Control Aids / Tabs
Balanced Control Surface
Control Tabs / Servo Tabs
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The simplest form of this assistance is the balanced control sur-face. In the case of the rudder, the balance portion, or overhang, deflects to the opposite side of the fuselage from the main rudder surface to produce an aerodynamic force that aids the pilot in moving the surface.
They are usually controlled with control tabs. The flight control column moves the tab on the control surface, and the aerodynamic forces caused by the deflected tab moves the main control surface.
Balance Tabs
The control forces may be excessively high in some aeroplanes, and in order to
decrease them, the manufacturer may use a balance tab. This tab is located in the same place as a trim tab and in many installations one tab serves the function of both
Anti-Balance Tabs
Stabilator surfaces do not have fixed stabiliser in front of them, and the location of their pivot point makes them extremely sensitive. To decrease this sensitivity, a full length anti-servo tab may be installed on the trailing edge. This tab works in the same manner as the balance tab except that it moves in the opposite direction.
Trim tabs are small movable portions of the trailing edge of the control surface. These tabs are controlled from the cockpit to alter the camber of the surface and create an aerodynamic force that will hold the control surface deflected.
Trim Tabs
Spring Tabs
Another device for aiding the pilot of high-speed aircraft is the spring tab. The control horn is free to pivot on the hinge axis of the surface, but it is restrained by a spring. For normal operation when the control forces are light, the spring is not compressed and the horn acts as though it were rigidly attached to the surface
Control Surface Mass Balancing
Most control surfaces are mass balanced. The purpose of this is to prevent control surface flutter.