BALANCED RUDDER

Description

Before the balanced rudder, all ships employed a rudder that was a simple flat piece of wood or metal, situated at the after end of the hull and hinged at the forward end, which could be angled to one side or the other to deflect the water passing it and hence provide an impulse to turn the ship. This required the exertion of significant force, as the passage of the water past the rudder tended to force it into a straight line in conformity with the flow.

The concept of a balanced rudder involved the shifting of the centre of rotation of the rudder to point approximately 1/2 of the way from the forward end to the after end. This meant that when the rudder was turned, the flow of water past the ship actively worked on the forward third to increase the angle of deflection, whereas the same flow acted on the after 1/2 to reduce the angle.

The mechanics of fluid dynamics produced a solution in which the turning force applied in one direction on the rudder by the passing fluid was balanced by the turning force applied in the other direction, allowing the rudder to be moved with only limited mechanical resistance.

The balanced rudder was soon adopted by the fledgling aircraft industry in the early 20th century, which often made use of the horn balance, in which a section of the rudder, usually at the top of the vertical stabiliser, projected into the airstream. Two illustrations of aircraft rudders published by Flight Magazine in 1920,^[1] illustrate both the conventional balanced rudder (at lower left on the Short Swallow) and with a large 'horn' (at left centre, in this case in the form of a semicircle, on the 'Short Sporting Type').

Different types of balanced rudder shown: 3 balanced, 4 semi-balanced, 5 non-balanced (hinged about axis 'A')