Commercial Pilots who don't know about piston engines

[Walter Atkinson]

***
All I was saying was if we could still get 100/130 fuel the majority may still prefer the extra power of 130 octane but the only way to get it would be ROP.
***
130 octane does not result in extra power over 100LL. Period. It does offer a wider detonation margin.

The 130 would run very nicely LOP.

One should understand that if I limit CHTs to a given temperature, say 380dF, I can get MORE power out of my engine LOP than ROP. I routinely fly my TNIO-550 at 85-90% power LOP. I can only get about 75% power ROP at that operational CHT limit. Obviously, I'm flying faster at 90% power than 75% power.

There are so many misconceptions about this stuff.

For example, operating an engine across the entire mixture spectrum has been a fact of science since the invention of the internal combustion engine. This is not new. It is not a theory. It is a fact of science, provable by any investigator--which has been done thousands of times.

Of course it is also true that no amount of science can overcome the comforts offered by a closely held superstition.

[Eddie Dean]

Indeed Walter, as well as tetra ethyl lead being a valve lubricant.

Tin hat on, waiting for incoming.

[sillograph]

So what happens when one of your engines egt probes fail on a system with a probe for each cylinder. Going off the gami supplement in Poh would that mean you now have to go back to ROP to be compliant as you now don't meet the requirements of the supplement until the probe is replaced. This could be any where from less than an hour to say 10 hours flying if you can't get to a shop due to scheduling. And what is the cost of said probe, roughly $200 each plus labour. The reason I say this we have installed such systems and this problem pops up every month or so.
Then there is the issue of 10 different drivers flying the aircraft I just can't see it working commercially due to this, looks fine for say owner pilot or maybe two pilots or owners.

Turbines are just better from every angle, and with the cost of the big lycomming the turbine is fast becoming a more viable option.

[Jabawocky]

Sillo,

Couple of things here, the calorific values of fuels varies by tiny amounts, not worth the discussion point. The different octane ratings means you get to use the fuel with higher boost or higher compression ratio to achieve more power, while maintaining detonation margins that are acceptable. And acceptable varies from airplane to race car and everything in between.

As for if an EGT probe fails? Well no, once you are "known to be LOP" a probe failure matters not, because validation from all the others, your fuel low etc…..means the EGT probe is just validation of a know state.

You can comply with the POH supplement without even looking at the egt info if you want. :ok:

[Aussie Bob]

Then there is the issue of 10 different drivers flying the aircraft I just can't see it working commercially due to this, looks fine for say owner pilot or maybe two pilots or owners.

This does about sum it up. Although I am an engine monitor and a LOP geek, it is not really a viable commercial option without extensive pilot education followed by extensive data downloading to see if the learning has sunk in.

Much as I hate to say it, it is a private owners thing mostly. Every flight review I conduct I casually ask about the pilots leaning policy, then I listen to "standard industry practice" or "that's what I was taught" and I ponder the task of changing established practices. That said, if ever I operate or manage an aviation business again, I would be looking at getting the education and doing the downloading because the savings would well be worth it subject to pilot turnover and other commercial considerations.

[Lead Balloon]

So let's say the deliberate decision is to "run ROP".

How do you know each cylinder is ROP?

And why would you make a deliberate decision to run each cylinder ROP, when the science and data prove that the mixture setting that will give the engine the hardest beating it can possibly be given is ROP?

It defies all logic. (Not an unusual circumstance in Australian GA though ...)

[Aussie Bob]

How do you know each cylinder is ROP?


I often run my engine with two cylinders ROP and two cylinders LOP. Great setting, CHT's all even, fuel flow better than book, engine exceptionally smooth. The paradox is; this is exactly where I would be if I had no monitor and simply leaned as per conventional wisdom. :sad:

[Lead Balloon]

Yes it is quite bizarre.

Apparently you'll be 'safe' and 'legal' if you believe all cylinders are ROP and cooler than they would be if LOP, but you'll be 'unsafe' and 'illegal' if you know that the cylinders are LOP and cooler than they would be if ROP.

[Jabawocky]

Gidday Aussie Bob,

There are several charter operators doing it quite successfully, and all with CASA approved ops manuals. I know, because I helped them do it ;)

It is not hard. As you know, running accurately LOP is much easier than ROP if you want to do it efficiently. I know one operator who is making several 6 figures more per year in less fuel and more importantly less maintenance. Here is what they did;

1. Chief Engineer did APS class.
2. Started fitting JPI's and GAMI's through the fleet (mostly twins) and installing better baffle kits.
3. Sent Chief Pilot to the next APS class.
4. Started to pay for the GAMI's, JPI's and Baffles in about 9 months or something like that.
5. Re-wrote ops manuals and educated pilots in house on simple and dare I say it "cook book" operations.
6. Reports to me that after 3 years they are doing a fraction of the cylinder work, and between better operating practises, better data analysis (not just asking pilots what they think is happening) they are saving several hundred thousand per year.

How to fly SAFER and make a profit in GA???? Well the cut throat competitors probably can't work it out, but they have not dropped their prices, so all of a sudden what was just profitable is now a viable business.

It is not rocket science, but it does involve a bit of science and not mythology. ;)


Hope you are having fun down there :ok:

[oggers]

For example, operating an engine across the entire mixture spectrum has been a fact of science since the invention of the internal combustion engine. This is not new. It is not a theory. It is a fact of science, provable by any investigator--which has been done thousands of times.

Walter this may seem trivial to you but for scientists and engineers 'theories' are models that have been proven to work, as opposed to an unproven hypothesis. A "scientific fact" is an observation, but if a model gives a useful approximation reliably, then its validity can be considered a 'fact'. You have already had this explained to you on this thread. Conflating a hypothesis with a theory is most definitely not a mistake that a scientist would make.

This video explains it: the scientific method (https://www.youtube.com/watch?v=zcavPAFiG14).

Please note #3, of the so-called 10 commandments: "Thou shalt back up thy statements with evidence...just claiming something is a fact doesn't make it a fact".

[Lead Balloon]

So what is your theory on why piston engines work, oggers, and what is your theory on what happens to EGT, CHT and ICP as the fuel air ratio is varied across the spectrum that will support combustion?

[Jabawocky]

oggers

You have been asked nicely on the previous page some simple questions to help in the education process yet you seem more intent on some asinine game of what is a scientific fact and a hypothesis.

I think you have just proven a fact……….an unintended consequence no doubt.

If I am grossly off the mark maybe Lead ballon or someone else can set me straight but I seriously thing you are wasting everyones time.

A "scientific fact" is an observation

Yes, and when this observation is repeatable and not some random result, it is….well…..it is what it is. Pretty much all the APS teachings are based on the "observations" of the likes of Pratt & Whitney, Curtis Wright, heck even Lycoming and TCM. Not to mention thousands of hours doing FAA certification testing etc at the Carl Goulet engine test facility.

So……have you a point? :confused:

[oggers]

Jabawocky

oggers, you are simply not correct....Time to put your glasses on, figure 8 clearly shows that statement is false.NACA-754 Figure 8:

72
Valve temp correlates very well with EGT. What glasses do you recommend to change that fact – beer goggles perhaps. Note the blue line I added where Walter Atkinson wrongly claims peak valve temp occurred is actually outside the range in which the report authors say it occurred.

This same data was repeated in tests done by Lycoming in the 1960's. I don't doubt that Lycoming have acquired plenty of data for their valves. But they did not draw the conclusion that you and Walter Atkinson have – quote: “EGT does NOT affect valve temperature...valve temperature does NOT track EGT...the two are not in any way related”.

Walter Atkinson:

According to the 1943 NACA report referenced, those who think that valve temp is in any way related to EGT must reconcile the fact that as EGT is going UP from 25dF ROP to peak EGT the valve temperature is going DOWN. This is definitive evidence that the two are NOT related.You are clutching at straws. Eyeballing the curve from the test with the thermocouple gives a peak valve temp at no more than 10ROP, not your 25ROP and definitely not the 40°ROP you claimed previously.

But that is beside the point. The knowledge that valve temperature is linked to both CHT and EGT is well and truly established in the engineering literature and the publicly accessible data.

reconcile the fact that as EGT is going UP from 25dF ROP to peak EGT the valve temperature is going DOWNEasy: the spread between where CHT and EGT peak as a function of mixture means the valve temp will not peak precisely at either but between them. :ugh:


This extract is from a document by Electronics International that is very well referenced throughout:

“During the exhaust stroke the high velocity of the exhaust gasses and the large surface area of the exhaust valve head cause the exhaust valve to absorb a significant amount of heat. The temperature of the hot exhaust gasses (EGTs) flowing over the valve has a direct affect on the temperature of the exhaust valve. The exhaust valve is heated during two of the four strokes of the engine (power and exhaust strokes). During the exhaust stroke, the valve loses its major cooling path (valve seat face to the seat insert).” http://buy-ei.com/wp-content/uploads/2013/06/Pilots-Manual.pdf

Meanwhile you have provided nothing to support the APS hypothesis that “EGT does not affect valve temperature...[and]...exhaust valve temperature is not related to EGT in any way”.

[sillograph]

Sillo,

Couple of things here, the calorific values of fuels varies by tiny amounts, not worth the discussion point. The different octane ratings means you get to use the fuel with higher boost or higher compression ratio to achieve more power, while maintaining detonation margins that are acceptable. And acceptable varies from airplane to race car and everything in between.

As for if an EGT probe fails? Well no, once you are "known to be LOP" a probe failure matters not, because validation from all the others, your fuel low etc…..means the EGT probe is just validation of a know state.

You can comply with the POH supplement without even looking at the egt info if you want. :ok:

Ok fair enough if the probe fails and you are LOP at that time I agree you where compliant when it was set so that's fine, but what of the next flight ie returning to base let's say it's a two hour flight. Surely you can't comply then with a failed probe, your only option is to run ROP to be compliant. All this talk about that you must have good monitoring gear to go LOP which I agree with but when it fails it's still ok to go LOP?.
I can't see casa being happy with that, I know it is knit picking but this is where we end up with the regulator sometimes.
So now you are ROP for a few runs here and there and when the hundred comes up it turns out all is ok with the engine, great. However if at the hundred all is not well and you have a burnt valve or fried waste gate etc where do we point the finger LOP or ROP. Like all aircraft things break or go u/s and I am yet to see a machine that has some sort of magical wizard induced spell with such 100% reliability, isn't that why we have mel's.
So you have a MEL shouldn't this be on the MEL and if so what does it say , I'd like to see that page.

[Lead Balloon]

Eyeballing the curve from the test with the thermocouple gives a peak valve temp at no more than 10ROP, not your 25ROP and definitely not the 40°ROP you claimed previously.Let us assume you have a well-calibrated eyeball, oggers, and that the peak in valve temperature is, in fact, at 10 (or 9 or 8..) degrees F ROP.

What is your theory on why valve temperature goes DOWN as the mixture is further leaned past that point - whatever it is - and EGT continues to go UP to peak?

Even on your own observation and interpretation of NACA-754 Figure 8, valve temperature starts going DOWN before the EGT peaks. How can that be so, if EGT 'drives' valve temperature?The knowledge that valve temperature is linked to both CHT and EGT is well and truly established in the engineering literature and the publicly accessible data. I trust that after your lecture on the scientific method, you're not suggesting the assertions made in what you quoted from EI constitutes "data"?

[Jabawocky]

Ok fair enough if the probe fails and you are LOP at that time I agree you where compliant when it was set so that's fine, but what of the next flight ie returning to base let's say it's a two hour flight. Surely you can't comply then with a failed probe, your only option is to run ROP to be compliant. All this talk about that you must have good monitoring gear to go LOP which I agree with but when it fails it's still ok to go LOP?.

Sorry, that is not the case. I know it is not your fault, you just don't get it. Maybe come for a fly with me and i can show you why.

But trust me on the return flight, using known data, you set the same MP/RPM and Fuel flow, and the 5/6 that still work will confirm you were back exactly where you were before.

Stop trying to find ways not to do things……the glass is half full. :ok:

And seriously, if you want to call me and thrash it out properly, drop me a PM or send me your number. Happy to point you in the right direction.

And whats this burnt valve thing got to do with anything…..seriously, there are many old wives tales that you could benefit from killing.

[Lead Balloon]

Ok fair enough if the probe fails and you are LOP at that time I agree you where compliant when it was set so that's fine, but what of the next flight ie returning to base let's say it's a two hour flight. Surely you can't comply then with a failed probe, your only option is to run ROP to be compliant. How will you know the cylinder is running ROP if the EGT probe has failed?

Think about what Jabba said. All your EGT probes are working. You set a mixture that results in all the cylinders being LOP. You have a known MP, RPM, density altitude, IAS fuel flow and CHT for each cylinder.

You then snip the connections to all the EGT probes. What changes in the engine? Nothing.

You then do a touch and go, and climb at full rich (not the most efficient way to get there, but let's not complicate things) and max RPM, and then level off at the same density altitude as before and set the same RPM and fuel flow as before. The MP is the same as before, and you note the IAS is the same as before and the CHT for each cylinder is the same as before.

It's very (very) probable that all the cylinders are at the same or nearly the same point LOP as they were before. And anything that would change that outcome would mean you couldn't be sure you were ROP and "compliant".

[Lead Balloon]

By the way, oggers, if you read the paragraph on the page after Figure 8 of NACA-754, it says:The high valve temperatures accompanying operation with fuel-air ratios in the region of 0.065 is one reason why lean-mixture operation is detrimental to valve life. Injection carburetors are frequently adjusted to give a fuel-air ratio of 0.070 for cruising. From the foregoing discussion it is evident that this mixture ratio imposes the most severe temperature on the exhaust valve. The valves would probably give more satisfactory service if operated with a leaner mixture.

And before you leap at the phrase "reasons why lean-mixture operation is detrimental to valve life", note (with your calibrated eyeball) where the fuel-air ratio of around 0.065 - 0.070 is on the lean curve in the graph: [b]rich of peak EGT.

When the report talks about "lean-mixture", it's not talking about lean of peak mixtures. It's merely talking about a mixture that is lean relative to another mixture that supports combustion. Every mixture that supports combustion is on the lean curve, somewhere. It's just that some are LOP, some are ROP and one is P.

