Which Engine?

[tomscub]

Hi Group,

 

There has probably been more experience collected on this site than any other in the world, regarding the Rotax 912 ULS, and the Jabiru 3300. These are my engine choices for my current project and I would like a consensus.

 

My thought:

 

The Jab has an extra 20 hp and more torque, but it is not as mature of a product.

 

Also, much less plumbing and a more simple engine.

 

It can happily burn 100LL

 

Single carb

 

Valve trouble as been noted.

 

There have been more than 15,000 912's built and they have a bullet proof lower end. Not sure about the top end. I understand that you can get in trouble up there by simply turning the prop backwards.

 

Also, some gearbox woes.

 

I sure would like to hear from some experienced users.

 

Thanks, in advance

 

Tom

 

 

[Guest Maj Millard]

To compare the 3300 with the 912 is like comparing the jab with a 737. One is well along in it's development cycle and emcompases many improvements and upgrades, whereas the other is still attempting to prove it's reliability. Which by the way, is the first thing an aircraft engine should be ....RELIABLE.

 

Without going too deeply, the 3300 needs two more cylinders to match the 912, more cylinders mean more fuel burn, and more parts. It has yet to even come close to matching the 912s in-service reliability, and has continuing problems with top ends, bottom end, rods, valves, pistons, oil pressure, cooling, carb ice, fuel pumps, etc. etc. not to mention all the unexplained stoppages throughout the range, usually around the 250 hr mark, or sooner. As an example: see report #1 in 'Pilot and Tecnical notes' Feb 09 RAA Mag.

 

The 912 will happily burn 100% avgas, and the operators manual will tell you that. They are also quite happy with Premium mogas, or a mix of both. You do need to select an oil that is suitable for 100% avgas, and change oil at 50 hrs. Most people do anyway. The Rotax gear box 'Woes' were the result of a bad batch of metal in the gears, is limited to a small % of production engines, and is easily checked for with a magnetic plug. Still I would rather have a gearbox than a broken crank any time. Turning the propellor backwards on any aircraft engine is not a real smart idea.

 

The Rotax 912 does not need to put itself agains the 3300. They already have thousands of safe operating hours all over the world behind them, and basically already have the 'runs on the board 'so to speak. I have not seen too many 3300s out bush doing the hard, hot yards, but I have replaced old 912s with thousands of hours on them, with brand new 912s. The owners, who use their 912s every day, in all temps, would have nothing else. When (if ever) the 3300 has a similiar history, then we can look back and compare the two, fairly, side by side. Don't get me wrong folks, I am stuanchly Australian, and will always support Aussie first every time if it's good. However I was also taught to call a spade a spade.............

 

 

[icebob]

Hi,

 

I would have to agree with Maj: Miller here, the 912 is a joy to do maintenance on. My main background is military aircraft and we all know how hard the maintenance on them is/can be.

 

Also another consideration I placed an order for Rotax parts and they arrived from interstate in four days with an appology for being slow. I also ordered Jab parts and four days later find them still on the way?????? Which would you choose?

 

The Rotax owners web site is also a gold mine of information plus videos of the latest maintenance activities,well worth it.

 

The Jab web site and engine maintenance is still in it's infancy so one should not expect the same or similar service information just yet but one then should ask how long has the Jab motors been around and why is there not more readily available information on day to day maintenance how to's on the Internet?

 

Sorry off the soap box now.

 

Bob.

 

 

[Guest brentc]

There's always 2 sides to the story and 2 ways to look at this! Whilst I do like the Rotax engine, I need to come to the defence of the 3300 as I've never in my life heard of these 250 hour stoppages! One of the biggest problems is user error, installation and maintenance.

