<VV> Fans and air flow

[BBRT]

Good comments. Thanks.

Chuck S
----- Original Message ----- 
From: <ScottyGrover at aol.com>
To: <virtualvairs at corvair.org>
Cc: <fastvair at yahoogroups.com>
Sent: Wednesday, August 01, 2007 4:23 PM
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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