Trapdoor hinge pin retainer

Over the last three days I finished a lot of prep work on the left tank in preparation for attaching the baffle. Got the outboard rib sealed and riveted, attached and wired the sender plates, and permanently installed the flop tube into the inboard leading edge.

I also had to find a way to secure the hinge pin that holds the trap door in place on the second inboard rib. The second rib and trapdoor form a sort of header tank that retains fuel when doing aerobatics. I can foresee a need to remove the hinge and door at some point, so I wanted to make a clip that I could reach just by removing the access plate. The little clip has a small hole for safety-wiring the hinge pin, there’s a little proseal on there as well.

Trapdoor hinge pin retainer

Fabricating a pickup screen

A couple of weeks ago I received the brass screen I ordered from McMaster-Carr. I needed to finish up the right tank’s fuel pickup, so I broke out the wire cutters, soldering iron and solder to fabricate a pickup screen.

This turned out to be a lot easier than I anticipated; the only trick was keeping the screen from unraveling while cutting and forming it. Running a bead of solder along one edge of the screen ‘locks’ the individual brass wires in place, making it easy to roll into a cylinder using a piece of 3/8″ aluminum tube as a mandrel. Solder the long side of the cylinder together with more solder, trim the excess screen away then close the end – and voila, a pickup screen.

Flop tube pickup with safety wire

Before somebody emails me, yes, I do know now that Van’s sells a pre-made fuel pickup with screen. But I already had the screen on order when I found out, so I decided to experiment – and it was easy to make an acceptable screen. I’ll probably continue to experiment with this over then next couple of days.

Cleanup items

With the end ribs in place, I worked on some of the cleanup items that needed doing before the tanks are sealed. One of those items is a Van’s service bulletin that calls for safety-wiring fuel pickup attachments. Fortunately, the pre-made flop tube I bought from Van’s already had a safety wire hole drilled in the flare nut, so all I had to do was attach the flop tube to the bulkhead fitting – using the proper torque, of course – then safety-wire the assembly.

Looks like this…

Flop tube pickup with safety wire

I was definitely out of practice with the safety wire pilers – took me a couple of tries to get a nice, tight twist on the wire.

Burned out on proseal

I’m getting burned out on proseal and the mess and cleanup that accompany it. So I’ve been pushing pretty hard to get the inboard ribs riveted into both tanks. The only ‘gotcha’ on these ribs is fitting the T-410 reinforcement plates and the T-405 attach angles to the rib. The plans don’t specify an exact location for the angle, it just fits as far as possible into the leading edge of the rib.

Some builders get into trouble by riveting both the angle and the plate in place before the rib is riveted; they then find out that there’s no room to squeeze those rib-to-skin rivets that lie between the angle and the rib. Take a look at the picture below and you’ll see how everything fits together.

T-405 riveted in place

For me, the best way to put this assembly together was to rivet the inboard rib in place with a minimum amount of sealant around the front of the rib. I held the T-405 angle in place and match-drilled through the top and bottom pilot holes into the rib, clecoing as I went. Then I removed the angle, taped the reinforcement plate in place inside the rib and match-drilled it through the holes just drilled in the rib. Finally, I clecoed both the plate and angle to the rib and match-drilled the remaining holes. For the left tank, the center hole also became the pilot for a 3/8″ hole which will accomodate the flop tube bulkhead fitting.

Right tank with the outboard rib riveted

The last rib sealing/riveting tasks are installing the end ribs on each tank. Here’s the right tank with the outboard rib riveted; there’s obviously some cleaning-up to do.

End rib riveted but not cleaned

The only detail worth mentioning on the outboard ribs is how to fit the T-410 nose reinforcement plate. With the rib clecoed in place, I laid out and drilled pilot holes in the reinforcement plate, then taped it in place against the inside of the rib with two-sided tape. That kept the plate in place while I removed the rib. It was easy, then, to match drill the plate and rib. The plate was sealed and riveted to the rib before the rib itself was riveted to the tank skin. Clear as mud, right?

Fabricated a fuel pickup for the right tank

Not too many more pictures to show; I’ve haven’t accomplished much on the airplane recently and what little I’ve done, I don’t have too many pictures of. But here’s one thing I did – fabricate a fuel pickup for the right tank, connecting to the fixed pickup and anti-rotation bracket I put together on 15 January.

Fixed pickup in the right tank

What’s missing here are the slots cut with a saw into the aft end of the pickup tube. I think this is a cheezy approach by Van’s – anything the size of the saw kerf or smaller will go straight to the gascolator or fuel filter. My tech counselor thought the same thing, so he bought some brass screen from McMaster-Carr and fabricated a pickup like those used in production aircraft. I ordered some of the same material – 16×16 brass screen – and I’m going to try my hand at doing the same thing.

Plumbed the vent line into the right tank

I’ve been on the road a lot recently, having started a new job. John and I finished riveting all the ribs in both tanks except for the inboard and outboard end ribs. With the interior ribs in place, I plumbed the vent line into the right tank. Here’s the inboard vent line fitting; the wire coming from the BNC connector attaches to the inboard capacitive sender plate, and it gets routed with and wrapped around the vent line.

Inboard vent plumbing

And here’s the outboard end affixed to the clip previously riveted to the fuel cap flange.

Outboard vent plumbing

Unfortunately, I didn’t get any pictures while I wired up the capacitive sender plates. The outboard plate is installed with the vent line, and the connecting wire from it is wrapped around the vent line as heads in toward the inboard sender plate. It connects there with the wire from the BNC connector installed on the inboard rib (see the first picture for this entry).

Anti-rotation bracket

While waiting for another rib riveting session with John, I worked on fabricating the fuel pickup anti-rotation bracket for the right tank. My airplane will have a flop tube pickup in the left tank for inverted flight, and a standard pickup in the right. The anti-rotation bracket keeps the fixed pickup from rotating around its bulkhead mount, raising the end of the pickup and making more fuel unusable. When I mount the pickup later, the bracket’s function will be clear.

Here’s the inside face of the sender plate with the bulkhead mount and bracket Prosealed and riveted.

Fuel tank antirotation bracket

Here’s the outside face of the sender plate; this is where the fuel pickup will attach to the rest of the fuel system.

Fuel tank antirotation bracket