Flying over square
43 inches,
From post #261:
Shockcooling not a problem within allowed temp ranges?
While I agree operations outside those ranges are wrong, don't assume no damage can be done inside them!
Glider tugs for instance can crack cylinders very easily if throttle reduced too quickly on descent, a steady reduction of power is needed.[along with help from modern CHT warning systems and cowl flaps can help]
From post #261:
Shockcooling not a problem within allowed temp ranges?
While I agree operations outside those ranges are wrong, don't assume no damage can be done inside them!
Glider tugs for instance can crack cylinders very easily if throttle reduced too quickly on descent, a steady reduction of power is needed.[along with help from modern CHT warning systems and cowl flaps can help]
Grandpa Aerotart
When trying to get your head around rich mixtures 'cooling' the engine it might be more productive to think about oxy acetylene torches. Pure acetylene produces a lazy, dirty (sooty) 'cool' flame. As you squeeze the oxygen trigger on the torch you're leaning the mixture and it burns hotter and cleaner. Keep adding oxygen and you get that hot blue flame - peak EGT if you.
That is exactly how a rich mixture 'cools' your engine - it's more correct to say 'produces less heat' than cools.
That is exactly how a rich mixture 'cools' your engine - it's more correct to say 'produces less heat' than cools.
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jas24zzk
leaner = hotter, richer = cooler is for the combustion chamber.
ROP rich of peak is for peak exhaust temperature
LOP lean of peak is also for peak exhaust temperature
This might be where some of the disagreements are coming from.
That might need some re-thinking. If LOP is best power, why does you POH show a higher TAS for ROP than it does for LOP??
ROP rich of peak is for peak exhaust temperature
LOP lean of peak is also for peak exhaust temperature
This might be where some of the disagreements are coming from.
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leaner = hotter, richer = cooler is for the combustion chamber.
Wouldn't that would make LOP operations impossible, because the engine would get too hot?
http://www.warmkessel.com/jr/flying/td/jd/images/pelperch_aps_leaning_chart.jpg
This chart is the similar to those published by Lycoming, Continental, and various regulators.
What damages an engine? Heat.
Quite simply, the data shows that around peak EGT, the cylinder head temperatures, and so the internal pressure (pressure and temperature being directly proportional) are at their maximum. The reason that people keep making a big deal out of all this LOP/ROP thing is that it shocks us that the engine manufacturers give advice that is EXACTLY opposite to what the data suggests.
On other matters: While I'm no expert, I am willing to debate the concept of LOP in a carburetted engine, or without an engine monitor.
I think either is perfectly acceptable.
If you operate where the POH suggests you are already operating at the worst possible place. If you're flying at 50ROP you are producing the highest CHTs, and coupled with a high-ish power setting these may be too high. If you fly at 50ROP at high altitude or with a low setting, then that of course may be fine.
My point is, if you have no idea what your EGTs/CHTs are, and you lean as per the flying school "till the engine is rough, then richen till smooth", you likely have cylinders that are LOP, and some that are ROP. The roughness was the leanest "falling off" the BHP curve as shown in the graph. So if you mixture distribution is good you may have part of your engine LOP anyway! This being without intending to operate beyond peak, because as everyone know, engines explode there.
So you have two options:
Lean as far as possible for fuel economy and to keep your engine clean, and at a sensibly low power setting to ensure that the cylinders close to peak are happy.
Or, fly conservatively rich at whatever setting you want. Noting of course that mixture alters the power produced, and most tables include the condition that best power is set.
These are only my opinions, largely collected from reviewing the data available, so feel free to disagree.
Last edited by Aerozepplin; 19th Oct 2011 at 02:54. Reason: quoting failure
The way I have always thought of it is fire needs fuel, air and heat (ie; spark). At a certain level these give the biggest flame (therefore hottest and most powerful). Any change to fuel or air (you can't change spark in flight) from this certain level will result in a cooler, less powerful and more 'wasteful' flame.
By wasteful I mean something won't be totally burnt at ROP this is fuel and therefore 'dirty' and LOP this is air therefore 'clean'.
Is this a fairly accurate simple summary?
By wasteful I mean something won't be totally burnt at ROP this is fuel and therefore 'dirty' and LOP this is air therefore 'clean'.
Is this a fairly accurate simple summary?
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Walls of China and others.....do we need to go through this all again? The hard part is explaining every little detail here in a post on pprune.
I am seriously thinking of start an APS type seminar process like they have in the USA, and I have thought about colaboration with one particular engine shop that has the gear. Other option is bring the boys from APS out, but that is not as easy as it sounds. I have talked to them about it.
So lets get a few things straight, and best you all learn to love this chart, this is not some GAMI produced slant on things (take note Trent) it is universally accepted and has been from day dot. It appears in some of your engine manuals and other engine manufacturer documents.
This one I believe is coutesy of TCM.
And study this one hard too, coutesy of Advanced Pilot Seminars
Some of you guys are really well off the track. A bit of your version of OWT's.
Walls Of China, can I suggest you contact me via PM, I am happy as always to help educate folk but it requires several things not possible on here I have found. Namely a lot of documentation, a long phone call or two, and some desire to go out and prove it to yourself. If you want to see why your leaner = hotter comments above raise my eyebrows I suggest you spend a few bucks and come up here so I can show you.....heck I might even let you do it yourself and watch with your own eyes.
In summary, looking at the TCM graph, a richer mixture is a lethagic mixture (hard to get going bang) and is containing more available BTU's than a leaner one. As you lean you get a mixture more volatile and it goes bang better and quicker giving you a bigger PPP and one closer to TDC, this is when you get more force and x crank distance torque and at a given RPM > Power. You also get a rising CHT. Going richer again just reverses all that and the CHT goes down again. As Chimbu chuck said, its not cooling, its just creating less heat to begin with.
As you lean past peak EGT you start getting a more lethagic mixture again, less of them BTU or calorie thingo's, less PPP and at a crank position further from TDC again, and guess what....dropping CHT's.
If anyone does not get this, I am serious at a cost sharing basis of flight and pay me for my time I will arrange a ad hoc seminar at YCAB, we can all go play....and no I do not think for one minute you will kill my IO540, and you can learn for yourselves. I have all the gear and it may just save your life one day, by knowing what your engine monitor tells you. If we get a small bunch of keen folk together it will be a fun day, or two, and will not cost everyone a fortune. I doubt I will retire on the proceeds, but it will be fun and educational for all of us.
Where is Warbo?......he was kind enough to let me fly his beautiful 185 while we did exactly this. Was a great exercise.
PM me if you are interested.......and bring your CFI/Gr 3 instructors along too
I am seriously thinking of start an APS type seminar process like they have in the USA, and I have thought about colaboration with one particular engine shop that has the gear. Other option is bring the boys from APS out, but that is not as easy as it sounds. I have talked to them about it.
So lets get a few things straight, and best you all learn to love this chart, this is not some GAMI produced slant on things (take note Trent) it is universally accepted and has been from day dot. It appears in some of your engine manuals and other engine manufacturer documents.
This one I believe is coutesy of TCM.
And study this one hard too, coutesy of Advanced Pilot Seminars
Some of you guys are really well off the track. A bit of your version of OWT's.
Walls Of China, can I suggest you contact me via PM, I am happy as always to help educate folk but it requires several things not possible on here I have found. Namely a lot of documentation, a long phone call or two, and some desire to go out and prove it to yourself. If you want to see why your leaner = hotter comments above raise my eyebrows I suggest you spend a few bucks and come up here so I can show you.....heck I might even let you do it yourself and watch with your own eyes.
In summary, looking at the TCM graph, a richer mixture is a lethagic mixture (hard to get going bang) and is containing more available BTU's than a leaner one. As you lean you get a mixture more volatile and it goes bang better and quicker giving you a bigger PPP and one closer to TDC, this is when you get more force and x crank distance torque and at a given RPM > Power. You also get a rising CHT. Going richer again just reverses all that and the CHT goes down again. As Chimbu chuck said, its not cooling, its just creating less heat to begin with.
As you lean past peak EGT you start getting a more lethagic mixture again, less of them BTU or calorie thingo's, less PPP and at a crank position further from TDC again, and guess what....dropping CHT's.
