US shows off robot plane

Previous pilotless drones have been plagued by problems, with at least eight crashing since the autumn.

The X-45 has been developed at a cost of $256m to carry weapons into combat and could be in service by 2010.

Officials expect the plane will be able to carry more than 3,000 pounds (1,350 kilograms) of bombs to drop on enemy radar and missile batteries.

"These have to buy their way in by performing as well in those missions as a manned asset would," said X-45 programme director, Colonel Michael Leahy.

Growth area

Boeing has built two X-45 prototypes. Only one of them has flown so far, reaching an airspeed of 195 knots and an altitude of 7,500 feet (2,290 metres). The second prototype is due to start test flights in the autumn.

The X-45 is designed to be partially autonomous. Its pilot, who may fly several planes at once, would remain on the ground, out of harm's way.

The two Y-shaped aircraft have been developed by the Defense Advanced Research Project Agency (Darpa), the Air Force and Boeing.

They both sport a gaping air intake instead of a canopy, with a slim, stealthy profile.

The target cost of each plane is between $10m and $15m or about one-third the cost of next-generation fighter planes.

The Darpa, which develops future technologies for the Pentagon, has at least half-a-dozen other drones under development, some no larger than a cake tin.

Experts predict the global market for military drones could be worth $7.5bn over the next decade.