Tip: Proseal ...The fact and the fiction

[David-aviator]

Rick,

If I see you at the next local chapter meeting, I'd like for you to look at what's going on with my quick built tanks. (I did not build them)

I've been over this with Van's and they say they have not seen it before, but just about every tank rivet is lifting the paint. There are no fuel leaks, but a blister of lifted paing. It would appear to be a gas formed at the rivet head.

Vans says it could the paint prep. But that doesn't make sense because it is happening only with fuel tank rivets, no where else. The final conclusion was it is filiform (sp) corrosion. Bu again, how come only with fuel tank rivets.

I wondered to Vans if the pro seal had been properly mixed and perhaps never cured? They said no way. What do you think?

dd

[Rick6a]

Originally Posted by David-aviator

..................what's going on with my quick built tanks..............but just about every tank rivet is lifting the paint. There are no fuel leaks, but a blister of lifted paing. It would appear to be a gas formed at the rivet head.............only with fuel tank rivets......What do you think? dd

Dave,

I have no real idea who builds Van's fuel tanks nor what kind of quality control is maintained during the assembly process. For all we know it could have been an unqualified worker filling in for someone who happened to call in sick that day or a new hire cut loose on his or her own to build your fuel tanks after some period of training and their required work processes not carefully inspected along the way....but of course, I'm just speculating. I do think it is unlikely the proseal was mixed incorrectly as a potential factor because even poorly mixed proseal will within limits, eventually set up. The fact that your fuel tanks have for some time continued to hold fuel without leaking would seem to support that. On this point, I tend to agree with Van.

From what you describe, I would be inclined to think it IS gas forming under the rivet heads and if so...."could" that possibily be due to a chemical reaction with the paint or its base preparation? I believe you painted your -7A with a HVLP....is that yellow color you applied an automotive type paint? Still, I'm inclined to think that during the fuel tank assembly process, either the rivets were not "wet installed" properly or the shop heads encapsulated to their respective dimples with sealer or possibly a combination of both omissions. I would think that if the tanks were properly sealed in the first place, it wouldn't matter what kind of paint process you used, but again I'm speculating.

I know you complained about a few instances of blistering in the past but your recent post seems to suggest the problem is growing to now include virtually all the tank rivets.

Sorry, I really cannot suggest anything approaching a "silvet bullet" fix to make the problem disappear. Perhaps if you have not complied with the recent SB yet, this would be a good time to inspect what internal tank area you can by peering through the access cover hole and see if you can determine if a good fillet seal and shop head encapsulation exists on those areas you can see with a flashlight and mirror. At that time you might want to drill out an easily accessed tank rivet and determine once and for all if sealer traces exist under the head of the removed rivet. Lacking traces of that mandatory sealer, I'd have another chat with Van.

I hope to see you at the next chapter meeting but tend to doubt that upon a casual visual inspection I can add anything more than the possibilities I have outlined here.

[Andrew M]

Hey all,
I to am a professional tin bender, so here goes;
1. I cut those thick shop paper towels into 2" squares to wipe sealent off the tail of the rivit before I hit it, saves on puppy feet.
2. Mix as follows, weight one cup and one stick-tare. add 25g base and total, add 2.5g to that total (number only) and wipe a little black stuff on the side of the cup until I reach that number. 25g does one rib.
3.Shoot everything wet, partly cured sealant is asking for working rivits in the future.( Chapter 51 ATR:Boing: Dehavaland and my personal experience ect..)Wipe as much sealant off the finnished rib as possible, to recoat after the assembly is complete. That way any rework(swag) has nothing to stick to.
4. barrier cream AFTER everything is clecoed, then I also keep a cup of baby poweder to dip my fingers in. Try it. It helps. Sticky fingers has it's advantages, figure that out!
5. To clean hands,Go-Jo liberally, then put on a pair of laytex gloves, then work gloves. Your hands will sweat the sealant out of you pours and if you used enough baby powder it will just roll right off with a scotch brite pad. It really works, Mother being the necessity for this invention. ( I love mom more tha proseal!)
6. Hold your toung just right and recite the riviters prayer "Though I buck in a mess of proseal, I shall fear no puppy feet, for rhine Is the MASS, POWER, and DURATION Amen."

