Lycoming, Continental and Rotax
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BSFC
Jabawocky
This is probably a more appropriate thread to discuss the rotax.
Rotax figures for the 912iS as per
http://fahrzeugtechnik.fh-joanneum.a...otax-912iS.pdf
show the figures of between .41 and .42 in cruise and .477 at full power
Performance
Maximum Power*
(5 minutes) 100HP / 73.5KW @ 5800 RPM
Maximum Power (sustained) 95HP / 69.0KW @ 5500 RPM
Maximum Torque 94ft-lb / 128NM @ 5100 RPM
If your Lycoming is returning .4 as you claim which I assume is LOP then the figures are almost identical given similar fuel management regime,
The operator manual for a 300 HP Lycoming IO-540-K, L, or M series engine shows a full power fuel flow of 24 GPH which is a BSFC of 0.474 ...
I repeat there is no such thing as a free lunch, the figures are almost identical. Considering you enjoy the advantages of scale and no gearbox losses it is a remarkable achievement for a little engine.
As for dollars per horsepower I agree the Rotax is more expensive and Rotax has become greedy but to be fair we are paying in euro exchange rates.
Aussie Bob
your argument re head temperatures is immediately proven wrong when you consider that a Rotax head operates at 85 to 95 c as opposed to 162 c for your heads. Add in thermal momentum for the liquid cooling = a more stable valve train. You might have got somewhere with arguments such as more cooling drag, increased complexity and weight but it is proven fact that liquid cooled engines enjoy more stable operating temperatures
This is probably a more appropriate thread to discuss the rotax.
Rotax figures for the 912iS as per
http://fahrzeugtechnik.fh-joanneum.a...otax-912iS.pdf
show the figures of between .41 and .42 in cruise and .477 at full power
Performance
Maximum Power*
(5 minutes) 100HP / 73.5KW @ 5800 RPM
Maximum Power (sustained) 95HP / 69.0KW @ 5500 RPM
Maximum Torque 94ft-lb / 128NM @ 5100 RPM
If your Lycoming is returning .4 as you claim which I assume is LOP then the figures are almost identical given similar fuel management regime,
The operator manual for a 300 HP Lycoming IO-540-K, L, or M series engine shows a full power fuel flow of 24 GPH which is a BSFC of 0.474 ...
I repeat there is no such thing as a free lunch, the figures are almost identical. Considering you enjoy the advantages of scale and no gearbox losses it is a remarkable achievement for a little engine.
As for dollars per horsepower I agree the Rotax is more expensive and Rotax has become greedy but to be fair we are paying in euro exchange rates.
Aussie Bob
your argument re head temperatures is immediately proven wrong when you consider that a Rotax head operates at 85 to 95 c as opposed to 162 c for your heads. Add in thermal momentum for the liquid cooling = a more stable valve train. You might have got somewhere with arguments such as more cooling drag, increased complexity and weight but it is proven fact that liquid cooled engines enjoy more stable operating temperatures
Last edited by Oracle1; 27th Jul 2013 at 10:54.
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Apples for Apples
Look here also for real world comparisons as to operating costs to other engines in its class,
Rotax Aircraft Engines - Fuel Economy
Rotax Aircraft Engines - Fuel Economy
Last edited by Oracle1; 27th Jul 2013 at 10:27.
so what is the difference about aircraft crankshafts as from automobile crankshafts. There is obviously something that makes autoconversions not very successful. I just cant find what it is. How can a crank that turns reciprocating power into rotary power have such different results.
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Auto Conversions
aircraft engines are designed to turn at slower RPMS because the speed is limited by the prop tips going beyond the speed of sound. Automobile engines develop rated horsepower at higher RPMS and therefore need a gearbox to spin the engine at enough RPM to develop rated power. Building a successful gearbox and beating torsional resonance is no mean feat as discovered by lycoming and continental with G0 300 and the geared 6 cyl in the navajo cheiftain. Hats of to the german engineers for making it work very well in the rotax.
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Even assuming no gearbox to reduce revs the automotive crankshaft is not designed for the sideways loading that a prop would give it.
Much more leverage from a prop than the straight drive to a flywheel or torque converter.
