A trim system is provided in the flight controls to lessen the need for constant effort on the part of the pilot to maintain the desired heading and altitude. The trim system stabilizes the aircraft during flight.

The aileron trim control system is shown in figure 9-42. The illustration represents a trim tab arrangement similar to that found on aircraft equipped with conventional aileron systems.

Operation of the lateral and longitudinal trim systems is usually controlled by a five-position, four-throw, momentary ON contact switch with a center OFF position. The switch is found on the control stick grip. This switch electrically energizes the trim control motor, which operates the trim control actuator to reposition the load-feel bungee and achieve hydraulic-powered actuation of the ailerons. At the same time, the actuator operates the cable drum mechanism. The cable drum mechanism operates the jack screw mechanism to reposition the follow-up trim tab to aerodynamically maintain the aileron surface in a position corresponding to that achieved by the hydraulic actuation.

The tab movement does not control the lateral trim of the aircraft while normal powered flight is maintained. This is accomplished by the hydraulic-powered displacement of the ailerons. When the manual flight control system is used, the follow-up trim tab position introduced during powered operation becomes effective and maintains the same trim as that provided by the powered operation. With the power system disconnected, further hydraulic trim control ends, and all future trim inputs are achieved through aerodynamic effect. This function depends upon selective follow-up tab position. Engaging the AFCS controls the trim actuator by electrical inputs.

Aircraft without trim tabs achieve lateral trim by repositioning the lateral control surfaces as necessary to achieve a balanced lateral flight condition. The trim actuator, located in the aileron trim and mixing linkage, normally acts as a series-connected, fixed-length rod in the aileron control system. The trim control switch on the stick grip controls the actuator length. Shortening or retracting the trim actuator (trim button to the right) supplies a left wing up input into the aileron control system linkage. Extending the actuator supplies a left wing down input. The trim actuator changes the neutral position of the aileron mechanism, allowing the control surfaces to deflect and trim the aircraft without moving the control stick.