Another Jab bites the dust.

[Louis Moore]

I should probably clarify what I mean- Generally it's not uncommon these days to see car engines go 300 000 k's without any work other than oil , filter & plugs (cam belts if fitted), which would roughly equate to 3000 hrs, how many piston aero engines see that without work.

Matter of perspective on that one! It is such a common argument, the automotive to aerospace comparison of mechanical parts and to be honest your comparing apple to oranges. Easiest thing to do is go and look at the Auto engine conversion being put into aircraft these days, they fair no better (in fact they usually do a little worse) than the designed for the purpose aero engines. That in itself should be a clear indication of the fact that the operating enviroment that exsist in front of your aircraft firewall is vastly different to the one in your car bonnet!

 

I think it also worth while to note though that I know MANY engines flying today that are well over a 1000 hours on condition and still running very strong. I also know engines that have been overhauled a couple of times that are running the same cylinders, pistons, crank etc... from new and not having any real issues. It's just the fact we have a mandatory overhaul period for aircraft that makes it appear aero engine will not last long, which is not true!

 

As for the jab engine banter going on, I know very little about it so not really going to jump in on that one Agree something needs to be address but thats about it! I will say this though, I read a book about pipers early days and in the original taylor's and eventually the early cubs they were flying they expected to get a WHOPPING 3 hours of the lycoming engines before they would fail. Even reading the biographies of the early aviation pioneers it would seem engine failures were par for the course of your daily flight! The jab engine was built in 1994, and from my understanding it is mostly the later model engine with issues? Teething problems are common enough with a new engine, it took continental and lycoming many years to sort their GA engines out. I am sure Jab will get there!!

 

 

[deadstick]

OK then deadstick, how about Briggs and Stratton stationary engines on elevators where life cycle exceeds 1000 hours?

Hi TP, not sure what your saying mate!

 

 

[Bubbleboy]

Hi TP, not sure what your saying mate!

I think he means we should fit B & S to our planes! Maybe the 24Hp twin I have on my mower might get my Pietenpol off the ground!

 

 

[old man emu]

For those that are interested, heres what the cylinder looks like when this occurs.[ATTACH=full]17404[/ATTACH]

Look at the silastic around the cylinder base. How the hell can you torque a cylinder head bolt if you have squishy stuff in between the mating surfaces?

This is what I have said before, and what Motz also said - Jabiru won't listen to those with experience in engine asembly. If they did, they would drop the use of silastic; torqu down onto metal-to-metal, and the problem would go away.

 

As for detonation - the jabiru con rods aren't strong enough to withstand bad detonation. They would bend.

 

What's an easy way to see if detonation has occurred? The top of the piston will not have the usual combustion deposits on it because the shock of the detonation will blow the scale off the top of the piston

 

My Boss is now going to read this thread and may post something over my signature.

 

Old Man Emu

 

 

[Old Koreelah]

ll cowl flaps?

problem is you have to get out what you get in ,

his problem was the air was dead heading,and could not get out quick enough and was not passing thu the motor as designed ,

 

having explained the theory he had larger cowl flaps made and the temp dropped down to a nice 160 to 170,

You are right on, Graham. The heads of my 2200 run very cool and after 65hrs are still shiny, not brown or black. The cooling air comes thru tiny intakes and exits via large outlets which, in my case, are mounted over the wing leading edge where the lowest pressure is, rather than underneath in the high pressure zone. Air gets sucked thru, even when ground running.

 

 

[damkia]

An interesting comparison of failure rates is that of the nitro funny cars. Apart from "idling" (well, more "failure to stall"), they have a life of perhaps a half a dozen runs before catastrophic failure or strip down and rebuild.

 

Consider this: they do a quarter mile in (say) 6 seconds = 1/10 minute, at 8000 rpm WOT = 800 revolutions per WOT run. Multiply this by the half doz runs and you have an engine that lasts less than 5000 revolutions at full power, or 1.5 mins equivalent for a Jab, and 1 minute for a Rotax.

