Engine Management Course
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Jack,
I doubt that even with mis-timed engines you could do that in one hour. Look at the Whyalla engine that was mis-timed, it took a beating for a couple of hundred hours (from memory) and in the end it just accelerated the onset of the crank failure.
Without knowing anything more of the failure it is possible to have cracks between the plug and injector from over tightening and it could be said that where ever the crack was starting was not visible. Perhaps the LAMEs were slack, maybe not. We do not have enough information to comment.
Trent
George is the smartest person I know, and I work with some seriously smart people, and the odd genuine rocket scientist....yes odd as well.
I doubt that even with mis-timed engines you could do that in one hour. Look at the Whyalla engine that was mis-timed, it took a beating for a couple of hundred hours (from memory) and in the end it just accelerated the onset of the crank failure.
Without knowing anything more of the failure it is possible to have cracks between the plug and injector from over tightening and it could be said that where ever the crack was starting was not visible. Perhaps the LAMEs were slack, maybe not. We do not have enough information to comment.
Trent
George is the smartest person I know, and I work with some seriously smart people, and the odd genuine rocket scientist....yes odd as well.
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Interesting reading to the causes of circumferential cracking at the head/barrel interface: http://www.eci.aero/pdf/12-2.pdf
My personal experience of cylinder cracking, low compressions at 100 hourly on newly reconditioned (very 2nd hand i suspect) cylinders, so I guess it can certainly happen within 100 hours.
Engines would be running fine but cylinders cracked around sparkplug to exhaust, went over to factory new cylinders and it didn't happen again.
Ive had one internal engine failure, on takeoff on a very short sector I thought one engine was making a very faint ringing sound, almost like a school bell tone but the sector was all of 10 minutes, no other indications.
A piston completely burned through on the very next takeoff, pressurised crankcase etc. that flight was about 90 seconds long.
I can only guess, but if the engine was detonating/preigniting on the previous takeoff it destroyed itself in about the time it took to do 2 takeoffs, I suppose it may have been in a failure mode for a long time prior but I dont know.
Engines would be running fine but cylinders cracked around sparkplug to exhaust, went over to factory new cylinders and it didn't happen again.
Ive had one internal engine failure, on takeoff on a very short sector I thought one engine was making a very faint ringing sound, almost like a school bell tone but the sector was all of 10 minutes, no other indications.
A piston completely burned through on the very next takeoff, pressurised crankcase etc. that flight was about 90 seconds long.
I can only guess, but if the engine was detonating/preigniting on the previous takeoff it destroyed itself in about the time it took to do 2 takeoffs, I suppose it may have been in a failure mode for a long time prior but I dont know.
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At my last 100-hourly three cylinders had cracks near the exhaust port on the O-320-D1A engine.
The fourth cylinder had a similar crack repaired with welding about 300 hours ago.
Second life engine with second life over-bored cylinders.
I was a bit pissed off and checked the Lycoming documentation, which said the cylinders had an expect life of 3,000 hours. The log books showed 3,100 hours, so I think the Lycoming engineers know their stuff.
New complete Lycoming cylinder kits only cost $1,350, so it's not that expensive to get a complete new top end on an engine.
A mag failed shortly before this, and I suspect it caused unburnt fuel to ignite in the exhaust port, giving much higher CHT temps and may have been the catalyst for the cracks.
The fourth cylinder had a similar crack repaired with welding about 300 hours ago.
Second life engine with second life over-bored cylinders.
I was a bit pissed off and checked the Lycoming documentation, which said the cylinders had an expect life of 3,000 hours. The log books showed 3,100 hours, so I think the Lycoming engineers know their stuff.
New complete Lycoming cylinder kits only cost $1,350, so it's not that expensive to get a complete new top end on an engine.
A mag failed shortly before this, and I suspect it caused unburnt fuel to ignite in the exhaust port, giving much higher CHT temps and may have been the catalyst for the cracks.
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Originally Posted by Jabawocky
A Squared, if you wish to share your experiences with me, PM me your details. Love to hear about your 24,000 hrs of LOP days
anyone with genuine questions not rubbish rock throwing wish to ask a question, they can be basic, but never a dumb question so long as its sensible.
What is occurring and what do you do when the MP is inexplicably out of Sync?
Why is setting 25/25 on a CMI engine in climb the ‘single most damaging thing’ you can do it?
"I’ve also learned that the mixture control doesn’t cut off the fuel on my engine." What does it do?