[RV8SQDN]

Rick6a,

I am new here but not new to sealing. You bring up several good points. I have a question though. In your pictures in your first post is the sealant shown all that you applied? I have done a lot of fuel tanks and it looks to me that the void area in the front of the ribs where there are cutouts for rib curvature there is not enough sealant to stop a persistant generated leak path. After your hours flying, are you totally leak free? Thanks.

[Rick6a]

Originally Posted by RV8SQDN

............In your pictures in your first post is the sealant shown all that you applied? I have done a lot of fuel tanks and it looks to me that the void area in the front of the ribs where there are cutouts for rib curvature there is not enough sealant to stop a persistant generated leak path. After your hours flying, are you totally leak free? Thanks.

RV8SQDN,

By viewing those early disposable camera pictures at the start of this thread, I concede it is very difficult to observe that the rib tip cutouts are completely filled in with sealer. You can barely discern a couple of black lines of sealer filling a few of those cutouts in the first picture of the series. See the photo below of a scrapped tank rib for illustration. In addition, because of the poor quality of the photos you cannot see the uninterrupted fillet seal around both the inboard and outboard edges of the tank rib flanges. I am pleased to report that to date, other than one intermittent weeping rivet on the top of the right tank when it is nearly full, the tanks continue to be leak free. BTW, I used medium weight Titeseal to seal the access covers.

[TShort]

Is it really necessary to completely fill those on the interior ribs? There are no rivets or holes to the exterior in that area. On the end ribs it is a different story...

Thomas

[cjensen]

Hey Thomas,

If you don't fill them, it will create a path to the row of rivets for that particular rib. They need to be covered to block that path.

[RV505]

Originally Posted by Rick6a

Working with proseal is no big deal.....really. It continues to rate right up there with canopy cutting as a chore many builders seem to dread with a vague sense of impending doom......shadows of ill-defined personal perception overwhelming the clarity of knowledge and reality. Who starts these wild overblown horror stories? Overrated piffle. The stuff of wasted worry.

For years, I worked with proseal daily, often for weeks at a time. Even after many years of working with a material used in far more applications than just fuel tanks, I still had to attend 3 days of sealer school to satisfy customer requirements for training when I did a stint on the C-17 program. The cockpit and nose section of the giant cargo plane is produced in St. Louis. It is proseal that makes pressurization possible. It made some sense to retrain when assigned to the C-17 program because the enormous size of the pressure vessel demanded proseal be applied precisely and application requirements were somewhat different that the routine techniques we commonly employed on the F-18. Interestingly, those persons skilled in icing a cake performed better with a filleting spoon than their polysulfide-challenged co-workers when requirements specified spreading proseal evenly over a surface without any interruptions or other defects. In the self-interest of limiting the mess to an absolute minimum and keeping my clothes unstained (rarely successful since I refused to wear an apron), I did manage to absorb a few helpful tricks over the years. Admittedly, most of the time I used a pneumatic Semco to apply the stuff, but the use of a Semco sealant gun does present a logistical nightmare for the average homebuilder because it can accept a dizzying array of accessories including various sized tubes, nozzles, extentions and such. Last but not least, the stock of limited shelf life sealer was mixed daily and manually stuffed into appropriately sized tubes by the friendly folk working the neighborhood sealer crib, stamped with an expiration date, then distributed plantwide into dozens of stategically located 40 degree below zero freezers for shop use. That was the way things were done for decades until a new age of economic fashion swept the nation. Not too many years ago, the powers-that-be decided proseal mixing should be subcontracted out to distant strangers, layoff notices soon followed, and the proseal mix is now shipped in from afar and stored in new 80 degree below zero uberfreezers!

