Total: 527.8 hours
Outboard leading edges: 25.7
Since last time: 15.5 hours
I was way overdue for a major flub and it happened. There’s this strip of metal that goes between the outboard leading edges and the fuel tanks. The strips get riveted to the outboard leading edge and then screwed to the tanks. This involves the installation of a bunch of nutplates. (A nutplate is basically a nut that gets fixed in place by rivets.)
The attach holes for these nutplates you have to countersink and the plans specifically say to machine countersink for a 3/32 flush rivet head. Only the strip of metal is really too thin to machine countersink without expanding the hole. I should have seen this problem despite the plans telling me what to do. Add to this that the strip is really flexible and the end result is countersunk holes that look more like ovals than they do circles. And the holes are way too big for the shank of the 3/32 rivet – even when the head fits perfectly flush. I knew these countersinks were coming out very bad, but I kept going on them mostly to try and understand why (I knew they would have to be fixed). Eventually I realized that I was allowing the thin metal to flex while running the countersink and also (and related) was that I had drilled a large hole in the wood bench to “receive” the tip end of the countersink bit. But because it was a large hole, it did nothing to hold the bit cenetered and as a result it drifted, resulting in ovals instead of circles.
My first thought at a solution was to drill out the nut-plates to receive 1/8 rivets. This would have worked fairly well, but would result in an edge distance issue in the nutplates which would make them prone to cracking. Nope. The only solution was to start over with new metal – only there was a problem with this, too. The strips come attached to the tank skins. Would I have to order new tank skins ( more than $115.00 each + huge shipping charges)? The answer was no. I contacted Ralph Hoover, EAA Tech. counsellor extraordinaire. he advised me to by the raw aluminum and he would help me rebuild the strips.
I was worried about this because there is a particular bend in the strips. How would this be duplicated? – not to mention the tight tolerance in the position of the holes. The original strips would be useless because they were bent, not allowing them to be laid flat onto another piece of metal to act as a guide for the holes and I had mangled the nutplate holes anyway. Not to worry, though. Ralph knows how to deal with all these things. For $7.00 + another $7.00 cutting fee (gotta love that) and shipping (low because I bundled the metal with other items I needed), I got the bare aluminum and brought it to Ralph’s shop. He marked the bends, made some measurements, then straightened the mangled strips (apparently, you can do this). We used the mangled strips as guides to drill holes for the attachment to the leading edge (the holes which weren’t mangled) and Ralph made a nutplate jig which in conjunction with the mangled strips allowed us to drill all the propoer holes in all the proper locations. Lastly, he used his markings of the bends in the original strips and put what look to me like precision bends in the new strips.
Finally, instead of machine-countersinking for AN426AD3 rivets (as called for in the plans), we countersunk for NAS1097AD3 rivets. These are “oops” rivets with 3/32 shanks and 1/16 heads. They allow us to countersink but not go so deep, so the holes don’t get enlarged. The new strips are perfect! I give a very hearty thanks to Ralph Hoover for helping me fix this issue and showing me how it’s done. It really feels bad when you mess something up. But it feels really good to fix it the right way.
Apart from this, there was nothing all that out of the ordinary in the other work done. Cleco, drill, deburr, dimple, etc. Next we’ll be priming and riveting it all together. The fix described in detail took about 4 hours. The rest of the time was all the normal stuff.
These are the strips with the mangled holes. Just look at them!
And this is what the new ones look like – beautiful:
And this is Ralph Hoover:
Some random pictures of the leading edge (mostly the right):
And what post could be complete without seeing a picture of Zach learning to use his new Christmas present: