Refueling an aircraft while it is flying can be a tricky-enough proposition but refueling an unmanned jet from another unmanned jet sounds like a scene for a James Bond movie.
But such a tricky procedure is apparently within reach as the Defense Advanced Research Projects Agency, this week said it successfully tested the technology needed to fly two drones close enough together in mid-air, at speed that one, acting as a tanker aircraft, could successfully refuel the other.
From DARPA: " During its final test flight, two modified Global Hawk aircraft flew in close formation, 100 feet or less between refueling probe and receiver drogue, for the majority of a 2.5-hour engagement at 44,800 feet. This demonstrated for the first time that High Altitude Long Endurance (HALE) class aircraft can safely and autonomously operate under in-flight refueling conditions. The flight was the ninth test and the first time the aircraft flew close enough to measure the full aerodynamic and control interactions. Flight data was analyzed over the past few months and fed back into simulations to verify system safety and performance through contact and fuel transfer-including the effects of turns and gusts up to 20 knots."
DARPA said that because HALE aircraft are designed for endurance rather than control authority, it expected only one of six attempts would actually achieve positive contact (17%). However, "the final analysis indicated that 60% of the attempts would achieve contact. Multiple autonomous breakaway contingencies were successfully triggered well in advance of potentially hazardous conditions."
The demonstration could open a world of longer duration drone flights as today's UAVs aren't designed to be refueled in flight. In 2007, DARPA teamed up with NASA to show that high-performance aircraft can easily perform automated refueling from conventional tankers, yet many unmanned aircraft can't match the speed, altitude and performance of the current tanker fleet. The 2007 demonstration also required a pilot on board to set conditions and monitor safety during autonomous refueling operations.
BACKGROUND: What the drone invasion looks like
Under a $33 million deal in 2010 with DARPA, Northrop agreed to demonstrate refueling with a pair of Global Hawks. Although air-to-air refueling was not originally part of the design for drones like the Global Hawk, Northrop then stated such technology offers a number of benefits.
A Global Hawk with a particularly heavy payload, for example, would be able to take off with less fuel, and be subsequently refueled in the air. In addition, a Global Hawk with a unique sensor package would be able to stay on station longer if equipped to receive fuel from another platform.
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