Quote:
Originally posted by Ari Hi Darren_UK,
After bunny hopping around terra firma, I started hovering and found it challenging close to the ground and wonderfully smooth at 3 to 10 feet.
Regards
Ari |
You probably know this already, but here it is again for the benefit of anyone else:
There's something called ground effect in hovering (so much so that it even has its own acronyms in full-sized helis: HIGE and HOGE: Hovering In/Out of Ground Effect)
At altitude, the rotor downwash goes down through the rotors with nothing but air under the heli to get in the way.
Near the ground, the rotor downwash hits the ground and forms a cushion of air. The helicopter wants to fall off the cushion of air, hence is more difficult to control when hovering in ground effect. The more height above the ground, the less ground effect - I think this disappears to all intents and purposes around 3 feet in a model heli and around 10 feet (might be wrong though) in a full-sized heli.
This ground effect also explains why you can raise the collective to lift off into the hover, and then if the collective is kept in the one place, the heli will rise to a given height and then remain at that height. To go higher, more up collective is needed.
This is an important consideration when settling back down onto the ground from a hover: Progressive and continuous down-collective movement is required to settle back down onto the ground to "get through" the increasing ground effect.
(As an aside: The "normal" hovering height, in both hovering and hover-taxying, is around 5 feet - high enough not to strike the ground, low enough to be able to settle with minimal impact in the event of an engine failure in the hover. When hovering backwards, a hover height of 10 feet is performed to remove the possibility of a tail fin strike)