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Understanding LOP Operations - A Summary of John Deakin's Knowledge

...Engines certified with a fixed pitch prop do not have the limitation. The only time they are right of the limitation line is for take off. My engine isn't even on the chart at 28" MP and 2180 RPM, but as soon as RPM is up to 2300, it doesn't matter, it would be right of the line if there were one...
Two things I'm having a hard time getting my head around (perhaps I have misunderstood your post):

1. How does the engine "know" that the RPM is being held back by a hydraulically variable blade angle or one that is forged that way from the factory, and why does it matter to ICP?

2. Using the chart shown (for an O-320), your engine is far to the "bad" side of the line at 28 inches and 2180 RPM, and will be for some time until you climb above the MP limit or speed up to let the engine spin. In theory, operating to the bad side of the line could last the entire flight... Why does the engine not self destruct?

There are so many general guidelines out there that people have turned into "rules" or "gospel", that I think the whole concept has been corrupted. I'm beginning to think that you really only need to worry about CHT, oil pressure and oil temp, and the ol' Lycosaurus will just keep pounding away.
 
I'm beginning to think that you really only need to worry about CHT, oil pressure and oil temp, and the ol' Lycosaurus will just keep pounding away.

That is most likely the rule for the "simple" engines we run in our RV's. I think we spend a lot of effort and dollar$$ micro-managing the ol' Lycosaurus that could be better spent just enjoying the ride. Keep the thing well maintained and it should run happily for a long time. If problems arise, the Lyc usually gives the attentive pilot plenty of warning.

I realize those relative few who have "caught" problems with fancy instrumentation will disagree with this view, but consider how many millions of hours have been accumulated in aircraft with only oil pressure and temp gauges. But....a lot of us really enjoy watching needles, graphs, and twiddling with controls, so my opinion will increasingly be in the minority as complex engine monitors become mainstream. :)
 
"So, the second question. If detonation risk is low, then what is the failure that brings on early cylinder replacement?"

I'll take a shot at that question:
Valve failure caused by poor valve geometry, angles not matching with the seat, valve not concentric with the seat leading to the valve not fully transferring it's heat to the head.

Bingo. Well done Don...exactly right.

Heat is transfered from the valve via two paths, the valve stem to the guide, or the valve head to the seat. Poor seat contact (for all the reasons Don stated plus seat width and flatness) results in a very hot valve and early failure.

Poor seating is common.....way too common, and the resulting poor cylinder life is not the operator's fault. Early failure was delivered brand new in the box.
 
Two things I'm having a hard time getting my head around (perhaps I have misunderstood your post):

1. How does the engine "know" that the RPM is being held back by a hydraulically variable blade angle or one that is forged that way from the factory, and why does it matter to ICP?

2. Using the chart shown (for an O-320), your engine is far to the "bad" side of the line at 28 inches and 2180 RPM, and will be for some time until you climb above the MP limit or speed up to let the engine spin. In theory, operating to the bad side of the line could last the entire flight... Why does the engine not self destruct?

There are so many general guidelines out there that people have turned into "rules" or "gospel", that I think the whole concept has been corrupted. I'm beginning to think that you really only need to worry about CHT, oil pressure and oil temp, and the ol' Lycosaurus will just keep pounding away.

My apologies for the confusion.

The engine doesn't know which prop is controlling RPM. Perhaps Lycoming could explain why the MP restriction line is on charts with CS props and not with FP props. I don't have the answer. (at least it appears the charts are different for that reason, for sure some 0360 charts have the restriction, some don't)

In theory the entire flight could be on the right side of the line but in fact it doesn't happen because the only way to keep it there would be to climb at a very low air speed at WOT. As soon as the nose is lowered speed builds up and so does RPM and in no time the operation is left of the line, no matter what the MP. That may be why the chart for the O360-A4M, for example, has no MP restriction line.

Also it may be because FP applications in the certified world had no MP gage. All power is a matter of setting a given RPM. The Cessna 150-172 and Cherokee 180 manuals have no reference to MP at all.
 
Poor seating is common.....way too common, and the resulting poor cylinder life is not the operator's fault. Early failure was delivered brand new in the box.

Except with engines from BPE.

Allen cuts the seats at several angles, the valves sit better and last longer. :)
 
The answer might be found elsewhere

"The engine doesn't know which prop is controlling RPM. Perhaps Lycoming could explain why the MP restriction line is on charts with CS props and not with FP props. I don't have the answer. (at least it appears the charts are different for that reason, for sure some 0360 charts have the restriction, some don't)"

I participated in a propeller certification process with my Rocket. The Techs doing the various tasks were candid with answers to a few questions that have been bothering me for a while - and they also knew their stuff.

While it is possible to build a 400HP 4 cyl engine, there exists no current technology to put a prop on the thing. This same problem (power stroke torque amplitude) restricts the diesel engines in that they can only have a cyl of a certain size/power output.

A PSRU has to be designed to absorb these pulses, and the clutch used by Bud Warren in his design was a clear winner in this aspect.

