"Maintenance Hourmeter"

[cwleach]

While reviewing the logs of an '82 M20K I came across an entry showing the replacement of the original mechanical tachometer with a new EI electronic unit. While that's not unusual, the entry refers to the aircraft time shown on the "Maintenance Hrmtr (lower console)". Further in the entry it reveals "removed console hour meter". Since it's apparently gone now, I was curious about the reason Mooney may have put a specific clock for maintenance purposes versus simply using tach time, and if this clock is actually required equipment. Any gurus out there with knowledge on this?

[LANCECASPER]

12 minutes ago, cwleach said:

While reviewing the logs of an '82 M20K I came across an entry showing the replacement of the original mechanical tachometer with a new EI electronic unit. While that's not unusual, the entry refers to the aircraft time shown on the "Maintenance Hrmtr (lower console)". Further in the entry it reveals "removed console hour meter". Since it's apparently gone now, I was curious about the reason Mooney may have put a specific clock for maintenance purposes versus simply using tach time, and if this clock is actually required equipment. Any gurus out there with knowledge on this?

Commonly referred to as a Hobbs meter just to keep track of cumulative time on the airframe.

At some point later on as tachs no longer had an hour meter built in, the tach sent an electrical signal to the Hour meter to record at a pre-determined rate. On some models 2500rpm equaled a 1 to 1 ratio. Lesser rpm would provide a lower ratio.

[cwleach]

I thought the same thing ... but there's a separate "hobbs" meter with different times from the "Maintenance Meter". 

[JimB]

Well typically a Hobbs hour meter is for billing/log book time and the tach is for tracking maintenance. A lot of newer Garmin systems provide "Air Time" and this is what you use for maintenance tracking. Never seen a maintenance meter. Maybe it was wired to a squat switch. 

[jlunseth]

If you google "tachometer time vs. Hobbs time" you will find explanations of the difference between the two. I am sure no expert, but tach time is synonymous with "maintenance time" as I understand it. Tach time changes with the RPMs of the engine and Hobbs does not, I believe. Tach time/maintenance time is what is used to determine inspections or TBO for example, such as a 100 hour inspection for commercially operated aircraft. As stated, Hobbs is used  for logging and counts the time the aircraft is being operated.

My aircraft has a tach meter on the lower right console. The reference to "Maintenance Hrmtr (lower console)" isn't something Mooney called it, it is what the A&P called it when he made the log entry.

[PT20J]

The original tach was probably not mechanical but a B&D electric tach which did not include an hour meter (tachs with hour meters are called "recording tachometers"). The remote meter was driven by the tach as @LANCECASPER described. It measured what is colloquially referred to as tach time. This is what is usually used for maintenance records. Hobbs meters are usually driven by on oil pressure switch or something similar and record hours that the engine is running. This is usually used by flight schools and rental airplanes for billing.

Neither tach time or Hobbs time are technically correct for maintenance or pilot flight time. According to FAR Part 1.

Time in service, with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.

Flight time means: 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.

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[kortopates]

The original Mooney hour meter you described was electrically connected to the original Mooney Tachometer/RPM gauge.
If an EI R1 tachometer was installed to replace your original RPM gauge it replaced both Mooney indicators.

It sounds like someone separately installed a hobbs meter; probably from it on a leaseback.


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[RoundTwo]

My ‘88J had the hour meter located in the console, down by the copilot’s calf. When the new panel was done, the electronic tach was lost and the hour meter was then switched over to come on with the master switch. I have since had that hour meter removed and now use the times that the JPI keeps for maintenance purposes.

[GeeBee]

Believe me, the airlines don't use a hobbs meter or tach time. Time off to time on. Time on the ground does not count to time in service.

 

[PT20J]

3 hours ago, GeeBee said:

Believe me, the airlines don't use a hobbs meter or tach time. Time off to time on. Time on the ground does not count to time in service.

 

The G3X EIS has a timer in it (actually two) and I set it to "flight time". The Part 135 outfit I flew for had a Hobbs hooked up to an air switch for all the fleet planes. You'd be surprised how much difference it makes. 

[Pinecone]

Just to muddle the waters even more, the console meter in a Mooney is technically a Hobbs Meter, as it was made by Hobbs company.

They make lots of different timers for different uses. 

In common aviation use, a Hobbs meter counts the actual time.  It may be wired to run when the Master is on, or when the engine oil pressure comes up or from when the gear goes up or an airspeed switch.

The best reason for replacing the meter on a Mooney, is putting a readout where one can see it without contortions. 

[jlunseth]

2 hours ago, Pinecone said:

The best reason for replacing the meter on a Mooney, is putting a readout where one can see it without contortions. 

Ain’t that the truth!