Hobbs vs. Tachometer

Discussion in 'The Okie Corral' started by bigjim, Mar 2, 2005.

  1. bigjim

    bigjim

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    I've been looking around at rental aircraft and flight instruction in my area, and I notice that they charge for rental time one of two ways, either tachometer or hobbs meter.

    Which one is the best value for the average renter?
     
  2. TimC

    TimC Uhavthecontrols

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    The one that shows the least amount of time after the flight is complete. :)

    Are you saying you have a choice in which hour meter by which you want your rental time to be charged? In my experience it has always been by hobbs meter. The tachometer is usually used only for engine purposes.
     

  3. bigjim

    bigjim

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    Thank you, Socrates. ;Y

    What I meant was, most places seem to charge by Hobbs time, but there was at least one flight club that charged by tachometer time.

    Doesn't one of them record all time that the engine is running and the other records only time when the aircraft is moving?


     
  4. Timotheous46

    Timotheous46

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    The Hobbs show actual clock time that the electrical system is turned on. The Tach meter shows clock time only at the max rated rpm of the engine. When you throttle back, the tach meter shows less time. I’ve noticed that if I fly 1 hour on the clock the tach meter will only show 45-50 minutes. Of course I tend to fly at lower rpms when I’m just poking holes in the sky with no destination in mind. A club that charges by the tach time may charge more for hour, but you may get more airtime per buck depending on how you fly.

    Tim
     
  5. TimC

    TimC Uhavthecontrols

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    Hobbs meters can be activated by various methods such as master electrical switch and some by engine oil pressure. On a helicopter the hobbs is activated by the collective pitch control. So, it depends on the particular aircraft as to exactly how much the hour meter runs per actual flight hour. It would be hard to say which would be "best" regarding the money factor without knowing that airplane. If there are airplanes that charge by engine tach time, I would rather pay that rental since it should only indicate engine run time. An oil pressure activated hobbs would be the same...
     
  6. sf340flyer

    sf340flyer

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    My answer would be depends...If you are at an airport where you spend a lot of time taxiing most likely tach time would be the way to go. They are calibrated to show proper time when the engine is at high rpm so at idle they barely move. Also if you are paying tach time and you cruise at a lower power setting you can also save a little money. I guess it depends how you are going to use it. Would make a difference if you primarily do X-country flying from small airports where taxi time is minimum, or pattern work in a busy tower controlled field.
     
  7. JonnyB

    JonnyB Millennium Member

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    GigJim:

    The answer is - it depends. If your goal is to add hours to the logbook - instruction, etc., the Hobbs time adds up quicker.

    If you're renting to have fun or to travel, you want to pay by the tach hour. The tach is accurate only at a given RPM - typical cruise RPM, generally. If you throttle back, you get more actual hours of flight for a given tach time. On takeoff and high cruise, the time adds up quicker.

    Most light plane Hobbs meters are controlled by oil pressure switches, so if the master switch is left on, you don't rack up any time.

    JB
     
  8. cfiguy31

    cfiguy31

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    I have been flying at places that charged via the tach time. I know this is the best way if your trying to save money. I also multiply tach time by 120% to get my hobbs time. This works almost all the time when I am up just doing touch and go's or just cruising around. If I go on a long cross country I just add an estimate of how much more time I spent than what the tach say's. Hope this helps!!

    Dave
     
  9. Wulfenite

    Wulfenite The King

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    Sounds like the hot ticket is to pay Tach time, fly slow, and log hobbs time by multiplying by 1.2, or just log the time by stopwatch.

    Either way you'd get maximum log book value for the least cost.

    Of course if you're paying CFI time at the same time it might be better to fly faster.
     
  10. flyandscuba

    flyandscuba

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    I recommend buyng your own airplane -- it isn't as difficult or as expensive and you might think. You can pick up an airworthy C-152 in the $15-18K range, or a VFR C-172 (possibly IFR) for $35-45K. Like boats, you can amortize a loan for 30 years. You'd be surprised what you can get for $300-350 per month. Considering many C-172s rent for $100+ an hour, you'd do well to buy even with tiedown/hangar, oil changes/routine maintenance, and insurance. The key is finding one with decent time remaining on the engine.

    Fly the snot out of it and then lease it back to a flight school, trade up to something else when you are ready, or sell it and recoup a significant portion of your investment.
     
  11. allanteman

    allanteman

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    Be careful with aircraft that have a Hobbs that runs off of electrical power ONLY. This means that anytime you flip on the master battery, you're paying for it. If you turn it on to check the lights, lower the flaps, play with the GPS, whatever, it's going on your tab. Also, if you leave it on by accident, things may get interesting when you and the owner/operator try to calculate the ACTUAL time.

    Wiring it only to the master battery is a cheap, easy way for an operator to pick up some extra money. Putting an oil pressure switch in the middle is the honest, but more expensive way.

    If you're running with only a tachometer, log flight time from "the moment the aircraft moves under its own power for the purposes of flight." That's straight out of FAR 1.1.

    -Jonathan