... four questions from this thread, provided without answers. They surely can't be "dumb questions" if you are posing some of them yourself
Last edited by Checkboard; 17th Feb 2013 at 20:45.
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Checkers, Good questions
If I answer them now folk will be getting a head start in the course
1. Quite easy when you do regular data reviews and know what you are looking at. Ironically John Deakin and I had some email banter overnight about several graphs of data on this very topic. Theses examples and many more are gone over with considerable time to study in the course.
Every owner should do this for every engine and in particular right before the LAME gets it for a 100hrly. Most problems give you ample warning, some 20-40 hours, some problems which could develop into major ones 2-400 hours later can be seen by the trained eye, if there is data and a trained eye.
The very reason I say, ROI for this training is huge, maybe drug running is a higher return, but the risk reward is not so good.
As for the failure Jack is referring to, that may never have been seen coming, but there is not enough information so far. We are investigating though.
2. Shut it down IMMEDIATELY and divert. No ifs buts or maybe's. You may not have time to even fiddle or dick about with it. A lot more of that in the course. Pictures too!
3. Another good question, not sure who asked it, but anyway, when you do the classes you will soon see why reducing MP delays the ICP and thats fine by itself, however reducing the RPM just moves the ICP back up to a similar theta PP and the double whammy kicks in all at a reduced fuel flow (TCM/CMI is rpm dependant) and even in a Lyc with a mass airflow fuel controller its still not good either.
This old wives tale, that is to this day taught by flying schools, I flew with young PyroTek once and after I chastised him for doing this we did a second go at things. Plane went up faster, forward faster, CHT cooler happy Jaba.
Despite all the APS data shown in the course material, I went and did a test at Watts Bridge, I had a VA B737 guy fly (coz he is gooderer at nailing the numbers) and I fiddled the levers. Using a constant IAs of 120, we did four climbs to 5500'. One was a APS target EGT, a full rich touch nothing, a 25/2500 as the schools teach, and another Target EGT run to prove the data was consistent with the first. You know which one was at TOC quicker, used less fuel etc.....and yes the two options of full rich or full rich 25/2500 were in order of unkind to the engine. Both in terms of deposits and the later deposits and CHT.
APS have nothing to sell you like a snake oil salesman, it is simply data backed science, methods proven over hundreds of millions, no billions of hours in flight, yet flying schools and people on pprune etc keep perpetuating the OWT's
One last point, there is a lot of stuff in an APS class that will never be discussed on an internet forum, some of it is just too hard to explain in one or two posts, and the consequences of doing so is that some half clued up genius gets it wrong.
It would be fair to say that you do not know what you do not know....I am a classic example of this all the time! But no matter what I say here, unless you attend, you will never appreciate it. I think this is why those who do know, sort of sound like some evangelistic nutter to the doubting Thomas folk. Unfortunately the ones who THINK they know it all and will never sign up, are the very ones who need to attend the most. This can't be taught here.
It all comes back to Return On Investment to me. My training has paid me back in my estimation between $25000 and $30000 so far in terms of fuel and maintenance costs, and most likely extended TBO, just on one aircraft alone in around 750 hours so far. My investment was a lot more than $1290 though, that trip cost me $35K (yeah Mrs Jaba and adult jabettes went too) but it has almost paid for that!!
If I answer them now folk will be getting a head start in the course
1. Quite easy when you do regular data reviews and know what you are looking at. Ironically John Deakin and I had some email banter overnight about several graphs of data on this very topic. Theses examples and many more are gone over with considerable time to study in the course.
Every owner should do this for every engine and in particular right before the LAME gets it for a 100hrly. Most problems give you ample warning, some 20-40 hours, some problems which could develop into major ones 2-400 hours later can be seen by the trained eye, if there is data and a trained eye.
The very reason I say, ROI for this training is huge, maybe drug running is a higher return, but the risk reward is not so good.
As for the failure Jack is referring to, that may never have been seen coming, but there is not enough information so far. We are investigating though.
2. Shut it down IMMEDIATELY and divert. No ifs buts or maybe's. You may not have time to even fiddle or dick about with it. A lot more of that in the course. Pictures too!
3. Another good question, not sure who asked it, but anyway, when you do the classes you will soon see why reducing MP delays the ICP and thats fine by itself, however reducing the RPM just moves the ICP back up to a similar theta PP and the double whammy kicks in all at a reduced fuel flow (TCM/CMI is rpm dependant) and even in a Lyc with a mass airflow fuel controller its still not good either.
