In preparation for closing the fuel tanks this weekend, Jenn gave me a hand with the six universal rivets holding the fuel tank attach bracket on.  For never having shot rivets before, she did a great job.  Afterward, I installed the remaining flop tube and put sealant over everything.

I got up early this morning before the kids were up to work on the plane a little.  It wasn’t enough time to get started on the fuel tanks, so I decided to fabricate these splice plates instead.  These will get riveted to the outboard leading edge wing skins and provide additional nutplates for the fuel tank to attach to.

Here is a closeup of one of the nutplates.  The skin is dimpled here to accept the fuel tank dimples and #8 flush screws.

I didn’t get any pictures of how the sealant is applied, but I just followed Van’s instructions.  I applied a <3/16″ bead just ahead of the skin to baffle rivets (where the long row of silver clecos are below) as well as sealant around each of the rib to baffle rivets and along the outer ribs.  Next, I dropped the baffle into place and clecoed every skin to baffle hole to ensure a tight fit (I’m really glad I have the pneumatic cleco gun).

Next, the upper and lower rib to baffle holes are pop riveted.

Then the z-brackets are pop riveted on.  Double check the orientation of each of these brackets because it varies and it would be really hard to change once they’re riveted on.  Just like other builders, I had to grind the nose of my crappy Harbor Freight pop rivet gun down to get to these pop rivets.

At the top of this picture, you can see the bead of sealant that gets formed when the baffle gets pushed into position.  I’m really glad I purchased a Semco sealant gun now.  It made it trivial to get a nice bead on the skin.

I came out into the garage a little later in the evening.  It was too late to get started sealing the other tank, so I took down one of the outboard leading edge skins and deburred it.  After finishing the tanks, these will be the next pieces to get riveted.

I deburred and dimpled the leading edge skin and ribs tonight (though you can’t tell that from this picture).

I only had a short time to work on the plane tonight, but I got the skin and ribs for the left wing’s outboard leading edge components dimpled.  The undimpled holes at the top edge of this skin are for attaching the wing tips.

I sealed the right fuel tank tonight.  I didn’t take any pictures, but it would look pretty much exactly like the pictures from the left tank that I closed a few days ago.  I’m going to give everything at least a week to cure before leak testing the tank.  In the meantime, I can go ahead and get the outboard leading edges riveted and installed.

I spent a few hours tonight deburring and dimpling the remaining components for the outboard leading edge sections of the wings.  These ribs are ready to be primed.

These wing skins are ready to rivet; hopefully, I can get these both done tomorrow.

My buddy Andre stopped by today and helped me rivet the outboard wing leading edges together.  Here, we’re riveting the inboard rib which includes an extra strip of aluminum with nutplates to hold on the tank.  The plans called for AN426AD3-4 rivets, but -4.5 worked better.

Here’s the completed left leading edge.

…and completed right leading edge.  I’m really enjoying getting back to basic aluminum work (without having to mess with tank sealant).  It’s nice how much faster structures like this go together.

I installed the outboard leading edges and the tanks to evaluate the joint between the two.  First the good news: the gap between the two is virtually nonexistent and the leading edges align perfectly.

Now the bad news.  Like many people have encountered, the flushness of the two skins is rather poor.  I need to probably shim the outboard skins out a bit to bring them flush with the tanks.  The worst is about 0.042″, but there are several places that are over 0.020″.

I started countersinking the spars for the rivets that will hold on the skins.  First up is to rivet the ribs to the spars using the forward holes in the tank attach section.  You can see one rivet set just above the cleco to the left and another countersink to the right that is ready to receive a rivet.  The plans don’t mention anything about these holes, but the tank will cover up this area, so it only makes sense to rivet these.

Here you can see all of the holes that must be countersunk along one side of one of the spars.  There are over 600 holes to countersink on both sides of both spars.  I’ll shoot some primer on these before riveting everything together.

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It’s been a week and a half or so since I finished sealing the last tank, so I thought now would be a good time to leak test the tanks.  I put some packing tape over the filler hole, put some caps over the return line and fuel pick up lines, and made a little elbow out of some 1/4″ soft aluminum tubing and attached it to the vent port along with some 1/4″ ID vinyl tubing to make a simple water manometer.

The fuel drain gets a special plug with a Schrader valve so that air can be pumped in with a bike pump.

After making sure everything was torqued down and sealed properly, I put in some water in the tube and pumped the tank up to just under 1 psi.  1 psi is about 27″ of water, so I pumped it up to about 24″.  Of course, as you pump air in such that the water rises in one part of the tube, it falls in the other part, so you only need to get a rise of about 12″ to create a 24″ water column.  Here you can see that I’ve made a mark on the tube right at the level of the water.

I’ve also grabbed our digital thermometer to get an accurate temperature reading in the garage since the pressure in the tank will vary with temperature.  The temperature at the start of the test was actually 82.9º, but I didn’t grab the camera until a few minutes later.

As the garage started to warm up in the afternoon, the water started to rise which is a good sign that the tank is not leaking.

Later this evening, I came out to the garage to see how the tank was holding up.  The water level is down about 3.38″ (6.76″ lower water column).  Running a quick pV=nRT calculation shows that this would be the correct water level for an 8.24º temperature drop.

An 8.24º temperature drop from the starting temperature of 82.9º would be 74.66º.  Given that a final temperature of 74.4º (shown below) would actually have made the water fall even further, I think we can safely conclude that the tank is leak free!  I didn’t actually expect it to even be this close since the temperature inside the tank wouldn’t precisely track the temperature outside the tank if it were changing very rapidly.

The test is running on the right tank now and it’s looking good so far, but it’s only been about 45 minutes so I’m not ready to claim it’s leak free.  I’ll check tomorrow morning and see how it held up overnight.