I think the russian shark design was pretty efficient in
some regions of flight but not in all.
Big long bendy blades with not that much hinge offset.(compared to the ABC)
As forward speed increased flapping did likewise. Add some g forces to it and clearances got smaller. A low speed heavy lifter great but a high speed attack helicopter no.
A few years back I sat in a similar rotored aircraft during runup. It had a video camera setup that looked down one of the blades while it rotated. (The blade was fixed in the line of site and the horizon spun around)
The big worry was that these blades would meet each other inflight at the higher end of the envelope. Apparently that's the speculation on what happened to the russian general in the shark.
