How Do They Defy Gravity?

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By Sharon Begley

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To maximize lift, jumpers can arch their backs to turn themselves into airplane wings. The greater the curvature, the greater the difference in pressure at the belly and the back, and the greater the lift. The same principle explains why airplanes stay aloft. "If you hit it right you feel a big suction into the air," says engineer Mike Holden of Calspan, Inc., an aerospace company that lent its wind tunnel to the ski team. In fact, ski suits that are pervious in front, but airtight behind, round the back so much that the skiers are practically sucked into the stratosphere.

To maximize horizontal speed, jumpers lift out of the back of their bindings on takeoff. They lean forward so that their bodies are almost parallel to their skis. That minimizes the size of their frontal area and therefore air resistance, or drag, enabling them to sustain much of their initial takeoff speed.

The position of the skis during a jump is controversial. Some jumpers swear by the V position, which is thought to simulate a delta wing, in which swirling air coming off the wing increases lift. Others believe in offsetting the skis relative to the body to increase the effective "wing area" and increase lift. Holden says he has found little difference between the two positions.

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