Hobbs Vs. Engine Time

Edit: Nevermind, you're not talking about Tach time. Looks like I can't delete my reply, so it'll just have to stay here, making me look dumb. :)

Hobbs is actual engine runtime, Tach is engine revolutions converted to time. There's a setting in the EMS setup to tell the Dynon what your cruise RPM is, and it'll calculate Tach time based on that. If you spend most of your time below that value (warming up, idling, taxiing, runup), or if the value is set higher than your actual cruise RPM, Tach will be lower than Hobbs.

Use Hobbs

What EMS brand is this?
If the "Engine" hours are ECU Hours, that is the Actual Engine running time.
A Mechanical HOBBS actuated by an Oil Pressure switch is also quite accurate.
The software HOBBS in the EMSs often is a Tach/Hobbs hybrid.
If the Software assumes 5200 rpm is full speed and you fly mostly at 5300, the software Hobbs will outrun the ECU hours.

I have an MGL brand EFIS that stops the HOBBS engine OFF/ Lanes ON,  but runs at 1/4 speed when the EFIS is ON and the LANES are OFF.
It records 0.1 hrs every 24 minutes.  Crazy !!!

I would interrogate the ECU to see if it matches what you are calling "Engine" hours.

Thanks, Bill.  I did, in parallel, run this past Dynon, my avionics manufacturer, and they just confirmed that they do generate the Hobbs time, which runs on sensing positive oil pressure and stops on shut down.  This all the more makes me wonder what ENGINE time means.  If it didn’t display on my EMS I’d be oblivious, but since it does I have to ask.  And it’s obviously coming from the ECU or it wouldn’t have shown 0.5 hours on first energizing the avionics.  Perplexing…

For my Dynon Skyview:

HOBBS

Whenever oil pressure is above 15 psi or engine is above 200 rpm.

TACH

Engine time normalized for cruise RPM (cruise RPM parameter must be properly set in system setup).

RUN TIME

Hobbs time for current flight. Resets first time engine is started after Skyview is powered on. This allows you to view previous flight’s engine run time any time before you start your engine.

AIR TIME

Runs any time SkyView determines the aircraft is in flight. Resets as SkyView detects that the aircraft has transitioned to “in the air.” This time is also optionally used to calculate the Switch Fuel Tank Reminder.

TRIP RUN

Hobbs time that can be reset by pressing ENGINE > CLR TMR.

AIR TRIP

Runs any time that SkyView determines that the aircraft is in flight, just like air total. Unlike air total, it can be reset by pressing ENGINE > CLR TMR

AIR TOTAL

Runs any time that SkyView determines that the aircraft is in flight. Can be reset or adjusted in the Aircraft information menu within SkyView Setup.