Engine Stress, Power and Fuel Mixture Management

[Petehdgs]

Understanding Engine Stress, Power, and Fuel Mixture Management (UESP&FMM Rev7) has been removed, for review.  

I ask that all existing copies be deleted.  

I further request that Mooneyspace.com delete this thread and related materials associated with it.  

Have FUN!  Fly SAFE!  Pete

 

 

 

 

Edited December 5, 2021 by Petehdgs
Revised

[201er]

Neat presentation.

 

Perhaps you can help settle a debate on how afterburn might affect cabin heat? Which of the following causes the most cabin heat to be produced and which causes the least?

50ROP

Peak

50LOP
 

Is 50ROP = 50LOP in terms of cabin heat?

What impacts cabin heat more, HP or EGT?

 

Do you have an opinion on cylinder break in leaning?

[exM20K]

5 hours ago, 201er said:

Neat presentation.

 

Perhaps you can help settle a debate on how afterburn might affect cabin heat? Which of the following causes the most cabin heat to be produced and which causes the least?

50ROP

Peak

50LOP
 

Is 50ROP = 50LOP in terms of cabin heat?

What impacts cabin heat more, HP or EGT?

 

Do you have an opinion on cylinder break in leaning?

Things get a little funky operating LOP in the flight levels.  I believe there are issues with the mass of the exhaust flow being insufficient, but I have never understood this note:

“Above 22,000 power settings above 2300 RPM must be operated at 1675* or richer”

That is for LOP

[Petehdgs]

On 11/29/2021 at 12:30 PM, 201er said:

Neat presentation.

 

Perhaps you can help settle a debate on how afterburn might affect cabin heat? Which of the following causes the most cabin heat to be produced and which causes the least?

50ROP

Peak

50LOP
 

Is 50ROP = 50LOP in terms of cabin heat?

What impacts cabin heat more, HP or EGT?

 

Do you have an opinion on cylinder break in leaning?

I must admit that never in a million years would I have thought the first question to be asked about UESP&FMM would be which settings would give you the most CABIN HEAT!!! LOL! SMH! To be truthful I have never really thought about it... until now.  Assuming that this IS a serious question, I will do my best to answer it so long as you understand that this is far from where my mind has been in writing it, and my answer is just an educated guess. So, It is worth what you paid for it.  ZIP. 

Based on my research I would not recommend running at 50ROP at any time for any reason unless the total load is less than 60%.  Why?  Because the peak cylinder pressure will be too close to TDC which builds more internal stress instead of producing more useful power.  IMHO 50ROP uses some energy to create stress that could otherwise be driving the airplane forward.  This is undesirable at best, damaging at worst.  If the load is low enough, then not damaging, but not as good a use of the fuel either.  I would also not run 50ROP at all during the break in period. NEVER! (but, I have not studied this specifically) 100 ROP or more is acceptable as is 15-100LOP.  Be sure to stay out of the RED FIN.  IMHO.  YMMV. 

In making useful cabin heat you are running cold air around an exhaust fed heat ex-changer and the design of this device has a lot to do with how well it works.  Temperature and mass flow both affect how fast it heats up and heats the cold air it is warming.  Mass Flow varies with MR number and load, with ROP having slightly more Mass Flow than LOP.  Once the heat ex-changer is hot, it is not likely to cool off rapidly unless it has been optimized for minimum weight (likely in an airplane) so again mass flow and temperature both affect it.  Having said all of this, 50ROP has slightly more mass flow than Peak EGT or 50LOP.  50LOP will definitely will produce less heat than either of the others, but it depends on how much mass flow is involved between the other two options.  If the mass flow is small, then Peak EGT will win out over 50ROP, but if the mass flow is higher then maybe not.  It might be a toss up at 50ROP vs Peak, but peak should win at 100ROP vs Peak EGT. 100LOP will be less than either of the other two.  IMHO> 

So I have now answered a question I never thought I would be asked.  One Miracle at a time! 

 

Edited December 1, 2021 by Petehdgs

[GeeBee]

How would you explain that the M20R POH and Continental has the IO-550G running best power at 75% at 50 ROP? 

Second, where does induction efficiency figure into engine stress? Would a more efficient induction system allow running closer to peak at 75% power?

