gyro pickoff signals cause the gimbals to rotate
to true north) changes as a function of longitude.
and cancel the pickoff error signals. The stable
The system operation is the same as a north-
element is torqued until the accelerometers show
pointing system. However, the wander angle is
a null or level condition.
taken into account by the computer with the north
and east sensored accelerations.
Alignment at Sea
Problems that arise in aligning an aircraft
inertial navigation system on aircraft carriers at
sea are, more complex than aligning the INS
ashore. This situation exists even though our
carrier-based inertial reference is another INS of
very high accuracy. The inertial navigation
reference system aboard an aircraft carrier is the
ship's inertial navigation system (SINS) and the
relative velocity computer (RVC). Outlets on the
flight deck make it convenient to pipe the SINS
reference information into the aircraft inertial
navigation system. However, one major problem
still remains that makes proper alignment
difficult. The accelerations experienced by the
ship's inertial navigation accelerometers located
below deck. These accelerometers are remote from
the aircraft accelerometers, and therefore do not
sense the same accelerations.
COARSE SEA ALIGNMENT. --During
coarse sea alignment, the best available true
heading is from the SINS and the RVC. Aircraft
carrier true heading goes to the RVC. Here a
manually selected aircraft heading angle, with
respect to the aircraft carrier, is inserted. The
combined signals then go to the heading computer
in the aircraft's inertial navigation system, thus
concluding the coarse sea alignment.
FINE SEA ALIGNMENT. --During fine sea
alignment, the accelerometers sense the aircraft
carrier movement in addition to gravity. Only the
gravity component is used in the leveling. This
allows accelerometer output caused by aircraft
carrier movement to be canceled. The SINS
and RVC accomplish this task by supplying
continuously computed corrections. The accel-
erometer error signals are integrated to supply
a velocity. The reference velocity supplied by
the RVC during sea alignment, actual aircraft
velocity, is subtracted from the accelerometer
derived velocity. The difference corresponds to
the gravity component sensed by the acceler-
ometer. After amplification it is applied to the
torquing coils of the gyros. The processing of the