I guess I see the potential path...
The way I did mine, I "buttered up" the rib with a good layer of proseal on all surfaces where there is a rivet hole. I then placed the rib carefully into position, and when clecoed / riveted in place the proseal squeezed out and made a nice fillet all the way around the rib and all the rivet holes. I did not put any proseal on the tabs at the very end where there are no rivet holes; the area you marked as "potential path" has plenty of proseal, however.

I'm 1/2 way done with the interior ribs, doing all the shooting and bucking solo, and this is not nearly as bad as I had anticipated.

Thanks for the tips!

Thomas

Weeping Rivet
 

RV-6A,

One rivet weeping. Not bad. Are you planning on a fix for that? And if so, what is your plan? Because I am not sure if I would have one in your place. Getting something under the rivet head is going to be very difficult. And going in through another way is not very appealing either.

There are a few options to try in my particular circumstance without tearing into the tank.
#1. Do not fill the tank above 15-16 gallons. I know this works but the single weeper only yields a very small amount of blue dye over a period of several days. It really is no big deal to wipe the dye away. In practice, I routinely top off the tank anyway.
#2. Apply Loctite Threadlocker Green (901?) to the rivet head which I am told sometimes works due to its superior wicking powers. I may try that sometime, if I ever get the tank really dry.
#3 Apply a vacuum to the tank to "suck" proseal in from the outside. Apparently this has been done successfully many times.
#4. At AirVenture this year, I was amazed to spot an RV-6A with a blind rivet protruding from the exact same hole location as my weeper. What do you suppose the odds of that are? You can bet it was installed to deal with a weeper. This is a very common fix. Still, a protruding rivet just isn't my thing.
Builders sometimes cut access holes into the rear baffle to deal with bad leaks or in the case of older RV's....peeling slosh. I really don't see removing
the tank and going through all that just to address one single rivet.

---------------------------------------------------------------------------

A day or so after I wrote those comments, using eyeball effort alone I mixed what I guessed to be an approximate 10-1 by weight dollop of sealer from what is left in a can of oh-so-long expired proseal purchased from Van in 2000. I applied a dab of it over the head of that weeping rivet and worked a popsicle stick back and forth over the area in an effort to shove some of the sealer underneath the less than perfectly seated rivet head. When in my imaginings I was reasonably sure I did as much as possible under the circumstances, I left the sealer glob to cure in place over the rivet and continued to fly the plane several times over the next few days. Later, I cleaned off the excess sealer from around the area and noticed a distinct halo of proseal remains around the perimeter of the noted weeper. The minimalist effort seems to have worked because since that time with the fuel tank constantly filled to the max, no traces of tell-tale dye have yet emerged from under that rivet. I?d rather be lucky than smart. As a back-up plan, I did manage to locate and purchase some very hard to find -1 grip length flush head Cherry rivets (CR9162-4-1) from Bon-Aero. At this point, my gut tells me it will not be necessary to eventually replace that rivet but as in all things, time will ultimately tell.

Rick,
Your method worked brilliantly. Wish I had known this on the 1st tank.
Much easier to deal with ... less mess and increased visual inspection of rivets.
A counter sink bit was all I needed to clean the dimple of sealant after cleco
removal.
One thing I did learn was not to discard the little nubs (from the inside
of the tank, after cleco removal) onto the floor... :eek: Use the garbage can!!
Steve 81604

This procedure seems pretty good. The only question I have is if you let the proseal partially dry with the cleco's installed and then when you go to rivet everything together later. Is there any chances for the skins to get a wave in them between the rivet because the dried proseal may prevent the space between rivets from compressing. Do the skin come out smooth down the rivet line on each rib by letting the proseal dry before riveting?

I can see when riveting the rib to the skin with wet proseal, the proseal will squeeze out and make a tight fit between the rib and skin. Is my thinking faulty?

OS rivets?
 

Rick,
For this application, wouldn't the oversize CherryMax CR3242 - which are easily available in the -4-1 size - be a better choice?

The existing hole, which I presume is double dimpled, will not have very parallel sides, which is of little effect to a standard driven rivet, but is not the best hole for pulled rivets, which prefer nice straight sides.... :)

It seems to me that drilling the hole out 1/64 and using a OS CherryMax rivet would give a better joint and also probably better sealing... with no effect on the fit into the existing dimple.

