U.K. start-up to demo serious flying robo-saucer in 2009

unmanned, but there is hope for the flying-car fanciers yet. Asked whether there was any aspiration to scale the tech up to manned versions, Broughton emphatically replied: “Yes. In fact if you ask our chairman he’d say that’s one of the reasons he’s involved.”

The jury’s still out on whether Hatton’s Coanda saucers are actually better than ducted fans — or indeed whether either will ever be mainstream flight technologies. You have to like GFS, though, for being willing to try something new. Rather than producing a duplicate rival to the Honeywell MAV and similar machines, they are offering altogether different technology which might actually be superior — breaking new ground rather than playing catch-up. Page says it would make sense for the MoD to put some of its scarce R&D funds GFS’ way — rather than giving BAE Systems plc huge, undisclosed sums to play catch-up and reinvent American wheels, as it’s doing right now.

The Coandă effect

The Coandă is the tendency of a fluid jet to stay attached to an adjacent curved surface. The principle was named after Romanian scientist Henri Coandă, who was the first to recognize the practical application of the phenomenon in aircraft development. In the instance of a stream of water attracting a spoon as it flows over the bowl, the Coandă effect is a result of surface tension, or Van der Waals forces, plus Newton’s second and third laws. The effect, in this case, is caused by attractive forces. In the instance of a gas flow over a convex curved surface in ambient gas, however, the Coandă effect is a result of the momentum of the gas and entrainment of ambient gas and has nothing to do with attractive forces. As a gas flows over a convex airfoil, the gas is drawn down to adhere to the airfoil by a combination of the greater pressure above the gas flow and the lower pressure below the flow. The lower pressure below is caused by an evacuating effect of the flow itself, which, as a result of shear flow, rarefies the slow-moving fluid trapped between the flow and the upper surface of the airfoil. Note that supersonic flows have a different behavior, and gas flows in a liquid, for instance, in submarine propulsion using the Coandă effect, are also more complicated.