It's been decades since I've flown and with too much time on my hands I took an interest in this V-22 thing. This is the first source of real technical debate I've found. I've spent over a hour skimming though these threads, and learned others have lots of time too!
I found this article by a V-22 pilot of interest:
Flying the V-22 | Vertical Magazine - The Pulse of the Helicopter Industry
I apologize if you all have discussed this before, but he mentions something odd:
"At this point, the Osprey is cruising along essentially as a twin-engine turboprop airplane, flying at the same speeds, altitudes and flight rules as traditional turboprops. The primary difference is the lack of ability to fly with one proprotor feathered, (which is one of the major training obstacles of multi-engine airplane transitions). Should a proprotor gearbox fail in airplane mode, causing the related proprotor to stop, the only recourse is to shutdown both engines and conduct a power-off glide and emergency landing; the adverse yaw is just too great for the rudders to overcome, leaving few options."
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That would seem to make long flights over water dangerous. A problem with just one gearbox requires that both engines shut down?