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Tank Gasket and Anti-Rotation Bracket

StuBob

Well Known Member
I'm getting started on the tanks of an RV 8. A couple of quick questions:

1) It seems to me that cork gaskets will have a finite and short life before they start leaking. Has that been a problem? Is there an reason why I can't substitute silicone of the same dimensions?

2) Photos below. Can I trim the T-715 attach angle to keep it from interfering with the rib? Maybe trim the hole in the rib a little? Or do I have to start over on a new rib and T-708 Access Plate?

Thanks in advance.

2016-06-24%2021.02.26-XL.jpg


2016-06-24%2021.03.08-XL.jpg
 
Tank

1. Why not relieve the rib to the edge of the ring?
2. Proseal instead of gasket or Titeseal with the gasket. No RTV.
 
1. Why not relieve the rib to the edge of the ring?
Can I do that? The circle on the rib is defined by a hump, which is present in the plans. Doesn't that hump add strength?

Are you saying to remove that hump all the way around, or only a small area to accommodate the bracket?
 
https://www.permatex.com/products/gasketing/gasket-sealants/permatex-permashield-fuel-resistant-gasket-dressing-flange-sealant/

Never use this product on your cover plate flanges. It's not certified, or recommended by Van's. All your friends will shun you, and all your children will be below average.

And everyone will call you lazy because it will be so simple to remove, clean up, and replace, when you need to open the tank to repair the leaking proseal.

Charlie

edit: Oh yeah; forgot the ;-)
 
Something seems wrong on this, it's been a little while since I did my tanks but I don't recall having to make a modification in this area.

I don't have plans in front of me, but are you sure how you have it laid out in the picture is correct?
 
Can I do that? The circle on the rib is defined by a hump, which is present in the plans. Doesn't that hump add strength?

Are you saying to remove that hump all the way around, or only a small area to accommodate the bracket?

Don't remove the hump, cut a flat on the edge of the circular plate so none of the plate rests on the hump.

The RV-6 plans show this flat.
 
Don't remove the hump, cut a flat on the edge of the circular plate so none of the plate rests on the hump.

The RV-6 plans show this flat.

Correct. Just looked at the plans again. Plans clearly show the hump. However, not to confuse the issue, but if you look at the photos in Section 7, Fig 7-13 shows the hump cut away and the rib web is cut to the edge of the ring. At least it looks that way.
 
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What Larry said.

I wouldn't pretend to speak for Van's, but it's my understanding that the flange around lightening holes is to stiffen the panel around the hole. If you add a doubler ring (plus the cover itself), the doubler ring and cover should be doing that job. It's been a long time, but IIRC, my 10+ year old -7 wing kit either had the flange cut away, or instructed the builder to cut it away. The final opening was the ID of the stiffener ring.

The anti-rotation bracket was a different design back then, too. IIRC, there may have just been an instruction on how to make one from a piece of angle.

On what sealant to use. Seriously, I'd at least take a look at the Permatex sealant I linked to in my previous post. I did some research on it about 18 months ago, and decided to use it when I had to open the 25 year old tanks on my -4. I applied it without a gasket, and put a match-head size drop in each screw hole prior to inserting the screw. No leaks around the flanges in 18 months, either tank. I did have to re-open one tank after a month or two because I missed a spot with my proseal work, and the flange sealant had remained soft and pliable. I was able to remove the cover by just slipping in a thin blade, and the old sealant was relatively easy to wipe off with a bit of solvent on a rag. It stands up to the no-alcohol premium mogas I typically burn, plus the rare bit of avgas I might have to buy while traveling.
 
The plot thickens.......

Here's the RV-8 drawing and the detail. They clearly show the hump:
2016-06-25%252020.54.51-XL.jpg


2016-06-25%252020.55.00-XL.jpg


But Figure 7-13 appears to show the whole hump trimmed away. And here are the RV-6 drawings, which show no hump:
2016-06-25%252020.55.38-XL.jpg


2016-06-25%252020.55.48-XL.jpg


It would appear I can cut that hump off, leaving the rib flush with the reinforcing ring. But it seems that, when the drawings differ, I should be following the later ones. :confused:
 
Actually, now that I look at it for the 1000th time, it appears the RV-8 Section B-B' shows the whole assembly inside the hump, which isn't possible.

Really tempted to just cut the sucker out and keep building..........



Edit: WAIT!!!That isn't the hump around the lightening hole, is it. It's the hump between the lightening holes. But it still shows the rib extending past the edge of the ring.

hmmmmm......
 
https://www.permatex.com/products/gasketing/gasket-sealants/permatex-permashield-fuel-resistant-gasket-dressing-flange-sealant/

Never use this product on your cover plate flanges. It's not certified, or recommended by Van's. All your friends will shun you, and all your children will be below average.

And everyone will call you lazy because it will be so simple to remove, clean up, and replace, when you need to open the tank to repair the leaking proseal.

Charlie

edit: Oh yeah; forgot the ;-)

Do you use the Permatex gasket stuff with the cork gasket, or instead of it?
 
I don't think that is the bead you are seeing in section C-C. Look closely at section B-B. It appears to me that one of the hidden lines in C-C is the inside edge of the reinforcement ring and the other hidden line is the edge of the hole. Section B-B does not show the bead.

It has been a while but I think if you cut a hole just big enough to remove the bead, there would be a little rib exposed inside the reinforcement ring. I think that is what C-C is showing although the hidden lines appear to be a little out of scale.

Just my $.02.
 
Agree with the others; you cut your access hole too small, or at least smaller than I did. My access holes are the same size as the ID of the doubler ring. I see no reason to preserve the "bead" or "hump" here - the doubler + cover should provide plenty of strength, and if you ever have to stick your hand in that hole, you're going to want all the room you can get.

Some pertinent posts from my build log: http://rv.squawk1200.net/2014/08/03/left-fuel-tank-stuff-senders-access-plates-oh-my/

There's also a better view of the inside of the rib with the doubler and cover in place here: http://rv.squawk1200.net/2014/08/07/left-tank-plumbing/

Another good look at the doubler on the rib: http://rv.squawk1200.net/2014/08/25/right-tank-misc-bits/
 
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Alright, this is making some sense.

I looked at your site, Phil, and I've got to say -- either you work really fast or you put in some long days. Thanks for the links.

Robert, good to see you here!
 
I toured the Van's factory couple months ago. The guy told me when I receive my wing kit, take the cork gasket and toss it as far as I can. FWIW
 
There's a special tank sealant for removable hatches. It's called access hatch sealant. Skygook.com sells it and that's what I used on my not-yet-flying RV-3B.

Other people have reported that regular tank sealant seals well (of course) and is removable if necessary. I botched one part and had to remove a rib and replace it, and found that using a hair-dryer makes removal much easier. I think I documented the entire process in the Tips section.

Dave
 
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