'Unleaded' For G/A..??
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Facts.
TEL does only one thing, Creamie is 100% correct. End of discussion.
TEL does only one thing, Creamie is 100% correct. End of discussion.
for avgas with TEL
correct mix burns light grey.
lean mix burns white and rich mix burns dark grey.
go fly a real aeroplane and take a bloody look!
Facts.
TEL does only one thing, Creamie is 100% correct. End of discussion.
TEL does only one thing, Creamie is 100% correct. End of discussion.
With all due respect, bollox.
TCM and Lycoming have ALWAYS used hardened seats
Tootle pip!!
Last edited by LeadSled; 2nd Aug 2013 at 09:36.
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leadie he is correct in that it was only intended to do one thing.
he is wrong about it being the only effect though. the muck in the burnt mixture really does slow valve seat recession in unhardened valve seats.
that is a well documented and experienced fact.
it also changes colour according to the mix.
40 years ago we used to check the tuning adjustment of the car by taking it for a run around the block. after a few miles the exhaust colour would confirm or otherwise whether the tune was ok. same for aircraft.
it also makes you clean out the lead nodules from spark plugs on a reasonably regular basis thereby increasing your opportunities for dropping them.
(I was once asked, almost as an exam question, what is the corner of a hangar for? answer; somewhere to kick dropped spark plugs so that you cant find them.)
he is wrong about it being the only effect though. the muck in the burnt mixture really does slow valve seat recession in unhardened valve seats.
that is a well documented and experienced fact.
it also changes colour according to the mix.
40 years ago we used to check the tuning adjustment of the car by taking it for a run around the block. after a few miles the exhaust colour would confirm or otherwise whether the tune was ok. same for aircraft.
it also makes you clean out the lead nodules from spark plugs on a reasonably regular basis thereby increasing your opportunities for dropping them.
(I was once asked, almost as an exam question, what is the corner of a hangar for? answer; somewhere to kick dropped spark plugs so that you cant find them.)
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we went from having multiple grades of avgas to all using just one (100/130) not because of CASA but because the fuel companies stopped making them.
I would suggest that the first task is to find a company prepared to produce and distribute it.
the engines were originally certified by the FAA so once they certify the fuel blend it should be an easy rubber stamp exercise for CASA.
I would suggest that the first task is to find a company prepared to produce and distribute it.
the engines were originally certified by the FAA so once they certify the fuel blend it should be an easy rubber stamp exercise for CASA.
"88" I reckon no fuel Co maker/distributor would make a specialist type fuel (as that's where all leaded fuel is heading) as there wouldn't be the volume there for them to produce it never lone market it to a dieing sector as GA, simply no money in it or a decent return on outlay.
GA in the not to distant future will only be for the elite with money to burn.
It's my understand that lead or fuel with a higher octane rating has a direct effect on ignition timing & therefor performance, sure did in motor vehicles of yesteryear. If you put 'std' fuel in a car that was tuned for 'super' it pinged it's head off at the std BTDC timing (usually around 6 deg's) so you had to back off the dissy 'till it stopped pinging & the result was a slug! Can't see the Aero engines being any diff but am here to learn from the "Master Jabba"
Wmk2
GA in the not to distant future will only be for the elite with money to burn.
It's my understand that lead or fuel with a higher octane rating has a direct effect on ignition timing & therefor performance, sure did in motor vehicles of yesteryear. If you put 'std' fuel in a car that was tuned for 'super' it pinged it's head off at the std BTDC timing (usually around 6 deg's) so you had to back off the dissy 'till it stopped pinging & the result was a slug! Can't see the Aero engines being any diff but am here to learn from the "Master Jabba"
Wmk2
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Leadsled, I would love you to show me the data to prove your claim but two different part umbers does not mean that they were not changed somewhat over the years, different manufacture is not uncommon, but they have always had a hardened seat because they were ALWAYS aluminium heads.
So please, don't be sucked in any longer.
W8......no I was correct entirely,
Right observation.....WRONG causation. Did you not read about the ag guys, latency etc. 
Go do the study. I am not paid to do this, and I do not do this for kicks, but FFS, the OWTs are hard enough to kill off as it is, so please be careful with the beliefs of OWT's.
As we say, Data is no weapon against the warm fuzzy feeling of a deeply held superstition.
So please, don't be sucked in any longer.
W8......no I was correct entirely,
the muck in the burnt mixture really does slow valve seat recession in unhardened valve seats.
Go do the study. I am not paid to do this, and I do not do this for kicks, but FFS, the OWTs are hard enough to kill off as it is, so please be careful with the beliefs of OWT's.As we say, Data is no weapon against the warm fuzzy feeling of a deeply held superstition.
