Tach time vs Hobbs time

AKBill

AKBill

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AKBill
I'm a little embarrassed to ask this question but what the heck my skin is thick. I talked to a CFI lately after a BFR and he asked me if I used tach time or hobbs time when making my logbook entries. I said tach time. He said I should use hobbs time as it is a true measurement of time. Tach time is not accurate for ground operations and does not represent total time of the flight.

I have logged 1000+ hours tach time on my plane over the last 20 years flying, if I would have used hobbs time what would that equate to?
 
AKBill said:
I'm a little embarrassed to ask this question but what the heck my skin is thick. I talked to a CFI lately after a BFR and he asked me if I used tach time or hobbs time when making my logbook entries. I said tach time. He said I should use hobbs time as it is a true measurement of time. Tach time is not accurate for ground operations and does not represent total time of the flight.

I have logged 1000+ hours tach time on my plane over the last 20 years flying, if I would have used hobbs time what would that equate to?
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Wow ya, tach depends on how fast the engine is spinning. You might have a lot more hours than you recorded.
 
Well... whatever your tach time is times 1.2.

but, really, do you care? If you're filling up the book to get to minimums for a rating or a job you may want the 1.2 upper.

The planes I fly the most do not have operational hobbs meters. Couple that with me being lazy and I sometimes log it Tach and sometimes log it Hobbs. Can't say that under reporting using tach would ever hurt me.
 
I did a little Google searching and found a couple of posts saying multiply by 1.3 for Hobbs time. But I don't don't really know other than the Googling.
 
Yeah you cheated yourself of a couple hundred hours in all likelyhood...


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AKBill said:
I used tach time or hobbs time when making my logbook entries.
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You should use Hobbs. Tach is for the mechanics and your engine logbooks. Your flight time includes ground movement which you are not recording if you use tach time.
 
Yeah, you kinda cheated yourself, basically if the engine is running a 50% max RPM youre logging 50% of an hour per clock hour, so 2 hours on your watch at 50% RPM = 1 hour on the tach.

I use my watch or timer, log prop start to prop stop.
 
James331 said:
Yeah, you kinda cheated yourself
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Cheated himself of what? We all know that log books are only required for time towards ratings and..... <- I don't need to quote it since it's all over the forum.

So yes, if he wants the shortest duration route to a measured goal he should use Hobbs. But I didn't get that from the original post.
 
Ravioli said:
Cheated himself of what? We all know that log books are only required for time towards ratings and..... <- I don't need to quote it since it's all over the forum.

So yes, if he wants the shortest duration route to a measured goal he should use Hobbs. But I didn't get that from the original post.
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Hours. Which may or may not be valuable to you. For lower insurance, or for a resume should you ever decide to make flying a career...


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Live and learn, for me it's just time in the log book not using the time to earn additional ratings. Just something I stumbled on talking to the CFI. So 1000 hrs equates to 1200 hrs. Big difference...
 
That's why it's best to use a clock and note the time. I've used tach, Hobbs, Hobbs with WOG switch and clock.

I'm more of a believer in quality over quantity anyway so I don't place much of an importance of one over the other.
 
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BrianNC said:
I did a little Google searching and found a couple of posts saying multiply by 1.3 for Hobbs time. But I don't don't really know other than the Googling.
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That ratio depends on the airplane (especially fixed vs C/S prop) and the type of flight. 1.3 is about right for a 172 doing touch and go landings and some other 1 hr training flights but the same airplane running high power on a long trip will actually get more time on the tach than the Hobbs meter. Each airplane with a mechanical tach/hourmeter has a specific RPM where tach time equals Hobbs time ( often but not always somewhere around 2300 RPM). Run the engine below that speed and the tach hourmeter runs slower than Hobbs, at higher speeds it's the other way around.

And on the "legal" side, if you really want to be accurate you should use a stopwatch or log the start and stop time on your flights and take the difference. The FARs say you can log the time from the first movement of the airplane (on the ground) until it's parked if a flight occurs (time spent taxiing without taking off doesn't count). For that reason Hobbs actually overstates the hours slightly unless you let the airplane roll forward a couple feet right after starting but I can pretty much guarantee that no one is going to come after you for including the time from engine start to the beginning of your taxi if you use the Hobbs.
 