So the report shows that the mixture ratio that imposes the most severe temperature on the exhaust valve is one that results in an EGT that is rich of peak. The report says the valves would probably give more satisfactory service if operated with a leaner mixture than one that results from a fuel air ratio of around 0.065 - 0.070.

The simple messages that APS tries to communicate are: if you're going to run ROP, run far far enough ROP; if you're going to run LOP, run far enough LOP; and the setting at which you're going to give your engine the hardest beating you can give it is ROP. Those messages are completely consistent with NAC-754 and all other relevant data.

[oggers]

Lead Balloon

What is your theory on why valve temperature goes DOWN as the mixture is further leaned past that point - whatever it is - and EGT continues to go UP to peak?

I gave the explanation in the very same post. But here it is again :rolleyes:

Easy: the spread between where CHT and EGT peak as a function of mixture means the valve temp will not peak precisely at either but between them.

It is a no brainer. The observation that exhaust valve temp - as a function of mixture - begins to fall slightly rich of peak EGT does not in any way invalidate the theory that valve temperature correlates with some combination of CHT and EGT. In fact, as the working fluid is the heat source and the cylinder head is the heat sink, it cannot be otherwise.

[oggers]

By the way, oggers, if you read the paragraph on the page after Figure 8 of NACA-754, it says:
Quote:
The high valve temperatures accompanying operation with fuel-air ratios in the region of 0.065 is one reason why lean-mixture operation is detrimental to valve life. Injection carburetors are frequently adjusted to give a fuel-air ratio of 0.070 for cruising. From the foregoing discussion it is evident that this mixture ratio imposes the most severe temperature on the exhaust valve. The valves would probably give more satisfactory service if operated with a leaner mixture.
[bolding added]

And before you leap at the phrase "reasons why lean-mixture operation is detrimental to valve life", note (with your calibrated eyeball) where the fuel-air ratio of around 0.065 - 0.070 is on the lean curve in the graph: rich of peak EGT.

When the report talks about "lean-mixture", it's not talking about lean of peak mixtures. It's merely talking about a mixture that is lean relative to another mixture that supports combustion. Every mixture that supports combustion is on the lean curve, somewhere. It's just that some are LOP, some are ROP and one is P.

So the report shows that the mixture ratio that imposes the most severe temperature on the exhaust valve is one that results in an EGT that is rich of peak. The report says the valves would probably give more satisfactory service if operated with a leaner mixture than one that results from a fuel air ratio of around 0.065 - 0.070.

...and you think I disagree with that part of the report why exactly?

[oggers]

The simple messages that APS tries to communicate are: if you're going to run ROP, run far far enough ROP; if you're going to run LOP, run far enough LOP; and the setting at which you're going to give your engine the hardest beating you can give it is ROP. Those messages are completely consistent with NAC-754 and all other relevant data.

Yes Balloon. But all you are doing there is tilting at windmills. Have Lycoming or TCM ever argued that running a fuel-air ratio of 0.07 results in a lower CHT than running either a richer mixture or LOP? Nope. They know that. That is why they do not recommend that mixture for high powers, generally above either 65% or 75%.

[Lead Balloon]

It is a no brainer. The observation that exhaust valve temp - as a function of mixture - begins to fall slightly rich of peak EGT does not in any way invalidate the theory that valve temperature correlates with some combination of CHT and EGT. In fact, as the working fluid is the heat source and the cylinder head is the heat sink, it cannot be otherwise.The increase in CO2 as a percentage of the atmosphere correlates with the decrease in the the number of pirates (as any practising Pastafarian knows). But the decrease in the number of pirates has not caused the increase in CO2 as a percentage of the atmosphere (as any practising scientist knows).

What causes the CHT to go DOWN even though the EGT keeps going UP?

[sillograph]

How will you know the cylinder is running ROP if the EGT probe has failed?

Think about what Jabba said. All your EGT probes are working. You set a mixture that results in all the cylinders being LOP. You have a known MP, RPM, density altitude, IAS fuel flow and CHT for each cylinder.

You then snip the connections to all the EGT probes. What changes in the engine? Nothing.

You then do a touch and go, and climb at full rich (not the most efficient way to get there, but let's not complicate things) and max RPM, and then level off at the same density altitude as before and set the same RPM and fuel flow as before. The MP is the same as before, and you note the IAS is the same as before and the CHT for each cylinder is the same as before.

It's very (very) probable that all the cylinders are at the same or nearly the same point LOP as they were before. And anything that would change that outcome would mean you couldn't be sure you were ROP and "compliant".

So in that situation we would revert back to old school using the TIT probe and lean the engine to peak egt and then richen by 125 degrees at say 65% power. Does a jpi monitor qualify for original aircraft certification? Not sure, still I wouldn't remove the TIT probe hence its still there as backup.

I am just trying to get a picture of how we would advise casa we could comply in the case of a engine monitor or probe failure, and what goes in the Ops manual. Obviously we can't always cruise at the same level or power setting due maybe traffic or a crossing time requirement etc, understanding casa only has to accept your method not approve it.

[Lead Balloon]

So in that situation we would revert back to old school using the TIT probe and lean the engine to peak egt and then richen by 125 degrees at say 65% power. You might earnestly believe and hope that that's what you're doing to "the engine", but you wouldn't know what's happening in each cylinder. However, you will have the warm inner glow that the regulator will consider you to be 'legal'. Does a jpi monitor qualify for original aircraft certification?Depends on the model.Not sure, still I wouldn't remove the TIT probe hence its still there as backup.I keep the original CHT probe and gauge for ****s and giggles too. I'm reminded what a joke it is every flight, because it rarely reaches the bottom (cold end) of the green arc, yet my hottest cylinder is much hotter but happens to be located on the opposite side to the original CHT probe. I reflect on how much safer I would be, and still legal, if I were flying blissfully ignorant of the fact that #6 cylinder is about to depart the crankcase.

I am just trying to get a picture of how we would advise casa we could comply in the case of a engine monitor or probe failure, and what goes in the Ops manual. Obviously we can't always cruise at the same level or power setting due maybe traffic or a crossing time requirement etc, understanding casa only has to accept your method not approve it.A very reasonable and justifiable concern.

I suppose you just have to pray that you find someone in CASA that isn't chock full of folklore. Lots of luck with that.

[oggers]

The increase in CO2 as a percentage of the atmosphere correlates with the decrease in the the number of pirates (as any practising Pastafarian knows). But the decrease in the number of pirates has not caused the increase in CO2 as a percentage of the atmosphere (as any practising scientist knows).

What causes the CHT to go DOWN even though the EGT keeps going UP?

Balloon, okay so you have come up with a new version of the old "correlation is not causation" cliche. Fair point but we do not have a direct indication of the temperature of the exhaust valve and yet it is the hottest component in the engine and highly stressed so it is useful to know how it correlates with CHT and EGT.

Now, the APS hypothesis brought to us here by Walter Atkinson is "valve temperature does NOT track EGT...[the NACA report with thermocouple in the valve] is definitive evidence the two are not in any way way related" is not supported by that report or any other piece of literature I have seen. The part of that report you and Walter both cite as definitive is the valve temp peaking slightly rich of EGT. But it does not follow that valve temperature does not track EGT. The correlation with EGT alone is a very good proxy for valve temperature as a function of mixture. When you add the influence of CHT (as indicated in figure 8 of that report by the spark plug bushing) it becomes apparent why the valve temp peaked slightly rich of EGT.

Now to illustrate the absurdity of Walter's logic let us also test the APS teachings against it:

"EGT is NOT the indication you're looking for. Pay attention to the CHT, and the valves take care of themselves.com." John Deakin; Fried Valves

Refer to figure 8 again. The CHT as represented by rear spark plug bushing. As a function of mixture it is going DOWN as the valve temp is still going UP. Now according to what you and Walter are saying this would be "definitive evidence" that CHT "does NOT track valve temperature and the two are in no way related". But of course, all it really means is that CHT - as a function of mixture - does not correlate with valve temperature as well on its own as it does when combined with EGT.

QED

[Lead Balloon]

[Y]et it is the hottest component in the engine and highly stressed so it is useful to know how it correlates with CHT and EGT. There is a scientific term for rubbish. It's: "rubbish". Like the usefulness of knowing there's a correlation between CO2 levels and at the number of pirates.

Now, the APS hypothesis brought to us here by Walter Atkinson is "valve temperature does NOT track EGT...[the NACA report with thermocouple in the valve] is definitive evidence the two are not in any way way related" is not supported by that report or any other piece of literature I have seen.Except for the fact that valve temperature does not track EGT. The part of that report you and Walter both cite as definitive is the valve temp peaking slightly rich of EGT."Slightly". Now there's a scientifically precise term. But it does not follow that valve temperature does not track EGT.True - it does not follow in principle.

However, valve temperature does not "track" EGT in fact. The correlation with EGT alone is a very good proxy for valve temperature as a function of mixture.And the correlation with CHT alone is an even better proxy for valve temperature as a function of mixture, because valve temperature more closely "follows" the CHT curve. One wonders at the scientific justification for preferring the EGT curve over the CHT curve as the "proxy".

Now to illustrate the absurdity of Walters logic let us test the APS teachings against it as well:

Quote:
"EGT is NOT the indication you're looking for. Pay attention to the CHT, and the valves take care of themselves.com." John Deakin; Fried Valves
Refer to figure 8 again. The CHT as represented by rear spark plug bushing. As a function of mixture it is going DOWN as the valve temp is still going UP. Now according to what you and Walter are saying this would be "definitive evidence" that CHT "does NOT track valve temperature and the two are in no way related". But of course, all it really means is that CHT - as a function of mixture - does not correlate with valve temperature as well on its own as it does when combined with EGT.Gosh, I wish I'd read this first, because I'm now embarrassed to realise this is just a pisstake! We know what the NACA report says about the rear spark plug bushing measurement.

Got me a beauty, oggers! (You're not a Pastafarian, by the way?)

[Walter Atkinson]

Well, well, well. If one says a stupid thing fifty million times, it is still a stupid thing. paraphrased from Anatole France.

If one looks at the CHT and ICP curves and valve temp, one would see a nice correlation. The EGT is a red herring. The NACA report does not show all of the issues. These issues have been clarified quite nicely by Lycoming in 1966 and in the Carl Goulet Memorial Engine Test Facility. The physics are everywhere the same.

The EI explanation has been proven wrong by multiple sources. Several other of EI's statements have been such.

"There are none so blind as those who will not see." It gets to be a waste of time to try to educate those folks. I only continue to respond to these acts of rubbish for those who are lurking and wanting to learn.

Now, back to your regularly scheduled programming.

[oggers]

Balloon

Except for the fact that valve temperature does not track EGT.

Hmm. As I have posted a couple of times already neither EGT nor CHT correlates perfectly with the valve temp on its own. But together they do. A sense of proportion is called for here. No, the valve temp does not exactly track EGT - I have never said that - but it does correlate very well. Yes, valve temp peaks slightly rich of EGT but that is because it is also inlfuenced by CHT. That is what the engineering literature tells us and it is what the NACA report shows us.

As long as you keep misrepresenting that I will keep correcting you.

Here again is the graph:

http://www.pprune.org/members/125420-oggers-albums-misc-picture257-fig8c.png

The position that you and Walter Atkinson have taken (and as far as I can tell it is an APS thing) is flat out wrong. Let me repeat your position "EGT and exhaust valve temperature are not in any way related". Wrong.

[oggers]

Walter Atkinson:

If one looks at the CHT and ICP curves and valve temp, one would see a nice correlation.

Sort of yes.

The EGT is a red herring.

No. The curve speaks for itself.


The NACA report does not show all of the issues. These issues have been clarified quite nicely by Lycoming in 1966 and in the Carl Goulet Memorial Engine Test Facility.

...but:

We have hard data to prove that. The data came from a 1943 top secret NACA report done during WWII.

...and a couple of posts back:

According to the 1943 NACA report referenced....This is definitive evidence that the two are NOT related.


...now the top secret NACA report does not show all of the issues :suspect: Well okay then let us be seeing this 1966 Lycoming clarification.

I won't ask for the Goulet stuff because you already said:

Go the the APS website and sign up for the online course where 16+ hours of hard DATA are presented. It is the equivalent of a semester course, not a simple SAE "paper." Where I went to school, one had to pay for the education.

This isn't school Walter. By refusing to bring any supporting evidence out from behind the paywall of your course, your opinion on valves is unsupported and therefore not credible.

[Volumex]

Just for giggles, I curve fitted the EGT and Valve temperatures using third order polynomials.
Turns out the peak EGT is at a F/A ratio of 0.0649, which allowing for various uncertainties explains how Lycoming nominate the figure of 0.0648 as the F/A ratio peak EGT in their "Power from Fuel Flow" document.
I thought it was interesting.

I will bow out and let the belligerents continue to argue past each other.

[vh-foobar]

The position that you and Walter Atkinson have taken (and as far as I can tell it is an APS thing) is flat out wrong. Let me repeat your position "EGT and exhaust valve temperature are not in any way related". Wrong. Reading NACA-754 in the context of varying mixture ratio i.e. figure 8 it is hard to see how EGT and valve temperature are not related. Its a pretty strong correlation. Though if you read the entire report it's clear that EGT (more precisely mixture) is not the only variable that effects the temperature of the exhaust valve.

One point that is interesting from the graph in figure 8 though is that for a given EGT when ROP the valve temperature is hotter than LOP.
i.e. at say 1400 degrees LOP results in valve temp of 1200 degrees and 1400 degrees ROP results in a valve temp 1300 degrees. i.e about 100 degrees hotter.

[Eddie Dean]

So how many Rastafarians can dance on the head of a pin?
Are the Pirates in the South China Sea, included in the paradigm?

A serious question, why is the exhaust valve exposed to the highest temperature during the combustion process, when exhaust is at the end of the Otto (modified) cycle?

[Jabawocky]

oggers, let me make it really simple.

YOUR hypothesis is true….until.

The valve temperature "tracks" the EGT, because as the mixture at any given mass airflow is leaned, the EGT goes up AND the CHT goes up. But why does the CHT go up? Because the peak cylinder pressures go up. Just like your air compressor in the garage.

Now at the moment your hypothesis is true right up until the moment they stop tracking each other and diverge. Hypothesis BUSTED. end of argument.

