Experimental unmanned canard rotor-wing flies
Boeing’s Phantom Works has sent its canard rotor-wing (CRW) prototype aloft for flight test. The unmanned 80-second flight, controlled by former USAF special operations pilot Stetson Cowan, took place at the company’s Yuma, Ariz. test facility on December 3 and is reported to have gone well.
The program manager for the X-50A Dragonfly CRW, Clark Mitchell, told AIN that flights will continue from now until around midyear, by which time he hopes that the aircraft will achieve a full conversion from rotary- to fixed-wing flight and back. “As an R&D project we are event driven–our goal is to make a conversion to fixed-wing flight and lock the rotor in place.”
CRW is a promising technology that combines hovering capability with high-speed performance. Turbine power is used to drive a rotor that, in forward flight, then becomes a wing. “Despite the fact that the power is expelled through blade tipjets,” explained Mitchell, “the handling technique is very much like that of a conventional helicopter. It has a traditional swashplate, there is full collective control to apply pitch to the blades and a cyclic for directional control. During takeoff the [remote] pilot slowly brings the collective up until the aircraft is light on the wheels–we have a camera mounted on the tailboom looking forward so that he can judge that moment. He then pulls on the collective to break free from ground effect and aims for a 12-foot hover.
“There’s very little yaw–a small amount of friction from the thrust bearings down the rotor mast, but it’s only 5 to 10 percent that of a conventional helicopter. Some of the power also goes back to port and starboard cruise nozzles, the openings of which are controlled by the yaw pedals. The automated flight-control system will trim out any residual torque but if the pilot wants to turn left or right he uses pedal as usual.”
CRW has been a “higher risk” program than Boeing first calculated. Technically, Mitchell said the main problem continues to be friction in the flight-control system.
“We’ve reduced it a lot but we still have more to do in that area. “However, the flight at Yuma, in a wind that began at three knots and built to four, showed a very stable flight condition,” Mitchell said. He admitted the December flight was technically not the aircraft’s first. “We did a pre-test flight hop on November 24. It lasted 23 seconds and we went up to 80 feet.”
During rotary-wing flight, the engine’s exhaust is diverted by the reaction drive system through the rotor system, exiting through small nozzles in the rotor tips. As forward speed increases beyond around 60 knots, and the canard and tail pick up the aerodynamic load of the aircraft, the exhaust is gradually diverted through a nozzle at the back of the aircraft. This propels it even faster forward. And at around 120 knots the rotor, by now not helping at all, stops and locks into place as a wing. The reverse occurs for conversion back to rotary-wing flight.”
Mitchell said that, as a new class of vehicle, there are no particular physical limitations that dictate the eventual size of a CRW. “It could be manned or unmanned, and grow to the size of a CH-53 if a customer wanted.”