Wave Drag is a force, or drag, that retards the forward movement of an airplane, in both supersonic and Transonic Flight, as a consequence of the formation of shock waves.
Wave drag is caused by the formation of shock waves around the aircraft in supersonic flight or around some surfaces of the aircraft whilst in transonic flight. Whilst in cruise, most civil jet aircraft fly in the mach .75 to .85 speed range. Although shock waves are typically associated with supersonic aircraft, they also form on an aircraft traveling at less than the speed of sound on areas of the aircraft, such as the aerofoils, where local airflow is accelerated to sonic speed and then decelerated, once again, back to subsonic speed. The shockwave (and associated wave drag) forms at the point the airflow becomes subsonic. As the aircraft continues to accelerate, the area of the wing experiencing supersonic flow increases, the shockwave moves further back on the wing and becomes larger. Boundary layer separation also increases with the increase in speed and if the speed is allowed to increase beyond the limiting mach number (MMO), severe buffeting, Mach Tuck, or "upset" (loss of control) may occur.
Shock waves radiate a considerable amount of energy, resulting in drag on the aircraft. This wave drag can be reduced by incorporating one or more aerodynamic design features such as wing sweep, ultra thin wings, fuselage shape, anti shock bodies and supercritical aerofoils.