Because of its profound effect on the development of warfare, mining, and thereby heavy industry, black powder, also called “gunpowder”, is considered by scholars in all fields to be one of most important inventions in the history of civilization. It is one of the oldest pyrotechnic mixtures known, and though its exact origins are uncertain, recognizable formulas for black powder first appear in the literature of the 13th Century. Black powder is a mixture of a chemical oxidizer (potassium nitrate or sodium nitrate), a simple fuel (a form of carbon such as coal or charcoal), and sulfur, which functions to some extent as a fuel, but mainly as a sort of melting-flux that helps the other ingredients burn faster. When combined in the proper proportions and ignited, its three components burn furiously, releasing great amounts of gas. smoke, and heat that are useful in dozens of military and industrial applications.
All the propellants in this topic are either modified forms of black powder, or closely related mixtures. The popular perception is that black powder is an explosive used only in blasting, gunnery, and fireworks. But black powder makes an excellent rocket propellant as well. It is. in fact, the exact propellant used in the “safe” model rocket engines sold in hobby shops. The secret lies in packing it tightly into a solid stick, a form in which it burns at a fixed and predictable rate, and a form in which its burn rate can be carefully controlled.
As you can see in Figure 1-1. a loose, teaspoon-size pile of the KG3 propellant burns very quickly. Though it generates a great amount of heat, and a large puff of smoke and gas. it does not explode.
When properly triggered, high explosives like nitroglycerine undergo a sudden and violent decomposition of their entire molecular structure, even when loose and completely unconfined. But black powder and the propellants described in this topic gain their explosive power only when burned in a tightly confined or totally sealed container, and are therefore not considered “high explosives”.
Figure 1-1. A small pile of the loose KG3 propellant burns very quickly. It generates a large amount of heat, gas. and smoke, but it does not explode.
Sensitivity to Impact
In small quantities, black powder made with potassium nitrate or sodium nitrate and a simple carbon fuel is comparatively insensitive to impact, and I’ve verified this many times with the following experiment. You can try it yourself if you wish, but because it involves striking a piece of steel with a hammer, you must wear safety goggles when performing this test.
As shown in Figure 1-2. place a tiny pinch of commercial black powder or one of the propellants in this topic on an anvil, or a large piece of iron or steel. Then begin striking it gently with a hammer. You will find to you amazement that you can increase the force of your blows to a point where you are in danger of chipping the hammer, and the powder will not explode. In fact, all you will succeed in doing is to pound it into a flat, gray-colored cake (Figure 1-3). Of course if you miss the powder and strike the anvil, the metal-to-metal impact could generate a spark that might ignite the powder. so never use more than a small pinch of powder, and be very careful when performing this test with other chemical mixtures, because unlike black powder, many of them are highly sensitive to impact.
Then why do the caps in a cap pistol make such a bang? Contrary to popular belief, the caps used in cap pistols are not made of black powder. The are made of another mixture similar in appearance but completely different in chemical composition. Antique muskets and flintlock rifles use black powder. What makes them work? The answer is that the hammer strikes a piece of flint that produces a spark. It is the spark that lights the powder, and not the impact of the hammer.
The fact is that none of the more common explosive fireworks, like firecrackers, cherry bombs, and M-80s. use black powder for the very reason that black powder is not sufficiently impact-sensitive or explosive enough to make them work. Black powder is used by the fireworks industry, but not for creating loud and violent explosions. It is used mainly as a skyrocket propellant. a lifting charge for mortars, and a bursting charge for scattering the stars and other special effects used in star shells. And. of course it is used in making fuse.
Sensitivity to Sparks and Static Electricity
In its loose form, black powder is extremely sensitive to sparks. It can be ignited by even the tiniest spark. Common spark sources to avoid are welding sparks, sparks from a grinding wheel, the sparks produced by striking together two pieces of iron or steel, and especially static electricity sparks. If you get up in the morning, walk across the carpet, and see a spark jump from your finger to the light switch as you reach to turn it on. this is not a good day to work with black powder. A few-years ago one of my readers toured a commercial rocket motor factory. He told me that they use an elaborate network of static electricity detectors. On days when this equipment tells them that the potential for static electricity is “high”, they shut the factory down. I think that this is an excellent policy, and I’d like everyone who reads this topic to adopt it.
