Rotax 912iS or 912ULS for Sling 2 ???

Talk about airplanes! At last count, there are 39 (and growing) FAA certificated S-LSA (special light sport aircraft). These are factory-built ready to fly airplanes. If you can't afford a factory-built LSA, consider buying an E-LSA kit (experimental LSA - up to 99% complete).

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cam737
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Rotax 912iS or 912ULS for Sling 2 ???

Postby cam737 » Fri Mar 09, 2018 8:04 pm

I am getting ready to build a Sling 2, 51% EAB, with Midwest Sky Sports.

I am torn between the 912ULS and 912iS. I have been thinking ULS for great history, lower cost, lower weight, etc…

But, I had a nice talk with a gentleman at Lockwood Aviation today about my decision and he made some good points about the iS: No worry about carb mx, no worry about auto gas sitting in carbs for a 3-week break in use, lower mx costs, and better fuel economy. I have heard about some of the growing pains as well. Maybe some of those problems were caused by install.

I would appreciate thoughts and inputs from owners.

Thanks, Cam
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby Sling 2 Pilot » Fri Mar 09, 2018 8:48 pm

Hey Cam, you already know where I stand on the subject. That said, the iS is constantly evolving, just as the ULS did. I was adamant about wanting the iS, even with the weight penalty. As you know, I went with the ULS after my visit to TAF. The airplane factory had to have a good reason for recommending the ULS over the iS, as we were told at the time of our visits. It’s not like they had a plane on the lot they wanted to get rid of.

We have both spoken to others, who swear by the iS and I believe them. Had I gone with the certified RV-12 S-LSA, when it becomes available again, it will only be offered with the iS. I guess Van’s Knows something TAF doesn’t.

By The Way, gas is gas, what makes the iS different in regards to worrying about fuel sitting for more than 3 weeks? Stale fuel is stale fuel. Instead of varnish in the float bowl, you could have clogged injectors. Or am I out of the loop on that?

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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby cam737 » Fri Mar 09, 2018 9:01 pm

Hey J,

Yeah, great question. The Lockwood gentleman said auto gas sitting over 3-weeks is not an issue in the ULS because of the gas sitting in the carbs for an extended period. He specifically said it is not a problem in the iS. I'm not smart enough to know why?

Anyone, anyone?
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby FastEddieB » Fri Mar 09, 2018 9:18 pm

I think its a really hard choice.

Fuel injection is the future, there's no doubt about that. Its just better. More efficient. And potentially much more reliable.

But on a long cross-country, if the fuel injection system does fault, one needs to find a ROTAX dealer with the right dongle to diagnose and then fix the problem. There are large swaths of the country where ROTAX dealers are few and far between. My impression is that carbs have problems more often, but the problems they do have are easily fixed in the field. Most common problems seem to be crud in the float bowls getting sucked into the main jet or interfering with the needle and seat.

Like I said, I'd agonize long and hard. If one has a ROTAX dealer with the right diagnostic equipment nearby, that can make a difference. If one is doing one's own maintenance, that can make a difference. And then there's the weight.

As an aside, in the 10 years I've owned my Sky Arrow I've had 93 octane ethanol-free fuel sit in my carbs for up to 6 weeks or so and never had a problem in that regard.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby Warmi » Fri Mar 09, 2018 9:49 pm

Interestingly, I kept hearing how expensive is that “special” diagnostic equipment for the IS version but then when I went for rotax training up there in Wisconsin ( basic owner maintenance ) it turned out to be just a $1000 cable/dongle + a windows laptop - not exactly a deal breaker heh
Flying Sting S4 ( N184WA ) out of Illinois

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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby cam737 » Fri Mar 09, 2018 10:43 pm

FastEd...thanks for the info. I wouldn't want to be lookin' for a Dongle in Des moines!

Warmi...agree.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby jetcat3 » Sat Mar 10, 2018 12:05 am

Sling 2 Pilot wrote:Hey Cam, you already know where I stand on the subject. That said, the iS is constantly evolving, just as the ULS did. I was adamant about wanting the iS, even with the weight penalty. As you know, I went with the ULS after my visit to TAF. The airplane factory had to have a good reason for recommending the ULS over the iS, as we were told at the time of our visits. It’s not like they had a plane on the lot they wanted to get rid of.

