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Buzz-Bombs/Helicopters
A very popular flying firework, the Buzz-Bomb
or Helicopter.
Both basically the same device, but the Buzz-Bomb explodes
with a loud report at the apex of its flight. There
are a large number of variations to this particular
firework,
several are covered in the procedure outlined below...
Procedure
The Helicopter is made from a 4 ounce rocket tube (
1/2" ID x 5" long). Like all rocket-type devices,
the tubes used must be parallel wound to prevent bursting,
due to the high internal pressures generated. Parallel
wound tubes do not have the spiral seam that goes down
the length of the tube ( like the tube from a roll of
paper towels or toilet paper has. ).
Once you've got the proper tube, the first thing you'll
need to do is make some tooling. The reason for the
tooling is to be able to form a hard plug & cavity
at the end of the tube.
When lit, hot gasses, sparks & flame shoot out the
small 1/8" vent hole at the bottom of the Helicopter
making it spin and lift off the ground. If you were
to make an exhaust hole in the cardboard casing
alone, the intense heat & flame would widen the
hole in a fraction of a second, reducing the thrust
and making the Helicopter just flop around on the ground.
What the tooling does is to form a cavity of heat resistant
Rocket Nozzle Mix at the bottom of the tube. With the
Rocket Nozzle Mix cavity in place, the flame & hot
gasses pass through the small vent hole in it, which
they cannot burn through, so the hole stays at 1/8"
all through the flight. See the illustrations below.
As you can see from the illustrations
above, the Plug/Cavity Ramming Tool is nothing more
than a wooden or metal rod with the end ground down
to a point, that slips easily into the cardboard tube.
The best choice for making the tool is Aluminum or steel.
You're going to be pounding on this thing with a hammer,
so one made of wood probably wouldn't last you all that
long. You'll also need to make an identical ramming
tool without a point on the end. This will be used for
compacting the propellant into the tube. The step-by-step
procedure follows....
Procedure
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Propellant: Most rocket propellants are
suitable, particularly those that produce interesting
sparks. The following composition works well,
and several more may be found in the composition
database
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Potassium nitrate
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68
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Charcoal
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14
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Sulfur
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9
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Aluminum
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9
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Clay: The
nozzle and end plug are formed from clay, much
like as is done in the construction of rockets.
As will be described shortly, the nozzle shape
is different though. Bentonite, kaolin and ground
kitty litter all work well.
Tools: A
sleeve and rammer, such as used in the construction
of rockets are used for this project as well.
Besides a flat-ended rammer an unconventional
rammer will also be needed (see figure). With
some patience it can be made by evenly filing
down one end of a straight rod. Alternatively,
you could drill a lengthwise hole of 5 mm diameter
in the center of a flat ended dowel and fix a
short length of 5 mm rod in that (much like as
is done in the construction of a spindle.
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Construction
Nozzle end
Buzzbombs differ from rockets in that the exhaust
from the nozzle is projected sideways, exerting
a torque. Clay is used to provide a more or less
erosion resistant exhaust hole.
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Propellant, end plug and exhaust
hole
Ram or press the propellant in small increments,
each no more than will give a layer as thick as
half the casings inner diameter to prevent wrinkling.
The other end of the casing is filled with clay
to form the end plug.
The exhaust hole is drilled through the side
of the casing. This is a somewhat dangerous operation
since it causes quite a lot of friction but as
we do not need to drill a great length through
the propellant and the propellant is quite insensitive,
I consider the risk to be acceptable. (of course,
a blast screen and proper protective clothing
should still be used). Carefully drill a1/8"
hole through the side of the casing about 5/8
from the end. Drill halfway through the casing
the hole should reach just into the (now propellant
filled) cavity in the clay plug, as illustrated.
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The wing
Wings
can be purchased from many pyro supply companies.
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Assembly
Glue
the wing to the casing with some hot melt glue.
Take care to orientate the exhaust hole properly
with respect to the wing. Insert a piece
of fuse into the exhaust hole (2 1/2" of
visco is adequate) and fix it in place with a
drop of hot melt glue
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Dangers
Place on the ground with the casing resting on the
ground and the wing on top. Light fuse and get away.
Keep well away from these items. They are somewhat unpredictable
and may bounce around on the ground instead of climbing
into the air. Like rockets, they may explode if the
propellant is not compressed well. The end plug or nozzle
may also be blown out which can be hazardous.
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