You might think your prop is a solid object, when in fact it is constantly flexing, something like a fishing pole. It could be that 28"/2100RPM produces enough of a power pulse to overstress the prop, assuming the crank nose is strong enough. It could also be that the reverse is happening: the prop could be stressing the crank nose section?

I would volunteer that FP props are likely stronger in the hub area when compared to a CS prop, so it follows that CS props are restricted from high MP/low RPM ops.

In any case, constant operation in that combination of MP/RPM will eventually cause failure on the tested engine/prop combination. So, the engineers tell you to not operate there. YMMV, of course.

Yes, BPE builds very good cylinders.

Carry on!
Mark
 
Mark,

The restrictions on MP/RPM/propeller and engine model are understood from a resonance perspective, and we also know that they are highly influenced by the specific powerplant configuration. However, the chart discussed here is quite generic and only seems to consider detonation (a function of ICP) as the limiting factor, not damage from resonance. If this is true, then it seems that Lycoming also completely ignores the loads imposed on ICP as a function of the aerodynamic properties of the fixed propeller. This makes no sense either.

It's like the old wives tale we've all heard concerning runnning a C/S prop equipped engine "oversquare" - we've all heard it is "bad", yet the "science" quickly evaporates when you realize most F/P engines spend much of their lives in that exact (oversquare) condition.

Like I said, there is enough conflicting information out there that anyone can assemble bits and pieces to create a "position" and still be technically credible. I wish I had the resources to test all these theories for myself!
 
The engine doesn't know which prop is controlling RPM...

In theory the entire flight could be on the right side of the line...

Also it may be because FP applications in the certified world had no MP gage...

Here's my problem with all the various charts and guidelines out there - If the engine will be damaged by operation in some condition (like high indicated MP), it is not acceptable to mitigate the condition by eliminating the M/P gage!

The fact that the "restriction" only applies to an engine equipped to monitor the condition (while other engines are ignored) leads me to the logical conclusion that it's not really a restriction at all.
 
I suspect its a simple as Lycoming feels that if you have the choice the power and rpm combinations should be provide the very best service life. Since with a FP prop you don't have RPM options they have no choice but to allow the operations. The difference might be a very small change in the average time between overhauls.

George
 
RV8R999
I see Mr. Deakin is a very experienced pilot but what about his engineering/test background? Maybe this short bio doesn't include his technical expertise or background - anybody know?

Ken, With the power of the internet, you could learn so much. John Deakin, George Brayly and Walter Atkinson combined are the worlds greatest resource in present times when it comes to this stuff. Much of it was known in the 50's but was lost in time.

I must have said this now at least 5 or 6 times now, attend an APS seminar.
http://www.advancedpilot.com/

Anyone who missed the one this week will need to book in for the next one!

The more I read these threads, I see folk who know some, know a lot, and those who clearly know very little. A lot seem to know what to do, but do not understand why. The key to it is understanding the why, from there you can vary the way you operate and when small anomolies come along you can diagnose and correct it before trouble strikes.

Toolbuilder
Quote:
Originally Posted by RV10inOz View Post
...And yes the low compression as you call it, or standard LYC can be run in detonation...
There are quite a few experts who would disagree with you... Not under "normal" circumstances anyway.

Also, while I'm not among the "experts", I do know that I have never seen detonation as evidenced by runaway CHT on any Lycoming I've flown - and I have done some dumb things with the mixture control over the years.

Just my (nearly) undeducated opinion here, but I'll bet if the engine has an STC or is otherwise capable of operating on the watered down Mogas, it's nearly impossible to induce detonation in that engine on 100LL.

Just because you have not seen it does not make you the expert. I have. And I can demonstrate it at will if you like. Yep happy to do it on my engine too.....just not for long! :eek:

As for this,
There are quite a few experts who would disagree with you... Not under "normal" circumstances anyway.

Well your quite a few experts are wrong too. refer back to my post #20. I talked about rapidly rising CHT's on takeoff and it was due to mixture not hitting full rich due to cables (too short in throw from Vans) and the mount flexing. This was detonation.

You are correct though in one point.....none of this is under "normal" circumstances. But this is my whole point, you need to be aware. All cylinder monitors saved this engine from serious trouble, may have taken a few years to fail or be severly damaged, but it would have happened had we had just 1 CHT probe on a cylinder not affected and an old analogue gauge.

Someone else here has posted a similar experience, and I suggest everyone makes a point of checking their mixture cables allow the FR and ICO stops to be made with some cable travel left over for when the engine rubbers sag or pull under load.

Just my (nearly) undeducated opinion here, but I'll bet if the engine has an STC or is otherwise capable of operating on the watered down Mogas, it's nearly impossible to induce detonation in that engine on 100LL.
Those that have a higher margin might be hard to detonate on AVGAS, but I do not know this for sure. Do you? Not by your statement above so why encourage others to do so when you do not know. I would ask George Brayly, ask about the engines STC'd for Mogas and how the would fair on 100LL on his engine test stand and see what he says. I would love to know the answer.

