[CSpaced]

Jungmeister,

On a helicopter, when a gyro is set to rate mode, as the tail turns the gyro increases or decreases the tail rotor throw to stop the tail movement.

When the gyro is set to heading hold, it will do the same thing only it will keep giving the throw until the tail is back to where it started.

Using it in either mode on a rudder I'm not entirely sure how it would affect performance on take off, but I have heard of people using gyro's on their rudders in the past. I hope this helps a little.