If anyone does not get this, I am serious at a cost sharing basis of flight and pay me for my time I will arrange a ad hoc seminar at YCAB, we can all go play....and no I do not think for one minute you will kill my IO540, and you can learn for yourselves. I have all the gear and it may just save your life one day, by knowing what your engine monitor tells you. If we get a small bunch of keen folk together it will be a fun day, or two, and will not cost everyone a fortune. I doubt I will retire on the proceeds, but it will be fun and educational for all of us.
Where is Warbo?......he was kind enough to let me fly his beautiful 185 while we did exactly this. Was a great exercise.
PM me if you are interested.......and bring your CFI/Gr 3 instructors along too
Jaba,
My experience with these engines was a long time ago, [Jets or gliders mostly last 20+ years
], the only independent cylinder EGT/CHT indicators showed a fair difference between cylinders at some times. Most EGT indicators were only on one cylinder from memory.
Do you lean on the hottest, coolest, richest, leanest, average?
My experience with these engines was a long time ago, [Jets or gliders mostly last 20+ years
], the only independent cylinder EGT/CHT indicators showed a fair difference between cylinders at some times. Most EGT indicators were only on one cylinder from memory.Do you lean on the hottest, coolest, richest, leanest, average?
On other matters: While I'm no expert, I am willing to debate the concept of LOP in a carburetted engine, or without an engine monitor.
There is another factor affecting effective leaning of an engine and that is vibration. The smoother you can get the engine to run the longer the engine componants and accesories will last. Too rich there is above normal vibration, and too lean in most engines it will run rough before it cuts out.
Quite simply, the data shows that around peak EGT, the cylinder head temperatures, and so the internal pressure (pressure and temperature being directly proportional) are at their maximum. The reason that people keep making a big deal out of all this LOP/ROP thing is that it shocks us that the engine manufacturers give advice that is EXACTLY opposite to what the data suggests.
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Lycoming has some good notes on the whole thing.
Lycoming Flyer Operations (4.5MB pdf)
Two entries in the flyer answer the original question;
page 43; An Explanation Of Power Settings
page 65; A Review of Old Wives Tales
43inches MAP + 2575 RPM = 350hp (ISA, SL) = Happy Chieftain at take-off
page 43; An Explanation Of Power Settings
page 65; A Review of Old Wives Tales
43inches MAP + 2575 RPM = 350hp (ISA, SL) = Happy Chieftain at take-off
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Jaba,
My experience with these engines was a long time ago, [Jets or gliders mostly last 20+ years
], the only independent cylinder EGT/CHT indicators showed a fair difference between cylinders at some times. Most EGT indicators were only on one cylinder from memory.
Do you lean on the hottest, coolest, richest, leanest, average?
My experience with these engines was a long time ago, [Jets or gliders mostly last 20+ years
], the only independent cylinder EGT/CHT indicators showed a fair difference between cylinders at some times. Most EGT indicators were only on one cylinder from memory.Do you lean on the hottest, coolest, richest, leanest, average?
So your question do you lean to???? How would you ever really know? You have no way of telling just from those instruments.
For a friend who recently aquired an RV6 with 0-320 and fixed pitch prop, I was able to calculate by looking at graphs and knowing what fuel flows should be, a suggested engine setting for cruising at 5500-9500. This worked rather well. He reported excellent speeds (faster than 2 x 7's and a 6 on the trip and less fuel burn.) and his CHT was a bit lower than running ROP. So you can assume I guessometrically calculated that spot on
.The other RV6 with a slower speed and way higher fuel burn must not know what the mixture knob is for.
So you can do it..........but I am not about to start trying to explain it on here, we have enough trouble getting the basics through
.43inches
There is no problem with heat at all LOP, if there is you must of exceeded your peak EGT limit on the way there.
Except for the TIT in your chieftan, there really is no such thing. Apart from anything else it will vary depending on probe location.
A float type carby would almost be impossible to get even fuel distribution to all pots,
Some will, and some won't and some will only if you experiment a heap to get it there.
The main point they make continuously is that non of their engines should be leaned at high power (above 75% non turbo or abv 65% turbo)
And from the Lycoming Flyer, I love the way TCM and Lycoming have tip toed backwards on LOP operations over the years, you can see it in the way they write stuff
, but what is rather disturbing is this little gem. Seems old habbits die hard
In the
climb configuration, we recommended full throttle throughout the climb for internal fuel cooling with RPM reductions initially to 3000 RPM and then 2750 RPM for prolonged climb.
climb configuration, we recommended full throttle throughout the climb for internal fuel cooling with RPM reductions initially to 3000 RPM and then 2750 RPM for prolonged climb.
What is your peak EGT limit 
Except for the TIT in your chieftan, there really is no such thing. Apart from anything else it will vary depending on probe location.
Except for the TIT in your chieftan, there really is no such thing. Apart from anything else it will vary depending on probe location.
The manufacturers write their books based on the lowest common denominator. They stay away from LOP because if they started even giving the slightest hint its ok we all know some pilots who would be sitting 50 LOP full power in the climb with the engine shaking itself off its mounts "But I'm saving fuel!". To their credit they do have a disclaimer there effectively saying that if you do have the right equipment to monitor the engine and know how to use it you may lean to your hearts desire....
Last edited by 43Inches; 19th Oct 2011 at 09:07.
Grandpa Aerotart
I have climbed my Bonanza LOP-was smooth as a baby's bum. The engine doesn't know what phase of flight it's in. As long as you keep your speed up it's fine-of course in a NA aircraft your ROC will be unacceptable by the time you're at 5000', but in a turbo you can climb LOP as high as you like.
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Agreed Chimbu Chuckles
Mind you the retard vehicle will climb at a few hundred feet per minute at 9-11k feet while LOP.
I am gong to "borrow" a phrase from George Brayly, and folks this is GOLD.
It's not how hard you run your engine, It's how you run your engine hard!
Mind you the retard vehicle will climb at a few hundred feet per minute at 9-11k feet while LOP.
I am gong to "borrow" a phrase from George Brayly, and folks this is GOLD.
It's not how hard you run your engine, It's how you run your engine hard!
Last edited by Jabawocky; 19th Oct 2011 at 10:39.
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Thinking about Jaba's quote...
The engineering in these things has always amazed me. You get talking to people 'that know' and they scoff at air cooling. (seems to work to me) They are then amazed that we tell them we run em at 75% power till the fuel runs out. (well ok almost)
They squat on the belief that no factory (unmodified) engine can do that, and insist its been modified.
You watch them shake their heads in disbelief when you tell em a 540 only makes 300hp or so. Then they really fall over when you tell em the operator (pilot) has control over mixture, normally answered with 'why the **** would they let you do that' Some (most) mechanics really should stick to changing oil.
TBH I really think few pilots really understand this stuff, and the attitude of most CPL's doesn't help, as most are too busy studying for the next rating to go take a sidestep for this stuff (and no not trying to wind anyone up), but surely they could ensure the student knows where to get it. If it was taught properly at PPL level there wouldn't be any OWT's floating about. Maybe the schools should look to appoint someone to teach this stuff as a specialist...from the get go.
If it's not addressed, and it has to be, as The info I see and hear too often, says that what is being taught is getting worse. Then engines are going to suffer, and owners will decide to either opt out, or decide that its cheaper to fit a FADEC, and the knowledge will become just another victory for the IT nerds.
Jas
The engineering in these things has always amazed me. You get talking to people 'that know' and they scoff at air cooling. (seems to work to me) They are then amazed that we tell them we run em at 75% power till the fuel runs out. (well ok almost)
They squat on the belief that no factory (unmodified) engine can do that, and insist its been modified.
You watch them shake their heads in disbelief when you tell em a 540 only makes 300hp or so. Then they really fall over when you tell em the operator (pilot) has control over mixture, normally answered with 'why the **** would they let you do that'
Some (most) mechanics really should stick to changing oil.TBH I really think few pilots really understand this stuff, and the attitude of most CPL's doesn't help, as most are too busy studying for the next rating to go take a sidestep for this stuff (and no not trying to wind anyone up), but surely they could ensure the student knows where to get it. If it was taught properly at PPL level there wouldn't be any OWT's floating about. Maybe the schools should look to appoint someone to teach this stuff as a specialist...from the get go.
If it's not addressed, and it has to be, as The info I see and hear too often, says that what is being taught is getting worse. Then engines are going to suffer, and owners will decide to either opt out, or decide that its cheaper to fit a FADEC, and the knowledge will become just another victory for the IT nerds.
