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NASA News
National Aeronautics and
Space Administration
Dryden Flight Research Center
P.O. Box 273
Edwards, California 93523
Phone   (661) 276-3449
FAX (661) 276-3566 
                        __
May 1, 2003

Alan Brown
NASA Dryden Flight Research Center
(661) 276-2665
alan.brown{at}dfrc.nasa.gov

RELEASE: 03-25

ACTIVE AEROELASTIC WING COMPLETES FIRST PHASE OF FLIGHT TESTS

With a final sonic boom reverberating over the desert north of 
Edwards Air Force Base, a NASA research aircraft has completed the 
first phase of the Active Aeroelastic Wing (AAW) flight research 
program.

NASA research pilot Richard Ewers flew the final two test points 
during the brief 35-minute flight in mid-April from NASA's Dryden 
Flight Research Center at Edwards. In all, 50 test missions were 
flown by two project pilots in the modified, highly instrumented 
F/A-18A over the course of five months since the first flight last 
November.  

The Active Aeroelastic Wing project seeks to determine the advantages 
of twisting flexible wings for primary maneuvering roll control at 
transonic and supersonic speeds. From flight test and simulation 
data, the program will develop structural modeling techniques and 
tools to help design lighter, more flexible high aspect-ratio wings 
for future high-performance aircraft. Greater freedom in wing design 
will enable more economical operation or greater payload capability.

Although similar in concept to the "wing warping" control system 
pioneered by the Wright brothers almost a century ago, AAW employs 
conventional control surfaces such as ailerons and leading-edge flaps 
to aerodynamically induce the twist, rather than mechanically 
twisting the wingtips as on the Wright Flyer.

"The first phase of flight tests focused on what we call parameter 
identification - essentially evaluating control surface effectiveness 
at rolling the aircraft or twisting the wing," said Dryden's AAW 
project manager Larry Myers. "We flew test points at altitudes 
ranging from 5,000 to 25,000 feet, and at speeds from Mach 0.8 to 
1.3."

Prior to the beginning of flight tests, the F/A-18's wings were 
modified to increase their flexibility, equivalent to the those on 
prototype and pre-production F-18s. Those early wings were deemed to 
be too flexible to meet Navy performance specifications at transonic 
and supersonic speeds due to a phenomenon known as aileron reversal. 
Aileron reversal occurs when high dynamic pressures cause a 
too-flexible wing to twist when the ailerons are moved up or down, 
severely reducing the aircraft's roll rate and maneuvering 
capability. The wing structure on production F/A-18s was then 
stiffened to help it meet the Navy's specifications.

"What we are trying to do in AAW is take what is traditionally a 
negative -- too much wing flexibility  --  and turn it into a 
positive," Myers added. 

Over the next two months, AAW engineers at NASA Dryden and at 
Boeing's Phantom Works division in St. Louis will analyze the 
extensive data recorded during the first phase of flight tests. Armed 
with that information, the Phantom works engineers will then write 
the control law software for the AAW research flight control 
computer. After an extensive period for verification, validation, 
integration and checkout of the new software with the aircraft's 
control systems, the second phase of AAW flight tests should get 
under way in early 2004.

While new flight control software is being developed, the AAW 
research aircraft will undergo inspection, maintenance and 
installation of additional flight test instrumentation. It will also 
be flown to the Midwest for display at several air shows during the 
summer in connection with Centennial of Flight activities. Those 
shows include:
* The Dayton International Air Show at Dayton, Ohio, July 17 - 20;
* The Grissom Air Force Base air show at Kokomo, Ind., July 26-27;
* The Experimental Aircraft Association's AirVenture 2003 at Oshkosh, 
Wis., July 29 - Aug. 4.  

AAW is jointly funded and managed by the Air Force Research 
Laboratory's Air Vehicles Directorate and NASA Dryden, with Boeing's 
Phantom Works division in St. Louis, Mo., the prime contractor for 
aircraft modifications and software development.

- NASA -

NOTE TO EDITORS / WRITERS:

Interviews with NASA Dryden AAW project manager Larry Myers or other 
project personnel can be arranged by calling (661) 276-2665. Still 
photos and video footage are available to support this release. 
Photos are available on the NASA Dryden Flight Research Center 
Internet website at: 
http://www.dfrc.nasa.gov/Gallery/Photo/index.html.  For photo prints 
or video dubs, please call (661) 276-2665 .

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