February 8, 2008

Back to work on the Tank - 4.25 hrs.

I dove back into working on the tank today. Sure feels good. I started by dismantling the whole thing. Most of the holes have been drilled to full size, and it all needs to come apart for deburring and dimpling. Plus, I needed to get inside to work on the stiffeners, the drain flange, and the fuel cap flange. But first, I worked for a while on the baffle plate; deburring every hole on both sides, and deburring and smoothing the edges of the plate all around. It is now finished, ready to install permanently. But it will be a little while, so I put it aside (no picture, sorry... how exciting is a deburred baffle plate?) and got busy with the main tank skin.

You're looking at the inside of the fuel tank. The hole on the top right is where the fuel filler cap will go. I clecoed all the stiffeners in place and drilled them to the skin. Then I marked them for positioning and took them back out for deburring and dimpling. As I explained earlier when I did this for the other tank, these stiffeners have an important role. This is the bottom of the fuel tank, which will hold 21 gallons of fuel. Think of how much 21 gallons of gas weighs, and you'll see why it's important to stiffen and reinforce the bottom of the tank. If you're in maneuvers and you're pulling 2 G's or more, all that gas weighs twice as much or more! I don't want my tanks bulging or straining. I want these stiffeners solidly in place doing their thing.

Next, I carefully positioned and clamped the drain flange in place. Then I drilled it to the skin, clecoing each hole as I went along. This will be the lowest point of the fuel tank, and this drain is in place to check the fuel each time you pre-flight, or, if you need to drain the tank for some reason. If any water has condensed inside the tank, it will run to the lowest point (being heavier than fuel) and when you open this drain briefly during pre-flight to look at a sample of fuel, it will remove it from the tank. It's a standard safety precaution. You obviously don't want to fly with water in your tank!

Next, I moved on to the fuel cap flange. The last time I did this was on October 13, 2007. I explained that I splurged a bit and got the deluxe locking fuel caps. They're really nice! Again, it's a matter of carefully rotating and positioning it in place, clamping it down, and drilling it to the skin.

All finished drilling. Then I took it apart. The rivet holes need to be deburred and dimpled, and the flange needs to be deburred and countersunk for the dimples.. When it was apart, I cleaned it up and deburred the opening. It's all polished and finished up real nice now.

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