Aileron
Ailerons are hinged control surfaces attached to the trailing edge of the
wing of a
fixed-wing aircraft. 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. The word
aileron is French for "little wing."
An unwanted side-effect of aileron operation is
adverse yaw â€" a
yawing moment in the opposite direction to the turn generated by the ailerons. In other words, using the ailerons to roll an aircraft to the right would produce a yawing motion to the left. It is caused by an increase in
induced drag due to the greater effective
camber of the wing with a downward-deflected aileron, and the opposite effect on the other wing. Modern aileron systems have minimal adverse yaw, such that it is barely noticeable in most turns. This may be accomplished by the use of
differential ailerons, which have been rigged such that the downgoing aileron deflects less than the upward-moving one.
Frise ailerons achieve the same effect by protruding beneath the wing of an upward deflected aileron, increasing drag on that side. Ailerons may also use a combination of these methods. Adverse yaw is also caused by the wing on the outside of the turn traveling faster than the inside wing and thus having more lift and drag. Once the desired angle of bank (degree of rotation on the longitudinal axis) is obtained, the pilot uses opposite aileron to prevent the aircraft from continuing to roll due to this increased lift. This minor opposite use of the control must be maintained throughout the turn. The pilot also uses a slight amount of
rudder in the same direction as the turn to counteract adverse yaw and to produce a "coordinated" turn where the
fuselage is parallel to the flight path. A simple gauge on the instrument panel called the
turn coordinator, also known as "the ball", indicates when this coordination is achieved.
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Ailerons are the trailing-edge control surface nearest the wing tip (although on some airliners they can also be found at the wing root). On this parked Piper Cherokee the aileron has deflected downwards. |
Modern airliners tend to have a second set of inboard ailerons much closer to the fuselage, which are used at high speeds. If the wings are also in a V shape and the aircraft enters a
stall, the ailerons on the inside will still be able to function as the stall will proceed from the tips of the wings to the body. In plane wings, the stall develops the other way so the ailerons are placed towards the tips of the wings. Large jet aircraft often have ailerons towards the tips of the wings to increase the moment of the aircraft so less force is required to pitch the aircraft. Some aircraft use
spoilers to achieve the same effect as ailerons.
Although the device first appeared on a monoplane, built by New Zealand inventor
Richard Pearse in 1902, the first aircraft that flew using a aileron was
14 Bis by
Santos Dumont.
It was later developed independently by the
Aerial Experiment Association, headed by
Alexander Graham Bell, and by
Robert Esnault-Pelterie, a
French aircraft builder. Ailerons superseded the earlier
wing warping technique, developed by the
Wright Brothers.
Another control surface that combines an
aileron and
flap is called a
flaperon. A single surface on each wing serves both purposes: used as an aileron, the flaperons left and right are actuated differentially; when used as a flap, both flaperons are actuated downwards. As an example of an aircraft using flaperons, see this
RJ.03 IBIS experimental aircraft. Please note that when a flaperon is actuated downwards (i.e. used as a flap) there is enough freedom of movement left to be able to still use the aileron function.
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Flight controls*
NASA Glenn Research Center aileron article with Java demo and more pictures