Now when the CHT tracks the valve temp hypothesis is tested in exactly the same way, and it does not diverge, it follows the valve temperature…..what can you make from that? Because when Lycoming did their test with far newer equipment they plotted even better curves showing this in detail. I do not have them at hand, but in several weeks I will be right there in the dyno room and will surely be able to get them, if I remember.

Now just so you know I am not making this stuff up, lets examine what else the NACA had to say about valve temperature. Remember they were not measuring ICP in those days, we can today. "The effect of spark advance on valve temperature is shown in Fig.9 This figure shows that at a F/A 0.08 the exhaust valve temperature is practically unaffected by variation of the spark advance in a range from 5-25 DBTDC. As the spark was advanced beyond 25DBTDC the valve temperature increased until at 45 DBTDC it was the highest observed in the cylinder".

Hmmmm :hmm: If we are intellectually honest with ourselves, we would ask ourselves what also tracks the same by advancing the spark timing. We know today because we can measure what they could not 8o years ago, that the ICP will rise considerably, and funny enough the CHT goes with it. Does that help prove what we are saying??? Thought not.

But wait, there is more…..we know you want more, like this set of steak knives!

In the above while advancing the timing and noting exactly the same results as the NACA were getting we not only got higher ICP tracking with CHT we had a constant decline in EGT. Yep thats right a decline in EGT!!!! :mad::mad::mad::mad::mad: Bugger….the timing went up, the ICP went up, the CHT went up, the VALVE temperature went up and the EGT went down! :ooh:

Walter…..over to you!

[Walter Atkinson]

Remember the purpose of the NACA report. Some US engineer during WWII decided that we needed to run the B-24 Liberator LOP to get the range AND increase the bomb load. Some General said, "That's ridiculous, everyone knows that leaner mixtures result in higher exhaust valve temperatures." The Top Secret study was undertaken to prove or disprove the adamant General's position. The general lost. The physics won. Along the way, it was discovered that EGT and exhaust valve temperature were not directly related as initially assumed. It looks like it might, but the red herring was chewed by researchers until we realized that valve temperature is most directly affected by CHT. Period. We also learned that there are actually mixtures where the exhaust gasses blasting past the exhaust valve were actually COOLING the valve. Depending on other factors, if one sets the mixture at 40dF ROP, the exhaust gasses can actually cool the exhaust valve! Try that fact on for size.

It's also worthwhile to note that science has the habit of slaying a beautiful hypothesis with an ugly fact.

(FWIW, the B-24 was the only airplane of WWII that was run LOP in cruise. It seemed to work quite well as it carried the highest bomb load the greatest distance.)

[Lead Balloon]

I'm not sure on what, if any, scientific issue/s we differ any more, oggers and Eddie, so I'll frame the discussion a different way.

Which of these mixture settings will, in your view, be better for a piston engine's longevity:

- 30 degrees F Rich of Peak

- 30 degrees F Lean of Peak.

[Walter Atkinson]

During a preignition event, the valve temperature is rising at the alarming rate of as much as 2 degrees per second. While this is happening, the EGT is going down significantly.

During detonation, EGT moves little or goes down slightly while exhaust valve temp goes steadily up.

How can that be if EGT affects valve temperature?

The correct observation that EGT and valve temp go up as the mixture is leaned from full rich to about 25dF ROP is the red herring. It's a correct observation with a misapplied causality.

We can hold the EGT steady on the test stand and reduce CHT and the valve temp goes down. We can raise the CHT and while holding the EGT steady and the valve temp goes up. If we hold the CHT steady and alter the EGT, the valve temp remains steady. Explain that and continue to insist that valve temp is related to EGT.

One other thing. As I have spent the last 15+ years studying this stuff, I have had to unlearn what I knew to be true, but wasn't. It was not a comfortable feeling.

[rutan around]

(FWIW, the B-24 was the only airplane of WWII that was run LOP in cruise. It seemed to work quite well as it carried the highest bomb load the greatest distance.) Um Walter maybe not? Well not the only one to run LOP.


ttp://www.475thfghf.org/Lindbergh.htm (http://www.475thfghf.org/Lindbergh.htm)


The second and critical passage made by the group concerned fuel consumption. With additional fuel cells in the J model P-38, Satan's Angels had been making six and one-half and seven-hour flights. On I July Lindbergh flew a third mission with the group, an armed reconnaissance to enemy strips at Nabire, Sagan One and Two, Otawiri, and Ransiki, all on the western shore of Geelvink Bay. Already Lindbergh's technical eye noticed something. After six and one-half hours flying time, he landed with 210 gallons of fuel remaining in his Lightning's tanks.

Two missions later, on 3 July, the group covered sixteen heavies on a strike against Jefman Island. Lindbergh led Hades Squadron's White Flight as they wove back and forth above the lumbering B-25s. After the attack the Lightning's went barge hunting.

First one, then two pilots reported dwindling fuel and broke off for home. MacDonald ordered the squadron back but because Lindbergh had nursed his fuel, he asked for and received permission to continue the hunt with his wingman. After a few more strafing runs, Lindbergh noticed the other Lightning circling overhead. Nervously the pilot told Lindbergh that he had only 175 gallons of fuel left. The civilian told him to reduce engine R.P.M.'s, lean out his fuel mixture, and throttle back. When they landed, the 431st driver had seventy gallons left, Lindbergh had 260. They had started the mission with equal amounts of gas.

Lindbergh talked with MacDonald. The colonel then asked the group's pilots to assemble at the recreation hall that evening. The hall was that in name only, packed dirt floors staring up at a palm thatched roof, one ping pong table and some decks of cards completing the decor. Under the glare of unshaded bulbs, MacDonald got down to business. "Mr. Lindbergh" wanted to explain how to gain more range from the P-38s. In a pleasant manner Lindbergh explained cruise control techniques he had worked out for the Lightning's: reduce the standard 2,200 rpm to 1,600, set fuel mixtures to "auto-lean," and slightly increase manifold pressures. This, Lindbergh predicted, would stretch the Lightning's radius by 400 hundred miles, a nine-hour flight. When he concluded his talk half an hour later, the room was silent.
The men mulled over several thoughts in the wake of their guest's presentation.

The notion of a nine-hour flight literally did not sit well with them, "bum-busters" thought some. Seven hours in a cramped Lightning cockpit, sitting on a parachute, an emergency raft, and an oar was bad, nine hours was inconceivable. They were right. Later, on 14 October 1944, a 432nd pilot celebrated his twenty-fourth birthday with an eight-hour escort to Balikpapan, Borneo. On touching down, he was so cramped his crew chief had to climb up and help him get out of the cockpit.

The group’s chief concern surfaced quickly, that such procedures would foul sparkplugs and scorch cylinders. Lindbergh methodically gave the answer. The Lightning's technical manual provided all the figures necessary to prove his point; they had been there all along. Nonetheless the 475th remained skeptical. A single factor scotched their reticence.

During their brief encounter, MacDonald had come to respect Lindbergh. Both men pushed hard and had achieved. Both were perfectionists never leaving things half done. And both had inquisitive minds. John Loisel, commanding officer the 432nd, remembered the two men talking for long periods over a multitude of topics beyond aviation. If, as MacDonald had informed his pilots, better aircraft performance meant a shorter war, then increasing the Lightning's range was worth investigating. Lindbergh provided the idea, but it was MacDonald's endorsement, backed by the enormous respect accorded him by the group, that saw the experiment to fruition. The next day, the Fourth of July, Lindbergh accompanied the 433rd on a six-hour, forty-minute flight led by Captain "Parky" Parkansky. Upon landing, the lowest fuel level recorded was 160 gallons. In his journal entry Lindbergh felt ". . . that the talk last night was worthwhile. " The 475th had lengthened its stride

[andrewr]

Which of these mixture settings will be better for a piston engine's longevity:
- 30 degrees F Rich of Peak
- 30 degrees F Lean of Peak.

An excellent question, and now we're getting to the real science. How would you test that?

[Lead Balloon]

An excellent question, and now we're getting to the real science. How would you test that?By running some engines for millions of hours at around 30 degrees rich of peak and running other engines for millions of hours at around 30 degrees lean of peak, then comparing the reliability of each group.

If only that had happened around 50 or 60 years ago.

Oh, wait....

[oggers]

vh-foobar

One point that is interesting from the graph in figure 8 though is that for a given EGT when ROP the valve temperature is hotter than LOP.
i.e. at say 1400 degrees LOP results in valve temp of 1200 degrees and 1400 degrees ROP results in a valve temp 1300 degrees. i.e about 100 degrees hotter.

Yes, but that set of runs was at 93% of the audible knock limit for each mixture setting and so the power was being varied. 1400LOP was an imep of about 170psi which is only 75% (!) of the 226psi they achieved at 1400ROP. Apologies but I cropped the imep curve out when I uploaded the image as I was only trying to show the EGT/valve temp curves.

[Jabawocky]

So….are you saying that pressure is actually the driver?

Surely not?

Refer my previous post as I think you are learning something.:ok:

[Jabawocky]

By running some engines for millions of hours at around 30 degrees rich of peak and running other engines for millions of hours at around 30 degrees lean of peak, then comparing the reliability of each group.

If only that had happened around 50 or 60 years ago.

Oh, wait....

Lead Balloon………….you wouldn't be suggesting an American Airline(s) would you?

[vh-foobar]

So….are you saying that pressure is actually the driver?

Surely not?I don't think oggers is saying that.

The report is pretty clear the variables that effect exhaust valve temp are Mixture, IMEP, speed, spark advance, and cooling.

[Walter Atkinson]

While Lindy did use a LOP setting to fly the Ryan across the Atlantic in 1927, the Lindberg myth about LOP in the P-38 persists even though it is contradicted by those who were there. According to M.F. Kirby, P-38 ACE from the Pacific who was present for two of Lindy's talks about extending range, he claimed that he never talked about mixture management at all. That's consistent with my own knowledge of the P-38 Allison set-up which could NOT be manually leaned. It had only four mixture positions: Emergency rich, Auto rich, Auto Lean and Idle cutoff. Auto lean like all other WWII aircraft was set for Best Power, 80dF ROP. One P-38 pilot who actually flew with Lindberg on a combat mission said that Lindy seemed to change his mind about slow-flying when he saw his first Zero up close and personal.

According to Kirby, Paul Murray and others, Lindy ONLY talked about using high MP with low RPM to extend range. After attending a Juvat Reunion (80th FG) with Kirby, I had that confirmed by at least a dozen other P-38 pilots from the time. ALL of them claimed that Lindy's method, while useful in peacetime was a disaster in combat. The reason was that it took too long to come up to dog-fight speed from the extended range speed when you saw the enemy. Not one of them said they knew anyone who used Lindy's recommendations. They kept speed up and S-turned behind the bombers they were covering, always ready to engage at a moments notice.

"I never was interested in saving gas. I was too busy trying to save save my arse."
M.F. Kirby

[oggers]

Jaba

oggers, let me make it really simple.

YOUR hypothesis is true….until.

The valve temperature "tracks" the EGT, because as the mixture at any given mass airflow is leaned, the EGT goes up AND the CHT goes up. But why does the CHT go up? Because the peak cylinder pressures go up. Just like your air compressor in the garage.

Now at the moment your hypothesis is true right up until the moment they stop tracking each other and diverge. Hypothesis BUSTED. end of argument

Haha, you wish. I have explained why the valve temp peaks just before the EGT twice already. It is because: "the spread between where CHT and EGT peak as a function of mixture means the valve temp will not peak precisely at either but between them." The valve is heated by the working fluid and cooled by the head -and ultimatley the air. Therefore one would expect the valve temp to peak between peak EGT and peak CHT.


Now when the CHT tracks the valve temp hypothesis is tested in exactly the same way, and it does not diverge, it follows the valve temperature…..

...but it does "diverge" as we can see:

http://www.pprune.org/members/125420-oggers-albums-misc-picture264-fig8div.png

...what can you make from that?

..that you really really want the report to show no "divergence" between CHT and valve temp even though it doesn't!

Because when Lycoming did their test with far newer equipment they plotted even better curves showing this in detail. I do not have them at hand, but in several weeks I will be right there in the dyno room and will surely be able to get them, if I remember.

We shall see. However, John Deakin already tried to make this point with Lycoming 'data' so maybe we already have it:

"It should be intuitively obvious then, that the valve temperature will correspond most closely with the cylinder head temperature (not the EGT), and indeed, old data from Lycoming (1966) confrirm this" he wrote, and here's the 'data':

http://www.pprune.org/members/125420-oggers-albums-misc-picture261-lycomingdata1966.png

...I added the pecked lines. There isn't actually a curve on there for the valve, but anyway he says:

"Note that CHT, valve guide, and valve head temperature all increase together, all peak at roughly the same point on the mixture curve (just rich of peak EGT), and all fall together."

...and they do sort of peak in the same place but there is a trend; The valve seat peaks leaner and hotter than CHT, and the guide leaner and hotter still and very much closer to peak EGT than peak CHT. And if the valve was on there it would definitely be hotter than the guide. And yet the APS opinion is that has nothing to do with the exhaust gas temperature.

I think most people can understand that if the guide - which isn't even in the combustion chamber - is running hotter than the valve seat, and the cylinder head, it is because it is being heated by the hot exhaust flow. Or bearing in mind that only 25% of the valve heat goes through the guide while 75% goes through the seat, why isn't the seat hotter than the guide? Because of the exhaust gas.


I find it very strange that you persist in arguing against this ground truth.

[Lead Balloon]

I'm not sure on what, if any, scientific issue/s we differ any more, oggers and Eddie, so I'll frame the discussion a different way.

Which of these mixture settings will, in your view, be better for a piston engine's longevity:

- 30 degrees F Rich of Peak

- 30 degrees F Lean of Peak.

[Jabawocky]

oggers,

You seem to be missing the point and confusing some things.

1. The centre of valve crown thermocouple is tracking the EGT more closely because it is basically an EGT probe. Look at where they positioned it :ugh: You are not looking at the relevant trace for a start.

2. The valve temperature that matters is the valve face/seat and the one represented by the back of the valve body. Stick to the important ones and don't confuse the two.

Please refer to my previous post about what happens when you advance the spark. ICP goes up, CHT goes up, valve temperature goes up and EGT goes down.

