Tank to Selector Fuel Lines, Round 2 – 2 hrs

Friday Jan 13, 2012

Today I ripped the whole fuel line out that I installed yesterday. After sleeping on it last night I decided that I could and should do better. One thing I was not satisfied with was the area under the fuel valve. Last time I formed the first bend before installing the tube on the spar but I formed the second bend after the tube was routed through the weldment and side wall. This resulted in a sloppy large bend. I decided to form the first two bends under the fuel valve before installing the tube. To get it right I made a short test piece from the AN fitting on the valve to a few inches beyond the first snap bushing. Actually it took two attempts to get this right but once I did I had a formula for a good fit. The tube makes a 90 degree bend 2.7 inches below the AN fitting going not perpendicular but at a 60 degree angle to the main spar. Then it turns 60 degrees to enter the first snap bushing. Both of these bends are made with my Imperial 470 tube bender so they are very clean bends with absolutely no kinking. I installed an AN fitting on the test piece to make sure it was engaging the valve correctly for fit purposes.

Then I took a new 40-inch long piece of tubing, slipped and AN819 sleeve on the end and flared it, then formed the first two bends like the test piece.  In the picture below you can see the test piece next to the 40 inch long piece to be installed. You can see how I duplicated the shape so I should not have to shape this area under the fuel valve once I get it routed.

Bruce Swayze did a great job of laying out how he installed his fuel lines on his web site. Following his lead I bent the line into a large arch and feed it through the first snap bushing. I removed the bracket for the second snap bushing from the spar to make pushing it through a little easier. It’s just slipped over the tube and floats until the tube is routed through the side wall. O yeah, don’t forget to slip the AN818 nut onto the tube before inserting it through the first snap bushing!

I also discovered another error I made last time – I ran the tube through the lowest hole in the weldment. Bruce ran it through the middle hole. Today I found that makes a huge difference in making it easier to route through the weldment and out the side hole. In the photo below you can see how the tube now routes through the weldment and out the side hole in a relatively gentle bend. It will not do that routed through the lowest hole. It must make a compound curve s-bend which is really difficult to work along the tube.

In this picture you can see how it now exits the side skin following that gentle arc.

Once I got the tube fully inserted I connected the fuel valve AN fitting which fit nicely this time.

Then I formed the s-bend between the weldment and the side wall. The s-bend makes it exit the side skin perpendicular to the surface but I only have to do this once now that the tube is in place. I used a 1/2 inch wood dowel and a cut-off broom handle – one between the tube and the side wall and the other down through that hole in the top of the weldment to get into the inside radius of each bend. I used the coiled wire bender for this process too of course so the tube would not collapse or kink while bending and to protect the tube from the sharp edges of the weldment and the side wall holes.

In the photo you can see how it now runs straight out the side hole and well centered on the hole.

Then I formed a 90 degree bend on the outside of the fuselage to run the tube forward toward the fuel tank fitting. I used the coiled wire bender here also and the broom stick handle against the side skin to form the radius. Now is the time to slip the rubber grommets on the tube and insert then into the side skin holes. The first grommet must be pushed through to the inside of the fuselage and then the second grommet installed on the outer skin as seen below.

This next picture shows the grommet installed on the inside doubler.

Finally tonight I removed the tank attach bracket on the side of the fuselage and finished forming the tube and tweaking it until it ran straight through the hole in the bracket. This took some trial and error, putting the bracket on to check alignment and taking it back off to make adjustments but I didn’t have to install the nuts each time so it only took a few minutes.

I’m almost home on this tube run but I still need to form the last bend and put an AN fitting on to mate to the tank. But that will have to wait until tomorrow.