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Please don’t make my fabric covering mistake

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  • Please don’t make my fabric covering mistake

    In the interest of safety I’m sharing a enormous screwup of mine that could have been disastrous. Last week on my second test flight, during climb out,
    I heard a loud boom. I thought perhaps I had blown out a window and checked, but all windows were good. A friend on the ground radioed and said he thought I was back firing so I thought I blew something in the engine. The engine instruments were all good, but I made an emergency landing and taxied to my hangar. When I exited the plane, I saw what the issue was, and it wasn’t the engine. The fabric on the fuselage above my head had filled like a balloon and loudly burst ripping the fabric. I couldn’t see any of this because I have a headliner that stayed intact. The backfiring was actually the fabric snapping in the wind like a flag in a windstorm. Upon closer examination it appears likely that where the fabric wraps around the windshield channel and is glued, that it didn’t hold. Either I didn’t have enough glue or didn’t scuff the channel properly in this area.
    In discussing this with airport friends I found out about an old Piper AD on several models that had the same issue in the seventies where a metal trim strip over the fabric and windshield was required. I’m sure that isn’t necessary on the BH when done properly, but obviously I screwed up. When you look at the attached pics you can see the damage. I believe i will have to recover the entire fuselage but if there is another suggestion on an easier or faster repair, I welcome any ideas. Thanks
    You do not have permission to view this gallery.
    This gallery has 4 photos.

  • #2
    Thanks for sharing this....

    Last edited by way_up_north; 02-16-2021, 04:51 PM.

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    • #3
      Huge thanks for sharing Tim and sorry to see this. Any idea how the air got between the headliner and the top skin ? Or do you think it was the lifting force of the airflow over the windshield and top skin that lifted the fabric ?
      Nev Bailey
      Christchurch, NZ
      Builders-log
      YouTube

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      • #4
        Thanks for sharing that. I am currently covering my fuselage and this made me rethink not rib stitching the top down.
        Just curious did you have the fabric tucked inside the windshield channel?

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        • #5
          What system? Looks like Polyfiber?
          It is a real good idea to stitch or rivet that area, there are tremendous forces working on the fabric, both lift and prop wash. Glad you made it down okay.
          Not to pile on but the fabric should go in the channel to the bottom and return so that the windshield pinches it in there.

          Comment


          • Battson
            Battson commented
            Editing a comment
            Oh - you beat me to it - my thoughts exactly.

        • #6
          I should start by saying - so sorry to see this Tim. To all the builders here, this is easy to relate to I am sure. A huge amount of work, now undone. Taking things apart again to repair is the last thing you want to be doing right now. But if it's any consolation, I have been there before too - and it will feel like no time before you're up and running again.

          The "Bearhawk hump" is a lifting surface, and needs to be rib-stitched (if I recall correctly). Exactly the same as the top of a fabric wing - which incidentally blow up like balloons if not stitched. There are some tales about people going flying without stitching the wing...

          That may be a big part of the problem - I don't see any stitching in the hump?

          You will be able to repair that without recovering the whole fuse - for certain.
          You just need a 6" overlap (again from memory) and to follow the instructions in the manual exactly and refer to AC43.13B as well.
          The repair will be almost invisible in that location, so I would not recover the whole thing, were I in your shoes.
          You can always recover the whole thing at any time, might as well go through all the testing and learning to fly the Bearhawk stages with the repair job. Just in case anything else happens.

          One final thought - as others have mentioned, in accordance with the manual, the fabric always needs to be wrapped around something, it almost looks like it was only glued to the top of the windscreen channel - trust me when I say, that would never last long, in any location. After a few hundred hours, any fabric glued to a flat surface will have separated. The only way to make a flat surface stick to fabric (long term) is the sandwich it between the fabric and a patch or plate.
          Last edited by Battson; 02-16-2021, 09:38 PM.

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          • Luke68
            Luke68 commented
            Editing a comment
            How far back should the hump be stitched?

          • N942VT
            N942VT commented
            Editing a comment
            All the way to the rear spar. Use AC43.13 for spacing in the prop wash, 2.5 I think.

          • Battson
            Battson commented
            Editing a comment
            Refer to the manual. If there is no help there, personally I would say to the end of the curved portion at least - no question about that. Maybe a few extra inches just to be sure. That is not based on practical experience with this problem, mind you, just my knowledge as a Mechanical Engineer.

