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Airspeed Hobbs Switch?


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Since I only have a Hobbs meter and not a tach timer, the hours on my airplane tend to accumulate faster than what the actual flying time represents.  My A&P suggested that if I had only a Hobbs meter, it would make sense to install an airspeed switch so that the Hobbs meter only runs at flying speeds.  I'm assuming this would tie into the pitot system to get the airspeed.  I hate that just warming up my engine adds 0.1-0.3 to my engine and airframe time.  

 

I like the idea of the switch, but I'm sure FD would require an MRA form, and I'm not sure they'd approve it since it "alters" aircraft time.  Anybody have experience or thoughts on this? 

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The hour meter only runs when the alternator switch is in the on position, and also when the alternator lamp bulb is good and in the socket. ;)

 

Rotax wants the hour meter running anytime the engine is running, using actual time and not tach time.

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You don't need to use the hobbs meter to track time. There's nothing in the regs that say you have to use *any* meter. Which is a good thing because there are airplanes without any meter still flying around!

 

You can literally write 1.5 hours if you flew 1.5 hours, from wheels off to wheels touch down (this is when TIS starts and finishes). Just make sure you keep a proper running tally.

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You don't need to use the hobbs meter to track time. There's nothing in the regs that say you have to use *any* meter. Which is a good thing because there are airplanes without any meter still flying around!

 

You can literally write 1.5 hours if you flew 1.5 hours, from wheels off to wheels touch down (this is when TIS starts and finishes). Just make sure you keep a proper running tally.

 

You are correct, as is what I stated above. I will say that having an hour meter to keep track of time is a much better solution than keeping time on you watch and writing it down. At least this is what I have seen in my experience working on and flying older airplanes.

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Also,when selling an airplane, prospective buyers want to see the tach time and hobbs time (if equipped) and be able to reconcile all the times with logbook entries.  I would look into adding an engine hour meter in addition to the hobbs meter.  I think it's simply a timer triggered off of oil pressure, unless I'm mistaken.

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You are correct, as is what I stated above. I will say that having an hour meter to keep track of time is a much better solution than keeping time on you watch and writing it down. At least this is what I have seen in my experience working on and flying older airplanes.

 

Sorry didn't actually read the other posts in the thread, just briefly read the top post and made a reply :)

 

Also, rotax changed their wording, they used to say something like "oscillating quartz timer" or something to that effect, now they just say "use a meter that begins recording on takeoff and stops when wheels touch down".

 

By the way, dynon D series, and I'm fairly certain the skyview system does too, does have a flight timer. It triggers @ 30-35 knots and stops when it drops below that.

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Also,when selling an airplane, prospective buyers want to see the tach time and hobbs time (if equipped) and be able to reconcile all the times with logbook entries.  I would look into adding an engine hour meter in addition to the hobbs meter.  I think it's simply a timer triggered off of oil pressure, unless I'm mistaken.

 

An hour meter triggered by an oil pressure switch is mostly there for people who are renting aircraft or logging pilot time, in most cases it serves no purpose in relation to keeping track of time on the aircraft.

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I may have them backwards.  All I know is when renting, they charge by hobbs meter which is running all the time the engine is running, I guess.  For maintenance, they use the engine hours meter which runs about 20 percent less.  Many non-rental planes don't have a hobbs meter.

 

The G300 in the SkyCatchers I fly (and rent) records both.  They charge based on the hobbs reading which is always higher, of course.

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I may have them backwards.  All I know is when renting, they charge by hobbs meter which is running all the time the master switch is on (I think or maybe the engine needs to be running).

Most GA aircraft I've encountered in the past have had the HOBBS meter wired directly to an oil pressure switch, and not running through the MASTER. That prevents a renter pilot from just switching off the MASTER while in flight to save money. It also allows the MASTER to be on with the engine off for preflight duties and the like without the HOBBS meter running.

 

Anyway, that was the norm. As we're seeing, today there are lots of different implementations.

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Most GA aircraft I've encountered in the past have had the HOBBS meter wired directly to an oil pressure switch, and not running through the MASTER. That prevents a renter pilot from just switching off the MASTER while in flight to save money. It also allows the MASTER to be on with the engine off for preflight duties and the like without the HOBBS meter running.

 

Anyway, that was the norm. As we're seeing, today there are lots of different implementations.

Yes, I think you're correct.  I was mistaken to say it runs with only the master switch on.

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I may have them backwards.  All I know is when renting, they charge by hobbs meter which is running all the time the engine is running, I guess.  For maintenance, they use the engine hours meter which runs about 20 percent less.  Many non-rental planes don't have a hobbs meter.

 

The G300 in the SkyCatchers I fly (and rent) records both.  They charge based on the hobbs reading which is always higher, of course.

 

I use the Hobbs time for rental in my Warrior because it reads in real time, and not based on engine RPM. Both basically start at the same time. For my CT the hour meter is connected to the generator master, and runs when it is on. There are a few seconds of run time each flight where the engine is running and the hour meter is not.

 

As for Hobbs meters on other aircraft I have come across quite a few that use one for maintenance times especially complex aircraft aircraft. They are triggered with pitot air pressure or a landing gear switch. Some of the light twins with combustion heaters have a separate hour meter for just the heater, but use just one for airframe and engine time.

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Hi Andy,

 

Don't you have a Dynon D120?

 

if so you have the choice of tach time or hobbs time. Tach time accumulates at different rates depending on the rpm. It can be 15%-20%. 

Hobbs time runs at a steady rate no matter what the rpm. It is triggered by the engine being over 15 psi oil pressure and that usually only happens with the engine running. If you have the D120 you should be using hobbs time.

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