DiggyDog, A while ago, I tried to replicate the same effect you want using the physic vehicle example.
Here it is - http://dl.dropbox.com/u/51270524/Physics - vehicle.capx
But unfortunately I couldnt do it, Whilst in the air things was not right, You'll see.
Maybe Kyatric could take a look at my test, and figure out what went wrong..
@Kyatric, Could you tell me that i was atleast close? ;D