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Tachometers and Flight Logging

Old 26th Feb 2022, 22:31
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Tachometers and Flight Logging

Hey Guys,

So I've been hiring out a few lighties which are charged on tacho time, and I'm told i should be logging tacho time as well. Can someone help explain the benefit of tacho time?, what actually makes it go up compared to a VDO? Some ppl have told me i should be logging chock to chock

TIA
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Old 26th Feb 2022, 23:07
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Originally Posted by q400link View Post
Hey Guys,

So I've been hiring out a few lighties which are charged on tacho time, and I'm told i should be logging tacho time as well. Can someone help explain the benefit of tacho time?, what actually makes it go up compared to a VDO? Some ppl have told me i should be logging chock to chock

TIA
It's very straight forward, flight time is considered from when the craft moves under its own power for the intention of flight to when it comes to a stop at the destination after completion, chock to chock. Tacho is for engine maintenance, the timer will vary according to engine load or RPM, Flight switch is for airframe maintenance and VDO is engine running time, usually a very close approximation, unless you spend 20 minutes warming up that is.
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Old 26th Feb 2022, 23:14
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As long as you're not adding swathes of time to your actual flights, nor making up flights you didn't do - no one cares. It's your logbook, and what you log is up to your honesty.
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Old 26th Feb 2022, 23:14
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43Inches is correct but in practice, a lot of people, including me, use tach time. Itís much simpler and easier. Just look at the tach hours after shutdown and subtract the previous value in the logbook.

Yes, I know the argument that I am wasting TBO hours, but itís minuscule in the grand scheme of things.
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Old 26th Feb 2022, 23:43
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Errrm, how does logging tach time mean you’re “wasting TBO hours”?

I’m having trouble in even understanding what “log” or “logs” this thread is referring to. Old timer’s disease I suppose….
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Old 27th Feb 2022, 00:11
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In all the types I've flown tacho time has always been less than the actual elapsed time, depends on the rpm at which you run the engine and time spent on the ground.
If you use the tach time for your pilot logbooks entries, you could be shorting yourself on your flight hours because tach time can be as much as 20 percent lower than the Hobbs time.
https://doublemaviation.com/hobbs-time-vs-tach-time/
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Old 27th Feb 2022, 00:30
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In theory if you used Tacho time for flight and duty compliance you would be exceeding your actual flight time limits if you were calculating to the maximum without an adjustment. Hence why there is a strict method for calculating flight time. Tacho 'time' is misleading as it does not measure hours and minutes, its a counter that measures engine usage. It does relate about 80% to real time, depending on things like length of flight and taxi, but obviously the lower the average RPM used for a particular flight the slower the counter will tick over. VDO/HOBBS would be the closest approximation to the legal requirement. For private operations, who cares, if you are building hours for your commercial or experience in general you will shaft yourself out of approximately 20% flight time.
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Old 27th Feb 2022, 01:15
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With respect, 43, you’ve got it the wrong way around, for the reason stated by megan.

Of course, so much depends on what kind of tacho we’re talking about. In the case of a ‘standard GA’ steam driven tacho, one hour only equals one hour at one specific RPM (usually around 2.350 as I recall, but someone will correct me if I’m wrong). A steam driven GA tacho is actually the same as a steam driven car speedo/odometer.

So, one hour taxiing around at 1,200 RPM results in less than an hour clocking over on the tacho. One hour cruising at 2,450 RPM results in more than an hour clocking over on the tacho.

And I’m still not sure if we’re talking about pilot logged time or aircraft logged time in service or whatever, none of which has any necessary relationship to how an aircraft owner chooses to charge for the use of the aircraft.
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Old 27th Feb 2022, 01:40
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The OP is hiring an aircraft and paying via the Tacho counter. He is asking if they should be logging the flight time (personal log) via the Tacho or chock to chock. I explained clearly that Tacho is a maintenance counter which generally under-reads block time. Chock to Chock is most accurately represented by VDO, if you don't actually record it via watch times, which is perfectly acceptable, we do that in airline operations. The other option to Tacho counter for maintenance is Air switch with a factor for engine time. As for airframe maintenance airborne time (airswitch) is all that matters in most cases. In airline ops you just manually enter watch time off and on block for personal logbook, and the airborne and landing times for maintenance. Then the smart guys in tech do fancy calculations based on how it flew as to what cycles and hours remain.
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Old 27th Feb 2022, 01:57
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I think we’re in heated agreement about the technicalities of what various things measure and those measurements’ correspondence or otherwise with various times recorded for regulatory purposes.

Not sure what flight and duty times have to do with a privately hired GA aircraft. But I take your point in the case of pilots logging flight time on the basis of a steam driven GA tacho that is, on ‘average’, run below the RPM at which 1 tacho hour equals 1 real hour, the logged flight time will usually be less than actual flight time. However, I reiterate that - as always - so much depends on what specific kind of tacho is fitted to the aircraft. Digital tachos don’t work the same as steam driven ones. And a steam driven tacho (and most ‘Hobbs’ meters) will record time spent warming up then taxiing to the fuel bowser to fill up before a flight, none of which time counts as flight time for the pilot nor time in service for the aircraft.

(And I still have no idea how logging tacho time as pilot flight time results in “wasting TBO hours” as suggested by India Four Two.)

