4 Model rocketry is a sport that involves designing, constructing and
5 launching self-made rockets. Model rockets vary greatly in size,
6 shape, weight and construction from detailed scale models of
7 professional rockets to lightweight and highly finished competition
8 models. The sport is relatively popular and is often cited as a
9 source of inspiration for children to become engineers and
12 The hobby started as amateur rocketry in the 1950's when hobbyists
13 wanted to experiment their skill with building rockets. Designing,
14 building and firing self-made {\it motors} was, however, extremely dangerous,
15 and the American Rocket Society (now the American Institute of
16 Aeronautics and Astronautics, AIAA) has estimated that about one in seven
17 amateur rocketeers during the time were injured in their hobby. This
18 changed in 1958 when the first commercially-built model rocket
19 motors became available. Having industrially-made, reasonably-priced
20 and safe motors available removed the most dangerous aspect of amateur
21 rocketry. This along with strict guidelines to the design and
22 launching of model rockets formed the foundation for a safe and
23 widespread hobby.~\cite[pp.~1--3]{stine}
25 Since then model rocketry has spread around the globe and among all
26 age groups. Thousands of rockets ranging from 10~cm high miniatures
27 to large models reaching altitudes in excess of 10~km are launched
28 annually. Model rocket motors with thrusts from a few Newtons up to
29 several kilo-Newtons are readily available. Since its forming in
30 1957, over 90\s000 people have joined the National Association of
31 Rocketry (NAR) in the U.S. alone.
32 % Model rocketry is used as an
33 %educational device in numerous of schools and by many youth
36 In designing rockets, the {\it stability} of a rocket is of central
37 priority. A stable rocket corrects its course if some outside
38 force disturbs it slightly. A disturbance of an unstable rocket
39 instead increases until the rocket starts spinning in the
40 air erratically. As shall be discussed in
41 Section~\ref{sec-stability}, a rocket is deemed
42 {\it statically stable} if its center of pressure (CP) is aft of its
43 center of gravity (CG)\footnote{An alternative term would be
44 {\it center of mass}, but in the context of model rocketry, we are
45 interested in the effect of gravity on the rocket. Thus, the term
46 center of gravity is widely used in model rocketry texts, and this
47 convention will be followed in this thesis.}.
48 The center of gravity of a rocket can be easily calculated in advance
49 or determined experimentally. The center of pressure, on the other
50 hand, has been quite hard to determine either analytically or
51 experimentally. In 1966 James and Judith Barrowman developed an
52 analytical method for determining the CP of a slender-bodied rocket at
53 subsonic speeds and presented their results as a research and
54 development project at the 8th National Association of Rocketry Annual
55 Meeting (NARAM-8)~\cite{barrowman-rd}, and later as a part of James
56 Barrowman's Master's thesis~\cite{barrowman-thesis}. This method has
57 become known as the {\it Barrowman method} of determining the CP of a
58 rocket within the model rocketry community, and has a major role in
59 determining the aerodynamic characteristics of model rockets.
61 Another important aerodynamic quantity of interest is the
62 {\it aerodynamic drag} of a rocket. Drag is caused by the flow of air
63 around the rocket and it can easily reduce the maximum altitude of a
64 rocket by 50--80\% of the otherwise theoretical maximum. Estimating
65 the drag of a model rocket is a rather complex task, and the effects
66 of different design choices are not always very evident to a
69 Knowing the fundamental aerodynamic properties of a rocket allows one
70 to simulate its free flight. This involves numerically integrating
71 the flight forces and determining the velocity, rotation and position
72 of the rocket as a function of time. This is best performed by
73 software designed for the purpose of model rocket design.
