Van's Air Force
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Hobbs meter ?
- Thread starter JimWoo50
- Start date
Isaac
Well Known Member
No. You need an oil pressure switch. Something like this
https://www.aircraftspruce.com/catalog/inpages/hobbsswitch.php?clickkey=3855
12V to the Hobbs meter is switched thru the pressure switch which activates when the engine is running and producing oil pressure.
https://www.aircraftspruce.com/catalog/inpages/hobbsswitch.php?clickkey=3855
12V to the Hobbs meter is switched thru the pressure switch which activates when the engine is running and producing oil pressure.
Jetmart
Well Known Member
I did the same using an air pressure switch.
works great.
I went with this one as I didn't see the Honeywell version.
https://www.aircraftspruce.com/catalog/inpages/switch11-13477.php
PilotjohnS
Well Known Member
Combo switch
I used a combo oil pressure switch. When the engine is running The normally open side grounds out the hobbs, and the normally closed goes to the idiot light on the panel. Both the light and hobbs are feed from fused bus from master switch, ( normally open is closed when engine is running)
I used a combo oil pressure switch. When the engine is running The normally open side grounds out the hobbs, and the normally closed goes to the idiot light on the panel. Both the light and hobbs are feed from fused bus from master switch, ( normally open is closed when engine is running)
It depends what you want to record.
If you are trying to log Time In Service, that definition is: "for maintenance time records, aircraft log records, and similar purposes, the elapsed time from the aircraft leaving the surface until touching it again on landing". In that case you would want an air-switch that would record time from T/O to Landing. Most GPSs do the same thing, logging time with airspeed above a certain setting (40 kts?)
If you want pilot time for your logbook, you want (essentially) engine start to engine shutdown. (Oil Pressure Switch)
FAA definition of Flight Time:
(1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing.
If you don't want a Hobbs at all, the GPS will give you airborne time (TIS) for your engine, airframe, and prop, and you can add 0.3 to that for your pilot time. Before T/O is +0.2 (10-15 min), and after landing is +0.1 (6 min, give or take).
Close enough!
Flight Time for pilots, and Time In Service for maintenance records, are not the same thing.
I have flown aircraft that had two Hobbs meters. One was actuated by an air-switch (TIS), and the other was actuated by an oil pressure switch (Flt Time.) Best of both worlds back before GPS units came along!
As always, YMMV.
If you are trying to log Time In Service, that definition is: "for maintenance time records, aircraft log records, and similar purposes, the elapsed time from the aircraft leaving the surface until touching it again on landing". In that case you would want an air-switch that would record time from T/O to Landing. Most GPSs do the same thing, logging time with airspeed above a certain setting (40 kts?)
If you want pilot time for your logbook, you want (essentially) engine start to engine shutdown. (Oil Pressure Switch)
FAA definition of Flight Time:
(1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing.
If you don't want a Hobbs at all, the GPS will give you airborne time (TIS) for your engine, airframe, and prop, and you can add 0.3 to that for your pilot time. Before T/O is +0.2 (10-15 min), and after landing is +0.1 (6 min, give or take).
Close enough!
Flight Time for pilots, and Time In Service for maintenance records, are not the same thing.
I have flown aircraft that had two Hobbs meters. One was actuated by an air-switch (TIS), and the other was actuated by an oil pressure switch (Flt Time.) Best of both worlds back before GPS units came along!
As always, YMMV.
