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One of the circular problems facing engineers developing unmanned aerial vehicles (UAVs) is fuel vs weight vs flight time.
Longer flight time means loading more fuel. Loading more fuel means more weight. More weight means more fuel is required to stay in the air.
Aircraft of any type are more useful in the air than on the ground, and this is particularly true for UAVs designed for defence and security-related surveillance and monitoring.
The well-established solution is mid-air refuelling. Unfortunately the manoeuvre requires highly skilled pilots flying in formation, defeating the purpose of autonomous, unmanned drones.
This week two separate research projects from separate sides of the world claimed to have achieved the first fully autonomous mid-air refuelling, thereby creating the drone that never has to land. Strangely, one is the result of a decade of work by a billion dollar US defence contractor backed by a multinational industrial consortium. The other is a four year research project by an Australian student for his PhD.
University of Sydney researcher Daniel Wilson with his UAV and drogue
The two projects seem to use almost identical approaches. According to Northrop Grumman, its AAR technology (autonomous air refuelling, for want of an acronym), “integrates both GPS and infrared imaging to enhance navigational precision and hedge against GPS disruption”. Daniel Wilson's PhD research uses “a combination of precise measurements from an infrared camera, with GPS and inertial sensors”.
Not to belittle the achievement of either, but the difference between the two projects for the same outcome couldn't be larger. One has involved Learjets, the US Navy's most cutting-edge UAV, and engineering expertise from firms such as Lockheed Martin, Pratt and Whitney and GKN Aerospace. The other was conducted at a remote airfield in the Australian outback and co-supervised by two University of Sydney lecturers.
“The biggest challenge is the highly accurate and reliable relative positioning performance to allow a second aircraft to dock with a small target, in the air, and amidst turbulence," says University of Sydney researcher Wilson, who sees his technology as being useful in search and rescue operations, or for using UAVs for communications.
"There are two autonomous aircraft, a leader and a follower. The leader tows a cone-shaped, parachute-like drogue. The objective is for the follower to autonomously dock its nose, within the drogue.
"Initially both the aircraft rendezvous to a formation position where the follower's infrared camera can observe infrared LED markers on the leader's wingtips and tail. Once docked, the follower is commanded to station for a certain amount of time.”
The US Navy demonstration uses the same probe and drogue technique, but between a significantly larger X-47B and a Omega K-707 tanker. Northrup Grumman believes that autonomous launch, recovery and refuelling will reduce operational costs in the future.
Capt. Beau Duarte, the Navy's Unmanned Carrier Aviation program manager, said: "AAR testing with the X-47B helps solidify the concept that future unmanned aircraft can perform standard missions like aerial refuelling and operate seamlessly with manned aircraft as part of the Carrier Air Wing.”
The difference between the two demonstration is during Wilson's demonstration the refuelling was simulated. So, despite Wilson's experiments being conducted earlier than the US Navy demonstration, late last year, the mantle of first actual unmanned refuelling goes to Northrup Grumman. Still the US UCAS-D (Unmanned Combat Air System Demonstration) isn't bad company for a PhD research project to be keeping. Unless there is some serious espionage going on somewhere its a great coincidence that both achieve virtually the same milestone with the same approach but in totally different places.