That must be one of the reasons why the six-bladed fan (the -8600 one) is also
not symmetrical in that the blade pairs are 180 degrees apart, but each of the
pairs are not spaced 60 degrees apart. The other reason would likely be noise:
If all the blades are equally spaced you would get a drone from the fan that was
very distinctly related to engine RPM, and that was of relatively pure tone.
Breaking up the spacing between the blades causes the noise to be generated at
multiple frequencies, and that tends to blur out the noise somewhat. Tire
designers also do this to tread patterns to keep the tires from having a
distinct whine.
Theo
Derek White wrote:
> One point not mentioned in this round of the Volvo fan discussion is that
> the asymmetrical blades cause an un-stable vortex that moves around the
> radiator instead of staying centred as is the case with a symmetrical design
> fan. This gives much better heat exchange-- greater surface area covered and
> higher temperature differential since you're not pulling most of the air
> through the same small area of the radiator core. Apparently infrared
> cameras show this clearly.
>
> This wisdom was passed on some years ago on the list. cheers, derek
>
> Derek White
> 37/2 Buller's Lane
> Colombo 7
> Sri Lanka
> Tel: 94 1 581175
> Cell: 94 777 475955
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