Jabiru engine life times

[motzartmerv]

Great stuff there Bob. thanx.

 

 

[Bob Llewellyn]

Great stuff there Bob. thanx.

No worries. One of the issues to consider is this: with a non-constant temperature around the barrel, the hot barrel deforms, generally to an egg shape. The piston & rings wear to this shape. The wearing process obviously ups the friction, but - less obviously - as the rings creep around the pistons, they leak a lot more than they should, losing compression, increasing temperatures, and generally being pests. From what I've heard about old Jab engines, they most all have issues with this.

 

 

[motzartmerv]

Yep. Have had one engine 'egg' twice now. Its on a bantam, which is not a good idea.

 

 

[Bob Llewellyn]

there is one of the new camit motors at my airport i seen it today. it had an alternator and black barrels but looked like a jabiru motor other than that. the guy said it had 20 hours on it at the moment. he said that he had 2 mates in qld that have them too with a fair number of hours so it wont be long before some reports come back if they are no good (or good for that matter)

Look fowards to hearing more - technically, cooling is an installation (airframe) issue, not an engine issue - eg the baffles on a Continental O-300 in a Cessna 172 are a Cessna product, not a Continental product. I do not know CAMIT's focus on the redesign, but I assume that the subcomponents and detail design is now virtually flawless (or they mean to find out and fix it immediately!)...

 

 

[jetjr]

Ok, read the Naca report, interesting stuff.

 

Re BL comments on cooling and warping of barrels, i think this is key stuff as it brings a few things together

 

Cooler running = longer life, Egg barrels, Lined up or jammed rings, All leading to early teardowns and ring barrel replacement

 

NOW throw in the odd other isssue like poor fuel, poor fuel distibution, few substandard bits and youve got seemingly random early failures .

 

SO how do we get cylinders cooling evenly?

 

From my duct fiddling....... i know a tiny dag of fibreglass can help or throw out air distribution, even worse in air filter to carb mouldings.

 

 

[Old Koreelah]

Ok, read the Naca report, interesting stuff.Re BL comments on cooling and warping of barrels, i think this is key stuff as it brings a few things together

Cooler running = longer life, Egg barrels, Lined up or jammed rings, All leading to early teardowns and ring barrel replacement

 

NOW throw in the odd other isssue like poor fuel, poor fuel distibution, few substandard bits and youve got seemingly random early failures .

 

SO how do we get cylinders cooling evenly?

 

From my duct fiddling....... i know a tiny dag of fibreglass can help or throw out air distribution, even worse in air filter to carb mouldings.

I'm tempted to toss out the standard fibreglass ducts and install a conventional horizontal fence around the engine, with a vertical wall behind the starter. It would need "gull wing" baffles between cylinders. Shouldn't be too hard to build, and once installed, getting at plugs etc should be a breeze. Perhaps this has been tried before?

 

 

[Camel]

I'm tempted to toss out the standard fibreglass ducts and install a conventional horizontal fence around the engine, with a vertical wall behind the starter. It would need "gull wing" baffles between cylinders. Shouldn't be too hard to build, and once installed, getting at plugs etc should be a breeze. Perhaps this has been tried before?

I was told it was done on a j230 at Cessnock by a well known L2, this was a while ago and I never followed it up to see how it went later but at the time he said it was good. I can't see why it wouldn't give better cooling.

 

 

[Oscar]

I'm tempted to toss out the standard fibreglass ducts and install a conventional horizontal fence around the engine, with a vertical wall behind the starter. It would need "gull wing" baffles between cylinders. Shouldn't be too hard to build, and once installed, getting at plugs etc should be a breeze. Perhaps this has been tried before?

Now a new thread on this where things can be discussed would be of great assistance to Jab. engine owners.

 

I also have the intention of doing some serious work to see how the whole cooling airflow can be improved, but it can be a tricky and frustrating business to get everything right. At the very minimum you'd want to have CHTs on all pots and a test flying area that will allow you to easily abandon a 'heavy-duty' test and quietly potter back home if something you're trying isn't working as well as you'd hoped, e.g. you find you get flow choking in certain situations. A test set-up that can measure relative pressures past each barrel/head is fairly advisable ( old ASI's will do it, but there are other ways). The advice I've had - from someone who has done rather a lot of this stuff for certification and modifications work - is to go at it fairly gently and seek firstly to make sure you're getting the best out of the standard set-up and then tune it progressively. It's a somewhat boringly repetitive task, I'm told, requiring pretty accurate flying and some work converting ambient temps to a normalised state to get the real figures that show progress / regress as you change things.

