From first-hand experience: The lawyers are going to get your house if you have an engine failure running your engine/s on folklore, in accordance with the POH or otherwise. The only difference is whether you have a provable cross-claim against the publishers of folklore in the POH. That argument will cost you your house, anyway.

I envy you your blissful ignorance.

A friend of mine works at Katherine Aviation where they operate 210s and Barons lean of peak with GAMIs fitted. Apparently it's all part of their SOPs/in their operations manual. CASA must have signed off on this right?

Lead Balloon

The POH is not folklore, but a legal document. The defence that a dentist at APS gave me operational engine management guidelines, not accredited by CASA, or the manufacturer, means you will end up enjoying the bliss of a trailer park, as you say.

Not actually correct, CASA do not approve Operations Manuals, they merely accept them.

You’re obviously sure of your opinion, tio540. Those reading PPRuNe will rely on it. :ok:

I am all for a robust discussion.

The PA31-350 POH actually permits LOP, one of three options for leaning, so here we might even agree. However, the actual Lycoming engine manufacturer does not approve LOP.

The Continental service bulletin cites engine longevity as an issue when describing LOP, and recommends this only in extreme long range operations, and only occasionally.

I should add I have absolutely no engineering quals, and am usually wrong with most things.

Leadballoon

In your opinion. Now for the facts:

If the engine has detonated visual signs like broken spark plug porcelains or broken ground electrodes are dead giveaways and call for further examination or engine disassembly. Engine Basics: Detonation and Pre-Ignition by Allen W. Cline

The typical cracked core nose condition shown may be caused by improper cleaning or gapping procedures and by detonation. Champion Aerospace Aviation Service Manual

Detonation is an explosion of the combustion charge in an uncontrolled sudden manner. This condition may damage the spark plug electrodes or crack the insulator nose as well as destroy the engine if permitted to continue. Tempest Aviation Spark Plugs

It is a fact that detonation causes cracked insulators. It is also a fact that running lean of peak at high power puts an engine inside its certified detonation envelope. Note I am not saying LOP causes detonation, I am saying LOP at high power can cause detonation, for instance when a pilot forgets to set the mixture full rich before take off or go-around on a hot day.

I wish I’d said that.

Oh wait, I did, or most of it to the extent it’s accurate:I listed the top 3 causes, not the only causes.

The most efficient way to punish an engine is to run it ROP, but not far enough ROP. As I said, the surest way to cause detonation in my engine is to run it where the POH says to run it.

You can also punish an engine if don’t you run it far enough LOP. But you will never be giving it as good a thrashing as you could ROP.

On my engine the throttle is left full from the start of the take off roll to joining the circuit at the destination. From the top of descent to the shut down the mixture control is at whatever the cruise setting was - usually LOP. (Sometimes I’ll have to give it twist or two richer, but I’ll be on the lean side of peak all the way down.)

Walk me through how I’d get detonation if I went to full throttle to go around, without touching the mixture. Note that the engine would in that case be set precisely where it was set when I arrived in the circuit. And I can see on the engine monitor that the CHTs are lovely and cool.

I might not have as much power as I could safely draw from the engine if I leave the mixture LOP, which is why I would as SOP go full rich. But note I’m not going full rich to avoid detonation LOP, but rather to get more power at a safe mixture.

And not I’m not setting the mixture to get maximum power - around 25C ROP - as that would be the mixture that would maximise the likelihood of .... detonation, particularly if I’ve forgotten to set the prop to maximum RPM.

My mistake, it is 50 ROP they describe as the worst place to run an engine. But peak is generally in their "Red Box".

It doesn't change the fact that this is where all engine designers intend the engine to run. What evidence do you have that it is bad?

You keep using words like "punishing" and "thrashing". These are just words, not evidence.

Again, a misrepresentation. As I said earlier, I ran at peak EGT during a flight on Monday. At 9,500’, normally aspirated, peak EGT ain’t in no ‘Red Box’.

