 The tab has a leverage advantage, being located well aft of the control surface hinge line, and thus its airflow deflection moves the control surface in the opposite direction, overcoming the resistance generated by the airflow deflection of the control surface.This has the effect of reducing the control force required from the pilot to move the controls.In some large aircraft, the servo tab is the only control that is connected to the pilot's stick or wheel, as in the Bristol Britannia and its Canadian derivatives.