Jas
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Good point about the FADEC there jas, the problem is the old mixture cable is more reliable in a mechanical sense. I am an automation person, heck it is what I do for a living, but automation relies on good inputs either digital or analog.
If I have an egt probe fail in some way, or if in fact they all do, I can still operate LOP just as the FADEC does however if it starts to lose a few sensory inputs it has no idea what to do and has to default to some preset performance.
Give me a properly tuned IO-XXX with manual controls and an EMS any day ov a FADEC.
I started to read that Lycoming Flyer closer last night, I read one paragraph out to Mrs Jaba and even she was shocked
, so my task apart from work today is go through it and highlight those little GEM's that are lurking in there as a result of a re-write that missed a lot of OWT's . They went to great trouble to dispell the myth of over square, but left so much behind.
PS jas that was not my quote.....it was George Brayly.
If I have an egt probe fail in some way, or if in fact they all do, I can still operate LOP just as the FADEC does however if it starts to lose a few sensory inputs it has no idea what to do and has to default to some preset performance.
Give me a properly tuned IO-XXX with manual controls and an EMS any day ov a FADEC.
I started to read that Lycoming Flyer closer last night, I read one paragraph out to Mrs Jaba and even she was shocked
, so my task apart from work today is go through it and highlight those little GEM's that are lurking in there as a result of a re-write that missed a lot of OWT's . They went to great trouble to dispell the myth of over square, but left so much behind.PS jas that was not my quote.....it was George Brayly.
Interesting to note that the Lycoming recomended procedure for economy leaning a normally aspirated engine will result in LOP operation in a good engine. The procedure requires mixture to be leaned until rough or significant loss of power occurs and then enrichen only sufficiently to regain smooth reasonable power operation. If the engine is able to run smoothly LOP then this procedure will result in LOP operation.
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Sit still Jabba, you're a moving target. Let's just stay with FADEC for the exercise. I decided to do some reading and found good support for LOP and long engine life in a number of reports. Didn't find any recommendation from Continental, and didn't find any empirical evidence for it. The Gami site firmly supported it, and although they are selling injectors, made sense in what they said. They gave an example of a Cirrus SR22 with Continental O-550N engine and FADEC (Full Authority Digital Engine Control) of 2200 hours against the only stated TBO I could find of 1700 hours.
That's one single case, but I read a lot of similar claims where the consensus was that with fuel injection, telemetry and control like FADEC the engine could be managed for a satisfactory life.
Bear in mind, with the pressure of reducing emissions such as cancer causing Nox and Particulates, engine manufacturers are using digital technology to do different things at different times of the stroke including multiple injector shots at different times with the intent of burning non combusted items etc. and also to allow operation at leaner mixtures to substantially reduce fuel consumption because of the ever growing cost of fuel.
Add all this together and LOP makes a lot of sense.
What DIDN'T have much support was running LOP on a carburetted engine because there is a lot less control accuracy, and the power output from each cylinder will be different, so you don't really know what you are doing to the engine with the settings you are using. Flow balancing, where the inlet side of the engine is modified so all cylinders produce the same power, is a way to get closer, but if you really want the reduced fuel consumption maybe the solution is to run the engine out then upgrade to the newer technology.
Maybe I shouldn't have jumped in with basic engine principles because this thread was all about operating an engine at reduced power and lower rpm compared to the full power output situation.
However, some of the comments strayed away from peak exhaust gas temperature and into the combustion chamber itself.
The Chart which Jabba attributed to TCP shows up all over the place, and is part of a powerpoint presentation called gregs_show, and shows a Cylinder Head Temperature curve related to Exhaust Gas Temperature curve in a typical less-than-full power manipulation of air/fuel ratio.
I agree, if I came up Jabba, you could show me how you could replicate this, but then I could show you how I could melt your pistons, because I've melted a few.
The relatively even cylinder head temperature you see on a gauge is the net result of a number of temperature changes dancing around the combustion chamber at various points in the cycle.
My original comments about lean being hotter and rich being cooler relates to gas temperature in the chamber in response to Clint's comment, and your #262 and #264.
