HOBBS meter vs. Tach Time
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Hi,
A very minor quibble, but having 2 HOBBS meters is redundant, and they will always read the same, since HOBBS is airframe time, not engine time. Tach Time is the measure of engine time, and could vary between engines. https://doublemaviation.com/hobbs-time-vs-tach-time/
Kat
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You're actually both half correct! Typically in smaller aircraft, there will be a Hobbs meter and a tachometer. The Hobbs meter counts at 1 hour per hour any time the master switch is on. The tachometer counts at a rate proportional to engine RPM, usually driven by a direct linkage from the engine's accessory gearbox.
"Hobbs", however, is a genericized trademark, coming from the original company that manufactured these counters. They can be installed in many ways, and there mere appearance of the name "Hobbs", does not necessarily indicate what they are counting. While I can't tell you exactly how these behave in the real aircraft (I'll ask one of the owners next time we're chatting), I can confirm that they came in several different layouts during the construction of the Duke. Some of them had only one, marked "Hobbs", and labeled "Flight". Some had two, marked "Hobbs", with one labeled "Engine" and one labeled "Flight", and some had two, marked "Hobbs", and labeled "Engine 1" and "Engine 2".
In MSFS, they are both correctly connected to their respective engines, so they will not always read the same. They will, however, also not behave exactly like tachometers, because that's just not how the variable works in MSFS. To quote from the SDK: "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."
I hope that answers some of your questions. Thanks for writing!
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Thank you for responding. The reason I mentioned the difference, in the state.cfg file, the HOBBS readings are identical (accumulated HOBBS time), but the engine times are different (accumulated time), both starting at 0. What's being displayed is the HOBBS time. So it seems the HOBBS meters in the Duke are displaying airframe time rather than engine time. Which is fine, if that's the intent.
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I'm looking at my state file too, and the "hobbs" times are also identical. Interestingly, they are 25% less than the "accumulated" time, which according to the documentation, should be the one that's not affected by RPM. The accumulated times are also different, unlike the "hobbs" times. I see evidence in other aircraft state.cfg's, that this may be the case for many or all aircraft. It's possible that the SDK is incorrect, or that I have not set some config value that triggers this behavior. I think I will switch over to using the total engine accumulated time since starting, at least for the Dukes, so that you can see two different numbers for the two different engines, even if they aren't 100% accurate to real world tachometer time accumulation.
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@Black-Square So you changed the time displayed as HOBBS time with the engine time with this update?
I stumbled across, because I set the Hobbs hours in the state.cfg of the Grand Duke to match the hours of my Duke in FSEconomy, right after my first installation after release.
But after the update it shows the engine time (the numbers don't match on the screenshots of the CFG and the hobbs meter, because I did one flight in between. But instead of the saved "57x.." hobbs time, it shows the "47x.." engine time.)
It's no problem, but I'm just curious to know if it's on purpose. Perhaps I edit the engine time in the cfg, to match my FSE Duke hobbs hours again. :)