...just a question... gil A

You are not really allowing the sealer to cure up hard, merely some degree of tack dryness and in my experience, no discernable waviness has ever been encountered.


Gil,

IF the hole were double dimpled (which it is not) the CR3242 would be a better choice. In this case however, the hole is of the standard DWG dimension complete with nice straight sides. :)

I shared this procedure with a friend of mine who is a A&P and he also sees nothing wrong with this way to seal the tanks, even though they (Duncan) rivet with the proseal wet. One thing he recommended was to spread proseal completely over the shop heads of the ribs flange instead of just wetting the rivet's shop head themselves with a q tip on the inside of the tank. He said a complete layer of proseal will lessen any chances of a individual rivet leaking later.

He was the one who questions the potential waviness between the rivets.

Those of you who used the pre-filled tubes method, how many does it take to do everything on both tanks?

Surface Prep of the Dimples
 

Thinking about the weeping rivets...we're told to Scotchbrite the fay surfaces between ribs/stiffeners and skin before sealing, but what about the fay between the rivet and outside skin dimple surface? Seems like the dimpling process is not a good adhesion-promoting prep. Could that be a reason for poor sealing and should we be addressing those?

A big glob of Prosealover the shop head...a generous filet along one side of the rib, and then along the flange/skin on the other... can't leak. Buy extra proseal.

Proseal Basics
 

-8A QB N192NM so I haven't had the fun assembling the tanks. However, it is time to install the float-type fuel senders.

I've got a tube of "stuff" from Vans that's supposed to work - if I can really figure out the mixing instructions. Some really basic questions:

1. Urban legand sez to toss the cork gaskets. Is that correct?
2. Bead size - what's appropriate? While subscribing to the "More is better" idea, what happens if the excess oozes from the cover plate into the tank and possibly breaks loose sometime in the future?
3. Rubber gaskets - just in case the **** thing doesn't work and I have to remove the sender, I intend to use the provided rubber gaskets without sealer, but put pleny of sealer on the screws before assembly. Good idea?
4. Shelf life - or more accurately - "After mixing useful life". How long do I have after mixing for useful application capability?

Proseal Basics
 

Hi Rick,

I just found your thread. Nice write up.

I did my RV-3 wing tanks Van's way 20+ years ago. Messy, but lasts a long time.
A friend of mine is also on the C-17 program.
I did my RV-4 wing tanks the same way you discribe. Much cleaner, and easier to inspect for possble leak paths.
In addition to placing a cleco in every rivet hole, I included a #6 nut against the inside of the wing rib to increase the cleco spring compression and distribute the cleco force around the dimple.
I usually waited a week (48 hours minimum) before I riveted the tanks.
I didn't clean the clecos or nuts. Just removed them. (You'd normally have to pay someone to provide these custom non-scratch clecos.)

I installed the rivets dry. Very easy this way.
Any potential for problems with the dry rivet installation? I understand the the shop head is self sealing.

I sealed around each rivet inside the tank, and formed a overlapping bead over the rib and onto tank skin by about 3/16" all around.

I also sealed the fuel line fitting and nut, instead of Van's safety wire method. 1/4" overlap on each part and .15 minimum thckness is supposed to meet the same standards on fuel fittings as safety wiring them.

Any comments, or suggestions?

Regards,
Jim Ayers

Jim,

No doubt it is easier to install the rivets dry but many, many field reports of weeping rivets and blistering paint suggest to me that the shops heads of the rivets are not necessarily self sealing when bucked into a thin dimpled stackup. In addition to any given builder's level of workmanship, there are other variables that determine overall quality such as rivet length...the callout is 3.5 and I prefer a 4....hole preparation...usually reamed with a #40 and I prefer a #41 to produce a slightly snugger fit...the quality of the shop head after bucking...some people leave bad rivets in place reasoning that they will cause more damage by replacing than leaving alone.....All the more reason to dab a touch of sealer around the countersink prior to seating the manufactured head, and then fully encapsulate the shop head after setting the rivet. Extra work...sure...but I'd rather pay now than pay later.

