Contributions of the 

Langley Research Center 

to U.S. Military Aircraft 

of the 1990s 

Joseph R. Chambers 

1

4
NASA SP-2000-4519 

Partners in Freedom 

Contributions of the Langley Research Center to

U.S. Military Aircraft of the 1990's 

By

Joseph R. Chambers 

Monographs in Aerospace History Number 19

The NASA History Series 

National Aeronautics and Space Administration

Office of Policy and Plans

NASA History Division

Washington, DC

2000
Library of Congress Cataloging-in-Publication Data 

Chambers, Joseph R. 

Partners in freedom contributions of the Langley Research Center to U.S. military 

aircraft of the 1990's / by Joseph R. Chambers. 

p. cm. -- (NASA history series) 

Includes bibliographical references and index. 

1. Langley Research Center. 2. Aeronautics, Military--Research--United 

States--History. 3. Airplaces, Military--United States--Design and construction. I. Title. 

II. Series. 

UG644.H36 .C43 2000 

623.7'46'072073--dc2 1

00-056072 

The use of trademarks or names of manufacturers in this publication is for accurate 

reporting and does not constitute an official endorsement, either expressed or implied, of 

such products or manufacturers by the National Aeronautics and Space Administration.
Acknowledgments 

I am sincerely indebted to the dozens of current and retired employees of the NASA 

Langley Research Center who consented to be interviewed and submitted their personal 

experiences, recollections, and files from which this documentation of Langley contributions was drawn. The following individuals contributed vital information to this 

effort:

Irving Abel

William J. Alford, Jr.

Jerry M. Allen

Theodore G. Ayers

Donald D. Baals

E. Ann Bare

Bobby L. Berrier

Ralph P. Bielat

James S. Bowman, Jr.

Francis J. Capone

Huey D. Carden

Stanley R. Cole

Mark A. Croom

Richard G. Culpepper

H. Benson Dexter

Robert V. Doggett

Robert H. Daugherty

Moses G. Farmer

Stuart G. Flechner

Charles H. Fox, Jr.

Charles M. Fremaux

William P. Gilbert

Sue B. Grafton

David E. Hahne

James B. Hallissy

Perry W. Hanson

Roy V. Harris, Jr.

Lowell E. Hasel

William P. Henderson

Charles M. Jackson

Lisa E. Jones

Joseph L. Johnson, Jr.

Donald F. Keller

Richard E. Kuhn

John E. Lamar

Laurence K. Loftin, Jr

Donald L. Loving

Linwood W. McKinney

James C. Newman, Jr.

Luat T. Nguyen

James C. Patterson, Jr.

John W. Paulson, Jr.

Edward C. Polhamus

Richard J. Re

Wilmer H. Reed, Jr.

Rodney H. Ricketts

Charles L. Ruhlin

Maynard C. Sandford

David S. Shaw

M. Leroy Spearman

Raymond D. Whipple

Richard T. Whitcomb

Thomas J. Yager

E. Carson Yates

Long P. Yip 

Special thanks to Bobby Berrier and Patricia A. West, who provided their superb technical editing and proofreading skills to the project. I would like to express my special gratitude to Noel A. Talcott and Jeffrey A. Yetter, who provided the inspiration to undertake 

this activity, and to A. Gary Price, who provided the mechanism. 

Thanks also to Percival J. Tesoro for the cover design, Leanna D. Bullock for assistance 

with the photographs, Peggy S. Overbey for manuscript preparation services, Cathy W. 

Everett for bibliography verification and formatting, Christine A. Ryan for printing 

coordination, and Gail S. Langevin for editing and document production coordination. 

Ultimately, however, the greatest thanks go to the thousands of current and retired 

employees of the NASA Langley Research Center, who provided the personal dedication, expertise, and innovation that enabled the legendary contributions covered in this 

work. 

Joseph R. Chambers 

Yorktown, VA 

April 20, 2000 

Acknowledgments
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Preface 

For over 80 years, Langley Research Center has exemplified the cutting edge of worldclass aeronautics research for civil and military aircraft. Established in 1917 as the 

nation's first civil aeronautics research laboratory under the charter of the National 

Advisory Committee for Aeronautics (NACA), Langley initially existed as a small, 

highly productive laboratory with emphasis on solving the problems of flight for the 

military and the civil aviation industry. During World War II (WWII), the Langley 

Memorial Aeronautical Laboratory directed virtually all of its workforce and facilities 

to research for military aircraft. Following WWII, a more balanced program of military 

and civil projects was undertaken. The emergence of the Space Age and the incorporation of the NACA and Langley into the new National Aeronautics and Space Administration (NASA) led to a rapid growth of space related research and the cultural change 

of the old laboratory into a major research center. Today, Langley research efforts 

encompass critical areas of both aeronautics and space technology. 

Throughout its history, Langley has maintained a close working partnership with the 

Department of Defense, U.S. industry, universities, and other government agencies to 

support the defense of the nation with fundamental and applied research. Many of the 

legendary contributions of Langley to military aircraft technology have been discussed 

and documented by specialists, the media, and historians. Langley contributions to 

famous military projects such as the aircraft drag cleanup studies of WWII, the advent 

of supersonic flight and the X-1, the development and tests of the Century-series fighters, the X- 15, and many, many others have been archived in detail. 

The objective of this particular undertaking is to document the contributions of Langley 

Research Center to specific military aircraft that were operational in the 1990's. Virtually all military aircraft that participated in Operation Desert Storm, Kosovo, and other 

peacekeeping missions of this era have Langley technical contributions to their design, 

development, and support. In some instances Langley research from one aircraft development program helped to solve a problem in another development program. At the 

conclusion of some development programs, Langley researchers obtained the research 

models to conduct additional tests to learn more about previously unknown phenomena. 

These data also proved useful in later developmental programs. Perhaps the most consistent element in all of the research programs is the length of time for the development 

and maturation of new research concepts before they are implemented in new aircraft. 

Many of the military aircraft in the U.S. inventory as of late 1999 were over 20 years 

old. Langley activities that contributed to the development of some of these aircraft 

began over 50 years prior. 

Preface
This publication documents the role—from early concept stages to problem solving for 

fleet aircraft—that Langley played in the military aircraft fleet of the United States for 

the 1990's. The declassification of documents and other material has provided an opportunity to record the contributions of Langley personnel and facilities and discuss the 

impact of these contributions on Department of Defense aircraft programs. This review 

is intended for the general public with an interest in aircraft development. For more 

technical information about specific aircraft and programs, please see the publications 

listed in the bibliography. 

Readers familiar with NASA and its research centers will note that the former Lewis 

Research Center is referred to by its new name, Glenn Research Center. The decision to 

use the new name was made to avoid confusion for those readers less familiar with the 

NASA centers and to avoid disruptive explanations in the text for all readers. 

Vi Preface
Contents 

Introduction . 1 

Langley Contributions to Selected Aircraft .............. 3

BAI Exdrone BQM-147A ............................ 5

Highlights of Research by Langley for the Exdrone .............. 5

Langley Contributions to the Exdrone BQM-147A...............7 

Background.......................................................7 

Langley Research Efforts ............................................7 

Subsequent Exdrone Vehicle Applications ...............................8 

Boeing AV-8 Harrier .............................. 11

Highlights of Research by Langley for the AV-8 ................11 

Langley Contributions to the AV-8............................13 

Background......................................................13 

Contributions to the P1127 .........................................13 

Contributions to the Kestrel .........................................16 

Contributions to the AV-8 ...........................................18 

Boeing C-17 Globemaster III ........................21 

Highlights of Research by Langley for the C-17 ................21 

Langley Contributions to the C-17...........................23 

The CX Competition ...............................................23 

The Externally Blown Flap Concept ..................................23 

TheYC-15 .......................................................24 

The C- 17 Supercritical Wing, Winglets, and Aerodynamic Studies ...........26 

Composite Materials...............................................27 

Fly-by-Wire Control System .........................................27 

Avoiding the Deep Stall ............................................27 

Recognition Visit..................................................28 

Contents vii
Boeing F/A- 18 Hornet . 29 

Highlights of Research by Langley for the F/A- 18 .............. 29

Langley Contributions to the F/A- 18 ......................... 31

Vortex Lift and Maneuvering Flaps ................................... 31 

Development of the YF-17 ........................................... 32 

F/A-l8AtoF/A-18D ..................................... 35 

Development of the F/A-18 .......................................... .35 

Cruise Drag ..................................................... 36 

High-Angle-Of-Attack, Spin, and Spin Recovery Characteristics ............ 36 

The NASA High-Angle-Of-Attack Technology Program.................... 38 

The Falling-Leaf Maneuver ......................................... 42 

Flutter Clearance and Tail Buffet..................................... 42 

Thrust-Vectoring Research .......................................... 43 

F/A-18E/F .............................................. 44 

The Super Hornet ................................................. 44 

Cruise Performance ............................................... 45 

Redesign of the Leading-Edge Extension ................................ 45 

High-Angle-Of-Attack Characteristics ................................. 46 

Spin Tunnel and Drop-Model Tests.................................... 47 

Flutter Tests ..................................................... 48 

WingDrop....................................................... 48

Boeing T-45 Goshawk ............................. 51

Highlights of Research by Langley for the T-45 ................ 51

Langley Contributions to the T-45 ........................... 53

 Early Configuration Development ....................................53 

Stall Characteristics ...............................................53 

Spin Characteristics ...............................................54 

Ground Handling .................................................55 

Inlet Performance .................................................56 

Fairchild Republic A- 10 Thunderbolt II ................ 57 

Highlights of Research by Langley for the A- 10 ................ 57

Langley Contributions to the A-lO ........................... 59 

The A-X Competition ..............................................59 

Spin Recovery ....................................................60 

General Dynamics F- ill Aardvark ................... 61

Highlights of Research by Langley for the F- ill ............... 61

Langley Contributions to the F- ill ........................... 63

 The Variable-Sweep Wing Concept....................................63 

The Tactical Fighter Experimental (TFX) Program .......................66 

Aerodynamic Performance ..........................................68 

Propulsion Integration .............................................70 

High-Angle-of-Attack Characteristics .................................72 

Spin Recovery ....................................................73 

viii Contents 
Flutter Tests .75 

Crew Escape Module ............................................... 76

Wing Box Problems ................................................ 78

The Transonic Aircraft Technology (TACT) Program ...................... 78

The Mission Adaptive Wing (MAW) Program ............................ 81

Grumman A-6 Intruder .............................83 

Highlights of Research by Langley for the A-6 .................83 

Langley Contributions to the A-6............................ 85

Speed Brake Studies................................................ 85

Spin Tunnel Tests .................................................. 85

The Composite Wing ............................................... 86

Grumman EA-6B Prowler...........................89 

Highlights of Research by Langley for the EA-6B ..............89 

Langley Contributions to the EA-6B .........................91 

Spin Tunnel Tests .................................................. 91

Maneuver Improvements ............................................ 91

Cooling Study .................................................... 94

Grumman F- 14 Tomcat .............................97 

Highlights of Research by Langley for the F-14 ................97 

Langley Contributions to the F- 14 ...........................99 

Early NASA Fighter Studies ......................................... 99

F-14 Source Selection ............................................. 100

NASA Independent Assessment ...................................... 100

Propulsion Integration ............................................. 100

High-Angle-Of-Attack and Spin Research. ............................. 102

Flutter Tests ..................................................... 106

F-14 Yaw Vanes .................................................. 107

Grumman X-29 ..................................109 

Highlights of Research by Langley for the X-29 ...............109 

Langley Contributions to the X-29 ........................... III 

Evolution of Forward-Swept Wing Configurations ....................... 111 

High-Angle-of-Attack Technology .................................... 112 

Spin Tunnel Tests ................................................. 115 

Drop-Model Tests ................................................ 117 

Engine Inlet Tests................................................. 119 

Aeroelastic Divergence ............................................ 119 

Advanced Engine Nozzle ........................................... 120

Lockheed C-5 Galaxy .............................123 

Highlights of Research by Langley for the C-S ................123 

Langley Contributions to the C-S ........................... 125 

C-5 Evaluation ................................................... 125

Research on Sting Interference Effects ................................ 125

Contents ix 
Research on Effects of Test Section Size ............................... 125

Propulsion Integration Research .................................... 127

Low-Speed and Wake Characteristics................................. 128

Tail Flutter ..................................................... 129

Load Alleviation ................................................. 131

Ditching Tests ................................................... 131

Wind-Tunnel Test to Flight-Test Correlation ........................... 133

Lockheed Martin C-130 Hercules....................135 

Highlights of Research by Langley for the C-130 ..............135 

Langley Contributions to the C-130 ......................... 137 

Composite Structures and Materials ................................. 137

Advanced Cockpit Displays ........................................ 137

Acoustics ....................................................... 137

Aerodynamic Technologies ......................................... 138

Recognition Visit ................................................. 138

Lockheed Martin C-141 Starlifter .................... 139 

Highlights of Research by Langley for the C-141 ..............139 

Langley Contributions to the C-141 .........................141 

Tail Flutter ..................................................... 141 

Aileron Reversal ................................................. 143 

Runway Grooving ................................................ 144 

Wind Tunnel and Flight Correlation .................................. 144 

Lockheed Martin F-16 Fighting Falcon ...............147 

Highlights of Research by Langley for the F- 16 ...............147 

Langley Contributions to the F-16 ..........................149 

Early Assessments ................................................ 149 

Transonic Performance ............................................ 149 

Vortex Lift ...................................................... 149 

High-Angle-Of-Attack Stability and Control ........................... 151 

Curing Deep Stall ................................................ 152 

Spin Recovery ................................................... 153 

Fly By Wire and Sidestick Controller ................................. 154 

Flutter Clearance ................................................ 155 

The F-J6XL ..................................................... 156

Lockheed Martin F-22 Raptor ......................159 

Highlights of Research by Langley for the F-22 ...............159 

Langley Contributions to the F-22 ..........................161 

The Advanced Tactical Fighter (ATF) Program ......................... 161 

Value of the Langley Database ...................................... 161

The YF-22 Program .............................................. 162

Letter of Appreciation .............................................. 163

The F-22 Program ............................................... 163 

Vertical-Tail Buffet ............................................... 165

x Contents 
Lockheed P-3 Orion . 167 

Highlights of Research by Langley for the P-3 ................ 167

Langley Contributions to the P-3 ........................... 169

169 The Lockheed Electra .............................................

Lockheed S-3 Viking .............................. 171

Highlights of Research by Langley for the S-3 ................ 171

Langley Contributions to the S-3 ........................... 173

173 Background .....................................................

173 Spin Tunnel Tests .................................................

174 Flutter Tests.....................................................

McDonnell Douglas F-4 Phantom II .................. 175

Highlights of Research by Langley for the F-4 ................ 175

Langley Contributions to the F-4 ........................... 177

Early Configuration Development.................................... 177

178 Maneuverability..................................................

179 High-Angle-of-Attack Stability ......................................

181 The Flat Spin ....................................................

183 Nose Vibrations ..................................................

184 Runway Grooving ................................................

McDonnell Douglas F-iS Eagle ..................... 185

Highlights of Research by Langley for the F- 15 ............... 185

Langley Contributions to the F-15 .......................... 187

187 The NASA Fighter Study ...........................................

188 F-IS Source Selection .............................................

188 Aerodynamic and Propulsion Integration Studies........................

190 High-Angle-Of-Attack and Spin Research..............................

191 Flutter Clearance ................................................

 The F-IS Short Takeoff and Landing and Maneuver Technology 

Demonstrator................................................. 192

Missiles ........................................ 195

Highlights of Research by Langley for Missiles ............... 195

Langley Contributions to Missiles .......................... 197

Background ..................................................... 197 

AIM-9 Sidewinder ................................................ 197 

AIM-7 Sparrow .................................................. 199 

AIM-J2OAMRAAM ............................................... 199 

Impact on Aircraft Characteristics ................................... 199

Northrop Grumman B-2 Spirit ....................... 201

Highlights of Research by Langley for the B-2 ................ 201

Langley Contributions to the B-2 ........................... 203

Contents xi 
Rockwell B-lB Lancer . 205 

Highlights of Research by Langley for the B- lB ............... 205 

Langley Contributions to the B-lB .........................207 

Early Strategic Bomber Studies .....................................207 

The B-lA Program......................................208 

High-Angle-of-Attack Research ...................................... 208

Cruise Drag .................................................... 210

Flutter ......................................................... 211

The B-lB Program......................................212 

Dynamic Loads on Engine Nozzle Flaps .............................. 212

Rockwell-MBB X-31 .............................213 

Highlights of Research by Langley for the X-31 ...............213 

Langley Contributions to the X-31..........................215 

Background ..................................................... 215

The HiMAT Program ............................................. 215

The SNAKE Program .............................................. 216

X-31 Configuration Evolution ....................................... 219

X-31 Flight Demonstration Program ................................. 221

Role of the X-31 in High-Angle-of-Attack Technology .................... 223

The Future—Investing in Freedom...................225 

Wind Tunnels—The Tools of the Trade...............227 

Langley 4- by 4-Foot Supersonic Pressure Tunnel..............228 

Langley 7- by 10-Foot High-Speed Tunnel ...................228 

Langley 8-Foot Transonic Pressure Tunnel ...................228 

Langley 30- by 60-Foot Tunnel ............................229 

Langley 16-Foot Transonic Tunnel .........................229 

Langley 20-Foot Vertical Spin Tunnel .......................230 

Langley 16-Foot Transonic Dynamics Tunnel.................231 

Langley Unitary Plan Wind Tunnel .........................232 

Bibliography ....................................233 

Index ..........................................243 

Monographs in Aerospace History ...................255 

About the Author ................................. 256

xii Contents
Introduction 

"The making available to agencies directly concerned with national defense 

of discoveries that have military value or significance ...... 

The foregoing statement is an excerpt from the National Aeronautics and Space Act of 

1958, which in part established the formal relationship between NASA and those 

responsible for the defense of the nation. Since its initial operations over 80 years ago, 

the Langley Research Center has maintained an appropriate priority within its research 

activities to ensure the quality, timeliness, and applications of its research in accordance 

with this congressional act. As a result, Langley and the Department of Defense (DOD) 

have maintained a strong and productive relationship. This critical teamwork has been 

nurtured by mutual respect and recognition that the close working arrangements have 

benefited both parties. 

Langley's support of specific military aircraft development programs and Langley's fundamental research have provided many benefits to the DOD. By virtue of its independent agency perspective, Langley's assessments of evolving technology and aircraft 

systems have provided, and continue to provide, the DOD with unbiased analysis, opinions, data, and extremely valuable recommendations for decisions about aeronautical 

technology issues in its aircraft programs. Langley's staff has been frequently called 

upon to participate or represent the DOD in early assessments and selections of competing aircraft designs. In addition, Langley's unique wind tunnels, simulators, and computational facilities have been extensively utilized for evaluations and development of 

military aircraft. The DOD benefits from the extensive experiences and corporate 

knowledge of the Langley staff as a result of Langley's participation in a vast number of 

aircraft development programs. The multidiscipline expertise at Langley is viewed as a 

unique capability and resource for the nation. 

The DOD frequently requests the participation of Langley on review boards and accident investigations. The DOD also recognizes that technical problem-solving exercises 

during aircraft development programs frequently do not provide the fundamental understanding or design tools necessary to avoid similar problems in future aircraft programs. 

Therefore, the DOD encourages Langley to conduct follow-on research and frequently 

assists NASA in obtaining the resources required for these efforts. 

Finally, the DOD and its supporting industries value the innovative concepts and technical capabilities provided by the ongoing fundamental research programs at Langley. 

Breakthrough concepts in aeronautics take years of dedicated research to bring to maturity and readiness for application. Many examples are discussed herein where Langley 

conceived, assessed, and reduced the risk of application of enabling technology when 

Introduction
that technology was critically needed for the development of major DOD aircraft 

programs. 

Providing support to the DOD in the development of military aircraft has provided 

Langley with very significant benefits. By responding to DOD's requests, Langley 

maintains relevance in research endeavors and receives test assets, valuable data, and 

validation of research concepts. For example, DOD normally provides wind-tunnel 

models for assessments in Langley's unique wind-tunnel facilities. (For more information about selected Langley wind tunnels, see the appendix.) After the critical objectives 

of aircraft development programs have been met, these models are frequently made 

available to Langley researchers for generic research and assessments of advanced concepts, which provides a mechanism for research studies that might not be otherwise 

funded within the Langley budget. 

By participating in problem-solving exercises with DOD, Langley researchers are 

exposed to a myriad of real-world requirements and constraints, thereby gaining valuable awareness of limitations in designing and conducting research within specific technical disciplines. Researchers also experience the implication of off-design flight 

conditions on new technologies, and thus obtain a much broader outlook for future 

research opportunities. Another valuable benefit to Langley is the application and validation of research concepts and technical analysis methods. By becoming a team member in DOD aircraft development programs, Langley researchers obtain highly valued 

flight-test data and feedback that is unaffordable within NASA budget constraints. 

The single most important benefit of the DOD and Langley partnership, however, is the 

application of new technologies to this nation's first-line military aircraft, thereby helping to ensure the continued supremacy of the airpower of the United States. 

Introduction
Langley Contributions to Selected 

Aircraft 

The recent declassification of many documents detailing research conducted at Langley 

during the 1960's, 1970's, 1980's, and 1990's has permitted a unique opportunity to collate and summarize the contributions of Langley researchers to several types of aircraft. 

The following pages document specific contributions of the NASA Langley Research 

Center to U.S. military aircraft. The discussion includes fighters, transports, trainers, 

missiles, and remotely piloted vehicles. The information, which has been gathered from 

documents, personal interviews, and other sources, emphasizes the highlights of Langley's support of specific programs. Research on developing aircraft is extensive and 

exhaustive. In many cases, additional projects or research was conducted on specific aircraft; however, not all activities are covered herein. 

The Langley research culture that produced these significant results flourished because 

of team participation and the personal dedication and contributions of many, many 

individuals. Despite the dangers of citing certain individuals and omitting others, 

names have been included for further guidance to those interested in expanding the 

information. 

The material is presented in two formats. These formats are 

• Single-page (back and front) overviews that summarize the major contributions of 

Langley to a specific aircraft 

• Multipage detailed discussions of individual contributions to a specific aircraft 

The discussion is intentionally at a level that can be understood by the nontechnical 

reader; however, additional publications are provided in the bibliography for those seeking more detailed technical information. 

Langley Contributions to Selected Aircraft 3
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Highlights of Research by Langley for the Exdrone 

SPECIFICATIONS 

Manufacturer 

BAI Aerosystems, Inc. 

Date in service 

Late 1980's 

Number built 

Over 500 to date 

Type 

Remotely piloted vehicle 

Crew 

Remotely piloted 

Engine 

8-hp 2-stroke gasoline 

engine. 2-blade wooden 

propeller 

MISSION 

Reconnaissance, communications jamming. and delivery of 

nonlethal payloads 

USERS 

U.S. Marine Corps and U.S. 

Naval Air Warfare Center 

DIMENSIONS 

Wingspan ............. 8.2 ft 

Length ............... 6.1 ft 

Height ............... 1.7 ft 

Wing area ......... 21.4 sq ft

WEIGHT 

Empty ................45 lb 

Max payload ...........46 lb 

PERFORMANCE 

Cruise speed .........90 mph 

Range.................() mi 

Endurance .............2 hr

BAT Exdrone BQM-147A 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE EXDRONE - - 

I. At the request of the U.S. Marine Corps. Langley conducted wind-tunnel and flight 

tests to solve unacceptable Exdrone low-speed flight characteristics. 

2. Langley identified configuration modifications to the wing airfoil, control surfaces, 

wing leading edge. and vertical tail that dramatically improved low-speed flight 

characteristics. 

BA! Evd rune BQM-147A 5 
Highlights of Research by Langley for the Exdrone 

The worldwide deployment of remotely piloted vehicles (RPV's) by military forces has 

dramatically increased. Several factors, such as elimination of threats to human pilots in 

hostile environments, cost-effectiveness for certain missions, and stealth for some applications, have stimulated the use of RPV's. The field-launched Exdrone RPV has proven 

to be an extremely effective battlefield option for the U.S. Marine Corps. During Operation Desert Storm, Exdrone was pulled from a research and development program. The 

Exdrone was pressed into reconnaissance service to find attack routes through Iraqi 

defenses, thus allowing a rapid ground advance into Kuwait. The NASA Langley 

Research Center made a critical and timely contribution during the development of the 

Exdrone that enabled highly successful deployments of the vehicle. 

In the mid-1980's, prior to the involvement of Langley, BAlAerosystems, Inc. manufactured the Exdrone RPV in accordance with a technical specification generated by Johns 

Hopkins University Applied Physics Laboratory. This version of the Exdrone was for an 

earlier mission (jamming of communications) that required high dash speeds, therefore, 

the configuration was not optimized for the low-speed flights that are necessary for 

extended reconnaissance missions. In fact, at slow speeds the vehicle was extremely dif -

ficult to fly and several crashes occurred during field trials simulating the reconnaissance task. 

In response to an urgent request from the Marine Corps in 1988, Langley conducted 

wind-tunnel and flight tests of the Exdrone to determine how the vehicle could be modified to enhance the flight characteristics in low-speed flight. Changes to the wing airfoil, 

control surfaces, wing leading edge, and vertical tail that were recommended by the 

Langley staff resulted in a configuration with outstanding low-speed flight characteristics. The changes were incorporated into the BQM-147A Exdrorie. The modified vehicle 

was an immediate success in reconnaissance missions in Operation Desert Storm. 

The overall aerodynamic configuration of the Exdrone has not been revised since 

Langley's study; however, the vehicle payloads and mission applications continue to be 

upgraded. The latest vehicle is referred to as the Dragon Drone. As technological innovations continue to evolve candidate payloads into smaller, more efficient packages that 

are suitable for small RPV's, the Dragon Drone's capabilities will likewise continue to 

be upgraded. The nucleus of the concept, however, remains the modified configuration 

that owes much to the improvements recommended by Langley's insightful researchers 

and their problem-solving efforts.

BAI Exdrone BQM-147A
Langley Contributions to the Exdrone BQM-147A 

LANGLEY CONTRIBUTIONS TO THE EXDRONE BQM-147A 

Background BAI Aerosystems. Inc. (BAI) of Easton. Maryland initially manufactured the Exdrone 

air vehicle in the late 1980's in accordance with a technical specification generated by 

the Johns Hopkins University Applied Physics Laboratory (JHU-APL). JHU-APL's 

delta-wing configuration was powered by a tractor propeller propulsion system. This 

configuration was effective for an earlier mission for jamming of communications that 

required high dash speeds, therefore the configuration was not optimized for the lowspeed flights that are necessary for extended reconnaissance missions. During evaluation for potential reconnaissance applications, the U.S. Marine Corps found that the 

vehicle exhibited poor stability and control characteristics and had a tendency toward 

severe lateral-directional instability near the stall, which resulted in numerous crashes. 

At the request of the Marine Corps in 1988, exploratory wind-tunnel and flight-test 

investigations of the Exdrone were conducted at the Langley Research Center by flight 

dynamics specialists under the lead of Joseph L. Johnson, Jr. Lead researcher for the 

study was Long P. Yip. 

Langley Research Efforts Results of wind-tunnel tests of the baseline Exdrone configuration in the Langley 

12-Foot Low-Speed Tunnel identified several aerodynamic deficiencies that contributed 

to the unacceptable low-speed flight characteristics experienced in the Marine Corps 

evaluations. For example, longitudinal control was insufficient to trim the Exdrone to 

the high-lift conditions required for low-speed flight. Yip recommended an increase in 

the chord of the elevator and thereby provided almost three times as much lift for lowspeed flight. To cure a wing-dropping tendency at high lift, Yip recommended a leadingedge "droop" modification to the outer wing panels. Increasing the rudder area and the 

size of the vertical tail solved deficiencies in directional stability and control. The original configuration displayed a bad combination of lightly damped rolling and yawing 

motions (sometimes called Dutch roll). but Yip eliminated this motion by increasing 

directional stability with the increased vertical tail and by adding wingtip skids. The 

wingtip skids also provided better flow over the ailerons and served as landing skids. 

which replaced the original drag-producing wire skids. 

Lan glev researchers Long P Yip and David Fratello 

with modified Exdrone during flight-lest evaluation. 

BA! Exdrone BQM-147A
Langley Contributions to the Exdrone BQM-147A 

One noteworthy modification contributed by NASA was a sawtooth notch on the wing 

leading edge near the wingtip. This notch and the leading-edge droop mentioned earlier 

were an outgrowth of the Langley General Aviation Stall-Spin Program. Yip and his 

peers had previously recommended the combination to certain general aviation companies for increasing stall departure and spin resistance with a minimal drag penalty. Thus, 

NASA research to improve light aircraft provided a critical improvement for military 

applications. As a result of these improvements, the Exdrone is easily flown by inexperienced pilots and very forgiving during training maneuvers. 

The results of radio-controlled flight tests conducted by Langley researchers at the 

Langley Plum Tree Test Site, located in nearby Poquoson, VA, showed that the modified 

configuration had excellent longitudinal and lateral-directional flight characteristics. 

The configuration was very maneuverable and responsive to control inputs, exhibited 

good damping characteristics, and was easily flyable through the stall with no departure 

tendencies. 

The modifications recommended by Langley were endorsed and applied to the Exdrone 

design, and the overall aerodynamic configuration of the Exdrone vehicle has not 

changed since these modifications. 

Subsequent Exdrone Vehicle In early 1990, approximately 30 of the newly configured BQM-147A Exdrone reconApplications naissance RPV's were sent to Operation Desert Storm. The Exdrones were successfully 

used to map Iraqi minefields and bunkers, which allowed the Allied ground forces to 

slip through in darkness. During the 1990's, several hundred Exdrone air vehicles were 

produced by BAT under contract to the U.S. Uninhabited Air Vehicle Joint Project Office 

(UAV-JPO). These vehicles were sent to Army and Marine Corps units as cost-effective 

devices for familiarizing new users with the benefits of tactical unmanned reconnaissance systems. 

Throughout the 1990's, the UAV-JPO directed BAT, the Department of the Navy, and the 

Army Research Laboratory to test and incorporate numerous payloads and system 

upgrades for the basic Exdrone aircraft. Some of those upgrades include Global Positioning System (GPS) (Exdrone was among the first military aircraft certified to use 

GPS for navigation), a communications relay, the Tactical Remote Sensor Suite (TRSS), 

an infrared and several other versions of down-looking reconnaissance sensors, and a 

parachute recovery system to protect the higher value payloads. 

In early 1997, the Marine Corps provided funds to BA! to create a new configuration of 

the Exdrone (referred to as Dragon Drone) for the Hunter-Warrior Advanced Warfighting Experiment at Twenty-Nine Palms, CA. Tests performed at NASA Wallops Flight 

Facility successfully identified and led to the elimination of onboard vibration interference with reconnaissance payloads. A belly-mounted pan-tilt-zoom television camera 

produced by BAI was then installed into Dragon Drone with several other improvements. 

During the Hunter-Warrior Experiment, Dragon Drones proved highly effective in identifying enemy command locations and troop movements at distances of up to 30 mi. 

Because of the success of the Hunter-Warrior Experiment, the Marine Corps funded the 

development of other upgrades to the Dragon Drone system, including 

Belly-mounted television camera equipped with laser range finder for enhanced 

targeting 

8 BA! Exdrone BQM-147A
Langley Contributions to the Exdrone BQM-147A 

• Belly-mount infrared camera equipped with laser range finder for enhanced targeting 

at night 

• Pneumatic launcher and deck-mounted net recovery system to enable shipboard use 

• Belly-mounted dispenser for insertion of nonlethal warfare agents (i.e.. tear gas) 

The Marine Corps' success with the Dragon Drone has sparked worldwide interest in 

the system. BAI Aerosystems. Inc. received the first international order for a Dragon 

Drone system from the Bahrain Defense Force (BDF) with delivery in late July 1999. A 

small Dragon Drone system is being leased to the Australian Marines for evaluation. 

The Ministry of Defense of the United Kingdom is investigating the feasibility of 

Dragon Drone providing turnkey fulfillment of their tactical UAV requirements. Several 

U.S. organizations, including the Air Force and Coast Guard, are actively pursuing these 

systems. 

Clearly, the future for the Dragon Drone is bright. As technological innovations continue to evolve candidate payloads into smaller, more efficient packages that are suitable 

for RPV's. the Dragon Drone's capabilities will likewise continue to be upgraded. The 

nucleus of the configuration, however, remains the vehicle configuration that came from 

the timely and responsive improvements recommended by insightful researchers at 

Langley.

An Exdrone undergoes weight and balance tests. 

BA! Exdrone BQM-147A
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Highlights of Research by Langley for the AV-8 

Boeing AV-8 Harrier 

SPECIFICATIONS 

Manufacturer 

Boeing 

Subcontractor 

British Aerospace 

Date in service

November 1983 

Type

STO close support 

Crew

One \ 

Engine

Royce F402-RR-408 

USERS 

U.S. Marine Corps, British 

Navy, British Air Force, Spanish 

Navy, and Italian Navy 

DIMENSIONS 

Wingspan ............ .30.3 ft 

Length .............47.75 ft HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE AV-8 - - 

Height .............. ll.6ft ----------------- ----- ----

Wing area ..........30.0 sq ft I. Free-flight model tests and powered-model studies of the P.1127 by Langley instilled 

WEIGHT confidence in Hawker's commitment and converted many skeptics in the United 

Empty ............14.867 lb Kingdom. 

Max VTOL ........20.595 lb 2. Flight tests and coordination by the Langley chief test pilot provided guidance to the 

PERFORMANCE British and kept the U.S. and NASA in partnership with leading-edge vertical and 

short takeoff and landing (V/STOL) developments. Max speed .....Mach number 

of 1.0 3. Langley flight research and engineering development of vectoring in forward flight 

(VIFF) provided the Harrier with unprecedented maneuver options in air-to-air 

combat. 

4. Langley provided independent tests and analysis of a deficient competing V/STOL 

fighter concept (XFV- 12A). 

5. Langley provided wind-tunnel database for design of AV-813 wing. including beneficial flap and power effects and supercritical airfoil which provide tremendous 

increase in STOL load carrying capability over previous versions of the AV-8.

Boeing AV-8 Harrier 11 
Highlights of Research by Langley for the AV-8 

The Langley Research Center has played a key role for over 40 years in the highly successful development of the Boeing (formerly McDonnell Douglas) AV-8 Harrier—the 

most advanced vertical and short takeoff and landing (V/STOL) high-performance aircraft in the world. Langley has been involved in the development of the Harrier since the 

conceptual and evolutionary stages and continuing through the P.1127 prototype, the 

Kestrel (XV-6A), the AV-8A, and the current AV-8B used by the U.S. Marine Corps. 

Langley's initial involvement with the Harrier began when the British Hawker Company 

designed a V/STOL prototype known as the P.1127 in 1957. Unfortunately, Hawker's 

revolutionary design was met with disinterest by the British government and a lack of 

government funding to proceed into development. At that time, experts at Langley had 

conducted extensive research on numerous competitive concepts for V/STOL flight, 

including aircraft-tilting (tail sitters), thrust-tilting (tilt rotors), thrust-deflection 

(deflected slipstream), and dual-propulsion (lift-cruise engines) concepts. The simplicity and elegance of the rotatable nozzle vectored-thrust concept of the P.1127 so 

impressed Langley management and researchers that a formal agreement for coopera -

tive testing was initiated with Hawker under the Mutual Weapons Development Program of NATO. Free-flying tests of a 1/6-scale model were conducted in the Langley 

30- by 60-Foot (Full-Scale) Tunnel to evaluate flying characteristics and to demonstrate 

the ease of converting between hovering flight and conventional wing-borne forward 

flight. These dramatic model flight tests provided confidence to the Hawker test pilots 

and design team and helped sway the opinions of skeptics in the United Kingdom. Transonic wind-tunnel tests of a powered P.1127 model were also conducted in the Langley 

16-Foot Transonic Tunnel. In recognition of his preeminent position as the world leader 

in flight testing of V/STOL aircraft, Langley chief test pilot John P. (Jack) Reeder was 

invited to evaluate the P.1127 aircraft and became a strong supporter of the concept. 

Following cooperative flight-test evaluations of the second-generation P.1127, the 

Kestrel, by military of the United Kingdom, the United States, and the Federal Republic 

of (West) Germany, Langley was provided with two aircraft. These aircraft were used to 

conduct extensive flight tests to develop more time- and fuel-efficient instrument 

approach procedures. Arguably, Langley's most significant contribution to the Kestrel 

was the flight research and engineering development of the vectoring in forward flight 

(VIFF) concept for enhanced maneuverability in air-to-air combat. This capability provides the Harrier pilot with unique maneuver options. Other Langley contributions 

included wind-tunnel databases to optimize wing-flap-nozzle aerodynamic interactions 

and the supercritical wing design methodology for the AV-8B. Langley's leadership role 

in V/STOL technology was transferred to the NASA Ames Research Center in 1973 

where NASA support for the AV-8 series continues. Langley supports the program in 

technical disciplines that are unique to Langley, such as spin tunnel tests of new 

variants. 

12 Boeing AV-8 Harrier
Langley Contributions to the AV-8 

LANGLEY CONTRIBUTIONS TO THE AV-8 

Background In the early 1950's, the Langley Research Center was recognized worldwide as a leader 

in fundamental and applied research on vertical takeoff and landing aircraft. Leaders in 

the Langley research efforts included John P. Campbell, Richard E. Kuhn, John P. (Jack) 

Reeder, and Marion 0. McKinney. The challenge of providing efficient vertical flight 

with minimal penalties and adequate payload produced a myriad of candidate concepts, 

including aircraft-tilting (tail sitters), thrust-tilting (tilt rotors), thrust-deflection 

(deflected slipstream), and dual-propulsion (lift-cruise engines) concepts. The Langley 

researchers had accumulated in-depth experience with each concept and had identified 

the limitations and complexities that constrained the satisfactory growth of vertical and 

short takeoff and landing (V/STOL) aircraft. In view of this vast experience and their 

innovativeness and visionary personalities, the researchers were actively sought for 

assessments and opinions of emerging V/STOL concepts. 

In the United Kingdom, Hawker Aircraft Ltd. was privately funding the development of 

a new V/STOL tactical strike aircraft known as the P.1127. Initial interest from the British government had been lukewarm, and Hawker aggressively pursued potential funding 

from the Mutual Weapons Development Program (MWDP) of the North Atlantic Treaty 

Organization (NATO) for development of the revolutionary P.1127 engine. This engine 

utilized four swiveling nozzles to redirect the engine thrust for vertical or forward flight. 

The U.S. members of the MWDP were particularly impressed with the P.1127 concept, 

and with their outspoken leadership, critical development funds were provided to Bristol 

Siddeley, the engine manufacturer, in June 1958. 

The support for the P.1127 project from the U.S. military (particularly the Marine 

Corps) and NASA has been a key element in the success of the Harrier, which continues 

to the present day. 

Contributions to the P.1127 As Hawker proceeded in the engineering development of the P.1127 from 1959 to 1960, 

numerous critical issues arose. These critical issues included the design of the flight 

control system; whether artificial stabilization was required; the lifting capability of the 

aircraft in ground effect; and the stability, control, and performance of the P.1127 in 

conventional flight. Perhaps the most daunting question was whether the aircraft could 

satisfactorily perform the transition from hovering flight (supported by the vertically 

directed engine thrust) to conventional wing-borne flight. Many skeptics—particularly 

in the British government—believed that the transition maneuver would be far too complex for the pilot or that the P.1127 would not maintain adequate lift to permit a safe 

conversion. 

John Stack, then Assistant Director of Langley and an active member of the MWDP, 

regarded the P.1 127 as the most significant advance since the achievement of operational supersonic speeds in fighters. Stack directed the Langley team to provide full support to the emerging P.1127 technology by conducting tests in the unique facilities at 

Langley. Two model test programs were initiated. One, free-flight tests of a 1/6-scale 

dynamically scaled powered model in the Langley 30- by 60-Foot (Full-Scale) Tunnel, 

was used to determine the characteristics of the P.1127 in the transition maneuver. The 

other program used a large-scale powered model (with simultaneous simulation of inlet 

and exhaust flows) for force tests in the Langley 16-Foot Transonic Tunnel to determine 

the complex propulsion and airframe interactions over the operational flight envelope. 

The 1/6-scale model was also used for tests on the Langley Control Line Facility (a 

Boeing AV-8 Harrier 13
Langley Contributions to the AV-8

Shielded bs' a protective panel, Lan glev researchers

Robert 0. Schade and Louis P Tosti hover the 116 -scale tree-flight

model in the airflow return passage of the Full-Scale Tunnel. 

large rotating crane equipped with control lines for testing powered models) to determine characteristics during rapid transitions to and from hovering flight. All tests were 

slated for completion prior to the initial flights of the prototype aircraft in 1961 

Under the direction of Marion McKinney, the free-flight model tests showed that the 

P.1127 model behaved extremely well when compared with other V/STOL designs 

tested by Langley. Transitions to and from forward flight were easily performed. and 

thrust management was relatively simple. Several problems were identified, however. 

including the fact that the model lacked sufficient lateral control power for satisfactory 

behavior during the transition. (The control power of the aircraft was increased as a 

result of these tests.)A tendency to pitch up due to longitudinal instability at high angles 

of attack was anticipated based on Hawker wind-tunnel tests and was readily apparent in 

the model flight tests. (This problem was subsequently cured by adding anhedral or 

droop to the horizontal-tail surfaces of the P.1 127 and subsequent variants.) Despite 

these shortcomings. the P.1127 was judged to be a superior performer by the Langley 

researchers. 

The free-flight model tests were witnessed by leaders of the Hawker design team, 

including William Bedford. the P.1127 test pilot slated to make the first conversion 

flights of the aircraft. While at Langley. Bedford flew Langley's variable stability 

research helicopter. which had been programmed to simulate the control powers and 

sensitivities of the P.1127 design. The variable stability features of the helicopter provided valuable information that was used by Hawker in the control system design of the 

P.1127. 

14 Boeing AV-8 Harrier
Langley Contributions to the AV-8 

Hovering flight tests of the P.1 127 were conducted in the United Kingdom on 

October 21, 1960, followed by the first conventional flight on March 13, 1961. Finally. 

on September 12. 1961, transition flights both to and from wing-borne to jet-borne flight 

were accomplished. The overall results of these flight programs agreed remarkably well 

with the Langley model tests and the helicopter in-flight simulations of 1960. John 

Stack witnessed transition flights in gusty conditions a week later and referred to them 

as the smoothest transition of any of the existing crop of V/STOL machines. Stack subsequently noted that the precursor Langley tests had, in fact, indicated that the P.1127 

would have better characteristics than any other concept previously investigated. 

Perhaps the most important compliment to the Langley contributions prior to the first 

flights came from Sir Sydney Camm. the Chief Designer of Hawker (designer of the 

Hawker Hurricane fighter of WW II), who said that the Langley wind-tunnel tests were 

the most important tests for the P.1127 project prior to flight. 

Despite the success of the P.1127 flight program. the British Royal Air Force did not 

consider the aircraft as a serious strike aircraft, citing an unacceptably small payload 

capability and low engine thrust. Aggravating the lack of interest, in March 1961 NATO 

requested proposals for a new V/STOL close-support fighter with supersonic speed 

capability. The Hawker design team responded with the P.1154, a configuration with 

twice the thrust, twice the speed. twice the weight. and twice the performance of the 

P.1127. While pursuing the P.1154. Hawker continued demonstrations of the subsonic 

P.1127 and kept the program alive. 

Langley chiet test pilot Jack Reeder era/noted the P 1127 in 1962. 

Boeing AV-8 Harrier 15
Langley Contributions to the AV-8

On June 13, 1962, Langley chief test pilot Jack Reeder became the first foreign pilot to 

fly the P.1127. Despite the fact that he had never flown in the military service, 

Reeder was vastly experienced, having flown over 177 different aircraft of which 7 were 

V/STOL research aircraft. His V/STOL flight experience was unrivaled and Hawker 

eagerly awaited his opinion of the P.1127. Reeder returned to the U.S. filled with enthusiasm for the P.1127 and he influenced many decision makers regarding the potential of 

the aircraft for military applications. 

The Labour government in the United Kingdom cancelled the P.1154 program and 

instructed the frustrated Royal Air Force to accept an upgraded version of the subsonic 

P.1 127—the Harrier. But first, the P.1127 was developed into an interim version known 

as the Kestrel. Nine Kestrel aircraft participated in a unique international collaboration 

that was designed to assess the practicality of V/STOL operations in the field. 

Contributions to the Kestrel Under the leadership of the MWDP, an agreement was signed in late 1961 by the United 

States, the Federal Republic of (West) Germany, and the United Kingdom to test an 

improved P.1127 concept in field conditions in the United Kingdom. Changes made to 

the P.1127 to upgrade it into the Kestrel included a new engine with increased thrust, a 

new swept wing with more fuel capacity than the P.1127 wing, a drooped horizontal tail, 

and improved reaction controls. The flight-test evaluations began in 1965. At the end of 

9 months of flight evaluations, the squadron pilots gave glowing reports about the flying 

qualities of the Kestrel. 

Jack Reeder was an active participant in the evaluation program, especially in discussions about required improvements in the Kestrel handling qualities. Following the 

international flight program, Reeder persuaded officials to provide Langley with two 

Kestrel aircraft for follow-on V/STOL research. Langley test pilots Lee H. Person, Jr. 

and Perry L. Deal flew the Kestrels (designated XV-6A) at Langley under the leadership 

of Reeder. 

Contributions of the Kestrel flight tests at Langley had profound impact on the operational usage of this unique vehicle in both the powered-lift regime, as well as in conventional maneuvering flight. Extensive flight evaluations of the efficiency of existing 

Kestrel instrument approach procedures led by researcher Samuel A. Morello identified 

new methods to permit safer, more fuel-efficient approaches and landings. However, the 

most valuable contribution made by the Langley team was the flight research and engineering development that permitted the rotatable nozzles to be deflected in maneuvering 

flight, thereby providing unprecedented maneuvering for air-to-air combat. 

In 1969, the Defense Department requested that Langley review and comment on a 

report written by Dr. John Attinello, an engineer of the Institute of Defense Analyses, 

that favorably discussed the potential of using thrust vectoring on P.1127-type aircraft to 

enhance the maneuverability of fighters in air combat. Although the application of vectoring in forward flight (VIFF) was fundamentally attractive, considerable engineering 

concern existed over potential control requirements, stability characteristics, and the 

physical well being of the engine in such maneuvers. 

The Langley team designed a flight-test program to develop and evaluate the VIFF concept with the Langley Kestrel. Person and Deal were assigned as project pilots and 

Richard G. Culpepper was assigned as project engineer. Hawker was initially very skeptical and very concerned over theflight-test objectives, with a special concern expressed 

over the internal air ducts leading to the reaction control "puffers" at the wingtips and 

16 Boeing AV-8 Harrier
Langley Contributions to the AV-8 

IANG[EY RESi ONO 

NCR CENTER 

Lee Person and Jack Reeder with the two Kestrel (XV-6A) aircraft assigned to Lan gle'c 

tail of the Kestrel. Operation of the reaction controls at high speeds could result in the 

internal ducts bursting. There was also concern about handling problems, especially at 

high angles of attack. 

The initial flight trials were conducted in straight and level flight, with Person carefully 

evaluating internal duct pressures, angle of attack, engine exhaust gas temperatures, and 

handling qualities. The flight envelope was gradually opened up to 250 knots, then up to 

450 knots, until the nozzles could be deflected from the horizontal (cruise) position 

downward through 90 deg to the breaking stop position. In level flight, the deceleration 

of the aircraft was extremely high and Person reasoned that the abrupt change in speed 

could be used to force an enemy pilot to over shoot and become the target. The Kestrel 

also experienced a nose-up trim change when VIFF was used, but forward stick could 

be used to maintain attitude. During simulated air combat maneuvers. Person would 

rotate the nozzles all the way down, roll the wings into the turn and create a very rapid. 

very high decelerating turn. Other Langley pilots who chased the Kestrel in a Langley T38 aircraft (including Robert A. Champine. noted X-1 pilot) observed that the Kestrel 

appeared to "turn a square corner" and added their enthusiasm to that of the test crew. 

This initial exploration of VIFF was conducted by Langley from January 1970 to the 

end of June 1970. 

Following the completion of the flight trials of VIFF in 1970, attempts to obtain a more 

modern Harrier aircraft for follow-on VIFF experimentation met with great disappointment because only six development batch Harriers were available, and all six were 

heavily involved in development flying in the United Kingdom. Former astronaut 

Neil A. Armstrong, then serving as Deputy Associate Administrator for Aeronautics at 

NASA Headquarters, used his influence to obtain a British Harrier and have it modified 

for VIFF research by NASA. A joint VIFF program between NASA and the Royal 

Boeing AV-8 Harrier 17
Langley Contributions to the AV-8

Aircraft Establishment was initiated in 1972, and flying in the United Kingdom continued through 1976. Results obtained in flight evaluations against a variety of highperformance adversary aircraft and analyses of evasive maneuvers provided by VIFF 

against enemy ground-to-air and air-to-air missiles resulted in overwhelming support 

for VIFF as a valuable tool for the AV-8 pilot. 

As far as the U.S. Marine Corps is concerned, the engineering contribution of NASA 

was invaluable in developing and proving the VIFF concept (ref. 1). 

Other studies of the Kestrel included wind-tunnel tests of a large, powered model in the 

Langley V/STOL Tunnel (later renamed the Langley 14- by 22-Foot Subsonic Tunnel) 

by a team led by Richard J. Margason with the objective of establishing wind tunnel to 

flight correlation. Although the test results were published in a NASA report, the flight 

correlation effort was not undertaken (ref. 6). 

Contributions to the AV-8 The U.S. Marine Corps has unquestionably been the strongest supporter of the Harrier 

concept. Most aircraft development programs, however, are driven by politics, service 

rivalries, and many factors other than technology. In the fall of 1972, the U.S. Navy 

issued a request for proposals of the next generation V/STOL aircraft. Unfortunately, 

the list of candidates did not include any further development of the Harrier. Instead, the 

Navy favored the North American Rockwell XFV-12A supersonic fighter design. The 

XFV-12A used a thrust augmentation scheme that diverted the total exhaust flow of the 

main engine and ejected it through a venetian blind arrangement in the wings to give 

vertical-lift capability. The concept was considered by many at Langley to be very risky 

when compared with the proven Harrier approach, but the Navy was prepared to fully 

fund the development of the aircraft and close out further development of the Harrier. 

Two activities subsequently transpired that resulted in Langley contributions to the AV-8 

program. First, Langley supported test and analysis of the XFV-12A. Second, Langley 

contributed airfoil design methods and wind-tunnel databases that played a key role in 

the development of the second-generation AV-813. 

Naval Air Systems Command requested Langley support for the XFV-12A Program. 

This support included testing a free-flight model in the Langley Full-Scale Tunnel and a 

spin model in the Langley 20-Foot Vertical Spin Tunnel and conducting a remarkable 

hovering test evaluation of an XFV-12A prototype at the Langley Impact Dynamics 

Research Facility (IDRF). This facility, previously known as the Langley Lunar Landing 

Facility, had been used to train astronauts for the reduced gravity levels of the moon's 

environment. Interest in using the IDRF was stimulated by the difficulty of mounting the 

XFV- 1 2A airframe on a more conventional pedestal mount for the hover test. 

The results of the free-flight model tests in 1974 in the Full-Scale Tunnel indicated that 

the projected thrust augmentation for the XFV-12A was considerably less than 

expected, and the thrust available for vertical flight was insufficient to permit poweredlift flights. Although the configuration flew well in conventional wing-borne flight, the 

Langley team expressed grave concern over the deficient V/STOL capability of the freeflight model. 

In early 1978, tethered hover tests of the full-scale XFV-12A on the IDRF were carried 

out by a joint team of NASA, Navy, and Rockwell personnel. Richard G. Culpepper 

served as the lead Langley engineer for the investigation. The IDRF had undergone major modifications to permit static and dynamic tethered hover tests for powered 

V/STOL aircraft. During 6 months of tests, it became apparent that major deficiencies 

existed in the XFV-12A for hovering flight, including marginal vertical thrust. Although 

18 Boeing AV-8 Harrier
r 

Langley Contributions to the AV-8 

Lwi1ev ic i iii,'i her William \'euIunhi it ithi i/Ic XIV- 124 live-flight

model it',th au,,Ientor doors on wing and canard open. 

XFV- 12A aircraft inounteultor tethered hover flights on

Lan glev Impact Dynamics Research Faciliri. 

Boeing AV-8 Harrier 19
Langley Contributions to the AV-8

the augmentation of flow at the wing augmentors was as predicted, large losses in the 

internal ducting and corners of the propulsion system seriously degraded the net thrust 

to the extent that only 75 percent of the weight of the vehicle could be supported in 

attempts to hover. The results of the tests at Langley influenced the Navy's decision to 

cancel the XFV- 12A Program. 

Meanwhile, faced with the potential end of the Harrier program, McDonnell Douglas 

and its partners launched a major redesign effort to provide a significant improvement in 

the VISTOL capability of the AV-8A. McDonnell Douglas engineers drew on two fundamental research efforts at Langley to assist them in redesigning the AV-8A into the 

AV-813. Under the leadership of Richard E. Kuhn, Langley researchers in the Langley 

VISTOL Tunnel conducted systematic wind-tunnel studies of the aerodynamic interactions that occur between rotatable fuselage-mounted nozzles and a high wing with a 

trailing-edge flap. The test variables included a range of geometric relationships 

between these components and showed that the resulting total lift for an aircraft similar 

to the Harrier could be significantly impacted (both favorably and unfavorably) by the 

positioning of these elements. Drawing on this database, the McDonnell Douglas engineers arrived at the current AV-813 wing-nozzle-flap configuration, which resulted in an 

increase of more than 6,000 lb of lift beyond that produced by the AV-8A arrangement. 

In addition, McDonnell Douglas used methods that had matured from the research of 

Dr. Richard T. Whitcomb for supercritical airfoils. The resulting AV-813 wing design has 

a thicker wing with better performance at high speeds, better fuel consumption, and provides an increase in internal fuel capacity of over 40 percent. 

After the decision was made by NASA Headquarters in 1973 to consolidate all V/STOL 

research under the leadership of the NASA Ames Research Center, additional windtunnel and V/STOL flight research on the Harrier was conducted by Ames, and close 

NASA involvement in the AV-8 Program continues today. 

Langley continues to support the program in areas unique to Langley expertise and 

facilities. For example, spin tunnel tests were conducted at Langley for the AV-813 in 

1984, as the external configuration, armament, and other important factors changed in 

the AV-8 fleet. 

20 Boeing AV-8 Harrier
SPECIFICATIONS 

Manufacturer 

Boeing 

Date in service 

January 1995 

Type 

Transport 

Crew 

Three 

Engine 

Pratt & Whitney Fl 17-PW100 turbofan 

USER 

U.S. Air Force 

DIMENSIONS 

Wingspan........... 169.8 ft 

Length ............. 174.0 ft 

Height .............. 55.1 ft 

Wing area .........3.800 sq ft

WEIGHT 

Empty ...........277.000 lb 

Max take-off ......585,000 lb 

PERFORMANCE 

Max speed .....Mach number

of 0.77

Range ............ 4,741 n mi

Highlights of Research by Langley for the C-17 

Boeing C- 17 Globemaster III 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE C-17 -- - -

I. Langley conceived, researched, and developed an externally blown flap concept that 

permits the C-17 to make slow, steep approaches with heavy payloads. 

2. The C-17 uses supercritical wing technology, developed at Langley, which enhances 

range. cruising speed, and fuel efficiency at transonic cruise conditions. 

3. The C-17 employs win glets, conceived and developed at Langley, for better cruise 

efficiency with a reduced wing span. 

4. Fly-by-wire technology, used by the C-17 as a lighter weight replacement for a 

hydraulic control system. was initially researched at Langley. 

5. Research led by Langley on the development of composite materials enabled the 

C- 17 to employ advanced composites for significant weight savings. 

6. Langley conducted flutter clearance tests for the C-17 wing and winglet configuration. 

7. Langley conducted fundamental research on deep-stall characteristics of 1-tail aircraft. providing McDonnell Douglas with background for the development of the 

C-17 angle-of-attack limiting system. 

Boeing c- I 7 GIo/e,nasrer 111 21 
Highlights of Research by Langley for the C-17 

The C-17 is the newest airlift aircraft to enter the Air Force inventory. The C-17 is capable of rapid strategic delivery of troops and all types of cargo to main operating bases or 

directly to forward bases in the deployment area. The aircraft is also able to perform theater airlift missions when required. Using advanced aerodynamics and an innovative 

NASA powered-lift concept, the C-17 combines the load carrying capacity of the C-5 

with the short takeoff and landing performance of the C- 130. McDonnell Douglas was 

recognized in 1994 for the innovative design of the C-17 with the prestigious Collier 

Trophy, which is awarded annually for the greatest achievement in aviation in the 

United States. 

Fundamental and applied aeronautics research conducted at Langley in the areas of 

advanced high-lift systems, aerodynamics, advanced composites, and aeroelasticity contributed to the success of the C-17. Decades of Langley research efforts had conceived, 

developed, and matured emerging concepts and design guidelines that helped 

McDonnell Douglas produce this outstanding military transport. Langley facilities associated with research for the C-17 included the 30- by 60-Foot (Full-Scale) Tunnel, the 

300-MPH 7- by 10-Foot Tunnel, the 16-Foot Transonic Dynamics Tunnel, the 8-Foot 

Transonic Pressure Tunnel, piloted simulators, and the Structures and Materials 

Laboratory. 

In an acknowledgement of Langley's involvement in the C-17, McDonnell Douglas and 

the Air Force brought a C-17 to Langley on May 24, 1996, for a special ceremony to 

thank the employees for their contributions to the design of the C-17. 

22 Boeing C-I 7 Globemaster III
Langley Contributions to the C-17 

LANGLEY CONTRIBUTIONS TO THE C-17 - - 

The CX Competition In the late 1970's, the U.S. military recognized a growing demand for rapid deployment 

of military forces and equipment that would exceed the capabilities of the existing 

C-141, C-5, and C-130 fleets. Early in 1980, the Department of Defense (DOD) issued a 

request for proposals (RFP) for a new Cargo Experimental (CX) Program. Boeing, 

Lockheed, and McDonnell Douglas submitted variants of civil transports, derivatives of 

the prototype YC-14 and YC-l5 aircraft, and completely new aircraft in response to the 

RFP. In August 1981, the Air Force announced that it had selected the Douglas Aircraft 

Company Division of McDonnell Douglas to develop the CX, now known as the C-17. 

Langley's contributions to the development of the C-17 included years of consultation 

and cooperative research with the Douglas team, providing unique test facilities, and 

several innovative technological concepts. 

The Externally Blown Flap The specifications for the C-17 transport required advanced concepts for superior short 

Concept takeoff and landing (STOL) performance. As a result of Langley research on powered 

high-lift systems for over 35 years, the innovative externally blown flap (EBF) concept 

had matured to the point that it could be incorporated in the C- 17 transport. The EBF 

enables the C-17 to make slow, steep approaches with heavy cargo loads to touch down 

precisely on the spot desired on limited runway surfaces. Because of this technology 

that was developed by Langley, the C-17 can carry the same loads as a C-S and use the 

same airfields as a C-130. 

John P. Campbell of Langley conceived the EBF concept in the mid-1950's as a relatively simple approach to augment wing lift for low-speed operations. In this concept, 

the exhaust from pod-mounted engines impinges directly on conventional slotted flaps 

and is deflected downward to augment the wing lift. The magnitude of lift augmentation 

is extremely large, and the resulting lift can be as much as twice the value for a conventional aircraft. However, no serious consideration was given to the EBF concept initially 

because of the severe high-temperature impingement on the wing and flap surfaces from 

the turbojet (no bypass or fan flow) engines used at that time. Also, the relatively small 

mass flow from such engines was a limiting factor for lift augmentation. In addition, 

considerable concern was expressed over potential control problems in the event that an 

engine became inoperative during flight at low speeds with high-power settings. With 

the advent of turbofan engines, however, the efflux from the engines was relatively cool, 

and large quantities of air became available for increased airflow through the flaps. The 

turbofan engine, therefore, provided the breakthrough mechanism that permitted 

Langley researchers to evolve and mature the applications of the EBF concept. 

At Langley, extensive wind-tunnel tests in the Langley 30- by 60-Foot (Full-Scale) 

Tunnel and the Langley 300-MPH 7- by 10-Foot Tunnel explored the fundamental liftaugmentation capability of the EBF for various wing-engine nacelle-flap combinations. 

These tests defined the optimum wing and flap geometries for application to aircraft 

configurations. Led by Joseph L. Johnson, Jr., a team of researchers in the Full-Scale 

Tunnel studied the aerodynamic performance of two- and four-engine EBF transport 

configurations. The scope of their research included detailed studies of projected aircraft 

performance, potential control problems and solutions, and design guidelines for the 

general geometric layout of the aircraft. The advantage of using a T-tail empennage configuration was identified as a desirable approach to avoid the large local downwash 

angles experienced at conventional tail locations due to the increased wing circulation 

Boeing C-i 7 Globemaster 111 23
Langley Contributions to the C-17

Langley researcher John P Campbell (1) and Gerald G. Kavten (r) of NASA Headquarters

inspect a free-flight model of an EBF configuration in the Langle y Full-Scale Tunnel. 

produced by the EBF concept. The engine-out control issue was addressed and solved 

by defining the vertical tail and rudder size required to maintain directional control. 

Dynamically scaled models of transport configurations vividly demonstrated the highlift potential of the EBF concept, while exhibiting satisfactory stability and control characteristics, in free-flight wind-tunnel tests. Aerodynamic data generated by these studies 

were then used for piloted-simulator studies of EBF transports at Langley, during which 

more realistic evaluations of the handling qualities could be conducted and flight control 

systems could be configured. Throughout the years that the EBF concept developed and 

matured. Langley researchers coordinated with U.S. industry and DOD. Langley 

provided briefings and invaluable technical reports that summarized the findings of 

the research studies and the revolutionary capability offered by this new concept in 

aeronautics. 

In the late 1960's, the progress on the EBF concept had advanced considerably, and 

most of the major issues had been adequately addressed and resolved. The concept was 

now ready for flight evaluation on an actual aircraft. Langley advocated for a special 

flight demonstrator program and conducted several studies of the feasibility of modifying existing aircraft as appropriate test beds. The Douglas A3 Skywarrior twin-engine, 

high-wing aircraft operated by the U.S. Navy appeared to be a desirable option; however, a new DOD program known as the Advanced Tactical Transport Program superseded the Langley plans. 

The YC-15 In 1972. the Air Force issued a request for proposals (RFP) for an Advanced Medium 

STOL Transport (AMST) that would ultimately replace the C-130 tactical transport. 

The program emphasized innovative technologies and the capability of conducting 

STOL operations from 2,000-ft runways. Boeing and McDonnell Douglas were each 

24 Boeing C- 17 Globemasrer III
Langley Contributions to the C-17 

awarded preliminary design contracts for the construction and testing of two transport 

prototypes, respectively designated YC-l4 and YC-l5. 

Boeing based their YC-14 design on another powered-lift concept known as upper surface blowing (USB), which had also been developed at Langley in efforts led by Joseph 

Johnson and Oran W. Nicks, Deputy Director of Langley. In the USB concept, the 

engines were mounted so that the exhaust spread over the upper surface of the wing for 

enhanced circulation and lift augmentation in STOL operations. 

