"Jaberoo" down (Mildura this time)

[Oscar]

Turbs - I did say - and underlined it: 4% of reported failures. I'm damn sure there are plenty of occurrences of people deciding even before start-up that they 'don't like the feel/sound of that' - and NOT proceeding to fly until the reason is discovered and rectified. I find it hard to accept that there is some huge pool of unreported genuine failures resulting in forced landings, though; from memory, and with far less access to back copies of the RAA mag., I seem to remember even forced landings determined to be icing or precautionary only tended to be reported (though there was a major and disturbing gap in reporting in, I think, 2013?).

 

Let's say that as many as 1 in 2 of 'failures' (or incipient failures picked up by attentive owner/operators) was in fact NOT reported, that would make it 8%. Let's round it up to 10%. That's way, way too many, we're in complete agreement here. In fact, if there were NOT a problem, what CAMit is doing - at a lot of expense, time and sometimes frustration - would make no sense. It's EXACTLY the reason I went to CAMit and re-built my engine there incorporating as many of their mods as I could afford at the time (I'll add later ones in due course) and spent days learning how to (and doing) the machining of the cases and heads; my engine is so early in origin that CAMit had to make some special jigs and tools to do that work (my heads are the earliest version of 2200 heads, and had to be machined to accept the later-style exhaust headers - Ian Bent personally hand-made a tool for me to cut the chamfers for the later exhaust tubes into the exhaust ports, that's how early they are!).

 

The point I am trying to make here is: the basic Jab engine is not fundamentally flawed, but it most certainly has detail stuff that doesn't work adequately except under near-perfect conditions of maintenance and use. What CAMit have been doing is going through the engine exhaustively (pun intended here!) and analysing the entire 'system' chain of failure points and rectifying them. The success of that work is undergoing both in-flight testing and is about to start a major programme of highly-controlled testing.

 

Jabiru made two HUGE mistakes, I believe, in introducing hydraulic lifters and the (now repudiated) 'lean running' carby jetting. Jabiru have also not done enough work on cooling installation detail, and that's a major, major area for improvement; there is more than sufficient research that has been done (principally, by NACA) on cooling design parameters for air-cooled engines that needs attention. Lycoming won't warranty their engines if the installation is not audited by them and been found to meet their criteria.

 

Cooling design for air-cooled engines does NOT correspond to 'intuition', and simply stuffing lots of air in the general direction of the engine is only marginally better than useless. Not only is it necessary to ensure that the airflow gets to the right areas with maximum effectiveness, but it also needs to be balanced against cooling drag if the aircraft is going to perform decently. You'll know very well how much ridiculously expensive effort goes into F1 aerodynamics - and a significant part of that is directed at cooling drag. In water (or water+oil) cooled engines, the heat can be transferred by the cooling medium to areas of maximum efficiency for heat transfer; with air-cooled engines, you have to try to get the cooling medium to the right parts of the engine. The LoPresti 'howl cowl' is way, way more than just two small round holes in the cowling...

 

 

[turboplanner]

mistakes, I believe, in introducing hydraulic lifters

Just in the installation perhaps; hydraulic lifters are very reliable in Holdens, but if valve timing is out the exhaust vale area can get hotter.

 

and the (now repudiated) 'lean running' carby jetting.

Tell us more about this; in petrol engine power increases as you lean the jets, but reaches a point where the combustion chamber overheats and seizing starts to occur. Conversely, I found that unburned fuel is by far the best medium for cooling an air cooled engine, and that was based on drag racing where people were extracting 12,000 horsepower out of engines designed for driving Miss Daisy.

 

Cooling design for air-cooled engines does NOT correspond to 'intuition', and simply stuffing lots of air in the general direction of the engine is only marginally better than useless.

That's been my point in talking about the difference between temperatures on the outside of the engine, and inside the combustion chamber.

What doesn't seem to come up in the reports is whether it is always the same cylinder on the engine where the valves and thru bolts fail, or whether it is random. If it was the same cylinder I would then be taking a close look at the mean length from the piston face to the carby jet for each cylinder and doing some calculations.

 

 

[Oscar]

Turbs, the hydraulic lifters altered the oil pressure distribution pattern throughout the engine. They, in effect, exchanged routine maintenance for exacerbating the problem areas. CAMit haven't gone back to solid lifters just on a whim, but on the basis of research.

 

Um, what drag racing engines are air-cooled? I remember - if my memory is faithful - Don Garlits? ( it may have been Don Jenkins, whose work I followed religiously in my own race engine developments) developing a ceramic-filled drag engine, but drag engines run what - 12 seconds max? - whereas our aircraft engines are supposed to hang in there at 75% - 80% max power for ever. As you say, rich is good for cooling; lean jetting was a major mistake for Jab. engines.

