Vortex Ring State and Windmill Brake State nicely explained
A good description of all this, and some very useful diagrams, are found in Wayne Johnson's book "Helicopter Theory", page 99 section 3-1.2.2 for Vortex Ring State, and on page 101 section 3-1.2.4 for Windmill Brake State. As I recall, at least some of this clear explanation originally derives from Prof. Norm Ham's excellent work (a colleague of Prouty).... (when both Wayne and Mike Scully were a graduate students of Norm's, back at MIT Course 16, in the late 60s and early 70s).