"220V Cooling Fan" of the three blades is why most of it? This is because if the number of blades of the fan is even, and the formation of a symmetrical arrangement, then the fan itself not only makes it difficult to adjust the balance, and easy to make "220V Cooling Fan" to produce more resonance at high speeds, causing Leaves can not withstand prolonged fatigue resonance eventually appear blade fracture and so on. And when the fan blade number is odd, it is impossible to achieve symmetry leaves an odd combination can bring more performance advantages over the blade combinations even. This principle is widely used, including parts of the helicopter propeller including a variety of "220V Cooling Fan" fan design.