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Brief description of the issue:
Direction Gyro Drift/Precession not working as it should
Provide Screenshot(s)/video(s) of the issue encountered:
N/A
Detailed steps to reproduce the issue encountered:
Load a flight:: Default Cessna 172, any place on earth, static on the ground, engine running & generator on so that the Directional Gyro is working. Use any variable watch program (Simvatwatcher, simconnect, axis & ohs, whatever). Monitor and log values for PLANE_HEADING_DEGREES_GYRO and GYRO_DRIFT_ERROR.
In reality drift/precession of the DG is comprised of several components:
- Electro-Mechanical Error - gives a cumulative build-up of error, also called ‘Real precession’. Modern systems typically have 1 degree per hour.
- Apparent precession - due to rotation of the earth. Is 0 at the equator, and 15 degrees/hr at the poles, magnitude is sin(latitude). To the right on North latitude, left on South latitudes.
- Earth transport precession - due to physically moving aircraft around the world. Is equal to approximately 1 degree for every meridian crossed.
So - it must be clear that a static aircraft at latitude 63°N would have the following:
- Real precession - random but up to 1°/hr (+ or -)
- Apparent precession: sin(63)*15 = 13.3°/hr (+)
- Transport precession: None, because aircraft is static.
Now, on logging the Sim data, we find that:
- GYRO_DRIFT_ERROR is very large and constant (typically up to 15° hr, positive and negative).
- The total PLANE_HEADING_DEGREES_GYRO error is also large, but not the same as GYRO-DRIFT_ERROR
- If we correct the PLANE_HEADING_DEGREES_GYRO with the GYRO_DRIFT_ERROR (i.e. we remove the GYRO_DRIFT_ERROR from the PLANE_HEADING_DEGREES_GYRO) , a very small and also constant value remains: typically in the order of 1 - 1.5°/hr.
- Further, it seems that for identical aircraft at identical positions, the GYRO_DRIFT_ERROR is different every session, leading to suspect it is a randomized value.
So we might conclude that GYRO_DRIFT_ERROR is actually the larger Apparent precession, and another smaller error (Real Precession) is implemented on the PLANE_HEADING_DEGREES_GYRO.
However, there is a problem with that. If GYRO_DRIFT_ERROR is The Apparent Precession, it must always have a positive value on the Northern Hemisphere. And it does not. Values of -10 and +14 have been observed at latitudes 51N and 37N respectively.
Alternatively, if the GYRO_DRIFT_ERROR is the Real Precession, it is a order of magnitude 10 too high.
It does not seem to make sense.
I am not aware of any other factors affecting gyro drift.
PC specs and/or peripheral set up if relevant:
Not relevant
Build Version # when you first started experiencing this issue:
SU11
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