by W D Adkins

Created on: April 30, 2008   Last Updated: May 05, 2008

The swept back wings of modern jet aircraft give them a graceful appearance that seems to be the physical expression of the great speeds these panes are capable of. This is a happy side effect of a design that is purely functional. The swept wing, in its various forms, makes high-speed subsonic flight more efficient by reducing drag, and is a vital element for any supersonic aircraft as a means of controlling the powerful shock waves supersonic speeds produce.

The origin of swept wing designs goes back to aeronautical engineers in Germany in the 1930s. Prior to World War II, they developed the basic concept and carried out wind tunnel tests. The goal was to solve a problem that was becoming worse as planes got faster. At low speeds, the straight wings of existing aircraft allowed air to flow smoothly over the curved upper surface. As speeds increased, so did turbulence and drag at the trailing edge of the wing. This is analogous to what happens if you pass your hand slowly through water: the water flows smoothly around your hand. If instead you push you're hand through the water fast, swirling turbulence and bubbles form in the wake of your hand's passage.

The swept wing design minimizes turbulence and drag by "tricking" the air into acting as if the aircraft were traveling slower than it is. The result is air flows more smoothly, allowing higher speeds. Because the Germans had done research years ahead of the British and Americans, they were able to produce the first operational jet fighter, the Messerschmitt 262-E, beginning in 1941.

Following the war, engineers faced a new problem. Planes and engines were still getting faster. But as speeds began to approach the speed of sound, they discovered that shock waves formed, particularly at the leading edges of the wings. This produces drag by absorbing energy from the aircraft. Even worse, the shock wave disrupt the slipstream (the layer of smoothing flowing air in actual contact with the aircraft), forcing it away from the aircraft, and away from the control surfaces that depend on interacting with the slipstream to work. It was becoming harder and harder to control an aircraft.

The answer was a combination of features. The wing of a supersonic aircraft is much thinner than that of slower aircraft. This reduces the surface area presented to the air, and so reduces the shock wave. This, in combination with a swept wing, also allows the air to flow over the wing more slowly (since it has less distance to travel), remaining

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