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Jabiru Bad experience

Old 20th Jan 2014, 05:37
  #41 (permalink)  
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Zanthrus, can I use that bottom line? very funny, thinking of ideas for side stripes on the 160...
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Old 20th Jan 2014, 05:50
  #42 (permalink)  
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XXX,
heres two of the reasons Jabiru gave me for the J160 heads failing, the other was to accuse me of running an additive. I quote Sue woods the business manager:-


"The word from the engine section regarding the heads is that there is evidence of overheating of the exhaust port areas probably from leaking exhaust pipes. This overheating has resulted in the valve seats dislodging and valve stem damage. They suggest the installation of EGT monitoring as an early warning for leaking exhaust pipes. Also carburettor jetting can be checked against the EGT measurements on the Mogas, Avgas and mixture of Avgas and Mogas. The cracks in the heads may have been caused by the overheating though they donít appear to have contributed to the engine failure. For any more information speak to Mark in the engine section."


XXX, point of note a full brief of equipment fitted and conditions at the time was sent, they missed the fact that it had the desired sensors, also if you read the report into my other engine, the 3300 you will note that Jabiru state that the seats will start to fall out at 250c. also they found that one head had an exhaust leak at the flange, gripping at straws if you think that effected all heads... So I politely pointed out the inconsistency in their conclusion and got this:-


"Hi Chad

The engine section has examined the heads and the piston and cannot see any manufacturing defect that has caused this damage therefore we will help as far as providing the 2nd hand heads as quoted. If you want to send us the EMS data file we would be interested to see the EGT measurements against what fuel was in use. "


I have considered driving the 7 hours to get the EMS file for them, but I can guarantee it will show that they have been kept within limits! further all Jabiru would say if I tried to use that as evidence is that its a non calibrated instrument.


Sue has informed me that they will not be returning my heads, only after I requested them back for a third party to inspect and report on, she quoted her requirement to hold them in quarantine for one year so CASA can inspect. I provided her with this from the section head of defect investigation at CASA:


Hi Chad,

This email formally notifies you that under Civil Aviation Regulation 52B(3) that your Jabiru cylinder heads are not required to be kept in a state which allows CASA to investigate the defect.


Still refuses to return my property.







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Old 20th Jan 2014, 05:51
  #43 (permalink)  
 
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Why would they need a log book to explain how and why an engine failed? Its simple. They pull it apart, find the broken bit. The blaming of the operator (need for log book) would come later yea? Thats the usual routine isnt it?
"oh, youve overheated it"
" umm, no I havnt, I have 4 channel EGT/CHT for entire life of (rebuilt) engine which clearly shows always in specs."
"Oh, well, in that case, you used the wrong fuel additives"
"Ummm, no, i dont use fuel additives"
Oh...fair enough, well, then im afraid youve overheated it"..
"Ummm..havnt we been over this?"..
"oh yea, sorry, i got confused who i was talking to. You must understand we deal with a lot of these failures every week, I got confused"
"ok, so can you please tell me why my factory engine died at 300 hours?"
" Yes, we probably can..But..Not right now..We want to quarantine the parts so casa can see them...one day..maybe."

"Ok, just let me know please..Now, can you put me through to the sales dept..i need to buy some new parts to fit to my factory engine that doesnt work anymore"
"yes certainly sir"


While you may think this is a joke, i assure you its not. every part of that conversation I have witnessed first hand.
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Old 20th Jan 2014, 06:34
  #44 (permalink)  
 
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All four in Jabiru 2200 aircraft.

Two engines cut out short final when power reduced to idle for landing.

One cut out during a stall practice at 4000ft in training area accompanied by a wing drop at the stall. Exciting! Restarted ok.
I chuckled when I read this, so you have had one genuine engine failure that can be attributed to the condition of the engine.

Adjustment of the idle stop is hardly a fault of the engine or engine manufacturer !
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Old 20th Jan 2014, 06:50
  #45 (permalink)  
 
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Yea, hafta agree. It seems your engines were idling to slow.
I once did the testing for a Jab powered homebuilt. For some reason, the engine would idle normally on the ground, but in flight would idle down and stop. Was strange and counter intuitive. I cant recall the reason. Sorry, getting old..
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Old 20th Jan 2014, 07:06
  #46 (permalink)  
 
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I have considered driving the 7 hours to get the EMS file for them, but I can guarantee it will show that they have been kept within limits! further all Jabiru would say if I tried to use that as evidence is that its a non calibrated instrument.
Well I would happily look at it for you, but can I say that there is no such thing as an EGT within limits, except when talking about a TIT, but that is not relevant here.

