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Al Downs

Grounding while fueling

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What is the best place to attach ground wire while fueling. The main wheels and tie down rings on the wings are places I see pilots using but on the CTLS I don't think those places go to ground. I have also heard people say it is not a good idea to use the exhaust pipe. It seems to me that on the CTLS the easiest is the exhaust pipe or the nose wheel. What do you use?

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I don't know Ed. I remember hearing it but don't know the reason. That is what I use. I see some of the pilots here using the other places and explain that they are not grounds (at least I don't think they are). I tell them to use the exhaust pipe.

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Use the exhaust. It is grounded to the battery or we wouldn't use it to charge or jump the aircraft. Plus to have a ground like some think you would need to drive a 6' copper rod into the ground and attach that to the plane just like hangars and homes that are grounded. Plus our planes are carbon fiber so it conducts electrical current so it can be grounded through the system. All you're trying to do is help prevent static build up.

Food for thought. :)

Let's look at realistic circumstances. There has never been a documented static fire in Tucson. Ladders that you use usually have rubber or plastic feet so it doesn't really touch the ground and you're standing on an un-grounded ladder. . The gas fill neck on the plane is epoxy'd in place so it really doesn't have carbon fiber contact because epoxy doesn't have the same electrical properties as carbon fiber. So the carbon fiber at the neck may not have electrical properties for the ground on the exhaust. So now you're standing on a non grounded ladder, with a nozzle from a truck that isn't grounded into the soil and a plane that isn't grounded to the soil.

What's the worry. LOL

Just fuel it.

 

p.s.

The grounds built into the plane, truck and pumps will prevent or safely discharge static build up. 

 

p.s.s.

Take a voltmeter and check continuity from the exhaust to the fuel filler neck.

I did this. Surprise is in your future. LOL

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I only know of one fire caused by static electricity. It was many years ago at the Birchwood airport in Anchorage. A guy I knew causally was defueling his beautifully restored Navion in a hangar that also housed a C-185 and another plane. It all burned to the ground. I don't know for sure if it was grounded or not.

That is why I never fuel or defuel in my hangar. Fires are very rare but do happen. It would be my luck to have a spark and a fire. Kind of like any line I am in at the store will be the one that takes the longest time.

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Grounding the aircraft is about as much use as changing the colour of your shirt, it does nothing. To prevent static build up you must bond the source to the aircraft tank. I realise that dose not answer the question but static builds up by the flowing fuel, the faster the flow the more static can happen. I bond the nozzle to the filter/funnel. A lot of people bond the exhaust to the fuel truck with a static line. This has nothing at all to do with grounding.

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I've done a continuity test to both of my fuel ports to the exhaust. It's 10-20 ohms.

The purpose of bonding the aircraft to ground is that it too can have a difference of potential from the supply tank. Flowing liquids do create static buildup as you said, but it's not the only source. Airplanes are separated from the ground with rubber, if they somehow get charged, now you have an issue.

You should be bonding /everything/ to ground, or at least to each other, not just the aircraft, or just the funnel, or just the canister.

That's why fuel trucks bond to the airplane..the hose is a special type of conductive hose so that the aircraft it's bonded to, and the hose itself, remains at equal protential.

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You are correct about the need to bond as I said but the difference in potential energy from the plane to ground is of no consequence. A spark could theoretically jump from the ungrounded plane to ground and no one would notice or care. I have worked in the petrochemical industry 40 years and understand static discharge hazards and can assure you that even jet airliners are not grounded but are bonded for fuelling.

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Big airplanes are usually grounded though. Not necessarily through the fueling system (some trucks do have static cables that drag from the rear axle, not really an ideal ground though, I question the effectiveness), but it could be through things like the GPU. The grounding isn't really just about the fuel.

I say should be grounded because it's ideal and covers a lot of bases. Not a necessity for fueling in itself. Bonding though, is a MUST. So we're on the same page.

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You must electrically connect the supply eg. the fuel truck or at least the nozzle to the fuel tank eg. the aircraft

Fuel truck hoses are tested for continuity on a regular basis enforced by law.

For the process of certification an aircraft fuel tank must be conductive and this can be achieved a number of ways. A glass fibre tank may have

an additive in the resin, or a copper strip inside the tank or any other method that will achieve conductivity. Or of course you could buy an aircraft with a carbon fibre

tank maybe a CT.?

To answer your question Al,  just bond with the static wire on the truck to your exhaust pipe. It is still ok if there is a bit of resistance at the connection because static

electric charge is very high voltage and low current.

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Static electricity is also governed in part by capacitance, and CT's are not exactly capacitors. So any charge that may be built up will be gone before you even realize you've touched the exhaust as well.

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The tank itself is probably grounded through the carbon fiber, but it is coated inside. I wonder if that coating is conducive? 

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