 

 

[turboplanner]

Deadstick, an argument was being made about aero engines pulling at constant full power vs car engines lasting longer because of intermittant loading.

 

I was giving the example of a stationary engine operating all it's life at full power and still getting a reliable life cycle.

 

Tomo is saying yes, but it's a heavier construction.

 

 

[jetjr]

Motz - fit the EGT probes, it seriously could have saved this problem and resultant outlanding

 

Re Deadsticks comments, just a few of my own to further confuse things

 

The black ooze from cylinder bases is very common, I have seen it be really bad and would warrant removal and reseal but sometimes stops and sets as a hard crud but doesnt get any worse. The problem seems to be that the seal here is on a very fine structure being wall of cylinder and they leak. Thermal expansion doesnt help obviously through bolts loose (or stripped) are a major problem too. The new bolt COULD help this by being less often over tightened. Keep in mind this can be close or even under spec torque on the old bolts and nuts according to Andy's work.

 

Until fairly recently these bolts were sometimes reused in rebuilds as there wasnt a known problem.

 

Re spark plug colour, in the Jabs I dont think this is a very good method to monitor things, does work well in other engines where mixture and flows are better sorted out.

 

On my EGT I see things move from very hot, through to too cool, just by changing power settings and the hot cylinder changes locations. ie No2 on WOT reaches 730, No 5 on descent reaches 750 but cools below 2400rpm. At altitude EGT cease being an issue. Its all to do with air flow.

 

I slightly back of the throttle just after rotation - no difference in rpm even - and EGT in No2 drops to safe levels. Carb heat also fixes issue and the whole engine EGT spread tightens up. Wouldnt even know there was an issue without EGT monitor. CHT dont vary.

 

The idea presented about hot starts and training use is quite possible.

 

A few inclusions of intake vanes, carb jetting or even tilting which can make the spread of EGT in the OK range. Jabiru USA have a nice article on Bing carb jetting and how they do it.

 

Multipoint EFI is the ideal but Jab cant present this as there are no certified ECU's and adds to complexity. 19 reg or experimentals can buy this today and there are reports of great results......... but $$$$$.

 

A whole another issue here is that this problem developed in hydraulic lifter engines. Rot#c have a video on valve bind and oil pressure issues which could result in mixture and breathing problems. This can further mess with mixtures at various rpm and altitudes. I dont know enough to work out how this might create cracked cylinder. What about a valve stuck shut?

 

Just because a Jab engine had a problem why does this become a competition with other engines, only the Rotax 912 is a competitor for the 2200 and its a very good one but not available at price point or in the aircraft chosen for this tough training job. Discussion on Lyc or Conti are largely irrelevant as they have 50+ years more development, way more development money also many more sold and besides wont fit in the RAA aircraft anyway let alone exorbitant cost. New engines might be great but just because 912 is a good engine doesnt mean 914 or 912is is infallible. Similar for new Light sport Lyc or UL.

 

 

[turboplanner]

An interesting comparison of failure rates is that of the nitro funny cars. Apart from "idling" (well, more "failure to stall"), they have a life of perhaps a half a dozen runs before catastrophic failure or strip down and rebuild.Consider this: they do a quarter mile in (say) 6 seconds = 1/10 minute, at 8000 rpm WOT = 800 revolutions per WOT run. Multiply this by the half doz runs and you have an engine that lasts less than 5000 revolutions at full power, or 1.5 mins equivalent for a Jab, and 1 minute for a Rotax.

That's really getting into a different area relating to extracting more and more power with a resulting shorter and shorter life.

 

I did a comparison many years ago which went something like this

 

Production engine 350 cu in, 250 hp - life cycle 800,000 km

 

Nascar/V8 Supercar 500 mile racing, 425 cu in, 600 hp - life cycle 800 km

 

Sprintcar, 40 lap racing, 380 cu in, 800 hp - life cycle 200 km

 

Top fueller drag racer 500+ km/hr, 500 cu in, 8,000 hp - life cycle 15 mins

 

So while you might argue that 80 hp in a Jabiru might not be enough engine, in that case other failures would be occurring.

