by Larine Barr
Air Force Research Laboratory Public Affairs
3/8/2005 - WRIGHT-PATTERSON AIR FORCE BASE, Ohio (AFPN) -- An experimental flexible-wing jet has embarked on a final phase of flights over Edwards Air Force Base, Calif., to demonstrate wing warping performance advantages for future aircraft.
During the final phase, which began in December and is expected to be completed in April, a modified Navy F/A-18A will fly about 30 test flights from NASA’s Dryden Flight Research Center at Edwards. Scientists will evaluate the flight control system designed to twist the wing and control the airplane.
The goal of the Active Aeroelastic Wing program is to demonstrate the design process, philosophies and concept, focused on taking advantage of the aeroelastic effects of the wing, said Dryden's project manager Larry Myers.
"To control the aeroelasticity of this wing, we have designed control laws that take advantage of the different inboard and outboard leading edge flaps to control them separately, to exploit the aeroelasticity of the wing," Mr. Myers said.
Since it began in 1996, the program has sparked the imagination and energy of its creators and onlookers alike. For the Air Force, the new technology represents a revolutionary approach to designing wings and is applicable to a wide variety of future air vehicle concepts under study -- from fighter aircraft to high altitude, long endurance concepts and high speed, long range vehicles, Air Force Research Laboratory officials here said.
"AAW is about managing the aeroelastic shape of the wing and represents a new philosophy for designing highly efficient wings in terms of structural weight, aerodynamic efficiency and control effectiveness," said Pete Flick, Air Force program manager assigned to the laboratory’s air vehicles directorate.
Mr. Flick said the benefits of the program depend on the specific application.
With wing warping, the control surface deflections can be chosen to produce an aeroelastic shape that minimizes the load on the structure which results in reduced structural weight, he said. It also minimizes the drag of the aircraft, improving range, or maximizes the maneuver rates of the aircraft, enhancing maneuverability, Mr. Flick said.
The research advances work by the Wright Brothers, who used a wing-warping control system on the 1903 Wright Flyer. Like the Wright Brothers, the program’s inventors recognize that today's aircraft could benefit from wing twist.
In 2002, during the first phase of testing, the team flew the aircraft through 50 parameter-identification flights to collect data and refine the team's aerodynamic and structural loads models of the aircraft, officials said.
"In Phase 1, our primary objective was to characterize the aeroelastic nature of the wing," Mr. Flick said. "We determined the effect of deflecting each of the four wing control surfaces (two leading edges and two trailing edges) across the flight envelope on structural loads, the degree of wing twist under those loads and vehicle maneuvering rates. With this data, we developed the (wing warping) control laws that we are now testing, which will demonstrate that aeroelastic wing twist can be effective in improving vehicle maneuverability and controlling structural loads," Mr. Flick said.
NASA's test pilot Dana Purifoy is flying the final phase of flights, and has defined 18 test points that start at 15,000 feet and Mach 0.85, going out to 25,000 feet and Mach 1.3, officials said.
Now about half-way through the flights, Mr. Purifoy said the aircraft is performing well.
"The flying qualities of the airplane are very good," he said. "From a piloting standpoint, the airplane is very predictable. I'm able to control it very precisely throughout all the envelope expansion maneuvers that we've done. From a performance standpoint, the simulation experience that I had prior to the flight was very close to what we saw in flight and that the airplane continues to perform flawlessly as we go through the final phase."
As the jet continues to prove the flexible wing concept, program officials are poised to call the program a success.
"We are extremely pleased with our final phase results to date," Mr. Flick said. "For the maneuvers and flight conditions evaluated, we have demonstrated that (wing warping) technology works. We are anxious to complete the remaining flight research to prove the technology over the entire research flight envelope."
Once the flight research is successfully completed, Mr. Flick said the inventors will turn toward spreading the design philosophy to the technical community.
"Transitioning (wing warping) will likely be a relatively long process since it represents a design philosophy. The application to future Air Force vehicles will depend on specific design requirements of those future systems. The benefits are greatest when a vehicle design is initiated with (wing warping) in mind, and limited when applied to an existing vehicle. We look forward to presenting the results of our successful program," Mr. Flick said. (Courtesy of Air Force Materiel Command News Service)