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Fuel Tank Build

November 12, 2011

I have been working hard on the tank.  Sorry for the infrequent posts.  When last I posted I had finished the Z-brackets.  Since then I’ve fitted all the ribs to the tank skin.

One thing that I’ve learned about the fuel tanks is that they are a sub section of the build all their own.  There are tons of little tasks that have to get done before you can even think about sealing the tank.

I had to order a new inner and outer rib becuase I didn’t like how they had been fluted.

Flutes seemed to deep.

I got a second opinion on VAF and decided to go ahead and get some new ribs for the two ends and get a different tool for fluting.

The inner most rib has a lot going on, so you spend alot of time just on this rib to get it ready.  After you get it fitting, like we did above, then its time to start attaching things to it.  On the tip of the rib are two parts.  One is an attach point that you will use to attach the inner front of the fuel tank to the fuselage.  The other is a reinforcement doubler.  The doubler is hidden and its a “Where’s Waldo” moment to figure out where they are.

Here they are!

Vans cuts them from a round circle of aluminum and you have to snap out the parts like you did with model parts when you were a kid.  The two doublers and the T408 rings are released.

The attach point, or T405, is something you have to fabricate yourself.  Oh goody.  You start with an 18″ or so piece of aluminum angle stock.  You draw out the rough dimensions of what you’re trying to build and then get to cutting and grinding.

This is the ginding part

Lots of fussing around and getting it fitting right.

Fits just right and the doubler (behind the rib) fits too.

You then drill some holes, which are roughly described on the diagram.  This took me a good days worth of work.  Mostly because I did both the left and right fuel tanks at the same time.


I was glad to have this behind me.  I’m not a big fan of the fabricating part.  I just dont think I’m very good at it.

Next up is getting the T708 reinforcement ring in place.  This step seems pretty “optional” to me.  I’m putting in flop tubes so my fuel pickup is on the tip of this rib and the fuel sending unit is in a completely different spot.  After puzzling over it, and almost skipping it altogether, I decided to proceed.  My logic is this.  *IF* in the future I have to open up the rib to fix something, I am not going to want to have to cut this hole when fuel has been in the tank.  That could be quite dangerous.  Better to do it now and hope I never have to take it off.

First off I have to cut a monstrous hole in my rib.

No hole, but there are stiffener ribs

So you have to find something to cut out that big ring (including the stiffener) on the left.  There just aren’t any drill bits that big.  So I needed to get a fly cutter…more on this widow maker later.

I needed to come up with the center of my future hole.  So this is how I puzzled it out.

Reminded me of elementary art class

Now that I have the center of my ring, I can find the center of the hole I want to cut.

So, here is the center.  I marked it with a Sharpie and then used a punch to make a nice dent in the middle for a drill to work with.  Hmmm….now if I had that drill bit.

The Widow Maker

The Fly Cutter, or hole cutter, is without a doubt one of the most dangerous tools I have ever used.  You can get seriously hurt with this thing.  I am sure that the pictures tell you all you need to know.

It does cut a nice hole, though

The job is done here, and you can see that it does do its job.  Just watch your hands, sleeves, fingers, tools and anything else that might get into the path of this thing.  The hole turned out perfect.

Here is the final piece with the 408 ring attached.

Next a little mindless scuffing of the parts that will be sealed. This I can do in about 15-minutes.  The ribs and the skin probably took 45-min or so.  Not so bad.

Ok, now back to some fabricating.  Maybe I”m getting better at this.

One of the issues you have to worry about with acro is fuel rushing down to the tips of your wings so rapidly that it starves  the engine for fuel.  To help with this you can add a little flapper gizmo to the rib beside the innermost one.  It doesnt have to make a perfect seal, just slow the fuel down that is running out of that compartment.  It really wasn’t hard to make.  A piece of scrap hinge and a 2″x2″ peice of scrap aluminum sheet.

Fabricate the hinge.Notice how the hinge has that little piece of turned up metal?  That is a stop to keep the flap from opening to much and getting stuck in the open position.

Now I have to attach it to the little piece of aluminum scrap.

Ok, so I skipped a few steps, but you get the point.  It really wasn’t that hard to build and only took an hour or so.

Here it is attached to the rib.

I also got my fuel sending unit hole cut and the sending unit mounted in the hole.

I thought i had more pictures than this.

Basically I cut a hole in the rear tank baffle between the 1st and 2nd rib, in the middle.  Then I riveted in some nut plates and that was it.  Took about and hour and a half, not including the trip to Lowes to get the hole saw.

Thats it.  Now you’re up to date.  Tomorrow is a marathon dimpling session.  I want to get everything on the right wing dimpled.  Shouldn’t be hard, just time consuming since there are hundreds of holes.








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