 

Personally I'll be starting with a proper oil-cooler and installation (rather as per kgwilson's ideas, though a ram-scoop rather than a NACA duct is more effective at actually getting decent air pressure into the oil-cooler), an oil-cooler outlet that doesn't exit into the main cowl cooling area thus reducing effective relative pressure on the extraction side and a decent bottom cowl-lip to generate more effective extraction from the cowl area. A spinner better matched to the intakes is also tops on the list. From there, tweaking the plenums and the plenum interconnect to balance pressure on both intake sides and after that, more sophisticated baffling to get the damn cooling air balanced and effective past front and rear heads. On the plus side - my circuits should get really well-practiced...

 

As a small aside re knocking up a set-up if using aluminium sheet: thin aluminium subject to vibration is a right bastard for fatiguing at any attachment points if they can cause it high stress levels. I found out the hard way when building racing cars just how quickly something can break off. I think just about every aircraft owner knows this - I'm sure you will - but it's oh, so easy to overlook it in designing a fitting when space is tight. Been there, done that, had the dead bits thrown into the back of the trailer...

 

 

[jetjr]

New thread in Jabiru section on cooling

 

 

[Old Koreelah]

Now a new thread...the whole cooling airflow can be improved...

I have learned some useful lessons worth considering by anyone installing a Jab engine in a low-wing airframe. My engine cooling air exits above the wing in the low-pressure zone. The CHTs have always run cool-even too cool-so I installed butterfly-type cowl flaps. (I plan to replace them with smaller longitudinal doors to improve streamlining at cruise or if I have to glide.) The intake area is of little importance compared to the exit.

 

...Personally I'll be starting with a proper oil-cooler and installation... an oil-cooler outlet that doesn't exit into the main cowl cooling area...

You are on the money, Oscar. My oil cooler shares the same exit as the rest of the engine, and oil temps nudge the maximum. The only way I can see to improve this is to seal a few air gaps.

 

...A spinner better matched to the intakes...

I can't understand peoples' fixation with tiny spinners. The bigger the better. Look at a 1912 Deperdussin. Narrow slits either side let in enough air and can be easily married into standard Jab head cowls.

My spinner is 340mm diameter and mounted on a robust alloy plate. One secondary aim was to add a little more inertia to the prop to assist it to smooth power pulses. I have heard dissenting views. One bloke thought this might add to the stresses on the crank. Way beyond my expertise. Time will tell.

 

 

 

[Oscar]

I have learned some useful lessons worth considering by anyone installing a Jab engine in a low-wing airframe. My engine cooling air exits above the wing in the low-pressure zone. The CHTs have always run cool-even too cool-so I installed butterfly-type cowl flaps. (I plan to replace them with smaller longitudinal doors to improve streamlining at cruise or if I have to glide.) The intake area is of little importance compared to the exit.You are on the money, Oscar. My oil cooler shares the same exit as the rest of the engine, and oil temps nudge the maximum. The only way I can see to improve this is to seal a few air gaps.

 

I can't understand peoples' fixation with tiny spinners. The bigger the better. Look at a 1912 Deperdussin. Narrow slits either side let in enough air and can be easily married into standard Jab head cowls.

 

My spinner is 340mm diameter and mounted on a robust alloy plate. One secondary aim was to add a little more inertia to the prop to assist it to smooth power pulses. I have heard dissenting views. One bloke thought this might add to the stresses on the crank. Way beyond my expertise. Time will tell.

Can you arrange an exit duct around the oil cooler that carries the air to an exit hole on the cowl with a lip in the air blast to create a bit of suction? That'd give you double benefit if you can (though it sounds like you have an abundance of low pressure inside the lower cowl, so you might not need the second bang-for-the-buck effect - lucky you!) Is your oil cooler intake getting decent high-pressure feed from the prop blast? - NACA-type ducts are great from a drag POV at getting low pressure air through a given size of opening, but they don't actually create much at all actual intake pressure. Might be worth sticking a few wool tufts just ahead of the oil cooler intake and watching the airflow there in the prop blast, though on the ground you'll be getting a different flow distribution to in the air. (Or better still, use a small camera mounted out of the direct airflow into the oil cooler and and record it in-flight - maybe one of those 'sport-camera' type things that one can clip to one's bike helmet. Even the old 'smear of oil and see what the traces have been doing' trick could work, possibly.

