Sender: <marv@lancaironline.net> (Marvin Kaye)
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Date: Mon, 30 Aug 2004 09:41:38 -0400
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From: "Gary Casey" <glcasey@adelphia.net>
Subject: Engine Cooling
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I'm about to figure out the cooling system on my ES, so all the recent
postings on cooling were very interesting, although none seemed to impart
any take-it-home factual information.  From what I can tell, there are no
real "secrets" on cooling systems, only a lot of obscure facts.  Here is
what I have gathered about the issue:
1.  Pressure recovery (converting the high velocity free-stream to low
velocity higher pressure air with minimum energy loss) is critical and it
looks like the Lancair cowl does this ahead of the entrance as the cowl
openings are larger than they could be.  This is probably a good, efficient
approach.  However, once the air enters the cowl, no attention at all was
given to pressure recovery.  Should there be?  I think so.  The idea is to
get maximum pressure above the engine.
2.  Eliminate all wasted air flow across the engine, primarily by
eliminating any leakage paths.  This is the most obvious point and one on
which everyone seems to agree.
3.  Control of air flow patterns inside the cowl is important, but here
again it looks like Lancair (and most other airframe builders) have given no
thought at all to this.  Their assumption must have been that once the air
is inside the cowl it will just magically get to where it needs to go.  The
air at this point is at a relatively low velocity so this as some validity,
but I'm not convinced.
4.  Exactly how the air gets around the cylinders has to be critical and
this seems to be done mostly by the engine-manufacturer-provided baffles,
but I'm not convinced these are optimized either.  The most important
airflow around the engine has to be across the fins between the valves and
I've never seen any directed effort at maximizing this flow path.  My
judgment is that the temperature around the cylinder head is nowhere near
constant, but how does one improve upon this?
5.  And finally, the airflow in the lower cowl has to be managed.  In most
systems I see zero effort in this regard.  Even Lancair, although they went
to the trouble to provide a curved, converging flow path at the top of the
cowl outlets, put sharp edges at the sides, which accounts for more than
half the entrance periphery.  As I see it, the objective of the first four
points above is to cool the engine while allowing the HIGHEST lower cowl
pressure to be maintained.  This pressure can then used as the energy source
to accelerate the air back up to somewhere near free-stream velocity, but it
can only do that if the exit nozzles are efficient.

I would appreciate any discussion on these points.

Gary Casey