Ray Prouty
If you read Prouty's "More Helicopter Aerodynamics" he has a chapter on coax and synchrocopter configurations. He mentions the S69 and how the rudder was swept aft, like a c172. In autorotation, the airflow was up the hinge line. Prouty makes some comment about how that would be a lesson learned for the next time around. If I can find the Prouty book I could post his statement more accurately, maybe somebody else has it.
-- IFMU