McDonnell Douglas used the EBF concept with a four-engine configuration and large 

double-slotted flaps that extended over 75 percent of the total span for the YC- 15 prototypes. The first of two YC-15 prototypes made its first flight on August 26. 1975, and 

was joined by the second prototype in December of that year. The YC- 15 demonstrated 

exceptional STOL performance in its flight-test program with an approach speed of only 

98 mph and a field length of 2.000 ft at a landing weight of 150.000 lb. 

During the flight-test program for the YC-15. Langley researchers participated in evaluations and analysis of STOL capabilities, including an assessment of lift augmentation 

in ground effect. In addition to participating in the flight tests of the YC-15. Langley 

conducted a cooperative wind-tunnel test in the Langley 8-Foot Transonic Pressure Tunnel to evaluate the effectiveness of the emerging winglet concept. which was developed 

by Langley, on the YC- 15 configuration. Dr. Richard T. Whitcomb's winglet designs are 

small, wing-like vertical surfaces located at each win-tip that enable an aircraft to fly 

with greater efficiency. Winglets are strategically located at the wingtip to produce a forward force on the aircraft, similar in many respects to the sail on a sailboat. 

Although the YC-15 was never placed into production, the experiences gained by 

McDonnell Douglas in advanced wing design (supercritical airfoil and winglets). the 

EBF concept, and advanced controls for STOL operations gave the company confidence 

in future applications of these technologies to the C- 17. 

YC- 15 model iii the Lw,'lev 8-Foot Transonic Pressure 

U

One of the McDonnell Douglas YC-15 prototepes intlig/it. 

Boeing C-I 7 Globernaster 111 25
/ I 

"I 

Langley Contributions to the C-17 

The C-17Supercritical Wing, The YC-IS was the first military transport to use supercritical wings, a major innovative 

Winglets, andAerodvnwnic technology conceived and developed through wind-tunnel research by Richard 

Studies Whitcomb at Langley. Whitcomb's supercritical wings incorporate advanced airfoils 

that enhance the range, cruising speed, and fuel efficiency of aircraft by producing 

weaker upper-surface shock waves, thereby creating less drag and permitting higher 

efficiency. McDonnell Douglas subsequently incorporated supercritical wing technology in the C- 17 design. 

Whitcomb's brilliant development of the winglet concept was another product of 

research at Langley that was ideally suited for the C-17. The C-17 is a large aircraft with 

a relatively small wing. The wingspan of the C- 17 was dictated by an Air Force requirement for three aircraft to maneuver on a ramp measuring 90 m by 122 in that is connected by a 15-rn-wide taxiway. The aerodynamic contribution of the winglets permits 

the C-17 to employ a shorter wing span while retaining the efficiency of a larger wing 

span. The C-17 winglets also employ supercritical airfoil sections. 

The successful application of wino lets to the C- I 7 also required consideration and analysis of the flutter characteristics of the wing-winglet combination. This area was of particular concern because flow separation in the wing-winglet juncture could provide an 

aggravating mechanism that might lower the flutter speed to within the flight envelope 

of the C-17. Led by Charles L. Ruhlin. a Langley. McDonnell Douglas. and Air Force 

team conducted flutter tests on the C-17 wing-winglet configuration in the Langley 

16-Foot Transonic Dynamics Tunnel and successfully cleared the aircraft for flight tests. 

Several cooperative wind-tunnel test studies were conducted by McDonnell Douglas 

and Langley in the National Transonic Facility (NTF) at the Langley Research Center to 

assess and optimize the cruise aerodynamic performance of the C- I 7. The unique capability of the NTF to more properly simulate full-scale aerodynamic flight conditions has 

been an extremely valuable contribution to the program. 

selluspall ! 1 l( 'Jel /(' I i/ic ( -- / / iiiiiL-iilIl'/ct configuration in the (- 17 iiioili'I ,llOu,l(ei// ill the National Thuiunic 

Langley 16-Foot Transonic Dynamics Tunnelfor flutter tests. Faiiliti at L.anglev for aerodynamic studies. 

26 Boeing C-/7 Gloheinaster Ill
Langley Contributions to the C-17 

Composite Materials The initiation of the Aircraft Energy Efficiency (ACEE) Program by NASA in 1976 in 

response to the energy crisis accelerated the development of concepts to improve the 

efficiency of advanced aircraft. New methods of producing unique, lightweight materials were one of the major thrusts of the ACEE Program, with emphasis on durable composite materials for aircraft structures. The Structures Division at Langley played a key 

role in developing the technology, which was ultimately incorporated on several components of the C-17. One of the most valuable Langley contributions in the ACEE Program was the development of graphite-epoxy upper aft rudders for the DC-b. The 

rudders have accumulated over 500,000 flight hours since they were introduced into regular airline service in 1976, thereby providing extensive experience for applications to 

other aircraft, including the C-17. 

Several major components of the C-17 are made of advanced composites (ailerons, rudders, elevators, vertical and horizontal stabilizers, flap hinge fairings, main landing gear 

pod panels, and winglets). Over 16,000 lb of composites are incorporated in the design, 

with composites accounting for about 8 percent of the structure. 

Fly-by-Wire Control System The extensive database and literature produced by pioneering research at Langley on 

fly-by-wire flight control systems and handling qualities of STOL transports provided 

McDonnell Douglas with a rich source of information in the development of the C-17 

flight control system. Although not directly involved in this facet of the C-17 development program, Langley contributed fundamental research information that helped build 

the confidence and risk reduction required for the application of the sophisticated C-17 

systems. 

Avoiding the Deep Stall The T-tail empennage configuration offers significant aerodynamic advantages over 

conventional designs. The relatively high location of the horizontal tail places the tail in 

a relatively undisturbed airflow at normal cruise conditions, thereby maximizing the 

contribution of the tail to stability and control. Many military and civil design teams 

have adopted this tail configuration very successfully. However, the application of the 

T-tail requires consideration of critical aerodynamic factors—especially an analysis in 

wind-tunnel tests to ensure satisfactory handling characteristics at extreme pitch attitudes. At high angles of attack associated with wing stall, the low-energy wake of the 

stalled wing can impinge on the horizontal tail and result in a loss of longitudinal stability (pitch up) and markedly reduced longitudinal control effectiveness. As a result of 

these flow phenomena, the angle of attack can increase to a deep-stall condition, in 

which the aircraft enters a stable but uncontrollable trim point with a very high rate of 

descent. 

In the early 1960's, a British BAC Ill T-tail transport experienced a fatal accident in 

which the aircraft entered a deep stall and descended in an uncontrollable condition at a 

very high rate of descent with an almost horizontal fuselage attitude until impact. 

Worldwide interest in the causes of this accident resulted in a research program at the 

Langley Research Center on the behavior of T-tail configurations at high angles of 

attack. Under the leadership of Robert T. Taylor and Martin T. Moul, extensive windtunnel and piloted-simulator studies were conducted to determine the aerodynamic 

characteristics associated with deep-stall trim conditions and to develop design methods 

and pilot techniques to recover from such conditions. A large number of aircraft configurations were studied in the Langley 7- by 10-Foot High-Speed Tunnel, with an emphasis on designs with aft-fuselage-mounted engine nacelles. Studies at Langley on the 

Boeing C-] 7 Globemaster 111 27
Langley Contributions to the C-i 7

1-tail deep-stall phenomenon provided a valuable database that has been used extensively in the design of numerous T-tail civil and military transport configurations. Perhaps the most valuable contribution of this work is the guidance and approach it 

suggests to the designer during early wind-tunnel tests and configuration layout. 

The C-17 design team was very familiar with the existing NASA database and design 

procedures for avoiding the deep-stall problem. The quadruple redundant digital fly-bywire flight control system of the C- I 7 provides automatic limiting of angle of attack for 

high-angle-of-attack conditions, thereby preventing any tendency of the aircraft to enter 

an uncontrollable deep-stall condition. 

Recognition Visit On May 24, 1996, McDonnell Douglas and the Air Force brought a C-17 of the Air 

Mobility Command from Charleston Air Force Base. S.C.. to Langley as a gesture of 

thanks to Langley and its employees for their contributions to the design of the new military jet transport. The visit and formal ceremony acknowledged the contributions of all 

four NASA Aeronautics Centers (Langley, Ames. Dryden. and Glenn) to the design and 

development of the C-17. The NASA research contributions cited by the visitors 

included the areas of powered-lift systems, short takeoff and landing control systems. 

head-up display technology. supercritical wing and winglet, fly-by-wire systems, engine 

technologies, and composite materials. 

Rt 

C-17 in front of the hangar during a visit at Langley on Ma y 24, 1996. 

28 Boeing C- I 7 Globe,nasrer III
Highlights of Research by Langley for the F/A-18 

Boeing F/A- 18 Hornet 

SPECIFICATIONS 

Manufacturer 

Boeing and Northrop Grumman 

Date in service 

1983 

Type 

Multirole fighter-attack aircraft 

Crew 

One or to k 

Engine 

F-1 8C .......General Electric V 

F404-GE-402 

F-I 8E .......General Electric 

F414-GE-400 

USERS 

U.S. Navy. U.S. Marine Corps, 

Canada, Australia, Spain. Kuwait, 

Switzerland. Finland. and

HIGHLIGHTS HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F/A- 18 - - 

DIMENSIONS 

Wingspan I. At the request of industry and the military. Langley participated in reviews and 

F-1 8C ............. 40.4 ft assessments from the YF- 17 prototype program to the development of F/A-I 8E/F. 

F- 18E ............. 44.9 ft 2. Langley provided wind-tunnel research on wing leading- and trailing-edge flap techLength nology for transonic maneuver optimization. 

F-18C ............. 56.0 ft 

F- 18E............. 60.3 ft 3. Langley contributed to cooperative studies of vortex lift with McDonnell Douglas 

Height and Northrop and participated in the selection of the wing leading-edge extension 

F-18C ............. 15.3 ft (LEX) shapes for all variants of the F/A-18. 

F-18E ............. 16.0 ft

4. Langley provided a solution (porous wing doors) to a severe wing-drop tendency for Win area 

F-18C .......... 400.0 sq ft the F/A-18E/F. thereby helping to avoid potential termination of the aircraft 

F- I 8E .......... 500.0 sq ft program. 

WEIGHT 5. Langley helped solve numerous F/A-18 developmental challenges including 

Empty

• Cruise performance 

F-18C ........... 23.407 lb

• Flutter clearance 

F- 18E ............30.500 lb 

Gross • High-angle-of-attack stability and control 

F-18C ........... .S 1,900 lb • Recovery from unusual out-of-control conditions 

F- 18E ........... 66.000 lb 6. Langley led the NASA High-Angle-of-Attack Technology Program, which provided 

PERFORMANCE valuable information on F/A- I 8 characteristics and design methodology for future 

Max speed .........hove Mach fighters. 

number of 1.8

Boeing F/A-18 Hornet 29 
Highlights of Research by Langley for the F/A-18 

The Langley Research Center has been an active participant in the development 

of the F/A-l8 series of aircraft for over 25 years, including contributions to the YF-17, 

F/A-18A, and the F/A-18E/F. With the exception of the F- Ill, no other fighter aircraft 

has been the subject of as many Langley wind-tunnel studies and analytical investigations. Working closely with Boeing (formerly McDonnell Douglas) and Northrop 

Grumman (formerly Northrop), Langley has contributed to aerodynamic performance, 

computational fluid dynamics, high-angle-of-attack stability and control, and aeroelasticity. Langley facilities used in the development of the F-18 included the 30- by 

60-Foot (Full-Scale) Tunnel, the 12-Foot Low-Speed Tunnel, the 20-Foot Vertical Spin 

Tunnel, the 8-Foot Transonic Pressure Tunnel, the 16-Foot Transonic Tunnel, the Jet 

Exit Test Facility, the 16-Foot Transonic Dynamics Tunnel, the 7- by 10-Foot HighSpeed Tunnel, the 14- by 22-Foot Subsonic Tunnel, the Differential Maneuvering Simulator, radio-controlled drop models, and computational facilities. 

Research contributions by Langley for the F/A-18 have increased lift for aggressive 

maneuvering, improved cruise performance, insured a high degree of spin resistance, 

provided flutter clearance, and enabled prompt recovery from out-of-control conditions. 

Recently, one of the most significant Langley contributions was providing a solution to 

an uncommanded wing-drop characteristic exhibited by the F/A-18EIF. Boeing was 

awarded the Collier Trophy in 1999 in recognition of the accomplishments in the 

F/A-I 8EIF program. 

Langley provided the lead advocacy and technical leadership for a highly successful 

NASA High-Angle-Of-Attack Technology Program based on the F/A- 18 configuration. 

The program aggressively accelerated progress in design methods for aerodynamics, 

flight controls, thrust vectoring, alleviation of empennage buffet, and test techniques. 

Extensive documentation and analysis of F/A-18 characteristics were significant byproducts of the program. 

30 Boeing F/A-18 Hornet
Langley Contributions to the F/A-18 

LANGLEY CONTRIBUTIONS TO THE F/A-18 

Vortex Lift and Maneuvering In the early 1960's. the Northrop Company noticed an improvement in the maximum lift 

Flaps of the F-5 aircraft because of a small flap actuator fairing that extended the wing root 

leading edge. This phenomenon spurred interest in the effects of inboard vortex 

flows and led to a cooperative NASA and Northrop study, which was conducted in the 

Langley 7- by 10-Foot High-Speed Tunnel with a group led by Edward C. Polhamus. 

The cooperative study of hybrid wings centered on the use of relatively large, highly 

swept wing extensions at the wing-fuselage intersection, which promoted strong beneficial vortex-flow effects. The scope of the study included parametric studies to maximize 

the lift- and stability-enhancing effects of the wing extension concept. which became 

known at Northrop as the leading-edge extension (LEX). Studies were also directed at 

cambering the leading edge of the LEX to suppress the vortex at low angles of attack, 

and thereby minimize drag at cruise conditions. Northrop applied a large highly swept 

LEX to the YF-17 prototype aircraft to enhance lift and stabilize the flow over the YF17 main wing at high angles of attack. 

From these initial cooperative studies with Northrop. Polhamus and his associates put 

together a world-class vortex-lift research program that became internationally recognized for its experimental database, analytical procedures, and aircraft applications. In 

addition to Polhamus, key members of this team included Linwood W. McKinney, 

Edward J. Ray, William P. Henderson, John E. Lamar. and James M. Luck-ring. Their 

extraordinary research into the fundamentals and applications of vortex flows placed the 

Langley Research Center in an excellent position to aid the U.S. industry in the design 

of highly maneuverable advanced fighters. This experienced pool of experts would subsequently provide invaluable guidance and analysis to industry design teams in the 

development of the F- 16 for the Air Force and the F/A- 18 for the Navy. 

F/A -18 with wing leading-edge flaps deflected 

and LEX vortices made visible by condensation. 

Boeing F/A-18 Hornet 31
Langley Contributions to the F/A-18

In Vietnam, the lack of maneuverability of U.S. fighters at transonic speeds provided 

key advantages to nimble enemy fighters. Industry, the Department of Defense (DOD), 

and NASA were all stimulated to sponsor research to achieve unprecedented transonic 

maneuverability while maintaining excellent handling qualities. Langley researchers, 

under the leadership of Polhamus, conducted studies in the 7- by 10-Foot High-Speed 

Tunnel to obtain near optimum aerodynamic maneuver performance for wings, including the use of fixed and variable camber concepts. Some of the earliest systematic windtunnel tests were conducted by the group to determine the most effective geometries for 

wing leading- and trailing-edge flaps. In addition to tests of aerodynamic performance 

and stability and control, buffet studies were conducted to understand and develop 

methodologies for the prediction and minimization of undesirable buffet characteristics. 

The program was closely coordinated with flight tests of actual high-performance fighters at the NASA Dryden Flight Research Center. Flight evaluations of the effects of 

maneuver flaps on a YF-17 were also later conducted in the Dryden program. 

Numerous discussions with Polhamus and his staff provided valuable guidance to the 

Northrop design team and the McDonnell Douglas team for the subsequent F/A-18 

design. The insight and understanding provided by the broad database from Langley 

tests permitted development of the extremely effective leading- and trailing-edge flaps 

used by the YF-17 and the F/A-l8. The F/A-l8 and similar high-performance fighters 

use specific, computer-controlled schedules of flap deflection with Mach number and 

angle of attack for superior maneuverability throughout the flight envelope. 

Development of the YF-17 On January 6, 1972, the Air Force issued a request for proposals (RFP) for a Lightweight Fighter (LWF) Program. In March 1972, the Langley Research Center was 

requested by DOD to participate in assessments and supporting tests of the competing 

YF-16 and YF-l7 designs for the LWF. Langley researchers became members of DOD 

source evaluation teams to assess and check technical claims by each of the contractors. 

The sponsoring LWF Program Office requested that certain services of Langley be made 

available on an equal basis to the two competing teams. This remarkable arrangement 

provided each team with analysis and support if they desired. 

Northrop placed a high priority on superior high-angle-of-attack characteristics and a 

high degree of inherent spin resistance for the YF-l7. The company had also placed priorities in these areas during the development of the F-5 and T-38 aircraft, which had 

become known for outstanding resistance to inadvertent spins. Langley support was 

therefore requested for tests in the 30- by 60-Foot (Full-Scale) Tunnel and the 20-Foot 

Vertical Spin Tunnel. 

To provide superior handling qualities at high angles of attack for fighter aircraft, 

Northrop provided the airframe with the required levels of aerodynamic stability and 

control characteristics without artificially limiting the flight envelope with the flight 

control system. This approach proved to be highly successful for the YF-17 and has 

been adopted by McDonnell Douglas (now Boeing) and used in all variants of 

the F/A- 18 aircraft. 

Researcher Sue B. Grafton conducted exhaustive tests in the Full-Scale Tunnel of the 

YF-17 configuration at high angles of attack in 1973. The results of the Langley tests 

revealed that Northrop had done an outstanding job in configuring the YF-17 design. 

The integration of the large LEX surfaces and the placement of the twin vertical tails 

provided exceptional tail effectiveness at high angles of attack. The small strakes added 

to the forward fuselage nose by Northrop resulted in extremely high directional stability 

at high angles of attack. Free-flight tests of the YF-17 model in the Full-Scale Tunnel 

32 Boeing F/A-18 Hornet
Langley Contributions to the F/A-18 

Project engineer Site Grafton with the free-flight inodel of the YF- 17 in 1973. 

confirmed the excellent flying characteristics predicted by the wind-tunnel data and provided Northrop with highly positive predictions for upcoming flight tests of the two 

YF- 17 prototypes at Edwards Air Force Base. The wind-tunnel data also formed the 

basis for piloted simulator studies at Langley and Northrop that helped Northrop design 

the flight control system for critical high-angle-of-attack conditions. 

Spin and recovery tests in the Spin Tunnel also provided positive results for the YF-17. 

The scope of the tests in the Spin Tunnel was relatively broad for the fast-paced LWF 

Program and included the determination of the size of the emergency spin recovery 

parachute that would be required for flight tests. The results of the Spin Tunnel tests 

showed that the YF- 17 would have remarkably good spin and recovery characteristics. 

In fact, the YF-17's characteristics were the best noted for any fighter configuration to 

that time. 

Although not specifically requested by the Air Force, Langley had already conducted 

Air Force approved studies of the high-angle-of-attack characteristics of the YF-16 in 

the Langley Differential Maneuvering Simulator (DMS) and approval was given to conduct similar studies of the YF-l7. Under the leadership of Langley researchers Luat T. 

Nguyen and William P. Gilbert, extensive studies were conducted in the DMS to verify 

the impressive behavior predicted by the wind-tunnel and free-flight model tests for 

more realistic air combat conditions. In addition, the simulation was used to refine certain elements of the flight control system for high-angle-of-attack conditions. The 

results of the simulator investigation showed the YF- 17 to be highly maneuverable and 

departure resistant throughout the operational angle-of-attack range and beyond maximum lift. 

Boeing F/A-18 Hornet 33
Langley Contributions to the FIA-18

A YF- 17 prot(')tvpe in flight with the open 

slots in the LEX adjacent to the fuselage. 

YE- 17 model in the Langle y 8-Foot Transonic 

Pressure Tunnel for drag assessment studies. 

34 Boeing F/A-18 Hornet
F/A-18A to F/A-18D 

The Langley predictions for the YF- 17 behavior were subsequently confirmed in 1974 

when two YF-17 prototypes began flight evaluations at Edwards Air Force Base. Handling characteristics at high angles of attack were excellent. The YF-17 could achieve 

angles of attack of up to 34 deg in level flight and 63 deg could be reached in a zoom 

climb. The aircraft remained controllable at indicated airspeeds down to 20 knots. 

Northrop consequently claimed that their lightweight fighter contender had no angle-ofattack limitations, no control limitations, and no departure tendencies within the flight 

envelope used for the evaluation. 

Langley researchers conducted a cruise-drag test of the YF-17 in the Langley 8-Foot 

Transonic Pressure Tunnel in 1973. The test was initiated when Northrop questioned the 

high transonic drag levels predicted by the Air Force, which were based on results from 

other wind tunnels. The Air Force agreed that an independent NASA analysis would be 

appropriate and requested the test. 

Langley researchers found that their results agreed with the Air Force predictions. 

Researchers then identified the major contributors to drag and provided recommendations to reduce it. Dr. Richard T. Whitcomb reviewed the YF-17 drag results and concluded that the wing design was the major factor in the unexpected drag levels. 

Whitcomb's suggestion for a wing redesign to solve the problem was unacceptable to 

Northrop. 

F/A-18A TO F/A-18D 

Development of the F/A-18 In April 1974, the LWF Program changed from a technology demonstration program to 

a competition for an Air Force Air Combat Fighter (ACF), and the flight-test programs 

for the YF-16 and YF-17 were rushed through in a few months instead of the planned 

2 years. On January 13, 1975, the Air Force announced that the General Dynamics 

YF-l6 would be the new ACE Congress decreed that the Navy adopt a derivative of one 

of the LWF designs as the new Naval Air Combat Fighter to complement the F-14. On 

May 2, 1975, the Navy announced that the YF-17 design would form the basis of their 

new F/A-18 fighter-attack aircraft. Northrop, inexperienced in the design of naval fighters, teamed with McDonnell Douglas, which had extensive experience with a highly 

successful line of naval aircraft, including the F-4 Phantom. McDonnell Douglas 

became the prime contractor for the F/A-18 with Northrop the prime subcontractor. 

The formidable task of converting the land-based YF- 17 lightweight day fighter into an 

all-weather fighter-attack aircraft capable of carrier operations with heavy ordnance 

loads required significant changes from the earlier configuration. Structural strengthening and a new landing gear design were required for catapult launches and arrested landings. The aircraft gross weight rapidly grew from 23,000 lb for the YF-17 to a projected 

weight over 33,000 lb. 

The required approach speeds for carrier landings resulted in modifications to the wing 

and LEX surfaces of the YF- 17 configuration to provide more lift. McDonnell Douglas 

consulted the Langley research staff, and several individuals participated in the analysis 

of wind-tunnel tests that had been conducted at NASA Ames Research Center and 

McDonnell Douglas facilities. As a result of the analysis, changes were made to the aircraft configuration. The geometric shape of the YF-17 LEX was extended farther forward on the fuselage and the plan view of the LEX was modified to produce additional 

lift while retaining the good high-angle-of-attack characteristics exhibited by the YF-17. 

Boeing F/A-18 Hornet 35
F/A-18A to FIA-18D

The deflections of the wing leading- and trailing-edge flaps were increased and the ailerons were programmed to droop in low-speed flight to augment lift. Finally, a "snag" or 

discontinuity was added to the leading edges of both the wing and horizontal tails to 

provide more lift. 

Formal Navy requests for specific NASA studies in support of the evolving F/A-18 configuration were received and accepted by Langley. The excellent correlation of Langley 

predictions for high-angle-of-attack and spin characteristics of the YF- 17 prompted the 

Navy to request the full suite of tests at Langley for these characteristics. A request for 

tests in the Spin Tunnel and the Full-Scale Tunnel and helicopter drop models was 

received in late 1976. 

The first preproduction F/A-18 made its first flight on November 18, 1978, and entered 

the initial phases of flight tests at the Patuxent River Naval Air Station in Maryland. The 

preproduction flight-test program lasted from January 1979 to October 1982, and the 

Langley staff was called on to help solve several critical developmental problems. 

Cruise Drag Initial results from flight evaluations at Patuxent River in 1979 indicated that the cruise 

performance of the F/A-18 was significantly below expectations, with a shortfall of 

about 12 percent in cruise range. The performance deficiency became a weapon for 

those who sought the termination of the F/A-18 Program. A number of reasons for the 

poor performance were identified. Modifications to the engines, computer-controlled 

schedules for the deflection of leading- and trailing-edge flaps, and other changes 

reduced the cruise range deficit to about 8 percent, but aerodynamic drag remained a 

problem. 

In response to this critical threat to the program, a Navy and NASA F/A-18 working 

group was formed in late 1979. The NASA members were all Langley personnel led by 

researchers Richard Whitcomb, Edward Polhamus, and William J. Alford, Jr. With the 

addition of members from the Navy, McDonnell Douglas, and Northrop, the group 

totaled about 20 participants. After consideration of several approaches to reduce the 

drag of the aircraft, the group recommended wind-tunnel and flight studies of modifications to several configuration features. Modifications included increasing the wing leading-edge radius, variations in the LEX camber, and filling in the slots in the LEXfuselage juncture. The Langley members identified the slots as a particularly undesirable feature with potentially high drag characteristics. Tests with favorable results were 

conducted in the Langley 8-Foot Transonic Pressure Tunnel in early 1980. These 

changes were implemented on the F/A-18 test aircraft at Patuxent River where they 

were found to favorably increase the cruise range of the aircraft. The impact of filling in 

the LEX slot on high-angle-of-attack characteristics was found to be acceptable in additional tests at Langley and F/A-l8 flight tests. 

High-Angle-Of-Attack, Spin, Langley responded to the Navy's request for stall-spin tests in support of the F/A-18 

and Spin Recovery with spin tunnel tests (1978), free-flight model tests (1978), and drop-model tests 

Characteristics (1979). The results of the Langley spin tunnel and drop-model tests were very favorable. 

The F/A-18 configuration was found to be extremely resistant to spins. (The pilot was 

required to maintain prospin controls for over 20 sec to promote a spin.) When 

spins were entered, recovery could be effected very quickly. In the spin tunnel tests, the 

F/A48 model demonstrated the best spin recovery characteristics of any modern U. S. 

fighter (as had the YF-17 configuration). During the limited model tests for spins, the 

phenomenon known as "falling leaf' was not encountered, but it became a problem in 

operational usage as will be discussed in a later section. 

36 Boeing F/A-18 Hornet
F/A-18Ato F/A-18D 

The F/A-18 free-flight model tests that were conducted in the Full-Scale Tunnel were 

very controversial; however, the model tests subsequently proved to be a major contributor to the success of the F/A- 18 development program. 

As previously discussed, early high-angle-of-attack tests had been completed in other 

NASA and McDonnell Douglas wind tunnels to tailor the geometry of the F/A- 18 for 

good flight characteristics. The removal of the stabilizing nose strakes that were on the 

YF- 17. which would have interfered with the radar performance on the F/A- I 8. and the 

revision of LEX shape had been carefully analyzed and designed from these results. 

When the Langley free-flight model underwent tests, the LEX and leading-edge flap 

schedule had been defined for flight tests. 

When the Langley model was tested, however, the results obtained with this particular 

model indicated that the F/A- 18 would exhibit a moderate yaw departure near maximum 

lift. Although not a flight safety concern, this result would infrin ge on the precision 

maneuverability of the aircraft. These undesirable results had been obtained at low 

wind-tunnel test speeds with a relatively large model and were dismissed with skepticism by the engineering community as having been caused by erroneous scale effects. 

In 1979. an F/A-l8 test aircraft at Patuxent River suddenly and unexpectedly departed 

controlled flight during a wind-up turn maneuver at high subsonic speeds. None of the 

baseline wind-tunnel data predicted this characteristic, and the F/A- I 8 Program was 

shocked by the event. The fact that the free-flight model had also exhibited such a trend 

did not go unnoticed, and a joint NASA. Navy, and McDonnell Douglas team was 

formed to seek solutions with the free-flight model at Langley. Following exhaustive 

wind-tunnel tests in the Full-Scale Tunnel. the team recommended that the wing leading-edge flap deflection be increased from 25 deg to 34 deg at high angles of attack. Following the implementation of this recommendation on the test aircraft (via the flight 

AA 

F/A-18 drop model prepared for flight in 1978. 

Boeing F/A-18 Hornet 37
F/A-18A to F/A-18D

The 1-/A- ISA Ieee-flight model during tesLs in the Lnnglev 30- by 60-1-not Wind Tunnel in 1978. 

control computers), no more departures were experienced, and the flap deflection schedule was adopted for production F/A- 18s. 

This was not the first time that results from large free-flight models in the Full-Scale 

Tunnel had proven to accurately predict the flight behavior of an aircraft at high angles 

of attack, despite the low speeds of the wind-tunnel tests. (See Lan glev Contributions to 

the F-Jo, for example.) 

The NASA High-Angle-Of- The emergence of a generation of highly maneuverable fighter aircraft such as the F-14, 

Attack Technology Program F- 15, F- 16. and F- 18 in the late 1970's resulted in a new perspective on operating highperformance aircraft at high angles of attack. Previous U.S. military experience with aircraft such as the F-4 and A-7 during the Vietnam era had been tormented with unacceptably high accident losses of these aircraft from inadvertent departures and spins from 

maneuvers at high angles of attack. Operational procedures required very careful and 

precise pilot inputs at high angles of attack to avoid loss of control, and handbook 

restrictions were placed on the operational use of angle of attack. With the advent of the 

new generation of fighters, flight at high angles of attack became a common occurrence 

and was no longer feared or avoided by pilots. Exploitation of high angles of attack provided the potential for new maneuvers and options for air combat tactics. These interests 

resulted in several major programs within DOD, industry, and NASA to develop the 

analysis and design methodologies for superior performance over an unlimited range of 

angle of attack. 

In the early 1980's, NASA initiated a High-Angle-of-Attack Technology Program 

(HATP) among the aeronautics research centers (Langley. Ames. Dryden. and Glenn). 

The program included all the critical elements of high-angle-of-attack technology: aerodynamics, flight controls, handling qualities, stability and control, and the rapidly evolving area of thrust vectoring. In recognition of its extensive accomplishments in this field. 

Langley was designated the technology lead center for the program. and Dryden was 

designated the lead for flight research and operations. The Langley leader in the initial 

phases of the program was William Gilbert, who was followed by Luat Nguyen in later 

years. 

38 Boeing F/A-/8 Hornet
F/A-18A to F/A-18D 

A critical element in the HATP plan was the correlation and validation of experimental 

and analytical results with results from flight tests of a high-performance aircraft. The 

NASA team considered several aircraft configurations for this important task, including 

the F-15. F-16, F/A-18. and the X-29 forward-swept wing technology demonstrator aircraft. The advantages and disadvantages of each aircraft for the NASA program were 

thoroughly considered, and the F/A- 18 was unanimously chosen as the desired test vehicle for several reasons. In flight, the F/A-l8 had shown aerodynamic and aeroelastic 

phenomena of interest (vortex flows and tail buffet), stall-free engine operation at high 

angles of attack, excellent spin recovery characteristics, an advanced digital flight control system, and a large angle-of-attack capability (up to 60-deg trim capability at low 

speeds). The Navy's response to a request from NASA for a preproduction F/A-l8 vehicle for the program was very positive. The Navy initially offered NASA an early production F/A-18A aircraft: however, NASA targeted the specially equipped 

preproduction F/A- 18 (ship no. 6) that had been used at Patuxent River for the spin evaluation phase of the development program. The aircraft had completed its spin tests and 

had been stored in a hangar and stripped of its major components as a spare-parts aircraft. However, this particular aircraft was equipped with a special emergency spin 

recovery parachute system worth several million dollars and a programmable digital 

flight control computer adaptable to the variations desired in the HATP. The Navy 

approved the transfer of the stripped aircraft to NASA, and it was trucked to Dryden and 

reassembled by experts at Dryden with the Navy's help into a world-class research aircraft to be known as the F/A-18 High Alpha Research Vehicle (HARV). 

F- 18 HARV during flow visualization studies using smoke 

ejected at apex of LEX and wool tufts on upper surfaces.

/ 

Boeing F/A-18 Hornet 39
F/A-18A to F/A-18D

The HATP studies were conducted in three phases. In the first phase, emphasis was 

placed on static and dynamic aerodynamic phenomena. This phase included extensive 

correlations of wind-tunnel and computational results with data from flight instrumentation on the HARV. These data correlations were conducted with common data sensor 

locations on the wind-tunnel models and the HARV. As a result of these aerodynamic 

experiments, the capabilities of emerging computational fluid dynamics tools and the 

interpretation of wind-tunnel test techniques were aggressively accelerated. Detailed 

studies of vortical flow structures emanating from the F/A-18 LEX and interactions with 

the vertical tail surfaces resulted in rapid progress in the understanding, prediction, and 

minimization of vertical-tail buffet phenomena. Finally, in-depth analysis of the flow 

fields shed by the nose and forebody of the F/A-18 resulted in wind-tunnel test procedures and validation of computational codes for future fighters. 

An excellent example of the impact of this fundamental research is the LEX uppersurface fences mounted on FIA-18C/D aircraft. These devices greatly alleviate the vertical tail buffeting associated with sudden bursting of the core of the strong vortical flow 

shed by the LEX at high angles of attack. McDonnell Douglas developed the fence during parametric wind-tunnel experiments in its own wind tunnel; however, they did not 

have the resources or time to identify the flow mechanisms created by the fence. Within 

the scope of the HATP, Langley developed a laser vapor screen flow visualization technique that permitted rapid, global assessments of interactive flow fields. Using this 

technique, Langley researcher Gary E. Erickson conducted diagnostic tests on an 

FIA-18C model in the Navy David Taylor Research Center (DTRC) 7- by 10-Foot Transonic Tunnel, and he precisely identified the vortex-flow mechanisms associated with 

the benefits of the fences. The success of the vapor screen system so impressed the Navy 

and industry that they requested the Langley vapor screen system on other tests to 

understand nonlinear flow behavior at subsonic and transonic speeds. 

In the second phase of the HATP, the HARV incorporated a relatively simple and cheap 

thrust-vectoring system for studies of aerodynamics at extreme angles of attack, and 

engineering development and evaluations of the advantages of thrust vectoring for highangle-of-attack maneuvers. Previous efforts with the Navy involving experiments with 

thrust-vectoring vanes on an F-14 inspired the NASA team to adopt this simple concept 

instead of a program to develop internal engine vectoring at a cost of many more millions of dollars. (See Langley Contributions to the F-]4.) Dryden managed and directed 

a contract with McDonnell Douglas to outfit the HARV with deflectable external vanes 

mounted behind the engines. The engine exhaust nozzle divergent flaps were removed 

and replaced with a set of three vanes for each engine, which resulted in both pitch and 

yaw vectoring capability. The specific vane configuration was analyzed and defined by 

tests of a powered model in the Langley 16-Foot Transonic Tunnel and the Langley Jet 

Exit Test Facility. Meanwhile, the aircraft flight computer was modified to permit 

research evaluations within a broad spectrum of thrust-vectoring parameters. The modification of the HARV proved to be extremely challenging, and several members of the 

staffs from Langley and Dryden assisted in the final implementation of the hardware and 

software of the thrust-vectoring system. 

Extensive piloted simulator evaluations of the HARV with thrust vectoring were conducted in the DMS, with results indicating that the implementation of both pitch and 

yaw vectoring provided powerful, unprecedented controllability and precision for 

maneuvers at high angles of attack. 

The results of the F/A-18 HARV thrust-vectoring flights were remarkable. The HARV 

became the first high-performance aircraft to conduct multiaxis thrust-vectoring flights, 

40 Boeing F/A-18 Hornet
F/A-18A to F/A-i 80 

Thrust-vectoring lane inta//aiion on the F- 18 /8 H.4RVtree-Jlight model nit/i

rectangular box above the vanes representing the container for the spin parachute. 

and the powerful effectiveness of thrust vectoring at high angles of attack was vividly 

demonstrated. The control precision of the aircraft at extreme angles of attack was significantly enhanced, and the vehicle could be stabilized at the conditions for high quality 

aerodynamic studies. 

In the final phase of the HATP, earlier studies to understand and predict the strong vortex flows emanating from the long pointed fuselage forebody of the F/A-18 were 

extended. The studies now included the ability to control these flows for aircraft maneuvers at extreme angles of attack, where yaw control provided by conventional aerodynamic rudders becomes relatively ineffective. Based on in-depth studies conducted by 

Langley in several wind tunnels, the HARV was equipped with deflectable foldout 

strake surfaces on the forward forebody, and the control system was modified to permit 

the pilot to use the strakes for roll control. The strake hardware was engineered and fabricated in Langley machine shops, and the flight computer interface was provided by 

Dryden. Results of the flight evaluation of the nose strakes were extremely impressive. 

The time required to roll the aircraft through a specific roll attitude change was significantly reduced due to the crisp, powerful control provided by the strakes. At the higher 

subsonic speeds, the effectiveness of the strakes approached levels provided by thrust 

vectoring in yaw. 

The HATP efforts represent a decade of invaluable research and development on key 

technologies that will be required for future highly maneuverable high-performance 

fighter aircraft, as well as the FIA-18 configuration. The data gathered by NASA has 

been widely disseminated among design teams at NASA sponsored national conferences and during site visits. The program has been cited for its high quality, pioneering 

value on numerous occasions by industry and DOD. The results of the program are 

being used in the development of the next generation F/A-18E/F and other military 

aircraft. 

Boeing F/A-18 Hornet 41
FIA-18A to F/A-18D 

The Falling-Leaf Maneuver The falling-leaf maneuver originated during World War I as a flight training exercise. In 

this exercise, pilots intentionally stalled the aircraft and forced a series of incipient spins 

to the right and left. The aircraft descends as it rocks back and forth, much as a leaf does 

falling to the ground. In the early 1980's, an unintentional falling-leaf mode surfaced as 

a severe out-of-control problem during developmental flight tests of the F/A-I 8A. The 

out-of-control falling-leaf mode is a highly dynamic mode where the aircraft oscillates 

so that it is very difficult to reduce angle of attack and recover. The term "alpha hangup" was used to describe this problem with the F/A- 18 and it was a key driver in establishing the aft center of gravity and the maneuvering limits for the aircraft. During early 

operational use of the F/A-18, the falling-leaf mode was rarely encountered; however, 

by the early 1990's increasingly aggressive maneuvering had exposed a susceptibility to 

the falling-leaf mode with numerous incidents and losses of aircraft. 

Langley began studying the falling-leaf mode in 1994 at the request of the Naval Air 

Systems Command, following an F/A-18 falling-leaf incident during a routine training 

flight that nearly resulted in loss of the aircraft. Under the technical leadership of 

Langley researcher John V. Foster, the cause for the falling-leaf mode was identified and 

linked to a common aerodynamic stability design method that had been used for many 

years. Using the DMS, the critical entry maneuver that excites the mode was identified 

and correlated with fleet incidents, and various recovery methods were studied. In addition, the necessary requirements for high-fidelity prediction of the falling-leaf motion in 

piloted real-time simulations were defined. 

In light of the growing falling-leaf problem on early models of the F/A-18, there was 

concern that the emerging F/A- 1 8E/F, which was then preparing for developmental 

flight tests, would have the same problem. In response, McDonnell Douglas proposed a 

control law design approach, supported by Foster's research, that specifically targeted 

falling-leaf suppression, which was later implemented on the aircraft. 

Because no methods existed specifically for falling-leaf flight tests, NASA again used 

the DMS facility to develop reliable flight-test techniques that were subsequently validated on the NASA F/A-18 HARV at Dryden. Using these test techniques, falling-leaf 

susceptibility was extensively evaluated on the F/A-18E/F during the high-angle-ofattack flight-test program. While the unaugmented aircraft was shown to exhibit the 

falling-leaf mode, the new control system design was shown to be very effective in suppressing the mode and the falling-leaf problem was considered solved for that aircraft. 

Largely due to the success of the F/A- 1 8E/F program, the Navy is considering retrofitting earlier models of the F/A- 18 with the updated control law for the purpose of eliminating the falling-leaf problem. 

While the F/A- 18 was the most visible recent manifestation of the falling-leaf problem, 

numerous other aircraft configurations have exhibited the mode. For example, the 

AV-813 exhibited a severe falling-leaf mode that the Foster criteria showed to be a result 

of a minor configuration change. As new highly maneuverable configurations are developed and the angle-of-attack envelope expands, Langley's F/A- 18 research has brought 

a necessary and timely focus to a critical flight problem. 

Flutter Clearance and Tail In a departure from most fighter programs, flutter clearance tests of both the YF- 17 and 

Buffet the F/A-18A were not conducted in the Langley 16-Foot Transonic Dynamics Tunnel. 

Research studies were, however, conducted in the areas of active flutter suppression and 

buffet alleviation. A cooperative NASA, Northrop, and Air Force research study was 

later conducted to assess the application of active controls for flutter suppression for the 

42 Boeing F/A-18 Hornet
F/A-18A to F/A-18D 

YF-17 wing-store-pylon combination in the tunnel in late 1977. The results indicated 

that active control of wing-store-pylon flutter was possible and that wing leading-edge 

surfaces could be effective in such a control system. In 1979 interest in the concept 

resulted in an international study of several active flutter suppression systems designed 

by British Aerospace and the Royal Aeronautical Establishment from the United 

Kingdom. the Office of National d'Etudes et de Recherches Aerospatiales from France, 

and Messerschmitt-Bolkow-Blohm from the Federal Republic of (West) Germany. The 

TDT tests showed that all the control systems were highly effective in supressing flutter. 

The YF-17 testing continued through 1982. 

The vertical-tail buffet experienced by the F/A- 1 8A and other high-performance aircraft 

resulted in cooperative research by industry, DOD. and NASA on buffet alleviation from 

smart materials and actively controlled rudders. Because international allies of the U.S. 

use the F/A-18, this research effort included Australia and Canada. The Actively Controlled Response of Buffet Affected Tails (ACROBAT) Program led by Robert W. 

Moses investigated the use of an actively controlled rudder, actively controlled piezoelectric devices, and other novel concepts to alleviate vertical-tail buffeting. For the 

ACROBAT Program. a 1/6-scale rigid full-span model of the F/A-18 A/B aircraft with 

flexible tails was tested in the 16-Foot Transonic Dynamics Tunnel. Numerous control 

laws were tested, and many demonstrated buffeting alleviation over a large angle-ofattack range. These tests have been followed up with international ground-based tests of 

a buffeting alleviation system on a full-scale F/A-l8. 

Thrust-Vectoring Research In the early 1970's. the Navy conducted a vertical and short takeoff and landing 

(V/STOL) nozzle study for potential applications to high-performance aircraft. Following this study, the augmented deflector exhaust nozzle (ADEN) was selected as the best 

nozzle concept for Navy V/STOL requirements. The ADEN nozzle had a hood, which 

deployed from a long upper ramp, that was capable of thrust vector angles from 0 deg to 

over 90 deg. Nozzles of this type (long flap on one side of the nozzle and no deploying 

hood without VTOL capability) were later called single expansion ramp nozzles 

(SERN).

qb1hh' 

F/A- /S model nit/i 2-1) co,iveri,'eiir-divergent (CD) 

nozzles tested in Lan g/ev 16-Foot Transonic Tunnel. 

Boeing F/A-18 Hornet 43
F/A-18E/F

In 1975, a joint DOD and NASA two-dimensional (2-D) nozzle workshop held at 

Langley formed an ad hoc interagency nonaxisymmetric nozzle working group that 

eventually recommended a flight test of 2-D, thrust-vectoring, in-flight thrust-reversing 

nozzles. To avoid duplication, studies on potential flight-test vehicles were split up 

among NASA (F- 15), the Air Force (F-Ill), and the Navy (YF-l7 and F/A-18). 

The first full-scale tests, which were sponsored by the Navy, of a 2-D nozzle (ADEN) 

were conducted in a Glenn Research Center altitude test cell in 1976. In support of the 

Navy studies of advanced nozzles. Langley conducted powered-model tests of an early 

F/A-18A configuration with 2-D nozzles in the Langley 16-Foot Transonic Tunnel. 

Since the F/A- 1 8A represented the state of the art in fighter design. Langley expanded 

the test objectives to include propulsion-airframe integration studies of a number of nozzle types (wedge, 2-D convergent-divergent (CD). SERN), thrust-vectoring concepts, 

and in-flight thrust-reversing concepts. The studies also examined F/A-18A vertical-tail 

loads, particularly during in-flight thrust-reversing operation. Unfortunately, Navy and 

NASA attempts to secure funding for the F/A-18A flight tests were unsuccessful, and 

the F/A- i 8A studies of thrust vectoring were terminated. 

F/A-18E/F 

The Super Hornet - - The F/A-i 8E/F Super Hornet was funded in June 1992 as the replacement for the cancelled Navy A-12 aircraft and as the replacement for the early F/A-18A aircraft and 

other Navy and Marine Corps aircraft. The F/A-18E/F is a larger version of the 

F/A-18C/D Hornet with extended mission capabilities. The ElF is roughly 25 percent 

larger than the CID, with a 25 percent increase in operating radius and a 22 percent 

increase in weapons load capability. First flight of the F/A-18E/F occurred on 

November 29. 1995, and preproduction flight tests began in February 1996. at Patuxent 

River.

F/4-18EfiigIit test aircraft prepares to land at Patuxent Rirer Naval Air Station. 

44 Boeing F/A-18 Hornet
F/A-i 8EJF 

CnusePertormance NASA's involvement with the F/A- lSE/F began in the early stages of the proposed aircraft development when the Office of the Secretary of Defense (OSD) became concerned with the accuracy of McDonnell Douglas' range estimates for the vehicle. At the 

request of OSD, a three-member NASA. DOD, and industry team conducted an independent review of McDonnell Douglas' F/A-18E/F fighter-escort mission range estimates in April 1992. Langley researcher Gary Erickson represented NASA and called 

on supporting analyses from several Langley specialists. Results of the independent 

review substantiated the McDonnell Douglas estimates and were briefed to the Assistant 

Secretary of Defense. The favorable results from this review were critical to the aircraft 

program proceeding to the Defense Acquisition Board for funding advocacy. 

Redesign of the Leading-Edge Many operational requirements were revisited as the F/A-18C/D grew to the larger, 

Extension heavier F/A-I 8EIF. Critical performance issues included lift requirements for carrier 

approach and wave offs, high-angle-of-attack stability, recovery from extreme attitudes, 

and minimization of adverse aerodynamic phenomena such as tail buffet. McDonnell 

Douglas explored a number of configuration changes to satisfy these requirements, 

including adding a snag to the wing leading edge, reshaping the LEX, and using moveable spoilers on the upper surfaces of the LEX to ensure recovery from extreme angles 

of attack. 

Low-speed wind-tunnel tests by McDonnell Douglas had indicated that a deflected 

spoiler on the upper surface of each LEX would alleviate buffeting of the vertical tails, 

promote good lateral-directional stability, and provide trim changes for nose-down control at extreme angles of attack. In May 1992, a series of tests were conducted in the 

Langley 8-Foot Transonic Pressure Tunnel to determine the effects of the spoiler concept at higher speeds (Mach numbers from 0.6 to 1.2). Unfortunately, results of the 

1/1- IE/i ,,u/cI ill S-I-i I/li1Hni( l'!'\sl!r( Tiii,,i'I

fr eraIuaiio, o/ i/u LL.\ spoiler concept. 

Boeing F/A-18 Hornet 45
F/A-i 8E/F

F/A- /8E/F (foreground) with redesigned LEX in tug/it wit/I I-/A - 1SC i/iose n/oral,. 

Langley tests indicated that the deployed spoilers would cause an unacceptable decrease 

in maximum lift of over 15 percent. With these negative results, a redesign of the LEX 

surfaces began. The LEX spoilers have been retained on the F/A- 1 8E/F as speed brakes 

and nose-down control devices. 

Redesigning the LEX was the job of a 15-member industry. DOD. and NASA team, 

which included Langley researchers Daniel G. Murri, Robert M. Hall. and Gary Erickson. This team, which was active for the first 6 months of 1993, initially explored small 

modifications to the size and shape of the original F/A-18C LEX to help provide the 

required lift and improve lateral-directional stability. However, subsequent wind-tunnel 

tests showed that this incremental approach would not be successful and much larger 

changes to the LEX configuration would be required. Based on his prior research with 

other configurations. Murri proposed more radical LEX candidates that would potentially satisfy these requirements. One of the LEX configurations with favorable windtunnel results that was recommended by Langley was accepted for further refinements 

and met all design goals. This configuration was the basis for the final design adopted as 

the wing LEX configuration for the production F/A-I 8E/F. 

Extensive tests of the F/A-18E/F with the redesigned LEX were conducted in several 

NASA and industry wind tunnels to completely define the aerodynamic characteristics 

of the configuration. Data from these tests were used to generate the aerodynamic databases for flight simulation and to develop the flight control software for the aircraft. 

NASA engineers worked closely with engineers from McDonnell Douglas and the Navy 

to assure that design requirements and national goals were met. 

High-Angle-0 -Attack - Stability and control characteristics of the F/A-18E/F at high-angle-of-attack flight conCharacteristics ditions were evaluated in numerous wind-tunnel tests at Langley. In the Full-Scale Tunnel, a combination of static, dynamic, and powered tests was conducted to define and 

develop a database for the high-angle-of-attack aerodynamic, stability, and control characteristics of the aircraft. In addition to tests of the basic configuration, tests were 

46 Boeing F/A-18 Hornet
F/A-i 8EJF 

conducted to study the impact of fuselage-mounted and wing-mounted stores on aerodynamic and stability characteristics, to assess aerodynamic damping characteristics, 

and to assess the magnitude of thrust-induced aerodynamic effects on the configuration. 

Free-flight tests were also conducted to provide confirmation of the stability and flight 

dynamic characteristics. 

This database has been used by McDonnell Douglas and the follow-on Boeing organization. NASA. and the Navy to conduct flight-simulation studies and to aid in the development of the aircraft's flight control system. An extensive unpiloted and piloted 

simulation of the F/A-I 8E/F has been implemented in the Langley DMS and is being 

used to analyze flight control modifications and the impact of aircraft parameters on 

high-angle-of-attack behavior. 

Spin Tunnel and Drop-Model Hundreds of tests in the Langley Spin Tunnel quantified the spin modes and spin recovTests cry characteristics of the F/A-18E/F. determined the acceptable emergency spin recovery parachute size, and identified the optimal spin recovery procedures prior to flight 

tests. Time histories of model motions from these tests were used by McDonnell 

Douglas to validate their spin simulation. Data from rotary-balance tests conducted in 

this facility provided inputs for an analytical assessment of spin modes, spin recovery 

characteristics, and a database for incorporating rotational aerodynamic characteristics 

into the flight simulation.

11 

F/A-18E/F drop model im,nediatelv after release I rom the helicopter 

Boeing F/A-18 Hornet 47
er-

: 

F/A-i 8E/F

A highly sophisticated F/A-18E/F drop model was tested by Langley at the NASA 

Wallops Flight Facility to provide risk reduction for the high-angle-of-attack part of the 

flight-test program. These tests, which used a 0.22-scale remotely piloted model, supplemented the aircraft flight-test program by providing flight dynamics data for the aircraft at conditions outside the planned operating envelope. 

Flutter Tests - - - - -- - F/A- 18E/F flutter clearance tests were conducted at Langley by Moses G. Farmer in the 

16-Foot Transonic Dynamics Tunnel during four tunnel entries from 1993 to 1995. 

Phase I tests insured that each pair of dynamically scaled surfaces (wings, horizontal 

tails, and vertical tails) was clear of flutter throughout the scaled flight envelope. Phase 

11 of the tests studied the configuration both with and without stores (bombs and fuel 

tanks) mounted on the wings. These tests used the unique two-cable-mount system of 

the tunnel, which allows the model to actually fly in the center of the tunnel with assistance from a pilot in the control room. The tests verified that the aircraft was free from 

aeroelastic instabilities, including flutter, within its flight envelope. As a result of the 

Langley tests, the number of expensive flight tests dedicated to flutter clearance could be 

minimized. 

In view of Langley's corporate knowledge of the F/A-18E/F and its predecessors, the 

Navy requested NASA involvement when the F/A-I 8E/F began flight tests. NASA continued to work closely with the Navy and McDonnell Douglas during the engineering 

and manufacturing development (EMD) phase. Langley support included flight-test 

planning and data evaluation, especially in the high-angle-of-attack regime. In 1997, 

Langley assigned an engineer to Patuxent River as a participant in the flight tests and as 

a liaison and technical consultant for the test team.

F/A-/8E/F model mounted tort/utter tests in time Langle y 16-Foot Transonic D ynamics Tunnel. 

Wing Drop The most recent Langley contribution to the F/A-I 8E/F Program explored the phenomenon known as wing drop. In March 1996. during flight tests at Patuxent River, 

an F/A- I 8E/F experienced wing drop—an unacceptable, uncommanded abrupt lateral 

48 Boeing F/A-18 Hornet
F/A-i 8E/F 

roll-off that randomly occurred and involved rapid bank angle changes of up to 60 deg. 

The problem was viewed as extremely serious and posed a threat to operational tests and 

the overall development schedule. During the first year of flight tests, the wing-drop 

phenomenon was only seen at high altitudes because load restrictions prevented the aircraft from reaching the relevant range of angle of attack at low altitudes. As the loads 

test program opened the flight envelope to 7.5g at all altitudes, the full extent of the 

wing-drop problem became evident. Objectionable wing-drop events occurred throughout the flight envelope at Mach numbers between 0.5 and 0.9, and this deficiency 

became a significant threat to the technical and political health of the F/A-I 8EIF 

Program. 

A joint Navy and McDonnell Douglas team concluded that the wing drop was caused by 

a sudden, abrupt loss of lift on one of the outer wing panels during maneuvering. 

Though the basic cause of the wing drop was determined, how to moderate the airflow 

separation differences between the left and right wings was not. A variety of solutions 

was explored. For example, 25 potential wing modifications were tested in wind tunnels, computational fluid dynamics studies were undertaken, and two of the potential 

fixes were flown with mixed results. In one approach, the use of stall strips in the vicinity of the wing-fold fairing eliminated wing drop, and the aircraft exhibited excellent 

flight qualities throughout the envelope. However, the impact of the stall strips on range 

and turn performance were severe, and they were discarded as a viable option. 

Langley engineer Robert Hall also served on a DOD blue ribbon panel to review the 

approach taken by McDonnell Douglas to resolve the wing drop. The panel also participated on various McDonnell Douglas and Navy "tiger teams" that were created to 

resolve issues related to the wing-drop problem. Roy V. Harris, a distinguished Langley 

retiree, was selected by DOD to head the blue ribbon panel, which subsequently cited 

the lack of technical understanding and design tools available in the technical community to address the high subsonic and transonic wing-drop problem. The panel strongly 

recommended that a research program be undertaken to develop the design methods 

required to avoid this problem in future fighter aircraft. The recommendation was 

accepted, and a joint NASA and Navy Abrupt Wing Stall (AWS) Program was initiated. 

Langley researchers Jeffrey A. Yetter and Robert Hall served as AWS Program Comanager and Technical Comanager, respectively, with their Navy partners. 

As a low impact "80-percent solution" to the FIA-18E/F wing-drop problem, a revised 

deflection schedule for the leading-edge flaps was evaluated in flight tests in early 1997, 

with very favorable results. Although the leading-edge flap schedule modification significantly reduced the magnitude of the problem, the aircraft still exhibited smaller wing 

drops at many test conditions. The original wing-drop problem had been viewed as a 

potential safety hazard and a roadblock to productive load tests. After the modification, 

the problem was reduced to a flying qualities issue that allowed other tests to continue. 

Wind-tunnel tests were conducted at sites other than NASA to evaluate wing changes 

that might eliminate the residual wing-drop tendencies. Langley researchers Gary 

Erickson and Robert Hall participated in the tests, which continued through the summer 

of 1997. 

During the winter of 1997 to 1998, the Navy asked NASA for additional assistance in 

resolving wing drop. In November 1997, a diagnostic flight test of an F/A-I8EIF with 

the wing-fold fairing removed was conducted and the results showed that wing drop had 

been eliminated from most of the flight envelope. The fairing-off configuration was not 

a viable approach for production aircraft, and Langley engineers led by Steven X. S. 

Bauer suggested that the flight program apply porosity, a passive technology developed 

Boeing F/A-18 Hornet 49
F/A-i 8E/F

at NASA, to the wing in the fold area. Langley researchers had been conducting experiments with passive porosity to control shock locations and other characteristics for 

several years. During the initial concept evaluation on the F/A-18E/F, the porous fairing 

was simply a standard wing-fold fairing with areas cut out and a screen mesh substituted. Langley provided design guidelines for the porosity and thickness of the mesh. 

This solution, refined by the NASA, Navy, and Boeing team, resolved the wing-drop 

problem and permitted continued production of the aircraft. 

Additional activities are being conducted to support the joint NASA and Navy AWS 

Program, including tests of an F/A- 1 8E/F model in the Langley 16-Foot Transonic Tunnel in September 1999 under the leadership of Robert Hall and S. Naomi McMillin. 

50 Boeing F/A-18 Hornet
Highlights of Research by Langley for the T-45 

Boeing T-45 Goshawk 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE T-45 

1. At the request of the Navy, Langley participated in an independent assessment team 

review of technical progress during early development. 

2. Langley conducted exploratory research to define potential wing leading-edge modifications to cure severe low-speed wing drop on the original configuration. 

3. Tests were conducted at Langley to determine the spin and spin recovery characteristics of the aircraft and its potential utility as a spin trainer. 

4. Langley provided critical tire characterization data that dramatically improved the 

modeling and analysis of pilot-induced oscillations during landing. 

5. Tests were conducted in the Langley 16-Foot Transonic Tunnel to identify potential 

candidates for a revised engine inlet configuration. 

SPECIFICATIONS 

Manufacturer 

Boeing 

Date in service 

January 1992 

Type 

Trainer 

Crew 

Two 

Engine 

Rolls Royce F405-RR-401 

USER 

U.S. Navy 

DIMENSIONS 

Wingspan ............ .10.1 ft 

Length ...............39.3 ft 

Height ..............14.0 ft 

Wing area ..........180 sq ft 

WEIGHT 

Empty .............9,394 lb 

Gross .............13,636 lb 

PERFORMANCE 

Max speed .....Mach number 

of 1.04

Boeing T-45 Goshawk 51
Highlights of Research by Langley for the T-45 

The Boeing (formerly McDonnell Douglas) T-45 Training System is the first totally 

integrated training system developed for and used by the U.S. Navy. It includes the T-45 

Goshawk aircraft built by Boeing, advanced flight simulators, computer-assisted 

instructional programs, a computerized training integration system, and a contractor 

logistics support package. The integration of all five elements produced a superior pilot 

in less time and at lower cost than previous training systems. The two-seat, singleengine T-45 Goshawk is the heart of the training system. The T-45 replaces the T-2 and 

TA-4 aircraft formerly used for Navy advanced jet trainers. The Goshawk's design is 

based on the British Aerospace Hawk land-based aircraft; however, design modifications have been made to the Goshawk that make the aircraft more suitable for carrierbased operations. The modifications include strengthened landing gear, the addition of 

an arresting hook, and catapult launch fittings. The latest version of the aircraft, known 

as the T-45C, includes a digital cockpit. 

Langley's involvement in the T-45 began with an independent assessment team review 

of technical progress during the initial development program in 1988. Subsequent activities included spin tunnel tests, wind-tunnel research on wing leading-edge modifications, characterization of landing gear tires for improved handling characteristics during 

ground rollouts on landing, and wind-tunnel assessments of new engine inlet designs. 

Langley facilities involved in support of the T-45 Program included the 16-Foot Transonic Tunnel, the 12-Foot Low-Speed Tunnel, the 20-Foot Vertical Spin Tunnel, and the 

Landing Loads Facility. 

52 Boeing T-45 Goshawk
Langley Contributions to the T-45 

LANGLEY CONTRIBUTIONS TO THE T-45 

Earli Configuration The U.S. Navy initiated the Advanced Trainer (VTX) Program in the early 1980's to 

Development replace the existing T-2 Buckeye and TA-4 Skyhawk advanced jet trainers. Industry 

responses to the Navy request for proposals (RFP) included several existing and new 

aircraft configurations. A team from McDonnell Douglas and British Aerospace proposed both a modification of the existing British Hawk land-based configuration and a 

new trainer. The VTX contract was awarded to the McDonnell Douglas and British 

Aerospace team in November 1981. The Boeing (formerly McDonnell Douglas) T-45 

Goshawk evolved from the Hawk design. 

Conversion of the Hawk land-based aircraft to a naval trainer with carrier capabilities 

involved considerable research and development. In addition to the necessary strengthening of landing gear components and the inclusion of arresting gear, development work 

was required in numerous areas that were critical for carrier-based operations. Some 

areas of concern included the handling qualities, engine response characteristics, and 

stall characteristics of the T-45. 

In 1988, following extensive preliminary flight-test evaluations by the Navy at the 

Patuxent River Naval Air Station in Maryland, the Navy cited several major deficiencies 

in the T-45. The deficiencies included high approach speed, slow engine thrust response, 

and longitudinal and lateral stability deficiencies. McDonnell Douglas and British 

Aerospace developed candidate solutions and recommended approaches to resolve these 

issues. In 1989 the Navy convened a blue ribbon independent assessment team to review 

the technical status and plans for the program. In response to a request from the Navy 

for Langley representation, Joseph R. Chambers served on the team. 

Stall Characteristics - The stall characteristics of the initial T-45 configuration were judged to be unacceptable 

by the Nav y on the basis of a severe wing-drop behavior at the stall and high approach 

Itt\ ted h\ rhc incrca'd v, e!11t ''1iiircd to stren g then the airframe folLangle_N ic iii/o/ie,.s Lo,o,' P }p and Ho//v M. Ross examine a T-45 model imith a

discontinuous leading-edge modification in the Lan glev 12-Foot Low-Speed Tunnel in 1989. 

Boeing T-45 Goshawk 53
Langley Contributions to the 1-45 

Spin Characteristics

carrier operations). During the Navy's flight evaluations, the wing drop was so severe 

that uncommanded roll motions often exceeded 90 deg. 

While McDonnell Douglas and British Aerospace explored various candidate solutions 

to the wing-drop issue. Langley proposed a joint research project to assess the effectiveness of a Langley concept for enhanced stall characteristics. As part of research to 

improve stall and spin characteristics of general aviation aircraft. Langley had conceived a wing leading-edge modification that significantly improved the lateral stability 

and spin resistance of several general aviation research aircraft during stall-spin 

research flight tests. The leading-edge modification consisted of a discontinuous "snag" 

at about the 75-percent span location that acted similar to an aerodynamic fence and 

maintained attached flow on the outer wing panel to very high angles of attack (beyond 

stall). Although the wing leading-edge radius of the T-45 was much smaller than those 

of general aviation aircraft, it was hoped that the modification would also be effective 

for the advanced trainer. 

