Rotax Stator Rumor

[gbigs]

In terms of complexity, the 912iS is actually a simpler engine when you consider the elimination of the dual self leaning carburetors which are finicky items that haven't been in cars (or in this case, dual carbs, so motorcycles) for decades.  

 

 

Yes. The 912iS is simpler to operate due to the fuel-injection system, the ECU and electronic ignition system (FADEC like).  The computer optimizes the operation of the engine.  It's a big reason why the engine has nearly a 30% higher fuel efficiency over the ULS version.  And why the operator need not worry about icing conditions or the troubles associated with carburetors.

 

New sales of planes with the option to either have the 912ULS or the 912iS engine are 100% 912iS.  The extra cost is quickly returned in fuel savings.

 

I no longer own the CTLSi...having sold it last month.  But it was a great plane and far simpler to operate than my new plane, a Cirrus SR22T.  Though the Cirrus is also fuel-injected it does not have a FADEC system and does not manage fuel flow like the 912iS did.

 

And welcome to the site.  Though most here own a plane with a Rotax engine they are mostly Flight Design CT owners.  There are a couple of guys here who are expert on the different permutations of the engine and can answer question well if you have any....

[Duane Jefts]

My experience is that  the 912iS engine vs the 912ULS experiences about a 15% fuel savings.  The savings are more pronounced at higher altitudes.

 

I fly a iS in formation with a ULS quite often and have a direct comparison.  Savings are not 30%.

 

Savings  were closer to 20% before the sport upgrade but after the upgrade, it added a little horsepower and the savings were somewhat reduced.

[IrishAl]

 after the upgrade, it added a little horsepower and the savings were somewhat reduced.

 

Interesting comment.

 

Am I right in thinking that the official power rating on the 912iS is still 100 hp?

 

Does anyone know what the actual difference is in power output compared to the ULS?

[Tom Baker]

Interesting comment.

 

Am I right in thinking that the official power rating on the 912iS is still 100 hp?

 

Does anyone know what the actual difference is in power output compared to the ULS?

 

Both are 100hp. The torque for the 912ULS is 94ft/lb and 912iS is 97ft/lb with the sport upgrade. Prior to the sport upgrade the 912iS was lacking in performance compared to the 912ULS. After the sport upgrade they are pretty even as best that I can tell sitting in the seat flying the airplane.

[912iS Fanatic]

Datasheet_Rotax 912 iS Sport_100hp_A4_red.pdf This is the best comparison, from Rotax. The 912iS Sport definitely feels much more powerful comparing it directly with the ULS in test flights.

[FlyingMonkey]

I think any performance gains are swallowed up by the additional weight.  The engine makes 4% more torque...but weighs over 14% more.

 

I consider the two engines to be equivalent in performance; overall airplane weight will have more effect that which engine is installed.  Nobody has shown any speed or climb gains in a CT.  I think fuel economy is the only measurable plus, and the additional $4000 price will pay for a lot of gasoline.

[912iS Fanatic]

The difference is significant due to RPM optimization. The torque curve has been optimized for the normal operating speeds of the engine. There is a similar series of graphs on Rotax-owner.com and the horsepower is also higher at the same range that the torque is higher for the 912iS versus the ULS. There is a lot of data on the Rotax website, too much to try to download on my iPhone to be sure.

[FlyingMonkey]

The difference is significant due to RPM optimization. The torque curve has been optimized for the normal operating speeds of the engine. There is a similar series of graphs on Rotax-owner.com and the horsepower is also higher at the same range that the torque is higher for the 912iS versus the ULS. There is a lot of data on the Rotax website, too much to try to download on my iPhone to be sure.

 

So then...where is the performance advantage in either speed or climb?  All of what you said might be true, but it still has to drag around 14% more weight than the 912ULS.  If it can't overcome that disadvantage with increased performance, it's a moot point.

[gbigs]

Interesting comment.

 

Am I right in thinking that the official power rating on the 912iS is still 100 hp?

 

Does anyone know what the actual difference is in power output compared to the ULS?

 

I didn't want to comment but the sport upgrade did not increase HP.  It increased torque.  The fuel efficiency as Rotax reports was experienced by us in the CTLSi.

[FastEddieB]

All of what you said might be true, but it still has to drag around 14% more weight than the 912ULS.

Well, to be fair, is it not just the engine and associated extras that weigh 14% more?

 

You're making it sound as if the whole aircraft is 14% heavier. That's not the case, is it?

[Ed Cesnalis]

Torque is not power, power is power.  Both engines have the same power ratings and same limitations allowing access to that power.

[912iS Fanatic]

There are a number of tangible benefits between the two. In our family my brother operates a ULS and I operating the iS sport. Different airframes so can't comment on in flight differential except fuel burns, and my airplane routinely operates below 4gph and is faster by about 12 knots and climbs out at 900+fpm when his is doing 500fpm. Likely that's more airframe than engine but when it's time for service, there is a big difference. He has had a lot of issues with the carbs and the need to balance them every 200 hours, replacing floats, and rebuilding and/or replacing them within the TBO interval of the engine. When he purchased his CT the iS wasn't an option but he would opt for the iS now for sure.

