SkyTruck wrote:I am by no means an expert, but the engine in my plane is the most important part so I treat it like I want it to get me home!

A correction,
The engine is the most important part unless the "Wife" is aboard. In that case, she is the most important part.... and the most expensive

Mark

SkyTruck wrote:

SkyTruck wrote:I am by no means an expert, but the engine in my plane is the most important part so I treat it like I want it to get me home!

A correction,
The engine is the most important part unless the "Wife" is aboard. In that case, she is the most important part.... and the most expensive

Mark

Those maintenance costs can run high.

Just for clarity, some seem to be explaining a procedure for leaning to peak EGT before T/O.... maybe not, but to be clear:

You don't want to lean for peak fuel economy, around maximum EGT - you'll get detenation, high CHTs, and damage the engine really fast!!

You do want to lean for peak fuel flow and/or RPM (fixed pitch), maximum power - to get the best performance from your engine while still keeping it as cool as possible.

More HP per Cubin Inch more fuel cooling is needed (maybe even lead or water injection)!

The variable are endless, unless you have a high speed computer!

Battson wrote:Just for clarity, some seem to be explaining a procedure for leaning to peak EGT before T/O.... maybe not, but to be clear:

You don't want to lean for peak fuel economy, around maximum EGT - you'll get detenation, high CHTs, and damage the engine really fast!!

You do want to lean for peak fuel flow and/or RPM (fixed pitch), maximum power - to get the best performance from your engine while still keeping it as cool as possible.

It slightly more complicated than that and not really true at all altitudes and your advice to lean to "max power" can be downright dangerous below 7-9k feet.

The most detonation prone mixture at ANY altitude is BEST POWER or around 50-80 degree ROP! Leaner or richer than that actually reduces the chance of detonation. That's not my opinion, that's scientific fact. With a naturally aspirated engine above 7-9k feet, it doesn't matter as much because the engine can't generate enough power to really cause heavy/severe detonation, which CAN lead to preignition. Which is much more destructive and is literallyy "game over" in seconds if corrective action is not taken immediately. Mild detonation is not really that dangerous and can actually be useful at times to help clean the plugs and cylinder. Within reason of course, and only mild detonation, but I digress.

For those interested, Mike Busch helps explain the Science behind leaning here. And while this is primarily a LOP/ROP article.It is very helpful in understanding why you lean at altitude and how to do so, while getting the most performance for your aircraft, while protecting and being kind to your engine at the same time.

https://www.jpinstruments.com/wp-conten ... ed-Fin.pdf

For those with a multi point engine monitor Advance Pilot Seminars has some great FREE information that explains the technique in easy simple to understand terms for those who aren't up to speed on LOP/ROP ops. Once there toggle "downloads", then "target EGT".

http://www.advancedpilot.com/tech.html

FWIW, and I'm not trying to turn this into a LOP vs ROP debate but, I've been running LOP almost exclusively for 4,000 hours now with 4 different Carbureted engines following APS advice and leaning techniques without any problems. Period! The science is sound, however, in some cases it can be very counter-intuitive to what we were taught but, if you'll take the time to educate yourself the fuel saving and peace of mind are undeniable!

IMO!

My data is from my own experience and is all 0-540 and smaller carburetor engines with fixed pitch props. Lycoming engines like lots of fuel to start and then run better leaned at any rpm or altitude. As MTV said, we lean any simple engine at high density altitude to get some percentage of full power. With 0-320 and 0-360 engines, we leaned to best rpm regardless of the density altitude on pipeline patrols. We had fewer plug fouling problems and valve problems and got an average of 3,000 hours between overhauls. For old senile guys, it was a lot easier not having to remember to lean when up high. We just leaned every time.

Little Continentals are easy to flood when starting, and as soyAnarchisto said, the Stromberg carburetor has to be in premium condition to lean. Some mixture controls are even safety wired off. The easiest way to start a little Continental is to get out and prop it. You can hear the proper mixture, set with the butterfly in the carburetor by throttle setting. Slurp, slurp is what you want with no drip.

Harpoon1 wrote:It slightly more complicated than that and not really true at all altitudes and your advice to lean to "max power" can be downright dangerous below 7-9k feet.

The most detonation prone mixture at ANY altitude is BEST POWER or around 50-80 degree ROP! Leaner or richer than that actually reduces the chance of detonation. That's not my opinion, that's scientific fact. With a naturally aspirated engine above 7-9k feet, it doesn't matter as much because the engine can't generate enough power to really cause heavy/severe detonation, which CAN lead to preignition. Which is much more destructive and is literallyy "game over" in seconds if corrective action is not taken immediately. Mild detonation is not really that dangerous and can actually be useful at times to help clean the plugs and cylinder. Within reason of course, and only mild detonation, but I digress.

