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Tanks: to fay or not to fay?

S

StaringSkyward

Member
I am not far from having to start on the tanks so I have been doing plenty of research. The tank building method in the build manual makes sense to me but does sound a little messy.

I like the sound of the fay sealing method but there's a little voice in my head saying: "if it is better, why don't Van's tell you to do it that way in the manual?".

I would be very grateful of any advice for and against the fay sealing method from those here who have perhaps made tanks using both methods and any other sagely advice before I start. I have plenty of MEK, clean lint-free cloths, popsicle sticks and dozens of pairs of latex gloves. Do I need anything else other than the usual industrial dose of proseal and patience?

Sorry if I'm covering old ground here.

Thanks,

Matt
Slow build RV-9 wings
South Yorkshire, UK.
 
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I fay-sealed

When building my fuel tanks, I'd mix a batch of sealant, butter-up two ribs, cleco them in place, and considered myself done for the day. I came back the following day, riveted them with little/no mess, and buttered two more ribs. It worked GREAT! The only leak I sufferred was in the baffle of my second tank. (I ran just a little short of sealant but thought I could still make it work. Tip: mix/have more sealant on hand than you think you'll need/use. It's cheap insurance.) For the ribs, I think I was measuring 50 grams of grey goo prior to adding the catalyst....

I put clecos in EVERY rivet hole to ensure enough pressure on the skin/ribs and pulled them one at a time as I riveted. It's possible to clean the sealant off the clecos but I didn't bother. I just passed them off to another builder who was getting ready to "goo-up" a fuel tank.

Good luck!
 
The fuel tanks were one of the few places I didn't follow Van's instructions. I was glad I used the fay method and would again. Be sure and read Rick Galatti's (sp?) posts. Zero leaks and wiser folks than me said they looked great. I was very careful to follow Van's instructions about keeping everything clean, measuring proseal carefully, etc. Oh, and a Semco sealant gun was a big help, too.

IMG_0439.JPG
 
Mel said:
Built 4 tanks (2 RV-6s) in 1992 exactly per plans. No leaks to date!
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Build them per the plans. Do NOT let the proseal harden then rivet! The rivets pull the skin tight, which can't happen if the proseal is hard.

When finished, do NOT wipe off the excess proseal with MEK or anything
else as the MEK can cause leaks.
 
I did it by the book.

And I only did two ribs at a time and then done for the day. ProSeal everywhere. I think I used a whole can on just one tank. I gooped up everything. I did it by the book, I made sure the surface was CLEAN -- CLEAN!!! -- before starting. I wasn't that concerned about how it looked after.

The tanks don't leak and at the end of the day, that's ALL I cared about, the tanks don't leak. If someone should someday open the fuel caps, look inside with a flashlight and, say "wow, kind of generous with the ProSeal, weren't you," I will have a clever retort handy.

"Shouldn't you be working on fixing your leaky tanks?"
 
I did the fay sealing and it worked out fantastic. You can certainly avoid much of the mess by taking your time and using the right tools and techniques.

I did a lengthy writeup of my tank building here.
 
N941WR said:
Build them per the plans. Do NOT let the proseal harden then rivet! The rivets pull the skin tight, which can't happen if the proseal is hard.
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I haven't built any tanks, but I think the idea is to put clecos in every hole, which would also pull the skins tight.
 
Snowflake said:
I haven't built any tanks, but I think the idea is to put clecos in every hole, which would also pull the skins tight.
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Mixed but not yet cured tank sealant is quite viscous.
Clecos do not have enough pull tension to squeeze out sealant to the point that the rib makes contact with the skin.
Riveting while the sealant is soft, does pull the rib in closer to the skin but even then it may not come into contact with it.
I have seen instances of people having difficulty installing the finished tanks because of sealant buildup. I do not believe that allowing the sealant between the ribs and skins to pre-cure would cause this, but I would caution builders about doing so with the rear baffle and Z brackets. Buildup of sealant on the back of the ribs and z brackets can cause the tank to be pushed further forward of the spar web than it was when initially assembled dry.
This is the reason the construction manual (I think) cautions to use minimal sealant at these locations.
 
