I think he is asking how to stop the pitch and roll of the flying unit matching the terrain it is on. If you look at a unit like a siege tank climbing a hill, it will rotate with the terrain instead of embedding its front into the hill or having the front float in mid-air when going downhill. I recall some sampling point field in the Arts section governing this behaviour.
I have problems recalling if flying units actually do this, although the flying machine does ring a bell.