Cardinal heading and static balance
RESTRICTED
Why
Sight, In
Precession
Run, Must
Face Card-
inal Head-
ing.
Theory
of Static
Balancing
of Gyro.
duce a precessing force
upon the east face of the
gyro; this, considering the gyro rotates Clockwise,
causes the south face to precess downward, which
in turn causes the bottom of the soin axis to move
northward.
of the
latitude taken
i use the formula 1%. 5 tares the cosit
the trig. tables.)
Likewise one must use
the optics as a means of
sighting for the precession, the optics being lin-
ed up with
a grid plate which is calibrated accord-
ing
to dimensions in mils.
If the latitude is not known, so that appar-
ent easterly precession can not
be computed in
balance the gyro so
that it precesses an
etual amount on opposite headings. The same ar-
plies to north hook.
If the gyro precesses equally on all four
headings, and the leveling
bubbles do
not move
more
than
1/4
a bubble length
two minutes from cen-
of reference mark on bubble tube, the gyro is pre-
cessing correctly.
making a
run, face on a cardinal
why must the sightheading? There
precession
are
three
reasons:
(1) in balancing
the gyro statically
while making a precession
run, it would
be necess-
ary to shift about both
sets
of centering weights
every time an adjustment was made if
the sight did
not face on a cardinal
heading.
This would
make
the adjustments extremely difficult.
(2) The more
the number of
bearings the gyro
reguires to tilt
as a
result of easterly precession,
the greater
will be the amount of north hook. And
if the sight
were not on a cardinal heading, the gyro would
tilt on the cardan gudgeon bearings, the gyro gud-
eon bearings, and the telescope cradle gudgeon bear-
ings.
Standardized readings for north hook have
been made only on cardinal headings and therefore
we have no way of knowing what the correct amount
or north hook
shoud be other than a cardinal head-
ing. (3)
East is the direction of apparent east-
erly precession,
and since east
is itself a card-
inal heading,
on a
headinai heading.
it is logical that the sight face
First,
cosine of the latitude
Paris arent eastery beed
multiplication of 17.45 mils by the
will give the correct num-
minutes. A close approximation of this figure on
120