Servo Tabs
Servo tabs move in the opposite direction of the control surface. The tab has a leverage advantage, being located well aft of the surface hinge line and thus can deflect the control surface in the opposite direction. This has the effect of reducing the control force required by the pilot to move the controls.
In the case of some large aircraft the servo tab is the only control that is connected to the pilot's stick or wheel. The pilot moves the wheel which moves the servo tab and then the servo tab, using its mechanical advantage, moves the elevator or aileron, which is otherwise free-floating. With a servo-tab variant named "geared spring tab", a pilot was able "to maneuver a vehicle weighing as much as 300,000 pounds flying at an airspeed of 300 miles per hour or more".
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