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Thread: Fuel Flow Testing

  1. #11
    Senior Member jiott's Avatar
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    Default Re: Fuel Flow Testing

    I agree, the hose to the fuel pump seems way more reasonable as a measuring point. The fuel pump may have a lot of resistance thru it when not turning. I will recheck flow at inlet to fuel pump.

    I would still like to hear some more numbers and how others did the testing.

    Jim

  2. #12
    Senior Member t j's Avatar
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    Smile Re: Fuel Flow Testing

    My Rotax engine installation manual lists a maximum fuel pump height above the fuel tank. I have a nose tank that serves as the header tank in my kitfox. The fuel pump is about level with the bottom of the header tank.

    The gascolator is the low point in the system and is well within the maximum height below the fuel pump.

    So, I tested the flow at the outlet of the gascolator, tail low, one gallon remaining in the nose tank (header) and zero fuel in the wing tanks. flow rate 14.3 gal/hr. Zero unusable.

    I then tested the rate from wing tanks to header tank to be sure the wing tank flow to header tank would keep up with the engine fuel burn should I forget to switch on a wing tank and run the header dry. Left tank 11.8 gal/hr. .75 gal unusable. Right tank 11.25 gal/hr, .75 gal unusable.

    I have since found that I can actually drain all the fuel in the wing tanks by slipping but I think the definition of unusable is in level flight so left the plackard on the wing tanks. I did subtract that unusable fuel weight from my empty weight though. 9 pounds
    Last edited by t j; 08-07-2013 at 12:16 PM.
    Tom Jones
    Classic 4 builder

  3. #13
    Senior Member SkyPirate's Avatar
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    Default Re: Fuel Flow Testing

    just my 2 cents worth,..just thinking if its a gravity test, due to concern of normal operation in flight if the fuel pump fails or is turned off,..wouldn't testing the system from the furthest point from the fuel tank be best,..ie carb inlet, to include flow thru the pump? or a by pass of the pump if needed?

  4. #14
    Senior Member t j's Avatar
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    Default Re: Fuel Flow Testing

    Don't know about the 912 but rotax two strokes won't run very good without a fuel pump in a kitfox.
    Tom Jones
    Classic 4 builder

  5. #15
    Senior Member jiott's Avatar
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    Default Re: Fuel Flow Testing

    Based on some of the comments here I did some additional fuel flow tests. In flight level attitude and 1/4 tank of fuel in each wing I measured the gravity flow right at the inlet to the mechanical fuel pump. It was 15.0 gph. I removed the inline fuel filter (Kitfox supplied) and did it again and got 16.8 gph. These values are over 200% of Rotax 912s max T/O consumption. I put it back together with a new inline fuel filter for good measure.

    These values sound real good to me; apparently there is quite a lot of resistance going thru a non-operating mechanical pump plus the additional smaller lines to the carbs (flow in this configuration was 5.80 gph as previously reported).

    What this tells me is that with a complete fuel pump failure (broken shaft, etc.) I will not get full T/O power, but all other flight conditions of cruise and descent should be fine.

    What do you think?

    Jim

  6. #16
    Senior Member Dorsal's Avatar
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    Default Re: Fuel Flow Testing

    Sounds good to me
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  7. #17

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    Default Re: Fuel Flow Testing

    I am surprised that your final inspection / Inspector does not ask for a fuel flow test or at least the report/results.

    Also testing with tail on ground is a good start but
    YOu should test at hose end at Carbs.
    in level flight
    again with tail on ground

    and again at max climb angle
    -I think that you will find that you will need to elevate your mains a fair bit to achive Max climb angle - try to at least 15/20 degrees.

    If you have fuel tank selector then try in every configuration

  8. #18
    Senior Member Dorsal's Avatar
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    Default Re: Fuel Flow Testing

    Dave, I am curious as to what one is testing for? clearly the system should be tested for any restrictions which arguably could be done at any attitude that give some head pressure. If the test is to insure full power in the event of a pump failure then that is a different story. I tested to insure that my engine can produce full power with the pump operating from the header tank alone (negative head pressure) and, in the event of a pump failure, I will have enough flow to maintain flight and land (to the sound of a low pressure alarm ). As an aside my DAR did not ask any questions about any of this other than my statement that I built to the manual.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  9. #19

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    Default Re: Fuel Flow Testing

    You are testing for fuel flow

    YOu will need 150% of the maximun fuel required at WOT for your engine on gravity feed

    125% I think on pump driven


    But if your pump fails you should knjow what flow you get with a failed pump with gravity alone.

  10. #20
    SWeidemann's Avatar
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    Default Re: Fuel Flow Testing, Aux Pump Necessary?

    I just finished a two day Rotax 912 Series service seminar (Leading Edge Airfoils in Lyons, WI) where it was pointed out that a auxiliary fuel pump is recommended in any installation using the 912.

    In my Model 5 Tri Gear, I do not believe I have a pump on board other than the mechanical engine driven one. It works fine, but now I'm wondering if I should put one in? Should I be doing fuel flow testing or just keep flying what I have? (It does have a lot of time on it with no known incidents of any kind.)

    Another point, is: Should I have a metal header tank instead of the plastic one ? My plastic one works however is a little "weepy" around the pipe joints.

    Skot
    N24V

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