wing tank questions

[FunkyMonkey]

so far ive only achieved a successful fuel transfer from the wing tanks to the main tank once. ive tried numerous times during cruise but the only success was in a dive. tried to make it work on the ground today. with engine shut down and about 2-3 gallons in the tank i opened the valve and listened but heard nothing after about ten minutes i measured the wire gauge with no change indicated. i then tried it with the tail raised to a cruising attitude, with the tank cap on, without it, and with it while blowing through the vent. all with no change. does the vent need a ram pressure greater then i can blow? i think i recall somebody saying they left their valve open and heard the fuel transfering while they were pushing back into the hanger. do i need more fuel in the tank to initiate a transfer. my thoughts are that there is something not right here. also my valves are mounted in the wing root if that helps at all. not sure whats going on. any suggestions are welcome.

[alwaysoar]

Re: wing tank questions

Be sure that your fuel cap gaskets are tight. You might be losing pressure there. Check to make sure that nothing is clogging the vent. Is this an original?

[FunkyMonkey]

Re: wing tank questions

i can blow through the vent relatively easily, the gaskets look good to me but i dont know what a bad one would look like. wont it drain on the ground with out the caps on?

[VictorBravo]

Re: wing tank questions

You have a clogged line or a clogged fitting. Sorry, but that's just about all it could be if it won't work with both fuel caps removed.

[Bob Waldron]

Re: wing tank questions

Funky Monkey,

The most puzzleing thing in your note, was that you were able to blow into the vent line, and not start a fuel flow. THAT indicates that you will probably NEVER be able to get the fuel to flow during flight.

In order for me to have reliable fuel flow (without having to dive and shake the wing and sing a magic song) I would follow this procedure: Fill the wing tank. Open the valve. Blow into the vent (to cause a flow). Shut the valve. Fill the header tank. Sounds like a pain, but it makes mine flow very reliably. I carry two feet of flexiable silicone model airplane fuel line in my pocket, for blowing into the vent line. I suspect that the smaller (1/4 inch) fuel line to the header is my problem.

To find the problem with YOUR airplane:

You should make sure that the gas cap vent tube is clear. You should feel NO pressure when you blow into the vent tube when the gas cap is removed from the tank.

A poor gasket will allow the air pressure (from you blowing on the fuel cap vent line when the cap is attached to the tank) to escape around the fuel tank filler neck. If the gasket does NOT leak, you should sense a pressure 'build up' when you blow into the vent tube. You do NOT have to blow hard.

If you can feel the pressure 'build up' and can hold it for a minute, and there is STILL no flow of fuel, then there is something blocking the flow.

By looking through the filler neck into an empty tank, you can see the finger screen that is inside the tank. It is rare that this screen would be so clogged that NOTHING will flow, so if the screen is the problem, you should be able to see the problem.

With the fuel tank empty, remove the line to the tank, and try to blow into the vent line again. You should NOT be able to build up any pressure when you blow into the vent line now. If you don't feel any pressure, go to the next paragraph. If you are able to build up pressure, the problem MAY be in the finger screen. Remove the gas cap and blow into the finger screen. If you don't feel any pressure build up, then the screen is OK. Now replace the fuel cap, and blow into the finger screen. You should feel some pressure and you should feel air coming out ot the vent line. If you don't then the gasket is somehow plugging the vent line.

If the vent line and finger screen are OK, try to blow into the fuel line (that was attached to the wing tank) and see if you can get air to bubble into the header tank. If you can, then I don't have a solution.

Hope you can trace the problem and solve it. It is GREAT to have the extra fuel when you need it.

[Sloanlow]

Re: wing tank questions

I'm new around here...But my T-Craft is currently disassembled and I'm looking at the wing tanks and the nose tank and I cannot see anything that would prevent fuel flowing from the wing tanks to the nose tank. From looking at this assembly, It would seem to me that, if you are having problems with both wing tanks flowing into the nose tank that you should examine the brass "T" fitting at the nose tank inlet for trash or other obstcle. The only other thing I see on mine it when the last time the wings were attached they smashed the fuel tubing (not enough to block the line), I guess to accomadate the wing fittment. I don't know why this happened but I assure you that it will be corrected on my rebuild.

[Dano"T"]

Re: wing tank questions

Look at the routing of your fuel lines from the wing tanks into the main tank....make sure they are not bent wrong or kinked...also make sure they are run so that gravity will allow flow.

[8708]

Re: wing tank questions

I had the same problem with my bc12d. I could get the lhs tank to flow but never the rhs tank. I could blow through the gas tank and hear it bubble in the main tank but it would never flow. It was not until I started my restoration that I figured it out. When I had the wings off I found the tube from the wing tank to the main tank had a large upward bend in it! In fact the tubing bent smoothly upward nearly to the top of the tank before it started down into the main tank. Gravity could not overcome that but still explained why I could force air through it. You usually cannot see the tube since it is hidden by the wing root cover. Take the covers off and see if you can see how the tube is running. Good Luck!

