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From what I've researched, a gyro compass is usually calibrated with with reference to a magnetic compass. Once you've engaged the gimbal locks, and start to rotate the compass to a magnetic heading; will it automatically compensate for true heading or will you not even reference a magnetic compass when calibrating?

Or are there cards used to indicate what's your position from true north, based on your magnetic indication?

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The directional gyro (DG) does not know about heading. Its gyroscope will hold its position (e.g. the heading you set from the magnetic compass) in space. The plane is turning "around it", but DG is holding its position, so you can read the heading from the scale fixed to the airplane while the gyroscope holds its position in space. Only friction and other forces (acceleration forced upon the aircraft) force the gyroscope to wander from its position. E.g. the gyro shows a magnetic heading if set using a magnetic compass and it shows a true heading if set using a GPS (or some map feature like a road with a heading visible on a map).

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    $\begingroup$ Some DG's are slaved to the magnetic compass, might be good to talk about it. And welcome to av.se :) $\endgroup$ – ymb1 May 3 '17 at 19:17
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A gyro compass utilizes physical forces, including the procession of the earth to determine direction. This provides a more useful north than a magnetic compass for navigational purposes.

A directional gyro can be slaved to a compass, but it is distinctly different from a gyro compass.

To be clear, a gyro compass does not use magnetic forces, and therefore is useful on boats where a steel structure might influence a magnetic based reading. https://en.wikipedia.org/wiki/Gyrocompass

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  • $\begingroup$ Aircraft are too fast for the auto-alignment of gyrocompass to work, so they don't have them. Inertial navigation systems do use the auto-alignment when powered up at the gate for initialization though (which is why it usually takes a couple of minutes). $\endgroup$ – Jan Hudec May 3 '17 at 21:48

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