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Old 04-12-2016, 08:35 AM
jeffw@sc47's Avatar
jeffw@sc47 jeffw@sc47 is offline
Join Date: Aug 2014
Location: Simpsonville, SC (SC47)
Posts: 408
Default Tip: My journey into fuel tank assembly

After studying and discussing the fuel tank assembly methodology options and getting past the reluctance to get started, I began with the ProSeal.

Method (Wet or Dry): I opted for the WET faying surfaces, and WET rivet set, one rib at a time.

Used the larger tank dimple dies on the skins and the sub-structure dimple dies on the tank ribs.

Set up tank cradle to raise tank about 8” above cradle base and tilted towards the bottom skin side about 10 degrees, this helped in setting wing leading edge top-side first couple of rivets that would otherwise be in awkward position for rivet gun and holding bucking bar (rectangular tungsten bar).

Fabricated a ¼” plywood spreader rib, with reliefs to span over the stiffeners, to spread the skin surfaces apart a bit to ease installation of rib with ProSeal spread on rib flanges. The line along the edge of the spreader rib is the outline of a tank rib (not a perfect representation), there is about 1/4" total added to the rib width for the width of the spreader at the trailing edge and it tapers down to zero at the leading edge. Start with the spreader outline a hair large and test it and adjust to where you feel comfortable with the amount of spread.

To stiffen fuel tank ribs for installation into tank, because they are a bit floppy, I fabricated two 3/8” plywood stiffener strips with through bolts and wing nuts placed through the rib lightening holes. I found that these stiffeners strips made handling the rib a little easier while applying ProSeal to the rib flanges and made setting the rib into the tank immensely easier. After the rib is clecoed in, the strips can be removed

When inserting the rib into the tank, with the stiffeners strips on the rib and the plywood spreader rib between the rib being installed and the next outboard rib, it is easy to keep the rib aligned with the skin rivet holes and to set the rib almost all the way into the leading edge of the tank. I then tapped lightly on the rear baffle flange bend of the rib with a dead-blow shot-filled plastic hammer, the rib set into the tank so that the trailing edge rib flange rivet holes top side and bottom side aligned to within a 1/32” of their corresponding dimpled skin rivet holes. It was easy then to insert a cleco into the two trailing edge rivet holes, and then alternating top to bottom skin insert all the clecos down to the leading edge rivet holes. Trying to start the clecos from the leading edge was much harder to get them started.

Applied ProSeal on faying surfaces of rib and surface of skin so there was a modest amount of PS squeezed out around flange edges. Mixed about 35g of PS to do one rib and skin faying surfaces, providing enough extra to set all rivets of a rib with about 3-4g left over. I was able to adjust down to 32g of mix. Good point Jerry F, I applied the PS to the rib flanges with the side of a popsicle stick first and then to the skin rivet line, then spreading the rivet line PS with a trimmed acid brush. A little less PS on the rivet line than the rib flange. I trim off the rounded end of the popsicle stick with the clippers of a large pliers so that the end is cut at about a 20 degree cutoff.

Ran a strip of clear packaging tape along outside surface of skin, inserted clecos through tape, skin and into rib; rolled tape up on itself as I set rivets. Started riveting at the leading edge, removed two clecos above each rivet being set, this gives good clearance for mushroom rivet set. Started at wing leading edge, alternating one rivet at a time for the first 4 or 5 rivets each side (top and bottom), then set two rivets one side then alternate side (cuts down on time spent moving from side to side. Also placed a 12” long piece of cardboard box material curved into the leading edge on both sides of rib to protect the skin in case I dropped the bucking bar.

I used a Q-Tip to fill rivet dimple; the mix cup held to work table surface with Velcro pad strip under cup (holds ProSeal cup down while pulling away Q-tip from the sticky stuff), a one-hand operation vs. holding the cup with other hand.

Only cleaned the bucking bar and the 1 7/8” diameter mushroom rivet set three or four times while doing one rib; small buildup of ProSeal residue on rivet set and bar not a problem.

Waited about 30 minutes after finishing riveting before wiping skin at rivet manufacture heads with acetone, and smoothing rib flange fillets with soapy watered finger.

Waited a day to cap rivet shop heads and add filet bead where needed along rib edges to previous installed rib, then installed next rib through to finishing riveting that rib and clean up again.

Capped each rivet shop head with small amount of ‘B’ type ProSeal, then when all the ribs are installed will cap each rivet and apply good fillets with an application of ‘A’ type ProSeal.

After three rib installs, a single person team, from start - one rib’s faying surfaces/rivets, a ProSeal mix of 35g total mix weight - to finish setting one rib’s rivets and then cleaning up the clecos > right at 2 hours (capping rivets and adding filleting is extra). Finally around 25g PS for one rib's faying surface, skin faying surface, skin rivet dimple seat, and thin spread of PS on shop heads and fillet edges. First full rib was 2 hours 30 minutes; second was 2 hours 15 minutes; third rib 2 hours 5 minutes. Then the rhythm set in at 2 hours per rib. Finally by the last two ribs, 1 hour 15 minutes for typical rib and the outboard rib 1 our 25 minutes (more rivets).