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Vex
Fleet wide STC ...... problem solved. CASA do not need to do anything, which is just as well 
So what do we need to do to get G100UL certified by CASA?
Would they accept the flight test reports of the flights that were witnessed by the FAA?
Would they accept the flight test reports of the flights that were witnessed by the FAA?
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Wally, on the topic of timing you can only reduce the timing so much, and in high compression engines the timing is retarded enough already.
Also on the larger high output engines there is a very thin line. Advance the timing, and you get into detonation margin, or into light detonation. The Chieftain engine is a classic example. they live there all the time. So you cant advance, but you ca't retard.
If you do retard the timing the problem is you run into TIT problems as the EGT goes up.
It is all about latency of the fuel.
Anyone interested in learning about this.... it takes more thna an internet post. Advanced Pilot Ask Volumex and creamie
Also on the larger high output engines there is a very thin line. Advance the timing, and you get into detonation margin, or into light detonation. The Chieftain engine is a classic example. they live there all the time. So you cant advance, but you ca't retard.
If you do retard the timing the problem is you run into TIT problems as the EGT goes up.
It is all about latency of the fuel.
Anyone interested in learning about this.... it takes more thna an internet post. Advanced Pilot Ask Volumex and creamie
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Jaba...
Excuse my ignorance, but where exactly is the TIT measured from (sensor placement) in the average engine(s), and what is the average reading in cruise, and what info does it give you that the EGT/CHT/oil temp/oil press combo can't give you?
Last edited by RatsoreA; 2nd Aug 2013 at 14:23. Reason: Clarification
Thread Starter
**** Me Guys & Gals,.....
Oi dinna wanna start WW3.....
T'was just a discussion on feckin' FUEL ....FCSs....
Now..... Exhaust valves at the ready...GO!
Oi dinna wanna start WW3.....
T'was just a discussion on feckin' FUEL ....FCSs....
Now..... Exhaust valves at the ready...GO!
--- but they have always had a hardened seat because they were ALWAYS aluminium heads.
Please go back and read what I have already posted --- all the Jaguar cylinder heads are aluminium --- that didn't automatically make the valve seats "hardened".
Are you really suggesting that Jaguar (and others) went to all the trouble of changing the material in production heads post the mid-'80's, and went to the trouble of producing valves and seats for retrofitting --- if there was no need?? As has already been mentioned, changing valve guide material is part of the above unleaded conversion.
TEL isn't always good, how many of you can remember the new heads we had to fit to Gypsy Majors, to cope with "high octane" leaded fuel.
As I said before, while I have the greatest of respect for the efforts of Pelicans Perch, in making know, in present times, what many of us have always known about the operation of piston engines. How do you think the Qantas "double daylight" services in the Catalina's made the range they did --- in fact, they very carefully operated right on peak CHT, to get every last drop of power out of the available fuel.
What we do have now, in little engines, that make it easier, are Gamijectors and good multi-point EGT or CHT --- but little else has changed in the last 70 or so years. The physics and chemistry certainly haven't changed.
Tootle pip!!
PS: Having been an operator of reasonably high performance car and bike engines, and aeroplane engines, since the late '1950's, and originally having an engineering background, I have not been sucked into anything.
Last edited by LeadSled; 2nd Aug 2013 at 16:01.
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Leadie, I have no idea what think Jaguar did with their heads, and frankly it has little to do with this debate. Lead does nothing to the valve or seats that cushions or protects. Perhaps they always had hardened valve seats 
Yes even back in the 1940's Leadie, the early XK120's etc, all had hardened valve seats. Here is what one Jaguar specialist has to say on the topic.
The key issue was ignition timing, why? Latency, it has nothing to do with lead as a lubricant, because it is not.
In latter years the XJS series in particular (have a friend who is an XJS fanatic) the biggest issue was valve seats dropping. This is entirely an overheating issue. End of story.
You have just proven this concept to yourself with the following statement.
TEL is never good for the engine. Why do you think they add in Bromine? Well to scavenge the lead after it finished with the latency issue they want it out! The result is Lead Oxybromide which is a salt. And when has a salt of anything made an excellent lubricant or any other active ingredient that is good for the internals of an engine? Besides that salt is gaseous and expelled at all but idling temperatures where a small amount can settle out in a cold engine. Once hot enough they are gone. Even the ATSB were fooled by OWT's on this one.
