Lean of Peak Operation On Australian Avgas?
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Lean of Peak Operation On Australian Avgas?
At a short morning smoko, it was mentioned that a certain speaker on care and feeding of engines, at a forum for owners of certain aircraft type, strongly advised against "Lean of peak EGT" operations even when fitted with a you beaut JPI instrument and GAMI injectors.
The reason being, according to this gentleman, is that Australian avgas is of inferior quality to American avgas, and that therefore there is less margin for error, and one is risking ones engine by using this dubious practice here. Furthermore, the apparent trap for young players is that when you lose a few horsepower going lean of peak, the tendency is to increase MAP to get the speed back, thus risking detonation.
At this point the argument got too technical and waltzed into altering the ignition timing or some such.
Is Aussie Avgas crap compared to the American product?
The reason being, according to this gentleman, is that Australian avgas is of inferior quality to American avgas, and that therefore there is less margin for error, and one is risking ones engine by using this dubious practice here. Furthermore, the apparent trap for young players is that when you lose a few horsepower going lean of peak, the tendency is to increase MAP to get the speed back, thus risking detonation.
At this point the argument got too technical and waltzed into altering the ignition timing or some such.
Is Aussie Avgas crap compared to the American product?
Grandpa Aerotart
If you're quoting said individual accurately he clearly has not the first clue on the subject.
Quite apart from his statement re avgas specs being doubtfull (do we really think it varies THAT much), if he understood the topic he would know that increasing 'MAP to get the speed back' leans the mixture further and further reduces the possibility of detonation...not the other way around
It is a little hard to see on the above graphic because I have reduced it down to fit here...the orange dashed line is detonation margin at redline CHT, the orange dotted line at 50F below redline CHT and the yellow dotted line is 100F below redline CHT.
Quite apart from his statement re avgas specs being doubtfull (do we really think it varies THAT much), if he understood the topic he would know that increasing 'MAP to get the speed back' leans the mixture further and further reduces the possibility of detonation...not the other way around
It is a little hard to see on the above graphic because I have reduced it down to fit here...the orange dashed line is detonation margin at redline CHT, the orange dotted line at 50F below redline CHT and the yellow dotted line is 100F below redline CHT.
Last edited by Chimbu chuckles; 29th Jun 2007 at 06:45.
Inferior Avgas
It is my understanding that Avgas is produced to meet a required specification, and that this is far more exact than car fuel in some countries. Therefore there should be no concern regarding the "quality" of Australian avgas, and hence no angst regarding LOP operations.
Mogas may be a different matter, as I understand that there are seasonal variations in the specifications for motor spirit (summer/winter).
Mogas may be a different matter, as I understand that there are seasonal variations in the specifications for motor spirit (summer/winter).
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Err..... Executive summary of the coroners findings
http://www.airsafety.com.au/whyalla/whyalla.pdf
few words at the end there about lean mixtures.....
http://www.airsafety.com.au/whyalla/whyalla.pdf
few words at the end there about lean mixtures.....
Grandpa Aerotart
One of the things that really annoys me on this website and in general is people's innability to read and comprehend the written word.
A quote from the POH for the Chieftain...as presented within the report linked above.
It is clear that the CP/Manager was experimenting with LOP operations...it is equally clear that the aircraft were not fitted with all cylinder monitors and balanced injectors...so the CP/Manager was flirting with LOP without the minimum equipment necesary to do so safely and successfully...and EASILY.
Having set the mixture to '50F LOP' the only cylinder that was actually 50F LOP was that one which the single probe EGT was attached to...the other 5 cylinders were operating somewhere else in the mixture spectrum and he had no idea where.
As a result some may well have been leaner than the reference cylinder while others were richer...it is highly likely that most were richer otherwise rough running would have been very evident and likely as not stopped him from experimenting with LOP ops.
