"Jaberoo" down (Mildura this time)

[reggie]

Dunno about an ignore button but we sure could use a W----r button.

 

 

[Dafydd Llewellyn]

I'll offer a crumb: The instruments used for measuring CHT are thermocouples. How many of you really understand how thermocouple instruments work?

 

What a thermocouple does, is measure the difference in temperature between its hot end ("hot junction") and its cold end ("cold junction"). If the cold junction is NOT at the temperature the instrument manufacturer designed it for, and if it is a simple instrument lacking "cold junction compensation", it will have an error; if the cold junction is located in a hotter place than the instrument manufacturer expected, the thermocouple instrument will read low. I suggest you look at your CHT instrument and find where its cold junction is located. Then look it up in the instrument maker's specifications, and find out what the assumed cold junction temperature is, that the instrument was designed for.

 

This is not likely to be an issue for the more sophisticated EMS-type instruments, because they usually have cold junction compensation (but read the fine print!). It's most likely to be an issue with a single-purpose instrument. VDO commonly assumes, as far as I can discover, that the cold junction will be at 30C. It will read wrongly by the amount the actual cold junction temperature differs from this.

 

I suspect some of the Jabiru problems may arise because their CHTs are reading low, from this cause. It would certainly account for the variability we hear so much about. People need to be careful about where the cold junction is located. Keep it cool.

 

 

[Butch]

Yes theres evidence of a number of things which break.........the whole point of analysing engines and flight data is this is possibly NOT the cause of the engine problem but the symptom.Make those bits stronger and it will break somewhere else

Its not like theres an answer there and with more pressure they will reveal it

 

Wouldnt it be interesting if facts said 75-80% of failures were in hydraulic lifter engines?

 

As far as you go Butch aounds like you should be flying a turbine, everything is sorted , nothing to touch.......bit more money and training required thats it. Dont approach any aircraft with the thought, nothing will go wrong its all sorted for me.

Hi jetjr,

 

I know nothings bullet proof, I had an early model Mazda ute.....let it overheat just once and the alloy head would warp.....new head gasket. This happened 3 times in a few years.

 

It was a known fault with this engine....what did Mazda do redesign the engine to improve or fix the problem.

 

My logic is why tempt fate with a product that has faults and the manufacturer seems not interested in fixing when there are other alternatives that may still fail but the law of averages of this happening are far less,

 

cheer's Butch

 

 

[bexrbetter]

Peter said this thread was making him sick

Peter did say the thread made him sick

 

But we know what makes that tick

 

It's a subject involving EGT

 

That ends up news on the ABC

 

Today a problem of a cylinder nut

 

That made the golfers afraid to putt

 

Previously it was the flywheel bolt

 

That made a few flyers revolt

 

And now we leave it in the hands of Bent

 

Lets hope for a resolve to all this vent!

 

 

[motzartmerv]

. How many of you really understand how thermocouple instruments work?I suggest you look at your CHT instrument and find where its cold junction is located. Then look it up in the instrument maker's specifications, and find out what the assumed cold junction temperature is, that the instrument was designed for.

I suspect some of the Jabiru problems may arise because their CHTs are reading low, from this cause. People need to be careful about where the cold junction is located. Keep it cool.

Or, we could ask the manufacturer to "learn all this cool stuff" hey, seeing as we are buying a certified Aeroplane engine. I think your question should be does the manufacturer know how a thermocouple works?. I dont need to know sh!t about my commodore, I turn the key and it works. Thermocouple schmermocouple.

 

 

[motzartmerv]

That being said. I have to agree, i think the CHT is a major cause of the problems. Thats not coming from any engineering back ground, just purely operational experience. Having had over half a dozen different model jabs over a few years, in different schools/ locations, Ive noticed the only engine I could say has been OK is the coolest running of them all. By far, and the one thats caused the least problems. I think the figures in POH etc are wrong. I dont think you can run these things at 180 deg's and expect them to last.

 

 

[Dafydd Llewellyn]

Or, we could ask the manufacturer to "learn all this cool stuff" hey, seeing as we are buying a certified Aeroplane engine. I think your question should be does the manufacturer know how a thermocouple works?. I dont need to know sh!t about my commodore, I turn the key and it works. Thermocouple schmermocouple.

