What is Gyro Drift?

Answer 1

^ Gyroscopic precession is how INS, at least the old type, works. But that explains nothing about how it fails.

In a perfect world where physicists could buy light inextensible strings and friction free bearings there wouldn't be any gyro drift. But in the real world the gyros never quite manage to move exactly as much as they should when the platform moves, there's a little bit of bearing friction and that gives you a bit of error. There's also just small imperfections in the way the gyros are read, you can't get perfect positional readings from the electronics that monitor them. Even optical inertial platforms, ring laser gyros, have small electronic errors which can either cancel or accumulate over time.

RLGs work by differencing standing waves in optical paths arranged as a ring, actually more like a triangle but it makes no difference. Anyway, they are very very expensive but rugged and reliable and great for missiles. The ones we used drifted a lot faster than mechanical gyros but they worked more often.

Answer 2

Simply, it is the tendency of a gyroscope to precess (drift) from its start position. It will cause your attitude indicator and any other gyro slaved instrument to slowly display erroneous information. That is what the re-cage function is for.

Answer 3

the flightsim site just says it happens not why!
It is really Gyroscopic precession




Gyroscopic precession is a phenomenon occurring in rotating bodies in which an applied force is manifested 90 degrees later in the direction of rotation from where the force was applied.

Although precession is not a dominant force in rotary-wing aerodynamics, it must be reckoned with because turning rotor systems exhibit some of the characteristics of a gyro. The graphic shows how precession affects the rotor disk when force is applied at a given point:


A downward force applied to the disk at point A results in a downward change in disk attitude at point B, and an upward force applied at Point C results in an upward change in disk attitude at point D.



Forces applied to a spinning rotor disk by control input or by wind gusts will react as follows:

This behavior explains some of the fundamental effects occurring during various helicopter maneuvers.

For example;

The helicopter behaves differently when rolling into a right turn than when rolling into a left turn.
During the roll into a left turn, the pilot will have to correct for a nose down tendency in order to maintain altitude. This correction is required because precession causes a nose down tendency and because the tilted disk produces less vertical lift to counteract gravity.
Conversely, during the roll into a right turn, precession will cause a nose up tendency while the tilted disk will produce less vertical lift.

Pilot input required to maintain altitude is significantly different during a right turn than during a left turn, because gyroscopic precession acts in opposite directions for each.

Answer 4

http://www.flightsimaviation.com/faq_9_q1_What_is_gyro_drift.html