aerodynamic center

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aerodynamic center

[‚e·ro·dī′nam·ik ′sent·ər]
(aerospace engineering)
A point on a cross section of a wing or rotor blade through which the forces of drag and lift are acting and about which the pitching moment coefficient is practically constant.

aerodynamic center (AC)

aerodynamic center (AC)click for a larger image
Moment about the aerodynamic center is constant with angle of attack. Aerodynamic center does not move with angle of attack.
The aerodynamic center is a point on the wing chord that results in a constant moment when the wing angle of attack is changed. An AC lies approximately at the quarter-chord position at subsonic speeds and at approximately the half-chord position at supersonic speeds.
References in periodicals archive ?
For a gust element we have:--the element aerodynamic centre, R--the distance from F to the Darrieus rotor axis, [theta]--the angle between the Ox axis and the R radius, z--the F height and [delta]--the angle of the normal element in F to the blade element and the horizontal Oxy plane (for cylindrical rotors [delta] = 0 ).
The spoiler also doubles as an airbrake: when the driver brakes heavily, it rises to an angle of 65 degrees, not only ensuring increased aerodynamic drag but also shifting the aerodynamic centre further towards the rear aiding stability.