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210:, in order to obtain upward lift on the wings, in reaction the air passing over them must be deflected downwards. At supersonic speeds this creates at least one shock wave and possibly more. Like any other airfoil, the Busemann biplane can be given a small positive angle of attack to generate lift in this way, however it will also now generate external shockwaves.
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The problems of off-design choking and hysteresis can be resolved by the use of variable-geometry devices, such as flaps and slats which may also serve as high-lift devices during takeoff and landing. Another approach is to modify the airfoil geometry to provide acceptable performance over a range of
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Wave drag has two causes, one due to the bulk or form of the plane and the other due to the lift generated. The
Busemann concept can eliminate form shock drag but not that due to lift. Busemann's original geometry eliminated all wave drag and hence also lift. Modern Busemann type designs can create
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destroys the constructive interference and results in shock choking and flow hysteresis effects, which greatly increase drag. In shock choking, the shockwaves reduce their backwards angle with each reflection off the tapered wing surfaces until they form a shock wall across the gap. This causes a
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lift, with its associated shockwave, while still eliminating much or all of the form drag, thus achieving considerable improvements in efficiency over conventional designs. They can also allow adequate performance over a range of speeds and angles of attack.
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Supersonic flow around a conventional wing generates compressive sonic shock waves at the leading and trailing edges, with an expansion wave in between them. These shock waves correspond to pressure changes which impede airflow, known as
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Busemann's original biplane consists of two triangular cross-section plates a certain distance apart, with the flat sides parallel to the fluid flow. The spacing between the plates is sufficiently large that the flow does not
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buildup of pressure and slowdown of flow speed, so that flow hysteresis occurs, in which the slowing of the air causes the choking to persist through and beyond the design point before it clears at a higher aircraft speed.
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either. A Busemann biplane concept, which provides adequate lift, and which can reduce the wave intensity and drag but not eliminate them, has been studied for a "boomless" supersonic transport.
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used a mixed compression inlet, a configuration sensitive to unstarts, ie shock expulsion giving an external bow shock-wave.
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The
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The
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boats with reduced wave-making resistance due to their so-called split hull configuration.
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off-design conditions, at the expense of some form drag even at the optimum design point.
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The internal alignment of the shock waves means that
Busemann's biplane produces minimum
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334:"Avoiding Choked Flow and Flow Hysteresis of Busemann Biplane by Stagger Approach"
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Busemann, A. (1935). "Aerodynamic Lift at
Supersonic Speeds",
272:(2006) "Busemann's Biplane", Tohoku University web site.
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Busemann's original biplane operating at its design point
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170:and supersonic flow is maintained between them.
193:Operation away from the design cruise speed or
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404:Busemann's Biplane - Explanation and Theory
305:Kusunose, Matsushima and Maruyama. (2011).
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360:, Vol.49, No.3. May–June 2012. pp.802 ff.
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307:"Supersonic biplane — A review"
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352:Wu, Jameson and Wang. (2012).
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134:configuration invented by
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189:Off-design conditions
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434:Aircraft wing design
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