Tell you what: Next time you take off around sea level on an ISA day with a big bore piston engine, lean the mixture so that you’re getting the maximum possible power out of the engine. (Hint: That’s a setting ROP.) And for good measure to perpetuate another OWT, pull the RPM back to 2,500. If you don’t believe you’re “punishing” and “thrashing” the engine at that setting, it won’t take long for you to see the evidence to the contrary.

Will you take up my offer to pay for your seat at the next APS in Australia?

(PS: You need to take care to include the unit of measurements in the numbers you quote. It’s 50F.)

That's why I said "generally" not "always".

That is a generous offer. Yes, I would be happy to.

Great. PM me when you make the booking, and I’ll arrange payment to APS.

Fair point, although I can only recall F being used in these discussions, with the exception of your posts.

How did you determine that?

From first-hand observation of measurements taken from a piston aero engine in a test cell.

Indeed, those measurements indicate that many big bore piston engines run in a state of mild detonation at settings that are uncontroversial from any perspective.

What size bore ?

For the edrumergated there is a great difference between a opposed engine used in ga and the large radials used in a time since past. While they both suck push bang blow thats basically where it starts and finishes.
The airlines did not invent running lop btw. It was used by the millitary mostly to cross the pond to the UK for delivery. In fact there is a great book on it were they were running lop and had to go to rop to make it.

There are no free rides everthing has its costs.

And it doesn’t go any further so far as the effect of mixture control is concerned. Varying the fuel/air ratio of what’s sucked into a cylinder that’s fitted to a radial engine has the same effect as varying the fuel/air ratio of what’s sucked into a cylinder that’s fitted to a horizontally opposed engine.

Or maybe the laws of chemistry and physics mean the fuel/air being sucked into a cylinder fitted to a radial engine combusts differently than if it’s being sucked into a cylinder fitted to a horizontally opposed engine. Maybe the compression is squashier or the spark sparkier? Hmmmm....But what happens when the aircraft to which the radial engine is fitted goes into a vertical climb or dive and the engine effectively becomes horizontally opposed? Does the fuel/air being sucked into the pistons ‘know’ to behave differently? Remarkable technology.

Walk us unedgumicated through it, Rod.

Page 180 in Fate is the Hunter makes reference to boffins getting the crews to operate at reduced RPM and MP so I imagine that operating LOP was part of it. EK Gann found that it was bollocks in practise, but then again what would he know.

How about this. Why dont you tell us why the radial and the opposed egines are the same. Now im sure younknow why this is as your an expert at all things and done the aps course and then i will respond to your comments. So back to you. Let see what you come up with. Im not holding my breath while i wait but as you also believe that a rich mixture burns slower than a lean mixture i dont hold much faith in you getting much right but who knows you may supprise

Waiting in suspense

Perhaps Lead Balloon is a complete idiot when it comes to his IO-520 engine management, Connedrod and andrewr?

But somehow, he manages to do a lot of GA flying and remarkably stays alive!

What I said was that varying the fuel/air ratio of what’s sucked into a cylinder that’s fitted to a radial engine has the same effect as varying the fuel/air ratio of what’s sucked into a cylinder that’s fitted to a horizontally opposed engine.

The reason is simple: The laws of physics are the same everywhere.

andrewr described my offer to pay for his spot on an APS course as “generous”. My motivation is pure self-interest.

The fewer people there are in GA perpetuating myths, intuition-based folklore, 60s marketing-hype, mule-stupid ‘wisdom’ and other mumbo-jumbo, the safer my wallet and I will be.

Absolutely spot on.:ok:

I haven't read Fate is the Hunter yet. (It's on my "to do" list) however I have read a number of articles about how Charles Lindbergh demonstrated lean of peak operation to greatly extend the range of navy aircraft operating in the Pacific.

I wondered why quite a number of pilots rejected the method until I read their reason for refusing to use it. It turns out it was because they were operating in an active war zone and were on high alert as soon as they were airborne even when the target of the day was a considerable distance away.

They weren't interested in stuffing around with mixtures when they needed instant power to escape a nasty situation or press on with an attack when they spotted a stray enemy aircraft.