Much more leverage from a prop than the straight drive to a flywheel or torque converter.
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Correct no axial loads are applied to an automotive crank hence the large plain bearing at the front of an aircraft crankshaft, however a gearbox absorbs the axial loads if correctly designed
Last edited by Oracle1; 27th Jul 2013 at 10:52.
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Rotax 912 crankshafts are pretty much indestructible, some are 1500 hr TBO, but the last 5 to 10 years they have been 2000hr TBO. a 1500 hr tbo engine can be upgraded to 2000 hr with the completion of a few Service bulletins.
the tbo cost is substantial, as the crankshaft, and piston conrods are manufactured as a one piece assembly that cant be disassembled. they do not use copper slipper type bearings, but sealed for life roller bearings.
Unlike continentals, the cylinder heads can be easily separated from the barrels for overhaul of each component. i am lead to believe that the heads on continental engines are screwed onto the barrels to complete the "jug" assembly, and ove these are screwed together, cannot be separated. (could be wrong though)
the tbo cost is substantial, as the crankshaft, and piston conrods are manufactured as a one piece assembly that cant be disassembled. they do not use copper slipper type bearings, but sealed for life roller bearings.
Unlike continentals, the cylinder heads can be easily separated from the barrels for overhaul of each component. i am lead to believe that the heads on continental engines are screwed onto the barrels to complete the "jug" assembly, and ove these are screwed together, cannot be separated. (could be wrong though)
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Building a successful gearbox and beating torsional resonance is no mean feat as discovered by lycoming and continental with G0 300 and the geared 6 cyl in the navajo cheiftain. Hats of to the german engineers for making it work very well in the rotax.
Just to be sure, the Chief had the TIO and LTIO 540, the Titan has the GTSIO 520..
Just to be sure, the Chief had the TIO and LTIO 540, the Titan has the GTSIO 520..
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ultralights the engines have totally different overhaul philosophies.
you are trying to compare apples, pears and oranges.
yes they are all fruit but none are the same.
I would not ever change my Continental O-200A to any other engine.
it is totally absolutely trustworthy.
btw TBO is a meaningless concept in privately owned cat B aeroplanes.
the engines are run on condition.
overhauled parts are for schmucks. real engines work on replacing worn bits.
I have sitting beside me 4 new O-200 cylinder assemblies. for $5200 I get new pistons, new rings, new wrist pins, new cylinders, new heads, new valves, new valve guides, new valve springs, new retaining clips. what I carry over from the old cylinders are the bits that don't wear hardly at all. rocker assemblies and such.
there is a flying school in florida that ran either lycomings or continentals on condition. with very regular flying one engine was run for over 4,000 hours.
dont believe the dinosaur rubbish. it will take you down the garden path.
you are trying to compare apples, pears and oranges.
yes they are all fruit but none are the same.
I would not ever change my Continental O-200A to any other engine.
it is totally absolutely trustworthy.
btw TBO is a meaningless concept in privately owned cat B aeroplanes.
the engines are run on condition.
overhauled parts are for schmucks. real engines work on replacing worn bits.
I have sitting beside me 4 new O-200 cylinder assemblies. for $5200 I get new pistons, new rings, new wrist pins, new cylinders, new heads, new valves, new valve guides, new valve springs, new retaining clips. what I carry over from the old cylinders are the bits that don't wear hardly at all. rocker assemblies and such.
there is a flying school in florida that ran either lycomings or continentals on condition. with very regular flying one engine was run for over 4,000 hours.
dont believe the dinosaur rubbish. it will take you down the garden path.
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the dinosaur rubbish i believe, is the fact the lycomings and continentals still run a magneto! carburettors disappeared in cars decades ago!! even so, carbys can be made to automatically adjust their mixture in reference to external air pressure, or lack of it,
why do they still use a manual mixture control? im still a little surprised Rotax have just come up with a multi point EFI. not exactly a new invention.
why do they still use a manual mixture control? im still a little surprised Rotax have just come up with a multi point EFI. not exactly a new invention.
