Major weaknesses addressed

[Old Koreelah]

Interesting, Oscar. Before finally fitting a Jab 2.2 I was hung up on the fear of glazing the bores. The little Jodel D-9 was first flown with 27 hp and most have a VW putting out 40-60 hp, so I was expecting to be cruising at about 2300 rpm.

 

We're told that's a bad rev band for a Jab, so mine gets 2800. I have forgotten about glazing. So far so good.

 

 

[facthunter]

ALL engines will have some "bad" RPM ranges depending on the prop used to some extent but caused by torsional harmonics. These are titled "AVOID" for extended periods but on some engines you go straight through them at all times.( with VARIABLE pitch) I would be more concerned about getting the engine cooled properly is a more draggy plane. I can't understand why Jabiru don't use between cylinder baffles to better direct the air like all other engines do. There is always a very hot parch near the exhaust valve on the Jab cylinders. Steel is not a real good conductor of heat, so the hot spots should be addressed if possible. Nev

 

 

[Old Koreelah]

Agree Nev. After spending weeks building a complex pair of fibreglass hoods for my previous engine (a VW 1600) I happened upon a Great Plains cooling kit. Absolutely simple and effective. If I had a similar horizontal fence around Jab engine it would be so easy to get at spark plugs, etc.

 

 

[jetjr]

Older engines do use baffles on top between cylinders, aim was to divert air to rear cylinders, at one stage it was directed to remove tham and fiddle with exit outlet to pull more air in, then theres newer fine finned heads which negate much of these dramas

 

Some have put old cooling baffles underneath cylinders and added baffles in the top of incoming air ducts (as per Jabiru usa tech note) and see even, constant head temps around 100 deg C :)

 

 

[Dafydd Llewellyn]

I've heard of it building up on the valve seats on liquid cooled motors, ( and then a small part comes loose and causes compression loss and seat damager sometimes. They would be running much cooler than the aircooled motors (even Yours) run. Nev

Interestingly, there was a published paper in which comparison was made between exhaust valve seat temperatures on air-cooled Vs liquid-cooled engines, by the RAE I think, back in the 1930s; if I recall correctly, the author was Roxbee-Cox. Both types had Stellite seats, i.e. very much current conventional practice. The result was that there was no practical difference in the seat temperature between the two. I've not come across any more recent research - what there is, is no doubt not in the public domain. However, it showed that one should not make assumptions on this sort of thing. I can only suppose the result was due to the very poor thermal conductivity of Stellite, but it's an area that I'd like to know more about.

 

Re cylinder glazing, this is a well-known problem in engines that have nitrided steel bores (as do almost all Lycomings and Continentals etc). However Lycoming at one stage supplied plain steel barrels for some models of their 0-320 - I had one such, in a PA28-140; they were mainly for flying school aircraft that got constant use. My engine ran its full life with full compression; not the slightest evidence of glazing - but I made a point of doing a couple of circuits in it at least once a week. It had to work hard in the Cherokee 140, all climbing had to be done at full throttle or it simply would not climb fast enough to get the high-power phase out of the way quickly. It ran at about 150 C below peak EGT when full rich, at full throttle, as I recall (by comparing the climb EGT at full rich, with the peak EGT at cruise power - NEVER try to find peak EGT at above 75% power!) However I did a lot of cross-country flights - Sydney-Tamworth, Sydney - Tocumwal etc and I always cruised at 60% power (around 2300 RPM) and leaned to 50C rich of peak EGT, so the climb phase was only about 10% of total flight time. I had no problems from lead fouling, tho the plugs were definitely due for cleaning at each 100-hourly. This was all on 100 LL, of course. So it was the case for that engine that there's nothing wrong with climbing at full throttle, provided you avoid doing so at minimum airspeed; keep the speed up so it gets better cooling, and get the climbing bit over as soon as possible. Having reached you cruise height, pull the power back until the engine is purring, instead of pounding - this is quite possible to "feel" in most aircraft I've flown - to about 65% to 70% power (many modern EMS gauges will show the % power).

 

One cannot check whether the engine is running on the rich or the lean side of peak EGT, with no manual mixture control; and as both the Jabiru and the Rotax 912 have CD carbies, they lack manual mixture control (the mis-use of which is a major cause of engine damage, in engines that have it) however the spark plugs will tell you. The difference is crucial; on the rich side of peak EGT, the exhaust gas has no free oxygen, but does have some carbon monoxide. The reverse is true, on the lean side of peak EGT. Carbon monoxide is lethal to humans, but kind to hot metal; it prevents oxidation of the metal (it's the basis for the blast furnace). Ask any welder what happens if he tries to weld something using oxy-acetylene, with the oxygen set too high. So check your spark plugs and NEVER let your engine run on the lean side of peak EGT if you can avoid this.

 

 

[Russ]

Camit have my vote, everything just sounds right. Will be ordering one SOON.

 

As to jab and camit again getting together , highly unlikely, as jab have been trialling a Chinese jab power plant for some time now, and "spies" tell me it,s not far off release.

