Lean of Peak Operation On Australian Avgas?
Grandpa Aerotart
An interesting PM from an old mate who has been flying Chieftains relatively recently...and for a smarter than average operation/CP.
My Chieftain manual does not appear to state any particular limit but.....
When I was doing casual work for XXXXX, company policy stated that the engines could be run flat out, ie full throttle and 2575rpm BUT at full rich mixture!!!!
Also; leaning in the climb (40''MAP 2400rpm) was streng verboten!!
Others have already covered this which is why I have'nt posted to this effect.
When I was doing casual work for XXXXX, company policy stated that the engines could be run flat out, ie full throttle and 2575rpm BUT at full rich mixture!!!!
Also; leaning in the climb (40''MAP 2400rpm) was streng verboten!!
Others have already covered this which is why I have'nt posted to this effect.
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The Cirrus uses an Avidyne engine monitoring system that allows the operator to manutally select via the red knob a mixture that is electronically monitored to achieve best economy, best power, etc, etc. I have heard of Cirrus's with severely damaged engines due to lean operation.
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Yes. I have heard of damage due to inappropriate operation. I have no idea how lean the operator ran it. The one I'm thinking of must have tried to save on his fuel bill.
All the radial engined airliners such as the Connies, DC-6, DC-7, Convairs etc etc., operated MILLIONS of hrs lean of peak, the only way they could achieve the range required for trans-Atlantic and trans-Pacific ops. Only they didnt have sophisticated EGT guages then, so they used BMEP instruments instead. Now that we have the technology tosee whats happening in the cylinder in real time, we discover that they were running LEAN OF PEAK.
I guess that millions of hrs experiance does not count for much in the light of conventional GA wisdom.
Count me in for the Advanced Pilot Seminar in Sydney.
I guess that millions of hrs experiance does not count for much in the light of conventional GA wisdom.
Count me in for the Advanced Pilot Seminar in Sydney.
Grandpa Aerotart
You can't just make sweeping statements like,
How do you know it wasn't a manufacturing quality control issue?
What damage have they suffered?
In who's opinion is it damage caused by 'leaning'?
What leaning practice was he using 'to save money on fuel bill'?
With respect your post makes no more sense than the post that started this thread.
I have heard of Cirrus's with severely damaged engines due to lean operation.
What damage have they suffered?
In who's opinion is it damage caused by 'leaning'?
What leaning practice was he using 'to save money on fuel bill'?
With respect your post makes no more sense than the post that started this thread.
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I was just saying that I knew of particular aircraft that were damaged by running too lean. The main one that I know of was confirmed as operator error. The purpose of the post I guess was because others made reference to the Cirrus being 'wizz bang' and I am saying that even a gucci alleged electronic masterpiece still suffers from cracked cylinders etc when run lean.
EMax Engine Monitor
From the Cirrus Design site. It would appear that the features are similar to a digital engine monitor with individual EGT gauges. So it still comes down to ham fisted operators not understanding what the machine is telling them if a Cirrus engine gets fried. It is not the fault of the technology, just the biological interface device
From the Cirrus Design site. It would appear that the features are similar to a digital engine monitor with individual EGT gauges. So it still comes down to ham fisted operators not understanding what the machine is telling them if a Cirrus engine gets fried. It is not the fault of the technology, just the biological interface device
Grandpa Aerotart
I knew of particular aircraft that were damaged by running too lean.
This is important...the biggest hurdle to understanding and practicing modern engine management (assuming aircraft capability-which the Cirrus has in spades) is precise language...and not just from relatively innexperienced pilots...veteran engineers/pilots are often the worst offenders.
The graph above is one of the ones used in the pilot seminars referenced earlier in the thread.
It is a portion of the mixture spectrum...left side is rich (but not full rich) and the right is lean (but not idle cutoff). It is important to realise that MP/RPM are held constant in this graph...25/25 from memory...the ONLY thing being varied is mixture.
From top to bottom the lines show EGT, CHT, ICP (internal combustion pressure in the cylinder), HP and 'mpg' for want of a better term...economy if you like. It is actually Brake Specific Fuel Consumption (BSFC= how much fuel it takes to make 1 hp for 1 hr) inverted so it peaks with the rest rather than curving the other way as less fuel is required to make 1 hp.
