CSAR DiscRotor -- DARPA/Boeing Retractable-Blade Helicopter

Boeing Develops Helicopter-Airplane Hybrid for DARPA

As part of a DARPA initiative, Boeing is developing a search-and-rescue aircraft that combines a helicopter's hovering capabilities with an airplane's long flight range. According to Aviation Week, Boeing will test a 20-percent scale model of the disc-rotor aircraft, called the CSAR DiscRotor, in a wind tunnel sometime next year.

The aircraft takes off vertically like a helicopter, with telescoping rotor blades extended, then converts to fixed-wing forward flight by retrating the blades into the disc, which is then stopped. The aircraft the flies on its swept wing and dual ducted propellers.

DARPA - Tactical Technology Office (TTO)

The goal of the DiscRotor Compound Helicopter program is to design and demonstrate the enabling technologies required to develop a new type of compound helicopter capable of high-efficiency hover, high-speed flight, and seamless transition between these flight states.
An aircraft capable of long range high speed (300-400 kts) and vertical take-off and landing (VTOL)/hover will satisfy an ongoing military interest, bridging the gap in helicopter escort and insertion missions by providing survivability, mobility, and responsiveness for troop and cargo insertion.

High-Speed VTOL Goes for a Spin

Developing a mechanism that will reliability and repeatably retract and extend the blades under flight loads (including centripetal forces) is the central technical challenge of the DiscRotor program,

The DiscRotor has an integrated propulsion system using two turboshaft engines fitted with fans so they can also generate forward thrust. Shaft power goes to the main gearbox to power the rotor and a pair of wing-mounted, cross-shafted ducted propellers that provide the majority of the thrust in fixed-wing mode.