the point Im making is that if you use the acceleration script that is shown in the Airwolf addon, you could modle a Osprey moving forwards at high speed without tilting the whole helicopter. I wouldn't suggest you moddle it with the rotars facing full forwards so that it would opperate like a plane, but half-forwards so it looks like it should be constantly moving forwards.
Basically, you create a V-22 in the helicopter class with the rotars in the full-upright hovering position. It operates like a normal helicopter in every way. Then, using the action menu, you can activate a script that accelerates the Osprey forwards and keeps it at a constant speed. At the same time, it models the rotars tilting to a 45 degree angle.
Try out the Airwolf Helicopter addon and you'll see what i mean, you activate the "turbo" function through the action menu and it accelerates the chopper forward and keeps it moving at about 500 km/h. It handles almost like a plane when you do that.
In short, don't try and make a plane into a helicopter; try and make a helicopter into a plane.