7.7.47 – 54 Closing the left fuel tank

Well the big day has arrived. I’ve put it off long enough and I think I’ve prepped all I can. One of things I did to prepare was read as many blogs as possible and read the Van’s instructions repeatedly.

Once I think I understood it all sufficiently I made a step by step list that was easy to read during the work.


My Dad came to help so I ran through all the steps one by one with him just so we were both clear. It also helped make sure I had everything lined up and ready. After that I mixed a Semco cartridge of sealant by hand as per their YouTube video. It took 60 strokes to get it all mixed! Once mixed I fitted the nozzle and trimmed the nozzle until I got it to match my 3/16 lines drawn on the pad.

Once my gun and eye were calibrated it was time to run sealant just in front the rivet holes.

I did the same on the end ribs and dabbed sealant around each of the rivet holes of the inner ribs.

After triple checking the sealant it was time to drop the baffle straight down onto the bed of sealant.

Then we immediately fitted the clecos in every hole of the tank skin as per the instructions. We also clecod the centre three rivet holes in the ribs to help square everything up.

Once everything was clecod in place we riveted every skin hole using the hand squeezer.

Next we blind riveted the inner ribs top and bottom holes with AD-41H rivets twirled in tank sealant.

Next we put some sealant on the face side of the z-brackets. The plans say to dab only the rivet holes but I decided to do the entire face for corrosion protection mainly. It was a very thin smear.

Once all the z-brackets were clecod we used the modified pop rivet tool to set all the blind rivets with AD-42H blind rivets. Once they were done we then had to rivet the outboard brackets. The outer 4 AN470AD4-4 rivets on each bracket could be done with the hand squeezer. Unfortunately the inner 4-5 rivets has to be set with the rivet gun which meant quickly firing up the compressor and rivet gun tools. It’s ok I just wasn’t prepared for that.

Once they were bucked I cleaned up the sealant in the outside corners and dabbed sealant on top of each blind rivet head. That was it, after a big cleanup the left fuel tank is finally closed. Looking inside and the sealant seems to have behaved as expected. Not such a bad bead there.

While the sealant cures I decided to leave the tank stood on its brackets. I don’t know if this will help the sealant leach into the joints better or not but it can’t hurt to try!

That’s it for the left tank! It’s pretty much ready to leak test. Yes, I know the access panel is off. I won’t seal that on until I’ve tested the tank. Just in case!

And the best bit? We get to do this all over again on the right tank! 😂

7.7.46 Clean & check left fuel tank

Just a quick session today cleaning any left over tank sealant from the back of the rib flanges. I don’t want anything that can interfere with the seating of the baffle.

Once that was done I gave the tank a good clean out with the vacuum cleaner.

That’s it for today.

7.7.46 Inspector passes tanks and leading edges

Before work this morning I checked the right tank for leaks, particularly the BNC connector. Great news, no leaks so I drained the tank of all water and left it to dry for the impending inspectors visit.

I also gave the workshop a thorough clean! I can’t believe how grubby it had gotten.

Later in the afternoon my inspector arrived and inspected both fuel tanks and leading edge assemblies. He gave me a few great tips and was happy for me to carry on to the next stage. Yay!

After that I JC5A’d and fitted the left leading edge to the main wing spar ready for riveting.

I ran out of time today to actually rivet the leading edge so I will do that another day. That’s enough for today.

7.7.46 & 53 Tank leak found and z-brackets prepared

I was very anxious walking up to the workshop today. Does the left tank leak like the right tank does or not?

I took a really good look around the tank and especially inside the BNC connector. Great news, no leak yay!!!

So, using my drill pump, I drained the tank of all water and set it aside upside down to dry.

Next, I carefully read and reread the instructions for closing the tanks in every detail. The instructions give a good overview but it definitely pays to read ahead. For example it says to check the z-brackets have nutplates attached but doesn’t say that they have to be debured and scuffed for a good bond. This is not what you want to be doing during the 2 hour sealant workability window! Currently the z-brackets look like this.

That’s no good for final fitting But after a quick wipe with MEK, debur both sides of the top flange and a scuff with maroon scotchbrite they now look like this.

Much better for fitting. Also the instructions go on to say that I may need to adjust the rivet puller tool so I thought I would check now. Again I don’t want to be doing this once the sealant is laid. Yep, it definitely needs grinding down to fit in the small gap.

Once ground I thought I would test it. I really don’t want anything to surprise me while I’m closing the tank. Good job I did test it as it didn’t work!!! After some head scratching I took the tool apart and found the grip head mechanism inside the pulled had melted due to the heat of the grinding. Doh!!!

