Prop RPM?

Does anyone know if it's possible to have the SkyView calculate & display the prop RPM? Anytime I see or adjust power using engine RPM, I find that I'm always wondering what that is in terms of the prop. I'm assuming that it's due to 30+ years of flying planes where engine=prop RPM.

A poster on a different thread (thanks, TomKK) had a great way of tucking a minor number inside a larger arc to not take up display real estate, so that's probably what I would do: tuck the prop RPM inside the engine RPM arc.

thanks,
-dbh

How can the prop RPM be any different than the engine RPM?

oops! didn't notice that this was a Rotax question.

gasman said:

How can the prop RPM be any different than the engine RPM?

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Unlike the Lycomings that power other RVs, the Rotax in the RV-12 is a geared engine, so the engine turns at a much higher rpm than the prop.

The gearbox reduction is something like 2.27:1, if I remember correctly. It's been a few years since owning/operating some 912's.

2.43:1 if this is correct http://www.rotaxservice.com/rotax_engines/rotax_912ULSs.htm

The ROTAX 912 ULS used in the RV-12 has a 2.43 to 1 engine/prop ratio. After you get a few hours operating a 912 you will have no need to think in terms of "prop rpm".

DHeal said:

The ROTAX 912 ULS used in the RV-12 has a 2.43 to 1 engine/prop ratio. After you get a few hours operating a 912 you will have no need to think in terms of "prop rpm".

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I agree. I jump back and forth between Lyc powered RV's and the RV-12's all the time. You just get used to it.

But to answer your question, the tach sensor for the Rotax is on the engine crankshaft, so the only way to change the reading to prop RPM would be to add a sensor to the gear box/prop shaft or get the manufacturer of the EFIS/EMS to write some special software code to divide the engine speed value by 2.43.

This is a test question in the Line maint. class. It is #18.
For this question we'll use the 912ULS since that is what most have.

What is the 5th trigger coil used for?
The answer is: It is the tach pickup/trigger.

There are 5 trigger coils off the flywheel. 4 are for the engine and equipment use and the 5th on the left side of the flywheel is for the tack. It doesn't come off the crank.

Prop rpm for most of our operations isn't that important as a rule. There are times it is, but not for your average everyday use.

The 912ULS gearbox ratio is indeed 2.43:1

So if you have an engine rpm of 5000 then the prop rpm is 5K divided by 2.43 = 2057 prop rpm.

You can make a small chart with some engine rpms around 200-300 difference and then put the prop rpms next to it.

Something like this and it could be used anytime one of those special needs pop up. Pick your own rpms.
5000=2057
5100=2098
5200=2139
5300=2181
5400=2222
5500=2263

While I originally had some idle curiosity about the prop RPM, I finally decided I just don't care. All I care about is engine RPM, just like in a Lycoming powered plane. I don't have to worry about the prop red line, just the engine red line. If I really want to know the prop RPM (and there's no practical reason I can think of) my phone has a calculator app, and I have a pencil if that's not available.

Sink said:

It doesn't come off the crank.

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Thank you for expounding your infinite knowledge Roger......

So what is the Flywheel attached to? The crank shaft!

So though the sensor is not directly sensing the rotation of the physical crank shaft, it is still sensing the rotation rate of the crank shaft. Which is all that is relevant to my post or this discussion thread.



It is interesting that you mention prop RPM being of little value, but you went to the trouble of doing the simple math for everyone??????

I used to own a Yak-52 that haD a gear box on the prop (PSRU). The tach read in % of max RPM so there it was pretty intuitive.

rvbuilder2002 said:

I agree. I jump back and forth between Lyc powered RV's and the RV-12's all the time. You just get used to it.

But to answer your question, the tach sensor for the Rotax is on the engine crankshaft, so the only way to change the reading to prop RPM would be to add a sensor to the gear box/prop shaft or get the manufacturer of the EFIS/EMS to write some special software code to divide the engine speed value by 2.43.

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It looks like there is not any code in Skyview to be able to perform the division and display it. That was really all I was looking for.

thanks all,
-dbh

The Diamond Katana as originally built only indicates prop rpm. I've flown one a few times but don't know just how this is accomplished.

Not sure if this would work and I've never used it but G3X offers a custom RPM selection:

Custom: This option allows the installer to enter up to 8 points of frequency-to-RPM calibration. The input accepts frequency values up to 1 kHz. This input supports any RPM sensor that has a known frequency output (up to 1 kHz). This input also supports RPM readouts that display in percent instead of RPM.

Walt said:

Not sure if this would work and I've never used it but G3X offers a custom RPM selection:

Custom: This option allows the installer to enter up to 8 points of frequency-to-RPM calibration. The input accepts frequency values up to 1 kHz. This input supports any RPM sensor that has a known frequency output (up to 1 kHz). This input also supports RPM readouts that display in percent instead of RPM.

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Thanks Walt
My comment was in the context of Skyview and AFS. I am not very familiar with G3X.