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Thread: Useable Fuel in the EX/FX3

  1. #1
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    Default Useable Fuel in the EX/FX3

    Well I had to drain the fuel in my EX3 with extended tanks (44 gallons total) to replace some bad o-rings in the fuel valve (came that way I guess). So I drained all the fuel with the plane in the 3 pt attitude (parked in the hangar) and drained it out at the gasolator valve. I the raised the tail and put it in a level attitude to see if any more fuel would drain out. NONE. I checked all 3 drain locations (rear fuse; behind the gasolator and at the gasolator) in both configurations. No more fuel would come out anywhere, in any configuration.

    After fixing the fuel valve I refilled it being sure to get all the tanks completely full. It took 41.5 gallons which means there was 2.5 gallons in the tanks that were not coming out in any configuration. The EX/FX3 is listed as having 39 gallons usable of the 44 ....for some reason, this is 1 less gallon than the EX2 has in useable fuel (it is 40 useable).

    One thing is that I drained it in the 3 point config so possibly, it would have drained out even less in level attitude? Will have to try that next time.

    I was told by Cubcrafters that the unuseable fuel was mostly due to putting the aircraft in a takeoff and turn situation where some of the fuel apparanetly would not drain but I was also told by someone that ALL of the fuel in the tanks would actually drain out if not in that configuration. That is wrong......no matter what.....2.5 gallons is not coming out in a static position. Perhaps when flying with air flowing in the fuel vents at the caps it would pressurize and push more out? I guess the only way to tell is to fly it till it runs out....
    Last edited by Daveembry; 07-12-2018 at 06:32 AM.
    Dave Embry
    "You only live once.....
    ..but if you do it right.....
    ....once is enough."..

  2. #2
    Senior Member TroyBranch's Avatar
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    Default Re: Useable Fuel in the EX/FX3

    Did you measure the total from the very first fill after the build? I wonder if the tank volume is incorrect?


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  3. #3
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    Default Re: Useable Fuel in the EX/FX3

    Troy, yes it took 43.8 and they call it 44 so pretty much right on.

    Quote Originally Posted by TroyBranch View Post
    Did you measure the total from the very first fill after the build? I wonder if the tank volume is incorrect?


    Sent from my iPhone using Tapatalk
    Dave Embry
    "You only live once.....
    ..but if you do it right.....
    ....once is enough."..

  4. #4
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    Default Re: Useable Fuel in the EX/FX3

    Another thing I could have tried might have been to rock the wings a bit to see if it might move some fuel around.
    Dave Embry
    "You only live once.....
    ..but if you do it right.....
    ....once is enough."..

  5. #5
    Senior Member Dan L's Avatar
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    Default Re: Useable Fuel in the EX/FX3

    When I put new O-rings in my valve there was some residual fuel left in the tanks but I don't think that much. I rocked my wings some and that probably helped.

    This is a good reason to do the weighing for an accurate empty weight before ever putting any fuel in the tanks.
    Flying Carbon Cub EX #11 since 2011

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