What does tripping do, actually? It shifts someone's feet so that their center of gravity is no longer over their feet, thus causing them to fall over.
Center of gravity does not affect your ability to float. If you 'trip' a magically flying creature, it's feet will be yanked a foot or so to the side, and it will laugh at you for wasting an action. If you 'trip' a winged flying creature, I'd say that you manage to disrupt its motion for one round, so that it stalls, but doesn't fall. But it will have to spend a move action next round to recover.