ORIGINAL: wws2010
no i am saying tht you route the engine in the center hole and the two fuel lines on the outer two, that would work right? The reason that i want such long flight times is that it will be a kind of uav for my senior project at school. And i really want to wow the teacher.
You're missing what I'm saying I guess. I agree that you hook it up that way. But when you've got the one side connected to the engine the other side is connecting its barb with the fuel line to an exhaust hole on the other side of the valve body opposite the barb. Your diagram DOES NOT SHOW THE TWO EXHAUST HOLES. But trust me, they ARE there. So the fuel from the non-selected tank would dribble out into the fuselage of the plane and the second tank would be empty when you try to switch to it.
The valve you show is the other style of 3way we use. In that one the exhaust ports out out the extreme ends of the body. Go back and look at your animated diagram again. Note how when it moves to one side that the other line is exposed to the open end? That would be fuel running out into your model's fuselage.
Using two tanks in the nose of the model would not be a good idea anyhow. That's 8 oz of fuel in the nose of the model that would be burned during flight. 8 oz of glow fuel weighs in at around 7 to 7.5 oz. That would be a lot of nose weight in a model of this sort to loose during a flight. Depending on the design the model may not be able to adjust to that big a shift in the CG location due to that shift. The flying charactaristics would change a lot due to this and it could easily end up outside of the ability of your systems to deal with. The other reason it's not a good idea is since it is a UAV that means no active pilot monitorying the flight. Who is going to notice that the fuel is running low and switch tanks?
If you need to make up a bunch of plumbing it's STILL better to do the float controlled constant level chamber and just let a higher placed larger tank at the CG feed that float chamber via gravity. Or play with and use the regulator so the engine sees a constant pressure over the whole tank.
Besides you still have not said how long a flight you are looking for in total. Two 4 oz tanks running on a .15 even at mid throttle won't last more than about 35 to 45 minutes at best. If you're after more then you need a larger fuel supply. And such a supply cannot be placed in the nose. It would have to be at the center of gravity due to the weight change during flight.