75 RockSim~\cite{rocksim} is one such piece of software. It is a
76 commercial, proprietary program that allows one to define the geometry
77 and configuration of a model rocket, estimate its aerodynamic
78 properties and simulate a launch with different rocket motors. It has
79 become the {\it de facto} standard software for model rocket
80 performance estimation. However, as a proprietary program, it is
81 essentially a ``black-box'' solution. Someone wishing to study or
82 validate the methods will not be able to do so. Similarly extending
83 or customizing the functionality or refining the calculations methods
84 to fit ones needs is impossible. The software is also only available
85 on select operating systems. Finally, the cost of the software may be
86 prohibitive especially for younger hobbyists, voluntary organizations,
89 Open Source software, on the other hand, has become an increasingly
90 competitive alternative to proprietary software. Open Source allows
91 free access to the source code of the programs and encourages
92 users with the know-how to enhance the software and share their
93 changes~\cite{oss-principles}. Success stories such as the Linux
94 operating system, the OpenOffice.org office suite, the Firefox web
95 browser and countless others have shown that Open Source software can
96 often achieve and even exceed the quality of expensive proprietary
100 \section{Objectives of the thesis}
102 The objectives of this thesis work are to:
105 \item Develop and document relatively easy, yet reasonably accurate
106 methods for the calculation of the fundamental aerodynamic
107 properties of model rockets and their numerical simulation;
109 \item Test the methods developed and compare the results with other
110 estimates and actual experimental data; and
112 \item Implement a cross-platform, Open Source model rocket design and
113 simulation software that uses the aforementioned methods, is at the
114 same time easy to use and yet versatile, and which is easily
115 extensible and customizable for user requirements, new types of rocket
116 components and new estimation methods.
119 The methods presented will largely follow the methods developed by
120 Barrowman~\cite{barrowman-rd,barrowman-thesis}, since these are
121 already familiar to the rocketry community. Several extensions to the
122 methods will be added to allow for more accurate calculation at larger
123 angles of attack and for fin shapes not accounted for in the original
124 paper. The emphasis will be on subsonic flight, but extensions will
125 be made for reasonable estimation at transonic and low supersonic
128 The software developed as part of the thesis is the OpenRocket
129 project~\cite{openrocket}. It is an Open Source rocket development
130 and simulation environment written totally in Java. The program
131 structure has been designed to make full use of object oriented
132 programming, allowing one to easily extend its features. The software
133 also includes a framework for creating user-made
134 {\it listener components} (discussed in Section~\ref{sec-listeners})
135 that can listen to and interact with the simulation while it is
136 running. This allows a powerful and easy way of interacting with the
137 simulation and allows simulating for example guidance systems.
139 One possible future enhancement that has also specifically been
140 considered throughout the development is calculating the aerodynamic
141 properties using computational fluid dynamics (CFD). CFD calculates
142 the exact airflow in a discretized mesh around the rocket. This would
143 allow for even more accurate calculation of the aerodynamic forces for
144 odd-shaped rockets, for which the methods explained herein do not
147 It is anticipated that the software will allow more hobbyists the
148 possibility of simulating their rocket designs prior to building them
149 and experimenting with different configuration, thus giving them a
150 deeper understanding of the aerodynamics of rocket flight. It will
151 also provide a more versatile educational tool since the simulation
152 methods are open and everyone will be able to ``look under the hood''
153 and see how the software performs the calculations.
155 In Chapter~\ref{chap-basics} a brief overview of model rocketry and
156 its different aspects will be given. Then in
157 Chapter~\ref{chap-aerodynamics} methods for calculating the
158 aerodynamic properties of a general model rocket will be presented.
159 In Chapter~\ref{chap-simulation} the aspects of simulating a rocket's
160 flight are considered. Chapter~\ref{chap-software} then explains how
161 the aerodynamic calculations and simulation are implemented in the
162 OpenRocket software and presents some of its features. In
163 Chapter~\ref{chap-experimental} the results of the software simulation
164 are compared with the performance of constructed and launched rockets.
165 Chapter~\ref{chap-conclusion} then presents a summary of the
166 achievements and identifies areas of further work.
projects / debian / openrocket / blob