Kitfox Static discharge Fire

[amerkarim]

Hi All,

Just a warning about refuelling, static electricity and fire.

At the end of last year, my Kitfox 7SS was being refuelled by a crew at a local airstrip. The person doing the fuelling was using an aluminium funnel and was filling from a jerrycan using a step ladder. I didn't see the incident as I was not there, but apparently the right tank filled just fine, but as he inserted the funnel into the left tank, a spark was discharged, there was an explosion, and the fuel in the left tank caught fire and poured out over the wing, burning right through the wing to the ground.

Fortunately no-one was hurt in the incident, and the fire was put out. The damage has been inspected and fortunately is limited to fabric alone.

I have had a really busy year and have now finally found the time to work on the repair and want some advice based on the photos, if I should patch this as per the Polyfibre manual with a 2 inch overlap, or take the fabric off all around and start again.

I also want to make others aware of the dangers of static when refuelling and to be sure you discharge all the static before thinking about refuelling.

I am also thinking of a small modification to earth the metal fuel tank lips or gas caps to the main airframe, so that any static that has built up around the wing tanks can be discharged by touching or clipping an earth cable to the exhaust pipe like in all aluminium planes.

Any advice or tips would be very welcome

Thanks and happy landings.

Amer

[aviator79]

Wow that stinks. Literally as well as figuratively, I'm sure.

I've never done a repair like that, but I did take the PolyFiber class recently and the instructor talked about how to make big repairs. An adequate repair should be possible without recovering completely, and can be done so that it's cosmetically almost undetectable if you make sure to put the seams at the ribs outboard of the repair area.

What is the top coat? If it's Poly Tone, you can use enough MEK to lift the finish tapes, make the repair underneath, and then replace the tapes. If you'd have to sand the top coat off, I think the amount of very careful sanding involved might make me lean toward just recovering the whole wing. Taking all the fabric off might also allow you to do a more thorough inspection.

Hopefully someone with actual experience can give you more authoritative advice.

[amerkarim]

Hi,

Its Polytone and I think I have all the chemicals and paints left over to do the repair and enough fabric.

I was going to patch as its quicker. I plant to cut out the burnt sections top and bottom. Use MEK to remove the paint, glue and tapes around, and then patch with a 2 inch overlap with fabric cement. Then do the rib stitching and apply the coats of poly brush , poly spray and polytone as per the manual.

For the modification I was going to put an earthing wire from the gas cap to an earthed section of the wing to bleed away any static in the future.

Thanks

[Dave S]

Amer,

First off - really sorry for your misfortune.

There is so much to consider with this. The repair is one thing; and, preventing this kind of thing is another.

On the repair, it is next to impossible to suggest partial or complete recovering other than in a general way from afar because the need is ability to accurately inspect - only a person on site/hands on can figure that out. One thing regarding fire damage - much of the residue can be a source of corrosion or rot down the road if it isn't all removed and cleaned up. I do know of a local person who had a wing fire not involving fuel on a fabric covered airplane due to misuse of a space heater (put the chimney up against the bottom of the wing) - in that case the mechanic removed the fabric on the entire wing to inspect and do the repair.


I think the incident should reinforce the care we need to take when fueling. 1) Always do it outside, 2) Have an adequate fire extinguisher handy, 3) Have some way of grounding the aircraft......+ other considerations?

One question I have is do you know what the humidity level was in the air at the time? Was it an extremely dry day?

When building our Kitfox, I thought about grounding the fuel cap rings since the rings are insulated from the frame and therefore won't be grounded by the method usually used when fueling, but didn't get it done:(. I think your idea of doing this has real merit. If anyone has any experience in how to ground the ring, or has done it, that would be very useful information.

Wishing you good luck with the repair - that is a tough deal.

[amerkarim]

Hi Dave,

Many thanks for your thoughts.

It was about midday and it was very hot and dry. There was probably lots of fuel vapour in the air and the wind was blowing, so the wing was probably generating lots of static.

As you are aware, the wing and gas tanks are an insulator and the only metal parts are the gas caps and the lips of the tank. I am sure that earthing the lip of the gas tanks or the gas caps, will help discharge static that builds up over the wing. If anyone was doing a new build, I would advise them to earth both the tanks from inside the wing by riveting an earthing wire from the underside of the gas tank lip on the outside, to the main metal spar or round in the wing.

