motzartmerv Posted December 12, 2014 Share Posted December 12, 2014 IWhy hasn't any one run colder plugs? It seems an obvious thing to try under the circumstances. If it doesn't soot up on long taxying it won't cause any trouble at other times..Nev Are they an approved engine part IAW with Jabs manuals? 1 Link to comment Share on other sites More sharing options...
facthunter Posted December 12, 2014 Share Posted December 12, 2014 Probably not, but it's one of the first things that should be investigated if detonation suspected. They lowered the compression and retarded the ignition timing, both of which would lose power and retarding the timing makes it run hotter. Another possible problem if the exhaust valve is pumping up or distorted it will get so hot because it isn't seating properly it can be an ignition source and again a detonation possibility. Nev 1 1 Link to comment Share on other sites More sharing options...
01rmb Posted December 12, 2014 Share Posted December 12, 2014 Did you guys go back to Avgas? Did this improve things?All our pilots have become experts at pre flights, which is a good thing. Almost ALL of our failures have been picked up during pre flights. In fact, the fly wheel bolts on our 170 were found to be sheared when my instructor heard a very very faint clicking noise when she pulled the prop through. I was very pleased that she picked this up, I couldn't hear it...(im on the other side of a fair few AC/DC concerts) .It was an ever so quiet click as the ring gear contacted a surface it normally wouldn't due to slop in the fly wheel. The pre flight is the LAST line of defence, and luckily for us, has almost always identified the issues before they cause more damage or worse. The problems were on avgas and went away once on mogas. It was the fouling of the exhaust valves and plugs from the avgas and resulting rough engine running which drove the use of Mogas. It gets run through a lot so is always fresh but still need to be careful to not let it get old. Need to be careful during climb to keep heat down and avoid pinging. The 4 cylinder ab initio jabs were getting the worse (accounts for two of the partial engine failures in the reports) but my 6 cylinder used just for cross country training didn't escape the exhaust valves being fouled on 2 cylinders and starting to burn through the stems - identified in preflight and replaced during a service. The thoughts were that the extended taxi/ idle plus the extensive circuits with low power idling landings along with another extended taxi and idle before being shut down was causing the problems more than somewhere where the aircraft does a quick taxi and then sits at 2800 revs for extended time and then just a short powered landing. There seemed to be a change in the avgas that made things worse - time of year or supply import I don't know. It was not unique to the jabs, a number of cessnas were fouling plugs and needing to be replaced but they are far more tolerant of the problem and will keep running if a bit more poorly. Added bonus is that using mogas keeps the oil in much better condition avoiding the lead contaminants. From what I understand that was the main reason behind the 25 hour oil changes. 1 Link to comment Share on other sites More sharing options...
01rmb Posted December 12, 2014 Share Posted December 12, 2014 Probably not, but it's one of the first things that should be investigated if detonation suspected. They lowered the compression and retarded the ignition timing, both of which would lose power and retarding the timing makes it run hotter. Another possible problem if the exhaust valve is pumping up or distorted it will get so hot because it isn't seating properly it can be an ignition source and again a detonation possibility. Nev This could have been something to do with the valve problems with my engine. The aircraft was initially run on avags but switched to mogas when the problems with the other aircraft were identified and then on my trip to Longreach we used avgas due to ease of availability and belief that avgas was not too bad in the 6 cylinders used for longer cross country flights. Tanks were pretty well empty at each time fuel was changed. The valves were probably already fouled and then the combustion and poorer valve cooling started to burn through the valve dropping compression very quickly and if not picked up would have dropped the valve head into the cylinder and causing major problems and a forced landing if it happened airborne. Link to comment Share on other sites More sharing options...
motzartmerv Posted December 12, 2014 Share Posted December 12, 2014 rmb. We have an almost identical history. We went from Avgas to mogas after finding lots of issues with it, not least of which was actually getting it at our airfield. Our engines were always cakked with crap, the oil looked like green goop. The tops of the pistons were almost silver, and looked like they had molten metal pored over them. Valves were crapped out and never wanted to seat properly. We also take steps not to run old fuel, we check for ethanol regularly, and only get fuel from one 'reputable' servo. Not a dodgy lookin indian 7/11. Have you seen a direct improvement since running mogas? Link to comment Share on other sites More sharing options...