Next and for those who say APS never give anything (data) for free here is a slide from the APS class. Look closely at the Cylinder 6 trace in blue. Note that the CHT is going through the roof. The ICP was definitely going through the roof (not shown but we know) and correspondingly the EGT fell considerably. What do you think the valve temperature was doing at the seat/face and the bulk of the valve body? Please answer this.

http://i849.photobucket.com/albums/ab58/jaba430/Screen%20Shot%202016-04-09%20at%204.39.52%20PM_zpsidzobnzc.pngCourtesy of Advanced Pilot Seminars

Your position has been that EGT is driving valve temperature, and that seems to be based on CORRELATION not CAUSATION. There is correlation for sure on the curve you keep showing above. However this is the wrong curve being observed in terms of an exhaust valves overall temperature and health. The appropriate one is the valve face/seat and the body represented by the back of the valve.

So Correlation some of the time does not support the facts. Causation is not from EGT, as has been shown in the NACA report on page 44 where EGT did not drive the valve temperature.

It is worth repeating, ICP is what drives valve temperature, and when you have high ICP you get high CHT, always. This is the best proxy you have for valve temperature in your plane. As is shown in the picture above.


Walter……anything to add? John Deakin perhaps?

[oggers]

Jaba

Your position has been that EGT is driving valve temperature, and that seems to be based on CORRELATION not CAUSATION.

Nope. I have never taken that position. I have been very careful to never say that EGT drives valve temperature. I have pointed out that there is a correlation, between EGT and valve temp, and that CHT also correlates.

http://www.pprune.org/members/125420-oggers-albums-misc-picture268-fig7tracking.png

I have said that exhaust gas heats the valve. Obviously combustion heats the valve too. The two are not mutually exclusive. Walter Atkinson's position was:

Walter Atkinson claims, quote:

EGT does NOT affect valve temperature....
those who think that valve temp is in any way related to EGT must reconcile the fact ...This is [B]definitive evidence that the two are NOT related....valve temperature does NOT track EGT. This is 1943 data, not ours. Lycoming verified it in 1966.

NACA:

http://www.pprune.org/members/125420-oggers-albums-misc-picture267-fig8tracking.png

[Lead Balloon]

I'm not sure on what, if any, scientific issue/s we differ any more, oggers and Eddie, so I'll frame the discussion a different way.

Which of these mixture settings will, in your view, be better for a piston engine's longevity:

- 30 degrees F Rich of Peak

- 30 degrees F Lean of Peak.

[oggers]

oggers,

You seem to be missing the point and confusing some things.

1. The centre of valve crown thermocouple is tracking the EGT more closely because it is basically an EGT probe. Look at where they positioned it :ugh: You are not looking at the relevant trace for a start.

So you now think that the valve thermocouple placed in the head of the valve 1/16" (1.5mm) from the face with the combustion chamber indicated a temperature more representative of EGT than valve? And also that placing the thermocouple as close as was physically possible to that face biased the temperature away from temperature in the combustion chamber toward EGT more than if it were where in the valve exactly?

And on that basis you reject the report data showing that EGT and valve temp correlated well. Bearing in mind that a few posts back APS cited this report as "definitive".

2. The valve temperature that matters is the valve face/seat

I am not sure how much closer you to the valve face than 1/16" you imagine the thermocouple should be so as not to be "basically an EGT probe" instead of a 'valve face probe'?

Why not simply accept what the report shows loud and clear - that valve temp for the most part correlated with EGT?

[rutan around]

Walter,
Thank you for making me aware that Auto Lean on those Allison engines is still 80 degrees ROP. I now understand that it simply means leaner than auto rich but not lean of peak EGT.

ALL of them claimed that Lindy's method, while useful in peacetime was a disaster in combat. The reason was that it took too long to come up to dog-fight speed from the extended range speed when you saw the enemy.Surely Lindy's method would have been useful en route to combat zones or when engaged in distant reconnaissance trips?

Cheers RA

[oggers]

I'm not sure on what, if any, scientific issue/s we differ any more, oggers and Eddie, so I'll frame the discussion a different way.

Which of these mixture settings will, in your view, be better for a piston engine's longevity:

- 30 degrees F Rich of Peak

- 30 degrees F Lean of Peak

Balloon, we disgree on the APS hypothesis that exhaust gas does not affect valve temperature...unless you have had an epiphany.

As you keep asking, it's 30 lean. I'm not aware that anyone has ever argued 30 ROP is the best place to run an engine for longevity. Sorry to shoot your fox.

[andrewr]

By running some engines for millions of hours at around 30 degrees rich of peak and running other engines for millions of hours at around 30 degrees lean of peak, then comparing the reliability of each group.

If only that had happened around 50 or 60 years ago.

Oh, wait....

Are those the same engines where according to flight engineers notes, they advanced timing from 20 to 30 degrees BTDC which favoured improved valve life when running leaner than 0.077 (which seems to correspond to about 50 ROP)?

R-4360Ops1 (http://www.enginehistory.org/r-4360ops1.shtml)

Also, interestingly, the target CHT was 230C (445F) which is high compared to the numbers people worry about here. I have no idea whether the materials are the same - but if they are different, it is another reason why the data may not be directly applicable.

Walter, in post 193:
One must be careful in comparing these engines and their engineering requirements to our GA engines.

Science is inconvenient: if your proposition is that data collected from large radials is equally applicable to today's GA engines, the question becomes how do you test that?

[Jabawocky]

Why not simply accept what the report shows loud and clear - that valve temp
for the most part correlated with EGT?
Why…? Because IT DOES NOT

You have failed to answer the simple questions repeatedly. You have failed to understand the reports, the history and for that matter when better equipped tests many years later have proved and refined the results, you have refused to accept them.

WHY is it that you find correlated things……yet when there is ZERO correlation as has been pointed out to you, you bury your head and start diversionary argument.

You are a lost cause. You refuse to open your eyes.

Reminds me of the saying….Confucius says, do not tell man something impossible when he is already doing it. :roll eyes:

Answer my questions with respect to the data provided (including that you and or others may have said we refused to provide) and prove beyond correlation that you are correct.

The facts are, it matters not whether you or I have the right opinion, it is what the data shows and how best we can use that to operate our engines. I have no opinion in this. But I do have many hours watching the data get collected, including FAA certification work doing detonation testing on aviation fuels. Maybe we are all wrong…..:E

[oggers]

Walter Atkinson

Remember the purpose of the NACA report. Some US engineer during WWII decided that we needed to run the B-24 Liberator LOP to get the range AND increase the bomb load. Some General said, "That's ridiculous, everyone knows that leaner mixtures result in higher exhaust valve temperatures." The Top Secret study was undertaken to prove or disprove the adamant General's position. The general lost. The physics won.

Now I'm not saying that some general and some engineer didn't have that debate but the reason for the report, strangely enough, is in the report:

"Direct measurement of valve temperatures would make possibe the accurate determination of the effects of the foregoing changes in cylinder design on the temperature of the exhaust valve. The developpment of a means of measuring valve temperatures was therefore undertaken"

They do not mention anywhere, anything about proving or disproving whether LOP results in higher valve temperatures.

Also it was not Top Secret it was confidential - the lowest classification apart from unclassified. It would be absurd to undertake that research as Top Secret - everyone involved would have needed to be develop vetted or whatever they called it then. Maybe some of them were already - I don't know - but the results would have had to be kept secret from virtually everyone who could have made use of them or declassified anyway. In anycase it was confidential. But we digress.

[vh-foobar]

oggers,

You seem to be missing the point and confusing some things.

1. The centre of valve crown thermocouple is tracking the EGT more closely because it is basically an EGT probe. Look at where they positioned it :ugh: You are not looking at the relevant trace for a start.

2. The valve temperature that matters is the valve face/seat and the one represented by the back of the valve body. Stick to the important ones and don't confuse the two.

Please refer to my previous post about what happens when you advance the spark. ICP goes up, CHT goes up, valve temperature goes up and EGT goes down.

Next and for those who say APS never give anything (data) for free here is a slide from the APS class. Look closely at the Cylinder 6 trace in blue. Note that the CHT is going through the roof. The ICP was definitely going through the roof (not shown but we know) and correspondingly the EGT fell considerably. What do you think the valve temperature was doing at the seat/face and the bulk of the valve body? Please answer this.

http://i849.photobucket.com/albums/ab58/jaba430/Screen%20Shot%202016-04-09%20at%204.39.52%20PM_zpsidzobnzc.pngCourtesy of Advanced Pilot Seminars

Your position has been that EGT is driving valve temperature, and that seems to be based on CORRELATION not CAUSATION. There is correlation for sure on the curve you keep showing above. However this is the wrong curve being observed in terms of an exhaust valves overall temperature and health. The appropriate one is the valve face/seat and the body represented by the back of the valve.

So Correlation some of the time does not support the facts. Causation is not from EGT, as has been shown in the NACA report on page 44 where EGT did not drive the valve temperature.

It is worth repeating, ICP is what drives valve temperature, and when you have high ICP you get high CHT, always. This is the best proxy you have for valve temperature in your plane. As is shown in the picture above.


Walter……anything to add? John Deakin perhaps?

From what I read here... you now seem to be saying that the valve temp measurements are misleading "because it is basically an EGT probe"? and the APS presentation has NO measurements of exhaust value temps, Hmmmm....

Not saying there might be some mistakes in NACA-752, or the the lycoming graph above, but it would be nice to see some actual valve temp measurements...

[vh-foobar]

oggers,

Please refer to my previous post about what happens when you advance the spark. ICP goes up, CHT goes up, valve temperature goes up and EGT goes down.



That is entirely understandable in the context of the report, the report lists the factors that affect exhaust valve temp, Mixture, IMEP, speed, spark advance, and cooling.

it never says the EGT is actually a factor though, it's simply a measurement, it shows that mixture effects valve temp, it also show that spark advance does to...

In the case of spark advancement, heat energy from the combustion process is being created earlier relative to a retarded ignition. As a result more of that heat energy is transferred by convection and radiation to the cylinder walls and valve faces, and less of the heat energy is dissipated in the expansion of the gas, relative to a more retarded ignition.

[oggers]

Jaba

and prove beyond correlation that you are correct.

I say there is a correlation. I cannot prove beyond correlation that there is a correlation. So every time you deny it I will simply rebut you with the graphic data.

Your opininon:

...for the most part correlated with EGT? Why…? Because IT DOES NOT

1943 data:

http://www.pprune.org/members/125420-oggers-albums-misc-picture267-fig8tracking.png



Your opinion:

for that matter when better equipped tests many years later have proved and refined the results, you have refused to accept them.


You have not provided any data from later and better tests.

[Walter Atkinson]

It was war-time. The Top Secret nature of the project was important to keep from the enemy. Afterward, It was reduced to confidential.

It matters not. The issue is that it has been widely accepted by the top researchers that valve temperature follows CHT and ICP and not EGT. The temp of combustion skyrockets. The ICP skyrockets. The CHT can go up 2 degrees per second. There has been confirming evidence posted as in detonation and preignition that this is true.

If one insists that EGT is a factor, please reconcile the preignition DATA that Jabba posted. We have a bucket full of these files and in every case, it is the same. Falling EGT, rapidly rising CHT. How can one with intellectual honesty suggest that during pre-ignition that the valve is running cooler because the EGT is falling?

This is not unlike those who insist that lead lubricates the valves. That's a religious fervor to support the unsupported.

[Walter Atkinson]

***
Surely Lindy's method would have been useful en route to combat zones or when engaged in distant reconnaissance trips?
***

One would think so, but as Kirby pointed out, "The whole damned place was a combat zone. You never knew where the bastards were going to show up."

I wasn't there. I'm just relaying what those who were there told me and I heard discussed among them at their Juvat reunion. As one of the P-38 ACEs said, "You could always tell which P-38 I was flying. There was a consistent, thin, brown mist coming out of the cockpit." Being around these guys is a treasured experience.

BTW, one of the things they all said was that the Aussies were the toughest, most tenacious men around. They said they thought it was the mutton and the vegemite that made 'em so disagreeable in the jungle.

[oggers]

andrewr

according to flight engineers notes, they advanced timing from 20 to 30 degrees BTDC which favoured improved valve life when running leaner than 0.077....Also, interestingly, the target CHT was 230C (445F)

That's interesting. The flight engineer knew that "lowered exhaust gas temperatures favored longer valve exhaust life". Whilst observing a CHT of 445F - and the cruise limit was even higher at 470!

[vh-foobar]

If one insists that EGT is a factor, please reconcile the preignition DATA that Jabba posted. We have a bucket full of these files and in every case, it is the same. Falling EGT, rapidly rising CHT. How can one with intellectual honesty suggest that during pre-ignition that the valve is running cooler because the EGT is falling?


It IS a factor, just NOT THE ONLY ONE... In the pre-ignition case considerably more heat energy is transferred to both valve and cylinder head and less is available in the exhaust gas, that is demonstrable. The heat is both generated and transferred to the cylinder head and valve earlier in the engine cycle.

The post from Jabawocky does not present any data with valve temps...

[Walter Atkinson]

The cruise limit on CHT was not that high. It was that high where it was measured--on the back side of the hottest cylinder, under the spark plug as a ring gasket. It was known that the CHT was actually much lower than that reading--by about 50dF. The CHTs were measured on only two of 18 cylinders, one in each row. When we put ceramic thermocouples on the cylinders, we found that the ring probe was reading higher by the referenced amount. The resulting operational CHT was in the range we now think optimal for longevity concerns. We know that cylinders operated under about 380-400dF retain a significant amount of metal strength over those operated at higher temps. We show that data in the new Master's Class given by APS.

The reason they advanced the timing in cruise was to place the thetaPP closer to optimal (16dATDC), while having a retarded timing for max power applications which allowed for a greater detonation margin and optimal crank-conrod geometry at that power. It was not about valve life. It had to do with optimizing the crank-conrod geometry for maximum torque on the given fuel burn LOP.

When running the TC-18 engines ROP, the TBO was 600 hours. When operating LOP, the TBO was 3600 hours. Why? Lower ICPs and CHTs resulted in greater longevity and fewer maintenance issues at the same power output. THAT was easier on the exhaust valves. They could not measure EGT on the engines as installed. That awaited the innovations of Alcor.

