Figure 7-46.-Platform on great circle route.
acceleration has taken place to cause a speed
coincidence of earth axis and pole implies earth
change. Thus, the centripetal correction circuit
dynamics in the phenomenon, but actually this
must simultaneously plant positive accelerations
is not a factor. Assume we shift the coordinate
in one axis if it plants negative accelerations in
systems to place the pole at New York. Now use
the other. Therefore, when canceling some of the
this city as the focal point of one accelerometer
north or south velocity, the system must add a
axis of an inertial navigator circling the city. The
sufficient increment of east or west acceleration.
accelerometer sensitive to this axis will report
This allows the reported total speed to remain
acceleration toward the city.
unchanged, while the reported direction of flight
In a spherical coordinate system, any linear
vehicle acceleration initially affecting both
bends toward the equator. As shown in figure
7-46, after a single north-east acceleration has
accelerometers will result in the vehicle NEVER
occurred, the north vector becomes progressively
reaching the pole. The vehicle follows a great
shorter. Note that the resultant speed vector is
circle track that first approaches one of the poles.
always of the same size.
It will fly due east or west for a brief period, and
In summary, you can see that an east or west
then depart the pole, as shown in figure 7-46.
acceleration in either hemisphere contains a
Although the velocity resulting from any given
hidden element of acceleration toward the
acceleration is initially computed correctly with
equator. Also, you can say centripetal correction
respect to space, the direction of the speed must
simply acts to reveal this element. When aircraft
be constantly altered. This is necessary if the
velocity is not due north or due south, in the
navigational system is to accurately report a great
Northern Hemisphere the centripetal correction
circle course that crosses both latitude and
manufactures a south velocity component. In the
longitude. On such a course, the aircraft does not
Southern Hemisphere, it manufactures a north
turn as it does following a line of latitude.
velocity component.
Therefore, it does not generate uniformly false
north acceleration signals. The centripetal
CORIOLIS CORRECTION. --As mentioned
correction circuit does, however, continue to plant
before, the scope of the centripetal correction
signals of acceleration toward the equator. This
makes no allowance for earth dynamics. Since the
has the effect of altering the reported speed (the
earth rotates toward the east, all points on the
result of velocity along both axes). No actual
7-38