CHAPTER 42 - Side Skins and Steps
Installing the forward side skins began with holding the skin in place and marking the rear wing attachment on the inside. That translated into a notch and it was a relief to see that Van's assertion that the skin would not be deflected too much to mark accurately was true. With the notch cut, I held the skin in place with a sidegrip as shown in the first photo and then added clamps where ever possible, as shown in the second picture. Next it was possible to mark along the longeron for trimming and then, with the longeron clamped to the skin, it was possible to mark the bottom (top as jigged) of the skin as well as the spar and aileron control cutouts. The final cutout was for the step's torque tube.
Once all the trimming was done, the drilling started. I began with the center section, drilling and clecoing to the seat ribs, longeron, F604 and F605 longerons. Next I worked aft as shown in the photo until I had reached the step. At this point, I clecoed on the bottom skin and inserted the step, drilling the forward two columns of rivet holes. Switching to the front, I started at the longeron and drilled up and forward as shown in the next photo. The following photo shows a closeup of the spar area and is a reminder - be careful where you drill forward of the spar so that your rivets do not interfere with the landing gear mounts. Returning to the step, the aft bottom corner of the mounting plate is trimmed to match the expected bend line and the remaining holes drilled.
Now the skin can be removed and the conical bend marked and begun. I had marked the skin where it overlapped at the aft bulkhead and trimmed it perpendicular from that point. I had also measured the circumference of the bulkhead there, divided it up evenly, and made marks along the trimmed skin. I also marked the forward end where the skin would sharply 'turn the corner' making the point of the cone. You can see in the photo how I am using a board to clamp the skin to a table and aligning the marks with the edge of the table I am bending the skin downwards. Be sure you are bending in the right direction (no, I didn't make that mistake). I did discover that I should have waited to trim the aft edge of the skin however. You can see in the next photo how the skin begins to conform to the curve you need. On this skin, the first one, I had drawn the bend lines full length so you can see how they radiate but it is really only necessary to mark the ends for alignment on your table.
The next photo shows why trimming the aft skin too soon produced an error. I had trimmed in a straight line and the conical bend caused the skin to miss the bulkhead by about 1/2". I corrected the error by backing the skin with a 1" strip of aluminum aligned on the bulkhead. It was drilled for a line of rivets matching the bulkhead and another, converging, line of rivets along the edge of the skin. The skin on the other side was done correctly and not trimmed until the bend was complete. Returning to the step area in the final photograph, the gradual bend acutally undercut the step plate by a small amount. However, a couple of raps on the corner of the plate with a 5 lb. hammer caused it to conform fairly well with the skin and the remaining gap along the bottom can be easily filled.