That was Siegfried Hoffman, not Karl Zimmerman. Just watched it three more times and am still wondering about the cause, as the rotor shows no movement toward a recovery, so I’ve always thought about other possible causes.
As to whether the roll rate or pitch rate was a problem, perhaps a few observations. We rented a BO-105 prior to the UTTAS fly-off with Boeing, to see what the competition rotor was like-advantages & shortcomings. It was what we expected in terms of the couplings, but just stronger, because of the higher effective blade flapping offset in the rigid rotor. Same counterclockwise rotation. So, get up to speed and pull back on the cyclic and the smart pitch rate is accompanied by a couple right roll…..same as our articulated rotors in say the S-67 but less in magnitude because of the lower odds set in the articulated rotor. Push forward on the cyclic and you get left roll. Put in pure right roll and you get nose down and the opposite with left roll. Gyroscopics at work. The problem with this flight path on the video is there does not appear to be any rotor movement toward correcting the flight path, and especially given the background of that pilot ( had the honor of flying a B-117 with him ) I’ve always been suspicious of some other factor at work here.
There was some comment re collective in maneuvering flight. NASA issued a contract to Sikorsky re investigating the maneuverability of the S-67 with and without wings and the effects on achievable max load factor. One of the interesting results was that independent of wings on/off, we achieved the max load factor ( talking about up and away speeds, beyond bucket speed,not hover ) at 70% collective. At higher collective, rotor stall effects were in play, and at lower collective, rotor thrust was in play. By the way, we used that approach doing all the structural demonstrations on the UH-60 and SH-60, with the concurrence of the military monitoring entities.