Originally Posted by
IFMU
Yep. 252 kts level flight for the X2 and something like 262 in a shallow dive.
There is far more to a full flight spectrum than straight and level flight, even high speed flight, nor is it a forgone conclusion that high speed flight is the worst regime from a vibration control standpoint. From released videos and statements, it appears the S-97 has performed a wider variety of maneuvers, Nz levels, etc. than the X-2 demonstrator did, even without yet hitting its top line speed goal. Sikorsky has been publicly pretty mum on what is has learned about vibration control on that aircraft, so it's hard to project much to SB>1.
However, that said, if vibrations on a rigid rotor can be significant, and I believe math and available evidence says they can be, then an AVC system has to be suitably powerful. An active system capable of (nearly) canceling large vibrations is technically capable of nearly doubling them with incorrect system operation. It might not need to be strictly flight critical, but it could well be mission critical.