Category Archives: Fuel Tanks

Time: 7 Hours

Today I started out by finishing up the deburring of the tank skin edges. So I broke out the bag of 1″ 3M wheels and my die grinder to accomplish this task.

I was able to finish both skins in an hour or so and moved on to the next task for the day, the tank baffle modifications. A brief history on why I’m going with the modification. It is said that it’s not “if” your Van’s fuel tanks will leak but more like “when”! These tanks are a “wet” design similar to the Lear I fly. That means that means all the tanks are built like any other part if the plane but just sealed with a product like caulk called ProSeal. This sealant is made to withstand chemicals like fuel. The problem is that it’s sometimes can be tough to get a “perfect” seal or one that lasts forever. Some tanks leak right away and you can fix while others can take days, weeks, months or years! So what do you do when you have sealed up your tanks and they start to leak down the road? Well the rear of the tanks there is a piece of aluminum called a baffle. This is just the rear piece that allows the tank to be sealed with the skin and ribs. Should you develop a leak (or when) Van’s has you empty the tank of fuel and drill a ~5″ hole in the baffle between the two ribs that would allow you access to the area that has the leak. Once you fix the said leak, whether it’s from a bad rivet or the seal between the baffle and skin, you cap off the hole you cut with a plate. This happens so often that Van’s has a tank repair kit that includes the required parts. The downside is you now have introduced metal shavings into your tank where you drilled plus the pain of doing this on a completed tank. So with that knowledge I have decided to be proactive with my tanks and prepare for my possible leaks, hoping that I never have any! There are 4 bays in the tank that would need access so I ordered 8 of each of the access plates and reinforcement rings that I used for the inboard ribs of the tanks. These will allow me to beef up the hole and add platenuts so that the in the future I would just have to break the ProSeal and unscrew the access plate to gain access to the bay that has the problem. So might say that I just introduced more placed for possible leaks and I would agree however fixing a leak at these areas would be very easy! So I spent a couple hours debuting the edges of the parts for the holes.

Then with several measurements I came up with the center of each bay on the baffles.

With the center marked I setup my hole cutter in the drill press to make the cuts.

The reinforcement rings have the platenut holes predrilled so I used them as a drill guide for the baffles. I found the center of the ring and drew lines on them. These lines will match up to the center lines on the baffles so that the access plates are lined up just right.

I started by drilling one hole and adding a clecko and then drilling another hole until I had all the holes done.

With all the #40 holes drilled for the platenut rivets I moved on to the #19 holes in the center of the platenuts for the #8 screws that will hold the access plates in place.

I took all the rings off the baffles and debured every hole on the baffles and the rings. I then grabbed my countersink cage with the #40 bit and set the depth so that the rivet would sit flush with the baffle web allowing the access plate to sit flush with the baffle.

I got all the holes countersunk on the right baffle and decided to call it a day, whew that was 7 hours of fun work. I will get back at it tomorrow and try to finish up this mod!!

Time: 6 Hours

I took Saturday off this weekend to let the mind rest. After a good visit with friends this morning I was able to get back into the Hangar. I needed to finish scuffing the rib flanges so that the ProSeal will adhere to them. I then loaded up the dimple dies into the pneumatic squeezer and dimpled all the rib holes.

the ribs are now all ready for assembly so I moved to the skins. First up was to debur all the inside holes. The punch process that is used to make the skins leaves a pretty big burr so before I used my debur bit I grabbed the die grinder with a 1″ 3M wheel and knocked down the edges.

Before I dimpled all the skin holes a scuffed the rivet hole lines first since it’s easier without the dimples.

I took care of both skins inside and outside deburring and scuffing. I then grabbed the DRDT machine to dimple all the skin holes. All the holes get dimpled except the row for the baffle as the are countersunk and the fuel drain holes. The perimeter holes get a #8 dimple for the screws that hold the tank to the spar. These holes are pretty big so I just took my time dimpling them so they didn’t crack the skin. They all came out perfect!

Here you can see a couple of the AN509-8R8 screws and how they sit flush with skin in their dimples.

Next up will be the baffles as I’m going to do some modifications to them, more on that later.

Time: 3 hours

I was able to get a little time in the Hangar today after working on my sons car. I got my new #40 countersink bit so first up was to finish the fuel filler cap flanges.

