What are Trim tabs?
Tim Tabs are small movable rectangles visible on the trailing edges of the control surfaces. They help the main control surfaces (i.e., aileron, rudder, and elevator) move to the desired position or angle. Imagine how hard it would be to deflect those larger control surfaces without the aid of trim tabs. A trim tab deflects to the opposite direction the pilot would want the main control surface to deflect to so it could push the control surface to the desired angle of deflection. For example: the pilot wants to make the aircraft nose up, the trim tabs on the elevators should be deflected downwards, assisting the elevators to deflect upwards, applying a downward pressure on the tail section of the plane, thus making the aircraft nose up and the aircraft would climb up.
From Wikipedia:
Trim tabs are small surfaces connected to the trailing edge of a larger control surface on a boat or aircraft, used to control thetrimof the controls, i.e. to counteract hydro- or aero-dynamic forces and stabilise the boat or aircraft in a particular desired attitude without the need for the operator to constantly apply a control force. This is done by adjusting the angle of the tab relative to the larger surface.
Changing the setting of a trim tab adjusts the neutral or resting position of a control surface (such as anelevatoror rudder). As the desired position of a control surface changes (corresponding mainly to different speeds), an adjustable trim tab will allow the operator to reduce the manual force required to maintain that position—to zero, if used correctly. Thus the trim tab acts as a servo tab. Because thecenter of pressureof the trim tab is farther away from the axis of rotation of the control surface than the center of pressure of the control surface, the moment generated by the tab can match the moment generated by the control surface. The position of the control surface on its axis will change until the torques from the control surface and the trim surface balance each other.
*Sources:
1. http://www.airplanedesign.info/18.htm
