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NASA has kicked off a flight test campaign to evaluate wing surfaces that can change shape in-flight. The Adaptive Compliant Trailing Edge (ACTE) joint effort between NASA and the US Air Force Research Laboratory (AFRL) hopes to bring a step closer the day when rigid control surfaces can be replaced by smoothly morphing surfaces, which would more closely mimic bird flight and promise to make future airliners quieter and more fuel efficient.
Researchers at the Armstrong Flight Research Center in Edwards, California replaced a Gulfstream III’s (below) conventional aluminium flaps with advanced, shape-changing assemblies that form seamless bendable and twistable surfaces. Flight testing will determine whether flexible trailing-edge wing flaps are a viable approach to improving aerodynamic efficiency and reducing noise generated during take-offs and landings.
The flaps, designed and built by FlexSys of Ann Arbor, Michigan, were locked at a specified setting during the initial ACTE flight, but different flap settings will be employed on subsequent flights to collect a variety of data demonstrating the capability of the flexible wings to withstand a real flight environment
DARPA began a three-phase program in January 2003 to design, build and control active, variable-geometry wing structures that can change substantially in flight....
Research has been ongoing for at least a decade into shape-changing designs, at the Air Force Research Laboratory (Wright-Patterson Air Force Base, Ohio), the Defense Advanced Research Projects Agency (DARPA, Arlington, Va.) and at military contractors Lockheed Martin (Palmdale, Calif.), Northrop Grumman (Los Angeles, Calif.), NextGen Aeronautics (Torrance, Calif.), Raytheon (Waltham, Mass.), Vought Aircraft Industries (Dallas, Texas) and at Cornerstone Research Group.
One promising material for flexible skins is reinforced shape memory polymer (SMP). SMPs consist of "multiphase" thermoset polymer networks that can be elongated up to 200 percent into a new shape when subjected to heat. If restrained while cooling, it retains the elongated shape. When reheated above a specific, tailorable “trigger temperature,” the material relaxes to its original shape, due to the elastic energy stored during the temporary deformation....
Currently working on DARPA’s MAS project as a partner with Lockheed Martin, CRG has developed a reinforced SMP wing skin that can soften within seconds of heating thanks to small, stretchy electrode heaters embedded within the carbon fiber laminate. The heated, softened skin moves in concert with the underlying substructure joint as it morphs to the desired position and shape. Once cooled in the new, stretched configuration, the polymer “rigidizes” in the new shape. Havens reports that this SMP, used in a wing designed to morph in chord (that is, elongating the distance between leading edge and trailing edge) weighs less than DARPA’s baseline wing design and recent wind tunnel tests have shown that it can deliver 80 percent increased lift. With an SMP-based gel coat, the wing maintains a smooth aerodynamic surface at strains up to 100 percent.