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lancenewman(at)comcast.ne
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 Posted: Wed Feb 01, 2006 12:11 pm Post subject: CYL high temp |
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Those temps sound reasonable to me. Frankly, I would wait until the seasonal
temps begin to heat up a bit and see how the airplane flies leaned back at
altitude. Remember that temps will come down as your altitude increases.
Your well below the recommended temp for maximum service life.
I'm flying an RV6 with a new 0320 D1A and an 80 pitch Sensenich FP. I'm
running about 374F at 65% cruise and 392F flat out. My climb temp is 428F
full throttle. Oil temp 176-194F. This is at 3000' and below. At 8000' and
above subract about 3-5 percent from those numbers. Here is the complete
list of CHT problems in case you don't want to read all the way through this
message before troubleshooting.
1. Spark plugs of improper heat rating
2. Cooling baffles, missing, broken or bent. Be sure you have the lycoming
baffles between the cylinders. Not just the baffling kit that came from
Van's.
3. Partially plugged fuel nozzle
4. Fuel lines of improper I.D. Should be .085 to .090 for lycoming engines.
Primer lines must have restrictor fittings.
5. Engine improperly timed.
6. Engine running too lean. Look for carbon deposits in the combustion
chamber, if there are none, the engine is being run continually too lean.
7. Improper rigging of mixture control. Ensure full travel capability.
8. Exhaust gas leak into the cylinder. Look for burned paint or white
deposits.
9. Loose or bad CHT leads. Only use bayonette style. Spark plug ring style
are junk.
Temps to remember
Oil Temp - 160F to 245F . At least 180 deg F to ensure vaporization of
moisture out of the oil.
CHT- Minimum in flight 150F. Cruise range 350-435F ( not to exceed 400F
for maximum service life)
EGT- 1200-1600F. (1400F for maximum service life)
Probe calibration
Forget about having to buy expensive thermometers to calibrate your probes.
Just emerse the probes in boiling water and look for consistancy around 212
deg F. If you have all 4 monitored, try swapping around to look for a change
in readings. Once you feel comfortable that your monitoring is accurate to
within 10 deg F or so you can begin to look for ways to bring the temps
down. The most common sources of problems lie in Mixture control and baffle
efficiency. Lets attack them one at a time
Mixture Questions
Which is your hottest cylinder, should be #3 or #4. The leanest running
cylinder is going to be the hottest. My experience is that #3 usually runs a
little leaner than the rest and therefore hotter. If you have carb heat, try
cracking it slightly to enrich the mixture and see if the temp comes down.
If this works, you might go with it. If your still worried, we will move on.
If your engine is running a bit lean at cruise rpm, the only way you can
improve this would be to bore out the jets by a tiny amount. This would be
the last option after you try all else. The mixture dial on the carb is only
for idle mixuture adjustment and will have no effect on cruise mixture.
Baffling Questions
Have you tried to tape vortex generators on the baffling just forward of the
entry to cyl 1 and 2. They will increase airflow past 1 and 2 and feed more
air back to 3 and 4. The comments about keeping the cylinder fins clean and
clear are good ones as well. You can also adjust the air exit velocity by
playing with your safety wire length under the baffles. If you want to get
real inventive, you can change the air exit velocity from the coweling by
cutting away about 1/4" at a time from the trailing edge of the scoop.
The biggest breakthrough I found was to put fiberglass boxes above the air
entry ports into the coweling using those funny looking layups that Van's
sends you with the finish kit. Pop rivet and glass those in and seal off the
open ends with more layups so that air can't circulate unterneath them.
Frankly, I would wait until the seasonal temps begin to heat up a bit and
see how the airplane flies leaned back at altitude. Remember that temps will
come down as your altitude increases.
Happy Landings
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Kellym
Joined: 10 Jan 2006
Posts: 1700
Location: Sun Lakes AZ
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| Posted: Wed Feb 01, 2006 12:43 pm Post subject: CYL high temp |
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I'm not sure the basis of your temp recommendations. The best
recommendations I know come from Advanced Pilot Seminars, where they
have more data to back their recommendations than anyone. Oil okay.
CHT, there is no minimum temp for max life, that is an OWT.
Maximum for any flight phase, including climb should be 400F.\
EGT, for normally aspirated, there is no maximum, especially none for
maximum life, but much over 1500 is unlikely. Turbos, totally different,
they do have TIT maximums. What matters is all cylinders peaking as
close to each other, in terms of fuel flow, not temp. You are only
looking for the peak on each cylinder, not an absolute temperature.
You are totally incorrect about why #3 on an O-360 or IO-360 runs
hottest. Has very little to do with mixture, and if it were leanest, it
would only be hottest on the rich side of peak, where you don't want to
be anyway. #3 runs hottest because of the way Lycoming designed the head
casting to have NO cooling fins on the back side of #3 (and front #2).