The chemical and physical properties of air don't change. When it's compressed it heats, when it expands it cools.
On the compression stroke, intake air is compressed and heats to a peak at top dead centre. The flame front then kicks in and there is a momentary second rise followed by a rapid fall as the gas expands.
If the mixture is too lean, it's all burnt and there is nothing left to cool the second rise, so it doesn't take long for any protrusions such as spark plug electrodes, piston edges and valves to start to deteriorate or melt.
If the mixture is rich, there is a flow of unburnt fuel over these items, cooling them.
Since gasolene has a very narrow band of tolerance for combustion, and doesn't have to be very rich for the engine to run rough, Jabba as you've found you don't see it dripping out the exhaust.
To make this easier to understand, let's look at methanol where the engine will make full power with an extremely rich mixture. Only a fraction of this is burnt, and the methanol is virtually like a garden hose turned on your engine.
I'm able to make an aircooled engine pump out maximum power reliably in an enclosed compartment with no vents, and if you look at a Top fueler dragster you'll see methanol streaming out at low rpm (it's turned into a gas at full power)
So in discussing the subject of this thread, the theory needs to stay out in the exhaust temp, cruise power, and mixture control area.
That's one single case, but I read a lot of similar claims where the consensus was that with fuel injection, telemetry and control like FADEC the engine could be managed for a satisfactory life.
Bear in mind, with the pressure of reducing emissions such as cancer causing Nox and Particulates, engine manufacturers are using digital technology to do different things at different times of the stroke including multiple injector shots at different times with the intent of burning non combusted items etc. and also to allow operation at leaner mixtures to substantially reduce fuel consumption because of the ever growing cost of fuel.
Add all this together and LOP makes a lot of sense.
What DIDN'T have much support was running LOP on a carburetted engine because there is a lot less control accuracy, and the power output from each cylinder will be different, so you don't really know what you are doing to the engine with the settings you are using. Flow balancing, where the inlet side of the engine is modified so all cylinders produce the same power, is a way to get closer, but if you really want the reduced fuel consumption maybe the solution is to run the engine out then upgrade to the newer technology.
Maybe I shouldn't have jumped in with basic engine principles because this thread was all about operating an engine at reduced power and lower rpm compared to the full power output situation.
However, some of the comments strayed away from peak exhaust gas temperature and into the combustion chamber itself.
The Chart which Jabba attributed to TCP shows up all over the place, and is part of a powerpoint presentation called gregs_show, and shows a Cylinder Head Temperature curve related to Exhaust Gas Temperature curve in a typical less-than-full power manipulation of air/fuel ratio.
I agree, if I came up Jabba, you could show me how you could replicate this, but then I could show you how I could melt your pistons, because I've melted a few.
The relatively even cylinder head temperature you see on a gauge is the net result of a number of temperature changes dancing around the combustion chamber at various points in the cycle.
My original comments about lean being hotter and rich being cooler relates to gas temperature in the chamber in response to Clint's comment, and your #262 and #264.
The chemical and physical properties of air don't change. When it's compressed it heats, when it expands it cools.
On the compression stroke, intake air is compressed and heats to a peak at top dead centre. The flame front then kicks in and there is a momentary second rise followed by a rapid fall as the gas expands.
If the mixture is too lean, it's all burnt and there is nothing left to cool the second rise, so it doesn't take long for any protrusions such as spark plug electrodes, piston edges and valves to start to deteriorate or melt.
If the mixture is rich, there is a flow of unburnt fuel over these items, cooling them.
Since gasolene has a very narrow band of tolerance for combustion, and doesn't have to be very rich for the engine to run rough, Jabba as you've found you don't see it dripping out the exhaust.
To make this easier to understand, let's look at methanol where the engine will make full power with an extremely rich mixture. Only a fraction of this is burnt, and the methanol is virtually like a garden hose turned on your engine.
I'm able to make an aircooled engine pump out maximum power reliably in an enclosed compartment with no vents, and if you look at a Top fueler dragster you'll see methanol streaming out at low rpm (it's turned into a gas at full power)
So in discussing the subject of this thread, the theory needs to stay out in the exhaust temp, cruise power, and mixture control area.
Last edited by Wallsofchina; 20th Oct 2011 at 00:51.