NASA and the US Defense Advanced Research Projects Agency (DARPA) have launched an eight-month study of an automated aerial refuelling (AAR) system for unmanned combat air vehicles (UCAV).

This is an extension of NASA's autonomous formation flight programme which was redirected towards AAR before entering its third phase after 11 September 2001. The effort is considered "number one on a list of 43" national defence priorities, and "will significantly affect the operability of UCAVs", says NASA programme manager Gerard Schkolnik. It will likely see a substantial involvement from the US Air Force Boeing X-45A/B and US Navy Boeing X-46 and Northrop Grumman X-47 UCAV demonstrator teams.

The programme involves measuring the in-trail automatic station-keeping capabilities of an aircraft behind a standard refuelling drogue basket. A NASA Boeing F/A-18 test aircraft is being fitted with a tanking pod and refuelling drogue assembly for the tests which will verify positional accuracy of an automatic system rather than measuring any drag reducing benefits of vortex riding.

Verification of this was measured in NASA's original programme which ended with a 1.5h long flight by two F/A-18s in which the trailing aircraft, flying in the wingtip vortex of the lead aircraft, burned 14% less fuel than the lead aircraft. NASA says the DARPA/USN UCAV-N team are showing interest in the potential fuel savings of formation flying because of the 12h plus station keeping mission requirements.

The USAF appears focused on the baseline station keeping concept, which depends on highly accurate satellite navigation-based positioning, high fidelity autopilot technology and advanced datalinks. The formation flying control system (FFCS) will be based on the NASA system architecture in which a wireless local area network datalink connected the FFCSs of each aircraft together, while a wireless modem datalink connected the two aircraft's independent separation measurement systems.

Source: Flight International