How does a balance tab move in relation to the flight control surface that it is coupled with?
Primary Controls are controls which rotate the aircraft about its three axes and thereby cause a change in the aircraft’s flightpath and/or attitude. Primary controls consist of elevator, rudder and ailerons plus roll control spoilers.
The primary flying controls in a manually operated control system are reversible. That is, a force applied to the cockpit control will move the control surface, and also, a force applied to the control surface will cause the cockpit control to move. This means that the air pressure on the control surfaces is felt by the pilot through the cockpit controls. This is not the case if the controls are fully power operated. A power operated control is irreversible, that is, a load applied to the control surface cannot move the cockpit control, and the system has no natural feel.
Because of this it is necessary to introduce feel to the system artificially. The artificial feel unit should increase the cockpit control load in proportion to the control deflection, and in proportion to the speed. A manually operated trimming tab is irreversible, once its position has been set by the trim wheel, it cannot be moved from that position by a load on the trimming tab.
Trim tab is a small adjustable surface set into the trailing edge of a main control surface. Its deflection is controlled by a trim wheel or switch in the cockpit, usually arranged to operate in an instinctive sense. To maintain the primary control surface in its required position, the tab is moved in the opposite direction to the control surface, until the tab hinge moment balances the control surface hinge moment.
A balance tab moves in the opposite direction to the flight control surface that it is coupled with.
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Austro Control