On 11/16/2022 11:21 AM, Jeff York via KRnet wrote:
Larry, Valid question and valid thoughts in my mind. For whatever
reason I did it, I also lowered the cowling in the front of my KR. It
slimmed the front profile. I am now wondering how that helps or hurts
cooling.
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I'm not an engineer, engine mechanic, or hold any special degrees so
take anything I say with a grain of salt and confirm using 2 different
sources before you believe it.
On engine cooling: I read, long ago, of an RV builder doing some tests
to verify engine cooling and ignition timing. His test results
convinced me that many aircraft cowlings have openings too large for
best cooling and drag reduction. He was running an 0-320 as I recall
and continued to reduce the inlet openings and recorded the results. He
found the best opening size for cooling and drag reduction to be smaller
than the openings in my Diehl 0-200 cowl. Given that I reduced the
opening in my cowl by several inches in width and never see the single
cylinder I monitor (it may be the coolest) to run more than 300 degrees
in cruise and less in cool weather. That might indicate that less might
be better. I'm not sure what the pressure differential above the engine
and below the engine should be for best cooling but with a couple of old
altimeters and some tubing you could measure the difference in your setup.
On electronic ignition: I'm convinced the greatest reward using
electronic ignition is the ability to vary the timing with rpm. It may
have been the same builder that ran cooling test on his engine but he
used his installation to test timing settings when timing advance is not
available such as magnetos. He tested up and down the scale and found
that, wait, drum roll........................25 degrees was optimal ,
just as Lycoming and Continental determined 50 or 60 years ago, without
computers. My 0-200 was originally set to 28 degrees but cylinder
issues required a change to 24 degrees. With the introduction of new
cylinders timing can go back to 28 degrees.
As far as dual plugs go, once a cylinder reaches a given diameter two
plugs give a better flame front progression than a single plug, hence
the rpm drop with mag check. I have no idea if a single plug fired with
a much hotter spark using electronic ignition eliminates that benefit or
not. I think it has more to do with cylinder diameter than spark
energy. I recall that something in the 4 inch range was given but that
was a long, long time ago I read that. I'm convinced that plug gap
using magnetos is more critical and if the gap gets too big the engine
doesn't run as smoothly at cruise rpm. Several times over the 800 hours
on my KR I sensed the engine wasn't running as smoothly as it could.
Adjusting plug gap to the lower end of the range seemed to smooth things
out a bit. As Always, your results may vary.
Back to the cooling issue. I seem to recall Mark Langford pointing out
to me years ago the difference in cooling fin area on VW cylinders
compared to the 0-200 and similar engines. The aircraft engines seem to
have a much cleaner air passage area and cleaner fin casting than the
VW. That might well add to the lack of cooling when extracting high
horsepower at continuous cruise RPM and the reason I recall Mark giving
attention to that area on his engine builds.
Larry Flesner
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