Heading Hold would imply that the heading of an aircraft would not change, ever. For instance, Try this: Fly your heli with the tail pointing in one direction, say north, and then switch to “heading hold” and then land. Now pick the heli up and turn the heli until it points east and then spool up the rotor. The heli would immediately rotate back to pointing north, if it were “heading hold”. Obviously with the gyros we are using that doesn’t happen so they are rate gyros.
The gyro holds the heading that you tell it to. If you land, turn the heli 90 degrees, and take off again it wont move because you didn’t move the stick to tell it to, it holds the tail where it is until you tell it otherwise. Go try to do a circuit in heading hold without touching the tail....you'll see that the gyro holds the heading that you told it to.
Heading Hold would imply that the heading of an aircraft would not change, ever
No, heading hold refers to a gyro that sees a movement, stops the tail from turning anymore, and brings it back to where it was. This is exactly what the Heading Hold gyros of today do. A normal rate gyro simply stops the unwanted movement, it does not bring the tail black. A HH gyro holds the heading until told differently by the tail rotor stick position.
Colin