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Thread: Repairing flaperons

  1. #11

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    Default Re: Repairing flaperons

    Hi Guy's. Luckily I came across this old article. I have the same fate as many I suppose where, the flaperons gets damaged when folding the wing in incorrectly and or carelessly. Mine was done by a guy that worked on my plane and his staff folded the wings. I understand the repair process although mine was bend on both sides no cuts. I don't have any pictures at this moment. I have 3 questions nl. 1. Will it not be better to just put a patch over the damaged areas with out cutting out the bend damaged sections to keep the structural strength? 2. Is aircraft grade aluminum sheeting required or can normal aluminum sheeting do the trick. 3.What thickness should the plate be?

  2. #12
    Senior Member jiott's Avatar
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    Default Re: Repairing flaperons

    I think its best to leave the bent parts for structural reasons, straighten as well as possible.
    For just a patch I don't think aircraft grade aluminum is necessary. If the patch requires any sharp bends be aware that the stronger, harder grades may crack at the bend line.
    Measure the thickness with a micrometer at one of the hinge slots; I think it is 0.012" but not sure.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #13
    patrick.hvac's Avatar
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    Default Re: Repairing flaperons

    Flaperons are 2024 T3 clad ams 4462 Kaiser aluminum .016
    🇨🇦CANADA
    Flying | SS7 | G3X | Edge 912

  4. #14
    Senior Member Eric Page's Avatar
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    Default Re: Repairing flaperons

    I'm in the same situation as @gizmos was in back in 2013 (first post, above), with several flaperon hinge slot ends damaged (some dented, some cut) by improper storage/transport. I'm also in the process of devising a solution, but the guidance in AC43.13-1b is, quite frankly, confusing gibberish.

    Starting with Figure 4-16, on page 4-32, we see the method for patching stressed sheet metal skins:

    AC43-13-1B Fig 4-16.jpg

    Notice that the crack length is 2.5" and they specify a patch size "not less than 2 times length of crack," so we can assume the patch shown is five inches long, measured "crack-wise." It appears that it might be a bit wider across the crack, but let's say 5" wide also.

    Now look at an excerpt from Table 4-10 and its notes, on page 4-38:

    AC43-13-1B Table 4-10.jpg
    AC43-13-1B Table 4-10 Notes.jpg

    Using their example with a skin thickness of 0.028" and 1/8" rivets, the table requires 4.9 rivets per inch of width. Note c. allows 75% of that number for a single lap sheet joint (3.675 rivets). If the patch is 5" wide, then the minimum number of rivets would be 5 times that number, or 18.375, which I would round up to 19.

    Now look at the patch in Figure 4-16 again. They used a total of 8 rivets across the width of the patch, and the note calls out "4 rivets reqd each side." Confusingly, the drawing also shows 4 rivets along each edge of the patch, so the meaning of "side" is somewhat unclear to me, but let's assume it means "on each side of the crack."

    The patch shown in Figure 4-16 has 32 total rivets. Does this mean that the calculated minimum of 19 is for the whole patch? If that's the case, then what guidance dictates the minimum of 4 rivets per side, and how is that calculated? What if the patch is much longer than it is wide; then how many rivets?

    It gets worse. Looking at paragraph 4-57.c., on page 4-19, and Figure 4-5, on page 4-20, we see that for single and triple/multiple row rivets, edge distance should be at least 2 times rivet diameter and spacing should be at least 3 times rivet diameter. For double row rivets, spacing is 4 times rivet diameter.

    AC43.13-1b Para 4-57c.jpg AC43.13-1b Fig 4-5.jpg

    Using the most space-efficient layout, with the rivets staggered to achieve the closest possible lateral spacing (a technique that is not shown in Figure 4-5, but is used in Figure 4-16), there doesn't appear to be any way to get the required number of rivets across any patch. For example:

    Spacing Example.jpg

    A patch of 1.03" width would require 4 rivets (4.9 x 0.75 x 1.03 = 3.78), but only three will fit, and only if they're staggered. The math just doesn't work, no matter what size patch or how many rows of rivets you use. Even a single row doesn't work; it would require 1/2" total width to achieve 1/4" edge spacing, but a 1/2" patch requires 2 rivets.

    If someone understands this and can offer a cogent explanation, I would both be very grateful.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
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  5. #15

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    Default Re: Repairing flaperons

    Hi Guy's Thank you for the info and feedback. I think my repair process will be to fold the patch over the crumpled area with the 2 ends meeting at the bottom end of the trailing edge. Basically like a book over. thereby ensuring minimum airflow disruption over the repaired section. What rivet sizes and spacing and will it be advisable to use an epoxy as well?

