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  • acceptable spar damage

    Asking for help being more productive than brooding, I'm just going to admit it.

    When putting the jury strut attach bracket on the front bracket, I was distracted while tightening the bolt. A few turns too many, and I felt the wood "crunch" underhand.

    After pouring cinders of shame on my head, I called the IA over. He said that ordinarily he'd reject the entire spar out of hand, as I broke the grain structure - but that there may be a way to save it. He didn't know; he'd have to research.

    Then he told me to disassemble half the wing, slide the front spar out, and put my left front spar in - and continue on the wing. I did so with the help of a few friends, and before we started, I tried to sufficiently impress on my friends that the spars must be completely undamaged. I held one end while we carefully moved the ribs a few inches at a time. When finished, I got down to the other end of the wing, only to see a deep scratch from the wing root to the fifth main rib in, where I must not have flattened the metal from a pulled brad sufficiently. I did not scream. Very carefully, I said to my friend, "Why didn't you tell me it was scratching?" I put my hand on the spar, and noted a few gouges on top, where he'd yanked a rib when it stuck. I did not strangle him.

    "Oh, it's just a scratch. Why? Is that a problem?"

    I did not kill him. Barely. But I did seriously consider crying, which I hate doing. Then I went home, slept on it, called in the IA, who says he doesn't know if it's salvageable or not, and looked through 43.13 which is bloody useless on acceptable damage for spars. Or I just don't know enough to figure it out.

    Aside from suggesting good places to bury a body, what I would very much appreciate right now are any references on how to determine acceptable damage. Because I refuse to give up; she will fly again.

    Thank you.
    Attached Files
    N69V (Formerly NC36462)
    1941
    BL12-65

  • #2
    Re: acceptable spar damage

    OK Dot, don't panic, don't maim any one, and take a deep breath. She WILL fly again. I have two spars with exactly the same kind of damage. I can't say they can or can't be saved yet, BUT there are things you may be able to do.
    My spars are from my 45 and were caused by the same dumb actions (dragging a rib off the spar). I have been working on the 41, so the damaged spars have just been sitting (for years now). What I plan to do is find out what the minimum drawing dimension is for the spar. We might just get lucky and find out they can be sanded without going to thin. first I plan to carefully remove the finish (from past wood work it is amazing how bad finish scrapes and scratches look that hardly touch the actual wood). If we can clean up the damage and stay within the drawing dimensions we are golden!
    Another thing you can do if there aren't any published damage limits anywhere is do a spar bending analysis and see how much loss of strength there is. Loss of extreme fiber (the top and bottom of the wood) is MUCH more of a problem than loss of section in the web. My scratches are in the center (web) and if you look at spars that are REALLY lightened, they mill away a LOT of that web to save weight (makes it look like an "I" beam). It is EXTRA material and not as big a deal to loose some. The only way to tell is get the design data (shear and bending moment for the original spars) and redo the analysis for a sanded or milled spar. If you are still within the limits for the plane the FAA should let you use the spars with an engineers analysis (we could probably use the same analysis).
    WORST case would be the spar is shot and even that isn't worth a homicide. You will need a really nice piece of Stitca Spruce and you have a great pattern for making a new spar. Good spruce is really fun to work with. Life is still good. This too will pass. Hug your friend and know you are better than someone who would beat the snot out of them. A friend who will help you with your plane is probably worth more than a spar.
    Hank

    Comment


    • #3
      Re: acceptable spar damage

      Dot; after spending a year looking for, finding, purchasing, and finally taking delivery of my new spars, you have my permission to throttle this person. As a matter of fact he/she should be removed from the gene pool!!!!
      Seriously, I really feel for you, hope it all works out. Larry
      "I'm from the FAA and we're not happy, until your not happy."

      Comment


      • #4
        Re: acceptable spar damage

        You should be able to drill out and insert a large spar bushing for the jury strut attach.... a 337/field approval would be needed. Bellanca uses about 1" dia. aluminum in the old Decathlons. Phenolic may work as well. As for the scratches... sand down a little bit on that side and see where you stand, it may or may not take care of the deep ones. GOOD LUCK

        I probably woulda at least punched the guy right in the kisser!

        Comment


        • #5
          Re: acceptable spar damage

          The comment about "milled" or machined spars looking like an I-beam is correct. It has been done on may airplanes.

          Engineers correct me if I'm wrong, but it's the upper and lower one third or one fourth of the spar that takes the most load, and the center area simply holds them a certain distance apart and holds against shearing.

          Although it is ultimately between you and your IA, I would not throw away the spar.

          The idea about putting in a bushing seems good, as does in-laying a large hardwood dowel and then putting thin plywood plate doublers on both sides. That may mean you have to modify your jury strut brackets, but that may be less money and time than a new spar.

          We have a lot of places to bury bodies down here. Bring your friend's corpse, I have one or two I have always wanted to add, and we'll have a nice evening out in the Mojave desert with a couple of shovels.
          Taylorcraft : Making Better Aviators for 75 Years... and Counting

          Bill Berle
          TF#693

          http://www.ezflaphandle.com
          http://www.grantstar.net
          N26451 (1940 BL(C)-65) 1988-90
          N47DN (Auster Autocrat) 1992-93
          N96121 (1946 BC-12D-85) 1998-99
          N29544 (1940 BL(C)-85) 2005-08

          Comment


          • #6
            Re: acceptable spar damage

            I had a good chat with my IA about this - and he says that putting a spacer in is a very probable fix - but he refuses to sign off on it unless I have some specs on dimensional tolerances. How big must the spacer be? How big is too big? What tolerance is needed for spruce? What for a different wood? What for bakelite and what for aluminum?

            On sanding the scratch out of the other spar - again, he wants data: minimum thickness acceptable - design data, etc. "It's not that the fix can't be done; it's that if we don't know what we're doing, and how much we can do, then how do we know we're doing it safely?"

            Also, he pointed out again where my friend gouged the top of the spar by yanking on the rib. What are the tolerances for sanding there?

            As for the friend, he gave me a beautiful CZ .22 rifle for a late Christmas present the day before the spar incident, but requested that maybe we should put off going to the range to shoot it until next weekend. I'm going to go to a gun show and then go shoot it Sunday with another friend, and remember that people who give me a gun, mead, and good coffee and are willing to help with the airplane are rare, and should not be shot. Just given heck for now until... someday when I forgive him.

            ANC-19 - Wood Aircraft Inspection and Fabrication looks like it might have some of the data I seek - but things published before WWII are darned hard to find on the net. Go figure. Has anybody read it and can tell me if it's what I need, or I need to look elsewhere?
            N69V (Formerly NC36462)
            1941
            BL12-65

            Comment


            • #7
              Re: acceptable spar damage

              Dorothy, I looked at your spar, its not that bad. I am back on the Island, call me some time or PM me your phone number. Tim
              N29787
              '41 BC12-65

              Comment


              • #8
                Re: acceptable spar damage

                Dot,
                Hang on to that IA. He's trying to keep you alive and being conservative is one of the best ways to do that. That said, if the damage to the spars doesn't make them unsafe you just have to prove it to him. Again, good for long life.
                If Forrest has the original spar dimensions and the shear and bending load analysis I should be able to re-run it with the reworked spar minimums and you (and your IA) will know for sure the spars are safe or good stock for wood stringers. I need to do this for my spars on the 45 eventually too but just got back in town today.
                Forrest, I know you are out there, got any original spar design analysis data?
                Hank

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