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Thread: The Aerodynamics of Wing Strut Fairings

  1. #1
    Senior Member DanB's Avatar
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    Default The Aerodynamics of Wing Strut Fairings

    I launched into the blue without my strut fairings so I'm now zeroing in on them. As I contemplate horizontal positioning between the trailing edge of the front one and the leading edge of the aft one, my question is one of best aerodynamic performance...
    Q: Should the trailing edge of the front fairing be positioned in relation to the aft fairing leading edge
    a. slightly to the top?
    b. center?
    c. slightly to the bottom?
    d. other

    I have seen this done all three ways and I would like to get a known physics answer. Any aeronautical engineers out there that could help?
    Dan B
    Mesa, AZ

  2. #2
    JimS's Avatar
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    Default Re: The Aerodynamics of Wing Strut Fairings

    Not an engineer Dan, but when I did mine I figured the spars are like a glider wing,(long and have a short cord), so I positioned the trailing edge of my fairings a tad low figuring this would give a bit of angle of attack and result in some lift being generated. Can't really say for certain that it was a good idea but it hasn't seemed to hurt.
    JimS

  3. #3
    Senior Member HighWing's Avatar
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    Default Re: The Aerodynamics of Wing Strut Fairings

    A couple of ideas. One guy elliminated the glue between the fairings and strut so the fairing would find it's own best position. No lift, but max drag reduction and that's the way he flew. I recall another guy from Florida who flew with the fairings and somehow discovered their preferred location in cruise and glued them in that position. I have wondered about an epoxy that would set in about an hour - place some in the unfinished fairings and go fly. When back on the ground do the finishing. Speaking of lift, the Florida guy talked about the lift and thrust being generated by the angle of the exhaust pipe.
    Lowell

  4. #4
    Senior Member t j's Avatar
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    Default Re: The Aerodynamics of Wing Strut Fairings

    I have a set of wood fairing that I attached with Duck tape to test the effect before purchasing the PVC type. I positioned them with the trailing edges centered with the struts. I didn't think to try different angles.
    Tom Jones
    Classic 4 builder

  5. #5
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    Default Re: The Aerodynamics of Wing Strut Fairings

    Not an engineer Dan, but when I did mine I figured the spars are like a glider wing,(long and have a short cord), so I positioned the trailing edge of my fairings a tad low figuring this would give a bit of angle of attack and result in some lift being generated. Can't really say for certain that it was a good idea but it hasn't seemed to hurt.
    JimS


    Jim, I agree a little positive angle of attack would be better than a little negative. Also, as I recall from the wing design section of an aircraft design book I read a few years back, a symmetrical airfoil acts as any other airfoil with a positive angle of attack, it provide lift and does so with little drag if the angle of attack is not too great.
    Roger

  6. #6
    Senior Member jiott's Avatar
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    Default Re: The Aerodynamics of Wing Strut Fairings

    I can't imagine needing any more lift on a Kitfox. The only condition it might help a little is on very slow flight; at cruise there is already more than enough lift from the wings and flaperons to hold the plane in the air. Therefore I think I would go for minimum drag at cruise, where you spend most of your time, rather than a little help at very slow speeds. Any increase in lift is always accompanied by an increase in drag, even if its very small. So I will set mine up for a neutral position in the cruise airstream and go for the most increase in speed possible. After all, isn't that the whole purpose of the strut fairings anyway.

    Jim

  7. #7
    Senior Member Dorsal's Avatar
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    Default Re: The Aerodynamics of Wing Strut Fairings

    Jim,
    I believe your thinking is quite correct as any lift generated by the fairings would be inefficient relative to the main wing and would increase drag. I used option B and second the notion that fairings should be tuned only to minimize drag.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  8. #8
    Senior Member Esser's Avatar
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    Default Re: The Aerodynamics of Wing Strut Fairings

    Quote Originally Posted by HighWing View Post
    A couple of ideas. One guy elliminated the glue between the fairings and strut so the fairing would find it's own best position...
    The exhaust thing is interesting. My girlfriend told me that on her plane the two exhausts add the equivalent of almost 10% in horsepower. It's almost 120hp from the exhaust thrust alone. This is a turbine engine mind you but still interesting. I had never really thought of it before she mentioned it to me

  9. #9
    Senior Member Peteohms's Avatar
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    Default Re: The Aerodynamics of Wing Strut Fairings

    Just make the strut fairings extra wide and call it a biplane. I'm sorry I just can't help myself.
    Pete
    Leander, TX
    Model III SN 1000
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    Grove

  10. #10
    Senior Member Dorsal's Avatar
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    Default Re: The Aerodynamics of Wing Strut Fairings

    Would increase your dihedral a bit
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

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