Wing twisting: the Wright stuff

Technology that enables wing 'warping' completes its first flight at Dryden

BY WILLIAM COLE


NASA, the U.S. Air Force and Boeing proved Friday, Nov. 15, that old aerospace ideas never die—they just wait for the right technology to come along.

A high-tech variation of wing-twisting— one of the earliest forms of flight control the Wright brothers pioneered a century ago—took its first outing aboard a highly modified flight-research F/A-18 Hornet. The aircraft took off from NASA's Dryden Flight Research Center, Edwards Air Force Base, Calif., at 2:05 p.m. During the one-hourand- eight-minute flight, NASA research pilot Dana Purifoy put the modified Navy fighter plane through an extensive functional checkout of aircraft flight controls, avionics systems, engine operation and newly installed test instrumentation. He also began evaluation of its aerodynamic flutter limits and the differential movement of the inboard and outboard leading edge flaps that AAW research uses.

The aircraft, configured to investigate and ultimately exploit Active Aeroelastic Wing technology, is able to alter the shape of its wing surfaces subtly in flight, providing a new measure of control and better performance. The technology could one day lead to a fully ''morphing'' aircraft that can actually change its shape in various ways during flight for optimum performance.

During the first flight, the team checked out the basic operation of the aircraft. Subsequent flights will gather specific information about the aircraft's performance. Dryden, U.S. Air Force and Boeing employees applauded as the aircraft came in to land.

''This first-flight milestone is one we've been waiting for, and it's only the beginning of a new chapter in the combination of aerodynamics, structures and flight controls into a single integrated system,'' said Bob Krieger, president of Boeing Phantom Works.

''Our AAW teaming effort with NASA and the Air Force is unique, and everyone has worked very hard to reach this point. I look forward to the next few months when we will verify this concept with additional AAW flight tests.''

Pam Drew, vice president of Boeing Phantom Works' Engineering and Information Technology organization, said, ''The future will show that this was a defining moment in the history of aerospace technology. The Wright brothers would have been proud of what we did here today. This flight represents a triumph of our team's creativity and know-how. We're pushing the boundaries of research, proving that if we can dream it, we can do it.''

Jim Guffey, Phantom Works program manager for AAW, said the flight was an ''historic milestone in the exploration of AAW technology.

''This first flight will demonstrate how to capture and exploit this technology for future applications,'' he said. The maiden voyage, he said, was the culmination of extensive ground testing that included extensive loads calibration, vibration and systems testing, taxi tests, and simulation and training.

The AAW program is putting a new twist on something that Orville and Wilbur Wright started almost 100 years ago.

During his historic flight in 1903, Orville Wright used pulleys and cables to ''warp'' the wings of his rudimentary plane to make turns and provide roll control. As aluminum replaced fabric in the construction of aircraft, airplane makers largely abandoned wing twisting in favor of ailerons, flaps and leading-edge slats flight controls. But those flight controls add weight and drag to the vehicle. Wings that can twist require fewer moving parts for controlling flight. They can be made thinner, lighter and more aerodynamically efficient than today's standard wings.

The first flight brought the Wright brothers' roll control solution full circle.

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 allows 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—provide the aerodynamic force needed to twist or ''warp'' the wing. In addition, project engineers have equipped the plane with highly sophisticated flight controls. They hope to obtain roll performance at transonic and supersonic speeds close to that of production F/A-18s, without using the stabilators (moving horizontal tails) and with smaller control surface deflections.

Project goals include demonstrating aircraft roll control by aerodynamically inducing 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.

The first flight followed extensive systems tests and simulation. 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 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.

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 manned 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.''

william.cole@boeing.com