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Jabiru engine failures

Old 14th Nov 2014, 13:09
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Where was he then and what was he doing?
Folks,
That is a very good question, I wonder when all the claimed shortcomings at RAA happened -- in the short time between him quitting and turning up at CASA, or on his watch.

The RAA has been much criticized, some of it justified, but much of the problems over certification of certain aircraft is a result of CASA changing the rules of the game, after the game is over, with a number of historic certification agreements being ignored, and effectively aircraft judged by current rules. That is a bit of an over simplification, but you get the drift.

If you did that (demanded compliance with current certification rules) to GA aircraft, it would ground most of the fleet. Only the GA 8 and a few recent types would survive. The great majority of Cessna, Piper and Beech would disappear from the skies.

Tootle pip!!
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Old 14th Nov 2014, 15:03
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Jaba,
As an 'innocent bystander' these days, I cant help wondering why these issues have not been adequately addressed up to this point.

I, myself, have declined invitations to fly behind one of those apparently beautifully engineered powerplants.

Who stuffed up? How? Why?
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Old 14th Nov 2014, 19:42
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Stanwell, I would say 80% of the issues are quality control. It's one crisis to the next. Valves, rockers, collets, what is next? CASA are addressing this with them.

The other thing is the owners complying with the SB's.

When your LAME services your Cessna and you get $11,000 of sticker shock, you have no option but to pay it.

On the other hand, what is compelling you to upgrade the thru bolts on your owner maintained Jab? God, I've known of people that don't even have an engine or airframe log book! (Being careful with my words there)
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Old 14th Nov 2014, 20:17
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My experience with Jabiru the factory and Jabiru the engine is mixed.
The factory do not want to know you if you purchase second hand, and even less so if their engine is not installed in one of their Tupperware airframes. I emailed them with details of engine serial number, to ask if they had any records of its modification status when it left the factory, and to ask whether it had the 1000 hour TBO or the later, higher TBO. Not even a simple reply to say they had no knowledge of where it went after it got shipped out in a box, but based on serial number it would be a 1000 hour TBO.

The engine, a 2200 serial number 65 is one of their first of that series. So far, so good. The only issues have been a badly cracked muffler due to poor welding and some ignition faults which I fixed by replacing both rotors, both distributor caps and all the HT leads. It is owner maintained on the basis of if it ain't broke I don't fix it. The usual regular oil and spark plug changes and and a good look around for leaks and cracks and monitoring of compressions and tappet clearances is all. I imagine that swinging a wrench on through bolts etc would do more to break them than never touching them.

If this was the automotive industry, with 10,000 units on the road, the authorities would require a general recall to have the safety issues rectified at factory expense. But, hey, this is aviation and it's easier for the authority in this case to simply shut the factory. For those of us stuck with the product, if we can't have empty skies, solo skies are the next best thing.

Last edited by Mach E Avelli; 14th Nov 2014 at 20:51.
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Old 14th Nov 2014, 20:30
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Is t true the V6 Commodore pistons in Jabs are mounted with the gudgen offset opposite to normal practice?
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Old 14th Nov 2014, 20:48
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Apparently there was a batch of engines where they got it the wrong way around and therefore some failures and other cylinder damage resulted. Don't know when this happened or any other details.
If true, it reflects very poorly on their training and QA and certainly should have been a general recall with free fix.
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Old 14th Nov 2014, 21:01
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There was a cir clip problem about 2 years back I think that was gudgeon pin related.

The piston is based on the old V6 Holden engine piston and is manufactured at the same factory where ACL makes all their pistons. There are a few machining differences, the cir clip grooves, and a wider ring groove.

Stanwell…….I really can't answer your question I am not involved enough, just have a lot of exposure through various avenues.
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Old 15th Nov 2014, 03:08
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Is t true the V6 Commodore pistons in Jabs are mounted with the gudgen offset opposite to normal practice?

Keep digging in this area. Check out the reason South Africa reportedly gets such good performance out of their engines
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Old 15th Nov 2014, 03:50
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More info and petition to minister here
https://www.change.org/p/the-hon-war...rcraft-engines
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Old 15th Nov 2014, 04:17
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There is a complex discussion paper on the Jabiru website regarding the piston installation. If you can read and understand it, your questions will be answered. Unfortunately I lost interest half way thorough because the end result didn't affect me.
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Old 15th Nov 2014, 06:06
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Jabs way in front, if the stats are complete (which they may not be, based on track record). Even if they aren't, it's a wide margin.
Statistically significant for what it's worth - p<0.001 using chi^2
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Old 15th Nov 2014, 06:59
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Looking at the most recent ATSB stats report (AR-2013-084), we can get a guestimate of the engine failure rate for GA by adding the accident, serious incident and incident counts for "powerplant/propulsion", and diving by the total hours. For 2012, we get a GA engine failure rate of 0.16 failures per thousand hours. Note that this includes single and multi engined aircraft, and both piston and turbine, so it's not exactly comparable to the jab/rotax numbers given by raa. Also, there's probably differences in counting engine failures vs prop failures.

There are RAA numbers in the same stats report, but those numbers look seriously suspicious.

While on the ATSB website, there's an open investigation by them into "light sport" engines (AR-2013-107). It was due to be released last month, but that has yet to happen. Perhaps that report has triggered CASA's action.

- S
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Old 17th Nov 2014, 05:50
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Consultation period extended by 7 days.