Luckily this is a cheap budget puller and amazon can deliver me a replacement next day. I’ll just swap the grip head when the replacement arrives.

Finally it was time to investigate the leak on the right tank. Remember that it was leaking through the BNC connector? I used my dentist mirror to very closely inspect the connector and sealant around it and I found this…

Look in the top left of the mirror and you can see the back side of the BNC plug is missing some sealant. Hopefully that’s it! So I mixed up 15g of sealant and very liberally applied it around the connector and wire. I also topped up the other connectors in the tank just in case.

Finally, a big tidy up again and that’s that for today. Now I’m off to research other builders logs for any tips on closing the fuel tanks.

7.7.46 Empty right tank and retest left tank

I rechecked the right fuel tank and the good news is that it is ONLY leaking from the BNC connector, the rest of the tank outer skin was bone dry after 24 hours full of water. I did some brief research on this and it seems to be a common issue with BNC connectors. I had hoped using top branded Amphenol connectors would prevent this issue but it seems not.

So, how to fix it? I drained the tank down completely and have left it upside down to dry thoroughly. Once it is dry dry I will reinspect the sealant around the connector. One forum I read suggested it might even be flowing from the other end of the wire in the tank. This is known as wicking. I can’t quite believe fluid could flow all that way but I will check the sealant at all the connections inside the tank as well as at the BNC itself.

Given my now detailed knowledge of water testing the fuel tanks I decided to retest the left tank. So I quickly filled the tank with tap water, dried all areas including the tank attach bracket and left a tissue under the BNC connector to capture any leaks.

That’s it for now. I’ll leave the right tank to dry and leave the left tank full of water. I’m going to hold my breath for 24 hours in the hope that the left tank won’t leak!

7.7.46 Water test results and leak found

So the right tank has been full of tap water for exactly 24 hours and it’s time to inspect the tank for leaks.

On first look the tank is still full of water which is a great start. Looking closely all around the tank and I spot a heart sinking sight. There is a pool of water at the bottom of the tank attach bracket point…

And a small pool of water inside the BNC connector…

Now, what I don’t know is, did I cause the pool of water at the tank attach bracket by over filling the tank yesterday or was that water spilled by filling the tank. It could even be water that has seeped from the BNC connector and collected there.

The only way to find out is to reduce the water level by a few millimetres so it can’t overflow, put some tissue under the BNC connector to collect the weep and rerun the test. This will tell me if there is a leak at the bracket.

However, the BNC connector is definitely leaking. I’m not sure yet how I’m going to fix this. I think I will try to find out how it’s leaking first and then try and fix it, probably with copious amounts of tank sealant!

7.7.46 Water test the right fuel tank

A quick thought occurred to me earlier, my inspection is imminent but I haven’t checked my right tank using the water test. So a quick dart up to the workshop and I put the right tank in the cradle then filled it with water.

The last time I tested the capacitive plates while emptying them, this time I thought I’d test them while I was filling them…

Once the tank was as full of water as I dare do I then made a mental note of the settled water level and checked for obvious and chatastriphic leaks. Nothing glaring so I let it settle for a few minutes more.

After a few minutes I felt all around the tank for any signs of water. None so far. I also carefully inspected inside looking for the tiniest of air bubbles. There were a handful but they all seemed static. If there was a leak I would expect more bubbles or expanding bubbles. Again nothing obvious.

OK, that’s it for today. I’ll leave the tank overnight and check the water level tomorrow. If the level is the same as I left it we’re good to go closing the tank. If not at least I’ll know where a leak is before closing the tank permanently.

7.7.46 Final checks of left & right tank before closing

After many, many, many hours working on the fuel tanks I think I can finally say they are ready for inspection. Tonight I rechecked everything I could think of on the tanks. I can’t see anything obvious that needs doing. I’ve checked the aerobatic flap door, the flop tube, the anti-hangup brackets, the electricals and the caps. All looks good to me.

I need to wait for the right tank sealant to set for a few days and then water test that tank like I did the left one.


7.7.42 – 45 Fit right capacitive plates, pickup tube & prepare baffles

Tonight I got to do the fun bit, fitting the capacitive fuel sender plates and pick up tube. With the experience of the left tank, fitting the right plates was a non-event really.

Once they were fitted I tested them for continuity with the test meter and made sure that they did not short with the fuel tank any where. They didn’t.

Next job was to fit the inspection plate and screw it in place. Once that was done I then spent the rest of the time deburing, scuffing and cleaning the baffles ready for fitting. I left the tanks upright so that any sealant that was still setting would be assisted by gravity.

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