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78. Tanks, but no tanks

26/10/2013

Two of the more difficult bits to manufacture are the tanks.

Forward fuselage, showing the position of the tanks. The oil tanks is so big because it uses so much oil!

Forward fuselage, showing the position of the tanks. The oil tank is so big because it uses so much oil!

They sit on the top of the fuselage frame in front of the pilot, and each has a flat bottom and a curved top, with more or less flat ends.

The oil tank made of brass, with about 300 rivets holding it together!

The oil tank made of brass, with about 300 rivets holding it together!

The oil tank is the simplest to manufacture and is made of brass, with vertical ends, a filler cap at the top, and a cone-shaped sump at the bottom. The joints are riveted and soldered which was standard practice on the petrol tanks of cars of the period. This means that the vertical ends have to be ‘flanged’ – bent over at right angles to provide a lip through which the rivets can go. The basic shape of the end is semi-circular, and as you will see if you try this with a piece of paper, there’s an enormous tendency for the flange on the curved bit to wrinkle. It’s possible to do it with very careful hammering, but it takes a lot of skill and care, and if once it starts to wrinkle. You’re likely to have to throw it away and start again. But the flange isn’t the only difficulty with it. If you leave the ends flat, they have a tendency to drum when there’s any vibration, and the way to fix this is to ‘dish’ them slightly – to make them bow outwards, which stiffens them up immensely at no extra weight.

We decided to have a go at this process ourselves, partly because we’d like to do as much of the work ourselves as possible, and partly to save cost…

Back in March (in 49 Bits & Pieces) we thought the first thing would be to do the dishing by squashing it in a big press with a wooden pattern underneath and a thick piece of rubber on top. Well, we tried it and even with a 60 ton press, the brass sheet wasn’t even dented a little bit!

So it was back to the drawing board and clearly time to call in the experts. A couple of phone calls led us to Ian Harris, who lives only a few miles away, and runs a 1903 Franklin car  and works on all sorts of others. When we went, there was a relatively modern 1909 Darracq and a positively space-age chain-drive Fraser Nash in his spotless workshop. Clearly we’d come to the right man, and Ian is going to be looking at both this and the petrol tank for us. We’ve already warned him that the oil tank in particular was renowned for leaking – here are a couple of pictures with the evidence – and we’ll be trying to make sure ours doesn’t suffer the same fate!

Of the two, the oil tank is the simpler. The petrol tank is made in steel, and widens out at the front to match the outline of the engine cowling. It also has a couple of internal baffle plates which need to be flanged…

The underside of the petrol tank. The two channels are for fixing it to the fuselage longerons, and you can see the horizontal lines of rivet heads that mark where the internal baffle plates are. It's sat on the front end for the picture, which as you can see is wider than the back, and you can see the cone for the petrol outlet that will have to be made up.

The underside of the petrol tank. The two channels are for fixing it to the fuselage longerons, and you can see the horizontal lines of rivet heads that mark where the internal baffle plates are. It’s sat on the front end for the picture, which as you can see is wider than the back, and you can see the cone for the petrol outlet that will have to be made up.

And whereas soldering the joints in the brass oil tank is fairly straightforward, the steel parts for the petrol tank will need to be made up all ready for riveting, then sent away for tinning, before riveting and soldering. All good clean fun, and we have every confidence that Ian’s the man to do it.

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From → Building, Technical

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