 

 

[planesmaker]

I could be wrong but yes jetjr is right in saying it is a relatively recent problem (thru bolts) early Jab engines did not have this problem, Jabiru need to go back and see what they changed (gosh that would take forever) that now causes the thru bolts to break. Eg have they changed the bolt manufacturer, the timing, the mixture? or something else that is causing this problem. I believe they are claiming a few more horsepower over the older 2200 engines is this adding to the problem? just my thoughts Regards Tom

 

 

[fly_tornado]

The bolts could just be aging and being weakened by heat cycles.

 

 

[RKW]

Hello Tom, The older motors were rated at 85hp, the later ones, only 80hp. From my observations most of the thru-bolt problems occured after they went to hydraulic lifters, though there are reports of failures on the solid lifter models as well. We will now have to wait to see if the 7/16 threaded thru-bolt alleviates the problem. This could take a while since they were released late last year. Regards, Bob

 

 

[alf jessup]

I should probably clarify what I mean- Generally it's not uncommon these days to see car engines go 300 000 k's without any work other than oil , filter & plugs (cam belts if fitted), which would roughly equate to 3000 hrs, how many piston aero engines see that without work.

M61,

 

I would roughly say for a 300,000 km auto engine it would have done about 5000 minimum.

 

Your basing the assumption on 100kph average, you got idling, stopping at lights different speed zones ect.

 

Not trying to be picky mate just clarifying it.

 

Alf

 

 

[Louis Moore]

Hello Tom, The older motors were rated at 85hp, the later ones, only 80hp. From my observations most of the thru-bolt problems occured after they went to hydraulic lifters, though there are reports of failures on the solid lifter models as well. We will now have to wait to see if the 7/16 threaded thru-bolt alleviates the problem. This could take a while since they were released late last year. Regards, Bob

I was told the same thing RKW at a Jabiru information evening for L2's a number of years ago. The presenter said that the majority of issues with the engines have come about due to the hydraulic lifters that Jab have installed. They went to hydraulic lifters due to the industry complaining about having to re-adjust tappets every 25 hours. If memory serves (I do not work on Jabs all that often and this old, second hand info that might have been twisted in my mind over time!) he said that the lifters had a tendency to over pressurise because they were designed for holden engines and not jab's (no idea how true that is, like I said second hand and old information!). Both continental and lycoming tried engines using automotive parts suppliers for ease of production, both engines where pretty big flops!

 

 

[M61A1]

detonation/pinging is 2 (or possibly more) flame fronts meeting within the combustion chamber. one ignited by the plug, the other from hot carbon deposits, or compression in an excessivly lean mixture, to low an OCTANE rating, or other such as advanced timing

When I was an apprentice armourer, we had the difference between an explosion and detonation defined roughly-

Explosion- a rapid expansion of matter (gas)

 

Detonation- total molecular disintegration -the rate is much higher from memory, upwards of 4000 metre/sec. (bear in mind this was 30 yrs ago)

 

In any case, it's destructive.

 

 

[eightyknots]

When I was an apprentice armourer, we had the difference between an explosion and detonation defined roughly-Explosion- a rapid expansion of matter (gas)

Detonation- total molecular disintegration -the rate is much higher from memory, upwards of 4000 metre/sec. (bear in mind this was 30 yrs ago)

 

In any case, it's destructive.

Apply the definition: The atomic bomb over Hiroshima: was it a detonation or an explosion?

 

 

 

[jcamp]

Apply the definition: The atomic bomb over Hiroshima: was it a detonation or an explosion?

Rapid burning of powder (the gun) followed by a (non chemical) rapid heating ie explosion.

 

Nagasaki was detonation (the explosive lenses) followed by a (non chemical) rapid heating ie explosion.

 

 

[Blue Skies]

Has anyone questioned whether the service bullitin JSB031-1 Through Bolt had been done?

 

 

[facthunter]

Making a comparison with car mileage and aeroengine life has no point to it. The car engine can still do the job when it is far beyond the condition an aircraft engine has to be in to survive.

