair of weighted wheels, which permitted it to be “leaned” out into space. At its base there was a “protractor” that

told you how far it could be angled without tipping over.) This sweaty business

often took some time. It was not the kind of operation I wanted the excitable

Munk to watch. Moreover, since no one else in the PRT section had ever started

an airplane engine by turning the propeller, I was the one who was going to have

to do it.

I brought my problem to Elton Miller, my boss, and to Henry Reid, the engineerin-charge. Together, we decided that the only thing to do was to make an end-run

around Munk and check out the tunnel balance system in his absence. This was

easily done, as Munk worked on theoretical problems in his room at a Hampton

boarding house every afternoon. We set up the test run and after a bit got the

engine started without any difficulty. We then experimented with it until we could

start it easily and felt ready for the final trial.

The problem of convincing Munk remained. We could not simply tell him

about the successful test, so we agreed to arrange another “first test” for Munk to

witness. Engineer-in-charge Reid escorted Munk to the tunnel the next morning.

I casually said, “Good morning,” clambered up the ladder, and pulled through

the Messenger’s prop. Luckily, the engine started on the first try. We then moved

the ladder away, ran the engine through its entire range with no vibration difficulty,

and then shut it down. Now, I wondered, what sort of explosion will we have? I

needn’t have worried. Munk walked toward me with his hand outstretched and

congratulated me on the success of the operation. Everything had turned out all

right. The balance system of the PRT operated satisfactorily with engines of up to

400 horsepower into the late 1930s, when it was replaced by a new and better one.

In 1926 Dr. Munk gave a number of lectures on theoretical aerodynamics to

a select group of young Langley engineers. I was very happy to learn these things

from him. Ever since graduation from the University of Illinois, I had thought

about taking some graduate courses in aeronautical engineering. While working
580 Chapter 2: Building a Research Establishment

for Tony Yackey, I had read in a magazine article about the graduate courses in

aeronautics offered at Massachusetts Institute of Technology. I had written MIT

for information and had received a letter back from Professor Edward P. Warner,

who had been Langley’s first chief physicist in 1919 and would later become assistant

secretary of the navy for aeronautics, editor of the magazine Aviation, and finally

president of the International Civil Aviation Organization (ICAO), which continues

to coordinate the rules and regulations for aeronautical activities throughout the

nations of the world. I had hoped still to find a way to work in some graduate

courses even after reporting to work at the Bureau of Aeronautics. But Dr. Lewis

had talked me out of the idea on the basis that formal aeronautical engineering

education was inferior to what I could learn if I went to work for the NACA at

Langley. I guess he was probably right in regard to the aeronautical courses per se,

but on occasion, in later years, I sorely missed the extra mathematics and physics

that would have been obtained in school.

As mentioned earlier, the power plant for the new PRT consisted of two

1,000-horsepower, six-cylinder in-line diesel engines taken from a T-2 submarine.

These engines were located end-to-end with crankshafts connected to a large

sheave or pulley between them. This sheave carried forty-four Tex-rope V-belts to

a similar sheave on the shaft of the propeller fan that drove the air through the

tunnel. The shaft of the propeller fan was 25 feet above the ground, and the two

sheaves were 55 feet apart center to center. Because we were concerned that some

destructive vibrations might occur in the crankshaft-sheave assembly, we decided

that a theoretical analysis of the torsional oscillations should be made, with Dr.

Munk outlining the problem and a new man, Dr. Paul Hemke, to work out the

solution. As a junior engineer, my assignment was to give the measurements and

sizes that I would get from the drawings of the engines and sheaves.

I had no difficulty giving them the measurements, but Dr. Hemke was never able

to get the gist of the torsional pendulum problem as described by Munk. This went

on for some time with no results being obtained. Finally, I looked into my mechanical

engineers’ handbook and into a couple of textbooks and found that considerable work

had been done on the problem and that the solution was not too difficult. I made the

computation myself, coming out with a natural frequency of 312 RPMs. Later on, after

the tunnel was in operation, some men came down from the navy shipyard in

Brooklyn with equipment to measure the torsional oscillations; they found exactly

the same natural frequency as I had computed. Hitting it exactly, of course, was a

matter of luck, but it helped give me a good reputation, whether I deserved it or

not. The success put me in good with Munk, but unfortunately Dr. Hemke was never

able to work satisfactorily with him. A short time later he left the NACA. Hemke

later joined the faculty of the U.S. Naval Academy, after holding a prestigious

Guggenheim Fellowship for research under B. Melville Jones at Cambridge.
Document 2-20(a–c) 581

Another problem I helped to solve was the design of the 28-foot propeller fan that

was to circulate the air in the propeller research tunnel. This fan needed to have eight

blades of normal width. The exact energy ratio of the tunnel was not known in

advance, so I desired to have blades that could be adjusted so that the pitch could be

set exactly right after trial runs. Aluminum-alloy blades therefore seemed the best

choice, but the blades we wanted were too large to be forged in the manner of the

aluminum-alloy propeller blades then being manufactured. Fortunately, the propeller

was to turn at only 375 revolutions per minute, which meant that the stresses would

be very low in comparison even with airplane propellers having large diameters. This

gave me the idea that a cast aluminum alloy might be used successfully, which it was.

I arranged with the Aluminum Company of America to cast the blades in

their plant at Cleveland, Ohio. Before the large blades were cast, however, the

company made two blades for a small ten-foot model that I then took to McCook

Field in Dayton, where they were tested by Army Air Service engineers on their

propeller whirl rig. This test showed the blades to be sufficiently strong.

[ . . . ]

We had gotten the diesel engines to run satisfactorily in a short time, but the

long Tex-rope drive, with its forty-four different V-belts, were always getting so

tangled up that they could not stay on the sheaves satisfactorily. It took several

months of experimenting with idling sheaves in various locations before the operation became satisfactory. The entire drive, with Tex-ropes and sheaves, had been

purchased from the Allis Chalmers Company and had been guaranteed to operate satisfactorily. After spending much money and time on this problem, the

NACA sued Allis Chalmers for a sizable rebate. My daily log of operations was

used as part of the testimony, and after one futile operation I had put down in

disgust, “No soap.” Although this was a generally used term in the Midwest,

where I came from, indicating failure, no one in the room, all of whom were from

the East, knew what I had meant. So I had to explain it in detail, an amusing

interlude in an otherwise dull trial.

[ . . . ]

Finally, in 1927, the Tex-rope problem was solved and the PRT was ready for

actual testing. The tunnel personnel included Donald H. Wood, a mechanical

engineer from Renssalaer Polytechnic Institute who was about my age and who

had been with the PRT section from the start; Melvin N. Gough, a young engineer

who had come to Langley directly from Johns Hopkins; William H. Herrnstein, Jr.,

an engineer who had come directly from the University of Michigan; and John L.

Crigler and Ray Windier, also engineers. The power plant and shop work under

Ted Myers, who was a little older than the rest of us, included George Poe and

Marvin Forrest. There were two or three others whose names I have forgotten. At

any rate, we had a good team and we all worked together very well.
582 Chapter 2: Building a Research Establishment

Just before testing actually started in the PRT, Langley experienced a rather

sad affair: a revolt against Dr. Munk, the head of our aerodynamics division.

Munk was a wonderful theoretical aerodynamicist, but, as the story of my design

of the PRT’s balance structure illustrates, he was also an extremely difficult supervisor,

not just for me but for all the section heads working directly under him.

Eventually all the section heads, including Elton Miller, decided they couldn’t

work with Munk any longer and handed in their resignations. Munk was then

relieved of his job, which I feel was a great loss. If Dr. Lewis could only have kept

him holed up in his little office in Washington, Munk could have produced a great

deal more of his useful theoretical work.

With Munk’s departure, Elton Miller became the chief of the aerodynamics

division, and I became head of the PRT section.

In the first months of PRT operation, just to get experience, we merely tested

the Sperry Messenger and obtained drag data with various parts of the airplane

removed. This was then written up and published as an NACA technical note.

Before we could actually make propeller tests, though, we had to design and build

a dynamometer that would support the engine and propeller up in the airstream

and measure the torque of the engine while it was operating. We mounted the

dynamometer in a long structural steel frame of small cross-section. Any engine

up to about 500 horsepower could be mounted ahead of it, and any fuselage form

could be put on over it. The engine torque we measured directly in foot pounds

on a dial-type Toledo scale.

For the first propeller tests, we slipped this dynamometer inside the fuselage

of a Vought VE-7 airplane. The engine was a 180-horsepower Wright E-2 liquidcooled unit, similar to the old Hissos. These tests were made primarily to compare

with the propeller data we had gotten from our flight testing and with the smallmodel data acquired previously from wind-tunnel testing at Stanford University.

Three full-size wooden propellers of the same type previously used on the same VE-7

airplane, and models of which had also been investigated in the Stanford tunnel,

were tested. The results agreed as well as could have been expected, considering

the difference in Reynolds number (the nondimensional coefficient used since

Osborne Reynolds’s pioneering experiments at the University of Manchester in the

1880s as a measure of the dynamic scale of a flow) between flight and tunnel testing.

An interesting sidelight about the accuracy of aerodynamic testing appeared

soon after we began PRT testing. In our final plots, the points of our wind-tunnel

data for the full-scale tests had substantial scatter about the curves, whereas the

small-model tests had the points right on the curves. I worried about this for a

while, until I found the answer. Our results at NACA were plotted with fine points

and fine lines at a large scale, and the model tests at Stanford were in printed

form with heavy lines and large points. When we plotted our results in the same
Document 2-20(a–c) 583

manner as the model test results, our accuracy was at least as good as Stanford’s.

I reported these results in NACA Technical Report (TR) 301, “Full-Scale Tests of

Wood Propellers on a VE-7 Airplane in the Propeller Research Tunnel,” in 1928.

TR 300, describing the tunnel and testing equipment, had been prepared just

previously by Donald H. Wood and me.

After the technique of making satisfactory propeller tests in the propeller

research tunnel had been worked out satisfactorily, one of the first things that I

wanted to investigate was the effect of high propeller tip speeds; after all, this had

been one of the main reasons for having the tunnel built in the first place. The

original propeller-testing setup with a 180-horsepower engine was not powerful

enough to cover the range desired in high tip speeds, but we did what we could

with it. The tests had to be made with a very low pitch setting that corresponded

to angles of attack of the cruising or level range of flight but not of climb or takeoff conditions. The range of the tests was from 600 to 1,000 feet per second, about

0.5 to 0.9 times the velocity of sound in air, or in modern terminology, from Mach

0.5 to Mach 0.9. Within the range of these tests, the effect of tip speed on the

propulsive efficiency was negligible, and there was no loss due to the higher tip

speeds. The results are given in my NACA Technical Report 302 (June 20,1928).

Later on, with a more powerful engine, we were able to test a whole series of propellers at tip speeds of up to 1,300 feet per second, which is well above the speed

of sound. The results of these tests are recorded in NACA TR 375 (November

1930) by Donald H. Wood.
584 Chapter 2: Building a Research Establishment

Document 2-21(a–c)

(a) Elliot G. Reid, “Memorandum on Proposed Giant 

Wind Tunnel,” 3 April 1925, National Archives, 

171.1, Washington, D.C.

(b) Arthur W. Gardiner, “Memorandum on Proposed Giant

Wind Tunnel,” 22 April 1925, National Archives, 

171.1, Washington, D.C.

(c) Smith J. DeFrance, The NACA Full-Scale Wind Tunnel,

NACA Technical Report 459, Washington, D.C., 1933.

By 1930, the VDT had proven that wind tunnel testing of models at high

Reynolds numbers produced data that accurately predicted the performance of

airfoils, and the PRT had shown the value of full-scale testing in determining the drag

characteristics and synergistic effects of integrating the various components of an

airplane. Yet, neither tunnel totally reproduced the conditions experienced by a

complete airplane in flight, so the NACA decided to build a still larger wind tunnel,

one capable of testing full-size aircraft. This was not a brand new idea. Shortly after

Max Munk proposed the twenty-foot-diameter PRT in March 1925, others at

Langley began to call for a ten-foot increase in its diameter to enable the tunnel

to test large- and full-scale aircraft components. Arthur W. Gardiner and Elliot G.

Reid, assistant aeronautical engineers at Langley, each prepared a “Memorandum

on Proposed Giant Wind tunnel” that applauded the idea of a facility suitable for

propeller research and suggested how such a “giant wind tunnel” could do much

more than test propellers. Their ideas had little effect on the design of the PRT,

which was built with a twenty-foot-diameter nozzle, but good ideas rarely die.

The Full-Scale Tunnel (FST), completed in 1931, was gigantic in all respects,

and it loomed over every other structure at the LMAL. Like the PRT, the FST was

a closed-circuit tunnel with an open test section and return ducts whose outer

walls formed the building walls. With its larger size, the FST design included dual

return ducts. The elliptical nozzle—a brilliant solution to the problems associated

with very large circular or rectangular designs—delivered an air stream that measured

thirty by sixty feet and attained velocities of up to 118 miles per hour. Two thirtyfive-foot-diameter propellers, each driven by a 4,000 horsepower electric motor,

circulated almost 160 tons of air through the 838-foot-long circuits. The FST

could handle airplanes or large-scale models with wingspans of up to forty-five
Document 2-21(a–c) 585

feet. While the FST’s speeds were not extraordinary, they were sufficient to enable

measurements that could be confidently extrapolated to cover the aircraft’s entire

speed range because no scale factor was involved. In addition to lift and drag

studies, the FST supported stability analysis and research into the interferences

between the various parts of an airplane. With the FST joining the VDT and PRT

in service, the NACA’s Langley Laboratory possessed the most extensive and versatile research facilities in the world. As with its earlier facilities, the NACA published a technical report discussing the FST and its capabilities.

Document 2-21(a), Elliot G. Reid, “Memorandum on 

Proposed Giant Wind Tunnel,” 1925.

MEMORANDUM ON PROPOSED GIANT WIND TUNNEL.

I have been thinking over the possibilities of a tunnel of the size and type suggested and have become very enthusiastic over the project. As requested, I am

outlining my ideas of the value of such an apparatus.

Below are listed a number of problems which I consider particularly suitable

for investigation in the large tunnel:

(A) Propeller research: 

(a) Tests of full size propellers, isolated, for determination of characteristics under the conditions of deformation imposed by air loads and

centrifugal forces.

(b) Investigation of the propeller slipstream, including confirmation or

rejection of the inflow theory and investigation of the phenomena

accompanying tip speeds greater than that of sound. 

(c) Tests of propellers with axes inclined to the wind.

(d) Tests of propellers on actual airplane fuselages for determination of

full scale interference characteristics.

(e) Pressure distribution tests on propellers.

(f) Investigation of the magnitude and causes of full size propeller deflections. 

(g) Tests of adjustable and reversible propellers and their operating

mechanisms under flight conditions.

(B) Testing of full size airplane parts which cannot be accurately reproduced

to the scale of present models. 

(a) Tests of radiators, air-cooled engine installations, etc.

(b) Tests of fuselages with and without slipstream for development of better forms. 

(c) Pressure distribution over full size wings under conditions either very

difficult or dangerous to obtain in flight. (Conventional airplane practice,

i.e., spars, ribs, and usual covering to be used in construction).
586 Chapter 2: Building a Research Establishment

(C) Strength and stiffness of wing cellules. 

(a) Tests of large models or full size half cellules for the purpose of measuring air load deflections and, if it is found possible to determine

aerodynamic characteristics under these conditions, improve the

structures in such ways as to eliminate dangerous or inefficient conditions.

(D) Power plant testing.

(a) Tests of air-cooled engines under flight conditions. To be made by

installing engine in fuselage and running in tunnel under propeller

load.

(b) Development of cowling and cooling controls for air-cooled engines.

(c) Heat dissipation tests on full-scale radiators.

(E) Testing of very large models of wings and complete airplanes.

Probably the one line of research to which the large tunnel would be the

greatest boon is propeller testing. It is known, of course, that models could be

tested in the Dense Air Tunnel [VDT] at Reynolds numbers equal to those existing

in the flight operation of full size propellers. This, however, is not the criterion

for complete dynamic similarity. Dr. Durand’s excellent analysis of the necessary

relations for the establishment of complete dynamic similarity, as given in N.A.C.A.

Technical Report No. 14, Part II, shows that dimensional homogeneity can be fulfilled

only by making the model of the same size as the original. While he does not take up

the possibility of testing in a different medium—as compressed air—the fulfillment

is still incomplete because the factors involving medium density are different.

It has been the feeling for some time that the deflections of full-scale propellers

were considerably different from those of their smaller prototypes and that

numerous failures to predict full-scale propeller performance arose from this fact.

Mr. Lesley was convinced that such a condition did exist and supported his belief

with the statement that model and full scale results were in better agreement in

the case of stiff bladed propellers than for limber ones.

Therefore it would seem not only desirable, but almost imperative to have

some means of testing full-size propellers and the large wind tunnel seems the

only possible solution.

With regard to tests of propellers with axes inclined to the wind, it would seem

that only small angles could be explored if the closed throat type of tunnel be used.

This is more particularly the case for propellers mounted on full size fuselages. The

wall effect would probably so modify these results as to make them misleading.

Interference and slipstream studies could be carried out with an accuracy

never before possible. The possibility of using a full size radiator directly behind

the propeller solves one of the most troublesome problems of such tests. 

Fuselage forms have received very little study up to the present. The Variable

Density Tunnel provides a means of eliminating the scale effect factor but the dif-
Document 2-21(a–c) 587

ficulty of producing accurate replicas of fuselages is great and to study their characteristics under the action of a slipstream is almost out of the question with this tunnel.

Static testing of wing cellules will give very good and reliable information on

the ultimate strength but only very approximate data concerning deflections. It is

of course known that wing characteristics may undergo large changes if any

deflections are introduced and yet very little attention has been paid to this matter.

By the use of a very large tunnel, it would be possible to test complete semi-span

cellules of the smaller machines and very large scale models of large ones. By the

use of proper strength relations, the deflections in full size cellules could be very

accurately predicted from tests of models sufficiently large to permit use of the same

type of construction. It would thus be possible to investigate the conditions which have

caused inefficient flight in some cases, failure of controls in others and accidents in

some few. The failure of monoplane wings in service during a dive is one of the latter.

The testing of aero engines under actual flight conditions is a thing which can

not be accurately done at present. It is known that the ideal conditions of the electric dynamometer test do not prevail in actual operation and just how much the

performance suffers is a matter of conjecture. As it would be possible to put an

entire plane, minus the outer portions of the wings, into the proposed tunnel, the

conditions of flight could be exactly simulated and the propeller testing equipment

utilized to measure the engine output.

Likewise the cooling of the air-cooled engine could be studied with an accuracy

and completeness quite out of the question in flight and it should be possible, as

a result of such testing, to devise much more efficient (from the aerodynamic

standpoint) cowling for such engines.

The testing of large-scale models of wings and airplanes is particularly desirable.

We feel quite sure that the much feared scale effect becomes almost vanishingly

small as the VL product rises to the range covered by actual airplanes and that in

this range the effects of turbulence are also practically negligible. If the maximum

value of this product could be brought to three or four times as large as that

obtainable in present tunnels, it should be quite safe to predict full-scale performance

directly from such test data. While the Variable Density Tunnel can, theoretically,

accomplish this very thing, there always exists the difficulty of reproducing the

airplane with sufficient accuracy in the small size necessary. Then, too, any extensive

pressure distribution investigation can be carried out only with an enormous

expenditure of time, apparatus, and labor.

The large tunnel would eliminate a number of these outstanding difficulties.

Models could easily be built to the required accuracy with only a little more pains than

is usually used in normal airplane construction. Their cost would be relatively small

and thru their use it would be possible to study a large number of problems which are

important but can not be undertaken for one reason or another at the present.
588 Chapter 2: Building a Research Establishment

The questions of size and general arrangement will naturally involve much

thought and planning. A few remarks on these subjects are appended.

The suggested 20 ft. throat diameter seems ample except for one possibility

which was not mentioned in the list above. It would be a marvellous asset to be

able to test scaled-down models of large airplanes and having the models capable

of actual flight. This could be done in many cases if the tunnel were to have a

throat of about 30 ft. diameter, but any model capable of carrying a pilot would

be too large for a 20 ft. tunnel. The comparison of flight and tunnel tests on the

same model would be just about the ne plus ultra of aerodynamic investigation.

The use of return ducts would effect such a great saving of power and make

possible a maximum speed so much higher, with any given power, that the open

circuit type of tunnel is completely out of the question. 

The outstanding advantages of the Eiffel chamber would seem to overbalance any

possible aerodynamic advantage inherent to the closed throat tunnel. Installation

and operation of measuring apparatus have few terrors in an Eiffel chamber but,

as a result of my experience in the atmospheric tunnel, I would expect many troublesome and expensive complications if the throat were to be closed.

With the use of an open balance room, the shape of throat is pretty well limited to a polygon or circle, as a free jet of air having a square or rectangular cross

section would be rather difficult to handle, particularly in the matter of collecting

after having traversed the balance room. The circular jet would eliminate several

difficulties attendant upon the propeller installation.

A single large propeller might be difficult to build but its operation would

doubtless be more satisfactory than any other system that could be devised. It is

thought that a multiblade fan of the inserted blade type, somewhat similar to the

one in use in the 5 ft. tunnel at McCook Field, offers the best possibilities for

adaptation to very large installations.

[signed] Elliott G. Reid

Elliott G. Reid,

Assistant Aeronautical Engineer

Langley Field, Va.

April 3, 1925.

Document 2-21(b), Arthur Gardiner, “Memorandum on 

Proposed Giant Wind Tunnel,” 1925.

MEMORANDUM ON PROPOSED GIANT WIND TUNNEL.

As requested, I submit herewith a brief memorandum on the proposed giant

wind tunnel indicating certain investigations for which such a wind tunnel would

seem to be peculiarly well adapted.
Document 2-21(a–c) 589

To my mind, a wind tunnel of the proposed proportions would fulfill a very

definite need in aeronautic research, and, if built, would have a threefold purpose:

(1) to aid in correlating the wind tunnel testing of models with the flight testing

of full-size airplanes, i.e., to duplicate, after a fashion, the function of our variable

density tunnel, but attacking the problem from the standpoint of increased linear

dimension, approaching or equalling full-scale, rather than from the standpoint

of increased air density; (2) to take over certain phases of flight research, thereby

substituting more accurate methods for the somewhat unreliable flight test methods,

and, at the same time, making it possible to exercise control of the operating conditions, and (3) to enable some very pertinent research problems to be investigated

which are not being undertaken at present due to the lack of suitable equipment.

To utilize a giant wind tunnel to fulfill the purpose mentioned under (1)

above might appear, at first thought, to be an unnecessary duplication of effort.

However, full-size, or nearly full-size, model testing would seem to have many

advantages over small model testing in a variable density tunnel, as full-size models

could be made in our own shops according to standard airplane construction

practice, thus effecting a great saving in time and enabling a greater variety of

model building. Also, it would seem that considerable time could be saved in the

actual testing of the model. The advantages accruing from either the direct application of wind tunnel test data from a giant tunnel or the application of the test

data with but a small correction for scale effect would be highly desirable in predicting flight performance.

The purpose mentioned under (2) above might also appear to be a duplication

of effort, but here again it would appear that certain phases of flight research

could be conducted in a giant wind tunnel much more expeditiously and with

greater accuracy than possible with flight testing methods. In addition, there are

cases where a greater range of investigation is possible in wind tunnel testing than

is permissible in flight testing. The fact that wind tunnel tests can be conducted

independent of weather conditions would also make for a saving in time.

The purpose to be fulfilled under (3) above is by far the most important. The

fact that a giant wind tunnel would enable certain investigations to be made,

which are not being undertaken at present due to the lack of suitable equipment,

might very well, in itself, be a sufficient reason for taking the pioneer step in constructing a wind tunnel of the proposed type. Some pertinent investigations that

could be conducted might include tests to determine: full-scale propeller characteristics, either with a free mounting or when mounted adjacent to full-size slipstream obstructions, the data obtained including all scale and installation factors;

performance of engine-propeller units mounted in full-size fuselages; the cooling

capacity of, and the heat distribution throughout the cylinders of air-cooled

engines when mounted with cowling in full-size fuselages; full-scale radiator per-
590 Chapter 2: Building a Research Establishment

formance under all conditions of mounting in or near a full-size fuselage (nose,

wing, and retractable mountings; drag characteristics of full-size landing gears

assembled to fuselage, the investigation to include a study of the retractable type

looking toward its general adoption; comparative performance of direct-driven

and geared propellers, gear efficiency included in results; the efficiency and general operating characteristics of adjustable and variable pitch propellers; drag

characteristics of full-size fuselages with a view to increasing the efficiency of

design; parasite resistance of full-size airplane parts either independently or in

assemblies; effect on airplane characteristics of such equipment as spoiler gears,

variable camber wings, etc., and the behavior of empenage assemblies (reference

is made to recent tests with the MO-1 tail unit).

One of the greatest benefits to be derived from the construction of a giant

wind tunnel would be its utilization in connection with the investigation of certain

power plant problems.

In connection with our analysis of airplane performance, the outstanding

need at present is a means for determining the power output during flight of normal, over-compressed and throttled, supercharged and geared engines. All of

these types of engines either are being investigated at the present time or are

included in our immediate future program of tests. As the purpose of the present

and proposed tests is to arrive at a definite answer as to the most efficient power

plant unit, it is extremely essential that means be provided for determining power

output during flight. In lieu of a suitable torque-meter, propellers, calibrated as

installed in the airplane, would serve the purpose. A giant wind tunnel would provide

a means for supplying the required propeller calibrations. 

The determination is a giant wind tunnel of the performance characteristics

of engine-propeller units mounted in full-size fuselages, complete with radiator

installation, et al, would aid materially in arriving at the efficiency of a given

power plant installation. There is some question as to whether or not accurate

torque and thrust measurements could be made with the vibrations of the engine

imposed on the measuring devices, but if the effect of engine vibrations could be

reduced to a negligible amount, the proposed method of engine-propeller calibration would seem to have many possibilities. It is thought that the problem of

handling the engine exhaust would not be serious. 

A giant wind tunnel would serve directly as a means for studying air-cooled

engines. If the required accuracy of measurement could be secured, a great

advantage would accrue from the direct testing of air-cooled engine-propeller

units mounted with cowling in full-size fuselages. We have felt the need for investigating such problems as heat distribution throughout air-cooled engine cylinders,

effect of fuel mixture on cylinder temperature, effect of cylinder temperature on

power, etc., in connection with our tests with the supercharged Lawrance J-1
Document 2-21(a–c) 591

engine, but have been unable to make any such tests due to lack of equipment. A

giant wind tunnel might serve to supplant the immediate necessity for securing

special equipment for testing air-cooled engines.

The study of adjustable and variable pitch propellers is tied up directly with

the power plant problem, especially with the supercharged engine problem. In

light of present knowledge, it would seem that variable pitch propellers must be

developed into safe and efficient units if the ultimate advantages of the supercharged engine are to be realized. In our tests with the Roots supercharger we

have felt a definite need for the variable pitch propeller, especially for high altitude operation. These two types of propellers could be carefully studied in a giant

wind tunnel, whereas their characteristics could not be investigated efficiently, if

at all, in a small model due to the difficulty of reproducing them to a small scale. 

In conclusion, I concur with the general opinion that the tentative size (20 ft.)

of the proposed tunnel be increased to such a size as to enable certain of the

smaller size airplanes, or specially built small size airplanes, being tested therein

in toto, and to permit accurate testing of large propellers (we are at present using

a propeller having a diameter of 13 ft.) such as are used with geared engines.

[signed] Arthur W. Gardiner

Arthur W. Gardiner,

Assistant Aeronautical Engineer

Langley Field, Va.

April 23, 1925.

Document 2-21(c), Smith J. DeFrance, The NACA Full-Scale 

Wind Tunnel, NACA Technical Report No. 459, 1933.

SUMMARY

This report gives a complete description of the full-scale wind tunnel of the National

Advisory Committee for Aeronautics. The tunnel is of the double-return flow type with a 30

by 60 foot open jet at the test section. The air is circulated by two propellers 35 feet 5 inches in diameter, located side by side, and each directly connected to a 4,000-horsepower slipring induction motor. The motor control equipment permits varying the speed in 24 steps

between 25 and 118 miles per hour. The tunnel is equipped with a 6-component balance

for obtaining the forces in 3 directions and the moments about the 3 axes of an airplane. All

seven dial scales of the balance system are of the recording type, which permits simultaneous

records to be made of all forces.

The tunnel has been calibrated and surveys have shown that the dynamic-pressure distribution over that portion of the jet which would be occupied by an airplane having a wing

span of 45 feet is within ± 1 1/2 per cent of a mean value. Based on the mean velocity of

118 miles per hour at the jet, the ratio of the kinetic energy per second to the energy input
592 Chapter 2: Building a Research Establishment

to the propellers per second is 2.84. Since it is generally recognized that a long open jet is

a source of energy loss, the above figure is considered very satisfactory.

Comparative tests on several airplanes have given results which are in good agreement

with those obtained on the same airplanes in flight. This fact, together with information

obtained in the tunnel on Clark Y airfoils, indicates that the flow in the tunnel is satisfactory and that the air stream has a very small amount of turbulence. 

INTRODUCTION

It is a generally accepted fact that the aerodynamic characteristics of a small

model can not be directly applied to a full-sized airplane without using an empirical

correction factor to compensate for the lack of dynamic similarity. Two methods

have been used to overcome this difficulty. One is to compress the working fluid

and vary the kinematic viscosity to compensate for the reduction in the size of the

model. This method is used in the variable-density wind tunnel where tests can

be conducted at the same Reynolds number as would be experienced in flight.

The other method is to conduct tests on the full-scale airplane.

The variable-density wind tunnel offers a satisfactory means for testing the

component parts of an airplane and is particularly suitable for conducting fundamental research on airfoil sections and streamline bodies. However, this equipment

has its limitations when the aerodynamic characteristics of a complete airplane

are desired, especially if the effect of the slipstream is to be considered. It is practically impossible to build a model of the required size that is a true reproduction

of a complete airplane. This difficulty is increased by the requirement that the

model withstand large forces.

It is apparent that the most satisfactory method of obtaining aerodynamic

characteristics of a complete airplane is to conduct a full-scale investigation.

Heretofore such investigations have been conducted only in flight. Because of the

variation in atmospheric conditions, it has been necessary to make a large number

of check flights to obtain enough data to average out the discrepancies.