 

Also, every bit of operating and maintenance data and fault data is stored by the computers and when you download them it is really easy to diagnose the engine or just see if it has ever been overheated, over revved or otherwise abused at any time during its lifetime. While new this may not seem important buying new, if buying a used plane you get the benefit of knowing exactly how it was treated.

 

My plane came equipped with a Rotax engine monitor: http://www.stockflightsystems.com/emu-912is.htmlThis allows you to have complete access to every engine parameter and there are some great writeups on various websites as to the capability this gives. This has also free'd up real estate on my G3X displays though I also have "steam gauge" backups and can use the G3X engine pages. This puts any faults into plain english instead of codes, allows you to see exactly what the engine is doing, and allows really simple downloads. If you don't get this and use your G3X or Dynon you still have access to more engine parameters than a ULS engine but in order to get the history data you need a "dongle" and software for your computer.

 

The dongle is a cable that plugs into the ECU (like the data port on your car), and the software reads it. The dongle and software sells for under $1000 and my Rotax mechanic has it. I don't own a code reader for my car but would consider it for my plane if I didn't already have the Rotax EMU. If you own an iS engine you can buy it yourself but any mechanic who works on your plane will need one. If your mechanic doesn't have one I'd buy it since I'm sure it'll pay for itself if there ever is a fault you need to diagnose.

 

My point is that not that this gear is necessary but that you are getting a truly modern engine, finally on par with what we've had in cars for years. Troubleshooting the engine is no longer reserved for an "expert" but can be done just like it is done at the car dealership, hook it up and let the computer tell you what is going on. The system is flawless and no other GA piston engine even gives you the capability. I don't know if you can order the Rotax EMU on a CT but if you can get one in your plane it is worth far more, to me at least, than additional glass displays in my VFR airplane.

 

For me this is a tangible benefit. It increases my confidence in the engine/airplane substantially and this capability, more so than the reduced fuel flow and increased performance and redundancy is why I am so thankful for Rotax's investment in making this modern engine a reality in GA. I'm certain there are those who will not think the cost benefit makes sense but for me it is a game changer. I have paid dearly for mechanics chasing down faults in GA airplanes over the years and this is long overdo and would have saved me thousands in maintenance in the last couple of decades. I think any tradeoff between the two engines should consider the whole picture on the iS.

[gbigs]

Well, to be fair, is it not just the engine and associated extras that weigh 14% more?

 

You're making it sound as if the whole aircraft is 14% heavier. That's not the case, is it?

 

The 912iS is about 35lbs heavier than the 912ULS.   Given the huge differences in fuel injection (none of the carb problems), dual alternators, better Iron Lithium battery, ECU (FADEC like control), fuel efficiency increase, increased torque, and solid state ignition that small weight delta is a non sequeter.

[FlyingMonkey]

Well, to be fair, is it not just the engine and associated extras that weigh 14% more?

 

You're making it sound as if the whole aircraft is 14% heavier. That's not the case, is it?

 

That was not my intention.  I meant the engine weighs 14% more.  That is a disadvantage that would likely be barely compensated for by a whopping 3 foot pounds of torque.

[FlyingMonkey]

The 912iS is about 35lbs heavier than the 912ULS.   Given the huge differences in fuel injection (none of the carb problems), dual alternators, better Iron Lithium battery, ECU (FADEC like control), fuel efficiency increase, increased torque, and solid state ignition that small weight delta is a non sequeter.

 

None of that is performance difference.  You can make any argument you want about better reliability, better technology, ease of operation, or fuel efficiency.  None of that has anything to do with how the engine performs when attached to an airplane.  Having a performance discussion and then claiming victory because of dual alternators is the real non sequitur.

 

BTW, my numbers were based on an 18lb weight delta.  If the actual weight difference is 35lb, that is actually a 28% weight difference.  As a politician might say: "That Yuuuuge!"

[FlyingMonkey]

There are a number of tangible benefits between the two. In our family my brother operates a ULS and I operating the iS sport. Different airframes so can't comment on in flight differential except fuel burns, and my airplane routinely operates below 4gph and is faster by about 12 knots and climbs out at 900+fpm when his is doing 500fpm. Likely that's more airframe than engine but when it's time for service, there is a big difference. He has had a lot of issues with the carbs and the need to balance them every 200 hours, replacing floats, and rebuilding and/or replacing them within the TBO interval of the engine. When he purchased his CT the iS wasn't an option but he would opt for the iS now for sure.

 

 

What type of airplanes are these?  They are clearly not CTs, or if they are the 912ULS powered plane is in sad need of maintenance or repair.  On a cold day my 912ULS powered CTSW sees 1100fpm, and gets 900fpm in the dead of 100°F Georgia summer.

