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It appears that Bygrave also came up with the idea for the "slaved gyro"
which is in common use in almost all planes with more than about six
seats. It consists of a compass element mounted out by the wing tip,
away from ferrous metals and electrical influences, connected to the
directional gyro (DG). In simpler instruments, the DG is free running
and precesses over time due to friction in the bearings. In addition to
this actual precession there is "apparent precession" due to the plane
moving over the surface of the earth. In addition, there is "earth
transport precession" caused by the earth rotating away from the
original plane of reference. So in an airplane sitting on the ground
with a frictionless perfect gyro the heading will appear to drift at a
rate of 15.04 degrees per hour times the sine of the latitude just like
a Foucault pendulum since they both maintain their orientations in
inertial space. So pilots periodically read the compass in the cockpit
and reset the DG. A compass in a plane can only be read in straight and
level unaccelerated flight. If the airplane is banked or if it speeds up
or slows down the compass card is moved away from horizontal and is then
caused to turn by the vertical component of the earth's magnetic field
giving erroneous readings. The slaved gyro's remote compass constantly
resets the DG while in level flight but is disconnected during turns and
accelerations and the gyroscope maintains its direction during those
short periods.

gl






douglas.denny@btopenworld.com wrote:
> source:
> The Journal of Navigation‎ - Page 136
> Institute of Navigation (Great Britain) - 1955
> article:
> "Automatic Dead Reckoning and Navigation Instruments for Aircraft" by H.C. Pritchard
> extract:
> ==============
>
> In fact it was published in 1956 in Vol. IX  of 'The Journal Of the Institute of Navigation'
>
> Here is the first page.
>
> Douglas Denny.
> Chichester.  England.
> >
>
>
> ------------------------------------------------------------------------
>


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