Flaps
A wing flap is defined as a hinged, pivoted, or sliding airfoil, usually attached near the trailing edge of the wing. The purpose of wing flaps is to change the camber of the wing and in some cases to increase the area of the wing, thus permitting the aircraft to operate at lower flight speeds for landing and take off. The flaps effectively increase the lift of the wings and in some cases, greatly increase the drag, particularly when fully extended. The plain flap, in effect, acts as if the trailing edge of the wing were deflected downward to change the camber of the wing, thus increasing both lift and drag. If the flap is moved downward sufficiently, it becomes an effective air brake. The plain may be hinged to the wing at the lower side, or it may have the hinged line midway between the lower and upper surfaces.
The split flap when retracted, forms the lower surface of the wing trailing edge. When extended, the flap moves downward and provides an effect similar to that of the plain flap. Plain flaps and split flaps may be attached to a wing with three or more separate hinges, or they may be attached at the lower surface with a continuous piano hinge.
Power Flap
The Power flap and others with similar operation are designed to increase substantially the wing area as the flap extended. When retracted, the flap forms the trailing edge of the wing. As this type of flap is when extended, it moved rearwards, often by means of a worm gear, and is supported in the correct position by means of curved tracks. The effect of the power flap, when extended, is to greatly reduce the stalling speed of the aircraft by the increase in wing area and change the wing cambers.
A multi element flap, such as the triple slotted flap employed on the Boeing 727 airplane, is a further development of the Power flap principle. the three elements of this flap are the force, mid and the aft flap. This design provides a maximum increase in wing area, thus enabling the airplane to land at a much lower speed than would otherwise be possible. The lift of the wing is increased because of the change in camber and the
greater wing area.