Jabiru engine failures
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WE HAVE ... Throttle body installed and direct port injection, 
have the data to prove the system works for us ....unleaded 95 octane fuels....Have a very happy Jabi Motor. With lean or rich mixture control in flight.
check out.......
AvCom ? View topic - Electronic Fuel Injection
have the data to prove the system works for us ....unleaded 95 octane fuels....Have a very happy Jabi Motor. With lean or rich mixture control in flight.check out.......
AvCom ? View topic - Electronic Fuel Injection
Last edited by flightstick; 4th Dec 2014 at 09:47.
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Apologies for repeating a post.
But; things changed Dec 01, 2014. IMO Jabiru could demand and, probably receive a new deal, given the facts. Perhaps if the affected parties all got together and presented a united, consolidated, comprehensive, cohesive, no pulled punches report to the new board; who knows.
Every time someone has their cage rattled; see what was promised and point out to the 'rattler' that the action they propose is contrary to the spirit and intent of the Truss acceptance of the Rev. Forsyths' little shopping list. None of the promised changes will happen if industry does not pull it's weight and make things happen. Jabiru can now dispense with the old method of simply copping it. Use the words to insist on an new deal, fresh eyes and proper homework being presented to Skidmore and his board. Make the buggers work.
'Jab' handled properly could do more to decimate the remnants of the McComic supported bastardry than Pel Air did. For starters, it's jobs and export $$ CASA intend to remove, that has legs. Prove the 'facts and circumstances' to be incorrect and take them directly to 'the man', argue the case and prove the vendetta was all about the CASA antagonist covering his arse, lest the duck-ups from his previous jobs reflect badly on his future well being. This is now contrary to the stated government policy of change. The tools are there, just pick 'em up and use them; without fear.
Just saying –
Mind you, I'd say just about anything to break the endless cycle of ROP/LOP 'discussions'...
...
Every time someone has their cage rattled; see what was promised and point out to the 'rattler' that the action they propose is contrary to the spirit and intent of the Truss acceptance of the Rev. Forsyths' little shopping list. None of the promised changes will happen if industry does not pull it's weight and make things happen. Jabiru can now dispense with the old method of simply copping it. Use the words to insist on an new deal, fresh eyes and proper homework being presented to Skidmore and his board. Make the buggers work.
'Jab' handled properly could do more to decimate the remnants of the McComic supported bastardry than Pel Air did. For starters, it's jobs and export $$ CASA intend to remove, that has legs. Prove the 'facts and circumstances' to be incorrect and take them directly to 'the man', argue the case and prove the vendetta was all about the CASA antagonist covering his arse, lest the duck-ups from his previous jobs reflect badly on his future well being. This is now contrary to the stated government policy of change. The tools are there, just pick 'em up and use them; without fear.
Just saying –
Mind you, I'd say just about anything to break the endless cycle of ROP/LOP 'discussions'...
...
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flightstick,
welcome and a very interesting post indeed.
I think if I may, a few subtle corrections and educational points, as you may have some assumptions based on correlation not causation.
The extra fuel delays the peak pressure by slowing the speed of the flame front. This means the peak occurs further from TDC, in a larger volume and thus a lower peak pressure. It is the peak pressure that determines the CHT and piston temperature. There is a bunch more explanation, happy to do it via phone Skype or in class, but that might be a long way for you to travel.
You are on the right track, just correlation is confused with causation. The actual EGT is not the problem. In fact as funny as it sounds, the valve and seat temperatures are cooler at peak EGT than they are at 50dF ROP or as you approach best power (12.5-13.5 roughly).
It is not the temperature of the valve, it is the distortion of the head and valve components and subsequent valve guide wear that causes the valve to not seat nicely, and thus the "rattling into place" that stresses the valve and breaks the head off.
Here are a few graphs that contain much of the knowledge that has been passed down.
Just to finish off, if you can control your fuel injection on each individual cylinder to match the air intake (volumetric) and maintain an AFR that is consistent across all 4 or 6 cylinders, and do this in real time closed loop, you will not only have a wonderfully smooth Jab engine but one that will run Lean Of Peak at the top of the brown BSFC curve above, all day long and with superb reliability.
I would be interested to chat with you about it if you can. You can use a Lamda probe or EGT for feedback. But the Lamda probe would make the processing easier, but cost a lot more.
Cheers
David Brown
welcome and a very interesting post indeed.
I think if I may, a few subtle corrections and educational points, as you may have some assumptions based on correlation not causation.
he excess fuel drops the combustion temperatures, EGTs and cools the piston crowns themselves, keeping them within their safe thermal limits.
these parts have thermal limits and high EGTs can decrease the life of these components. Rich mixtures decrease EGTs and exhaust valve temperatures.
