Re-fueling - What do you use for ground?

[0TreeLemur]

I didn't watch the video and saved minutes of my life to do something else!    Unpainted metal is the requirement.  I too use the tow-bar hole in the nose gear.

[MikeOH]

3 hours ago, GeeBee said:

A lot of St. Elmo's off the prop at night would confirm it.

Interesting troubleshooting technique

[PeteMc]

5 hours ago, gevertex said:

But it does get a little bit in the way of the fuel hose as I drag it to the opposite wing.

Note to Self...   Pull a LOT more of the grounding wire out than you need and sort of whip it under the wing and then back out to your grounding point on the nose wheel.  you'll never walk over or drag the hose over the grounding wire again. 

And that also means no more of those accidental disconnections when the wired gets pulled with the hose. 

[MikeOH]

Ok, finally made it out to the hangar and measured resistance to the fuel cap retainer ring from the exhaust stack: 13 ohms. From the muffler it is less than 1 ohm. My conclusion is the resistance is entirely due to the spring loaded ball joint. Note I have a PowerFlow exhaust.

[N201MKTurbo]

56 minutes ago, MikeOH said:

Ok, finally made it out to the hangar and measured resistance to the fuel cap retainer ring from the exhaust stack: 13 ohms. From the muffler it is less than 1 ohm. My conclusion is the resistance is entirely due to the spring loaded ball joint. Note I have a PowerFlow exhaust.

I think any charge big enough to make a static spark, would make that spark across the ball joint before you got the fuel nozzle anywhere close to the airplane. The charge would actually flow through the 13 ohms quite rapidly. If we knew the size of the charge, we could figure it out. I’m thinking sub-millisecond.

[MikeOH]

5 minutes ago, N201MKTurbo said:

I think any charge big enough to make a static spark, would make that spark across the ball joint before you got the fuel nozzle anywhere close to the airplane. The charge would actually flow through the 13 ohms quite rapidly. If we knew the size of the charge, we could figure it out. I’m thinking sub-millisecond.

Exactly!  As someone else pointed out, ESD wrist straps have a much larger series resistor and are still quite effective for their intended purpose of static charge dissipation.

I'm sticking with grounding the exhaust stack.  By the time you put on the ground clamp and get around to putting the nozzle in the filler neck quite a few milliseconds have elapsed

[EricJ]

I was helping a friend with their Cherokee today (like in the vid) and took the opportunity to measure the resistance from the exhaust pipe to the airframe:   0 ohms.   

That guy either just isn't doing it right, there's something wrong with his airplane, or there's so much crud on his exhaust that he couldn't get a measurement.    If the ground/bonding straps are not right, that's definitely something to get sorted out so that they're configured functionally, especially if you're getting too much radio static or engine instruments are flaky.

I'll suggest that if you've been using your exhaust (like I do), there's no reason to change habits.    If you get an open-circuit measurement when you check it, it might be worth it to figure out why.   

 

[Pinecone]

On 12/13/2024 at 8:26 AM, GeeBee said:

RE: Touching the nozzle to the aircraft as recommended by the video.. Yes that creates zero potential at that time. However, the act of pumping fuel through a hose creates a static charge so touching the nozzle against the aircraft before fueling is almost worthless.

 

Except the nozzle and hose have a ground connection and conductivity.

The problem is the first contact, if the plane is charged with static, you get a spark to the nozzle.

[GeeBee]

13 minutes ago, Pinecone said:

Except the nozzle and hose have a ground connection and conductivity.

The problem is the first contact, if the plane is charged with static, you get a spark to the nozzle.

 

[N201MKTurbo]

https://en.wikipedia.org/wiki/Triboelectric_effect

[Pinecone]

13 minutes ago, GeeBee said:

 

Exactly.  You need to keep the fueling nozzle in contact with the fuel port.

But if you do not bond the airframe to the fueling rig before putting the nozzle against the fueling port, you get a spark then.

 

[Fly Boomer]

1 minute ago, Pinecone said:

But if you do not bond the airframe to the fueling rig before putting the nozzle against the fueling port, you get a spark then.

I don't know what the voltage or amperage is inside an ohmmeter, but it seems possible that touching the fuel filler opening might generate a spark.

[Pinecone]

That is what I said.  When you make the first contact with the fuel nozzle to the aircraft, you could get a spark if the two are not bonded together.

