On J230, the heat, and suitability of the Rotax 912ULS

[Bruce Tuncks]

While I understand Turb's worry about shock cooling, I reckon that this is more likely to cause cracking with a more brittle alloy than the Jabiru heads were made of.

But why increase the water? I thought the first system gave you the bit of extra cooling you needed. Minimal flow-rate gives less weight of water to carry.

Anyway, we sure appreciate the work you are doing on this project.

[Old Koreelah]

3 hours ago, Bruce Tuncks said:

…why increase the water? I thought the first system gave you the bit of extra cooling you needed…

Good point Bruce. The first version delivered a water/fuel ratio of about 1:5 and didn’t cool the heads as much as I’d like. Anticipating very hot weather, I set the second one to a ratio of about 1:2 and it does an excellent job, but I hadn’t considered the shock cooling risk. 
 

As outlined in my previous post, I plan to relocate the nozzle to downstream of the carby and come up with some way of gradually “ramping up” the water rate with revs, in order to reduce shock cooling.

 

I’d also like to find a better position for the water tank, so it doesn’t reduce legroom. Making these modifications was pretty easy when my plane lived on it’s carrier in my shed but now it means a trip to the airport and lots of standing on my head to reach under the panel.

[onetrack]

Old K, it's a shame there's not a readily available source of the information gathered up by Cyril Kleinig, who was one of Australia's best engineering innovators, as well as a very good race car driver.

Cyrils "Mist-Master" water/alcohol injection unit was advertised in the "Modern Motor" magazine for decades, from the late 1940's.

It was simple and it worked - although it did have its risks if it malfunctioned, as it would pool water inside the engine. I wonder if you could even find an old Mist-Master unit, and utilise it?

I don't know how heavy they are. Of course, they did also work on gravity feed alone, so more potential problems there, as compared to an electrically-driven water injection unit.

Today, Snow and Aquamist provide high-tech WI systems for current-model vehicles - but they're all designed to work with engines that use an ECU (or PCM, depending on which company terminology you're using) - which is all automotives engines today.

 

https://primotipo.com/tag/frank-kleinig/

[Old Koreelah]

2 minutes ago, onetrack said:

…Cyrils "Mist-Master" water/alcohol injection unit was advertised in the "Modern Motor" magazine for decades, from the late 1940's.

It was simple and it worked - although it did have its risks if it malfunctioned, as it would pool water inside the engine.

That’s why I mounted my water tank in the lowest place available, after discovering it would syphon, even thru the tiny spray orifice. 
 

One of club members is from your part of the continent and he tells me the combustion chambers of his Ford were shiny after a few hundred thousand km with a manifold-mounted “steam injection” system.

[facthunter]

You are not really shock cooling something when you prevent the temp rising to what it would have if there was no extra cooling... Nev

[Jase T]

An Allison 250 would solve most problems here..

[Bruce Tuncks]

Here's the deal on fatigue and frp...  THE STUFF DOES NOT FATIGUE.

There is a type of overload failure where the resin can turn to powder and gradually a greenstick failure will ensue.

Fatigue is a metal failure where cracks grow between metal grains.

Look up the story about Blanik gliders, wooden gliders, the Janus project etc .

Fiberglass "fatigue" is an invention of bureaucrats which has no basis in reality or evidence.

 

[turboplanner]

7 hours ago, Bruce Tuncks said:

Here's the deal on fatigue and frp...  THE STUFF DOES NOT FATIGUE.

There is a type of overload failure where the resin can turn to powder and gradually a greenstick failure will ensue.

Fatigue is a metal failure where cracks grow between metal grains.

Look up the story about Blanik gliders, wooden gliders, the Janus project etc .

Fiberglass "fatigue" is an invention of bureaucrats which has no basis in reality or evidence.

 

So the thousands of boat transom failures over the years was invented by bureaucrats?

[Bruce Tuncks]

I don't know anything about boats turbs. Of course you can under-design anything . Bet I too could under-design a boat part.

The earliest fatigue tests they did on FRP consisted of a rotating shaft of FRP with a cantilever end carrying a weight.

So the inboard end of the shaft had a cycle of tension and compression for each rotation, and the weight and geometry gave any stress you wanted. And you can compare different metals with FRP using this.

Set the thing to be driven, and you get millions of cycles of stress in time. 3,000 rpm gives over 4 million cycles in a day.

This was done over 60 years ago, and the main finding was what I said. FRP does not fatigue, well not in the way metals do. The individual strands of glass are crack-stoppers and they don't form a contiguous medium in which a crack can grow. 

Sure enough though, if the stuff is over-stressed, the resin powders over time and the part fails as the glass strands are left unsupported. This is called a greenstick fracture and I guess this is what happened to those boat transoms.

