Rotax 912 iS Sport Engine time vs Hobbs.

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bluesideup

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bluesideup
Hi everyone.

Known. Hobbs defined as Start 15PSI Oil pressure.

Engine time, is not defined anywhere that I know of, is supplied by the Rotax ECU.



Is there a possibility when / where Engine time is higher than Hobbs time?

If Yes, what is the explanation?

Does any one know how Engine time is defined by Rotax?

Thanks.
 
Well, someone with Rotax experience can correct the details, but, I would assume engine time is tach time.

Tach time can be higher than Hobbs, though it would be pretty unusual for that to be true overall, especially for small aircraft that don't have long endurance. Tach time is typically set to be one hour when the engine turns the same number of times as it would in cruise flight in an actual hour. So, whatever RPM is typical for cruise for that engine would be selected, and if you ran one hour at exactly that RPM, you'd get one tach hour. If you run higher, it will be higher. It's typically 2400 or 2500 RPM for traditional aircraft engines, but I couldn't tell you what it is for the Rotax, which, of course, turns a much higher RPM.

If you are consistently running higher RPM, tach can exceed Hobbs. If the plane tends to cruise high and far, generally tach can exceed Hobbs, as the RPM allowed up high is generally higher and by traveling the full endurance of the tanks, you maximize the time at this high RPM. That's why I'd imagine it would be unusual for a Rotax powered aircraft, as they tend to be short range flyers that don't head too high.

Well, that's how it can happen if it's basically just tach time. I'll admit I don't have specific knowledge of Rotax.
 
Pilot flight time is elapsed time (on your watch or whatever) from the time the aircraft first moves under it's own power for the purpose of flight until it comes to rest at the destination.

Time in service (in general) for maintenance purposes is that time that the aircraft is off the ground.

I don't know much about ROTAX but if they say their engine time is something different (like engine running time) then you're obliged to follow that. Otherwise, it's the time in service definition above.

A Hobbs is just an electric clock that counts time when it's got power applied to it. There are a number of ways to switch it on in aircraft. It could be just on the master, it could be on an oil pressure switch so that it comes up shortly after engine start, it could be on a gear switch (as later Bonanzas and my Navion does). The latter is the closest you'll come to the time in service definition in my opinion.

The FAA has always allowed any reasonable approximation of the time, such as tach time, for time in service as long as you're consistent about it.
 
arnoha said:
Tach time is typically set to be one hour when the engine turns the same number of times as it would in cruise flight in an actual hour.
Click to expand...
For mechanical tachometers.

Rotax typically uses an electronic tach.
 
Capt. Geoffrey Thorpe said:
Does it add up "hours" by counting revolutions or does it have an actual clock?
And, can you say that "they are all like that"?
Click to expand...

If it's a tach, electronic or not, it's by counting engine revolutions. That's the definition of a tachometer. There's different ways to get that count, but they all count the same thing.

There is that assumption that it's actually tach time. That I'm not sure of.
 
Hi everyone.
Rotax dictates that:
>>All of the maintenance intervals, such as the 100 hr. inspection and the engine TBO, relate to the number of operating hours of the engine.<<

>>The operating hours are defined as follows in order to prevent miss understandings and to ensure safety:
- All time during which the engine is running is counted towards the total number of operating hours.
- The time is counted irrespective of the load factor of the engine, such as idling or take-off power.<<

>>Maintenance and overhaul intervals are always dictated by the readings of the engine control unit (ECU).<<

The questions are:
1-How is that time defined / displayed in the Dynon Skyview?
2-Assuming that this is the Engine Time, how is it defined / counted?
3-Can this ever be higher than Hobbs time that is Defined as Start at 15PSI, Stop_key Off or less than 15PSI?

Tach Time dependent on Load factor / RPM which is Not used by Rotax as Maintenance time / clock, for anything that I know of.
Thanks.
 
arnoha said:
If it's a tach, electronic or not, it's by counting engine revolutions. That's the definition of a tachometer. There's different ways to get that count, but they all count the same thing.
Click to expand...
Nope.
One example. There are others.
https://www.aircraftspruce.com/catalog/pdf/15-05211s.pdf

"In addition to RPM, the LCD displays total
accumulated engine (Hobbs) time"

Now, what I am not finding is what is the trigger for the timer behind the CAN message "ECU Hours" which is sent by the 912 si ECU. But given how much stuff is sync'd to the real time clock in the ECU, I would be amazed if they messed with the hours calculation to try and scale it with engine speed.
 
bluesideup said:
Hi everyone.
Rotax dictates that:
>>All of the maintenance intervals, such as the 100 hr. inspection and the engine TBO, relate to the number of operating hours of the engine.<<

>>The operating hours are defined as follows in order to prevent miss understandings and to ensure safety:
- All time during which the engine is running is counted towards the total number of operating hours.
- The time is counted irrespective of the load factor of the engine, such as idling or take-off power.<<

>>Maintenance and overhaul intervals are always dictated by the readings of the engine control unit (ECU).<<

The questions are:
1-How is that time defined / displayed in the Dynon Skyview?
2-Assuming that this is the Engine Time, how is it defined / counted?
3-Can this ever be higher than Hobbs time that is Defined as Start at 15PSI, Stop_key Off or less than 15PSI?

Tach Time dependent on Load factor / RPM which is Not used by Rotax as Maintenance time / clock, for anything that I know of.
Thanks.
Click to expand...

Interesting. That implies that "Engine time" is fundamentally the same as Hobbs time.
 
Hi.
>>Interesting. That implies that "Engine time" is fundamentally the same as Hobbs time.<<

That would be acceptable / almost logical.
The problem comes when some of the Dynon glass / 912iS shows / displays a higher Engine Time value than Hobbs Time, which is what triggered this question / post.
 
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