Tach time or Hobbs time?

[RV8Squaz]

Hello Gang,
When deciding when to change the oil, or when an AD based on time comes due or anything else based on hours... Do you use the tach time or the Hobbs time?

For logging my flying time in my pilot logbook, I've been using the stantard Air Force technique of takeoff to landing plus 5 minutes to account for ground ops. I do it this way because I don't actually have a Hobbs and I feel like it would be pretty close to Hobbs time if I had one installed and pretty close to actual engine operating time.

I have a VMS VM1000C and it logs tach time only when the RPM is above 1500. So there is quite a bit of difference between my VM1000C tach time and the flying time I am logging. The flying time I've been logging runs about 15% more than my VM1000C tach time. So do I change the oil at 50 hrs tach time ( which is about 58 hrs actual engine operating time) or 43 hrs tach time ( which is about 50 hrs actual engine operating time).

Jerry
RV-8 N84JE 90.9 hrs ( actual engine operating time, 79.0 hrs tach time ) since 4 Feb. :-)

[gasman]

Originally Posted by RV8Squaz

Hello Gang,
When deciding when to change the oil, or when an AD based on time comes due or anything else based on hours... Do you use the tach time or the Hobbs time? :-)

Get a hobbs, hook it up to a 12v power and let it run till it has the same hours as the motor has now. Then install it and use it for ALL OF YOUR times (except for standard rate turns ). The Hobbs will still be in the aircraft long after every thing else has been changed out. It is the standard.
Warren

[Rivethead]

I don't fly enough hours in a quarter to need an oil change based on time so my engine gets an oil change four times a year. That said, if I did fly enough I would base my oils time on the Hobbs and base all other engine maintenance on tach time.

[jcaplins]

For me and my Cessna (still at negative 10,000 hours on the RV)... All times that are entered in the aircrafts logbooks (engine, airframe, prop) are from the TAC. All my pilot logbook entries come from the Hobbs.

All AD's are complied with based on the TAC time.

Best Regards,
Jeff

[Rick6a]

There are several ways to measure time and all are are different. I find that Hobbs time is way too fast...no wonder flight schools love to charge you by referring to it. The VM1000 is better, but like you said it only measures time above 1500 RPM. Then there is flight time automatically logged on the Garmin 296 and you can always refer to a watch. Lately, I've been in the habit of using the stop watch function on the GTX-327 transponder to measure time from start up to shut down.

Want to exaggerate your total flight experience? Use Hobbs. Want to sell your engine with the lowest declared hours? Use VM1000 time. Want to be truly accurate? Use your watch.

I log my personal flight hours by what the GPS records automatically and I make airframe and engine logbook entries by splitting the difference between Hobbs and VM1000 readings. YMMV.

[rv6rick]

I've got way too much invested in my Lycoming(s) to change the oil at 50hrs.....it gets changed at 25hrs along with the filter. I've watched folks dump their oil at 50hrs and it doesn't look real good . My opinion only, based on 30yrs of refining experience. I think 25hrs would be about the 'norm' among the RV group although I'm sure some folks will disagree but, hey....oil and a filter is cheap insurance.

I go by the hobbs which means the oil has only about (or so) 23 hrs 'tach time'.

[osxuser]

Originally Posted by rv6rick

I've got way too much invested in my Lycoming(s) to change the oil at 50hrs.....it gets changed at 25hrs along with the filter. I've watched folks dump their oil at 50hrs and it doesn't look real good . My opinion only, based on 30yrs of refining experience. I think 25hrs would be about the 'norm' among the RV group although I'm sure some folks will disagree but, hey....oil and a filter is cheap insurance.

I go by the hobbs which means the oil has only about (or so) 23 hrs 'tach time'.

If you fly often, 50 hrs works fine. Lycs run to 2400 regularly at 50hr intervals.