It just may be that the materials between boats and planes differs too...  planes are,or should be, made of high glass to resin layups with glass cloth and ( usually ) epoxy resins.

These days, the glass has largely been replaced by carbon, which gives good and bad changes to what i've been saying.

But not in Jabirus, thank goodness.

[turboplanner]

1 minute ago, Bruce Tuncks said:

The earliest fatigue tests they did on FRP 

FRP stands for Fibreglass Reinforced Plastic

The dominant material is Plastic, fibreglass just being the reinforcement

The product is a composite so you have to test the composite for fatigue.

 

I understand your description of the definition of fatigue in a metal, which is not a composite, so the issue may be the misapplication of the word "fatigue" which you are saying relates to a contiguous medium, but the application we are discussing uses a composite, so I'm happy to use the term Deterioration test instead of fatigue.

 

60 years ago when your test occurred, as I mentioned earlier we were all working in a new frontier. I was doing design drafting where I would draw up a component showing laminates, scarfing laminates, roving and steel reinforcements and components bonded together using epoxy adhesive as well as bolting and clamping. We were watching our products in the field like hawks. On one occasion there was a news report of a 20'0" ISO Container accident where, prior to the invention of twistlocks a refrigerated container had slid off a semi trailer and rolled on to a Holden ute. At the real the ute tray and rear window area looked normal but when the container had been craned off the windscreen area, engine and guards had been squashed down to tyre height. There was no collaps of the container walls, just deep scratches. So our assessments then were as crude as that.

 

Today there should be so much comprehensive history and data on composites which now use hundreds of different base materials, that you should even be able to get deterioration test and impact test results on the plastics by themselves to help select the ideal one.

 

 

 

 

1 minute ago, Bruce Tuncks said:

FRP does not fatigue, well not in the way metals do. The individual strands of glass are crack-stoppers and they don't form a contiguous medium in which a crack can grow. 

Correct; it fatigues "not in the way metals do"

The plastic cracks, disintegrates and buckles and the component fails catastrophically.

After the failure you could remove the failed resin and your would have a chopped strand mat in your hands which flipped or flopped or waved in the breeze, and if non-critical could be impregnated with a new batch of resin and be used again.

 

The boat transoms are not under designed; they would all pass a structural test, but the composite which produces the finished part can vary widely as I tried to explain in my previous post.

 

If we remove the word "fatigue" to remove any misunderstanding

 

1 minute ago, Bruce Tuncks said:

Sure enough though, if the stuff is over-stressed, the resin powders over time and the part fails as the glass strands are left unsupported. This is called a greenstick fracture and I guess this is what happened to those boat transoms.

It just may be that the materials between boats and planes differs too...  planes are,or should be, made of high glass to resin layups with glass cloth and ( usually ) epoxy resins.

These days, the glass has largely been replaced by carbon, which gives good and bad changes to what i've been saying.

But not in Jabirus, thank goodness.

 

[onetrack]

There's plenty of information available as regards "fatigue" testing of FRP - and all composities, in fact. They've been in use for decades now, so performance, damage and repair criteria is established. 

Turbo is right on all counts, FRP does not "fatigue" the same as metals, so the comparison is apples to oranges.

Metal fatigue shows up initially as cracks, then the cracks propagate to component failure, if left unattended.

FRP does not necessarily show initial surface cracking under fatigue, it can sometimes fracture with little warning, because the fracture point is actually debonding within the component.

FRP performance and life under cycling loads can be quite variable, because the end product is dependent on the level of professionalism in the construction, the types of resins and fibres used, and the levels and periods of exposure to UV light and heat/cold cycles.

Vacuum bagging techniques are now used extensively, and "Vacuum bagging failures" is a good area to research.

FRP performance is also related to the types of strengthening materials used. Boats originally used light wood beams (usually Balsa) covered with FRP for strength - but water ingress into the timber is a major factor in the life of a boat component.

Then foam was used for cores, and then advances led to a range of exotic core materials. Nowadays, if you want the ultimate core, you use Nomex honeycomb core.

Not surprisingly, boat builders were quick to pick up on advances in aircraft composite materials, and boat-building has advanced considerably in recent years, thanks to that.

 

https://onlinelibrary.wiley.com/doi/10.1002/pc.24177

 

This Chinese writer has written up a good, and a very comprehensive outline, of the huge amount of FRP and composite construction types and materials in boats.

 

https://www.linkedin.com/pulse/what-materials-frp-boats-杰-任?trk=read_related_article-card_title

[turboplanner]

I should have mentioned that Composites in non-structural applications are a whole lot less complicated.

