SPECIAL AIRCRAFT TOOLS
7-1. General. The tools described in this chapter are
all used in specific applications on Army aircraft. Some
of these tools, such as inspection mirrors, make basic
tasks simpler, and others are used for critical
maintenance tasks, like the cable tensiometer.
7-2. Protractor. The protractor assembly may be used
to measure propeller blade angle, control surface
movement, or any other angle.
a. Description. The protractor, shown in figure 7-1,
consists of an aluminum frame in which a steel ring and
a disk are mounted. Spirit levels are mounted on both
the frame and disk. Locks are provided for locking the
ring to the frame or the disk. Scales are marked on the
disk and the ring. Zeros of the scales provide reference
marks between which the angle may be read. Hand
adjusting screws are provided so that the ring and the
disk may be rotated in relation to the housing and to
each other. Functioning parts of the protractor are
described in the following paragraphs.
(1) Indicating surface. The indicating surface of the
protractor is the bottom edge opposite the upper curved
(2) Primary level. The level at the lower left corner
of the protractor is the primary level and is parallel with
the indicating surface. This level has two positions:
against the face, and at the right angle to the face.
(3) Secondary level. The level at the center of the
protractor is a secondary level functioning with the inner
and vernier dials.
(4) Lock assembly. The lock assembly detents and
engages the inner protractor dial with the vernier scale
at zero alignment only.
(5) Ring-to-frame lock. The knob locks, by tension,
the other vernier scale at any rotary position in relation
to the indicting surface of the protractor.
Figure 7-1. Protractor