The original funding for the refuelable UCAS came from Northrop Grumman and later by the Defense Advanced Research Programs Agency (DARPA) Joint Unmanned Combat Air System (J-UCAS) program, which was a joint research collaboration program between the Air Force and Navy. Both departments were interested in deploying a common UCAS. However, in 2005 the Quadrennial Defense Review, a study conducted by the U.S. Department of Defense, ordered the J-UCAS program to be terminated and created two separate objectives for the military branches to better fulfill the needs of the departments for long-range stealth vehicles. The Air Force pursued a long-range stealthy bomber while the Navy continued the J-UCAS research under a new program called the unmanned combat air system demonstrator (UCAS-D) program, focused on developing a long-range, carrier-based unmanned aircraft capable of refueling in the air. The U.S. Naval Air Systems Command (NAVAIR) in Patuxent River, Md., named Northrop Grumman as the prime contractor for the UCAS-D program and funded two X-47B aircraft with one craft capable of refueling in the air.

Carrier-capable solutions

The X-47B is the first developmental unmanned program to provide a carrier suitable solution. It is structurally different from other UCAS aircraft to handle the loads from landing on an aircraft carrier. The load paths must be strong enough to withstand the arrestment gear loads when landing and the catapult launch loads when taking-off on a carrier deck. All the parts on the aircraft endured structural and durability tests to ensure they would withstand the loads for the carrier operations. “The UCAS structure must be strong enough to support the force of being catapulted into the air,” says Saunders. The Navy aircraft requirements used on the carrier-capable supersonic fighter jets F-18 and F-35 were applied to X-47B.

The X-47B carbon epoxy composite skin is manufactured at the GKN Aerospace facility in St. Louis, Mo., using conventional lay-up with several layers of ply to create the skin. GKN Aerospace, a tier one supplier for the aviation industry, is one of the members of the Northrop Grumman team that also includes Lockheed Martin, Pratt & Whitney, Eaton, General Electric, Hamilton Sundstrand, Dell, Honeywell, Goodrich, Moog, Wind River, Parker Aerospace and Rockwell Collins. The contract to design the composite skins was written in 2006 during the J-UCAS program and continued into UCAS-D. The composite parts are constructed using normal composite manufacturing techniques similar to the approaches used today on other aerospace legacy systems. The X-47B also uses carbon fiber composite skin on the leading edges and controlled surfaces of the aircraft, such as the wings, fuselage and doors. The Northrop Grumman team chose to implement the composite skins to provide weight savings and corrosive-resistant controlled surfaces on the leading edges, says Saunders. Each wing supports the elevon, aileron and spoiler flight control surfaces used to perform the flight patterns of the UCAS in flight.