As they say, or you can also use chain and sprocket or belts and pullies to gear them up faster than the blades would turn them mounted directly.
I have a 75lb 2hp 180V 11-16amp DC motor sitting here still I am trying to figure out what to do. Electric vehicle, wind gennie, riding mower?? For a Wind gennie I would run large blades of 8'-12' for torque and use large pully on them and small on the motor I think. With a tread mill motor that is what I would do anyway but smaller set.
Some low Rpm motors you can mount blades right on the motor shaft, others not good to do. Some have bearings, some only brass bushings, so that makes alot of difference how long they may last which way.
If I mounted that 75lb 2Hp as a gennie it will produce alot of power with the correct setup! But then that's alot of weight in the air, and I am thinking it would be good for several ground uses.