As the climax of a long winter project at work begins to wind down, I once again have sometime to build models and contribute to modeling as a whole. One large area that I believe needs support is the commercial availability of racing equipment or at least the information needed to produce your own. This article will be the first of many trying to accomplish just that. Below is the procedure that I use to fabricate fuel tanks. The method is the same for all of my models, the only things that vary are the venting configurations and possibly the inclusion of fast fills. So, here goes:
I begin by designing my fuel tanks in a 3D solid modeling program called Autodesk Inventor. I know virtually none of you have access to this program so I will provide information for alternatives. The program is not necessary to build fuel tanks, it just allows me more of a visualization of what I'm trying to achieve. Pictured here is the tank after several hours of designing.
Pretty straightforward design. The tank body is mocked up at 33cc but the target amount will be 30.5cc to be within the 3.1cc max rule. This extra space allows me to trim the tank to final size for things like tubing compensation. From the above design, I create a drawing that is the tank laid out flat as shown below.
The tank is printed out to scale which gives me templates to work from. I usually build tanks like this in three-pieces. This allows me to construct the main body of the tank and leave the rear open for plumbing/cleaning.
The above template is Scotch 77 spray glued to the tank material. I personally prefer to use the K&S Easy Solder Tin sheet as it is readily available and is easy to work with. Shown at right is the layout. I should note that anyone with a ruler, calculator, and paper can get to this point as it is pretty straight forward. Again, the solid modeling program is my own personal choice.
The tank is then cutout from the sheet stock with a standard pair of tin snips. The edges should be de-burred on a belt sander or equivalent. Pictured at right are the tank components, ready to be bent.
My dad came up with the concept of using sheet metal pliers made by ViseGrip®. They can be purchased from most hardware stores and are invaluable. They are about 3" in width, measured across the blade. We have taken several pairs and trimmed them down to various sizes as needed. Break parts along the lines of the templates.
Here we can see all of the components after bending. The adhesive and paper templates can be removed at this point. Brakleen® or Acetone® works well for this.
At this point we begin to actually assemble this thing. Depending on how well you did with the prep work, this could either be smooth sailing or a complete nightmare. Either way, forward we go ... I begin by assembling the main body of the tank. I use Staybrite® Silver Solder throughout with acid flux as it is the best I've used to date. One must take care in neutralizing the acid with baking soda after soldering otherwise you could develop leaks in the joints after some time. A tip here is to make sure the joints are clean. This is the particular reason why I use the Brakleen® or Acetone® rinses. Also, make sure your iron can melt the solder reasonably well. If cold, the solder will react poorly and give tremendous headaches while working.
Next, the tank venting is added. A good reference here is to place the tank into the intended location on the model and see where things need to go. Mark with a pen and drill the holes with a bit that is about a 1/16" diameter smaller than the intended tubing that is going in that location. Use a tapered punch or something similar to wallow out the holes to size. The reason for this is that it provides a slight more amount of material for the tubing-to-tank contact area and gives more reinforcement of this joint.
A good thing to do before installing the tubes is to roll them against an abrasive sheet or belt-sander to roughen them up. This gives the fuel tubing a more slip resistant surface and keeps the tubing from coming loose in flight.
Place the pickup tube first as it will be the reference for the uniflow vent. This should be placed about 3/16" from the rear of the tank at the lowest outboard position. The uniflow is then placed on the bottom of the tank about 3/16" further forward of the pickup tube. Any closer and bubbles can be introduced into the fuel line when flying. This can give tremendous fluctuations in needle settings throughout the flight so take extra care here. Also, make sure to solder the tubes to both the floor and the entry location of the tank, ALWAYS SOLDER IN TWO PLACES! These tubes will take quite a bit of abuse over their lifespan, especially the uniflow (fill) vent. Lastly, add the overflow tube which is located in the highest part of the tank when the model is at rest. Take the completed tank and submerge it into a bath of baking soda and water. Use an acid brush to completely neutralize it to prevent corrosion.
Here is a picture of the completed tank minus rear cover and accessories.
This is where things can get really exciting. Here you have a completed tank and it is time to check capacity. With maximum volume events such as clown, BTR, or F2C, this step is crucial. An easy method to perform this check is to seal the rear of the tank with a piece of plastic backed by a sheet of balsa clamped into position. This will provide a way for us to check the tank capacity without having to add the rear cover.
Now fill the tank completely with water and then suck out through the pickup tube the volume enclosed in the tank. If lucky, this should be the exact amount desired or within 1cc over the amount. My tank came in around 31.5cc which is just too big.
After a quick calculation, I found that my tank needed to be trimmed about 1mm to get down to the volume needed. Just trim the back of the tank by placing it against a disc sander for a few seconds. After de-burring and cleaning, the tank is now ready for soldering.
The tank is now finished and should again be immersed in a pot of hot water and baking soda to neutralize the acid. Use a syringe to fill and empty the tank several times. Dry the tank with air and proceed to the next step.
The tank is once again checked for volume. I first repeat the procedure that was used for the initial measurement check and I then perform a volume test similar to what will be (should be) used during processing. I fill the syringe with the maximum allowable volume for the event, in this case 31cc. The tank is then filled through the uniflow vent while the pickup tube is plugged. Before the syringe is empty, fuel must come out of the overflow or else your tank is too big. The above picture shows the results from the first test, dead-on at 30.5cc. The second test showed a burst of fuel from the overall just as the syringe emptied.
At this point the tank is completed except for the external accessories that will be used for competition. I use an alligator clip to plug the overflow tube as it is the quickest way we've found for pitting.
Also, the tank will have to be mounted. I have used all ways of mounting including rubber-bands and hard-mounting with straps. Either way, make sure to use some form of vibration dampening material such as foam or Silicone under the tank to stabilize the run.
Here is a picture of a simple brass mounting strap that can be used for hold-down.
That concludes the final building of the tank. The tank should now be cleaned by flushing soda pop through it three times followed by three cycles of fuel. The soda is somewhat acidic and therefore has a Ph that is similar to the flux used for soldering. The similar Ph's will allow the two to mix and then be flushed away. The oil in the fuel will then act as a corrosion preventative. Make sure to use filters with the new fuel tank as debris can come from inside for some time. I always use filters on my equipment and found them to be invaluable for consistent running. Finally, plug two of the vents with tubing and force air into the other tube to pressurize the tank. Place the tank into a bowl of water to see if any air bubbles are present. Hopefully there aren't any leaks. If so, re-solder the area and check again. Make sure to clean if any more work is done.
This concludes the methods used for tank fabrication. As can be seen, it is a pretty simple and straightforward process. I hope that this will help those with questions.
Thanks for reading, -Todd Ryan Phone: 541-292-4580
This page was upated March 22, 2006