![]() wave drag ( aerodynamics) is caused by the presence of shockwaves and first appears at subsonic aircraft speeds when local flow velocities become supersonic.lift-induced drag appears with wings or a lifting body in aviation and with semi-planing or planing hulls for watercraft.For example, the Douglas DC-3 has an equivalent parasite area of 23.7 sq ft and the McDonnell Douglas DC-9, with 30 years of advancement in aircraft design, an area of 20.6 sq ft although it carried five times as many passengers. It is used for comparing the drag of different aircraft. Parasite drag is often expressed in terms of a hypothetical (in so far as there is no edge spillage drag ) "equivalent parasite drag area" which is the area of a flat plate perpendicular to the flow. For aircraft, pressure and friction drag are included in the definition of parasitic drag. A body is known as bluff (or blunt) if the source of drag is dominated by pressure forces and streamlined if the drag is dominated by viscous forces. Also shown is a flat plate illustrating the effect that orientation has on the relative proportions of skin friction and pressure difference between front and back. The effect of streamlining on the relative proportions of skin friction and form drag is shown for two different body sections, an airfoil, which is a streamlined body, and a cylinder, which is a bluff body. ![]()
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