seat tank mini explosion

[snowbird1]

I had a real scary thing happen to me yesterday- I was flying for and hour in my single seat snobird, and landed with 2 gallons left in the seat tank. I taxied up to the hanger and parked on the concrete, stopped the rotor blades and prepared to get out of the gyro. I took my gloves and helmet off, placed my hand under one leg against the seat tank and as soon as I put one of my feet on the ground, the seat tank hissed real loud and inflated like a balloon! it forced me forward then stopped. I looked back and the front of the seat expanded, pushing me almost off the seat and it was still hot and soft. I pushed it and it went back into shape. The gas cap was not blown off but thankfully it was vented. Looking at the seat afterwards, you couldn't tell this happened once I pushed it back into shape.
I figured somehow static electricity built up while the blades were spinning while sitting on the concrete. Once I stepped off, it grounded from my foot to my hand which was on the seat. I use the electronic fuel guage with the long sensor rod, but even after this incident, the guage still works fine.
I went for another flight today without incident, although I was nervous.If that seat were to split apart, gas would have sprayed everywhere, possibly burning me really bad and definetly destroying the gyro!!
Anybody have any thoughts on what caused this????

[All_In]

Wow thanks for the heads up.

I think you nailed it!

How far is the overflow line that could vent fumes from your foot or hand and the spark?

Could be prevented with a metal ground strap dragging on the ground?

[SnoBird]

Sounds like you already know what caused it. Static buildup during your flight, and when you put your foot on the ground the spark discharged. Not sure how it managed to discharge internally inside the tank. But odds are the electric sensor you have inside somehow generated an arc and ignited the fuel vapor inside the tank. The only other way it could have happened is if the vent was close to where an arc occurred externally.

As an aside, I took a Naval Aviation Survival class where we were trained on how to be picked up in the water by a helo. We were instructed to never touch the winch cable as it came down, always let it hit the water (and ground) prior to swimming to it and latching onto the hook (or jumping in the ring).

PS>>Oh yeah how do you like flying your snobird? Got any pics?

[DennisFetters]

This is the first time I have every heard of this happening, but of course I can see how its possible.

What make of seat tank was it? Snowbird have their own?

[dhubbs]

I am not sure what caused your tank to bubble out like that, but i am almost sure you did not have a small explosion inside of there. The upper explosive limit for gasoline is a concetration of only 7.6% in the air. The concentration inside of a fuel tank is well above that, meaning that there is not even oxygen to support even a quick flash. I have seen this proven as I have been on a few vehicle arson fires where paper towels or a rag was stuffed inside of the fill hose and lit. The paper towels self extinguished before any of the fuel vapors ignited. When you see tanks explode due to fire exposure, it is a result of the fire heating the product inside until the vapor pressure is higher than what the tank can handle. Its called a BLEVE. Boiling Liquid Expanding Vapor Explosion.

[Alan_Cheatham]

Perhaps as the pilot removed his weight from the seat tank the tank expanded and drew in some air through the vent with just enough oxygen to support a quick flash.

[phantom]

This has happened to a number of snowmobile tanks in the past few years and the tank splits wide open and the machine is almost always destoryed by the fire.

[earthbnd misfit]

Scary stuff. The theory behind mobile phone explosion in petrol stations is, that someone was filling up the tank, the phone rang in the car, so they slid back in the car to answer it, then stepped out without touching anything, then touched the nozzle, causing the static charge to discharge through the nozzle, causing a fire. So fitting an static strap isn't a bad idea.

[Jean Claude]

No inflammation. Just a heating local of the pipeline too close to the engine. After the shutdown, no ventilation .
If the fuel heats up too much in the pipeline near the engine, then it boils and increases the pressure in the tank. it is my opinion.

[brett s]

Jean Claude's post makes sense to me - don't think a true explosion wouldn't have ended the same way.

[snowbird1]

No inflammation. Just a heating local of the pipeline too close to the engine. After the shutdown, no ventilation .
If the fuel heats up too much in the pipeline near the engine, then it boils and increases the pressure in the tank. it is my opinion.

Sorry, I don't think that was even close to what happened. My gyro has a completly open fram/engine with the fuel lines on the intake side of the engine and nowhere near touching anything. I can put my hand on the engine right after flying and its very warm buy not too hot to touch. The day this happened, the outside temperature was 56F degrees so the seat did not heat up from the engine/sun either. The fuel I use is really freezing cold because the gas stations underground tanks are still very cold from the winter. A simple tank pressure expansion would not have heated the front of the seat tank to almost melting temperature and make the gas vent cap very hot- actually melting the edges. This whole episode happened in about 2 seconds and then it was over-it was very violent. I flew this gyro in Arizona briefly in 107F weather and also never had this happen before.
I am going to install a ground strap behind the tail on the frame, this should eliminate any further static problems...

