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  #1  
Old 10-31-2020, 07:37 PM
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MacCool MacCool is offline
 
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Location: central Minnesota
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Default Total time....Hobbs or Tach?

Here's a bonehead question. When stating total time on airframe/engine, does one quote Hobbs, or Tach? For me, the difference is considerable.

Hobbs.....442.22
Tach.......364.22
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  #2  
Old 10-31-2020, 07:43 PM
gasman gasman is online now
 
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Hobbs is 100%. Tach time is a percentage based on rpm.

Most all rentals are based on hobbs time.
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  #3  
Old 10-31-2020, 07:59 PM
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Yup..this I know.

If you were selling your airplane, to the prospective buyer would you quote Hobbs, or Tach?

To put it another way, if you were buying an airplane, would you be more interested in Hobbs time, or Tach time?
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  #4  
Old 10-31-2020, 08:05 PM
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rvanstory rvanstory is offline
 
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Quote:
Originally Posted by MacCool View Post
Here's a bonehead question. When stating total time on airframe/engine, does one quote Hobbs, or Tach?
I’ve always assumed tach time is the more accurate indicator of useful life. Not sure what the “official answer” is, or if there is one. I’d use tach.
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  #5  
Old 10-31-2020, 08:11 PM
georgedouglas georgedouglas is offline
 
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Quote:
Originally Posted by MacCool View Post
Here's a bonehead question. When stating total time on airframe/engine, does one quote Hobbs, or Tach? For me, the difference is considerable.

Hobbs.....442.22
Tach.......364.22
According to the FAA it is up to the owner to determine and record aircraft time. You could use a stop watch for that matter, but the normal for non commercial use is tach time.
george
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  #6  
Old 10-31-2020, 08:13 PM
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PaulvS PaulvS is offline
 
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Default Times

Hobbs time for the airframe. For the engine and prop, tach time and time remaining to overhaul. Also interested in calendar age of the airframe and engine to calculate average hours flown per year.

I'm accustomed to Lycoming maintenance e.g. oil change and 100 hourly per tach time. But Rotax appears to be different and needs to be serviced based on Hobbs time.
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  #7  
Old 10-31-2020, 08:13 PM
okdonn okdonn is offline
 
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Quote:
Originally Posted by georgedouglas View Post
According to the FAA it is up to the owner to determine and record aircraft time. You could use a stop watch for that matter, but the normal for non commercial use is tach time.
george
Tach time for maintenance and use records. Hobbs time for your log book and rental use.
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  #8  
Old 10-31-2020, 08:14 PM
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Foghorn Foghorn is offline
 
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Quote:
Originally Posted by MacCool View Post
Here's a bonehead question. When stating total time on airframe/engine, does one quote Hobbs, or Tach? For me, the difference is considerable.
Tach for me. Neither aircraft has a Hobbs meter so it’s easy.
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  #9  
Old 10-31-2020, 09:25 PM
PCHunt PCHunt is offline
 
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Someone will correct me if I'm wrong, but here's how I remember it:

Time In Service (TIS) for maintenance that is related to hours, (i.e. a 100-hour inspection) is calculated or recorded as time from takeoff to landing. That includes engine hours TIS.

Logging pilot time, or Flight Time, is from start of taxi, to end of taxi after landing. Or near enough, engine start to engine shutdown.

Tach time approximates TIS. Hobbs time approximates Flight Time.

Most GPS's will give you a time based on liftoff and landing. That should be close to tach time.

Or, you can look at your watch 4 times during the flight......... Start, Roll, End of rollout, and stopping before shutdown.

Nothing is ever easy!

So, when advertising a plane for sale, the buyer should be interested in the Time In Service (Tach), rather than the pilot flight time.
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  #10  
Old 10-31-2020, 11:30 PM
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RV7A Flyer RV7A Flyer is offline
 
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Quote:
Originally Posted by PCHunt View Post

Or, you can look at your watch 4 times during the flight......... Start, Roll, End of rollout, and stopping before shutdown.
ACARS used to (and maybe still does) call this OOOI...Out, Off, On, In. Out of the gate, off the ground, on the ground, in the gate.

I use the most conservative approach for maintenance items, that is, Hobbs time. I figure the engine is turning, plugs are firing, etc. So I change oil a little bit more often, or clean/rotate the plugs a little sooner, etc. In the grand scheme, it's just easier to keep one set of numbers for everything, and I treat my engine a little nicer.
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