When working with black powder, the greatest danger exists when you are sifting it or pouring it from one container into another. If you were standing directly over it, and if anything more than a small amount were accidentally ignited, it would not explode, but it would burn so quickly and violently that you could probably not jump out of the way fast enough to avoid being seriously burned. The most likely cause of such an ignition would be static electricity, and you can minimize the risk of a static electricity accident by following these rules.
1. Always ground yourself before touching anything that contains black powder. You can do this by reaching down, and momentarily touching a water pipe or the ground.
2. When sifting black powder or pouring it from one container into another, place all the tools and containers on the ground, and lei them to sit on the ground for several minutes before you begin. This allows time for any static charge that these items might contain to drain away.
3. Never operate a powder mill on top of a table, but always on the ground. If you are outside, set the mill on the dirt. If you have a patio, set it on the concrete.
4. Avoid working in dry and windy weather.
5. When handling black powder in its loose form, work slowly and deliberately.
Sensitivity to Friction
In 1992 I met another rocket maker who has worked extensively with black powder, and he told me the following story. He was loading dry black powder into a large motor one day when he became impatient with loading and tamping it in small doses. In an attempt to save time, he poured a large amount of powder into the motor casing, and tried to compact it all with one gigantic blow of the hammer.
As he rammed the tamp downward into the casing, the sudden compression of the air underneath forced a jet of air and loose powder upward between the sides of the tamp and the casing wall. The result was a momentary hissing sound followed by a loud “PHOOOM!” The tamp was blown high into the air. The powder that remained in the motor burned like a flare. The motor did not explode, and though startled, he was not injured. Of course the immediate question is. “What happened?”
We already know that black powder is relatively insensitive to impact. We also know that, when spread over the comparatively large area of the motor casing, the concentration of force and impact applied by his hammer was only a small fraction of that applied during the impact test described earlier. And we also know that the cushion of compressed air under the tamp would have prevented it from sharply impacting the powder already in the casing.
1 can only make an educated guess at what actually happened, and my best guess is that the friction between the tamp moving downward and the thick film of dry powder moving upward generated enough heat to ignite the mixture. It is also possible that the jetting of the dry powder up the sides of the tamp acted like an electrostatic generator, creating a spark that ignited the powder. It would take a series of carefully designed experiments to find out exactly what happened, but an exact understanding of the mechanism isn’t necessary. Just rememberwhen loading your own motors to exercise common sense, and follow these rules.
1. Don’t use commercial black powder. Use only the slower-burning, homemade propellants described in this topic. Though even commercial black powder is comparatively insensitive to impact, it burns much fasterthan these homemade propellants. If an accidental ignition should occur, the chances of an explosion and serious injury are correspondingly greater.
Figure 1-2. A simple impact test for the KG3 propellant. A tiny pinch is placed on a steel block and struck with a hammer. Safety goggles must be worn during this test.
Figure 1-3. The result of the impact test. The propellant does not explode. It is simply pounded into aflat, gray cake, and in this demonstration, stuck to the face of the hammer.
2. Don’t try to ram in a large amount of propellant with a single hammer blow. When loading my own motors, I do it in small doses. I first give the tamp a few light taps to squeeze out any trapped air. Then 1 ram the propellant into a state of complete compaction.
3. Never use a metal tamp. Always make tamps from a lightweight material like wood or plastic. In the event of an accidental ignition, the tamp must be light enough to be blown out the front of the motor casing before the pressure in the casing can build to a dangerous level. Tamps made of metals like brass, steel, and even aluminum, are heavy.Jhelr inherent resistance to motion, aka “inertia”, can allow the pressure in the casing to build to the point of explosion.
4. Never stand directly over the tamp or look directly down on it while you are working.
The Piezoelectric Effect
The piezoelectric effect is the tendency of some crystalline substances to generate an electric current when struck sharply. The most notable example is quartz, whose ability to respond in this way is used in electrical devices ranging from frequency-controlling crystals to piezoelectric cigarette lighters. Many years ago an explosives expert told me that there is some evidence that potassium nitrate crystals are slightly piezoelectric. If this is true, it would be theoretically possible for a large barrel of black powder to contain enough crystals to generate an internal spark if dropped or shocked in just the right way.
As far as he knew at the time no one had performed the experiments needed to test this theory. He seemed to think it more likely that the known cases of dropped barrels exploding were caused by the sparks generated when the iron barrel hoops hit the ground. In any case it’s an interesting theory, and one that might cause a person to use extra care when handling black powder in large amounts.
