Notice I am showing Tygon fuel line as well as clear plastic tubing from the hardware store. Both are acceptable. To determine the length of the upward bend of the vent tube, just estimate it by placing the tube as shown, fro the lower edge of the stopper opening and the top of the tank. Some tanks have a raised dimple on the top of the tank for the vent tube to fit up into. Just make sure you do not install the vent tube so it contacts the inside surface of the tank, Vibration will cause the tube to damage the tank wall.
Above right. Here the tube has been bent to 75 degrees using the bending tool. Assemble the stopper and tube assembly and estimate the length of the outlet and vent tube lengths. The rotary cutter compresses the tube and this mustt be opened out so fuel floe is not restricted.
Cut the output tube to length and use fine sandpaper to smooth the ends of the tubes so they do not chafe the flexible fuel lines. Cut the length of the pick up tubing so the clunk just clears the back of the tank and is free to flop around as the model moves during flight.
Make sure to leave the fuel lines extra long so you can feed them into the model and out of the firewall and vent holes. Feed a flexible pushrod into the firewall hole and snake it into the fuselage. Place the tank in the wing saddle and attach the fuel out tube to the end of the pushrod and pull the tubing back out of the hole as shown Above right.
Here you can see the fuel tank installed on a support plate right side of the wing saddle. I use stick on double sided foam tape and heavy duty Velcro to hold the tank in place while making it easily removable if needed. Also remember, when looking into the bottom of the wing saddle, your tank should be upside down.. When the fuselage is upright on its gear, the tank will be rightside up. When you install the fuel fitting to full and empty the fuel tank, make sure to install the fuel lines so the fuel flows into the tank when the fueling probe is attached to the fitting.
A fuel filter should be installed between the fuel fitting and the carburetor. But what is it, exactly? Simply put, it is the amount of 2-stroke engine lubrication oil measured in ounces added to a gallon of gasoline.
Here are some common ratios used with RC gasoline engines. With a couple of flips of the prop to prime the engine, It took only a few flips of the prop to start the engine. Check the fuel flow and watch for bubbles in the fuel lines. Any bubbles indicate you may have a pinhole somewhere or a loose fitting bleeding air. Let the engine warm up for a few minutes and then adjust the throttle trim for a solid reliable idle.
Adjust the low end needle-valve so you have a smooth transition to full power. The first step to having a successful flight is installing your fuel system properly! Hope you found this helpful! What are you waiting for? Go fly something! Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.
Do you have a video to share with Model Airplane News? Usually the instructions for the plane indicate the best position for the tank in that airframe. I try to locate the tank so its centerline is on the same level as the centerline of the engine. The idea is to prevent having to suck the fuel uphill for any great distance.
Pumping carburetors will pull fuel uphill but it is not wise to count on that any more than is necessary. In this case, close usually works just fine.
Another consideration with tank location is its effect on the CG center of gravity. To reduce the chance of a tank rubbing against the airframe and developing a hole, tanks are usually mounted on a layer of foam rubber.
I also put a strip of the double-sided tape between the tank bottom and the foam to further keep everything in place. Double straps made from hook and loop material hold the tank firmly but allow it to be removed if necessary.
Between the foam, tape and straps my tanks have stayed in place no matter what I have done with the plane in the air. Two or Three Lines? All fuel systems must have a line to the carburetor and a vent line. As fuel is drawn out of the tank it must be replaced with air at normal atmospheric pressure through a separate line. This vent line prevents the tank going into a vacuum state that shuts off the fuel flow to the carb.
Foam under the tank isolates it from some vibrations and helps prevent it from rubbing a hole in the tank of the surrounding wood. To prevent the tank from emptying itself to the outside environment through siphoning the vent line runs from its outlet on the tank and then up so it is slightly above the top of the tank. Most will run the vent line around the top of the tank and then down to exit through the bottom of the plane.
In this configuration, when the plane is inverted the tank can still draw air in to equalize the pressure within the tank without dumping fuel. Simple but very important! Of course, we must deliver the fuel to the carburetor. Modern gasoline engines use a pumping carburetor that literally sucks fuel through the line coming from the tank.
Though we can seldom run the supply line straight to the carb, with a little thought we can find a path that eliminates substantial deviations up, down or sideways.
Crap Trap Yes, that is the name of the device made by Sullivan Products I use to filter the fuel one last time before it gets to the carb.
This is a very simple filter that can be easily fit to most planes. I also like this filter because it is virtually bulletproof and if the lines are secured to its barbs, will never leak.
Lots of folks will add another Crap Trap to the fill line coming from their gas can through which they fill the tank in the plane. This is a cheap way to add a little more protection to prevent getting junk in the system.
The orifices in a carburetor are very small which means that tiny pieces of debris can plug it up. Adding a couple filters to your filling and flight fuel systems is not overkill or paranoia. The good news is that nearly all modern fuel tanks are very capable if assembled and maintained correctly. The solution for the changing attitude was remarkably simple, put a weighted end on the pickup line inside the tank.
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