The faster the prop spins on the nose of the plane, the more centrifugal force, and thus more stability. If the plane is very light weight then he would need less pitch to keep the plane up and would be able to keep the blades almost flat, resulting in more rpm's and thus more stability. The "4d" pilot can thus make it look like a long controlled hover. The pilot can also fly the plane back a bit and then fly down again to adjust the plane straight during the temporary reverse and foward flight. It is not really possible at this time to control a planes surfaces during face down hovers because during those hovers there is a vacum aroung the tail. I would suggest for backwards flight though by trying to think of the plane as literally being already flying foward in the other direction except the throttleand rudder are reversed.

Hope this helps.[8D]