 

Jab made a serious blunder yrs back, they should have "optioned" a Rotax 4 banger to buyers, this alone would have seen the jab sales go ballistic , and the ongoing negative reports re "that jab engine" would simply faid away. The higher buying price would be tolerated by pilots, simply because it was powered by Rotax.

 

The jabs look great, comfortable, strong, good endurance....they are brilliant.

 

Powered by Rotax, they would be a world beater.

 

Just my view...

 

 

[Oscar]

Russ, I think that just about anybody involved in Recreational Aviation in this country - even those who harbour a deep-seated antipathy towards anything Jabiru - would admit that without them here, we'd be a far less successful sector of aviation. They're a bit like Commodores /Falcons / Camrys - they're not the BMW's, Mercedes, Porsches of the sector, but when you want to haul the family on a holiday instead of run down to the local social hot-spot and be seen as cool, they do the damn job - and they do it pretty well. You can (if you treat them half-reasonably), pretty much pack everybody in, head off to the destination and have a reasonable expectation of arriving there when you expected to. And if they do hiccup on the way, then there's somebody around who can get you back on the road again before your holiday is ruined.

 

Yes, CAMit and Jabiru are headed on different paths regarding engine supply for Jabirus. Just what the 'Chinese' engine will deliver is something I suspect only Jabiru know at this time - we'll all have to wait and see what that is, in the experience of real-time use. We all have no idea of not just performance but even price! Will it be a simple retro-fit for existing engines? You'd have to think yes, it would be - but again, that is something we don't yet know.

 

CAMit are not building an engine based on the idea that it will replicate a Rotax. I am one who welcomes that; I have deep-seated reservations about using a basic reciprocating concept that depends on a crankshaft manufacturing technique that has grown from small, short-life two-strokes in a four-stroke environment. I'm happy to acknowledge that that is a prejudice reinforced by the knowledge that there are no high-performance four stroke engines that use this form of crankshaft, from heavy-equipment diesel engines through to ultra-high performance drag racing engines. That said, I recognise that - generally speaking (though the recent Rotax emergency bulletins effectively recalling a large number of crankshafts is a bit of a reality check) - Rotax engines are a decent thing. I'm looking forward to flying a unique aircraft powered by one - but just personally, I don't want one turning the prop of the device I'll be using as a commuter between my place and another location 1,000ks away over some tiger country.

 

What CAMit are currently developing, is a potentially better Jabiru engine. That it IS a better engine will be either proven or negated by real-time testing - and that is happening right now. Real-life operational results are coming in. If you have the interest to research the changes CAMit have made - they can tell you what, why and how those changes work. Absolutely nothing beats going to the source - and if you have/can create the opportunity to go to CAMit and see, feel, examine, discuss those changes, you can make up your own mind with the real dirt under your fingernails from pretty much forensic-level investigation. To me, that just HAS to be worth the time and expense - and in our case, we drove something like 1500k's one-way, spent two weeks (copping the accommodation charges), and got not just dirt under the fingernails but several days of full-body kerosene wash just from cleaning our old engine ready for the upgrade work!) And the prawns available in Bundaberg from the local fisherman's co-op make any trip there worthwhile.

 

All of that was more than worth it for us personally - because we are both techo-nerds, we wanted to know all the nitty-gritty. I personally find the PR blurb for engines and aircraft to be so much marsh-gas - call me an old-fashioned cynic, but for me two weeks of exposure to every little detail about the manufacture of an engine from a lump of metal through to a delicate finished component beats two paragraphs of web-page blurb. About 99% of my own flying experience has been in aircraft in which I absolutely knew that engine failure was not going to happen - because it didn't have a damn engine. And,yes, I've outlanded in paddocks surrounded by trees and infested with cows..

 

A visit to CAMit is phenomenally instructive. Next best is talking to them. They are there, on the end of a phone call/email. You don't have to just pay your money and see what happens.

 

 

[fly_tornado]

You're assuming that the prevalence of engine failures has no impact on RAA activities.

 

 

[Dafydd Llewellyn]

You're assuming that the prevalence of engine failures has no impact on RAA activities.

No, just that it's a separate subject to this thread. This thread, I say again, is about CAMit's initiatives. It's NOT about "Wot should RAA do about (putative) Jabiru engine problems." The first post on it was a question to the effect that if CAMit have addressed major weaknesses in the engines they are building under their own name, why can't Jabiru do likewise. That's a rhetorical question, firstly because whilst there's been a lot of scuttlebut about Jabiru engines, none of its perpetrators seem able to produce valid engineering proof of any "major weaknesses"; and secondly because, if & when a proven weakness can be demonstrated, only Jabiru could answer the question.

So the real purpose of the post was to draw people's attention to the existence of CAMit's engine, which is at this stage only suitable for fitment to -19 registered RAA aircraft, and homebuilt VH-registered aircraft, but which we all hope will prove to be somewhat more durable, in the hands of the type of usage meted out by RAA members, than the Jabiru engines are, fairly or not, reputed to be.

 

A lot of disinformation and mis-direction has been directed at the thread; but I hope most of its readers by now have a reasonable understanding of what it's about.

