The CRW is propelled in both rotary-wing and fixed-wing modes using a conventional turbofan engine. A diverter valve directs the exhaust gas produced by the engine either to the rotor or aft to the jet thrust nozzle, or to both during transition. A two-bladed teetering rotor is used to generate the required lift for hover and low-speed forward flight. The CRW would spin a center wing to take off like a helicopter.The vehicle would then accelerate to about 120 knots when flaps would deploy from the front and rear wings. Once the rotorcraft is at a sufficient forward velocity, the required lift generation is transferred from the rotor to a canard and horizontal tail. Flap deployment would off load the spinning center wing, which could then stop rotation and be locked into a position across the fuselage to perform as a third wing. The flaps on the other two wings would then be retraced and all three wings would share the lift loads in a fixed wing flight mode. A reverse of these events would transition the CRW back to its rotary wing--VTOL mode for landing on small landing areas.
By using a reaction-drive rotor system, the CRW concept eliminates the need for a mechanical drive train and transmission, as well as the need for an anti-torque system. Eliminating these typically heavy, maintenance-intensive systems will greatly reduce vehicle weight, maintenance, complexity, and cost. Because the CRW's rotor is stopped to allow high-speed forward flight, the rotor's airfoil cross section must be elliptical. This is a compromise between the optimum airfoil shape for conventional rotor flight and that for high-speed stopped-rotor flight.In June 1998 a $24 million agreement between the Defense Advanced Research Projects Agency (DARPA) and The Boeing Company funded a 37 month effort by the Boeing Phantom Works to design, build and fly two technology demonstrators to assess and validate this advanced rotorcraft. DARPA and Boeing agreed to a 50/50 cost share agreement to validate this revolutionary concept in a joint advanced technology demonstration program known as "Dragonfly". Each will contribute $12 million toward the program, leading to flight demonstration in early 2001.
