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Thread: Fuel Tank Calibration

  1. #1
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    Fuel Tank Calibration

    I am flying an RV-6A with dual AF-3400's, and have calibrated my tanks in flight configuration. Meaning I jacked my plane up until the longerons were level. During my initial test flights, I would only fill my tanks half way and the levels seemed to be correct. Now I have been flying with full tanks and when I land I get "check fuel computer" alert, and the gages do not seem to be correct.
    Since RV-6A's sit a bit tail low when on the ground, should I calibrate my tanks while on the gear? Do you think this difference in attitude could be causing inaccurate readings on the ground?
    Thanks for your input.

  2. #2
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    I have a similar issue. My tanks were calibrated with the aircraft in both the tail-low and in-flight position. When I refuel, I press the 'Fill Mains' button, and the computer reflects the full amount, 42 gallons. However some times I still get the 'Check Fuel Computer' alarm. Any idea what is causing this? thanks
    Jim Shannon
    RV-8 N52VV
    Charlottesville, VA

  3. #3
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    Go into your fuel computer calibration screen and set the fuel gauge cross check to a larger number. It is probably set to 5. I kept moving mine to a larger number until I no longer get the error. What is happening is that wing dihedral is keeping the floats in the full poistion even though you are burning fuel, which the fuel computer recognizes and is accounting for. Sometimes you can burn up to 5 -7 gallons in each tank before the gauges will start to register. Hence, the disparity between the fuel totalizer and the gauges.

  4. #4
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    Thanks Vic, I'll take a look. If I understand this correctly, the number ought to be at least as high as the number of gallons that must be burned before the calibration values change, correct?
    Jim Shannon
    RV-8 N52VV
    Charlottesville, VA

  5. #5
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    Thanks Vic. I'll give that a try.

  6. #6
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    yes, that's right... the value needs to be large enough to allow for the indicators to move off of full. As an example, in the RV-10 that could be as much as 7 gallons per side, so if you take off on one tank and then change tanks within 30 minutes and have burned less than 7 gallons, and are now running on the opposite full tank, it, too, could need to burn more than 7 gallons before there is any indication on the fuel tank gauge. Hence, a 15 gallon disparity. If you have tip tanks installed, which give an extra 15 gallons of fuel, the problem is magnified. I currently have my fuel gauge cross check set at 25 gallons, and have not had any more warnings.
    Vic

  7. #7
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    Mine is set at 8. Think I'll try 25 which seems to work for you. Thanks again Vic.
    Jim Shannon
    RV-8 N52VV
    Charlottesville, VA

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