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George is wrong.
If you
can open up a 1.5 inch hole in your baffling and see no change in the cooling of
your air cooled engine in all regimes it was meant to effectively operate, you
have an inefficient cooling system. You have way too much air coming in
and have created a high cooling drag situation. George
is an expert in running "lean of peak" for reducing the power available (HP)
thus, the heat (BTU) generated. Be very careful for what you wish for -- I
happen to like to run at best power -- best power that the engine was designed
for and is capable of delivering forever. It must be cooled to to achieve
that high power condition at the altitudes that the airplane was designed to be
most efficient. Period. It must do this whilst minimizing the
cooling drag. Period. IMHO, Everything else is just screwing around
and messing around. What the devil are we flying high performance
airplanes for anyway? Huh? Huh?
Enjoy,
Scott
Krueger
N92EX
Fuel is the least expensive component aviation!
***********************************
Scott,
Please, let's not mix apples and oranges
here. The cooling air flow discussion has nothing to do with mixture
settings, LOP, ROP, "Best (poor term, better is 'Max') Power", BTU's
etc.
So,
let's take the issues, your raise, one at a time.
First: With respect to cooling air flow,
here is the proposition:
For
ANYBODY's cowling on any six cylinder air cooled engine: If you find
a spot on the back of the cowling that is as remote from any particular
cylinder as possible, and open up a 1.5" hole - - what will be the "before and
after" affect on the measured cylinder head
temperatures?
From the testing I have done on Bonanzas,
Cessnas, Pipers, and various homebuilts, the measured effect is
very small. A few degrees at worst. 2, 3, maybe
5.
I have
not seen anybody run this test (other than myself), nor even claim to have
run this test. So I have not seen any data to the
contrary.
Now,
on the other hand, if you put this 1.5" air leak NEAR a specific cylinder
or cylinders, then it WILL adversely affect the specific cylinders by affecting
the local pressure drop and the local airflow.
If
anybody has any data to the contrary, I would like to hear about the test
and how it was conducted and the results.
It is,
therefore, based on the foregoing, my view that creating inordinate future
maintenance problems by using ungodly amounts of RTV on parts that will,
inevitably, have to be removed for routine maintenance, is a very bad
idea. Much better to design the parts to seal up the air flow in the
first instance, without the RTV caulking.
NEXT, with respect to your short exhortation
about why we fly high performance airplanes, let me take this a phrase at a
time:
>>George is an expert in running "lean of peak" for reducing
the power available (HP) thus, the heat (BTU) generated.
<<
That
is not a correct or accurate statement of either my position or the combustion
engineering involved. The purpose of operating these turbocharged engines
at cruise at A/F ratios of 17, 18,19, or 20:1 is to allow the engines to
operate at HIGHER horsepower settings that they could otherwise be operated
at while at rich of peak A/F ratios (14, or 13, or 12:1) - -
given the same constraints for cylinder head temperatures and peak internal
cylinder pressures. I routinely do this - - and practice what
I preach in this regard - - by operating rated 300 Hp engines at 85 to 90%
of rated horse power (255Hp to 270 Hp) for extended periods at very
high altitudes - - with the hottest CHTs < 380F.
>>Be very careful for what you wish for -- I happen to like
to run at best power -- best power that the engine was designed for and is
capable of delivering forever. It must be cooled to to achieve that high
power condition at the altitudes that the airplane was designed to be most
efficient. Period. <<
Please, be specific. Pick a horsepower
at which you wish to operate the engine. Let me presume the
familiar TSIO-550 engine. Is it 262.5 Hp
? (0.75 x 350) ? Now, please, go out and set your
mixture up to the book "best power" mixture for that horsepower and you will
(according to the "book", TCM Form X30614) be at 21.7
gph. Is that how you would run that
engine?
Or,
would you set it up at exactly the same 262.5 HP and operate it at 50F LOP and
burn 17.9 GPH with CHTs that are about 30 to 35F cooler?
If the
engine is operated 35F cooler (than at some other mixture setting at the
same HP) - - then it means that you could have reduced the cooling drag by a
significant amount if you were willing to tolerate the higher CHTs that are
inherent in operating the engine at "best power" as described
above.
[In
practice, operating the engine at "best power" mixture settings results in
such excessive CHTs (and peak cylinder pressures) that the
operator is forced to use a mixture setting that is much richer than the "best
power" mixture setting in order to even slightly moderate the
CHTs.]
On the
other hand, if your goal is to achieve the same CHTS rich of peak as
lean of peak, maintaining the same HP, then the 21.7 gph fuel flow
(best power mixture) will not be sufficient to do that. it will require
something like 24 to 26 gph to drop the CHTs down to the same (constant cooling
drag) CHTs as the same engine engine enjoys when 50F LOP at the same
HP at 17.9 gph.
The
above is not my opinion. It is all hard data which is published by
TCM. I have verified its correctness by my own extensive
testing.
Scott, I invite you to come by and visit our
facility and go fly with me and see for yourself. I can demonstrate
absolutely everything you see above, in a one hour flight in my
airplane.
THIRD,
and last:
Scott, you say: >>Fuel is the least expensive component aviation!
<<
To
which I respond: Air is the least expensive component in
aviation!
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