 

[EricJ]

On 11/29/2021 at 10:09 AM, Petehdgs said:

Replying to a recent thread on POA made me realize there is an interest for more understanding in the area of fuel mixture management. I think I have a good enough understanding of this subject to teach a class on it, which I intend to do for the local EAA chapter in January. In preparation for the class I wrote 45 paragraphs with illustrations, including a new RFFA chart of my own design. The big improvement is this new RFFA chart can be easily adapted to any piston engine at any power level.

Understanding Engine Stress, Power, and Fuel Mixture Management (UESP&FMM Rev6) is presented here for your enjoyment. It is copyrighted, and paragraph 45 includes a terms of use license granting any private pilot the ability to post and copy as required for personal use. I ask that MooneySpace allow this material to be shared on this website. 

Have FUN!  Fly SAFE!  Pete

UESP&FMM Rev6 Nov2021.pdf 1.1 MB · 63 downloads

Haven't read it yet, but an initial skim shows that the figures have no numbers, titles or captions, and the axes are generally un-labelled and have no units.    This makes them far, far less useful than they could be and much less able to convey information by themselves.

[jaylw314]

On 11/29/2021 at 9:09 AM, Petehdgs said:

Replying to a recent thread on POA made me realize there is an interest for more understanding in the area of fuel mixture management. I think I have a good enough understanding of this subject to teach a class on it, which I intend to do for the local EAA chapter in January. In preparation for the class I wrote 45 paragraphs with illustrations, including a new RFFA chart of my own design. The big improvement is this new RFFA chart can be easily adapted to any piston engine at any power level.

Understanding Engine Stress, Power, and Fuel Mixture Management (UESP&FMM Rev6) is presented here for your enjoyment. It is copyrighted, and paragraph 45 includes a terms of use license granting any private pilot the ability to post and copy as required for personal use. I ask that MooneySpace allow this material to be shared on this website. 

Have FUN!  Fly SAFE!  Pete

UESP&FMM Rev6 Nov2021.pdf 1.1 MB · 64 downloads

Do we actually have any data that supports the conclusion that high cylinder combustion pressures are associated with decreased longevity?  It seems that is the underlying assumption in discussions about "engine stress," yet it's not clear that anyone has produced or collected data to quantify what that stress really does.  Do we, for example, actually have strong evidence that motors fail at a rate proportional to the amount of time spent at higher powers, time spent with higher internal cylinder pressures, or time spent with higher CHT's?  Certainly those all sound like reasonable claims, but are these just examples of the sort of things we think we know, but don't really?

I always caution my students that there are four kinds of "knowledge", and it's important to know which category any particular one falls into:

• The stuff we know
• The stuff we think we know
• The stuff we want other people to think we know
• The stuff we can't know in the first place

Didn't mean to get all epistemological, but it's been something nagging at the back of my mind whenever I hear this talk about engine management

Edited December 1, 2021 by jaylw314

[Hank]

It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.

Mark Twain

[Petehdgs]

1 hour ago, GeeBee said:

How would you explain that the M20R POH and Continental has the IO-550G running best power at 75% at 50 ROP? 

Second, where does induction efficiency figure into engine stress? Would a more efficient induction system allow running closer to peak at 75% power?

 

>>>How would you explain that the M20R POH and Continental has the IO-550G running best power at 75% at 50 ROP? >>>
Based on the research I did, I would tend to disagree.  It is clear that when your POH was written they figured that 50ROP was the place to run.  The FA Ratio chart that I used in UESP&FMM is a Lycoming chart, and it clearly shows best power is 100-150ROP with increased stress and CHT at 50ROP compared to 100ROP.  The Advanced Dynomometer Testing that identified the RED BOX concept puts 50ROP near the center of the RED BOX and identifies it as likely to be an undesirable area to run the engine.  The concept is that engine stress increases as a result of fast burning fuel mixtures generating Peak Internal Pressures too close to TDC, and that 40-50ROP is near the center of the maximum stress area, and that is an undesirable place to run depending on the load.  Having said all of that, if your POH says you can run there, then you can... but running richer, or leaner, should reduce engine stress and drop CHT.  As long as the engine is maintaining operating temperatures, lower CHT and engine stress should mean longer engine service life.  That's what you want isn't it?