Have you been using Avgas? Mogas? and which sort and where from?

And just in case you are wondering ....which do you think has the highest EGT and which is the better off the two?

And just before you think I have any involvement with Jabiru, I do not. But I might be able to offer rational understanding of engines the data and they fuel used. Gidday Wally!
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Old 20th Jan 2014, 07:23
  #47 (permalink)  
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Jabbawocky,
mogas, higher EGT than avgas.
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Old 20th Jan 2014, 07:24
  #48 (permalink)  
 
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M,

For some reason, the engine would idle normally on the ground, but in flight would idle down and stop. Was strange and counter intuitive.
My best 'guess' would be induced prop drag due airspeed. I used to operate a C206 that would slow the idle when turning right due (I'm told) to gyroscopic propeller influences. Never occurred when turning left.

An aerodynamicist or engineer may have a more qualified answer.
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Old 20th Jan 2014, 09:10
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Deadstick 1 you have one more guess. I'll let Jabba explain why. Cheers RA

Hint:- Compare what happens after the spark event using the two different fuels. Especially look at peak pressure and where it occurs and what happens to CHTs The timing and RPM should be the same for both fuels when you do the comparison.

Last edited by rutan around; 20th Jan 2014 at 09:42.
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Old 20th Jan 2014, 09:21
  #50 (permalink)  
 
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Adjustment of the idle stop is hardly a fault of the engine or engine manufacturer !
Yea, hafta agree. It seems your engines were idling to slow.
Nothing like judgement by your peers

The two J160's I have time in both have a peculiarity. If the idle is set correctly and a ham fisted pilot heaves the throttle shut the engine stops. If the idle speed is set high so the engine can't stop with a hard yank on the throttle then excessive braking is required or you need to instruct to pull the throttle very hard and keep the pressure on. There is a flex in the system somewhere that I have NEVER encountered in any GA aircraft. Gifted engineers have looked at these two aircraft, the best they come up with (failing modification) is a compromise, high idle or an engine that can be stopped by hauling hard on the throttle.

I know the problem Zanthrus, I have seen it, having a prop stop on final or on the runway is not really my cup of tea.

That said, both aircraft have had no engine problems, both have 2200 hours and both have had engines replaced (in lieu of a top overhaul) every 1000 hours.
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Old 20th Jan 2014, 10:23
  #51 (permalink)  
 
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hey Bob. No judgment mate. Just a possible explanation to his woes..Which you subsequently provided further evidence for. Judgment? or discussion..?

Ive not come across that problem in jabs. You must have some strong handed pilots there, pulling on that throttle.
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Old 20th Jan 2014, 10:30
  #52 (permalink)  
 
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Rutan around..... Good work there. Clearly not rutanaround at the back of the class were you. Unlike a couple of other ppruners

deadstick
The shorter latency of mogas Vs Avgas means that the peak pressure is higher and so is the CHT. Neither of these things is optimal.

The spark timing is fixed at 25DBTDC and being a direct coil on the flywheel system this will mean the spark (in theory) will fire sooner than that of a conventional magneto, but only a little. It could be said that the plugs location partially offsets this, but I do not know that for sure. (Flame front propagation).

High CHT, poor fuel quality, and with MOGAS there is not guarantee, there could be increased peak pressure and thus CHT. Add to this induction leaks and or the ordinary fuel distribution and how you know what was happening.

My suggestion is that with Mogas compared to Avgas all things being equal, you had higher CHT and lower EGT.

There is a large difference in Octane rating. So specifically which Mogas were they using and from where?

So getting back to the failure with a rapidly rising CHT and the two instructors on board, have you any photo's of the failed cylinder?
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Old 20th Jan 2014, 10:33
  #53 (permalink)  
 
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Hey hold on, I was up the front

There might have been a bit of rooting around but I got the most important question right
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Old 20th Jan 2014, 10:39
  #54 (permalink)  
 
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Do Jabiru certify mogas in their engines? If so are there any modifications needed (IAW with the maintenance manuals) to account for this issue?
Another question. How do other aircraft engines that allow both types of fuel handle the issue? Im assuming the engine manufacturers have similar or dare I say it, better knowledge about these problems?
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Old 20th Jan 2014, 10:49
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Another question. How do other aircraft engines that allow both types of fuel handle the issue? Im assuming the engine manufacturers have similar or dare I say it, better knowledge about these problems?
There is a bucketload of material on this. Try this to start. You'll find more with the EAA, possibly AOPA and I think the Cafe Foundation.

