How to make the best windmill blade?

Question

in a small windmill(15in.X15in.) what demension and shape of blade will give me the fastest rpm. its source of power will be power a 20" fan. thank you

Answer 1

The wind energy to power your mill is greater than the energy needed to drive the fan producing the same air movement.

As a system, this scheme will only reduce the wind speed to a value lower than it was at start.

Answer 2

I think the multi blade ones, like  on those small windmills , used on farms for centuries to pump water.   It'd catch more wind than a 2,3 or 4 blade

and looks easier to build.  with a small diameter you can only catch so much wind - but it'd be less likely to fly apart in a high wind, less need for fancy graphite propellers.