Right wing tank line leak

[rdwater]

My '46 BC-12D has developed a fuel leak where the flexible line attaches to the wing tank. The flexible line is copper and is flared. Apparently the flared end doesn't seal well with the brass fitting. Perhaps theres a small crack.

Questions:
- Is copper the right material for this line? It looks old, if not original, and has a rubber-like material through the bend at the top of the door.
- Is the flare the aircraft or automotive angle?
- Can I just cut off the end with a tube cutter and re-flare?

Thanks for the help!

Bob

[Mark Julicher]

Re: Right wing tank line leak

Bob,
The copper may very well be original. Especially if the brass fitting you speak of has a flare inside a female threaded section. These are still common, but obsolete.

At any rate, copper is known to work-harden. Eventually, you do that one, last installation and the flare just cracks. If you have sufficient copper line, you might be able to just cut it and re-flare it - aircraft flare please - not automotive. You may want to anneal the copper before flaring so that the old, hardened copper does not crack while flaring; however, do that off the plane lest we lose a member of the tribe due to explosion.

A better solution would be to go back with aluminum tube and fittings if you can.

[rdwater]

Re: Right wing tank line leak

Thanks Mark. The brass fitting is as you say - flare inside the female threaded section - so this is probably original and in need of annealing before reflaring. If that doesn't work, then aluminum it will be! Thanks, Bob

[Hank Jarrett]

Re: Right wing tank line leak

Copper tube was used back in WW-I and was replaced after WW-II. It is really is obsolete. If you can I would replace it. Explosion isn't what will get you. I had a friend who burned to death in an in flight fire. It wasn't nice and quick like an explosion. The cause was traced back to the copper fuel line he used in his WW-I replica (to keep it just like the original). Copper work hardens from the engine vibration and cracks.
If you decide to re-flare, the tube the fittings and tube SHOULD both be aircraft, BUT DON'T COUNT ON IT! If the fitting is an automotive flare and you use an aircraft flare on the tube IT WILL CRACK. If you get one of those old time mechanics who says you can use the wrong flare angle and it will finish the flare process to the right angle as you tighten the fitting, IMMEDIATELY throw a cup of fuel on him and take out your lighter. Tell him if he EVER shows his face to you again you will light him up like a Roman Candle.
I lost one friend to a death too horrible to imagine, I don't want to loose another. DON'T SCREW WITH HALF A**ED FUEL SYSTEM REPAIRS!
Hank

[rdwater]

Re: Right wing tank line leak

Thanks for the good advice, Hank! We normally don't use the wing tanks and definitely don't use that one now given the small leak.

I've been looking in Spruce at the AN fittings and tubing. The AN fittings to get are obvious, except for material. Is the blue-finished aluminum good for this application, or is brass or steel needed?

What tubing is needed is less clear. There are two types I see.
(1) 3003-O Versatube soft aluminum tubing (3/8" good for 520psi max working pressure) and
(2) 5052-0 rigid aluminum alloy tubing ("this tubing will withstand a higher pressure than 3003-0 tubing").
Both say they are for fuel systems (and other applications).

The 3003-0 tubing is 500x stronger than necessary and would be easier to bend into that tight, contorted run. In more modern a/c, you usually see the rigid tubing with nice bends. Is the 3003-0 tubing an acceptable material for this application?

Thanks, Bob

[Hank Jarrett]

Re: Right wing tank line leak

I actually used the braided flexible fuel line from the wing tank to two 90* AN fuel fittings at the root leading edge on the fuselage (up just in front of the front spar attach fittings). That was where I found the hidden kink in my line that was giving all the problems for so long in fuel transfer. The two 90* fittings let me do an easy transfer from the flex line between the tank and the fittings. I used soft aluminum fuel line from the top fitting down to another 90* fitting at the intersection of the panel and "A" pillar (the door hinge tube) followed by another soft aluminum line to the shut off valve. From the shut off valve is the next soft line to the main tank. It sounds more complex, but the AN fittings allowed me to adjust the lines so they could be well secured with Adel clamps without stressing the lines. I am pretty sure the original was a hard line from the wing tank to the valve, and another from the valve to the main tank, but that way was a royal PAIN to put in. The flex section allows me to pull the wing out a few inches and unhook the line without damaging the fuel line when the wing comes off again too.
Hank

[Mark Julicher]

Re: Right wing tank line leak

Bob,
Hank's solution with the braided fuel line is elegant. If, however, you do want to go with solid line, use the 3003 versatube. You will also need a tube bender (or sand-fill the tube) a tube cutter (better than a hacksaw) and a flare tool. The inexpensive flare tools work fine once you get the knack, although a $$ Parker flare tool will spoil you forever.