So much has been published about assembling the tanks and using ProSeal that it gave me too much to consider and there is an equal amount of opinions across the spectrum. ProSealing and riveting-in the fuel tank ribs is not nearly as bad or as difficult as I was imagining it was going to be. What happened with me was that it caused me to procrastinate too long with starting this task. The best part about this set of steps in the build process is that when it is done it feels like you’ve reached a significant plateau in the project and you’re so much closer to completion.
Jeff Warren
Simpsonville, SC (@SC47 > 10nm NW Triple Tree)
RV14A (N14ZT), Ser#140195
Start 10/11/14; AWC Rcvd 7/21/21
Contribution made 12/2/20 (USArmy 2/67-2/70)

Last edited by jeffw@sc47 : 05-07-2016 at 09:11 PM. Reason: a little clarification
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Old 04-12-2016, 09:01 AM
wirejock's Avatar
wirejock wirejock is offline
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 4,755
Default Tank instructions

Nice write up.
Save a tracing of that spreader rib. I'm sure other builders will be asking for it. That's a great tip.
Larry Larson
Estes Park, CO
wirejock at yahoo dot com
Donated 01/01/2021, plus a little extra.
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Old 04-13-2016, 07:17 AM
Jerry Fischer's Avatar
Jerry Fischer Jerry Fischer is offline
Join Date: May 2007
Location: Winder Ga
Posts: 934
Default Nice work Jeff

While building tanks for RV's, I found some easier methods for starting pro-seal on inner most ribs first as I do it solo. My secret is painting the thinned sealant on the rivet lines for the rib & the skin with an acid brush. Then painting sealant on the shop heads and seams of the ribs after riveting. Seems to work very well. RV9 tanks are the most difficult due to the shorter ribs and tighter curves of the nose. I also specify the 2 hour sealant as it has a longer working time when ordering. Believe it or not, I enjoy building tanks for RV's
Jerry Fischer KW4F
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Old 04-13-2016, 11:44 AM
sblack sblack is offline
Join Date: Dec 2009
Location: Montreal
Posts: 1,520

thank you for posting this. I need to build a tank in the next few weeks.
Scott Black
Old school simple VFR RV 4, O-320, wood prop, MGL iEfis Lite
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Old 04-13-2016, 02:40 PM
jeffw@sc47's Avatar
jeffw@sc47 jeffw@sc47 is offline
Join Date: Aug 2014
Location: Simpsonville, SC (SC47)
Posts: 408

Originally Posted by Jerry Fischer View Post
. . . My secret is painting the thinned sealant on the rivet lines for the rib & the skin with an acid brush. . . .
How much do you thin the ProSeal and what do you use as a thinner? And, after applying a thinned PS layer on the ribs and skin, do you add any full bodied PS on either surface prior to riveting?
Jeff Warren
Simpsonville, SC (@SC47 > 10nm NW Triple Tree)
RV14A (N14ZT), Ser#140195
Start 10/11/14; AWC Rcvd 7/21/21
Contribution made 12/2/20 (USArmy 2/67-2/70)
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Old 04-14-2016, 08:10 AM
longranger's Avatar
longranger longranger is offline
Join Date: Mar 2007
Location: 45G, Brighton, MI
Posts: 1,921

I applied UNthinned sealant with an acid brush trimmed to 1/4 inch or less for stiffness. Worked fine.
Miles (VAF# 1238, Paid up as of 12/20)
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Old 04-14-2016, 01:06 PM
jeffw@sc47's Avatar
jeffw@sc47 jeffw@sc47 is offline
Join Date: Aug 2014
Location: Simpsonville, SC (SC47)
Posts: 408
Default Few more journey notes

About the clear shipping tape over the skin dimples >
Make sure you remember to start rolling up the tape as you start to rivet, it is easy to forget until you might have more than a few rivets set and they would be through the tape.

About inserting a rivet through the skin into the rib flange >
Do not force the rivet if it doesn't slip right through. It is possible that you can push the flange a little away from the inside of the skin which doesn't make the best arrangement for setting the rivet. After I have all the clecos inserted I tap a few more times with the plastic hammer at the trailing edge end of the rib to set the rib in as far as it will go.

I have been drift aligning the first 5 or 6 rivet holes on both top and bottom skin surfaces starting at the leading edge before trying to insert rivets in those holes. I apply the PS into the dimple after I drift the hole. As I get farther towards the trailing edge the rivets generally slide in without drift aligning. The ones that do not slide right through the rib flange I drift with a small point diameter nail set, then they go right in. The nail set is tapered which works better than a nail to drift the two parts into alignment.
Jeff Warren
Simpsonville, SC (@SC47 > 10nm NW Triple Tree)
RV14A (N14ZT), Ser#140195
Start 10/11/14; AWC Rcvd 7/21/21
Contribution made 12/2/20 (USArmy 2/67-2/70)
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