Special Tools
support push-pull tubes and guide them through holes
in structural members.
Each aircraft has a set of special tools for flight
control maintenance that may include rigging fixtures,
Bungee
pins, blocks, throwboards and protractors. Other
Bungees are tension devices used in some rigid
common equipment, such as micrometers, pressure
gauges, push-pull gauges, feeler gauges, tensiometers,
systems that are subject to a degree of shock or
and calipers may also be required. These are usually
overloading. They are similar to push-pull rods, and
maintained in the toolroom and checked out when
perform essentially the same function except that one
needed.
of the fittings is spring-loaded in one or both
directions. That is, a load may press so hard
TENSIOMETER.The tensiometer is an
(compression) against the fittings that the bungee
instrument used in checking cable tension. Tension is
spring will yield and take up the load. This protects the
the amount of pulling force applied to the cable. The
rest of the rigid system against damage. The internal
amount of tension applied in a cable linkage system is
spring may also be mounted to resist tension rather
controlled by turnbuckles in the system.
than compression. An internal double-spring
A tensiometer is a precision cable tension
arrangement will result in a bungee that protects
measuring device, but it has limitations and can be
against both overtension and overcompression.
awkward to use. It is inaccurate for cable tension under
30 pounds. When you take tension measurements, the
TROUBLESHOOTING
instrument must not be pressed against any part of the
aircraft, it can't be pushed or pulled against the cable,
When the cause and remedy for a reported
and the cable must not be pressed against fairleads or
malfunction in a control system are not immediately
any part of the aircraft. Any one of these actions may
obvious to you, it may be necessary to troubleshoot the
lead to inaccurate measurements. A major advantage
system. Most aircraft MIMs provide troubleshooting
of cable linkage is its minimal space requirement and
charts that list some of the more common malfunctions
the ease in which it can be routed around, through, and
in a system. Each discrepancy is accompanied by one
behind aircraft structures and components. This can
or more probable causes, and a remedy is prescribed
make access difficult and the tensiometer awkward or
for each cause. The troubleshooting charts are
difficult to use. Adequate clearance for the tensiometer
organized in a definite sequence under each possible
is necessary. All tensiometers must be certified by a
trouble, according to the probability of failure and ease
calibration laboratory for accuracy at least once a
of investigation. To obtain maximum value from these
month.
charts, they should be used systematically according to
One type of tensiometer is shown in figure 16-23.
the aircraft manufacturer's recommendations.
This instrument works on the principle of measuring
the amount of force required to deflect a cable a certain
Since most aircraft use some form of electrical
distance at right angles to its axis. The cable to be
control or hydraulic boost in their flight control
tested is placed under the two blocks on the instrument,
systems, maintenance of these systems must include
and the lever assembly on the side of the instrument is
the related electrical circuits and hydraulic systems.
pulled down. Movement of this lever pushes up on the
Although an AE or AM is generally called upon to
center block, called a "riser." The riser pushes the
locate the correct electrical or hydraulic troubles
cable at right angles to the two clamping points. The
respectively, you should be able to check circuits for
force required to do this is indicated by a pointer on the
loose connections, perform continuity checks, and
dial. Different risers are used with different size cables.
perform minor troubleshooting of the hydraulic
Each riser carries an identifying number, and is easily
system.
inserted in the instrument.
RIGGING AND ADJUSTING
Each tensiometer is supplied with a calibration
table to convert the dial readings into pounds. One of
The purpose of rigging and adjusting a primary
these calibration tables is shown in figure 16-23. For
flight control system is to ensure neutral alignment of
example, if the pointer on the dial indicates 48 with a
all connecting components and to regulate and limit
No. 2 riser and a 3/16-inch diameter cable, the actual
tension on the cable is 100 pounds. With this particular
the surface deflection in both directions.
16-27
