Dave,
Have You ever consider idea of Variable Solidity Rotor, ... instead of Variable Diameter Rotor ?
Mirek,
No meaningful consideration about variable solidity.
My closest consideration has been that of high solidity and variable tip speed, such as;
DESIGN: UniCopter ~ Rotor - Disk - Large Chord & Low Tip Speed.
We are both posting on the new thread 'A New Rotorcraft Called a Tiltplane' on another rotarywing forum. I will post a response to Variable Solidity there.
Dave