        • #7
          Hi guys, just to clarify some of the questions posed, I did have the fabric tucked in the channel and pinned in with the windshield. However I did not have the hump area rib stitched, which unfortunately I was unaware was needed. Thanks all for the encouragement and comments and Battson thanks for the repair suggestion, I think I will at least try that first before redoing the entire fuselage.

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          • #8
            Hey Tim,

            So sorry to hear that happened. Great job getting it back to the airport. Really glad the damage was limited to just that. Also, having made a few repairs to my fabric due to rocks and such, it's not that big of a deal. Battson is right, totally repairable.

            I noticed you don't have any safety wire on your aileron carry through turnbuckle. Perhaps you took it off after the incident... if not, you really need to put some on there IAW with AC43.13.
            Last edited by swpilot3; 02-16-2021, 11:06 PM.
            Bobby Stokes
            4-Place Kit Builder
            Queen Creek, AZ
            http://azbearhawk.com

            Comment


            • robcaldwell
              robcaldwell commented
              Editing a comment
              It appears to me that the turnbuckle is the clip lock type. I think I can barely make out the blue clips on the bottom of the barrel.

          • #9
            Thank you Tim for sharing, and great job flying the airplane with a pretty huge distraction.

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            • #10
              So sorry to hear this but the important thing is that you got back on the ground safely and the plane will fly again. I agree that you should be able to make the repair without it being real noticeable.

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              • #11
                Sorry to hear about your blowup, but thankful you are save, and as swpilot3 mentioned, if you didn't have safety wire on that turnbuckle then you might view it as providence as that for sure could have caused a serious accident.

                Tell us more about your trim system! I see that it's electric, show us what you did please!

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                • #12
                  Originally posted by swpilot3 View Post
                  Hey Tim,

                  So sorry to hear that happened. Great job getting it back to the airport. Really glad the damage was limited to just that. Also, having made a few repairs to my fabric due to rocks and such, it's not that big of a deal. Battson is right, totally repairable.

                  I noticed you don't have any safety wire on your aileron carry through turnbuckle. Perhaps you took it off after the incident... if not, you really need to put some on there IAW with AC43.13.
                  ...And you should have 3 crimps on the cable sleeve.
                  You do not have permission to view this gallery.
                  This gallery has 1 photos.

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                  • #13
                    Originally posted by Aero_tango View Post

                    ...And you should have 3 crimps on the cable sleeve.
                    And the order of the three crimps is very important too "particular order in which multiple crimps are to be made: first in the middle, then nearest the loop, and last the tail end"

                    Two crimps will not hold full tension, and neither will crimps made in the wrong order. These issues could lead to a broken control cable, and total loss of control of the aircraft.

                    Please refer to these visual instructions on the required method for forming control cable crimps (scroll down the page quite a ways, past the cautionary tales)
                    https://www.kitplanes.com/the-big-squeeze/

                    Next item...

                    I am also concerned by the lack of thread engagement on the turnbuckle - Tim - had you already started disassembling that turnbuckle?

                    The AC only allows for three to four threads showing for a new installation. The pictures make it look like there would only be three or four threads engaged, with no safety wire, this is a horrifying thought! Please read the AC carefully - if one of these things fails, you are gonna get yourself killed.

                    Here is the relevant part from the AC

                    Screenshot (4).png
                    Last edited by Battson; 02-17-2021, 03:26 PM.

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                    • #14
                      For some reason I remembered that fabric doesn't have to be stitched to stringers? Is that incorrect, or it only needs stitched to the hump? All the other stringers are also convex curved.

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                      • #15
                        You're right, it doesn't normally need to be stitched to the stringers. However, I stitched mine on the hump. I remember some sort of specific guidance on this... like how far back it needed to be stitched. I thought it was a bear track article, but I can't find anything about it now.
                        Bobby Stokes
                        4-Place Kit Builder
                        Queen Creek, AZ
                        http://azbearhawk.com

                        Comment


                        • svyolo
                          svyolo commented
                          Editing a comment
                          I have a skylight back to the rear spar, and my headliner aft of that is already installed so it would be tough to stitch it to the upper stringers until aft of the cargo bulkhead.

                        • swpilot3
                          swpilot3 commented
                          Editing a comment
                          I think the issue was just the hump. The hump creates lift and lifts the fabric. Even with mine stitched I can see it raise quite a bit in flight since I don't have a head liner.
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