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Ailerons are hinged flaps attached to the trailing edge of an airplane wing, usually near the wingtips. They are used to control the aircraft in roll. The two ailerons are interconnected so that one goes down when the other goes up: the downgoing aileron increases the lift on its wing while the upgoing aileron reduces the lift on the other wing, producing a rolling moment about the aircraft's longitudinal axis.

An unwanted side-effect of aileron operation is a yawing moment, caused by the downgoing aileron producing more drag than the upgoing aileron. One way of minimising this is to arrange for the upgoing aileron to move further than the downgoing aileron, to try to balance out the drag forces generated.

Modern airliners tend to have a second set of inboard ailerons much closer to the fuselage, which are used at high speeds. Some aircraft use spoilers to achieve the same effect as ailerons.