Two colleges are doing two pre-rotators projects for PRA. In horsepower terms to spin 30-foot blades, it takes 3HP for 150 RRPMs. It takes two-speed transmission and 3HP to spin it up to 170 so far. The class ended before we change the gearing for the 2nd time to learn just how fast we could spin them. With the transmission, it is like 5HP.
The 2nd college just started the phase of ordering the parts for a lightweight state-of-the-art prerotator and the math show us that we need a 7.2 HP motor to spin the same 30-foot blades to 220 RRPM. I have most of the parts and an 8HP motor sitting in my living room waiting for the SDSU semester start 8/27.