NASA AERONAUTICS BOOK SERIES

Bruce I. Larrimer

AIAA HISTORY MANUSCRIPT AWARD 2013
.

Bruce I. Larrimer
Library of Congress Cataloging-in-Publication Data

Larrimer, Bruce I.

 Thinking obliquely : Robert T. Jones, the Oblique Wing, NASA's AD-1 

Demonstrator, and its legacy / Bruce I. Larrimer.

 pages cm

 Includes bibliographical references.

1. Oblique wing airplanes--Research--United States--History--20th 

century. 2. Research aircraft--United States--History--20th century. 

3. United States. National Aeronautics and Space Administration--

History--20th century. 4. Jones, Robert T. (Robert Thomas), 1910-

1999. I. Title.

 TL673.O23L37 2013

 629.134'32--dc23

 2013004084

Copyright © 2013 by the National Aeronautics and Space Administration.

The opinions expressed in this volume are those of the authors and do not 

necessarily reflect the official positions of the United States Government or 

of the National Aeronautics and Space Administration.

This publication is available as a free download at

http://www.nasa.gov/ebooks.
iii

Introduction v

Chapter 1: American Genius: R.T. Jones’s Path to the Oblique Wing .......... ....1

Chapter 2: Evolving the Oblique Wing ............................................................ 41

Chapter 3: Design and Fabrication of the AD-1 Research Aircraft ................75

Chapter 4: Flight Testing and Evaluation of the AD-1 ................................... 101

Chapter 5: Beyond the AD-1: The F-8 Oblique Wing Research Aircraft ....... 143

Chapter 6: Subsequent Oblique-Wing Plans and Proposals ....................... 183

Appendices

Appendix 1: Physical Characteristics of the Ames-Dryden AD-1 OWRA 215

Appendix 2: Detailed Description of the Ames-Dryden AD-1 OWRA 217

Appendix 3: Flight Log Summary for the Ames-Dryden AD-1 OWRA 221

Acknowledgments 230

Selected Bibliography 231

About the Author 247

Index 249
iv

This time-lapse photograph shows three of the various sweep positions that the AD-1's unique 

oblique wing could assume. (NASA)
v

On December 21, 1979, the National Aeronautics and Space Administration 

(NASA) AD-1 Oblique Wing Research Aircraft (OWRA) took off from 

the main runway at Edwards Air Force Base (AFB), CA, for a 45-minute 

checkout flight. It marked the world’s first flight of a piloted oblique-wing 

airplane. This historic flight, which was flown with the airplane’s wing 

at its “straight” (0-degree angle) position, was soon followed by flights at 

wing angles of 15 degrees, 20 degrees, 45 degrees, and finally on April 24, 

1981, at the 60-degree-angle design goal, thus proving the aerodynamic 

concept of an airplane with an oblique-wing configuration. This initial 

oblique-wing program, which ran from 1976 through 1982, was a joint 

effort between NASA’s Ames Research Center and Dryden Flight Research 

Center, CA, thus giving rise to the aircraft’s name—Ames-Dryden AD-1 

Oblique Wing Research Aircraft.1 Extensive research, wind tunnel and 

computer-code testing, and model-building and testing projects were 

undertaken at Ames, and flight simulation, flight testing, and flight evaluation were conducted at Dryden. While the concept of the oblique wing 

was developed during World War II, and the landmark wind tunnel tests 

of John P. Campbell and Hubert M. Drake were undertaken just following the end of the war, most aeronautical attention in the postwar era 

concentrated on the continuous refinement of symmetrical point-forward 

swept-wing aircraft.

Serious attention, however, once again turned to the oblique wing 

in the 1970s, resulting in the research activities discussed in this book. 

Chapter 1 reviews the life of NASA aerodynamicist Robert T. Jones and 

his path to the oblique wing. Chapter 2 covers the extensive wind tunnel, 

model, computer-code, and simulation testing, first at Langley and later at 

Ames, as well as a number of NASA industry design contracts undertaken 

by Boeing and Lockheed. Chapter 3 reviews the design and fabrication of 

the AD-1 Oblique Wing Research Aircraft and its subsequent proposed 

use as a joined-wing demonstrator. Chapter 4 describes the flight testing and flight evaluation of the AD-1. Chapter 5 reviews the supersonic 

F-8 followup oblique-wing program. And, finally, chapter 6 reviews the 

subsequent oblique-wing plans and proposals. Appendices present the 

physical characteristics of the AD-1 aircraft, a detailed description of it, 

and a summary flight log of its flight research program.
vi

Thinking Obliquely

Writing the history of the AD-1 proved both a challenge and a pleasure. I 

am very grateful to all who have assisted me in this endeavor. A listing of those 

who were particularly helpful follows the appendices.

Bruce I. Larrimer

Columbus, OH

March 12, 2012

 1. From September 27, 1959, until March 26, 1976, NASA Dryden was known as the NASA Flight 

viii

NACA-NASA research scientist Robert T. Jones. (NASA) 
1

CHAPTER 1

American Genius

R.T. Jones’s Path to the Oblique Wing

Robert Thomas “R.T.” Jones was born on May 28, 1910, in the farming community of Macon, MO, and died on August 11, 1999, in Los Altos Hills, CA. 

In the intervening 89 years, Jones more than fulfilled the definition of genius, 

and his lifetime in aeronautics constituted a particularly productive and welllived life. In his progression to distinction, Jones resembles far more the 17th 

century’s largely self-taught and broadly interested “natural philosopher” than 

the rigorously educated, university-trained STEM (science, technology, engineering, and mathematics) über-specialized professional of the modern era.1

Jones’s lifelong consuming interest in aviation started at an early age when 

he built rubberband-powered model airplanes and assembled airplane models 

with scaled drawings from the Ideal Model Airplane Supply Company. In his 

rural Macon, MO, high school, Jones acquired an interest in mathematics 

from his math teacher, Iva Z. Butler, who guided him “along the intricate 

path through exponents, logarithms, and trigonometry.”2 Following the 

nationwide increase in interest in aviation resulting from Charles Lindbergh’s 

nonstop transatlantic flight in 1927, Jones was readily able to purchase the 

magazines Aviation and Aero Digest in his hometown of Macon. These publications contained technical articles, which Jones read with great interest, as well as notices of Technical Reports (TRs) of the National Advisory 

Committee for Aeronautics (NACA, the forerunner to NASA), which Jones 

was able to purchase from the Government Printing Office for as little as 

10 or 15 cents. In regard to his interest in aviation, Jones noted that he 

must have puzzled his high school English teacher with all the essays he 

wrote on aeronautics-related subjects. After graduation, Jones attended the 

University of Missouri to study engineering but left college after the first year 

because the university did not offer courses in aeronautics and he “found the 

other subjects rather uninteresting.”3

 In dropping out of college after a year, 

Jones followed in the footsteps of his father, who also had quit after 1 year,

and then read the law and passed the bar examination to practice as an 

attorney in Missouri.
2

Thinking Obliquely

The Evolution of a Practical Engineer-Scientist

After leaving college, Jones returned to Macon, working for the Marie Meyer 

Flying Circus. In exchange for odd jobs, such as fueling its Curtiss JN-4 Jenny 

aircraft and patching its often-damaged fabric-covered lower wingtips, Jones 

received free flying lessons—although it would take another 50 years before 

he would make his first solo flight and subsequently receive his pilot’s license. 

In 1929, at the age of 19, Jones was hired as the chief and only engineer of 

the Nicholas-Beazley Airplane Company, Inc., of Marshall, MO, after Charles 

Fower, a friend of Jones’s, told Russell Nicholas that Jones “knew everything 

there was to know about airplanes.” Jones obtained this engineering position due 

to the departure of Walter Barling, who had been the principal designer of the 

company’s NB-3 of 1928, a low-wing, single-engine, two-place, open-cockpit 

monoplane of straightforward design that enjoyed brief, modest commercial 

success. Later, the company hired Thomas Kirkup, a certified engineer from 

England who taught Jones how to undertake stress calculations. At its peak 

production, Nicholas-Beazley, which Jones noted was well-placed to become 

the center of small airplane production in the United States, was producing an 

airplane per day, but the company failed during the Great Depression and Jones 

soon found himself back in his hometown of Macon. During this time back in 

Macon, Jones continued his self-study by reading books on aeronautics, including Max M. Munk’s Fundamentals of Fluid Mechanics for Aircraft Designers, his 

introduction to an individual who was himself a towering figure in aeronautics 

and who would have a profound effect upon Jones’s life and work.4

During the depth of the Depression, Jones, desperate for work, hitched 

a ride to Washington, DC, with some neighbors. Once in Washington, he 

immediately visited his local Congressman, who secured for him a position 

as an elevator operator in the House Office Building. Jones took advantage of 

this welcome security to further his study of mathematics by studying books 

from the Library of Congress and attending evening classes in aerodynamics taught by Max Munk at Catholic University. A decade previously, Munk 

had introduced modern scientific airfoil development to America. Munk was 

born in Hamburg, Germany, in 1880. He studied under Dr. Ludwig Prandtl, 

was a contemporary of Theodore von Kármán, received two doctoral degrees 

from the Göttingen University, and moved to the United States in 1920 to 

join the National Advisory Committee for Aeronautics’s Langley Memorial 

Aeronautical Laboratory (now NASA Langley Research Center). After a productive if tempestuous time with the NACA, Munk left the agency to take up 

a teaching position at Washington’s Catholic University and to serve as technical editor of the magazine Aero Digest.

5

 Soon after arriving in Washington, 

Jones paid a visit to Munk and informed the professor that he had read his 
American Genius

book on fluid dynamics for aircraft designers. Listening to Jones, Munk, a brilliant if irritable personality, was impressed to the point of promptly inviting 

his young visitor to take his course in aerodynamics. When Jones modestly 

demurred, stating that he lacked an undergraduate degree, Munk challenged 

him to define a derivative of a function. When Jones promptly did so, Munk 

equally promptly admitted him to the course.

Jones realized that in order to become a successful engineer, he would need 

to know more about mathematics. Fortunately, his status as a congressional 

employee, coupled with the close proximity of the House Office Building to the 

Library of Congress, readily enabled Jones to obtain works on various branches 

of mathematics. He read Hermann Grassmann’s Die Ausdehnungslehre, one of 

the most influential texts in the history of mathematics, written by an individual who was, in his broad range of interests and largely self-taught abilities, very 

much like Jones himself, though, sadly, unrecognized for his contributions in 

his lifetime.6

 In particular, Jones became fascinated with the “time plus space” 

theory of quaternions (four-element multiples of real numbers consisting of 

a scalar [time] element and three vector [space] elements), first derived by the 

Anglo-Irish mathematician Sir William Hamilton, which contributed much of 

the underpinning of quantum theory.7 Jones credited the scholarship of both 

men with helping him during his years with the NACA.

In addition, while at the Library of Congress, Jones made the acquaintance 

of Dr. Albert F. Zahm, a physicist and influential aerodynamics researcher 

who had established America’s first wind tunnel–equipped research laboratory at Catholic University in 1901 and, later on, helped found another at 

the Washington Navy Yard. By the time he met Jones, Zahm was managing 

the Library’s aeronautics collections, though he still undertook some research 

and maintained a determinedly future-focused mindset. One of the topics 

he pursued was the challenge of upper-atmospheric near-space flight, and 

he invited Jones to assist him.8 Impressed, he subsequently furnished Jones 

a contact who was to help the young Midwesterner obtain his job with the 

NACA—Congressman David J. Lewis. Lewis took to Jones for, like the young 

man, he had achieved his own success without formal education, and he was 

likewise fascinated with mathematics. Subsequently, Jones tutored Lewis in 

mathematics, impressing the Congressman with his extraordinary knowledge. 

Having impressed Munk, Zahm, and Lewis, Jones had no difficulty securing 

their recommendations to obtain, in 1934, a temporary 9-month appointment 

as a Junior Scientific Aide at the NACA’s Langley Aeronautical Laboratory 

under a Roosevelt-era employment program.

The temporary appointment lasted until Jones’s supervisors were able to 

make it permanent. At Langley, Jones first worked under Fred E. Weick, a wellknown engineer who in the 1930s continued earlier work on inherent stability 

3
4

Thinking Obliquely

undertaken by Jerome C. Hunsaker and E.B. Wilson. Weick was also interested 

in designing an airplane with a simplified “two-control” (independent pitch 

control but interlinked roll and yaw control) pilot operation, and Jones was 

given the task of making the dynamic calculations. Jones’s calculations indicated that Weick’s two-control operation, subsequently employed on Weick’s 

two-control Erco Ercoupe that Jones enjoyed flying in later years, would be 

better achieved by placing primacy upon the ailerons instead of the rudder 

as the principal control device driving directional changes. Weick, according to Jones, also realized that a two-control system would need dynamically 

stable landing gear, driving his development of a tricycle gear with fixed wheels 

behind the center of gravity and a steerable nose wheel ahead.

While Weick was not the first to develop such a configuration—for example, it had appeared before the First World War in the pusher designs of Glenn 

Curtiss—the Ercoupe certainly encouraged its use and almost universal subsequent adaptation. As for Jones, his work on two-control flight control systems 

later influenced his wartime work on guided weapons.9

Once Jones’s 9-month appointment expired, the Langley staff found a way 

to retain Jones by skipping him a grade above junior engineer, which required 

a college degree, to the next higher professional engineering position, which 

already assumed that the candidate had a college degree and thus failed to list 

a degree as a position requirement. This led to Jones’s long career with the 

NACA and NASA.

William R. Sears, himself a noted aeronautical engineer, noted of Jones 

that during his long civil service career, Jones had become “one of the world’s 

leading aerodynamicists, [who] made discoveries that have changed the history 

of aeronautics, and received important honors.”10 In 1947, the Institute of the 

Aeronautical Sciences (one of two professional societies—the other being the 

American Rocket Society—that merged to form the American Institute of 

Aeronautics and Astronautics [AIAA]) awarded Jones its 1946 Sylvanus Albert 

Reed Award “For his contributions to the understanding of flow phenomena 

around wings and bodies at speeds below and above the speed of sound.”11 In 

1971, Jones was awarded an honorary doctorate degree by the University of 

Colorado for his contributions to aeronautics, and in 1973, he was elected to 

the National Academy of Engineering. Jones received the Prandtl Ring award 

from the German Aeronautical Society in 1978. In 1981, the Smithsonian 

Institution selected Jones to receive its prestigious Langley Medal (named for 

Smithsonian Institution Secretary and pioneer astrophysicist Samuel Pierpont 

Langley, himself a notable pioneer of flight), which is awarded for “especially 

meritorious investigation in the field of aerospace science.”12 The Langley 

Medal was awarded to Jones in recognition of his “extensive contributions in 

theoretical aerodynamics, particularly with regard to development of the swept 
5

American Genius

The first production Ercoupe, at its College Park, MD, plant, 1939. (NASM)

wing, supersonic area rule and, more recently, the oblique wing.”13 In 1981, 

Jones received the President’s Award for Distinguished Civilian Service, which 

read in part as follows: “Of major consequences are his triangular wing concept, 

the independence principle for the three-dimensional boundary layers, and the 

concept of the oblique wing boom-free supersonic airplane.”14

Jones’s Other Interests

In addition to aeronautics, R.T. Jones had a wide range of other areas of interest and expertise, again reflecting, to an almost uncanny degree, Hermann 

Grassmann and Sir William Hamilton, whose work had furnished so much 

insight for his own work. Jones’s polymath tendencies are evident in at least 

nine reports prepared while at the NASA Ames Research Center and at least 

four reports prepared at the Avco-Everett Research Laboratory, MA, during 

his approximately 7 years of voluntary absence from NASA. At NASA Ames, 

these reports covered such varied topics as:

• 

• 

• 

• 

• 

• 

modified Gregorian and Cassegrainian mirror systems,

time calculations for interplanetary travel,

work on lenses and telescopes of an unusual optical design,

extending the Lorentz Transformation by characteristics coordinates,

a review of some selected space-science problems 

and accomplishments,

analysis of accelerated motion in the theory of relativity,
6

• 

• 

• 

• 

• 

• 

Thinking Obliquely

conformal coordinates associated with uniformly accelerated 

motion, and

conformal coordinates associated with space-like motions.

His studies at Avco-Everett Research Laboratories included the following 

topics:

wide-angle lenses with aspheric correcting surfaces,

motions of a liquid in a pulsating bulb with application to problems 

of blood flow,

a theory of synchronous arterio-arterial blood pumps, and

studies of blood flow (as a followup, he undertook a study of fluid 

dynamics of heart assist devices).

Even in leisure and family pursuits, Jones could not resist the opportunity 

to study and learn new things—and then to improve upon them. When his 

daughter developed an interest in violins, Jones even built a number of violins, making a detailed acoustical study of each. In testing two of the violins, 

Jones concluded that “It will be noted that the second violin has accentuated 

overtones in the 2000 to 3000 Hz [hertz] range, the main body resonance is at 

450 Hz, and the air resonance peak is somewhat lower in amplitude,” adding 

(with just a touch of obvious pride), “This violin is preferred by musicians who 

have tried both.”15

Jones, however, never left his lifelong interest in aeronautics. He returned to 

NASA Ames in 1970 and worked there until his retirement in 1981. During 

this time period, Jones concentrated mostly on his oblique-wing concept and 

its potential development as a high-speed transport. After retiring from NASA, 

Jones joined the faculty of Stanford University, where he served until 1997 as a 

consulting professor in the Department of Aeronautics and Astronautics while, 

at the same time, maintaining an informal relationship with NASA Ames. 

While at Stanford, Jones’s work on the oblique-wing concept moved toward 

developing a pure oblique flying wing, an idea he had long nurtured. After 

Jones’s death in 1999, Walter G. Vincenti, a veteran NACA-NASA engineer 

and distinguished historian of technology, noted in his Biographical Memoir of 

Robert T. Jones (written for the prestigious National Academy of Sciences) that

[t]hose who worked with R. T. marveled at how he arrived at his 

ideas, seemingly intuitively and frequently in terms of physical 

models and analogies. He could use highly sophisticated mathematics deductively when necessary, but he did so mostly to 

support his ideas and explore their consequences. In the initial 

report on his concept of sweepback he began conventionally with 

a mathematical derivation followed by three physical arguments 

and explanations. Events at the time suggest that the mathematics 
7

American Genius

Robert T. Jones at home, making a violin. Note the oblique-wing radio-controlled model airplane 

and a reflector telescope, also made by Jones, July 30, 1982. (Photograph © Roger Ressmeyer/

Corbis Images)

actually came to R. T.’s mind after the physical concepts and had 

been put into the report in response to editorial-committee objections. Whatever the situation, the fact is that things that seemed 

clear and obvious to him in his physical explanations often caused 

the rest of us difficulty and struggle to master.16

Jones’s Early Work at Langley Aeronautical Laboratory

Jones established his reputation between 1936 and 1946, when he worked on 

a number of different engineering assignments and wrote entirely or coauthored at least 21 NACA reports, notes, and studies covering a wide range of 

topics. Taken together, they constitute a prodigious output and extraordinary 

technical and scientific accomplishment. If he had done nothing else, this 

work, culminating in his enunciation of the thin, high-speed slender delta 
8

Thinking Obliquely

wing and the swept wing, would have on its own sufficed to secure his place 

in aviation history.

Viewed sequentially to the point just prior to his commencing research on 

swept planforms, his corpus of accomplishment included:

• 

• 

• 

• 

• 

• 

• 

• 

• 

• 

• 

• 

• 

• 

Report No. 560 (1936), reviewing a simplified treatment of the 

application of mathematician and physicist Oliver Heaviside’s operational methods to problems of airplane dynamics.

Report No. 570 (1936, coauthored with Fred E. Weick), analyzing 

the lateral controllability of an airplane in which both the static rolling and yawing moments supplied by the controls and the reactions 

due to the inherent stability of the airplane were taken into account.

Report No. 579 (1936), examining the two-control operation of 

an airplane.

Technical Note (TN) No. 586 (1936, with Albert I. Nerken), studying the reduction of aileron operating force by differential linkage;

Report No. 605 (1937, a Fred E. Weick report to which Jones 

contributed), examining a resume and analysis of NACA 

lateral-control research.

Report No. 635 (1938, coauthored with Henry A. Pearson)—examining the theoretical stability and control characteristics of wings 

with various amounts of taper and twist.

Report No. 638 (1938), studying the influence of lateral stability 

of disturbed motions of an airplane with special reference to the 

motions produced by wind gusts.

Technical Note No. 667 (1938), addressing the operational treatment of the nonuniform lift theory in airplane dynamics.

Report No. 681 (1940), studying the unsteady lift of a wing having 

finite aspect ratio.

Technical Note No. 771 (1940, coauthored with Leo F. Fehlner), 

reviewing the transient effects of the wing’s turbulent wake on the 

horizontal tail of an airplane.

Report No. 709 (1941, coauthored with Doris Cohen), analyzing 

the stability of an airplane with free controls.

Report No. 722 (1941, coauthored with Doris Cohen)—studying a 

graphical method of determining pressure distribution in two-dimensional flow.

An article (1941), examining the theoretical correction for the lift of 

wings having an elliptical planform.

Technical Report No. 837 (1941), addressing problems involved in 

the stability and control of tailless airplanes.
9

• 

• 

• 

• 

• 

• 

American Genius

Wartime Report L-464 (1942, coauthored with Milton B. Ames, Jr.), 

covering wind tunnel testing of beveled trailing edges to reduce the 

hinge moment of a control surface.

Report No. 731, (1941, coauthored with Doris Cohen), examining a theoretical analysis to determine the optimum planforms for 

control surfaces.

Wartime Report L-233 (1943, coauthored with Joseph W. Wetmore), 

dealing with emergency measures for increasing the range of 

fighter airplanes.

Report No. 798 (1943, coauthored with Harry Greenberg), covering the effect of hinge-moment parameters on elevator stick forces in 

rapid maneuvers.

Wartime Report L-651 (1943, coauthored with W.J. Underwood), 

involving a wind tunnel investigation of a beveled aileron shape 

designed to increase the useful deflection range.

Report No. 801 (1943), presenting a method for studying the hunting oscillations of an airplane with a simple type of automatic flight 

control system.17

Jones’s NACA activities during this time period included important work 

in the emerging field of guided weapons research, and it was this work that 

led him, eventually, to conceptualize the American delta and swept wing. In 

1944, he was assigned to work at Eglin Field to help the U.S. Army Air Corps 

develop guided missiles, including a glide bomb designed to be launched from a 

B-17. The glider was equipped with a heat seeker developed by Franklin Offner 

and an autopilot made by Laurens Hammond, designer and manufacturer of 

electric organs. The initial tests, however, were not very successful because the 

bomb was guided to its target by rudders, which imparted directional control 

(yaw control, i.e., left-right control) but still did not ensure sufficient accuracy. 

Drawing upon his earlier experience with two-control flight control systems 

with Weick at Langley, Jones recommended using aileron (roll) control, which 

greatly enhanced delivery accuracy.

In 1944, Jones was detailed to join a U.S. Army Air Force’s Air Technical 

Service Command (ATSC, forerunner of the modern U.S. Air Force [USAF] 

Materiel Command) team sent to Eglin Field (now Eglin Air Force Base) in 

Florida to test the pulsejet-powered Republic JB-2 Loon guided missile. An 

American copy of the Fieseler FZG-76 (better known to history as the infamous Nazi V-1 Buzz bomb—the V standing for Vergeltungswaffe, or “Revenge 

Weapon,” its Nazi propaganda designation—that savaged London in 1944 

through early 1945), the JB-2 was America’s first jet-age cruise missile.

Unlike the preset V-1 (which could deviate as much as 8 miles over approximately 120 miles), the JB-2 used ground radar tracking and radio-controlled 
10

Thinking Obliquely

Republic JB-2 ready for flight. (USAF) 

guidance to reduce its course deviation to just one-quarter mile at a range of 

100 miles—extremely accurate by the standards of the day.18 While the V-1 

employed a launching sled and steam catapult (with the steam produced by the 

reaction of concentrated hydrogen peroxide poured over potassium permanganate), the JB-2 was boosted to flight speed by solid-fuel rockets, considered 

both safer and less complex for the launching team. It seemed a simple matter 

to modify the missile for rocket boost: simply by aligning the thrust vector of 

the rockets through the missile’s center of gravity, the test team could launch 

the JB-2 into the air.

But at the time, the JB-2 was in trouble. It took many attempts before the 

team determined the proper configuration, to prevent the powerful rockets 

from tearing the missile apart during launch. Initially, only 20 percent of all 

missiles launched successfully. Thanks in large measure to Jones and a more 

analytical approach to the missile’s launch dynamics, by war’s end, the figure 

had increased to 80 percent.19 Jones also used gyros from the JB-2 to devise a 

bilaterally symmetric flight control system to improve the one developed by 

Hammond for the Northrop Company’s rival JB-10 flying wing “flying bomb.”

In regard to this wartime service, an Army Air Forces Air Technical Service 

Command letter commending Jones for his service stated:

It will be noted that the Air Technical Service Command desires to 

commend Mr. Robert T. Jones of the Langley Memorial Aeronautical 

Laboratory for his assistance in the successful initiation of this project. This office also wishes to take this opportunity to commend 
11

American Genius

JB-2 launch accident. (USAF)

Mr. Jones for his efforts which resulted in the NACA making very 

valuable contributions to the success of the JB-2 flying bomb project 

of the Army Air Forces Air Technical Service Command.20

Overall recognition of R.T. Jones’s contributions during his time at Langley 

is found in George W. Lewis’s October 14, 1947, letter to Jones (who had 

transferred the previous year to the Ames Aeronautical Laboratory, now NASA’s 

Ames Research Center) noting the following:

I am attaching a clipping from the Washington Sunday Star, 

which is very interesting to me because I well remember the day 

Congressman Lewis of Maryland called on me and said that 

something must be done about Bob Jones—he must have an 

opportunity to use his talents in a scientific organization. It was 

a fortunate day for the Committee, for you and Mrs. Jones have 

brought credit to the Committee with the many contributions 

that you have made.21
12

Thinking Obliquely

Jones’s Great Discovery: 

The American Delta and Swept Wing

By the time Lewis penned his note, Jones had contributed two landmark technical studies—his singular greatest and most influential technical accomplishment—that influenced, arguably, what still constitutes the greatest aerodynamic 

transformation following the invention of the airplane in 1903, which made 

Jones’s name and gave him a truly international reputation: NACA Technical 

Reports numbers 835 and 863, published in 1946 and 1947, respectively.

They had a remarkable genesis. In 1935, leading aerodynamicists met in Rome 

for the Volta Congress on high-speed flight. During the prestigious conference, 

Adolf Busemann, a young German fluid dynamicist, unveiled the concept of 

using a sweptback wing to delay the onset of high-drag rise afflicting conventional 

straight wings, thus making the attainment of supersonic flight a practicality. 

Busemann’s paper attracted little notice at the time, perhaps because the modest 

wing-sweep angles that he presented and the concepts underlying them seemed 

far less revolutionary than they were. Also, the moderately sweptback wing had 

been a feature of aircraft design since before the First World War, but it was used 

for reasons of stability rather than to achieve high-speed flight. (With a moderate sweptback wing, a designer could build a tailless aircraft, several different 

types of which appeared over the previous quarter century.) Thus the Busemann 

study dropped out of sight to be resurrected a decade later, when the Allies 

sifted through the rubble of Germany’s wartime aeronautical research establishment, discovering the tremendous investment that the Nazi regime had made 

in developing jet-and-rocket-powered swept- and delta-wing designs for aircraft 

and missiles. Only the punishing Allied strategic bomber offensive, coupled with 

the rapid overrunning of Germany itself in 1944 to 1945, had prevented some 

of these from entering service.22

Jones, in an unpublished autobiography, recounted his own progression to 

the swept wing, using as a departure point an experimental configuration he was 

asked to review:

One day near the end of the war an engineer from the Sikorsky 

Company stepped into my office with a design for a fighter plane 

having a narrow wing of triangular planform, proposed by Michael 

Gluhareff.23 He had applied Prandtl’s theory to calculate the lift and 

pressures on the sections, but had some misgivings since Prandtl’s 

theory was based on the assumption that the wing was long and 

narrow in the direction perpendicular to the flight direction [e.g., 

a high-aspect-ratio planform], so that the flow over the airfoil 

sections, parallel to the flight direction, could be considered two 
13

American Genius

dimensional. He asked if I could think of a better way to determine 

the characteristics of such a wing, long and narrow in the flight direction [e.g., a low-aspect-ratio planform]. I remembered a paper by my 

teacher Max Munk in which the flow in planes perpendicular to the 

flight direction was considered two-dimensional. I also remembered 

a paper by H. S. Tsien24 in which it was pointed out that Munk’s 

“slender body” theory remained applicable at supersonic speeds.25

 All that remained to convert slender body theory to a wing theory was to find a way to impose the Kutta condition. I reasoned that 

a portion of the wing behind the section of maximum width would 

develop no lift, since its boundary condition would be satisfied by 

the wake from sections ahead. At first I thought the assumptions 

too crude to be of much interest and I put the report in my drawer. 

Later I found that the results were insensitive to the Mach number, 

whether subsonic or supersonic. I then collected my formulas and 

observations in a paper entitled “Properties of Low Aspect Ratio 

Pointed Wings at Speeds Below and Above the Speed of Sound” 

(NACA Tech. Report No. 835, May 1945.26) This paper became 

instrumental in the design of supersonic aircraft.

27 [Emphasis added.]

Jones added that he recalled an observation by Max Munk “that the air 

forces on a sweptwing panel would depend only on the component of flight 

velocity in the direction perpendicular to the leading edge and were independent of the flow in the direction of the long axis.”28 From this, Jones concluded 

that Munk’s independence principle would enable sweeping the wings back 

within the Mach cone generated by an airplane’s passage through the air at 

supersonic speeds, thus placing the wings within a subsonic and relatively 

low-drag flow.

As longtime Jones associate Walter Vincenti noted, it followed from Jones’s 

analysis that

the effective Mach number, on which the air forces depend, 

decreases continuously with increasing sweep; it follows that, even 

at supersonic flight speeds, the air forces can be made to have the 

advantageous properties found at low subsonic Mach numbers 

simply by introducing sufficient sweepback. In particular, that 

the enormously increased drag of conventional unswept wings 

at supersonic speeds can be reduced to subsonic levels. R.T. thus 

discovered the theory of high-speed sweepback, which William 

Sears describes as “certainly one of the most important discoveries 

in the history of aerodynamics.” The planform of every high-speed 
14

Thinking Obliquely

Jones's slender delta, from NACA TR 835, 1946. (NASA)

transport one sees flying overhead embodies R.T.’s idea. When it 

became known, it came as a mind-boggling surprise to the rest of 

us working in aerodynamics.29

Jones subsequently built a small test model resembling a dagger, measuring 

4 inches in length with a span of just 11⁄2 inches, testing it to Mach 1.75 in 

a small Langley supersonic tunnel; as predicted, it had much less drag than a 

conventional higher-aspect-ratio wing. Its configuration is illustrated in the 

following drawing, from Jones’s subsequent technical report.30

Jones immediately expanded upon this work, deriving from it a bilaterally 

symmetric and sharply sweptback ∆-profile wing. Thus, whereas in Germany 

the discovery of the transonic swept wing had preceded that of the classic delta 

wing, in the United States the exact reverse was true: the invention of the transonic delta preceded the invention of the transonic swept wing.31

Despite the attractiveness of his discovery, Jones did not immediately win 

converts to the swept-wing cause. Indeed, the results were so controversial that 
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Jones's sharply swept-back wing, from NACA TN 1033, 1946. (NASA)

Jones encountered official skepticism that delayed dissemination of his ideas. 

He recalled the following:

As customary, an editorial committee was appointed to go over 

my paper and approve it if they found it correct. The committee 

was composed of experts on compressible flow, who had made 

complex studies of high-speed flow over straight wings. (It may 

be remembered that our first supersonic airplane, the [Bell] “X-1” 

had straight wings). I was no expert on compressible flow, but I had 

a simple solution to their problem. It is perhaps natural that they 

did not believe it. Surprisingly, they did believe my slender wing 

theory and I was encouraged to publish this without reference to 

the sweep theory. During the course of the meetings, a 1935 paper 

by Adolf Busemann was discovered by one of the members and 

brought to the attention of the committee. Busemann had used 

the independence principle but had not considered wings swept 

behind the Mach cone where I thought a subsonic type of flow 

would arise (though he later did so).32

As a result of the committee’s action my paper on slender wing 

theory was published (NACA TR no 835, 1945), but my paper on 

sweep theory, entitled “Wing Planforms for High Speed Flight[,]” 

was delayed.33 NACA’s Director, George W. Lewis, proposed that 

we make experiments to see whether the theory was correct. In 

one such experiment, wings were attached to a balance inside a 

heavy cylindrical body which was dropped from a high altitude 

and the balance readings transmitted to the ground. At Mach 
16

Thinking Obliquely

One [the speed of sound], the wings with 45 degrees sweep had 

less than one-tenth the drag of the straight wings!

 Earlier, at the end of the war a group of American scientists 

boarded an Air Force plane to Europe for the purpose of studying 

the accomplishments of German wartime research. According to 

George Schairer [a Boeing design engineer subsequently responsible for the swept-wing design of the company’s XB-47 Stratojet 

bomber], one of the group, much of the time on the long flight was 

devoted to a debate on the merits of my sweep theory. By the time 

they reached Germany they decided that it was correct. On going 

through the German research they found that, thanks to Busemann, 

many experiments had been made on swept wings, although the idea 

had not yet had time to influence the manufacturers.34

In a signed and witnessed statement that apparently was part of his patent 

submission, Jones stated the following:

I have discovered a form of construction and a method of determining the correct proportions of airfoils whereby the large increases 

of air resistance associated with the formation of shock waves is 

avoided, and whereby an airplane embodying this form of construction will be enabled to fly at speeds greater than those now attained, 

without undue expenditure of power and thrust. The object of my 

invention is therefore the improvement of the design of the airfoil 

surfaces or wings for airplanes flying at high speeds.

Jones added, “An airfoil surface embodying my invention requires also a 

certain angle of inclination or sweep in planview relative to the direction of 

flight.”35 His signed statement was typed on March 14, 1945, and the witness 

acknowledged receipt of the information on February 27, 1945.

Jones’s NACA Report 835, published in 1946, spawned American research 

on thin, sharply sweptback wings, using the example of an extremely slender 

delta planform (his NACA Report 863, a year later, extended his work to cover 

sharply swept wings). Jones reviewed previous theories regarding disturbances 

in two-dimensional potential airflows, including his mentor Munk’s thin-airfoil 

theory and a later compressible-incompressible airflow corrective approximation 

method, commonly called the “Prandtl-Glauert rule,” derived by Germany’s 

Ludwig Prandtl and Britain’s Hermann Glauert.36 The Prandtl-Glauert approximation “reduced the equation for compressible flow to the same form as the 

equation for incompressible flow”37 and enabled comparison of the boundary 

conditions of both as well.
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But unlike previous researchers, examining these in relation to conventional high-aspect-ratio wing planforms (wings characteristically having a 

large span and small, narrow chord such as those on a long-range transport or 

a light personal airplane) at subsonic speeds, Jones examined instead the case of 

low-aspect-ratio wings (wings characteristically having a short span and a larger, 

broader chord such as a supersonic jet fighter) having pointed planforms and 

at supersonic speeds (that is, at speeds in excess of the speed of sound, Mach 

1 in aerodynamic shorthand).

Reviewing conventional wing theory, Jones noted that “At speeds above 

the speed of sound, application of the [Munk and Prandtl-Glauert] assumptions leads to [Swiss fluid dynamicist Jakob] Ackeret’s theory according to 

which the wing sections generate plane sound waves of small amplitude,” 

adding, “As is well known, the Ackeret theory predicts a radical change in the 

properties of such wings on transition to supersonic velocities.”38 Examining 

the properties of low-aspect-ratio wings in compressible flow at transonic and 

supersonic speeds, Jones concluded in early May 1945 (before Americans had 

the opportunity to avail themselves of Germany’s impressive wartime sweptand delta-wing research) that

1. The lift of a slender, pointed airfoil moving in the direction of its 

long axis depends on the increase in width of the sections in a downstream direction. Sections behind the section of maximum width 

develop no lift.

2. The spanwise loading of such an airfoil is independent of its 

plan form and approaches the distribution giving a minimum 

induced drag.

3. The lift distribution of a pointed airfoil traveling point-foremost is 

relatively unaffected by the compressibility of the air below or above 

the speed of sound.39

The Emergence of the Oblique Wing

The uncovering after the Nazi collapse of the staggering extent of German sweptwing work before and during the Second World War confirmed Jones’s work and 

added greatly to his stature.40 Edward C. Polhamus and Thomas A. Toll recalled 

the multinational development of high-speed swept-wing theory in 1981, stating that the “concepts of both fixed-sweep and variable-sweep high-speed aircraft trace their beginnings to aerodynamic research carried out in Germany 

during the latter half of the 1930s and early 1940s,”41 adding that,
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Thinking Obliquely

while the Germans, during World War II, were the first to apply 

sweptwings to high-speed aircraft and had periodically considered 

variable sweep, other pressures during the war and the dismantling of their aeronautical industry after the war precluded any 

serious research relative to variable-sweep aircraft.... [Afterward] 

aerodynamic researchers in the United States discovered and 

verified the advantages of sweep independently of the German 

research, although some five years later, and in 1945 as our 

research effort was expanding and the German swept-wing results 

became available, the aerodynamic technology required for successful variable-sweep high-speed aircraft began to evolve.”42

Independent development likely occurred because aerodynamicists read 

many of the same papers written by earlier and current experts in their fields 

and built upon that base of work with their own formulations and concepts, 

and their work was expedited by the added pressure caused by World War II. 

As a further indication of independent development, Jones noted in a tribute to 

Adolf Busemann after the latter’s death that

[d]uring the war years communication with German scientists was 

lost, and my own somewhat belated discovery of the sweep effect, 

which emphasized subsonic sweep, was not immediately accepted 

by American aerodynamicists, including those who had attended 

the Volta Congress. Consequently, the first American supersonic 

airplane, the X-1, had no sweep.43

R.T. Jones’s development of his oblique wing theory followed upon his 

discovery of the swept-wing concept. The oblique wing is a single continuous 

wing surface with a central midspan pivot attached to the top of the fuselage. 

An aircraft with such a wing appears as a conventional straight-wing (i.e., 

perpendicular to the direction of flight) design during takeoff and landing. 

But as the pilot increases speed, the wing pivots so that one wingtip (typically 

the right) advances forward as the other wingtip translates aft. At cruise speed, 

therefore, an oblique-wing aircraft has the appearance of an open pair of scissors, hence its nickname, scissors wing. The aeroelastic structural behavior 

and lateral-directional (roll-yaw) stability characteristics of the oblique wing 

are complex, blending those of the traditional swept wing (for the trailing aftswept wing) and the more radical forward swept wing (for the leading wing).

As with the classic V foremost swept wing itself, the concept of the oblique 

wing appears to have been another example of mutual (if not simultaneous) 

discovery, once again in both Germany and the United States.
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Vogt’s Blohm und Voss P 202 oblique-wing-fighter proposal, from USAAF, Foreign Equipment 

Descriptive Brief, August 1946. (USAF)

In 1942, Richard Vogt, chief engineer of the Abteilung Flugzeugbau of 

the Blohm und Voss Schiffswerft—the Aircraft Manufacturing Department 

of Blohm and Voss (BuV] Shipworks—proposed the P 202, a jet fighter 

having a straight, pivoted variable-sweep wing. At takeoff and landing, 

it would fly at a 0-degree sweep. But at high-speed, it would pivot to 35 

degrees, becoming an oblique swept wing. While concept drawings as well 

as a number of other references of the proposed aircraft exist, no prototype 

of the fighter was ever built, and no German Air Ministry aircraft designation was assigned for the BuV project—an indication of its lowly status.44

Vogt’s proposed BuV fighter airplane had a sweep angle of 35 degrees with 

the left wingtip forward; a top-mounted wing spanning 39.4 feet when straight 

and 32.84 feet at a 35-degree sweep; a wing area of 215 square feet; two BMW 

003 jet engines enclosed in a bulged lower fuselage, sharing a common intake 

and nose; and a proposed armament consisting of one MK-103 30-millimeter 

(mm) and two MG-151 20-mm cannons.45
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Thinking Obliquely

Vogt’s penchant for aeronautically unconventional designs was well established, his best known design being an experimental asymmetric observation aircraft, the Bv 141, which had its cockpit mounted in a small pod 

on the wing separate from the fuselage. (Luftwaffe procurement officials, 

despite how its technical staff might otherwise have been impressed with 

his technical acumen, chose a more conventional symmetrical design, the 

Focke-Wulf Fw-189, instead).46 Altogether, including the P 202, Vogt and his 

engineering team came up with as many as 33 asymmetrical aircraft designs 

between 1938 and 1945. Ironically, of all those generated, arguably it was the 

P 202 that presented the most logical and worthwhile case for development. 

But Vogt was not alone in his pursuit of the oblique wing; other so-called 

sheared elliptical-wing concepts were conceptualized at the Aerodynamische 

Versuchsanstalt (the Experimental Aerodynamics Establishment at Göttingen) 

and by German manufacturer Messerschmitt’s advanced concepts team under 

Woldemar Voigt, architects of some of Germany’s most radical and advanced 

future aircraft designs. Their P 1101/XVIII-108 (also referred to as the P 

1109) featured two axisymmetrically pivoted oblique wings, one on top and 

one under the fuselage. At takeoff and landing, the P 1101/XVIII-108/P 

1109 would be, effectively, a biplane. But at high speed, the upper wing 

would sweep its right wingtip forward as the lower wing would sweep its left 

wingtip forward, producing the planform of a compressed X shape whose 

legs were swept at 60 degrees. In addition to the two-wing design, there was 

a single-wing variant with the right wingtip swept forward at maximum 

sweep. Messerschmitt also explored a fixed X-wing concept using two fixed 

oblique wings that were axially superimposed, one above the other, with one 

mounted on top of the fuselage, and the other mounted below.47

The leading German aeronautical aerodynamicist, Dietrich Küchemann 

(who after the Second World War became chief scientific officer and aerodynamics department head for the Royal Aircraft Establishment [RAE] in 

Farnborough, England, where he pioneered slender-wing research influencing the aerodynamics of the Concorde supersonic transport) noted that,

[once] the application of sweep was proposed, it became clear 

that the aerodynamic problems concerned not only the cruise 

design but also the increasingly unsatisfactory characteristics at 

low speeds...[and] thus the concept of variable sweep almost 

suggested itself as a possible remedy.48

Erich von Holst, a pioneer in behavioral physiology who undertook 

extensive research on bird-like ornithopters (flapping-wing aircraft) at 

Göttingen in association with Küchemann, suggested in an unpublished 
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1942 paper that a skewed wing was the simplest way of obtaining variable sweep. Küchemann noted that von Holst actually built and flew 

models to demonstrate “their generally satisfactory stability and flying 

characteristics.”49 He added that the models “included not only asymmetrical configurations, without and with a fuselage, but also symmetrical 

arrangements with scissor-like biplanes.”50 Küchemann noted, however, 

that while Germany’s wartime collapse “prevented the completion of an 

actual aircraft with a slewed wing,” in the postwar era, the slewed wing was 

effectively “invented” again by the NACA’s R.T. Jones, tested at Langley 

by John P. Campbell and Hubert M. “Jake” Drake (who tunnel tested its 

stability characteristics), and resurrected in the 1970s by R.T. Jones (by 

then at Ames Research Center), who provided the rationale and justification for possibly applying it to high-speed supersonic transports (SSTs).51

The NACA Commences its Own Skewed-Wing Exploration

While the German efforts existed as intriguing drawings (and perhaps, in the 

case of Erik von Holst, as hobbyist models), they did not reach the prototype 

piloted aircraft construction stage. That had to await the independent conceptual and development work of Robert T. Jones. Jones’s oblique-wing concept 

was being wind tunnel tested by John P. Campbell and Hubert M. Drake at 

Langley as early as 1945 (as discussed below). As with his other swept-wing 

and delta-wing research, Jones’s work resulted in extensive study, wind tunnel 

testing, and model building, and it finally led to the design and fabrication of 

a proof-of-concept jet-propelled aircraft—the Ames-Dryden AD-1 Oblique 

Wing Research Airplane, which to date remains the only piloted oblique-wing 

aircraft ever flown.

Walter G. Vincenti, who knew Jones well and worked with him over a 

period of years, has addressed the independent oblique-wing concept development issue and Jones’s role in influencing Campbell and Drake to undertake 

their wind tunnel investigation of an oblique-wing model. Vincenti stated that

[w]hether the concept of the oblique wing was original with R.T. 

is not clear. The idea was current in the sweep developments in 

Germany during the war. The first mention in the United States 

is in a NACA report, dated in mid-1946, by John P. Campbell 

and Hubert M. Drake on stability-and-control tests of an obliquewing airplane model in the Langley low-speed free-flight wind 

tunnel (Campbell and Drake 1947). The report states in typical 

NACA impersonal fashion that ‘it has been proposed’ that such 
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Thinking Obliquely

an airplane be flown, but R.T. has confessed that he promoted 

the tests, though somewhat secretively from Langley management. 

Whether he had heard of the German work before these tests we 

do not know. In any event, the idea was—and is—startling because 

as R.T. wrote, “Artifacts created by humans show a nearly irresistible tendency for bilateral symmetry.”... A large body of work has 

grown up concerning the oblique-wing airplane in the past half 

century, much of it at Ames and Stanford under R.T.’s inspiration.52

Wind tunnel model testing of the oblique-wing concept started at NACA 

Langley shortly after the end of the Second World War, blending the conceptual development work of R.T. Jones with the methodical tunnel research of 

John P. Campbell and Hubert M. Drake. This work was followed by a series of 

other tests, first at NACA Langley and later NASA Ames, the results of which 

were well documented by the NACA and NASA in future references that served 

as building blocks for continued study and testing, which, in fact, is still in 

progress today. The wind tunnel tests validated the anticipated aerodynamic 

performance of the oblique-wing concept, thus encouraging further study. 

Specific areas covered included wing-body tests, lift-to-drag (L/D) ratio assessment, and airfoil and planform studies. Aircraft industries, universities, and 

conceptual studies (undertaken by R.T. Jones and other aeronautical engineers 

with NASA) analyzed these findings and further refined the oblique-wing 

concept. These efforts led to the fabrication of the AD-1 oblique-wing demonstrator and, later, in followup designs and proposals, including one to modify 

an obsolete U.S. Navy jet fighter as a potential transonic low-supersonic test 

bed (the F-8 Oblique Wing Research Aircraft program covered in chapter 5) 

and more recent design applications for potential high-speed civil air transport 

aircraft (reviewed in chapter 6).

NASA engineer-historian Joseph R. Chambers has noted that “virtually 

every technical discipline studied by the NACA and NASA for application to 

aerospace vehicles has used unique and specialized models, including the field 

of aerodynamics, structures and materials, propulsion, and flight controls....

The most critical contributions of aerospace models are to provide confidence 

and risk reduction for new designs and to enhance the safety and efficiency 

of existing configurations.”53 There are two major categories of aeronautical 

modeling techniques: physical wind tunnel test models and computer models 

and codes. Both were used in the AD-1 Oblique Wing Research Aircraft 

program. In addition, there are remotely piloted models or vehicles, such as 

the oblique-wing model used by R.T. Jones to demonstrate the oblique-wing 

concept. A physical model generally refers to the model used in experimental 

analysis of a larger full-scale vehicle. Wind tunnel models are routinely used 
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in many applications, including aerodynamic data gathering for the analysis 

of full-scale aircraft designs, proof-of-concept demonstrators for analysis of 

aeronautical concepts, and problem-solving exercises for vehicles already in 

production. Physical wind tunnel models are generally classified as either 

static or dynamic depending on their configuration and testing purpose. 

Static models of aircraft are used to obtain detailed aerodynamic data for 

analysis of their full-scale versions under specified flight conditions. Static 

tests are normally conducted with the model fixed to an internally mounted, 

force-measuring device known as an electrical strain gauge, which in turn is 

mounted to a sting support system. Dynamic model investigations represent an extension of conventional static tests to include the effects of vehicle 

motions assessed in free flight (hence the term dynamic). The primary objective of free-flight testing is to evaluate the inherent flight motions of a configuration and its response to various control inputs. Computer models and 

codes consist of various computer programs and combinations of programs 

designed to model various design concepts and vehicle performance. All of 

these techniques were used in the development and flight testing of the AD-1 

Oblique Wing Research Aircraft.

In a 1981 survey of variable-sweep research, Edward C. Polhamus and 

Thomas A. Toll noted:

By combining information from various sources—the theoretical findings of Busemann and Jones, the German experimental 

data at subsonic and supersonic speeds, and the NACA transonic 

data—a perspective of the benefit of wing sweep was developed. 

[As a result] [t]he conclusion drawn by many in the United States 

during 1945 and 1946 was that the best of all worlds would 

involve having straight-wing characteristics at low speeds and 

swept-wing characteristics beyond the point where compressibility effects began to appear.54

Polhamus and Toll added, however, that: “The oblique-wing (or skewedwing) concept was a somewhat different matter, since there were widespread 

reservations about the flying qualities of highly unsymmetrical aircraft, and 

a free-flight investigation of an oblique-wing model was undertaken during 

March 1946.”55
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Thinking Obliquely

Phase One: The Campbell-Drake Trials of 1947

This wind tunnel testing of an oblique-wing airplane model was conducted 

in the free-flight tunnel at the Langley Memorial Aeronautical Laboratory 

(LMAL, now NASA Langley Research Center [LaRC]) by John P. Campbell 

and Hubert M. Drake. Their findings were published as NACA Technical 

Note 1208 in May 1947, and the model they tested is shown in the 

following drawing.

In undertaking their tests, Campbell and Drake noted that

[i]n order to gain the advantages of sweep at high speeds without 

experiencing the difficulties introduced by sweep at low speeds, 

it has been proposed that an airplane be equipped with a wing 

pivotally attached to the fuselage so that it can be set at right 

angles to the fuselage for take-off, landing, and low-speed flight 

and at some angle of sweep for flight at high speeds. In one suggested design the wing is skewed or pivoted as a unit so that one 

side of the wing is swept forward and the other side swept back.56

Their tests consisted of in-flight tests, force tests, and damping-in-roll 

tests of a model with an oblique wing that could be set at various angles of 

skew ranging from 0 degree to 60 degrees. In undertaking the tests, the two 

NACA engineers noted that the investigation was a “preliminary and qualitative indication or whether such a design could be flown” and that the tests 

did not represent a “complete and comprehensive”57 discussion of the stability 

and control problems involved in skewed- (oblique-) wing designs. To address 

those problems, Campbell and Drake indicated that higher-scale tests on 

skewed-wing models more representative of high-speed aircraft designs would 

probably be needed in order to obtain an accurate and detailed analysis.

The flight and force tests were conducted in the Langley free-flight tunnel 

using an inclined airstream to enable a continuous gliding flight. Force tests 

were made on the free-flight tunnel balance, which measured forces and 

moments about the stability axes. The values of the damping-in-roll derivatives were determined by rotation tests in the Langley 15-foot free-spinning 

tunnel. Controls for the model were actuated by electrical pulses through a 

flexible trailing cable, as with all Langley spinning-test models.

The model itself weighed between 4.73 pounds (lb) and 5.03 lb. It had a 

wing area of 2.67 square feet; a wingspan of 4 feet at a 0-degree skew, 3.07 

feet at a 40-degree skew, and 2 feet at a 60-degree skew; an aspect ratio of 6.0 
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Configuration of Campbell-Drake oblique-wing wind tunnel model, from NACA TN 1208, 1947. (NASA)
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Thinking Obliquely

at a 0-degree skew; and a mean aerodynamic chord of 0.70 feet at a 0-degree 

skew, 0.91 feet at a 40-degree skew, and 1.40 feet at a 60-degree skew. The 

ailerons were of the plain type with an area of 0.19 square feet. The horizontal 

tail had an area of 0.53 square feet, an aspect ratio of 4 feet, and a tail length 

(hinge line to center of gravity) of 2 feet. The vertical tail had an area of 0.4 

square feet, an aspect ratio of 2 feet, and a tail length (hinge line to center of 

gravity) of 2 feet.58

The wind tunnel testing included force tests for longitudinal (pitch) and 

lateral (roll) stability and control and rotational tests for evaluating its spin 

characteristics. Afterwards, Campbell and Drake reported, encouragingly, that:

1. In general, the results indicated that an airplane wing can be skewed 

as a unit as great as 40° without encountering serious stability and 

control difficulties.

2. Longitudinal stability and control:

(a) The longitudinal stability and control characteristics were 

satisfactory in flights made with 40° skew over a lift-coefficient 

range from 0.3 to 1.0 even for very low values of static margin.

(b) Only a slight change in longitudinal trim occurred with 

increasing skew, but an appreciable increase occurred in the 

glide angle required at a given lift coefficient.
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3. Lateral stability:

(a) The values of effective dihedral for the wing skewed as a unit 

were considerably less than those encountered on wings with 

large amounts of sweep-forward or sweep-back.

(b) Skewing the wing caused sizable changes in the lateral trim 

which varied with lift coefficient and skew angle.

4. Lateral control:

(a) The aileron control effectiveness was only slightly reduced 

by skew for angles less than 40° because the damping in roll 

decreased approximately the same amount as the aileron rolling 

moments. At 50° skew, however, the aileron control effectiveness was noticeably reduced, and at 60° it was so weak that 

sustained flights could not be made.

(b) The force tests indicated that for the 40° skew angle the 

ailerons produced large pitching moments. In the flight tests, 

however, no pitching tendencies were observed in aileron rolls, 

apparently because the lift forces on the wing produced by rolling introduced pitching moments that were equal and opposite 

to the aileron pitching moments.59

The positive impact of Campbell and Drake’s tests are evident not only 

from the findings outlined in the resulting NACA Technical Note, but also in 

the numerous citations by R.T. Jones and other experts in subsequent writings 

and oblique-wing designs over the next 50-plus years. Campbell and Drake’s 

wind tunnel tests, however, did not bring about an immediate effort to develop 

oblique-wing aircraft. Instead, primary attention was directed toward further 

work on symmetrical variable-sweep development. Wind tunnel study at 

Langley, however, resumed later under the direction of Charles J. Dolan, using 

a modified X-1 research airplane model with a fixed pivot point on the fuselage 

centerline to conduct sweepback tests at 0-degree, 15-degree, 30-degree, and 

45-degree angles.60 The initiation of Campbell and Drake’s wind tunnel tests 

appears to have immediately followed or overlapped the wind tunnel testing of the swept wing. In a March 14, 1945, letter to R.T. Jones, George W. 

Lewis, the committee’s legendary Director of Aeronautical Research at NACA’s 

Washington Headquarters on H Street NW, stated that

[t]he result of your theoretical analysis in arriving at the correct 

principle of design of a supersonic, or transonic, wing I consider 

most important....Mr. Crowley [John “Gus” Crowley, a Lewis 

associate at NASA Headquarters who specialized in flight testing 

and flight research] was in the office today and I mentioned your 
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Thinking Obliquely

Jones's depiction of an oblique-wing elliptical planform, 1952. (AIAA)

letter to him. He said that he had discussed this matter with you 

and that he had suggested you prepare a memorandum, which is 

to be followed later by some tests.61

It is not clear whether this letter referred only to the swept-wing testing or 

to both the swept-wing tests and Campbell and Drake’s investigation of the 

oblique wing. As reviewed above, however, Walter Vincenti stated that “R. 

T. [Jones] has confessed that he promoted the [oblique-wing] tests, though 

somewhat secretively from Langley management.”62 In reviewing the early history of the oblique-wing concept, Ilan Kroo, a Stanford University professor 

of aeronautics, also signaled Jones’s role in the undertaking of Campbell and 

Drake’s study, noting, “He [Jones] built balsa wood models of oblique wings 

while at Langley field in 1945 and inspired the first published wind tunnel 

tests of the concept by J. Campbell and H. Drake.”63
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Phase Two: Jones’s Progression to 

the Oblique Wing, 1946–1958

Between 1946 and 1958, R.T. Jones steadily expanded his studies on sweptand delta-wing aerodynamics, making notable contributions to understanding 

the relationship between planform choice and aerodynamic performance and 

contributing notably as well to studies of wing-body effects, a subject of vital 

importance in the early years of transonic aircraft design. Initially, whatever 

other interest he might have had in Vogt-like skewed wings, Jones was firmly 

committed to the study of bilaterally symmetric swept-wing shapes. Thus, for 

example, a 1946 paper entitled “Thin Oblique Airfoils at Supersonic Speed” 

was not, as the title might seem to imply, a paper on the skewed AD-1-style 

oblique wing but, rather, a paper extending his research (enunciated in his TR 

835 issued that same year) on bilaterally symmetric swept wings.64

But in 1952, Jones deviated from the bilaterally symmetric path to address 

the case of the elliptical wing. The elliptical wing is one of the oldest and most 

pleasing aerodynamic shapes, and if inevitably associated with the Supermarine 

Spitfire of Reginald Mitchell (whose wing was, in fact, a broken rather than 

pure ellipse), its origins actually date to the First World War. In the prewar era, 

it appeared in its purest form on the interwar Bäumer Sausewind light aircraft, 

which inspired Heinkel’s (Germany’s manufacturing company) later He 70 

Blitz. Earlier in his career, Jones had studied the conventional elliptical wing, 

and now, in the early supersonic era, he returned to study it, finding that the 

drag of an elliptical wing set at an oblique angle not only had a highly desirable 

uniform lift distribution, but a greatly reduced drag as well.65

Jones continued his pursuit of the elliptical oblique wing, and in a conference on high-speed aeronautics held at the Polytechnic Institute of Brooklyn 

in January 1955, he presented his views on the future of high-speed transport 

airplanes, noting that the “wing of elliptic planform” had “especially simple 

mathematical properties at supersonic speeds” with a uniform distribution of 

lift “over whatever elliptical area is allotted.”66 He added that an elliptical wing 

“yawed behind the Mach cone”—that is, flying forward but presenting an 

oblique planform when viewed from above, such as on the AD-1 demonstrated 

a quarter century later—“enables the requirements of minimum pressure drag 

and minimum friction drag to be satisfied simultaneously.”67 He concluded,

At large angles of sweep or yaw the drag due to lift becomes in a 

large measure independent of the exact distribution, but depends 

primarily on the span b and the length l [report references] of the 

wing[, thus the] minimum drag occurs when both the lengthwise 

and spanwise loadings are elliptical.68
30

Thinking Obliquely

For supersonic speed we thus require the maximum span b and 

Thus, a decade after enunciating the bilaterally symmetrical swept planform—whether a slender delta or a bent V-planform wing—Jones was now 

enunciating the pure simplicity of the straight elliptical wing, skewed obliquely 

to the line of flight, effectively acting as an aircraft with both a forward-swept 

and aft-swept wing. Ten months after his Brooklyn presentation, Jones spoke 

before an international aerodynamics conference held, fittingly, at Göttingen. 

There he presented his findings on the benefits of the oblique elliptical planform, noting as well the contributions of his mentor Max Munk to his analysis 

of induced drag reduction.70

Model aircraft have a long and distinguished history of contributing to the 

development of aeronautics, from Alphonse Pénaud’s rubberband-powered 

model of 1871, which demonstrated that a powered aircraft could successfully 

fly through the inherently stable steam-powered Aerodromes of Smithsonian 

Secretary Samuel Langley, and numerous other examples in the 20th century. 

