Powered controls

Nowadays all but small aircraft are usually fitted with power-actuated control surfaces which are very easy to operate even on large airliners. Because such controls offer virtually no natural resistance, they are given some form of arti­ficial ‘feel’, a resistance which is designed to increase with flight speed (or more precisely with dynamic pressure) so that the control system feels like a direct mechanical linkage. Without such feel it would be quite literally possible to pull the control surfaces off at high speed.

The control column often incorporates a ‘stick shaker’ which operates when the aircraft approaches a stalled condition. This reproduces the shaking that normally occurs on simple mechanical systems due to the buffeting of the control surfaces caused by turbulence. It is intended to trigger the pilot’s con­ditioned response. On some aircraft, if the pilot fails to respond correctly by pushing the column forward, the controls take over and a ‘stick pusher’ does the job for him! With the advent of advanced and reliable electronic devices, it has become possible to make control systems of immense complexity that respond smoothly over a very wide range of flight conditions and contain many built-in safety features. In order to prevent loss of control in the event of power failure the systems are usually duplicated, triplicated or even quadru­pled.