Pro-sealing venture...

[David-aviator]

My first serious venture into this world occurred during the last three days and I must say it is no big deal. But that can be said only after absorbing comments and advice on the subject from forum members and especially Rick Galati.

The time to install the ribs was about 2 hours including mixing 40 gram batches of sealant. It takes about 22 grams to butter up one rib. Over half the time was spent inside the tank filling all the corners and smoothing out the sealant as best I could.

The result so far is most gratifying but of course the real test will be the balloons when it is all together.

I think I've solve the problem of matching the Z brackets to the wing spar shear web. I will use the old brackets. Preliminary measurements indicate the CNC drilled tanks (old vrs new) are identical so the brackets should fit. We shall see.



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[David-aviator]

Things look a bit in disarray but the job was pretty well organized. I had everything lined up ready to go, gram scale, cleaned parts, acetone (much less expensive than MEK and it works), a clamp in the vise to hold a rib while buttering the mating surface, and lots of gloves, change gloves frequently.

If any of you have built a composit airplane, you'll know of what I speak - this job is a piece of cake compared to doing a wing lay up.






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[wrongway john]

Excellent pics, and gives me an idea of what will be going on here. You seem to be enjoying this aspect, and I detect a bit of a smile. When the time comes, I?ll let you do mine.

[flion]

Organization is key. It's not difficult if you are prepared and don't rush. Plenty of time to get everything right, given how long it takes to set up. I didn't find the tanks on my -6A all that difficult and other prosealing tasks since then have been a snap. Nice shop, by the way.

[Rick6a]

Originally Posted by David-aviator

My first serious venture into this world occurred during the last three days and I must say it is no big deal.

Glad to hear it is working out so well Dave. Assuming your shop is a cool environment, you can rest easy knowing you've got a few DAYS to finish shooting all the rivet locations now clecoed.

BTW. Even though the rivets will be wet installed, don't rule out using rivet tape if you have to.

[David-aviator]

Originally Posted by flion

Organization is key. It's not difficult if you are prepared and don't rush. Plenty of time to get everything right, given how long it takes to set up. I didn't find the tanks on my -6A all that difficult and other prosealing tasks since then have been a snap. Nice shop, by the way.

Thanks for the kudos.

I was concerned about set up time but it is a none issue, at least at 75F and using Flame Master out of the can. The stuff was still workable after an hour but it was getting stiff.

For those just tuning in, this effort is motivated by chronic paint blisters at rivets in the fuel tanks. I am replacing QB tanks built in 2002. The cause of the phenomenon is not known and is under study by some guys here and at Vans.

In the background of the second image is a view of the one of the old tanks after I opened it with a 5" hole saw. The sealant work done back in 2002 actually looks good although it does appear it was thinned and there definitely was less of it used that what I am using. Until the interior could be examined I was undecided on whether to repair the old tanks with more sealant, as has been done successfully, or rebuild.

What prompted the decision to rebuild is completely unrelated to the blisters.

What I found in the left tank were 4 of the 7 ribs deformed and slightly collapsed. That was self induce by me before the airplane first flew back in 2003. Some fuel had been poured into that tank to facilitate test running the Subaru engine just installed. When it came time to weigh the airplane, the remaining fuel was removed by disconnecting the fuel line at the engine and pumping the fuel out with the electric pump. While this was merrily going on I heard this ominous whomp sound - wow, the top of the tank was slightly indented. I immediately stopped the pump and opened the cap and it all popped back to it original shape. What happened was the result of a piece of masking tape across the fuel vent line to keep mod dabbers out.

Much to my surprise, the event did not result in any fuel leakage for quite some time, like maybe 4 years. When it did come near the leading edge, it was repaired by sucking some green lock tite at each leaking rivet. There were 4 or 5 and it worked.

Now did that event have anything to do with the blisters appearing? I don't know. The evidence would indicate not. The right tank actually has more blisters than the left tank with the damaged ribs. Most of blisters are at the aft bulkhead flange, top and bottom. Almost every rivet at the right aft bulkhead has blistered top and bottom.

The sealant used in 2003 was definitely thinned. The final finish is very smooth and the color a light tan. Clearly, it had been applied with a brush. I believe this is a technique used in some production aircraft and is not a local anomaly. Perhaps the stuff had been thinned a bit too much, there is some cracking evident at corners and some crimped rib edges are open where right tank rib rivets have blistered. Curiously, left tank rib rivets have not blistered as much and there are open edges everywhere after the vacuum damage to the ribs.

Perhaps, as one theory goes, it could all be caused by external contamination. I don't know.

I do know what I am assembling now will have a lot more sealant everywhere and none of it will be thinned.

[David-aviator]

re "Glad to hear it is working out so well Dave. Assuming your shop is a cool environment, you can rest easy knowing you've got a few DAYS to finish shooting all the rivet locations now clecoed.

BTW. Even though the rivets will be wet installed, don't rule out using rivet tape if you have to." Rick Galati.

Thanks for all the help and encouragement, Rick.

The venture (adventure) continues. It took 3.5 hours - ribs 2-6 are installed in one tank. One hundred, seventy rivets were set this afternoon.

A 6? round skewer stick, slightly larger than a tooth pick, was used to swirl a bit of sealant into each rivet hole. The rivets were soaked and rinsed in acetone, dried on a piece of cloth and then inserted into each hole with a small surgical pliers. The little buggers were untouched by human hand as per Vans instructions.

Hopefully, all this attention WILL result in no leaks, but I am not holding my breath. This process is somewhat black magic for me at this point.

Each shop head will be covered with a generous swirl of sealant after tank two is riveted. Seems like if the fay is sealed, fillet is sealed, rivet machine head and shop head are sealed, there should be no leaks, right? Will be finding that out in a week or so....I need to get flyin' again and am motivated to get this done.



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[jimbower]

Dave's a good friend and valuable source of wisdom with regards to all things fiberglass (he built a Cozy Mk. IV before coming over from the dark side). I'm glad to see him enjoying the process of building tanks, since his original ones were QB. I'm another proponent of the Rick Galati method of tank building in which you liberally apply ProSeal and then 100% cleco all the ribs into the skins and allow the ProSeal to set up (I waited a week). This method is WAAAAY cleaner than riveting the ribs into the wet ProSeal. It will involve removing dried ProSeal from the dimpled areas, but that's easier than having your rivet gun and bucking bar slip-sliding all over the place during the riveting process. I'm a super-slow builder and my tanks were done almost 10 years ago. They do not leak (at least not on the ground). Using this method caused building tanks to be kind of a non-event (as opposed to the ordeal some said it was).

Jim Bower
RV-6A Slow build
N143DJ
Nearly ready for DAR inspection

[trackdom]

Hi,

I am unable to finf Rick Galati's post about the best fuel tank proseal method...First proseal and cleco then riveting.

thanks for your help

[Dave Taylor]

Try this:
http://www.vansairforce.com/communit...ht=wet+install

Originally Posted by trackdom

Hi,

I am unable to finf Rick Galati's post about the best fuel tank proseal method...First proseal and cleco then riveting.

thanks for your help