Fuel Tanks

[paul330]

I am just starting the dreaded fuel tanks and thought I understood how everything was sealed. However, there are places on the front of the rib flanges where the curvature is greatest where the flanges are notched. In common with all nose ribs, I have found it necessary to slightly blend the ends of these notches to get the ribs to fit and not bulge the skin. Even without this, it appears there is a gap in this area and the nose ribs never fit particularly well anyway.

To my point - do you get a seal simply by running a good fillet of tank sealant along the 2 outside ribs? Will this stay good over the years with flexing? I am particularly concerned about the inboard area which will always be soaked with fuel.

I understand how everything else is sealed with beads of sealant along the flanges and rivets dipped in sealant. It's just really the front of the 2 outer ribs that concerns me.

 

[FredMagare]

Paul,

I'm building a -9A and part of sealing the fuel tank end ribs was to fabricate a couple of doublers which are riveted and prosealed to the nose end, inside of the end ribs. There are likely a couple of small holes on the end ribs which will be at the rear baffle - these could benefit with a similar precaution of a small doubler in the corners. I used the "fay sealing" method to assemble my tanks which took longer but not as messy by far! (Do a search in the forums for fay sealing.)

Good luck.

 

[paul330]

I think you are talking about the tooling holes which are documented in the plans (scrap plate/rivet & proseal). I need to seal around the heavily curved area at the front of the ribs where the fit is not perfect and the notches in the flange would allow fuel to leak out.

 

[derLuigi]

Hi Paul,

have a close look at the plans, I bet you have the doubler in the nose area too. For the RV-7 they are called "reinforcement plates" and have the part no. T-410. They are shaped like the nose section of the tank (maybe 4" * 2.5") and get riveted and sealed on the inside of the end ribs. On the -7 the parts are "in the middle" of the reinforcement ring of the tank access cover when we get the parts, so we just have to break them out.

Mario

 

[flion]

No, the RV-10 plans do not include them. However, as Paul noted, the plans on page 18-5, Step 2, instruct you to make scrap plates to cover the tooling holes. I intend to make the cover plate like my RV-6A reinforcement plates. Mario describes them pretty well. To fabricate them, assemble the ribs into the tank skin. Hold your scrap aluminum up to the end of the skin to trace the shape of the nose. Cut out the piece and shape it to fit inside the tank up against the rib; on the -6A I trimmed until it fit against the skin (with a strip of electrical tape as a spacer so as not to create a stress point). I pre-drilled the rib with #40 holes for the attaching rivets (#30 would be Ok, too, and either universal or countersunk heads) and then held the plate in place and drilled it carefully, avoiding my fingers. At the time I riveted the tank stiffeners to the skin, I also prosealed and riveted the plates to the rib. When the ribs are riveted to the skins, run a proseal fillet along the inside of the joint; the scrap plate will cover the tooling holes and the flange notches.

You'd have to ask Van's why they discarded the rib nose plates on the RV-10 fuel tanks but I suspect that proseal is sufficient to hold in the small gaps created by the flange notches. Still, the plates are easy to fabricate (they're not structural) and give you good control over the gap at the leading edge. Maybe some builders who've been there before can give some perspective.

 

[paul330]

Thanks for the info.

There are other areas (where the tank attach bracket exits and the rear baffle corners) where there are gaps. The plans mention the rear corners as a source of possible leaks and to put a good glob of proseal in the area.

I suspect the answer is that you just seal all the gaps with extra proseal - surely some of you 100+ guys who have actually built a -10 can come up with the answer!!

 

[rleffler]

Thanks for the info.

There are other areas (where the tank attach bracket exits and the rear baffle corners) where there are gaps. The plans mention the rear corners as a source of possible leaks and to put a good glob of proseal in the area.

I suspect the answer is that you just seal all the gaps with extra proseal - surely some of you 100+ guys who have actually built a -10 can come up with the answer!!

Yes, plenty of sealant should applied to the holes and gaps as required.

 

[bobmarkert]

Two more thumps on the dead horse

Ok so I will crack the seal on the pro-seal this weekend. Convince me that the proseal will fill these gaps?????
Click thumbnail for larger pic


Thanks
Bob

 

[rleffler]

Ok so I will crack the seal on the pro-seal this weekend. Convince me that the proseal will fill these gaps?????

Thanks
Bob

I had to flute some of my ribs and proseal worked just fine.

Here are a couple pics

For more details about all my opportunities chasing leaks on the fuel tanks, you can read them here. The gaps at the rear baffle corners are probably larger than what you are showing at the leading edge. You will see from my photos that I was pretty liberal with the proseal.

 

[[email protected]]

Ok so I will crack the seal on the pro-seal this weekend. Convince me that the proseal will fill these gaps?????
Click thumbnail for larger pic


Thanks
Bob

All I can say is I used a lot of proseal, 70+ hours on my plane and the only leak I have is one rivet, right tank, top inside front of the "walk plate".

