Setting up a gas tank
Tutorials > Setting up a gas tank
|Plan||Components||Bottle||Lines||Install||Connect||Three line system|
An airplane with a two-stroke gasoline engine requires a fuel tank, a way to get the fuel to the carburetor, a method of filling the tank and a way to vent it. There are different ways to do it; this tutorial describes an approach has worked well for me - a two line system based on a Fiji water bottle.
Photos were taken from two different setups so two different bottle sizes will appear - 500 mL for a 50cc engine, and 330 mL for a 20cc engine.
Plan the system
It's essential to plan the system beforehand to determine what parts and supplies you'll need and the placement of the tanks and lines.
Here's a look at a fuel system ready for installation.
Assemble the components
Time to get all the stuff together!
Everything starts with the bottle. Fiji bottles are light, strong and square and are available in varying sizes - 360 mL, 500 mL and 1L.
This cap from PSP Manufacturing is a perfect fit for Fiji bottles and features outer and inner barbs.
The single barb vent, also from PSP Manufacturing, is ideal for connecting the vent line.
My choice of pickup is the Walbro felt clunk.
For extra insurance I put a fuel filter in between the tee and the carburetor.
This fuel dot is made by McFueler.
I use this part from Hangar 9 as a vent line fitting.
A package of fuel tees - only one is required.
Tygon tubing for everything outside of the tank.
Viton tubing for the in-tank line.
An assortment of zip ties; I use a small size.
The tank should sit on foam.
Velcro is a good way to secure the tank.
Prepare the bottle
Start by testing the cap - I came across a bottle that the cap would not thread onto.
Drill the vent hole - make sure the location suits the planned installation. I use a brad point drill bit because the spurs scribe a nice clean hole; I turn it with my fingers for better control.
A nice clean hole.
Time to install the barb. Start by dropping it into the bottle.
A piece of wire helps guide it into position.
There's an internal keyway for a hex driver - insert that...
...then hold onto it while tightening the nut with a wrench.
Configure the lines
Take a minute to determine the required length of the lines for the clunk, carb, vent and fill. Be generous - better too long than too short!
Here's a carburetor line.
And here a vent line is marked.
Attach the felt clunk to the Viton line and inner cap barb.
Install the cap and ensure that the clunk reaches as far as possible without catching on the inside of the bottle.
Attach the vent line to the barb.
Build the supply ine to the carb, incorporating the tee for the fill line and the filter. Note the missing zip tie on the tee side of the filter - that was installed after the photo was taken.
The fuel system, ready to install.
Install the tank
Installing the tank is a quick job. Be sure to route the vent line down and along the side of the tank - this prevents gas from leaking out of the vent line during flight.
Connect the system
The final piece of the puzzle - making the connections.
Connect the carburetor supply line.
Don't forget the zip tie!
Route the vent line and connect it to the fitting.
Connect the fill line to the tee and route it out of the fuel dot housing.
Connect the fuel dot.
Three line system
Since I started flying gas airplanes in 2012 I've used a two-line gas system. I use a filter in the gas can, a felt fuel clunk in the gas tank, and an in-line filter in the supply line to the carburetor. It was recently pointed out to me that this might not be the best approach; consider the following diagram:
The blue arrows indicate five additional points for potential air leaks. A three line system requires neither the T-fitting nor the inline filter (pumping gas into the tank through the felt clunk negates its effect as a filter, which is why I add a separate one in the supply line). I've switched to 3-line setups.