For example you can easily laminate a panel with the holes neatly recessed my making a mould starting with laminate tabletop ply, drilling for a bolt on mandrell at each hole centre, and turning plaster with an aluminium profile until it sets for each recess.

 

The other non structural application is composite attached over a steel space frame.

[Bruce Tuncks]

I've never heard of an aircraft failure due to debonding, although I have heard ( but not seen ) a Jabiru undercarriage leg which went "soft" due to disbonding within the leg. This leg did not fail, but was nasty to handle on the ground.

Anyway, a question for you boat experts... Are those black sails on some leading ocean racers made of carbon? Since when did carbon fiber become used for sails? are they much lighter? what about their porosity?

Could ( should ) I consider carbon u/c legs for a Jabiru?

[Old Koreelah]

The three common reinforcing fibres have quite different properties.

Glass fibres are easy to wet out, making it ideal for hand laminating.

Glass will stretch a little, giving useful flexiblity.

Kevlar is a bugger to cut and wet out, has lots of give when stressed, but will return to original shape, making it ideal for crash-prone components.

The strongest is Carbon, but it’s plurry hard to properly saturate (unless you use vacuum bagging). Carbon is very stiff, but when it breaks, you are left with dangerous micrfibres. 
 

Jabiru are wise to stick with glass fibre; it suits the job and it easy to repair.

[onetrack]

Bruce - Yes, the ocean racer sails are carbon fibre. It's been used in sails since at least 1992, when it was introduced on an Americas Cup entrant. Yes, they are very light and very strong. Their porosity is low when new, but it deteriorates over time, as the materials become affected by stretch, salt, and UV light exposure.

 

https://www.northsails.com/sailing/en/2020/02/why-are-racing-sails-black

 

https://en.wikipedia.org/wiki/Sailcloth

 

Carbon U/C leg design is a minefield, you could spend a lot of time and money trying to get the correct level of springiness.

[Jim188]

I have enjoyed reading this posts about a Jabiru transplant, I know where such a Jab was out past Warwick for sale some time back. What really interested me about this, no one was actually really that interested in buying it from what I was told.   

 

I have read a lot of this thread and it seems many people are having too much fun tinkering with their Gen2 and Gen 3's in looking for the answers to their issues and I am wondering what they would do if they had no issues to fix. 

 

I wonder why no one has mention what is the easiest answer of all. 

 

RF, you need to take a look at this equation, (Gen2 + Gen3)-1 = Gen 4, sell your Gen 2 or 3 and buy a Gen 4. I own one and it has no temp issues at anytime and I have 6 CHT, 6 EGT and Oil Temp. 

 

I realize many people on this forum love the challenge of tinkering with their Gen 2 or 3's, and these engine for them are a match made in heaven for those amongst us.

 

But my advice for those of you who are tied of scrolling through such place looking for answers to solve your frustration of temp issues, get your Jab into a Gen 4 and instead of you watching your temps, you can start watching the scenery going by. 

 

Cheers to All

Jim188

 

Edited January 11, 2022 by Jim188

[Old Koreelah]

...and miss out in all the fun?

[RFguy]

Hi Jim

I'd like to see a few more years of Gen4 and wringing the problems out before I would buy one. There are still issues .

I have a late Gen3, now with LCH. Am pretty happy that I understand all of the issues of the Gen3 . I have a Rotax coming along, slowly getting all the ancilliaries together.... That might end up in this Jab, or another plane.  - glen

Edited January 11, 2022 by RFguy

[Jim188]

Well Glen, 

 

I am not sure how long you would need to wait before installing a Gen 4, when your are talking about spending money on a  912 to put in your Jab.  

 

My Gen 4 was installed in late 2017 and has low average hours, being 4 years of age . 

 

Here are some Stats,

 

Less an 200 hours. 

Uses no oil between 25 hour oil changes.

Before HD piston change, at 2.5 years old, leak downs where 72-75 over 80.  

Since the HD piston recall, last 2 annuals, one recently, the leak downs have been 77-80 over 80.  

 

Temperatures,  OAT 19-34. 

DA at average 3000-4500FT

With a 75knts climb to circuit height and then cruise climb, CHT spread across the 6, 106c to 121c.

If you pushed very very hard to see the temp envelope by an extended 70 knot climb, I found it is very hard to get it up near my orange range.  

My EGT's spread across the 6, are in the range of  619c to 677c. 

My oil temp is always stable, but gets a bit cold during the winter months. 

 

I had a HD pistons recall, they contacted me, great service from all the staff.  Even offered a car to see the sights of Bundaberg at no costs for the one and half days I was there.  

 

I know someone will want to know about my EFIS instrumentation. All my EGT and the CHT read the same temp before the engine is started and the OAT sensor reads within one degree of them before pulling the plane out of the hangar.  

