Felt like I made a lot of progress this week. Finally finished up the right fuel tank, and over the weekend (with Becca's help) I was able to finish riveting the top skins in place. I also found a couple of leaks in the tank and applied a fix. Have to wait a few days to see how that works out.
Started out the week finishing up the fuel tank.
Final cut the vent tube to length. I deliberately left it a bit long so that I could be sure it would fit after all the bending and final fitting.
Basically the vent line is connected to a bulkhead fitting through the end rib, then extends the length of the tank through tooling holes with nylon bushings to prevent wear. The end is attached to a small aluminum clip that is riveted to the filler cap flange.
Here's the bulkhead end. (yes, i know it's messy. no, i don't want it to leak. ever)
The far end connects to the clip which is held on by one of the filler cap flange rivets.
Once that was done the final task was to install the fuel pickup tube and fitting in the T708 end plate. There is an anti-rotation bracket that holds the tubing nut and is riveted to the end plate to prevent it from coming unscrewed.
On the outside is the connection where the fuel tube will carry into the fuselage structure and eventually to the engine.
Once that was done and everything test fitted one last time, I did a final cleanout of the tank (air gun, then vacuum, then a wipedown with acetone) to get it as clean as possible. Then I mixed up a big batch (used 60gms) of proseal and got to work installing the baffle plate and attach angles. There is really no way to stop this process once you start, since everything has to be riveted together in one shot (around 200 rivets total) and the proseal is hardening the whole time (still plenty of working time, but don't dawdle and I wouldn't want to try it on a hot day since heat seems to accelerate the proseal setting up). Don't have any pictures - with 4+ hours of work there is no time and you're too covered with proseal anyway.
Here's the final result.
Two things I think I've decided about proseal - if there is a next time I will try the "A" type, which is brushable. Regular proseal is about the consistency of and about as easy to work with as hot bubble gum (like you find in a parking lot in the summer) and it as *least* as stringy and gooey. Oh - and it sticks (like bubble gum) tenaciously to anything it touches, and is very hard to clean up. The other part I really don't like is the cleanup. Most of the tank isn't that bad, but when doing the baffle plate you need to use around 170 clecos and then you get to clean all those dudes up with MEK/Acetone or something. Gets very tedious.
I was a bit disappointed with the fit of the rivets on one side in particular (top side). They are slightly proud of the surface. Not sure if it was slight under countersinking or if the proseal underneath was a bit thicker and it made them stand slightly high. Hopefully I can correct this later.
Once that's done, you screw the tank to the main spar, then start installing the top skins.
I did the skins twice before I was happy with the fit between the skin and the L.E./Tank.
Note from later: I read where some folks taped over the proud rivets with stainless tape then hit it with various abrasives (dremel tool seemed to be one of the more popular ones). I tried it with plain old blue painters tape and very slow hand sanding and was very pleased with the results. I'll be trying more of this later.
Here's the finished tank attached to the spar. Once that's done it's on to the top skins, so the skins are clecoed on one last time prior to riveting. Things are starting to come together....
Becca is my expert wing riveter, and although she was pretty beat from a week of marching all day every day this week (band camp) she graciously agreed to help me rivet the skins. It's at least twice as fast as doing it by yourself, and there are bits you just can't do by yourself.
After clecoing the skins on I didn't like the fit at the leading edge/tank juncture so I re-did the whole thing, starting with the complete top row first (and snugging it up) then continuing down toward the trailing edge. Came out *much* better.
Back riveting worked pretty well on the left wing. Either I'm getting pickier, or something was up, cause I wasn't happy with the back riveting on the few we tried so we bucked the whole thing. The shot below is after the inboard panel is mostly finished.
And here's about 75% done.
Closeup of a line of rivets. This will polish out just fine.
And here's the completed wing. Really glad to have the main bits done. Next is the flap and aileron attach brackets.
The fuel tank was removed from the last shot cause I tested it for leaks and discovered a couple of slow leaks along the lower edge of the baffle plate.
The procedure for testing for leaks is pretty straightforward.
First, seal all the holes, then put some air in it and see if it leaks.
I ordered a fuel tank testing kit from Van's a while back ($6 i think), you get a fuel line cap/seal, an air valve (like a bike tube valve) with a tapered pipe fitting on the end that fits the fuel drain flange, and some instructions.
Basically you install the valve in the drain flange:
Put the cap on the fuel line:
Install the filler cap and tape it tightly shut:
Then install a balloon on the vent line. I made up a short piece of aluminum tubing to the assembly to make it easier.
Once that is done, fill with *very* low pressure air. 1 or 2 pounds max or you'll pop the tank.
I set my regulator to 5 and went very slowly just a quick shot at a time and watching the balloon carefully the whole time.
Theoretically the balloon will pop before the tank does, but I wasn't taking any chances.
Once I knew I had a slow leak, I mixed up some dish soap with water and started painting joints and rivets - anywhere something might leak.
I kept thinking I saw something when I wasn't, but as soon as I got to a real leak it was extremely obvious. Turned out there were two small ones along the bottom edge of the baffle plate. One leak was in bay 3 and the other in 5 (counting from 1 being the inboard tank bay). Didn't think to take a picture of the bubbles, but here's what the fix looks like (both are virtually identical). The great news was none (at least so far) of the really difficult places to fix were leaking.
The leaks were actually only an inch or so (just the bit between two rivets) but I made the patches much bigger hoping to contain them in one go.
Here's the overall view after prosealing. I also prosealed the rivets along the attach angles more thoroughly since I had some extra proseal from the batch I made for patching.
I'll let this set up a day or two then retest for leaks. Pretty hopeful at this point. I also still need to test the left tank. Probably do that next week as well.
