The function of a servo tab is very
different from a balance tab.
With a servo tab control system
movement of the pilot’s flight controls moves the servo tab.
The servo tab at the trailing edge of
the main flying control surface produces a aerodynamic
force to move the control surface.
The servo tab is displaced in the
opposite direction in which the flight control surface moves. ie if you wish to pitch the
aircraft nose up, servo tab is deflected down and moves the elevator up.
The system requires airflow from
leading edge to trailing edge, when taxiing in a tailwind the effectiveness of
this type of control is reduced.