I am planning to rivet a wire to the gas caps themselves and then pass that through the wing and to a metal earthing point.

Regarding the repair, I am sure I can cut out anything that is fire damaged and do a patch. The plane has already been inspected by an engineer, and he has said it is only fabric damage. He offered to do the repair, but I want to do it myself.

Thanks

[Dave S]

Amer,

Sounds like you are well on your way to getting this solved:).

I think the value of a poly tone finish is certainly shown in the case for an easier repair.

Good to know it was just fabric damage.

Dave

[jiott]

I would suggest earthing the gas tank filler neck rather than the gas caps. You remove the gas caps when refueling. I was thinking that the copper self adhesive tape that is used for ground planes in composite aircraft would be good to use. It is very thin and would not show under the fabric, compared to a wire.

[Slyfox]

first off glad nobody was hurt.

a note on refueling. it scares the bejesus out of me when I see someone using a funnel. I have always used one of those plastic jugs (5gal) with a long spout on them. they are used to refuel 4 wheelers. at least I find them at the motorcycle shops. I always transfer with metal jury cans with a nice neck into this and then into the airplane(touch the steel can spout to the plastic jug). always, I say always let the neck of the jug touch the opening of the airplane fuel tank, that grounds the two together, thus eliminating a static spark. I use this jug to fuel both airplanes, the rv and the kitfox.

onto the repair. you are going to have to remove the wing and rip off all the fabric, then using a heat gun soften the glue and remove the ribs. then start over with new ribs and then refabric the wing.

[dholly]

As you are aware, the wing and gas tanks are an insulator and the only metal parts are the gas caps and the lips of the tank. I am sure that earthing the lip of the gas tanks or the gas caps, will help discharge static that builds up over the wing. If anyone was doing a new build, I would advise them to earth both the tanks from inside the wing by riveting an earthing wire from the underside of the gas tank lip on the outside, to the main metal spar or round in the wing.

I'm confused... the lips of your tanks are metal?

[edit] Sorry, I assume you meant filler neck. I personally like Jim's idea, but stripping the entire wing and removing/replacing ribs etc., not so much. If there is no evidence of adhesive failure and inspector says recover and go, that's exactly what I would do..

[Slyfox]

thoughts here. I know this was done with a funnel. when you go to a fuel pump at an airport where do you ground for fueling? I'm thinking at the fuel tank opening. why? how does the tank ground to the aircraft, even worse to the exhaust on the engine? food for thought

[ken nougaret]

thoughts here. I know this was done with a funnel. when you go to a fuel pump at an airport where do you ground for fueling? I'm thinking at the fuel tank opening. why? how does the tank ground to the aircraft, even worse to the exhaust on the engine? food for thought

Exactly! All this time i've been grounding at the exhaust. I guess from now on i'll clip the ground to the top of the gas neck. Then move it to the other wing before fueling it.

[aviator79]

The possible downside here is that your plane may have already accumulated quite a charge in flight, and when you touch the bonding clamp to the filler neck, you could jump a spark where a potentially ignitable fuel/air mixture exists. So you may want to touch it to the wing somewhere else (doesn't necessarily need to be metal, charge can still equalize) before touching it to the filler neck.

There are really two hazardous voltage sources:
1) Accumulated charge prior to filling (Airplane moving through air or jug sliding around on your plastic bedliner)

2) Accumulated charge during filling (result of fuel flowage/swirling/sloshing).

[zadwit]

static discharge fires are real common in Alaska due to the dry air.. .one guy put a piece of copper welding rod to the bottom of his red jerry jug of fuel. The top is epoxyed in to preven leakage. Then when refueling the plane, he clips the rod in the red gas jug to the plane and the plane to ground...

IN most every case the person said when he went to install the metal funnel, he heard a pop and funnel blew out. SOmetimes hyou can put hyour hand over the gas cap and the fire will go out.. most of the time the fueler is startled and drops the gas can and fuel goes every where..

Also, when aluminum is exposed to heat like a fire you need to find out what the main spar aluminum is, what the heardness is and then get a hardness tester and check it in the burn area to make sure the fire has not weakened the spar...most hardness testers are a little pointed thing with a dial guage and you press on the metal, the compare the reading to a chart that shows the hardness for the aluminum. Dont want to fly with a weakened spar!!