 

Advice I've been given is absolutely get the biggest spinner on there that comes as close to the edges of the intake duct(s) as possible.

 

You probably can't do much harm with a decent thickness of alloy plate as the spinner hub since its mass will be small compared to the prop. mass and it'll have low gyroscopic couple, but it's a very good idea to not change the prop. mass by much; the 2200's are very sensitive to the whole prop. characteristics and not just the anti-friction tension on the prop hub from the beleville washer pack but the whole flange attachment and shaft can be affected. That 'avoid this rpm range' thing is down to harmonics in the shaft and you pretty definitely don't want to change those from what's been found to be safe. Way better 'smoothing' is to use the CAMit alternator and toothed belt set-up, that's been developed with full understanding of the shaft harmonic issues (though you probably won't feel any difference, but the shaft will!)

 

Once again (and Ian Bent is probably cursing me by now for keeping on making suggestions to contact him, but I know he's happier to give advice than hear of problems people have by not seeking advice!)- Ian makes the shafts and he is the best authority on what will and won't do harm etc. Jabiru will likely just say: 'don't do anything we don't recommend' - and because of their liability situation, one can appreciate why - but in my experience, Ian will not just tell you what's the go but tell you why it's the go..

 

 

[Old Koreelah]

Can you arrange an exit duct around the oil cooler that carries the air to an exit hole on the cowl with a lip in the air blast to create a bit of suction? ... Is your oil cooler intake getting decent high-pressure feed from the prop blast? ...

As you can see from the pic, the intake is just below the spinner, so wool tufting is not an option. I have been experimenting with closing off the head/cylinder intakes, so that more air comes in via the oil cooler.

 

Advice I've been given is absolutely get the biggest spinner on there that comes as close to the edges of the intake duct(s) as possible.

Right on; why not squish the ducts out to allow a bigger spinner?

 

...it's a very good idea to not change the prop. mass by much; the 2200's are very sensitive to the whole prop. characteristics and not just the anti-friction tension on the prop hub from the beleville washer pack but the whole flange attachment and shaft can be affected. That 'avoid this rpm range' thing is down to harmonics in the shaft and you pretty definitely don't want to change those from what's been found to be safe...

Agreed, but I'd like to know more about the "danger zone". Rod Stiff told us he was horrified to learn the US military run Jab engines in their drones at about 2400 rpm to get the best range. He didn't mention any after effects, but I guess they are considered almost disposable in that role. I recall one poster on this forum has had a good run cruising way below 2800rpm.

I will follow your suggestion to get some advice from Ian Bent. I am impressed with his energy and accessability.

 

...Way better 'smoothing' is to use the CAMit alternator and toothed belt set-up, that's been developed with full understanding of the shaft harmonic issues...

What's wrong with the crank-mounted alternator? I thought that was an inspired design; doing two things at once (adding to flywheel effect and generating adequate juice). Besides, many of us can't afford the extra weight or find the space for another alternator behind the engine.I read of a simple modification to the standard Jab alternator which involved effectively doubling the length of the winding. It was claimed to greatly increase output, but I haven't heard a thing since.

 

 

 

[01rmb]

I read of a simple modification to the standard Jab alternator which involved effectively doubling the length of the winding. It was claimed to greatly increase output, but I haven't heard a thing since.

Here is the modification from Jabiru for changing the voltage output of the alternator by doubling the stator winding length.

 

http://www.jabiru.net.au/Manuals/Engine/AVDALSR087-1_12_Pole_Alternator_Mod.pdf

 

 

[Oscar]

As you can see from the pic, the intake is just below the spinner, so wool tufting is not an option. I have been experimenting with closing off the head/cylinder intakes, so that more air comes in via the oil cooler.Wow - yep, you can't get much more effective intake positioning than that! Maybe look to the extraction side and see if you can get an exhaust duct than empties below the cowl with a wee lip on it? From the Jab engine install stuff, that only needs to be about 1/2" deep. That whole duct arrangement would probably need to come along the sides of the oil cooler to the very front of the intake to be most effective and of course be sealed off against the sides of the cooler. I've recently been working on the air intake for a Victa engine conversion and we thought of changing that over completely (the owner is putting in an IO360 which radically changes the intake/hot air box arrangement so the old intake was almost begging for the oil cooler installation, but the standard Victa oil cooler arrangement works just fine so why bugger around with it?

