Page 494 - PPL-engelsk 2025

Principles of flight

Rudders can also be equipped with a "horn" placed in front of the rudder itself.

In this horn it is possible to place balance weights, so that you simultaneously

statically balance the rudder.

5.7.6.3 Servo tab

Instead of making an aerodynamic balancing of the rudder, you can make a servo

rudder.

The illustration shows an example of a servo rudder.

It works by the fact that when the

rudder is moved downwards, it

automatically causes the small flap to

go up.

When the tab goes up, a downward

force is created, which eases the

rudder deflection.

These are mainly elevators with a fixed surface (stabilizer).

5.7.6.4 Anti servo tab

If we take an aircraft like a Piper 28, it has a tailplane where the entire surface

rotates around a certain point.

This means that the area in front of the hinge line and behind the hinge line are

almost equal.

When they are, you need to have a damping so
that the rudders do not become too easy to move.

You have then mounted an “anti servo tab”, which

automatically moves in the same direction as the

rudder itself.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 494