Commercial Pilots who don't know about piston engines

[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

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…..

[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]

Originally Posted by 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 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.

Courtesy 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]

Originally Posted by Jabawocky

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:





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]

Originally Posted by Walter Atkinson

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 Peak

oggers 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 ways

Precisely.

[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.