So for the punters reading this;
1. How does TEL (not lead) in fuel lubricate the valve stems on the inlet or exhaust valve when it does not come in contact with either? And if it were to come in contact say through worn guides? The fuel is a solvent on the inlet side and that makes a poor lubricant, and under the suction of the intake stroke it would not get sucked into the valve guide anyway. Myth Busted.
Now lets look at the exhaust valve, it is closed during all but the expelling of hot exhaust gas, which now contains a compound called Lead Oxybromide. If that gets into the valve guide, the guides will really wear fast, and then the valve rattles around and wears it more and before long you have a valve failure. Sound familiar?
2. The reason engines designed to run on higher octane (not leaded because they need the octane not the lead) when run on ordinary ULP had valve issues was that of Internal Cylinder pressures. The problem is the latency of the fuel, the time it takes for the fuel to burn and the pressure in the cylinder to rise. If this happens quicker, after the spark event, the gas expansion occurs sooner and with the piston rising this happens in a progressively smaller chamber. So what follows is a much higher peak pressure. This does not generate more HP by the way as much of the extra pressure generated goes into doing the compressive effort in the other cylinders, and the peak is now closer to TDC than before, thus less Torque is generated by the crank angle being less, and less torque means less power at any given RPM.
With all that understood, these higher pressures, much higher, and the resulting higher temperatures were the reason for valve recession and valve jobs. The solution in many cases was simply back off the timing to compensate for the latency. A premium unleaded PULP of a similar octane and latency will run an "old school" engine just fine and it will run longer on the PULP because it has less deposits. Just as pointed out above with the Tiger Moth engines. My race car engine has SOFT cast iron heads an no problems on PULP, because it was timed right, the compression ratio was right, the cooling was right....heck I even put the thing together myself! That was the biggest risk!
Some years ago the FAA tested side by side a twin with one engine on AVGAS and one on unleaded, and they ran it for several hundered hours. What a surprise, two identical engines and one had more wear and degradation than the other. You can guess which one was the healthier one.
The only reason we have the lead fuel is to have a latency suitable for high HP engines so that they can have sufficient detonation margin without suffering a loss of performance. When you see a Chieftan engine run on PULP you soon realise you can extract a lot of HP out of it without an issue, but you simply can't extract full rated power out of it without it detonating to the point where it is dangerous. If you cure the detonation, you don't get the power. And all the piston twin pilots will tell you that they need every pony they can get to meet the minimum certification single engine performance numbers as it is. So either you have a fuel that works, or planes are grounded. It is that simple. And they burn the most volume of the fuel so if you ground them, AVGAS or an UL version of it disappears anyway.
Tiger Moths and O-320's and other low compression engines have STC's for low octane fuel, and they are best run on it. IF you can. Rotax actually specify more frequent oil changes is Avgas is used. You are better without the lead.
Bottom line is there is no hard data to prove leaded fuel has any benefit other than latency and if there was I am sure we would have found it by now. Smarter folk than I have never found it because it does not exist. there are plenty of superstitions that are tightly held onto though.
Yes even back in the 1940's Leadie, the early XK120's etc, all had hardened valve seats. Here is what one Jaguar specialist has to say on the topic.
The fitting of an electronic 'U' box from AJ6 engineering is another good solution if your engine tends to 'ping' on unleaded fuel. Don't have an 'unleaded cylinder head conversion' unless you are overhauling the head anyway. If you want to give money away we can suggest a very good charity.
In latter years the XJS series in particular (have a friend who is an XJS fanatic) the biggest issue was valve seats dropping. This is entirely an overheating issue. End of story.
You have just proven this concept to yourself with the following statement.
TEL isn't always good, how many of you can remember the new heads we had to fit to Gypsy Majors, to cope with "high octane" leaded fuel.
So for the punters reading this;
1. How does TEL (not lead) in fuel lubricate the valve stems on the inlet or exhaust valve when it does not come in contact with either? And if it were to come in contact say through worn guides? The fuel is a solvent on the inlet side and that makes a poor lubricant, and under the suction of the intake stroke it would not get sucked into the valve guide anyway. Myth Busted.
Now lets look at the exhaust valve, it is closed during all but the expelling of hot exhaust gas, which now contains a compound called Lead Oxybromide. If that gets into the valve guide, the guides will really wear fast, and then the valve rattles around and wears it more and before long you have a valve failure. Sound familiar?
2. The reason engines designed to run on higher octane (not leaded because they need the octane not the lead) when run on ordinary ULP had valve issues was that of Internal Cylinder pressures. The problem is the latency of the fuel, the time it takes for the fuel to burn and the pressure in the cylinder to rise. If this happens quicker, after the spark event, the gas expansion occurs sooner and with the piston rising this happens in a progressively smaller chamber. So what follows is a much higher peak pressure. This does not generate more HP by the way as much of the extra pressure generated goes into doing the compressive effort in the other cylinders, and the peak is now closer to TDC than before, thus less Torque is generated by the crank angle being less, and less torque means less power at any given RPM.