 

Right on; why not squish the ducts out to allow a bigger spinner?

 

Alan Kerr did a lot of work on the Jab. engine installation for Boeing Aus. when they were contending for the Aus. military drone project; he found that the pressures on the 'departing' side of the prop direction were quite a bit different to those on the 'approaching' side. ( He also found that in certain sidewind conditions, the cooling airflow actually reversed on the downwind side of the engine, which is why holding on taxi can be a really fraught time for the cooling side-to-side). The Jab. engine install manual gives some figures of areas for intake and exhaust volumes which should be a useful guide; of course, if one looks at the LoPresti 'howl cowl' idea (which has a bit more marketing hype than being the 'Holy Grail' it suggests, but the buggers do work) the actual intake area for the size of engines it cools appears really small - we can deduce that you don't need gaping maw sizes of intake if everything is well balanced!

 

Agreed, but I'd like to know more about the "danger zone". Rod Stiff told us he was horrified to learn the US military run Jab engines in their drones at about 2400 rpm to get the best range. He didn't mention any after effects, but I guess they are considered almost disposable in that role.

 

Ahem - in the Predator programme, many Rotax 912/914's are failing within 50 hours - so if you accept (and I do) that Rotaxii are a way more tolerant engine of cooling situations, it becomes fairly obvious that the US military do, indeed, regard engines as McEngines: drive-through for a new one..

 

I recall one poster on this forum has had a good run cruising way below 2800rpm.

 

Yep, but cooling and harmonic vibration in the crankshaft are entirely separated issues. I'd not be running any engine in the 'danger zone'. The harmonic vibration issue is a whole different bag of snakes. Jabiru's comments that around 2800 rpm for 75% or so cruise speed is mainly to do with cooling efficiency on Jab. aircraft; but it also takes the crank well out of harmonics issues. The old 'system' issue is well in play here: all the important stuff needs to work in harmony to get the best sum of the parts.

 

I will follow your suggestion to get some advice from Ian Bent. I am impressed with his energy and accessability.

 

Yes, he's seriously 'available' to discuss Jab and Jab. design based (his) engines. You'll learn more in one hour with Ian at CAMit about Jab. engines than all the posts on any site (including mine).

 

What's wrong with the crank-mounted alternator? I thought that was an inspired design; doing two things at once (adding to flywheel effect and generating adequate juice). Besides, many of us can't afford the extra weight or find the space for another alternator behind the engine.

 

I read of a simple modification to the standard Jab alternator which involved effectively doubling the length of the winding. It was claimed to greatly increase output, but I haven't heard a thing since.

 

Nothing at all 'wrong' with the standard Jab. alternator if it gives you the herbs you need, it's just that the CAMit alternative (and probably also, to a slightly lesser degree because it uses a v-belt rather than a toothed belt, the Rotec version) does provide some crankshaft harmonic damping. It's also a bit kinder to the ring-gear bolts, but with the steel starfish ring-gear centre, there's no issues anyway). The other advantages of going that route are a more reliable (in terms of voltage spikes) regulator set-up and less RF interference, which is likely to be beneficial if you run iPads etc. and also, some noise-cancelling headsets (though in the latter case, the TX/intercom module can be the critical factor - some headsets (mine is an example, a Lightspeed-manufactured third-party beastie, that just won't work happily with a MicroAir setup).

 

P.S - should we move this conversation to the new 'Jab cooling' thread - it might be worth having it there as a reference for later readers?

[biggles]

 

biggles, those temps look great, and nice and even aswel. Are they as marked? 3 and 4? One of our jabs (170) has always ran very cool in CHT and oil temp. While the 160 has always been a hot engine. CHT's routinely 30 or 40 deg's hotter than the 170, but still within the specs. The hottest engine (j) we have seen was in a 230 a few years ago. Always hot, always pushing the limits of the quoted specs. Pilots needed to fly it very particularly or risk over heating it. It never suffered a breakdown while online with us, but did suffer valve failure some years later when with another school.Just 1 month ago a member bought an LSA 55 and had it delivered to the airfield. After .9 of an hour of flying it too suffered a valve seat failure. Both pilots stated it never got hot and the previous owner stated it was always a cool runner. To be fair, this aeroplane had not done alot of work in the previous year.

