bexrbetter Posted May 22, 2017 Share Posted May 22, 2017 Thanks for that, I'll make a Note of it.Alan. Was my Key thought for today. Link to comment Share on other sites More sharing options...
bexrbetter Posted May 22, 2017 Share Posted May 22, 2017 I ride a Yamaha ag bike on the farm. It is an air-cooled 4 stroke, like the Jab engine, but the airflow over the engine is nowhere near as good. Yet is has shown no overheating problems.And it doesn't run on avgas or need aeroshell oil. Why is this so? And why does it just use normal oil and not need special air-cooled engine oil? Exhaust out front. Surface area both external, air, and internal, oil. Roller bearings are lower friction than slipper bearings. 'As cast' rough finning far superior to smooth. No radiant heat from other cylinders. 1 Link to comment Share on other sites More sharing options...
aro Posted May 22, 2017 Share Posted May 22, 2017 I ride a Yamaha ag bike on the farm. It is an air-cooled 4 stroke, like the Jab engine, but the airflow over the engine is nowhere near as good. Yet is has shown no overheating problems. Fuel use rate is probably a good approximation of the amount of power and heat being generated. I would wager that you would have trouble using fuel at the Jabiru rate for a sustained period on the bike. Airflow on the bike is probably better than you think. People worry a lot more about cooling drag in aircraft, so low speed cooling (especially on the ground) may be marginal. 1 Link to comment Share on other sites More sharing options...
Old Koreelah Posted May 22, 2017 Share Posted May 22, 2017 ...and don't forget car and motorcycle engines are cast with a grade of alloy which copes with higher temperatures than that which Jab engines are cut from. 1 Link to comment Share on other sites More sharing options...
facthunter Posted May 22, 2017 Share Posted May 22, 2017 The main reason is you are not operating at a high power output (75%) continuously. Many of those motors overheat with mud on the engine when the OHC cam bearings suffer most. Nev 1 Link to comment Share on other sites More sharing options...
Jaba-who Posted May 22, 2017 Share Posted May 22, 2017 The main reason is you are not operating at a high power output (75%) continuously. Many of those motors overheat with mud on the engine when the OHC cam bearings suffer most. Nev Yep - Same reason you can't compare auto engine reliability with aviation engines. An auto engine in probably all but a very cars/bikes never runs full throttle for ten or so minutes let alone doing it every time it's run. Very little of an aviation engine cycle is at idle while auto and bike engines run at idle for lots of a usage cycle. 1 Link to comment Share on other sites More sharing options...
coljones Posted May 22, 2017 Share Posted May 22, 2017 I ride a Yamaha ag bike on the farm. It is an air-cooled 4 stroke, like the Jab engine, but the airflow over the engine is nowhere near as good. Yet is has shown no overheating problems.And it doesn't run on avgas or need aeroshell oil. Why is this so? And why does it just use normal oil and not need special air-cooled engine oil? The dynamics would change if you replaced wheels with an air cushion. That would require the engine to work a lot harder 100% of the time. 1 Link to comment Share on other sites More sharing options...
SDQDI Posted May 22, 2017 Share Posted May 22, 2017 An auto engine will run at 75% power all day every day with no hassles at all. An aero engine is built right on the limits in regards to weight which causes compromises. Auto engines aren't limited by anywhere near that extent. 1 1 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted May 22, 2017 Share Posted May 22, 2017 Thanks guys. Well the new Jab engine looks good and shows less friction when cold for some reason. If this is true for all engines, they should be a easier to start. I understand that this friction will not increase as it gets hot which should lead to a bit more power as well as running cooler. It is being installed to replace a Jab engine which easily made TBO. I'll keep you posted. 1 2 Link to comment Share on other sites More sharing options...
Old Koreelah Posted May 22, 2017 Share Posted May 22, 2017 An auto engine will run at 75% power all day every day with no hassles at all... Take it from me, SD has proven this. 1 1 Link to comment Share on other sites More sharing options...
coljones Posted May 23, 2017 Share Posted May 23, 2017 An auto engine will run at 75% power all day every day with no hassles at all.An aero engine is built right on the limits in regards to weight which causes compromises. Auto engines aren't limited by anywhere near that extent. It would be interesting to see a fuel rate graph over time in a variety of driving situations. My fuel use on inner west roads is a lot more than when cruising the highways, fuel rate being a crude measure of power expended. (Perhaps I could claim that the savings in petrol pays for my flying whenever I drive out to The Oaks) Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted June 26, 2017 Share Posted June 26, 2017 The new engine is operating fine and has about 15 hours at the moment. When you try to turn over the hot engine ( taking care of course in case it fires) it still feels "bouncy" and is easy to move. In comparison, the older steel-cylinder engines feel very stiff when hot. In fact they feel so stiff that my intuition says they should just about seize up. More heat=more tightness=more heat etc. Since these older engines don't do that, my intuition is obviously faulty. 2 Link to comment Share on other sites More sharing options...
turboplanner Posted June 26, 2017 Share Posted June 26, 2017 I ride a Yamaha ag bike on the farm. It is an air-cooled 4 stroke, like the Jab engine, but the airflow over the engine is nowhere near as good. Yet is has shown no overheating problems.And it doesn't run on avgas or need aeroshell oil. Why is this so? And why does it just use normal oil and not need special air-cooled engine oil? Combustion chamber temperature; which is much hotter than, but not a direct correlation to, cylinder head temperature. Combustion chamber temperature varies substantially with time and amount of power demand, and fuel available for cooling. Link to comment Share on other sites More sharing options...
