I think you're asking a question about rotor rpm in autorotation. If you review your books about autorotation you'll see that the rpm is governed by the relationship between the driving and the driven regions of the rotor disk. I know nothing about R-22's but generally in a properly rigged aircraft the maximum rpm will be obtained right around the max r/c airspeed (correspond to the minimum rate of descent airspeed for autorotation), as you slow below that airspeed rpm will decrease, as you go faster rpm will decrease. The rpm should stay in the green unless you exceed the max airspeed for autorotation.
Specific aircraft performance and limitations can vary significantly but generally most helicopters fall in these parameters.
If that wasn't your question, disregard.