Abstract: A fan for attachment to fan clutch housing members having supporting shoulders at two different radial distances from their axis, respectively. The fan comprises a plurality of fan blade supporting arms extending radially outward from a hub and a central opening formed through the hub. The central opening is defined by a plurality of angularly spaced apart inner arcuate edges located at a first radial distance from the axis of the hub and a plurality of angularly spaced apart outer arcuate edges located at a second radial distance from the axis of the hub, wherein the second radial distance is greater than the first radial distance.

Abstract: Disclosed is a multi-blade fan assembly and method for manufacture, the fan assembly having a central hub having means for being attached to a driving assembly and having a plurality of fan blades connected therewith and extending radially therefrom; and further characterized by having the fan blades manufactured in accordance with subcritical aerodynamic air foil criteria so as to be efficient for moving ambient air at low relative speeds between the fan blade assembly and the air and for minimum power consumption and noise at high relative such speeds. Each of the fan blades has a length to width ratio L/W within the range of 1-9; has a length L in the range of 6-18 inches; has an artificially reduced chord thickness to length ratio within the range of 0.03-0.12; has a chord that is totally contained within a perpendicular planar cross section of the blade at the chord location and has a twist for obtaining a substantially uniform flow of air throughout the length of the blade.