[Dusty]

Corrosion would be a concern here.Any material that burns leaves a harmful residue,also what was used to put the fire out? If in doubt recover the whole wing, as later corrosion will be hard to detect.
Sad to see the damage but glad the fire was delt to promptly.

[HighWing]

I would suggest earthing the gas tank filler neck rather than the gas caps. You remove the gas caps when refueling. I was thinking that the copper self adhesive tape that is used for ground planes in composite aircraft would be good to use. It is very thin and would not show under the fabric, compared to a wire.

What Jim suggests is exactly what I did. The tape is also used in Leaded glass projects and is where I discovered it. I did it on the second Model IV after fuelling for the 900 hours I put on the first one and every time thinking in my mind that connecting the ground to the exhaust stack was only cosmetic to satisfy the "is the aircraft grounded" question at the pump. What I did is remove the adhesive from a length of the tape with solvent then wrapped it around the filler neck for sizing. I then shortened it a tad to ensure a tight fit and soldered the ends together. The end of the rest of the adhesive backed tape was then soldered to the ring at a 90° angle. The inside of the ring and the filler neck was sanded lightly with a very fine sandpaper to create a good contact surface and the ring was forced onto the neck. The adhesive backed tape was then run to the end of the wing where it was soldered to wire that then led to a bolt to fuselage near the wing. The Aerothane I used on the plane was then carefully brush painted on the neck to create - hopefully - a water tight seal. I check it from time to time with an Ohm meter and it has always shown "0" Ohms from neck to exhaust stacks.

The picture was taken during an annual when I detected a suspected crack in the paint seal.

[efwd]

Odd that this isn't discussed in the build manual. I would think that if I made a small diameter steel cable, looped it around the gas filler neck before removing the cap, ground the cable and then fill the tank, this would suffice. Too late for me to pull off what Lowell did.

[PapuaPilot]

The of lack of bonding has crossed my mind, but I never thought something like this would happen. I am going to check my plane between the airframe and the gas filler neck to see if there is any bonding. If there isn't a proper ground then we need to think of a way to bond our fuel tank necks to the airframe.

On a related subject. Please realize that the use of plastic fuel jugs doesn't guarantee you are free from hazards from sparks. Even though plastic is non-condictive it readily stores static electricity. If a jug is charged it could easily cause a spark between the jug and filler neck. An easy way to take care of this is to wipe plastic jugs with a damp rag or spray/wipe a little water over the jug.

[bholland]

I agree with Phil. I work in the fire service and have been to several calls where people were filling plastic cans in the back of a pick up with a plastic bed liner and a fire was started by static electricity. It is always recommended to fill the plastic cans on the ground not in the bed of the truck. This whole conversation has made me realize that the A240 I sometimes fly has the same problem. Scary stuff:confused:

[Av8r3400]

I'm not very smart so help me out here a little.

If the static charge in a plastic can can be dissipated by placing it on the ground by the fuel pump (standard procedure) or grounding through your body to earth with a damp cloth, doesn't the fiberglass fuel tank in the plane ground to the wing spars and the rest of the airframe the same way, if the plane is grounded to the exhaust (standard procedure at all airport fueling pumps)?

Isn't all of this extra grounding to fix an extremely rare occurrence a little over blown?

[jiott]

Maybe someone will put an ohmmeter on a standard Kitfox and measure resistance between the metal filler neck and some point on the fuselage. If its near zero then we are overblowing it.

[Av8r3400]

The resistance will be very high. For sure.

My point is the resistance from the filler neck of a plastic gas can to its base will also be very high. But that will ground static just fine. Why won't this also apply to grounding the exhaust of the plane?

