Fuel System Details

[rodsmith]

Finally finished my fuel system from the wing roots to the firewall. Took way too much time and I have a pile of discarded tubing. I found this one of the most challenging parts of the project so far. One of my goals was to use one piece of tubing from the wing root to the T, eliminating the need for inspection panels on the interior fabric. I accomplished that but it wasn't easy. Before painting the fuselage I thought I had accounted for all the mounting tabs I needed but not quite. Had to add a couple and cut off a couple that weren't quite in the right location. I found routing the front tubes to be fairly straight forward. At the top I routed the tubes outside the fuselage. You have to make sure you make the bend above the point where the windshield is still flush on the door posts. I wanted to route the rear tubes in the door post channel. At the top you can not route the tubes outward because that would interfere with the flap pulley and cable. That means you have to first bend the tube inboard to clear the doorpost tube and then back outboard. I attempted those bends with smaller pieces of tubing and could not get something I was satisfied with. On the right side you also have the rear door to contend with. Maybe others have been able to accomplish that. At Oshkosh I saw a Bearhawk with the tubing running on the inside of the door posts which I hadn't considered but it made sense as an easier way to do it. I started out with 12' lengths of 5052 tubing that I bought when I bought the fuselage steel. After I wasted most of that I used the coiled 3003 versatube because I didn't want to pay shipping on oversize parcels. The one piece rear tubes are nearly 7' long. My method using the 3003 is to roll it out and get it as straight as possible. Then I use a tubing bender for all the bends. It was easier to work with than the 5052 because if your bend is a bit off you can tweak it into place. One thing to remember when planning is you need a minimum of 1 1/2" of straght tubing past a bend to install a fitting and flare the tube. Anywhere the tubing was in contact with structure I used 3:1 heat shrink tubing to protect it. When shrunk the heat shrink is about .040 thick. Where I ran the tubes down the rear doorposts I used 3" gaffer tape to anchor it. The gaffer tape doesn't leave the sticky residue like duct tape, I checked it with an iron and it didn't shrink or melt. This will be covered with a layer of fabric and a finishing tape. I located the fuel selector centered on the pilots side so I can reach straight down to it. I explored several locations for the gascolator to ensure it was the low point in the system and that it wouldn't be below the bottom skin contour. As it is located, just the drain fitting extends below the skin. The actual low point is the tubing just in front of the inlet. Hope this may help some who haven't tackled this yet. I am curious as to what provisions exist on the kit fuselages for mounting tubing, fuel selector, gascolator etc. I know a lot can be done with adel clamp combinations but I thinks a small .040 tab is just as light if you are scratch building your fuselage.

[whee]

Great job Rod!

It’s a challenging task to do right and have look good. Luckily my dad has skills and I allowed him the opportunity to run our fuel lines.😁 I gave him the sketch and he got it done. I too wanted one solid tube from root to tee but also required 1/2” rear fuel lines. He said next time it’s my turn...

[nichzimmerman]

Whee, have you done any fuel flow testing with your 1/2" lines yet? I've always been curious how much difference they made.

[svyolo]

I started making mine in multiple pieces until I get it right, out of 3003. When I get it perfect I will try to copy it in 1 piece. It is a work in progress.

[James]

I inherited a fair few lengths of 5052, plus rolls of 3003 tube with my kit second-hand. I have one poor old length of 3003 which I've bent, then restraighted about 4 times, just to get the distances right between a bends. Then once I'm happy, I replicate this in 5052. So far, not much wastage. I ran the aft lines through the vertical door sill, with a 90deg bulkhead fitting. There will be about 2" where the tube goes slightly horizontal / uphill because of the 90 degree angle, but that should be fine. I've seen photos of other builders with the same routing. Hardest part was packing the fitting out away from the cargo door sill, to clear a stiffening bar for the forward door hinge.

Great tip about getting the front fuel line to clear the windshield, I might not have thought about that before. Thanks Rod!

Edit - Update on wasted on 5052 tubing:
RH Aft line - one attempt
LH Aft Line - one attempt
RH Fwd Line - one attempt
LH Fwd Line - five attempts (!!)

If you're using the imperial tube bender (highly recommended), periodically sand it with very fine sand paper - a couple of these attempts, I found that the soft material of the bending dies picked up aluminium and galled it around the bend.

[Bcone1381]

Here is another thread on fabricating a pattern for the fuel lines that you might be interested in. Every "bend" has three dimensions, the bend angle, clocking of the bend in relation to other bends, and third, the placement of the bend longitudinally on the tube.

https://bearhawkforums.com/forum/tools-technics-and-best-practices/32690-fuel-line-fabrication-pattern

[spinningwrench]

I adapted Brooks technique on my Patrol and it worked great. I have continuous 5000 tubing from wing root down to the T fitting. I found welding a few additional tabs down in the vicinity of the fuel selector greatly simplified my final installation.