Lots of legal weasel words, not much substance - what happens when you get lawyers involved.
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Old 17th Nov 2014, 06:26
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Would you care to elaborate on that? I did already, you just failed to copy and paste the rest of the answer.

Formation of CO2 releases more than 3x the energy of CO. OK, and by running richer and richer you generate a lot more CO.
The rest of the answer didn't say anything about the amount of energy released.

When rich by definition you are limited by the amount of O2. If you produce CO instead of CO2, you can only get 2 x CO for every CO2. Not "lots" - exactly 2.

2 x 1/3 = 2/3, which is less than 1. For each 2 CO you produce, you lose about 1/3 the energy you would get if it was less rich and the O2 ended up as CO2.

My high school chemistry calculations (admittedly with 25+ years of rust) Don't worry….I am worse off suggest that 10% excess fuel reduces the energy (heat) released by about 3%.

Not really, it slows down the burn rate, and the peak pressure occurs later, therefore at a lower peak pressure.
Yes, really. The energy (heat) released is well documented. More CO = less heat.

The chemistry says less energy is released.
By definition, EGT is lower when richer than peak EGT.
Full rich generally gives lower CHT.

So I don't understand the claim that fuel doesn't cool. If richer mixture doesn't cool, where does the heat go with all these cooler temperatures?

Maybe "fuel doesn't cool, it just heats less"? Of course it may not be the most efficient way of cooling, but it doesn't mean the effect doesn't exist.
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Old 17th Nov 2014, 08:52
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By definition, EGT is lower when richer than peak EGT.
By definition, EGT is also lower when leaner than peak EGT.
Full rich generally gives lower CHT.
Full lean always gives lower CHT. Any mixture that's leaner than about 50 degrees F ROP will also give a lower CHT than at 50 degrees ROP.

So, taking away fuel can also cool, and adding fuel can also heat, depending on where you are on the lean curve before you start taking the fuel away or adding the fuel.
So I don't understand the claim that fuel doesn't cool. If richer mixture doesn't cool, where does the heat go with all these cooler temperatures?
If you start at peak EGT, and add fuel (make the mixture richer) so that the EGT goes down by about 50 degrees F, your CHT will go up. So in this example, adding fuel doesn't cool.

If you start at 50 degrees F lean of peak, and add fuel (make the mixture richer) so that the EGT peaks and then goes down 50 degrees F on the rich side of peak, your CHT will go up. Lots. So in this example, adding fuel still doesn't cool.

Making your mixture increasingly rich from around 50 degrees F ROP will result in lowering of CHTs, because all other things being constant, as the mixture is made richer from around 50 degrees F ROP the peak pressure point in the combustion cycle becomes later, and therefore the peak pressure becomes lower. (Using a higher RPM will help as well.)
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Old 17th Nov 2014, 10:19
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andrewr

if you have an engine at peak EGT and you make it richer, which by your example means it will get cooler, why then does it get hotter (CHT) when the EGT is falling? And once past about 50 or so dF CHT will drop again.

When you get the concept here, the rest of my answer will make sense.

Not trying to be a smart ass, just want you to challenge the thought processes.

Creamie is onto it.
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Old 17th Nov 2014, 10:28
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shhh. yr rihgt will be here in a minute!
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Old 17th Nov 2014, 21:21
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Why dose cht rise. Because the energy is being released into the Cylinder chamber and not out the exhaust. Hence that's why you don't get burnt exhaust valves when running rop. But then again what would I know !!!
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Old 17th Nov 2014, 21:33
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But then again what would I know !!!
Right on cue!

You’ve demonstrated, time and time again, that you don’t know much about how engines run. That’s because you’re a piano tuner, not a piano player.

I can prove it.

Try this quick quiz, yr right.

(1) When will CHT be higher:
(a) When the mixture is leaned to peak EGT?
(b) When the mixture is leaned to 50 degrees F rich of peak EGT?

(2) How does a pilot know when the engine is running ROP?

The answers should be short and sweet, for someone of your enormous experience and knowlege.
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Old 17th Nov 2014, 22:01
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if you have an engine at peak EGT and you make it richer, which by your example means it will get cooler, why then does it get hotter (CHT) when the EGT is falling? And once past about 50 or so dF CHT will drop again.
The total energy released reduces as you produce CO instead of CO2. Total energy is divided between turning the prop (power), heating the engine (CHT) and out the exhaust (EGT).

CHT can increase while total energy decreases if there is a reduction somewhere else e.g. power or EGT. As you said, keep adding fuel and CHT drops too. No-one said that all temperatures had to drop in synchronization.

You can't create or destroy energy. The peak pressure point is a furphy - it cannot change the amount of energy you have, just where it ends up. If the peak pressure is later and CHT goes down, it means more energy goes out the exhaust or (possibly) turning the prop instead of heating the engine.

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.

Lean mixtures causing detonation is something that has been documented for a long time in many different engine types. Maybe George Braly has shown that Continentals/Lycomings have enough detonation margin to run LOP without detonation. (You might however ask the question whether that margin belongs to the engineer or is the end user's to use.) That doesn't mean that every engine has the same margins.

I somehow doubt that he has done extensive testing of Jabiru engines and their detonation margins. Without that testing, suggesting that Jabiru engines would be more reliable if they ran leaner is dangerous guesswork.

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.
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