Well, I got to work finishing the top wing skins (Section 16-02). It took a while to strip off the blue plastic (14 ribs x 2 wings plus 3 horizontal stripes). I finally got that done and finished the countersinks for the wing walks. My wife came by for lunch (and to keep me from spending all day with the plane — she’s a bit jealous and calls the plane, my “mistress“). She took a picture so the FAA will know that it was me sweating over these skins in the garage.
Doing the countersinks for the wing walk doublers… the instructions caution to make sure these don’t go too deep. The skin is right on the borderline of too thin to countersink, but it works better to deal with the top skin/doubler/rib sandwich.
Next, I had to pull the skins off to make a scarf joint along the forward edge of the skins. I’m starting with the right wing. It’s easier to leave the skins on the rib skeleton as I have no better place to store them.
I found the illustration very confusing. The shape on the bottom does not nest with the shape on the top. It took me a while, but I finally figured out that they just wanted the two skins to lay flat on the spar. Once I saw that, it was easier to figure out how to shape the corner.
The inner top skin sits underneath the outer top skin. The gap between the spar and outer top skin is too big if you just let it overlap. So, we file and sand and polish a bit off the inner skin and then remove a matching amount off the outer skin and try for a flat joint.
I clecoed my skins to the tables to get them lined up and then filed and sanded the corners. I used my bastard file since you have to carefully remove a surprising large amount of material. Still had to be careful. Several bloggers reported removing too much and having damaged or rounded corners. I used some sandpaper and a paint stir stick to finish it off.
The joint is a lot flatter after the adding the scarf — not sure this picture does it justice.
There is a lot of dimpling to do on the skins. The inner skin has almost 250 dimples to make (in addition to the 70-80 countersinks). The outer skin has over 450! My son dropped by (for lunch) and I enlisted his help in doing the dimpling on the DRDT-2. It can reach all the dimples and it made nice crisp ones.
The blue X’s are reminders not to dimple the wing tip attach holes quite yet.
With the dimpling done, it was time to prime the skins. I ran a line of primer over the rivet lines and filled in with a light coat of primer. You can see the large outer skin, the smaller inner skin, and the two wing walk doublers (those are primed on both sides).
I also needed to finish the J-stiffeners that go down the middle of the wing. These were match drilled in the very first wing task a few months ago. I stripped off the blue plastic, and ran a deburring bit through the holes. Then they got shot with some primer. They’re not in the wing yet, but that should not take long on the next build day.
So, the wing is just about ready to rivet. With the dimples in place, the wing really feels solid. It’s amazing how much just dimpling adds to the sheer resistance for the skins. They really lock in tight!
I also had one last minute task on the right wing. One of my rib flange holes was a bit enlarged when I double clutched the dimpler. I reamed this out to 1/8″ (hence the copper cleco) and marked it for an “oops” rivet. The tape goes over the cleco depressor, so I’ll be sure to remember to swap in the NAS 1097 rivet for this one hole. The head is a normal 3/32″ size, so it won’t be noticeable.
Next, I have to slide the J-stiffeners into the right wing and then do all the dimple and prep work for the left wing skins. Then, it will just be a lot of riveting to finish this section.