downwash from the wing when the flaps were deployed, necessitating a small "SMURF" surface fixed to the fuselage, such that it aligned with the stabilizer leading-edge root at the critical angle. Active stability Using a computer to control the elevator allows aerodynamically unstable aircraft to be flown in the same manner. Aircraft such as the F-16 are flown with artificial stability. The advantage of this is a significant reduction in drag caused by the tailplane, and improved maneuverability. Mach tuck At transonic speeds, an aircraft can experience a shift rearwards in the center of pressure due to the buildup and movement of shockwaves. This causes a nose-down pitching moment called Mach tuck. Significant trim force may be needed to maintain equilibrium, and this is most often provided using the whole tailplane in the form of an all-flying tailplane or stabilator. Control A tailplane usually has some means allowing the pilot to control the amount of lift produced by the tailplane. This in turn causes a nose-up or nose-down pitching moment on the aircraft, which is used to control the aircraft in pitch. Elevator: A conventional tailplane normally has a hinged aft surface called an elevator, Stabilator or all-moving tail: In transonic flight shock waves generated by the front of the tailplane render any elevator unusable. An all-moving tail was developed by the British for the Miles M.52, but first saw actual transonic flight on the Bell X-1; Bell Aircraft Corporation had included an elevator trim device that could alter the angle of attack of the entire tailplane. This saved the program from a costly and time-consuming rebuild of the aircraft. Transonic and supersonic aircraft now have all-moving tailplanes to counteract Mach tuck and maintain maneuverability when flying faster than the critical Mach number. Normally called a stabilator, this configuration is often referred to as an "all-moving" or "all-flying" tailplane. See also Aircraft flight control system Flight control surfaces Stabilizer (aeronautics) T-tail Trim tab References Aircraft controls