Rotax 912 iS
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Rotax 912 iS
Hi,
I'm part of an LSA build and need to make an informed decision regarding engine choice.
We have reluctantly decided to give the Jabiru 3300 a miss due to reliability concerns. This seems to have left us with a choice of either a Rotax 912 ULS or Rotax 912 iS.
We have developed a bias towards the fuel injected 912 iS as the fuel savings would cover the higher purchase cost.
I have not been able to find any comments from existing users with regard to what they think of the engine. May be it's just too new for any impressions/feedback to be available.
I would welcome any thoughts or comments from the forum.
Thanks
NTB
I'm part of an LSA build and need to make an informed decision regarding engine choice.
We have reluctantly decided to give the Jabiru 3300 a miss due to reliability concerns. This seems to have left us with a choice of either a Rotax 912 ULS or Rotax 912 iS.
We have developed a bias towards the fuel injected 912 iS as the fuel savings would cover the higher purchase cost.
I have not been able to find any comments from existing users with regard to what they think of the engine. May be it's just too new for any impressions/feedback to be available.
I would welcome any thoughts or comments from the forum.
Thanks
NTB
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My thoughts are that any fuel saving is outweighed by the complexity of the engine and its fuel system :-
The basic weight of the 912is is 7kgs heavier than the carb version and this is before the extra weight of the very complicated fuel sysytem is installed which will add more extra weight.
Doing any future maintenance work on it yourself will be ruled out due to the complexity of the injection/electronics needing specialist diagnostic equipment. So any problems incurred in the future are going to cost more.
The conventional 912 carburettor version is in my opinion a far better bet for an LAA machine where the maintenance will be in the main carried out by the owner/s. I am all for keeping it simple.
This is before taking price into consideration, the simple fact is that the 912is intial cost is 5K more than the 912uls!....it is a no brainer IMHO
The basic weight of the 912is is 7kgs heavier than the carb version and this is before the extra weight of the very complicated fuel sysytem is installed which will add more extra weight.
Doing any future maintenance work on it yourself will be ruled out due to the complexity of the injection/electronics needing specialist diagnostic equipment. So any problems incurred in the future are going to cost more.
The conventional 912 carburettor version is in my opinion a far better bet for an LAA machine where the maintenance will be in the main carried out by the owner/s. I am all for keeping it simple.
This is before taking price into consideration, the simple fact is that the 912is intial cost is 5K more than the 912uls!....it is a no brainer IMHO
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Thank you for your thoughts SF.
The maintenance aspects I had not considered, the 7kg of additional weight I viewed as being offset by not needing to carry as much fuel. Rotax are claiming 20 - 30% less fuel burn.
The reliability of the 912 iS design is of concern at this early stage in its life with little history.
The 912 iS is claimed to be much smoother running with lower vibration.
The drawbacks of the 912 ULS as I understand it are:
Carb rubber mounting splitting
Carb balancing issues
Having only operated Lycomings in the past I only have Internet information relating to the Rotax engines.
NTB
The maintenance aspects I had not considered, the 7kg of additional weight I viewed as being offset by not needing to carry as much fuel. Rotax are claiming 20 - 30% less fuel burn.
The reliability of the 912 iS design is of concern at this early stage in its life with little history.
The 912 iS is claimed to be much smoother running with lower vibration.
The drawbacks of the 912 ULS as I understand it are:
Carb rubber mounting splitting
Carb balancing issues
Having only operated Lycomings in the past I only have Internet information relating to the Rotax engines.
NTB
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>> Carb Balancing Issues
Not really an issue - buy a carb balancing kit, about £35. The process is very simple and only needs to be done once a year or so. After the first time I found that very little (if any) adjustment was required at later checks.
I would agree that for a permit aircraft the carb version is more practical from a maintenance POV.
>> Carb rubber mounting splitting
Again not a major issue if regularly checked (at 100 hour service) not difficult to replace but they are relatively expensive - if I remember rightly about £120. the pair BUT I would not expect to have to replace them more often than every 3 - 4 years, so not exactly a major expense concern and would definitely be less than the extra costof 3rd party mintenance for the fuel injection system.
Hope this helps
Not really an issue - buy a carb balancing kit, about £35. The process is very simple and only needs to be done once a year or so. After the first time I found that very little (if any) adjustment was required at later checks.