If you can't be bothered let me know, I will ask. Your time zone is much closer than mine ;)
 
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I talked about rapidly rising CHT's on takeoff and it was due to mixture not hitting full rich due to cables (too short in throw from Vans) and the mount flexing. This was detonation.

Serious question David; why are you sure it was detonation?
 
...Those that have a higher margin might be hard to detonate on AVGAS, but I do not know this for sure. Do you? Not by your statement above so why encourage others to do so when you do not know...

First off, if anyone reads a statement that begins with the disclaimer "this is just my (nearly) uneducated opinion..." as even the slightest form of encouragement, then they have a lot more to worry about in life than proper engine management!

Second, I'm no expert, and have NEVER promoted myself as such in this field. My complaint is that the "experts" have let all of us down because they can't seem to agree on much of anything. So in such a case, I'm forced to sift through all the BS published and try to find the few things that ARE held as universal truths among all the engine guru's, compare that to my own experience, and go from there. Though I have never seen detonation, I know how to read a CHT gauge... I expect that this will serve me as well as it has the hundreds of thousands of other pilots over the last 60 years or so. This may not be the perfect solution, but I like my odds.

Finally, the relatively newfound ability to monitor multichannel CHT and EGT to 1 degree resolution does NOT increase the chance of detonation - so even if the Lycoming DOES detonate under certain conditions, it's obviously been doing it for 60 years without any real problem - so when it's all said and done, we're no worse off than the previous generations of pilots, so who cares?
 
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Moura
Since Don from AFP was mentioned, I did replace my restrictors and they were perfect. Only replaced 3 for 25 dollars (I think that is what I paid) each.
But you know what puzzles me, Don mentioned he would never run not even an inch above 24MAP when LoP!! Should I be confused?
Moura

Yes I think you should be confused!!! :confused: What on earth would make Don say that? He should know better. How do you think the big old radial airliners did it? This is exactly how Old Wives Tails begin.

As for down low , Toolbuilder has it pretty much nailed. WOT unless for some reason you need to pull way back. Pulling the throttle back is not unlike a clogged air filter, and you would not run around with a clogged up filter would you?

So set the RPM where you want, and slower is theoretically less power (Torque x RPM) but its a slower piston speed and closer to detonation ;) but anything like 2000+ is not that much of a deal, but if you choose more go, more RPM, a bit less, use less. Then set LOP according to this,

________________________________________
Outside the Box
? At 65% power, use richer than 100 ROP, or leaner than peak EGT.
? At 70%, use richer than 125?F ROP, or leaner than 25?F LOP.
? At 75%, use richer than 180?F ROP, or leaner than 40?F LOP.
? At 80%, use richer than 200?F ROP, or leaner than 60?F LOP.
________________________________________

How hard can that be?
 
Dan,

A few tests, downloaded data sent to John Deakin, much discussion about all the likely things to do with pre-ignition first of all as that is really bad, such as a defect with a plug, helicoil, timing etc.

If it was not detonation of a mild kind what else could it be? and let?s be realistic here, it?s hard to determine without an engine test stand like GAMI have what is mild-med-high levels of detonation.

The way one or two or three CHT's all ran away at a very rapid rate compared to the normal 1 degree every few seconds during a take-off and climb were pretty obvious, and the data looked like what they get on their data.

We found the problem, and that explained it pretty darned well.

This was not just a few folk at the airfield shooting from the hip kind of investigation. I was lucky having had some acquaintance with John Deakin and good access to him to diagnose it. As usual he was onto it!
 
I went and had a dig around, and this explains why the tell tail sign of rapidly rising CHT's is worth watching out for! One post I read recently this is what he saw and did the right thing immediately.


http://www.avweb.com/news/pelican/182132-1.html

It was too long an article to copy into this post, so please read this, several times even until it sinks in. Thats the only way I seem to learn.

And can I say again....attend the classes.
 
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I did some more testing yesterday. One question quickly came to mind. I post the chart on page 1 of this thread in the my aircraft. Had to go to 9500 feet for ATC and went to the chart to decide where to run the engine. I appears based on the chart on the first page of this thread that you can't fun LOP above 9000 feet and in fact they recommend 50 ROP at least. I am trying in my mind to understand the reason behind this since MAF is dropping as you climb and you are in the region where in past LOP writings you can't hurt the engine at any mixture setting. Any comments or ideas? Anyone running LOP at higher altitudes?

George
 
...Anyone running LOP at higher altitudes?..

Yes. This is LOP:

xmtt03.jpg
 
First off, if anyone reads a statement that begins with the disclaimer "this is just my (nearly) uneducated opinion..." as even the slightest form of encouragement, then they have a lot more to worry about in life than proper engine management!

Second, I'm no expert, and have NEVER promoted myself as such in this field. My complaint is that the "experts" have let all of us down because they can't seem to agree on much of anything. So in such a case, I'm forced to sift through all the BS published and try to find the few things that ARE held as universal truths among all the engine guru's, compare that to my own experience, and go from there. Though I have never seen detonation, I know how to read a CHT gauge... I expect that this will serve me as well as it has the hundreds of thousands of other pilots over the last 60 years or so. This may not be the perfect solution, but I like my odds.

