Tourist - The increase in Nr is due to the higher ROD
Not sure that's strictly true (although I agree that a higher ROD, and more airflow through the disc would increase rpm), I think it's more the higher disc loading, impact on coning angle, and conservation of angular momentum. In order to contain the higher NR collective pitch is increased. The inner 'blade stall' area will grow outwards, the outer blade 'drag' area will move inwards slightly, the overall autorotative force section will diminish enough that NR can be maintained. Even though the outer 'drag' area of the blade has grown it is still producing more lift too, along with the increased lift in the 'autorotative force' section. So overall result - same RPM, more lift.
[IMG]
I guess the apparent resultant reduction in ROD airflow further confuses things, moving the autorotative force section more inboard...?
All a stab in the dark, but it makes some sense in correlating with what has apparently been shown. I'm keen to go and try now at different weights...