2.4. Trim.

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2.4.1. There are many factors in various conditions of flight that affect the forces felt in the controls. Trim is needed to compensate for these control stick forces to prevent fatigue, increase smoothness, and enable multitasking. When properly trimmed, an aircraft can and should be flown with just the fingertips on the control stick to allow slight out-of-trim conditions to be easily felt.

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2.4.2. Trim tabs are small movable surfaces attached to the primary flight control surfaces (rudder and elevator) that act as levers to equalize pressure exerted on either side of the parent control surface. To equalize pressure, the rudder and elevator tabs move in opposite direction from the parent control (Figure 2.2.). The amount of trim tab displacement determines the magnitude of the parent surface deflection. When trimming the ailerons the entire control surface is moved to equalize the pressure.

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2.4.2.1. Trimming is a continuous process. When pressure on the controls is relieved and aircraft attitude is maintained, the aircraft is correctly trimmed. In the T-6, subtle power changes normally do not require large, immediate changes in control pressure. The need for trim, is gradually evident as airspeed, power, and pitch change.

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2.4.2.2. Without proper rudder trim, the aircraft flies in a slip or a skid as indicated by the turn and slip indicator (the ball is deflected while the needle is centered). The longitudinal axis of the aircraft is not aligned with the direction the aircraft is traveling. In effect, the aircraft is flying sideways through the air (proportional to the deflection of the ball). To correct this, first apply rudder to center the ball (while holding the turn needle centered) and then relieve pressure using rudder trim in the direction of the ball/foot pressure.

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2.4.2.3. To correct either forward or aft control stick pressure or to maintain a stabilized attitude, use elevator trim in the direction needed to push or pull on the control stick.

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2.4.2.4. To correct wing heaviness or rolling tendencies, adjust aileron trim opposite the direction of the “heavy” wing. Unlike the elevator and rudder, aileron trim inputs physically reposition the ailerons. Aileron trim tabs are preset by maintenance personnel and do not adjust in flight.”

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2.4.2.5. Trim in the following order: rudder, elevator, and aileron.

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2.4.2.6. The trim aid device (TAD) assists rudder trim to help maintain coordinated flight during power and airspeed changes. Using engine torque, altitude, airspeed, and pitch rate, the TAD computes a desired rudder trim tab position and applies it to the rudder trim tab actuator. During large transitions of the four parameters, the TAD will lag the desired trim position requiring pilot input to ensure coordinated flight. The TAD will not completely trim the aircraft in yaw.

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2.4.2.7. A properly trimmed aircraft is trimmed for a specific airspeed and power setting. It flies at the trimmed airspeed hands off with little or no force applied to the control stick or rudder pedals. Changes to airspeed require additional trim input potentially in all three axes but predominantly in elevator and rudder (pitch and yaw) trim. For example, if the PCL is retarded to slow from 200 to 120 KIAS in level flight, the nose of the aircraft drops to seek 200 KIAS. Back stick pressure is required to maintain level flight until nose-up trim relieves the back stick pressure and left rudder may be necessary to accommodate the power decrease. A trimmed aircraft reduces pilot fatigue and allows the pilot to devote more attention to task management and development of SA on events occurring outside the cockpit. Large changes in airspeed in a short amount of time will require large changes in elevator trim and will require “running” the trim or many rapid clicks of trim. After heavy forces are trimmed off, fine tune the trim by loosening grip on the control stick and note the direction that the nose or wings travel. A properly trimmed aircraft is much easier to fly but don’t sacrifice basic aircraft control to focus on perfect trimming.

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2.4.2.8. Apply trim in the opposite direction to nose or wing movement. For example, if the nose drops, apply aft elevator trim. If the aircraft rolls left, first confirm slip indicator is centered, then add right rudder trim as necessary for coordinated flight. If the slip indicator is centered and the aircraft still rolls left, apply right aileron trim.

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