Finally, the relatively newfound ability to monitor multichannel CHT and EGT to 1 degree resolution does NOT increase the chance of detonation - so even if the Lycoming DOES detonate under certain conditions, it's obviously been doing it for 60 years without any real problem - so when it's all said and done, we're no worse off than the previous generations of pilots, so who cares?

Michael,

I have not compared every statement and written word by Deakins and Busch, but they generally are in agreement. They advocate LOP is a better way to go but the gist of what is put forth is applicable mostly to 6 cylinder, high powered engines. Their theory is somewhat at odds with Lycoming but in fact Lycoming has come around somewhat to their way of thinking on leaning after a major flight school had to shut down operations with almost new airplanes a few years back due to fowled plugs.

To transfer the theory of LOP operations to the 4 cylinder low compression engines is not all that critical or complicated. If in doubt, follow Lycomings recommendations to the letter. But evidence seems to indicate LOP works. Mike Busch's Cessna twin is 200% beyond TBO.

The discussion here has drifted off into detonation. So how is detonation controlled in modern auto engines? By a computer that monitors knock and when it is detected timing is retarded until it detects no knock. If you minitor timing, as I did with an OBD scanner hooked up to the Subaru engine, it always ran more advanced than 25 degrees (magneto timing) even when flying around with WOT and 1700 rpm.

I don't think detonation is much of an issue with Lycoming unless an EI systm looses its brain. It does not monitor knock but it does respond to MP and RPM inputs. Unfortunately, the program could get out of wack with high MP (calling for 25 degrees advance) and low RPM (perhaps calling for 35 degrees advance). I don't know what advance the system would call for. I had a dwell meter hooked up with Electoraire when I used it and it sure responded well to normal MP and RPM with a fixed pitch prop. It was always advanced except for take off power.

With magnetos the timing is fixed and retarded considerably from where Ei and ECU computers normally set it. Mag timing is really out of the detonation range. If CHT goes up on take off due to a lean mixture, it is a matter of inadequate fuel and air flow cooling. I would be surprised if there is detonation. I suppose there could be, put how would one know?

These engines are low rpm, big displacement like an old farm tractor, it was very difficult to get them to detonate even under heavy load pulling a 3 bottom plow. They would get hot but did not detonate until RPM got really low and one did not shift to a lower gear quick enough. :)
 
A few tests, downloaded data sent to John Deakin, much discussion about all the likely things to do with pre-ignition first of all as that is really bad, such as a defect with a plug, helicoil, timing etc.

Ahh. Given the concern with preignition, you pulled the plugs and looked in the cylinder?

BTW, you are running the standard 8.5 compression and mags at 25, and burning 10LL? Was OAT 100F+, and CHT 400+?

It appears based on the chart on the first page of this thread that you can't fun LOP above 9000 feet and in fact they recommend 50 ROP at least. I am trying in my mind to understand the reason behind this.......

Good question. George refers to this graphic; yellow circle added for emphasis.

 
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I'm interested it what he thinks is going on between 8-9K to develop the severe knee in the curve? Everything is linear up to this point and all of a sudden a big discontinuity...
 
Michael, 395 and 380 EGT aren't too high for LOP ops?

...I think you mean 395 and 380 CHT...

As far as I'm concerned, that's too high for continuous ops, period. However, there is no chance of detonation at this altitude, so any side of peak EGT makes the CHT cooler. I just picked LOP because it has the same effect on CHT (on this airplane) as ROP, but is much cheaper. The high CHT shown (or more to the point, the wide spread between cylinders) is another issue I'm trying to resolve. I have yet to determine if I have a baffle problem, incorrect fuel scheduling, the wrong nozzles or something else. As pointed out in the thread where this picture originates, it may be a combination of multiple problems.

For the purpose of this thread however, the engine seems perfectly happy running LOP at altitude.
 
I'm interested it what he thinks is going on between 8-9K to develop the severe knee in the curve? Everything is linear up to this point and all of a sudden a big discontinuity...

...And why does it go perfectly flat at 9.5? No data?
 
...And why does it go perfectly flat at 9.5? No data?

The answer is power and speed. Here's what he has to say about it.

The same chart can be used for illustrating the climb, if you climb as I suggested a couple of columns ago. Leaning to that target EGT as you climb produces pretty much what you see on the second chart, just rich of the red box. Once you get to your altitude (the example is at 4,500 feet), do the "big mixture pull," and set LOP. The green lines show a good area to be in when running LOP, up to about 9,000 feet altitude. At and above that point, you probably want to switch over to ROP to keep the power up as much as possible.

For efficiency LOP is very good. Fuel mileage is up, consumption is down, and so are EGT's and CHT's.

His chart is an illustration of going LOP in climb which I think is a bit over the edge. Why sacrifice power in climb to be LOP and then go ROP for power and speed in cruise? This all just talking stuff. It makes more sense to me to get to altitude ASAP and cruise at whatever you want - speed or efficiency.