Storage of Black Powder
When you buy black powder at a gun shop, it usually comes in a metal can. The theory says that in the event of a lightning strike or a fallen power line, the can will act like a Faraday cage, conduct the electricity around the powder, and reduce the chance of ignition. Whether or not this really works is open to question, but it never hurts to be safe. So when storing your own black powder, keep it in a lightweight metal container. If the powder ever ignites, you want the container to blow its lid and not explode, so look for a light weight can with a loose fitting top. like a thin, sheet metal, tea or cookie box.
Disposal of Black Powder
To safely dispose of black powder, dissolve it in water. Fill a bucket with warm water and a dash of laundry detergent. Stir the powder in with a spoon. Let it soak for a few hours, and stir it again to insure that it’s completely dissolved. Then filter the solution through a sieve lined with paper towels. The sulfur and the charcoal will remain in the towels, which you can place in a plastic bag. and put in the trash. Then use the nitrate solution as a fertilizer in your garden, or dispose of it in the same way that you’d normally dispose of any unused nitrate fertilizer.
Handling and Storage of Finished Motors
Once black powder has been compressed into a solid stick, its sensitivity to ignition is reduced, and finished rocket motors with the solid propellant sealed inside are even less hazardous. When handling and storing them, you should follow the same safety procedures recommended for storing and handling commercially-made model rocket engines, which are:
1. Keep finished rocket motors away from all fire and flame, and do not smoke in their presence.
2. In case of a fire near or among the rocket motors, use water or a foam fire extinguisher to
prevent their ignition.
3. Store finished rocket motors in a cool, dry place, and never expose them to temperatures above 150° Fahrenheit.
4. Dispose of damaged, defective, or unwanted motors by soaking them in water.
<• Safety During Propellant Preparation and Motor Construction
1. Work out of doors whenever possible. If you confine your mixing and loading activities to a workbench in the back yard, you reduce the risk of a fire in the event of an accidental ignition.
2. Never keep large amounts of rocket propellant on your workbench. Bring only what you need for the immediate task at hand.
3. Never operate a powder mill indoors. Always set it on the ground outside at a safe distance from your house and other buildings, and surround it with a sandbag wall {Figure 1-4). In the event of an explosion, the sand will absorb most of the heavy debris, and everything else will be directed upward out the top of the enclosure. At the time of this writing, empty sand bags cost 25 cents each, and you can buy them at hardware-lumber yards like Home Depot and Lowe’s. Fill each bag 1/2 full, fold over the open end, lay it flat, and butt the folded end against the next bag in the row. As you finish each row, you can flatten and level it by walking on its upper surface. When you add a new row, stagger the joints as you would if you were building a brick wall. The powder mill’s electric cord passes through a short length of 2″ PVC water pipe placed in the bottom row.
When you make this enclosure, leave plenty of air space around the powder mill. The enclosure in the photo is square, and it’s sufficient for a 1/2 gallon mill. It is 8 rows high with 8 bags per row. It took 64 bags, and a little more than “a yard” of sand to make. For a 1 gallon mill make a taller, rectangular enclosure by adding 3 more rows, and an extra bag along two sides of each row. With 10 bags per row it will take 110 bags to make. The extra bags will more than double the enclosure’s internal volume. For a permanent installation, dig a pit in the ground, and line it with cement blocks.
Figure 1-4. A sandbag enclosure greatly reduces the chance of injury or property damage if the powder mill ever explodes. Sandbags are inexpensive. In the event of an explosion, they absorb most of the heavy debris, and everything else is directed upward out the top of the enclosure.
4. Mix only enough propellant for the motors that you plan to build in the next day or two, and avoid storing large quantities of unused propellant for any length of time.
5. Wear a respirator or a dust mask when handling or working with propellants. Though the chemicals in these propellants are nontoxic or mildly toxic, all of them are irritating to the lungs and nasal passages. Long term exposure to charcoal, coal dust, and carbon black can cause black lung and other serious respiratory diseases.
6. Handle finished rocket motors gently. Black powder propellant grains are hard and brittle.They can easily be broken or cracked. A cracked propellant grain will cause a motor to explode shortly after ignition. The long and narrow motors like the NV6-83-G44 should be stored and transported in plastic bubble wrap (See the PACKAGING SUPPLIES headings in The Yellow Pages). If you accidentally drop a motor, you should assume that the propellant grain has cracked, and you should destroy the motor by soaking it in water.
