Damage caused by 12 point nut AD

[Guest Maj Millard]

I've always believed that the root cause is the fact that the case is soft machined alloy, with a steel rotating crankshaft inside, and the whole lot trying to be held together with undersized steel studs. All with differing rates of thermal expansion and contraction.. But what would I know, I 'm just a rabid Jab-basher !....I did however spend two years operating large precision CNC mills making similar precision parts from alloys and other metals. Most other engine manufacturers recognise the fact that engines should initially be run in test cells to distraction, and then improved accordingly for long-term reliability. Has the Jab engine manufacturer ever done this ??.............Maj...

 

 

[dazza 38]

I've always believed that the root cause is the fact that the case is soft machined alloy, with a steel rotating crankshaft inside, and the whole lot trying to be held together with undersized steel studs. All with differing rates of thermal expansion and contraction.. But what would I know, I 'm just a rabid Jab-basher !....I did however spend two years operating large precision CNC mills making similar precision parts from alloys and other metals. Most other engine manufacturers recognise the fact that engines should initially be run in test cells to distraction, and then improved accordingly for long-term reliability. Has the Jab engine manufacturer ever done this ??.............Maj...

Hi Ross, CAMIT p/l do have a state of the art computerised Dynamometer on which they test every engine. But I don't know if they have ever tested one to destruction.

 

 

[Guest Maj Millard]

Additionally in between the soft alloy case and the hard rotating steel crank , you've got relatively soft bearing material doing it's best to survive, with oil that's often not getting cooled correctly..............Maj...

 

 

[Guest Maj Millard]

Thanks Dazza, dynos are or normally used for testing horsepower or performance improvements. I've recently read books on the development of the Rolls Royce aircraft engines, including the Merlins and Griffins. Even in the midst of war when those engines were needed NOW, they still tested to destruction and made the appropriate improvements, which made those engine the classics they are. We are basically in a peacefull stage in this country right now aren't we ????...........Maj....

 

 

[Old Koreelah]

Hi Ross, CAMIT p/l do have a state of the art computerised Dynamometer on which they test every engine. But I don't know if they have ever tested one to destruction.

When Jodel builders first started fitting Peugeot diesel engines, one Frenchman came up with an expected life. He had tested a batch of engines to destruction. The first had a valve failure at 12,700 hours, so he conservatively came up with 10,000 hours. I presume he worked for PSA. I doubt Jabiru has the resources to do this. I get the feeling that when they set out to make engines they never imagined selling so many, so went the small-run path of using CNC. With hindsight they might have invested the extra funds in casting them, which may have delivered a better engine.

 

 

[Guest Maj Millard]

They do have the resources Old Korellah, and in fact they accepted several large government grants or low interest industry development loans, over the years. And they found the cash to promote their products internationally. Either way, they are producing aircraft power plants, that people bet their lives on. The excuse that we don't have the resources, or facilities, to properly test their engines before they sell them wholesale, to the general public, just doesn't cut the mustard for me......they found the dollars to develope the airframes didn't they, and to seek certification, for their products...........Maj.......................

 

 

[Old Koreelah]

?..Rolls Royce aircraft engines, including the Merlins and Griffins. Even in the midst of war when those engines were needed NOW, they still tested to destruction and made the appropriate improvements, which made those engine the classics they are. We are basically in a peacefull stage in this country right now aren't we ????...........Maj....

Good point, Maj, but how long were those Merlins meant to last? I have read that they needed a lot of TLC, just like Jabs. Wartime production was done under a different value system; very complex products designed for a very short service life, being built with cheap labour (especially the women).

 

The Taree community, like many others throughout the empire, raised the funds to buy one Spitfire (about £50,000- a bloody fortune then) little knowing that dozens of them would be shot down in a single day.

 

 

[Old Koreelah]

They do have the resources Old Korellah, and in fact they accepted several large government grants or low interest industry development loans, over the years..

That changes the complexion of the debate, Maj. I wasn't aware of Jabiru receiving public funds. If the money was targeted at improving safety/reliability then they should have done the testing, but it would not surprise me if the beaurocracy wanted the money spent on an export drive, assuming the product had been fully developed.

 

 

[motzartmerv]

The new engine in the 230 (3300) looks a cut above evrything I have seen from them so far. Im no engineer, but to me it looks and sounds like a real aeroplane engine now. Time will tell, but at least for now I will be testing something a little more substantial in key areas (thru bolts and nuts) for them.

 

Jab have a good product waiting to be completed in my view. Its right there, ready and waiting. They are let down constantly by one thing. Quality assurance. But the product itself is good. How else can we xplain 2 identical engines, maintained by the same people, run in the same school, at similar hour states, one engine lasting 900 hours, the other lasting 150?

 

 

[Guest Maj Millard]

Good point, Maj, but how long were those Merlins meant to last? I have read that they needed a lot of TLC, just like Jabs. Wartime production was done under a different value system; very complex products designed for a very short service life, being built with cheap labour (especially the women).The Taree community, like many others throughout the empire, raised the funds to buy one Spitfire (about £50,000- a bloody fortune then) little knowing that dozens of them would be shot down in a single day.

Well if they were designed for a short life, it's even more impressive then, that they did the destruction testing on them. The real fact is Rolls Royce engineers only knew one level of quality, the best....which is why there are still many Merlins and Griffins operating daily in the warbirds they were designed for, often pulling many more inches of manifold pressure than was ever intended. In fact if you read about the wartime production of those engines in many satellite facilities,you'll note that Rolls Royce were very fussy about not letting their quality and tolerances drop. The difference is they had standards and high quality in the first place....................Maj....

 

 

[Old Koreelah]

?..there are still many Merlins and Griffins operating daily in the warbirds they were designed for........Maj....