Petersen Aviation | Auto Fuel STC

In short (aside from octane issues) Mogas compatibility has to do with fuel pump configuration and fuel line fitting metal composition. The engine itself doesn't care much, its all about getting it to the engine.
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Old 20th Jan 2014, 10:50
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It is impossible to pull the throttle rotating mechanism past the stop located on the side of the carburetor, basic physics that one!

If the engine stops when the throttle is pulled out of the dash regardless of the strength of the pilot(s), then the idle stop is incorrectly set. Pretty simple really.

What will be wrong in the instances of stoppages mentioned above, is that the location of the cable assembly is incorrect both where it passes through the firewall and also through the holder attached to the carby. In all honesty if your mechanic can't get this right, they should stick to lawn mowers and I'm not referring to ultralights either. Failing that the problem will go away after replacing the throttle cable. I would be more than happy to demonstrate the correct fitting of the cable whenever I next pass through wherever this problem exists.


You will never ever get me back in that piece of $hit wing cracking, engine failing, random flap retracting, small wheelled uncomfortable aircraft.
Would love to hear more on the wing cracking and random flap retraction. Both of those if reported would probably warrant an SB. As for random flap retraction, they are either manual flaps on an old LSA55 or electric in the J160 onwards and short of some shoddy maintenance I can't imagine why the flaps would randomly retract. No wonder these aircraft are getting a bad name when mechanics can't seem to look after them properly.
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Old 20th Jan 2014, 10:55
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Yes yes. I get that. But, im saying that clearly there are engines that are designed to run on both types of fuel. My question is, what, if any measures do operators of these engines have to take when running the different fuels to account for these problems.. Apart from the rotax schedule of extra oil changes. Whats the difference. if its enough of a difference for some of you to blame the fuel for overheating the engine to FAILURE, then surely it would be enough of a difference to warrant standardised handling of the engines with different fuels.. of which there is non that im aware. Please tell me if im wrong.
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Old 20th Jan 2014, 11:15
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Heat comes from energy. Its about how much power the engine produces and how effective the cooling, not the fuel that supplies the energy. I have only half been following this thread, but I think some of the failures may not fit the symptoms. I struggle to see how fuel type would play a role. Ignition timing might (come in Jaba).

As a rule of thumb car sump oil runs about 20 degC hotter than the water temp. Modern cars can easily run over 100 degC, so an acceptable operating temperature for oil is 120 degC (say 250 degF) for as long as you like. Use Synthetic and you'll go a lot higher. Higher temperature causes mineral oil molecular chains to break down. A modern car will happily do this on a synthetic blend oil for 30,000 km which equates to about 150 hours (an overall average of 50 km/h is a reasonable guess for an average suburban based driver with a mix of city, suburban and freeway driving). The Jabiru (I believe) uses automotive oil not the old mineral cr*p that certified engines use.

Oil is a major part of the cooling of any engine (even water cooled ones). I forget the proportion of cooling done by oil, but it might be circa 20%. Automotive oil will have better " wetting" properties and I would expect would transfer heat more effectively that aviation oils.

We should be able to design & build engines to cope with this and I struggle to see how through bolt issues are related to operating temperature. If I were to investigate this, I'd start by looking at the operating practices.

As I said, I haven't really paid full attention. These are off the cuff ideas. I might have something wrong.
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Old 20th Jan 2014, 11:15
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Hey XXX

Glad I gave you a chuckle and I agree engine cuts on idle power may not be classed an engine failure. I can tell you it was a big surprise and very sudden. It was not as a result of ham fisted yanking closed either.

The flaps were manual on left side of roof. Half a broom handle and a bush which kept popping out of the hole holding the flap setting. Sudden bang and loss of lift which really scared the student in left seat!

Wing root cracks starting in windscreen. I was told that is just the gel coat she'll be right. Still not a good look and I never totally believed them. I have never seen this type of defect in other composite ga aircraft. Seems ultra light are a different breed.

Z!
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Old 20th Jan 2014, 11:21
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Yea, sudden uncommanded flap retraction makes the aeroplane unserviceable in my opinion. If you flew it in that state...more power to ya brother.
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