Opps!
Post #22 on http://www.pprune.org/forums/showthr...=252205&page=2 and most of the following posts on that thread should have been posted on this thread. 
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It was mentioned by IMFU, in a different thread, that Sikorsky's new X2 coaxial ABC will have multiple-speed rotors, as did its predecessor, the XH-59A ABC.
However, the possibility of using single-speed, low-rpm rotors with wide chord blades (large
solidity ratio) for tomorrow's high speed rotorcraft appears to have significant advantages.
Two bits of information have come to light while digging deeper into this subject.
1/ A cursory review of the technical papers on the XH-59A ABC show that the 'solidity ratio' is much used in the evaluation of many variables. However, I cannot find any place where the solidity ratio, itself, was evaluated as a variable.
2/ Stepniewski considers the rpm of the rotors as a variable in his conceptual Intermeshing ABC, but it appears that this evaluation was only to pick the optimum single-speed RPM.
Can anyone suggest one or more potentially viable reasons for using multiple-speed main rotors?
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Another bit of uncovered trivia, from the Spring 2001 AHS publication of Vertiflite;
"
I [Glidden Doman]
committed office and shop space to him [Anton Flettner
".. at a relatively advanced age"]
for the construction of a unique intermesher with no hinges. When the project did not go ahead I hired his top engineer and lost contact."
Apparently, Kellett was not the only person at that time to consider an intermeshing configuration with rigid rotors.
Dave