Original URL: http://www.theregister.co.uk/2010/01/13/airmule_hover_tests/

Israeli ducted-fan robo sky-jeep in hover trials

Not a flying car, but perhaps a flying mule

By Lewis Page

Posted in Science, 13th January 2010 09:02 GMT

The Israeli designers of a radical flying jeep style vertical-takeoff-and-landing "fancraft" have announced long-belated flight tests. However, the trials of the pilotless "AirMule" have so far seen the aircraft tethered and restricted to just two feet off the ground.

The AirMule in initial hover testing. Credit: Urban Aero

Surly bonds of Earth still in place for now.

"Fancraft" technology - so referred to by its developers to distinguish their creations from hovercraft, which can't actually fly - involves the use of a long-touted basic idea: that of ducted fans, essentially enclosed helicopter rotor discs.

It was once thought that ducted-fan aircraft would soon become widespread, perhaps acting as military air-jeeps able to flit about easily in urban areas or other restricted terrain found tricky by helicopters. In the event it was found that small thrust discs mean very low efficiency, leading to aircraft with unacceptably poor fuel endurance and payload even in the context of helicopters. Secondly, many decades ago when most of the tests took place, the ducted-fan machines were almost impossible to control.

Engineers at Urban Aeronautics of Israel believe they've cracked the second snag, however. Their fan ducts feature venetian-blind style arrays of tilting slats, allowing air flow to be redirected without any need to tilt the thrust disc as a normal rotorcraft must. Thus the designers believe that one of their fancraft will be able to hover accurately even in strong, gusty winds while remaining entirely stable and level.

Combining the proprietary slats with modern fly-by-wire automated controls, the Urban Aero boffins contend that their machines will not only be easy to fly, but actually able to fly themselves. The initial AirMule is a crewless design. (This may be a case of necessity being mother to invention, though, as Urban Aero lack major backing and unmanned aircraft are seen as cheaper and quicker to develop than manned ones.)

A turbine-powered, unmanned AirMule prototype was assembled last year, and Urban Aero execs told the Reg at last summer's Paris Airshow that flight tests could be expected "within two months".

In the event that expectation wasn't met, but the AirMule - according to an Urban Aero release no doubt erroneously dated next Friday - has now completed the "first phase of flight testing".

Manned version offering "comfortable access" to high-rise windowsills

Admittedly this was tethered and to heights of only two feet, but Urban Aero says that this is "just outside of ground effect for this particular configuration"*. The firm goes on to say that the trials have confirmed the AirMule's potential ability to hover rock-steady in 50 knot gusty winds. The statement adds:

Based on the success of these initial hover tests the vehicle is now being readied for the next phase which will include vehicle position stabilization in X,Y and height above ground. During this upcoming phase the safety wires that are now connected to the tarmac will be removed.

The initial idea for the unmanned AirMule is that it could airlift crucial supplies to troops fighting in built-up areas where helicopters would struggle to reach them. It might also extract battle casualties; obviously nobody would normally be keen to ride in an unpiloted aircraft, but if the alternative was avoidable deaths from wounds the decision might be made. Israeli troops do more fighting than most in urban areas, so Urban Aero may find a market if the AirMule can be made to work.

In the event of success, the AirMule is intended to develop into manned, multi-purpose "X-Hawk" craft. These would have most of the attributes of the long-coveted flying car: VTOL, robo-autopilot requiring almost zero skill from the pilot, "comfortable access to... the window of a high-rise building".

However, though Urban Aero claims that "the aircraft’s ducted-fan design makes it significantly quieter than any helicopter", one might doubt whether a turbine-powered craft is ever going to really be quiet enough for residential areas. Furthermore, the need to keep the fan discs large for reasonable efficiency is such as to dominate the design of the craft - perhaps to the point of making it unsuitable for many tasks.

Still, though: one to watch. ®

*Vertical-thrust craft gain additional lift and stability when "in ground effect", ie close enough to the ground that its presence affects the behaviour of the air blasted down through the thrust disc. In helicopters, ground effect drops away sharply to insignificance above a height of half the rotor-disc diameter; the Urban Aero statement chimes roughly with the dimensions of the craft's fans.