CASA - Draft Proposal for Jabiru Aircraft

[jetboy]

Kenaviator asked (post 1485):

" How many flywheel bolt failures have there been since the upgrades were introduced? Are these failures happening to both solid lifter and hydraulic lifter engines?"

 

Again Ross, Are you able to provide an answer from the RAA files? I assume that as you raised these failures in post #1480 today you must have some facts that you could share?

Flywheel bolts. its unclear whether any of the Jabiru upgrades have helped to change the occurence rate of flywheel bolt problems. More likely the publishing of the extra inspections required and reinspections after any prop strike / stoppage incidents may have helped, as the rate of failures lately seems small.

This I know:

 

failures were becoming notable by 2006. By the end of 2006, The UK repair agents had changed bolt installation procedure to loctite and torque=30 ft-lbs. their problems first came to light on aircraft with a coarse pitch composite propeller. BMAA did vibration tests with various props and using mogas and avgas. the vibrations were different for each, "significantly it showed the vibration differed with the change of fuel"

 

In NZ there had been 3 failures - one reportedly with an over heavy (non standard) prop, and 2 to an installation that included a non-Jab prop extension fitting.

 

This had prompted Rex Kenny of CAA to visit CASA and Jabiru about getting a fix and resulted in an AD for NZ engines.http://www.caa.govt.nz/Airworthiness_Directives/Airworthiness_Directives_Engines.htm

 

Similarly RAANZ were looking into it for their members along with an engineering firm who had now reworked about 20 engines with flywheel bolts torqued to 40 ft-lb. The RAANZ report and supporting data is conveniently here. http://contrails.free.fr/engine_jab_bolts.php

 

To the present situation: Yes there have been bolts breaking on new engines with starfish, on engines with dowels, on engines maintained by LAME, on engines owned by the dealer, etc. Point is, most of these would be torqued to the Jabiru engine specs, either because they had to, or didnt know about or consider "UK" or "RAANZ" method. I'm not aware of any "nonstandard" maintained engines, fed & watered with correct fuel and prop loads, dowels or not, giving trouble.

 

For clarity: NZ avgas is only available in 100/130 grade (green) Is this what is being used in Australia?

 

What I hope to come from this new CASA awakening: the finite point engineering analysis done by Jabirus consultants on this joint and the reasons why the fix was justified. They produced this type of data within 2 weeks for the Raaus over the head cracks so they must have similar thoughts about flywheels, throughbolts etc.

 

Ralph

 

 

[jetjr]

There are a few trolls on here, they come on, make a few inflammatory statements without backing, their mates support their comments. Often they have no contact or current knowledge on the issues. Some arent even RAA members, Jabiru owners or maintainers. In some cases arent even current pilots.

 

Being voted to the board doesnt change who you are. In fact doesnt take that many votes to get there either.

 

Dont waste time responding

 

There has been maybe 40 of 70 pages discussing problems, plenty of useful comment on modes and causes. The idea that someone is hiding or ignoring issues is laughable. Theres noting new in the last few pages I assure you.

 

This thread is about the Proposed action by CASA and most agree it isnt the right way to go if real fixes are to be achieved. Its potentially going to promote patch up fixes.

 

Re through bolts, firstly not all engines needed to have them changed, I think solid lifters were not included in directive (few were included, as they extended serial number range backwards to ensure they were all captured). Engines made after this time had them fitted as standard. Jabiru claim there has not been a failure with new bolts fitted.

 

Merv has one example of an aircraft which didnt perform upgrade then it failed, I assume it was in training use, so yes they exist in LSA fleet. maybe even LAME maintained that one?

 

Jabiru have been surveying FTF to find out current status of compliance, guess through bolts would be the main one.

 

I think there are two issues within this too, LONGER through bolts and LARGER through bolts. Two upgrades. Quite possible the earlier longer ones wont achieve much.

 

The issue with retaining washers has been documented and theres an SB so shouldnt be an issue anymore, everyone is inspecting or more sensibly replacing the washers right?

 

Re flycut pistons, valves dont stick and stay stuck open, they release and continue working until next time. Some could do this for hundreds of hours with no sign other than odd EMS data for a few seconds or a little "miss" noise. By allowing valve to stick and then free itself it could easily prevent an engine failure. This isnt a good situation but beats a chewed up piston and stoppage.

 

Yes there needs to be efforts to fix the real cause but adapted pistons are a good measure in any case.

 

Flywheel bolt failures are in my mind the biggest problem, several reasonable efforts have been made to rectify the problem and its still happening.

 

A highly possible outcome is that CASA could demand all training aircraft are LAME maintained. At least some solid records could be accumulated on all types.

