Thanks all. I am just trying to understand how the disc continues to be driven without without negative collective pitch. And please excuse my ignorance of the physics going on here. I have limited hours in an R22 but concerned at the moment with the mathematical properties of rotors. I have read about the driven and driving sections of the blades but can't quite understand how the energy is imparted to the in-plane axis; rather than the lift axis which, given positive pitch, (therefore a lifting angle of incidence to the airstream) will control the rate of descent.
The weight of the helicopter will pull it down through the airstream and this flow through the disc will impart energy to the blades according to their pitch - and if positive or "fine" will no doubt generate enough lift to control the rate of descent.
I am trying to see it in terms of a propeller pulled through a fluid. A positive pitch (in this instance) will not spin faster (in a given direction) but rather slow and reverse, but a negative pitch will "spin-up" accelerating in the direction the propeller is already turning in.