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engineers will now have more freedom in designing more efficient,
thinner, higher aspect-ratio wings for future high-performance air-
craft while reducing the structural weight of the wings by 10 to 20
percent.”
Research teams working on DARPA's Morphing Aircraft Struc-
tures project are even more ambitious. Cornerstone Research Group,
Inc. (CRG) and Lockheed Martin are testing a wing capable of with-
standing changes of up to twice the length. The wing's skin is made of
a shape-memory polymer designed by CRG scientists and engineers.
When heated by flexible wires hidden in the structure, the material soft-
ens in a few seconds and morphs into a new shape. As it cools, the poly-
mer sets, keeping its shape until another change is needed.
FlexSys, Inc., funded by a U.S. Air Force program called Small Busi-
ness Innovation Research, has made and tested a wing with a trailing
edge that can flex up and down as much as 10 degrees. The adaptive sys-
tem consists of aluminum and composites—standard aeronautic mate-
rials—driven by actuators. Flight tests began in 2006, using an airplane
called the White Knight, which was built by Scaled Composites, Inc.
(White Knight is the airplane from which SpaceShipOne launched in
2004—SpaceShipOne was the first private vehicle in space.) The wing is
not actually used for lift at this early testing stage; instead, a small ver-
sion of the wing, measuring 30×50 inches (75×125 cm), is attached to
White Knight's underside. FlexSys researchers are studying the wing's
behavior as indicated by gauges and sensors connected to the surface.
Further testing will be needed to determine if a full-scale version can lift
and control an airplane in flight.
A number of important issues remain unresolved. Drastic changes
during flight raise a number of problems. Highly adaptable structures
such as morphing wings may be perfectly stable and controllable while
set in one shape or another, but the transition between shapes might
cause trouble in flight. As an analogy, imagine two people in a narrow
canoe. The craft is stable in the water as long as one person stays in the
front and one person in the rear. But there is a problem if they want to
switch seats—while passing each other in the middle, the boat is liable
to tip over. For an airplane in flight, instability during a transition can
have consequences a lot more tragic than getting wet.
But flight stability with morphing wings is possible—consider the
peregrine falcon. Swifts are another kind of acrobat flier. Researchers
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