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