The US defense advanced research projects agency (DARPA) has completed autonomous refuelling trials with two Northrop Grumman RQ-4 Global Hawks, demonstrating that unmanned air vehicles (UAV) can refuel mid-air.
The success of the experiment has the potential to revolutionise large UAV manufacturing and operations.
The two aircraft flew in close proximity during nine high-altitude test flights, and while the aircraft were never physically linked and no fuel was passed, DARPA analysis shows that the aircraft could have done so on up to three-fifths of the attempts. DARPA had anticipated a 17% success rate given the nature of the aircraft – capable of great altitude and endurance, but not manoeuvrability – and the difficulty of precision flight at 44,000ft, where the tests took place.
“The goal of this demonstration was to create the expectation that future HALE aircraft will be refuelled in flight,” says Jim McCormick, DARPA programme manager. “Such designs should be more affordable to own and operate across a range of mission profiles than systems built to satisfy the most stressing case without refuelling.”
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The unusual refuelling system consisted of a hose-and-drogue used worldwide, however in this case the receiver deployed the hose, while the tanker would push fuel upwards. The fuel system was tested on the ground and certified as fully functional, but there are no imminent plans to actually transfer fuel in midair using these vehicles.
Autonomous refuelling was preceded by low-altitude tests using a modified Boeing F/A-18. Plans are moving forward to use the Northrop Grumman X-47, a test bed for unmanned combat vehicle technologies, for autonomous refuelling from manned tankers upon completion of its current aircraft carrier landing trials.
