ABSTRACT
The control surfaces, called ailerons, control the rolling motion of an airplane. When the aileron is displaced downward, the lift over the wing increases and when it is displaced upward, the lift over the wing decreases. In order to maximize the rolling moment, the ailerons on either side of the wing are deflected opposite to each other. But aileron deflection also affects the pitching moment. An aileron deflected downward creates a nose-down aerodynamic pitching moment, which twists the wing in a direction that tends to reduce lift and so the rolling moment. As the elastic stiffness of a wing is independent of flight speed and aerodynamic force varies with U2, there exists a critical speed at which the aileron becomes completely ineffective. This critical speed is called aileron reversal speed. When air speed is above this critical speed, the control is reversed. This means that a downward deflection of an aileron on the starboard wing produces a rolling moment, which moves the starboard wing tip downward instead of upward as intended. Closer to critical speed, aileron control is ineffective.
