The Wright brothers pioneered flight with aircraft that twisted, or warped, their wingtips to induce a bank instead of using now-conventional hinged ailerons for the purpose. Over time, hinged ailerons and rigid wings became the dominant means of aircraft roll control; and wing warping was retired as an impractical anachronism to a place of veneration in museums.

But, as speeds increased in the jet age, wing warping occasionally returned unintentionally. Pilots of the sleek, slim-wing B-47 Stratojet encountered a phenomenon at high speeds where aileron deflection caused the limber wing to twist in the opposite way, reversing the direction of roll input. Called aileron reversal, this trait was also discovered on pre-production F/A-18 jets, prompting production versions to have stiffer wings.

Now NASA’s Active Aeroelastic Wing (AAW) program capitalizes on unique pliable wings to initiate roll in the modified AAW F/A-18 flown to EAA AirVenture 2003. The AAW test bed has been operated at speeds up to Mach 1.3 as engineers map the flexibility of the special wings this year. Armed with that knowledge, the testers will devise flight control software to capitalize on the AAW phenomenon in a phase of tests next year.

Soon, new flight control software will prompt the ailerons and movable leading edge control surfaces to respond to normal pilot stick inputs by causing the AAW F/A-18’s wings to deflect. The roll induced in this manner will make the AAW aircraft independent of horizontal stabilizer inputs to keep the aircraft on course in a roll.

Fittingly, this modern takeoff on the Wrights’ wing-warping idea made the NASA AAW F/A-18 the first aircraft authorized to wear the official Centennial of Flight insignia. But, there’s much more to AAW than nostalgia. The ability to use computer flight control programs and state-of-the-art flexible, yet strong, wing structures could lead to future high-performance aircraft with lighter, less mechanically complex wings, possibly even using seamless control surfaces to induce wing twisting. The ability to maneuver at high speeds could become simpler, and more efficient through wing warping. Benefits could include lighter weight, which may translate into other desirable traits: increased speed, range, or payload.

Wing warping could become one more tool for NASA and industry designers who seek the ultimate morphing airplane, with an airframe that can change shape to constantly seek optimum flight parameters throughout a wide speed range, or in the face of changing atmospheric conditions.

The AAW program is conducted by NASA’s Dryden Flight Research Center located on Edwards Air Force Base in California’s Mojave Desert. It is jointly funded and managed by NASA Dryden and the Air Force Research Laboratory’s Air Vehicles Directorate. Boeing’s Phantom Works division in St. Louis, Missouri, is the prime contractor for AAW aircraft modifications and software development. Lockheed-Martin developed the AAW research flight control computer.

On the flight east from Dryden earlier this month, NASA pilots Dick Ewers and Dana Purifoy received permission to make a low pass over the U.S. Air Force Academy campus near Colorado Springs, Colorado, in the AAW jet and its F/A-18 chase plane, honoring a tradition of such salutes to Air Force Academy cadets by the crews of interesting aircraft.

A team of AAW specialists and pilots from NASA Dryden can often be found beside their special research F/A-18 jet at AeroShell Square this week, describing their high-speed world and answering questions for EAA AirVenture visitors.

July 30, 2003

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