Virtually all aeronautical engineers began their careers in flight by building 

flying model airplanes in their youth. Thus, it was natural that when Jones 

sought to validate his ideas regarding an oblique wing, he turned to the elegance 

and deceptive simplicity of the traditional balsa-wood model airplane, demonstrating the concept of an oblique flying wing with a balsa-wood glider that he 

flew at the first International Congress of the Aeronautical Sciences (ICAS), 

held in Madrid, Spain, in September 1958. In recalling this in a 1972 paper 

for the American Institute of Aeronautics and Astronautics, Jones said, “Some 

years later the present writer demonstrated the rather surprising stability of 

the slanted wing by flying models at the first ICAS meeting in Madrid.”71 The 

“surprising stability” that Jones referred to was likewise implicit in the findings 

of Campbell and Drake, which Jones described as “Perhaps the earliest experiments to test the flight stability of such an arrangement.”72

In his 1958 paper, Jones reviewed the state of contemporary supersonic 

design, noting at the outset that

[i]n its earlier development the subsonic airplane showed a great 

variety in the arrangement of airfoils, bodies, and other parts. 
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American Genius

For the past 15 or 20 years, however, those airplanes which have 

passed the tests of experience have shown little alteration in basic 

form. The aerodynamic principles which have determined this 

form seem now to be well understood and agreed upon.73

 The situation is different in the case of the supersonic airplane. 

Here the aerodynamic rules seem more complex. No clear direction toward a specific form is evident. Our theoretical investigations have taken a rather wide range—seeming in some cases 

rather far removed from practical questions.74

Jones added that in this paper he was going to “review some of the recent 

theoretical and experimental work in supersonic aerodynamics with its practical application in mind.”75 Central to his review was a comparison of yawed 

and swept wings. In making this comparison, Jones noted:

With planar wings the wave drag is reduced as the lift distribution is extended in the flight direction, while the vortex drag is 

reduced by extending the span. At the same time the friction 

drag is reduced by diminishing the exposed area of the wing. At 

subsonic speeds the last two considerations are effective and they 

lead to wing forms approaching a lifting line perpendicular to the 

flight direction. At supersonic speeds the added condition on the 

length leads to a long, narrow wing placed at an angle of yaw.76

 It is interesting to analyze the yawed lifting line in terms of 

its area of entrainment. The forward and reversed Mach waves 

are simply circular cones drawn from the ends of the line. At 

subsonic angles of yaw the cones are displaced laterally so that 

the contour of their inter-section, which outlines the equivalent 

jet, is an ellipse. The area of this ellipse vanishes rapidly, however, 

and disappears completely as the lifting line approaches the Mach 

angle. The area of entrainment is zero and the wave drag given by 

the theory is infinite at supersonic angles of yaw.77

Jones then noted that if a yawed wing is converted into a swept wing (by 

bending the wing at the middle), its length in the flight direction is reduced to 

about one-half, thus increasing the wave drag “so that the potential lift-drag ratio 

is invariably smaller for the bilaterally symmetric arrangement.”78 (Emphasis added.)

In understanding Jones’s quest to reduce supersonic drag, the perspective 

of the great Hungarian aerodynamicist Theodore von Kármán affords a useful 

insight, offered near-contemporaneously with Jones’s oblique-wing work:
32

Thinking Obliquely

Even before any manned aircraft had pierced the sound barrier, 

it was apparent from a theoretical point of view that the most 

important factor in the design of a supersonic plane is the new 

source of drag, which we aerodynamicists have come to call “wave 

drag.” This type of drag is analogous to a phenomenon which is 

familiar to every motorboat operator. At low speed the boat’s keel 

rides deep in the water. As the operator increases the speed, the 

boat encounters greater resistance, which arises from the waves 

created by the boat. Similarly, in the case of flight, as indicated 

earlier, the resistance of the air rises appreciably when the airplane 

begins to approach the speed of the air waves created by it. Once 

the plane goes through this speed, the flow around it smooths 

out to some extent.

 The difference between the motorboat and the airplane lies 

in what one can do to overcome this new resistance. A speedboat 

can rise on its “step,” and move along in the water with most of 

the boat in the air, so a great part of the water drag is lessened. 

But an airplane cannot move on the step; it is already operating 

in three dimensions....Other means have to be found to reduce 

the new resistance arising out of the high speeds.79

It may be said that Jones’s progression toward the oblique-wing configuration certainly represented just such an “other means.”
33

American Genius

Endnotes

1. See, for example, Frederick L. Nussbaum, The Triumph of Science and 

Reason, 1660–1685 (New York: Harper & Row, Publishers, 1953), 

7–8; Thomas P. Hughes, “From Deterministic Dynamos to SeamlessWeb Systems,” in Engineering as Social Enterprise, ed. Hedy E. 

Sladovich (Washington, DC: National Academy Press, 1991), 7–24.

2. For insights into Jones, see his Robert T. Jones, “Learning the Hard 

Way: Recollection of an Aeronautical Engineer,” unpublished 

autobiography, copies in NASA Dryden Flight Research Center 

Library, NASA Ames Research Center Archives, and Stanford 

University Library Special Collection no. 876 (Papers of Robert 

T. Jones); Walter G. Vincenti, “Robert T. Jones, 1910–1999: A 

Biographical Memoir,” Biographical Memoirs 86 (2005); Walter G. 

Vincenti, “Robert T. Jones, One of a Kind,” Annual Reviews of Fluid 

Mechanics 37, no. 1 (2005): 1–21; William R. Sears, Introduction 

to the “Collected Works of Robert T. Jones,” NASA Technical 

Memorandum (TM) X-3334 (February 1976), vii–xii; James R. 

Hansen, Engineer in Charge: A History of the Langley Aeronautical 

Laboratory, 1917–1958, NASA Special Publication (SP)-4305 

(Washington, DC: NASA 1987); and Robert T. Jones, “My 

Adventures in Aeronautics,” undated and unpublished draft of autobiography, Department of Special Collections, Stanford University 

Libraries, box 11, folder 11.

3. Ibid.

4. Max M. Munk, Fundamentals of Fluid Dynamics for Aircraft 

Designers (New York: The Ronald Press Co., 1929).

5. For the Prandtl-Munk connection, see Michael Eckert, The Dawn 

of Fluid Dynamics: A Discipline Between Science and Technology

(Weinheim, Germany: Wiley-VCH Verlag, 2006), 73–76, 102–105. 

For Munk at Langley, see the previously cited Hansen, Engineer in 

Charge, 72–95.

6. Hermann Grassmann, Die Ausdehnungslehre: Vollständig und 

in Strenger Form Begründet (Berlin: Enslin Verlag, 1862); for 

Grassmann’s extraordinary work, despite contemporary lack of 

appreciation, see Gert Schubring, Hermann Gunther Grassmann: 

Visionary Mathematician, Scientist and Neohumanist Scholar (New 

York: Kluwer Academic Publishers, 1996).

7. For Hamilton, see Thomas L. Hankins, Sir William Rowan Hamilton

(Baltimore, MD: The Johns Hopkins University Press, 1980); see 
Thinking Obliquely

also W.W.R. Ball, A Short Account of the History of Mathematics (New 

York: Sterling Publishing Co., 2001 ed.), 472–474.

8. In his “Aerodynamic Design for Supersonic Speeds,” in Advances in 

the Aeronautical Sciences Proceedings of the First International Congress 

in the Aeronautical Sciences, Madrid, September 8–13, 1958 vol. 

1, eds. Theodore von Kármán, A.M. Ballantyne, and R.R. Dexter 

(New York: Pergamon Press, 1959), Jones recollected assisting Zahm 

by making figures and drawings for Zahm’s “Superaerodynamics,” 

Journal of the Franklin Institute 217 (1934): 153–166.

9. Jones, “Learning the Hard Way: Recollection of an Aeronautical 

Engineer.”

10. Sears, “Introduction,” in “Collected Works of Robert T. Jones,” vii.

11. Robert R. Dexter, Secretary, Institute of Aeronautical Sciences, letter 

to Dr. Robert T. Jones, January 3, 1947, Stanford, box 35.

12. Award Presentation citing January 6, 1981, award signed by 

President Jimmy Carter, NASA Ames Research Center History 

Office, Archives Reference Collection, Collection Number 

AFS1070.8A.

13. Phillip S. Hughes, Acting Secretary, Smithsonian Institution, letter 

to Dr. Robert T. Jones, February 24, 1981, Department of Special 

Collections, Stanford University Libraries, box 35, folder 10.

14. Ibid.

15. NASA, “Collected Works of Robert T. Jones,” 885–1025. The quotation is on 1022.

16. Vincenti, “A Biographical Memoir,” 15.

17. See the R.T. Jones, “Collected Works of Robert T. Jones.”

18. Details on the JB-2 are from Kenneth P. Werrell, The Evolution of the 

Cruise Missile (Maxwell AFB, AL: Air University Press, September 

1985), 65–67.

19. Indeed, as of November 2011, the remains of one such JB-2 missile 

fatally damaged during launch are still rusting away amid scrubwood-covered sand dunes at the Sandestin, FL, wartime test location, now the Coffeen Nature Preserve on Florida’s Emerald Coast. 

Information from Dr. Richard P. Hallion, who visited the site and 

inspected the wreckage on November 16, 2011. Loss statistics are 

from Werrell, Evolution of Cruise Missile, 65.

20. G.W. Lewis, “Memo from NACA to Langley Laboratory,” February 

14, 1945, Robert T. Jones Papers, Stanford University Libraries, 

Department of Special Collections, box 35, folder 16. 

Jones, “My Adventures in Aeronautics,” 10–11.

34
35

American Genius

21. Letter from G.W. Lewis to Robert T. Jones, October 14, 1947, 

Robert T. Jones Papers, Stanford University Libraries, Department 

of Special Collections, box 35, folder 16.

22. For this progression, see Richard P. Hallion, “Sweep and Swing: 

Reshaping the Wing for the Jet and Rocket Age,” in, NASA’s 

Contributions to Aeronautics, vol. 1, ed. Richard P. Hallion, NASA 

SP-2010-570-Vol 1 (Washington, DC: NASA, 2010).

23. It is worth noting that on this point, Jones’s memory that the Sikorsky 

engineer came to him with a drawing of a “fighter plane” is incorrect; he came with a drawing of a proposed glide bomb based upon 

an earlier Sikorsky fighter proposal by Michael Gluhareff. Gluhareff 

had conceptualized a futuristic delta-wing fighter powered by a pusher 

propeller. This remarkable concept (more suitable for turbojet propulsion) was not developed, though several years later, it spun off a proposal for a 2,000-lb guided glide bomb, or “glomb.” It came to Jones’s 

attention because of his work on guided-weapon issues for the NACA. 

Richard P. Hallion, who interviewed Jones for his article “Lippisch, 

Gluhareff, and Jones: The Emergence of the Delta Planform and the 

Origins of the Sweptwing in the United States,” (Aerospace Historian 

26, no. 1 [Spring 1979]: 1–10)—the first historical examination of 

Jones’s work and the context of swept-wing research in Germany and 

America—was drawn to Jones’s work by discovering a wind tunnel model of the Gluhareff fighter proposal in the collections of the 

National Air and Space Museum, Smithsonian Institution, in 1976. 

For a more expanded review and drawing of Gluhareff’s proposed 

1941 rounded delta planform and subsequent “glomb” missile design, 

see the previously cited Hallion, “Sweep and Swing: Reshaping the 

Wing for the Jet and Rocket Age,” 8–11.

24. A von Kármán research associate at the Guggenheim Aeronautical 

Laboratory of the California Institute of Technology (GALCIT), 

Tsien Hsue-shen undertook significant high-speed research, later 

concentrating his work in rocketry and hypersonics and, subsequently, became the architect of the People’s Republic of China 

missile program. Two of his papers relating to Jones’s interests 

are: “Two-Dimensional Subsonic Flow of Compressible Fluids,” 

Journal of the Aeronautical Sciences 6 (1939); and (with L. Lees) 

“The Glauert-Prandtl Approximation for Subsonic Flows of a 

Compressible Fluid,” Journal of the Aeronautical Sciences 12 (1945).

25. Jones, “My Adventures in Aeronautics.”
36

Thinking Obliquely

26. The paper was drafted in May 1945 and published the next year as 

“Properties of Low-Aspect-Ratio Pointed Wings at Speeds Below and 

Above the Speed of Sound,” NACA Report No. 835 (1946).

27. Jones, “My Adventures in Aeronautics.”

28. See Max M. Munk, “Note on the Relative Effect of the Dihedral and the 

Sweepback of Airplane Wings,” NACA Technical Note No. 177 (1924).

29. Vincenti, “Robert T. Jones, One of a Kind,” 7.

30. Jones retained this model and used it as a letter opener! When he 

mentioned this to Richard P. Hallion during Hallion’s interview with 

him, Hallion persuaded him to donate the model to the National 

Air and Space Museum, and it was subsequently accessioned into the 

museum’s collections.

31. See the previously cited Hallion, “Sweep and Swing: Reshaping the 

Wing for the Jet and Rocket Age,” 13–17.

32. This was Busemann’s milestone Volta Congress paper in which 

he enunciated the theory of high-speed swept wings, printed 

as “Aerodynamische Auftrieb bei Überschallgeschwindigkeit,” 

Luftfahrtforschung 12, no. 6 (October 3, 1935).

33. It subsequently appeared as “Wing Planforms for High-Speed 

Flight,” NACA TR No. 863 (1947).

34. Jones, “My Adventures in Aeronautics.”

35. Robert T. Jones, signed statement titled “The Shaping of Wings to 

Minimize the Formation of Shock Waves,” witnessed as explained by 

Jones on February 27, 1945, and typed on March 14, 1945, NASA 

Ames History Office, Moffett Field, CA.

36. See Max M. Munk, “Elements of Wing Section Theory and of the 

Wing Theory,” NACA Report No. 191 (1924); Hermann Glauert, 

“The Effect of Compressibility on the Lift of an Aerofoil,” Reports & 

Memoranda No. 1135, Aeronautical Research Committee (United 

Kingdom) (1927); Ludwig Prandtl, “General Considerations on the 

Flow of Compressible Fluids,” NACA TM No. 805 (1936).

37. Quote from Hans Wolfgang Liepmann and Allen E. Puckett, 

Introduction to Aerodynamics of a Compressible Fluid (New York: 

John Wiley & Sons, Inc., 1947), 172. See also R. Giacomelli and 

E. Pistolesi, “Historical Sketch,” in Aerodynamic Theory: A General 

Review of Progress Under a Grant of the Guggenheim Fund for the 

Promotion of Aeronautics, vol. 1, ed. William Frederick Durand 

(Pasadena, CA: Guggenheim Aeronautical Laboratory of the 

California Institute of Technology, 1943 ed.), 383–394; Theodore 

von Kármán, Aerodynamics: Selected Topics in the Light of Their 
37

American Genius

Historical Development (New York: McGraw-Hill Book Company, 

1963 ed.), 56–57, 115, 129–30.

38. Jones, “Properties of Low-Aspect-Ratio Pointed Wings at Speeds 

Below and Above the Speed of Sound,” 59. Ackeret’s work was 

published by the NACA as “Air Forces on Airfoils Moving Faster 

than Sound,” TM No. 317 (1925), translated from Zeitschrift für 

Flugtechnik und Motorluftschiffahrt (February 14, 1925).

39. Ibid., 63.

40. Hallion, “Sweep and Swing,” 11–13.

41. Edward C. Polhamus and Thomas A. Toll, “Research Related to 

Variable-Sweep Aircraft Development,” NASA TM 83121 (1981), 1.

42. Ibid.

43. Robert T. Jones, “Adolf Busemann: 1901–1986,” Memorial 

Tributes: National Academy of Engineering 3, (1989): 65.

44. Headquarters, Freeman Field, Air Materiel Command, “German 

Aircraft and a List of Foreign Aircraft Brought to the United 

States,” Foreign Equipment Descriptive Brief, archives of the 

National Museum of the USAF, serial No. 46-6B (August 1946), 

1, 8–9.

45. Headquarters, Air Materiel Command, Wright Field, “German 

Aircraft, New and Projected Types,” reprint of British Air Ministry 

A.I.2(g) Report No. 23, January 1946 (June 1946).

46. William Green, The Warplanes of the Third Reich (Garden City, NY: 

Doubleday & Co., 1970), 83, 192.

47. See Michael J. Hirschberg, David M. Hart, and Thomas J. 

Beutner, “A Summary of a Half-Century of Oblique Wing 

Research,” a paper presented at the 45th AIAA Aerospace 

Sciences Meeting and Exhibit, Reno, NV, January 8–11, 2007, 

AIAA paper no. 2007-150 (2007), 2–3; Hans-Ulrich Meier, ed., 

German Development of the Sweptwing, 1935–1945 (Reston, VA: 

AIAA,[in cooperation with the Deutsche Gesellschaft fur Luft und 

Raumfahrt Lilienthal-Oberth e.V.], 2010).

48. Dietrich Küchemann, The Aerodynamic Design of Aircraft

(United Kingdom: Paragon Press, 1978). Quotation from 12. In 

regard to Küchemann, see Andrew Nahum, “The Royal Aircraft 

Establishment from 1945 to Concorde,” in Cold War, Hot Science: 

Applied Research in Britain’s Defence Laboratories 1945–1990, eds.

Robert Bud and Philip Gummett (London: Science Museum, 

2002), 50–52; Kenneth Owen, Concorde: Story of a Supersonic 

Pioneer (London: Science Museum, 2001), 36–42.
38

Thinking Obliquely

49. Von Holst is not one of the better known interwar aerodynamics 

and flight control researchers, but in his work one can see the roots 

of today’s interest in insect- and bird-like micro-Remotely Piloted 

Aircraft (micro-RPA). See his essay (coauthored with Küchemann) 

“Biologische und Aerodynamische Probleme des Tierfluges,” Die 

Naturwissenschaften 29 (1941): 348–362. He was arguably better known among the model aircraft and youth airmindedness 

movement within the Third Reich; see, for example, his “Tierflug 

und Modellflug,” Luftfahrt und Schule: Zeitschrift zur Förderung 

der Luftfahrt und des Luftschutzes an deutschen Schulen 6, issue 3 

(December 1940): 24–26. Reproductions of his remarkable models 

periodically reappear and amaze anew.

50. Ibid.

51. Küchemann, Aerodynamic Design of Aircraft, 12.

52. Vincenti, “Robert T. Jones, One of a Kind,” 9.

53. For a detailed review of wind tunnel testing and modeling, see 

Joseph R. Chambers, Modeling Flight: The Role of Dynamically Scaled 

Free-Flight Models in Support of NASA’s Aerospace Program, NASA 

SP-2009-575 (Washington, DC: NASA, 2009), quote from 2.

54. Polhamus and Thomas, “Research Related to Variable Sweep Aircraft 

Development,” 5.

55. Ibid.

56. John P. Campbell and Hubert M. Drake, “Investigation of Stability 

and Control Characteristics of an Airplane Model with Skewed 

Wing in the Langley Free-Flight Laboratory,” NACA TN No. 1208 

(May 1947), 2.

57. Ibid., 2.

58. Ibid., 12–13.

59. Ibid., 10.

60. Polhamus and Toll, “Research Related to Variable Sweep Aircraft 

Development,” 5.

61. Letter from G.W. Lewis to R.T. Jones, March 14, 1945. NASA 

Ames History Office.

62. Vincenti, “Robert T. Jones, One of a Kind,” 9.

63. Ilan Kroo, “The Aerodynamic Design of Oblique Wing Aircraft,” 

AIAA paper no. 86-2624 (1986), 1.

64. Robert T. Jones, “Thin Oblique Airfoils at Supersonic Speed,” 

NACA TR No. 851 (1946).

65. Robert T. Jones, “Theoretical Determination of the Minimum Drag 

of Airfoils at Supersonic Speeds,” Journal of the Aeronautical Sciences

19, no. 12 (December 1952).
66. R.T. Jones, “Possibilities of Efficient High-Speed Transport 

Airplanes,” in Proceedings of the Conference on High-Speed 

Aeronautics, Antonio Ferri, Nicholas J. Hoff, and Paul A. Libby, eds. 

(New York: Polytechnic Institute of Brooklyn, 1955), 151–153.

67. Ibid.

68. Ibid.

69. Ibid.

70. Robert T. Jones, “Some Recent Developments in the Aerodynamics 

of Wings for High-Speeds,” Zeitschrift für Flugwissenschaften 4, no. 8 

(August 1956). The conference was sponsored by the Gesellschaft für 

angewandte Mathematik und Mechanik (GAMM), the Verein Deutscher 

Ingenieure, and the Wissenschaftlichen Gesellschaft für Luftfahrt.

71. R.T. Jones, “Reduction of Wave Drag by Antisymmetric 

Arrangement of Wings and Bodies,” AIAA Journal 10, no. 2 

(February 1972): 174.

72. Jones’s balsa-wood models are on display at NASA Ames. NASA 

Ames archivists have published instructions that show the actual size 

of each glider model part along with instructions on how to make 

an oblique-wing glider. The glider, which is made of 1/16-inch balsa 

wood, has an oblique wingspan of 63⁄4 inches with a rounded-up 

trailing edge. The left end of the wing, which is pointed forward, has 

a smaller fin perpendicular to the wing, while the right side of the 

wing has a larger fin. A critical part of the glider is the 2-inch boom 

consisting of a 3/32-inch stick with a nose weight made of clay or 

wax. The boom is glued at either a 30-degree or 45-degree angle to 

the wing. A handhold is glued under the wing immediately next to 

the boom.

73. Jones, “Aerodynamic Design for Supersonic Speeds,” 34.

74. Ibid.

75. Ibid.

76. Ibid., 40.

77. Ibid.

78. Ibid.

79. Theodore von Kármán and Lee Edson, The Wind and Beyond: 

Theodore von Kármán—Pioneer in Aviation and Pathfinder in Space

(Boston: Little, Brown and Company, 1967), 220–221.
40

Jones-Gadeburg radio-controlled oblique-wing free-flight model. (NASA)
41

CHAPTER 2

Evolving the Oblique Wing

For aerodynamicists, the Swinging Sixties meant more than a cultural transformation: it was the decade in which practical variable-wing-sweep went 

mainstream, typified by new aircraft—such as the American F-111, Soviet 

MiG-23 and Su-24, and French Mirage G—and imaginative concepts for 

variable-sweep supersonic transports and lifting reentry spacecraft. It was also 

the decade in which engineers first applied the single-pivot oblique planform 

to air transport design thanks to British aeronautical engineer G.H. Lee. If 

imitation is indeed the sincerest form of flattery, R.T. Jones had every reason 

to feel well-praised.

Lee, then deputy chief designer of Handley Page, Ltd. (Britain’s oldest 

aeronautical firm), had heard Jones’s Madrid presentation, during which the 

American had “demonstrated very convincingly” the oblique-wing concept 

using his small balsa-wood models.1

 He returned to the United Kingdom 

determined to undertake his own examination of the concept and as a result, 

developed a plan for a Mach 2 flying wing transatlantic airliner that he 

believed could increase “payload by between 50% and 100% if a slewed-wing 

layout were adopted.”2 Lee argued that when aerodynamicists and aircraft 

designers considered future high-speed designs,

[t]he usual solution is to have a highly swept arrow-head type of 

planform arranged with a joint somewhere on the inner part of 

the wing so the tips may be moved forward for subsonic parts 

of the flight where span is required, while they are moved back 

again to give a highly sweptwing for the supersonic phases....

The main penalty for such a layout is that major shear and 

bending loads have to be taken through the moving joints, with 

subsequent severe mechanical and structural problems.3

As a solution, Lee proposed a slewed all-wing planform containing the 

passengers and fuel with a crew cabin at the forward wingtip. Its vertical fin 
42

Thinking Obliquely

and rudder were at the rearmost wingtip, and four engines in ventral pylonmounted nacelles were under the central portion of the wing set (like the crew 

cabin and vertical fin and rudder) to always be parallel to the line of flight, 

whatever the wing’s skew (oblique) angle. Lee noted that with this configuration, unlike a bilaterally symmetrical variable swept wing, only comparatively 

secondary loads would be taken through moving joints. Longitudinal and 

lateral control would be provided by elevons (combined ailerons and elevators) and the rudder. Lee noted that,

[w]ith regard to the performance to be expected from such an 

aeroplane, the lift/drag ratio in supersonic flight at a Mach No. 

of, say, 2.0 may be expected to be approximately 10 or 11, which 

is probably 10% or 20% better than might be obtained with 

the corresponding slender wing configuration. Subsonically, the 

slewed wing would have a lift/drag ratio of about 24, which is 

very much better than could be obtained with the slender wing.4

Despite the promise of the oblique wing and its apparent maturity, it 

would take more than another decade to appear. In retrospect, Lee admitted, the oblique wing, despite its attractiveness, “bristled with magnificent 

problems,”5 particularly in stability and control, because with an oblique 

wing, any deviation in pitch immediately resulted in rolling and yawing as 

well, thanks to “an inescapable, built-in coupling between all three motions.”6

For his part, Jones left NASA for a period of 7 years to work as a principal 

research engineer with the Avco-Everett Research Laboratory in areas other 

than aeronautics, though he continued his own individual research, publishing yet another analysis of thin oblique-wing aerodynamics in 1965.7

In 1970, Jones returned to NASA’s Ames Research Center as a senior staff 

scientist. By the late summer of 1971, he had formulated a compelling argument for considering oblique wings for future supersonic aircraft, resting on 

a detailed and provocative examination of wave drag and the comparative 

performance of bilaterally symmetric V-foremost sweptwings and antisymmetric oblique wings.8

Jones’s Progression Toward a 

Suitable Flight Configuration

Acknowledging that “[o]ne of the unspoken assumptions in aircraft design is 

that of bilateral or mirror symmetry,” Jones argued that there was “no rational 

discussion”9

 of its merits, and that, indeed,
43

Evolving the Oblique Wing

once the velocity of sound is exceeded, the laws of aerodynamics 

change in such a way as to make it seem inadvisable to arrange the 

components of an airplane side by side or abreast in a supersonic 

stream unless there are compelling reasons for such an arrangement. Both the transonic area rule and the supersonic small disturbance theory show large adverse interference effects for bodies 

or wings in mirror-symmetric arrangements.10

He demonstrated his argument by showing the results of applying supersonic wave-drag theory to two airplanes—in two different formations—flying in 

close formation at a slightly supersonic Mach number. Alone, one airplane had 

a measured wave drag of 1. When flying side by side (bilaterally symmetrically) 

with another airplane of similar type, the two aircraft would produce a combined 

drag of 4 as the drag of each aircraft would be doubled by interference from 

the other. But if they flew in a classic military “leader and wingman” formation 

(with one slightly ahead of the other), producing an oblique, antisymmetrical 

formation, the total drag of both aircraft was 1. In short, the two airplanes had 

a wave-drag count equivalent to just a single aircraft.11 In an obvious critique of 

contemporary thought, then wedded firmly to the delta or sharply swept bilaterally symmetric arrow wing, Jones pointedly noted that “[t]he arrow shape, which 

seems intuitively correct for supersonic speed, nevertheless has a predicted wave 

drag many times larger than the antisymmetric arrangement.”12

Jones illustrated his paper with compelling plots and graphs and showed 

two possible supersonic oblique-wing configurations: one with a single fuselage 

and pivoted wing and horizontal tail and a second with two parallel fuselages 

joined to a wing and horizontal tail, each with a pivot so that, like a parallel 

rule, the aircraft could translate one fuselage ahead of the other, forming an 

aircraft with an oblique wing and an oblique tail. In both of these cases, the 

tendency in 1960s to 1970s air-transport design of mounting engines aft on 

the fuselage worked to keep the engines oriented so that their inlets and thrust 

were always aligned with the line of flight.

Jones concluded his paper by conceding that

it is admittedly surprising that aerodynamics and simple mechanics would lead to an antisymmetric form for supersonic flight. The 

difficulties with such forms may, however, be more conceptual 

than real and it is hoped that our analysis, though incomplete, 

will show that such configurations deserve more serious study.”13

To obtain additional experience in the control and stability of obliquewing aircraft, Jones (assisted by Burnett L. Gadeburg of NASA Ames, who 
44

Thinking Obliquely

Jones's concept for a single-fuselage oblique-wing SST, 1971. (AIAA)

Jones's concept for a twin-fuselage, oblique-wing, "antisymmetric" SST, 1971. (AIAA)
45

Evolving the Oblique Wing

served as project pilot) fabricated and tested several radio-controlled models. 

The radio control system, which was acquired from Kraft Systems of Vista, 

CA, provided linear, proportional deflection of all surfaces and, in addition to 

normal control channels, had an extra channel that permitted variation of the 

wing-skew angle in flight. (The wings were, of course, in a straight position 

for takeoff and landing). Afterward, Jones noted: “Variations of wing angle 

up to and beyond 45 deg produced no apparent changes in stability and only 

slight change in lateral trim—requiring a 1- or 2-deg offset of the ailerons.

Elevator and aileron effectiveness remained normal and we observed no change 

in longitudinal trim.”14 Maneuvers such as loops and rolls were performed 

without difficulty at angles of 45 degrees. He noted that coupling between 

longitudinal and lateral motions did not occur in aileron rolls but was apparent 

in the response to elevator control (pitch), thus indicating aileron deflection 

had to be employed simultaneously with pitch application.

Jones concluded that varying the sweep of a single wing had several practical 

advantages over the swing-wing design, including:

1. Turning the wing as a whole keeps the wing structure continuous 

across the pivot and places the primary load on the pivot tension 

(separate wing panels pivoted at the root places much greater loads 

on the pivots);

2. Likewise, turning the wing as a whole does not displace the centroid 

of area relative to the center of gravity;

3. The optimum fuselage shape for an oblique wing is more nearly 

cylindrical than the swept wing, which, conforming to the “area rule,” 

requires a somewhat localized and deep indentation in the fuselage;

4. An oblique wing would enable flight at different Mach numbers 

with greater efficiency, thus enabling overland flights at speeds slow 

enough to avoid sonic booms (Mach 1.0 to 1.2 with the wings at 45 

degrees) and over-water flights at Mach 1.4 with the wing at 60- to 

65-degree angles.15

Finally, while the oblique-wing aircraft would take off with a straight wing 

position, the wing’s higher aspect ratio would require less takeoff energy than 

conventional jets.16

Over the next several years, Jones continued to proselytize for the obliquewing configuration while, back at Ames, Lawrence A. Graham and Frederick 

W. Boltz tested his ideas in the Center’s 11-foot Transonic Wind Tunnel (a 

variable-density, closed-return, continuous-flow tunnel), from Mach 0.60 to 

Mach 1.40, to determine the aerodynamic characteristics of a high-aspect-ratio 

oblique wing in combination with a high-fineness-ratio Sears-Haack body.17

Longitudinal and lateral-directional stability data were obtained at wing yaw 

angles from 0 degrees to 60 degrees over a test Mach number range from 0.6 
46

Thinking Obliquely

to 1.4 for angles of attack between –6 degrees and +9 degrees. The effects of 

changes in Reynolds number, dihedral, and trailing-edge angle were studied 

along with the effects of a roughness strip on the upper and lower surfaces of 

the wing. In addition, flow-visualization studies were made to determine the 

nature of the flow on the wing surfaces.

The models consisted of elliptical planform wings mounted on top of a 

Sears-Haack body. Each wing was pivoted in the horizontal plane about the 

0.4 root-chord point in order to obtain oblique angles of 0 degrees, 45 degrees, 

50 degrees, 55 degrees, and 60 degrees relative to the body’s longitudinal axis. 

All of the tested wings had elliptical planforms with a straight 25-percent 

chord line. The basic wing section was an NACA 3610-02,40 perpendicular 

to the upswept chord line. The experiments indicated that an oblique wing 

of high aspect ratio can give exceptionally high values of lift-to-drag ratio at 

all Mach numbers from 0.60 to 1.40 and that these values are significantly 

higher than those previously obtained with bilaterally symmetric swept or 

delta wings. Additional findings indicated that the upward curvature of the 

wing was effective in reducing the changes in trim with changes in yaw angle 

to very low values within the cruising range and that at higher angles of attack, 

significant trim changes occur, apparently due to stalling of the downstream 

tip.18 The finding relating to upward curvature was very important and was 

noted in Jones’s first patent. Curving the wing upward enabled achieving and 

maintaining a symmetrical lift distribution even during maneuvering flight. 

As the load factor (the gravitational, or “g” loading on the aircraft) increased, 

the upward wing’s deflection proportionately increased to furnish the correct 

effective twist necessary to maintain the symmetrical distribution. It was further elaborated and refined in subsequent wind tunnel testing at Ames and was 

incorporated on the design of the aeroelastically tailored wing on the AD-1 

wind tunnel model at NASA Ames by Ronald C. Smith.

Graham, Jones, and Boltz conducted an additional experimental investigation in the Ames 11-foot Transonic Wind Tunnel in order to determine 

the aerodynamic characteristics of three different high-aspect-ratio oblique 

wings in combination with a high-fineness-ratio Sears-Haack body.19 The 

shape parameters for the airfoil were selected on the basis of previous wind 

tunnel tests. All three wings had the same elliptical planform and baseline 

curvature, but they had different airfoil sections. The first wing had an airfoil 

section designed to have a lift coefficient of 1.0 at a Mach number of 0.7; the 

second wing was designed to have a shock-free supersonic flow over the upper 

surface; and the third wing was designed to have a lift coefficient of 1.3 at a 

Mach number of 0.6. For the investigation, longitudinal and lateral directional 

stability data were obtained at wing yaw angles of 0 degrees, 45 degrees, and 

60 degrees over a test Mach number range from 0.6 to 1.4 for angles of attack 
47

Evolving the Oblique Wing

between –7 degrees and +9 degrees. Reynolds numbers for the study were 4 

million and 6 million per foot. Flow-visualization studies were made to examine the nature of the flow on the wing surface.

The results of the tests, published in April 1973, found a notable difference in the aerodynamic characteristics of the three wing-body combinations, 

especially in their lateral directional characteristics. The aerodynamic efficiency 

of the three wing-body combinations was in most instances approximately the 

same. Two of the wings generally exhibited slightly higher maximum values. 

The other wing was slightly more efficient at Mach numbers where supercritical flow existed on the wings. Wing numbers 1 and 3 both had a maximum 

lift-to-drag ratio of 11 at Mach 1.4 and 60 degrees of sweep. Wing number 2 

had a lift-to-drag ratio of 31 at Mach 0.80 and zero wing sweep. Wing number 

2, which was designed to operate with shock-free supersonic flow over the 

upper surface, showed the expected behavior. At a 60-degree sweep, however, 

the crosswise component of Mach number 1.40 is only 0.70, which is not sufficient to achieve the design condition of the wing. Thus, further refinement 

of the airfoil selection for oblique wings would depend on the extension of 

three-dimensional wing theory beyond the linearized formulas now in use and 

probably also on more detailed wind tunnel studies. The study also identified 

another noteworthy feature: a remarkably small shift of center of pressure 

for wing-sweep variations from 0 degrees to 60 degrees. A comparison of the 

pitching moment of the straight wing at Mach 0.70 with the same wing at a 

60-degree angle reflected only moderate changes even though the fore and aft 

dimension (streamwise chord) of the wing increased nearly tenfold when the 

wing was swept. Finally, the study noted that with conventional swept-back 

wings, stalling of tips caused the airplane to pitch up, whereas with an oblique 

wing, only one tip stalls and thus the airplane may be expected to roll.20

NASA Ames conducted several programs involving the analysis, wind 

tunnel testing, radio-controlled model testing, and, finally, testing of a remotely 

piloted oblique-wing vehicle. The purpose of these programs was to determine 

the application potential of the oblique-wing concept for the actual design 

and fabrication of an oblique-wing airplane. The data obtained during these 

programs served as the basis for NASA contracts with the Boeing Airplane 

Company and the Lockheed-Georgia Company for preliminary design studies relating to supersonic transport applications. The contract studies in turn 

provided practical design data relating to structures, stability and control, and 

overall performance. The information from these studies was used in the development of a wind tunnel model at NASA Ames and, later, in the actual design 

and fabrication of a low-speed, low-cost, piloted research airplane—the AmesDryden (AD-1) Oblique Wing Research Aircraft. This airplane was to have 

the general design of one of the configurations developed during the Boeing 
48

Thinking Obliquely

Oblique-wing transonic wind tunnel model tested in the 11-foot Ames Research Center Transonic 

Wind Tunnel at Mach numbers from 0.6 to 1.4 and angles of attack between –7 and +9 degrees 

at 0-, 45-, and 60-degree sweep angles. (NASA)

studies. After construction of the AD-1, NASA Ames conducted a number 

of tests, including a wing proof-loads test to compare the static deflection of 

the wing under a distributed load with design values, a ground vibration test 

to document the principal structural modes considered necessary for the flutter clearance of the airplane, and a moment-of-inertia test to document the 

principal moments of inertia and the product inertia about the body axis.21

NASA-Contracted Industry Design and Mission Studies

In addition to the various wind tunnel tests, remotely piloted vehicle flights, 

and NASA technical reports reviewed above, NASA contracted for a number 

of industry studies, including four reviewed in this section. The three Boeing 

studies resulted in conceptual designs for potential development of a transonic 

oblique-wing transport, and the Lockheed study reviewed the various missions 

suited for oblique-wing subsonic aircraft.
49

Evolving the Oblique Wing

Boeing Studies of Transonic Aircraft Design Concepts (1972–1973)

Following Jones’s model testing at NASA Ames, the Boeing Commercial 

Airplane Company was awarded a NASA contract to undertake an initial 

design study of high-transonic-speed aircraft. This was the first of three contract studies, plus a follow-on report extension, awarded by NASA—two to 

Boeing, plus one contract extension, and one to Lockheed—for the evaluation of the oblique-wing aircraft concept and for configuration development that led to the recommendation to design and fabricate the AD-1 

Oblique Wing Research Airplane. The work on these studies was undertaken 

between June 1972 and December 1973 for Boeing and from August 1975 

until July 31, 1976, for Lockheed. The studies were intended to provide the 

technical readiness for service introduction in 1985 for an oblique-wing 

transport airplane.

The objectives of the first Boeing study were to develop five specific 

configuration types suitable for cruise in the high-transonic regime, make 

cross-comparisons of each, conduct design tradeoff sensitivity studies, and 

identify critical research areas pertinent to the development of high-transonic transport aircraft. The Boeing study team selected the following five 

design concepts for evaluation and comparison: (1) aircraft with a fixed 

swept wing, (2) aircraft with a variable-sweep wing, (3) aircraft with a delta 

wing, (4) aircraft with a twin-fuselage oblique wing, and (5) aircraft with a 

single-fuselage oblique wing.

The study, which was conducted between June 20, 1972, and May 20, 

1973, incorporated past programs and earlier studies, including Boeing’s 

work on supersonic transport development and work done under NASA 

Langley’s sponsored contracts for the “Study of the Application of Advance 

Technologies to Long-Range Transport Aircraft.” In addition, the aerodynamic development accomplished by NASA’s Ames Research Center on 

oblique-wing concepts provided essential background data for the Boeing 

study. The Boeing project study team included Robert M. Kulfan, E.C. 

Nobel, James L. Stalter, and James K. Murakami (aerodynamics and performance considerations); Mark B. Sussman (propulsion and noise characteristics); John P. McBarron (weight and balance estimates); Alan R. Mulally 

(flight stability of the unsymmetrical configurations); James W. Nisbet and 

David W. Gimmestad (structural and aeroelasticity studies); and Frank D. 

Neumann (general arrangements).

The following design objectives applied to all configurations studied:22

Cruise Mach number: Mach 1.2 (to minimize sonic boom)

Range: 3,000 nautical miles (nmi)

Aircraft noise goal: 15 effective perceived noise decibels 

 (EPNdB)
50

Thinking Obliquely

Below Federal Air Regulation 36

Passenger payload: 40,000 lbs

Cruise altitude: 39,000 feet

Approach speed: 180 knots (kt)

Technology level: 1985 (subject to pace of technology 

 development)

The study results indicated that the oblique-wing configuration, due to 

its superior low-speed aerodynamics, has a big advantage in takeoff and landing performance. Furthermore, the variable-sweep and high-aspect-ratio wing 

of the oblique-wing configuration provides a 20-percent range improvement 

for subsonic cruise over its Mach 1.2 design range. The study noted that the 

stability and control responses of oblique-wing airplanes are unique but that 

flight control systems could be developed to give swept-wing aircraft handling 

qualities that are similar to those of more conventional aircraft. All five of the 

airplane concepts evaluated used a graphite-epoxy honeycomb structure. In 

this regard, the study noted that the critical structural design conditions for the 

oblique wings were gust and maneuver loads rather than aeroelastic divergence. 

Finally, the study noted that the oblique-wing aircraft presented unique design 

and integration problems and that coordinated theoretical-experimental studies are required to determine whether the predicted performance characteristics 

are actually achievable.

Due to the promising potential of the single-body oblique-wing concept, 

the study team recommended that a program be undertaken to verify and 

further develop the concept’s potential. They recommended a three-phase 

development plan to establish the full potential of the oblique-wing concept.

Phase One called for conducting analytical studies that followed directly 

from the Boeing study. This phase would include the following tasks:

1. Determine the best structural design speed placard by studying the 

trade between airframe weight and aerodynamic performance.

2. Develop an alternate configuration that would simplify the engine 

and landing gear installation while retaining aerodynamic efficiency.

3. Develop a low-transonic-speed yawed-wing configuration to 

compare directly to the ATT [Advanced Transport Technology] 

configuration.

4. Match the engine cycle, the amount of noise suppression required, 

the flap system, and the takeoff and landing procedures to minimize 

the community noise for the synthesized basic and alternate yawedwing configurations.

5. Conduct an analysis of the stability and control characteristics of a 

flexible yawed-wing airplane to identify control system requirements.
51

Evolving the Oblique Wing

6. Conduct a theoretical and experimental wing development study to 

fully identify the maximum practical wing thickness/chord ratio and 

the minimum achievable drag due to lift.

7. Analyze operational characteristics of a yawed-wing commercial transport in airline operation and estimate total operating costs. Compare 

these costs with wide-body and ATT operating costs for similar payload/range categories.23

Phase Two called for undertaking the following tasks:

1. Verify the performance of the best Mach 1.2 configuration identified 

in Phase One through a coordinated theoretical-experimental program 

covering both the low- and high-speed flight regimes.

2. Conduct a market analysis to determine potential total airline fleet 

requirements.

3. Based on the results of the Phase One stability and control study and 

available test data, develop a moving base simulation of the airplane to 

evaluate flight control systems.

4. Perform an aeroelastic model wind tunnel test to confirm the wing 

divergence and flutter characteristics.

5. Develop detailed plans, including the design criteria for a yawed-wing 

flight test vehicle.24

For Phase Three of the program, the study team recommended the design, fabrication, and flight testing of an oblique-wing flight-test airplane.

In addition to the work outlined above for the oblique-wing configuration, 

the study team suggested that the advanced technology programs recommended 

as part of the Advanced Transport Technology (ATT) Study should be pursued 

since they apply nearly universally to this concept, especially in regard to structures, flight control, and power systems that require the projected technology 

advances to achieve the potential identified in the study.

The Boeing study recommendation for further consideration of the singlefuselage oblique-wing concept led to a 5-month contract extension that started 

on July 1, 1973, and ended on December 1, 1973. This extended contract 

study had the three following objectives: Task One was to develop an alternate 

single-fuselage, oblique-wing configuration arrangement with a simplified engine 

arrangement; Task Two was to determine the structural design speed placard 

that would allow the engine-airframe match for optimum airplane performance; 

and Task Three was to conduct an aeroelastic and control analysis of the flexible 

oblique-wing configuration. The original study evaluated four different engine 

arrangements—one for four engines, one for three engines, and two configurations involving two engines. The three-engine arrangement of the initial study 

was used as the design starting point for the extended study. Based on the findings 
52

Thinking Obliquely

from this followup study, a two-engine arrangement was selected with NASA 

Ames’s concurrence of a more detailed design and evaluation.25

These studies all greatly increased confidence in the practicality of the 

oblique-wing concept and were crucial to its gaining acceptance to the point 

that the Government and industry were willing to proceed to fabrication 

and flight testing of a specialized oblique-wing test bed. In 1974, Jones and 

Boeing’s James W. Nisbet noted that while the oblique wing can generate 

higher lift-to-drag ratios in the transonic range, prior to the above study, 

it was still not clear that the oblique-wing configuration could be successfully adapted to a real airplane. A question that needed to be answered, for 

example, was could factors such as increased structural weight and aeroelastic 

instability nullify a purely aerodynamic advantage? They also noted that 

the transonic transport study found that the assigned flight mission could 

be performed by any one of the five concepts evaluated: swept wing (fixed 

geometry), variable sweep, fixed delta wing, oblique wing with two bodies, 

and oblique wing with single body. They added, however, that the airplane 

size and weight for the five different concepts varied widely.26

Jones and Nisbet noted the following points regarding the study and 

earlier test findings:

1. Operation just below sonic ground speed eliminates the sonic 

boom associated with overland supersonic flight thus enabling 

flight operations at speeds nearly 50-percent greater than subsonic 

jets.

2. The oblique-winged aircraft introduced some new problems, 

and considerable effort was devoted to finding a good general 

arrangement with major emphasis on the engine and landing gear 

placement.

3. Structural weight of the oblique wing also received considerable 

study because of the concern over aeroelastic stability.

4. Reducing the aspect ratio to 10.2 (8:1 ellipse) and increasing the 

wing-root thickness to 12 percent improved the prior excessive 

structural weight problem.

5. Selection of the structural materials for all five evaluated wing 

configurations was based on the Advanced Transport Technology 

study results. Graphite-epoxy honeycomb was selected for the 

wing, fuselage, and vertical tail primary structure. Titanium was 

selected for the wing pivots and pivot-support structure. Using the 

graphite-epoxy material, as opposed to aluminum, resulted in a 

weight savings of 35 percent for the oblique wing.

6. The oblique-wing pivot differed significantly from a variablesweep pivot. A variable-swept-wing pivot transfers wing-bending 
53

Evolving the Oblique Wing

moments through the pivot bearings. This was avoided on the 

oblique-wing pivot by placing the bearings below the wing and 

maintaining continuous upper- and lower-wing surfaces to transfer 

the bending moments. In addition, the pivot diameter was made as 

large as possible in order to keep the bearing loads low.27

Jones and Nisbet concluded their article by noting the following:

This technically oriented [Boeing] study has yielded, we believe, a 

realistic performance comparison of the five wing-planform concepts and gives insight into areas unique to the oblique-wing configuration. The oblique-wing offers desirable performance, but 

further analysis and wind-tunnel work will be needed to develop a 

rounded picture of its potential. In particular, future work should 

include an economic evaluation of the consequences of oblique 

wing’s ability to increase today’s cruise speeds 50%.28

Just months later, in a May 1974 article published in the Canadian 

Aeronautics and Space Journal, Jones made the following additional interesting points regarding transonic transport flight:

1. An airplane designed for transcontinental flight ideally should be 

capable of efficient flight at various speeds from subsonic to supersonic, but flight at supersonic speed entails some loss of aerodynamic 

efficiency. Jones noted, however, that the loss of aerodynamic efficiency at transonic and low supersonic speeds need not be as great as 

the loss at higher supersonic speeds because it seems possible that the 

increased utilization of the aircraft and the time saving for the passengers could make up for a moderate increase of energy consumption per mile of flight.29

2. Jones added that the loss of lift-to-drag ratio begins at Mach 0.7 or 

0.8, and in order to minimize the loss at higher speeds, it is important to consider the shape of the wing. In this regard, Jones noted 

that “The surprising answer given by aerodynamic theory is that the 

narrow straight wing of high aspect ratio, ideal for low speed flight, 

already has the right shape for supersonic speeds provided it can be 

turned so as to move through the air obliquely.”30

3. The significant advantage of the oblique wing is the ease that the 

sweep angle can be varied to suit flight conditions. For example, 

during takeoff or holding, the wing should be straight and in this 

configuration the load-to-drag ratio was approximately 30 to 1; 

that could lead to a very low power requirement and thus minimize 

power consumption in an airport environment.31
54

Thinking Obliquely

Lockheed Study for a Subsonic Oblique-Wing Transport (1975–1976)

As a followup to the Boeing high-transonic-speed aircraft studies reviewed 

above, NASA awarded a contract to the Lockheed-Georgia Company for 

an analytical study involving a subsonic oblique-wing transport concept. 

Lockheed’s approach consisted of a survey of commercial and military missions, the selection of a number of mission possibilities, the application of 

the oblique-wing concept to these missions, the selection of the best missionconfiguration combination, an analysis of the selected configuration, and 

a technical assessment to define key parameters and technological requirements. The three missions selected by Lockheed were a commercial passenger 

transport, an executive transport, and a large military cargo transport. The 

background data used by Lockheed to predict technology availability were 

obtained from the two Boeing contract studies and from oblique-wing concept 

development work undertaken by NASA Ames. Lockheed’s study started on 

August 1, 1975, and was completed on July 31, 1976.

The determination of the methodology for assessing aeroelastic effects on 

wing weight and the selection of the cruise Mach number for all oblique-wing 

airplane studies were made at an August 1975 conference held at NASA Ames 

between NASA and Lockheed-Georgia representatives. The methodology for 

conducting the study consisted of a program plan that divided the study into 

the following four related elements: mission selection, configuration design and 

analysis, final analysis, and technical assessment. At a followup December 10, 

1975, meeting at NASA Ames, the group conducted a review of the progress 

and reached an agreement on the selection of the final configuration for the 

oblique-wing airplane concept. The study was undertaken at the LockheedGeorgia Company under the direction of Roy H. Lange, Transport Design 

Department manager. The study manager was Edward S. Bradley, who along 

with J. Honrath, W.W. Warnock, and P. Shumpert, was assigned responsibility for aerodynamics, structures, propulsion, and design integration. Other 

contributors were C.M. Jenness (aeroelastic analyses), K. Tomlin (stability and 

control analyses), and G. Swift (acoustic analyses).

At the beginning of the study, a literature data search was undertaken to identify possible missions applicable to the oblique-wing concept. Approximately 

1.7 million Government and private technical abstracts of potential interest 

to the study team were reviewed using the Lockheed DIALOG computerized 

data retrieval system. Additional data also was obtained from the Defense 

Documentation Center, the Advanced Systems Directorate of the National 

Aeronautics and Space Council (NASC), the Air Force Development Plans 

and Analysis Group, and the Air Force Systems Command Headquarters 

Requirements Office. Finally, commercial airplane data were obtained 

through Lockheed-Georgia Company operations research and commercial 
55

Evolving the Oblique Wing

Lockheed-Georgia conceptualization of a six-engine subsonic oblique-wing military airlifter, from 

CR 137896, 1976. (NASA)

sales organizations and from a Lockheed project titled “Future Wide-Body 

Dedicated Freighter Aircraft-Payload/Cargo Handling Design Guidelines,” 

or “Project INTACT.”

The airplane structural characteristics used by Lockheed relied on the ability to utilize the maximum level of filamentary composite materials primarily 

consisting of graphite-epoxy and Kevlar 49. Aerodynamic characteristics relied 

on supercritical airfoil technology, which, due to the oblique-wing concept, 

depended on a high degree of stability augmentation and a flight control system 

that would account for cross-coupling effects. Propulsion-system data were 
56

Thinking Obliquely

based on the Pratt & Whitney STF 433 (bypass ratio 6.5 turbofan), which 

was the engine design consistent with the airplane technology timeframe 

for noise and emissions and for thrust-weight and specific fuel consumption 

improvements. The maximum thrust level achievable for 1985 was estimated 

to be 65,000 pounds. The wing planform was trapezoidal with a taper ratio of 

0.33 and a constant thickness-chord ratio from root to tip. The wing volume 

between the spars would provide fuel tankage for mission fuel. If necessary, 

additional fuel volume would be provided in the fuselage. The wing design 

called for trailing-edge flaps. If necessary, leading-edge devices would be 

added to augment the maximum lift. The Lockheed report noted, however, 

that because of the variable geometry feature of the oblique-wing concept, 

the wing contours must remain unencumbered by any protuberance so that 

the aerodynamic efficiency of the wing is not impaired. This would require 

the leading-edge and trailing-edge lift devices to be contained within the 

wing airfoil contours except at those prescribed conditions of flight requiring 

deployment of the devices. The empennage configuration was designed to be 

a tee-tail arrangement with a horizontal stabilizer of conventional configuration articulating in the pitch axis only.

The Lockheed evaluation team concluded that the mission-configuration 

combination best suited to the oblique-wing concept was the commercial 

passenger transport due to freedom from design integration problems, freedom from balance and loadability problems, and propulsion systems that 

were within the technology limitations and close to the base engine characteristics. The passenger-transport mission used for the study involved transporting 200 passengers a distance of 3,000 miles at a Mach 0.95 cruising 

speed. The team concluded that for this mission, oblique-wing airplanes 

did not appear to present any insurmountable design integration problems. 

Lockheed’s final configuration called for a “three engine, transcontinental 

range, high speed, pressured commercial transport with provision for a flight 

crew of two, pilot and copilot, a cabin crew of 6 attendants and a maximum 

payload consisting of 200 passengers together with their baggage and 4,536 

kg (10,000 lb) of cargo.”32

The results of the study indicated that the upper-swept aspect-ratio limit 

was 6.0 in order to ensure divergence-free characteristics for the wing without 

incurring weight penalties. Additional results indicated that the oblique-wing 

concept would have 7 percent less takeoff gross weight, 5 percent less direct 

operating costs, and lower total installed thrust and block fuel, and it would 

require less takeoff distance than the equivalent conventional configuration. Furthermore, the variable-geometry feature would permit a maximum 

increase in range at off-design conditions of 10 percent and increased endurance capability up to 44 percent.
57

Evolving the Oblique Wing

The Lockheed study team noted that the airplane design for commercial 

passenger transport application is also shown to have military mission capability as either an Air Force tanker or a Navy antisubmarine warfare (ASW) 

airplane. The Air Force tanker and command post and Navy land-based ASW 

missions resulted in configurations that were about the same size as the aircraft for the commercial transport mission. The team noted further that the 

tanker airplane would benefit from the oblique-wing-concept advantages of 

greater endurance, increased ability to fly mission profiles involving loiter and 

high-speed segments, and greater capability to match the speed and altitude 

requirements of receiver aircraft during refueling. The command post application could make use of the higher endurance capability and lower gross weight, 

while the land-based ASW airplane could benefit from the high-speed cruise 

and improved on-station loiter capability. The study team, however, concluded 

that the oblique-wing application was precluded for military cargo transports 

due to propulsion-system size, wing-flap-system integration problems, center 

of gravity, and loadability limitations.

The Lockheed team made the following recommendations for followup work 

on its study: conduct further aeroelastic analyses to determine structural characteristics of wings at aspect ratios greater than 6.0, investigate active flutter 

suppression systems as a means of achieving higher aspect ratios, continue development of the commercial passenger transport to further improve the design and 

performance, investigate the short-haul potential of the oblique-wing concept, 

and further develop the executive transport configuration with emphasis on Navy 

carrier–borne applications.33

Additional Boeing Oblique-Wing Configuration 

Development (1976–1977)

The Boeing Commercial Airplane Company was awarded the third study under 

NASA Ames project-readiness contracts. This study, which involved design and 

trade studies that were incorporated into the final definition of an oblique-wing 

transport, investigated wing planform and thickness; pivot design and weight 

estimation; and climb, descent, and reserve fuel.34 A tapered, high-aspect-ratio 

wing planform was selected following aerodynamic, structural, and weight evaluations of several planforms, each of which had a graphite-epoxy primary structure. Ten different pivot-design concepts were evaluated, and a Teflon-coated 

turntable bearing was selected. Based on the above evaluations and the two previous contract studies, Boeing designers evolved the final Boeing 5-7 configuration.

The Boeing 5-7 design was an elegantly streamlined and extremely large aircraft with an empty weight of 248,070 lb, a payload of 40,000 lb, and a takeoff 

gross weight of 428,910 lb. It could carry 190 passengers (28 in first class and 

162 in tourist class) and had 1,050 cubic feet of cargo space. It cruised at Mach 
58

Thinking Obliquely

Boeing 5-7 oblique-wing SST design study, adapted from NASA CR-151928, 1977. (NASA)

1.2 with an approach speed of 140 kt, and it was powered by four afterburning 

turbofan engines fed by two large inlets, each engine producing a thrust of 35,200 

lb. The Boeing 5-7 design had an overall length of 287 feet, and an unswept 

wingspan of 202.3 feet, which when pivoted to maximum sweep, reduced to 

130.6 feet. The wing had an area of 3,040 square feet, double-slotted flaps (a 

feature of Boeing transport design), spoilers for lateral (roll) control, and variablecamber leading-edge flaps to enhance lift during takeoff and landing. To adjust 

trim at supersonic speeds, it incorporated an aft fuselage tank to and from which 

balancing fuel could be transferred. Its supersonic cruise lift-to-drag ratio was 

13.4—better than any of the alternative configurations Boeing studied and more 

than half better than the best traditional tailed bilaterally symmetric delta-wing 

configuration, the Boeing 3-2a, which had a supersonic cruise L/D of 8.8. It 

had a wheelbase of 134.5 feet between its forward and main landing gears, could 

operate from a 7,430-foot runway, and had the best community noise characteristics. Because of all its advantages, the Boeing 5-7 design formed the basis for 

the aerodynamic configuration of the AD-1 Oblique Wing Research Aircraft.35

Possible Military Applications of the Oblique-Wing Planform

In addition to the civil aviation advantages and missions applications noted in 

the above industry studies, a number of potential military mission applications 

were identified in studies conducted by the Advanced Vehicle Concepts Branch 

at NASA Ames. To assist in identifying these mission applications, NASA Ames 

engineers used a modularized computerized synthesis program (ACSYNT) 

that was developed by the Ames Research Center in order to provide rapid 
59

Evolving the Oblique Wing

conceptual design information at the early stages of vehicle definition. The 

synthesis program consisted of a control module and technology modules 

for geometric, aerodynamic, propulsive, mass, and economic information. 

Additional modules provided automatic design convergence, sensitivity, and 

optimization calculations in addition to graphical input. As of September 

1976, NASA Ames identified the following potential military mission applications of the oblique wing:

1. Land based antisubmarine warfare (ASW) aircraft, which could 

increase time-on-station (loiter time) for the same total crew time 

and provide longer ranges for the same crew time;

2. Air-mobile missile launch concept;

3. Carrier-based aircraft, which would provide improved loitering 

performance and require less storage space (the wing can be aligned 

with the fuselage while on deck);

4. Remotely piloted vehicles ranging from very small surveillance 

systems to large military combat vehicles, including an oblique 

all-wing configuration; and

5. A number of other military concepts, including advanced tactical 

fighters, cruise missiles, and an airborne battle platform consisting of 

a very large cargo-type aircraft that carries, launches, and recovers a 

large number of oblique-wing microfighters.36

Glimmerings of Something Greater: 

Planning for an Oblique-Wing Test Bed

Even before construction of the AD-1 Oblique Wing Aircraft, Jones was already 

looking beyond to a genuine transonic and supersonic demonstrator. Several 

possibilities presented themselves, one being a conversion of an expendable 

target drone, the Teledyne-Ryan BQM-34F Firebee. The Firebee was a small 

swept-wing jet-powered target drone that, during the Vietnam War, had been 

modified to fulfill a variety of intelligence-collection functions.37 Afterward, 

Firebees were employed for a variety of experimental purposes, including dropping bombs and firing air-to-surface missiles. NASA looked at the Firebee as 

the basis for several small, low-cost unpiloted test projects, one of which was 

a test bed for Jones’s oblique wing.

