Originally Posted by
Jack Carson
IFMU
I agree in principle. Igor Sikorsky flew the Grand, a 4 engine, 5 ton machine in 1913. Sixty years later that vehicle evolved into the 747. Similarly, he flew the VS-300 in 1939. 35 years later Sikorsky flew the 35 ton CH-53E. However, some subsets of rotorcraft technology may approach physical limits due to power requirements or material limitations. To draw a slightly different analogy, I believe that the VTOL Harrier and F-35 are approaching practical limits for turbo-fan thrust born flight. Co-axial rotor systems may have just such a boundary.
Jack
Jack, your comment is spot on. The boundary you are refering to is compressibility. By opting for a counterrotating main rotor system you avoid the retreating blade stall, but the limit you now hit is the advancing blade shock wave formation. Improved modelling and damping of blade modes will allow Nr to reduce at higher speeds without fear of structural divergence. Eventually the machine will operate at speeds approaching turboprops, so Sikorsky are being sensible with a 250kias start - remember it has to work.
One day in the distant future speed might get into the turbofan arena. Much work on blade dynamics will be required - likely with active systems. This is similar to commercial fixed wing struggling to justify projects over M1...
Mart