A fan has a hub and a plurality of blades each having a medial line, a root region secured to the hub and extending radially outwardly to a tip region, with a leading edge and a trailing edge of each blade having a respective surface portion which is tangential to a respective radius of the fan, the leading edge and the trailing edge of each blade at the tip region being circumferentially behind, with respect to a first direction of rotation, the leading edge and trailing edge at the root region whereby the fan is rearwardly skewed wherein each blade has a dihedral angle formed between a plane perpendicular to a center axis of the fan and a line tangent to the medial line, each blade having a surface which is curved so that the dihedral angle decreases along the span of the blade moving from the root to the tip over a portion of the span equal to about 50% of the total span and wherein the dihedral angle increases over the remaining portion of...
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