Firework Anatomy
Repeating Aerial Tube
devices are little more than several aerial
shells fused together to go off in sequence, with a few seconds of delay
between each shell. There are usually anywhere from 3 to 7 tubes which are
glued down to a thick wooden base to stabilize the device. Each tube
contains a typical aerial shell in the bottom, protected by a cardboard disk
and a cap at the top of the tube. Holes are drilled in the bottom of each
tube, and small chunks of fuse connect each shell to the tube adjacent to
it. The tube on the end has a long fuse that runs outside for a few inches.
When that fuse is lit, the first shell fires. The lift charge of that shell
ignites the chunk of fuse leading into the next tube, which in turn ignites
a shell about four seconds later, and so on.
Repeaters
contain smaller "effect tubes" that are usually about one-third to half
the length of the main "launching tubes". Each of these has a
construction very similar to a shell. When the lift charge in the
launching tube fires, it ignites a time fuse and (usually) a coloured star
composition in the bottom of the effect tube. The star composition burns
brightly as the tube rises, and at the at its maximum altitude, the burst
charge ignites the effects. The diagram at the right shows stars, which
would look like a small, uneven shell burst when ignited. But if you have
ever lit off a repeater before, you would know that there are dozens of
possible effects: effects tubes that go up and explode, ones that whistle,
ones that crackle, ones that spin around on the way up, and even ones that
give off parachutes. Next time you light a repeater, come back to that
area the next morning and look at the ground around where you set it off -
you will see dozens of these spent effects tubes (with nothing but the
clay plug left).
Mines
are basically a ground-level aerial shell burst
that is directed upwards. The bottom of the tube contains a black powder
lift charge, similar to that found in a shell. When ignited, the lift charge
engulfs the stars in flame, igniting them as it propels them out of the tube
in a V-shaped pattern. The "spread" of the stars in the sky depends on both
the length and the width of the mortar.
Consumer mines are typically one-shot-per-tube devices that are bunched
together, resembling repeaters. Professional mines, however, are reloadable
- the lift powder and stars are put in bags, which are lowered into the
mortars and ignited.
Single Tube Fountains
consist of a cardboard tube (which may be inside
of a cone) that stands vertically on a plastic base. The tube is charged
with a composition designed to make lots of sparks, flame, and gas. At the
end of the tube there is a clay plug with a hole drilled into it, forming
what is known as a "choke". Without a choke, the fountain would only give
off a weak spray of sparks. With a choke, however, a lot of pressure builds
up inside of the tube, which forces the gas and sparks out of the fountain
with a much greater velocity. Very small fountain tubes (i.e., 1/4 in
diameter) don't require chokes.
The fountain composition is often layered as to produce different effects at
different stages in the burning. For instance, one layer may burn to produce
orange sparks, followed by a layer that produces white sparks and green star
fragments.
Repeating Aerials
are just as complex as aerial shells because that's basically what a
repeater is - many tubes of mini-"shells" all in one unit. These
clusters of tubes each have a clay plug in the bottom and a black powder
lift charge. There are two holes in the side of each tube, and as the
device is
being constructed,
small chunks of fuse are used to connect each tube to its neighbor.
This way, when the first lift charge ignites and sends the effect into the
air, the tube next to it ignites shortly afterwards, and so on. Most
devices have several parallel-fused tubes towards the end of the "fire
trail", so that several tubes ignite simultaneously (or in very rapid
succession) at the end of the performance in order to intensify the display.
Aerial Shells
are one of the most beautiful and certainly one of the
most complex types of fireworks. A shell consists of main parts: a
container, a lift charge, a time fuse, a burst charge, and stars/effects.
The container, or shell casing, is a strong wall that protects the contents.
The lift charge propels the shell out of the tube, and the time fuse ignites
the burst charge at the right altitude. The burst charge then ignites the
effects.
Shells are launched from a tube known as a mortar. A string loop is often
attached to consumer firework shells so it can lowered into the mortar by
the fuse. When the fuse enters the shell, it ignites the burst charge,
creating an explosion that ignites the time fuse and shoots the shell high
into the air.
As the shell ascends, the time fuse burns towards the burst charge. At the
precise altitude - usually where the shell is briefly hanging in the air -
the time fuse ignites the black powder burst charge, causing the shell to
explode. The powerful explosion blasts apart the shell casing and ignites
the stars, scattering them in all directions across the sky. These stars
burn brightly and give off sparks, creating a huge spherical pattern in the
sky.
Aerial Parachutes
have a complex internal construction very
similar to that of an aerial shell. Parachutes can come in the form of
single tubes with a base, or clusters of tubes that look like a tall
repeater. The launch tube is usually quite thick to withstand the forces of
the powerful, noisy lift charge. When the lift charge ignites, it blasts a
"parachute tube" high into the air. Meanwhile, a time fuse is burning inside
of the parachute tube, which in turn ignites a tiny burst charge when the
tube reaches the highest point in its flight. Much like a model rocket, this
burst (or "ejection") charge blasts the parachutes from the parachute tube.
There is often a small piece of paper "wadding" between the burst charge and
the parachutes to prevent the chutes from burning up. The tissue parachutes
are attached to small chunks of tube filled with clay to serve as weights.
They can be packed together tightly, which enables several parachutes to be
put inside of one parachute tube.
Sometimes the weight tube is filled with a smoke composition. A short piece
of fuse transfers fire from the parachute tube's burst charge to the
composition in the weight, which smokes as it drifts down from the sky.
Nighttime parachutes use a steady-burning star or strobe composition in
place of smoke composition
Roman Candles
seem like a simple firework, the construction
process is quite complex and difficult. After a clay plug at the bottom, the
roman candle tube consists of alternating layers of lift charge, stars, and
delay compositions. When the fuse enters the tube, it activates a
slow-burning delay composition that makes its way down. Within seconds, the
delay charge reaches the first star, simultaneously igniting both it and the
lift charge below it, which blows the star out of the tube. This ignites
another layer of delay composition, which will light a star and the lift
charge to blow it out a few seconds later. This continues until every star
has been blown out of the tube
Wheels
consist of a cardboard frame to which are
attached several small rockets, or "drivers". The device is usually attached
by a nail to a wooden post. When the burning fuse enters each driver, the
propellant burns rapidly to give off gas, which is forced out of the small
nozzle to create thrust. This thrust spins the device around its axis.
Unlike most rocket propellants (which are designed to lift the rocket up
into the air and not give color), the propellant used in wheel drivers burns
to produce rich colors, sparks, crackle, etc. Because the wheel spins so
fast, it appears that there are "rings" of fire. When each driver is
exhausted, the fire is transferred by another fuse to the next driver, which
starts up again and continues the process (usually with a different effect).
This usually happens so fast that the wheel doesn't have time to stop
spinning
Rockets
are the second oldest type of firework that were
originally discovered by mistake - the Chinese discovered that an open-ended
firecracker propelled itself along the ground, rather than exploding. Since
then, their construction has become much more complex. Rockets and missiles
operate the same way; the only difference being in the method of
stabilization (either fins or a stick). When the burning fuse enters the
end, the cone-shaped chamber ignites within a fraction of a second. The
shape of this chamber provides a very large surface area for burning to take
place, creating a large volume of gas which is forced out of the back to
create thrust. As a result, the rocket/missile travels in the opposite
direction. Because of the rapid burning, the fuel is exhausted in a matter
of seconds. The casing of the rocket is usually fairly thick so it can
withstand the high pressures of the burning fuel. The internal time fuse
then transmits fire to the burst charge, which explodes to break open the
rocket casing and ignite the stars or reports inside.
