Bill Freeman wrote:

Paul,

I think the key to cooling is to decelerate the air while raising the
pressure (diffuser) efficiently and then have the pressure differential
move the air thru the radiator, then re-accelerate the air back up
to near free-stream velocity.  Easy to say, hard to do.  The
90 turn does not make as much difference if the air is slowed
enough. Since drag is a V^2 affair, slowing is  very good to lower the
losses thru the rad.

Also, using a airspeed indicator is a lot less messy than a bunch
of manometers.  Used that on setting up the cooling system on
the 150 hp Long EZ.  Works well when you listen.

Bill

Excellent and concise description of what happens in the 
duct Bill. Thanks.

Here is a little diagram from Hoerner Fluid Dynamic Drag
that illustrates this situation. You could also plot
velocity along the duct as well as just pressure is shown
here. P1 X V1 = P2 X V2.

The funny looking squiggly line is Hoerner's
symbol for loss coefficient. Sometimes I wish people
would use alpha characters for this sort of thing. I would
have a much easier time remembering what everything meant.
I guess I am just not an icon kind of guy. 
I never liked the MAC.

On the other hand Hoerner uses w for average velocity in one 
place and V for a different  velocity in another. What is 
the German word for velocity?

fluiddy1.jpg
 
Paul Lamar
 
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