The Boeing X-50A Dragonfly Canard Rotor Wing advanced technology demonstrator made its first fight on December 3 at Yuma Proving Grounds. The 80-second, 12-ft hovering flight at Yuma Proving Grounds started an incremental flight test program aimed at translating from rotary- to fixed-wing flight and back again. According to Boeing X-50A Dragonfly Program Manager Clark Mitchell, translational flights could take place early next year. "The one lesson that I and the team have learned is to look at the broader scope. When you look at flight test, it always takes longer than anyone expects."

In a jointly-funded effort with the Defense Advanced Research Projects Agency (DARPA), the Boeing Phantom Works built two X-50A demonstrators to evaluate the potential of the CRW in piloted and unmanned air vehicles (UAVs). The remotely-piloted CRW takes off, hovers, and lands with a tip-driven teetering rotor system, and then translates to high-speed flight on the lift of its fixed canard and tail surfaces.

A single Williams International F112 turbofan (developed for the AGM-129 cruise missile and used in the X-36A sub-scale tail-less fighter demonstrator) provides both tip thrust for the rotor and forward thrust for fixed-wing flight. Without a mechanical transmission, the CRW promises lighter, less complex aircraft with helicopter-like VTOL performance and efficient jet cruise speeds. Though the X-50A demonstrator is capable of 220 kt with the current engine, program plans limit maximum speed to 150 kt. "We're actually testing a very small portion of the capability of the machine," says Mr. Mitchell.

The 12-ft diameter rotor of the X-50A has a hydraulically-actuated swashplate for cyclic and collective control in rotary-wing flight, and conventional control surfaces for fixed-wing maneuvering. The jet exhaust nozzle opens and closes for directional control. "It's all tied in with speed," explains Mr. Mitchell. "That's what sets the cruise nozzle open." At 0 to 60 kt, the nozzle is closed, and the rotor provides all lift and thrust. From 60 to 120 kt, the CRW is in compound flight and transfers from rotary- to fixed-wing lift and power. Above 120 kt, the Dragonfly is a fixed-wing jet, and the rotor indexes and brakes perpendicular to the fuselage. The translation is reversed as the aircraft slows for landing.

Wind tunnel testing shows the current elliptical airfoil rotor provides no lift when fixed for cruising flight, and its blunt trailing edge generates a 10% drag penalty. Mr. Mitchell says, "We are looking at ways to solve that problem and have airfoils that will be configurable depending on flight mode."

The X-50 has a flight path command system that enables the pilot to fly the vehicle through a sidearm controller and head-up display. The pilot's ground control station was adapted from the X-36 program. A Honeywell flight management computer and Boeing airframe interface unit also borrowed from the X-36 host the X-50A flight control laws. The laws themselves were derived from Boeing work on the Rotorcraft Pilots' Associate program. A dedicated rotor processing unit controls the CRW rotor rpm and braking position.

The rotor design was one of the main challenges for the X-50A team. At a tip speed of 1,170 rpm or 5,735 fps, the short rotor generates high centrifugal forces. In addition, exhaust gas temperatures in the blades top 800 F. The high G loads and high temperatures required innovative structural solutions. "I think we've learned a new respect for rotary-wing UAVs," says Mr. Mitchell.

Another demanding feature of the demonstration effort is the flight control laws that operate the exhaust mass flow valve to determine where the gas is directed. Dragonfly engineers had to develop valve control software to maintain relatively constant backpressure on the engine.

X-50A test plans call from a gradual progression in speed from hovering flight to fixed-wing translation. Mr. Mitchell explains, "Each step of the way, we're looking at the data to make sure it matches the simulation." The test vehicle has three antennas to downlink some 800 test parameters to a data collection system adapted from the X-36 program.

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