Is the CHT instrument included in the engine parts catalog? I didn't think it was . . . That being said, I agree you cannot expect the engines to tolerate 180C on the CHT gauge continuously - especially if the cold junction of the CHT system happens to be exposed to heat. Putting a multi-probe EMS into one of these aircraft is, I suspect, cheap insurance. There has been a big change in thermocouple instrument designs in recent years; 20 years ago, the typical aircraft CHT instrument used a massive-wire thermocouple, and it came with a set of calibrated leads, made from the thermocouple alloys, not copper wire, that must not be cut to length. That was because its meter was a simple milliamp meter that measured the current in the circuit that resulted from the voltage generated by the temperature difference. For that style of instrument, the cold junction was at the instrument itself. Those instruments are invariably self-powering, that is, they need no external power, unless it's for the instrument's internal lighting - they will give a reading even if the master switch is off. More recently, the instruments use fine-wire thermocouples, and they have an amplifier chip in them, so they measure the circuit voltage directly. By doing so, they have a very high impedance - which means they draw almost no current from the thermocouple circuit - so variations in the electrical resistance of that circuit have vastly less effect on their accuracy. This style of instrument won't give a reading with the master switch off. Ideally, the leads are still made from the thermocouple wire, all the way to the instrument, which puts the cold junction at the instrument.

However, thermocouple alloys are expensive - especially the K-type (Chromel/Alumel), which is almost universally used in modern instruments, because it behaves linearly over a very large temperature range, so some manufacturers use copper wire to carry the circuit back to the instrument. In such a situation, the cold junction is where the wires change from the thermocouple alloys to copper. That's the type that can easily give grossly wrong readings. The instrument manufacturers do not point out this subtlety.

 

In the last year or two, EMS systems have started to appear that have an intermediate module, that can be located in the engine bay. The thermocouple wires run to it, and it contains the cold junction and the amplifier module, and it sends the data on to a display in the cockpit. It needs to include cold junction compensation; in effect, the cold junction compensation is a separate sensor that tells the intermediate module how hot it is; the thermocouple tells it how much hotter the cylinder head is, and it adds the two together and sends that on to the display. Provided all that works correctly, the result can be very accurate. All this post-dates the original certification of the Jabiru.

 

I'm not an instrument expert - but I have had to learn this stuff in the process of doing certification flight testing, because I have always found that the most difficult aspect of that work is getting instruments that do not tell lies.

 

 

[turboplanner]

If you're correct (and I'm not suggesting that you're not). Then if CASA was to launch an investigation into the common failure points of the J2200 engine either on it's own motion or in response to a request from the RAA, wouldn't they, if they're only going to look at the "what" not the "why", limit their investigation to determining whether the engines and all their component parts are still being manufactured to the design standards they were built to when the J2200 gained certification? I would've thought that the "what" is obvious. Surely it's the "why" that's important. If the RAA (and by that I mean not just the Organisation but us, the members) hopes to gain anything out of petitioning CASA to "do something" they/we need to provide a wealth of in-depth accurate and intellectually rigourous reporting on the cause(s) of the failures. If CASA decides develop new standards or raise the bar, surely they need to understand why the existing standards are insufficient. Simply saying that through bolts break and should therefore be made stronger isn't improving the engineering standard, it's just spackling over the cracks. Is that spending the taxpayers money wisely?From what I've seen, Ian Bent is going to great lengths to identify and understand the root causes of the failures and use that information to improve the engineering and design of his engine. I imagine that when/if he seeks certification for his engine all that information will be provided to CASA as justification for the changes. So I suppose Ian is doing what the RAA is asking CASA to do. Investigate. The expense must be horrendous. I sure hope he gains adequate rewards for his efforts.

 

And before the crabs (not you Turbs) respond to that bit of bait I should assert that I have no financial interest in either Jabiru or CAMit, though I wouldn't mind buying shares in CAMit if Ian was offering..... I do have shares in a Jab and I am very keen to have it fit on the "no problems" side of the ledger.

I'm not sure why RAA would step back from self administration and ask CASA to do its work. It has to power under its incorporation with the ACT Department of Justice to expand its constitution and rules o ensure safe operations.

 

I'm not sure that CASA would "launch an investigation"

 

There would be procedures to ensure an engine remained as certified, however a certified engine can still have problems which could result in safety issues.

 

The reason the Government doesn't get involved in the "why" is that it would cost money, and if they decided they knew why and issued instructions to modify, for example, timing, camshaft gear etc. they would then bear the liability costs if their design failed.

