aileron(redirected from Alerion)
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a control surface that constitutes a certain fraction of the rear portion of a wing of an airplane or a glider. Ailerons can be deflected upward or downward and are used to control an aircraft with respect to its longitudinal axis. When deflected, an aileron produces a difference in lift between the right and left wings of an aircraft.
Ailerons are usually differential—that is, are deflected through a greater angle upward than downward—in order to reduce yawing moments when banking and to increase the control effectiveness near critical angles of attack. Ailerons provide lateral stability and make it possible to fly along curves—for example, to make a 360° banked turn—without slipping.
Ailerons may be double-slotted or triple-slotted. They may be supplemented by spoliers, trim tabs, or trimmer-flatteners (seeHIGH-LIFT DEVICES). In design, an aileron is similar to a wing.