Airfoil

An airfoil (in American English, or aerofoil in British English) is the shape of a wing or blade (of a propeller or ship's screw or sail) as seen in cross-section. It is used to provide lift or downforce, depending on its application. Subsonic-flight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, and often with camber.

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To understand lift itself, see lift. As well as the wing, an aircraft's horizontal and vertical stabilizers are airfoils as well. Airfoils are also found in propellors, fans, compressors and turbines. Sails are also airfoils, and the underwater fins of sailboats, such as centerboards, are also lifting foils and operate on the same principles as airfoils (technically they should called hydrofoils, but this term has already been taken; generally they are just referred to as "foils"). Bird wings also have airfoil shapes.

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An inverted airfoil will create a downward pressure on an automobile or other motor vehicle, improving its traction and keeping it on the ground. The term "lift" can mean a force generated in any direction in any medium. Any thin object with a positive angle of attack, such as a flat plate or the deck of a bridge, will generate lift. Airfoils though are more efficient, generating lift with the least drag. A lift and drag curve obtained in wind tunnel testing is show on the right.

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Airfoil design is a major facet of aerodynamics. Various airfoils serve different flight regimes. A supercritical airfoil, with its low camber, reduces transonic drag divergence, while a symmetric airfoil may better suit frequent inverted flight. Supersonic airfoils are much more angular in shape and can have a very sharp leading edge.

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While sharper leading edged airfoils produce stiffer and lighter wings, large rounder edges increase wing volume for fuel. Moveable high-lift devices, flaps and slats are fitted to airfoils on most aircraft. New airfoil design techniques continue to develop.

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Various systems have been devised to describe and characterise airfoils — the most common and prevalent is the NACA system. Before this, various ad-hoc systems were used. An example of a general purpose airfoil that finds wide application, and predates the NACA system is the Clark-Y.

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American English: American English (AmE) is the form of the English language used mostly in the United States of America. It is the primary language used in the United States. As of 2005, more than two-thirds of native speakers of English use various forms of American English. American English is also sometimes calle...

British English: British English (BrE) is a term used loosely to refer to the form of the English language written in the British Isles, and more narrowly as spoken in the south of England (extending elsewhere with varying degrees). For historical reasons dating back to the rise of London in the 9th century, the var...

Wing: In computing, WinG (pronounced Win Gee) was an API to provide fast graphics performance on Windows 3.1. It was later built-in to Windows 95. In Win32, the equivalent of WinG functionality is provided via API calls such as CreateDIBSection(), SetDIBColorTable(), BitBlt(), and StretchBlt()....