Attaching The Fuel Filler Flange

Tonight I was going to fly to the local EAA Chapter 80 meeting in Omaha, but I got a wild hair to knock out another session with tank sealant.  Since when is sealing fuel tanks more fun that going flying and talking about airplanes????  I must be breathing to many MEK vapors.

Now that I have my fuel pick-up fitting and anti-rotation bracket mounted to the inspection cover, I installed my newly fabricated fuel pick-up tube.  It fit better than Van's original pick-up tube, BUT....  I still am not super happy with the clearance between the tubing and the nutplate.  They don't touch each other, but that can't be more than the thickness of a couple of sheets of paper between the two.


I think that I am going to fabricate yet another fuel pick-up tube.  As you can see there is plenty of clearance between the stiffener and the tubing, but I had to work hard to see that the tubing and the nutplate don't touch.


Otherwise, I am really happy with how the fuel pick-up sits in the fuel tank.


The fuel pick-up sits nicely along the end rib and clear of the tank drain.  I guess this is a good example of why it is a good idea to sump your tank before flight.  If there is any water in the tank, the fuel pick-up sits very near what would be the lowest point in the tank when on the ground.

Anyway, I had enough tubing to attempt two new fuel pick-up fabrications.  I had one absolutely perfect so that the fuel pick-up was nearly centered in the clearance between the fuel tank stiffener and the pesky nutplate.  However, YOU MUST REMEMBER that when working with tubing, you must put the AN sleeve on AFTER you make the bend in this tube and BEFORE you flare the end.  I made that same mistake X2!!!!!!! Dam-it....  It only cost me about 2 foot of tubing (a whole $1.38), but it was the last 3/8" tubing I had.  Okay, time to surf Wicks Aircraft Supply.


Okay, now that my fuel pick-up is not a done deal yet, I decided to move onto prepping and sealing the fuel tank filler flange and vent tubing clip.  I had everything ready on the fuel filler flange, so all I had to do before sealing was to finish fabricating the vent line clip.

I made this clip a fair amount shorter (less than 3/4", but noticeably shorter than the right tank).


When I clecoed the vent clip to the filler flange, I looked down the tank and it lined up almost perfectly with the tooling hole for the vent line.  In the background, you can see my vent and fuel return fittings on the inboard rib.


Where the vent clip butted up against the neck of the fuel filler flange, I radiused it slightly.  My thought here was to allow it to "hug" the neck of the filler flange which would keep it from twisting.  The vent clip is only held by one rivet and it doesn't take to much effort to twist it.  It is kind of a mute point after you put the vent line through it.  It becomes pretty immobilized after that.


Pretty happy how this is looking so far.  Alright, where's the tank sealant?


Let the sealing fun begin....  I am rather generous when I put on tank sealant.  I have seen builders who have really small fillets and sealant lines that look like a work of art (which is very difficult if you have ever worked with this messy, sticky stuff).  Then they go to leak test their tanks and sure enough, they leak.  My approach has been to fully encapsulate rivet heads and flanges.  What I work hard to stay away from is to have "stringy" messes all over the inside of the fuel tank.  Those little chunks of sealant that can become dislodged and make their way to the fuel pick-up.


I got the fuel filler neck riveted and sealed.  Then I spent about as much time again cleaning the area so I had none of those small, stingy, blobs of sealant I was talking about.


Nothing is fun about riveting this flange in.  Van's calls out AN426AD3-4 rivets for this fuel flange (when you are using the kits standard, non-locking flange).  The problem is that I upgraded my fuel cap to the locking style which has a different flange.  It is thicker on the sides and thinner on the forward and aft sides of the flange.  I reviewed my log entries for the right fuel tank and I didn't make any mention of trouble with rivet length.  It was clear that the rivets Van's called out were going to be to short in some of the areas around the flange (see my rivet call out below).

I saved the forward rivet that holds the vent clip until last.  This rivet gave me a hard time on the last tank and on this tank, I didn't have any problems.  As I detail in my right tank, the best solution I could come up with for riveting the forward rivet that holds the vent clip was to use the rivet hammer with the back rivet attachment on the shop head side of the rivet.  I used the bucking bar on the skin side of the rivet.  The reason I saved this rivet until last, was that in order to get the rivet hammer on the inside of the tank, you have remove the fuel tank from the cradle and set the skins on the table.  The tank skins open up enough to get the rivet hammer on the inside.


Here is my unofficial rivet call out I used for my fuel filler flange.  The 3-5 rivets were a little long, but the 3-4.5 rivets were a little short.  Why does it have to be so complicated?  I ended up bending over one of the 3-5 rivets, so I did have to drill one rivet out.  That was better than last time, when I drilled the same rivet out 3 or so times.


I should have went up to the EAA meeting.....  I feel pretty good about having the fuel filler flange riveted and sealed.  One more tank sealant session behind me...  WooHoo...