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Principles of flight

5.6.2 Trim

To facilitate the maneuvering of an aircraft, trim tabs are attached.

There are fixed trim tabs on the rudder, which can be adjusted when the aircraft
is on the ground.

The trim tabs are adjusted so that the aircraft flies correctly at normal cruising

speed. There is also adjustable trim that must be adjusted via trim wheels from

inside the cockpit.

The figure here shows elevator trim.

The way it works is that a small tab
at the back of the rudder is

activated and causes the main

rudder surface to move.

If the tab is moved downwards,

this creates a curved surface upwards, which sucks the control upwards.

This causes a more curved underside of the elevator, and we get a downward

tail force, which causes the nose of the aircraft to move upwards.

Here is a picture of the trim wheel in the cockpit of a Cessna

172. Remember to set the trim in the correct position before

take-off.

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Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 483