While I think heat is a contributing factor in some of the problems, I dont think it explains it all. We have several other jab engines we have run for extended periods with our school that have had varying degrees of success and failures. But to date the longest lasting engine is the 170, which has just clocked 900 hours. It snapped a through bolt stud at about 750 hours only 30 hours after the mandatory mod was performed. jabiru copped to that one explaining that the wrong parts were sent and installed. They warranted the damage due to their stuff up. There was simply no way out of it for them as the wrong part was sent and we still had the engine so they couldn't run. But..Im confidant that engine would have made the 1000 hrs. Out of 5 aircraft we have operated (significantly) one of them 'probably' would have made it to top end overhaul. The rest did not.

 

The stats in this poll, while only being 3o or so samples, dont look favourable at all, and certainly my own personal experience with them would align quite closely with the 10% of engines making top end of 1000 with no major problems (indicated in this poll)

 

Small samples such as this are still quite usable when looking purely at stats, although admittedly there are many more not represented. However, 30 samples, spread across a range of users is statistically quite ok to get a general idea of things. Dont hang your hat on them, but certainly dont chuck the results out with the bath water.

 

If this thread proves nothing else, it should serve as a prompt for any potential Buyer to go into the whole thing with eyes wide open. You will most probably, at some stage be spending money on your engine. You may not have to, but at least now you can't say you didnt know it was a 'possibility', some would say a high probability.The mods that 'learned' people speak of certainly do seem to offer a more reliable platform, although, this 'theory' cant be tested in the same way 24 rego'd school aeroplanes (think of taxis) can test the waters.

 

Again, im only commenting on personal experience and the results of this poll, not offering an opinion. (as per my promise) for what its worth.

 

http://www.measuringusability.com/blog/stats-usability-errors.php

Yes Andrew , CHT 4 is on the left as indicated , and CHT on the right to mimic their actual positions . I did little to the individual forced air ducts , other than glue strips of foam , approx. 25 x 25 mm on the upper and lower cowls to minimise leakage . The rubber strips on the ducts actually "bed " into the foam , and as can be seen , there would be quite a gap otherwise .Have just returned from a trip to YORB today ,which is actually located on the beautiful East Gippsland Coast at Marlo . The pic shows Lakes Entrance town just ahead , and through the sun reflection , you can see the CHT's a little over 210 oF . They moved only slightly higher during climb - out , with an OAT around 23 o C . So many stories about Jabiru engines , but I firmly believe that inadequate cooling and running consistently high temp's ,is the cause of many failures . While it is possible for an owner/pilot to ensure adequate airflow , it is not always possible to get this message through to students/hirers , although some flying schools do seem to have remarkable results . I have enclosed a few pics from today and , as you can see climbing out at over 90 kts ( normally 80 kts and around 30 l/hr ) and the CHT's are around 210 o F. I use only 100 LL Avgas , as recommended by Jabiru .The other pics show the sealing strips . Bob

 

 

 

 

 

 

 

 

 

 

[motzartmerv]

Thanx bob. Great stuff. Although the only thing you can get through to flying schools is to operate iaw the jab manuals. Anything else is lot aloud. Unfortunately.

 

 

[Oscar]

Yes Andrew , CHT 4 is on the left as indicated , and CHT on the right to mimic their actual positions . I did little to the individual forced air ducts , other than glue strips of foam , approx. 25 x 25 mm on the upper and lower cowls to minimise leakage . The rubber strips on the ducts actually "bed " into the foam , and as can be seen , there would be quite a gap otherwise .Have just returned from a trip to YORB today ,which is actually located on the beautiful East Gippsland Coast at Marlo . The pic shows Lakes Entrance town just ahead , and through the sun reflection , you can see the CHT's a little over 210 oF . They moved only slightly higher during climb - out , with an OAT around 23 o C . So many stories about Jabiru engines , but I firmly believe that inadequate cooling and running consistently high temp's ,is the cause of many failures . While it is possible for an owner/pilot to ensure adequate airflow , it is not always possible to get this message through to students/hirers , although some flying schools do seem to have remarkable results . I have enclosed a few pics from today and , as you can see climbing out at over 90 kts ( normally 80 kts and around 30 l/hr ) and the CHT's are around 210 o F. I use only 100 LL Avgas , as recommended by Jabiru .The other pics show the sealing strips . Bob