[bholland]

I don't know if this helps but I have attached a few links discussing this subject. It seems like grounding the aircraft would help just as setting the can on the ground would but what happened to Amer is concerning especially since our tanks are fiberglass. I would like to know if they remembered to ground it before filling. There are many more articles discussing this phenomenon if your interested you can google and many pop up.

cdc.gov/niosh/docs/98-111/pdfs/98-111.pdf

alabamacounties.org/wp-content/uploads/2012/.../2008-05-Truck-Bed-Liners.pd

Brett

[airlina]

As an added measure I made up a 10' wire lead with alligator clips on each end. If fueling at a fuel farm I always clip one end to the metal tank filler while the other goes to my exhaust stack. Then the fuel farm ground cable goes to the exhaust stack as well . On occasion I have to fuel from a jug , so I then clip one alligator clip to the tank filler and this time the other goes to a 2 foot ground "T" stake that I drive in the ground by the hangar. the T allows an easy pull out of the ground. Bruce N199CL

[HighWing]

...doesn't the fiberglass fuel tank in the plane ground to the wing spars and the rest of the airframe the same way...? Isn't all of this extra grounding to fix an extremely rare occurrence a little over blown?

Through the silicone? I don't think so. But as suggested, an Ohm meter will tell the tale. What motivated me - printed circuit boards are typically fiberglass and with the voltages used, the slightest conductivity would seriously impact all the gadgets we use for navigation, communication and forum chat.

[ken nougaret]

I'm going with the 10' wire and alligator clips as Bruce suggests. At least during the winter months when the air is dry.

[Av8r3400]

Through the silicone? I don't think so. But as suggested, an Ohm meter will tell the tale. What motivated me - printed circuit boards are typically fiberglass and with the voltages used, the slightest conductivity would seriously impact all the gadgets we use for navigation, communication and forum chat.

I will agree fiberglass is insulating in nature. So is polycarbonate plastic. Why does sitting a polycarbonate gas can on the ground considered a safe practice, then? Is silicone calk more insulating than a polycarbonate gas can? What about the carbon-black fuel line attaching the tank to the airframe? What about the silver coating in the fabric covering the tank, will that conduct the static charge away?

Static charges are an odd thing. They don't behave like normal electric potiential.

[David47]

..... What about the carbon-black fuel line attaching the tank to the airframe? ....


The fuel line is ok. In order for there to be an explosion, you need fuel vapour together with a spark from a static charge, brought about by a potential difference between two objects. Liquid fuel is too rich a mixture.

[LSaupe]

I would have to do some digging but I think it is more of a static type charge and discharge. Like the experiment of generating a charge using a glass rod and rabbit fur. Stripping off the valence electrons. Surface effect. Just needs a path to displace itself (or come back into equilibrium) with its surroundings.

Similar to static wicks on the trailing edge of wings etc to dissipate any stored voltage.

Very interesting topic.


I will agree fiberglass is insulating in nature. So is polycarbonate plastic. Why does sitting a polycarbonate gas can on the ground considered a safe practice, then? Is silicone calk more insulating than a polycarbonate gas can? What about the carbon-black fuel line attaching the tank to the airframe? What about the silver coating in the fabric covering the tank, will that conduct the static charge away?

Static charges are an odd thing. They don't behave like normal electric potiential.

[Av8r3400]

The fuel line is ok. In order for there to be an explosion, you need fuel vapour together with a spark from a static charge, brought about by a potential difference between two objects. Liquid fuel is too rich a mixture.

I referenced the fuel hose not as a source of fire or explosion, but as a source of static conductivity to the airframe, in order to discharge it through the "normal" grounding procedure of grounding the exhaust pipe.

[Wheels]

I'm not very smart either, but ... I operate a hydro electric generation company.
Static electricity is unforgiving of fuel vapor. The less distance from a source of fuel to a ground, the better for me. I"m grounding twice, once at the aircraft to discharge the airframe from its potential, then the filler neck to make dang sure.
(unless someone who IS smart can educate me as to my error)

[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.

[amerkarim]

Hi All,

Thanks for all your comments and the developing discussion on this subject, and for your tips about fixing my wing. Fortunately all the insides were fine so its just fabric and paint, that should be easy to fix. Will post some pics when its done.

For my 2 cents ... I think this is potentially a very serious problem. It certainly has me paying attention to grounding on my airplanes now. I had also emailed John McBean about it with the possibility of him adapting the his kit to allow for better earthing of the tanks. I will get back to him once my plane is fixed with the mod that I am going to do.

Having your plane burn to the ground, or worse... having someone or yourself get burnt by a fuel fire is no fun, and I have had the misfortune of seeing 2 pilots in hospital with severe burns fighting for their lives after catching fire in a plane crash.