Those cylinders LOP EGT were operating cooler and cleaner than those operating ROP EGT...those operating ROP EGT were likely sitting right in the hottest part of the mixture spectrum...30-80 ROP EGT...PEAK CHT!
Had the engines been fitted with balanced injectors they ALL would have been Lean of Peak EGT...and thus ALL exposed to less heat and wider detonation margins.
Mr Hat you do understand the definition of "PEAK"?
In the tables on page 88/89 of that report it is obvious that most of the Chieftain operators canvassed operated the engines LEANED at climb power settings...only 2 from memory used full rich mixture at climb power. They also ALL used 2400 rpm.
It is quite obvious in the report that the CP/Manager applied significant pressure on his pilots to save fuel...thus it can be reasonably certain that his pilots used the lower numbers in the fuel flows quoted by that CP/Manager as 'recommended' by himself.
Plot those fuel flows/MAPs on the graph I posted above and you will see that all the operators, bar the 2 that use full rich, are flirting with detonation throughout every climb.
It is entirely likely that the reduced RPM further raised combustion chamber pressures/temps and reduced the already super slim detonation margins in this configuration to near zero...the likelyhood of preignition caused by rich mixture slightly fouling the plugs being heated up by the excessive pressure and heat caused by innappropriate leaning at climb power is high.
Can anyone post the max continuous RPM for a Chieftain?
LOP had not one thing to do with this accident...Leaning (but still ROP) on climb certainly caused long term damage to the cylinders and pistons...they were very likely operating in 'light' detonation on most climbs...when one engine failed due to a crankshaft failure the young pilot bumped up the power on the remaining engine (possibly not adjusting the mixture) and that engine stressed by 100s of hours of abuse gave out on him too...via heat damaged pistons at least one of which had a massive hole melted right through it.
A quote from the POH for the Chieftain...as presented within the report linked above.
When leaning below best power is permitted (refer to Maximum Manifold Pressure Vs. Altitude graph in Section 5 – Performance), the engines may be operated at peak EGT or on the lean side of peak EGT as long as stable engine operation results without exceeding any engine limitations during steady state or transient conditions.
Having set the mixture to '50F LOP' the only cylinder that was actually 50F LOP was that one which the single probe EGT was attached to...the other 5 cylinders were operating somewhere else in the mixture spectrum and he had no idea where.
As a result some may well have been leaner than the reference cylinder while others were richer...it is highly likely that most were richer otherwise rough running would have been very evident and likely as not stopped him from experimenting with LOP ops.
Those cylinders LOP EGT were operating cooler and cleaner than those operating ROP EGT...those operating ROP EGT were likely sitting right in the hottest part of the mixture spectrum...30-80 ROP EGT...PEAK CHT!
Had the engines been fitted with balanced injectors they ALL would have been Lean of Peak EGT...and thus ALL exposed to less heat and wider detonation margins.
Mr Hat you do understand the definition of "PEAK"?
In the tables on page 88/89 of that report it is obvious that most of the Chieftain operators canvassed operated the engines LEANED at climb power settings...only 2 from memory used full rich mixture at climb power. They also ALL used 2400 rpm.
It is quite obvious in the report that the CP/Manager applied significant pressure on his pilots to save fuel...thus it can be reasonably certain that his pilots used the lower numbers in the fuel flows quoted by that CP/Manager as 'recommended' by himself.
Plot those fuel flows/MAPs on the graph I posted above and you will see that all the operators, bar the 2 that use full rich, are flirting with detonation throughout every climb.
It is entirely likely that the reduced RPM further raised combustion chamber pressures/temps and reduced the already super slim detonation margins in this configuration to near zero...the likelyhood of preignition caused by rich mixture slightly fouling the plugs being heated up by the excessive pressure and heat caused by innappropriate leaning at climb power is high.
Can anyone post the max continuous RPM for a Chieftain?
