An axial fan for a cooling blower of a vehicle engine has fins with leading and trailing edges, and aeroacoustic optimization is provided by each of the leading edges and trailing edges having a strong forward sweep followed by a strong backward sweep in the manner of a bird's wing or by a straight forward...http://www.google.co.uk/patents/US5961289?utm_source=gb-gplus-sharePatent US5961289 - Cooling axial flow fan with reduced noise levels caused by swept laminar and/or asymmetrically staggered blades
