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BOEING'S NEW UNMANNED AIR VEHICLES

While the military planners are already dreaming of fleets of unmanned fighters, practical experience of armed unmanned air vehicles (UAVs) is extremely limited even in the USA. This is now set to change with Boeing's X-45 alias Unmanned Combat Air Vehicle (UCAV). At the Dryden Flight Research Center at Edwards AFB, California the final preparations are currently under way for the first flight of the futuristic flying vehicle which is scheduled to take place in the spring.

"During the trials we shall be releasing bombs and guided missiles," says George K. Muellner, general manager of Boeing's Phantom Works, emphasising the importance of the programme. For this purpose, the X-45 has two weapons bays which, for example, can each take a 450kg Joint Direct Attack Munition (JDAM) bomb. In fact UCAV is far from being toy-sized. Its 10.26m wing span is actually bigger than that of F-16, although the fuselage is only 8.05m long. Empty weight is stated at 3,530kg and maximum take-off weight is to be 6,800kg.

The X-45 will be powered by a Honeywell F124 turbofan, without afterburner. It has a single thrust-vectoring nozzle, which assists in controlling the tailless air vehicle about the vertical axis. To reduce costs, UCAV has a very simple structure, with milled bulkheads and single section panelling made out of composite materials above and below. The wings, which do not hold any fuel, are similar to surfboards and are built out of a foam rubber core with fibre matting.

They can be easily removed and reassembled again within 30 minutes, as one of the basic ideas behind the UCAV development is that it should be possible to store and ship the air vehicles in containers. Six of them could be carried in a single C-17. They would only be flown every few years.

UCAV does not need a proper pilot, but instead there is a console with two large screens on which an operator can follow the tactical situation and system status of the unmanned aircraft. One operator would control three or four UCAVs at the same time.

One particular problem here is co-ordination with manned fighters during combined operations. For this reason a major portion of the trials will entail flying several UCAVs at once. Until the second X-45 is ready towards the end of the year, a Boeing-owned T-33 will assume the role of "wingman". It has already had the UCAV software installed in it, 40% of which is based on code from the AWACS, Apache and JDAM.

In the meantime, according to Muellner, funding has also been secured for a third X-45, which will incorporate improved stealth technology. It should then be possible to demonstrate quite realistically the capability of a UCAV to attack air defence positions or other ground targets, enabling a seamless transition to development of a production machine. Whether it comes to this, however, is uncertain since apparently Lockheed Martin is working on a secret rival UCAV.

But the X-45 is not the only unusual design currently being pursued by Phantom Works. In the plant in Mesa, Arizona, the Canard Rotor Wing (CRW) concept demonstrator is nearly finished. As the name suggests, this is a flying vehicle with movable canard wings, a two-bladed rotor powered by hot gases and a wing at the rear which incorporates large winglets.

The Canard Rotor Wing should exceed the maximum speed possible with a helicopter and achieve around 600 km/h. After a vertical take-off, during which the rotor bears the entire load, the CRW transitions to fixed-wing aircraft configuration in the region between 130 and 230 km/h. The lift is transferred to the canard and rear wing, while the rotor is stopped and secured. In this way the exhaust gases produced by the engine (a Williams F112 with 37.5 kN thrust) are diverted aft to provide forward thrust instead of driving the rotor.

"A flying vehicle like the Canard Rotor Wing is only feasible with the technologies that are available today," says George Muellner. Above all the flight control system would not be feasible without computers. The CRW is also pretty complicated. In particular, it took a lot of wind tunnel testing to arrive at a satisfactory rotor profile. The highly loaded rotor hub had to be redesigned last year. "There is probably a maximum size to which the CRW can go," says Muellner.

Despite all the simulations a lot of unknowns remain, for example as regards the UAV's vibration characteristics. Therefore extensive ground trials are scheduled before the CRW lifts off in Mesa towards the end of the year.

What happens when the present $24 million funded programme (50% of which is being borne by Boeing) finishes is still wide open. But one prospective buyer could be the US Marine Corps, which needs a fighter escort for its V-22 Osprey.

From page 62 of FLUG REVUE 5/2001