Furthermore, in flight testing the scope of experiments is often limited by the fact

that the possible alterations that can be made are restricted to those that do not

seriously affect the weight or airworthiness of the airplane. In order to provide a

means of full-scale investigation by which the conditions can be controlled and

alterations made without serious limitations, the full-scale wind tunnel has been

erected. Of course, only the steady-flight conditions can be readily investigated in

the wind tunnel, but the execution of this work in the tunnel will facilitate full-scale

testing and allow the flight-research personnel of the laboratory to concentrate on

those problems possible of solution only in flight.

The full-scale wind tunnel may be used to determine the lift and drag characteristics of a complete airplane, to study the control and stability characteristics
Document 2-21(a–c) 593

both with and without the slipstream, and to study body interference. In addition,

equipment has been installed to determine the direction and velocity of the flow

at any point around an airplane. Aircraft engine cooling and cowling problems

can also be investigated under conditions similar to those in flight.

The design of the full-scale wind tunnel was started in 1929. Since this was to

be the first wind tunnel constructed with an elliptic throat and with two propellers

mounted side by side, a 1/15-scale model was constructed to study the flow problems.

Very satisfactory flow conditions were obtained in the model tunnel. This piece of

equipment is now being used for small-scale testing. Construction of the full-scale

wind tunnel was started in the spring of 1930; it was completed and operated for

the first time in the spring of 1931.

DESCRIPTION OF TUNNEL

The general arrangement of the tunnel is shown in figure 1 and an external view

of the building is given in figure 2. The tunnel is of the double-return flow type with

an open throat having a horizontal dimension of 60 feet and a vertical dimension

of 30 feet. On either side of the test chamber is a return passage 50 feet wide, with

the, height varying from 46 to 72 feet. The entire equipment is housed in a structure, the outside walls of which serve as the outer walls of the return passages. The

overall length of the tunnel is 434 feet 6 inches, the width 222 feet, and the maximum height 97 feet. The framework is of structural steel and the walls and roof

are of 5/16-inch corrugated cement asbestos sheets. The entrance and exit cones

are constructed of 2-inch wood planking, attached to a steel frame and covered

on the inside with galvanized sheet metal as a protection against fire.

Entrance cone.—The entrance cone is 75 feet in length and in this distance

the cross section changes from a rectangle 72 by 110 feet to a 30 by 60 foot elliptic

section. The area reduction in the entrance cone is slightly less than 5:1. The shape

of the entrance cone was chosen to give as far as possible a constant acceleration

to the air stream and to retain a 9-foot length of nozzle for directing the flow.

Test chamber.—The test chamber, in which is located the working section of

the jet, is 80 by 122 feet. The length of the jet, or the distance between the end

of the entrance cone and the smallest cross section of the exit-cone collector, is 71

feet. Doors 20 by 40 feet located in the walls of the return passage on one side

provide access for airplanes. In the roof of the test chamber are two skylights, each

approximately 30 by 40 feet, which provide excellent lighting conditions for daytime operation; eight 1,000-watt flood lights provide adequate artificial illumination for night operation. Attached to the roof trusses and running across the test

chamber at right angles to the air stream and also in the direction of the air

stream are tracks for an electric crane which lifts the airplanes onto the balance.

Exit cone.—Forward of the propellers and located on the center line of the

tunnel is a smooth fairing which transforms the somewhat elliptic section of the
594 Chapter 2: Building a Research Establishment
Document 2-21(a–c) 595

single passage into two circular ones at the propellers. From the propellers aft, the

exit cone is divided into two passages and each transforms in the length of 132 feet

from a 35-foot 6 1/2-inch circular section to a 46-foot square. The included angle

between the sides of each passage is 6°.

Propellers.—The propellers are located side by side and 48 feet aft of the

throat of the exit-cone bell. The propellers are 35 feet 5 inches in diameter and

each consists of four cast aluminum alloy blades screwed into a cast-steel hub.

Motors.—The most commonly used power plant for operating a wind tunnel

is a direct-current motor and motor-generator set with the Ward Leonard control

system. For the full-scale wind tunnel it was found that alternating current slipring induction motors, together with satisfactory control equipment, could be

purchased for approximately 30 per cent less than the direct-current equipment.

Two 4,000-horsepower slip-ring induction motors with 24 steps of speed between

75 and 300 r.p.m. were therefore installed. In order to obtain the range of speed

one pole change was provided and the other variations are obtained by the introduction of resistance in the rotor circuit. This control permits a variation in air

speed from 25 to 118 miles per hour. The two motors are connected through an

automatic switchboard to one drum-type controller located in the test chamber.

All the control equipment is interlocked and connected through time-limit relays,

so that regardless of how fast the controller handle is moved the motors will

increase in speed at regular intervals.

The motors are provided with ball and roller bearings, which reduce the friction

losses to a minimum. Roller bearings of 8.5- and 11.8-inch bores are provided at

the slip-ring and propeller ends respectively, while the thrust of the propellers is

taken on a ball bearing at the rear end of each motor shaft. The motors are

mounted with the rotor shafts centered in the exit-cone passages. The motors and

supporting structure are enclosed in fairings so that they offer a minimum resistance

to the air flow.

Guide vanes.—The air is turned at the four corners of each return passage

by guide vanes. The vanes are of the curved-airfoil type formed by two intersecting

arcs with a rounded nose. The arcs were so chosen as to give a practically constant

area through the vanes.

The vanes at the first two corners on back of the propellers have chords of 7 feet

and are spaced at 0.45 and 0.47 of a chord length, respectively. Those at the

opposite end of the tunnel have chords of 3 feet 6 inches and are spaced at 0.41

of a chord length. By a proper adjustment of the angular setting of the vanes, a

satisfactory velocity distribution has been obtained and no honeycomb has been

found necessary.

Balance.—The balance, which is of the 6-component type, is shown diagrammatically in figure 3. Ball and socket fittings at the top of each of the struts A hold
596 Chapter 2: Building a Research Establishment

the axles of the airplane to be tested; the tail is attached to the triangular frame

B. These struts are secured to the turntable C, which is attached to the floating

frame D. This frame rests on the struts E, which transmit the lift forces to the

scales F. The drag linkage G is attached to the floating frame on the center line

and, working against a known counterweight H, transmits the drag force to a

scale J. The cross-wind force linkages K are attached to the floating frame on the

front and rear sides at the center line. These linkages, working against known

counterweights L, transmit the cross-wind force to scales M. In this manner forces

in three directions are measured and by combining the forces and the proper

lever arms, the pitching, rolling, and yawing moments can be computed.
Document 2-21(a–c) 597

The scales are of the dial type and are provided with solenoid-operated printing

devices. When the proper test condition is obtained, a push-button switch is momentarily closed and the readings on all seven scales are recorded simultaneously,

eliminating the possibility of personal errors.

The triangular frame B is caused to telescope by electrically operated screws which

raises and lowers the tail of the airplane and thereby varies the angle of attack. By

a similar mechanism the turntable C can be moved so as to yaw the airplane from

20° left to 20° right.

The entire floating frame and scale assembly is enclosed in a room for protection

from air currents and the supporting struts are shielded by streamlined fairings which

are secured to the roof of the balance room and free from the balance. In figure

4 it can be seen that very limited amount of the supporting structure is exposed to

the air stream. The tare-drag measurements are therefore reduced to a minimum.

Survey equipment.—Attached to the bottom of the roof trusses is a 55-foot

structural steel bridge (fig. 5), which can be rolled across the full width of the test

chamber; mounted on this bridge is a car which can be rolled along the entire

length. Suspended below the car is a combined pitot, pitch, and yaw tube which

can be raised or lowered and pitched or yawed by gearing with electrical control
598 Chapter 2: Building a Research Establishment

on the car. This arrangement permits the alinement of the tube with the air flow at

any point around an airplane. The alinement of the tube is indicated by null readings

on the alcohol manometers connected to the pitch and yaw openings in the head

and the angle of pitch or yaw is read from calibrated Veeder counters connected

to the electric operating motors. This equipment is very valuable for studying the

downwash behind wings and the flow around the tail surfaces of an airplane.

CALIBRATIONS AND TESTS

The velocity distribution has been measured over several planes at right

angles to the jet, but the plane representing approximately the location of the wings

of an airplane during tests was most completely explored. The dynamic-pressure

distribution over the area that would be occupied during tests by an airplane with

a wing span of 45 feet is within ±1? per cent of a mean value. It is possible to

improve the distribution by further adjustment of the guide vanes. However, tests

already conducted in the tunnel indicate that the present distribution does not

detrimentally affect the results. This fact has been shown by the excellent agreement

which has been obtained between the tunnel and flight results.

A survey of the static pressure along the axis of the tunnel showed that the

longitudinal pressure gradient is small, as evidenced by the fact that between 11 and
Document 2-21(a–c) 599

36 feet from the entrance cone the variation of the static pressure is within ± 1 per

cent of the mean dynamic pressure at the test section.

Two wall plates with static orifices are located in each return passage just

ahead of the guide vanes at the entrance-cone end of the tunnel. The orifices are

connected by a common pressure line, which is led to a micromanometer on the

control desk in the test chamber. The other side of the manometer is left open to

the test-chamber pressure. This installation has been calibrated against the average

dynamic pressure determined by pitot surveys of the jet at the test location and it

is used to determine the dynamic head during tests.

A series of Clark Y airfoils of the same aspect ratio, but with spans of 12, 24, 36,

and 48 feet, have been tested at the same Reynolds number to determine the jetboundary correction. Tests have also been made to determine the blocking effect

of an airplane in the jet. The results of the complete investigation will be presented in a separate report.

Using the mean velocity across the jet of 118 miles per hour for computing

the kinetic energy per second at the working section and dividing this by the

energy input to the propellers per second gives an energy ratio for the tunnel of

2.84. This ratio, considering the length of the open jet, compares very favorably

with the most efficient open-throat tunnels now in operation and exceeds the efficiency expected when the tunnel was designed.
600 Chapter 2: Building a Research Establishment

Before force measurements are made on an airplane, the airplane is suspended from the roof trusses by cables and held within one half inch from the balance

supports while the tare forces are measured. The tare-drag coefficient determined

in the above manner has been of the order of 25 per cent of the minimum drag

coefficient of the airplanes tested.

When testing airfoils the airplane supports are replaced by those shown in

figure 6. The angle of attack is changed by displacing the rear support arms and

rotating the airfoil about pins in the top of the main supports. The rear support

arms are moved by linkages, which are connected to long screws on the back of

the main supports, and the screws are operated by hand cranks inside the balance

house. The tare drag of this support system is exceptionally small and amounts to
Document 2-21(a–c) 601

only 3 per cent of the minimum drag of a 6 by 36 foot Clark Y airfoil.

The lift and drag characteristics have been measured in the tunnel on several

airplanes which had been previously tested in flight and their polars determined.

These tests were conducted to obtain a check between the tunnel results and those

from flight tests. A comparison of the results from the two methods of testing for

one of the airplanes, the Fairchild F-22, is shown in figure 7. The wind-tunnel

results are shown by the solid lines and the flight results are presented by the

experimental points. These curves are representative of the results obtained with

the different airplanes.

The agreement that has been obtained between the flight and full-scale tunnel

results, together with the consistent manner in which measurements can be

repeated when check tests are made, has demonstrated the accuracy and value of

the equipment for aeronautical research.

LANGLEY MEMORIAL AERONAUTICAL LABORATORY,

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS,

LANGLEY FIELD, VA., March 13, 1933.
602 Chapter 2: Building a Research Establishment

Document 2-22

Max M. Munk, memorandum on “Recommendations 

for New Research,” 16 November 1926, AV400-1, 

LaRC Correspondence Files, NARA, Philadelphia, PA.

This letter from Max Munk, chief of the Aerodynamics Division at Langley,

to George Lewis, the NACA’s director for research in Washington, furnishes an

intriguing glimpse into Munk’s vision for himself and the Langley Laboratory.

Five days earlier, Lewis had issued instructions that all recommendations for new

research projects from the Langley technical staff be forwarded to his office, via

the engineer-in-charge, for consideration by the appropriate subcommittee.

While this appeared to be an innocuous request to streamline the process, Munk

took decided issue with a process that could bypass him. Noting that Langley was

“at present pretty well filled up with problems; we are really overstocked,” Munk

downplayed the need for the Langley staff to make such recommendations. He

expressed concern over his staff ’s need to instead focus “the fullest amount of

thought and interest” on current projects, and suggested that a staff member

should only propose projects “derived directly from the problem he is engaged in

at the time.” Such suggestions from subordinates would, of course, be reviewed by

Munk. Given Munk’s uncompromising faith in himself and his commanding

methods, one senses that this may have been more of an effort to retain control

over the research program at Langley than an expression of real concern over

workload and a possible compromise of research quality.

Document 2-22, Max M. Munk, memorandum on 

“Recommendations for New Research,” 1926.

November 16, 1926

Comment of Dr. Munk.

Subject: Recommendation for new research.

Reference: NACA Let. Nov. 11, 1926. 21-1.

1. The type of wings of reference has been discussed at the last meeting of the

Subcommittee on Aerodynamics.

2. As a comment to the memorandum of Mr. E. G. Reid, and to Mr. Lewis’ letter,

I wish to call to Mr. Reid’s and to Mr. Lewis’ attention, that we are at present pretty

well filled up with problems, we are really overstocked. Each problem should

receive the fullest amount of thought and interest and should be carried through

as far as can be. Otherwise, we might degenerate into a mere test factory. From
Document 2-22 603

this point of view it is desirable to have only as many problems being turned over

from outside as absolutely necessary. It is further desirable that each staff member propose chiefly such new problems as are derived directly from the problem

he is engaged in at the time. Otherwise, the conclusion can not be avoided that

he does not concentrate his entire mind on his problem; and furthermore, he is

less prepared to know about the desirability of his proposed problem, if it does

not belong to his present work in investigating.

3. To sum up, we need on the side of our staff members the serious will and

the intense interest necessary to solve problems, rather than reflecting on new

problems to be solved by somebody else.

[signed] Max M. Munk

Technical Assistant
604 Chapter 2: Building a Research Establishment

Document 2-23(a–b)

(a) Daniel Guggenheim, letter to Secretary of Commerce

Herbert Hoover, 16 January 1926, reprinted by Reginald M.

Cleveland in America Fledges Wings (Chicago: Pittman

Publishing Co., 1942), pp. 3–7.

(b) California Institute of Technology, “Development of

Aeronautics,” August 1926, Historical Files, Folder A1.1,

California Institute of Technology Archives, Pasadena, CA.

While the Federal government’s investment in aeronautical research facilities

grew throughout the 1920s, other wind tunnels were built with private funding.

While “airmindedness” and a general interest in the possibilities of commercial

aviation were on the rise during this period, no one could be sure of its future.

Flying remained a risky business, and aircraft manufacturers found it difficult to

attract investment capital until some of the safety issues could be resolved. There

was a pressing need for trained aeronautical engineers in 1925, but only five

American schools offered aeronautical-engineering courses, and among them

only MIT and the University of Michigan awarded degrees in aeronautical engineering. Such programs required wind tunnel laboratories for instruction and

research, but the colleges were either private or state institutions and Federal

funding was generally unavailable in the mid-1920s.

Into this void stepped Harry Guggenheim and his father, Daniel. Daniel

Guggenheim was an American businessman who, along with his brothers, had

acquired a large fortune managing mining operations started by his father. Harry,

who had served as a pilot during World War I and maintained a keen interest in

aviation after the war, determined that a committee of wealthy men should underwrite

research that would lead to safer airplanes. Over lunch one day, the younger

Guggenheim heard of a plan by New York University to raise $50,000 to endow a

new aeronautical engineering program. Rather than a public appeal, he proposed

that New York University Chancellor Elmer E. Brown write his father—Harry would

personally deliver the letter—and request a gift from the Guggenheim family.

Rather than involve his brothers, the elder Guggenheim decided to make the donation himself, and NYU opened its Guggenheim School of Aeronautics in 1925. 

Daniel Guggenheim soon began to think beyond NYU, however, and in a letter

to Commerce Secretary Herbert Hoover he offered to underwrite a larger, nationwide

program, the Daniel Guggenheim Fund for the Promotion of Aeronautics, and

endow it with $2,500,000, a substantial sum for the day. Established in 1926, the
Document 2-23(a–b) 605

Guggenheim Fund relied on a board of distinguished aviation personalities to

determine the fund’s distributions. Between 1926 and 1930, the Guggenheim

Fund awarded major grants totaling $1,693,000 to seven engineering schools: the

California Institute of Technology (Caltech), Leland Stanford University, the

University of Michigan, MIT, the University of Washington, the Georgia Institute

of Technology (Georgia Tech), and the University of Akron. A large portion of

these grants went into construction of wind tunnel laboratories, but, significantly,

some funds were earmarked for the hiring of exceptional professors and

researchers. A Guggenheim grant allowed Clark and Robert Millikan to woo

Theodore von Kármán, Germany’s outstanding theoretical aerodynamicist (and

Prandtl protégé), into moving to California and assuming the directorship of

Caltech’s Guggenheim Aeronautical Laboratory (GALCIT), where he would play

a dominant role in shaping the growth of theoretical aeronautics in the United

States. While the Guggenheim wind tunnels were generally unremarkable,

exhibiting no significant technical innovations, they were a vital part of programs

that began to supply the professional engineering talent that American aviation

so badly needed. By midcentury, over 90 percent of the nation’s leading aeronautical engineers were graduates of Guggenheim-funded colleges.

Document 2-23(a), letter from Daniel Guggenheim to Herbert Hoover, 1926.

Honorable Herbert Hoover

Secretary of Commerce

Washington, D. C.

My Dear Mr. Secretary:

Under your general direction the United States Government has made substantial progress in the promotion of civil aviation. I am venturing to advise you,

therefore, by this letter, of my purpose to establish a Fund which will cooperate

with you and with all agencies of the Government and the public generally in

advancing the art and science of aeronautics and aviation.

This action is taken particularly in view of the very wise endorsement by the

President of the United States of the recommendation by the National Advisory

Committee for Aeronautics that a Bureau of Air Navigation be established in the

Department of Commerce. President Coolidge stated that: 

“The outstanding weakness in the industrial situation as it affects national

defense is the inadequacy of facilities to supply air service needs. The airplane

industry in this country at the present time is dependent almost entirely upon

Governmental business.”

The Department of Commerce, in studying the need for commercial aviation,

reported:
606 Chapter 2: Building a Research Establishment

“There are indications of a great change in the last few months which has

given an impetus to plans for developing American civil aeronautics that is bound

to produce permanent results. The extent of our country, its physical characteristics and its intimate contact with Canada, Mexico, and the West Indies are such as

to make air service highly desirable. The success of the transcontinental air mail

service operated by the Post Office Department and the general approval which

has greeted its operations indicate that the choice of a method for developing

civil aeronautics in the United States is the question demanding immediate solution. There is every reason to hope that before the end of the present year, civil

aviation in the United States will have taken a long step forward toward a position

of permanent security.”

You, yourself, have pointed out that a Government public service must be

provided to cooperate with aviation in a manner comparable to the cooperation

our Government now gives to shipping, and you have very properly pointed out that

without such service “aviation can only develop in a primitive way.” There is undoubtedly a function in this situation which the Government alone can perform.

I have also been much impressed by the question raised and the answer

given, in the report of the President’s Aircraft Board which, as of November 30,

1925, said:

“How can the civilian use of aircraft be promoted? This . . . may well be the

most important question which aviation presents in its far-reaching consequences

to our people. A great opportunity lies before the United States. We have natural

resources, industrial organization, and long distances free from customs barriers.

We may, if we will, take the lead in the world, in extending civil aviation.”

Such considerations as the foregoing have convinced me that there is a function

which can only be performed by private enterprise aside from the proper function

of the Government. So much remains to be done before civil aviation can realize

the possibilities before it, that everyone must recognize that there intervenes a

period of necessary study and experimentation. 

In these circumstances I have decided to establish the Daniel Guggenheim

Fund for the Promotion of Aeronautics and to place at its disposal the sum of

$2,500,000. The Fund will be administered by a Board of Trustees composed of men

of eminence and competence. 

I shall place the sum of $500,000 immediately in the hands of the trustees to

defray the expense of their studies and any work they may decide immediately to

undertake. In addition, I will hold myself in readiness to supply any additional

sum, up to a total of a further $2,000,000 as and when the judgment of the

trustees may indicate that the money can be used wisely to promote the aims of

the Fund. The trustees will have unrestricted power to do anything which in their

judgment may develop aeronautics, the only condition being that the Fund shall
Document 2-23(a–b) 607

not be a profit-making enterprise. Any earnings the Fund may realize from its

efforts will go back into the Fund to carry on the work for which it was created. 

The trustees are to have the power to spend the principal sum thus contributed and there is no purpose to establish a permanent foundation. The

thought is, rather, that, the whole art and science of aeronautics and aviation

being now in its infancy, it will be possible with the sums thus contributed, to bring

about such an advance in the art that private enterprise will find it practicable and

profitable to “carry on” and thus render a continuous and permanent endowment

for this purpose unnecessary.

You will perhaps recall that last year I established a School of Aeronautics at

New York University, my desire in making that gift being more quickly to realize

for humanity the ultimate possibilities of aerial navigation, and to give America the

place in the air to which her inventive genius entitles her. This school is already

making gratifying progress, and the studies that have been made in connection

with it have indicated clearly the enormous field of opportunity which unfolds

itself to the pending development of air transportation. The establishment of

additional schools such as that at New York University may well be warranted in

the future. 

Among the most important objects which I would now like to see accomplished at the earliest possible moment is the development of opportunities for

new fields of employment for American young men. My family, as you know, has

long been identified with exploration beneath the earth. We have tried to assist in

development which would make mining more safe as well as more profitable, and

therefore, of the greatest economic and value. Not the least desirable results which

have followed from this effort have been the opportunities for the profitable

employment of able engineers and workmen generally. My hopes, therefore, are

that, through the impetus which the Daniel Guggenheim Fund for the Promotion

of Aeronautics will give, attractive opportunities for men to work and serve in the

air may develop far more rapidly than would otherwise be the case. 

The general purposes to which I trust the new Fund will devote itself may be

broadly defined as follows: 

1. To promote aeronautical education both in institutions of learning and

among the general public.

2. To assist in the extension of fundamental aeronautical science.

3. To assist in the development of commercial aircraft and aircraft equipment.

4. To further the application of aircraft in business, industry, and other economic and social activities of the nation.

I am hopeful without desiring in any sense to restrict their own freedom of

judgment, that the Trustees of the Fund will govern themselves as far as possible

by the following principles: 
608 Chapter 2: Building a Research Establishment

1. Restrict the work to civil activities.

2. Avoid duplication of effort with other aeronautical organizations.

3. Avoid work which is properly a Government function.

4. Plan carefully to concentrate effort and to carry an investigation or project

through to definite conclusions.

5. Maintain a simple, inexpensive directing organization depending on outside established agencies wherever possible, to carry out the aims of the Fund.

I have confidence that the Fund can serve an important purpose. Recent

events in the United States have stimulated much discussion of aviation. The time

is ripe for action. There is urgent need in our country for immediate, practical,

and substantial assistance to aviation in its commercial, industrial, and scientific

aspects. No less urgent is the need to awaken the American public, especially our

business men, to the advantages and possibilities of commercial aircraft—in a

word, to make the American public in a very real sense, “air-wise.”

In closing, Sir, may I express my delight at the intelligent and constructive

interest you yourself are manifesting in the development of aeronautics as one of

the most important new agencies of civilization. In making my deed of gift to the

trustees of the Fund, I shall accordingly request that the trustees cooperate with

your Department in every possible manner.

With best wishes, I am, Mr. Secretary,

Yours very truly,

Daniel Guggenheim

January 16, 1926

Document 2-23(b), California Institute of Technology, 

“Development of Aeronautics,” 1926.

DEVELOPMENT OF AERONAUTICS

It has been announced that the Daniel Guggenheim Fund for the Promotion

of Aeronautics has made a gift of $300,000 to the California Institute of Technology,

and an equivalent gift to Stanford University. News of this gift was received at the

California Institute in the following telegram from Harry F. Guggenheim,

President of the Daniel Guggenheim Fund:

“It gives me great pleasure as President of the Daniel Guggenheim Fund for

the Promotion of Aeronautics to advise you that the Trustees of the Fund have

authorized a grant amounting altogether to approximately $300,000 for the erection

of a permanent building at the California Institute of Technology to be devoted

to the study of aeronautics and including a provision of fifteen thousand dollars

a year for a term of years for the conduct of study and experiments in this rapidly

developing science and art. May I remark that this gift is made in recognition not
Document 2-23(a–b) 609

merely of the opportunities for study and research which the climatic and other

conditions in California make possible, but also as a tribute to the distinguished work

in science and education of yourself and associates, and because of our belief that you

are developing in Southern California an institution which is destined to make very

great contributions to the progress not only of our own country but of the whole world.”

On the basis of this gift the California Institute has established the Daniel

Guggenheim Graduate School of Aeronautics at the California Institute of

Technology, and there will be constructed immediately a new Aeronautics

Building containing a new ten-foot High-speed wind tunnel, the total construction

involving an expense of approximately $200,000.

The California Institute has just announced the programs:

1. The extension of the Institute’s theoretical courses in aerodynamics and

hydrodynamics, with the underlying mathematics and mechanics, taught by

Professors Harry Bateman, Edward T. Bell, and Paul S. Epstein.

2. The initiation of a group of practical courses conducted by the Institute’s

experimental staff in cooperation with the engineering staff of the Douglas

Airplane Company, with the aid of the facilities now being provided at the

Institute combined with those of the Douglas plant.

3. The initiation of a comprehensive research program on airplane and motor

design, as well as on the theoretical bases of aeronautics.

4. The immediate perfection of the new stagger-decalage, tailless airplane

recently developed at the Institute, primarily by one of its instructors in aeronautics,

A. A. Merrill, a radical departure from standard aeronautical design, which in

recent tests has shown promise of adding greatly to the safety of flying.

5. The establishment of a number of research fellowships in aeronautics at the

California Institute.

6. The building and testing, not only of models for wind tunnel work, but also

of full-size experimental gliders and power planes for free flight work.

It is considered of especial importance that the facilities of the Douglas

Airplane Company in Santa Monica, with its large corps of engineers, will be

added to those of the Institute for both instructional and research purposes in the

effort to make a center of the first importance in Southern California for the

development of both the theoretical and practical phases of aeronautics.

The Daniel Guggenheim Fund for the Promotion of Aeronautics was established

by Mr. Daniel Guggenheim last February with provision for supplying $2,500,000

as needed by the Fund, the Fund being unique among the great foundations of

the country in that its founder did not contemplate a permanent foundation but

merely provision for sums which would make possible experimentation and development in the field of aeronautics and aviation during the infancy of this art and

science as a civil enterprise.
610 Chapter 2: Building a Research Establishment

Last year Mr. Guggenheim established the School of Aeronautics at New York

University, with a principal fund of $500,000; and now one of the first acts of the

new Guggenheim Fund is to make financial provision of equal amount in order

that the scientific experience and the equable climatic conditions of California

may be utilized to supplement the work of eastern and European institutions in

the study of this important subject.

A further announcement was made today that Dr. von Karman of Aachen,

Germany, one of the foremost mathematical physicists and one of the most outstanding aeronautical engineers of Europe, has accepted the invitation of the

Daniel Guggenheim Fund to visit the aeronautical centers of this country in the

near future. He will go immediately to Pasadena for the sake of advising with the

aeronautical staff of the Institute, both as to the best type of aeronautical installation and as to the design of new planes already being perfected there.
Document 2-24(a–b) 611

Document 2-24(a–b)

(a) C. G. Grey, excerpts from “On Research,” 

Aeroplane 35, No. 21 (21 November 1928): 837–840.

(b) C. G. Grey, excerpts continued from “On Research,”

Aeroplane 35, No. 22, (28 November 1928).

Before the end of the 1920s, the American model for aerodynamics research

had become the standard by which much of the industrialized world judged its

own efforts. While the empirical and theoretical contributions of other nations,

particularly Great Britain and Germany, were substantial, critics condemned their

governmental agencies and longed for research organizations and facilities like

those in the United States. The criticism in England is especially interesting since

that nation’s Advisory Committee for Aeronautics served as the model for the

American NACA. In 1928, Aeroplane Editor C. G. Grey penned a two-part editorial in response to comments by C. W. Brett, managing director of Barimar Ltd.

Brett had called for an aeronautical research laboratory independent from the

government agencies, which he felt could not address the needs of independent

inventors. He proposed that it be funded and managed by a consortium of three

existing British aviation organizations. Grey agreed that such a facility was needed, but he doubted that Brett’s organization plan would work and instead called

for a wealthy benefactor to underwrite the facility, much like Daniel Guggenheim

had done in America. Such a laboratory never came to pass in England, but this

editorial called attention to the fact that “ad hoc” research—research focused on

solving practical problems, such as that practiced in American universities and the

NACA—had produced some outstanding results.

Document 2-24(a), C. G. Grey, excerpts from “On Research,” 1928.

AS THINGS ARE.

The official reply to Mr. Brett’s suggestion, if a Question were asked about it

in the House of Commons, would be that any inventor who has an idea, whether

patented or not, for the improvement of anything aeronautical, has only to take it

to the Air Ministry, and that if the official experts judge it to be of any value it will be

tested impartially on behalf of the Air Ministry either at the Royal Aircraft Establishment at Farnborough or at the National Physical Laboratory at Teddington.

But the trouble is, as Mr. Brett suggests, that the Air Ministry grant for purely

experimental work is in fact too small,—in spite of the half million or so pounds
612 Chapter 2: Building a Research Establishment

per annum spent by the R.A.E. at Farnborough. And so an undue amount of time

passes before experiments can be made.

The N.P.L. at Teddington is always far behind in its experimental work, owing

to pressure of work and likewise lack of money. Moreover it is not primarily interested

in aeronautics. And so aeronautical experiments have to take their turn with all

other branches of engineering.

As for the R.A.E., there is always the suspicion that if an inventor submits a

really good idea his invention may be held up for months, and even for years,

while the bright brains at Farnborough, who are in fact paid for producing new

ideas themselves, try to invent some better way of doing the same thing as the

inventor has done. Even when there is no suspicion of that sort the R.A.E. is so

busy experimenting with its own inventions that it does take a long time to test

anybody else’s. For example, the Pobjoy engine, which recently passed its type-test

successfully, was actually sent to Farnborough last March, and was only put

through its tests a few weeks ago.