In November 1974, Teledyne-Ryan submitted a proposal to NASA to 

undertake an 8-week engineering and design study on modifying a BQM34F for NASA’s oblique-wing aircraft technology programs. The proposal 

noted that “Teledyne Ryan fully supports NASA’s long-range goal of using 

sub-cost, remotely piloted vehicles to minimize the time span for obtaining 

flight-proved, low-risk, technology test data applicable to various types of aircraft programs.”38 The proposal outlined four tasks:
60

Thinking Obliquely

• 

• 

• 

Task I—NASA would provide an initial basis for defining a wing size 

that can be matched to the BQM-34F system;

Tasks II and III—design tasks with support from the technical analyses specialty areas such as stress, loads, aerodynamics stability/control 

systems; and

Task IV—utilize tasks I, II, and III to ascertain schedules and ROM 

costs in support of NASA’s planning on the oblique wing program.39

Teledyne-Ryan would modify the Firebee to have an oblique wing mounted 

on the top of the fuselage that was capable of being rotated from an unswept position to a sweep angle of 60 degrees. Like the company’s other Firebees, it would be 

air launched from either a Lockheed DC-130 Hercules (the same kind of launch 

system used in Vietnam with the Firebee reconnaissance drones) or from one of 

two prototype Northrop YA-9A aircraft that NASA had acquired after it lost out 

to the rival Fairchild-Republic A-10A for an Air Force attack aircraft contract. 

Like other Firebees, the oblique-wing test bed would be parachute recovered, 

snatched in midair by a helicopter, and returned to the ground.40 After reflection, 

however, NASA chose not to proceed with the Firebee oblique-wing demonstrator, though it did use Firebees for aeroelastic and flutter control research.

Though the Firebee proposal went nowhere, another attracted far more attention, lasting well over a decade. NASA was fortunate that the 1970s coincided 

with the U.S. Navy’s gradual retirement of the Vought F-8 Crusader fighter 

from fleet service. The F-8, a highly successful fighter, had a unique high-wing 

configuration that enabled it to be easily removed and replaced. Already, NASA 

had modified one F-8 to test Richard Whitcomb’s supercritical wing (SCW), 

a complex airfoil section and wing planform that enabled a dramatic increase 

in transonic cruising speeds by raising the so-called critical Mach number and, 

hence, delaying the onset of high drag rise. Another F-8 was being flown as a 

test bed for electronic flight controls. Jones thought that the F-8 would be an 

ideal test bed for his oblique wing.

Jones arranged for construction of a 0.087-scale model of an actual F-8 

airplane fitted with an oblique wing, and he then tested it in the Ames 11-foot 

Transonic Wind Tunnel. These tests, which predated the beginnings of a 

planned AD-1 followup F-8 oblique-wing program (see chapter 5), were conducted because earlier free-flight handling tests on oblique-wing models had 

indicated a considerable reduction in roll control for wing yaw angles greater 

than 45 degrees. Also, prior tests were conducted at low speed and low Reynolds 

numbers that were not necessarily representative of actual flight characteristics. 

This new series of tests was designed to answer questions regarding the available 

aileron-control power of oblique-wing aircraft with the wing yawed at angles 

of 50 degrees to 60 degrees in the Mach number range of 0.6 to 1.4 and at a 

Reynolds number range from 14.8 to 19.7 x 106/m.
61

Evolving the Oblique Wing

Proposed oblique-wing modification to a Teledyne-Ryan BQM-34F Firebee Drone, 1974. (NASA)

The model consisted of an elliptical planform wing mounted on top of the 

fuselage of a 0.087-scale model of an operational Navy F-8 fighter. The wing 

was pivoted in the horizontal plane about the 0.4 root-chord point in order 

to obtain sweep angles of 0 degrees, 45 degrees, and 60 degrees. The wing had 

a maximum thickness-chord ratio of 12 percent and consisted of an elliptical 

planform having an elliptic axis ratio of 8:1. It had an unswept aspect ratio of 

10.2 and a straight 25-percent chord line. It employed a NACA 3612-02,40 

airfoil section at the center, perpendicular to the 25-percent chord line. The 

wing trailing-edge region was cut out for ailerons that extended from 52 percent to 89 percent of the wing semispan. The ailerons were sealed-gap plain 

flaps hinged at approximately the 75-percent chord line. The horizontal and 

vertical tail surfaces retained their original NACA 65A006 airfoil sections. The 

horizontal tail was all-movable and thus could be set at various angles relative 

to the body centerline.

As researchers Ronald C. Smith, R.T. Jones, and James L. Summers reported:

Results of aileron and horizontal tail control power tests of an F-8 

model equipped with an 8:1 elliptical-wing indicate no apparent or unpredictable control power deficiencies. Deflection of 

the ailerons induced significant pitching moments with the wing 

swept. Because this pitching moment arises from the unbalanced 
62

Thinking Obliquely

Proposed oblique-wing modification to a Vought F-8 Crusader naval fighter, 1974. (NASA)

loading about the x axis, it is expected to disappear whenever the 

spanloading is once again balanced in steady roll motion. Large 

deflections of the horizontal tail induced some side force and 

yawing moment, the origin of which is not known.41

Toward the AD-1

Over the mid-1970s, NASA Ames moved steadily toward defining and 

refining its concept for a small demonstrator oblique-wing test aircraft. In 

preparation for flights of the demonstrator, which by 1977 had been designated the AD-1, reflecting the shared partnership of the Ames and Dryden 
63

Evolving the Oblique Wing

Configuration of a 0.087-scale model of an F-8 oblique-wing aircraft tested in the 11-foot Ames 

Transonic Wind Tunnel. (NASA)

research Centers, engineers began a detailed assessment of its anticipated 

handling qualities and, particularly, its aeroelastic stability, a central concern 

when considering the flying qualities and behavior of oblique-wing vehicles. 

The AD-1’s development occurred at a time when the growing power of the 

computer revolution was first being applied to detailed analysis of aircraft 

behavior and motions. While some early work in this area had been accomplished by the NACA, the Air Force, and industry analysts as early as the 

mid-1950s (particularly in support of the early X-series research aircraft), 

the 1970s constituted a period in which computational analysis of structures 

and aeroelastic response received great attention.

From 1976 to 1977, Ames researchers undertook a pioneering 

aeroelastic-stability analysis of the AD-1, covering the behavior of the 

oblique wing alone and the oblique wing with ailerons. The wing with ailerons was included in the tests in order to study their effects on the aeroelastic 

stability of the AD-1. The tests were performed using the latest version 

of the MacNeal-Schwendler Corporation’s NASTRAN computer code 
64

Thinking Obliquely

AD-1 configuration showing range of oblique-wing sweep. (NASA)

(MSC-V43) and the Ames programs for PASS and FLUT. The application 

of the NASTRAN capability to the oblique-wing configuration served to 

substantiate the results obtained from PASS/FLUT and to evaluate two different flutter analysis methods available in the NASTRAN aeroelastic package (KE-method and PK-method). NASTRAN is a large, general purpose, 

finite-element computer program for structural analysis. PASS is a structural 

analysis program and FLUT is a flutter analysis program.42 The tests run 

on these computer codes helped to validate the oblique wing’s potential for 

increased aerodynamic efficiency over conventional swept-wing aircraft due 

to reduced wave drag at transonic and low supersonic speeds. In addition, 

the tests conducted at NASA Ames, which were also supported by NASA 

contract studies, demonstrated the mission flexibility of the oblique wing 

for both civilian and military applications. Finally, the report noted that, 

if funding became available, a Lockheed F-104 Starfighter aircraft might 

be fitted with an oblique wing to validate the concept at transonic speeds, 

though, in fact, researchers were far more interested in using the more easily 
65

Evolving the Oblique Wing

converted Vought F-8 Crusader than the more challenging (if potentially 

higher performance) Lockheed design.43

The OWRPRA Flight-Test Program (1976)

Robert Jones had built a small 51⁄2-foot-span radio-controlled oblique-wing 

model to assess the oblique wing’s basic flying qualities, but this small model 

did not, on its own, suffice to give confidence for progressing with a much 

larger and more complex vehicle. Instead, what was needed was a larger and 

much more comprehensively instrumented test bed, and thus, in order to 

investigate the feasibility of flying an oblique-wing aircraft, NASA Ames and 

NASA Dryden sponsored construction and flight testing of a small variablesweep propeller-driven Oblique Wing Remotely Piloted Research Aircraft 

(OWRPRA). NASA issued a $200,000 development contract to Developmental 

Sciences, Inc., of City of Industry, CA, and its development took 3 years, from 

1972 to the end of 1975. Constructed primarily by hand-laid-up fiberglass 

and epoxy resin (furnished by the Fiber Resin Corporation of Los Angeles) 

with steel, aluminum, and magnesium structural components, the resulting 

vehicle had a 22-foot, 4-inch wing capable of being skewed up to 45 degrees 

with the left wing foremost, and it was flown in both a short-tail and long-tail 

configuration. The aircraft was powered by a 90-horsepower four-cylinder aircooled two-stroke McCullough 4318B reciprocating engine driving a ducted 

midfuselage three-bladed, 4-foot-diameter propeller with a cruise speed of 

approximately 3,600 revolutions per minute (rpm). A fixed tricycle landing 

gear enabled horizontal takeoffs and landings on a dry lakebed.44

The remotely piloted model was equipped with an all-movable tail and 

conventional rudder and aileron surfaces. Artificial stability was furnished 

via a two-axis, gyro-stabilized autopilot. Telemetry links were used to send 

pilot control inputs to the vehicle and to return aircraft response data to the 

ground. Additionally, a television camera was mounted in the vehicle’s nose. 

The augmentation system consisted of pitch-and-roll attitude feedback. All of 

the standard stability and control variables were instrumented, including static 

and total pressures, control-surface positions, vehicle attitudes, angular rates, 

linear accelerations, and angles of attack and sideslip. The moments of inertia 

for the long-tail configuration were estimated from swing tests of the assembled 

vehicle after the last flight. Those for the short-tail configuration were estimated 

by subtracting the predicted differences from the long-tail values. The angleof-attack and sideslip measurements were taken from standard boom-mounted 

metal pitch and yaw vanes. The control surface positions were measured by 

control position transducers on the control surface. The data was acquired 

at 200 samples per second using an 8-bit pulse-code modulator system and 

telemetered to the ground for recording.
66

Thinking Obliquely

Basic configuration of the NASA FRC Developmental Sciences Oblique Wing Remotely Piloted 

Research Aircraft (OWRPRA) test bed, from NASA TP 1336, 1978. (NASA)

Early testing at Bicycle Lake, in the Mohave Desert, CA, was not without 

problems; a loss of signal during a high-speed taxi run resulted in the craft 

flipping over, and it was so badly damaged that it required significant rebuilding. Flight testing commenced on August 6, 1976, with an 0615 takeoff from 

Dryden. The flight constituted the first time that Dryden had flown a remotely 

piloted vehicle using a pilot located in a remote van. The project manager 

was Rodney O. Bailey and the Ames test pilot was James “Jim” Martin, who 

was controlling the OWRPRA. Martin had earlier completed over 30 remote 

takeoffs and landings with a NASA Piper Twin Comanche (with safety pilot 

Einar Enevoldson on board) to get a feel for remote vehicle operation. The 
67

Evolving the Oblique Wing

The OWRPRA test bed in its original short-tail configuration, on the ramp at NASA DFRF, August 

2, 1976. (NASA)

practice proved most fortunate as Martin literally had his hands full with the 

little OWRPRA once it became airborne. It was so unstable that the horizon 

continuously oscillated up and down in the television monitors, and afterward, 

Martin described his piloting experience as “intense;”45 accordingly, he prudently limited the wing sweep to just 15 degrees, returning the little research 

vehicle safety to the ground after 24 minutes. Before the vehicle’s next flight, 

technicians increased the size of its tail surfaces and moved them aft, thus creating both a short-tail and long-tail variant. The OWRPRA flew only two more 

times, on September 16 and October 20, thus limiting its total flight program 

to three flights of approximately 1 hour each. The remote pilot controller performed 87 maneuvers for stability and control data acquisition during the three 

flights. Elevator doublets were used for longitudinal maneuvers. Each lateral 

directional maneuver included a rudder doublet and an aileron doublet. 

Fortunately, following its early flight-test difficulties, the OWRPRA’s last two 

flights permitted the acquisition of data validating the performance of the 

oblique wing at 30-degree and 45-degree sweep angles, greatly encouraging 

developers as they moved toward the larger, faster AD-1.46

Predictions of the static derivatives were based on data obtained from 

full-scale tests conducted in the Ames 40-by-80-foot wind tunnel. The actual 
68

Thinking Obliquely

The OWRPRA (in long-tail configuration) in flight with its oblique wing in skewed position, 1976. 

Note its special bicentennial commemorative markings scheme. (NASA)

flight vehicle in both the short-tail and long-tail configurations was tunnel 

tested, permitting subsequent comparison of tunnel-test results with flighttest results. However, postflight analysis indicated a large scattering of the 

data, reflecting limitations in the Ames tunnel’s data acquisition system, with 

predictions in some cases varying “by a factor of 2 or 3 for the same flight 

condition.”47 Additionally, design of the tail boom to ease tunnel testing of 

the long-tail variant made it so flexible that “long[-]tail [tunnel] data were 

judged unusable.”48 (By contrast, the actual flight vehicle had a much more 

rigid boom). The short-tail variant had less flexibility, but analysts conceded 

“it still opens the validity of the predictions to question.”49

Fortunately, testers acquired reliable data during the actual flight-test 

program. The flight tests and resulting data analysis incorporated an imaginative technique that estimated aircraft aerodynamic derivatives by separating 

the analysis of longitudinal and lateral directional motion even in the presence of the moderate cross-coupling characteristics of oblique-wing aircraft. 

Engineers digitally filtered the data acquired during the tests and then used it 

to estimate the aircraft’s stability and control derivatives. This technique was 

determined to have several advantages over the usual five-degrees-of-freedom 
69

Evolving the Oblique Wing

approach for some situations. The separation technique was applied to obtain 

a complete set of stability and control derivative estimates from flight data 

for a small remotely piloted oblique-wing aircraft. This complete set of flightdetermined estimates was presented and compared to predictions. The maximum likelihood estimation method was used to analyze the oblique-wing 

data. The results of the above analysis demonstrated that this relatively simple 

approach was adequate for obtaining usable estimates of the aerodynamic 

derivatives of oblique-wing aircraft. This application represented the first 

time that aerodynamic derivatives had been estimated from flight data for 

an oblique-wing aircraft.50
70

Thinking Obliquely

Endnotes

1. G.H. Lee, “Slewed Wings,” Flight International (June 15, 1972): 870.

2. G.H. Lee, “Slewed-Wing Supersonics,” The Aeroplane and 

Astronautics (March 3, 1961): 240–241.

3. Ibid.

4. Ibid.

5. Lee, “Slewed Wings,” 870.

6. Ibid.

7. See, for example, R.T. Jones, “Three-Dimensional Wings of 

Minimum Pressure Drag,” in Theory of Optimum Aerodynamic 

Shapes, ed. Angelo Miele (New York: Academic Press, 1965), 

125–134; R.T. Jones, “Reduction of Wave Drag by Antisymmetric 

Arrangement of Wings and Bodies,” AIAA Journal 10, no. 2 

(February 1972): 171–176.

8. R.T. Jones, “Reduction of Wave Drag,” 171–176.

9. Ibid., 171.

10. Ibid.

11. Ibid.

12. Ibid.

13. Ibid., 175.

14. Robert T. Jones, “New Design Goals and a New Shape for the SST,” 

Astronautics and Aeronautics 10, no. 12 (December 1972): 69.

15. Ibid., 68–69.

16. Ibid., 69.

17. Lawrence A. Graham, Robert T. Jones, and Frederick W. Boltz, 

“An Experimental Investigation of an Oblique-Wing and Body 

Combination at Mach Numbers Between 0.60 and 1.40,” NASA 

Technical Memorandum (TM) X-62207 (December 1972).

18. Ibid., 1–6.

19. Graham at al., “An Experimental Investigation.”

20. Ibid., 1–5.

21. W.H. Andrews et al., “AD-1 Oblique Wing Aircraft Program,” 

a paper presented at the Aerospace Congress & Exposition, Los 

Angeles, CA, October 13–16, 1980, 1–2.

22. Robert M. Kulfan et al., Boeing Commercial Airplane Company, 

“High Transonic Speed Transport Aircraft Study: Final Report,” 

NASA Contractor Report (CR) 114658, (1973).

23. Ibid.

24. Ibid.
71

Evolving the Oblique Wing

25. Robert M. Kulfan, Boeing Commercial Airplane Company, “Study 

of the Single-Body Yawed-Wing Aircraft Concept,” NASA CR 

137483 (May 1974).

26. Robert T. Jones and James W. Nisbet, “Transonic Transport 

Wings—Oblique or Sweep?” Astronautics and Aeronautics 12, no. 1 

(January 1974): 1.

27. Jones and Nisbet, “Transonic Transport Wings,” 41–43.

28. Ibid., 47.

29. R.T. Jones, “Aircraft Design for Flight Below the Sonic Boom Speed 

Limit,” Canadian Aeronautics and Space Journal 20, no. 5 (May 1974).

30. Ibid., 226.

31. Ibid.

32. E.S. Bradley et al., The Lockheed-Georgia Company, “An Analytical 

Study for Subsonic Oblique Wing Transport Concept, Final 

Report,” NASA CR 137896 (1976), 41.

33. Ibid.

34. Preliminary Design Department, Boeing Commercial Airplane 

Company, “Oblique Wing Transonic Transport Configuration 

Development, Final Report,” NASA CR 151928 (1977), 1–3.

35. Ibid., Table 1, 18–19, and Figure 66.

36. Walter P. Nelms, Jr., “Application of Oblique-Wing Technology—

An Overview,” AIAA 76-943, a paper presented at the AIAA Aircraft 

Systems and Technology Meeting held in Dallas, TX (September 

27–29, 1976), 5–7.

37. For the Firebee story, see William Wagner and William P. Sloan, 

Fireflies and Other UAVs (Arlington, TX: Aerofax, 1992).

38. H.A. James, and C. B. Spangler (Teledyne-Ryan Aeronautical), 

“Proposal for Oblique Wing Feasibility Study for the BQM-34F 

Firebee II,” vol. 1, Technical Proposal, Report No. TRA 29308-26A 

(November 1, 1974), 1-1, copy in Dryden Flight Research Center 

(DFRC) Archives.

39. Ibid.

40. Ibid., 2-19 and 5-1.

41. Ronald C. Smith, Robert T. Jones, and James L. Summers, 

“Transonic Lateral and Longitudinal Control Characteristics of an 

F-8 Airplane Model Equipped with an Oblique Wing,” NASA TM 

X-73103 (March 1976).

42. Michael J. Rutkowski, “Aeroelastic Stability Analysis of the AD-1 

Manned Oblique-Wing Aircraft,” NASA TM 78439 (October 

1977), 1–12.

43. Ibid.
72

Thinking Obliquely

44. Technical details of this aircraft can be found in Rodney O. Bailey 

and Peter A. Putnam, “Oblique Wing Remotely Piloted Research 

Aircraft,” a paper presented at a meeting of the National Association 

for Remotely Piloted Vehicles, Dayton, OH, June 3–4, 1975.

45. No author. “Ames’ Part in Successful Oblique Test,” The Astrogram

(NASA Ames Research Center) 18, no. 26 (September 9, 1976): 2.

46. See Peter W. Merlin, “The Evolution of Remotely Piloted Vehicles,” in 

NASA’s Contributions to Aeronautics 2, ed. Richard P. Hallion, 496–498.

47. Rutkowski, “Aeroelastic Stability Analysis of the AD-1 Manned 

Oblique-Wing Aircraft,” 8.

48. Ibid.

49. Ibid.

50. Richard E. Maine, “Aerodynamic Derivatives for an Oblique 

Wing Aircraft Estimated From Flight Data by Using a Maximum 

Likelihood Technique,” NASA Technical Paper (TP) 1336 (October 

1978), 1–17.

74

Cockpit and instrument panel of the AD-1 Oblique Wing Research Aircraft. The wing sweep 

"skew" gauge is center-left on the lower row of panel instruments; the sideslip gauge is centerright on the lower row; the angle-of-attack gauge is center-right on the top row. The dual-engine 

throttles are on the left side, and the dual-engine instruments are on the lower right side. Note 

as well the centerline control stick capped by a stabilizer-trim switch. (NASA)
75

CHAPTER 3

Design and Fabrication of 

the AD-1 Research Aircraft

In his NASA Technical Memorandum titled “Role of Research Aircraft in 

Technology Development,” Kenneth J. Szalai, who was chief of the Dryden 

Research Engineering Division and later became the director of NASA Dryden, 

noted the importance of research aircraft to advances in aviation and the resulting technology spinoff into other fields of scientific development. He pointed 

out that

[t]he history of research and experimental aircraft in the United 

States is a rich one.... These aircraft have ranged from exotic forms 

designed to expand the overall knowledge of aerodynamic configurations, to complex systems aircraft designed to explore improved 

efficiency or improved mission effectiveness. Some of these aircraft were forerunners of military aircraft; others, such as the Lunar 

Landing Research vehicle which prepared astronauts for lunar landings, were important trainers.... Flight research has been a vital and 

continuous part of this nation’s aeronautical research program since 

the inception of the National Advisory Committee on Aeronautics 

(NACA) in 1915. Flight research with both highly modified service 

aircraft and new experimental aircraft has contributed to many of 

the aeronautical advances over the past several decades, drawing on 

a strong partnership between NACA/NASA, the Department of 

Defense (DOD), and industry.1

Small Is Beautiful: Undertaking the AD-1’s Development

In the early 1970s, the British economist E.F. Schumacher (drawing upon the 

thinking of his mentor, the Austrian Leopold Kohr) popularized the notion 

that small is beautiful in a book of essays of the same name. Schumacher’s 

emphasis upon appropriate technology and simplicity as opposed to complexity in approach could have served as a pattern for the development of the AD-1 
76

Thinking Obliquely

Oblique Wing Research Aircraft, which stood in marked contrast to the large 

and complex underpinnings of most experimental aircraft programs. In fact, the 

AD-1’s development fit very well into the traditional model of flight research 

as practiced by Walter Williams, Paul Bikle, and their successors at the Dryden 

Flight Research Center, previously known as the NASA Flight Research Center 

and the NACA High-Speed Flight Station before that. For over three decades, 

the Center and its personnel, led by Walter Williams, Paul Bikle, Lee Scherer, 

Dave Scott, and Isaac T. “Ike” Gillam IV, had mastered the art of using models, 

small specialized test rigs, and aircraft to evaluate larger and, in some cases, 

highly significant concepts. This included testing reaction controls, developing experimental lifting bodies, and fabricating a jet-and-rocket-powered lunar 

landing trainer that gave astronauts the requisite skills to land on the Moon. The 

AD-1 development effort thus constituted a natural extension of the Center’s 

organizational culture and operational philosophy.2

Referring to the Ames-Dryden AD-1 Oblique Wing Research Aircraft, 

Szalai noted: “In the case of oblique-wing technology, wind tunnel tests had 

shown potential performance benefits transonically and supersonically when 

an oblique-wing aircraft was compared with an equivalent variable-sweep

aircraft.”3

 Regarding issues that needed to be resolved by flight testing,

Szalai added,

[a]side from uncertainties regarding the aerodynamic performance, 

there were those related to the low-speed handing qualities of an 

oblique-wing aircraft, including the ability of a pilot to land an 

aircraft with a large wing-skew angle; the stability and control of 

an oblique-wing aircraft, especially with cross coupling; and finally, 

dynamics and trim characteristic effects on overall flying qualities.4

Szalai noted that NASA’s approach to investigating these issues was to build 

a small, low-cost manned research vehicle that demonstrated that the return on 

investment could be very high for small and inexpensive flight research vehicles. 

To accomplish this, NASA contracted with leading designers and builders of 

small aircraft to build a foam-and-fiberglass piloted aircraft powered by two 

fan turbine engines. To hold down costs, light airplane avionics and simple 

mechanical controls were used; instrumentation consisted of a multichannel 

pulse-code modulator system with structural and dynamic sensor data sent 

to the NASA ground station. Szalai reviewed the flight research accomplishments, which included obtaining significant high-quality stability, control, and 

flying-qualities data that helped validate predictions of the characteristics of 

oblique-wing aircraft; estimating the unique cross-coupling terms of this type of 

vehicle from flight data; establishing side force and trim requirements; obtaining 
77

Design and Fabrication of the AD-1 Research Aircraft

handling-quality data; and developing pilot techniques and trim sequences for 

various wing-skew angles. In regard to technology spinoff, Szalai emphasized 

the refinement of parameter identification techniques for asymmetrical vehicles 

that would be mandatory for any future asymmetrical vehicle.5

While NASA engineers realized that the aerodynamics performance benefits 

of an oblique-wing configuration occur at transonic speeds, they determined 

that many of the characteristics associated with asymmetry are not strongly 

related to compressibility and, therefore, to a limited extent, could be evaluated 

at low speeds. Accordingly, the purpose of the AD-1 program was to investigate 

the low-speed characteristics of an oblique-wing configuration. This enabled the 

AD-1 to be designed and fabricated as a low-speed, low-cost airplane. Low speed 

allowed the use of a low-technology structure, fixed landing gear, and a mechanical control system that in turn permitted the fabrication of a low-cost aircraft.

The specific technical objectives of the AD-1 program were the assessment 

of the unique handling and flying qualities of an unaugmented, low-speed, 

oblique-wing vehicle; general appraisal of the nature and complexity of a flight 

control system on an oblique-wing configuration; verification of the static aeroelastic design criteria for the wing; and comparison of the flight-determined 

aerodynamic data with predicted values.6

 But who could build such a craft, 

and do so quickly, cheaply, and to the highest standards of creativity and 

technical acumen?

Enter Burt Rutan and the Rutan Aircraft Factory

The answer was Elbert Leander “Burt” Rutan, a remarkably gifted aerospace 

engineer who was born in Oregon, raised in California, and educated at 

California Polytechnic State University at San Luis Obispo. Burt Rutan had 

served as a flight-test engineer at the Air Force Flight Test Center, had been 

director of development for Jim Bede’s aircraft company (maker of the BD-5, 

a tiny speedster that attracted a great deal of attention in the early 1970s), and 

then established his own aircraft company in Mojave, CA, where he produced a 

string of imaginative aircraft, most having a canard (tail first) configuration. He 

was unconventional, innovative, open to new ideas, and unbureaucratic—and 

thus perfect for the job.

Rutan biographer Vera Foster Rollo noted the following:

One of Burt’s important strengths is his “can do” attitude. It didn’t 

matter to him, out there in the Mojave Desert, with no money 

to speak of, a relatively unknown designer at the time, that he 

planned to do what aircraft manufacturers spend millions of dollars, with hundreds of engineers and craftsmen, do—design, build 
78

Thinking Obliquely

and land test a new aircraft design with materials not widely used 

at all in aviation.7

While NASA was looking to build an inexpensive basic airplane to test 

Robert Jones’s oblique-wing theory, there apparently was no official contract with Rutan that could be considered a response to a formal Request for 

Proposals (RFP) to undertake a feasibility study for the preliminary design of 

the AD-1. Instead, in 1975, with the AD-1 program gestating at both Ames and 

Dryden (then called the Flight Research Center), two college friends, Charles 

Van Norman and Richard Fisher, who both had graduated from California 

Polytechnic State University 1 year ahead of Rutan, approached Rutan with 

the feasibility study and design idea. According to Rutan, Van Norman, who 

worked for the Air Force, and Fisher, who worked at NASA Dryden, informed 

him that NASA was not in a position to put out a formal proposal, but asked 

him to submit an unsolicited proposal to undertake a feasibility study. They 

thought Rutan would be the ideal choice due to his having designed and 

built the VariEze airplane, which used composite materials and was built in 3 

months. As a result of this informal process, NASA selected Burt Rutan and 

his Rutan Aircraft Factory to conduct a feasibility study for the fabrication of 

a small, low-cost, subsonic, yawed-wing experimental aircraft.8

The results of the feasibility study were presented in a December 1975 

report by Burt Rutan and George Mead. The study, which Rutan completed in 

the remarkable time of just 40 work hours, examined the following concepts:

1. Evaluation of the feasibility of building a small piloted research aircraft using the transonic airliner [Boeing design] geometric envelope;

2. Preliminary design of the general structural arrangement and general 

air-load estimation;

3. Preliminary weight and balance summary;

4. Formulation of the general arrangement of the flight control, landing gear, propulsion, wing yaw, and egress systems;

5. Preliminary estimation of flight performance; and

6. Preliminary estimation of the schedule and cost for detail design and 

construction of the prototype research aircraft.9

The study proposed that the basic configuration should be that of a transonic, single-body, yawed-wing transport of an already defined configuration 

(this was, of course, the Boeing 5-7 configuration discussed in chapter 2). The 

aircraft would be a 14-percent-scale size of the above configuration with the 

forward fuselage upper mold line raised to provide adequate forward visibility 

and adequate room for the pilot. Also, changes in the geometric shape would 

be required in order to provide adequate static and dynamic stability since 

the proposed full-size airliner design used a fly-by-wire control system that 
79

Design and Fabrication of the AD-1 Research Aircraft

could compensate for an otherwise unstable configuration. In the case of the 

proposed AD-1, sufficient static and dynamic stability would be provided by 

an increase in tail volume and a forward shift of the wing, achieved by moving 

the wing yaw pivot forward from its 50-percent chord location.

The oblique-wing configuration would be a composite sandwich glass-onfoam-on-glass semi-elliptical wing with the following dimensions: a mean chord 

of 34 inches, a span of 35.3 feet, an area of 98.9 square feet, and an aspect ratio 

of 12.6 (in straight, not oblique, configuration). The control configuration would 

consist of mechanical ailerons with no high-lift devices. The wing-pivot mechanism would be an electric screw-jack with manual backup permitting a 0-degree 

(wing straight) to 60-degree (oblique swept) capability. The horizontal stabilizer 

would have a mean chord of 41 inches, a span of 7.7 feet, and an area of 26.2 

square feet. The control mechanism would consist of a mechanical elevator and 

electric screw-jack stabilizer trim. The vertical stabilizer would have a mean chord 

of 45 inches, a span of 45 inches, and an area of 14.1 square feet. The control 

mechanism would be a mechanical bungee-rudder trim. The fuselage would 

have a length of 426 inches and a maximum diameter of 31 inches. The landing 

gear would have retraction by electric actuators, differential brake steering, and 

composite spring energy absorbers. Propulsion would consist of two Microturbo 

TRS-18 turbojet engines, each producing 220 lbs of thrust. The AD-1 would 

have an empty weight (including data systems) of 1,015 pounds and an enginestart weight (pilot and 11⁄2 hours of fuel) of 1,565 pounds.

Overall performance was estimated as:

Stall speed at take off: 60 knots

Stall speed at landing: 54 knots

Takeoff distance: 1,400 feet (at 3,000 feet altitude)

Rate of climb S/L [sea level]: 1,400 feet per minute

Single engine rate of climb: 400 feet per minute

 (at 5,000 feet altitude)

Maximum level flight speed: 260 knots (at 15,000 feet altitude)10

The basic structure would be a composite sandwich airframe utilizing the 

highly contour-adaptable fiberglass-on-foam-on-fiberglass techniques developed by the Rutan Aircraft Factory. The basic aircraft structure consists of two 

skins of unidirectional fiberglass separated by a rigid foam core. Rutan noted 

that the “structural viability of this technique has been proven over a series of 

three general aviation aircraft designed and fabricated by RAF [Rutan Aircraft 

Factory].” He added that “the workability of the basic structural materials enables 

the fabrication of a one-off prototype employing extensive compound curvatures 

without the expensive molds and form tooling required for other structures.”11
80

Thinking Obliquely

This technique enabled Rutan to develop the prototype aircraft with an 

oblique wing and an area-ruled (i.e., complex curve) fuselage at a low cost. He 

described the process as follows:

The wing, horizontal, and vertical tail are formed from several 

straight tapered foam cores, jig assembled, and locally contoured 

to shape using templates. A tapered glass/graphite box spar is then 

layered up into the inboard 2/3 of the span (the outer 1/3 being full 

monocoque) followed by a skin which consists of two spanwise unidirectional glass layers and two layers of bidirectional glass oriented 

at 45 degrees to provide torsional stiffness.... Structural efficiency 

is excellent since the tapered spar caps are optimally separated at 

the contoured wing skin surface and are supported by foam against 

local buckling. The shear web fibers are oriented at 45 degrees for 

primary shear and the shear panel is foam supported on both sides. 

A very conservative design approach is used: instead of reaping the 

benefits of the improved structural efficiency as a weight savings, the 

wing is built at about the same weight as an all-aluminum wing, but 

with extremely large structural safety margins. Surface durability, 

stiffness and fatigue life are thus greatly increased. Development 

costs can be greatly reduced since with a design safety factor of 

three, and a conservative design load (6-g limit)[,] the requirement 

for proof load testing is obviated.12

As for the rest of the aircraft, Rutan noted that the fuselage would be built as 

a square box of rigid foam slabs, contoured as required inside to clear equipment. 

The inside of the box would be glassed before assembly. The outside would then 

be carved to the required contour using templates. The outside skin would be layered up using fiber orientation to provide the desired stiffness and strength. Local 

stiffness and strength for attachments would be provided by high-density foam 

and multiple-layer glass layups. Rutan noted further that the resultant structure 

would be safer than an all-metal structure since multiple redundancy would be 

provided and cracks could not propagate across layers within the composite. Fuel 

tanks built into the structure using the glass-on-foam-on-glass sandwich would 

not flex and fatigue, and thus fuel-tank-leakage problems would be eliminated. 

The wing would be mounted by attaching the main spar box, which would be 

stiffened locally by aluminum extrusions in the lower corners, to a flange on an 

8-inch length of 7-inch-diameter aluminum tube. The bearing surface would take 

all asymmetrical bending, torsion, and lift loads from the wing. Wing rotation 

about the pivot point would be controlled by an electrical screw-jack at the bottom 

of the large tube. The screw-jack could also be operated manually by the pilot.
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Design and Fabrication of the AD-1 Research Aircraft

In regard to pilot safety, Rutan noted that the design criteria would result 

in a docile flying aircraft at zero wing-angle of incidence and that the low wing 

loading and relatively low indicated cruise speed would place the aircraft more 

in the category of a medium-performance general aviation aircraft than that of a 

contemporary jet. With the engines out, the rate of sink would be approximately 

500 feet per minute at 75 knots, allowing a near sailplane-like lift-to-drag sinkrate condition for glide and landing without power.13

The table on the following page shows the preliminary time and charges 

estimate for development of the AD-1 (RAF 35) aircraft. The feasibility study 

noted that a more refined cost estimate should be made during the detail-design 

phase. The final contract cost totaled $261,350 and consisted of a preliminary 

design study ($560); an initial airplane design ($9,970); a design modification 

($4,590); an aircraft fabrication contract ($218,000); a fabrication contract 

modification ($21,930); and the delivery ($6,300). Although higher than the 

initial feasibility study estimate, the final total was still remarkably low for a 

jet research airplane and fulfilled the NASA program objective for a low-cost, 

low-speed, oblique-wing flight demonstrator.

The final cost of the actual design and fabrication, Rutan recalls, was considered so low that when final approval was given, a number of NASA personnel 

thought they were approving the construction of a remotely piloted vehicle, 

not a piloted aircraft.14

The estimated time to develop the prototype aircraft was 9 months based 

on the following schedule:

7. Verification of adequacy of flying qualities of the selected configuration, including NASA-conducted wind tunnel model test program 

to verify adequate static margins, controllability, and predicted 

dynamic stability of the modified Boeing 5-2-4 configuration at the 

Mach and Reynolds numbers expected. Time Duration: Unknown 

at time of estimate.

8. Detail loads prediction, structural design, and system design. Time 

Duration: 850 engineering hours over an 11-week period.

9. Prototype construction. Time Duration: 1,800 work hours over a 

time period of 24 weeks.

10. Final surface contouring and finishing. Time Duration: 90 work 

hours over a 2-week period.

11. Engine installation, wiring and checkout. Time Duration: 160 work 

hours over a 2-week period.15

Burt Rutan followed up his first phase feasibility study with a second phase 

consisting of more detailed design plans and drawings that resulted in NASA 

issuing a formal Request for Proposals to fabricate the AD-1. NASA had expected 

the Rutan Aircraft Factory to bid on the project, but according to Rutan, his 
82

Thinking Obliquely

Estimated Cost and Work Hours for AD-1 Fabrication by Task

Task Cost Hours

Loads Prediction, Structural Design, and System Design $11,900 850

Components1 $42,480 --

Two TRS 18 engines: $38,000 -- --

Wheels, tires, brakes, axles: $780 -- --

Control system hardware: $335 -- --

Landing gear struts, mechanism, and actuators: $525 -- --

Fuel system, gauging, fittings, low-level warning: $310 -- --

Wing yaw and pitch trim actuators: $200 -- --

Electrical system components: $250 -- --

Canopy jettison actuators: $150 -- --

VFR instrumentation transponder and com radio: $1,930 -- --

Structural Materials $3,670 --

Glass and graphite: $680 -- --

Epoxy: $280 -- --

Rigid foam: $380 -- --

Canopy, vendor-formed to RAF mold $280 -- --

Wing pivot machined parts: $360 -- --

Control system machined parts: $150 -- --

Engine mounts and alum nacelles: $230 -- --

Misc. hardware: $400 -- --

Misc. materials: $550 -- --

Finishing/contouring materials: $360 -- --

Construction Labor—Basic Structure and Systems $25,200 1,800

Engines Installation, Wiring and Checkout $2,240 160

Final Surface Contouring and Finishing $1,260 90

Flight Test Data Instrumentation and Check2 -- --

TOTALS $86,750 2,900

Burt Rutan, “Feasibility of a Small, Low Cost, Subsonic, Yawed-Wing Experimental Aircraft,” 20-2.

1. Acquired via “off-the-shelf” procurement.

2. To be accomplished by NASA, not the contractor. 
83

Design and Fabrication of the AD-1 Research Aircraft

company only had two or three employees and could not meet the RFP technical 

requirement that limited the percentage of new hires that could be made simply 

to fulfill a NASA contract. To get around this provision, Rutan asked Herb 

Iverson, who was his partner in the founding of aeronautics company Scaled 

Composites and who was president of the Ames Industrial Corporation, to 

respond to the RFP. Rutan thought Ames Industrial could fulfill the contract 

with Rutan’s assistance, especially on the use of composite materials since Ames 

Industrial’s experience was in using aluminum, not composite materials. NASA 

awarded the contract to the Ames Industrial Corporation of Bohemia, NY. The 

AD-1, which Rutan designated as RAF 35, was assigned the NASA registration 

N805NA (800-numbers being reserved by the agency for flight-test aircraft 

flown at Dryden) and was built on budget and delivered to NASA on March 

11, 1979.16 The actual program schedule called for the completion of the initial 

design study on February 2, 1976; completion of the actual airplane design 

from May 28, 1976, until September 8, 1976; and fabrication and manufacture 

of the airplane from November 18, 1977, to March 11, 1979.

Jones Secures Patent Recognition for His Oblique Wing

On July 27, 1976, as conceptual work on what would become the AD-1 

moved ahead, the U.S. Patent Office granted a patent assigned to the U.S. 

Government (as represented by NASA) recognizing Robert T. Jones as the 

inventor of

[a]n aircraft including a single fuselage having a main wing and 

a horizontal stabilizer airfoil pivotally attached at their centers to 

the fuselage. The pivotal attachments allow the airfoils to be yawed 

relative to the fuselage for high speed flight, and to be positioned 

at right angles with respect to the fuselage during takeoff, landing, 

and low speed flight. The main wing and the horizontal stabilizer are upwardly curved from their center pivotal connections 

towards their ends to form curvilinear dihedrals.17

Jones had originally filed for the patent on August 12, 1974, and his application claimed the following:

The instant invention relates to an aircraft having a single continuous wing mounted above a single fuselage and pivoted at 

the wing center so that it can be rotated from the straight wing 

perpendicular to the fuselage at take-off to various oblique angles 

at higher speeds. Half the wing is thus pointed more towards the 

direction of flight at high speeds and the other half trails. The wing 
84

Thinking Obliquely

Jones’s 1974 oblique-wing jet transport, showing the wing at 0-degree sweep. Note the 

“skewed” engine nacelles flanking the tail cone and the subtle curvilinear dihedral of the main 

wing and horizontal tail. From US Patent 3,971,535 (1976). (NASA)

Jones’s 1974 plot of predicted aerodynamic benefits of the single-pivot oblique wing, measuring 

drag rise vs. an oblique wing. From US Patent 3,737,121 (1973). (NASA)
85

Design and Fabrication of the AD-1 Research Aircraft

has a small amount of upward curvature forming a curvilinear 

dihedral which—when the wing is yawed—is equivalent to twist 

and affords an increased angle of attack for the forward portion 

and a decreased angle for the rearward portion.18

Varying the sweep by turning the wing as a whole has several 

practical advantages over the usual “swing wing” design. In the 

former case, the wing structure is continuous across the pivot and 

the primary load on the pivot is tension. With separate wing panels 

pivoted at the root, however, the loads developed on the pivots 

are much greater. Also, sweeping the wing panels back for high 

speed flight displaces the center of lift rearward, compounding the 

normal rearward center of pressure shift at these speeds. Turning 

the wing as a whole, however, does not displace the centroid of 

area relative to the center of gravity. Even with fixed geometry, the 

structure of the bilaterally symmetric wing is less favorable because 

of the unbalanced torsion at the wing root. The unbalanced torsion 

may be equated approximately to increased beam length for the 

swept wing. Also, conforming to the “area rule,” the swept wing 

requires a rather localized and deep indentation of the fuselage to 

form a tuck-in or “wasp waist”. The optimum fuselage shape for 

the oblique wing, however, is much more nearly cylindrical. That 

means more cargo space or passenger space can be provided.19

Jones’s 1976 patent was preceded by an earlier patent he had applied for on 

December 9, 1971, and received on June 5, 1973, for a dual-fuselage obliquewing aircraft, though, for reasons explained subsequently, he soon went back 

to a single-fuselage concept rather than the twin.

His application described the aircraft as follows:

Briefly, the present invention includes an airframe in which a parallelogram principle is utilized to achieve an efficient selective angular 

disposition between a pair of airfoils (a main wing and a horizontal 

stabilizer) and a pair of fuselages. The main wing and the horizontal 

stabilizer form one set of parallel sides of the parallelogram while the 

two fuselages form the other two sides. The two airfoils are pivoted 

to the spaced fuselages and enable two important in-flight changes 

in aircraft configuration to be effected: The first is the skewing or 

yawing of the airfoils relative to the direction of flight for high speed 

flight; the second is the lateral spreading of the weight distribution 
86

Thinking Obliquely

Jones’s conceptualization of a dual parallel-fuselage oblique-wing SST, 1971. (NASA)
87

Design and Fabrication of the AD-1 Research Aircraft

to minimize the bending stresses of the wing. The increased extension of the aircraft components in the fore and aft direction serves 

further to reduce the drag at supersonic speed. Another feature of 

the present invention is the upwardly curved main wing configuration which compensates for any roll tendency caused by the yawed 

positioning of the wing.20

In his February 1972 paper titled “Reduction of Wave Drag by Antisymmetric 

Arrangement of Wings and Bodies,” Jones determined that a single-fuselage 

oblique wing was more efficient than the dual-fuselage oblique-wing configuration. In this paper, Jones stated the following:

One of the unspoken assumptions in aircraft design is that of 

bilateral or mirror symmetry. At slow flight speeds, this assumption seems on rather secure ground, partly because of the indications of aerodynamic theory, but also because it agrees with the 

observed evolutionary forms of birds. Although it is perhaps natural to extrapolate the forms of birds and animals to the supersonic 

flight regime, there has been no rational discussion of the merits of 

bilateral symmetry for supersonic flight. In fact, once the velocity 

of sound is exceeded, the laws of aerodynamics change in such a 

way as to make it seem inadvisable to arrange the components of 

an airplane side by side or abreast in a supersonic stream unless 

there are compelling reasons for such arrangement. Both the transonic area rule and the supersonic small disturbance theory show 

large adverse interference effects for bodies or wings in a mirrorsymmetric arrangement.21

Jones stated further that

[t]he favorable properties of the oblique wing depend, first of all, 

on the maintenance of a subsonic type of section flow at supersonic 

speeds, and this requires that the wing be placed at an angle of yaw 

such that the component Mach number normal to its long axis be 

subsonic. If one assumes that the critical “drag divergence” Mach 

number of the wing sections is 0.7, then the angle of yaw must be 

such as to reduce the component Mach number to this value.... 

The advantage of the yawed wing over the swept wing depends 

on an increased extension of the wing in the flight direction. As 

is well known, spreading the lift over a greater length diminishes 

both the sonic-boom intensity and the drag. For a given structural 
88

Thinking Obliquely

General arrangement drawing of the AD-1 Oblique Wing Research Aircraft. (NASA)

slenderness, the single yawed wing panel may have nearly twice the 

projected length of the corresponding swept wing.22

Jones studied three different trims for dual-fuselage oblique-wing configurations as well as the single-body configuration and noted that “[t]he use of 

two bodies connected across by the wing and horizontal tail in a parallelogram 

arrangement has certain advantages over the usual arrangements of variable sweep. 

[For example,] [s]hearing the parallelogram does not displace its center of 

gravity and only slightly displaces the center of lift.”23 When comparing the 

dual-body configuration with the single-body configuration, however, Jones 

concluded that “[s]ince the single fuselage at the center of the wing has almost 

negligible inertia in roll, one arrives at the surprising conclusion that the onebody arrangement has greater aeroelastic stability than the two-body arrangement.”24 Thus, Jones and NASA proceeded forward with the development of 

the single-fuselage oblique-wing design.

The AD-1 Described

The general layout of the AD-1 airplane consists of a high-fineness-ratio fuselage with two French Microturbo TRS-18 engines, each with a sea-level thrust 

rating of 220 pounds. The engines are mounted on short aft pylons on the side 
89

Design and Fabrication of the AD-1 Research Aircraft

of the fuselage and consume 72 gallons of jet fuel stored in two fuselage tanks 

installed fore-and-aft of the wing pivot. The AD-1 has conventional horizontal 

and vertical tails, fixed gear, and a high-aspect-ratio aeroelastic oblique wing. 

The wing can be pivoted in flight from a 0 degree to 60 degree sweep (with the 

right wing forward) on a pivot point at the 40-percent root-chord location. 

The center of gravity while in flight was generally within a few percent of the 

nominal quarter root-chord position.

Structurally, the airplane consists of a fiberglass-reinforced-plastic sandwich 

with a core of rigid foam. The thickness varies from 17 plies at the wing root 

to 4 plies at the tip. Except for the wing pivot, all other components were 

designed to a 6 g-load limit capacity. The wing pivot was designed to withstand 

+/–25.0 g-loading. The airplane weighs approximately 2,100 pounds and has 

potential performance speeds up to 175 knots and flight at altitudes of up to 

15,000 feet. The above specifications were considered conservative since the 

aircraft was not expected to exceed 5 g-loading or 150-knot speed in order to 

accomplish the program’s research goals.

The pilot of the AD-1 sat semireclined in a manner similar to the seating 

in a high-performance sailplane. The AD-1 has a conventional aileron, elevator, and rudder that were actuated using a mechanical control system. The 

rudder pedals were mechanically linked to the upper rudder, and yaw trim 

was provided by the electrically operated lower rudder. Pitch and roll trim 

were obtained from electrically operated tabs located on the elevator and right 

aileron. Throttle control was provided through an electronic engine control 

monitor, and wing sweep was initiated by using a switch on the instrument 

panel. The wing could be returned to the unswept position by using either the 

switch or a trigger located on the pilot’s center stick. Because it was intended 

to operate only in visual flight rules (VFR) clear-skies flight-test conditions 

over the Edwards R-2508 range, the aircraft had a very basic instrument panel 

containing readings for altitude, airspeed, normal acceleration, angles of attack 

and sideslip, wing-sweep angle, engine parameters, and rudder trim position. 

Three separate instruments furnished information on angle of attack (“α” or 

nose pitch), angle of sideslip (“β” or nose yaw), and wing-sweep angle (“Λ” or 

skew angle). All handling-quality maneuvers had to be performed using visual 

heads-up external references because there were no attitude instruments such 

as an artificial horizon. The electrical system consisted of an engine-driven 

generator that powered the battery for engine start, the cockpit gauges, the 

trim motors, and the onboard data acquisition system.25 The battery was used 

to start the engine, and once the engines were started, the generator recharged 

the battery and provided electrical power for the various electrical components.

The AD-1 was instrumented with a multichannel pulse code modulation 

(PCM) system with a 32,000-bit-per-second rate with an 8-bit word, 20-word 
90

Thinking Obliquely

frame length, and a 16-frame data cycle. The data were transmitted to a ground 

station and recorded on tape. The monitored parameters were related to stability and control, wing-root bending loads, and wing and empennage accelerations. The structural acceleration data were monitored during flight in a 

spectral analysis facility (SAF) for real-time flutter envelope clearance.26

Detailed physical characteristics of the AD-1 are contained in appendix 1, 

and a detailed description is contained in appendix 2.

NASA AD-1 Developmental Tunnel Research

Although NASA had already assembled a comprehensive database for the 

oblique-wing design (in part because of the many industry studies run on the 

configuration), development of the AD-1, as with any new aircraft, required 

that the little research airplane have its own wind tunnel development program, 

complementing analytical and computational studies run on the configuration 

as well. Accordingly, wind tunnel testing for the AD-1 oblique-wing configuration was conducted in the NASA Ames 12-foot Pressure Wind Tunnel using 

an aeroelastic one-sixth-scale model of the craft. Two wings were tested: one a 

stiff, solid aluminum wing, and the other a fiberglass-epoxy composite wing 

that was designed by Ronald C. Smith to have the necessary flexibility to produce the correct curved dihedral at a 45-degree wing sweep to accommodate 

a range of structural loadings. This constituted an early example of aeroelastic 

tailoring of composite wing structures.27

Full-scale real-world Reynolds numbers, as well as full-scale wing flexibility, were obtained when operating at 4.5 atmospheres—approximately 66.15 

pounds per square inch (psi)—and at a Mach 0.3 (approximately 230 miles per 

hour [mph]) flow speed. Limited data were obtained at lower Mach numbers 

or tunnel pressures in order to obtain vehicle characteristics at higher angles of 

attack or off-nominal wing flexibility. Damping derivatives predictions were 

obtained using computational methods. A six-degrees-of freedom fixed-base 

digital simulator was developed using these predictions for safety of flight planning. A spin tunnel test of a one-thirteenth-scale model also was performed 

at NASA Langley. Most of the wind tunnel data were obtained over an angleof-attack range from –4 degrees to 11 degrees. The presented predictions were 

digitized at every 4 degrees of angle-of-attack. The wind tunnel data were 

obtained at wing-sweep angles of 0 degrees, 25 degrees, 45 degrees, and 60 

degrees. The data from these angles were interpolated to obtain predictions at 

15 degrees and 30 degrees.

Interference between a wind tunnel model’s support system and the model 

itself has been a frequently encountered problem in tunnel testing, and the 

AD-1 proved no exception in this regard. The first wind tunnel tests were 

conducted with a bottom-mounted blade support and a straight midchord 
91

Design and Fabrication of the AD-1 Research Aircraft

Ronald C. Smith of the NASA Ames Research Center with the AD-1 oblique-wing wind tunnel 

model. (NASA)

aluminum wing. While these first tests produced a reasonably complete set 

of wind tunnel data, the results were unrealistic because of apparent losses 

in elevator control effectiveness accompanied by a 30-percent increase in 

static margin. As a result, a second set of tests were conducted that, through 

flow-visualization studies and a model component buildup, revealed that the 

bottom-mounted blade model support was producing aerodynamic interference in the region of the aft fuselage and horizontal tail. The interference 

affected pitching moment and, to a lesser degree, rolling moment. The impact 

on yawing moment was unknown. The problem with pitching and rolling 

interference was resolved by using a top-mounted blade support system. The 

top-mounted system interfered with the vertical tail so data from the bottommounted support system still had to be used to define yawing moment, sideslip, 

and rudder characteristics.

The primary tool for estimating damping derivatives was the STBDER 

computer program. The main application of this program is to compute static 

and dynamic derivatives for oblique-wing vehicles in the subsonic flight regime. 
92

Thinking Obliquely

STBDER uses lifting-line theory for the wing configuration and classical methods for the remaining vehicle components. The MMLE3 computer program 

was the primary flight-data analysis tool. This computer program uses a maximum likelihood estimation method of analysis. For the AD-1 analysis, the 

program was modified to include an aerodynamic model that separated the 

longitudinal and lateral directional equations of the motion while also including the aerodynamic cross-coupling terms. As a result of the investigation, a 

“best preflight set of predictions was estimated based on both wind tunnel and 

computational analysis results.”28

Dryden’s Ike Gillam Defends the Program to Headquarters

Even with the wind tunnel tests, model development, and industry studies 

well under way, NASA apparently still had concerns regarding the AD-1 program. Over many years, Dryden’s enthusiastic pursuit of small “on the cheap” 

development activities (encouraged by its founding directors who shaped its 

institutional culture, Walter Williams and his successor Paul Bikle) had occasioned scrutiny from higher headquarters. At the beginning of 1978, the AD-1, 

like such projects as the Parasev paraglider, the M2-F1 lifting body before it, 

attracted equivalent headquarters attention. Dryden’s director, Isaac T. “Ike” 

Gillam IV, concerned that the program might fatally stall, responded to Dr. 

James J. Kramer, then NASA’s Associate Administrator running the Office of 

Aeronautics and Space Technology, vigorously arguing for the program: “We 

appreciate your concern,” Gillam bluntly stated. “We firmly believe that the 

AD-1 program should be continued as planned.”29 He noted:

1. The program would provide meaningful information on whether or 

not the oblique-wing concept has potential;

2. Theoretical and wind tunnel studies have demonstrated that the 

concept has promise;

3. The aeronautical industry has identified potential applications with 

military and civil aviation through the conduct of preliminary 

design studies; and

4. Several remotely piloted vehicle programs have further substantiated 

the feasibility of the concept.30

Gillam added that the AD-1 airplane and flight-test program was conceived 

as an interim step to the final verification of the concept, noting that “the 

transonic speed regime, where the true advantages of oblique wing technology 

are realized, cannot be explored with AD-1” and that “the wing structural aeroelastic behavior cannot be assessed.”31 These areas of investigation, according 

to Gillam, would require a vehicle capable of flying in the Mach number range 

of 1.4 to 1.6. He concluded, however, that the “AD-1 will provide a means for 

evaluating the handling qualities and preliminary control system requirements 
93

Design and Fabrication of the AD-1 Research Aircraft

in conjunction with a more systematic assessment of the dynamic aero characteristics than was possible with previously conducted RPV [remotely piloted 

vehicles] programs.”32

Gillam allayed Headquarters’ concern over program risks by noting that 

both Ames and Dryden had pursued a risk-reduction strategy that included:

1. Three series of wind tunnel tests had been conducted with the AD-1 

model in the Ames 12-foot tunnel to establish the static aerodynamic stability and control characteristics (This information was 

provided to the designer who, in turn, provided the detailed airplane 

drawings being used to build the aircraft).

2. NASA Ames completed a flutter analysis of the AD-1 configuration.

3. A six degree of freedom simulation has been mechanized and periodically run at NASA Dryden with the assigned pilot performing 

the evaluations tasks.

4. The simulation was used to develop the flight plans that will be used 

to progressively explore the flight envelope of the vehicle for various 

speed and altitude conditions associated with each of the wingsweep settings.

5. The simulation will be upgraded with test flight results and then 

used as a problem-solving tool during the flight envelope expansion 

period.

6. Considerations are being given to conducting full-scale tests in the 

Ames 40 x 80 wind tunnel with the flight hardware.

7. Although the AD-1 is considered to be over designed from a structural standpoint, consideration will be given to conducting ground 

vibration and static loads tests at Dryden.33

8. Prior to flight, the Dryden standard center management and technical staff reviews will be performed to establish the flight readiness 

of the AD-1 and the actual conduct of the program will be initiated with the necessary taxi tests and the subsequent flight envelop 

buildup through systematic variations of configuration with the 

speed and altitude.34

Based on the above process and the fact that the testing was not driven by a 

critical time schedule, Gillam stated that “it is felt that the AD-1 program can 

be conducted in a safe and orderly manner” and it “will provide the next step 

essential to successfully verify the feasibility of the oblique wing concept.”35

NASA Headquarters obviously concurred as fabrication of the AD-1 proceeded 

forward, bringing the concept from tunnel to flightline.
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Thinking Obliquely

Overseeing Fabrication

A review of the monthly project update reports to NASA Dryden directors from 

William H. Andrews (from June 1, 1978, through September 9, 1981) and 

then Weneth D. “Wen” Painter (from October 8, 1981, through September 10, 

1982) indicates that program engineers closely and conscientiously monitored 

the progress of the AD-1. The June 2, 1978, monthly report noted, under the 

section “New Concepts,” that a May 22 visit to Ames Industrial Corporation 

confirmed that construction of the AD-1 was “essentially on schedule and the 

airplane is approximately 40 to 45% percent complete.”36 The July 5, 1978, 

monthly report added that the contractor was still on schedule; that the wing 

assembly component was completed and was “being worked with cores cut and 

fiberglass lay in progress”; 37 that the control system, fuel system, and landing 

gear were being worked; and, finally, that there were no major problems anticipated at the present time. The September 6, 1978, report mentioned that “Bill 

Andrews and Tom McMurtry [NASA’s AD-1 project pilot] of Dryden visited 

Ames Industrial Corporation (AIC) to observe the status of the manufacturing. 

The airplane is approximately 80 percent complete.”38 The November 2, 1978, 

monthly report stated that the “wing-attach plates and pivot bearing have been 

installed. The wing pivot actuator was delivered to DFRC where the actuator 

mechanism is to be fabricated and then the entire assembly will be shipped to 

Ames Industrial Corporation (AIC) for installation....At this time the February 

delivery schedule still appears firm.” The December 4, 1978, report noted that 

the major effort in November had been “to complete the fabrication of the 

control system surface and begin the linkage with the cockpit controls, install 

wiring and fuel system plumbing to the nacelles and complete the engine 

installation.”39 A wing proof-loads test also was conducted. The report added 

that “[i]n the month of December the principal effort will be directed towards 

completion of the systems installations and overall airplane surface finishing.”40

The January 4, 1979, report noted that fabrication of the airplane was 

still on schedule but that several minor problems became evident during the 

engine runs. These problems included an exhaust plume impingement that 

was enough to cause a noticeable buffet, and with both engines running, there 

was a tendency for one of the generators to drop off line, which could limit 

the capacity of the airplane’s electrical system. The exhaust plume problem was 

thought to be caused by the engine’s close proximity to the ground in the static 

runup condition and was scheduled for further evaluation. The tail buffet from 

the generator problem was to be resolved by a design change to the currently 

installed simplified relay system. Finally, the report noted that a meeting was 

held at NASA Ames on December 20 “to review the airplane development 

status, discuss Dryden fixed-based simulator results, discuss the Ames AD-1 
95

Design and Fabrication of the AD-1 Research Aircraft

flutter analysis, and firm up plans for a moving base simulation at Ames prior 

to the first flight of the AD-1.”41

The February 5, 1979, monthly report noted the following:

During the week of January 8 the project engineer, airplane 

crew chief, and inspector spent several days at Ames Industrial 

Corporation (AIC) to conduct preliminary inspection of the 

assembled airplane. This resulted in a nine page write-up that 

identified items that required attention. On January 22 and 23, 

Bill Andrews and Tom McMurtry visited AIC and at that time a 

major portion of these items had been corrected....The current 

schedule shows the airplane being completed and ready for shipment by February 23, 1979.42

The March 2, 1979, report added that the “manufacturing of the AD-1 

was essentially complete on February 22, with a semi-formal roll-out at Ames 

Industrial Facility at Bohemia, New York. During the earlier portion of the 

week Dryden representatives completed a preliminary inspection and acceptance of the airplane that was to be performed before shipment to Dryden.... 