It is not the temperature of the valve, it is the distortion of the head and valve components and subsequent valve guide wear that causes the valve to not seat nicely, and thus the "rattling into place" that stresses the valve and breaks the head off.
Here are a few graphs that contain much of the knowledge that has been passed down.
Just to finish off, if you can control your fuel injection on each individual cylinder to match the air intake (volumetric) and maintain an AFR that is consistent across all 4 or 6 cylinders, and do this in real time closed loop, you will not only have a wonderfully smooth Jab engine but one that will run Lean Of Peak at the top of the brown BSFC curve above, all day long and with superb reliability.
I would be interested to chat with you about it if you can. You can use a Lamda probe or EGT for feedback. But the Lamda probe would make the processing easier, but cost a lot more.
Cheers
David Brown
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David,
Thanks for that explanation. I have a better understanding now. For me this is a steep learning curve. Just a quick change in subject. Im not particularly interested in all the BS going on with JAb . Why stress over something that is totally out of my control. Whatever happens happens. We that's my son and myself decided to go for it ourselves and try and make our J400 " Robust " to suite our mission which is touring, not flying around the patch. We wanted efficiency and reliability. We all know that cooling, engine management, fuel delivery is the key. I think we have managed this. We have gone from Avgas to Mogas successfully without an issue. We are able to control cooling , fuel flow to a point, right now we working on baffling/ ducting with some success.
Anyway the system does not allow the injectors to be individually tuned, they are pulsed in pairs. The main problem on some engines such as the Jab is that the intake manifold probably does not flow equal amounts of air so the AFR is slightly different in each cylinder, even with EFI. Some expensive systems like Motec allow individual cylinder trim for fuel but they are over $4K for the ECU I believe. Programming becomes very complex as the trim amount may vary with rpm and throttle opening. EGTs may not be a totally reliable guide for tuning either.Only way to do this is to change an injector to suite the data. I did request this from the developers but as you well know development and RD costs dearly. We have a Lamda sensor in the system sits about 20 cm on the exit side of the exhaust so its an accumulative reading of exhaust gases. The software does allow for O2 logging which is particularly useful for the WOT settings and cruise settings. Basically the system is mapped on the ground to WOT every 250 RPM using an external lamda probe, LM 2 . The fine tuning is done in flight by adjusting the mixtures and computing the differences . No changes are made in flight. All done in the map programming.
Anyway would really like to chat, don't think this is the place send me an email with your skype contact and we can knock heads.
cheers
Gary
Thanks for that explanation. I have a better understanding now. For me this is a steep learning curve. Just a quick change in subject. Im not particularly interested in all the BS going on with JAb . Why stress over something that is totally out of my control. Whatever happens happens. We that's my son and myself decided to go for it ourselves and try and make our J400 " Robust " to suite our mission which is touring, not flying around the patch. We wanted efficiency and reliability. We all know that cooling, engine management, fuel delivery is the key. I think we have managed this. We have gone from Avgas to Mogas successfully without an issue. We are able to control cooling , fuel flow to a point, right now we working on baffling/ ducting with some success.
Anyway the system does not allow the injectors to be individually tuned, they are pulsed in pairs. The main problem on some engines such as the Jab is that the intake manifold probably does not flow equal amounts of air so the AFR is slightly different in each cylinder, even with EFI. Some expensive systems like Motec allow individual cylinder trim for fuel but they are over $4K for the ECU I believe. Programming becomes very complex as the trim amount may vary with rpm and throttle opening. EGTs may not be a totally reliable guide for tuning either.Only way to do this is to change an injector to suite the data. I did request this from the developers but as you well know development and RD costs dearly. We have a Lamda sensor in the system sits about 20 cm on the exit side of the exhaust so its an accumulative reading of exhaust gases. The software does allow for O2 logging which is particularly useful for the WOT settings and cruise settings. Basically the system is mapped on the ground to WOT every 250 RPM using an external lamda probe, LM 2 . The fine tuning is done in flight by adjusting the mixtures and computing the differences . No changes are made in flight. All done in the map programming.
Anyway would really like to chat, don't think this is the place send me an email with your skype contact and we can knock heads.
cheers
Gary
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Jetjr,
Yes that is the "ideal outcome" and even a Lycming or Continental does not have equal air flow. That is the problem with mainstream aero engines. They all spray equal fuel but the air part of the ratio is not perfect. Usually the fuel is, or close enough.
The problem is fixing the air in is the difficult thing, so it i.e. easier to fix the fuel thing.
That above = George Braly & the GAMIjector.
Now back to your last post, that is why equal electronic injection is not the answer.
Hope that helps.
Yes that is the "ideal outcome" and even a Lycming or Continental does not have equal air flow. That is the problem with mainstream aero engines. They all spray equal fuel but the air part of the ratio is not perfect. Usually the fuel is, or close enough.
