Section 21

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  Final flap assembly

  Flap Section 21 Wing

  May 10, 2021

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  Getting the trailing edges cut and trimmed to butt together perfectly took a little bit of time using hand tools, but pretty happy with the result.

  

  Much of the flap assembly required to cleco the entire assembly together to final drill, then disassemble for cleanup. I ended up 3D printing a spacer for the hinge brackets to avoid putting in appropriate washers during assembly.

  

  I used the squeezer to double-flush rivet the hinge brackets. They didn't come out quite as pretty as I was hoping, but look pretty flush in the end.

  

  For the final riveting of the trailing edge, the instructions didn't provide much information on. I ended up back riveting all the trailing edge rivets, which worked quite well. The only trick was to initially drive the rivets along the axis of the rivet, then finally setting them parallel to the trailing edge.

  

  The final flap turned out pretty square along both the hinge and the trailing edge.

  

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  Flap tool fabrication

  Flap Section 21 Wing

  May 10, 2021

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  In the flap plans, there are a few callouts to fabricate tools and jigs to countersink and drill the trailing edge at a precise angle. While outright precision probably isn't necessary here, I decided to hop on the CAD and 3D print all these parts instead of fabricating them out of aluminum.

  

  One challenge was machine countersinking the trailing edges. I noticed that Cleveland Aircraft Tools sold a jig to hold the trailing edge at the right angle to use a countersink cage with. $42 seemed like a lot for such a simple part, and I decided to draw one up and 3D print it also, which worked great.

  

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  Flap prep

  Flap Section 21 Wing

  May 10, 2021

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  While the flaps seemed fairly straight forward, there were a few new and interesting tidbits in the plans that haven't come up in previous parts. First was the use of duck-bill pliers to eliminate "pucker" in the ribs. I didn't actually own any duck-bill pliers by that name, but had a small pair of flat (non-grooved) surface pliers that I put some tape over to not damage the aluminum and straightened out the bend as best I could. It was pretty subtle to start with, but it came out slightly more flush so I suppose mission accomplished.

  

  And "pucker removed"!

  

  Next were the inboard leading edges that required doublers and a large nutplate. Pics still need to be deburred, but everything went together nicely.