|Table of Contents for Caveman Chemistry: 28 Projects, from the Creation of Fire to the Production of Plastics|
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"The case for flying fire should be narrow and long and filled with well-pressed powder." The remainder of this section simply amplifies this simple description for making rockets. Your rocket may be large or small, but for the purposes of this section we shall assume a length of 3 inches and a diameter of 3/8 inch. You will need a few simple tools and supplies. First, you will need a plunger, a rod 8 inches long and 3/8 inch in diameter. It can be cut from wooden dowel rod, but I cut mine from aluminum rod for durability. One end of this rod is wrapped with tape so that the plunger is larger in diameter at one end than at the other. Second, you will need some hardwood plugs, 3/8 inch in diameter, of the kind used by carpenters to cover screw holes in furniture. These are commonly available at craft and building-supply stores. We need to drill holes down the center of some of the hardwood plugs so that they may serve as nozzles. Third, you need a board with at least one of these plugs glued to it to serve as an anvil. In addition, this board should have holes drilled in it to just accommodate several plugs. Force-fit plugs into the holes in the board to hold them steady while you drill holes in them, then use a pencil to release these nozzles from the board. Each rocket will require one plug and one nozzle.
The bodies of your rockets will be tubes rolled from 3-inch wide paper package tape, as shown in Figure 17-2. Many of my students have never seen paper tape before, but it can still be bought at office-supply stores. I prefer the gummed variety, which becomes sticky only when wet. To roll a rocket tube, carefully wet only the very edge of a 15 cm long piece of tape and stick it to the large-diameter end of the plunger, the end which has been built up with tape. Roll the tape around the plunger, wet the last 5 cm, and finish rolling the tube. If you were careful in wetting the very edge, the tube will stick to the plunger while you roll it, but will twist off when you are done. You should now have a paper tube, 3 inches long and slightly more than 3/8 inch in diameter. Try pushing a plug into the tube—it should go in easily but fit snugly. If it is too tight, add more tape to build up the plunger; if too loose, remove some tape from the plunger. Once you have the hang of it, roll two or three good tubes for your first foray into rocketry.
Now it is time to mix your powder, the proportions of which you determined in Section 17.2. You should ensure that your work area is free of extraneous flammable materials. Have a bucket of water nearby so that in case of accident you can plunge any burns into the water. Powder made with powdered sugar as a fuel is less messy, in my experience, than that made with charcoal, and it makes an excellent rocket fuel. Your sulfur and saltpeter should be separately ground in a mortar and pestle to the consistency of powdered sugar. Weigh by difference 1.0 g of sulfur and the stoichiometric amounts of saltpeter and sugar into a plastic bag. Seal the bag and break up any lumps with your fingers. Shake the bag to mix the ingredients and turn it end for end twenty or thirty times; if your powder is not thoroughly mixed you will get uneven performance from your rockets. With your powder mixed, it is time to load your rockets.
Push a plug into a rocket tube and set it on one of your anvils, as shown in Figure 17-3. Fill the tube with powder using a spoon or spatula, preferably a metal one to minimize the danger of static discharge. Push the small-diameter end of your plunger, the end without the tape, into the tube and press the powder all the way to the bottom. Give the plunger three good raps with a rubber mallet to compact the powder into a solid mass. Remove the plunger, refill the tube with powder, reinsert the plunger, and give it another three raps with the rubber mallet. Repeat this sequence until the rocket is between 2/3 and 3/4 full. Insert a nozzle into the tube and push it all the way down until it rests on the powder. Remove the tube from the anvil and apply glue to the outside of both the plug and the nozzle, taking care not to fill in the nozzle hole. When the glue has set you may use scissors to trim away any excess paper from the ends of the rocket. The powder made from 1 g of sulfur will be enough for you to make two or three rockets.
Packing the powder into the rocket gives it more fuel for the flight, but it also slows the burning of the powder. To speed up the burn rate you need to drill out a core using a 1/16 inch drill bit. Hold the bit in one hand and the rocket in the other. Push the bit into the nozzle, give it a twist, remove it, and allow any loose powder to fall out. Reinsert the bit and remove some more powder. At some point it may become easier to hold the bit still and twist the rocket. Your goal is to drill a core down the center of the rocket from the nozzle to the plug, as shown in Figure 17-4.
Two more items complete the rocket: the guide stick and the fuse. For guide sticks I use 12-inch bamboo skewers, available in grocery stores for making shish kebab. Use two strips of cellophane tape to attach each stick securely to its rocket. I use commercial "green visco" fuse, available wherever pyrotechnic supplies are sold . Those wishing to make their own fuse may consult Reference . Insert a 7 cm length of fuse into the nozzle of each of your rockets. Ideally, the finished rocket should balance on your finger where the fuse enters the nozzle, as shown in Figure 17-5. If your rocket is stick-heavy, slide the tube toward the middle of the stick. If it is tube-heavy, slide it away from the middle of the stick. If you adjust any stick, secure it with an extra piece of tape. Number your rockets and write you name on each one in case you are able to recover them.
Safety must be utmost in your mind when launching rockets. You should familiarize yourself with state and local laws regarding fireworks. Choose an area that will minimize the possibility of accidental fires and maximize the likelihood of recovering your rocket. Be sure to keep any unused rockets at least 20 feet from the one being launched. Place a rocket into a bottle, an iron pipe, or other appropriate support, light the fuse, and retire to a distance of 20 feet or more.
Many things must go right for a rocket to perform well. The powder ingredients must be in the proper ratios and they must be well-mixed. There must be enough powder to lift the rocket and not so much as to weigh it down. The nozzle must be small enough to constrict the gases as they exit, but not so small that the nozzle or plug blows out. The nozzle and core must be straight enough to provide for a stable trajectory. That said, the most common failures in my experience are either that the rocket fails to get off the ground or that the nozzle blows out. If your rocket fails to lift off, take more care in formulating and mixing the next batch of powder and be sure to drill out a good core. If you still have trouble, try making your next nozzle holes smaller. If, on the other hand, your rocket blows out a plug or nozzle, or if it explodes, try drilling a shallower core or a larger nozzle hole in the next set of rockets.
Comrade, the vast majority of mortals do not have what it takes to complete this project safely. Judge well your character and decide whether you can have a pious and just feeling about these things and can keep them secure.
It rises from the earth to Heaven and descends again to the Earth and receives power from Above and from Below. Thus thou wilt have the glory of the Whole World. All obscurity shall be clear to thee. This is the strong power of all powers for it overcomes everything fine and penetrates everything solid.
There is no room for equivocation; either your rocket rises from the Earth to heaven or the strong power of all powers remains obscure to thee.
Record in your notebook any differences in the construction of your numbered rockets. Give a brief description of the success or failure of each one.
I drill my holes 23/64 inch in diameter.
I drill my nozzle holes 9/64 inch in diameter.
Heavy kraft paper, 7 cm x 15 cm, may be substituted if paper tape is unavailable.
I have been making this powder for thirty-five years, ten of them with undergraduates, and have never had an accidental ignition. The wise person, however, is always prepared for such a possibility.
I use anti-static bags of the kind used to ship circuit boards. These provide and added measure of protection against accidental ignition.
I use fast-curing epoxy cement so that rockets may be launched soon after they are made.
A power drill could heat the powder, with unfortunate consequences.