A Bit of an Issue and Rivet Removal Tips
I was assembling the tanks to the wing before riveting on the tank baffles, just to be sure, and the left tank no longer fit on the outboard leading edge's splice strip. Remember that it was built in place on the wing, with the outboard leading edge attached. This time it didn't fit.
Turns out that the outboard tank rib interfered with the splice strip. Here's the rib and the skin. You can see how close the rib and the reinforcement piece are to the dimpled holes.
This shows the splice strip and how much it would need to be trimmed to fit - clearly a problem.
Later, I marked where I'd need to trim the splice strip and it was very close to those holes. I contacted Van's support and they recommended replacing the outboard tank rib and relocating the leading edge reinforcement plate to the inside of the tank. This didn't please me - I'm not that great at drilling out rivets. So I took a break to think about it.
For my break, I had a friend over and we set the -4 rivets that hold the main ribs to the spar web behind the tank. During the process, I got to replace a few of these and it went reasonably well. Then came the aha! moment. Drilling out these rivets, I was using a #40 drill bit as a pilot drill.
When those were all finished, I went back to the tank and tried to drill out the -3 flush rivets using a pilot drill. This worked a lot better.
This photo shows a few of the first rivets drilled out and the tools I used.
The basic approach is:
1. Center punch the center of the rivet head.
2. Pilot drill just a bit deeper than the head. Use a drill bit that’s 10 number sizes smaller than the nominal one. In this case, for the -3 rivets which used a #40 bit, I used a #52 bit to pilot-drill them.
3. Drill just the head with the correct size drill, in this case #40.
4. Using the unfluted end of the #40 drill bit, pop the head off.
5. Use the pin punch and a very small hammer to punch out the rivet body. That hammer, by the way, has earned its scars. This is its fourth homebuilt airplane.
6. If you’re my age, the magnifying glass comes in handy, and if you didn’t get the head exactly, the needle nose pliers are helpful pulling it off.
That left the rib firmly sealed to the tank. Think glue. Here are the top rivet holes with no more rivets:
How to get the rib out? I bought a set of plastic picnic knives and they were of little use. The sealant was just too tough. I made a sealant knife by wrapping a piece of music wire around a couple of pieces of 1” dowel. I used several pieces of music wire: .015 was too weak. It cut well but broke easily. The .020 was the compromise that worked. The .032 was sturdy but cut poorly in the sealant at room temperature. Going across the dimples was especially difficult.
Then a friend suggested heat. I’ve got an 1,800 watt hair dryer and a few minutes with that let the .020 wire cut through the rest of the sealant. Using a piece of 1/2" plywood as a sort of wedge helped a lot, too, forcing the joint apart. I've got some serious respect for tank sealant now.
These are the tools I used.
Now the rib’s out and parts are on order. They should be here on the 29th.
That light at the upper left of the photo is a sweet thing. It’s a 9 watt florescent under-the-counter light and makes a handy shop light.
Merry Christmas, everyone!
Dave