AS9120B, ISO 9001:2015, and FAA AC 0056B ACCREDITED

Different Types of Trim Devices Used on Airplanes

A majority of aircraft are equipped with trim devices, which are adjustable flight control surfaces that enable pilots to change the aerodynamic forces that aircraft are exposed to. With the application of trim devices, pilots do not need to constantly apply pressure to control systems. As airplanes vary in design, there are many different types of trim devices on the market, some of which we will outline in this blog.

1. Trim Tabs

Trim tabs are adjustable flight surfaces that are located on the back of an aircraft’s elevators or rudders. Pilots can raise or lower the trim tabs by turning a wheel or crank inside the cockpit. Trim tabs can either be fixed or adjustable. Fixed trim tabs are usually positioned on the rudder or aileron of light aircraft, while adjustable trim tabs can be changed during flight, using cockpit controls to counter changes resulting from airspeed, center of gravity, and more.

2. Servo Tabs

Servo tabs are hinge-like devices that allow a pilot to control aircraft with ease. Also called balance tabs, servo tabs move in the opposite direction of the control surface to which they are affixed to. They operate by deflecting airflow so that the control surface is exposed to a greater force. It is important to note that servo tabs are commonly found on elevators and ailerons. Some servo tabs may be found on the tail assembly and others may be positioned on the wings, depending on the aircraft type.

3. Anti-Servo Tabs

Alongside servo tabs, there are anti-servo tabs. These trim devices allow pilots to control aircraft in the opposite way of their servo counterparts. While servo tabs move in the opposite direction of the control surfaces that they are affixed to, anti-servo tabs move in the same direction of the control surfaces to which they are attached. Anti-servo tabs are primarily utilized to make the controls heavier in feel to the pilot, providing more resistance and increased stability. Furthermore, they may also function as a trim device to relieve control pressure and maintain the stabilizer in the desired position.

4. Bungee System

A bungee system is a type of trim device that leverages a spring-like cord to change the aerodynamic forces to which an aircraft is exposed. Generally, most bungee systems are connected to a cockpit lever, which can be pulled to engage the system.

5. Stabilizers

The last trim device we will cover are stabilizers. Stabilizers are moveable control surfaces that are designed to, as their name suggests, stabilize the airplane. There are different types of stabilizers. For example, horizontal stabilizers are one type that have a horizontal design, whereas vertical stabilizers feature a vertical and upright design. Their main purpose is to provide longitudinal (pitch) and/or directional (yaw) stability and control.


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