Rotax 912 iS

[NoTurningBack]

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

[Shoestring Flyer]

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

[NoTurningBack]

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

[funfly]

I had a heated carb inlet when I has a Rotax which helps with any concerns about carb icing on a non injected engine, if that's a factor in your decision.

[Choxolate]

>> 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

[Sir George Cayley]

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

[Shoestring Flyer]

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!

[lutonvarieze]

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??

[patowalker]

TBO on a new Rotax 912 is 2000 hours.

[Monocock]

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.

FLYER Forums ? View topic - Rotax V. Jabiru (http://forums.flyer.co.uk/viewtopic.php?f=40&t=87113)

[cockney steve]

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"

[gasax]

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.

[EDMJ]

Rotax are claiming 20 - 30% less fuel burn.

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?

[aviate1138]

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

SKYDRIVE :: Products (http://www.skydrive.co.uk/products.asp?cat=36)

[cockney steve]

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?


UK Mogas is ,locally ~£1.25 a litre...£5.68 per Imperial gallon (4.546 L)
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!

[Silvaire1]

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!

The carbs fitted to the Rotax 912 are Bing motorcycle carbs, as fitted to BMW R-Series bikes from the early 70s through mid 90s. The venturi size is slightly different, but not much else.

[NoTurningBack]

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

[Shoestring Flyer]

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.

[Mickey Kaye]

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.

[Baywatcher]

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.

[Cows getting bigger]

I've sat behind various versions of the Rotax 912. Whilst the iS is a technological step forward, I'm not sure it is true to the relative simplicity of the 912 design and do you really need to sip even less fuel than can be achieved by the carb version? Personally, I think the best engine is the plain old 912 as it runs more smoothly than the 912S. I would go for this one unless you feel that you need the extra 20 or so horses.

[Baywatcher]

Rotax replaced some fuel pumps and we replaced some filters but later there are no complains registered is the reply from Pipistrel. There are now over 60 912iS Pipistrel flying.........

[bartonflyer]

Flight Design offer both the Carb & injected versions on the CTLS range. In the USA since the arrival of the injected version I think that has been the only option chosen.

If you take a browse around Flight Design CTSW CTLS CTLSi C4 Forum (http://ctflier.com) you'll find plenty of discussion there. Warning!!! Ignore any posts there from a guy called 100hamburgers - he's a ******** (I think it's obligatory for all forums to have at least one!)

FWIW I am very happy with the carburetted version in my CTLS ~ 450 hours now from new and still purring along. The weight penalty and extra complication (needs fuel header tank etc) seem too great for the gains claimed.

[Rod1]

What Shoestring Flyer said.

Operated my 912uls for the last 9 years with zero issues. You will use 18.5lph.

Rod1

[Colibri49]

D-Motor promises to be the future for small light aircraft. It's a marriage of very old and modern technologies to produce plenty of power, while being light and economical. It will fit directly into frames designed for Jabiru engines, occupying less space inside the cowls due to the absence of overhead valve gear. Also becoming available as a 6 cylinder. https://www.youtube.com/watch?v=wxK_GcZ3RSQ

[letpmar]

I built own and operate a Sportcruiser with a 912uls and gave also just finished a Bristell with a 912is.
I think the remarks made that the ULS is a lot simpler are very true and cheaper if you do the usual low annual flying if mist users. There is a lot to be said for the ULS and I don't think you would be disappointed, It's by far and away the mist used 4 stroke out there, and I firmly believe in following the herd. We deliberately aimed for a very top speck aircraft with the Bristell with Twin Garmin Glass and autopilot, we chose the IS to match. So far we have only ground run it and it's smoother than the ULS. Rotax staff have told me it actually produces 105 horse but we will see. So far we are very happy with it but it's very early days. Having done both now the IS is a lot more complicated to install and we needed professional help, I would happily do a ULS myself. I use Gary Masters (air masters) and I give him our Sportcruiser every year for an annual as I like someone else to look at it. So the maintenance costs to us aren't that different. Give me a call if you want to look at both engines, I would suggest with less experience and fir a lot of people's flying the ULS is the best start.
Pete 07976262833

[Jan Olieslagers]

D-Motor promises to be the future

... as so many have promised ...
Not that I believe my countrymen's work to be poor, nor the resulting offer (=product+price+service). But I'd prefer to see the promise proven.