facthunter Posted December 12, 2014 Share Posted December 12, 2014 I'm not trying to be picky but some of the descriptions of the condition of parts don't do it for me. Most of the engines are probably lean and hot. If the valves overtemp they stretch and develop stress cracks in the stem. If the seat is lost you have gas leakage and power loss and erosion of the seats. IF the engine has run very hot you may see blue colour in the cylinder bore adjacent to the exhaust port. Are there scratches in the bore and any carboning in the ring lands. ALL these signs mean the engine won't be reliable. It's not happy Alice. Pull,the prop through and if the compression just bleeds away reject it. Ask your L2 to show you what a good cylinder feels like. (if he/she knows. You don't have to do a leakdown test unless you need figures or to back up what you feel doing it by hand. When we hand propped most planes you would notice a sick cylinder as a matter of course when priming and starting it. Nev 1 1 Link to comment Share on other sites More sharing options...
motzartmerv Posted December 12, 2014 Share Posted December 12, 2014 No, they dont look blue. Theres no carbon deposits anymore. Not since changing to Mogas. 1 Link to comment Share on other sites More sharing options...
facthunter Posted December 12, 2014 Share Posted December 12, 2014 The only thing that will show blue is the top and side of the steel cylinder near the exhaust valve.. If you aren't getting any carbon at all you are running lean. The oil should darken slightly during it's life because of blow by in a slightly rich engine. You get blowby in a lean running engine as well , probably more as more oil is oxidised from the surfaces, and oil helps form the seal...Nev 1 Link to comment Share on other sites More sharing options...
01rmb Posted December 12, 2014 Share Posted December 12, 2014 Merv - The experience was exactly the same - fouled cylinder heads, valves (especially exhaust) and plugs. Valve and plug fouling and many little rough running niggling issues has completely gone now that mogas is used. The photo below was at 300 hours. You can see the lead build up and the burning on the exhaust valve near the plug (the one that has been removed). The cylinders had similar thick light brown build up. After a good clean and running on mogas the heads and cylinders are still clean 100 hours later when one of the heads came off again to replace a compression ring in one cylinder stuck and needed replacing. (The cylinders were not touched when the heads were cleaned so it was possibly still a legacy from the avgas. Probably should have done the lot at the time.) I have had a few long chats with a long time family friend who was head of Shell aviation - he also identified that the lead from the avgas from the blowby gas will contaminant the lubrication oil and will combine with water to become an acidic paste. With such a low oil volume in the jabs, it doesn't take much to completely contaminate the oil to become a sludge and cause loss of lubrication, rusting and increased component wear. I believe that Jabiru after consulting a few people and in discussions with Shell changed the oil change schedule to 25 hours from the original 50 hours. Below are a couple of references that are worth a read. Note they specifically mention Rotax being designed for unleaded fuels and the potential that a hotter plug could be used to reduce lead fouling if avgas is used. http://www.shell.com/global/products-services/solutions-for-businesses/aviation/aeroshell/knowledge-centre/technical-talk/techart18-30071600.html http://transairpilotshop.wordpress.com/2011/11/03/winter-and-the-oil-in-your-aircrafts-engine/ I have spoken with Jabiru about avgas and whilst they acknowledge these issues they are uncomfortable with the variability of mogas and the increased potential for other issues such as detonation. I also feel that they don't want to alienate those that have avgas on hand at the airfield. It is far easier for me to fill up with Avgas than have to lug jerry cans of mogas but the experience has been way better on mogas and I would not go back to avgas given the issues that myself and the flight school has experienced. As long as the mogas is 95 or greater (we use 98), has no ethanol, is kept fresh, and not push the cylinder temps too high there should not be too many problems. But don't let it dry out - Where somebody has spilt some on a wing and left it to dry there is an awful syrupy residual mess that was hard to clean off so I would hate to see what it would look like inside a carburettor if it were left to dry out. Bring on unleaded avgas!! 2 Link to comment Share on other sites More sharing options...
motzartmerv Posted December 12, 2014 Share Posted December 12, 2014 Carbon copy of how ours used to look. Infact some looked worse in places. I can't find the pics I have of th pots after running Mogas. So much cleaner looking and more uniform coloration Link to comment Share on other sites More sharing options...
