Sikorsky has begun turning the tail-mounted propeller on its X2 Technology demonstrator, in preparation for high-speed flight tests, but there are no signs yet of a near-term application for the 250kt-cruise coaxial-rotor helicopter.Photo: Sikorsky
But the Office of Naval Research (ONR) has issued a request for information on a cargo unmanned aircraft system that might just fit the X2. ONR is looking for a vertical takeoff and landing UAV that can operate from U.S. Navy ships to support geographically dispersed U.S. Marine Corps combat units. It wants a vehicle that can carry at least 1,600lb of payload over a radius in excess of 285nm at a cruise speed of at least 250kt. ONR is seeking ideas for vehicles that could be fielded within 5 years, 5-10 years and 10-15 years.
Sikorsky plans to demonstrate the X2's 250kt cruise capability by year-end, so it could be a near-term contender. Getting the prop turning is a key step along the way. For the three-flight initial low-speed test phase late last year the variable-pitch prop was disconnected. On the demonstrator, the prop now is directly connected to the main transmission, so it turns when the rotors turn. But a production X2 would have a clutch, so that the prop could be disconnected on the ground and when its thrust is not needed.
The prop's pitch-change mechanism is now connected to the X2's fly-by-wire system. The next step is to add the rotor-hub fairings and gear-retraction mechanism to reduce drag. Then the X2's forward-flight envelope will be opened up in three phases: from 40kt to 120kt will use rotor thrust; 120-180kt will use a combination of rotor and prop thrust; 180kt upwards will use the prop, with the rotor producing only lift at maximum speed.