>>>Second, where does induction efficiency figure into engine stress? >>>

Increased induction efficiency, increases volumetric efficiency, and increases total load available.  This should make things heat up more and make the RED BOX larger unless the designers offset the power increase with increased cooling capacity, or oversized the components such that higher CHT can be tolerated while the strength of the engine structure has been reduced.  The RED BOX is based on internal engine stress and loads that make it likely to have 400F CHT because that is the point that alumimum loses half its strength. 

>>>Would a more efficient induction system allow running closer to peak at 75% power?>>>

I don't think running closer to Peak EGT is the desirable goal here.  Running with reduced engine stress is, and so is better fuel economy when doing so prolongs engine life as well.   To this end you can run above or below the RED FIN.  According to the RFFA chart paragraph 34 , 185ROP at 75% load or 50LOP are both completely out of the RED FIN.  Of course, while monitoring CHT you could lean closer to Peak EGT, but the best fuel economy will be 75% load at about 50LOP with 51MR, saving 25% of your fuel at 185ROP, or saving 16% at 100ROP, and run 30F cooler CHT while doing it. 

Edited December 1, 2021 by Petehdgs

[Petehdgs]

1 hour ago, EricJ said:

Haven't read it yet, but an initial skim shows that the figures have no numbers, titles or captions, and the axes are generally un-labelled and have no units.    This makes them far, far less useful than they could be and much less able to convey information by themselves.

I believe you are incorrect about that.  The first page opens up with a FA Ratio chart with 4 curves, with clear scales on 3 sides. 

[EricJ]

2 minutes ago, Petehdgs said:

I believe you are incorrect about that.  The first page opens up with a FA Ratio chart with 4 curves, with clear scales on 3 sides. 

Yes, the plots that were taken from elsewhere are better, for certain.   That's an example of how better to do it.

[Petehdgs]

1 hour ago, jaylw314 said:

Do we actually have any data that supports the conclusion that high cylinder combustion pressures are associated with decreased longevity?  It seems that is the underlying assumption in discussions about "engine stress," yet it's not clear that anyone has produced or collected data to quantify what that stress really does.  Do we, for example, actually have strong evidence that motors fail at a rate proportional to the amount of time spent at higher powers, time spent with higher internal cylinder pressures, or time spent with higher CHT's?  Certainly those all sound like reasonable claims, but are these just examples of the sort of things we think we know, but don't really?

I always caution my students that there are four kinds of "knowledge", and it's important to know which category any particular one falls into:

• The stuff we know
• The stuff we think we know
• The stuff we want other people to think we know
• The stuff we can't know in the first place

Didn't mean to get all epistemological, but it's been something nagging at the back of my mind whenever I hear this talk about engine management

Your questions are addressed in paragraph 3, 9, & 10. 

[jaylw314]

1 hour ago, Petehdgs said:

Your questions are addressed in paragraph 3, 9, & 10. 

With all due respect, that was not my question.  You cited the theoretical basis for assuming CHT and ICP decrease longevity of cylinders, which I agree makes sense on an intuitive level.  I was asking if we have any data on outcomes that confirms this.  If that data exists, it might also suggest how strong the effect is (which would be useful to know).

[Petehdgs]

2 hours ago, jaylw314 said:

With all due respect, that was not my question.  You cited the theoretical basis for assuming CHT and ICP decrease longevity of cylinders, which I agree makes sense on an intuitive level.  I was asking if we have any data on outcomes that confirms this.  If that data exists, it might also suggest how strong the effect is (which would be useful to know).

The easiest way to get the answers you seek is to take the advanced pilot class at https://www.advancedpilot.com/ .  I took their class about 18 months ago.  It cost me about $500 then.  I think it is less now.  The class is way longer than my 45 paragraphs in 10 pages, and I think it is worth it.  It was for me anyway.  The information presented is not theoretical, but confirmed in practice with advanced engine monitoring and dynamometer testing.   

Edited December 2, 2021 by Petehdgs

[PT20J]

This seems to be a reasonable summary of other people’s work — without attribution, I note.

Most of this is information presented and published by Advanced Pilot Seminars, and especially John Deakin. APS is the originator of the concepts of ICP, red box, big mixture pull.

The red fin was popularized in the Cirrus community, I believe, by Gordon Feingold. 

Some of this also appears to derive from writings by Mike Busch.