 

Let's compare:

 

912 80 HP, 4 Cylinders, 1.2 Litres capacity

 

912s 100 HP, 4 Cylinders, 1.4 litres capacity

 

914 115 HP, 4 Cylinders, 1.2 litres capacity

 

RPM Continuous ~ 5100RPM

 

MAX continous power for 5 minutes only

 

Gearbox that has to be treated well to prevent rebuild

 

Water and Air Cooled

 

Lots of extra plumbing

 

Runs on any fuel

 

Requires cylinder de-coke every 400 hours when on Avgas

 

Requires 25 hourly oil changes on Avgas

 

Very expensive parts (valves $280 each)

 

Dual carbies are sometimes troublesome to balance

 

Complicated and expensive electronic ignition

 

Jabiru 3300, 120 HP, 6 cylinders, 3.3 litres capacity.

 

RPM Continuous ~ 2850RPM

 

Runs on 95+ octane

 

Runs happily on Avgas with no extra servicing required

 

Parts are cheap (Valves are $45 each)

 

Single carby, no balancing issues

 

Simple alternator and regulator with distributors

 

Direct drive so no gearbox overhaul cost come rebuild time

 

 

[BigPete]

Hmmmmmm......

 

I can see this thread going down the gurgler and becoming a "mine is better/bigger than yours" heated debate (debakle??) argument.

 

Suffice to say that some of us love :heart: Jabirus and will defend them until the cows come home and vice versa. :thumb_up:

 

I'd love to see a 100hp 4 cylinder Jab of around 2600cc and maybe a larger 6 as well (140hp and 3800cc - to move it away from the new 100hp 4). :big_grin:

 

I do envy the way the Rotax engined (100hp) aeroplanes perform at take off and climb out. That extra 15 - 20hp does make a difference.

 

regards

 

:big_grin::big_grin:

 

 

[gofastclint]

I guarantee if the Jabiru aircraft came with a Rotax option they would sell more, they have the runs on the board and have a lot of happy customers. I prefer the gearbox over direct drive any day, people will tell you that there are more things to go wrong with a gearbox but with direct drive, if there is any balance issues with the prop the crank will be effected more and the inertia will always transfer the load onto the one side of the crank that is hevier, with a gearbox the load will be spread out over all different points on the crank due to the gear ratio being different from 1to1.

 

From another direction, if you had 2 identical spec engines. same bore, same stroke, same bearing area but the only difference being 6 cylinder and the other 4 cylinder like an EJ22 and an EG33 from Subaru. the EG is just an EJ with 2 extra cylinders. The 6 would always last a lot longer due to the balence of the crank. In a 4 cylinder engine every 180 degrees the pistons are all totally stopped, this never happens with a 6 and as such the engine runs a lot smoother, this smothness adds to engine, gearbox and prop life.

 

If I was a manager for Rotax I would push for a 912 with 2 extra cylinders. oh yeah!!

 

Like the Maj said, "back the Aussie products when you can, but a spade is a spade"

 

 

[Guest Crezzi]

912 80 HP, 4 Cylinders, 1.2 Litres capacity

912s 100 HP, 4 Cylinders, 1.4 litres capacity

 

914 115 HP, 4 Cylinders, 1.2 litres capacity

 

RPM Continuous ~ 5100RPM

 

MAX continous power for 5 minutes only

 

Gearbox that has to be treated well to prevent rebuild

 

Water and Air Cooled

 

Lots of extra plumbing

 

Runs on any fuel

 

Requires cylinder de-coke every 400 hours when on Avgas

 

Requires 25 hourly oil changes on Avgas

 

Very expensive parts (valves $280 each)

 

Dual carbies are sometimes troublesome to balance

 

Complicated and expensive electronic ignition

In the interests of accuracy - max takeoff rpm for 912 is 5800 (for 5 mins only) & max continuous is 5500rpm. Operating on avgas for more than 30% of the time requires oil change at 50 hours rather than 100 - the relevent SB doesn't mention anything about a 400 hour de-coke though ?

 

Cheers

 

John

 

 

[Guest Maj Millard]

Actually a five cylinder engine is smoother than a six. Ever drive an Audi 5000, with the five cylinder engine ? I have often wondered which would have sold more, the Jab or Rotax, if Stiffie had offered both engines. There were two 912 powered Jabs at Hedlow field years ago, and they were pretty popular with the users...........

