Waterproof Cooling Fan blade design

"Waterproof Cooling Fan" Tip Gap: How to adjust the gap that exists between the fan and the fan frame design is a major problem. Here the gap is too small will make the airflow and blade, frame friction, increasing noise; increase the gap is due to the influence of the flyback airflow and so reduce fan efficiency.
"Waterproof Cooling Fan" blade Arc: In addition to having a curvature of the blade in cross-section, the plane is not in the plan view extends along the radial straight, but slightly bent toward the direction of rotation, was a certain arc. If the blades radially extending straight, driven by rotation of the fan at the outlet side of the air show a widely scattered, air distance is short, and the "power" is not focused; slightly curved as the current product version, you can ensure that the blowing airflow focus within the columnar space in front of the outlet, adding "Waterproof Cooling Fan" blowing away with the wind pressure.