  6. #16
    Senior Member PapuaPilot's Avatar
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    Default Re: Repairing flaperons

    Eric,
    I agree that the information on AC43-13 is lacking clarity. This is one of the more frustrating things an A&P has to learn to get the rating. The issue with the number of rivets isn't an issue for what you want to do, that figure is for lap joints. I don't think the flaperon skins would be considered stressed skins, which means it is a simple patch/doubler repair in my eyes.

    If I were to do a repair I would stop drill the crack or clean out the damaged area by elongating the slot slightly. The repair needs to be done with 2024-T3 aircraft aluminum of the same thickness. I would make a patch wide enough to cover the slot on both sides and extend in front of the current slot. Size the patch with enough edge distance for 3/32" rivets (2D = 3/16"), which would be approximately 1" wide and 2" long (size as needed). I would make it with a new slot that puts it back in the original position. Drill the holes with the correct edge distance and spacing. Use pull rivets and Hysol to install it.

    Here is a drawing I made that might be clearer. BTW I would radius the corners of the patch.


    Patch.jpg
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  7. #17
    Senior Member Maverick's Avatar
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    Default Re: Repairing flaperons

    Something else to consider, if you haven't already installed the weights is, move the counter balance weight outboard until it is right in front of the outboard hinge and install there. This puts a harder metal at the forward part of the slot creating a stop against over rotating the flaperon when folding the wing.

    1-8-2021 9-33-41 AM.jpg
    Fred
    EAA, AOPA
    KF5 (N49FK & N36KJ)
    Phoenix, AZ

  8. #18
    Senior Member jrevens's Avatar
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    Default Re: Repairing flaperons

    Just a thought - I think I would be hesitant to relocate the balance weight to that position. There is probably a reason that they are specifically located where they are, directly over an internal foam rib ... stiffness, distribution of forces, conformity of shape? Changes of that nature on a control surface also have to be looked at considering a possible effect on flutter.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
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  9. #19
    Senior Member Maverick's Avatar
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    Default Re: Repairing flaperons

    I can understand your reservation and one should follow their own mind about about it. And, this is pertaining to a series 5. I don't know about the later series or the 1-4.

    I did this on my first Kitfox and it's still flying 18 years later. As well, I know of others in the Phoenix area that have also done this. So far, none off them have fallen out of the sky. As for the location as advised by the factory, I don't know how they came to that decision. Mabey it was aesthetics. I am not concerned about flutter because the flaperons are well balanced with the two weights on both flaperons and the balance wouldn't change based on the location of the weights on the flying surface, inboard or out board. Many designers add the weights at either the outboard end of the flying surface or inboard at the beginning of the surface. In the case of the Kitfox, it's sort of both. As long as the offsetting weight of the attachment is ahead of the pivot point of the flying surface and there is static balance, flutter is highly unlikely in an airplane that flies the speeds of a Kitfox. The strength of the attachment of the weights isn't going to be affected much by the location because of how they are designed. I can see that it wouldn't be wise to put the two weights close together, i.e. side by side but them being far apart, the stress of the weights would well dispersed.

    It's just a suggestion. I've yet to have the problem of the hinges cutting/denting the aluminum.
    Fred
    EAA, AOPA
    KF5 (N49FK & N36KJ)
    Phoenix, AZ

  10. #20
    Senior Member Eric Page's Avatar
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    Default Re: Repairing flaperons

    Quote Originally Posted by PapuaPilot View Post
    If I were to do a repair I would stop drill the crack or clean out the damaged area by elongating the slot slightly. The repair needs to be done with 2024-T3 aircraft aluminum of the same thickness. I would make a patch wide enough to cover the slot on both sides and extend in front of the current slot. Size the patch with enough edge distance for 3/32" rivets (2D = 3/16"), which would be approximately 1" wide and 2" long (size as needed). I would make it with a new slot that puts it back in the original position. Drill the holes with the correct edge distance and spacing. Use pull rivets and Hysol to install it.
    Thanks for the clarification, Phil. I was hoping one of you A&P guys would chime in. I'll do as you described. Most of my damaged slots are dented/cut at the forward end, so I don't have enough room for the row of three rivets. With that in mind, would you recommend wrapping the patch around the leading edge and putting those three rivets on the bottom side? I could probably dummy up a wood buck with the flaperon nose profile to get the right bend (or maybe use the fiberglass tip to get it close...).

    Quote Originally Posted by Maverick View Post
    Something else to consider, if you haven't already installed the weights is, move the counter balance weight outboard until it is right in front of the outboard hinge and install there. This puts a harder metal at the forward part of the slot creating a stop against over rotating the flaperon when folding the wing.
    That's something to think about. I had the same question as John mentioned, regarding the effect on balance, but it's hard to argue with 18 years of safe flying. Thanks, Fred.
    Last edited by Eric Page; 01-08-2021 at 05:41 PM.
    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

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