Andre stopped by tonight and helped me get started on the tank ribs.  We managed to get four done this evening.  With an earlier start tomorrow, we should easily finish up all of the internal ribs on both tanks by the end of the night.

Here you can see the inside of the tank and the next to last outboard rib (the outboard rib is removed in this picture.  I still need to form filets on both sides of the ribs and encapsulate each rivet head in sealant.

Andre stopped by again tonight and knocked out the remaining six interior tank ribs in about four hours.  I can pretty much finish the remaining rivets on the tank by myself from this point.

I fabricated the tank vent lines tonight.  These are the lines that will let air back into the tank as fuel is pumped out during flight.  First up was to flare one end of the 1/4″ tubing using the Parker Rolo-Flair flaring tool.  This will flare aluminum, copper, and stainless steel in sizes ranging from 1/4″ to 3/4″.

Here is what one of the flares looks like on the 1/4″ aluminum tube.  I’m using 5052 tubing instead of the 3003 tubing that comes with the kit.  It seems to be easier to work with and isn’t as prone to cracking when flared.

The holes that the vent line passes through the interior ribs doesn’t line up with the fitting in the end rib (I had to move it over to make room to mount the fitting.  The tube has to jog over 1 1/4″ in the inboard bay.  I needed a little bit of straight tubing at the fitting, so I determined that the jog could take up 5 5/8″ of the inboard bay.  A little quick trigonometry (arctan of 1 1/4 divided by 5 5/8″) yielded about 13º for the bends (I know I wrote arcsin below.  Give me a break; it’s been 20 years since I used this stuff.  I’m entitled to be a little rusty).

Here is the bending tool I’m using.  It’s an Imperial 470FH.  It can do 180º bends in 1/4″, 3/8″, and 1/2″ tubing.

And here is the resulting shape in tubing.

You can see how accurate the bend was here.  The flare lines up perfectly with the fitting without having to use any force to hold it there.

Here’s what the inboard bay looks like.  You can see that the bend goes almost all the way to the second rib.

Here is the outboard bay.  You can see how the clip I fabricated earlier supports the tubing.  I’ll give a slight upward bend to the end of the tube after installing this for the last time to get the end of the tube as high up in the tank as possible.  After spending about an hour fabricating this for the right tank, it only took about another 20 minutes to repeat the process for the left tank.

I fabricated the tank fuel return lines.  Since I may put an engine on at some point in the future that requires a high flow fuel return line, I’m running the same size return line as the supply line (3/8″).

Unfortunately, I wasn’t thinking about the location of the capacitive fuel sender plates when I drilled the holes for the return lines, so I had to modify the plates to provide room for the lines to run through.  I kept the same clearance from the line as from the ribs/stiffeners.

The return line dumps fuel into the last bay so that hot fuel returned from the engine won’t immediately be picked up and returned to the engine.