"Jaberoo" down (Mildura this time)

[Dafydd Llewellyn]

The principle of interrupted fins was used on the Wright R 1820 and 3350 cylinder barrels, using stamped aluminium-sheet fins pressed or clipped onto the barrel. It was NOT used on the cylinder heads, which retained the classical "Pompadour" fin style. You do not find this sort of interrupted finning on a Lycoming or a Continental engine, which run around 50 horsepower per cylinder. Nor was it used by Pratt & Whitney, BMW, Bristol, etc. I think the development of air-cooled aircraft engine cylinders up to around 200 horsepower per cylinder, is a rather more appropriate datum for an aero engine, than motorcycle practice. The Jab engine is running 20 HP per cylinder, so it's making rather conservative use of this established practice.

 

The merit or otherwise of the finning style depends on many factors, but the main one is how the overall airflow for cooling is to be managed. Normal pressure-cowled aircraft practice, is to recover the dynamic pressure from the speed of the airflow relative to the aircraft, in a duct or chamber on one side of the cylinders, and use that to force the flow between the cylinders, aided by whatever depression can be provided by the cowl outlet. With horizontally-opposed or in-line engine layout, that involves turning the flow through 90 degrees; with a radial, no turn is necessary. The form of cylinder-head finning you describe seems more appropriate to uncowled cylinders, i.e. 1920 aero-engine practice. Things have moved on from there.

 

The form of the cooling provisions in the test cell is a consequence of the form of finning airflow adopted by the engine designer, not the cause of it.

 

Let's see some test cell results for your cooling concepts, Rex? Preferable results witnessed by CASA.

 

 

[pmccarthy]

A very interesting and informative thread, thanks everyone.

 

 

[motzartmerv]

Good onya Bex, thanks!!!

 

 

[winsor68]

Which "they" are you referring to? And which CASA schedule?

The schedule that Lycoming follows...

 

 

[Dafydd Llewellyn]

The schedule that Lycoming follows...

Um - I'm still somewhat in the dark. Every GA aircraft has its maintenance system identified in the Log Book Statement - on the first page of its log book. If it has a Lycoming engine, the Log Book Statement will normally specify the appropriate Lycoming maintenance manual. If it's a VH-registered Jabiru, it will specify the appropriate Jabiru maintenance manual. The specification of these in the Log Book Statement makes them mandatory. An owner or operator can apply to CASA to alter or vary the maintenance system; fleet operators often develop their own maintenance system.

I have no idea how RAA handles that - or even if it does address it at all.

 

Does that answer your question?

 

 

[David Isaac]

Silly question - If you bother to think about it, it should be obvious that the engine test cell cooling system cannot be the same as the aircraft cooling system, because it's not moving through the air at 70 knots or so.

Great post Dafydd, good info. Not really that silly a question though because even though we both know there is an engine test cell where the engine is setup for initial static testing, there is also an installed test that you have ably described. It is the final installation of the cooling configuration that I am highlighting and perhaps that configuration changed from the test configuration or perhaps it may need improvement if subsequent operating experience indicates the engines are running on peak or too close to peak temps. Of course what is defined as peak could also be pivotal in the survivability of the engine. I think if they can improve the cooling, many of the problems which are symptomatic of high temps will go away.

 

The LSA models are not supervised or oversighted by CASA; and I have no knowledge of exactly what was done in their case. So I do not understand why you say " the consumer should be able to rightly rely on the CHT instrument accuracy, especially on factory built LSA models." . If anything, the level of surety should be higher for the certificated models.

My mistake, I meant to actually say 'factory built models' which would include the certificated models and the LSA. By that comment I am suggesting that the factory built models should have properly functioning cooling installations and properly functioning CHT instrumentation which is fit for the purpose of operating the aircraft in accordance with the POH. Of course in the kit built versions, anything could happen and the factory would not be responsible. My understanding is that the factory built Jabs are also experiencing over heat symptoms.

Hell when they finally get this right, it will be a fabulous little engine and should do Jabiru and Australia proud. I personally want them to succeed and I really believe most of us feel the same. Hopefully many of the resolutions will be available soon.

 

 

[Dafydd Llewellyn]

Great post Dafydd, good info. Not really that silly a question though because even though we both know there is an engine test cell where the engine is setup for initial static testing, there is also an installed test that you have ably described. It is the final installation of the cooling configuration that I am highlighting and perhaps that configuration changed from the test configuration or perhaps it may need improvement if subsequent operating experience indicates the engines are running on peak or too close to peak temps. Of course what is defined as peak could also be pivotal in the survivability of the engine. I think if they can improve the cooling, many of the problems which are symptomatic of high temps will go away.

My mistake, I meant to actually say 'factory built models' which would include the certificated models and the LSA. By that comment I am suggesting that the factory built models should have properly functioning cooling installations and properly functioning CHT instrumentation which is fit for the purpose of operating the aircraft in accordance with the POH. Of course in the kit built versions, anything could happen and the factory would not be responsible. My understanding is that the factory built Jabs are also experiencing over heat symptoms.