Russ Posted December 12, 2014 Share Posted December 12, 2014 One issue I have on Mogas is at shutdown, it sometimes, just as it's about to stop, it reverse runs for a couple of prop revolutions. Why ?? Trialling different shutdown methods to stop this. Link to comment Share on other sites More sharing options...
dodo Posted December 12, 2014 Share Posted December 12, 2014 October 1922, Sir Sefton Brancker, Director of Civil Aviation,: "We have two immediate ends to attain in connection with navigation: 1.Eliminate engine trouble 2.Perfect the wireless. Both are possible - and quite soon." 1 Link to comment Share on other sites More sharing options...
01rmb Posted December 12, 2014 Share Posted December 12, 2014 And just to tie this back into the thread topic - the recommendations I suggested to CASA et al was for Jabiru to undertake better investigation of engine problems (incidents and those identified during maintenance) as well as to better investigate problems with running on avgas. And not just running avgas in a test mule that gets fired up and left to run for several days but in an aircraft that gets hammered at at training school with multiple extended taxi and low power landing approaches per hour - for many hours per week. From what I have seen I feel that fuel problems accounts for a number of the identified incidents - I know for a fact that there would be 2 fewer partial failures on the list this year if they had not been running on avgas. Link to comment Share on other sites More sharing options...
01rmb Posted December 12, 2014 Share Posted December 12, 2014 I've only ever used Avgas in mine and have never had fuel related issues. And this is what the maintenance guys couldn't explain - why some people have no problems. They could only guess that for us it had something to do with the amount of time idling/low power whilst circuit training, taxiing etc. Link to comment Share on other sites More sharing options...
Old Koreelah Posted December 12, 2014 Share Posted December 12, 2014 Keep this going please, people. One of the most useful discussions in recent times. Correct me if I have got this wrong: Fuel seems to be a major factor for some. Schools' experience may not be directly relevant to those of us who may only fly once a month, or even less. Mogas is viable, as long as only the best and freshest is used and the engine temperatures are kept under control. It is also a good idea to run the carby dry after each flight. Avoid storing Mogas, (or an aeroplane containing it) where it can get hot and evaporate off its volatile components. 1 1 Link to comment Share on other sites More sharing options...
Guest Ornis Posted December 12, 2014 Share Posted December 12, 2014 I've only ever used Avgas in mine and have never had fuel related issues. Thanks for answering my earlier query about sensors for CHTs. I didn't realise you had a CAMit core, not a Jabiru engine. (I know where the holes are, but don't use them.) We are closing off all escape routes, allowing air only through the fins - the opposite to you. Won't have any results for a few weeks. Here's the thing: air in the duct undergoes very little compression. As you found, it's necessary to lower the pressure in the cowl, to "suck" the air down through the fins. That's why a fully enclosed engine with a fan is better. Link to comment Share on other sites More sharing options...
Captain Posted December 12, 2014 Share Posted December 12, 2014 Here's the thing: air in the duct undergoes very little compression. As you found, it's necessary to lower the pressure in the cowl, to "suck" the air down through the fins. That's what I found. It is as much (if not more) about helping the air to get out of the cowl as it is getting it in. Once you get good airflow through the ducts and cowl it's then about getting more of the air down over 3 and 4 on the 3300. I wish I had done a bit more on a deflector in the duct to facilitate that, as I always had more then enough/too much cooling going past 3 & 4 and on to 5 & 6. Link to comment Share on other sites More sharing options...
Guest Ornis Posted December 12, 2014 Share Posted December 12, 2014 Jabiru 3300, serial 2xx, 8:1. Number 1 head had been off earlier, but at ~800 hours had a top end overhaul, using some factory-reconditioned heads; new solid-lifter heads unavailable. (In retrospect all cylinders should have had reconditioned heads.) All exhaust valves new, and pistons. Tightened down the rear of the ramairducts and used aluminium scoops between the heads on the left side and baffles on the duct on the right - because the exhaust port on the right is towards the front. No EGTs as none supplied with engine or recommended at the time and CHT thermocouple under #6 sparkplug only - fitted 6 CHT sensors. All CHTs green so I sometimes ran the engine harder during cruise. At ~1100 hours #5 exhaust valve head broke off at full power climbing prior to crossing a rugged mountain range. After discussions with people I trust I binned the engine. I considered ULPower and Rotax but settled for CAE. I don't think it's as good as it could be but I believe I can keep it happy for 1000 hours - and that will "see me out". Have made two new tight-fitting ramairducts with no scoops or baffles - yet. All the air escaping the duct is forced against the heads, none is "wasted". That is the principle of an orthodox airbox. I've had two forced landings and walking away was as much good luck as good management. Knowing what you're doing is a necessary condition but it's not a sufficient condition. Link to comment Share on other sites More sharing options...
