9.3.4 Bulkhead Fuel Fittings

The first step is to prep the inside of the fuselage for the hardpoints. In my installation there are a total of three. The round one on the left is for the digital fuel sensor and associated electronics. The two square ones on the right are for the fuel vent line (top) and fuel tank output line (bottom). 

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Prepping the inside walls for installation of the hard points for the fuel tank fittings.

The factory supplies all of the hardpoints pre-tapped for the fuel line fittings. All I need to do is embed them in a mixture of EZ-poxy and Micro.

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These hardpoints also get covered with two layers of BID to help lock them into place. Once everything cures it’s time to install the fuel lines and fuel tank vent lines. Section 9.3.5 covers the installation of the vent lines while Section 9.5.0 covers the fuel lines to and from the sump tank.

In the meantime, I also need to fit and install the fuel tank level sensors. Again, this is a modification to the original manual since the factory no longer supplies the sight gauges. A quick discussion with the factory cleared up any questions I had and, in fact, the procedure is fairly easy.

You can see in the photo above that I’ve already cut out the hole for the hardpoint. One factory recommendation was to add 10-32 nuts to the bottoms of the hardpoints even though the hardpoints are already tapped. Why? Well, these hardpoints aren’t made out of the thickest aluminum so it’s always possible to strip one of the threads. The nuts help to strengthen each bolt hole. The nuts also act as a standoff so that the hardpoint doesn’t lay too deeply in the wall of the fuselage. Once these hardpoints are embedded into the Microballoon mixture, they will be firmly locked into place.

You’ll notice that I’ve marked one of the bolt holes with a black Sharpie mark. That indicates the top hole. Even though it looks like these hole are equidistant from one another, they are not! So, the hardpoints need to be aligned with the sensor before they are installed. The screws are just temporarily holding the nuts in place. They’ll be removed once the epoxy cures.

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The factory supplies the hard points for the digital fuel senders but the senders themselves have to be purchased separately.

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Test fitting the fuel sender hard point.

The fuel sensors come from the manufacturer as straight pieces. However, the first 5 inches from the electronics on down is bendable. They mark the bendable area. The idea is to carefully bend that section so that the true sensor area fits properly. Doing that was an interesting exercise, at least for the first one. Not only did I need to bend it to fit properly, but also so that I can pull it out or reinstall it should it need to be replaced. The end result looks like the photos below. (Bending the second one was easy - I just copied the first!) I used tubing bender springs around the tube to help with the bend and to keep it from kinking.

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Here's one of the digtal fuel sensors. In the upper left corner you can see the fuel strainer (finger strainer) which filters out any large particals hopefully never get into the system!

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And here's the fuel level sensor installed in the other tank.

The capacitive sensors are designed to just about touch the bottom of the tank. There is unusable fuel in each tank so I aimed to end of the sensor to match, as closely as I could, the bottom of the finger strainer. The top of the sensor just about touches the top of the tank. We don’t want the sensor to touch the top to keep it from rubbing.

The next step before sealing up the tanks is to install the fuel system venting. That process is covered in Section 9.3.5.

ui© John Trautschold 2018