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Old 09-27-2021, 10:28 PM
RFSchaller RFSchaller is online now
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 3,168

I have the D180. When my oil pressure sensor failed in flight I was about an hour away from an airport. That hour did not register on my display labeled “HOBBS”.
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Old 10-01-2021, 09:09 AM
Amadeus Amadeus is offline
Join Date: Nov 2020
Location: Basalt, CO/Lexington, KY
Posts: 86

After 30 years of flying Cessna and Diamond aircraft where tach time is always significantly lower than Hobb's time this has confused me, too. I know that ECO mode is still 97% power but 97% is still less than 100% so it seems that tach time should be lower, if just minimally, than total time (especially since I often cruise at less than 97% power to burn just 3.9gph).

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Purchased N112DR E-LSA flying with 28.2 hours - Thank you David (CraftingN112DR) for putting your skills, knowledge and attention to detail in this RV-12iS!
Dropped at paint shop this morning (July 15, 2021)
Picked up from paint shop (August 14, 2021)
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Old 10-01-2021, 01:09 PM
Jake14 Jake14 is offline
Join Date: May 2014
Location: Seattle
Posts: 390

AF-5000 Pilot's Guide - Advanced Flight Systems

Tach Time: Hours on engine above 1250 RPM.
Hobbs Time: Hours on engine above 0 RPM.
RV-14A flying 520 hrs
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Old 10-01-2021, 01:23 PM
AlpineYoda AlpineYoda is offline
Join Date: Nov 2019
Location: Boulder, CO
Posts: 334

Originally Posted by Desert Rat View Post
Hobbs just ticks over .1 hours every 6 minutes. Some of them are wired to start ticking when you turn the master on, some are on a switch so they don't start until oil pressure comes up.

Assuming 'engine" time is the same as what the certified world calls "Tach time," it works like on a tractor or other random farm equipment- i.e. it ticks .1 hour every 6 minutes at full power but when you reduce r.p.m. it slows down proportionally.

Traditionally, you log hobbs time in your logbook but schedule maintenance by tach time.

Edit- I'm not talking specifically about your airplane, just industry standard.
To date, all my experience has been in the certified world and the above is exactly right. I flew a rental C172 this morning to stay proficient whose tach time was about 70% of the Hobbs time. All these reports of virtually identical hobbs and engine time mean that engine time is accruing too quickly for most people. If you religiously follow 100 hour maintenance, 500 hour mag, and 2000 hour overhaul rules, I think you will be early in all cases, incurring costs before they are really needed. If you can set the EFIS to use a % of max power calculation for engine time / tach time, you might extend parts' effective life per the schedule by 10-30%.
RV-10 build blog --
Started 12/19/2019
Engine hung 1/9/2021
Panel hopefully coming fall 2021

N1814T reserved with FAA
Donated Jan 11 for 2021, EAA and AOPA member
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Old 10-01-2021, 03:58 PM
printbr printbr is offline
Join Date: Oct 2019
Location: Richland, WA
Posts: 68

Originally Posted by Jake14 View Post
AF-5000 Pilot's Guide - Advanced Flight Systems

Tach Time: Hours on engine above 1250 RPM.
Hobbs Time: Hours on engine above 0 RPM.
On a Rotax that would be pretty much the same thing.
Bruce Rawlins
Richland, WA
RV-12 Flying
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