December 6, 2005 Boeing’s second canard rotor/wing (CRW) X-50A Dragonfly unmanned air vehicle (UAV) has successfully completed a four-minute hover flight at the U.S. Army’s Yuma Proving Ground reaching an altitude of about 20 feet above ground. The aircraft combines the vertical takeoff/landing capabilities of a rotorcraft with the high-subsonic cruise speed and agility of a fixed-wing airplane. As its name implies, its versatility is achieved by having a specially designed rotor for vertical takeoffs and landings that can be stopped in flight to serve as a fixed wing for jet cruise. Under an agreement with DARPA, Boeing Phantom Works has built and flight-tested two pilotless demonstrators to assess and validate the advanced rotorcraft concept and according to Clark Mitchell, Boeing Phantom Works program manager for the CRW prototype, the flight was “a significant achievement toward validating the new stopped-rotor technology.”
Under joint development by Boeing Phantom Works and the Defense Advanced Research Projects Agency (DARPA), the CRW is a revolutionary aircraft that combines the speed and range of fixed-wing flight with the flexibility of rotary-wing flight. It also incorporates tip jet propulsion and stopped rotor technologies.
“The most significant objective met was verification that software compensation effectively reduces the rotor control issue we were having, or cross coupling,” he said. The phenomenon of cross coupling was a finding in the mishap investigation of Ship 1 in 2004 that led to wind tunnel tests for Ship 2 at the Boeing helicopter facility in Philadelphia earlier this year.
Ship 2 then completed ground checkout testing at the Boeing facility in Mesa, Ariz., where it was configured for flight. After a flight readiness review, the vehicle was shipped to Yuma where it completed a preparatory “pop up” flight Nov. 4. The flight lasted only about 30 seconds during which the aircraft stabilized briefly at 16 feet above the ground and then landed. Success with the initial flight led to the hover flight Dec. 2.
Mitchell said that flight tests are expected to continue into early next year. The flight-test schedule calls for 11 flights. Under the remote control of a pilot in a ground station cockpit, the X-50A Dragonfly will gradually perform more extensive hover flights, then forward-moving rotary wing flights.
The test program will culminate with the first ever “conversion” from rotary wing flight to fixed-wing flight and back again to rotary wing flight for landing. The conversion requires the main rotor to stop turning in flight, and lock in place to become a fixed wing for high speed flight.
The X-50A Dragonfly vehicle is 17.7 feet long and 6.5 feet high and weighs 1,460 pounds. In addition to its 12-foot-diameter rotor/wing, it also has an 8.9-foot-span canard and an 8.1-foot-span horizontal tail. It is propelled by a conventional turbofan engine combined with Boeing’s unique reaction drive rotor system.
During rotary-wing flight, the engine’s exhaust is diverted by the reaction drive system through the rotor system to exit through small nozzles in the rotor tips. As forward speed increases and the canard and tail pick up the aerodynamic load of the aircraft, the exhaust is gradually diverted completely through a nozzle at the back of the aircraft, propelling it even faster forward and allowing the rotor to stop and lock into place for fixed-wing flight. The reverse then occurs for conversion back to rotary-wing flight.
The CRW reaction drive rotor system eliminates the need for the traditional mechanical transmission, drive train and anti-torque device. Reaction drive makes the CRW much lighter, simpler and more affordable to operate and support than traditional rotorcraft. Its greater speed, range and flight-mode flexibility will make it suitable for a wider range of missions.
Further expanding CRW’s flexibility and versatility is the fact that it can be scaled for both manned and unmanned applications. As an unmanned air vehicle, the CRW would be able to perform such missions as reconnaissance, communications and data relay. In a manned configuration, it would be ideal for armed escort, command and control, logistics re-supply and medical evacuation.
Ship 1, the first Dragonfly prototype vehicle, was involved in a flight mishap on March 23, 2004, that led to a joint investigation by Boeing and DARPA. The findings identified cross coupling of the rotor controls as the main cause of the mishap. Since then, improvements have been incorporated into Ship 2 that address design issues related to findings. These include changes such as new rotor torsion springs for increased control power, new flight control software and a flight data recorder.