There certainly is no problem LOP at altitude unless you need a warmer EGT for cabin heat. :)

The temps will run very cool which is a life extended for these engines, no doubt about it.
 
LOP at altitude

Deakin has his little green lines move to ROP at altitude for speed and power reasons - I run LOP at altitude all the time... There is no "red box" at altitude - no risk of detonation.

Hans
 
Michael,

...I have not compared every statement and written word by Deakins and Busch, but they generally are in agreement...

Thank you for taking the time to write that response David. I am certainly an advocate of LOP ops when appropriate, and do not fear it at all. The only possible danger of running lean that I can see is detonation, and this is where most of the confusion and arm waving is found. Take detonation out of the picture, and the advantage of running LOP is clear - cooler, cleaner, cheaper flying. However, the detonation issue clouds things up and injects fear into the debate. Some will say with near certainty that "our" engines have a very wide detonation margin, while others take a more cautious approach. Lycoming itself publishes "limitations" based on the ability to monitor the engine: If you have a MP instrument, then the limits apply, if you don't, then don't worry about it. And let's not also forget that Lycoming also endorses operating continuously at PEAK EGT!

Anyway, the fact that this discussion has turned to detonation is the right one IMHO. Detonation is really the only important factor in the entire LOP subject, and the one that seems to have the most mystery surrounding it.

I suspect that resolution would lift the fog surrounding LOP ops once and for all.
 
The only possible danger of running lean that I can see is detonation, and this is where most of the confusion and arm waving is found. Take detonation out of the picture, and the advantage of running LOP is clear - cooler, cleaner, cheaper flying. However, the detonation issue clouds things up and injects fear into the debate. Some will say with near certainty that "our" engines have a very wide detonation margin, while others take a more cautious approach ....

Detonation is really the only important factor in the entire LOP subject, and the one that seems to have the most mystery surrounding it.

I dont see how detonation can be occuring without associated high CHTs. Since we can monitor CHT on all cylinders with modern equipment, why the fear and mystery?


erich
 
"For efficiency LOP is very good. Fuel mileage is up, consumption is down, and so are EGT's and CHT's."

How do you define efficiency?
 
Dan

Yep! Like I said we did a very through check of everything. OAT would have been pretty warm coming into our summer time, but I do not recall now. CHT's on a couple of cylinders went racing past 400. In the time it took to get to 500' and look at the EMS and say WTF??? and then pull back the MP to 20-23" and come back round and land.

And while I think of it, our standard IO540, including the grey paint from Lycoming is 260HP. On a per cylinder basis its slightly less than the IO360 180HP, so you guys with anything more per cylinder than me, who think it can't happen, think again. Think about the differences in our engines....not many are there? When all is running well, and you are getting correct fuel flow on takeoff at FULL EVERYTHING, I agree its pretty hard to get, but it only takes one small thing. EMS devices pay for themselves. Ours owes us nothing now.

By the way, fuel flow needs to be in a standard atmosphere your HP divided by 10 in GPH when full bore. In my case 26GPH +/- 5%.
 
I dont see how detonation can be occuring without associated high CHTs. Since we can monitor CHT on all cylinders with modern equipment, why the fear and mystery?

This is my point.......not everyone does and can. The next point is you have to know what the instrument is telling you. What any changes or trends mean, and why some good value education is important. Most of us do not know enough, we all know too many OWT's and not enough fact. Too many years of stories bantered around flying schools and aeroclubs....Chinese Whispers if you like.

Now maybe I am being picky, and you may not have meant it this way, but Detonation will occur without high CHT's, .....but not for very long. the rapidly rising CHT is a symptom of detonation, its how you spot it happening. A CHT steady all round at 420F does not mean you have detonation, but when they should all be 330 and one or more are racing through 400 and beyond like the EGT numbers do when you start up....:eek:
 
Detonation is really the only important factor in the entire LOP subject, and the one that seems to have the most mystery surrounding it.I suspect that resolution would lift the fog surrounding LOP ops once and for all.

Yep.

Refer back to post #41 and the standard Lycoming power chart.

I don't know if Lycoming meant that line to be a detonation line or not....

Oh ye of little faith ;)

Lycoming offers some discussion of the limit line in Lycoming Flyer Key Reprints (page 44, lower left), but like some of you I prefer straight data. The following charts are from a Lycoming test cell, detonation runs made with 100LL for baseline comparison to the same IO-360 on an ethanol fuel. It takes more than three charts to illustrate the entire limit line as found on the power charts, but you can get a taste.

Look close at the operating temperature conditions. All the runs are made in accordance with FAR 33.47 and its companion AC 33.47-1 dealing with how detonation tests shall be conducted. At least one CHT must be at max and the others close to it, oil temp is near max, and intake air temperature is ~100F......pro-detonation conditions.

