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reason why somebody should build his own tank shall not be discussed here.
There’s another story which cares about this topic. Here you’ll
find a step by step instruction about how it can be done. There are other
- and maybe better - ways to do it. What follows is my way of building tanks,
according to my preferred ideas, materials, and methods. I’ll not
try to mention specific materials, tools, and trade names since these will
be completely different in other parts of the world.
Starting the project begins with some mathematics. Usually the tank compartment poses some limits on tank design. A pocket calculator is very helpful to find out the overall dimensions of our tank, once the required capacity is known. If a different engine is to be used and the required numbers are not available from previous designs, an exactly timed bench run with a tank of clearly designated volume may give some basic advice to calculate the right tank capacity.
|. Since I’m always trying to keep the fuselage nose very short I don’t have much freedom in tank length, so I have to vary the other dimensions. After these have been found I draw a rough sketch and put down the numbers. This is necessary to find the length of the wedge shape ( the calculator will precisely tell you the capacity, but it cannot tell you the dimension of the wedge ) . Only this will allow me to draw the mantle of the tank right on the tin sheet. After cleaning the sheet with some abrasive stuff ( kitchen cleaning powder ) the lines can be applied with a felt marker. Don’t forget a small strip ( about 5 mm wide ) which serves as an overlap to complete the tank mantle. After this has been drawn completely it can be cut out. Now the bending begins.|
|For this I’m using a rigid metal ruler and two strong C clamps. Also a small rigid plate of wood or metal is required to make precise bends. At first the narrow “overlap” portion of the sheet is clamped to the edge of the workbench, with the rest of the sheet pointing away from you. Make sure that it is clamped quite safely. If it can slip the bend will be neither correct nor sharp.|
Bending by hands only will not do the job properly; that’s why I insist
on using a strong plate to get a real clean bend along the full dimension.
After this first bend we’ll have to remove the sheet from under the
ruler and insert it the opposite way: the first bend will now point away
from us, and the rest of the sheet points to our stomach ( try to get it
out of the way ). The next bends follow, one after the other, according
to our sketch. After each bend slightly loosen the clamps, slide the tin
sheet under the ruler to the next spot ( line ) and tighten the clamps again.
Some bends are rectangular, some are less, one can be more ( the tip of
the wedge ). Usually I try to come close to the required angle, but that’s
not so important. The correct angles can be adjusted later with suitable
pliars. It’s quite helpful to get the final correct shape of the mantle
prior to soldering. It’s easier to solder if the tank doesn’t
have to be held down under tension, and it helps to prevent a “warped”
or “crooked” tank.
I prefer to get some solder on both matching areas before I begin to join these. After fixing both ends together slightly I heat the overlap area with a clean soldering iron from the outside, thus connecting both ends of the mantle safely. If necessary ( visual inspection mandatory ) some additional solder is applied from inside. Now the mantle is finished. The next step will be adding the front wall. Long ago I've given up working from a sketch. It can never be exact enough to work from it. Instead I prefer to put the mantle on a piece of tin plate. With a very sharp scriber I "scratch" the tank's outline from inside the mantle.
scratched drawing is cut out oversize to allow for some small “overlap”
soldering lugs about 3 mm wide. Bending these overlap lugs is always a nightmare
for me. If the gaps in the mantle are too big you’ll need tons of
solder to fill them. If you make the wall too big you’ll have no chance
to insert it into the mantle. By now you’ll have noticed that I solder
the front and back wall INTO the tank mantle. I prefer this method because
I believe I have better control over solder flow this way. Anyway, after
careful bending and re-bending, the front wall is pushed into the tank mantle
into it’s correct position. With the tank standing on its rear end
a lot of solder is applied to all edges. It looks as if way too much solder
is used. Now the tank mantle is heated from the outside with a carefully
cleaned soldering iron. All this surplus solder will flow into all gaps
now. You’ll see this since all the “mountains” of solder
will quickly disappear. Give some additional attention to the corners. Usually
I check the tank inside and add some additional solder to the tank corners.
