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I still think the Fairey Rotodyne could fulfill a category somewhere between standard helicopters and the highly technical and exotic Boeing V-22 Osprey
The Fairey Rotodyne is fairly simple technology , it is a heavy lifter , reasonably fast , and if you are not flying it downtown the noise would not matter so much.
I have the David Gibbings book on the Rotodyne and it has plenty of info , pictures and mechanical component drawings etc.
Post WW2 we had a surplus of aircraft manufacturers in a world that needed farm tractors , cars , and washing machines. That is why a lot of those good projects were set aside.
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