 

 

[dan3111]

I think a alot of this has come to ahead with casa as they have slowly been cracking down on certified RAA aircraft with paper work and compliance as they can be used for hire and reward, just much the same type of paper work a any boat used the hire way . General public riding in those TIF flights don,t know any history of jab,s just pay for a flight lesson etc . You would have to dumbest person on earth if you did a quick look at the raa records not to pick up on jabs engines have a few problems as CASA would have had a good look by now . I think if they were just all home built aircraft with no hire or reward they would care so much, but a big number are certified factory built aircraft so they do have a duty of care to see those aircraft meet certification engine as well . Much the same thing happen when alot of the rushed LSA aircraft got on the register certified then got pulled after the safty audit as didn,t comply . You can jump up and down as much as you like, but paper work records reflect the facts and trends on engine life so that all CASA can go on. Unless someone has magic records they don,t know about,what are they ment to do turn a blind eye and end up on 60 mins down the track .

 

 

[kasper]

much snippingA highly possible outcome is that CASA could demand all training aircraft are LAME maintained. At least some solid records could be accumulated on all types.

Begs two questions:

 

On what basis do you make a statement that it's 'highly possible' that CASA would remove L2s from training aircraft?

 

On what basis is the LAME suddently expected to have a better sucess rate at keeping a Jab engine going than an L2?

 

Q2 is only there to avoid the other implication in the L2 vs LAME that I have disregarded - that a LAME is inherantly better as a person that the L2 ... why else would us L2s not be reporting what we see when you expect LAMES to report it?

 

Focus on the issue - its the engine not the L2's that is at issue here.

 

 

[motzartmerv]

Lames are not currently aloud to perform work on RAA 24 reg aircraft. They MUST be L2's also.

 

 

[Guest Ornis]

If you fly a twin ... you have ... twice the chance of having a motor bring you to grief

Yes, and if you buy two Lotto tickets you have twice the chance of not winning?

 

 

[facthunter]

Can't see the connection there. Again quoted out of context. The context WAS .. IF ANY engine failure results in an aircraft that cannot continue to hold height, you DO have double the chance of an engine making a problem for you.

 

Your question which seems quite witty, at first glance,. shows you don't know how to apply probability. IF you buy two tickets you have double the chance of winning NOT losing. Nev

 

 

[Guest Ornis]

And you can hold height if the engine in a single fails?

 

I've just read the rest of your comment. It's not a question of probability though, is it. It's a matter of reasoning.

 

Yes, if you have 2,3,4 engines you have doubled, trebled and quadrupled your chances of having a problem with an engine. So?

 

Conversely, if you have no engine, like a glider, you have zero chance of an engine failure.

 

You're simply analysing the "problem" the wrong way.

 

 

[facthunter]

Was that ever suggested as being possible and is it a relevant question? I would regard it as self evident. Nev

 

 

[Downunder]

Re flycut pistons, valves dont stick and stay stuck open, they release and continue working until next time. Some could do this for hundreds of hours with no sign other than odd EMS data for a few seconds or a little "miss" noise. By allowing valve to stick and then free itself it could easily prevent an engine failure. This isnt a good situation but beats a chewed up piston and stoppage.

Yes there needs to be efforts to fix the real cause but adapted pistons are a good measure in any case.

 

QUOTE]

Well....I'm flabbergasted. How can anyone in their right mind think any of this is OK?

 

Are we talking about the Jabiru AIRCRAFT engine or a Jabiru lawn mower engine....?

 

If any of this is true, what little respect I had for Jabiru just flew out the window

 

 

[facthunter]

Ornis, this matter has been considered a lot over the years, with design concepts and I would suggest you might make reference to knowledgeable sources . We are off topic here. It's about Jabiru engines. Nev

 

 

[Guest Ornis]

There are two issues here. One is the amount of maintenance required to keep the engine going, the other is the risk of a catastrophic failure in flight of a well maintained engine.

 

I'm prepared to take some risk but I'm not going to be fobbed off with numbers on a bit of paper when I know from direct observation the prevalence and seriousness of several problems.

 

I understand one problem very well: flywheel bolts. The early engines had an aluminium vacuum drive and an aluminium flywheel; the bolts (SHCS) were torqued to 24 ft-lb with Loctite 620. The vacuum drive has gone and the flywheel has a steel centre. Yet the bolts are still only 24 ft-lb. They should be at least 36 ft-lb, or more, especially as they are now bigger bolts, using grease - so they can be retorqued. Forget the dowels, the joint still need friction which means proper clamping. Secondly, flat gear wheels.

 

 

[gandalph]

And you can hold height if the engine in a single fails?

Yep!

 

 

Hope the link works!

 

 

[Guest Ornis]

Well....I'm flabbergasted. How can anyone in their right mind think any of this is OK?

It's called enginerring...

 

 

[facthunter]

To ERR is ERR... Human Especially with those INFERNAL Combustion engines of the reciprocating kind Nev

 

 

[ianboag]

There's a basic point here that gets a bit lost in the noise.