The average GA aircraft doesn't have the Navy's wartime problems so it makes sense to run your engine where it's happy, cool and giving you the best bang for your buck in the fuel and maintenance department.

My first post in this thread was in support of following the flight manual, so let's keep it to settings approved by the POH.

What about 24" MP, 2400 RPM - about 70% power on an IO-360 - at peak EGT as approved by the Lycoming manual. Thrashing or punishing?

There are settings in the manual that I would consider punishing, e.g. 2000 RPM at 26" MP (about 60%). If you are looking for detonation, you won't necessarily find it at maximum RPM and full power. You are more likely to find it at these lower RPM and power settings along the "Limiting manifold pressure for continuous operation" line.

Andrewr this is a genuine question. Do you own your own aircraft or do you fly someone else's?

Neither, provided all cylinders are at peak. However, you could move to thrash or punish territory if you were to change the mixture to around 25C ROP. If you have an all-cylinder engine monitor, you will see it before your very eyes.

What’s the fetish with “as approved by the Lycoming manual”? Is 24.734” MP and 2,355 RPM “approved”?

Correct. That’s one of the reasons why reducing RPM to 2,500 after take off, IAW the OWT, increases risk. It has the effect of reducing thetaPPP. I.e. it moves the peak pressure point closer to TDC.

This is also why the AWB highlighting LOP operations and not the operations that are more likely to cause problems is mumbo-jumbo.

What an interesting line. I’ve never heard of it.

As I said in an earlier post, my SOP is wide open throttle from the commencement of the take off roll until entering the circuit at my destination. In other words, the MP is continuously as high as it could possibly be. In cruise I just set the RPM to wherever the engine feels smooth - it’s interesting to note how this varies with different propellers - I imagine it has something to do with resonance and other esoteric issues. I haven’t a clue what the POH says about RPM and MP, and I’m not inclined to waste my time reading it. My SOPs are based on science and the evidence of the instruments in front of me.

It wasn't LOP he introduced. Normal squadron practice was to fly at 2,200 to 2,400 RPM with mixture auto rich. Lindbergh introduced the practise of 1,600 RPM and auto lean.

2,300 RPM was the change over point for auto lean/auto rich operation according to the manual. Lean allowed a max of 34.5", rich 38" at 2,300. The manuals provide data for auto lean cruise, so wonder why the squadron didn't use it?

Just out of interest I had a look at the AP website and I noted that the staff were people who happened to be pilots. Other than the ex 747 pilot the other two are from non-aviation backgrounds. I would have expected some engineering background. I noticed that two of them flew for the CAF. I wonder what that organisation uses as their SOP for mixture control? I also noticed that there are no upcoming courses.

I don't have an opinion one way or the other on the issue of LOP or ROP but I have learnt from experience that wandering off the reservation in terms of POH puts one in test pilot territory. I have never subscribed to the theory "Its ok everyone does it this way" when its not stated in the manual.

Just like I expected the POH in my 210 to be written by engineers and expected my brand new IO520 designed by engineers to have all 6 cylinders put out pretty equal power whatever the mixture. Luckily 3 non engineers sorted out both problems and saved me a bucket of $$$$$$$.

PS The engineers actually recognized the problems but were not funded to fix them. I wonder how many extra engines that shiny pants decision sold for their company.

This thread has some interesting theories and pontification a from so called experts: mostly flying other people's aircraft.

We operate an aircraft with GTISO 520 engines. Our SOPs are simple 55% power setting and slightly rich. Fuel is cheap but an overhaul is expensive.

I reckon that 'rutan around' and 'Lead Balloon' fly their own single engine aircraft which are both fitted with IO-520 engines. What about you, 'andrewr'?

...hmm. Certification of the engine requires the manufacturer to demonstrate that the engine can be run detonation free at the leanest fuel flow approved for each power setting in its manual, up to 103ºF and down to sea level. At leaner settings the engine may detonate up to so-called limiting detonation but those settings are, by definition, not recommended. In this buffer range, the fuel must be able to be reduced by 12% from recommended before limiting detonation occurs.

