Sender: "Marvin Kaye" <marv@lancaironline.net>
To: lml@lancaironline.net
Date: Sun, 17 Oct 2004 18:11:50 -0400
Message-ID: <redirect-476400@logan.com>
Received-SPF: pass
 receiver=logan.com; client-ip=207.109.1.8; envelope-from=Christopher.Zavatson@udlp.com
From: "Christopher Zavatson" <Christopher.Zavatson@udlp.com>
Subject: Re: [LML] Re: Keeping Ada Cooling Cool
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

To plenum or not to plenum, that seems to be the question lately.
I wanted to add a few comments to the mix.  
Merely having a plenum says nothing about how well an engine is being
cooled.  The plenum itself is only a small piece in a much larger
picture.  You need to consider the inlet, the transition to the plenum
chamber, the detailed baffling around the cylinders and finally the
exit.  Mess up any of these components and a plenum isn't going to save
you.  
The Ada cooling seminar focused on the detail baffling around the
cylinders.  It was amazing to find out that certified installations,
such as the Bonanza, had so many fundamental flaws.  Unfortunately the
IV's and ES's adopted many of the same shortcomings.   Those issues
cannot be fixed with plenums.  It doesn't matter if you have unlimited
air at your disposal, if you don't get it through the cooling fins
correctly.  

To take the next step and go beyond the engine baffle improvements, in
particular for the Bonanza, would be an enormous undertaking given both
the geometry of the installation and the FAA.  In the experimental world
however, I feel there is much more potential for improvement.
Not all plenum installations are successful.  To make generalizations
about their effectiveness based on poorly executed examples is
meaningless.  I have come across plenum installations that span the
spectrum of CHTs, from having the lowest to the absolute highest CHTs I
have ever heard of, on any engine.  -So then why the difference.  All
the parts in the chain from inlet to exit have to be right.  As I said
earlier, merely having a plenum says nothing about how well an engine is
being cooled.  

When I went about designing my system, 99% of the effort was devoted to
the inlets and the transition to the plenum.  The primary reason behind
using a rigid plenum was simply due to the ease of sealing the "plenum"
chamber above the engine to the inlets. The rigid plenum also offers the
opportunity to get a guaranteed seal around the perimeter of the "plenum"
chamber.

The original inlets suffered from the effects of a rapid expansion into
the upper plenum chamber around a most of the inlet circumference.  This
generated all kinds of turbulence, which translates into wasted energy. 
You have to pay for this energy somewhere.  It will cost you in terms of
higher temperatures or reduced airspeed.  
So what can cleaning up the inlets buy you?   All I can report on is the
before and after for my installation.  The Ada trip was my first
opportunity to check higher altitudes.  It turns out the benefit
improves the higher I fly.  Down low the highest CHTs have dropped 30
deg F, but up at 17,500 the difference was 42 deg F.  Bear in mind that
this is with smaller inlets, reduced exit area, and higher EGTs over the
original installation.  I have made no changes to the cylinder baffling
as of yet.  If some of the Ada mods can be employed these numbers may
get even better.  The decreased inlet and exit areas provided another
welcome side effect: an increase in airspeed.  In an indirect way, you
could say that improving cooling efficiency has increased airspeed.
The RV George mentioned obviously has issues. But remember, merely
having a plenum says nothing about how well an engine is being cooled. 
It was certainly poorly designed if it takes two man-hours to remove the
plenum.  Mine comes off in less time than it takes be to remove the
cowl.  It's all in the design.  
In terms of bang for the buck, over the years I had made many small
changes that netted some improvement.  The new cowl was a big a change,
but hit the jackpot in terms of cooling.  Making all the molds for these
parts, and especially, the cowl was a lot work, but I would certainly do
it again.  In fact, if I had known the magnitude of the resulting
improvement, I wouldn't have waited six years to get started.
I would encourage everyone to keep an open mind and not evaluate the
merits of a concept based on examples where that concept was poorly
executed.
Chris Zavatson
N91CZ, running cooler than ever
360 std


Christopher Zavatson
Mobility Technologies
United Defense
(408)289-4329