Message-ID: <007801c3bf9a$592a0260$1702a8c0@WorkGroup>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2885292@logan.com>
Subject: Re: [FlyRotary] Re: K&W Streamline duct vs 7 deg optimum duct
Date: Wed, 10 Dec 2003 22:53:33 -0500
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> Subject: [FlyRotary] Re: K&W Streamline duct vs 7 deg optimum duct
> > Good question, Joe.  I honestly don't have a clue.  The key
> > (according to
> > K&W)
> > appears to be having the side wall diverge just enough so that the
> > pressureincrease along the wall (caused by friction slowing the
> > airstream) is
> > matched by the centrifugal force of the air flowing around the
> > curve of the
> > wall.
> >
>
>
> Another conundrum.  What is the effect of a twisted plenum?
>
> Nearly all the pictures I've seen show a radiator that is something other
than 90degrees to the intake.  Often, the radiator face and intake are
parallel.
>

 I believe you are referring to what K&W calls an "oblique" duct.   They do
have a bit on that subject that I am still trying to digest.  In one case,
my interpretation of what I read (which could be incorrect) is that
"obliqueness" is not as significant a factor on cooling as you might tend to
think.  One place they appear to suggest that a obliqueness of up to 60 Deg
has very little effect in of itself compared to other factors.

Perhaps that is an additonal reason for slowing down the airflow and
converting it to pressure.  Once it is converted to pressure across the
front of the core surface, then it would appear that the flow through the
core is basically dependent on that pressure difference across the core.  So
how the air got there and changed into  pressure (so long as it does)
may be of little "interest" to the core.

 I would expect that would put more emphasize on a good pressure recovery
duct.  Another of their diagrams appears to show an oblique duct in which
the inner duct wall appears straight, but the outer wall follows the
Streamline Duct coordinates which produces a very slight outward buldge as
it nears the radiator face.

So I don't have an answer, but, from my interpretation it appears that if
your duct design is good at converting air velocity to pressure near the
face of the duct, you are probably going to be OK.  Some of the later part
of the chapter starts to talk about "Correction" factors to Cooler Core size
to account for the "Real" world.  Perhaps I will find that an oblique duct
has its own correction factor.

Ed Anderson