Hobbs meter

fosl

Hello,

Does the fact that the Hobbs meter always resets to zero for every new flight cause any issues with the MTBF failures? Or does the BS 114 keep a separate running total somewhere for proper MTBF failure simulation.

Thanks

rinkerbuck

It shouldn't be resetting. Mine did that once, so on my second flight it was back to 0, which made me think maybe it was per livery for that, but then the next couple of flights it has continued to save and is the same across all liveries of the variant (turbo/non turbo).

jmarkows

I am apparently differing from everyone else who is having issues with the Hobbs meter not saving between sessions, my Hobbs meter is not incrementing at all...

jmarkows

@Black-Square any thoughts on why the Hobbs isn't increasing at all for me? It's only at 0.1 hours when I've had the master battery on for far longer; at least the hour I've put on the engine.

Edit: seems like it's only counting time I'm in the air?

fizzboy

The Hobbs meter in MSFS only increments when a certain threshold such as airspeed or RPM is met.

jmarkows

There's no way they did that... did they? That doesn't sound like that's how it's supposed to work.

fizzboy

https://docs.flightsimulator.com/msfs2024/retail/programming-apis/simvars/aircraft-simvars/aircraft-engine-variables/#GENERAL-ENG-HOBBS-ELAPSED-TIME

This records the time the engine has been running, but instead of taking a % of the time based on the Pct/RPM this takes the full time, but only if a threshold RPM/speed is reached.

fizzboy

The way MTBF works is there isn't an "accumulated time" for any given component. It's more like on some particular interval the universe rolls dice and if it rolls all ones then the component fails. Also, there are a lot of dice and they have a lot of faces and the size of the dice depend on that MTBF number. Each roll is independent of all of the previous rolls (there is no memory).

So the Hobbs meter in MSFS is just a fun role-play thing you can look at while you imagine you're taking your fake plane to the fake mechanic to have your fake inspection. It's not implemented correctly but it also really doesn't matter at all.

jmarkows

That's the engine meter, I'm talking about the general one on the center pedestal that's supposed to tick onwards as long as the battery master switch is on.

fizzboy

Well... you're right in that the manual on page 48 states:

The included Hobbs timer in the aircraft runs from when the master switch is activated, to when it is shut off.

The XML code for the subpanel gauges on the Commander 114 all use the GENERAL ENG HOBBS ELAPSED TIME simvar (the same one as the documentation I linked to above) to determine what numbers to display on the Hobbs meter (the 6 digit gauge with a maximum of 99999.9 hours). Flipping the battery master on, I can observe that the value for that variable does not change at all (the floating point value will be accurate down to like the 10,000th of a second or so). Some time later if I'm especially curious I'll figure out what the rough RPM/speed threshold is to get it to start incrementing.

So either the manual gets updated to reflect how Asobo accumulates time to that variable or something. I doubt Asobo will ever change how that simvar records time.

The XML also refers to a gauge with 5 digits (TachometerDigit1 through 5 so a maximum of 9999.9 hours) and that uses GENERAL ENG ELAPSED TIME which is "Total elapsed time since the indexed engine was started." according to the simvar docs. I don't think it's actually on any of the panels or gauges, however. I could have missed it, though.

fizzboy

pfft... the tach hours are on... the tach. obviously.