You could touch the fuel nozzle to the cap before opening it to bring the two potentials close.

[EricJ]

38 minutes ago, N201MKTurbo said:

https://en.wikipedia.org/wiki/Triboelectric_effect

This is why styrofoam packing peanuts should be outlawed.   Photographic evidence at the link. 

[DCarlton]

First of all, I'm a big proponent of safety procedures.  However, does anyone else wonder why this is so critically important for aircraft fueling but it's completely overlooked for automobile refueling?  What's the technical difference between the two platforms?  

[EricJ]

2 minutes ago, DCarlton said:

First of all, I'm a big proponent of safety procedures.  However, does anyone else wonder why this is so critically important for aircraft fueling but it's completely overlooked for automobile refueling?  What's the technical difference between the two platforms?  

Cars are always in contact with the ground (well, supposed to be), so they dissipate charge as it is accumulated.    Even though the tires have significiant electrical resistance, they still conduct, so the charge gets dissipated.

[MikeOH]

5 minutes ago, DCarlton said:

First of all, I'm a big proponent of safety procedures.  However, does anyone else wonder why this is so critically important for aircraft fueling but it's completely overlooked for automobile refueling?  What's the technical difference between the two platforms?  

I've wondered the same. Best I can come up with is that aircraft are more prone to build up a higher charge since they are not in contact with the ground.

EDIT: I don't type as fast as @EricJ

[DCarlton]

21 minutes ago, EricJ said:

Cars are always in contact with the ground (well, supposed to be), so they dissipate charge as it is accumulated.    Even though the tires have significiant electrical resistance, they still conduct, so the charge gets dissipated.

Ahh.  So we're primarily concerned about electrical charges that build up in flight.  

[EricJ]

16 minutes ago, DCarlton said:

Ahh.  So we're primarily concerned about electrical charges that build up in flight.  

Yes, so if you refuel immediately after a flight, the ground strap is very important.    If refueling and the last flight was a long time ago, it's not a big deal.   The additional case of refueling without touching the dispenser to the tank when the dispenser nozzle isn't grounded via the hose is also worth mitigating with a ground clip.    So it's a good habit to get into regardless.

[201er]

So are you guys saying that the ground wire could just as well be removed after initial contact? Just to get the initial charge off and the the nozzle leaning on the filler is grounding for fuel flowing static?

[EricJ]

1 hour ago, 201er said:

So are you guys saying that the ground wire could just as well be removed after initial contact? Just to get the initial charge off and the the nozzle leaning on the filler is grounding for fuel flowing static?

You don't know how long it'll take to fully drain the charge, since you don't know how much there is or the impedance of the ground path, and mitigating the charge from the triboelectric effect during pumping is still a good idea.   The best practice is the normal practice of always connect it to a good conductive path, leave it there until you're done.

Also, walk it back to the reel rather than let it go so that the clip pops off the end and the next guy just gets a frayed wire. 

[201er]

15 hours ago, EricJ said:

You don't know how long it'll take to fully drain the charge, since you don't know how much there is or the impedance of the ground path, and mitigating the charge from the triboelectric effect during pumping is still a good idea.   The best practice is the normal practice of always connect it to a good conductive path, leave it there until you're done.

Also, walk it back to the reel rather than let it go so that the clip pops off the end and the next guy just gets a frayed wire. 

It makes sense to leave it on till the end of fueling just in case. But is all the "action" really just happening in the first second?

Is the fuel hose creating a ground for the fueling and the ground wire discharging the airframe for the fuel hose to approach?

[EricJ]

2 hours ago, 201er said:

It makes sense to leave it on till the end of fueling just in case. But is all the "action" really just happening in the first second?

Is the fuel hose creating a ground for the fueling and the ground wire discharging the airframe for the fuel hose to approach?

For the most part, yes.   All of it is to prevent a static discharge spark when the fuel nozzle is near the rim of the fuel tank opening.  

It'd be cool if we could visibly see the static field around things, (like Geordi LaForge or something) and be able to watch them build and drain and see how big or small they are, but we can't so we just have to assume it's there.   If the field gets really big you can feel them sometimes, especially if they make your hair stand up, and you can see discharge sparks when they happen, but otherwise we're stuck just having to assume the worst.   That's SOP in aviation, though, so NBD.