Led by Langley's Long P. Yip, tests were conducted on a 0.15-scale T-45 model in the 

Langley 12-Foot Low-Speed Tunnel. The test techniques included conventional static 

force tests as well as single-degree-of-freedom free-to-roll tests to determine wing-drop 

tendencies. The results of the investigation indicated that the wing modification was 

effective in minimizing wing-drop tendencies for the cruise configuration: however, the 

modification was not effective for the landing configuration with the wing trailing-edge 

flaps deflected. The 1-45 Program subsequently adopted a wing redesign, which incorporated wing leading-edge slats. The slats virtually eliminated the wing-drop tendency 

and lowered the carrier-approach speed to a more acceptable value. 

Flight-test experience with the British Hawk aircraft had indicated that the aircraft was 

very reluctant to spin and that attempts to intentionally spin the aircraft usually resulted 

T-45 model undergoing test in the Langley Spin Tunnel. 

54 Boeing T-45 Goshawk
Langley Contributions to the T-45 

in a spiral with rapidly increasing airspeed. The Hawk recovers from the high-speed spiral when controls are neutralized. Spin tests of the T-45 in the Langley 20-Foot Vertical 

Spin Tunnel by Langley researcher Raymond D. Whipple indicated that the Goshawk 

would exhibit similar characteristics. In fact, it was virtually impossible to obtain spins 

for the T-45 model in the normal upright attitude because, after being hand launched 

with prerotation into the vertical airstream, the model would immediately nose over and 

rapidly increase airspeed beyond the test capability of the Spin Tunnel. 

Full-scale flight tests of the T-45 subsequently verified the predictions of the Langley 

Spin Tunnel tests. During spin attempts, airspeed rapidly increased, and stabilized spins 

could not be obtained. As a result of this spin resistant behavior, the T-45 is not used for 

spin training. (The T-2 and TA-4 had been used for spin training.) 

Ground Handling In 1999. the Navy requested that Langley provide data, analysis, and recommendations 

to eliminate a severe pilot-induced oscillation (PlO) resulting in erratic yaw behavior of 

the T-45 during runway rollout in land-based landing operations. The Navy also 

requested assistance in determining the cause of uncontrollable aircraft yaw when tires 

failed. 

In response to the Navy requests. Langley researcher Robert H. Daugherty led a 

Langley effort that conducted over 160 aircraft main and nose tire tests to define cornering and braking behavior in the T-45. The Langley team conducted on-site tests at 

Patuxent River with a special truck apparatus in a program that included evaluations of 

various tire states, including normal and blown tires. The tests determined the effect of 

aircraft roll attitude on uncommanded tire cornering force, identified the drag behavior 

of failed main gear tires and the reason for lack of yaw control, and provided models of 

-

Lj

- -'" -.

--

The T-45 tire characteristics during landing rollout nere studied b y Langley. 

Boeing T-45 Goshawk 55
Langley Contributions to the T-45

physical tire behavior for analysis. A particularly valuable output of this effort was a 

dramatic improvement in the modeling capability of T-45 landing operations and the 

inclusion of the data generated by Langley in the T-45 rollout and training simulators. 

After the Langley data had been incorporated in the simulator, the landing dynamics of 

the simulated aircraft were significantly more realistic. The T-45 Program was especially complementary in recognizing this effort as a timely, critical, and valuable NASA 

contribution to the program. 

Inlet Performance Flight-test experience with the T-45 has demonstrated that the aircraft sometimes experiences undesirable propulsion system characteristics during certain maneuvers. In particular, the aircraft engine has experienced self-clearing "pop" stalls, pop surges, and 

occasional locked-in surges during simulated air-combat maneuvers and recovery 

maneuvers from aircraft (wing) stalls. 

As a result of concern over these characteristics, the Navy requested that Langley provide support to, and participate in, wind-tunnel tests of the engine inlet behavior of the 

T-45. In support of this request, a Langley, Navy, and Boeing Team conducted two separate T-45 test entries (May 1998 and July 1999) in the Langley 16-Foot Transonic Tunnel. Langley researcher E. Ann Bare led the test operations. 

The 0.26-scale inlet distortion model used in the tests consisted of the T-45 forebody, 

fuselage contour to the wing trailing edge, and wings. The model was powered with an 

aft-mounted ejector and included extensive instrumentation to measure steady state and 

dynamic pressure distortion characteristics. The scope of the test program included evaluations of minor and moderate inlet changes for the cruise and power approach configurations of the T-45. 

T-45 inlet performance model in the Lan glev 16-Foot Transonic Tunnel. 

56 Boeing T-45 Goshawk
SPECIFICATIONS 

Manufacturer 

Fairchild Republic 

Date in service 

March 1976 

Type 

Close support and attack 

Crew 

One 

Engine 

General Electric TF34-GE1 OOA 

USER 

U.S. Air Force 

DIMENSIONS 

Wingspan ............ 57.5 ft 

Length .............. 53.3 ft 

Height .............. 14.7 ft 

Wing area ..........506 sq ft

WEIGHT 

Empty ...........18,591.0 lb 

Typical combat . . . .23.498.0 lb 

PERFORMANCE 

Max speed .....Mach number

of 0.56

Radius of action.....695 n mi

Highlights of Research by Langley for the A-10 

Fairchild Republic A- 10 

Thunderbolt II 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE A- 10 

1. At the request of industry and the Department of Defense, Langley personnel participated in reviews and assessments during competitive stages of Attack Experimental 

(A-X) Program. 

2. Langley conducted wind-tunnel tests and provided data for all competing designs in 

A-X Program. 

3. Langley and Fairchild conducted joint tests of a powered A- 10 model in the 7- by 

10-Foot High-Speed Tunnel to determine the effects of engine exhaust on aerodynamic characteristics. 

4. Fairchild consulted with Langley personnel on A-lU wing airfoils, stall characteristics, high-lift aerodynamics for low-level maneuvers, and spin characteristics. 

5. Langley conducted extensive spin tunnel tests of the A-lU for a variety of external 

store configurations. 

Fairchild Republic A-JO Thunderbolt 11 57 
Highlights of Research by Langley for the A-b 

The Fairchild Republic A-10 was the result of the Air Force's A-X competition that 

began in 1967 for a close-support aircraft capable of withstanding the highly lethal environment near the front lines. During the A-X competition, the Department of Defense 

(DOD) requested that Langley participate in mission analyses, conduct supporting 

wind-tunnel tests, and provide analyses of the competing designs. During the summer of 

1967, tests were conducted in the Langley 7- by 10-Foot High-Speed Tunnel on designs 

submitted by Grumman, Northrop, McDonnell, and General Dynamics. In 1970, the 

requirements for the A-X mission were changed, and the Air Force issued a new request 

for proposals (RFP). Six companies responded to the RFP, and designs by Fairchild and 

Northrop were selected for further development. In preparation for a competitive fly off 

under the "fly before buy" philosophy, Langley conducted performance and spin tunnel 

tests of the Fairchild Republic and Northrop configurations, known as the YA-10A and 

the YA-9A, respectively. 

After the Air Force selected the A-10 as its close-support aircraft in January 1973, 

Langley conducted extensive tests in the Langley 20-Foot Vertical Spin Tunnel of the 

production configuration with a large variety of external stores. Langley facilities used 

in support of the A- 10 Program also included the 7- by 10-Foot High-Speed Tunnel. 

58 Fairchild Republic A-JO Thunderbolt II
Langley Contributions to the A-10 

LANGLEY CONTRIBUTIONS TO THE A- 10 

The A-X Competition In the Vietnam conflict concentrated small-arms fire, ground-to-air missiles, and other 

more sophisticated defenses were particularly lethal to aircraft flying close-support missions. This situation resulted in dramatic changes in philosophy for the capabilities of 

aircraft conducting these missions. Specialists at Langley were asked to identify technologies that could be applied to a hard-maneuvering aircraft with a relatively high 

degree of survivability. In March 1967. the Air Force released a request for proposals 

(RFP) for a new Attack Experimental (A-X) Program. In 1967, numerous wind-tunnel 

tests were conducted in the Langley 7- by 10-Foot High-Speed Tunnel to obtain analysis 

data for designs by Grumman, Northrop. McDonnell. and General Dynamics. The tests 

were led by William P. Henderson and Linwood W. McKinney, who conducted extensive briefings for the Department of Defense (DOD) and the industry competitors on the 

merits of each configuration. 

In the years following 1967, the A-X mission requirements began to change as the threat 

of Soviet armor and all-weather operations became embedded in military priorities. In 

1970, a new A-X RFP was released by the Air Force and six companies responded. 

After a formal study, Northrop and Fairchild were named as final competitors for a fly 

off competition at Edwards Air Force Base. 

In 1971, tests of a powered model of the Fairchild A-10 were conducted in the 7- by 

10-Foot High-Speed Tunnel by Vernon E. Lockwood. The principal objective of the 

tests was to determine the effects of engine exhaust flow on aerodynamic characteristics 

in high-power conditions. The tests were conducted with a special model installation in 

which the powered engine nacelles were not mounted directly to the airframe, but to a 

separate sting that included air supply lines for the simulation of power. Critical data 

were obtained on the impact of power on performance and stability of the configuration, 

including ground effects. 

EA

0 

Powered-model tests of the Fairchild A-JO nit/i engines SU/)IOrted b y an 

auxiliary upper sting in the Lan glev 7- b y 10-Foot High-Speed Tunnel. 

Fairchild Republic A-JO Thunderbolt 11 59
-t. 

Langley Contributions to the A-10 

Spin Recoi'err -- - In 1972. tests were conducted in the Spin Tunnel by Stanley H. Scher for the competing 

Northrop (A-9) and Fairchild (A-b) A-X configurations. Results of these tests were 

used for evaluations and planning for the competitive fly off that occurred at Edwards 

Air Force Base later that year. In addition to providing information on advantages and 

disadvantages of each configuration, these results provided spin and recovery characteristics for pilots of the respective vehicles. 

The Fairchild aircraft was announced as the winner of the competition on January 18. 

1973, and a formal request for tests in the Langley Spin Tunnel for the development program was received from the Air Force. A large number of tests were conducted because 

of the variety of external stores, tanks, and armament carried by the aircraft. 

High Reynolds number tests were performed with an A- 10 model at spin attitudes in the 

NASA Ames Research Center 12-Foot Pressure Tunnel prior to the spin tunnel tests to 

determine whether the model would exhibit significant scale effects, and if so, what 

modifications might be made to correct for these effects. Results of the tests at Ames 

showed no appreciable scale effects for angles of attack below about 75 deg, but appreciable scale effects (more prospin yawing moments at low Reynolds numbers) for 

angles of attack above 75 deg. Nose strakes were sized to artificially compensate for the 

scale effects, but no flat spins (angle of attack greater than 75 deg) were evident and the 

strakes were not used.

Spin tunnel tests of the A- 10 configuration. 

60 Fairchild Republic A-JO Thunderbolt II
SPECIFICATIONS 

Manufacturer 

General Dynamics 

Date in serv!e 

June 1967 

Type 

Crew 

Tw 

Engni 

F- !III. 

TF30-P- I H 

USERS 

U.S. Air Force (retired 1996) 

and Australian Air Force 

DIMENSIONS 

Wingspan 

unswept........... 63.0 ft 

fully swept ......... 1.9 ft 

Length .............. 73.5 ft 

Height .............. 17.1 ft 

Wing area ...........525 sq ft

WEIGHT 

Empty ............ 47.481 lb 

Gross ............100,000 lb 

PERFORMANCE 

Max speed ........bove Mach

number of 2

Range ............ ..925 n mi

Highlights of Research by Langley for the F-1 11 

General Dynamics F- ill Aardvark 

AL 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F- ill 

I. Langley conducted studies to enable the variable-sweep wing that was employed by 

the F- Ill and subsequent variable-sweep aircraft such as the F- 14 and 13- 1. 

2. Langley staff conducted wind-tunnel tests, identified major problems, and recommended critical improvements to the aerodynamic performance of the F- Ill. 

3. Langley personnel presented key technical results in congressional and high level 

Department of Defense investigations of the technical merit of the F- Ill. 

4. Langley led studies to provide solutions to major propulsion integration problems 

exhibited by the F- ill, which were used on all subsequent high-performance fighters, such as the F-14, F- 15, and F-22. 

5. Langley identified critical deficiencies in the high-angle-of-attack characteristics of 

the F-Ill. 

6. Langley detected the presence of a dangerous flat spin for the F-i II and precipitated the development of a stall inhibitor system to protect against inadvertent 

spins. 

7. Following a catastrophic wing fatigue failure of an operational F-Ill, Langley conducted critical materials tests, and Langley personnel served on advisory boards to 

recommend approaches to ensure safety of the fleet. 

8. Langley conducted tests to improve the robustness and landing loads of the F- Ill 

crew module. 

9. Langley wind-tunnel tests to determine the flutter characteristics of the F- Ill identified a potential tail flutter problem that resulted in modifications to the aircraft. 

10. Langley supercritical wing technology was applied to the F- 111 and demonstrated 

during the TACT and MAW Programs. 

General Dynamics F- Ill Aardvark 61 
Highlights of Research by Langley for the F-1 11 

The General Dynamics F-I II was a multipurpose supersonic tactical fighter-bomber 

aircraft. The F- ill was one of the more controversial aircraft in the U.S. military inventory, yet it achieved one of the safest operational records in Air Force history. It was 

regarded as a highly effective, all-weather interdiction aircraft. As the result of a high 

level government directive in 1961, both the Navy and Air Force became committed to a 

common Tactical Fighter Experimental (TFX) Program. The TFX Program called for 

developing a single aircraft to fulfill a Navy fleet defense interceptor requirement and an 

Air Force supersonic strike aircraft requirement. The mission requirements were impossible to achieve, especially since planners placed priority upon the Air Force requirement, and then tried to tailor a heavy land-based aircraft to the demands of carrier-based 

naval aircraft. The naval version, the F- Il IB, was never placed into production. The Air 

Force aircraft was produced in a variety of models, including the F-I hA, F- il ID, 

F-il IE, and F-il IF fighter-bombers; the FB-I I IA strategic bomber; the F-li 1C for 

the Australian Air Force; and an EF- lii electronic warfare version. The U.S. Air Force 

versions were retired in 1996, but the Australians plan to operate their fleet until well 

into the twenty-first century. 

Arguably, the political and technical issues associated with the F- Ill program resulted 

in more research activities at the Langley Research Center than any other production 

military aircraft in Langley's history. The staff participated in top level assessments of 

the aircraft's capabilities (including briefings at the highest levels of the Department of 

Defense (DOD) and government), identified several critical problems, and provided recommendations for solutions. Significant Langley technical contributions included the 

variable-sweep wing concept, and test activities in aerodynamic performance enhancements, high-angle-of-attack characteristics, spin recovery, flutter, propulsion integration, wing structures and materials, and robustness of the crew escape module. Finally, 

Langley was a major participant in the joint NASA and Air Force F- ill Transonic Aircraft Technology (TACT) Program and the Mission Adaptive Wing (MAW) Program 

that applied supercritical wing technology, which was developed at Langley, through 

flight tests of a modified F- li I research aircraft at NASA Dryden Research Center. 

Langley facilities that contributed to the F-ill program included the 7- by 10-Foot 

High-Speed Tunnel, the 4- by 4-Foot Supersonic Pressure Tunnel, the Unitary Plan 

Wind Tunnel, the 16-Foot Transonic Tunnel, the 8-Foot Transonic Pressure Tunnel, the 

26-Inch Transonic Blowdown Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, the 

20-Foot Vertical Spin Tunnel, the 16-Foot Transonic Dynamics Tunnel, the Fatigue and 

Fracture Laboratory, the Impact Dynamics Research Facility, the 12-Foot Low-Speed 

Tunnel, and radio-controlled drop models. 

62 General Dynamics F-]]] Aardvark
Langley Contributions to the F-1 11 

LANGLEY CONTRIBUTIONS TO THE F-I II 

The Variable-Sweep Wing The F-I II was the first production military aircraft to capitalize on years of Langley 

Concept research to develop a variable-sweep wing aircraft. Variable-sweep wings provide significant benefits to the aerodynamic performance of aircraft that operate over a wide 

range of altitudes and airspeeds. An excellent summary of the history of Langley's role 

in the development of this breakthrough concept was given by Edward C. Polhamus 

(contributor to variable-sweep research and the F-I 11 program) in his 1983 American 

Institute of Aeronautics and Astronautics (AIAA) Wright Brothers Lecture (ref. 4). 

As the advantages of wing sweep for enhanced aerodynamic performance became 

known near the end of World War II, designers considered several approaches to providing variable sweep for efficient characteristics at both low and high speeds. The German 

Messerschmitt P-1101 research configuration had provisions for three groundadjustable sweep angles however, the aircraft was only carried to the prototype stage 

and flight tests were never conducted. Although it never flew, the P-I 101 was captured 

and brought to the United States, where it was later evaluated by Bell Aircraft Corporation in a study that strongly influenced the design of the Bell X-5 research aircraft. 

The first wind-tunnel tests of variable-sweep concepts were conducted at Langley in the 

mid-1940's. These tests included the now familiar symmetric variable-sweep wing, as 

well as the variable oblique-wing concept (free-flight model tests by John P. Campbell). 

Researcher Charles J. Donlan, who would later become Deputy Director of Langley, initiated tests of an existing model of the famous Bell X-1 (first aircraft to exceed the 

sound barrier) in the Langley 300-MPH 7- by 10-Foot Tunnel in 1947 to explore the 

challenges of variable sweep. The results of the study, which used a single centerline 

pivot for the wing, clearly showed that such an arrangement resulted in excessive longitudinal stability and marginal maneuverability with the wings swept aft. To be successful, the variable-sweep concept would have to minimize the dramatic increase in 

stability. Several methods were explored, and it was concluded that some type of variable longitudinal translation of the pivot point was required—although this solution was 

undesirable from a weight and complexity perspective. 

Tune-lapse photograph of the Bell X-5 shows the wing at various sweep angles. 

General f)vnainics F- Ill Aardvark 63
1 d 

Langley Contributions to the F-1 11

The radieal British Swallow configuration in the Lang/er 16-Foot Transonic Tunnel

with variable sweep arrow wing and over and under wing-mounted engines. 

In the late 1940's, under somewhat reluctant Air Force sponsorship and based on the 

German and U.S. studies, the Bell X-5 became the Air Force and the National Advisory 

Committee for Aeronautics (NACA) workhorse for variable-sweep studies. Wing sweep 

on the X-5 could be continuously varied from 20 deg to 60 deg through the use of a 

translating wing-pivot mechanism. The X-5 configuration was tested in the Langley 

300-MPH 7- by 10-Foot Tunnel. the 8-Foot Transonic Pressure Tunnel. the 4- by 4-Foot 

Supersonic Pressure Tunnel, and the 20-Foot Vertical Spin Tunnel. The first flight of the 

X-5 was made on June 20. 1951. At about the same time, interest in variable sweep was 

growing in the United Kingdom. and discussions between Langley Assistant Director 

John Stack and the British resulted in exchanges of data and proposed cooperation for 

research efforts. 

In 1952, the Grumman XF-IOF variable-sweep aircraft began flight tests. (The XF-IOF 

had also been tested in the 7- by 10-Foot High-Speed Tunnel at Langley.) Although the 

aircraft was underpowered and subsonic, it demonstrated the aerodynamic performance 

advantages of variable sweep. However, the wing-pivot translation feature added considerable weight to the configuration, and the performance of the XF- I OF could not 

compete with the rapid increase in supersonic performance that was being demonstrated 

on most military aircraft of its size. 

At this point, military interest in the variable-sweep concept rapidly decreased. It 

appeared that supersonic flight could not be sustained with state of the art engines at that 

time. Also the heavy, complicated translating wing-pivot mechanism was not an acceptable penalty when compared with the performance of a moderately swept fixed wing. 

However, as has been the case throughout Langley's history, a few visionaries correctly 

anticipated the future military aircraft requirements for sustained supersonic flight and 

successfully advocated for fundamental research to continue to develop and optimize 

64 General Dynamics F- I// Aardvark
Langley Contributions to the F-i ii 

the variable-sweep concept. Led by John Stack and Charles Donlan. Langley researchers joined with the British in a North Atlantic Treaty Organization (NATO) sponsored 

cooperative study of variable-sweep concepts that included extensive tests in the 

Langley 7- by 10-Foot High-Speed Tunnel and the 16-Foot Transonic Tunnel. 

The British and Langley cooperative tests in 1958 included work on the British Swallow 

configuration, which was a radical tailless slender arrow-wing configuration with variable-sweep wings and pivoting wing-mounted engines. The Swallow exhibited numerous stability and control problems. Langley brought three variable-sweep configurations 

to the study, including two that used pivot locations in the fuselage near the trailing edge 

of the inner wing and folding tail control surfaces to maintain stability levels. 

Thomas A. Toll, responsible for the stability portion of the variable-sweep program. 

assigned William J. Alford, Jr. and Edward Polhamus to the task. In 1959 they arrived at 

the breakthrough solution, which was to locate the pivots of the movable wing panels to 

positions outboard of the fuselage. With this outboard wing-pivot arrangement, sharing 

of lift between the fixed inner wing and the movable outer wing panels minimized the 

movement of the aerodynamic center of lift. A fourth configuration, known as configuration IV, was added to the research program to confirm this design concept. The configuration was tested across the speed range in Langley tunnels with great success. 

Encouraged by their success, the Langley team conducted in-depth analyses of variablesweep aircraft representative of configurations for Navy and Air Force missions. Tests 

of all types—force and moment, dynamic, and free flight—were conducted in virtually 

all of the major tunnels at Langley. Variable-sweep configurations applicable to the 

Navy combat air patrol mission were studied in a program known as CAR and the Air 

Force tactical aircraft mission was the basis for configurations studied in a program 

known as TAC. Extensive wind-tunnel tests and analysis by Langley researchers had 

matured the variable-sweep concept. 

Alford and Polhamus became internationally recognized for their research on the outboard wing-pivot concept, and they mutually hold the U.S. patent on this revolutionary 

discovery, which has been successfully applied to numerous U.S. and foreign military 

aircraft. 

Configuration I % which was the Incakth long/I .Iwne.s L. Hassell, Jr nit/i a tree-/light LI I' model that 

model for variable-sweep technology. was flown in the Lang/er Full-Scale Tunnel. 

General Dynamics F-ill Aardvark 65
Langley Contributions to the F-1 11 

The Tactical Fighter In 1957, the U.S. Navy requested industry responses for the design of a low-altitude 

Experimental (TFX) Program strike fighter. John Stack briefed senior Navy managers that a proposed British lowaltitude strike fighter, the NA-39, would be much more advanced than the Navy aircraft. 

He also suggested the application of variable sweep to leapfrog the capabilities of the 

NA-39. Following briefings by Langley personnel to the Navy, the mission specifications for the new Navy fighter were expanded to include multimission capability with a 

requirement that variable-sweep applications be studied. The request for proposals went 

to industry in early December 1959 and set the stage for what would ultimately become 

the Tactical Fighter Experimental (TFX) Program. 

Meanwhile, the Air Force Tactical Air Command (TAC) Requirements Division at 

Langley Air Force Base (adjacent to the Langley Research Center) was attempting to 

define a replacement for the F-lOS fighter-bomber aircraft. TAC was interested in an aircraft that could carry nuclear weapons internally, fly transatlantic routes without refueling, operate from semiprepared fields in Europe, have a top speed of Mach number of 

2.5 at high altitudes, and fly at high subsonic speeds at low altitudes. The aircraft would 

perform a "low-low-high" mission, wherein it would cruise into the vicinity of the target 

at low altitudes and subsonic speeds, perform a low-altitude dash to the target at high 

subsonic speeds, and perform a high-altitude, long-range cruise back to base at subsonic 

speeds. The Mach number of 2.5 capability would be used for high-altitude engagements against enemy fighters. Initial analysis by industry of the request indicated that a 

fixed-sweep aircraft capable of meeting the requirements would weigh in excess of 

100,000 lb (too heavy for unprepared fields) and demand the attributes of low sweep for 

transatlantic flight, but high sweep for the high-speed requirements. TAC was therefore 

in a stalemate without a viable design approach to its requirements. 

John Stack approached the TAC planners in 1959 with the benefits of variable sweep to 

enable an aircraft to meet the requirements. The extended ferry range that is provided by 

variable sweep was of prime importance to TAC, since estimates indicated that transatlantic range might be possible. Together with the commander of TAC, Stack laid out a 

realistic set of aircraft performance requirements that included the desired low-altitude 

dash capability at high subsonic speeds. Unfortunately, as the requirements went 

through the TAC system for approval, the final specifications called for a 210-n-mi, sea 

level dash at a speed that had increased from a Mach number of 0.9 to a Mach number 

of 1.2. Upon learning of the supersonic low-altitude speed requirement, Langley quickly 

informed the Air Force that this capability was impossible to meet for the range specified. Nonetheless, TAC was committed to the unrealistic specification. (In flight tests of 

the F- il 1A in 1969, the actual low-altitude supersonic dash performance of the aircraft 

was only 30 n mi.) 

In 1960, the Air Force and the Navy were both attempting to develop new fighter aircraft. The Kennedy administration's Secretary of Defense, Robert McNamara, ordered 

the development of a single aircraft for both the Air Force and the Navy (to be led by the 

Air Force), called the Tactical Fighter Experimental (TFX). Mr. McNamara defined the 

basic mission requirements when the Air Force and Navy could not agree, and in October 1961, a request for proposals (RFP) was issued to industry. Boeing won all four 

stages of the competition that followed, but McNamara overruled the source selection 

board and decreed on November 24, 1962, that the General Dynamics and Grumman 

Team would build the TFX. 

Langley's variable-sweep wing concept was nationally recognized as the technical key 

that would unlock the capabilities of the TFX. McNamara said (ref. 27) 

66 General Dynamics F-Ill Aardvark
Langley Contributions to the F-1 11 

New developments in engine performance and in aerodynamics, particularly the variable-geometry wing concept evolved by NASA, now 

make it possible to develop a tactical fighter that can operate from 

aircraft carriers as well as from much shorter and cruder runways, 

and yet can carry the heavy conventional ordnance loads needed in 

limited war 

As an example of the plaudits given Langley for the variable-sweep contribution to the 

evolving TFX program, the following comments of editor Robert Hotz of the internationally acclaimed Aviation Week magazine appeared in the magazine on December 3, 

1962:

Underlying the whole TFX concept is one of the solid, basic technical 

explorations of the old National Advisory Committee for Aeronautics 

(NACA) that did so much to keep this country the international leader 

in supersonic aircraft development. Without the fundamental research 

into the variable-sweep wing and the detailed development of this 

principle by the Langley research laboratory group headed by John 

Stack, the current TFX concepts of both final competitors would have 

been impossible... When Congress convenes again and begins carping 

over the Fiscal 1964 NASA budget for aeronautical research, the full 

story of the Langley contributions to the TFX program should be hammered home as an example of how these research and development 

investments eventually pay substantial benefits. 

After the TFX contract was awarded, Langley, Ames, Glenn, and Dryden all supported 

the F- Ill development program. Because of the strong interest in this aircraft, and the 

large magnitude of NASA support, the program was rigorously managed and documented, beginning in November 1962. Mark R. Nichols, Laurence K. Loftin, Jr., 

Edward Polhamus, Jack F. Runckel, Theodore G. Ayers, and M. Leroy Spearman were 

the leaders and spokesmen for the F-I 11 support activities at Langley. In addition, 

Poihamus served as the Langley focal point for overall F-I 11 activities and spent considerable personal time in coordination of tunnel requests and NASA, industry, and 

DOD joint meetings. 

In 1963, political turmoil surfaced as a special Senate subcommittee chaired by Senator 

McClellan of Arkansas held hearings on the award of the TFX Program. This committee 

gathered a considerable amount of Langley data, briefings, and testimony during various 

phases of the hearings, which took place over several years. 

For the first 3 years of the F- 111 development program (1963 to 1965), a total of nearly 

20,000 hr of tests were conducted in NASA wind tunnels (about 15,000 hr at Langley). 

Over 15 wind tunnels were utilized, making the F-1 11 program the most extensive 

wind-tunnel support effort ever provided for one aircraft by NASA or the NACA. By 

1968, over 22,000 hr of tunnel tests had taken place at Langley. (In contrast, Langley 

expended 5,000 hr for development of the F-lOS.) The large number of test hours was 

the result of the multiple versions of the aircraft (F-lilA, F-IIIB, RF-111, and 

FB-I 11), the addition of wing sweep as a test variable, a vast number of external store 

configurations, and concentrated technical assaults on a multitude of problems—

especially the transonic drag issue. During the development effort, the Langley staff also 

participated in numerous F- Ill advisory and assessment teams and briefings for DOD, 

Congress, and industry. For example, Edward Polhamus presented the scope and results 

of the NASA effort to the McClellan Committee during its second session in 1970. 

General Dynamics F-li] Aardvark 67
A4 

Langley Contributions to the F-1 11

The first F- Il IA flew in December 1964, and the first F- Il I flew in May 1965. The 

most positive result from early flight evaluations was the very satisfactory behavior of 

the variable-sweep wing system. However, the aircraft were judged to be sluggish and 

underpowered. Furthermore, the engines exhibited violent stalling and surging characteristics. 

An outstanding, in-depth discussion of the details of the initiation and early years of the 

F- Ill development program is given in the book Illusions of Choice by Robert F. 

Coulam and Robert S. McNamara (ref. 27). 

AerodvnamicPeifrr,nance On December 19, 1962, representatives of General Dynamics and Grumman visited 

Langley for discussions of the supersonic performance of the F- Ill. The manufacturers 

were informed that the supersonic trim drag of the aircraft could be significantly 

reduced and maneuverability increased by selecting a more favorable outboard wingpivot location. Unfortunately, the manufacturers did not act on this recommendation, 

and it was subsequently widely recognized that the F-I 11 wing pivots were too far 

inboard. (It should be noted that the F-14 designers, aware of this shortcoming, designed 

the F-14 with a more outboard pivot location.) The F-1 11 subsequently exhibited very 

high levels of trim drag at supersonic speeds during its operational lifetime. 

In March 1963, the initial supersonic tests of the F- ill in the Langley Unitary Plan 

Wind Tunnel by David S. Shaw confirmed the Langley expectations of high trim drag at 

supersonic speeds. A month later, tests conducted by Theodore Ayers of a 1/24-scale 

F- Ill model at transonic speeds in the Langley 8-Foot Transonic Pressure Tunnel indicated that the transonic drag was considerably higher than General Dynamics predictions. Therefore, a large drag reduction had to be accomplished to meet mission 

requirements. Several discussions between Langley and General Dynamics were also 

held to define approaches to improve supersonic maneuverability. Langley continued to 

emphasize the importance of wing-pivot location and recommended a change in pivot 

location and a forward shift of the wing as a solution to the problem. It was decided that 

the modified wing suggested by Langley would be built and tested. Supersonic tests of 

the Langley wing modification indicated a large increase in maneuverability that would 

allow the F-I 11 to approach the proposed maneuverability levels. However, because of 

changes in maximum cross-sectional area, some transonic drag penalty would be 

Supersonic tests of the ear/v F- Ill design in the

Langley Unitary P/au Wind Tunnel in 1963. 

68 General Dynamics F-Ill Aardvark
Langley Contributions to the F-1 11 

expected with the modification. At a later meeting in June between Langley, the F- ill 

Systems Program Office (SPO), and General Dynamics, the positive results of the modified wing were discussed, but the F- Ill SPO expressed concerns over any possible 

transonic drag penalty, the engineering effort required for the change, and potential 

schedule slippage. The Air Force cancelled further studies of the wing modification. 

Meanwhile, a controversy erupted over the discrepancy of transonic drag estimates 

between the data obtained by Theodore Ayers in the Langley 8-Foot Transonic Pressure 

Tunnel and data obtained in the Cornell Aeronautical Laboratory 8-Foot Transonic Pressure Tunnel. The Langley staff investigated these differences and concluded that the 

lower drag measured in the Cornell facility was probably due to interference effects 

caused by an oversized model and the large, blunt support sting. Langley offered to 

investigate the problem by testing a mock-up of the Cornell support system. In October 

1963, special tests were conducted in the Langley 8-Foot Transonic Pressure Tunnel 

with a mock-up of the Cornell support system. The results of the test indicated a very 

large buoyancy effect, which accounted for the erroneous low transonic drag measurements in the Cornell tunnel. As Langley's support for the F- Ill continued, the staffs of 

the 16-Foot Transonic Tunnel and the 8-Foot Transonic Pressure Tunnel remained sensitive to wind-tunnel accuracies, and numerous tests were conducted with the same model 

in these two tunnels to establish confidence in the Langley projections of transonic drag. 

With a much higher level of drag established, emphasis was placed on reducing the transonic drag. The drag problem included large afterbody and nozzle drag components 

caused by high closure slopes (rapid variations in external aircraft contours), high drag 

components of the cockpit and inlets, and very high boundary-layer spillage drag. 

Dr. Richard T. Whitcomb and his staff conducted exhaustive tests of engine alignment, 

wing and tail twist, and even antishock bodies to reduce drag. Studies by Ayers concluded that the area ruling for the F- Ill was unsatisfactory. 

Also in 1963, an F- Ill aerodynamic consulting group consisting of Air Force, Navy, 

and NASA members met and concluded that the transonic aerodynamic performance of 

the F- Ill would be considerably below the requirements for the projected missions. 

Calculations based on Ayers' drag measurements predicted that the aircraft would only 

have a range of about 20 to 30 n mi for flight at low altitudes and speeds of a Mach number of 1.2, in contrast to the 220 n mi capability predicted by General Dynamics. Actual 

flight tests later verified Ayers' projection. The group, which included Polhamus and 

Spearman, recommended that aft-end modifications suggested by Langley should be 

studied for transonic drag reduction. 

As concern over the aerodynamic performance of the F- Ill increased, Charles Donlan 

and Edward Polhamus briefed the Assistant Secretary of the Air Force in April 1964 on 

the situation. They recommended that the staff of the Langley 16-Foot Transonic Tunnel 

define the benefits of Langley conceived aft-end modifications. It was also suggested 

that the wing with the longer span of the Navy aircraft be used on the Air Force aircraft. 

Polhamus and Spearman also briefed Air Force General Schreiver and Navy Admiral 

Schoech a month later on the transonic drag problem. 

During May 1965, representatives of Grumman visited Langley several times to discuss 

methods of improving the acceleration and maneuverability of the Navy F-I 1 lB. 

Modifications considered by Grumman included several of the early Langley suggestions, such as a modified wing and pivot location, a straightened tailpipe, and an 

improved interengine fairing. In addition, Grumman examined a modified horizontal 

tail, alternate missile arrangements, and an aft-fuselage modification. Although these 

modifications never came to fruition for the F- Il [B, the discussions had a large impact 

General Dynamics F-Ill Aardvark 69
Langley Contributions to the F-1 11

on the later design of the F-14 by Grumman, which became an outstanding Navy 

aircraft. 

Langley also assessed the effect of the bomb bay cavity and doors on directional stability in the Unitary Plan Wind Tunnel; the impact of missile carriage at supersonic speeds 

in the Unitary Plan Wind Tunnel; the aerodynamic damping during subsonic, transonic, 

and supersonic flight in the 30- by 60-Foot (Full-Scale) Tunnel, the Unitary Plan Wind 

Tunnel, and the 8-Foot Transonic Pressure Tunnel; the transonic and supersonic flight of 

the strategic bomber (FB-11l) and reconnaissance (RF- lll) versions of the F- Ill in 

these same wind tunnels; and the development of the F- il I by the Navy, until it was 

cancelled on July 10, 1968. Over 25 test entries in the Unitary Plan Wind Tunnel were 

made for the F- Ill variants. 

Propulsion Integration Hot-jet tests of a 1/9-scale ejector nozzle at transonic speeds were conducted in April 

1963 in the Langley 16-Foot Transonic Tunnel to begin what would become an 

extensive series of F-ill propulsion integration studies. (The staff ultimately conducted 17 entries of F- ill models or components during the program.) Later that year, a 

1/6-scale inlet model was tested to determine the effects of aircraft nose shape (Air 

Force and Navy) and engine inlet spike configuration. Following this test entry, the inlet, 

cowl, and spike geometry were revised. 

In 1964, General Dynamics, in consultation with the 16-Foot Transonic Tunnel staff, 

completed fabrication of a 1/12-scale model designed to investigate propulsion-airframe 

integration characteristics. This model represented the most realistic and complex 

model of a military fighter ever tested in the 16-Foot Transonic Tunnel. The model had 

multiple strain-gage balances and balance arrangements to independently measure 

thrust, drag, and thrust minus drag. It also contained three independently controlled 

internal flows to simulate the F- Ill blow-in-door ejector exhaust system: a hot hydrogen peroxide primary-jet flow system, a high-pressure air secondary-flow system, and a 

low-pressure air boundary-layer bleed system. In addition, the model contained fully 

variable, aerodynamically actuated blow-in doors and ejector shroud flaps on the nozzles. Tests in 1964 on this model in the 16-Foot Transonic Tunnel indicated a significant 

nozzle-thrust deficiency that was associated with an adverse fuselage afterbody flow 

field. At the end of the year, additional tests of the hot-jet model were directed at a wide 

range of ejector nozzle geometries in an attempt to solve nozzle-thrust and flutter problems. Langley also initiated studies directed toward reducing the large base drag associated with the short interengine fairing (interfairing). Relatively large drag improvements 

were obtained with a long interfairing design conceived by Langley. 

Unfortunately, the naval F- lI I configuration was too long to met the requirements for 

aircraft carrier elevator spotting (compatibility of the aircraft dimensions with the elevator on the aircraft carrier that transports aircraft to and from the flight deck and the lower 

hangar area). Follow-on tests of the 1/6-scale inlet model during 1964 included studies 

of the effects of an extended nose (for the RF-1 11), a weapons bay pod, and bleed doors. 

Jack Runckei and Edward Polhamus briefed Air Force management in October 1964 on 

the ejector nozzle problems of the F- ill. Since the nozzle problem was associated with 

the aircraft aft-end flow field and since the aft-end drag was relatively high, the Langley 

representatives recommended that improvements to the back end of the aircraft be 

investigated as a high priority item. Runckel subsequently became a key figure in a joint 

F- ill nozzle committee that included the F- ill SPO, the Bureau of Naval Weapons, 

Pratt and Whitney, General Dynamics, and NASA. In a meeting of this committee in 

70 General Dynamics F-Ill Aardvark
Langley Contributions to the F-i ii 

1,i/ei leLs o/ an F-Ill model in the Langle' 16-Foot Transonic Tunnel. 

January 1965, Runckel proposed that a truncated, concave base interfairing be investigated as a means of reducing drag at transonic speeds, while still meeting the length 

restriction imposed by the F- ill B naval version. 

In February 1965, tests of the 1/12-scale hot-jet model indicated large improvements in 

transonic performance because of airframe changes in the region between the nozzles. 

This model configuration had the best aerodynamic characteristics to date in the program. A few months later, a meeting was held at Langley with representatives from the 

F- Ill SPO. the Bureau of Naval Weapons, General Dynamics, Grumman. Pratt and 

Whitney. and Langley. At that meeting, it was agreed that emphasis should quickly 

move to reducing transonic drag by developing an optimum engine interfairing and 

speed bumps (additional area added to shape the aircraft to comply with Whitcomb's 

area rule). In December 1965, the hot-jet model was tested to develop the interfairing 

and define a configuration that would be flight tested in early 1966. The aft-end modifications from this effort were ultimately adopted and resulted in a significant improvement in transonic drag. 

The early F-I I IA exhibited numerous engine problems, including compressor surge 

and stalls. NASA was a participant in finding solutions to these problems, as its pilots 

and engineers flew test flights of the aircraft to determine inlet pressure fluctuations 

(dynamics) that led to these events. Eventually, as a result of NASA, Air Force, and 

General Dynamics studies, the engine problems were solved by a major inlet redesign. 

The F- Ill program brought many difficult challenges in propulsion-airframe integration to the staff of the Langley 16-Foot Transonic Tunnel. These problems were 

extremely complex and demanded timely solutions in a highly visible, controversial 

national program. However, the staff responded with outstanding technical expertise and 

innovation. By the end of 1967, 19 F-I 11 related model entries had been completed in 

the 16-Foot Transonic Tunnel, and over 283 configurations were investigated during 

12.5 months of tunnel occupancy. This effort ultimately required participation of almost 

every 16-Foot Transonic Tunnel staff member. Staff members who made significant 

General Dvna,nics F-ill Aardvark 71
Langley Contributions to the F-1 11

contributions to the F-I 11 program included Richard J. Re. Odis C. Pendergraft, Jr.. 

Richard G. Wilmoth, Charles E. Mercer, Francis J. Capone. and Bobby L. Berrier. As a 

result of the F-I 11 program, the research capability on aft-end transonic drag problems 

greatly increased. This research capability contributed to all subsequent highperformance military aircraft and placed Langley in a position of world leadership in 

this critical technical area. 

HighAngleo:A ttack - - - Initial free-flight model tests of the F-Ill configuration were led by Peter C. Boisseau 

Characteristics in the Langley 30- by 60-Foot (Full-Scale) Tunnel in October 1964. During the flight 

tests, the wing sweep was varied from 16 deg to 72.5 deg. In December, the model was 

flown to determine the effects of stability augmentation in roll and pitch for the clean 

and landing configurations. The flight tests were extended to high angles of attack, 

including the stall. 

When the model was flown to high angles of attack with the wings at the SO-deg and 

72.5-deg sweep conditions, the model exhibited a sudden, uncontrollable yaw divergence prior to maximum lift. General Dynamics personnel, including the test pilot who 

was scheduled to make the first high-angle-of-attack flights with the aircraft, witnessed 

the tests. 

The model free-flight tests also indicated an unusual unsteadiness in lateral behavior at 

moderate angles of attack for the landing configuration. The unsteadiness was 

apparently caused by an unsteady flow off the wing root glove (the fixed, highly swept 

inner wing). In early 1965, extensive flow visualization tests were made in the Langley 

12-Foot Low-Speed Tunnel in an effort to change the vortex-flow field set up by the 

glove and to delay separation on the inner wing for the landing configuration. This work 

Time-lapse photograph of the F- I / IA free-flight model at several 

wings sweep angles during tests in the Langle y Full-Scale Tunnel. 

72 General Dynamics F-I I I Aardvark
Langley Contributions to the F-i ii 

included an investigation of a rotating glove vane, which was then evaluated during the 

free-flight model test in the Full-Scale Tunnel. The glove vane cured the roll unsteadiness previously noted and was subsequently incorporated into the F-111 landing 

configuration. 

As F- Ill operations expanded within the Air Force in the late 1960's, a rash of incidents involving unexpected departures from controlled flight during maneuvers at high 

angles of attack occurred. The Air Force requested industry and NASA assistance in 

analyzing and solving the problem, which was viewed as a significant flight safety issue. 

Langley researchers Joseph R. Chambers and James S. Bowman, Jr. served on an Air 

Force, industry, and NASA committee that identified a shortcoming in the F- lI 1 flight 

control system that promoted the unintentional departures. The F-111 had been 

designed with a g-command flight control system that provided g-forces in direct proportion to the deflection of the pilot control stick. However, in providing the pilot with 

the level of g-force, the system would increase the angle of attack of the aircraft. Unless 

the pilot was monitoring the angle of attack, the aircraft could enter a range of high 

angles of attack where a loss of directional stability resulted in an unintentional yaw 

departure and spin entry. These findings led to an Air Force program in 1973 to develop 

a stall inhibitor system (SIS) for the F- Ill. Langley participated in the design and analysis of this system. The SIS was designed to automatically monitor and limit the angle 

of attack of the aircraft during flight maneuvers and was incorporated into the F-1 11 

fleet. 

Spin Recover)' Another area of controversy within the F- 111 development program arose in the early 

1960's—in the area of spin and spin recovery technology. The conventional approach to 

assessing and improving spin characteristics of new military aircraft was to conduct 

tests of dynamically scaled models in the Langley 20-Foot Vertical Spin Tunnel to determine spin and spin recovery characteristics, as well as the size of the emergency parachute required for spin test aircraft. In conjunction with these tests, radio-controlled 

drop-model tests were conducted to assess spin-entry tendencies and to assess the effectiveness of out-of-control recovery procedures. 

For the F- Ill program, General Dynamics proposed to assess spin recovery characteristics with analytical methods, in lieu of the traditional dynamic scale model tests. In 

addition, General Dynamics requested over 1,000 hr in Langley tunnels to provide the 

data required for the proposed study. Langley's reaction to this proposal was extremely 

negative because analytical procedures for spin studies had not been validated, and in 

the opinion of James Bowman and the Spin Tunnel staff, could not be trusted for such 

an important aircraft program. However, the Air Force accepted Langley's recommendation to-terminate the General Dynamics plans for the analytical approach and elected 

to continue with the traditional Spin Tunnel and drop-model tests. 

At the request of Langley, a 1/24-scale model of the F-I 11 was tested in the Ames 

12-Foot Pressure Tunnel in early 1964 to examine Reynolds number effects at high 

angles of attack and sideslip. The results of these tests necessitated forebody modifications for the spin tunnel model to simulate, at the low Reynolds numbers of spin tunnel 

investigations, the cross-flow characteristics approximating the Reynolds number conditions of full-scale flight. 

During the period from October 1964 to May 1966, extensive spin tunnel tests were 

made by James Bowman and Louis White on 1/40-scale models of the F-1 1 IA and 

F-I II B aircraft to determine spin and recovery characteristics. Tests were conducted for 

General Dynamics F-il] Aardvark 73
Langley Contributions to the F-1 11

wing-sweep angles of 20 deg. 26 de-, 50 deg. and 72.5 deg. The results of the tunnel 

tests indicated that the F-I II would exhibit several spin modes, including steep oscillatory spins from which recovery could be accomplished and a fast flat spin from which 

recovery was marginal or impossible using aerodynamic controls. The flat spin was 

especially stable. A number of radical approaches to breaking the spin were attempted, 

including sweeping the wings forward and rearward during the spin. For these tests, the 

model was equipped with a small electric motor that was remotely actuated to drive the 

wing-sweep angle. However, the flat spin could not be slowed or stopped using this 

technique. All of these spins (including the flat spin) were subsequently encountered in 

F-I 11 spin tests at Edwards Air Force Base and in fleet operations. Bowman served on 

several spin accident investigation committees formed by the Air Force. 

Extensive studies were made of the spin entry and post-stall motions of the F- Ill A by 

Charles E. Libbey with two 1/9-scale helicopter drop models. Over 50 successful drops 

were made with wing sweeps varying from 16 deg to 72.5 deg. Results of these tests 

showed that certain pilot inputs following the yaw departure at high angles of attack (as 

previously discussed for the wind-tunnel free-flight model) would promote the fast flat 

spin. These results were discussed with Air Force representatives for inclusion in the 

pilot handbook procedures for avoiding this extremely dangerous condition. 

Several F-I 11 aircraft were lost in spin accidents during fleet operations: however, the 

subsequent implementation of the SIS prevented stalls and eliminated spins as an operational concern. 

During the late 1960's. Langley researcher William P. Gilbert conducted fundamental 

research on automatic spin prevention systems for fighter aircraft. Gilbert's work was 

stimulated by the fact that flight control systems were beginning to use flight parameters 

(such as angle of attack and yaw rate) that would permit the mechanization of spin prevention for routine operations in highly redundant systems. Previously, the concept of 

The F- 11/A divj model prior to launch/mm a helicopter/am a spin-entr y text. 

74 General Dvnan,ics F- Ill Aardvark
Langley Contributions to the F-1 11 

automatic spin prevention was a highly desirable concept, but the mechanization would 

have required a special system that might be prone to failure and would only be utilized 

on very rare occasions. With the emergence of the new operational control system components. Gilbert became interested in demonstrating the effectiveness of spin prevention 

systems. Following a series of analytical studies, Gilbert teamed with Charles Libbey to 

implement and test the prototype system on an F-I ii drop model. With the system 

engaged, the spin-prone model could be maneuvered to extreme angles of attack without entering a spin, even with full prospin control inputs from the pilot. 

On one occasion, Gilbert briefed NASA Administrator. Dr. James Fletcher. on the very 

positive results of his study. Fletcher praised the work as a forerunner of future systems 

that would enable carefree maneuvering of military aircraft. Gilbert's work with the 

F- ill model represented one of the first efforts to develop the highly sophisticated control systems that are now used in virtually every domestic and foreign fighter aircraft to 

prevent spins during strenuous air combat maneuvers. 

Flutter Tests In early 1963, flutter trend models were tested in the Langley 26-Inch Transonic Blowdown Tunnel to determine the general flutter boundary for the isolated wing and tail surfaces of the F-I 11. Several tests were conducted in this facility, before a dummy 

(stability) model of the complete F-ill configuration was tested in the Langley 16-Foot 

Transonic Dynamics Tunnel (TDT) in August 1963. The initial TDT tests were to check 

out the wind-tunnel suspension system for future flutter tests. Subsequent tests of the 

isolated wing and horizontal tail in the Blowdown Tunnel revealed that the horizontaltail design had an inadequate margin of safety for flutter at low supersonic speeds, and 

the geometry of the F- Ill tail configuration was changed. 

Flutter clearance tests of the F- ill empennage model and a 1/8-scale complete flutter 

model of the F- Ill were made in the TDT during February 1965. Flutter tests continued 

through 1965 and subsequent years to examine the effects of a number of external store 

configurations on flutter boundary. External stores for the F-I II included combinations 

F- Ill niodel in ilie I,iinIev I O- hnn /nhILnnhj( I)v,ui,iii x Ini,ul

in 1963. (Tail surtuces were later changed to avoid flutter.) 

General Dynamics F-Il / Aardvark 75
.4 

Langley Contributions to the F-i ii

FR- / / / flutter model illustrating the wide wupe at

eutenuil lures that were tested in the program. 

of bombs, missiles, and fuel tanks. The wing pylons pivoted as the wings swept hack, 

keeping the ordnance parallel to the fuselage. F-I II tests led by Charles L. Ruhlin, 

Maynard Sandford. and Irving Abel ultimately included 13 test entries in the TDT of 

versions such as the F- Il IA. F-I I lB. and FB-I II. 

Crew Escape Module The two crew members in the F- Ill sat side by side in an air conditioned, pressurized 

cockpit module that served as an emergency escape vehicle and a survival shelter on 

land or in water. In emergencies, crew members remained in the cockpit, an explosive 

cutting cord separated the cockpit module from the aircraft, small rocket engines ejected 

the module from the aircraft, and the module descended by parachute. The ejected module included a small portioii of the inner wing glove to stabilize it during aircraft separation. Air bags cushioned the landing impact and helped to keep the module afloat in 

water. After separation, the air bags were inflated with nitrogen (stored behind the 

pilot's seat). 

The module could be released at any speed or altitude—even under water. For underwater escape, the air bags raised the module to the surface after it had been severed from 

the plane. Initial concerns for the module design centered on potential windbIast however, this threat was properly addressed in the design. Unfortunately. impact of the level 

of acceleration on the crew during landing proved to be a problem. The nominal descent 

rate of the module on the parachute was about 32 ft/sec. 

As a result of a number of hack injuries to crew members during use of the recovery system and undesirable postinipact overturning, the Air Force requested that the NASA 

Crash Dynamics Group conduct drop tests of the F-I II crew escape module at the 

unique Langley Impact Dynamics Research Facility (IDRF). The facility had initially 

been used to train astronauts for moon walks as part of the Apollo Program. when it was 

known as the Lunar Landing Training Facility. After the successful Apollo Prograni. the 

Langley staff recognized the value of the tall, large gantry structure for simulating 

ground impact of large aircraft structures and full-scale general aviation aircraft and 

rotorcraft. The Air Force provided F- Ill crew escape modules and air bags for the tests 

that were conducted at the facility. 

76 General Dynamics f_J 1/ Aardvark
Langley Contributions to the F-1 11 

Huey D. Carden and Lisa E. Jones led the F-I II module tests at Langley. The tests 

(between 60 to 70 drops) spanned from the early 1980's to 1995. The objectives of the 

tests were to assess 

• Impact loads that were generated by the air bag attenuation system 

• Structural loads that were transmitted to the seats and occupants 

• Module stability under various impact attitudes which could exist due to drift from 

winds 

• Design changes to the air bag attenuation system or seats. 

Tests with controlled pitch, yaw, and roll orientations of the module relative to the forward velocity vector were conducted to account for various attitude envelopes of the 

module during descent. Additional vertical tests were also performed. Impact velocities, 

structural impact loads, air bag pressures, and loads transmitted to the seats and dummies representing the crew were measured and provided to the Air Force for 

assessment. 

Additionally, impact and postimpact behavior of the module was provided via extensive 

onboard and ground-based cameras, which also provided module stability information. 

The last series of drop tests in 1995 assessed the performance of and qualified an 

entirely new air bag design that was required for a new parachute design. 

The results of the Langley tests were analyzed and provided to the Air Force and the 

industry contractor for continual refinement of the system. As a result of the data provided to the Air Force, load attenuating crew seats were included in the F-I II and air 

bag and blowout plug design changes were made in the original air bags. Various 

changes to the module led to the design of a new air bag system, which was tested for 

qualification on the F-1 II in the final series of tests prior to the retirement of the U.S. 

F- Ill fleet.

E 

/:_ 111 crew escape iu/uIt , (/u ,in' !es 1.s cli rice 

La,is.,'Iev Impact D ynamics Research Facility. 

General Dynamics F- ill Aardvark 77
Langley Contributions to the F-i ii 

Wing Box Problems The F- Ill airframe utilized a significant amount of high-strength D6ac steel in the wing 

carry-through structure. This component was heat treated to a tensile strength of 

220,000 psi and designed for -3g to 7.33g with design flight life goals of 4,000 hr and 

10 years of service. However, a full-scale static test program that was conducted over a 

6-year period encountered several failures, including a failure at the wing-pivot fitting. 

Various modifications, including the first use of an advanced boron-reinforced composite doubler to reduce stress levels, coupled with an extension of the structural tests to 

40,000 hr, were believed to have provided for 10,000 hr of safe operations. 

In December 1969, an F-I 11 experienced a catastrophic wing failure during a pull-up 

from a simulated bombing run at Nellis Air Force Base. This aircraft only had about 

100 hr of flight time when the wing failed. The failure originated from a fatigue crack, 

which had emanated from a sharp-edged forging defect in the wing-pivot fitting. As a 

result of the accident, the Air Force convened several special committees to investigate 

the failure and recommend a recovery program. James C. Newman, Jr. and Herbert F. 

Hardrath represented Langley on the recovery team deliberations, and along with 

Charles M. Hudson and Wolf Elber, they conducted fatigue crack growth and fracture 

tests on specimens made from the D6ac steel used in the aircraft. These tests were conducted in the Langley Fatigue and Fracture Laboratory under conditions that simulated 

aircraft operations. The original material had low fracture toughness due to the heattreatment process. The committee recommended that every F-I 11 be subjected to a lowtemperature proof test. This proof-test concept had been developed and successfully 

used in the Apollo program, as well as other missile and space efforts. To screen out the 

smallest possible flaw size, the F-I 11 full-scale proof tests were conducted at temperatures of about -40° F, where the fracture toughness of the D6ac steel was lower than the 

fracture toughness at room temperature. The heat-treatment process was also corrected 

to provide improved toughness for the D6ac material in newer aircraft. A decade later, 

the same material with improved toughness was also successfully used in the Space 

Shuttle solid rocket boosters. As a result of the revised proof-test approach and the 

improved toughness material, there were no F-I 11 aircraft lost due to structural failure 

in almost 30 years of operations before the aircraft was retired from service in 1996. 

The F- ill failure was most responsible for the U.S. Air Force developing the damagetolerant design concept, where flaws, such as a 0.05-in, crack, are assumed to exist in 

critical aircraft components. The structural components must then be tolerant of these 

defects during flight conditions. This concept relies on fatigue crack growth and fracture 

criteria to establish an inspection interval to insure the safety and reliability of the 

aircraft. 

The Transonic Aircraft Richard Whitcomb's pioneering research and development efforts on supercritical airTechnology (TACT) Program foils for enhanced transonic performance, which began at Langley in 1964 and continued until the 1980's, included extensive wind-tunnel and flight evaluations for potential 

military applications. After flight tests of a modified F-8 Crusader validated the benefits 

of supercritical wing technology that had been predicted by theory and wind-tunnel 

experiments for potential civil applications, NASA and the Air Force became interested 

in assessing the benefits of supercritical wing applications to high-performance aircraft 

during transonic maneuvers. Significant increases in the drag-divergence Mach number, 

the maximum lift coefficient for buffet onset, and the Mach number for buffet onset at a 

given lift coefficient were demonstrated for the supercritical airfoil when compared with 

a NACA 6-series airfoil of comparable thickness. Theodore Ayers, in cooperation with 

General Dynamics, conducted exploratory tests in the Langley 8-Foot Transonic 

78 General Dynamics F-il] Aardvark
too 

Langley Contributions to the F-1 11 

Pressure Tunnel in 1966 to test the effects of a slotted supercritical airfoil on a 

1/15-scale model of the F-Ill with the existing flap system. Although the overall results 

were not satisfactory because of high subcritical drag levels, the results encouraged 

additional studies of an integral or unslotted supercritical airfoil. Tests of a 1/24-scale 

F- 111 model showed significant benefits to drag-divergence Mach number, maneuver 

drag, and buffet onset characteristics. These tests also spurred additional interest by 

General Dynamics in potential improvements of the F- Ill. 

Following these exploratory tests at Langley. interest in supercritical applications continued to increase and a joint NASA and Air Force study that included ground and flight 

activities was proposed. Specific objectives of the study included the effects of supercritical wings on transonic drag, buffet onset and magnitude, and handling qualities. In a 

study known as the Transonic Aircraft Technology (TACT) Prograni, several candidate 

military aircraft were examined for potential modifications to provide flight validation 

of supercritical wing military applications. 

The program was ultimately based on the application of supercritical technology to the 

F- Ill configuration, which had outer wing panels that could be relatively easily 

replaced with modified supercritical sections. In addition, the potential retrofit of 

advanced wings to enhance performance of the F- 111 fleet was an interest in some areas 

of the Air Force. The TACT Program, which started in 1969, included NASA Langley. 

Dryden. and Ames Research Centers, and the Air Force Flight Dynamics Laboratory. 

Theodore Ayers served as the Langley focal point for TACT activities, which included 

extensive experimental development work of the modified wing in the 8-Foot Transonic 

Pressure Tunnel by Ayers and James B. Hallissy (with considerable oversight and participation from Dr. Whitcomb), tests of a propulsion model in 1973 in the 16-Foot Transonic Tunnel by Charles Mercer, and flutter tests led by Charles Ruhlin and Maynard 

Sandford in 1971 in the 16-Foot Transonic Dynamics Tunnel. 

.h,nie.s B. HaIIi.s,sv in,spects the I- iii T1 (T model in F- / 11 TACT model in the Langley unitary 

the Lan glev 8-Foot Transonic Pressure Tunnel. Plan Wind Tunnel for supersonic tests. 

General Dynamics F- 111 Aardvark 79
'I 

I 

Langley Contributions to the F-1 11

F- Ill TACT model mounted for flutter tests in the Lang/er

16-Foot Transonic Dvnamus Tunnel in 1971. 

The NASA and Air Force F-Il / TACT aircraft during flight tests at Drvden. 

The F-i ii TACT aircraft began flight tests at Dryden in 1972. Flight-test results showed 

that the supercritical wing generated up to 50 percent more lift during maneuvers than 

the conventional F- Ill wing and significantly delayed the onset of wing buffet to higher 

angles of attack. Special flight tests were also conducted to demonstrate that the carriage 

of external stores on the wing pylons did not significantly degrade the benefits of the 

supercritical wing. Although the Air Force decided not to retrofit the F-I 11 fleet, the 

supercritical wing technology had dramatically demonstrated its benefits for incorporation into future military aircraft. 

80 General Dvna,nics F- Ill Aardvark
P 

Langley Contributions to the F-1 11 

The Mission Adaptive Wing In 1976. Theodore Ayers transferred from Langley to Dryden, where he accepted a posi-

(MAW) Program tion as Director for Aerodynamics. Ayers continued his interest in advanced wing configurations. Working with his technical peers within NASA, DOD, and industry, he 

advocated for another important flight program with the modified F- Ill at Dryden. 

After the TACT Program ended in the 1980's. the Air Force and NASA engaged in a 

new technology development program known as Advanced Fighter Technology Integration (AFT!). One element of this joint program was the modification and flight tests of 

the F-I 11 TACT aircraft with a Mission Adaptive Wing (MAW). The MAW used flexible wing skin and internal hydraulic control mechanisms to recontour the wing shape as 

a smooth variable-camber wing for varying flight conditions. The objective was to provide the technical confidence for significant performance improvements with a wing 

system that varied the wing contour in flight as a function of pilot inputs, flight conditions, and structural loads. The wing box of the existing TACT aircraft was equipped 

with flexible wing leading and trailing edges. A high-lift section was used for low-speed 

landing conditions, and the wing was recontoured to a supercritical shape for transonic 

flight and adjusted to a symmetrical section for supersonic flight. Boeing. Grumman. 

and General Dynamics bid on the request for proposals for the aircraft modification. 

Tests of the competing configurations in the 8-Foot Transonic Pressure Tunnel were 

conducted by James Hallissy. Boeing was awarded the contract in 1979. The MAW Program was managed by the Flight Dynamics Laboratory of the Air Force Wright Aeronautical Laboratories with Dryden as the responsible flight-test organization. Langley 

supported this activity with exploratory tests of smooth variable-camber concepts in the 

8-Foot Transonic Pressure Tunnel, which were conducted by James C. Ferris. Langley 

also actively participated in the flight-test program, including conducting additional 

tests with a 1/24-scale model. Langley personnel were also assigned temporarily at 

Dryden during the flight program. The F- Ill MAW flight research was conducted from 

1985 to 1988 and included an assessment of automatic camber modes. 

The F-Ill Mission Adaptive Wing (MAW) aircraft during flight tests at Drvden. 

General Dynamics F- i/i Aardvark 81
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Highlights of Research by Langley for the A-6 

Grumman A-6 Intruder 

SPECIFICATIONS 

Manufacturer 

Grumman 

Date in service 

A6A 196 

A6E 1972 

Type 

Attack 

Crew Z4 Two 

Engine r 

Pratt & Whitney J52-P813 .....----

USERS 

U.S. Navy and U.S. Marine 

Corps (retired in 1997) 

DIMENSIONS

Wingspan............ 53.0 ft 

Length .............. 54.7 ft 

Height .............. 15.5 ft 

Wing area...........529 sq ft HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE A-6 

WEIGHT

I. Wind-tunnel studies of aerodynamic and thermal characteristics in the Langle y 16- Empty ............ 28.000 lb Foot Transonic Tunnel provided data for selection of the configuration for the fuse- . 

Gross ............. 58,600 lb

lage-mounted speed brakes. 

PERFORMANCE 2. Tests of A-6 configurations in the Langley 20-Foot Vertical Spin Tunnel determined 

Max speed ......... 563 knots that spin recovery characteristics were significantly enhanced by enlarging the rudder and increasing the deflections of the horizontal tail and rudder. 

3. Flutter clearance tests for a composite wing for the A-6E were successfully conducted in the Langley 16-Foot Transonic Dynamics Tunnel.

