Balanced rudder

Balanced rudders are used by both ships and aircraft. Both may indicate a portion of the rudder surface ahead of the hinge, placed to lower the control loads needed to turn the rudder. For aircraft the method can also be applied to elevators and ailerons; all three aircraft control surfaces may also be mass balanced, chiefly to avoid aerodynamic flutter.

Ships

A balanced rudder is a rudder in which the axis of rotation of the rudder is behind its front edge. This means that when the rudder is turned, the pressure of water caused by the ship's movement though the water acts upon the forward part to exert a force which increases the angle of deflection, so counteracting the pressure acting on the after part, which acts to reduce the angle of deflection. 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. This allows the rudder to be moved with less effort than is necessary with an unbalanced rudder.