Proseal basics
 

I second the queries of pvalovich, as I am in the same position about to install/seal the float senders and would like to know what works and what is less likely to work

Floating rivet heads
 

I installed the rivets dry so the rivet head wouldn't float up on wet seal.
C-17 program. NEVER shoot wet seal. ?

I didn't see the need to dimple extra deep to allow room for the floating rivet head. Seems contrary to rivet structure considerations.

I shot my RV-3 wing tanks per Van's instructions for shooting wet seal. I still got one rivet that blistered the paint around the rivet head. It seems like there are no guarantees with that method, either.

Jim

I started out back riveting tank stiffeners (wet) but most were being left slightly proud on the outside. Thinking the workbench may be giving somewhat, I moved the backrivet plate from the bench to the concrete floor and got slight improvement, but still not as flush as I'd like to see. I got even better results with the mushroom set and bucking bar with the skin in the cradle. I did notice that after 3 or 4 rivets they started sticking up again. That's when I started wiping the set after each rivet and had no more problems. (I assume the layer of sealant holds the set off the skin slightly?) Slower this way, but the results are worth it.

BTW, I seemed to be able to better control the right end of this bucking bar while shooting solo than I did with my new titanium bar, resulting in fewer clinched shop heads.

Thinned Sealer?
 

Rick,
I'll start sealing this weekend and plan to use your suggested 100% cleco process and post-semi-cured rivets. Two questions: is it easier to just do the ribs that way but not the stiffeners, and 2) would it be a good idea to thin the pro-seal a little for wet installing the rivets?

Bill,

You can do the stiffeners that way but their installation counts among the easiest jobs in fuel tank construction and I just install them wet. The ribs are another story. As the photo shows, I prepped all the internal ribs in both tanks at the same time and shot the rivets over the next few days. I have no experience with thinning proseal so I won't go there.

Proseal Tip
 

Use the method Rick has shown.
I did and had no leaks.


Thx Rick

Fuel Sealing: It Begins
 

Hey, how come nobody told me this was a messy process?!:rolleyes:
Well, I installed the first four stiffeners last night and learned a ton. I want to say thanks to you guys for the collective suggestions (double gloves, ziplock on the scale, etc.) on tank sealing. I felt like I knew what I was doing right from the get-go because of this forum. I know I've got more to learn this weekend as I move to the ribs but I'm having a blast! I was a little dissappointed to find the new "quart" can of pro-seal only 5/8 full. And for those in the market for a digital postal scale, Staples just put their $35 unit on sale for half price. Since I know you've never seen the process I'll post pix later!:D

Sam Buchanan thinned sealer with MEK and got good results. I tried it a couple of days ago and couldn't get it to mix thoroughly. I may have added the MEK too long after initial mixing. I'm just going to stick (no pun intended!;)) with straight sealer.

Thanks Rick!
 

Rick, great information on the sealing of the tanks. Much appreciated. I don't know if this is overkill, but I really don't want to do all this work and have a leaky tank. So, I completely encased the shop heads and the flange with proseal...too much?

Any comments would be appreciated.

Here's a link to my pics:

http://mykitlog.com/display_project.php?project_id=820

Thanks

Don

Looks like mine!
 

Thats what I did. Two tanks and no leaks :D

Good Job
 

Looks okay to me Don. Since you are inviting comments, I will remark on something you wrote:

"Later tonight, I'll go in and proseal and 100% cleco another rib, and then rivet the rib I prosealed...."

My question (if I interpret your comment correctly) is why invest in the extra time and effort to install the internal ribs singly or one at a time? Unless you feel you would have difficulty accessing all the rivet holes, on the next tank why not install all 5 of the internal ribs in one session? Doing so will provide you with the following benefits: By clecoing all 5 of the internal ribs in place in one session, starting with the nose of the ribs and then "wrapping" the fuel tank skin around them as shown in my series of photographs (selectively abbreviated below) you will greatly reduce the chance of generating voids in the faying surfaces as opposed to "sliding" each wet rib into place one at a time. Also, installing all 5 ribs at once will minimize the number of times you have to mix up a batch of proseal.



In any event, it is always gratifying to hear from other builders who have learned that by working smarter rather than harder, the horror stories about "black death" we sometimes hear are completely overblown. You are learning for yourself that working with proseal is not that big a deal if the task is approached efficiently. Good luck to you Don, by the looks of your encapsulation method and supposing your fay seal surfaces are without void, I am virtually certain you are building at least BLISTER free fuel tanks.