This old wives tale, that is to this day taught by flying schools, I flew with young PyroTek once and after I chastised him for doing this we did a second go at things. Plane went up faster, forward faster, CHT cooler happy Jaba.
Despite all the APS data shown in the course material, I went and did a test at Watts Bridge, I had a VA B737 guy fly (coz he is gooderer at nailing the numbers) and I fiddled the levers. Using a constant IAs of 120, we did four climbs to 5500'. One was a APS target EGT, a full rich touch nothing, a 25/2500 as the schools teach, and another Target EGT run to prove the data was consistent with the first. You know which one was at TOC quicker, used less fuel etc.....and yes the two options of full rich or full rich 25/2500 were in order of unkind to the engine. Both in terms of deposits and the later deposits and CHT.
APS have nothing to sell you like a snake oil salesman, it is simply data backed science, methods proven over hundreds of millions, no billions of hours in flight, yet flying schools and people on pprune etc keep perpetuating the OWT's
One last point, there is a lot of stuff in an APS class that will never be discussed on an internet forum, some of it is just too hard to explain in one or two posts, and the consequences of doing so is that some half clued up genius gets it wrong.
It would be fair to say that you do not know what you do not know....I am a classic example of this all the time! But no matter what I say here, unless you attend, you will never appreciate it. I think this is why those who do know, sort of sound like some evangelistic nutter to the doubting Thomas folk. Unfortunately the ones who THINK they know it all and will never sign up, are the very ones who need to attend the most. This can't be taught here.
It all comes back to Return On Investment to me. My training has paid me back in my estimation between $25000 and $30000 so far in terms of fuel and maintenance costs, and most likely extended TBO, just on one aircraft alone in around 750 hours so far. My investment was a lot more than $1290 though, that trip cost me $35K (yeah Mrs Jaba and adult jabettes went too) but it has almost paid for that!!
Yes Jabba - it was Clinton who mentioned the "other two" questions 
- You may have guessed that by now!
I was a flying instructor in the early 90's and knew, and taught, that leaning is cooler, if you are already lean of peak EGT. The CFI had some old (60's) Lycoming engine manuals which clearly explained all of that pretty clearly. (Of course, practically, the lesson was rich of peak on the pa28s we used).
Same thing for me, when I was flying Navajos on freight ops in the mid-90s, after the instructing gig - and that I operated lean of peak.
I signed up to Avweb, and read Deakin's articles as each was first published in the late 90s with interest (I also loved his oxygen series, using welder's oxygen and pulse oxymeters combined with cannulas.), but but by then I was flying for Ansett, and my piston days where behind me.
I'd love to attend the course - but I am in the UK now (visiting Australia in November).
P.S. - I always simulated engine failure with mixture.
- You may have guessed that by now! I was a flying instructor in the early 90's and knew, and taught, that leaning is cooler, if you are already lean of peak EGT. The CFI had some old (60's) Lycoming engine manuals which clearly explained all of that pretty clearly. (Of course, practically, the lesson was rich of peak on the pa28s we used).
Originally Posted by Tinstaafl
A 1980 PA31 Navajo I operate is approved to operate 50deg LOP - and that's directly from the AFM/POH. The manual even details a procedure to get to a LOP power setting if the EGT temp limit is reached prior to LOP being achieved (in a nutshell, reduce MP, continue leaning to 50-75 deg LOP then add back the MP).
I signed up to Avweb, and read Deakin's articles as each was first published in the late 90s with interest (I also loved his oxygen series, using welder's oxygen and pulse oxymeters combined with cannulas.), but but by then I was flying for Ansett, and my piston days where behind me.
I'd love to attend the course - but I am in the UK now (visiting Australia in November).
P.S. - I always simulated engine failure with mixture.
Last edited by Checkboard; 18th Feb 2013 at 09:35.
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Howdy Checkers,
This is not an attempt at being picky but just for your curiosity and general knowledge. Did you know that CHT actually starts dropping prior to peak EGT, so once you are past about 40ROP the ICP and CHT is actually dropping.
Welding O2 When you come to my hangar you will think I do a LOT of welding....but the Acetylene bottle is away being refilled....apparently
break break
Apparently 25% booked already 3 months to go! So don't muck around or if you know folk who want to attend don't muck around. Advanced Pilot
I was a flying instructor in the early 90's and knew, and taught, that leaning is cooler, if you are already lean of peak EGT.
