Hobbs Time vs G1000 tach time

[OneAuburnFan]

Good evening all. I’m looking at planes and considering an upgrade. I looked at an Acclaim and the Hobbs on the rear bulkhead was at 1400ish while the tach was at 900 ish in the G1000. The spread seems very high. I would have guessed maybe 20%. Is this a normal spread?  Thanks in advance.

[kortopates]

Let Google be your friend, type the below into your browser for a Google search:

Mooneyspace.com: G1000 time vs hobbs time

You'll find at least 4 threads on the topic - the first one is perhaps the more complete.

The summary is the rear bulkhead meter is NOT a Hobbs meter but the Mooney Hour meter which records actual flight time - its wired into the airspeed safety switch per your POH. This is what you want for maintenance times or TIS - Time in Service. Before the airspeed safety switch was used, Mooney had the same hour meter wired to the Mooney tachometer to drive it. 

The G1000 time is elapsed engine time. i.e. clock time between engine start and shutdown. For all practical purposes it works just like the Hobbs meter you used on rental airplanes that relied on oil pressure for them to run and is also good for logging pilot time. 

Overtime the G1000 engine time >> Mooney Hour meter as you would want.  

Edited August 18, 2020 by kortopates

[wpbarnar]

6 hours ago, kortopates said:

Overtime the G1000 engine time >> Mooney Hour meter as you would want.  

The Acclaim he is looking out has the opposite.     The rear bulkhead or flight time is greater than the engine time on the G1000 by a significant amount.  

@OneAuburnFan what do the log books say?  Airframe and engine time should both be noted.   Did the difference slowly evolve over time or something else trigger it.

Bill

Edited August 18, 2020 by wpbarnar

[Guest]

So in this case the flight time per the hour meter has more recorded time than the engine meter in the G1000.  This Acclaim must have spent hundreds of hours as a glider.

Something doesn’t make sense.

Clarence

[Danb]

56 minutes ago, M20Doc said:

So in this case the flight time per the hour meter has more recorded time than the engine meter in the G1000.  This Acclaim must have spent hundreds of hours as a glider.

Something doesn’t make sense.

Clarence

Doesn’t make sense seems something was removed and replaced without updating the hours properly. My hours meter and G1000 meter are very close, within a couple hours there’s no doubt my ground times exceeds the difference between the two timing devices.

[Davidv]

8 hours ago, kortopates said:

Let Google be your friend, type the below into your browser for a Google search:

Mooneyspace.com: G1000 time vs hobbs time

You'll find at least 4 threads on the topic - the first one is perhaps the more complete.

The summary is the rear bulkhead meter is NOT a Hobbs meter but the Mooney Hour meter which records actual flight time - its wired into the airspeed safety switch per your POH. This is what you want for maintenance times or TIS - Time in Service. Before the airspeed safety switch was used, Mooney had the same hour meter wired to the Mooney tachometer to drive it. 

The G1000 time is elapsed engine time. i.e. clock time between engine start and shutdown. For all practical purposes it works just like the Hobbs meter you used on rental airplanes that relied on oil pressure for them to run and is also good for logging pilot time. 

Overtime the G1000 engine time >> Mooney Hour meter as you would want.  

You learn something new everyday...

In my case the meter is in the left side of the passenger foot well (92 Bravo).  Is mine also measuring off the airspeed safety switch?

[buddy]

Check and make sure that the Hobbs meter is not running after shutdown. I found mine did and I just disconnected it, pulled one wire of the back of it. You can also hear if the Hobbs meter running if you put your ear close to it.

[Hank]

24 minutes ago, buddy said:

Check and make sure that the Hobbs meter is not running after shutdown. I found mine did and I just disconnected it, pulled one wire of the back of it. You can also hear if the Hobbs meter running if you put your ear close to it.

If you have Tach Time, you don't need a Hobbs. Unless you're renting out your plane . . . . My Mooney never had a Hobbs.

[RLCarter]

I installed a Hobbs meter in my “E”, I use it for keeping track of flight time

[kortopates]

3 hours ago, Davidv said:

You learn something new everyday...

In my case the meter is in the left side of the passenger foot well (92 Bravo).  Is mine also measuring off the airspeed safety switch?

No, before G1000's the Mooney Hour meter ran off the tach - you can see that from your schematic. Its 1:1 at a cruise RPM less than max RPM - its should be about .2 lower than actual elapsed time, per flight,  if you significant taxi an runup time like I do.

