This non-technical paper may be of interest;
Recent Development of Rotorcraft Configuration
Mart,
The above paper relates to our previous discussion on this thread.
Going a little deeper into the subject,
this page has information on Sikorsky's Variable Diameter Tilt Rotor.
In the past, link #2 provided the article for free. Currently, there are numerous links to it on Goggle, but all, or most, want money.
Dave