Description
Ailerons are a primaryflight controlsurface which control movement about thelongitudinal axisof an aircraft. This movement is referred to as "roll". The ailerons are attached to the outboard trailing edge of each wing and, when a manual or autopilot control input is made, move in opposite directions from one another. In some large aircraft, two ailerons are mounted on each wing. In this configuration, both ailerons on each wing are active during slow speed flight. However, at higher speed, the outboard aileron is locked and only the inboard or high speed aileron is functional.
B727 Flight Control Surfaces. Source: Wikicommons. Origin: FAA(USA)
Function
Moving the flight deck control wheel or control stick to the right results in the aileron mounted on the right wing to deflect upward while, at the same time, the aileron on the left wing deflects downward. The upward deflection of the right aileron reduces thecamberof the wing resulting in decreasedlifton the right wing. Conversely, the downward deflection of the left aileron results in an increase in camber and a corresponding increase in lift on the left wing. The differential lift between the wings results in the aircraft rolling to the right. On some aircraft, ailerons are augmented byroll spoilersmounted on the upper surface of the wing.
Adverse Yaw
In the functional example above, the increase in camber of the left wing results in an increase in lift but this, in turn, also causes an increase indrag. This added drag causes the wing to slow down slightly resulting in rotation, referred to as yaw,around the vertical axis. To overcome this yaw and thereby maintaincoordinated flight,rudderinput is required while entering and exiting a turn. To minimise the amount of adverse yaw produced during a turn, engineers have developed various aerodynamic and mechanical solutions includingdifferential aileronsandcoupled ailerons and rudder.
