Fuel Lines page 1
November 15, 2011
The material that I used for the fuel lines is 3003-0 3/8" Aluminum tubing
(Aircraft Spruce calls it "Versatube").. It is very flexible, so that
allowed me to make fairly long uninterrupted runs of it without having
to add a lot of connectors. The Fuel line routing and information is
located in the 2007 Bearhawk Patrol Newsletter. Here is a scan of
it:
Also, there was an Engineering Notice in the January 2011 Issue that allows you to mount the "Tee" in the fuel line lower which results in a better downhill flow of the aft fuel lines. click on the linked text in the last sentence for that notice.
The proper flares for an aircraft is 37 degrees. Automotive ones are 45 degrees. Make sure that you purchase or borrow an aircraft flaring tool to assure that you have 37 degree flares.
Here is the procedure for flaring the tube ends to accept An fittings. All fittings used were aluminum.
After cutting the tube to the proper length, debur the end with a regular
debur tool or large drill bit. Slide the AN818 Coupling Nut and the
AN819 Coupling Sleeve on to the tubing as shown
here:
Using a 37 degree flaring tool, make the flare on the end of the
tube:
The finished product. One is a 3/8" fuel line, the other is a 1/4"
brake line:
The sleeve slides up against the flare. No sealer or lubrication is
needed. When you tighten the nut down, it presses the flare against
the AN fitting you are attaching the tube to and makes a liquid tight
seal.
Ok now for the fuel line routing. The goal here is to make sure that all fuel lines run downhill to the low point in the system, the Gascolator. There should be no valleys or low points, just a nice downhill slope all the way. Watch out for any "U" shapes in your tubing runs. This can create a pocket where water and debris can collect when the airplane is sitting still.
Let's start at the top and work our way down. There are two fuel ports
coming out of each wing tank, an aft one and a forward one. This is
a great design as it will allow fuel flow when the plane is in a climb and
when its in a descent. The fuel lines begin at the top of the fuselage
where the wing mounts. Let me apologize in advance for all the arrows
you will see in the following pictures. It is difficult to photograph
tubing structures and have it come out where you can see where you are supposed
to be looking. Here are the fuel inlets that will be attached to the
tank via rubber hoses:
Click here to see the wing tank outlets.
To secure the fuel lines, I used a combination of Adel clamps (rubber cushioned
clamps) and flat waxed nylon cord with a piece of clear plastic tubing the
fits over the fuel line. Here is the nylon cord and clear tubing
piece:
I decided to run my aft fuel lines down the inside of the door frame tube.
It will later be fabric covered, rendering it invisible. Here
we are making the transition at the
top:
