Guest Bruce Knowles Posted November 18, 2014 Posted November 18, 2014 hello Brian all "standard" are you sure about that I remember some body had ceramic coated barrels in his Jab for what ever reason perhaps to address high temps:wave:
dazza 38 Posted November 18, 2014 Posted November 18, 2014 I honestly think CASA didn't have a choice., although they went a bit over board initially. Having a engine that is likely to fail twice as much as the Rotax ( I assume both 4 stroke and 2 stroke engines were used in compiling the total hours) according to the figures released this week. That isn't exactly something to write home about. 2
Jaba-who Posted November 18, 2014 Posted November 18, 2014 I honestly think CASA didn't have a choice., although they went a bit over board initially. Having a engine that is likely to fail twice as much as the Rotax ( I assume both 4 stroke and 2 stroke engines were used in compiling the total hours) according to the figures released this week. That isn't exactly something to write home about. Have they released the proper stats? My understanding is they haven't. Simply saying " twice as many failures" means nothing. Two is twice as many as one but two in a million is no different statistically to 1 in a million. And why are you assuming 4 stroke and two stroke were used in the figures. As far as i can tell CASA have refused to release that information even to Jabiru. For all we know it is selected sub-types of only one type of jabiru engine. And it seems there is no benchmark to say that rotax is or has an acceptable standard to aim for. CASA does not have a benchmark for what is an acceptable rate of failure in an engine.
bexrbetter Posted November 18, 2014 Posted November 18, 2014 Who gives a toss about stats when the actual real owners are reporting in their experiences. 1
Jaba-who Posted November 18, 2014 Posted November 18, 2014 Yea the stats are out. Can you advise where I can find them? Thanks
Bruce Tuncks Posted November 18, 2014 Posted November 18, 2014 The "clarification" is clearly the result of Truss's office sending a "What the hell have you guys done" to CASA. But CASA have not told us what the problems are. Is it through-bolts? Why didn't they say? IF it is the bolts, I reckon the fact that many SMALLER through-bolts have gone for years without failing is highly relevant.It shows that detonation or pre-ignition is the real cause of larger through-bolts failing. Now these problems have to be related to fuel and/or operating too hot. The geographic evidence is interesting too... What if some places get different fuel? We don't see these failures in Adelaide but apparently it happens all the time in NZ. If you do the calculations, you will find that the small original through-bolts were ok for the design cylinder pressures in normal operation, but not for pre-ignition or detonation pressures, which can be 3 times normal pressures. CASA would have had these calculations when they certified the engine. I'm interested where Ungermann got his engineering degree, or if he even has one. Does anybody know? 1 1
01rmb Posted November 18, 2014 Posted November 18, 2014 A holden engine won't last as well as a mercedes engine - that doesn't make it unsafe or unreliable just not as reliable. At twice the price I would expect better from a mercedes or a rotax. At 1 failure in 3,300 takeoffs/landings, whilst half as good as Rotax it is the same as the other engine types. Will this mean that every other engine other than Rotax should have the same restrictions imposed? I would still like to have better from the engine with fewer failures but are the draconian measures from CASA reasonable? CASA along with Jabiru would be better off undertaking an analysis of each failure and determine if a fix, improved maintenance or better handing could have prevented the failure. The trouble with overreacting is that the response is over the top as well. I don't agree that the response from Jabiru is correct but that is what happens when you get hit with a big stick - you hit back in defence. If only things were kept in control and proper analysis was carried out I am sure improvements could be made. 2
01rmb Posted November 18, 2014 Posted November 18, 2014 I still lay a lot of the variability of outcomes based on handling, maintenance and most critically fuel. Without proper analysis - you will never get to the bottom of the problem. CASA hasn't said because they don't have a clue - only that they think it is not good enough. 1
motzartmerv Posted November 18, 2014 Posted November 18, 2014 How can a pilot " handle " the jab engine in a way to minimize through bolt failure? Genuine question. 2 1
dlegg Posted November 18, 2014 Posted November 18, 2014 There was major discussion a while ago about pistons being in the wrong way around, and being bandied about as the cause of bolt failures. Do South African dealers turn these pistons around on new engines as rumoured? They have an excellent run out of their Jabs.
01rmb Posted November 18, 2014 Posted November 18, 2014 Possibly - If the engine is pinging away from pre ignition or detonation - slow down the climb rate. The trouble is many people will (If it is a hired aircraft) just fly it like they stole it - Works the same as with hire cars. I have known pilots to just jam full power and reef the stick back to climb as fast as possible for as long as possible without concern for odd noises and rising temperatures. 2
bexrbetter Posted November 18, 2014 Posted November 18, 2014 So could anyone confirm to me that the throughbolt failures occur only on the lower rows next to the pushrod tubes (as Bruce pictured above) please? 1
Bruce Tuncks Posted November 18, 2014 Posted November 18, 2014 motzart, you have to avoid pre-ignition or detonation. Run it cool on the right fuel. Don't have a lean cylinder. Running it cool may mean tweaking the cooling system. Let me know if you want some advice or references here.
