5.8 Hours -
There are many small tasks that need to be completed on the tanks before they can be sealed up. Because of this, I was able to accomplish quite a bit today, even if it doesn’t look like it. I wasn’t planning on spending 6 hours in the garage today, but the next thing I knew…
I started off by doing a final fit check on the tank attach brackets prior to drilling them to the inboard tank ribs. For the most part, the fit was good, but I had to do a bit of filing near the corners to make sure there will be enough room for the rivet heads that will attach the skin to the rib.
Once the brackets were fitted, I clamped them in place on the rib along with the reinforcement plates (T-410) that go on the other side of the rib. The bracket, plate and rib were then all final drilled together using the holes in the bracket as a guide.
To fit the tank attach bracket, I had to check the fit, file, check the fit, file again, etc.
A reinforcement plate is on the inside of the inboard rib. The rib and reinforcement plate are drilled with the bracket as a guide.
Next, I moved on to the fuel tank access holes. The inboard ribs do not have a pre-cut hole for these, so a large hole has to be cut using a fly-cutter. Using the fly-cutter is simple enough, but it is still a bit of a scary process. My basic strategy is to clamp everything in place on the drill press, turn on the drill, and then stand as far back from the drill press as I can while still being able to operate the press. The cutter makes a lot of racket as it cuts and it throws large shards of aluminum everywhere. Once the circle is cut, the danger isn’t over as you still have two razor sharp pieces to deal with!
Fly cutter time! Clamp the rib down, turn on the drill, and stand as far away as you can while still being able to opperate the drill press.
Despite the chaos created by the fly-cutter, it does produce a nice hole.
After the access holes were cut, I set the access plates (T-708) in place and used them to drill all of the screw holes in the ribs. Once the screw holes were drilled, I replaced the access plates with the stiffener rings (T-407), and used it to drill all of the nutplate rivet holes in the ribs. Finally, I deburred everything, countersunk the stiffener rings, dimpled the ribs and installed the stiffener rings and nutplates on the ribs. These are the only rivets in the tanks that don’t get set with sealant since the access cover plate (with sealer) will seal them.
The last thing I did on the inboard ribs was to drill a 7/16” hole for the vent line fitting. I used a step drill to make this hole and I came very close to drilling one of the holes on the lower portion of the rib instead of the top. Fortunately, I caught this before I had to start planning a fix!
The tank access cover is clamped into place so the screw holes can be drilled into the rib.
After the screw holes are drilled, the access reinforcement ring is clamped into place and used as a guide to drill the nutplate rivets.
The rivet holes in the reinforcement ring are countersunk while the ones in the rib are dimpled.
The reinforcement ring and nutplates are riveted on now (they'll get sealed by the access cover), and I also drilled the hole for the vent line fitting.
After dealing with the inboard ribs, I also drilled a reinforcement plate to the leading edge of the outboard rib on each tank.
The outboard tank rib also has a reinforcement plate installed in the nose.
Next, I turned my focus to the right tank, since it was still in the cradle, and drilled both the drain flange and cap flange to the skin. The drain flange is simply lined up over the hole in the skin and drilled using the flange as a guide. However, the fuel cap is slightly more involved.
To drill the drain flange, you just line it up over the drain hole and use the flange as a guide to drill the skin.
I’m using the standard Van’s fuel cap. It’s a little rough looking and hard to open, but it seals well and it’s cheap. The flange for the cap has two slight bends in it to help it conform to the tank skin. The bends are subtle, but it was fairly easy to figure out how best to orient the flange in the skin. Once I figured out the orientation, I clamped the flange in place and started drilling it using the holes in the skin as a guide.
I'm using the standard Van's fuel cap. Not pretty and hard to open, but they work and they are cheap.
The cap flange has a slight bend in it, so you have to take some time to line it up correctly. Once aligned, drill away using the skin as a guide for drilling the cap flange.
Tackling the vent lines was my next task. I started by fabricating the vent line clips. These are simply two small clips (one per tank) that will be used to hold the vent line towards the top of the tank in the outboard bay. I made the clips from some scrap .025” x 0.5” aluminum as per the plans. To make the curved portion, I bent the aluminum around a 1/4” bit. The upper portion of each clip has a single #40 hole that will be used to attach the clip to the fuel cap flange.
The vent line attach clips are fabricated from .025" x .5" scrap aluminum. Bending them is fairly straight forward. Now I just have to remember to rivet them in place when I install the fuel cap flanges.
Next, I made the actual vent line for the right tank. While this was just a rough fitting, I was surprised how easy it was to bend the correct shape into the inboard end of the line (it has to make a slight jog from the second inboard rib to the inboard most rib. I’ll have to make some final length adjustments once the bulkhead fitting is in place.
Making the vent line was simple...I couldn't believe it when I made the bend correctly on the first try. I'll have to fine tune the length during once the bulkhead fitting is in place.
Finally, I started deburring some of the pieces to the right tank. I deburred all the stiffeners and I think I’ll deburr and dimple pieces as I take the right tank assembly apart. I’ll also have to complete a few more tasks on the left tank before I start final assembly.
