It is commonplace for airplanes to meet up with an airborne tanker and refuel mid-flight. This allows the aircraft to extend the amount of time they can spend aloft. NASA and DARPA showed these aircraft can conduct refueling autonomously in 2007. This same capability is being testing for implementation into Unmanned Aerial Vehicles, or UAVs.
September 30th concluded DARPA’s Autonomous High-Altitude Refueling, AHR, program. The purpose of the test, as the name implies, was to explore the possibility of UAVs to refuel autonomously at high altitude. For this testing two Global Hawks were modified, one equipped with the refueling drogue and one with the receiving probe. The Global Hawks used in the testing were High Altitude Long Endurance, HALE, aircraft. In order to achieve the enhanced endurance the planes operate more autonomously, allowing the computers to optimize fuel efficiency whereas many of the UAV’s in service currently are piloted remotely by a human. The actual flight test consisted of the UAV’s flying in a formation, separated approximately 100 feet between the drogue and receiver conducted at an altitude of 44,800 feet.
The initial expectation was that the drones would be able to connect with an approximate success rate of 17%. After the flight data was run through various simulations that estimate was raised all the way up to 60%. The fuel systems themselves were integrated and tested on the ground. According to Jim McCormick, DARPA Program Manager, “The goal of this demonstration was to create the expectation that future HALE aircraft will be refueled in flight. 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 refueling. The lessons from AHR certainly extend beyond the HALE flight regime, and insights into non-traditional tanker concepts may offer further operational advantages.”
The HALE Global Hawks are operated by NASA after having had been acquired from the U.S. Air Force. These variants have an 11,000 mile range and can stay aloft for 32 hours. NASA uses these planes to carry various sensors for various studies and tests as well as study parts of the planet that are hard to access by conventional means. While the AHR capabilities would complement these activities, it would certainly be beneficial to military UAV’s as well. The ability to dwell on a target for extended periods or patrol various locations would certainly increase the already high effectiveness achieved by the drones in combat situations.