Figure 7-48.-Coriolis and centripetal corrections.
compensating for the decreasing eastward velocity
generated by aircraft speed. The Coriolis correc-
of the earth's surface.
tion accounts for the additional force generated
The train traveling north stops at a latitude
by the earth's rotation. For example, if the earth's
where the earth's tangential velocity is 600 knots.
tangential velocity at latitude L is 700 knots and
This is 200 knots less than the tangential velocity
aircraft speed 350 knots, total speed is 1,050
at the point of its initial alignment. The velocity
knots. Centripetal correction offsets the accelera-
computer will continue to report that the vehicle
tion caused by the centrifugal force of a 350-knot
is traveling west at 200 knots even though it is
turn of this radius. Coriolis correction offsets the
perfectly static. The Coriolis correction prevents
force of a 700-knot turn. In this case, the two
this from happening. It creates enough east
corrections are summed.
acceleration signal to offset the continual west
If the course is reversed and the plane flies
acceleration generated by the east-west accel-
west, the correct ions become opposite in polarity.
erometer as it travels north. The east and west
The centripetal signal is still south, but Coriolis
accelerations cancel, thus, there is no change in
is north (to the right of the track). Therefore, only
longitude to report. Of course, on the return trip,
a part of the larger correction is effective.
the platform is under the delusion that 600 knots
east is zero velocity. So as it travels south, the
Schuler-Tuned Loop
increasing earth tangential velocity causes it to
constantly report east acceleration. In this case,
The Schuler-tuned loop is a closed loop circuit
the Coriolis correction also reverses. It now
between the accelerometer, velocity integrator,
manufactures a west acceleration that exactly
and stable element. It prevents large velocity and
voids the east acceleration.
distance errors caused by misalignment of the
In both of the above cases, the Coriolis
stable element. Figure 7-49 shows a simplified
correction supplies an artificial signal of accelera-
Schuler-tuned loop with the platform aligned.
tion to the right side of the actual track. This is
The output of the accelerometer is integrated
the nature of the Coriolis correction, regardless
to provide a velocity signal. The velocity signal
of the direction of travel in the Northern
is multiplied by 1/R where R equals the earth's
Hemisphere. Look at figure 7-48. When the track
radius. This operation derives an angular velocity
is east along a latitude line, centripetal correction
about the earth's surface, V/R. The system uses
offsets the increment of north acceleration