Welding O2
When you come to my hangar you will think I do a LOT of welding....but the Acetylene bottle is away being refilled....apparently break break
Apparently 25% booked already 3 months to go! So don't muck around or if you know folk who want to attend don't muck around. Advanced Pilot
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Gentlemen:
This thread has some spirited discussion within and that is almost always educational. It's been fun to read. There are, however, some posts which do not comply with the known physics, and since , according to Sir Isaac Newton, "the physics are everywhere the same", this presents some interesting contradictions.
First of all, several of the Lycoming publications quoted have been recently recanted by Lycoming and have become a sort of embarrassment to them. They are trying to soft-shoe their way around these difficult contradictions. They are making the transition to being on board with the scientifically valid concepts of engine management. We welcome them to the party. The problem for them was that several of their publications were not in harmony with their own engineering data. Between believing the Marketing Department and the Engineers, I'm going to go with the engineers. This has been a problem for Lycoming and apparently a few of this forum's members. Going with the repeatable, hard data is never a bad choice.
Secondly, please do not believe anything I say. For that matter do not believe anything anyone says. Believe the hard data. The hard data does not lie. In some cases, one must be adequately schooled to be able to interpret the data in meaningful manner, but it is there for everyone to see and interpret on their own.
We spent about five years amassing the data for use in the APS class from many sources, including but not limited to Pratt & Whitney, Wright Aeronautical, Lycoming, TCM, and the most advanced engine test facility in the world. We make NO attempt to convince anyone of anything. We simply offer a fire hose of information for each participant's digestion. We have had thousands of pilots, LAMEs, aircraft manufacturers, engine manufacturers and overhaulers as well as engine monitor engineers come to the class. We even had a group of auto engine test facility fellows join us. In not a single instance has anyone offered any data which contradicts what we present nor has anyone taken issue with any of the data we present. Believe the data. Opinions are always suspect. "A person without data has nothing more than an unsupported opinion."
I have not joined the forum to promote anything. If anyone has an engine management question, I will be more than happy to try to present the data or science which answers their question and let each make their own decision as to the proper conclusion.
It may be helpful to remember that, as Boswell said, "It's not what you don't know that hurts you; it's what you know that isn't so..."
I will be traveling from Colorado to Brisbane and Melbourne to be at the APS classes in May and look forward to meeting those of you who will be attending. I can promise you an enjoyable time packed with information that will be useful in saving you money, maybe your engine, and possibly your life.
I look forward to your engine management questions; and working through the answers.
This thread has some spirited discussion within and that is almost always educational. It's been fun to read. There are, however, some posts which do not comply with the known physics, and since , according to Sir Isaac Newton, "the physics are everywhere the same", this presents some interesting contradictions.
First of all, several of the Lycoming publications quoted have been recently recanted by Lycoming and have become a sort of embarrassment to them. They are trying to soft-shoe their way around these difficult contradictions. They are making the transition to being on board with the scientifically valid concepts of engine management. We welcome them to the party. The problem for them was that several of their publications were not in harmony with their own engineering data. Between believing the Marketing Department and the Engineers, I'm going to go with the engineers. This has been a problem for Lycoming and apparently a few of this forum's members. Going with the repeatable, hard data is never a bad choice.
Secondly, please do not believe anything I say. For that matter do not believe anything anyone says. Believe the hard data. The hard data does not lie. In some cases, one must be adequately schooled to be able to interpret the data in meaningful manner, but it is there for everyone to see and interpret on their own.
We spent about five years amassing the data for use in the APS class from many sources, including but not limited to Pratt & Whitney, Wright Aeronautical, Lycoming, TCM, and the most advanced engine test facility in the world. We make NO attempt to convince anyone of anything. We simply offer a fire hose of information for each participant's digestion. We have had thousands of pilots, LAMEs, aircraft manufacturers, engine manufacturers and overhaulers as well as engine monitor engineers come to the class. We even had a group of auto engine test facility fellows join us. In not a single instance has anyone offered any data which contradicts what we present nor has anyone taken issue with any of the data we present. Believe the data. Opinions are always suspect. "A person without data has nothing more than an unsupported opinion."
I have not joined the forum to promote anything. If anyone has an engine management question, I will be more than happy to try to present the data or science which answers their question and let each make their own decision as to the proper conclusion.
