[Big Al]

and my apologies for letting a bit of sarcasm sneak in. The point I was trying to make (not very well ) was that fans , propellors , turbines all have the same basic problem of trying to couple mechanical movement to fluid movement and what works fluid- to- mechanics ought to work mechanics-- to- fluid.Or does it ??? Sounds like we need one of those philosopher /mathematicians to answer that . The sort of guy who can tell me if Bett's law can be broken by a wind turbine blade that almost reverses the flow ( a la Pelton wheel ). Its probably not relevant to wind but I believe Peltons , working with a nice chunky fluid like water , achieve efficiencies in the nineties.
I agree that the maths at first make the jet turbine claim to be the equivalent of a normal turbine twice the diameter seem impossible but if the vortex produced at the back of the jet turbine sucks in flow that would normally pass the turbine--hey who knows ?? Maybe not twice the diameter but maybe part way there.
Anyway I think it looks awful nice , the sort of turbine one could take home to your mother.