Abrams SC-1, Technical Manual

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MAINTENANCE MANUAL
star at night when
it
is
not cloudy. So
it
is
the complement of,
and
does
not replace the magnetic compass.
The
land navi
gator must
be
equipped
with
both, using the sun compass
whenever possible, and reserving the magnetic
compass
for
cloudy periods.
c.
The
sun compass is attached
to
the vehicle
by means
of
a
universal gimbal mounting (figure
1,
item
1)
which
allows tip
ping the instrument
in
any direction
to
make
it
level.
A
level
vial
(item 2) attached to the extended arm of the gimbal
mounting indicates when the instrument is
level.
A
circular
protractor
plate (item 3) is
secured
to the
gimbal mounting.
A
date bar (item
4),
an oval shaped solar plate (item
5),
and
a
shadow bar (item 6) are mounted successively on top of the
protractor
plate.
A
pivot bolt (item
7)
acts as
a
pivot for
these
parts.
The
date
bar
can be rotated
a
full
360
degrees to
any desired setting on the protractor. The
solar plate can
be
slid
along the date bar
to
the proper date mark.
The
shadow
bar can
be
rotated
a
full
360 degrees
over the surface
of
the
solar plate
to
the proper time-latitude setting.
The solar
plate
and the date bar are clamped at the desired settings by
a
star-
shaped clamping nut
on
the lower
end
of
the
pivot bolt.
A
vertical gnomon rod (item 8) is mounted
in
the center of
the
pivot bolt.
It
casts
a
shadow which
falls
on
the shadow bar
when the proper adjustments have
been made.
This
gnomon
rod
is
used
in
conjunction with
a
sighting rod (item 9) on the
gimbal mounting arm, to obtain
a
foresight
or to sight
on a
star.
2.
DETAILED
DESCRIPTION.
a.
Oimbal Mounting.
—
The gimbal mounting (figure
1,
item
1)
frictionally
prevents the compass
from tilting,
but
allows
it
to be
readily
leveled.
The
holes provided
for
the mounting
bolts
in
the bottom support
of
the gimbal mounting are made
slightly
oversize
to
provide an adjustment in aligning
the com
pass
parallel
to the centerline
of
the vehicle.
Wing
nuts
on
the pivot bolts
of
the support can
be
tightened to
rigidly
secure
mounting
after
it
has been leveled.
6.
Level Vial.
—
The
level
vial
(item 2)
is
a
round, heat re
sistant
glass
vial,
enclosed
in
a
metal
cap
and mounted
on
the
Gimbal arm.
It
provides
a
ready means for
leveling the
com-