Precession check
RESTRICTED
N.O.P.
#650
FORMED. PREVIOUS STEPS IN CAE
PRECESS ON CHECK• BEFORE MAKING A PRECESSION
MUST BE PER-/
1..
Check flexible leads, pigtails and all
other wiring in gyro.
2.
Work all gudgeon bearings to distribute
oil and to
insure freedom.
3.
minutes to attain run-
ning temperature
(140° F.).
4.
Set zero drift and place sight on one car-
dinal heading.
5.
Before starting each run, uncage gyro and
spiral cross hairs
to center of grid with leveling
knobs,
making last movement always in same direct-
ion.
6.
Start stop watch and plot for two minutes.
Repeat this on opposite heading.
7.
From these
two readings, determine in
which direction the weights must be moved to ob-
tain proper
apparent easterly precession for this
latitude.
One method of determining which way the
weights on top of gyro should be moved is: to ad-
just for lateral or transverse precession, move
the weights on the longitudinal or fore and aft
screw. Move the weights forward if the cross
hairs
precess to the right.
Move the weights to
the rear if the cross hairs precess to the left.
To adjust for fore and aft precession, move the
weights on the transverse screw.
Move weights to
left if cross hairs precess forward.
Move the
weights to the right if the cross hairs precess
rearward.
When moving weights,
always count the
number of turns givem. This will give an approx-
imation of the amount needed to turn the weight
for a desired change in precession. Make another
run as in steps above
8. When apparent easterly precession is close
to the same on the two headings above for two min-
ute
take two minute
runs on the other two
headinas
(easterly precession). When easterly pre-
cession is approximately equal for the four head-
ings,
take four minute
runs for fine
adjustment.
Disregard north hook when making adjustment; it
will be corrected automatically as easterly pre-
cession is adjusted.
If north hook is excessive,
or not approximately equal on all headings, it
probably indicates that the bearings need cleant
RUN
ALL
PREVIOUS
STEPS
FORMED.
Let
gyro
runs,
ing.
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