jetjr Posted June 26, 2017 Share Posted June 26, 2017 The new engine is operating fine and has about 15 hours at the moment.When you try to turn over the hot engine ( taking care of course in case it fires) it still feels "bouncy" and is easy to move. In comparison, the older steel-cylinder engines feel very stiff when hot. In fact they feel so stiff that my intuition says they should just about seize up. More heat=more tightness=more heat etc. Since these older engines don't do that, my intuition is obviously faulty. No they just wear a great deal - early life high leak downs, low time overhauls....... Its supposably due to differing materials, pretty low grade alloy pistons inside steel barrels (which tend oval when fitted), wide ring gaps. New engine should have less of these troubles assuming Jabiru have their product development process together. For interest sake CAE went with round barrels (when fitted) and tighter rings, same pistons though, and they feel pretty much the same hot or cold. Theres a few ways to address the same problem Good to hear its going well. 1 Link to comment Share on other sites More sharing options...
SSCBD Posted June 26, 2017 Share Posted June 26, 2017 most of use rotax or jab engines etc as that is what we can afford in these planes and that is what they have. I personally love the sound and to fly Pratt and Whitney Radial engines whilst flying amphib beavers in aus. - but I don't own one personally as I am not that rich. But they even broke. And yes even RAA pilots understand revs versus stress. (edited...mod) 3 Link to comment Share on other sites More sharing options...
Camel Posted June 26, 2017 Share Posted June 26, 2017 I operate a Lyc O235 with a TBO of 2400 hrs, this is a very under stressed low revving engine, there in lies the reliability hence I chose not to sit behind a Jab motor, personal choice. (Play the topic not the person...if you have a problem with the person do so privately, not here....mod) 2 2 1 Link to comment Share on other sites More sharing options...
turboplanner Posted June 26, 2017 Share Posted June 26, 2017 (edited...mod) Link to comment Share on other sites More sharing options...
Keith Page Posted June 26, 2017 Share Posted June 26, 2017 I ride a Yamaha ag bike on the farm. It is an air-cooled 4 stroke, like the Jab engine, but the airflow over the engine is nowhere near as good. Yet is has shown no overheating problems.And it doesn't run on avgas or need aeroshell oil. Why is this so? And why does it just use normal oil and not need special air-cooled engine oil? The oil does a lot of internal cooling, hence the short life of the oil. OR.. It should be changed regularly. KP. 1 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted June 26, 2017 Share Posted June 26, 2017 Hi Wally, my son has a Lycoming in his Lancair. I said don't buy that just fly the family Jabiru for nothing but he said the Jabiru is too small and slow. This Lycoming max CHT of 190C would scare me on the Jabiru where I keep it under 160C. (Well I try to and generally succeed. ) But my bottom line is to buy Australian if possible and I just don't understand people who think differently. Link to comment Share on other sites More sharing options...
coljones Posted June 26, 2017 Share Posted June 26, 2017 I ride a Yamaha ag bike on the farm. It is an air-cooled 4 stroke, like the Jab engine, but the airflow over the engine is nowhere near as good. Yet is has shown no overheating problems.And it doesn't run on avgas or need aeroshell oil. Why is this so? And why does it just use normal oil and not need special air-cooled engine oil? You might find that your AgBike is only using a fraction of peak RPM most of the time, unlike an aero engine. 2 2 Link to comment Share on other sites More sharing options...
jetjr Posted June 26, 2017 Share Posted June 26, 2017 Theres lots of analysis here of the CASA - not ATSB - claims as to Jabiru reliability, have a read. ATSB actually claimed Rotax and Jabiru had "around the same" numbers of failures in their preliminary report. Promoting your engine choice here (which is much heavier and more costly than the 2200 which this thread is about) would appear to serves little purpose 1 2 Link to comment Share on other sites More sharing options...
jetjr Posted June 26, 2017 Share Posted June 26, 2017 Yep your opinion, start a thread and go for it 1 3 Link to comment Share on other sites More sharing options...
Bruce Tuncks Posted June 27, 2017 Share Posted June 27, 2017 I don't think I have ever bought an overseas product when there was a much cheaper Australian version. I do admit to buying imported products when they are cheaper than local stuff. As for the Jabiru engine, it runs just fine and always has, well once I overheated it with improper ground running but that was my fault and not the engines. If I were so rich that money didn't matter, I would still fly with the Jabiru engine. 2 Link to comment Share on other sites More sharing options...
facthunter Posted June 27, 2017 Share Posted June 27, 2017 If you got a Lyc 0-360 and carefully blueprinted it after about 100 hours running you would probably have one of the most reliable piston engines available. today... Comparing a Lancair to a Jabiru is a little unfair..The Lancair is fast and critical and unsuited for other than fairly long sealed strips You can even have a turboprop pressurised version to play airliners with if you are silly enough, because it's still slow compared with Grumman's latest jets. Jabiru meets the safe and affordable tag quite well considered as a package. That's the aim of the organisation isn't it? You have to be a good if not "ACE" pilot to fly them too and you can fly across Australia in a 230 comfortably. If the "new" cylindered motor goes well it will be even better. Nev 1 Link to comment Share on other sites More sharing options...
gandalph Posted June 27, 2017 Share Posted June 27, 2017 few years ago the ATSB did a study on light A/C engine failures, Can you provide the reference for that study please Capt Wally? 1 Link to comment Share on other sites More sharing options...
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