<VV> Fans and air flow

Wed Aug 1 16:54:57 EDT 2007

Grrr.  This subject just won't go away.

Well, I think we all agree that the stock Corvair blower uses a lot of
horsepower - so much so that replacing it with an electric motor is not
practically feasible.  

However, there has been much discussion about improving airflow by opening
up the finned passages, adding external oil coolers, etc.

I think another thing we can all agree on is that GM was not putting a lot
of effort into improving the airflow through the engine, adding external oil
cooling, etc.  The car was expensive enough to mass produce as it was and
they certainly weren't going to do anything more than they had to.  Also,
consider that most folk back then only kept a car for a few years, so they
weren't making them for longevity either.

Having said all that, it is therefore likely that the horsepower requirement
of the stock Corvair cooling system is probably higher than it needs to be,
as the factory would have designed in excess capacity to overcome the
restricted airflow, etc.

So what have we learned?  The electric fan setup, as sold, does not properly
cool a stock Corvair engine.  No big surprise there.  

But do we know for certain that you cannot cool the engine with an electric
fan IF you optimize airflow, fan/blower and shrouding characteristics, and
use external oil cooling, RAM air flow, etc. etc.?

Well, here is where I side with "the Curmudgeon".  As far as I am concerned
it is all speculation until somebody actually builds a contraption and
proves it to work.

Yes, I know the engineers out there will pull out their charts, tables, and
slide rules (oops!  I mean calculators!) and prove on paper that it can't be
done, given the heat output of the engine, the density and thermal
properties of the air, etc. etc.  So if you are an engineer, just sit back
and relax with that smug look on your face and consume your personal
favorite beverage (or "cooling system" as we doctor types like to call it).

As for the rest of you - go out to your garages and start building
something.  Let us know when you have succeeded and we will watch all the
engineers swallow their slide rules and choke on their beverages.

Meanwhile, I will continue to wonder how those great big metal airplanes
actually fly while my patients keep telling me they know their bodies and
that only the latest and greatest drug will work on them.

Now, can we give this topic a rest?  Please?

Bill Hubbell

-----Original Message-----
From: virtualvairs-bounces at corvair.org
[mailto:virtualvairs-bounces at corvair.org] On Behalf Of ScottyGrover at aol.com
Sent: Wednesday, August 01, 2007 4:23 PM
To: virtualvairs at corvair.org
Cc: fastvair at yahoogroups.com
Subject: <VV> Fans and air flow

I have been reading this line of comments and maybe I could add a little  
something.  For my credentials--I don't have a ME degree But what I do have
is 
45 years as an estimator reading HVAC plans and specs.  OK??
An axial fan (prop) is fine mounted on a floor stand or in an outside wall  
where there is little or no ductwork attached to it; it can circulate quite
a  
lot or air.  When it is ducted (duct-axial or vane-axial) it can move air  
against air resistance (called static pressure) but the horsepower
requirements  
are quite high; airlines have lots of horsepower to spare so that's how they

run  those FAT jet engines on modern planes.  Now centrifugal fans
(sometimes  
called squirrel-cage blowers) need--ideally--a scroll-shaped casing and send

the  air parallel to the outside wall of the scroll.  Centrifugal toilet 
exhaust  fans (the kind you see in a restroom with the stamped grille
showing) don't 
have  a scroll but as long as they are in a box they can put up pressure 
which will  force3 the air out of any available opening.  Corvairs use a 
centrifugal  fan of a rather crude design (at least the magnesium fans are)
which is 
using  the shroudwork as its plenum.  They would work better if there was
less  
clearance at the top of the "turkey roaster" but the wheel design uses much 
more  power to get the job done than it should.  Maybe the early model fan 
wheels  should be used as a mold to make a lightweight plastic fan modified
to make 
sure  it fits is the roaster but with a minimun clearance.  
I have not seen photos of the prop. fan that was used in the test but one  
report stated that the fan was blowing on a flat plate and was observed to
blow  
upwards; this is a total SNAFU.  There should never be an obstruction like
a 
flat plate near a prop. fan; any ductwork downstream of the fan should be  
carefully angled to bend the flow of air outward and direct it to the
cylinder  
fins.  
Also, as several people have stated, the fins should be cleaned up to  
minimise the obstruction to air flow; this probably lowers the HP
requirements  of a 
stock fan also.  Anyone trying to use an electric fan should take all  steps

necessary to lower the power requirements of the engine before they mount
the 
electric setup; however, this was not part of the test requirements; it  
would be interesting to mount the electric system on a properly cleaned-up
engine 
and see what that would do in the way of changes.

Scotty from Hollyweird

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