David Paule
Well Known Member
Every once in a while we've got to get into a tank for some reason or other. I had a problem on one of my RV-3B tanks so that I had to remove and replace an end rib. I'm copying most of this from my commentary in the "My RV Build Project," since I figure that most people facing this might not catch it over there.
The first step was drilling out the rivets.
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.
I'd ordered some Polygone polysulfide remover from Van's along with the new end rib. While I was waiting for that to arrive, I took after the tank sealant with the plastic picnic knives and the hair dryer, holding the hair dryer on the outside of the tank skin partly to heat the skin/sealant interface, partly because the plastic knife will soften and partly to keep my hands from roasting. This got a lot of the remaining sealant.
The Polygone remover really works on tank sealant. It's a translucent jelly, slightly golden, that seems quite similar to paint remover except that it can be cleaned off with rags and soap and water. I'm using one of the plastic picnic knives to spread it on and encourage it. It dissolves the sealant quickly.
This is after I spread the first bit on.
After all the sealant was lifted, I wiped the Polygone off with a number of small cut-up rag pieces. Then into the kitchen for a wash and bath in the sink- really. Being of course very careful not to contaminate the kitchen -- I'm the cook.
I've still got to go over the areas with Scotchbrite again and lacquer thinner before I install the new rib.
The Polygone instructions suggested that some plastics weren't compatible, including acrylic, but these knives did just fine. They are compostable ones from Whole Foods.
Dave
The first step was drilling out the rivets.
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.
I'd ordered some Polygone polysulfide remover from Van's along with the new end rib. While I was waiting for that to arrive, I took after the tank sealant with the plastic picnic knives and the hair dryer, holding the hair dryer on the outside of the tank skin partly to heat the skin/sealant interface, partly because the plastic knife will soften and partly to keep my hands from roasting. This got a lot of the remaining sealant.
The Polygone remover really works on tank sealant. It's a translucent jelly, slightly golden, that seems quite similar to paint remover except that it can be cleaned off with rags and soap and water. I'm using one of the plastic picnic knives to spread it on and encourage it. It dissolves the sealant quickly.
This is after I spread the first bit on.
After all the sealant was lifted, I wiped the Polygone off with a number of small cut-up rag pieces. Then into the kitchen for a wash and bath in the sink- really. Being of course very careful not to contaminate the kitchen -- I'm the cook.
I've still got to go over the areas with Scotchbrite again and lacquer thinner before I install the new rib.
The Polygone instructions suggested that some plastics weren't compatible, including acrylic, but these knives did just fine. They are compostable ones from Whole Foods.
Dave
Last edited:
