single rotating assembly 190 the single rotating assembly 190 is driven by a motor 230 coupled to the hub 210 via a bracket 240 the fan operates similar to the mixed flow fan described above so that air enters in a generally axial direction 250 at an entrance of the rotating shroud 220 and is driven axially and outwardly by the rotating blades 200 to emerge in an exit direction 260 the blade angle can be easily adjusted in the fan shown in fig8 this is because the hub 210 or at least that part 270 which contacts the blades 200 forms part of the surface of a sphere centered around a point 280 the edge 290 of each blade 200 which mates against the hub 210 is arranged to fit against the spherical surface of the hub 200 in this example it is a segment of a circle centered on the point 280 the inner surface of the shroud 220 or at least the part 300 which contacts the blades 200 forms part of a sphere centered around the point 280 finally the outer edge 310 of each blade is again arranged to fit against the spherical surface of the shroud 220 and in this example forms a segment of a circle centered around the point 280 in fact at least a part of each of the hub 210 and the shroud 220 in this embodiment is frusto spherical in shape each blade is attached.