Fuel Tank Ground

Bcone1381

Bcone1381

Finished Patrol
Today as I am reading thru part of Eric Newtons Bearhawk Builder's Manual. (Specifically the Volume 1 Wing Manual, part 8, p.13) Eric Newton adds a grounding lug to the fuel tank to facilitate grounding the tank to the wing because he uses rubber as a cushion between the fuel tank straps and the tank.

This is the first I've thought of grounding the tank.Are others grounding the fuel tank? If so, by what method?

I am thinking maybe an AN472 aluminum loop clamp around the AL fuel line near the tank. Then a wire with a ring terminal on each end to ground the loop clamp to a rib. Is there a industry standard that demands it be attached directly to the tank?
 
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Ya the MDRA inspector in Canada says it’s mandatory. I used a regular 10ga wire, pulled 8” of the cover off one end and used a foil tape to adhere it to the tank
 
Ya fuel tanks need to be grounded to the aircraft, otherwise that grounding wire you attach when you fuel is doing nothing to prevent a spark at the tank hole when you bring the nozzle up.
 
Great point! My first thought was it is grounded though the fuel lines. The I remembered that many, including myself, use a short section of rubber fuel hose at the wing tank so that ground path doesn't exist. I have some copper foil tape I made my antenna out of. Maybe I'll bond the tank to the wing with that.
 
This is clearly something that needs to be addressed so thanks for bringing it up! Maybe the kit tanks could include a grounding tab in the future, as it stands now I'll need to figure a way to include a jumper on mine.
 
I wrapped large copper wire/cable around the welded tank nozzle many times, and secured it tightly by twisting it back on itself and adding a very small amount of solder. I left the insulation on the cable for wear protection, and terminated the other end onto the wing structure with a ring terminal and bolt.

I think we had a thread about this before? As noted, if you used rubber hose in your fuel line then you need to earth the tank (you have rubber grommets in the wing ribs).

My local IA has seen a homebuilt fireball when the fuel tank was not grounded and a spark occurred. The pilot / refueller was terribly burnt.
 
How about soldering or silver soldering a wire to the outside of one of the brass tank strainers? I have never tried soldering something directly to aluminum. I will give it a shot.
 
I haven't looked, but I was thinking there might be room to drill and tap a small hole (maybe #8) on the surface of one of the bungs and not interfere with the strainer. Have to see when I get home.
 
We should think about high resistance oxidation of materials as well as corrosion issues between different metals. I like to see tight (screwed or clamped) connection of very clean materials that have been coated with an electrical antioxidant compound such as Noalox or No-ox-id.
 
marcusofcotton said:
We should think about high resistance oxidation of materials as well as corrosion issues between different metals. I like to see tight (screwed or clamped) connection of very clean materials that have been coated with an electrical antioxidant compound such as Noalox or No-ox-id.
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With the materials we are discussing, galvanic corrosion is only a problem if an electrolyte is present. Inside the wing is pretty dry. No problems so far with copper, aluminium alloy, and steel all close together.

I totally agree with your point though, a welded tab from the factory would be a valuable addition. Perhaps something to share with Mark Goldberg
 
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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.
 
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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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...
 
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Suggest you make make sure the clamp is tight, so it doesn't vibrate and slowly wear a hole through the fuel line.
 
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.
 
Mark Moyle said:
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...
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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!
 
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
 
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...
 
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
 
James said:
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
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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.
 
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.
 
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
 
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.
 
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.
 
kestrel said:
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.
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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.
 
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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.
 
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
 
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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/ref=cm_sw_r_cp_apa_i_2Wy6Cb8ZWWY22
 
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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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.
 
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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.
 
I understand about the rubber hose interrupting the ground at the wing roots, but I have installed aux tanks with Facet pumps between the aux and main tanks. Would that not ground both the aux and main tank through the aluminum fuel line to the Facet pump with is mounted to a wing rib?
 
See the concern expressed in post #19. I will be checking all my fittings to see if the electrical continuity is effected as it travels thru anodized AL fittings the pipe thread sealant. I still like the solution in post #28.
 
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
 
After pondering this thread, I ended up just using an AN742-D16 clamp on the outlet bung of each tank (with No-Ox applied to all mating surfaces). Equivalent to post #28 but saved me a bit of fab time vs making my own clamp out of scrap (which I have plenty of!). :D
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Per AC 43-13B:

11-191. FUEL SYSTEMS. Small metallic
objects within an aircraft fuel tank, that are not
part of the tank structure, should be electrically
bonded to the structure so as to dissipate static
charges that may otherwise accumulate on
these objects. A practical bonding design
would use a flexible braided jumper wire or
riveted bracket. In such situations, a DC resistance
of 1 ohm or less should indicate an
adequate connection. Care should be taken, in
designing such connections, to avoid creating
continuous current paths that could allow
lightning or power fault currents to pass
through connections not designed to tolerate
these higher amplitude currents without arcing.
Simulated static charge, lightning, or fault current
tests may be necessary to establish or verify
specific designs. All other fuel system
components, such as fuel line (line to line) access
doors, fuel line supports, structural parts,
fuel outlets, or brackets should have an electromechanical
(bonding strap) secure connector
that ensures 1 ohm or less resistance to the
structure. Advisory Circular 20-53A Protection
of Aircraft Fuel Systems Against Fuel Vapor
Ignition Due to Lightning, and associate
manual DOT/FAA/ CT-83/3, provide detailed
information on necessary precautions.​
 
OK, I need a layman’s explanation.

Luckily BrokenStraw brought this to my attention as I missed it in the build process. I have braided ground material that I used to ground the engine to the fuselage. If I put an adel clamp on the fuel tank and use this braided material, what should I attach it to? A wing rib? I am at a total loss on this. Please help as this has come up just in time for me to get it done prior to hanging wings.
 
I would like some clarification as well. I understand the clamp and the no-lox but what size ground wire needs to be used and does it go to a rib or back to the fuselage to a ground block?
 
I would use a three inch long piece of 20 awg tefzel wire and crimp on PIDG ring terminals on each end. One ring for 3/16” bolt on the loop clamp. One for #6 machine screw. I then would drill a 9/64” hole in the wing rib and attach the wire to it. Then check it for continuity. Keep it small simple and light.

if you don’t have a crimper, PIDG terminals, or wire lying around wait on it until you do your electrical. You’ll have all that stuff in your inventory then.
 
I didn't use this, but I saw an all metal Adel clamp onto a hard fuel line. Clean the oxidation off the line and cad plating or whatever off the clamp. Seemed like an easy solution. Check anything you do with a multimeter for continuity/resistance.
 
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