Originally Posted by
SASless
What are the issues that exist for the 97 but did not seem to limit the 53,64. and 67 or the Cheyenne?
What is unique to the ABC concept that other Rotor Systems do not share when it comes to size increases?
ABC craft, by definition, utilize a closely spaced high hinge offset rigid rotor system. This means no flapping or lead/lag hinges, and therefore colossal moments through the rotor head and into the mast, even for small diameter rotors and smaller gross weights.
As I alluded to before, why is it that you've never seen a rigid rotor from a Bo105 installed on a helicopter much larger than a light twin (topping out at ~12k lbs), much less in a closely spaced stacked arrangement? Because the loads into the structure increase exponentially, to a point where the required construction to carry them becomes prohibitively sized. The amount of blade flapping also will increase, as there are no materials which maintain the stiffness to weight ratios required at larger radii. This drives greater rotor spacing, which is a poison pill to the ABC concept meeting its stated performance. Then there is also the complex aeroelastic tuning aspect.
The comparison to Kamov is getting tiresome; the only commonality between these designs is the usage of a coaxial drivetrain. The Russian designs are all articulated, hinged rotor systems (hinges and flapping alleviate loads). There is no doubt you can scale something like that up to CH53 size, though to clear flapping it would on the order of 50 feet tall!