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Jabiru engine failures

Old 17th Nov 2014, 22:12
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andrewr, you have to remember that heat transfer is a function of temperature and temperature in a piston engine is a function of pressure, so you can dramatically shift the heat energy flow by raising and lowering the pressure by shifting the Pmax point with ignition angle or burn rate.

On an aero engine, ignition angle is fixed. The ignition delay is variable with air-fuel ratio as is the burn rate, so air-fuel ratio will have a large influence on the magnitude of and angle at which Pmax occurs, which in turn influences whether the heat goes to the cylinder head, makes mechanical work or heads out of the exhaust.

Oh, and exhaust valves burn when they leak. That's pretty much the only way you will overheat them without melting the cylinder head at the same time.
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Old 17th Nov 2014, 22:44
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I'm not arguing with those factors - just the proposition that fuel doesn't cool. It does, unless you are LOP.
What if you are at peak EGT and you add fuel until the EGT is 50 degrees F rich of peak?
The thing that worries me about this whole LOP thing is the number of pilots who think that every engine can be run LOP without danger, and that LOP is the answer to all engine problems. There is too much evidence to the contrary for me to believe that.
’Evidence’ eh?

So, it follows from that 'evidence' that to avoid those dangers and problems, you run your engine ROP.

How do you know your engine is running ROP?

This is what I find perpetually hilarious about these folklore-driven discussions. Let’s assume it’s cookd clys all the way and your wings will drop off if you don’t operate ROP.

How do you know your engine is running ROP?
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Old 17th Nov 2014, 22:50
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Originally Posted by andrewr
Adding fuel when you are limited by O2 (rich) means that the amount of energy released is reduced. Listing other factors that also result in a cooler engine doesn't change this fact. I'm not arguing with those factors - just the proposition that fuel doesn't cool. It does, unless you are LOP.
Just re-read your post and must comment on this. You might think it's semantics, but cooling refers to dumping waste heat to the environment. Running rich is not chemically generating the heat in the first place, so to call it cooling is disingenuous.

Sure, it runs cooler, but it isn't cooling any more than reducing the power level is cooling.
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Old 17th Nov 2014, 22:57
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Exactly. Also demonstrated by the fact that you make the engine cooler by making the mixture leaner.
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Old 17th Nov 2014, 23:01
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You might think it's semantics, but cooling refers to dumping waste heat to the environment. Running rich is not chemically generating the heat in the first place, so to call it cooling is disingenuous.

Sure, it runs cooler, but it isn't cooling any more than reducing the power level is cooling.
See my post #74:
Maybe "fuel doesn't cool, it just heats less"?

So yes I agree, in part. But you could also say that cooling is "lowering the temperature" i.e. making it cooler. If you are trying to reduce your engine temperature you may not care.
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Old 17th Nov 2014, 23:05
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So you're going to run your engine ROP to avoid the dangers and problems of LOP. Great.

How will you know your engine is running ROP?

Last edited by Creampuff; 17th Nov 2014 at 23:28.
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Old 17th Nov 2014, 23:14
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Originally Posted by andrewr
See my post #74:
Maybe "fuel doesn't cool, it just heats less"?

So yes I agree, in part. But you could also say that cooling is "lowering the temperature" i.e. making it cooler. If you are trying to reduce your engine temperature you may not care.
But the objective is not to cool the engine. It's to produce sufficient power without overheating the engine and its components.
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Old 18th Nov 2014, 01:37
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But the objective is not to cool the engine.
My objective is just to understand the statement "FUEL DOES NOT COOL" when the chemistry says otherwise.
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Old 18th Nov 2014, 01:48
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Thread drift! The whole LOP/ROP debate was done elsewhere only a month or so back.
I am completely sold on the benefits of LOP, and was when I did my DC 3 ground school nearly 50 years ago.
But this is about Jabiru engines. How can we run a standard Bing carburettor LOP? My understanding is you get whatever it thinks you need, and that will usually be well rich of peak.
Jabiru did try some lean burn jetting for a while, but I believe that it was too imprecise and caused more problems than it was worth.

The only way I could see to run a Jabiru LOP would be to get rid of the standard Bing set up and perhaps fit a Rotec. I would be grateful to hear from anyone who has done this and how has it worked out?
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Old 18th Nov 2014, 01:49
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"Sure, it runs cooler", but it isn't cooling any more than reducing the power level is cooling.

Those four words are vital for someone running a little engine with a little carby with mixture controlled by the main jet, less piston clearance than the engine which originated the piston, a "lean" jet setting, and a "continuous loading" application.
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Old 18th Nov 2014, 01:55
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Walls, as the redhead once famously said "Please exPLAIN?."
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Old 18th Nov 2014, 01:57
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So you're going to run your engine ROP to avoid the dangers and problems of LOP. Great.

How will you know your engine is running ROP?
Not sure where you're going with this question. I would suggest you start full rich, and if leaning increases EGT you are ROP.

Personally, I would just operate according to the Lycoming recommendations, but I'm not making any recommendations about what you do.

I was discussing this topic with a guy who designs ECUs for a living. His comments were that
1) Peak EGT is very lean already and
2) EGT is a terrible way to set mixture. You have no idea what the actual lambda (mixture) is at e.g. 50F ROP/LOP. However, it is the best we have in aircraft due to the lead in the fuel.

