Supercritical airfoil

A supercritical aerofoil (supercritical airfoil in American English) is an airfoil designed primarily to delay the onset of wave drag in the transonic speed range.

Supercritical airfoils are characterized by their flattened upper surface, highly cambered ("downward-curved") aft section, and larger leading-edge radius compared with NACA 6-series laminar airfoil shapes.^[1] Standard wing shapes are designed to create lower pressure over the top of the wing. Both the thickness distribution and the camber of the wing determine how much the air accelerates around the wing. As the speed of the aircraft approaches the speed of sound, the air accelerating around the wing reaches Mach 1 and shockwaves begin to form. The formation of these shockwaves causes wave drag. Supercritical airfoils are designed to minimize this effect by flattening the upper surface of the wing.

The origins of the supercritical airfoil can be traced back to the German aerodynamicist K. A. Kawalki, who designed a number of airfoils during the Second World War. Following the end of the conflict, multiple nations continued research into the field, including Germany, the United Kingdom, and the United States. In particular, Hawker Siddeley Aviation designed a number of advanced airfoils that were, amongst other programmes, incorporated into the Airbus A300. In America, the aerodynamicist Richard Whitcomb produced supercritical airfoils similar to Kawalki's earlier work; these were used to devise a supercritical wing that was, in turn, incorporated into both civil and military aircraft. Accordingly, techniques learned from studies of the original supercritical airfoil sections have been used to design airfoils for several high-speed subsonic and transonic aircraft, from the Airbus A310 and Boeing 777 airliners to the McDonnell Douglas AV-8B Harrier II jumpjet.