9 timers, No Hobbs
I don't have a Hobbs, because I have too many clocks and timers already. Do we need a Hobbs meter at all?
Thinking about it, I have: 3 clocks, 3 flight timers and 3 elapse timers in my RV, with out even trying. Every electronic goodie seems to throw in at least a clock or timer or two:
(2) EFIS: Clock & count-up/down timer
(2) EIS (engine monitor): Engine time (RPM limited), Flight timer based on RPM
(3) 3-in-1 panel clock: Clock, count-up elapse timer & flight timer (air or gear activated)
(2) GPS: Clock time & time in motion
The above does not include the watch on my wrist, which is what I really use when I write my block times down for the purpose of logging pilot time, which is all I would use a Hobbs meter for if I had one.
For pilot flight time I use block to block, as most do. I just look at the clock and write the times down, after engine start and shut down. Some times I use one of many elapse timers. If I forget to write the time down or start a timer, I just use flight time that the EIS automatically records and retains till after yhe flight and up to next flight power up for 3 minutes. Other wise the total engine/hobbs time is always retained in no-volatile memory.
Flight Time (actual airborne) and Engine-time are one in the same. I use the electronic engine monitor. It accumulates flight time in memory for maintenance and airframe time. It is based on engine RPM's above a min RPM I set. Below this RPM it records no time, e.g.: taxi, run-up and short approach (low RPM). The EIS also uses this time flight time for the purpose fuel burn. It clears the flight time every flight. The flight time is used with the fuel flow totalizer. If you remember to reset the fuel quantity after fill-up with know quantity, it gives you fuel endurance time based on Fuel Flow. This is most accurate and accounts for actual fuel used.
I guess the Hobbs would be a nice back up, but could not justify adding a 10th clock.
HOBBS AND TACH
Could a particular brand or model of Hobbs meter be more inaccurate or just off calibration more than others? Is the pressure switch set to activate at low oil pressure? Hobbs is just an electric clock turned on and off with a pressure switch, right. It would seem well with in the area of technology to make it accurate, if you wanted to.
Agreed, the traditional Hobbs is too conservative for maintenance. You don 't need to measure time unless in flight, i.e. high RPM/high power. The Tach hour-meter always is going to be less over time from the Hobbs, because it's rate of time accumulation is less at lower RPMs, like taxi, low or idle power, as was stated above. I think that is what the FBO's do. Charge on Hobbs and do maintenance on Tach. George