Grumman A-6 Intruder 83 
Highlights of Research by Langley for the A-6 

The Grumman (now Northrop Grumman) A-6 Intruder was an all-weather, two seat, 

subsonic, carrier-based attack aircraft. Designed in the late 1950's, the Intruder played a 

critical role in the Vietnam War with over 35,000 combat sorties by 1973. The last version of the aircraft, the A-6E, was widely regarded as the best all-weather precision 

bomber in the world. As an example of its effectiveness, during the strike on Libyan terrorist-related targets in 1986, A-6E Intruders penetrated sophisticated Libyan air 

defense systems, which had been alerted by the high level of diplomatic tension and 

rumors of impending attacks. Evading over 100 guided missiles, the strike force flew at 

low altitude in complete darkness and accurately delivered laser-guided and other ordnance on target. Composite wing replacements and upgraded systems and weapons 

improvement programs maintained the A-6's combat capability until its retirement from 

the fleet in early 1997. 

Langley's contributions to the A-6 Program began in 1959. Studies of the aerodynamic 

and thermal characteristics of candidate designs for the fuselage-mounted speed brakes, 

which were located adjacent to the hot efflux of the turbojet engines, were conducted in 

the Langley 16-Foot Transonic Tunnel. Tests were also conducted in the 20-Foot Vertical Spin Tunnel to determine the spin and recovery characteristics of the aircraft and to 

determine the size of parachute required for the spin test aircraft. Initial Langley tests 

indicated that spin recoveries were significantly improved with an enlarged rudder and 

more deflection angles for the horizontal tail and rudder. The rudder was enlarged, and 

the control system was modified to provide the extended deflections. Follow-on spin 

tests were also conducted over the years to determine the effects of new external stores 

and new weapons on spin recovery characteristics. 

Arguably, the most important contribution of Langley to the A-6 Program was a series 

of two test entries in the Langley 16-Foot Transonic Dynamics Tunnel (TDT) to ensure 

flutter clearance for an advanced composite wing that was incorporated into the A-6E 

fleet to extend the fatigue life and capabilities of the aircraft. Initial tests in the TDT 

ended in flutter failure of the model wing, but a revised wing design passed flutter demonstration requirements and permitted the fleet to utilize the advanced wing. 

84 Grumman A-6 Intruder
A 

Langley Contributions to the A-6 

LANGLEY CONTRIBUTIONS TO THE A-6 

Speed Brake Studies In May 1959, a team from Langley and Grumman led by Langley researcher Charles E. 

Mercer conducted powered-model tests in the Langley 16-Foot Transonic Tunnel to 

determine the optimum configuration for fuselage-mounted speed brakes—thrust spoilers 

for the A-6 (then designated the A2F- I). The speed brake panels were located immediately behind the engine exhaust nozzles on the rear fuselage, which caused concern over 

the aerodynamic loads and the thermal environment of the speed brakes during highpower conditions. To further complicate the engineering issues, the original aircraft also 

had a tilting tailpipe to increase lift at low speeds and thereby reduce approach speeds. 

The test examined several candidate configurations, including a perforated panel design, 

which was subsequently incorporated into the early A 6A and EA 6A. Later variants of 

the A-6 used symmetrically deflected split ailerons at the wingtips for speed brakes, and 

the original speed brake panels were inactive or deleted. 

The A-6 prototype made its first test flight in April 1960. The Navy was satisfied with 

the 90-knot approach speed, so the deflectable nozzle design feature was eliminated in 

production aircraft. The Langley staff, however, continued research on thrust vectoring, 

which later contributed to more advanced fighter designs.

Powered-model tests in the Langley 16-Foot Tnuinih 

Tunnel evaluated several speed brake configurations. 

Spin Tunnel Tests Initial evaluations of the spin and spin recovery characteristics of the A-6 by Henry A. 

Lee in the Langley 20-Foot Vertical Spin Tunnel indicated that spin recoveries could be 

significantly enhanced by an enlarged rudder and by additional deflections of the rudder 

and horizontal tail. The original A-6 design had incorporated extended throws on the 

rudder and horizontal stabilizer for the power approach configuration, so an assist spin 

recovery switch was installed so the pilot could extended deflections for the cruise 

Griininian A-6 Intruder 85
Langley Contributions to the A-6

configuration. The Langley tests determined that the greater horizontal-tail deflection 

angle (trailing-edge up) provided a better flow field on the vertical tail during spins, 

thereby increasing the effectiveness of the rudder to terminate the spin. The rudder of 

the production aircraft was enlarged as a result of these tests. 

The Composite Wing By the rnid-1980's. the A-6 was beginning to show its age. The accumulated stress of 

high-g catapulted takeoffs and arrested landings on carriers and the long exposure to salt 

water were beginning to take a toll on the life of airframe components. Studies were 

underway for a new wing design, and inspections of the A-6 structure revealed major 

corrosion problems. In January 1987, a fatal accident resulted in an investigation of the 

structural health and projected lifetime of the A-6 fleet (ref. 5). 

At the time of the accident. U.S. Marine Corps First Lieutenant Bob Pandis and his 

bombardier/navigator. Lieutenant Colonel John Cavin. were practicing dive-bombing 

missions at the El Centro Naval Base in California. During a 40-deg diving run at about 

500 knots, the left wing of their A-6E broke off the aircraft at an altitude of about 

8.000 ft and the aircraft began to spin wildly out of control. When the wing separated 

from the aircraft, fuel from the severed fuel cells in the aircraft immediately ignited in a 

giant fireball, adding to the severity of the rolling motion. The violence of the roll 

caused the empennage to separate from the aircraft, which started cartwheeling endover-end. Pandis ejected from the out-of-control aircraft and suffered major injuries, 

while Cavin died in the crash. 

Pandis later recalled that the two other A-6's in his flight had noticed fuel venting from 

his left wing during the run for the dive. About halfway into to the dive, the crews of the 

two aircraft saw a dramatic increase in fuel venting and were shocked to see the left 

wing tear off the aircraft. 

Prior to this terrible accident. 72 A-6 aircraft had been temporarily grounded and 

another 109 were operating under flight restrictions. The Boeing Company had begun 

to design a new wing under a Navy contract that was awarded in 1985. With a 

-00!0— 

—w r 

7 

: 

/ lutier u.s is of the lieu A-6 composite wing in the Langley 16-Foot

Transonic Dynamics Tunnel included numerous external store loadings. 

86 Grumman A-6 intruder
Langley Contributions to the A-6 

carbon fiber—epoxy resin torsion box, light alloy control surfaces, and some titanium 

components, the new wing was much lighter and designed for four times the fatigue life 

of the existing wing. In addition to becoming a retrofit for the A-6E fleet, the wing was 

also intended for a new, advanced version of the A-6 to be known as the A-6F. (The 

A-6F was later canceled in the prototype stage when the Navy decided to replace the 

A-6 fleet with the stealth A-12 aircraft). 

At the request of the Navy, tests were conducted in the Langley 16-Foot Transonic 

Dynamics Tunnel (TDT) in February 1986, to ensure that the new wing would not 

exhibit flutter within the flight envelope. The preflight flutter clearance tests required 

two separate entries in the TDT under the leadership of Langley researchers Stanley R. 

Cole and Jose A. Rivera, Jr. The first composite-wing model was lost in a catastrophic 

flutter event while testing a "pencil" store configuration that represented the fuel tanks. 

Pencil stores are slender metal rods that simulate the moments of inertia of the real fuel 

tanks while minimizing aerodynamic effects. The test of the pencil store configuration is 

part of the flutter clearance test; however, the result was much more severe flutter than 

expected and the model was destroyed. Based in part on these results, Boeing modified 

the structural design of the A-6 composite wing. A second model incorporating the new 

wing design was fabricated and tested in the TDT in June 1987. This second model 

demonstrated no flutter incidents within the scaled flight envelope plus a safety margin. 

A unique aspect of both models was that they were semispan models (only one half of 

the aircraft was modeled); however, Boeing designed a unique root constraint to simulate the carry-through structure of the wing at the fuselage. The semispan model was 

larger than a full-span model, thereby permitting more accurate representation of the 

structural characteristics at model scale. Also of interest with regard to model design, 

the first model had a very clean wing surface. However, the decision was made to 

include the bumps, fences, and other wing features that were present in the actual flight 

hardware on the second model. 

Subsequent to the Langley tests, the composite wing was retrofitted to about 200 A-6E 

aircraft, which significantly increased the aircraft's capability, safety, and operational 

life. 

By 1988, the team of McDonnell Douglas and General Dynamics began to build the A-6 

replacement called the A-12 Avenger. Unfortunately, Defense Secretary Richard 

Cheney cancelled the $57 billion project after cost overruns exceeded $2.7 billion dollars in the development phase. Nonetheless, the decision to retire the A-6 was 

unchanged, and the F/A- 18 Hornet became the replacement aircraft for the Intruder. The 

last flight of the A-6 Intruder occurred in early 1997. 

Grumman A-6 Intruder 87
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Highlights of Research by Langley for the EA-6B 

Grumman EA-6B Prowler 

SPECIFICATIONS 

Manufacturer 

Grumman 

Date in service 

1971 

Type 

Electronic warfare 

Crew 

Four 

Engine 

Pratt & \Vhitncy J52-P-408A

USERS 

U.S. Navy and U.S. Marine 

Corps 

DIMENSIONS 

Wingspan............ 53.0 ft 

Length .............. 59.8 II 

Height .............. 16.3 it 

Wing area .......... 529 sq ft 

WEIGHT 

Empty ............ .34,300 lb 

Gross ............. 61.500 lb 

PERFORMANCE 

Max speed ..... Mach number 

of 0.72

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE EA-6B - 

I. Tests in the Langley 20-Foot Vertical Spin Tunnel resulted in increased control surface deflections for spin recovery. 

2. Langley cooperated with the Navy and Grumman to determine configuration modifications that significantly improved maneuver aerodynamics, high-angle-of-attack 

characteristics, and low-speed high-lift capability. 

3. Aft-fuselage ram-air cooling scoops were designed with data from tests in the 

Langley 7- by 10-Foot High-Speed Tunnel. 

Grumman EA-6B Prowler 89 
Highlights of Research by Langley for the EA-613 

The Grumman (now Northrop Grumman) EA-613 Prowler is a unique national asset that 

can be deployed from land bases and aircraft carriers to monitor the electromagnetic 

spectrum and actively deny an adversary the use of radar and communications. This aircraft is included in every aircraft carrier deployment and has a primary mission to protect fleet surface units and other aircraft by jamming hostile radar and communications. 

The EA-613 played a key role in suppressing enemy air defenses during Operation 

Desert Storm for U.S. and allied forces. The Department of Defense (DOD) has now 

assigned all radar jamming missions to the Prowler. 

The EA-6B airframe is a derivative of the A-6E Intruder. Although the fuselage was 

stretched to permit space for four crew members, the wing area is the same as that used 

on the A-6E. The basic mission, external stores, and electronic suites of the Prowler are 

considerably different from those of the A-6E. Also, the EA-613 is considerably heavier 

than the A-6, which results in a significant reduction in maneuvering capability. As a 

result of an alarming increase in accident rates for the EA-613 fleet in the early 1980's, 

the Navy requested support from Langley to define modifications that might improve 

maneuver aerodynamics, high-angle-of-attack stability and control, and low-speed highlift systems. During follow-on Navy flight tests, these modifications to the wing airfoil, 

vertical tail, wing leading and trailing edges, and roll control devices significantly 

enhanced the capabilities of an EA-613 demonstrator aircraft. Langley also supported a 

Navy and Grumman request to conduct wind-tunnel tests to define fuselage ram-air 

cooling scoop concepts for additional aerodynamic cooling of electronic systems. The 

significant improvements predicted by the results of Langley tests were verified during 

Navy flight evaluations of a modified A-6F aircraft. 

Langley facilities that supported the EA-613 program included the 20-Foot Vertical Spin 

Tunnel, the National Transonic Facility (NTF), the 7- by 10-Foot High-Speed Tunnel, 

the 16-Foot Transonic Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, the LowTurbulence Pressure Tunnel (LTPT), the 6- by 28-Inch Transonic Tunnel, and the 

12-Foot Low-Speed Tunnel. 

90 Grumman EA-6B Prowler
Langley Contributions to the EA-613 

LANGLEY CONTRIBUTIONS TO THE EA 6B

Spin Tunnel Tests The EA-613 aircraft is a four-seat, electronic warfare derivative of the A-6E Intruder. 

The major external differences between the EA-613 and the two-seat A-6E are a 54-in. 

fuselage extension for two additional crew stations, a large pod on the vertical tail to 

house electronic countermeasures equipment, and a canted refueling probe. The EA-613 

is more than 10.000 lb heavier than the A-6E, and carries large pods for electronics on 

wing pylons. In view of these significant configuration changes, the Navy requested that 

Langley conduct tests to determine spin and recovery characteristics of the EA-613. 

Henry A. Lee and James S. Bowman. Jr. conducted the investigation in 1971. 

As discussed in Langley Contributions to the A-6, a cockpit switch had been implemented in the A-6 to provide the pilot with the option of increasing horizontal-tail and 

rudder deflections for spin recovery. The results of the tests of the EA-613 indicated that 

the existing 23-deg rudder deflection was not sufficient for satisfactory spin recovery. 

The rudder deflection on production aircraft was increased to 35 deg with the A-6 assist 

spin recovery switch, which was also implemented on the EA-613. 

Maneuver Improvements The EA-613 has a significantly higher design gross weight than the A-6E; however, the 

EA-613 employs the same wing to carry the increased load. This increased wing load 

contributed to an alarming number of EA-613 accidents in the early 1980's. During that 

period the EA-613 aircraft experienced accident rates in fleet operations that were nearly 

three times higher than all other Navy and Marine aircraft combined. The majority of 

these mishaps were attributed to out-of-control flight and resulted in the loss of the aircraft after the pilots were unable to recover the aircraft and were forced to eject. These 

losses prompted many fleet squadrons to restrict the EA-613 from intentional maneuvers 

at high-angle-of-attack conditions. While the restrictions substantially reduced the accident rates, they also imposed constraints on evasive maneuvers while operating in high 

threat environments. 

In late 1984. the Navy approached Langley to undertake a research program to improve 

the EA-613. with emphasis on increasing maximum usable lift, maintaining lateraldirectional stability near stall, and maintaining lateral control near stall. Langley agreed 

to lead this effort, under the cognizance of the Navy. Grumman joined the effort and 

provided additional technical support to Langley, as well as participating in additional 

wind-tunnel tests at NASA Ames Research Center for the high-lift configuration. This 

program evaluated the EA-613 in ten NASA and Grumman facilities. 

Grumman EA-6B Prowler 91
Langley Contributions to the EA-613

Laiiglev researcher David E. Ha/we with the EA-6B free-flight model. 

Langley research activities on the high-angle-of-attack stability and control characteristics of the EA-6B were led by Joseph L. Johnson. Jr. and his staff of the Low Speed 

Aerodynamics Division. The efforts to improve maximum lift and maneuver performance were led by Percy J. (Bud) Bobbitt and his staff of the Transonic Aerodynamics 

Division. 

Johnson's team conducted extensive tests in the Langley 12-Foot Low-Speed Tunnel 

and the Langley 30- by 60-Foot (Full-Scale) Tunnel with flow visualization and force 

and moment measurements. The Langley leaders in this effort were Frank L. Jordan, Jr. 

and David E. Hahne. The results of these tests showed that the vertical tail was 

adversely affected by flow emanating from the fuselage and wing root areas for highangle-of-attack conditions, which resulted in a severe loss of directional stability. The 

problem was resolved by extending the vertical tail above the existing fin pod. adding 

leading-edge droop to the inboard wing, and adding a strake to the wing-fuselage intersection. Roll control at high-angle-of-attack conditions was augmented by using the 

existing wingtip speed brakes as additional ailerons. These modifications were tested 

with a 0.12-scale free-flight model in the Full-Scale Tunnel. The results clearly demonstrated the potential of these modifications to improve the flight characteristics of the 

EA-6B at high angles of attack. 

Bobbitt's team worked to improve maximum lift. This task was a challenge as changes 

in wing contour were limited to the leading-edge slat and trailing-edge flap to keep retrofit costs low. Several advanced airfoil designs were tested by William G. Sewall. 

Robert J. McGhee. and James C. Ferris in the Langley 6- by 28-Inch Transonic Tunnel 

and in the Langley Low-Turbulence Pressure Tunnel (LTPT). The results of the airfoil 

92 Grumman EA-6B Prowler
Langley Contributions to the EA-613 

studies were used to design advanced slats and flaps for the EA-6B that produced a substantial increase in lift, as well as decreased drag at cruise Mach numbers. Edward G. 

Waggoner and Dennis 0. Allison led computational and experimental studies to design 

the wing configurations to increase the low-speed maximum lift capability of the EA-6B 

with minimal degradation in high-speed performance. Their work ranged from the 

application of low-speed and transonic computational methods to experimental verification tests in the Langley 7- by 10-Foot High-Speed Tunnel and the National Transonic 

Facility (NTF) at Langley. The integrated efforts of these two teams identified new 

leading- and trailing-edge configurations that dramatically improved the high-lift performance of the EA-6B. The modifications defined by the Johnson and Bobbitt teams 

were then tested on a model at Ames to assess the impact on the high-lift configuration. 

Spin tunnel tests were also conducted to evaluate the impact of the changes on spin and 

spin recovery characteristics. No degradation was noted during the tests, and the existing spin characteristics of the EA-6B were projected to remain unchanged. The final 

tests included wing loads tests led by Langley researcher Charles Mercer in the Langley 

16-Foot Transonic Tunnel. Tests of a full-size, EA-6B semispan wing in the Full-Scale 

Tunnel led by Jordan and Hahne validated the effectiveness of using the speed brakes as 

ailerons and provided additional loads data. Because the A-6E had significant problems 

with fatigue life, it was important to assess the impact of the modifications on wing 

loads and wing root bending moments to ensure that the EA-6B wing fatigue life would 

not be degraded. 

The impact of the Langley-led test program was substantial. Test data indicated the 

potential for a 25-percent increase in maximum usable lift in the cruise configuration. 

Lateral and directional stability could be maintained to angles of attack well beyond 

stall. Lateral control could be maintained beyond stall by using the speed brakes as ailerons. A performance improvement due to decreased drag could be realized at medium 

EA-6B model being prepared tor tests in the National Transonic 1-acuity at Lan g1e 

Grwnmnan EA-6B Prowler 93
Langley Contributions to the EA-6B

EA-6B Vehicle E#lhan( en/en! Program ( VEP)

test aircraft during flight evaluation. 

and high altitudes where a majority of the EA-613 missions are flown. Approach speeds 

could be substantially reduced at existing landing gross weights, and growth capability 

was provided for higher gross weights. Finally, an extensive, unprecedented aerodynamic database for the EA-613 had been produced and was ready for incorporation into 

simulators for EA-613 pilot training. 

The results of this outstanding NASA. Navy, and Grumman joint program were summarized in several technical papers in 1987. The effort received such positive national 

attention that in the 1987 Applied Aerodynamics AIAA meeting, an entire session was 

dedicated to the EA-613 effort with five papers presented. Aircraft modifications defined 

by the joint EA-613 program were directed at an advanced version of the aircraft known 

as the EA-613 ADVCAP (Advanced Capability), which included a myriad of improvements such as new engines and electronic upgrades. as well as the airframe modifications. Flight tests of a modified EA-613 designated the Vehicle Enhancement Program 

(VEP) test aircraft were conducted to evaluate the effects of the airframe modifications 

derived from the Langley-led joint studies. Flights began on June 15. 1992, and the final 

flight occurred on April 4. 1994. The flight evaluation of the test aircraft validated all 

projections of the research program. and the performance, stability, and control 

characteristics of the modified aircraft were judged to be far superior to those of the 

basic EA-613. The aircraft performed flawlessly. Unfortunately, fiscal constraints and 

other programmatic issues restrained the Navy from funding the upgrades. EA-613 simulators, however, have been upgraded with the data from Langley. 

COO/lug Study - The continuing evolution of the EA-613 and the demands of the all-weather warfare mission involved a continuous upgrade of advanced electronic systems that demand adequate cooling for satisfactory operations. In particular, the projected Advanced 

Capability (ADVCAP) version of the aircraft included a significant electronics upgrade 

that required additional cooling. Langley participated in a joint NASA. Navy, and 

Grumman wind-tunnel study of new aft-fuselage ram-air scoops to satisfy the cooling 

requirements. Langley researcher William Sewall led these tests, which were conducted 

in the Langley 7- by 10-Foot High-Speed Tunnel. The scoop configuration derived from 

the tests was evaluated in flight tests of a prototype of another advanced A-6 derivative 

known as the A-6F. The scoop configuration was to be included in the overall ADVCAP 

package, which was not funded for continued development. 

94 Grumman EA-6B Prowler
Langley Contributions to the EA-613 

EA-6BJiieIage and empennage model in the Langley 7- by

10-Foot High-Speed Tunnel for air scoop studies. 

A -oF prototYpe with aft-fuselage scoops. 

Grumman EA-6B Prowler 95
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Highlights of Research by Langley for the F-14 

Grumman F-14 Tomcat 

SPECIFICATIONS 

Manufacturer 

Grumman 

Date in service 

November 1974 

Type 

Carrier-based multirole 

Crew 

Two 

Engine 

F-14B/D ... General Electric 

F-ll0-GE-400 augmented 

turbofan with afterburner 

USER 

U.S. Navy 

DIMENSIONS 

Wingspan 

unswept........... 64.2 ft 

swept............. 38.2 ft 

Length .............. 61.9 ft 

Height .............. 16.0 ft 

Wing area ...........S65 sq ft

WEIGHT 

Empty ............41.700 lb 

Max takeoff ........ 74,349 lb 

PERFORMANCE 

Max speed .....Mach number 

of 2.3 

Unrefueled 

range ............3,450 n mi

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F- i 4 

1. The F-14 employs the variable-sweep wing developed by Langley to meet wide 

ranging mission requirements. 

2. Langley conducted wind-tunnel tests to collect data for the competitive source selection team. 

3. Langley personnel participated in the evaluation process. 

4. At the request of the Department of Defense, Langley led a multidiscipline assessment of the F- 14 in early development and reported the results to the Navy. 

5. Langley conducted propulsion integration studies to improve the subsonic cruise 

efficiency that resulted in a redesign of the aft end. 

6. Langley studies of the high-angle-of-attack and spin characteristics identified a 

potential flat spin and an innovative flight control system modification that dramatically reduced the spin susceptibility of the aircraft. 

7. Tests in the Langley 16-Foot Transonic Dynamics Tunnel identified potential flutter 

of the F- 14 over-wing covers, which Grumman solved with external strake stiffeners. 

8. Langley provides technology, expertise, and facility support on a continual basis, 

such as providing numerical models for pilot training simulators. 

Grumman F-14 Tomcat 97 
Highlights of Research by Langley for the F-14 

The multirole F-14 fighter employs many Langley technical concepts that permit it to 

accomplish diverse requirements such as supersonic dash and landing on an aircraft carrier in adverse conditions. Grumman relied on existing NASA databases and consultation during the design of the F-14. Langley staff tested and analyzed the competing 

designs in the Navy Advanced Fighter (VFX) Program competition that resulted in the 

F-14. Technical contributions to the F-14 from Langley include the areas of aerodynamic performance, high-angle-of-attack and spin characteristics, and flutter suppression. Langley facilities used in F-14 studies included the 30- by 60-Foot (Full-Scale) 

Tunnel, the 20-Foot Vertical Spin Tunnel, the 4- by 4-Foot Supersonic Pressure Tunnel, 

the 8-Foot Transonic Pressure Tunnel, the Unitary Plan Wind Tunnel, the 16-Foot Transonic Tunnel, the 16-Foot Transonic Dynamics Tunnel, the 7- by 10-Foot High-Speed 

Tunnel, the Differential Maneuvering Simulator, and radio-controlled models dropped 

from a helicopter. In addition, Langley provided leadership for high-angle-of-attack 

F-14 flight experiments in a joint NASA, Navy, and Grumman program at NASA 

Dryden Flight Research Center. 

Following the selection of the Grumman design at the completion of the VFX Program, 

the Department of Defense requested that NASA provide an independent assessment of 

the F-14. A NASA team of 45 professionals that was led by Langley briefed their findings to the Navy and helped shape the development of the aircraft. Over 11,000 hr of 

wind-tunnel tests were conducted in Langley facilities during the subsequent F-14 

development program. 

98 Grumman F-14 Tomcat
Langley Contributions to the F-14 

LANGLEY CONTRIBUTIONS TO THE F-14 

Early NASA Fighter Studies During the development of the variable-sweep wing at the Langley Research Center, 

researchers recognized the advantages of applying the concept to multimission aircraft. 

One ideal application was for naval fleet defense fighters, which must be able to quickly 

intercept threats and yet slowly approach aircraft carriers to land. Variable-sweep wings 

in the fully swept (high-speed) configuration permit efficient supersonic dash and the 

carrier-approach requirements could be met with the wing in the unswept (low-speed) 

position. Inspired by the potential of this application of variable-sweep technology, 

Langley conducted several in-house studies of fighter configurations for naval applications. In 1967, Langley published the results of in-house studies of a variable-sweep 

fighter configuration known as LFAX-4 that incorporated several features that are evident in the F- 14 aircraft. Some of these features are 

• Short propulsion package to minimize weight 

• Engines placed forward for balance 

• Horizontal ramp engine inlets for good performance at high angles of attack 

• Tailored twin-engine aft-end spacing and interfairing for efficient subsonic cruise 

conditions 

Results of studies of the performance, stability, and control characteristics of the 

LFAX-4 obtained across the speed range of a representative advanced naval fighter were 

outstanding, and Langley researchers conducted extensive briefings of their findings at 

industry and Department of Defense (DOD) sites. 

One result of the LFAX-4 study that the Langley team emphasized was the critical location of the pivot for the movable wing panels. To minimize drag during transonic 

/ 

The Langley LFAX-4 fighter configuration. 

Grumman F-14 Tomcat 99
Langley Contributions to the F-14

maneuvers typical of air-to-air combat, the pivots must be located in a relatively outboard position. Langley's experience with the test and analysis of the F- ill revealed 

that large penalties in trim drag occurred if this key design factor was not adequately 

appreciated. Although the F-I 11 incorporated the variable-sweep concept, the full 

advantages of the concept were not realized because the pivot locations were relatively 

inboard. As a result, the F- ill suffered excessive trim drag at transonic and supersonic 

conditions. The designers of the F- 14 were made aware of the significance of pivot locations by NASA briefings. Comparison of the NASA results for the LFAX-4 to those of 

the F- ill helped convince Grumman to locate the F- 14 pivots in a more favorable outboard position. 

The LFAX-4 studies also pointed out the importance of the placement of the horizontal 

tail relative to the wing for stability and control. These recommendations were also 

included in the F-14 design. 

F-14 Source Selection Following the disastrous attempt to achieve interservice aircraft commonality with the 

F- 111, the Navy issued a request for proposals (RFP) for a new VFX fighter in July 

1968. Competitors included Grumman, General Dynamics, Ling-Temco-Vought, 

McDonnell Douglas, and North American Rockwell. At the request of the Navy, the 

competing configurations were evaluated with wind-tunnel data from the Langley 

8-Foot Transonic Pressure Tunnel, the 7- by 10-Foot High-Speed Tunnel, the Unitary 

Plan Wind Tunnel, and the 16-Foot Transonic Tunnel. Langley personnel also participated in briefings of their results to the industry teams and the Navy. 

NASA Independent Assessment On January 14, 1969, the Navy announced the award of the contract for the VFX fighter, 

now designated F-14, to Grumman. The Assistant Secretary of the Navy requested that 

NASA make a timely independent assessment of the technical development of the F-14. 

A NASA F-14 Study Team of over 40 Langley personnel led by Langley researcher 

William J. Alford, Jr. was organized. A briefing of the study results was given in August 

1969 at the Naval Air Systems Command by a team led by Laurence K. Loftin, Jr., 

Mark R. Nichols, and William Alford. This briefing (which covered results in cruise and 

maneuvering performance, aeroelasticity and flutter, propulsion integration, stability, 

and control) identified several areas where further research would enhance the F- 14's 

capabilities. Following the briefing, Dr. John Foster, Director of Defense Research and 

Engineering, requested the support of Langley in the development of the F-14. 

Propulsion Integration Initial flight-test evaluations of the performance of the F-14 by the Navy revealed higher 

drag levels at high subsonic and transonic speeds than had been predicted by Grumman 

wind-tunnel tests. The Navy requested Langley support in analyzing and providing solutions to the problem. Langley experience with the F- 111 and other advanced fighter concepts indicated that an extremely large portion of the high subsonic and transonic cruise 

drag of modern twin-engine fighters is contributed by the aft end of the configuration. 

For example, a relatively poor aft-end design could produce almost 50 percent of the 

cruise drag for some configurations. In the course of the F-1 11 development program, 

Langley researchers in the 16-Foot Transonic Tunnel had developed test techniques and 

analysis methods to minimize this problem, and they went to work on the aft-end aerodynamic characteristics of the F- 14 configuration. 

100 Grumman F-14 Tomcat
Langley Contributions to the F-14 

Based on their extensive experience, the 16-Foot Transonic Tunnel team conducted tests 

in 1972 to determine the characteristics of the critical engine-fuselage fairing (pancake) 

at the rear of the aircraft. Several geometric variations were evaluated to determine more 

effective pancake shapes, with an appreciation of the trades that are necessary to minimize component interference drag while adhering to the area rule developed by Langley 

researcher Dr. Richard Whitcomb. In addition, certain regions had to be preserved for 

the F-14 fuel jettison system and the landing arrestor hook. The researchers cut away 

areas of the pancake, reshaped the geometry and added a "handle" in the shape of a bulbous pod at the rear of the pancake. The design recommended by the Langley tests 

proved extremely effective in reducing cruise drag and was incorporated into the F-14 

configuration. 

In addition to the pancake modification. Langley researchers recommended that generous "speed bump" (area added to shape the aircraft to comply with Whitcomb's area 

rule) fairings be added to the forward bottom area of the vertical tails. The suggestion 

was accepted by Grumman and incorporated into the production F- 14 fleet. 

Pancake configurations evaluated in cruise-drag studies in the 

Lan glev 16-Foot Transonic Tunnel. Original shape is at left. 

4ft-enl /)aJu(,ke haiullc wul vertical tail root speed bumps on 1-14 aircraft. 

Grumman F-14 Tomcat 101
Langley Contributions to the F-14 

High-Angle-Of-Attack and 

Spin Research

In early 1970. initial tests conducted in the Langley 20-Foot Vertical Spin Tunnel at the 

request of the Navy indicated that the F-14 would exhibit two types of spins. The first 

spin involved relatively steep, nose-down spins from which recovery would be relatively 

easy for the pilot. However, the results also showed that the F-14 might exhibit a relatively flat unrecoverable spin in which the aircraft would rotate rapidly (2 sec per turn) 

about a vertical axis through its center of gravity, while descending vertically with the 

fuselage in a relatively horizontal attitude. Because of the high rate of rotation of the flat 

spin, the g-forces at the cockpit location would be very high (approximately 6.5 longitudinal g's outward) and would probably incapacitate the pilot if sustained for even a 

moderate period of time. Under the direction of Langley researcher James S. Bowman, 

Jr. exhaustive spin tunnel tests were conducted to define a spin recovery procedure, but 

the aerodynamic control surfaces of the F- 14 were ineffective at these flat attitudes. In 

fact, even a scaled version of a very large 35-ft diameter spin recovery parachute (the 

largest that could be carried by the F- 14 was 21 ft) could not recover the model from the 

spinning motions. The only concept that provided marginal recovery was the simulta- neous application of normal recovery controls, deployment of the emergency parachute, 

and extension of auxiliary canards on the nose of the model. 

Unrecoverable flat spins have been exhibited by many fighter configurations in the 

Langley Spin Tunnel, and such characteristics are viewed with concern. However, additional types of model tests are required to judge the seriousness of the problem. In particular, drop-model tests are conducted to determine if the aircraft can enter the spin 

from initial flight conditions. Spin tunnel tests are conducted with the model launched in 

a flat attitude into a vertically rising airstream—conditions very favorable for the spin to 

stabilize. However, in actual flight conditions, many aircraft lack the control power 

required to reach these conditions. For example, although the F-S aircraft exhibited a flat 

spin in Langley Spin Tunnel tests, it was virtually impossible for pilots to intentionally 

enter the flat spin. 

Il .1 

- - -. 

F-14 model in Spin recovery tests in the Lan glev Spin Tunnel. 

102 Grumman F-14 Tomcat
Langley Contributions to the F-14 

I

I. 

I 

E-14 drop model being calibrated uitbglit electronics lab prior toflig/it texts. 

Two F-14 drop models were under fabrication when the spin tunnel results became 

known. The Langley. Grumman. and Navy team had planned to equip the models with 

extensive instrumentation to measure flight variables for correlation with analytical 

studies of the spin, but the installation process would have taken several months. 

Because the Navy required an immediate answer about the susceptibility of the F- 14 to 

enter flat spins, Marion 0. McKinney directed the team to install limited instrumentation in one of the models, and to obtain answers as quickly as possible. With the 

approval of this approach by the Navy. Charles E. Libbey and his team installed a miniature movie camera in the engine inlet of the model and pointed it forward, where it 

could monitor the relative angle of a simple wooden angle-of-attack vane mounted on a 

nose boom. This innovative approach gave the Navy answers in a few weeks, rather than 

months. The team conducted as many as 4 drop tests a day in a very successful test 

series. More refined instrumented model tests were completed later for a total of 55 drop 

tests in the program. 

Libbey and his team concentrated their initial studies on the susceptibility of the F- 14 

model to enter the spin by manipulating the controls after the model had been dropped 

from a helicopter. Results of the tests showed that the model could be pitched up in an 

aggressive manner with no tendency to enter either the steep or flat spins. However, if 

the roll control (differential deflection of the horizontal tails) was used in normal fashion 

to pick up a down-going wing at high angles of attack, the model would depart controlled flight in a direction opposite of the intended input because of adverse yaw caused 

by large yawing moments produced by the horizontal tails. If the pilot held in the roll 

control, the model would enter a flat spin. Recovery from flat spins requires the use of 

an emergency parachute, special nose canards, and full differential tail deflections. 

Grumman F-14 Tomcat 103
Langley Contributions to the F-14

Although the drop-model results predicted that entry into the flat spin was possible, it 

was recognized in this test technique that the ground-based pilot controls the model 

from a remote position, thereby losing the natural physical cues available to the pilot of 

the actual aircraft. In addition, the scaled model moves much faster than the full-scale 

aircraft, so the time available to the pilot of the model for recovering from an impending 

spin is very limited. The analysis of the F-14 therefore turned to the use of the Langley 

Differential Maneuvering Simulator (DMS) where the actual human environment could 

be more accurately simulated. 

In 1972, a team headed by Langley researcher Luat T. Nguyen programmed the DMS 

with aerodynamic data from Langley wind-tunnel test results and F- 14 aircraft mass 

characteristics. Arrangements were made for Langley research pilots and the Grumman 

chief test pilot Charles Sewell to participate in the evaluation. Simulated maneuvers 

flown in the DMS confirmed the drop-model results—that is, the aircraft could be 

aggressively pitched to extreme attitudes without loss of control, but if roll control was 

maintained at high angles of attack, the aircraft would depart from controlled flight. In 

addition, with simulation of full-scale conditions, it appeared that the pilot had time to 

make corrective controls before hazardous spin-entry conditions occurred. 

Nguyen and his team had participated in the development of the flight control system for 

the F-15 for high-angle-of-attack conditions. (See Langley Contributions to the F-15.) 

They recognized that the concept used by the F-15 to reduce the adverse effects of the 

horizontal tails as roll control devices at high angles of attack would be an ideal solution 

to the F-14 problem. With this knowledge, an automatic rudder interconnect (ART) for 

the F-14 was implemented and evaluated in the DMS. The AR! system automatically 

phased out movement of the tails for roll control and phased in deflections of the rudders at high angles of attack. The concept was refined and matured in the simulator studies. The pilots who flew the F-14 with the ARI system were enthusiastic, and the system 

allowed the pilot to maneuver the aircraft without regard to angle of attack or switching 

from differential tails to rudders. The Grumman team regarded the ART concept developed by Langley as a highly desirable addition to the F-14 aircraft. The production contract for the early F-14 aircraft called for the implementation of an ARI system. At this 

point, Langley closed out its F-14 research, while Grumman pursued the development 

of the final ARI system. 

Unfortunately, the early F-14 aircraft also included another late developing preproduction concept—deployable wing leading-edge maneuver slats for improved maneuverability. Early Grumman flight tests revealed that the F-14 modified with both the ARI 

system and the maneuver slats displayed unsatisfactory air combat maneuvering characteristics because the ARI rudder inputs aggravated lightly damped rolling oscillations 

(wing rock) induced by the slats during maneuvers. Because of this incompatibility, the 

Navy deactivated the ART systems on all fleet F-14 aircraft. 

The F-14 proved to be a relatively forgiving aircraft to fly, and pilots adapted to manually switching from using differential tails for roll control at low angles of attack to 

using rudders at high angles of attack. However, the F-14 fleet began to experience spin 

losses at the rate of about one aircraft per year. In 1978, a joint NASA, Navy, and 

Grumman program was initiated to develop a new ARI system to increase the spin resistance of the F-14. Nguyen and his team once again examined the F-14 and used the 

DMS to develop a new ART that provided adequate damping of the wing rock, while 

retaining the spin resistance of the original ART system developed by Langley. A flighttest F-14 was modified with a spin parachute, battery driven hydraulic pumps for 

emergency power, and the special foldout canards on the fuselage forebody that were 

104 Grumman F-14 Tomcat
Langley Contributions to the F-14 

recommended by the earlier spin tunnel tests. Fitted with the new ARI. flight tests were 

conducted over a 2-year period at NASA Dryden Flight Research Center with Langley 

personnel on site for the flight tests. Over 100 flights by 9 pilots were made up to low 

supersonic speeds. 

The results of the flight-test program were extremely impressive. Wing rock was suppressed, inadvertent spins were eliminated, and the handling qualities throughout the air 

combat envelope were improved. Several years passed before funding constraints permitted the Navy to develop the AR! within plans to equip the F-14 fleet with a new 

advanced digital flight control system (DFCS). Following further refinements during 

Navy flight evaluations at Patuxent River Naval Air Station in Maryland, the Navy 

implemented the DFCS with the ARI. The first F-14 deployments with the AR! 

occurred during the Kosovo operations, and glowing reports from the F-14 squadrons 

indicated that the new system was a success. 

The F-14 responds to an abrupt stick pull bY Drvden test pilot Fitz Fulton

(luring evaluations of the Langle y designed Automatic Rudder

Interconnect (A RI) control s ystem at Dryden. 

Grumman F-14 Tomcat 105
#4 4 . 11

Oft 

Langley Contributions to the F-14 

Flutter Tests Flutter clearance tests of the F- 14 in the Langley 16-Foot Transonic Dynamics Tunnel 

required five entries from 1970 to 1973 under the leadership of Moses G. Farmer. The 

utilization of variable-sweep wings by the F-14 introduced a unique flutter problem that 

had been unanticipated prior to the tests. The challenge of providing an upper-fuselage 

covering for the variable-sweep wing panels had been addressed by Grumman with relatively flexible inner wing covers. Early in the flutter tests, large deflections and buffeting of the over wing panels were observed and viewed as a potentially serious flutter 

problem. 

With knowledge of the Langley results. Grumman engineers designed a set of external 

stiffening strakes for the wing covering that eliminated the flutter problem. An additional favorable impact of the strakes was local straightening of the airflow over the 

upper fuselage, which resulted in performance benefits. With the strake modification. 

the F-14 passed flutter clearance tests in the Langley tunnel. Initially, it was proposed 

that this modification would only be applied to the preproduction flight-test F- 14 aircraft 

while a redesign of the wing cover could be accomplished. However the modification 

proved to be extremely robust and similar strakes were incorporated in all production 

F-14 aircraft. 

During the flutter tests, the Langley staff observed considerable buffeting of the vertical 

tails, particularly at moderate angles of attack. The staff of the 16-Foot Transonic 

Dynamics Tunnel modified the cable-mount system to permit tests at high-angle-ofattack conditions where the buffeting became more intense. Langley expressed concern 

that damage to the structural integrity of tails or tail-mounted avionics and antennae 

might be encountered, but Grumman did not accept this concern as an issue. Subsequently. the F-14 fleet experienced structural damage and the replacement of tailmounted radar warning units. As a result, the vertical tails of F-14 aircraft were stiff -

ened. 

The experience of the engineering community with vertical-tail buffeting in the F- 14 led 

to the development of design analysis tools and special wind-tunnel test techniques for 

follow-on aircraft including the FIA-18 and F-22. 

F-14 model ,floii,?1e/ in prep1rI!!ofl 10r.flutter te.s 1. Close-up u/dc of the externuul ode, utin' Over

in the 16-Foot Transonic D ynamics Tunnel. strakes added to prevent pane/flutter 

106 Grumman F-14 Tomcat
Langley Contributions to the F-14 

F-14 Yaw Vanes In the early 1980's, researchers in the Navy community became interested in the potential benefits of using thrust vectoring for control augmentation of the F-14. Their interest 

had been spurred by a cooperative Langley and Navy piloted simulator study that was 

conducted in the Langley DMS. The study defined the benefits to a representative fighter 

aircraft of maintaining the control power required for satisfactory V/STOL flight in conventional flight. In this study, an existing Langley simulator model of the F-14 was modified to incorporate the control modifications under the leadership of Luat Nguyen. 

Langley and DOD pilots flew the simulated flights. 

Results of the simulator study showed that the most important benefit occurred when the 

yaw control was augmented at high angles of attack (normally, yaw control provided by 

conventional rudders is markedly reduced at high angles of attack). With the increased 

yaw control capability, pilots could consistently win against a variety of adversaries in 

simulated air-to-air combat. Analysis of the desired control levels in the simulator 

results indicated that deflecting the engine thrust on aircraft similar to the F-14 would 

provide the necessary control. 

To pursue the development and demonstration of the effectiveness of yaw vectoring, the 

Navy conducted a series of tests to evaluate the turning effectiveness and structural 

integrity of external vanes mounted behind the nozzles of the F-14 engines. These activities were augmented by tests led by Bobby L. Berrier and David E. Reubush in the 

Langley 16-Foot Transonic Tunnel. Data obtained in these tests were used to define the 

geometry and thrust-vectoring effectiveness for the Navy evaluations. 

Full-scale vanes were fabricated and initially ground tested behind an F-14 aircraft at 

the Patuxent River facility. Flight tests of a modified F-14 were subsequently conducted 

to demonstrate the structural integrity and thrust-vectoring performance of the vane concept over a limited flight envelope. 

F-1 .4 Jno(/e/ equipped itith dcl leciithle \uw iw,e.s in the Lung/cr 16-Foot Transonic Tunnel. 

Grumman F-14 Tomcat 107
Langley Contributions to the F-14

[-14 tIi/z eXperimoltal

.Nall . rc,ne, in flight ore,' Pat oven! Ri,'er Ala vol Air Station. 

Further applications of the yaw vane concept to the F-14 did not develop beyond this 

exploratory program, but the concept of external vanes as relatively inexpensive devices 

for thrust vectoring at high angles of attack was successfully used in the NASA F- I 8 

High-Angle-of-Attack Technology Program and the DARPA X-31 Enhanced Fighter 

Maneuverability Program. 

108 Grumman 1-14 Toiticat
SPECIFICATIONS 

Manufacturer 

Grumman 

First flight 

December 1984 

Type 

Experimental demonstrator 

of advanced forward-swept 

wing and relaxed stability 

Crew 

One 

Engine 

General Electric F404-GE400 

PARTICIPANTS 

Grumman, DARPA. U.S. Air 

Force. and NASA

DIMENSIONS 

Wingspan............ 27.1 ft 

Length .............. 53.9 ft 

Height .............. 14.3 ft 

Wing area ........ l88.8sqft 

WEIGHT 

Empty ............ 13.800 lb 

Gross ............. 17.800 lb 

PERFORMANCE 

Max speed ..... Mach number 

of 1.6

Highlights of Research by Langley for the X-29 

Grumman X-29 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE X-29 - 

1. Langley, Grumman, Defense Advanced Research Projects Agency (DARPA), and 

U.S. Air Force cooperated to validate analytical methods for aeroelastic divergence 

of forward-swept wings. 

2. Tests in the Langley 16-Foot Transonic Dynamics Tunnel of the X-29 resulted 

in advances in design methods for aeroelastically tailored forward-swept wing 

configurations. 

3. Langley studied the high-angle-of-attack behavior of the X-29 and identified potential problems such as wing rock, divergent rolling motions at post-stall angles of 

attack, and longitudinal tumbling motions, which permitted timely design of a robust 

flight control system. 

4. Critical information on engine inlet performance at high angles of attack was 

obtained during tests in the Langley 14- by 22-Foot Subsonic Tunnel. 

Griinunan X-29 109 
Highlights of Research by Langley for the X-29 

The Grumman (now Northrop Grumman) X-29 demonstrated the feasibility of several 

advanced technologies, including the aeroelastically tailored forward-swept wing, and 

the ability to routinely operate with extremely high levels of inherent longitudinal instability (relaxed static stability). Under the Defense Advanced Research Projects Agency 

(DARPA) sponsorship, Grumman designed two X-29 aircraft that underwent joint 

DARPA, Grumman, NASA, and U.S. Air Force flight tests at NASA Dryden Flight 

Research Center from 1984 to 1992. The exhaustive flight-test program covered aspects 

such as structural and aerodynamic performance, as well as high-angle-of-attack 

maneuverability. The X-29 aircraft flew 422 research missions. The joint X-29 Program 

obtained a vast amount of detailed data and analysis methods that will be applied to 

future high-performance aircraft. 

Langley cooperated with DARPA and Grumman in the areas of flight dynamics and 

engine inlet performance at high angles of attack and aeroelastic divergence of forwardswept wings. Highlights of these tests included early and accurate projections of aerodynamic, stability, and control characteristics that allowed for resolution of problems 

before flight tests; rapid acceleration and validation of design methods for the avoidance 

of wing divergence for forward-swept wing configurations; and risk reduction for 

engine operations at high angles of attack. 

Langley facilities used to support the X-29 program included the 30- by 60-Foot Tunnel, 

the 20-Foot Vertical Spin Tunnel, the National Transonic Facility, the 16-Foot Transonic 

Dynamics Tunnel, the 14- by 22-Foot Subsonic Tunnel, radio-controlled drop models, 

and the Differential Maneuvering Simulator. 

110 Grumman X-29
Langley Contributions to the X-29 

LANGLEY CONTRIBUTIONS TO THE X-29 

Evolution of Forward-Swept Research on the swept wing as a drag-reducing mechanism for high subsonic and tranWing Configurations sonic speeds during the late 1930's and early 1940's resulted in some of the first conventional aft-swept wing aircraft during World War II. At that time, it was also recognized 

that forward-swept wings (FSW) could produce the same beneficial effect for performance. Furthermore, the FSW also promised improved low-speed controllability. Stalls 

were expected to start at the wing root rather than the tip (in contrast to aft-swept 

wings), thereby maintaining the effectiveness of outboard ailerons and their contributions to roll control at low speeds. The onset of shock waves at high speeds was also 

expected to begin at the wing root, which again maintains aileron effectiveness at high 

speeds. With lateral control effectiveness assured across the operational envelope, there 

would be no need for drag-producing leading-edge high-lift devices. Finally, the general 

layout of the FSW resulted in a more aft location of the wing spar carry-through structure in the fuselage, which results in more fuselage internal volume. 

During 1942. the German Junkers Design Bureau initiated studies of an FSW bomber 

designated the Ju-287. First flown in 1944. the Ju-287 exhibited several problems. the 

most serious of which was a tendency to increase g-loading during a turn without control inputs from the pilot. The analysis of the problem by Junkers revealed that the cause 

was wing structural deformation from the aerodynamic loads on the forward-facing 

wingtip panels. At high speeds, the deformation was predicted to become very severe, 

exceed structural limits, and result in wing failure. This potentially catastrophic phenomenon was referred to as aeroelastic divergence. Further analysis indicated that the 

structural modifications required to avoid the divergence problem for the aluminum 

wing of the Ju-287 would result in excessive weight and unacceptable performance penalties. Other interest in FSW configurations during World War II came from the 

American Cornelius Aircraft Company, which worked on several configurations, including the XFG-l. a piloted towable glider used to transport fuel. 

Researchers at Langley also investigated FSW as part of a program to develop variablesweep wings. In one of these investigations, an existing wind-tunnel model of the Bell 

X- I was equipped with a variable-sweep wing, and tests were conducted for a FSW version of the aircraft in the Langley 300-MPH 7- by 10-Foot Tunnel. 

Following World War II, the only significant FSW aircraft built was the German 

Hansajet business jet. which was designed by the same chief engineer who designed the 

Ju-287. The aircraft never enjoyed a large market. 

The German Junkers Ju-287 forward-swept-wing bomber 

Grumman X-29 III
Langley Contributions to the X-29

The problem of aeroelastic divergence stood squarely in the progress of FSW options 

for relatively high-speed aircraft, and the challenge of providing sufficient rigidity versus weight turned many designers away from the concept. 

In the 1970's, two activities coupled to stimulate interest in FSW configurations. First, 

Grumman became interested in conducting aerodynamic research to determine methods 

to improve its Highly Maneuverable Aircraft Technology (HiMAT) configuration, 

(which had lost in the design competition to Rockwell) including revolutionary wing 

configurations. The second activity was the remarkable advocacy and influence of 

Dr. Norris J. Krone, Jr., a retired Air Force pilot who had written his doctoral thesis on 

eliminating aeroelastic divergence of FSW configurations by using advanced tailored 

composites for structural rigidity. Krone subsequently became a manager at the Defense 

Advanced Research Projects Agency (DARPA), and Krone's discussions with the 

Grumman managers led to a resurgence of interest in an examination of the FSW concept. During 1977, DARPA released a request for proposals (RFP) for a highly 

advanced technology demonstrator that would integrate advanced aerodynamics (with 

emphasis on the FSW) and advanced flight controls. Responses were received from 

Grumman, Rockwell, and General Dynamics. 

On December 22, 1981, DARPA announced that Grumman had been selected to 

develop the new technology demonstrator, to be known as the X-29. 

High-Angle-of-Attack Initial information exchanges between DARPA and Langley on independent high-angleTechnology of-attack evaluations of the competing FSW configurations occurred in early 1980, 

when Krone visited Joseph R. Chambers and his staff at the 30- by 60-Foot (Full-Scale) 

Tunnel. Langley agreed to provide support in this area as requested for all three competing industry teams. General Dynamics proposed an FSW version of the F-16 as a candidate design for the DARPA competition. Exploratory static wind-tunnel data had 

already been generated by cooperative tests led by Langley researcher Sue B. Grafton in 

the Langley 12-Foot Low-Speed Tunnel in 1978. Final tests of the General Dynamics 

design occurred in the Full-Scale Tunnel in April 1980. Rockwell's FSW configuration 

underwent preliminary static and dynamic tests in the Full-Scale Tunnel in March 1981. 

Grumman's FSW configuration was tested in the same tunnel during three entries beginning in November 1980. As a result of these tests, DARPA was provided with a timely, 

independent assessment of the high-angle-of-attack characteristics of all three competing designs. Langley gained considerable experience with the unique aerodynamic, stability, and control characteristics of FSW configurations at high angles of attack. 

Following the award of DARPA's X-29 contract to Grumman, Langley's support in the 

area of high-angle-of-attack technology expanded to include additional dynamic force 

tests and free-flight model tests in the Full-Scale Tunnel, spin and spin recovery tests in 

the Langley 20-Foot Vertical Spin Tunnel, control system development studies and 

piloted assessments of high-angle-of-attack behavior in the Langley Differential 

Maneuvering Simulator (DMS), and assessments of spin-entry and post-stall motions 

using a radio-controlled drop model. 

One of the most important, unexpected results of the X-29 high-angle-of-attack study 

came during preliminary static and dynamic tests of a 0.16-scale free-flight model in the 

Full-Scale Tunnel. The X-29 government and industry team (and the entire technical 

community) had expected the X-29 to be heavily damped in roll at high angles of attack 

as a result of the tendency of the FSW to maintain attached airflow at the wingtips 

during stall. However, when Sue Grafton conducted the first dynamic force tests to 

112 Grumman X-29
Langley Contributions to the X-29 

Sue Gm//on with the 1- JO Jorwarcl-swept-wing model. 

measure aerodynamic damping in roll, the results indicated that the X-29 configuration 

would exhibit very unstable values of roll damping at angles of attack above about 

25 deg. This result came as a complete surprise, and additional tests were quickly 

planned to confirm the suspected impact of the unstable damping. Grafton conducted a 

special "free-to-roll" test, in which the X-29 model was mounted to a sting assembly 

that contained a roll bearing which provided a 360-deg roll capability. The test technique evaluated the tendency of the model to display unsatisfactory roll characteristics 

at high angles of attack. At low angles of attack, the model was very stable, with no tendency to oscillate or diverge (in agreement with the results of the dynamic force test). 

When the angle of attack of the model was increased to about 25 deg, however, the 

model suddenly exhibited large amplitude wing rocking motions of a periodic nature. 

The wing rock was a nonlinear phenomenon. in that the model motions were selfinitiating and built up to a limited amplitude independent of the magnitude of the initial 

disturbance. 

The early identification of the wing rock led to more tests, wherein it was determined 

that the wings of the X-29 were indeed working as predicted. That is, the airflow 

remained attached at the wingtips. However. vortical flow shed from the long, pointed 

forebody of the X-29 was found to be interacting on the upper fuselage and inner wing 

and causing the unstable dampin g. which was so large that it overwhelmed the stabilizing influence of the attached flow at the wingtips. Interestingly, the X-29 incorporated 

Grumman X-29 113
Langley Contributions to the X-29

the forward fuselage of the Northrop F-5A, which is also known to exhibit wing rock at 

low speeds and high angles of attack because of the same phenomenon. With the cause 

of the instability identified, the X-29 flight control system could be modified to increase 

the level of the artificial roll damping provided by feedback to the flaperons. Fortunately, the flaperons of the X-29 retained their effectiveness because of the favorable 

flow patterns of the FSW at high angles of attack. Estimates indicated that sufficient 

damping could be provided by the flight control system via the roll damper, which utilized the flaperons. 

Free-flight tests of the X-29 model were first conducted in the Full-Scale Tunnel in 

January 1982. A special challenge faced the Langley team, since the X-29 airframe was 

designed for a very high level of aerodynamic instability in pitch (relaxed static stability) with a highly responsive, redundant flight control system that provided stability 

augmentation. The X-29 would be unflyable without the stabilizing inputs of the stability augmentation system. No other aircraft (and no other free-flight model) had ever 

flown with such a high level of relaxed stability. The X-29 incorporated a level of 

relaxed longitudinal stability (-32 percent at low speeds) that was an order of magnitude 

more unstable than the F- 16. Under the leadership of Luat T. Nguyen, the staff programmed the X-29 control laws into the Langley computer that was used to replicate 

full-scale controls for the model flight tests. With a vane on the model nose boom providing information on angle of attack, the control system of the model performed 

flawlessly during the entire test program. The X-29 model became the first flying vehicle with such a level of relaxed stability. 

X-29 free-flight model undergoing tests at high angles ofattack in the Lan glev Full-Scale Tunnel. 

114 Grumman X-29
Langley Contributions to the X-29 

During the free-flight tests led by Daniel G. Murri and Sue Grafton, the model exhibited 

large amplitude wing rock near an angle of attack of 25 deg when the roll damper component of the flight control system was turned off, as had been observed in the free-toroll tests. The wing rock became more severe with increasing angle of attack, and flights 

usually resulted in loss of control of the model near an angle of attack of 30 deg. The 

amplitude and frequency of the motions were in close agreement with the preliminary 

tests. When the roll damper was engaged, the motions quickly damped out and the 

model displayed satisfactory characteristics. 

The timely identification of the unstable roll damping of the X-29 configuration was a 

major contribution of Langley for the aircraft. If the full-scale aircraft flight program 

had begun without the provision for adequate control system gains and an awareness of 

a possible roll-damping problem, the high-angle-of-attack characteristics of the X-29 

could have been unacceptable. Ultimately, the X-29 did display the wing rock tendency 

in flight (although not to the degree of severity indicated by the model tests). However, 

the controls of the full-scale aircraft were even more effective than those of the freeflight model, and the control system had been designed with provision to increase the 

gain of the roll damper. The two X-29 aircraft subsequently exhibited entirely satisfactory characteristics in flight, and the technical community learned a lesson regarding 

the integrated aerodynamic contributions of FSW configurations with long, pointed 

fuselages. 

In 1983, Luat Nguyen led a piloted assessment of the X-29 at high angles of attack in 

the DMS. The objectives were to study the high-angle-of-attack flying characteristics of 

the aircraft and its susceptibility to departure under maneuvering conditions, identify 

and develop control law concepts to provide good flying qualities and a high level of 

departure-spin resistance, assess the effectiveness of the Grumman flight control laws at 

high angles of attack and provide recommendations for modifications, and provide support for flight-test planning and coordination with NASA Dryden Flight Research 

Center. 

A priority issue in the DMS studies was the effect of Reynolds number on aerodynamic 

characteristics. Results of high Reynolds number tests in the NASA Ames 12-Foot Pressure Tunnel indicated that significant effects of Reynolds number on pitching moments 

and yawing moments existed for the X-29 configuration. Working with flight control 

team members from Grumman and Dryden, Nguyen completed an in-depth study of 

X-29 handling qualities at high angles of attack and provided numerous recommendations for the specific design of the flight control system for high-angle-of-attack conditions. Control law concepts were identified for control surface interconnects for 

optimum roll coordination, wing rock suppression, and automatic departure and spin 

prevention. 

Spin Tunnel Tests Tests of the X-29 in the Langley 20-Foot Vertical Spin Tunnel, which began in 1981 

under Raymond D. Whipple, concentrated on three areas. First, the developed spin and 

spin recovery characteristics of the X-29 were determined for various aircraft loadings 

and erect and inverted spins. As previously mentioned, large Reynolds number effects 

had been predicted for the X-29 configuration. These effects were very noticeable at 

very high angles of attack (near 90 deg), where the model might exhibit critical spins. 

To correct for these effects (which were caused by the unique forebody shape that was 

incorporated from the F-5A) at the low speeds involved in the Spin Tunnel conditions, 

the Langley staff employed auxiliary strakes on the nose of the X-29 spin model. The 

Grumman X-29 115
Langley Contributions to the X-29

X-29 model exhibited two types of spin. One type was flat, with an angle of attack of 

about 85 deg. with marginal to unsatisfactory spin recovery. The second spin was very 

oscillatory, with satisfactory to excellent recovery characteristics. 

The second area of interest was determination of the size of the emergency spin recovery parachute required for the number 2 aircraft, which would be used in the high-angleof-attack flight-test program. Working with Grumman and Dryden. Whipple and the 

X-29 team arrived at a recommended parachute size, truss structure, and deployment 

mechanism. As a result of the outstanding maneuverability and spin resistance exhibited 

by the X-29. the emergency parachute system was never utilized in flight tests to ternhinate post-stall maneuvers. 

The third area of interest in the Spin Tunnel test program involved concern over the possibility of a longitudinal tumbling phenomenon for the X-29. This concern had risen 

because of the high level of inherent longitudinal instability designed into the X-29. 

Specifically. Langley researchers expressed concern over whether the combination of 

very low airspeed and very high angle of attack (such as during recovery from a "zoom 

climb" to zero airspeed) might result in the aircraft pitching over into an end-over-end 

tumbling that would result in incapacitating g-levels for the pilot. The Spin Tunnel staff 

first addressed this issue in free-spinning tests wherein the X-29 model was launched 

tail first, without rotation, into the vertically rising airstream. The results of these 

exploratory tests showed that, without inputs from the control system. the model would 

indeed pitch over and develop a continuous tumbling motion about its center of gravity. 

The wild gyrations quickly caused the spin tunnel model to impact the walls of the tunnel, so an additional test technique was developed to study the issue under more controlled conditions. In these tests, the model was mounted on a special single-degree-offreedom test apparatus that permitted 360-deg free-pitching motions. The additional 

The spin parachute and truss assembl y on the X-29 during high-angle-of-attack tests at Drvden. 

116 Gruinnian X-29
Langley Contributions to the X-29 

\-2 ,u11 In(u,lfl(l on 

pitch-tumble test appuiatus in the Lun'/ev .S'pin Tunnel. 

studies of tumbling on this apparatus provided insight to a possible solution to the problem. The X-29 flight control system included aft-fuselage strake flaps, which were 

intended to be used only as trimming devices. However, during the tumbling tests it was 

found that the strake flaps were extremely efficient in promoting recovery from the tumble motions. In view of this result, the control system was modified to permit use of the 

strake flaps as control devices. This approach prevented the X-29 from entering the 

uncontrollable tumbling motions. 

Drop-Model Tests In 1987. Langley upgraded its drop-model test technique and conducted studies of the 

high-angle-of-attack and post-stall characteristics of a 0.22-scale model of the X-29. 

The high degree of relaxed stability of the X-29 made high-fidelity simulation of the 

control system a mandatory feature of the drop model. Langley had never flown an 

unstable model before the X-29 program. The Langley staff, led by Mark A. Croom, 

upgraded nearly every element of the drop-model operation, such as the model control 

actuators, transmitters and receivers, data encoders and decoders, and operational displays including a new cockpit display and operations monitor. The advanced X-29 control laws developed in the DMS study were programmed into a ground-based computer 

for proper simulation of control effects. This activity was by far the most challenging 

drop-model project ever conducted by Langley to that time. 

Grumman X-29 117
Langley Contributions to the X-29

The results of the drop-model program further confirmed the need for special control 

system concepts for high-angle-of-attack conditions. Without artificial stability augmentation in roll, the drop model exhibited the same type of large amplitude wing rock 

motions previously displayed by the wind-tunnel free-flight model. In the case of the 

drop model, when the angle of attack was increased to 30 deg and beyond, the oscillations became so divergent that the model exhibited uncontrollable 360-deg rolls that 

evolved into a roll departure and post-stall gyrations. When the wing rock suppression 

system was engaged, the motions were damped and the model was controllable to very 

high angles of attack. 

During some flights at extreme angles of attack, asymmetric yawing moments were 

encountered that caused the model to yaw and generate relatively high rotational rates. 

When the pilot intentionally applied prospin control inputs during these conditions, the 

model sometimes entered the unrecoverable flat spin mode exhibited by the spin tunnel 

model. With the departure and spin prevention system engaged, the model was highly 

resistant to intentional spins and was extremely maneuverable at high angles of attack. 

Another valuable contribution of the X-29 drop-model program was a parameter identification effort conducted by David L. Raney and James G. Batterson of Langley, in 

which they analyzed the wing rock motions of the drop model and extracted values of 

the critical aerodynamic parameters that caused the motions. This complex analysis 

required the identification of rapidly changing aerodynamic derivatives over a range of 

angle of attack. The results of the study clearly identified unstable values of aerodynamic damping in roll to he the cause of the wing rock motions. 

X-29 drop model mounted 00 launch apparatus onside

of helicopter prior to release for post-stall tests. 