[vh-foobar]

If EGT does not effect exhaust valve temperature, wouldn't you expect to see the same temperatures with the intake valves and similar failure/damage rates?

Perhaps in the NACA study they should have put a probe in the inlet valve as well.

I understand Lycomming engines have sodium filled exhaust valves, do they go to the same trouble with the inlet valves?

[andrewr]

But why does the CHT go up? Because the peak cylinder pressures go up. Just like your air compressor in the garage.

This is exactly backwards. Your engine is not an air compressor.

In an air compressor, the piston is adding energy to the gas (compressing it) which heats the gas. In an engine, the piston is extracting energy from the compressed gas which actually cools the gas and lowers the EGT.

You can see this in e.g. CO2 engines which run from compressed gas without combustion. They get (very) cold, not hot. The more power and higher pressures from the engine the colder they get. The cylinders have fins to try to avoid the engine getting too cold, which causes the power to drop off.

In an IC engine the temperature creates the pressure, not the other way around.

The NACA report 754 alludes to this in the section on the effect of timing on valve temperature:
"The rise in valve temperature with greatly retarded spark is probably caused by the higher exhaust-gas temperature resulting from a decreased expansion after combustion"

Earlier combustion = higher pressures but greater expansion after combustion (i.e. piston stroke after combustion) = more energy extracted from the gas = lower EGT but yes, probably higher CHT.

So increased pressure correlates with higher CHT, but it's NOT like an air compressor.

[Lead Balloon]

I asked:Which of these mixture settings will, in your view, be better for a piston engine's longevity:

- 30 degrees F Rich of Peak

- 30 degrees F Lean of Peakoggers finally replied:As you keep asking, it's 30 lean.Is the correct answer! Well done oggers.

0ggers went on to say:I'm not aware that anyone has ever argued 30 ROP is the best place to run an engine for longevity. Gosh. You haven't been paying much attention to the detail of the 'debate' Downunda, have you. For example, Eddie Dean said at post 242 of this very thread:I have worked with several operators and Chief Engineers over recent years, all of them are against the APS LOP theory and have warned their pilots of such.There is no "APS LOP theory". There are merely data to prove that an EGT 30 degrees LOP is better for an engine's longevity than 30 degrees ROP.

Anyway, we got to the practical bottom line eventually. The fact that you might believe that an EGT of 30 degrees lean is better for engine's longevity than 30 degrees rich because EGT has a causal connection to valve temperature is of no practical consequence.

[andrewr]

The reason they advanced the timing in cruise was to place the thetaPP closer to optimal (16dATDC) ... It was not about valve life.


I agree about optimizing the PP. On valve life, the flight engineer instructor says it favoured longer life, you say it doesn't. I have no way of confirming either way. It might annoy you that I don't just "believe" but that's OK.

But if you advance the timing to keep the same theta PP, you (obviously) start burning earlier BTDC and will burn more of the mixture before top dead centre (i.e. timing 20 degrees BTDC you have 36 degrees of rotation before the theta PP, 30 BTDC gives 46 degrees. At 20 degrees you are half way there at 4 degrees BTDC, 30 degrees half way is 9 degrees BTDC.

Does this not increase ICP? Not that I think increased ICP is a problem, within design parameters, but you seem to be aiming to reduce it?

But my original statement was simply that we do need to be careful when applying specific data from these engines to current GA engines - and agreeing with your post saying the same thing.

In particular, I believe that the statement that operating according to engine manufacturer recommendations will result in a decreased service life deserves better data than service information from radial engines 50 years ago.

Is it not possible that Lycoming has incorporated some of the information that was discovered to improve their engines and eliminate many of the causes of failure?

[Perspective]

Jabawocky.
Quote: "like all TROLLS before you"
He has a differing opinion. You are better than that.
I really don't have a dog in this one, but in my opinion the jury is far from out
On this. Why?. I think there is a lot of validity in what you are saying about LOP guys,
Unfortunately we are still seeing damaged engine components due to, what would
Probably be best described as mishandling. Not intentional Of course. Have had quite a few
Guys proudly telling me how they read all of this literature on LOP and practice it, then we go about changing cracked cylinders, burnt out valves, barrels knackered, worn out guides, is it poor manufacturing, poor application, i.e. Set and forget to monitor?
I tend to think it is weighted to poor application and monitoring more than manufacturing, but I don't know definitively, forget about super Connies or 6's they had a guy whose job was to monitor and the Radials seem far more robust anyway, but until I see everyday folk running LOP not damaging engines I'll be suspicious. Yes it is demonstratively (is that a word!) cooler, anyone can follow that, unfortunately there are many variables to what seems a simple operation.
What's really frustrating is that we are in 2016 still talking about all this, this is where I find the certification process so counterproductive it's a joke, there is so much technology out there we could be adopting to control all this stuff, along with synthetic vision for panels etc.
Archaic industry in so many ways

[Lead Balloon]

Guys proudly telling me how they read all of this literature on LOP and practice it, then we go about changing cracked cylinders, burnt out valves, barrels knackered, worn out guides, is it poor manufacturing, poor application, i.e. Set and forget to monitor?

I tend to think it is weighted to poor application and monitoring more than manufacturing, but I don't know definitively, forget about super Connies or 6's they had a guy whose job was to monitor and the Radials seem far more robust anyway, but until I see everyday folk running LOP not damaging engines I'll be suspicious. Yes it is demonstratively (is that a word!) cooler, anyone can follow that, unfortunately there are many variables to what seems a simple operation.That's why it's very important not to confuse trying to run LOP, or believing an 'engine' is LOP, for each cylinder being LOP.

Given that the data prove that all cylinders being at an EGT LOP is better for engine longevity than an EGT ROP - or at least an EGT ROP that is not far enough ROP - and given that we know why, the cause/s of the damage to which you refer inexorably follow. They are alluded to in your post. What's really frustrating is that we are in 2016 still talking about all this, this is where I find the certification process so counterproductive it's a joke, there is so much technology out there we could be adopting to control all this stuff, along with synthetic vision for panels etc.

Archaic industry in so many waysPrecisely. :(

[Ultralights]

Guys proudly telling me how they read all of this literature on LOP and practice it, then we go about changing cracked cylinders, burnt out valves, barrels knackered, worn out guides, is it poor manufacturing, poor application, i.e. Set and forget to monitor? i think the problem with these guys, is they "think" they are LOP, one or 2 cylinders might be, but the others could well be right in the danger zone about 50 ROP. to run reliably at LOP, you need good monitoring, and a conforming engine. without that, you see the results, damage caused by those that think, but arnt running all cylinders LOP.

[Jabawocky]

andrewr….yes correct but I can't get oggers to answer a few simple questions, so very basic analogy attempts were the best I could get. ;)

Refusal to accept that increasing pressure and dropping EGT means the correlation he observes does not equate to causation.

All Swans were white……until they found black swans.

[vh-foobar]

andrewr….yes correct but I can't get oggers to answer a few simple questions, so very basic analogy attempts were the best I could get. ;)

Refusal to accept that increasing pressure and dropping EGT means the correlation he observes does not equate to causation.



I attempted to answer it, not on oggers behalf mind...

I wrote:
In the case of spark advancement, heat energy from the combustion process is being created earlier relative to a retarded ignition. As a result more of that heat energy is transferred by convection and radiation to the cylinder walls and valve faces, and less of the heat energy is dissipated in the expansion of the gas, relative to a more retarded ignition. Unfortunately my post needed to be approved by mods or something,

[Jabawocky]

nahh mate you were doing fine :ok:

[Walter Atkinson]

***
Your engine is not an air compressor.

In an air compressor, the piston is adding energy to the gas (compressing it) which heats the gas. In an engine, the piston is extracting energy from the compressed gas which actually cools the gas and lowers the EGT.
***

The exact same thing is happening in an internal combustion engine. The IAT is heated during the compression stroke.

***
You can see this in e.g. CO2 engines which run from compressed gas without combustion. They get (very) cold, not hot.
***
This is due to the fact that the air is never heated and the EXPANSION on the power stroke is cooling significantly.

***
In an IC engine the temperature creates the pressure, not the other way around.
***
The "temperature" does not create the pressure. The expansion of the burning gas that creates the pressure, the increasing pressure affects the heating. It's a small nit, but it's real.

***
The NACA report 754 alludes to this in the section on the effect of timing on valve temperature:
"The rise in valve temperature with greatly retarded spark is probably caused by the higher exhaust-gas temperature resulting from a decreased expansion after combustion"
***
They got this "probably" wrong. This is a perfect example of a correct observation leading to an incorrect assumption of causality. The later thetaPP of a retarded spark has the resultant EGT higher at a much reduced pressure. The rising valve temp in these conditions are caused by the still burning 3800dF combustion gasses going past the open valve. There was no time for the gas to expand after burning and lower the EGT. We can see this effect in very well-balanced F:A engines that are leaned beyond optimal. This is not a "normal" condition.

***
Earlier combustion = higher pressures but greater expansion after combustion (i.e. piston stroke after combustion) = more energy extracted from the gas = lower EGT but yes, probably higher CHT.
***
Correct.

[Walter Atkinson]

***
I agree about optimizing the PP. On valve life, the flight engineer instructor says it favoured longer life, you say it doesn't. I have no way of confirming either way. It might annoy you that I don't just "believe" but that's OK.
***
We can confirm this if we understand the difference between the higher EGT very late in the cycle as I explained in the post above and the engineer's reasoning being correct and a higher EGT in a normal combustion cycle which is what I have been talking about. We are not in disagreement, just talking about two very different conditions--one normal, the other abnormal. The standard takeoff timing was so late during cruise operation as to have the valve opening while the gas was still burning. That is not good and is bad for valve life, as the engineer correctly surmised. That's not what I was talking about in the normal combustion event. They advanced the timing to allow the valve to be closed during combustion event and not have the extremely hot gasses flow by the valve face. We show these different conditions on leaning traces in the APS class.

***
But if you advance the timing to keep the same theta PP, you (obviously) start burning earlier BTDC and will burn more of the mixture before top dead centre (i.e. timing 20 degrees BTDC you have 36 degrees of rotation before the theta PP, 30 BTDC gives 46 degrees. At 20 degrees you are half way there at 4 degrees BTDC, 30 degrees half way is 9 degrees BTDC.
***
By measurement, half of the F:A mixture is consumed at the thetaPP. If the thetaPP is the same the same amount of gas has been burned regardless of the spark event timing. The reason this works is two-fold. The flame front is organized slower and the burn is slower. SO, the amount of increased pressure on the up-stroke is not significantly different.

***
Does this not increase ICP? Not that I think increased ICP is a problem, within design parameters, but you seem to be aiming to reduce it?
***
See explanation above. The ICP is "increased" from a very low number, very late in the cycle to the designed ICP at the right place in the stroke. These ICPs are still much lower than those seen at 50dF ROP, hence the desire to lower them to this level.

***
In particular, I believe that the statement that operating according to engine manufacturer recommendations will result in a decreased service life deserves better data than service information from radial engines 50 years ago.
***
The physics are everywhere the same. Sir Isaac Newton.
There are more similarities than differences in radials and flat engines. They had 400 MILLION flight hours of data. We have more than 4 million flight hours of data on the flat engines and it is all in a agreement. (Thank you to Sir Isaac!)

***
Is it not possible that Lycoming has incorporated some of the information that was discovered to improve their engines and eliminate many of the causes of failure?
***
One would hope so.

[vh-foobar]

***
The "temperature" does not create the pressure. The expansion of the burning gas that creates the pressure, the increasing pressure affects the heating. It's a small nit, but it's real.


That's not truly accurate either... the total gas is not expanding until top centre, sure the the volume of gas that has ignited is expanding.


***
The NACA report 754 alludes to this in the section on the effect of timing on valve temperature:
"The rise in valve temperature with greatly retarded spark is probably caused by the higher exhaust-gas temperature resulting from a decreased expansion after combustion"
***
They got this "probably" wrong. This is a perfect example of a correct observation leading to an incorrect assumption of causality. The later thetaPP of a retarded spark has the resultant EGT higher at a much reduced pressure. The rising valve temp in these conditions are caused by the still burning 3800dF combustion gasses going past the open valve. There was no time for the gas to expand after burning and lower the EGT. We can see this effect in very well-balanced F:A engines that are leaned beyond optimal. This is not a "normal" condition.
Correct.

I would agree with that, now that your considering the valves exposure to the flame, I would submit that this is also why the valve temperature curve is reasonably flat from 5 to 25 degrees, even though EGT increases, the valve face exposure to the advancing flame is reducing as the volume of the gas expands and moves away from the face.

[oggers]

Lead Balloon

0ggers went on to say:

I'm not aware that anyone has ever argued 30 ROP is the best place to run an engine for longevity.


Gosh. You haven't been paying much attention to the detail of the 'debate' Downunda, have you. For example, Eddie Dean said at post 242 of this very thread:

I have worked with several operators and Chief Engineers over recent years, all of them are against the APS LOP theory and have warned their pilots of such.

Well, I don't speak for Eddie Dean, but that quote most definitely doesn't mention 30ROP being the best place to run an engine for longevity, which is an argument you seem strangely keen for someone, anyone, to take up!

[andrewr]

i think the problem with these guys, is they "think" they are LOP, one or 2 cylinders might be, but the others could well be right in the danger zone about 50 ROP. to run reliably at LOP, you need good monitoring, and a conforming engine. without that, you see the results, damage caused by those that think, but arnt running all cylinders LOP.

That's why it's very important not to confuse trying to run LOP, or believing an 'engine' is LOP, for each cylinder being LOP.

This is what concerns me about the LOP debate. Any problems are attributed to "people not doing it right". Even if that's true, people who try and fail should be included in the reliability statistics.

Otherwise you also have to exclude engines from the non-LOP camp too: those who don't lean, those who lean but not in accordance with manufacturer's instructions, any engines that have suffered overheating, engines with bad baffling...

If you start excluding those who fail to follow instructions correctly, pretty soon reliability data is meaningless.

[andrewr]

***
Your engine is not an air compressor.

In an air compressor, the piston is adding energy to the gas (compressing it) which heats the gas. In an engine, the piston is extracting energy from the compressed gas which actually cools the gas and lowers the EGT.
***

The exact same thing is happening in an internal combustion engine. The IAT is heated during the compression stroke.

