Control Cables and Terminals
Cables are the most widely used linkage in primary flight
control systems. Cable-type linkage is also used in engine controls, emergency
extension systems for the landing gear, and various other systems throughout
the aircraft.
Cable-type linkage has several advantages over the other
types. It is strong and lightweight, and its flexibility makes it easy to route
through the aircraft. An aircraft cable has a high mechanical efficiency and
can be set up without backlash, which is very important for precise control.
Cable linkage also
has some disadvantages. Tension must be adjusted frequently due to stretching
and temperature changes. Aircraft control cables are fabricated from carbon
steel or stainless steel. Cable Construction The basic component of a cable is
a wire. The diameter of the wire determines the total diameter of the cable.
Several wires are preformed into a helical or spiral shape
and then formed into a strand. These preformed strands are laid around a
straight center strand to form a cable. Cable designations are based on the
number of strands and the number of wires in each strand. The most common
aircraft cables are the 7 × 7 and 7 × 19. The 7 × 7 cable consists of seven
strands of seven wires each.
Six of these strands
are laid around the center strand. This is a cable of medium flexibility and is
used for trim tab controls, engine controls, and indicator controls. The 7 × 19
cable is made up of seven strands of 19 wires each. Six of these strands are laid
around the center strand.
This cable is extra flexible and is used in primary control
systems and in other places where operation over pulleys is frequent. Aircraft
control cables vary in diameter, ranging from 1 ⁄16 to 3 ⁄8 inch. The diameter
is measured as shown in Figure 7-68. Cable Fittings Cables may be equipped with
several different types of fittings, such as terminals, thimbles, bushings, and
shackles.
Terminal fittings are generally of the swaged type. They are
available in the threaded end, fork end, eye end, single shank ball end, and
double shank ball end. The threaded end, fork end, and eye end terminals are
used to connect the cable to a turnbuckle, bell crank, or other linkage in the
system.
The ball end
terminals are used for attaching cables to quadrants and special connections
where space is limited.
the various types of terminal fittings. The thimble,
bushing, and shackle fittings may be used in place of some types of terminal
fittings when facilities and supplies are limited and immediate replacement of
the cable is necessary.