OK, So why an engine tach & a Hobbs?

kontiki

kontiki

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Kontiki
Just wondering?
 
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My understanding: the tach measures "engine time"(based on propellor revolutions) and is useful for engine related things(oil changes, over hauls, etc), whereas the hobbs is a measure of "airframe time" and based on actual time the plane is "being used" and is useful for things not related to engine time, renting being the main one.
 
mechanical tach time will always be less than hobbs time

electronic tach time will be closer to hobbs time but not equal

hobbs time is real time so it works well for logs & billing
 
I record POC time based on Hobbs, which is usually 20% more than tach hours.
 
Yup, you can't measure mileage meaningfully in an airplane, so you count engine revolutions to decide how "old" an engine is.
 
Clark1961 said:
mechanical tach time will always be less than hobbs time
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only if your hobbs reads engine running time. Ideally the hobbs will only read flight time. For hour-dependant AD's, inspections, etc, time running on the ground is free.
 
MAKG1 said:
Yup, you can't measure mileage meaningfully in an airplane, so you count engine revolutions to decide how "old" an engine is.
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Yeah, guess it would be difficult to cut the engine in half and count "rings.":wink2:
 
Neither the Hobbs or the Tach is technically time in service by the FAA definition, but the FAA will accept either as long as you are consistent.

The time in service is the time the aircraft is off the ground. In my plane, I have the hobbs connected to the gear so that's about as good as you're going to get. (My tach came out of a bonanza so it's not a recording one).

It's a fallacy that the engine only has some fixed amount of rotations in it's life. Wear is determined by many things PRIMARILY HEAT.
 
"A man with a watch always knows what time it is; a man with two is never quite sure." :D
 
MAKG1 said:
Nope. Just takes a bandsaw.

And if you have a 4banger, odds are you have eight compression rings and four oil control rings.
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Your bandsaw must be bigger and stronger than mine!:wink2:
 
Use one for flight time ,the other (lower ) for billing time.
 
Taxi the plane takes more care and skill than flying it straight and level. In my opinion, the time on the ground with the engine running is part of piloting. The flight isn't over until the engine is stopped. (And its not really over until its in the hangar or tied down.)
 
tinerj said:
Taxi the plane takes more care and skill than flying it straight and level. In my opinion, the time on the ground with the engine running is part of piloting. The flight isn't over until the engine is stopped. (And its not really over until its in the hangar or tied down.)
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depends on the purpose of counting time. For counting hours toward an inspection or a life limited part, the flight is indeed over when the wheels touch the ground.
 
JHW said:
flight is indeed over when the wheels touch the ground.
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Wheels, tires, and brakes don't think so, but I do understand what you are saying. It's really what needs to be measured.

For purposes of my pilot logbook time, elapsed time from engine start to engine shutdown (provided an actual flight is made) is what I record.
 
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tinerj said:
Taxi the plane takes more care and skill than flying it straight and level. In my opinion, the time on the ground with the engine running is part of piloting. The flight isn't over until the engine is stopped. (And its not really over until its in the hangar or tied down.)
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Pilot flight time is the time from which the aircraft first moves under it's own power for the purpose of fight until it comes to a rest.

Time in service (maintenance) was already described in my earlier post.

Neither the tach or hobbs are precisely either one of these numbers in most cases.
 
Does anybody remember when Hobbs' meters first appeared in GA? I know it happened after I started, but no exact recall.
 
flyingron said:
Pilot flight time is the time from which the aircraft first moves under it's own power for the purpose of fight until it comes to a rest.

Time in service (maintenance) was already described in my earlier post.

Neither the tach or hobbs are precisely either one of these numbers in most cases.
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yep, and that's why I have a timer built into my yoke. My last plane didn't have a hobbs and I owned the one I have now for a while before I noticed it did. It's in an awkward place and I can't say that I've read the numbers on it.
 
tinerj said:
For purposes of my pilot logbook time, elapsed time from engine start to engine shutdown (provided an actual flight is made) is what I record.
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Me as well. My ticket is in jeopardy for my actions from engine start to engine stop. So that's what I record.
I know, movement to end of movement. But the plane moves when the engine starts (just not longitudinally).
 
wabower said:
Does anybody remember when Hobbs' meters first appeared in GA? I know it happened after I started, but no exact recall.
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It appeared when FBOs realized they could generate more revenue based on a clock than engine revolutions!!
 
JHW said:
only if your hobbs reads engine running time. Ideally the hobbs will only read flight time. For hour-dependant AD's, inspections, etc, time running on the ground is free.
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Most hobbs meters I've dealt with are electric, with some including an oil pressure switch so they start running when power is applied and there is oil pressure. Others forego the pressure switch and run the meter as long as the master is one.
 
All hobbs meters are electric. They're electric elapsed time meters which run as long as they have power. The question is what controls the power that feeds them. Some wire them to the master or the oil switch as noted. The one in my plane (and I presume most of the modern Beech stuff) is wired to the gear.
 
LDJones said:
Most hobbs meters I've dealt with are electric, with some including an oil pressure switch so they start running when power is applied and there is oil pressure. Others forego the pressure switch and run the meter as long as the master is one.
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and some (mine included) are on an airflow switch on the belly and count time over 40mph give or take
 
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