118 Gruiniiiaii X-29
Langley Contributions to the X-29 

Engine Inlet Tests - - - - - Grumman requested support from Langley in assessing the static and dynamic pressure 

conditions that might be experienced by the engine inlets during the high-angle-ofattack flight tests of the X-29. The data were required to ensure satisfactory engine operation and avoid engine stalls that could result in loss of hydraulic power during the spin 

maneuvers. Langley responded with tests of a powered X-29 model in the 14- by 

22-Foot Subsonic Tunnel. The model was equipped with a propulsion simulator, flowthrough inlets, and extensive instrumentation. These tests occurred in 1991 under the 

leadership of John W. Paulson, Jr. 

X-29 penciec/-inlet model tesis in the

Lan i'Iev 14- hr 22-Foot Subsonic Tunnel. 

AeroelasricDit'ergence - The phenomenon of aeroelastic divergence had dramatically constrained international 

interest in the application of conventional metal FSW concepts. Franklin W. Diederich 

and Bernard Budiansky of Langley studied and summarized the major challenges of the 

divergence phenomenon in a NACA Technical Note in 1948 (ref. I). However, the emergence of composite materials and the aggressive advocacy of Norris Krone to utilize 

aeroelastic tailoring to reduce divergence led to cooperative studies of FSW technology 

by the staff of the Langley 16-Foot Transonic Dynamics Tunnel (TDT). Rodney H. 

Ricketts, Robert V. Doggett, and Wilmer H. Reed, Jr. planned and participated in numerous studies with DARPA, the Air Force, and industry to develop and verify analytical 

predictions of the divergence phenomenon. The studies investigated systematic generic 

wings and specific configurations, including the Rockwell and Grumman FSW designs. 

Grumman X-29 119
Langley Contributions to the X-29

1. SIR 

C

- 

Riuliu'v Rit keirs ui/li the (1unuuuiuuuIl I' SR uiwulel during aeroelastic 

divergence tests in the Lang/er 16-Foot Transonic Dvna,nius Tunnel. 

The analyses and tests of generic wing models with variations in aspect ratio, airfoils, 

and sweep provided invaluable data and methods that significantly expanded the database, especially in the transonic regime. Six subcritical response test techniques were 

formulated and evaluated at transonic speeds for accuracy in predicting static divergence. and two divergence stoppers were developed and evaluated for use in preventing 

structural damage of wind-tunnel models during divergence tests. 

Ricketts led cooperative tests of the proposed Grumman and Rockwell FSW configurations in the TDT in 1979. NASA. DARPA. the U.S. Air Force, and the industry teams 

participated in the cooperative tests. The Rockwell model consisted of a seniispan wing 

mounted to a splitter plate on the tunnel sidewall. The Grumman model included a 

representative fuselage shape. Conclusions from the divergence tests included dramatic 

demonstrations that aeroelastic tailoring was extremely effective in suppressing divergence for FSW configurations and that new nonlinear aerodynamic theories were 

required for complete analysis of the phenomenon. After the DARPA X-29 contract was 

awarded to Grumman, additional tests were conducted in the TDT in 1983 which demonstrated the potential coupling of the wing structural modes with the rigid body pitch 

mode to create an instability called body-freedom flutter. Techniques were developed to 

analyze these wing-body interactions, and the wing divergence prediction methods 

developed at Langley were used in the flight-test program of the X-29 at Dryden. 

Advanced Engine Nozzle - In the early 1970's, an advanced thrust-vectoring nozzle for V/STOL aircraft was 

designed by the General Electric Company under a contract funded by the Navy. The 

nozzle was designed with a deflectable internal hood to permit large pitch thrust-vector 

angles for V/STOL operations, while deflection of the single expansion ramp could he 

used for smaller thrust-vector angles during air-to-air combat. This nozzle, known as the 

augmented deflector exhaust nozzle (ADEN). received considerable test and developmental support in the technical community during the 1970's and early 1980's. Much of 

this activity was advocated by the Department of Defense (DOD). NASA. the U.S. Air 

120 Grumman X-29
Langley Contributions to the X-29 

Simple ADEN-like ,u):zlc iinii,'uratjon (pitch and van' i'e(torjln,')

flon'n on X-29 free-flight model in the Full-Scale Tunnel. 

Force, and the U.S. Navy ad hoc interagency nonaxisymmetric nozzle working group 

that included Langley researcher Bobby L. Berrier as the NASA representative. The 

Propulsion Aerodynamics Branch at Langley conducted much of the development work 

on the ADEN under the direction of William P. Henderson and Bobby Berrier. Numerous cooperative ADEN research programs with DOD and industry were conducted to 

optimize nozzle performance and define suitable propulsion-airframe integration methodologies on a series of generic and specific (e.g.. F-18) fighter configurations. The first 

full-scale nonaxisymmetric nozzle test was conduced at the Glenn Research Center in 

1976 by running an ADEN nozzle attached to an augmented General Electric YJIOI 

engine in an altitude test cell. Thus, by the time of the DARPA X-29 award to Grumman 

in 1981, a mature thrust-vectoring nozzle design was available. 

During the early phases of the X-29 program, NASA Headquarters expressed interest in 

the application of the ADEN to the canard configured X-29 as an exploratory flight-test 

bed, since the canard of the X-29 could counterbalance the effects of the deflected 

ADEN nozzle. The NASA interest in the X-29 ADEN was to promote technical 

progress in vectorable nozzles and ensure that a sufficient number of candidate nozzles 

were considered for further development. 

Grumman X-29 121
Langley Contributions to the X-29

NASA Headquarters requested Langley's assessment of the X-29 ADEN configuration 

for further advocacy discussions with Grumman and DARPA. Although no induced lift 

or aerodynamic wing lift augmentation would occur for this configuration, the addition 

of vectoring was believed by Langley to improve high-angle-of-attack controllability. In 

response to this request from Headquarters. Joseph L. Johnson. Jr. and his staff at the 

Full-Scale Tunnel quickly modified their X-29 free-flight model and conducted exploratory evaluations of the handling qualities of the X-29 ADEN at high angles of attack in 

1984. During these tests, a yaw-vectoring side-door capability (a concept defined and 

tested by the Propulsion Aerodynamics Branch in the Langley Jet Exit Test Facility) was 

added to a simplified ADEN-type nozzle to provide both pitch and yaw vectoring, and 

the resulting flight tests demonstrated a dramatic improvement in controllability and 

agility of the X-29 at extreme angles of attack. The model could be flown with precise 

and effective control to angles of attack as high as 85 deg. These positive results were 

typical of those that had been obtained with several different aircraft configurations 

equipped with other thrust-vectoring nozzles. The national progress in nonaxisymmetnc, thrust-vectoring nozzles led to interest in other nozzle configurations and the eventual successful F- 15 short takeoff and landing and maneuver technology demonstrator 

(STOL/MTD), F-18 High Alpha Research Vehicle (HARV). and X-31 flight-test 

programs. 

X-29 i)1\ model /1\ in,, , (a an angle at attack of 80 deg in the Langle y Full-Scale Tunnel. 

122 Grumman X-29
Highlights of Research by Langley for the C-5 

Lockheed C-5 Galaxy 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE C-5 

I. The aerodynamic performance of three competing industry configurations for the 

C-S contract was determined by model tests in the Langley 8-Foot Transonic Tunnel. 

2. Aerodynamic interference between the wing and the large engine nacelles and 

pylons were measured during tests in the 8-Foot Transonic Tunnel. 

3. Parametric tests in the Langley 16-Foot Transonic Dynamics Tunnel of a clippedspan C-S model identified an abrupt drop in tail flutter speed at transonic Mach numbers that required increased stiffening of the fin spar. 

4. An active load alleviation system was developed in the Langley 16-Foot Transonic 

Dynamics Tunnel. 

5. Powered-model tests in the Langley 30- by 60-Foot (Full-Scale) Tunnel provided 

information on C-S airdrop (wake) characteristics and power effects for the landing 

configuration. 

6. Tests of a C-5 model were conducted to determine an optimum ditching cotifiguration. 

SPECIFICATIONS 

Manufacturer 

Lockheed 

Date in service 

C-5A.......December 1969 

C-SB ......... January 1986 

Type 

Transport 

Crew 

Six 

Engine 

General Electric TF39-GE-IC 

USERS 

U.S. Air Force (Active, Air 

National Guard, and Reserve) 

DIMENSIONS 

Wingspan...........222.8 ft 

Length .............247.8 ft 

Height ..............65.1 ft 

Wing area ........6.200 sq ft 

WEIGHT 

Empty ............370.000 lb 

Max takeoff ....... 837.000 lb 

PERFORMANCE 

Cruise speed ........563 mph 

Range ............ .3,000 n mi

Lockheed C-5 Galaxy 123
Highlights of Research by Langley for the C-5 

The Lockheed (now Lockheed Martin) C-5 Galaxy heavy-cargo transport provides strategic airlift for the worldwide deployment and supply of combat and support forces. The 

C-5 can carry unusually large and heavy cargo for intercontinental ranges at high subsonic speeds. The aircraft can take off and land in relatively short distances and taxi on 

substandard surfaces during emergency operations. The C-5 is one of the largest aircraft 

in the world. It is almost as long as a football field and is as tall as a 6-story building 

with a cargo compartment about the size of an 8-lane bowling alley. The C-5 and the 

smaller C-141B Starlifter are strategic airlift partners. Together they can carry fully 

equipped, combat ready troops to any area in the world on short notice and provide the 

full field support necessary to maintain a fighting force. The C-5 can carry a payload 

that is more than twice as heavy as the C- 141 payload. The lower deck of the C-5 has an 

unobstructed length of 121 ft and width of 19 ft that enables it to carry any piece of 

Army equipment, including self-propelled howitzers, personnel carriers, and tanks—

none of which can enter the payload bay of the C-l4l. 

Langley's contributions to the C-5 program included wind-tunnel tests and performance 

analysis of the competing industry designs during the Cargo Experimental–Heavy 

Logistics System (CX–HLS) Program that resulted in the C-5. Langley conducted windtunnel assessments of engine and wing aerodynamic interactions; flutter studies of the 

1-tail configuration; flutter clearance tests for the complete configuration; wind-tunnel 

studies of an active load alleviation concept; flow surveys behind the configuration for 

analysis of airdrop characteristics; assessments of power-induced effects in the landing 

configuration, including studies of potential applications of the externally blown flap 

concept (subsequently incorporated in the C-17 transport); and model tests to determine 

the optimum ditching configuration. Langley facilities involved in C-5 tests included the 

8-Foot Transonic Tunnel, the 16-Foot Transonic Dynamics Tunnel (TDT), the 16-Foot 

Transonic Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, and the Langley Impacting 

Structures Facility (Tow Tank). 

124 Lockheed C-5 Galaxy
Langley Contributions to the C-5 

LANGLEY CONTRIBUTIONS TO THE C-5 

C-5 Evaluation In 1964, the Air Force awarded study contracts to Boeing, Douglas, and Lockheed for 

the design of a heavy-lift transport for the Cargo Experimental—Heavy Logistics System 

(CX—HLS). In December 1964, the three manufacturers were invited to submit proposals for the new transport, which was intended to carry bulky and heavy military equipment that could not be accommodated in the C-141. All three industry designs 

incorporated high-wing configurations with four large turbofan engines in underwing 

nacelles and front and rear doors with ramps for flow-through loading and unloading. 

The Boeing and Douglas designs had conventional tail configurations, whereas the 

Lockheed design incorporated a T-tail configuration. 

At the request of the Department of Defense (DOD), Langley conducted aerodynamic 

assessments of all three designs in the Langley 8-Foot Transonic Pressure Tunnel in 

1965 under the leadership of Langley researcher Dr. Richard T. Whitcomb. The results 

of these tests were provided to a committee to select the winning C-5 design. In an 

extremely controversial decision based on proposal cost estimates, industry workloads, 

and geopolitical considerations, the Air Force announced in October 1965 that 

Lockheed had been selected to proceed with development of their C-5 design. 

The C-5 design submitted by Boeing was found to have superior aerodynamic cruise 

performance in the transonic wind-tunnel tests performed at Langley. Boeing's experience with the C-S competition coupled with Boeing management's vision of the marketability of jumbo civil transports (and interest from Pan American Airlines) led to the 

development of the Boeing 747, which enabled Boeing to dominate the world market 

with a new product line. Although the 747 was a completely new aircraft design (low 

wing, passenger-carrying civil aircraft), the general configuration influence of the earlier 

C-S candidate is in evidence. 

Research on Sting Interference Analysis of the data from the Langley 8-Foot Transonic Pressure Tunnel tests of the 

Effects three C-5 configurations indicated that the high degree of aft-fuselage bottom upsweep 

of all the configurations increased cruise drag (especially the Douglas design, which 

had 19 deg of upsweep). Because of the critical nature of the aft-end drag, concern 

arose over potential interference effects caused by the model support sting on drag 

measurements. 

Donald L. Loving and Arvo A. Luoma conducted tests in 1965 of all three configurations with conventional stings, dummy stings, and dorsal strut-support systems over a 

limited range of test variables from just below to just above the design cruise condition 

of each configuration. The results of their investigation indicated that the sting interference effects were of very small magnitude. 

Research on Effects of Test Also in 1965, a study was conducted by Langley researchers Arvo Luoma, Richard J. 

Section Size Re, and Donald Loving to address concerns over the effect of model size during transonic tests of large models in the 8-Foot Transonic Pressure Tunnel. In wind-tunnel 

tests, the largest model possible is generally desirable so that higher model Reynolds 

numbers are obtained, but if the model is too large potential tunnel wall effects and data 

corrections become concerns, especially at high subsonic and transonic speeds. Comparative aerodynamic data were obtained for the same 5-ft-span model of the C-S in the 

Lockheed C-5 Galaxy 125
Langley Contributions to the C-5

ConieIu,g (-5 ((nlflguratio,is clilli/Ig tests ill the Lan g/ev -Ioot l,an.an,u 

Pressure Tunnel. 

figurations

to bottom: Douglas. Lockheed, and Boeing designs. 

126 Lockheed C-5 Galax
/ 

Langley Contributions to the C5 

C-5 model mounted /or tunnel levi section stud y in the Langley 16-Foot Transonic Tunnel. 

Langley 8-Foot Transonic Pressure Tunnel and the Langley 16-Foot Transonic Tunnel 

for Mach numbers from 0.75 to 0.83. The 5-ft-span model was two to three times larger 

than usual models tested in the Langley 8-Foot Transonic Pressure Tunnel. 

The results of the study indicated that the data obtained in the two tunnels were in good 

agreement and that large models could be tested in a slotted tunnel such as the 8-Foot 

Transonic Pressure Tunnel at subsonic speeds with acceptable results. 

Propulsion Integration In 1966, Langley researchers James C. Patterson, Jr. and Stuart G. Flechner conducted 

Research parametric studies in the Langley 8-Foot Transonic Pressure Tunnel to determine the 

effects of large high-bypass engines on the interference drag of wing-nacelle configura -

tions at cruise conditions. In the study, a large powered semispan model that incorporated tip-driven, nitrogen-powered engine simulators was used. The baseline model 

configuration represented the C-5; however, the horizontal and vertical positions of the 

engines relative to the wing were varied so the effects of the engine exhaust wakes could 

be studied in detail. The results of the study indicated that the interference drag 

effects could actually be beneficial for certain combinations of wing-nacelle geometric 

parameters. 

Ponered C-5 selni,vpan model in the Lung/er -luui 1iu,iniu Lu uleic ijmnmiel. 

Lockheed C-5 Galax y 127
Langley Contributions to the C-5 

Low-Speedwid Wake - In late 1965. the Air Force requested that tests he conducted in the Langley 30- by 

Characteristics 60-Foot (Full-Scale) Tunnel to investigate the application of the externally blown flap to 

the C-S aircraft. Close examination of the C-S configuration indicated that the engine 

exhaust would blow strongly on the trailing-edge flaps and that the aircraft would probably have considerable jet-flap lift effect in its basic configuration. The jet-flap lift effect 

might be sufficient to promote marked improvements in takeoff and landing performance that had not been anticipated. However, the jet-flap effect could induce pitch and 

roll trim problems that were also not anticipated. The Air Force request included tests of 

a semispan powered model, as well as a full-span powered model. 

The examination by Langley of the C-S configuration indicated that several features of 

the wing and flap did not lend themselves well to adaptation of a high efficiency jet-flap 

arrangement. For example, the flap configuration was not optimum for blown flap applications. As a result of concern expressed by Langley, a two phase program was conducted. The first phase of the program measured the effects of power on lift and drag 

characteristics and the effect of power (and engine-out conditions) on the longitudinal 

and lateral trim requirements. control, and stability of the basic C-S configuration. The 

second phase of the research program consisted of modifying the wing and flap system 

to provide a more optimal configuration for an efficient jet flap. 

In 1966, a powered semispan model of the C-S underwent two test entries in the FullScale Tunnel to determine a limited amount of power effects, including the effects of 

thrust reversers. Unfortunately. Lockheed changed the trailing-edge flap system of the 

C-S from a double-slotted configuration to a Fowler flap configuration, and the tests had 

to be conducted with an outdated flap system. 

In 1967, a full-span 0.057-scale model of the C-S was tested in the Full-Scale Tunnel to 

determine the effect of the externally blown flap concept on the aircraft. The initial work 

was done with the original, nonoptimized double-slotted flap design. Subsequent work 

was done with a new flap system that was designed specifically for the blown flap concept by the Langley staff under the leadership of Joseph L. Johnson, Jr. 

Pooered C-5 model mounted in the Lwmglev Full-Scale Tunnel

for external/N, blowim flap as.sess,oents %tit/i the

double-slotted flap configuration. 

128 Lock/iced C-5 Galax'
Langley Contributions to the C-5 

Lan glev engineer Charles C. Smith, Jr. conducts flow

visualization studies on the modified C-5 model. 

The results of the wind-tunnel study indicated that, as had been predicted by Langley. 

the blown flap effectiveness for the original double-slotted flap configuration was relatively modest. Modifications required to obtain a more optimal externally blown flap 

configuration were fairly extensive, including new trailing-edge flaps, relocation of the 

horizontal tail, and resizing of the vertical tail and rudder for control of engine-out conditions. Although such modifications were beyond the scope and interests of the C-5 

program. Langley conducted additional wind-tunnel tests of the modified C-5 configuration, including free-flight model tests and piloted simulator studies. Although not 

applied to the C-S. this research provided critical information, design guidelines, and 

solutions to engine-out issues that were extremel y helpful in the risk reduction and ultimate development of the C- 17 transport. 

At the request of the Army. a survey of the flow in the wake of the C-S full-span model 

was made in early 1968 in the Full-Scale Tunnel to define the dynamic pressure and 

flow angularity for analyses of the airdrop capability of the C-S. 

Tail Flutter The staff of the Langley 16-Foot Transonic Dynamics Tunnel (TDT) led research on 

flutter characteristics of the T-tail configuration as a design feature of large transport aircraft with transonic cruise capabilities in the late 1950's. Although several aerodynamic 

theories had been developed for predicting subsonic and supersonic flutter of T-tails. the 

transonic regime posed special challenges because transonic flutter speeds tend to be 

lowest and are accompanied by complex shock patterns that make flutter analyses difficult. TDT staff members Charles L. Ruhlin and Maynard C. Sandford had been actively 

involved in the flutter issues that faced the C-141 and had contributed to the databases 

for the design of flutter-free T-tails for future aircraft. Their pioneering efforts in the 

C-141 program resulted in new test procedures. validation of computational methods, 

and fundamental research of the complex aerodynamic and structural coupling for the 

new tail designs. Two types of T-tail flutter had been identified by research: symmetric 

tail flutter, which was dominated by pitching-type relative motions of the surfaces, and 

antisymmetric flutter, which was characterized by yawing and rolling relative motions 

of the tail surfaces. Antisymmetric flutter is especially complex, and more data were 

needed to advance the understanding and design tools. 

Lockheed C-5 Galaxy 129
1104 

00' 

0 100 

Langley Contributions to the C-5

Clipped wing model of the C-S in the Lang/er 16-Foot Transonic Tunnel for flutter tests. 

II 

iø 

Full-span model of the C-S in the Lang/er 16-Foot Transonic Dvna,nics Tunnel. 

Ruhlin and Sandford developed an innovative approach to testing large, isolated-tail and 

aft-fuselage models, which permitted more accurate simulation of structural and aerodynamic properties of full-scale aircraft. In late summer of 1966. they began studies of an 

isolated 1/13-scale model of the C-5 empennage, fuselage, and inner wings in the TDT. 

The T-tail, fuselage, and inboard wings were geometrically, dynamically, and elastically 

scaled. Two models of the T-tail were tested—one was built with the C-5 design stiff -

ness. while the second had only half the design stiffness. 

The tail flutter speeds for the designed C-5 empennage were beyond the required flutter 

demonstration speeds: however, a pronounced decrease in flutter speed was observed 

slightly above the maximum Mach number (between 0.92 and 0.98). As a result of these 

tests, the fin spar stiffness was increased, and flutter clearance for the full-span C-5 

model in the TDT was subsequently obtained. 

130 Lockheed C-5 Ga/an
Langley Contributions to the C-5 

Load AlIetation - In the initial design of the C-5, Lockheed implemented an aggressive weight reduction 

program to meet performance requirements. The wing weight was reduced by using 

higher design stress levels and reducing primary component thickness. The higher stress 

levels proved to be a problem, and wing cracks were found early in full-scale ground 

fatigue tests in July 1969. After the aircraft had been in service several years, a wing 

tear-down inspection on one aircraft with a high number of flight hours revealed significant cracks. Lockheed proposed several approaches to restore C-S wing fatigue life to a 

specified level of 30.000 flying hours. These approaches included (1) an active aileron 

system to alleviate gust loads on the wing. (2) local wing modifications to improve 

fatigue. and (3) redistribution of fuel within the wing to reduce bending moments. 

Langley researchers Ruhlin and Sandford conducted tests of the C-S active lift distribution control system (ALDCS) in the 16-Foot Transonic Dynamics Tunnel in 1973. The 

results of this study validated the use of active control technolo gy for the minimization 

of aircraft aeroelastic response and showed that scaled aeroelastic wind tunnel models 

can be used in developing active control systems. 

Active ailerons were retrofitted to 77 C-S's in 1975 through 1977. That approach, however, was superseded by a redesign of the wing that included a new center wing, two 

inner wing boxes, and two outer wing box sections, which were manufactured from 

advanced aluminum alloys that were unavailable when the original wings were produced in the late 1960's and early 1970's. As a result, all C-S aircraft were modified with 

the new wings.

2 eI 

, I 

' 

I0 

041P,O 1.0 

Active load alleviation test of the C-5 in the 

Lan glev 16-Foot Transonic D ynamics Tunnel. 

Ditching Tests Langley conducted ditching investigations for military and civil aircraft (including the 

Space Shuttle) for many years in a water tank facility known as the Langley Impacting 

Structures Facility. Following World War II, aircraft shapes and sizes did not vary significantly from the existing database that was generated by the Langley research. However, the introduction of the C-S and other large wide-body civil transports required the 

prediction of ditching characteristics for heavier and larger configurations that were not 

Lockheed C-5 GaIax 131
Langley Contributions to the C-5

C-5 model in Lan glev Impacting Structures Facility for ditching tests. 

C-5 ditching model Hit/I .S j,1!l1la/ed sinictural SkI,? on bottom of model. 

132 Lockheed C-5 Galaxy
Langley Contributions to the C-5 

included in the database. The design configuration and structural features of large cargo 

and transport aircraft also required that a dynamic model be investigated to determine 

overall motions, accelerations, and the approximate location and amount of damage that 

might be expected during a ditching at sea. In addition, the large number of main landing gear wheels (24) for the C-5 and the ability of the landing gear to be extended to various positions offered the possibility of an optimal ditching configuration, since 

previous wheels-down dynamic-model investigations had shown a wide variation of 

ditching performance with landing gear extended. 

At the request of the Air Force, Langley researcher William C. Thompson conducted 

ditching studies of a 1/30-scale model of the C-5 in the Impacting Structures Facility in 

1969. The model was highly instrumented to measure accelerations, and a special 

scaled-structure lower fuselage was included to determine the structural damage 

incurred in ditching. The tests included various impact attitudes, flaps up and down, and 

landing gear retracted and down in simulated calm and rough (simulated sea state 4) 

water. Results of the study indicated that the most favorable condition for ditching was a 

7-deg nose-high attitude with the flaps down 40 deg, the nose gear retracted, and the 

main gear fully extended. For these conditions, damage to the fuselage bottom would 

occur, and most of the main landing gear would probably be torn away. 

Wind-Tunnel Test to Flight- Analysis of flight data obtained with the C-5 indicated that significant differences 

Test Correlation existed between pressure measurements made in the wind tunnel and flight. Similar 

issues had previously arisen during the C- 141 program. These issues involved difficul -

ties with scaling effects in wind-tunnel tests. Extensive fundamental research was initiated in the Langley 8-Foot Transonic Pressure Tunnel under the direction of Richard 

Whitcomb. The research was initiated to develop an approach of simulating high 

Reynolds number flows by using specific placement of artificial boundary-layer trip 

strips on the wing upper and lower surfaces of the wind-tunnel model. The test program, 

which was conducted by Donald Loving, Arvo Luoma, and James A. Blackwell, Jr., successfully identified a methodology that more properly simulated the appropriate boundary-layer thickness in transonic wind-tunnel tests. This technique was used extensively 

in the development of the supercritical airfoil. 

Lockheed C-5 Galaxy 133
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Lrlj

'All 

SPECIFICATIONS 

Manufacturer 

Lockheed Martin 

Date in service 

C- 130A .............1956 

C-130E .............1962 

C-130J .............1996 

Type 

Transport 

Crew 

Three 

Engine 

Allison T56-A- 15 turhoprop

I 

USERS 

U.S. Air Force (Active.Aii

National Guard, and Rcxi c 

U.S. Navy. U.S. Marine Corps. 

U.S. Coast Guard, and over 

65 countries 

DIMENSIONS 

Wingspan........... 132.6 ft 

Length .............. 97.8 ft 

Height ...............38.4 ft 

Wing area ........ 1.745 sq ft

WEIGHT 

Empty ............75,743 lb 

Max takeoff ....... 175.000 lb 

PERFORMANCE 

Cruise speed .........36() mph 

Range ............ ..700 n mi

Highlights of Research by Langley for the C-130 

Lockheed Martin C-130 Hercules 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE C-130

1. Lockheed used aerodynamic computational codes developed by Langley in the configuration development of models of the C- 130. 

2. Under a Langley contract in the early 1970's, Lockheed produced an advanced 

boron reinforced metal center wing box for the C-130 that was flight tested on three 

C- i 30E aircraft. 

3. In the 1980's. Lockheed tested a composite center wing box for the C-130, which 

was not implemented but provided expertise for applications of advanced composites to other Lockheed Martin products, including the F-22. 

4. Lockheed, under contract to Langley. developed piloted simulators and interacted 

with Langley researchers to develop advanced cockpit liquid crystal flat-panel displays for the C- I 30J. 

Lock/teed Martin C- 130 Hercules 135 
Highlights of Research by Langley for the C-130 

The Lockheed (now Lockheed Martin) C-130 Hercules is arguably the most versatile 

military transport aircraft ever built. The aircraft is capable of operating from rough, dirt 

strips and is the prime transport for air dropping troops and equipment into hostile areas. 

C-130's fulfill a wide range of operational missions in both peace and war, with specialized versions of the aircraft that perform an enormous number of roles. The C-130J 

incorporates state-of-the-art technology to reduce manpower requirements, lower operating and support costs, and provide life cycle cost savings over earlier C-130 models. 

Langley's contributions to the C-130 program include composite structures and materials, noise reduction, cockpit displays, and aerodynamic technologies. Lockheed has 

extensively used basic and applied research studies conducted by Langley in the continuous evolution of the C- 130. For example, aerodynamic analyses of wing performance, 

stall characteristics, and loads have been accomplished with computational methods 

developed by Langley. Also, Langley methodology has been used to predict C- 130 exterior noise and to reduce interior noise. Lockheed's participation in the design and development of advanced simulators at Langley and Langley's research on advanced cockpit 

displays led to the adoption of liquid crystal flat-panel displays for the C- 1 30J. The most 

interactive Langley and Lockheed studies of the C- 130 have occurred in applications of 

composite structures and materials. Under Langley sponsored contracts in the 1970's, 

Lockheed fabricated and tested a boron reinforced metal center wing box to improve the 

fatigue life by a factor of three and reduce the weight by 300 lb. The modified wing box 

was subsequently flight tested on three C- 130 aircraft, which are still in routine fleet service. In the 1980's, a subscale all-composite C-130 center wing box was designed, fabricated, and structurally tested as part of the Langley Advanced Composites Technology 

(ACT) Program to validate the potential for increased load levels with reduced weight. 

On November 6, 1998, Lockheed Martin arranged for a C-130J to visit Langley for a 

special ceremony in honor of NASA's continuous contributions to the C-130 Hercules. 

136 Lockheed Martin C-130 Hercules
Langley Contributions to the C-130 

LANGLEY CONTRIBUTIONS TO THE C-130 

Composite Structures and Lockheed Martin has had an interest in Langley research on the development of 

Materials advanced composite structures for the past 30 years. Working under a long series of 

Langley contracts, Lockheed has developed composite flaps, wing trailing edges, and 

propellers for the C-130J. As a result of extensive experience from these efforts, Lockheed has also developed composite process improvements for reduced costs. 

In 1968, thorough inspections of the Air Force C-130 fleet revealed that almost half of 

the 619 aircraft in operational service had fatigue cracks in the center wing section. The 

technical community offered numerous recommendations to update and repair this vital 

aircraft. 

In the 1970's, Lockheed conducted a five-phase program under a Langley contract to 

develop and demonstrate the selective reinforcement of conventional metallic structures 

with boron composites. This program, under the direction of Langley researcher 

H. Benson Dexter, was designed to demonstrate that advanced filamentary boron composites could improve static strength and fatigue endurance with less weight than would 

be possible with metal reinforcement. Contract activities included the development of a 

basis for structural design, selection, and verification of materials and processes; manufacturing and tooling development; and fabrication and test of full-scale portions of the 

center wing box. The baseline C-I 30E aluminum center wing box design was modified 

by removing aluminum and adding unidirectional boron reinforcing laminates bonded 

to the crown of the hat stiffeners in the wing structure. The center wing sections on three 

C-I 30E fleet aircraft with fatigue cracks were replaced with the new stronger aluminum 

wing box. This hybrid design improved the fatigue life by a factor of three while reducing the weight by 300 lb over the conventional metallic wing. Flight tests of the modified center wing structure were later conducted on three C-130E fleet aircraft. These 

aircraft were entered into routine fleet service in 1974 and are still operational. Unfortunately, the Air Force was not ready to commit to the new technology. 

In the 1980's, Lockheed actively participated in several contracts for the development of 

composite wing and fuselage structures that led to the Langley Advanced Composites 

Technology (ACT) Program. Working under a Langley contract managed by Randall C. 

Davis, Lockheed designed and fabricated a full height, half-chord, all-composite center 

wing box for the C- 130. This wing box was designed, fabricated, and successfully tested 

at the higher load requirements of the special operations aircraft. The resulting wing box 

weight was lower than the conventional metal wing box. Funding reductions for the 

ACT Program terminated the potential C- 130 applications, and the remaining advanced 

composite program elements were applied to other aircraft such as the F-22. 

Advanced Cockpit Displays Under NASA contract, Lockheed built three individual simulators that are located at 

Langley, NASA Ames Research Center, and Lockheed. Interactions with the Langley 

staff regarding NASA research on advanced cockpit displays led to the development of 

head up display (HUD) technology and liquid crystal flat-panel displays, which provide 

integrated instrument information and significantly reduce pilot workload and increase 

maneuver precision for the C- 130J. 

Acoustics As a result of certain mission specific requirements, the external and interior noise characteristics of the C-130 have received considerable attention from Lockheed. The utilization of the aircraft for special missions requires that the exterior noise be minimized. 

Likewise, the interior noise for missions that transport combat troops or sensitive instrumentation must be controlled through accurate acoustic analysis. In accomplishing these 

tasks, Lockheed used noise prediction and control methods developed by Langley. 

Lockheed Martin C-130 Hercules 137
Langley Contributions to the C-130 

Aerodvnwnic Technologies The aerodynamic development of the C-130 by Lockheed included the utilization of 

advanced databases of Langley experimental and computational studies. Although no 

wind-tunnel tests of the C-130 configuration have been conducted in Langley flicilities, 

discussions of the interpretation and application of Langley aerodynamic concepts and 

data to the C-130 were common during the development of the aircraft. For example, 

Lockheed's interest in providing short takeoff and landing capabilities to the C-130 

stimulated discussions on all facets of Langley research on high-lift systems. including 

trailing-edge flaps, propeller-induced effects, and powered-lift concepts. Lockheed 

remained particularly informed and interested in potential applications of the externally 

blown flap (EBF) and the upper-surface blowing (USB) powered-lift concepts conceived and developed at Langley. Numerous discussions with Langley researchers took 

place, especially with John P. Campbell and Joseph L. Johnson. Jr. for the EBF concept, 

and with Johnson for the USB concept. 

Lockheed has applied computational codes developed by Langley to assess and improve 

aircraft characteristics, including the stall characteristics of the C-130J. Aerodynamic 

loads and several other significant aerodynamic topics have been investigated with the 

computational code USM3D, which was developed by Neal T. Frink of Langley. 

Another Langley aerodynamic code. FUN2DL was used by Lockheed to simulate the 

effects of leading-edge ice shapes on the C-I 30J wing and empennage lifting characteristics. In this particular application, the code significantly reduced the number of tests 

required to support Federal Aviation Administration (FAA) certification. 

Recognition Visit As a gesture of goodwill and recognition of the contributions of all the NASA research 

centers (Langley. Ames. Glenn, and Dryden)to the development of the C-130 Hercules, 

Lockheed Martin arranged for a visit of a C- 1 30J to the Langley Research Center on 

November 6, 1998. The C-130 flew to Langley from the Lockheed Martin facility in 

Marietta. Georgia. Langley Director Dr. Jeremiah Creedon welcomed representatives 

from Lockheed Martin, Congress, NASA Headquarters, and the Air Force Air Combat 

Command, as well as Langley employees in a formal ceremony at the Langley flight 

hangar. Mr. James A. (Micky) Blackwell. Jr., President of Lockheed Martin's Aeronautics Sector, recognized the contributions of NASA employees to the C- 130 and the fruitful partnership between NASA and industry that it represented. Mr. Blackwell's 

compliments were especially meaningful to the Langley staff because he began his aerospace career as a NASA employee at Langley in 1962 and worked with Dr. Richard 

Whitcomb at the Langley 8-Foot Transonic Pressure Tunnel. 

Lan glev researcher Mary Beth Wusk and her daughter 

complete their tour of the C- 130J at Lan glev in 1998. 

138 Lock/iced Martin C-/30 Hercules
SPECIFICATIONS 

Manufacturer 

Lockheed

Date in service 

May 1964 

Type 

Transport 

Crew 

Six 

Engine 

Pratt \\ hitnc 1F LI-7 

USERS 

U.S. Air Force (Active. Air 

National Guard, and Reserve 

DIMENSIONS 

Win g span ........... 160.() it 

Length ............. 168.3 ft 

Height .............. 39.6 ft 

Wing area .........3,228 sq ft

WEIGHT 

Empty ...........140.882 lb 

Gross .............343.000 lb 

PERFORMANCE 

Max speed .... . Mach number

of 0.83

Range............2,550 n mi

Highlights of Research by Langley for the C-141 

LockheedMartin C- 141 Starlifter 

ra 

.d5I Z ' 

%--AWN _%^N4 

• 

• - .. .. .5. . 

- ..- . . 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE C- 141 

I. Parametric tests in the Langley 16-Foot Transonic Dynamics Tunnel (TDT) of an 

isolated-tail model advanced the understanding of T-tail flutter at transonic conditions. 

2. Although the tail design did not flutter in initial TDT tests, the parametric tests identified several issues. including a large area of transonic flow separation at the juncture of the vertical and horizontal tails that promoted early flutter for some 

configurations. 

3. When an unpredicted elevator-induced flutter problem in flight was exhibited. TDT 

tests identified key factors and solutions. 

4. The isolated-tail tests permitted flutter clearance for a complete model of the C-141 

in subsequent TDT tests. 

5. Langley developed a technique to test dynamically scaled models in TDT to assess 

an aileron reversal problem. 

6. Joint Langley and Air Force runway performance tests with a C-141 aircraft established grooving as an effective solution to hydroplaning accidents. 

Lockheed Martin C- 141 Starlifter 139 
Highlights of Research by Langley for the C-141 

The Lockheed (now Lockheed Martin) C- 141 was the first jet aircraft designed to meet 

military standards as a troop and cargo carrier. It was also the first military aircraft to be 

developed with a requirement for FAA type certification in the contract. The Starlifter is 

the workhorse of the Air Mobility Command. It fulfills a vast spectrum of airlift requirements through its ability to airlift combat forces over long distances, place those forces 

and their equipment either by conventional landings or airdrops, resupply employed 

forces, and extract the sick and wounded from a hostile area. The current C-141B is a 

stretched version of the original C-141A with in-flight refueling capability. The C-141B 

is about 23 ft longer than the C-l4lA, with cargo capacity increased by about one-third. 

The C-141 force, nearing seven million flying hours, has a proven reliability and longrange capability. 

Several critical flutter tests for the C-141 were conducted in the Langley 16-Foot Transonic Dynamics Tunnel (TDT). During these tests, parametric experimental and computational research was conducted on the flutter characteristics of T-tail configurations 

with full-span models and unique isolated-tail models of the C-141 configuration. Studies of the aeroelastic mechanisms responsible for inducing flutter led to significant 

improvements in the prediction and analysis of T-tail flutter at transonic conditions and 

the development of specific modifications to cure flow separation near the intersection 

of the vertical- and horizontal-tail surfaces. During early service, the C-141 exhibited 

tail flutter that was precipitated by large elevator deflections. This phenomenon was also 

replicated and analyzed in the TDT. Langley also conducted research in the TDT to 

assess tendencies of the C-141 to exhibit the aeroelastic phenomenon known as highspeed "aileron reversal". 

The C-141 aircraft was a test subject during joint NASA and Air Force runway traction 

studies, which demonstrated the effectiveness of a runway grooving concept developed 

by Langley. Fifty grooved and ungrooved runway surfaces were tested and grooving 

was established as an effective solution to hydroplaning accidents. Subsequently, runways and highways worldwide were grooved for better traction in inclement weather. 

140 Lockheed Martin C-141 Starl(fter
Ilk 

in 

Langley Contributions to the C-141 

LANGLEY CONTRIBUTIONS TO THE C-141

Tail Flutter In the 1950's, several domestic and foreign high-performance aircraft configurations 

were developed that incorporated T-tail empennage configurations. Unfortunately. operational experiences with some of these aircraft indicated that tail flutter could be a critical problem for this configuration at high subsonic speeds. In July 1954. a British 

Handley Page Victor bomber experienced severe T-tail flutter and crashed during a lowaltitude, high-speed flight test when the tail began wobbling and then tore off the aircraft, which dove into the ground. Noted aviation periodicals, including Aviation Week, 

stated that the accident raised doubts on the high placed T-tail configuration (ref. 6). In 

addition, jet-powered T-tail flying boats had been developed for the Navy that also experienced flutter problems. 

The staff of the Langley 16-Foot Transonic Dynamics Tunnel (TDT) was cognizant of 

the T-tail problem as the C-141 configuration entered the developmental process. The 

complex aeroelastic and aerodynamic factors that had allowed tail flutter to occur were 

discussed and researched in considerable depth by TDT staff members Frank T. Abbott, 

Charles L. Ruhlin. Maynard C. Sandford. and E. Carson Yates, Jr.. The Langley team 

and their peers recognized that the flutter mechanisms of T-tails were not well understood, particularly at critical transonic flight conditions where flutter margins were minimal. In addition, they identified certain geometric parameters, such as dihedral and 

sweep of the horizontal-tail surfaces, to be particularly critical. Carson Yates conducted 

extremely complex analytical calculations that identified the critical parameters and flutter modes for T-tails, and the results of his calculations highlighted the dramatic flutter 

challenge for transonic conditions. 

A formal request from the Air Force for flutter clearance tests of the C-141 in the 

Langley TDT was received. In view of the relatively poor understanding of 1-tail flutter, 

the Air Force, Lockheed, and Langley team agreed to conduct special tests of a dynamically scaled model of the empennage and rear fuselage in the TDT. These tests 

Flutter tnodel of C-14/ empennage in the Langle y 16-Foot Transonic

Dynamics Tunnel in 1961 with highly streamlined original bullet

fairing at the juncture of the horizontal and vertical tails. 

Lockheed Martin C-141 Starlifter 141
Langley Contributions to the C-141

C- 141 model heinç' prepared for flutter tests in the Transonic Dynamics Tunnel in 1962. 

permitted parametric studies and correlation with theory before the full-span model flutter clearance test. Flutter tests of this unique C- I 41 empennage model began in the TDT 

in late 1961. The design configuration did not flutter within the Mach number and 

dynamic pressure ranges tested. A matrix of structural parameters and test conditions 

was covered to determine the relative sensitivity of flutter to variations in physical features such as the stiffness of the horizontal-tail pitch trim actuator, stiffness of the fin 

spar, roll and yaw stiffness of fin-stabilizer joints, rotational stiffness of elevators and 

rudder, and stabilizer mass and yaw and roll. 

During the isolated-tail tests, the NASA and industry team encountered an unexpected 

flow phenomenon on the tail at transonic speeds. The C-141 tail had been designed with 

a streamlined bullet-shaped fairing to improve airflow at the juncture of the vertical and 

horizontal tails. However, at transonic speeds the bullet shape caused adverse pressure 

gradients and shock-induced flow separation over the aft portion of the fin-stabilizer 

juncture. Tufts on the vertical tail illustrated the dynamic and massive flow separation 

regions as the tail fluttered over relatively large amplitudes. The flow separation acted as 

a forcing function to encourage certain flutter modes of the entire tail surface. Yates recommended a redesign of the bullet. including a nonstreamlined shape and a blunt "boat 

tail". Vortex generators on the fin were also evaluated. With the vortex generators and 

bullet modifications, results of the test indicated that the vertical-tail flow separation was 

entirely eliminated and any tendency for flutter was pushed significantly beyond the 

flight envelope. 

The results of the isolated-tail model tests significantly increased the understanding of 

T-tail flutter prediction. and provided extremely valuable background for the upcoming 

flutter clearance test of the complete configuration. When the full-span flutter clearance 

142 Lockheed Martin C-141 Starlifter
Langley Contributions to the C-141 

model of the C- 141 was tested in the TDT in 1962, no flutter was encountered within the 

flight envelope (flutter was pushed beyond 120 percent of design dive speed), and the 

value of the isolated-tail model tests was recognized by the participants. 

After the C- 141 entered service, an unexpected unstable oscillation of the horizontal tail 

was experienced during high-altitude flight tests. The flutter was precipitated by a 

deflection of about 8 deg of the elevator relative to the stabilizer no fix was found in 

flight tests. Analysis by Lockheed indicated that the flutter speed could be raised significantly by increasing the elevator mass balance, and this approach was used to eliminate 

the problem. This elevator-induced flutter mechanism was studied by Maynard 

Sandford and Charles Ruhlin with the isolated-tail model in the TDT, where they found 

that the flutter was reproduced by the model. The tests also verified the effectiveness of 

elevator mass balancing to eliminate tail flutter. 

In summary, Langley's contribution to the C-141 program in the area of flutter generated extensive advances in experimental techniques and analytical methods for funda - mental understanding of T-tail flutter characteristics. The highly successful flutter 

studies of the C-141 resulted in significant advances in the development of T- tail configurations. 

Aileron Reversal - Evaluations of the C-141 indicated that for certain flight conditions the aircraft experienced the phenomenon known as aileron reversal. This phenomenon occurs when a 

deflection for roll control of the aileron at the wing trailing edge results in aeroelastic 

twisting of the wing to the extent that the control effectiveness is nullified or actually 

reversed. That is, a pilot's input to intentionally roll the aircraft results in little or no 

response. In some cases, the effects of aileron reversal can actually roll the aircraft in the 

direction opposite to that intended by the pilot. Accurate predictions of this phenomenon require precise estimates of the aerodynamic behavior of the wing and aileron system under dynamic conditions and at high speeds. The difficulty of estimating 

aerodynamics at transonic conditions made this problem a significant challenge for the 

designers of emerging large, flexible transports such as the C-14I and C-5. 

G 141 /1,0(1(1 In Ililni000 I)viiw,iiis Tuniicl /111 ni/own iee,siil 1,vts in 1966. 

Lockheed Martin C- 141 Starlifter 143
Langley Contributions to the C-141

Langley researcher Irving Abel developed an innovative experimental technique to evaluate aileron reversal tendencies with an aeroelastically scaled C-141 model in the TDT 

during 1964 and 1966. Abel used a cable-mount system in the TDT that had been developed by Wilmer H. Reed. Jr. and Frank Abbott to permit more realistic flutter tests by 

allowing the structural modes of the models to be simulated in free-flight conditions. 

Abel's results for the C-141 model agreed well with flight results and provided a new 

test method to the capabilities of the TDT. 

Runwa y Grooving - In the 1950s. Langley researchers at the Langley Aircraft Landing Dynamics Facility 

focused their research on aircraft braking and directional control performance on wet 

runway surfaces. This effort was led by Langley researchers Walter Home and 

Thomas J. Yager. The phenomenon of tire hydroplaning was identified as a contributory 

factor for unsatisfactory tire traction on wet runways. The associated losses in tire traction in water were defined for a variety of test parameters. A technique that appeared 

promising for improved water drainage at the tire and pavement interface was to modify 

the pavement surface with slots, or grooves, similar to the grooves in aircraft tire treads. 

Basic parametric research on the groove concept was conducted at the Aircraft Landing 

Dynamics Facility. The very positive results led to full-scale, instrumented aircraft tests 

at the landing research runway at the NASA Wallops Flight Facility in 1968. 

In a joint program with the Air Force. Langley evaluated the effects of 50 grooved and 

ungrooved runway surfaces on the braking performance of a C-141 aircraft. On the 

basis of these test results and other aircraft evaluations, the application of grooving to 

runways and the nation's highways has been accepted as an efficient means for minimizing wet pavement skidding accidents.

L A 

C-141 braking tests in a joint NASA. Air Force, 

and FAA program at Wallops Flight Facility. 

Wind Tunnel and Flight During early flight tests of the C-141, the wing pressures and pitching moments were 

Correlation found to be considerably different from those predicted in wind-tunnel tests at supercritical Mach numbers. These discrepancies resulted in several national efforts to establish 

reasons for the differences, with emphasis on wind-tunnel test procedures. At Langley, 

Dr. Richard T. Whitcomb participated in the analysis of the data discrepancy and concluded that wind-tunnel scale effects were the problem. Under the direction of 

Whitcomb, Donald L. Loving led a study in 1965 that focused on the impact of 

144 Lockheed Martin C- 141 Starlifter
Langley Contributions to the C-141 

C-141 model with dorsal strut and lower strut support in the 

8-Foot Transonic Pressure Tunnel for drag correlation studies. 

shock-induced boundary-layer separation. Differences in the relative magnitudes of 

shock-induced flow separation resulted in large differences in aerodynamic loads on the 

wing. Unfortunately, the phenomenon was difficult to model and extremely complex. 

The problem was differences between the relative thickness of boundary layers on models and full-scale aircraft. The importance of artificially locating transition on a model to 

produce the same relative boundary-layer thickness at the trailing edge of the wing was 

highlighted. However, locating the transition point at the appropriate place on the model 

proved to be more an art than a science. The major recommendation from the study was 

to conduct wind-tunnel tests for several artificial positions of transition to evaluate the 

sensitivity of shock-induced separation to modifications of the boundary-layer conditions. Later, James A. (Micky) Blackwell, Jr. of Langley contributed an approach to 

scaling and transition-fixing that was accepted as producing accurate simulations for 

wind-tunnel practice. 

In a tunnel-to-flight study. Langley awarded a contract to Lockheed in 1970 to conduct 

analytical studies on drag estimation for the C- 141 and to obtain a set of fully corrected 

wind-tunnel data on a 0.0275-scale C- 141 model in the Langley 8-Foot Transonic Pressure Tunnel. Lockheed's experience in the C-S program with new transition-fixing techniques and model support systems was applied to the C-141 test data to obtain the 

accuracy required for the study. Model support interference corrections were evaluated 

through a systematic series of tests, and the fully corrected model data were analyzed to 

provide details of the model component interference factors. The results of the investigation indicated that the predicted, subcritical minimum profile drag of the complete 

C- 141 configuration was within 0.7 percent of flight-test data. 

Lockheed Martin C-141 Srarlifter 145
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Highlights of Research by Langley for the F-16 

Lockheed Martin F- 16 Fighting 

Falcon 

SPECIFICATIONS . .

oli 

Manufacturer 

Lockheed Martin . Date in service 

January 1979 

Type 

Fighter-attack 

Crew , .-.. .. . 

One or Two . Enaine

& Whitney

.-

(1 Gone ii FlLc 

Ft ?ii3I_ 

USERS 

U.S. Air luicc. f S. '\Li\ \. .•. . .. -- . , 

Bahrain. Belgium. Denmark, 

Egypt, Greece, Indonesia, Israel, HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F- 16 

South Korea. Netherlands,

Norway. Pakistan, Portugal, I. At the request of industry and Department of Defense. Langley staff participated in 

Singapore. Taiwan. Thailand, F- 16 reviews, from the YF-16 prototype to the current F-16 variants. 

Turkey, and Venezuela 2. The F-16 uses Langley wind-tunnel research on leading- and trailing-edge flap techDIMENSIONS nology for transonic maneuver optimization. 

Wingspan ............ .3l.Ot't 3. Langley's fly-by-wire technology and sidestick controller are incorporated in the 

Length .............. 49.3 ft F-16 Height .............. 16.7 ft 

Wing area .........300.() sq ft 4. Lockheed Martin Tactical Aircraft Systems (LMTAS) sought Langley's guidance 

and accepted recommendations for a wing-body strake that provides superior 

WEIGHT

and

through the aerodynamic phenomenon known as vortex lift. 

Empty ........... 18,591.0 lb 

Typical combat ......3,498.0 lb 5. Langley helped solve numerous F- 16 developmental challenges including 

Flutter clearance 

PERFORMANCE 

Max speed .......above Mach • Spin recovery 

number of 2.0 High-angle-of-attack stability and control 

Radius of action • Recovery from a deep stall 

Air patrol ...... . 866 ii mi 

Typical strike . . . . 676 n mi 6. Langley provided supersonic wing design methods and developmental tests in a 

cooperative program with LMTAS for the F-I 6XL supersonic cruise prototypes. 

Lockheed Martin F- 16 Fighting Falcon 147
Highlights of Research by Langley for the F-16 

The conception, development, and deployment of the F-16 by the Lockheed Martin Tactical Aircraft Systems (LMTAS) Division (formerly General Dynamics) included a 

close working relationship with Langley Research Center. Throughout the design and 

deployment of the F-16, Langley personnel participated in evaluations, wind-tunnel 

tests, and special studies—all of which helped to insure superior maneuverability and 

performance for this first-line U.S. fighter-attack aircraft. The LMTAS and NASA partnership began with the YF- 16 Lightweight Fighter (LWF) Program in 1971. The YF- 16 

concept of a relatively small, highly maneuverable day fighter ultimately evolved into 

the multimission, all-weather F-16, which has been deployed worldwide by numerous 

countries. General Dynamics was awarded the Collier Trophy for 1975 in recognition of 

accomplishments in the development of the F-16. The F-16, with its primary mission as 

a strike aircraft, complements the Air Force F- 15 air superiority fighter. The aircraft has 

been a workhorse for several nations in recent conflicts including Operation Desert 

Storm, Bosnia, and Kosovo. 

Designers of the F-16 frequently interacted with the Langley staff and used Langley 

facilities during the development cycles for the YF- 16 and the F-16. Existing NASA 

data and additional cooperative tests were used to optimize aerodynamic performance, 

stability and control, and aeroelasticity. Langley facilities used by the LMTAS and 

NASA team included the 30- by 60-Foot (Full-Scale) Tunnel, the 20-Foot Vertical 

Spin Tunnel, the Unitary Plan Wind Tunnel, the 16-Foot Transonic Dynamics Tunnel, 

the 7- by 10-Foot High-Speed Tunnel, and the Differential Maneuvering Simulator. 

Langley was involved in research on several variants of the F-16, including the highly 

impressive F-I6XL, which was a derivative that can cruise efficiently at supersonic 

speeds without use of an afterburner. Although not put into production, the F-16XL 

demonstrated the validity of Langley design methodologies for supersonic cruise 

vehicles. 

148 Lockheed Martin F-16 Fighting Falcon
Langley Contributions to the F-16 

LANGLEY CONTRIBUTIONS TO THE F-16 

Early Assessments In early 1972, the Langley Research Center was requested by the Department of 

Defense (DOD) to participate in assessments and tests of competing YF-16 and YF-17 

designs for the Air Force Lightweight Fighter (LWF) Program. Langley researchers, as 

members of DOD source evaluation teams, assessed technical claims of each of the 

competing contractors. The YF-16 configuration underwent extensive wind-tunnel tests 

at Langley, especially in the 30- by 60-Foot (Full-Scale) Tunnel, the 20-Foot Vertical 

Spin Tunnel, the 7- by 10-Foot High-Speed Tunnel, the 16-Foot Transonic Dynamics 

Tunnel, and the Unitary Plan Wind Tunnel. Extensive studies of enhanced control systems for high-angle-of-attack conditions were also conducted in the Langley Differential Maneuvering Simulator (DMS) with pilots from Langley, Lockheed Martin Tactical 

Aircraft Systems (LMTAS) Division, and the Air Force. The results of these studies provided information on the capabilities of the YF-16. Following the selection of the YF-16 

for production as the F-16 in 1974, the precursor tests served as an excellent knowledge 

base for development of the new F- 16 fighter. 

Transonic Performance The air war experience in Vietnam, where the lack of maneuverability of U.S. fighters at 

transonic speeds provided advantages to nimble enemy fighters, was the stimulus for the 

YF-16 program. The Air Force and designers of the YF-16 therefore placed great 

emphasis on achieving unprecedented transonic maneuver capability with excellent 

handling qualities. At that time, Langley researchers under the leadership of Edward C. 

Polhamus were conducting in-depth studies in the 7- by 10-Foot High-Speed Tunnel of 

approaches to obtain near optimum aerodynamic maneuver performance for wings, 

including the use of fixed and variable-camber concepts. Some of the earliest systematic 

wind-tunnel tests determined the most effective geometries for leading- and trailingedge wing flaps. In addition, studies were conducted to develop methodologies for the 

prediction and minimization of undesirable buffet characteristics. The program was 

coordinated with flight tests of actual high-performance fighters at the NASA Dryden 

Flight Research Center. 

Polhamus and his group (including Edward J. Ray, Linwood W. McKinney, Blair B. 

Gloss, and William P. Henderson) provided valuable guidance to the LMTAS design 

team. The insight and understanding provided by the broad database from Langley tests 

permitted development of the extremely effective leading- and trailing-edge flaps used 

by the F- 16. The F- 16 (and most other high-performance fighters) uses specific schedules of flap deflection with Mach number and angle of attack for superior maneuverability at transonic conditions. 

Vortex Lift In the early 1960's worldwide interest in the phenomenon known as "vortex lift" 

increased as a result of aerodynamic studies of highly swept configurations such as the 

Concorde supersonic transport. Two events contributed to the initiation of a world-class 

Langley vortex-lift research program led by Edward Polhamus. 

The first event was a detailed experimental and theoretical study of canard configurations at high subsonic speeds led by researcher Linwood McKinney. McKinney became 

interested in the favorable effects of vortex on lift that were demonstrated during development of the Swedish Viggen canard configured aircraft. McKinney's study indicated 

Lockheed Martin F-16 Fighting Falcon 149
Langley Contributions to the F-16

F-16 in a hard turn with wing leading-edge flaps deflected and ortices produced 

hr the sharp wing-bodr strakes illustrated b y condensation. 

that the favorable effects of the canard trailing vortex on the lifting capability of a closecoupled wing might also be extended to higher angles of attack by the strong leadingedge vortex flow of a slender lifting surface. 

The second event that led to the vortex-lift work at Langley was a cooperative Langley 

and Northrop study of hybrid wings that centered on the use of relatively large, highly 

swept wing extensions at the wing-fuselage intersection to promote strong beneficial 

vortex-flow effects. 

Stimulated by the promise of this revolutionary aerodynamic concept. Polhamus and his 

associates put together a vortex-lift research program that became internationally recognized for its experimental database, analytical procedures, and aircraft applications. In 

addition to Poihamus and McKinney, key members of this team included Edward Ray, 

William Henderson, John E. Lamar. and James M. Luckring. Their research into the 

fundamentals and applications of vortex flows allowed Langley to aid U.S. industry in 

the design of highly maneuverable advanced fighters. 

The evolution of the YF- 16 design at LMTAS included studies of configuration variables such as wing design, maneuvering devices, number and location of engines, control surfaces, number and location of tail surfaces, and structural concepts. As the 

configuration options matured, two candidate configurations competed for priority. The 

first configuration was a simple wing, body, and empennage design, while the second 

design was a twin-tailed, blended-wing body with vertical and horizontal tails on 

booms. The LMTAS team selected the best features of both configurations for the final 

YF-16 design. After considerations of performance, stability, and control were 

addressed, the YE- 16 configuration incorporated a rather wide, blended forebody that 

produced strong vortices at moderate angles of attack. LMTAS had attempted to weaken 

the strength of the vortices by promoting attached flow, but these attempts were not 

successful. 

A team from LMTAS visited the Polhamus group and requested guidance for control of 

the vortical flows emanating from the forebody of the YF- 16. In a historically significant meeting, the Langley team suggested that a completely different approach be used 

150 Lockheed Martin F- 16 Fighting Falcon
Langley Contributions to the F-16 

to control the vortical flow. Specifically. Langley suggested that the leading edge of the 

blended forebody be sharpened to increase (rather than decrease) the strength of the vortices, which could be exploited for additional lift. This modification allowed the forebody vortices to dominate and stabilize the flow field over the aircraft at high angles of 

attack, improve longitudinal and directional stability for the single-tail configuration, 

and stabilize the flow over the outer wing panels. The LMTAS team accepted the recommendation, and subsequent wind-tunnel tests verified the lift-enhancing effect of the 

sharpened wing-body strake. In addition, the sharpened strake significantly reduced buffet intensity at transonic maneuvering conditions. The wing-body strake of the F-16 is 

regarded as a key contribution to its success as a maneuvering fighter. 

When the YF-16 team analyzed the effects of deflected leading- and trailing-edge flaps 

and the sharp-edged wing-body strake on directional stability at high angles of attack, 

they found that the stability contributions of a single vertical tail were significantly 

enhanced. However, the contributions of twin vertical tails were markedly degraded. As 

a result of this analysis, the YF-16 was configured with a single vertical tail. Thus, the 

Langley recommendation for a sharpened wing-body strake favorably impacted other 

configuration features of the aircraft. 

High-Angle-Of-Attack - Increased maneuverability for the YF-16 necessitated extended flight at high angles of 

Stability and Control attack where aerodynamic deficiencies caused by separated airflow can result in sudden 

decreases in stability and controllability. Therefore, special emphasis was placed on 

tests in Langley facilities to insure that the YF- 16 could provide the pilot with "carefree" maneuverability. Langley facilities used included the Full-Scale Tunnel, the Spin 

Tunnel, and the DMS. Helicopter drop-model tests for the YF- 16 and the F- 16 were not 

conducted at Langley because of concurrent resource demands of the B-I and F- I 5 programs and the fast pace of the LWF Program. 

RerIu,- tti//ii,ii I íi. I tith dic tr(e-tIu.i/,i ,n(u/(/

the Yl- -16 used in tests in the Full-Stale Tunnel. 

Lockheed Martin F- 16 Fighting Falcon 151
Langley Contributions to the F-16

To provide superior handling characteristics at high angles of attack, any undesirable 

handling characteristics were pushed out of the operating envelope of the aircraft and 

the flight envelope was limited with an advanced fly-by-wire flight control system by 

LMTAS. This concept has proven to be highly successful and has been used in all variants of the F-16. 

Researchers in the Full-Scale Tunnel conducted exhaustive tests of the YF-16 and the 

F-16 configurations at high-angle-of-attack conditions. Data gathered in these studies 

identified the aerodynamic contributions of components of the airframe, deficiencies in 

stability and control, and potential solutions to these deficiencies. These data also 

formed the basis for piloted simulator studies at Langley and LMTAS that helped 

LMTAS design the flight control system for critical high-angle-of-attack conditions. 

Langley and LMTAS engineers recognized that reliance on the flight control system to 

insure satisfactory behavior at high angles of attack required research on the ability of 

fly-by-wire control systems to limit certain flight parameters during strenuous air combat maneuvers. The YF-16 and F-16 employ the concept of "relaxed static stability" in 

which the aircraft is intentionally designed to be aerodynamically unstable while the 

flight control system provides integrated stability by sensing critical flight variables and 

making the control inputs required to stabilize the aircraft. Cooperative piloted simulator studies were conducted in the Langley DMS to identify critical control system components, schedules, and feedback gains to stabilize the aircraft and pilot system for the 

most demanding maneuvers for high-angle-of-attack conditions. Of particular concern 

was the ability of the horizontal tails and longitudinal control system to limit the aircraft's angle of attack during maneuvers with high roll rates at low airspeeds. Such 

maneuvers are critical because rapid rolling maneuvers produce large nose-up trim 

changes due to inertial effects, whereas the aerodynamic effectiveness of the horizontal 

tails becomes significantly reduced at low airspeeds and high angles of attack. 

Under the leadership of Langley researchers Luat T. Nguyen and William P. Gilbert, 

extensive studies were conducted in the DMS with pilots from Langley, LMTAS, and 

the Air Force. These studies verified the effectiveness of the flight control system and 

identified critical maneuvers that would be tested during the flight development program. Gains in the flight control system were modified and incorporated into the aircraft 

system. New control elements, such as a yaw rate limiter, a rudder command fade-out, 

and a roll rate limiter that maximized the maneuvering envelope with minimal adverse 

effects were developed. The DMS was flown by the LMTAS YF-16 and F-16 test pilots 

who later flew the prototypes. These pilots cited the accuracy of the preflight predictions 

and the valuable training and exposure to potentially hazardous flight-test conditions 

provided by the DMS. 

Curing Deep Stall Early in Langley research, tests of a YF-16 model in the Full-Scale Tunnel indicated 

that if angle of attack was not limited by the flight control system, the aircraft could 

pitch up and attain an undesirable trimmed condition at very high angles of attack with 

insufficient nose-down aerodynamic control to recover normal flight. The Langley 

researchers viewed this "deep" stall as a serious problem that would require significant 

research for resolution. The ability of the YF-16 to enter this deep stall was demonstrated in piloted simulation with the Langley DMS and the results were formally 

reported to the LMTAS team and the Air Force. Unfortunately, other NASA and industry wind-tunnel tests of YF-16 models contradicted the Full-Scale Tunnel results—indicating that the problem would not exist. The engineering community generally agreed 

152 Lockheed Martin F-16 Fighting Falcon
Langley Contributions to the F-16 

that the deep stall was not an issue for the F-16. Flight tests of the YF-16 aircraft were 

not extensive enough to determine susceptibility to deep-stall phenomenon. However, 

the follow-on flight-test program for the F- 16 proved that the favorable projections were 

wrong and that the deep-stall condition actually existed for the aircraft. 

