Fuel Tank Assembly

[dons]

I have now entered the ProSeal club, just starting out, but at least I've reached the point where the fuel tank pieces are being put together.

So far, but I am just starting this, I found as long as I had everything planned ahead I could manage to keep things clean. I put all the stiffeners on using just one pair of gloves and didn't get any myself, but I went through several gloves doing the drains because of all the solvent I used cleaning up the outside area. The acetone I was using would cause rips to form in the gloves pretty quick.

Here is the progress so far:

• Scuffed the skins for stiffeners, ribs, filler cap, and drain
• Cleaned rivets and held them in the stiffener holes with rivet tape
• Weighed a batch of sealent on a piece of cellophane using a postal scale (I first tried mixing in a small cup, but I found doing it on a flat surface made it easier to get a good thorough mixed batch)

• Spread some sealant on the stiffeners (it really is completely covered, those are just reflections giving the brownish colour)
• Push down the stiffeners to make sure they are well seated

• Made a custom back rivet setup that is easy to keep clean (only things that gets close to the sealant is easy to clean, a normal back rivet set gets sealant where it is hard to clean)
• Place the set (from a C-Frame) on the shop head
• Lower the block to apply pressure and rivet
• Set revit and the only extra sealant is on the end of the all metal set where any excessive build-up can be easily cleaned as required. I found I could do 5 to 10 rivets before having to clean the end of the set to prevent sealant from getting anywhere it wasn't needed.

• Cover up the shop head so fuel can't wick out along the rivet
• Put a bead of sealant along the edges using a syringe (really cuts down on the mess using one of these, I first tried with just a stick, but that wasn't as good a method in my opinion)
• The bead of sealant as applied by the syringe, a lot more consistent than just using a stick
• Smooth out and press the sealant against the stiffener, I just used a toothpick

• Scuff up the area around each shop head (tried to leave the alclad around where the water might sit and just scuff it up where required)
• Scuff up the outside of the fuel tank skin where the drain fitting attaches
• Seal in the drain fitting
• Once again cover the shop heads leaving room for liquid to reach the drain from all angles

So far I'm happy with the results, but I have a long way to go on these things. Thanks for all the tips I have seen posted has made this a lot easier than it would have been otherwise.

[jwyatt]

Looking good!

Thanks for the pictorial guide -- I'll be tackling this in the next couple of weeks, and I've read much of the commentary on tank sealing, but seeing it in pictures is a good "huh, that doesn't look too bad after all" moment.

What did you use to scuff the stiffener and rib lines? Looking forward to seeing the rest of the process.

[Brantel]

Most excellent looking job! Looks like you are taking very much care in your work!

If you manage to keep it that neat thru till the end, you will be declared the new tank building expert!

[dons]

What did you use to scuff the stiffener and rib lines? Looking forward to seeing the rest of the process.

I used a maroon scotch-brite pad and either the original plastic or blue (green the picture below) 3M masking tape to define the areas to be scuffed.

• Scuffing the rib lines with a scotch-brite pad
• Scuffing the shop head side of the stiffeners using a mask
• Scuffing the shop head side for the drain rivets using sandpaper

Most excellent looking job! Looks like you are taking very much care in your work!

Thanks! I know I spend too much time on most things, but it's just the way I am ... maybe I'll learn different ... maybe not, I'm guessing not.

[BSwayze]

Don,

It's really looking good! If it's any help, I just launched my website and you can check out my pages on tank construction. Both of them went together without any leaks. There are lots of pics and details. I used the "fay sealing" method after trying it the traditional way, and would highly recommend it. Having done it both ways, if I ever build tanks again, I will do it that way for sure.

Hope this is helpful! Keep up the good work.

Bruce's RV-7A site: http://www.BrucesRV7A.com

[dons]

Thanks Bruce. That is a nice website, you put some serious work into that! The stuff about why build should be very helpful to those sitting on the fence.

I've looked at quite a few sites that include pictures of fuel tanks, yours included, thanks.

[RV7Factory]

Holy Cow!

I've been accused of having very clean tanks, but mine are nothing in comparison to yours. Nice work!!!

[Spike]

Wow dude, that is nice work! Quite impressive.

[dons]

Thanks for the comments Brad and Spike.

