Fuel Tank Ground

[svyolo]

A few minutes of googling did find some solders meant for aluminum. I think soldering a wire or welding a tab onto one of the tank bungs will be my solution.

Some of the solders melted at a very high temp, like 1000F. Some of the others were a 300 F. I would definitely choose the lower.

[Bcone1381]

Tigging tabs is trivial for some, but Its beyond my current skill level. I don't want to weld/braze anything onto my tanks. Soldering would be my second choice.

SO I will plan to use an Aluminum AN742 loop clamp applied at the red arrow (The tubing I use is 3/16DIA rigid 5052 AL tubing), and two ring termials with the application of some electrical anti-oxident. If this method seems negligent or not prudent, please advise.

Brooks
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[Battson]

Suggest you make make sure the clamp is tight, so it doesn't vibrate and slowly wear a hole through the fuel line.

[Bdflies]

I like your idea Brooks. All of the cautions are right (getting loose and wearing, electrical conductivity) but are easily checked at annual. A quick look and shake would reveal a loose clamp, not to mention the telltale smoky dust and a quick check with a multimeter would confirm continuity.
If one is concerned about the effects of vibration, I'd suggest avoiding "Aluminum solders". Strength is highly dependant on joint design and elongation(flexibility) isn’t good.


Bill

[Mark Moyle]

Kent White at TM Technologies has different aluminum brazing and welding rods as well as special fluxes for different aluminum types.....and don’t forget to ask about his gas welding lens...if welding aluminum from my perspective you’ll want Kent’s lens to see what you’re doing....

For corrosion prevention I like using dielectric compound and self vulcanizing tape to seal the connection or prevent exposure to the atmosphere.. for a connection like a tank ground cut square pieces..apply. Warm it up with a heat gun to soften, knead it to shape and fill the voids until you’re happy with the sealing of the connection...

[svyolo]

I am not sure how well a clamp on the fuel line would work. The clamp looks anodized (you can fix that), but that line goes to a anodized fitting, which goes to a brass fitting, which goes to the aluminum tank. Sealant on all the threads. It might have a lot of resistance to overcome, which might get worse over time.

It might work. I am not sure.
I think my second choice would be to try some kind of thin hose clamp on the filler neck or one of the bungs. I will either solder or TIG if my aluminum TIG skills allow it. Not there yet.

[JimParker256]

At the very least, I'd check the resistance from the fuel tank to the grounding wire to see what all those "minor" things add up to. You don't even need to wait until it's installed to check it out. If the resistance is higher than you'd like, go to Plan B...

[Bcone1381]

Kent White at TM Technologies has different aluminum brazing and welding rods as well as special fluxes for different aluminum types.....and don’t forget to ask about his gas welding lens...if welding aluminum from my perspective you’ll want Kent’s lens to see what you’re doing....

For corrosion prevention I like using dielectric compound and self vulcanizing tape to seal the connection or prevent exposure to the atmosphere.. for a connection like a tank ground cut square pieces..apply. Warm it up with a heat gun to soften, knead it to shape and fill the voids until you’re happy with the sealing of the connection...

I've got Kents video on aluminum welding. The flux is corrosive and needs to be cleaned off after welding. I've always wondered about the inaccessible areas not getting cleaned. "Would I have a corrosion problem there?"

I like your vulcanizing tape idea! I will be using that!

[James]

Yep, I was thinking about this the other day, because my factory tanks don't have the tangs. My solution was to source (or make) an aluminium ring terminal with an ID large enough to accept the AN union at the outlet of the tank, and then sandwich the terminal between the union and the tank. If it was a soft material and had a large surface area, I don't think it would leak. I would then run it to the frame.

Questions for experts:

What should my fuel tank bonding check be? 3 mOhms?

My little C150 has grounding tabs that protrude through the wing surface to connect your fuel nozzle ground onto. What do BH guys do to ground the gun?

Thanks in advance,

James

[davzLSA]

if its 3 m ohms to ground that is not much of a ground, ideally you need to see less than 1 ohms, 3 m ohms is 3 million ohms, The lower the resistance between your tank and ground the better.

[kestrel]

davzLSA, under "PREFIXES", check 'milli' vs. 'mega'

http://www.learnalberta.ca/content/memg/Division03/International%20System%20of%20Units/index.html

[zkelley2]

Yep, I was thinking about this the other day, because my factory tanks don't have the tangs. My solution was to source (or make) an aluminium ring terminal with an ID large enough to accept the AN union at the outlet of the tank, and then sandwich the terminal between the union and the tank. If it was a soft material and had a large surface area, I don't think it would leak. I would then run it to the frame.

Questions for experts:

What should my fuel tank bonding check be? 3 mOhms?

My little C150 has grounding tabs that protrude through the wing surface to connect your fuel nozzle ground onto. What do BH guys do to ground the gun?

Thanks in advance,

James

The ground wire at the fuel pump is connected to the fuel nozzle. The hose has a wire wrapped in the rubber that makes that connection.

[James]

Hi DavzLSA - yeah, nah I was talking about 3 milliohms, ie 1/300th of an ohm. My modern keyboard doesn't seem to have an omega key! :-) :-)

zkelley2 - not sure how the specs work in your part of the world, but here in Aus, you have a ground lead you run out to the aircraft from the pump, but then the fuel nozzle also must also be grounded to the airframe prior to transfer of fuel. Same goes for Avtur / JetA1.

All the refuel systems here have another short bonding lead from the gun to the airframe, and I'd say that's probably the most important of them all, given possible static build-up with the fuel flowing down the rubber hose. I'm not sure if our fuel hoses also have a grounded shield/mesh built in like your hoses do. Interesting the different solutions offered in different parts of the world.