Upon delivery at Dryden plans are being made to begin preliminary ground 

testing and installation of the data acquisition systems.”43 Finally, the April 23, 

1979, monthly report confirmed that

[t]he airplane was delivered from the Ames Industrial Corporation 

facility on Long Island, New York, to Dryden by an Air National 

Guard C-130 on March 11, 1979. Subsequent to delivery, the 

wing was installed and an inspection was made for final acceptance. Following the activity, several taxi runs were made to a 

speed of approximately 25 mph to evaluate the steering capability, using brakes in conjunction with asymmetric power. The 

responses were satisfactory to the pilot.44

The May 16, 1979, update report, which followed acceptance of the aircraft, 

noted that the ground vibrations tests previously reported were now completed 

and that all modes “compared favorably with the design analysis except the 

wing torsional frequency...[which] were somewhat less than predicted and as 

a consequence, the analysis performed to establish the flutter margins will be 

recomputed.”45 The report added that the airplane was now being instrumented 

and prepared for flight test.

The June 22, 1979, update report added that flight-test instrumentation 

was still being added and that modifications were made to the landing gear 
96

Thinking Obliquely

brake assembly plate, the rudder pedals, and control stick and that “all of the 

control surfaces are being statically balanced as they were not balanced properly on delivery.”46 The report also noted that a moving base simulation was 

performed at Ames Research Center and that “in general the tests verified the 

fixed based simulation results obtained at Dryden Flight Research Center.”47 The 

July 24, 1979, report noted that as a result of a Headquarters briefing on May 

14, 1979, coordination was undertaken with Langley regarding the feasibility 

of conducting a spin tunnel test of the higher sweep-angle configuration. The 

report covering the month of July 1979 recounted a telephone conference with 

Dryden, Ames, and Langley scheduled to discuss Langley’s William Gilbert’s 

recommendation regarding the stall-spin characteristics. It was generally agreed 

that Langley would develop a model and conduct spin-recovery tests and that if 

“the spin tunnel test has not been completed by the time the flight envelope has 

been expanded to a sweep angle of 45 deg, an assessment will be made before 

continuing beyond this sweep angle.” The September 13, 1979, report informed 

the director that the flight instrumentation installation was completed and that 

the cockpit canopy was being reworked to use an aft-mounted hinge arrangement that would enable better pilot egress. The December 12, 1979, report noted 

concern regarding the strength of the landing gear system due to the increased 

airplane gross weight over the design. Nine days after this report, however, the 

AD-1 made its first flight at Edwards AFB. Flight testing of the AD-1 was now 

under way at NASA Dryden.48
97

Design and Fabrication of the AD-1 Research Aircraft

Endnotes

1. Kenneth J. Szalai, “Role of Research Aircraft in Technology 

Development,” NASA TM 85913 (November 1984), 6.

2. See Richard P. Hallion and Michael H. Gorn, On the Frontier: 

Experimental Flight at NASA Dryden (Washington, DC: 

Smithsonian Books, 2003).

3. Szalai, “Role of Research Aircraft in Technology Development,” 7.

4. Ibid.

5. Szalai, “Role of Research Aircraft in Technology Development,” 6–8.

6. Alex G. Sim and Robert E. Curry, “Flight Characteristics of the 

AD-1 Oblique-Wing Research Aircraft,” NASA TP 2223 (1985), 1.

7. Vera Foster Rollo, Burt Rutan: Reinventing the Airplane (Lanham, 

MD: Maryland Historical Press, 1991) 35.

8. Interview of Burt Rutan by the writer, July 21, 2011.

9. Burt Rutan and George Mead, “Feasibility of a Small, Low Cost, 

Subsonic, Yawed-Wing Experimental Aircraft,” December 1975, 

Dryden History Office, folder L1-5-4-8, 2–3.

10. Ibid., 6.

11. Ibid.

12. Ibid., 6–7.

13. Ibid., 1–17.

14. Telephone interview of Burt Rutan by the writer, July 21, 2011.

15. Rutan and Mead, “Feasibility,” 19.

16. Telephone interview of Burt Rutan by the writer, July 21, 2011; 

see also Dan Linehan, Burt Rutan’s Race to Space: The Magician of 

Mojave and His Flying Innovations (Minneapolis, MN: Zenith Press, 

2011), 58–59, 158–159.

17. Robert T. Jones, Oblique-wing supersonic aircraft, US Patent 

3,971,535, filed August 12, 1974, issued July 27, 1976.

18. Ibid. The patent also referenced Vogt’s patent that represented an 

aircraft having a single fuselage with two sets of rotatable mounted 

integral wings (one for subsonic flight and one for supersonic flight) 

and the Hubschman patent wherein the wing-to-fuselage angle of 

separate left and right wings can be independently adjusted by the 

pilot.

19. Ibid.

20. U.S. Government as represented by NASA, Dual-fuselage aircraft 

having yawable wing and horizontal stabilizer, US Patent 3,737,121, 

filed December 9, 1971, issued June 5, 1973.
98

Thinking Obliquely

21. R.T. Jones, “Reduction of Wave Drag by Antisymmetric 

Arrangement of Wings and Bodies,” AIAA Journal 10, no. 2 

(February 1972): 171.

22. Ibid.

23. Ibid., 174–175.

24. Ibid.

25. Sim and Curry, “Flight Characteristics of the AD-1 Oblique-Wing 

Research Aircraft,” 3; W.H. Andrews et al., “AD-Oblique Wing 

Aircraft Program,” SAE International, TP 801180, 2–3.

26. Andrews et al., “AD-Oblique Wing Aircraft Program,” 3. Records 

give three different communication channel numbers for this—35, 

40, and 41.

27. For a comprehensive review of the testing, see Alex G. Sim and 

Robert E. Curry, “Flight-Determined Aerodynamic Derivatives 

of the AD-1 Oblique-Wing Research Airplane,” NASA TP 2222 

(1984), 4–11. The information on the two wing types was furnished 

to the author by Stephen C. Smith.

28. Ibid., 11.

29. Isaac T. Gillam IV, “NASA Dryden Letter to Dr. James J. Kramer, 

NASA Headquarters,” January 31, 1978, Milton O. Thompson 

Papers, NASA Dryden History Office, box L1-5-8, folder 16.

30. Ibid.

31. Ibid.

32. Ibid.

33. In a July 21, 2011, telephone interview with the author, Burt Rutan, 

who did the design work on the AD-1, noted in regard to structural 

divergence that while the test indicated that the wing was 6-percent 

too flexible, NASA approved the wing, noting that they had made 

the requirement 400-percent higher than the amount necessary to 

avoid structural divergence of the forward swept wing. Rutan stated 

that this caused the wing to be made much stiffer than necessary, 

which greatly increased wing weight and resulted in poor flight performance, particularly its single-engine climb rate.

34. Gillam, “NASA Dryden Letter to Dr. James J. Kramer, NASA 

Headquarters.”

35. Ibid.

36. Gene J. Matranga, “Aeronautics Update Memorandum—May 

1978,” June 2, 1978, Dryden History Office, box L3-4-4B, 4.

37. Ibid.

38. Gene J. Matranga, “Aeronautics Update Memorandum—October 

1978,” November 2, 1978, Dryden History Office, box L3-4-4B, 4.
99

Design and Fabrication of the AD-1 Research Aircraft

39. Gene J. Matranga, “Aeronautics Update Memorandum—November 

1978,” December 4, 1978, Dryden History Office, box L3-4-4B, 4.

40. Ibid., 5.

41. Gene J. Matranga, “Aeronautics Update Memorandum—December 

1978,” January 4, 1978, Dryden History Office, box L3-4-4B, 4.

42. Gene J. Matranga, “Aeronautics Update Memorandum-January 

1979,” February 5, 1979, Dryden History Office, box L3-4-4B, 3–4.

43. Gene J. Matranga, “Projects Update Memorandum—February 

1979,” March 2, 1979, Dryden History Office, File Box L3-4-4B, 

4–5.

44. Gene J. Matranga, “Projects Update Memorandum—April 1979,” 

April 23, 1979, Dryden History Office, box L3-4-4B, 6.

45. Ibid., 5.

46. Gene J. Matranga, “Projects Update Memorandum—May 1979,” 

June 22, 1979, Dryden History Office, box L3-4-4B, 6.

47. Ibid.

48. “Monthly Memorandums to the Director of Dryden Flight Research 

Center,” June 2, 1978, through April 23, 1979, Dryden History 

Office, box L3-4-4B.
100

The AD-1 at 60-degree wing sweep, during its 30th flight, on July 1, 1981, for stability and 

control evaluation, piloted by Tom McMurtry. This is the program’s iconic photograph. (NASA) 
101

CHAPTER 4

Flight Testing and 

Evaluation of the AD-1

The flight testing and evaluation phase of the AD-1 program consisted of 

NASA preflight tasks, flight operations, flight program evaluations, postflight 

testing, and studies undertaken to compare actual results with predictions. 

NASA preflight tasks were divided between three NASA Centers. Ames continued its wind tunnel test and structural dynamics predictions; Langley was 

conducting spin tunnel tests; and Dryden was undertaking instrumentation 

installation, moment-of-inertia tests, ground vibration tests, component loads 

tests (excluding wing), and flight simulation.

Ground Testing the AD-1

Following delivery of the AD-1 to Dryden and prior to flight testing of the 

AD-1, a proof of loads test was performed on the wing and a ground vibration 

test was performed on the entire vehicle. The purpose of the wing-loads test 

was to check wing deflection and to obtain a calibration of the root-bendingmoment strain gages for symmetrically and antisymmetrically distributed 

loads. Shot bags were used to produce loads equivalent to 0.9 g, 1.7 g, and 4.7 

g’s. Measurements were made at 11 wingspan stations and chord locations of 

the leading edge, 40 percent of chord, and the trailing edge. These tests indicated that the wing was 10-to-15-percent stiffer in bending than was indicated 

by the design. Also, a separate torsional rigidity test was conducted on the wing. 

For this test, three levels of torque were applied to the wing near the tip, and 

the resulting angle of twist was measured at several spanwise stations inboard 

of the applied torque. The test results indicated that at lower levels of torque, 

the wing’s torsional rigidity compared very well with the prediction produced 

from NASTRAN computational structural analysis. At the higher level of 

torque and near the tip, the wing appeared to have less torsional rigidity (more 

deflection) than the analysis program predicted.
102

Thinking Obliquely

The AD-1 undergoing a ground vibration test at the Dryden Flight Research Facility, March 15, 

1979. (NASA)

After the proof-loads test, a ground vibration test was performed. For this 

test, the airplane was suspended from an I-beam frame through an airbag 

system that was connected to a rigid plate attached to the wing pivot. A shaker 

unit was then attached to the right and left wing sections just inboard of the 

aileron. Several accelerometers were used to sense the discrete responses of the 

various components of the aircraft. Wing sweep angles of 0 degrees and 45 

degrees were used for the test. Symmetrical and antisymmetrical vibrations 

were applied to the airplane at frequencies that varied smoothly from 0 hertz to 

60 hertz. The response was measured on the wing, fuselage, engine nacelles and 

pylons, horizontal and vertical tails, and control surfaces. In addition, discrete 

frequency inputs were made to determine the shapes of the wing modes at a 

0-degree wing-sweep angle. The response was pronounced near frequencies of 

15 hertz and 43 hertz, indicating that the antisymmetrical responses at these 

two numbers were related to the second wing-bending and the first wingtorsional modes, respectively.1

Finally, during the fabrication of the AD-1, a six-degrees-of-freedom (longitudinal, lateral, and vertical correction at three different rotations) fixed-base 

simulator was assembled in order to obtain a preliminary assessment of the 

airplane’s flying qualities and to evaluate the vehicle’s control system requirements. The simulator’s cockpit instrument display was nearly identical to the 
103

Flight Testing and Evaluation of the AD-1

The Cooper-Harper Pilot Rating Scale

Aircraft 

Characteristics

Demands on the Pilot in Selected Task or 

Required Operation

Rating

Excellent (highly 

desirable)

Pilot compensation not a factor for the desired 

performance

1

Good (negligible 

deficiencies)

Pilot compensation not a factor for the desired 

performance

2

Fair (some mildly 

unpleasant 

deficiencies)

Minimal pilot compensation required for desired 

performance

3

Minor but annoying 

deficiencies

Moderate pilot compensation required for desired 

performance

4

Moderately 

objectionable 

deficiencies

Considerable pilot compensation 

required for adequate performance

5

Very objectionable 

but tolerable 

deficiencies

Extensive pilot compensation required for adequate 

performance

6

Major deficiencies Adequate performance not attainable with 

maximum tolerable pilot compensation. 

Controllability not in question.

7

Major deficiencies Considerable pilot compensation 

required for control

8

Major deficiencies Intense pilot compensation required to 

retain control

9

Major deficiencies Control will be lost during some portion of required 

operation

10
104

Thinking Obliquely

The AD-1 Oblique Wing Research Aircraft on the Dryden Flight Research Center ramp, April 17, 

1980. (NASA)

one used in the final airplane design; however, a pitch-and-roll attitude display 

was included in the simulator in order to give the pilot some outside reference. 

Also, a moving-base simulation was performed at NASA Ames. This simulation 

provided a check on the fixed-base simulation and enabled the effects of motion 

on the various piloting tasks to be evaluated. For the moving-base operation, 

the attitude display was replaced with a television display. The equations of 

motion used in both simulators utilized the static aerodynamic derivatives 

obtained from wind tunnel tests. The data were corrected for the effects of 

aeroelasticity. The pilot ratings, based on the Cooper-Harper rating scale (see 

table on previous page), for the above simulations at a 45-degree wing-sweep 

angle at an altitude of 10,000 feet and indicated airspeeds from 100 knots to 

160 knots, generally ranged between 3 and 5. The introduction of motion in 

the simulator slightly increased the pilot’s difficulty in accomplishing the task. 

At the 60-degree angle, however, the introduction of motion appeared to aid, 

not hamper, task accomplishment.2

With satisfactory completion of the above tests and simulations, the program was ready for actual test flights of the AD-1. Simulations, however, continued during flight testing in order to familiarize additional pilots with the 

airplane and to assess the need for a more sophisticated control system. Several 

taxi runs were made at a speed of approximately 25 mph in order to evaluate 
105

Flight Testing and Evaluation of the AD-1

NASA research pilot Thomas C. “Tom” McMurtry and the AD-1. (NASA)

the steering capability. These test results were used to validate the input data 

used in the design flutter analysis. After completion of the vibration test, a 

torsional loading was applied and the results of the test indicated that the 

torsional stiffness compared well with predictions. The instrumentation was 

then installed and the plane readied for flight.3

The Program and its Pilots: An Overview

The primary objectives of the flight-test program that began in December 1979 

were to assess the aircraft’s unique handling and flying qualities; learn the nature 

and complexity of oblique-wing flight control; verify the aeroelastic design of 

the wing; and compare the vehicle’s aerodynamic characteristics with predictions. Altogether, the AD-1 completed a total of 79 flights between December 

21, 1979, and August 7, 1982. Seventeen pilots flew the AD-1, including the 

two Dryden program pilots and 15 guest pilots.

NASA’s two AD-1 program pilots were Thomas C. McMurtry and Fitzhugh 

L. “Fitz” Fulton, Jr., both extraordinarily gifted and experienced airmen who had 

flown a wide variety of experimental and operational aircraft during their careers. 

Both were enthusiastic airmen who flew privately as well as professionally, and 
106

Thinking Obliquely

NASA research pilot Fitzhugh L. “Fitz” Fulton and the AD-1. (NASA)

thus both were ideally qualified to test and assess the radical little AD-1. Fortynine of the 79 flights were flown by Thomas McMurtry and 15 were flown by 

Fitzhugh Fulton; the remainder were flown by various guest pilots.

Born in Crawfordsville, IN, on June 4, 1935, McMurtry received his bachelor of science degree in mechanical engineering from the University of Notre 

Dame in June 1957. Before joining NASA, McMurtry had served as a naval 

aviator flying the Douglas A-3 Skywarrior and then flew the Lockheed U-2 

for Lockheed. McMurtry was a graduate of the U.S. Navy Test Pilot School 

(TPS) in Patuxent River, MD. While with NASA, McMurtry successively 

held a number of different positions at NASA Dryden, including chief pilot, 

director of flight operations, associate director for operations, and acting chief 

engineer. As director of operations, he supervised the Avionics, Operations 

Engineering, Flight Crew, Quality Inspection, Aircraft Maintenance and 

Modification, and Shuttle and Flight Operations support branches. In addition to his role with the AD-1, McMurtry served as project pilot for the F-15 

Digital Electronic Engine Control (DEEC) project, the KC-135 Winglets 

project, and the F-8 Supercritical Wing program, for which he received NASA’s 

Exceptional Service Medal. He also served as coproject pilot on the F-8 Digital 

Fly-By-Wire (DFBW) program. In 1982, he received the Iven C. Kincheloe 

Award from the Society of Experimental Test Pilots (SETP), the international 
107

Flight Testing and Evaluation of the AD-1

Robert T. Jones meets his creation: Jones inspecting the AD-1 at Ames Research Center, 

December 1981. In the cockpit is NASA research pilot Tom McMurtry. (NASA)

professional society for test pilots, for his contributions as project pilot on the 

AD-1 Oblique Wing program. In 1999, McMurtry was awarded the NASA 

Distinguished Service Medal. McMurtry retired from NASA, following a 

32-year career, on June 3, 1999.4

Fitz Fulton was born in Blakley, GA, in 1925. A graduate of Golden Gate 

University and the Air Force Test Pilot School, Fulton had served 23 years as a 

pilot in the U.S. Air Force before joining NASA as a civilian research pilot at 

Dryden, where he flew two decades for the Agency from August 1, 1966, until 

July 3, 1986. While with the Air Force, he received the Distinguished Flying 

Cross and five Air Medals for flying 55 missions in the Berlin Airlift and then 

as a B-29 bomber pilot in Korea. He was also awarded three Distinguished 

Flying Crosses for his test pilot work with the Air Force. Fulton was arguably 

the world’s most experienced multiengine large-aircraft test pilot at the time of 

his work with the AD-1. He had flown aircraft as diverse as the B-52 launch 

aircraft for the X-15 and lifting bodies, the Mach 2+ Convair B-58 and the 

Mach 3+ North American XB-70A Valkyrie, and the exotic Lockheed YF-12A 
108

Thinking Obliquely

Blackbird. He was the project pilot on all early tests of the 747 Shuttle carrier 

aircraft used to air-launch the Space Shuttle Enterprise in the approach and 

landing tests (ALTs) undertaken at Dryden in 1977. For this program, Fulton 

received the first of two NASA Exceptional Service Medals, and in 1977, he, 

like McMurtry, was awarded the SETP’s prestigious Iven C. Kincheloe Award 

as the test pilot of the year. At the time of his retirement from NASA, Fulton 

had accumulated over 15,000 flying hours in over 200 different types of aircraft—from light sport planes to high-performance fighters, bombers, and 

experimental test beds.5

Tom McMurtry was first to fly the AD-1, making his first two flights 

on December 21, 1979; the first flight was an unplanned 5-minute excursion occurring during a high-speed taxi test. This was followed on the same 

day by the first official flight, which took 45 minutes, to check out the aircraft. McMurtry also flew all four of the first oblique-wing translations. The 

15-degree wing-sweep test flight was made on April 2, 1980, followed by 

the 20-degree wing-sweep flight on April 25; the 45-degree flight on May 

28; and finally, the 60-degree flight on April 24, 1981. In addition to these 

flights, McMurtry flew 6 performance test flights (one of these also included 

handling qualities), 8 stability and control flights, 4 flutter clearance flights, 

1 handling-qualities test flight, 2 oil-flow visualization flights, 12 flights 

to ferry the AD-1 to and from demonstration sites, and 10 demonstration 

flights. These included a flight to Ames Research Center, where McMurtry 

completed two demonstration flights and oblique-wing pioneer Robert T. 

Jones inspected his creation first hand.

The last eight flights of the AD-1 were at the Oshkosh air show in Wisconsin 

in August 1982. The last Oshkosh air-show flight, which also (according to 

the flight log summary) was the last flight of the AD-1, was flown on August 

7, 1982, thus making McMurtry both the first and last pilot to fly the AmesDryden AD-1 Oblique Wing Research Aircraft.

Fitzhugh L. Fulton, Jr., flew 15 of the test flights, making his first flight 

(pilot checkout and aircraft performance mission) on January 25, 1980. This 

flight was followed by a second performance checkout flight on February 20; 

five flutter clearance flights between July 9, 1980, and May 12, 1981; six stability and control test flights between July 1, 1981, and September 3, 1981; and 

two oil-flow visualization study test flights in June 1982.

NASA Dryden offered various Air Force, Navy, Marine Corps organizations 

and NASA Centers the opportunity to each have two pilot familiarization 

flights. These guest pilots, who each flew a single sortie, were

• 

• 

• 

Einar Enevoldson, NASA Dryden pilot

John Manke, flight operations director, NASA Dryden

William Dana, NASA Dryden
109

• 

• 

• 

• 

• 

• 

• 

• 

• 

• 

• 

• 

Flight Testing and Evaluation of the AD-1

Richard Gray, NASA Dryden6

Don Mallick, NASA Dryden

Captain John Small, Air Force Flight Test Center

Major Robert Cabana, U.S. Marine Corps, Naval Air Test Center, 

Naval Air Station (NAS) Patuxent River

Commander John Watkins, Naval Air Test Center, NAS Patuxent River

James Martin, NASA Ames

G. Warren Hall, NASA Ames

Captain Denny Mohr, USAF TPS instructor

Philip Brown; NASA Langley

Major William Neely, USAF NASA Langley

Colonel William J. “Pete” Knight, vice commander, Air Force Flight 

Test Center (AFFTC)

Steven Ishmael, NASA Dryden7

Fittingly, Tom McMurtry flew the last eight flights of the AD-1 at the 

Experimental Aircraft Association meeting and air show held in Oshkosh 

between July 31 and August 7, 1982. Wen Painter narrated the flights, which 

each lasted approximately 10 minutes. R.T. Jones was present for the flight 

demonstrations, and the air show flights were reported in the August 20, 1982, 

edition of the Dryden X-Press with the following commentary:

The airplane that proved the concept of oblique winged flight flew 

its last flights before an audience totaling more than 600,000 in 

Oshkosh, Wisconsin recently. The unique scissor wing craft flew 

daily to the delight of attendees at this year’s Experimental Aircraft 

Association meet in the Dairy state.8

Amongst the 12,000 aircraft at the gathering, there was no 

question as to which one was the show-stopper, as NASA Dryden 

Chief Pilot Tom McMurtry put the AD-1 through its swingwing paces before impressed and skyward looking crowds. On 

the ground, the Oblique Wing garnered a continuous circle of 

the curious and knowledgeable wanting to know more about 

the plane. On hand to answer the questions were Wen Painter[,] 

AD-1 Project Manager, Tom McMurtry[,] and Walt Vendolosky, 

AD-1 Crew Chief.9

The flights certainly accomplished their purpose. One young onlooker, 

Thomas Beutner, was so impressed with the sight of the AD-1 flying confidently through the Wisconsin skies that he determined, at that point, to devote 

his engineering career to studying oblique wings, subsequently studying with 

Jones and some of his associates later that decade.10
110

Thinking Obliquely

The AD-1 at 20-degree wing sweep, during its 13th flight, on April 25, 1980, for flutter clearance, piloted by Tom McMurtry. (NASA)

After the air show, Walter Vendolosky and Mike Bondy trailered the 

AD-1 to NASA Langley in Hampton, VA, where the aircraft was scheduled 

to undergo wind tunnel testing. It is not clear, however, from Langley 

records and personnel whether the wind tunnel tests were, in fact, ever 

conducted.11

In regard to the AD-1 management team and ground crewmembers, 

William Andrews served as the first project manager, Weneth D. “Wen” 

Painter was responsible for flight control and stability augmentation systems and served later as project manager, George Nichols was the instrument technician, and Walter Vendolosky served as aircraft crew chief.

NASA Dryden’s Monitoring and 

Oversight During AD-1 Testing

The record of monthly AD-1 progress and situation reports sent to the 

Dryden Center director offers clear evidence of NASA’s close oversight 

of the AD-1 program as it underwent its flight research phase.12 These reports 

also provided valuable additional test-flight and flight-evaluation information. 

The following extracts and summaries (by report date) are a representative 
111

Flight Testing and Evaluation of the AD-1

sampling of reports reflecting key contemporary updates as they occurred and 

were reprinted subsequently.13

January 14, 1980: On December 20, a series of taxi runs were 

made on the Edwards main base runway to evaluate the ground 

handling qualities up to a nose wheel lift off speed of approximately 65 knots. On December 21, 1979, two flights were performed with the wing locked in the zero sweep position. The first 

flight was just down the runway at approximately 50 feet to check 

the wing structural response. The second flight was accomplished 

with a maximum speed and altitude of 140 knots and 10,000 feet 

attained respectively. The testing involved flutter clearance, performance evaluation, and stability and control testing. The flight 

was very successful and the airplane landed with only minor maintenance squawks on the longitudinal trim and rudder controls. 

These squawks will be corrected and Flight No. 3 is scheduled for 

January 10, 1980.14

February 1, 1980: Since the last report six flights have been flown 

for a total of nine flights to date and about an equal number of 

flight hours. The first eight flights, which were flown at a 0 deg 

wing sweep, involved a flight envelope at altitudes of 12,500 and 

5,000 feet and over a speed range of up to 178 knots. The ninth 

flight, which was flown at a wing sweep angle of 15 deg, consisted 

primarily of establishing a flutter envelope clearance at 12,000 

and 7,500 feet altitude for speeds up to 150 knots.15

April 17, 1980: Three additional flights had been flown. The first 

flight was to check out another pilot and the next two flights were 

devoted to completing the evaluation of the 15 deg sweep angle 

configuration and obtaining data at high angles of attack (12 deg 

to 14 deg) for 0 deg and 15 deg wing sweep angles. Pilot evaluation from these flights revealed that “From a flutter standpoint, 

the wing exhibits low damping and caution is being observed as 

higher sweep angles are explored.”16

May 12, 1980: The latest flight flown was Number 13, which 

was accomplished on April 25, 1980. The purpose was to open 

the flight envelope to a sweep angle of 20 deg. The testing was 

conducted at altitudes of 7,500 and 12,500 feet and airspeeds 
112

Thinking Obliquely

The AD-1 at 45-degree wing sweep, during its 14th flight, on May 28, 1980, for flutter clearance, piloted by Tom McMurtry. (NASA)

up to 150 knots indicated. Flutter checks were made at five knot 

increments. At 7,500 feet the testing was terminated at 125 knots 

and at 12,500 feet it was terminated at 140 knots. The reason for 

discontinuing was due to very low damping in wing structural 

response in the frequency range of 15 to 16 Hertz. The wing had 

exhibited this behavior at lower sweep angles, but it appeared to 

be more persistent at 20 deg. Currently, the design flutter analysis 

and ground vibration test data are being reviewed as well as a more 

complete analysis of the flight data is in progress. As a result of 

this experience, the next flight has not been scheduled.17

June 11, 1980: Flight 14 was flown on May 28, 1980. As in the 

previous flights, the purpose of the flight was to expand the flight 

envelope relative to sweep angle and explore the low damped 

wing structural response noted in earlier flights.18

October 9, 1980: There was a lower damped left wing structural 

response on flight 19 as compared with previous flights. This factor was not readily explained. As a result, the wing skin was to be 

checked for delamination and a series of ground vibration tests 

were scheduled to be performed.19
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Flight Testing and Evaluation of the AD-1

December 8, 1980: A ground vibration test was scheduled in order 

to define the aileron influence and wing pivot free-play effects on 

the wing structural responses observed in flight.20

February 6, 1981: This report identified the suspected source of 

the structural vibration discussed in the previous report as the 

lateral control system.21

March 9, 1981: This report added that, based on recommendations of a Lockheed consultant and the flutter vibration group, a 

linear snubber is being installed on the aileron in order to remove 

the effects of slop in the system.22

April 8, 1981: This report noted that the ground vibration testing analytical model did not show any flutter potential within 

the region that the AD-1 would be flown. In addition, the 

installation of the aileron damper noted last month was effective in increasing the stiffness between the aileron and wing 

responses. This report also advised the director that two additional flights (flights 20 and 21) were flown on March 31. These 

flights explored the flight envelope at 110 to 120 knots in 5-knot 

increments and from sweep angles 0 deg to 50.5 deg. The sweep 

angles between 15 deg and 25 deg still indicated that the low 

amplitude, low damped 15 Hz responses on the left wing existed 

but that flying qualities at the higher sweep angles were as good 

as or slightly better than observed on the fixed base simulator.23

May 8, 1981: This update reported on flights 22 and 23, both 

flown on April 24. On these flights the flight envelope was 

explored between 120 and 150 knots for sweep angles from 15 deg 

to 25 deg. These flights cleared the AD-1 to fly at speeds of 130 

knots and sweep angles up to 55 deg and to perform a preliminary 

evaluation of the flying qualities at 60 deg to evaluate basic stability, damping and cross-coupling effects. The report noted that 

“The results appeared to be similar to that observed on the fixed 

base simulator; however, the real world motion cues naturally 

enhanced the flying characteristics over those predicted.24

June 9, 1981: The report noted that three additional flights had 

been flown bringing the total up to 26 flights. These flights concentrated on obtaining basic stability data in the sweep range from 
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Thinking Obliquely

30 deg to 60 deg in the speed ranges from 130 to 145 knots. This 

included a series of longitudinal and lateral-directional handling 

qualities tasks performed out to 60 deg sweep. The overall assessment was that the airplane continued to perform well and the 

flight operation was to be expanded to one flight per week.25

July 7, 1981: This update reported on four additional flights that 

increased the total flight number to 30. The principal testing now 

centered on performance in the 50 deg to 60 deg sweep range 

and on obtaining pilot performance ratings for specified tasks.26

August 10, 1981: This report noted that an additional four flights 

were performed in the 50 deg to 60 deg sweep range and that successful landings were made at the wing sweep angles of 15 deg, 30 

deg, and 45 deg. On the last flight, however, trouble developed in 

the right-side engine and that the Ames Industrial Corporation 

had been contacted for a new rental engine.27

September 9, 1981: This update reported that the new engine had 

been received and two additional flights flown bringing the total 

number of flights up to 37. The objective of these flights was to 

continue the pilot evaluation program especially in the high sweep 

angle range. Consideration was also being given to checking out 

additional pilots in order to expand the experience data base. 

Finally, this report noted that in conjunction with the current 

handling qualities evaluation, the fixed base six-degree of freedom 

simulator is being used to evaluate the effect of incorporating 

stability and damping augmentation.28

October 8, 1981: Weneth D. Painter reported that the AD-1 flight 

research program had been completed and that the program team 

was currently awaiting approval of a “Guest Pilot” program.29

February 10, 1982: Painter reported on the guest pilot familiarization program noting that Air Force pilots would fly the AD-1 the 

week of February 1; Navy pilots would fly the week of February 

8; and Ames pilots would fly the week of February 15.30

April 9, 1982: The report noted that 13 guest pilots had flown 

the AD-1 and that 1 to 3 additional pilots might still get the 

flight opportunity.31
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Flight Testing and Evaluation of the AD-1

May 10, 1982: This report noted that the AD-1 was scheduled to 

fly to Ames on May 14 for a static display and that 4 more guest 

pilots were scheduled to fly the airplane on May 19 and 20, at 

which time the program would be completed.32

June 10, 1982: This report added that the pilot familiarization 

was successfully completed and the program team was awaiting 

approval for 4 additional flights on June 8 and 9 in order to conduct oil flow visualization studies on the oblique wing.33

July 12, 1982: Guest flights have been completed. NASA will display 

and fly the AD-1 at the annual Experimental Aircraft Association 

convention in Oshkosh, Wisconsin later in the month.34

August 9, 1982: In this update, Kenneth E. Hodge, Chief of 

Dryden’s Aeronautical Project Office, reported that the AD-1 

was trucked to Oshkosh for participation in the air show and 

that “Following the EAA event, it is planned to truck the AD-1 

to Langley in response to their request for its use in wing aerodynamics research in the 30-by-60-foot wind tunnel. The loan 

agreement stipulates that the AD-1 will be returned to Dryden in 

airworthy condition upon completion of wind-tunnel testing.35

September 10, 1982: The update reported that the AD-1 was at 

Langley being prepared for wind tunnel testing and would be 

returned within the next year.36

First Look: The AD-1 Team’s 1981 

End-of-Program Evaluation

Less than a month after Weneth Painter had reported the AD-1 research program complete and 3 months before the onset of the guest-pilot evaluation, 

the AD-1 team offered an initial quick-look assessment of the program at a 

prestigious international flight-testing conference sponsored by the American 

Institute of Aeronautics and Astronautics, the Society of Experimental 

Test Pilots, the Society of Flight Test Engineers, the Society of Automotive 

Engineers, the International Test and Evaluation Association, and the Institute 

of Electrical and Electronic Engineers.37 In evaluating the AD-1 flight program, 

McMurtry, by now director of flight operations at Dryden, and aerospace 
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Thinking Obliquely

The AD-1 at 60-degree wing sweep, during its 32nd flight, on July 14, 1981, for flow visualization study (note the tufted wing), piloted by Fitz Fulton. (NASA)

engineers Alex Sim and William H. Andrews reminded their audience that 

the principal purpose of the flight-test program initiated in December 1979 

was to demonstrate the flight and handling characteristics of the oblique-wing 

configuration, especially in the wing-sweep angle range of 45 degrees to 60 

degrees.38 A six-degrees-of-freedom fixed-based simulation of improvements 

could be realized by incorporating advanced control system technology augmented the flight operations. McMurtry, Sim, and Andrews noted that development of the AD-1 Oblique Wing Aircraft was a good example of the need for 

complementary advances in technology in other fields in order to implement 

new engineering principles. In this regard, they noted that,

[t]heoretically, this configuration, which Robert T. Jones conceived 

of many years ago, offers aerodynamic, structural and operational 

efficiency unequalled by conventional designs. The development of 

a vehicle which would incorporate these new features has been considered impractical, however, because of the structural divergence 

problems inherent in the forward swept wing sections. However, 

with recent advances in the state of the art composite structural 
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Flight Testing and Evaluation of the AD-1

design and the advent of active control systems, the advantages of 

this concept may be realized in the future.39

The NASA Dryden team noted the following aerodynamic characteristics 

of the AD-1:

1. The lateral-directional trim changes consisted of change in sideforce, 

rolling moment, and yawing moment as a function of angle of 

attack and the wing sweep angle.

2. The changes in sideforce flight data and predicted data were due to 

the difference in construction between the wind tunnel model and 

the actual airplane. The effect of the sideforce is that either nonzero 

bank angle or sideslip angle must be maintained to hold a constant 

heading, thus resulting in an airplane that can be trimmed using 

many combinations of aileron, rudder, and elevator control.

3. Wing-stiffness problems impacted the plane’s dynamics, causing 

significant effect on vehicle handling qualities and making the AD-1 

less stable for large maneuvers involving load factor than for small 

maneuvers. Also, turbulence tended to amplify the flexibility effects 

and thus degrade the handling qualities. The handling qualities, 

however, would be improved by switching the wing construction 

from fiberglass, which was necessary to use for the AD-1 due to the 

low technology scope of the program, to carbon-fiber material.

4. Other aerodynamic concerns, including pitching moment due to 

aileron deflection and sideslip, as well as cross damping, such as 

pitching moment due to roll rate. These were not shown to have 

a significant effect on handling qualities, although the aeroelastic 

response tended to mask any effect they had.40

In order to examine the handling qualities associated with an oblique-wing 

airplane, the following set of tasks were used for the flight tests of the AD-1: 

trim to constant airspeed, altitude, and heading with zero sideslip; perform 

windup turns to 1.5 g and change heading 180 degrees while maintaining 

constant airspeed; descend 500 feet and level off, maintaining constant airspeed and heading; and perform moderate rate rolls to a bank angle of 30 

degrees and return to level flight, maintaining constant airspeed and altitude. 

The above tasks were considered simple since there was no assigned mission 

for the aircraft. The tasks were evaluated at wing-sweep angles of 0 degrees, 

35 degrees, 45 degrees, and 60 degrees. The NASA team noted that the tasks 

were performed within a range of 11,000 feet and 13,000 feet (the nominal 

altitude was 12,500 feet) and that this altitude was chosen primarily to allow 

for pilot egress in case of loss of control. Finally, the Cooper-Harper rating 

scale, as defined previously, was employed to evaluate the tasks.
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Thinking Obliquely

Use of the rudder to control roll of the AD-1 when aileron effectiveness was 

reduced at the higher oblique-wing sweep angles was considered important 

by the pilots because the static directional stability of the airplane was weak. 

This characteristic of the AD-1 was noted at all wing-sweep angles, and use of 

the rudder proved very helpful. Pilots also noted an additional characteristic 

while performing windup turns. When the wing-sweep angle was 50 degrees 

or higher, the airplane showed a tendency to increase in bank angle as the 

maneuver was performed to the left. When the maneuver was performed to 

the right, the airplane tended to roll out due to pitch coupling. Pilots indicated 

that the tendency for the AD-1 to roll out of the turn was more desirable than 

the tendency for the bank angle to increase. When increasing the load factor 

above 2.0 g’s during windup turns, the left roll tendency would exceed the roll 

authority of the full right aileron unless the pilot used an increasing amount 

of right rudder.

Pilot ratings were obtained at several different airspeeds. Landings were 

performed with the wing at 45 degrees of sweep. Pilots noted that the approach 

and touchdown speed had to be increased slightly. The approach, flare, and 

touchdown were made with a slight right bank. At touchdown, the airplane 

generally rocked over until the left main gear touched the runway. The pilots 

concluded, however, that the approach and landing of the AD-1 were easily 

completed with the wing at a 45-degree sweep angle. In regard to flight evaluation, pilot ratings indicated that for all maneuvers, the performance of the 

AD-1 declined as the sweep angle increased. Some of the poorer ratings, however, related to tasks that were performed in light turbulence where the wind 

gust response of the airplane was typical of a low-wing-loaded aircraft. When 

gusts were encountered, the roll oscillations were large and roll damping 

was low.

Pilot ratings were also given to the handling qualities evaluated on a sixdegrees-of-freedom simulator. Using the same tasks as used on the actual flight 

tests, the performance ratings given to the simulation of the basic airplane 

revealed the same trends as the ratings given to the AD-1 in flight. At 60 degrees 

of wing sweep, however, the pitch-damper-only configuration had better handling qualities than the basic airplane for all evaluation tasks. Likewise, the 

roll-damper-only configuration had better handling qualities than the basic 

airplane. A configuration of a pitch damper and a roll damper resulted in the 

best handling qualities. A yaw damper, however, appeared to have little, if 

any, effect. The above results on the simulator tests indicated that a control 

system using state-of-the-art technology could be tailored to produce a transonic oblique-wing airplane with satisfactory handling. In their concluding 

evaluation, McMurtry, Sim, and Andrew noted the following:
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Flight Testing and Evaluation of the AD-1

The AD-1 flight test program has demonstrated the flight characteristics of an oblique wing configuration to 60° of wing sweep[;]

 Pilot evaluations indicated that acceptable handling qualities 

were experienced at up to 50° of wing sweep[;]

 An evaluation of control system augmentation on a fixed 

based simulator has indicated that significant improvements in 

flying qualities may be realized on an oblique-wing airplane to 

wing sweep angles of at least 60°[;] and

 The aerodynamic data derived from flight has verified the 

feasibility of utilizing aeroelastic tailoring to satisfy design 

cruise criteria.41

Summary Review of the AD-1’s Flight Experience

In 1983, Alex Sim and Robert Curry, following up on their TP 2222 

(reviewed in chapter 2), reviewed flight operations with the AD-1 aircraft, 

including basic flight characteristics, both traditional and nontraditional; 

pilot ratings and comments; envelope-expansion flight results; and controlsystem augmentation.42

Flight operations

Normally, the AD-1 was taxied using one engine to conserve fuel. Pilot ratings 

of 5 to 6 were obtained for single-engine taxi while ratings of 3 were obtained 

when both engines were running. Takeoff consisted of lifting the nosewheel 

at a speed of approximately 60 knots and holding a pitch attitude of about 3 

degrees until takeoff occurred at a speed of about 85 knots. Prior to nosewheel 

lift-off, a slight forward stick pressure was often used to prevent nosewheel 

bouncing. Pilot ratings of 2 to 3 were obtained for takeoff. After takeoff, the 

aircraft would climb to 12,500 feet before research testing started. Since the 

best rate of climb was performed in the airspeed range between 100 knots and 

120 knots, most of the climb was performed at a speed of 110 knots. The rate 

of climb at 3,000 feet was about 1,000 feet per minute. This rate decreased to 

about 660 feet per minute at 12,000 feet. Although the initial climbs to the 

test altitude were performed with a 0-degree wing sweep, the rate of climb 

remained reasonably constant to about a 35-degree wing sweep. The climb task 

usually received a pilot rating of 2. Most of the research flying was conducted 

at an altitude of 12,500 feet and terminated when the airplane dropped below 

10,000 feet. Maneuvers were performed to expand the flight envelope for 

flutter, divergence, and loads; to analyze the aerodynamics; and to evaluate 
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Thinking Obliquely

the handling qualities. Structural excitation for flight-flutter testing consisted 

primarily of stick raps. Maneuvers for the analysis of aerodynamics, flight 

loads, and handling qualities consisted of doublets, windup turns, slow sideslip 

variations, 1-g decelerations, pull-up push-overs, descents, and aileron rolls.43

Return to base consisted of a descent with the engines at idle and the 

wing at either a 0-degree or 45-degree sweep. The approach to landing was 

usually long and flat because of the moderately high lift-to-drag ratio and the 

high idle thrust. Speedbrakes or spoilers would have improved flying qualities but were not on the AD-1 because they were not considered necessary 

for either the research or flight operational tasks of the aircraft. An 80-knot 

touchdown speed was used to provide attitude that allowed for adequate forward visibility and avoided the scraping of the tail that occurred at a pitch 

attitude of 7.5 degrees. Pilots compared the landing of the AD-1 with that of 

a low-performance sailplane. Pilot ratings were usually a 3. A chase plane pilot 

augmented the AD-1’s forward visibility and provided all nonresearch-related 

communications. Control room engineers monitored both the ground track 

and operational flight limits.

Traditional characteristics

The maximum lift-to-drag ratio decreased at the higher wing sweeps, causing 

increased speed stability and decreased maneuver performance. Since verification of oblique-wing aerodynamic performance was not an objective of the 

AD-1 program, additional precautions were not taken to minimize drag. At 

initial climbout, the available thrust-to-weight ratio was approximately 0.20, 

and at test altitude, the thrust-to-weight ratio was approximately 0.16. These 

numbers indicate that the AD-1’s performance was comparable to that of a 

light general aviation airplane. At airspeeds below 100 knots, the control forces 

were comparable to a low-performance sailplane. The transient response to a 

rudder input took about three cycles to damp out and was a result of the low 

directional stability derivative. As a result, the aircraft tended to wander or 

search directionally, and this characteristic became greater at high sweep angles 

and high angles of attack. For operational flying, the directional stability was 

considered adequate, although for precise maneuvering, the low directional stability often contributed to degraded handling qualities. The transient response 

to elevator inputs was nearly deadbeat, and the transient response to aileron 

input increased spiral instability. The spiral instability was primarily the result 

of the effective dihedral derivative and a strong positive value for the damping 

in roll due to the yaw-rate derivative.
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Flight Testing and Evaluation of the AD-1

Nontraditional characteristics

In addition to traditional flight characteristics, oblique-wing configurations’ 

handling qualities are affected by a number of nontraditional stability and 

control characteristics. With an increasing angle of attack, the resulting aerodynamic forces on a wing rotate forward and become approximately perpendicular to the wing-sweep angle. With an oblique wing, an increasing angle 

of attack creates a sideforce that must be neutralized by using either sideslip, 

bank angle, or a combination of the two in order to maintain a constant heading. In regard to the AD-1 sideforce problem, Sim and Curry noted in their 

technical paper that

[m]ost of the apparent side-force and the resulting trim requirements could have been eliminated by tilting the wing pivot axis 

forward about 5 deg and increasing the unswept wing incidence 

to maintain the same unswept geometry....This modification 

would cause the bank angle of the wing to increase as wing sweep 

increased, thus allowing the fuselage to remain straight and level. 

This was not realized during the AD-1 design phase.44

For a trimmed flight, both the moments and the sideforce must be neutralized. This can be obtained by using a number of combinations of elevator, 

aileron, and rudder trim. At high wing sweep, the most common technique for 

obtaining trimmed flight was to use sufficient right (negative) rudder trim in 

order to allow the center stick to be laterally neutralized. At a 60-degree sweep 

and 140 knots, this rudder trim procedure brought about a trimmed flight 

condition with about 1 degree of nose-right (negative) sideslip and 7 degrees 

of right-wing-down (positive) bank angle.

In comparing the yaw of the AD-1 with the anticipated yaw based on wind 

tunnel tests of the spin model, Sim and Curry noted that

[t]he AD-1 spin model had a “yaw into the leading wing” (yawright) established spin mode from which recovery was difficult 

without first unsweeping the wing. Reference 9 [in the report] also 

indicated that the AD-1 model with the wing highly swept would 

not sustain a spin into the trailing wing (yaw left). However, 

experience with the airplane has been that at low speeds, the 

trailing (left) wing stalled first and caused the airplane to roll and 

yaw left, away from the potential spin problem. If recovery were 

not attempted, indications are that the airplane would go into 

a steep spiral to the left. Rapid pull-ups to stall at high airspeed 

were not attempted.45
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Thinking Obliquely

The report added that the “negative yawing moment increment due to load 

factor has an ‘adverse yaw’ effect for right turns and a ‘proverse yaw’ effect for left 

turns. Thus, right rudder was needed to coordinate either left or right turns.”46

Pilot ratings and pilot comments

Sim and Curry, as did other NASA engineers and pilots (discussed subsequently), also reviewed the pilot findings and comments from the actual flights 

of the AD-1. Pilot ratings were obtained from the envelope-expansion flights 

and from the guest pilot program flights. Ratings from the two pilots who flew 

the envelope-expansion flights, Thomas McMurtry and Fitzhugh Fulton, were 

obtained near the end of the flights after each pilot had previously flown in each 

rated flight condition. Pilots in the guest pilot program only had one flight in 

which to evaluate and rate the handling qualities of the AD-1, and their flight 

evaluations were obtained primarily for the trim task. Sim and Curry noted:

Although the AD-1 geometry was chosen for its similarity to 

supersonic oblique-wing transport designs, many of the maneuvers performed to evaluate the handling qualities were not 

transport-aircraft maneuvers. For example, windup turns are 

often used to evaluate the capability of a maneuvering airplane. 

Because deficiencies in transport-aircraft handling qualities tend 

to be amplified in maneuvers like windup turns, these types of 

maneuvers are excellent for highlighting deficiencies and for ascertaining the need for stability augmentation.47

Flight envelope expansion tasks were performed for trim, descent, aileron rolls, windup turns, pull-up push-overs, landings at a 45-degree sweep, 

and turbulence encounters. For trim below 30 degrees of wing sweep, pilot 

ratings and comments indicated satisfactory handling qualities. Pilot ratings 

remained satisfactory at higher angles, but increased pilot compensation was 

required. Elevator trim authority runs out at airspeeds below 85 knots, requiring the pilot to hold back the stick. At sweep angles of 45 degrees and above, 

proper trim had to be used or it was possible to run out of aileron trim and 

even aileron authority. Due to these factors, the AD-1 was trimmed every 5 

degrees of sweep for angles above 45 degrees. Pilots noted that at a 60-degree 

sweep, the aircraft exhibited “a little lateral hunting which required constant 

watch.”48 Pilot ratings and comments for descent maneuvers indicated that the 

AD-1 was generally satisfactory below 30 degrees of wing sweep but degraded 

at higher angles. One pilot noted that at a 60-degree sweep and an airspeed 

of 84 knots, there was “no problem holding the descent”49 but that coming 

out of the descent, the AD-1 developed some pitch and roll “oscillations and 
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Flight Testing and Evaluation of the AD-1

cross couples.”50 The pilot added that at below 45 degrees of sweep, the task 

“required minimal compensation and did not produce significant coupling.”51

For aileron rolls, pilot ratings indicated that there was good command of bank 

angle with good roll rate and no tendency to overshoot at sweep angles lower 

than 45 degrees. At 30 degrees of sweep, only slight pitch coupling was noted, 

and at sweep angles of 45 degrees and higher, the AD-1 resisted rolling to the 

right and often required rudder action to adequately perform the maneuver. 

Pilots generally indicated that rolls to the left were slightly easier than rolls to 

the right, although there was a tendency to overshoot the desired bank angle. 

A number of pilot comments, however, indicated that the aircraft wandered 

(primarily directionally), making it difficult to maintain coordinated flight 

using the rudder.

Windup turns were the most difficult handling task because they required 

close attention to pitch, roll, and yaw. Below the 45-degree sweep angle, pilot 

comments indicated that there was no tendency to overshoot the desired 

g-force and that the maneuver required minimal pilot workload. Above the 

45-degree sweep angle, however, the AD-1 exhibited different characteristics 

when turning right than when turning left. When the pilot increased bank 

angle to the right, the aircraft “seemed to want to roll out of the turn.”52 At 60 

degrees of sweep, if proper rudder trim was not used, it was possible to run out 

of right aileron control authority before attaining the desired 1.5 g-force. When 

turning to the left, the aircraft would tend to roll farther into the turn than the 

pilot had commanded. This situation often required the right aileron to be held 

in place in order to counter the increased roll tendency. At a 60-degree sweep 

angle, liberal right rudder was often needed in order to roll back to a straight 

heading. Primarily during left turns, an oscillation would be superimposed on 

the maneuver, causing the pilots to refer to the maneuver as “jerky” or “ratchety,” 

and proper rudder coordination could not cause a smooth maneuver.

While pull-up push-over maneuvers were not pilot-rated, pilot comments 

indicated that at low sweep angles, the AD-1 was able to attain a target g-level 

“quickly and precisely,” but at sweep angles above 45 degrees, the maneuvers were 

“sloppy since cross controlling of pitch was necessary.”53 Several landings were 

made with the wing at a 45-degree sweep angle with pilot comments indicating 

“good control authority in all axes with no adverse ground effects,”54 but the 

comments also indicated that forward visibility was poor and that a 3-to-4-degree 

bank was needed to maintain constant heading. Pilot ratings increased from 3 

for 0-degree sweep-wing angle landings to 5 for 45-degree sweep-wing landings. 

The pilots also noted that throughout the envelope expansion, the presence of 

light turbulence degraded the handling qualities by two to three pilot ratings, 

often resulting in overall unacceptable handling qualities. The major cause of the 

poor turbulence response was the dynamics resulting from the wing aeroelastics.
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Thinking Obliquely

Control system augmentation

A stability augmentation system using rate feedback, though not implemented 

on the AD-1, was incorporated into a pilot simulation. This simulation was 

mechanized in a fixed-base, six-degrees-of-freedom simulator containing aerodynamic data. Using only one of the program pilots, pilot ratings were obtained 

from the unaugmented simulation at an air speed of 140 knots. The simulator 

test results indicated that a control system using only rate feedback was sufficient 

to yield acceptable handling-qualities ratings at high wing-sweep angles.

Sim and Curry concluded:

The basic flight characteristics of the AD-1 airplane were discussed, 

including several stability and control characteristics that have 

either traditionally affected handling qualities or that are unique 

to an oblique-wing vehicle. Of particular significance were the low 

directional stability, the unusual trim requirements, the roll-pitch 

couplings, the dynamics resulting from the wing aeroelastics, and 

the stall. Pilot ratings that document many of the vehicle’s handling 

qualities were presented. At or below 30 deg of wing sweep, ratings 

indicate satisfactory handling qualities. Between 30 deg and 45 

deg of sweep, ratings increase, generally indicating the beginning 

of a degradation in handling qualities caused by wing sweep. The 

primary degradation in handling qualities occurred between 45 

deg and 60 deg of sweep. Light turbulence degraded the handling 

qualities by up to three pilot ratings. A control system using rate 

feedback was mechanized on the AD-1 simulator. Simulation 

studies indicated that only rate feedback was necessary to yield 

acceptable handling qualities at the high wing sweeps.55

In a 1984 follow-on study to their earlier survey of AD-1 flight experience, 

Sim and Curry compared flight data with preflight predictions in order to provide, along with their two earlier studies, a complete aerodynamic data package 

for the AD-1 research vehicle.56 This final paper reviewed wind tunnel data with 

flight data noted in the earlier reports and made comparisons and formulated 

their overall conclusions. The two NASA engineers concluded by noting,

The flight results were compared with predictions based on wind 

tunnel model data. The correlation was generally good, although 

it was less favorable for the drag and yaw moment components. 

The data also indicated significant flow separation and spanwise 

vortex flow effects which were verified by flow visualization at 

high angles of attack.
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Flight Testing and Evaluation of the AD-1

 The static aeroelastically tailored wing design criteria resulted in 

As early as 1980, program team members had concluded:

The oblique wing concept has potential applications, particularly as related to supersonic cruise vehicles. The unconventional 

aspects of the configuration require that a concentrated effort be 

made to prove that the potential indicated by theoretical and wind 

tunnel predictions can be realized in flight. The flight program 

described in this paper is only a minor step toward establishing 

the practicality of the configuration. An advanced vehicle should 

be developed and tests should be performed to extend operational 

experience and a full-scale data base into the supersonic regime.58

Indeed, NASA did proceed forward with a plan to move from the AD-1 

program into the supersonic regime through the follow-up F-8 Oblique Wing 

Research Aircraft (OWRA) program covered in Chapter 5. The OWRA program overlapped NASA’s F-8 fly-by-wire program that was a necessary step in 

the followup oblique-wing program due to the need for computer augmentation for a supersonic or transonic oblique-wing aircraft. NASA engineers, 

however, were not finished with the planned use of the AD-1 airplane. The 

engineers thought that the AD-1 aircraft, which actually had very limited flight 

use, would be an ideal test bed for analyzing the potential for joined-wing aircraft, and so this was the next—and final—direction that the AD-1 program 

took involving the small, low-cost airplane.

Last Chance for the AD-1: 

The Joined-Wing Research Aircraft Effort

Following the completion of the AD-1’s oblique-wing program, NASA Ames 

planned for the additional use of the AD-1 airplane as a joined-wing flight demonstrator. The oblique wing would be removed from the AD-1 and replaced 
126

Thinking Obliquely

by a joined wing, and the aircraft would be redesignated as the JW-1 JoinedWing flight demonstrator or, in NASA shorthand, the JWRA (for JoinedWing Research Aircraft). Basically, the “new” aircraft would utilize the fuselage, 

engines, and undercarriage of the existing AD-1. This arrangement was considered a more practical solution to building a separate low-cost proof-ofconcept demonstrator. The aerodynamic design of a joined-wing demonstrator 

was accomplished by NASA Ames in collaboration with ACA Industries, of 

Torrance, CA, undertaken pursuant to a Small Business Innovation Research 

(SBIR) program consisting of the two following phases: Phase One was to complete a feasibility study for a joined-wing research airplane during 1984, and 

Phase Two was a 1986 contract to design and fabricate a joined-wing research 

aircraft based on the AD-1. The objectives of the joined-wing research program 

were to demonstrate good handling qualities on a realistic configuration and 

to validate existing design methods for joined-wing configurations.59

The Joined Wing: An Overview

As defined in 1987 by Stephen C. Smith and Susan Cliff, of NASA Ames’s 

Advanced Vehicle Concepts Branch, and professor Ilan Kroo, of the Aerospace 

Engineering Department at Stanford University:

The joined wing is a novel aircraft configuration with a rear wing 

surface which acts both as a horizontal tail and as a strut brace 

for the forward wing. This rear wing is attached near the top of 

the vertical tail, and is joined to the trailing edge of the forward 

wing, typically somewhere along the outboard half of the span. 

The projected angle between the two wings created by the vertical 

separation between the two wing roots, when viewed from the 

front, allows the rear wing to act as a strut, providing bendingmoment relief for the forward wing.60

The joined wing, as noted 2 years earlier by Julian Wolkovitch, a pioneer 

of the joined-wing concept and founder of ACA Industries, Inc., “incorporates tandem wings arranged to form diamond shapes in both plan and front 

views.”61 The joined wing has a long legacy of interest, with small-scale experimental examples dating to the early interwar period following the First World 

War. The attractiveness of the joined wing is precisely what Stephen C. Smith 

and his colleagues noted in the text above—namely, that it offers an ideal 

tradeoff between aerodynamic performance, weight, and structural efficiency. 

By combining the aerodynamic functions of a wing and a tail while combining the bracing function necessary to support a high-aspect-ratio wing, the 
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Flight Testing and Evaluation of the AD-1

Configuration drawing of a joined-wing wind tunnel model evaluated by Rockwell, from CR 

177543, 1989. (NASA)

joined-wing concept furnishes an opportunity for designers to fulfill a variety 

of possible civil and military mission applications.62

By the mid-1980s, the joined wing, if not necessarily the next big thing 

in aerodynamic design, offered the potential of a novel concept that, like the 

oblique wing, could furnish efficient, low-drag flight. A number of research 

and industry studies (including by Rockwell International, the former North 

American Aviation concern, the University of Kansas, California Polytechnic 

State University, Stanford University, and NASA) were under way to examine 

its possible application for a range of aircraft from agricultural crop dusters to 

transonic and supersonic aircraft.63

NASA’s interest in the joined wing began when Wolkovitch approached 

Joseph Johnson of the Dynamic Stability Branch at Langley Research Center 

in 1979 to request cooperative testing of a propeller-driven agricultural aircraft 

concept conceived by the AD-1 designer Burt Rutan. The joined wing seemed 

particularly valuable for such an aircraft because the exceptionally rugged structure greatly enhanced the structural “crashworthiness” of the design—always 

a concern for crop-dusting aircraft. Accordingly, Langley tested the design 
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in its 12-foot-low-speed tunnel, and the results encouraged further studies. 

Simultaneously, Stephen Smith, of NASA Ames, and Ilan Kroo and John 

Gallman, of Stanford University, were pursuing derivation of a structural and 

aerodynamic analysis code to ease analysis of joined-wing configurations. Their 

work eventually resulted in a mission-synthesis model that could be used to 

undertake vehicle optimization.64

As well as assisting in vehicle conceptualization, computational-based analysis played a significant role in refining understanding of the joined wing’s aerodynamic performance. Indeed, traditional wind tunnel testing of the joined 

wing was not without difficulty, and the peculiarities of its design made it more 

suitable to the newly emerging field of computational fluid dynamics (CFD). 

In 1985, Wolkovitch explained,

The structural design of joined-wing wind tunnel models has 

been a recurring source of difficulty. The wings of wind-tunnel 

models are typically machined from slabs of uniform (solid) 

material. Hence they do not have the optimum concentration 

of structural material... Relative to comparable “solid” cantilever wings, “solid” joined wings contain less volume of structural 

material, and it is not as well distributed to resist lift loads. The 

problem is compounded by the standard practice of using simple 

beam formulas to calculate stresses in wind tunnel models. This 

is adequate for cantilever wings but is not acceptable for joined 

wings. Any wind-tunnel program involving joined wings must 

include adequate stress analyses by finite-element methods, to 

check model safety and to predict aeroelastic deflections.65

In his advocacy of the joined-wing planform, Wolkovitch argued 

persuasively that

1. The joined wing provides advantages over a conventional wingplus-tail arrangement, including lighter weight and higher stiffness, 

less induced drag, reduced transonic and supersonic drag, and builtin direct lift and sideforce capability.66

2. Experimental data show that the joined wing has good stability and 

control in normal flight and at the stall.

