the article crutschow linked:
https://www.warlock.com.au/10kwgenerator-abstract.htm
I'm going to be generous and give them 3KW at 515 rpm. at 50% efficiency.
32 magnets, each 2 inches by 1 inch by .5 inches.
that is 32 cubic inches of magnet.
with 1.5 cubic inches of magnet, I got 138 watts from this:
**broken link removed**
at only 8.5% voltage drop, and used not even one pound of copper.
which means there's 11 watts lost in the copper.
probably 50 watts lost in the iron, but i don't have an iron loss number yet.
so if i pick a reasonable number like 50 watts copper loss that comes out to a 300 watt machine, at 500 rpm, and 75% efficiency. 400 watts in, 300 out.
so divide 3 kw by 32 cubic inches of neodymium and you get 93 watts per cubic inch.
about the same as what i got.
now surprisingly we get about the same value, but mine is running at 8.5% copper losses, theirs at 50%.
but one relatively unknown property of electrical machines is they are supposed to scale at the 4/3rds power of the specific size.
axial machines also scale torque with radius cubed, as opposed to radial machines with the radius squared.
because air core machines are always copper limited,an axial machine that uses 32 cubic inches of magnet, and is on the order of 16 inch diameter, 15 poles, should generate something on the order of 38 horse power, at 500 rpm.. at 95% efficiency.
i think there's something wrong with that number but one benchmark you can use is the toyota prius pulls 80HP out of a 4 pole motor using 18 cubic inches of neodymium magnets at about 600 hz or 9000 rpm iirc.
a 16 pole motor would spin at 2250 rpm to generate that much power and you would have to double the radius of the machine, but you would use exactly the same amount of magnet, and copper to get the same mechanical power.