You are right that the central part of the rotor is stalled. There may some confusion over terminology here. So here goes.. If we ignore geometric blade twist for now and look at the rotational velocity of an element and the inflow to the rotor, these factors combine to give the angle of attack, for a given blade angle. If, for simplicity, we consider a uniform inflow over the disk, then we need only look at the effect of the rotational velocity along the blade. At the hub centre it is zero and increases linearly to the tip. With the net inflow coming from beneath the rotor and the rotor speed horizontal, the resultant airflow onto the blade element is angled from below. As the blade element velocity increases along the radius, the angle of attack reduces. This means that as the centre region is stalled, as we move along the radius, the angle of attack reduces. As you pass through the mid sections of the blade the angle of attack allows the total reaction to be tilted forward driving the rotor. As you close on the tip, the blade element velocity increasing, the total reaction moves past vertical and therefore acts to slow the rotor.
Hope that makes it a little clearer. As for the negative comments above, well there is no such thing as a bad question. As for my knowledge of helicopter aerodynamics, well, I think I can safely say that I have read a one or two books on the subject. As for the suggested title, it is okay but does muddle a lot of different theories together and in some instances makes some serious mistakes. Look for any of the ‘Helicopter Aerodynamics’ books by Ray Prouty or ‘The Helicopter’ by John Fay. (If you’ve got good maths knowledge, at least A-Level, try ‘Fundamentals of Helicopter Aerodynamics’ by S.J. Newman , ‘Aerodynamics of the Helicopter’ by Gessow and Myers, its old but still good or ‘Helicopter Performance, Stability and Control’ also by Prouty).
Good question about co-axials. With co-axial rotors the yaw is via differential collective, increasing on one and decreasing on the other to maintain constant thrust but have different rotor torques producing yaw. In autorotation, with power off, the aerodynamics described above come into play. The yaw control is adjusted for the power on condition where the lift force on a blade section is tilted backwards and the torque has to overcome this and the other sources of drag. In autorotation, the lift force is tilted forwards, thus the torque is now coming from the lift. This means the yawing moment, via the pedals, is set for power on whereas in autorotation where the lift forces have changed direction, results in a control reversal. Does that make any sense to you?
Steve