Thanks guys,
James

[zkelley2]

Ya, your hoses must be constructed without an internal wire. You can't even buy those here. Even the fuel hoses at the hardware shop that I assume are made in China have them.

[James]

Actually, thinking about it, our hoses must have the wire mesh as well... because they're all made OS.
So, the second bonding lead on the gun must be to double the connection pump-hose-airframe.

[kestrel]

I most often see a separate ground cable that is attached to anything on the airframe that is part of the airframe ground. In the unusual case (for me) that there is a short ground cable attached to the fuel nozzle, I have been able to reach it to the tiedown ring of that wing.

zkelley2:
I'm not a big fan of grounding through the nozzle. It is true that most static build up doesn't occur until pumping, but not all and there may be build-up from the prior guy pumping. Or your airplane may have a charge on it from flying through the air. The moment you touch the nozzle to the edge of the filler neck, you could get a spark in an environment with a healthy mixture of oxygen and fuel vapor.

Growing up pumping gas at our family run airport, we didn't make much use of ground wires and nothing ever came of it. Now I'm older and I hope wiser. I presume that all these grounds are required because someone got blown up. I've changed my procedures.

[zkelley2]

I most often see a separate ground cable that is attached to anything on the airframe that is part of the airframe ground. In the unusual case (for me) that there is a short ground cable attached to the fuel nozzle, I have been able to reach it to the tiedown ring of that wing.

zkelley2:
I'm not a big fan of grounding through the nozzle. It is true that most static build up doesn't occur until pumping, but not all and there may be build-up from the prior guy pumping. Or your airplane may have a charge on it from flying through the air. The moment you touch the nozzle to the edge of the filler neck, you could get a spark in an environment with a healthy mixture of oxygen and fuel vapor.

Growing up pumping gas at our family run airport, we didn't make much use of ground wires and nothing ever came of it. Now I'm older and I hope wiser. I presume that all these grounds are required because someone got blown up. I've changed my procedures.

You're not grounding through the nozzle. At least not initially. You ground with the ground wire that you attach to the airplane prior to even touching the hose. That wire and the wire that runs through the hose and is connected to the metal threads the nozzle is threaded to(or crimped as you may have). Those two wires are connected. Connecting the first wire is the same electrically as touching the nozzle to the aircraft.
The entire static charge potential is neutralized when you connect the first wire and can never build because they are connected the entire time. The correct term would be bonding, not grounding since you're not dissipating any charge, just making the potential between the two objects 0.

They used to do a lot more actual grounding to earth, but we figured out with big metal airplanes getting fueled with storms in the vicinity, that turning an airplane into a lightning rod is a bad idea.

[way_up_north]

what follows is land lubber related....but might be food for thought

was assisting a friend do some wiring around his house and learned a few interesting things...that might be common knowledge here but was new to me...

aluminum is an excellent conductor but the oxide film formed on the surface...does not conduct electricity at all and is a good insulator...and has been the cause of some house fires....as aluminum wires in a connection marett..twist connector or other wise may oxidize over time and the electrical resistance creates heat....

do to a shortage of copper during the Vietnam war many homes built at that time were wired with aluminum or worse...a hybrid... a house wired with copper and aluminum together...

the procedure for making an aluminum connection safe....is cover the aluminum wire end with conducting grease(cant remember what specific kind of grease it was)...wire brush the aluminum surface while its covered by the grease...so it never comes into contact with air..as the oxidizing process can happen very fast..the copper and aluminum wires are then put into the marett/connector together with the grease...this process is excepted by the province of Ontario as making an aluminum connection safe to pass electrical inspection(probably the same other places)...an aluminum wired house here cant get insurance without this process ...

I would consider any un-protected electrical connection with aluminum a weak point over time

[alaskabearhawk]

Noalox is used for home wiring: https://idealind.com/shop/noalox.html

[Archer39J]

Your house is still fed with aluminum conductors, and most of our electrical infrastructure is aluminum. The problem with using Al and Cu together is their different thermal expansion rates, in connections they'd work themselves apart and would arc as they lost contact, that's what was burning houses down.

Put some dielectric grease on Al joints for good measure, I don't know what wire brushing through the grease would get you.

Permatex 22058 Dielectric Tune-Up Grease, 3 oz. Tube https://www.amazon.com/dp/B000AL8VD2..._2Wy6Cb8ZWWY22

[svyolo]

My straps are being painted and the tanks will be going in for good. I happened to have a thin strip of .040 Al in my (growing) scrap heap. That piece took all of 30 seconds to make. A bare Adel would work as well. Maybe a dab of urethane on 25% of the surface to make sure it doesn't vibrate off.




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[James]

Well, my initial thought was to sandwich a terminal lug between the tank and the union, but as Brooks pointed out, because it's a tapered thread, it won't pull up tight. So, I'm going with this clamp method as well, and shaving down the clamp to sit under the boss. You can buy aluminium Adel Clamps, they're quite expensive, but probably a good investment. - James

[S Lathrop]

I am posting this solution to solicit responses.

Why not weld say a 1/2 diameter boss into all the tanks? My plane has aux tanks. So I would have a boss on each aux tanks and 2 bosses on the main tanks. The bosses would be drilled and tapped 1/4 20, blind holes. I would then run a ground strap or wire from the aux tank to the outside of main tanks and the other boss on the main tank (inside face) would be grounded to the root of the wing near the spar attachments to the fuselage. The ground straps would contact a 1/2 inch diameter surface of the boss and be secured with a 1/4 bolt. I think that this system assures a strong connection and one that should not have corrosion issues.

[svyolo]

Obviously will work, but it is still relying on a mechanical connection to make the electrical connection. If I was going to weld/braze/solder, why not directly attach the ground wire/strap to the tank? No oxidation issues.

[alaskabearhawk]

Noalox is used for home wiring: https://idealind.com/shop/noalox.html