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Flamethrowers
How Flamethrowers Work
BY TOM HARRIS
Fire is one of the most useful natural
phenomena in the world.
When early humans first captured fire
from naturally burning areas, and later generated flames themselves, their
lives changed dramatically.
With this understanding of nature,
they could have light and heat after nightfall, and they could cook their
food.
But fire is also one of the most
dangerous phenomena in the world, and this fact wasn't lost on early humans.
Archeological evidence suggests early
hunters used fire to flush out their prey, and some groups may have used it to
fight other humans.
Throughout history, fire has proven
to be an extremely effective, devastating weapon.
One of the most interesting
developments in fire weaponry was the flamethrower.
The modern flamethrower came about in
the early 20th century, but the original idea is actually thousands of years
old.
In this article, we'll look at these
early pyrotechnic weapons, as well as their modern counterparts, to understand
what they do and how they do it.
Feel the Burn
Fire is caused by a chemical reaction between two or more
substances, typically oxygen in the air and some sort of fuel (gasoline, wood, or coal for example).
This reaction is triggered by extreme
heat, often caused by another flame or a spark. The fire's own heat is
sufficient to keep the chemical reaction going as long as there is fuel to burn.
The
basic idea of a flamethrower is to spread fire by launching
burning fuel.
The
earliest flamethrowers, dating roughly from the 5th century B.C., were long
tubes filled with burning solid material (such as sulfur or coal).
These
weapons worked in the same way as a blow-gun -- warriors just blew into one end
of the tube, propelling the burning matter toward their enemies.
A
more sophisticated sort of flamethrower came into widespread use in the 7th
Century.
In
this era, the Byzantine Empire added "Greek
fire" to its arsenal.
Greek
fire was probably a mixture of liquid petroleum, sulfur, quicklime and other
elements. In any case, it was a highly-flammable, oil-based fluid.
In
combat, Byzantine forces would pump this substance from a large reservoir,
through narrow brass tubes.
These
tubes concentrated the pressurized liquid into a powerful stream, the same way
a hose and nozzle concentrate water into a narrow jet.
The
soldiers lit a fuse at the end of the brass tubes to ignite the fluid stream as
it shot out. The fluid stream carried fire dozens of feet through the air.
The
Byzantines mounted these weapons along the walls of Constantinople, as well as
the bows of their ships.
Since
the flammable substance was oil-based, it would still burn even when it hit the
water, making it a particularly effective weapon in naval battles.
Initially,
the Byzantines' enemies were mystified by this horrific weapon, but before
long, others were copying the technology.
The
Chinese applied their advanced technology to take the idea to the next level.
The
Byzantines used a very basic pump, like the sort used to drive water out of an
underground well.
This
kind of pump only pushes out fluid on the downstroke, so the Byzantine
flamethrower could only shoot fire in short bursts.
The
Chinese had developed a more advanced pump, the double-acting
bellows.
Double-acting
bellows consist of a pivoting pedal that drives two pumping chambers.
When
the pedal is pushing down on one chamber (the downstroke), it's lifting up on
the other (the upstroke).
In
this way, the pump is constantly pushing out fluid, allowing a continuous
stream of fuel (and therefore a constant blast of fire).
Soon
after this sort of weaponry came into use, it was eclipsed by another
pyrotechnic technology: gunpowder.
Over
the next thousand years, gunpowder revolutionized the world of warfare, and
flamethrowers more or less fell by the wayside.
But
as we'll see in the next section, flamethrowers were eventually reintroduced
into the world's combat arsenal, in a modified form.
Fight Fire With Fire
In World War I, the German army rediscovered the
flamethrower and added it to their arsenal (in a new and improved form).
By World
War II, forces on both sides used a range of flamethrower weapons on the
battlefield.
The most
impressive innovation was the handheld flamethrower. This long, gun-type weapon has an attached fuel tank that soldiers can
carry on their back.
Handheld Flamethrowers
The backpack
contains three cylinder tanks. The two outside tanks hold a flammable, oil-based liquid
fuel, similar to the material used to make Greek fire.
The tanks have screw-on caps, so they
can be refilled easily. The middle tank holds a flammable, compressed gas (such
as butane). This tank feeds gas through a pressure regulator to two connected
tubes.
One tube leads to the ignition system
in the gun, which we'll discuss later on. The other tube leads to the two side
fuel tanks, letting the compressed gas into the open area above the flammable
liquid.
The compressed gas applies a great
deal of downward pressure on the fuel, driving it out of the tanks, through a
connected hose, into a reservoir in the gun.
The gun housing has a long
rod running through it, with a valve plug on the end.
A spring at the back of the gun
pushes the rod forward, pressing the plug into a valve seat. This keeps the
fuel from flowing out through the gun nozzle when the trigger lever is
released.
When the operator squeezes the
trigger lever, it pulls the rod (and the attached plug) backward. With the
valve open, the pressurized fuel can flow through the nozzle.
A flamethrower like this one can
shoot a fuel stream as far as 50 yards (46 meters).
As it exits the nozzle, the fuel
flows past the ignition system.
Over the years, there have been a
variety of ignition systems used in flamethrowers. One of the simpler systems
was a coil of high-resistance wire.
When electrical current passed
through these wires, they released a lot of heat, warming the fuel to the
combustion point. The gun in the above diagram has a slightly more elaborate
system.
When the ignition valve is open, compressed flammable gas from the middle
cylinder tank on the backpack flows through a long length of hose to the end of
the gun.
Here it is mixed with air and
released through several small holes into the chamber in front of the nozzle.
The gun also has two spark plugs positioned
in front of the nozzle, which are powered by a portable battery.
To prepare the gun, the operator
opens the ignition valve and presses a button that activates the spark plug.
This creates a small flame in front of the nozzle, which ignites the flowing
fuel, creating the fire stream.
Tank-mounted Flamethrowers
In World Wars I
and II, as well as in the Vietnam war, flamethrower designs similar
to the handheld models were mounted on tanks.
Typically, the fuel in these weapons
was driven by rotary or piston pumps, powered directly by the tank engine.
With greater pumping power,
tank-mounted flamethrowers had better range, and with more fuel tank space,
they had a larger ammunition supply.
Civilians With Fire
Military forces
continue to use these sorts of weapons today, but the technology is more
commonly used for nonviolent civilian purposes.
Most notably, foresters use
flamethrowers in prescribed burning, and farmers use it to clear fields.
Some car enthusiasts install
low-range flame throwers at the back of their cars, to release an impressive
ball of fire when they take off.
Rock stars and other entertainers
often include flamethrowers as part of elaborate pyrotechnic displays.
One of the most widely known
flamethrower technologies today is actually the simplest.
"Fire breathers" turn their own bodies into flamethrowers by pouring
fuel (typically kerosene) into their mouth and holding an ignition system
(typically a torch) in front of them. When they spit out the kerosene, the
torch ignites it, creating a dazzling stream of fire (only professionals should
attempt this -- it is extremely dangerous).
The technique is definitely low-tech,
but the operating principle is exactly the same as in the most expensive
military flamethrowers!
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