 

Your point about the difference between temps registered on the outside of the engine (CHT, specifically) and what's happening inside, is valid - but the thermodynamics involved in extracting heat from critical areas means that you can't ignore CHT's as an indicator of the general cooling performance. Ian Bent explained this at Temora this year, people need to take that on board.

 

 

[turboplanner]

The only point about the drag racing reference was using fuel to cool an engine. Yes the rest is not relevant here.

 

Did anyone ever check plug colours?

 

Ian Bent is entitled to his explanations; I'm looking in a different direction, but need more accurate data.

 

 

[Oscar]

Turbs: yes, Ian Bent has 5,000+ engines manufactured (to Jabiru's specifications, admittedly) and a vast amount of research to back up his explanations - but the proof will be in the results.

 

However - have you seen this?: http://flightdesign.com/files/Media/The Aviation Consumer - LSA Accidents.pdf It provides some interesting statistics, drawn from the FAA database.

 

Amongst the notable points: Cessna 152 accidents from engine failures (that good, old, mature, reliable Lycoming 0-235): 19%. Overall accidents: Cessna 152, 2.2%, Jabiru,: 3.5%, Cessna 172: 8%, Evektor a staggering 27.7%.

 

LSA class causes combined: engine 10% - which seems to be about median with our projected - but not reported - Jab engine problem rate.

 

So either we have a global conspiracy that the FAA has embraced to under-represent Jab. engine failures, OR Jab engine failures are not as epidemic as imagined.

 

You choose.

 

 

[fly_tornado]

US has a lot more cold weather than Aus, so a lot more carb ice.

 

 

[Oscar]

Riiight,

 

And Cessna 152's don't have carby heat, that'd be it?

 

 

[motzartmerv]

Why are FAA stats relevant Oscar? Have I missed something?

 

 

[motzartmerv]

US has a lot more cold weather than Aus, so a lot more carb ice.

Back to the books FT.

 

 

[DrZoos]

Its not just a cold weather event...

 

http://www.casa.gov.au/wcmswr/_assets/main/pilots/download/carburettor_icing_chart.pdf

 

 

 

[Oscar]

Why are FAA stats relevant Oscar? Have I missed something?

Merv: it's still the same Jab aircraft and engine over there as over here (though it seems Jab USA have done a bit more for engine cooling installation). As far as I am aware, air and associated stuff over there is pretty much the same as here (I certainly haven't noticed much difference in five visits), so I suggest it's reasonable to add FAA statistics to our own re Jab engine failures, in terms of getting a handle on the problem.

 

Once again, I add: is the failure rate of Jab engines acceptable? - and I join with those who say: 'NO'. But when it comes to the suggestion that we're looking at an Ebola-type epidemic catastrophe vs. a disturbingly noticeable incidence, then the statistics show that just isn't realistic.

 

 

[Oscar]

Its not just a cold weather event...[ATTACH=full]31638[/ATTACH]

Um, I think you and Merv have a fundamental disagreement. CASA is just CASA, with responsibilities to provide accurate information. Merv is a CFI.

 

 

[motzartmerv]

Yea Oscar, I Just wonder how relevant the figures are. How many Jabs are in the USA?

 

 

[DrZoos]

I was referring to FT

 

I didnt want people assuming colder equals more carb ice...

 

 

[Oscar]

Yea Oscar, I Just wonder how relevant the figures are. How many Jabs are in the USA?

No idea - but the figures are %ages, so unless there are just a few, and they've all been amazingly lucky, you're not comparing raw numbers.

 

 

[motzartmerv]

Oh ok. Its percentage by 1000 hours flown, extrapolated from small numbers. Not ver usefull, but can indicate an early trend I spose.

 

Looks like they are still a safe plane to prang in over there aswel.

 

Do we have any numbers yet that we can compare? per thousand hours etc? Sorry, been working for a few days havnt read the last few pages of this thread.

 

 

[dazza 38]

I have a quick question, how does the 3300 engine go in the Lightning?. It is a fast machine and I have personally never heard of cooling issues. So I am wondering wether their climb and cruise speed nullify the cooling issues and/or their engine cowling design being a efficient design.

 

 

[deadstick]

Daffyd, during the cooling tests were the barrel temps ever monitored? The reason I ask is that every jab engine I have overhauled showed signs of cylinder out of round, blued heat indications and the pistons showed heating around the ring lands. Also was an air dam cooling setup tested as this is what is being used in the states and South Africa I beleive.

 

Cheers...

 

 

[Dafydd Llewellyn]

Daffyd, during the cooling tests were the barrel temps ever monitored? The reason I ask is that every jab engine I have overhauled showed signs of cylinder out of round, blued heat indications and the pistons showed heating around the ring lands. Also was an air dam cooling setup tested as this is what is being used in the states and South Africa I beleive.Cheers...