I would be interested in a chart of lambda vs EGT - particularly if it showed whether it varied with rpm and manifold pressure but I can't find one.
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Old 18th Nov 2014, 01:59
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How do we know when you run lop or rop. We don't we all dills us lames we have zero idea.
Panio tuner may be. But your not even a player Clinton. Your a sheep. Your just passing on information that you have be taught.

Funny thing is you can't lie to an engineer. You may try we may think you have told us a furthy but in the end we know what happens the aircraft tells us what happens they talk to us. We don't always need fancy gauges to tell us what's happen. You may think we are all fools but at the end of the day your only cheating and lying to your self.
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Old 18th Nov 2014, 02:12
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Not sure where you're going with this question. I would suggest you start full rich, and if leaning increases EGT you are ROP.

Personally, I would just operate according to the Lycoming recommendations, but I'm not making any recommendations about what you do.
That’s what’s so hilarious. You’ll be confident of where you think the engine is running, but blissfully ignorant of where the engine is actually running.

More comedy gold:
1) Peak EGT is very lean already and
2) EGT is a terrible way to set mixture. You have no idea what the actual lambda (mixture) is at e.g. 50F ROP/LOP. However, it is the best we have in aircraft due to the lead in the fuel.
Seriously: that’s the funniest thing I’ve read in weeks.
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Old 18th Nov 2014, 02:35
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I know exactly what you mean, yr right.

When I find the tools under my carpet out of a 100 hourly, the tooth fairy put them there. When the temperature probe is left disconnected out of a 100 hourly, the Unicorn did it. When the magneto advance is 2 degrees too far advanced out of a 100 hourly, the cat did it.

Engineers never make mistakes. Manufacturers never make mistakes.

The problem is never the appalling quality control or competence of manufacturers or LAMEs. Those cookd clys are always the pilot’s fault.

It must be the pilot’s fault, because the manufacturers and the LAMEs say so.

I’m begging you to save other pilots from the lies that I’m telling.

You know how to prevent cookd clys.

Explain the throttle, mixture and propeller settings that pilots should use, and what indications pilots should expect, to operate a piston engine the safe, yr right way.

Please.
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Old 18th Nov 2014, 03:10
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That’s what’s so hilarious. You’ll be confident of where you think the engine is running, but blissfully ignorant of where the engine is actually running.

More comedy gold: Quote:
1) Peak EGT is very lean already and
2) EGT is a terrible way to set mixture. You have no idea what the actual lambda (mixture) is at e.g. 50F ROP/LOP. However, it is the best we have in aircraft due to the lead in the fuel.
Seriously: that’s the funniest thing I’ve read in weeks.
I'm happy to entertain you. Perhaps you can tell me what lambda corresponds to 50F ROP and 50 LOP?

How does lambda at peak EGT compare to the lambda for maximum power? Maximum efficiency?
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Old 18th Nov 2014, 03:28
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I have no idea nor interest in what the lambda is, because I know, from first hand measurements of the EGT and CHT of each cylinder, where each cylinder is on the lean curve, and I know what to do to put and keep each cylinder where I want it to be on the lean curve, to get the power and efficiency I need for various phases of flight.

But that’s not the point: Remember – I have no clue what I’m doing. Many years and hours behind an engine that I’m incompetently managing, and the lack of cookd clys has been mere luck. The cool CHTs have been a product of the cooling effect of the lead on the valves and the unicorn fart additives in the oil.

I’m just fascinated to know what it is you propose to actually do about your concerns, and how you will be able to work out whether your concerns have actually been addressed. Presumably as some stage you’ll be sitting in a cockpit in proximity to a reciprocating engine, with some knobs to play with and some dials to watch.
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Old 18th Nov 2014, 03:41
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Just remember Creamie, if the knob in your hand is red, you're probably doing it wrong
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Old 18th Nov 2014, 03:45
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Andrewr, what are you doing on the 27-29th of March 2015?
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Old 18th Nov 2014, 03:55
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How do we know when you run lop or rop. We don't we all dills us lames we have zero idea.
Panio tuner may be. But your not even a player Clinton. Your a sheep. Your just passing on information that you have be taught.

Funny thing is you can't lie to an engineer. You may try we may think you have told us a furthy but in the end we know what happens the aircraft tells us what happens they talk to us. We don't always need fancy gauges to tell us what's happen. You may think we are all fools but at the end of the day your only cheating and lying to your self.
You're is a contraction, that is, it shortens two words. In this case the word 'you' and the word 'are', hence: you're. An example could be; 'You are a fool'. We can use the contraction to shorten that statement (contract = reduce/shorten) to 'You're a fool". Easy!

'Your' is a pronoun, (possessive in this case).

How do we know when you run LOP or ROP? We don't. We are all dills us LAMES, we have zero idea.

Panio tuner may be. But you're not even a player Clinton. You're a sheep. You're just passing on information that you have be taught.

Funny thing is, you can't lie to an engineer. You may try, we may think you have told us a furphy, but in the end we know what happened. The aircraft tells us what happened, they 'talk' to us.

We don't always need fancy gauges to tell us what's happened. You may think we are all fools, but at the end of the day, you're only cheating and lying to yourself.


That might be a bit easier to read now.

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