AERONAUTICAL INSTRUMENTATION ****MODULE4
Thus, to an observer on the earth having no sense of the earth's rotation, the gyroscope would appear to veer
or drift, called as apparent drift.
b) Real Drift
Red drift results from imperfections in a gyroscope such as bearing friction and gimbal unbalance. Such
imperfections cause unwanted precession which can only be minimized by applying precision engineering
techniques to the design and construction.
c) Transport wander
Consider a horizontal-axis gyroscope which is set up initially at the North Pole, with its input axis aligned
with that of the earth, and then it will exhibit an apparent drift equal to we. Assume now that the gyroscope
is transported to lower latitude, and with its input axis aligned with the local vertical component of we.
During the period of transport, it will appear to an observer on the earth that the spin axis of the gyroscope
has tilted in a vertical plane, until at the new latitude it appears to be in the position, termed as transport
Apparent tilt, or transport wander would also be observed if, during transport, the input axis were aligned
with either a local N-S component, or a local E-W component of we.
Transport wander will appear simultaneously with drift, and so for a complete rotation of the earth, the
gyroscope as a whole would appear to make a conical movement.
The limitations of a displacement gyroscope are:
a) Gimbal Lock
This occurs when the gimbal orientation is such that the spin axis becomes coincident with one or other of
the axes of freedom which serve as attitude displacement references. Consider example, the case of the spin
axis of the vertical-axis gyroscope becoming coincident with the ZZ1, axis of the outer gimbal ring.
This means that the gyroscope would lose its spin axis, and since the rotor plane of spin would be at 90⁰ to
the ZZ1 axis but in the same plane as displacements in roll, then the stable roll attitude reference would also
If, in this 'locked' condition of the gimbal system the gyroscope as a whole were to be turned, then the forces
acting on the gimbal system would cause the system to precess or topple.
Chetan Ghatage, Asst. Prof
Department of EIE, RNSIT