What would it matter if a vacume is caused behind the blades when there is only so much pressure in front of the blades to begin with? It's not going to pull any more air through than what is available. I would understand if there was a ventura in front of the blades to increase pressure/flow..
The law of leverage is going to be a hard one to beat. long blades = torque. I can move a lot of weight with a cinder block and a 4"x4"..