 

Hell when they finally get this right, it will be a fabulous little engine and should do Jabiru and Australia proud. I personally want them to succeed and I really believe most of us feel the same. Hopefully many of the resolutions will be available soon.

Thanks, David. If the installation detail design changes in a type-certificated aircraft, the cooling tests are required to be re-done. Jabiru builds its certificated aircraft under a CASA Production Certificate; and the issue of "Conformity" - i.e. making each one in strict compliance with the Type Design - is something CASA polices assiduously, at least now they have come to grips with Part 21, and set up a manufacturing QA branch i.e. since about 2008 or so.

 

LSA models can be modified with much less formality - which makes that option much more attractive to a manufacturer - so they should not be mentioned in the same breath as certificated models; they are chalk and cheese.

 

Overall, I agree with you that the cooling system can be improved. I doubt there is any designer who considers his design perfect; the problem is when to decide to stop fiddling with it. Type certification is usually that point.

 

The suitability of instruments for their purpose is not a subject that arises in certification, certainly under the relaxed standards for recreational aircraft; perhaps it should. However, cost comes into that to a considerable degree; the cost of TSO'ed CHT instrument is probably about ten times that of a VDO commercial-grade instrument; multiply that by all the instruments in the panel, and you have a substantial increase in cost. Making the safest aircraft in the World achieves nothing if nobody buys it. You all accept low-grade Chinese altimeters and airspeed indicators. Is the Jabiru any different to the rest of its competition in that regard?

 

The Blanik has military-standard instruments, which is one of the reasons I like it. But people are happy to buy gliders with the cheapest instruments available, because they cost less. The plain truth is that the market has to require a common standard across the board, or no manufacturer can afford to supply anything but the lowest common denominator.

 

You wanted cheaper aeroplanes - and you got them. The Jab is amazing value for its price. Make up your B minds!

 

 

[Guest Andys@coffs]

Dafydd

 

You are right, I did accept Chinese altimeters and ASI's and I purchased a 230 because nothing else had the carrying capacity......but that was in a time when engine failure wasn't as widely known about and with regard the Chinese instruments....not anymore.....in fact never again....the fact that its aviation doesn't change the basic tenets, once bitten twice shy! Which isn't to say that I wouldn't buy a quality Chinese instrument, but rather the word quality and the instruments you refer to should never be used in the same sentence unless its describing lack thereof.

 

As Bex once pointed out, its unfair that I pick on them as Chinese when they are in reality Cheap Sh!t that just happens to be made in China. I agree, pay what you have to so you need only buy an item once, buy cheap sh!t if happy to replace over and over such that your final investment in purely $ value is way more than the better alternate.....

 

Which arguably could be applied to Rotax vs Jabiru Engines.......were it possible to buy a 120hp Rotax and if it was for less than a small nations GDP

 

Andy

 

 

[poteroo]

There is hardly anything in the world that some man cannot make a little worse, and sell a little cheaper: and the people who consider price alone are this mans lawful prey.

 

John Ruskin, (1819-1900)

 

 

[winsor68]

Um - I'm still somewhat in the dark. Every GA aircraft has its maintenance system identified in the Log Book Statement - on the first page of its log book. If it has a Lycoming engine, the Log Book Statement will normally specify the appropriate Lycoming maintenance manual. If it's a VH-registered Jabiru, it will specify the appropriate Jabiru maintenance manual. The specification of these in the Log Book Statement makes them mandatory. An owner or operator can apply to CASA to alter or vary the maintenance system; fleet operators often develop their own maintenance system.I have no idea how RAA handles that - or even if it does address it at all.

 

Does that answer your question?

No. What I was referring to is that if my memory serves me correctly the Jab motor attracted controversy when it was first designed because it was not certified to the same standard as previous aero engines...I believe Lycoming etc had a much more rigorous test regime to achieve certification.

This was contentious "back then"...and today's outcomes were expected by the pilots I knew.

 

 

[David Isaac]

There is hardly anything in the world that some man cannot make a little worse, and sell a little cheaper: and the people who consider price alone are this mans lawful prey.John Ruskin, (1819-1900)

Profound quote Potts,

What I guess is enlightening to me is that he said that back in the 1800s. Seems like 200 years later, human nature is still the same.

 

 

[bexrbetter]

The Jab engine is running 20 HP per cylinder, so it's making rather conservative use of this established practice..

And yet here we are with all the overheating problems, go figure ....

 

The form of cylinder-head finning you describe seems more appropriate to uncowled cylinders, i.e. 1920 aero-engine practice. Things have moved on from there..

bahahahahaha, the whole foundation of your post is from 1920! - and no, with the exception of a couple of brands, they haven't moved on from there.

 

Let's see some test cell results for your cooling concepts, Rex? Preferable results witnessed by CASA.

Zafydd, how did that work out for Jab?

