Step 5.9 Fuel tank stiffeners

After excitement of match drilling the Z brackets, this post may seem a little tame.  That was quite an ordeal that will not soon be forgot. We laughed, we cried, and after just the right amount of pain and agony was experienced, we eventually we got it done!  Now it's time to push on to the fuel tank stiffeners.

The stiffeners are short pieces of aluminum angle that are riveted span-wise along the bottom of the tank for additional support against the weight of the fuel.  There are two rows of stiffeners in between each rib.

As was the case with the empennage, the stiffeners arrive in the kit in long pieces that are cut to length and then the edges are dressed with the Scotch-brite wheel.

There are four different lengths of stiffener and the angle stock is not marked for which is which.  In addition, three of the four types have the same number of holes.  This would seem to make identifying  the B, C, or D types rather difficult.  The faithful reader of this blog may be thinking that this sounds suspiciously like a diabolical plan to encourage the builder to make grievous fabrication errors that would naturally lead to the purchase of additional parts from the man himself, Mr. Van. I'm sure that the omission of any identifying information is innocent enough [wink], and in any case, (after some pondering and sufficient time had elapsed) I discovered that Van has actually slipped up this time -- It seems that the pre-punched holes have different spacing and can only fit in certain bays within the tank.  OK, I get it.  Never mind.

  

So here they are.  24 shiny stiffeners ready for match drilling to the tank.  Not quite ready, first they and the matching tank skin need to be uniquely marked so that after drilling and deburring they can be reassembled into the same location.  Now they're ready.

Drill, drill, drill, drill, drill, drill, drill, drill, drill...














Next on the list is machine counter sinking the row of rivet holes that attach the rear tank baffle.  Shown below is the micro-stop counter sink cage with a #40 piloted counter sink bit.  I put the skin on some scrap plywood and drilled through the skin in to the plywood.  The holes in the plywood guide the counter sink pilot so that the bit doesn't get to wobble about chattering and making oblong holes (this is the secret desire of a counter sink bit).  So after some preparation, very nice, round counter sinks result.

Following all of the counter sinking of the tank skins, I drilled screw holes around the periphery that will attach the tank to the spar and to the W-423 splice plate.  And finally, the screw holes are dimpled for a #8 counter sunk screw.  At this point, the tank skins are nearly ready for final assembly with ribs and the black death also known as Pro-Seal (epoxy sealer).  There are a number of other things that go into the tank before we're ready to assemble, so the skins will be set aside for now.  

The final step for this posting is to attach the nutplates to the W-423 splice plate.  The splice plate is shown above sticking out from the leading edge section.  In the photo, I have the nut plates clecoed to the outside where I am using them as a drill guide for their attachment rivets.  Each nut plate is fastened with two flush rivets, so after the holes are drilled they must be counter sunk.  The screw holes are then enlarged to #19 and dimpled.  Finally, the nut plate is riveted to the inside of the splice plate completing the assembly.