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Bob Y 09-19-2021 08:36 AM

912iS - Hobbs vs. ENGINE Time
1 Attachment(s)
I'm pretty sure this is a 912iS only item...

What's the difference between Hobbs vs. "ENGINE" time in the EMS? When I first energized my HDX system, the Hobbs showed zero, naturally, but there is a timer labeled "ENGINE", which showed 0.5 hours. I naturally assumed this was from the factory break-in period. Slowly, Hobbs has overtaken the ENGINE time. With over 100 hours on the engine, the Hobbs has gained about 45 minutes over the ENGING timer - now 112.5 on the Hobbs vs. 112.3 on ENGINE time. See attached screenshot of my EMS screen.

I've checked the Rotax manuals, floated this question to Dynon and on the Rotax Owner's forum, but no good answers, so, I'm reaching out to you iS engine guys with two questions:

1. Does anyone know the real meaning of ENGINE time?
2. How do Hobbs vs. ENGINE times compare on your aircraft?

Desert Rat 09-19-2021 02:38 PM

Hobbs just ticks over .1 hours every 6 minutes. Some of them are wired to start ticking when you turn the master on, some are on a switch so they don't start until oil pressure comes up.

Assuming 'engine" time is the same as what the certified world calls "Tach time," it works like on a tractor or other random farm equipment- i.e. it ticks .1 hour every 6 minutes at full power but when you reduce r.p.m. it slows down proportionally.

Traditionally, you log hobbs time in your logbook but schedule maintenance by tach time.

Edit- I'm not talking specifically about your airplane, just industry standard.

rvbuilder2002 09-19-2021 05:18 PM

On G3X engine time is the same as the traditional aircraft tach time.
Rotax specifically states that all engine inspection and maintenance is to be done based on Hobbs time.

Desert Rat 09-19-2021 05:33 PM

Scott, thanks for the clarification re; Rotax. I love learning new stuff.

Bob Y 09-19-2021 08:34 PM

1 Attachment(s)
Guys, I get Hobbs vs. tach time and understand maintenance is based upon Hobbs. These are produced from the HDX and run per the conditions indicated on the attached from the HDX user manual. This “ENGINE” time is generated by the Rotax ECU, not the Dynon system. That’s why it showed 0.5 hours when the HDX was first powered up - it was served up to the Rotax EMS from the ECU. So, I’ll repeat my second ask in my initial post: Can I ask those of you with an iS, and maybe an HDX, if it’s Dynon specific, how your Hobbs vs. “ENGINE” times compare. And certainly if someone REALLY knows what “ENGINE” time means, please share. Thanks in advance for your support.

jcl777 09-20-2021 09:18 AM

After the flight home when I took delivery of my RV-12iS, my G3X Touch showed 19.9 engine and 19.3 total. Today it shows 122.2 engine and 122.9 total.

Bob Y 09-20-2021 09:39 AM

Thanks, John. So your numbers correlate well with mine. Glad to know the delta between them is not unique to me. So, the mystery remains as to what ENGINE time means. Hopefully I’ll get to a Rotax maintenance course soon and can ask the question.

fehdxl 09-20-2021 01:04 PM

4 Attachment(s)

Originally Posted by rvbuilder2002 (Post 1556543)
On G3X engine time is the same as the traditional aircraft tach time.
Rotax specifically states that all engine inspection and maintenance is to be done based on Hobbs time.

I think these screen captures from the Rotax Maintenance Manual Line agree with that statement…. But, a related question is does the Rotax FADEC provided “Engine Time” accrue like a mechanical tachometer where the ‘tach time’ isn’t equal to watch time except at a certain RPM -OR- like a hobbs where it records watch time once it’s powered from a sensor (oil pressure, master switch, wow, etc)



P.S. Added a picture of our RV-12iS times from a couple weeks ago…. The G3X is set to record Total Hours using the airborne option (i.e. GPS and IAS derived).

jrtens 09-27-2021 09:38 AM

I couldn't find a purpose for that engine time either so I just removed it from the display.

Bob Y 09-27-2021 09:53 AM

I still haven’t found an authoritative answer to this question either, but I’m starting to wonder if it might start timing when the oil hits the magical 120 degree point? Would sort of correlate better with the Hobbs readings.

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