Sunday, July 1, 2012

Don't Sweat the Do-Over.

Last week, after destroying my rudder skin, I almost ordered a new one from Van's. New rudder skins are $70, but I just happened to have a new piece of .016" 2024 squirreled away in the garage from a long-forgotten project. I decided, what the hell, I'll make a new one from scratch. I used the original skin as a pattern and cut it out on the garage floor using the air shear. It took all of a half hour to cut it and bend the trailing edge using a 2x6 and an extra set of hands. In fact, it went so fast, I forgot to take a picture of it. Imagine that, me forgetting to take a picture! The flange on the one side was easily done at work on the sheet metal brake.

One week later, as I look at my new skin, I realize that my booboo was actually a good thing. While I was happy with the original one, there were a few things I had wished I'd done differently.

One thing is the dimpling. I set the DRDT-2 up so that it created a crisp dimple, but even after the rivets were driven, there was a slight bit of an upturn on the very edges of each dimple. I know the instructions for the DR say you can't overdimple with it, but this is really thin metal, and I believe they actually were over done just a bit. So, this time I relaxed the preload on the DR and ended up with smoother looking dimples.

I made all new stiffeners for it instead of drilling off the ones I used on the original skin. One night last week, I  tried to drill the first two and ended up with (what I thought were) horribly crooked rivet lines. I just couldn't get the drill to do what I wanted it to that night. I came in the house and complained to Ben about it and he pointed out that the bend radius of a stiffener fits a corner of a 2x4 perfectly, so why not clamp one to the drill press and drill all the stiffeners in the "jig?" He's smart. I remade the two that I drilled by hand (again) and used the 2x4 trick. I was a little mad that I didn't think of it myself. This made the rivet lines straighter.

Another thing I thought of halfway through the last rivet job was the fact that I had no primer and a lot of hand prints on the metal. Last year I decided not to prime the new components of the plane because the fuselage and wings aft of the spar are not primed. No need for all that extra work and money just to have the tail survive after the fuselage corrodes away, right? :-P  However, I did not think to clean the skin or stiffeners before riveting, which can be a bad thing because skin oils can be corrosive. Once you rivet the stiffeners in, oils and dirt trapped between them and the skin is there forever. This time around, I had a few scuffs to clean up anyway with the Scotchbrite, so I cleaned all the parts thoroughly, lightly scuffed them and gave them a quick shot of self-etching primer to protect any areas where the alclad got worn off during the scratch buffing process. This would also protect them from greasy mitts during the assembly process.

The backriveting went fine this time due to increased vigilance and situational awareness. Ben helped hold the other half of the skin out of the way for the aft rivets, and that helped as well. Now it's time to freak out about squishing the finished skin in the archaic hinged wood device according to Van's instructions to form the final trailing edge radius.  Eek!

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