I would agree that for a permit aircraft the carb version is more practical from a maintenance POV.
>> Carb rubber mounting splitting
Again not a major issue if regularly checked (at 100 hour service) not difficult to replace but they are relatively expensive - if I remember rightly about £120. the pair BUT I would not expect to have to replace them more often than every 3 - 4 years, so not exactly a major expense concern and would definitely be less than the extra costof 3rd party mintenance for the fuel injection system.
Hope this helps
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Interested in your comment about the Jab. I'm aware the early engines did have some problems but speaking to someone at the Flying Show the claimed the quality and reliability was much improved.
Is your opinion based on facts such as comparisons of Mean Time Between Failures or comments from other pilots?
I've no connection with any engine manufacturer and have as my favourite they good ol' Vee Dub.
SGC
Is your opinion based on facts such as comparisons of Mean Time Between Failures or comments from other pilots?
I've no connection with any engine manufacturer and have as my favourite they good ol' Vee Dub.
SGC
Last edited by Sir George Cayley; 19th Jan 2014 at 10:05. Reason: spellink 'n punctuation
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NTB
Carb balancing is a yearly or less regular maintenance none event, so I wouldn't worry about it at all.
As for carb sockets splitting...true there have been some issues with them splitting but this is usually caused by the aircraft manufacturer not utilising the Rotax or similar airbox.These type of installations merely have an air filter hanging off a flexibly mounted carburettor, which is totally inadequate, hence in time the socket splits and the rumour starts that Rotax carbs sockets are a problem...
With the correct airbox utilised they do not split. My guess and I may be wrong is you are talking about an engine installation in a Bristell which comes with a Rotax copy ( their own)airbox which will do the job admirably and should cause you virtually no issues.
As for not fitting the Jab....wise decision IMHO regardless of what Farry says!
Carb balancing is a yearly or less regular maintenance none event, so I wouldn't worry about it at all.
As for carb sockets splitting...true there have been some issues with them splitting but this is usually caused by the aircraft manufacturer not utilising the Rotax or similar airbox.These type of installations merely have an air filter hanging off a flexibly mounted carburettor, which is totally inadequate, hence in time the socket splits and the rumour starts that Rotax carbs sockets are a problem...
With the correct airbox utilised they do not split. My guess and I may be wrong is you are talking about an engine installation in a Bristell which comes with a Rotax copy ( their own)airbox which will do the job admirably and should cause you virtually no issues.
As for not fitting the Jab....wise decision IMHO regardless of what Farry says!
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Don't the Rotax 912 s suffer problems with the crankshafts that require the unit to be stripped down every 300 hrs to check for cracks or have they sorted that problem out now??
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You're thinking about the 2 stroke Rotaxes.
The 9 series of four stroke engines are completely different and are superb power plants.
It might be worth reading the thread below which gives some more detail about ULS problems and other views on the Jab. You bought to consider the UL Power engine too. No gearbox, no water coolant system and fuel injected. If I specifically wanted fuel injection it's the way I'd go personally. Rotax are charging jut to much for the 9 series now IMHO.
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The 9 series of four stroke engines are completely different and are superb power plants.
It might be worth reading the thread below which gives some more detail about ULS problems and other views on the Jab. You bought to consider the UL Power engine too. No gearbox, no water coolant system and fuel injected. If I specifically wanted fuel injection it's the way I'd go personally. Rotax are charging jut to much for the 9 series now IMHO.
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You could look at the "pacific" sub-forum here...there's quite a tale about Jab engines,the lack of factory support and the total denial that the engines are less than perfect......a real lesson in "how to ruin a reputation and kill a business"
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I have a friend with a 3300 Jabiru, he operates it carefully - but after one long taxiing session it still dropped three valve seats. This is after various misfiring and generating issues. Would be a good engine - if they actually engineered it properly and did not fiddle about. I know a guy with the original 80hp - who had no problems until he fitted the Jabiru 'economy' jets and then promptly had a partial seizure.....