Rolf Posted December 13, 2014 Share Posted December 13, 2014 There have been multiple claims in this threat about Jabiru having the toughest most survivable airframe of all aircraft on the market. I would be interested if anyone could back this up with some factual technical data (please not an Australian fatality statistic). I am interested in technical facts like What's the structure of the safety cell are there crash test studies or safety ratings (local/internationally) available for aircraft to backup this claim and shed some light. Or should we make this a new threat. No bashing please really interested in facts :) 1 Link to comment Share on other sites More sharing options...
jetjr Posted December 13, 2014 Share Posted December 13, 2014 New fine finned heads for solid lifter are available?? Full EGT is essential with the known fuel distribution problems Jabiru ignored uneven EGT until few years ago, i reckon many earlier problems (probably some of current ones) are related to hot and lean running in some cylinders. Users dont even know theres a problem until too late Ive had one forced landing and yes luck was a big part, landed back on runway I just left. Link to comment Share on other sites More sharing options...
rgmwa Posted December 13, 2014 Share Posted December 13, 2014 Motz, which type of mogas do you use in your aircraft - 95 or 98? rgmwa Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted December 13, 2014 Share Posted December 13, 2014 I feel half the problem with running Avgas in our engines is that we are running automotive plugs ...not the massive electrode type aviation plugs run in GA aircraft, which are more specifically designed for use with Avgas. On my trip earlier this year to Natfly I ran 100% Avgas for a lot of the time in the 912, as approved by the manufacturer with increased oil change frequency requirements. ( every 50 hrs instead of 100 ). Although it seems to take about 30 or so hours to do so, there is no doubt that the lead contained in Avgas does eventually foul the automotive type plugs, whereas with mogas usage they'll easily make 100 hrs before requiring attention. In answer to RGMWAs question above. I used to run 98 octane mogas, however was advised that the content used to boost the octane in 98 is subject to variation and constant change. I was also noticing that the actual performance varied a bit from fuel load to fuel load. Additionally I was advised that the 95 octane is a more stable product and I have run that ever since with consistently good and reliable performance. My preferred mix is 50/50 avgas and mogas ( 95)....the engine also runs cooler and smoother on that mix. Additionally aviation spark plugs are often cleaned, regapped, tested, and refitted or replace every 50 hours to remove and minimise lead buildup and fouling on the plugs Link to comment Share on other sites More sharing options...
Guest Ornis Posted December 14, 2014 Share Posted December 14, 2014 ... claims that Jabiru have the toughest most survivable airframe on the market ... anyone back this up with technical data ... What's the structure of the safety cell ... crash test studies or safety ratings ... to backup this claim ... If you stall/spin or fly into terrain nothing is going to save you, naturally. If you make a heavy landing onto rough ground you'll probably be okay - look at some photos and you'll "get the picture" - the fuselage is very strong. Fibreglass tends to absorb energy and eventually mush - much better than carbon which snaps and metal which bends. I know this is not the information you seek, merely the opinion of a pilot who would never buy another Jabiru, but gives credit where credit is due. Link to comment Share on other sites More sharing options...
motzartmerv Posted December 14, 2014 Share Posted December 14, 2014 Motz, which type of mogas do you use in your aircraft - 95 or 98?rgmwa Always 98 octane. 1 Link to comment Share on other sites More sharing options...
Kyle Communications Posted December 14, 2014 Share Posted December 14, 2014 I am not sure if you have it down south but we have the "UNITY" branded in selected garages up here now selling 100 octane Mogas Link to comment Share on other sites More sharing options...
Recommended Posts