Two possible experiments later this year are poised to tackle the challenge of refuelling unmanned air vehicles in flight. A "smart" drogue designed by Smiths Aerospace enters windtunnel tests later this month, and a go-ahead is expected in June on the demonstration of a satellite-guided approach system invented by Sierra Nevada (SNC).

Both projects focus on different aspects of the final two steps in the in-flight refuelling process - aligning the refuelling and receiving aircraft on an identical heading, and precisely closing the final inches between the receiver's probe and the tanker's basket.

To address the alignment requirement, SNC is awaiting approval by the Defense Advanced Research Projects Agency to launch its demonstration programme. SNC has pioneered precision landing systems for UAVs and is proposing a derivative technology for autonomous refuelling. Based on differential GPS, which corrects for positioning errors between moving aircraft and a fixed location, SNC's concept uses relative GPS to transmit navigation corrections between two or more moving aircraft.

If approved, the SNC demonstration could serve as a starting point for Gulfstream's plans to convert its G550 business jet into an unmanned vehicle. The G550 is expected to be chosen by SNC to conduct the autonomous rendezvous experiments with a manned tanker. Gulfstream says the G550's existing avionics already allow for autonomous operation in all phases of flight except take-off, initial climb and landing. The G550 can also be converted back to manned mode to avoid airspace restrictions. Gulfstream plans to enter the unmanned G550 in the US Navy's Broad Area Maritime Surveillance (BAMS) competition, which is scheduled to begin next month.

Meanwhile, a model of Smiths' smart drogue goes into the windtunnel at the University of Michigan in late May. Tom Crawford, business development manager at Smiths, declines to give greater details on the concept, but says the design gives the refueling aircraft the ability to autonomously guide the drogue to meet the receiving probe, correcting for the often-turbulent motion of the basket. The technology is expected to be offered exclusively on the Boeing KC-767 tanker, which has launched Smiths' drive into the hose-and-drogue market as a competitor to Cobham's Sargent Fletcher and Flight Refuelling subsidiaries.


Source: Flight International