 

Yes, accidents - whether or not due to the design of the engine, the manufacture of the engine, the operation of the engine, fuel mis-management, fuel exhaustion, carbie icing, or any of perhaps a dozen other causes of "engine failure" that have nothing to do with the quality of the engine itself - do have an impact on RAA activities.

 

What are RAA's options? The Jabiru 2200 has a Type Certificate issued by CASA. That means, the onus of proof would be on the RAA to show that the engine either does not comply with its certification basis (i.e. that CASA wrongly issued the TC); or to demonstrate to CASA that there is a fault or faults that require CASA to issue an AD. The RAA is, quite candidly, completely incapable of doing either of these things. RAA cannot, under the terms of CAO 95.55, refuse to register Jabiru aircraft that have a TC and conform to their Type Design (or which have proper approval of any modifications), so RAA is free of liability in that regard.

 

So, why are you raising this as an issue in this thread? What do you imagine anybody can do about it in this Forum? If you want to pursue that, FFS start another thread.

 

 

[Oscar]

You're assuming that the prevalence of engine failures has no impact on RAA activities.

OK., how about you and I hold fire on our differences in the interests of the greater good here? I'm prepared to come out of my trench in the Christmas Truce situation..

 

Are you saying that RAA activities have been - or should be - impacted by the statistics of Jabiru engine failures? It's a fair question - but surely that is something that RAA needs to answer, since it is the only authority with the full access to the statistics. Are these reputed failures of sufficient impact that something really radical should be done? I'm happy to acknowledge that RAA has had a lot on its plate in simply trying to sort out the registration mess - but is it in fact the case that Jabiru engine failures are causing deaths/injuries at the rate that needs specific RAA safety focus? That's a question that RAA should answer, officially - not just as a casual comment. How about we ask them directly? How about you pose that question to the new Tech. Manager? Let's have it all out in the open, rather than one side hurling invective and the other side postulating 'no serious problem'.

 

How about we both work to improve the information available to prospective users of Jabiru products, rather than beat our own specific drums? Just where on the scale of safety / economic problems do Jsbiru engine failures rank - and what are the real causes of those problems? What are putative solutions to those problems and how reliable are these?

 

If the occurence (let's walk away from the emotive-laden 'prevalence' word in the absence of quantitive analysis of failure rate/hours flown data for now, ok?) of Jabiru engine failures moderated by the discovery of actual causes is impacting the activity for RAA - let's hear all about that. Let's have the damn factual evidence. Anything less than that is really nothing more than false advertising for/against the product.

 

 

[fly_tornado]

I agree we shouldn't lump Camit into the Jabiru problems.

 

 

[Oscar]

I agree we shouldn't lump Camit into the Jabiru problems.

OK! - we have a point from which to move forward. Can we agree that:

 

1) if the statistics demonstrate that there is a problem of sufficient magnitude in terms of user safety, RAA should take whatever action is appropriate to maximise user safety;

 

2) that RAA is the appropriate authority - rather than the 'court of public opinion' ('aka forum threads') for the delivery of whatever 'evidence' - be that authoritative analysis by reputable entities or personal opinion - that ought to be considered;

 

3) that discussion of potential changes to the existing situation constitutes exchange of information;

 

4) that statements purporting to convey a summary or statement of expert opinion/extrapolation of 'fact' from anecdotal / published sources without the supporting evidence are a waste of everybody's time.

 

Let's strip away the bias, personal prejudice etc. and provide as much fact / information useful to establishing fact, for the users / potential users of Jabiru engines as we can assemble. For instance: I won't claim that the through-bolts issue is dead and buried until there is a statistically reliable source for making such a statement. Will you refrain from claiming that through-bolt failure was the cause of an engine failure without being able to document all the circumstances of the engine in question that MAY have caused the through-bolts to give up and shown that it was, in fact, an 'unprovoked' failure of the bolts, not e/g. operating outside limits? This is important stuff.

 

 

[DrZoos]

China makes lots of good stuff now, but they also make a lot of crap with very poor quality control in some areas. Yes they are getting better and better.

 

If Jabiru are not all over this in terms of quality control including material quality control this could be dangerous and disastrous... And i know Ian has expressed this in similar terms.

 

Im wondering who will be brave enough to buy and fly the first few years worth of Chinese Jab engines...

 

 

[Camel]

China makes lots of good stuff now, but they also make a lot of crap with very poor quality control in some areas. Yes they are getting better and better.If Jabiru are not all over this in terms of quality control including material quality control this could be dangerous and disastrous... And i know Ian has expressed this in similar terms.

 

Im wondering who will be brave enough to buy and fly the first few years worth of Chinese Jab engines...

Are you aware that Cessna 162 is made in China, Cirrus is now made in China. I'm sure there will be more, I am certain that Camit are taking the opportunity and I'm am glad they have . You are right about one thing, they will have to prove reliability or I think this could be a disaster for them.

 

 

[Dafydd Llewellyn]

Cut the waffle - supply some facts. In effect, put up or shut up.