True, but the effect is very small compared to the heat from combustion. Try turning an engine with a motor at WOT without fuel, and compare the CHTs.

The "temperature" does not create the pressure. The expansion of the burning gas that creates the pressure, the increasing pressure affects the heating. It's a small nit, but it's real.

No, that's just plain wrong. Pressure in a gas depends on 2 things - the number of molecules and the temperature. Burning fuel breaks up big hydrocarbon molecules and combines them with oxygen into many smaller H2O, CO and CO2 molecules, AND releases a lot of energy as heat. Both contribute to the pressure rise. This stuff isn't new, it's been known since before the internal combustion engine was invented and is part of basic chemistry.

***
The NACA report 754 alludes to this in the section on the effect of timing on valve temperature:
"The rise in valve temperature with greatly retarded spark is probably caused by the higher exhaust-gas temperature resulting from a decreased expansion after combustion"
***
They got this "probably" wrong. This is a perfect example of a correct observation leading to an incorrect assumption of causality. The later thetaPP of a retarded spark has the resultant EGT higher at a much reduced pressure. The rising valve temp in these conditions are caused by the still burning 3800dF combustion gasses going past the open valve. There was no time for the gas to expand after burning and lower the EGT.

I'm not sure what you are saying is wrong here, since your explanation is pretty much exactly the same. You talk about still burning gas, but in fact it doesn't matter whether it is still burning or not.

A flame is just hot gas anyway. The 3800F heat doesn't just disappear once the burn is complete. The gas remains at that temperature until it loses the energy to something else.

There are basically 5 places that energy can go:
1) Turning the propeller by expanding against the piston - this is obviously where we want the energy to go
2) Out the exhaust (EGT)
3) Into the cylinder head/valves
4) Into the piston
5) Into the cylinder barrel.

That's it. All that 3800F heat has to go down one of those paths.

The earlier you burn the more the gas can expand against the piston and the more energy goes down the useful path - and the sum of all the other energies must be less (even if e.g. CHT is higher).

If the burn finishes late much more energy (heat) remains in the gas or is transferred to other engine parts. EGT is higher and as you say this will heat the valves. CHT may be lower because the heat is spread through a larger volume in the cylinder, but I would be very interested to see measurements of cylinder barrel temperatures in particular. I would expect them to rise as the CHT decreases with leaner mixtures. You can look at the fins to see which part is intended to receive most heat.

All the explanations need to follow the principles of chemistry and conservation of energy. If they don't e.g. some energy just disappears there is something missing from the explanation.

[Lead Balloon]

I see, oggers. When Eddie referred to all those operators and Chief Engineers who've "rejected the APS LOP theory and have warned their pilots of such", he meant (of course) that those operators and Chief Engineers were warning against operating engines 30 degrees F rich of peak.

I picked 30. I could have picked 40. Or 47.397. Or 27.3333. The number matters not (except, perhaps, for the purposes of whatever it is you're arguing) until all cylinders are far enough ROP.

Andrewr: You are in my view absolutely correct. The 'data' derived from multi-cylinder engines with a single EGT probe and a single CHT probe and no way of calculating accurate % power measurements are absolutely meaningless for the purposes of deciding whether ROP is "better" than LOP for a multi-cylinder engine. That's one of the reasons why opinions about the causes of the unreliability of and damage to a piston engine with a single EGT probe and single EGT probe are also absolutely meaningless.

[oggers]

Walter Atkinson,

Andrewr posted

In an IC engine the temperature creates the pressure, not the other way around.
...you posted

The "temperature" does not create the pressure. The expansion of the burning gas that creates the pressure, the increasing pressure affects the heating. It's a small nit, but it's real.

No Walter you are not right about this at all. In a heat engine there is this thing called a 'heat addition process' - ie when combustion happens. It is not called a 'pressure addition process'. Heat and temperature are not the same thing but andrewr is absolutely correct that "the temperature creates the pressure not the other way around". The pressure rises because the heat of combustion raises the temperature of the gas and the pressure therefore has to go up and/or expansion occur.

The "expansion of the burning gas" does not "create the pressure". The expansion of the gas reduces the pressure. You cannot argue with that, it is the gas law. That is not to say that pressure cannot rise while expansion takes place, but that is different and not what you claim.

It would be fair to say the burning of the gas is creating the pressure, or causing the expansion. In neither case is the "expansion of the burning gas creating the pressure".

It's a small nit, but it's real

Sorry Walter but this is not a small nit it is thermodynamics 101 and you have it wrong.

[oggers]

Lead balloon

I see, oggers. When Eddie referred to all those operators and Chief Engineers who've "rejected the APS LOP theory and have warned their pilots of such", he meant (of course) that those operators and Chief Engineers were warning against operating engines 30 degrees F rich of peak.

I picked 30. I could have picked 40. Or 47.397. Or 27.3333. The number matters not (except, perhaps, for the purposes of whatever it is you're arguing) until all cylinders are far enough ROP

as I posted:

Lead Balloon


0ggers went on to say:

I'm not aware that anyone has ever argued 30 ROP is the best place to run an engine for longevity.

Gosh. You haven't been paying much attention to the detail of the 'debate' Downunda, have you. For example, Eddie Dean said at post 242 of this very thread:

I have worked with several operators and Chief Engineers over recent years, all of them are against the APS LOP theory and have warned their pilots of such.

Well, I don't speak for Eddie Dean, but that quote most definitely doesn't mention 30ROP being the best place to run an engine for longevity, which is an argument you seem strangely keen for someone, anyone, to take up!

[gerry111]

I suspect that 'Lead Balloon' may be a rather junior aeromodeller, perhaps flying his first Enya 15 powered model aircraft?

So he'd have no idea of how an IO520 engine in a family owned Bonanza would operate? Things like how to run the engine at its most efficient leisure. And how to keep his life and that of his pax safe?

Clearly, he doesn't have a clue.. :ok:

[oggers]

So he'd have no idea of how an IO520 engine in a family owned Bonanza would operate? Things like how to run the engine at its most efficient leisure. And how to keep his life and that of his pax safe?

Clearly, he doesn't have a clue..

Yes I've always been a big believer in the concept that if someone hasn't killed themselves, and they own an aeroplane, they must certainly know more about engine ops than all the engineers and test pilots of the manufacturers combined. :ok:

[oggers]

Walter Atkinson:

When running the TC-18 engines ROP, the TBO was 600 hours. When operating LOP, the TBO was 3600 hours. Why? Lower ICPs and CHTs resulted in greater longevity and fewer maintenance issues at the same power output. THAT was easier on the exhaust valves. They could not measure EGT on the engines as installed. That awaited the innovations of Alcor.

That claim about TBO is unverified and therefore suspect. When I do a search to verify that claim, the only links I get are ones to you making the same claim on other forums without any evidence.

They could not measure EGT on the engines as installed. That awaited the innovations of Alcor.

Who say:

"The exhaust valve is usually the most critical with respect to excessive temperatures.

When the mixture is enriched at powers above 65% to maintain constant exhaust valve temperature, the EGT versus power curve is as shown in Figure 9. As illustrated, the EGT at 100% power needs to be 100°F lower than peak EGT at 65% if the exhaust valve is to be maintained at the same temperature as it is at peak EGT for 65% power." redskyventures.org EGT Procedures ALCOR pdf (https://www.redskyventures.org/doc/cessna-maintenance-manuals/EGT_Procedures_Nutshell_ALCOR_06_14_2010.pdf)


So the "innovators" at Alcor have identified a correlation between EGT and exhaust valve temp.

Figure 9:
http://www.pprune.org/members/125420-oggers-albums-misc-picture270-alcoregt.png

[rutan around]

Oggers said:-
The expansion of the gas reduces the pressure.What you and others seem unable to get your heads around is that BEFORE top dead centre (TDC) the size (volume) of of the container holding the gas is decreasing. Even without igniting the gas the pressure and temperature increase. You know-same number of molecules squeezed into a smaller space.

How much anti-work pressure ( pressure trying to make the engine go backwards) depends on where you light the fire. Remember all the way up the upstroke the volume of the part of the cylinder containing the gas is decreasing. So if you light the fire early the pressure increases sooner. The worst / hardest you can be on your engine is to burn all the fuel/air mixture before TDC . At that point your combustion chamber is the smallest it's going to get and you've added ALL the the energy from combustion plus the normal heat from compressing the intake gas to 12% of it's original volume.
This gives a very high temperature and internal cylinder pressure (ICP) but because of the geometry of the piston / con rod / crankshaft at that point no work is being done. The piston is pushing straight down on top of the crankshaft (trying to push it through the bottom of the sump) but giving NO rotational force.

Once past TDC the pressure starts to do some useful work. Unfortunately the greatest mechanical advantage occurs when the con rod is at right angles to the crank web (BTW Not 90* after TDC ) This is no use as by the time the crank reaches that angle the combustion chamber is many times larger and the pressure many times smaller and not worth using.

So the trick is to have peak ICP occur where there some mechanical advantage but the volume of the combustion chamber hasn't grown big enough to adversely effect the pressure to an unacceptable extent.

This "sweet spot" occurs when the fuel/air mixture finishes burning at 12* to 15* after TOD. As a fair bit of the combustion and hence energy increase takes place after TDC where the combustion chamber is starting to increase in volume it is obvious the ICP and temperature wont be as high as it would be if that energy had been added at or before TDC.

Anyone trying to get their head around piston engines must keep in mind the constantly changing volume of the combustion chamber and also the speed of the combustion event along with the factors affecting it.

Here's a good pub quizz to win a couple of beers.

After fuel ignites in an internal combustion engine what is it's average burn speed?

A 60 k/h
B 100 k/h
C 500 k/h
D 950 k/h
E Almost instantaneous. Can't be measured.

[Lead Balloon]

So oggers, because I'm a dumb pilot with no other qualifications, please tell me which of one the alternative EGT settings will all those wise "engineers and test pilots of the manufacturers combined" say is the best setting for the longevity of the engines on which my life relies:

- 30 ROP
Or
- 30 LOP.

(Or if you like:

- 40 ROP
Or
- 40 LOP

Or if you would prefer:

- 47.397 ROP
Or
- 47.397 LOP

Or perhaps instead:

- 27.3333 ROP
Or
- 27.333 LOP.)

What is a dumb pilot to do when the wise manufacturer's recommendations are contrary to what the data prove?

[Jabawocky]

oggers

You are reduced to publishing alcor's material now as gospel.

The game is up. You will not take the advice of Walter, yet you will stand on the old Alcor advertisement material ……. :ugh:

As for the TBO….perhaps Walter might just have done a lot of work with and has a lot of papers from the guys that flew them. I have in my office an excellent publication from Curtis Wright which is not easily found where they talked heavily about what we know today to be true. Some folk from the DC-7 and Connie days could help you fill in the blanks. APS are just lucky to have one such gentleman, his name is John Deakin.

American Airlines would be an excellent source. Give them a call. :ok:

[rutan around]

Re pub quizz
Oops
None are correct so pick the one nearest.

Note to self. If you're going to celebrate the removal of a much hated Airport Manager by drinking heavily don't post on Pprune.:E

[oggers]

Rutan around:

What you and others seem unable to get your heads around is that BEFORE top dead centre (TDC) the size (volume) of of the container holding the gas is decreasing. Even without igniting the gas the pressure and temperature increase. You know-same number of molecules squeezed into a smaller space.

Sure, I would assume everyone gets that. It is obvious but it is beside the point. Walter Atkinson wrote - as a rebuttal to andrewr - The expansion of the burning gas creates the pressure which is a misunderstanding of how an engine works thermodynamically and an equally incorrect understanding of the gas laws. That is the point.


Jabawocky

oggers

You are reduced to publishing alcor's material now as gospel.

The game is up. You will not take the advice of Walter, yet you will stand on the old Alcor advertisement material …….

I have not claimed that Alcor document is gospel. Walter said "Alcor are innovative" so I simply reproduced some of their material. Somehow I didn't think you would like it. :ok: "Gospel" is your word - I wouldn't use it. If there is a part of that document you wish to rebut then feel free; I may or may not agree with your opinion.

As for the TBO….perhaps Walter might just have done a lot of work with and has a lot of papers from the guys that flew them. I have in my office an excellent publication from Curtis Wright which is not easily found where they talked heavily about what we know today to be true.

Ok, so the calim by APS is "TC18 engines only made 600hrs TBO when run ROP, and they made 3600hrs when run LOP". If you have the documents from Wright where they verify this you will be able to post it here.

[Lead Balloon]

God I hate it when I'm sucked in by a troll.

You are correct, oggers. :ok: Best wishes for the rest of your life. :ok:

[Walter Atkinson]

oogers:
The 600 to 3600 hour TBO information came from "Basic Theory", a publication by Wright Aeronautical (known as the WAD manual). It was published in (IIRC) 1957, and was based on 400 million flight hours of data collected by American Airlines. This has been confirmed by pilots and flight engineers who flew these engines during their heyday.

The US Military ran 'em ROP. As a general rule, changed one or two cylinders after every ocean crossing (according to Ralph Requa who flew them) and American Airlines did the same--until running them with a 10% BMEP drop (about 50dF LOP) when the TBOs extended to 3600 hours (according to the WAD manual and Captain John Miller who had 80,000 hours flying them, four at a time.)

Lead Balloon:
I guess I got sucked in by the troll as well. The difference is that over the last 15 years we have educated more than few by dealing with the trolls.

[vh-foobar]

So far in summary...

The only data posted in this thread that has real measurements of exhaust valve temps is the naca report below.




from the NACA report
http://www.pprune.org/members/125420-oggers-albums-misc-picture264-fig8div.png



It makes the point that mixture has the biggest effect of valve temp. It notes that a mixture of 0.66 results in the highest temp observed and the graph shows this very close to peak EGT. A mixture of .112 (indicative of full rich) give the lowest valve temp and the lowest EGT. While a lean mixture of 0.52 gives a substantial reduction of valve temp, EGT and also power (if knock is to be avoided) verses .066.

It also shows that both CHT and EGT do not always correlate with Exhaust valve temp, but in the case where mixture is varied alone there is strong correlation between EGT and exhaust valve temp.

That seems pretty conclusive, perhaps they made some errors...