The really wily inventor can, certainly, get his invention tested in other ways.

If he happens to have a friend on the spot he may have tests made at South

Kensington or at Cambridge, provided that his invention comes within the scope

of the experts at those places. Or if he is a good enough salesman (which few

inventors are) he may induce one or two manufacturers to test his invention in

their own experimental shops, or on their machines.

All these methods have their objections, and at the [finish] the inventor who

manages to get his invention properly tested within a reasonable time must be

something of a specialist in the gentle art of wangling,—without which in peace

as in war, achievement of a desired end is difficult.

Therefore there is a great deal to be said for Mr. Brett’s suggestion that a central and completely equipped laboratory and experimental station which exists

entirely by, with and from aviation is desirable. The only question is, who is going

to pay for it?

The Aircraft Industry certainly has not the money. And if it had the money,

individual members of the industry would certainly not cooperate in anything

which might help general progress and so help their rivals. The British Taxpayer

obviously could not be asked to fork out money for the purpose so long as there

are doles and pensions to be paid.

There remains then only the dim hope that some British millionaire, possibly

of extraneous origin, such as Sir Basil Zaharoff, who has already founded the

Chair of Aviation of the London University, might be induced to put his hand in his

pocket for the purpose much in the same way as that good hundred-per-cent

American, Mr. Daniel Guggenheim, has done in establishing the Daniel

Guggenheim Fund for Aeronautics.
Document 2-24(a–b) 613

[ . . . ]

WHAT RESEARCH MEANS.

Research is of two kinds, that which is known as basic research, and that which is

known as ad hoc research. In the former kind seekers after truth dig around blindly,

working on more or less established, scientific facts, in the hope that something

may turn up. In the latter kind deliberate research is made to discover a certain

thing,—ad hoc meaning “to this,” the word “object” or “end” being understood.

Occasionally in ad hoc research for one thing quite a different thing, or a different application of the same thing, may be discovered accidentally,—as, for

example, the usefulness of the Handley Page slot in assuring control below

stalling point, when in fact search was being made for a method of improving lift

and slowing landing speeds. Basic research may, by sheer luck, discover something which revolutionizes the whole industry, or science, with which it is concerned. But, on the whole, the cheapest and quickest way of making progress is

by means of ad hoc research.

That is just where the Americans have scored over us so far. Over and over

again their practical aeronautical engineers have started out with one definite end

in view, and they have pursued that end until they have got it.

The present improved performances of aircraft practically all over the World

is due primarily to the search for the proper stream-line shape of fuselages and

engine housings for high-speed racing machines in the Curtiss Company’s wind

tunnel. The Curtiss designs were brought to this country by Mr. C. R. Fairey five

years ago, and those lines dominate the design of the machines with the highest

performances all over the World.

Further search for improved performance, and consequent economy of running,

caused the invention of the high-pressure wind tunnel (300 lbs. to the square

inch) by a German engineer who was imported to the States just after the War.

And the high-speed wind tunnel with its air-stream of 100 miles an hour, and 20

feet diameter, which the American National Advisory Committee for Aeronautics

have at Langley Field was built because the N.A.C.A. wanted to experiment with

engines and airscrews on fuselages under flying conditions.

The N.A.C.A. has had its high-pressure wind tunnel for five years or so, and

it has discovered all kinds of things about interference effects as between fuselages

and planes and struts and undercarriages and tail units, of which we in this country

know but little. We are just beginning to build a high-pressure wind tunnel.

If only we had a completely equipped laboratory and full-scale experimental

station, such as Mr. Brett has suggested, and if we only had the money to run it,

regardless of expense, and if we only had the man at the top and a staff to spend

that money efficiently and to get results from it, we certainly could make as much

progress in the next five years as we are likely to make in the next twenty-five.
614 Chapter 2: Building a Research Establishment

This is said without belittling in any way the splendid work which is being done

by the Department of Supply and Research at the Air Ministry. There everything

possible is done, even to the point of being unconstitutional, to hasten experiments

and to urge research. But there are limits to what any Government Official can

do. And private enterprise has no limits except those imposed by finance.

Nor are there any limits to the things to be discovered, if Aviation is to progress

as it should. Next week we will consider some of these.—C.G.G.

(To Be Continued.)

Document 2-24(b), C. G. Grey, excerpt continued from “On Research,” 1928.

THINGS TO BE DISCOVERED

One of the interesting facts which has been discovered in the N.A.C.A.’s highspeed tunnel is that by totally enclosing a radial engine in cowling the speed of a

machine can be increased beyond anything which mere calculation would show to

be possible, and yet the engine can be kept cool. A machine of the popular cabinmonoplane type which, with a 200 h.p.Whirlwind engine and normal cowling

covering about three-quarters of it, has a speed of 125 m.p.h., has had its speed

up to up to 133 m.p.h. with complete cowling. And, incidentally, as photographs

show, the appearance of the machine is improved. 

Figures quoted in THE AEROPLANE recently from an American paper gave

the improvement as being from 118 m.p.h. to 137 m.p.h., and a scientific critic

proved that the higher speed was impossibly high. The true figures, as herein

quoted on reliable authority, are startling enough. No doubt they also could be

proved by pure or applied mathematics to be impossible. And quite possibly the

higher figure may be reached by further improvements.

Experiments have gone that far, but there is still more to be done in the way

of discovering what shape of cowling best suits particular forms of fuselages. Also

the shape of spinner which best suits particular forms of cowling has to be discovered,—and whether, with certain airscrews and cowling, any kind of spinner is

worthwhile has to be proved.

Then there are experiments to be made as to the best shapes of fuselage

which can be made big enough to include a cabin. And there is the question of

the best way of fixing a wing in relation to a cabin fuselage.

Naturally all our own experimentalists have been and still are engaged on

these problems. Some of them try to get there with slide rules and the Prandtl

Theory. Some of them try to do it in wind-tunnels with such low speeds that the

results may be quite misleading. And some of them try to do it on actual aeroplanes,

in which all sorts of errors are likely to occur because a combination of undercarriage,

wing, fuselage, engine, and cowling which gives a certain performance may have
Document 2-24(a–b) 615

that performance entirely upset by altering any one of the components, though

altering other components to fit in with the first alteration might give a vastly

improved performance. 
616 Chapter 2: Building a Research Establishment

Document 2-25(a–c)

(a) Frank A. Tichenor, “Why the N.A.C.A.?” 

Aero Digest 17, No. 6 (December 1930): 40, 124–134.

(b) Frank A. Tichenor, “The N.A.C.A. Counters,” 

Aero Digest 18, No. 2 (February 1931): 50, 122–126.

(c) Edward P. Warner, “Speaking of Research,” 

Aviation 30, No. 1 (January 1931): 3–4.

While the NACA’s continued expansion of its research programs and facilities

was generally applauded, both at home and abroad, it was not without controversy

and criticism. The NACA’s founding legislation had charged the committee to

“direct the scientific study of the problems of flight, with a view to their practical

solution,” but this mandate was interpreted differently by different people. By 1931,

the NACA tended to emphasize the last phrase, and its efforts were largely directed

toward finding practical solutions to well-known problems. Critics, including Aero

Digest Editor Frank Tichenor, argued that Congress intended something else

entirely. In two of his “Air—Hot and Otherwise” columns, Tichenor blasted the

NACA for its failure to continually generate new, purely scientific knowledge,

something he claimed its charter demanded. The NACA’s chief of aerodynamics,

Elton Miller, prepared a response for both his boss, Henry Reid, and Aviation

Editor (and NACA Committee on Aeronautics member) Edward Warner, who

based a rebuttal editorial on it. Although glossing over the fundamental science

issue, they countered that the NACA saw its development work as science with a

purpose, but legitimate science nonetheless. In truth, the argument was really

over the difference between science and engineering, a distinction frequently

missed in the era, even within ranks of the NACA. Tichenor’s criticism had little

long-term effect on the NACA, and Warner received numerous compliments for

his stand, but the exchange did serve to illustrate that aeronautical research had

come to play a visible, important, and growing role in aviation development, even

if it was not purely, or even primarily, one of fundamental science.
Document 2-25(a–c) 617

Document 2-25(a), Frank A. Tichenor, “Why the N.A.C.A.?” 1930.

AIR—HOT AND OTHERWISE

Why the N.A.C.A.?

By Frank A. Tichenor

HERE is a matter of such vital importance to the industry that we can not

write of it save with plain words of considerable solemnity. It is a matter to which

we respectfully would call the attention of the President. Indeed, we do so explicitly and respectfully, refraining from anything except such a statement as will

make facts clear.

In this period of industrial readjustment, particularly in the aviation industry,

our thoughts turn to a very important basis of technical enterprise, experimental

aeronautical research. A young industry is more dependent on research, and at

the same time less able to provide for it, than older and better established industries. Because the Government has been well aware of this situation, nearly all

aeronautic research in this country has been financed and carried on by the

Federal Government. Foremost in this activity has been the National Advisory

Committee for Aeronautics, for which Congress has provided funds. The

N.A.C.A. has obtained from Congress funds for the largest, the most splendidly

equipped and the most modern laboratories, and facilities for aeronautic

research. To all practical purposes aeronautic research in America means N.A.C.A.

research. Our thoughts turn in this hour to this research activity, and with full concern for conditions in the aeronautic industry, we ask ourselves whether the

N.A.C.A. has discharged its duty well, whether it has given to the industry the full

return to which it is entitled for these appropriations.

How greatly aeronautic progress depends upon research has indeed been

fully realized by those in charge of N.A.C.A. work, as is indicated in the annual

report of the N.A.C.A. for 1921 (page 5) :

“Substantial progress in aeronautical development must be based upon the application to the problems of flight of scientific principles and the results of research.”

Research activity of the N.A.C.A. has been going on for more than ten years.

The first appropriation for a wind tunnel having been made in 1917, this tunnel

was reported to have been completed in 1918. Experts tell us that a year is ample

time to build an ordinary small wind tunnel. Nevertheless, although the wind tunnel

was completed, it was not then put into operation. In 1919, the tunnel was again

reported not yet in operation. Finally, in 1920, the same tunnel originally reported

as finished in 1918, was once more reported as finished. The year 1920, therefore,

we are entitled to consider as the beginning of research activity, particularly inasmuch

as an engine laboratory and free flight test facilities had been announced as completed in 1919.
618 Chapter 2: Building a Research Establishment

This fact is important because the results of research can not be judged from

the activity of one day, or one month or even one year. After ten years of uninterrupted activity, however, with continuous liberal financial support, the N.A.C.A.

can be judged according to the results derived from its research work and an estimate

can be made of what we have a right to expect in the future. Let us, therefore,

review these results and ascertain what the N.A.C.A. has achieved.

The standard by which the results of research should be appraised is defined by

the N.A.C.A. itself. Repeatedly, its annual reports have stressed scientific research as

of paramount importance. For instance, almost all reports close like that of 1927

(page 76) : “Further substantial progress is dependent largely upon the continuous

prosecution of scientific research,” and farther below on the same page, “its (the

N.A.C.A.’s) work in the fields of pure and applied research on the fundamental

problems of flight.” The latest report, that for 1929, states (page 87) : “The most

important active influence upon aeronautics has been the farsighted and constructive policy of the Federal Government, liberally supported by Congress and

the President, in providing for the continuous prosecution of organized scientific

research.” In the 1926 report we find (page 69), “The more fundamental investigations are undertaken by the Committee in its own laboratory,” and (page 68),

“to conduct investigations of a truly scientific character.” (The italics are mine.)

We could easily quote other passages from N.A.C.A. publications to the same

effect. The N.A.C.A. is not an aircraft factory; it is not interested in the properties

or the development of any particular airplane. More general scientific investigations

are its domain. It is charged with the responsibility of furnishing information concerning aeronautics as a science.

Nor do the annual reports of the N.A.C.A. leave any doubt about what is

meant by “scientific research.” That of 1922 (page 48), defines the term clearly:

“By scientific research is meant the investigation by trained men in a properly

equipped laboratory of the fundamental phenomena of nature. . . . All progress

depends upon the acquisition of knowledge, of new knowledge. This can be

obtained only by long continued investigations directed by men who know the problems and the methods used for their solutions.”

Perhaps the best standard by which to judge the results of ten years of

N.A.C.A. research is in terms of returns for the funds spent. Even with a small

appropriation there is no upper limit to what can be obtained in the way of

research if that research is directed “by men who know. . . . ” There is, however, a

lower limit to what ought to be obtained for a given amount of money. It stands

to reason that we can expect more for an expenditure of $2,500 than for one of

$250, and more for one of $25,000 than for one of $2,500.

The N.A.C.A. has spent on each of its research items undertaken more than

$100,000, and we have a right to count on important results from $100,000
Document 2-25(a–c) 619

researches. This average expenditure for each problem investigated is computed

by dividing the sum of the money spent by the number of problems undertaken.

Thus far the N.A.C.A. has received $4,936,370 in appropriations. Approximately

$4,800.000 has been spent (presuming the expenditure of the whole sum of

$1,508,000 appropriated for 1930). The results of its research are laid down in

eighty-eight Technical Reports. All other N.A.C.A. Technical Reports contain

information obtained from outside sources, the N.A.C.A. acting only as publisher.

This means that more than $30,000 has been spent for each report on a research

project. It means much more per research, for at least four reports are always

issued on the same research. This would give $200,000 per research item.

Allowing for those research projects not yet completed for which no reports have

yet been published and allowing also deductions for other expenses of the

N.A.C.A., we are certainly justified in estimating that more than $100,000 has

been spent for each research undertaken. Since 1925, and until 1930, the annual

appropriation for the National Advisory Committee for Aeronautics has been

approximately $500,000. This year it was increased to $1,508,000. No one can

claim that during any one of the last four years more than five research problems

have been finished and the results made available to the public. One hundred

thousand dollars per research is perhaps too moderate an estimate.

It is pertinent to ask whether really useful scientific results have been obtained,

and if not, to inquire about the reasons why research so liberally supported failed

to furnish an adequate return. This sum can not be considered exorbitant if valuable

results have been obtained from it.

If we make a more detailed analysis of the N.A.C.A.’s research of the past ten

years, we find that it can be classified into wind tunnel research, free flight

research on actual airplanes, and engine laboratory research.

In the engine laboratory, tests have been conducted with a view to improving

the efficiency of gasoline aircraft engines by the choice of the best compression

ratios, richness, and mixtures, and the like. That work would be valuable if important

results had been obtained, but we doubt whether, lacking this research, any one

existing engine would be worse. To say the least, this study and experiment has

not been of a scientific nature. In addition, the Diesel engine was studied, likewise

not a scientific or new phenomenon, and no tangible results were achieved,

except possibly in the case of the spray research with solid injection.

The free flight researches gave valuable information concerning the maximum

accelerations and maximum pressures occurring in maneuvers. Also some practical

information regarding the ice hazard and similar subjects was obtained.

Apparently the only fact demonstrated in the study of the supercharger was that

such a device increases the available horsepower, and that was known before. This

can hardly be considered an outstanding success. On the whole it can, nevertheless,
620 Chapter 2: Building a Research Establishment

be said that the free flight research has been the most beneficial conducted by the

N.A.C.A. At the same time it can be said that no free flight test has been a scientific

test nor dealt with investigation of fundamental phenomena of nature. Test flights

conducted over a period of ten years, with the aid of good instruments, can not

but yield some valuable information, especially at a time when flying is new, but

they are not likely to advance fundamental science.

The class of wind tunnel research should correspond most to the description

“scientific.” Therefore, we ought to consider it in more detail in order to find there

at least some of the promised scientific work. In this category the pressure distribution

work of the N.A.C.A. showed only that wings should be rounded at the tips, which was

known before, and which could be and was demonstrated in the course of natural

industrial development. Merely to make pressure distribution measurements is not

scientific. We are sometimes inclined to believe that it would be better for wind

tunnel research if it were more difficult to do this kind of work; an abundance of

patience is necessary but not much creative mental effort. The results are not of

great practical value, because they are made under steady wind tunnel conditions,

whereas the largest pressures occur under unsteady flight conditions. For this reason,

the pressure measurements made in flight tests are much more valuable.

In addition there have been wind tunnel tests on complete airplane models,

and drag measurements on airplanes and airplane parts. This research can not

yield new results of general value, and is therefore outside the scientific research

the N.A.C.A. is charged to undertake.

During all of the ten years, much time and effort has been spent on a series of

tests undertaken to standardize wind tunnels throughout the world. This work showed

merely that different wind tunnels give slightly different results and that these differences can not be predictedæwhich facts we knew before. Tests referring to wind

tunnel technique are secondary anyhow. Someone has claimed that all wind tunnels could continue to do research even if no airplanes existed. They could, but

we would not accept such work as useful unless science had been advanced.

Propellers have been investigated and found to possess a certain thrust and

torque. Interesting, but again not scientific progress, not even technical progress.

We come at last to the research having most of the scientific element in

itæthat dealing with the rotating cylinder. This stirred the imagination when the

first tests were made and showed undreamed-of lifts. Right now, a very prominent

manufacturer is making experiments along that principle. Unfortunately, the first

tests along this line were not made by the N.A.C.A. On the contrary, the N.A.C.A.

refused a suggestion in 1921 to measure this phenomenon. Several years later, it

did repeat measurements made abroad without adding one new thought or result.

The Autogiro is the most painful subject in connection with the N.A.C.A.

research. The N.A.C.A. had the priority in this new and perhaps most important
Document 2-25(a–c) 621

invention of recent years. Autogiro models were investigated in 1922. It is hard to

believe, but nevertheless true, that these tests were never published in a Technical

Report. Five years later, after the practical value of the Autogiro had been demonstrated abroad, the results were published in mimeographed form, giving evidence

of an opportunity to contribute to scientific progress which was woefully neglected.

In the investigation of auto-rotation of wings, it was demonstrated that, in a

wind tunnel, wings can be made to rotate like windmills. This has hardly any bearing

on or connection with the spinning of airplanes. It can hardly be called a research,

but rather only making pretense of research. No airplane designer gives any attention

to such tests, and science rejects them entirely.

A study of boundary layer control is on the program of the N.A.C.A., according

to its statement, but no report has appeared in print on the results and we have not

been apprised of any progress. This should be the most important subject of the

work, but in fact hardly anything seems to have been done except the repetition

of some work abroad.

Finally there is the wing section research. This is the only line in which the

N.A.C.A. has contributed to aeronautics by way of its own experimental research.

The M wing sections were developed by the N.A.C.A., in its wind tunnel, and at least

two of them have been adopted in practice, being considered superior to older ones.

Accordingly, the N.A.C.A. report for 1924 (page 50) says: “satisfactory progress

has been made in the science of aerodynamics during the past year. . . . One important result of wind tunnel investigations has been the development of a number

of remarkably efficient wing sections of adequate thickness for economical structures. It is desirable that this development continue substantially along the present course.”

This was indeed desirable for the investigation was intended only as the first

and preliminary step of a more systematic research. Much better wing sections

were expected from the next series of tests, as the report indicates (page 59), “It is

believed that a fruitful field for research lies in the determination of these sections

which have a stable flow with good aerodynamic properties.” In the interim, however,

there has been no evidence of further work and the M section research, so

admirably begun, has never been, continued.

We do not believe that we have overlooked a major research item of the

N.A.C.A.: we are certain we have not overlooked a successful one. The N.A.C.A. was

officially awarded the congressional medal for its low drag cowling. Apparently, even

the friends of the N.A.C.A. consider this the most outstanding of the research

projects completed. Yet, in the true sense, this cowling work was a development

rather than an original work. Moreover, because it had reference to special airplanes

and engines, it can not be regarded as having general value. Therefore, it can not

be considered scientific work. It does not involve the study of new and fundamental

phenomena of nature. Its doubtful value in this connection is clearly contrasted
622 Chapter 2: Building a Research Establishment

with the research of similar aimthough along entirely different linescarried on at

the same time in England. The Townend Ring is definitely superior to the

N.A.C.A. cowling. It is the outcome of strictly scientific research carried on with

scientific spirit, involving the systematic exploration of new and fundamental

phenomena, and incurring relatively little expense. It represents more brain and

less expenditure than for the N.A.C.A. cowling research.

The results of the N.A.C.A. experimental research are not, in our opinion, an

adequate return for the money spent. There is hardly one research project of scientific value, and only a few of technical value. There is an enormous gap between

the principles of research laid down and those applied.

It can not be denied that there is keen feeling of disappointment throughout

the industry about the outcome of the N.A.C.A. research. Every year the industry

gathers at Langley Field to acquaint itself with the latest results of the research

going on, but every year it is presented with stone rather than with bread. New

laboratories and instruments are exhibited but no new results worth speaking of.

Responsibility for the N.A.C.A.’s failure to make substantial contributions to

aeronautic science does not rest entirely on the organization itself. General supervision of the research undertaken is in the hands of committees, which are composed of members serving without compensation. Under these circumstances,

they can not give much time to this research; and after all, they are not to be

blamed for its shortcomings. Scientific knowledge can not he amassed by a committee any more than an opera can be written by a committee. The capable and

patriotic members of the several research committees feel that they can give best

service by keeping their hands off, by assisting with advice and suggestion only,

without showing too much initiative.

The real responsibility would seem to rest, therefore, upon the director of

research. Is he one who knows “the problems and the methods used for their solution”? We fear not. But then it must be remembered that this director exercises

the direction of the research from a distance of 200 miles, and as an auxiliary duty

only. His primary duty, is that of an executive. In the first place he must practice

diplomacy and exercise organizing talent: only secondarily need he exhibit any

scientific spirit. Most of his direction of the research is done over the long-distance

wire, or on occasional visits. These facts, together with his normal duties which stand

in distinct contrast to the duty of research supervision, and require entirely different

capabilities, make it plausible to believe that the director of research is not in a position properly to discharge his duty. As one important reform that will improve the present conditions, we suggest that the Langley Field laboratory be separated entirely

from the Washington political office of the N.A.C.A. and be put in charge of a capable

research engineer who would be fully responsible for the research and for it only.

As it is, the true initiative must come from the local head of the laboratory,
Document 2-25(a–c) 623

and from the heads of the single divisions. We expect most from the aerodynamic

sections. It is now a fact that both positions, the head of the L.M.A.L. and of the

aerodynamics division, have been occupied in recent years by men who are decidedly

not research engineers at all. Neither of them has ever contributed anything to science,

and neither of them expects to do so. They are mere routine engineers, and hardly

that; they are mere bureaucrats, signing letters and unwrapping red tape.

This brings us to the question of the N.A.C.A. staff. Friends of the N.A.C.A.

have claimed that the staff has suffered great losses because the industry has

induced its best men to leave by offering them lucrative positions. This does not

sound probable. In the first place, a capable research engineer does not leave his

work if he has found favorable working conditions, and is progressing satisfactorily in his work. The fact that nearly all good research engineers have left the

N.A.C.A. constitutes in itself a reproach to the management. From inside information we know that most engineers left of their own initiative, because they were

dissatisfied with the management. They are now employed in industry, and most

of them did not leave as friends of the Committee. During these ten years, the

head of the laboratory at Langley Field has changed four times, and two and a

half years is about the average time the engineers used to stay. There must be a

reason for this state of flux in the personnel. Most of the research engineers are

young graduates, and the few older men who have stayed with the organization

are for the greatest part less capable than those who left. Jealousy and petty politics

have always played too great a part in the activities at Langley Field. The spirit of

research and scientific work was never really encouraged by the management.

Nobody can carry on research work successfully if he is compelled to devote a

great part of his time to fighting for the cooperation of others to which he has a

right, and fighting off the aggressiveness of his colleagues. The failure of the

National Advisory Committee for Aeronautics is the failure typical of so many

public organizations. There is no effective check on what is accomplished. If the

results of the N.A.C.A. could be computed according to their worth in dollars and

cents, the Committee would long ago have been bankrupt. But it is not a moneymaking organization; it is a money-spending organization. That leaves much

energy free, and unfortunately the conditions in such a case are favorable to the

survival of those most unsuitable for carrying on scientific research.

The activity of the N.A.C.A. has become a mere building of new laboratories

without distinct ideas of what to do with them after they are built, and it has

become a mere weighing and measuring of less value than the weighing of a grocery

clerk. No concerted efforts are made to advance science; no efforts are made to

apply the results of the tests to any logical system, to digest them, and to interpret

their significance in the sum of general knowledge. The truth is that the tests can

not be interpreted that way because the program has not been guided by scientific
624 Chapter 2: Building a Research Establishment

reasoning. Weighing for weighing’s sake is not scientific research, but at the best

a kind of indoor golf.

We urge that radical changes in the management be made with the view to

improving the conditions to the end that real and honest talent be attracted to

the N.A.C.A. Only then will there be some prospect of an intelligent use of the

research equipment and a reasonable return on the money spent.

Let’s devote a period of thought to wondering if these large appropriations

devoted to the N.A.C.A. have served, are serving, or will serve the industry.

Let’s hope that Congress, yes, and even the President of the United States,

will give consideration to the self-same subject.

Let us spend money, certainly—no detail of aviation should be stinted but let

us have men in charge of its expenditure who will see to it that the money which

we spend shall count.

Document 2-25(b), Frank A. Tichenor, “The N.A.C.A. Counters,” 1931.

AIR—HOT AND OTHERWISE

The N.A.C.A. Counters

Frank A. Tichenor

IN these columns in December, I reviewed the conditions prevailing in the

National Advisory Committee for Aeronautics which prevent it from functioning

in a manner useful to the best interests of the industry it purports to serve. The

discussion has disclosed evidence of widespread interest in this question. It

becomes ever more apparent that the points touched on have for some time been

a subject of concern to many. The importance of a wise and honest expenditure

of public funds appropriated specifically for scientific research and not for a

cheap substitute for it, is generally recognized. The conditions which urged us to

stress this vital phase of aeronautical development have found sympathetic

response among all who have at heart the good of aviation and the country.

The comments of those who concur in our contentions contain little that has

not already been said in these columns. As a matter of fact, little more can be said

concerning these conditions which have lasted so long and about which informed

public opinion fairly agrees. It was with interest and curiosity, however, that we

awaited replies of defenders of the present N.A.C.A. management. We had hoped

that some bright spots might be brought to shine on the otherwise dark picture,

that perhaps things are not quite as bad as they appeared to us. Unfortunately we

were disappointed in this hope. Although the management of the N.A.C.A. has

an advocate who apparently tries to defend its policy, actually he only concurs in

the broad picture which we painted. Indeed, we fear the picture is even darker

after his defense than it would have been without it. We are disposed to believe
Document 2-25(a–c) 625

now that conditions are even worse than we at first suspected, and that the trouble

is not only lack of ability, but also absence of an honest attempt to accomplish the

laudable task which the N.A.C.A., through its presiding body, has assigned itself.

This seems to be another case in which a feeble attempt to defend a weak

cause serves only to render its defects more vulnerable. It almost looks as though

the defender of the N.A.C.A. management in his own heart agrees with us; and

although he finds it expedient to depreciate our criticism, he writes as though he

himself would like to see reform effected. He does not call attention to one successful research, nor one scientific advancement which can be credited to the

N.A.C.A., nor even one technical advance which we may have overlooked. Nor

does he suggest that such advances can be expected in the near future. Indeed,

there is not even the assurance that they will eventually be forthcoming or that

anything is being done to hasten that day. Our principal criticism, the absence of

scientific research, is tacitly admitted. Such research, he contends, is the proper

sphere of universities, not of the N.A.C.A.

Now, we have not, merely as the result of our own judgment, specified scientific

research as the task of the N.A.C.A.; we quoted this as the N.A.C.A.’s task from

the Committee’s own annual reports. The defender of the N.A.C.A. can not logically

ignore this point altogether, as he does, for it is the most important consideration,

the keynote of the N.A.C.A.’s shortcomings. This is not a question of opinion

only: rather, it is far more a question of keeping faith, of loyalty to duties defined

by the supervising body of the N.A.C.A. The policy of conducting scientific

research was adopted ten years ago by the presiding Nominee Committee, made

up of the foremost experts of the country. In all annual reports since then, it has

been recorded as the accepted policy of this body. It has been pleaded for in hearings

before congressional committees. It has formed the basis for public appropriations.

Does the defender of the N.A.C.A. mean to imply that there is one policy for

obtaining appropriations and for general advertising and publicity purposes and quite

another one for the actual service and activity within the walls of the N.A.C.A.?

We are referring chiefly to a reply to our article expounded under the sponsorship

(and probably under the personal authorship) of one who is himself a member of

the supervising body of the N.A.C.A. Having been appointed by the President to

serve as a member of the group prescribing the policy of the N.A.C.A., he certainly

can not plead ignorance of that policy. His words would indicate that he is

opposed to the policy of scientific research, that he prefers something easier and

cheaper. If that is so, he can well argue that everyone has a right to an opinion of

his own. It is, however, one thing to advocate a change of policy and quite another

to advocate disobedience to a policy established by authority, laid before Congress

and the nation, for the execution of which policy appropriations have been made.

No ordinary citizen should advocate disobedience to rules established by authority;
626 Chapter 2: Building a Research Establishment

he ought rather to satisfy himself by urging and pleading for reforms. How much

more shocking is it that a member of the Committee should defend the management’s

activities when they are in direct contrast to the policies promulgated by the presiding body! Our opponent’s failure to acknowledge the authorized policy of the

Committee has greatly intensified our conviction that something is wrong with

the N.A.C.A.

We expected the defender of the N.A.C.A. to give us evidence (or at least to

try to give us evidence) that we had erred, and that the N.A.C.A. after all is true

to its avowed ideals. Instead he denounces these ideals, admitting thereby the justification of our criticism. He joins us so far as the facts are concerned; he concedes

the point that the N.A.C.A. has made no “contribution to pure science” and merely

tries to make that failure appear insignificant.

This thing is not insignificant, however. If money is appropriated for scientific

research, can we consider it of no consequence that those funds are spent for

something else? The presiding body of the N.A.C.A., Congress, the industry—all

of us expect the N.A.C.A. to be a bright torch of science; we have a right to expect

that. We know that a great national organization is needed as a guiding light for

a prosperous aviation industry, not as a satellite which merely reflects faintly the

illumination of more brilliant bodies. This point is not one for which compromise

can suffice. Either there is scientific research or there is not, and authority has

decreed that the N.A.C.A. should conduct scientific research.

