Northrop Grumman rolled out the X-47B UCAS-D (unmanned combat air system-demonstrator) in December 2008 and since then has been busy preparing the first of two vehicles for its maiden flight, expected shortly. Low- and high-speed trials have been completed at Air Force Plant 42, Palmdale, California, where the second X-47B is in final assembly. The first vehicle has been moved to Edwards Air Force Base for high-speed taxi and rejected takeoff trials, in preparation for its first flight.

The X-47B has been funded by the U.S. Navy to demonstrate the feasibility of a carrier-capable unmanned combat air vehicle. Quite apart from the unmanned element, the type’s low-observable configuration also presents something of a challenge, especially in terms of approach control, as the X-47 will be the Navy’s first tailless carrier aircraft since the days of the Vought Cutlass and Douglas Skyray.

Flight control software has been tested in manned surrogate aircraft, such as the F/A-18 Hornet, including hands-off recoveries, launches and patterns around the carrier. Two Navy carriers have already had the X-47B’s mission management system installed so that they are ready for sea trials. Other than that, the X-47B is entirely compatible with existing carrier systems and infrastructure. “The ship sees it just as it would a manned platform,” said Gene Fraser, vice president and general manager of NG Aerospace’s Advanced Programs and Technology Division.

As a demonstrator for carrier compatibility, the X-47B does not carry any mission-specific sensors and systems, although integration work has been performed on manned testbeds.

The first X-47B vehicle will undertake its initial flight test campaign from Edwards AFB, after which it will transfer to the U.S. Naval Air Warfare Center Aircraft Division at Patuxent River, Maryland, to undertake carrier compatibility trials. It is due to arrive at NAWCAD next spring, where it will operate from the center’s shore-based simulated carrier deck.

Trials at NAWCAD will be conducted in a similar fashion to those of any manned aircraft, including steam ingestion and barrier engagement trials at Lakehurst, New Jersey. A key part of the shore trials are so-called “off-nominal” approaches to the deck, with the aircraft deliberately approaching in varying attitudes and at different speeds and directions. This, in itself, raises some interesting issues. “The airplane just doesn’t do off-nominal,” explained Fraser. “We have to program it specially to fly these approaches, otherwise it will just fly a perfect glideslope every time.”

Beyond UCAS-D
The X-47B demonstrator is the first step toward a carrierborne UCAV. Next comes UCLASS (unmanned carrier launched airborne surveillance and strike). In March, the deputy chief of naval operations (DCNO) issued a request for information dominance, which has drawn responses from a number of companies, including Boeing with a Phantom Ray-based proposal and General Atomics with the Sea Avenger. Northrop Grumman has, of course, responded with a proposal drawing on its X-47 technology and expertise.

The UCLASS RFI covers the provision of four to six vehicles with multi-sensor and weapons capability, and an 11- to 14-hour endurance. They would enter service around 2018 and provide a limited operational capability. More importantly, they will form a stepping stone to a full system design and development program for a carrier-capable UCAS. A Navy response to the UCLASS proposals might come late this year, leading to an RFP.