[James]

From my many years in the natural gas industry and as a state certified fire fighter, I say it could have happened just like Snowbird1 described. Remember the airliner that exploded over the water and they blamed fuel vapors inside the middle tank, and we are talking about kerosine here. When he got off the tank, it could have sucked in enough air through the vent to be an explosive mixture. After it ignited for some reason it could have burned it self out, (used up all of the oxygen) before blowing the tank apart. In other words, it used the burnable mixture until all the oxygen was used and went out because it became to rich to burn. Snowbird1, It would be wise to find out if it were your fuel sender or find some way to ground the tank, if it happens again you might not be as lucky as this time.

James Lee
Gallatin, TN

[dhubbs]

After hearing more about it, I would ave to agree that upon getting off of the seat, it could very well have sucked air into the tank through the vent. Just enough of it to create what would be considered a relatively small explosion. Not enough air to create a large enough explsion to actually rupture the tank, or do any more damage.

[Heron]

Is it possible that the mixture have ignited itself when enough O2 was present?
thanks
Heron

[James]

Snowbird1, the most important thing here is to figure out the source of ignition and elimanate it.

[lanichol]

I may add a grounding strap to the keel in the near future similar to the ones I have seen on pickups.

[mceagle]

I would seriously doubt the possibility of an explosion. If it did occur then a plastic seat tank would not contain it and I do not think that you would be here to talk about it. I have had the backrest of a seat tank "pop" out on me before after I leaned away from it. I assumed it was from pressure build up after landing from a partial blockage of the vent. It "boinked" back into position a minute later. That thump in the back though sure gives you a wake up call.

[Udi]

How much fuel was inside the tank at that time? If combustion really took place inside the tank, the ignition -- the spark -- had to happen at the vapor space, not in the liquid. Where did the spark come from and where did it go to? For a spark to occur, there has to be a charged surface and a grounded surface. The grounded surface has to be conductive to electricity. Polyethylene - the seat material - is not conductive.

I think it is very unlikely that a spark would go thru the insulating polyethylene sidewall of the seat tank. In my opinion the spark was most likely caused by the fuel probe. Is it possible that, as you were getting ready to get off the gyro, you placed your hand on top of the fuel probe - possibly discharging static from your own body into the fuel probe?

I would treat the level probe as the main suspect. The capacitance fuel probe has three wires connected to it - positive, negative, and a level signal wire going to the gauge. The negative wire has to be grounded. The probe contacts should be covered - not exposed.

Do you have a metal fuel cap? How close is the fuel cap to the level probe? Is it possible that you were touching the fuel cap with your hand, causing a spark to jump from the fuel cap to the probe?

A grounding strap is not going to help if the cause of the spark was any of the above. What would help is grounding yourself or removing metal parts that can conduct electricity into your tank.

[snowbird1]

As I said in the first post- there was just under 2 gallons left in the 7.5 gallon tank, the mini explosion melted the ends of the gas cap and heated/expanded the front for the seat tank. This seat was very hot to the touch and I was able to mold it back into shape. These snobird tanks are very strong and pretty thick material so for this to happen would take a lot of pressure. I don't use the electronic fuel level sensor anymore, its completly disconnected. I'll just install a tube on the side of the tank. My 618 burns almost exactly 5 gals an hour and I usually fly for one hour at a time and still have 20 mins of reserve.

[reelmule]

? dumb question--Do vented fuel caps work only as a one way check valve, allowing air in to replace fuel burned, or do some vent both in and out?? Many F/W aircraft have static discharge wicks to prevent a static charge build up. This might offer more protection than a ground strap. Snobird1, what clothing material were you wearing? Nylon and other synthetics are much worse than cotton and wools for static buildup. I find it hard to believe that you actually flew it again the next day without more analysis! Lady Luck isn't always so forgiving. Your hearing this from someone that lost a C-310 to an inflight fire which killed the pilot and mechanic because they doubted my concern about a surging engine when the turbo was engaged. Afer all, I had a brand new multi-engine rating and just didn't understand these planes!! I believe that is why they asked for my permission to check the plane out in the air! I've never owned another turbo charged aircraft nor will I.

[SnoBird]

Snowbird1 I believe you when you say it experienced an explosion. And it does sound like the fuel probe was probably the culprit. Somehow the voltage was discharged into the probe and/or its wiring and was enough to cause an arc inside the tank. The reaction of your tank with it blowing out and getting hot etc is a sure sign you did have combustion inside the tank.

