Builder Log: Lots of Plumbing

It’s been a week since my last build session in Torrance, and while the progress might not look as dramatic this time, a lot of detailed work took place—especially in the fuselage and firewall-forward area. Think of it as less “big leaps” and more “careful choreography.”

During the week in between my visits, the Sling team focused on the elevator rigging, including the pushrod assemblies, the control mechanism, and the joystick assembly. Over at the tail, the parachute box cover was also checked and fitted on top of the empennage.

Control Stick and Elevator Pushrods

My Work: Fuel Plumbing 101

My main project this week was all about plumbing the fuel system. This meant running lines from the firewall to the gascolator, then on to the fuel pump and filter.

Sounds simple? Not quite.

These lines start life as straight aluminum tubing, which then gets coaxed into shape using forming tools. The tricky part is that each component lives on a slightly different plane, so the lines have to weave and bend just right. At the ends, each line was flared and fitted with AN6 Female-to-Male fittings.

One challenge I discovered: the exact placement of firewall components seems to vary a bit from plane to plane. For example, on my build the gascolator’s input/output lines are parallel to the ground, while on others they’re vertical. Add to that the Airplane Factory’s philosophy of minimizing AN fittings (fewer potential points of failure), and you end up with more complex routing and geometry. A fun puzzle… if you enjoy puzzles that fight back.

In addition to the lines, this week also included finalizing the fuel pump assembly. I had already done the initial pipe forming and test assembly, but now I finalized the pump’s placement on the firewall—which required a modification to the mounting bracket—and completed the electrical cabling preparation, installation, and connection. The pump is powered directly by Alternator A from the engine, so getting this right was a critical step.

My Work, Part 2: Big Cables, Small Gymnastics

After plumbing came electrical cabling. These are the thick lines connecting the battery to the engine accessories and other key components. Unlike the custom fuel lines, the cables are thankfully standardized: I had a list of lengths, gauges, terminals, and placement points to follow.

Still, running them wasn’t always straightforward. Routing the cables around the engine and its accessories occasionally required some “builder yoga”—stretching, reaching, and contorting to get things into place. Once installed, the cables were bundled neatly, wrapped, and laid on soft plastic covers to prevent any chafing from vibration.

Lessons Learned

This week was a crash course in two critical systems:

Fuel lines: routing, flaring, and fittings, and how placement decisions affect the geometry.
Battery cables: sizing, routing, and securing for long-term reliability.

Working on both systems gave me a much better understanding of how the components interact and why small placement details matter so much.