February 6, 2008

Wrapping up some Details - 4.0 hrs.

I decided to take care of a couple of details today that have been nagging at me. So I started by scuffing, cleaning and priming the 408-I end rib and the splice plate for the leading edge. While they were drying, I drilled out the hole in the bottom of the leading edge skin for the tie-down ring. Finally, I riveted the nutplates on the splice plate and clecoed it and the end rib in place on the leading edge.

Here's the end rib and splice plate, primed and ready to go with all the nutplates riveted on.

Close up shots of the nutplates and rivets, front and back sides.

Here's the hole in the leading edge skin, drilled out for the tie-down ring. This is more time-consuming than just drilling a hole. The black lines were drawn according to the plans to make sure the hole was centered in the right place. Mine was off by just a smidgen, which means that in order to finish with it centered, it took some time and patient work. I drilled it undersized first, so you can look through the hole and see where you're at. Then I used my Dremmel tool with a small cylindrical sanding drum to slowly enlarge the hole in the right direction, Finally, one more plunge with my unibit finished enlarging it to the right size. The leading edge had to be taken on and off, of course, while drilling and sanding so no damage would be caused to the threads in the tie-down block. Finally, the edges of the hole were deburred and smoothed.

Here's the tie-down ring being installed for a trial fit. The problem with this system is that these rings aren't made to fit as well as they could be. The flat flange at the top of the threads can't push on the skin on the wing as you screw it in, or it will push it in making a big dent. This is because there's a gap behind the skin between the skin and the tie-down block. It's about 1/4". If you made the hole big enough for the flange to fit inside, it would not only be a much bigger hole than you would like, but the edges of the ring would hit and rub on the skin before the flange is screwed down tight against the block inside. So that won't work either. So what do you do? I stole an idea from another builder. I made a spacer. I bought a hard white nylon cylindrical piece at Home Depot, drilled and tapped the hole so it would thread onto the bolt, cut about 1/4" length off, and threaded it on the bolt as you see above. The hole I drilled in the skin is just big enough for this piece to fit through it. Now I can screw the ring down tightly against this spacer and the flange is just at the skin. Should work great. The picture above looks a bit off... as though it doesn't line up with the hole. But it's sloppy and flops around in the hole until it's down tight, so it does fit very well. I don't plan on flying with these tie-down rings in place. Besides the tiny bit of extra drag they would cause, I still don't think they'll stay in place. I don't want to lose them or bomb somebody's house. So I would like to find a flat plug of some kind that would securely screw in to cover the hole while flying. Any ideas would be appreciated.

Finally, I clecoed the end rib and splice plate in place on the leading edge. I'm not going to rivet it on yet, until I do the final fitting of the tank joint when I get the tank finished. I want to have the option of using a shim here and there if necessary to bring the skins flush with each other.

This is kind of a cool shot. I like this perspective. Except for the rivets on this rib, the leading edge is finished. Now I feel like I can dive into the tank and get it finished. I can't wait. By the way, if you're noticing different colors in the above two pictures, you're very observant. The interior ribs are primed in gray, and the end one is green. It's the same primer, just a different color. I prefer the gray, but I had a spray can of the green that I wanted to use up. Nobody sees this anyway, so who cares.

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