The problem is fixing the air in is the difficult thing, so it i.e. easier to fix the fuel thing.
That above = George Braly & the GAMIjector.
Now back to your last post, that is why equal electronic injection is not the answer.
Hope that helps.
Jabiru have just let off a Cylinder head inspection program:
http://www.jabiru.net.au/images/JSL0...spection_4.pdf
The through bolt business was dealt with last year, assuming that fix was effective:
http://www.jabiru.net.au/images/JSB0...ough_Bolts.pdf
It is difficult to understand what more Jabiru can do to satisfy CASA in the short term.
The question now seems to me to be if CASA will unconditionally withdraw its proposed regulation.
If it does, the next question is what CASA might do to try and rebuild any semblance of trust and cooperation with industry, since, arguably, threatening the existence of Jabiru ( and the owners of 2000 odd aircraft) marks a new low point in its behaviour.
http://www.jabiru.net.au/images/JSL0...spection_4.pdf
The through bolt business was dealt with last year, assuming that fix was effective:
http://www.jabiru.net.au/images/JSB0...ough_Bolts.pdf
It is difficult to understand what more Jabiru can do to satisfy CASA in the short term.
The question now seems to me to be if CASA will unconditionally withdraw its proposed regulation.
If it does, the next question is what CASA might do to try and rebuild any semblance of trust and cooperation with industry, since, arguably, threatening the existence of Jabiru ( and the owners of 2000 odd aircraft) marks a new low point in its behaviour.
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Since CASA and ATSB are working hand in glove thanks to their memorandum of understanding, the ATSB conclusions from any report into such matters as engine failures are tainted and can safely be ignored as evidenced by the ATSBs disgraceful performance - on - demand Pel - Air ditching report.
To put that another way, we already know what the ATSB is going to report; - that Jabiru engines are lethally unsafe. That is what CASA have already pronounced.
Great Christmas present for the Jabiru workers, pink slips and a referral to Centrelink..
To put that another way, we already know what the ATSB is going to report; - that Jabiru engines are lethally unsafe. That is what CASA have already pronounced.
Great Christmas present for the Jabiru workers, pink slips and a referral to Centrelink..
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What's acceptable risk
The graphs from ATSB show Jabiru well in the lead when it comes to rate per 000's. If you take Jabiru out of the equation there will always be a particular engine that will be less reliable than others. So, what is the acceptable risk of failure for any one of these engines? Until CASA locks itself into a position of acceptable risk on this matter, this argument could go on forever with the ever changing goalposts afforded by being non-committal.
Excellent question, Blueyonda.
It again highlights the fundamental flaw in the structure of aviation regulation in Australia.
CASA is not competent to decide what the acceptable risk is.
The decision is a political decision, not a technical decision.
The decision requires consideration of matters that CASA does not know and cannot find out.
The only option CASA has to deal with “safety” issues is to make the standards ever-more-stringent, without knowing or caring about the opportunity costs.
ATSB could dust off the junk science that was the original investigation into the Whyalla tragedy. Perhaps Jabiru engines have over-dosed on lead oxybromide and swirl marks on the top of the pistons…
It again highlights the fundamental flaw in the structure of aviation regulation in Australia.
CASA is not competent to decide what the acceptable risk is.
The decision is a political decision, not a technical decision.
The decision requires consideration of matters that CASA does not know and cannot find out.
The only option CASA has to deal with “safety” issues is to make the standards ever-more-stringent, without knowing or caring about the opportunity costs.
ATSB could dust off the junk science that was the original investigation into the Whyalla tragedy. Perhaps Jabiru engines have over-dosed on lead oxybromide and swirl marks on the top of the pistons…
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What's acceptable risk?
This investigation is ongoing and will analyse a number of additional aspects including, but not limited to:
a comparison between VH-registered light sport aircraft with the same engine models;
a comparison of factory built and amateur-build aircraft;
an analysis of the different engine models from Jabiru and Rotax;
an analysis of the engine failures with respect to both the total engine hours and the hours since last service;
an examination of the causes of the failures, to identify any potential systemic failure mechanisms;
an examination of the effect recent engine changes made by Jabiru have affected engine failures and malfunctions.
a comparison between VH-registered light sport aircraft with the same engine models;
a comparison of factory built and amateur-build aircraft;
an analysis of the different engine models from Jabiru and Rotax;
an analysis of the engine failures with respect to both the total engine hours and the hours since last service;
an examination of the causes of the failures, to identify any potential systemic failure mechanisms;
an examination of the effect recent engine changes made by Jabiru have affected engine failures and malfunctions.
