<July 1, 2006>
Tank Drilling Tasks
Lots and lots of tank stuff got done today. Let's see... I finished riveting the inboard ribs, drilled the cap flanges, fabricated the vent line clips, drilled the skin for the drain flanges, match-drilled the stiffeners to the right wing skin (not pictured), countersunk the filler-cap flanges, and drilled the holes for the vent line and vapor return line fittings. I am moving along and should be ready to seal these things up very soon.
Here are the two inboard ribs with the reinforcing rings and nutplates riveted.
To drill the cap flange I first drew a line on the flange bisecting the filler opening, from forward to aft. The flange is curved to match the curve of the tank skin, so I had to be sure to get the alignment correct.
I then carefully clamped the flange in place, making sure the cap was centered in the hole in the skin (not pictured). The tape was just there to keep it from moving around as a put the clamps on.
I match-drilled the cap flanges using the skin as a guide and clecoing as I went. No problems here, and the alignment looks great. In case you are wondering, these are the deluxe caps from Van's... aren't they nice?
To bend the clips that hold the vent tube, I compressed some .025 around the shank of a 1/4" drill bit. This made the curve of the clip nice and round without any flat spots.
The clips turned out good I think. In this shot you can get a better idea of the curvature of the cap flange. If you look closely you will see it is thinner fore and aft (left and right in this shot).
To hold the VA-112 in place I just used a scap 1/4" bolt I had laying around. I wrapped the threads of the bold to thicken the shank of the bolt and to protect the threads inside the flange.
I then used a wing nut and washer to hold the flange snugly against the skin for drilling.
I removed the bolt after drilling and you can see the tape that I had wrapped around the bolt still in the hole of the flange.
I then started countersinking the cap flange holes, but after about four holes, the pilot of the countersink cutter broke off in the hole and took a nasty little chunk out of the flange. Fortunately, I had a spare cutter so I was able to continue, and since these holes accept the dimples in the tank skin, this little boo-boo isn't a big deal.
After I drilled the holes for the vent line fittings in the inboard ribs, I needed to figure out where I was going to place the fittings for my vapor return lines. I put my flop tupe on the AN fitting to determine the best location, one where it wouldn't interfere with the flop tubes. This picture shows the flop tube in the inverted (flight) position, so I elected to put the fittings for the vapor return lines just below and forward of the vent line fittings.
I am not sure if was such a good idea, but I have decided to install vapor/fuel return lines in the tanks now. I am unsure what fuel injection system I will be using, but some of the newer systems (e.g. ECI) return fuel to the tanks during certain operations. Some builders just put a tee in the fuel lines ahead of the fuel selector valve, but some put return lines directly to the tanks. In my case, for the most in long-term flexibility I have decided to go with -6 return lines. They are probably overkill, and I may regret my decision, but now that the holes are drilled, there's no going back.
Here is where I mounted the fitting for the vapor return. In this picture the flop tube is again in the inverted flight position, and there should be no problems with interference with the vapor return lines.
Here is what the -6 fitting looks like from the outside.