[FunkyMonkey]

Re: wing tank questions

all these sound like good ideas ill give them a try next time i get there. an hour drive means it might be alittle while though. it would be nice to have those working. more fuel means more options.

[jrzangger]

Re: wing tank questions

Before you tear the plane apart checking fuel lines, try putting three or four gallons in a wing tank with the valve open. With the cap off, seal your mouth on the wing tank and pressurize the tank. (Don't chew gum while doing this!) If your lines are not blocked, you should hear the air bubble flow into the main tank. Once the air is out of the line, flow should be normal. I used this procedure for quite some time until Forrest said to check the gaskets on the caps. I had new cork gaskets but replaced them with the white neoprene type. Since I did that I have yet to have a problem. The caps are very tight to put on, but they flow everytime I open the valve now. Of course, if you're lines are misrouted, crushed or otherwise blocked this won't work either, but will get you on your way to finding the problem.

[VictorBravo]

Re: wing tank questions

The gasket thing makes sense on another level. Remember from basic flight school aerodynamics that the wings have low pressure above them. The lowest pressure will be close to the thickest part of the wing on top, and that just happens to be where the fuel cap is. So, if you have a "vented" automotive style gas cap but not the little pitot tube, then the low pressure could be sucking the inside of the tank instead of blowing. If you do have a pitot vent but also have a bad gasket, the low pressure around the cap could be sucking away the pressure that the pitot is supposed to be providing. This is probably one of the reasons that the Gilberti / Harer conversion tells you to hook up all sorts of new vent lines. But the real solution is to have a positive vent on the fuel cap IMHO.

[Guest]

Re: wing tank questions

so far ive only achieved a successful fuel transfer from the wing tanks to the main tank once. ive tried numerous times during cruise but the only success was in a dive. tried to make it work on the ground today. with engine shut down and about 2-3 gallons in the tank i opened the valve and listened but heard nothing after about ten minutes i measured the wire gauge with no change indicated. i then tried it with the tail raised to a cruising attitude, with the tank cap on, without it, and with it while blowing through the vent. all with no change. does the vent need a ram pressure greater then i can blow? i think i recall somebody saying they left their valve open and heard the fuel transfering while they were pushing back into the hanger. do i need more fuel in the tank to initiate a transfer. my thoughts are that there is something not right here. also my valves are mounted in the wing root if that helps at all. not sure whats going on. any suggestions are welcome.

Hi, let me ask you something. If you put the cap on and then drain fuel out of the sump drain at the rear of tha tank thru the curtiss drain valve or whatever type you have is the flow vigorous or whimpy?

If it's vigorous for 30 seconds or more then I suspect your vent system is ok. If it is not vigorous I would remove the drain valve and check it then clean (if dirty) and reinstall and test again. If still no vigorous flow then the vent system is suspect.

I wonder if you will find that the vent system is ok and the drain valve is plugged with sloshing compound. If so the same compound could be plugging the fuel transfer plumbing. If somene put fuel with alchohol in the tank or added some dry gas that could cause this problem.

Also yo may just have a improper plumbing.

I would like to hear what you find.

Dave.

[FunkyMonkey]

Re: wing tank questions

the tanks have had fuel stuck in them for awhile and out of habit i drain them before every flight. When using a strainer it seems to flow fairly quickly and without a problem. i have yet to investigate further since starting this thread due to a long drive to the airport, poor weather, and the shorter days but i plan to get up there this weekend and take a closer look. thanks again for all the helpful ideas.

[fearofpavement]

Re: wing tank questions

This has been an interesting thread as I have also been trying to figure out a fuel tank not draining down on a BC-12D. The right wing tank empties into the main nicely and predictably. The left wing tank sometimes drains down partially, sometimes hardly at all and never quickly. Have had the lines loose at the different connections and good fuel flow there. I am going to investigate the bernoulli situation mentioned and see if maybe the low pressure on the wing top in flight is the culprit. the caps have sort of a home made vent tube device on them and I am also going to try switching the caps from one side to the other although I think that was tried previously. The plane is down for an annual now so while doing the inspection I am also going to check out the routing of the lines in the wing root. The way it was acting, I was thinking that perhaps there was something in the tank intermittently plugging the outlet. Not sure of what type of tank outlet screen there is. I had left my Bic lighter at home and couldn't see in there.

[Pearson]

Re: wing tank questions

If you are going to disconnect the fuel line from where it attaches to the wing tank there can still be a quart or two of fuel in an "empty" tank that could slosh out. Drain the quick drain valve until nothing comes out.

Good luck! And let us know what you find.