Out of interest, if you take GA Jabiru and Rotax engines out of the annual ATSB statistics, do stats for conventional GA engines improve or deteriorate?
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Well on a slightly different note however still theoretically relevant, I guess another comparative between RA-Aus vs CASA ways of dealing with acceptable risk would be that as adopted by RA-Aus with respect towards Pilots medicals, which is (as copied from the RA-Aus website):
Now if (when dumbed down) the definition of risk basically is "The effect of uncertainty on objectives.." and taking this context when balanced against the plethora of CASA medical requirements for flight under the VFR I just wonder which is the more prudent mechanism for management of an acceptable risk of a pilot's medical status for example.
I guess the same definitive could be used with this engine argument. But then again I'm only guessing, hang on, guessing and risk management? Surely not....
Stiky
An aviation medical certificate is not required but an RA-Aus pilot must be medically fit to a standard equivalent to that required to hold a private motor vehicle driver’s licence in Australia. It is the responsibility of all Pilot Certificate holders to report to RA-Aus any change in their health status which would cause them to be below that minimum health standard required.
I guess the same definitive could be used with this engine argument. But then again I'm only guessing, hang on, guessing and risk management? Surely not....
Stiky
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Fair-minded aviation consumers can only welcome the ATSB analysis and publication. As I've said a number of times, the scandal has been that even the top-level comparative stats have not been openly available, having been hidden in the RA Aus mire. I made my own choice based on what data I could pull together myself, and if having this present data available leads to others more easily doing the same, that's progress.
I don't expect anyone else (incl. CASA) to make the choice on my behalf but if there's a clear outlier in terms of unreliability at a given state of the engine art, I don't have a problem with the national aviation safety body highlighting the issue and pushing for the improvement that both RA Aus and the manufacturer had previous opportunities to achieve.
Operating my Rotax-powered VLA as a VH machine, I suspect that I have still taken a (hopefully small) hit in reliability relative to traditional aero engines in the other aircraft I fly, but it's a corner of the operational space that might yield some interesting stats, assuming there are more than a handful of aircraft included in the Rotax/VH category. I'll be interested to see what the continuing ATSB analysis comes up with, not because I think there's any magic reliability cut-off but because I want the opportunity to make choices on the best data available.
I don't expect anyone else (incl. CASA) to make the choice on my behalf but if there's a clear outlier in terms of unreliability at a given state of the engine art, I don't have a problem with the national aviation safety body highlighting the issue and pushing for the improvement that both RA Aus and the manufacturer had previous opportunities to achieve.
Operating my Rotax-powered VLA as a VH machine, I suspect that I have still taken a (hopefully small) hit in reliability relative to traditional aero engines in the other aircraft I fly, but it's a corner of the operational space that might yield some interesting stats, assuming there are more than a handful of aircraft included in the Rotax/VH category. I'll be interested to see what the continuing ATSB analysis comes up with, not because I think there's any magic reliability cut-off but because I want the opportunity to make choices on the best data available.
Last edited by tecman; 11th Dec 2014 at 08:45. Reason: typo
Let me fix the opening sentences for you:
Fair-minded aviation consumers can only welcome an objective analysis by disinterested experts, and publication of their peer-reviewed findings. It is to be hoped that the ATSB has the necessary corporate integrity and competence to do that. …
I can't believe that took so long to produce, I could have written it up in a couple of hours.
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Rotax 912
Operating my Rotax-powered VLA as a VH machine, I suspect that I have still taken a (hopefully small) hit in reliability relative to traditional aero engines in the other aircraft I fly, but it's a corner of the operational space that might yield some interesting stats, assuming there are more than a handful of aircraft included in the Rotax/VH category.
I have probably tens of thousands of hours of Rotax time with my signature on it. (maintenance) I will take the Rotax over the American air cooled engines any day and twice on Sunday
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Oracle, I take your comments to mean you're speaking from a maintenance perspective and that you don't have a workshop full of burnt Rotax cly's 
. As I said, I'm comfortable with my choice but nonetheless interested in your observation. The reason I'd like to see the stats for the VH Rotaxes is that I suspect the maintenance regime is significant. If it goes the way conventional wisdom would predict (VH = more and/or better maintenance), the resultant Rotax rate might indeed be better than the other engines, the 'contaminating' stats from less expert maintenance regimes having been removed.
Of course it might go the other way, opening a whole other can of worms!
. As I said, I'm comfortable with my choice but nonetheless interested in your observation. The reason I'd like to see the stats for the VH Rotaxes is that I suspect the maintenance regime is significant. If it goes the way conventional wisdom would predict (VH = more and/or better maintenance), the resultant Rotax rate might indeed be better than the other engines, the 'contaminating' stats from less expert maintenance regimes having been removed.Of course it might go the other way, opening a whole other can of worms!