Welcome to the forum.

I am familiar with the material you're referencing. I think you've confused the information presented by Mike with the context of the conversation here?

If you don't lean to max RPM (as the instructional course materials suggest....) and you obviously don't keep it full rich or lean for peak EGT - then please enlighten me - what exactly do you lean for.....?

Battson wrote:

Harpoon1 wrote:It slightly more complicated than that and not really true at all altitudes and your advice to lean to "max power" can be downright dangerous below 7-9k feet.

The most detonation prone mixture at ANY altitude is BEST POWER or around 50-80 degree ROP! Leaner or richer than that actually reduces the chance of detonation. That's not my opinion, that's scientific fact. With a naturally aspirated engine above 7-9k feet, it doesn't matter as much because the engine can't generate enough power to really cause heavy/severe detonation, which CAN lead to preignition. Which is much more destructive and is literallyy "game over" in seconds if corrective action is not taken immediately. Mild detonation is not really that dangerous and can actually be useful at times to help clean the plugs and cylinder. Within reason of course, and only mild detonation, but I digress.

Welcome to the forum.

I am familiar with the material you're referencing. I think you've confused the information presented by Mike with the context of the conversation here?

If you don't lean to max RPM (as the instructional course materials suggest....) and you obviously don't keep it full rich or lean for peak EGT - then please enlighten me - what exactly do you lean for.....?

Thank you, I've actually posted here before over the years, many times, just not lately!

Mikes article covered where you should lean, focus on the Red Fin, its a visual aid. And If you'll look at it carefully you'll find your answers on the ROP side of the curve/graph. It is exactly like leaning when climbing out. For a specific power, you need to be a specific number of degrees from peak. The higher the power, the further from peak.

Again, at high altitude, when a naturally aspirated engine cannot make more than 65-75% power, say ABOVE 7-9k feet (depends on whether you take Continental advice and 65% or Lycomings 75% power), then best power is the place to be.

At lower altitudes, it depends. The higher the power production, the further from PEAK/Best power you need to be.

At sea level, somewhere around 250-300 ROP is a pretty good place to be.

Between SL and 7-9k feet, it's a sliding scale. And that's where the Advance Pilot Seminar is helpful in explaining the theory and giving some visual aids. In general with a multi-point engine monitor, at those altitudes below 7-9k feet, you would lean to the same target EGT that you have at sea level. Above that, then best power.

So that raises several interesting point to discuss - the 7-9k ft DA part of it. If we delve past the "whether to lean or not" question from the OP:

As you climb you need to advance the throttle to maintain a certain power output, which is obviously a function of manifold pressure (CS prop setup). The starting point being the manufacturer's design point, full rich at sea level. If you think about the stoichiometry, at the altitude the throttle touches the full-open stop - as you go higher then engine is progressive recieving more and more fuel than it needs, as the air gets less dense.

So to maintain the same combustion stoichiometry as at sea level and during the lower part of the climb, you would start leaning after the throttle touches the firewall. Most don't do that, they'll wait and lean in a larger step. But either way, you typically start leaning at around 4-6k ft depending on the DA and your method, would you agree?

Waiting until 7-9k to start leaning would put you a long way back from maximum performance, and you'd be shovelling unwanted fuel into the cylinders (which would of course keep them cooler and prevent pre-ignition).

Battson wrote:So that raises several interesting point to discuss - the 7-9k ft DA part of it. If we delve past the "whether to lean or not" question from the OP:

As you climb you need to advance the throttle to maintain a certain power output, which is obviously a function of manifold pressure (CS prop setup). If you think about the stoichiometry, at the altitude the throttle touches the full-open stop - as you go higher then engine is progressive recieving more and more fuel than it needs, as the air gets less dense.

So to maintain the same combustion stoichiometry as at sea level and during the lower part of the climb, you would start leaning after the throttle touches the firewall. Most don't do that, they'll wait and lean in a larger step. But either way, you typically start leaning at around 4-6k ft depending on the DA and your method, would you agree?

Waiting until 7-9k to start leaning would put you a long way back from maximum performance, and you'd be shovelling unwanted fuel into the cylinders (which would of course keep them cooler and prevent pre-ignition).

I personally use the "target EGT" leaning technique described by advanced pilot seminars. That is when I climb ROP, however, I'll often climb LOP but thats for another discussion. My EGTs are around 1300 at sea level and I lean to maintain 1300 and keep my cht's below 380-400 throughout the climb until passing through @8k, give or take. Where I then lean for best power and keeping my CHT's under control for the remainder of the climb.