The real proof is during the leak test which at my speed is many weeks away. While keeping things neat and clean doesn't in itself mean good quality, the process of doing that in my case tends to make me a bit more careful and meticulous about the task which hopefully improves the quality and likelihood of a functional pair of tanks. Is this neatness necessary to make a perfectly acceptable and functional fuel tank, absolutely not. I'm treating it as a challenge to see if I can keep things (including myself) relatively clean of ProSeal, except for the clecos of course, they are going to need some clean up if I ever intend to use them again.

Brad, glad to see you get a least a few minutes now and then for the aviation/computer related activity.

[RV7Factory]

Brad, glad to see you get a least a few minutes now and then for the aviation/computer related activity.

I'll be back in the shop soon, very soon!

[dons]

This past weekend I managed to do some more prep work and a little bit of sealing.

• scuff up the mating surface between the outboard rib and doubler
• the use of the tape keeps the alclad in good shape where there won't be sealant
• made sure the shop head sides had a good scuffed area, the tooling hole also got some scuffing after this shot

Installing of the fuel filler ring required three different rivet lengths due to the machined shape. This is one of the 'deluxe' fuel cap assemblies.

• all the rivets were held in place with rivet tape and the ring covered in sealant
• after back riveting, covering the shop heads, and adding a bead around the edge
• after cleaning up the sealant on the top the of fuel tank skin

[dons]

It's been a while since I posted anything about my fuel tanks, so at last I have some progress to share:

• Typical interior rib just after setting the rivets
• Non-flange side of an interior rib just after setting the rivets
• Before smoothing out the sealant
• After covering one of the shop heads

• After adding some sealant and smoothing out a filet, the shop heads all get covered as well
• Removing the tape, and no I don't always wear gloves, if you are careful it isn't messy
• Finished up non-flange side with extra sealant and the tape removed
• A typical finished interior rib

• Outboard capacitive sender plate, used tape to hold the wire while the sealant cured
• Inboard capacitive sender plate, wires sealed in place

• Outboard rib sealed in place, used a large rivet to fill the tooling hole
• Fitting the inboard rib with attachment angle
• Details of attachment angle, note the releaf areas for rib shop heads, I installed the angle after the rib was riveted

• Inboard rib ready for the capacitive sender BNC connector
• Interior side of the inboard rib with the BNC connector installed
• Added some extra sealant around the connector base
• Exterior side of the inboard rib with the BNC connector installed and sealed

• Interior side of the inboard rib ready for the vent line fitting
• Exterior side of the inboard rib ready for the vent line fitting
• Interior side of the vent line connector after adding some sealant
• Exterior side of the vent line connector after adding some sealant

• The inspection hole doubler riveted on and sealed around the outter perimeter
• The ring fully sealed to the inboard rib

• When finished with the cleos I put them in small cups, then a bag, then the freezer for later cleaning, this kept the sealant from getting all over the cleos or cleco pliers etc.
• This is how I kept the rivet gun clean, a piece of rivet tape over each rivet head
• Pulling the tape off leaves a small easy to clean area on the outside of the tank skin

• Intial cleanup with small pieces of shop towel and acetone
• A final wipe with a clean cotton rag and acetone
• A rib line riveted and cleaned

Next comes the rear baffle and z brackets ...

[Spike]

Thats like a work of art!!

[dons]

Thanks Spike! I'm likely over doing it a bit, but it's my plane.

There may actually be an end to the sealing of the fuel tanks, not yet, but getting a lot closer:

• Scuff the inside of the rear baffle
• Scuff the outside of the rear baffle
• Remove the tape and plastic to expose the scuffed areas
• Clean, clean, and clean some more

• Apply sealant where the shop heads of the rivets will be
• Apply sealant to the skins and then the ribs
• Added the small bead just forward of the skin to baffle rivet holes
• Used a pair of clecos as handles to postion the baffle, also added some tape to the outside of the skins along the rivet line to keep the sealant from oozing out the holes while positioning the baffle.

• Add a lot of clecos and then rivet the skins to baffle
• Added the z-brackets
• A bit more cleaning up and this one is has a rear baffle

• Scuff and clean the inspection plates and associated parts
• Add the fuel pickup parts to the plates
• More of the same
• Waited for the sealant to cure a few days, added the flap (didn't want any sticky sealant to contact the flap), I'm not putting in a flop tube, but the flap would be very hard to do later, so why not.

