Hobbs vs. Tach vs. average flight distance

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Alex Hartunian

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Dec 11, 2018
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Alex H
I'm new to Pilots of America. Hi all. I wanted to post some information about hobbs vs. tach. I'm joining a local flying club and they charge tach time vs. hobbs. After reading a few forums and articles on the web I thought this post would be beneficial to some seeking the same information. I noticed many articles discussed a factor of 1.2 - 1.3x tach to get a ballpark hobbs time. There was a pilot that recorded his logbook entries based on tach and the advise most gave him was multiply all your entries by 1.2 - 1.3x to get a more accurate number (hobbs).

I found recently that this varies greatly on your typical flight. If you are a pilot that flies within 40 - 70 miles of your home airport on average then your factor may be more like 1.7 - 1.8x your tach time. I flew this past weekend from Van Nuys to Camarillo and back for a hobbs time of 1.0 and a tach time of 0.6. Full stop at Camarillo. This is attributed to time on the ground (startup, clearance, taxi, run-up, etc.). If you fly in busier environments and fly IFR it's going to take you longer to get going and get a release. All that time the engine is spinning but not that fast since your RPM is low and the tach turns slower.

I think if the average flight for me was 75 miles or so (Van Nuys to Santa Barbara for example) then I would guesstimate my factor would be around 1.6x in that case. The longer legs you fly to your destination the closer you will get to the 1.2 - 1.3x factor. Would love to hear and comments and some good discussion if this post is worthy. Thanks!
 
You actually log time by what you see on your watch. The Hobbs meter is pretty much the same as your watch as far as keeping time.

All a tach does is count engine revolutions. As you have found, tach time varies widely depending on RPM.

Don't over think it. If the airplane has both tach and Hobbs, record tach time on the airplane log and Hobbs time in your logbook. If there is no Hobbs meter, note the time on your watch. Simple as that.
 
It also depends on the airports you fly from. I take off from a deserted (mostly) grass strip and go to other sleepy pilot controlled fields so usually add 0.1 to each end of my flight track as recorded on FlyQ (it starts and stops recording at 20 mph). I know that rarely am I not off the ground 6 minutes into the flight. 3 minutes to taxi and 3 minutes for run up (overall average times). Maybe a bit more for warming up now that it is winter.
 
Not to mention, what the Hobbs is attached to!

I just found out my plane's Hobbs meter is attached to the master switch. We log Tach time for billing and inspection purposes.
 
I take a note of both Hobbs and tach, from a fairly busy delta that I fly out of the difference is exactly 1.3, pretty much 90% of the time. If I am taking off a podunk airport it’s either .1 more than Hobbs or about the same. In one flight I had tach more than hobbs
 
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