Basically, the folks at Sikorski think that technological advances have made the advancing blade helicopter viable, most notably composites, active fly by wire control systems to reduce vibration, and improved propulsion (the late 1970s version X-59A ABC used two turbojets for forward thrust) (see also here)

By offloading the retreating blade, they hope to achieve cruise speeds in excess of 250 kts, and improved range.

I’m rather more sanguine on this than I am on the tilt rotor concept myself, because the tilt-rotor is really a plane that can take off vertically, while this is a helicopter that can fly faster.

It appears to have fewer compromises, and should have superior performance in the hover and low speed flight regime, which is the helicopter’s raison d’etre.

As Sikorski is self-funding this, I expect progress to be slow, they can’t afford a crash.

They’ve already pushed back first flight a couple of years from 2006, and now there is talk of pushing it back to 2009.

Also, Av Week‘s Bill Sweetman noticed a special ops mockup model of the concept at Farnborough: