Even in the sometimes-wacky world of next-generation drones, Boeing's X-50A Dragonfly was a bit of an oddball. Helicopter-ish blades "that operated on the same principle as a rotating lawn sprinkler" would spin, to lift the thing off of the ground. Then, the blades would lock in place, forming a wing, so the 18-foot, 1500-pound, turbofan-powered Dragonfly could buzz around fast, like an airplane.Officials at Darpa were hoping that the machine would provide "a high-speed, rapid response capability from a VTOL [vertical take-off and landing] air vehicle with significant range and stealth improvements."But for now, those hopes have been dashed. The program has been axed, Aero-Net News reports. "The decision marks the end of the $51.8 million program, with Boeing using the leftover funds to compile a report on just what went wrong."Right from the start, the Dragonfly was troubled. More standard, VTOL plane combos, like the tilt-rotor Osprey and Harrier jump jet, were tough enough to handle. But the X-50A's "canard rotor/wing" was particularly tricky. In copter mode, it called for "exhaust from the aircraft's turbofan engine [to be] directed up the rotor assembly and through outlets at the rotor tips to cause the rotor to spin," Aviation Week notes. "For fixed-wing flight, the exhaust was directed out the aircraft's tail, causing the rotor to stop spinning and act as a wing, while additional lift was provided by the aircraft's fuselage."The Dragonfly's first test flight -- in December, 2003 -- came a year later than expected. Another flight, fifteen months after, ended disastrously; cross-coupling in the rotor controls caused the drone to crash.A second, back-up vehicle was enlisted. And in December, 2005, the Dragonfly successfully flew. But by April of this year, there was more bad news: another crash. "18 minutes in," Aero-Net News says, "the prototype once again lost control during a transition attempt [from fixed-wing flight to rotor]."
DARPA says the second prototype was lost due to poor low-speed control authority, as well as extreme sensitivity to wake strength off the vehicle's rotor. The agency states the accident occurred after rotor wake hit the fuselage, and caused the Dragonfly's nose to pitch up violently -- and in excess of the abilities of the control system to recover.