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[Fwd: [canard-aviators] Re: COZY: Re: Cylinder Head Temps]
Hi Folks !
Reprint with permission from C.W.Wright, webmaster, Canard-aviators, is
Nat Puffer's thoughts on CHTs, in case any of you missed it.
IMHO, CHTs can be kept in check by
1) a general tightening up around the plenum & cowl,
2) allow for which side of cyl your probes are located per Nat's info,
knowing that our plenums are down-draft, not up-draft.
3) Check out V-Views "super-cooling" armpits (I don't have the issue
4) Do it like Simon did
5) Did you de-burr (or see any need to) the Franklin cooling fins ?
Also, for David Doshay & other water cooled guys, I'll get the issue #
of Central States Assoc newsletter that has fascinating article/drawings
on ram-cooling the radiator with "exhaust augmentation"...minimizes
cooling inlet drag & seems to actually provide (in theory) a slight
amount of thrust... that was on a rotary.
General question: Does anyone have the phone number of the rotary guys
that spoke at Sun-n-Fun banquet ? They may have some hot deals on
300-400hp rotaries (they were claiming 300-600hp I think, depending on
how crazy you want to get) as they really want to get one of theirs
flying. (I'll most likely opt for an IO-540, but the power
potential/drag reduction possible with a rotary is very intriguing).
Also, did anyone actually see their engine(s) ? I couldn't find them,
but they said the be running the rotary & a turbine off/on thru the day.
XL-RG N411JB just a-buildin'
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[The Canard Aviators's Mailing list]
Dear Ken and Builders,
One time on the way to Sun and Fun, we overnighted with a Long EZ
builder at Ft. Stockton. He was complaining about high cylinderhead
temperatures. The next morning I checked over his installation. His
engine baffling wasn't the best, but the first thing I noticed was that
he had rather large openings around his exhaust pipes. I explained to
him that these openings were letting a lot of cooling air escape, which
reduced the pressure inside the cowling and reduced the amount of air
flowing through the engine. When builders experience high cylinder head
temperatures, there is usually a reason. When they call me with a
complaint like this, without being able to inspect their installation,
all I can do is ask them about it. I can verify that my 0-360 Lycoming
is installed and baffled as I show in the plans. When I rebuilt my
Lycoming, I used a B & C spin-on oil filter adapter, so I could no
longer mount the oil cooler so the air exited at the top of the cowling.
So I mounted it at the wing root with the air exiting out the bottom of
the cowling. I am using a 13-row cooler, and my oil temperature usually
runs below 180 deg F in cruise (2600 rpm) at altitude in the summer. My
cylinder head temperatures run from 290 deg F to 335 deg F measured with
probes at the bottom of the cylinders with updraft cooling. That is
what they ran with my 1800 hour Lycoming before I rebuilt it, and that
is what they run now with about 65 hours on my Lyc after rebuild to new
With updraft cooling, the probes are no longer on the hottest side of
the cylinder, so you have to mentally add about 40 degrees before
comparing the readings to Lycoming specs. If you are using themocouples
under the plugs, they read about 40 degrees higher than the bayonet
probes would read. So if you are using thermocouples under the bottom
plugs, you can compare those readings directly with Lycoming specs. If
you are using them under the top plugs, you need to subtract 40 degrees
before comparing them to specs. Lycoming says that you should not run
an engine continuously with cylinder head temperatures over 400 degrees,
if you expect to get the best life out of the engine. Optimum oil
temperature is 180 degrees F, and I believe you should not accept oil
temperatures over 200 degrees. The cylinders close to the fire wall
usually run the hottest, because the least pressure drop for the cooling
air is to go through cylinders #1 and #2, so it is necessary to install
baffles in the bottom cowling to intercept the high velocity air which
piles up at the aft of the cowling, and redirect it through cylinders #3
and #4. You should measure the temperatures in all cylinders so you can
balance them. The airflow changes at different speeds, so you balance
them at one particular speed and accept the variation at other speeds.
It is not necessary to put vent holes in the top of the cowling
(unsightly) if you do the correct baffling in the bottom cowling, UNLESS
you have a restriction in your top cowling. I experienced this with the
Franklin engine, because it was a longer engine, and solved the problem
by making the blisters a little taller so there was more room for the
air to get out. One last thought, oil provides one-third of the
cylinder cooling, so it you are running with too high an oil
temperature, you will probably have cylinder head temperatures which are
too high as well.
It increases drag to use more air than the minimum necessary to cool the
engine. The NACA flush scoop shown in the plans provides more than
enough air to cool the cylinders and oil for an 0-360 engine. If your
temperatures are too high, you need to study your installation. You may
have too small an oil cooler, or lines that are too small, or leaks that
let air escape without cooling, or restrictions which won't let the air
get out. There could be many causes.
> From: Ken Reiter <firstname.lastname@example.org>
> Hello Mark,
> Thanks for the quick reply. I have 11.6 hours on my CozyIII and
> things are working almost fine. The plane is a joy to fly!
> Many thanks Nat and Burt.
> Slight issue with the alternator - going for a replacement.
> Oil temps are high - tried the MarkIV way but just did not
> have enough room for air flow ( have the B&C spin-on filter ).
> Switched to the PLAN'S way ( Nat does have know how) and oil temp
> is now down to 180 at 3000' at 2200 rpm.
> CHT 2 is high (446) / 1 is low (374) - I made ramps as big as
> possible and now in process of sizing down and matching temps.
> I am using probes under plugs on top. I think it is accepted
> that (ref is 500 max measured at bottom tap with up draft cooling)
> the bottom tap reads 50 low on the cool side; while the plug
> reads 50 higher than tap. Sooo, my 446 on top plug is really
> 396 as lycoming specs??
> Please let me know how the top opening are working.
> Ken Reiter
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