 

 

[kgwilson]

Seriously - and not wishing to be in any way combative - is the 'run hard' and 'don't baby it' thing more conventional wisdom handed down from person to person than actually what Jabiru says? I can only comment from the J120 POH, because that's what I have access to, but those terms don't appear in it - and there's really nothing about engine operation that suggests it. They're both very subjective terms anyway! However, here's some quotes from the 'Jaba Chat' of September 2011 that might provide a bit of perspective on what Jabiru actually are saying - and some of it is worth reading carefully, because they are fairly comprehensive explanations of a difference between 'run it hard' as most might interpret it vs. 'let it spin freely':

 

CLIMB OUT SPEEDS

 

There appears confusion on best climb out speeds. Manual specifications for best rate of climb

 

for J160 and J230 is 68 and 75 knots respectively.

 

This means this air speed will give the best chance of clearing obstacles if the need arises.

 

However the rate of climb for best engine management has been largely left to operators.

 

The quickest way between two sets of traffic lights is to floor the accelerator and race the engine

 

– but it’s not the way most of us do things because we understand that driving that way will use

 

more fuel and wear the engine out faster. Similar arguments apply to climb speeds with a Jabiru

 

Engine. The 4 cylinder engine will look after you better with better air/oil cooling if climbed around

 

80 knots while the 6 cylinder will think highly of you at a 90 knot climb or above. If flying a J430/

 

J450, climb speeds for load will differ especially according to load. Once heading to that cross

 

country destination cruise climb at elevated speeds (shallow angle of climb) contributes to good

 

engine management. At these higher speeds not only is there more air available to cool the engine

 

but the RPM is higher, allowing the engine to rev more instead of “lugging”. This significantly

 

reduces the stress on the engine and makes it less likely to suffer detonation or other

 

long-term maintenance issues.

 

 

 

OPERATING RPM

 

Historically we have always recommended that operators allow their engine to rev rather than

 

lug. Done properly this approach works very well, however in certain cases it can also be damaging

 

as it has been over-simplified and does not necessarily consider percentage power.

 

For example, consider a Jabiru J200 with a Jabiru engine, propeller and cowls. In a full power,

 

straight and level run at sea level this aircraft should reach speeds in the 130 – 140 KIAS range

 

and the engine will be revving to around 3100 – 3200RPM. In this aircraft – which is fairly sleek

 

and fitted with a well-matched propeller – cruising at 2900 rpm is fine because it will be at a relatively

 

low power setting.

 

In comparison, the same engine and propeller could be fitted to a bush plane with slats, flaperons,

 

tundra tyres and the aerodynamics of a brick. In this case the static RPM and RPM on takeoff

 

would be similar to the J200 – but flat out straight and level at sea level the aircraft won’t do

 

much more than 100 knots and the engine will be stuck at about 2900 – 3000 RPM or less. In

 

this case trying to cruise the engine at 2900 RPM would be disastrous as it would be a very high

 

percentage power setting.

 

The above examples are deliberately extreme but their message can be applied across all airframes

 

and engine models.

 

It's not like keeping a diesel engine under decent load to avoid glazing the bores! What Jabiru are saying, basically, is: let them rev decently, don't beat them to death. It's not difficult to see that this is quite different to 'use

 

them hard' - if 'use them hard' is taken by the pilot to mean 'load them up and make them work all the time at the top end of limits'. So I don't think you are 'babying' your engine, but rather using it intelligently! If it's toddling along at lower revs and the CHTs are good - then surely you're giving the engine its best chance of returning you the sort of life you expect.

 

One has to wonder - how many Jab. engines are bought to premature ends because the operators thought they were doing what Jabiru says, based on 'conventional wisdom' handed out by a mate, someone on the field etc. - rather than actually operating them according to the manufacturer's recommended techniques?

Spot on. This run hard BS shows complete ignorance. It is always horses for courses. A mate of mine has just bought an early Jab SP6 with the thick finned solid lifter 3300 engine. The original builder did a simple job of getting the cooling airflow right & didn't put any gull wing deflectors in or a fence to force air over the top of the cylinders but left a nice big hole in the bottom cowl with a decent lip to aid suction. I'd say that exit area would be 3 to 4 times that of inlet area. He cruised at 2600 rpm with excellent fuel consumption (has run entirely on 95 Mogas) & the engine has not been touched other than standard maintenance & has 850 hours TTIS. From the takeoff near Geelong to final destination South Grafton via Temora & Narromine, oil top-up was only 200 ml & his comments were that Ts & Ps never got out of the green. There is no EGT & only a single CHT probe under the plug of the rear LH cylinder.

 

 

[rankamateur]

Jab made a serious blunder yrs back, they should have "optioned" a Rotax 4 banger to buyers, this alone would have seen the jab sales go ballistic , and the ongoing negative reports re "that jab engine" would simply faid away. The higher buying price would be tolerated by pilots, simply because it was powered by Rotax.

You can't say things like that out loud!

 

 

[turboplanner]

Cut the waffle - supply some facts. In effect, put up or shut up.

Very well said.

 

When the products eventually get on to the market, and if those products establish a commercially reliable performance, then that will be the time to crow about it.

 

I wish both manufacturers well with their plans.

