Tach time sync with G3X

[hais]

Our ovation has a Hobbs meter in the baggage area that runs at lower rate on low rpm. I would like to find out what the parameters are so that I can configure G3X engine time meter to count the same.

How do I figure out the rpm settings? 

[PT20J]

You could check with Frank Crawford service@mooney.com for the proper number, but if it is like my M20J, the installed meter reads 1:1 at 2500 rpm.

if you are using the G3X to record time in service for maintenance, you are better off to set it for flight time which agrees with the time in service definition in FAR Part 1 and gives you lower numbers than tach time.

The G3X has two timers, so I set Engine Time to be 1:1 at 2500 and Total Time to be flight time. Eventually, I deleted the Engine Time timer because I got tired of explaining it to maintenance people that are used to recording tach time fir maintenance.

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[Pinecone]

I checked with Frank about my M20K 252, and he said that pretty much all of them use 2500 as base.

However, with my JPI 830, I set it to 2500, but it is not tracking the physical meter.  After about 8 hours, it is about  0.3 off.  So will try 2490.

[PT20J]

55 minutes ago, Pinecone said:

I checked with Frank about my M20K 252, and he said that pretty much all of them use 2500 as base.

However, with my JPI 830, I set it to 2500, but it is not tracking the physical meter.  After about 8 hours, it is about  0.3 off.  So will try 2490.

It might be that the time/rpm curve isn’t quite linear. Someone posted a calibration chart for the B&D tachs a while back.

[hais]

13 hours ago, Evan said:

Are you wanting to use the G3X to track engine time or keep using the baggage compartment one?

Wanted to use G3X, but since we have the other one still, it's nice if they match. 

[PeteMc]

13 hours ago, Evan said:

Our ovation has a Hobbs meter in the baggage area that runs at lower rate on low rpm.

Sounds like it's a voltage problem if the Hobbs meter if it's running slow at low RPM.  A Hobbs meter is just supposed to run in real time once it's turned on like a stopwatch.  Typically it turns on with the Master, but sometimes it turns on with a squat switch for flight hours.  It is not supposed to vary in time like Tach Time, which runs slow, in sync or fast compared to time of day pending what RPM the engine is running at.

Even with the lower voltage at low RPM, I'd be surprised if the batter dropped below 12v.  I guess it could happen pending the load, but just surprised the Hobbs runs slow enough for you to notice.

 

Edited June 10, 2023 by PeteMc

[PT20J]

1 hour ago, PeteMc said:

Sounds like it's a voltage problem if the Hobbs meter if it's running slow at low RPM.  A Hobbs meter is just supposed to run in real time once it's turned on like a stopwatch.  Typically it turns on with the Master, but sometimes it turns on with a squat switch for flight hours.  It is not supposed to vary in time like Tach Time, which runs slow, in sync or fast compared to time of day pending what RPM the engine is running at.

Even with the lower voltage at low RPM, I'd be surprised if the batter dropped below 12v.  I guess it could happen pending the load, but just surprised the Hobbs runs slow enough for you to notice.

 

If it's connected to a B&D electric tach, it isn't really a traditional Hobbs hour meter. It has a third wire connected to the tach and it reads tach time calibrated 1:1 at 2500 rpm. A true Hobbs hour meter doesn't run slower with lower voltage -- it should either run or quit if the voltage is too low.

[PT20J]

1 hour ago, hais said:

Wanted to use G3X, but since we have the other one still, it's nice if they match. 

There's an old saying: A person with one watch knows what time it is, but a person with two watches is never sure. 

[hais]

2 hours ago, PT20J said:

There's an old saying: A person with one watch knows what time it is, but a person with two watches is never sure. 

Well, I think a scotch tape on the G3X will resolve the uncertainty:)

[Pinecone]

14 hours ago, PT20J said:

It might be that the time/rpm curve isn’t quite linear. Someone posted a calibration chart for the B&D tachs a while back.

That was me.  That was the chart that Frank gave me.  And it was pretty linear over the normal operating range.

I am sure there is some slight variation from tach to tach, just based on tolerances.  I just want to get the proper number before that tach is removed with the my install of a G3X with EIS.

[Pinecone]

9 hours ago, PT20J said:

If it's connected to a B&D electric tach, it isn't really a traditional Hobbs hour meter. It has a third wire connected to the tach and it reads tach time calibrated 1:1 at 2500 rpm. A true Hobbs hour meter doesn't run slower with lower voltage -- it should either run or quit if the voltage is too low.

There is a problem with terminology.  Hobbs is a company that makes meters that count.  They may be triggered by various means and may count hours or they may count pulses or other things.

We CALL a meter a Hobbs Meter that counts hours, most times in aviation, directly hour for hour.

I suspect that our meters count pulses that even out to 2500 RPM reading 1 hour for 1 hour at that RPM.  On most other aircraft, that counting is done inside the Tach and is called Tach Time.   Mooney Tach Time is read out on a meter made by Hobbs Company.

 

[PT20J]

The G3X also has a setting for the rpm that must be exceeded to begin counting. 

[hais]

9 hours ago, Pinecone said:

That was me.  That was the chart that Frank gave me.  And it was pretty linear over the normal operating range.

I am sure there is some slight variation from tach to tach, just based on tolerances.  I just want to get the proper number before that tach is removed with the my install of a G3X with EIS.

Thanks for coming forward - can you share the link?

[hais]

9 hours ago, Pinecone said:

There is a problem with terminology.  Hobbs is a company that makes meters that count.  They may be triggered by various means and may count hours or they may count pulses or other things.

We CALL a meter a Hobbs Meter that counts hours, most times in aviation, directly hour for hour.

I suspect that our meters count pulses that even out to 2500 RPM reading 1 hour for 1 hour at that RPM.  On most other aircraft, that counting is done inside the Tach and is called Tach Time.   Mooney Tach Time is read out on a meter made by Hobbs Company.

 

I had to scratch my head a bit to figure out how to write the original post without messing up the terminologies...

[PeteMc]

22 hours ago, PT20J said:

it should either run or quit if the voltage is too low.

Exactly!!

[PeteMc]

3 hours ago, hais said:

Mooney Tach Time is read out on a meter made by Hobbs Company.

Interesting historical tid bit....   So you're saying the company that built the Tachs for Mooney, when they built the instruments, installed a Hobbs brand counting mechanism/dial display?  Or were the all of the guts in the Tach supplied by Hobbs?

I honestly don't remember the brand of my original Tach, but I'm sure it wasn't Hobbs.  Guess it wasn't the original and was just what was in there when I bought the plane, but it failed not too many years after I got the plane and replaced it with a Horizon and it hasn't failed me yet.

[PT20J]

A guy named Hobbs invented an hour meter widely used in aircraft  manufactured by a company he founded using the same name. Because the face of the meter had the company name on it, everyone called it a Hobbs meter. 

Mechanical 3-1/8" diameter recording tachometers have an hour meter built in that records 1:1 at some rpm (depends on the tach). Because most all airplanes used to have one of these, it was commonly used for tracking maintenance time. And, since the meter is part of the tachometer, it became commonly referred to as tach time.

The smaller 2-1/4" electric tachometers didn't have space for an hour meter. The B&D tachs used by Mooney used a meter that looked like a standard Hobbs meter, but actually is different electrically, to record tach time in the same manner as a recording mechanical tachometer. 

According to Wikipedia, the Hobbs product line was purchased by Honeywell at some point and discontinued in 2022.

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[Pinecone]

21 hours ago, hais said:

Thanks for coming forward - can you share the link?