My Wooden Airplane
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7/21/2010 - 7/29/2010

Gluing Wing Skins

I'd have to say, without a doubt, that this was the most challenging part of the whole project so far. Even though the wing skins were "pre-bent", they still didn't go on very well. I used the same clamping process as I did when I bent them, but not everything lined up the same way.
I think I was able to fix most of it with careful trimming and lots of sanding, but I know there's still "scalloping" between the ribs, and I probably won't know the full extent of the problems until it's covered and painted.

Here is a picture of some of the pieces I trimmed off. These were between the ribs, aft of the spar. See all the warping? It was completely uncontrolled: sometimes up, sometimes down.
The plans don't say anything about trimming these pieces off, but if I had left them on there,
it would have truly looked awful.

Lessons Learned:

   1) Glue the bottom before the top. I thought I'd glue the top first, since it seemed to form to the airfoil shape more readily, but this made it much more difficult to attach the strut brackets afterward.

   2) Be careful how the wing is "twisted" when gluing the skins! During most of the wing assembly, the spars were resting on some old batteries to keep the wing a uniform distance above the workbench. However, when attaching the wing skins, I had to relocate the batteries because they would have interfered with attaching the skins. The problem was, I guess they weren't positioned equally, because there's now a permanent twist to my wing, and it's not even in the right direction! (Normally, the wing is twisted in such a way as to make the trailing edge higher at the tip than at the root. This is called "washout" and helps maintain controllability during a stall. Mine is now twisted so that the trailing edge is lower at the tip than at the root.) I didn't pay too much attention to it because I was planning on setting the washout by adjusting the length of the struts when attaching the wing to the fuselage. However, now that the skins are attached, the wing is MUCH stiffer than it was before, and I think I'm going to have a tough time setting the 2 degrees of washout that is necessary!

   3) The president of our local EAA chapter suggested putting some aluminum between the skins and the ribs when bending the skins. This might have helped to alleviate the "scalloping" between the ribs. Unfortunately, his suggestion came a little too late, since I had already glued the skins in place.

   4) I think a much better way to approach skinning the wings would be to do it the way it was done on the Horizontal Stabilizer. This way, there is no special bending or forming to be done, and the top and bottom skins are completely independent of each other, so a misalignment of one doesn't necessarily affect the alignment of the other. I'm sure it's heavier, and is most likely the reason why the designer chose to do it this way, but I would gladly pay that price in exchange for all the head-scratching this has caused. In fact, if I ever have to rebuild the wings, that is how I will skin the leading edge!

Total Time: 18.5 hrs.