Boeing was looking at flexible and bending wing technology with the use of composites

Boeing was looking at flexible wing technology and the use of composites. The story of how Seattle planemaker Boeing used a McDonnell Douglas F/A-18 Hornet for Active Aeroelastic Wing (AAW) development. When man first dreamed of flying, he studied how birds maneuvered through the air and noted how they flexed and bent their wings.

The Wright Brothers used pulleys and cables on their rudimentary plane to perform turns similar to how birds did. Wing twisting was eventually abandoned as an idea for flight control after wings were fitted with ailerons, flaps, and leading edge slats. An example of wing warping can be seen in the drawing above.

A US Navy F/A-18 was selected for the tests
An Active Aeroelastic Wing integrates controls, structures, and aerodynamics at high speeds and pressures to control aeroelastic twist. Aeroelastic twist can be harnessed using aerodynamic tabs with multiple leading and trailing edge controls to provide wing control power.

When studying what aircraft to use for the tests, Boeing determined that a pre-production version of the F/A-18 would be the ideal plane because of its high-wing aspect. Working with the Air Force and NASA, Boeing modified the F/A-18 to allow two leading-edge controls to work two trailing-edge controls for high-speed rolling performance. The technology was developed from knowing that the aeroelasticity of the wing caused by deflecting one of the control surfaces could be offset by deflecting another control surface.

The tests took place in California
Almost all modern planes use some form of slat along the leading edge to provide additional lift during certain flight portions. Deploying the slats simultaneously as the ailerons cause a twisting effect on the wing’s main structural parts. Engineers knew that if used correctly, the wing would twist less.

After modifying the aircraft for the tests, flights took place at NASA’s Dryden Flight Research Center at Edwards Air Force Base in California. When being interviewed in May 2002, Via Boeing Frontiers, commander of the Air Force Research Laboratory, Paul Nielsen said:

“The program takes us back to the future.” This reference noted earlier attempts by the Wright Brothers and other aviation pioneers in wing twisting. Nielsen added: “The team will attempt to harness wing aeroelastic flexibility in a high-performance aircraft in a new and beneficial way.”

Before the test flight, Boeing sent the F/A-18 to its Phantom Works facility in St. Louis, where it used composite material and lightweight aluminum to modify the Hornet’s wings. The modifications would allow the plane’s wing’s to twist up to five degrees. The project aimed to demonstrate roll control by using aerodynamically induced wing twists on a fighter jet. It was also a test to see how new composite materials could be used in aircraft manufacturing.

Engineers saw many benefits in having a flexible wing
Engineers at NASA thought that building a plane that could flex and bend its wings would create an aircraft that could change shape for maximum efficiency. They concluded that the benefits would be the following:

• A better performance
• Reduced drag
• Improved fuel efficiency
• The ability to carry heavier payloads
• A weight reduction of up to 25%

When speaking about what the tests could lead to, Boeing’s vice president of Engineering and Information Technology, Pam Drew said:

“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.” simpleflying.com