Hobbs meters

MikeD

MikeD

Administrator
Staff member
Curious as to the different methods everyone has come across for how the Hobbs meter's (if equipped) are installed in their personal aircraft/FBO rental/flight school fleet, etc.

I personally have seen it one of three ways (maybe there's more)

1. Electrical. Wired to the battery/master switch, so it starts clicking when electrical power is applied.

2. Oil ppp. Senses oil pressure from the engine running and begins working.

3. My former airline had them as a squat switch relay on the left mainmount. When the switch sensed weight-off-wheels on takeoff, it would begin working and vice versa.

That being said, which method do most agree with when they rent aircraft, or log hours?

MD
 
In the UK we used to record the hobb times, however we were billed from take off to landing, taxing was free. Ofcourse I taxied and did my run up very slowly, so I could log some free time. Considering I was paying $130 an hour for a Tomohawk, it all helped!
 
Most of the aircraft that I fly it is hooked up to the oil pump...I like this one the best, because it is the most flexible. Allthough...I did fly a 210 a long time ago that it was connected to the master switch, and I didn't like it at all because you get charged if you just want to see what the date is on the gps
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Most of the planes I have flown use an oil pressure switch to activate the Hobbs only while the engine is running. Some places do use the master switch-Flightsafety does this on the Seminoles-for mostly revenue reasons. On the single engine planes, the revenue Hobbs is run by an oil pressure switch, but the maintenance Hobbs is activated by a squat switch on the nosegear.
 
We don't need to know how Hobbs meters are installed. We need to know how they can be uninstalled!
 
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We don't need to know how Hobbs meters are installed. We need to know how they can be uninstalled!

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Thats the beauty of the having the hobbs run off of the master switch....A guy rented the 210 that I used to fly (the hobbs ran off the master) for a long x-c trip to the bahamas or somewhere like that, and somewhere over the gulf of mexico, when he wasnt talking to anybody, he thought that he would be swift and switch off the master and save a few bucks.....only problem was that the tach time ran off of the oil pressure switch (I think), but anyway...when the master goes off, the tach time would keep running as long as the engine was running....long story short, when he got back, the hobbs read like 12 hours or so, but the tach time showed about 16 or so....when the aircraft was examined, the hobbs ran fine....and the tach meter was also ok....when both are working right, it would take an act of god to make the tach time more than the hobbs
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[ QUOTE ]
[ QUOTE ]
We don't need to know how Hobbs meters are installed. We need to know how they can be uninstalled!

[/ QUOTE ]
the tach time ran off of the oil pressure switch (I think), but anyway

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Nope the tach runs directly (mechanical) off the engine. Prop turning, Tach running. that is why the maintenance is all done by tach time, not hobbs.
 
And because the tach is mechanically linked to the engine it turns at a variable speed. If you go flying for an hour the hobbs meter will read an hour but the tach will read something less - maybe .7 or .8 or so because part of that hour is spent taxiing(very low engine power) and on approach/landing(fairly low engine power) and the tach is 'turning' slower than real time. The only time the tach will match the hobbs is if you start the egine and keep it at max power for the whole flight. There will always be a difference between the two meters - but not usually 4 hours on one trip - if the guy was going to cheat he should have at least reached behind the panel and unscrewed the cannon plug input to the tach
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Jason
 
I've seen them both ways. About half and half between the oil pressure and the master switch.

FSI also had "maintenance hobbes" meters attached to the strut. This was used to determine flight time for inspections, not for billing!

We all know about the Hobbes meter, but where is the Calvin meter?
 
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