 

As to the accuracy of my sensors, I bench tested the CHT and EGT probe against a Fluke quality multimeter and thermocouple/ sensor. I did this with the CHT's and EGT's sensors still attached to EFIS and using a heat sink with brackets made to hold either a EGT or CHT probe.  Then using a variable heat source to vary the heat temperature, I check each sensors and EFIS reading across the whole temp range and against the Fluke meter reading. 

 

I had to replaced all EGT's and one CHT sensor. Yep, all the sensor worked, but their readings were out by as much as +- 15%.     

 

What are these Gen 4 issues you talk about Glen? 

 

I have no compression issues, caused by the rusting of the steel barrels from irregular flight hours and I would be a prime candidate for that. My CHT could be seen as being to cold and EGT are not even worth watching. I had the HD pistons recall what else can I say.

 

Happy Days so far and an easy 100 hourly inspection with a Gen 4.   

 

Cheers

Jim188 

Edited January 12, 2022 by Jim188

[RFguy]

Hi Jim

You have had a good experience.  That is great

 

Why  I am not going to buy : I would have liked to have  seen the failures that occur in the Gen4s  be more public, instead of the failures (and I know of alot of them) being carefully (IMO) hidden from view.  From my POV, there just isnt enough transparency on Jabiru's part with shortcomings. If there was transparency, then I would be much more comfortable  regardless of ther problems, because I would be more comfortable that various issues are not being swept under the carpet and hidden. .......and then would certainly buy a Gen4.  Bad example :  The O rings that are fitted between the head and the inlet manifold are only Nitrile, they are NO WHERE NEAR rated for the temperatures they encounter against the head-  and two aircraft I know have developed hardened O rings and lost sealing there (high EGTs) . When I brought this up with Jabiru, and I suggested they used Viton material , they were dismissive. Well if that's there attidude, to knowly use the incorrect product for the job ,  I wont buy their engine  product regardless of its good or bad reputation.

 

That's why I've stayed with the Gen3- much is known. The engine community knows pretty much as much as can be known on any shortcomings and their mitigation strategies.

 

I've been scratching together the 912 slowly as I find things at the right price - got a mid hour engine, now got engine mount, exhaust system, inlet box etc etc

 

Again, Jabiru  airframe is marvellous, support is great, and they are very forthcoming on issues. Like a different company.....

Edited January 12, 2022 by RFguy

[Jim188]

Hi RFguy, 

 

I am please you have found yourself an aircraft and it is a Jabiru 230. 

 

So the Gen 4 has been flying for 5 years now and it's continuing to prove itself, and as it does the value of your airframe is also slowly heading up.  

 

As a Jabiru owner, if you are not flying regulars hours each and every month with your Gen 2 or 3's engine, you are most likely going to have steel barrel/corrosion/compression issues. It's not a big deal, but can cause owners to have higher workshop hours in maintaining their compressions with in specs. Most flying school don't have issues with this or for those who fly regular hours every other week, as their barrel don't have time for surface rusting causing compression issues.  

 

For me, my Gen 4 is now 5 years old years and just been through GA annual. The Gen 4's have Nikasil coated barrels which don't rust. So with low irregular flight hours between annuals as my aircraft has done to date, this past issue of steel barrel/corrosion/compression is a thing of the past and proving to be a non issue with compressions being in the 77-80/80 leak down range some five years later. 

 

RFguy, are you right about the Plenum O-rings and their operating temperature?

 

My CHT are just getting to 125c, so I am wondering if the plenum in a Gen 4 is not getting anywhere near that temperature you talked about. As the plenum has vast amounts of air flowing around and through its, so being cooled. This is just a though I had why Jabiru may not have be so willing to listen to your theory about the need to up-grade plenum O-rings.   

 

Cheers

Jim188

Edited January 20, 2022 by Jim188

[RFguy]

Hi Jim

Not the inlet plenums.

 

THE O RINGS BETWEEN THE HEAD AND THE INLET MANIFOLD TUBES. 

 

YES, THERE ARE O RINGS THERE. iN THE PAST, THERE WAS A GASKET.

 

These O rings are in contact with the head.

 

cheers

 

[Jim188]

Hi RFguy,

 

Oh dear, sorry RFguy, I had read another post recently on FB about the intake O-rings in the plenum and incorrectly mixed the two replies up as I did not reply immediately at the time of reading each posts. I can see very clearly which area of the engine you are talking about, sorry.

 

Cheers

Jim188 

 

 

 

 

[RFguy]

Hi Jim.

yeah those are not so bad, a leak there is not as bad  (for mixture leaning == hot EGTs) as a leak at the head. That is a cool region, no hotter than the oil.