By Graham Warwick  in Washington DC

Experimental programmes suffer double blow as Dragonfly loss follows hard on heels of Eagle Eye accident

The crash of Boeing’s second X-50A Dragonfly experimental canard rotor/wing (CRW), just a week after the loss of Bell Helicopter’s TR918 Eagle Eye tiltrotor demonstrator, is a setback for advanced unmanned rotorcraft development.

The X-50A crashed on 12 April while in low-speed rotary-wing flight over the Yuma Proving Grounds in south-west Arizona. The demonstrator lost control 18min into the flight, at 200ft (60m). The second X-50A was on its sixth flight, and was still operating in helicopter mode. The goal of the programme was to transition from vertical to forward flight by stopping the rotor, which would then act as the wing.

The future of the X-50 programme, and CRW high-speed rotorcraft technology, is under review by Boeing and the US Defense Advanced Research Projects Agency (DARPA). The first X-50 crashed in March 2004 after a few hover flights because of a cross-coupling issue with the tip-driven rotor. The modified second vehicle first flew in December 2005.

The full-scale Eagle Eye crashed on 5 April, when it lost power while hovering at Bell’s Fort Worth, Texas test centre (Flight International, 18-24 April). Tiltrotor and stopped-rotor CRW are different designs for high-speed rotorcraft. Another approach, the coaxial advancing-blade rotor, is to be flight-tested by Sikorsky this year with its manned X2 Technology demonstrator.

Boeing is continuing tests of the A160 Hummingbird optimum-speed rotor, long-endurance unmanned helicopter for DARPA. The A160, which has a rigid rotor that can operate over an RPM range of 50% to 100%, is flying with a modified automotive gasoline engine. The next steps are to install a diesel engine in the fifth air vehicle, and Pratt & Whitney Canada PW207 turboshaft in the sixth and eight in a bid to push endurance beyond 24h.

Source: Flight International