LOP had not one thing to do with this accident...Leaning (but still ROP) on climb certainly caused long term damage to the cylinders and pistons...they were very likely operating in 'light' detonation on most climbs...when one engine failed due to a crankshaft failure the young pilot bumped up the power on the remaining engine (possibly not adjusting the mixture) and that engine stressed by 100s of hours of abuse gave out on him too...via heat damaged pistons at least one of which had a massive hole melted right through it.
Last edited by Chimbu chuckles; 29th Jun 2007 at 10:15.
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Sorry Chimbu - not as expert on the topic as you are. ROP worked okay for me. Anyway doesn't matter as I'll never fly one again.
The gauges in alot of the machines weren't ideal so I wasn't about to re invent the wheel...
The gauges in alot of the machines weren't ideal so I wasn't about to re invent the wheel...
Grandpa Aerotart
Nor should you have...the OEM triplex gauges are not anywhere near good enough..especially not in commercial operations.
Anything less than full rich on climb in these aircraft and 100F ROP in cruise is flirting with danger....UNLESS fitted with all cylinder monitors and balanced fuel injectors...and the pilot trained to use them.
Anything less than full rich on climb in these aircraft and 100F ROP in cruise is flirting with danger....UNLESS fitted with all cylinder monitors and balanced fuel injectors...and the pilot trained to use them.
Ah CC, there’s nothing like banging one’s head against the wall.
YesTAM: The August 2005 Australian Aviation included an air test of a Cirrus aircraft. At page 61, the report of the test says:
Bolding added.
Could you ask your learned friend why Cirrus aircraft aren’t falling out of Australian skies each day, as a consequence of the terrible consequences of burning evil antipodean Avgas in that heart of darkness at lean of peak?
I might add I’ve chosen that test as one example. There are numerous other sophisticated GA aircraft that remove the dangers of pilot superstition, old wive’s tales and ‘morning smoko’ stupidity, by automatically leaning the engine to lean of peak without the pilot knowing.
Mr Hat: I commend to you Mr John Deakin’s article ‘Lead in the Hogwash’.
YesTAM: The August 2005 Australian Aviation included an air test of a Cirrus aircraft. At page 61, the report of the test says:
By further leaning to best economy (35-40degrees lean of peak) that speed drops by 5 to 10kt, but with a 15 per cent fuel burn improvement.
Could you ask your learned friend why Cirrus aircraft aren’t falling out of Australian skies each day, as a consequence of the terrible consequences of burning evil antipodean Avgas in that heart of darkness at lean of peak?
I might add I’ve chosen that test as one example. There are numerous other sophisticated GA aircraft that remove the dangers of pilot superstition, old wive’s tales and ‘morning smoko’ stupidity, by automatically leaning the engine to lean of peak without the pilot knowing.
Mr Hat: I commend to you Mr John Deakin’s article ‘Lead in the Hogwash’.
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Mr Chuckles
I seem to recall reading somewhere that the wise ones from the states are doing a seminar in oz ,I thought it was october? but can't lay my hands on the original read.Any ideas?
cheers
cheers
Doesn't Cirrus have a Fadec and also electronic ignition?
It’s lean of peak and running on Australian Avgas. Why aren’t Cirrus aircraft falling out of the sky?
Grandpa Aerotart
Cessna Pilots Association Australia have invited Walter Atkinson and George Braly to hold one of their Advanced Pilot Seminars in Australia...12-14th October in Sydney.
Google CPAA for details.
I don't think Cirrus have a FADEC as such...Cirrus do schedule RPM automagically but pretty sure mixture is still manual...stand to be corrected on that though. What I do know is they are fitted with balanced injectors, probably Gamis, and digital engine monitors.
I think the only true FADECs fitted to light aircraft are in the diesel powered aircraft coming from Europe. Stand to be corrected on that too.
Personally I prefer knowing what to do with the throttle/prop/mixture...FADEC is a sop for lazy pilots.
Google CPAA for details.
