CJ Eliassen thanks. The gearbox and tail rotor do consume a small amount of the energy, which would have otherwise gone toward a slower autorotation.
At very low differential collective settings the greater drag should be in the CW turning rotor (driven rotor) and the yaw will be CW, as desired. This very low differential collective probably has little yaw authority.
The problem appears to come about when a greater amount of differential collective is applied. In this situation, the stall region on the CCW turning rotor (driving rotor) will probable be so large that it will consume all the torque that its driving region is producing. The implication is that the yaw may now reverse and be CCW.
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The first quote below seems to support the above. The second quote give no reason as to how the problem was solved.
In an old thread, CRAN said ~
"Dr. Gareth Padfield picked the Russian engineers up on this point [weak yaw control during autorotation] at the conference and they sheepishly said that ...'yes, it is a problem, and we achieve direction control in autorotation with the moveable fins...' or words to that effect."
"The problem of coaxial-rotor helicopters' directional stability in autorotation has been solved in full." ~ Quote from Kamov web page. They do not say how it has been solved.
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Assuming that the above problem is correct, the following web page is submitted as a solution to this problem. It is submitted for;
1/ critique by the
and
2/ to put this idea into the public domain and thereby deter its patent.
Rotor - Disk - Autorotation Yaw w/ Separate Root and Tip Control