Yet the Lycoming data posted, while they have not measured the valve temps, they have measured the guide and seat, these support the measurement provided in NACA-754.





http://www.pprune.org/members/125420-oggers-albums-misc-picture261-lycomingdata1966.png



Perhaps my summary is all rubbish, if so there must be some scientific data, with actual valve temp measurements to show its rubbish?

[vh-foobar]

When running the TC-18 engines ROP, the TBO was 600 hours. When operating LOP, the TBO was 3600 hours. Why?

Would be nice to see that data, but it appears entirely plausible given that it appears this engine was designed for LOP at cruise power.

I would suggest your explanation leaves an important bit out, spark advance. Those engines had variable timing, albeit operated by the FE and he had two choices 30 and 20 degrees. At the cruise setting 30 degree BTDC and a mixture close to peak EGT, combustion would start and finish too early. Using the data from NACA-754, 30 degree and mixture at .08 results in CHT and EGT higher than at 20 degree.

[Walter Atkinson]

***
Would be nice to see that data, but it appears entirely plausible given that it appears this engine was designed for LOP at cruise power.
***
It was operated ROP for a number of years. Poor results lead to the understanding that if operated with a 10% BMEP drop, the engines would last longer... six times longer to be exact.

***
I would suggest your explanation leaves an important bit out, spark advance. Those engines had variable timing, albeit operated by the FE and he had two choices 30 and 20 degrees. At the cruise setting 30 degree BTDC and a mixture close to peak EGT, combustion would start and finish too early. Using the data from NACA-754, 30 degree and mixture at .08 results in CHT and EGT higher than at 20 degree.
***
I explained that earlier. Please reference the explanation as to higher EGT very late in the combustion stroke and poor valve life. The spark advanced was added to the TC-18 variant, not originally present in the 3350.

BTW, our flat engines were DESIGNED to be run LOP. They have not been until recently since, as delivered, they had poor F:A balance and would run rough on the lean side. Since GAMI fixed that, they run as they were designed to be run. See the Malibu TSIO-520 history on that fubar.

Alcoa's development of the EGT probe allowed us to see that the 10% BMEP drop was about 50dF LOP. It allowed for more accurate leaning on engines without torque converters.

FWIW, when the crank is 20dBTDC on the up-stroke, the piston is very, very close to TDC--it's not 20 degrees more travel up. The piston movement is very, very small from 20dBTDC to 20dATDC on the crank. It's so close that it's hard to tell that it's not AT the top. Another thing we have shown to the many APS students. These things help in one's understanding.

[vh-foobar]

***

It was operated ROP for a number of years. Poor results lead to the understanding that if operated with a 10% BMEP drop, the engines would last longer... six times longer to be exact.


http://www.pprune.org/newreply.php?do=postreply&t=573902
I would say your not acknowledging important details... An earlier version of the engine, run ROP lasted 600 hours operated by the military, and a later model that incorporated at least variable timing operated by an airline operated LOP lasted 3500 hours.

Who was the physicist that said ?

'Everything should be made as simple as possible, but not simpler'

***

BTW, our flat engines were DESIGNED to be run LOP.

I would believe that, if I had the skills and was asked to design an engine I would design it LOP as well, doesn't mean when it got built there might be some limitations not intended that are either inherit in the design and/or manufacture that now must be observed.

[Walter Atkinson]

***
I would believe that, if I had the skills and was asked to design an engine I would design it LOP as well, doesn't mean when it got built there might be some limitations not intended that are either inherit in the design and/or manufacture that now must be observed.
***

That's a weird approach. If you thin that might be true, and intellectually honest, you should say why that *might* be the case. It's not the case. The only issue was that they did not provide the product with balanced F:A ratios like the design called for. Had they, we would have been running these engines for 50 years like they were intended to be run--LOP. GAMI fixed that and a small group of pilots don't seem to be able to "get it."

Be well. Go on as you see fit.

[Zaphod Beblebrox]

i has discussed this technickal question at length about the whys and wherefores of operating reciprocating piston powerplants of various type with my good friend Delmar O'Donnel and he says, "I'm with you fellers."http://www.wearysloth.com/Gallery/ActorsN/45204-25320-0.jpg

[Ultralights]

I guess I got sucked in by the troll as well. The difference is that over the last 15 years we have educated more than few by dealing with the trolls.

yes, i have done the APS course, even though the engines i operate have no mixture controls, i still find these conversations with "trolls" entertaining and learn a little bit, or refresh previous learned knowledge.

[oggers]

Walter Atkinson

That's a weird approach. If you thin that might be true, and intellectually honest, you should say why that *might* be the case. It's not the case. The only issue was that they did not provide the product with balanced F:A ratios like the design called for. Had they, we would have been running these engines for 50 years like they were intended to be run...a small group of pilots don't seem to be able to "get it."

In your opinion.

[oggers]

The graph Alcor produced:

http://www.pprune.org/members/125420-oggers-albums-misc-picture270-alcoregt.png

...is validated by the data from the NACA series of tests:

http://www.pprune.org/members/125420-oggers-albums-misc-picture273-valve-v-power.png

[andrewr]

Poor results lead to the understanding that if operated with a 10% BMEP drop, the engines would last longer... six times longer to be exact.


I hate to muddy the waters further, but I looked for information on BMEP change with mixture.

3 different sources I found show 10% BMEP drop from best power putting you at peak EGT or just lean (maybe 10F). Right at the best economy mixture.

10% additional BMEP drop from peak EGT looks closer to 50F lean (which the same sources suggest is 20-25% less BMEP than best power).

I am not trying to troll, just trying to relate what APS is teaching to data from other sources - which is what science is supposed to be about.

[vh-foobar]

***
I would believe that, if I had the skills and was asked to design an engine I would design it LOP as well, doesn't mean when it got built there might be some limitations not intended that are either inherit in the design and/or manufacture that now must be observed.
***

That's a weird approach. If you thin that might be true, and intellectually honest, you should say why that *might* be the case. It's not the case. The only issue was that they did not provide the product with balanced F:A ratios like the design called for. Had they, we would have been running these engines for 50 years like they were intended to be run--LOP. GAMI fixed that and a small group of pilots don't seem to be able to "get it."

Be well. Go on as you see fit.

I don't get all this troll talk!

I am being honest, I would design it LOP, I can understand that when it got built it might not work out like that, maybe one day I would get a chance to fix it... I have designed and built complex stuff as a team and seen that pattern before.

I applaud your efforts to improve education, and advance technology appreciating that part of it is 'back to the future'...

However there are some important statements in this thread that relate to safety, that are in conflict with the verifiable data presented!

Pilots sometimes do the right thing for the wrong reason, what's important is they do the right thing! That is why I would suggest that if you want to do something different that relates to safety you need some scrutiny to ensure that the real reason that perhaps the pilot was blissfully unaware, is still not a concern.

My last statement also applies to engineers equally.

Who said 'to err is human'?

[Ultralights]

a good source of peer reviewed journals, and scientific texts on pretty much anything
ScienceDirect.com | Science, health and medical journals, full text articles and books. (http://www.sciencedirect.com/)
just got to know the search terms
Assessment of Flame Transfer Function Formulations for the Thermoacoustic Analysis of Lean Burn Aero-engine Combustors (http://www.sciencedirect.com/science/article/pii/S1876610214001507)

[oggers]

Alcoa's development of the EGT probe allowed us to see that the 10% BMEP drop was about 50dF LOP. It allowed for more accurate leaning on engines without torque converters.

Walter Atkinson; the "torque converters" transmit the turbine power to the crankshaft. The BMEP was measured by torque gauges.

[megan]

torque convertersHe is talking of the means by which the torque on a shaft is converted into a signal that can be measured on a gauge. It's a really simple piece of gear, at least the theory behind the concept.

[Jabawocky]

Effectively a load cell in todays language. The gauge indicates the torque, not measures it. To be pedantic.

[oggers]

megan


torque converters

He is talking of the means by which the torque on a shaft is converted into a signal that can be measured on a gauge. It's a really simple piece of gear, at least the theory behind the concept.

Nope. A "torque converter" is not a torque meter, it is a fluid coupling like that in an automatic transmission that is used to transmit drive. A torquemeter does not transmit the drive - though it is of necessity in the transmission. The old TC18 engines he was referring to had fluid couplings (torque converters) to transmit drive from turbine to crankshaft. Those torque converters had nothing whatsoever to do with the torquemeter that was “indicating” BMEP.


Turbine Drive System

...the gears reduce the turbine speed, and transmit the power through a fluid coupling to a pinion which drives the crankshaft...; Facts About the Wright Turbo Compound

http://www.pprune.org/members/125420-oggers-albums-misc-picture284-torqueconverter.png

http://www.pprune.org/members/125420-oggers-albums-misc-picture285-torquemeter.png

[vh-foobar]

I have learnt a few things from the NACA report presented in this thread, along with Cpt Deakin's articles and have been reflecting on my own professional experience operating some of these engines, though that was a long time ago and unlikely to be repeated.

Someone said earlier something to the effect of, which is better?

- 30 degrees F Rich of Peak

- 30 degrees F Lean of Peak.I would agree that if everything is working and you can safely get ALL cylinders to 30 degrees from a peak, 30 LOP is probably better than 30 ROP for your engine in cruise, Probably at least.

But as an example of possibly not thinking through ALL factors, what mistakes might you make from the descent onwards that might make 30 ROP better than 30 LOP? i.e. which might be more error tolerant?

Or perhaps to put it another way, what mistakes might you make from descent onwards that might make operating at a best power mixture with higher cylinder temps, higher ICP and maybe higher valve temps at say perhaps 100 ROP etc compared to say a safe LOP of perhaps 50 LOP.

Perhaps in my example, you might just consider a turbocharged example like a chieftain, or a big normally aspirated engine with alt compensation fuel pump, such as found in baron or bonanza, though the same problems or different problems may apply with smaller training aircraft.

[Jabawocky]

foobar,

With a better understanding of things it would be easier to explain, but a forum post will not do your inquisitiveness justice. In terms of error tolerance on descent? LOP, far more tolerant in every case.

Abridged version;
In a conforming engine take off, full rich, climb leaning to a target EGT (Turbos full rich the whole way up, same for ACFP), level out, big mixture pull (another story) leave red knob alone until at the hangar door or if you must for your own desires, full rich when you put the gear down or turn final or whatever you prefer.

There are some extra comments and in the class room it is easy to discuss. Or pick up the phone and call me.

Is that answering your question? Hope it helps

[Walter Atkinson]

Here's a thought about the dangers of screwing up the mixture.

1) There is nothing one can do when LOP that hurts the engine. Period.
2) There are any number of things one can do to harm the engine when ROP.

So, the question is: "Why are pilots comfortable with ROP mixtures, and seem to be resistant to/uncomfortable with LOP ops?

Maybe because they "have always done it that way" with little to no understanding of what they are doing? Maybe the fact that engine manufacturers were intellectually dishonest on the subject for a long time? (We've finally gotten CMI and Lycoming on board to agree with their own data.)

As the King of Siam noted, "'Tiz a puzzlement."

[vh-foobar]

foobar,

In terms of error tolerance on descent? LOP, far more tolerant in every case.


The example that I had in mind was advancing the throttles to full, with the mixture still set at a sensible LOP setting (whatever that might be), as opposed to an appropriate ROP setting. For example in a chieftain won't both examples result in ROP with the former more likely to be at risk of some detonation?

Perhaps if you do it once it won't hurt, perhaps it doesn't matter the detonation margin is big enough, or perhaps they are both equally bad.

It's as much an illustration that other factors can influence the outcome, or its not always as straight forward as it might seem.

[Jabawocky]

Depends on the fuel control unit, but generally no it won't. How can it? The typical Lycoming is a mass air flow device so it will advance the fuel flow with it roughly (they are not perfect for the nit pickers) and maintain the F/A ratio.

Typical TCM's the RPM controls fuel pressure which is delivery so it actually gets leaner.

What is a BIG problem is when you are ROP on say a Chieftan but not anywhere near rich enough, and you get away with it in the cruise but you push it full forward on the throttle, and forget the red knob :eek:

That has been done before :sad:

[vh-foobar]

Depends on the fuel control unit, but generally no it won't. How can it?

In those engines full throttle, enriches the mixture, to maintain an adequate detonation margin, I understood there was a extra jet in the FCU...

As I said previously perhaps this doesn't make much difference, or maybe I am flat out wrong about the engine. Its as much an example of how other factors can have a less than obvious effect.

[Walter Atkinson]

***
The example that I had in mind was advancing the throttles to full, with the mixture still set at a sensible LOP setting
***

Lycoming got it right on their full controller. When one advances the throttle when LOP, the mixture gets LEANER--exactly what we want to happen. Since no one set LOP could effectively advance the throttle to WOT as on takeoff, any enrichment feature is moot. The engine as set up will not run LOP above about 33" MP, so fuel enrichment is not an operational issue. We have tried to define why most of the engines will not run smoothly above about 32-33"MP LOP. (The exception being the GTSIO engines which runs smoothly LOP up to about 36" MP.) We have come up with some pretty good theories, all of which when tested, were wrong. (I hate when that happens)

Lycoming said the opposite--that the mixture got richer when the throttle was advanced. When we told them that's not how their how their fuel controller worked, they insisted that it did the opposite. We sent them the DATA on the TIO-540-J2BD from the test stand and they now agree that when the throttle is advanced from a LOP setting, that the mixture gets leaner--as it should.

Some fuel enrichment features are accomplished with an extra jet, others with a cam arrangement. As Jabba said, "it depends on the controller."

[vh-foobar]

***

Lycoming got it right on their full controller. When one advances the throttle when LOP, the mixture gets LEANER--exactly what we want to happen. Since no one set LOP could effectively advance the throttle to WOT as on takeoff, any enrichment feature is moot. The engine as set up will not run LOP above about 33" MP, so fuel enrichment is not an operational issue. We have tried to define why most of the engines will not run smoothly above about 32-33"MP LOP. (The exception being the GTSIO engines which runs smoothly LOP up to about 36" MP.) We have come up with some pretty good theories, all of which when tested, were wrong. (I hate when that happens)

Lycoming said the opposite--that the mixture got richer when the throttle was advanced. When we told them that's not how their how their fuel controller worked, they insisted that it did the opposite. We sent them the DATA on the TIO-540-J2BD from the test stand and they now agree that when the throttle is advanced from a LOP setting, that the mixture gets leaner--as it should.


