About Refueling, Jerry Cans and Bonding

Jacko wrote:

Can anyone point to reliable airplane and automobile fueling accident records which would justify the disparity in behaviour of airplane operator and car driver?

There’s no disparity, fires also happen occasionally with cars

I think the reason for the traditional concern with aircraft fueling is that aircraft fuel pumps flow at a much high rate, leading to higher static electricity production.

Airplanes have a much greater potential (there is is again) to accumulate a static charge while flying through air which contains particles. Though my knowledge of physics in this regard is rather pedestrian, I think it’s because of their large surface area. Non metallic structures can hold a charge. The balloon rubbed in the hair accumulates and retains a noticeable static charge, yet neither is “conductive” in the electrical system sense. I am also aware that some composite airframes have had conductivity problems – they did not conduct a charge away quickly enough, and got very hot instead. One composite airplane I can think of had a copper mesh “window screen” applied all over before final finish, to assure conductivity. Most radomes, which are always composite, have those rows of dots to conduct a charge away – lightning strike consideration I expect.

I recall during my work on the gasoline committee during my Mogas testing days, reports of certain General Motors cars, which were known to spontaneously catch fire in the left rear wheel well. ’Turns out that the plastic fuel line had no bonding filament, and a charge would build up on the inside of the fuel line. Sparks would go to chassis ground through the fuel line, burning very tiny holes in the fuel line, which would then weep fuel, and be a fire risk. So one day, as I was called in my capacity as a volunteer firefighter to a car fire, I knew what to look for, and that was found to have been a factor in the fire – my fellow firefighters extinguished it so as to preserve enough to inspect.

So, I’ll use the jerry cans as their design intends, though I’m certain to maintain the best bonding path possible during fueling, and have not had a problem.

Refueling the P2008 you need a good, steady ladder. There is no way to crawl up like on the Cessnas.

We use a trailer very much like this one, its MOGAS for our aeroclub ULM :
(I will have a look later today about how its grounded etc)

Silvaire’s video link surely shows static discharge between the woman and the car not between the pump and the car, which I think is the equivalent concern of this topic.

As to my own machine the only possible conductive path between my fuel tank and the engine, assuming the wooden structure to be non-conductive, are the fuel lines themselves which may be, to some extent, conductive. But there are several joints, connections and gaskets between one and the other which makes me think that conductivity would be very poor and unreliable as an earth bonding path. But I have never attempted to check that.

One last observation about my own experience. I do remember when it was not uncommon to get a static jolt when touching a car, but I have never had a static jolt from touching any part of my aeroplane, nor any other I’ve flown, even just after a flight when static might be assumed to have built up.

ChuckGlider wrote:

One last observation about my own experience. I do remember when it was not uncommon to get a static jolt when touching a car, but I have never had a static jolt from touching any part of my aeroplane, nor any other I’ve flown, even just after a flight when static might be assumed to have built up.

This still happens. In warmer weather I routinely get quite large static shocks from the car door when pushing it closed after getting out. They become regular and unpleasant enough that I sometimes take to pushing the door closed with fingers on the glass. In theory one can let the charges balance out by holding the door frame as one gets out, but the paint is probably insufficiently conductive as the spark still jumps as I let go. There is no bare metal to touch.

Never known it happen with an aeroplane.

In warmer weather I routinely get quite large static shocks from the car door when pushing it closed after getting out.

I believe this is mostly caused by the pants rubbing over the car seat when getting out of the car. This is also what must have happened in the video.

Once while flying a Piper Aztec through heavy snow, I reached out toward the windshield. As my fingers came within a few inches of the inside of the windshield, “sparks” like those of a plasma globe, extended from my finger tips, to the windshield. This was sustained for a second or so, rather than a single spark. It made enough light that a passenger in the back audibly spoke out in surprise. Electrical potential difference between me, and the airframe – my butt was in the seat, hand on the control wheel, and feet on the pedals, and still the electrical potential difference.

Most of us who fly from home started with jerrycans and soon graduated to a small (1,400 – 2,000 litre) bowser. In the scheme of things, they are not expensive to buy second-hand. I have to tow mine 3 miles to the nearest proper road to have it filled, but that’s just quid pro quo for not living on top of our neighbours.

I do always “ground” airplane to bowser when refuelling, but have never seen or heard a spark. So I do suspect it’s more of a “potential” risk than a real one.

Interestingly, when the (suitably qualified) articulated tanker driver fires 400 gallons of 100LL through a 4” hose into my bowser, there’s never any sign of a grounding wire…