The supercritical airfoil, below, maintains a lower Mach number over its upper surface than the conventional airfoil, above, which induces a weaker shock.

A supercritical airfoil 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 (curved) aft section, and greater leading edge radius as compared to traditional airfoil shapes. The supercritical airfoil was created in the 1960s, by then NASA scientist Richard Whitcomb, and was first tested on the TF-8A Crusader. While the design was initially developed as part of the supersonic transport (SST) project at NASA, it has since been mainly applied to increase the fuel efficiency of many high subsonic aircraft. Research in 1940 by DVL's K. A. Kawalki led to subsonic profiles very similar to the supercritical profiles, which was the basis for the objection in 1984 against the US-patent specification for the supercritical airfoil. ^[1] The supercritical airfoil shape is incorporated into the design of a supercritical wing. For the kite, see foil kite. ... Wave drag is an aerodynamics term that refers to a sudden and very powerful form of drag that appears on aircraft flying at high-subsonic speeds. ... Transonic is an aeronautics term referring to a range of velocities just below and above the speed of sound. ... The Leading Edge is a Speculative fiction magazine founded in 1981, located in Provo, Utah, and which has published stories by Dave Wolverton and Orson Scott Card, among others. ... The 1960s decade refers to the years from the beginning of 1958 to the end of 1974. ... For other uses, see NASA (disambiguation). ... Richard Whitcomb is an aeronautical engineer. ... The F-8 Crusader (originally F8U) was a single-engine aircraft carrier-based fighter aircraft built by Chance-Vought of Dallas, Texas, USA. It replaced the Vought F-7 Cutlass. ... The Concorde supersonic transport has a delta wing, a slender fuselage and four underslung Olympus engines. ... For other uses, see NASA (disambiguation). ...

Research aircraft of the 1950s and 60s found it difficult to break the sound barrier, or even reach Mach 0.9, with conventional airfoils. Supersonic airflow over the upper surface of the traditional airfoil induced excessive wave drag and a form of stability loss called Mach tuck. Due to the airfoil shape used, supercritical wings experience these problems less severely and at much higher speeds, thus allowing the wing to maintain high performance at speeds closer to Mach 1. Techniques learned from studies of the original supercritical airfoil sections are used to design airfoils for high-speed subsonic and transonic aircraft from the Boeing 777 to the McDonnell Douglas AV-8B Harrier II. The 1950s decade refers to the years 1950 to 1959 inclusive. ... The 1960s decade refers to the years from the beginning of 1958 to the end of 1974. ... A United States Navy F/A-18E/F Super Hornet in transonic flight. ... Wave drag is an aerodynamics term that refers to a sudden and very powerful form of drag that appears on aircraft flying at high-subsonic speeds. ... Mach tuck is an aerodynamic effect, whereby the nose of an aircraft tends to pitch downwards as the airflow around the wing reaches speeds close to Mach 1. ... The Boeing 777 is an American long-range wide-body twin-engine airliner built by Boeing Commercial Airplanes. ... DC-10, retired from American Airlines fleet at gate McDonnell Douglas was a major American aerospace manufacturer, producing a number of famous commercial and military aircraft. ... See also Hawker Siddeley Harrier The Harrier II is a second generation, vertical/short takeoff and landing (V/STOL) light_attack jet aircraft used by the United States Marine Corps, Royal Air Force, Spanish Armada and Italian navy. ...

NASA TF-8A in 1973

Supercritical airfoils have four main benefits: they have a higher drag divergence Mach number,^[2] they develop shock waves farther aft than traditional airfoils,^[3] they greatly reduce shock-induced boundary layer separation, and their geometry allows for more efficient wing design (e.g., a thicker wing and/or reduced wing sweep, each of which may allow for a lighter wing). At a particular speed for a given airfoil section, the critical Mach number, flow over the upper surface of an airfoil can become locally supersonic, but slow down to match the pressure at the trailing edge of the lower surface without a shock. However, at a certain higher speed, the drag divergence Mach number, a shock is required to recover enough pressure to match the pressures at the trailing edge. This shock causes transonic wave drag, and induces flow separation behind it; both have negative effects on the airfoil's performance. Shock Waves is a horror movie from 1977 directed by Ken Wiederhorn. ... In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface. ... Critical mach is a aeronautics term that refers to the speed at which some of the airflow on a wing becomes supersonic. ...

Supercritical airfoil Mach Number/pressure coefficient diagram. The sudden increase in pressure coefficient at midchord is due to the shock. (y-axis:Mach number (or pressure coefficient, negative up); x-axis: position along chord, leading edge left)

At a certain point along the airfoil, a shock is generated, which increases the pressure coefficient to the critical value C_p-crit, where the local flow velocity will be Mach 1. The position of this shockwave is determined by the geometry of the airfoil; a supercritical foil is more efficient because the shockwave is minimized and is created as far aft as possible thus reducing drag. Image File history File links Supercrit2. ... Image File history File links Supercrit2. ... An F/A-18 Hornet breaking the sound barrier. ... The pressure coefficient is a dimensionless number used in aerodynamics. ... An object moving through a gas or liquid experiences a force in direction opposite to its motion. ...

In addition to improved transonic performance, a supercritical wing's enlarged leading edge gives it excellent high-lift characteristics. As a result, aircraft utilizing a supercritical wing have superior takeoff and landing performance. This makes the supercritical wing a favorite for designers of cargo transport aircraft. A notable example of one such heavy-lift aircraft that uses a supercritical wing is the C-17 Globemaster III. For the Lockheed aircraft with this designation, see C-17 Super Vega. ...

See also

• Whitcomb area rule
• NACA airfoil

The Whitcomb area rule (sometimes just called the area rule) is a design technique used to reduce an aircrafts drag at transonic speeds, speeds between about Mach 0. ... The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics (NACA). ...

Notes

External links

• Supercritical airfoil at Aerospaceweb
• Supercritical airfoil at century-of-flight