Advanced Pilot Seminars also advocates FULL throttle climbs, the altitude will limit power production and rather quickly no need to restrict the airflow to the engine with partial MP, let the engine breath. This also is why leaning to a "target EGT" is so effective.

Unfortunately it's more complicated to explain in a few short paragraphs than actually do but, if you'll browse through their website and Mike Busch's articles, it's all there, chapter and verse. The how's and why's.

So the thinking behind the (ROP) climb with constant EGT is that the combustion reaction maintaining the same temperature must therefore have the same stoichiometry? I guess that makes sense, I need to go through that seminar again. You can get the same temperature LOP too, but with a much higher risk of detonation, does that therefore give the same results for the engine - I don't know if that rule holds? Oviously you would know you're LOP, given the instruments you typically want to run those ops safely.

Your earlier comment is right, detonation isn't going to destroy the big end bearing in minutes like pre-ignition could, but it's still something I would tend to avoid at all costs. I was interested to read your remark about a little detenation being "good"?

Battson wrote:You don't want to lean for peak fuel economy, around maximum EGT - you'll get detenation, high CHTs, and damage the engine really fast!!

Not really. At the DA discussed, the engine can be run well lean of peak if so inclined without detonation. The CHT's will go down, markedly, LOP and at peak EGT. And peak EGT doesn't coincide with max CHT's according to the Lyc or TCM data...not by a long shot. Below 65% BHP,which is what we are talking about at full throttle for the DA described, TCM says it is fine to run at peak EGT. I can't see why a person wouldn't be safe to run peak EGT at the same DA during takeoff. But you really probably want best power anyway, not peak EGT, in conditions where your takeoff run is already nearly 2.5 times that at sea level due to DA.

If you are down low, then the power developed might mean the valves cant reject enough heat and the mixture needs to be adjusted.

So the thinking behind the (ROP) climb with constant EGT is that the combustion reaction maintaining the same temperature must therefore have the same stoichiometry?

Yes!

And why anyone should lean at any altitude, given they have an egine monitor or at least a single point EGT/CHT to verify.

Getting late here, gotta go. Will check in tomorrow.

Peace.

Do all you guys really run this shit through your heads as you takeoff ? I know it's in our brains but really ? Mixture is where it is from experience and different temps altitude ect. If I have painted myself into a corner and cant remember where my mixture was when I landed or somehow forgot everything the "elders" have told me then maybe I should not have landed somewhere where this comes into play.Engines like what they like and every single one is different ...I'm not debating numbers on engine science , how does it FEEL when you punch it. ? Does it bog , or purr really nice and mabye push your hed back when u go .?Feel the plane. Do the Bull dance.

Head not hed

lesuther wrote:Not really. At the DA discussed, the engine can be run well lean of peak if so inclined without detonation. The CHT's will go down, markedly, LOP and at peak EGT. And peak EGT doesn't coincide with max CHT's according to the Lyc or TCM data...not by a long shot. Below 65% BHP,which is what we are talking about at full throttle for the DA described, TCM says it is fine to run at peak EGT. I can't see why a person wouldn't be safe to run peak EGT at the same DA during takeoff. But you really probably want best power anyway, not peak EGT, in conditions where your takeoff run is already nearly 2.5 times that at sea level due to DA.

With the EGT vs CHT, my comment was premised on the fact that detonation was happening (which drives the CHT way up if it's serious). With normal combustion then you're right, they are quite some way apart. Once again you are quite right, if you're unable to develop high power, then detonation is a non-issue, but I assumed there are altitudes in the mid-range where they two can overlap (high power and leaning for T/O), thus my comment - better to be safe than $25k in a hole if you cook your engine. Maybe I am guilty of over-dramatising the risk?

The heart of my point was, taking-off at peak EGT would be almost as pointless as at full rich, from a getting-off-the-ground-fast point of view (at altitude). You're short changing yourself in terms of performance.

Harpoon1 has gone for the night, but he raises a good point about the risk of pre-ignition. I am rusty on that topic, but I thought it typically takes plug fouling or some hotspot to get into that territory under normal ops without extreme CHTs.

Some pilots get shit-scared of this stuff and run back to ROP ops whenever they can. I think Mike Busch is onto it, a good understanding of what's really happening inside your engine and solid knowledge goes a long way past the good 'ol "she'll be right" attitude and hearsay about cracked cylinders etc. Scare-mongering. Conversations like this are a great way to learn which is what I love.

You can get the same temperature LOP too, but with a much higher risk of detonation, does that therefore give the same results for the engine - I don't know if that rule holds?

Ah......not exactly, LOP does NOT have a much higher risk of detonation! I don't know where your getting that notion from. Again, the most Detonation prone mixture for ANY power setting is found at Best Power, which is around 50-80 ROP. Richer or Leaner than "Best Power" and the risk of detonation goes DOWN. That includes LOP mixture settings.