When I was a kid (after school when my parents weren't home) I used to put a small amount of alcohol in an empty jelly jar with a metal cap. Then I'd cut a small hole about 1/2" in diameter in it. Put my thumb over the hole and shake it up to generate fuel/air vapor inside. Then put a match to the hole and watch what happened: The mixture inside would instantly ignite and you could see the internal pressure of the combustion by the metal cap bowing out (occasionally it would blow the cap off altogether). A jet of hot gases would blow out of the hole and it would resonate at a particular frequency that would gradually change as the fuel/air was consumed. You could see through the glass how the flame pattern progressed as the fuel/oxygen inside the jar were consumed. If you held the jar in your hand you could also feel the thrust and heat that was generated. And yes the glass would sometimes crack, and yes it is dangerous - "don't try this at home kids!" etc.

The simple jelly jar was basically a mini-pulse jet that was an amazing little aerospace propulsion lab all by itself. I would find out many years later a man named Francois Reynst did the same thing many years earlier as a child and then grew up to more fully develop and patent his "Reynst Pot" idea.

Anyway, your seat explosion was probably a Reynst jam jar for a few moments. Here's a vid of what was happening inside - talk about being in the hot seat. :)

http://www.youtube.com/watch?v=AePLpM5SnqE

[dcarr4321]

:boom:Rotorcraft generate a tremendous amount of static electricity. The larger the rotors and fuselage the more static it is capable of generating and holding. All aircraft surface areas can act as a capacitor and capable of retaining and discharging several thousand volts. When watching helicopters land at night on the carrier deck, a spark would jump from the static discharge wire hanging down form the tire. The wire is designed to be the first contact point from the helicopter to the ground. The spark would jump about 6 inches before the wire touches the ground / ship's deck. Mind you, what I observed was in a damp environment while underway at sea. The electrical charge would certainly be more pronounced in dry cold air. On occasions when the wire would break or was missing, I have heard of stories that persons first touching the aircraft or stepping off would receive a static electrical jolt.

I believe there was an explosion in the tank and resultant short duration fire. The fact that the tank was well ventilated probably prevented it from rupturing.

I will add a grounding wire/strap to my gyro biased on this incident. If that practice is good enough for all of our nations Naval Aviation fleet, it sounds like a good practice for me. It will be a stainless steel wire bonded to the frame of the left wheel. I believe that is the one that will fly low and contact the ground first in a gyrocopter.:boom:

[gyrodrifter]

Wow thanks for the heads up.

I think you nailed it!

How far is the overflow line that could vent fumes from your foot or hand and the spark?

Could be prevented with a metal ground strap dragging on the ground?


All out,

I like a smart thinker, I lack that quality sometimes :D

Nice going, exellent idea, remove the charge before it can spark in a fume situation.
It's on the list. (Car anti static strip?)

Regards John.

[gyrodrifter]

Snowbird1,

I think you were looked after when that happened, I think you came close to a disaster, but it didn't happen.
That's a good thing.

I would only be guessing at it myself if I offered any thoughts, So instead I'll just say, I hope that never happens to you again, that was a close call all around.

Regards,
John.

[EI-GYRO]

This link is in the same ball-park, I think;

http://www.pprune.org/rotorheads/309803-helicopter-static-charge.html

[snowbird1]

thanks everyone for you comments! Its interesting to hear everyones opinions, thats what this site is all about. I do know that the day this happened, it was cloudy with cumulus clouds but no rain, there may have
been a more than usual charge in the air. I was also parked on concrete, resting on the 3 air filled rubber tires, I usually stop on grass where it would seem the moisture in the grass would try to ground out the gyro better. I also
will make it practice to get out with my hand touching the frame and not the seat before touching the ground with my feet. I was wearing a full snomobile suit but took off my gloves and touched the seat when I put my feet on the ground when the seat ignition happened. Actually, during the warmer weather i could fly nakid, that way I wouldn't creat any static between the plastic and my butt...although i would create some staic with the neighbors.....

[Alan_Cheatham]

Actually, during the warmer weather i could fly nakid, that way I wouldn't creat any static between the plastic and my butt.....

If you have a lot of body hair that might not be true.......:D

[EI-GYRO]

Have a word with Martin-Baker. You could be onto something there..... :)

[robertstodaro]

I think I'll remove my fuel probe from my seat tank based on this event.

[All_In]

I think I'll remove my fuel probe from my seat tank based on this event.If your not using it, I would!!!

[automan1223]

For those of you who can read this should be old news to you.

If you ever read any of the fueling instructions at a filling station it says to put your fuel can on the GROUND. DO NOT fill it while in the back of your pickup truck especially if it has a plastic bed liner in it.

All aircraft can generate static electricity if conditions are ripe.

If you have ever gotten fuel at an airport, they put a GROUNDING cable on your airframe to prevent the boom boom from happening.

