The principle of a typical symmetry. The
precise figures, tolerances, and checkpoints for a particular aircraft are
found in the applicable service or maintenance manual.
On small aircraft, the measurements between
points are usually taken using steel tape. When measuring long distances, it
is suggested that a spring scale be used with the tape to obtain equal tension.
A five-pound pull is usually sufficient. On large aircraft, the positions at
which the dimensions are to be taken are usually chalked on the floor.
This is done by suspending a plumb bob from the
checkpoints and marking the floor immediately under the point of each plumb
bob. The measurements are then taken between the centers of each marking.
Cable Tension :
When it has been determined that the aircraft
is symmetrical and structural alignment is within specifications, the cable tension
and control surface travel can be checked. To determine the amount of tension
on a cable, a tensiometer is used.
When
properly maintained, a tensiometer is 98 percent accurate. Cable tension is
determined by measuring the amount of force
needed to make an offset in the cable between two hardened steel blocks called
anvils. A riser or plunger is pressed against the cable to form the offset. Several
manufacturers make a variety of tensiometers, each type designed for different
kinds of cable, cable sizes, and cable tensions.
