US Patent 7585155 Axial flow fan

Blades mounted on a circumferential outer surface of a hub of an axial flow fan do not deform even when rotated at high speed, thus promoting structural stability. The direction of the sweeping angle of each blade alternately changes between the blade root and tip. A chord length between the blade leading and trailing edges gradually decreases from the blade root to an intermediate portion of the blade, and the chord length gradually increases from a predetermined position on the intermediate portion of the blade to the blade tip.