Great stuff, and absolutely indicative of the fact that small differences can have major effects. One of the real problems with Jab reported reliability, I believe, is that many people don't realise how what appears as a minor thing can have such a major effect. Of course, there is the extreme other end of the scale; I remember a report on (from memory) that 'Jab engine failure and crash' site that recounted a recently RAA-converted GA pilot who hired a Jab and on climb-out saw the CHT hit the red and 'climbed as hard as I could in case the engine failed so I'd have height for a turn-back' - at Warnervale, I think. Warnervale is NOT a nice place for a low EFATO, but guess what? - this guy's engine blew the through-bolts! Who would have though that likely?

 

Most modern cars have an ECS that includes a recording element. If we had more consistent installation of recording EMISs, (such as the MGL Extreme we intend to use) we'd be able to get decent histories of actual engine conditions during use, which would give some really useful quantitative data. The motoGp bikes have data recording of everything and from that, trained engineers can determine every damn thing that happens during a ride -with GPS track position reporting, down to just about which square foot of track whatever happened at. Those things are seriously ballistic (300+kph, accelerating, cornering and braking at 2g's or more); we don't need anything like that data performance recording, but even quite crude figures can provide a vastly improved picture of what happens and happened. If I had any aircraft on the line, I'd have one of these at least in it so I damn well KNOW what use it had had.

 

Boeing, for many, many years now have had major data recording capability (from the early 747's onwards, I believe) and that data gets downloaded to Boeing Seattle, analysed, and maintenance information sent out to the aircraft operator on an aircraft-by-aircraft basis. An old Qantas Captain mate of mine told me that early on, some pilots were a bit freaked because Boeing could identify which pilots had 'soft hands' on the stick vs. other ones (well, which flights by date and time, and therefore the pilots could be identified). Quite a bit of the move towards more automated 'heavy' flying has come about from the realisation of just how much difference individual pilot technique can make to an aircraft's performance and maintenance requirements - and on those guys, shaving maintenance costs is big $$..

 

 

[turboplanner]

I remember a report on (from memory) that 'Jab engine failure and crash' site that recounted a recently RAA-converted GA pilot who hired a Jab and on climb-out saw the CHT hit the red and 'climbed as hard as I could in case the engine failed so I'd have height for a turn-back' - at Warnervale, I think. Warnervale is NOT a nice place for a low EFATO, but guess what? - this guy's engine blew the through-bolts! Who would have though that likely?

Well certainly not me.

 

 

[Bob Llewellyn]

I was told it was done on a j230 at Cessnock by a well known L2, this was a while ago and I never followed it up to see how it went later but at the time he said it was good. I can't see why it wouldn't give better cooling.

Okay... the heat carried away by moving air (forced, i.e. faster than convection) varies as the velocity to the 0.78th power; so increasing the velocity increases the heat transfer, but less than proportionally. Now, for a circular (finned) cylinder, a duct of ~1.2 times the sectional area between the fins (on both sides of the cyl), blending smoothly into a pair of arcs that start above the tips of the fins and converge as they wrap around the cylinder, then blend into an exhaust of 0.8 times the inlet duct area, will give near perfect cooling. This is because, as the cooling air gets hotter moving past the cylinder, the contracting passage speeds it up enough to maintain virtually constant heat transfer. The baffles on Austers, and to a degree on Tiger Moths, come close to this ideal.

By contrast, the "let the air in over the top, then hit the firewall and drop - stunned - through the fins, rattle out of the lower cowl any old how" is pretty lame. The NACA C-75 exercise shows at least converging inlet baffles / ducts, and an inverted "V" to turn a bit of the outflow past the back of the cylinders must be presumed.

 

Given the known advantages of streamlined struts - the airflow doesn't separate - compared to cylindrical - it does separate - I do not understand how anyone expects cooling air to adhere to the "back" half of a round(ish) cylinder without a great deal of help.