Fortunately for the RV builder, the job of sealing got much easier with the introduction of this handy device. http://tinyurl.com/egfol I highly recommmend using one. Such a device sure beats using a common alternative a homebuilder has traditionally been reduced to using...a paper cup and a popsicle stick or tongue depressor.

As for proseal itself, if you get the stuff on your clothes...forget it. Nothing out there will remove proseal without also discoloring your shirt or pants. I take that back. Methylene chloride will "sometimes" work (depending upon the fabric) but its dubious use is best served for a much more noble cause...to decaffinate coffee. Otherwise its just too toxic a chemical and not worth the risk to health from needless exposure. Prior to using proseal, rub some barrier cream or lotion into your skin to more easily remove the stuff from your hands after a sealing session. Wear latex gloves anyway.

When I assembled my leak free fuel tanks, I proceeded exactly as I would at work. There is no compelling reason to wallow around in wet sealer needlessly! I would commonly apply the proseal to the mating surfaces of the parts (called fay-sealing), 100% cleco the assembly together, then allow it set up somewhere between tack dry and full cure. That's it. Walk away. Upon returning to work the next day or even better....after the weekend, I would then remove every second or third cleco from the assembly, wet install and shoot the rivets, then repeat the process over and over again until all the rivets were set.


The above pre-digital pictures make a poor attempt to illustrate the procedure I used on my 6A fuel tanks. First, after roughing the local fay sealing surfaces with maroon scotchbrite and thorough cleaning with MEK, the ribs were fay sealed and secured to the skin by 100% clecoing into place. I insured adequate squeeze-out (smoothed into an uninterrupted fillet seal) existed around the ribs and skin (and previously installed stiffeners) without any voids whatsoever. Session complete. I felt no need to have extra sealer arbitrarily slopped all over the place as a sort of voodoo talisman employed to ward off leak demons. In my mind, excessive and weighty sealer needlessly laying about in perpetuity simply displaced that much more fuel the tanks would otherwise hold. A day or so later, the rivets were wet installed by first removing the clecoes from alternate holes. When all rivets were finally set and while I still had interior access, AND to further insure against leaks, using a Q-tip or a toothpick, I swirled a dollop of sealer around the shop head of each rivet to encapsulate it to its dimple. Next came attaching the rear baffle to the tank skin. As shown, I routinely 100% clecoed and clamped assemblies together. I then allowed the freshly (fay) sealed assembly to set up overnight before moving on to and completing the final riveting. This procedure greatly reduced mess and bother when I worked with wet proseal during this interesting phase of construction. Correctly applied, proseal is truly a tough and awesome material.

As in all aspects of our personal construction experience, we should strive for perfection knowing we will never really achieve it. Prosealing need not be the nightmare scenario some would have you believe. Far from it. There are more pleasant sheet metal tasks to do...sure...but...whoever said building an airplane was not going to be a challenging experience from time to time?

Rick Galati RV-6A "Darla" 124 hours

RicK: You have some of the best and knowlegeable info on this site!!!! I was taught the same way , different production line!!!

[TShort]

Originally Posted by cjensen

Hey Thomas,

If you don't fill them, it will create a path to the row of rivets for that particular rib. They need to be covered to block that path.

I'm not sure I get that. No different than the fillet that is next to the row of rivets along the length of the rib ... the proseal has to "end" somewhere.
Look at the pictures in the wing construction section of the manual from Van's. They don't have proseal in the very nose section of the tank (at least on the internal ribs). I can't see a good reason to seal this area... ?

Thomas

[Rick6a]

Originally Posted by TShort

I'm not sure I get that. No different than the fillet that is next to the row of rivets along the length of the rib ... the proseal has to "end" somewhere.............Thomas

Thomas,

Perhaps this edited photo will help you visualize why it is important to fill in those
rib tip cutouts with sealer. In this situation, simply fillet sealing the edges of the rib
flanges will not "surround" the rivet locations on the rib tip cutouts, hence the
(potential) pathway if the entire cutout is not plugged with proseal.