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Thread: Bonding ribs, horizontal stab

  1. #1
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    Default Bonding ribs, horizontal stab

    When bonding horizontal stabilizer ribs into place, do I bond the sections where the welded structure passes through the ribs? How do I know if I need stiffeners? The ribs are all strait, but will they bend with an air load, or when the fabric is shrunk?

  2. #2
    Senior Member jrevens's Avatar
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    Default Re: Bonding ribs, horizontal stab

    Hi Steve,

    FWIW, I installed stiffeners on most all of the ribs that weren't in contact with one of the steel "ribs"... that includes the elevator ribs. I also bonded to the structure that passes through them.
    Here's a representative picture -
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    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  3. #3
    Senior Member Esser's Avatar
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    Default Re: Bonding ribs, horizontal stab

    I did my rudder with no stiffeners only to find out the humidity caused them to swell and warp. In my opinion, stiffeners are not optional unless you are bonding it to something along side it.
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  4. #4
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    Default Re: Bonding ribs, horizontal stab

    Half (just under) of the horizontal stab done. I need to go glue the ribs with weldments through them. Was waiting to hear/see back from you guys. Dinner, then trimming the ribs for the other side.

    After gluing, I went upstairs to show neighbor wings and fuselage, and noticed that KF uses a lot of adhesive to bond the wing ribs in. Did I use enough adhesive to bond in my ribs?

    Tomorrow, I will install stiffeners on today’s work and install ribs in the other half.
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    Last edited by Flyboy66; 06-09-2018 at 05:33 PM.

  5. #5
    Senior Member jiott's Avatar
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    Default Re: Bonding ribs, horizontal stab

    By all means, use stiffeners on all ribs not otherwise stiffened by a steel structural member. The kit typically does not include enough stiffener material so you will be tempted to skip it on some ribs, but go buy some 1/8" ply from the local hobby shop and cut some more. I skipped some on my elevator and was sorry I did. The fabric shrink process pulled the outer steel tubing in just enough so that some of my unstiffened ribs took on an "S" curve. Not a show stopper, but not good in my book.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  6. #6
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    Default Re: Bonding ribs, horizontal stab

    I am sold on stiffeners, but it raises another question. How do you clamp the stiffener in place while the adhesive sets?

    Any pictures?

    The outboard 8 ribs are now installed on the stab. Tomorrow is stiffener day as well as elevator rib day. Also, what about foam versus balsa wood for the outer edge of the stabilizer?

  7. #7
    Senior Member jiott's Avatar
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    Default Re: Bonding ribs, horizontal stab

    I used small spring clamps to hold the stiffeners.
    I highly recommend balsa rather than foam on the stabilizer tips as well as the elevator tips. Much more resistant to hangar rash in these very vulnerable places. Foams OK on the top of the rudder and vertical stab.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  8. #8
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    Default Re: Bonding ribs, horizontal stab

    Recommend you also put stiffeners on the elevator ribs. I didn’t on mine initially and had to go back and do it because they bowed with moisture uptake over time. Suggest you Put the stiffeners on ribs first before you locate and bond in place.
    David
    SS7 Builder

  9. #9
    Senior Member efwd's Avatar
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    Default Re: Bonding ribs, horizontal stab

    I just put a bit more flox in to make sure gravity didn't take advantage of the situation. I put the stiffener on and just wrapped tape around it in a couple spots along the length. Everything turned out well.
    I too would recommend Balsa wood. I won't ever use foam anyplace if I do this again. I have mentioned before, If your using Oratex, foam will melt when forming the fabric around those surfaces.
    Eddie
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  10. #10
    Senior Member Delta Whisky's Avatar
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    Default Re: Bonding ribs, horizontal stab

    Steve - after bonding in the ribs in my VS, and then adding the stiffeners, I changed the process a bit when doing the rudder. I first "dry fitted" the ribs (using the ribs in the VS for alignment), then added the stiffeners using a table top to ensure a flat rib, and then bonding them in their final resting places.


    As you can see in the pictures, I'm fond of using my most used tool - clamps from the aviation department in Harbor Freight.



    Bonding while on the table top also made the job tons easier due to access.


    More details can be seen on my build site.
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