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Fuel Tanks

asw20c

Well Known Member
My next session in the shop will be the first time where I will be using the fuel tank sealant. I'm sure I would eventually work out a "system", but I thought I would solicit advice here first. I'm trying to envision what this will be like so I can anticipate how to set quality, non-leaking rivets while keeping up with the mess. So I have lots of questions. Just how much sealant do you put between mating parts? Run a bead down the middle and let it squish out? Completely butter the contact surface? Put sealant on both parts to be mated or just one of them? How do you apply sealant to the rivet? Just put a dab in the dimple? Put it on the rivet? What about backriveting? I plan to use backriveting for the stiffeners but I'm expecting that my backriveting steel plate is going to get covered in goo. Do you have to clean all surfaces after every rivet? Clean the bucking bar between rivets? How do you apply the sealant? Section 5 talks about putting it in a sandwich bag, cutting the corner off and using it like a chef. I'm guessing popsicle sticks might be helpful.
These may sound like naive questions but I'm terrified of having leaks at the end because I suspect fixing a leak will be much harder than doing it right the first time. Any advice from those who have gone before is much appreciated.
 
After making sure everything was ready I just buttered up all the ribs except the inboard one and carefully placed them in position. The proseal expressed itself after clecoing into the counter sunk topskin which I cleaned out with ear buds. It then took about an hour and a half to rivet all the ribs which was within the two hours available. Then did the inboard rib and drag link plus fuel cap receivers. Swirled a dollop of proseal on all rivet heads.
I copied a process mentioned in another post and taped the rear bulkhead in place and gently pressurised. Only had one leak up underneath the drag link fitting which was still easily accessible.
The rear bulkhead goes on real easy as instructed.
Then had a party with some balloons. 🎈
 
I found this thread to be one of the most informative, and it formed the basis for the process I used.
http://www.vansairforce.com/community/showthread.php?t=7602

The key to the "fay sealing" method described is to apply the pro seal, 100% cleco the parts and then let the pro seal set up before riveting - much less mess.

Also, rather than using bulk pro seal in a can, for the tanks I bought the caulking gun tubes (Aircraft Spruce http://www.aircraftspruce.com/catalog/appages/ps890.php P# 09-04643) - the entire tube is activated so its no good for small jobs, but outstanding for the work on fuel tanks if you plan your activities.
 
Pro seal

Go to VAF Forums page then down to RV building tips/techniques. The very first one tells all you need to know.
 
Wear a long sleeve shirt. Expect to throw away your clothes after it's all done. You'll be amazed how many places it's spread too. If I did it over again I would cover interior skins. I think the instructions say one strip of tape on either side of the ribs. Check the bottom of your shoes, or better yet take them off before going in the house.
 
I found unfortunately that the trick to sealant is practice. It took me a while but one of the things I learned with my first tank is when sealing over rivet shop heads was to dab some sealant on top of the shop head then use a popsicle stick and swirl it both clockwise and counterclockwise around the shop head to make sure that the sealant has contact on all of the surfaces as well it being even distributed.

And IMHO don't be afraid to use too much. I use 1 quart per tank (which may seem excessive) but I've never had a leak wherever I've applied sealant. Besides a few extra pounds of seal is worth the peace of mind.
 
I didn't have any success with a foam roller and used a two inch hard plastic printers roller. Worked a treat and is a fast way of applying the proseal.
 
Update

Ok, so yesterday was my first time using the fuel tank sealant, and I have to say as much as I was dreading it, it was even worse than what I imagined. First, even though I spent a few hours thinking about what I would need to do and in what sequence so as to plan out all my movements, I still messed things up. I had planned to use my pneumatic squeezer to rivet the finger strainer flanges, but only when I had the goop on did I realize the yoke wouldn't fit and had to buck them instead. Messed up a few rivets and had to drill them out leaving shavings in the goop. Tried putting the 470-6-5 rivets in the tooling holes using my dimpling tool and only managed to lean them over. Mess everywhere despite going through about a hundred rubber gloves. I spent hours getting two flanges and one anti-rotation bracket riveted to a single rib. I'm disgusted with the outcome. It was a comedy of errors, nothing but problems, and frankly the worst build session I've had since starting the project. Just short of a disaster. Here it is more than 24 hours later and the goop still has not set up (although admittedly my shop is about 40 degrees inside). Not sure how I'm going to power through finishing the tanks now that I know how miserable it is working with fuel tank sealant, and how long it is going to take if I have to go in baby steps the whole way. This stinks.
 
Not sure how I'm going to power through finishing the tanks now that I know how miserable it is working with fuel tank sealant, and how long it is going to take if I have to go in baby steps the whole way. This stinks.

It'll take days or weeks to cure at that temperature. Either work on something else until temperatures rise, or carry the tanks into a nice warm room in your house. Alternately, make a plastic bag tent over 'em and put a cube heater under the tent. 80F for a day or so will do wonders.

The tanks aren't *that* bad. Really. Positive thoughts and all... 10,000 people have completed them before. You can too.
 
Don?t despair, it is a steep learning curve with Proseal and tanks. I was dreading building them but after I got going, actually enjoyed it.
 
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