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). 

IMG 2250

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.

IMG 2251

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.

IMG 2257

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

IMG 2258

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.

IMG 2270

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!

IMG 2271

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 the end of the sensor to match, as closely as I could, to 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 photo below shows the completed fuel tank feed lines as well as the vent lines. Venting is covered in the next section. Since the Velocity uses a gravity feed system the fuel lines all need to curve down towards the sump tank. The installation isn’t as pretty that way, but you’ve got to do what you’ve got to do to make it all work! There’s a line coming from the bottom of each fuel tank, passing through a maintenance shutoff valve and then into the sump tank. Those two shutoff valves are only used for maintenance purposes so they normally will be tie wrapped in the open position, just to prevent them from closing due to vibration. (There’s a separate feed from the sump to the engine that does have a cockpit emergency shutoff control. See below.)

Wings - Fuel System - Fuel Lines

Completed fuel and vent lines in the back of the fuselage.

The factory does not supply a remote control cable for the shutoff valve. They do provide the valve though. Some builders just use the valve as a manual maintenance shutoff but I always worry about being able to shut off the fuel to the engine should there be a fire. Therefore, this remote control cable. I purchased the cable from McMaster-Carr and it comes with a large, bright red knob!

Fuselage - Emergency Fuel System Cutoff

Emergency fuel system cutoff cable installation.

Fuselage - Emergency Fuel System Cutoff 1

Painting the emergency fuel shutoff stop bracket.

Fuselage - Emergency Fuel System Cutoff 2

Completed emergency fuel system shutoff stop bracket before installation.

I’m not quite finished with this part of the project yet. Once completed, I’ll post a photo showing the complete assembly as well as the shutoff valve and control cable.

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