The Defense Advanced Research Projects Agency is investigating ways that new materials could be used to create an aircraft able to change shape in flight. This would provide benefits in low-observability and performance. The fixed shape of an aircraft determines what mission it is best suited for and how it will perform. A shape good for speed may be bad for range; a shape harder to spot on radar may cost performance or weapons load. The only workable design-change aircraft to date have been the "swing wing" designs such as the F-111, B-1, and F-14, but these designs have a major problem (the weight of the wing-change gear box is considerable) and they have only a couple of options on their shape. What DARPA wants as a first step is an unmanned recon aircraft with a wing span under 40 feet that can fly at high subsonic speed. They want this aircraft to be capable of a 200 percent change in aspect ratio, a 50 percent change in wing area, and a 20-degree change in wing sweep. Most of the change will be in the wings, but other structures could change in more advanced versions. The engine inlets could be reconfigured for different speeds and altitudes, and the fuselage might even contract as fuel is burned. Another fascinating concept is the "virtual rudder", which could be extended when the aircraft needs to maneuver and retracted when cruising in straight and level flight. Control surfaces are major problems for a stealthy aircraft as they cause more reflection than a smooth surface. The B-2 uses split flaps to turn, and when they are deployed the aircraft is much easier to spot on radar. Making radical maneuvers in an attack run actually make the B-2 vulnerable to enemy air defenses.--Stephen V Cole