Such is the defense the management of the N.A.C.A. summons, a defense

worse than none. It begins with mild mocking on the degree of courage necessary

for attacking scientists—as if any scientists were attacked. The absence of scientists

on the staff of the N.A.C.A. was attacked, and the politicians who occupy positions

rightfully belonging to scientists were attacked. Certainly it takes more courage to

defend their presence there than to criticize the absence of scientists. It takes

more courage to disclaim the policy laid down by authority of office and public

consent than to plead for it. It takes more courage to advocate a use of public

funds other than that for which they were appropriated. It takes more courage to

sacrifice the interest of the industry and to advocate administrative measures foreign

to American spirit than to ask for a clean policy. Pleading weakness and inability

to defend oneself in a case like this, where the defense would be easy if the criticism

were unjust, is inadvertently an admission of guilt. Where are the advances of science

made by the N.A.C.A. at Langley Field? Why not enumerate them, if there are

any, instead of lapsing into disputes about personal courage?

Let us review, in short, what results the champion of the N.A.C.A. is able to

point out. As the most conspicuous achievement, he mentions the Townend Ring

and the fuselage cowling, admitting that the N.A.C.A. did not invent the latter.

With the evolution of the cowling, the N.A.C.A. had nothing whatsoever to do. It
Document 2-25(a–c) 627

is nevertheless seriously suggested that neither cowling nor ring would have been

adopted by the industry had it not been for the N.A.C.A. The industry is alleged

to be so timid that the information about improvements available is not sufficient

to induce it to adopt them; the industry needs the guiding hand of the N.A.C.A.;

the industry does not trust and has no confidence in its own speed tests made by

its own pilots. The implication is that, instead, it waits until the N.A.C.A. measures

in pounds and ounces the diminishment of the drag in consequence of some

improvement and then computes the increase in the speed. The industry, it is

seriously alleged, has more confidence in such computed speed gain than in a

speed gain directly observed. How grotesque! We really have cause to admire the

courage of one who advances such opinions. He dignifies this business of measuring

by calling it “determination of relative merit,” which must have something to do

with the theory of relativity. At least we must confess that we fail to understand it fully.

As further useful research of the N.A.C.A., our attention is called to the pressure

measurements of floats. There is certainly some use in such measuring. A tailor

taking down the measurements of his customer also does something useful.

Measuring pressures is but a secondary duty of the N.A.C.A.; its chief duty is to

measure pressures (if any) in such a connection that scientific theory is advanced

thereby. This was not done in the case mentioned.

As a third citation of successful activity of the N.A.C.A., another pressure

measurement is mentioned, one which likewise failed to advance science—the

pressure measurement over the dirigible Los Angeles. Although genuine contribution to science is in fact not claimed for this work, it is contended that these measurements have proved indispensible for practical purposes, and that the new

Goodyear Navy airships will be stronger and lighter in consequence of them. We

doubt whether the design staff or the Goodyear-Zeppelin Company will agree.

The strength and weight of a dirigible depend upon structural improvements and

aerodynamic progress. The air force loadings assumed for the structure of a dirigible

are based chiefly on theoretical aerodynamic developments (to which no research

at Langley Field has ever contributed), together with one numerical factor, based

on operation experience. It is a curious fact that the Goodyear-Zeppelin Company,

after its experience with more than 120 airships, arrived at a different factor than

the U.S. Navy with its experience with two airships. A commendable research

project would have been an attempt to clear up that discrepancy. Instead, the

N.A.C.A. made some pressure measurements, leaving the whole question as it was

before. No harm done; dirigibles will continue to be improved without the assistance of the N.A.C.A. But, after all, why all the measurements?

It is obvious, therefore, that our arguments have been strengthened by those

of the advocate of the N.A.C.A. We stand in line with the supervising body of the

N.A.C.A. and insist with it that scientific research is the proper and chief domain
628 Chapter 2: Building a Research Establishment

of N.A.C.A. activity. We advocate that capable scientists be encouraged to join, not

to leave, the N.A.C.A. staff. We heartily agree with the able and patriotic chairman

of the N.A.C.A. that the N.A.C.A., to borrow his own words, “undertake investigations

directed by men who know the problems and the means of their solution” and

that such changes be effected as are necessary to bring this about. We insist that

is not the function of the N.A.C.A. to gape and squint at what others are doing,

like a loafer standing on the street, and do at best a little measuring to see

whether the work was done right, but that it should be the purpose of the

N.A.C.A. to do things itself. Aeronautics has not yet reached its goal. The final

shape of airplanes will eventually be quite different from what we have now. We

want that development hastened. We want a critical and scientific survey, an

exploration of all known possibilities. It may be possible (it probably is possible)

to increase the specific lift to ten times what we have now, and we want a central

institution of research to give us light on that. It may be possible to reduce the

specific drag to one-tenth what we have now; the theory of air motion producing

drag is still entirely in the dark. Friction of air, as such, does not account for more

than one-twentieth of actual drag. We want to have some light on that too. We

want knowledge concerning boundary control, concerning the effect of rotating

cylinders, of vibrating surfaces, of lubrication, of autogiros, of Flettner cylinder,

of jet action, of shooting action, of sound wave action, and of chemical action.

Indeed the possibilities are without limit. We want a national agency to explore

these unexplored regions, and to do so with scientific spirit, systematic thought,

and honest endeavor. We are not satisfied with useless pressure measurements

and with the building of wind tunnels which will never be really usefully

employed. Build small laboratories and do big things in them; not the other way.

Only then will the nation attain high rank in world aviation.

Our conviction as to the failure of the N.A.C.A. is not an original idea. The

conditions existing have been recognized by none other than General John J.

Pershing, who states in the third chapter of the story of his war experiences,

appearing in the New York Times, Wednesday, January 14, “...we had some fiftyfive training planes in various conditions of usefulness—all entirely without war

equipment. Of these planes it is amusing now to recall that the National Advisory

Committee for Aeronautics, which had been conducting an alleged scientific

study of the problem of flight. . . . ” General Pershing was in a position to know

and no one can question his sincerity.

Document 2-25(c), Edward P. Warner, “Speaking of Research,” 1931.

Nothing is easier, and nothing demands less courage, than attacking scientific

work for the benefit of a non-scientific audience. The general public, and even most
Document 2-25(a–c) 629

of us who are engaged in applying science to industry, have little understanding

of scientific theories or of laboratory work, and it is immensely consoling to feel

that people who pretended to be so much wiser than ourselves, and claimed to

“understand all that stuff,” were wrong all the time.

To assail the scientist is the safest of pursuits, for he has neither the inclination

nor the equipment for rebuttal. Reasoned and orderly discussion in reply to a vindictive assault on the caliber of work done in a laboratory is quite impossible

before an audience that has no background or experience of its own to give it an

understanding of the nature of the controversy.

The National Advisory Committee for Aeronautics has had its share of vilification.

Perhaps no answer, and not even passing comment, is necessary. The steady

growth of interest in the industry’s pilgrimages to Langley Field, annual since

1926, and the lively discussions that take place there, give evidence of the esteem

in which manufacturers and operators hold the N.A.C.A. Nevertheless it is worth

recalling how much influence that body’s activities have already had on American

aeronautical development. Let us take an example.

The venturi and ring cowlings are the most conspicuous of recent contributions

to aerodynamic efficiency. They are the exclusive invention of no individual or

group. Their genesis can be traced back at least to 1920. They have appeared in

various forms here and abroad,—but the most important single step in practical

application was the direct quantitative proof of the reduction in resistance they

permitted. Without the tests that were made at Langley Field, the new forms of

cowl might have been suggested and argued and perhaps tried in a small way, but

their general acceptance would have been a matter of many years. Even in

England, the original home of the ring, its adoption as a standard feature of airplane

design has been enormously accelerated by the American laboratory work, which

has given generalized in place of specialized results, and definite measurements

of resistance in place of speculations based on a measurement of maximum

speed. The most important function of the Committee, in short, was not to invent

a new type of cowling, but to determine the relative merits of all available types

and to make the determination on a scale which no other laboratory in the world

was prepared to duplicate.

It is a good general rule that there are three types of research work, and they

are adapted to three different types of organization. First, and in the very long run

most important, is contribution to pure science and underlying theory, perhaps

most generally the product of members of the staffs of educational institutions or

of laboratories endowed by private capital or by especially farsighted industries. At

the other extreme is the study directed to solve a particular and specialized problem

of particular design, or to lead directly to the invention of a new proprietary

device, and that is the proper sphere of the research department of a corporation.
630 Chapter 2: Building a Research Establishment

It is a sphere, be it said in passing, not as yet sufficiently exploited by American

airplane manufacturers, for in the face of the great affluence of the industry in

1928 and 1929 the absence of research departments in most airplane factories

remained a proper ground for surprised comment by foreign visitors and for

shame-faced acknowledgment by American engineers.

Between the two extremes there is a third class of work, the conduct of “practical”

studies, general but immediate in their application. That is the particularly fitting

task for a government laboratory.

To produce a theory of heat flow which will make it possible to calculate the

cooling characteristics of an air-cooled cylinder is the function of an individual

mathematical physicist, and it is on a college faculty that he will most often be

found. To determine the cause of repeated spark-plug failure in the XYZ engine is

the responsibility of the XYZ Engine Company. But to find out by actual measurement

on a group of typical engines how temperatures are typically distributed in cylinders

and how they are affected by changing conditions of flight, information that can

be applied to the XYZ engine or any other, is work most profitably to be undertaken for the general good, and for general dissemination of the results, by such

a body as the Advisory Committee.

The determination of design data may not be inspiring or spectacular. It does

not appeal to the imagination as does an invention, but it is extraordinarily

important. Without it, design does not progress.

The structural design of every airplane built in the United States today is

dependent to some degree upon the N.A.C.A. work on pressure distribution and

air loads in flight. The structure of seaplanes has gained a rational foundation for

the first time through the studies made on pressure distribution on float bottoms.

The airship being built at Akron will be a stronger and a lighter craft than would

be possible without the N.A.C.A. measurements on the Los Angeles. Examples

can be multiplied without number.

Science is a term that covers a multitude of widely different things. Not the

least important among them is the skillful devising of means for accumulating

data upon which the designers of engineering material may lean.

The Advisory Committee has acquired the material and the personnel to do

that work for American aviation, and has been doing it. Aeronautical engineers

in Europe are quick to express their envy of their American colleagues’ good fortune

in having at their disposal an institution of such resources.
Document 2-26 631

Document 2-26

Joseph S. Ames and Smith J. DeFrance, remarks at the 

dedication of the NACA Full-Scale Wind Tunnel in 

“Report of Proceedings of Sixth Annual Aircraft Engineering

Research Conference,” Langley Field, Virginia, 27 May 1931,

NACA, pp. 20–26, Historical Archives, NASA Langley.

As the NACA’s research capabilities, physical plant, and budget grew, the

committee clearly understood that continued public, and especially industry, support

would be crucial. The committee also knew that it needed a way for the emerging

civil aviation industry to bring its problems to the attention of the NACA. In a

brilliant stroke, Director of Research George Lewis and Executive Secretary John

Victory devised a conference where civilian and military leaders would be brought

to Langley for a first-hand look at the facility and an opportunity to talk directly

with NACA people. The first conference, with 38 invited guests in 1926, proved

popular, and it quickly grew into the Annual Aircraft Engineering Conference. By

1931, the conference had become a well-staged and -attended event hosting over

a hundred guests—including a number of prominent aviation journalists—to

ensure publicity, and the NACA used the event to show off its latest technology.

In 1931, the latest technology was the Full-Scale Tunnel, a thirty- by sixty-foot

monster of a wind tunnel, and the committee made the dedication of the FST the

highlight of that year’s conference. This excerpt from the conference report outlines the carefully scripted dedication program. The dedication opened with a

brief review of the history of aeronautical research by Joseph Ames, followed by a

report by tunnel chief engineer Smith J. DeFrance, and culminated with a live

demonstration of the new tunnel. 

While the actual number of research projects that resulted from industry

inputs at these conferences was small—less than two dozen in all—the conferences succeeded in projecting the NACA’s best image to the aviation industry and

the public, and they helped ensure essential congressional support.

Document 2-26, Joseph S. Ames and Smith J. DeFrance, 

remarks at the dedication of the NACA Full-Scale Wind Tunnel in “Report of

Proceedings of Sixth Annual Aircraft Engineering Research Conference,” 1931.

DEDICATION OF FULL-SCALE WIND TUNNEL.

The members of the conference then proceeded to the new full-scale wind tunnel,

where a Vought Corsair airplane was mounted on the balance in position for test.
632 Chapter 2: Building a Research Establishment

DR. JOSEPH S. AMES.

The tunnel was dedicated by Dr. Ames, who presented the following statement:

Before putting this new wind tunnel into operation I would like to say a few

words with regard to the history of wind tunnels and something with regard to the

design and study of equipment of this type. The problem is to find the resistance

offered to the passage of a solid body through the air. Early experiments along this

line were attempts to study the effect of wind on the human body by determining

how far a man could jump with the wind and how far against the wind.

The beginning of the science of aerodynamics probably dates back to the year

1661, when Hooke read a paper before the Royal Society of London, on the resistance of the air. The material in this paper was based on experiments Hooke had

conducted by throwing different shaped bodies horizontally from the top of a

tower and observing the time they remained in the air before striking the ground.

Similar experiments were made by Sir Isaac Newton in 1710, with spherical bodies.

In 1746, Benjamin Robins, an Englishman and a distinguished mathematician,

developed an early form of whirling table and accumulated considerable data on

air resistance and on the motion of bodies projected into the air.

Although these investigations were concerned chiefly with ballistics and had

little bearing on the aerodynamics of flight, they led to the statement of the pressure

velocity law by Charles Huttin about 1790, that pressure varies as the square of

the velocity, and to the importance of aspect ratio.

The whirling table, or whirling arm, and straight-away towing arrangements,

were used for the investigation of problems in aerodynamics until the beginning

of the twentieth century. These devices were supplemented by the actual flight of

models, man-carrying gliders, and in some cases engine-driven airplanes. The

era of gliding, from the time of Lilienthal, did much to lay the foundation of

flight and the principles of stability.

Langley, early in his career, conducted research on the sustentation of bodies

by inclined planes with a view to determining the fundamental data as to lift and

drag of airfoils and the probable efficiency of air propellers.

About 1890, Sir Hiram Maxim constructed a wind tunnel with a three-foot

square throat.

In 1901, Orville and Wilbur Wright set themselves to solve various problems

of flight and started a lengthy series of experiments to check previous data on

wind resistance and lift of curved surfaces, besides problems on lateral control.

They built a wind tunnel at their home in Dayton, which had a 16-inch square

throat and was 6 feet long. In this tunnel they measured the lift and drag of over

200 miniature wings. In the course of these tests they produced comparative

results on the lift of square and oblong surfaces, with the result that they rediscovered the importance of aspect ratio.
Document 2-26 633

It was not until 1909 and 1910 that organized research was undertaken, and wind

tunnels were constructed at the National Physical Laboratory in England, at the Eiffel

Laboratory in France, and at the Aeronautical Research Institute at Göttingen.

In the United States, wind tunnels were constructed at the Washington Navy

Yard, at the Massachusetts Institute of Technology, and at the Bureau of

Standards, and the first wind tunnel constructed by the National Advisory

Committee for Aeronautics was completed in 1919.

In 1927 the Committee placed in operation the present propeller research wind

tunnel. This wind tunnel was designed and constructed largely for the purpose of

investigating the characteristics of full-sized airplane propellers. A large number of

propeller investigations have been completed in this wind tunnel, but the major

portion of the operating time has been taken up in the study of other than propeller

problems. The investigation of large wing models, the study of the cowling and

cooling of engines, the study of engine-nacelle-wing arrangements, the investigation

of different forms of airship models, and many other projects have so filled this

program that in 1928 the Committee submitted to the Director of the Bureau of the

Budget a request for authority to expend $5,000 for the development and procurement of a design of a wind tunnel suitable for research on full-sized airplanes. With

the approval of the Bureau of the Budget, authority was obtained from Congress for

the expenditure of $5,000 for the study and design of a full-scale wind tunnel on

May 16, 1928.

Preliminary designs and estimates were prepared and submitted to the Bureau

of the Budget, and by act approved February 20, 1929, the Congress provided an

appropriation to extend over a period of two years the construction of a full-scale

wind tunnel.

The contract was awarded for the construction of this wind tunnel on

February 12, 1930, and we are here today to place in operation this important

equipment. With the completion of this equipment we now have available a

means for actually studying a full-sized airplane under flight conditions.

The ideal method of investigating the stability and control characteristics of

an airplane would be to place on the airplane in flight means of measuring the

lift, drag, and moment characteristics. This, of course, would be very difficult to

accomplish so as to obtain accurate measurements. In this wind tunnel we have

practically done the same thing by placing the airplane on a balance capable of

measuring all the changes, and providing the air stream flowing past the airplane.

The completion of this wind tunnel opens up a new vista of important problems,

the solution of which I am confident will mean much toward increasing the safety

and efficiency of aircraft. The Committee has received many suggestions for

research problems from the military services and from aeronautical engineers,

which will provide a research program that will keep this piece of equipment in
634 Chapter 2: Building a Research Establishment

continuous operation for a long period of time.

The Executive Committee in 1928 authorized the preparation of a preliminary design, and Mr. Smith J. DeFrance, of our technical staff, was placed in

charge of this project. Mr. DeFrance, with his assistants and other members of our

technical staff, has been responsible for the design and construction of the completed equipment. I wish to add at this point the appreciation of the members of

the Committee to the staff of the Committee and to Mr. DeFrance for the excellent manner in which they have carried through this enterprise.

Mr. SMITH J. DeFRANCE.

The Chairman then called on Mr. DeFrance, who described the operation of

the full-scale wind tunnel, referring, as he spoke, to diagrams of the plan of the

tunnel and balance. His remarks were as follows:

After what Dr. Ames has said I am sure that you are all familiar with the principle

of the wind tunnel. You have seen small wind tunnels in operation. This tunnel is

in many respects similar to a small tunnel but of course much larger. The crosssectional area of the throat is five times that of the next largest wind tunnel in the

world, the propeller research tunnel.

This is the first wind tunnel ever constructed for the purpose of testing complete

full-sized airplanes, and as such it will fill a very important place in the field of

aeronautics. Its principal use will be in the determination of the lift and drag

characteristics of an airplane. Previously it has been necessary to do this from

glide tests in flight, and sometimes the tests have been very lengthy because of

inability to control test conditions. Here we will be able to control the test conditions, and to obtain the polar of an airplane in approximately one hour whereas

it might take a month in flight. 

In this tunnel we will be able to study control, especially control at low speeds

and at high angles of attack; and the drag of air-cooled engines, and of water-cooled

engines with radiators, under practically the same as flight conditions.

The dimensions of the tunnel are 30 by 60 feet at the throat, and, as may be

seen from the chart, the tunnel is of the double-return flow type. The velocity of

the air stream may be varied up to 115 miles per hour. This stream is produced

by two 35 1/2-foot propellers, each directly connected to a 4,000-horsepower

motor of the slip ring induction type. The speed of the motors may be varied

between 75 and 300 r.p.m. in twenty-four equal steps.

The airplane is mounted on a six-component balance through tubular struts.

The chart shows the arrangement of the balance and struts, which are at present

streamlined by fairings. Eventually the fairings will be separately supported and

merely serve as shields for the tubes, thereby reducing the support drag to a minimum.

The tubes in turn are secured to a floating structural steel framework, which is

connected by linkages to six recording scale heads. The lift is taken on two scales
Document 2-26 635

forward and one in the rear, the drag on one scale, and the side-wind force on two

scales. From the lift readings it will be possible to compute the pitching and

rolling moments, and from the side-wind readings the yawing moments.

Mounted on top of the floating frame is a turntable by means of which it will

be possible to turn the airplane from 15 degrees left to 15 degrees right while the

tunnel is in operation. We will also be able to vary the angle of attack from 5 degrees

to +20 degrees, thereby taking the airplane through the stalled condition and

making it possible to obtain data so difficult to obtain in flight.

The scales are equipped with electrical recording devices which are operated

from a single control stand. The amounts of the forces are printed on cards from

all scales simultaneously, thereby eliminating errors which may arise from readings.

The cards are moved from time to time as readings are made. 

Because of the amount of power required to operate the tunnel and the small

capacity of the local power plant, we are compelled to take the power on off-peak

load, or between midnight and 6:00 a.m. The amount of power permitted during

the day is 750 kilowatts, which will give an air speed of 55 miles an hour. This

afternoon we are operating at that speed. Before the tunnel is started, the pilot

will climb aboard the airplane and after the air stream has been started he will

start the airplane engine. Readings will be taken on the scales, and you will be

notified by placards when the cards are moved and when the angle of attack and

the angle of yaw of the airplane are changed.

The pilot will now go aboard the airplane. Dr. Ames, I ask you, as Chairman

of the National Advisory Committee for Aeronautics, to dedicate this full-scale

wind tunnel.

Dr. Ames.

This Committee started its work in 1915. I regard this moment as probably

the most important moment in the history of the Committee, because it is to set

in operation a piece of apparatus which promises to give in the shortest time the

most important information desired in the development of aerodynamics; an

instrument which is unique in the world, and which we owe to the ingenuity of our

engineers and to a Congress and a Budget Committee who understood our problem

and were willing to cooperate with us.

The pilot having climbed aboard the airplane, Dr. Ames pressed the button

and propellers were rotated, starting the air stream. The pilot started the engine

of the airplane and readings were taken on the balances, the members of the conference being notified by placards as to the variation of the attitude of the airplane

with respect to the air stream. 
636 Chapter 2: Building a Research Establishment

Document 2-27

Minutes of the Second Technical Committee Meeting, United

Aircraft and Transport Corporation, 5 December 1929, pp.

522–531, Boeing Company Archives, Seattle, Wash.

Once the merits of wind tunnel testing had become apparent, as they had by

the late 1920s, American aircraft builders began to think seriously about constructing major new tunnels for their own research and development work. The

Curtiss Aeroplane & Motor Company had been operating a private wind tunnel

for two decades with some notable results, including designs for Schneider Cup

racers, but most manufacturers were content with the data coming from the

NACA and university laboratories. Aircraft building was a risky endeavor in 1920,

and the fledgling firms engaged in it did well to merely survive. As the decade

drew to a close, however, the future of aviation seemed much more assured, thanks

to a combination of federal regulation, greater public acceptance and enthusiasm, and

technological progress. The aircraft industry, especially the larger companies formed

through consolidation, could also support greater investments in research facilities. 

The United Aircraft and Transport Corporation established a technical committee made up of prominent individuals in aviation to identify technical trends

and recommend actions for the company to take. At the committee’s second

meeting in December 1929, the minutes recorded a discussion about wind tunnels.

These minutes provide unique insight into the thoughts of several influential

people in the aeronautical community concerning the role of private versus government laboratories, the state of intercompany cooperation, and the overall

understanding of wind tunnels. While no two situations can be exactly alike, these

minutes, and especially the debates over the desired size and costs, reveal much

about the decision process for governing and managing boards. 

Document 2-27, minutes of the Second Technical Committee Meeting, 

United Aircraft and Transport Corporation, 1929.

CHAIRMAN MEAD: Another question which has been brought up a number

of times was that in the group we have no aerodynamic facilities in which to

deposit all the information we have gotten so far, and the next decision is whether

with as much money as we have in aviation we can rely on the outside sources of

information whenever we need such data.

I have no brief either way, but it just seems peculiar not to have some facilities

of that kind in our own outfit, and I would like to hear what you think about that.
Document 2-27 637

I have incidentally heard a good deal of criticism of having some work done

outside because of the leaks which occur; everybody knows about it before you do.

MR. MONTEITH: Before you go into the aerodynamic research, I think that

everybody in the group who is doing flight testing of production ought to be

equipped with decent barograph and calibration instruments.

CHAIRMAN MEAD: Tomorrow, we want to have you, if you will, get your

gang together on this flight testing and see if you can not come to some conclusions

as to both how to do it and what equipment is required. Then we could get the

various units so equipped, because that certainly is most important.

MR. SIKORSKY: I think that is very important, and I would even add the suggestion that maybe we can order some entirely identical instruments, because it

will help if we can know the instruments; it will simplify the comparison of the test.

MR. McCARTHY: We bought a barograph recently which is the same as the

Navy uses at Anta Costa. It was quite expensive, of course.

MR. SIKORSKY: As a central unit, it seems to me a simple method to install

a method of correcting these instruments.

MR. CHATFIELD: The operation for calibrating an ordinary barograph is not

very elaborate, ten or fifteen dollars will buy one. We use mercuro-chrome with a bell

jar. Apparently the temperature areas are not important enough to worry about.

MR. McCARTHY: I think we ought to talk a little about wind tunnels before

we go away. It seems to me that the United can well afford to buy one wind tunnel

somewhere in the East for the use of our outfit.

MR. MONTEITH: Why the East?

MR. McCARTHY: Well, it would certainly have to be in the East or West to be

of any use to anybody.

—You will have to get your own facilities out there. I don’t see how we could

have one wind tunnel to serve everyone.

But, for a fairly modest sum we can put up about an eight-foot tunnel that

would serve all the Eastern units and probably excluding Stearman.

MR. SIKORSKY: I am very much in favor of it. I think it is simply a necessity

for us to arrange our own research laboratory of such size as would give reasonable

service. As was stated here, the very important fact of secrecy,—and we know that

it is almost impossible to get it,—is sufficient.

Besides this, simply the service is sometimes very hard to get. The data is not

so reliable and not comparable with each other, and I believe the wind tunnel will

simply pay back its cost in one year or so to everyone of us, besides the special

work for every unit the wind tunnel would do, and the general work everyone

would be interested in.

Again, it is interesting both so to speak in a positive and a negative way.

Today, for example, we asked the question about these new wheels; who knows
638 Chapter 2: Building a Research Establishment

accurately what the data is? With our own wind tunnel, we could test it correctly

and have reliable information available.

The same thing holds true with the new shape of stresses which come out, the

results would be the actual tests of such new refinements, ideas and so on which

may come out. Because, probably one of the strongest things which United may

have is to keep leading the industry, and to do it accurately, I believe a research

laboratory would be of considerable value, it is certainly worth spending twenty

or thirty thousand dollars on, or whatever it would cost.

CHAIRMAN MEAD: There is quite a variance in opinion as far as I can gather

as to what kind of a wind tunnel it should be, and how large.

MR. McCARTHY: I don’t think you want to go below eight feet.

MR. CHATFIELD: I think the central tunnel should be,—I favor going a little

larger than eight feet, with the idea that possibly some of the individual plants

may have smaller tunnels and would like a larger one in which to take those problems

which can not very well be handled in a four or five foot tunnel.

CHAIRMAN MEAD: I think we want to interrupt Chat just a second—I realize

that this gang around here is being looked upon to provide the equipment which

will return a good profit on the investment in United, and therefore it is a much

different picture than those of us individually faced before when we have all

pinched the pennies here because we have had to. Now, by pooling,—everyone

giving a bit to this project, we certainly can afford better equipment than we could

ever think of having ourselves, and I don’t think we ought to look at this thing in

too niggardly fashion.

What we really should have is desirable equipment, or at least ask for it, and

if the money is not forthcoming that is too bad and we will have to trim our sales

accordingly.

I feel that if you want a wind tunnel, I certainly want it to be a good one whatever size that might be. I don’t know anything about wind tunnels so I can’t advise

as to size.

MR. CHATFIELD: I would like to have Mr. Weick’s opinion on that point.

MR. WEICK: Well, I think that size is more important than velocity for

instance. You can put money into a wind tunnel in two ways, one is in size and the

other is in power to obtain velocity, and while of course, you want to get as near

to full scale results as you can in both cases, the size when you are dealing with all

sorts of models is more important than just velocity, and the power goes up very

quickly with increased velocity. I think that Mr. Sikorsky’s point is worth emphasizing that one wind tunnel, if you are going to rely on wind tunnel work which

apparently you are to some extent, one wind tunnel in which all of these various

models can be tested in by uniform methods under uniform conditions would be

greatly valuable, because as it is with some testing in one tunnel and some testing
Document 2-27 639

in another you can not prepare those models with any degree of exactness, you

can’t expect to be able to compare them.

CHAIRMAN MEAD: We can take for definite example, Boeing Company

developed something here in the wind tunnel that might exist at the University

of Washington. The result of that test might go readily to Hartford to be checked,

or wherever this other tunnel would be, so that our data would all be alike.

MR. WEICK: That would be very well.

MR. MONTEITH: I am pessimistic about shipping wind tunnel models. We

used to ship them to Atlantic, or M I T, and the Railroad Company used them like

they were cord wood.

MR. CHATFIELD: We have had fairly good luck recently at M I T with models

coming in.

CHAIRMAN MEAD: We have not answered the question of how big or how

fast here.

MR. McCARTHY: You would not want to answer it in one gulp, would you?

MR. MONTEITH: It depends on how much money you have.

CHAIRMAN MEAD: Well, let’s put down two or three operations here, and

let’s see then how much money we can get; we will go out and canvas the crowd.

MR. MONTEITH: I think you have only two operations. You have either the

full sized wind tunnel, or a reasonably sized tunnel like eight or ten feet; eight feet

preferably. I think the four foot tunnel is absolutely out of the question except for

very minor tests.

CHAIRMAN MEAD: Your optional one is how big then? Would you say this

big fellow?

MR. MONTEITH: It is twenty feet like NACA.

MR. WEICK: That is very good because you can put all full scale bodies into it,

and propellers and so forth, and the only thing you can’t get in full scale is the wings.

CHAIRMAN MEAD: How low speed in a twenty-foot tunnel is going to be any

earthly good?

MR. MONTEITH: Sixty miles an hour anyhow.

MR. WEICK: You ought to have at least I would say eighty. You see the tunnel

there has only one hundred ten as an absolute maximum at the present time, and

one hundred is what we call top speed for testing, and that was quite satisfactory

for almost all conditions.

CHAIRMAN MEAD: Can I tell again what is the top limit on this thing?

MR. MONTEITH: I don’t think you should go above one hundred.

MR. McCARTHY: What did it cost to put in that unit down there?

MR. WEICK: It is hard to say exactly, because the power units were put in by

the Navy with a couple old submarines.

MR. McCARTHY: I think the eight or ten foot tunnel is about the limit.
640 Chapter 2: Building a Research Establishment

MR. WEICK: The only thing I can say about the ten-foot tunnel is what someone here said the other day about the cost of the Berliner-Joyce tunnel. They have

one which cost $37,000.00.

MR. CHATFIELD: California Tech’s actually cost $60,000.00.

CHAIRMAN MEAD: And what velocity in a ten-foot tunnel?