[Hank Jarrett]

Re: Right wing tank line leak

Just make sure you get the correct flare angle. The stronger aluminum lines are for fuel systems that are under pressure. Our system is just gravity feed so the extra strength isn't really needed and the harder tube is actually a bit harder to bend. A tube bender is REALLY nice and there is one kind that looks like a spring that slides over the tube to keep it from kinking. Once it is bent you just slide the spring back off. I can even bend hard brass tube with mine, at least in the smaller sizes. I just tried to eliminate as many bends as I could so I could adjust everything to the airframe. I don't really like the sand method for fuel or hydraulic systems since I can never really convince myself I got ALL of the sand out. Any microscopic bits in a hydraulic system could cause bad problems down the line.
Hank

[rdwater]

Re: Right wing tank line leak

These all sound like great solutions. I do have all the bending, cutting and flaring tools. I assume the aluminum AN fittings work here. Now, about the paperwork! Is a field approval required? Is this a minor mod with logbook entry? All of these solutions are certainly increases in safety, so everyone should want to support having it done! I really appreciate your help, Mark and Hank! Bob

[Hank Jarrett]

Re: Right wing tank line leak

You are replacing what WAS approved with an approved set of parts from new materials, so I would think if anything you would only need a log entry. It really isn't a true "Mod", it is just updating the old copper lines with new modern materials, but it is your A&Ps call. I haven't found ANYONE (and we have some picky (nosey) people around here) who thought aluminum fuel fittings were a problem behind the firewall and only one A&P who "claims" you have to have steel fittings in front of the firewall. He was not convinced that you didn't need steel in the engine compartment even though there were aluminum lines, an aluminum gascolator, an aluminum carburetor and a MAGNESIUM REAR ENGINE CASE! I have aluminum fittings throughout with braided flex lines from the firewall penetration to the gascolator and from the gascolator to the carb, but he isn't my A&P. That is in addition to the braided flex line from the wing tank to the top of the "A" Pillar where the two 90* fittings take it through the leading edge fuselage rib and turn down the "A" Pillar. I REALLY like the flex lines since they really do take a lot of load off of the fuel lines that could contribute to a fatigue crack in a line. I also like how easy it is to route the lines and tie them down in the engine compartment, plus they look like they would be safer than the rubber fuel hose that was there when I bought the plane.
One thing I DON'T like about the braided fuel lines is if the rubber inside the hose breaks down, the braiding will hide it. I plan to look at those hoses VERY carefully at each annual and do a THOROUGH check if I ever smell or see fuel. I think a fuel flow test would be a good idea at each annual to check for internal hose collapse and will be adding it to my annual list.
Hank

[rdwater]

Re: Right wing tank line leak

I talked to my IA this weekend and he agrees with Hank that this is a minor repair, so we'll make the fix with modern parts. Thanks everyone for your help! Bob

[Bird]

Re: Right wing tank line leak

Hank, will this ethanol crap come into play with the rubber, I seem to remember having trouble when this crap 1st came out on my olds.

[Hank Jarrett]

Re: Right wing tank line leak

One of the reasons we are NOT allowed to use fuel with alcohol is it can attack some of the older chemistry rubbers in our planes fuel systems. There are lots of other reasons not to use it, but one of them is how it may react with the rubbers in our seals and carburetors. I have also seen it soften the old sloshing compounds in fuel tanks. I have an old Porsche and it is not supposed to be compatible with alcohol fuels. The factory says will soften the fuel lines and cause bits to come off of the insides of the lines and screw up the injectors.
Bottom line though is that it really doesn't matter if it will damage your system or not. It is illegal to use it. The chemistry is complex for the different rubbers and different types of alcohols and I worry about the non-chemists who keep saying there is no problem. They DON'T know! I don't use it, and I recommend you don't either.
Hank

[N96337]

Re: Right wing tank line leak

Amen, Hank!!

[cvavon]

Re: Right wing tank line leak

AS John said I also agree with Hank as far as alcohols made from corn first field corn is for cows and corn flakes but a little for making corn whiskey is the only human use i need Chuck