With all that understood, these higher pressures, much higher, and the resulting higher temperatures were the reason for valve recession and valve jobs. The solution in many cases was simply back off the timing to compensate for the latency. A premium unleaded PULP of a similar octane and latency will run an "old school" engine just fine and it will run longer on the PULP because it has less deposits. Just as pointed out above with the Tiger Moth engines. My race car engine has SOFT cast iron heads an no problems on PULP, because it was timed right, the compression ratio was right, the cooling was right....heck I even put the thing together myself! That was the biggest risk!
Some years ago the FAA tested side by side a twin with one engine on AVGAS and one on unleaded, and they ran it for several hundered hours. What a surprise, two identical engines and one had more wear and degradation than the other. You can guess which one was the healthier one.
The only reason we have the lead fuel is to have a latency suitable for high HP engines so that they can have sufficient detonation margin without suffering a loss of performance. When you see a Chieftan engine run on PULP you soon realise you can extract a lot of HP out of it without an issue, but you simply can't extract full rated power out of it without it detonating to the point where it is dangerous. If you cure the detonation, you don't get the power. And all the piston twin pilots will tell you that they need every pony they can get to meet the minimum certification single engine performance numbers as it is. So either you have a fuel that works, or planes are grounded. It is that simple. And they burn the most volume of the fuel so if you ground them, AVGAS or an UL version of it disappears anyway.
Tiger Moths and O-320's and other low compression engines have STC's for low octane fuel, and they are best run on it. IF you can. Rotax actually specify more frequent oil changes is Avgas is used. You are better without the lead.
Bottom line is there is no hard data to prove leaded fuel has any benefit other than latency and if there was I am sure we would have found it by now. Smarter folk than I have never found it because it does not exist. there are plenty of superstitions that are tightly held onto though.
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Leadsled,
I would like to see the data for that , as the scientific fact is to get the very last drop of range/fuel they did not operate at peak CHT or peak EGT. They would have had to operate at BSFCmin. And that is way LOP. And far from peak CHT. If they ran at peak CHT, it was because they had no way of telling BMEP or EGT, and that I can believe. So if that was the case what they did was sub-optimal but they knew no better.
To get the most or peak power, they would have operated at a setting that was around 75dF ROP. The peak CHT would have been fractionally less, and maybe that is what they did, but it would have been sub-optimal. Perhaps on those aircraft they could not define the difference. I assume they did not measure BMEP either like in the Connie or other big R3350 installs.
If you have the manuals for these particular operations I would happily study them and compare it to the R3350 which was carefully operated with BMEP, because back then they did not have EGT instruments like we do now.
This is major thread drift....sorry
How do you think the Qantas "double daylight" services in the Catalina's made the range they did --- in fact, they very carefully operated right on peak CHT, to get every last drop of power out of the available fuel.
, as the scientific fact is to get the very last drop of range/fuel they did not operate at peak CHT or peak EGT. They would have had to operate at BSFCmin. And that is way LOP. And far from peak CHT. If they ran at peak CHT, it was because they had no way of telling BMEP or EGT, and that I can believe. So if that was the case what they did was sub-optimal but they knew no better.To get the most or peak power, they would have operated at a setting that was around 75dF ROP. The peak CHT would have been fractionally less, and maybe that is what they did, but it would have been sub-optimal. Perhaps on those aircraft they could not define the difference. I assume they did not measure BMEP either like in the Connie or other big R3350 installs.
If you have the manuals for these particular operations I would happily study them and compare it to the R3350 which was carefully operated with BMEP, because back then they did not have EGT instruments like we do now.
This is major thread drift....sorry
161octane
Does this mean I will once again hear the noise of a Merlin at full song? I am getting all wet just thinking about it.
Does this mean I will once again hear the noise of a Merlin at full song? I am getting all wet just thinking about it.
Last edited by OZBUSDRIVER; 2nd Aug 2013 at 22:10.
There is been a fact based discussion about this on AVWEB for a year or more. Its a complex issue. Many GA engines could switch tomorrow. The main problem is the slowness of the US labs in testing fuels. Its been the subject of debate in congress. Other engines will never run on unleaded fuel and if you read the documents put out on this subject by both lycoming & Continental they concede that it would mean the retirement of many aircraft - including my Seneca. It got quite a bit of attention when a fringe group in California started a court case seeking the immediate ban on the sale of AVGAS
While admire John Deakin, lets just remind ourselves of his qualifications. Engine calibration is the single most difficult part of vehicle development and experienced engine calibrators are highly sought after globally. The number of good ones in Australia could be counted on the fingers of one hand. The best guys work for Ricardo, AVL or FEV. There are even fewer fuel technologists.