 

 

[gofastclint]

Actually a five cylinder engine is smoother than a six. Ever drive an Audi 5000, with the five cylinder engine ? I have often wondered which would have sold more, the Jab or Rotax, if Stiffie had offered both engines. There were two 912 powered Jabs at Hedlow field years ago, and they were pretty popular with the users...........

With regards to a 5 cylinder engine, it has a secondary balance issue that causes it to have a slight vibration. A 6 cylinder of the straight or horizontaly opposed configuration has no ballance issues making it a smooth running engine. That is why a V12 can have any Vee angle and still run smooth as it has theoreticaly 2 straight 6 motors that are balanced perfectly sharing the same crank.

 

 

[Guest brentc]

John, hence my use of the '~' symbol.........

 

One important part not really mentioned in detail is cost.

 

Last time I looked at the cost of a Rotax when I built my Jab with a view to install a 912S was that it was close to $20k and that didn't include the muffler etc. The Jab engine was $18,337 and included everything and came with another 20 horses.

 

Don't under-estimate the gearbox either. Usually at around 1,000 hours a 912 gearbox will require much work to be performed on it, particularly if it has been used on bitumen runways and taxiways. Why? Because they don't like being operated at low RPM as they 'chatter' and this causes damage. A good example of this would be the 2 Gazelle's that used to operate out of Point Cook. As they were opeating on bitumen they were run at low RPM to keep the taxi speeds down, rather than wear out the brakes. At just on 1,000 hours both of these aircraft required over $1k of gearbox repairs. Whereas the Gazelle's out at Sunbury operating on grass at higher taxi speeds were still chugging along with no issues at all. Will be interesting to hear how the Sportstars go in this regard at Moorabbin.

 

All I can say is that the most common engines in the world in aircraft, aka the Lycoming and Continentals don't run a gearbox and they don't rev at 5,800rpm! They chug along at a low rpm well within their limits and they practically last forever.

 

John - I would never run a 912 to 100 hours for an oil change no matter what fuel I was using. Is this in the service manual? I used to change mine at 50 hours when on unleaded or sooner on Avgas. The cylinder de-coke was required in my maintenance manual for the 912A.

 

 

[Guest Crezzi]

John, hence my use of the '~' symbol.........

Noted but I thought you'd appreciate the precise values ;-)

 

John - I would never run a 912 to 100 hours for an oil change no matter what fuel I was using. Is this in the service manual?

Yes, from the service manual for 912UL (which I believe also applies to the ULS) quotes oil change interval as 100 hours reducing to 50 hours if frequently run on avgas. No mention of decoke that I could find either. Interesting that its different from the certified engine .

 

Cheers

 

John

 

 

[gofastclint]

Sorry Brent '~'

 

 

[eightyknots]

There's always 2 sides to the story and 2 ways to look at this! Whilst I do like the Rotax engine, I need to come to the defence of the 3300 as I've never in my life heard of these 250 hour stoppages! One of the biggest problems is user error, installation and maintenance.Let's compare:

 

912 80 HP, 4 Cylinders, 1.2 Litres capacity

 

912s 100 HP, 4 Cylinders, 1.4 litres capacity

 

914 115 HP, 4 Cylinders, 1.2 litres capacity

 

RPM Continuous ~ 5100RPM

 

MAX continous power for 5 minutes only

 

Gearbox that has to be treated well to prevent rebuild

 

Water and Air Cooled

 

Lots of extra plumbing

 

Runs on any fuel

 

Requires cylinder de-coke every 400 hours when on Avgas

 

Requires 25 hourly oil changes on Avgas

 

Very expensive parts (valves $280 each)

 

Dual carbies are sometimes troublesome to balance

 

Complicated and expensive electronic ignition

 

Jabiru 3300, 120 HP, 6 cylinders, 3.3 litres capacity.

