Quiet fan with non-radial elements

Claim 1

In an axial flow apparatus of the type described, in combination: a rotor unit and a stator unit each comprising a circumferential array of vanes; said rotor unit being rotatable in axial adjacency to said stator unit for imparting energy to an axial flow through the apparatus; one of said units having a frame comprising inner and outer supports; said vanes of one unit including a plurality of non-radial vanes of airfoil cross-section which are similarly oriented in nonradial positions leaning circumferentially away from the radial in a common direction throughout their radial extent; said vanes being secured between said supports; the vanes of the other unit being oriented in positions angularly related to the positions of said non-radial vanes; said non-radial vanes comprising a first circumferential array of vanes all similarly oriented in positions leaning circumferentially away from the radial in one direction and a second circumferential array of vanes leaning away from the radial in an opposite direction; whereby the pulsations created by the vanes of said rotor unit passing the vanes of said stator unit will be attenuated by the radial progressions of the crossings of the relatively moving vanes, thereby reducing noise.