So, at this point 39 people have viewed this, and not one has any problem with the fact that Gyroscopic HI/DI will not work on the flat earth, yet in reality they work just fine?
I have heard Dave Murphy drone on endlessly about how he, quite mistakenly as a matter of fact, believes that a gyroscopic AI should not work on a spherical earth and proudly presents that as a definitive proof that the earth is not spherical.
Well, here is my attempt to resolve this paradox. We all know gyroscopes and magnetic compasses work. They have for hundreds of years in the case of gyroscopes and thousands of years in the case of magnetic compasses. They have also worked in agreement, within the error of the magnet poles WRT the axial poles, in aircraft for decades and continue to do so.
The only sound and sensible conclusion one can come to is, the earth is not flat.
This document details how aircraft instrumentation works. The discussion on gyroscopes starts on page 52. Attitude Indicators (AI) begins on page 56. Heading Indicators/Direction Indicators (HI/DI) are mentioned on page 58.