A variety of "Waterproof Cooling Fan" section curve of the blade, angle and other basic similar, each blade width often depends on the height blades. In order to ensure the blade pitch will not be too large, the impact of wind pressure, diameter and height is relatively small (ie relatively thin) to increase the number of fan blades to use more methods to compensate. Regardless of the number of blades "Waterproof Cooling Fan" is more than a little, but the number of axial fan blades are often 3,5,7,11 and so odd, which is due to the use of a symmetrical shape even-piece blades, but did not adjust the balance , it is easy to make the system resonance, if the blade material is unable to resist fatigue vibration, will make "Waterproof Cooling Fan" broken blade or mandrel, so much designed as an odd piece about the axis of asymmetric blade design. This principle is widely used in a variety of designs including some helicopter propeller blades, including the.