I also fabricated a couple of clips that hold the end of the fuel vent line right by the filler caps. I used a 1/4″ drill bit in my vise and shaped them. After several try’s I finally got two that I was happy with.

I also shaped the reinforcement plates for the last outboard ribs of the tanks and drilled them for the 6 rivets that hold them in place. I then used them as templates for match drilling the ribs.

I then had a visit by my friend Glen Vokac so that he could take a look at my anti-hang up guides for the flop tubes. He said all is well except that he would have waited to rivet them to the access plates until I had some ProSeal. So I took his advice and drilled out the 3 rivets that hold them in place. I’m getting pretty good at this task!

The other day I grabbed a couple of -6 rivets, they are pretty big, to plug the tooling holes in the last outboard rib.

I just placed the rivet in the hole for you to see, I will wait for ProSeal for these too! Not a long day but anytime in the Hangar is good!

Time: 6 hours

Today I decided to do more research on the topic if covering up the middle hole in the second inboard rib of the fuel tanks. The lower hole has the trap door but I couldn’t find any description in the plans for covering the upper hole. I tried several searches on vansairforce.net and finally came up with one builders blog that had an email reply from Van’s Aircraft support:

After I decided that I would cover those holes I match drilled the covers to the rib and countersink them for riveting. I used flush rivets so that there wouldn’t be any chance the flop tubes could get hung up on them.

I then started the work on the anti-hang up mods for the inboard rib. The flop tube has the opportunity to get snagged or caught on the nutplates of the access plate. You can see in this photo this risk.

Van’s has you make a guide that sits proud on the nutplates like a bridge that gets riveted to the top and bottom of the access plate stiffening ring. The downside to that design is that it restricts you access through the hole as there would now be a 1/2″ wide strip of aluminum in the center of the hole. That would make using that hole in the future, should I need it, a lot tougher. Other builders have built a two piece guide that has one piece riveted to the access plate and one piece riveted to the stiffening ring. What this does is allow most of the guide to come out with the access plate and allow full access through the hole. I took my time and made several measurements to come up with a design that I was happy with.

I installed one of the flop tubes to see how it looked and fit.

With one side done I just copied the pieces for the other side, again building both wings at the same time is a great idea.

To remove the access plate you just need to slide the plate up and pull the lower portion out before pulling the top out.

It was a long day in the Hangar, I find that when I have to design and build a part from scratch it takes me a while to make sure I get it just right. I’m getting closer to the dreaded task of sealing the tanks. I ordered most of the supplies for that as well as a few more parts to make some modifications to the tanks baffles, more on that later.

Time: 6 Hours

Today I had a list of tasks I wanted to complete on the tank ribs and z brackets. My order of nutplates from Aircraft Spruce came so I riveted one to the last z bracket since I had ran short when I was working on them. Next was to finish up the capacitor fuel sending plates since I received my electrical tools. The outboard plate are connected to the inboard plate with an 18 Awg wire. They then are both connected to the fuel gauge system via a BNC connector. I soldered a BNC connector to 15″ of wire for the connection to the inboard plate. I then marked and drilled the 7/16″ hole for the connector on the inboard rib.

The outboard plate gets a 48″ wire bolted to it with a terminal end. The other end, as well as the end of the BNC wire, will also get terminals later when the tanks are riveted. This allows you to fish the wire through the bushings that hold the fuel vent, something you couldn’t do if the terminal ends were in. So with my new crimper I attached the the terminals as well as soldered them per the plans.

I then drilled the holes for the fuel vent line elbows in the inboard rib. This allows air to replace the fuel that is being used by the engine.

Next was to finish up the fabrication on the trap doors for the second ribs.

One other modification that some builders have done is to cover the lightening hole the is in the middle of the second rib, above the trap doors. This also helps keep fuel in the first bay for the flop tubes to pick up when doing aerobatics. I still haven’t decided weather I’m actually going to do this until I research it a little more but I made the plates anyways.

I decided that I would call it a night as it was approaching 10:30 pm but before I did I connected one of the flop tubes to see how it looked. I still need to fabricate the anti-hang-up guides that cover the access panel to prevent the flop tube from hanging on the nutplates.