If you want to understand this, then get do a paper search on places like the library of Ricardo engineers, The SAE and the NASA Langley library.
While admire John Deakin, lets just remind ourselves of his qualifications. Engine calibration is the single most difficult part of vehicle development and experienced engine calibrators are highly sought after globally. The number of good ones in Australia could be counted on the fingers of one hand. The best guys work for Ricardo, AVL or FEV. There are even fewer fuel technologists.
If you want to understand this, then get do a paper search on places like the library of Ricardo engineers, The SAE and the NASA Langley library.
I am perpetually fascinated by the propensity of highly intelligent people to confuse correlation for causation.
When the traffic lights turn green, the cars start moving. Therefore, the green light causes the cars to move …
The lack of lead does not cause the problems that people keep citing. The detonation does.
If you take the lead out, the combustion event happen more quickly, moving the peak pressure point closer to TDC and increasing the absolute peak pressure. It’s not the ‘removal’ of the ‘valve lubrication’ or ‘valve cooling’ that’s causing the problems: it’s the advance in the PPP and the increase in the PP caused by the quicker combustion in the absence of the lead.
You can create exactly the same problems by advancing the timing. Leave the lead in, and slowly advance the timing to e.g. 30 degrees BTDC instead of 22 and see what happens (not on my engine, please). (Hmmmm, perhaps the magneto timing is lubricating the valves
)
You can take the lead out and make the problems go away by retarding the timing. (Therefore, the magneto timing is definitely lubricating the valves) But if you do that, you’ll create other problems.
When GAMI gets G100UL certified, no doubt the received wisdom will become that the secret herbs and spices are 'lubricating the valves'.
When the traffic lights turn green, the cars start moving. Therefore, the green light causes the cars to move …
The lack of lead does not cause the problems that people keep citing. The detonation does.
If you take the lead out, the combustion event happen more quickly, moving the peak pressure point closer to TDC and increasing the absolute peak pressure. It’s not the ‘removal’ of the ‘valve lubrication’ or ‘valve cooling’ that’s causing the problems: it’s the advance in the PPP and the increase in the PP caused by the quicker combustion in the absence of the lead.
You can create exactly the same problems by advancing the timing. Leave the lead in, and slowly advance the timing to e.g. 30 degrees BTDC instead of 22 and see what happens (not on my engine, please). (Hmmmm, perhaps the magneto timing is lubricating the valves
)You can take the lead out and make the problems go away by retarding the timing. (Therefore, the magneto timing is definitely lubricating the valves
) But if you do that, you’ll create other problems.When GAMI gets G100UL certified, no doubt the received wisdom will become that the secret herbs and spices are 'lubricating the valves'.
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Lead In Rotax's
Having seen the inside of a Rotax that has been run on Avgas I can tell you that is is a serious contaminant within the engine. It leaves a paste of abrasive which cloggs the internals and the first thing that happens is the starter system which uses fine springs to disconnect the starter as the engine fires fails. I can tell if a rotax has been running Avgas just by looking at the oil, you can see the lead suspended in it.
In my 0-300 D I am convinced that the lead actually DAMAGES valves. Because it is a low compression engine the heads do not get hot enough to scavenge the lead. It actually forms deposits under the valve seat causing leakage and the valve starts to burn.
In my 0-300 D I am convinced that the lead actually DAMAGES valves. Because it is a low compression engine the heads do not get hot enough to scavenge the lead. It actually forms deposits under the valve seat causing leakage and the valve starts to burn.
Well, from this thread I am convinced enough to go out and purchase a Peterson STC for my Scout. Then I can legally run PULP mogas. I can't currently get lean of peak cause she misses too much and doesn't really sound well. My multi point thingie Jabba convinced me was a good idea is still in the mail.
So perhaps someone could tell me, do I treat PULP like avgas? Do I lean as aggressively? Do I just fly and hope for the best. Given the nature of the machine I am seldom above 3000, but occasionally (like when over water) I like to climb up to the 9500 range of nose bleeding altitude.
So perhaps someone could tell me, do I treat PULP like avgas? Do I lean as aggressively? Do I just fly and hope for the best. Given the nature of the machine I am seldom above 3000, but occasionally (like when over water) I like to climb up to the 9500 range of nose bleeding altitude.