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Thread: Question about KF 4 wing repair

  1. #1
    Senior Member
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    Default Question about KF 4 wing repair

    I am in the middle of repairing the wings on my KF 4 and ran into an issue that I wanted some advice on. The plane that I bought was flipped over in a corn field years ago and got pretty crunched. The wings suffered minor damage to the tips but the fusealage had to be completely rebuilt. Fast forward to now...I with the help of a fellow Avid builder I have repaired the wings structurally (replaced 3 ribs, trailing edge) and have started the covering process. I only recovered the outter two rib bays on each wing tip since the fabric is in good shape everywhere else and I could see inside the wing and saw no other damage. (plane had 17 hours on it when crashed) Yesterday I was looking at the attachement points for the jury struts and noticed that on one wing, the attachment brackets both stick out of the fabric about 1 inch below the fabric. On the other wing, one sticks out about 1 inch and the on the other one, the top of the bracket sticks out maybe a 1/4". (Not enough to see the bolt hole without pushing the fabric down) It seems like when you would bolt the jury strut in, the bolt would be inside the fabric. I checked the bracket and it is still attached to the spar and nothing looks bent or warped. It looks like the original bracket and is riveted in what looks like the original location. The fabric is still good and tight and the rib stitching is still intact so it's not as if the fabric came loose. Any thoughts? Is this some kind of "offset" or something? Can't find anything in the manual but then again the 1990's manual is very lacking. Thanks.

  2. #2
    Senior Member t j's Avatar
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    Default Re: Question about KF 4 wing repair

    I have one wing like that too Jerry. I built the plane and know exactly why it happened that way. I swear I followed the directions in the manual to a T.

    I didn't see the problem until I was working on the second wing. I called the factory then...back in 1994...and asked them what I did wrong because it looked like the bolt on the top of the front leg on that jury strut would be inside the fabric. The guy I talked too said that is a common error in building...even some of their planes were a tight fit on that bolt.

    The jury strut brackets are located to their position on the spar with great attention to being sure they are perfectly vertical and the wing struts perfectly straight. There was no mention in the instructions to check how the fabric would lay at that location.

    I had to make slightly longer than specified brackets and install the jury strut at a slightly less than vertical position to make the hole in the bracket end up on the outside of the fabric while still keeping the wing struts perfectly straight on the second wing.

    The bolt on the short bracket wing is a pain in the butt to install. The factory guy suggested cutting a hole in the fabric to install the bolt then make an aluminum sheet cover to put over it but I didn't like that idea. I just push the fabric up and put the bolt in. The fabric has good "Memory" and will return to nice and straight after a couple minutes.
    Last edited by t j; 09-14-2010 at 07:55 AM.
    Tom Jones
    Classic 4 builder

  3. #3
    Senior Member HighWing's Avatar
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    Default Re: Question about KF 4 wing repair

    Jerry,

    My wings on the new project are pretty much as you describe. The forward spar being somewhat forward of the lift strut has the attachment directed aft so it doesn't penetrate the fabric to the same extent as the aft more vertical angled bracket. I didn't build this wing set, but my first Model IV was the same. Not a problem after the challenge of putting in the bolts.

    Lowell

  4. #4
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    Default Re: Question about KF 4 wing repair

    Well this is good news. I was just worried that I might have had some unseen damage or an improper rigging. It's weird that it would only be one wing and only one of the brackets. If I remember correctly it's the left wing. So I guess it would be OK to just extend the bracket so that it does protrude equal to the others? I don't really care about the jury strut not sitting perfectly vertical. I do care more about making the fabric look nice around the brackets. Thanks.

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