First up, 26.8 MAP and 2700 RPM. From the top down you have CHT, EGT, power, BSFC and detonation. The detonation graph is expressed as a percentage of firing events. In this test they pulled mixture from rich through peak to 40-60 degrees LOP. Detonation percentage is zero:



Let's make things more difficult, full throttle, 28.5 MAP and 2700 RPM. Again mixture is pulled from bog rich to LOP. There's a slight nibble of detonation right at peak EGT (less than 5% of firing events) and well lean of best power:



Ok, let's see that detonation limit. This run is again 28.5 MAP, but the RPM is hauled back to 2400 RPM....ouch. It detonates 10%, maybe 12% at ~25 ROP, a little lean of best power. You could even argue power fell off because it started to detonate. Whatever, it's the limit:



28.5 and 2400, the upper end of the limit line on the power chart. There's your red box for a low compression NA Lycoming on 100LL:



Keep it cool and pay attention to what you do with the prop control, and it becomes difficult to hurt it with the mixture control. You don't need twenty pages of Deakin or a trip to charm school. You really don't need to understand much more than the basics, the very first graph in the first post of this thread.....information published by both GAMI and Lycoming.



Of course if you run more ignition advance, less octane, high compression pistons, a turbo, or anything else which steps away from the base version, you get to find your own detonation limits.
 
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Now maybe I am being picky, and you may not have meant it this way, but Detonation will occur without high CHT's, .....but not for very long. the rapidly rising CHT is a symptom of detonation, its how you spot it happening.

Absolutely. Thanks for fine tuning my previous statement.

erich
 
Yep.


2vaf6hc.jpg


Ok, let's see that detonation limit. This run is again 28.5 MAP, but the RPM is hauled back to 2400 RPM....ouch. It detonates 10%, maybe 12% at ~25 ROP, a little lean of best power. You could even argue power fell off because it started to detonate. Whatever, it's the limit:

dexxf7.jpg


28.5 and 2400, the upper end of the limit line on the power chart. There's your red box for a low compression NA Lycoming on 100LL:

2n5edv.jpg

looks like you could use a rule of thumb..........

RPM/100 + 4 as an absolute limit,

2000 rpm, max MAP 24

2300 rpm, max MAP 27

etc,
 
Dan,

Great work!

You don't need twenty pages of Deakin or a trip to charm school.

As for the trip to charm school, well thats a bit unfair. You and I might understand test data, and in this case you have explained a lot of stuff with a page or two, but we are only talking about one small matter of running an aero engine. APS do not spend two days talking about this one thing.

What charm school does is educate people on the wholistic understanding of engine operation and fault finding. not sure what you do but I guess you work for lycoming or somewhere where good data and knowledge exists, or are just one of the few real enthusiasts. Either way many aircraft owners are not degree qualified engineers specialising in areas that make this stuff easy to pick up and understand. Most Lawyers and accountants would struggle with the concept of torque on a bolt and nut and how that relates to tension in the bolt. Let alone any of this.

So Charm school as you call it is about the only available resource anywhere in the world, and for those of us on the other side of the planet the online version is about as good as it gets. trust me in a so called 1st world country, I only know of one engine shop in Australia that understands this stuff and has a similar dyno stand, albeit without all the sensors plugged into an engine as GAMI do.

Anyway, do you have the same test charts for an engine at say 350F. This would be more representive of how we all operate, and while detonation margin is a semi-fluid thing, it would show a smaller red zone no doubt.

Again....I appreciate your input, you have more patience or time to find all this stuff than I do.
2thumbs.gif
 
...At least one CHT must be at max and the others close to it...

So do we mean 500 degrees for CHT as the "max"? If so, then I would suspect a huge detonation margin at even the "too hot" 400 that most of us use as a limit, let alone the more typical mid 300's.

I would expect the thing to detonate at idle with a CHT at the limit!
 
So do we mean 500 degrees for CHT as the "max"?

Look at the very top of all three charts Mike. AC33.47-1 requires one cylinder be within +-10 degrees F of maximum when leaned to highest CHT, and all others must be with 50F of the hottest one.

Anyway, do you have the same test charts for an engine at say 350F. This would be more representive of how we all operate, and while detonation margin is a semi-fluid thing, it would show a smaller red zone no doubt.

No doubt.

Having been schooled, can you tell us why the suggested mixture setting on the red box graphic suddenly shifts to ROP above 9000 MSL?
 
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Having been schooled, can you tell us why the suggested mixture setting on the red box graphic suddenly shifts to ROP above 9000 MSL?

It's been awhile, but I went through the Deakin articles (although not the school) pretty carefully in the past, and I don't recall this shift to ROP being recommended or discussed. Does someone have the reference for this?

Regards

Erich
 
You guys are smarter than this, or is this a bait?

Once you get to a height where say 60% is achieved, you can put the mixture/RPM wherever you like it to achieve the speed or MPG as you choose.

I get a bit of RAM AIR effect compared to say a C182 might, so the difference of 7500-9000' is a bit variable but even my RV does not generate enough MP at 8500+ to be an issue. So I would suggest from 9000' onwards you can do what you like. No risk. 50ROP gets a nice TAS up high for no more fuel flow than down lower at 20-40LOP and a lower TAS.

