Sump tank low fuel sender and drain hole | 10.9.2020

Inside the cabin behind the main gear is a ~3 gallon fuel header (sump) tank. This tank is fed by lines from the two main tanks in the strakes via gravity and then this tank feeds the engine. This tank also provides the sump drain where you can drain some fuel out the bottom into a tester to ensure there's no water in the tanks before flight. Water is heavier than fuel, and should settle to the bottom of this tank.

Since this is a 3 gallon tank at the low point in the system that feeds the engine directly, we can put a last minute warning device here to alert us of a critically low fuel condition. Assuming it alerts at 2 or 2.5 gallons, it gives us at least 15 - 20 minutes (at cruise power) to get the plane on the ground before we run out of fuel. We can tie this sender into the electronic instrumentation that we plan on using and it will give us an audio and visual alert if fuel is low and we need to get on the ground. To be clear, typical aviation fuel planning should never result in this situation, but it's an easy to add "Nth layer" safety measure.

The aluminum hardpoint in the tank had already been installed, all I needed to do was apply some Permatex #2 and thread it in.

Here it is installed. (black with yellow wires)

I also drilled the hole in the bottom of the fuselage that will allow us to sump the tank during pre-flight.

You can see the drain fitting up through the hole.

 

Short day with not much done, but the little progress adds up!

- Jeff