Busemann's Biplane
Busemann's Biplane is a conceptual airframe
The airframe of an aircraft is its mechanical structure. It is typically considered to include fuselage, wings and undercarriage and exclude the propulsion system...

 design invented by Adolf Busemann
Adolf Busemann
Adolph Busemann was a German aerospace engineer and influential early pioneer in aerodynamics, specialising in supersonic airflows...

 which avoids the formation of N-type shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...

s and thus does not create a sonic boom
Sonic boom
A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion...


It 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 choke
Choked flow
Choked flow is a compressible flow effect. The parameter that becomes "choked" or "limited" is the velocity or the mass flow rate.Choked flow is a fluid dynamic condition associated with the Venturi effect...

 and supersonic flow is maintained between them.

Usually with supersonic flow a positive pressure shock wave is generated at the front and a negative pressure shock wave at the rear. In Busemann's biplane, the high pressure shock wave is created internally and reflects symmetrically between the two plates. This cancels/fills the expansion fan forming at the rear, leaving no external shock waves to propagate to infinity. The flat upper and lower surfaces generate no shock waves because the flow is parallel.

The internal alignment of the shock waves means that Busemann's biplane produces minimum wave drag
Wave drag
In aeronautics, wave drag is a component of the drag on aircraft, blade tips and projectiles moving at transonic and supersonic speeds, due to the presence of shock waves. Wave drag is independent of viscous effects.- Overview :...

. However, the flat external surfaces and internal symmetry also mean that the airfoil does not produce any lift. Hence, no implementation has yet flown, although the concept has been successfully tested in wind tunnels and for ammunition.

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