Go try it for yourself. Early FL's will show you. Or attend the course and ask the question of the APS team. Of which I am not one of! :)

Seen this before anyone? :rolleyes: Take note of the second line....of text that is :D

________________________________________
Red Box = No Fly Zone
• At and below about 60% power, there is no red box. Put the mixture wherever you want it.
• At about 65% power or so, 100ºF ROP to Peak.
• At about 70%, 125ºF ROP to 25ºF LOP.
• At about 75%, 180ºF ROP to 40ºF LOP.
• At about 80%, 200ºF ROP to 60ºF LOP.
________________________________________


________________________________________
Outside the Box
• At 65% power, use richer than 100 ROP, or leaner than peak EGT.
• At 70%, use richer than 125ºF ROP, or leaner than 25ºF LOP.
• At 75%, use richer than 180ºF ROP, or leaner than 40ºF LOP.
• At 80%, use richer than 200ºF ROP, or leaner than 60ºF LOP.
________________________________________


PS: RE the 60% >>> With cool most of the engines we use, between 60 and 65% its probably OK, it should be remembered these are not hard and fast numbers, bit of give and take is allowed here.
 
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It's been awhile, but I went through the Deakin articles (although not the school) pretty carefully in the past, and I don't recall this shift to ROP being recommended or discussed. Does someone have the reference for this?

Regards

Erich

Down the page, titled "Where I left you last month."

http://www.avweb.com/news/pelican/183094-1.html

John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
You guys are smarter than this, or is this a bait?

It's just a question. I think you'll find the real answer to be holistic, as in "whole engine". You don't actually believe Mr. Deakin, the LOP advocate, is recommending you abandon all the benefits of LOP (which, BTW, I think are real) at 9000 ft or so because he wants you to have more power? What about "cleaner" and "cooler" and "3% less speed for 15% less fuel" (or whatever is is)?

Seen this before anyone? :rolleyes:

Why yes....yes we have. Let's look at reality. Your "No Fly Zone" list forbids a range from 200?F ROP to 60?F LOP at 80%.

The very first chart posted above is 26.8 MP and 2700 RPM....about 92% power. Peak EGT is 1480 on the hot cylinder, full rich is 1220 and the leanest reading is 1420. They pulled mixture from 260 ROP to 60LOP, with the engine temps at their limits, without detonation.

Let's go a little further. The "No Fly Zone" list is based on percent power. Again look at the real data:

26.8/2700 = no detonation at any mixture....at 92%
28.6/2400 = 10%-12% detonation when leaner than best power ....at 87%

The detonation limit is seen at the lower percent power. The same MP/RPM relationship exists as you move down the power scale, because detonation margin isn't a function of percent power. The simple, easy to remember truth is right there on the instructions that came with the engine......don't run it radically oversquare.

All right, a few notes.

I think very highly of George Braly and his crew.....smart people all. If I had a big bore turbo motor (routinely oversquare and higher induction air temperatures) I'd run it with the "Red Box" prohibitions in mind. If an RV owner insists on slavish adherence to the Deakin "forbidden power settings" list, well, fine. For a basic NA Lyc it is extremely conservative. You'll spend a lot of time and effort sweating details of EGT and power that don't matter, but it won't hurt. Just don't run into anything while your head is down.

The detonation survey charts are for a stock IO-360-A. They're here for illustration. The other plain vanilla low compression models won't be a lot different, but you be conservative as you like. As before, with high compression, more ignition advance, etc, you're an experimenter. You get to gather your detonation data with a boroscope.

Some recent engine operating charts don't have a limiting manifold pressure line. My IO-390 is an example. It's not because those engines don't have a limit. When I wrote Lycoming last year and asked, the response was (quote) "No we do not have anything as of yet for the IO-390 like you are requesting." Since then the 390 has become a certified model, so maybe the data is now available. Or maybe Lycoming has no intention of publishing it anymore. I don't know.
 
BSFC data from these charts is most interesting.

These engines really do run .42 at peak to just LOP. That is as about as good as it gets with any engine, new or old technology.

I wonder about the timing of the test engine set at 20 degrees. That in itself would give an extra margin before detonation.

We operate at 25 degrees, at least I do, wouldn't that tighten the detonation margin?
 
Just don't run into anything while your head is down.
<snip>
As before, with high compression, more ignition advance, etc, you're an experimenter. You get to gather your detonation data with a boroscope.

The two best quotes from this entire thread. As a hard-core LOP guy, I have found that with a little practice the "big pull" can be accomplished with a minimum of head down time by knowing about where the lever is going to be and using fuel flow as a reference, then fine tuning the EGT.

The borescope remark is very true. Several people have advanced the theory that you can see a "rapid rise" in the CHT during detonation. True, but too late, the damage may have already happened.

John Clark ATP, CFI
Aviator & Gearhead
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
...detonation margin isn't a function of percent power.