dazza 38 Posted November 18, 2014 Posted November 18, 2014 Have they released the proper stats? My understanding is they haven't.Simply saying " twice as many failures" means nothing. Two is twice as many as one but two in a million is no different statistically to 1 in a million. And why are you assuming 4 stroke and two stroke were used in the figures. As far as i can tell CASA have refused to release that information even to Jabiru. For all we know it is selected sub-types of only one type of jabiru engine. And it seems there is no benchmark to say that rotax is or has an acceptable standard to aim for. CASA does not have a benchmark for what is an acceptable rate of failure in an engine. Because the stats that came out a few days ago from the RAA showed engines over the fleet total time for the last 12 months. It was broken down as Jabiru, Rotax and others ( others as in auto conversions and low volume engines). I don't have the figures with me but they were posted on this site. Anyway Rotax flew the most hours. 71 000 or something so I assume that includes all Rotax model engines. Jab were second in total time over the fleet. It worked out close to Jabiru engines failed twice as many times than Rotax when taking into consideration the number of failed engines compared to the number hours flown.
motzartmerv Posted November 18, 2014 Posted November 18, 2014 Thanx Bruce. My engineer is doing a jab course as we speak. Hopefully they will juice him up. As a school, we can ONLY maintain IAW the published jab procedures, so I'm interested to know how any tweaks can be done an still be IAW te manuals.
Old Koreelah Posted November 18, 2014 Posted November 18, 2014 Surely Australia possesses the facilities and people needed to properly develop this engine? If cost is the issue, there are so many funding programs and grants available for all sorts of unproductive projects, why can't some be allocated to saving and growing a unique Australian business? Other countries must be laughing at the way we regularly throw money at old industries and ignore the new ones. We've been here before, with even the great Barry Jones making excuses ("it just doesn't fit the guidelines") for not supporting promising new industries. 1
Jabiru Phil Posted November 18, 2014 Posted November 18, 2014 Yea the stats are out. Also Answer the question from this statement please. On another thought that just hit me, if we didn't have the Jab discussions these past weeks, this site hits would be down over 500% ( not having a a go at the site owner) It's a pity that we have lost GENUINE debate of late because of some forum members posting, just for a stir! Phil 1 1
motzartmerv Posted November 18, 2014 Posted November 18, 2014 The stats have een posted in this thread. Look back a few pages.
Bruce Tuncks Posted November 18, 2014 Posted November 18, 2014 motzart, at the very least you must be able to put in a monitoring ( data-logging) system which will tell each cylinder CHT and EGT history. I bet you can also adjust the ram-air ducts to block any areas where air can escape without getting close enough to the fins to remove heat. If you think about how heat transfer happens at the molecular level, you will see that the air must actually get right onto the hot fins. I don't know who you could ask, if it was me i'd just do it. And you can make sure that taxi and holding procedures don't cook the engine. On the ground a different cylinder might be the hottest, and this can depend on the wind. The students would need to be shown how to review the record from the datalogger. They would like to see how well they operated from the record of temperatures. It would make looking after the engine a point of pride. Dunno how much this would cost but cheaper than an incident for sure.
Guest Maj Millard Posted November 18, 2014 Posted November 18, 2014 Surely Australia possesses the facilities and people needed to properly develop this engine?If cost is the issue, there are so many funding programs and grants available for all sorts of unproductive projects, why can't some be allocated to saving and growing a unique Australian business? Other countries must be laughing at the way we regularly throw money at old industries and ignore the new ones. We've been here before, with even the great Barry Jones making excuses ("it just doesn't fit the guidelines") for not supporting promising new industries. OK, Jab did recieve federal grant money at some time in the past...or low- interest loans
aro Posted November 18, 2014 Posted November 18, 2014 The stats have een posted in this thread. Look back a few pages. A few numbers have been posted. They suggest that Jabiru have a greater failure rate than some others, but leave many questions unanswered. I would hope there are MUCH more detailed stats somewhere to justify this level of action. 2
Old Koreelah Posted November 18, 2014 Posted November 18, 2014 OK, Jab did recieve federal grant money at some time in the past...or low- interest loans Thanks Maj. Maybe they need some more, lots more. 1
Jabiru Phil Posted November 18, 2014 Posted November 18, 2014 There was major discussion a while ago about pistons being in the wrong way around, and being bandied about as the cause of bolt failures. Do South African dealers turn these pistons around on new engines as rumoured? They have an excellent run out of their Jabs. Don't know about South Africa. I read the article recently and asked an Independent Guru about his take on this. He said that this theory has been going on for 15 years. The presumption did not take into account that there was a propeller up front. Basically the pistons have an arrow pointing to the front and Jabs have them pointing rearward as they turn anti clockwise. Phil
Jaba-who Posted November 18, 2014 Posted November 18, 2014 How can a pilot " handle " the jab engine in a way to minimize through bolt failure?Genuine question. Choice of fuel? Mogas vs avgas Choice of warm up prior to applying full power ( I know a guy who has had an engine failure who didn't know for three years that jabs should not have full power applied till engine temps were over 50 degrees. He used to take off at any temp over 15 degrees. ( the minimum operating temp) Climb out speeds Cruise settings - many opt for fuel economy but that runs engines hotter Probably more
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