But the 912ULS is a very expensive engine. I have to say I love mine, I finally have an aircraft engine which requires only servicing, no routine replacement of worn out or badly engineered parts. The only downside is that it is frankly grossly over priced. I've looked at the 912iS and it is a very complicated 'solution'. The complexity is as yet unproven in terms of reliability and in the last couple of years it has become apparent that Rotax quality control is little better than Lycoming or Continental - so much for certification.
On that basis I would not go for the 912iS. If there are issues then the Rotax warranty is less than generous and their approach to claims is difficult. The ULS is a pretty good engine if operated carefully and serviced as it should be. The ability to fault find the iS is going to be much less widespread and require equipment that individual owners are unlikely to be able to afford. If the iS systems had 5 years of faultless service I would plump for them immediately - but they do not and even Rotax tend to use 'early adopters' as guinea pigs.
But the 912ULS is a very expensive engine. I have to say I love mine, I finally have an aircraft engine which requires only servicing, no routine replacement of worn out or badly engineered parts. The only downside is that it is frankly grossly over priced. I've looked at the 912iS and it is a very complicated 'solution'. The complexity is as yet unproven in terms of reliability and in the last couple of years it has become apparent that Rotax quality control is little better than Lycoming or Continental - so much for certification.
On that basis I would not go for the 912iS. If there are issues then the Rotax warranty is less than generous and their approach to claims is difficult. The ULS is a pretty good engine if operated carefully and serviced as it should be. The ability to fault find the iS is going to be much less widespread and require equipment that individual owners are unlikely to be able to afford. If the iS systems had 5 years of faultless service I would plump for them immediately - but they do not and even Rotax tend to use 'early adopters' as guinea pigs.
Rotax are claiming 20 - 30% less fuel burn.
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Skydrive supplied me with a carb heat kit for my 912UL and once fitted [it warms the carb body thus preventing any ice formation] I never had any indication of icing even in wintry weather. I did wait for coolant temp to steady on v. cold days. Sky Arrow 650T
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Considering that the 912UL sips cheap Mogas at a very low rate, and all the other sundry costs related to aircraft ownership/building, would this alleged saving be of any significance?
Assume a "normal,carburetted" burn of 3 GPH, and assume the saving
is 25% with injection, that would be 3.4 Lph....(£4.26 )
a hundred hours a year would save £425, so well over 10 years to recoup the extra cost, even ignoring the loss of interest or cost of the extra 5K initial purchase.
Personally, I'm a big fan of injection....beautiful clean burn must be good for the engine as well as the wallet. It's normally robust and maintenance free, doesn't wear unpredictably like carbs...and , usually, doesn't falloff or introduce mystery induction leaks due to perished mountings.
Having said that, The rotax application is IMO, grossly overpriced,
though I have just seen a price for overhauling a pair of Rotax carbs and it made my eyes water...I really did lose my way, mending cars and motorcycles!
I have just seen a price for overhauling a pair of Rotax carbs and it made my eyes water...I really did lose my way, mending cars and motorcycles!
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Thank you to the contributors of this thread,
I will spend a some time mulling over what has been said, particularly the ability to maintain the engine your self.
Currently still leaning towards the iS.
The UL Power engine has not been approved/designed in to the airframe yet.
NTB
I will spend a some time mulling over what has been said, particularly the ability to maintain the engine your self.
Currently still leaning towards the iS.
The UL Power engine has not been approved/designed in to the airframe yet.
NTB
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NTB
Are you sure that the LAA have approved the installation of a 912is in the particular aircraft that you are building?...I would give them a call otherwise you could be months/years getting it approved. Whilst it may have been designed/approved outside of the UK by another authority, getting it through the LAA treacle usually takes lots of time.
Are you sure that the LAA have approved the installation of a 912is in the particular aircraft that you are building?...I would give them a call otherwise you could be months/years getting it approved. Whilst it may have been designed/approved outside of the UK by another authority, getting it through the LAA treacle usually takes lots of time.
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I would have though that the 912is main area will be in aircraft used at flight school were 500 hours is the norm (p2006 ?) And in that environment the reduced fuel burn will pay for the extra initial cost within a couple of years.
I also expect that at some point the tbo will increase further.
I also expect that at some point the tbo will increase further.
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Whatever you do, steer well clear of Jabiru. I am leaning towards a Pipistrel Virus SW with a Rotax 912 iS. But reading the problems arising with overheating and power loss and am now not sure.