 

RPM Continuous ~ 2850RPM

 

Runs on 95+ octane

 

Runs happily on Avgas with no extra servicing required

 

Parts are cheap (Valves are $45 each)

 

Single carby, no balancing issues

 

Simple alternator and regulator with distributors

 

Direct drive so no gearbox overhaul cost come rebuild time

One important consideration in any comparison is the 'true' weight (i.e. all fluids in the engine and essential added parts attached). I wonder how good the weight comparison is between these two engines? Also there is now the ULP Power engine competing in the same market: it has EFI / FADEC / no carby.

 

 

[facthunter]

Comparo.

 

Without getting into the never ending thing about Jabiru and Rotax, you would want a more even handed and comprehensive analysis than presented there as a quote. Nev.

 

 

[HEON]

A nice Ford/Holden discussion...or is it?

 

When I finished my pilots certificate I wanted to buy a aircraft...asked the CFI at the school that ran both Rotax and Jab powered trainers about engines as I had heard stories about Jab reliability...told none of his Rotax's had broken: all of his Jab's had!

 

I know that Rotax cost more (just paid around $25,000 for 80hp with bits) but I now own three...80, 100, and 115hp. If I thought that Jab's were even equal I doubt that all would be Rotax's.

 

Gearbox problems?...do not run under 1800rpm/better around 2200. Yes in a Drifter that makes a rapid taxi speed which Drifter drivers know the brakes (????) are not much use in keeping in check...think/plan/stop engine if required. My 914 had the gears replaced (no cost) as in the bad batch. That is the only part ever replaced excluding filters.

 

Have said before a Jab 170 with 100hp Rotax IN MY OPINION would be a terrific Australian aircraft.

 

 

[Dieselten]

I have two aircraft, one powered by the Rotax 912 ULS, the other powered by a Jabiru 2.2 with hydraulic lifters but solid push-rods. I have some observations to make on these engines, for both of which I have the greatest respect. They are both good engines.

 

As the Jab engine had reached 500 hours and one cylinder was ever-so-slightly low on leak-down test (about 10psi), I decided to pre-emptively replace the exhaust-valves. This proved wise because one exhaust valve was on the way out and wouldn't have made it to the 1000 hour top-end overhaul, the rocker-rods were slightly worn and there was metal transfer from the rocker-bushes onto the rocker rods.

 

All these items were replaced, the inlet-valves were re-lapped, and the cylinder-heads were lapped to the cylinders for a good seal. The oil-cooler hoses were also replaced, as were the distributor-rotors, these being either scheduled items (oil-cooler hoses) or pre-emptive (rotors).

 

As the engine had run on Avgas until the last 25 hours when it ran 98-octane BP Ultimate as an experiment to see how much carbon and lead-oxide use of mogas, admittedly for a relatively short time, would remove.

 

The answer was "not much". My conclusion is to keep a clean engine you need to run 98-octane mogas all the time, although in my experience on this particular installation this makes the engine very susceptible to carburettor-icing, especially in the early morning at low ambient temperatures and high relative humidities - perfect conditions for carby-ice to form, especially when the engine has just started and there is no heat in the muffler to make the carby-heat effective.

 

The engine is less prone (but not immune) to carby-ice when running on Avgas, but engine deposits will build up due to the lead. These are easy to remove.

 

Result? I am now confident this particular engine will do another 500 hours with no issues (it did its first 500 hours perfectly trouble-free) and at 1000 hours the same process will occur, with a probable upgrade to high-flow hydraulic-lifters and hollow-push-rods.

 

Turning to my 912 engine, it has about 200 hours, has has oil changed every 25 hours for the first 100 hours, then at every 50 hours using Aeroshell SPort Plus 4 oil. It has also been trouble-free. The parts cost for a top end will greatly exceed that of the Jabiru, but it will need just the routine line maintenance until that time.

 

I can assure users that with the Rotax you will not be "putting the spanners to it" as frequently as you do with the Jabiru, but any engine is only as good as the way it is operated and the way it is maintained.