MR. WEICK: I would say you want one hundred miles an hour.

CHAIRMAN MEAD: Well, now, that is the way to go at it and we can ask them

for what we feel we need. Is there any use of having an intermediate size here?

That is, the cost of these things seem to go up as the sixth power.

MR. MONTEITH: No use going beyond ten feet if you can’t go to the full size.

CHAIRMAN MEAD: Well, isn’t NACA apt to go at things in rather an expensive

manner? As long as you are out of it, Weick, you can perhaps feel this is not criticizing, and we could not perhaps build a big tunnel for much less expense. As an

example, Cline’s tunnel down here, he admits for certain reasons that it is very

expensive and apparently could be well cut down to $30,000.00 or $35,000.00.

Do you think there is any chance of the NACA’s being very elaborate,—very

much more than would be necessary?

MR. WEICK: I don’t think the NACA tunnel could be classed elaborate in any

sense of the word. It is built of only a single thickness of board on a steel framework

for the walls, and it was sort of a factory job in construction all the way through

with no trimmings whatever.

CHAIRMAN MEAD: I would think from what little I could see that the cost

is in the machinery and not in the tunnel itself.

MR. McCARTHY: They got the machinery for nothing.

MR. MONTEITH: How much power have they there?

MR. WEICK: 2000 horsepower is all.

CHAIRMAN MEAD: Now, wouldn’t it be worthwhile, we seem to be interested

in wind tunnels, to make Chat the dog again and have him go around again and

see or get information on what it really might cost to build these tunnels based on

actual cost of other places and examination of NACA’s, and discussion with them as

to production and costs, and so on, and then we can put up a figure which looks

reasonable and let the Executive Committee decide what they want to do about it.

MR. WEICK: I think that is a good idea.

Incidentally, they are now building another tunnel at NACA which would give

better information than our tunnel, but you see when you double the linear

dimension of a tunnel, which is done in that one, then you go up as a cube in volume

and the price of your building goes up to beat the band.

MR. McCARTHY: That type of tunnel is not usable for a lot of things. The

small tunnel is too.

CHAIRMAN MEAD: We might find a grandpa to give us these things, who knows?
Document 2-27 641

MR. SIKORSKY: I believe a ten-foot tunnel would do all right, because in a

big tunnel simply the speed with which you can make big tests and actually put

models in,—I think it may be a little too big.

CHAIRMAN MEAD: Of course, we could do this, we could start off in a modest

fashion and take the ten-foot, then if we kept growing and there was any need for

a bigger one and we found it was desirable we could build it perhaps.

MR. WEICK: I would certainly recommend starting with a ten-foot tunnel.

CHAIRMAN MEAD: What else in the way of equipment do we have to

have,—or is the desirable equipment to have, is the better way perhaps to put it?

Here is one wind tunnel—

MR. CHATFIELD: (Interrupting) There is a point in the operation, I think a

great many wind tunnels are limited in their usefulness, not in their ability to conduct

the test, but in their ability to get them written up afterwards.

To get the full use of a tunnel, I think it ought to have a larger personnel than

many wind tunnels have so as not to have the delay in the making of the tests and

the reporting of the results.

MR. McCARTHY: I think that is a secondary question. If you get the

Executive Committee to approve of the construction of a wind tunnel, you merely

go out and hire people to run it, that follows naturally.
642 Chapter 2: Building a Research Establishment

Document 2-28(a–b)

(a) A. L. Klein, “The Wind-Tunnel as an Engineering

Instrument,” S. A. E. Journal 27, No. 1 (July 1930): 8–90.

(b) A. L. Klein, letter to V. E. Clark, 14 August 1934, Klein

Collection, Folder 3.2, California Institute of Technology

Archives, Pasadena, California.

At a Los Angeles meeting of the Society of Automotive Engineers (a leading

professional society for aeronautical as well as automotive engineers) in 1930,

A. L. Klein, an aerodynamics professor at Caltech, presented “The Wind-Tunnel

as an Engineering Instrument,” which briefly discussed some of the ways wind tunnels could be used, with particular emphasis on research to enable high-speed

planes to land on short fields. The paper itself is mildly interesting, but the discussion that followed—moderated by former Langley Laboratory Engineer-inCharge Leigh M. Griffith—ventured into several contemporary issues concerning

wind tunnel design and operation. The discussion concerning the problems with

small, high-speed electric motors with model propellers explained part of the

rationale for building the PRT and FST at Langley, and other comments, primarily by Griffith, noted both problems and successes with the VDT. Considering his

background with the NACA, two of his remarks are especially interesting. Griffith

opened the discussion with, “The wind-tunnel is more or less of a mystery to

many who are otherwise well versed in aeronautics. I have personally had some

experience with it, and it is still a mystery to me.” His ensuing comments belie

that self-effacing remark, and his final comment at the end of the discussion sums

up his belief that “It is only a question of time, I think, when we shall be able to

design aircraft upon the basis of tunnel tests and not miss the computed performance

on the full-scale machine by more than 2 or 3 per cent.” Time would prove him right.

While Klein’s 1930 S. A. E. paper shows his interest and mature understanding

of wind tunnels and research techniques, a letter he wrote to Virginius E. Clark in

1934 went into greater detail concerning many of the practical considerations for

wind tunnel work. Klein’s letter, the result of years of experience with Caltech’s

tunnel, outlined a careful procedure for testing new aircraft designs and included

an itemized estimate of the costs associated with wind tunnel testing. The dollar

amounts appear miniscule today, but at a time when an engineer might earn $15

per week, spending $800 to $1,200 on a test series was not something to be taken

lightly, and the planning of test programs grew increasingly complex to ensure

the greatest possible benefits.
Document 2-28(a–b) 643

Document 2-28(a), A. L. Klein, 

“The Wind-Tunnel as an Engineering Instrument,” 1930.

Of the many problems that arise in the design of an airplane, those in connection with the wings can be most easily investigated in the wind-tunnel. The

determination of the mean aerodynamic chord of an unorthodox wing cellule is

one of the most obvious types of wind-tunnel problems. It is highly desirable that

the wing cellule of the airplane be investigated independently, as only by determining the polars of the wing cellule alone and then repeating the measurements

with the fuselage, nacelles and other parts in place, can the interference between

them be measured. By following this procedure and then trying different types of

filleting, marked improvements in the characteristics of the complete airplane

can be obtained. Muttray [Assistant Professor of Aerodynamics, California

Institute of Technology] has shown that an improperly filleted fuselage can have

a marked effect upon the wing-fuselage interference. [See National Advisory

Committee for Aeronautics Technical Memorandum No. 517.] A badly designed

fuselage and fillets cause a great decrease in the equivalent span of the airplane.

The interference drag can be almost completely eliminated by correct design. It

is well known that anything attached to the upper surface of a wing has a very

detrimental effect. If protuberances can not be avoided, a model of sufficient scale

should be constructed and their design worked over so that they will have the least

effect. All re-entrant angles and small gaps, especially up above the wing, should

be avoided. The recent work of the National Advisory Committee for Aeronautics

has shown that a properly mounted wing-engine has only one-sixth the drag of

the present normal type of engine nacelle. [See National Advisory Committee for

Aeronautics Technical Note No. 320.]

Miscellaneous Drag Problems

The present type of landing-gear has very large drag, principally because of

acute angles between the struts. Landing-gears can be tested at full-scale in a large

wind tunnel or at half scale in a smaller wind-tunnel. The N.A.C.A., in its brilliant

development of the Venturi cowling, has pointed the way for a more scientific

attack upon drag. The British townend ring, though different in principle from

the N.A.C.A. cowl, produces similar results.

A newer type of drag problem has arisen in connection with very high-speed

airplanes. This type of plane is necessarily so clean that its gliding angle is very

flat. This characteristic, combined with some of the ways in which the tendency

toward low-wing monoplanes, has produced airplanes having great floating tendencies. These planes are very difficult to land in small fields over obstructions.

There are three possible methods of landing them, all unsatisfactory: (a) The pilot

may glide into a field steeply, picking up speed all the time and then floating a
644 Chapter 2: Building a Research Establishment

long distance before making contact; (b) he may glide in at his minimum glidingspeed and touch the ground at approximately the same distance from the

obstruction as before; or (c) use the last method which is to squash into the field

and pull out just before contact, thus making a short landing.

The first two methods are impossible in small fields, while the last method

requires great skill and is very dangerous in bumpy air. Side-slipping a high-speed

airplane is not very effective, as the fuselage used in this type is a very good streamline body at any ordinary angle of yaw. A few calculations will show that enough

flat-plate area to decrease the lift-drag ratio to a reasonable value will be almost

impossible to obtain in a safe and controllable manner. The usual form of spoiler

is likewise inadvisable as it decreases the lift markedly, thus increasing the sinking

speed. The only reasonably safe way to decrease the lift-drag ratio is to use some

form of interference-drag device that will not spoil the lift and yet will produce a

large increase in drag. This is an ideal wind-tunnel problem, and the polar and

pitching-moment curves of any contemplated device can be easily determined.

High-lift devices should always be investigated to determine their effectiveness.

Enough tests have been made with models and with the corresponding full-scale

airplane to prove the reliability of the wind-tunnel methods.

Dynamical Stability Difficult To Test

All of the foregoing tests can be made with the ordinary three-component

wind-tunnel balance. To investigate the complete airplane with its six degrees of

freedom, a six-cylinder balance is necessary. The model of the complete airplane

can be tested for stability and control, the effectiveness of the controls measured

and the statical stability investigated. The problem of stability, power on, is more

difficult. The statical stability of the airplane can be determined without the slipstream, and after the coefficients have been determined the moments of the gravity forces and the propeller thrust can be added in. To work with the slipstream a

small high-speed motor is necessary. To date no satisfactory power unit has been

developed, although a number of laboratories have designed or purchased apparatus for this purpose.

The study of dynamical stablity is very difficult, as it requires an entirely different type of set up than any of the foregoing tests. The model must be free to

oscillate and it must be dynamically as well as geometrically similar to the fullscale airplane to be investigated.

The problem of wing or tail flutter is very difficult to investigate, as the model

must be constructed so as to have the same geometrical shape, structural rigidities and mass distribution as the airplane. Work of this nature has been done and

more will be done in the future. The surface texture of airfoils is now being

worked on in the world’s laboratories, and definite data on the effect of corrugations, rivet heads and the like will be available in the near future.
Document 2-28(a–b) 645

It is well to mention that propellers are being constantly tested in the laboratories

that specialize in this work and our present remarkably high propeller efficiency

has been achieved as a result of their efforts.

The writer does not believe that all of the tests mentioned are necessary for

the design of a conventional airplane, but every plane should have its polars, moment

curves and static stability determined. The rules now extant for dynamic stability

give satisfactory results and those for the prevention of dangerous spinning characteristics are sufficient for the designer in most cases.

THE DISCUSSION

CHAIRMAN L. M. GRIFFITH [M.S.A.E.—Vice-president, general manager,

Emsco Aero Engine Co., Los Angeles]:— The wind-tunnel is more or less of a

mystery to many who are otherwise well versed in aeronautics. I have personally

had some experience with it, and it is still a mystery to me. One thinks the building of a tunnel is a simple sort of job. He sees a tunnel running, notes its character, gets the dimensions and drawings and builds one like it. If he has had no

experience, he says, “In two months we will have the tunnel finished and start

making tests.” But after the tunnel is completed in the two months, usually a year

or two years is required to find out whether it is a good tunnel or not. There seem

to be many things to contend with when one deals with air at high velocity

through a wind-tunnel; the air does not follow the nice, smooth lines that were

laid down on the drawing-board. Information resulting from wind-tunnel tests of

all kinds, however, forms the real basis of our aerodynamic advance. We discover

many things with full-size machines but can not very conveniently measure them.

The quantities involved can not be determined readily, as we found at Langley

Field; therefore we are dependent for much of our information upon the results of

tests in wind-tunnels on models and parts of airplanes.

DR. A. L. KLEIN:— I can echo what Mr. Griffith has said, since, after the tunnel

at the Institute was built, we found that one place inside of its perfectly conical

body the air was moving upstream. We were much astounded; then we did a few

things and got the air to go in the same direction over all of the tunnel.

Full-Scale Application of Tunnel Results

CHAIRMAN GRIFFITH:— Many airplane designers who have had a little experience are prone to think that the wind-tunnel is suitable only for the use of

research men working on problems that have no bearing on the actual airplane.

On the other hand, there may be one or two designers who have implicit faith in

any result that comes from a wind-tunnel. Somewhere between these two views is

a happy medium where the work of the designer is guided, not controlled, by

wind-tunnel results. All such results are subject to interpretation and modification

as necessary to suit the actual full-scale design, taking into consideration the difference
646 Chapter 2: Building a Research Establishment

in operating conditions between the flight of the full-size airplane and the passage

of air around the small model in the wind-tunnel.

STANLEY H. EVANS [Aeronautic Engineer, design staff, the Douglas Co., Santa

Monica, Calif.]:— What model airscrew speed can you get in the tunnel, Dr. Klein?

DR. KLEIN:— Our largest models will be of 6-ft. span, and an airscrew of the

same proportional size as that used in an airplane would be approximately 18 in.

in diameter. To run that propeller at the same V/D ratio as the actual propeller

would require a speed of 10,000 to 15,000 r.p.m. Great difficulties have been

experienced with the small electric motors at such speeds because of overheating.

We hope soon to have a high-frequency generator to drive a three-phase motor

at any speed up to 20,000 or 25,000 r.p.m. and to be able to control its speed by

controlling the speed of the motor generator. Such apparatus is very expensive

and the sets built to date have not been very satisfactory.

MR. EVANS:— I assume you could use a much larger propeller and only a

small portion of the airplane model.

DR. KLEIN:— That could be done, but we were thinking of running the propeller in the stability tests of the airplane as a whole. If you were developing

nacelles, you could make a model of just the parts of the structure adjacent and

use a larger propeller; this would require more horsepower. The only successful

work of this type has been done in England and Germany, and one of the aerodynamical laboratories in this Country received a duplicate of one of these motors

and found that it ran red hot.

Trouble with High-Speed Electric Motors

WELLWOOD E. BEALL [Jun. S.A.E.—Assistant chief engineer, Walter M. Murphy

Co., Pasadena, Calif.]:— The motor to which Dr. Klein refers was imported from

Germany by Prof. Alexander Klemin of New York University. It was about 2 1⁄2 in.

in diameter and about 9 in. long. It operated on 500 cycles and required a special

converter, also of German manufacture. This small motor developed, as I recall,

about 1 3

⁄4 hp. and was similar to one the Navy experimented with some time ago.

This motor was intended to be mounted in a wind-tunnel model and drive a

propeller so that conditions approximating actual powered flight could be simulated.

It was designed for operation at 40,000 r.p.m. with the propeller geared down to a

suitable speed. However, operation at this speed was found to be impracticable, due

to the motor overheating. It was then adjusted to turn at 36,000 r.p.m. With the motor

mounted by itself in the laboratory and when it was turning a small propeller which

threw considerable air upon it, this speed proved to be practicable. However, as

soon as it was mounted inside a model for test, where no air current could strike it,

it immediately became hot and after 45 sec. of running became too hot to operate.

The propeller reduction-gears were mounted on the motor in such a way that

the torque reaction, and consequently the power delivered to the propeller, could
Document 2-28(a–b) 647

be measured. This reduction-gear train was carried by a frame that pivoted in

such a way that the torque reaction tended to rotate it. This rotation was

restrained by a calibrated spring and the torque was indicated by a long, thin arm.

This torque indicator operated satisfactorily in still air but, when placed in the

slipstream of the propeller or in the wind-tunnel, it became inoperative due to the

impact of the wind on it. This prevented the indication of the torque and consequently the calculation of the power.

This motor was also equipped with a revolution counter consisting of a worm-gear

train and a small disc about an inch in diameter with one mark on its circumference.

To obtain the speed of the motor, it was necessary to watch this disc, count its revolutions and calculate the result. This method is suitable for obtaining the speed

of the motor before it is mounted in the model but very inconvenient when

mounted in the model and in the tunnel. The reasons for this are obvious.

Although this motor was rather disappointing, it did arouse considerable

interest and at least has provided a start in obtaining data for predicting the effect

of the propeller slipstream and wash by means of wind-tunnel tests. The motor, I

believe, has been sent back to its manufacturers to be rewound and rebuilt to

operate at lower temperatures under load. A new system of distance-type indicating

devices for the speed and torque is also being devised. With this rebuilt motor it

is hoped that many valuable data may be obtained.

CHAIRMAN GRIFFITH:— The difficulty of running small-motor tests in the

wind-tunnel is one of the factors that led to the present large tunnel at Langley

Field and is leading the National Advisory Committee for Aeronautics to plan the

construction of a much larger tunnel. I understood that the size of this was to be

in the neighborhood of 30 ft. high and 40 ft. wide, but Dr. Klein tells me it has

been increased to 30 x 60 ft. It is interesting to note that the 20-ft. tunnel takes

about 2000 hp. to drive it.

With reference to Dr. Klein’s comment about the detrimental effect of protuberances on top of the wing, I have been curious to know how much the Dornier-X

speed might be below that of a similar airplane having the engines mounted within

the wing itself.

DR. KLEIN:— German engineers have made some tests but the results have not

been completely published. They showed that locating the propeller completely above

the wing does not interfere with the wing. Before he built the flying-ship, Dr. Dornier

expected to get a considerable increase in lift at take-off, because the slipstream

would be entirely above the wing and increase the circulation about the wing.

QUESTION:— Has any work been done on an airplane which has some variabledrag device to increase the drag on landing so as to reduce the landing speed?

DR. KLEIN:— I do not know of any that has been done. We expect to try several devices of our own and of other people for this purpose. I think personally that
648 Chapter 2: Building a Research Establishment

the only feasible means is to use some interference-drag device; any other way is

open to objections on the ground of reduction of controllability.

Variable-Density Wind Tunnels

QUESTION:— What is the situation in regard to increasing the air density,

using a closed pressure-system?

DR. KLEIN:— That is one way of achieving a large Reynolds Number, which is

our criterion of scale effect. A tunnel 5 ft. in diameter that can be pumped up to

20 atmospheres has been built at Langley Field and has been very successful. The

British are contemplating building a similar tunnel. The Langley Field tunnel was

exceedingly expensive. I imagine a high-pressure tunnel would cost about five

times as much as an open tunnel of the same size. Our tunnel has a 10-ft. diameter,

and we get an increased scale-factor by running at air-speeds up to 200 m.p.h. I

think that our tunnel, without the building, cost approximately $75,000. We did

not expect to get such high speeds but are pleased that we can get them. We build

wind-tunnels and get astonishing results; nobody has very clear-cut ideas as to

what the ideal wind-tunnel is.

CHAIRMAN GRIFFITH:— An interesting item about the variable-density windtunnel at Langley Field is the tank in which the tunnel was placed. It was a very

good piece of ship-plate work. The shell is 15 ft. in diameter and about 30 ft.

long, with hemispherical ends, and weighs 43 tons. The side plates are 1 1

⁄4 in.

thick. This tank was tested to a pressure of 450 lb. per sq. in. and showed very little

leakage. It cost $24,000, and $1,200 more was spent to get it from the place where

it was built to the site of the tunnel. When we got it there, we began to figure how

much more money we would have to spend. We had enough to put up a building

and, through the cooperation of the Navy Department, used Navy equipment

that originally cost about $80,000 and had been used in the helium plant at Fort

Worth, Texas. Consequently, we were able to do a relatively big job for a small sum

of money.

Plans for Huge Tunnel at Langley Field

A MEMBER:— Is that very large tunnel at Langley Field actually being constructed

and is it possible to make a guess as to the power that will be required? 

DR. KLEIN:— I believe that the National Advisory Committee for Aeronautics

obtained from the Congress an appropriation of $900,000 for it and expects to

use about 8000 hp. The Committee was considering the larger tunnel very seriously

and was debating how to build it.

CHAIRMAN GRIFFITH:— This wind-tunnel problem is really very interesting.

When we built the 5-ft. variable-density tunnel at Langley Field we thought we

would be in an excellent position to investigate all kinds of aerodynamic problems

in the tunnel. Shortly after that tunnel was finished, we started the 20-ft. tunnel

with the idea that we would then be able to make tests at the same Reynolds number
Document 2-28(a–b) 649

but with different air densities and model scales. The interior of the high-pressure

tunnel burned out several times and we found that wood was not a suitable material

at 20 atmospheres, or a pressure of about 300 lb. per in., as combustion is

extremely energetic at that pressure and air velocity.

All this time the Committee was carrying on full-scale work with airplanes

with about 17 different varieties of recording instrument and found the limitations

of that method. Having completed the 20-ft. tunnel, it is now building one 30 x 60 ft.

To the industry the world over it looks as if it were going to be worth a lot of

money. I really believe that, with proper coordination between full-flight tests with

all the instruments that can be crowded into the cockpit, tests of the model airplane in a variable-density tunnel and tests in an ordinary tunnel, we can produce

a mass of coordinated data that will tie up rather closely the various testing means.

In any case we can look forward to the increasing use of the wind-tunnel and

to its influence being reflected in greater aerodynamic efficiency of aircraft. That

is very definite. We know that the wind-tunnel has given us the basis on which we

have built most of our aerodynamic progress and is going to be the main instrument

for further development. It never will take the place of free-flight development,

but it is coming closer to it. It is only a question of time, I think, when we shall be

able to design aircraft upon the basis of tunnel tests and not miss the computed

performance on the full-scale machine by more than 2 or 3 per cent.

Gerald Vultee [Chief engineer, Lockheed Aircraft Co., Burbank, Calif.; now

with Detroit Aircraft Corp., Detroit]:— The result of my experience in flying airplanes is that, if one sometimes could be sure of hitting within 25 per cent of calculations, he would feel much better.

Present Landing-Speeds Seem Safe

JOHN K. NORTHROP:—Will the new landing rules of the Department of

Commerce necessitate the use of variablelift devices, or will it be possible to bring

a full-scale machine to a landing much slower than the theoretical figures would

indicate?

MR. VULTEE:—As I remember the rule, unless the theoretical landing-speed

was below 60 m.p.h. the Department required special flight-tests to prove the

practicability of the design. If those were passed, and they were not particularly

stringent tests, the design was approved. However, I believe from the experience

we have had that the plane can be brought in at a considerably lower speed than

would appear from theoretical considerations.

It is natural to assume that most manufacturers’ performance figures on landingspeeds are somewhat optimistic; checking the maximum lift–coefficients of existing

commercial planes against the performance that is claimed for them, the maximum

lift–coefficients are found to run in the neighborhood of 0.0040 or higher. These

are rather high figures. We encountered something similar to that in trying to
650 Chapter 2: Building a Research Establishment

reduce the landing-speed we had. We found we could not get any assurance of

being able to reduce the landing-speed appreciably with any normal wing-section,

as by actual flight-tests we already had a maximum lift-coefficient of about 0.0040.

However, I believe that a good pilot can bring a plane in rather more slowly than

the theoretical figures indicate.

Perhaps we have become used to seeing planes coming in at 60 and 65 m.p.h.

and it looks like 45. The landing-speeds we are using now seem to be satisfactory

as regards safety. The planes get in and out of fairly small fields and do not average

a large per centage of crack-ups on landing; therefore, as an increase in landingspeed will make possible a greater increase in high speed, it seems that we should

go a little slowly in drawing conclusions regarding specifying slower landingspeeds. Planes designed for a landing-speed of about 40 m.p.h. would look rather

queer compared with the planes that are being built at present. All the builders,

I believe, are making a little increase in the allowable landing-speed in their

designs except for airplanes that are built for special purposes, such as training,

for which a lower landing-speed is absolutely necessary.

Document 2-28(b), letter from A. L. Klein to V. E. Clark, 1934.

August 14, 1934

Mr. V. E. Clark

30 Rockefeller Plaza

New York City

Dear Mr. Clark:

You will please find enclosed a copy of our wind tunnel specifications together

with some additional blueprints and addenda to bring them up to date.

In answer to the first point in your letter, I would state that the maximum

span of models which we have tested in our tunnel is 7 3

⁄4 ft.; any size up to this

will be satisfactory. We usually try to pick a model span of some simple ratio to the

full scale airplane, in order to simplify the computation of the model dimensions.

The wind tunnel corrections are now in such good order that we have found that

this size of model, 77 1⁄2%, gives perfect satisfaction. The only reason we do not

try to go to a larger model is because we are afraid that our velocity distribution

will not be satisfactory very much nearer the walls. This size of model results in

approximately a 1⁄7th scale model of a modern single engine transport.

Your question 2 is covered, I think, in the wind tunnel model specifications.

Our normal procedure in testing airplane models is to test the wing alone

first, in order to find its characteristics, then to build up the model part by part,

putting on the fuselage first and filleting it with wax in order to get the minimum

detrimental effect, then adding the engine and landing gear, etc. Finally, having
Document 2-28(a–b) 651

made a complete test of the model less horizontal tail surfaces, we add the horizontal

tail surfaces and take measurements with three positions of the stabilizer in order

to determine the optimum stabilizer setting. After making the stabilizer tests with

the elevator fixed, we work with the elevator set at various angles for its effectiveness,

and similarly with the ailerons and rudder. If control tabs are used on the elevator,

we make elevator free tests, in which case the elevator must be mounted on ball

bearings and counterweighted so that it is in static balance. These tests are made

at several tab settings in order to get the tab effectiveness.

We have found from experience that the following gives a fairly accurate estimate

for experiments on normal airplane models:

a) A fixed cost of about $120 for preparing the model for the tunnel, making

the preliminary calculations for reducing the data, etc.

b) A running cost of approximately $28 per Run, a normal Run consisting of

a series of three or six component measurements at about 15 angles of attack and

at one air speed.

Our costs are based on the following items:

a) 1.5 times our labor cost.

b) A wind tunnel charge of $6.00 per hour for all time in which the tunnel is

tied up for the investigation.

c) Electrical power used at 1.2 cents per K.W.H. (about $2 or $3 per Run).

We prefer to base our charges directly on the above costs, but if you prefer, we

will make a definite bid based on a detailed list of exactly the tests you desire.

In order to quote on a single set of lift, drag and pitching moment curves corrected for Reynolds’ Number and turbulence, it will be necessary for us to make

at least three runs at various speeds in the wind tunnel and then to extrapolate to

full scale. This will cost in the neighborhood of $200 to $225 on account of the

large overhead of one test. The unit cost of a small number of runs is rather large.

Our costs have been as small as $20 per run for investigations that were of some

length, i.e. from 60 to 100 runs on the model. We have found that the normal cost

of a complete test on a model as mentioned is from $800 to $1200.

I hope that the foregoing will give you all of the necessary information which

you desire.

Sincerely yours,

A. L. Klein
652 Chapter 2: Building a Research Establishment

Document 2-29

Starr Truscott, Aeronautical Engineer, memorandum 

to Engineer-in-Charge [Henry J. E. Reid], “Work in 

connection with special aerodynamic tests for Bureau of

Aeronautics which has been requested by Mr. Lougheed,” 

5 April 1932, RA file 210, Historical Archives, NASA Langley.

As noted elsewhere in this chapter, there is a close link between hydrodynamics

and aerodynamics, and the latter discipline frequently benefited from theoretical

and experimental work in the former. The NACA constructed two model-towing

tanks at Langley for the express purpose of investigating the behavior of seaplanes

during takeoff and landing, but some rather unusual tests were performed in the

tanks on occasion. One such test involved a study of seagull flight characteristics

for the U.S. Navy’s Bureau of Aeronautics (BuAer). BuAer’s Victor Lougheed devised

a program to capture several seagulls, freeze them with outstretched wings, and test

their aerodynamic characteristics by towing them submerged through one of the

seaplane tanks. Always cooperative, the NACA approved the project but, as this

memo shows, the Langley staff wanted to be sure that the navy assumed most of

the responsibility and risk for such an unorthodox program. The tests were run,

but there is no evidence that they contributed anything of significance to aeronautical engineering.

Document 2-29, Starr Truscott, “Work in connection with special aerodynamic tests

for Bureau of Aeronautics which has been requested by Mr. Lougheed,” 1932.

April 5, 1932

MEMORANDUM For Engineer-in-Charge.

Subject: Work in connection with special aerodynamic tests for Bureau of

Aeronautics which has been requested by Mr. Lougheed.

1. On the morning of Wednesday, March 30, Mr. Lougheed appeared at the tank.

The special dynamometer for use in making the tests in which he is interested had

been received the day before. Under Mr. Lougheed’s direction the dynamometer

was unpacked and a rack made especially to suit it. He also explained the operation

in detail.

2. In view of the general delicacy of the device and the ease with which the

small spring hinge “knife edges” could be put out of adjustment, it was decided

to leave the balance exactly as it was received, with all motions locked, until the

work of assembling it to its support and on the carriage had been completed. The
Document 2-29 653

support has not yet been received from the Norfolk Navy Yard, although it is

understood that it is completed.

3. After discussing the installation and the precautions to be observed in this

work and in the operation of the balance, Mr. Lougheed gave an outline of the

further work which would be required to prepare for and carry out the tests.

4. A working platform across the fan end of the tank is required. On this is to

be carried the freezing box for freezing the birds, two protractors for measuring

the angle of attack of the wings, a projecting walk for reaching the balance on the

spur projecting from the carriage, a receptacle for liquid air, two scales, two scale

pans, and fine shot for calibrations of the balance.

5. The freezing box must be about 8 or 10 feet long and 4 feet wide. In plan

form it should taper from the center to the ends so as to reduce the volume to be

filled with liquid air. The depth of the box should be as little as will accommodate

the birds, for the same reason. This box can be made of insulite or some other

insulating board with wood batten stiffening.

6. The two protractors can be made or bought. They can be relatively crude

in construction but must include blades 12 inches to 18 inches long to extend

under the wings to measure the slope of the wing chord relative to some level line.

Two are required so that one can be held while the other is being used to set the

other wing.

7. The projecting walk is required to provide access to the calibrating screw

which lies under the balance and some 4 feet back from the tip of the spike on

which the models are supported—or on which the birds are impaled.

8. The receptacle for the liquid air will probably be the one in which it is

received, but it must be supported in such a manner as to make access easy and

replacing simple.

9. The two scales are required for weighing the birds, or models, and for

weighing the calibrating loads. This balance has no calibrated springs or lever

balances. On each test run the device is brought to a null point and left there.

After the run the model is removed and the forces required to restore the null are

measured by dead loading with shot.

