Tip speed of class 3 fan is approx 16000 fpm about 2400 rpm for the fan yoiu discribe Horsepower will increase to approx 40 at 2400 rpm . to Direct drive at 2 pole (3500 rpm)appox 50 hp approx 22500 fpm tipspeed . Best reference for this Buffalo Forge Handbook Oops I mean Howden Forge . Think...