'Forward' or 'backward' is not a sensible way of putting it.... if it faces 'forwards' at the top, it faces 'backward' at the bottom and vice versa....
The way to think about this is as a 'concept'. The air is not PUMPED though your disk, it's DRAGGED through it because of centrifugal (centripetal) force. It's NOT trying to use the outer edge to 'scoop' air through like a lawn mower blade.....
The simplest way is to think of it like a Catherine Wheel. The 'spokes' (sparks) of a firework catherine wheel 'trail behind' the centre of the wheel. That's how your venting should look... so mount the disk so it looks like a catherine wheel as it's rotaing (while moving forward).
That's with the part of each 'vane' that's nearest the axle being 'in front' (further 'ahead' in the rotation) than the outer edge of the same 'vane'.
Ian
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