That is interesting, I wonder if it was be design or by luck... I would suggest for at least one Lycoming engineer is was luck;)

[Walter Atkinson]

***
That is interesting, I wonder if it was be design or by luck... I would suggest for at least one Lycoming engineer is was luck
***
I have a very high level of confidence that it was not luck, but by design. Sadly, the corporate memory seemed to have been lost and the current understanding was flawed.

[vh-foobar]

While studying for something else, I found these if some are interested.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930081891.pdf

and

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091891.pdf

you can find everything from NACA on exhaust valves here (http://naca.larc.nasa.gov/?N=0&Ntk=All&Ntt=exhaust%20valve%20temperature&Ntx=mode%20matchallpartial&Nm=123|Collection|NASA%20STI||17|Collection|NACA||125|Collec tion|NIX)

The former has a chart showing CHT, exhaust valve temperature, while mixture is varied and power held constant, Figure 8. It also has EGT (though not enough data points to see the peak properly) the significance of the graph is that’s its at a constant power. The engine is watercooled.

Its reinforced that while some of the OWT may be tales, some of the POH leaning procedures for these old aircraft is still appropriate, YMMV.

I still agree for updated engine i.e. appropriate instrumentation and fuel delivery, different leaning procedures would be appropriate.

The later report has a method of calculating the valve temperatures, but its not a simple read...

[Walter Atkinson]

Thanks for posting those links. I'll comment as I get a chance to review them.

http://ntrs.nasa.gov/archive/nasa/ca...9930081891.pdf

I have taken a cursory look at the issues on the ink above and found several interesting issues.

1) The "assumption" by the researchers that the observed increase in EGT with respect to RPM is flawed. The measured change in combustion temperature with increasing RPM is actually lower due to the delayed thetaPP during the higher RPMs, therefore so is actual EGT. The effects are actually very small but the reading changes are significant. Why, then are they (and we in instrumented aircraft) seeing higher EGT READINGS with increases in RPM? The reason this is the case is that the probe has less refractory time to cool between pulses of hot air.--it will read the same (or even a lower) temperature as higher. This has only recently become appreciated (the last 20 years or so).

2) If one looks at the change in exhaust valve temperature as CHT is altered while holding everything else consent, one quickly sees the most direct correlation of CHT-EVT as compared the other factors.

3) The unusually high EGTs in this study are due to the low compression (6.5:1) of the engine. As expected.

4) Research and analysis of hundreds of events of pre-ignition have debunked the "assumption" during this test that pre-ignition is caused by high exhaust valve temperature. This is simply not supported by reams of data from pre-ignition events where engine monitors have been present to record the events.

5) Some of the "assumptions" from the 1930s and 40s are taking a long time to dispel (recently a CMI representative giving a talk to 300 LAMEs in the US assigned effects of pre-ignition to having been, incorrectly, detonation--and that's not an uncommon error).

There is, however, some very good data in this study which has been confirmed in the decades following.

Thank you for posting this 1947 study.

[Ultralights]

An interesting video, that mentions something i have not heard mentioned before in the discussions on engine ops, combustion etc,

the thing that actually influences your CHT temps. and why higher combustion pressures are the real killer, not mixture.

The boundary layer.. or sidewall cooling

_TNSUIsjdpY

[Jabawocky]

UL……You HAVE heard it mentioned before. 10th of November 2013, roughly 10am?

[Ultralights]

yes, i heard it then, but not on online discussions here.

[Walter Atkinson]

Mixture affects thetaPP and ICPs, which affect the thermal boundary layer, which affects the rate of heat transfer from the combustion gasses into the wall of the combustion chamber.

This is discussed in detail during the APS class

[oggers]

Walter Atkinson:

I have taken a cursory look at the issues on the ink above and found several interesting issues.

1) The "assumption" by the researchers that the observed increase in EGT with respect to RPM is flawed. The measured change in combustion temperature with increasing RPM is actually lower due to the delayed thetaPP during the higher RPMs, therefore so is actual EGT. The effects are actually very small but the reading changes are significant. Why, then are they (and we in instrumented aircraft) seeing higher EGT READINGS with increases in RPM? The reason this is the case is that the probe has less refractory time to cool between pulses of hot air.--it will read the same (or even a lower) temperature as higher. This has only recently become appreciated (the last 20 years or so).

You have overlooked where they specifically state that the EGT is "not the true exhaust gas temperature but merely indicated the temperature that may be attained by an engine part subjected to the flow of exhaust gases at the same position"; which is more relevant than instantaneous gas temperature. Nonetheless it stands to reason that EGT would increase with RPM, like it does with retarded timing.

"Mass-averaged exhaust temperatures are higher than time-averaged or thermocouple determined temperatures. All these temperatures increase with increasing speed, load, and spark retard, with speed being the variable with the greatest impact". Heywood JB, Internal Combustion Engine Fundamentals, chap 6, p234, 1984.

What you describe as "it will read the same (or even a lower) temperature as higher" is actually thermocouple equilibrium temperature approaching the temperature of the "pulses of hot air" as RPM increases.


The measured change in combustion temperature with increasing RPM is actually lower due to the delayed thetaPP during the higher RPMs, therefore so is actual EGT.

It does not follow that EGT is lower. In the test they maintained imep as they varied RPM. In the diagram below the red pecked line represents the pressure trace with retarded PP. For the EGT to be cooler the red pecked line would have to drop into the brown area. That cannot happen whilst maintaining imep.

http://www.pprune.org/members/125420-oggers-albums-misc-picture404-retarded-pp.png

2) If one looks at the change in exhaust valve temperature as CHT is altered while holding everything else consent, one quickly sees the most direct correlation of CHT-EVT as compared the other factors.


They did not do a test to alter CHT and EGT while holding everything else constant. I would be very interested to know how you think one would go about such a test...

3) The unusually high EGTs in this study are due to the low compression (6.5:1) of the engine. As expected.

The CR was 6.65 which was normal for that engine and seemingly typical for blown engines of that time, eg the Wright TCs (CR 6.7). Therefore the EGTs in the test were representative under the conditions stated. The mixture temp was 200°F which would be modest based on NACA estimates:

http://www.pprune.org/members/125420-oggers-albums-misc-picture395-naca-blower-outlet-temps.png

In the test of variable CR the difference between CR of 6.65 and 7.5 (typical GA turbo) was 55°F:

http://www.pprune.org/members/125420-oggers-albums-misc-picture393-egtvcr-nacavga.png

...not huge and the point of the test was to investigate how all the temps respond, not establish absolute figures for any specific CR.

4) Research and analysis of hundreds of events of pre-ignition have debunked the "assumption" during this test that pre-ignition is caused by high exhaust valve temperature. This is simply not supported by reams of data from pre-ignition events where engine monitors have been present to record the events


A proper reading of the report reveals that the valve temperature was actually lower when they experienced preignition, due to the insulating effect of the valve deposits. It is those deposits that is the problem they identified rather than the valve temperature per se; "The foregoing results indicate that the scale and deposits probably reached a temperature sufficiently high to cause preignition whereas the temperature of the valve steel as measured by thermocouple remained substantially below this temperature". All backed up by the engineering literature:

"The source of preignition is usually the exhaust valve covered with mineral deposits coming from fuel and lubricant additives" Guibet JC, Duval A, New Aspects of Preignition in European Automotive Engines, SAE Technical Paper, 1972.

"Preignition is caused by the mixture igniting as a result of contact with a hot surface such as an exhaust valve." Stone R, Introduction to Internal Combustion Engines, chap 3, p74, 1992.

"The parts which can cause preignition are those least well cooled and where deposits build up and provide additional thermal insulation: primary examples are spark plugs, exhaust valves....Under normal conditions using suitable heat range spark plugs, preignition is usually initiated by an exhaust valve covered in deposits". Heywood JB, Internal Combustion Engine Fundamentals, chap 9, p453, 1984.

...but perhaps no longer the same problem as with the fuels of 1947.

5) Some of the "assumptions" from the 1930s and 40s are taking a long time to dispel (recently a CMI representative giving a talk to 300 LAMEs in the US assigned effects of pre-ignition to having been, incorrectly, detonation--and that's not an uncommon error)

Interesting anecdote but it has nothing to do with this test. On the two occasions when they encountered preignition, had that actually been detonation they would have recognised it due to audible knock. Your opinion that these experienced NACA researchers mistook preignition for detonation is not supported by studying the series of tests undertaken at the Cleveland lab to explore those very issues.

[Lumps]

Damn! I'd like to thank everyone for providing us all with excellent reading, trolls included.

I have a question relating to the fuel enrichment on the J2B, in the piper manual it calls for a maximum normal operating power (can't remember exact acronym) of something like 40" MAP 2400RPM (for climbs etc). This is still quite a lot of power % and would require very rich mixture, however by pulling the throttles back to 40' do we loose the fuel enrichment function? Would it be better to leave everything on the stops?

I'm aware of how the Continental enrichment set up works but didn't know the fuel metering in the J2B had a similar function (I take it most Lycomings do not)

[Tinstaafl]

The J2B (or is it a J2BD? I forget) in the 1980 PA31-325Navajo** I operate specifies 43" nominal MAP/2575/full rich for max power, then set 38"/2400/ US 28-32GPH for climb power. I never use less than US 32GPH for climb, erring on richer than that to ensure never leaner. Even so, I'm now tending towards full rich even for climb power.

For the last 7 or 8 years I've run it LOP for cruise. Nearly always 33"/2200 RPM /27 US GPH which gives a TAS of 170kts +- 2 kts at A120.

**It's a Mike Jones 'Lock & Key' Colemill Panther Navajo, with 350HP engines. Nicest Navajo I've ever flown.

[Jabawocky]

Tins,

You are correct, full rich is the only place to be in the climb. I have just run the dyno data and you should have about 34GPH at your 38/2400 setting. Leave it full rich and that is where it should stay for takeoff, climb and any time you take the whip out.

Some tips for the cruise, try 32-33" /2400 and no more than 17GPH. At 30" about 15.5GPH. This will be around 80dF LOP. :ok:

Some folk stress out too much about TIT, so if you would rather set up 30"/2400 and then 80dF LOP then add back 2-3" then do it that way. The FCU will look after the rest.

If you want to see an hour or so of various stuff on the dyno, and Georges famous words with a nasty climb power setting where he says frankly this is not good for the engine, shortly followed by but it is consistent with the POH recommendations :eek: all the while you are watching the pressure traces :eek::eek: just drop me a line.

The banter machine is not a TKR machine?

[Tinstaafl]

Hiya Jabba. I should clarify that FF is 27 GPH total ie 13.5 GPH /side, and done without GAMIs. Can't get it leaner without roughness. Owner isn't inclined to spend more just now (see below re autopilot).

I'd love to see dyno data on this engine. This plane is an early-ish Mike Jones 'Lock & Key', so apart from the Colemill mods, it had an expensive restoration from Mike Jones. It was done before glass panels became common, so still steam driven gauges (except it has a nice King EHSI that I rather like). It has 530 & 430 WAAS GPS, Avidyne MFD, XM weather, radar & stormscope so nav. is a breeze. Digital FF + an EDM760 so fuel & engine management is catered for too.

Two biggest hassles are the autopilot & Cyl 3 & 4 run hotter than the others.

Autopilot is a KFC200. Usually a good unit, but 1980 and later PA31s were required to include an accelerometer in the installation. Can't find a replacement for a reasonable price. Honeywell will build one as a special order - for only US$20,000! Used serviceable ones are rare as hen's teeth. We have our eye on one for US$7000...

[Jabawocky]

If it gets to 13.5 per side that is outstanding.

I dare say that is not needing GAMI's. You are almost at ICO :}

[Tinstaafl]

When I took over managing it, I recommended to the owner that he have an EDM fitted so that LOP could be done (the POH has it using the factory single point EGT but apart from a one experiment to see how it would run on an empty leg, and a single demo to the owner to show the fuel savings, I've never run LOP without the EDM). At the time I said GAMIs might be needed post-EDM but we should have a trial period to see. That was 7 or 8 years ago

Probably a bit late to start recommending GAMIs now. Anyway the engine is only a couple of hundred hours to TBO. Maybe post overhaul I'll revisit the topic.

[Jabawocky]

By the sounds of it being able to run that far LOP it does not need GAMI injectors at all.

And by the way, you do not need the EDM to run LOP......you already are doing sans EDM.

If you look at the logic of it, to run ROP safely you need the EDM more. The opposite of popular myth ;)

If you are unsure give me a call. :ok:

[Tinstaafl]

I think I wasn't clear. I had the owner install the EDM 8 or 9 years ago. It was most instructive! Before then, I could get it to what I knew was LOP by some amount based on the single point EGT but I had no way of knowing if all cylinders were sufficiently LOP. Also CHT temps were a factor. I can easily see with the EDM whether or not I'm sufficiently LOP. Can't do that with the single point. Based on EDM info I'm pretty confident that sans EDM cyl 3 & 4 on each engine weren't sufficiently LOP. 50 deg LOP on the single point isn't 50 deg LOP for the richest cylinders!

Fuel flow to 50 deg LOP on the single point is about .7-1.0 USG greater than every cylinder at least 50 deg LOP on the EDM.

As an aside, that EDM paid for itself within the 1st year of installation. The plane had a cracked LH #2 injector line that showed in odd temps on the EDM. I could see the temps going awry compared to the other 5 cylinders, even as I enrichened to compensate. I was thinking a return to base might be on the cards. A few minutes later it broke completely (not that I knew the cause at the time, but I could see it was a single cylinder issue) and I shut the engine down.

Because I knew it was a single cylinder problem, and there wasn't a fire, I elected to return to base - saving a lot of $$$ in transport for the pax & myself, finding a local mechanic to fix it, fetching the plane afterwards etc. I roughly estimate that those costs would have been about the purchase price of the EDM. Add in the fuel savings and it's been a no-brainer for the last 8 years or so.

[Jabawocky]

:ok:

and some words :ok::ok:

[Lumps]

so is there an 'enrichment' device on the J2B(D - makes no difference) engines? I'm sure I read it on this thread even... If there is, even full rich at the reduced throttle max continuous power as per POH may not be enough, depending on how it works.

Anyone?