Amateur Rocket Motor Construction by David Sleeter
About this review:
I have never made motors like the ones described in the book, and I don't plan to. Therefore, this review does not provide a technical critique. Other 'experts', such as Professor Terry McCreary, have given it good marks. However, the other reviews I have seen are rather short and don't provide much detail on the contents. I thought that others who might be pondering its purchase might be interested in a little more detail.
Quoting the cover, this book is "A Comprehensive Guide to the Construction of Homemade Sold Fuel Rocket Motors." Here, solid fuel refers to packed powder as opposed to composite propellant. Somewhat to my surprise, none of the propellants presented in the book are purely black powder, a point that Sleeter is careful to make (here 'purely' means a stoichiometric mix). The book is a whopping 526 pages with tons of photos, illustrations, and technical drawings. It includes 54 tested motor designs using 5 proven propellant formulations. The motors range from a C6 (3/4"x 3 1/4") to an I65 (2" x 14.5"). I'd love to see one of those puppies fly!
This book is well written and is professionally presented. Not surprisingly, it is written for a novice. No background in chemistry is required but access to a lathe would be most helpful (almost necessary) to effectively produce these motors. There isn't much theory, as this is a hands-on book that represents over 10 years of experimentation by the author. I will walk you through the book, giving my opinions as I go. As you will see I only included a photo of the cover. A few photos of the insides, as well as two brief reviews, appear on Aerocon's site.
Chapter 1 -- Important Information and Safety Procedures
This chapter starts with a highlighted inset identifying chemicals which must be avoided and which will be dangerous if mixed with those described in the book. One thing I liked is his safety discussion is not limited to the first chapter. He repeats and emphasizes this information throughout. The chapter continues with a brief history of the rocket beginning in China in 1232 A.D. and through Oberth and Von Braun in the 1960's. It's always interesting to read a tad of history. He then discusses the efforts through recent years to squash amateur rocketry and discusses the safety history. In brief, the author indicates that the safety record of amateur rocket propellant is not as bad as is often portrayed. Much of its bad rap came back when chemicals were available at your corner drug store and the experimenters mixed them without any knowledge of their characteristics. This discussion was interesting and I'm sure would be controversial in some circles. The history material ends with a very brief discussion of Tripoli and the Reaction Research Society. The discussion then moves to a discussion of black powder: what it is, what it is not, and its sensitivity to impact, friction, and static. Much of this discussion is safety related and is very important. He covers storage, disposal, handling, and the safety record. He points out that while four of his five propellants are modified forms of black powder, they employ a burn rate suppressant and are slower burning. He warns not to use commercial black powder! The fifth propellant is sugar-based.
Chapter 2 -- Basic Concepts
This covers the basic operation of a rocket motor (i.e. Newton's 3rd Law), its components (paper tube, clay nozzle, etc), and terminology (thrust, burn time, etc). The material is tailored to the type motors in the book and makes ample use of diagrams and thrust curves. He talks about end and core burners, time delays, and staged rockets. Because large end burners are very difficult to make, all the motors in the book are core-burners. About the only math is showing how to size and position delay elements.
Chapter 3 -- Tools You Buy
As the name implies, there is a list of equipment you must buy to build these motors, starting with a good scale. Other items include a powder mill, vacuum pump, and other minor items. He provides recommendations on what to buy and potential sources.
Chapter 4 -- Tools You Make
It might be good to provide an overview of how these motors are made. A cardboard tube is inserted into a steel retainer to prevent it from expanding during packing. The tube sits on a nozzle mold, which has a core spindle in its center. A powdered clay mixture is tamped into the bottom of the casing to form the nozzle. The propellant is then tamped in, a small bit at a time. A delay charge, clay closure, and ejection charge follows. Finally, the metal tooling is withdrawn. So, the main tools you need are: nozzle molds, case retainers, core spindles, and tamps. The choice of materials is very important. For instance you need a non-sparking material, such as nylon, for the tamps. He shows how to make these, and even how to improvise if you don't have access to a lathe or a machinist buddy. In my opinion, the improvised tools will still be a lot of work. He closes with instructions on how to make a vacuum chamber and other processing tools.
Chapter 5 -- Tools Drawings
This chapter provides detailed fabrication drawings and instructions for 84 tools. I feel that a lathe should be part of the 'tools you buy' list.
Chapter 6 -- The Chemicals
The main chemicals include oxidizers, fuels, sulfur, and binders. He describes the various forms and grades of these ingredients, how to find them, and if necessary how to make some of them. Extracting these chemicals sounds like a nasty business, requiring ammonia-rated respirators and other safety gear. Luckily, they are easily available. Other chemicals discussed are burn rate suppressants, solvents, and ingredients to make nozzle clay.
