Again if you don't want low wind performance and want the cheapest solution for high winds then slotted cores are fine.Manufacturers sell on cost and rated power output so they use them but in many cases the low wind performance is not optimum.
I think decent low wind performance is going to be an important issue for most people. Not everyone is fortunate enough to live in Kansas where the standard wind speed indicator is a length of log chain nailed to the top of a fence post, and if that log chain is at 45 degrees to the post you have a light spring breeze, and standing straight out from the post it means a real wind might pick up later.
It appears that's where the iron core I experimented with won't work that well. With a 13 foot rotor the machine, I don't think, would not start turning at all until a 10-12 mph gust hit and it would take a 14-18 mph breeze to get the output on par with a dual rotor axial at the same wind speed.
We're kind of in the dog days of summer here and it takes a thunderstorm to get any real wind this time year. But I would love to mount this generator I got on a 13 foot turbine and fly it to see what it actually does in real world conditions. I would have to rewind it with half the turns of heavier wire to do that but I think I need to know how it actually performs on a turbine before I attempt another core design. I've had things before that I thought wouldn't work based on bench testing (like stators designed for IRP) - but putting them on a turbine yields a different result.
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Chris