Skip

 

[Petehdgs]

13 hours ago, PT20J said:

This seems to be a reasonable summary of other people’s work — without attribution, I note.

Most of this is information presented and published by Advanced Pilot Seminars, and especially John Deakin. APS is the originator of the concepts of ICP, red box, big mixture pull.

The red fin was popularized in the Cirrus community, I believe, by Gordon Feingold. 

Some of this also appears to derive from writings by Mike Busch.

Skip

 

To the best my knowledge what Skip says is all true.  The object of the paper is to teach an understanding of the subject matter.  It is rather complex.  The origin of this knowledge comes from advanced pilot seminars and the gami-injector people.  Who did what I couldn't say, because I don't really know.  I do know that the writing and organization is my own, and I designed the RFFA chart towards the end, but my basic understanding of this subject comes from the advanced pilot traing class that I took about 18 months ago, followed by hours of research and analysis and experience with my own airplane to create the RFFA chart that can be tailored to any engine.  The material is copyrighted to ensure it is not altered, insuring the reader receives a pure dialog.  I am receiving no compensation, and am not asking for any.  

If you feel I have acted improperly, and want me to take this post down,  I will.  If you want me to add an addendum that properly credits the people that created understanding that we now consider to be fact, I can do that too, but I'll need help doing that.  

Edited December 2, 2021 by Petehdgs

[PT20J]

George Braly, John Deakin and the late Walter Atkinson deserve the credit for popularizing LOP operation through the Advanced Pilot Seminars. APS, LOP and GAMIjectors go together. You can't run LOP on many engines -- especially the big Continentals -- without GAMIjectors, and you can't convince people to buy them if they think LOP is damaging to their engine. 

Spark ignition internal combustion engines are complicated and a deep understanding involves delving into aspects of chemistry, combustion dynamics, and thermodynamics. Pilots are not going to sit through lectures on specific heats and enthalpy. APS uses a simple, easily described parameter -- ICP -- to illustrate what they want to teach. The concept is readily conveyed using graphs and simple mechanical principles. But it does not adequately or completely explain many aspects of engine operation. Though central to APS presentations, peak pressure is barely mentioned in most textbooks except in connection with abnormal combustion such as detonation and preignition because it is a design parameter, not an operational parameter.

The red box idea follows a logical progression. First, there is no red box if one follows engine manufacturer recommendations of reducing power to 75% for most Lycomings, and 65% for most Continentals before leaning. The problem with this procedure is that if you lean much past peak EGT the power falls off rapidly. Now, it's hard to sell injectors that turn your Bonanza into a Cherokee speed-wise. So the idea was to increase the power once safely LOP and thereby get your speed back while reaping the benefits of LOP operation. However, now there definitely is a red box because if you richen the mixture toward peak, the power will increase above the 75% or 65% allowed for lean mixtures. The big mixture pull is simply a means to simplify the procedure: rather than reduce power, set the mixture LOP and increase power, just pull the mixture back and zip through the red box before anything bad can happen.

The problem is that the red box has become expanded to include areas the manufacturers consider normal operation and we are told that to operate there is damaging to our engine. To accept this is to buy the idea that the manufacturers don't understand their product. Some have claimed this is because they didn't have the knowledge or instrumentation to understand what we know today. I think this is hogwash. If you want to learn how much was understood way back in 1940, look up NACA TN-772.

Skip

[ilovecornfields]

8 hours ago, jaylw314 said:

Didn't mean to get all epistemological, but it's been something nagging at the back of my mind whenever I hear this talk about engine management

Now you’ve done it! You went and got all epistemological on us. Now who’s going to clean up this mess?

I won’t comment on the technical aspects discussed above (except to agree that the APS course is well worth the cost) but I believe that copyrighting other people’s original work without crediting them for it is usually frowned upon at best.

[MikeOH]

31 minutes ago, ilovecornfields said:

Now you’ve done it! You went and got all epistemological on us. Now who’s going to clean up this mess?

I won’t comment on the technical aspects discussed above (except to agree that the APS course is well worth the cost) but I believe that copyrighting other people’s original work without crediting them for it is usually frowned upon at best.

Hmm, I might point out that the "other people" merely popularized LOP....hardly their "original work."

That NACA tech note is but one example of much earlier work.

