Thursday, January 05, 2006

Making Flamethrowers

I came across the below entry in the London UK newspaper, the Guardian, and it reminded me of the time I built a flamethrower.

From the Monday January 2, 2006
edition of The Guardian:
The Freedom of Information Act, hailed by Lord Falconer, the constitutional
affairs secretary, as "a giant step forward" in sweeping away official secrecy, is one year old today.

Over the past 12 months, it has led to the release of much information formerly kept from public view. Here, the Guardian gives a taste of what has been disclosed so far: from serious matters to lighter ones; from the top of Whitehall to the outer reaches of government.

Here is one entry of the information released under the act:

"More than 300 weapons were seized from Scottish school pupils last year, including air pistols, claw hammers, knuckle dusters, knives, swords, and an improvised flamethrower."

Now, I know US public schools are tough, probably tougher than British schools. Still, it makes me wonder about a student who would bring a sword to school. It seems impractical as well as imprudent.

As far as the improvised flamethrower goes, I built one once for my warrior robot, Tosca. Tosca wasn't much of a fighter, but for a short while, it had a flamethrower. Although Battlebots dissallowed flamethrowers, other tournaments allowed them.

The knowledge regarding flamethrower building is arcane to say the least. How does one build one from scratch? A robot builder I met, named Jon, spent some time experimenting with flamethrowers and he got pretty good at it. I'll skip the mechanical details, but here's some interesting chemistry tidbits regarding flamethrowers from Jon:

. . . there is a direct relationship between flash point of the fuel and length of the flame. Low flash point fuels like toluene burn up before the fuel is projected more than one or two feet. In fact, a very low flash point fuel like ether can vaporize within the system and back up into the tank, so the pump is trying to move gas instead of fluid and produces limited amounts of fire. High flash point fuels, say, xylene, will stay together longer and so project farther. But very high flash point fuels, for example kerosene, do not burn completely, so it’s messy because unspent fuel is winds up spewing everywhere.”

Eventually, I wound up simply using propane because it was the easiest to project. Using the vapor pressure inside the cylinder of propane we could get a six to eight foot flame. It never did much damage to the other bots, but the flamethrower was mostly for pleasing the crowd, anyway. I remind all that, for the vast majority of people, building your own flamethrower is a very, very bad idea.

But if you have built one in the past (and remember, I don't advocate that you do) I'd like to hear about it.

The photo above is that of mechanical artist Christian Ristow's Subjugator -- it's a great flamethrower/ robot.


Anonymous said...

In college We (royal use) built a flamethrower out of a super-soaker water gun. We filled it with rubbing alcohol. After pumping it up, the stream was too powerful for lighter to ignite it. So, we took an aerator off a water faucet and secured it tot he tip of the soaker.

Full pressure, and a lighter at the tip, we ignited a HUGE fireball. It went from floor to ceiling (about 10 feet tall) all from the tip of the Soaker.

The ceiling and carpet were singed (did I mention we did this inside!).

Luckily, we stopped after the great fireball of doom.

Definatly not safe or prudent. In hindsight, the plastic Soaker could have melted, the alcohol could have weakend the tank, explosion etc etc. Nothing good could come of that experiment.

thurston said...

Let's just say, the first time you figure out how to mount a Tire valve on any sort of re-usable pressurized tank is a beautiful thing.

Anonymous said...

Ragnar's Big Book Of Homemade Weapons has a chapter on flamethrowers.

Anonymous said...

Why do Super Soakers always provoke this kind of behaviour. :-)

We filled ours with windshield-washer fluid (glycol) which doesn't dissolve plastic and burns like alcohol.

One of those little catalytic (ie. very hot) lighters set the stream on fire quite nicely.

Anything within about 20 feet could be set on fire with this configuration. Further away, it would only scorch.

Nasty, dumb, and oh-so-cool.

Bill Gurstelle said...

To Thurston and other interested "tankers":

I believe the best way to attach to a schrader valve (bicycle tire-type valve) to any tank is to install what's called a "tank valve." Available at larger hardware stores, look for a Schrader Bridgeport “Camel” Model 38-900 or a Tru-Flate 47-951.

Charles said...


Far be it for me to lead anyone down the path of mayhem. (disclaimer: I AM an original member of the Austin, Texas "Torque & Recoil Club")

but these may be some interesting links. And by interesting, I do mean "Kids, don't try this at home"

and should you be in a more interesting country....

all my best....