10. One scale should read up to 5 pounds by 1

⁄4 ounce; the other should have

a capacity of 1⁄2 to 1 pound and should read to 5 grains.

11. With the balance there have been supplied stirrups for supporting scale

pans in which the shot may be placed, but the scale pans must be supplied. Mr.

Lougheed suggests paper cups as easy and light.

12. In addition to the material to be used in connection with the tests, there

will also be required a supply of birds for testing. Mr. Lougheed suggested 5 gulls

and 5 turkey buzzards. These could be obtained by local trapping he thought and

probably boys might be interested in getting them.
654 Chapter 2: Building a Research Establishment

13. For keeping these birds a small menagerie will be required. The cages

must be large enough to permit the birds to spread their wings to preen them. If

the birds do not have sufficient space they will disarrange and break feathers by

pushing them against the walls of the cages. Mr. Lougheed estimated that a cage

about 12 feet long, 5 feet high, and 5 feet deep would suffice. This should be

divided by a solid partition into a section 7 feet long and one 5 feet long. The

larger section is for the buzzards, the smaller for gulls. Perches should be provided.

14. The birds will require to be fed to keep them in condition. The gulls get

fish and the buzzards meat in the form of spoiled meat or carrion.

15. Mr. Lougheed now has one gull and one buzzard in the zoo at Boston

which will be shipped down here.

16. I called his attention to the protection against killing or taking which is

given these birds by State and Federal laws. He said he would get the necessary

permits issued to himself and supply copies of the original to anyone who undertook

to catch birds for this job.

17. Discussing the balance and its method of operation, Mr. Lougheed

referred to the adjusting of speed, while the carriage was in motion, to suit the

model or bird. I called his attention that we could not do it from the carriage. He

replied that he understood that, but that by fitting two colored lights which could

be seen by the operator at the desk and which would indicate plus or minus

speed, it ought to be possible to do it. These lights would be operated by contacts

on the balance. I recalled to him that we had told him in the beginning that it was

not possible to change speed while running. He said the speed wasn’t critical and

if it didn’t work out it would simply mean more runs!

18. He requested that we install the balance on the balance support which is

still at the Navy Yard. This would require installing the wiring from the contacts, the

fitting of lamps, with condensers (if required) and batteries, for signalling the

operator on the carriage, and the fitting of signal lamps for the operator at the desks.

19. After we had the balance installed we should play with it, mounting discs

or other objects on the spike and determining their resistance, etc. A box of wing

models which could be fitted was also on its way to the laboratory.

20. Mr. Lougheed inquired about a local supply of liquid air. I told him I had

no information but doubted that it could be obtained locally or even in Norfolk.

He said it could be obtained in Washington and how it could be transported. I

suggested the Ludington Line airplanes if it was urgent. He replied that probably

the boat would be all right.

21. When the recital of this list of things to be done began I, of course, acquiesced

in the items of the freezing box and the access platform. The first was relatively

simple, requiring only a few sheets of insulite and a little carpenter work, while

the second we have in the form of our small portable bridge.
Document 2-29 655

22. However, as the list kept increasing in length—and obviously in cost—I

thought it might be better to let Mr. Lougheed complete his tale before commenting.

When this involved the provision of the menagerie and keepers, to say nothing of

trappers, I decided that it would be better to make no objections but simply to get

the picture well in mind, study it, and then make proposals as to what we should

do and what the bureau should provide.

23. Accordingly, I suggest the following:

A. The Bureau of Aeronautics should be informed that Mr. Lougheed has visited

the laboratory in connection with this work and has discussed the equipment

required in addition to the balance and also the method of taking the birds.

Certain items of this material can be supplied by the laboratory but others should

be supplied by the bureau because they are of types which are not used at or easily

available to the laboratory. These items are:

(1) The birds required for experiment

(2) the liquid air for freezing them

(3) the protractors for measuring angle of attack of wings

(4) two scales, one reading 5 pounds to 1

⁄4 ounce, the other reading 1 pound

to 5 grains

The bureau should also be reminded that in the course of the conferences

before these tests were authorized, the representatives of the bureau were

informed that the speed of the carriage was not controllable from the carriage

and hence could not be varied during the run. From the recent discussion with

Mr. Lougheed it has been learned that the operation of the balance which has

been provided requires that the speed of the carriage shall be adjusted while running.

This will require the fitting of some small items of equipment not contemplated

in the original plan and the adopting of a method of operation which will make

heavy demands on the control operator. The laboratory is willing to attempt this

method of operation, but of course can not promise certain success.

B. The laboratory will assemble the balance to its support, provide all incidental

fastenings, wiring, lights, extensions of control rods, batteries, and other items connected with the operation of the balance, and will install the balance on the carriage

in the manner described by Mr. Lougheed on his recent visit. It will also provide and

have ready the means of access to the balance, the freezing box, and one or more cages

for the birds. When the birds are received it will provide for their feeding. (It is assumed

that requisitions covering the necessary meat and fish will get by the Comptroller.)

24. It will be noted that this calls for the bureau to supply the birds. It seems

to me they should do this because it will require quite a bit of arranging. Mr.

Lougheed spoke of putting an advertisement in the papers. Such a thing would

only start trouble. Some group or person either well intentioned or seeking notoriety

would protest and the resulting troubles would keep us busy.
656 Chapter 2: Building a Research Establishment

25. A further thought is that Mr. Lougheed warned me that the gulls might

easily put out an eye for anyone who handled them, as they always strike for it,

while the buzzards can bite off a finger without trouble, thanks to their “tinsnip”

jaws. I would just as soon others should handle such birds while catching them.

Feeding them will be bad enough.

26. A further thought is that if this work is to be kept at all confidential the

purpose of the birds must not be advertised. This would surely occur if the birds

ere taken locally. It would be much better to take them around Washington and

ship them here. It might even be feasible to handle the taking at the Naval Air

Station.

Starr Truscott,

Aeronautical Engineer
Document 2-30(a–b) 657

Document 2-30(a–b)

(a) Edward P. Warner, “Research to the Fore,” 

Aviation 33, No. 6 (June 1934): 186.

(b) “Research Symphony: The Langley Philharmonic in 

Opus No. 10,” Aviation 34, No. 6 (June 1935): 15–18.

Aviation Editor Edward P. Warner was clearly a big fan of the NACA. He extolled

the virtues of the committee, its research methods, and the products of that research

in numerous columns, but Warner, who served on the NACA’s Committee on

Aeronautics, knew what he was talking about. Thus, his comments and conclusions

are worthy of consideration as more than simply those of an apologist.

The final documents presented in this chapter both come from the pages of

Aviation; the first a Warner editorial, and the second an article likely written—and

certainly approved—by him as well. They were published about the time of the

NACA’s 1934 and 1935 Annual Aircraft Engineering Research Conferences at the

Langley Laboratory, and both dealt with the rise of aeronautical research to a

leading role in aircraft design. In 1934’s “Research to the Fore,” Warner observed

that “every group in the aircraft industry” had come to “a new appreciation of the

vital importance of the scientific fundamentals of aircraft design. Research has

ceased to be the servant of aeronautical development, and has become its guide.”

Journalistic hyperbole aside, Warner’s observation had some solid evidence, in

the form of recently built wind tunnels and new aircraft designs, to back it up.

Aviation took a whimsical tone in its report on the tenth (1935) conference,

titling it “Research Symphony: The Langley Philharmonic in Opus No. 10” and

using musical analogies to categorize the research work being done under the

baton of “Conductor Joseph S. Ames” and his able “Concert Master George W. Lewis.”

Nevertheless, this “brief recapitulation of some of the principal movements”

included a wealth of information on the current state of aeronautical research and

its impact on the aviation industry. Reading it, one will quickly sense how far aviation

technology had come in the two decades since the NACA’s founding, thanks in no

small part to that organization’s increasingly sophisticated research program. 

Document 2-30(a), Edward P. Warner, “Research to the Fore,” 1934.

Research to the Fore

About this time each year the aircraft industry prepares to move in force on

Langley Field and the laboratories of the N.A.C.A. This springtime visit has
658 Chapter 2: Building a Research Establishment

become an annual habit, and out of the annual attendance of 200 or 300 at the

N.A.C.A. field day the majority are veterans who have acquired the habit so thoroughly that they never think of missing the trip. In the last two or three years

those old timers have been sensing a change in the atmosphere of the meeting,

for an interest in the detail of research equipment, method, and results that was

once concentrated among scientists has spread to every group in the aircraft

industry. The representatives of the builders of aircraft for the military market

attend in steadily growing numbers, and the manufacturers of light commercial

craft and the operators of airlines, though they came comparatively late to the

roster of the meeting, are finally beginning to play a part.

All this is quite a compliment to the National Advisory Committee, but it is

much more than that,—it is evidence of a new appreciation of the vital importance

of the scientific fundamentals of aircraft design. Research has ceased to be the servant

of aeronautical development, and has become its guide. One need not go to the

very remote past to find that research, like God and the doctor in the ancient jungle,

was valued by the man of strictly practical interests principally in time of trouble,

when he had run into an unexpected obstacle and needed to have it removed in

a hurry. Now he has learned not only to avoid the obstacle by a sufficiently intense

preliminary study, but to make certain that he is really getting the best possible

result from his product, and not merely a passably good one, by trying out the

whole range of possible alternatives under laboratory conditions. On a modern

high-speed transport the difference between a wing-fuselage fillet casually faired

in to look about right and one determined as the ideal through a long series of

studies in the wind tunnel may be 3 m.p.h. in maximum speed. On a 12-passenger

twin-engined transport that means a saving of about $2,500 a year in operating

cost on a single plane. On an order for twenty such planes, the saving in a single

year would be enough to pay the cost of building and equipping a first-class wind

tunnel in which to do the work. That fact has made itself felt, and whereas no

more than four or five years ago it was rather an extraordinary thing to have any

extensive wind-tunnel testing done before building a new ship it has now become

the general rule. Not only the wind tunnel, but the seaplane channel as well, has

become an accepted and an almost necessary instrument of the designer in his

preliminary planning of a new type.

Aviation has suffered at all times from a delusive belief, which one may still

encounter here and there, that research and analysis in airplane design are futile

frills and that what is needed is to have a good practical man with an extended

experience as a pilot and a good eye for line draw a picture of the new airplane

and build it accordingly. There was a time when that went so far that the very

making of engineering drawings for an experimental machine was considered to

fall under the head of “frills,” and one pioneer builder used to boast “he could
Document 2-30(a–b) 659

start in the middle and work outwards and not decide what anything on the plane

was going to be like until he came to it.” That certainly is one way of doing it, but

not the best way. How far it is from being the best becomes apparent when the

practical man scornful of theory and of research has done his best and when

another designer unhampered by any such scorn, but possessed of wind tunnels

and believing their results, takes the same set of specifications and produces a

machine to be put into the competition. The airplane built by inspiration and by

seasoned judgment is prone to look extremely foolish, under those conditions, as

against the ship in which judgment is backed by careful application of science and

of laboratory technique.

Already it is true that a majority of America’s foremost airplane builders

either have wind tunnels of their own or have access to the tunnels of neighboring

universities. We predict that within another three or four years the company that

fails to own and operate its own tunnel will be quite out of the running, and that

an aerodynamic section attached to every engineering staff, with its personnel

concerning themselves exclusively with aerodynamic research and with the analysis

of aerodynamic problems handed over to them by the designers, will be no questionable extravagance but quite as much of a necessity as the stress analysis group

is today. The compass points that way, and the wise management will make its

plans accordingly.

Document 2-30(b), “Research Symphony: 

The Langley Philharmonic in Opus No. 10,” 1935.

Research Symphony

The Langley Philharmonic in Opus No. 10

With conductor Joseph S. Ames insisting on inflexible adherence to tempo

and Concert Master George W. Lewis getting brilliant performance from his individual group and solo performers, the Tenth Annual Engineering Research

Conference of the National Advisory Committee for Aeronautics proceeded with

all the smoothness of a major symphonic ensemble in action. The audience was the

aviation industry in numbers that strained the facilities of the isolated Tidewater

Peninsular at Old Point Comfort almost to the limit. It is impossible within our

space limitations to reproduce each nuance in the detailed development of every

research theme. That we leave to the extensive literature of the committee. All we

can do here is to give a brief recapitulation of some of the principal movements.

Spinning Song

Most fascinating number of this year’s performance was the demonstration of

the brand new tunnel where model airplanes may spin freely in a vertically rising

air jet of controllable velocity. Most remarkable are the models themselves, miniature
660 Chapter 2: Building a Research Establishment

airplanes that are not only geometrically similar to their full scale counterparts,

but also must have identical mass distribution and similar dynamic characteristics.

To add wonder to wonders, into each model has been built delicate timing

machinery connected to controls to reset rudder, elevators, ailerons at predetermined intervals during spinning to promote recovery from the spin, or to change

its characteristics. To watch these intricate models swimming in the air stream like

goldfish in a bowl, reproducing well-known spinning maneuvers as though under

the control of a miniature human Pilot, was an experience that few of this year’s

visitors will soon forget.

Thanks to Public Works Administration funds which made possible the installation of the new tunnel and its accessory equipment, the 800 factors which contribute

to spins outlined some five years ago by Fred E. Weick, may now be subjected to

exacting laboratory tests, reducing by many times the expense and the danger

involved in full-scale spinning research.

Wings; Crescendo

Long before the Department of Commerce undertook a program of private

flying encouragement through equipment purchases, the NACA had been at

work on the fundamentals of what makes flying simpler. Five years of work on

variable lift devices for lowering landing speed and on surer lateral controls had

gradually split the boundaries of knowledge, and the conference revealed for the

first time a new series of results.

Particularly important was the report of flight trials on designs so far tried

only in the wind tunnel. Flaps and variable area wings, generally considered only

as a means of reducing minimum speed, are established on a new footing as

proven aids to performance in getting off and climbing. On a standard Fairchild

monoplane, the installation of a Fowler wing (sliding a flap out of the lower surface

of the wings to rear and at the same time pulling it down so that both the area

and the camber are increased) reduced take-off distance from 500 ft. to 330 ft. in

still air. The total distance to clear a 50-ft obstacle came down from 910 ft. to 720,

the calculated distance to accomplish the same take-off and climb with a heavily

loaded twin engine ship, from 1,500 ft. to 840. On the twin engine take-off, the

use of a simple split flap without area increasing features would reduce the space

needed for take-off only from 1,500 ft. to 1,100 ft.

A trend toward variable lift devices of higher efficiency than the plain hinged

flap, a readiness to accept as necessary whatever mechanical complications their

virtues might involve, were plainly indicated in the report and their discussions

by the engineers in attendance. Area variation, for example, is clearly a matter of

practical interest for the near future.

Most elaborate and most effective of devices so far known is boundary-layer

control, sucking off the air from the surface of the wing into its interior through
Document 2-30(a–b) 661

slots parallel to the span along the upper surface. The committee’s studies show

that with a fixed wing with a single slot halfway back on the cord, burbling can be

eliminated, a steady flow and a steadily increasing lift be maintained up to an

angle of attack of over 50 deg., a maximum lift coefficient of 3.0 be attained with

an application to the blower of less than 3 per cent of the engine power. That

would make it possible to land at 55 m.p.h. with a wing loading of 23 lb. per sq.

ft. Even with a thin tapered wing well suited for high speed use the same lift could

be secured with expenditure of about 6 per cent of the total power.

Interesting experiences with the handling of flap-equipped airplanes came

out in the course of discussion. The committee’s pilots have found that if the flaps

are pulled down suddenly to steepen tile glide path in coming in over an obstacle,

the immediate effect is exactly the opposite of what is wanted. The increase of lift

by the flaps sets the ship to climbing above its original course, and with a light airplane

fully 850 ft. had to be covered before the flight-path dropped below the level that

would have been reached if the flaps had not been used at all. To overcome any such

reversal of effect it was suggested that the flaps be pulled down to very large angles,

as much as 80 deg., where there will be a pure air-brake action with no further

increase of lift. One experimental machine of private-owner type has been fitted

with such a control for trial.

Another way of increasing the lift, well known to test pilots trying to meet a

minimum speed specification but seldom made the subject of research, is by pulling

back into a full stall and then opening the throttles wide to blow the slip-stream

across the wings and to carry a part of the weight directly on the propeller thrust.

Measurement on a typical plane in the propeller research laboratory at Langley

Field showed an effective increase of 0.3 in the lift coefficient from such a maneuver,

a possible reduction of about 10 per cent in minimum speed.

The effect of large flap angles on stability has proved to be bad throughout,

even when the flap extends over only a part of the span. The Fairchild with the

Fowler flap became longitudinally unstable both with free and with fixed controls

at all speeds above 70 m.p.h. with the flap clear down. Fortunately the stability

characteristics prove to be best in the part of the speed range where the flap is

most likely to be wanted, but at low speeds there is an extreme sloppiness of rudder

control that requires as much as 11 deg. of rudder to hold a straight course. In

some cases, in fact, the machine could not be flown at all at minimum speed with

full flap effect because of the impossibility of keeping it straight even with full rudder.

Mr. McAvoy of the Committee’s technical staff and Temple N. Joyce debated flap

landing technique and agreed that it differed from normal practice in that the

machine need never be brought anywhere near a stalled attitude. The drag being

so large that the nose call be put down sharply without picking up much speed,

the angle of attack can be kept small until the very last instant of flattening out.
662 Chapter 2: Building a Research Establishment

For that reason, the abrupt collapse of the lift coefficient at angles beyond the

burble point that characterizes all flap arrangements makes no trouble in practice.

The NACA slot lip control is a new and most promising addition to the long

list of lateral controls developed especially for use in conjunction with flaps and

to be effective beyond the stall. A combination of slot and spoiler, it is a small flat

plate lying flush with the upper surface and hinged at its forward edge. So placed

as normally to block very largely but not entirely the exit of air from a slot through

the wing just forward of mid-chord, its raising cuts down the lift with none of the

time lag that marks the action of an ordinary spoiler.

Drag; Diminuendo

Few of the committee’s programs have been as extensive or as fruitful of practical

results as the relentless pursuit of drag. First notable contribution to aerodynamic

efficiency was the familiar NACA radial engine cowling, then a long series of investigations on nacelle position, interference, correlated with more highly theoretical

studies of air flow, scale effect and turbulence.

In the course of recent research the laboratories have dipped deeply into fundamentals without losing sight of visual manifestations of flow phenomena. For

example, the smoke streamer studies of flow separation from airfoil bodies have

revealed that a turning propeller in optimum position (tractor or pusher installation)

improves the airflow in normal flight and at high angles of attack.

Optimum position for engine installation has been found to be within the

structure or in leading edge nacelles. An ideal installation would have the engine

completely enclosed in the structure fitted with extension shaft. Rear extension of

the shaft gives best net efficiency at low speeds but, at 200-300 m.p.h. is worse

than one with propeller ahead of the leading edge.

Tests on in-line engine installation in wing-nacelle combinations have yielded

slightly higher drag figures than for radials, although it appears probable that

with higher power concentration in a given nacelle, conditions may be reversed.

Bombshell for retractable landing gear advocates was the news that clean

fixed landing gears had only slightly lower drag than fully retracting types. In

terms of top speed, the difference was approximately 3 per cent. Airline engineers

pointed out in conference that 6 m.p.h. at the upper end of the range was the

equivalent to 10 per cent power, asked for study of fixed landing gear effect on

stability and spinning qualities. Investigation of the take-off characteristics of airplanes

with normal retracting gear extended as compared with fixed faired gears was

suggested by T. P. Wright.

To run down the influence of various fuselage-wing combinations on drag

and therefore on speed, a series of tests was run in the variable density tunnel to

determine optimum wing position with respect to fuselage. Beginning with a bare

fuselage with an uncowled radial engine in the nose and a rectangular wing in the
Document 2-30(a–b) 663

best low-wing position, refinements were added successively. Engine cowling, wing

root fillets, complete housing of engine in the wing, adaptation of a symmetrical

airfoil (rectangular then tapered), and finally a shift of the wing up to a high mid-wing

position, boosted the potential high-speed of the combination (for constant

engine power) from 145 up to 205 m.p.h. The addition of a trailing edge flap naturally did not add to the top speed but gave, as would be expected, a greatly

increased speed range.

New sources of efficiency were promised by Eastman N. Jacobs, whose airfoil

family increases yearly. Ideal offspring, NACA 23012, is symmetrical, has maximum

camber relatively far forward. In such airfoils, maximum camber may be moved

forward beneficially to 15 per cent of chord length, harmlessly to 5 per cent.

Stresses, Giros, Boats; Miscellany

Heretofore the study of gust loads has been confined to effects on wings.

Recent flight research has indicated, however, that gust loads on tail surfaces are

much greater than has been June, suspected. Accelerometer readings give an

average for the action of a gust over the entire wing span but since the wave

length of the gust may be much shorter than the wing span, the peak loads

imposed by the gust may be much higher than the average recorded for the entire

wing. Where the wing may extend beyond the boundaries of a single gust wave,

the shorter span tail surfaces may take the full gust impact. On an O2H machine,

for example, where an average wing gust of 13 ft. per second was recorded, simultaneous readings on the horizontal and vertical tail surfaces showed 33 and 45 ft.

per second gusts respectively. An extensive investigation of tail loading to supplement

the results so far obtained from acceleration readings on transport planes in actual

service is now under way.

Work with rotating wing systems, although apparently not as active as a year

ago, still has a place in the research program. Recent investigations have covered

the selection of airfoil sections for rotor use, also plan form modifications for

maximum values of L/D. Thin cambered sections show higher efficiency than the

symmetrical types; for example, NACA 4412 was found to be some 13 per cent more

efficient than NACA 0018. Although it was suspected that greater rotor efficiencies

might be obtained by cutting out portions of the effective blade area near the hub,

experiment soon indicated not only that maximum L/D’s were obtained with a full

span blade, but also that greater efficiencies might be expected from tapered plan

forms where the chord at the blade root was considerably greater than at the tip.

The ability of an autogiro to take off vertically on energy stored in an over

speeded rotor was demonstrated with a 10 ft. electrically driven model. During

initial rotation the blades were held at zero lift position then suddenly released to

a high angle of attack position. The model rose vertically to a height of 20-25 ft.

It was shown that the vertical distance attained during the initial jump is a function
664 Chapter 2: Building a Research Establishment

of disk loading. Tests on the model showed that, with a 392 ft. per second tip

speed and a disk loading of 2 lb. per sq. ft., the initial rise is only 1 ft. Cutting the

disk loading in half, however, the initial jump goes up to 15 ft. 

The research program which led to the discovery of the beneficial effects of

pointed main steps for flying boat bottoms (announced in 1934) was extended to

cover steps of varying depths, and to study the effects of changes in the angle of

dead rise and after-body keel. Shallow steps were shown to perform better at low

speeds, deeper steps at higher speeds. Relatively flat after-body angles (the range

between 0 and 8 deg. has so far been investigated) appear more advantageous at

low speeds, low loadings. Dead rise angles did not seem critical, however, for the

characteristics of similar hulls with bottom angles of 15, 20 and 25 deg, were

essentially alike.

Most important result announced concerned the effect of various shapes of rivet

heads in bottom plating. By towing metal planing surfaces with a standard pattern

of dimpled, brazier and button headed rivets, the advantage of keeping bottoms

as smooth as possible became evident. The resistance of dimpled rivets was 5 per

cent over the smooth plate, brazier heads 12 per cent, button heads 17 per cent.

Power plants; Energico

Some twenty forms of NACA cowl with varying ratios of nose opening to overall diameter and rear gap area are being studied at full scale in the 20 ft. tunnel.

Charts will shortly be available from which designers will be able to select cowl

characteristics for all desired engine and flight conditions. As suggested by airline

operators who experience cooling troubles at normal angles and speeds of climb,

the program will be extended to include rang of angles of thrust in line to flight

path of from 0 to 10 deg.

Preliminary test results indicate that cylinder cooling at constant power output

is independent of altitude as long as the mass movement of air over the cylinder is

constant. The cooling effect per unit of cooling surface seems to vary approximately

as the square root of the airflow in terms of pounds per second per square feet of

area covered. Studies of variation of cylinder temperatures with changes of cooling

air temperatures indicate that the variation is linear, independent of brake mean

effective pressure, mass flow.

Cooling fins should run at least eight to the inch, should be closely jacketed

to force airflow to follow the fin and the wall closely. The shape of the jacket and

the size of the intake and outlet openings are being investigated not only for free

air flow cooling but also for blower cooling.

Interest in completely housed-in engines for drag reduction prompts

research in blower cooling. Of chief interest is the cost of blower operation in

horsepower. Some 30 to 35 per cent of total horsepower goes into the cooling of

a bare engine, 13 to 16 per cent to cool the same engine with a properly designed
Document 2-30(a–b) 665

NACA cowl. Calculations based on skin friction of the average radial engine indicate

that the absolute minimum of power required is about 1? per cent of the total

horsepower. Therefore, the range in which blower designs must work is between

1? and 13 per cent of the total horsepower. On the basis of 65 per cent blower efficiency, the cooling loss should not be over 5 per cent.

Where long range performance is required, the low specific fuel consumption

of the compression ignition engine put is independent of altitude as long as is

very attractive since 40 to 45 per cent of initial useful load of an airplane may be

required for fuel alone. Work has progressed far enough to indicate that it is possible

to obtain the same power for the same displacement and r.p.m. for carburetor

and for compression ignition engines with reduction of specific fuel consumption

of some 20 per cent.

Shape of combustion chamber affects the efficiency of compression ignition

engines. Spherical or disk type mixture chambers were found not as effective as a

new displacer type recently developed by the laboratories. A solid boss cast on top

of the piston projects into the mixture chamber at top dead center, causing a high

velocity air flow in the narrow clearance between boss and sidewall and great turbulence in the chamber at the instant of fuel injection.

Among questions submitted for consideration of the committee: Best cooling

arrangement for six-cylinder in-line engines? How can airflow inside an NACA

cowl be restored to the outside flow most efficiently?—through an open slot or

through louvers?—is it permissible to support the skirt of the cowl on the fire

wall? Are internal guide vanes permissible? How may the accessories on an in-line

engine best be cooled? What is the effect of a propeller spinner on the cooling of

an in-line engine? How best to cool a flat engine—where to take in the air, where

to discharge it? What is the drag of openings such as the ends of exhaust stacks,

facing aft,

Propellers; Vibrato

Resonance with frequencies originating in the engine rather than aerodynamic

flutter is now recognized as the cause of vibrations frequently leading to fatigue

failures in propellers. It is demonstrable that true flutter can occur only at speeds

far in excess of the speed of sound. The natural frequency of a rotating propeller

is quite different from one at rest, due to the blade tension induced by centrifugal

forces. For full scale propellers, therefore, vibration analysis by accoustical [sic]

methods becomes the only practical method.

A method of scaling down propeller vibration effects for study was shown. A

propeller of full-scale diameter was prepared with the aluminum alloy blades

reduced to one-tenth normal width and one-tenth normal thickness. It is mathematically demonstrable that the vibration characteristics of such a propeller when

rotated at one tenth normal revolutions per minute are exactly similar to those of
666 Chapter 2: Building a Research Establishment

the normal propeller at normal speeds. It is therefore possible by rotating the

propeller (with blades completely enclosed in steamline tubes to eliminate all air

effects) and imposing at the same time axial vibrations of known frequencies on

the hub, to determine the resonant frequencies of the modified blades. Results

scale up to full size by simply multiplying all data by ten.

It was stated that undesirable resonances had been eliminated in some cases by

changing the mounting of a propeller from a position parallel to the engine crank

throw to one 90 deg. away, but the desirability of such a method of correction was

seriously questioned by propeller and engine manufacturers. 

A new light on the composition of propeller noise was obtained by filtering

out certain frequencies (or combinations of frequencies) from the sound picked

up by microphone 50 ft. away from an electrically driven full scale propeller. It

was evident that the troublesome ranges were (1) the higher frequency harmonics

and (2) the vortex noises which produce the characteristic tearing sounds emitted

by a propeller at high speed. It was shown that the basic frequency filtered out

from all the super-imposed harmonics and vortex noises was a musical note of low

pitch. This is the note normally heard by an observer at a relatively great distance.

The unpleasant frequencies are filtered out by the intervening atmosphere. This

effect was produced electrically to conclude the demonstration.
NASA History Series

Reference Works, NASA SP-4000:

Grimwood, James M. Project Mercury: A Chronology. NASA SP-4001, 1963.

Grimwood, James M., and C. Barton Hacker, with Peter J. Vorzimmer. Project

Gemini Technology and Operations: A Chronology. NASA SP-4002, 1969.

Link, Mae Mills. Space Medicine in Project Mercury. NASA SP-4003, 1965.

Astronautics and Aeronautics, 1963: Chronology of Science, Technology, and Policy.

NASA SP-4004, 1964.

Astronautics and Aeronautics, 1964: Chronology of Science, Technology, and Policy.

NASA SP-4005, 1965.

Astronautics and Aeronautics, 1965: Chronology of Science, Technology, and Policy.

NASA SP-4006, 1966.

Astronautics and Aeronautics, 1966: Chronology of Science, Technology, and Policy.

NASA SP-4007, 1967.

Astronautics and Aeronautics, 1967: Chronology of Science, Technology, and Policy.

NASA SP-4008, 1968.

Ertel, Ivan D., and Mary Louise Morse. The Apollo Spacecraft: A Chronology,

Volume I, Through November 7, 1962. NASA SP-4009, 1969.

Morse, Mary Louise, and Jean Kernahan Bays. The Apollo Spacecraft:

A Chronology, Volume II, November 8, 1962–September 30, 1964.

NASA SP-4009, 1973.

Brooks, Courtney G., and Ivan D. Ertel. The Apollo Spacecraft: A Chronology,

Volume III, October 1, 1964–January 20, 1966. NASA SP-4009, 1973.

Ertel, Ivan D., and Roland W. Newkirk, with Courtney G. Brooks. The Apollo

Spacecraft: A Chronology, Volume IV, January 21, 1966–July 13, 1974. 

NASA SP-4009, 1978.

Astronautics and Aeronautics, 1968: Chronology of Science, Technology, and Policy.

NASA SP-4010, 1969.

Newkirk, Roland W., and Ivan D. Ertel, with Courtney G. Brooks. Skylab: A

Chronology. NASA SP-4011, 1977.

667
668 The Wind and Beyond: Volume 1

Van Nimmen, Jane, and Leonard C. Bruno, with Robert L. Rosholt. NASA

Historical Data Book, Volume I: NASA Resources, 1958–1968. NASA SP-4012, 1976,

rep. ed. 1988.