 

I would rather pay for a set of heads, mod them and give them to someone in the forum to test who is having real world issues. If successful I would make them from scratch including a bit of redesign, I believe there would be a handy market for them.

 

So who's up for that in a couple of months time? Could be a waste of time or could be the best thing since sliced bread ...

 

 

[David Isaac]

Maybe Cammit are doing something similar Bex. Are you planning on using these heads on your engine maybe????

 

 

[Oscar]

Hey, why don't you just DO that? There's over 5,000 Jab engines been produced, that's 20,000+ heads! Got to be a great market. I believe Rotec have sold 83 sets of heads already.

 

The Jab engine owner world awaits you!

 

 

[bexrbetter]

Maybe Cammit are doing something similar Bex. Are you planning on using these heads on your engine maybe????

I have no idea what Camit are doing, but best to them for any relief they may bring to some obviously frustrated owners.

 

I can't see them doing a total head redesign though, Oscar has previously indicated they are concentrating on the known issues in his posts, but you know, I'm not privvy to their business.

 

And nothing to do with any engines of mine, pure business item, like Rotec's water cooled heads, I think there's a market out there but without the plumbing and radiator hassles.

 

 

[Dafydd Llewellyn]

No. What I was referring to is that if my memory serves me correctly the Jab motor attracted controversy when it was first designed because it was not certified to the same standard as previous aero engines...I believe Lycoming etc had a much more rigorous test regime to achieve certification.This was contentious "back then"...and today's outcomes were expected by the pilots I knew.

Ah - why didn't you say that the first time?

The certification basis for the Jabiru 2200 is JAR 22H. The same certification basis was used for the Rotax 912 A series. It's au fond, a European standard for motor-glider engines - which was deemed appropriate for other recreational aeroplanes. The standard for Lycomings etc, is FAR Part 33; and this standard also is used for the Rotax 912F and S series.

 

JAR 22H is very similar to FAR 33 except that the endurance run is 50 hours, versus 150 hours for FAR 33. However, JAR 22H makes it much easier for the manufacturer to use commercially-available components - whereas FAR 33 build requirements mean the manufacturer has to have traceability practically back to the ore from which the metal was smelted.

 

 

[Oscar]

And the Rotax 912 series, other than the A, F, S and iSc are ( as of recently, at least) uncertificated. The 912 F is certificated to FAR 33. The 912 ULS is, as far as I am aware, still uncertificated.

 

 

[Guest Andys@coffs]

So the F model was certificated to FAR33 and the A model was only certificated to JAR22 and the 912 UL is uncertificated......

 

So if I was to put all that aside and look at the design is there any difference in the engine other than the parts and hence the engine itself is ultimately traceable back to OEM and the OEM's material supplier....

 

To me, as an uneducated observer, with what's been said above if the engine meets the FAR33 requirement in terms of tests then given that they are more difficult can it then meet JAR22 without being formally tested? Or is it simply a marketing tool used to set a premium (JAR22) or an even bigger premium(FAR33) where logically to me if you for both cases have to be able to show traceability so that like all Rotables it can be returned to known starting point and its usage life is total known and reportable

 

 

[alf jessup]

And the Rotax 912 series, other than the A, F, S and iSc are ( as of recently, at least) uncertificated. The 912 F is certificated to FAR 33. The 912 ULS is, as far as I am aware, still uncertificated.

Uncertified and ultra reliable is far better than certified and Unreliable, I know which one I'd rather fly behind.

 

50,000 Rotax 912's have been produced in the last 25 years and been pretty darn reliable from day 1 compared to 5000 J engines in the last 20 odd years which have shown a not so good record, obviously a certain brand knows how to make them right and doesn't throw it back in the maintainers face from their own production inadequacies.

 

Alf

 

 

[David Isaac]

I often marvel at that little engine screaming its ass of at 5,800 RPM for hours and and hours with many still going way beyond the rated TBO.

 

A lot of money behind Bombardier though and you pay for what you get.

 

 

[alf jessup]

I often marvel at that little engine screaming its ass of at 5,800 RPM for hours and and hours with many still going way beyond the rated TBO.A lot of money behind Bombardier though and you pay for what you get.

David,

 

5800 max continuous for 3 mins, 5500 continuous all day every day until you need to do the scheduled servicing, then it goes again and again pretty much until TBO & beyond unless there is the odd failure.

 

Alf

 

 

[Dafydd Llewellyn]

Here we go again. Ta Ta

 

 

[bexrbetter]

I often marvel at that little engine screaming its ass of at 5,800 RPM for hours and and hours with many still going way beyond the rated TBO..

Because it's not "screaming", the piston speed is near identical to a Lycoming.

 

Here we go again. Ta Ta

door ass way out hit

 

 

[David Isaac]

Ha Ha yep, well I don't fly behind one, mine is max continuous at 21oo RPM. Cruise 1900 RPM. I guess that is why I marvel at the little ones.

 

 

[rick-p]

 

STILL PLAYED TO THE TUNE OF "THE LONG AND WINDING ROAD"