AKBill said:
I have logged 1000+ hours tach time on my plane over the last 20 years flying, if I would have used hobbs time what would that equate to?
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Depends a lot on the kind of flying you did. Was it all cross country stuff, or did you spend a lot of time doing pattern work?

In a typical single/flat engine, if all your flying was x-country, then you probably didn't miss too much time logging off the tach, unless you did a lot of flying from a busy class B airport with long ground run times.

If you did a spent a lot of time in the traffic pattern (especially doing power off approaches) you may have missed out on a lot of valid time.
 
BrianNC said:
I did a little Google searching and found a couple of posts saying multiply by 1.3 for Hobbs time. But I don't don't really know other than the Googling.
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1.2-1.3 is pretty typical multiplier for flying clubs/rentals that don't have a Hobbs meter.
 
Coupl'a 1.3 rentals round here I reckon.
 
I log Garmin time. It starts recording above 30 knots and 250' agl and stops below 30 knots. I "cheat" myself out of all my ground ops. I don't care. Logging "flight" time when you're sitting on the ground is shady anyway. ;)
 
A lot depends on how far back you pull the blue knob. Tach hour meter just counts how many times the prop turns.
 
If I'm flying a tach only aircraft I usually just multiple by 1.2. It's almost always spot on with the clock doing that. I believe I even found that in the AIM or somewhere in an FAA document.
 
Fearless Tower said:
Depends a lot on the kind of flying you did. Was it all cross country stuff, or did you spend a lot of time doing pattern work?

In a typical single/flat engine, if all your flying was x-country, then you probably didn't miss too much time logging off the tach, unless you did a lot of flying from a busy class B airport with long ground run times.

If you did a spent a lot of time in the traffic pattern (especially doing power off approaches) you may have missed out on a lot of valid time.
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Depends on the time of year. Example in the winter I preheat engine, start and warm up maybe 10 to 15 minutes before taxi. Not a lot of time in the pattern. Mostly warm engine and taxi for departure. Guessing taxi time is 5 to 10 minutes per flight.
 
Yep, 1.2 is close enough, unless your crashing-and-dashing, where it seems 1.3 or even 1.4 is more accurate. We don't have a Hobbs in our airplane, and I don't much note the exact time anymore. If you don't have a Hobbs, and use 1.2 to build time for a rating, the FAA will be fine with it. It's honest, and defensible.
 
Thanks for asking, this is always something I wondered as well, and I have noticed a large disparity when just doing touch-and-go's. I've always logged Hobbs and will sometimes pull the plane out and angle it differently so that prop wash doesn't hit anyone else pre-flighting, I guess that would count as "first movement"
 
Tantalum said:
Thanks for asking, this is always something I wondered as well, and I have noticed a large disparity when just doing touch-and-go's. I've always logged Hobbs and will sometimes pull the plane out and angle it differently so that prop wash doesn't hit anyone else pre-flighting, I guess that would count as "first movement"
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No that doesn't count. What he means is any time spent at the controls of the aircraft with the engine running, whether it be on the ground or in the air.
 
^thanks, I assumed as much, it was kind of tongue in cheek lol
 
These are my numbers from last year flying a plane that only has a tach.

Tach Hours: 25.15
Clock of Hobbs Hours: 32
Factor: Just shy of 1.3
Landings: 129 (I try to get 3 landings at least each time I fly)

More time in the pattern 1.3ish outside the pattern 1.2ish
 
Your flight time is the time under which the aircraft first moves under it's own power for the purpose of flight until it comes to rest at the end of the flight. Ideally as soon as you start taxiing you'd push a button on a stop watch and when you pull into park afterwards you'd press stop.

That being said, the FAA will allow just about any reasonable estimate. Since many Hobbs meters run with the engine start, that is an accepted way to do it. Note that a Hobbs meter is just an electric clock, so you have to know is it just connected to the master, an oil pressures switch, the gear, the heater?

