Right Fuel Tank - Plumbing

I worked on the plumbing and access plates today.  Everything is done except for sealing the access cover.

Right Fuel Tank - Leading Edge Rivets

I still had maybe 9 or 10 remaining rivets to do in the very leading edge of the tank.  The awkward angle of bucking and using the gun when the tank was in the vertical position meant that I bent over the shop heads more often than not, which is why I got help on the previous tank.  I'm impatient though, so instead of waiting for help, I figured I'd give it another shot myself.  This time I took the tank out of the jig and tried riveting with it just laying flat on the table.  This allowed me to hold the rivet gun much more normally.  Reaching around and into the nose with my bucking hand was just on the edge of physical limits, but in the end it actually worked out great.  I was able to finish up all of the rivets just fine.  I wish I had tried this approach on the last tank!  Oh well, next plane I guess.  Tomorrow I will seal all of the rivet heads and should be able to get all of the plumbing finished up.

Right Fuel Tank - Sealing (4)

I riveted the two ribs I had prosealed yesterday then did the inboard and outboard ribs.

I had a senior moment and put the rivets in backwards for the nose doubler and the patch that seals up the tooling hole.  Well, there really is no backwards, except that I would generally put the shop head on the inside where it is hidden.  I wasn't thinking and put the shop heads on the outside of the rib.  They'll never be seen unless the tank has to be removed from the wing of course.  Next up is the plumbing and baffle, and then the tanks will both be done!  

Right Fuel Tank - Sealing (3)

Nothing too exciting to show, but I got two more ribs gooped up and clecoed in.  For a split second I thought about going ahead and riveting them with the proseal wet, then I came to my senses.  I'll wait until tomorrow!

Right Fuel Tank - Sealing (2)

This afternoon I riveted the three ribs that I prosealed last night.  All in all it went pretty well.  I'm done with these ribs except for the couple of rivets along the very nose of the tank.  I attempted to do those by myself, but just like on the other tank, the rivets came out pretty bad because of the awkward angle required.  I'll get some help doing these.

Fuel tanks - Leak Testing & More Sealing

Time to see if all of the work has paid off.  After a few false starts due to caps that weren't quite tight enough and were leaking, I got things sorted out and started the leak test on the left tank.  All this involves is putting a schrader valve in the drain opening, capping the fuel pickup fitting, and putting a balloon on the vent line.  It only takes 1-2 psi to do the check, so just enough to blow up the balloon a little bit is all that is needed.

One thing that Van's calls out is the need to cover the filler cap with tape, since it's not perfectly air tight.  Laughably, this turned out to be the hardest part of the whole process.  I tried packing tape, but no matter what I did, I couldn't keep it from leaking (sprayed it with soapy water to test).

I finally switched over to heavy duty Gorilla tape.  That seems to be working, but we'll see what things look like in the morning.  The only problem with the balloon test is that it'll inflate and deflate depending on temperature.  I did spray the entire tank down with soapy water and didn't see any leaks beyond the filler cap, but if tomorrow the balloon is deflated and I can't tell if it's because of temperature or a leak, I may switch to using a water manometer instead.  At least with that you can mark the water level at a specific temperature and then wait as long as you need to for that temperature to be hit again to recheck the level.  Given what I've seen so far, I'm cautiously optimistic.  I think may actually have a leak free tank.

I went ahead and got started on the ribs of the right tank.  It's amazing how much faster things go the second time around.  I prosealed and clecoed 3 ribs.  I'll shoot the rivets tomorrow night.

Right Fuel Tank - Sealing Begins

Here we go again!  Same story, different tank - scuff, clean, and start with the goop.  Having one tank under my belt (although not leak tested yet) definitely made this go faster.  I back riveted the stiffeners and fuel tank filler flange and squeezed the rivets on the drain. 

The fuel filler was the last piece I riveted on, and of course I only had enough proseal left to do half of it.  So I mixed up a small batch that turned out not to be so small.  This is what the sealing looks like when you have leftover proseal.  I figure it doesn't seal much sitting in the trash, so why not make use of it.  Not like adding extra on the fuel filler should matter much.  If you have a leak here, you might be putting in a tad much fuel!

A lot of proseal on the inside, but nice and clean on the outside.

Left Fuel Tank - Done?

I bit the bullet and decided today was the day to fully seal the left tank!  I went through the normal motions of ensuring mating surfaces were scuffed and cleaned, then just to make cleanup easier, I taped off the skins just above where the baffle will set.  I've seen two methods of sealing the baffle - the Orndorff method that lays down proseal along the entire width of where the baffle flange will go, and the Van's method of only putting a bead down just inside the rivet holes.  I get why Van's does it the way they do, but given that the rear baffle is the most common source of leaks, I kind of wanted to err on the side of more surface area than less.  Maybe for the next tank I'll do it differently, but for this one I put proseal over the entire surface that the baffle flange will rest against.

