Tech Counselor Visit and more Fuel Tank Rib Fabrication

Had a little lull over the new year holiday - cold temps, getting sick, holiday obligations - blah! Nice to get back to airplane building for a change. Picking up where I left off, per Vans input about the hinge for the trap door assembly I decided to do the same - leave the rear hinge pin bent to 90 degrees and leave a small amount of excess on the other side of the hinge without bending it or peening it, etc. The idea is that the rear hinge pin will hit up against the rear baffle plate without ever coming out of the hinge, as long as there is a sufficient amount of pin left on the other side to keep from coming out or causing the hinge to hang up.

So I straightened the bent part of the hinge pin a bit more to keep that end from binding against the eyelets of the hinge, and then I made a mark on the other end after setting the bent end along the rear flange of the rib, simulating where it would hit the rear baffle plate:

 Then I cut the hinge with the dremel tool cutting wheel and deburred the end on the scotch brite wheel:

The piece of metal sticking up one the left is actually a reinforcement plate that goes on the forward part of the most inboard and outboard ribs. In this case it served quite well as a mock baffle plate so that I could verify the length of the hinge pin was correct.

Next came the cover plate for the open hole also seen in the above pic. Vans says that with the flop tube assembly this hole also needs to be covered with a patch plate so that fuel is only allowed through the trap door location. of course this is NOT in the instructions or the plans, so it begs the question, if someone was building the kit with very little or no outside help, they would never cover up this hole. How would they know f they needed to. Vans once again fails to impress me with its lack of updates to the plans of its older models that are still being built and flown. The hole is about 1.5 inches wide, so I reasoned that a 2 inch square patch plate over this hole with 4 AN426AD3 flush rivets in each corner should doe the job. this allows me to maintain 1.4 inch edge distance at each corner of the patch plate:

I cut the plate from scrap .025 inch thick aluminum sheet and deburred it on the scotchbrite wheel. then marked the location for the plate over the hole in the rib, as well as the location for the 4 rivet holes as shown above.

After drilling the 4 rivet holes in the plate, I had to match drill the holes in the rib. So I used the clamps to secure the plate on the rib and got that all done. then I deburred all the holes:

Now I get to decide which side of the rib to mount the plate. the general idea for this is that you want to put the plate on the side of the rib that might encounter the most force due to the amount of fuel in the bay at any given time. I need to decide this because I am using flush rivets to mount this thing. It is not structural so there is no need for AN470 rivets for this, and I am also trying to minimize the amount of space taken up by things other than fuel inside the tank. A rivet seems like a minute detail, but it all adds up in the end - excess sealant, excess hardware, excess rivets, and so on...... It all means less fuel in the the tank.

Since I am using AN426 rivets I will need to dimple the skins, and I have to decide which side of the rib I want  to do this.

This past weekend I had my technical counselor Jim Elliot come out again to review my plans for the cutout of the leading edge skin. He was satisfied with my planned approach. So now I am almost ready to remove the LE and make the big cut. In the coming weeks you will finally start to see what I have been planning to do all along. To think of all the research, design work, and safety evaluations I have gone through to make this seemingly rather small mod makes my head hurt. So I'll leave it at that for now.

My big problem now is that I have the fuel tank in prep mode in my only LE cradle, so in order to take off my LE I have to figure out what to do with the fuel tank. I think I may be making another cradle this weekend to give me some flexibility with handling these big parts. Not really a big problem, just yet another one that I have to deal with on this never ending journey...

KPR