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Trimmable Horizontal Stabiliser
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The design of the majority of airliners and transport aircraft incorporates a trimmable horizontal stabilizer. Like a stabilator, the trimmable stabilizer features a fully moving horizontal tail surface. However, unlike the stabilator, the trimmable stabilizer does not move in response to control column or control stick movement. Instead, it is fitted with elevators which respond to pilot or autopilot input to control pitch and adjust the aircraft attitude and the entire horizontal tail assembly moves in response to the trim system to stabilize the aircraft in the pitch axis.
The trimmable stabilizer's primary advantage is that it provides tremendous trimming power over the full speed range of the airplane. The system also reduces drag as the stabilizer surface and the elevator are in alignment whenever the aircraft is in trim. The stabilizer trim is normally adjusted to compensate for centre of gravity position prior to takeoff to ensure optimum elevator effectiveness.
In most cases, a trimmable stabilizer is either manually or electrically controlled and hydraulically actuated. In some Fly-By-Wire equipped aircraft, the stabilizer automatically adjusts to a one G loading without the need for pilot action.
- "Do you really understand how your trim works?" - Captain Alex Fisher