 

To give you an example of how things operate within the same government department CASA belongs to, the government specifies performance requirements for vehicle braking, and performance requirements for some of the key systems. It's up to the manufacturer to design his system with the components of his choice. If the manufacturer has a series of brake failures, he hasn't met the performance standard so the government just sanctions him until he does. They don't start getting into a discussion of how brand X valve is better than brand Y valve which is having all the failures - they just make him spend his own money on design and testing until he can show he meets the standard.

 

So if the issue WAS through bolts, I couldn't see CASA telling someone to make them bigger as you say, but would expect a broader performance requirement, which would allow the manufacturer to continue to use the same bolts if he found the cause was not in fact undersize bolts, but excessive intermittent forces which he could prevent by action X.

 

A government might develop new standards if the existing standard was obviously inadequate, for example where statistics showed that a significant number of people were dying from head injuries in side collisions a government may introduce a requirement for head protection in those incidents to a performance standard, and a manufacturer may respond by using an airbag design, or body structure - its up to him.

 

I've seen speculation/claims on what some engine manufacturers are going to do, but I've seen no tested-in-service (and I mean hundreds of engines over thousands of hours) examples from the people making the claims, and after several decades of experience with the manufacturing and operations of many engines by some of the world's best builders I like to wait for that result before getting excited. I'm not saying someone who is diligently working will not be able to achieve success right out of the box - Phil Irving/Jack Brabham/Repco/GM did, I'm just pointing out that designing and building an engine is an incredibly complex process.

 

 

[johnm]

specify nothing specifically ............. but, encompass the whole thing (an unknown things) in a performance requirement that has to be achieved - yuck

 

 

[turboplanner]

specify nothing specifically ............. but, encompass the whole thing (an unknown things) in a performance requirement that has to be achieved - yuck

If the government sees from its statistics that a lot of Make X cars are having brake failures it doesn't spend taxpayers money on extensive durability and trial testing to find the faulty component, and it doesn't employ design engineers whose job it is to design a better component than the manufacturer who developed the product, then specify that that component has to be fitted, and so take over public liability for any failures on their redesign, at our (taxpayers) expense. They're smarter than that, so they just come up with a standard which requires the manufacturer to stop the failures, and he has to do the diagnosis, redesign and in-field testing at HIS expense. It's his business (and quite often commercial in confidence) what he does.

 

 

[Dafydd Llewellyn]

I'm not sure why RAA would step back from self administration and ask CASA to do its work. It has to power under its incorporation with the ACT Department of Justice to expand its constitution and rules o ensure safe operations.I'm not sure that CASA would "launch an investigation"

 

There would be procedures to ensure an engine remained as certified, however a certified engine can still have problems which could result in safety issues.

 

The reason the Government doesn't get involved in the "why" is that it would cost money, and if they decided they knew why and issued instructions to modify, for example, timing, camshaft gear etc. they would then bear the liability costs if their design failed.

 

To give you an example of how things operate within the same government department CASA belongs to, the government specifies performance requirements for vehicle braking, and performance requirements for some of the key systems. It's up to the manufacturer to design his system with the components of his choice. If the manufacturer has a series of brake failures, he hasn't met the performance standard so the government just sanctions him until he does. They don't start getting into a discussion of how brand X valve is better than brand Y valve which is having all the failures - they just make him spend his own money on design and testing until he can show he meets the standard.

 

So if the issue WAS through bolts, I couldn't see CASA telling someone to make them bigger as you say, but would expect a broader performance requirement, which would allow the manufacturer to continue to use the same bolts if he found the cause was not in fact undersize bolts, but excessive intermittent forces which he could prevent by action X.

 

A government might develop new standards if the existing standard was obviously inadequate, for example where statistics showed that a significant number of people were dying from head injuries in side collisions a government may introduce a requirement for head protection in those incidents to a performance standard, and a manufacturer may respond by using an airbag design, or body structure - its up to him.

 

I've seen speculation/claims on what some engine manufacturers are going to do, but I've seen no tested-in-service (and I mean hundreds of engines over thousands of hours) examples from the people making the claims, and after several decades of experience with the manufacturing and operations of many engines by some of the world's best builders I like to wait for that result before getting excited. I'm not saying someone who is diligently working will not be able to achieve success right out of the box - Phil Irving/Jack Brabham/Repco/GM did, I'm just pointing out that designing and building an engine is an incredibly complex process.

The word is "certificated" - i.e. having a Type Certificate.