[Davidv]

1 minute ago, kortopates said:

No, before G1000's the Mooney Hour meter ran off the tach - you can see that from your schematic. Its 1:1 at a cruise RPM less than max RPM - its should be about .2 lower than actual elapsed time, per flight,  if you significant taxi an runup time like I do.

Thanks, good for know.  I suspected it was a little less from my logbook entries.  Since you either need to be an Olympic gymnast or crawl on your stomach through the passenger footwell to get a reading, I usually just check it periodically for my oil changes ect...

[JimB]

I can't speak to the Mooney installation but the G1000 installed in most other aircraft indicates "Flight Time". It is determined by on-ground and off-ground states within the G1000.  The hobbs meter is usually wired to the master, engine master or ignition switch. 

You base the maintenance intervals off of flight time. You bill rentals off of hobbs time. 

Edited August 18, 2020 by JimB

[StevenL757]

6 hours ago, M20Doc said:

So in this case the flight time per the hour meter has more recorded time than the engine meter in the G1000.  This Acclaim must have spent hundreds of hours as a glider.

Something doesn’t make sense.

Clarence

Ditto.

@OneAuburnFan, Are the logbooks complete?  Are there gaps, and if so, how big are the gap?

Also, curious to know your intended mission for the Acclaim...living in GA.  A jump from a "J" to a "TN" is a quantum leap in capabilities.

[skykrawler]

The club DA-40 I flew for a while had a considerable spread between the tach time and the hobbs.   The tach time came from the VM1000 engine monitor which didn't clock time until it was over 1500 rpm.  Hobbs meter tracked elapsed time with oil pressure or power on.   Mechanical tach count revolutions - so time idling and low rpm count up less time.   That airplane had the engine overhauled at 1900 hours tach.   The hobbs had something like 2600.  Tach time says nothing about how many cold starts you have made.

So  a spread is not unusual.

[exM20K]

1 hour ago, skykrawler said:

The club DA-40 I flew for a while had a considerable spread between the tach time and the hobbs.   The tach time came from the VM1000 engine monitor which didn't clock time until it was over 1500 rpm.  Hobbs meter tracked elapsed time with oil pressure or power on.   Mechanical tach count revolutions - so time idling and low rpm count up less time.   That airplane had the engine overhauled at 1900 hours tach.   The hobbs had something like 2600.  Tach time says nothing about how many cold starts you have made.

So  a spread is not unusual.

also, if battery voltage drops low enough during storage, the DA40 hobbs will run on its own.  ask me how i know:-)

[exM20K]

1083 vs 1089 (bulkhead vs G1000) for mine.  Perhaps the G1000 doesn't record below a threshold rpm. Hardly worth noting....

I use G1000 for logging and MX.

What section of POH addresses these gauges? 

-dan

[GeeBee]

There is nothing to say a Hobbs meter is correct time. I have seen many run fast and run slow. In fact, they are notoriously unreliable for keeping proper time. 

 

 

[OneAuburnFan]

9 hours ago, StevenL757 said:

Ditto.

@OneAuburnFan, Are the logbooks complete?  Are there gaps, and if so, how big are the gap?

Also, curious to know your intended mission for the Acclaim...living in GA.  A jump from a "J" to a "TN" is a quantum leap in capabilities.

The logs were complete as far as I could tell on a quick review. I didn’t dig too deep to find a possible source for the disparity I’m asking about here. It was an initial visit. 
 

My mission is primarily trips to Daytona and Vero beach. I would like an Acclaim for the flexibility of being able to climb and go fast if I want. If I’m in no hurry, I’ll dial it back and cruise. Seems to be a pretty flexible machine. 
 

Thanks for all the replies. Super informative.

[OneAuburnFan]

9 hours ago, skykrawler said:

The club DA-40 I flew for a while had a considerable spread between the tach time and the hobbs.   The tach time came from the VM1000 engine monitor which didn't clock time until it was over 1500 rpm.  Hobbs meter tracked elapsed time with oil pressure or power on.   Mechanical tach count revolutions - so time idling and low rpm count up less time.   That airplane had the engine overhauled at 1900 hours tach.   The hobbs had something like 2600.  Tach time says nothing about how many cold starts you have made.

So  a spread is not unusual.

This answer seems most likely given the much higher Hobbs number. Thanks.  
while I’m just looking at this point, it never hurts to know such things to the best extent possible.  

[carusoam]

Find the section in the POH... each instrument gets a paragraph...

The flight timer will describe what it is tracking and what turns it on...

The G1000 will have several pages for its operation... each function being covered...

PP thoughts only, not a CFI...

Best regards,

-a-