If there is a simple solution that requires a bit of planning or forethought, or a simple modification that can be done afterwards to our planes that will reduce the risk of this happening, then that is a worthwhile investment of our time. I promise you, even if the chance is 1 in a billion, it is worth it. You don't ever want to be that guy in the hospital bed.

I was thinking of going with the modification of wrapping some wire around the filler neck, but the way my fabric is done, I would have to strip the other wing as well, and I am not keen on that. I am going to see how well earthed the flapperon mounts are. I may just end up drilling a hole in the gas caps and then riveting an earth cable from them to the flapperon mounts (they are in contact with the tank lips from the inside), and then hide the cable under a strip of fabric. By having a simple small connector and a few cm of slack, one could disconnect the gas caps if needed. An earthing strap from the engine block or airframe, to one of the exhaust pipes should then be sufficient to bypass any gaskets that act as resistors. A multimeter should confirm the earthing before I start. and then a short earth rod and a crocodile clip to the exhaust should discharge all the static before I start fuelling in the future.

That tip about wiping plastic jerrycans with a wet cloth is also one worth remembering for next time.

Thanks and regards to you all

[Rodney]

This has been a really valuable discussion. I've learned a lot from all the posts.

I'm not much good with electricity so tell me if you think this would work, ok?

I checked continuity between a bolt that holds the "N" strut on and the exhaust pipe. Good continuity there. I checked between the filler neck to the bolt and then the filler neck to the exhaust pipe and no continuity, as expected.

So I bought a static discharge wrist strap like computer tech's use when handling mother boards which I guess can be ruined by a static electrical discharge.

I clip the alligator clip to the "N" strut bolt and as I take the fuel cap off I make sure to touch the exposed metal on the fuel filler neck with my hand that has the wrist strap on. Then, when I pick up the fuel nozzle in the other hand I make sure I touch the filler neck again with the hand that has the wrist strap on it. I hope that makes sense.

Am I right in thinking I have now equalized the potential between the fuel filler neck, the rest of the airplane and also the fueling nozzle??

Thanks
Rodney

[rv9ralph]

I have been following this thread, and re-read the initial post about the sequence of the incident. Here are some thoughts. The static discharge happens when there is a difference of electrical potential, that has been agreed upon. In this instance the discharge happened when the fueler touched the aluminum funnel to the fuel tank causing the discharge (ignition spark). If he had discharged his potential to the airframe away from the fuel tank, there would not have been the spark to ignite the fuel fumes.

I was talking to the owner of the FBO at KLVK and discussed this event. We agreed that the solution is to make a connection of the fueling apparatus (funnel, fueler, nozzle) to the airframe away from the combustable fumes.
The grounding clip at the fueling stations does not ground the aircraft, but connects the aircraft to the fueling nozzle, eliminating the potential for a spark at the fuel tank. (The fuel hose has a conductor from its base to the nozzle).

I hope this make sense.
Ralph

[amerkarim]

I agree with the principal that static electricity builds up over the wing and concentrates at the filler necks, or can be contained within the fuelling can.

The problem is the discharge of the static from the filler neck of the fuel tank to the can or to the person who is acting as the earth. This discharge can be large enough to produce a spark if the tanks are not grounded in some way and the static has not been discharged beforehand.

In principal, you can just tough all around the wing with your hand and touch the filler neck and gas caps.. by doing so you are the earth and you are discharging the static through your body to the ground, but even this action can create a spark between your hand and the filler neck. As you are most likely to have fuel vapour around the gas caps / filler neck ... in the right conditions of dry air, high temp, this can start a fire.

The spark will only happen at the point of contact of the earth to the statically charged airframe. As the airplane is sitting on rubber tyres, it is insulated from the earth anyway. and so will tend to collect static electricity all over the airframe. This static can be discharged by making a contact from the airframe to the ground either by touching the airframe or using a grounding wire and a crocodile clip. The key is to ground away from the fuel source... so even if a large spark is generated on contact... it is away from the fuel vapour source.

By connecting the fuel tank filler necks to the airframe.. when the static is discharged by touching the exhaust pipe or any earthed part of the airframe away from the fuel vapour source.. as long as their is continuity between the wing and the airframe.. all the static will be discharged, even that around the wing and fuel filler caps.. and any spark generated will be away from the fuel vapour.