If your tank is not grounded, it is hard to ground a plastic tank anyway. Static electricity can and will find its way to a ground point, your fuel probe in the tank makes an excellent return path. Is the wire to your fuel probe shielded with a metal braid to ground ?

As far as why you are still here and currently dead or in orbit I would suggest going to church this Sunday, and realize that fumes do need a perfect scenario to burn effectively and your air fuel ratio was not just right.

Flexible Ground strap on the frame to ground would be a good idea if you are lucky enough to pickup that much static electricity.



You

[karlbamforth]

The main reason for not filling a gas tank in the back of a pick up truck is because fuel vapour is heavier than air. The vapour can fill the bed of the truck and not get blown away, it is worse with a plastic bed liner sealing the hinge lines along the side. Filling in the open allows even the slightest breeze to disperse the vapour.

[fiveboy]

The fuel probe didnt cause that.

[snowbird1]

So, last week I decided to test out the theory of static electricity on my snobird gyro. I disconnected the seat tank electric fuel sender,faced the gyro into the wind and got the rotors spinning pretty good- it was windy so there was definetly enough to keep the brakes held and often tilting the rotor forward to keep from sliding backwards...anyway, after about 10 mins, I stopped the rotors and took off my gloves (I wore a different flight suit than I wore the day the origional explosion happened). I started to touch the metal frame- not the seat this time and as soon as I stepped on the ground, my right thumb was shocked so hard it hurt! i couldn't believe the kick I got! so, its definetly a static buildup problem and it was also overcast with cumulus clouds above, just like before. So, I figured out these things:
1. the fuel probe didn't cause the explosion- it probably provided a place for the spark to goto ground with me still touching the seat when I touched the ground the first time.
2. the rubber tires dont dissapate the static, even when sitting on grass.
3. I think there may be something to do with the cumulus clouds overhead...both times it looked like it was going to rain.
4. the blizzard suit I was wearing may also be a contributor, but the first time it happened, I was wearing a full snowmobile suit.

I will try a ground strap next- strange, I never had this probem during the winter months, although its usually cold and wet here in Michigan. Oh and the rotor blades I have are aluminum rotordyne's and a powerfin prop. Also, the clouds were nothing near thunderstorms, not even any rain was falling from them.

[fiveboy]

What is the surface of your seat made from. My hunch is its a build up from your suit against the seat when you get on and off.

[freebird]

What you are describing is very interesting. I have been a "spark maker" for most of my life.

If this was happening to me, I would look at several things like my sight gauge, softness of the seat (worn out), fuel probe, baffles, etc.

Drops of liquid can generate a charge of amazing proportions.

Here http://www.eskimo.com/~billb/emotor/kelvin.html is a device that you can build to demonstrate this principle.

Whatever is the cause, this makes a good case for getting deto-stop or a similar product into the tank.

[All_In]

Oh I just remembered, maybe another solution!

In the computer old days, we used to have to spray the carpeted floors with fabric softener to assure that there were no static discharges to the computer that would shut it down!

Fabric softener on your seat and clothes will work too!!!

[freebird]

hang some bounty cloths off your rotor and make the whole countryside cling free and springtime fresh

[All_In]

I though of saying something about "And you'll smell so sweet!"

Not necessarily a good thing if you are a guy!

[CLS447]

I was just reading this scary thread again........So what have we learned ?

When it is dry out, I get shocks from alot of different cars. I slide off the seat & touch the body or door frame & ZAPPP ! I am real bad for this.

Never on my gyro . I do have a seat cover though. If this was a common thing, we would all be getting blown up !

So whatever happened here ?

[500e]

Some plastic extrusions have a proportion of metal Incorporated, could this be a factor?.
Some ABS/plastic boxes are so high in aluminum content that a low power RF device wont show any RF power on the external surface.
Bonding of parts could help including tank, we have had interference problems on electronics, that were cured by grounding plastic assemblies :der: also might be worth measuring for ANY resistance between component parts of frame/Engine.
Nylon cloths don't help :rip: not good for flying, remember nylon melts & sticks to you in fires, cotton or wool if not Nomex

[hillberg]

put a static wick off the frame to the ground below rubber tires keep the charge build up ready to "spark" the ejection seat tank.:rip:

[okikuma]

David, Sorry that I missed your post three years ago. Don is right, perhaps you should install a couple of aircraft static wicks on your gyroplane.

Wayne

[WHY]

speaking of static build up, would composite/fiberglass blades be more inclined to build up static charge that metal ??

Tony

[CLS447]

I'd sure like to know what happened ? Is anyone else even the least bit concerned that it could happen to them ?

I suppose that if it did not happen to me yet, it ain't gonna happen !

[scandtours]

[QUOTE=(I wore a different flight suit than I wore the day the origional explosion happened). [/QUOTE]

What kind of material is your flight suit made of?