The US Navy's X-47B Unmanned Combat Air System Demonstration (UCAS-D) aircraft has gone out on a high note (and added yet another acronym to the military lexicon) by conducting the first ever Autonomous Aerial Refueling (AAR) exercise. The autonomous aircraft rendezvoused with an Omega K-707 tanker plane off the coast of Maryland and Virginia, successfully taking on 4,000 lb (1,814 kg) of jet fuel as it completed the project's final test objective.

At a press conference, Captain Beau Duarte, the Navy’s Unmanned Carrier Aviation program manager, confirmed that on April 22, the X-47B carried out the last of four refueling exercises. During Wednesday's test, the robotic aircraft became the first to autonomously approach a tanker, secure a refueling drogue, take on fuel, and disconnect. This was the last in a series of demonstrations to show that an unmanned aircraft can carry out standard Carrier Air Wing operations.

Duarte emphasized that the X-47B was not remotely piloted during the refueling. Instead, the ground controller and tanker crew gave commands for the aircraft to carry out tasks and the onboard computers executed the maneuvers, handling not only navigation, but also the rapid movements of the two aircraft and the resulting feedback loops.

During the exercise, the X-47B carried out Navy-style refueling, which uses a probe-and-drogue method where the tanker plane trails a fueling tube that ends in a conical basket, or drogue, while the following aircraft extends a probe into the basket to link up and take on fuel.

This is a tricky exercise even for a human pilot, but the X-47B accomplished the task using an infrared camera linked to a new visual computer to home in on the basket, a government-designed Refueling Interface System (RIS) aboard the tanker to communicate between the two aircraft, and a combination of GPS and inertial navigation systems.

This system allowed the X-47B to approach the tanker, close the distance, find the basket, insert the probe, and fly in formation for 11 minutes while it took on fuel before ground control ordered it to disconnect and return to base.

Under a contract with the US Navy, Northrop Grumman built two X-47B demonstrators named Salty Dog 501 and Salty 502. Though the X-47B is unmanned, it is not a drone. Instead, it’s an autonomous aerial vehicle, which means that it flies missions according to pre-programmed instructions rather than being under constant control by a ground-based pilot.

The aircraft were designed to demonstrate autonomous carrier operations including launch, recovery and operations within 50 nautical miles (57.5 mi, 92.6 km) of the carrier. Only one of the two demonstrators built is designed for autonomous aerial refueling operations using the Air Force “boom/receptacle” approach as well as the Navy probe and drogue method. No weapons were carried by either aircraft and no sensor tests were conducted.

The Navy says that the next step as far as refueling goes will be to develop a more robust and reliable system that can operate outside of land range and in a variety of weather conditions, which might mean using different approaches than the one used on Wednesday. However, this will have to wait because efforts will now concentrate on the Navy's Unmanned Carrier-Launched Airborne Surveillance and Strike (UCLASS) aircraft.

The X-47B is a demonstrator and its design is very different from UCLASS and the Navy contends that it would be impractical to rebuild it for the UCLASS program. The Navy will instead use what remains of the program's budget to conduct further testing before the aircraft are mothballed or sent to a museum.

"What we accomplished demonstrates a significant, groundbreaking step forward for the Navy," says Duarte. "The ability to autonomously transfer and receive fuel in flight will increase the range and flexibility of future unmanned aircraft platforms, ultimately extending carrier power projection."

The video below shows Wednesday's test.

Source: US Navy

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