I can recall seeing the downward deflecting retreating side blade tip of the upper rotor passing very close to the upward deflecting advancing side blade tip of the lower rotor. While the X2 blades are fairly short, this problem will get more difficult as the blades get longer.
Precisely. Take note, sikorsky has almost completely abandoned the marketing of a HGW X2 configuration, especially compared to about 4-5 years back.
There is always talk from them about the X2's "scalability". Thats true...aerodynamically speaking the coaxial rigid rotor system is quite scalable. Building an ultra-stiff blade set that maintains the efficient spacing and doesnt not incur tip-path-divergence issues? Thats an entirely seperate can 'o worms.
IMO the 11-12000 GW range is probably the upper end of the envelope without some radical blade material innovation. And I do mean
radical.