 

 

[Camel]

Kgwilson

 

"The run the Jabiru engine hard " was direct from Jabiru and they say operate at 2850 rpm and do not baby it. This is not BS but fact. You say complete ignorance, is very harsh having owned two J 230's am a motor mechanic, L2 and not deaf and was told by Rod Stif and Don at Jabiru. I have been very interested in Jabiru engines for a long time and have a keen interest in them. I am supportive of Camit upgrading the engine the concept of the engine is good but Jabiru have refused to listen to good advice and practices. If Jabiru had taken notice of recommendation from such things as below their product may be without knockers. I believe Camit with do well as long as Jabiru don't make the decisions.

 

http://nvsr.com.au/articles/article10.html

 

Jabiru Ultralight Aircraft - Oops!

 

Jabiru produce a range of Ultralight and Light Sports aircraft right here in Australia. They're popular with enthusiasts and flying schools alike because they are easy to handle and fairly robust - with one exception. The dummies have installed the pistons backwards! The offset pistons used were designed for clockwise rotation whereas the Jabiru rotates anticlockwise.

 

A quick lesson in 4 stroke engine operation

 

1. Induction Stroke

 

With the exhaust valve closed and the inlet valve open the piston is pulled down drawing air & fuel into the combustion chamber.

 

2. Compression Stroke

 

Both valves are closed and the piston is pushed up to compress the air and fuel to a fraction of its original size.

 

3. Ignition Stroke

 

The excitement starts on the third stroke when the sparkplug fires causing the fuel and air mixture to explode! The rapidly expanding gases push the piston back down again.

 

4. Exhaust Stroke

 

The fourth and final stroke completes the cycle by moving upwards pushing the exhaust gas out via the now open exhaust valve.

 

My late father, an Aeronautical Engineer with the Royal Australian Navy for 35 years, simplified this process by referring to it as "Suck Squeeze Bang Blow". That term pretty well sums up the 4 Stroke engine!

 

The amount of force exerted on pistons as they travel up and down is enormous, and like any "up and down" motion there has to be a “Top and Bottom”! By that I mean the piston must stop at the top before it can travel to the bottom and visa versa. Pistons with a 90 mm stroke at 3000 RPM travel at 9 meters (29 feet) per second and have to come to a dead-stop in an instant at the top and bottom of the stroke. This stopping and starting causes a hammering affect and creates stress on gudgeon pins, con-rods, big-ends, and more. The hammering is particularly horrific during the Ignition Stroke when the explosive force of the burning fuel literally "blows" the piston down.

 

Easing the strain

 

Traditionally pistons were connected to con-rods right in the middle but to ease the strain when the piston stops and comes back down they are offset in the direction of engine rotation, the connection between con-rod and piston is off centre. The crown of each piston is marked with an arrow indicating which direction the piston should be installed. By offsetting in this way you are giving the piston a bit of a headstart on its journey.

 

Engines with offset pistons run better! They're more durable, reliable and quieter but ONLY if you've put them in the right way.

 

Jabiru have it wrong

 

For some reason, as yet unexplained logically, Jabiru have chosen to put their pistons in reverse. They were made for General Motors motor vehicles, all of which run clockwise, which is correct based on the offset, but Jabiru engines rotate anticlockwise meaning they are all installed wrong. Any mechanical engineer will tell you what happens when you don't install your offset pistons correctly - you get problems, you shorten the life of your engine, it makes more noise, and they just become crappy in general.

 

One of the symptoms, and it is common to all Jabiru engines, is that when you shut-down there is a distinctive clunk-clunk before it stops completely. This clunk-clunk is caused by the engine trying to run itself in reverse as a result of the offset pistons.

 

By installing pistons in accordance with the Jabiru manual the offset is working against the flow and actually creating durability issues and potentially safety problems. Interestingly, a number of people have chosen to install their pistons in the opposite direction and claim their engines perform better and are significantly quieter.

 

Who knows about this

 

The Australian Civil Aviation Safety Authority (CASA) and the Australian Transport Safety Bureau (ATSB) were advised by various Jabiru owners and maintenance staff, but both organisations have chosen to do nothing. The engines were certified to fly and deemed appropriate for the aircraft type. I've been informed that engines are tested at idle and cruise RPM only! They did not test them through the full rev range, which was a mistake that should be rectified.

 

Jabiru have been made aware of this issue on multiple occasions and have cleverly devised a cover story “The pistons are installed in reverse due to the forces applied by the Prop”. What a load of cods-wallop. Every engineer I've spoken to about this issue has given me multiple reasons why these pistons should be turned around. My late father was very interested in discovering why Jabiru believe that an opposite offset could be beneficial. With 35 years of experience behind him working with various aircraft engines he could find no reason why Jabiru would pursue the opposite of what, from an engineering point of view, seems to be ridiculous.

 

Safety

 

The definition of a good pilot is “One whom has the same number of take-offs as they have landings” and most people when they go flying want to make certain they land in one piece. The secret to keeping yourself alive when flying light aircraft is more than just your own skills! Maintenance of your aircraft is vital to safe flying and going up in an aircraft that has such a design floor, in my mind, is madness.

