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Wings

Inverted flight fuel tank mods – part 2

Today I continued on with the inverted flight fuel tank mods. I started by clecoing the inner 2 and outer ribs onto the left skin. I only put clecoes in the bottom side as I wnted to keep access inside the tank. I did this to see how the anti-hang up strip I made yesterday looked and to see how the flop tube would slide up and down this strip. I wanted to make sure it would not get caught anywhere. I was happy with how things looked to I proceeded on to making the next strip.

Flop tube test fit

I picked out one of the spare 0.5″ strips I cut yesterday and trimmed one end to be roughly 45 degrees. I positioned the strip roughly in position and bent up the other end so that it would lie flush with the rib web. I erred on the side of slightly longer than required to allow for some play in the rib.

Rib strip test fit

I then grabbed the second spare strip and make a mirror image of the the strip I had just bent. I then rounded the corners, broke the edges, drilled holes in each end and deburred the holes.

New strips finished

I then held the strip into position then marked and drilled the hole in the stiffener. Using a cleco to hold the strip in place, I then marked where the hole needed to be drilled on the rib web. My first mark didn’t give enough play for the rib so I ended up adjusting things and marking a second position.

Rib hole marking

I then drilled and deburred the hole in the rib and clecoed the new anti-hang up strip into position. I moved the flop tube around to see how it would slide around to ensure it wouldn’t get stuck anywhere. It looked all okay to me.

Another flop tube test

I got to thinking that it might be a little tricky to rivet the new strips into position with the tankin the cradle and the ribs in the way. So I decided I would rivet the strip to the stiffener now. The other end should be pretty easy to rivet in situ. I dimpled the stiffener and strip as well as I only had countersunk AD3 sized rivets.

Strip riveted on

I then put the right tank rib back-to-back with the left rib and match drilled the new strip rivet hole. After deburring the new holes I dimpled the rib hole so it’s ready to rivet on the anti-hang up strip.

Ribs drilled and dimpled

I haven’t got the piano hinge and 0.020″ Alclad to make the trap doors yet so I decided to break the edges on the skins and tank baffles. First I filed off the tooling marks and rounded the corners and edges. I then went over all the edges with some fine grit sand paper to make everything nice and smooth.

Nice and smooth

In order for the tank sealant to stick well, I used some Scotchbrite and scuffed up the mating surfaces on all the stiffeners.

Scuffed stiffeners

I then scuffed the mating surfaces on the skins and tank baffles.

Scuffed tank skins

After I make the trap doors, I’m ready to clean everything and start riveting the tanks together. My tank sealant and wiring conduit arrived from Vans during the week so I’m almost ready to put these things together.

Build time 3 hours.

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About gstrack

Husband and father of 2. Control & Instrumentation Engineer. Flying nut. Gadget geek.

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