High-angle-of-attack test results obtained on the early production version of the F-16 

configuration in the Full-Scale Tunnel showed the same deep-stall trimmed condition 

that was noted in the YF-16 results. Again, contradictory wind-tunnel results obtained 

elsewhere convinced the engineering community that the aircraft would not exhibit the 

problem. However, in subsequent high-angle-of-attack flight evaluations at Edwards Air 

Force Base, an F-16 that had been subjected to rapid rolls at diminishing airspeeds in 

vertical zoom climbs suddenly entered a stabilized deep-stall condition and the pilot 

was unable to recover the aircraft with normal aerodynamic controls. The conditions for 

the deep stall agreed very well with predictions based on the earlier test results from the 

Langley Full-Scale Tunnel. Fortunately, the test aircraft was equipped with an emergency spin recovery parachute that was deployed to recover the aircraft to normal flight 

conditions. This event brought all high-angle-of-attack flight tests of the F- 16 to a standstill while a solution to the deep stall could be found. 

The excellent correlation of the Langley wind-tunnel data with the events that occurred 

in flight and the ongoing evaluation of the F-16 in the DMS at Langley provided the 

tools to work the problem. A joint NASA, LMTAS, and Air Force team arrived at 

Langley and aggressively sought interim and permanent fixes under Nguyen's lead. 

Working with the evaluation pilots, the team devised a "pitch rocker" technique in 

which the pilot pumped the control stick fore and aft thereby setting up an oscillatory 

pitching motion that forced the aircraft out of the deep stall and allowed recovery to normal flight. The concept was adopted and validated in the F-16 flight-test evaluation at 

Edwards and was incorporated in the flight control system as a pilot selectable emergency mode. A longer term fix was developed in cooperative wind-tunnel tests in the 

Full-Scale Tunnel and in LMTAS wind tunnels. The ultimate fix for the problem (which 

also improved takeoff performance) was increasing the size of the horizontal tail about 

25 percent. This solution has been incorporated in all F-16 production aircraft. 

Langley also identified and developed an automatic spin prevention control system concept that could prevent inadvertent spins for the F-16. Nguyen and his group demonstrated the effectiveness of the system with the DMS and analytical studies. The 

fundamental elements of the system were further refined by LMTAS and incorporated in 

the F-16 fleet. 

As a result of Langley supporting analysis and tests, the advanced fly-by-wire flight 

control systems of the YF-16 and F-16 were designed with confidence that inadvertent 

loss of control incidents that had plagued many earlier fighters would be eliminated. 

Spin Recovery The YF-16 and F-16 configurations underwent extensive tests in the Langley Spin Tunnel to determine spin and spin recovery characteristics, especially for the configurations 

with external store loadings. In addition, these tests determined the size of emergency 

spin recovery parachute that is required for the flight trials. The results of these tests 

indicated trends that were fairly typical of high-performance fighters. The models predicted two types of spins—one spin was a relatively well-behaved moderate spin from 

which recovery was easily effected, and the second spin was a potentially serious flat 

spin at very high angles of attack with poor recovery. The success of the sizing of the 

spin recovery parachute was proven in its successful deployment in the unexpected 

Lockheed Martin F-16 Fighting Falcon 153
- —

,rc 

Langley Contributions to the F-16

deep-stall encounter. The parachute can be credited with saving the invaluable test aircraft as well as the pilot. The development and implementation of the production automatic spin prevention system by the Langley and LMTAS team has minimized 

operational encounters with spins. 

Fly B' Wire and Sidestick In 1954, flight tests of the first fly-by-wire aircraft, a modified F9F Panther jet, were mi- - Controller tiated at Langley. The primary objective of the tests was to evaluate various automatic 

control systems, including those based on rate- and normal-acceleration feedback. However (as is the case in many research investigations), the most valuable result of the 

flight test was related to secondary objectives—in this case the introduction and evaluation of fly by wire and a sidestick controller for pilot inputs. 

In a serendipitous approach, Langley researchers decided to avoid the relatively large 

expense and time required to modify the existing hydraulic flight control system for the 

F91F. Instead they chose to implement an auxiliary system based on a fly-by-wire analog 

concept and a small (4 in.) sidestick controller mounted at the end of the armrest at the 

side of the pilot. The sidestick controller was used as the maneuvering flight controller 

throughout the investigation. Rapid and precision maneuvers such as air-to-air tracking, 

ground strafing runs, and precision landings were evaluated. 

Lan glev test plot William L. AIfwl cliect.s out i/ic side-sric/ coiii,-ol/ei In 1954 studies. 

154 Lock/iced Martin F- 16 Fighting Falcon
'I 

000!:^, ,01 

3 

Langley Contributions to the F-16 

The objectives of the flight program were completed with great success, and the information on various types of automatic control feedback was used for numerous aircraft 

development programs. However, the very successful use of the rudimentary fly-by-wire 

and sidestick controller concepts generated considerable excitement within the research 

community, especially those visionaries that anticipated the weight saving advantages 

for future aircraft. Additional research was conducted at Langley on these systems, 

including the use of a sidestick controller for the Apollo mission. The concept of the flyby-wire control system was later refined and greatly improved in cooperative efforts 

between Langley and Dryden that used a modified Vought F-8 Crusader and surplus 

Apollo di gital computers. 

Flutter Clearance Flutter clearance tests of both the YF- 16 and F-16 were conducted in the Langley 

16-Foot Transonic Dynamics Tunnel (12 tunnel entries for the F-16) under the leadership of Moses G. Farmer. Raymond G. Kvaternik, Jerome T. Foughner. and Frank W. 

Cazier. Numerous external store configurations were investigated and several potential 

flutter problems were identified and solved. LMTAS requested a large number of flutter 

tests to identify critical conditions that would be demonstrated in flight, thereby minimizing very expensive flight-test time. The YF-16 and F-16 did not demonstrate flutter 

within their flight envelopes in the tunnel tests, but valuable improvements in flutter 

margins were identified. For example, a fuel-usage sequence was established for the 

three-bay external tanks that significantly raised the flutter speed. Mass balancing of the 

win-tip missile launcher corrected a potential flutter problem with the wingtip missile 

and underwing missile combination. Several TDT studies were directed at active flutter 

suppression for the F-16 with stores. Beginning in 1979, a joint NASA, General 

Dynamics. and U.S. Air Force Wright Aeronautical Laboratories team initiated a series 

of tests that continued over an 8-year period. These highly successful studies progressed 

through an evaluation of a digital adaptive (no prior knowledge of the aircraft configuration) system. A Langley concept for flutter suppression known as the "decoupler pylon" 

was designed and evaluated by Wilmer H. Reed. Jr.. Cazier, and Farmer, including flight 

tests on an F-16 aircraft-, however, the concept as not implemented in the F-16 fleet. 

J(lO/11( 1: Pint ghner checks out the J-16 model with external stores 

mounted in the 16-Foot Transonic D ynamics Tunnelfor flutter tests. 

Lockheed Martin F-16 Fighting Falcon 155
Langley Contributions to the F-16 

The F-/6XL In the niid-1970's the U.S. Air Force became interested in a fighter aircraft capable of 

"supercruise"—the ability to cruise supersonically without an afterburner while retaining respectable maneuver, takeoff, and landing characteristics. The supercruise requirement drove aircraft configurations to highly swept wing platforms. LMTAS appreciated 

the fact that the modular construction of the YF-16 allowed for relatively simple 

replacement of the outer wing panels and that a supercruiser demonstrator aircraft with 

a highly swept wing would undoubtedly attract considerable interest within the Air 

Force. 

Langley's staff had developed a research program known as the Supersonic Cruise Integrated Fighter (SCIF) Program under the leadership of Roy V. Harris, Jr. As participants 

in previous national and NASA civil supersonic transport programs (SST), the Langley 

staff were leaders in the development of databases and design methods for efficient SST 

configurations. Several in-house supercruiser fighters were designed and tested across 

the speed ranges at Langley. Subsequent to the SCIF program. Langley joined several 

industry partners in cooperative. nonproprietary studies of supercruiser configurations. 

In 1977 Langley and LMTAS agreed to a cooperative study to design a new crankedarrow wing for the F-16 to permit supersonic cruise capability. Personnel from LMTAS 

worked alongside the NASA researchers under the direction of Charles M. Jackson at 

Langley during the studies. The project leader for supersonic design was David S. 

Miller. The results of the wind-tunnel and analytical studies indicated that a viable wing 

could be designed to satisfy the supersonic and transonic requirements. With these 

results, LMTAS initiated a company funded development of an F-16 derivative with 

supersonic cruise capability. Following the spirit of the previous wing design cooperative venture with NASA, a cooperative agreement was signed for mutual efforts on the 

new demonstrator, which was called the Supersonic Cruise and Maneuver Prototype 

(SCAMP).

Project engineer Sue B. Gia/nnz with the free-flight model ot the E-I6XL. 

156 Lockheed Martin F-16 Fighting Falcon
I 

Langley Contributions to the F-16 

F- IOXL protorpe in flight. 

Extensive tests for SCAMP took place in Langley facilities, including the Unitary Plan 

Wind Tunnel, the 7- by 10-Foot High-Speed Tunnel, the 16-Foot Transonic Dynamics 

Tunnel. the Full-Scale Tunnel. the DMS, the Spin Tunnel, and a helicopter drop model. 

During these tests, a team led by researcher Joseph L. Johnson, Jr. identified low-speed 

stability and control issues that required modifying the wing apex with a rounded 

planform. Research on the SCAMP configuration by Langley researchers identified 

numerous advanced concepts for improved performance, including the application of 

vortex flaps on the highly swept leading edge for improved low-speed and transonic performance, automatic spin prevention concepts, and optimized wings for supersonic 

cruise. The final configuration became known as the F-I6XL (later designated the 

F-1 6E), which displayed an excellent combination of reduced supersonic wave drag, 

utilization of vortex lift for transonic and low-speed maneuvers, low structural weight, 

and good transonic performance. The F-I 6XL flutter envelope was cleared in the 

16-Foot Transonic Dynamics Tunnel by Charles L. Ruhlin without significant problems. 

Two (a one-seat and a two-seat) F-I6XL demonstrator aircraft were subsequently built 

and entered flight tests in mid-1982. In recognition of Langley's many contributions to 

the F-I6XL, LMTAS management sent letters of recognition to Langley and senior 

NASA management. Marilyn E. Ogburn of Johnson's group was an invited participant 

at flight-test evaluations of the F-I6XL at Edwards Air Force Base. The results of flight 

tests validated the accuracy of Langley wing design procedures., wind-tunnel predictions, and control system designs based on DMS tests. Unfortunately, the interest in 

Lockheed Martin F- 16 Fighting Falcon 157
Langley Contributions to the F-16

supersonic cruise was replaced by an urgency to develop a dual role fighter with ground 

strike capability. Although the relatively large wing of the F-16XL carried a significant 

amount of weapons, the Air Force ultimately selected the F-15E in 1983 for developmental funding and terminated interest in the F-I6XL. 

158 Lockheed Martin F-16 Fighting Falcon
LI . .—:. 

Highlights of Research by Langley for the F-22 

Lockheed Martin F-22_ Raptor_____ 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-22 

I. At the request of industry and the Department of Defense. Langley personnel participated in reviews from the genesis of the Advanced Tactical Fighter (ATF) Program 

and the YF-22 Prototype Program to the production F-22. 

2. The F-22 utilizes the results of Langley research and development of thrust-vectoring nonaxlsymmetric nozzles and afterbody integration for enhanced maneuverability and reduced drag. 

3. Langley research of the high-angle-of-attack characteristics of the YF-22 and F-22 

proved to be highly accurate and contributed to the outstanding agility and spin 

resistance of the configuration. 

4. Supersonic drag and performance wind-tunnel measurements by Langley agreed 

within 1 percent with flight measurements, which ensured supersonic cruise without 

afterburner. 

SPECIFICATIONS 

Manufacturer 

Lockheed Martin 

Type 

Air superiority lighter 

Crew 

One 

Engine 

Pratt & Whitney Fl 19-PW-100 

USER 

U.S. Air Force 

DIMENSIONS 

Wingspan............44.5 ft 

Length ..............62.1 ti 

Height ..............16.4 ft 

Wing area ..........840 sq ft

WEIGHT 

Empty ............31670 lb 

Max takeoff ......... 60.00 lb 

PERFORMANCE 

Max speed ........hove Mach 

number of 1.7

Lockheed Martin F-22 Raptor 159
Highlights of Research by Langley for the F-22 

In the late 1980's, concern arose among military planners about the aging design (first 

flight in 1972) of the F-is and the possible loss of future air superiority of the fighter. 

Soviet fighters such as the MiG 29 and Su-27 had demonstrated remarkable maneuverability and performance. In addition, fighter technology had taken enormous strides forward with the introduction of stealth, or low observable, technology. There was also 

growing concern over the increased effectiveness of the Soviet air defense system that 

posed a highly lethal environment for the F-Is. Therefore, the Air Force initiated an 

Advanced Tactical Fighter (ATF) Program to develop a replacement for the F-is. The 

request for proposals (RFP) was sent to industry in September 1985, and Lockheed and 

Northrop were chosen in October 1986 to develop two prototype air vehicles designated 

YF-22 and YF-23, respectively. Lockheed teamed with Boeing and General Dynamics, 

while Northrop teamed with McDonnell Douglas. 

The Air Force asked that Langley provide support for the YF-22 and YF-23 development programs on an as requested, equal basis. Within their program funds and interests, Lockheed requested Langley's support in two key areas: supersonic cruise 

performance and high-angle-of-attack and spin technology. Langley facilities used in 

the development of the YF-22 and the F-22 included the Unitary Plan Wind Tunnel, the 

30- by 60-Foot (Full-Scale) Tunnel, and the 20-Foot Vertical Spin Tunnel. The ATF Program was initially conducted at the highest levels of classification, and Langley demonstrated once again that it could make significant contributions in a highly controlled 

environment. 

Langley's contributions to the development and demonstration of the YF-22 were cited 

in a letter of appreciation from the Lockheed Vice President for ATF, James A. (Micky) 

Blackwell, Jr. to the Langley Center Director, Richard H. Petersen in March 1991. 

Blackwell praised the Langley efforts and support of the YF-22 and cited the accuracies 

of Langley wind-tunnel predictions and the dramatic demonstrations of the performance 

and agility of the prototype. Follow-on Langley support for the production F-22 was 

conducted in these same areas. 

160 Lockheed Martin F-22 Raptor
Langley Contributions to the F-22 

LANGLEY CONTRIBUTIONS TO THE F-22 

The Advanced Tactical Fighter By the late 1980's, concern arose among military planners about the aging design (first 

(ATF) Program flight in 1972) of the F-15 and the possible loss of future air superiority of the fighter. 

Soviet fighters such as the MiG 29 and the Su-27 had demonstrated remarkable maneuverability and performance, and were provided to Third World countries. Also, fighter 

technology had taken enormous strides with the introduction of stealth, or low observable, technology. There was growing concern over the effectiveness of the Soviet air 

defense system, because new surface-to-air missiles posed a highly lethal environment 

for the F- 15. Therefore, the Air Force initiated an Advanced Tactical Fighter (ATF) Program to develop a replacement for the F-15. Throughout this planning and competitive 

period, members of the Langley staff were involved in briefings and discussions with 

Department of Defense (DOD), Air Force, and industry teams about technical issues 

and concepts to be exploited by the new aircraft. In October 1985, the Air Force issued 

the original ATF request for proposals (RFP) to seven competing companies. The next 

month, the Air Force revised the RFP to include more stringent low observable requirements. In June 1986, Lockheed, Boeing, and General Dynamics signed a teaming memorandum of agreement, but continued to compete individually for the ATF contract. 

Prime contracts were subsequently awarded by the Air Force to Lockheed and Northrop 

for the development of flying prototypes. Lockheed's design was designated the YF-22, 

and Northrop's design was the YF-23. 

Value of the Langley Database The YF-22 and F-22 aircraft benefited from basic and applied aeronautics research conducted at Langley over the 20-year period prior to the evolution of the programs. In particular, Langley research in nonaxisymmetric thrust-vectoring nozzles, supersonic 

cruise without afterburner, and "carefree" maneuverability with unlimited angle of 

attack had produced concepts, data, and assessments of advanced technologies that ultimately provided the YF-22 and F-22 with superior characteristics. 

The staff of the Langley 16-Foot Transonic Tunnel had long been recognized as the 

world leaders in conceptual research on nonaxisymmetric thrust-vectoring nozzles and 

aft-end aerodynamic integration for advanced fighters. Fundamental studies of isolated 

nozzle performance and vectoring efficiency were coupled with specific configuration 

evaluations during the 1960's, 1970's, and 1980's to the point that risk was considerably 

reduced, along with dramatic predictions for improvements in fighter maneuverability, 

cruise performance, and takeoff and landing performance. 

The contributions of Langley researchers in the prediction and reduction of supersonic 

drag were also well recognized, including fundamental theories and design methods to 

reduce supersonic wave drag. Langley researchers also participated in in-house and 

cooperative studies with industry on supersonic civil and military aircraft. These 

researchers, who used the supersonic capabilities of the Langley 4- by 4-Foot Supersonic Pressure Tunnel and the Langley Unitary Plan Wind Tunnel, conducted years of 

research that came to fruition in the F-22 Program. 

The Langley research program on high-angle-of-attack characteristics of fighter aircraft, 

which was initiated in 1969 in response to an alarming number of fighter aircraft accidents due to deficient characteristics, provided proven test techniques, design concepts, 

and advanced technology for use by the YF-22 and F-22 design teams. The staffs of the 

Langley 30- by 60-Foot (Full-Scale) Tunnel and the Langley 20-Foot Vertical Spin 

Lockheed Martin F-22 Raptor 161
Langley Contributions to the F-22

Tunnel worked closely with industry in generic and specific applications of their 

technologies. 

The YF-22 Program During the ATF competition. the Air Force established that each contracting team could 

draw upon NASA's unique expertise and facilities on an equal basis. The Lockheed 

YF-22 team intended to place considerable emphasis on achieving unlimited angle-ofattack capability and supersonic cruise for their design. Lockheed requested tests in the 

Langley Unitary Plan Wind Tunnel, Spin Tunnel, and Full-Scale Tunnel in support of 

this goal. 

In mid-1989, static and dynamic tests of the YF-22 began in the Full-Scale Tunnel under 

the direction of Sue B. Grafton to determine stability and control at high angles of 

attack. Data was also obtained to develop aircraft control laws. Free-flight tests of a 

YF-22 model to determine low-speed longitudinal and lateral-directional response characteristics and departure resistance were also conducted. The Langley Spin Tunnel was 

used to determine the spin and recovery characteristics of the YF-22 in 1988 and to validate the geometry of the emergency spin recovery parachute. Tests were also conducted 

in the Spin Tunnel to determine rotational aerodynamics during simulated spinning conditions for use in the development of control laws. 

The first flight of the YF-22 prototype occurred on September 29, 1990, and the flighttest phase of the competition ended on December 28, 1990. 

Free-flight tests of the YF-22 model in the Lan gler bull-Scale Tunnel in 1990. 

162 Lockheed Martin F-22 Raptor
Langley Contributions to the F-22 

Letter of Appreciation The success and quality of Langley's contributions to the YF-22 Program were emphasized in a March 12, 1991, letter from James A. Blackwell (Vice President and General 

Manager of the Lockheed ATF Office) to Richard H. Petersen, Director of the Langley 

Research Center. In the letter, Blackwell stated 

On behalf of the Lockheed YF-22 Team, I would like to express our appreciation of the contribution that the people of NASA Langley made to our successful YF-22 flight test program, and provide some feedback on how well the 

flight test measurements agreed with the predictions from your wind-tunnel 

measurements. 

Briefly, the flight test program was an enormous success, and we achieved all 

of our objectives. Between first flight on September 29, 1990, and the last 

flight on December 28, 1990, we flew the two prototypes from 80 knots and 

60' angle of attack to Mach 2+. 

We relied on the NASA Langley Unitary Tunnel to provide the final supersonic 

drag and stability and control data that were used for performance predictions and the flight control law design. We demonstrated supercruise on both 

the GE and P& W-powered prototypes as predicted. The supersonic drag 

determined from flight test agreed within one percent of the predictions that 

were made using the Langley Unitary Tunnel data. The supersonic flying 

qualities were rated excellent; we flew to 15' angle of attack supersonically; 

and we did 360'full-stick rolls demonstrating excellent roll rates and roll 

response. 

The highlight of the flight test program was the high-angle-of-attack flying 

qualities. We relied on: aerodynamic data obtained in the 30- by 60-Foot FullScale Wind Tunnel to define the low-speed, high-angle-of-attack static and 

dynamic aerodynamic derivatives; rotary derivatives from your Spin Tunnel; 

and free-flight demonstrations in the Full-Scale Wind Tunnel. We expanded 

the flight envelope from 20' to 60' angle-of-attack, demonstrating pitch attitude changes and full-stick rolls around the velocity vector in 7 calendar days, 

December 11 to December 17. The reason for this rapid envelope expansion 

was the quality of the aerodynamic data used in the control law design and 

pre-flight simulations. 

Without the help of the NASA Langley people and your unique test capabilities, it would have been impossible to complete our YF-22 flight test program 

in the time available. We look forward to working with you and your people 

when we win the Full-Scale Development contract to build the F-22. 

The Lockheed, Boeing, and General Dynamics team was announced as the winner of 

the ATF competition on April 23, 1991. 

The F-22 Program Although not immediately apparent to the uninitiated observer, the external geometry of 

the F-22 changed significantly from the YF-22 prototype. Specifically, the wingspan 

was increased, the wing leading-edge sweep was decreased, the vertical tails were 

reduced in area and moved aft, and the horizontal-tail surfaces were reconfigured. These 

changes were considered significant enough to warrant specific tests of the F-22 in the 

same unique Langley facilities as the YF-22. 

High-angle-of-attack tests of the F-22 were conducted in the Full-Scale Tunnel in 1992, 

and spin and rotary-balance tests were conducted in 1993 in the Spin Tunnel. In the 

F-22 Program, a free-flight model was not built, and tests in the Full-Scale Tunnel were 

limited to conventional static force and dynamic (forced-oscillation) tests. 

Lockheed Martin F-22 Raptor 163
Langley Contributions to the F-22

Sue Grafton with the F-22 force test model for the Lonmlev Full-Scale Tunnel. 

[-22 mod/cl (lIII'in ic is in the Lniit,'Iev Spin Timminel to determine

the size of e,nergencv parachute required for spin recom'er'. 

164 Lockheed Martin F-22 Raptor
Langley Contributions to the F-22 

F-22 model mounted for supersonic test in the Lao glev unitary Tunnel. 

Performance, stability, and control tests at supersonic speeds were accomplished in the 

Langley Unitary Plan Wind Tunnel in 1991. 

A contribution from the Langley Spin Tunnel to the F-22 Program involved a relocation 

and assessment of the attachment point for the emergency spin recovery parachute. 

Evaluations of the original F-22 parachute truss structure and attachment point were 

accomplished in 1994: however, the attachment point had to be moved forward a 

distance of 3 ft on the full-scale aircraft to clear the exhaust plume of the vectored 

engine in afterburner. These tests were urgently requested by the Air Force and 

Lockheed to complete the installation on the flight-test aircraft before spring of 1999. 

The staff of the Langley Spin Tunnel provided timely and critical contributions, including the fabrication of a new parachute truss for the existing F-22 spin model, conducting 

free-spinning tests in the Spin Tunnel, and evaluating a broad range of store loadings 

and mass asymmetries. 

Vertical-Tail Buffet - In collaboration with the F-22 System Program Office and the Air Force Research Lab 

at Wright-Patterson Air Force Base. Langley researcher Robert W. Moses conducted tail 

buffet tests in the Langley 16-Foot Transonic Dynamics Tunnel. These tests assessed the 

vertical-tail buffet environment and explored the potential application of advanced buf -

fet alleviation systems. In these tests, the 13.5-scale model of the F-22 that had been 

used for tests in the Full-Scale Tunnel was refurbished with a new starboard flexible 

vertical-tail surface that included a rudder driven by a hydraulic actuator. A rigid, portside vertical tail was instrumented with pressure transducers for measurements of 

unsteady pressures. 

Lockheed Martin F-22 Raptor 165
Langley Contributions to the F-22

I 

F-22 model with instrumented vertical tails undergoes 

buffet tests in the 16-Foot Transonic D ynamics Tunnel. 

166 Lockheed Martin F-22 Raptor
Highlights of Research by Langley for the P-3 

Lockheed P-3 Orion 

SPECIFICATIONS 

Manufacturer 

Lockheed

Date in service 

July 1962 

Type 

Antisubmarine warfare 

Crew 

6 minimum 

II normal 

Engine 

Allison T56-A-14 turboprop 

USERS 

U.S. Navy, New Zealand, 

Australia, Norway, Spain, Iran, 

Japan. Netherlands. and 

Portugal 

DIMENSIONS 

Wingspan............99.7 ft 

Length .............116.8 ft 

Height ..............33.8 ft 

Wing area ........1,300 sq ft 

WEIGHT 

Empty ............67,486 lb 

Gross ............139,760 lb 

PERFORMANCE 

Max speed ..........450 knot

Mission duration ........over

14 hr

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE P-3 

I. Tests in the Langley 16-Foot Transonic Dynamics Tunnel (TDT) identified a catastrophic propeller-whirl flutter that had caused two fatal accidents of the Electra civil 

transport on which the P-3 was based. 

2. Engine mount modifications suggested by the results of the TDT tests cured the 

problem and the Electra (and the derivative P-3) safely completed service without 

further flutter issues. 

Lockheed P-3 Orion 167
Highlights of Research by Langley for the P-3 

In late 1958, Lockheed began production of a new four-engine turboprop civil transport 

named the Electra. About 170 were subsequently built and supplied mainly to U.S. and 

South American airlines. The Navy called for design proposals for a new aircraft to 

replace the aging P-2 Neptune for maritime patrol and antisubmarine warfare (ASW) in 

August 1957. To save cost and permit service introduction as quickly as possible, the 

Navy suggested that a variant of an existing aircraft or one in an advanced design stage 

would receive favorable consideration if suitable for the missions. Lockheed proposed a 

militarized version of the Electra, and in April 1958, the Navy awarded Lockheed a contract to develop the aircraft. The P-3V Orion entered the inventory in August 1962, and 

over 35 years later it remains the Navy's sole land-based antisubmarine warfare aircraft. 

It has gone through one designation change (P-3V to P-3) and three major models: 

P-3A, P-313, and P-3C. The latter model is the only one now in active service. The last 

P-3 came off the production line at the Lockheed plant in April 1990. 

Langley's contribution to the P-3 program involved powered-model tests of the predecessor Electra configuration in the Langley 16-Foot Transonic Dynamics Tunnel (TDT). 

During 1959 and 1960, two catastrophic Electra accidents occurred with evidence that 

the aircraft had experienced violent flutter and the wings had been torn from the aircraft. 

Working under great pressure (about 130 Electras were in service at the time), a NASA 

and industry team conducted tests in the TDT along with analytical calculations. The 

driving mechanism behind the catastrophic structural failure was discovered to be propeller-whirl flutter. The phenomenon of propeller-whirl flutter involves a complex interaction of engine mount stiffness, gyroscopic torques of the engine and propeller 

combination, and the natural flutter frequency of the wing structure. The results of the 

TDT tests very accurately simulated the Electra scenarios. Based on these results, the 

engine mount structure on all Electras was strengthened, and the aircraft (and the derivative P-3) continued in service thereafter with great success and safety. 

168 Lockheed P-3 Orion
Langley Contributions to the P-3 

LANGLEY CONTRIBUTIONS TO THE P-3 

The Lockheed Electra In the fall of 1958, Lockheed began deliveries of a new four-engine turboprop Model 

L.188 civil transport to U.S. airlines. The sleek airliner, known as the Electra, set a new 

pace for luxury and speed for propeller transports. Over 170 Electras were built by 

Lockheed and delivered to U.S. and South American airlines. 

In August 1957, the U.S. Navy called for design proposals for a new advanced aircraft 

for maritime patrol and antisubmarine warfare (ASW) to replace the aging P-2 Neptune. 

The Navy strongly suggested that a variant of an existing aircraft or one in the advanced 

design stage be used to save cost and permit rapid introduction into fleet service. 

Accordingly. Lockheed proposed a military version of the Electra. In April 1958, the 

Navy announced that the Electra derivative had won the competition. Known initially as 

the P-3V, the aircraft was redesignated in 1962 as the P-3 Orion. The Orion retained the 

wings, tail unit, basic fuselage structure, power plant, and many subsystems of the 

Electra, although its fuselage was about 7 ft. shorter than the Electra's. 

Soon after introduction to the civil transport fleet, the Electra suffered two widely publicized fatal accidents with suspicious wreckage that raised concern over the structural 

integrity of the aircraft. On September 29. 1959, a Braniff Electra cruising near Buffalo, 

OF

4#

/ 

Powered model of the Lockheed Electra mounted in the

Lan glev 16-Foot Transonic D ynamics Tunnel for flutter tests. 

Lockheed P-3 Orion 169
Langley Contributions to the P-3

Texas, disintegrated without survivors. Investigation of the dispersal of aircraft wreckage revealed that the left wing had failed and separated from the aircraft in flight. On 

March 17, 1960, another Electra crashed in Indiana, with startling similarity to the 

Texas accident. Its right wing was found over 11,000 ft from the crash site, which indicated that it had also been torn from the aircraft. Over 130 Electras were operating in the 

civil fleet at the time, and authorities immediately reduced the cruise speed of the airliners while the investigation attempted to identify the cause of the fatal crashes. 

Langley had recently completed the conversion of the Langley 19-Foot Pressure Tunnel 

into the world's first aeroelastic test tunnel, known as the Langley 16-Foot Transonic 

Dynamics Tunnel (TDT). The TDT had just been calibrated, and a 0.125-scale powered 

model of the Electra was quickly prepared for flutter tests. Senior researchers I. Edward 

Garrick, Philip Donely, Robert W. Boswinkle, and D. William Conner led the planning 

for the investigation. Frank T. Abbott and Robert M. Bennett led the experimental work 

in the TDT. Wilmer H. Reed, Jr. and Samuel R. Bland led analytical studies to model 

and predict the phenomenon. 

Lockheed and Langley flutter experts were concerned that the propeller driven Electra 

may have exhibited the phenomenon known as propeller-whirl flutter, in which the stiffness of the engine mounts interacts with the gyroscopic torques produced by the engine 

and propeller combination. This interaction results in an unstable wobbling motion that 

could resonate with natural frequencies of the wing structure and could cause catastrophic flutter of the wing. 

The industry and NASA team reduced the stiffness of the outboard engine mounts on 

the model and found that the wobbling motion indeed coupled with the natural flutter 

frequency of the wings. The fatal resonance could build up and tear the aircraft apart in 

30 sec. Based on these results, the engine mounts on all Electra aircraft were strengthened, and the Electra and its derivative P-3 aircraft have since operated safely. 

170 Lockheed P-3 Orion
Highlights of Research by Langley for the S-3 

Lockheed S-3 Viking 

SPECIFICATIONS 

Manufacturer 

Lockheed 

Date in service 

February 1974 

Type - 

Antisubmarine warfare, 

antisurface warfare, electronic 

warfare, and antimine warfare - ---- .•t 

Crew -

Four 

Engine .

• •,..

r1il. 

General Electric TF34-GE-400 . . , 

DIMENSIONS

USER 

U.S. Navy

68.7 ft

Length ..............53.3 ft

Height ..............22.8 ft HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE S-3 

Wing area ..........598 sqft 

WEIGHT 1. Flutter clearance was obtained for the S-3 during tests in the Langley 16-Foot TranEmpty ............26.864 lb

sonic Dynamics Tunnel.

Max takeoff ........ .52,539 lb 2. Spin and spin recovery characteristics of the S-3 were evaluated and found to be satPERFORMANCE

isfactory during tests in the Langley 20-Foot Vertical Spin Tunnel. 

Max speed .........450 knots 

Range............2,300 n mi 

Lockheed S-3 Viking 171
Highlights of Research by Langley for the S-3 

Lockheed (now Lockheed Martin) S-3 Viking aircraft are tasked by carrier battle group 

commanders to provide antisubmarine warfare (ASW), antisurface warfare (ASUW), 

surface surveillance and intelligence collection, electronic warfare, mine warfare, coordinated search and rescue, and fleet support missions such as airborne refueling. The 

S-313 aircraft carries surface and subsurface search equipment with integrated target 

acquisition and sensor coordinating systems that can collect, process, interpret, and 

store ASW and ASUW sensor data. It has a direct attack capability with a variety of 

armament, including the Harpoon missile. 

During operation Desert Storm, the versatility of the S-3 enabled it to serve a variety of 

roles. It flew hundreds of sea surveillance missions to enforce the economic blockade of 

Iraq and secure the seas surrounding the battle groups. Mine detection was an especially 

critical mission in the Persian Gulf, and the S-3 also served as the primary logistic transport for carriers. The S-3 had a direct combat role in which it electronically monitored 

active missile sites prior to air strikes. It also participated in the hunt for Scud missiles. 

Perhaps the most important contribution of the S-3 during the conflict was its airborne 

tanking capability. In this role, it employed a hose-and-drogue refueling system that 

resulted in more efficient refueling operations and more U.S. aircraft getting to their targets. In recognition of its broad applications, the designation of the S-3 Viking squadrons has been changed from Air Antisubmarine Squadron to Sea Control Squadron. 

At the request of the Navy, Langley conducted wind-tunnel tests to provide flutter clearance and spin recovery evaluations for the S-3 prior to flight tests. The phenomenon of 

aileron "buzz" was encountered in the flutter test and eliminated, and flutter clearance 

was successful. Results of the spin tests indicated satisfactory characteristics, and no 

major modifications were made to the aircraft. Based on the data from the Langley tests, 

Lockheed and the Navy were able to proceed into flight-test development of the S-3 

with increased confidence. 

Langley facilities used in support of the development of the S-3 were the Langley 

16-Foot Transonic Dynamics Tunnel and the Langley 20-Foot Vertical Spin Tunnel. 

172 Lockheed S-3 Viking
NN 

Langley Contributions to the S-3 

LANGLEY CONTRIBUTIONS TO THE S-3 

Background In 1964, the Navy announced a requirement for a new carrier-based antisubmarine warfare aircraft (designated VSX) to replace the aging Grumman S-2 Tracker. The new aircraft was to have twice the speed, range. and altitude capability of the S-2. Development 

of the S-3 Viking began in 1969 when Lockheed was awarded the VSX contract. 

Remarkably, only five years elapsed from the time of contract award until the first aircraft was delivered to a fleet squadron in 1974. 

With the decline of the Soviet Union, and a subsequent reduction in the submarine 

threat to the U.S. fleet, the S-3 took on many new missions, including antisurface warfare, electronic surveillance, and airborne refueling. 

Spin Tunnel Tests In 1972, spin and spin recovery evaluations of the S-3 configuration were conducted in 

the Langley 20-Foot Vertical Spin Tunnel by Henry A. Lee and W. Louis White. Results 

of the tests indicated satisfactory characteristics would be expected of the S-3, and no 

modifications to the basic design were recommended. Although numerous stalling tests 

of the S-3 were conducted during the full-scale flight-test development program, intentional spins were not deemed necessary and were not attempted. 

Operationally, the S-3 has not experienced stall-departure or spin problems 

S-3 model launched into the vertical1' rising airstream in the Lan glev Spin Tunnel. 

Lockheed S-3 Viking 173
.4 C' 

Langley Contributions to the S-3 

Flutter Tests Langley researchers Jean Gilman, Moses G. Farmer, and Charles L. Ruhlin conducted 

flutter tests of the S-3 in the Langley 16-Foot Transonic Dynamics Tunnel in late 1970 

and early 1971. During the tests, the condition known as aileron "buzz" was encountered in which the S-3 ailerons exhibited very high frequency undamped oscillations. 

The problem was solved with a design modification to balance the ailerons, and flutter 

clearance for the complete configuration was demonstrated in mid-1971. 

S-3flutter model in the Lan glev 16-Foot Transonic Dvnan?ics Tunnel. 

174 Lockheed S-3 Viking
Highlights of Research by Langley for the F-4 

McDonnell Douglas F-4 Phantom I1 

Manufacturer 

McDome11 Douglas 

Date in service 

December 29,1960 

Type 

Fighter 

Crew 

mo 

Engine 

General Electric J79-GE-17 

USERS 

U.S. Navy, U.S. Marine Corps, 

U.S. Air Force, Egypt, Israel, 

Iran, Greece, Spain, Turkey, 

South Korea, West Germany, 

Australia, Japan, and Great 

Britain 

DIMENSIONS 

Wingspan. ........... 38.4 ft 

Length. ............. 63.0 ft 

Height .............. 16.6 ft 

Wing area ... .530 sq ft 

WEIGHT 

Empty ........... .31,360 lb 

Gross ............ .58,000 Ib 

PERFORMANCE 

Max speed. .... Mach number 

of 2.0 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-4 

1. Studies in the Langley Unitary Plan Wind Tunnel revealed that the configuration 

exhibited lateral-directional stability problems at supersonic speeds, which resulted 

in McDonnell redesigning the wing and vertical tail. 

2. Langley conducted studies of the stall departure and flat spin and identified causes of 

the poor stall-spin behavior of the F-4. 

3. Langley, McDonnell Douglas, the Air Force, and the Navy investigated wing modifications to improve the maneuverability and handling characteristics, which resulted 

in incorporation of leading-edge slats on later versions of the aircraft. 

Langley provided a solution to a severe nose buffet problem for the reconnaissance 

version. 

Langley and Air Force braking performance tests conducted with an F-4 aircraft 

established runway grooving as an effective solution to hydroplaning accidents. 

McDonnell Douglas F-4 Phantom I1 
Highlights of Research by bangley for the F-4 

The McDonnell Douglas (now Boeing) F-4 was an exceptional fighter aircraft, which 

was used for air superiority, interdiction, and close air support. Originally developed by 

the Navy as a supersonic fleet defense fighter, the F-4 was also put into service by the 

Air Force and served a variety of roles in the Vietnam conflict. The final application of 

the F-4 by the U.S. was in the "Wild Weasel" role for suppressing enemy air defense 

systems. F-4 production ended in 1979 after over 5,000 had been built-more than 

2,600 for the U.S. Air Force, about 1,200 for the U.S. Navy and U.S. Marine Corps, and 

the rest for friendly foreign nations. Later versions of the aircraft were in the U.S. Air 

Force inventory until December 1995. They are still flown by other nations. 

NASA Langley Research Center contributions to the F-4 program began during the 

design stages when supersonic wind-tunnel tests at Langley identified stability issues 

that required redesign of the airframe, including adding dihedral (angle between horizon 

and wing panels from frontal perspective) to the outer wing panels and increasing the 

size of the vertical fin. Another contribution from Langley resulted in the development 

and incorporation of wing leading-edge slats for enhanced maneuverability and 

increased safety for high-angle-of-attack conditions. 

Langley facilities used in the development and support of the F-4 program included the 

Langley Unitary Plan Wind Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, the 20-Foot 

Vertical Spin Tunnel, the 16-Foot Transonic Dynamics Tunnel, the 7- by 10-Foot HighSpeed Tunnel, piloted simulators, and radio-controlled drop models. 
Langley Contributions to the F-4 

LANGLEY CONTRIBUTIONS TOTHE F-4 

In 1954, the Navy selected McDonnell Aircraft to design and develop an all-weather 

supersonic fighter. The fighter, designated the F4H, was to be a fleet defense fighter that 

could take off from an aircraft carrier, have a cruise distance of 250 mi, intercept intruders, and then return to the carrier 3 hs after takeoff. The aircraft was to be armed with 

missiles and would not carry guns. It would operate as a high-speed (Mach number of 

2), standoff missile launcher that would not engage in close-in combat. 

In mid-1955 the full-scale engineering mock-up of the twin-engine aircraft featured a 

swept wing with no dihedral, and the horizontal tails drooped down at an angle of 

15 deg. At the request of the Navy, tests began in the Langley Unitary Plan Wind Tunnel 

under the direction of Melvin M. Carmel to determine the supersonic performance and 

stability and control characteristics of the original configuration. Three separate entries 

in the Unitary Tunnel were made to evaluate the early F4H design. 

Results of the first phase of tunnel tests indicated that the F4H exhibited serious deficiencies in lateral-directional stability characteristics at supersonic speeds, including 

unstable dihedral effect and marginal directional stability. To cure these problems, 

McDonnell introduced 12 deg of geometric dihedral into the outer wing panels (which 

were foldable for carrier operations) and increased the size of the vertical tail. Analysis 

had indicated that only 3 deg of geometric dihedral across the entire wing would solve 

the problem, but the same effect was achieved with less redesign and developmental 

effort by changing the outboard panels. Additional tests in other wind tunnels had indicated an undesirable pitch-up characteristic at transonic and low speeds, which was 

solved by adding chord to the outer wing panels (producing a leading-edge snag or "dog 

tooth") and by increaiing the droop of the horizontal tail to 23 deg. The final phases of 

the F4H study in the Unitary Tunnel were directed to the integration of external stores at 

supersonic speeds. 

Engineerilzg mock-up of the original F4H Pha~ltoin ~tlithout 

dihedral in ozrter wings and 15-deg droop of the horizontal fail. 
Langley Contributions to the F-4 

F4H model arfrer n~odijcatiolls ~vitlz dihedral 

in outer ~t~ings and increased vertical tail. 

After the development process, the F4H was placed into operations with the U.S. Navy 

and Marines under the new designation F-4 and set several speed and altitude records. 

The Air Force began to acquire F-4's in 1962, and this famous fighter became a mainstay in the air forces of friendly nations, with several variants produced by the 

McDonnell Douglas Corporation. 

Mnrzeznlel.rrbility During the first few years of the Vietnam conflict, the U.S. found itself engaging enemy 

aircraft such as the MiG-17 and MiG-19 that were relatively agile and could easily outmaneuver the heavier 'U.S. aircraft (F-4 and F-105) that had been designed without 

requirements for close dogfighting or close weapons such as a gun. Initial tactics used 

by U.S. pilots to try and turn with enemy aircraft had been relatively unsuccessful, and it 

had become apparent that missiles in use at that time were relatively unreliable at long 

ranges. Pilot training and revised tactics were ultimately employed to blunt the threat 

and use U.S. aircraft to an advantage, but the lack of maneuverability and a gun for 

close-in combat became issues for the Air Force. A new Air Force version known as the 

F-4E was equipped with a nose mounted M61 cannon, and additional deliveries to the 

Air Force began in October 1967. 

McDonnell Douglas became interested in wing modifications for the F-4 that would 

improve buffet onset and increase lift and turning performance, while retaining satisfactory characteristics for approach and landing. Langley researcher Edward J. Ray led a 

cooperative Langley, McDonnell Douglas, and Air Force study of F-4 maneuver and 

buffet characteristics in the Langley 7- by 10-Foot High-Speed Tunnel in 1969. Candidate configurations included the use of wing leading-edge flaps, leading-edge camber, 

trailing-edge flaps, and other devices; however, the most effective modification was a 

two-position leading-edge slat. Two slats were mounted on the leading edge of each 

wing panel in place of the earlier leading-edge flap. The inner slat was fully retractable 

at high speeds, but the outer slat remained deployed in both the cruise and high-lift configurations. With the slats deployed, the F-4 could make tighter turns, and approach 

speeds were also reduced by a significant amount. Another benefit of this modification 

was a dramatic improvement in the lateral-directional handling characteristics and spin 

resistance at high angles of attack. 
Langley Contributions to the F-4 

** F^ 

F-4E model in the Lan glev 7- by 10-Foot High-Speed Tunnel for evaluation

Of wing leading-edge modifications for enhanced maneuverability 

The slat configuration was evaluated during flight tests (known as Project Agile Eagle) 

of a modified F-4 test aircraft with extremely impressive results. The wing leading-edge 

slats were incorporated on all F-4E aircraft built during and after 1972. Later, the Navy 

received a slat equipped version of the aircraft known as the F-4S. 

The F-4G Advanced Wild Weasel, which inherited most of the features of the F-4E 

including the wing slats, was one of the last versions of the F-4. Working in "hunterkiller" teams of two aircraft, such as F-4G and F-16C, the F-4G hunter could detect, 

identify, and locate enemy radar then direct weapons to ensure destruction or suppression of the radar. The technique was effectively used during Operation Desert Storm 

against enemy surface-to-air missile batteries. 

High-Angle-of-Attack Stability Military strategists had procured the F-4 design as a standoff missile launcher with no 

requirement for strenuous maneuvering at high angles of attack. At that time, the need 

for close-in air combat maneuvering was thought to be obsolete, due to the advent of 

air-to-air missiles. Operations prior to Vietnam had stressed the supersonic mission for 

the F-4, and the initial safety record for the aircraft was extremely good. 

The return of close-in air-to-air combat during Vietnam unfortunately exposed a deficiency in the flying characteristics of the F-4. During hard turns to engage or escape 

enemy aircraft, pilots began to fly the F-4 at high angles of attack where they experienced a marked deterioration in lateral-directional stability and control characteristics. 

McDonnell Douglas F-4 Phantom 11 179
Langley Contributions to the F-4

Inadvertent loss of lateral-directional control and spin entries occurred, with an alarming number of accidents and losses of crew and aircraft during training and combat. The 

Navy, Marine Corps, and Air Force suffered over 100 high-angle-of-attack and stallspin accidents over the lifetime of the F-4 aircraft. 

In 1967, representatives from the Air Force Aeronautical Systems Division met with 

Langley researchers Edward C. Polhamus and Joseph R. Chambers to discuss the growing concern over the high-angle-of-attack and stall-spin accidents (at that time, about 

10 aircraft had been lost). Analysis of the problem by the Air Force was particularly dif -

ficult because the limited interest in high-angle-of-attack maneuvers had resulted in no 

wind-tunnel tests (other than spin tunnel tests) of the F-4 configuration for such conditions. Langley agreed to conduct diagnostic high-angle-of-attack wind-tunnel tests of 

the F-4. Tests in the Langley 12-Foot Low-Speed Tunnel and the Langley 30- by 

60-Foot (Full-Scale) Tunnel thoroughly documented the aerodynamic factors that produced the loss of lateral-directional stability at high angles of attack. 

Chambers and Sue B. Grafton conducted two free-flight model investigations of the F-4 

for high-angle-of-attack conditions in the Full-Scale Tunnel. In the first study. flight 

tests of a model of the Air Force F-4C demonstrated an abrupt loss of directional stability (nose slice) near wing stall, and most of the flights ended with the model going out of 

control. Analysis of wind-tunnel data indicated that massive flow separation on the 

swept wing caused adverse flow fields at the tail, thereby degrading the stabilizing influence of the vertical fin at high angles of attack. No simple fixes could be found for the 

problem, short of a redesign of the wing. 

When interest in wing leading-edge modifications for enhanced maneuverability 

became known. Langley conducted free-flight tests of a model of the later F-4E configuration. The test program, which was conducted by Edward Ray in the 7- by 10-Foot 

High-Speed Tunnel, was closely monitored. The results obtained from the Full-Scale 

Tunnel by Chambers and Grafton for high-angle-of-attack characteristics were fed back 

Researcher Sue Grafton with the slatted F-4E model used for

free-flight tests in the Lan glev Full-Scale Tunnel. 

180 McDonnell Douglas F-4 Phantom 11
Langley Contributions to the F-4 

_L1 -

-- -;

1 

F-4 drop model inoiinieJ on the Lin'Iev helicopter drop rig for a spin entry test. 

to Ray and others interested in maneuver performance. The results of the free-flight 

model test indicated that the incorporation of wing leading-edge slats markedly 

improved the high-angle-of-attack behavior of the F-4 by eliminating the severe nose 

slice tendency of the basic configuration. 

Langley also conducted studies on the high-angle-of-attack characteristics of the F-4 

with a radio-controlled model and a piloted simulator. The radio-controlled model was 

used by Charles E. Libbey to determine aircraft motions after loss of control at high 

angles of attack and to demonstrate the beneficial effects of the leading-edge slat modification. The simulator study of the F-4 by Frederick L. Moore was one of the first 

attempts to develop a simulator to study high-angle-of-attack behavior. The application 

of piloted simulators to this area is now a routine development tool. 

The Flat Spin - - - - Tests of an F-4 model by James S. Bowman, Jr. in the Langley 20-Foot Vertical Spin 

Tunnel in the early 1960's indicated that the F-4 configuration would exhibit several 

types of spins. In addition, the recovery characteristics from these various types of spins 

differed greatly. For example, one spin involved a relatively steep nose-down fuselage 

attitude with large oscillations in roll during the spin motion. Recovery from this spin 

was relatively easy with normal pilot control inputs. In contrast to this spin recovery, the 

F-4 also exhibited a relatively fast, flat spin in which the aircraft descended vertically in 

a rapid spin motion with an almost horizontal (flat) fuselage attitude. Recovery from the 

flat spin with normal aircraft controls was found to be impossible. During these spin 

tests, Langley determined that a 30-ft diameter emergency spin recovery parachute 

would be required for the test aircraft. 

McDonnell Douglas F-4 Phantom II 181
Langley Contributions to the F-4

Spin tunnel tests are conducted by hand launching a model into a vertically rising airstream with an artificial spinning motion. The question remains as to whether the aircraft could enter such spinning conditions from conventional flight. Langley, therefore, 

conducts outdoor radio-controlled drop-model tests to evaluate this tendency. Drop tests 

were considered mandatory to confirm the potential for fiat spins for the F-4. Fortunately, the results of the radio-controlled F-4 drop-model tests by Libbey indicated that 

the aircraft would have a dominant tendency to enter a steeper, recoverable spin rather 

than the fiat, unrecoverable spin. In fact, the flat spin was only obtained once in over 

20 aggressive attempts to spin the drop model. 

The Navy and Air Force both conducted full-scale aircraft spin tests of the F-4, with 

aggressive control inputs to seek out the various spin modes. The Navy had expressed 

doubts over the existence of the fiat spin at the beginning of their F-4 spin program. The 

agreement of the precursor Langley Spin Tunnel tests with the flight tests was remarkable. The steep, oscillatory spin mode was normally encountered and recovery was satisfactory as predicted by the Spin Tunnel tests. Unfortunately, the fast, fiat 

unrecoverable spin was encountered in both test programs. The respective test aircraft 

were lost in crashes at Patuxent River Naval Air Station, Maryland, and Edwards Air 

Force Base, California, when the emergency spin parachute systems failed to operate 

properly. In the case of the Navy tests, the parachute failed to inflate properly, while in 

the Air Force tests, the mechanical system malfunctioned and released the parachute 

prematurely. 

Although accident statistics for the F-4 indicated that the accidents involved about an 

equal number of approach-to-landing and up-and-away maneuvers, the Air Force and 

Navy expressed great interest in determining what features or factors of the F-4 were 

responsible for the unrecoverable flat spin mode. A request was made to Langley for 

assistance in determining these factors, and a contract was given to McDonnell Douglas 

to analytically study the flat spin. 

During tests of the F-4 in the Full-Scale Tunnel, Chambers noted that a prospin yawing 

moment existed for the configuration at the attitudes associated with the fast, fiat spin. 

Results from these tests also indicated that the prospin tendencies were produced by the 

aft end of the aircraft. An innovative, inexpensive test was used by Langley to identify 

the responsible aircraft components and the primary mechanism of the fiat spin. 

Chambers mounted a commercially available 1/48-scale plastic hobby model of the F-4 

on a spindle assembly with a shaft through the top of the fuselage. The model was free 

to rotate as it would in a flat spin. When the hobby model was tested in the wind tunnel 

in a simulated fiat spin attitude, researchers found that it would immediately spin up to 

the angular rates exhibited by the spin tunnel model and that the hobby model would do 

this to the right or left when released from a nonrotating condition. The researchers 

found that the driving mechanism for the flat spin tendency was adverse aerodynamic 

interactions between the drooped horizontal tail and the vertical fin. When the drooped 

tails were inverted (that is, the tails had 23 deg of positive geometric dihedral) the model 

would no longer accelerate into the spin condition and would stabilize without rotating. 

The results of the hobby model tests were checked out in the Langley Spin Tunnel with 

the dynamically scaled F-4 model previously used for spin tests. The initial tests were 

conducted with the baseline F-4 configuration, and as expected, the model exhibited the 

fast flat spin. However, when the horizontal tails were inverted, the model would no 

longer spin flat, even though it was hand launched with conditions associated with the 

fast fiat spin. Instead, the model would nose down into the steeper, recoverable spin. It 

182 McDonnell Douglas F-4 Phantom II
Langley Contributions to the F-4 

was also found that increasing the deflection angle of the horizontal tail to 55 deg or 

greater eliminated the prospin aerodynamic interference effect for the basic configuration, which would no longer spin flat. 

The results of these tests to identify the cause of the flat spin and other concepts identified by Langley (including an automatic spin prevention control system) were evaluated 

by the military. The recommended modifications to the F-4 fleet were considered too 

drastic at that time in the operational life of the aircraft, but the important adverse effect 

of the tail interference phenomenon was noted for subsequent aircraft development 

programs. 

In the mid-1980's, the Navy approached Langley with reports that Marine pilots were 

recovering from flat spins by lowering the landing gear. The Navy requested spin tunnel 

tests and funded an F-4S model to determine the effects of operating the landing gear 

during the flat spin. Spin tunnel tests by Bowman showed that lowering the gear actually 

increased the spin rate in the flat spin! Based on these tests, the Navy did not incorporate 

lowering the gear as a spin recovery technique in the pilot handbook. Perhaps the most 

significant result from this test was that it alerted researchers to the potential adverse 

effects of components such as landing gear, gear doors, and weapons bay doors on spin 

recovery. The effects of such components had not been routinely tested in decades. This 

experience later proved very valuable during other programs. 

The contributions and participation of Langley in the F-4 high-angle-of-attack and stallspin efforts are also noteworthy because they formed the impetus within Langley to 

form a cohesive suite of test techniques designed to extract the maximum amount of 

information in this difficult and complex area. Following the F-4 program, Langley 

greatly increased commitments to this area and embarked on a research program with 

industry and DOD that has benefited the development of high-performance U.S. aircraft 

to this day. 

Nose Vibrations In late November 1965, the staff of the Langley 16-Foot Transonic Dynamics Tunnel 

(TDT) was urgently requested to assist the Air Force with a buffet problem that was 

experienced by the RF-4 reconnaissance version of the aircraft during combat operations in Vietnam. When pilots attempted to perform high-speed pre- and post-strike photographic reconnaissance missions, they found that the nose mounted cameras in the 

RF-4 were being literally shaken to pieces, seriously degrading the clarity of the photographic information and ruining the mechanical operations and operational lifetime of 

the cameras. Langley researchers Robert V. Doggett and Perry Hanson conducted windtunnel tests of the front fuselage of an RF-4 model in the TDT in early 1966 to measure 

fluctuating pressures in the area near the camera lens and housing. The results of the 

study indicated that aerodynamic flow separation on the lower forebody over the camera 

installation produced large vibratory loads that were the source of the problem. Doggett 

and Hanson, working with McDonnell Douglas and the Air Force, developed a modified 

camera ramp angle and revised camera enclosure fairing that eliminated the problem 

and was incorporated on later models of the RF-4. The fairing, which rounded the flat 

lower surface of the baseline nose, also resulted in increased internal nose volume and 

allowed larger cameras to be utilized. 

McDonnell Douglas F-4 Phantom 11 183
Langley Contributions to the F-4

The RF-4 reconnaissance version of the F-4 with camera

fairing under the forward nose section. 

Siinpliitied ,nodel oJRF-4 nose tested in the Lan glev 16-Foot Transonic Dvna,nics Tunnel. 

Runway Grooving In the 1950's. Langley researchers at the Aircraft Landing Dynamics Facility focused 

their research on aircraft braking and directional control performance on wet runway 

surfaces. This research, led by Langley researchers Walter Home and Thomas J. Yager, 

included ground handling tests of an F-4 test aircraft. Comparative tests of the effects of 

runway grooving on braking and handling characteristics provided clear demonstrations 

of the effectiveness of the grooving concept. 

184 McDonnell Douglas F-4 Phantom II
...- ... -.r._-- •.. 

AL 

USERS 

U.S. Air Force, Israel, Saudi 

Arabia. and Japan

DIMENSIONS 

Wingspan............ 42.8 ft 

Length .............. 63.8 ft 

Height .............. 18.5 ft 

Wing area .......... 608 sq ft 

WEIGHT 

Empty ............ 40.000 lb 

Typical combat ..... 68,000 lb 

PERFORMANCE 

Max speed ....... above Mach 

number of 2.0 

Unrefueled ........ 3.450 n mi 

range

Highlights of Research by Langley for the F-15 

McDonnell Douglas F- i 5 Eagle 

SPECIFICATIONS 

Manufacturer 

McDonnell Douglas 

Date in service 

November 1974 

Type 

Air superiority, dual role 

Crew 

One or two 

Engine 

F- I SC . . . Pratt & Whitney 

F100-PW-220

ri 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE F-I 5 

1. At the request of the Department of Defense, Langley responded to a request for proposals with candidate fighter configurations of which one, known as LFAX-8, 

strongly influenced the winning design by McDonnell Douglas. 

2. Langley conducted over 6,000 wind-tunnel test hours to collect data for the competitive source selection team and participated in the evaluation process. 

3. Langley conducted studies to improve the subsonic cruise efficiency with emphasis 

on propulsion integration, which resulted in a substantial improvement in perforfiance by the removal of ventral fins and modification of the vertical tails. 

4. Langley conducted studies of high-angle-of-attack and spin characteristics to 

develop and demonstrate a high level of spin resistance. 

S. Tests in the Langley 16-Foot Transonic Dynamics Tunnel identified potential flutter 

of the horizontal tails, which resulted in modifications of the tail geometry and subsequent flutter clearance. 

6. Langley provided technology, expertise, and facility support for upgrades to the F- 15 

fleet on a continual basis including development of the F-15E and the F-15 short 

takeoff and landing and maneuver technology demonstrator (STOL/MTD). 

McDonnell Douglas F-15 Eagle 185 
Highlights of Research by Langley for the F-15 

One of the most illustrative examples of the benefit of NASA aeronautical research for 

military aircraft is the impact of NASA studies on the F- 15 air superiority fighter. NASA 

studies ranged from conceptual configuration studies that employed aggressive technologies to developmental studies of aerodynamic performance, high-angle-of-attack and 

spin characteristics, flutter, and advanced derivative aircraft. Langley facilities used in 

the F- 15 studies included the Langley 30- by 60-Foot (Full-Scale) Tunnel, the Langley 

20-Foot Vertical Spin Tunnel, the Langley 4- by 4-Foot Supersonic Pressure Tunnel, the 

Langley Unitary Plan Wind Tunnel, the Langley 16-Foot Transonic Tunnel, the Langley 

16-Foot Transonic Dynamics Tunnel, and the Langley 7- by 10-Foot High-Speed 

Tunnel. 

In 1968, the Department of Defense (DOD) asked NASA to respond to the F- 15 request 

for proposals (RFP) in a manner similar to the contractors to define the possible impact 

of advanced technology on the industry proposals. Under Langley's leadership, a NASA 

team of about 70 professionals colocated at Langley designed a series of advanced fighters that would meet the F-is mission requirements. One of these configurations, 

LFAX-8, was of great interest to the McDonnell Douglas proposal team, which adopted 

many of the configuration features in the winning F- 15 design. 

Langley also participated in the source selection process by conducting over 6,000 test 

hours in eight wind tunnels to define the characteristics of competing F-lS designs and 

serving on the source selection evaluation board. During the development of the F-is, 

Langley provided continuing advice to the Air Force and provided a member to the F- 15 

Program Office. Langley's contributions to the F-iS in the areas of aerodynamics, propulsion integration, stability and control, aeroelasticity and flutter, and flight controls 

have helped the nation maintain superiority in advanced fighter aircraft. 

186 McDonnell Douglas F-15 Eagle
Langley Contributions to the F-15 

LANGLEY CONTRIBUTIONS To THE F-15 

The NASA Fighter Study Many of the basic design features of U.S. fighter aircraft have resulted from technology 

pioneered at the Langley Research Center. Some examples are the area rule, the variable-sweep wing, wing maneuver flaps, and efficient afterbody-nozzle integration. 

NASA continues to ensure that breakthrough concepts are quickly transferred to industry and DOD. 

In 1967, Langley disseminated the results of in-house studies of a fighter configuration 

known as LFAX-8, which incorporated several features that would later be evident in 

the F- 15 aircraft. Some of these features were 

• Short propulsion package to minimize weight 

• Engines placed forward for balance 

• Horizontal ramp engine inlets for good performance at high angles of attack 

• Horizontal tails located far aft on booms for increased stability and control 

• Tailored twin-engine aft-end spacing and interfairing for efficient subsonic cruise 

conditions 

Many industry design teams studied the database provided by Langley and these features were incorporated into many high-performance aircraft designs. 

In 1968, the Department of Defense (DOD) requested that NASA respond to the F-is 

request for proposals (RFP) in a manner similar to the industry contractors. The key person behind the NASA participation was Dr. John Foster, Director of the Defense Department Research and Engineering organization. He requested the participation for two 

reasons. First, Foster felt that NASA's aircraft designs for the F-is mission would 

embody advanced technology and serve as the upper limit of technology for industry 

proposals. Second, NASA and its problem-solving expertise could minimize risks and 

problems later in the development program.

—::Z<* 

LFAX-9 Io

'I 

/ I 

'I 

'I 

Fighter concepts developed by NASA for the F-15 mission requirements. 

McDonnell Douglas F-15 Eagle 187
Langley Contributions to the F-15

In response to Foster's request, NASA organized a design team of about 70 professionals from the Langley, Ames, Glenn, and Dryden Research Centers. The team was cobcated at Langley under the leadership of Langley researcher William J. Alford, Jr. 

Roy V. Harris, Jr. and A. Warner Robins of Langley were members of a subteam responsible for configuration design and many other Langley researchers served on other subteams. The team spent about 4 months at Langley developing several fighter concepts 

directed at the F-15 mission requirements. The breadth of studies included analytical 

and wind-tunnel tests for the most promising configurations. Four fighter concepts were 

studied in great detail: 

• LFAX-4—a variable-sweep configuration 

• LFAX-8— a fixed-sweep version of LFAX-4 

• LFAX-9—wing-mounted twin-engine configuration 

• LFAX-10—similar in external shape to Soviet MiG-25 Foxbat 

Industry design teams visited Langley during the efforts and were continually updated 

on the advantages, disadvantages, and technical maturity of the configurations. The 

NASA team also briefed high ranking DOD officials. The LFAX-4 and LFAX-8 embodied features that would subsequently be evident in the McDonnell Douglas F-15 and 

Northrop Grumman F-14 aircraft. 

