builder jim

I have a high wing mono plane and need to place the tank very low and almost to the firewall sideways. it has the os160 twin and to be able to scale out the interior this is the arrangment I came up with, but the question is three lines from the tank. one is vent top one the other is to carb the lowest one the other for the fill cap. both the carb and the fill lines are clunked, can the carb line be only half way back? this leaves me to believe that on banked turn the fuel at half full will run to the turning side and eng will starve or guit , I think I need some help here... PLEASE builder jim

Campy

My Feedback: (1)

With the carb line only 1/2 way back you are going to have problems, especially once you get below 1/2 tank. Any manuver (except straight and level flight) is liable to move the fuel away from the clunk.

When I do my 3 line tanks I do them as follows:

One line to the vent/pressure tube (from the muffler)

The other 2 lines are clunked and all the way to the back of the tank. I have not had any problems with the lines tangling or falling forward (even with an "unscheduled" landing
)

This way, as long as I know which is my vent/pressure line, it makes no difference which of the other lines go where. FWIW, I also use 3 different colors for my lines, one for each function.

da Rock

There is a good reason to have the pickup line to the carb with a clunk on it. The same reason applies to why that line should go to the back of the tank, not just halfway. The fuel line that runs to the engine's carburetor should reach to within 1/4" of the back of the tank and needs to be clunked.

There is really not much reason to have the fill line clunked. The fill line is only in use while filling and is stoppered when the tank is full. Why would it matter where the fuel pours out inside the tank? The fill line can stop just inside the stopper. It can go anywhere inside the tank but why bother. Once the tank is full and you stopper the fill line, it ceases to affect the way the tank works or the engine runs.

You need a line to indicate when the tank is full. That line usually runs to the top of the tank so when the tank is full, it overflows. It's often the muffler pressure line because it then doesn't need to be capped or otherwise touched.

With those three lines, you simply unplug the fill line, hook it to your fuel pump line, fill the tank, plug the fill line, and you're ready to crank the engine.

If you put the tank below the carb, you're going to have engine troubles. If you must position the tank below the centerline of the carb, the usual solution is to run a small secondary tank that is close to the engine and pressurize the main tank so that it's fuel is forced upward to the secondary tank which then feeds the engine.

vertigo72480

On the plane that I have a three line system installed, my carb line is the only one "clunked." My fill line just barely clears the stopper so when it comes time to defuel I just tilt the plane forward and hit the switch. No problems.

builder jim

[&:]OK, thanks guys better do it the right way dont want any problems, thank you, builder jim

allanflowers

It seems like everybody is missing the main question originally asked. The clunk in a tank mounted sideways is not going to function properly and, as the questioner suspects, the engine may starve in some flying conditions. In actuality, this may not happen so much in a banked manever but certainly would in a knife-edge.
Maybe the two tank option with a checkvalve would work.
Allan

Cub Man

My Feedback: (50)

in my 1/4 cub I took two tanks fixed each tank as they should. The vent from the first tank went to the pickup of the second tank. This works great

builder jim

wow, now were talking thought that my question wasnt clear .how did you guys do the two tank system? really would like to know as the plane looks nice except fot the tank going into the interior. thanks allenflowers and cub man......builder jim

builder jim

could I ask a favor and that is could this tank system be explained in detail or even a diagram, sure would help me as the tank now when installed will be in the cabin and am wanting to leave that area for the seat and dash, thanks very much....JIM[&o]

builder jim

[&:]ANYBODY,

2slow2matter

My Feedback: (1)

For two tanks, it's pretty simple. The muffler pressure goes from the muffler to your main tank (usually the larger of the two tanks). Then, the clunk (pickup) line goes from the main tank to the vent line of the secondary (smaller, "header") tank. Then, the pickup line (clunked) of the header tank goes to the carb. In this fashion, pressure entering the main tank forces fuel to go out of the the clunk, and into the secondary tank. Fuel entering the secondary tank creates a pressure that helps push fuel to the carb. This is a very elementary explanation of it, but it should get you going.

When you fill a system like this, you take the line off of the carb, and fill it. This forces fuel into the small tank. When the small tank over flows, fuel will run out of the vent, and into the larger tank. When the larger tank is full (therefore, both tanks are full), fuel will run out of the large tank vent, and you will see that they are full. Hook the lines back up to the muffler and carb, and go fly.

The advantage of a system like this is that is allows you to place a relatively small tank near, and level with the carb--therefore usually creating more positive fuel flow. It also helps to eliminate leaning of the engine in high G maneuvers and such, as the smaller tank is almost always full, and fuel cannot flow away from the clunk. However, once the large tank empties, then the smaller tank will begin to empty, and leaning can occur. I would time it so that the flight ends when the large tank is about empty, this gives you some "reserve" for go arounds and such, and almost assures you of a consistent mixture during the whole flight. Header tanks are usually 2 to 4 ounces, depending upon the size of the plane and engine.

Hope this helps.