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Trim tabs are small, secondary flight control surfaces that are attached to the trailing edge of a larger, primary control surface such as an elevator or rudder. The trim tab is used to "trim", or counteract the aerodynamic force on, the control surface and thus stabilise the aircraft in the axis of rotation associated with the primary control. Trim tabs can be either flight adjustable or fixed.
By adjusting the angle of the trim tab relative to the larger control surface, the neutral position of the control surface is changed. This occurs because the distance from the control surface hinge at which the trim tab is mounted provides sufficient moment or force to move the larger surface.
Fixed trim tabs are most often encountered on the rudder or aileron of a light, single engine aircraft. A fixed tab is ground adjusted (bent) to the desired position to overcome any unwanted roll or yaw tendencies of the aircraft. Adjustable trim is virtually always installed to adjust control loading associated with the pitch axis and may also be used to trim for yaw or roll. The position of an adjustable trim tab can be changed in flight, using cockpit controls, to counter any variation in control loading resulting from changes in airspeed, centre of gravity, aircraft configuration or due to an engine failure. Trim tabs can be manually or electrically controlled (or both), depending upon the aircraft installation.
- "Do you really understand how your trim works?" - Captain Alex Fisher