Compression buoyancy

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North American XB-70 in flight with wing tips down

In aerodynamics , compression lift describes a lift force in supersonic flight . The shock wave in the Mach cone is used .

The shock wave occurs when the speed of sound is exceeded ; a specially designed supersonic aircraft can thus fly with a smaller angle of attack and thus with low induced drag .

history

The phenomenon of compression lift was first described by the NACA engineers Clarence A. Syvertson and Alfred J. Eggers in 1956. They examined the deviations from the ballistic curve in re-entry bodies and uncovered the principle behind compression buoyancy.

Comparison with the glide of boats

The compression lift is similar to the planing of boats when a boat in planing conditions , the hull speed approaches to the bow wave slides up and is thus partially lifted out of the water. In aircraft, however, this is more difficult to implement, because the shock wave only develops during supersonic flight, is strongly swept (see Mach's cone ) and its opening angle changes greatly with speed. This makes it difficult to design an aircraft that can gain lift from the shock wave over a wide range of speeds.

Technical implementation

The North American XB-70 was the first to use compression lift on an airplane. The shock wave created by the air intake is guided under the wings. In this way, lift could be increased by 30% without additional air resistance during supersonic flight. On the XB-70, this was additionally supported by the wing tips when they were fully folded down by generating an additional 5% compression lift. The folded-down wing tips increased the directional stability, so that the XB-70 could be used with a smaller rudder than would otherwise have been possible. Only in this way was it possible to achieve the desired low resistance and thus acceptable ranges at Mach 3.

So-called lifting bodies use the same principle to generate buoyancy. Newer maneuverable re-entry vehicles (MARV nuclear warheads) use this effect in part to change direction within the atmosphere in order to make interception more difficult and to increase target accuracy.

The American project of the Rockwell X-30 spacecraft that took off like an airplane was also based on compression lift, which was never developed beyond the concept phase .

The Boeing X-51 demonstration aircraft with ramjet propulsion made use of the compression lift.

Web links

Individual evidence

  1. ↑ Dennis R. Jenkins, Tony R. Landis: Warbird Tech Series Volume 34, North American, XB-70 VALKYRIE. Specialty Press, North Branch, Minnesota, USA 2002, ISBN 1-58007-056-6 , p. 17.
  2. ↑ Dennis R. Jenkins, Tony R. Landis: Warbird Tech Series Volume 34, North American, XB-70 VALKYRIE. Specialty Press, North Branch, Minnesota, USA 2002, ISBN 1-58007-056-6 , p. 76.