3. The joined wing can provide reduction in parasite drag through 

smaller lifting surface areas, reduced wing-fuselage interference, and 

stability for thin airfoils. These beneficial effects offset the effects of 

lower wing Reynolds Numbers, such that overall savings in parasite 

drag can be achieved.
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4. Although the joined wing is synergistic with new developments 

such as composite materials, laminar flow airfoils, and control 

configured vehicles, it does not depend on new technology. Hence it 

can provide the above advantages with short development times and 

low risk.67

Initial NASA feasibility studies indicated that one of the most promising 

applications of the joined wing was a medium-range commercial jet transport. 

As a result, Agency researchers conducted a transport design study to determine what an optimized joined-wing transport should look like. An additional 

aspect of the design study was to quantify the potential fuel savings offered 

by the joined-wing configuration. An existing aircraft analysis and synthesis 

program, which had been developed to study the effect of tail size and stability 

requirements on direct operating costs of transport aircraft, was modified to 

include structural weight and aerodynamic models suitable for the analysis of 

joined wings. Eleven different design variables were selected for testing with 

the modified analysis and synthesis program. These included wing area, wing 

aspect ratio, wing sweep, wing-thickness-to-chord ratio (commonly expressed 

as “thickness-chord ratio”), wing taper, wing twist, tail area, interwing point 

location, tail-root height, tail twist, and tail taper. The mission requirement 

provided for a flight range of 1,500 nautical miles, a flight speed of up to 

Mach 0.80, and a capacity to carry 155 passengers. A balanced field length 

and second-segment climb were imposed for each selected aircraft configuration. Each candidate was permitted to operate at its best cruising altitude. Two 

aft-mounted engines with moderately high bypass ratios were appropriately 

sized for each design. The aerodynamic analysis used a vortex-lattice model 

of the nonplaner surfaces to compute the trimmed drag and static margin; an 

aerodynamic computation was used to determine the loading for structural 

weight estimation along with a simplified joined-wing structural model that 

was also used for weight estimation; and the high-angle-of-attack load conditions were examined with various fuel and passenger loadings.

The results of the above tests, which were confirmed by a followup study, were:

1. The optimal joined-wing design would exploit the inherently 

improved structural efficiency to increase the span so that the structural weight was comparable to a conventional configuration;

2. The optimum cruising altitude was somewhat higher than conventional transport configurations because of the higher aspect ratio and 

similar wing loading;

3. The wing sweep, wing area, and tail-to-wing area ratio were similar 

to conventional aircraft, and the optimum interwing joint location 

was at approximately 60% of the wing semispan; and
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Thinking Obliquely

Side perspective of the proposed NASA-ACA JW-1 Joined-Wing Research Aircraft, 1987. (NASA)

4. The tail aspect ratio was somewhat higher as a consequence of the 

joint location and tail area.68

Modifying the AD-1 into the Joined-Wing Research Airplane

The goal of the planform design process was to find a joined-wing planform that 

was both representative of a commercial transport and satisfied the geometric 

constraints imposed by the AD-1 fuselage. The NASA Ames design study 

indicated that the basic planform should have the following design values: a 

wing sweep of 30 degrees; a wing aspect ratio of 14; a tail-to-wing area ratio of 

0.30; an interwing joint location at 60 percent of the wing semispan; a static 

margin of 0.35; and a pair of dihedral angles for the wing and tail of 5 degrees 

and –20 degrees, respectively. The AD-1 fuselage, however, imposed several 

constraints on the planform design that would require modification of the 

aircraft. The existing vertical and horizontal tails of the AD-1 would need to be 

removed at a convenient fuselage bulkhead, and a new 15-percent-larger vertical tail would need to be installed 2 feet ahead of the original. The wing sweep 

would need to be increased to 30.5 degrees, and the tail would need to be swept 

forward 32 degrees so that the planform would fit the fuselage and vertical tail 

with the desired center-of-gravity location. Depictions of the former AD-1, as 

modified as the high-aspect-ratio JW-1 variant of the Joined-Wing Research 

Airplane, together with a three-view drawing of the medium-aspect-ratio JW-2 
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Flight Testing and Evaluation of the AD-1

Top perspective of the proposed NASA-ACA JW-1 Joined-Wing Research Aircraft, 1987. (NASA)

Drawing of the proposed NASA-ACA JW-2 Joined-Wing Research Aircraft, from CR 177543, 

1989. (NASA)
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Thinking Obliquely

variant with an interwing joint location at 80 percent of the wing semispan, 

are shown below.

Once the fuselage modifications were determined, the wing and tail incidence 

distribution had to be addressed. The feasibility study assumed a linear wing 

twist to reduce computation time and determined the best twist for the cruise 

design point. A detailed design effort refined the wing incidence distribution to 

include a climb or maneuver design point, stalling characteristics, and fuselage 

constraints. Next, the total wing-system incidence was selected so that high lift 

coefficients for takeoff and landing could be achieved with no fuselage contact 

with the ground. In this regard, it was noted that the AD-1 landing gear was 

very short and that the aft area of the fuselage could contact the ground at 7 

degrees of fuselage rotation. To start the design process, the completed joinedwing planform was used as an input to the MultOp computer program, which 

is an inverse, multilifting surface, vortex-lattice method of solving the incidence 

distribution that produces minimum-trimmed drag at a specified lift coefficient and static margin. As a result, the joined-wing planform was modified 

using 30 spanwise, full-chord panels for the wing and 18 spanwise, full-chord 

panels for the tail. Another important wing-design characteristic that needed 

to be analyzed was the lift-coefficient distribution that occurs near maximum 

lift. Special airfoil sections were designed for the JW-1 using two-dimensional 

airfoil design methods. The design goals for these airfoils were to maintain a 

conservative degree of natural laminar flow at cruise lift coefficients and achieve 

maximum section lift coefficients of 1.5 for the wing sections and 1.0 for the 

tail section. The airfoils, which were constrained to be 14-percent thick, were 

oriented perpendicular to the 25-percent chord line. The airfoils were designed 

using NACA 6-series airfoils that were modified to satisfy design objectives. 

Airfoil shapes were modified and smoothed using the PROFILE program, 

which permits the designer to add various analytical shape functions to alter an 

airfoil shape subject to a thickness constraint. Candidate airfoils were analyzed 

at their design-lift coefficient using PROGRAM H to predict forces, moments, 

pressure distribution, and the extent of laminar flow on the upper and lower 

surfaces. This program is a two-dimensional airfoil analysis program that uses 

the full-potential equations and the von Kármán integral boundary-layer solution. The CLMAX vortex-panel code was used to estimate the maximum lift 

coefficient of each airfoil.69

A one-sixth-scale wind tunnel model of the joined-wing aircraft was built 

at NASA Ames using the fuselage of the existing AD-1 wind tunnel model. 

This model was tested in the Ames 12-Foot Pressure Wind Tunnel to measure 

aerodynamic performance, stability, and control characteristics. The model was 

supported on a swept blade–type strut mounted on a bipod support system. The 

blade was swept back 50 degrees from the normal axis of the model and was 
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Flight Testing and Evaluation of the AD-1

contoured with a 15-percent-thick low-speed airfoil. The model had removable 

outer wing panels to represent three different joined-wing configurations—designated JW-1, JW-2, and JW-3.

The high-aspect-ratio JW-1 had outer wing panels installed at the interwing 

joint located at 60 percent of the semispan; the medium-aspect-ratio JW-2 wing 

had shorter outer panels so that the joint was located at 80 percent of the semispan; and the low-aspect-ratio JW-3 wing configuration had the outer panels 

removed so that the interwing joint was located at 100 percent of the semispan. 

The wing geometry was produced by locating each airfoil perpendicular to the 

25-percent chord line and lofting straight lines between these defining sections. 

The joined-wing configurations were fitted with five control surfaces on each 

side, representing various arrangements of flaps, elevators, and ailerons. The 

vertical tail was fitted with a conventional rudder. The wings were designed so 

that small underside leading-edge fences (called vortilons) could be mounted at 

the three span stations, and the engine pylons were designed so that speedbrakes 

could be installed between the fuselage and nacelles.70

The testing conditions and procedures were done at the following numbers: 

Mach number of 0.35; a test Reynolds number of approximately 2.2×106/foot; 

a chord Reynolds number of approximately 1.0×106; the angle of attack was 

varied from –7 degrees to 14 degrees, and the angle of sideslip was varied from 

–5 degrees to +2.5 degrees. The testing results found that the joined-wing aircraft 

had acceptable levels of stability and control, especially with the vortilons 

installed, and that all of the control surfaces maintained sufficient effectiveness 

to control the joined-wing aircraft well above the stall angle of attack. A small 

speedbrake arrangement installed on the engine pylons was found to produce 

a significant amount of drag, which provided a convenient means of glidepath 

control for landing.71

Smith, Cliff, and Kroo noted that considerable attention was given to 

the stall characteristics during the design of the JW-1 because of its highaspect-ratio swept wing without any leading-edge high-lift device. Wind tunnel 

data were used to evaluate stall characteristics by examining the change in pitching moment caused by small changes in angle of attack from a trimmed condition 

near stall. The tests revealed that the JW-1 model had a minor, unstable pitchup 

at stall that was addressed in the design phase by installing simple vortilons on 

the wings. The final conclusion in regard to these tests and the overview of the 

engineering team’s testing of the JW-1 model was that “Good agreement of the 

test data with the design predictions confirmed that the relatively simple design 

methods used for the JW-1 are suitable for joined-wing configurations.”72
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Thinking Obliquely

The three JW-1, -2, and -3 wing planform configurations, from TM 101083, 1989. (NASA)

“A Sorry State of Affairs”: Termination of the AD-1/JW-1 Program

Due primarily to financial concerns relating to ACA Industries running out of 

SBIR funds to fabricate the JW-1 and to more limited issues involving operational safety and airworthiness concerns regarding the modified AD-1 aircraft, 

NASA terminated the joined-wing program just prior to the start of the AD-1 

aircraft modification phase. In regard to program costs, William Ballhaus, Jr., 
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noted in a June 1987 memorandum to NASA Headquarters that NASA Ames 

had examined a number of different management approaches to minimize the 

cost of supporting the program. NASA Ames had originally estimated that 

costs to support the program would be $7 million, which would include staff 

time, the cost of additional independent analysis, and various ground tests to 

ensure that the vehicle was airworthy. He added that a project team of 12 to 

15 personnel would be necessary to work with the contractor and conduct or 

participate in various tests and analysis to establish the airworthiness of the 

vehicle to NASA standards. Ballhaus added that this total investment would 

be way out of proportion to the small investment by SBIR to complete the 

program. He noted further that a second study to reduce the cost and staff 

decreased the “bare bones” commitment to $1.5 million and fewer than 10 

staff members, but even at this level, the approach was unacceptable. The letter 

contained a proposed solution to permit the program to continue by giving 

the problem of flight safety responsibility to ACA Industries. Ballhaus noted 

that “this is the only viable solution to our problem because even if we were 

provided the necessary funding, we could not properly staff the project without 

taking personnel from higher priority programs.”73 ACA initially considered 

assuming this responsibility but later said they were not able to accept the 

liability. Ballhaus also outlined some of NASA Ames’s concerns regarding the 

use of the AD-1, stating that

[t]he SBIR proposal of ACA Industries to construct and test a 

Joined Wing Aircraft by modifying the NASA AD-1 aircraft was 

approved approximately a year and a half ago. Since that time 

the contractor has completed a preliminary design and is currently finalizing his design in preparation for modification of the 

AD-1 to a Joined Wing Aircraft. We at Ames have supported 

ACA Industries with wind tunnel tests and independent analysis. 

We have also assumed Project Management responsibilities for 

NASA’s efforts in the program and more notably also assumed 

flight safety responsibility. We did not take on flight safety responsibility without some soul searching, but we believed that we 

could not absolve ourselves of that responsibility since NASA 

was sponsoring the program. The magnitude of the funding and 

resource problem created by assuming flight safety responsibility 

is now very apparent and we believe, not acceptable.74

In regard to safety and his concerns about being overly cautious, Ballhaus 

concluded his memo by stating the following:
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Thinking Obliquely

[w]hether we care to admit it or not, the current post-Challenger

environment will not allow NASA to take risks particularly with 

flight vehicles. NASA cannot survive many more flight accidents. 

This is really a sad situation for NASA. If you are not taking some 

risks, you are not taking big enough steps. You are not challenging the technology. If this situation continues, we will have to 

rely on someone else like ACA [NASA’s industry partner in the 

joined-wing program] or DARPA [Defense Advanced Research 

Projects Agency] to take the risks and make the breakthroughs. 

A sorry state of affairs.75

In a September 12, 1989, memo from Milton O. Thompson, Dryden’s chief 

engineer, to Theodore G. Ayers, Dryden’s deputy director for flight operations 

and research, Thompson recommended that the AD-1, due to airworthiness 

concerns, be grounded and used only for display purposes. In his memo, 

Thompson noted,

The AD-1 was last flown on Aug 7, 1982, over seven years ago. 

Since that time, the aircraft has been shipped around the country 

on numerous occasions, for use as a wind tunnel model and for 

static display. Although some care has been taken to avoid damaging the aircraft during these movements, we are aware of several 

incidents in which the vehicle was damaged during shipping... 

[The AD-1] has served its original purpose. The Government has 

received a substantial return on its investment and the vehicle 

should now be retired.76

Thus, as NASA’s research on joined-wing planforms went forward, the 

AD-1 did not share in the journey.77 Originally placed in storage on August 

11, 1982, the AD-1 was transferred to Ames, where it remained on display 

until it was transferred, pursuant to a loan agreement, to the Hiller Aviation 

Museum in San Carlos, CA. There, it remains as of the date of this writing.
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Endnotes

1. W.H. Andrews et al., “AD-1 Oblique Wing Aircraft Program,” SAE 

International, TP 801180 (1980), 3–4.

2. Ibid., 3–5.

3. Gene J. Matranga, “May 16, 1979, Memorandum to the Director of 

Dryden Flight Research Center,” NASA Dryden History Office, box 

L3-4-4B.

4. NASA Official Biography, “NASA People: Thomas C. McMurtry,” 

NASA Dryden Flight Research Center Web site, http://www.nasa.

gov/centers/dryden/news/Biographies/Pilots/bd-dfrc-p011.html, accessed 

November 28, 2011.

5. NASA Official Biography, “NASA People: Fitzhugh L. Fulton Jr.,” 

NASA Dryden Flight Research Center Web site, http://www.nasa.

gov/centers/dryden/news/Biographies/Pilots/bd-dfrc-p005.html, accessed 

November 28, 2011.

6. Richard “Dick” Gray served as an aerospace research pilot at NASA’s 

Johnson Space Center from November 1978 until November 1981, 

when he transferred to NASA’s Ames-Dryden Flight Research 

Facility. In addition to one flight, as a guest pilot, on the AD-1 

Oblique Wing Research Aircraft, Gray was a pilot for the F-8 Digital 

Fly-By-Wire and Pilot Induced Oscillations investigations. He also 

had flight experience flying the F-104 and F-15. He was fatally 

injured when his T-37 jet airplane crashed on November 8, 1982, 

during a spin-training exercise. Gray was a remarkable airman and 

one of the Navy’s earliest (and finest) F-14 pilots, and his passing 

was a great tragedy.

7. See “Ames Dryden AD-1 (N805NA) Flight Log,” Peter W. Merlin, 

compiler, December 2002, NASA Dryden History Office, box 

L1-3-7B, folder 1.

8. “AD-1 Makes Farewell Flight to Oshkosh,” Dryden X-Press, NASA 

Dryden Flight Research Center, Edwards AFB, August 20, 1982.

9. Ibid.

10. Thomas J. Beutner and Richard P. Hallion, telephone conversation, 

December 7, 2011.

11. Joseph Chambers to Tom McMurtry (with copy to author), e-mail 

message, October 24, 2011.

12. These reports are in the historical archives of the DFRC.

13. The following items were excerpted from monthly “Projects Update” 

documents located in the NASA Dryden History Office archives, in 

box L3-4-4B. The citations to follow are identified by title and date.
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14. “Projects Update—December 1979,” January 14, 1980, 4–5.

15. “Projects Update—January 1980,” February 1, 1980, 4–5.

16. “Projects Update—March 1980,” April 17, 1980, 6.

17. “Projects Update—April 1980,” May 12, 1980, 3–4.

18. “Projects Update—May 1980,” June 11, 1980, 4–5.

19. “Projects Update—September 1980,” October 9, 1980, 4.

20. “Projects Update—November 1980,” December 8, 1980, 4.

21. “Projects Update—January 1981,” February 6, 1981, 5.

22. “Projects Update—February 1981,” March 9, 1981, 5.

23. “Projects Update—March 1981,” April 8, 1981, 4.

24. “Projects Update—April 1981,” May 8, 1981, 4–5.

25. “Projects Update—May 1981,” June 9, 1981, 3.

26. “Projects Update—June 1981,” July 7, 1981, 3.

27. “Projects Update—July 1981,” August 10, 1981, 4–5.

28. “Projects Update—August 1981,” September 9, 1981, 3.

29. “Projects Update—September 1981,” October 8, 1981, 4.

30. “Projects Update—January 1982,” February 10, 1982, 4.

31. “Projects Update—March 1982,” April 9, 1982, 3.

32. “Projects Update—April 1982,” May 10, 1982, 6.

33. “Projects Update—May 1982,” June 10, 1982, 3.

34. “Projects Update—June 1982,” July 12, 1982, 6.

35. “Projects Update—July 1982,” August 9, 1982, 5.

36. “Projects Update—August 1982,” September 10, 1982. Apparently, 

Langley did not carry through with the plan to wind tunnel test the 

AD-1 as Center records reflecting such tests taking place have not 

been located. The author thanks Joseph Chambers for his tireless 

efforts to sort out the Langley side of this story.

37. Thomas C. McMurtry, Alex G. Sim, and William H. Andrews, 

“AD-1 Oblique Wing Aircraft Program,” AIAA paper no. 81-2354, 

presented at the first AIAA–SETP–SFTE–SAE–ITEA–IEEE Flight 

Testing Conference, Las Vegas, NV, November 11–13, 1981.

38. As recalled by Richard P. Hallion, who attended the presentation.

39. McMurtry, et al., “AD-1 Oblique Wing Aircraft Program,” 1.

40. Ibid., 2.

41. Ibid., 4.

42. Alex G. Sim and Robert E. Curry, “Flight Characteristics of the 

AD-1 Oblique-Wing Research Aircraft,” NASA TP 2223 (March 

1985). The paper was completed in February 1983, published in 

March 1985, and held for general release until March 31, 1987.

43. Ibid., 4.
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44. Ibid., 6.

45. Ibid., 4–7.

46. Ibid.

47. Ibid., 7.

48. Ibid., 8.

49. Ibid.

50. Ibid.

51. Ibid.

52. Ibid.

53. Ibid., 9.

54. Ibid.

55. Ibid., 9–10.

56. Robert E. Curry and Alex G. Sim, “In-Flight Total Forces, 

Moments, and Static Aeroelastic Characteristics of an Oblique-Wing 

Research Airplane,” NASA TP 2224 (1984). This represented a final 

supplement to their earlier AD-1 studies. It was written in June 

1983, published in October 1984, and held for general release until 

October 31, 1985.

57. Ibid., 9.

58. Andrews and Smith, “AD-1 Oblique Wing Aircraft Program,” 6–7.

59. In an exchange of e-correspondence with the writer, Stephen C. 

Smith, a NASA aeronautical research engineer extensively involved 

in the joined-wing project, noted that in parallel with the NASA 

joined-wing project, there was substantial conceptual design optimization studies under way with Ilan Kroo and John Gallman, both at 

Stanford University, and Stephen C. Smith, at NASA. He added that 

John Gallman later joined NASA and, along with Smith, completed 

the research studies on the joined wing.

60. S.C. Smith, S.E. Cliff, and I.M. Kroo, “The Design of a JoinedWing Flight Demonstrator Aircraft,” AIAA paper no. 87-2930 

(1987), 1.

61. Julian Wolkovitch, “The Joined Wing: An Overview,” AIAA paper 

85-0274 (1985), 20–21.

62. For a discussion of the joined wing, see Joseph R. Chambers, 

Innovation in Flight: Research of the NASA Langley Research Center 

on Revolutionary Advanced Concepts for Aeronautics, SP-2005-4539 

(Washington, DC: NASA, 2005), 227–244.

63. Wolkovitch, “The Joined Wing: An Overview.”

64. Chambers, Innovation in Flight, 233–234.

65. Ibid. Wolkovitch added that A. Shyu and H. Miura of NASA Ames 

performed comprehensive structural analyses of joined wings using 
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the EAL, SPAR, and NASTRAN computer programs. He noted that 

buckling was checked using the differential stiffness option of the 

NASTRAN computer model and NASA Ames was able to obtain 

usable wind tunnel findings.

66. Direct lift and sideforce control were topics of great interest in the 

late 1970s and into the 1980s, exemplified by research programs 

such as the F-16 Control Configured Vehicle (CCV); the Advanced 

Fighter Technology Integration (AFTI) F-16 (later Advanced Flight 

Technology Integration); and the NF-15B STOL Maneuvering 

Technology Demonstrator (the “Agile Eagle”).

67. Ibid., 21–22.

68. Smith et al., “The Design of a Joined Wing Flight Demonstrator 

Aircraft,” 2–3.

69. Ibid., 2–6.

70. Stephen C. Smith and Ronald K. Stonum, “Experimental 

Aerodynamic Characteristics of a Joined-Wing Research Aircraft 

Configuration,” NASA TM 101083 (April 1989), 1–2.

71. Ibid., 9–10.

72. Smith et al., “The Design of a Joined Wing Flight Demonstrator 

Aircraft,” 7.

73. William F. Ballhaus, Jr., memo to NASA Headquarters, June 11, 

1987, NASA Dryden History Office, box L1-5-4, folder 8.

74. Ibid.

75. Ibid.

76. Milton O. Thompson memo to Theodore G. Ayers dated September 

12, 1989, Milton O. Thompson papers, NASA Dryden History 

Office, box L1-5-8, folder 16. Unfortunately, Thompson died before 

he could be interviewed for this project, but Richard P. Hallion, who 

knew him well, is convinced that he must have been upset that the 

joined-wing AD-1 did not go forward. Thompson, a former Dryden 

research pilot of broad experience and great influence, was a strong 

advocate of such experimental programs and a veteran of several of 

them, including the Parasev and M2-F1 lifting bodies. He had advocated for many in his career. In his memo, he did acknowledge “a 

recurring interest” in modifying the AD-1 to a joined-wing configuration, which likely reflected his own wistful hopes.

77. See, for example, John W. Gallman, Stephen C. Smith, and Ilan 

M. Kroo, “Optimization of Joined-Wing Aircraft,” Journal of 

Aircraft 30, no. 6 (November–December 1993): 897–905; John H. 

McMasters, David J. Paisley, Richard J. Hubert, Ilan Kroo, Kwasi K. 

Bofah, John P. Sullivan, and Mark Drela, “Advanced Configurations 
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Flight Testing and Evaluation of the AD-1

for Very Large Subsonic Transport Airplanes,” NASA CR 198351 

(October 1996); and Robert C. Scott, Mark A. Castelluccio, David 

A. Coulson, and Jennifer Heeg, “Aeroservoelastic Wind-Tunnel 

Tests of a Free-Flying, Joined-Wing SensorCraft Model for Gust 

Load Alleviation,” NASA Technical Reports Server (NTRS) Doc. 

ID 20110009997, Report/Patent No. NF 1676L-12256 (2011), 

http://ntrs.nasa.gov, last accessed November 30, 2011. This does not 

include numerous academic studies on the subject. The previously 

cited Chambers, Innovation in Flight, has a concise summary of 

NASA work after the AD-1 effort.
142

Rockwell concept for a Mach 2+ oblique-wing, twin-engine, two-seat, carrier-based, multimission fleet air defense fighter for the U.S. Navy’s VFMX study effort, 1985. (NASA)
143

CHAPTER 5

Beyond the AD-1

The F-8 Oblique Wing Research Aircraft

Coincident with NASA work on the AD-1, various companies had been 

studying possible application of the oblique wing for commercial and military aircraft. One such firm was Rockwell International. Rockwell was a 

company with a distinguished lineage, going back to the pre–World War 

II era and development of North American Aviation’s T-6 trainer and the 

B-25 bomber. Then came the legendary P-51 Mustang, arguably the finest 

all-around, propeller-driven fighter ever built, and the postwar (and equally 

legendary) F-86 Sabre, of Korean War fame. Among other accomplishments, 

the company had produced the F-100, America’s first supersonic jet fighter; 

the hypersonic X-15, its most successful research airplane; the Apollo spacecraft and the Saturn’s engines; the OV-10 counterinsurgency airplane; the B-1 

strategic bomber; and, of course, the Space Shuttle orbiter, its best-recalled 

achievement. But in the late 1970s and 1980s, it had its share of disappointments. Rockwell was unsuccessful in entering the stealth field, lost out to 

Grumman to build what became the X-29, and confronted a full measure of 

challenges with its B-1 and the Space Shuttle. And then there was the abortive 

XFV-12A thrust-augmented wing (TAW).

An ambitious attempt to produce a complex, experimental, vectoredthrust-and-augmented-lift Mach 2+ vertical/short takeoff and landing (V/

STOL) fighter for the Navy, the XFV-12A used off-the-shelf components 

(including the nose of an A-4 Skyhawk and the basic wing structure and 

inlets of the F-4 Phantom II) joined to a complex suction and blowing system 

involving multiple vanes and flaps—the whole conglomeration powered by a 

single large jet engine. But when installed in the Impact Dynamics Research 

Facility (the former lunar landing test rig) at Langley Research Center for testing in 1978, its actual flow-augmented thrust proved insufficient for vertical 

flight. The sight of the huffing and puffing design, engine thundering away, 

inspired skeptics of the concept to unkindly dub its much-trumpeted thrustaugmented wing the “thrust-tormented wing.”1

 The program died in 1981.
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The North American–Rockwell XFV-12A augmented-wing V/STOL test bed at Columbus, OH, 

with its wing in VTOL configuration, 1978. (USN)

Rockwell hoped to have better luck with Jones’s oblique wing, and it 

launched a study program for a Mach 1.8 Fleet Air Defense fighter (to meet 

a proposed Navy requirement to succeed the F-14) using either conventional 

bilaterally symmetric variable-sweep wings or an oblique wing, and it drew 

heavily on the aerodynamic design of the much larger variable-sweep B-1 

bomber. Studies indicated that the oblique wing would be lighter and have 

greater range than an equivalent symmetrical-sweep design.2 In retrospect, this 

large twin-engine, two-seat aircraft (dubbed “VFMX” after the Navy’s shorthand for the program effort) was not in congruence with the Navy’s plan for 

its fighter future, a future ultimately based on derivatives of the conventional 

McDonnell-Douglas F/A-18 Hornet. Nevertheless, for a brief period, the 

VFMX and Rockwell’s design study influenced the course of NASA research 

on oblique wings.

One result of the Navy-Rockwell studies was a recommendation that NASA 

and the Navy jointly examine oblique-wing technology, leading to issuance 

of a joint NASA-Navy Memorandum of Understanding (MOU) executed 

in May 1984. From this, in November that year, evolved the Oblique Wing 

Research Aircraft program, which was created to develop and flight-test a 

supersonic aircraft equipped with an oblique wing. As mentioned in chapter 

2, since the early 1970s, NASA already had anticipated the potential need for 

a supersonic research aircraft and had explored the possibility of using either 
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Beyond the AD-1

the NASA Digital Fly-by-Wire F-8 research aircraft modified with an oblique 

wing or one of Dryden’s F-104s. Of the two, the F-8 made greater sense, given 

the location of its wing and the ease with which it could be modified as well as 

its electronic (if rudimentary, at that point) fly-by-wire flight control system.

Rockwell Confirms the F-8’s Suitability as a Supersonic OWRA

Accordingly, NASA contracted with Rockwell International for a feasibility 

design study of an F-8 Oblique Wing Demonstrator. Rockwell confirmed 

that the F-8 provided a unique capability in that its general configuration 

would easily allow modification for an oblique wing. The purpose of the study 

was to show the feasibility of modifying NASA’s F-8 fly-by-wire aircraft for 

demonstration of high-speed oblique-wing technology. The study defined the 

size, shape, arrangement, and modifications of the demonstration aircraft as 

well as the limitations to adapting the F-8 DFBW aircraft to an oblique-wing 

demonstrator. It also addressed the design constraints of divergence, flutter, 

strength, minimum weight, control trim, and roll-pitch coupling. Rockwell 

noted that this was twice as many design constraints as required for other wing 

configurations. A subsystem feasibility review was conducted in order to study 

proposed modifications of flight control and supporting subsystems on the 

NASA F-8 aircraft. The study used as much of the F-8’s existing subsystem 

hardware as possible within the requirements of still satisfying the goals of the 

demonstration program. Two finite element models were developed to support 

the design and analysis effort of the F-8 oblique wing.

Researchers of the F-8 OWRA sought the following goals:

1. The successful design, fabrication, and flight test of a composite, aeroelastically tailored, high-aspect-ratio wing at supersonic, 

medium-altitude flight conditions.

2. The confirmation of predicted performance benefits through a 

combination of experimental and analytical results.

3. The achievement of satisfactory handling qualities at combat conditions and improved low-speed characteristics compared to presentgeneration naval combat aircraft.3

The specific aerodynamic design goals of the F-8 OWRA were to eliminate 

roll trim at the design-point supersonic cruise (M=1.4 at 40,000 feet), minimize sideforce at the design point, minimize roll trim throughout the flight 

envelope, provide a stable aircraft at all flight conditions, and minimize trim 

drag throughout the flight envelope.4

The wing planform developed for the study differed from the transport 

wing explored earlier with the AD-1 and first postulated for the F-8 over a 

decade before. Instead of an elliptical planform, it was a high-aspect-ratio, 

high-thickness-ratio oblique wing with a straight leading edge and strongly 
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Thinking Obliquely

Rockwell Concept for an oblique-wing F-8 test bed, from TP 2874, 1988. Note the differences 

between this oblique-wing planform (with a straight leading edge and highly tapered trailing 

edge) and earlier 1970s concepts for an elliptical oblique-wing modification to the F-8. (NASA)

tapered trailing edge designed for two primary wing-angle positions—0 degree 

(straight) and 65 degrees (swept).

The underlying Navy Fleet Air Defense mission requirements for the airplane 

were long loiter time, high-speed dash, and carrier suitability. Aerodynamically, 

these requirements represented low-subsonic vortex drag, low-volume wave 

drag, and a high lift capability.

Rockwell’s February 1, 1984, final report concluded:

1. The F-8 Oblique Wing Demonstrator has been preliminarily 

analyzed by the k-method for flutter and divergence and by the 

p-method for rigid body-wing structural mode coupling assuming a 

flexible wing and pivot, but with a rigid fuselage and empennage.

2. The structural modes have adequate flutter speed margins with 

respect to the critical flight condition of M=0.95 at sea level for the 

three skew angles analyzed (Ʌ=0, 45, and 65 degrees).

3. Adequate divergence speeds were calculated for yaw angles 45 and 65 

degrees with respect to M=0.95 at sea level. For 0-degree skew, adequate 

divergence speeds were calculated with respect to M=0.60 at sea level.

4. Dynamic analyses of the flexible F-8 Oblique Wing Demonstrator 

with the wings swept 65 degrees with and without SAS [Stability 

Augmentation System] operating revealed no tendency toward bodywing structural coupling instabilities at the high dynamic pressure 

M=0.90 flight conditions investigated. Since dynamic pressure is the 
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Beyond the AD-1

Wing geometry at maximum and minimum sweep, and basic structural and internal layout, for a 

modified F-8 Oblique Wing Research Aircraft, from TM 86808, 1986. (NASA)

key aeroelastic parameter, these M=0.90 results are judged to be representative of the maximum Mach number flight conditions where 

the same high dynamic pressure exists.

5. More detailed analyses should be performed including flexible 

fuselage and empennage. The influence of fuselage should be 

investigated.

6. Although not considered as critical as the M=0.95 condition, analysis should be performed for supersonic mach numbers to determine 

flutter margins and characteristics.5

Rockwell noted that the above demonstrations were “to be achieved in a 

minimum cost program commensurate with the overall objectives [and that] 

the output of the program will be the confidence required to incorporate this 

technology in a future operational weapon system.”6

Oblique Wing Pros and Cons in Light of the AD-1 Experience

Developing a supersonic oblique-wing aircraft was eased by the experience of 

the AD-1 and the growing amount of tunnel and computational fluid dynamics data on oblique-wing performance, but it still involved significant challenges that made it far from a certain thing.

Four years after the AD-1 ceased flying, Ilan Kroo identified the challenges 

remaining after 30 years of technology development.7 He noted that the results 
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Thinking Obliquely

of the previous 30 years of research and testing illustrated the importance of the 

interaction between aerodynamics, structures, and controls in the overall design 

process. Kroo provided a concise assessment of the oblique wing, drawn from 

its evolution and historical experience, again noting both its advantages and 

ongoing challenges:

1. The oblique wing has reduced supersonic wave drag as compared with 

a conventional symmetrically-swept design. Fundamentally, this is due 

to the increased length of an oblique wing, which is twice as long as a 

symmetric wing. As the sweep angle increases, however, the differences 

are smaller so that the oblique wing might be more desirable at lower 

Mach numbers.

2. “In addition to the drag savings associated with the increased wing 

length, wing wave drag is also reduced by eliminating the ‘kink’ at the 

wing centerline where isobars are unswept and drag may be increased 

considerably. This difference is less apparent for wing and fuselage 

combinations, although even in this case the oblique wing system does 

not require such severe changes to fuselage cross-section to obtain a 

desirable area distribution.”

3. There is also an important practical advantage provided by the utility 

of a variable geometry arising from the mismatch of configuration 

optimized for low speed and high speed flight. A variable sweep 

design permits exceptional performance at low speeds with important 

implications on reserve fuel requirements. The oblique wing provides 

a method of achieving a versatile and efficient aircraft over a wide 

range of operating conditions with smaller aerodynamic and structural 

penalties than with conventional variable symmetric sweep.8

In regard to advantages of oblique-wing variable swept aircraft over conventional variable swept aircraft, Kroo noted the following:

Only a single pivot structure is required and the pivot is loaded 

primarily in tension, while each pivot of a conventional design must 

support the full root bending moment of each semispan. Similarly, 

the actuator loads are reduced since the aerodynamic forces on each 

side of the aircraft are balanced.

 Additional savings in structural weight and manufacturing 

simplicity accrue from the absence of a “kink” at the center section of the wing. This enables tip-to-tip composite material layups, 

straight, unbroken spars, and reduced fuselage carry-through loads.

 Furthermore, the centroid of the wing area need not change 

position as the wing is swept obliquely while symmetric change of 

sweep produces a rearward shift in center of pressure. This shift is in 
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the same direction as the shift associated with supersonic flow and 

results in the well-known problem of excessive longitudinal stability 

for the variable sweep wings. The problem has been addressed in 

several ways, including outboard pivots, glove vanes, translating pivot 

mechanisms, and others—all of which introduce some mechanical 

complexity or reduce the effectiveness of the wing sweep.

 Finally, the high wing oblique design enables the wing to be 

“overswept” to angles that are not of use for efficient flight but 

which provide convenient storage and a low “spotting factor.” 

[The latter is an extremely important requirement for carrierbased aircraft, as even on a so-called “supercarrier,” flight deck 

and hangar deck space is at a premium].9

But as well as enumerating the advantages of the oblique wing, Kroo indicated the difficulties in acceptance of the concept, noting that while the oblique 

wing clearly offered many advantages, it had not won acceptance for an operational design. Kroo believed a combination of factors had worked to delay its 

introduction into operational service, noting the following:

First the concept is extremely unconventional. There is a lack 

of precedent for asymmetrical designs leading to the perception 

of high risk, and the advantages, although numerous, are of a 

sort which are seldom properly recognized in a conceptual design 

study. Several more fundamental technical difficulties do, however, accompany the oblique wing concept and it is these that 

current research efforts are focused.

 The nearly complete decoupling of the longitudinal and lateral motions which arises in the case of symmetric aircraft in 

normal flight greatly simplifies their control. In the case of oblique 

wing aircraft, the motions are coupled by aerodynamic and inertial moments, requiring a non-intuitive combination of control 

inputs to produce desired maneuvers. This situation constituted 

a major obstacle to oblique wing development thirty years ago, 

but the development of automatic control systems has reduced 

the problem to the more tractable challenge of control law design.

 Another factor partially responsible for retarding the development of oblique wing aircraft was the concern over undesirable aeroelastic effects.... The phenomenon was investigated 

analytically and in free-to-roll wind tunnel tests at NASA Ames 

Research Center in the 1970s, demonstrating stable, controllable properties well above the clamped divergence speed. Thus, 
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Thinking Obliquely

while aeroelasticity still introduces some complexity in control 

law design (rolling and pitching moments vary with load factor), 

and some dynamic instabilities are possible at higher dynamic 

pressures, the problems are not as severe as was first imagined.10

Kroo raised the three following questions in his 1986 paper: Could a control 

system be devised that would provide good, not just flyable, handling qualities? 

Are aeroelastic and structural considerations likely to be a problem at supersonic speeds and high dynamic pressures? Can an oblique-wing airplane truly 

operate efficiently over a wide envelope suggested by the conceptual design 

studies? He answered these questions by stating: “Sponsored jointly by NASA 

and the Navy, the Oblique Wing Research Aircraft Program is intended to 

answer these questions and provide the basic technology necessary to implement this innovative concept.”11

The F-8 OWRA Program

Following the numerous theoretical studies, wind tunnel tests, low-speed flight 

models, and, finally, the low-speed piloted demonstrator—the AD-1—NASA 

was well prepared to assist the Navy and Rockwell International in developing 

an oblique-wing supersonic aircraft using an F-8 airplane. A paper outlining 

the program objectives, the testing and experiments to be conducted, and 

the program schedule was prepared by Glenn B. Gilyard, NASA Oblique 

Wing Research Aircraft program chief engineer.12 The specific objectives of the 

program were to establish the technology necessary to translate oblique-wing 

theoretical and experimental results into practical, mission-oriented designs; 

design, fabricate, and flight test an oblique-wing aircraft throughout a realistic 

flight envelope; and develop and validate design and analysis tools for asymmetric aircraft configurations. Based on the work of the AD-1 program that had 

preceded the OWRA program, NASA engineers considered an oblique-wing 

configuration to be well suited for a Navy Fleet Air Defense mission and for 

a civilian supersonic transport. Accordingly, the program was directed toward 

the development and flight testing of a full-scale supersonic oblique-wing 

demonstrator that would address key technological challenges.13

As noted above, theoretical studies had indicated that in supersonic conditions, the oblique wing has a significant advantage over symmetrically swept 

wings due to less wave drag because the wing volume is distributed over a 

greater length. In addition, an oblique-wing configuration does not produce 

the aerodynamic center shift that occurs in a symmetrically swept configuration. Both trim drag and tail loads are reduced, thus resulting in a lighter 
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Beyond the AD-1

F-8 OWRA configuration model depicted in flight, 1985. Note the “mirror image” wing orientation contrasted to F-8 OW studies a decade earlier, as well as its nonelliptical planform. (NASA)

structure and elimination of center-of-gravity control as a function of wing 

sweep. Also, an oblique-wing configuration has some significant structural 

advantages over a symmetrically swept-wing configuration. One pivot point, 

as opposed to two, results in cost and weight reduction and minimizes bending 

and torque loads transmitted through the pivot.

Preparation for the proposed F-8 OWRA required undertaking a variety of 

tests and experiments that were to be followed by others once it entered construction and proceeded into flight testing. These tests included the following:

1. Conducting a number of unsteady pressure measurement experiments to follow up on the excellent test results that had been 

obtained using an F-15 experimental aircraft. The F-15 was also 

used for unsteady pressure transfer function analysis.

2. Since the unique aerodynamic characteristics of oblique-wing 

configurations have the potential for producing unusual flutter-type 

characteristics and other instabilities, a flutter-model wind-tunnel 

test was planned to provide data for validation of aeroelastic analysis 
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Thinking Obliquely

Load advantages of a single-pivot oblique wing over a dual-pivot, symmetrical variable-sweep 

wing. (NASA) 

codes prior to the first test flight and to support an efficient and 

rapid envelope-clearing process. There were also tentative plans to 

obtain limited unsteady pressure measurements for both code validation and correlation with flight results. In this regard, an interdisciplinary analysis code (STARS) capable of performing flutter and 

aeroservoelastic analysis was developed.

3. It was also noted that as the angle of attack increased, the F-8 

OWRA would exhibit nonlinearities in all flight axes—at high 

wing sweeps the increase in spanwise flow and the formation of a 

leading-edge vortex can occur at relatively low angles of attack (6 to 

8 degrees). Due to the asymmetry of the vehicle, these effects will 

not be balanced in the lateral directional axis. Furthermore, at higher 

angles of attack, areas of spanwise flow also form in an asymmetric 

pattern, generally progressing from the trailing wingtip. It addition 

to the above characteristics, which impact vehicle flight dynamics, 

other unusual features, including the interaction of parallel spanwise 

vortices on the leading wing panel, have been observed in water tunnel studies. Due to the above, program engineers determined that 

additional water tunnel studies needed to be undertaken. To address 

the above issues, a computational fluid dynamics analysis was under 
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Beyond the AD-1

way at Ames in Moffett Field, CA, to develop a Reynolds NavierStokes solution of the complete vehicle. During the flight-test 

program, unsteady pressure data would be used to identify vortex 

and regions of separate flow.

4. NASA project engineers also noted that an accurate determination of the deflected wing shapes in flight was required to validate the wing stiffness and load distribution predictions, which, 

because of the wing’s unconventional attitude, could produce 

some unpredicted pressure distributions. Accordingly, the objective of these tests was to evaluate the ability of analytical codes to 

predict structural-loads deflections and pressure distributions. The 

approach was to measure in-flight deflections to correlate with 

predictions and define in-flight shape for correlation pressure data 

with CFD codes.

Instrumentation for Unsteady Aerodynamics 

and Aeroelastic Research

The F-8 OWRA would, of course, differ considerably from the basic F-8 

airframe. A variable skew wing and pivot assembly would replace the F-8’s 

variable-incidence high wing. The original mechanical flight control system 

was completely removed. The existing all-moving F-8 horizontal stabilizer, 

operated symmetrically for pitch control, was to be modified to operate differentially for roll control as well, giving the airplane a so-called rolling tail, 

like the X-15, for use when the wing was so sharply swept that it could not 

employ wing ailerons for roll control. The modified flight control system 

included appropriate sensor sets, triplex control primary and backup digital 

computers, interface units, and secondary actuators that provided the commanded inputs to the primary actuators.14

The F-8 would, like all research airplanes, itself function as a research 

instrument, using the sky as its laboratory. Accordingly, NASA engineers 

planned to instrument it carefully to address the issues discussed above and 

others as well. In particular, fulfilling its role as a test bed for the examination of unsteady aerodynamics, it would have three special instrumentation 

systems for surveying unsteady pressures, flutter, and deflections.15

For measurement of unsteady pressures, researchers planned to install 

a pressure-sensing system capable of measuring both static and unsteady 

pressures via electronically scanned pressure modules arrayed in front of 

the forward-wing spar and aft of the rear-wing spar. They were particularly 

interested in studying flow effects and interactions when the wing was fully 

swept to 65 degrees with the left outer wing nearly overlaying the left horizontal stabilizer, and so in addition to the pressure orifices located in the 
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Thinking Obliquely

Flow distribution around a model of the F-8 Oblique Wing Research Aircraft with an experimental 

Ames wing design having unsymmetrical tip shapes, 1984. (NASA)

wing, pressures would be measured along two chord locations on the left 

horizontal tail.

To measure modal response and correlate predicted with actual flight-test 

results, the F-8 OWRA would have an array of accelerometers installed in 

the wing, fuselage, and left horizontal stabilizer. These would be employed 

to identify bending and torsion of the fuselage, leading-edge suction forces, 

and in-plane wing motions, contributing to understanding the oblique wing’s 

flutter and aeroservoelastic stability characteristics.

The F-8 OWRA would also have an imaginative electro-optical flightdeflection measurement system to evaluate bending and twisting of the wing. 

Light-emitting targets (16 on each wing) located on the upper surface of the 

wing above the front and rear spars would be read by a light-sensitive receiver 

located in a raised, streamlined blister mounted on the top of the wing pivot. 

This system was designed to be removable, with engineers ensuring that it 

would not interfere with the complex static and unsteady pressure measurement system installed in the plane’s wings.

Preparing the Way Forward

In a July 18, 1985, presentation to a subcommittee of the Congressional 

Advisory Committee on Aeronautics, NASA Ames presented a timeline and 

a proposed budget and funding program for the planned F-8 OWRA effort. 

This timeline stressed that the F-8 OWRA program was a planned supersonic 
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Beyond the AD-1

F-8 Oblique Wing Research Aircraft planned sensor distribution for measuring static and 

unsteady pressures. (NASA)

airplane followup to the earlier subsonic AD-1 Oblique Wing Research Aircraft 

program—effectively, an assurance to Congress that this did not represent some 

big new and ill-defined effort but rather that it constituted a logical extension of 

decades of previous work. The history portion of the presentation emphasized 

this earlier work, particularly the various design studies from 1972 and earlier 

through 1976, the wind tunnel tests from 1972 through 1976, the simulations from 1974 through 1976, the Remotely Piloted Vehicle flight program 

from 1976 through 1977, the AD-1 flight program from 1978 through 1983, 

and the proprietary studies from 1980 through 1984.16 The planned OWRA 

project schedule provided for wing construction from July 1987 to July 1990 

(the preliminary design phase was already completed); systems checkout from 

July 1990 to April 1991; and finally, a planned first flight in May 1991.17

As noted in previous chapters, this historical background timeline, while 

a close approximation, was not the exact timeline actually followed by the 

AD-1 program. The F-8 portion of the timeline provided for the following: 

(a) feasibility and design work from 1983 through 1986 to modify NASA 

Dryden’s TF-8C Digital Fly-By-Wire test bed aircraft to an oblique-wing 

aircraft, (b) modifications and flight testing of the TF-8C from 1986 through 

1989, and (c) technologically ready-for-flight-test status by the end of 1989.18
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Thinking Obliquely

F-8 Oblique Wing Research Aircraft planned accelerometer array to measure modal response. 

(NASA)

In regard to the budget and division of responsibilities between NASA and 

the Navy, under the terms of the NASA-Navy Memorandum of Understanding, 

a $36 million budget for fiscal year (FY) 1985 through FY 1989 was to be 

divided 50-50. The NASA responsibilities (via the Ames-Dryden Flight 

Research Center19) were program management and development and flight 

testing. The Navy responsibilities (executed via Naval Air Systems Command) 

included technology assessment for Navy applications and support development and flight testing.

Rockwell’s F-8 oblique-wing program manager was C.D. Wiler and the 

project engineer was S.N. White. Ron Murphy and Robert Traskos served as 

the Navy’s program managers, and Erwin Roeser and Henry Lystad served 

as Navy project managers. For their part, NASA’s flight research professionals looked forward to the chance to apply the oblique wing to the F-8, and 
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Beyond the AD-1

F-8 Oblique Wing Research Aircraft planned wing deflection measurement system. (NASA)

in announcing the initial staffing of the F-8 Oblique Wing program to the 

Dryden staff, Kenneth J. Szalai stated that

I am personally extremely excited about this program. It has all 

the elements of an outstanding flight research program including 

the challenges in three aeronautical disciplines as well as an opportunity to further advance the state of the art in design of highly 

interactive systems. Tom Gregory has been working oblique wing 

technology for a decade at Ames North, and I share with him 

the expectation that Ames can and will play a significant role in 

developing this technology, which has a tremendous potential for 

strongly impacting future aircraft design.20
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Thinking Obliquely

Component breakdown of F-8 Oblique Wing Research Aircraft. (NASA)

To run the program, one of Dryden’s most experienced flight testers, Cal 

Jarvis, was appointed acting project manager, with Tom Gregory his deputy 

project manager. A core research engineering group was formed under Mike 

DeAngelis. The engineering group was “chartered to lead the Dryden technical effort in planning the experiment, participating in the joint NorthSouth vehicle syntheses activity, and in preparing the statement of work.”21

Additional research engineering staff would be “matrixed to the project in the 

normal manner.”22 The initially designated team members were John Bresina 

(simulation), Harry Chiles (instrumentation), Robert Curry (aerodynamics), 

Glenn Gilyard (structural dynamics), Dale Mackall (flight systems), and Joe 

Pahle (flight controls). All of these people were experts in their field, their 

expertise honed by having worked other programs with shared interactions 

and responsibilities.23
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Beyond the AD-1

Challenges: Cross-Coupling, Flutter, 

Controls, and Simulation

As the F-8 effort went forward, engineers and researchers confronted a series of 

explicit technical challenges, including the inherent longitudinal-lateral (pitchroll) cross-coupling encountered with any oblique-wing vehicle, the unique flutter characteristics of oblique wings, the development of flight control technology 

and software for the OWRA, and the process of undertaking simulation.

Cross-Coupling

NASA engineers Robert W. Kempel and Joseph W. Pahle, together with 

Gurbux S. Alag, an associate professor of electrical engineering at Western 

Michigan University, studied the problem of cross-coupling related to asymmetrical oblique-wing aircraft. While recognizing the “substantial aerodynamic 

performance advantages”24 offered by oblique wing aircraft, they also noted (as 

earlier engineers likewise had recognized) that the oblique wing “has significant aerodynamic and inertial cross-coupling between the aircraft longitudinal 

and lateral axes.”25 As a result of their studies, they developed a technique 

for synthesizing a decoupling controller while providing the desired stability 

augmentation. They noted that then-current typical design procedures synthesized aircraft controllers based on 2-degrees- or, at most, 3-degrees-of-freedom 

solutions but that the NASA-Navy OWRA program had to address at least 5 

degrees of freedom simultaneously.

This study team recognized that a significant component of the OWRA program would be the synthesis of a control system that would provide acceptable 

stabilization and decoupling across the F-8’s “Mach [number, M], angle-ofattack [AoA, α,] and wing-skew [sweep angle, Λ] envelope”26 and that NASA’s 

F-8 DFBW aircraft offered the opportunity to apply modern control theory 

techniques for solving problems associated with oblique-wing aircraft. They 

added that model-following has been a popular method for the design of multivariable control systems and that “[i]n this method, the desired behavior of 

the plant is provided by an ideal model, and that the problem is one of designing a suitable controller for the plant so that its response follows that of the 

model.”27 The three engineers proposed to integrate two previously developed 

techniques—the Yore model and the eigenstructure assignment. In the Yore 

model, the synthesis procedure consisted of constructing an ideal model, 

designing feedback gains by quadratic optimization, and designing feedforward gains. The noted disadvantage of this procedure, however, was that 

the method of selecting the feedback gain is an “iterative and time-consuming 

process”28 and the determination of the gain becomes a more complex problem 

when all states are not available, thus causing output feedback to be used. The 
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Thinking Obliquely

eigenstructure assignment technique involves interpreting the performance 

specifications in terms of the eigenvalues and eigenvectors or the closed-loop 

system.29 The study added that J.R. Broussard and P.W. Berry used the equivalent of this technique to the design model-following systems.

Alag, Kempel, and Pahle defined the model-following problem as follows:

The concept of model-following is useful when an ideal set of 

plant equations of motion can be specified. The ideal objective of 

model-following flight control is to force the aircraft to respond 

as the model would to a given pilot command. It is often desirable to simulate the model dynamics in the flight computer and 

to generate the aircraft control signal using the aircraft outputs, 

the pilot input commands, and the model states. This situation is 

sometimes referred to as the pilot flying the computer, while the 

computer is flying the aircraft....There are two configurations of 

model-following, one is implicit model-following, and the other 

is real model-following (RMF). In implicit model following, the 

model is part of the system. In RMF, however, the model is part 

of the system as control law requires the states of the model. The 

technique of RMF has been shown to be amenable to the solution 

of many aircraft control problems.30

The study team, while noting that the conditions for perfect model-following 

are not attainable, pointed out that Y.T. Chan derived an asymptotic RMF 

control law for the class of plants and models whose output vectors are identical 

to their state vectors. Chan, therefore, showed that, even if the conditions for 

perfect model-following are not satisfied, the use of perfect model-following 

gains can yield a control capable of keeping the error between the model and 

plant to a small region of state. Next, the team noted two widely used synthesis 

techniques of modern control theory—linear quadratic regulator design and 

the modal control theory involving pole placement or eigenvalue assignment. 

The team pointed out that the difficulty in incorporating specifications such 

as damping, natural frequency, and decoupling within the quadratic performance index makes the eigensystem synthesis procedure a “promising design 

alternative”31 and that other engineers have successfully demonstrated the use 

of the eigenstructure assignment procedure for aircraft control system design.

As a result of their investigation, Alag, Kempel, and Pahle concluded,

A method is presented to obtain a decoupled control for a highly 

coupled asymmetric aircraft. The method utilizes a real modelfollowing control law in which gains for perfect model-following 
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Beyond the AD-1

are used even when the conditions for perfect model-following are 

not satisfied. The feedback gain, using output feedback, is computed by using eigenstructure assignment. The results indicate 

that the method does obtain the decoupling incorporated in the 

ideal model for the flight condition considered.

 Future investigations will be conducted to evaluate the control algorithm under nonlinear 6-degree-of-freedom flight conditions. These investigations will consider such factors as nonlinear 

aerodynamic data, control system surface rate and position constraints, and system hysteresis.32

Addressing the Challenge of Flutter

Flutter has been an insidious problem in aeronautics since the earliest airplanes. 

The advent of the monoplane highlighted the dangers of control surface and 

tail and wing flutter. Flutter can take many forms, and it persists through the 

hypersonic regime, even affecting extremely robust flight structures. With this 

legacy of danger, it is understandable that NASA’s aeroelastic and structural 

researchers took the risk of flutter with the proposed F-8 OWRA very seriously.

John J. Burken and Glenn B. Gilyard, NASA Ames aerospace engineers, 

and professor Gurbux S. Alag (who also worked on the cross-coupling problem 

reviewed above) addressed the challenge of oblique-wing flutter, examining 

a mode that develops under flight conditions of Mach 0.70 and altitudes 

of 3,048 meters (10,000 feet).33 The three engineers identified the following 

problem to be solved:

The unsymmetric configuration and forward sweep of one 

semispan result in aeroelastic behavior distinctly different than 

that of straight, swept-back, or swept-forward wings. It should be 

noted that in addition to unsymmetric modeling characteristics, 

unsymmetric configurations will typically have significantly larger 

plant formulations since all degrees of freedom must be adequately 

represented. Separation of an unsymmetric model into two smaller 

models (as is possible for symmetric and antisymmetric modes of 

a symmetric aircraft) is not possible, because the response motion 

is coupled and not separated.34

In order to evaluate the analytical tools required for the analysis of an 

oblique-wing configuration, the researchers developed a generic skewed-wing 

model of the aeropanels and node points with a wing-skew angle of 45 degrees 

operating at M=0.70 and 10,000 feet. The objective of the testing was to 
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Thinking Obliquely

Generic 45-degree skewed-wing model using simple beam representation of the F-8 Oblique 

Wing Research Aircraft wing and fuselage, from TM 86808, 1986. (NASA)

demonstrate the control synthesis design process required to develop a practical control law for stabilization of the oblique wing’s flutter mode. The process 

involved the formulation of the state-space model, including the independent 

wing actuators, a Dryden gust model,35 and the S-plane approximations of 

unsteady aerodynamics; optimal full-scale-control-law determination; robust 

output-feedback control-law determination; reduced-order (practical) controllaw formulation; and critical evaluation of the practical control law.36

The model used in the system synthesis process was a simple beam representation of the fuselage and wing. The aircraft aeroelastic characteristics were 

modeled using the now-common NASTRAN computational analytical tool. 

At the assumed flight conditions, the unaugmented aircraft had a flutter mode 

characterized primarily by wing bending but with some torsion. The formulation of the complete, integrated (structures, aerodynamics, and controls) 

state-space model for use in the analysis and design process followed the Peele 

and Adams process. Left- and right-wing actuators were modeled independently because the synthesis process determined unique control laws for each 

surface. The active control synthesis was based on LOG theory modified to 
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Beyond the AD-1

accommodate the high-order model of the aircraft. The design process involved 

the following steps: state-space-model generators, full-state-feedback design, 

estimation of states from available measurements, and development of the 

reduced-order controller.

The engineering team’s conclusions were:

An implementation flutter controller for the 45°-skew obliquewing aircraft mathematical model was designed using the LOG 

design methodology. Kalman estimators produced low stability 

margins, however, the Doyle-Stein procedure for robust estimator 

design can be used to improve these margins to acceptable values 

without excessive surface activity. A modal residualization technique was used to obtain a reduced-order controller that satisfied 

the performance requirements and can be implemented.37

The bottom line was simply this: the team had evaluated a potentially serious danger-to-flight flutter mode, creatively explored how to address it, and, 

using complex mathematical analysis, developed a flight control law that could 

be implemented by the F-8 OWRA to suppress the flutter before it reached 

potentially dangerous divergent levels.38

Ensuring Adequate Flight Control for the F-8 OWRA

In 1986, Dale F. Enns and Daniel J. Bugajski, of the Honeywell Systems and 

Research Center, and Martin J. Klepl, of Rockwell North American Aircraft 

Operations, reviewed the development of multivariable control laws for the 

F-8 Oblique Wing Research Aircraft. They noted that the aircraft control 

laws were scheduled for piloted moving-base simulations at NASA Ames 

for early 1987 (subsequently discussed). It was crucially important that the 

control laws decouple the longitudinal from the lateral directional motions 

of the F-8 aircraft. If not, all motions of the highly skewed oblique-wing 

aircraft would be highly coupled, seriously degrading its performance and 

preventing satisfying conventional handling-qualities specifications. Other 

objectives for control of the aircraft were gust attenuation, desensitization, 

good command tracking (a measure of precise flight control), stability augmentation, good handling qualities, and stability robustness with respect to 

model uncertainty.39

The control laws were developed using a loop-shaping methodology 

involving three loops—roll, pitch, and yaw. There are five control-surface 

actuator commands—left elevator, right elevator, rudder, left aileron, and 

right aileron. There are seven sensor outputs—roll rate, pitch rate, yaw rate, 

lateral acceleration, normal acceleration, roll angle, and pitch angle. A matrix 
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Thinking Obliquely

transfer function combines the seven sensor outputs into three regulated 

variables that represent the basic flight control objectives for the three axes. 

The pilot commands the roll variable with the lateral stick, the yaw variable 

with the rudder pedals, and the pitch variable with the longitudinal stick. 

A number of different models, which were all obtained through Rockwell, 

were used for the control-law development. The simplest model was a standard eight linearized model of the rigid-body dynamics. The most complex 

model used was a simulation of the aircraft dynamics, including nonlinear 

kinematics and aerodynamics as well as actuator dynamics. This simulation 

model was used for assessing the performance of the control laws in the presence of nonlinearities. The pilot objectives were identified as maintaining 

wing level, heading hold, altitude hold, and velocity hold. Care was taken to 

maintain bandwidths within the limits of what a human pilot could perform. 

Bandwidths were selected at 1 radian per second for heading and bank angle, 

0.5 radian per second for velocity, and 0.3 radian per second for altitude.

Enns, Bugajski, and Klepl summarized their investigation by noting,

The loop shaping procedure for designing the control laws was 

presented. The performance and stability robustness objectives 

for the control laws were presented in terms of singular values 

and structured singular values of specific frequency responses. 

