Introduction to Rocket Design

1. Introduction At the time of this writing, I have designed, built, and flown my own amateur experimental rockets over a period of nearly 50 years. The design and construction of my rockets evolved greatly over the years.The main factors that influenced the evolution of my rockets was knowledge and experience gained over time. Knowledge refers to those aspects of rocketry that comes with educating yourself about the subject, such as the physics of rocket flight, aerodynamic effects such as drag and how if impedes the motion of a rocket, rocket motor performance and how this relates to the flight, ensuring stability, improving reliability, etc. Experience relates to putting this knowledge into effect and continually striving for improvement. This is perhaps the most challenging aspect of rocketry, applying all these ideas into actual working hardware that behaves as you hope and expect. The problem here is that knowledge is never complete or all-encompassing. We need to continually learn and to 'fill in the gaps' in our knowledge and this often means improvising, and this is where creativity (and, yes, intuition) comes into play. With regard to experience, this often means learning what works and what does not work. I also learned to never give up. Experiences, both positive and negative, are part of the design equation. It's easy to move forward with this hobby when things go right. Sadly, that is often not the case, as with so many things in life. Early on in my quest, many of my rockets returned to earth as "lawn darts", and in the process, got largely destroyed (or lost), when the recovery system failed. Occasionally, a rocket turned out to be unstable, flipping around in the air after leaving the launch pad. Under such circumstances, it becomes easy to quit. Fortunately, I tend to be a rather stubborn person and my passion for rocketry provided needed impetus to keep going. Nowadays, my rockets have had a impressive recovery rate. My last "lawn dart" recovery was over 15 years ago (representing something like 67 flights). There are many reasons for this improved record of success. As mentioned, learning combined with experience were two important factors. Curiously, two other key factors were rather serendipitous: the advent of the internet and the revolution in microelectronics. When I first turned my attention to rocketry, sources of information relating to the subject of rocketry were very sparse. The local libary (and later, the engineering library) had some books that dealt with the principles of rocketry, but there was next to nothing relating to amateur rocketry. I was pretty much on my own and was forced to improvise and to be creative, which was too often dead-ended when things didn't work out as expected. The wealth of information that became available via the internet, combined with sharing knowledge and experiences through e-mail, has transformed learning about all aspects of rocketry. With regard to electronics, which is one of the key elements for reliable rocket recovery, my brother and I struggled to design and build our own parachute recovery devices. Today's tiny and affordable rocket flight computers and GPS recovery systems are a godsend to the experimental rocketeer. Safe recovery of our rockets become a less daunting challenge. As I began writing these pages on experimental rocket design, it became apparent that "experimental rocket" is a very broad term, and as such, the design philosophy will not be the same for all experimental rockets. An experimental rocket can range from a small and simple rocket that can be considered one step beyond model rocketry. At the other end of the spectrum, an experimental rocket can be a highly advanced design that can reach the boundary of Space. I felt that it would be useful, in terms of design approach, to break down the range of experimental rockets into four classes. Rather than categorize experimental rockets in terms of motor power, such as is done with commercial rocketry (model rocketry, mid-power, hi-power, etc), a more useful approach would be to classify an experimental rocket on the basis of its expected maximum velocity. The reasoning behind this approach is that the maximum velocity a rocket is designed to achieve is a strong driver in its design. As a rocket vehicle gains velocity, aerodynamic effects become much more significant both in terms of drag and structural loading, aerodyanmic heating, stability, etc. As such, greater care is required when designing such rockets. The four classes of experimental rockets that I will refer to in these web pages is given in Table 1. Table 1: Experimental rocket classification All of the rockets that I have designed, built and flown belong to either LoPER class or MiPER class. My involvement in the Sugar Shot to Space program (2004-2011)provided me with a wealth of experience in helping to design rockets in the HiPER class and ViPER class. In this series of web pages, my goal is to "distill and compile" my knowledge gained over the years, fortified by my rocketry exeriences, into a guide for likewise passionate individuals and teams who wish to design and build their own experimental rockets. I should clarify that by "rockets" I am refering to the flight vehicle powered by a rocket motor. The design of the rocket motor will not be discussed here, other than in general terms (such as total impulse and thrust) required as input for the rocket's design. For convenience, throughout this series of web pages, the term EX rocketry will be used in place of the rather cumbersome Amateur Experimental Rocketry. Before delving into the details of EX rocket design, I would like to present a few general tips that have served me well. In fact, I would consider these more than merely tips, rather, things that are necessary to counter the rather capricious nature of experimental rocketry. Keep notes of everything, being as concise as possible. I have kept notebooks since "day one" and am currently on my 30th notebook. Design details are readily forgotten and if something works well, it is of great value to be able to look back on your notes on how something was made or configured (including calculations), what materials you used, weight and dimensions, etc. Such notes can be of even greater value if something goes wrong. You want to fix what went wrong, not repeat it. It is great to have the knowledge and resources to confidently design something. But a design that cannot be built by the designer is of limited value. As such, the first step is an assessment of one's capacity to design and build an amateur experimental rocket. Such factors are: •Tools and ability to use them. Tools can refer to either hardware for building a rocket, or software as a design aid. •Availability of materials. When designing a rocket, one needs to know what materials are available, either on-hand or obtainable. This greatly influences the rocket design. •Budget and cost for materials and other resources. •Time. Clearly, the amount of time one has available to invest in EX rocketry plays a role in design. Learn the basics of rockety first. I found that model rocketry served me very well in this regard. As a first EX design, a simple LoPer class rocket is recommended. Next--Goals