Copper Fuel Lines

[Hank Jarrett]

Re: Copper Fuel Lines

Woody had a closed casket funeral. That was back in 1983.

Hank

[otrcman]

Re: Copper Fuel Lines

I agree that copper fuel lines can be a real hazard. And yet most older airplanes did use copper. My current project is a 1929 Curtiss Robin, which I'm trying to make as authentic as possible. Right down to "AC" type fuel fittings. So, to copper or not to copper ? And Hank, I also well remember Woody Clapp's terrible end.

My solution was to use automotive steel fuel line material, but to have it copper plated for appearance. The fuel line was cheap, but the plating wasn't. Plating cost was $250. But that's a small part of restoring a large project.

As to the question of which type materials are subject to fatigue cracking or hardening and then cracking, I have copied a bit out of a Wikipedia article on the subject. See below. In a nutshell, metals fall into two categories: Those which eventually fail if repeatedly stressed even a small amount, and those which do not fail providing you don't stress them beyond their "endurance limit". Copper definitely falls into the first category, while steel falls into the second category. That's one of the reasons you see springs made of steel but not copper or aluminum.

Can you make copper lines last a long time ? Yes. The trick is to immobilize them so that they are not flexing at all. Lots of support clamps so they don't vibrate even a little bit. But with steel, the worry is reduced immeasurably.

Dick

[Hank Jarrett]

Re: Copper Fuel Lines

Dick,
Great idea. You get the look and the improved resistance to cracking.

I would recommend two more additions. First is a fuel cut off right at the tank so you can shut off all fuel at the source if there ever is a leak. Second, check to see what happens when you copper plate stainless. I don't know what type stainless you used, but high strength steels are prone to hydrogen embrittlement (stainless is not normally considered "high strength"), which is when hydrogen atoms are interlaced in the iron and alloying elements putting pressure on the bonds between them. It was usually a problem with HIGH STRENGTH steels, and stainless tube is usually pretty mailable, so you are probably OK, but we used to heat soak the materials after plating for 24 hours at 350-375 degrees F. You had to put the parts in the oven within 30 minutes of coming out of the plating solution for the embrittlement relief to work reliably. Lower strength steels would self relieve over time and I used to have tables that showed what percentage of parts would crack over what time before they were self relieved. The nice thing about a restoration project is you get LOTS of time for self relieving to happen. ;-)

If the plate shop did an embrittlement relief you should be safe from embrittlement.

It has been quite a few years since I was a plating engineer (late 70s) but I remember that the Ultra High Strength steels (like 300M) would split in an hour if not taken to the ovens. An F-14 landing gear was sitting on a Bull Dog cart and the transport guy went to lunch. An hour later it sounded like a shot gun blast when the cylinder split. Really showed the floor guys we were NOT kidding about embrittlement relief requirements.

Again, we DID NOT plate stainless, so I don't know what the effect on stainless would be from copper plate, but the shut off valve would be nice to control how much fuel gets into the cockpit.

Hank

P.S.
There are a lot of lovers of other types here, one being the Robin. How about a thread in "Hangar Mates" on your Robin? I would really love to see more of your Robin project.

P.P.S.
If the shop used IVD plating (vacuum deposit) there is no acid solution so no Hydrogen. If they did that, you are MUCH safer! I LOVED IVD! Didn't work for chrome, which was our bread and butter, but IVD Aluminum almost COMPLETELY replaced CAD plate and we did use LHE plating (Low Hydrogen Embrittlement) on a lot of parts, but at the time it was developed it was pretty much a military only process. Should be pretty wide spread by now.

[otrcman]

Re: Copper Fuel Lines

[QUOTE=Hank Jarrett;78636]Dick,
Great idea. You get the look and the improved resistance to cracking.

I would recommend two more additions. First is a fuel cut off right at the tank so you can shut off all fuel at the source if there ever is a leak. Second, check to see what happens when you copper plate stainless. I don't know what type stainless you used,.....

Hi Hank,

The tubing I used was ordinary low carbon steel, not stainless. Incidentally, I was surprised to read that stainless steel fits into the "will eventually fatigue crack" category just like copper and aluminum. Carbon steel and titanium seem to be unique in their ability to flex within some limit forever without experiencing fatigue. Of course that's not counting wood. My understanding is that wood can be flexed repeatedly right up to its yield point without fatigue. Good reason to use wood spars, providing you don't have termites.

Dick (another retired NASA Aero engineer)

[Hank Jarrett]

Re: Copper Fuel Lines

Been a LOOOONG time since I was a plating engineer and we never even tried workng with stainless (in fact there was very little stainless in any of the Navy planes I worked on). We did do a lot of copper plate in the "fill and cap" process I helped develop. When the chrome on a steel part was spalled we would grind the area our, fill in to flush with LHE copper select plate until teh area was flush, then put a select plate Nickel-Tungston cap over the copper. We salvagd a LOT of landing gear pistons in the field with the technique, right on the plane. You could spot the planes from across the ramp because the chrome piston looked like it had a stain on it where the copper was showing through. Watched a line division guy work like mad trying to clean the stain off before I could explain what it really was. The Nickel Tungston was REALLY TOUGH..

Hank

Funny how high tech guys are drawn to low tech planes. I got a lot of teasing that I had a plane with no starter on weekends and a space craft at work. Guess which one I liked best. ;-)

[otrcman]

Re: Copper Fuel Lines

Funny how high tech guys are drawn to low tech planes. I got a lot of teasing that I had a plane with no starter on weekends and a space craft at work. Guess which one I liked best. ;-)

Hank, please excuse my edit of your post. What was saved is the part I wanted to reply to.

I never saw myself as a high tech guy drawn to low tech planes. I was always drawn to steel tube (or wood) & fabric airplanes. NASA was just a way to make money to pay for my real interests. Most of the planes I worked around at NASA were either jets or rockets. The jets smelled like an old school bus and you didn't dare smell the rocket fuel because it might kill you. The only airplane there that really turned me on was our C-47. Well, I guess the start cart for the SR-71's was pretty cool as well. It had two Buick V-8's to crank the SR engines.

This is not to totally discount my professional years. I was fortunate to rub elbows with some really smart people, learning a tremendous amount about materials, systems and aerodynamics that I'm able to apply to the airplanes that we work with now.

Working as a flight test engineer, I had the opportunity to fly (and log stick time) as a back seater in lots of different different types, most notably the T-33 and F-104. They were interesting, but nowhere near as much fun as my L-2.

Dick

[Hank Jarrett]

Re: Copper Fuel Lines

Hank, please excuse my edit of your post.

Dick

Certainly not a problem for me. ;-)



They were interesting, but nowhere near as much fun as my L-2.

Dick[/QUOTE]

COMPLETE agreement!

Hank

They never did let me fly Orion, of course no one else has yet either. Guess that means I could hold the current altitude record for her. ;-)