The handling qualities of the closed-loop system were analyzed 

with the equivalent systems technique. Time histories of the 

closed-loop response to pilot inputs were examined. The analyses using highest fidelity models available showed that the design 

goals were achieved.40

Simulations of Decoupling Control Laws and OWRA Motions

Simulation has always played a significant role in flight testing and flight 

research, both for its own sake and as a tool for research into how a new 

aircraft will behave. Thus, it is not surprising that NASA Ames undertook an 

extensive simulation of the proposed F-8 Oblique Wing Research Airplane, 

using the Center’s large Vertical Motion Simulator, to evaluate the decoupled 

handling qualities of the proposed flight control system. When combined with 

expert opinion from test pilots “flying” the simulator, the Vertical Motion 

Simulator provided a valuable means of realistically evaluating the preliminary handling qualities of the oblique-wing research airplane. The Vertical 

Motion Simulator, in conjunction with realistic large-motion and visualsimulation systems, provided a unique capability to investigate the OWRA’s 

anticipated dynamic characteristics early in the control system design phase. 
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The goals of the simulation tests were to obtain preliminary pilot evaluations 

of a prototype flight control system designed to provide decoupled handling qualities, identify important response variables in the evaluation of the 

oblique-wing configuration, and develop criteria and requirements for use 

in future control laws for highly coupled airplanes. Accordingly, five discrete 

flight conditions were evaluated, ranging from low-altitude subsonic Mach 

numbers up to moderate-altitude supersonic Mach numbers.41

Six pilots participated in the evaluation with each required to perform a 

variety of maneuvers and tasks and to provide pilot ratings for each maneuver. 

The control law was a prototype system based on the loop-shaping approach 

with the objectives of decoupling the longitudinal and lateral directional 

motions of the aircraft as well as satisfying the conventional flight control 

objectives, including gust attenuation, stability augmentation, good command tracking, good handling qualities, and stability robustness. All simulation flights were flown at a fixed wing skew and were limited to relatively 

small variations in Mach number, altitude, and angle of attack. The study 

team noted the following:

1. The results of the evaluation should be considered preliminary and 

not necessarily characteristic of a final OWRA configuration or 

typical of an operational oblique-wing configuration;

2. The preliminary aerodynamic data base used was for a wing area 

that was only 67% of the most recent OWRA wing design and 

that since cross-coupling is largely dependent on angle-of-attack 

change required for maneuvering, the increased wing area would be 

expected to result in reduced coupling; and

3. The five flight conditions selected for evaluation were at moderate 

to high dynamic pressures that would tend to aggravate unusual 

dynamic characteristics.42

The weight of the NASA DFBW F-8 ranged from a loaded weight of 23,500 

pounds to an empty weight of 18,800 pounds, and the simulation study used 

a weight of 21,116 pounds, which represented 50-percent fuel loading. The 

airplane’s aerodynamic controls consisted of the following movable surfaces: 

wing ailerons for roll control,43 symmetric and differential stabilizer for pitch 

and roll control, rudder for yaw control, and flaps.

Based on the simulation testing and analysis of the data, the study team 

reached the following conclusions:

1. Participating pilots were unanimous that the high levels of sideforce 

or lateral acceleration in pitch maneuvers were unsatisfactory.

2. Pilots were more critical of left turns than they were of right turns. 

At the higher dynamic pressure conditions, the difference was as 

much as 2 pilot ratings. Pilots indicated that the airplane rolled into 
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Thinking Obliquely

the bank angle in left turns and rolled out of the bank angle in 

right turns.

3. Pilot comments and ratings deteriorated with both increasing wing 

skew and dynamic pressure. The most favorable comments were 

received for the lowest dynamic pressure and wing skew condition, 

and the most unfavorable comments were received for the highest 

dynamic pressure and wing skew condition.

4. Roll-to-pitch coupling was not a significant problem.

5. Pitch-to-roll coupling in the open loop configuration was substantial 

and was a major concern in the control law design. This coupling 

caused only minor handling qualities problems in the closed 

loop airplane.

6. The flight control system provided satisfactory pitch-to-roll decoupling at all flight conditions, but did not provide acceptable pitchto-sideforce decoupling.

7. The use of a motion-based simulation with visual cues provided 

handling qualities conclusions for this vehicle that were not obvious 

using a fixed-base simulation with no visual cues.44

The overall finding was that “the flight control system was effective in generally decoupling the airplane.”45 Clearly, however, refining the flight control 

of the F-8 OWRA to address sideforce and lateral acceleration issues during 

pitch maneuvers would have required considerable work.46

Investigating the Aerodynamic Characteristics 

of an Oblique Wing for the F-8 OWRA

In addition to the 300-square-foot Rockwell oblique-wing proposal, a number 

of other oblique-wing designs for the F-8 model were tested at NASA Ames, 

including two smaller 250-square-foot wings and an additional wing with 

an 8-to-1 elliptical planform. A number of these designs, however, were not 

directly comparable with each other due to differences in inlet fairing, tail 

incidence angle, presence of ventral fins, and method of wing attachment.47

In addition, NASA Ames undertook in own oblique-wing design and tested 

and compared this NASA design with the Rockwell design. Indeed, the testing indicated that the NASA wing performed better than the Rockwell wing. 

“Had the F-8 OWRA project continued,” NASA engineer Stephen C. Smith 

noted afterwards, “it is most certain that this wing would have been the wing 

selected for the airplane, over Rockwell’s mild objection that it was slightly 

more expensive to manufacture.”48
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Beyond the AD-1

During June and July 1987, NASA Ames engineers conducted an experimental study of the aerodynamic performance and the stability and control 

characteristics of a 0.087-scale model of an F-8 airplane fitted with a NASA 

Ames–designed tapered (10.47 aspect ratio) wing that used specially designed 

supercritical airfoils with a 14-percent-thickness-chord ratio at the root and 

a 12-percent-thickness-chord ratio at the 85-percent span location. The tests, 

which were conducted in the NASA Ames 11-foot Transonic Wind Tunnel, 

were part of the OWRA program undertaken in conjunction with Rockwell 

International. The Ames-designed wing was tested at two different mounting 

heights above the fuselage. The performance of this wing was compared with 

the performance of the oblique wing designed by Rockwell International and 

tested by NASA Ames as part of same development program. The test objectives were to examine the performance and stability characteristics of the Amesdesigned wing, provide timely information on the effects of the wing height 

and pivot axis inclination angle proposed by Rockwell, examine the benefits 

of varying the wing camber with wing sweep for efficient roll trim, measure 

the effectiveness of deflected tips as an alternative to ailerons for roll control 

at high sweep angles, and test a simple fuselage-mounted vortex generator.49

In designing the wind tunnel model, the fuselage, empennage, and ventral 

fins were based on the Ames-Dryden F-8C Digital-Fly-by-Wire test bed vehicle. The model engine inlet was faired over and the wing was mounted above 

the fuselage on a pivot shaft instead of being submerged within the fuselage. 

The horizontal and vertical tail surfaces had NACA 65A006 airfoil sections 

and a 45-degree sweep as measured at each surface’s quarter-chord line. The 

horizontal tail was mounted at a 0.0-degree incidence relative to the fuselage 

centerline. The oblique-wing airfoils were modern, thick, supercritical sections. 

Lofting of the wing surface was linear from the root to the planform break 

at 85-percent semispan and the wing leading edge was then sheared forward 

4 degrees. There were 2 degrees of washout between the reference axes of the 

defining airfoil sections. The wing was lofted with a small amount of dihedral 

so that the upper surface was flat along the 40-percent chord line. The wing 

pivot axis was inclined so that the wing banked as it swept (right tip forward 

and down). The pivot axis inclination of 7.894-degrees forward and 5-degrees 

right was chosen by Rockwell International in order to counteract a sweepdependent sideforce observed in previous wind tunnel tests. High and low 

mounting posts were used to simulate the two selected wing heights.

The wing had flaps, ailerons, and deflectable tips that consisted of detachable 

segments machined at fixed angles. The tips were hinged along a chord line at a 

85-percent semispan, and the trailing-edge devices were hinged at a 70-degree 

chord. The ailerons extended laterally from a 58-percent to 85-percent 

semispan. The flaps were built in two segments in order to permit evaluation 
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Thinking Obliquely

of the effectiveness of inboard versus outboard location and for testing their 

effect on cruise drag. The outboard flap segments covered a 34-percent to 

58-percent semispan and the inboard flaps ran from 9 percent to 34 percent. 

The left inboard flap could not be deployed in a positive (downward) sense when 

the wing was swept. The left-hand and right-hand side-control surfaces had the 

same chordwise and spanwise dimensions.

The study team, consisting of Robert A. Kennelly, Jr., Ralph L. Carmichael, 

Stephen C. Smith, and James M. Strong from NASA Ames and Ilan M. Kroo 

from Stanford University, concluded the following:

1. As in the case of the previously reported Rockwell wing, the high 

pivot caused excessive drag with little reduction in wing/fuselage 

interference and was less stable in pitch for high angles of attack.

2. Simple models of lift and drag based on airfoil characteristics and 

simple sweep theory, with extensions for separated flow, provide a 

useful characterization of oblique wing performance.

3. The overall F-8 OWRA drag is rather high, but most of this is caused 

by the large, blunt fuselage with abruptly faired-over engine inlet.

4. Side force and the three moments are complex functions of sweep, 

Mach number, and lift. The underlying flow mechanisms are similar 

to those observed on conventional, symmetrically swept wings, but 

they manifest themselves differently because of the asymmetric wing 

and its interactions with the fuselage.

5. The directional stability of the F-8 OWRA with the wing swept is 

only slightly degraded in comparison to the zero-sweep configuration.

6. The performance benefits of variable geometry were confirmed for 

sweep angles up to 60-degrees at Mach 1.40; higher speed testing will 

be required to check whether higher sweeps are desirable.

7. The thick, high-lift, supercritical airfoils designed for the Ames 300 

sq ft wing appear to have achieved their design objectives. Both the 

wing drag-rise characteristics and performance envelope at the various sweep angles are in agreement with expectations based on simple 

sweep theory. No off-design penalty attributable to the use of supercritical sections was observed.

8. Cruise and loiter flaps were found to be ineffective in reducing drag 

for the limited set of flap deflections tested. Asymmetrical deflection 

of cruise flaps can be useful for roll trim with negligible drag penalty.

9. (High lift performance with segmented plain flaps was measured. 

Although maximum lift was somewhat improved by flap deflection, 

the largest effects were an increase in drag and a shift of α for maximum lift to lower values. The maximum lift coefficient was strongly 

affected by Mach number.
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10. Deflected [wingtips] were found useful for roll control and are superior to ailerons at high sweep angles. Both deflected tips and ailerons 

have side effects on pitching and yawing moments.

11. A pitch-up was observed for intermediate sweep angles at transonic 

Mach numbers. The pitch-up is associated with the increase in lift 

loading on the rear wing panel as angle of attack is increased, leading 

to buffet and/or stall of the rear wing panel. This pitch-up is typical of 

conventional swept wings except for the coupled nonlinearities in rolling and yawing moment due to the asymmetric configuration.

12. A fuselage-mounted vortex generator positioned ahead of the center of 

the wing did not significantly affect the nonlinear characteristics of the 

oblique wing as various portions of the wing stalled.

13. With the exception of drag, the forces and moments were not significantly affected by variation in Reynolds number. The decrease of drag 

with increasing Reynolds number was typical of models tested at these 

Reynolds numbers.50

Program Monitoring and Project Termination

Review of the monthly update reports indicates that NASA Dryden monitored 

very closely the progress of the OWRA program and indicated that project funding became a critical problem that eventually led to the cancellation of the project 

that was well along the road to being completed. After the Navy withdrew funding, NASA approached the Air Force and DARPA for help in continuing the 

program. When these efforts failed, NASA was forced to terminate the program.

A sampling of monthly reports offers insight into the program’s progression, 

its challenges, and its accomplishments:

• The June 12, 1984, monthly report reflected the program startup, noting that an overview briefing of the F-8 Oblique Wing Program was 

presented to management and disciplinary personnel at both AmesDryden and Ames North; task teams that would comprise the project 

office were currently being established at both sites; and the program 

Memorandum of Understanding was formally approved and signed 

by both NASA and Navy management, thus establishing funding and 

schedule commitments by both agencies. The report also noted that 

wind tunnel testing of a scale F-8 Oblique Wing model was scheduled 

to begin in the Ames 11-foot wind tunnel on June 11, 1984, and a 

statement of work had been completed for the development of the initial F-8 Oblique Wing Aero Model and for support in establishing an 
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Thinking Obliquely

F-8/OWRA operational “Iron Bird” (a ground simulator for piloted 

controls evaluation).51

The September 12, 1984, update added that an August 30 meeting 

with the Charles Stark Draper Lab (CSDL) was held in order to discuss required hardware and software modifications to the F-8 primary 

digital flight control system and that a meeting was held with Sperry 

Flight Systems to discuss required modifications to the F-8 backup 

flight control systems. Contractor wind tunnel tests were completed 

in the Ames 11-foot Transonic Wind Tunnel, and the results were 

presented at Ames. Flow-visualization tests were planned for September 

using the Ames-Dryden water tunnel. Planning continued in order to 

define the approach and requirements for in-house research and testing 

development in support of the OWRA program. A visit was made to 

the Ling-Temco-Vought Corporation by NASA Ames and Navy representatives in order to acquire baseline loads data on the F-8, and the 

Phase B (preliminary design) procurement activity was on schedule.52

The February 22, 1985, report added that the final aeromodel was 

received from Rockwell for the Oblique Wing fuselage configuration 

and that a presentation was given to the Ad Hoc Congressional Review 

Committee regarding program objectives and technology development 

items in support of the study.53

The March 7, 1985, update reported that a “correct and complete” 

aerodynamic model for the F-8 oblique-wing program had been 

received and was in the process of being implemented into simulations 

at Ames and Dryden.54

The June 10, 1985, report noted that the only final actions remaining to implement the oblique-wing preliminary design contract were 

project plan approval, project funding release, and contract award. 

Also, the “batch simulation” of Rockwell’s aerodynamic model was now 

operational at Dryden, and five check cases had already been evaluated 

with satisfactory results.55

The July 8, 1985, update reported that Dr. Gupta, of the Ames-Dryden 

Aerostructures Branch staff, had completed an aeroelastic modeling 

of the 250-square-foot oblique wing and noted that the results of the 

investigation with the analytical approach “appear realistic.”56

The August 12, 1985, monthly report reviewed the following program 

progress: a piloted simulation, which can be flown at all wing-skew 

angles, of the F-8 OWRA was activated at Dryden, and it was anticipated that “controls augmentation” would be added to the simulator in 

August; Rockwell had completed a wind tunnel test of its wing model 

incorporating the 4-degrees of leading-edge sweep as recommended 

• 

• 

• 

• 

• 

• 
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Beyond the AD-1

from the NASA in-house wing design; and a smaller scale model 

of the in-house wing was being fabricated for Dryden Flow 

Visualization Facility (water tunnel) testing.57

The September 12, 1985, update identified the three following additional work items: a real-time, six-degrees-of-freedom simulation was 

now operational, and computational pressure data that agreed with 

water tunnel test results had been generated; the final award of the 

oblique-wing preliminary design activity was awaiting release of FY 

1985 funds; and the project plan document was being reviewed for 

final approval by the Navy.58

The December 12, 1985, update added that the preliminary design 

contract for the oblique wing was awarded to Rockwell and that a 

water tunnel model of the in-house oblique-wing design had been 

constructed and was ready for testing at Dryden.59

The January 10, 1986, monthly update reported on a review meeting 

attended by Rockwell, NASA, and Navy representatives held at Ames 

on December 18, 1985, in order to review Rockwell’s progress and to 

compare Rockwell’s proposed design with NASA’s in-house design. 

The report added that Rockwell was now leaning toward a larger wing 

that would be canted on the fuselage to minimize the out-of-trim 

moments resulting from the wing skew.60

The February 10, 1986, report noted that NASA Dryden, Rockwell, 

and Honeywell had been independently studying different control-law 

methodologies, and while no particular methodology had been selected, 

it appeared that the loop shaping and model-following would be the 

prime contenders. Also, the report indicated that acceptable OWRA 

control characteristics were achievable without major difficulties.61

The March 7, 1986, update reported that the release of Navy funding 

appeared imminent.62

The April 10, 1986, report indicated that the Navy funding had been 

released to the NAVAIR program and was in the process of being 

transferred to NASA.63

The August 11, 1986, monthly update reported that the NASA 

project team was continuing its in-house development in order “to 

assure that the Rockwell selections are appropriate or if necessary to 

redirect them.”64

The September 15, 1986, report reflected how far along the program 

was. The synopsis for the oblique-wing final design and fabrication was 

released, a vertical motion simulation was planned to be accomplished 

early in October, and the project team had finished assimilating the 

results of the wind tunnel tests of the in-house wing. The in-house 

• 

• 

• 

• 

• 

• 

• 

• 
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Thinking Obliquely

wind tunnel tests indicated that the oblique wing was “somewhat more 

efficient at the loiter cruise condition than the wing design previously tested.”65

• 

• 

• 

• 

• 

• 

The October 8, 1986, update noted that a 3-year contract for the 

control system modifications to accommodate the flying wing was 

awarded to the Charles Stark Draper Laboratory. The proposed flight 

control computer system was a “quadraplex computer with strapped 

triplex sensors and actuators.” The October report also added that 

NASA Ames was designing two simple force-and-moment wind 

tunnel models for testing in January 1987 and that these tests 

would enable a direct comparison of the performance of the NASA 

technology developed for the oblique wing with the contractor’s 

(Rockwell International) oblique wing as well as identifying any 

problems that the contractor’s wing might encounter.66

The November 12, 1986, monthly report, however, revealed the first 

major problem that threatened to end the F-8 OWRA program. The 

Navy’s funding of the program, while included in the Congressional 

authorization bill, was omitted from the appropriations bill.67

The March 13, 1987, report added that the Navy had withdrawn 

from the F-8 OWRA program. The Navy indicated that it still 

supported the technology that the program would develop but that 

overall budgetary constraints precluded the funding of their portion of the program.68

The May 11, 1987, report noted that a Memorandum of 

Agreement for the conduct of a joint DARPA-NASA Oblique 

Wing Research Aircraft program was in circulation for review.69

The June 12, 1987, monthly update report noted that Rockwell 

had initiated a contract with Honeywell for control-law development and that approximately 160 hours of wind tunnel testing 

were planned on the NASA-designed 300-square-foot oblique 

wing. The report added that negotiations were still under way to 

secure DARPA funding for the project.70

The July 8, 1987, monthly update stated that the Ames wind 

tunnel tests of the 300-square-foot NASA-designed oblique wing 

were completed and that the test revealed some difficulties with the 

aerodynamics of the pivot design that supported the wing above 

the fuselage. Preliminary analysis of the problems indicates that the 

Rockwell-proposed design would need to be modified to eliminate the pivot extension. The report added that negotiations were 

still under way to find a funding partner and that the Air Force 
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Beyond the AD-1

had expressed interest in the program as it would pertain to the 

Conventional Defense Initiative.71

The August 12, 1987, monthly update status report noted, in 

regard to the F-8 OWRA program, that a Critical Design Review 

for the flight control computers, which were being procured 

from the Charles Stark Draper Laboratory, was held at Dryden in 

August and concluded that the CSDL work was now technically 

ready to start fabrication. The report added that discussions were 

still under way with the Air Force to secure a funding partner for 

the project.72

The October 13, 1987, update report noted that the wind tunnel tests planned for September had been deferred until October 

and that these tests were designed to enable a comparison of the 

aerodynamics of Rockwell and in-house wing designs, although it 

was noted further that even these tests would not be of sufficient 

scope to enable the development of a complete aerodynamic model 

for the simulation scheduled to be developed in Phase C of the 

project (which was recently canceled). Finally, the report informed 

the Dryden Director that the Honeywell control laws, which were 

generated using a 200-square-foot-wing-area database, should be 

delivered in October.73

• 

• 

But by now, the program had already collapsed; a month earlier, Dryden’s 

September 9, 1987, update report had signaled the end of the program with 

the following directive:

Direction from NASA Headquarters to cease further cost obligations on the Oblique Wing Research Aircraft project was received 

on August 27, 1987. We have been informed that a request for a 

Termination Plan to terminate the project in an orderly manner 

will be forthcoming from Code RX at Headquarters. The acceptance of this plan will enable limited expenditures for those items 

that are desirable to complete.74

The report added that the wind tunnel tests of the Rockwell designed wing 

would be completed in September.

Termination of Navy funding and the subsequent withdrawal of DARPA 

and Air Force interest ended NASA’s F-8 OWRA program, which was poised 

to enter its next to final phase, thus ending a very promising effort to realize 

NASA’s plan to have a supersonic oblique-wing airplane to follow the Agency’s 

earlier subsonic AD-1. In retrospect, the cancellation was an unfortunate one 

because the F-8, despite what challenges may have existed as it made its way 
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Thinking Obliquely

Comparison of a high vs. low pivot location for the proposed F-8 Oblique Wing Research Aircraft, 

from TM 102230, 1988. (NASA)

toward flight, would most likely have demonstrated the benefits of a supersonic 

oblique-wing aircraft. The cancellation stemmed in part from cost overruns 

that the Navy experienced on another program for an experimental “X-Wing” 

stopped-rotor research aircraft, which itself failed to go forward.75

Even without flying the F-8 demonstrator, the program added measurably 

to the oblique-wing technology base, particularly by identifying and projecting 

solutions for most of the previously identified stability and control problems. 

For a while, F-8 inspired research played out within the Agency. For example, 

in July 1988, almost a year after cancellation, Ames researchers tested a 0.087-

scale model of an F-8 fitted with an oblique wing designed by Rockwell in the 

Center’s 11-foot Transonic Wind Tunnel (as hinted at in the October 1987 

progress report). Unlike the earlier Jones-style elliptical transport wing, this 

wing had a straight taper (as discussed previously), with an aspect ratio of 10.3 

and a thickness-chord ratio (t/c) of 14 percent. The wing was evaluated over a 

Mach range of 0.25 to 1.40 at Reynolds numbers ranging from 3.2 to 6.6×106/

feet; at 0-, 30-, 45-, 60-, and 65-degree sweep angles; and at a range of angles of 

attack from –5 degrees to +18 degrees. Most flights were at a 0-degree sideslip, 

“but a few runs were made at sideslip angles of ±5 deg.”76 On the basis of these 

tests, the research team found that wing location was crucially important to 

the aircraft’s aerodynamic performance. The wing, which employed a Langleyderived SC (2)-0714 airfoil section, was designed to produce a lift coefficient 
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Beyond the AD-1

of 0.70 at Mach=0.735. It was tested in two mounted positions—one low to 

the top of the fuselage and one higher.

Surprisingly, the higher location proved to have greater interference and a 

smaller lift-to-drag value than the lower location. Overall, the straight leadingedge, forward-swept trailing-edge Rockwell wing proved inferior to the earlier 

Ames-modified elliptical configuration, which “offers higher L/D ratios at most 

conditions, higher CL (max) [maximum coefficient of lift], and more moderate force and moment breaks than the present [Rockwell] design does.”77 The 

team concluded that the tests raised issues meriting further investigation. In 

this, they were both prescient and fortunate, as interest in the oblique-wing 

concept certainly did not end within the Agency, as illustrated by the followup 

studies, proposals, and designs reviewed in the next chapter.
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Endnotes

1. Including rival British Aerospace V/STOL Sea Harrier designer 

John Fozard, who informed Richard P. Hallion of this after the 

British designer had visited Langley and observed the XFV-12A 

in action. (Hallion recollection to the author). See “XFV-12A: 

V/STOL in Need of a Lift,” Flight International (January 20, 

1979): 171.

2. See the previously cited Michael J. Hirschberg, David M. Hart, 

and Thomas J. Beutner, “A Summary of a Half-Century of 

Oblique Wing Research,” a paper presented at the 45th AIAA 

Aerospace Sciences Meeting and Exhibit, Reno, NV, January 

8–11, 2007, AIAA paper no. 2007-150 (2007), 21–22.

3. Rockwell International (S.N. White, project engineer). “Feasibility 

Design Study of an F-8 Oblique Wing Demonstrator,” NASA 

Contract NAS-11409 (February 1984).

4. Ibid.

5. Ibid., 5–58.

6. Ibid., 1-1.

7. Ilan Kroo, “The Aerodynamic Design of Oblique Wing 

Aircraft,” a paper presented at the AIAA-American Helicopter 

Society- (AHS)American Society for Engineering Education 

(ASEE) Aircraft Systems Design and Technology Meeting, 

Dayton, OH, October 20–22, 1986, AIAA Paper 86-2624, 1 

(internal references in quotation omitted). Ilan Kroo is an individual who has featured prominently in this work. He worked 

at NASA Ames during much of the time period that involved 

the F-8 Oblique Wing Research Aircraft program, and later, as 

a professor at Stanford University, he continued his association 

with the program. He gave special acknowledgment in his paper 

to the work undertaken at Ames and the previous studies “by 

many government, industry, and university researchers” noted 

in the references to his paper. For this paper, he gave particular 

acknowledgment to Robert Kennelly (Sterling Software) and 

Ralph Carmichael (NASA Ames) and stated that “frequent discussions with R.T. Jones were always enlightening.”

8. Ibid., 1–2.

9. Ibid.

10. Ibid., 2–3.
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Beyond the AD-1

11. Ibid., 1–3. Kroo added that a large number of engineers at three 

NASA Centers, Navy installations, universities, and contractor 

sites were already involved in the effort.

12. Glenn B. Gilyard, “The Oblique-Wing Research Aircraft: A Test 

Bed for Unsteady Aerodynamic and Aeroelastic Research,” NASA 

N89-19253.

13. Ibid., 396.

14. The proposed flight control system for the actual F-8 oblique-wing 

aircraft called for replacing the triplex primary and triplex backup 

computers with a quadruplex fault-tolerant computer architecture, 

including a software backup system. The existing sensor sets, interface units, and secondary and primary actuators were planned to be 

used but were to be modified as required. The control law would 

be an entirely new design that would make use of the differential 

horizontal stabilizer for roll control at high skew angles and trim to 

all surfaces. This was not a normal F-8 aircraft function. See Robert 

W. Kempel, Walter E. McNeill, Glenn B. Gilyard, and Trindel A. 

Maine, “A Piloted Evaluation of an Oblique-Wing Research Aircraft 

Motion Simulation with Decoupling Control Laws,” NASA TP 

2874 (November 1988), 5.

15. Ibid., 401–402, 410.

16. NASA Ames Presentation to Congressional Advisory Committee on 

Aeronautics.

17. Gilyard, “The Oblique-Wing Research Aircraft,” 413.

18. NASA Ames Presentation to Congressional Advisory Committee on 

Aeronautics.

19. From 1981 to 1991, Ames Research Center and Dryden Flight 

Research Center were merged into a single bureaucratic and organizational entity, with Dryden referred to officially as the Dryden 

Flight Research Facility (DFRF). However much sense this seemed 

to make to decision makers at the time, in retrospect, it made very 

little sense, as the two Centers, beside being 288 miles apart (as the 

crow flies) shared little in common. After a decade, Dryden was 

again restored to independent status.

20. Kenneth J. Szalai, “Memo for Distribution, Subject: F-8 Oblique 

Wing Staffing,” June 20, 1984, Dryden History Office.

21. Ibid.

22. Ibid.

23. Ibid., 1.
178

Thinking Obliquely

24. Gurbux S. Alag, Robert W. Kempel, and Joseph W. Pahle, 

“Decoupling Control Synthesis for an Oblique-Wing Aircraft,” 

NASA TM 86801 (June 1986), 1.

25. Ibid.

26. Ibid., 2.

27. Ibid.

28. Ibid., 2.

29. In linear algebra, an eigenstructure is a set of eigenvalues presented 

in a matrix. An eigenvalue is the changed magnitude of a vector 

that does not change direction under a linear transformation. An 

eigenvector is a vector that is not rotated while undergoing a linear 

transformation.

30. Alag, Kempel, and Pahle, “Decoupling Control Synthesis for an 

Oblique-Wing Aircraft.”

31. See T.B. Cunningham, “Eigenspace Selection Procedures for Close 

Loop Response Shaping with Modal Control,” Proceedings of the 

IEEE Conference on Decision and Control, December 1980, 178–186; 

A.N. Andry, E.Y. Shapiro, and J.C. Chung, “On Eigenstructure 

Assignment for Linear Systems,” IEEE Transactions Aerospace and 

Electronic Systems, September 1983, 711–729.

32. Ibid.

33. Ibid. For a period in the 1970s to 1980s, NASA adopted metric measurements for its technical reports and publications 

before returning to a more traditional and accessible approach 

subsequently.

34. John J. Burken, Gurbux S. Alag, and Glenn B. Gilyard, “Aeroelastic 

Control of Oblique-Wing Aircraft,” NASA TM 86808 (June 1986), 

2.

35. See John C. Houbolt, Roy Steiner, and Kermit G. Pratt, “Dynamic 

Response of Airplanes to Atmospheric Turbulence Including Flight 

Data on Input and Response,” NASA TR R-199, 1964.

36. Burken et al., “Aeroelastic Control of Oblique-Wing Aircraft,” 2.

37. Ibid., 5. Burken et al., “Aeroelastic Control of Oblique-Wing 

Aircraft,” 5.

38. See also Gurbux S. Alag, John J. Burken, and Glenn B. Gilyard, 

“Eigensystem Synthesis for Active Flutter Suppression on an 

Oblique-Wing Aircraft,” NASA TM 88275 (1986).

39. Dale F. Enns, Daniel J. Bugajski, and Martin J. Klepl, “Flight 

Control for the F-8 Oblique Wing Research Aircraft,” a paper 

presented at the 1987 American Control Conference, Minneapolis, 

MN, June 1987, 1112.
179

Beyond the AD-1

40. Enns et al., “Flight Control for the F-8 Oblique Wing Research 

Aircraft,” pp. 1113–1116, quotation from 1116.

41. Kempel et al., “A Piloted Evaluation,” 1.

42. Ibid., 2–15.

43. For the record, use of wing ailerons was not evaluated in the simulation study.

44. Kempel et al., “A Piloted Evaluation,” 14–15.

45. Ibid.

46. Indeed, in a Ph.D. dissertation on developing integrated flight control for oblique-wing vehicles, Stephen Morris of Stanford University 

bluntly noted, “In the case of the NASA-Rockwell Oblique Wing 

Research Aircraft, attempts to improve the handling qualities by 

implementing a stability augmentation system have produced 

unsatisfactory results because of an inherent lack of controllability in 

the proposed design.” (Emphasis added.) See Stephen James Morris, 

“Integrated Aerodynamic and Control System Design of Oblique 

Wing Aircraft,” NASA CR 192614 (January 1990), abstract.

47. Robert A. Kennelly, Jr., Ralph L. Carmichael, Stephen C. Smith, 

James M. Strong, and Ilan M. Kroo, “Experimental Aerodynamic 

Characteristics of an Oblique Wing for the F-8 OWRA,” NASA TM 

1999-209579 (September 1999), 1.

48. Stephen C. Smith, recollection to the author, January 2012.

49. Kennelly, et al., “Experimental Aerodynamic Characteristics,” 1–2.

50. Ibid., 11–12.

51. Kenneth E. Hodge, “Project Update—May,” June 12, 1984, Dryden 

History Office, box L3-4-4B, p. 2. Note: The following “Project 

Update” documents are located in the aforementioned Dryden 

History Office box. The documents will be identified by title and 

date.

52. “Projects Update—August 1984,” September 12, 1984, 7.

53. Ibid.

54. “Projects Update—February 1985,” March 7, 1985, 5.

55. “Projects Update—May 1985,” June 10, 1985, 5.

56. “Projects Update—June 1985,” July 8, 1985, 5.

57. “Projects Update—July 1985,” August 12, 1985, 5.

58. “Projects Update—August 1985,” September 12, 1985, 5.

59. “Projects Update—November 1985,” December 12, 1985, 4.

60. “Projects Update—December 1985,” January 10, 1986, 5.

61. “Projects Update—January 1986,” February 10, 1986, 3.

62. “Projects Update—February 1986,” March 7, 1986, 3.

63. “Projects Update—March 1986,” April 10, 1986, 6.
180

Thinking Obliquely

64. “Projects Update—July 1986,” August 11, 1986, 5–6.

65. “Projects Update—August 1986,” September 15, 1986, 6.

66. “Projects Update—September 1986,” October 8, 1986, 5.

67. “Projects Update—October 1986,” November 12, 1986, 5.

68. “Projects Update—February 1987,” March 13, 1987, 5.

69. “Projects Update—April 1987,” May 11, 1987, 5.

70. “Projects Update—May 1987,” June 12, 1987, 4.

71. “Projects Update—June 1987,” July 8, 1987, 4.

72. “Projects Update—July 1987,” August 12, 1987, 4.

73. “Projects Update—September 1987,” October 13, 1987, 4.

74. Dryden monthly projects update report, September 9, 1987, 2.

75. Hirschberg, Hart, and Beutner, “A Summary of a Half-Century of 

Oblique Wing Research,” 24.

76. Robert Kennelly, Jr., Ilan M. Kroo, James M. Strong, and Ralph L. 

Carmichael, “Transonic Wind Tunnel Test of a 14% Thick Oblique 

Wing,” NASA TM 102230 (August 1990), 1.

77. Ibid.

182

First takeoff of the Northrop B-2A Spirit, July 17, 1989, Palmdale, CA. (R.P. Hallion)
183

CHAPTER 6

Subsequent Oblique-Wing 

Plans and Proposals

The previous chapters reviewed the theoretical studies and concept development of the oblique-wing idea; the wind tunnel models and testing that demonstrated that the oblique-wing idea was feasible, thus laying the groundwork 

for further study and development; the computer modeling that was used to 

augment the wind tunnel testing and to compare test data with predictions; 

the development of remotely piloted oblique-wing models that demonstrated 

the feasibility of flying larger-scale piloted aircraft; the development and use 

of flight simulators to prepare pilots for flying an actual oblique-wing aircraft; 

and finally, the building and flying of a piloted proof-of-concept obliquewing research aircraft—the Ames-Dryden AD-1. The NACA and its successor, 

NASA, played the leading role in this effort, starting with the remarkable concept developmental work of Robert T. Jones and the first wind tunnel testing 

of the concept by John P. Campbell and Hubert M. Drake that eventually led 

to the building and flying of the AD-1.

The engineering advantages of the oblique-wing concept that resulted 

in NASA’s building and flying the AD-1 were summarized concisely in the 

following historical survey of oblique-wing research undertaken by Michael 

Hirschberg, David Hart, and Thomas Beutner:

An oblique wing...can vary the wing sweep with a single pivot 

that is primarily loaded in tension, trading aspect ratio for fineness ratio by sweeping one wing tip forward and the other wing 

tip back. This design allows a greater reduction in the wave drag, 

automatically accounts for area ruling, and reduces pivot torque 

and bending loads as well as fuselage loads. In addition, asymmetric sweep can increase the fineness ratio of the wing more 

significantly than symmetric designs.1

It is thus both somewhat ironic and intriguing that, even given the engineering advantages outlined above and all of the work done the previous 40-plus 
184

Thinking Obliquely

years (including, most notably, building and flying the AD-1), the potential 

for supersonic and transonic oblique-wing aircraft has not yet been fulfilled. It 

reflects an oft-encountered situation within aeronautics and, indeed, virtually 

all scientific and technological fields, though perhaps to a greater and more 

surprising extent because fewer ideas have so clearly demonstrated their value. 

In retrospect, AD-1 team members Tom McMurtry, Alex Sim, and William 

Andrews appear prescient in light of remarks they made in addressing this 

issue in 1981:

There is often a delay between the discovery and the application 

of new engineering principles. Usually such principles must be 

widely known and accepted before designs begin to reflect them. 

Furthermore, complementary advances in technology in other 

fields are often necessary before new discoveries can be applied. In 

the field of aerodynamics, the oblique swept wing aircraft design 

concept serves as a good example. Theoretically, this configuration, which Robert T. Jones conceived of many years ago, offers 

aerodynamic, structural and operational efficiency unequaled by 

conventional designs.2

While the potential outlined above has not yet been realized, work has 

continued on a number of proposed designs and projects, including a variety 

of examples outlined below, starting, once again, with R.T. Jones.

Jones’s Inspired Ames-Stanford 

Oblique-Flying-Wing SST Concepts

One of the most enduring dreams in aeronautics has been the idea of a pure 

flying wing, dating to the conceptualizations of the German engineer and 

thermodynamicist Hugo Junkers prior to the First World War. The flying 

wing, a pure lifting surface, constitutes the most efficient form of flight vehicles. Junkers, Britain’s John Dunne and Barnes Wallis, Germany’s Alexander 

Lippisch and Reimar and Walter Horten (the Horten brothers), and America’s 

Vincent Burnelli and Jack Northrop all envisioned large propeller- (and later 

turbojet-) powered military and civilian flying wings. Jones was likewise 

entranced with the purity of the all-wing concept, having advocated such a 

design in passing at an international aerospace congress held in Spain in 1958. 

“Oblique flying wings were where he always was going,” recalled obliqueflying-wing advocate Thomas J. Beutner, who heard Jones extol their virtues 

during a graduate seminar at Stanford.3

 The advent of computer-controlled 
185

Subsequent Oblique-Wing Plans and Proposals

flight and fly-by-wire flight control made the flying wing (which previously 

always had a tendency toward persistent pitching and annoying Dutch roll 

lateral directional coupling) a practicality, evidenced by the first flight of the 

Northrop B-2A flying-wing stealth bomber, on the morning of July 17, 1989, 

at Air Force Plant 42 in Palmdale, CA.

In 1990, R.T. Jones, 45 years after his initial conceptualization of the swept 

wing (and at the mature age of 80), returned to the idea. Over the previous 

decade he had reinvigorated his own research on oblique wings, particularly 

an oblique-flying-wing supersonic transport. In an article on a flying-wing 

supersonic transport, published in 1991 by the prestigious Royal Aeronautical 

Society, Jones noted that the flying wing was “simply a straight wing of high 

aspect ratio and of sufficient size to contain passengers comfortably. Such a wing 

can be steered to different sweep angles and thus adaptable to efficient flight 

over a range of Mach numbers.”4 Jones added that G.H. Lee, of Handley Page, 

Ltd., had reviewed the advantages of this configuration at a subsequent meeting, 

acknowledging his intellectual debts to Jones, beginning with the latter’s demonstration of a small balsa glider oblique wing at the Madrid meeting. Jones stated,

Artifacts created by humans show a nearly irresistible tendency 

for bilateral symmetry. Thus we envision the supersonic transport 

as having the symmetric shape of an arrow, traveling naturally 

point foremost.

 Aerodynamic theory however discloses no preference for such 

symmetry, but shows instead a distinct preference for fore and 

aft symmetry. Thus the theorems of Kármán and Hayes indicate 

that the drag of a thin body having given lift and volume ought 

to be the same if the direction of flow is reversed. Surprisingly, 

even though the Mach waves at supersonic speed show a definite 

direction and trail backward from the nose of a body, all known 

shapes satisfying the requirements of minimum wave drag show 

fore and aft symmetry, that is they present the same aspect flying 

in either direction....

 According to theory if a lifting surface is to achieve the minimum drag[,] every loading projected along oblique characteristic 

lines should be elliptical....[And that] calculation shows that an 

arrow elliptic wing turned with its long axis inside the Mach cone 

has less drag than other distribution of lift or volume within a wide 

constraint area.

5 [Emphasis added.]

Jones then compared his oblique-flying-wing concept with the Concorde 

SST, a slender ogee delta planform then in airline service with British Airways 
186

Thinking Obliquely

and Air France. He noted that the Concorde, due to its fixed short-span, 

low-aspect ratio planform, was inherently inefficient at low speeds, requiring 

afterburning for takeoff, and wasted fully 40 percent of its fuel for low-speed 

operations. The oblique flying wing, however, could minimize its drag over 

a wide range of speeds, subsonic or supersonic, by simply skewing to different angles. He added that subsequent to G.H. Lee’s paper, studies at NASA 

Ames and Stanford University had greatly improved the understanding of the 

aerodynamic properties of the oblique flying wing, testing models that had 

elliptical wings of a 10-to-1 axis ratio with subsonic airfoil sections in Ames’s 

11-foot Transonic Wind Tunnel. The wings, which were mounted on a small 

body, could be set at various angles of yaw. Three different airfoil sections were 

used for the tests. Jones noted that the propulsion system would need to be 

adapted to a wide range of conditions necessitating the need for variable cycle 

or variable bypass engines for the supersonic transport. Jones added, however, 

that at high Mach numbers, such as between 2 and 3, the narrowing Mach 

cone limits the volume of air that can be influenced by the wing and lifting 

efficiency declines, but at slower speeds, around Mach 1.5, “it seems possible 

that fuel economy approaching that of subsonic transports could be achieved.”6

In 1989, NASA awarded a contract to Alexander J.M. Van der Velden, 

of the University of California at Berkeley, to undertake a performance and 

economics analysis of a Mach 2 oblique-flying-wing transport aircraft suitable for replacing the already venerable Boeing B747 passenger airliner. 

In undertaking the contract, Van der Velden rightly credited Jones with 

proposing the concept of an oblique flying wing in 1957, adding that in 

connection with his study, Van der Velden met with Jones in Los Altos in 

1987, discussing its reintroduction in view of the emerging technology of 

artificial stabilization and fly-by-wire flight control. The oblique supersonic 

flying wing synthesizes three challenging concepts—the oblique wing, the 

flying wing, and the supersonic passenger aircraft. The oblique-wing concept 

provides high lift-to-drag ratios at all speeds and therefore greatly increases 

the low-speed performance for aircraft designed for maximum efficiency at 

high speeds. The flying wing has higher cruise lift-to-drag ratios and lower 

empty weights due to the reduced wing-bending moment. The supersonic 

passenger aircraft, such as the Concorde, presented economic problems that, 

as Van der Velden noted, “led to the abandonment of the idea of commercial 

supersonic flight, even though everyone recognizes the importance of reducing the current long-haul flight time.”7

The baseline configuration for Van der Velden’s conceptual design accommodated 462 passengers and 16 cabin crewmembers who could be seated at a 

35-inch pitch, 12 abreast. Windows were located in the nose and emergency 

exits, reached by access ramps leading up to the top of the wing, positioned 
187

Subsequent Oblique-Wing Plans and Proposals

in the nose and trailing-edge side of the passenger cabin. Two entrance doors 

were in the wing nose. The study concluded that it did not make sense to 

design a protruding cockpit structure. Instead, the cockpit space, housing 

both pilots, was located on the left end of the cabin, affording the pilot good 

visibility during approach and climb, his field of vision encompassing from 

70 degrees left to 70 degrees right. If additional cabin space was desired, 

sections could be added at the area of maximum thickness, which actually 

worked to increase the configuration’s lift-to-drag ratio. The wing had an 

elliptical planform with a near-elliptical spanwise thickness-to-chord distribution, resulting in minimum wave drag for a given volume. The wing had 

some upward curvature to maintain uniform distribution of lifting pressures. 

In order to achieve the necessary lift coefficient with minimal drag and a low 

floor incidence, the center of lift during cruise had to be as far back as the 

artificial stability and control system would permit. Like other supersonic aircraft, center-of-gravity location would be maintained from subsonic through 

transonic and into the supersonic regime by shifting fuel.

The proposed oblique flying wing had a conventional monocoque and honeycomb structure, using the same aluminum alloy employed on the Concorde. 

The airframe life, however, would be significantly longer than the Concorde’s. 

This would be accomplished by reducing the maximum speed to Mach 2, 

which would reduce the equilibrium skin temperature and hence the progressive “aging” of the structure. The ceiling to floor connectors were placed every 

10 feet in order to enable the structure to carry the loads of pressurization while 

maintaining a near-unobstructed wide-body-cabin appearance. In order to 

increase one-engine-out yaw control and to minimize the wave drag and wind 

stress, the engines would be podded in four nacelles. The nacelles, distributed 

optimally along the span, could be pivoted over a 35-degree range. The engines 

could either be a refanned Rolls Royce Olympus (the same type used in the 

Concorde) or a double- scale GE F101/110 engine (the basic engine of the B-1 

bomber). The undercarriage would have six legs with four 40-by-14-inch tires 

each. The legs could be redesigned so the oblique flying wing could operate 

from the same runways as the Boeing 757, which would increase the number 

of potential flight destinations. Stability and control around the x and y axis 

would be provided by a 10-percent multi-segmented edge flap similar to one 

proposal earlier by NASA for another transport. The flying-wing configuration 

had three “all-flying” vertical fins mounted on the engine pivots. In order to 

ensure static stability around the z axis, the flying wing would have two rear 

vertical tailplanes. The vortilons could be used to control the boundary layer at 

the high angle of attack that might be produced during heavy wind gust conditions. The proposed flying planform and center cabin section are illustrated in 

the following drawings.
188

Thinking Obliquely

Van der Velden conceptual design for a supersonic oblique flying wing, from CR 177529, 1989. 

(NASA)
189

Subsequent Oblique-Wing Plans and Proposals

Internal cabin arrangement of the Van der Velden supersonic oblique flying wing, from CR 

177529, 1989. (NASA)

Van der Velden concluded by noting the following:

1. As compared to contemporary subsonic aircraft of the same size its 

operational characteristics are superior. The Aircraft can fly at the 

same holding speeds as today’s subsonic transports, and requires 

only half the takeoff field length.

2. The total cost of development of the aircraft is going to be higher 

than any other aircraft so far (around 10 billion (’86) USD), but 

due to the high blockspeed the direct operating costs of the aircraft 

are going to be comparable to the Boeing 747’s.

3. It is therefore proposed that further research is done to validate 

the results presented in this study and to expand the database on 

oblique flying wing configurations.8

Van der Velden extended his work in association with Ilan Kroo with 

a follow-on study prepared for Ames Research Center that was issued in 

1990, featuring a more-refined wing than previously examined. This later 

study explicitly presented the advantages of the oblique flying wing versus 

conventional bisymmetrical configurations as employed by the high-subsonic 

Boeing B747 (conventional swept wing with podded engines), and the HighSpeed Civil Transport (HSCT), with a highly tailored arrow wing.

Aerodynamically, it had a higher L/D ratio over its entire operating envelope, from Mach 0.2 to Mach 2.0. Structurally, it had less weight than any 

conventional configuration because the cabin was enclosed within the lifting 

surface, avoiding the penalties of the classic “tube and wing” airliner. In the 
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Thinking Obliquely

Van der Velden and Kroo supersonic oblique flying wing, from CR 177552, 1990. (NASA)

all-important area of passenger load and runway accessibility, it could carry 

almost twice as many passengers (462 versus 247) yet use a runway almost 

half that of the HSCT design (2,000 meters [6,500 feet] versus 3,600 meters 

[12,000 feet]). Additionally, its payload fraction (percentage of maximum 

takeoff weight) at Mach 2 was as high—14 percent—as that of the Boeing 

B747 at Mach 0.86 and almost twice as high as the bisymmetric HSCT.9

Following on NASA Ames’s preliminary studies of an oblique allwing transport, at cruise Mach numbers between 1.6 and 2.0, a group of 

NASA,industry, and academic investigators from Ames, the Eloret Institute, 

Stanford, Santa Clara University, and Sterling Software undertook a detailed 

assessment of Ames’s work on the oblique-flying-wing concept, examining 

all aspects of its design and conceptualization, including the wing planform, 

cabin and cargo bay layout, airfoil cross section, cockpit design, engine placement, landing gear configuration and location, and vertical tail placement. 

The baseline geometry of the vehicle was as follows10:
191

Subsequent Oblique-Wing Plans and Proposals

Aspect Ratio 10

Wing Maximum Thickness/Chord Ratio 0.16

Passenger Cabin Span 149 ft

Taper Ratio 0.4

Leading Edge Ratio 0.32

Tip Ratio 0.50

Total Wingspan 406.8 ft

Chord in Payload Section 51.4 ft

Chord at Tip 20.6 ft

Maximum Wing Thickness 8.22 ft

Total Planform Area 16,542 sq. ft

Vertical Tail Plan Area/Wing Planform Area .059

Leading Edge Sweep Angle 4.75°

Trailing Edge Sweep Angle 10.02°

Wing Planform—The study team noted that the most important thing to recognize in an oblique all-wing configuration is that once the wing-thickness-chord 

ratio and aspect ratio have been selected, the major dimensions of the wing, 

including wingspan and planform, are determined by the need for the 

passengers to be able to stand inside the aircraft. Therefore, the ratio of aircraft takeoff weight to planform area becomes a necessary parameter in any 

analysis. The engineering team selected a rectangular plan for the passenger 

cabin with straight taper sections outboard to the wingtips. The tips are 

completed with a short dual-ellipse shape. Cargo and fuel are stored in the 

tapered sections. The wing geometry is defined by specifying the absolute 

values of the maximum wing thickness and the length of the payload cabin, 

the thickness-to-chord ratio of the section, the aspect ratio and taper ratio 
192

Thinking Obliquely

of the planform, the tip ratio, and the ratio that sets the leading-edge and 

trailing-edge-wing-sweep angles for the taper section. Finally, the engineering 

team noted that with a low taper ratio, the chord length near the tip would 

become very short. Furthermore, the spanwise lift distribution is assumed 

to be elliptical, and thus the section lift coefficient must be increased near 

the tip to achieve the necessary lift, which might require unacceptable wing 

twist and camber variations. For this study, the wing-taper ratio was limited 

to a minimum of 0.4.

Cabin Arrangement—The proposed cabin arrangement constitutes a 

second rectangle within the rectangular center section of the wing. Seats 

and cross aisles would be arranged in chordwise bays. Entry doors would 

open to four of the bays, and each bay would be divided into a fore cabin by 

a single main spanwise aisle. A lavatory would be located within each bay, 

and emergency exits would be located at the end of each aft cabin bay. Seat 

and aisle dimensions would define the bay plan size, and the bays would be 

arranged side by side to build up the total cabin space.

Cargo Bay Section—Cargo containers, which would be arranged in chordwise rows, would be stored outboard of the cabin in the taper section of the 

wing. Loading of containers would be done through the wing leading edge 

or through the wing lower surface.

Fuel Tanks—The inboard edge of the fuel tank would be just outboard 

of the cargo section. This would provide the best distribution of weight for 

the structural design. The engineering team noted that since the fuel volume 

required for a typical long-range mission is considerably less than the available space, there is a lot of freedom in locating the fuel tanks.

Wing Cross Section—The maximum thickness-to-chord ratio for the proposed airfoil section is nominally 16 percent. A thinner section would result 

in a longer chord and thus a longer span for a given aspect ratio, and a 

thicker section might result in an adverse chordwise shift of the center of 

gravity aft. This shift, however, can be avoided if the number of rows in the 

cabin is reduced. Control of the chordwise shift of the center of gravity is a 

critical design requirement. For stability reasons, the study team estimated 

that the center of gravity should never be farther aft than 32 percent of the 

chord. Also, the wing-section leading edge must be as blunt as aerodynamic 

considerations will allow so that the passenger cabin can be integrated into 

the wing as close to the leading edge as possible. In addition, the forward 

landing gear must be stowed in the wing leading edge. The entry door height 

and location would establish the maximum thickness of the wing for a given 

wing section. The proposed aircraft’s entry door would be cut on a diagonal so 

that the required 72-inch opening could be located farther aft on the chord. 

The door would cut the structure at the floor at 10 percent of the chord and 
193

Subsequent Oblique-Wing Plans and Proposals

cut the ceiling of the cabin at 15 percent of the chord. The proposed internal 

heights in the cabin are 63 inches ahead of the first row of seats, 72 inches 

at the top of the entry door, 80 inches at the maximum point in the fore 

and aft cabins, and 77 inches at the intersection of the two structural lobes.

Access/Egress—The proposed aircraft would have four Type A exits (floor 

level, width of 42 inches, height of 72 inches, direct access from main isle, 

and a 32-inch-wide passage from the opening to the main aisle). These exits 

would also serve as main entry doors. In addition, the aircraft would have a 

Type I exit at the rear of each aft cabin (floor level, width of 24 inches, and 

height of 48 inches). For emergencies, there would be stairs to the top of the 

wing and access to an escape slide from each cabin bay.

Cockpit—The engineering team pointed out that with the oblique allwing aircraft swept on takeoff and landing, the pilot would experience unconventional motion and visual cues and that the best location for the cockpit is 

not clear. They added that a convenient location would be at the wing leading 

edge adjacent to any one of the four entry doors. In addition, the study team 

thought it desirable to locate the cockpit at or near the aircraft’s centerline 

in order to minimize potential problems for landing. The plan that the team 

developed has the cockpit oriented at 40 degrees to the wing’s leading edge. 

This swept angle was dictated by the spanwise position of the landing gear. 

The cockpit location, however, would displace a number of passenger seats, 

and the pilot’s visibility from the cockpit would be considerably reduced from 

the visibility that currently exists for subsonic transport aircraft. Recognizing 

these disadvantages, the engineers noted that there might be better locations 

for the cockpit, including on top of the aircraft with access through a spiral 

staircase at the intersection of the center cross aisle and the main span aisle.

Engine Placement—The proposed aircraft would have four engines located 

symmetrically on the planform. The engines would be pivoted 68 degrees for 

cruise flight. The inboard engines would be mounted just beyond the passenger cabin and the outboard engines would be located approximately 24 feet 

farther outboard on the span. This spacing is dictated by engine separation on 

the trailing wing in cruise. The engines would be mounted on pivots that are 

at 9 percent of the chord and tied directly to the primary structure. The precise 

location of the engines raised several questions. At the 9-percent chord position, 

the engines would create a yawing moment if they were located symmetrically 

on the span. The engines could be located at the 32-percent chord line, but 

this location would cut into cargo or fuel volume, and the engine inlets would 

have to be longer to reach beyond the wing leading edge at cruise speed. The 

yawing moment could be counteracted by pivoting all the engines to toe in, 

but approximately 7 to 9 degrees would be required, which would increase the 

required engine thrust by about 1 percent, and the profile drag of the nacelles 
194

Thinking Obliquely

also would likely increase. The engineering team’s proposed solution to the above 

problems was to vector the gross thrust of the exhaust nozzles. They explained 

that this solution would have a much more powerful effect because gross thrust 

rather than net thrust is acting, and typically only 3 degrees of thrust vectoring 

would also be a positive factor in vertical tail sizing for the engine-out case at 

takeoff. Another issue raised by the engineers was that the vertical position of the 

nacelle below the wing was thought to have been an important parameter that 

would have a strong influence on the interference drag. They added, however, 

that there was no available data to either support or refute this concern. The 

team concluded that it would be desirable to tuck the engines as close to the 

wing as possible to reduce the length of the pivot and the length of the landing 

gear. In regard to the positioning of the engines, the study team added:

The correct positioning of the engines both on the planform and 

vertically with respect to the bottom of the wing is a major unknown 

in the OAW [oblique all-wing] aircraft configuration definition. 

There is no reason to necessarily locate the engines symmetrically on 

the wing. Factors that must be considered are the interference with 

wing, interference between nacelles, effect on the center of gravity 

both spanwise and chordwise, and the potential yawing moment 

produced by the engines without thrust vectoring.11

Landing Gear Number and Placement—The engineering team noted that 

the landing gear for an oblique all-wing aircraft would require more consideration than for a conventional aircraft configuration. There must be a minimum of four struts with steerable trucks. The gear for the proposed aircraft 

design are just fore and aft of the passenger cabin, and the forward and aft 

gear share the load of the aircraft weight nearly equally. Due to this load on 

the struts, a forward gear is not possible. Furthermore, when runway pavement loading constraints are considered, eight struts (four ahead of the cabin 

and four behind the cabin), each with four tires, likely would be required. In 

order to locate the gear farther out on the span, this study planned to sweep 

the wing to 40 degrees for takeoff.

Vertical Tail Sizing and Placement—In this study, the vertical tail is sized 

assuming that the tail must create a restoring moment with a lift coefficient 

of 1.0 to balance the loss of one outboard engine at takeoff. The added drag 

of the unpowered engine is included in the study team’s analysis. The two 

tails would be mounted on pivoting supports located nominally 90 percent 

of the semispan from the aircraft centerline. The vertical tails are assumed 

to have an aspect ratio of nominally 1.0 and the leading- and trailing-edge 

sweep angles are assumed to be 45 degrees and 30 degrees, respectively.
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Subsequent Oblique-Wing Plans and Proposals

The engineering team concluded its study by noting the following:

It must be emphasized that this paper represents a first step in 

defining the configuration details of an OAW aircraft, and thus it 

is premature to draw any definitive conclusions about the viability of the concept or even a “best” design. One fact is clear—the 

aircraft is large, and it should be designed for a large payload.

 The basic performance of the OAW aircraft is considered to 

be excellent. For a flight Mach number of 1.6, the lift-drag ratio 

at cruise is high—nominally 11.5, and the wing unit weight is 

reasonably low compared to conventional wings—nominally 

6.5 pounds per square foot of surface area. Verifying these 

performance estimates is the primary focus for the continuing research at NASA Ames. Aerodynamic efficiency would be 

improved at a reduced cruise Mach number; and included in 

the plan for continued study is a detailed economic evaluation 

of the OAW aircraft at different Mach numbers. Finally, the 

research is to be expanded to include a detailed evaluation of 

low and high speed stability and control requirements.12

Altogether, the early 1990s were a particularly fruitful time for obliquewing studies, both for conventional “tube and wing” and pure flying-wing 

designs. A 1995 survey tracing the past history of oblique-flying-wing proposals, the work accomplished in the NASA Oblique All-Wing program, 

and future planned activity (including Stephen J. Morris’s then-ongoing 

radio-controlled (RC) model work), enumerated the many NASA and 

industry activities undertaken between 1991 and the end of 1994 (and it is 

worth remembering that, even prior to NASA’s direct involvement in Jones’s 

oblique flying wing, important predecessor work was carried on at Stanford 

University from 1988 to 1990, with grants from NASA Ames). See the following table.13

Samples and Examples: Extrapolating 

Beyond Jones’s Inspired Work

Van der Velden and Kroo’s work, joined with that of others in NASA, academia, and industry, encouraged subsequent work by Ames, defining a range 

of possible transonic and supersonic oblique flying wings for various civil air 

transport missions, carrying up to 500 passengers, and spawning a series of 

industry studies, including those by McDonnell-Douglas and Boeing.14 The 
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Thinking Obliquely

Activity Completed

Systems Analysis Study at NASA Ames July 1991

Conceptual Design by Frank Neumann of Boeing December 1991

AIAA Papers—Structural/Aero and Economics by NASA Ames August 1992

Configuration and Airport Interface Study by Boeing June 1993

Design Study by the University of Kansas June 1993

Wind Tunnel Test Design Team established at NASA Ames July 1993

Aerodynamics and Stability-Control Study by 

McDonnell-Douglas

October 1993

20-Foot Ground and Flight Test by Stanford University May 1994

Supersonic Wind Tunnel Test at NASA Ames August 1994

Mission Analysis Study by McDonnell-Douglas December 1994

following indicate the sweep of research inspired by Jones’s oblique-flying-wing 

work and his oblique-wing research in general.

General Electric Mach 2 Oblique-Flying-Wing High-Speed Civil Transport

In 1991, three General Electric Aircraft Engines company engineers—D.W. 

