Anti Servo Tab: What Is It? What are the Purposes & Functions?

What is an Anti servo tab, and how does it work?

Do you know how the pilot keeps the plane stable? Unfortunately, sometimes flights become overcontrolling, and pilots feel challenged to control. Thus, here comes the need for Tabs in flight. Moreover, there are many tabs for proper functioning and balance of the plane. We will discuss all those tabs, thus, starting from the anti servo tab.

So, talking about the anti servo tab, it is a movable surface on the trailing edge of the stabilator. It provides stability to the plane and puts the aircraft’s pitch under the control of the pilot. Moreover, airplanes with light control or aircraft requiring stability in pivot point use anti servo tabs.

However, the anti servo tab works in the same direction as that of the stabilator. Therefore, when the stabilator moves down, this tab moves along and creates a force to raise the edge. Moreover, with this raising force, the anti servo tab reduces the sensitivity. Thus, it gives resistance to the pilot when they move the stick.

The purpose of anti servo tab

 It would be easier to change the pitch without the anti servo tab. But, along with this, there would be a possibility to overstress the plane, as it becomes over-controlling. Thus, anti servo tab serves the purpose of:

  • It Provides stability to aircraft by giving resistance to sticking.
  • It reduces sensitivity and puts the plane under the control of the pilot.
  • It maintains the position of the stabilizer.
  • It relieves the control pressure of the aircraft.

Anti-Servo Tab vs. Servo Tab vs. Trim Tab vs. Balance Tab vs. Geared Tabs

Summary Comparison Table

 Anti servo tabServo tabTrim tabBalance tabGear tab
LocationThe trailing edge of the stabilatorControl surfaces of aircraft like wings and tail assembly.Outer edges of ailerons, rudders, and elevatorThe trailing edge of the elevatorAhead of control surface
PurposeIncrease stability, resistance, control pressure of aircraftProvide mechanical advantage to pilot by reducing the control forceReduces manual energy and work to stabilize aircraftHelps to control flight movement, assists with force required to position control surfaces.It gives flight control movements. It changes flight control forces, over-controlling them or decreasing them.
FunctionIt maintains flight control by aiding the stabilator. It moves in the same direction as of stabilator to create resistanceIt deflects airflow and generates a force on the control surface to move in the desired direction.It counteracts the aerodynamic force to stabilize the aircraft with primary control.It moves opposite to trail edge and provides force for flight controlIt gears to move at a set ratio in the same direction as the anti servo tab and control flight movement.
ConsWhen the anti servo tab moves in the elevator's direction, there is no reduction in hinge moment. Thus, it makes it difficult to make changes in the control surface by the pilot.It reduces control effectiveness at low IAS.Loose trim results in vibration and pitch up of aircraft.
They are unbalanced and prone to flutter. They may cause a slight rolling motion.
It may cause a possible increase in drag.
Increase in size of control surfaces
It sometimes makes the pilot put more effort into changing the control surface.

What is a servo tab?

A servo tab is a small device that hinges on the control surfaces of the aircraft. These devices do not put any negative feedback to maintain the control surface in position. Moreover, you may find a servo tab on the control surfaces like wings and tails.

How does the servo tab work?

The servo tab works by giving mechanical advantages to the elevator or aileron. That means servo tabs move in the opposite direction of the control surface. Thus, causing deflection in airflow and generating force in the direction of the control surface. This force overcomes the resistance of airflow deflection. Therefore, it reduces the control force to move the control of an aircraft. However, the pilot controls the servo tab from the cockpit by either lowering or raising them. For example, if the pilot raises them, it will make air move from the top of the control surface. Thus, causing aircraft to move down. Likewise, if the pilot lowers the tab, airflow will be from the bottom of surfaces, causing the plane to move upward.

What is the purpose of a servo tab?

The servo tab serves the easy movement of the control surface of aircraft. In addition, the tab provides a mechanical advantage by allowing the pilot to create resistance according to need.

What is a trim tab?

Trim tabs are secondary flight controls and minor in size. You may find these tabs on the trailing edge of control surfaces such as the elevator and rudder. Moreover, it is of two types: either fixed trim tab or flight adjustable.

How does the trim tab work?

The trim tab works by moving a small wheel in the cockpit. Moreover, when the pilot moves the tab, it causes the airflow to deflect.  And this deflects the elevator in the opposite direction. So, for example, if you move the tab down, the aircraft’s nose will move up and vice versa.

What is the purpose of a trim tab?

Trim tab in aircraft serves to reduce the pilot’s energy and work to stabilize the plane. Moreover, trim tabs protect the plane from wear and tear by reducing stress and pressure.

What is a balance tab?

The balance tab is a small device present on the control surface linkage.

How does the balance tab work?

The balance tab works opposite to the control surface direction. That means, if the elevator or control surface moves up, the balance tab moves down. Thus, reducing the control load of the aircraft’s wheel and allowing the aircraft to fly efficiently. In addition, the balance tab works automatically in the plane when there is a need to control surface movements.

What is the purpose of a balance tab?

The balance tab serves to generate force to assist with movements of flight control.

What is the gear tab?

The geared tab is a secondary flight control tab that links with a fixed surface ahead of the flight control surface.

How does the geared tab work?

The geared tab works in a set ratio that moves in both directions. They move in the opposite direction, like the balance tab or the same direction as the anti servo tab. Moreover, the control surface connects it through pedals or sticks. Thus, deflection in the geared tab causes movement in the flight control.

What is the purpose of a geared tab?

The Geared tab serves to change flight control forces. They either increase or decrease the forces. Thus, it helps in efficient flight control movement.


Aircraft have a complex flight control system. However, this article clarifies the anti servo tabs and many other flight control tabs essential for efficient movement. Moreover, the anti servo tab is a movable surface on the trailing edge. It works in the same direction as of stabilator, creating force in the opposite direction. Thus, the force produces resistance that reduces the sensitivity of flight control. Thus, the anti servo tab increases the stability of the aircraft. However, it mainly makes control feel heavier to the pilot.


What are the disadvantages of the servo tab?

The disadvantage of the servo tab is that at low IAS, it reduces control effectiveness. After giving input, the servo tab deflects and produces force. Then, this aerodynamic force governs flight control. But, at low IAS servo tab fails to maintain control effectively.

What is the difference between the trim tab and the servo tab?

The trim tab and servo tab may seem to be similar but operate differently.

  • The trim tabs have a light wire that attaches to them with the control surface. In contrast, the servo tabs have a large tab on the back of the control surface, which usually hangs down while parking.
  • The trim has independent control, and the pilot may readjust to control aerodynamic force. In contrast, the servo tab integrates within the flight operating system like steering.
  • The trim tab serves to counteract the aerodynamic force and stabilize the aircraft’s control. In contrast, the servo tabs deflect the airflow on the flight control surface and make the desired movement.

What is the spring tab in aviation?

The spring tab is the same as the servo tab with spring in the linkage that causes the tab position to vary according to stick force. However, under average flight load, it has no role. But, in heavy loads, it moves opposite the control surface and aids in a smooth movement.

What is the ground adjustable trim tab?

A ground adjustable trim tab corrects the tendency to fly with a fuselage. It slightly misaligns with the relative wind. Moreover, these tabs are adjustable on the grounds. In addition, this tab keeps coordination of aircraft with the flight level.

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