Tracy Crook wrote:

Jeff Spitzer wrote:

Tracy Crook wrote:

BTW, that cooling system chart that Neil sent looked odd to me. 
 I thought
outlet area was always supposed to be larger than the inlet.  Mine is.
Have I got it all wrong?

Maybe and maybe not.  It all depends on the system.  If the system uses
mostly internal diffusion (as opposed to external) then the outlet will
usually be bigger than the inlet.

Jeff Spitzer

Thanks Jeff, [and Fred] very interesting thread here.  I think I learned something.
This also explains why Everett removed the spinner on their rotary powered
plane when they were racing.  They were using an annular ring inlet and
without the spinner in place it "looked" draggy as hell.   Obviously  looks
can be deceiving.   My cooling system is using the internal diffusion scheme
which was the only one I was aware of before this discussion started.

Tracy Crook   rws@altavista.net

I don't think Everett was quite THAT sofisticated :-). I think it did
not cool
all that great. The rads where in there horzontal so a lot of the
diffusion was
done internally. I think he originally felt if he dumped the air into a 
well sealed plenum and exited into another plenum below the engine 
everything would work fine. We discussed it and he told me it needed 
re-design but he had not got around to it.

Removing the spinner was just a bigger hammer. Rare Bear has a huge
spinner.

One of the problems was the rads were picking up heat through radiation
from the exhust system. Another problem with dumping hot air into the
cowl 
is the heat from the rad (as Jeff pointed out, it should be nearly as
hot as 
the water) adds to the general heat around the engine and makes it 
that much more difficult to cool. 

IMHO It is better to duct the air out of the rads like a P51 type system
and NOT into the engine cowl. If you can fit them in there, ducts that
carry
the rad air  out the sides of the cowl and back to the low pressure
area, 
above the wing, would be better. At idle, without these ducts,
all this hot air is probably flowing out through the rads, back to
front.
 

With an air cooled engine it is practical to allow the exit air to go 
into a lower plenum as it has already passed over the engine and done
its 
job. Also the exhaust pipes are below the engine which is probably 
the reason updraft cooling does not work too well.

The fastest RV's in the country, right at the moment, Tracy Saylor and
Dave 
Anders, have spent a tremendous amount of time refining the internal
diffusion
systems on their airplanes. Tracy Saylor is using two holes about 3.5
inches
in diameter on his Rv6. I was going to take a picture yesterday but 
Mr. Saylor took off before I had a chance. Maybe today. Dave Anders 
holes are only slightly larger and he is cooling at least a 250 HP 
engine.

BTW all this cooling development illustrates one of the advantages 
of racing that has not be mentioned on here before.

Paul Lamar
 
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