Helping MIke Rettig with Fuel Tanks and Back in House Hell Again

Over the course of the past couple of weeks I had decided to cough off some bucks to have a contractor take care of refurbishing two bathrooms in the house - you know, so I could spend more time building the airplane for a change. Unfortunately what I feel has become an all too common theme in America these days is that there is no quality of service anymore. Long story short, and then I will get back to some positive airplane building stuff, I ended up firing the contractor, and I am now fixing everything he screwed up. So now I get to spend time dealing with that instead of working on the plane - a pretty typical sob story for me I'm afraid. Just can't seem to catch a break to have a relatively prolonged spurt of building activety.

I guess this sort of thing kind of bleeds over into some of the same reasons I chose to build my own airplane. The only sure way for me to know the true airworthy state and condition of any airplane that I wish to fly is to be familiar enough with it by building and maintaining it myself. Anything short of that in today's world, and you are possibly putting your life or the lives of others at risk. I just can't help but feel that way after witnessing many counts of shoddy workmanship and less than competent maintenance practices from some maintenance shops over the years.

Anyway, on a positive note, I spent a short time on Saturday helping friend and fellow builder Mike Rettig do some riveting on his RV10 auxiliary fuel tanks. This was a great opportunity for me to get my feet wet with the process of working with the Proseal and the rivetting techniques for the fuel tanks. Here is the star of the show just before we commenced:

The process is somewhat the same as any other skin riveting task. The only real difference is that the stem of each rivet is covered in thick black proseal, which is the sealant that is used to keep the fuel from leaking out of the riveted metal fuel tanks. All of the ribs are coated in the thick goo and clecoed to the skin in preparation for riveting. The clecos are removed one at a time, covered in the same goo, and a rivet is placed in each hole. You use the same bucking bar, rivet gun, or squeezer process that is used for other rivets, but for the fuel tanks this is notably messier. It is also a challenge to set each rivet correctly because the rivet stem is covered in proseal, and you cannot see the shop head forming very well, since it will be covered in proseal. So you really must have a good feel for riveting and must be very familiar with how your tools are working before you get to this point in the build process.

The bucking bar gets most of dirty work, since it must be placed on the proseal-covered rivet and will inherently also get proseal on it from any nearby point of the rib or skin during the bucking process. Everything has to get wiped down after each rivet is set to keep from making a complete mess. We used Mike's 3x rivet gun shown here with a mushroom set encased with a rubber boot around the edge. I also have one of these but have not used it yet, so I was curious as to how well it would set the rivets. We discussed air pressure settings and the need to do practice riveting. After Mike had demonstrated the timing to use (about a 1 second trigger pull), I then tried it on the surface of the work bench, everything felt about the same as with my rivet gun, so we decided to proceed without doing any practice rivets before hand.

We did most of the riveting with the tank in the cradle. We started on the bottom side since that is the flatter side of the rib, and it is the easiest to buck. I worked the rivet gun while Mike did the bucking. The truth is that there were not very many rivets to set because Mike had done most of the them the night before. Only the harder to reach rivets around the nose of the tank remained. We used a fairly standard method for riveting with two people that seems to work well for most other builders. It is all done using a 3 count process. The person on the gun calls "One" when the gun is positioned over the rivet and held firmly in place. The bucker calls "Two" when the bucking bar is in position and is ready for driving. The person on the gun then calls "Three" and on completion of that count, presses the trigger on the gun to set the rivet. The bucker then checks the rivet and calls for additional driving of the rivet if needed, or verifies if the rivet is good or needs to be drilled out, which is not something you want to do when doing the fuel tanks.. Then you wash, rinse, and repeat the process for the next rivet, after cleaning up the tools as needed.

Here is a pic of the ribs all prosealed and clecoed in place. Mike had prosealed them all in place the night before, to allow the proseal to stiffen up just a bit for riveting.

Next are some more details about the riveting process. First you remove the cleco, and then the rivet gets inserted into the hole. In most cases, pulling the cleco out of the hole draws sufficient proseal into the hole so you don't necessarily have to pre-coat the rivet first, but sometimes you need to do this if the hole is dry for some reason. Once the rivet is inserted into the hole, a hefty amount of proseal will come out of the hole, covering the dimple and most of the rivet head. The rivet is checked fo proper seating in the dimple and excess proseal is wiped away. Occasionally we had to use the rivet gun to lightly tap a rivet into its final resting place in the dimple, but most of them inserted right into the hole with no problem. You use your finger pressure to ensure that the rivet is as far down in the dimple as possible. Then the gun is placed on the rivet head and the bucking process commences. Afterward, you get a result that looks like this on the manufactured side of the rivet:

For leading edge ribs it is easiest to start on the bottom which is flatter, followed by the top. The most challenging rivets to set are always the two most forward rivets, since they are the ones that are formed around the extreme curved edge of the skin. Even setting the gun in the correct position on these rivets is a bit of challenge, since the goal is to place the mushroom flat rivet set at a 90 degree angle to the manufactured head of the rivet. Trying to figure out what 90 degrees is to a curved surface simply by eyeballing it is a bit tricky, but you can generally figure out the angle by looking at it.

Another key detail item concerns using the cradle when riveting the tanks or leading edges. While the manufactured heads were relatively easy for me to reach with the gun while the tank was in the cradle, bucking them is another story. Mike was standing on a small step ladder to allow him to get up high enough to be able to comfortably reach down inside the tank to buck the rivets. With me pushing on the rivet gun to maintain pressure while setting the rivet, Mike also had to push back on the tank with his free hand to keep the tank from sliding out of the cradle. This was a bit of trick, but he had obviously figured out how to manage it very well. Just another in a long line of acrobatic contorsionistic moves that one must make to complete this job properly.

When it came time to do the most forward rivets, we needed to take the tank out of the cradle and lay it down on a blanket on the work bench. The only other option is to raise it up out of the cradle so the nose is high enough to get the rivet gun in there. But by the time you do that, you lose all of the holding power of the cradle, so it essentially becomes useless and is more inthe way than anything at that point.

The black marks around the rivet heads in the above pic are easily cleaned up with acetone, as long as the proseal is still wet. So this has to be done soon after the rivets are set. The last two pics show the completed fuel tank rivets after cleaning off the excess proseal on the exterior:

Note the little black ring around the rivet heads in the above pic. This pic is a bit deceiving since it shows the reflection of the speckels on the epoxy floor, so just ignore that and focus on the flush rivets. This is a sign of a properly sealed rivet head on a fuel tank. I was pleased with the way this turned out. Mike is not using tank dimple dies on his tanks, and while some rivets do sit proud from time to time, all of these rivets that we set seemed to be nice and flush with the skin, so I am now more confused than ever as to the never-ending-debate about using special tank dies or regular dimple dies for the fuel tank dimples. I purchased a set of tank dies long ago, and I am still mulling over if I am going to use them or not.

On a cleanup and shop prep note - you will need lots of rags, paper towels, and most importantly rubber gloves. You need to stage these items in such a way that you can use or shed them when necessary and dawn new ones to keep everything as clean as possible. Proseal is some very sticky stuff, and it has to be when you consider that it must be resilient enough to withstand aviation grade fuel. Tools and clecoes get cleaned up after all the work is done.

Thanks Mike for the opportunity to help out with this. What a great experience. Lots of builders make this one of the 49% of the entire build that can be literally built by someone else, and still qualify as a homebuilt airplane that was "built" by you, as required for issuance of an Experimental Airworthiness Certificate. I plan on doing my own tanks, and being able to get some hands on with another builder helps emmensely with understanding what it takes to do this successfully.