Time in service (for maintenance issues) is determined differently. It's that time that the aircraft is flying. Some planes like later model Bonanzas and my Navion have a Hobbs meter that is on the gear switch. That's pretty much as close to the FAA time in service definition as you're going to get. The FAA will accept the numbers from recording tachs as well or just about anything else as long as you are reasonably accurate and consistent.
 
flyingron said:
Your flight time is the time under which the aircraft first moves under it's own power for the purpose of flight until it comes to rest at the end of the flight.
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I'm not arguing this, but it seems counter intuitive to me. To me, "flight time" doesn't include time spent taxiing. If it did, wouldn't we all be entering the few minutes one spends taxiing the plane from the hangar to the shop? Or to the gas island?

I note the time when I'm cleared for takeoff, and I note the time I pull off the runway at my destination. That's what I enter in the books. I may be cheating myself, but I'm quite sure no one will ever be able to challenge the hours I have in my logbook. (Not that I'd care.)
 
Rykymus said:
I'm not arguing this, but it seems counter intuitive to me. To me, "flight time" doesn't include time spent taxiing.
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The Hobbs is the standard clock to record flight time in the log book. The Hobbs meter will run during taxiing, takeoff, flying, landing and taxiing again.
  1. It can measure the time that the electrical system is on.
  2. It can be activated by oil pressure running into a pressure switch, and therefore runs while the engine is running.
  3. It can be activated by another switch, either an airspeed sensing vane under a wing or a pressure switch attached to the landing gear.
  4. It can be activated when the engine alternators are online (as in the Cirrus SR series).
 
Rykymus said:
I'm not arguing this, but it seems counter intuitive to me. To me, "flight time" doesn't include time spent taxiing. If it did, wouldn't we all be entering the few minutes one spends taxiing the plane from the hangar to the shop? Or to the gas island?
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CFR 1.1
Flight time commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing. So you wouldn't be able to log the time spent taxiing to the self serve or to the mx hangar if that was your only purpose.
 
I wouldn't call it "standard", since plenty of airplanes don't have a Hobbs, and one isn't required.

For practical purposes, if the engine is running for the purposes of flight, count it, if you care to. I know a high time guy that doesn't log anything, except what's required for currency - three takeoffs and landings, six approaches, etc., and the rest he doesn't bother with putting in his log book.
 
Rykymus said:
I may be cheating myself...
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You definitely are in regards to obtaining a rating or being hired to fly. It's what the FAA allows as flight time that can be counted toward a rating, or as used for qualifying for a particular job such as 135 or 121.
 
I just thought hobbs time was invented so flight schools could start charging you as soon as to flick the switch, knowing that new students will usually be sitting there for 10 minutes going through the checklist. ;)
 
OkieFlyer said:
I just thought hobbs time was invented so flight schools could start charging you as soon as to flick the switch, knowing that new students will usually be sitting there for 10 minutes going through the checklist. ;)
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Yeah, me too. You want to be count tach time when you're paying for the plane and/or instructor, but hobbs time for ratings. ;)
 
My experience was only a 15% boost from tach to actual with my old C182. Your mileage may vary
 
BrianNC said:
You definitely are in regards to obtaining a rating or being hired to fly. It's what the FAA allows as flight time that can be counted toward a rating, or as used for qualifying for a particular job such as 135 or 121.
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Except that I have no aspirations to take a pay cut and become a commercial pilot. To me, it's about time flying, not about time taxiing. If I was seeking that magic 1500 hrs, you bet I'd be counting every second I legally could.
 
Rykymus said:
I'm not arguing this, but it seems counter intuitive to me. To me, "flight time" doesn't include time spent taxiing. If it did, wouldn't we all be entering the few minutes one spends taxiing the plane from the hangar to the shop? Or to the gas island?
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Intuition has absolutely nothing to do with the regulations. The regs are what they are. As for the gas island, you didn't read what I said (or the actual regulation). It says FOR THE PURPOSES OF FLIGHT.
Maybe in your 172, taxiing isn't an innate part of flight, but as they say with regard to conventional gear, the flight ain't over until she's tied down. If the FAA wanted it to be solely the time in the air, they'd have written it that way (as I stated, that's how time in service is defined).
I note the time when I'm cleared for takeoff, and I note the time I pull off the runway at my destination. That's what I enter in the books. I may be cheating myself, but I'm quite sure no one will ever be able to challenge the hours I have in my logbook. (Not that I'd care.)
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You are cheating yourself, and there's no "challenge" to the log book because the FAA defines it as we have stated.
 
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