 

How many accidents have occurred as a result of the offset issue. Just last week a good friend of mine was flying a Jabiru when a thru-bolt broke and he had to land with a faulty engine. It could have been much worse, the engine could have failed completely. These bolts are known to fail in Jabiru aircraft and in my mind this is a direct result of excessive stress placed on them by the ridiculous offset issue.

 

Certification

 

Jabiru are popular with flying schools because they offer easy shared access to controls via a v-shaped stick between the left and right seat. When an aircraft is used for training purposes it is considered "Certified" which means that under no circumstances can the aircraft be modified from manufacturer specifications. So even if they wanted to turn their pistons around to improve reliability and reduce maintenance costs they cannot by law. Private owners that rent their aircraft to flying schools are in the same boat. Owners that do not rent their aircraft are free to do whatever they like and some have already turned their pistons in the opposite direction with amazing results. Despite these results Jabiru continue to maintain that their manual is correct.

 

What should happen now

 

CASA should ground every Jabiru airplane! It's that simple. The ATSB needs to review any previous accident reports involving Jabiru, particularly when engine failure was considered a possible cause.

 

Jabiru should look carefully at their engines and if necessary swallow their pride and turn the pistons in right direction. They would probably find that maintenance costs would fall, performance would rise, and their customers would be very happy.

 

On a more personal note

 

I have spoken with a number of Jabiru owners whom tell me it's rare for an engine to go more than 250 hours before it requires serious and expensive repairs. I've seen evidence of excessive wear on cylinder walls and pistons. I've seen first hand the damage done to big-end shells as a result of excessive belting when the piston is trying to go in the opposite direction to engine rotation. Jabiru are unlikely to accept responsibility because they would then be liable for fixing the problem – that could be expensive!

 

Published 5 June 2013

 

Read a review of the Jabiru 160 on Aviator: Click Here.

 

 

[kgwilson]

I am well aware of the recommended cruise RPM from Jabiru but they do not say anywhere "Run it Hard". The airflow and performance envelope of the particular aircraft will determine the best cruise RPM for optimum engine operation.

 

The pistons have not been installed backwards. Anyone can publish articles on the internet & many are completely wrong while others have a lot of good information but fail to get the one crucial aspect of their theory right. The Jabiru engine does not have a flywheel like a conventional car engine. The propeller is the flywheel so the engine is running clockwise in relation to its flywheel.

 

 

[Oscar]

Wow - a lot there to contemplate!

 

I think that the Jaba Chat stuff I posted above explains what Jabiru MEAN when they say 'run it hard'; let's be realistic, 'run it hard' is not a technical specification for operation but a very loose term that lacks any sort of quantification. It's a bit like 'torque it to really bloody tight' or 'belt the crap out of it', isn't it? Rod Stiff just may have unwittingly condemned lots of his engines to an early grave by using a term he thought would be understood to mean one thing but has (not unsurprisingly) been taken to mean something else! The POH (at least for the J120) certainly provides a far more definitive specification for normal engine operation in climb and cruise modes, and I think it's not unreasonable to suggest that that Jaba Chat explanation exists because Jabiru realised they needed to provide a batter explanation of things than just a three-word slogan. There's an old slogan that goes something along the lines of: 'I know you heard what I said, but I am not sure you understood what I meant' - and surely Jabiru published that explanation because they realised more explanation was needed. Rod Stiff is a man of mostly few words, and possibly in this case, a few too few!

 

As for the piston direction thing - I've had the geometry involved explained to me and I'm certainly one of those that believes that the Jabiru piston install direction is incorrect. It's a fairly simple case of looking at the line of force reacted by the downwards-travelling con-rod when projected through the crown of the piston at peak combustion pressure loading, and you can see why a gudgeon-pin offset helps to keep that line of force in the centre of the piston thus holding it straight in the bore (or perhaps more accurately, why an offset gudgeon pin placed on the wrong side will increase the rocking force imparted by the combustion pressure on a piston where the line of force reaction is off-centre) thus driving the piston skirt and crown against the sides of the bore. Changing the piston install direction around to 'normal' isn't a silver bullet thing as suggested, but one of a number of incremental changes that are entirely likely to be beneficial.

 

 

[fly_tornado]

Jab's response http://www.jabiru.net.au/images/AVDALSR088-1_Piston_Offset.pdf

 

 

[Dafydd Llewellyn]

Kgwilson"The run the Jabiru engine hard " was direct from Jabiru and they say operate at 2850 rpm and do not baby it. This is not BS but fact. You say complete ignorance, is very harsh having owned two J 230's am a motor mechanic, L2 and not deaf and was told by Rod Stif and Don at Jabiru. I have been very interested in Jabiru engines for a long time and have a keen interest in them. I am supportive of Camit upgrading the engine the concept of the engine is good but Jabiru have refused to listen to good advice and practices. If Jabiru had taken notice of recommendation from such things as below their product may be without knockers. I believe Camit with do well as long as Jabiru don't make the decisions.

http://nvsr.com.au/articles/article10.html

 

Jabiru Ultralight Aircraft - Oops!

