I started today’s session by finishing the countersinking on the Top Inboard Skin (FWD-Wing Walk) area. The four vertical rows of holes on the right side of the Skin have now all been countersunk and according to the guage, are .005 too shallow as recommended in the plans. The three horizontal rows of holes (top, middle, and bottom of the Skin) will all get dimpled in the next few steps. On the far right side of the Skin, there will be seven nutplates attached on the underside of the Skin. The rivet attach holes for these nutplates were also countersunk for the head of a AN426AD3-4 flush rivet. Lastly, the #19 holes (for the #8 screws) will also be countersunk in a future step.
The plans state, “remove material thickness from the top outboard forward edge of the W-00002 Top Inboard Wing Skin and the bottom inboard forward edge of the W-00003 Top Outboard Wing Skin”. Below is the figure referenced in the plans:
Since I’m a visual dude, I wanted to see how the two Skins fit together in this area before I started removing anything, much less material. So, I temporary clecoed the Top Outboard Wing Skin to the Left Wing. In the two pictures below, the Top Outboard Wing Skin still has the blue plastic protective coating. I did notice that some of the holes between the Skins and the Wing Ribs did not “exactly” match up. Upon further inspection, I determined the Main Spar still has a “slight” bend in it. I suspect this bend will be removed when all the Skins are clecoed on and the rivets are installed.
Here is a close up of where the Top Inboard Skin (on bottom, .032 thick) and the Top Outboard Skin (on top, .025 thick) overlap. Those two Skins together have a thickness of .057. The “problem” that exists is the Tank Skin (which mounts right in front of the overlap) is .032.
So, the Skins aren’t “even” in this area. This is why some material has to be removed as described above. So, I made a small gauge that is .032 to match the thickness of the Tank Skins. The first picture below is the Skins BEFORE I removed any material.....
.....and here is the AFTER. This took ALOT longer than it probably should have, but I “had” to make it better.....it’s a disease! I started by using 220 grit sandpaper to get the pattern I wanted. Then I used a hand file to remove most of the material. Finally, I used various grits of sandpaper (80, 120, 220) to get the final result that I wanted. I CAN’T WAIT TO DO THE OTHER SIDE!
This is the two rows of holes that the Skins will share when riveted together. The row on the left will also be riveted to the Wing Rib below it. The row on the right, best I can tell, will only have the two skins riveted together (minus the Spars and J-Stiffeners).
There are only a couple of steps left before the Skins get treated with Alumiprep, Alodine, and are Akzo primed. I still need to do the edge work on the Skins, dimple the Skins, dimple the top flanges of the Wing Ribs, and dimple the Wing Box J-Stiffeners. Since I just did all the sanding on the area where the Skins overlap, I am OVER sanding right now. So, I’m going to start by dimpling the Wing Ribs (except Ribs #1 - #4–Wing Walk Doublers will go there). In the picture below, the Wing Rib on the right has been dimpled with my Substructure Dimple Dies. The two Wing Ribs next to it have not been dimpled yet. If you look close to the holes in the right Wing Rib, you can see the Akzo primer flaking off after the dimpling was completed. Earlier in the build, the plans recommended priming at a certain point.....which was just prior to the Wing Ribs being riveted it the Main Spar. However, at that time, only the lower holes were dimpled in the Wing Ribs. I suspected when I reached the step to dimple the top holes, the primer would flake off. I will use a nylon brush to brush off the flaked primer and touch up the holes prior to riveting on the Skins.