Chapter 7 -- Chemicals Preparation
Now the book turns to the process of making motors. Chemical preparation included steps like drying, milling, precipitation as an alternative to milling. The actual formula and process for making the nozzle clay is also provided. This material is similar to what commercial manufacturers use, but has an extra ingredient to help it pack.
Chapter 8 -- Motor Casings
The cardboard cases used in these motors are thick, convolute wound cases like the Quest/Estes motors. Spiral wound tubes will not work. This chapter includes everything you would ever need to know about buying (what and from whom), or making (materials and techniques) motor tubes. The discussion on paper types and building techniques might even come in handy in other areas of rocketry.
Chapter 9 -- Working with Propellants
First thing out of the gate: chemical safety warnings! He then describes the process for mixing and milling a propellant. The final process is the addition of solvent. He shows how to calculate the optimal amount and how to test your mix. He walks through the procedure he followed in detail, to arrive at one of his propellants, which is useful if you want to make your own formulations. The last section is a description of his sugar propellant, which is also packed unlike the now more common candy/sugar motors.
Chapter 10 -- The Motor Building Process
This chapter provides an illustrated outline of how to build a motor and walks the reader through a step-by-step description of building a sample motor from start to finish. Because the propellant is impregnated with solvent, it must be allowed to dry. It can take up to 84 hours to air dry a big motor, which is why a vacuum pump was in the 'tools you buy' list. Using a vacuum can speed the process by a factor of 10 to 30 times. He continues by discussing how to test time delays and making booster motors. His approach is not merely to have the propellant exposed like in an Estes C6-0 for example. This is interesting and I am pondering if his techniques might be adapted for commercial motors. Although he has not perfected end-burning motors, there is a section that shows how to go about making one. This includes procedures for making reusable steel De Laval nozzles. Additional fabrication drawings are provided.
Chapters 11 through 15 -- Propellant and Motor Designs
Each of these five chapters covers one propellant formulation each. They include safety warnings (again), the detailed formula, and a discussion of their preparation. There is a lot of detail on modifying the base formula in your own experiments. Each propellant has approximately 10 proven motor designs. Documentation for each includes a technical drawing along with references to the required tool drawings, the physical specs, and the performance specs. In addition, there is a thrust curve for each and two sample simulations. One is for a minimum diameter rockets and one for what the author considers typical for the given motor. These chapters span 188 pages.
Chapter 16 -- The Original 1983 Motor Building Process
This chapter discusses refinements to the processes presented in his earlier book for those who have been using these techniques.
Chapter 17 -- Electric Matches and a Homemade Ignition System
Several types of scratch built igniters are presented. The most interesting is a bridge wire igniter that uses a match head. Finally, plans for a simple launch controller are included.
Chapter 18 -- Test Equipment
In this chapter, Sleeter shows how to build and use a mechanical motor test stand and an improvised strip chart recorder. These items would certainly have wider applicability than just the motors presented in the book. He shows how to use the graphs from this equipment to get a thrust curve and find total impulse, average impulse, maximum thrust, burn time, and ISP. Safety during the testing of new designs is always important and he provides guidelines.
Chapter 19 -- Flight
There is no great purpose to build amateur motors unless you fly them and this will be an area that a majority of the readers will already be knowledgeable of. Nevertheless, this chapter felt like an afterthought. He describes 'stick rockets' which resemble bottle rockets and barely touches on the stability of 'regular' rockets (CP, CG, etc.). This is the only chapter I found lacking. A reference to The Handbook of Model Rocketry would have been in order.
It's hard for me to give this book a rating since it depends on the readers interests. If you make packed-powder motors, or would like to, this book is a '5'. If you only want information you can directly apply to other areas, then it's probably a '1' or '2'. If you are merely inquisitive like myself, I'd have to say it's a '3 ½'. I would have liked to see a bit more theory and the huge quantity of drawings and even the motor designs will mostly be of interest to those who are serious about making these things. Taking these out, you still have about 300 pages of reading.
I enjoyed this book because I find the general topic interesting. The book is well written, easy to read, and I learned a couple of things that I may apply to my personal projects. Will I ever apply the bulk of the information contained in the book? Probably not. Then again, I've read books on artificial life and fractals and will most likely never apply those either.
Finally, this review is not an endorsement of this type of motor. I am not convinced that these motors can be made as safely as other types, and it is up to each individual to make his or her own decision on this. However, if you are interested in BP motors and want a kick start, then this book is a 'must have'.
3 out of 5