<VV> Re: fan tests, vanes TV observation of fan design..

[Rick Loving]

Regarding shape of the cooling fan....
Just the other day I was watching the episode of Mythbusters where they
we building a personal hovercraft or levitation machine.  They had
purchased commercial grade leaf blowers for an air source.  When they
were disassembling the fan to "see" how it pushed air they found a
plastic fan that was about 8" in diameter (estimation, judged from TV)
and shaped similar to our cooling fan. The biggest difference is that
the vanes, instead of straight, were slightly curved at the ends.  It
looked like a cross between a turbo scroll and our cooling fan.

I wonder how much testing the blower company did to model their fan
blade design to push air flow.....

Rick Loving    

<SNIP>
Subject: <VV> Re: fan tests, vanes,etc

snipped and bottom posted

-------------- Original message -------------- 
> Subject: Air distribution on cylinders - stock Corvair 
> 
> 
> >I do not believe the air distribution is equal on all cylinders. The
stock 
> >type of fan, the direction of air flow, the crudeness of the shroud
shape > >lacking internal flow vanes (like a Porsche) lead me to believe
the > >cylinders and heads do not cool evenly. The direction of flow
will dictate > >if R and L side heads mirror each other, especially if
direction of fan 
> >rotation are different. I haven't seen the SAE papers. Perhaps Bob
could > >comment. The average on each side may be similar, but I expect
exacting > >measurements would show differences. I would like to see
both sides > >measured in the upcoming fan tests. Matter of fact, I'd
love to see > >individual cylinder tests. 
> > 
> > Chuck S 

The SAE Corvair paper (authored by Benzinger) has a couple of pages on
the development of the original cooling system.

1- One stated advantage of the vertical shaft fan location is it
automatically provides more "uniform flow to the cylinders." Makes sense
to me, at least to each bank of cylinders, with full peripheral
discharge.  The Germans have to load their ductwork with turning vanes
work to coax  their vertical fans to provide flawed but acceptable
cooling for their simplified two cylinder banks. We clever Yankees have
spent some time "fixing" it.
http://www.sbw.org/assets/index/vw/$file/enginefront.jpg

http://www.evozine.com/images2/911.fan.jpg

http://www.i405.com/vw/stand/FanHouse_OffSetOil02.jpg

http://www.aircooledtechnology.com/type1/dtm/
http://www.aircooledtechnology.com/type1/dtm/DSCN0200.JPG

2 - Chevy started with several flow directing scrolls/diffusers inside a
clear shroud and developed them to achieve uniform pressure distribution
with better blower efficiency (10-15% expectation).  But on a running
engine the cylinders far from the diffusers were not getting enough air
flow. So they ended up cutting back and then removing the diffusers.
"As it was, blower power consumption remained unchanged with or without
(the not optimized) diffusers"

Mr B's speculative explanation for diffusers instant failure was the
lack of space available.  This makes sense to, since the generic rules
for fan inlet and outlet ducting is 10 fan diameters of straight duct
are necessary for reasonable flow patterns to develop
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