Jerry Hey wrote:

Paul,    I have been designing and dreaming about my cooling system
for six months and still don't have it designed. I have defined large
areas of ignorance that I will never bridge without the help of the
engineers on this list. The goal is to avoid increasing cooling drag
over what an air cooled aircraft engine requires and to have the
engine run at the proper temp regardless of outside conditions.
Sometimes I feel these two goals are mutually exclusive.
Additionally,  hanging ugly, draggy looking, scoops out in the air
stream is not really an option. I want my Tailwind to be SLICK,
period.   I don't care how much work is involved or, within reason,
how much it costs.  Effort is not the issue, ingenuity is.

Instead of scoops ducting air into the fuselage, I could build a more
roomy cowl to put the rad up front.  The result is the same, however.
MORE DRAG.   And the beautiful lines  of the Tailwind would be
destroyed.

I realize that I am just venting the frustration that most people
feel when trying to hang a auto engine.  To be honest.  most of the
"solutions" I have seen are hard to accept.  Because of cooling drag,
the aircraft  end up going slower.

Would it be   possible to deliver sufficient air to a fuselage
mounted radiator using NASA ducts on the belly of the fuselage?  In
the Tailwind, internal structures limit the length of the 7º ramp of
the NASA duct to about 20 inches which would provide about 10 sq.
inches of inlet per duct.  I could put four of these side by side
across the bottom of the fuselage for a very clean looking
installation.  But that is only 40 sq in. of intake.

I recall you writing that the inlet size should be at least 25% of
the size of the rad.  This seems impossibly large to me.  I am not
sure if this refers to the volume of the core or just its surface but
it is much more than required for an air cooled engine either way.  I
just walked down to measure the intake openings on my friends 182,
which has, I think, a 470  cu in Lyc.  They are about 80 sq. in.
total.  To cool an equivalent auto engine using say a 1000 cu in RAD,
would the inlet have to be 250 sq in?   I must have this wrong. Does
a water cooled  engine require three times as must air as an air
cooled  engine?

A streamlined belly scoop could be made for the Tailwind.  It could
be 20"/30"  wide easily, but the airplane's looks would be destroyed
if the thing has to hang down 4 or 5 inches.  What if I combined NASA
ducts with a  two  inch deep scoop.  In all cases except taxiing, we
can assume a minimum of 125 mph relative air steam.  That must be
worth something.

Thanks for listening,  Jerry

Not to worry Jerry. I think we finally have a handle on why so many people
are having trouble with cooling. It has to do with a pressure build up
inside the cowl that Chuck discovered. More messages on this subject today
as I have done a bit of research. More on your message too when I get some
of this other stuff out of the way.

Paul Lamar
 
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