Aircraft rudder

The hinged rear portion of an airplane's vertical tail. The vertical tail is composed of the vertical stabilizer and the rudder. The vertical stabilizer is mounted to the fuselage and is fixed relative to it. The rudder is hinged to the rear of the vertical stabilizer (see illustration) and moves to the left or right in response to control inputs from the rudder pedals or from an automatic stability and control system.

Vertical tail of an airplane, showing location of the rudder.

The rudder provides an aerodynamic moment about the aircraft's center of gravity for the purpose of yaw control. When the rudder turns clockwise, for example, as viewed from above, its trailing edge moves to the left, effectively adding camber to the vertical tail. The result is that an aerodynamic side force is produced on the vertical tail to the right. This force, in turn, produces a counterclockwise yawing moment about the airplane's center of gravity, resulting in a turn to the left. See also Airfoil.

An additional, small, movable surface, known as a trim tab, may be hinged to the rudder. When deflected to a fixed position, the tab causes the rudder to deflect to, and hold, a desired angle.