Therefore, a conforming engine run at the manufacturer's recommended settings (and fuel octane rating) is proven not to detonate. The flip side is that at the most critical recommended settings you do not have to stray far from the strictly controlled conditions of the test in order to induce incipient detonation to a class of APS delegates.

Understanding the certification requirement may also help people understand why the manufacturers do not recommend running lean of peak, even though they acknowledge it is perfectly feasible with the correct equipment. The engines were simply not tested for it as originally certified. Now, GAMI must know this as they finally did get an STC in 2015, and as per their website:
Nonetheless, the fact remains that a conforming engine is proven not to detonate when run at the settings recommended.

Poeple pushing the lop line really are only going of the aps course and indoctrination of that. When they dont even know that difference between flame front speeds between rich and lean and push push push the wrong answer proven wrong will not addmit they were wrong and then delete a complete thread to cover their tracks.
When a person cant even tell the difference between a radial and a opposed engine. Wow he flys a io520 so that makes him an expert on the whole engine in the aviation fleet.

They say 75% rop is the same as 75% lop how so how much harder is the lop engine working to maintain that power.

They continue to claim lower exhaust temperatures but dont understand that the lower power settings that they are achieving is mainly because all the energy is is not used due to the slower burn rate of the lean mixture. So now energy is lost because its exiting past the exhaust valve. This is why you have burnt valves. This is why you have exhaust leakage on a leak rate test. This is why we check it iaw ad eng 4 and why both major manufacturers say you must do tnis check with zero leakage. To get around this the cult say this is not required and dismiss it. Totally agaist the AD.
Real world environment has shown and proven not only to myself but ask just about lame the same question what the results are from extreme leaning. Thier answer it not your fault its what you all been learnt from trade school etc and manuals. Wtf you think we all dumb sheep. We see feel smell whats going on we can make or own decessions and assessment on maintenance.

Fact is the leaner the mixture the slower tbe flame front burn rate is. With this the mixture is still emiting energy to the exhaust valve on opening where as in a richer mixture the energy is wholly consumed in the chamber, and even though it my be hotter it is NOT burning the valve because its engry is already been consumed.

They say running rop you will damage your engine and running lop ypu will not. Nothing could be further from the truth. 99% off engines in GA in aust do not run lop. So were are all these damaged engines then.
Go ask any lame that looked after a late model plastic fantastic with an io550 in it with lean assit and ask them what they have found over the years.

The other state they mention is it was proven by the airlines running the large radials running lop how they extended there engine o/h life from the millitary version. Wtf . Really. Not.
This is a play on words. Commercial avaition could never operate on millitary o/h periods. The P&w 985/ 1340 for example had an millitary o/h life by memerory of approx 300 hours, ( wil try and locate the 1st issue book i have on it to confrim) now its up to 1200 hours in cilivian life. Millitary have a zero expence rule where commercial well we have to pay so we make things last.
For the most part aps plays on words dyno testing is not reworld testing and never will be.

Cavite emptor i think it is let the byer be were.

And with these late model plastic aircraft with first life engines we dont see many if ever clyinder head cracking we do see exhaust valve destress and a lot off it.

Both lyc and cont have put alot of work on to their engines of late. While they may retain the outward appearance they are made of better materials than past engines. When you do your o/h replace the cylinders with new.
I recently was talking to a frim tnat they done two o/h with 2nd life cylinders and had failures at periodic inspection since they replace them all with new and get a full run out the engine till next o/h.
So who here has ever detenated an aviation engine. The last one i know off was across the spencer gulf in the chieftan because he didnt push the red knob first. And before a certain individuals say but the crank was cracked on that engine the crank did not fail so tnat is tottaly irrelevant. It failed because it was to lean and went into self destruct mode period. The evidence is quite clear on this fact.

If you ever get to have a look at an aircraft crank rod bearings they are extremely lagre for the power they produce against a cars of the same power.
Manufacturers make them like this for a reason and produce a manual for the engine for the same reason.