It may be helpful to remember that, as Boswell said, "It's not what you don't know that hurts you; it's what you know that isn't so..."
I will be traveling from Colorado to Brisbane and Melbourne to be at the APS classes in May and look forward to meeting those of you who will be attending. I can promise you an enjoyable time packed with information that will be useful in saving you money, maybe your engine, and possibly your life.
I look forward to your engine management questions; and working through the answers.
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G'day Walter,
I'm probably putting the horse before the cart. I'll be running in an IO540 shortly. Previous run-ins I've been involved in have you going flat knacker (75%) for 10 hours of flying at full throttle height. I'd be interested in your thoughts reference running in my IO540 and running LOP? When? Right from the start? I'll also be using the GAMI injectors, should they be installed before the run-in or after? My engine monitoring will be via the Garmin G3X.
Regards.
I'm probably putting the horse before the cart. I'll be running in an IO540 shortly. Previous run-ins I've been involved in have you going flat knacker (75%) for 10 hours of flying at full throttle height. I'd be interested in your thoughts reference running in my IO540 and running LOP? When? Right from the start? I'll also be using the GAMI injectors, should they be installed before the run-in or after? My engine monitoring will be via the Garmin G3X.
Regards.
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Sorry, also,
Just say you are part of a syndicate that has a C182, IO540, injected with engine monitoring. Does it matter if one syndicate member is running LOP and the 30 other syndicate members are leaning the 'usual' way? Guess what I'm trying to say, should everybody lean the same way, will there be any engine damage if the one fella is running LOP?
Ta.
Just say you are part of a syndicate that has a C182, IO540, injected with engine monitoring. Does it matter if one syndicate member is running LOP and the 30 other syndicate members are leaning the 'usual' way? Guess what I'm trying to say, should everybody lean the same way, will there be any engine damage if the one fella is running LOP?
Ta.
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I have a genuine question about cylinder head temperature gauges hopefully to be answered by someone with expertise in these instruments. ( Jabba come back )
What temp. does a CHT gauge actually show?
1 Is it the true temperature of the cylinder at the probe position? ie no matter how hot or cold the ambient temp happens to be the gauge reads the true CHT.
2 Alternatively does it simply read the temp difference between the thermocouple ends? ( one end, the cold one, is out in ambient air and the hot end is under a spark plug or screwed into the cylinder head )
If 1 is the case then the gauges must have some sort of device in them that compensates for ambient variations.
This is important because ambient temps vary widely. Often there is a 60* F difference from sea level to 10K. A gauge with no compensation, reading true at SL, would be over reading by 60* F at 10K on that particular day.
I have read that El Cheapo automotive gauges have a middle of the road ambient temp where they read true but are inaccurate at all other ambient temps.
Are our u beaut Alcors or JPIs compensated or are they wrong above and below the temp chosen for calibration?
Cheers RA
What temp. does a CHT gauge actually show?
1 Is it the true temperature of the cylinder at the probe position? ie no matter how hot or cold the ambient temp happens to be the gauge reads the true CHT.
2 Alternatively does it simply read the temp difference between the thermocouple ends? ( one end, the cold one, is out in ambient air and the hot end is under a spark plug or screwed into the cylinder head )
If 1 is the case then the gauges must have some sort of device in them that compensates for ambient variations.
This is important because ambient temps vary widely. Often there is a 60* F difference from sea level to 10K. A gauge with no compensation, reading true at SL, would be over reading by 60* F at 10K on that particular day.
I have read that El Cheapo automotive gauges have a middle of the road ambient temp where they read true but are inaccurate at all other ambient temps.
Are our u beaut Alcors or JPIs compensated or are they wrong above and below the temp chosen for calibration?
Cheers RA
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Jack:
Greetings. We do have a lot of experience with the IO-540. It's a terrific engine and as delivered almost always has adequate FF set-up (unlike the TCM engines) which makes breaking in the engine a straightforward process. The old method of break-in at 75% power and full rich works. For over a decade we have been breaking them in LOP at higher power settings up to 87% and find that to have several advantages. 1) the mean pressures are higher and the rings seat in five hours or so, 2) the peak cylinder pressures are occurring further down the barrel out of the choke area, and 3) the combustion chamber stays much cleaner, and 4) of significance is the fact that CHTs will be lower. All are nice things to have happening. The BIG thing to avoid during this time if running ROP is leaning away from full rich. While being very rich results in excess unburned hydrocarbons which are dirty, it keeps the other factors at bay somewhat. If you break it in rich, stay very rich.
