<VV> Plastic radiator fans
wrokit at hotmail.com
Sat Feb 3 17:57:02 EST 2018
Plastic Radiator fans have been a mixed bag... in some applications, they seem to last a long time, in others not very long.
The big differences are how high the peak temperature is, how high the peak rpm is, and how hard is the shock from changing
rpms, and of course how much horsepower they have to use. None of those factors favor usage in a air cooled engine application.
They certainly have been tried for racing, and it doesn't seem to take long for the blades to bend, just from aerodynamic forces!. Usually, when fans have the exact same strength and stiffness there isn't much difference in weight, steel vs plastic. It is only when it is possible to compromise on stiffness that big weight reductions are possible... I really need a stiff fan for a design like this! modern turbo's would look exactly like mine do at the tips, the reason they don't is because of tip flutter from pressure... something I don't have to worry about as the pressures that this fans is supposed to run at are much lower, but still far higher than any "propeller"type design can do. I designed this fan to be grenade proof even if it is run up to 28" and has been spun up as high as 11000 rpm, just short of some OE Porsche tip speeds... and as I discovered recently, is probably way more output and pressure than any aircooled engine can really use. It seriously needs to be geared down a lot for most applications, which is part of what I was after, as lower tip speed is the most effective way to deal with inertia. Also, notice those huge scallops in the tips
of the fan- those scallops have a fairly sizable impact on the inertia of the fan, but doesn't change the weight very much- there's
also flow and efficiency reasons for those scallops being there, but my big reason for doing that was for inertia reduction.
Just in case any of you are curious, the level of effort required to accelerate my fan with a stock sized pulley seems to be identical
to accelerating the alternator with its pulley.
63 Turbo EFI daily driver
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