Fri Nov 3 2006

Tank skin gap problem

I got one of the fuel tanks clecoed up. Man, was that a bitch. It's really hard to get the prepunched holes in the skin to line up with the prepunched holes in the ribs.

I match drilled the spar web to the main rib flanges before setting the tank on. I was running the drill rather slowly for this match drilling and I noticed the drill left a spiral down through the hole. I think I'll use a faster speed when match drilling from now on.

Here's the tank set in place.

I opened up the hole for the tiedown ring. I didn't follow Van's instructions for how to make sure the hole is centered. When the hole was 3/8" (the size of the threaded tiedown ring), it wasn't quite centered up. I enlarged it to 1/2" and it's perfectly centered now. I think that'll be fine having that 1/16" clearance all around. It looks like the tiedown rings have a shoulder that's larger than 3/8" anyway.

...not as much glare on this pic.

When I set the tank on the spar, I noticed a gap between the fuel tank skin and the main skin.

I realized it was just the tip of the inboard two clecos resting on the main spar member. Once I took those clecos out, the skins fit tightly together. Yay!

...but what's this?!? When I insert a Z bracket under the baffle, the gap is back... maybe even a little worse.

It seems like the Z brackets are about 3/64" too high. I'm going to have to ask the list about this.

Instead of worrying about that right now, I drilled the fuel drain to the skin.

I marked the centerlines of all the Z brackets. Chris had put the long lines on before he went back to California, but I transferred them to the edges... I could align the brackets with these centerlines on the baffle.

Once the Z brackets were lined up I used masking tape to hold them in place.

However, I realized that as soon as I flipped the tank over, the brackets would just flop around. So I added a second piece of masking tap to hold them in place while setting the tank on the spar.

Here all the brackets are lined up along the outboard edge of the tank.

Also lined up at the inboard edge.

I read on Dan's website that it's difficult putting the blind rivets in to attach the Z brackets to the baffle. Here's the shoulder clearance that'll be required for my blind rivet puller.

...and here's the clearance required for a rivet puller I borrowed from Ken at work. It's a full 1/8" better. I'll probably end up using this one, but it doesn't have a swivel head, I'll have to pay close attention to the order in which I rivet the Z brackets to the baffle.

Here's what Ken's rivet puller looks like...

...compared to mine.