I can't add too much to the conversation (and besides, I'm not even flying yet), but I seem to remember from my long-ago education that detonation is a function of mean effective pressure. Does that make sense?

Edit
Pulled out my calculator... MEP: At 2700 rpm & 92%, 134.9 psi. At 2400 rpm & 87%, 143.6 psi. Not a big difference, but it goes the right way. More MEP, more likelihood of detonation.
 
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I wonder about the timing of the test engine set at 20 degrees. That in itself would give an extra margin before detonation. We operate at 25 degrees, at least I do, wouldn't that tighten the detonation margin?

True and yes. Recall notes about "more ignition advance".

Some angle valve motors are 20 (IO360 A1B6D, A3B6D, or my IO-390) and others are 25. Parallel valve is 20, 23, or 25?
 
Look at the very top of all three charts Mike...

Yep, took the easy way out and didn't study the chart, thanks.

I would sure like to see a detonation curve for this engine between 300 and 500 CHT. I'd bet it is far from linear.
 
Dan

I think we are missing the point a little here, mind you I did get the detonation margin debate going so who else can I blame :) but its about margin. Now you have shown some graphs which show a very generous margin. The APS/GAMI data and suggestions is generic and will cover everyones needs.

Anyone who publishes a a set of guidlines and leaves one group out on thin ice is not very responsible. APS/GAMI info covers 95% or more of the fleet with a comfortable margin on most and a thin one no doubt for others.

You should also consider what happens to an engine with lead fouling in the bottom plug or one not erfect in timing or a helicoil thats being a glow plug, and there are plenty of threads about helicoils on the internet and this board, so it can and does happen.

In addition to this, the APS/GAMI information is also about running sensible CHT's for long cylinder/head life especially when not all heads are assembled equal.

If you were to adopt the run as close as you can to the red line in your graphs (which I know you are not pushing) what do you think your typical CHT's would be? Not in the 300F range for sure!

Next point is.....if you and I wish to improve air flow and CHT cooling, we go out to the hanger and start adding seals, cutting baffles, making all the mods we want and go try them. If you own a Cessna/Piper/Beech etc. or an RV that you did not build and do not have authority to modify, you can not do this. (I know who would know on an RV...but thems the rules). So you get an STC baffle kit for your Bonanza or something but thats about it.

So....... with that in mind, you would not be suggesting to folk in their C210 or A36 to go exploring the edges of the red line on the graph and running CHT's at 400 or whatever that would get you.

I think that is why the APS/GAMI info is what it is. It makes a logical argument wouldn't you say?

These guys have done more research than anyone I know of and publish their data for all to share and learn from. They have come under much scruitiny from all corners of the globe and at the end of the day, even TCM and Lycoming are sheepishly coming out of the closet so to speak.


Quote:
Originally Posted by David-aviator View Post
I wonder about the timing of the test engine set at 20 degrees. That in itself would give an extra margin before detonation. We operate at 25 degrees, at least I do, wouldn't that tighten the detonation margin?
True and yes. Recall notes about "more ignition advance".

Some angle valve motors are 20 (IO360 A1B6D, A3B6D, or my IO-390) and others are 25. Parallel valve is 20, 23, or 25?

Dan...are you sure? I know there are always exceptions on exceptions, but the majority of IO360A engines are 25 degrees, and I note the IO360 A1B6D is one of the engines that does not have an option for 20 degrees.

Just a question, where did those graphs come from and what was the purpose for their production?
 
Dan...are you sure? I know there are always exceptions on exceptions, but the majority of IO360A engines are 25 degrees, and I note the IO360 A1B6D is one of the engines that does not have an option for 20 degrees.

Nope, working from memory. Let's go to the TC's:

http://rgl.faa.gov/Regulatory_and_G...0619753f0fec87862575e6004f3dac/$FILE/1E10.pdf

Ok, A1B6D, A3B6D, and a few others are limited to 25, the majority have a 25 or 20 option, and some are limited to 20.

http://rgl.faa.gov/Regulatory_and_...6c4425821f8625770a004aeed8/$FILE/E00006NY.pdf

IO-390 is 20.

Just a question, where did those graphs come from and what was the purpose for their production?

As stated previously, an ethanol study. It's been floating around the net for quite a while. Takes 60 seconds to find; it turns up in the first page of Google results. Try "lycoming detonation survey"

http://www.cgar.org/Data/Projects/47/Files/Appendix 3 Detonation Testing Report3792.doc
 
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Interesting how the ethanol based fuel compared, 48% more fuel was required and 15 degrees BTDC :eek: Not exactly good range from a tank of that stuff.

Thanks Dan:)
 
Questions for some one learning about leaning

I'm still learning about leaning. So one of my questions were what happens if all the clyinders are not at the same tempature. Do you lean on ROP to the hotest cylinder and use it's EGT to set the whole engine. And then what do you use on the LOP side do you still use the hotest cylinder? So if your engine has a spead of CHT's what do you use because if you use the wrong CHT then you could have the other cylinder running in the red zone I think.
 
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