Logic dictates that all the plumbing has to be done now. The feed tube is installed first. It ends at about 10 % of the total tank length short of the rear wall. There are flyers who prefer a different position. So far I’ve had satisfying results with this method. I have to add that I mount the tank very carefully and make sure that it is at least mounted parallel to the circle tangent; better yet tilted somewhat so that the rear end is shifted slightly outward ( I’ve also built tanks which were wider at the rear than at the front end ). Since I like to mount my tanks with a central bolt there has to be a central tube, positioned right in the middle of the tank. A 8 mm diameter hole is drilled through tank top and bottom side which takes a short piece of 8 mm copper tube; a 6 mm RC nylon bolt will then mount the tank to the tank floor. Next addition is the Uniflow vent and the overflow tube. From the pictures this may appear to be a complicated task. The reason for these fancy looking tubes is the fact that I mount the tank from the bottom of the fuselage; and not from the front as many Americans prefer to do. This demands that the Uniflow vent and the overflow pipe must exit the fuselage at exactly the place where the fuselage and the engine cowl meet : at their separation line ( I have to add that I hate fuel line connections from the tank to fuselage mounted outer tubes. I want to install and remove my tank very quickly and easily without any circumstantial plumbing). For other tank mounting methods the tubing system may be much more convenient. I have used brass tubings for many years without any problems. But suddenly I had experienced severe problems with these; obviously the manufacturers had switched to low quality material, and the fuel simply ate up my tubes. I have switched to copper now. For bending I use a simple tool available from Graupner. For 3 and 4 mm tubes this is a big help. All tube ends are fixed with some solder inside the tank. This will greatly reduce the danger of vibration cracks. Since this is the last time we can take a look into our tank let’s use this opportunity to carefully clean the inside with some kind of thinner and do some overall inspection of the work done so far. Those who believe in a baffle should install this now. Since a baffle is effective at the end of the flight only, it’s width needs not be more than one third of the tank width. That leaves us with the task of the tank rear wall. Basically it's the same procedure as with the front wall; this time scratched from the outside of the tank. Try to bend the overlap lugs as precisely as possible. Your workmanship and the long term tightness of the tank will depend on this work.
|By trial and error try to get the best fit of the rear wall. You’ll have no chance to check whether your soldering work is perfect. I do it the same way as I did the front wall, except perhaps for some additional solder applied. This will build up weight, but will build up trust, too. When you have reached this point you’ve deserved a big break and a relaxing glass of (…call me for more detailed information ).|
forget to check whether your tank is airtight. There are two ways to do
it. Plug all the tubes except one; connect a fuel line to this tube. Put
the tank into a big pot filled with water. Put the other end of the fuel
line into your mouth and try to press air into it. If air bubbles come out
of the depth of the sea, try to locate the spot and re-solder. The other
method is the vacuum test. Again plug two tubes and connect one tube with
a fuel line. Put the end into your mouth. Try to “suck” as strong
as possible. Put the end of the fuel line on your tongue. Only then open
your mouth ! If the tank is airtight it will keep the vacuum as long as
you hold the fuel line to your tongue. If you remove it you will clearly
hear a sound when the air is re-entering the tank. If the tank is not tight
you will not feel the vacuum on your tongue, and you will not hear anything
because there’s no air stream filling a vacuum. If you do this job
in your bathroom in front of the mirror, and if the tank is tight, you can
actually see the tank top ( or bottom ) side bending inwards as long as
you suck air. A soothing sight, really! It prooves that all the work wasn't
done in vain.
A few more minutes should be spent for cleaning the tank thoroughly from solder flux and any other imperfections. I usually stick a small piece of coloured tape on the tank and write down the capacity and the name of the airplane which the tank is intended for. This helps me to find the tank in my tank scrap box if I have ever replaced it.
Okay, all this work is not an easy task, nor is it a quick shot affair. Building a new tank usually takes me about four hours. But if you need a special solution for a special problem there's no other way than to do it by your own. My tanks have exactly the correct size ( dimensions), capacity, function, and tube arrangement as I want to have them. As you can see in the last photo it takes quite a number of tools to accomplish the task. After the job is done my workbench has always turned into a huge chaos, and my camera has got it's share of solder flux finger prints. Oh, these helpers are not what they used to be.
|I have to admit that I have stolen the idea of the two helpers from Dave Clarkson, who has hired them several decades ago for making photos. Seems neither the idea nor the helpers have aged much since. Thanks, Dave!|