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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Nomore767
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby Nomore767 » Thu Mar 22, 2018 7:05 am

drseti wrote:The Rotax generator is really a cool design. (OK, I'll admit I'm a technology nerd.) They embed permanent magnets in the circumference of the flywheel. Thus, spinning magnetic field. Then, they place a total of seven stationary coils around the periphery of the flywheel housing. Since the coils are stationary, there's no need for slip rings or brushes.

The spinning magnetic field induces currents into the stationary coils. If you properly connect to a pair of coils spaced physically 180 degrees apart around the flywheel, you get a raw voltage. So, one pair of those coils generates power for one capacitive discharge ignition module. A second pair does the same for the other CDI module, and a third feeds the voltage regulator module that powers the main bus.

That leaves a single coil to produce a pulse of voltage each time the flywheel makes a revolution. And that pulse, students, drives the tachometer.

Pretty cool, no? Class dismissed.


Is this going to be on the exam? :(

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

Postby chicagorandy » Thu Mar 22, 2018 7:31 am

No brushes IS a big deal in making magic smoke machines, kudos to the generator design folks.

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

Postby MrMorden » Thu Mar 22, 2018 7:49 am

FastEddieB wrote:I came here for an argument!


Just standby, one is coming. You can bet the farm on it! :lol:
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby drseti » Thu Mar 22, 2018 8:50 am

Nomore767 wrote:Is this going to be on the exam? :(


No, Howard, this is a lab course. The final exam will consist of disassembling a Rotax generator down to its component parts, reassembling it, and successfully firing it up.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby Sling 2 Pilot » Thu Mar 22, 2018 9:11 am

Now my Sling is equipped pretty much the same as Cam’s, less a chute and Cam has a Garmin Nav/Com between his dual screens. I have an internal GPS. TAF tells me I’m fine with the stock setup, no need to add the aux generator. Go figure! They could have sold it to me and I asked several times. So, we shall see.

My question to the Dr, if need be, can it be added later?

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

Postby drseti » Thu Mar 22, 2018 9:26 am

It's a fairly easy add-on, but will require an LoA if you're going the SLSA route. And, you'll have to redo wt/bal, since the extra wt on the gearbox pulls the CG forward a bit.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby Wm.Ince » Thu Mar 22, 2018 12:04 pm

cam737 wrote:. . . The plan is to use a 40 amp external alternator.

Good deal! Hope that works out.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby 3Dreaming » Thu Mar 22, 2018 12:20 pm

drseti wrote:The Rotax generator is really a cool design. (OK, I'll admit I'm a technology nerd.) They embed permanent magnets in the circumference of the flywheel. Thus, spinning magnetic field. Then, they place a total of seven stationary coils around the periphery of the flywheel housing. Since the coils are stationary, there's no need for slip rings or brushes.

The spinning magnetic field induces currents into the stationary coils. If you properly connect to a pair of coils spaced physically 180 degrees apart around the flywheel, you get a raw voltage. So, one pair of those coils generates power for one capacitive discharge ignition module. A second pair does the same for the other CDI module, and a third feeds the voltage regulator module that powers the main bus.

That leaves a single coil to produce a pulse of voltage each time the flywheel makes a revolution. And that pulse, students, drives the tachometer.

Pretty cool, no? Class dismissed.


Paul, the coils that produce power for the generator and ignition are inside of the fly wheel not outside. There are 10 poles of which 2 are for powering the ignition. The other 8 are for generator power. There is only 1 pole for each side of the ignition.
Outside of the flywheel are two each triggering coils for each side of the ignition, a total of 4, and one triggering coil for the tachometer.

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

Postby WDD » Thu Mar 22, 2018 12:36 pm

cam737 wrote:Oh yeah. I knew that. :shock:

dr...my eyes are so glazed over I can barely type. But, I got through the first 2 sentences. :)



All you need to know is that if you can get up to 1.21 gigawatts you can do time travel........

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

Postby TimTaylor » Thu Mar 22, 2018 12:36 pm

Hope the generator never fails.
Commercial Pilot Airplane Single & Multiengine Land; Instrument Airplane; Sport Endorsement Airplane Single Engine Sea; Flight Instructor Airplane Single And Multiengine; Ground Instructor Advanced Instrument

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

Postby drseti » Thu Mar 22, 2018 12:43 pm

WDD wrote:All you need to know is that if you can get up to 1.21 gigawatts you can do time travel........


That's 1.21 gigajoules per second, Marty.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby drseti » Thu Mar 22, 2018 12:47 pm

3Dreaming wrote:Paul, the coils that produce power for the generator and ignition are inside of the fly wheel not outside. There are 10 poles of which 2 are for powering the ignition. The other 8 are for generator power. There is only 1 pole for each side of the ignition.
Outside of the flywheel are two each triggering coils for each side of the ignition, a total of 4, and one triggering coil for the tachometer.


Thanks for the corrections, Tom. Obviously, I was working from memory (I should have listened to Brian and pulled out the manual...)

It's still a pretty cool design, isn't it?
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 » Thu Mar 22, 2018 1:20 pm

WDD wrote:
cam737 wrote:Oh yeah. I knew that. :shock:

dr...my eyes are so glazed over I can barely type. But, I got through the first 2 sentences. :)



All you need to know is that if you can get up to 1.21 gigawatts you can do time travel........


Don't know about you, but in my Sling the "Flux Capacitor" is standard.

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

Postby drseti » Thu Mar 22, 2018 1:29 pm

Sling 2 Pilot wrote:Don't know about you, but in my Sling the "Flux Capacitor" is standard.


Damn! I had to pay extra for mine, and still needed an LoA.
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Re: Rotax 912iS or 912ULS for Sling 2 ???

Postby Nomore767 » Thu Mar 22, 2018 2:13 pm

Jeez guys.....I thought it was all ball bearings?!!


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