Monday, December 30, 2013

Aft Fuel Return Line Completed

During the last short but fruitful work session the positioning and length of the aft fuel return line was finalized. Final positioning of the fuel lines under the opening in the right baggage floor was determined by making the upper portion of the fuel line modification from the T up. The short 1 3/4" pipe that fits between the fuel tank and T was fabricated and attached onto the T to aid in determining positioning and clearance measurements. (Incidentally, the shortest 3/8" pipe that can be made with the Parker Rolo 37 degree flaring tool is 1 3/4" long).

Using the dimensions in the drawing (posted in the previous post) it shows the fitting for the fuel supply line needs to be 13/16" under the baggage floor … got the idea of using a block of wood that size to use as a spacer to position the T at the right level. As luck would have it, the first piece of scrap wood I grabbed was the perfect thickness.
Masking tape used to hold the T to tank assembly onto the 13/16" wooden spacer block.

The above mentioned drawing shows the center of the main supply line in line with the first rivet hole in the side of baggage floor and the return line is to be positioned 1 5/8" aft of that. Using the strings stretched out between the rivet holes (see previous post) the return fuel line was positioned 1 5/8” aft of the first string.
Return fuel line positioned adjusted to match the measurements in the drawing from the forward string.
With both the T assembly and return fuel line in position, the threads on the T can be seen. To the left of that is the main fuel line that will be flared and connected to the T. Overall, the alignment looks good.

The overall alignment was very good and placing the return fuel line on top of the supply line did not create any unforeseen issues with alignment or interference. At this point the two fuel lines were clamped together with hose clamps using 3/4" pieces of rubber tubing as cushions between the fuel lines to prevent chafing.  The assembly was set back in place to test the alignment once again and the final cut and flare was made for attaching the return fuel line to the AN837-4D fitting at the F-1204D center section bulkhead.
Main supply and return fuel lines clamped together with fabricated cushion clamps.

See no point to install this assembly at this time because it will need to come out again to make the final cut and flare for attachment to the T being placed under the fuel tank for the modification. Could probably do that now, but will hold off until the tank is built or at least with the fittings installed on the bottom plate. Feel it best to wait and obtain the exact positioning prior to making the final cut on the supply fuel line.

Having completed the aft return fuel line, work began on the forward return line. This line will be challenging because it is one piece and just shy of 6 feet long. The forward return line requires a handful of bends at the firewall and then it is a straight shot back to the center section where it will be a challenge to be sure.

The forward return line was purposely cut a little long and the first 90 degree bend at the firewall was set in place before deciding to call it quits for the day.