For all developers: how the magnetical compass works (because often done wrong)

[CharlieFox00]

Hello, I posted an explanation of this in another thread and it should apply here:

@CharlieFox00

If it helps, we can think of the compass and directional gyro as fairly fixed in space (disregarding compass acceleration/dip errors and DG precession) and the airplane moves around them.

The difference is you’re looking at the horizontally-mounted compass from behind. If we mounted the DG horizontally (some older DGs are mounted this way) and looked at it from the butt-end, it would behave the same way (appear to be moving opposite). To prove this is an illusion of perspective, imagine reading the DG from the bottom lubber line, but marked with the reciprocal headings so it’s technically showing the correct heading at the bottom lubber line. When you make a turn it would appear to be moving opposite the turn because we’re viewing it from the opposite end, but it’s still correct, like the compass.

To follow up: The gyro of the DG is still mounted in the horizontal axis, but the card we read is geared and flipped vertically so we see it as a top-down view. However, the whiskey compass, as the OP says, is still mounted horizontally and we’re looking at it from the rear-end, so the adjacent numbers appear in reverse orientation.

Is not the seagoing compass viewable from above so you can see the far lubber line and not just the back end? Now imagine only looking at it from the back end, but mark the numbers with the reciprocals of the headings.