Autorotational question

[Shenanigan]

Does anyone know what specific effects an increase or decrease in Rotor RPM during a descent has on the touchdown at the end?

Obviously it is known that if a full down collective steady state autorotation results in a increased rotor RPM than there will be an increase in rate of descent. This can be compensated for by increasing collective thus reducing rate of descent and increasing glide however at the touchdown point there will be a negative effect as there is now a smaller margin of collective left for cushion.

So if you found yourself in the situation where collective is needed to maintain 100% RPMR, and from my experience it is not uncommon is it more beneficial to let it rise some (10% or so) and convert that energy at the bottom? Or to use than energy during the descent despite having less energy for the cushion?


Disclaimer

I am not a student looking for an explanation of how to perform an autorotation. I think we can all appreciate that if you follow the parameters of RPM and airspeed set forth by the manufacturer you will achieve a successful autorotation. It is an aerodynamics question asked so i can better understand the relationship between rotor rpm vs angle of attack and why certain combinations can result in more lift for an equivalent torque as seen in variable rotor systems. And what these effects have in autorotation.

I am not talking about overspeeding the rotor until it is damaged. While I'm sure it is theoretically possible in autorotation to keep increasing the RPM until it falls off it has been my experience that the rotor RPM will stabilize even if slightly above 100% and the place where it stabilizes will normally be in the acceptable range except in extreme cases of DA and GWT. For this question assume the increase in rpm is within the acceptable range of the rotor.

I am not talking about practice autos where you may want to have a tighter parameter to reduce long term damage. I'm talking about an actual emergency where survival is a higher priority than long term durability of components.


I'm sure we have all heard from someone at some point in time that they believe that a high Rotor RPM is beneficial when it comes time for a touchdown. So is it more beneficial to arrive at your cushion with more potential energy but a greater rate of descent or to arrive with a lower rate of descent but less potential energy for cushion? Why?