Last edited by Lead Balloon; 27th Feb 2022 at 02:08.
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Old 27th Feb 2022, 02:08
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However if you were ever questioned about logging your flight time and responded I just logged the VDO time, CASA would not give a damn. However in a commercial operation if you used Tacho you could find yourself having exceeded flight time limitations, I'm only stateing where the logging of flight time becomes a strict process that CASA will care about. As I stated earlier for private ops, who cares. The only issue being if you are logging it for experience purposes you will shaft yourself out of hours needlessly. Standard factors we'd apply in the old days is .2-.3 for tachos and .3-.4 for airswitch for say a session of circuits, reduced number for say navex. that's if you couldn't be arsed looking at your watch at blocks on/off. CASA seemed happy with that. Engineers had factors for converting Tacho use for airframe calcs and for reverse flight switch back to engine time with no tacho. The reason I went further to explain commercial reasoning is that inevitably someone will ask that question if you just focus on private ops. In any case the same rule applies for both as to how flight time is calculated, just one is more critical legally.

(And I still have no idea how logging tacho time as pilot flight time results in “wasting TBO hours” as suggested by India Four Two.)
Yeah that one I have no idea, in a private operation anyway, it would only waste TBO if you owned the aircraft and wanted to minimise cost per logged hour for experience, maybe that's the angle. For a hired aircraft you would just waste unnecessary hire time if you logged 20% less each flight for experience gaining.
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Old 27th Feb 2022, 02:20
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And what of digital tachos that measure real time at anything over e.g. 1,000RPM?
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Old 27th Feb 2022, 02:35
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And what of digital tachos that measure real time at anything over e.g. 1,000RPM?
No idea, out of my league, all this fancy modern stuff. I mean its pretty easy to just use your own watch. The only question I have there is you are probably getting ripped off for maintenance if its recording higher numbers than the conventional tacho, unless there's some calculation for that as well.
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Old 27th Feb 2022, 02:44
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To make it complex, ~90% of RAAus aircraft have just a gauge on the VDO / Rotax branded hour meter that ticks over as soon as the engine starts. Add to that, some of them have a flight/air-switch that starts ticking over when the aircraft exceeds a specific speed. Some maintenance organisations use that figure for engine maintenance.

Some manufacturers such as Jabiru, specifically state that the engine maintenance must be based on the VDO time, which is engine runtime hour-for-hour. Otherwise, if the aircraft is a circuit queen in a training environment, it could hit the 1,000 TBO and have actually had the engine running for 1,400 hours.
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Old 27th Feb 2022, 03:33
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The tacho clock is just a convenient method of recording time; what ever time you want it to be. It is an American invention for convenience.

Before American aircraft/helicopters became the the majority; most British or European aircraft had no time recording clock fitted !

Aircraft maintenance and pilot logged flight time is based upon honesty.

For maintenance: Engine and airframe time is based upon wheels' off' to wheels 'on'; simple as that. (for simplicity - operators may fit an air switch to start recording at a pre determined airspeed - for helicopters that may be a torque setting or similar)

Pilot log book time: Based upon Start taxi to finish taxi at conclusion of each sector or flight. In commercial Operations where flight and duty time may be an issue over a 30/90/365 day period, CASA may accept via the approved Ops Manual; wheels on to wheels off + 5 minutes or 0.1 if logging digital time.

That's it ....

If you see aircraft sitting idling whilst conducting maintenance runs; waiting for take-off etc, none of that time is recorded for maintenance.

Flight schools need to make a dollar to cover overheads, power, light, air-con, admin staff, rent etc so they may well fit a VDO or Hobbs meter which would be oil pressure operated at engine start. They would bill the student or client by this method as they require money to make the business work.

If you check out the big name flight schools; you will find two Hobbs meters; one is for engine running time (billing hours) and the other is for airframe/engine maintenance. It is quite possible to have a C172 in a flight school with say 2000 hrs total time for engine/airframe maintenance; but showing 3000+ hours for billed out engine running time to the student or private hire. In this example the 3000+ hours has nothing to do with eng/airframe maintenance.

If you are a responsible owner/operator you do not require ANY time clocks in your flying machine. IF you carry out commercial operations the contract client may require a time clock to verify billed time is indeed maintenance time, otherwise you would have operators idling for 20 or 30 minutes to pad the billing time.

If in doubt refer to the CASA regs..
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Old 27th Feb 2022, 03:41
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Don't know how digital tachs handle the recording of time in operation, the old mechanical tachs are set to a particular RPM for the recording of one hour, manual I have has tachs ranging from 1,800 to 3,000 RPM for that one hour setting, typical Cessna is set at 2,566.
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Old 27th Feb 2022, 04:42
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Look at your watch the moment the engine kicks over, write the time down. As soon as you pull the mixture to shut the engine down, again look at your watch, note the the time. Secure the aircraft, while you're sitting down with your brew of choice calculate the time you will then enter your logbook.
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Old 27th Feb 2022, 10:44
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I don't recall the name of the flying club at Biggin Hill (Sportair?) who operated Fournier RF 3s in the 70s. The hire cost was the engine by tachometer and the chock to chock airframe time by the hour. On one occasion someone hired one of these and learnt soaring very quickly and stayed aloft for over 6 hours having used the engine for less than half an hour. He was able to log 6+ hours P1 powered flight and was very unpopular with the club and the 5 people who never got to fly the aircraft that day. I forget the aftermath but I think the CAA put a stop to this practice. Bitches. On a different matter, I think there were a few English Electric Lightning pilots who were able to get automatic multi engines stamped on their UK civil PPL licence until some spoil-sport advised the CAA that the Lightning engines were one above the other and not side by side. Bitches.
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Old 28th Feb 2022, 04:47
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When hiring an aircraft, log what you are asked to pay for, otherwise chock to chock.
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Old 28th Feb 2022, 04:57
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The obligation to log flight time, as defined, in the regulations is unaffected by how an aircraft hirer chooses to charge for the use of the aircraft.
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