Isf aps is so good why dont they start producing their own manuals our even get their courses and manuals for operating engines approved. Just like everyone else has too.

:ugh::ugh::ugh::ugh::ugh::ugh::ugh::ugh::ugh::ugh:

Nonetheless, the fact remains that conforming engines have been proven to detonate when run at some of the settings recommended.

Could you walk us through the test equipment used and cite the data produced by the engine manufacturers during certification mid-last century to "prove" that a conforming engine never detonates at any of the recommended settings? A very sophisticated test cell used contemporarily proves otherwise.

When GAMI obtained the STC and corresponding POH supplement for LOP operations from the FAA, how did all those engines (like mine) fitted with GAMIjectors that had been run LOP for years before suddenly 'know' that it was 'safe' to do so?

Why have I never had a plug with a cracked ceramic insulator (at least not after I've run it - I make damned sure they aren't fitted with defects)? I've had a few fail at altitude and quite a few defective new out of the packet, but no cracked insulators.

Could you identify the posters who fly other people's aircraft? For my part, it's my engine. My life depends on it.

So why have my engines gone hundreds of hours past TBO when run on "interesting theories" rather than your evidently scientifically-based "55% power setting and slightly rich"?

Oggers mentioned certification. My engine is certified to run at maximum rated power, continuously, to TBO. Whether it will do that in fact depends on the quality of manufacture (sadly deteriorating) the quality of maintenance (can be variable) and the nut behind the wheel operating it in accordance with the laws of physics, hopefully supplemented by input from an engine monitor, rather than POH-enshrined and regulator-perpetuated folklore.

Of course there are variations in how the fuel/air combusts in different engines. Differences in bore, stroke, compression ratio, piston speed, head design, piston design, manifold pressure, spark timing, spark plug location all affect combustion and in particular influence the likelihood of detonation.

The fact that different Lycoming engines use different timing is evidence that there are differences even between engines that appear very similar.

The assertion that all engines are the same is one of the those statements that just fall apart if you look at the evidence.

The flow of gas inside the cylinder during compression is influenced by cylinder and head design, and is a very important factor in engine design. It directly influences the likelihood of detonation. So yes, it certainly could be different.

I read some notes on operating the big radial engines. Part of the leaning procedures was to advance the timing to improve valve life. Maybe they were the earliest victims of the OWT about LOP causing valve problems? Or maybe there is something there?

In any case yes the spark was certainly earlier running LOP.

I reread one of John Deakin's columns where he was describing a Lycoming engine where Lycoming had approved operation LOP. One interesting tidbit was that the timing was advanced compared to engines where LOP operation was not approved.

Many engines run LOP, but I don't know of any engines with variable spark timing that would not advance the spark when running LOP.

And all of that can happen whether the engine is radial or horizontally opposed.

Do you own the aircraft you fly? Does it have an engine monitor?

Punishing? Really? This is exactly the range where engine manufacturers design the engine to be run. I don't understand this idea that aircraft engines are light, powerful, reliable, efficient, wonders of engineering and the designers are incompetent and don't know what they are doing.

It was leaning at that power setting I was referring to, not the power setting itself. As opposed to your example, where the manual tells you to run full rich. The RPM and MP was simply chosen because it's corresponded approximately to 70%, was in the middle of the power chart, and the numbers were easy to follow.

24.734” MP and 2,355 RPM is fine, but harder to read off the chart.

It's on the Lycoming power charts.

Or they convinced you there is a problem with a perfectly good engine.

I hate to burst your bubble, but on the lean side of peak power i.e. if you lean at all, power is more dependent on fuel quantity than air. So if the airflows to each cylinder are uneven it doesn't matter much.

A bit more air moves you further from peak power mixture, a bit less air moves you closer to peak power mixture. If the fuel flows are even the power from each cylinder will be reasonably even.

If you make the mixtures the same, the power from each cylinder will be uneven, matching the uneven airflow. But you can get leaner overall before the first cylinder gets too lean to run.