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Blowdarts of Fire: How to set a Hydrogen filled balloon alight with a blowdart?

Question asked by Sam Jones in #Mechanical on Jul 31, 2020
Sam Jones
Sam Jones · Jul 31, 2020
Rank E2 - BEGINNER

Sooo (don’t laugh) but at home my family has informal Blowdart target shooting competitions.

These are done with a popular brand of Blowdart gun, big-bore, .625 internal diameter (well they are called .625). You put a dart in the tube, you take a big breath and you blow it out, striking a target 20 feet away. The tube is aluminum, 4 foot long. 

Darts can be, bamboo BBQ skewers, or steel, both have a little plastic cone fitted on the back end to provide an air-tight seal, allowing the dart to be driven by the force of your breath. Darts can travel around 150 ft/sec.  

We often use balloons as targets. For fun and to amaze the children (and myself), I thought I could fill one of these party balloons with some homemade hydrogen and then pop it with a hot or flaming blowdart causing it to deflagrate. 

I am turning to you for help because, for the life of me, I can’t think of a method that will provide a dart of this nature. 

I am open to any suggestions, thermal, chemical, electrical, that will provide a dart that will ignite a balloon full of hydrogen. And while the solution does not have to be child proof (I will be the only one using it) I don’t want to be putting some lit phosphorus compounds near my mouth or permanently contaminating or destroying my tube. 

I have turned my mind to wrapping some cotton wool around the end of a dart, dripping some alcohol on it, and having a lit flame mounted outside the end of the blowgun pipe to ignite it on exit.  I haven’t tried this yet as I am extremely skeptical that the flame will ignite the alcohol as the dart speeds past. Or that a flame of this nature would stay alight as the dart sped through the surrounding air. 

Posted in: #Mechanical
Ramani Aswath
Ramani Aswath · Aug 1, 2020
Rank A1 - PRO

When the dart hits the balloon bursts and the hydrogen disperse too fast. It may not ignite. If the balloon is filled with a Hydrogen-air mix it might catch fire.

You may have better luck if you fit something like an incense stick on the point of the dart. The burning end is not a flame but a glowing ember. It will not affect the aerodynamic behaviour of the dart in flight.

Caution:

If a live dart swerves and hits (God forbid, in the eye) someone it can be a disaster. Indoors has other hazards of curtains and such catching fire.

In my childhood I put an iron nail on the end of the dart, placed a fire cracker behind the dart, closed the back end of the tube with a paper plug with the wick of the cracker sticking out. Sighting along the length of the tube I aimed the ‘gun’ at a brass bucket about 50 feet away and lit the wick and darted away to a distance. The cracker burst, the dart took off and hit the bucket with a loud clang. Unfortunately the nail punctured the bucket and I got roundly ticked off by my grandma with a ban on all such experiments in the future.

Sam Jones
Sam Jones · Aug 1, 2020
Rank E2 - BEGINNER

Thanks Ramani, and for the humorous stories of your childhood. A piece of incense stick is a good suggestion and I could try it. But I am thinking that even the glowing tip of the incense (or at least it's exterior surface) would be cooled completely by the rush of air during the flight of the dart? It might not be hot enough when it hits? What do you think. 

Ramani Aswath
Ramani Aswath · Aug 2, 2020
Rank A1 - PRO

Another personal story. I used to be a nicotine addict. 200 a day. In 1965 there was a cyclone that hit Madras. I went to the beach to see the waves. I lit a cigarette in those heavy winds. The speed of the wind was so high that when I inhaled the cigarette caught fire.

Similar thing may happen with your application too. Highly unlikely that the incense stick goes dead. Check it out in the yard or other open space.

Sam Jones
Sam Jones · Aug 3, 2020
Rank E2 - BEGINNER

Haha Ramani, great story about the cigarette. I will try the insense stick and report back. I will try and find something very flammable and shoot it into that initially to see how it goes.

Sam Jones
Sam Jones · Aug 3, 2020
Rank E2 - BEGINNER

Haha Ramani, great story about the cigarette. I will try the insense stick and report back. I will try and find something very flammable and shoot it into that initially to see how it goes.

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