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Thread: Help with Model III Spar question

  1. #1

    Join Date
    Dec 2020
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    KAVC VA.
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    Default Help with Model III Spar question

    I am building a Model III and have been following the manual to the letter. When riveting the spar inserts in place the manual says to use a round file to gently spot face the outside of the spar to help seat and strengthen the SS rivets. That's what I did. This morning, I'm cruising the Kitfox site and happen to read the online portion of their assembly manual for the wing. In bold print is says, "DO NOT use a file on the exterior or interior of the wing spar". Is this going to be a problem?

  2. #2
    Senior Member Dave S's Avatar
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    Oct 2008
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    St Paul, MN
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    1,833

    Default Re: Help with Model III Spar question

    William,

    A couple things to think about that may ease your mind a bit.

    First off, the statement in the current manual not to use a file on the inside or outside of the spar may be in a different context than the instruction in you Model III manual regarding the rivet holes. There is a difference between deburring a rivet hole and using a file on open areas of the spar on a surface imperfection. Filing the outside of a spar to remove an imperfection can leave a scratch which can result in a stress riser, particularly if the scratch is perpendicular to lenght of the spar.

    The Manual is pretty clear about using scotchbright to polish up the exterior of the spar to avoid scratching a spar rather than using a file.

    The inside of the spar can be easily damaged using a file for any reason there. This could mess up any chance of installing the spar insert, if the III has one, and result in galling which could destroy both the spar and insert. The insert has to slide in without binding.

    If in doubt, Calling up Kitfox after they get back from Oshkosh should be the final authority.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  3. #3

    Join Date
    Dec 2020
    Location
    KAVC VA.
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    5

    Default Re: Help with Model III Spar question

    Thanks for the response. I've not used anything on the inside. The spar insert is in place. Actually....the rivets that hold it in place are the ones my manual said to spot face with a round file. I did. Wasn't overly aggressive with the file but now I'm worried.

  4. #4
    Senior Member jiott's Avatar
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    Jun 2010
    Location
    Portland, OR
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    2,960

    Default Re: Help with Model III Spar question

    If your spotfacing is no more aggressive than a deburring tool I think you will be fine.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

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