Can someone tell me how to convert this raw tach time number?

[chriscalandro]

engine_type=ENGINE_LYCOMING
engine_type_uses=ENGINE_TYPE_USES_CHT
horsepower=180
redline_rpm=2700
cruise_rpm=2400
tach_time=615423843
hobbs_time=15425033
rotax_engine_time=0.00

 

[RV8JD]

I took the raw numbers from one of my saved User Config Files that I knew the Tach Time and Hobbs Time for (also a Lycoming 180 HP), and came up with the formulas below. The raw times in the User Config File appear to be in seconds, hence the 3600 number to convert from seconds to hours.

For your numbers:

- For tach_time=615423843: (615423843 / 10 / 3600 / 4) = 4273.8 Tach Hours

- For hobbs_time=15425033: (15425033 / 3600) = 4284.7 Hobbs Hours

Does that sound right for your airplane?

 

[chriscalandro]

That looks about right, and that's what I came up with based on a couple of tests, Thanks!

 

[swatson999]

I thought Tach Time was pulses from the mag...

615423843 revs / 2400 revs/min /60 min/hr = 4273.77 Hrs

?

 

[maartenversteeg]

True, Tach time normally references an engine running time that is normalized to the nominal RPM of the engine, so that when the engine is only run at 60% of its nominal rpm that the tach time only counts 60% of the actual time spend running at that rate. THis matches the idea that tch time is used for engine maintenace and the wear of the engine is related to the number of revolutions that the engine makes