 

Keep the maintenance up to the Jabiru engine and it will run willingly and hard, but aircraft engines are consumable items. The great engine designer and thermodynamicist Sir Stanley Hooker once famously said "a four-stroke engine has one stroke to make power and the other three to wear it out!"

 

The two engines are very different designs and a direct comparison is difficult. I can only report on what I have experienced with the 2.2 Jabiru engine, and for those using them I would suggest a 500-hour "mini top-end" such as I outlined above as e a very wise precaution to give the best possible chance of reaching the 1000 hours for a full top-end overhaul. A few hundred dollars spent at 500 hours may save many thousands later on.

 

 

[alf jessup]

John, hence my use of the '~' symbol.........

All I can say is that the most common engines in the world in aircraft, aka the Lycoming and Continentals don't run a gearbox and they don't rev at 5,800rpm! They chug along at a low rpm well within their limits and they practically last forever.

 

Brent,

 

Very true about the lyc's and continentals.

 

Cars dont run direct drives and neither do bikes and they can rev out to upwards of 18000 rpm and they have gearboxes, have water cooling with plenty of hoses and they dont wear out all that often.

 

I used to see the difference between water cooled and air cooled bikes when i had them over the years, the air cooled ones all used to loose there crispness over a period of time due to the expansion and contraction of the cylinders, where as the liquid cooled ones had a more uniform temprature rage all the time and lasted much longer

 

What we have in the 912 is a very proven engine over a very long time.

 

I am sure the Jab's will prove themselves over time as they are relativley new on the scene and might i say are going a might fine job.

 

Yes I know I am comparing car engines to aircraft ones but all in all they all are a just a peice of metal with lots of moving bits to create some form of momentum for us to harness.

 

Cheers

 

Alf

[Sloper]

Ok l'll throw this into the mix.

 

Home

 

l am serioursly considering both the Honda and Suburu conversion from this place.

 

regards Bruce

 

 

[Guest milton56]

912 for me, seems to have less problems than some other's.

 

 

[Sloper]

Looking at using one in a experimental. :)

 

If you look carefully at the power and tourqe curves they are much better than a Jab 6 at 75% throttle.

 

regards Bruce

 

 

[eightyknots]

I know that Rotax cost more (just paid around $25,000 for 80hp with bits) but I now own three...80, 100, and 115hp. If I thought that Jab's were even equal I doubt that all would be Rotax's.

Heon, you're the only person I know who owns all three four-stroke Rotax variants. I'm looking at an engine for a kit plane I want to build of 'around 100 hp'. I would love to hear your thoughts and experiences as a comparison for these three engines.

 

 

[HEON]

Of the three four stroke Rotax, which one?

 

Personally the 914 is great (with adjustable prop) to shorten take off, and also get up high. Mine in Speed seems happy around 5100rpm for around 21L/hr. Have to question however the large purchase price difference to 912.

 

Have not put a lot of time on 912ULS (100hp) as yet but it seems happy at around 5200rpm for around 19.5L/hr. Is the smoothest of the three I own but that could well be the mounts etc.

 

The 912UL (80hp) being in a Drifter is used at much lower rpm (around 4600 for around 13L/hr) due to the aircraft thus hard to do direct comparison with the others. From third hand reports this engine will often go twice TBO without problems.

 

Myself if lighter aircraft 80hp, otherwise the 100hp. The small increase in price of 100hp rearly makes you question is the purchase saving worth 20% less power for the 80hp. I know the 80hp can use standard unleaded over the others requirement for 95/98 however this advantage is of less advantage now as standard is increasingly having ethernol added.

 

If you can afford the extra price go 115hp as you can never rearly have too much power, and it's there if you need it. More now in use as the gyro's like them. They do not like Avgas 100; 100LL is OK.

 

All now 2000hr TBO thus Rotax must think they will all get there or they would not have raised the TBO's.

 

I personally would have any one...you rearly have to chose the best for your usage. You probably should not put a 914 in a Drifter (excessive power), or a 912UL in a LSA (excessive MTOW) for instance...you could do it but not best choise in my opinion.