While Mike Busch may be "onto it", these guys broke the code! Again! Or, more precisely George Braly, Walter Atkinson and John Deakin (the 3 instructors behind Advanced Pilot Seminars) re-introduced the science and benefits of operateing LOP and precise Mixture Control. No old wives tale, half truths, superstitions or "awe shucks, I just lean it till it pops" crap. It's centered around scientific fact, without prejudice or "feelings".

These Deakin Columns may help unravel some of the confusion and old wives tales that come from well meaning old timers that abound around "mixture control".

"Detonation Myths"

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

"Mixture Magic"

http://www.avweb.com/news/pelican/182084-1.html

All of Johns columns on engine management are worth reading, again and again, until they connect ALL of the dots for you. IMO!

Harpoon1 wrote:Ah......not exactly, LOP does NOT have a much higher risk of detonation! I don't know where your getting that notion from. Again, the most Detonation prone mixture for ANY power setting is found at Best Power, which is around 50-80 ROP. Richer or Leaner than "Best Power" and the risk of detonation goes DOWN. That includes LOP mixture settings.

I will take a look at those materials, thank you for posting. I am getting my info from printed literature at home (can't hyperlink sorry!).

I prefix all this with "My understanding is" I'm here to learn!

The reason they say best power mixture is most detonation prone is because you're generating the most heat (highest temperatures & pressures) in the cylinders, and the air-fuel charge may become too hot before it is ignited, which may cause explosive combustion instead of a steady 'burn'.

The reason detonation (and pre-ignition) are both more likely at leaner mixture (not necessarily LOP, but leaner mixtures) settings is because there is less latent cooling from the fuel in the cylinders which richer mixture settings have. This allows the cylinders to get hotter, and the charge can heat up before it combusts and/or hotspots can form, especially if the plugs are fouled etc. Both of those are causes for detonation / pre-ignition.

If you know what you're doing and have a well instrumented engine, I accept detonation may be no more likely. For a stock-standard aircraft, especially with INOP posted on those "less useful" gauges like CHT - I'm sure you know what I mean, rental aircraft are rife with it - there is an increased risk of detonation and preignition if you lean agressively and don't know what's happening to your engine temps.

I agree that LOP there is so little fuel in there, that high temps would appear to be less of a problem. I think Mike says 50 ROP is the worst place to operate for that reason? About 50 ROP is also the EGT most pilots fly at, some with no problems at all - my good friend's engine is at 1000hrs over TBO and has run 80% of them 50 ROP.

A few things first.

I guess we need to define which "high temperature" you are referring too. High EGTs are basically irrelevant, only an X value. High CHTs otoh are not!

And they don't neccessarily go hand in hand. 50 LOP vs 50 ROP are the exact same EGT but result in much different CHT's. WHY? Internal cylinder/combustion pressure! Edited: Because 50 ROP produces higher ICP because the combustion event is more powerful than the 50 LOP combustion event. More fuel than air ROP. High internal cylinder pressure is the real problem, not high EGTs.

Respectfully, at the risk of sounding condescending, please read through Deakin's engine management columns first, then if you have any more questions I'll try to answer them.

It's not that this is that complicated but there is a lot of new ground to cover. New concepts to learn, old wives tales to forget/dismiss. Takes time.

Harpoon1 wrote:A few things first.

I guess we need to define which "high temperature" you are referring too. High EGTs are basically irrelevant, only an X value. High CHTs otoh are not!

And they don't neccessarily go hand in hand. 50 LOP vs 50 ROP are the exact same EGT but result in much different CHT's. WHY? Internal cylinder/combustion pressure! High internal cylinder pressure is the real problem, not high EGTs.

Respectfully, at the risk of sounding condescending, please read through Deakin's engine management columns first, then if you have any more questions I'll try to answer them.

It's not that this is that complicated but there is a lot of new ground to cover. New concepts to learn, old wives tales to forget/dismiss. Takes time.

Sir - I have read all those columns at length over a year ago, and I re-read them after my last post. I maintain my position, there is an increased risk in some situations. Those articles are carfully written, but do 'gloss over' other aspects which don't suit the point of their argument.

I was referring to CHT or combustion temp/pressure, as you say EGT does not factor in that particular discussion.

The point is made in your literature that "if detonation does not occur at 50 ROP, it will never occur at those power settings and CHTs" (paraphrase). That is the case on a particular TCM IO-470 with GAMI injection which I fly in sometimes. It will not detonate unless you fail to manage the engine. Other engines are not so forgiving, such as carburated engines with a hot cylinder - in those situatuations I suggest the risk is increased.