7. Keep all rocket propellants and finished rocket motors away from children. Children are fascinated by rockets, and that is good. But if you intend to involve anyone who doesn’t own a valid driver’s license, be sure that you lay down a strict set of safety rules, and never let them mix or handle rocket propellants without close supervision. I’ve always had a problem with the idea that people magically become mature at 18 to 21 years of age. I think it is more sensible to tie the making of homemade rocket motors to the possession of a valid driver’s license.
If the State you live in thinks you are mature enough to operate a 4,000 pound killing machine (aka a car), you are probably responsible enough to build homemade rocket motors. If, by the same token, you are 40 years old, and your license has been revoked for drunk driving, you are clearly nor a responsible person. You are a danger to yourself and the people around you, and you have no business engaging in amateur rocketry.
Aren’t You Afraid That a Terrorist Will Use a Homemade Rocket?
My answer to this question is only in the movies. In real life homemade rockets are worthless as weapons. First of all they are very inaccurate. When fired horizontally, small variations in performance cause most of them to either overshoot their target or fall unacceptably short. Also consider that the fact that the process of making and testing rockets is exactly the kind of high-profile activity that a terrorist avoids. It takes unacceptable amounts of time. It involves noisy, smoky experiments, and it leaves a trail of material purchases that is easv for the authorities to follow. In the few cases where terrorists have successfully used rockets, they’ve been professionally made, and either stolen, or purchased on the black market. From a terrorist’s point of view, it is simpler and cheaper to park a truck filled with explosives next to a public building, then quietly walk away.
Additionally, the rocket motors in this topic have progressive thrust-time curves. Their low starting thrust results in a beautiful and very realistic lift-off in vertical flight. But if you try to launch them at a low angle from a tube (like a “Bazooka”), as they exit the tube they will drop unpredictably, or fall to the ground. I’ve designed these rocket motors to cany cameras and scientific equipment in vertical flight. They are the exact opposite of the kind used in weapons.
Won’t Someone Use Homemade Black Powder to Make a Bomb?
The people who fear this eventuality have a limited knowledge of chemistry. What they don’t understand is that you don’t need a well known explosive like black powder to make a violent explosion. Even if black powder were outlawed, the supermarkets and hardware stores of America contain dozens of products that are just as powerful, the most obvious example being matches. Since the bombing at the 1996 Summer Olympics, there have been so many descriptions of pipe bombs in the news that I’m sure I’m not revealing anything new when I explain that, for less than S100. anyone anywhere can buy the pipe fittings and enough matches to make a similar device. Likewise, anyone who saw the 1995 medical thriller. Outbreak, starring Dustin Hoffman, will remember the horrendous explosion at the end ot the film caused by a device called a “fuel-air” bomb. Fuel-air weapons actually exist, and are powered by a fine mist of air and gasoline. Frustrating though it is. the kind of weak and dysfunctional personalities that make and use bombs know all of this, and at least for now. aside from “good intelligence” or the threat of punishment, there is little you can do to stop them.
Therefore, outlawing hobbies like amateur rocketry, preventing the public from making homemade rocket propellant. and limiting the public’s access to anything that might be misused would be completely ineffective, and it would also be wrong. For every person who abuses these things there are thousands who put them to good and creative use. For example, we all know that in 1996 ammonium nitrate was used to bomb the Murrah federal building in Oklahoma City. But ammonium nitrate is a cheap and excellent fertilizer, and it’s also a precursor chemical used in the production of many other chemicals. A healthy and vibrant America needs ammonium nitrate, and later in this topic I will teach you how. with home-lab techniques, to convert ammonium nitrate into sodium nitrate, the main ingredient in the slow-burning NG6 and HV6 propellants.
Since I started this work in 1983 I’ve met at least a dozen professional rocket engineers. Every single one of them built his first rocket motor b\ the time he was seventeen, and several have told me that it was their early experience with homemade rocket motors that lead them to pursue rocket engineering as a career. Most of the people who tinker with these tilings do so in a responsible manner with benevolent intentions. As a group they are unusually intelligent, self motivated, and highly creative. When allowed to pursue their interests freely and without interference, their creativity blossoms in ways that benefit America as a whole. These people represent the best among us. To den\ them access to the knowledge and materials needed to pursue their hobby would do our country far more harm than good. Instead of tr\ nig to restrict our citizens’ involvement with technology, we should establish more severe punishments for those who misuse it!
