LOS ANGELES – NASA plans to dynamically test flexible wing technology on a modified Gulfstream III later this year after successfully completing initial trials of a morphing flap at the agency’s Armstrong Flight Research Center in California.

Under the Adaptive Compliant Trailing Edge (ACTE) program, NASA and the U.S. Air Force Research Laboratory (AFRL), along with morphing flap developer FlexSys, completed 22 test flights of an agency-owned Gulfstream fitted with flexible trailing edges. Flights began in November with flaps set at zero deg. and culminated six months later with the flaps set at the maximum angle of 30 deg. Tests were also conducted with flaps set at -2 deg.

The tests were aimed at proving the airworthiness of the flexible structure and its ability to withstand high dynamic pressures and aerodynamic loads up to 11,500 lb. per flap segment at high deflection angles. The 19-ft. long ACTE test section on each wing replaced the existing Gulfstream flap as well as the ground spoiler and flight spoiler/speedbrake and, although designed to morph throughout the entire range of motion, each test was conducted at a single fixed setting.

The morphing surface, which is joined to the wing with flexible transition surfaces, was tested as part of NASA’s broader Environmentally Responsible Aviation initiative and has the potential to cut cruise drag by around 3% on retrofitted aircraft or up to 12% on all-new designs. The concept also offers weight savings and lower noise over conventional flap configurations.

The shape-morphing mechanism exploits the inherent elasticity of the composite material from which it is made and contains no moving parts. By using evenly distributed devices rather than flexural hinges, the morphing flap requires less power to actuate than conventional flaps. As actuation devices are contained within the structure, the flap forms a continuous bendable surface. It therefore forms a seamless transition region with the wing, eliminating a major source of airframe noise generation.

The morphing flap would provide larger system-level weight benefits for all-new designs rather than retrofits because it could be used to twist the wing span-wise to reduce loading as well as reduce wing-bending moment.

NASA is planning a follow-on flight test program starting in the third quarter of this year that will evaluate moving the flaps in flight. This will require refitting flap actuators that were removed for the initial tests. Should further research be initiated beyond the currently envisioned program into tests of moving flaps on an all-new wing, however, the actuation requirements will be higher, as such a design would also incorporate a span-wise twist for gust load alleviation.