 

Balancing is not an "issue", it's regular maintenance that takes about ten minutes.  There was a float service bulletin, but it was a lot easier to comply with that the 912iS stator service bulletin...     My point is that no airplane is maintenance or trouble free, and one can make the argument that all of the redundancy in the 912iS provides more components for failure, which might raise maintenance costs. 

 

I like the iS engine, but I tend to like the "simpler is better" philosophy where possible, and don't think the advantages outweigh the costs at this point.

[Anticept]

When 100LL goes away, rotax plans on implementing live tuning with o2 sensors. That is when things will get interesting.

 

I wonder how well a throttle body injection system would work on a ULS...

[pointpergame]

From the peanut gallery an innocent question:

   35 lbs seems like a big switch for taking out a couple carbs and putting in a black box and some injectors.   In a few words, where does the increase of weight come from in the change from ULS to iS  ?

[Anticept]

The two engines are quite different. While the iS is inspired by the ULS, much of it is a ground up redesign.

 

Does anyone know if they switched to roller tappets? Those are pretty heavy compared to flat tappets.

 

The shift to two alternators and gearing to drive them adds up too.

[FastEddieB]

Doesn't the installation also call for a second, backup battery?

[912iS Fanatic]

goto flyrotax.com. Do the math on the two engines and its less than 16#. Dig into the spec sheets and compare away, much more engine. Compare horsepower and torque curves, not point values, much more informative. You get dual alternators and other features and redundancy not only the elimination of the carbs. There is too much conjecture going on here to base a purchase decision on when you can simply go to their website and compare for yourself. For me, no comparison, for others it is a mission decision. We have 4 pilots flying in the family. It took me a long time to accept Rotax versus the old standards but no time at all to understand the benefits of the most modern engine. My dad took a long time to get over radials and go to flat engines. All 4 of us will go back to single engine turbines and suffer low altitude fuel burns if class 3 comes out as expected. It's all a choice.

[Anticept]

Performance curves don't do a thing for anyone if they are similarly performing in the operating range. You're cherry-picking the things that back your bias and downplaying others. That's what marketers do, not engineers.

 

I looked at the datasheets. They are incredibly misleading. The torque graph goes from 110 to 135. At take off RPM, which is generally around 5000-5200rpm, there's a whole 6-7Nm difference of the iS vs ULS. That's a little over 4 foot pounds. We're already talking about 130ish newton meters, saying you've got 6-7 more just makes me go "neat", not "wow". Plus for some people on this forum who live at higher altitudes, that datasheet shows that the iS would perform WORSE at higher altitudes for takeoff torque.

 

Is the iS the better engine? In many ways, yes. But you're kind of making it sound like it's god's gift to the planet (again, like another person here). I like where it's going, but it's not enough of a difference to convince me to switch. If I was a new airplane buyer? I'd probably go for the iS. But the benefits just aren't there for switching yet.

 

How you are saying things is kind of rubbing me a little bit. I don't know how others feel so I'll try not to speak for them. I'm still welcoming you to hang around and debate by all means, but you're ignoring the points others are making (where is the climb realization as someone asked?) while continuing to restate the same points again and again that we've already acknowledged.

 

Anyways, the parts catalog shows it has flat tappets. Some parts look pretty beefy though compared to the ULS in the parts catalog, but take that with a grain of salt.

[FastEddieB]

goto flyrotax.com. Do the math on the two engines and its less than 16#.

Again, I think the larger (and more realistic) numbers are coming from including the required ancillary equipment.

 

The Flight Design USA site lists these empty weights:

 

CTLS: 730 lbs.

 

CTLSi: 810 lbs.

 

It also shows the same climb rate and cruise speed for each.

 

In the world of Light Sport, 80 extra lbs of empty weight is non-trivial.

 

Stipulated that the CTLSi might carry more standard equipment, but still...

[Roger Lee]

Depending on the aircraft MFG the weight gain is 16-20 lbs. This depends on things like mounting hardware, cowl re-makes, ect...

 

The 912is engine is better in some areas and the same as the ULS in others. In a couple items it's worse.  

 

Overall it's better and most likely to evolve as the UL did into the ULS and then the ULS evolved into it's own for years to come since it's inception.

 

Time will tell. 

[Tom Baker]

I own a CTLS, and have flown several others. I have flown 2 different CTLSi's. Prior to the sport upgrade I thought the performance of the CTLSi was doggy compared to my CTLS. Now having flown one with the sport upgrade the performance was very similar.

 

Flight Design stated a increase of 22 pounds for the 912is version of the airplane. This included the header tank, additional plumbing, cowling modifications, and they added electric pitch trim as part of the package. The bigger issue with weight on these are that the also have other additional options added making them 50-60 pounds heavier than a standard CTLS. The standard CTLS was about 40-50 pounds heavier than a CTSW.

 

I was quoted the cost of the dongle at $1500 when they first came out. Maybe the prices have come down since then.

 

For a LSA to be 12 kts faster than a CT one of 2 things must happen.

1. It is exceeding the regulatory limits of a LSA.

2. There is something wrong with the CT.

My CTLS operates right at the upper limits allowed by regulation and still be a LSA.