When it comes to the external tubes for a metal uniflow tank, it's pretty much up to you where they are for your convenience. The tank manufacturers like GRW and such ( I'm not really sure just now many they are ) have all sorts of configurations with the feed tube exiting the tank on top, bottom and places in between. The overflow works the same way but the tube can exit out the front, and just poke through the top or the tank and as long as the nose of the model is high enough, you will get a full tank to over flow. For the uniflow, and short tube can exit the front of the tank next to the over flow, and the tube ends in the usual place that is near the end of the pick up. I install short lengths of 1/8" copper tube in the inboard side of the fuselage, one bent into a curve and facing forward, and one straight tube just behind the curved tube, and leave a 3/8" length sticking out inside the fuselage. I connect these tubes with the corresponding tube on the tank. The curved tube goes to the uniflow tube on the tank, the straight tube connects to the over flow tube on the tank, and the straight portion outside the fuselage is capped after filling. In this configuration I can leave the curved tube open to the ram air of the prop wash and forward flight, and I make sure when building the fuselage this far that I can access it to the muffler pressure tap of the muffler for using muffler pressure if desired.. I have put these tubes in before and after painting. The pick up tube can exit as needed also and will not affect the run. If you have a close fit to the firewall or the engine, the tube can exit out the bottom of the wedge portion of the tank for convenience. This is all part of the planning when building the model. Al Rabe has some interesting videos and writings on making tanks in his collection of writing. With the unique scale models he built and flew, the tanks had to be custom made for the model and were all sorts of different shapes, but they worked just fine!! So, whether is a profile or a full fuselage model, there are few standards to abide by, but as long as the location of the actual pick up is in the right place in relation to the venturi and such on the engine, everything else can be put where you need it. If I need a custom tank for a model, I mage a wooden block replica of the tank to use as a form to wrap the sheet tin stock around. Once you have that all bent up and soldered together, you can use the wood form to make the end caps also. Figure out where you need the exit tube, and the I like to use an old ice pick to punch the holes through the tin. Old ice picks were made out of good, hard steel with a sharp point and a very shallow, smooth taper. Carefully poke the ice pick through the tin at the desired spot, and gently keep pushing it in until you get to the size you need for a good, tight fit of the 1/8" tube. When you push through the tin, it will leave a small flange like edge that will help with making a good solder joint. For solder, I use 1/32" diameter electrical solder for everything "normal" that I solder so that I don't have to worry about using the wrong stuff on the wrong part, For flux for use on tanks, I love the stuff called Ruby Fluid. It can be hard to find but a little bit goes a long way so a can or two will last a life time. You don't need gobs of flux to solder a tank. It's not one of those things where if a little is good a lot is better!! Nokrode ( however it's spelled ) is the easiest to find but I find it's a bit "dirty" , but still works. I fit the parts of the tank together and apply flux to the outside only. When putting the end caps on, I make sure they are seated with no big gaps, dab a small but of flux where I want it and apply heat with a broad tip soldering iron, usually a 40 watt iron. As the flux and tin heat up, the flux will liquify and run the length of the joint. If you have the tip tinned well, some will flow off the tip and you will know when to add in some more. This is where the small size comes in. If the solder is too big it tends to cool off the joint and it won't flow and probably leak. Work your way around the various joints and wipe everything clean with a rag. Then I water test the tank with a bowl of water, a length of fuel line and some plugs for the other tubes, and a fuel syringe. Submerge the tank and apply some air pressure with the syringe and watch for bubbles. If you have a leak, just a tiny dab more of some flux and resolder and then retest. When finished, just add it to the model.
Type at you later,
Dan McEntee