is widely used in hang gliders, powered hang gliders, and ultralight aircraft. Flight with disabled controls has been successful in a small number of aviation incidents. Reaction control valves as used in the Harrier family of military aircraft. Top rudder: this device was fitted to the British Army Aeroplane No 1. It comprised an all-flying fin mounted above the upper wing and pivoted about a vertical axis. In operation it applied a side force approximately above the centre of pressure, causing the craft to roll. The design also had all-flying ailerons between the wing planes, but these were removed at the time it made the first official flight of a British aircraft and roll control during the flight was achieved solely by use of the top rudder. Combinations with other control surfaces A 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. When a flaperon is actuated downward (i.e., used as a flap), there is enough freedom of movement left to be able to still use the aileron function. Some aircraft have used differentially controlled spoilers or spoilerons to provide roll instead of conventional ailerons. The advantage is that the entire trailing edge of the wing may be devoted to flaps, providing better low speed control. The Northrop P-61 Black Widow used spoilers in this manner, in conjunction with full span zap flaps and some modern airliners use spoilers to assist the ailerons. On delta-winged aircraft, the ailerons are combined with the elevators to form an elevon. Several modern fighter aircraft may have no ailerons on their wings but provide roll control with an all moving horizontal tailplane. When horizontal tailplane stabilators can move differentially to perform the roll control function of ailerons, as they do on some modern fighter aircraft, they are termed 'tailerons' or 'rolling tails'. Tailerons additionally permit wider flaps on the aircraft's wings. Aileron struts combined movable surfaces with an airfoil shaped wing strut. Acting in the propeller slipstream increased their effectiveness, although their mechanical advantage is lowered due to the inboard location. See also Aircraft flight control system Elevator (aeronautics) Flap Flaperon, a control surface combining both a flap and an aileron Spoiler, a flight control surface occasionally confused with ailerons