aileron

An aileron is a hinged control surface mounted on the trailing edge of an aircraft wing, used to control roll about the aircraft's longitudinal axis. In conventional configurations, a pair of ailerons on opposite wings move in opposite directions; when one aileron deflects downward and the other upward, the resulting change in lift between the wings creates a rolling moment that tilts the aircraft.

The effect depends on speed, wing design, and control system. Deflecting an aileron downward on one wing typically increases that wing's lift, while the opposite wing's aileron reduces lift, producing roll toward the wing with less lift. The roll rate is influenced by factors such as wing camber, wing twist (washout), and airspeed. To reduce adverse yaw, many aircraft employ differential ailerons (more deflection in one direction on one wing than the other) or combine aileron deflection with rudder input; some designs use spoilers or flap-ailerons.

Ailerons are usually located near the wingtips on the trailing edge, though some designs place them closer to the wing roots or integrate them with flaps (flaperons) or with elevons on tailless aircraft. They are actuated by mechanical linkages, hydraulics, pneumatics, or fly-by-wire electronic systems, and may include trim tabs or servo tabs to ease pilot workload.

Historically, ailerons were developed in the early 20th century and became standard on most fixed-wing aircraft. They are the primary means of roll control, supplementing the rudder for coordinated turns and aerobatic maneuvers.