What principle does the heading indicator work off of?

The correct principle that the heading indicator works off of is rigidity in space. This principle refers to the ability of a gyroscope to maintain its orientation regardless of the movements of the mount or the aircraft. In the case of the heading indicator, a spinning gyroscope remains fixed in its orientation relative to inertial space. As the aircraft turns, the gyroscope's axis of rotation stays constant, allowing the heading indicator to show the aircraft's direction relative to true north or magnetic north, depending on the type of heading indicator used.

The reliance on rigidity in space is fundamental to the operation of gyroscopic instruments. As the aircraft changes attitude, the heading indicator displays how much the aircraft has turned from its original heading, providing essential information to the pilot during flight, particularly in instrument conditions when visual cues are limited. Understanding this principle is crucial for interpreting how the heading indicator functions and the navigational information it provides.