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. The Busemann biplane configuration can still be used to minimize the energy of these shock waves and the associated drag. 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 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. 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 off-design conditions, at the expense of some form drag even at the optimum design point. The Busemann biplane concept has been studied as a concept for a "boomless" supersonic transport. See also Pratt & Whitney J58 used a mixed compression inlet, a configuration sensitive to unstarts, ie shock expulsion giving an external bow shock-wave. Catamaran boats with reduced wave-making resistance due to their so-called split hull configuration. References External links Busemann's Biplane - Explanation and Theory Biplanes Aerodynamics Wing configurations Aircraft wing design