If the baffling is tight against the cylinder head, it will run 30-50
degrees hotter than if you leave a 1/8" to 1/4" gap for air to get through.
KM
A&P
DO NOT Archive
lancenewman wrote:
| Quote: |
Those temps sound reasonable to me. F
Temps to remember
Oil Temp - 160F to 245F . At least 180 deg F to ensure vaporization of
moisture out of the oil.
CHT- Minimum in flight 150F. Cruise range 350-435F ( not to exceed 400F
for maximum service life)
EGT- 1200-1600F. (1400F for maximum service life)
Probe calibration
Forget about having to buy expensive thermometers to calibrate your probes.
Just emerse the probes in boiling water and look for consistancy around 212
deg F. If you have all 4 monitored, try swapping around to look for a change
in readings. Once you feel comfortable that your monitoring is accurate to
within 10 deg F or so you can begin to look for ways to bring the temps
down. The most common sources of problems lie in Mixture control and baffle
efficiency. Lets attack them one at a time
Mixture Questions
Which is your hottest cylinder, should be #3 or #4. The leanest running
cylinder is going to be the hottest. My experience is that #3 usually runs a
little leaner than the rest and therefore hotter. If you have carb heat, try
cracking it slightly to enrich the mixture and see if the temp comes down.
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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD |
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dan.beadle(at)inclinesoft
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| Posted: Wed Feb 01, 2006 12:43 pm Post subject: CYL high temp |
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I am not flying the same engine, but the oil temps look great.
The CHT seems a little high on climb out - I shoot for 400 degrees max,
using cowl flaps. One engine runs 375 (gages have been calibrated
recently). Generally, cooler is better for CHT. Oil Temp should get to 180
or so to boil off moisture in it.
So your temps all sound pretty "Normal"
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skylor4(at)yahoo.com
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| Posted: Thu Feb 02, 2006 10:25 am Post subject: CYL high temp |
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Kelly,
Actually, John Deakin suggests that 420F should be the
upper limit of CHT's, with the engine monitor alarm
set to 400F. 380F should be the cruise target
maximium.
See the text that I attached below...
Skylor Piper
RV-8QB Under Construction
--- Kelly McMullen <kellym(at)aviating.com> wrote:
| Quote: |
<kellym(at)aviating.com>
I'm not sure the basis of your temp recommendations.
The best
recommendations I know come from Advanced Pilot
Seminars, where they
have more data to back their recommendations than
anyone. Oil okay.
CHT, there is no minimum temp for max life, that is
an OWT.
Maximum for any flight phase, including climb should
be 400F.\
EGT, for normally aspirated, there is no maximum,
especially none for
maximum life, but much over 1500 is unlikely.
Turbos, totally different,
they do have TIT maximums. What matters is all
cylinders peaking as
close to each other, in terms of fuel flow, not
temp. You are only
looking for the peak on each cylinder, not an
absolute temperature.
You are totally incorrect about why #3 on an O-360
or IO-360 runs
hottest. Has very little to do with mixture, and if
it were leanest, it
would only be hottest on the rich side of peak,
where you don't want to
be anyway. #3 runs hottest because of the way
Lycoming designed the head
casting to have NO cooling fins on the back side of
#3 (and front #2).
If the baffling is tight against the cylinder head,
it will run 30-50
degrees hotter than if you leave a 1/8" to 1/4" gap
for air to get through.
KM
A&P
|
Grads,
Some of you may be getting a little too concerned over
CHT "limits," and while that won't harm your engine,
it may not allow you to get all the power you want.
A very well-informed person wrote recently:
Oversimplified, TCM set a redline around 460 degrees
and knowledgeable folks at Ada Oklahoma, using highly
instrumented engines have determined that 380 is a
safer maximum.
Not quite true. We're running into this a lot, which
means we may have been "too successful."
460F is a common TCM redline for CHT, and 500F is
common for Lycomings. We have LOTS of data that
suggest engines that go to those temperatures for a
very short period of time suffer little or no harm
from that specific event in the short term, IF
PROMPTLY CONTROLLED and brought right back down. We
also have data that suggests that any engine that goes
beyond those CHTs for even a short period of time WILL
suffer damage, often catastrophic damage. George
Braly has put hundreds of hours of detonation on the
test-stand engines without hurting them, some of it
very, very ugly, without damage. The secret to that
is inducing the detonation, recording the data, then
getting OUT of the detonation before the CHTs exceed
the factory limits. Maybe this is what the factories
had in mind??
Engines operated often and/or for long periods just
barely within those factory limits probably suffer
long-term damage that greatly reduces TBO and
reliability. We think those limits are much too high
for those reasons. TCM and Lycoming obviously agree,
for they have verbiage in many of the manuals about
"Maximum recommended CHT," and similar, but the
numbers vary, sometimes even within the same manual!
Where to set "reasonable" limits? Where to run?
I have personally seen two engines that will do what
we call a "thermal runaway" when the CHT is
deliberately run up to the high 420s. My old IO-520
was like this, and I demonstrated it many, many times.
