Hobbs - why?

Ed Haywood

Ed Haywood

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Big Ed
I'm going to replace my mechanical oil pressure gauge with an electric gauge, with sender forward of the firewall. The oil P line under the panel, which will be removed, has a switch plumbed to turn on a Hobbs.

If I have a recording tach, and I do not ever intend to rent my plane, is there any reason to keep the Hobbs, or can I toss it?

If I keep it "just because", can I wire the Hobbs to trigger from the new oil P sender?

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Ed Haywood said:
If I have a recording tach, and I do not ever intend to rent my plane, is there any reason to keep the Hobbs, or can I toss it?
Click to expand...
Do you track any maintenance, recurring ADs, etc with your hobbs time? If so make logbook entry converting your hobbs mx times to whatever new method you will track time-in-service of the aircraft.
Ed Haywood said:
If I keep it "just because", can I wire the Hobbs to trigger from the new oil P sender?
Click to expand...
Probably not unless your new electronic system has a separate provision for it as electronic systems use some sort of variable signal/resistance to the indicator vs a steady system voltage to run the hobbs.
 
What time do you use for your logbook?
 
Maintenance time in service is time the wheels are off the ground in general. Pilot time is time from when the plane first moves under its own power for purpose of flight until it comes to rest. Neither the tach nor the Hobbs connected to an oil pressure switch or master fit the definition of this time (some Bonanzas have the Hobbs on the gear squat so that's about as close as you come to time in service).
The FAA will allow you to use these approximations if you want, as long as you're consistent.
 
Me too -- Hobbs for pilot, tach for MX. Ditch the Hobbs. If you want to continue to use clock time, get a kitchen timer.
 
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