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Bearhawk Patrol Update - February 2020

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  • Bearhawk Patrol Update - February 2020

    Bob has issued an Engineering Change for the Patrol only:
    http://bearhawksafety.com/Patrol/february2020.html

    This update relates to a wing skin stiffener, to be applied to new construction going forward.

    For technical questions about this update, please contact Bob at 540-473-3661.

  • #2
    channel.jpg
    stiffener channel stiffener is .020 2024-T3 Aluminum, 3/4 inch wide with 5/16 inch flanges.

    Is this correct?
    Stan
    Austin Tx

    Comment


    • #3
      That's my understanding. I figure 134.75 inches between the centers of each end rib. If two sheets of .020 skin fit on a 4x12 there will be margin material available to make these.
      Regarding 4" in front of the spar web... I would have to look at the existing flutes on the nose ribs and just find the closest rivet.

      Was this in response to a single occurrence, or is it a known issue with every Patrol flying?
      Mark
      Scratch building Patrol #275
      Hood River, OR

      Comment


      • #4
        skinsheets2.jpg 020 material of this length is possible if wing skin sheets are cut long ways first
        trailing edge was cut from 025 sheet used for ribs and is not shown.
        Last edited by sjt; 02-20-2020, 11:59 AM.
        Stan
        Austin Tx

        Comment


        • Chewie
          Chewie commented
          Editing a comment
          Nice graphic! You're making your tip ribs from .032?

        • sjt
          sjt commented
          Editing a comment
          The 032 is for the root. For some reason I numbered the sheets from right to left. I guess the small color differences wash out in the picture. The color was meant to show what goes where.

        • Chewie
          Chewie commented
          Editing a comment
          No it's not the color, it shows up great. I just see two full-size outlines on the .032 sheet. Just happened to notice it, made me double check what I made mine out of!

      • #5
        A little background on this engineering running change. It is non mandatory and not a safety issue. In some pictures taken from above a flying Patrol, some oil canning of the nose rib skin was noted. This is not structural but aerodynamic. Bob feels like this oil canning is slowing down the Patrol by some small amount of MPH.. Bob also has seen the same nose rib skin oil can as it sits on the ground in the heat of the day with the red paint (on Bob's Patrol) getting hotter than the white rest of the wing. This skin stiffener will cure it.

        For those of you flying your Patrols - I would not worry about it. My new Patrol will not get anything done to it. If you have a set of wings from the kit factory (with the nose rib skin already closed up) - it is possible to bond in (not rivet) a skin stiffener in the place Bob calls for. One in each bay - not a long piece as Bob shows for new construction. In the bays on both sides of where the wing strut attaches where you have access.

        Bob and I have discussed how this might be done on our existing kit wings, and if builders are interested I can detail how to do it. Mark

        Comment


        • Pbruce
          Pbruce commented
          Editing a comment
          I will be starting on my QB wings soon and would like details on how to accomplish this. Thanks. I will watch this forum for details and I will contact you directly if I get to close-out before you have published them.

      • #6
        Wondering how this .020 lump is going to look on an otherwise smooth leading edge. It might fair out but I'm somwhat concerned.
        Gerry
        Patrol #30

        Comment


        • #7
          At the factory we tested this and found it invisible. The only thing is to not place rivets close to where the "transition" is. We had seen something similar many years ago when we used to place an .032 "shim" on the flange of the false spar behind the fuel tank. But we found that with even a strip of .032 missing (to level out) that it was not noticeable if the rivets were placed away from the "step". Mark

          Comment


          • #8
            Mark, would the best method for installing this be to flush rivet the strip to the rib flanges first and then skin it along with everything else?

            Comment


            • Mark Goldberg
              Mark Goldberg commented
              Editing a comment
              There is a drawing with Bob's engineering change that shows what he wants when building up a wing. Not sure who you are. If you have our kit wings, then another strategy would be required since the nose section is closed up more or less. Mark

          • #9
            Rob Hansen, Frederick MD

            I have a rib and spar kit.

            Comment


            • Mark Goldberg
              Mark Goldberg commented
              Editing a comment
              Bob's drawing with this engineering change should answer your questions Robert. Mark
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