Elliot, R.D. Hoskins, and R.F. Miller—outlined their findings regarding 

oblique-wing aircraft. They noted that NASA’s goals for the High-Speed Civil 

Transport Study were to identify a cruise Mach number, a certification date, and 

the relevant technologies required to support an HSCT aircraft. The primary 

contracted participants were airplane builders Boeing and McDonnell-Douglas 

and aircraft engine manufacturers General Electric (GE) Aircraft Engines and 

Pratt & Whitney. The specific identified goals were a 2005 certification date, a 

5,000-nautical-mile range, and a 300-passenger capacity. As background, the 

GE engineers noted that environmental constraints (takeoff noise, emissions, 

and sonic boom) were playing a significant role in sizing the airframe and 

engine combination. They added that even though the HSCT appeared to be 

a point-design system with over three quarters of the fuel burned in a single 
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Subsequent Oblique-Wing Plans and Proposals

condition (Mach 2.4), neither the cycle nor the engine size was optimized for 

cruise in a fixed-wing configuration. To meet the environmental challenges and 

HSCT performance goals, the engine companies headed by GE and Pratt & 

Whitney joined forces in 1990 to provide the airframers with an acceptable 

engine. This effort included working nozzle-suppressor schemes and exotic 

variable cycles to meet the noise standards, designing combustors that would 

reduce emissions indexes by 10 times the current subsonic designs, and circumventing the sonic boom with lower fuel consumption for efficient subsonic 

operation over populated areas.15

The GE engineers also noted that the airframe companies, working independently, both had fixed-wing baseline configurations reminiscent of the 

1970s Aeronautical and Space Technology (AST) configurations. In this regard, 

the GE team posed the question, “Is the level of aerodynamic and propulsion 

efficiency sufficient to produce a viable HSCT and meet the environmental 

constraints of 2005?”16 At this point, the GE engineers noted that “[g]ranting 

the need for variable geometry, the oblique wing concept envisioned by R.T. 

Jones in the late 1950s offers even more advantages by eliminating some of the 

major drawbacks of the conventional variable sweep designs exemplified by 

the F-14, F-111, and B-1.”17 In response to their own question, the GE team 

noted several advantages of using an oblique-wing configuration. For one, 

they noted that area ruling of the fuselage was not necessary, thus allowing 

a constant section and ease in extending the fuselage (“plugging”) for future 

growth. By contrast, an area-ruled fuselage, necessary on fixed-wing configurations, required varying frames and compound surface contours that are difficult to plug economically. Also, the landing gear is expected to be shorter 

by mounting the engines Caravelle style (e.g., off the sides of the aft fuselage, 

in the fashion of the French Caravelle, an early twin-jet airliner), since the 

nozzle of the wing-mounted engines were currently setting the tail down line. 

The GE team added, “The safety benefit related to the variable geometry is 

the fact that an oblique wing malfunction in the swept cruise position would 

not compromise the landing (but necessitate a higher speed) since the gear is 

independent of the wing sweep.”18

A unique feature of the oblique-wing configuration reviewed in the paper 

was the location of the oblique wing under the pressurized passenger compartment and above the landing gear bay. The GE team noted that this configuration solved the most aggravating problem in utilizing the oblique wing, which 

was fairing the wing to the fuselage. The engineers noted that this problem was 

so severe that a past Navy high-wing design had considered raising the wing for 

low speed and lowering the wing to set in a fixed fairing for supersonic flight. 

The configuration reviewed had a lazy Susan bearing above and below the wing, 

thus eliminating the loads associated with canter levering the wing on a post 
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Thinking Obliquely

above or below the bearing set. Also, the midwing location on a constant section fuselage makes the fairing a very simple hinged and/or sliding-door-type 

closeout. In regard to weight, the team noted that the major weight savings of 

an oblique-wing configuration was due to the approximately 15-percent-lessfuel requirement over a fixed wing. The takeoff advantages of an oblique wing 

were due to the high aspect ratio available in the unswept position and the need 

for only a simple single-slotted flap (whereas a fixed wing requires both leading 

and compound trailing edge devices to make up for the high sweep and low 

aspect ratio). An oblique wing’s takeoff speed could be as much as 30 knots 

slower and at a 3-degree-smaller angle of attack than that of a conventional 

bisymmetric wing.

The GE team concluded,

The estimated improvements throughout the total flight regime, 

allied with the reduction in potential problem areas demand a 

serious and timely assessment of an oblique wing HSCT. The 

positive attributes far outweigh the negative aspect of this concept. The liabilities have been identified and many studies have 

addressed both the aerodynamic characteristic and flying qualities 

peculiar to oblique wings; there should be no surprises. In this 

industry where percents in single digit are eagerly pursued, the 

double digit gains to be realized with the oblique wing concept 

must be pursued.19

California Polytechnic State University HSCT Project

California Polytechnic State University at San Luis Obispo has always had a 

robust reputation in aeronautics, enhanced by the number of distinguished 

graduates and alumni—Burt Rutan being one such—who have graced its halls 

and laboratories. In 1992, six aeronautical engineering seniors at California 

Polytechnic State University, as a required senior project, responded to a NASA 

Request for Proposals for a preliminary design of a 300-passenger, Mach 1.6, 

5,000-nautical-mile-range high-speed transport. The six aeronautical engineering students designated their High-Speed Civil Transport design, which 

included a variable-geometry oblique wing, the RTJ-303. The overall length of 

the proposed aircraft was 325 feet with an unswept wingspan length of 231 feet. 

If the wing was swept during all ground operations other than takeoff, the aircraft 

was much more slender than conventional winged aircraft. The projected wing 

area was 5,235 square feet. The determining factor for the wing-area choice was 

the thrust-to-weight ratio that was limited to 0.30 in order to use reasonably 

sized engines. The study noted that while no supersonic flight-test data had been 
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Subsequent Oblique-Wing Plans and Proposals

obtained to date, supersonic wind tunnel data had been obtained by NASA 

for Mach numbers up to 1.4 with wing-sweep angles up to 60 degrees. Also 

noted were the subsonic flight tests conducted by NASA using remotely piloted 

aircraft and the low-cost piloted AD-1 Oblique Wing Research airplane. The 

aeronautical engineering students added that the payload of 300 passengers was 

a compromise between length restrictions on the aircraft and the desire to remain 

competitive in the market with the maximum number of passengers carried for 

each flight. The 5,000-nautical-mile range was based on a flight model of 4,700 

nautical miles from Los Angeles to Tokyo plus a 300-nautical-mile reserve to 

reach an alternate airport. This range requirement necessitated a fuel volume that 

must be carried mostly in the wing. The students concluded that “this aircraft 

could be built with today’s technology and does not rely on vague and uncertain 

assumptions of technology advances.”20

The proposed aircraft configuration for the RTJ-303 resulted from a combination of a series of industry oblique-wing studies. Altogether, it was a much 

more traditional oblique-wing design than the pure flying-wing conceptions 

popular at the time, with a tube-and-wing approach strongly reflecting the 

early work of Jones and his initial conceptualizations. But appearances could 

be deceiving, and the RTJ-303 had a number of interesting features. Two of 

the attractive features identified for the configuration were the constant crosssection fuselage and the variable-wing geometry. The fuselage did not have 

the area-ruled bottleneck appearance characteristic of many conventional airplane designs, thus allowing a fuselage of constant cross-section to be utilized, 

which simplifies the fabrication processes and enables the fuselage to be easily 

lengthened. The design featured an elliptical variable-geometry oblique wing 

with a high aspect ratio (10 to 1) with conventional tail-aft control surfaces. 

The maximum sweep angle of 62 degrees was selected because beyond this 

angle, a dramatic loss of aileron control effectiveness exists, as does the occurrence of aeroelastic divergence problems on the forward swept wing. At the 

62-degree angle, the wing leading-edge normal Mach number was just below 

drag divergence for the airfoil section of the wing. The fuselage nose and tail 

cones consisted of modified paraboloids joined by a cylindrical center section. 

The proposed RTJ-303 would have four mixed-flow turbofan engines grouped 

into two separate pods staggered and mounted on either side of the fuselage. 

The vertical and horizontal tail surfaces were swept at 65 degrees in order to 

facilitate the use of rounded leading edges on conventional NACA airfoil sections. A retractable tricycle-design landing gear would be used on the RTJ-303.

The study included a cost analysis based on 1992 U.S. dollars. The estimated price for each airplane was $183 million ($295 million in 2011), which 

included the costs from the initial research and development through the production of the aircraft. The price estimate was based on a production run of 300 
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Thinking Obliquely

RTJ-303 student design project for an oblique-wing SST, California Polytechnic State University, 

from CR 192054, 1992. (NASA)

aircraft. The estimated per airplane life cycle cost (LCC) was $2.6 billion ($4.2 

billion in 2011). This number included research, development, testing and 

evaluation; manufacturing and acquisition; operation cost; and disposal cost.

The study team concluded their report with the following observations and 

recommendations:

Having such a long list of benefits, one should wonder why 

supersonic oblique wings are not flying today. The answer to this 

question would most likely be the fact that industry is reluctant to 

make large investments in a configuration which has not proven 

itself yet. Furthermore, real concerns have been brought up in 

the past regarding the aerodynamic problems and controllability 

of such an asymmetric design. However, problems previously 

thought to be insurmountable are believed to be solvable with 

today’s technology. The highly cross-coupled nature of the plane 

can be easily solved with current fly-by-wire technology. The 
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Subsequent Oblique-Wing Plans and Proposals

pilot need never know that he is flying an oblique wing aircraft. 

An aeroelastically tailored composite wing using unidirectional 

carbon fibers drastically reduces the problem of aeroelastic twisting and divergence.

 Recommendations for the HSCT design program are that 

supersonic flight tests be performed and performance characteristics be studied, research into synthetic vision be carried 

out, and composite wing tailoring be tested for effectiveness of 

reducing aerodynamic twisting and divergence. Further studies 

should be made as to the economics of variable sweep HSCT 

that carries fewer passengers in order to reduce the overall length 

and weight of the plane.21

Oblique Options: Pros and Cons of “Tube and Wing” or “All Wing”

As the Stanford and California Polytechnic State University (Cal Poly) studies 

showed, considerable divergence of thought existed as to the likely future of 

oblique technology as applied to air transport design. That conundrum—

which road to choose—led Thomas Galloway, Paul Gelhausen, and Mark 

Moore, of NASA Ames, and Mark Waters, of the Eloret Institute, to examine the respective technical and economic characteristics of two supersonic 

transport concepts—one an oblique wing-body configuration that carries 

the passengers in a traditional cylindrical-cross-section “tube” fuselage and 

the other an oblique all-wing configuration that accommodated the passengers within the wing structure à la Jones, Van der Velden, and Kroo. They 

compared these oblique-wing-on-fuselage and oblique-all-wing configurations with Boeing’s 300-passenger 767 and 777 and the 400-plus-passenger 

747. The study parameters included passenger capacities from 300 to 500, 

a design range of 5,000 nautical miles, a standard international fuel-reserve 

requirement, design Mach numbers of 1.6 and 2.0, a production quantity 

of 500 aircraft, a development period of 5 years, and a 15-year delivery 

schedule.22

Although designed for a maximum range of 5,000 nautical miles, the 

concepts were evaluated for economic analysis based upon an average trip 

distance of 3,800 nautical miles. The computer model used was the ACSYNT 

design synthesis program, which estimated the aircraft performance and sized 

the aircraft to meet the specified mission requirements reviewed above. The 

cost modules in ACSYNT estimated the aircraft price, operating costs for 

the mission, and the overall return on investment to the airline and aircraft 

manufacturer. The economic viability was assessed based on the average passenger revenue (cents-per-revenue passenger-mile) required for the airline to 
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Thinking Obliquely

make a 12-percent return on investment when the aircraft is priced so that 

the manufacturer also makes a 12-percent return on investment.23

The study’s conclusions were summarized as follows:

The study focused on identifying the economic potential of supersonic OWB [oblique wing-body] and OAW [oblique all-wing] 

designs compared to equivalent passenger size subsonic concepts. 

At the smallest passenger size studied (300), the Mach 2.0 OWB 

required the least increase in revenue above the subsonic baseline. 

As the passenger sizes increased to the largest size studied (544) 

the Mach 1.60 OAW required revenue only 9 percent above the 

subsonic concept. The variable sweep capability of the oblique wing 

designs offers the flexibility to cruise subsonically, if required because 

of sonic boom constraints, and suffer no penalty in the aircraft’s 

range capability. Since the oblique wing designs can meet takeoff 

field length requirements with significantly throttled engines, current Stage 3 noise levels can be met without major noise suppression 

devices. At the supersonic speeds of the study current aluminum 

airframe can be used to keep manufacturing costs low. In summary, the oblique wing concepts offer supersonic flight with trip 

times one-half the subsonic aircraft, needs only a modest increase in 

revenue, and have operational features that allow efficient subsonic 

operation and minimize noise around the airport.24

Stephen Morris and Small-Scale Radio-Controlled 

Oblique-Flying-Wing Flight Test

In his advocacy of the oblique-flying-wing concept, R.T. Jones cited the 

encouragement and assistance that he had received from Stephen Morris, then 

a doctoral student at Stanford, where, among others, he worked with Ilan Kroo. 

It would be Morris who would undertake a notable step forward in obliqueflying-wing studies by actually constructing and flying two radio-controlled 

flying wings, a significant first in aviation history arguably equivalent in significance to Alphonse Pénaud’s first flight of a powered model airplane in 1871. 

In the late 1980s, Morris and Kroo had studied aircraft design optimization, 

looking at interactions between weight, aerodynamic performance, and handling qualities using various design examples, including the proposed F-8 

OWRA and the challenge of dynamic mode decoupling. At the time, Morris 

was completing a doctoral dissertation on integrated aerodynamic and control system design for an oblique wing, looking at the challenge of ensuring 

adequate stability, control, and handling qualities at sweep angles above 30 
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Subsequent Oblique-Wing Plans and Proposals

Ames study for an oblique-wing “Turn and Glide-Back” space launch booster recovery system, 

1999. (NASA)

degrees, where the highly asymmetric nature of a swept oblique wing induced 

aerodynamic and inertial couplings that degraded both stability and handling 

qualities. Eventually, as part of his research, Morris built a 10-foot-span, radiocontrolled, statically stable oblique flying wing powered by a small two-stroke 

engine. Though initial flight trials were disappointing, Morris persisted until 

he had refined a stable configuration whose wing could be swept between 25 

degrees and 65 degrees. He followed this in 1994 with a more complex, statically unstable, twin-ducted-fan, radio-controlled model with a three-axis rate 
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Thinking Obliquely

gyro. Though it completed only a single flight before NASA funding shortfalls 

ended the program, it did demonstrate satisfactory handling qualities up to a 

50-degree sweep, a notable accomplishment.25

Beyond Civil Air Transport: 

Oblique Wings for Other Mission Areas

The advent of the oblique wing, coming as it did coincident with the revolutions in electronic flight control; lightweight, resilient, and strong composite 

materials; advances in command, control and sensor architectures; the onset of 

the Unmanned Aerial Vehicle (UAV), formerly, the Remotely Piloted Vehicle 

(RPV), and subsequently, the Remotely Piloted Aircraft (RPA); the era of 

space transportation and routine access to space; and the precision-weapon 

and cruise-missile eras, ensured that the planform would soon be evaluated 

for far more than simply its suitability to civil air transports.

One area of appeal involved something far afield from conventional air 

transport: using an oblique wing to enable recovery of the Space Shuttle’s 

booster system. NASA already recovered the burned-out solid-rocket boosters 

(SRBs) after each launch via a parachute-and-floatation-bag system, but it was 

complex, entailed search and recovery costs, and then extensive refurbishing 

and processing costs as well, since they were thoroughly soaked in the Atlantic 

Ocean. The appeal of recoverable first stages was long-standing within the 

astronautics community because recovering and then reusing a first stage could 

considerably reduce the operational costs associated with space launch and 

routine access to space. Fly-back boosters and recoverable booster concepts 

featured prominently in early Shuttle concepts, but the complexity of such 

systems and the penalty they imposed upon vehicle configuration, weight, and, 

hence, performance, dissuaded the designers from using them. But nearly two 

decades after the first orbital flight of the Shuttle, the technical situation, and 

rising concern over the cost of space launch (particularly the Shuttle), led to 

a resurgence of interest in fly-back boosters. The oblique wing, a much more 

suitable wing configuration than some sort of fixed delta wing, lifting body, 

or variable-geometry approaches, had decided appeal.

Accordingly, in 1999, Stephen C. Smith, Robert A. Kennelly, Jr., and James 

Reuther of the NASA Ames Research Center Aeronautics Directorate studied 

the feasibility of a “Turn and Glide-Back” system using an oblique wing to 

make the Shuttle’s solid-rocket boosters, and other spacecraft first-stage boosters, more easily recoverable, including running a series of tunnel tests on a 

suitable configuration. Unlike conventional bisymmetric swept wings, which 

posed daunting structural, storage, and deployment challenges, the oblique 
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Subsequent Oblique-Wing Plans and Proposals

wing stowed lengthwise on a booster with minimum impact on its ascent 

configuration. When deployed, the oblique wing could operate efficiently from 

a highly swept low-aspect-ratio profile at high supersonic speeds (L/D=3.5 to 

4.0) down to a subsonic high-aspect-ratio, high-lift profile (L/D=10 to 15), 

thus furnishing adequate L/D across a wide Mach number range from M=0.35 

to 2.35.26 The oblique wing remains an intriguing possible approach to reduce 

the cost and increase the flexibility of space access.

Another area constituting a natural field for oblique-wing utilization has 

been the steadily emerging field of remotely piloted aircraft. In 2000, R.K. 

Nangia, a consulting engineer with Nangia Aero Research Associates, and 

D.I. Greenwell, then principal scientist with the United Kingdom’s Defense 

Evaluation Research Agency (DERA), addressed potential military applications of oblique-wing combat UAVs and piloted aircraft.27 Their paper 

focused on design for transonic cruise at low altitudes, noting that “for 

oblique wing aircraft, the intuitive feeling is that the main problems are more 

likely to do with ensuring adequate control rather than drag reduction,”28

and concluding:

The Oblique Wing (OW) concept remains a proposition for 

meeting rigorous aerodynamic performance goals for Mach 

numbers to about 1.7 over a wide flight envelope up to 40,000 ft. 

With appropriate wing sweep, high efficiencies can be obtained 

at low speed. The handling, stability and control issues remain 

a strong design challenge to ensure adequate stability in pitch, 

yaw and roll. This has led to a work programme with the objective of assessing the suitability of such concepts for manned and 

UAV combat aircraft applications.29

In this vein, in August 2005 (following upon an encouraging earlier 

study on the prospects of supersonic oblique flying wings undertaken for the 

Defense Advanced Research Projects Agency by the Massachusetts Institute 

of Technology and Desktop Aeronautics), DARPA issued a Request for 

Proposals for an Oblique Flying Wing experimental aircraft (OFW X-Plane) 

that meets the following “non-tradable” design requirements:

• 

• 

• 

• 

• 

reusable conventional takeoff and landing (CTOL) using a retractable landing gear,

conventional air-breathing propulsion,

max Mach greater than or equal to 1.20,

tailless configuration,

variable-oblique-wing sweep from 30 degrees to greater than or 

equal to 60 degrees,
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• 

• 

Thinking Obliquely

aspect ratio greater than or equal to 7 at minimum sweep, and

wingspan greater than or equal to 40 feet at minimum sweep.30

On March 16, 2006, this resulted in the agency awarding a $10.3 million, 

20-month contract to Northrop Grumman for risk reduction, testing, and 

preliminary design of an OFW X-Plane demonstrator aircraft. (Subsequently, 

funding was increased to 14.5 million, and Northrop Grumman contributed 

$7 million of its own.)

Though not directly tied to the Air Force’s contemporary interest in precision long-range strike, the DARPA effort noted the oblique wing’s promised range of flight efficiency from subsonic through supersonic velocities, 

guaranteeing a favorable combination of speed, range, and endurance that 

would be desirable in any long-range strike system. The result of this study 

was an 18,334-lb gross weight, twin-engine subscale oblique-flying-wing 

design powered by two afterburning GE J85-21 turbojet engines (the same 

kind used in the Northrop F-5E/F Tiger II lightweight fighter) mounted in 

swiveling pods with an unswept span of 56 feet 4 inches. Its aspect ratio (AR) 

varied from 7.2 at minimum sweep to 1.33 at maximum (65 degrees) sweep. 

Over the length of the study effort, more than 1,000 wind tunnel test runs 

were performed on the configuration. Unfortunately, though the program 

satisfactorily completed its preliminary design phase, DARPA canceled it in 

May 2008, before it was actually fabricated and flown, a decision that appears 

unfortunate given the value such a flight demonstration could have had.31

The oblique wing has also received consideration for use on basic weapons 

such as projectiles and missiles. Because (as with space launch, discussed 

earlier) the oblique wing can easily be rotated to a fully streamlined position where the span of the wing is aligned parallel to the longitudinal axis 

of a projectile and missile, it offers an attractive means of giving a ballistic or near-ballistic weapon a high lift-to-drag ratio, thus greatly extending 

its engagement range and affording standoff to the launching system from 

enemy defenses.

In 2005, ZONA Technology, Inc., proposed that the U.S. Navy extend 

the range of its standard 5-inch, 54-caliber naval cannon (typically used 

on destroyers and cruisers) by modifying its shell with a “body-conformal 

oblique wing/tail with smart-structure (actuator) control.”32 The Navy was 

working on an Extended Range Guided Munition (ERGM) 5-inch precision round, the EX-171, scheduled to reach initial operational capacity. The 

Navy was considering achieving the extended range through a combination 

of rocket assistance and gliding flight. The rocket motor, however, would 

have a negative impact on payload, cost, safety, and reliability, so the Navy 

design strategy under their Naval Surface Fire Support (NSFS) program was 

to eliminate the rocket motor while at the same time trying to satisfy most 
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Subsequent Oblique-Wing Plans and Proposals

of the extended-range requirement. ZONA’s work was sponsored by a Navy 

contract (N00178-00-C-1051) awarded under a Small Business Innovation 

Research (SBIR) phase II program. NASA Langley and NASA Ames assisted 

one of the ZONA engineers in setting up and using PEGUS overset grid 

data. ZONA Technology noted that their innovative oblique-wing projectile “would maintain the maximum lift-to-drag ratio (L / D) throughout its 

gliding phase and achieve an extended range which exceeds the maximum 

range required for the rocket-assisted ERGM [Extended Range Guided 

Munition].”33 The study pointed out that

[t]he oblique wing has superior aerodynamic characteristics 

because it can maintain a subsonic leading edge throughout the 

supersonic/transonic ranges and significantly reduce the wave 

drag. In fact, it can achieve a much higher lift-to-drag ratio at all 

Mach numbers than virtually any other wing. For supersonicflight deployment of the wing near the apogee, maintaining 

the maximum lift-to-drag ratio of the projectile throughout the 

whole gliding phase requires the oblique wing to move in a 

continuously [sic] manner at each optimal sweepback position 

with a simple, light-weight mechanism.34

In conducting their study, the ZONA engineering team made extensive 

Navier-Stokes computations to search for the best sweepback positions of 

the oblique wing for the given pairs of Mach numbers and the angles of 

attack in the supersonic and transonic gliding phases. The engineers used 

the NASA CFL3D v6 computer code, which was developed and supported 

by NASA Langley. The CFL3D code is a three-dimensional, thin-layered, 

Reynolds-averaged Navier-Stokes code that uses an implicit approximately 

factored, finite-volume, upwind, and multigrid algorithm. Through the use 

of this code, after generating all component grids at one wing angle, it was 

only necessary to rotate the wing and wing-cap grids for different wing positions. The study results, reported at the 23rd AIAA Applied Aerodynamics 

Conference in Toronto, Canada, in June 2005, concluded the following:

Extensive Navier-Stokes computations have been performed to 

determine the optimal scheduling of the oblique-wing for a 

projectile during the supersonic and transonic gliding phases. It 

is found that using the oblique-wing technique, a guided projectile can achieve the maximum lift-to-drag ratio throughout its 

gliding phase and therefore extend its range beyond the target 

100 nm without rocket gliding assistance.35
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In January 2008, two Air Force Institute of Technology researchers presented study results of wind tunnel tests of an oblique-wing-missile model. 

In undertaking their study, Captain Matthew J. Dillsaver and Milton E. 

Franke found that

[e]ver since Chuck Yeager broke the sound barrier in 1947, aerial 

vehicle designers have been looking for wing designs that perform 

well at both subsonic and supersonic speeds. One way to accomplish this goal is through wing morphing of some kind providing 

variable wing geometry. One purpose of wing morphing is to 

provide a high aspect ratio for low-speed flight and loitering and 

a low aspect ratio for high-speed flight.

 A variable geometry concept currently garnering more 

research is the oblique wing design. In 1952, Jones proved that for 

any flight Mach number the minimum drag for a given lift could 

be achieved by an oblique swept wing with an elliptic planform. 

Other wind tunnel tests have shown that oblique wings are very 

effective at reducing wave drag at supersonic speeds. In 1958 Jones 

noted that wave drag and induced drag could be minimized by a 

variable sweep oblique wing with an elliptical lift distribution. At 

supersonic speeds drag on an aircraft is dominated by wave drag. 

One major advantage of oblique wings for supersonic flight is 

that for equivalent span, sweep, and volume the wings distribute 

the lift over twice the length of a more conventional sweep wing 

planform. This reduces lift dependent wave drag by a factor of 

four and volume dependent wave drag by a factor of 16. Jones 

also showed that the induced drag of an oblique wing at optimal 

sweep is half of that for a delta wing of the same span.36

Dillsaver and Franke noted that from 1979 to 1982, NASA successfully 

flew the full-scale demonstrator, the AD-1, for a total of 79 hours. They also 

noted that NASA’s F-8 oblique-wing program confirmed that controllability was a major issue to be addressed when dealing with oblique wings. In a 

comment on tunnel testing and test-result fidelity, the two engineers recognized 

the limitations of using a ground plane in a wind tunnel because the boundary 

layer buildup on the plane’s top surface can distort flow, compromising accurate 

data acquisition. As a possible solution, they recommended incorporation of a 

boundary layer removal system.

Dillsaver and Franke undertook their wind tunnel testing in the Air Force 

Institute of Technology (AFIT) 3-by-3-foot low-speed wind tunnel at WrightPatterson AFB, OH, employing an aluminum missile model. The model had a 
209

Subsequent Oblique-Wing Plans and Proposals

length of 28.44 inches with a projected diameter of 2 inches. The missile model, 

which had previously been used for joined-wing testing, had four identical tailfins, two horizontal and two vertical, employing a symmetric airfoil. The oblique 

wing had a span of 17.5 inches, with no twist or dihedral; its chord was 2 inches; 

and it had a blunt leading edge. The wing section had a positive camber. The 

oblique wing was installed on the missile with the pivot point near the model’s 

center of gravity. The wing-sweep angle was measured from 0 degrees to 90 

degrees. (Zero degrees was defined as when the wing was perpendicular to the 

missile body—i.e., fully spread—and 90 degrees was defined as the wing being 

aligned parallel to the longitudinal axis of the missile body.) A ground plane, 

consisting of two steel plates supported by eight cylindrical steel legs, was installed 

in the tunnel to simulate the missile separating from an aircraft. The missile and 

wing were tested in two different flight conditions. Simulated launch effects from 

an aircraft were performed by inverting the missile above the ground plane to 

determine the forces caused by the simulated inground effects.

Based on the wind tunnel test results, Dillsaver and Franke concluded that

[t]he oblique wing model presents an alternative to missile range 

extension and may allow a way to provide range extension. The 

tests herein, however, are preliminary tests as additional information is required at higher speeds to take possible advantage 

of the oblique wing both in release and in flight. Also, to get an 

understanding of the separation and stall, additional testing will 

need to be accomplished using pressure transducers and some 

flow visualization.37

Afterword: Robert T. Jones, the 

Oblique Wing, and His Legacy

Conceptualizing and refining the oblique wing constituted the culminating 

achievement of Robert T. Jones, an individual whose place in the pantheon of 

American aerospace pioneers is secure, together with colleagues such as Max 

Munk (airfoil theory and the variable-density tunnel), John Stack (supersonic 

research aircraft), and Richard T. Whitcomb (area rule).

Ironically, while he achieved great success with the bisymmetrical swept 

and delta planform, the same has not been true of the oblique wing, despite 

its obvious advantages. This has not been lost on his admirers, either before 

Jones’s death or after.
210

Thinking Obliquely

In his Introduction to the Collected Works of Robert T. Jones, written before 

Jones’s passing, William R. Sears (commenting on why no transonic obliquewing transports had yet been built) noted the following:

The aeroelastic properties of the oblique wing have frightened 

a number of engineers, for the upstream panel surely wants to 

deflect aeroelastically upward and the downstream panel downward. To Bob it seems obvious that these effects simply do not 

occur in flight. A study of the equilibrium of rolling moments 

will confirm that he is right. The details are left to the reader; it 

must be said that the conclusion is not quite “obvious,” even to 

most aeronautical engineers!38

In his 2005 biographical review of R.T. Jones, written as a memorial tribute, 

the engineer-historian Walter G. Vincenti (himself a notable NACA-NASA 

pioneer), in reviewing the legacy left by Jones in regard to the oblique-wing 

concept, noted the following:

Thanks to R.T.’s impetus and vision, there now exists a large 

body of knowledge of possible oblique-wing airplanes in both the 

pivoted and flying-wing versions. In the course of this work, the 

stability-and-control and aeroelastic problems that accompany 

the oblique wing have been solved. Sears writing in 1976 with 

regard to the pivoted wing said “I, for one, fully expect to see 

future transport airplanes with Jones oblique wings.” Though 

aircraft companies have studied the possibilities, what Sears 

expected has not, for a complex of reasons, come to the pass 

with either version.39

It is pleasant to record that Jones did more than theoretically conceptualize the oblique wing. Through his advocacy and persistence, he ensured that 

it actually did appear in flight, most notably, of course, with the AD-1 but, 

significantly as well, with subscale radio-controlled models and as a conceptualization that attracted the attention of major design firms and national agencies. 

It is even more pleasant to note that he was an observer to, and a participant 

in, such accomplishment, having witnessed the flights of oblique-wing test 

beds, particularly, again, his AD-1.

In their assessments, both Sears and Vincenti identified some points worth 

pondering and exploring. Sears noted the tendency toward design conservatism. Just as the comfortable traditionalism of the tube-and-wing airliner has 

persisted long after the era of electronic flight control has made the flying wing 
211

Subsequent Oblique-Wing Plans and Proposals

a practicality, so too has the seductive mirror image of bisymmetric sweep 

inhibited the creativity of many who should look to the barrier-breaking 

oblique wing with greater enthusiasm than they do. Vincenti, in acknowledging what has come to pass, rather than what might have been, has illuminated 

a future that has not, to date, been realized—but a future that will because the 

advantages of the oblique wing are simply too great to ignore. For any flight 

vehicle operating in the high transonic-supersonic regime, for any conventional 

space launch system boosting into space or returning from it, for any projectile 

or weapon that has to fly a distance at supersonic speeds, the oblique wing 

offers a simplicity of concept and fabrication that makes it more acceptable 

than other forms of variable sweep.

Reviewing the history of the oblique wing, its application to the AD-1, and 

its subsequent history since that milestone aircraft, one can see that the actual 

flight demonstration—in an inhabited aircraft, and not simply a model or 

rudimentary remotely piloted aircraft—was an important moment in NASA 

research. Jones had conceived the oblique wing, and his reputation ensured it 

would be taken seriously. But nothing was more convincing than the sight of 

the AD-1—an SST configuration, if flying at only a quarter of the speed—

coursing through the air, its wing sharply swept, a veritable flying scissors.

The legacy of Robert Jones—and those he inspired, influenced, and mentored—is this: While the transonic or supersonic oblique-wing transport, either 

as a pivoted wing on a fuselage or as a flying wing, has not yet been built, 

the promise of the oblique-wing configuration, as evidenced by the many 

design proposals and projects this work has enumerated, remains attractive to 

many in the aerospace community for a number of applications, ranging from 

advanced airliners and remotely piloted aircraft to missiles, rockets, and shells. 

That oblique-wing vehicles will fly is not in doubt. The only question is when.
212

Thinking Obliquely

Endnotes

1. Michael J. Hirschberg, David M. Hart, and Thomas J. Beutner, “A 

Summary of a Half-Century of Oblique Wing Research,” a paper 

presented at the 45th AIAA Aerospace Sciences Meeting and Exhibit, 

Reno, NV, January 8–11, 2007, AIAA paper no. 2007-150 (2007), 2.

2. T.C. McMurtry, A.G. Sim, and W.H. Andrews, “AD-1 Oblique 

Wing Aircraft Program,” AIAA paper no. 81-2354, AIAA/SETP/

SFTE/SAE/ITEA/IEEE, 1st Flight Testing Conference, November 

11–13, 1981, Las Vegas, NV, 1. 

Even though, they hopefully concluded (as discussed in chapter 4): 

“The development of a vehicle which would incorporate these new 

features has been considered impractical, however, because of the 

structural divergence problems inherent in the forward swept wing 

sections. However, with recent advances in the state of the art composite structural design and the advent of active control systems, the 

advantages of this concept may be realized in the future.”

3. Thomas J. Beutner with Richard P. Hallion, telephone conversation, 

December 7, 2011.

4. R.T. Jones, “Technical Note—The Flying Wing Supersonic 

Transport,” The Aeronautical Journal 95, no. 943 (March 1991): 103.

5. Ibid.

6. Ibid., 103–106.

7. Alexander J.M. Van der Velden, “The Conceptual Design of a Mach 

2 Oblique Flying Wing Supersonic Transport,” NASA CR 177529 

(May 1989), 2.

8. Ibid., 13.

9. Alexander J.M. Van der Velden and Ilan Kroo, “The Aerodynamic 

Design of the Oblique Flying Wing Supersonic Transport,” NASA 

CR 177552 (June 1990), figs 5.1–5.4.

10. M.H. Waters, M.D. Ardema, C. Roberts, and I. Kroo, “Structural 

and Aerodynamic Considerations for an Oblique All-Wing Aircraft,” 

a paper presented at the AIAA Aircraft Design Systems Meeting, 

Hilton Head, SC, August 24–26, 1992, AIAA paper no. 92-4220 

(1992), 1–3, 13. The study team noted that the configuration would 

undoubtedly continue to change as more constraints and requirements become clear.

11. Ibid., 5.

12. M.H. Waters, “Structural and Aerodynamic Considerations for an 

Oblique All-Wing Aircraft,” 4–12.
213

Subsequent Oblique-Wing Plans and Proposals

13. Thomas L. Galloway et al., “Large Capacity Oblique All-Wing 

Transport Aircraft,” a paper presented at the Transportation Beyond 

2000: Engineering Design for the Future conference, NASA Langley 

Research Center, Hampton, VA, September 26–28, 1995, 462–464. 

The work at the University of Kansas was done independently as 

part of a grant from the NASA Advanced Design Program.

14. These are enumerated in Hirschberg, Hart, and Beutner, “A 

Summary of a Half-Century of Oblique Wing Research,” 26–28. 

McDonnell-Douglas was soon absorbed into the Boeing Company. 

Boeing’s interest was understandable as it had sponsored the socalled “Spanloader” studies for over a quarter-century.

15. D.W. Elliott, P.D. Hoskins, and R.F. Miller, “A Variable Geometry 

HSCT,” AIAA paper no. 91-3101 (September 1991), 1.

16. Ibid., 2.

17. Ibid., 5.

18. Ibid., 5.

19. Ibid., 12.

20. H.M.S/L.E.O. Design Team, “RTJ-303: Variable Geometry, 

Oblique Wing Supersonic Aircraft,” Aeronautical Engineering 

Department, California Polytechnic State University, NASA CR 

192054 (1992), 1.

21. Ibid., 79–80.

22. Thomas Galloway, Paul Gelhausen, Mark Moore, and Mark Waters, 

“Oblique Wing Supersonic Transport Concepts,” AIAA paper no. 

92-4230 (August 24–26, 1992), 1–10.

23. Ibid.

24. Ibid., 5.

25. For Morris’s work, see Stephen Morris and Ilan Kroo, “Aircraft 

Design Optimization with Multidisciplinary Performance Criteria,” 

in Jean-François M. Barthelemy, Recent Advances in Multidisciplinary 

Analysis and Optimization, NASA CP 3031, pt. 3 (Washington, 

DC: NASA, 1989), 1219–1220; Stephen J. Morris, “Integrated 

Aerodynamic and Control System Design of Oblique Wing 

Aircraft,” NASA CR 192614 (January 1990); and Stephen J. Morris 

and B. Tigner, “Flight Tests of an Oblique Flying Wing Small Scale 

Demonstrator,” a paper presented at the Guidance, Navigation, 

and Control Conference, Baltimore, MD, August 7–9, 1995, AIAA 

paper no. 95-3327 (August 1995). His work is summarized in 

Hirschberg, Hart, and Beutner, “A Summary of a Half-Century of 

Oblique Wing Research,” 29–31.
214

Thinking Obliquely

26. Stephen C. Smith, Robert A. Kennelly, and James Reuther, 

“Oblique-Wing Glide-Back Booster for Shuttle Reusable First 

Stage,” Ames Research Center Aeronautics Directorate (July 1999), 

http://www.ntrs.nasa.gov, accessed December 5, 2011.

27. R.K. Nangia and D.I. Greenwell, “Wing Design of an Oblique 

Wing Combat Aircraft,” in Proceedings of ICAS Congress, ICAS2000 (2000), 161.1–7. Shortly afterward, on July 2, 2001, DERA 

was disestablished and its constituent elements reformed into two 

organizations, QinetiQ and the Defence Science and Technology 

Laboratory (DSTL).

28. Ibid., 161.4.

29. Ibid.

30. Information provided to the author by Stephen C. Smith, NASA 

Ames.

31. Graham Warwick, “Northrop Grumman to Fly Supersonic 

Oblique Flying-Wing by 2010 in $10 million Study,” Flight 

Global, March 28, 2006, http://www.flightglobal.com/news/articles/

northrop-grumman-to-fly-supersonic-oblique-flying-wing-by-2010-in10m-205690/, accessed December 5, 2011; Graham Warwick, 

“DARPA Kills Oblique Flying Wing,” Aviation Week (October 1, 

2008), http://www.aviationweek.com/aw/generic/story.jsp?id=news/

OBLI10018c.xml&headline=DARPA%20Kills%20Oblique%20

Flying%20Wing&channel=defense, accessed December 5, 2011; 

Hirschberg, Hart, and Beutner, “A Summary of a Half-Century of 

Oblique Wing Research,” 33.

32. Lei Tang, Danny D. Liu, and P.C. Chen, “Extension of Projectile 

Range Using Oblique-Wing Concept,” AIAA paper no. 2005-4600 

(June 6–9, 2005), 1.

33. Ibid.

34. Ibid.

35. Ibid., 11–12

36. Matthew J. Dillsaver, USAF, and Milton E. Frank, “Wind Tunnel 

Study of Oblique Wing Missile Model,” AIAA paper no. 2008-318 

(January 7–10, 2008), 2.

37. Dillsaver and Frank, “Wind Tunnel Study of Oblique Wing Missile 

Model,” 8.

38. William R. Sears, “Introduction,” in “Collected Works of Robert T. 

Jones,” NASA TM X-3334 (1976), xi.

39. Walter G. Vincenti, “Robert T. Jones, One of a Kind,” Annual 

Review of Fluid Dynamics 37 (January 2005): 11.
215

APPENDIX 1

Physical Characteristics of the 

Ames-Dryden AD-1 OWRA1

Description Specification

Total height 6.75 feet (ft)

Total length 38.80 ft

Wing reference and actual planform area 93 square (sq) ft

Wing reference and unswept span 32.30 ft

Wing reference and unswept chord (root) 4.28 ft

Wing aspect ratio 11.2

Wing airfoil NACA 3612-02, 40 (constant)

Wing dihedral angle 0°

Wing twist –2°

Wing root incident angle 2°

Wing quarter chord sweep angle 0°

Wing leading edge sweep angle 2°

Wing average chord 2.90 ft

Wing sweep (yaw) angle range 0° to 60°

Horizontal tail planform area 26 sq ft

Horizontal tail span 8 ft

Horizontal tail average chord 3.30 ft

Horizontal tail root chord 5.40 ft

Horizontal dihedral angle 0°

Horizontal incidence angle 0°

Horizontal tail leading-edge sweep angle 45°

Vertical tail area (exposed) 14.4 sq ft

Vertical tail span (exposed) 3.70 ft

Vertical tail average chord 3.90 ft

 1. “AD-1 Owner’s Manual,” 1-4 and 1-5 (December 11, 1979).
Thinking Obliquely

216

Vertical tail root chord 5.80 ft

Vertical tail leading-edge sweep angle 43°

Aileron hinge line 0.75 chord

Aileron total span 12 ft

Aileron area 23 sq ft

Aileron root station 0.62

Aileron root chord 0.65 ft

Aileron range (each) +/–25°

Elevator hinge-line sweep angle 0°

Elevator area 5 sq ft

Elevator average chord 0.62 ft

Elevator root chord 0.75 ft

Elevator range 25° up to 15° down

Rudder hinge-line sweep angle 0°

Rudder area 31.2 sq ft

Rudder average chord 0.71 ft

Rudder root chord 0.92 ft

Rudder range +/–25°

Empty mass 1,122 lb

Useful load 600 lb

Fuel load 400 lb

Gross weight 1,722 lb

Engines Two TRS-18-046

Engine sea level static thrust (each) 220 lb
217

APPENDIX 2

Detailed Description of the 

Ames-Dryden AD-1 OWRA2

The Airplane The AD-1 is a very small, low-subsonic aircraft whose 

purpose is to explore the aerodynamic and aeroelastic 

response characteristics of an oblique-wing design. The 

principal distinguishing feature of this craft is a top-mounted, 

high-aspect-ratio wing, which pivots on the fuselage from a 

conventional straight-wing position to a skew angle of 60 degrees.

The Engines Two 220-pound-thrust TRS-18-046 centrifugal-flow turbojet 

engines power the AD-1. Engines are pod-mounted to each 

side of the fuselage in a midships position. Pilot control of the 

engines consists of starting, thrust selection, and stopping. 

Engine functional parameters are displayed on the instrument 

panel. An onboard battery provides self-contained ground and 

inflight starting capability for both engines.

Electronic Engine 

Controls

The electronic control unit for each engine automatically 

modulates fuel flow to maintain operation within prescribed 

limits. The cockpit-mounted thrust lever positions a 

potentiometer for throttle control. This is, in effect, a fly-bywire throttle. No backup control for the electronic control unit 

is provided. The operator must maintain supervisory vigilance 

of the engine functional parameters and shut the engine down 

in the event of unsatisfactory operation.

Engine-Oil System Each engine-oil system consists of an internal sump reservoir, 

pressure pump, and distribution network. The oil pump is 

actuated by compressor bleed air. Usable oil capacity is 

one pint. Oil pressure for each engine is displayed on the 

instrument panel. Additionally, a low-pressure-warning 

light for each engine is provided. Since the pump is driven 

by compressor bleed air, oil pressure will vary with engine 

revolutions per minute (RPM) and density altitude.

 2. “AD-1 Owner’s Manual,” 1-10 and 1-19 (December 11, 1979).
218

Thinking Obliquely

Fuel System All fuel for the AD-1 is carried internally in two integral, 

tandem cells. The capacity of the forward cell is 40 gallons. 

Aft-cell capacity is 32 gallons. The left engine normally feeds 

from the forward cell while the right engine feeds from the 

aft cell. For single-engine operation, a solenoid-operated 

equalizing valve may be opened to allow fuel to gravity flow 

from one tank to the other. The equalizing valve is normally 

left closed in flight to prevent fuel from draining to one tank 

because of fuselage attitude. Fuel gravity flows from each tank 

to a nacelle-mounted electric fuel pump and thence to the 

engine. Excess fuel is bypassed by the fuel control and routed 

back into the fuselage cells. Fuel flow back is at a rate of 

approximately 25 gallons per hour.

Electric Power 

Supply System

Electric power for the onboard aircraft and data systems is 

supplied by a single 6.5-amp-hour, 24-volt Ni-Cad battery. 

The battery is maintained in a fully charged state by an 

engine-driven starter generator on each engine. Each starter 

generator feeds a single, common electrical power distribution 

subsystem (BUS) without regard to the status of its mate. The 

starter generators are each capable of delivering 20 amps, 28 

volts at maximum engine RPM.

Flight Control 

System

The AD-1 Flight Control System is an all-mechanical, 

nonboosted system. Stick and rudder pedals control ailerons, 

elevator, and rudder in a conventional fashion. Three-axis 

electric trim is provided through tabs on the aileron and 

elevator and through a separate surface rudder. Pitch and 

roll trim controls are conventionally located on the top of 

the control-stick grip. Yaw trim is controlled by means of a 

spring centering toggle switch mounted just forward of the 

throttles on the left console. All trim controls are of the “beep” 

style. There are no cockpit trim indicators, so in order to set 

the trims for takeoff, the pilot must (1) physically look at tab 

positions; or (2) take direction from the crew chief, who is 

looking at the tabs; or (3) take direction from NASA 1, which is 

looking at tab positions on telemetry. The Roll Control System 

linkage is designed so that the stick-to-surface relationship 

does not change with wing-skew angle.
219

Detailed Description of the Ames-Dryden AD-1 OWRA

Wing Skew 

System

The AD-1 wing pivots on a single, 14-inch-diameter roller 

bearing. The pivot assembly is designed so that the wing will 

remain attached to the fuselage if a catastrophic bearing 

failure occurs. Actuation of wing skew is by a dual electricmotor-gearbox assembly that is built into the pivot. Pilot 

operation of the wing skew is by a spring toggle switch. In 

order to skew the wing, the operator must hold the switch 

to the right. Full skew will be achieved in approximately 

20 seconds. Wing motion will stop as soon as the switch 

is released. Actuation of the wing back to its conventional 

position is accomplished by moving the skew switch to the 

left of center. The skew switch will remain in the left (unskew) 

position with no further pilot action. Emergency unskew can be 

commanded by depressing the trigger switch on the stick grip. 

Electrical limit switches at the wing pivot limit wing movement 

at 0 degrees and +60 degrees. Hard mechanical stops are 

placed at –2 degrees and –62 degrees on the pivot to prevent 

overtravel in case of a runaway actuator.

Landing Gear The AD-1 employs fixed, tricycle landing gear. Main gear 

consists of an epoxy-fiberglass strut protruding from each 

side of the fuselage. A single 5.00-by-5 wheel and 4-ply 

tire are mounted to each strut. Landing-shock absorption 

is accomplished by the flexing of the composite struts and 

by tire deflection. The nose landing gear is a simple epoxyfiberglass-composite strut that is internal to the fuselage. 

A single, steerable wheel is mounted to the nose strut. The 

nosewheel is capable of steering 20 degrees left or right by 

conventional rudder. The calculated maximum-landing sink 

rate is 5 feet per second. Landings at sink rates in excess of 

5 feet per second may result in the blowout of the main tires, 

damage to the wheel rims, and in severe cases, abrasion of 

the fuselage bottom.

Wheel Brake 

System

The AD-1 employs individually toe-operated main-wheel 

disc brakes. Hydraulic brake lines are routed from the brake 

pedals, back through the fuselage, and down the composite 

main landing gear struts. No boost is provided.

Instruments All flight instruments for day VFR flight and research flight 

tests are located on the main instrument panel. Angle-ofattack, sideslip, and wing-skew indicators are driven by the 

Data System.
220

Thinking Obliquely

Data System A research flight test Data System is installed in the aircraft. 

Except for remote sensors and the cockpit displays, the 

Data System is located on a single pallet in the upper third of 

the fuselage between F.S. 240 and F.S. 275. All flight data are 

transmitted to a ground receiving-and-recording station. No 

onboard data recording is provided. The Data System is turned on 

by means of a single switch on the instrument panel. It is possible 

to run the onboard Data System without transmitting data. Circuit 

breakers for this purpose are on the Data System pallet.

Pilot Seating and 

Restraint

Seating in the AD-1 is semisupine. The seat-back angle is 45 

degrees. Conventional seat belt, shoulder harness, and crotchstrap restraints are employed. The seat is designed to be used 

in conjunction with the Security Model 250-EPA parachute. No 

survival kit is provided. Adjustment for pilot size is by means of 

seat cushions.

Canopy The AD-1 is fitted with aft-hinged, manually operated canopy. 

Entry and exit is from the left side of the aircraft. The canopy 

latch is a two-point restraining device that may be operated 

either from inside the cockpit or from the outside. From inside 

the cockpit, the canopy is locked by moving fully forward until 

a spring-loaded detent is engaged. Locking of the handle may 

be checked by attempting to move the handle aft. To unlock 

the canopy, pull the handle inboard and move fully aft. An 

external canopy handle is mounted on the left-fuselage side 

just below the canopy sill. To open from the outside, push the 

button and rotate handle counterclockwise. Partial opening of 

the canopy for ventilation during taxi may be accomplished by 

lifting the canopy, slightly engaging the canopy lock handle, 

and lowering the canopy onto the closed hooks. Taxiing with 

the canopy partially open should be done with considerable 

care as there is nothing to prevent the canopy from fully 

opening due to wind or aircraft motion. The pilot should not 

unlock the canopy in flight except for purposes of canopy 

jettison. While no flight demonstration has been made, it is 

expected that the canopy will depart the aircraft immediately if 

it is unlocked in flight.
221

APPENDIX 3

Flight Log Summary for the 

Ames-Dryden AD-1 OWRA3

Flight

Number Date Pilot Organization TimeDuration Remarks

1 Dec. 21, 

1979

Thomas C. 

McMurtry

NASA DFRC 0:05 Resulted from 

high-speed taxi 

test

2 Dec. 21, 

1979

Thomas C. 

McMurtry

NASA DFRC 0:45 First official 

flight; aircraft 

checkout

3 Jan. 11, 

1980

Thomas C. 

McMurtry

NASA DFRC 0:45 Performance; 

handling 

qualities

4 Jan. 21, 

1980

Thomas C. 

McMurtry

NASA DFRC 0:50 Performance

5 Jan. 21, 

1980

Thomas C. 

McMurtry

NASA DFRC 0:50 Performance

6 Jan. 23, 

1980

Thomas C. 

McMurtry

NASA DFRC 0:20 Performance

 3. The information in items 48–79 was taken from:
222

Thinking Obliquely

7 Jan. 23, 

1980

Thomas C. 

McMurtry

NASA DFRC 0:55 Stability and 

control

8 Jan. 25, 

1980

Fitzhugh L. 

Fulton

NASA DFRC 1:00 Pilot checkout; 

performance

9 Feb. 1, 

1980

Thomas C. 

McMurtry

NASA DFRC 1:15 Performance

10 Feb. 20, 

1980

Fitzhugh L. 

Fulton

NASA DFRC 0:55 Performance

11 Mar. 7, 

1980

Thomas C.

McMurtry

NASA DFRC 0:40 Performance

12 Apr. 2, 

1980

Thomas C. 

McMurtry

NASA DFRC 1:05 First 15-degreewing-sweep 

flight; evaluate 

stability at high 

angle of attack

13 Apr. 25, 

1980

Thomas C. 

McMurtry

NASA DFRC 0:50 First 20-degreewing-sweep 

flight; flutter 

clearance

14 May 28, 

1980

Thomas C. 

McMurtry

NASA DFRC 1:30 First 45-degreewing-sweep 

flight; flutter 

clearance

15 July 9, 

1980

Fitzhugh L. 

Fulton

NASA DFRC 1:15 Flutter 

clearance

16 July 9, 

1980

Thomas C. 

McMurtry

NASA DFRC 1:15 Flutter 

clearance
223

Flight Log Summary for the Ames-Dryden AD-1 OWRA

17 July 17, 

1980

Fitzhugh L. 

Fulton

NASA DFRC 1:15 Flutter 

clearance

18 July 17, 

1980

Thomas C. 

McMurtry

NASA DFRC 1:15 Flutter 

clearance

19 Aug. 12, 

1980

Thomas C. 

McMurtry

NASA DFRC 0:40 Flutter 

clearance

20 Mar. 31, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:15 Flutter 

clearance

21 Mar. 31, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:20 Flutter 

clearance

22 Apr. 24, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:10 Flutter 

clearance

23 Apr. 24, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:30 First 60-degreewing-sweep 

flight; flutter 

clearance

24 May 12, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:10 Flutter 

clearance

25 May 12, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:05 Flutter 

clearance

26 May 28, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:00 Handling 

qualities
224

Thinking Obliquely

27 June 11, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:10 Stability and 

control

28 June 16, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:10 Stability and 

control

29 July 1, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:15 Stability and 

control

30 July 1, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:20 Stability and 

control

31 July 7, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:10 Stability and 

control

32 July 14, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:15 Stability and 

control

33 July 28, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:20 Stability and 

control

34 July 30, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:10 Stability and 

control

35 Aug. 18, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:10 Stability and 

control

36 Aug. 20, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:20 Stability and 

control
225

Flight Log Summary for the Ames-Dryden AD-1 OWRA

37 Aug. 31, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:05 Stability and 

control

38 Sept. 3, 

1981

Fitzhugh L. 

Fulton

NASA DFRC 1:15 Stability and 

control

39 Oct. 9, 

1981

Thomas C. 

McMurtry

NASA DFRC 0:30 Ferry flight from 

Edwards AFB to 

Lancaster, CA 

(Fox Field), for 

air-show static 

display

40 Oct. 13, 

1981

Thomas C. 

McMurtry

NASA DFRC 0:30 Ferry flight from 

Lancaster, CA, 

to Edwards AFB

41 Nov. 8, 

1981

Thomas C. 

McMurtry

NASA DFRC 0:30 Ferry flight from 

Edwards AFB 

to Norton AFB, 

CA, for air-show 

static display

42 Nov. 8, 

1981

Thomas C. 

McMurtry

NASA DFRC 0:35 Ferry flight from 

Norton AFB to 

Edwards AFB 

43 Dec. 4, 

1981

Einar K. 

Enevoldson

NASA DFRC 0:50 Pilot 

familiarization; 

guest pilot

44 Dec. 4, 

1981

John A. 

Manke

NASA DFRC 1:00 Pilot 

familiarization; 

guest pilot

45 Dec. 8, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:10 Ferry flight from 

Edwards AFB to 

Paso Robles, CA 

(refueling stop)
226

Thinking Obliquely

46 Dec. 8, 

1981

Thomas C. 

McMurtry

NASA DFRC 0:50 Ferry flight from 

Paso Robles 

to NASA Ames 

Research Center 

(Moffett Field)

47 Dec. 9, 

1981

Thomas C. 

McMurtry

NASA DFRC 0:20 Demonstration 

flight at NASA 

Ames 

48 Dec. 10, 

1981

Thomas C. 

McMurtry

NASA DFRC 0:20 Demonstration 

flight NASA 

Ames 

49 Dec. 10, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:05 Ferry flight from 

NASA Ames to 

Paso Robles 

(refueling stop)

50 Dec. 10, 

1981

Thomas C. 

McMurtry

NASA DFRC 1:00 Ferry flight from 

Paso Robles to 

Edwards AFB

51 Jan. 5, 

1982

William 

H. Dana

NASA DFRC 1:00 Pilot 

familiarization; 

guest pilot

52 Jan. 22, 

1982

Richard 

Gray

NASA DFRC 1:05 Pilot 

familiarization; 

guest pilot

53 Jan. 22, 

1982

Donald L. 

Mallick

NASA DFRC 1:00 Pilot 

familiarization; 

guest pilot

54 Feb. 5, 

1982

Capt. 

John Small

USAF AFFTC 1:05 Pilot 

familiarization; 

guest pilot

55 Feb. 11, 

1982

Maj. 

Robert 

Cabana

USMC NATC 1:15 Pilot 

familiarization; 

guest pilot
227

Flight Log Summary for the Ames-Dryden AD-1 OWRA

56 Feb. 11, 

1982

Cmdr. 

John 

Watkins

USN NATC 1:15 Pilot 

familiarization; 

guest pilot

57 Feb. 24, 

1982

James 

Martin

NASA ARC 1:10 Pilot 

familiarization; 

guest pilot

58 Feb. 24, 

1982

Warren Hall NASA ARC 1:10 Pilot 

familiarization; 

guest pilot

59 Mar. 5, 

1982

Capt. 

Denny Mohr

USAF TPS 1:10 Pilot 

familiarization; 

guest pilot

60 May 14, 

1982

Thomas C. 

McMurtry

NASA DFRC 1:20 Ferry flight from 

Edwards AFB 

to Paso Robles 

(refueling stop)

61 May 14, 

1982

Thomas C. 

McMurtry

NASA DFRC 1:10 Ferry flight from 

Paso Robles 

to NASA Ames 

(Moffett Field)

62 May 17, 

1982

Thomas C. 

McMurtry

NASA DFRC 1:00 Ferry flight from 

NASA Ames to 

Paso Robles 

(refueling stop)

63 May 17, 

1982

Thomas C. 

McMurtry

NASA DFRC 1:00 Ferry flight from 

Paso Robles to 

Edwards AFB

64 May 19, 

1982

Phil Brown NASA LARC 1:00 Pilot 

familiarization; 

guest pilot

65 May 19, 

1982

Maj. 

William 

Neely

USAF/NASA 

LARC

1:00 Pilot 

familiarization; 

guest pilot
228

Thinking Obliquely

66 May 20, 

1982

Col. William 

J. Knight

USAF AFFTC 1:05 Pilot 

familiarization; 

guest pilot

67 May 20, 

1982

Steven P. 

Ishmael

NASA DFRC 1:00 Pilot 

familiarization; 

guest pilot

68 June 8, 

1982

Fitzhugh 

L. Fulton

NASA DFRC 1:05 Oil-flow 

visualization 

study

69 June 8, 

1982

Thomas C. 

McMurtry

NASA DFRC 1:05 Oil-flow 

visualization 

study

70 June 11, 

1982

Fitzhugh 

L. Fulton

NASA DFRC 1:00 Oil-flow 

visualization 

study

71 June 11, 

1982

Thomas C. 

McMurtry

NASA DFRC 1:05 Oil-flow 

visualization 

study

72 July 31, 

1982

Thomas C. 

McMurtry

NASA DFRC 0:10 Oshkosh 

air show 

demonstration 

flight

73 Aug. 1, 

1982

Thomas C. 

McMurtry

NASA DFRC 0:10 Oshkosh 

air show 

demonstration 

flight

74 Aug. 2, 

1982

Thomas C. 

McMurtry

NASA DFRC 0:10 Oshkosh 

air show 

demonstration 

flight

75 Aug. 3, 

1982

Thomas C. 

McMurtry

NASA DFRC 0:10 Oshkosh 

air show 

demonstration 

flight
229

Flight Log Summary for the Ames-Dryden AD-1 OWRA

76 Aug. 4, 

1982

Thomas C. 

McMurtry

NASA DFRC 0:10 Oshkosh 

air show 

demonstration 

flight

77 Aug. 5, 

1982

Thomas C. 

McMurtry

NASA DFRC 0:35 Oshkosh 

air show 

demonstration 

flight

78 Aug. 6, 

1982

Thomas C. 

McMurtry

NASA DFRC 0:10 Oshkosh 

air show 

demonstration 

flight

79 Aug. 7, 

1982

Thomas C. 

McMurtry

NASA DFRC 0:10 Oshkosh 

air show 

demonstration 

flight; Final 

flight of AD-1
230

Acknowledgments

Many individuals went to great lengths to furnish crucial information in the 

form of documents, recollections of Robert T. “R.T.” Jones and the AD-1 

effort, insights, photographs, and reviews of the author’s work. The following 

individuals were especially helpful, indeed crucial, to the author’s research and 

manuscript preparation, and I am most grateful for their assistance.

At NASA Ames Research Center, Moffett Field, CA: John W. “Jack” Boyd, 

April D. Gage, Ronald C. Smith, and Stephen C. Smith.

At NASA Dryden Flight Research Center, Edwards, CA: Karl A. Bender, Alion 

Bowers, Freddy Locharno, Thomas “Tom” McMurtry, Peter Merlin, Joe Pahle, 

and Weneth “Wen” Painter.

