Angle of attack
| Angle of attack ： ウィキペディア英語版
In fluid dynamics, angle of attack (AOA, or (Greek letter alpha)) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is moving. Angle of attack is the angle between the body's reference line and the oncoming flow. This article focuses on the most common application, the angle of attack of a wing or airfoil moving through air.
In aerodynamics, angle of attack specifies the angle between the chord line of the wing of a fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere. Since a wing can have twist, a chord line of the whole wing may not be definable, so an alternate reference line is simply defined. Often, the chord line of the root of the wing is chosen as the reference line. Another choice is to use a horizontal line on the fuselage as the reference line (and also as the longitudinal axis). Some authors〔John S. Denker, ''See How It Flies''. http://www.av8n.com/how/htm/aoa.html#sec-def-aoa〕〔Wolfgang Langewiesche, ''Stick and Rudder: An Explanation of the Art of Flying'', McGraw-Hill Professional, first edition (September 1, 1990), ISBN 0-07-036240-8〕 do not use an arbitrary chord line, but use the zero lift axis instead — zero angle of attack corresponds to zero coefficient of lift.
Some British authors have used the term ''angle of incidence'' instead of ''angle of attack''. However, this can lead to confusion with the term ''riggers' angle of incidence'' meaning the angle between the chord of an aerofoil and some fixed datum in the aeroplane.〔Kermode, A.C. (1972), ''Mechanics of Flight'', Chapter 3 (8th edition), Pitman Publishing Limited, London ISBN 0-273-31623-0〕
==Relation between angle of attack and lift==
The lift coefficient of a fixed-wing aircraft varies with angle of attack. Increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases.
As the angle of attack of a fixed-wing aircraft increases, separation of the airflow from the upper surface of the wing becomes more pronounced, leading to a reduction in the rate of increase of the lift coefficient. The figure shows a typical curve for a cambered straight wing. A symmetrical wing has zero lift at 0 degrees angle of attack. The lift curve is also influenced by the wing shape, including its airfoil section and wing planform. A swept wing has a lower, flatter curve with a higher critical angle.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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