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Old 7th Apr 2018, 00:59
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The scenario you gave was:
What about 24" MP, 2400 RPM - about 70% power on an IO-360 - at peak EGT as approved by the Lycoming manual.
I said that if you enriched the mixture to around 25C ROP, you could move to thrash or punish territory. It is certainly the worst place to set the mixture if you're interested in engine longevity.
This is exactly the range where engine manufacturers design the engine to be run. I don't understand this idea that aircraft engines are light, powerful, reliable, efficient, wonders of engineering and the designers are incompetent and don't know what they are doing.
It is indeed patently clear you don't understand. What's worse, you won't understand.

I pity the wallet of the poor bastard who owns the aircraft you fly.
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Old 7th Apr 2018, 01:12
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I said that if you enriched the mixture to around 25C ROP, you could move to thrash or punish territory. It is certainly the worst place to set the mixture if you're interested in engine longevity.
It's where the engine designers designed the engine to run! What evidence do you have that this affects engine longevity, assuming you observe the other engine limits e.g. CHT?

I suggest you do not attach a data logger to your car. It will do your head in to see what mixtures it runs, and when you are most likely to see knock detected.
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Old 7th Apr 2018, 01:15
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If the fuel flows are even the power from each cylinder will be reasonably even.
That's the whole problem with IO520 engines as they come out of the factory.The bloody fuel supply to the cylinders is all over the place. THAT is what GAMI injectors rectified. More reading by you required.
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Old 7th Apr 2018, 01:30
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That's the whole problem with IO520 engines as they come out of the factory.The bloody fuel supply to the cylinders is all over the place. THAT is what GAMI injectors rectified. More reading by you required.
My understanding was that the injectors were matched from the factory to flow the same amount of fuel.

The GAMI lean test matches the injectors so the EGTs of all cylinders peak at the same time i.e. matches the mixture. That's perfect if you have equal airflow to each cylinder. If you don't then equal fuel flow is better (more even power) than matching EGT.

Am I incorrect?

If the injectors don't flow the same amount of fuel then maybe they need to be matched - but by fuel flow, not EGT.

(The proviso of course that there may be inequalities by design, it is quite possible that there are reasons fuel flows don't match. So any adjustment needs to be according to and within tolerances allowed by maintenance documentation.)
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Old 7th Apr 2018, 01:32
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Genuine question here LB - Are you suggesting that Cessna are telling their aircraft owners to run their engines 50deg ROP to deliberately reduce the potential life of their engines..? Or that there have been no advancements in the companies engineering knowledge in the last 50 years..?


The reason I ask is that the POH in the latest C182T with all the bells & whistles including lean assist etc is still recommending leaning to 50deg ROP like all the older models. Are they in denial or do they genuinely believe this is the best way to treat their engines..? (Presumably backed up by exhaustive testing and maintenance records).
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Old 7th Apr 2018, 02:04
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As I said before, for the marketing departments a few knots on the competition makes a difference. They want you to achieve the cruise speeds and fuel consumption figures in the glossy brochures.

The data prove that at a mixture of around 50F ROP you're giving the engine the hardest thrashing you can give it. Many engines tolerate the abuse. Some don't. If you're interested in maximising the longevity of an engine, it's better to sacrifice some fuel efficiency by going further ROP, or better still to sacrifice a few knots in return for greater efficiency by running LOP.

The reason aircraft manufactures and engine manufacturers and maintainers don't really care is because everyone knows what causes any and all engine problems: Pilots.
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Old 7th Apr 2018, 02:07
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All my piston leaning experience was simply putting the lever to auto lean, so excuse my ignorance. One method of leaning is leaning to the point of roughness (misfiring cylinder because it's too lean), so if you enrichen to the point of removing roughness would that particular cylinder not be running LOP? I notice reading FAA safety information they give the impression of giving their imprimatur to LOP, with the caveat of having proper instrumentation and calibrated yearly.
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Old 7th Apr 2018, 02:18
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Originally Posted by Lead Balloon View Post
If you're interested in maximising the longevity of an engine, it's better to sacrifice some fuel efficiency by going further ROP, or better still to sacrifice a few knots in return for greater efficiency by running LOP.
What evidence do you have that this improves longevity? By how much?

According to one of John Deakin's articles, Lycoming said they have collected data that indicates more problems with engines run LOP.

Deakin's conclusion was that Lycoming didn't know what they were talking about and it was because the pilots weren't doing it right.

But Lycoming are in the best position to collect that data. What evidence is there that they don't understand the data they are collecting? Alternatively, would they really lie?

If Lycoming really wanted to sell more engines or parts they could just reduce the TBO, or require mandatory replacement of certain parts like Rotax with their 5 year rubber & fuel pump replacements.

And I have already given my opinion on the APS attitude that if you DO have problems when following their recommendations it must be the pilot's fault.
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Old 7th Apr 2018, 02:24
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Hi Megan: The "roughness" is not caused by "misfiring". It's caused by different amounts of power being produced by the individual engines - each cylinder - bolted to the same crankshaft.