 

The flywheel setup is a clamp joint - also known as a bolted joint - a sandwich where the bits are tensioned together and friction keeps them that way. Not dowels, not Loctite, not sellotape - FRICTION. The bits in the sandwich should have no relative movement. If they move, then as they move the clamping bolts get bent backwards and forwards a tiny bit lots of times. Eventually the bolt(s) snap from BENDING fatigue at the junction between the moving parts. Rolled threads, cut threads, waisted/shanked bolts are not the issue - the fastener fails from bending (back and forth) fatigue because the bits of the sandwich move relative to each other.

 

That's how clamp joints fail. Google "bolted joint" or "clamp joint" if this is hard to accept. So if a bolted joint fails, it's because there was not enough clamp. It's that simple. Detonation, harmonics, phases of the moon, phooey. Not enough clamp to handle whatever happens.

 

Same analysis holds for the through bolts - another clamp joint. If you can see oil round the base of the cylinders, the joint is moving .......

 

Shoot me down someone ...

 

 

[facthunter]

I think keeping oil away from the joint would be a good thing. Nev

 

 

[ianboag]

Don't the flywheel have dowels these days? The Camit version has an entirely different mating surface.

Dowels schmowels trowels ... friction is what holds a joint together. Think of it as a zillion tiny dowels. Dowels can be handy for location but not much else.

 

 

[Guest Ornis]

Don't the flywheel have dowels these days? The Camit version has an entirely different mating surface.

CAMit CAE: Crankshaft, gearwheel, steel-centred aluminium flywheel, 3 of 1/4" dowels, 6 of 3/8" SHCS. Torqued to 24 ft-lb with Loctite. My engine is 50 N-m (37 ft-lb) with grease, so the capscrews can be retorqued.

 

Pretty sure Jabiru is the same now, the aluminium vacuum drive and flywheel aluminium centre has gone.

 

If the joint is not clamped properly the dowels and bolts will break.

 

 

[ianboag]

I think keeping oil away from the joint would be a good thing. Nev

You get oil leaking from between the crankcase halves when they start to fret. Because of insufficient clamp. And of course once the fretting starts - some metal disappears - which reduces the clamp - which makes things move some more ..... yadda yadda yadda Pop!

More (initial) clamp (torque) required. What's hard about this concept?

 

 

[ianboag]

Now I remember, Camit have a starfish collar securing the flywheel.Whilst I'm at it, thicker thru bolts than Jab standard, piston squirters, angled rocker cams and much more. It's the whole package and includes steak knives. I believe additional cooling mods are also included in the package.

Back in the bad old days of breaking through bolts, I did some sums about a starfish configuration and concluded it was no better or worse. The sensible solution seemed to me to be - biff the Loctite (a unique Jab thing) and reef the bolts up some more. I had a local mate on the field who wondered about pulling the thread out of the crank, but some more sums indicated this was pretty unlikely ...

 

The (former) NZ dealer who flew his (brand new) (starfished) 230 across the Tasman subsequently had the bolts break .... aircraft became a kitset, but noone was hurt. So I guess that makes it OK ... and the J120 he had also flown across the Tasman didn't throw a pot until a month later ... it was in the circuit so noone died.

 

Anecdotal. That's why we don't have an NZ dealer any more. Noone wants it.

 

 

[ianboag]

I think keeping oil away from the joint would be a good thing. Nev

The oil is 'pumped' out because the pots are moving.....

 

 

[Teckair]

Can't see the connection there. Again quoted out of context. The context WAS .. IF ANY engine failure results in an aircraft that cannot continue to hold height, you DO have double the chance of an engine making a problem for you.Your question which seems quite witty, at first glance,. shows you don't know how to apply probability. IF you buy two tickets you have double the chance of winning NOT losing. Nev

I thought this was regarded as off topic. Maybe we need a new thread?

 

 

[facthunter]

Tecky I've mentioned it being off thread at least 3 times...

 

Ian, re the oil. I'm talking about the flywheel joint. Clamp it is. How would a very thick high tensile washer under the bolt heads be? Locktite would exclude the oil getting between the two surfaces . Wouldn't greasing the bolt threads get into the joint? Nev

 

 

[ianboag]

Tecky I've mentioned it being off thread at least 3 times...Ian, re the oil. I'm talking about the flywheel joint. Clamp it is. How would a very thick high tensile washer under the bolt heads be? Locktite would exclude the oil getting between the two surfaces . Wouldn't greasing the bolt threads get into the joint? Nev

When tensioning up a bolted joint, normal practice is to lubricate the fastener. This gives a reproducible relationship between the torque and the bolt tension. I am told by people who should know that dry-torquing is a total nono. You can get galling of the mating surfaces and the torque-tension relation is all over the shop.

 

ARP (who ought to know) supply their own special lubricant - Continental say threads should be lubricated with engine oil etc etc. When a thread is lubricated and not welded, you can check for loss of tension .... and you know that x torque is y tension. Torquing it up with a non-lubricating substance that sets like concrete in a few minutes is - I am told - unusual.

 

Not really hard. People have been doing it that way forever. Go figure.