Once proseal was in place on the skins, outside ribs, and around the outside rivet holes of each rear rib flange, I set the baffle in place and went to town with clecos.  This is where using a full width of proseal gets pretty nasty.  If you do the Van's method and just place it inside of the rivet line, when you push the baffle into place, it moves the proseal away from the rivet holes and makes a nice clean way to rivet.  By putting proseal on the entire surface, a good bit of proseal gets pushed out through the rivet holes.  All of that has to be cleaned up, otherwise the rivets will set proud in the countersinks.  I used strips of paper (like in the Van's video) to scoop out the majority of the proseal from the holes, then learned that a quick spin with a Q-tip (even after it gets covered in proseal) is enough to clean out the countersink to where the proseal doesn't affect the rivets.

Thankfully, all of these skin/baffle rivets can be squeezed, which makes it go very quickly.  To lock in the baffle, first I put the solid core pop rivets in the outside holes of each rib/baffle.  With those done, I moved to squeezing the skin/baffle rivets.  That's a lot of rivets!  The top side went just fine, but for some reason the baffle was ever so slightly off on the bottom side.  I had to put a punch into almost every hole to pull the baffle down a tiny bit.  I suppose that could easily just be due to proseal buildup, even if it's super thin.

The Z brackets were next.  I put a very thin layer of proseal on the bottom side (just enough to cover - I'm guessing 1/32" thick) and pop riveted them into place.  The inboard and outboard brackets get regular rivets.

The last piece to go on was the access panel.  I took one last look at it to hopefully catch anything stupid I'd done, slathered it up with proseal, and put it into place.  In hindsight, I used way more proseal than I needed to.  I basically put enough proseal on the ring to span the entire contact area of the rib.  In reality, the only thing I need to do was put a bead around the outside portion, just beyond the screws, since based on where the nutplate rivets are, that would be enough to stop all leak paths.  It doesn't really matter, other than this access panel will be a lot harder to remove if the need every arises.  The final sealing is just a matter of dipping the screws in proseal and tightening them down until a nice ring of sealant squeezes out under the screw head as well as around the access plate.

I didn't get a picture of it before I closed everything up, but a quick peak inside looked pretty good.  Most of the areas of the baffle I could see had a nice bead of sealant that had been pushed in place as the baffle was seated.  The only area that I think is just a tiny bit iffy is on the outboard rib flange to baffle joint.  There's definitely sealant there, but not as much as in other areas.  The good news is that if that ends up being a leak path, it would be pretty easy to fix since I could just reach in through the fuel filler opening and spread proseal onto the rib from the inside.  Hopefully not a problem, but nice to know it's not terrible if it is.  I'll use a little more proseal in that area on the right tank.

So that's it for the left tank!  Now it needs to sit for a few days to let the proseal cure.  It's going to be a little cool for the next few days, so I'll probably give it until mid-week before I leak test it.  I'll use Van's leak kit (just a balloon and a few caps over the fittings, then a bicycle pump to put a whopping 1 psi into the tank, followed by a soapy water spritz).  I need to order some fuel friendly lube (EZ-Lube from Aircraft Spruce) for the fuel drain valve, so I won't put that it quite yet.

Left Fuel Tank - Plumbing (2)

I got to wade around in proseal today!  That's always a good time.  To kick things off, I cut and bent the fuel float sender wire and got it as close to "good" as I could (probably need to play around with it a bit yet though).  The float is supposed to lie within 1/8" of the top and bottom skins as it moves back and forth, but because of the curve of the top skin, if I get it within 1/8" on the bottom, then the angle of it as it's in the full position puts part of it at almost 1/2" from the skin (the other end of the float still almost touches).  I'm not sure if that's a big deal or not, considering I'd rather it be super accurate towards empty than at full.  I'll always use a dipstick anyway, and I'll also be putting a fuel totalizer in, so the float senders aren't the only game in town.  I'll look at it with fresh eyes another time.  I retested the sender across the entire range from full to empty to make sure the resistance readings were correct.

