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:

Click here to go to Fuel Lines page 2