Ultralights, it is easy to build a carby to automatically adjust mixture but with manual mixture control and a good EGT gauge, far more accurate adjustments can be made from on board. You may well want an engine that dumbs down everything but I don't. Tell me, how do you run LOP with auto mixture? Sure, magneto technology is old, but it sure is simple and in some ways I would prefer it to a bunch of electronic black boxes.
As a final note, have you ever seen just how easy it is to prop start an aircraft engine? My O360 will start with a barely perceptible movement of the prop. It is stunning to see just how easy it can be to start under the right circumstances. Using the mixture to stop the engine provides a margin of safety over and above ignition switches.
As a final note, have you ever seen just how easy it is to prop start an aircraft engine? My O360 will start with a barely perceptible movement of the prop. It is stunning to see just how easy it can be to start under the right circumstances. Using the mixture to stop the engine provides a margin of safety over and above ignition switches.
Last edited by Aussie Bob; 28th Jul 2013 at 05:18.
There was a recent failure of a 912 resulting in 2 deaths, but this was prop related apparently.
If this is the loss I think it is, the problem was an interaction between the type of prop. fitted and the engine, the result was a serious mechanical failure in the engine.
Always read the engine manufacturer's words of wisdom on props. very carefully, harmonics can ruin your whole day.
Tootle pip!!
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Variable Pitch Props
This failure was allegedly caused by a previous operator over stressing the crank by turning up (coarse) the variable pitch prop and raising the BMEP beyond limits. (time trial racing) The subsequent buyer then suffered an engine failure when the crank failed and a forced landing was unsuccessful. I have seen the photos of the crank in the report to the coroner (original copy by the author) and one of the recommendations of the coroner's report was that all RAA aircraft running a variable prop must be fitted with manifold pressure gauges.
Never seen a failure like it before or since
Never seen a failure like it before or since
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Course pitch effects BMEP ?? Peak pressure slightly, but I can show you these effects on dyno runs, and it is barely worth discussing. 
Please explain that, just because a coroner allegedly accepted it does NOT make the laws of physics change.
The reason the two died was because the pilot screwed up, big time. End of story.
The reason the crank failed was most likely due to significant problems induced by the deceased owner and his amazing maintenance problems. Read the coroners report closely and see why this is true.
The alleged damage from any time related records has nothing to do with it.
This was not a Rotax fault, nor the previous owner. The previous owner might have had some paperwork and regulatory issues, but the crank failure was not paper induced.
Plenty of people have survived a engine failure, despite crank failures, it was what they did after that that mattered.
How any of this can wind up BMEP on a Rotax is .....well tooth fairy stuff.
And a MP gauge in a NA aircraft is of very little value anyway, apart from calculating % power when ROP.
Please explain that, just because a coroner allegedly accepted it does NOT make the laws of physics change.
The reason the two died was because the pilot screwed up, big time. End of story.
The reason the crank failed was most likely due to significant problems induced by the deceased owner and his amazing maintenance problems. Read the coroners report closely and see why this is true.
The alleged damage from any time related records has nothing to do with it.
This was not a Rotax fault, nor the previous owner. The previous owner might have had some paperwork and regulatory issues, but the crank failure was not paper induced.
Plenty of people have survived a engine failure, despite crank failures, it was what they did after that that mattered.
How any of this can wind up BMEP on a Rotax is .....well tooth fairy stuff.
And a MP gauge in a NA aircraft is of very little value anyway, apart from calculating % power when ROP.
Last edited by Jabawocky; 28th Jul 2013 at 11:44.
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I'm not going to fuel what's coming across as essentially a religious debate (being happy to fly routinely with a Rotax 912 and the more traditional engines). However, Aussie Bob's assertion re unintended starts needs correction. With the supplied Rotax ignition system, you cannot in fact hand start the engine: it needs to swing at a few hundred rpm before the electronic module generates any spark at all. As a matter of fact, I've tended to regard this as a disadvantage.
I'm also quite happy to use a mixture control but I'd be surprised if I could improve much on my typical 15lph in the Rotax.
I'm also quite happy to use a mixture control but I'd be surprised if I could improve much on my typical 15lph in the Rotax.
