Читать книгу Flight Theory and Aerodynamics - Joseph R. Badick - Страница 87

Trim systems are designed to alleviate the pressures on the primary flight controls as experienced by the pilot during aircraft operation. Usually located on the trailing edge of these devices, the pilot (or autopilot) operates the respective trim system in order to position the flight control where minimum pressures are exerted in the system. The two most common trim systems are trim tabs and antiservo tabs.

A trim tab is usually found on the trailing edge of the elevator or rudder, and unlike the antiservo tab, the trim tab moves in the opposite direction to which the primary control moves (Figure 3.10). An antiservo tab is found on the trailing edge of a stabilator, and moves in the same direction as the primary control to which it is attached (Figure 3.11). As previously mentioned, the antiservo tab serves to reduce the sensitivity of the stabilator during pitch to the pilot, as well as reducing control pressure as needed.

Figure 3.10 Trim tabs.

Source: U.S. Department of Transportation Federal Aviation Administration (2008a).

Some smaller aircraft may incorporate a different type of trim tab that does not involve an independent mechanical linkage, this type of trim tab consists only of a metal plate attached to the trailing edge of a primary flight control. When set correctly, this allows the pilot to fly “hands‐off” the flight control while in straight and level flight. Figure 3.12 provides a summary of the many secondary flight controls available, including their location on the aircraft and function.