It is not necessary to use mineral oil, but do not use any of the oils with anti-wear additives. Single weight or multi-weights without these anti-wear additives are fine and have some advantages over mineral oil. (we can discuss these further if needed)
As far as mixture management across multiple users is concerned, it is not a factor and has no downsides. We have found that if an engine is run LOP at least some of the time, it will stay cleaner with the rich of peak deposits being burned off rather than continuing to be deposited. The differences between engine being run ROP and LOP at the same power include, lower CHTs, cleaner oil, cleaner combustion chambers, healthier rings and much fewer spark plug deposits in the LOP engines. We have not found any advantages for the engine to running ROP at the same power settings.
I would install the GAMIjectors immediately. The engine is designed to have balanced F:A ratios and doing that is moving toward that end.
Change the oil at 5 hours, cut the filter, and inspect. Change the oil again at another 15 hours and inspect the filter, then as usual thereafter. Run the GAMI Lean Test after the first oil change at 5 hours and have the injectors tweaked if needed.
Holler if I can help further or clarify anything above.
Greetings. We do have a lot of experience with the IO-540. It's a terrific engine and as delivered almost always has adequate FF set-up (unlike the TCM engines) which makes breaking in the engine a straightforward process. The old method of break-in at 75% power and full rich works. For over a decade we have been breaking them in LOP at higher power settings up to 87% and find that to have several advantages. 1) the mean pressures are higher and the rings seat in five hours or so, 2) the peak cylinder pressures are occurring further down the barrel out of the choke area, and 3) the combustion chamber stays much cleaner, and 4) of significance is the fact that CHTs will be lower. All are nice things to have happening. The BIG thing to avoid during this time if running ROP is leaning away from full rich. While being very rich results in excess unburned hydrocarbons which are dirty, it keeps the other factors at bay somewhat. If you break it in rich, stay very rich.
It is not necessary to use mineral oil, but do not use any of the oils with anti-wear additives. Single weight or multi-weights without these anti-wear additives are fine and have some advantages over mineral oil. (we can discuss these further if needed)
As far as mixture management across multiple users is concerned, it is not a factor and has no downsides. We have found that if an engine is run LOP at least some of the time, it will stay cleaner with the rich of peak deposits being burned off rather than continuing to be deposited. The differences between engine being run ROP and LOP at the same power include, lower CHTs, cleaner oil, cleaner combustion chambers, healthier rings and much fewer spark plug deposits in the LOP engines. We have not found any advantages for the engine to running ROP at the same power settings.
I would install the GAMIjectors immediately. The engine is designed to have balanced F:A ratios and doing that is moving toward that end.
Change the oil at 5 hours, cut the filter, and inspect. Change the oil again at another 15 hours and inspect the filter, then as usual thereafter. Run the GAMI Lean Test after the first oil change at 5 hours and have the injectors tweaked if needed.
Holler if I can help further or clarify anything above.
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Rutan Around:
The probes are thermo-couples which read the temperature at the tip of the probe and are not very sensitive to ambient air temp, other than the affect this has on refractory rate of cooling. This is seldom enough of a problem to be of operational concern. They are very accurate across the range of operating temperatures AT THE PROBE LOCATION. The problem is that many baffle designs are so poor that the cylinders operate at widely varying temperatures around their circumference. This results in round pistons going up and down in egg-shaped cylinders. That's not a good thing.
In our baffle research we used a 36-probe CHT set-up to measure CHTs around the cylinder. You do want a round cylinder.
In our experience in our research, we have found the CHT probes to be quite accurate and trustworthy.
The only engine monitor probes we do not like are the EI standard response EGT probes. They react too slowly to be useful in diagnostics. Their fast-response probes are like everyone else's and work appropriately.
The probes are thermo-couples which read the temperature at the tip of the probe and are not very sensitive to ambient air temp, other than the affect this has on refractory rate of cooling. This is seldom enough of a problem to be of operational concern. They are very accurate across the range of operating temperatures AT THE PROBE LOCATION. The problem is that many baffle designs are so poor that the cylinders operate at widely varying temperatures around their circumference. This results in round pistons going up and down in egg-shaped cylinders. That's not a good thing.
In our baffle research we used a 36-probe CHT set-up to measure CHTs around the cylinder. You do want a round cylinder.
