NASA Facts

National Aeronautics and 

Space Administration 

Dryden Flight Research Center 

P.O. Box 273

Edwards, California 93523 

Voice: 661-276-3449 

FAX 661-276-3566 

pao@dfrc.nasa.gov FS-2005-03-061 DFRC 

‘Back to the Future’ 

Active Aeroelastic Wing Flight Research 

How differential deflection of the inboard and outboard leading-edge flaps affected the handling qualities of this modified 

F/A-18A was evaluated during the first check flight in the Active Aeroelastic Wing program at NASA's Dryden Flight 

Research Center. NASA Photo: EC02-0264-19. 

Project Summary 

NASA's Dryden Flight Research Center, Edwards, Calif., in cooperation with the U.S. Air Force Research Laboratory 

(AFRL) and Boeing Phantom Works, researched a high-tech adaptation of the Wright Brothers rudimentary "wingwarping" approach to aircraft flight control in the Active Aeroelastic Wing (AAW) flight research program. The focus of 

AAW research was on developing and validating the concept of aircraft roll control by twisting a flexible wing on a fullsize aircraft. The test aircraft chosen for the AAW research is a modified F/A-18A obtained from the U.S. Navy in 1999. 

The aerodynamic forces acting on the F/A-18s traditional aircraft control surfaces, such as ailerons and leading-edge flaps, 

were used to twist a more-flexible wing to provide aircraft roll maneuvering control. 

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Historical Background 

When Orville Wright first took to the air on Dec. 17, 1903, he 

didn't have ailerons or flaps to control his airplane. Instead, the 

Wright brothers had chosen to twist or "warp" the wingtips of 

their craft in order to control its rolling or banking motion. Rather 

than using one of the craft's two control sticks to make the 

wingtips twist, they had devised a "saddle" in which the pilot lay. 

Cables connected the saddle to the tips of both wings. By moving 

his hips from side-to-side, the pilot warped the wingtips either up 

or down, providing the necessary control for the Wright Flyer to 

make turns. 

Current Status 

Begun in 1996, the AAW flight research program was completed 

in the spring of 2005. After completion of detailed design and 

wing modifications required for the program in the late 1990s, 

the test aircraft was extensively instrumented and reassembly was 

completed by early 2001. Over the course of the year, the AAW 

test aircraft was subjected to extensive structural loads, wing 

stiffness and vibration tests, installation of the initial control 

software into the aircraft’s research flight control computer, 

systems checkout and flight simulation activity. 

The first-phase parameter identification flights in the two-phase 

flight test program began in late 2002 and concluded in April 

2003 after 50 research flights. These flights were used to 

measure the forces available from each surface to twist the wing 

and control the aircraft. That was followed by a year-long period 

of data analysis and control software redesign to optimize the 

performance of the flexible wing. The final phase of flight tests 

to evaluate the AAW control laws and evaluate the handling and 

performance qualities available from the flexible wing concept 

began in late 2004 and concluded in March 2005. About 25 

research missions were flown in the second phase, covering 18 

test points ranging from speeds of Mach .85 to Mach 1.3 and 

altitudes ranging from 5,000 to 25,000 feet. Several additional 

flights were flown to re-evaluate several test points with different 

gains in the control laws and to evaluate the ability of the system 

to alleviate structural loads on the wing before AAW flights 

Comparison of conventional and active aerolastic wings. 

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concluded. Analysis of flight data and preparation of technical 

reports is expected to continue for some time into the future as 

staff time is available. 

Goals and Results 

The AAW program's goal was to demonstrate improved aircraft 

roll control through aerodynamically induced wing twist on a 

full-scale high performance aircraft at transonic and supersonic 

speeds. Data was obtained to develop design information for 

blending flexible wing structures with control law techniques to 

obtain the performance of current day aircraft with much lighter 

wing structures. The flight data included aerodynamic, structural 

and flight control characteristics that demonstrated and measured 

the AAW concept in a comparatively low cost, effective manner. 

The data also will provide benchmark design criteria as guidance 

for future aircraft designs. 

Over the course of the second phase of flight tests, roll rates 

adequate for lateral control, or within 15 to 20 percent of that 

obtained by a production F/A-18, were obtained by use of active 

control of wing flexibility alone, without use of the differential 

rolling horizontal tail used by standard F/A-18s at transonic and 

supersonic speeds. Roll rates at 15,000 feet were highest at Mach 

.85 and Mach 1.2, and lowest at Mach .95, similar to a conventional F/A-18. 

With landing gear and flaps down, NASA Dryden's Active 

Aeroelastic Wing F/A-18A research aircraft rolls towards 

final approach to the Edwards Air Force Base Runway at 

the end of a test flight. NASA Photof: EC03-0039-7. 

Aircraft Modifications 

The wings from NASA's now-retired F-18 #840, formerly used in 

the High-Alpha Research Vehicle (HARV) program, were 

modified for the AAW flight research program and installed on 

the AAW test aircraft. Several of the existing wing skin panels 

along the wing box section of the wing just ahead of the trailingWith a long flight data probe extending from its nose, this 

F/A-18A has been modified to conduct flight research in 

the Active Aeroelastic Wing (AAW) project at NASA's 

Dryden Flight Research Cetner, Edwards, California. 

NASA Photo: EC01-0288-5. 

edge flaps and ailerons were replaced with thinner, more flexible 

skin panels and structure, similar to the prototype F-18 wings. 

Original F-18 wing panels were comparatively light and flexible. 

During early F-18 flight tests, however, the wings were observed 

to be too flexible at high speeds for the ailerons to provide the 

specified roll rates. This was because the high aerodynamic 

forces against a deflected aileron would cause the wing to deflect 

in the opposite direction. 

In addition, the F/A-18’s leading-edge flap was divided into 

separate inboard and outboard segments, and additional actuators 

were added to operate the outboard leading-edge flaps separately 

from the inboard leading-edge surfaces. By using the outboard 

leading-edge flap and the aileron to twist the wing, the aerodynamic force on the twisted wing provided the roll forces desired. 

With AAW control technology, a flexible wing will now have a 

positive control benefit rather than a negative one. 

In addition to the wing modifications, a new research flight 

control computer was developed for the AAW test aircraft, and 

extensive research instrumentation, including more than 350 

strain gauges, was installed on each wing. 

Funding 

The AAW project receives its funding from NASA’s Office of 

Aerospace Technology, as well as from the U.S. Air Force 

Research Laboratory. The Boeing Company’s Phantom Works 

division in St. Louis, Mo., performed the AAW wing modifications, installed portions of the wing instrumentation and assisted 

in software development under contract with the Air Force 

Research Laboratory and NASA. Lockheed-Martin developed the 

AAW research flight control computer. The total budget for the 

entire AAW project is approximately $41 million, including 

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about $25 million in direct monetary outlay and about $16 

million for in-kind support, spread over eight years. 

Technology Commercialization 

With the successful demonstration of actively controlled "wing 

warping" techniques for aircraft roll control at transonic speeds in 

the Active Aeroelastic Wing project, engineers will now have 

Three-view drawing of AAW.

more freedom in designing more efficient, thinner, higher aspectratio wings for future high-performance aircraft while reducing 

the structural weight of the wings by 10 to 20 per cent. This will 

allow increased fuel efficiency or payload capability, along with 

potentially reduced radar signature. The technology also has 

application to a variety of other future aircraft, such as highaltitude, long-endurance unmanned aircraft, transports, and 

airliners. 

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