I believe the oddly spaced fan blades chopped up the running audible tone of the fan. Ever seen the Chrysler air raid siren? Its a rotating disk with slats in it that produces a loud tone. The blades that had a high blade count were probably like to move air as the were shorter blades and the center was so big. My 65 came with a X looking fan, 4 blades! Listen to a Huey 2 blade chopper and then a Sikorsky CH-53 that has 6 blades. Whap whap whap compared to a dull roar.
