Fin (aeronautics)

An aircraft stabilizer is an aerodynamic surface, typically including one or more movable control surfaces, that provides longitudinal (pitch) and/or directional (yaw) stability and control. A stabilizer can feature a fixed or adjustable structure on which any movable control surfaces are hinged, or it can itself be a fully movable surface such as a stabilator. Depending on the context, "stabilizer" may sometimes describe only the front part of the overall surface.

In the conventional aircraft configuration, separate vertical (fin) and horizontal (tailplane) stabilizers form an empennage positioned at the tail of the aircraft. Other arrangements of the empennage, such as the V-tail configuration, feature stabilizers which contribute to a combination of longitudinal and directional stabilization and control.

Longitudinal stability and control may be obtained with other wing configurations, including canard, tandem wing and tailless aircraft.

Some types of aircraft are stabilized with electronic flight control; in this case, fixed and movable surfaces located anywhere along the aircraft may serve as active motion dampers or stabilizers.

A longitudinal stabilizer is used to maintain the aircraft in longitudinal balance, or trim: it exerts a vertical force at a distance so that the summation of pitch moments about the center of gravity is zero. The vertical force exerted by the stabilizer to this effect varies with flight conditions, in particular according to the aircraft lift coefficient and wing flaps deflection which both affect the position of the center of lift, and with the position of the aircraft center of gravity (which changes with aircraft loading). Transonic flight makes special demands on horizontal stabilizers, since the crossing of the sound barrier is associated with a sudden move aft of the center of lift.

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