Checking to see any news on X2, came across this article:
http://aeronode.com/aero/18/sikorsky...run-in-october
Aviation Today reports that Sikorsky plans a ground run in October of its X2 concept demonstrator, only 16 months after the program’s inception. The ground run should test basic mechanical and avionics functionality without flight. The X2 uses contra-rotating rotors along with an aft pusher-prop to expand the speed envelope of rotorcraft, with 250 knots a possibilty.
Although quarter 2, this had a good article on page 3:
http://www.sikorsky.com/file/popup/0,3038,1875,00.pdf
Although the picture initially had me fooled, top rotor is same diam as lower rotor. One point about coaxials is that downwash contraction from the upper rotor will alter flow through centre region, but not the tips, of the lower rotor. I'm sure the engineers at Big Sky have done lots of corellated CFD simulations to get it right...
Other resources, since i couldn't find the original thread:
http://www.sikorsky.com/details/0,30...TI2088,00.html
http://www.flug-revue.rotor.com/FRtypen/FRSikX2.htm
http://www.aerospace-technology.com/projects/model333/
Mart