Elevator Trim Tabs

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

CHAPTER EIGHTEEN

WORKBOOK

Trim Tabs

Trim tabs allow the pilot to correct an unbalanced flight condition without exerting continuous

pressure on the primary controls. They are small moveable tabs on the trailing edge of each

primary control surface.

Trim Controls

Trim tab controls are located at the forward end of the left console in both cockpits. Position of

the rudder trim knob, elevator control wheel and aileron control wheel present a logical display

for use. Rotation of trim knob or wheels will effect movement of the trim tab through chain and

cables and push-pull tubes and will move controls in both cockpits simultaneously. The rudder

trim tab knob incorporates a numbered circular scale representing degrees of deflection.

Elevator and aileron trim tab wheels utilize an adjacent plastic window indicating degrees of

deflection.

Elevator Trim Tabs

Elevator trim tabs are designed to impart a clockwise rotation to the fuselage to offset torque

effect or "left-turning tendency." On preflight with elevator trim set at "0" the right tab will be

4 up and the left tab will be 4 down. As the trim control is moved in the cockpit, the trim

tabs will move up or down accordingly, but will remain with a 9 split between the two tabs.

With movement of the control stick and elevator, the elevator tabs will remain in their adjusted

position in relation to the elevator.

Rudder Trim Tab

When the rudder trim tab knob is set "0," the tab is aligned with the rudder. Rotating the trim tab

knob deflects the trim tab and the rudder is deflected in the desired direction. Moving the

rudders with the pedals causes the tab to move in the same direction, thereby creating artificial

feedback or feel. This is referred to as antiservo action.

Aileron Trim Tabs

When the aileron trim tab wheel is set at "0," the left trim tab is aligned with the trailing edge of

the left aileron. The right tab is set by the manufacturer or maintenance action, and is not

adjustable. Both ailerons move due to mechanical connection. When moving the ailerons with

the control stick each trim tab moves in the opposite direction (lag) of its aileron, acting as a

lever to assist the aileron movement. This is referred to as servo action.

Strakes and Ventral Fins

The strakes are an extension of the horizontal stabilizer forward alongside the empennage. The

ventral fins form a "V" beneath the empennage. The strakes and ventral fins limit the aircraft's

spin turn rate.

FLIGHT CONTROL SYSTEMS

18-3