Set the power and mixture to run 425F, no problem.
Change the mixture slightly (lean it more if LOP,
enrich it if ROP), and the CHT comes right down. 427,
the same. Just above that, 428, 429, 430 or so, and
the CHT would not stabilize there, it would keep on
ticking up, degree by degree, very slowly increasing
in rate of increase. Tweak the mixture as for the
slightly lower CHTs, and there is no effect, it just
keeps on rising, very slowly at first, then faster.
All the data we have suggests that will continue right
on past the factory redline, and well into the 500+
range, with damage. It takes a LARGE change in
mixture or MP to stop this "runaway."
We think that's from the usual uneven cooling around
the cylinders. The hottest parts of the cylinder
weaken a bit somewhere north of 420F, and it goes very
slightly out of round. The piston remains round, and
that starts a "scuffing" on the narrow part of the
cylinder, increasing the friction, and the heat,
becoming a self-feeding event.
We've not seen that happen when the CHT is controlled
below 420, except when there is a clear cut case of
preignition.
This is the basis of the GAMI/TAT/APS "limit" of 420F
on all these engines. Some may run happily at higher
CHTs, and heck, some engines we don't know about may
not even do the runaway anywhere near 420F! But 420F
makes a pretty decent upper limit, above which we
strongly suggest the pilots DO SOMETHING RIGHT NOW TO
GET IT BACK DOWN.
We take that a step further, and say that if you never
want to run above 420F, then it's probably a good idea
to set the engine monitor to alarm at 400F, giving
lots of time to spot it, figure it out, then take
action.
Now, if you try and run 399 or a bit less, you'll have
constant nuisance warnings from the 400F alarm, and
you'll be come so accustomed to it, you'll sooner or
later stop paying attention to it, and you may not
even hear it when it blows for real. So finally, the
crux of the matter, we say that when you're
controlling the mixture for cruise, use 380F as a
TARGET (370 is fine, 399 is fine). It also happens to
be a CHT where we're comfortable with the ICP
(Internal Combustion Pressure) and thetaPP (the angle
at which peak pressure occurs) in most of these
engines. The big TIO-540, and the TSIO engines are on
the hairy edge there, but it's still a decent set of
numbers.
Trouble is, folks take that 380, figure it's "The
Limit," and start adding a buffer to it. Not our
intention, we've ALREADY put the "buffers" in place!
Never allow the CHT to exceed 420F.
Set your monitor to alarm at 400F
Use 380F as a "target" for "Go Fast Mode."
Oh, and while I'm at it, feel comfortable running
1650F on your TIT (if you have a turbo) all day long,
that one is very conservative already!
Best...
John Deakin
Fly-Bye-Knight Press http://www.flybyeknightpress.com
Advanced Pilot Seminars http://www.advancedpilot.com
Index to all columns:
http://www.avweb.com/news/columns/182146-1.html
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Kellym
Joined: 10 Jan 2006
Posts: 1700
Location: Sun Lakes AZ
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| Posted: Thu Feb 02, 2006 11:49 am Post subject: CYL high temp |
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I have no issue with Deakin's recommendation or logic. His collegue at
APS, Walter Atkinson to the best of my recollection has advocated 400.
That may be difficult in some planes. Cooler is better, at least down to
around 225 degrees. I have no difficulty keeping below 400 with my IO360,
operating in Arizona. I would also agree with his alarm recommendation, as
you want to be making a change if the temp climbs above 400. I certainly
wouldn't try to "optimize" at 380 for cruise however. If your plane will
run at 370, or 340, that is fine, leave it alone...it gives you margin for
those extra hot days. Lycomings in particular suffer from high CHT, which
forced them to modify the 270 hp TIO540 used in the Mooney TLS to include
oil cooling of the valve guides, because they were seeing guide/valve
failure in under 300 hours when operated in accordance with factory
recommendations.
Obviously, at some point you have to balance cooling drag with your CHT,
so you want to have your baffles/cowling/plennum designed to have your hot
day CHT near 350-380 in cruise and under 400 in climb, mostly to minimize
drag, not because it would be any worse on engine longevity.
Do Not Archive
Skylor Piper said:
| Quote: |
Kelly,
Actually, John Deakin suggests that 420F should be the
upper limit of CHT's, with the engine monitor alarm
set to 400F. 380F should be the cruise target
maximium.
See the text that I attached below...
Skylor Piper
RV-8QB Under Construction
Never allow the CHT to exceed 420F.
Set your monitor to alarm at 400F
Use 380F as a "target" for "Go Fast Mode."
Best...
John Deakin
Fly-Bye-Knight Press http://www.flybyeknightpress.com
Advanced Pilot Seminars http://www.advancedpilot.com
Index to all columns:
http://www.avweb.com/news/columns/182146-1.html
|
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http://www.matronics.com/Navigator?RV-List |
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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD |
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