TSMOH

[smlynarczyk]

OK - this was clear in mind until I ran across log books for a plane (1990 era Mooney) I am looking at. TSMOH is listed in the sales ad but I am having a difficult time correlating this to the logs.  I see TT as a higher number than Tach but lower than Hobbs. Reading up about this, it seems this is less definitive than I thought. What should the TSMOH hours be based on?  Thx.

[gsxrpilot]

Might have to ask the guy who posted the ad, what he meant by that non-standard acronym. And how to reconcile the logs.

[Andy95W]

I've seen the acronym fairly often (Time Since Major Over Haul).

The answer should be the number of hours since the engine was overhauled.  This can get complicated as tachometers and Hobbes meters get switched out with new (that begin counting again at 0).

[smwash02]

There's two main numbers when referring to engines, which are TTSN and SMOH.

TTSN -- Total Time Since New

SMOH (TSMOH) - [Time] Since Major OverHaul

When your engine is either 1) made or 2) factory overhauled, your TTSN and SMOH goes to 0.

When your engine is overhauled by anyone else TTSN keeps ticking up and SMOH is set to 0.

Maintenance is done by tach time, so we can/should disregard the hobbs time here. Hobbs is 1:1, Tach is based on a ratio of your RPM to the number noted on the back of your tach. I think it's ~2500rpm is 1:1, but check the tach to confirm.

Hobbs and Tach gauges have multiple points of failure. Tach line, fuses, oil pressure switches, gauges themselves. If the tach stops working because gauge failed or cable snapped, tach stops ticking. If the tach stops working entirely, a new one is put in... these aren't always set to where the old one was and start at 0.

If the engine is replaced, the tach may or may not be, so you could have a 0 TTSN engine with 1500 on the tach and hobbs.

The engine logbook is the only way to get the story of why the numbers are what they are.

[smlynarczyk]

Paul, Controller uses this in any ads posted there so I thought it was clear to me until the figures and acronyms I see in these specific logs. Thanks!

[smlynarczyk]

Thanks smwash02. This makes sense and more in line with what I had thought.  I will ask the seller about the numbers they published. The TACH is less than the TSMOH figure they posted. Funny but Googling the topic brings up some varying opinions.

[smwash02]

Just now, smlynarczyk said:

Thanks smwash02. This makes sense and more in line with what I had thought.  I will ask the seller about the numbers they published. The TACH is less than the TSMOH figure they posted. Funny but Googling the topic brings up some varying opinions.

I would suspect that either:

1) Tach failed and didn't run for a period of time or was replaced with new

2) Engine failed early and was swapped for one with more hours

[Skates97]

The numbers on my plane from tach to engine to SMOH don't line up. At one point in its history it had a different engine (higher total time but lower SMOH time) put in it. However, everything is noted clearly in the logbooks.

In addition to the logbooks I keep a spreadsheet that has all the numbers in it which is easier to track than just using the logs. I put in the beginning/ending tach time for each flight and it keeps track of TT on the engine, time since overhaul, time since 500 hr mag inspection was done, time since oil change, time on the prop, as well as a column where I note how much oil I added and then it tracks the time between adding oil so I can easily see how much it is burning. Excel is a great tool. 

[RobertGary1]

I've swapped by my Hobbs and my tach for serviceable units in the past. You need to follow the log entries to know what the correction is. Engine time is always based on tach, never Hobbs . In fact Hobbs in a pilot's toy and has no FAA purpose at all.

 

-Robert

[Skates97]

21 minutes ago, RobertGary1 said:

I've swapped by my Hobbs and my tach for serviceable units in the past. You need to follow the log entries to know what the correction is. Engine time is always based on tach, never Hobbs . In fact Hobbs in a pilot's toy and has no FAA purpose at all.

 

-Robert

After my time in my PPL training and renting a plane I was surprised when I bought my plane and saw it didn't even have a Hobbs meter. Then I realized that nobody was keeping track of how much time I was in the plane to charge me for it. I could use it as much as I wanted, sit on the ground playing with the avionics, whatever I wanted to do! 

[Bob_Belville]

2 hours ago, Skates97 said:

After my time in my PPL training and renting a plane I was surprised when I bought my plane and saw it didn't even have a Hobbs meter. Then I realized that nobody was keeping track of how much time I was in the plane to charge me for it. I could use it as much as I wanted, sit on the ground playing with the avionics, whatever I wanted to do! 

Love it. A kid with a new toy. Doesn't get better than that!

[Skates97]

43 minutes ago, Bob_Belville said:

Love it. A kid with a new toy. Doesn't get better than that!

I tell my wife that guys never outgrow toys, they just get more expensive.

[smlynarczyk]

Thank guys. Went through the logs again and yes the tach was replaced. Now all the numbers do make sense.

[carusoam]

Now get a feeling for what is recorded by the tach time...

Some Long Bodies don't have a tachometer with an hour meter... Just a timer that is turned on by a switch, oil pressure or other...

Expect a lot of things to come out of the logs. Build a timeline when reviewing them. Even well kept logs can be a challenge to follow.

Good luck with the hunt!

Best regards,

-a-

Edited June 11, 2017 by carusoam

[mpg]

I still havent got to play with my plane yet,,  but I have gone through the logs twice,,  and made some notes of odd things!

Its a 66 and some time back the original engine was put in another plane, no telling how my plane kept on flying!

Some time goes by and my engine is reinstalled in my plane!?!?!!!

I havent tried to figure out tach time,,  especially with the engine swap... 

[cujet]

On 6/9/2017 at 3:59 PM, RobertGary1 said:

I've swapped by my Hobbs and my tach for serviceable units in the past. You need to follow the log entries to know what the correction is. Engine time is always based on tach, never Hobbs . In fact Hobbs in a pilot's toy and has no FAA purpose at all. 

From a practical standpoint, large aircraft use "flight time" to track engine time .  We commonly use a Hobbs meter that tracks flight time. Often it's configured to count time through the nose/main gear gear squat switch and an oil pressure switch. Ground operations do not affect recorded flight time. For example, both of our Pilatus PC-12's are configured this way. As is our EC-135 helicopter (uses collective pitch to start the timer) . Our larger aircraft, a G650ER and G550 both use the FMS for flight time, calculated by, you guessed it, oil pressure and squat switch. 

Tach time can also be mechanical or electronic. The mechanical tach is available with configurations such as, 1:1 = 2556RPM or 2300 RPM. Clearly the engine RPM chosen and the type of tach installed make a big difference. Many small aircraft have the wrong tach installed. 

 

Edited June 13, 2017 by cujet