rvbuilder2002 said:
Mixed but not yet cured tank sealant is quite viscous.
Clecos do not have enough pull tension to squeeze out sealant to the point that the rib makes contact with the skin.
Riveting while the sealant is soft, does pull the rib in closer to the skin but even then it may not come into contact with it.
I have seen instances of people having difficulty installing the finished tanks because of sealant buildup. I do not believe that allowing the sealant between the ribs and skins to pre-cure would cause this, but I would caution builders about doing so with the rear baffle and Z brackets. Buildup of sealant on the back of the ribs and z brackets can cause the tank to be pushed further forward of the spar web than it was when initially assembled dry.
This is the reason the construction manual (I think) cautions to use minimal sealant at these locations.
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I agree with RVbuilder on this one, in the heavy iron/light jet aircraft world, tank fasteners must be installed and torqued before the sealant sets. This is required for the parts to be pulled into their proper position. We used to drive heavy duty screw type clecos in with screw guns (with washers on the back side to protect the skins) and that still would not pull the skins all the way down. Sealant is installed to "seal" the surface, not "glue" it together (even though pro-seal works great as "glue" that is not the reason we use it when building fuel tanks).

So I'm in the messy but "assembly required before sealant sets" group.
 
Everybody has a fay seal if they put sealant on the flange before placing the rib. "Fay" simply refers to sealant between the flange and the skin. The term has nothing to do with allowing the sealant to cure before riveting, or riveting while wet.

We now return you to the usual debate ;)
 
Well if you want to get technical, class 'C' sealants are generally considered fay surface sealants while the class the 'B' sealants are "fillet" sealants :p
 
I've done it both ways

I had my first tank finished when I learned about the fay sealing method. I did the second tank that way. So I've done it both ways. Both methods work, but I wholeheartedly recommend fay sealing. It's so much less of a mess. You don't wait until the sealant is hard, just much less gooey and messy. I did the riveting when the proseal was rubbery but soft. You could still push it around a bit. I used a cleco in every hole while waiting. I have a lot of details, pics, and discussion on my web site if you care to check it out. Good luck, whatever you choose to do.
 
DanH said:
Everybody has a fay seal if they put sealant on the flange before placing the rib. "Fay" simply refers to sealant between the flange and the skin. The term has nothing to do with allowing the sealant to cure before riveting, or riveting while wet.

We now return you to the usual debate ;)
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Thank you, Dan. I was starting to think some folks were advocating NOT putting sealant on faying surfaces, preferring to only fillet seal their tanks. :eek:
 
krw5927 said:
Thank you, Dan. I was starting to think some folks were advocating NOT putting sealant on faying surfaces, preferring to only fillet seal their tanks. :eek:
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No, not at all. What I'm saying is don't put the proseal on the ribs, cleaco the tank together and let the proseal cure prior to riveting.
 
Wet

I've done more than a fair share of wet wing work. Assemble and shoot wet. I use a short acid brush to wipe up the excess, no wet chemical cleaning while assembling (interior). Try riveting some dimpled scrap together then drill it apart to see how set rivets change the shape of everything. Clecos can't do that. As far as mess, well O.K. it's messy. Problem? No cure before shooting a fay seal.
 
Thanks fellas.

This is obviously one of those topics that can rumble on forever (and always a tricky one for first timers like me). I'll take it all on board and make a decision when it comes to doing the first tank shortly.

I am hoping it will be yet another task that I fretted about and it turned out to be a non-issue.


Thanks again!

Matt.
 
Did one of each

Exactly what Bruce said - both techniques work fine, but using the "fay" mething was a lot less stressful and neater. Believe me - it's tought using and mixing fresh sealant while you're working with bucking bars and rivet guns. Tools need to be cleaned periodically and sealant tends to get everywhere. Fay, 100% cleco, set is aside for a day or two (depending on temperature), then rivet.
 
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