Aligning and Mounting the Flaps   February 2nd, 2010

After ordering a wider piano hinge from Aircraft Spruce, I was able to ‘pull out’ the flap enough to make it match the aileron trailing edge.

At this point the wing is upside down in a wooden cradle, so there is no good way to hold the flap while the hinge is drilled. I used the following method:
  • First, cut two scraps pieces of hinge, long enough to cover about 9-10 rivet holes on each end of the flap. Cleco the bottom skin to the wing and to the flap brace. Put a cleco in every skin-to-flap brace hole, except for the few holes on each end where the scrap piano hinge will sit.
  • Attach the pieces to the flap and mount on the wing using cleco clamps.
  • To check the alignment with the aileron trailing edge, first make sure the aileron is set to its neutral position, and then lightly clamp the flap and aileron together.
  • Before drilling, use a long straightedge (like the red level in the picture below) to make sure the flap and aileron’s trailing edges are aligned. I went one step further and used a digital level to make sure the angle of the aileron trailing edge was the same as the flap trailing edge (don’t expect this angle to be 0 degrees, as the wing will probably not be level with the ground while in the cradle.
  • After I was 100% positive the two trailing edges matched, I very carefully drilled each hole of the two scrap hinges, putting a cleco in every hole as I went.
  • Remove the flap, separate the scrap hinge pieces, and use a dremel tool cutoff disk to remove the loops on the scrap hinge.

  • Now lay the scrap on top of the full-length hinge to be drilled. Match drill the holes from the scrap to the full-length hinge. I used the loop tabs to line up the two pieces, and then clamped them together before drilling.

  • After both ends of the hinge are match-drilled, simply cleco the full-length hinge back on the wing and match-drill the rest of the holes.
The other flap was mounted with the same method, and I was very happy with the resulting alignment on both flaps.
And by the way, I didn’t come up with this method of mounting the flaps — I read it at 🙂
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