We have both spoken to others, who swear by the iS and I believe them. Had I gone with the certified RV-12 S-LSA, when it becomes available again, it will only be offered with the iS. I guess Van’s Knows something TAF doesn’t.

By The Way, gas is gas, what makes the iS different in regards to worrying about fuel sitting for more than 3 weeks? Stale fuel is stale fuel. Instead of varnish in the float bowl, you could have clogged injectors. Or am I out of the loop on that?


That’s really interesting. How recently did you visit the factory when they recommend the ULS over the iS?

I too, ageee this a very tough call. I really enjoy the latest and greatest and you definitely get that with the iS. But my office is practically built upon a ULS engine as I’m in Sportcruiser’s 5 hours everyday. I can’t argue with the reliability I’ve had so far and simplicity that comes with them. John Hurst has teamed up Dynon to have the HDX show the actual faults on the actual displays when you have a Lane A or Lane B issue right. That should go a long ways in helping overcome those worries on long cross countries.

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MrMorden
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby MrMorden » Sat Mar 10, 2018 10:33 am

It's not just the dongle, it's finding somebody qualified to work on the iS. The number of Rotax mechanics trained on the iS is a fraction of the number trained on the ULS series.

The good news is both are great engines, you probably can't make a "wrong" choice. If the airplane empty weight is already portly, I might tend toward the ULS, and if the empty weight is low I'd conversely favor tge iS. But the higher weight of the iS engine is partially offset by lower fuel burn at moderate throttle settings, so still a tough choice.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby drseti » Sat Mar 10, 2018 11:29 am

The kilobuck dongle is definitely a dealbreaker for me - and I'm a Rotax authorized heavy Maintenance repair center. With iS training. All my customers have ULS. If I ever get a customer with an iS, and he or she is willing to front the cost of the dongle, then maybe I'll consider working on one.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby Sling 2 Pilot » Sat Mar 10, 2018 11:37 am

In reality, fuel burn would be the least of my worries, especially if you’re burning auto fuel. Just me 2 cents.

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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby Warmi » Sat Mar 10, 2018 1:25 pm

drseti wrote:The kilobuck dongle is definitely a dealbreaker for me - and I'm a Rotax authorized heavy Maintenance repair center. With iS training. All my customers have ULS. If I ever get a customer with an iS, and he or she is willing to front the cost of the dongle, then maybe I'll consider working on one.

Just a few months ago I paid 6K for the 5 year rubber,annual and 200 hours inspection - given these prices being charged by mechanics a relatively minor 1K investment is pretty reasonable imho.
Flying Sting S4 ( N184WA ) out of Illinois

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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby drseti » Sat Mar 10, 2018 1:30 pm

Well, obviously, I'm not charging enough.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby 3Dreaming » Sat Mar 10, 2018 1:40 pm

Warmi wrote:
drseti wrote:The kilobuck dongle is definitely a dealbreaker for me - and I'm a Rotax authorized heavy Maintenance repair center. With iS training. All my customers have ULS. If I ever get a customer with an iS, and he or she is willing to front the cost of the dongle, then maybe I'll consider working on one.

Just a few months ago I paid 6K for the 5 year rubber,annual and 200 hours inspection - given these prices being charged by mechanics a relatively minor 1K investment is pretty reasonable imho.


I think the person who did yours was the same person who told me you couldn't do a CT for less than $5,000. Having done several CT's I simply have to disagree with him. My normal charge is just a little more than half of that.

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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby 3Dreaming » Sat Mar 10, 2018 1:45 pm

MrMorden wrote:It's not just the dongle, it's finding somebody qualified to work on the iS. The number of Rotax mechanics trained on the iS is a fraction of the number trained on the ULS series.

The good news is both are great engines, you probably can't make a "wrong" choice. If the airplane empty weight is already portly, I might tend toward the ULS, and if the empty weight is low I'd conversely favor tge iS. But the higher weight of the iS engine is partially offset by lower fuel burn at moderate throttle settings, so still a tough choice.


Andy, any Rotax trained mechanic who has done recurrent training, and is up to date is qualified to work on the 912iS.

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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby drseti » Sat Mar 10, 2018 1:45 pm

Well, Tom, obviously you're not charging enough either! ;)
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