[PT20J]

It’s certainly true that APS did not invent LOP, but I believe we should give credit where credit is due. John Deakin readily gave credit to previous work by Pratt & Whitney and Curtis Wright and even made reprints of their out of print publications available at nominal cost. This acknowledgement added a certain verisimilitude to their presentation. Pointing out that P&W and the airlines and military had used LOP routinely helped sell the notion that it wasn’t some new fangled idea cooked up by a lawyer, a dentist and an airline pilot.

George Braly did original work to determine the cause and remediation of mixture maldistribution in Continental’s intake design and also gathered much original data in his test cell using a spark plug modified to incorporate a pressure transducer of his design.

The original team created the APS courseware unlike any other at the time using a combination of previously published information and original work and designed a simplified presentation that was sufficiently accurate for their purposes and that was well received by the pilot community. 

Skip

[ilovecornfields]

9 minutes ago, PT20J said:

It’s certainly true that APS did not invent LOP, but I believe we should give credit where credit is due. John Deakin readily gave credit to previous work by Pratt & Whitney and Curtis Wright and even made reprints of their out of print publications available at nominal cost. This acknowledgement added a certain verisimilitude to their presentation. Pointing out that P&W and the airlines and military had used LOP routinely helped sell the notion that it wasn’t some new fangled idea cooked up by a lawyer, a dentist and an airline pilot.

George Braly did original work to determine the cause and remediation of mixture maldistribution in Continental’s intake design and also gathered much original data in his test cell using a spark plug modified to incorporate a pressure transducer of his design.

The original team created the APS courseware unlike any other at the time using a combination of previously published information and original work and designed a simplified presentation that was sufficiently accurate for their purposes and that was well received by the pilot community. 

Skip

Epistemological?! Verisimilitude?! You guys are driving me crazy with the big words. It’s making my brain hurt.

In all seriousness, Skip, thank you for explaining this better than I could. While no ones work is competent “original” as it is built upon the work of others, I agree that the APS guys are responsible for bringing it to the masses in a way that most pilots are able to understand and apply the principles. They certainly didn’t invent LOP but they did do a lot to popularize and make it understandable. 

[aviatoreb]

4 hours ago, ilovecornfields said:

Epistemological?! Verisimilitude?! You guys are driving me crazy with the big words. It’s making my brain hurt.

Especially when epistemological and verisimilitude are said in juxtaposition.

[Hank]

6 hours ago, PT20J said:

It’s certainly true that APS did not invent LOP, but I believe we should give credit where credit is due. John Deakin readily gave credit to previous work by Pratt & Whitney and Curtis Wright and even made reprints of their out of print publications available at nominal cost. This acknowledgement added a certain verisimilitude to their presentation. Pointing out that P&W and the airlines and military had used LOP routinely helped sell the notion that it wasn’t some new fangled idea cooked up by a lawyer, a dentist and an airline pilot.

George Braly did original work to determine the cause and remediation of mixture maldistribution in Continental’s intake design and also gathered much original data in his test cell using a spark plug modified to incorporate a pressure transducer of his design.

The original team created the APS courseware unlike any other at the time using a combination of previously published information and original work and designed a simplified presentation that was sufficiently accurate for their purposes and that was well received by the pilot community. 

Skip

What has always bothered me about all of this is that they never delve into ICP, they just say "look, running here is high ICP, but running here is lower ICP, and that has to be better." Calculate theoretical ICP, juxtapose it against material stress-strain curves, then take some measurements to prove your math is correct. How much ICP is bad? How much is it reduced going from 50ROP to 100ROP or 50LOP? What forces on the pistons are our engines designed to handle? Surely there's a minimum piston force that's part of the design criteria too, where does it appear on the tables? "Reducing ICP is a good thing. Here it's higher than over here, so you want to run where it's lower" is not a universal truth.

I probably could have knocked the math out in a hour back in my senior year of college, but I haven't done much of anything with thermodynamics, heat transfer, combustion chemistry, etc., since I finished my BSME lo these many years ago . . . . 

[N201MKTurbo]

It seems like everybody wants more power. The only way to increase your power is to increase cylinder pressure.

[Hank]

16 minutes ago, N201MKTurbo said:

It seems like everybody wants more power. The only way to increase your power is to increase cylinder pressure.

Or do like Clarence and get more cylinders!