Tourbillions are one of my favourite pieces. Simple and quick to construct, and fun. They consist of propellant-loaded tubes with a side directed nozzle and an attached helicopter wing. Spinning quickly, they climb several meters into the air untill they run out of propellant and ignite the effect charge. Their lifting capacity is marginal, so the effect charge in my tourbillions usually consists of a bit of flash powder for a healthy bang, perhaps with bit of titanium for sparks. This page will show you how to build a 12 mm tourbillion with a flash heading. If desired, larger or smaller tourbillions can be made using the same method.
Casing: For a 12 mm tourbillion we need a casing of 12 mm inner diameter, 3 mm wall thickness and 90 mm length. This is a bit longer than used for a rocket of the same caliber. The extra length will be used to accomodate the effect charge.
Propellant: Most rocket propellants are suitable, particularly those that produce interesting sparks or colors. The following composition works well, and several more may be found in the formula database.
Effect charge: A little bit of flash powder will be used for the report. Please do keep in mind that flash powders are among the most sensitive -and- powerfull mixtures used in fireworks. They should be treated with extra care. Pay extra attention to your methods to avoid static electricity and friction as much as possible. Also, do not prepare any more than a few grams at a time. A little goes a long way. Our tourbillion will only required 0.3 grams for a respectable BANG. There are many flash powder compositions that work. The most commonly used flash powder is probably flash #2 from the composition database, a mixture of 70 parts potassium perchlorate and 30 parts aluminum powder. To obtain the best results, use a very fine and reactive grade of aluminum, preferably german black. If you like, you can add a little bit (say +5%) of titanium to add some interesting sparks to the effect.
The wing: Coffee stirrer bars are perfect for forming the wing. They are cheap and easy to find at least where I live. If you have a hard time finding these, any other piece of thin, light wood will do. Use a piece of approximately 11 cm length, 1 cm width and 1 mm thickness.
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 (see rocket tools section) 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, also described in the rocket tools section).
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. The clay is pressed in two stages. First, a 12 mm plug of clay is rammed or pressed into the casing using the flat rammer. A sleeve may be used for more consistent results. Then, using the rammer from figure 1, a second layer of clay, approximately 10 mm thick is formed. This layer should have a cylindrical cavity of 10 mm depth and 5 mm diameter. The cutaway view in figure 2 illustrates the principle.
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 (i.e. 6 mm) to prevent wrinkling. The first two increments are compacted using the extended rammer, the rest with a normal flat rammer. The last 12 mm of the casing are 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 unsensitive, I consider the risk to be acceptable. (ofcourse, a blast screen and proper protective clothing should still be used). With the drill set at low speed, drill a 3 mm hole through the side of the casing, 17 mm from the end. Drill halfway through the casing (i.e. 9 mm deep, assumin the casing is of 18 mm outer diameter), the hole should reach just into the (now propellant filled) cavity in the clay plug, as illustrated.
Plastic Wings may be purchased or made per instructions below.
Forming the wing
As said, the wing is formed from wood. Wood can be bent by means of a method used to build ship hulls a few centuries ago. The wood is heated, slowly bent into shape and kept that way for some time. It is then allowed to cool. When it is then removed from the clamps it retains its shape. Hold the wood by the ends between thumb and finger and apply heat to the middle by means of a hot air gun or candle flame. Heat it well, but take care not to cause charring. Then, twist by an angle of approximately 45 degrees. Hold the wood in this shape for a short while, still applying heat . Then, keeping it twisted, allow it to cool down.
The direction of the twist is important. Though both left-handed and right-handed propellers will work it is best to decide on one direction in order to prevent yourself from getting confused. It will be assumed that a right-handed propeller is used from here on to prevent things from getting uneccesarily complicated. To determine the twist of a propeller look lengthwise along the propeller, keeping the end nearest to you horizontal. The schematic drawing on the left shows what both propellers should look like.
Glue the wing to the casing with some hot melt glue. Take care to orientate the exhaust hole properly with respect to the wing. The situation shown is as it should be for a right-handed wing. For a left-handed wing, rotate the casing 180 degrees around it's lengtwise axis. Insert a piece of fuse into the exhaust hole (5 cm of visco is adequate) and fix it in place with a drop of hot melt glue or red gum bound blackpowder (5% red gum, 95% black powder).
Use and dangers
Place on the ground, as illustrated above with the casing resting on the ground and the wing on top. Light fuse and retreat. Keep well away from these items, at least 10 meters. If the wing is accidentially attached in the wrong orientation, the tourbillion will 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 extra hazardous since it will be projected horizontally instead of up- or downward as in the case of a rocket.