Brief Outline- Cable Control Systems - Flight Controls II

Cables
We know control cables are made up of corrosion resistant steel wires, but how exactly are they ‘wired’ up? I have a very simple way of keeping tabs on this:
Wires around a single central wire = Strand.
Strands around a single central strand = Cable !
Just how many wires, and how many strands? That’s where cable classification comes in. Different applications require cables of different diameters and that is based on 2 aspects:
Cable loading – or the amount of load the cable application will require;
Cable Flexibility – based on the route and distance the cable must travel.
The classification is therefore given in diameter (in inches) and the number of strands/wires in the cable. So ¼ 7x19 would imply 1/4 inch diameter, 7 strands in each cable, 19 wires in each strand.

A very important aspect in understanding how cables take loads is knowing that a cable can transmit a force that is unidirectional only; that is, via Tension or a pulling force. That however does not restrict it only to pulling applications. It can exert a pushing force, or compression, as well. In order to do this however, it has to form a ‘loop’ that allows counter pulling, in the opposite direction.

EXAMPLE: In regards to the primary flight controls in the smaller training aircrafts today, an action to lower an aileron on one wing, causes an opposite aileron movement on the other wing. With the rudders and elevators this may not seem apparent, but if you examine at how pulling and pushing the control column in the cockpit operates the control surface, you will realize that the cable control applies the pulling and pushing motion of the control column to the actual control surface, via a pulling action (Tension load).