John,
Re: Autorotation;
From; Department of the Army Historical Summary - FY 1976, on the Coaxial - Sikorsky ~ S-69 (XH-59) ABC
"Flight testing of the XH-59, advancing blade aircraft, resumed during the year. The tests confirmed certain advantages and shortcomings of the advancing blade concept, which is a coaxial counterrotating, hinge-less rotor system. The aircraft control system was quite responsive, noise levels were low, retreating blade stall was virtually eliminated, and hover performance was improved by the absence of a tail rotor. Structural loads in the rotor and control system ranged from low to moderate and indicated potential for substantial weight reduction. Weak directional control power in partial power descents and autorotation was observed. In future testing, improvements in autorotation directional control at low collective settings and high flare angles will be emphasized."
In autorotation, it will be interesting to see how the; Driven, Driving and Stall Regions play out, if the blade profile on above posting #102 is used.
Dave