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UAVs Advance In-flight Refuelling Tests

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Making Connections At 45,000 Feet: Future UAVs May Fuel Up In Flight

(Source: DARPA; issued October 5, 2012)

DARPA completes close-proximity flight tests of two modified RQ-4 Global Hawk unmanned aerial vehicles, demonstrates technology enabling autonomous aerial refuelling. (Darpa photo)

Currently global military aviation relies on a key enabler – aerial refueling. Fighters, bombers, reconnaissance and transport aircraft use “flying gas stations” to go the extra mile. Increasingly, UAVs are conducting combat and ISR operations, but UAVs aren’t designed to be refueled in flight.

In 2007, DARPA teamed up with NASA to show that high-performance aircraft can easily perform automated refueling from conventional tankers, yet many unmanned aircraft can’t match the speed, altitude and performance of the current tanker fleet. The 2007 demonstration also required a pilot on board to set conditions and monitor safety during autonomous refueling operations.

Today DARPA has addressed this capability gap. DARPA’s two-year Autonomous High-Altitude Refueling (AHR) program, which concluded Sep. 30, explored the ability to safely conduct fully autonomous refueling of UAVs in challenging high-altitude flight conditions.

During its final test flight, two modified Global Hawk aircraft flew in close formation, 100 feet or less between refueling probe and receiver drogue, for the majority of a 2.5-hour engagement at 44,800 feet. This demonstrated for the first time that High Altitude Long Endurance (HALE) class aircraft can safely and autonomously operate under in-flight refueling conditions. The flight was the ninth test and the first time the aircraft flew close enough to measure the full aerodynamic and control interactions. Flight data was analyzed over the past few months and fed back into simulations to verify system safety and performance through contact and fuel transfer–including the effects of turns and gusts up to 20 knots.

Since HALE aircraft are designed for endurance at the expense of control authority, the program started with the expectation that only one of six attempts would achieve positive contact (17%). The final analysis, however, indicated that 60% of the attempts would achieve contact. Multiple autonomous breakaway contingencies were successfully triggered well in advance of potentially hazardous conditions. Fuel systems were fully integrated and ground tested, demonstrating a novel “reverse-flow” approach with the tanker in trail. This approach opens valuable trade space for future developers to choose between various fixed and modular implementations of proven probe and drogue hardware.

“The goal of this demonstration was to create the expectation that future HALE aircraft will be refueled in flight,” said Jim McCormick, DARPA Program Manager. “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.” (ends)

Two Global Hawk Unmanned Aircraft Fly In Close Formation, Move AHR Program Closer to Autonomous Aerial Refueling

(Source: Northrop Grumman Corp.; issued October 5, 2012)

SAN DIEGO --- Northrop Grumman Corporation (NOC), the Defense Advanced Research Projects Agency (DARPA) and NASA Dryden Flight Research Center have successfully completed a series of flight demonstrations, moving DARPA's Autonomous High-Altitude Refueling (AHR) program closer to demonstrating the first autonomous aerial refueling between two unmanned, high-altitude aircraft.

The flights, which used two NASA Global Hawk unmanned aircraft -- one configured as a tanker and the other as a receiver -- were conducted at Edwards Air Force Base, Calif.

During the flights, which spanned Jan. 11 to May 30, the AHR team achieved many milestones, including:
• The lead receiver aircraft extended and retracted its aerial refueling hose several times, completing all planned tests to validate the associated program hardware and software.
• The trail tanker aircraft successfully demonstrated precision control in formation with manual and automated "breakaway" maneuvers -- important safety features and criteria of the test program.
• Two Global Hawk unmanned aircraft successfully flew for the first time in close formation -- as close as 30 feet.
• During the close-formation flight, the aircraft rendezvoused and flew for more than 2.5 hours under autonomous formation control, with the majority of the time within 100 ft (or one wingspan) of each other.

"The technical developments that enabled these two high-altitude, long-endurance unmanned Global Hawks in close formation is an outstanding accomplishment for the AHR program," said Fred Ricker, vice president and deputy general manager for Northrop Grumman Aerospace Systems' Advanced Programs & Technology. "Coupled with the advanced design and technical implementation of aerial refueling systems on board both aircraft, the demonstration has truly brought a concept to life, which has the potential to change the operations for unmanned aircraft utility and enable mission flexibility never before realized."

Northrop Grumman and NASA Dryden Flight Research Center conducted several demonstration flights in the buildup to the close formation flight, which included tanker and receiver first flights and a distant formation flight. The Northrop Grumman-NASA-DARPA team worked closely to ensure that all safety precautions and measures were taken when preparing for and conducting all of the ground and flight demonstrations. Preparation included a calculated approach to ground and flight tests, which included extensive analysis, simulations, laboratory and ground tests as well as multiple safety review boards.

The $33 million DARPA AHR program aims to demonstrate autonomous fuel transfer between two Global Hawks, enabling flights of up to one week endurance. AHR is a follow-on to a 2006 DARPA Autonomous Aerial Refueling Demonstration (AARD), a joint effort with NASA Dryden that used an F/A-18 Hornet as a surrogate unmanned aircraft to autonomously refuel via a probe and drogue from a 707 tanker.

As part of the U.S. Navy's Unmanned Combat Air System Carrier Demonstration program, Northrop Grumman is also developing AAR technology to help extend the operating range and flight duration of future carrier-based unmanned systems. The company plans to conduct AAR demonstrations in 2014 using the Navy's X-47B unmanned demonstrator aircraft.

In partnership with NASA in the Space Act Agreement, Northrop Grumman supports the operations and maintenance of the two Global Hawks used in the AHR program and is responsible for all engineering design, as well as modification of both aircraft.

Northrop Grumman is a leading global security company providing innovative systems, products and solutions in aerospace, electronics, information systems, and technical services to government and commercial customers worldwide.