You are right, Maj about RR standards, but those few surviving warplanes have had squillions spent on them. I bet the maintenance cost is beyond most of us. We would all love to see Jabiru improve their quality control, but what would it do to their prices?

 

 

[geoffreywh]

I read Merlins had a service life around 1937 of 600 hours. The TBO varied enormously with the duties it performed. Better look at the Bristol Hercules sleeve valve radials with a TBO of 5000 hrs...or the Napier Lion broad arrow That had (I believe) the longest TBO of any aero engine..BUT I heard news yesterday that the new 3300 had MANY sensible improvements, Very encouraging indeed....

 

 

[Guest Maj Millard]

The Merlins in 1937 were still very early on their development stage. They were developed very rapidly in the next few years as war occurred, with almost a doubling of HP, as fuel and supercharger technology advanced.

 

You must remember also that they were developed to deliver maximum power, often at very high altitude, not longevity. Prime requirement of the military was power, not high TBO...600 hrs TBO on any aircraft in wartime was huge, but I'm sure if you check on the TBO of a Merlin in say 1946, you'll find it was much higher............Maj...

 

 

[frank marriott]

A Mustang doing joy flights here 4 or 5 years ago (based from down south somewhere) had a 500hr engine life - at least according to the operator?

 

 

[dazza 38]

The Packard built RR Merlin V-1650 has a TBO of 600 hours in civilian use (USA) bottom end .Top end would probably need some work at around the 300 hour mark. If the engines were fitted with Transport heads .The top end would easily out last the 600 TBO.

 

IRT to when they were used in anger during WW2- It is a crystal ball thing. Some engines would need a rebuild after 80 hours or so if flogged in battle.

 

I think the record for a Single piston engine fighter during WW2 was a P 47 Thunderbolt. One engine ( it had 2 different ones fitted during its career) lasted 870 odd hours.

 

 

[airangel]

Good point, Maj, but how long were those Merlins meant to last? I have read that they needed a lot of TLC, just like Jabs. Wartime production was done under a different value system; very complex products designed for a very short service life, being built with cheap labour (especially the women).The Taree community, like many others throughout the empire, raised the funds to buy one Spitfire (about £50,000- a bloody fortune then) little knowing that dozens of them would be shot down in a single day.

I believe the merlins had a tbo of 400hrs if they made it that far.

 

 

[facthunter]

Aircraft engines used in a real military situation have very short overhaul times. The output figures Boost and RPM limits are raised ( for obvious reasons). Civilian versions of the same engines were de rated significantly and had much higher overhaul lives in civilian transport use where cost and reliability are more important, and many go 2,500 hours TBO

 

The Merlin was not certified for civilian use in many countries due to the shared drive of the two magnetos, which even in wartime was a source of engine failure. Not that often, but enough for the feature to preclude it's use.The gear would shear and neither magneto would operate, and it would all go very quiet with all pressures and flows normal.

 

The motor also scuffed the cam followers sometimes on start up as they didn't have rollers as most of the other liquid cooled OHC V12's did. (American and German). The basic engine was very strong allowing more power to be extracted in later versions, and the connecting rods ( fork and blade) are a work of art. Side by side are a lot cheaper to produce and probably more practical, but Rolls Royce had their standards. A version of the engine is used in the Centurion Tank .Nev

 

 

[Old Koreelah]

I came across a couple of slightly used Allison engines in Darwin last week.

 

I was surprised to see OHC and 4-valve heads, plus roller cam followers:

 

 

 

[facthunter]

The Allison is relatively simple. The rollers prevent scuffing on start-up when the oil hasn't made it. The German stuff is better engineered. Their supercharging was more sophisticated. Nev

 

 

[Guest Maj Millard]

The Allisons were pretty high-tech for their time, and didn't they sound nice. Look what they were used in, the P-38 Lightning and the Bell Aerocobras and King Cobras. There is also an Allison motor in the RAAF Townsville air museum in better shape than yours. It was found on one of the mudflats south of Townsville and came from an Aerocobra. The original lock wire is sill in place on it.

 

The first time I saw and heard a P-38 Lightning take off at the Reno Air Races, I said to myself "that's not a fighter, that's a light bomber" because the twin Allisons sounded like a bomber.

 

My daughters' second name is Allison...had to get it in there somewhere!!!..............Maj...

 

 

[facthunter]

They are made by General Motors. The L-188 Electra has Allison turboprop engines in them. C-130 Hercules also. Famous name eh Maj? Nev

 

 

[Guest Maj Millard]

Didn't Rolls Royce buy Allison at some point ?....I'm pretty sure the engine in the new Robinson R66 is a Rolls Royce Allison......I'll have to go back and read those RR books again....it's all in there somewhere!...........Maj...coffee:

 

 

[Old Koreelah]

The Allison is relatively simple. The rollers prevent scuffing on start-up when the oil hasn't made it. The German stuff is better engineered. Their supercharging was more sophisticated. Nev

The Germans, Russians and others seemed to like upside-down engines, presumably so their valve gear could run in pools of oil. Daimler Benz learned a lot about supercharging during their pre-war car-racing campaign.

 

 

[Guest Maj Millard]

The upside down Benz in the Me 109 : in the Roll Royce book they tell of a visit to the factory in the mid 30s of a German delegation of engineers. RR was still playing with the Merlin design, and there was a block in the main engineers office but it was sitting upside down. The Germans saw this and shortly after return to Germany the upside down Benz appeared in the 109 and others.

 

As it turned out, it wasn't a bad idea as it gave better viz around the nose then some Merlin fighter installations !!....Maj....

 

 

[facthunter]

I can't think of any "later" in line or Vee motors that weren't upside down. Visibility over the nose and prop ground clearance would dictate that. Nev