Page 694 - PPL-engelsk 2025

Aircraft general knowledge

8.3.7 Control and stabilization

To help control and stabilize the aircraft, we have various aids.

- Trim tabs

- Flaps

- Slots

- Slats

8.3.7.1 Trim tabs

Trim tabs (servo) are secondary moving surfaces that are placed on the trailing

edge of the control. The trim tab causes the control to move up or down.

Some of them are so-called trim tabs, which are responsible for keeping the

control in a desired position so that the pilot does not have to use unnecessary

force to maneuver the aircraft.

The servo tab automatically moves when the control is moved. It is a trim tab

that has the opposite deflection of the control surface and makes operation

easier.

The illustration shows the principle of

servo tab.

An anti-servo tab automatically deflects to the same side as the rudder. This

dampens the rudder's movements.

When the trim tab is moved up, the elevator is pulled down, and we get a curved

surface. Here, the air moves faster over it than on the underside, and static

negative pressure is created, which provides lift on the tail. As a result, the tail

of the aircraft moves up and the nose of the aircraft moves down.

Flyveteori PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 694