Think of this being for just a one cylinder engine...the reality is that this mixture sweep represents an average of 6 cylinders with balanced injectors...but for the sake of clarity think of it as just 1 cylinder.
As you lean from richer towards leaner the EGT, CHT, ICP and HP all rise and the engine becomes more efficient...HP, CHT and ICP peak first...so the most heat and pressure experienced by that 1 cylinder happens before peak EGT...about 50F before (ROP) peak EGT.
That is why 50F ROP is deadly for engines above 65% power...because there is enough oxygen to mix with all that fuel so that those peak CHTs/ICPs are high enough to weaken the cylinder metal or cause imperfections like a busted helicoil tang to get hot enough to set off the next intake fuel/air charge prematurely (pre ignition)...which can lead to detonation and engine failure.
Now we lean a bit further...at peak EGT our CHT, ICP, HP are all falling away- a cooler, less stressed engine developing a little less HP...but economy is still improving.
A fraction leaner is where most engines start to run rough...and where we have been taught historically to stop leaning and enrichen "2-3 graduations" on the old EGT gauge...typically each graduation on an GT gauge = 25F...that takes you straight back to peak heat and pressure at about 30-80F ROP EGT
Now a single cylinder engine doesn't run rough..only a bunch of cylinders developing different HP run rough. This is because standard injectors can have up to +/- 4% variation from nominal flow rates. Look at the above graph and imagine that the 1 cylinder of your 6 cylinder engine that has an EGT & CHT probe shows you have just hit peak EGT...freeze the action...now think about all the other cylinders that have different flow rates from the other individual injectors...those flowing at a higher rate will be producing a richer mixture in their respective cylinder and those with a lower flow rate will be producing a leaner mixture in their respective cylinder....6 cylinders all developing different HP, CHT and ICP...and economy for that matter...all bolted together causing the engine to shake like a dog passing a watermelon.
As we have 'frozen the action' at peak EGT which cylinders are better off?
Tell me again about 'too lean'?
Last edited by Chimbu chuckles; 3rd Jul 2007 at 01:54.
Grandpa Aerotart
A typical engine with standard injectors would have 5 other sets of identical curves all in the same relationship to one another but dissplaced left and right of the central peak EGT dotted line of the one cylinder you can read about on the instruments.
That was the way my engine was before the Gamijectors were installed...a flow rate difference (Gamispread) between the richest and leanest injectors of approx 2-3usg/hr...with the gamis it is .3usg/hr.
Now when I lean my engine all the EGTs/CHTs rise in lock step just like the graph above...and all fall LOP in lock step-like the graph above...CHT is also a direct indication of ICP an once LOP there is a direct correlation with HP. 6 cylinders acting as one.
The engine doesn't 'run rough' so I can just keep on leaning...I get the first hint of roughness at around 80F LOP EGT. Look on the above graph and see what 80F LOP EGT equates to CHT, ICP and HP wise. The HP is so low it is past the point of efficient unless you're only concerned with endurance rather than range...so I operate around 50F LOP.
Too lean?
Engines are not damaged by 'too lean' as such...they just stop running.
They can however be damaged by not being lean enough...or rich enough.
They are most likely to be damaged by operating as per what pilots have for decades perceived to be 'by the book'. That is they forgot, or were not told, that 50F ROP was ONLY acceptable at 65% power and below...say 21/23...not at 23/24...at 23/24 100 ROP would be the minimum...look at the grpah above and see how ROP you need to be to make a difference.
The reference point for lean or rich is peak EGT...without a reference point words like 'too lean' are meaningless.
Now think about those Chieftains being operated leaned at climb power...think about 1 or 2 injectors being at the low end of the acceptable range of flow rate...that cylinder would be a lot leaner than the others so that cylinder would be developing much higher CHT and ICP...and with 38in MP (LOTS of air) all that fuel would be quite capable of producing LOTS of CHT/ICP...and without an all cylinder monitor you haven't the first fecking clue.
Enough CHT/ICP can cause pre ignition all by itself...without a busted helicoil or lead fouling to provide a glowplug like effect for the next charge of fuel and air through the inlet valve...like a diesel it just explodes earlier than it should...very, VERY bad news for the piston/crankshaft/Cylinder head...and pilot
That was the way my engine was before the Gamijectors were installed...a flow rate difference (Gamispread) between the richest and leanest injectors of approx 2-3usg/hr...with the gamis it is .3usg/hr.