In our experience in our research, we have found the CHT probes to be quite accurate and trustworthy.
The only engine monitor probes we do not like are the EI standard response EGT probes. They react too slowly to be useful in diagnostics. Their fast-response probes are like everyone else's and work appropriately.
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Walter, thanks for your reply. I understand that thermocouples produce a current when there is a difference in temperature between the two ends. This current is measured and is shown on our gauge as a temperature. The larger the temperature difference between the two ends, the larger the current, and the higher the temperature we read on our gauge.
There are three ways to produce a higher current. Increase cooling of the cold end of the thermocouple, OR increase the heat on the hot end, OR do both. If the temperature shown on the gauge in the cockpit is to accurately reflect the temp of the metal in the cylinder head, the temp of the cold end would have to be kept constant. If that wasn't possible, then some device is needed to adjust the reading up or down whenever the cold end (ambient) temp changed from the temp used for it's calibration.
eg If 70*F was the temp where the gauge was calibrated, then at 70*F a CHT reading of 400*F would be true, ie a 330*F differential between the hot and cold ends of the thermocouple produces a reading of 400*F.
If the ambient temperature dropped to, say, 40*F, then a reading of 400*F would actually mean only 370*F.
If the ambient temp happened to be 100*F, and the reading was 400*F, the true CHT would be 430*F.
If we knew that our gauges were not compensated, and we knew the ambient temperature at which they were calibrated, we could easily calculate what the CHTs really were.
Number of degrees lower than calibrated temp - subtract from the gauge reading.
Number of degrees above calibrated temp - add to the gauge reading.
Knowing whether our gauges are compensated and if not, the ambient temp at which the gauge reads true, would be very useful. If it's not compensated and the pilot doesn't know that, then in the second example above, Mr Pilot, on seeing 400*F, reduces his temperature to 380*F and is happy. Unfortunately, the engine is not, because the true CHT is still 410*F - not good
.
My interest in CHT gauge accuracy started when I was trying to control high CHTs in a home-built. Lately it's been in my normally-aspirated C210M. At high altitude (above 10K) in cold air and with relatively low power, 18" MP, 2500 rpm, and peak EGT, the CHTs hover around 400*F. Can they really be that high given the cool temperature and low power setting, or is my CHT gauge telling me porkies?
Sometime ago I emailed Alcor about this but got no reply.
Cheers, RA
(Don't let this put you off, but I have enrolled in your engine seminar in Caboolture.)
There are three ways to produce a higher current. Increase cooling of the cold end of the thermocouple, OR increase the heat on the hot end, OR do both. If the temperature shown on the gauge in the cockpit is to accurately reflect the temp of the metal in the cylinder head, the temp of the cold end would have to be kept constant. If that wasn't possible, then some device is needed to adjust the reading up or down whenever the cold end (ambient) temp changed from the temp used for it's calibration.
eg If 70*F was the temp where the gauge was calibrated, then at 70*F a CHT reading of 400*F would be true, ie a 330*F differential between the hot and cold ends of the thermocouple produces a reading of 400*F.
If the ambient temperature dropped to, say, 40*F, then a reading of 400*F would actually mean only 370*F.
If the ambient temp happened to be 100*F, and the reading was 400*F, the true CHT would be 430*F.
If we knew that our gauges were not compensated, and we knew the ambient temperature at which they were calibrated, we could easily calculate what the CHTs really were.
Number of degrees lower than calibrated temp - subtract from the gauge reading.
Number of degrees above calibrated temp - add to the gauge reading.
Knowing whether our gauges are compensated and if not, the ambient temp at which the gauge reads true, would be very useful. If it's not compensated and the pilot doesn't know that, then in the second example above, Mr Pilot, on seeing 400*F, reduces his temperature to 380*F and is happy
. Unfortunately, the engine is not, because the true CHT is still 410*F - not good.My interest in CHT gauge accuracy started when I was trying to control high CHTs in a home-built. Lately it's been in my normally-aspirated C210M. At high altitude (above 10K) in cold air and with relatively low power, 18" MP, 2500 rpm, and peak EGT, the CHTs hover around 400*F. Can they really be that high given the cool temperature and low power setting, or is my CHT gauge telling me porkies?
Sometime ago I emailed Alcor about this but got no reply.
Cheers, RA
(Don't let this put you off, but I have enrolled in your engine seminar in Caboolture.)