 

Jabiru produce a range of Ultralight and Light Sports aircraft right here in Australia. They're popular with enthusiasts and flying schools alike because they are easy to handle and fairly robust - with one exception. The dummies have installed the pistons backwards! The offset pistons used were designed for clockwise rotation whereas the Jabiru rotates anticlockwise.

 

A quick lesson in 4 stroke engine operation

 

1. Induction Stroke

 

With the exhaust valve closed and the inlet valve open the piston is pulled down drawing air & fuel into the combustion chamber.

 

2. Compression Stroke

 

Both valves are closed and the piston is pushed up to compress the air and fuel to a fraction of its original size.

 

3. Ignition Stroke

 

The excitement starts on the third stroke when the sparkplug fires causing the fuel and air mixture to explode! The rapidly expanding gases push the piston back down again.

 

4. Exhaust Stroke

 

The fourth and final stroke completes the cycle by moving upwards pushing the exhaust gas out via the now open exhaust valve.

 

My late father, an Aeronautical Engineer with the Royal Australian Navy for 35 years, simplified this process by referring to it as "Suck Squeeze Bang Blow". That term pretty well sums up the 4 Stroke engine!

 

The amount of force exerted on pistons as they travel up and down is enormous, and like any "up and down" motion there has to be a “Top and Bottom”! By that I mean the piston must stop at the top before it can travel to the bottom and visa versa. Pistons with a 90 mm stroke at 3000 RPM travel at 9 meters (29 feet) per second and have to come to a dead-stop in an instant at the top and bottom of the stroke. This stopping and starting causes a hammering affect and creates stress on gudgeon pins, con-rods, big-ends, and more. The hammering is particularly horrific during the Ignition Stroke when the explosive force of the burning fuel literally "blows" the piston down.

 

Easing the strain

 

Traditionally pistons were connected to con-rods right in the middle but to ease the strain when the piston stops and comes back down they are offset in the direction of engine rotation, the connection between con-rod and piston is off centre. The crown of each piston is marked with an arrow indicating which direction the piston should be installed. By offsetting in this way you are giving the piston a bit of a headstart on its journey.

 

Engines with offset pistons run better! They're more durable, reliable and quieter but ONLY if you've put them in the right way.

 

Jabiru have it wrong

 

For some reason, as yet unexplained logically, Jabiru have chosen to put their pistons in reverse. They were made for General Motors motor vehicles, all of which run clockwise, which is correct based on the offset, but Jabiru engines rotate anticlockwise meaning they are all installed wrong. Any mechanical engineer will tell you what happens when you don't install your offset pistons correctly - you get problems, you shorten the life of your engine, it makes more noise, and they just become crappy in general.

 

One of the symptoms, and it is common to all Jabiru engines, is that when you shut-down there is a distinctive clunk-clunk before it stops completely. This clunk-clunk is caused by the engine trying to run itself in reverse as a result of the offset pistons.

 

By installing pistons in accordance with the Jabiru manual the offset is working against the flow and actually creating durability issues and potentially safety problems. Interestingly, a number of people have chosen to install their pistons in the opposite direction and claim their engines perform better and are significantly quieter.

 

Who knows about this

 

The Australian Civil Aviation Safety Authority (CASA) and the Australian Transport Safety Bureau (ATSB) were advised by various Jabiru owners and maintenance staff, but both organisations have chosen to do nothing. The engines were certified to fly and deemed appropriate for the aircraft type. I've been informed that engines are tested at idle and cruise RPM only! They did not test them through the full rev range, which was a mistake that should be rectified.

 

Jabiru have been made aware of this issue on multiple occasions and have cleverly devised a cover story “The pistons are installed in reverse due to the forces applied by the Prop”. What a load of cods-wallop. Every engineer I've spoken to about this issue has given me multiple reasons why these pistons should be turned around. My late father was very interested in discovering why Jabiru believe that an opposite offset could be beneficial. With 35 years of experience behind him working with various aircraft engines he could find no reason why Jabiru would pursue the opposite of what, from an engineering point of view, seems to be ridiculous.

 

Safety

 

The definition of a good pilot is “One whom has the same number of take-offs as they have landings” and most people when they go flying want to make certain they land in one piece. The secret to keeping yourself alive when flying light aircraft is more than just your own skills! Maintenance of your aircraft is vital to safe flying and going up in an aircraft that has such a design floor, in my mind, is madness.

 

How many accidents have occurred as a result of the offset issue. Just last week a good friend of mine was flying a Jabiru when a thru-bolt broke and he had to land with a faulty engine. It could have been much worse, the engine could have failed completely. These bolts are known to fail in Jabiru aircraft and in my mind this is a direct result of excessive stress placed on them by the ridiculous offset issue.

 

Certification

 

Jabiru are popular with flying schools because they offer easy shared access to controls via a v-shaped stick between the left and right seat. When an aircraft is used for training purposes it is considered "Certified" which means that under no circumstances can the aircraft be modified from manufacturer specifications. So even if they wanted to turn their pistons around to improve reliability and reduce maintenance costs they cannot by law. Private owners that rent their aircraft to flying schools are in the same boat. Owners that do not rent their aircraft are free to do whatever they like and some have already turned their pistons in the opposite direction with amazing results. Despite these results Jabiru continue to maintain that their manual is correct.