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Jabawocky
your tone is becoming a little extreme isn't it? Keep in mind I have a lot of hours on these engines with my signature on it. When was the last time you pulled one to bits? Those really in the know are aware of the aircraft's history and I have cleaned up the mess before of the previous owners attempts at maintenance on aircraft in commercial service, done with no entry in the maintenance manual. Yes the pilot screwed up the landing but he is not here to defend himself is he?
Everybody knows what happens when you try and hill start a vehicle in 5th gear
Still claiming your naturally aspirated lyco is making .4?
your tone is becoming a little extreme isn't it? Keep in mind I have a lot of hours on these engines with my signature on it. When was the last time you pulled one to bits? Those really in the know are aware of the aircraft's history and I have cleaned up the mess before of the previous owners attempts at maintenance on aircraft in commercial service, done with no entry in the maintenance manual. Yes the pilot screwed up the landing but he is not here to defend himself is he?
Everybody knows what happens when you try and hill start a vehicle in 5th gear
Still claiming your naturally aspirated lyco is making .4?
Last edited by Oracle1; 28th Jul 2013 at 12:06.
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Explain your claim on how prop pitch has made a detrimental effect (increase) in BMEP.
I can calculate the BSFC really easy of my IO540 thanks, and show you the DATA.
How about you do the same?
I can calculate the BSFC really easy of my IO540 thanks, and show you the DATA.
How about you do the same?
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BMEP
The brake mean effective pressure differential (BMEPd) can be experimentally calculated if we know the engine power available at the crankshaft (brake horsepower, P) and the measured volumetric flow rate (Qm) of the air entering the engine's intake system:
BMEPd = P/Qm
we know from calculating the stings time over a set course that the engine was run at maximum power not max continous for an extended period of time so we know that BMEP would be higher than normal. Read my post carefully Jabba I did not say that the coarse prop caused the failure, I said the prop was coarsed to take advantage of the extra power and maintain a higher speed brought on by a higher BMEP over time. Yes peak pressures would have increased but as we have not got a dyno run of a rotax I think its a moot point don't you? Are you in a position to infer that any level of change in peak pressure wont affect the operation of a crank especially its harmonics and given we are already at higher than normal BMEP and this engine is running a gearbox?
RE MP gauges Q is a function of MP pressure and therefore gives an indication of BMEP.
Back off mate it doesn't make for a friendly forum
BMEPd = P/Qm
we know from calculating the stings time over a set course that the engine was run at maximum power not max continous for an extended period of time so we know that BMEP would be higher than normal. Read my post carefully Jabba I did not say that the coarse prop caused the failure, I said the prop was coarsed to take advantage of the extra power and maintain a higher speed brought on by a higher BMEP over time. Yes peak pressures would have increased but as we have not got a dyno run of a rotax I think its a moot point don't you? Are you in a position to infer that any level of change in peak pressure wont affect the operation of a crank especially its harmonics and given we are already at higher than normal BMEP and this engine is running a gearbox?
RE MP gauges Q is a function of MP pressure and therefore gives an indication of BMEP.
Back off mate it doesn't make for a friendly forum
Last edited by Oracle1; 28th Jul 2013 at 13:10.
Would the standard Continental and Lycoming engines benefit from the application of direct fuel injection and a small increase in compression ratio.
The Lycoming rep at the airshow told me that the Ie2 series full FADEC engines have not disappeared, just that the engines are being prepared fro military use and the US DoD is bankrolling its development, after which it will be released for public purchase. I belive the Ie2 does use direct injection.
How efficient are the 2 valve cylinderheads on standard C & L engines. In light of todays complex 4 valve , pentroof, stratified charge, tumble swirl cylinder heads of todays automotive engines, the aircraft cylinderheads seem very plain and low tech/inefficient.
Any comments?
The Lycoming rep at the airshow told me that the Ie2 series full FADEC engines have not disappeared, just that the engines are being prepared fro military use and the US DoD is bankrolling its development, after which it will be released for public purchase. I belive the Ie2 does use direct injection.
How efficient are the 2 valve cylinderheads on standard C & L engines. In light of todays complex 4 valve , pentroof, stratified charge, tumble swirl cylinder heads of todays automotive engines, the aircraft cylinderheads seem very plain and low tech/inefficient.
Any comments?