When you plot the power output of a cylinder against mixture, you see that the curve is 'steeper' on the lean side of peak. That means that smaller changes in mixture on the lean side cause greater changes in power than the same change in mixture on the rich side. That's why trying to run LOP highlights the extent to which engines come 'out of the box' with poorly balanced fuel/air across cylinders. Running ROP 'hides' the imbalance. That's also why successful LOP operations usually entail testing and swapping injectors (on injected engines) to get all of the cylinders close to each other on the lean curve. For those who achieve the nirvana of perfect balance, there is no 'lean missfire'. As the mixture is leaned on the lean side, each cylinder produces progressively less - but the same - power output, until the mixture is so lean that it can't sustain combustion and all cylinders simply cease to produce power.

andrew: Please save your questions for the APS.
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Old 7th Apr 2018, 02:51
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Originally Posted by Lead Balloon View Post
It is indeed patently clear you don't understand.
You are correct.

When I first read John Deakin's articles on Avweb 15 or so years ago, I was convinced LOP was good and I was happy.

But I was good at physics and chemistry at school, and Deakin posted a couple of things where the physics and chemistry were obviously wrong. I didn't understand. So I did some reading from other sources.

Since then I have read all the Deakin articles, various NACA reports, articles by Lycoming, other engine designers, engine tuners, information about the big radials, talked to a guy who does engine management system consulting for various manufacturers and race teams, and basically anything else I can get my hands on. It's a subject that interests me.

There is a lot out there from a lot of different sources that contradicts what APS have in their public materials.

That's one reason why I asked (unanswered) what sources other than APS have you used for your information?

On the other hand I have found nothing apart from the Deakin & APS information that contradicts what is in the engine manuals.

My conclusion is that yes, I don't understand. What I do know however is that it is a very complex subject, much more complex than APS indicate.

I certainly don't understand enough to be confident ignoring the manufacturers recommendations. From what I have seen of APS I doubt they could change that.

andrew: Please save your questions for the APS.
Will they answer them, or just give an answer like "Well it stands to reason, cooler is better"

Do they actually have real data gathered from engines in the field, with at least a basic level of correction for uncontrolled variables?
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Old 7th Apr 2018, 03:01
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No. APS just make it up. Based on their amateur intuition. They do not have access to the most sophisticated piston aero engine test cell on the planet and they do not show videos of the actual measurements taken in that cell during a real engine run in which fundamental variables like timing and mixture are varied. And even if they did show those videos, the measurements would be faked because - well, what interest would they have revealing the real measurements.

Alas, I think my first call was the correct one.
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Old 7th Apr 2018, 03:05
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Just about any engine can run past tbo. Running lop will not and never will make it go padt tbo any more than running rop.
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Old 7th Apr 2018, 03:44
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"Engines in the field" is different to engines in a test cell. The test cell can't tell you whether what is measured results in greater longevity in service or how much.

the most sophisticated piston aero engine test cell on the planet
Who told you that? I haven't done a survey, but this sounds like marketing fluff rather than true facts.

The guy who consults to the auto engine manufacturers and race teams told me that this stuff is well enough understood that test cells are not used as much anymore by manufacturers. Most of it can be modeled by computer. The test cells are mostly used to validate the important data points.
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Old 7th Apr 2018, 05:16
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I think the horizontally opposed vs radial question may have been interoperated wrongly?


If the question was in relation to the difference in size and stroke of a HO vs a big radial, then the difference is in the time/s the spark are set and changes in valve overlap and use of gearboxes. These are all based on the combustion burn rate in design stage and not normally pilot adjustable.
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Old 7th Apr 2018, 05:42
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Andrew

If the injectors don't flow the same amount of fuel then maybe they need to be matched - but by fuel flow, not EGT.
Before I or anyone else take the time and effort to explain the induction and fuel injection system used in IO 520 aircraft engines please let us know whether or not you know roughly how it works. If you do know give us a brief rundown of how the fuel and air end up in the cylinders ready for compression. It is very important you understand this because not understanding makes you say silly things which later will embarrass you.
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Old 7th Apr 2018, 06:07
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Fuel flow increases on most IO-520 when a nozzle is partially or fully blocked.
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Old 7th Apr 2018, 06:11
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Originally Posted by Bend alot View Post
Fuel flow increases on most IO-520 when a nozzle is partially or fully blocked.
Or Perhaps not the fuel flow its self, one could say it "indicates" due to the mode of operation.
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Old 7th Apr 2018, 06:13
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Oh dear .... all this on a 1940 technology , low compression , glorified VW industrial engine !

Andrewr I wouldn't bother ... these guys have been cult members pushing this barrow for awhile .... clearly they know best and pilots have been destroying engines prematurely for 70 years...
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Old 7th Apr 2018, 06:40
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So leadie as you fail to provide an answer to the previous questions what about this two.

What is cause for an opposed engine for the uneven breathing of each cylinder make it easy for you as you an expert on the io520 we will use this engine

Now
What is the change that gami make to even out fuel flow and what is the difference between them an a cont nozzles

Ok 2 basic simple questions im sure your able to find an answer too.

Then will go back to a radil of large scale to to opposed ga engine.
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Old 7th Apr 2018, 08:44
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It is over 30years since I flew an injected twin.
My flying now is in carbureted engines with no EGT indication.
I lean until rough, richen until smooth, the richen another centimetre of throttle movement or so.
What am I doing wrong?, or at least how can I improve things?
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