 

What should happen now

 

CASA should ground every Jabiru airplane! It's that simple. The ATSB needs to review any previous accident reports involving Jabiru, particularly when engine failure was considered a possible cause.

 

Jabiru should look carefully at their engines and if necessary swallow their pride and turn the pistons in right direction. They would probably find that maintenance costs would fall, performance would rise, and their customers would be very happy.

 

On a more personal note

 

I have spoken with a number of Jabiru owners whom tell me it's rare for an engine to go more than 250 hours before it requires serious and expensive repairs. I've seen evidence of excessive wear on cylinder walls and pistons. I've seen first hand the damage done to big-end shells as a result of excessive belting when the piston is trying to go in the opposite direction to engine rotation. Jabiru are unlikely to accept responsibility because they would then be liable for fixing the problem – that could be expensive!

 

Published 5 June 2013

 

Read a review of the Jabiru 160 on Aviator: Click Here.

This is another example of picking one point without considering the context, and assuming it's the whole answer. The argument ignores an important piece of context - i.e. the piston/cylinder clearance. With the sort of clearance one finds in a Lycoming, the above argument is valid. However the Jab. engine has a much smaller clearance, and this means the piston slap effect of the change in side load on the firing stroke is not large enough to be the major effect it's made out to be - and it also alters the timing of that occurrence relative to the peak gas pressure. You have to look at issues like this holistically, not in isolation, or you come up with the wrong answer.

 

I'm not saying that Jabiru is necessarily correct - or incorrect - in either its piston orientation or its piston clearance - I do not have sufficient data to answer that. I do know that Jabiru did NOT blindly put the things in "the wrong way around" - they thought about it and decided there was a good reason for doing it that way, in their engine. That's more than the pundits who are pushing this wheelbarrow have done. And yes, the propeller IS the flywheel, so get the argument right way around, too.

 

More conventional practice would be to use a larger piston clearance - and it then becomes advisable to turn the pistons the other way around. Where the best compromise lies, I do not know. We may learn this from CAMit's accumulating experience. Now put the damn wheelbarrow away, and learn something by watching the CAMit engines.

 

 

[DrZoos]

The Chinese themselves acknowledge that engine making is a massive problem due to a lack of quality from the engine makers components, and more so by the engine component material suppliers. Last year China ordered several hundred Russian AL-31FN engines to go in its J-10 fighters because even this program cant get the quality they are after made in China. Despite over a decade of design and test work on their own engine they gave up , admitting they had failed to get quality components that could last.

 

Recently Chinese officials made an issue of the Chinese inability to manufacture turbine blades for high-performance jet engines. They admitted they have no problem building the engines to specifications, but they have a massive problem with metal failure rates.

 

The cessna 162 was built in China but it has been a miserable failure. They test flew it with a Rotax 912 (non Chinese engine)and claimed they saved $71K per aircraft and would be selling them for under $100k . This claim had to be a crock because the engine costs arround $20K so they must have made the aircraft for $9k. They crashed the prototype and then the redesigned prototype. Then they launched it, took orders and when they realised the thing took so much quality control to get it right they upped the price to $149K and subsequently lost most their orders. After 4 years of production of prototypes and initial orders Cessna moved production back to Kansas. In 2012 Cessna issued a Mandatory service bulliten for cracks in the wing ribs and issues with the wing attachments in 228 planes less then 2 years old.

 

I know Cessna happily have some parts made and assembled in China for other aircraft , but citing Cessna as an example of aircraft success in China is a bit of a double edged sword.

 

If Cessna got it this far wrong how the hell is Jabiru going to get it to work. The problem is not Jabiru. The problem is a country where material quality is a poor distant cousin to volume and price.

 

If you need 3000 sheets of colourbond order it from China, but if you need 50 quality components to last the stresses of an aircraft engine, look elsewhere, primarily because the volumes of the material manufacturers preclude the care needed to get it right.

 

My best mate is the chief process metallurgist in Perth and he has toured many of these blast furnaces in China. His exact words where "they are built for volume not quality " and thats all they do well. When he starts telling me whats involved to get quality steel and alloys and how long it takes to get it right you can understand why the Chinese metals are so substandard.

 

 

[facthunter]

The principle of equalising forces (in this case sideloads ) on the cylinders has been around for ages. It used to be done by offsetting the cylinder axis ( called De Saxxe principle). This is not practical in a horizontally disposed cylinders where some (if not all) of the cylinder hold down studs are common with the main bearing alignment.

 

It's come and gone and then returned again, but regardless it is a small issue in the big scheme of things.

 

The offset piston gudgeon pin centre is there to TILT the piston as there is more Area on one side of the piston than the other. ( Consider it wanting to rotate around the gudgeon axis).

 

Short connecting rods are a bigger factor than what we are talking about here. They are more likely to be employed to make the engine width less. than for torque increase reasons. Side load is inevitable when power is delivered and as the piston travels about TDC it transfers from one side to the other. Piston rock is a cause of barrel facing of rings which makes them seal less effectively. Nev