 

Car engines spend a lot of their life at very low load. To cruise at 110 K's probably uses about 25% of it's max HP.

 

Continuous load at 75% is another matter especially when it was preceded by full throttle for about 5 minutes with minimum warm-up, to get to cruise.

 

Aircraft engines have to be minimum weight or nobody would buy them.

 

Holden red motors last no time on cement mixers. They are driven hydraulicly now. Nev

 

 

[eightyknots]

Making a comparison with car mileage and aeroengine life has no point to it. The car engine can still do the job when it is far beyond the condition an aircraft engine has to be in to survive.Car engines spend a lot of their life at very low load. To cruise at 110 K's probably uses about 25% of it's max HP.

Continuous load at 75% is another matter especially when it was preceded by full throttle for about 5 minutes with minimum warm-up, to get to cruise.

 

Aircraft engines have to be minimum weight or nobody would buy them.

 

Holden red motors last no time on cement mixers. They are driven hydraulicly now. Nev

My first car had a 186 Holden motor in it. I owned it 10 years and had to have it reconditioned twice in that period; this is despite the fact that I serviced this car every 3.000 miles -without fail- changing the oil and the oil filter. It let me down quite a few times and I am very pleased that this motor wasn't turning a prop on my aeroplane otherwise I would have done a few forced landings. Another Holden I owned had the 3.3 litre blue motor. I also had a few issues despite regular servicing. It also had to be rebuilt. Both of these cars would have had a low duty cycle, usually operating at far less than 100% power.

 

I have often thought about this when auto engine 'conversions' are sold as aeroplane engines. I really wonder how successful this is? However Raven, Viking and others seem to be OK from the sound of it.

 

 

[facthunter]

Short trips ruin them, and make sure the thermostat is working . It doesn't help aeroengines to run them for a short while on the ground either. It usually takes about an hout to get an engine to full heat and get some of the condensation out of it, and you need an oil temp around 85 degrees C Nev

 

 

[jetjr]

Short trips ruin them, and make sure the thermostat is working . It doesn't help aeroengines to run them for a short while on the ground either. It usually takes about an hout to get an engine to full heat and get some of the condensation out of it, and you need an oil temp around 85 degrees C Nev

I kind of thought this might be why training Jab aircraft tend to have less problems than private ones - this event goes against that trend though

 

 

[motzartmerv]

I was going to start a new thread, but I figured this was a good a place as any to get the message across.

 

EFATO is probably the second biggest threat that we all face. The first (IMHO) being some form of inflight structural failure. Im not saying the later is more likely, just more dangerous if we could weigh up the dangers.

 

High wing loading aircraft such as the J160 require a significant turn of speed to produce the lift required to achieve a good takeoff. Takeoff performance is limited by (among other things) thrust, but to be more specific, thrust in excess of that required to overcome the drag. In this way the power provided by the engine is the limiting factor with regard to maximum 'level' speed. The faster the aircraft goes the more thrust required to overcome the drag, eventually the thrust vector is balanced by the drag vector and no further increase in speed is possible without lowering the nose and using gravity.

 

All takeoffs, particularly in a high wing loading aeroplane, have what could be called a critical phase. This is the phase of flight after liftoff and before sufficient height can be gained to manourvre the aeroplane either back to the runway, or into an area where a path of least resistance can be navigated. Having an engine fail in this critical phase is the bain of our existence, and surviving this situation is where your instructor would have spent a great deal of time and effort during your training.

 

The situation can be broken down into two sperate phases and if thought about in these two distinct sections, you will give yourself the best chance to walk away with a cool story to tell your mates

 

Phase 1. Surviving the initial few seconds after the failure.

 

Unfortunately, this is where many people come unstuck. During the climb out your angle of attack is only moderately higher than in the cruise. Nothing too nasty here and generally nothing to be concerned with as the thrust vector angled skywards is aiding with getting you airborne.

