Sender: <marv@lancaironline.net> (Marvin Kaye)
To: flyrotary
Date: Thu, 20 Mar 2003 21:59:56 -0500
Message-ID: <redirect-2081795@logan.com>
Reply-To: "Tracy Crook" <lors01@msn.com>
From: "Tracy Crook" <lors01@msn.com>
References: <list-2081444@logan.com>
Subject: Thick or Thin? The debate continues
Organization: Real World Solutions Inc.
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> >Posted for Fred Breese <brecab@bellsouth.net>:
> >
> >Rusty, Increase the radiator thickness to around 4"(this is why Tracy's
> >airplane works so well) and your cowling clearance problems will go away.
>
>   This is the approach Neil used on his failed experiment with his Lancair
> and Setrab oil/water exchanger. Maybe his problem was due to airflow
> issues, but the arguments I've heard against extremely thick radiators
make
> good intuitive sense to me. If at all possible I'd attempt to gain core
> volume by increasing frontal area before adding thickness.
>
> Mike Wills

OK, here's my take on the thick vs thin rad argument.

I agree that the thinner radiator is 'more efficient' in terms of
dissipating a given number of BTUs with the fewest square inches of fin area
*IF* the volume of air used to do the job is ignored.  This whole argument
hinges on that 'if'.  Every thing I have read on the subject of drag
reduction (related to cooling) points to using the *minimum number of cubic
feet* of airflow to do the job, so, my premis is that the name of the game
is using the *least* amount of air to do the job.

When the amount of air used is the limiting factor, the entire picture
changes.    Every cubic foot of cooling air used represents a fair amount of
energy.  Remember that these cubic feet of air we are using were moving at
around 200 MPH (in the case of an RV class airplane).  That's a lot of
energy .  To minimize the energy lost  means transfering as many BTUs into
each cubic foot of air as possible, and this requires a thicker radiator.
This I will assume for now is intuitive to everyone.  True, the thicker
radiator will require more square inches of fin area and therefore will
weigh a bit more than a thin rad (assuming construction technique is the
same) but the thick rad will require fewer cubic feet of air to do the job,
and that's the whole point!

Some have suggested that we want to minimize the air resistance through the
rad in order to minimize the drag (implying that a thin rad is better).  The
simple fact is that every bit of energy represented by the air flowing
through the rad is lost, gone, kaput, no matter how thin or thick the rad.
You squirt air into anything as disruptive as a radiator and it comes out
with all its energy disipated.  I welcome arguments to the contrary.

So, I see the choice as:  Do you want an 'efficient' radiator or an
efficient airplane?

Tracy Crook