Northrop Grumman has selected Pratt & Whitney to provide the propulsion system for the X-47B unmanned combat air vehicle (UCAV) demonstrators to be produced under the US Air Force and Navy Joint Unmanned Combat Air System (J-UCAS) programme.

The Northrop Grumman-led team, which includes Lockheed Martin, has yet to decide which engine will power the demonstrators and later "spirals" of the vehicle. Candidates range from the commercial PW800 and PW6000 to the military F100 and F135. Sources say the F100-220 is the leading candidate to power the demonstrators, which will fly in February 2006. Boeing has selected General Electric's F404 to power its X-45C J-UCAS demonstrators.

The propulsion system and air vehicle will be highly integrated, "even more so than in the Joint Strike Fighter", says Kevin Farrell, P&W's general manager, small military engines. The Northrop Grumman team is looking across a wide thrust range of 10,000lb to 20,000lb (45-90kN), because of uncertainties about vehicle size, range and endurance, and the power extraction required to drive the payload.

The US Navy surveillance mission requires an endurance of at least 12h, which demands a low specific fuel consumption (sfc), which favours a larger-diameter single-stage fan, while take-off and manoeuvre thrust requires a high fan pressure-ratio, which favours a smaller-diameter multi-stage fan. "This is not a typical thrust/drag problem," says Farrell. "We need power to run a wide range of payloads."

The team's plan is to use an off-the-shelf engine with minor modifications to power the demonstrators, then in later spirals make changes within the same space to improve sfc, weight and low observability. These could include a better fan, a new low-pressure spool or even a new core, says Farrell. The resulting engine is likely to be a hybrid of civil and military propulsion technologies, he says.

The UK Ministry of Defence has also received information on the J-UCAS programme, with Northrop Grumman and competitor Boeing understood to have supplied information. An MoD source says information has been sought on J-UCAS and other "emerging technologies" from European companies including BAE Systems.

US sources say UK participation could mirror the Joint Strike Fighter programme with the UK being the only Level 1 participant.

Source: Flight International