Then I started with a bunch of proseal.  I cleaned and scuffed all of the parts up and started with the fittings on the inboard rib and access plate.  I didn't get many pictures of the process, since once the proseal comes out I don't really want to be messing with my phone.  With the 90 degree fuel pickup fitting and straight vent fitting in, then I moved to the inside portions and installed the pickup tube itself and hooked the vent line up.  Lastly, I installed the fuel sender body in the access plate.  It just gets a ring of proseal as a gasket, and the screws just push through the sealant and gush out to create a barrier of proseal as well.  The instructions call out that one screw needs to seat metal to metal though, so I kept one clean.  I'm not really sure why that is the case, since there's nothing about it that would ground it or complete any kind of circuit.  I'll have to reread that section and see if I can figure out why.  It's possible that they just meant that the center screw has to stay clean.

I probably didn't need to proseal over the nutplates on the fuel sender attachment, but I had a bunch left over, so figured I may as well.  Based on the leak path, I don't know that I would otherwise do it if I didn't have proseal that would be wasted.  I globbed proseal on fittings for the same reason.  If all goes well, once I close the tank up, nobody will ever see the inside again anyway!  Next up will be checking things over one last time and putting the baffle on!

One thing that I noticed while looking at my right tank skin is the fact that there are a number of holes that ended up kind of oblong.  That was the first tank I drilled and was before I had figured out the secret behind getting the ribs in place. I think a lot of the ribs were under major tension and the clecos probably went in at an angle.  Since the rib material is way stiffer than the skins, the rib holes dictated where the drill went.  That meant the ribs turned out just fine, but the skin holes sometimes got elongated as the drill angled to find the rib hole.  Most of the holes are fine, and for the few that are sprinkled around the tank, I can just use the "oops" rivets to upsize the holes.  However, for whatever reason, both end rib locations were worse than anywhere else.  It's totally fine to use oops rivets, but not too many in one place.  So instead of going overboard on the end ribs, I decided to just up the size of rivets to 4-4 instead of the 3's.  I re-drilled all of the end rib holes to 1/8" and re-dimpled to #40.  It's probably overkill to do that many, but I figured it would look better to have a whole row of the larger rivet heads vs random ones.  Not that it'll be noticeable anyway,  but I'd know!

Left Fuel Tank - Plumbing

Today I got a lot of "education" done, but not much actual work.  I got my flaring tool the other day, so figured I'd hammer out the tank plumbing today and be ready to seal the left tank in the next day or two.  Instead, I spent a few hours dialing in the flaring tool and a few hours researching torque ranges for fittings (it took hours because no reference seems to agree with the others).

The Rigid flaring tool works great, although I did have to modify how it is supposed to be used because of how soft the aluminum tubing is.  The aluminum tubing Van's supplies is 3003 aluminum, which is very soft, at least relative to something like 5052, which is more commonly used in aircraft.  For something as ho hum as a fuel vent line that will see no pressure or stress, the 3003 is actually nice though, because it's easily bent and worked through the ribs of the tank.  The gotcha is that it's really easy to over flare using the Rigid tool.  The tool has a clutch built it that is disengages the pressure at the "correct" amount of flare.  I'm sure it works great for stainless steel or copper, but it's too aggressive for the 3003.  It took me a lot of playing around to figure out just how many turns of the handle made the perfect flare (4.25).  This was a couple of turns before the clutch would have normally released.  After a bunch of experimenting, I was able to get pretty consistent flares though.  Like anything, prep was key - cut the tubing, square it off with a file or on the sander (the tubing cutter has an angle to the cut), deburr, then lubricate with oil/Boelubeto help the flare die move smoothly.

I found someone had posted a nice chart on VAF to show what the flare diameter should be based on tubing size.

Once I had flaring figured out, I flared the end of the roll of aluminum tubing that comes in the kit and then started figuring out how much to cut off for the vent line.  In the end I had to insert then pull the tube out 3 or 4 times and cut off more and more until I got it right.  The only reason it was a little iffy and not a straight forward measurement was because of the angles that are required in the inboard bay where it attaches to the bulkhead union fitting.

I was hoping to get all of the fittings prosealed in place today, but figuring out what the appropriate torque settings are for all of these different size nuts and fittings took hours of research.  My aircraft maintenance book talks about torque settings, but not specifically enough for these aluminum fittings.  At this point I have enough information on torque ranges that I can move forward at least, but doing the research really blew most of the day.  When I was ready to actually put my research into action, I had a "well duh" moment - I need a crowfoot wrench in order to be able to use my torque wrench here.  So yet another pause until I get the tools I need.  I'm getting there though!  It was actually a lot of fun figuring it all out, but it's still a bit maddening how long the head scratching takes relative to actual building.  Fingers crossed I can remember all of my lessons learned on this take and the next one is faster.

The picture below is just the vent line setting in place - nothing attached yet.