Twin Tanks Now and again you get a model where the distance between the firewall and the next former isn't enough to fit a decent sized tank. It's a real pain when you're restricted to a short flight because of the tank size. It's nice to have a long flight and have a good reserve for go-rounds if others are taking off or dead stick or whatever. What's needed is a short fat tank, but of course, nobody makes them to that shape do they? So twin tanks can be a good solution to this. The first time I tried this was on a Cambria Pioneer,  which was a Bleriot type vintage monoplane. It was fitted with a 4 oz tank which was suitable for the .20 size engine for which it was intended, but it had gained so much weight with numerous repairs that I'd ended up with a Merco .35 in it. Obviously a 4 oz tank didn't last very long feeding a .35! There wasn't enough room to fit a larger, and obviously longer tank, so I moved the original tank off to one side of the fuselage and fitted a second tank on the opposite side. The schematic below shows the plumbing method. As you can see exhaust pressure forces fuel from Tank 2 into Tank 1 which then feeds the engine. I've used this method in helicopters as well as 'planes with no problems, always using the carb' line to fill with. Provided you can get at your carb' line you can delete the filler line altogether. This, however, is the weak point of the system. If your engine is cowled and you can't get at your carb' line you'll have to use the filler pipe to fill. This will cause fuel to flow to the carb' while you're filling up. It's not only wasting fuel it's also probably flooding your engine too! If you can get a finger to the carb' line you can press it against something to seal it while you fill. If not, then you may be able to close the trim on your throttle and lock off the carb' that way. That's what I do on my Extra 300, but it won't work on the airbleed type carb's. You could screw in the needle valve every time you fill but I sure wouldn't want to be bothered with all that! Or fit one of those fueler valves they advertise; probably the best solution. If you have to use the seperate filler line make sure you plug it when you've filled your tanks or you'll lose your pressure. No doubt, some of you will be thinking of placing a fairly large tank over the C.of G and a smaller one in the nose. I've never tried it in a normal aircraft and I don't think it would work too well with that kind of head. I did it in a pusher delta once but the main tank was always still half full when the engine quit. I would recommend you keep the tanks as close together as possible. In some cases it can help to have a small tank near the engine if the main tank is a good distance away. My Extra has a 16 oz tank in the fuselage as usual, and a 3 oz tank mounted between the engine bearers. The small extra (?) tank was fitted to help the fuel head. With just the 16 oz I would start the flight so rich I could barely get airborne and later in the flight be going  too lean with half the tank still unused, (there's a fair distance between the tank and carb') so I fitted the smaller 3ozs as well, this almost cured the problem, at least I could get a fifteen minute flight without problems, but I've also got big vibration problems with this model too and I think that this is at the root of the problem. I knew I should have changed that lite ply firewall! G :-) FF 27.09.01