Jeep
Those who will adapt most readily to tiltrotors are dual rated pilots, followed very closely by helicopter-only pilots. Airplane-only pilots on the other hand, would be a distant third, as they would have to learn rotorcraft basics (hovering skills etc.) while helicopter-only pilots will have no difficulty performing enroute fixed-wing tasks.
The main advantage of having rotorcraft pilots with at least some f-w experience is stall recognition and recovery ability when nacelles are in the horizontal position. There may be times during slow speed maneuvering in the airplane mode that not being able to recognize an imminent stall could spell disaster. There are a few negative-transfer habits that come from helicopter flying (stall recognition being the only one of a potentially critical nature), but nothing that good training and experience will not overcome.
The FAA in Part 61 (Certification of Pilots and Flt Instructors) has already issued powered-lift requirements, and I believe Part 141 is complete now also. Requirements for Part 142 still need to be determined. The Bell training facility will be operating under Part 142, and for entry into the program they are requiring pilots to be in possession of three ratings: helicopter, airplane, and an instrument rating in either helicopters or airplanes. I don’t know if they have determined whether or not a multi-engine rating will be req’d, and I’m not sure whether the category ratings (airplane & rotorcraft) will both have to be commensurate with the rating sought (i.e., is it OK to have a commercial helicopter license with only a private airplane rating when seeking a commercial tiltrotor rating).
As far as flying the aircraft itself: when you are in the helicopter mode, it flies just like a helicopter; when you’re in the airplane mode, it feels just like a twin-engine airplane. And although I can’t claim to be an expert, the transition phase feels suprisingly natural, and something that can be adapted to without much difficulty. I must say that in a hover the XV-15 felt much more stable than any helicopter I’ve ever flown. There is virtually no weather vaning tendency at all, perhaps a characteristic of all tandem rotor systems in general. You can hardly tell which way the wind is coming from – you set the cyclic and the a/c just sits there like a rock. As far as the airplane characteristics, the stall is very benign with no radical tendencies. Standard recovery procedures of lowering the nose and adding power apply, although if you are in an intermediate mode (i.e. 60 degrees as we practiced it) the more efficient recovery technique is to simply push the nacelle switch forward and fly out of it.