McDonnell Douglas was especially interested in the NASA fighter study as an 

extremely valuable adjunct to the company's design effort on the F-15. The LFAX-8 

design made an indelible impression on the McDonnell Douglas design team, which 

embraced the fundamental layout of the NASA configuration. The cranked-wing design 

of the LFAX-8 had to be modified by McDonnell Douglas as the requirements for transonic maneuvering became more important. Another modification to the LFAX-8 

involved the installation of a larger radar dish in the nose than the NASA team had 

allowed for in their design. The installation required a larger diameter nose cone, and 

although the NASA researchers deplored the increased supersonic drag caused by the 

larger nose, the final design incorporated the larger dish. 

F-is Source Selection Following the NASA fighter study, 41 of the 70 NASA researchers became participants 

in the detailed evaluation of the industry proposals by McDonnell Douglas, Fairchild, 

and North American Rockwell. The studies and evaluation efforts, as well as developmental efforts at Langley, required over 6,000 hr in Langley facilities including the 

Unitary Plan Wind Tunnel, the 4- by 4-Foot Supersonic Pressure Tunnel, the 7- by 

10-Foot High-Speed Tunnel, the 16-Foot Transonic Tunnel, the 16-Foot Transonic 

Dynamics Tunnel, the 20-Foot Vertical Spin Tunnel, and the 30- by 60-Foot (Full-Scale) 

Tunnel. During the development of the F-is, Langley personnel acted as consultants to 

the Air Force, and Langley provided a permanent member to the F- 15 Program Office in 

Dayton, Ohio for improved liaison and communications. 

Following the award of the F-is contract by the Air Force to McDonnell Douglas in 

December 1969, Langley supported the development of the aircraft in several key areas. 

Aerodynamic and Propulsion Previous experiences with the F- 111 and other advanced fighter concepts indicated that 

Integration Studies an extremely large portion of the subsonic cruise drag of modern twin-engine fighters 

is contributed by the aft end of the configuration (approaches 50 percent for some 

configurations). Langley researchers learned that careful tailoring of the engine interfairings and tail surfaces could prevent excessive aft-end drag. In the course of F- ill 

188 McDonnell Douglas F-15 Eagle
Langley Contributions to the F-15 

Aft-end configurations of F-15 models before (top) and after (bottom) Lan glev modifications

such as removal of ventral fins. taller vertical tails, and nozzle interfairing. 

development. Langley researchers in the 16-Foot Transonic Tunnel under Blake W. 

Corson. Jr. had developed test techniques and analysis methods to minimize this 

problem. 

A Langley team led by Bobby L. Berrier conducted extensive tunnel tests on a 4.7-scale 

model of the F- 15 for a critical assessment of aft-end drag on the baseline configuration, 

which at the time had large ventral fins below the aft fuselage. Mutual adverse aerodynamic interference effects were evaluated for the aft-end components, including the 

tails, tail booms, nozzles, and fuselage. After several tunnel entries, the Langley and 

McDonnell Douglas research team recommended configuration changes that significantly reduced the subsonic cruise drag of the aircraft. Specifically, the ventral fins were 

removed, the height of the vertical tails was increased to compensate for the resulting 

loss of directional stability, and nozzle interfairings (between the nozzles and also 

between the nozzles and tail booms) were added. Following briefings by Berrier to Air 

Force and DOD managers (including Dr. John Foster, Director of Defense Research and 

Engineering, and Robert Seamens. Secretary of the Air Force) of the test results and recommendations, the modifications (except for variable interfairings) were accepted for 

all production aircraft. The variable interfairings were actually built for flight-test evaluations. but were never flown after it was learned that the modified production aircraft 

met all critical mission requirements without the interfairing modification. 

Upon completion of the drag clean-up studies. Berrier's team also provided the subsonic, transonic, and supersonic aerodynamic data package for the production aircraft. 

These data were obtained during multiple entries in the 16-Foot Transonic Tunnel 

and the 4- by 4-Foot Supersonic Pressure Tunnel. The final aerodynamic data package 

delivered by Langley included wind tunnel sting and distortion corrections and jet 

exhaust correction increments. Performance predictions of the final production aircraft 

were based on this data package. 

McDonnell Douglas F-15 Eagle 189
Langley Contributions to the F-15 

High-Angle-Of-Attack and 

Spin Research

In addition to studies of the production F-IS, the Langley team conducted exploratory 

tests of the performance benefits of two-dimensional (2-D) nozzles and other advanced 

propulsion integration concepts. These research studies provided the largest U.S. database for advanced nozzle integration and served as a valuable foundation for development of the 2-D thrust-vectoring nozzles used by the F-15 short takeoff and landing and 

maneuver technology demonstrator (STOL/MTD) aircraft and the F-22 fighter. 

Langley personnel conducted two other significant propulsion integration studies on the 

F-IS. The first study was a wind tunnel to flight correlation of a highly instrumented 

powered model in the 16-Foot Transonic Tunnel and flight tests conducted at Dryden 

Flight Research Center. The second effort was a study of acoustically induced loads on 

the F-IS nozzles in the 16-Foot Transonic Tunnel and the Langley Acoustic and 

Dynamic Laboratory. The stimulus for this study, led by Langley researcher John M. 

Seiner, was the in-flight loss of external nozzle leaves ("turkey feathers") from operational F- 15 aircraft as a result of structural fatigue. The cause and fix for this phenomena 

was identified during the Langley studies, but an alternate approach, at the expense of 

cruise drag, of simply removing the nozzle external leaves before they could fatigue and 

fall off was adopted by the Air Force. 

The Air Force and the Navy had expressed notable dismay over the relatively poor and 

unforgiving characteristics of the F-4 aircraft at high angles of attack. The F-4 exhibited 

a sudden directional divergence (nose slice) and other control-induced characteristics at 

high angles of attack that made the aircraft susceptible to loss of control and inadvertent 

spins. The two services lost a combined total of over 100 F-4's to accidents involving 

these characteristics during the operational life of the aircraft. Understandably, 

McDonnell Douglas approached the design of the F- 15 with the intention of providing a 

high level of stability and spin resistance for the new air superiority fighter. 

_E Li 

Lan glev technician Ronald White iith one of iwo F-15 drop

models used for research on spin -entry characteristics. 

190 McDonnell Douglas F-15 Eagle
Langley Contributions to the F-15 

William P. Gilbert and James S. Bowman, Jr. led Langley research on the high-angle-ofattack and spin characteristics of the F- 15. Facilities used for the effort included the 

Full-Scale Tunnel, the Spin Tunnel, and a helicopter-launched, radio-controlled drop 

model. McDonnell Douglas had done considerable homework as a result of the F-4 

experience, and entered the F-15 development program with an appreciation of the stability and control features required. 

In addition to careful layout of the airframe for satisfactory high-angle-of-attack stability of the F-15, McDonnell Douglas adopted a unique control augmentation system 

(CAS) in which movement of the control stick for lateral control resulted in deflections 

of the rudders, rather than the ailerons, at high angles of attack. With this approach, 

McDonnell Douglas restricted spin inducing aileron inputs while retaining adequate roll 

response. Initial analyses of this control concept by Langley researchers indicated that it 

would greatly enhance the spin resistance of the F-15. A demonstration of the spin resistance of the aircraft through the use of dynamically scaled free-flying models was still 

required. In addition, Langley was requested to identify the potential spin and recovery 

characteristics of the F- 15 and the size of the parachute required for emergency spin 

recovery for a flight-test aircraft. 

Results of tests of a 1/30-scale model in the Spin Tunnel indicated that the F-15 would 

exhibit developed spins if it exceeded the capability of the CAS to prevent spin entry. 

However, the ability of the aircraft control surfaces to recover the F-iS from spins was 

predicted to be very good. Meanwhile, tests in the Full-Scale Tunnel in 1971 on a 

0.10-scale free-flying model and with a 0.13-scale model dropped from a helicopter 

indicated that the F-15 would be very stable at high-angle-of-attack conditions and that 

spin entry would be very difficult with the CAS active. Using the drop model, Langley 

researchers led by Charles E. Libbey defined a very limited range of control inputs and 

aircraft attitudes that enabled entry into a spin. In summary, the superior high-angle-ofattack behavior that had been anticipated by the McDonnell Douglas designers of the 

F- 15 was validated and vividly demonstrated by the Langley dynamic-model tests. 

In 1972, the Dryden Research Center assessed the impact of model size and Reynolds 

number on the results of the Langley tests. Dryden built and conducted drop tests with a 

0.38-scale unpowered model, which was launched from a B-52. Results of the test program correlated well with the results obtained from the smaller model at Langley, and 

further substantiated the spin resistance of the F- 15 configuration. 

Flutter Clearance Flutter clearance testing of the F- 15 in the Langley 16-Foot Transonic Dynamics Tunnel 

required four tunnel entries. The tests were conducted in 1971 and were led by Langley 

researcher Moses G. Farmer. McDonnell Douglas provided a full-span F-is model for 

the initial tests in the facility. Unfortunately, the F-is was among a class of modern 

fighters that encountered tail flutter problems that were related to the pioneering use of 

composite materials in high-performance aircraft. The tunnel tests indicated that the 

original F- 15 design would exhibit horizontal-tail flutter within its operational envelope. 

The early detection of this potentially catastrophic deficiency was a valuable contribution of Langley to the program. With the Langley results in hand, McDonnell Douglas 

engineers conducted flutter tests of the tail components in their own facilities. The problem was solved by redesigning the horizontal-tail geometry to control the aerodynamic 

center and mass balancing of the tail surface. By removing part of the inboard leading 

edge of the horizontal tail and adding additional balancing weight, McDonnell Douglas 

was able to clear the envelope of flutter for the development program. McDonnell 

McDonnell Douglas F-15 Eagle 191
'0

0 

.1 

L 

i4 

Langley Contributions to the F-15

Lan g/ev resea,cl,er Mo.e,s 1-anne,' with F- 15 model in jn/niiatioiz 

for flutter tests in the 16-Foot Transonic Dviwnucs Tunnel. 

Douglas also removed a portion of wing near the wingtips to alleviate an objectionable 

buffet characteristic at transonic maneuvering conditions however, the requirements for 

this modification came from flight-test evaluations. 

The F-15 Short Takeoff and In 1984. the Fli ght Dynamics Laboratory of the Air Force Aeronautical Systems DiviLanding and Maneuver sion awarded a contract to McDonnell Douglas for an advanced development STOL/ 

Technology Demonstrator MTD experimental aircraft. The idea behind the program was to develop an aircraft that 

could land and takeoff from sections of wet, bomb-damaged runway under bad weather 

conditions and severe crosswinds without active ground-based navigational assistance. 

The F- 15 STOLIMTD aircraft was a direct adaptation of a configuration developed in 

Langley sponsored programs conducted in the 1970's. Government and industry studies 

of nonaxisymmetric two-dimensional (2-D) nozzles in the early 1970's had identified 

significant payoffs for thrust-vectoring 2-D nozzle concepts. To better integrate the various 2-D nozzle technology programs and also to exchange data on this concept, a joint 

NASA and DOD workshop was initiated and sponsored by Langley in September 1975. 

To strengthen program integration and develop recommendations for further development of 2-D nozzles, an ad hoc interagency nonaxisymmetric nozzle working group was 

formed at the workshop. Langley researcher Bobby Berrier was appointed as the NASA 

representative to this group, which also included a member from the Air Force, the 

Navy, and the Defense Advanced Research Projects Agency (DARPA) organizations. 

The group advocated for a flight research program on the thrust-vectoring 2-D nozzle 

concept. 

The working group provided reviews and progress reports to senior management officials throughout the mid-1970's to early 1980's. The working group advocated for studies on three potential flight research vehicles. To avoid duplication, the Air Force 

studied the F- Ill vehicle, the Navy studied the YF-17/F-18 vehicle, and Langley studied the F- 15 vehicle. In 1977, Langley initiated a system integration study of thrust-vectoring, thrust-reversing. 2-D nozzles on the F-IS with McDonnell Douglas. A 

192 McDonnell Douglas F-15 Eagle
Langley Contributions to the F-15 

companion study of 2-D nozzle integration with the engine was initiated with Pratt and 

Whitney by the Glenn Research Center. The eventual F-Is STOL/MTD aircraft with 

thrust-vectoring, thrust-reversing. 2-D nozzles and a canard for trim of thrust-vectoring 

forces is a direct descendent of the configuration developed in these studies funded by 

NASA. In addition, multiple tests for both the F-15 generic and the F-Is STOL/MTD 

were conducted at the Langley 16-Foot Transonic Tunnel to study propulsion integration and power effect of thrust-vectoring, in-flight thrust-reversing (including methods 

for trim). 2-D nozzles on the F- 15. As a result of its key role in developing the technology. Langley provided nearly all the features of the F- 15 STOL/MTD aircraft. 

The 16-Foot Transonic Tunnel team, led by Bobby Berrier, Francis J. Capone, 

Richard J. Re, Odis C. Pendergraft, Jr.. Mary L. Mason, Laurence D. Leavitt, and others 

developed during the 1980's the most extensive design database in the world for low 

observable, thrust-vectoring, thrust-reversing (yaw and pitch). 2-D nozzles. 

In recognition of Langley's leadership role in thrust-vectoring technology, the Air Force 

and McDonnell Douglas consulted frequently with the Langley staff, particularly with 

the propulsion integration experts under William P. Henderson at the 16-Foot Transonic 

Tunnel and the flight dynamics experts at the Full-Scale Tunnel. Free-flight tests conducted by Joseph L. Johnson. Jr.'s group in the Full-Scale Tunnel demonstrated that the 

aircraft would have excellent handling characteristics at high angles of attack. The most 

impressive research results in flight dynamics, however, occurred when the Langley 

researchers equipped the free-flight model with special 2-D nozzles that provided thrust 

vectoring in yaw as well as pitch. The superior control provided by the multiaxis vectoring was demonstrated when the model was easily flown at angles of attack up to about 

85 deg without vertical-tail surfaces. 

The first flight with the thrust-vectoring nozzles took place on May 16, 1989. The aircraft was transferred to Edwards Air Force Base for joint fli ght tests by the Air Force 

and McDonnell Douglas. The 2-D nozzles were first tested in flight on March 23, 1990. 

Test flights demonstrated a 25-percent reduction in takeoff roll, and the thrust-reversing 

feature made it possible for the F-is to land on just 1,650 ft of runway (7.500 ft is 

The E-15 STOL/IvI TD f/vuo,' with canards and ihru.si-ertorj,it ,uizzIe.s. 

McDonnell Douglas F-15 Eagle 193
Langley Contributions to the F-15

required for the standard F-15). In addition, thrust reversal was used during up-andaway flight to produce rapid decelerations—a useful feature for close-in air-to-air combat. During the flight program, the F-15 STOLIMTD made vectored takeoffs with rotation demonstrated at speeds as low as 42 mph. The program ended on August 15, 1991, 

after accomplishing all of the flight objectives. 

194 McDonnell Douglas F-15 Eagle
Highlights of Research by Langley for Missiles 

Missiles 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR MISSILES 

I. From the 1950's Langley has worked to improve aerodynamic performance and roll

characteristics of the Sidewinder missile, which resulted in rollerons on the tail fin. 

2. Langley wind-tunnel studies assessed the effects of mounting Sidewinders on 

wingtips and pylons on fighter aircraft stability and maneuverability. 

3. Langley participated in the development of the Sparrow missile in the early 1950's 

with flight tests to improve booster performance and supersonic wind-tunnel studies 

that resulted in changes to the nose and fin design. 

4. Langley determined Sparrow missile carriage and separation loads for several 

aircraft. 

5. Langley studied of the aerodynamics and relative drag of certain carriage configurations of the Advanced Medium Range Air-to-Air Missile. 

6. Langley provided aerodynamic data from wind-tunnel tests during development of 

the Patriot missile. 

7. Langley helped improve the stability problems of the early Hawk missile by proposing cutouts in the wings. 

8. At the request of the Department of Defense, Langley assesses the impact of missiles 

and external stores on aircraft performance, spin recovery, and flutter. 

Missiles 195
Highlights of Research by Langley for Missiles 

As a result of unique supersonic wind tunnels and broad expertise across several technical disciplines, the NASA Langley Research Center has conducted extensive fundamental and applied research on missile configurations. Langley also conducts investigations 

to define the characteristics of specific missiles when requested by the Department of 

Defense (DOD). Langley typically addresses the aerodynamic performance, stability, 

and control characteristics of missile configurations; the aerodynamic phenomena associated with the carriage and release of missile shapes; and the effects of missiles and 

other external stores on the performance, stability and control, spin recovery, and 

aeroelasticity characteristics of the aircraft. Contributions have included the analysis 

and enhancement of missile shapes, the development and validation of advanced computational methods for missiles, and the development of unique wind-tunnel techniques 

for efficient and insightful tests. Langley has contributed to missile configurations for 

over 45 years in partnership with DOD and industry. These contributions are continuing 

for programs such as the Sidewinder, Sparrow, Advanced Medium Range Air-to-Air 

Missile (AMRAAM), Hawk, and Patriot missiles. 

Langley facilities that supported research on advanced missile configurations included 

the 4- by 4-Foot Supersonic Pressure Tunnel, the Unitary Plan Wind Tunnel, the 16-Foot 

Transonic Tunnel, the 8-Foot Transonic Pressure Tunnel, and the Mach 6 High 

Reynolds Number Tunnel. Langley researchers also utilized the facilities at the NASA 

Wallops Flight Facility for missile testing. 

196 Missiles
Langley Contributions to Missiles 

LANGLEY CONTRIBUTIONS TO MISSILES 

Background In support of the Department of Defense (DOD), Langley Research Center is frequently 

requested to assist in the assessment and development of missiles. Langley provides 

support in the areas of aerodynamics, stability, and control for the isolated missile configuration, as well as in areas that might be affected by the carriage and release of the 

missile (aircraft performance, spin recovery, and flutter). 

Langley became involved in the development of missile systems in the early 1950's, 

when a detachment of Langley researchers formed the core of what would become the 

NASA Wallops Flight Facility. These pioneering researchers used booster rockets to 

assess the aerodynamic characteristics of evolving air-to-air military missiles. 

When large-scale supersonic wind tunnels were put into operation at Langley, special 

tests and test techniques were developed and validated for basic research for specific 

missile programs. Langley's leader in these early efforts was M. Leroy Spearman, who 

maintained a close working relationship with DOD and other agencies. In the 1960's 

and 1970's, Charles M. Jackson and Wallace C. Sawyer led the Langley missile program, which focused on a number of technical issues that were within the interests of 

the NASA program. The program included an expansion of the database for missile 

design (led by Jerry M. Allen and Adolphus B. Blair, Jr.), the development and validation of computational codes for missile aerodynamics (led by David S. Miller and Richard M. Wood), store carriage and separation (led by Robert L. Stallings, Jr.), and 

experimental techniques (led by William Corlett). 

The vast majority of work in the Langley missile program involved research on representative missile shapes; however, very significant contributions were made to specific 

missile programs. 

AIM-9 Sidewinder In 1953, the Naval Ordnance Test Section requested assistance from Langley in the 

development of a short range, guided air-to-air missile for close-in combat. Known as 

the Sidewinder, the missile was to be heat seeking—that is, able to lock on to a target's 

heat producing sources, and featured forward canards for improved control. 

At Wallops Island, Langley researchers conducted flight tests to improve the roll characteristics at supersonic speeds of the Sidewinder. During the tests, the missile was 

mounted atop a rocket test section. Langley developed special dampers, known as rollerons, for the rear control surfaces of the missile, which eliminated undesirable oscillatory roll tendencies. In 1956, Langley researchers studied how fighter aircraft would 

perform at supersonic speeds with various numbers of Sidewinder missiles stored in 

underwing locations and wingtip hard points. These studies were conducted in the 

Langley 4- by 4-Foot Supersonic Pressure Tunnel. The tests helped to establish limits on 

the external store capability of aircraft destined to carry the missile. 

Through the years, programs have improved the maneuverability and range of the 

Sidewinder missile, and Langley has conducted numerous wind-tunnel test programs in 

the Langley Unitary Plan Wind Tunnel in cooperation with the Naval Weapons Center, 

China Lake, California. The most recent efforts in 1990, led by Blair and Allen, were 

Missiles 197
p 

Al 

Langley Contributions to Missiles

conducted in the Unitary Plan Wind Tunnel and focused on the potential benefits of 

reduced tail span for enhanced supersonic maneuverability. The Langley and Navy team 

also examined a long range Sidewinder configuration, which incorporated an increased 

body diameter for more booster fuel. 

Air Force c,-eit loads a Sidewinder

Sidewinder missile research model in the Langley Unitary Plan Tunnel. 

198 Missiles
Langley Contributions to Missiles 

AIM-7 Sparrow In August 1948, Langley assisted the Navy and its contractors, the Sperry Corporation 

and the Douglas Corporation, in the development of the nation's first medium range 

guided air-to-air missile system. Langley constructed two uninstrumented development 

models of the missile, the XAAM-N-2 Sparrow I. The models were flown at the rocket 

range at Wallops to solve early booster problems. Refinements to the nose and fin sections of the missile were completed through subsonic and supersonic tests in Langley 

wind tunnels during the early 1950's. 

Once the aerodynamics of the Sparrow configuration had been proven, the launching 

characteristics from positions under the wings, on the wingtips, and under the fuselage 

of the aircraft had to be determined for factors that might hinder aircraft and missile performance. With scale models, realistic simulations of missile launches were conducted 

during the mid-1950's in the Langley 7- by 10-Foot High-Speed Tunnel. Various fighter 

designs with the missiles carried externally (including the F-4) were tested at supersonic 

speeds in the Langley Unitary Plan Wind Tunnel to determine the aerodynamic loads on 

the missiles, as well as other external stores. Reliable and extremely accurate, the 

Sparrow later became the medium range workhorse for the Navy and Air Force. 

Updates of the Sparrow missile system, such as the Sparrow III, also were tested in Langley wind tunnels. Initial tests of the advanced version began with an examination of the 

aerodynamic characteristics of the missile at supersonic speeds in the Unitary Plan 

Wind Tunnel in 1977. During the early to mid-1980's, further studies of the separation 

characteristics from simulated aircraft were conducted again in the Unitary Plan Wind 

Tunnel at speeds in excess of a Mach number of 2. 

AIM-120AMRAAM By the mid-1980's, the military hoped to gradually replace the air-to-air medium range 

guided missile mainstay, the AIM-7 Sparrow with a more advanced weapons delivery 

system that would be carried by the next generation of fighters with supersonic cruise 

capability. The new missile, produced by McDonnell Douglas was designated the 

AIM-120 Advanced Medium Range Air-to-Air Missile (AMRAAM). 

Initial aerodynamic studies of the AMRAAM at Langley focused on the missile itself, 

with scale models studied on a weapons palette. Extensive studies were conducted at 

supersonic speeds in the Langley Unitary Plan Wind Tunnel, first on a generic wingbody configuration and later on an advanced fighter configuration to determine the optimum external carriage locations. Researchers examined such factors as the amount of 

drag produced by missile arrangements and the amount of space required between missiles for effective weapons launch. 

Today, the AMRAAM dominates the active radar missile field. Export orders for the 

AMRAAM totaled more than 7000, which is more than ten times the orders of its competitors combined. 

Impact on Aircraft Since Langley is usually requested to support the development of high-performance airCharacteristics craft, the Center is in an excellent position to assess the impact of missiles and other 

external stores on characteristics of the aircraft. Thus, assessments of the impact of missile configurations are normally included in performance evaluations in transonic and 

supersonic wind tunnels, studies of spin recovery characteristics in the Langley 20-Foot 

Vertical Spin Tunnel, and flutter clearance tests in Langley 16-Foot Transonic Dynamics 

Tunnel. 

Missiles 199
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Highlights of Research by Langley for the B-2 

Northrop Grumman B-2_ Spirit_____ 

SPECIFICATIONS 

Manufacturer 

Northrop Grumman 

Date in service 

December 17. 1993 

Number built 

21 on order through year 2000 

Type 400^ 

Multitole bomber 

Crew 

Two (provisions for third) 4 Engine -. 

General

:

100 

USER 

S. Air Force 

DIMENSIONS \\ 1• 

Wing area ........5,140 sq ft 

WEIGHT 

Empty ...........153.700 lb 

Weapon load 40,000 lb zk Max takeoff ....... 376.000 lb

PERFORMANCE

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE B-2 Speed..........high subsonic ------------ — -------- ---- - 

Range ............ 6.000 fl mi I. At the request of the Air Force. Langley specialists participated as members of B-2 

technical review teams during design and early development stages. 

2. Langley provided critical wind-tunnel tests with multiple entries in 5 Langley tunnels during the development program. 

3. Areas addressed in the Langley tests included propulsion integration, high-angle-of -

attack and low-speed stability and control, cruise performance, and spinning. 

Northrop Grumman B-2 Spirit 201 
Highlights of Research by Langley for the B-2 

The B-2 Spirit's low observable, or stealth, characteristics give it the unique ability to 

penetrate an enemy's most sophisticated defenses and threaten its most valued, and 

heavily defended, targets. Northrop Grumman successfully met enormous technical 

challenges in blending the features and concepts required for low observability with the 

features required for high aerodynamic efficiency and large payload. In recognition of 

the significant accomplishments in the development of the B-2, Northrop Grumman was 

awarded the Collier Trophy in 1991. The NASA Langley Research Center provided key 

information for the design and development process by Northrop Grumman. 

Some of the more obvious B-2 design challenges are apparent, including the efficient 

operation of highly integrated engine inlets; providing satisfactory stability, control, and 

handling characteristics for a flying-wing configuration without tail surfaces; and meeting mission performance specifications with high aerodynamic efficiency. 

At the request of the Air Force, Langley researchers participated in preproduction technical reviews of the B-2 and later provided tests in several unique facilities at Langley 

during the development process. Langley facilities used for B-2 tests included the 

National Transonic Facility (NTF), the l6-Foot Transonic Tunnel, the 16-Foot Transonic 

Dynamics Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, and the 20-Foot Vertical Spin 

Tunnel. 

202 Northrop Grumman B-2 Spirit
Langley Contributions to the B-2 

LANGLEY CONTRIBUTIONS TO THE B-2 

NASA supported Northrop Grumman in the aerodynamic design and development of 

the B-2 for over 15 years. Some of the more critical configuration development tests 

included the B-2 planform, the shielded upper-surface engine inlets, and the flight control system. At times, this effort approached 20 percent of the test operational schedule 

for some facilitates. 

B-2 node/ during tests in the National Transonic Facilit y (NTF) at Langley. 

Free-spin and spin 1e('o('rv tests o/ the B-2 in the Lang/er Spin Tunnel. 

Northrop Grumman B-2 Spirit 203
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Highlights of Research by Langley for the B-i B 

Rockwell B-lB Lancer 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE B- lB 

I. At the request of the Air Force. Langley participated in early studies and assessments of configurations that led to the B-IA and B-lB, including the Advanced 

Manned Strategic Aircraft (AMSA) Program. 

2. The B-1 utilizes the variable-sweep wing concept that was matured by Langley. 

3. Langley assessments of the high-angle-of-attack stability and control characteristics 

of the B-IA identified an undesirable longitudinal instability (pitch-up) that was 

eliminated by modifications to the flight control system. 

4. Langley conducted several investigations of aft-end propulsion integration and the 

application of supercritical wing aerodynamics to reduce the cruise drag of the 

B- IA. 

5. At the request of the Air Force. Langley conducted diagnostic wind-tunnel tests to 

analyze high loads on the engine nozzle flaps for the B- lB. 

6. Flutter clearance tests and analysis of a unique wing oscillation problem were conducted at Langley. 

SPECIFICATIONS 

Manufacturer 

North American Aircraft of 

Rockwell International 

Date in service 

B-IB ... June 1985 

Type 

Bomber 

Crew 

Four 

Engine 

General Electric F 101-GE-I 02 

with afterburner 

USER 

U.S. Air Force 

DIMENSIONS 

Wingspan...........137.2 ft 

Length .............145.8 ft 

Height ...............33.6 ft 

Wing area ........1,946 sq ft 

WEIGHT 

Empty ...........186.234 lb 

Gross ............477,000 lb 

PERFORMANCE 

Max speed .....Mach number

of 1.2

Range.......Intercontinental,

unrefueled

Rockwell B-lB Lancer 205
Highlights of Research by Langley for the B-i B 

The Rockwell (now Boeing) B-IB is a multirole, long range bomber, capable of flying 

intercontinental missions without refueling, then penetrating sophisticated enemy 

defenses. The B-lB's electronic jamming equipment, infrared countermeasures, radar 

location, and warning systems complement its low radar cross section and form an integrated defense system for the aircraft. Rockwell was awarded the Collier Trophy in 

1976 in recognition of accomplishments for the B-I development program. 

Langley's association with the B-i began with Air Force requests for active NASA 

involvement in several Air Force studies for advanced manned strategic bombers in the 

mid-1960's. Langley's involvement in advanced supersonic transports significantly 

enhanced the technical capabilities of the Air Force and Rockwell. As the B-IA Program progressed, the Langley staff conducted extensive tests and analysis of cruise-drag 

reduction, high-angle-of-attack behavior, and flutter. Following the cancellation of the 

B-IA Program and the initiation of the B-lB Program, Langley contributed to a joint 

NASA, DOD, and industry flight and wind-tunnel study to determine the cause of 

extremely high loads on the engine nozzle flaps for the B-lB aircraft. 

Langley facilities involved in support for the B-lA and B-IB Programs included the 

Langley 30- by 60-Foot (Full-Scale) Tunnel, the 16-Foot Transonic Tunnel, the 8-Foot 

Transonic Pressure Tunnel, the 16-Foot Transonic Dynamics Tunnel, the 20-Foot Vertical Spin Tunnel, piloted simulators, and radio-controlled drop models. 

206 Rockwell B-lB Lancer
Langley Contributions to the B-i B 

LANGLEY CONTRIBUTIONS TO THE B-IB 

Early Strategic Bomber Activities that led to the development of the B-I B bomber began in 1961, when the Air 

Studies Force initiated studies under the Subsonic Low Altitude Bomber (SLAB) Program. The 

mission requirements and name of the bomber program continued to change during the 

early 1960's and became the Advanced Manned Strategic Aircraft (AMSA) Program in 

1965. NASA's contributions in the definition of the FX Advanced Tactical Fighter 

(F-15) Program had not gone unnoticed by Air Force leaders involved in the AMSA 

Program. The close working relationships and mutual respect that existed between the 

Air Force and NASA are exemplified in excerpts from letters of request from the Air 

Force to NASA Headquarters for NASA participation in the AMSA effort. 

From Lieutenant General Holzapple (Deputy Chief of Staff, Research and Development) to Dr. Mac Adams (NASA Associate Administrator for Advanced Research and 

Technology) on March 27, 1968: 

It appears appropriate to have an independent review of the technical status 

of the (AMSA) air vehicle/engine configurations that have evolved. Informal 

discussions with Mr Mark Nichols of NASA Langley indicate that NASA may 

be able to make a significant contribution in the form of evaluation and constructive criticism. Specifically, we have in mind verification of the latest preliminary designs and associated performance calculations and wind-tunnel 

results to ensure that our optimism is justified. In addition, such activity, by 

NASA at this time would provide the appropriate background for NASA participation in any contractor source selection that might eventually come to 

pass. 

From General McConnell (Air Force Chief of Staff) to Mr. James Webb (NASA Administrator) on June 13, 1968: 

The continued technical support that NASA has provided the Air Force in 

defining the FX Advanced Tactical Fighter has been most useful. I feel that 

our cooperative efforts have resulted in a very positive gain for the Air 

Force... Because of the value we place in NASA's expertise I would also ask 

you to consider supporting our AMSA effort. This should serve not only to 

improve our product but also to increase the confidence of others in our work. 

In response to these requests, Langley participated extensively in AMSA reviews, planning discussions, and exploratory wind-tunnel tests of candidate configurations. The 

expertise of the Langley staff in supersonic aerodynamics, and their active participation 

in the U.S. Supersonic Transport Program were especially valuable to the AMSA Team. 

The evolving requirements for the AMSA included challenging mission capabilities at 

supersonic speeds and low altitudes. As the studies began, it became obvious that application of the variable-sweep wing concept developed at Langley to the candidate 

bomber configurations was extremely beneficial. 

Rockwell B-1B Lancer 207
The B-lA Program

THE B-I A PROGRAM 

In June 1970. the Air Force awarded development contracts to North American 

Rockwell to build the B-IA bomber airframe and to the General Electric Corporation to 

provide the engines for the advanced bomber. Four B-IA prototypes were ordered for 

the development program. Langley immediately received a request from the Air Force 

to assist in the assessment and development of the 13- IA. 

High-Angle-otAttack - The Air Force requested that Langley conduct the complete suite of tests for highResearch performance military aircraft, including wind-tunnel free-flight model tests, spin tests, 

and radio-controlled drop-model tests. Rockwell engineers were interested in the potential variation of handling characteristics with wing-sweep position and were anxious to 

uncover any problems, along with the solutions. 

Free-flight model tests of the B- IA were conducted in the Langley 30- by 60-Foot (FullScale) Tunnel in 1972. by Langley researchers William A. Newsom, Jr. and Sue B. 

Grafton. Preliminary wind-tunnel tests of the model indicated that a severe longitudinal 

instability (pitch-up) would be encountered for angles of attack immediately above wing 

stall. This undesirable result was attributable to the relatively high position of the horizontal tail, which placed it in an adverse flow field at post-stall angles of attack. Subsequently. Langley radio-controlled drop-model tests by Charles E. Libbey vividly 

demonstrated the undesirable pitch-up characteristic. Piloted simulator studies were 

Langley researcher Wi//ian, Nearen, with the B-IA /iee-f1ii/,i ,nrelel. 

208 Rockwell B-IB Lancer
I 

The B-lA Program 

B- IAmodel in free-flight tests in the Langle y Full-Scale Tunnel in 1972.

I 

-

r 

'

f-. 

B-IA drop model being prepared for helicopter drop test in 1974. 

Rockwell B-/B Lancer 209
The B-lA Program 

Cruise Drag

conducted at Langley by William D. Granthani and Langley pilot Perry L. Deal to evaluate the stall recovery characteristics of the B- IA under simulated mission conditions, 

such as hook-up and disengagement during air-to-air refueling. Grantham and his team 

of Langley and Air Force research pilots found that recovery from the pitch-up was very 

demanding and that a high potential for inadvertent secondary stalls (and pitch-ups) 

existed for the basic aircraft. The Langley. Rockwell. and Air Force team evaluated several control system concepts to artificially limit the angle of attack of the B-IA and 

thereby eliminate the post-stall instability from the operational envelope. Based in part 

on the Langley studies, an angle-of-attack limiter was subsequently incorporated into 

the B- IA flight control system. 

Free-spin tests of a B-IA model were conducted in the Langley 20-Foot Vertical Spin 

Tunnel by James S. Bowman. Jr.: however, the angle-of-attack limiter system precluded 

serious concern of inadvertent spins with the B-IA. 

At the request of the Air Force. Langley researchers analyzed and measured the cruisedrag characteristics of the B-IA during the design process and the development 

program. 

At the request of the Air Force. Langley researchers William P. Henderson and Bobby 

L. Berrier participated in a special B-IA drag audit in the summer of 1972. The audit, 

which was requested by the B-I Systems Program Office (SPO), consisted of a detailed 

assessment of the external and internal drag and installed thrust of the B- IA to evaluate 

the progress of the program and identify any high risk areas. The audit team consisted of 

12 members from the Air Force and NASA. 

Drag reduction studies for the B- IA were also conducted in the Langley 8-Foot Transonic Pressure Tunnel under the leadership of Theodore G. Ayers. The studies were 

directed at two objectives: the reduction of aerodynamic drag caused by the relatively 

large over-wing fairing and the potential application of supercritical wing aerodynamics. A cooperative Langley and Rockwell investigation of supercritical aerodynamics 

promised significant results: however, the Air Force directed Rockwell to turn their 

design information over to General Dynamics for possible application to the FB-1 11, 

and the B- IA application was not revisited. 

B-IA model in the Langle y 16-hno Ira,mso,ii Tunnel. 

210 Rockwell B-/B Lancer
1.11 

The B-lA Program 

Aircraft such as the B-lB that incorporate advanced configuration features such as 

variable-sweep wing and variable nozzle throat and exit areas for engines have detailed 

configuration features that can result in excessive drag at cruise conditions. For example, variable-sweep wings can have steps and gaps in the wing and glove juncture that 

can produce high drag. Variable exhaust nozzles when closed down to cruise settings 

often have large boat tail angles that result in high drag. Also, for twin-engine configurations with closely spaced exhaust nozzles, the large surface slopes in the gutter between 

the nozzles can cause flow separation and high drag. 

To improve the drag characteristics of the 13- IA. an investigation of several modifications on a 0.06-scale model was conducted in 1974 in the Langley 16-Foot Transonic 

Tunnel. Langley researchers Richard J. Re and David E. Reubush. with Rockwell and 

Air Force participants conducted tests to determine the effects of nozzle configuration, 

wing and glove fairings, fuselage underfairings, and other configuration modifications. 

Flutter - - The B- IA configuration underwent tests in the Langley 16-Foot Transonic Dynamics 

Tunnel (TDT) during several entries to determine flutter characteristics of the tail surfaces, obtain flutter clearance for the complete configuration, and investigate a unique 

outer wing oscillation phenomenon. Langley researchers Charles L. Ruhlin and 

Moses G. Farmer led these tests, which began in late 1972. Flutter clearance for the 

B- IA was obtained during this test program, and flight tests of the aircraft proceeded. 

During the flight tests at high altitude maneuvering conditions, an unusual aeroelastic 

phenomenon was encountered in which the outer wings of the aircraft exhibited a relatively low frequency, low amplitude undamped oscillation for certain values of wing 

sweep and flight conditions. Several entries in the TDT were conducted from 1973 to 

1987 to further analyze the driving mechanism, which was identified as periodic shockinduced separation. The oscillations occurred near critical Mach number conditions for 

the wing airfoil and only at high positive angles of attack. The instability was demonstrated in the wind tunnel, however, at slightly different conditions than in flight. 

On June 30 1977, President Jimmy Carter announced that the United States would not 

proceed with the production of the B- IA bomber. However, flight tests of the four B- IA 

protot y pe aircraft continued until April 1981.

13- 1, k flutter Im)I(1 /H()lUt1e1 in 1/u Lan glev 16-Foot Transonic D ynamics Tunnel. 

Rockwell B-I B Lancer 211
The B-1B Program

THE B- lB PROGRAM 

As the B-IA Program was terminated, the DOD initiated a study through the Air Force 

Scientific Advisory Board to determine the need and direction for future strategic bombers. The results of the study concluded that a derivative of the B-I A. the B-i B. was the 

best candidate to fulfill the nation's needs within the envisioned mission requirements 

and the projected deployment date. Although the B- lB retained the same general geometrical shape of the B- IA. the shift in emphasis on penetration of highly defended targets resulted in modifications to the more crucial aircraft systems, especially defensive 

systems. The B-I B has a maximum speed of only half that of the B- IA. but it incorporates many more advanced concepts for enhanced survivability. Then known as the 

Long Range Combat Aircraft (LRCA). the B-IB was selected as the next strategic 

bomber and endorsed for production by President Ronald Reagan in October 1981. 

Dynamic Loads on Engine The B-I B experienced excessive dynamic loads on the engine external nozzle flaps. 

Nozzle Flaps which led to premature failures of the flap attachment system. In 1987, a joint Langley, 

Rockwell. and Air Force wind-tunnel and full-scale flight investigation of dynamic 

loads on engine nozzle flaps was conducted. A 0.06-percent full-span model of the B-I B 

with powered engine nacelles was tested in the Langley 16-Foot Transonic Tunnel under 

the leadership of Langley researchers John M. Seiner, Francis J. Capone. and Odis C. 

Pendergraft, Jr. The Langley researchers had previously participated in similar dynamic 

loads tests for the F-15. (See Langley Contributions to the F-15.) Seiner had led analysis 

of the principal mechanisms responsible for high loads on the external flaps that are 

caused by twin-plume supersonic resonance phenomena. The results of the B-I B study 

were similar to the previous F-15 analysis and contributed further understanding for 

improved design and analysis methods. Although the study team identified several solutions to the dynamic loads problem. the Air Force eventually decided to fix the problem 

by permanently removing the external flaps from the nozzles, which increased cruise 

drag, but reduced weight. 

FId

B-/B model in an inverted position for nozzle flap

load investigation in the Lan glev 16-Foot Transonic Tunnel. 

212 Rockwell B-IB Lancer
Highlights of Research by Langley for the X-31 

Rockwell-MBB X-31 

II 

HIGHLIGHTS OF RESEARCH BY LANGLEY FOR THE X-31 

I. Langley contributed to exploratory studies of a fighter configuration designed to

exploit high angles of attack in a precursor to the X-31 Program with Rockwell. 

2. Working with Rockwell. Langley identified unacceptable characteristics of the initial 

design and successfully revised the configuration. 

3. At the request of the Defense Advanced Research Projects Agency, Langley participated in the International X-31 Program and provided information on stability and 

control, control system effects, configuration effects, thrust-vectoring system, spin 

recovery, and recovery from out of control conditions. 

4. During flight tests of the two X-31 research aircraft at NASA Dryden Flight 

Research Center, Langley provided facility support and technical consultation and 

analysis. 

5. On two occasions. Langley provided timely solutions to critical X-31 deficiencies 

that had stopped the flight program. 

SPECIFICATIONS 

Manufacturer 

Rockwell 

First Flight 

October 1990 

Type 

Experimental demonstrator 

of combat utility of flight at 

extreme angles of attack 

Crew 

One 

Engine 

General Electric F404-GE400 

USERS 

NASA (Langley and Dryden). 

Rockwell, DARPA, U.S. Navy, 

Deutshe Aerospace-MBB, and 

German Ministry of Defense 

DIMENSIONS 

Wingspan............23.8 ft 

Length ..............48.8 ft 

Height ..............14.6 ft 

Wing area ..........226 sq ft 

WEIGHT 

Takeoff ............ 16,100 lb 

PERFORMANCE 

Max speed .....Mach number 

of 1.28

Rockwell-MBB X-31 213
Highlights of Research by Langley for the X-31 

The Rockwell (now Boeing) and Messerschmitt-Bolkow-Blohm (MBB) X-31 

Enhanced Fighter Maneuverability (EFM) Demonstrator was designed to demonstrate 

the effectiveness of controlled maneuvers at extreme angles of attack during certain 

close-in air combat scenarios. The first International (U.S. and Federal Republic of 

(West) Germany) X-Plane Program showed the value of using thrust vectoring (redirecting engine exhaust flow) with advanced flight control systems to provide unprecedented 

levels of controlled flight to very high angles of attack. Whereas many previous fighters 

experienced loss of control in this regime, the X-31 was able to maneuver without fear 

of loss of control or inadvertent spins, which provided the pilot with new tactical 

options. The X-31, along with the NASA F-18 High Alpha Research Vehicle, was used 

in extensive flight tests at NASA Dryden Flight Research Center in the 1990's to provide the technologies and tactical evaluations to remove the high-angle-of-attack 

"barrier." 

Langley became involved in the X-31 Program in 1984 in a cooperative research program with Rockwell to develop a fighter configuration capable of highly agile flight at 

extreme angles of attack. Free-flight model tests at Langley led to a major redesign of 

the Rockwell candidate configuration. When Rockwell, the Defense Advanced Research 

Projects Agency (DARPA), and the West Germans formed the X-31 Program, the staff 

at Langley was requested to participate in the configuration development. Langley 

researchers conducted extensive studies of the stability, control, and thrust-vectoring 

system of the vehicle. Langley remained active in the program as Dryden became the 

responsible test organization during the flight tests of two X-31 demonstrator aircraft. 

Flight tests began at Dryden in February 1992 and concluded in 1995. 

During the flight evaluation tests at Dryden, Langley provided technical support and on 

two occasions provided rapid solutions to critical stability and control problems that had 

stopped the flight tests. 

Langley support of the X-31 included tests in the 30- by 60-Foot (Full-Scale) Tunnel, 

the 20-Foot Vertical Spin Tunnel, the 12-Foot Low-Speed Tunnel, the 14- by 22-Foot 

Tunnel, the 16-Foot Transonic Tunnel, the Jet Exit Test Facility, a radio-controlled drop 

model, and piloted simulators. 

214 Rockwell-MBB X-31
Langley Contributions to the X-31 

LANGLEY CONTRIBUTIONS TO THE X-31 

Background Langley participated in the X-31 Enhanced Fighter Maneuverability (EFM) Program 

during four separate activities. From 1973 to 1984. Langley was active in the planning. 

testing. and analysis of the remotely piloted Highly Maneuverable Aircraft Technology 

(HiMAT) research vehicle. From 1984 to 1985. Langley cooperated in a program with 

Rockwell International to develop a representative fighter configuration that could demonstrate the advantages of exploiting high-angle-of-attack maneuvers during close-in air 

combat. From 1986 to 1991, Langley participated in the analysis and configuration 

development of the International (United States and Federal Republic of (West) 

Germany) X-31 Program. From 1991 to 1995. Langley supported the flight-test program, which was conducted at NASA Dryden Flight Research Center by the International Test Organization. 

The HiMAT Program Following the Vietnam conflict and renewed emphasis on close-in air-to-air combat, the 

U.S. military became interested in aircraft maneuverability. As a result, the requirement 

for high speeds, long considered the key factor in successful air combat, became a secondary objective. NASA initiated a joint program with the Air Force known as the 

Highly Maneuverable Aircraft Technology (HiMAT) Program. The staffs of the 

Langley. Ames. and Dryden Research Centers all participated in planning the HiMAT 

Program, with William P. Henderson serving as the technical lead and coordinator for 

Langley. The focus of the HIMAT Program was flight research and maneuverability 

demonstrations of a representative advanced configuration in the form of a remotely 

piloted subscale vehicle at Dryden. The goals of H1MAT included a 100-percent 

increase in aerodynamic efficiency over 1973 technology, and maneuverability that 

would allow a sustained 8-g turn at a Mach number of 0.9 and an altitude of 25.000 ft. 

The program ultimately achieved all goals. 

E_

0 

The on'n,oI IIitl1T model with the thrust- vectoring,

wedge nozzle in the Liinglev 16-Foot Tunnel. 

Rockwell-MBB X-31 215
Langley Contributions to the X-31

HiMAT during flight tests at Drvden. 

In August 1974. Rockwell International was awarded a contract to construct a reduced 

scale model of the H1MAT design. Rockwell submitted a canard configuration with twin 

vertical tails on a highly swept wing and a high aspect ratio, pitch thrust-vectoring, 

wedge nozzle. The thrust-vectoring wedge nozzle was later replaced with a fixed. axisymmetric nozzle to reduce program costs. The first flight of the HiMAT occurred on 

July 27. 1979, and research continued through January 1983. The success with the 

HiMAT configuration inspired Rockwell to examine the benefits of a derivative fighter 

that exploits high angles of attack for new tactical maneuvers during close-in air 

combat. 

The SNAKE Program - In 1984. Rockwell proposed a cooperative program to Langley to assess and develop a 

Rockwell advanced design known as the Super Normal Attitude Kinetic Enhancement 

(SNAKE) configuration. Joseph R. Chambers and Joseph L. Johnson. Jr. determined 

that the proposal was in concert with many Langley research interests in high-angle-ofattack technology, and the cooperative program on the SNAKE configuration was 

begun. Langley researcher Mark A. Croorn was assigned the role of lead engineer, and 

he began a decade of personal participation in the X-31 evolution and flight-test 

programs. 

The initial SNAKE configuration bore a superficial resemblance to the earlier HiMAT 

design (canard and wing-mounted twin vertical tails): however, the new configuration 

was designed analytically with computers and a minimum amount of wind-tunnel tests. 

Unfortunately. Croom's aerodynamic tests of the initial SNAKE configuration in the 

Langley 30- by 60-Foot (Full-Scale) Tunnel indicated unacceptable stability and control 

characteristics. The configuration was unstable in pitch, roll, and yaw for all angles of 

attack. 

Based on their extensive experience with stability and control characteristics of 

advanced fighters. Croorn and Johnson provided the Rockwell team with several 

recommendations to cure the problems exhibited by the SNAKE configuration. The 

216 Rockwell-MBB X-31
Langley Contributions to the X-31 

The original Rockwell SNAKE configuration with 

downiurned win grips and thrust vectoring paddles. 

ihe niothjicd SNAKL configuration a/icr the Lan glev tests with iqnurned oingtips, wing

leading-edge flaps, enlarged vertical rails, enlarged wing-fuselage strake, and nose strokes. 

Rockwell-MBB X-31 217
Langley Contributions to the X-31

Modified SNAKE model firing at extreme angle of attack using

thrust vectoring in the Lang/er Full-Scale Tunnel. 

configuration modifications resulted in satisfactory characteristics, and the aerodynamic 

deficiencies of the initial SNAKE design had been eliminated. Rockwell was grateful 

for the guidance and innovation contributed by Langley in the evolution of the SNAKE 

configuration. 

In the early 1980's. an awareness of the benefits of thrust vectoring for dramatically 

improved control at high angles of attack surfaced. In addition to studies of advanced 

engine concepts with vectoring nozzles, interest arose over the use of simple thrustvectoring paddles in the engine exhaust to deflect the thrust for control augmentation. 

As discussed in Lang/er Contributions to the F-14. the Navy, with Langley's assistance, 

had taken the lead in this area with flight tests on an F-14 modified with single-axis 

yaw-vectoring paddles. In addition, during a cooperative program with Rockwell led by 

Langley researcher Bobby L. Berrier. Langley provided design data for multiaxis thrustvectoring paddle configurations using the Jet Exit Test Facility in 1985. Based on these 

fundamental research studies, Rockwell incorporated multiaxis thrust-vectoring paddles 

into the SNAKE configuration. Free-flight tests of the modified SNAKE model in the 

Full-Scale Tunnel by Croom's team in 1985 provided an impressive display of the effectiveness of thrust vectoring at extreme angles of attack. 

In West Germany. Dr. Wolfgang Herbst of Messerschmitt-Bolkow-Blohm (MBB) 

aggressively touted the advantages of post-stall technology (PST) for increased 

218 Rockwell-MBB X-31
Langley Contributions to the X-31 

effectiveness during close-in air combat. Herbst's conclusions were based on windtunnel tests of a German advanced canard fighter configuration known as the TKF-90 

and piloted simulator studies during which the application of simulated thrust vectoring 

resulted in rapid directional turns at high angles of attack had increased the turn rate by 

over 30 percent. Technical discussions between the Rockwell SNAKE Program managers and Herbst were initiated in 1983, and planning for a mutual program on PST 

ensued. Discussions with the Defense Advanced Research Projects Agency (DARPA) 

were very positive. When funding for collaborative international activities became available from the U.S. (the Nunn-Quayle research and development initiative in 1986) and 

West German governments, the technical expertise of Rockwell and MBB were joined 

under DARPA sponsorship in the X-31 Program. In view of Langley's extensive experience in high-angle-of-attack technology, unique test facilities, and contributions to the 

Rockwell SNAKE Program, DARPA requested in 1986 that Langley become a participant in the X-31 development program. 

X-31 Configuration Evolution The Rockwell and MBB X-31 design team merged their configuration candidates into a 

canard fighter powered by a single General Electric F404 engine with a single vertical 

tail. The initial design included an F-16 canopy for cost-saving purposes. Extensive tests 

of the initial X-31 configuration were carried out at Langley during 1987. These tests 

included static wind-tunnel tests and configuration component evaluations in the 

Langley 14- by 22-Foot High-Speed Tunnel, rotary-balance tests in the Langley 20-Foot 

Vertical Spin Tunnel to determine aerodynamic characteristics during spins, and 

dynamic force tests in the Langley Full-Scale Tunnel. Unfortunately, in 1988 the X-31 

configuration was revised, and an F-18 canopy was incorporated. This change was 

regarded as significant, and a major portion of the previous wind-tunnel tests had to be 

repeated for the revised configuration. 

Rotary-balance tests of the revised configuration were conducted in 1988, and spin tests 

and static and dynamic tests were completed in 1989 for the updated configuration. In 

1989, a 0.19-scale model of the X-31 underwent extensive aerodynamic and free-flight 

tests in the Langley Full-Scale Tunnel. Results from these ground-based studies indicated that the X-31 might have marginal nose-down control at high angles of attack and 

that the configuration might exhibit severe, unstable lateral oscillations (wing rock) that 

would result in a violent, disorienting roll departure and an unrecoverable inverted stall 

condition. Fortunately, the results also indicated that a simple control law concept could 

prevent the aircraft from entering a spin. The awareness that such phenomena might 

exist for the full-scale aircraft enabled the X-31 design team to configure the flight control system for maximum effectiveness. 

An exhaustive test, which included 498 paddle and nozzle configurations of the multiaxis thrust-vectoring system, was conducted by Langley researcher Francis J. Capone in 

the Jet Exit Test Facility during 1988. These data were used to select the final paddle 

and nozzle multiaxis thrust-vectoring configuration. These data were also critical to the 

design of the X-31 flight control system, since vectored thrust imposes large forces and 

moments in addition to the normal aerodynamic parameters. 

A 0.27-scale drop model was used by Langley to evaluate the post-stall and out-ofcontrol recovery characteristics of the configuration. The model, which weighed 

about 540 lb and included extensive instrumentation, was flown without an engine 

to assess the capabilities and characteristics of the basic airframe. The objective was 

to demonstrate that the X-31 would be agile and have satisfactory characteristics withOut the additional augmentation provided by thrust vectoring. The drop-model test identifies characteristics and large amplitude flight motions that cannot be assessed in 

Rockwell-MBB X-31 219
Langley Contributions to the X-31

loom 

X-31 Ivilh F- 10ano/\ iliiri,i' tests in the Lan/ev 14- by 22-Foot Low-Speed Tunnel. 

Free-flight tests qttlie X-31 in the Langle y Full-Scale Tunnel. 

220 Rockwell-MBB X-31
Langley Contributions to the X-31 

conventional wind or spin tunnels. In the X-31 Program, the technique proved to be 

invaluable as an early indicator of the highly unconventional behavior of the configuration. In particular, the violent roll departure indicated by tests of the free-flight model 

was encountered during the drop-model tests. Several control schemes were evaluated 

to eliminate this problem. In addition, the drop-model test technique provided solutions 

to barrier problems during the full-scale flight-test program. 

X-31 Flight Demonstration The first flight of the first X-31 aircraft occurred at Palmdale. California. on October II. 

Program 1990, and the second aircraft made its first flight on January 19, 1991. During the initial 

phase of flight-test operations at the Rockwell facility at Palmdale, the two aircraft were 

flown on 108 test missions. On the test missions, the aircraft achieved thrust vectoring in 

flight and expanded the post-stall envelope to 40-deg angle of attack. Operations were 

then moved to Dryden in February 1992, at the request of DARPA. 

At Dryden. the International Test Organization (ITO) expanded the flight envelope of 

the aircraft, including military utility evaluations that compared the X-31 to similarly 

equipped aircraft for maneuverability in simulated combat. The ITO, managed by 

DARPA. included NASA, the U.S. Navy, the U.S. Air Force, Rockwell Aerospace. the 

Federal Republic of Germany. and Deutsche Aerospace (formerly MesserschmittBolkow-Blohm). The first NASA flight under the ITO took place in April 1992. As the 

X-3 I full-scale aircraft flight tests began at Dryden. the Langley staff maintained a close 

support role for consultation and ground testing capability. 

Two problems surfaced during the X-31 flight-test program, and both were considered 

significant enough to curtail flight tests until solutions were found. The first problem 

was encountered in the flight-test program when it became apparent that the pitch 

control effectiveness of the aircraft at post-stall conditions (particularly at aft center of 

gravity conditions) was marginal. Pilots reported that their ability to obtain positive, 

crisp, nose-down aircraft response was unsatisfactory and that increased control effectiveness was required if the X-31 was to be considered tactically responsive at high 

angles of attack. As part of the X-31 Team. Langley was requested to conduct windtunnel tests to explore options to provide the increased control at high angles of attack. 

Mark Croom and his team quickly responded and evaluated 16 configuration modifications to improve nose-down recovery capability in the Full-Scale Tunnel. Results of the 

One at the X-31 aircraft in flight. 

Rockwell-MBB X-3I 221
ci 

Langley Contributions to the X-31

I!!

-

\

Lan glev researcher Mark Coni (1) discusses the X-31 m 

drop-model program with an X-31 prograin manage!: 

' jMark Croom points to the aft-fuselage si rakes (IcfI;le(.I 1)1

Langley tests and subsequent/v incorporated on the X-31 aircraft. 

222 Rockwell-MBB X-31 
Langley Contributions to the X-31 

investigation recommended that a pair of 6- by 65-in. strakes be mounted along the fuselage afterbody to promote nose-down recovery. The Langley recommendations, which 

were given within a week of the test request, provided a timely solution to the problem. 

The aft-fuselage strakes were incorporated in the X-31. and the pilots reported that the 

nose-down control was significantly improved. 

The second problem that occurred in the X-3l full-scale flight test was caused by large 

out of trim asymmetric yawing moments at high angles of attack. Shortly into the highangle-of-attack, elevated-g phase of the envelope expansion, a departure from controlled 

flight occurred as the pilot was performing a maneuver at 60-deg angle of attack. Data 

analysis by the X-31 team indicated that a large asymmetric yawing moment, in excess 

of the available control power, had triggered the departure. In response to an urgent 

request for solutions. Croom and the Langley team conducted tests in the Langley FullScale Tunnel to design nose strakes that would minimize the problem. Once again. 

Langley responded rapidly with a strake configuration that permitted the flights to 

continue. 

The X-31 Program logged an X-plane record of 524 flights in 52 months with 14 pilots 

from NASA. the U.S. Navy, the U.S. Marine Corps. the U.S. Air Force, the German Air 

Force, Rockwell International, and Deutsche Aerospace. 

Evaluation of the X-31 as an enhanced fighter maneuverability demonstrator by the ITO 

concluded in early 1995. 

Role of the X-31 in HighAngle-of-Attack Technology

The accompanying photograph shows three thrust-vectoring aircraft, each capable of 

flying at extreme angles of attack, cruising over the California desert in March 1994. 

The F-18 HARV (to/)), the X-31 (middle), and the F-JO MATV (bottom) in flight. 

Rockii.'ell-MBB X-31 223
Langley Contributions to the X-31

The aircraft were flown in different programs and were developed independently. The 

NASA F-18 HARV was a test bed for aerodynamic and buffet data at high angles of 

attack to validate computer codes and wind-tunnel research. The X-31 was used to study 

the ability of thrust vectoring and advanced displays to enhance close-in air combat 

maneuvering. The F-16 Multiaxis Thrust Vectoring (MATV) aircraft was a demonstration of how thrust vectoring could be applied to an operational aircraft with an 

advanced engine that has a vectoring nozzle. 

224 Rockwell-MBB X-31
The Future Investing in Freedom 

As it looks to the future, the Langley Research Center intends to maintain a critical role 

in support of industries and government agencies that are responsible for the development of technology for the defense .of the United States. However, there are several challenges in striving to maintain this critical role. 

The level of Langley support for military research and development is dynamic and flexible. Langley participates as requested in response to the unpredictable international and 

domestic political and technical factors that influence our world as we enter a new millennium. 

The reduction of U.S. military forces and plans for mergers or elimination of federal 

research laboratories complicate planning for aeronautical research programs. The 

numerous industrial mergers of the 1990's have consolidated the number of aircraft 

companies that request the results of NASA's aeronautics efforts. Diminishing budgets 

and personnel reductions have forced NASA to choose between space exploration and 

aeronautics when placing priorities, which has resulted in fewer resources for traditional 

military related research within NASA. Finally, maintaining world-class facilities in the 

face of increasingly competitive foreign facilities is a great challenge. 

The end of the Cold War has diminished the intensity of the arms race. However, the 

alarming growth in international sales of sophisticated aircraft and arms to less developed countries and the development of advanced aircraft within nations such as the 

former Soviet Union and China continue to pose a technological challenge to the air 

supremacy of the United States. 

The emergence of terrorist operations on a worldwide scale has changed the scope of 

the potential threat to the United States. This change in scope demands a new look at the 

adequacy of our military readiness and the requirements for new technology. For example, our experiences with uninhabited reconnaissance aircraft in Operation Desert Storm 

and European peacekeeping missions were highly successful. This success highlights 

the probability that uninhabited aircraft will increase in number in the future inventory 

of the United States. Uninhabited aircraft permit unprecedented deviations from existing design constraints and radical improvements within technical disciplines such as 

aerodynamics, structures, and flight controls. 

Finally, the aging of the military aircraft fleet of the United States continues, and 

replacement aircraft will eventually be required. Nearly all military aircraft that participated in Operation Desert Storm, Kosovo, and other peacekeeping missions of the 

The Future—Investing in Freedom 225
1990's were over 20 years old. Some research activities that contributed to the development of these aircraft began over 50 years prior. 

Future military aircraft development programs for the United States will begin from the 

extensive database of computer analyses, wind-tunnel tests, and flight-test results of past 

and present military aircraft. Information is added to this database by fundamental 

research conducted by Langley researchers. Very often this fundamental research points 

the way to the solution of any problem that may occur in an aircraft development program. Shrinking budgets and staff reductions further encourage the use and expansion of 

this database. 

The staff at NASA Langley Research Center with their extensive aeronautical database 

and experience is ready to provide the research that is needed to maintain the air superiority of the United States. With adequate funding, Langley will continue in partnership 

with the Department of Defense, other government agencies, industry, and universities 

to develop the next generation of high-performance military aircraft. 

226 The Future—Investing in Freedom
Appendix 

Wind Tunnels The Tools of the 

Trade 

NASA Langley Research Center's world-class stature in aeronautics is a direct result of 

the combination of the expertise and dedication of its staff and the unique test capabilities provided by its facilities. Throughout its long history, Langley has strived to anticipate requirements for new testing facilities, to conduct pilot testing of evolving facility 

concepts, and to provide updated test capabilities during new aircraft development programs. As a result of these efforts, Langley offers high quality, unique test capabilities in 

the areas of fundamental aerodynamics, aerodynamic performance, flight dynamics, 

aeroelasticity and flutter, spinning, structures and materials, impact dynamics, aircraft 

landing dynamics, and piloted simulators. 

The discussion of Langley contributions in the text of this document illustrates the critical roles and responsibilities that were assigned to the Langley facilities during the 

development of these specific military aircraft. As might be expected, wind-tunnel facilities played a key role in the development process. Today, Langley operates wind tunnels that provide critical aerodynamic, flight dynamic, and aerothermodynamic data at 

speeds ranging from low subsonic conditions to hypersonic conditions. Donald Baal's 

and William Corliss' excellent review of NASA wind tunnels will provide the reader 

with extensive information on these wind-tunnel facilities (ref. 5). 

The discussion of the military aircraft in this document reveals that certain Langley 

wind tunnels provided most of the data for the development of these military aircraft. 

These wind tunnels included the 

• Langley 4- by 4-Foot Supersonic Pressure Tunnel 

• Langley 7- by 10-Foot High-Speed Tunnel 

• Langley 8-Foot Transonic Pressure Tunnel 

• Langley 30-by 60-Foot (Full-Scale) Tunnel 

• Langley 16-Foot Transonic Tunnel 

• Langley 20-Foot Vertical Spin Tunnel 

• Langley 16-Foot Transonic Dynamics Tunnel 

• Langley Unitary Plan Wind Tunnel 

New wind-tunnel test capabilities, such as those provided by the National Transonic 

Facility (NTF) at the Langley Research Center, and reductions in the NASA aeronautics 

operating budgets in the 1990's have resulted in the closure or transfer of the first four 

Langley wind-tunnel facilities on this list. The remaining wind tunnels on the list are 

still operating and providing valuable data for another generation of aircraft. Brief 

descriptions of the listed wind-tunnel facilities follow. 

