Flying with one tank Dry?

C

CraigH

New member
:?: I am wondering if my '75 7GCBC will start sputtering if one wing tank is dry and the other has between 1/4 and 1/2 fuel remaining? I've got about a 1/4 tank more in the right tank, and would like to run the left tank dry to replace a dripping quick drain. Have any of you actually flown with fuel in only one tank?

I know it should work in theory, but would rather rely on someone elses experience rather than try it myself.
 
My recently purchased Citabria ('73 GCAA) burns fuel completely uneven. On fill-up, one tank will take 18 gallons and the other will only take 5 gallons. Although I can't see for sure, but I think one tank is empty or very close to empty before it starts burning off the other tank. The fuel gauges bounce around a lot, but they seem to indicate one tank stays nearly full while the other goes down much quicker. I've also noticed that in the tank that doesn't burn as much fuel; the fuel seeps out and around the fuel cap pretty bad (not good on the surrounding fabric). For now, I've switched the caps on the tanks to see if one tank is not venting properly causing the uneven fuel flow.

Is the uneven fuel flow common in Citabrias? Do I need a new fuel cap to prevent the leaking? Any comments or suggestions are appreciated.

Thanks,
Brian Vulgamore
Scott City, KS
 
Brian,
Mine burns fairly evenly - MUCH more evenly than my Taylorcraft did. Sounds like you may have a venting issue or something restricting one of your fuel lines. Does your vent tube on the left wing have the little plastic buffer in front of it like it is supposed to?
 
I fixed the uneven fuel burn on my 7gcbc by replacing the gaskets in the filler caps.
Jay
N14WL
 
In the process of taking my wings apart this summer, I unscrewed the vent checkvalves and looked inside to see what makes them tick. They are hex shaped and have an "UP" orientation stamped on one side. Neither was pointed directly up on my plane-- one was rotated about 1/6 turn forward and the other about 1/6 turn aft. I suppose this is because they have pipe threads and so you just tighten them on until you think they have sealed OK. They worked fine before I took them apart, and they work again now.

Anyway, there's a delicate little flapper thingy inside each one that has a cute little spring and a gnomish red gasket. The assembly is supposed to pass air without passing gas. Err... you know what I mean. They look like they could get gummed up really easily. Then it seems that any of the symptoms described in the above posts would be possible.

I scraped mud dauber wasp residue from my vent intake halfway to the flapper. Scary. Any I think I'll forget about every taking a chance on mo-gas. Too many tales of gum and varnish.

The checkvalves are located just outboard of your gas cap. You may be able to feel them thru your fabric. Theoretically, you can replace these with minor fabric work.

Does anyone have a test procedure to recommend?

-Alex
 
Thanks for the info. Yes, I've got the plastic buffer, but I think I definitely have one bad gasket. I will replace both gaskets and see if that helps.

Alex, that's some good info on the check/valve. At some point, my plane has had some wasps in the wings. Maybe I've got some buildup or a partially plugged check/valve. I wonder if I can inspect the check valve without removing fabric?

Does anyone know why the fuel tanks have a vent on the left side (proceeded by the little plastic buffer), and also have these check/valves?
 
The posts on this topic are interesting and give good solutions to the problem of one tank draining faster than the other (usually a cracked gas cap gasket?) but no one has answered the original question.

Has anyone run one tank dry and demonstrated that the other tank will continue to feed the engine?
 
Yes, I think you can run on one empty tank. I discovered this unintentionally b/c of my uneven fuel flow problem. On my last fill up, I put 18 gallons in the left tank, and it only holds 18 gallons (actually, 17.5 usable). My right tank only took 5 gallons. Apparently, I had been flying on one empty tank.

Where are some places a guy can get Citabria parts?

Thanks, Brian
 
FYI-

I would consider a 5 gal flow imbalance normal, a 10 gal imbalance cause for concern. There is no gurantee that whatever caused the imbalance will magically disappear and allow the full tank to suddenly begin flowing after the other tank runs dry. Flying with drastic imbalances expecting, hoping actually, that the full tank will begin feeding is foolish.

While some earlier Citabrias had an upper wing vent system, all of the later ones have a vent under the LH wing. This vent is protected from impact icing, in freezing rain, by a plastic ice deflector, this is the same reason most high wing Cessna fuel vents are just behind the lift strut. Both tanks are vented from a point outboard of the filler cap on the upper edge of the outboard end of the tank. A check valve is threaded into the tank, a line leads from the RH tank across the cockpit at the upper rear of the windshield, this vent line then attaches to a similar line from the LH check valve and exits the lower surface of the wing just aft of the ice deflector. The check valves are designed to prevent fuel loss in uncoordinated flight, when parked on uneven terrain, etc. I've never seen Champion/Citabria vent line check valves that functioned satisfactorily. I regularly see fuel streaming from my vent in slips, this with a new aircraft.

Because the tanks are vented the caps are NOT vented.

Uneven flow can be caused by leaking caps allowing the lower pressure on the upper wing surface to form a partial vacuum in the tank, a cracked filler neck (always do your own fuel, NEVER allow the nozzel to hang from the filler neck), a clogged vent line, a malfunctioning check valve.

Tom-
 
About 1.5 years ago, a mud dauber built a nest not just in the fuel vent on the left wing but in the cross over pipe, running across the upper windshield area, between the tanks. Also, during a recent wing rebuild we found our check valves to be gummed up. All this apparently caused the left tank to burn much faster than the right (the one with the gage gave us a too-high reading).

Even with the gummed up valves, though, the tanks have always burned evenly, except when the crazed mud dauber's nest was in the crossover.

Charlie
 
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