Ezell, Linda Neuman. NASA Historical Data Book, Volume II: Programs and

Projects, 1958–1968. NASA SP-4012, 1988.

Ezell, Linda Neuman. NASA Historical Data Book, Volume III: Programs and

Projects, 1969–1978. NASA SP-4012, 1988.

Gawdiak, Ihor Y., with Helen Fedor, compilers. NASA Historical Data Book,

Volume IV: NASA Resources, 1969–1978. NASA SP-4012, 1994.

Rumerman, Judy A., compiler. NASA Historical Data Book, 1979–1988: Volume V,

NASA Launch Systems, Space Transportation, Human Spaceflight, and Space Science.

NASA SP-4012, 1999.

Rumerman, Judy A., compiler. NASA Historical Data Book, Volume VI: NASA Space

Applications, Aeronautics and Space Research and Technology, Tracking and Data

Acquisition/Space Operations, Commercial Programs, and Resources, 1979–1988.

NASA SP-2000-4012, 2000.

Astronautics and Aeronautics, 1969: Chronology of Science, Technology, and Policy.

NASA SP-4014, 1970.

Astronautics and Aeronautics, 1970: Chronology of Science, Technology, and Policy.

NASA SP-4015, 1972.

Astronautics and Aeronautics, 1971: Chronology of Science, Technology, and Policy.

NASA SP-4016, 1972.

Astronautics and Aeronautics, 1972: Chronology of Science, Technology, and Policy.

NASA SP-4017, 1974.

Astronautics and Aeronautics, 1973: Chronology of Science, Technology, and Policy.

NASA SP-4018, 1975.

Astronautics and Aeronautics, 1974: Chronology of Science, Technology, and Policy.

NASA SP-4019, 1977.

Astronautics and Aeronautics, 1975: Chronology of Science, Technology, and Policy.

NASA SP-4020, 1979.

Astronautics and Aeronautics, 1976: Chronology of Science, Technology, and Policy.

NASA SP-4021, 1984.

Astronautics and Aeronautics, 1977: Chronology of Science, Technology, and Policy.

NASA SP-4022, 1986.
NASA History Series 669

Astronautics and Aeronautics, 1978: Chronology of Science, Technology, and Policy.

NASA SP-4023, 1986.

Astronautics and Aeronautics, 1979–1984: Chronology of Science, Technology, and

Policy. NASA SP-4024, 1988.

Astronautics and Aeronautics, 1985: Chronology of Science, Technology, and Policy.

NASA SP-4025, 1990.

Noordung, Hermann. The Problem of Space Travel: The Rocket Motor. Edited by

Ernst Stuhlinger and J. D. Hunley, with Jennifer Garland. NASA SP-4026, 1995.

Astronautics and Aeronautics, 1986–1990: A Chronology. NASA SP-4027, 1997.

Astronautics and Aeronautics, 1990–1995: A Chronology. NASA SP-2000-4028, 2000.

Management Histories, NASA SP-4100:

Rosholt, Robert L. An Administrative History of NASA, 1958–1963. 

NASA SP-4101, 1966.

Levine, Arnold S. Managing NASA in the Apollo Era. NASA SP-4102, 1982.

Roland, Alex. Model Research: The National Advisory Committee for Aeronautics,

1915–1958. NASA SP-4103, 1985.

Fries, Sylvia D. NASA Engineers and the Age of Apollo. NASA SP-4104, 1992.

Glennan, T. Keith. The Birth of NASA: The Diary of T. Keith Glennan. J. D. Hunley,

editor. NASA SP-4105, 1993.

Seamans, Robert C., Jr. Aiming at Targets: The Autobiography of Robert C. Seamans, Jr.

NASA SP-4106, 1996.

Garber, Stephen J., editor. Looking Backward, Looking Forward: Forty Years of U.S.

Human Spaceflight Symposium. NASA SP-2002-4107, 2002.

Project Histories, NASA SP-4200:

Swenson, Loyd S., Jr., James M. Grimwood, and Charles C. Alexander. This New

Ocean: A History of Project Mercury. NASA SP-4201, 1966; rep. ed. 1998.

Green, Constance McLaughlin, and Milton Lomask. Vanguard: A History. NASA

SP-4202, 1970; rep. ed. Smithsonian Institution Press, 1971.

Hacker, Barton C., and James M. Grimwood. On the Shoulders of Titans: A History

of Project Gemini. NASA SP-4203, 1977.
670 The Wind and Beyond: Volume 1

Benson, Charles D., and William Barnaby Faherty. Moonport: A History of Apollo

Launch Facilities and Operations. NASA SP-4204, 1978.

Brooks, Courtney G., James M. Grimwood, and Loyd S. Swenson, Jr. Chariots for

Apollo: A History of Manned Lunar Spacecraft. NASA SP-4205, 1979. 

Bilstein, Roger E. Stages to Saturn: A Technological History of the Apollo/Saturn

Launch Vehicles. NASA SP-4206, 1980, rep. ed. 1997.

SP-4207 not published.

Compton, W. David, and Charles D. Benson. Living and Working in Space: A

History of Skylab. NASA SP-4208, 1983.

Ezell, Edward Clinton, and Linda Neuman Ezell. The Partnership: A History of the

Apollo-Soyuz Test Project. NASA SP-4209, 1978.

Hall, R. Cargill. Lunar Impact: A History of Project Ranger. NASA SP-4210, 1977.

Newell, Homer E. Beyond the Atmosphere: Early Years of Space Science. NASA 

SP-4211, 1980.

Ezell, Edward Clinton, and Linda Neuman Ezell. On Mars: Exploration of the Red

Planet, 1958–1978. NASA SP-4212, 1984.

Pitts, John A. The Human Factor: Biomedicine in the Manned Space Program to 1980.

NASA SP-4213, 1985.

Compton, W. David. Where No Man Has Gone Before: A History of Apollo Lunar

Exploration Missions. NASA SP-4214, 1989.

Naugle, John E. First Among Equals: The Selection of NASA Space Science

Experiments. NASA SP-4215, 1991.

Wallace, Lane E. Airborne Trailblazer: Two Decades with NASA Langley’s Boeing 737

Flying Laboratory. NASA SP-4216, 1994.

Butrica, Andrew J., editor. Beyond the Ionosphere: Fifty Years of Satellite

Communication. NASA SP-4217, 1997.

Butrica, Andrew J. To See the Unseen: A History of Planetary Radar Astronomy.

NASA SP-4218, 1996.

Mack, Pamela E., editor. From Engineering Science to Big Science: The NACA and

NASA Collier Trophy Research Project Winners. NASA SP-4219, 1998.

Reed, R. Dale, with Darlene Lister. Wingless Flight: The Lifting Body Story. 

NASA SP-4220, 1997.
NASA History Series 671

Heppenheimer, T. A. The Space Shuttle Decision: NASA’s Search for a Reusable Space

Vehicle. NASA SP-4221, 1999.

Hunley, J. D., editor. Toward Mach 2: The Douglas D-558 Program. 

NASA SP-4222, 1999.

Swanson, Glen E., editor. “Before this Decade Is Out . . .”: Personal Reflections on the

Apollo Program. NASA SP-4223, 1999.

Tomayko, James E. Computers Take Flight: A History of NASA’s Pioneering Digital

Fly-by-Wire Project. NASA SP-2000-4224, 2000.

Morgan, Clay. Shuttle-Mir: The U.S. and Russia Share History’s Highest Stage. NASA

SP-2001-4225, 2001.

Leary, William M. “We Freeze to Please”: A History of NASA’s Icing Research Tunnel

and the Quest for Flight Safety. NASA SP-2002-4226, 2002.

Mudgway, Douglas J. Uplink-Downlink: A History of the Deep Space Network

1957–1997. NASA SP-2001-4227, 2001. 

Center Histories, NASA SP-4300:

Rosenthal, Alfred. Venture into Space: Early Years of Goddard Space Flight Center.

NASA SP-4301, 1985.

Hartman, Edwin P. Adventures in Research: A History of Ames Research Center,

1940–1965. NASA SP-4302, 1970.

Hallion, Richard P. On the Frontier: Flight Research at Dryden, 1946–1981. 

NASA SP-4303, 1984.

Muenger, Elizabeth A. Searching the Horizon: A History of Ames Research Center,

1940–1976. NASA SP-4304, 1985.

Hansen, James R. Engineer in Charge: A History of the Langley Aeronautical

Laboratory, 1917–1958. NASA SP-4305, 1987.

Dawson, Virginia P. Engines and Innovation: Lewis Laboratory and American

Propulsion Technology. NASA SP-4306, 1991.

Dethloff, Henry C. “Suddenly Tomorrow Came . . .”: A History of the Johnson Space

Center. NASA SP-4307, 1993.

Hansen, James R. Spaceflight Revolution: NASA Langley Research Center from

Sputnik to Apollo. NASA SP-4308, 1995.
672 The Wind and Beyond: Volume 1

Wallace, Lane E. Flights of Discovery: 50 Years at the NASA Dryden Flight Research

Center. NASA SP-4309, 1996.

Herring, Mack R. Way Station to Space: A History of the John C. Stennis Space

Center. NASA SP-4310, 1997.

Wallace, Harold D., Jr. Wallops Station and the Creation of the American Space

Program. NASA SP-4311, 1997.

Wallace, Lane E. Dreams, Hopes, Realities: NASA’s Goddard Space Flight Center, The

First Forty Years. NASA SP-4312, 1999.

Dunar, Andrew J., and Stephen P. Waring. Power to Explore: A History of the

Marshall Space Flight Center. NASA SP-4313, 1999.

Bugos, Glenn E. Atmosphere of Freedom: Sixty Years at the NASA Ames Research

Center. NASA SP-2000-4314, 2000.

General Histories, NASA SP-4400:

Corliss, William R. NASA Sounding Rockets, 1958–1968: A Historical Summary.

NASA SP-4401, 1971.

Wells, Helen T., Susan H. Whiteley, and Carrie Karegeannes. Origins of NASA

Names. NASA SP-4402, 1976.

Anderson, Frank W., Jr. Orders of Magnitude: A History of NACA and NASA,

1915–1980. NASA SP-4403, 1981.

Sloop, John L. Liquid Hydrogen as a Propulsion Fuel, 1945–1959. NASA

SP-4404, 1978.

Roland, Alex. A Spacefaring People: Perspectives on Early Spaceflight. NASA 

SP-4405, 1985.

Bilstein, Roger E. Orders of Magnitude: A History of the NACA and NASA,

1915–1990. NASA SP-4406, 1989.

Logsdon, John M., editor, with Linda J. Lear, Jannelle Warren-Findley, Ray A.

Williamson, and Dwayne A. Day. Exploring the Unknown: Selected Documents in 

the History of the U.S. Civil Space Program, Volume I, Organizing for Exploration.

NASA SP-4407, 1995.

Logsdon, John M., editor, with Dwayne A. Day and Roger D. Launius. Exploring

the Unknown: Selected Documents in the History of the U.S. Civil Space Program,

Volume II, Relations with Other Organizations. NASA SP-4407, 1996.
NASA History Series 673

Logsdon, John M., editor, with Roger D. Launius, David H. Onkst, and Stephen

J. Garber. Exploring the Unknown: Selected Documents in the History of the U.S. Civil

Space Program, Volume III, Using Space. NASA SP-4407, 1998.

Logsdon, John M., general editor, with Ray A. Williamson, Roger D. Launius,

Russell J. Acker, Stephen J. Garber, and Jonathan L. Friedman. Exploring the

Unknown: Selected Documents in the History of the U.S. Civil Space Program, Volume

IV, Accessing Space. NASA SP-4407, 1999.

Logsdon, John M., general editor, with Amy Paige Snyder, Roger D. Launius,

Stephen J. Garber, and Regan Anne Newport. Exploring the Unknown: Selected

Documents in the History of the U.S. Civil Space Program, Volume V, Exploring the

Cosmos. NASA SP-2001-4407, 2001.

Siddiqi, Asif A. Challenge to Apollo: The Soviet Union and the Space Race,

1945–1974. NASA SP-2000-4408, 2000.

Monographs in Aerospace History, NASA SP-4500:

Launius, Roger D. and Aaron K. Gillette, compilers, Toward a History of the Space

Shuttle: An Annotated Bibliography. Monograph in Aerospace History, No. 1, 1992.

Launius, Roger D., and J. D. Hunley, compilers, An Annotated Bibliography of the

Apollo Program. Monograph in Aerospace History, No. 2, 1994.

Launius, Roger D. Apollo: A Retrospective Analysis. Monograph in Aerospace

History, No. 3, 1994.

Hansen, James R. Enchanted Rendezvous: John C. Houbolt and the Genesis of the

Lunar-Orbit Rendezvous Concept. Monograph in Aerospace History, No. 4, 1995.

Gorn, Michael H. Hugh L. Dryden’s Career in Aviation and Space. Monograph in

Aerospace History, No. 5, 1996.

Powers, Sheryll Goecke. Women in Flight Research at NASA Dryden Flight Research

Center, from 1946 to 1995. Monograph in Aerospace History, No. 6, 1997. 

Portree, David S. F. and Robert C. Trevino.Walking to Olympus: An EVA

Chronology. Monograph in Aerospace History, No. 7, 1997.

Logsdon, John M., moderator. Legislative Origins of the National Aeronautics and

Space Act of 1958: Proceedings of an Oral History Workshop. Monograph in

Aerospace History, No. 8, 1998.

Rumerman, Judy A., compiler, U.S. Human Spaceflight, A Record of Achievement

1961–1998. Monograph in Aerospace History, No. 9, 1998.
674 The Wind and Beyond: Volume 1

Portree, David S. F. NASA’s Origins and the Dawn of the Space Age. Monograph in

Aerospace History, No. 10, 1998.

Logsdon, John M. Together in Orbit: The Origins of International Cooperation in the

Space Station. Monograph in Aerospace History, No. 11, 1998. 

Phillips, W. Hewitt. Journey in Aeronautical Research: A Career at NASA Langley

Research Center. Monograph in Aerospace History, No. 12, 1998. 

Braslow, Albert L. A History of Suction-Type Laminar-Flow Control with Emphasis on

Flight Research. Monograph in Aerospace History, No. 13, 1999.

Logsdon, John M., moderator. Managing the Moon Program: Lessons Learned From

Apollo. Monograph in Aerospace History, No. 14, 1999. 

Perminov, V. G. The Difficult Road to Mars: A Brief History of Mars Exploration in

the Soviet Union. Monograph in Aerospace History, No. 15, 1999. 

Tucker, Tom. Touchdown: The Development of Propulsion Controlled Aircraft at NASA

Dryden. Monograph in Aerospace History, No. 16, 1999.

Maisel, Martin D., Demo J. Giulianetti, and Daniel C. Dugan. The History of the

XV-15 Tilt Rotor Research Aircraft: From Concept to Flight. NASA SP-2000-4517, 2000.

Jenkins, Dennis R. Hypersonics Before the Shuttle: A Concise History of the X-15

Research Airplane. NASA SP-2000-4518, 2000. 

Chambers, Joseph R. Partners in Freedom: Contributions of the Langley Research

Center to U.S. Military Aircraft in the 1990s. NASA SP-2000-4519, 2000.

Waltman, Gene L. Black Magic and Gremlins: Analog Flight Simulations at NASA’s

Flight Research Center. NASA SP-2000-4520, 2000.

Portree, David S. F. Humans to Mars: Fifty Years of Mission Planning, 1950–2000.

NASA SP-2001-4521, 2001.

Thompson, Milton O., with J. D. Hunley. Flight Research: Problems Encountered

and What They Should Teach Us. NASA SP-2000-4522, 2000.

Tucker, Tom. The Eclipse Project. NASA SP-2000-4523, 2000.

Siddiqi, Asif A. Deep Space Chronicle: A Chronology of Deep Space and Planetary

Probes, 1958–2000. NASA SP-2002-4524, 2002. 

Merlin, Peter W. Mach 3+: NASA/USAF YF-12 Flight Research, 1969–1979. 

NASA SP-2001-4525, 2001. 
Essay Title Please Replace 675

Renstrom, Arthur G. Wilbur and Orville Wright: A Bibliography Commemorating the

One-Hundredth Anniversary of the First Powered Flight on December 17, 1903. NASA

SP-2002-4527, 2002.

No monograph 28.

Chambers, Joseph R. Concept to Reality: Contributions of the NASA Langley Research

Center to U.S. Civil Aircraft of the 1990s. SP-2003-4529, 2003.

Peebles, Curtis, editor. The Spoken Word: Recollections of Dryden History, The Early Years.

SP-2003-4530, 2003.

Jenkins, Dennis R., Tony Landis, and Jay Miller. American X-Vehicles: An InventoryX-1 to X-50. SP-2003-4531, 2003.
676 Chapter 1: The Achievement of Flight
Ader, Clément, 14, 180, 181

Adlershof. See Deutschen Versuchsanstalt für

Flugwesen, Adlershof. 

Advanced Group for Aeronautical Research

and Development (AGARD), lxi

Aerial Experiment Association,

Hammondsport, N.Y., 230

Aerial Transport Company. See Henson and

Stringfellow airplane. 

Aero Club of America, 230, 453

Aeronautical Society of Great Britain, 18, 58,

59, 84, 126, 196, 232, 241

Ahlborn, Friedrich, 300

Air Commerce Act, 478

Air Force Aeronautical Systems Center (ASC),

U.S., xlvi

Air Force Flight Dynamics Laboratory, U.S., xlvi

Air Force Flight Test Center History Office

(AFFTC/HO), U.S., xlvii

Air Force Historical Collection, U.S., xxxvii

Air Force Historical Research Agency

(AFHRA), U.S., xlvii

Air Force History Support Office, U.S., xlvi

Air Force Institute of Technology (AFIT),

U.S., 265

Air Force Museum, U.S., xlvii

Air Force, U.S., xviii, xliii, xlvi, xlvii, lxvi

Air Mail Service, U.S., 444, 453, 479, 480

Air Production Board (World War I), 249

Air University, Maxwell AFB, Ala., xlvii, lvi

Albatross airplane, 463

Allegheny Observatory (Penn.), 131, 133, 241

Allen, James, 225, 229

Allis Chalmers Co., 581

Ambrosian Library, Milan, Italy, 5

American Association for the Advancement

of Science (AAAS), 17, 137, 147

American Astronomical Society, 233

American Institute of Aeronautics and

Astronautics (AIAA), lvi, lvii

American Mathematical Society, 233

American Nautical Almanac Office, 233

American Society of Civil Engineers (ASCE), 17

American Society of Mechanical Engineers

(ASME), lvii

Ames Aeronautical Laboratory. See Ames

Research Center, NACA/NASA.

Ames Collection, Milton, xl, xli, xlii

Ames, Joseph S., 247ill., 249, 253ill., 255,

360, 445, 454, 465, 467, 468, 469, 470,

472, 536, 538, 631, 632, 635, 657, 659

Ames Research Center, NACA/NASA, xxxix,

xli, xliv, xlv, 467

Anderson, John D., Jr., xviii, xxiii, lviii, lix, 3,

5, 7, 23, 240

Archimedes, 3

area rule, xli-xlii

Aristotle, 3

Army Air Service, U.S., 264, 581

Army, U.S., 225, 247, 248, 251, 265, 294,

306, 310, 362, 385, 441, 445, 450, 451,

452, 453, 457, 476, 479

Arnold Engineering Development Center

(AEDC), lxix

Arnot, Matthias, 149

Associated Press, 221, 223

Atmospheric Wind Tunnel, NACA Langley,

249, 250ill., 428, 445, 481, 484ill., 498, 577

Atmospheric Wind Tunnel, 7 x 10-Foot,

NACA Langley, 261ill., 261, 262, 263, 435

Auburn University, xii, xiii, xxxv, lvi, lvii,

xlvii, lxvii, lxx

Austin Co., 577

Auteuil, France, 245, 403

autogiro, 620-21

Automobile Club of America, 289

Avery, Norm, lxvi

Avery, William, 20, 210, 211

Avion III (Ader), 14 

Baals, Donald D., and Corliss, William, lxiv

Bacon, David L., 487, 531

Baden-Powell, Baden Fletcher Smyth, 126

Badin Double Venturi Head, 371, 372, 372ill.

677

Index
678 The Wind and Beyond

Bairstow, Leonard, 312, 316

Bane, Thurman H., 247ill., 362, 374, 445, 454

Barimar Ltd., 611

Barlow, Jewel B., and Rae, William H., Jr., lxiv

Bateman, Harry, 466, 468, 609

Battle of Britain (World War II), 339

Bauer, Eugene E., lxvi

B. E. 2C airplane, 319, 324, 344

Beall, Wellwood, E., 646

Becker, John V., lxiv

Bell aircraft:

Model 204/VH-1, xlvii 

X-1, xxxiii, xxxviii, xlii, xliv, xlvii, lxii

XS-1. See X-1.

X-series, xliv

XV-15 Tilt Rotor Research Aircraft, xxxiv, lxi

Bell, Alexander Graham, 10, 130, 145, 146, 230

Bendemann, Friedrich, 300, 304

Berlin, Don, lxvi

Berliner-Joyce wind tunnel, 640

Bernouilli, Daniel, 6

Bernouilli’s theorem, 398, 399, 400, 401, 417

Betz, Albert, 391

Bilstein, Roger (historian), lx, 234

Board of Ordnance and Fortification, U.S.

Army, 226, 227

Boeing Co., xxxv, l, li, lii, lxv, xli

Historical Archives, xlix, l, 636

Historical Services, lxv 

Boeing aircraft:

Boeing 247, xxxii, l

Boeing 707, xxxiii, l

Boeing 747, l

B-17, xxxii, l

B-29, xxxiii, l

B-47, xxxiii, l

B-52, l

Model 299, l

Model 367-80, l

Boeing Field, xxxviii

Boeing North American, lii

Bolling AFB, D.C., xlvi

Bostonis, Ronald G., lxiii

Boulton & Watt steam engine, 35, 49

Boushey, Homer A., 268ill.

Bowers, Peter M. (historian), lxvi

Braslow, Albert L., lxiii

Brett, C. W., 611, 612, 613

Brewster aircraft:

F2FA, xxxiii

Briggs, Lyman J., 441, 445, 452, 454, 465, 468

Brinkley, W. C., 222

British Advisory Committee for Aeronautics

(ACA), 302, 305, 316, 318, 467, 475, 476

British Aircraft Production Technical

Department, 366

British Air Ministry, 614

British National Physical Laboratory, 244,

246, 248, 249, 286, 297, 300, 302, 311,

312, 313, 316, 317, 319, 379, 380, 387,

391, 405, 411, 412, 416, 417, 447, 448,

451, 467, 473, 475, 476, 481, 483, 485,

486, 487, 490, 499, 611, 612, 633 

Brown, Elmer, 604

Bryan, George Hartley, 392

Bugos, Glenn (historian), lxi

Bureau of Aeronautics, U.S. Navy, xlii, 271,

576, 652, 655

Bureau of Aircraft Production, 376

Bureau of the Budget, 633

Bureau of Construction and Repair, U.S.

Navy, 309, 445, 450, 451

Bureau of Mines, 385, 480

Bureau of Navigation, U.S. Navy, 286, 605

Bureau of Standards, xxvi, 289, 306, 309,

441, 442, 443, 444, 451, 452, 453, 455,

457, 462, 471, 476, 633

Burnham, Walter E., lxvii

Busemann, Adolf, xxv

Busteed, Mr., Squadron Commander, 353

California Institute of Technology (Caltech),

xviii, xix, lv, lxv, 265, 604, 605, 608, 609,

640, 642

Caltech wind tunnel, 609

Cambridge Electric Light Co., England, 315

Cambridge Scientific Instrument Co.,

England, 316

Cambridge University, 580

Caproni Co., 384

Caquot, Albert, 381 

Carnegie, Andrew, 273, 284
Index 679

Cartwright, Edmund, 36

Castellazi, Lt., 400, 403, 412, 422

Cathers, Richard, liii

Catholic University of America, 244, 248

Cayley, George, xi, xx, xxi, 6, 7, 8, 12, 15, 33,

57, 79, 188, 240, 241, 268

Cayley glider of 1804, 7, 8

Centennial of Flight Commemoration Act

(Public Law 105-389), xxvii

Century Series fighters, xliv, xlvii

Chambers Report (U. S. Navy), 287

Chambers, Washington Irving, 246, 286, 287,

288, 296

Champs de Mars, France, 245

Chanute-Herring glider of 1896, 21ill., 23

Chanute, Octave, 15, 17, 17ill., 18, 19, 22,

107, 126, 147, 148, 149, 163, 171, 179,

187, 189, 195, 196, 197, 198, 200, 203,

208, 225, 229, 244, 273, 275, 282, 284

Chapman, William, 35, 36

Chatfield, James S., 637, 638, 639, 640, 641

Chattock gauge, 491

Churchill, Winston, 384

Civil Aeronautics Authority. See Federal

Aviation Administration.

Clark, Kenneth (historian), xx

Clark, Virginius E., 445, 642, 650

Clark Y airfoil, 592, 599, 601

Cleveland, Reginald M., 604

Clinton, William J., xxvii

Coffin, Joseph G., 466, 467, 468, 470, 472

Cogswell, John, Dr., 223

Cold War, xliv, xlvii, l, liii

Collier Trophy, Robert J., xlii, lxiv, 258

Columbus, Christopher, 4

Commission for Aeronautics, U.S., 474

Committee for the Scientific Survey of Air

Defense, 339

Cone, Hutchinson, 264ill.

Congress of Mathematicians, Heidelberg

(1904), 475

Congress, U.S., xxvi, 238, 246, 296, 305, 306,

307, 361, 616, 617, 624, 626, 633, 635, 648 

Consolidated B-24 Liberator, xxxiii

Consolidated Vultee, liii

Convair, liii

Convair aircraft:

Convair 240, liii

Convair 340, liii

Convair 440, liii

Convair 880, liii

Convair 990, liii

B-36, liii

B-58, xxxiii

XFY-1 Pogostick, liii

XF2Y Sea Dart, liii

F-102, xxiv, xxxii, xxxiii, xliv

F-106, xxiv, xxxi, xxxiii, xliv 

XF-92, xxiv, xxxi, xxxiii

Cook, William, li

Cooper, Bertram, 355

Copernicus, Nicolas, 7

Corn, Joseph J. (historian), lxvi

Council of National Defense, 376

cowling, NACA, xxxii, xli, 258, 614, 626,

627, 643, 662, 664, 665 

Crigler, John L., 581

Crocco, Antonio, 405, 412

Crouch, Tom D. (historian), lix, 10, 23, 25,

148, 241, 243

Crowley, John W., 575

Curtiss Aeroplane and Motor Co., 470, 472,

613, 636

Curtiss aircraft:

AT-5 airplane, xxxii

JN4H Jenny, xxxii, 251, 448, 449, 450,

455, 459, 460, 461, 463, 481, 490, 495, 498

NC-4, xxxii

Curtiss Engineering Corp., 446

Curtiss, Glenn H., 149

Curtiss wind tunnels, 403, 411

Curtiss-Wright Corp., liv, lxvi

Cygnet, 230

Daedalus, 1

Daniel Guggenheim Fund for the Promotion

of Aeronautics, lv, 264ill., 265, 266, 605,

606, 607, 609

Daniel Guggenheim Graduate School of

Aeronautics at the California Institute of

Technology, 609, 612

Daniels, John T., 222, 223
680 The Wind and Beyond

Daniels, Josephus, 306

Darwin, Charles, 7

Da Vinci, Leonardo, xi, xix, xx, 1, 4, 5, 239,

240, 245

Davison, F. Trubee, 264ill.

Dawson, Virginia P. (historian), lxviii

Dayton Press, 221

Dayton-Wright RB-1, xxxii

DeBothezat, George, 373, 374, 450

DeFrance, Smith J., 584, 591, 631, 634

Degen, Jakob, 34, 36, 41, 49, 52

DeHavilland DH.4 airplane, 397, 448

De Houthulst, Willy Coppens, xxxv

Department of Commerce, 605, 660

Department of Transportation, xxvi

Detroit Aircraft Corp., 649

Deutschen Versuchsanstalt für Flugwesen,

Adlershof, 300, 302–304, 395

Dines, W. H., 342

Dobson, B. Palin, 356

Dornier, Claude, 647

Douglas aircraft:

A-1 Skyrocket, liv

A4D Skyhawk, liii

A-20, liii, liv

A-26, liii, liv

C-17 Globemaster, liii

C-47, liii

C-54, liii

D-558, liii, xliv, liv, lxii

DC series, xxiv, xxxi, lii, lxvi

DC-1, xlvii

DC-2, xxxii, xlvii

DC-3, xxxii

F4D Skyray, liv

O2H, 663

SBD Dauntless, liii, liv

TBD Devastator, liii

X-3, liii

Douglas Aircraft Co., lii, liii, liv, xlvii, 609, 646 

Douglas, Donald W., liii

Dough, W. S., 222

“Dragonfly” engine, 378

Dryden Flight Research Center

(NACA/NASA), xxxix, xl, xliii, lxii, lxiii

Dryden, Hugh L., lxii

Drzewiecki method, 314, 421

Drzewiecki theory of propeller action, 401,

407, 408

Durand, William F., 250, 264ill., 306, 360,

376, 400, 441, 445, 446, 455, 466, 467,

468, 472, 474, 575

Du Temple, Felix, 14

Edson, Lee, xvii, xxx, lvii

Edwards Air Force Base, Calif., xxxviii, xxxix,

xliii, xlvii

Egtvedt, Claire, li

Eiffel, Gustav A., 245, 251, 253, 268, 287,

291, 294, 296, 297, 298, 303, 318, 381,

405, 412, 422, 446, 473, 481, 485, 499,

556, 588

Einstein, Albert, 263

EMSCO Aero Engine Co., Los Angeles, 645

Engelhardt, Lloyd, liv

Engineering Research Corp. (ERCO), xlii

Eole (Ader), 14, 14ill.

Ercoupe, xlii

Erie Railroad, 17

Etheridge, A. D., 222

Euclid, 4

Euler, Leonhard, 6

Evans, Stanley H., 646

Ewing, Susan E., xlviii

Experimental Techniques Branch, NASA

Langley, xliii

Fairchild F-22 airplane, 600, 601

Fairey, C. R., 613

Fales, Elisha N., 466, 468

Farren, William S., 355

Federal Aviation Administration (FAA), xxvi

Ferri, Antonio, xxv

Fifth International Aeronautic Congress, 289

Fishamend Laboratory, Vienna, Austria, 558, 559

Fliegner, Albert, 417

Flight Research Center. See Dryden Flight

Research Center.

