Fuel vent question...
 

I'm connecting up my first gas engine(BME G90) and have a newbie type question. Is there a preffered placement for the fuel tank vent? I can just see the fuel draining out of the tank when doing aerobatics...I keep thinking this is a stupid question and there must be a simple answer but beats me if I can come up with it...Thanks in advance for any explanation...

RE: Fuel vent question...
 

On gasoline tanks, I found that having the vent line at the interior top of the tank with it exiting the tank and then the model at a point lower than the bottom of the tank works fine. That way, if inverted, no fuel will leak from the tank yet the tank is free to vent to the atmosphere. Some use two vent lines, one as above with the second one being at the bottom interior of the tank and exiting the model at a point higher than the top of the tank. Again, if either upright or inverted, no fuel leakage yet open to atmospheric pressure. I've found no advantage in having two vent lines.

RE: Fuel vent question...
 

I also have the vent line going to the top inside the tank then a tube exiting through the bottom of the fuse. When I fly a down line, sometimes I notice a little spray of fuel from the vent.

RE: Fuel vent question...
 

Put a loop in your vent line that goes back past the back end of the tank that way when your plane is point down the fuel can't get out of the tank because the fuel can't run higher than the back of the tank to get out;)
Larry S.

RE: Fuel vent question...
 

Picture is worth a thousand words.

This is a 3-line tank.

Line 1 is the clunk--that is on the left side of the stopper in these pics.
Line 2 is the vent--thats the right side line
Line 3 is the filler--thats the one on the bottom of the stopper in these pics.

Take your vent line and run it up around the back of the tank, then run it down and out the bottom of the plane.

You can see in these pics that I have 2 tanks. 1 for gas and 1 for smoke oil. I ran the vent lines side-by-side and wrapped them back around the tanks and then made a little lite ply bracket and used some CA to attach it to the bottom of the plane. Put a couple brass tubes on the vent lines and epoxy them in. Makes a clean setup. Your tank is full when the vent line pukes out fuel.

The filler line just goes in the tank and makes a turn straight down to the bottom of the tank in the front. I used a clunk on them. The fuel line on this filler line is only about 1" long, and then it connects to the clunk. When I want to completely drain the tanks--tip the plane up on it's nose and pull the fluid out.

The reason why you do it like this is because the fuel won't leak out--no matter how theplane is oriented. You can have a full tank of fuel and tip the plane on it's nose without leaking fuel. The fuel would have to run uphill in the vent line and around the tank and then back down again to leak out. Highly unlikely.

RE: Fuel vent question...
 

hello on ocasion I would notice a long stream of fuel exiting my plane, at the time , was just running the vent from the tanl down to the bottom of the plane. Got to thinking about this problem, oil residue on the bottom of the plane, so I now run the vent to the very back ,and low point of the fuselage . Problem solved, no more oil residue on the bottom, and if I want to tilt the plane up on its nose, the vent line does not have to be clamped. This little idea has worked on all sizes of giant scale planes I fly, from 2.5 c i to 11.6 c i engines. I use a nylon tube from near the overflow vent and a piece of fuel line to the nylon tubing., Usually try to exit as far aft as possible. Give this a try, I think you will like it. regards jack

RE: Fuel vent question...
 

I have the same setup as RCpilet except I don't have a smoke unit (maybe some day I will). I also have a fuel filter before the vent exits the plane. I don't know if it's really necessary but it's supposed to stop dirt/dust from getting into your tank.

RE: Fuel vent question...
 

Thanks for all the input and pictures...I really appreciate it. Certainly makes sense now!

Regards,

Pete