I remember once observing a thread in a discussion forum by someone trying to build a backpack helicopter. Various people warned him about sprung-weight-vs-unsprung-weight, hazards of stability and flight control, etc. But ever since reading about James Dyson's bladeless fan and the well-known Coanda Effect, I've been wondering whether it could be adapted for propulsion purposes, into some kind of personal transportation device. http://www.aviationweek.com/aw/blog...&plckScript=blogScript&plckElementId=blogDest http://www.geeky-gadgets.com/dyson-bladeless-fan-13-10-2009/ I'd like to know - are there any inherent limits on using Coanda Effect and this bladeless fan idea for propulsion? Coaxial helicopters in particular have a smaller footprint because the counter-rotating blades eliminates the need for a tail-rotor, and of course the dual blades generate more thrust within that disc space. Would it be possible to make the bladeless fan ring work the same way as coaxial contra-rotating rotors, by linking 2 of them together somehow? The impeller inside the Dyson bladeless fan seems to present low sprung weight, and the airflow ultimately produced is smooth, as opposed to the choppier airflow of the helicopter's blades. Presumably this would add to flight stability. Crucially, the lack of external rotating blades would make it safer than any hypothetical helicopter backpack. Dyson's fan is also supposed to be fairly quiet. But what are the drawbacks to this impeller-with-coanda design? Does it trade off power-to-weight efficiency enough to make it infeasible for propulsion purposes?