Floyd L. Thompson Technical Library, NASA

Langley, lvi, xliii

Focke, Heinrich, 297

Fokker D-VII airplane, 535
Index 681

Fokker Tri-Motor 5-AT airplane, xxxii 

Ford, Henry, liv

Ford Motor Co., liv

Ford Trimotor airplane, liv

Forrest, Marvin, 581

Fort Meyer, Va., 226, 228

Fowler flap, 661 

Fowler wing, 660

Francillon, René, lxvi

French Academy of Sciences, 39, 56

French Aeronautical Technical Service, 380, 381

Freud, Sigmund, xx

Fuhrmann, H., 297, 304

Full-Scale Tunnel, NACA/NASA Langley,

xxxviii, xliii, 258ill., 259ill., 259, 260ill.,

260, 261, 584, 585, 591, 592, 593, 594ill.,

595, 596ill., 597ill., 598ill., 599ill., 631,

634, 635, 642

Galilei, Galileo, 3, 5

Gallaudet, Edson Fessenden, 23

Gardner, Lester D., 501

Gardiner, Arthur W., 584, 588, 591

Gates Learjet Model 55, xxxiv

Geer, Mary Wells, lxv

General Aviation Collection, University of

Texas at Dallas History of Aviation

Collection, lv

General Aviation Manufacturing Corp., li, lii 

General Dynamics aircraft:

F-16, xxxiv

F-111, xxxiii, xlii

Georgia Institute of Technology, 265, 266, 605

German Society of Mechanical Engineers, 300

German Wright Co., 297

Gillette, Aaron K., lxiii 

Glauert, Heinrich, 464, 575

Glazebrook, R. T., 312

Glenn Research Center at Lewis Field, NASA,

xxxix, lxvii

Goin, Kenneth, lxiv

Goodyear Navy airships, 627

Goodyear Zeppelin Co., 627

Gorn, Michael (historian), lxii, lxv, 270

Göttingen airfoils, 459, 502

Gough, Melvin N., 581

Gray, George W., lx

Greenwood, John T. (historian), lix

Grey, C. G., 237, 264, 611, 614

Griffin, Robert S., Admiral, 385

Griffith, Leigh M., 259, 521, 577, 642, 645,

647, 648

Grumann aircraft:

X-29, xxxiv

Guggenheim Aeronautical Laboratory at the

California Institute of Technology (GALCIT), xviii, xxxvii, liii, lv, 265, 270, 605

Guggenheim, Daniel, 264ill., 265, 604, 610

Guggenheim, Harry, 264ill., 604, 608, 612 

Gull, Lloyd Dake, xxxvi, xxxvii

Gwynn-Jones, Terry (historian), lix

Halley, Edmond, 363

Hallion, Richard P. (historian), lxii, lxiii, 265

Handley-Page Co., 378

Handley-Page wing slot, 613

Hanle, Paul A. (historian), lxv, 269

Hansen, James R. (historian), xi, xii, xxxv, xl,

xliii, lvii, lix, lx, lxi, lxxi, 239, 257, 258, 263

Hargrave, Thomas/James, 149, 162, 163,

164, 180, 185

Hartman, Edwin P., lxi

Harvard University, 233

Hayford, John F., 247ill., 360, 441, 445, 454

Hebbert, C. M., 398

Heinemann, Edward H., lii, liii, liv

Helium Board, 385

Hemke, Paul A., 580, 

Henderson, Paul, 247ill.

Henry Ford Museum and Greenfield Village

Archives, Dearborn, Mich., liv

Henson-Stringfellow airplane, 12, 13

Henson, William, 12

Herring, Augustus M., 15, 19, 19ill., 20, 147,

148, 149, 156, 173, 190, 196, 209, 210, 211

Herring glider of 1896. See ChanuteHerring glider of 1896.

Herrnstein, William, Jr., 581

Hicks, Frederick C., 383, 384

Hicks, Harold, liv

Higgins, George J., 577
682 The Wind and Beyond

Highly Maneuverable Aircraft Technology

(HIMAT), xxxiv, xliv

High-Speed Civil Transport (HCST) program, liii

High-Speed Flight Station (NACA). See

Dryden Flight Research Center.

History of Aviation Collection at the

University of Texas at Dallas, xxxvii

Holden, Henry M., lxvi

Hooke, Robert, 632

Hoover, Herbert, 604, 605

Houston, Robert S., lxiii

Huffaker, Edward C., 24ill., 187, 200, 202, 283

Huffman Prairie, Dayton, Oh., xxxviii, 27, 28

Hughes H-1 aircraft, xxxiii

Hunley, J. D. (historian), lxii

Hunsaker, Jerome C., 245, 246, 250, 251,

255, 270, 286, 287, 296, 301, 306, 311,

317, 359, 383, 445, 454, 463, 465, 497,

499, 500, 501, 536, 537

Hunt, Franklin L., 445, 454

Huttin, Charles, 632

Huyghens, Christian, 5

Hyper-X (X-43), NASA/Industry, xliv

Icarus, 1

Ide, John Jay, 266, 375, 376, 377, 380, 382

Indiana Dunes, Ind., 17, 19, 20, 147

Institute Aerotechnique de St. Cyr, France,

302, 303, 304, 387, 392

International Aeronautic Commission, 289

International Civil Aviation Organization

(ICAO), 580

Internet, xxxvi, xxxvii

Issy-les-Moulineaux, France, 375, 380

Jacobs, Eastman N., 663

Jakab, Peter (historian), lix, 22

Jamestown Exposition of 1907, 230

Jefferson, Thomas, 57

Jenkins, Dennis R., lxiii

Johannistal flying grounds, Germany, 301

Johns Hopkins University, 233, 581

Jones and Paterson method of airfoil design, 322

Jones, B. Melville, 580

Joukowski, Nicolai, xxv, 253, 270, 272

Joyce, Temple N., 661

Junkers Co., 394

Junkers laboratory at Dessau, Germany, 394

Junkers wing, 395

Kaiser Foundation (Germany), 297, 303

Kaiser Prize (Germany), 300, 304

Katydid (Chanute glider), 19, 20, 147

Kelvin, Lord, 10, 125, 128, 543, 546

Kemper, Carlton, 577

Kilgore, Robert, xliii

Kindelberger, James H., “Dutch,” lii

Kinney, Jeremy (historian), lxxi

Kitty Hawk, N.C., viii, xxvii, xxviii, xxx, 1, 2,

20, 23, 24, 26, 28, 130, 187, 192, 198, 199,

200, 204, 208, 212, 221, 222, 223, 231,

244, 284 

Klein, Arthur L., lv, 359, 642, 643, 645, 646,

647, 648, 650, 651

Klemin, Alexander, 646

Knight, Montgomery, 265

Knight, William, 416, 474

Krell manometer, 419

Laboratoire Aerodynamique Eiffel, 302, 499, 506

Lamar Files, William, xlvi

Lanchester, Frederick William, xxv, 270, 392

Land, Emory S., 576

Langley Aerodromes:

Great Aerodrome of 1903, 28, 29ill., 30ill., 130

No. 0, 134

No. 1, 135

No. 3, 136

No. 4, 136, 137

No. 5, 10, 11ill., 130

No. 6, 9ill.

Langley Aeronautical Laboratory. See

Langley Research Center, NACA/NASA.

Langley Field, Va., 237, 247, 248, 249, 306,

400, 403, 410, 411, 417, 418, 422, 441,

446, 447, 455, 456, 458, 461, 469, 481,

496, 522, 560, 561, 575, 588, 591, 601,

613, 623, 626, 627, 629, 631, 648

Langley Memorial Aeronautical Laboratory.

See Langley Research Center, NACA/NASA.

Langley Research Center, NACA/NASA, xxiv,

xxxi, xxxviii, xxxix, xlii, lvii, lx, 29, 256
Index 683

Langley Research Center, NACA/NASA

(continued), 257, 258, 259, 260, 261, 263,

265, 266, 267, 270, 272, 362, 375, 376,

398, 426, 445, 446, 448, 468, 478, 481,

502, 521, 522, 556, 575, 576, 577, 580,

585, 601, 602, 622, 623, 642, 657 

Langley, Samuel P., 9, 10, 12, 22, 26, 28, 31,

89, 107, 126, 127, 128, 130, 131, 141, 145,

149, 179, 180, 181, 187, 205, 217, 221,

238, 241, 283, 284, 293, 632

Lapresle, Charles, 303

Launius, Roger D. (historian), xxvii, lxiii

Law of Bairstow and Booth, 502

Lawrance J-1 engine, 590, 591

Le Bris, Jean Marie, 16

Lee, J. Lawrence (historian), lxxi

Lee, William D. B., 57

Les Hanuadières, France, 31ill.

Lesley, Everett P., 575, 586

Lessing, Sam, 148

Leviathon (Maxim biplane of 1894), 13, 14,

13ill., 127

Lewis, George W., 271, 466, 476, 497, 502,

506, 521, 556, 557, 576, 580, 602, 631,

657, 659

Lewis Research Center, NACA/NASA, xli

Liberatore, Eugene K., lxii

Liberty engine, 436, 484

Library of Congress, xxxvii

Lilienthal, Gustav, 101-02

Lilienthal, Otto, xi, xxi, xxii, 10, 15, 16, 17,

18, 22, 25, 89, 91, 92, 101, 102, 103, 104,

105, 106, 126, 153, 154, 155, 158, 159,

166, 172, 174, 177, 182, 184, 185, 187,

188, 189, 192, 193, 194, 195, 196, 197,

198, 199, 200, 201, 202, 203, 204, 207,

209, 212, 214, 215, 242, 273, 275, 280,

283, 284

Lindbergh, Charles A., 264ill.

Link, Edwin A., lv

Link trainers, lv

Lippisch, Alexander, xxv

Littlewood, William, 68, 248

Locke, C. N. H., 575

Lockheed aircraft:

Air Express, xxxii

Lockheed aircraft (continued):

F-104, xxxiii, xliv

F-117, xxxiv

L1049/C-69, xxxiii

P-38, xxxiii, xlvi

P-80, xxxiii

U-2, xxxi

Vega, xxxii

YF-12/SR-71, xxxiii

Loftin, Laurence K., Jr., xxxi, xxxii, lix

Logsdon, John M., xxvii

London University, 612

Lougheed, Victor, 652, 653, 654, 655, 656

Luddington Line airplanes, 654

Luftfahrzeug Gesellschaft, 297

Luftwaffe, 538

Mach number, 583

Macintosh screw propeller, 72

Mack, Pamela E. (historian), lxiv, 258

Maclaurin, Richard, 246, 311

Malina, Frank, 268ill.

Mansfield, Harold, lxv

Marey, Étienne-Jules, 196

Margoulis, Wladimir, xxv, 253, 497, 499, 506, 507

Mariotte, Edme, 5

Martin B-10 airplane, xlvii

Martin, H. S., 454

Marvin, Charles F., 247ill., 275, 282, 309,

445, 454

Massachusetts Institute of Technology (MIT),

242, 246, 265, 266, 300, 311, 360, 361,

455, 458, 471, 476, 497, 537, 580, 604,

605, 633, 639

Maurain, Charles, 303

Maxim, Hiram, 13, 14, 107, 126, 128, 135,

149, 179, 180, 181, 217, 242, 302, 632

Maxwell AFB, Ala., xlvii

McAvoy, William H., 661

McCarthy, Charles, 637, 638, 639, 640

McCook Field, Oh., xlvi, 248, 249, 263ill.,

264, 265, 362, 363, 373, 374, 403, 404,

411, 445, 450, 451, 452, 455, 458, 581,

588. See also Wright Field and WrightPatterson AFB.
684 The Wind and Beyond

McDonnell aircraft:

F-4, xxxiii

F-101, xliv

McDonnell Douglas Corp., lii, liii, liv, xlix, lxvi 

McDonnell Douglas aircraft:

DC-10, liii

MD-11, liii

MD-90, liii

McFarland, Marvin W., lvii, 187, 273 

Mead, George, 636, 637, 638, 639, 640, 641

Meiler, John, 148

Merrill, A. A., 609

Meurthe, Deutsch de la, 303

Middle Ages, The (European), 2

Millar, G. H., 354

Miller, Elton W., 256ill., 498, 523, 531, 577,

578, 579, 582

Miller, J. W., 264ill.

Miller, Ronald, and Sawers, David (historians), lix

Millikan, Clark B., lv, 265, 268ill., 605

Millikan, Robert, 264ill., 265, 270, 605

Missouri Historical Society Archives, liv

Mixson, Ralph E., 575

Moedebeck, Hermann, 214, 275

Moffett Field, Calif., xxxix

Moffett, William A., 247ill.

Montgolfier brothers, xxi

Montgomery, John Joseph, 16

Montieth, Charles N., 637, 639, 640

Moore, Johnny, 222

Morgan, William C., 521

Motorluftschiff-Studien-Gesellschaft, 296,

297, 303

Mouillard, Louis-Pierre, 16, 187

Mozhaiski, Alexander, 13, 14

Muenger, Elizabeth A. (historian), xliv, lxi

Munk, Max M., xxv, lxv, 253, 255, 257, 266,

267, 267ill., 269, 270, 271, 272, 391, 395,

396, 464, 497, 498, 499, 500, 501, 502,

511, 521, 522, 523, 535, 556, 557, 559,

577, 578, 580, 582, 602, 603

M (Munk) wing sections, 621

Muttray, M., 643

Myers, Ted, 581

NACA 4-digit airfoils, 663

NACA annual manufacturers conferences,

260ill., 631, 657, 659

NACA Report Server, lvi

NACA slot lip, 662

NACA Wind Tunnel No. 2. See VariableDensity Wind Tunnel.

NASA Center for Aerospace Information

(CASI), lvi

NASA Marshall History Office, lxviii

NASA Technical Report Server, lvi

National Air and Space Act of 1958, xxxix

National Air and Space Museum (NASM),

Washington, D.C., xxxv, xxxvi, xxxvii, xlviii, lix

National Archives and Records Aministration

(NARA), xxxv, xliv, xlv, xlvi, lxviii

National Bureau of Standards. See Bureau of

Standards.

National Physical Laboratory at Tedington.

See British National Physical Laboratory.

National Research Council, 376

National Signal Bureau, 212

Naval Academy, U.S., 580

Naval Aircraft Factory, Philadelphia, Pa., 450

Naval Appropriations Act of 1916, 306, 385

Naval Historical Center at the Washington

Navy Yard, Washington, D.C., xlviii-xlix

Naval Observatory, Washington, D.C., 233

Navy Bureau of Construction and Repair,

U.S., 250

Navy, U.S., xliii, xlvii, xlviii, 246, 251, 265,

286, 294, 309, 311, 359, 361, 385, 445,

457, 458, 460, 461, 479, 537, 627, 646, 648

Nayler, J. L., 379, 380

Newcomb, Simon, 233, 234, 235

Newcomen, Thomas, 132

Newport News (Va.) Shipbuilding & Dry

Dock Co., 531

Newton, Isaac, xx, xxi, 5, 6, 7, 55, 71, 240,

241, 525, 632

New York Public Library, xxxvii

New York University Guggenheim School of

Aeronautics, 604, 607, 610

Nieuport “Nighthawk,” 377, 378

Norfolk (Va.) Navy Yard, 653, 654

North American Aviation, Inc., lii, lxvi 
Index 685

North American Aviation aircraft:

AT-6, li

B-25, li

BT-9, li

F-86, xxxiii, li

F-100, xliv, li

F-107, xliv

FJ-1, li

Model NA-16, li, lii

Model NA-73, lii

P-51, xxxiii, xlii, xlvi, li, lxvi 

X-15, xlii, li, lxiii, lxiv

X-15A, xxxiii

XB-70, xxxiii, xliv, li

XFJ-1, lii

XP-51, xl

North American Rockwell Corp., xlix, li, lxv

Northrop aircraft:

HL-10, xxxiv

N-1M, xxxiii

Northrop, John K., “Jack,” li, lii, 649

Norton, Frederick H., 266, 271, 398, 426,

463, 466, 467, 468, 469, 481, 497, 500,

502, 521, 537

Office of Aeronautical Intelligence, NACA,

253, 266, 375, 376, 377

Pannell, J. R., 525, 535

Parseval airship, 296, 298, 299

Pascal, Blaise, 5

Pénaud, Alphonse, 8–10, 133, 134, 140, 150,

184, 188, 209

Pennell, Maynard, li

Pershing, John, 628

Phillips, Horatio, lviii, 59, 115, 116, 180,

181, 242, 268

Pilcher, Percy, 126, 128, 177, 182, 184, 190,

191, 196, 197, 200, 209

Piper aircraft:

Cub, xxxii

Pawnee, xliii

Piper Aircraft Corp., xlii

Pitcairn PCA (Cierva), xxxii

Pitot tube, 313, 363, 364ill., 365, 365ill., 367,

371, 419, 427, 471, 573

Pobjoy engine, 612

Poe, George, 581

Pope, Alan, lxiv

Post Office, U.S., 480, 606

Powers, Sheryll Goecke, lxiii

Prandtl, Ludwig, xxv, lxv, 244, 245, 249,

253–255, 257, 269-70, 272, 287, 288, 296,

297, 303, 386, 387, 391, 394, 466, 467,

469, 470, 474, 475, 499, 535, 536, 537,

538, 578

Propeller Research Tunnel (PRT), NACA

Langley, 256, 257, 258, 259, 260, 261, 

271, 376, 500, 556, 557, 560, 561, 561ill.,

562ill., 563ill., 564ill., 565ill., 566ill.,

567ill., 568ill., 569ill., 570ill., 571ill.,

572ill., 573ill., 575ill., 576, 577, 579, 

580, 581, 582, 584, 642

Public Works Administration (PWA), 660

Pupin, Michael I., 247ill., 360

Quittner, P., Dr., 299

Radio Direction Finding (RADAR), 339

R.A.F. airfoil sections:

R.A.F. 6, 324, 471

R.A.F. 15, 458, 459, 463, 467, 476

R.A.F. 19, 459

R.A.F. Mark IV airspeed indicator, 371, 372 

Rathbun, Richard, 187

Rawdon, Herb, lxvii

Rayleigh, Lord, 10, 125, 302, 524

Raymond, Arthur E., lv

Reed, R. Dale, lxii

Reid, Elliot G., 265, 584, 585, 588, 602

Reid, Henry J. E., 577, 579, 616, 652

Renaissance, The (European), xix, 2, 239

Renard, Paul, 289

Republic aircraft:

F-105, xliv

P-47, xxxiii

P-47B, xlii

XP-47 Thunderbolt, 78

Reynolds Law, 515, 517

Reynolds number, 252, 255, 257, 259, 455,

459, 498, 499, 500, 501, 502, 505, 507,

508, 509, 510, 513, 515, 516, 517, 518, 
686 The Wind and Beyond

Reynolds number (continued),

519, 520, 521, 522, 523, 528, 529, 530,

533, 556, 574, 584, 586, 592, 599, 648, 651

Reynolds, Osborne, 251, 252, 498, 518, 528,

535, 582

Reynolds velocity, 514, 518

Riabouchinski, Dimitri, xxv

Robins, Benjamin, 37, 47, 240, 632

Robinson Collection (University of Texas at

Dallas History of Aviation Collection), lv

Rockwell International, li, lii

Rockwell International aircraft:

B-1, xxxiv, li

X-31, li

Rockwell Space Transportation System 

(STS), xxxiv

Rockwell Standard Corp., li

Roland, Alex (historian), lx, 239

Root, Elihu, Jr., 264ill.

Roots supercharger, 591

Rosendahl Collection (University of Texas at

Dallas History of Aviation Collection), lv

Royal Aeronautical Society (British), lvii, 59, 84

Royal Aircraft Establishment (RAE) at

Farnborough, England, 378, 379, 391, 

611, 612

Royal Aircraft Factory (British), 302, 340, 397

Royal Air Force (RAF), 339, 342, 355, 356,

377, 384, 385

Royal Flying Corps (Canadian), 339, 340

Royal Society of London, 240, 632

Ryan aircraft:

Dragonfly YO-51 STOL, liii

Fireball FR-1, liii

NYP Spirit of St. Louis, xxxii, liii

SV-5A, liii

SV-5B, liii

Vertiplane V/STOL, liii

X-13 Vertijet, liii

Ryan Aircraft Co., liii

Ryan, John D., 264ill.

Sabine, W. C., 376

San Diego Aerospace Museum, liii

Sarah Clark Collection (National Archives),

lxv, lxviii

Schmid, Edgar, lxvi

Schultz, James, lxi

Science Technology Corp., Hampton, Va., xxvii

Scientific Revolution, The, xx, 4, 8

Scott, Catherine (historian), xxxvii

Scriven, George P., 305, 306, 307, 309, 310

Seely, General, 384

Selfridge, Thomas E., 226, 230

Serling, Robert J., lxv

Seversky, Alexandre, xxv

Sharp, Edward R., 577

Shoemaker, Eugene, 576

short takeoff and landing (STOL), liii

Siddeley Co. of Coventry, 377

Siddeley “Siskin” aircraft, 377

Signal Corps, U.S. Army, 225, 226, 227, 228,

229, 231, 232, 369, 522

Sikorsky aircraft:

S-42, xxxii

S-60/64, xxxiii

VS-300, xxxi

Sikorsky, Igor, xxv, li, 637, 638, 641

Silberman, Paul E., xlviii

Smeaton, John, 37, 203, 240, 273

Smith, Richard K. (historian), lix, 221

Smithsonian Institution, Washington, D.C.,

10, 22, 31, 91, 127, 130, 131, 145, 147,

187, 188, 246, 287, 288, 293, 301, 305, 36,

310, 311, 386, 395

Society of Automotive Engineers (SAE), lvii, 642

sound barrier, xli, lxii

Space Shuttle (NASA), xxxiv, lxii, lxiii, lxiv

Sperry M-1 Messenger airplane, xxxii,

256ill., 534, 573, 575, 578, 579, 582

Sperry Venturi speed meter, 372

Spratt, George A., 200, 202, 244, 273, 274

Stack Collection, John, NASA Langley, xlii

Stack, John, xl, xlii, lxiv

Stanford University, 247, 250, 257, 266, 306,

389, 403, 411, 412, 441, 445, 446, 450,

455, 461, 472, 556, 582, 605, 608 

Stanton, C. I., 454

Stanton, T. E., 525, 535

Stearman Co., l

Stearman, Lloyd, 637

Stillman, Wendell H., lxiii
Index 687

Stout Metal Airplane Co., liv

Stratton, Samuel W., 376

Stringfellow, John, 12

supersonic transport (SST), l, liii, xxxix, xlii 

Sundry Civil Act of 1920, 385

Sydenham, Lord, 353, 358

TACT, xxxiii

Tactical Fighter Experimental (TFX). See

General Dynamics F-111.

Talay, Theodore A., lix

Tate, Dan, 24ill., 200

Tate, W. J., 200

Tatin, Victor, 180

Taylor, David W., 246, 247ill., 248, 287, 383,

384, 386, 481

Taylor, D. Bryan (historian), lxxi

Taylor, Geoffrey I., 318

Taylor Cub, xxxii

Technische Hochschule, Aachen, Germany,

270, 298, 383, 386, 392

Teddington, England. See National Physical

Laboratory.

Teledyne Ryan, liii

Texas A&M University, xlii

TFX (Tactical Fighter Experimental). See

General Dynamics F-111. 

Theater of the Royal Society of Arts, 

London, 353

Theodorsen, Theodore, xi, xxv

Thomas-Morse MB3 airplane, 455, 460

Thompson, Milton O., lxii

Tichenor, Frank, 272, 616, 617, 624

Tizard, Henry T., 339, 340, 353, 354, 355, 358

Torricelli, Evangelista, 5

Toussaint-Lepère airspeed meter, 368

Townend ring cowling, 622, 629, 643

Travel Air aircraft:

Model R Racers, lxvii

Mystery Ship, lxvii 

Travel Air Co., lxvii

Treaty of Versailles, 558

Triaca, Albert C., 230

Truscott, Starr, 652, 656

Tsien, Hsue-tsen, xxv

Tunison, Frank, 221

United Aircraft and Transport Corp., xlii, li, 636

University of Akron, 265, 605

University of Dessau (Germany), 383, 386,

394, 395

University of Göttingen (Germany), lxv, 244,

250, 253–255, 286, 287, 296, 297, 298,

300, 301, 302, 303, 304, 383, 386, 389,

390, 394, 396, 438, 448, 474, 500, 501,

518, 537, 578, 633

University of Illinois, 579

University of Manchester (England), 252, 582

University of Michigan, 265, 581, 604, 605

University of Paris (France), 296, 303

University of Texas at Dallas History of

Aviation Collection, lv

University of Washington, 265, 605

U.S. Army (U.S.A.) 16 wing section, 475

U.S.S. Los Angeles (dirigible), 627, 630

Variable-Density Wind Tunnel (VDT), NACA,

xli, 254ill., 255, 256, 257, 258, 259, 260,

267, 267ill., 271, 467, 476, 497, 498, 499,

523, 535, 556, 559, 577, 584, 586, 587,

592, 642, 648

Venturi cowling, 629

Venturi, Giovanni Battista, 5

Venturi tube, 364ill., 365, 367, 372, 372ill., 443

Verein Deutschen Ingenieure, 304

Versuchsanstalt für Flugwesen der königliche

technische Hochschule, Berlin, 299

Vertical/short takeoff and landing (V/STOL),

xxxix, xlii, lxi

Vertical Wind Tunnel, 5-Foot, NACA, 261,

262ill., 263

Vertol aircraft:

CH-46, l

CH-47, l

Vertol Aircraft Co., l

Vickers Sons, 302, 379

Victory, John F., 631

Vincenti, Walter G., lix

Volta Congress on High-Speed Aeronautics, xxvi

Von Helmholtz, Ludwig, 525, 546, 547, 549

Von Parseval, Major, 299, 300

Von Kármán, Theodore, xi, xvii, xviii, xix,

xx, xxi, xxii, xxv, xxx, lv, lvii, lxv, 268ill.
688 The Wind and Beyond

Von Kármán, Theodore (continued), 269,

270, 392, 393, 536, 558, 610

Von Zeppelin, Ferdinand, 183, 298

Vought aircraft:

F8-U Crusader, xxxiii, xliv

O3U-1 Corsair, 259ill., 631

VE-7, 455, 459, 571, 582, 583

Vultee, Gerald, 649

Wagner, Ray (historian), lxvi

Walcott, Charles D., 247ill.

Walker, Lois E., and Wickam, Shelby E., lxv

Wallace, Lane E. (historian), lxii

Wallops Island, Va., xli

Ward Leonard motor control system, 595

Warner, Edward P., 253, 272, 383, 386, 398,

426, 441, 445, 454, 497, 506, 580, 616,

628, 657

Washington Navy Yard, Washington, D.C.,

246, 247, 248, 249, 250, 265, 287, 295,

305, 306, 309, 440, 445, 450, 451, 455,

458, 466, 469, 475, 633

Watson (James) and Crick (Francis), 7

Watson-Watt, Robert A., 339

Weather Bureau, U.S., 295, 306, 309, 479

Weick, Fred E., xl, xlii, xliii, li, lvii, 257, 271,

500, 556, 557, 560, 575, 576, 638, 639,

640, 641, 660 

Weick W-1A airplane, xlii

Wells, A. J., 242, 266

Wenham, Francis H., lviii, 25, 58, 59, 77, 78,

80, 83, 84, 85, 87, 241, 268

Western Society of Engineers, 192, 208

Westland “Wagtail” (British), 377

Whitcomb, Richard T., xli

Whitcomb winglet, xxxiv

Whitter Aviation Library and Archives of the

San Diego Aerospace Museum, N. Paul, liii 

Wichita State University, lxvii

Williams, H. M., 359

Wilson, E. B., 466, 468

Wilson, Woodrow, 255

Windler, Ray, 581

Wood, Donald H., 556, 560, 581, 583

Wooster, Stanton, 576

World War I, xxxv, 20, 234, 244, 245, 261,

264, 287, 306, 383, 500

World War II, xli, xlii, xliv, xlvi, liii, 339, 383, 386

Wright brothers, xi, xxv, xxvii, xxx, xxxviii,

xlii, lvii, lix, 1, 6, 8, 10, 12, 15, 22, 23, 24,

26, 28, 31, 89, 130, 148, 149, 202, 203,

208, 212, 215, 218, 225, 226, 230, 231,

232, 233, 234, 237, 238, 239, 242, 244,

245, 268, 286

Wright brothers’ aircraft:

Flyer of 1903, xxxii, 23, 27ill., 29, 192,

223, 224, 238

Flyer of 1905, 28

Glider of 1900, 23, 201

Glider of 1901, 24

Glider of 1902, 25, 26ill., 26, 192 

Wright Brothers Memorial Trophy, xlii

Wright Centennial Anniversary, xi, xxviii

Wright-Curtiss patent dispute, 287

Wright drag balance, 243ill.

Wright Field, Oh., xlvi

Wright, Katherine, 244

Wright, Milton, 1, 188, 192, 193, 223

Wright, Orville, 1, 21, 24, 26, 27, 91, 183,

187, 188, 192, 208, 211, 221, 222, 223,

225, 226, 229, 238, 242, 243, 264ill., 632

Wright Patterson Air Force Base, xlvi, xlvii,

lxviii, 27, 265

Wright State University, xxvii

Wright, Theodore P., 662

Wright Whirlwind engine, 614

Wright, Wilbur, 1, 10, 21, 24, 26, 27, 31ill.,

91, 126, 130, 183, 187, 188, 189, 192, 193,

208, 211, 218, 221, 222, 223, 225, 229,

238, 242, 244, 273, 274, 275, 282, 284,

286, 632

Wright wind tunnel, 239ill.

X-series aircraft, xlvii 

X-43. See Hyper-X. 

XYZ Engine Co., 630

Yackey, Tony, 580

Young, Pearl I., 18
Index 689

Zaharoff, Basil, 612

Zahm, Albert F., 244, 246, 248, 250, 265,

268, 270, 286, 287, 288, 301, 305, 445,

454, 455, 465, 467, 468, 469, 470, 475

Zahm Pitot-Venturi tube, 369

Zeppelin Airship Co., 385, 395, 396, 511

Zeppelin Versuchsanstalt, Friedrichshafen,

298, 386, 389, 395, 396