Moving Tailplanes

Publisher Summary This chapter describes the concept of moving tailplanes. Tailplanes that are adjustable for trimming purposes are much in favor for transonic and supersonic airplanes, since they obviate the difficulties associated with large changes of tab effectiveness at high Mach numbers. On low-speed airplanes, the only aerodynamic advantage is that the adjustable tail plus elevator may have slightly less profile drag under certain conditions of flight than the fixed tail/elevator/adjustable tab arrangement. On the other hand, the mechanism required to provide adjustment of the tail setting will tend to be heavier than that associated with a tab. High-speed airplanes frequently use all-moving tails, where the angle ηT is directly controlled by the movements of the pilot's control column. If the tailplane is moved via an irreversible power-control system, stick-free stability is no longer of significance, and suitable stick-forces can be arranged by artificial means. The object of such an arrangement is to avoid the difficulties associated with large changes of elevator effectiveness at high Mach numbers.