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Flush bolts or pan head for cowling

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  • Flush bolts or pan head for cowling

    Im looking for input and opinions. Is it worth the extra work to have flush cowl screws at the firewall/boot cowl and nose bowl. Is there any reason why i should not use one or the other. Also, are people using flush rivets for cowling fab or regular round head rivets. Preferences there? Any input would be appreciated to help me with my decision. Thank . Gary

  • #2
    It's all personal preference, but the rest of the aircraft is flush everything. I figure if you've spent the time to dimple everything up to now, why stop? Keep the drag down.

    There's a reason this airplane goes faster than most bush planes at the top end.

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    • #3
      What i was thinking

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      • #4
        not only that I just think it looks better with flush eveything.

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        • #5
          The top of the boot and engine cowling is .032, on top of .032, on top of .040 firewall flange. #8 screws. I don't think I can dimple .032 2024 very well for a #8 screw. No problem for a smaller rivet. I haven't tried it yet.

          So would it be better to just countersink the whole 3 layers, and use a tinnerman washer under the #8 screw?

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          • #6
            I would not recommend countersinking there. The whole cowl is cantilevered from that point and having the dimples greatly increases the shear strength. I had no trouble dimpling with the #8 screw die, one layer at a time of course.

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            • #7
              Originally posted by svyolo View Post
              The top of the boot and engine cowling is .032, on top of .032, on top of .040 firewall flange. #8 screws. I don't think I can dimple .032 2024 very well for a #8 screw. No problem for a smaller rivet. I haven't tried it yet.

              So would it be better to just countersink the whole 3 layers, and use a tinnerman washer under the #8 screw?
              No, you want to dimple that, one layer at a time.

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              • #8
                OK. I will give #8 dimpling a try.

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                • #9
                  Here is a tip most might already know. Easily make your own dimple dies. By drilling and counter sinking a hole in a extra bucking bar . Use the fastener as the male part and hit a few times with your rivet gun and a flush set or a ball peen gamer.

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