Let’s twist again!

Technology that enables wing 'warping' rolled out at Dryden

BY WILLIAM COLE

The Wright brothers would have been proud.

When NASA, the U.S. Air Force and Boeing recently rolled out a technology that will allow an aircraft to improve its performance by changing the shape of its wings, they were putting a new twist on something that Orville and Wilbur Wright started almost 100 years ago.

For their historic flight in 1903, the Wright brothers used pulleys and cables to "warp" the wings of their rudimentary plane to make turns and provide roll control. While simple and elegant in approach - emulating the flight of birds - wing twisting was eventually abandoned as fabric evolved into metals, and rigid wings were equipped with ailerons, flaps and leading edge slats.

But new technology may be changing all that again.

Gleaming under the hangar lights at NASA's Dryden Flight Research Center, Edwards Air Force Base, Calif., a highly modified flight research F/A-18 Hornet was unveiled March 27 to the applause of some 200 guests.

The aircraft, equipped with Active Aeroelastic Wing (AAW) technology, will have the ability to alter the shape of its wing surfaces subtly in flight, providing a new measure of control and better performance.

The program takes us "back to the future," said Maj. Gen. Paul Nielsen, commander of the U.S. Air Force Research Laboratory, noting early attempts at wing twisting. In honor of the Wright brothers and other aviation pioneers, the newly painted aircraft sported a "Centennial of Flight" logo provided by the Centennial of Flight Commission. Now, said Nielsen, the team will attempt to harness wing aeroelastic flexibility in a high performance aircraft in a "new and beneficial way."

Boeing Phantom Works modified the test aircraft wings at its St. Louis facility with additional actuators, a split leading edge flap and thinner wing skins. That would allow the outer wing panels, made of composite material and lightweight aluminum, to twist up to five degrees. The traditional wing control surfaces - trailing edge ailerons and the outboard leading edge flap - will be used to provide the aerodynamic force needed to twist or "warp" the wing. In addition, the plane is equipped with highly sophisticated flight controls. Project engineers hope to obtain roll performance at transonic and supersonic speeds close to that of production F/A-18s, without using the aircraft's stabilators (fully moving horizontal tail flight control) and with smaller control surface deflections.

Project goals include demonstrating aircraft roll control through aerodynamically induced wing twist on a full-scale combat aircraft and investigating the use of the lighter-weight flexible wings for commercial as well as military airplanes. Following extensive systems tests and simulation, the AAW F/A-18A will begin first phase flight testing by mid-year. Flight test results will ultimately provide benchmark design criteria as guidance for future aircraft designs.

The aircraft represents the future of aircraft that can flex and bend their wings in much the way that birds do. The ultimate extension of the idea is a NASA 'morphing' aircraft that can change its shape for peak efficiency at specific altitudes and under certain flight conditions. The end result: better performance, reduced drag, improved fuel efficiency, greater payloads and weight reductions of up to 25 percent.

"The best minds in aerospace have long dreamed of an aircraft not restrained by the physical limitations of rigid, inflexible wings ... an airplane that can change its features and structures and soar like an eagle," said Pam Drew, Boeing vice president of Engineering and Information Technology.

Other speakers noted the historical symbolism of the occasion. NASA's Active Aeroelastic Wing project manager Denis Bessette said that the Wright brothers flew the first research aircraft of the 20th century.

"This F/A-18 will be the first research aircraft of the 21st century," he said, characterizing the technology as the first research stepping stone to dramatically improved performance and safety that NASA intends to pursue for the 21st century aircraft.

Ed Pendleton, AAW program manager for the Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, said, "Active Aeroelastic Wing both returns aeronautics to it's beginnings, and opens the way to new avenues of lifting surface research in the future."

Pam Drew concluded: "What we see here today is a triumph of our team's creativity and know-how. It shows that there are no limits to the imagination."

EMPLOYING THE BEST OF THE BEST
It might just be the perfect partnership. While the F/A-18 Hornet test aircraft was the star of the Active Aeroelastic Wing rollout, the project team received almost as much praise as did the technology it seeks to demonstrate.

Jointly supported and managed by Boeing Phantom Works, NASA and the Air Force, the AAW program aptly illustrates the new philosophy, adopted by all three team members, of mitigating risk by drawing on the best available minds and talent to achieve results.

"This is an excellent example of collaborative research," said Maj. Gen. Paul Nielsen, commander of the U.S. Air Force Research Laboratory, noting three factors:

• The U.S. Air Force "focused its efforts on leading the design of experiment and funded most of the aircraft modification."
• Boeing "completed modifications to the wings, control actuation and the flight computer and will complete development of a set of experimental control laws."
• NASA "conducted some of the modification work and will lead the ground and flight research efforts."

Pam Drew, Boeing vice president of Engineering and Information Technology, drew an analogy between an eagle's natural flight controls and the power of team effort. "In a sense our individual efforts as team members blend to produce the right results much as the eagle's individual feathers serve to facilitate the perfect unfettered flight," she said. Phantom Works, she said, has adopted a best-of the-best approach to reaching technology solutions that extends well beyond the enterprise's borders.

Boeing AAW program manager Jim Guffey, said:, "The AAW program is a prime example of how Phantom Works functions. We understood the challenge, drew on talent from across Boeing and the AAW program partners, and then applied that technical expertise to achieve results."

NASA's program manager for the AAW, Denis Bessette, said, "We have a great team made up of Boeing, Air Force and NASA people. There isn't a government group, a contractor group or an Air Force group.

"We have all worked as one team."