Air flowing over the top of a wing of an airplane travels farther and faster than air flowing under it. As a result, air pressure is lower over the wing, which produces lift. This is the scientific theory, but the proof is in the pudding, which is why U.S. Army Yuma Proving Ground is extensively testing NASA's prototype parafoil for the X-38 aircraft. The unusual shape of the fiberglass X-38, which has no conventional wings, has led to its nickname, the Flying Potato.
Designers say it is truly a gliding phenomenon.
The X-38 glides through the air on wind currents flowing beneath its carefully sculptured, sleek, underbody. The shape is not as efficient in generating lift as the conventional airplane wing, but it provides enough to keep the craft airborne for a return flight to earth from space. Steering will take place by maneuvering a wing-like parachute, or parafoil, suspended above the craft. Gliding reduces the impact of gravity on astronauts. The X-38 skims through the atmosphere, thereby subjecting its crew to only about one and a half times the pull of gravity, as compared with forces six or eight times that of normal gravity felt in a ballistic entry capsule.