Rotax iS vs ULS

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drseti
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Re: Rotax iS vs ULS

Postby drseti » Mon Feb 27, 2017 8:56 am

FastEddieB wrote:As an aside, none of this discussion is meant to "diss" the 912is or electronic fuel injection in general. I think both represent the future


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Re: Rotax iS vs ULS

Postby 3Dreaming » Mon Feb 27, 2017 10:19 am

For the 912iS the engine is controlled by the ECU. This covers both ignition and the fuel injection. Power for the ECU comes from the battery for start up, and then switches to the engine once the first stator is on line. When the second stator comes online it then takes over engine operation, and the first stator now supplies electrical power for the aircraft. If the stator on which the engine is operating were to fail it will automatically switch to the other stator. If both were to fail you can then switch to battery power for the ECU. With this system after starting the engine provides power for all operations, and a back up of operations is also provided by the engine if the first were to fail, with a final back up provided by the battery.

For the 912ULS you have one stator with 2 poles providing power for the ignition. If one or the other of the 2 poles fails you lose the corresponding ignition. If the whole stator were to fail you lose both. There is no battery back up.

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Re: Rotax iS vs ULS

Postby cogito » Sun Mar 26, 2017 2:37 pm

MrMorden wrote:The iS engine is very nice, but it's $3000 more than the ULS (current CPS pricing) and weights ~22lb more. The extra cash is probably not a huge deal when you are already spending $17k on an engine or $100k+ on a new airplane, but on an LSA 22lb can be significant. It's 3.5 gallons (45min) of fuel, or an extra overnight bag.

The 912ULS is a great engine and pretty easy to keep running, but the iS is probably the future direction Rotax is going, and it would not surprise me to see the carb'ed engines stop being made in 5-10 years. I just wish it were a bit lighter. For now, either engine will do great on an LSA or other small airplane.


IMHO it's worth the extra $4,000 initial cost of the iS. ($3,000 more for engine, $1,000 for the dongle.) After 3.5 hrs of each flight the weight equals that of the ULS when you consider the lower fuel burn. And now that I have 1,000 hrs on my iS I've saved possibly 1,000 gallons of fuel which, at current fuel prices, is about the extra cost of the iS.

A properly in-sync ULS is about as smooth as an iS.

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Re: Rotax iS vs ULS

Postby Ed Rawlings » Sun Mar 26, 2017 4:04 pm

This is an interesting thread to me. I am currently awaiting delivery of a new Bristell and went through a lot of mental gyrations over ULS vs IS. I the end I decided on the ULS with the primary reason being weight. I would prefer the new technology of the IS and the cost is not a big factor when you compare it to the cost of a new LSA. However, 30 lbs is a big deal and I wanted to keep the empty weight under 800lbs with a chute and the dual G3X panel. The only way to do that was with the ULS. ( it is 798lbs). It sounds like from what I am reading here is that the IS may actually be more fail safe from an electrical standpoint than the ULS. I'm not sure I understand the difference between a Stator and a Pole but it can't be good if you only have one Stator vs two. If anyone can explain I would appreciate it.

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Re: Rotax iS vs ULS

Postby roger lee » Sun Mar 26, 2017 6:13 pm

Should have been separate systems. One for the engine and one for electronics and then you have the battery. If Diamond put the gear on the wrong circuit it may have dropped the voltage too low.
So far most of the 912iS problems have been Mfg caused by not following Rotax wiring specs.
There have been two Rotax issues and that was the stator and the gearbox.
Roger Lee
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Re: Rotax iS vs ULS

Postby Wm.Ince » Sun Mar 26, 2017 6:19 pm

roger lee wrote:Should have been separate systems. One for the engine and one for electronics and then you have the battery. If Diamond put the gear on the wrong circuit it may have dropped the voltage too low.
So far most of the 912iS problems have been Mfg caused by not following Rotax wiring specs.
There have been two Rotax issues and that was the stator and the gearbox.

Hi Roger,

If someone was thinking about ordering an airplane with a 912is engine, what tips would you suggest to them?
Thank you in advance for your answer.
Bill Ince
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roger lee
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Re: Rotax iS vs ULS

Postby roger lee » Mon Apr 03, 2017 6:37 pm

First I would never buy a first production run of an aircraft with this engine. Several of the aircraft Mfg's using this engine thought they knew more than Rotax and tries to wire it different. It didn't turn out so well and customers and the companies have had a bunch of issues. I would then pick an aircraft that has been out while and check its track record.
Roger Lee
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