Plane Gravity Fueling System

Fuel pumping systems don’t always work, but I guarantee you that gravity will always be there. The biggest drawbacks to gravity fueling have been the time it takes and having to hold the fuel supply above the plane. Well, I have an answer, crazy as it might sound, or look, or be. The only prerequisite is having the fuel in a container of 1-quart/liter or smaller. A translucent plastic bottle is best. This, by the way, is good fuel management in high humidity areas such as the Texas coast. Pour that fresh fuel into smaller containers when you first open it. Fit the cap with clunk and vent line connections. I pull the lines through undersize and heat smoothed holes in the cap, then connect to the lines with plastic fittings or plugs. Use metal bottles for long term storage of diesel fuel to avoid loss of the ether; I use Sigg bottles. They don't have caps that can be adapted for fuel servicing so I transfer the fuel to a translucent plastic bottle before going to the field. Back to the fueling operation. You need 3 each, 3/8” diameter wooden dowels, 4 ft long. Bundle the dowels and wrap a #64 rubber band around them (double it several times) about 8” from one end. A shoestring is shown in the photo but a rubber band gives you more flexibility in setting the tripod legs. Add a second rubber band for security in case one breaks. Spread the dowels at the far end and stand them tripod-like over the airplane. Tie a string with a loop on it to the neck of the fuel bottle. You can drop the loop over the S-hook or dowel as appropriate. Hang the fuel bottle high. Route a long line from the clunk line connection to the plane’s fueling connection. A nice alternative to the above tripod is a davit made of 3/4” pvc pipe standing in a socket on your field box. For a socket, I used a fishing rod holder with a section of foam rubber pipe insulation inserted. The pipe will fit snugly in the insulation. I incorporated a holder for my planes in the figure below. To start flow, temporarily close the vent connection and tilt or squeeze the bottle. When fuel reaches the aircraft, reopen the vent and release the squeeze. Now, with fuel flowing, connect a second line from the tank pressure/vent port to the bottle vent port. THIS LINE IS SHOWN CONNECTED TO A SMALL OVERFLOW TANK IN THE PHOTO -- DON'T DO IT THIS WAY. Connecting the second line to the fueling bottle’s vent will assure that fueling will stop when the tank is full. Now, you can go about the business of preparing the aircraft for flight; fueling will take care of itself. When fueling is complete, you will notice that the vent line will be filled to the level of fuel in the bottle. Lower the bottle to the ground and watch as fuel in the vent line begins returning to the aircraft fuel tank. After it reaches the tank disconnect the fueling system, sealing all lines as necessary. To deservice, leave the servicing bottle on the ground below the aircraft, hook up the fueling line only, squeeze the bottle, block the bottle vent, and release the squeeze. When fuel reaches the fueling bottle reopen the vent. Disconnect and seal all fittings Deservicing is not necessary for glow fuel. Just disconnect the airplane's fuel feed and pressure lines and connect them to each other. For diesel fuels, after a day of flying drain the plastic fueling bottle into a metal fuel storage tank with a good seal. I like Sigg camper's fuel bottles. How to make RC Airplanes