Dimpled the Cover Plate for the Fuel Tank rib

Well I suppose that's a long enough break since my last post. Time for some updates. In my previous post I was trying to decide what side of the tank rib to place the cover plate over the hole in the web about half way up the width of the web. After mulling that over a bit, I decided to put it on the outboard side of the rib web instead of the rib web. My reasoning for this was that MOST of the time the wings should be level, and there is a slight dihedral angle in the wing where the tip will be just a bit higher than the root.

This, combined with a slightly positive angle of incidence of the wing while it is in sustained level flight, lead me to believe that pressure from the fuel inside the tank will be greater on the outboard sides of each rib most of the time, while the small holes at the bottom rear of each rib will allow fuel to slowly escape to the next inboard bay. Since the fuel pressure should be greater on the outboard sides of each rib due to the reasons I mentioned previously, I decided to put the cover plate on the outboard side of the hole in the rib web, so that any pressure from the fuel against that rib and the patch plate would tend to push the patch plate tighter against the rib web, keeping the fuel from entering that hole, and forcing it to go through the trap door instead, as intended.

Having finally decided where to put the plate, the next step was to dimple the holes for the rivets. This turned out to be yet another exercise in "imaginative problem solving." If you haven't guessed by now, I am documenting this entire tank rib trap door fabrication process because almost nobody documents this to the level of detail that satisfies me, and as it turns out, the steps required to complete this little side assembly are a little more involved than you might think.

First problem - decide which side to put the dimples for the 4 AN426AD3-3.5 rivets. I decided to use flush rivets for this since that should be sufficient for holing this small plate in place, and flush rivets take up less space inside the tank than an AN 470 rivet. Remember, I am trying to stuff as much fuel as possible in these tanks, so every little bit helps, even if that does seem a bit anal.

I decided to put the manufactured head of the rivet on the outboard side of the rib web. Again, this is because fuel pressure will tend to push the rivet head against the rib head, instead of pushing it away.

So I put the dimple dies in my hand squeezer and set the dimples in the over plate:

Next problem -I would need to use my C-Frame tool and table to set the dimples on the rib web. None of my yokes were long enough to reach the holes in the rib web. Then another problem cropped up. The trap door was getting in the way. In hindsight, all I had to do was remove the hinge, but stupid me likes to do everything the hard way. The rib sits awkwardly on the table because of the trap door.Another problem was that my C-Frame table had been setup with the male dimple die on the bottom and the female die on the top. With this application they would need to be reversed so that the male die is on the top and the female die is on the bottom. Why is this a problem - the female die is longer than the male die, so my table no longer sits "flush" with the dimple dies in this reversed state.

So the combination of the trap door interference and the reversed setup of the dimple dies on my C-Frame table presented some challenges:

Here you can see the female die sitting very proud of the table

And it looked like this sitting on the table as a result of the trap door interference:

So how do I get the rib to set level on the dimple dies so I can pound these dimples properly: I was not concerned about the proud dimple die situation, but I did not want the dimples to be improperly set at an angle, so leveling the rib web was a concern. My solution was to place a couple of the fuel tank access plates on the other side of the rib to level it out just enough for me to set the dimples properly.

And here are the pics with all the dimples set in both parts:

I will have to use the rivet gun and a bucking bar to set these rivets. this will be the first time I have picked up the gun in a very, very long time. I will have to do some practice rivets on some scrap first, to make sure my air pressures are set properly, and I get my timing back. I want to set all of these rivets perfectly so I can move on with other much more important tasks. This little adventure has certainly resulted way too much of a time suck on the build.




I also finally called my tech counselor Jim Elliot ad he came out for another visit to help me finalize plans for the mod to the Leading Edge. I think I now have all the info that need to be brave enough to drill the final rivet and nut plate holes in the skin and the subskin, so that I can take it off the wing spar and make that all important cutout. More on that visit and the next steps for that tomorrow.

KPR