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Thread: Low Fuel Sensor

  1. #21
    mooreaa's Avatar
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    Default Re: Low Fuel Sensor

    Thank you for sharing these experiences. Wasn't something that was on my radar until reading your comments here. Interesting point about the steep descent attitude preventing fuel flow to the headers.

    I assume the issue is mostly the same regardless of carbureted or fuel injected engines. I like the idea of having the low fuel sensor mounted directly to the header tanks. Does the fuel return path affect this at all? Curious what the installation options are and what to watch out for.

    Thanks!
    Aaron & Ashley
    Newbie pilots working towards our PPL. Kitfox ordered (OSH19)!
    Corvallis, OR

  2. #22
    Senior Member jiott's Avatar
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    Default Re: Low Fuel Sensor

    Why is everyone shying away from the factory optional low fuel sensor with its separate little reservoir? It works perfectly and is super easy to install with no modifications to the header tank. Just curious.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #23
    Senior Member Eric Page's Avatar
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    Default Re: Low Fuel Sensor

    In the immortal words of Colin Chapman, "Simplify, then add lightness."
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  4. #24
    Senior Member Slyfox's Avatar
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    Default Re: Low Fuel Sensor

    years ago I was coming back from Seattle and was flying in the area of Ellensburg, wa. well the engine quit. now before I go any further I have valves that turn off each tank, well I only fly on one tank, why, why not. not only that response, but my rv has a left and right and you can't have both on a low wing plane. but anyway, I ran out on the left tank. the engine quit. I switched to the other tank, it starts back up. everything ok. But... when I got home I put in the low fuel sensor and put a light on the dash. fast forward, through the years that has proved to be very nice for me, many times the light would come on, to find that one tank or the other would quit flowing for one reason or another. right now I had it come on just a couple days ago, I thought wait a minute the tank I'm on is full. I looked at the vent line, mine is clear, and I could see that the line was empty of fuel, than I saw fuel come back up and than the light went off, than the light came back on and yup no fuel again. I took the screen out of that tank and sure nuff it was plugged. so take what you want on this low fuel light, I love it.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  5. #25
    Senior Member Dave S's Avatar
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    Default Re: Low Fuel Sensor

    Quote Originally Posted by mooreaa View Post
    Thank you for sharing these experiences. Wasn't something that was on my radar until reading your comments here. Interesting point about the steep descent attitude preventing fuel flow to the headers.

    I assume the issue is mostly the same regardless of carbureted or fuel injected engines. I like the idea of having the low fuel sensor mounted directly to the header tanks. Does the fuel return path affect this at all? Curious what the installation options are and what to watch out for.

    Thanks!
    Regarding descent attitude and what a person can count on for fuel feed is something a person can and should figure out during build and fuel system proofing. Since the fuel feed from the wing tanks is located near the rear of the wing tanks, the design indicates that nose down attitudes will, at certain descent angles, unport the fuel feed from the rear of the tank. The attached photo shows the Kitfox in a nose down attitude of 10 degrees (courtesy of removing some bricks in the driveway and digging a hole), estimated to be twice the nose down that would be experienced during normal operations. What this test revealed is that a 10 degree nose down attitude will start to unport the fuel tank with 6 gallons in a tank (or 12 gallons between the two tanks) which is just a tad less than half tanks. It is better at 5 degrees nose down with approximately 3 gallons per tank or 6 considering both tanks.

    Many aircraft have fuel system limitations that are accounted for and as long as a pilot knows what those are (hopefully published in the POH), operations can be performed in agreement with the limitations.

    The header tank on a Kitfox is a really good deal for a number of reasons including this one.

    The low fuel sensor is certainly a good idea and saves a person from having to do math in their head to keep from exceeding the capacity of the header tank on a long steep descent.
    Attached Images Attached Images
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  6. #26
    mooreaa's Avatar
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    Default Re: Low Fuel Sensor

    Quote Originally Posted by jiott View Post
    Why is everyone shying away from the factory optional low fuel sensor with its separate little reservoir? It works perfectly and is super easy to install with no modifications to the header tank. Just curious.
    Hi ya Jim, not so much shying away from the factory as much as trying to see the creativity and wisdom of others on this forum. I have no doubt that the factory solution works, but I do also like the idea of the sensor being integrated into the header tank.


    Dave, wow thats really very interesting. No fuel flow at half tank with just -10 degrees doesn't seem like much. If my maths right, thats 65mph at a -1000fpm is around -10 deg. Maybe thats an aggressive descent but still. Just out of curiosity, what about mounting the low fuel sensor in the wing tank or, maybe having two ports on the tank (I understand its not necessary, but would it mitigate this)? I suppose you can lose 1000fpm with wings level so... that aside, the point would be that this is equivalent with respect to coming down at that angle.
    Aaron & Ashley
    Newbie pilots working towards our PPL. Kitfox ordered (OSH19)!
    Corvallis, OR

  7. #27
    Senior Member Dave S's Avatar
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    Default Re: Low Fuel Sensor

    The only time during phase 1 (and afterwords) the nose down ever got near 10 degrees was VNE testing.

    I doubt that anyone will be getting beyond 5 degrees nose down for any normal operation - a power off best glide is considerably less than that - at least on our bird.

    If a person considers the Kitfox fuel placard - the no takeoff band is right about 3 gallons if I recall correctly.

    I feel that the design of the Kitfox fuel system on the S7 is solid.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  8. #28
    Senior Member rv9ralph's Avatar
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    Default Re: Low Fuel Sensor

    Quote Originally Posted by mooreaa View Post
    Just out of curiosity, what about mounting the low fuel sensor in the wing tank or, maybe having two ports on the tank.
    If there are 2 ports in the wing tank, the port with the least resistance will be the one that flows... in other words, if there is a unported pickup, the the fuel draw sill suck air. That is why you can't burn off both tanks on a low wing aircraft. Low fuel sensor in the wing will be inaccurate due to the sloshing and shifting of the fuel when changing pitch or yaw.

    An option for fuel sensor is from Belight. The have several fuel sensors that will indicate low fuel status that can be used in the header tank.

    Ralph

  9. #29
    Senior Member 109JB's Avatar
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    Default Re: Low Fuel Sensor

    You can have two ports on a high wing fuel tank but each port has to be independent until well below the tank. Easiest would be to run each outlet all the way to the header.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  10. #30
    Senior Member rv9ralph's Avatar
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    Default Re: Low Fuel Sensor

    ou can have two ports on a high wing fuel tank but each port has to be independent until well below the tank.
    After thinking about your comment, I stand corrected. However, to do as you recommend, it would take another fuel line from tank to header which could interfere with the wing folding. Also, it would have to tee in before the header tank due not any available ports on the header. Not an elegant solution.

    Ralph

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