I don't know, for the original certification work. They certainly will be, this time. We're looking quite hard at improving the baffling under the cylinder barrels. Ian Bent has been most recently researching exactly this point. Re an air dam cooling setup, I can't delve into that in the test cell, it has to be done in flight. But the whole cooling system is under review in this program. I've no idea at this stage where that will take us.

 

 

[Dafydd Llewellyn]

I should perhaps qualify that, by pointing out that there are two separate aspects here; the first one is to qualify the mod. package that constitutes the CAMit-modified engine. An undercylinder baffle may well be a mandatory part of that, if it works.

 

How the air gets delivered to the engine and the oil cooler, is not part of the engine; it's part of the airframe. So precisely where the engine stops and the airframe begins is not as yet determined, for the CAMit package. Modifying the airframe part of that would involve an STC for each airframe model; and of course that cannot apply to the models built under LSA. So that side of the question is a separate program; and it has second place to getting the engine package done.

 

 

[planedriver]

Merv: it's still the same Jab aircraft and engine over there as over here (though it seems Jab USA have done a bit more for engine cooling installation). ]I'd agree that Jab engine failures need more investigation as they are basically a great little aircraft, but carb-icing mentioned by Dr Zoos is common to so many aircraft and would probably be found to be a problem more associated with the conditions within which a pilot chooses to fly.

 

However, cooling problems are another thing entirely.

 

Exhaust valve failure which unfortunatly has shown it's ugly head far too often, is normally temperature related, which leads me to think that a more stable cylinder head temperature offered by liquid-cooled heads, may have a significant advantage to overcome this particular problem, over what the manufacturer is currently offering.

 

It would be interesting to know what the temperature related failures are for those flying in much cooler climates.

 

I used to drive an Austin 1800 automatic when I lived in the UK, and even rallied it a few times. I ran it till it had about 300,000km on the clock with next to no troubles at all.

 

When I first arrived in Oz I bought another one, which caused me so many dramas in hot weather I pi**ed it off.

 

It was all temperature related problems to what was otherwise a good product.

 

Through bolts which have already been addressed to some extent are one thing, but temperature problems are another, and we can only wind up with a champion product when each individual problem is sorted out.

 

Hopefully this will be soon.

 

The Jabiru fully-sorted would have to have a worthy place in the record books surely, as far as light sport aircraft are concerned, but I think there is still a little way to go yet.

[rick-p]

I have a quick question, how does the 3300 engine go in the Lightning?. It is a fast machine and I have personally never heard of cooling issues. So I am wondering wether their climb and cruise speed nullify the cooling issues and/or their engine cowling design being a efficient design.

Good point Dazza.

 

I have the 2200 installed in my Lambada and don't appear to have any cooling issues.

 

The air induction system is very good delivering a cool air flow to not only to the front cylinders but also the rear.

 

Even in the middle of summer here in central Queensland I don't have a problem.

 

I have also installed an oversized oil cooler.

 

And thanks to Nev and Myles I'm using 50mls of 2 stroke outboard motor oil to 20 litres of avgas.

 

All runs great, 300 hrs and not a problem but I still have my fingers crossed because it's always for me when it happens and not if it happens!

 

Also have the luxury of a 30-1 glide ratio.

 

 

[dazza 38]

Good point Dazza.I have the 2200 installed in my Lambada and don't appear to have any cooling issues.

The air induction system is very good delivering a cool air flow to not only to the front cylinders but also the rear.

 

Even in the middle of summer here in central Queensland I don't have a problem.

 

I have also installed an oversized oil cooler.

 

And thanks to Nev and Myles I'm using 50mls of 2 stroke outboard motor oil to 20 litres of avgas.

 

All runs great, 300 hrs and not a problem but I still have my fingers crossed because it's always for me when it happens and not if it happens!

 

Also have the luxury of a 30-1 glide ratio.

Thank you Rick for the feed back. And it is great to here that you are not having cooling issues, sounds like your airframe / engine combination is working well.

 

 

[Dafydd Llewellyn]

from what we read is seem that onlythe six cylinders has the cooling problemsThere are not many lightnings around to compare really

That's not what the statistics - such as they are - show (assuming - as I do - that valve failures are likely to be related to cooling, due to a thermal runaway effect; not all of them will be, of course. Turbs has a different view).

 

 

[01rmb]

I have raised this before (see http://www.recreationalflying.com/threads/another-engine-failure.118777/page-3#post-431173).

 

In my case, if not for being picked up during the 300 hr service I would have had a full engine failure, possibly in flight, due to the exhaust valve stem breaking off inside the cylinder. The problem was traced to burning of the exhaust valve and stem as a result of lead fouling from avgas preventing a proper seal of the valve. This inhibited cooling of the exhaust valve leading to the valve being burnt away exposing the valve stem to the combustion heat which within a few more hours would have broken off. I would not have expected CHT to pick up this problem only EGT.

 

Identified, fixed and no longer using avgas with no further issue.