Now when I lean my engine all the EGTs/CHTs rise in lock step just like the graph above...and all fall LOP in lock step-like the graph above...CHT is also a direct indication of ICP an once LOP there is a direct correlation with HP. 6 cylinders acting as one.
The engine doesn't 'run rough' so I can just keep on leaning...I get the first hint of roughness at around 80F LOP EGT. Look on the above graph and see what 80F LOP EGT equates to CHT, ICP and HP wise. The HP is so low it is past the point of efficient unless you're only concerned with endurance rather than range...so I operate around 50F LOP.
Too lean?
Engines are not damaged by 'too lean' as such...they just stop running.
They can however be damaged by not being lean enough...or rich enough.
They are most likely to be damaged by operating as per what pilots have for decades perceived to be 'by the book'. That is they forgot, or were not told, that 50F ROP was ONLY acceptable at 65% power and below...say 21/23...not at 23/24...at 23/24 100 ROP would be the minimum...look at the grpah above and see how ROP you need to be to make a difference.
The reference point for lean or rich is peak EGT...without a reference point words like 'too lean' are meaningless.
Now think about those Chieftains being operated leaned at climb power...think about 1 or 2 injectors being at the low end of the acceptable range of flow rate...that cylinder would be a lot leaner than the others so that cylinder would be developing much higher CHT and ICP...and with 38in MP (LOTS of air) all that fuel would be quite capable of producing LOTS of CHT/ICP...and without an all cylinder monitor you haven't the first fecking clue.
Enough CHT/ICP can cause pre ignition all by itself...without a busted helicoil or lead fouling to provide a glowplug like effect for the next charge of fuel and air through the inlet valve...like a diesel it just explodes earlier than it should...very, VERY bad news for the piston/crankshaft/Cylinder head...and pilot
Last edited by Chimbu chuckles; 2nd Jul 2007 at 16:07.
I was just saying that I knew of particular aircraft that were damaged by running too lean
When operating an engine at 70°LOP you are about 170°F away from peak engine temps, peak pressures, peak power, peak everything. The engine runs cool, it runs clean and the CHT's are way, way down. You won't junk the cylinders, you won't bugger up the valves and you'll have a nice light gray/brown exhaust pipe at the end of your trip (it's usually the first thing I do after exiting the aircraft at the completion of a long leg - the wife still doesn't understand why I get so excited when inspecting the end of exhaust pipe and noting the nice uniform shade of light gray up inside the end of it).
The LOP debate has been going on here for some time now and this thread has nothing new to add. So to save us all from having to type out a reply to the post, do an LOP search, read the posts and if you've got something fresh and new to add we're listening.
CC, I agree with your sentiment, but this applies only to the greasy, whizzy, spinny bits. As far as engine control is concerned, an engine is an engine is an engine.
The key difference between automotive and aerospace electronic engine control is that aerospace demands fail-safe and/or backup in all situations to prevent falling out of the sky. Actually, it might surprise you how much you can disconnect before an automotive ECU gives up, but unfortunately the fuel pump isn't part of this list.
A
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PA 31 Climb
It is interesting that the Chieftain POH states leaning to 30 GPH in the climb.
There is however a limit of 1500 deg F EGT, which is rarely reached.
Many pilots actually lean to the 1500 deg F, ignoring the 30 GPH POH requirement.
There is however a limit of 1500 deg F EGT, which is rarely reached.
Many pilots actually lean to the 1500 deg F, ignoring the 30 GPH POH requirement.
Folks,
ALL avgas produced in Australia conforms to exactly the same ASTM standard as in US, and I would suggest that, after the Mobil fuel contamination of late 1999, very close attention is paid to QC by the remaining refiners.
There is NO difference between the octane ratings of 100LL and 100/130.
Perhaps somebody else would like to let the "LOP don't work" brigade know what 100/130 actually means.
Tootle pip!!
ALL avgas produced in Australia conforms to exactly the same ASTM standard as in US, and I would suggest that, after the Mobil fuel contamination of late 1999, very close attention is paid to QC by the remaining refiners.
There is NO difference between the octane ratings of 100LL and 100/130.
Perhaps somebody else would like to let the "LOP don't work" brigade know what 100/130 actually means.
Tootle pip!!