The normal way these things usually go, is that CASA asks the manufacturer to put out a Service Bulletin. If CASA is not satisfied with the SB, it can withdraw or suspend the manufacturer's Production Certificate, under CASR 21.002. If CASA is satisfied that a defect exists, the manufacturer was aware of it, and failed to report it to CASA, it can prosecute the manufacturer under CASR 21.003.

 

CASA may elect to make a SB mandatory, by issuing an Airworthiness Directive under CASR Part 39.

 

You are quite correct that CASA will NOT design a modification itself. It will lean on the manufacturer instead - and it can lean very heavily indeed.

 

 

[motzartmerv]

Yes, see the R44 fuel tank bladders for a perfect example of how that all plays out. And interestingly, how pressure from the public (thanks Andy) can sway the actions of the regulator.

 

Those things killed dozens of people world wide, and CASA finally stepped up and changed the mod from an SB to an AD.

 

 

[planedriver]

That was another action that was long overdue

 

 

[AVOCET]

That was another action that was long overdue

Seems that people have to die before casa feels its necessary to step in . And maybe commercial in-confidence talks have already been put in place between jab and cam .

After all , all we will ever find out on a forum is folks opinions and thoughts .

 

 

[gandalph]

I dont need to know sh!t about my commodore, I turn the key and it works. Thermocouple schmermocouple.

Yeah but you surely don't transfer that mindset to your flying or instructing, do you?

 

 

[gandalph]

I'm not sure why RAA would step back from self administration and ask CASA to do its work. It has to power under its incorporation with the ACT Department of Justice to expand its constitution and rules o ensure safe operations.

 

I agree that the RAA has the power but does it have the expertise or the resources and will to gain the expertise?

 

 

[motzartmerv]

Yeah but you surely don't transfer that mindset to your flying or instructing, do you?

No, but I dont think I need to re design an engine or its instruments after Ive purchased a certified aeroplane.

 

 

[Dafydd Llewellyn]

No, but I dont think I need to re design an engine or its instruments after Ive purchased a certified aeroplane.

I'm not suggesting that you should. I'm trying to help prevent further accidents. If you choose to ignore what I provided on principle, that's fine by me.

 

 

[motzartmerv]

What would you have me do Daffyd? Play with the instruments on a certified aeroplane? Get an EO to change the location of a sensor? Im not chosing to ignore anything, you know very well we cant just fiddle with things on the word of a forum post.

 

Write me an EO, and ill get my engineer to do it.

 

 

[Dafydd Llewellyn]

What would you have me do Daffyd? Play with the instruments on a certified aeroplane? Get an EO to change the location of a sensor? Im not chosing to ignore anything, you know very well we cant just fiddle with things on the word of a forum post.Write me an EO, and ill get my engineer to do it.

I suggest you locate the cold junction of your CHT instrument, and make sure it's not being exposed to hot air. I'm retired from the CAR 35 game, so I can't write you an EO; but see what it says in the Jabiru engine installation instructions for your model. For the 2200, the relevant info is on Page 21.

 

 

[turboplanner]

I agree that the RAA has the power but does it have the expertise or the resources and will to gain the expertise?

I think the expertise is there, among the members, the resources are there, through volunteers the same as any other association, and the will I'll leave up to you.

 

 

[alf jessup]

Interesting read in Jabba Chat

 

I think J owners should have a read if your a tinkerer

 

http://www.jabiru.net.au/images/jaba/Contrary_to_local_rumour.docx

 

 

[motzartmerv]

Lol.. What a champion..

 

 

[alf jessup]

Dont expect action like the blader tanks the 44 is a certified helicopter

Qld state based news reported yesterday that jabiru is under investigation by CASA and Sue Woods was making coments and apparently said (this was secnd hand info) that the jab in Qld that crashed recently its engine was stil running so it was not the engine that failed and the one at Mildura was owner manetainer so they do not have enuff information to know what broke on it yet

 

I repeate this was second hand info from someone they watched the news

All we know for sure Deb is in both cases they could not defy the pull of gravity and gravity won in both cases

 

 

[AVOCET]

What would you have me do Daffyd? Play with the instruments on a certified aeroplane? Get an EO to change the location of a sensor? Im not chosing to ignore anything, you know very well we cant just fiddle with things on the word of a forum post.Write me an EO, and ill get my engineer to do it.

Maybe a bit of tweaking , i could give a rats .if its wrong fix it .