flap (helicopter rotor blade movement). Up-and-down movement of the tip of a helicopter rotor blade.
flaperon (aircraft control). Controls used on some swept wing airplanes that serve as both ailerons and wing flaps. The flaperons on both wings can be lowered together to increase the lift and drag of the wings. This is the flap function. The flaperons can also be moved differentially: one moves up, while the other moves down. This is the aileron function.
flap extended speed. 14 CFR Part 1: “The highest speed permissible with wing flaps in a prescribed extended position.”
flap overload valve. A valve in the flap system of an airplane that prevents the flaps being lowered at an airspeed which could cause structural damage. If the pilot tries to extend the flaps when the airspeed is too high, the opposition caused by the airflow will open the overload valve and return the fluid to the reservoir.
flapper valve. A form of hinged check valve that allows fluid to flow through it in one direction only. Fluid can flow in the direction which forces the valve off its seat, but it cannot flow in the direction which forces the flapper against its seat.
flapping (helicopter rotor blade). The vertical movement of a helicopter rotor blade about its delta, or flapping, hinge.
flapping hinge (helicopter rotor). The hinge with its axis parallel to the rotor plane of rotation.