You wouldn't throw away a perfectly good fuel tank would you?
I'm not sure if I am the only one who suffers leaks from around the bung in the front of the popular plastic types of tank available from most hobby shops. Perhaps I’m heavy-handed with the screwdriver when tightening the centre screw to seal the tank, but in most cases the damn thing will leak at some point.
At the cost of up to £5-8 or more each for these things (depending on size), it’s a little annoying as I must do my modelling 'on the cheap' because I cannot afford to lash out and spend big money on ARF’s that include all the fittings. So, what to do?
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As most of my models are scratch built prototypes (usually without plans – plans, who needs them!) they can be engineered to include a fuel tank made from either a empty baked bean tin or a ‘soup for one’ tin depending on what engine size is to be used.
I'll refer back to these tins later, as they are the same diameter. At present I am flying a .25 sized trainer using a 125g sweetcorn tin as the fuel tank and can usually obtain flights of 10 mins or longer with judicious use of throttle. On one occasion another club member easily got a 30-minute flight out of this aircraft although there was a lot of thermal lift on the day.
My recently completed semi-scale Comper Swift has a 'soup for one' tin as it’s fuel tank with a Thunder Tiger .46 up front, as does my semi-scale Macchi 202 Folgore. Both of these aircraft will stay up for 15-20 mins, although I’ve never tested the full flight time.
Construction
The tins I have previously referred to are the ring-pull type, which when open, leave a convenient shelf on which to solder a new front. I have tried cutting out other front sections from thin galvanized plate but it is harder to solder, and as I keep collecting these tins, there’s always a ready supply. If the bottom of one tin is cut-out with a tin opener, this then forms the front of the fuel tank on another tin.
As mentioned previously 220g baked bean tins and soup for one tins are conveniently the same diameter. I rough up the inside of the bottom with sandpaper where the soldering is to be done (ie: around the edge and in the centre where the pipes are to be fixed) and usually place the fuel feed pipe in the centre and the overflow/exhaust feed pipe vertically above it with the customary bend towards the inside top. This arrangement seems to work well.
Two suitable sized holes are then knocked in this end plate to take the 1/8th brass fuel pipes. I just use a nail and a hammer, to do this, but you can drill it if you wish. I find by using a nail you can get the hole to be a firm fit for the brass pipe. Bakers soldering fluid is then applied around the area to be soldered and these pipes are then soldered into position on both the inside and the outside. Make sure you cut the brass pipes long enough as too short will result in the clunk pipe coming adrift – 12-15 mm either side is sufficient.
A clunk can be recycled from a leaking plastic tank, turned up on a lathe (if you have one) or purchased from a hobby shop. Fit a length of one of the rubber fuel tube (blue or green are OK) to the fuel feed pipe and the clunk to the other. The critical thing at this point is to make sure that the tube is not too long as to impede movement of the clunk. Several trial fittings may be necessary. When satisfied with the fit we can now solder the front on.
Remember the shelf: to get a good solder joint we must run a bead of solder around this lip. Firstly we need to scrape the coating off using a screwdriver or some other sharp object, then we can apply some soldering fluid (or flux) and a thin bead of solder. The front plate, with all the pipes tube and clunk attached is then fitted in position and the two soldered edges are sweated together.
When cool, fit two pieces of scrap fuel tube to the outside pipes and after immersing the tank in water, blow in both tubes simultaneously. If there are any leaks then bubbles will appear. Simply resolder that point and repeat the process until the leaks disappear.
I have calculated that the 220g baked bean tin holds around 9oz of fuel and suspect that a 'soup for one' tin may hold as much as 14-15oz. The small amount of extra weight from the metal tin is not an issue as most R/C aircraft are light in the nose anyway, so the weight of the tin substitutes for ballast.
Just another little recycling tip; Don't throw away those broken hacksaw blades as they can be reshaped into hinge-slotting tools, ground to a sharp knife blade with a bench grinder or used simply as stirrers for epoxy. I use a lot of DUBRO medium hinges so simply use my sharpened hacksaw blade to push into the marked hinge position, withdraw it, and then insert my old hacksaw blade hinge slotter, push and pull it through a few times and voila’, we have a perfect slot for the hinge.
Don't be afraid to experiment with a few recycling ideas as it can save you a lot of the folding stuff.
