Kitfox Static discharge Fire

[Guy Buchanan]

Well I'm sorry to say you've made me feel a lot better about the silly-ass grounding wire I always get kidded about when I refuel. I've been using it for about 12 years now and occasionally think about giving it up. Not so much, now.

[PaulSS]

I, too, like the idea of the 10' wire with crocodile clips but I was thinking about the order of connection of the wires and real world practice, rather than electrical theory. It's not really something I'd thought about until this thread.

You know how sometimes if you touch a live wire (our statically charged fuel filler lip in this case) and a ground you get a spark, well clearly that would be a bad thing with our open filler cap and fuel vapour. Now I'm certainly guilty of grounding the exhaust pipe, then taking off the filler caps and filling up. Not a problem at the moment because I'm flying an RV, so all the wigglies go straight to ground when I connect to the exhaust pipe. BUT if I was in a Kitfox with my 10' wire, connected ground to the exhaust pipe, crocodile clip to the exhaust pipe, then up to the wing where the filler cap comes off and I then clip the other end of the 10' wire to the filler cap lip, it strikes me that is the time when I'm going to get a spark at the filler cap, as the static electricity at the cap connects to ground through the croc clip, which is a bad thing.

I reckon the 10' wire is a great idea but, if it's not blatantly obvious and I'm the only one who has never thought about it before, I think you need to ensure that you first connect the crocodile clip to the (open) filler cap lip, then to the exhaust pipe and/or direct to ground. This way the static wigglies are already queued up in the wire from the filler cap and will travel to ground when the wire is connected to the exhaust/ground. If we get a spark there then there's no problem, unlike if we do it the other way round.

As I say, probably obvious to everyone else but I'm glad of this thread for making me think about it

[PapuaPilot]

Hats off to you Guy. You aren't being silly. I still need to test my plane with aa ohmmeter between the filler necks and the exhaust stacks (and ground too).

The other day at work I checked a Cessna 206 with a precision tester for bonding to test how the bonding a certified plane is. I checked it from a good airframe ground to the exhaust and the results were not good, it had infinite resistance. Next I checked it from a wheel axle bolt to ground and got .003 ohms (which just meets certified specs for bonding). FYI it is our standard practice (where I work) to hook the ground cable to the axle bolts when refueling.

What this tells me is that using an exhaust system isn't a good idea, even if there is proper bonding to the tank filler neck. I think there are several reasons. Stainless steel is not a good conductor and there are slip joints and gaskets the may be filled with exhaust residue.

Using the landing gear on a Kitfox with the Grove gear would not a good solution because of the plastic mounting blocks and paint. Even if there is bonding from the fuel tanks you would need to find a proper airframe ground to attach the fuel ground cable to.

FYI bonding is making the entire plane one potential. It is needed for several reasons: for static dissipation, to provide a path for lightening strikes and prevention of sparks when refueling. Bonding is done by connecting all of the components together with bonding straps. When you hook up a ground cable before refueling it makes the aircraft the same potential as the fuel pump system, which should be hooked to earth ground too.

In a Kitfox I really doubt there is any bonding obtained through the fiber glass tanks, nor through the fuel lines (I have rubber hoses from the wing tanks to the header tank). I think the only way to get proper bonding would be to connect the filler necks to the airframe or to connect directly to the filler neck as some are doing.

[Esser]

Now maybe this is an oversimplification since the fuel flowing out of the Jerry-can can create static but couldn’t you just touch the Jerry can spout to the top of the fuel cap BEFORE you open the cap and now the two items will have equal charge?

[jiott]

Josh I was thinking the same thing; jerry can or fueling hose nozzle.

[Dave S]

Josh & Jim,

Been studying up on this deal a bit and found some old military information on refueling - a lot had to do with refueling under less than ideal conditions - One of the recommendations was that before a person pulls off the fuel cap - touch the dispenser or funnel to the upwind side of the fuel cap to equalize the charge between tank and the dispenser so if a spark occurs, it will not be in the midst of the fuel vapors- then pull off the cap and attach the funnel or touch the dispenser to the ring and keep it there till the fuel is done flowing - the idea on the second part is to process any charge that might develop once the fuel starts flowing.