At NASA Langley Research Center, Hampton, VA: Joseph R. Chambers.

At NASA Headquarters, Washington, DC: Gail Carter-Kane, Richard P. 

Hallion, Cynthia Miller, Anthony Springer, Christopher Yates, and Janine Wise.

At the National Museum of the United States Air Force, Wright-Patterson Air 

Force Base, OH: Brett Stolle.

At Stanford University, Stanford, CA: Daniel Hartwig.

I particularly want to thank Burt Rutan, designer of the AD-1 airplane, 

who very graciously consented to an interview and furnished much helpful 

information on the varied challenges he and his remarkable team faced in 

building this unique and frontier-expanding design.
231

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247

About the Author

Bruce I. Larrimer holds B.A. and M.A. degrees in history from The Ohio 

State University. Mr. Larrimer served on active duty as a U.S. Army officer 

assigned to the Intelligence Staff, U.S. Army Pacific (USARPAC), and later 

served in various positions with a Federal regulatory commission. He currently 

lives in Columbus, OH, where he has his consulting practice. Mr. Larrimer’s 

previous writings include the history of NASA’s participation in the Federal 

Wind Energy Program and NASA’s development and testing of high-altitude, 

long-endurance (HALE), solar-powered remotely piloted aerial vehicles.
248

The AD-1 cruising over the Mojave in 1980 with its oblique wing set at a 60-degree sweep. (ASA)
249

Index

Numbers in bold indicate pages with photos or figures

747 aircraft, 108, 186, 189, 201

757 aircraft, 187

767 aircraft, 201

777 aircraft, 201 

A

A-3 Skywarrior, 106

A-4 Skyhawk, 143

A-10A attack aircraft, 60

ACA Industries, 126, 133–36

Ackeret, Jakob, 17

ACSYNT program, 58–59, 201–2

AD-1 Oblique Wing Research Aircraft (OWRA)

actuation of wing skew, 219

airworthy condition of, 115, 136

characteristics and specifications, 78–80, 

88–89, 117–19, 215–20

cockpit, 74

cost of development and fabrication, 77, 

81, 82

defense of program, 92–93

delivery to Dryden, 95

design and development of, 21–22, 47–48, 

57–58, 58, 75–83, 183, 210, 211

duration of program, v

end-of-program evaluation, 115–19

entry to and exit from, 220

F-8 OWRA follow-up to, 125, 147, 150

fabrication of, 93–96

feasibility study, 78–81, 82

first flight of, v, 96, 221

flight control and flight control systems, 74, 

80, 89, 94, 95, 96, 218, 219

flight tests, 93, 96, 100, 104–5, 108–10, 

208, 221–29

goals and purpose of program, 76–77, 

92–93, 115–19

grounding of and display of, 136

JWRA, modifications for, 125–26, 129–30, 

132, 133–36, 140n76

management team and ground crew, 110

naming of, v

oversight of program and progress reports, 

110–15

performance goals, 79, 89

photos of, iv, 100, 105, 106, 107, 248

pilot safety and design of, 80–81

pivot assembly, 79, 80, 89, 94, 219

program schedule, 83, 93–96

RFP and contract award, 81, 83

risk-reduction strategy for development of, 

92–93

stability, handling, and control, 78–79, 

117–19

studies to support design and development 

of, 49–62

success of, 125, 210, 211

summary review of flight experience, 

119–25, 138n42, 139n56

takeoff and landing performance, 118, 119, 

120, 123

upward curvature of wings, 46

wing angles and flights of, v

wing sweep positions and range, iv, 64, 88, 

100, 108, 111–12, 112, 113–14
250

Thinking Obliquely

Advanced Design Program (NASA), 213n13

Advanced Fighter Technology Integration (AFTI), 

140n66

Advanced Flight Technology Integration, 140n66

Advanced Transport Technology (ATT) study, 50, 

51, 52

aerodynamics

AD-1 computer code analysis, 63–64, 91

F-8 characteristics, 145, 146–47, 151–53, 

166–69, 202

joined-wing aircraft and, 126

oblique flying wing and, 42, 185, 186, 196

oblique wing benefits and engineering 

advantages, 23, 53, 64, 77, 116, 144, 

147–49, 183–84, 200–201, 207, 209–11, 

212n2

RC model designs and testing of, 202–3

separation technique to estimate aerodynamic 

derivatives, 68–69

supersonic flight, aircraft design for, 29–31

symmetry and, 185

Aerodynamische Versuchsanstalt (Experimental 

Aerodynamics Establishment, Göttingen), 

19–20

aeroelastic properties

AD-1 OWRA, 62–64, 117

computers and analysis of aircraft behavior 

and motions, 63–64

divergence and divergent loads, 50, 56, 

98n33, 119–20, 146, 199, 212n2

F-8 OWRA characteristics, 146–47, 151–52

oblique-wing concepts, 148–49, 200–201, 

209–10

See also flutter and flutter control

Aeronautical and Space Technology (AST) 

program, 197

agricultural aircraft, 127

ailerons

AD-1 flight control and flight control system, 

63–64, 79, 89, 117–18, 218

directional change and two-control system, 4

F-8 oblique-wing model and wind tunnel 

testing of, 60–62, 63, 167–68

Jones research and reports on, 8, 9

loop-shaping methodology for control law 

development, 163–64

oblique-wing model tests, 26

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65

RC oblique-wing free-flight model testing, 45

snubber/damper on, 113

wing structural response, influence on, 

112–13

aircraft

agricultural aircraft, 127

bilateral symmetry/mirror symmetry, 27, 29, 

30, 42–43, 86, 87–88

commercial passenger joined-wing transport 

study, 129

commercial passenger oblique-wing 

transport study, 49, 54–57, 55

conservatism and traditionalism in design, 

210

development and design of, 29–31

flight-test aircraft numbering and 

designations, 83

research and experimental aircraft, important 

role of, 75, 140n76

supersonic flight, aircraft design for, 29–31

symmetrical variable-sweep development, 

26

Air Force, U.S.

Development Plans and Analysis Group, 54

F-8 OWRA program, 172, 173

Fulton career with, 107–8

Lockeed subsonic transport mission 

capabilities, 57

long-range strike capabilities, aircraft with, 

206

Material Command (Army Air Force Air 

Technical Service Command), 9–10
251

Index

Systems Command Headquarters 

Requirements Office, 54

Air Force Flight Test Center, 77

Air Force Institute of Technology, 207–9

air shows

ferry flights to and from, 108, 225

Oshkosh air show, 108, 109–10, 115, 

228–29

Alag, Gurbux S., 159, 160–61

American Institute of Aeronautics and 

Astronautics (AIAA)

Applied Aerodynamics Conference, 207

flight-testing conference, 115, 212n2

formation of, 4

oblique-flying-wing research, 196

American Rocket Society, 4

Ames, Milton B., Jr., 8

Ames-Dryden AD-1 Oblique Wing Research 

Aircraft (OWRA). See AD-1 Oblique Wing 

Research Aircraft (OWRA)

Ames-Dryden Flight Flight Research Center, vi 

n1, 156, 177n19

Ames Industrial Corporation, 83, 93–96

Ames Research Center/Ames Aeronautical 

Laboratory

ACSYNT program, 58–59, 201–2

AD-1 OWRA demonstration flights at, 226

AD-1 OWRA ferry flights to and from, 226, 

227

AD-1 OWRA role, v, 62, 101

Advanced Vehicle Concepts Branch, 58–59

balsa-wood models at, 38n72

Dryden, merger with and connection to, vi 

n1, 177n19

FLUT flutter analysis program, 63–64

joined-wing concepts, computational-based 

analysis of, 139–40n65

Jones career at, 5, 6, 11, 42

Jones research and reports, topics of, 5–6

Kroo career at, 176n7

oblique flying wing follow-on study, 189–90

oblique-flying-wing research, 190–95, 196

oblique technology, future of, 201

oblique-wing concepts research, 45–47, 48

PASS structural analysis program, 63–64

Pressure Wind Tunnel, 12-foot, 90–91, 91, 

92

Transonic Wind Tunnel, 11-foot, 45–47, 48, 

60–62, 167, 169, 170, 174, 186

Turn and Glide-Back space launch booster 

recovery system, 203, 204–5

Vertical Motion Simulator, 164–66

wind tunnel, 40-by-80-foot, 67–68, 93

Wind Tunnel Test Design Team, 196

Andrews, William H. “Bill,” 93, 94, 110, 115–19, 

184

angles of attack

AD-1 OWRA handling and, 120–21

F-8 OWRA handling and, 152–53, 165

joined-wing concepts, 133

oblique-wing model tests, 46–47, 48

antisubmarine warfare (ASW) aircraft, 57, 59

Apollo spacecraft, 143

area rule

AD-1 OWRA design, 79

development of, 209

HSCT fuselage design, 197

mirror symmetry and, 43, 87

oblique flying wing and, 197

oblique-wing aircraft fuselage shape, 45

Army Air Force Air Technical Service Command, 

U.S. (Air Force Material Command, U.S.), 9–10

arrow elliptic wing, 185

aspect ratio

high-aspect-ratio wings, 12, 16, 46–47, 53

joined-wing concepts, 133

Jones research and reports on, 8, 208

low-aspect-ratio wings, 12–13, 16–17

oblique wing engineering advantages, 45, 

183

OFW X-Plane demonstrator aircraft, 206

speed and, 53
252

Thinking Obliquely

Avco-Everett Research Laboratory, 5, 6, 42

Ayers, Theodore G., 136

B

B-1 bomber, 143, 144, 187, 197

B-25 bomber, 143

B-52 launch aircraft, 107

B-58 aircraft, 107

Bailey, Rodney O., 66

Ballhaus, William, Jr., 133–36

Barling, Walter, 2

Bäumer Sausewind light aircraft, 27

BD-5 speedster, 77

Bede, Jim, 77

Bell X-1 aircraft, 14

Berry, P.W., 160

Beutner, Thomas J., 109, 183, 184

Bicycle Lake, 65

Bikle, Paul, 76, 92

Blohm und Voss P 202 fighter concept, 18–19, 

19

Blohm und Voss Schiffswerft, Abteilung 

Flugzeugbau, 18–19

Boeing 747 aircraft, 108, 186, 189, 201

Boeing 757 aircraft, 187

Boeing 767 aircraft, 201

Boeing 777 aircraft, 201

Boeing Company/Boeing Commercial Airplanes/

Boeing Airplane Company

HSCT airframe development, 196, 197

McDonnell-Douglas merger, 195

oblique-flying-wing research, 195, 196

oblique-wing 5-7 configuration, 57–58, 58, 

78

oblique wing SST concept, 47–48

Spanloader studies, 195

transonic aircraft design concepts, 49–53

Boeing XB-47 Stratojet bomber, 15

Boltz, Frederick W., 45–47

Bondy, Mike, 110

BQM-34F Firebee drone, 59–60, 61

Bradley, Edward S., 54

Bresina, John, 158

British Aerospace V/STOL Sea Harrier, 176n1

Broussard, J.R., 160

Brown, Philip “Phil,” 109, 227

Bugajski, Daniel J., 163–64

Burken, John J., 161

Burnelli, Vincent, 184

Busemann, Adolf, 12, 15, 16, 35n32

Butler, Iva Z., 1

C

Cabana, Robert, 109, 227

California Polytechnic State University (Cal Poly)

joined-wing wind tunnel model, 127

oblique technology, future of, 201–2

RTJ-303 oblique-wing concept, 198–201, 

200

Rutan education at, 77, 78, 198

Campbell, John P., v, 20, 21–22, 23–27, 25, 

29, 183

canopy, 220

Caravelle aircraft, 197

Carmichael, Ralph, 168, 176n7

CFL3D computer code, 207

Chambers, Joseph, 22

Chan, Y.T, 160

Charles Stark Draper Laboratory, 169–70, 172, 

173

Chiles, Harry, 158

Chinese missile program, 34n24

Cliff, Susan, 126, 133

CLMAX vortex-panel code, 132

cockpit

AD-1 OWRA, 74, 89, 96

oblique flying wing, 187, 193

Coffeen Nature Preserve, 33n19

Cohen, Doris, 8, 9

commercial passenger joined-wing transport 

study, 129
253

Index

commercial passenger oblique-wing transport 

study, 49, 54–57, 55

computer modeling and code

ACSYNT program, 58–59, 201–2

AD-1 OWRA design and use of, 22–23

advances in and analysis of aircraft behavior 

and motions, 63–64

CFL3D computer code, 207

CLMAX vortex-panel code, 132

computational fluid dynamics, 128

concept of, 22–23

EAL program, 139–40n65

FLUT flutter analysis program, 63–64, 93, 

94

joined-wing concepts, 127–28, 139–40n65

MMLE3 computer program, 91

MultOp program, 132

NASTRAN structural analysis program, 

63–64, 101, 139–40n65, 162

PASS structural analysis program, 63–64

PROFILE program, 132

PROGRAM H, 132

SPAR program, 139–40n65

STBDER computer program, 91

Concorde supersonic transport, 20, 185–86

control surfaces

AD-1 OWRA, 79, 95

F-8 OWRA, 163–64

Jones research and reports on, 9

JWRA models, 133

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65

See also ailerons; elevators; rudder; tails and 

tail surfaces; wing edge flaps

Convair B-58 aircraft, 107

Cooper-Harper pilot rating scale, 103, 104, 117

coupling, cross-coupling, and decoupled control

AD-1 characteristics, 76, 91, 113, 118, 

122–23, 124

F-8 characteristics, 146–47, 149, 159–61, 

163–66, 179n46

HSCT characteristics, 200–201

oblique wing characteristics, 42, 45, 68

RC oblique flying wing characteristics, 

202–3

stability augmentation and flight control 

system to manage, 45, 55, 113, 159–61, 

163–64, 179n46

Crowley, John “Gus,” 26–27

Curry, Robert

AD-1 OWRA summary review of flight 

experience, 119–25, 138n42, 139n56

F-8 OWRA role, 158

Curtiss, Glenn, 4

D

Dana, William H., 108, 226

data collection and analysis

AD-1 system and instruments, 89, 95, 

98n26, 220

AD-1 wind-tunnel data compared to flighttest data, 124–25, 139n56

computer programs for, 22–23, 63–64, 91

F-8 systems and instruments, 153–54, 155, 

156, 157, 177n14

flight research vehicle instrumentation, 76

maximum likelihood estimation method, 69

OWRPRA test flights, 65, 67–68

OWRPRA wind tunnel testing, 67–68

separation technique to estimate 

aerodynamic derivatives, 68–69

DC-130 Hercules, 60

DeAngelis, Mike, 158

Defence Science and Technology Laboratory 

(DSTL, United Kingdom), 214n27

Defense Advanced Research Projects Agency 

(DARPA), 135–36, 172, 173, 205–6

Defense Documentation Center, 54

Defense Evaluation Research Agency (DERA, 

United Kingdom), 205, 214n27

delta-wing concepts and aircraft

drag and, 43, 208
254

Thinking Obliquely

fighter concept, 12, 34n23

Jones research on and development of, 7, 9, 

11–17, 27, 35n30, 208, 209

research report on, 11

slender delta planform, 13, 14, 16, 35n30

swept wing development and, 14

transonic aircraft design concepts, 49–53

Desktop Aeronautics, 205

Developmental Sciences, Inc., 65

dihedral, 26, 83, 84, 120, 215

Dillsaver, Matthew J., 207–9

divergence and divergent loads, 50, 56, 98n33, 

119–20, 146, 199, 212n2

Dolan, Charles J., 26

Douglas A-3 Skywarrior, 106

Douglas A-4 Skyhawk, 143

drag

delta-wing concepts and, 43, 208

F-8 oblique-wing model, 167–69

joined-wing aircraft and, 128

oblique flying wing and, 186, 187, 195

oblique-wing concepts and, 43, 148, 

150–51, 183, 208

supersonic flight and, 30–31, 148, 150–51

swept-wing concepts and, 13, 15, 17, 30, 

43

symmetry and, 43, 185

wave drag, 30–31, 42, 43, 148, 150

See also lift/drag ratios

Drake, Hubert W. “Jake,” v, 20, 21–22, 23–27, 

25, 29, 183

Dryden Flight Research Center/Flight Research 

Center/High-Speed Flight Station

AD-1 OWRA delivery to, 95

AD-1 OWRA flight tests, 101, 221–29

AD-1 OWRA role, v, 62, 101

Ames, merger with and connection to, vi n1, 

177n19

flight research culture and tradition at, 76, 

92

flight-test aircraft numbering and 

designations, 83

Fulton career at, 107–8

McMurtry career at, 106–7

name changes and naming of, vi n1

naming of, 76

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65–69

dual-fuselage oblique-wing aircraft, 85–88, 86, 

97n20

Dunne, John, 184

E

EAL program, 139–40n65

edge flaps. See wing edge flaps

Eglin Air Force Base/Eglin Field, 9

eigenstructure assignment technique, 159–61, 

178n29

eigenvalues, 160, 178n29

eigenvectors, 160, 178n29

electric power supply system, AD-1 OWRA, 89, 

94, 218

elevators

AD-1 OWRA, 79

AD-1 OWRA flight control system, 89, 122, 

218

Jones research and reports on, 9

loop-shaping methodology for control law 

development, 163–64

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65

RC oblique-wing free-flight model testing, 45

elevons, 42

Elliot, D.W., 196

elliptical wing, 27–29, 28, 185, 186

Eloret Institute, 190–95, 201

Enevoldson, Einar K, 66, 108, 225

engines and engine placement

AD-1 OWRA, 79, 88, 94, 217

AD-1 OWRA engine controls, 74, 89, 217

AD-1 OWRA engine-oil system, 217
255

Index

AD-1 OWRA engine trouble, 114

Boeing 5-7 configuration, 58

Boeing oblique-wing concept, 51–52

Lockeed subsonic transport study, 55–56

oblique flying wing, 42, 186, 187, 193–94

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65

RTJ-303 oblique-wing concept, 199

vectoring gross thrust of exhaust nozzles, 

193–94

Enns, Dale F., 163–64

environmental constraints and noise, 50, 

196–97, 202

Erco Ercoupe aircraft, 4, 5

Experimental Aerodynamics Establishment, 

Göttingen (Aerodynamische Versuchsanstalt), 

19–20

Experimental Aircraft Association meeting, 

109–10, 115

Extended Range Guided Munition (ERGM), 206, 

207

F

F-4 Phantom II, 143

F-5E/F Tiger II lightweight fighter, 206

F-8 Crusader fighters

Digital Fly-by-Wire (DFBW) electronic flight 

controls test bed, 60, 106, 125, 137n6, 

144–45

oblique wing test, modifications for, 64, 

144–45, 155

pilot induced oscillations research, 137n6

retirement of, 60

supercritical wing (SCW) program, 60, 106

wing configuration and ease of modifying, 60

F-8 Oblique Wing Research Aircraft (OWRA)

AD-1 program follow-up, 125, 147, 150

aerodynamics and, 145, 146–47, 151–53, 

166–69, 202

Ames-designed wing, 154, 166–67, 171, 

172, 173, 174–75

budget and funding for program, 156, 171, 

172, 173

contributions to oblique-wing technology, 

173–74

control laws, 163–64, 165, 166, 171, 172, 

173

cross-coupling and decoupled control, 

146–47, 149, 159–61, 163–66, 179n46

data collection instruments and sensors, 

153–54, 155, 156, 157, 177n14

design and development of, 22, 144–47, 

146, 150–58, 151, 152, 154, 166–73

design constraints, 145

F-8 DFBW modifications for, 64, 144–45, 

155

feasibility study, 145–47

flight control and flight control systems, 

153–54, 159–66, 172–73, 177n14, 

179n46

goals and purpose of program, 145–47, 150

management team and ground crew, 

156–58, 169

model of, 62, 151

model wind-tunnel testing, 60–62, 63, 

166–69, 170, 172, 173, 174–75

program monitoring and progress reports, 

169–73

program schedule and timeline, 154–55

recommendation for development of, 

144–45

Rockwell-designed wing, 144–47, 146, 

166–68, 170, 171, 172, 173, 174–75

simulation testing, 163, 164–66, 169, 170

stability, handling, and control, 145, 152–53, 

159–69, 179n46, 208

structure and components, 158

termination of program, 173

tests and experiments for development of, 

151–53

wing planform, 145–46, 146, 151, 166–69, 

174
256

Thinking Obliquely

wing sweep positions and range, 146, 147

F-14 fighter, 137n6, 144, 197

F-15 fighter

Digital Electronic Engine Control (DEEC) 

project, 106

Gray flight experience, 137n6

tests and experiments with, 151

F-16 (Advanced Flight Technology Integration), 

140n66

F-16 Control Configured Vehicle (CCV), 140n66

F-86 Sabre, 143

F-100 jet fighter, 143

F-104 Starfighter, 64, 137n6, 145

F-111 aircraft, 41, 197

Fairchild-Republic A-10A attack aircraft, 60

Fehlner, Leo F., 8

Fiber Resin Corporation, 65

Fieseler FZG-76 bomb (V-1 Buzz bombs), 9–10

fighter aircraft

delta-wing concept, 12, 34n23

Jones research and reports on, 9

Firebee drone, 59–60, 61

flight control and flight control systems

AD-1 OWRA system and instruments, 74, 

80, 89, 94, 95, 96, 218, 219

advances in and oblique wing applications, 

204

electronic flight controls (fly-by-wire) test 

bed, 60, 106, 125, 137n6, 144–45

F-8 OWRA systems and instruments, 

153–54, 159–66, 172–73, 177n14, 

179n46

flight research vehicles, 76

Jones research and reports on, 8, 9

model-following flight control, 160–61

oblique flying wing, 184–85

oblique-wing concepts and, 200–201

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65

pitch control, 4

RC model designs and testing of, 202–3

roll and yaw control, interlinked, 4

stability and damping augmentation 

technology and systems, 114, 116, 118, 

119, 122, 123–25

two-control system, 4, 8

flight tests

AD-1 flutter clearance flights, 110, 111–12

AD-1 OWRA flights, 93, 96, 100, 101, 

104–5, 108–10, 208, 221–29

air show and demonstration flights, 109–10, 

115, 225, 226, 227, 228–29

ferry flights, 108, 225, 226, 227

flight readiness reviews, 93

flutter clearance flights, 48, 108, 222–23

oblique flying wing, 196

oversight of AD-1 program and progress 

reports, 110–15

performance flights, 108, 114, 221–22

pilot familiarization/guest pilot flights, 108–9, 

111, 114–15, 225, 226–28

pilot performance ratings, 114, 117–19, 

122–23

pilots for, 105–10, 221–29

stability, handling, and control during, 

78–79, 117–19, 120–21

stability, handling, and control flights, 100, 

105, 108, 113–14, 221, 222, 224–25

summary of flight operations, 119–20

takeoff and landing performance, 118, 119, 

120, 123

taxi runs, 104–5, 108, 111, 221

windup turns, 117–18, 122–23

wing-sweep flights, 108, 111–12, 112, 

113–14, 222, 223

flow distribution and effects

AD-1 OWRA characteristics, 124

AD-1 OWRA flow-visualization studies, 90, 

108, 115, 116

F-8 OWRA flow characteristics and 

measurements, 153–54, 154, 155, 170
257

Index

Jones contribution to understanding of 

effects, 12–17

oblique-wing flow-visualization studies, 

46–47

oil-flow visualization studies, 108, 115, 228

understanding of effects, 4

FLUT flutter analysis program, 63–64, 93, 94

flutter and flutter control

AD-1 flutter clearance flights, 48, 108, 110, 

111–12, 222–23

AD-1 OWRA computer code analysis, 

63–64, 93, 94

F-8 OWRA characteristics, 146, 147, 

151–52, 161–63

Firebee oblique wing test bed research, 60

generic skewed-wing model and control law 

development to address, 161–63, 162

flying wing, 184

Focke-Wulf Fw-189 aircraft, 19

Fower, Charles, 2

Fox Field air show, 225

Franke, Milton E., 207–9

fuel systems and tanks

AD-1 OWRA, 79, 94, 218

Boeing 5-7 configuration, 58

oblique flying wing, 188, 191, 192

Fulton, Fitzhugh L. “Fitz,” Jr.

AD-1 OWRA flights, 105–6, 108, 222–25, 

228

awards, medals, and honors earned by, 107

education and career of, 107–8

experience and expertise of, 107–8

performance ratings for tasks, 122

fuselage

AD-1 OWRA, 79–80, 130

area rule and HSCT fuselage design, 197

area rule and oblique-wing aircraft fuselage 

shape, 45

dual-fuselage oblique-wing aircraft, 85–88, 

86, 97n20

fairing oblique wing to, 187–88

RTJ-303 oblique-wing concept, 199

single-fuselage oblique-wing concept, 43, 

44, 49–53, 85, 87–88

twin-fuselage oblique-wing concept, 43, 44, 

49–53

wing-body designs compared to all-wing 

designs, 201–2

G

Gadeburg, Burnett L., 43, 45

Gallman, John, 127–28, 139n59

Galloway, Thomas, 201

Gelhausen, Paul, 201

General Electric (GE)

GE F101/110 engines, 187

HSCT engine development, 196–97

J85-21 turbojet engines, 206

oblique flying wing HSCT, 196–98

German Aeronautical Society, 4

Germany

elliptical wing designs, 27

oblique-wing aircraft, development of, 

18–20, 19, 21

sweptback wings, development of, 12, 14, 

15–16, 17–18

variable-sweep research by, 17, 23

Gilbert, William, 95

Gillam, Isaac T. “Ike,” Jr., 76, 92–93

Gilyard, Glenn B., 150, 158, 161

Gimmestad, David W., 49

Glauert, Hermann, 16–17

glide bomb (glomb), 34n23

Gluhareff, Michael, 12, 34n23

Graham, Lawrence A., 45–47

Grassmann, Hermann, 3, 5

Gray, Richard “Dick,” 109, 137n6, 226

Greenberg, Harry, 9

Gregory, Tom, 157, 158

ground tests

ground vibration tests, 48, 93, 95, 102, 102, 

112–13
258

Thinking Obliquely

plans for and scheduling of, 95

wing proof-loads test, 48, 93, 94, 98n33, 

101–2

Grumman X-29 aircraft, 143

guided weapons, design and development of, 

9–10, 10, 11, 33n19, 34n23

H

Hadley Page, Ltd., 185

Hall, G. Warren, 109, 227

Hallion, Richard P., 34n23, 35n30, 140n76, 

176n1

Hamilton, William, 3, 5

Hammond, Laurens, 9, 10

Handley Page, Ltd., 41

Hart, David, 183

Heaviside, Oliver, 8

Heinkel He 70 Blitz, 27

High-Speed Civil Transport (HSCT)

California Polytechnic State University RTJ303 oblique-wing concept, 198–201, 200

cost estimates, 199–200, 201–2

environmental constraints on, 196–97, 202

GE oblique flying wing HSCT, 196–98

oblique flying wing advantages for, 189–90, 

200–201

performance goals of program, 196–97, 

198, 199, 201

wing-body designs compared to all-wing 

designs, 201–2

Hiller Aviation Museum, 136

Hirschberg, Michael, 183

Hodge, Kenneth E., 115

Honeywell Systems and Research Center, 163, 

171, 172, 173

Honrath, J., 54

Horton, Reimar, 184

Horton, Walter, 184

Hoskins, R.D., 196

Hunsaker, Jerome C., 4

I

Impact Dynamics Research Facility, 143, 176n1

implicit model-following flight control, 160

independence principle, 5, 13, 15

Institute of Electrical and Electronics Engineers, 

115

Institute of the Aeronautical Sciences, 4

International Congress of the Aeronautical 

Sciences (ICAS), Madrid, 29, 41, 185

International Test and Evaluation Association, 

115

Ishmael, Steven P., 109, 228

Iven C. Kincheloe Award, Society of Experimental 

Test Pilots (SETP), 106–7, 108

Iverson, Herb, 81, 83

J

Jarvis, Cal, 158

JB-2 Loon guided missile, 9–10, 10, 11, 33n19

JB-10 flying wing “flying bomb,” 10

Jeness, C.M., 54

Johnson, Joseph, 127

joined-wing aircraft

advantages of, 128, 140n66

aerodynamics and, 126

applications for, 126, 127, 129

computational-based analysis of concepts, 

127–28, 132, 139–40n65

concept and characteristics of, 126–29

drag and, 128

feasibility study, 129

high-speed aircraft designs, 41

research on and development of, 126, 136, 

139n59, 140–41n77

stability, handling, and control, 128, 133, 

140n66

wind tunnel models and testing, 127, 127, 

128, 132–33, 139–40n65

Joined-Wing Research Aircraft (JWRA)
259

Index

AD-1 modifications for, 125–26, 129–30, 

132, 133–36, 140n76

airfoil design, 132–33

computational-based analysis of concepts, 

132

cost of program, 134–35

goals and purpose of program, 126, 129–30

JW-1 configuration, 130, 130, 131, 132–33, 

134

JW-2 configuration, 130, 131, 132–33, 134

JW-3 configuration, 132–33, 134

landing gear, 132

stability, handling, and control, 133

takeoff and landing performance, 132, 133

termination of AD-1 modification, 133–36, 

140n76

wind tunnel testing, 132–33

wing design and structure, 130, 132–33

Jones, Robert T.

AD-1 OWRA, inspection of, 107, 108

Ames career of, 5, 6, 11, 42

autobiography of, 12–13

Avco-Everett Research Laboratory career of, 

5, 6, 42

aviation and aeronautics, lifelong interest 

in, 1, 6

awards, medals, and honors earned by, 4–5

balsa-wood model of, 27, 29, 38n72, 41, 

185

on Boeing transonic aircraft design concepts, 

52–53

death of, 1, 6

delta-wing and sweapt-wing concepts and 

aircraft, 11–17

early employment of, 2–3

early life and education of, 1–3

Experimental Aircraft Association meeting 

and AD-1 flights, 109

experts in engineering and aeronautics, 

contact with and influence of, 2–4, 5, 33n8

F-8 oblique-wing model and wind tunnel 

testing, 61–62

flying lessons and training, 2

interests and areas of expertise of, 5–9, 7

JB-2 Loon development, 9–10, 10, 11

Junior Scientific Aide appointment, 3–4

Langley career of, 3–4, 7–11

legacy of, 4–5, 11, 209–11

natural philosopher character and, 1

opinions about, 4, 6–7, 11

patents for oblique wing, 16, 46, 83–88, 84, 

86, 97n18, 97n20

photos of, viii, 7, 107

professional engineering position and college 

degree requirement, 4

RC models, 7, 40, 43, 45, 65

self-study by, 2, 3

violin building by, 6, 7

wartime service of, 9–10

Junkers, Hugo, 184

K

KC-135 Winglets project, 106

Kempel, Robert, 159, 160–61

Kennelly, Robert A., Jr., 168, 176n7, 204

Kirkup, Thomas, 2

Klepl, Martin J., 163–64

Knight, William J. “Pete,” 109, 228

Kohr, Leopold, 75

Kramer, James J., 92–93

Kroo, Ilan

career of, 176n7

F-8 OWRA model testing, 168

joined-wing aircraft research, 126, 127–28, 

133, 139n59

Jones, relationship with, 176n7

oblique-flying-wing concepts, 189, 195, 

201, 202

oblique-wing concepts, Jones role in 

development of, 27

oblique wing pros and cons, 147–50
260

Thinking Obliquely

research aircraft, program for development 

of, 150, 177n11

Küchemann, Dietrich, 20

Kulfan, Robert M., 49

L

landing gear

AD-1 OWRA, 79, 96, 219

Joined-Wing Research Aircraft, 132

oblique flying wing, 187, 194, 197

RTJ-303 oblique-wing concept, 199

tricycle configuration, development of, 4

wheel brake system, 219

Lange, Roy H., 54

Langley, Samuel Pierpont, 4, 29

Langley Medal, 4–5

Langley Research Center/Langley Memorial 

Aeronautical Laboratory

AD-1 OWRA research and testing, 101, 110, 

115, 138n36

CFL3D computer code, 207

Dynamic Stability Branch, 127

free-flight wind tunnel testing at, 23–27

Impact Dynamics Research Facility, 143, 

176n1

joined-wing agricultural design testing, 127

Jones career at, 3–4, 7–11

Jones research and reports, topics of, 7–9

Junior Scientific Aide appointment for Jones 

at, 3–4

low-speed tunnel, 12-foot, 127

Munk’s work at, 2

Pressure Wind Tunnel, 12-foot, 132–33

professional engineering position and college 

degree requirement, 4

wind tunnel, 30-by-60-foot, 115

Lee, G.H., 41–42, 185, 186

Lewis, David J., 3, 11

Lewis, George W., 11, 15, 26–27

Library of Congress, 2, 3

lift

direct lift, 128, 140n66

F-8 oblique-wing model, 167–69

Jones research and reports on, 8

oblique flying wing and, 187, 195

oblique-wing concepts and, 208

oblique-wing model tests, 24, 26

swept-wing concepts and, 12–13, 17

upward curvature of wings, 46

lift/drag ratios

AD-1 OWRA handling and, 120–21

losses at higher speeds, 53

oblique flying wing, 42, 186, 189, 195

oblique wings, 46, 47

Lindbergh, Charles, 1

Ling-Temco-Vought Corporation, 170

Lippisch, Alexander, 184

Lockheed DC-130 Hercules, 60

Lockheed F-104 Starfighter, 64, 137n6, 145

Lockheed-Georgia Company

oblique-wing SST concept, 47

subsonic oblique-wing transport study, 49, 

54–57, 55

Lockheed U-2 aircraft, 106

Lockheed YF-12A Blackbird, 107–8

loop-shaping methodology for control law 

development, 163–64, 165, 171

Lystad, Henry, 156

M

M2-F1 lifting body program, 92, 140n76

Mach numbers

oblique flying wing, 189–90, 195

oblique-wing concepts and aircraft, 205

oblique-wing model tests, 45, 46–47, 48

swept-wing aircraft and, 13, 15

Mackall, Dale, 158

MacNeal-Schwendler Corporation, 63

Mallick, Donald L., 109, 226

Manke, John A., 108, 225

Marie Meyer Flying Circus, 2

Martin, James “Jim,” 66–67, 109, 227
261

Index

Massachusetts Institute of Technology, 205

McBarron, John P., 49

McCullough 4318B engines, 65

McDonnell-Douglas, 195, 196, 197

McDonnell-Douglas F-4 Phantom II, 143

McMurtry, Thomas C. “Tom”

AD-1 manufacturing and visit to Ames 

Industrial Corporation, 94

AD-1 OWRA flights, 100, 105–6, 108, 109, 

110, 221–29

AD-1 OWRA program evaluation, 115–19

AD-1 OWRA program goals, 115–16

awards, medals, and honors earned by, 

106–7

education and career of, 106–7

oblique wing applications, 184

performance ratings for tasks, 122

photos of, 105, 107

Mead, George, 78

Messerschmitt oblique-wing concepts and 

aircraft, 20

Messerschmitt P 1101/XVIII-108/P 1109, 20

Microturbo TRS-18 turbojet engines, 79

MiG-23 aircraft, 41

military applications

Air Force long-range strike capabilities, 206

J85-21 turbojet engines, 206

Lockeed subsonic transport study, 55, 56

oblique-wing concepts and aircraft, 58–59, 

205

oblique-wing missile, 206–9

Rockwell VFMX fleet air defense fighter 

concept, 142, 144

See also weapons and missiles

Miller, R.F., 196

Mirage G aircraft, 41

Mitchell, Reginald, 27

Miura, H., 139–40n65

MMLE3 computer program, 91

model concepts and aircraft

AD-1 OWRA model, 22, 90–91, 91, 92

applications for wind tunnel models, 22

balsa-wood models, 27, 29, 38n72, 41, 185

contributions of to development of 

aeronautics, 29

dynamic models, 22

F-8 oblique-wing model, 60–62, 62, 63, 

151, 166–69, 172, 174

joined-wing models, 127, 132–33

mounting system for models, 90–91

oblique-wing missile model, 208–9

powered model airplanes, 202

RC oblique flying wing designs and testing, 

195, 202–3

RC oblique-wing free-flight model, 40, 43, 

45, 65

static models, 22

von Holst work in, 20, 21, 37n49

weight of, 24

model-following flight control, 160–61

Mohr, Denny, 109, 227

moment-of-inertia test, 48, 101

Moore, Mark, 201

Morris, Stephen J., 195, 202–3

Mulally, Alan R., 49

MultOp program, 132

Munk, Max M., 2–3, 12–13, 16–17, 29, 209

Murakami, James K., 49

Murphy, Ron, 156

N

Nangia Aero Research Associates, 205

NASTRAN structural analysis program, 63–64, 

101, 139–40n65, 162

National Academy of Engineering, 4

National Academy of Sciences, 6

National Aeronautics and Space Administration 

(NASA)/National Advisory Committee for 

Aeronautics (NACA)

AD-1 OWRA program, concerns about at 

NASA Headquarters, 92–93

Advanced Design Program, 213n13
262

Thinking Obliquely

Distinguished Service Medal, 107

Exceptional Service Medals, 108

flight research, important role of in, 75, 

140n76

flight-test aircraft numbering and 

designations, 83

metric measurement use by, 178n33

Oblique All-Wing program, 195

safety concerns and flight accidents, 

135–36

See also Ames Research Center/Ames 

Aeronautical Laboratory; Dryden Flight 

Research Center/Flight Research Center/

High-Speed Flight Station

National Aeronautics and Space Council (NASC), 

Advanced Systems Directorate, 54

National Air and Space Museum, Smithsonian 

Institution, 34n23, 35n30

Naval Surface Fire Support (NSFS) program, 206

Navier-Stokes computations, 207

Navy, U.S.

F-8 OWRA program, 144–45, 150, 156, 

169–73

Fleet Air Defense aircraft mission, 146, 150

Lockeed subsonic transport mission 

capabilities, 57

Naval Air Systems Command, 156

oblique-wing missile, 206–9

VFMX fleet air defense fighter concept, 142, 

144

XFV-12A thrust-augmented wing (TAW) V/

STOL fighter concept, 143, 144, 176n1

Neely, William, 109, 228

Nerken, Albert I., 8

Neumann, Frank D., 49, 196

NF-15B STOL Maneuvering Technology 

Demonstrator (Agile Eagle), 140n66

Nicholas, Russell, 2

Nicholas-Beazley Airplane Company, 2

Nicholas-Beazley NB-3 aircraft, 2

Nichols, George, 110

Nisbet, James W., 49, 52–53

Nobel, E.C., 49

noise and environmental constraints, 50, 

196–97, 202

North American B-25 bomber, 143

North American F-86 Sabre, 143

North American F-100 jet fighter, 143

North American P-51 Mustang, 143

North American–Rockwell OV-10 

counterinsurgency aircraft, 143

North American–Rockwell XFV-12A thrustaugmented wing (TAW) V/STOL fighter 

concept, 143, 144, 176n1

North American T-6 trainer, 143

North American X-15 aircraft, 107, 143

North American XB-70A Valkyrie, 107

Northrop, Jack, 184

Northrop B-2A Spirit stealth bomber, 182, 185

Northrop F-5E/F Tiger II lightweight fighter, 206

Northrop Grumman OFW X-Plane demonstrator 

aircraft, 205–6

Northrop JB-10 flying wing “flying bomb,” 10

Northrop YA-9A aircraft, 60

Norton Air Force Base air show, 225

O

Oblique All-Wing program, 195

oblique flying wing/oblique all-wing (OAW)

aerodynamics and, 42, 185, 186, 196

area rule and, 197

balsa-wood model of, 27, 29, 38n72, 41, 

185

cabin arrangements, 41–42, 186–87, 188, 

189, 190, 192

cargo section, 188, 191, 192

cockpit, 187, 193

cost of development, 189

design and conceptualization, analysis of, 

190–95, 212n10

drag and, 186, 187, 195

edge flaps, 187, 198
263

Index

engines and engine placement, 42, 186, 

187, 193–94

entry to and exit from, 189, 192–93

flight control and flight control systems, 

184–85

flight range of, 196, 198, 199, 201, 202, 

206

flight tests, 196

fuel tanks, 188, 191, 192

GE oblique flying wing HSCT, 196–98

Jones research on and development of, 6, 

184–86

landing gear, 187, 194, 197

Lee design for, 41–42

lift and, 187, 195

lift/drag ratios, 42, 186, 189, 195

Oblique Flying Wing experimental aircraft 

(OFW X-Plane), 205–6

oblique wing-body compared to, 201–2

performance advantages, 206

RC model designs and testing, 195, 202–3

research and development to support design, 

195, 196, 213nn13–14

stability, handling, and control, 42, 187, 196

structure and materials, 187

supersonic transport application, 185–95, 

188, 189, 190

takeoff and landing wing position, 188, 190, 

198

vertical tailplanes, 187, 194

wind tunnel testing, 186

wing cross section, 192

wing planform, 187, 191–92

oblique wing

actuation of wing skew, 219

development of concept of, v

fairing wing to fuselage, 187–88

patents for, 16, 46, 83–88, 84, 86, 97n18, 

97n20

stability, handling, and control, 24, 26

wind tunnel tests of models, v, 20, 21–22, 

23–27, 25, 29, 45–47, 48, 183

oblique-wing concepts and aircraft

acceptance of and reservations about, 23, 

147–50, 209–11

Ames research on, 45–47

applications for, 47, 54, 58–59, 183–84, 

204–9, 212n2

benefits and engineering advantages of, 23, 

53, 64, 77, 116, 144, 147–49, 183–84, 

200–201, 207, 209–11, 212n2

design and concept of, 18

drag and, 43, 148, 150–51, 183, 208

dual-fuselage oblique-wing aircraft, 85–88, 

86, 97n20

engines and engine placement, 51–52

fixed X-wing concept, 20

flight control and flight control systems and, 

200–201

flight range of, 129, 196, 198, 199, 201, 

202, 206

future of oblique technology, 116, 125, 

201–2, 209–11

German research on and development of, 

18–20, 19, 21

Jones research on and development of, 18, 

20–23, 27–31, 28, 42–47, 183, 197, 

199, 201, 209–11

lift and, 208

lift/drag ratios, 46, 47

oblique-wing missile, 206–9

pivot assembly, 52–53, 148

RTJ-303 oblique-wing concept, 198–201, 

200

single-fuselage concept, 43, 44, 49–53, 85, 

87–88

speed and wing position, 18, 20

stability, handling, and control and, 18, 42, 

148–49, 205, 210

success of, 52

sweep angles, 199, 200
264

Thinking Obliquely

sweep of single wing, advantages of, 45

takeoff and landing wing position, 18, 20, 45

twin-fuselage concept, 43, 44, 49–53

upward curvature of wings, 46

wing-body designs compared to all-wing 

designs, 201–2

Oblique Wing Remotely Piloted Research Aircraft 

(OWRPRA), 65–69, 66, 67, 68

Oblique Wing Research Aircraft (OWRA). See 

AD-1 Oblique Wing Research Aircraft (OWRA); 

F-8 Oblique Wing Research Aircraft (OWRA)

oil-flow visualization studies, 108, 228

Oshkosh air show, 108, 109–10, 115, 228–29

OV-10 counterinsurgency aircraft, 143

P

P-51 Mustang, 143

Pahle, Joseph W. “Joe,” 158, 159, 160–61

Painter, Weneth D. “Wen,” 93, 109, 110, 114, 

115

Parasev paraglider program, 92, 140n76

PASS structural analysis program, 63–64

patents for oblique wing, 16, 46, 83–88, 84, 86, 

97n18, 97n20

Pearson, Henry A., 8

Pénaud, Alphonse, 29, 202

People’s Republic of China missile program, 

34n24

pilots

AD-1 OWRA design and pilot safety, 80–81

AD-1 OWRA flight tests, 105–10, 221–29

performance ratings for tasks, 114, 117–19, 

122–23

pilot seating and restraint system, 220

Piper Twin Comanche aircraft, 66

pitch and pitching

AD-1 OWRA flight control system, 218

F-8 OWRA characteristics and flight control 

system, 163–66

loop-shaping methodology for control law 

development, 163–64, 165, 166

oblique-wing concept and, 42, 205

two-control flight control system, 4

See also coupling, cross-coupling, and 

decoupled control; stability, handling, and 

control

pivot assembly and location

AD-1 OWRA, 79, 80, 89, 94, 219

F-8 OWRA, 158, 174–75, 174

oblique-wing concepts and aircraft, 52–53, 

148, 151, 152

variable-sweep aircraft, 52–53, 148

Polhamus, Edward C., 17, 23

Polytechnic Institute of Brooklyn, 28, 29

Prandtl, Ludwig, 2, 12, 16–17

Prandtl-Glauert rule, 16–17

Prandtl Ring award, 4

Pratt & Whitney

HSCT engine development, 196–97

STF 433 engine, 56

President’s Award for Distinguished Civilian 

Service, 4

PROFILE program, 132

PROGRAM H, 132

Q

QinetiQ (United Kingdom), 214n27

quantum theory, 3

quarterions and time-space theory, 3

R

radio-controlled (RC) models

oblique flying wing designs and testing, 195, 

202–3

oblique-wing free-flight model, 40, 43, 45, 

65

real model-following (RMF) flight control, 

160–61

Remotely Piloted Aircraft (RPA)/Remotely Piloted 

Vehicle (RPV). See Unmanned Aerial Vehicle 

(UAV)/Remotely Piloted Aircraft (RPA)/Remotely 

Piloted Vehicle (RPV)
Index

265

Republic JB-2 Loon guided missile, 9–10, 10, 

11, 33n19

research and experimental aircraft, important 

role of, 75, 140n76

Reuther, James, 204

Rockwell B-1 bomber, 143, 144, 187, 197

Rockwell International

aircraft development by, 143

F-8 OWRA wing design, 144–47, 146, 

166–68, 170, 171, 172, 174–75

joined-wing wind tunnel model, 127

VFMX fleet air defense fighter concept, 142, 

144

Roeser, Erwin, 156

roll and rolling

AD-1 OWRA characteristics and flight control 

system, 122–23, 218

F-8 OWRA characteristics and flight control 

system, 163–66

loop-shaping methodology for control law 

development, 163–64, 165, 166

oblique-wing concept and, 18, 42, 205

two-control flight control system, 4

See also coupling, cross-coupling, and 

decoupled control; stability, handling, and 

control

Rollo, Vera Foster, 77

Rolls Royce Olympus engines, 187

Royal Aeronautical Society, 185

Royal Aircraft Establishment (RAE), 20

RTJ-303 oblique-wing concept, 198–201, 200

rudder

AD-1 OWRA flight control system, 89, 

117–18, 121, 218

directional change and two-control system, 4

JWRA models, 133

loop-shaping methodology for control law 

development, 163–64

Rutan, Elbert Leander “Burt”

AD-1 feasibility study, 78–81, 82

aircraft design and innovation by, 77, 78

education of, 77, 78, 198

joined-wing agricultural aircraft design, 127

wing design and structure, 98n33

Rutan Aircraft Factory

AD-1 feasibility study, 78–81, 82

composite-sandwich construction technique, 

79–80

RFP and contract award, 81, 83

Rutan Aircraft Factory 35 aircraft, 81, 83

S

Sandestin, Florida, 33n19

Santa Clara University, 190–95

Saturn rocket engines, 143

Scaled Composites, 81, 83

Schairer, George, 15

Scherer, Lee, 76

Schumacher, E.F., 75

scissors wing, 18. See also oblique-wing 

concepts and aircraft

Scott, Dave, 76

Sea Harrier V/STOL, 176n1

Sears, William R., 4, 13, 209–10

Sears-Haack body, 45–47

seating and restraint system, 220

Shumpert, P, 54

Shyu, A., 139–40n65

Sikorsky Company, 12, 34n23

Sim, Alex

AD-1 OWRA program evaluation, 115–19

AD-1 OWRA program goals, 115–16

AD-1 OWRA summary review of flight 

experience, 119–25, 138n42, 139n56

oblique wing applications, 184

simulation testing

AD-1 OWRA, 90, 93, 94, 95, 102, 104

F-8 OWRA, 163, 164–66, 169, 170

fixed-base simulation, 90, 94, 102, 104, 

113, 114, 124, 166

moving-base simulation, 94, 95, 104, 163, 

166
266

Thinking Obliquely

pilot performance ratings, 118–19

stability and damping augmentation 

technology and systems, 123–25

slender body theory, 12–13, 15

slender-wing concepts, 20

slewed wing, 20. See also oblique-wing 

concepts and aircraft

Small, John, 109, 226

small disturbance theory, 43, 87

small is beautiful concept, 75

Smith, Ronald C., 46, 61–62, 90, 91

Smith, Stephen C.

F-8 OWRA model testing, 166, 168

joined-wing aircraft research, 126, 127–28, 

133, 139n59

Turn and Glide-Back space launch booster 

recovery system, 204

Smithsonian Institution

Langley Medal, 4–5

National Air and Space Museum, 34n23, 

35n30

Society of Automotive Engineers, 115

Society of Experimental Test Pilots (SETP), 

106–7, 108, 115

Society of Flight Test Engineers, 115

solid-rocket boosters and oblique-wing recovery 

systems, 203, 204–5, 210–11

Space Shuttle program

747 Shuttle carrier aircraft, 108

orbiter, development of, 143

solid-rocket boosters and oblique-wing 

recovery systems, 203, 204–5, 210–11

space transportation, oblique wing applications 

for, 204

Spanloader studies, 195

SPAR program, 139–40n65

Sperry Flight Systems, 170

spin tunnel tests, 95–96, 101

Spitfire aircraft, 27

stability, handling, and control

AD-1 OWRA characteristics, 78–79, 

117–19, 120–21

AD-1 OWRA computer code analysis, 63–64

AD-1 OWRA flight tests, 100, 105, 108, 

113–14, 221, 222, 224–25

computers and analysis of aircraft behavior 

and motions, 63–64

F-8 OWRA characteristics, 145, 152–53, 

159–69, 179n46, 208

joined-wing aircraft, 128, 133, 140n66

Jones research and reports on, 8

oblique flying wing, 42, 187, 196, 202–3

oblique-wing concept and, 18, 42, 148–49, 

205, 210

oblique wing model tests, 24, 26

pilot performance ratings, 117–19, 122–23

RC oblique-wing free-flight model testing, 

43, 45, 65

sideforce control, 128, 140n66

simulation testing, 90, 93, 94, 95, 102, 104, 

113, 114

stability and damping augmentation, 114, 

116, 118, 119, 122, 123–25, 179n46

structural materials and handling qualities, 

117

swept-wing concept and, 12, 18

wing angle and, 45

See also coupling, cross-coupling, and 

decoupled control

Stack, John, 209

Stalter, James L., 49

Stanford University

joined-wing concepts and aircraft research, 

127, 127–28, 139n59

Jones faculty position at, 6

Kroo career at, 176n7

oblique-flying-wing research, 6, 186, 

190–95, 196

oblique technology, future of, 201–2

STBDER computer program, 91

Sterling Software, 190–95

STF 433 engine, 56

Strong, James M., 168

structural materials

AD-1 OWRA, 79–80, 89, 117

aluminum, 52, 80, 83, 90, 187, 202

Boeing 5-7 configuration, 57

Boeing transonic aircraft design concepts, 

52
267

Index

composite materials, 52, 55, 78, 79–80, 83, 

90, 148, 201, 204, 212n2, 219

flight research vehicles, 76

handling qualities and, 117

Lockeed subsonic transport study, 55

oblique-flying-wing concept, 187

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65

Su-42 aircraft, 41

subsonic oblique-wing transport study, 49, 

54–57, 55

Summers, James L., 61–62

supercritical wing (SCW) program, 60, 106

Supermarine Spitfire aircraft, 27

supersonic flight

aerodynamic efficiency and, 53

aircraft development and design for, 29–31

drag and, 30–31, 148, 150–51

lift/drag ratio losses at higher speeds, 53

oblique-wing concepts and, 147–51, 

210–11

research aircraft, program for development 

of, 144–45, 150, 177n11

swept-wing concepts and, 12, 13, 16–17

See also F-8 Oblique Wing Research Aircraft 

(OWRA)

supersonic transports (SSTs)

Boeing 5-7 configuration, 57–58, 58, 78

economics of, 186

oblique-flying-wing concept, 41–42, 

185–90, 188, 189, 190

oblique wing applications, 20, 47

single-fuselage oblique wing concept, 43, 44

twin-fuselage oblique wing concept, 43, 44

Sussman, Mark B., 49

swept-wing concepts and aircraft

bilaterally symmetric shapes, 27, 29, 30

controversy surrounding, 14–15

delta wing development and, 14

drag and, 13, 15, 17, 30, 43

fixed-sweep aircraft, 17

German research on and development of, 

12, 14, 15–16, 17–18

Jones research on and development of, 7, 9, 

11–17, 18, 27

lift and, 12–13, 17

point-forward swept-wings, v

research report on, 11, 13, 35n26

stability and, 12, 18

transonic aircraft design concepts, 49–53

variable-sweep aircraft. See variable-sweep 

aircraft

wind tunnel testing, 26–27

yawed-wing concepts compared to, 30

Swift, G., 54

Sylvanus Albert Reed Award, 4

symmetry

aerodynamics and, 185

aircraft and bilateral (mirror) symmetry, 27, 

29, 30, 42–43, 86, 87–88

drag and, 43, 185

human tendencies for bilateral designs, 185, 

210

symmetrical variable-sweep development, 

26

Szalai, Kenneth J., 75, 76–77, 157

T

T-6 trainer, 143

T-37 jet aircraft, 137n6

tailless aircraft, 8, 12

tails and tail surfaces

AD-1 OWRA, 88, 130

F-8 oblique-wing model and wind tunnel 

testing of, 61–62, 63

Jones research and reports on, 8

JWRA models, 133

Lockeed subsonic transport study, 55

oblique flying wing vertical tailplanes, 187, 

194

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65, 66, 67–68, 67, 68

RTJ-303 oblique-wing concept, 199

Teledyne-Ryan BQM-34F Firebee drone, 59–60, 

61

Thompson, Milton O., 136, 140n76

Toll, Thomas A., 17, 23

Tomlin, K., 54

transonic flight

aerodynamic efficiency and, 53
268

Thinking Obliquely

aerodynamics and wing-body effects, 27

aircraft design concepts for, 49–53

F-8 OWRA for, 22

lift/drag ratio losses at higher speeds, 53

Traskos, Robert, 156

TRS-18 turbojet engines, 79

Tsien Hsue-shen, 12, 34n24

Turn and Glide-Back space launch booster 

recovery system, 203, 204–5

U

U-2 aircraft, 106

Underwood, W.J., 9

University of Colorado, 4

University of Kansas, 127, 196, 213n13

Unmanned Aerial Vehicle (UAV)/Remotely Piloted 

Aircraft (RPA)/Remotely Piloted Vehicle (RPV)

Firebee drone oblique wing test bed, 59–60, 

61

micro-RPA, 37n49

oblique wing applications, 59, 204, 205

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 65–69, 66, 67, 68

V

V-1 Buzz bombs (Fieseler FZG-76 bomb), 9–10

Van der Velden, Alexander J.M., 186–90, 195, 

201

variable-sweep aircraft

development of, 17–20, 19, 41–42

German research on and development of, 

17, 23

oblique-wing variable sweep advantages 

over conventional variable sweep, 148–49, 

150–51, 152

pivot assembly, 52–53, 148

symmetrical variable-sweep development, 

26

transonic aircraft design concepts, 49–53

VariEze aircraft, 78

Vendolosky, Walter “Walt,” 109, 110

Vertical Motion Simulator, 164–66

vertical/short takeoff and landing (V/ STOL) 

aircraft, 143, 144, 176n1

VFMX fleet air defense fighter concept, 142, 144

Vincenti, Walter G., 6–7, 13, 21, 27, 210

Vogt, Richard, 18–19, 27, 97n18

Voigt, Woldemar, 20

Volta Congress, 12, 18, 35n32

von Holst, Erich, 20, 21, 37n49

von Kármán, Theodore, 2, 30–31

vortilons, 133, 187

Vought F-8 Crusader fighters. See F-8 Crusader 

fighters

V/ STOL (vertical/short takeoff and landing) 

aircraft, 143, 144, 176n1

W

Wallis, Barnes, 184

Warnock, W.W., 54

Waters, Mark, 201

Watkins, John, 109, 227

wave drag, 30–31, 42, 43

weapons and missiles

advances in and oblique wing applications, 

204

Extended Range Guided Munition (ERGM), 

206, 207

guided weapons, design and development of, 

9–10, 10, 11, 33n19, 34n23

oblique wing advantages, 211

oblique wing applications, 59

oblique-wing missile, 206–9

Weick, Fred E., 3–4, 8

Western Michigan University, 159

Wetmore, Joseph W., 9

wheel brake system, 219

Whitcomb, Richard T., 60, 209

White, S.N., 156

Wiler, C.D., 156

Williams, Walter, 76, 92

Wilson, E.B., 4

wind tunnel facilities

Ames 11-foot Transonic Wind Tunnel, 

45–47, 48, 60–62, 167, 169, 170, 174, 

186

Ames 12-foot Pressure Wind Tunnel, 90–91, 

91, 92

Ames 40-by-80-foot wind tunnel, 67–68, 93

Catholic University, 3
269

Index

Langley 12-foot-low-speed tunnel, 127

Langley 12-foot Pressure Wind Tunnel, 

132–33

Langley 30-by-60-foot wind tunnel, 115

Langley free-flight wind tunnel, 23–27

Washington Navy Yard, 3

Wind Tunnel Test Design Team, 196

wind tunnel testing

AD-1 OWRA developmental tunnel research, 

90–91, 91, 92

AD-1 OWRA full-scale testing, 93, 110, 115, 

138n36

applications for, 22

F-8 oblique-wing model, 60–62, 63, 

166–69, 170, 172, 173, 174–75

force tests, 24, 26

free-flight testing, 22

joined-wing concepts and models, 127, 128, 

132–33, 139–40n65

Jones promotion of testing, 21, 27

oblique flying wing, 186

oblique-wing missile model, 208–9

oblique-wing model tests, v, 20, 21–22, 

23–27, 25, 29, 45–47, 48, 183

Oblique Wing Remotely Piloted Research 

Aircraft (OWRPRA), 67–68

slender delta test model, 13, 14, 35n30

swept-wing concepts and aircraft, 26–27

wing-body effects, 27

wing edge flaps

Boeing 5-7 configuration, 58

F-8 oblique-wing model and wind tunnel 

testing of, 167–68

Lockeed subsonic transport study, 56

oblique flying wing, 187, 198

wing proof-loads test, 48, 93, 94, 98n33, 101–2

wings

arrow elliptic wing, 185

arrow wing shapes and drag, 43

deflectable wingtips, 167–68

Jones research and reports on, 8

speed and aspect ratio, 53

variable wing geometry, 208

wake of, 8, 13

Wolkovitch, Julian, 126, 127, 128, 139–40n65

Wright-Patterson Air Force Base, 208

X

X-1 aircraft, 14

X-15 aircraft, 107, 143

X-29 aircraft, 143

XB-47 Stratojet bomber, 15

XB-70A Valkyrie, 107

XFV-12A thrust-augmented wing (TAW) V/STOL 

fighter concept, 143, 144, 176n1

X-Plane, Oblique Flying Wing (OFW X-Plane), 

205–6

Y

YA-9A aircraft, 60

yaw and yawing

AD-1 OWRA, 121, 218

F-8 OWRA characteristics and flight control 

system, 163–66

loop-shaping methodology for control law 

development, 163–64, 165, 166

oblique-wing concept and, 18, 42, 205

two-control flight control system, 4

upward curvature of wings, 46

See also coupling, cross-coupling, and 

decoupled control; stability, handling, and 

control

yawed-wing concepts, 30, 50–51, 78, 87

YF-12A Blackbird, 107–8

Yore model, 159

Z

Zahm, Albert F., 3, 33n8

ZONA Technology, Inc., 206–7