•This is of course the same way trim tabs work. Therefore, you can think of this system as being like trim tabs if they were connected to the control wheel instead of a separate control wheel.•Note that in a tab controlled system there is no direct connection between the control column and the control surface.
Servo TabA servo tab is similar to a balance tab in location and effect, but it is designed to operate the primary flight control surface, not just reduce the force needed to do so. It is usually used as a means to back up the primary control of the flight control surfaces
Spring Tab•A control surface may require excessive force to move only in the final stages of travel. When this is the case, a spring tab can be used. •This is essentially a servo tab that does not activate until an effort is made to move the control surface beyond a certain point. •When reached, a spring in line of the control linkage aids in moving the control surface through the remainder of its travel.
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.
Spring Tabs•Like servo tabs are usually found on large aircraft that require considerable force to move the control surface.•The spring tab provides a boost, aiding in the control movement.•At high speeds, the spring is compressed by the pilot input and the tab moves the surface, diminishing the control force required by the pilot.•Note the control horn is connected to the control surface by springs.Under normal flight loads, a spring tab has no role to play and remains streamlined to the control surface. However, when air loads are high and a large force is required to move the control surface,the spring tab moves in the opposite direction to that of the control surface on which it is mounted,and this aids the pilot in moving the control surface.
Geared tab> With a servo-tab variant named "geared spring tab", a pilot is able "to maneuver a vehicle weighing as much as 300,000 pounds flying at an airspeed of 300 miles per hour or more.> Tab is linked to the main surfacein opposition to control motion,reducing the hinge moment withlittle change in control effect
Geared Servo tab•The geared spring tab is used in conjunction with an elevator, the force per g may be made independent of speed, no matter what the stiffness of spring used.