 

Now think about the attitude, dont confuse attitude with angle of attack, where is the nose in relation to the horizon. Its high, but while ever you are climbing the angle of attack is not too bad. Happy days. Now consider that same attitude with the thrust line (vector) removed completely. A low inertia aeroplane will stop climbing almost instantly, this results in a large change in the angle of attack. So within seconds you have gone from a situation where the angle of attack is only moderately high, induced drag and parasite drag are both in a region where the thrust has sufficient in reserve to effect the climb- to a situation where the angle of attack has just jumped up remarkably, and with that comes an increase in induced drag. Most of us would of heard and know of the requirement to lower the nose to maintain flying speed, but in the heat of the moment precious seconds can be lost while your panicked brain attempts to make sense of the situation. A tendency is to freeze on the controls, ie, hold the stick where it is. Without the thrust, most training aircraft should lower the nose automatically due to the coupling of the forces and the cofg, but you are taking off, you dont want the nose down, you want it up, and pointing away from the row of trees in front of you, so you come back on the stick instinctively. This obviously doesn't help matters, it increases the angle of attack and the drag even further. Its at about this point the average pilot will remember, only moments ago he was on a nice smooth, obstacle free runway, and that runway will call out to him. So with the stick still back, the angle of attack high, and the induced drag high, the pilot rolls on a steep turn. As normal, in a steep turn the nose trys to drop, the pilot reacts by coming back further on the stick. Now the pilot is really asking too much of the wing, the decent rate increases to alarming levels. Without immediate corrective actions, the inside (lower wing) stalls and the rest is history.

 

This situation has killed more pilots than the spitfire. So I thought id offer some tools to help you through this first phase of a low level EFATO. None of this is new stuff, but I reckon you can't hear this enough.

 

Your probably expecting me to say "lower the nose" first.. But back it up a bit.. Back to while you were lined up on the runway. We should ALL be giving ourselves a pre takeoff safety brief. Not a robotic speech, but a real briefing on what your actions will be in the event of an engine failure. Say it out loud, I will immediately lower the nose to maintain flying speed. Point to the airspeed indicator at about best glide speed. Hopefully doing this will remind your brain where the needle needs to be. What options are available to you?..On THIS strip, in this direction. Where are the best paddocks, roads, paths of least resistance. Where is the wind coming from. Is the best paddock straight ahead?..left or right of the centerline.? Are there any options at all??.. sometimes there aren't.

 

In this situation I can only offer this advice.. If you control the arrival, you stand a good chance of survival. And that goes for all these scenarios. Fly the plane. Concentrate on the attitude. Attitude attitude attitude. But what Im trying to get across here is make it a normal everyday part of your flying routine. Think about it, talk about it just before you roll.

 

A comment from Cory after this accident really sticks out to me.. He said " man, you know what was weird?.. I was just talking about it, then 20 seconds later I was doing it, when I glanced down I already had the thing at 70 kts and was in a slight left turn towards the paddock I was just talking about." If its been months or years since you thought about what your going to do if the music stops playing, your reactions, or rather, in actions could be very costly.

 

HAVE A PLAN. Even a bad plan is better than no plan.

 

Phase 2. The touchdown.

 

We would all like to think we are good under pressure, and we hope we would react with speed and intelligence in a crisis situation. I can tell you, and im sure Cory would agree, performance is going to be degraded. Your not going to be flying well, your not going to be thinking clearly. Concentrate on these two things...

 

Attitude, touchdown point. And thats it.. Maintain the attitude for best glide. And drive the aeroplane down to the ground. Put the cockpit in the best position you can, ie, if your going to strike obstacles, get the airframe to bare the brunt, not the cockpit. Thats it.. KISS principle is never more important. keep it simple stupid.

 

Its all about the energy. You need to dissipate as much energy as you can. velocity in most physics equations conforms to the inverse square law. A reduction in velocity equates to the square of that velocity being reduced from the total energy (force ) involved. Half the speed and you have 4 times less energy involved. For every second you spend on the ground, even rough, bouncy, shrub ridden ground, the energy is dissipating rapidly.

 

Cheers... Fly safe

 

 

[planesmaker]

How can fitting hydraulic lifters break thru bolts?

 

 

[deadstick]

Well said Motz!!!