 

[paul330]

Bob's picture shows exactly the area I was concerned about. I am going to fill the slots with proseal and use a good fillet on the other side. I intend also to mask so I can get a neat edge to the proseal and not get it everywhere! Prep work is all done so I will be starting today - wish me luck

 

[rleffler]

Bob's picture shows exactly the area I was concerned about. I am going to fill the slots with proseal and use a good fillet on the other side. I intend also to mask so I can get a neat edge to the proseal and not get it everywhere! Prep work is all done so I will be starting today - wish me luck

Paul, here's another set of pictures to use as a reference. This is Mike Cencula's 7a build site. Mike is very detail orientated and very neat in his work. You may get some ideas of how to proseal with neat edges. I wasn't so neat in my applications.

bob

 

[RV10Man]

re: thin it

I just built my tanks, as per plans. I had a couple of experienced guys helping.
Before the proseal set up completely, I mixed up a batch of proseal and thinned it to a thick, "pastey" like paint with mek and brushed it on all the seams, rivet lines, etc, (inside the tank) where there could possibly be a leak. As for the rear baffles I put a pretty good sized bead, glob, being more like it, on the edges where the plans said to, and sealed'em up. I didn't have any leaks when I tested them. I've got them on the wings but I haven't put the wings on the fuse yet.
FWIW, I wouldn't worry too much about what the outside of the tank looks like on the ends, as they'll be closed in.

Marshall Alexander
RV10 N781DM
fuse/wiring

 

[egohr1]

Build mine per the plan. No leaks yet. I am up to 15 gallons in each side. Should go to 30 per side after the 1st flight.

Eric Gohr
N410EG

 

[paul330]

Yuck...

Finally started putting the first tank together on Friday. Then yesterday, I took it all apart again. Guess who didn't read the instructions properly on the semkit.... Doesn't set if you don't mix it properly. Fortunately, no damage (other than my pride) - just wasted a day and a half. All part of the learning experience I suppose.

Anyway, did all the parts on the ribs and the stiffeners on one wing today. It actually went together really well but - jeez - that stuff is STICKY!!! Lots of gloves and acetone.

Now I see what the Proseal is actually like, I can understand how it will fill the gaps at the rib leading edges. As usual, worrying about nothing.

Anyway, thanks for all the input

 

[paul330]

Leak Check

The dreaded fuel tanks are almost finished - at least up to my LAA inspection point before the rear baffle goes on.

Now, this may sound stupid but is there any way to leak check BEFORE you close up? Now I have sealed every joint, dipped every rivet, encapsulated every shop head, filled every gap and been up to my elbows in ProSeal so it SHOULDN'T leak. However, I'm sure every builder thinks the same and yet leaks occur. By the time the baffle is on, it's a bit late to use the time-honoured balloon because you can't get at anything should a leak be apparant.

Can it be as simple as putting the tank in a cradle, blocking all the holes and filling it with water? Then if there is a leak from a rivet you can drill it out and reseal it. Naturally, one would put on a blanking plate in place of the fuel sender ........

Are there any pitfalls to trying this? Does anybody know any other way?

Finally, the plans call for ProSeal when fitting the sender. It comes with a rubber gasket. Would this suffice as leak-proof or do you need to smear sealant on as well? Or should you omit the gasket and just use sealant? Strikes me as it might be a bit difficult to get off in the future if you need to change the sender.

 

[rleffler]

Now, this may sound stupid but is there any way to leak check BEFORE you close up?

Not really, otherwise it's only a partial leak test. You should install the rear baffle and the fuel sender, as well as seal the tool holes on the end ribs, and plug the various fuel and vent lines.

Can it be as simple as putting the tank in a cradle, blocking all the holes and filling it with water? Then if there is a leak from a rivet you can drill it out and reseal it. Naturally, one would put on a blanking plate in place of the fuel sender ........

Are there any pitfalls to trying this? Does anybody know any other way?

A couple things, first if there is a leak around a rivet, you don't need to drill it out. It would be impossible to buck after the rear baffle is installed. You can use green loctite to seal any problems around a rivet. This process is documented in many threads here on VAF.

For testing, Van's does sell a test kit. It's on their web store. You could probably obtain the parts locally in the UK quicker and less expensive. A good overall write up using a manometer can be found at Mike Cencula's RV-7a buld site. http://www.our7a.com/20070911.html If you read the week before write ups you'll see the process he went through trouble shooting leaks in his tanks. The RV-7's tanks are a little different that ours, but the theory is the same.

Finally, the plans call for ProSeal when fitting the sender. It comes with a rubber gasket. Would this suffice as leak-proof or do you need to smear sealant on as well? Or should you omit the gasket and just use sealant? Strikes me as it might be a bit difficult to get off in the future if you need to change the sender.

My sender came with a cork sender. I believe the consensus is to throw away the cork gasket and just use the sealant.

 

[johngoodman]

Mine came with the rubber gasket. I used it with Fuel Lube. I'm still under construction, but my leak test went fine. Now that I have to get back into the tanks for return lines, I'm glad I didn't Proseal them.
John

 

[paul330]

Thanks John, I'll try it with the gasket first.

Bob, I understand what you are saying and realise you cannot drill out a leaking rivet once the baffle is on. I also intend to do the full pressure leak check when the tank is sealed.

However, it strikes me that by filling the tank with water BEFORE putting the baffle on, you can have 90% confidence about bad rivets and replace any that show a leak. Any problems around the baffle later can probably be solved with a good dollop of Proseal.

So, I ask the question again - is there any downside or issue with putting the complete tank less baffle in a cradle and filling it with water?