Any helo folks out there who can explain this:

Sikorsky’s breakthrough X-2 high-speed helicopter likely can’t be scaled up to the size of a heavy-lift helo, a Sikorsky executive told reporters Sept. 14.

“There is a question on the scalability on the X-2 technology at the medium class,” said Scott Starrett, Sikorsky’s vice president for government business development. “When you get to the utility-medium or attack-medium class, it scales nicely.” However, with size and weight increases “you starting getting up to that kind of payload and physical size and it gets to be a different challenge for the technology.”

Starrett said that the company’s CH-53K, which Sikorsky is developing for the U.S. Marine Corps, could fit into the Defense Department’s Joint Multi-Role (JMR) requirement for the heavy-lift helicopter.

Certainly, one explanation here is that Sikorsky is big on the CH-53K, which is under budget and ahead of schedule, but under threat from the V-22 mafia, who see it as a threat (it equals or bests the V-22 in everything but speed with less deck space and lower cost), and they don’t want this as a distraction.

The other alternative is that coaxial rotors simply do not scale well.

When one looks at large twin main rotor helicopters, the Chinook and the (huge) Mil MV-12, it seems that spaced, rather than coaxial or intermeshing (Kaman) rotors are the architecture of choice.