Balanced rudder

A degree of semi-balance is normal to avoid rudder instability i.e. the area in front of the pivot is less than that behind.

[3] Control of aircraft is complicated by their motion in three dimensions, yaw, pitch and roll, rather than one but there is a similar need to reduce loads, tackled in the same way as on a ship with some part of the surface extending forward of its hinge.

In addition, because aircraft control surfaces are mounted on flexible structures like wings, they are prone to oscillate ("flutter"), a dangerous effect which can be cured by bringing the centre of gravity (c.g.)

If the centre of gravity is behind the hinge, the surface can move like a pendulum and undergo forced simple harmonic motion with increasing amplitude.

Adding balancing weights which make the centre of gravity and hinge line coincident solves the problem.