One last thing...be extra mindful when you get around to installing that rear baffle. That seems to be the one area of fuel tank assembly many builders report leaks to emanate from, particularly the corners.

Very timely post, and thank you for it, nothing beats experience, except a cold beer. I'm starting my 9 tanks once the proseal arrives from Vans.

Wrapping
 

Hey Rick,

I started the prosealing 2 ribs at a time, then saw your wrapping technique afterward. I'm doing my left tank exactly as you suggested by wrapping it to avoid any voids at all.

It will be much easier doing one big batch, verses small batchces that I've been doing.

Again, MUCH thanks!


Cheers,

Don

Assembly Sequence
 

Don,

It will become apparent to you that key steps in the wet assembly process will become much easier to accomplish and sometimes even fun. When you get to the point all the internal ribs are 100% clecoed into place....relax. It is important to understand that (within reason, of course) there are no pressure or time constraints. Reaching this stage of assembly, you enjoy the satisfaction of knowing you can set all the rivets at your leisure. For now, concentrate on fashioning an acceptable fillet seal around each rib making certain no voids, interruptions or other defects exist. If you simply must shoot rivets and can set them in a few hours, that's wonderful. Consider yourself Superman. If you can set all those rivets in a freshly sealed and very wet assembly in those same few hours and do all that without making a sloppy mess, you are indeed a Superman. Most of us are not that fast or talented. For most of us, it would take all day or several days to finally get all the rivets properly set, and that's a perfectly fine plan of action. For instance, in my experience with the freshly prosealed/100% clecoed fuel tank shown below, I did not start the riveting process until the next day. Actually, what the photo does not show is that I assembled both fuel tanks at the same time. Then, it took approximately 2-3 days spread out over several sometimes brief work sessions to complete the riveting on both tanks. Because there are no time constraints, I took my time. As often as not, I walked away from it when I got frustrated or tired. I did not hesitate to remove and replace even the slightest marginal rivet throughout the process. When the proseal is tack dry (which is the state of cure I prefer to work it), you will likely find that aluminum chips and rivet chunks produced by drilling out unacceptable fasteners is not much of a problem.

Enjoy the process for what it is Don. Long after your RV is painted and flying, I'm sure you will be continually pleased with the lasting high quality performance of your fuel tanks as a result of your efforts.

End ribs
 

Rick, just curious as to why you wouldn't do the end ribs at the same time.

I am in the process of building new tanks for my -4 (only 3 internal ribs) and anticipated doing the internal ribs and the end ribs all at the same time, leaving them clecoed while the sealant set up.

Also, on the internal ribs is there a good reason to seal up the nose past the last rivet?

Thanks for sharing you knowledge!

Mark,

My general suggestions are influenced to some degree by the physical dimensions of the 6, 7 and -8 series fuel tank designs.
I am not familar with RV4 fuel tank design dimensions so please keep that fact in mind and bear with me.

The technical answer to your first question is...yes...it is possible to install the end ribs at the same time. Accessability becomes an issue though, most particularily at the inboardmost rib location, an area where rib to rib spacing (RV8) is narrow. As shown in the photo on the left, the spacing is not much wider than the filler flange! Following installation of the end rib, inner access to the immediate area becomes severely limited and just reaching a lot of rivets can be a dark and difficult challenge. I suppose one could argue that some rivets could be accessed through the large cover plate hole in the side of the end rib but that approach seems comparatively more difficult to me. By leaving the end rib off for now, the builder enjoys much better illumination and the entire series of rivets attaching that inboardmost internal rib can be accessed and shot much easier, even comfortably, in reality making that rib the easiest of all the internal ribs to work. You lose that considerable advantage with the end rib installed.

Again, my comments do not reflect a familarity with RV4 fuel tanks. If you find that accessability is not an issue and falls within your personal comfort zone, then by all means install the end ribs the same time as all the others.