My latest method for weighing and mixing the sealant, works a lot better than cups or bowls.

• Using "Freezer Paper" to weigh the sealant on (poor mans butcher paper)
• Tape the weighed mixture to a flat surface and mixed with a popsicle stick

I'm going to let it cure a bit before putting the inspection plates on and then some cure time and the leak tests.

[BSwayze]

Don,
You are way over the top, man. NICE WORK! Can't wait to see the results of your leak tests. It's a very big day when your fuel tanks are finished and tested. Be sure to let us know.

[cjensen]

Man Don! I almost can't even get past how nice your POSTS look, let alone the tanks! JEEZ! NICE!

[Speed3Guy]

Wow--you've turned ProSeal into some sort of art medium! I'm feeling really bad about myself now--I only thought I was picky. (My wife uses a different work to describe me--it begins with the letter "A")

I'm gonna have to go flying now, just to get my self confidence back!

Nice work.

Guy

[dons]

Don,
You are way over the top, man. NICE WORK! Can't wait to see the results of your leak tests. It's a very big day when your fuel tanks are finished and tested. Be sure to let us know.

I know it's over the top, but I wanted to prove to myself it could be done without getting sealant all over the shop and myself after watching a video on how to do it (accidents not withstanding, those things happen, we won't bring up any names though ). Thanks Bruce, I'm looking forward to the leak test and saying their done.

Man Don! I almost can't even get past how nice your POSTS look, let alone the tanks! JEEZ! NICE!

I like experimenting with my posts too, thanks Chad.

...turned ProSeal into some sort of art medium...

Nah, not me, I have no artistic bent, more along the "A" you mentioned . Thanks Guy.

[dons]

I hope this is the last chapter in my fuel tank saga. The inspection plates were installed almost three
weeks ago and this past week I did the leak tests.


The last assembly task was to install the inspection plates, I did not use a cork gasket, just sealant. I
do admit I used NAS1097AD3 flush rivets to hold the nut plates so the mating surface would be as flat
as possible. I figured if I had dimpled it, it wouldn't have been as easy to seal without a gasket.

• Apply sealant to the mating surface and the inside lip
• Loosely install all the screws
• Tighten everything down and spread sealant along the edges and around the screw heads
• Repeat for the other tank

Leak Testing

My testing idea was to set both tanks side by side, pressurize them the very same and watch for the
same behavior as the temperature and outside pressure varied with time. The hardest part was getting
rid of the leaks in the test setup. One of my air valves leaked quite a bit, one the transitions from 1/4 OD
to 1/4 ID tube leaked a bit, and one of the fuel caps wasn't tight enough. Soapy water finds those very
fast. Once the fuel caps were tight enough, there were no bulges under the tape. My test lasted about
a day and a half once the testing leaks were resolved and I observed the water level go up and down
past my reference mark by several inches as the weather system and thus pressure changed. When I
declared victory the levels were within less than a 1/10 of each other and higher than the original
reference mark (slightly lower outside pressure than when I started the test).

• Top half of the leak test setup I used
• Bottom half of the leak test setup
• Covered the filler cap with aluminum tape and then clear packing tape
• Pressurized both tanks such that the difference in water level was 27 inches and marked the
  levels with tape

The Finished Tanks

After all the work these tanks involved I was about to just put them away, but decided to clean them
up and cap the holes to keep the creepy crawlers out over the next many (too many) years.

• Top surface and filler cap end
• Top surface and inboard end
• Bottom surface
• Aft surface where it mounts to the spar

Nothing in this tank process was overly difficult, it was just very time consuming the way I did it, but it
seems to have worked.

[bruceh]

I'm right in the middle of doing the tanks on my 9A. This post with pictures has been a HUGE help and inspiration.
Yesterday I got the cap, drain and stiffeners riveted in after fay sealing them the day before. The back riveting didn't go so well. It was hard to get the rivets to set straight. I ended up drilling out a bunch. It took awhile to get the air pressure set correctly and my technique figured out for dealing with the slippery goo. Even using a pneumatic squeezer on the rivets I could reach was challenging with the sealant on there.