Wind Tunnels—The Tools of the Trade 227
Langley 4- by 4-Foot Supersonic Pressure Tunnel 

LANGLEY 4- BY 4-FOOT SUPERSONIC PRESSURE TUNNEL 

Design work on the first large supersonic wind tunnel at Langley began in February 

1945, with an effort to develop a 4-by 4-ft wind tunnel capable of providing test speeds 

up to a Mach number of 2. Delayed by labor strikes and other difficulties, the tunnel did 

not begin operations until May 1948. Initially powered by 6,000-hp motors (because of 

limited electrical power at the time), the facility was repowered in 1950 with 45,000-hp 

motors. Many historically significant military aircraft configurations and missiles were 

tested in the facility, including the Century Series fighters (F-100, F-102, F-104, and 

F-lOS), the TFX (precursor to the F-1 11), and the B-58 Hustler supersonic bomber. 

The 4- by 4-Foot Supersonic Pressure Tunnel was dismantled in 1977, and its drive 

motors, cooling towers, and support facilities were used in the construction of the 

National Transonic Facility (NTF), which was built on the same site. NASA saved an 

estimated $20 million in construction costs by utilizing the components of the old tunnel 

to provide key elements for the new cryogenic NTF facility. 

LANGLEY 7- BY 10-FOOT HIGH-SPEED TUNNEL 

In 1945, Langley initiated operations in two 7- by 10-ft wind tunnels, which were built 

side by side in the same building. One of these tunnels, known as the Langley 300-MPH 

7- by 10-Foot Tunnel, was used for basic and applied aerodynamic research at speeds up 

to 300 mph. The second tunnel, known as the Langley 7- by 10-Foot High-Speed Tunnel, was used for research at transonic test conditions. 

The 7- by 10-Foot High-Speed Tunnel was the site of some of the most important 

Langley aerodynamic research for military aircraft. Researchers utilized the facility to 

conceive and develop breakthrough technical concepts such as the variable-sweep wing 

and vortex-lift strakes. It was also used to assess and support the development of most of 

the high-performance U.S. military fighters. 

Regarded as one of the most productive research wind tunnels ever operated at Langley, 

the 7- by 10-Foot High-Speed Tunnel was closed and dismantled in 1993 because of 

limitations in operating budgets and workforce. 

LANGLEY 8-FOOT TRANSONIC PRESSURE TUNNEL 

Put into operation in 1953, the Langley 8-Foot Transonic Pressure Tunnel was used to 

produce some of the most important aeronautical breakthroughs for civil and military 

aircraft. Located on the original NACA property (East Area) at the Langley Air Force 

Base, the facility was a follow-on to the 8-Foot High-Speed Tunnel and incorporated the 

breakthrough slotted-wall concept for transonic testing. The new slotted tunnel was used 

to develop supercritical wing technology, winglets, and other innovative concepts that 

are now routinely used by military aircraft. Special test techniques, including the fluorescent oil flow visualization concept, were also developed and matured in the facility. 

The tunnel was utilized extensively for the support of military aircraft programs, including the assessment of competing designs, analysis of the performance capabilities of 

new configurations, and development of improvements and problem-solving concepts 

for evolving aircraft. 

Following a multiyear research investigation of hybrid laminar flow control, the 8-Foot 

Transonic Pressure Tunnel was closed in 1995. The National Transonic Facility at the 

Langley Research Center and the Langley 16-Foot Transonic Tunnel have now taken on 

the transonic test workload. 

228 Wind Tunnels—The Tools of the Trade
Langley 30- by 60-Foot Tunnel 

LANGLEY 30- BY 60-FOOT TUNNEL 

The design of the Langley 30- by 60-Foot (Full-Scale) Tunnel was initiated in 1929, and 

the tunnel was put into operation in 1931 for the intended purpose of obtaining fullscale aerodynamic data for the biplane configurations of the day. The tunnel contributed 

to military, commercial, and general aviation aircraft technology for over 64 years with 

a wide variety of test techniques including free-flight tests of remotely controlled, 

dynamically scaled models. 

In 1985, the Langley Full-Scale Tunnel was named a National Historical Landmark. 

NASA closed this historic wind tunnel in 1995 as a cost-saving action. It was subsequently transferred to the Old Dominion University, which now operates the facility for 

a diverse customer base, including race car enthusiasts. 

LANGLEY 16-FOOT TRANSONIC TUNNEL 

Since becoming operational in 1941, the Langley 16-Foot Transonic Tunnel has undergone a series of improvements and upgrades. Initially capable of speeds up to a Mach 

number of 0.7, the tunnel can now test over a speed range of up to a Mach number of 

1.29. The 16-Foot Transonic Tunnel is an atmospheric, closed-circuit tunnel with an 

octagonal test section that measures 15.5 ft across the flats. Twin 34-ft-diameter drive 

fans provide power, and the tunnel has an exceptionally low disturbance level through 

the transonic Mach number range. 

From its earliest operations, the facility has specialized in propulsion-airframe integration issues, ranging from propeller research and engine cooling research during World 

War II to the design and integration of today's advanced multiaxis thrust-vectoring and 

reversing propulsion concepts. The breakthrough nonaxisymmetric (2-D) nozzle and 

thrust-vectoring nozzle technologies were primarily developed in this facility. The availability of high-pressure airlines, water cooling lines, and hydraulic lines permit this 

unique facility to conduct in-depth studies of powered advanced military configurations. 

Because of the large test section, which results in low blockage values for typical models. this facility has also been extensively utilized for transonic aerodynamic studies on a 

wide range of military aircraft. 

The 16-Foot Transonic Tunnel is operational and continues to contribute to military aircraft development programs. This tunnel operates in conjunction with an auxiliary test 

IIi /oI / 1/1c JI(H/('
Langley 20-Foot Vertical Spin Tunnel 

facility, known as the Jet Exit Test Facility, to provide design information for the development and maturation of innovative nozzle-propulsion system concepts and to support 

specific NASA and Department of Defense aircraft development programs. 

LANGLEY 20-FOOT VERTICAL SPIN TUNNEL 

Following the initial operations of a 15-ft-diameter spin tunnel in 1935, Langley 

designed and developed the Langley 20-Foot Vertical Spin Tunnel (Spin Tunnel) 

and initiated operations in 1941. The Langley Spin Tunnel is a closed-throat, annular 

return wind tunnel that operates at atmospheric conditions. The 12-sided test section is 

20-ft across by 25-ft high. The test section velocity can he varied up to approximately 

85 ft/sec. A 3-bladed, fixed-pitch fan powered by a 400-hp direct-current motor that is 

located above the test section produces test section airflow. This motor is equipped with 

a control system designed to allow rapid changes in fan speed, which results in rapid 

flow accelerations in the test section. 

Dynamically scaled, free-flying models are used to investigate the spin and spinrecovery characteristics of aircraft configurations. To study spin characteristics, the 

model is hand launched with prerotation into the vertically rising air stream. The tunnel 

operator varies the tunnel speed so that the spinning model remains in equilibrium in 

front of video cameras for documentation of results. Direct observation of the test article 

is possible during tunnel operations via panoramic control room windows. The spinrecovery characteristics of aircraft are studied by using remote actuation of the model 

aerodynamic control surfaces. The size of emergency spin-recovery parachutes systems 

for flight test aircraft is also determined with specialized tests of scaled parachutes. 

Free-spin data have been acquired in the Spin Tunnel and used by nearly all U.S. military fighter programs during and since World War II. The tunnel has now logged over 

500 different aircraft studies. Nearly all U.S. attack and jet trainer programs have used 

Langley free-spin test data. 

In addition to free-spin tests, the facility permits the measurement of aerodynamic 

forces and moments during spin conditions with a unique rotary-balance apparatus. In 

addition to providing aerodynamic input data for analyses and theoretical studies of 

spins, the rig has been used to provide electronically scanned pressures on models during simulated spin motions. 

230 VVi,id Tunnels—The Thu/s oft/u' Trade
Langley 16-Foot Transonic Dynamics Tunnel 

The Langley 20-Foot Vertical Spin Tunnel is the only facility in the United States currently configured for free-spin tests and determination of emergency spin-recovery parachute requirements for military aircraft. The facility continues its service to the nation 

for both military and civil spin studies. The majority of work, however, supports high 

priority military aircraft programs. 

LANGLEY 16-FOOT TRANSONIC DYNAMICS TUNNEL 

The NASA Langley 16-Foot Transonic Dynamics Tunnel (TDT) became fully operational in 1960. It is now internationally regarded as the leading wind tunnel for performing flutter tests of large aeroelastically scaled full-span models at transonic speeds. The 

TDT is the only facility in the world capable of studying a full range of aeroelastic phenomena at transonic speeds. The tunnel is used by the aircraft industry to clear new 

designs for safety from flutter, to evaluate solutions to aeroelastic problems, and to 

study aeroelastic phenomena at transonic speeds. The TDT is used to perform flutter 

clearance investigations and to investigate flutter trends and aeroelastic characteristics 

of fixed-wing and rotorcraft configurations. The TDT is also used to perform a variety 

of active controls tests, to determine the effect of ground-wind loads on launch vehicles, 

and to make steady and unsteady aerodynamic pressure measurements to support computational fluid dynamic (CFD) code development. 

The TDT is a closed-circuit, continuous-flow wind tunnel capable of tests at stagnation 

pressures from near zero to atmospheric and over a Mach number range up to 1.2. The 

test section of the TDT is 16-ft square with cropped corners. One feature of the TDT 

that is particularly useful for aeroelastic testing is a group of bypass valves that connect 

the test section area to the opposite leg of the wind-tunnel circuit downstream of the 

drive fan motor. In the event of model instability, such as flutter, these quick-actuating 

valves are opened, which causes a rapid reduction in the test section Mach number and 

dynamic pressure, which may result in stabilizing the model. Other features that make 

the TDT uniquely suited for aeroelastic testing include high visibility of the model from 

the control room, a highly sophisticated data acquisition system, flow oscillation vanes 

upstream of the test section that can be used to generate sinusoidal gusts, a variety of 

model mounting and suspension systems such as cantilever sidewall mounts for component models and a 2-cable-suspension system for full-span free-flying models, safety 

screens that protect the tunnel fan blades from debris in case of a model failure, and 

state-of-the-art instrumentation and test equipment. 

h/jul TuuuuL— I/ic Tools of the Trade 2$ 1
Langley Unitary Plan Wind Tunnel

Tests can be performed in the TDT with air as the test mediuim however, the most distinguishing feature of the tunnel is the use of a heavy -as. presently R-134a refrigerant, 

as the primary test medium. R-134a is about four times as dense as air, and yet sound 

travels half the speed in R- I 34a as it does in air. These properties of higher density and 

lower sonic speed have beneficial effects on the design, fabrication, and testing of 

aeroelasticall y scaled wind-tunnel models that must accurately represent full-scale 

counterparts. Physically larger models may be built, thereby simplifying the model fabrication process. The scaled natural frequencies of these larger models are lower, resulting in lower flutter frequencies. thereby reducing the risk of model destruction during 

flutter. Other advantages resulting from the use of a heavy gas are a nearly three-fold 

increase in Reynolds number and a lower tunnel-drive horsepower requirement. 

The TDT has played a key role in the development process for virtually all military aircraft in the U.S. inventory, including transports and high-performance fighters. The 

facility is extremely active and supports civil and military programs. 

LANGLEY UNITARY PLAN WIND TUNNEL 

The Langley Unitary Plan Wind Tunnel has been in continuous operation since construction was completed in 1955. Congressional approval for the tunnel was provided by 

the Unitary Wind Tunnel Plan Act of 1949, which stated that the objective was to "Promote the national defense by authorizing a unitary plan for construction of transonic and 

supersonic wind-tunnel facilities..." 

Developmental tests of virtually every supersonic military aircraft, missile, and spacecraft in the current U.S. inventory were performed in the Unitary Tunnel. In addition. 

methods for predicting supersonic aerodynamic performance have been developed 

through basic experimental fluid mechanics research conducted in the Unitary Tunnel. 

The Unitary Tunnel is a closed-circuit pressure tunnel with two 4-ft by 4-ft by 7-ft test 

sections, and a Mach number capability ranging from 1.47 to 4.63. 

The Langley Unitary Plan Wind Tunnel participates in advanced military aircraft and 

missile research.

00000 

111100 

o il 0100 

232 Wind Tunnels—The Tools of the Trade
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3. Alford, William J.; and Henderson, William P.: NASA Assessment of the United States Navy 

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4. Assistant Secretary of the Navy: Letter to NASA Administrator. May 1968. 

5. Putnam, Lawrence E.: Effect of Nozzle interfairings on Aerodynamic Characteristics of a 

Twin-Engine Variable-Sweep-Wing Fighter Airplane at Mach 0.60 to 2.01. NASA TM 

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10. Reubush, David E.; and Carlson, John R.: Effects of Installation of F101 DFE Exhaust Nozzles on the Afterbody-Nozzle Characteristics of the F-14 Airplane. NASA TM-83250, 1982. 

II. Reubush, David E.; and Berrier, Bobby L.: Effects of the Installation and Operation of JetExhaust Yaw Vanes on the Longitudinal and Lateral-Directional Characteristics of the F-14 

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12. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000- 1768, 2000. 

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1680, 1948. 

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Lockheed Martin C-130 Hercules 

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AIAA-64-596, 1965. 

6. Victor Crash. Aviat. Week & Space Technol., vol. 61, no. 4, July 26, 1954, p. 16. 

7. Loving, Donald L.: Wind-Tunnel—Flight Correlation of Shock-Induced Separated Flow. 

NASA TN D-3580,1966. 

Bibliography 239
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Predictions With Flight Measurements on the C-141A Aircraft-Phase II, Wind Tunnel Test, 

Analysis, and Prediction Techniques. Volume 1-Drag Predictions, Wind Tunnel Data Analysis and Correlation. NASA CR-2333, 1974. 

9. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000- 1768, 2000. 

Lockheed Martin C-5 Galaxy 

1. Luoma, Arvo A.; Re, Richard J.; and Loving, Donald L.: Subsonic Longitudinal Aerodynamic Measurements on a Transport Model in Two Slotted Tunnels Differing in Size. NASA 

TM X-1660,1968. 

2. Loving Donald- L.; and Luoma, Arvo A.: Sting-Support Interference on Longitudinal Aerodynamic Characteristics of Cargo-Type Airplane Models at Mach 0.70 to 0.84. NASA 

TN D-4021, 1967. 

3. Patterson, James C., Jr.; and Flechner, Stuart G.: Jet-Wake Effect of a High-Bypass Engine on 

Wing-Nacelle Interference Drag of a Subsonic Transport Airplane. NASA TN D-6067, 1970. 

4. Parlett, Lysle P.; Fink, Marvin P.; and Freeman, Delma C., Jr. (appendix B by Marion 0. 

McKinney and Joseph L. Johnson, Jr.): Wind-Tunnel Investigation of Large Jet Transport 

Model Equipped With an External-Flow Jet Flap. NASA TN D-4928,1968. 

5. Grantham, Willaim D.; Deal, Perry L.; and Sommer, Robert W.: Simulator Study of the 

Instrument Landing Approach of a Heavy Subsonic Jet Transport With an External-Flow JetFlap System Used for Additional Lift. NASA TN D-5862,1970. 

6. Ruhlin, Charles L.; and Sandford, Maynard C.: Experimental Parametric Studies of Transonic T-Tail Flutter. NASA TN D-8066, 1975. 

7. Thompson, William C.: Ditching Investigation of a 1130-Scale Dynamic Model of a Heavy 

Jet Transport Airplane. NASA TM X-2445, 1972. 

8. Blackwell, James A., Jr.: Preliminary Study of Effects of Reynolds Number and BoundaryLayer Transition Location on Shock-Induced Separation. NASA TN D-5003, 1969. 

9. McWhirter, H. D.; Hollenback, W. W.; and Grosser, W. F: Correlation of C-5A Active Lift 

Distribution Control System (ALDCS) Aeroelastic Model and Airplane Flight Test Results. 

NASA CR-144903, 1976. 

10. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000- 1768, 2000. 

11. Perry, Boyd, III; Noll, Thomas E.; and Scott, Robert C.: Contributions of the Transonic 

Dynamics Tunnel to the Testing of Active Control of Aeroelastic Response. AIAA-2000-

1769, 2000. 

Lockheed Martin F-16 Fighting Falcon 

1. Jackson, Charles M.: NASA/General Dynamics Cooperative Research Leading to and 

Involving SCAMP. NASA Internal Report, May 1980. 

2. Polhamus, E. C.: Application of Slender Wing Benefits to Military Aircraft. AIAA-83-2566, 

1983. 

3. Buckner, J. K.; Benepe, D. B.; and Hill, P. W.: Aerodynamic Design Evolution of the YF-16. 

AIAA-74-935, Aug. 1974. 

4. Nguyen, Luat T.; Ogburn, Marilyn E.; Gilbert, William P.; Kibler, Kemper S.; Brown, Phillip 

W.; and Deal, Perry L.: Stimulator Study of Stall/Post-Stall Characteristics of a Fighter Airplane With Relaxed Longitudinal Static Stability. NASA TP-l538, 1979. 

5. Peloubet, R. P., Jr.; and Haller, R. L.: Wind-Tunnel Demonstration of Active flutter Suppression Using F- 16 Model With Stores. AFWAL-TR 83-3046, Vol. 1, 1983. 

6. Foughner, J. T., Jr.; and Bensinger, C. T.: F-16 Flutter Model Studies With External Wing 

Stores. NASA TM-74078, 1977. 

7. Perry, Boyd, Ill; Noll, Thomas E.; and Scott, Robert C.: Contributions of the Transonic 

Dynamics Tunnel to the Testing of Active Control of Aeroelastic Response. AIAA-2000-

1769, 2000. 

240 Bibliography
Lockheed Martin F-22 Raptor 

1. Mullin, Sherman N.: The Evolution of the F-22 Advanced Tactical Fighter. Wright Brothers 

Lecture, AIAA92-4I88, 1992. 

2. Aronstein, David C.; Hirchberg, Michael J.; and Piccirillo, Albert C.: Advanced Tactical 

Fighter to F-22 Raptor-Origins of the 21st Century Air Dominance Fighter AIAA, 1998. 

Lockheed Martin P-3 Orion 

1. Baals, Donald D.; and Corliss, William R.: Wind Tunnels of NASA. NASA SP-440, 1981. 

2. Abbot, F. T., Jr; Kelly, H. Neale; and Hampton, Kenneth D.: Investigation of PropellerPower-Plant Auto-Precession Boundaries for a Dynamic-Aeroelastic Model of a FourEngine Turboprop Transport Airplane. NASA TN D- 1806, June 1963. 

3. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-20001768, 2000. 

Lockheed Martin S-3 Viking 

1. Lee, Henry A.; and White, William L.: Spin-Tunnel Investigation of a 1132-Scale Model of 

the Lockheed S-3A Airplane-COORD No. N-AM-161. NASA TM SX-3057, U.S. Navy, 

1974. 

2. Rivera, Jose A.; and Florance, James R.: Contributions of 'Träñsonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000-1768, 2000. 

McDonnell Douglas F-4 Phantom II 

1. Carmel, Melvin M.; and Gregory, Donald T.: Preliminary Investigation of the Static Longitudinal and Lateral Stability Characteristics of a.Model of a 45° Swept Wing Airplane at Mach 

Numbers of 1.59, 1.89, and 2.09. NASA MEMO 3-30-59L, 1959. 

2. Carmel, Melvin M.; and Turner, Kenneth L.: Investigation of Drag and Static Longitudinal 

and Lateral Stability and Control Characteristics ofa Model of a 450 Swept Wing Airplane at 

Mach Numbers of 1.57, 1.87, 2.16, and 2.53, Phase II Model. NASA MEMO 3-31-59L, 

1959. 

3. Oehman, Waldo I.; and Turner, Kenneth L.: Aerodynamic Characteristics of a 450 SweptWing Fighter-Airplane Model and Aerodynamic Loads on Adjacent Stores and Missiles at 

Mach Numbers of 1.57, 1.87, 2.16, and 2.53. NACA RM L58C 17, 1958. 

4. Chambers, Joseph R.; and Anglin, Ernie L.: Analysis of Lateral-Directional Stability Characteristics of a Twin-Jet Fighter Airplane at High Angles of Attack. NASA TN D-5361, 1969. 

5. Chambers, Joseph R.; Bowman, James S., Jr.; and Anglin, Ernie L.: Analysis of the Flat-Spin 

Characteristics of a Twin-Jet Swept-Wing Fighter Airplane. NASA TN D-5409, 1969. 

6. Ray, Edward J.; and Hollingsworth, Eddie G.: Subsonic Characteristics of a Twin-Jet SweptWing Fighter Model With Maneuvering Devices. NASA TN D-6921, 1973. 

7. Moore, Frederick L.; Anglin, Ernie L.; Adams, Mary S.; Deal, Perry L.; and Person, Lee H., 

Jr.: Utilization of a Fixed-Base Simulator To Study the Stall and Spin Characteristics of 

Fighter Airplanes. NASA TN D-6117, 1971. 

8. Newsom, William A., Jr.; and Grafton, Sue B.: Free-Flight Investigation of Effects of Slats on 

Lateral-Directional Stability of a 0.13-Scale Model of the F-4E Airplane-COORD No. 

AF-AM-113. NASA TM SX-2337, U.S. Air Force, 1971. 

9. Doggett, R. V.; and Hanson, P. H.: Wind Tunnel Buffet Pressure Investigation on the Lower 

Nose Portion of the RF-4C Aircraft. NASA LWP-227, 1966. 

Missiles 

1. Blair, A. B., Jr.; Allen, Jerry M.; and Hernandez, Gloria: Effect of Tail-Fin Span on Stability 

and Control Characteristics of a Canard-Controlled Missile at Supersonic Mach Numbers. 

NASA TP-2157, 1983. 

2. Blair, A. B., Jr.; and Rapp, G. H.: Experimental and Analytical Comparison of Aerodynamic 

Characteristics of a Forward-Control Missile. AIAA-80-0374, 1980. 

Bibliography . 241
Rockwell B-i Lancer 

I. Newsom, William A., Jr.; and Grafton, Sue B.: Free-Flight Investigation of a 1117-Scale 

Model of the B-i Airplane at High Angles of Attack—COORD No. AF-AM-128. NASA TM 

SX-2744, U.S. Air Force, 1973. 

2. Grantham, William D.; Deal, Perry L.; and Libbey, Charles E.: Piloted Simulator Study of the 

Stability and Control Characteristics of the B-I Airplane at High Angles of Attack—COORD 

No. AF-AM-128. NASA TM SX-3381, U.S. Air Force, 1976. 

3. Re, Richard J.; and Reubush, David E.: Effect of Several Airframe/Nozzle Modifications on 

the Drag of a Variable-Sweep Bomber Configuration. NASA TM-80129, 1979. 

4. Seiner, John M.; Manning, James C.; Capone, Francis J.; and Pendergraft, Odis C., Jr.: Study 

of External Dynamic Flap Loads on a 6 Percent B-IB Model. ASME-PAPER-9 1 -GT-236, 

1991. 

5. Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000- 1768, 2000. 

Rockwell X-31 Enhanced Fighter Maneuverability Demonstrator 

1. Croom, M. A.; and Schnellenger, H. G.: High-Alpha Flight Dynamics of the X-31 Configuration. NASA CP-3 149, 1990. 

2. Knox, Fred D.: X-31 Flight Test Update. AIAA-92-1035, 1992. 

3. Banks, Daniel W.; Gatlin, Gregory M.; and Paulson, John W., Jr.: Low-Speed Longitudinal 

and Lateral-Directional Aerodynamic Characteristics of the X-31 Configuration. NASA 

TM-4351, 1992. 

4. Scott, William B.: X-31 Completes Post-Stall Test. Aviat. Week & Space Technol., vol. 138, 

no. 20, May 17 1993, pp. 29-30. 

5. Croom, Mark A.; Fratello, David J.; Whipple, Raymond D.; O'Rourke, Matthew J.; and 

Trilling, Todd W.: Dynamic Model Testing of the X-31 Configuration for High-Angle-ofAttack Flight Dynamics Research. AIAA-93-3674, 1993. 

6. Cobleigh, Brent R.: High-Angle-of-Attack Yawing Moment Asymmetry of the X-31 Aircraft 

From Flight Test. NASA CR-186030, 1994. 

Appendix 

I. Perry, Boyd, III; Noll, Thomas E.; and Scott, Robert C.: Contributions of the Transonic 

Dynamics Tunnel to the Testing of Active Control of Aeroelastic Response. AIAA-2000-

1769, 2000. 

2. Cole, Stanley R.; and Garcia, Jerry L.: Past, Present, and Future Capabilities of the Transonic 

Dynamics Tunnel from anAeroelastic Perspective. AIAA-2000-1767, 2000. 

3. Schuster, David M.; Edwards, John W.; and Bennett, Robert M.: An Overview of Unsteady 

Pressure Measurements in the Transonic Dynamics Tunnel. AIAA-2000-1770, 2000. 

4, Rivera, Jose A.; and Florance, James R.: Contributions of Transonic Dynamics Tunnel Testing to Airplane Flutter Clearance. AIAA-2000- 1768, 2000. 

5. Baals, D. D.; and Corliss, W. R.: Wind Tunnels of NASA. NASA SP-440, 1981. 

242 Bibliography
I -nr0 ro 

A A- 10 Thunderbolt II (Fairchild Republic) 57-60 

A-12 Avenger (McDonnell Douglas and General Dynamics) 44, 87 

A3 Skywarrior (Douglas) 24 

A-6 Intruder (Grumman) 83-87, 90, 91, 93-95 

A-7 (Ling Temco Voight) 38 

A-9 (Northrop) 60 

Abbott, Frank T. 141, 144, 170 

Abel, Irving 76, 144 

Abrupt Wing Stall (AWS) Program 49, 50 

acoustic loads 137, 190 

active lift distribution control system (ALDCS) 131 

Actively Controlled Response of Buffet Affected Tails (ACROBAT) Program 43 

Advanced Capability (ADVCAP) EA-613 aircraft 94 

Advanced Composites Technology (ACT) Program 136, 137 

Advanced Fighter (VFX) Program 98, 100 

Advanced Manned Strategic Aircraft (AMSA) Program 205, 207 

Advanced Medium Range Air-to-Air Missile (AMRAAM) 195, 196, 199 

Advanced Medium STOL Transport (AMST) Program 24 

Advanced Tactical Fighter (ATF) Program 159-163, 207 

Advanced Tactical Transport (ATT) Program 24 

Advanced Trainer (VTX) Program 53 

aeroelastic divergence 109-112, 119 

aileron buzz 172, 174 

aileron reversal 139, 140, 143, 144 

air bag 76, 77 

Air Combat Fighter (ACF) 35 

Air Force Flight Dynamics Laboratory 79, 81, 192 

Air Mobility Command 28, 140 

Aircraft Energy Efficiency (ACEE) Program 27 

Aircraft Landing Dynamics Facility, see Langley Aircraft Landing Dynamics Facility 

Alford, Jr., William J. 36, 65, 100, 188 

Alford, William L. 154 

Allen, Jerry M. 197 

Allison, Dennis 0. 93 

Ames Research Center 12, 20, 28, 35, 38, 60, 67, 79, 91, 93, 137, 138, 188, 215 

Ames Research Center 12-Foot Pressure Tunnel 60, 73, 115 

antisubmarine warfare (ASW) 167-169, 171-173 

area rule 71, 101, 187 

Armstrong, Neil A. 17 

artificial stabilization 13 

Attack Experimental (A-X) Program 57-60 

Index 243
Attinello, Dr. John 16 

augmented deflector exhaust nozzle (ADEN) 43, 44, 120-122 

Australia 29, 43, 167, 175, 245 

automatic rudder interconnect (ARI) 104, 105 

AV-8 Harrier (Boeing) 11-13,16-18,20,42 

Aviation Week and Space Technology 67, 141 

Ayers, Theodore G. 67-69, 78, 79, 81, 210 

B B-i Lancer (Rockwell) 61, 151, 205-212 

B-2 Spirit (Northrop Grumman) 201-203 

BAC 111 27 

BAT Aerosystems, Inc. 5-9 

Bare, E. Ann 56 

Batterson, James G. 118 

Bauer, Steven X. S. 49 

Bedford, William 14 

Bell Aircraft Corporation 63 

Bennett, Robert M. 170 

Berrier, Bobby L. 72, 107, 121, 189, 192, 193, 210, 218 

Blackwell, Jr., James A. 133, 138, 145, 160, 163 

Blair, Jr., Adolphus B. 197 

Bland, Samuel R. 170 

blow-in door 70 

Bobbitt, Percy J. 92, 93 

Boeing 11, 12, 21, 23, 25, 29, 30, 32, 47, 50-53, 56, 66, 81, 86, 87, 125, 126, 160, 161, 

163, 176, 186, 206, 214 

Boisseau, Peter C. 72 

Boswinkle, Robert W. 170 

Bowman, Jr., James S. 73, 74, 91, 102, 181, 183, 191, 210 

Bristol Siddeley 13 

British Aerospace 11, 43, 52-54 

Budiansky, Bernard 119 

buffet 30, 32, 39, 40, 42, 43, 45, 78, 79, 80, 106, 149, 151, 165, 166, 175, 178, 183, 

192,224 

C C-130 Hercules (Lockheed Martin) 22-24, 135-138 

C-141 Starlifter (Lockheed Martin) 23, 124, 125, 129, 133, 139, 140-145 

C-17 Globemaster III (Boeing) 21-28, 124, 129 

C-5 Galaxy (Lockheed) 22, 23, 123-133, 143, 145 

cable-mount 48, 106, 144 

camber, variable 32 

Camm, Sir Sydney 15 

Campbell, James F. 150 

Campbell, John P. 13, 23, 24, 63, 138 

Canada 29, 43, 245 

canard 19, 102-104, 121, 149, 150, 193, 197, 216, 219 

Capone, Francis J. 72, 193, 212, 219 

Carden, Huey D. 77 

Cargo Experimental (CX) Program 23 

Carmel, Melvin M. 177 

Cazier, Jr., Frank W. 155 

Chambers, Joseph R. 53, 73, 112, 180, 182, 216, 245 

Champine, Robert A. 17 

Cheney, Richard 87 

cockpit display 117, 136, 137 

244 Index
Cole, Stanley R. 87 

Collier Trophy 22, 30, 148, 202, 206 

composite material 21, 27, 28, 119, 191 

computational fluid dynamics 30, 40, 49 

Concorde 149 

Conner, D. William 170 

control augmentation system (CAS) 191 

convergent-divergent (CD) nozzle 43, 44 

Corlett, William 197 

Cornelius Aircraft Company 111 

Cornell Aeronautical Laboratory 8-Foot Transonic Pressure Tunnel 69 

Corson, Jr., Blake W. 189 

cranked-wing 188 

Creedon, Dr. Jeremiah F. 138 

crew escape module 62, 76, 77 

Croom, Mark A. 117,216,218,221-223 

Culpepper, Richard G. 16, 18 

D D6ac steel 78 

Daugherty, Robert H. 55 

David Taylor Research Center (Navy) 40 

Davis, Randall C. 137 

DC-10 27 

Deal, Perry L. 16,210 

deep stall 21, 27, 28, 147, 152-154 

Defense Advanced Research Projects Agency (DARPA) 108-110, 112, 119, 120-122, 

192, 213, 214, 219, 221 

Defense Department Research and Engineering 187 

Department of Defense (DOD) 1,2,23,24,32,38,41,43-46,49,57-59,61,62,67, 

81, 90,97-99, 107, 120, 121, 125, 147, 149, 159, 161, 175, 183, 185-189, 192, 

195-197,206,212,226,230 

Deutsche Aerospace 221, 223 

Dexter, H. Benson 137 

Diederich, Franklin W. 119 

digital cockpit 52 

digital flight control system (DFCS) 39, 105 

dihedral 141, 176-178, 182 

ditching tests 131, 132 

dog tooth 177 

Doggett, Jr., Robert V. 119, 183 

Donely, Philip 170 

Donlan, Charles J. 63, 65, 69 

Dragon Drone 6, 8, 9 

drooped horizontal tail 16, 182 

drop model 30, 36, 37, 47, 48, 62, 74, 75, 103, 110, 112, 117, 118, 157, 176, 181, 182, 

191, 206, 209, 214, 219 

Dryden Flight Research Center 28, 32, 38-42, 62, 67, 79, 80, 81, 98, 105, 110, 115, 

116, 120,138,149,155,188,190, 191,213-216, 221 

Dutch roll 7 

E EA-6 Prowler (Grumman) 85, 89-95 

Edwards Air Force Base 33, 35, 59, 60, 74, 153, 157, 182, 193 

EF-111 62 

effects of test section size 69, 125 

Elber, Wolf 78 

Index 245
electronic warfare 62, 89, 91, 171,172 

elevator 7, 27, 70, 139, 140, 142, 143 

empennage 23, 27, 30, 75, 86, 95, 130, 138, 141, 142, 150 

engine inlet 51, 52, 56, 70, 99, 103, 109, 110, 119, 187, 202, 203 

engine-fuselage fairing (pancake) 101 

Enhanced Fighter Maneuverability (EFM) Program 108, 214, 215 

Erickson, Gary E. 40, 45, 46, 49 

Exdrone BQM-l47A (BAt) 5-9 

externally blown flap (EBF) 21, 23-25, 124, 128, 129, 138 

F F/A- 18 High Alpha Research Vehicle (HARV) 39, 40-42, 122, 223, 224 

F/A-18 Hornet (Boeing) 29-32, 35-46, 87, 106 

F/A-i 8EIF Super Hornet 29, 30, 41, 42, 44-50 

F-105 (Republic) 66, 67, 178, 228 

F- ill Aardvark (General Dynamics) 30, 44, 61-63, 66-81, 100, 188, 192, 228 

F-l4Tomcat (Grumman) 35, 38, 40, 61, 68, 70, 97-108, 188, 218 

F-IS Eagle (McDonnell Douglas) 38, 39, 44, 61, 104, 122, 148, 151, 158, 160, 161, 

185-194,207,212 

F- 15 Short Takeoff and Landing and Maneuver Technology Demonstrator (S TOLL 

MTD), see Short Takeoff and Landing and Maneuver Technology 

Demonstrator (STOLIMTD) 

F- 16 Fighting Falcon (Lockheed Martin) 31, 38, 39, 112-114, 147-153, 155, 156, 179, 

219, 220, 223 

F- 16 Multiaxis Thrust Vectoring (MATV) aircraft 223, 224 

F-16E 157 

F-16XL 147, 148, 156-158 

F-22 Raptor (Lockheed Martin) 61,106,135, 137, 159-161,163-166,190 

F-4 Phantom II (McDonnell Douglas) 35, 38, 175-184, 190, 191, 199, 245 

F-S (Northrop) 31, 32, 102, 114, 115 

F-8 Crusader (LTV) 78, 155 

F9F Panther (Grumman) 154 

Fairchild Republic 57, 58 

fairing 27, 31, 49, 50, 69, 70, 101, 141, 142, 183, 184,210,211 

falling leaf 36 

Farmer, Moses G. 48, 106, 155, 174, 191, 192,211 

fatigue 61, 78, 84, 87, 93, 131, 136, 137, 190 

Fatigue and Fracture Laboratory 62, 78 

Federal Republic of (West) Germany 12, 16, 43, 214, 215 

Ferris, James C. 81, 92 

fin 92, 123, 130, 142, 176, 180, 182, 195, 199 

flap hinge 27 

flaperon 114 

flat spin 60, 61, 74, 97, 102-104, 118, 153, 175, 181-183 

Flechner, Stuart G. 127 

Fletcher, Dr. James 75 

flight control computer 37, 39 

flight control system 13, 24, 27, 28, 32, 33, 39, 47, 73, 74, 97, 104, 105, 109, 114, 115, 

117,152-154,203,205,210,214,219 

Flight Dynamics Laboratory, see Air Force Flight Dynamics Laboratory 

flight envelope 13, 17, 26, 32, 35, 48, 49, 87, 107, 142, 143, 152, 155, 163, 221 

flow field 40, 70, 86, 151, 180, 208 

flutter 21, 26, 29, 30, 42,43,48, 61, 62, 70, 75, 76, 79, 80, 83, 84, 86, 87, 97, 98, 100, 

106, 120, 124, 129, 130, 139, 140-144, 147, 155, 157, 167-172, 174, 185, 186, 

191, 192, 195, 197, 199,205,206,211,227,231,232 

246 Index
fly by wire 154 

forward-swept wing (FSW) 39, 109-115, 119, 120 

Foster, Dr. John 100, 187, 188, 189 

Foster, John V. 42 

Foughner, Jerome T. 155 

Fowler flap 128 

Fratello, David 7 

free-flight model tests 11, 14, 18, 33, 36, 37, 63, 72, 112, 129, 208, 214 

Frink, Neal T. 138 

Full-Scale Tunnel, see Langley 30- by 60-Foot (Full-Scale) Tunnel 

G Garrick, I. Edward 170 

General Aviation Stall-Spin Program 8 

General Dynamics 35, 58, 59, 61, 62, 66, 68-73, 78, 79, 81, 87, 100, 112, 148, 155, 

160, 161, 163, 210 

General Electric 29, 57, 97, 109, 120, 123, 147, 171, 175, 201, 205, 208, 213 

General Electric F404 engine 219 

General Electric YJ1O1 engine 121 

Gilbert, William P. 33, 38, 74, 75, 152, 191 

Gilman, Jean 174 

Glenn Research Center (Lewis) 28, 38, 44, 67, 121, 138, 188, 193 

Global Positioning System (GPS) 8 

Gloss, Blair B. 149 

Grafton, Sue B. 32, 33, 112, 113, 115, 156, 162, 164, 180, 208 

Grantham, William D. 210 

graphite-epoxy 27 

ground effect 13, 25, 59 

Grumman 58, 59, 64, 66, 68-71,81, 83-85, 89-91,94, 97, 98, 100, 101, 103, 104, 106, 

109, 110, 112, 115, 116, 119, 120-122, 173 

H Hahne, David E. 92, 93 

Hall, Robert M. 46, 49, 50 

Hallissy, James B. 79, 81 

Hanson, Perry 183 

Hardrath, Herbert F. 78 

Harris, Jr., Roy V. 49, 156, 188 

Hassell, James L. 65 

Hawk aircraft 54 

Hawk missile 195 

Hawker Aircraft Ltd. 13 

head-up display 28 

Henderson, William P. 31, 59, 121, 149, 150, 193,210,215 

Herbst, Dr. Wolfgang 218, 219 

High-Angle-of-Attack Technology Program (HATP) 29, 30, 38-41, 108 

Highly Maneuverable Aircraft Technology (HiMAT) 112, 215, 216 

horizontal tail 16, 27, 36, 48, 69, 75, 83-85, tOO, 103, 104, 129, 139, 142, 143, 150, 

152, 153, 177, 182, 183, 185, 187, 191, 208 

Home, Walter C. 144,184 

Hudson, Charles M. 78 

hybrid wing 31, 150 

hydraulic control system 21 

hydroplaning 139, 140, 144, 175 

Index 247
Impact Dynamics Research Facility, see Langley Impact Dynamics Research Facility 

inlet 13, 51, 52, 56, 69-71, 99, 103, 109, 110, 119, 187, 202, 203 

Institute of Defense Analyses 16 

interfairing 70, 71, 99, 187-189 

International Test Organization (ITO) 215, 221, 223 

Jackson, Charles M. 156, 197 

Johns Hopkins University Applied Physics Laboratory (JHU-APL) 6, 7 

Johnson, Jr., Joseph L. 7, 23, 25, 92, 93, 122, 128, 138, 157, 193, 216 

Jones, Lisa E. 77 

Jordan, Jr., Frank L. 92, 93 

Ju-287 (Junkers) 111 

K Kayten, Gerald G. 24 

Kestrel (XV-6A) 12, 16-18 

KronefJr., Dr. Norris J. 112, 119 

Kuhn; Richard E. 13, 20 

Kvaternik, Raymond G. 155 

L Lamar, John E. 31,150 

landing gear 35, 52, 53, 133, 183 

Langley 12-Foot Low-Speed Tunnel 7, 30, 52-54, 62, 72, 90, 92, 112, 180, 214 

Langley 14- by 22-Foot Subsonic Tunnel 30, 109, 110, 119 

Langley 16-Foot Transonic Dynamics Tunnel (TDT) 22, 26, 30, 42, 43, 48, 62, 75, 76, 

79, 80, 83, 84, 87, 97, 98, 106, 109, 110, 119, 120, 123, 124, 129-131, 

139-144, 148, 149, 155, 157, 165-172, 174, 176, 183-186, 188, 191, 192, 199, 

202,206,211,227,231,232 

Langley 16-Foot Transonic Tunnel 12, 13, 30, 40,43,44,50-52,56,62,64,65,69-72, 

79, 83-85, 90, 93, 98, 100, 101, 107, 124, 127, 130, 161, 186, 188-190, 193, 

196,202,206,210-212,214,227-229 

Langley 20-Foot Vertical Spin Tunnel (Spin Tunnel) 18, 30, 32, 33, 36, 47, 52, 54, 55, 

58,60,62,64,73,83-85,89-91,98,102,110,112,115-117,148,149,151, 

153, 157, 160-165,171-173,176,181,182,186,188,191,199,202,203,206, 

210, 214, 219, 227, 230, 231, 245 

Langley 26-Inch Transonic Blowdown Tunnel (Blowdown Tunnel) 62, 75 

Langley 30- by 60-Foot (Full-Scale) Tunnel 12-14, 18, 22-24, 30, 32, 36-38, 46, 62, 

-65,70,72,73,90-93,98,110,112,114,121-124,128,129,148,149, 

151-153, 157,160-165,176,180,182,186,188,191,193,202,206,208,209, 

214,216,218-221,223,229,245 

Langley 300-MPH 7- by 10-Foot Tunnel 22, 23, 63, 64, 111, 228 

Langley 4-by 4-Foot Supersonic Pressure Tunnel 62, 64, 98, 161, 186, 188, 189, 196, 

• 197, 227, 228 

Langley 6- by 28-Inch Transonic Tunnel 90, 92 

Langley 7- by 10-Foot High-Speed Tunnel 27, 30-32, 57-59, 62, 64, 65, 89, 90, 93, 94, 

98, 100, 148, 149, 157, 176, 178-180, 186, 188, 199, 227, 228 

Langley 8-Foot Transonic Pressure Tunnel 22, 25, 30, 34-36,45,62, 64,68-70, 79, 81, 

98, 100, 125, 127, 133, 138, 145, 196, 206, 210, 227, 228 

Langley Acoustic and Dynamic Laboratory 190 

Langley Aircraft Landing Dynamics Facility 144, 184 

Langley Control Line Facility 13 

Langley Differential Maneuvering Simulator (DMS) 30, 33, 40, 42, 47, 98, 104, 107, 

110,112,115,117,148,149,151-153,157,245 

Langley Impact Dynamics Research Facility 18, 19, 62, 76, 77 

248 Index
Langley Jet Exit Test Facility 30, 40, 122, 214, 218, 219, 230 

Langley Low-Turbulence Pressure Tunnel (LTPT) 90, 92 

Langley Plum Tree Test Site 8 

Langley Unitary Plan Wind Tunnel (Unitary) 62, 68, 70, 79, 98, 100, 148, 149, 157, 

160-163, 165, 175-177, 186, 188, 196-199,227,232 

Langley V/STOL Tunnel 18, 20 

leading edge 5-8, 11, 31, 36, 37, 43, 45, 49, 51-54, 92, 104, 150, 151, 157, 163, 

177-180,191,217 

leading-edge extension (LEX) 29, 31, 32, 34-37, 39, 40, 45, 46 

leading-edge slats 54, 92, 175, 176, 178, 179, 181 

Leavitt, Laurence D. 193 

Lee, Henry A. 85, 91, 173 

LFAX-10 188 

LFAX-4 99, 100, 188 

LFAX-8 185, 187,188 

LFAX-9 188 

Lewis Research Center, see Glenn Research Center 

Libbey, Charles E. 74, 75, 103, 181, 182, 191, 208 

Lightweight Fighter (LWF) 32, 33, 35, 148, 149, 151 

liquid crystal flat-panel display 135-137 

Lockheed 23, 123-126, 128, 131, 135-141, 143, 145, 160-163, 165, 167-173 

Lockheed L.188 Electra 167-170 

Lockheed Martin 124,135-140,147-149,159,172 

Lockwood, Vernon E. 59 

Loftin, Jr., Laurence K. 67, 100 

Long Range Combat Aircraft (LRCA) 212 

Loving, Donald L. 125, 133, 144 

Luckring, James M. 31, 150 

Luoma,ArvoA. 125, 133 

M main landing gear 27, 133 

maneuvering flaps 31 

Margason, Richard J. 18 

Mason, Mary L. 193 

mass balancing 143, 155, 191 

McClellan Committee 67 

McDonnell Douglas 12, 20-23, 25-30, 32, 35-37, 40, 42, 45-49, 52-54, 87, 100, 160, 

175, 176, 178, 182, 183, 185, 186, 188-193, 199 

McGhee, Robert J. 92 

McKinney, Linwood W. 59, 149, 150 

McKinney, Marion 0. 13, 14, 103 

McKinney. Linwood W. 31 

McMillin, S. Naomi 50 

McNamara, Robert S. 66, 68 

Mercer, Charles E. 72, 79, 85, 93 

Messerschmitt-Bolkow-Blohm (MBB) 43, 213, 214, 218, 219, 221 

Miller, David S. 156,197 

missiles 3, 18, 59, 76, 84, 161, 172, 177-179, 195-197, 199, 228 

Mission Adaptive Wing (MAW) Program 61, 62, 81 

Moore, Frederick L. 181 

Morello, Samuel A. 16 

Moses, Robert W. 43, 165 

Moul, Martin T. 27 

multiaxis vectoring 193 

Murri, Daniel G. 46, 115 

Mutual Weapons Development Program (MWDP) 12, 13, 16 

Index 249
N NA-39 66 

NACA 6-series airfoil 78 

nacelle 23, 27, 59, 123, 125, 127, 212 

NASA Headquarters 17, 20, 24, 121, 122, 138, 207 

National Advisory Committee for Aeronautics (NACA) 64, 67, 119, 228 

National Aeronautics and Space Act 1 

National Transonic Facility (NTF) at Langley 26, 90, 93, 110, 202, 203, 227, 228 

Naval Air Systems Command 18, 42, 100 

Naval Weapons Center, China Lake, California 197 

Newman, Jr., James C. 78 

Newsom, Jr., William A. 151, 208 

Nguyen, Luatl. 33, 38, 104, 107, 114, 115, 152, 153 

Nichols, Mark R. 67, 100, 207 

Nicks, Oran W. 25 

noise 136, 137 

nonaxisymmetric nozzle 44, 121, 159, 192 

North American Rockwell 18, 100, 188, 208 

North Atlantic Treaty Organization (NATO) 12, 13, 15, 65 

Northrop Grumman 29, 30, 84, 90, 110, 188, 201-203 

nose vibrations 183 

nozzle 12,13,16,17,20,40,43,44,69-71,85,107,120-122,159,161,187,189, 190, 

192, 193, 205, 206, 211, 212, 216, 218, 219, 224, 229, 230 

nozzle, two-dimensional, see two-dimensional (2-D) nozzle 

0 Ogburn, Marilyn E. 157 

Operation Desert Storm 6, 8, 90, 148, 179, 225 

oscillation 104, 118, 143, 163, 174, 181, 205, 211, 219, 231 

P P.1127 (Hawker Siddely) 11-16 

P.1154 15,16 

P-1101 (Messerschmitt) 63 

P-2 Neptune 168, 169 

P-3 Orion (Lockheed) 167-170 

Patriot missile 195, 196 

Patterson, Jr., James C. 127 

Patuxent River Naval Air Station 36, 37, 39, 44, 48, 53, 55, 105, 107, 108, 182 

Paulson, Jr., John W. 119 

Pendergraft, Jr., Odis C. 72, 193, 212 

Persian Gulf 172 

Person, Jr., Lee H. 16, 17 

Petersen, Richard H. 160, 163 

pilot-induced oscillation (PlO) 51, 55 

pitch rocker technique 153 

pod 23, 27, 70, 91,92, 101 

Polhamus, Edward C. 31, 32, 36, 63, 65, 67, 69, 70, 149, 150, 180 

porosity 49, 50 

powered-lift 16, 18, 22, 25, 28, 138 

Pratt and Whitney 21, 61, 71, 83, 89, 139, 147, 159, 185, 193 

Project Agile Eagle 179 

R radar 37, 90, 106, 179, 188, 199, 206 

Raney, David L. 118 

Ray, Edward J. 31, 149, 150, 178, 180, 181 

250 Index
Re, Richard J. 72, 125, 193, 211 

recognition visit 28, 138 

Reed, Jr., Wilmer H. 119, 144, 155, 170 

Reeder, John P. (Jack) 12, 13, 15-17 

relaxed static stability 110, 114, 152 

Remotely Piloted Vehicle (RPV) 3, 5, 6, 8, 9 

Reubush, David E. 107, 211 

Reynolds number 60, 73, 115, 125, 133, 191,232 

Ricketts, Rodney H. 119, 120 

Rivera, Jr. Jose A. 87 

Robins, A. Warner 188 

rollerons 195, 197 

rotary-balance 47, 163, 219, 230 

Royal Aircraft Establishment 17 

rudder 7,24,27,41,43,83-86,91, 104, 107, 129, 142, 152, 165, 191 

Ruhlin, Charles L. 26, 76, 79, 129-131, 141, 143, 157, 174, 211 

Runckel, Jack F. 67, 70, 71 

runway grooving 140, 144, 175, 184 

S S-3 Viking (Lockheed) 171-174 

Sandford, Maynard C. 76, 79, 129-131, 141, 143 

sawtooth notch 8 

Sawyer, Wallace C. 197 

Schade, Robert 0. 14 

Scher, Stanley H. 60 

Seamens, Robert 189 

Seiner, John M. 190, 212 

semispan model 26, 87, 127, 128 

Sewall, William G. 92,94 

Sewell, Charles 104 

Shaw, David S. 68 

Short Takeoff and Landing (STOL) 11, 22, 23, 25, 27, 28, 138 

Short Takeoff and Landing and Maneuver Technology Demonstrator (F-IS STOL! 

MTD) 122, 185, 190, 192-194 

sidestick controller 147, 154, 155 

Sidewinder missile 195, 197, 198 

single expansion ramp nozzles (SERN) 43, 44 

skid, landing 7 

slat 14, 54, 93, 104, 178-180 

snag 36, 45, 54, 177 

spar 111, 123, 130, 142 

Sparrow missile 195, 199 

Spearman, M. Leroy 67, 69, 197 

speed brake 46, 83-85, 92, 93 

speed bump 71, 101 

spin 8, 12, 18, 20, 30, 32, 33, 36, 38, 39, 41,42,47, 51, 52, 54, 55, 57, 58, 60-62, 

73-75,83-86,89,91,93,97,98,102-105,112, 115, 116, 118, 119, 147, 153, 

154, 157, 159, 160, 162-164,171-173, 175, 178, 180-183, 185, 186, 190, 191, 

195-197,199,203,208,210,213,214,219,230,231,245 

spin recovery parachute 33, 39, 47, 102, 116, 153, 162, 165, 181 

stabilizer, horizontal 27, 85 

stabilizer, vertical 27 

Stack, John 13, 15, 64-67 

stall 7, 8, 36, 39, 49, 53, 54, 56, 57, 74, 91, 93, III, 112, 119, 136, 138, 173, 175, 180, 

183, 210, 219, 245 

Index 251
stall inhibitor system (SIS) 61, 73, 74 

Stallings, Jr., Robert L. 197 

stealth 6, 87, 160, 161, 202 

sting interference effects 125 

stores 47, 48, 58, 60, 75, 76, 80, 84, 87, 90, 155, 177, 195, 196, 199 

strakes 32, 37, 41, 60, 106, 115, 150, 217, 222, 223, 228 

Structures Division 27 

Subsonic Low Altitude Bomber (SLAB) Program 207 

Super Normal Attitude Kinetic Enhancement (SNAKE) configuration 216-219 

supercritical wing technology 21, 26, 61, 62, 78, 80, 228 

Supersonic Cruise and Maneuver Prototype (SCAMP) 156, 157 

Supersonic Cruise Integrated Fighter (SCIF) Program 156 

Swallow configuration 64, 65 

T T-45 Goshawk (Boeing) 5 1-56 

Tactical Fighter Experimental (TFX) Program 62, 66, 67, 228 

tail flutter 61, 123, 129, 130, 140-143, 191 

Taylor, Robert T. 27 

tethered hover test 18 

Thompson, William C. 133 

thrust vectoring 16, 30, 38, 40, 41, 44, 85, 107, 108, 193, 214, 217-219, 221, 224 

thrust-vectoring vanes 40 

tires 52, 55 

titanium 87 

Toll, Thomas A. 65 

Tosti, Louis P. 14 

trailing edge 20, 29, 32, 36, 54, 56, 65, 81, 86, 90, 92, 93, 128, 129, 137, 138, 143, 145, 

147, 149, 151, 178 

transition 13-15, 145 

transition point 145 

Transonic Aircraft Technology (TACT) Program 61, 62, 78-81 

trim drag 68, 100 

T-tail 21, 23, 27, 28, 124, 125, 129, 130, 139-143 

tumbling 109, 116, 117 

turbofan 21, 23, 97, 125,201 

turbojet 23, 84 

turboprop 135, 167-169 

two-dimensional (2-D) nozzle 44, 190, 192, 193, 229 

U U.S. Air Force 9, 21-24, 26, 28, 31-33, 35, 42, 44, 57-62, 64-66, 69-71, 73, 74, 

76-81, 109, 110, 112, 119, 120, 123, 125, 128, 133, 135, 137-141, 144, 

147-149, 152, 153, 155, 156, 158-162, 165, 175, 176, 178, 180, 182, 183, 185, 

186, 188-190, 192,193,198,199,201,202,205-208,210-212,215,221,223, 

228,245 

U.S. Army 8, 124, 129 

U.S. Marine Corps 5-9, 11-13, 18, 29, 83, 86, 89, 135, 175, 176, 178, 223 

U.S. Navy 8, 18, 20, 24, 29, 31, 35-37, 39, 40, 42-44,46-56, 62, 65, 66, 69, 70, 83, 

85-87,89-91,94,97,98,100,102-105,107,120,121,135,141,147, 

167-169,171-173,175-180,182,183,190,192,198, 199,213,218,221,223, 

245 

Uninhabited Air Vehicle Joint Project Office (UAV-JPO) 8 

United Kingdom 9, 11-13, 15-18, 21, 43, 64, 245 

upper-surface blowing (USB) 25, 138 

upper-surface shock waves 26 

252 Index
V vapor screen system 40 

variable-sweep wing 61-63, 65-68, 97, 99, 106, 111, 187, 207, 211, 228 

Vectoring in Forward Flight (VIFF) 11, 12, 16-18 

Vehicle Enhancement Program (VEP) 94 

ventral fin 185, 189 

Vertical and Short Takeoff and Landing (V/STOL) 11-16, 18, 20, 43, 107, 120, 245 

vertical tail 5-7, 24, 32, 40, 43-45, 48, 86, 90-92, 101, 106, 129, 141, 142, 151, 163, 

165, 166, 175, 177, 178, 185, 189, 193, 216, 217, 219 

Vietnam 32, 38, 59, 84, 149, 176, 178, 179, 183, 215 

vortex 31, 142, 149, 150, 157 

vortex flow 31, 39-41, 72, 150 

vortex lift 29, 31, 147, 149, 150, 157, 228 

W Waggoner, Edward G. 93 

Wallops Flight Facility 8, 48, 144, 196, 197, 199 

wedge nozzle 215, 216 

Whipple, Raymond D. 55, 115, 116 

Whitcomb, Dr. Richard T. 20, 25, 26, 35, 36, 69, 71, 78, 79, 101, 125, 133, 138, 144 

White, Ronald 190 

White, W. Louis 73, 173 

Wilmoth, Richard G. 72 

wind tunnel to flight correlation 18, 144, 190 

wing box 78, 81, 131, 135-137 

wing drop 7, 29, 30, 48-51, 53,54 

wing pivot 64, 65, 68, 78 

wing rock 104, 105, 109, 113-115, 118,219 

wing stall 27, 180, 208 

winglet 21, 25-28, 228 

wingtip 7, 8, 16, 25, 85, 92, 111-113, 155, 192, 195, 197, 199, 217 

Wood, Richard M. 197 

Wusk, Mary Beth 138 

X X-1 (Bell) 17, 63, 111 

X-29 (Grumman) 39, 109-122 

X-31 (Rockwell-MBB) 108,122,213-216,219-224 

X-5 (Bell) 63, 64 

XF-IOF (Grumman) 64 

XFG- 1 (Cornelius Aircraft Company) 111 

XFV-12A (North American Rockwell) 11, 18-20 

y YA-IOA 58 

YA-9A 58 

Yager, Thomas J. 144, 184 

Yates, Jr., E. Carson 141, 142 

YC-14 23,25 

YC-15 23-26 

Yetter, Jeffrey A. 49 

YF-16 32,33,35,147-153,155,156 

YF-17 29-37,42-44,149,192 

YF-22 159-163 

YF-23 160, 161 

Yip, Long P. 7, 8, 53, 54 

Index 253
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Monographs in Aerospace History 

Launius, Roger D., and Gillette, Aaron K. Compilers. The Space Shuttle: An Annotated Bibliography. (Monographs in Aerospace History, No. 1, 1992). 

Launius, Roger D., and Hunley, J.D. Compilers. An Annotated Bibliography of the Apollo Program. (Monographs in Aerospace History, No. 2, 1994). 

Launius, Roger D. Apollo: A Retrospective Analysis. (Monographs in Aerospace History, No. 3, 

1994). 

Hansen, James R. Enchanted Rendezvous: John C. Houbolt and the Genesis of the Lunar-Orbit 

Rendezvous Concept. (Monographs in Aerospace History, No. 4, 1995). 

Gorn, Michael H. Hugh L. Dryden's Career in Aviation and Space. (Monographs in Aerospace 

History, No. 5, 1996). 

Powers, Sheryll Goecke. Women in Aeronautical Engineering at the Dryden Flight Research Center, 1946-1994 (Monographs in Aerospace History, No. 6, 1997). 

Portree, David S.F. and Trevino, Robert C. Compilers. Walking to Olympus: A Chronology of 

Extravehicular Activity (EVA). (Monographs in Aerospace History, No. 7, 1997). 

Logsdon, John M. Moderator The Legislative Origins of the National Aeronautics and Space Act 

of 1958: Proceedings of an Oral History Workshop (Monographs in Aerospace History, No. 8, 

1998). 

Rumerman, Judy A. Compiler U.S. Human Spaceflight: A Record of Achievement, 1961-1998 

(Monographs in Aerospace History, No. 9, 1998). 

Portree, David S.F. NASA's Origins and the Dawn of the Space Age (Monographs in Aerospace 

History, No. 10, 1998). 

Logsdon, John M. Together in Orbit: The Origins of International Cooperation in the Space Station Program (Monographs in Aerospace History, No. II, 1998). 

Phillips, W. Hewitt. Journey in Aeronautical Research: A Career at NASA Langley Research Center (Monographs in Aerospace History, No. 12, 1998). 

Braslow, Albert L. A History of Suction-Type Laminar-Flow Control with Emphasis on Flight 

Research (Monographs in Aerospace History, No. 13, 1999). 

Logsdon, John M. Moderator Managing the Moon Program: Lessons Learned from Project 

Apollo (Monographs in Aerospace History, No. 14, 1999). 

Perminov, V.G. The Difficult Road to Mars: A Brief History of Mars Exploration in the Soviet 

Union (Monographs in Aerospace History, No. 15, 1999). 

Tucker, Tom. Touchdown: The Development of Propulsion Controlled Aircraft at NASA Dryden 

(Monographs in Aerospace History, No. 16, 1999). 

Maisel, Martin D.; Demo J. Giulianetti; and Daniel C. Dugan. The History of the XV-15 171! Rotor 

Research Aircraft: From Concept to Flight. (Monographs in Aerospace History, NASA SP-2000-

4517, 2000). 

Jenkins, Dennis R. Hypersonics Before the Shuttle: A History of the X-15 Research Airplane. 

(Monographs in Aerospace History, NASA SP-2000-4518, 2000). 

Monographs in Aerospace History 255
About the Author 

Joseph R. Chambers is an aviation consultant who lives in Yorktown, Virginia. He 

retired from the NASA Langley Research Center in 1998 after a 36-year career as a 

researcher and manager of military and civil aeronautics research activities. He began 

his career as a specialist in flight dynamics as a member of the staff of the Langley 30-

by 60-Foot (Full-Scale) Tunnel, where he conducted research on a variety of aerospace 

vehicles including V/STOL configurations, reentry vehicles, and fighter aircraft configurations. He later became a division chief with responsibilities for all research projects 

in the Full-Scale Tunnel, the 20-Foot Vertical Spin Tunnel, drop-model tests, and piloted 

simulator studies in the Differential Maneuvering Simulator (DMS) at Langley. When 

he retired from NASA, he was manager of a division that conducted systems analysis of 

the potential payoffs of advanced aircraft concepts and research investments. 

Mr. Chambers participated in the development of virtually every Air Force and Navy 

aircraft of the past 30 years, including all fighter-attack aircraft. He is the author of over 

50 technical reports and publications and coauthor of NASA Special Publication SP-514 

on the subject of airflow condensation patterns for high-performance aircraft. He has 

made presentations on research and aircraft development programs to audiences as 

diverse as the Von Karman Institute in Belgium and the annual Experimental Aircraft 

Association (EAA) Fly-In at Oshkosh, WI. He has served as a representative of the 

United States on international committees for military research and has given presentations in Japan, China, Australia, the United Kingdom, Canada, Italy, France, Germany, 

and Sweden. 

Mr. Chambers received the Exceptional Service Medal and the Outstanding Leadership 

Medal, two of NASA's highest awards. He received the Arthur Flemming Award in 1975 

as one of the 10 Most Outstanding Civil Servants for his management of NASA stallspin research for military and civil aircraft. He also was a corecipient of the 1973 

H.J.E. Reid Award presented by Langley for the most outstanding technical paper (an 

analysis of the lateral-directional stability of the F-4 fighter aircraft at high angles of 

attack). In 1977, he was a corecipient of the Mechanics and Control of Flight Award of 

the American Institute of Aeronautics and Astronautics. This awarded was presented for 

his contributions to technology to predict high-angle-of-attack, stall, and spin characteristics for aircraft and for improving those characteristics through combined aerodynamic and automatic control design. Mr. Chambers has a bachelor of science degree in 

Aeronautical Engineering from the Georgia Institute of Technology and a master of science degree in Aerospace Engineering from Virginia Polytechnic Institute and State 

University (Virginia Tech). 

256 About the Author

National Aeronautics and

Space Administration

Langley Research Center