To help answer your question about prosealing the tips of the ribs, I refer you to my comments and detail photograph included
in post #40:

http://www.vansairforce.com/communit...2&postcount=40

Another Fay Fan
 

Just finished my right fuel tank using the fay method that Rick described. Much easier and neater than the left tank which I did following the manual. I 100% clecoed everything Friday, then riveted today (Sunday). The weather has been cool so by today the proseal I used on Friday was like soft tar. I used a toothpick to push the little "nit" of proseal out of the hole, then used another toothpick to dab some fresh proseal in the dimple before riveting. MUCH neater and MUCH less stressful way of sealing and riveting the tank. Most importantly, you can visualize the shop head of the rivet MUCH better with this technique.

Filling the dimple with a little dab of fresh proseal


This method allows for a very neat job




P.S. - what looks like streaks of Proseal on the tank skin in the last picture is the reflection of the rib's lower flange

Thanks Rick.

tank leak proseal trick
 

An IA I know that works with Mooneys helped me with a small seam leak in the back of my tank. He said rather than cut a hole and fill from inside, you could suck proseal into crack. He talked to the company that produces it and they said you can thin proseal with Toulene since it is soluble in toulene. Ironic part of this is is that Toulene is what keeps the blue dye in suspension in 100LL. Once proseal is set up, it's ok, but if it isn't completely set when you add fuel, you're going to have problems.

Anyway, here's what I did.
1. Sealed off tank except for vent tube and put a shop vac hose in filler hole. I left the vent tube open to avoid pulling too much suction and damaging tank.

2. Cleaned area of leak with MEK and used vac to suck some MEK into leak and let it evaporate.

3. Mixed up some proseal and thinned to consistency of about Karo syrup or some of that running "natural peanut butter".

4. Put the proseal on and used shop vac to suck it into leak. I let that cure for a few days and leak checked and it was good.

5. To be extra sure put more proseal on outside. I know a few tanks that have been done this way with small leaks on seams and none have failed to date. One has been about 4 years.

I actually have a photo from inside tank that shows where the proseal streamed back along bulkhead.

jjet

Add another Fey Fan
 

Just finished my first tank( right ), and leak tested. No bubbles. Have had balloon on vent for over 48 hours and balloon is still inflated!

Thanks so much to Rick for sharing this method. I had been reluctant to start the sealing process till I read Rick's post. Can honestly say it was fun.

Steve

handy device, essentially a caulking gun
 

Rick's original post in this thread refers to "handy device, essentially a caulking gun" but the tiny url link is broken. Would someone please post/describe which caulking gun device he was recommending?

Not sure if it is the same one he was linking to, but HERE is a calking gun meant for use with Sem kit sealant cartridges.

Forgive my inexperience, but why would one not back rivet ribs to one side of the skin from the inside, before wrapping the skin? It seems that this would be easier and faster.

One reason is that you wouldn't be able to shoot and buck solo. Since you wouldn't be able to use a flat backriveting plate on the curves of the ribs, and it would be next to impossible to control an offset backrivet set solo, you'd need someone on the outside with a bucking bar - and maybe a third to hold the skin open for you...

Another (and maybe more pressing) reason would be the difficulty of clecoing the second side of the skin to the ribs after you've riveted one side. It's difficult enough dry; I can't imagine what it would be like with sealant slathered all over the parts. The instructions have you dry cleco all the ribs into the skin then remove one at a time for sealing, letting the others hold the shape.

Sealing the tanks is not really as bad as many make it out to be. For me the worst part is measuring and mixing, but even that is OK once you've worked out a process. I did my first tank solo with reasonable results, and only minor cleanup. I'm in process on the second, and plan to do it the same. One thing I've found that I didn't see here or any builders' logs is to wipe the outside of the rivet of sealant before setting it; it greatly improves (for me at least) the flushness of the finished rivet.

First half
 

I used Ricks method for the first half (ribs to skins) and I must say...all my fears of ProSeal really were for nothing. This is pretty clean way to get the bulk of the sealant done on the tanks.

I hope to have both tanks riveted during this week sometime. Wish I had done it sooner! Thanks Rick!

How many clecoes did you need to do that? I'd like to lay all the ribs in at once but I don't know if I have enough clecoes to be able to fill every hole on the interior ribs...

340 total will take care of both RV-7 tanks!

I had to borrow some from a buddy to make it work and still leave my top skins and leading edges together.