I don't think Cirrus have a FADEC as such...Cirrus do schedule RPM automagically but pretty sure mixture is still manual...stand to be corrected on that though. What I do know is they are fitted with balanced injectors, probably Gamis, and digital engine monitors.
I think the only true FADECs fitted to light aircraft are in the diesel powered aircraft coming from Europe. Stand to be corrected on that too.
Personally I prefer knowing what to do with the throttle/prop/mixture...FADEC is a sop for lazy pilots.
FADEC is to engines what GPS/FMS is to planning and navigation. A work-load reducer, a durability enhancer and therefore a safety feature - if only the aviation industry would wake up and smell the coffee.
BTW, the Cirrus (SR22, at least) is not FADEC - only a mechanically linked throttle/CSU. The red knob is still there.
A
BTW, the Cirrus (SR22, at least) is not FADEC - only a mechanically linked throttle/CSU. The red knob is still there.
A
Grandpa Aerotart
if only the aviation industry would wake up and smell the coffee.
I agree it is a safety improvement in terms of replacing magnetos with solid state, multiple redundant variable electronic ignition etc but the big drive, Prism aside, still smells of dumbing down...the other systems all claim 'single lever' engine operation...I cannot think of a single good reason not to have direct control of RPM and mixture.
BTW Yestam....my Bonanza runs beautifully LOP on Australian Avgas and has been doing so for 5 years. It never gets plug fouling and the boroscope at each annual shows the engine LOVES it.
BTW, I think we have had a very similar discussion some time ago.
Perhaps I should approach this issue another way, YesTAM.
Let’s assume running lean of peak with Australian Avgas is risky for engines and is to be avoided.
How does a pilot know the ‘engine’ isn’t running lean of peak?
If your answer is that the circa 1940s technology single EGT gauge is telling the pilot so, I’m afraid that’s called ‘blissful ignorance’.
There is extensive, irrefutable evidence to show that the fuel flows to, and therefore the mixtures being delivered to, each cylinder in a bog standard GA engine can be substantially different. A single point EGT gauge merely tells you the approximate EGT of some cylinders on one side of an engine. It does not tell you whether each cylinder is running rich of peak.
GA engines generally survive because they are almost completely idiot proof, whether you’re running them ROP, at peak or LOP. If they have some fuel and some oil, you have to be trying really hard, or have to have made a really big mistake, to break them.
The usual way in which this spectrum of treatment manifests itself is not in accident statistics (thankfully), but in fuel and maintenance costs.
QED.
Let’s assume running lean of peak with Australian Avgas is risky for engines and is to be avoided.
How does a pilot know the ‘engine’ isn’t running lean of peak?
If your answer is that the circa 1940s technology single EGT gauge is telling the pilot so, I’m afraid that’s called ‘blissful ignorance’.
There is extensive, irrefutable evidence to show that the fuel flows to, and therefore the mixtures being delivered to, each cylinder in a bog standard GA engine can be substantially different. A single point EGT gauge merely tells you the approximate EGT of some cylinders on one side of an engine. It does not tell you whether each cylinder is running rich of peak.
GA engines generally survive because they are almost completely idiot proof, whether you’re running them ROP, at peak or LOP. If they have some fuel and some oil, you have to be trying really hard, or have to have made a really big mistake, to break them.
The usual way in which this spectrum of treatment manifests itself is not in accident statistics (thankfully), but in fuel and maintenance costs.
[CC’s] Bonanza runs beautifully LOP on Australian Avgas and has been doing so for 5 years. It never gets plug fouling and the boroscope at each annual shows the engine LOVES it.
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Can anyone post the max continuous RPM for a Chieftain
Typical settings for CLB was 39"MAP/2400RPM.
I stand to be corrected.
When I operated them, I made a recommendation to the aircraft owner that the aircraft be upgraded with the GAMI/JPI set up, but was told it was too expensive. So we were instructed to run the motors at 150 degrees ROP instead.
