One time I was playing with a treadmill motor, I had a 6' 2 blader I had made up for a not finished genny laying on the workbench. Gears started grinding, it just so happened I also had the right hub size to fit the treadmill motor. I set it all up clamped in the vice, balanced the blade as well as I could, ran some long cords just in case, and powered it up.
I was 25' away from this thing and it was pelting me with stuff it was blowing around. I don't think it got much over a 100-200 rpm but it certainly was moving air, and anything else not heavy or locked down.