Technical Report for Water Bottle Rocket

EDITOR'S NOTE: For a change, the comments are being left ON. I welcome and would appreciate your thoughts -- this technical report has not been scored yet, so it will be interesting for your feedback to compare & contrast with the judges. Just keep it (pardon the pun) constructive! :D

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TEAM SILVER Technical Report on Water Bottle Rocket excerpt

Introduction
In the 2009/2010 SECME competition, our mission was to construct an efficient water bottle rocket that could remain airborne for the longest period of hang time. In order to achieve this goal, we had to not only go through the process of trial and error, but also, apply our knowledge of physics. We needed to have a mastery of areas such as aerodynamics, Newton’s Laws of Motion, gravity, acceleration, air resistance, momentum, inertia and the ability to make precise and accurate calculations and plan each step accordingly. In the process of building these rockets, we enhanced our life skills, such as responsibility, hard work, teamwork, and of course, ingenuity.

Design Background
In the process of building the water bottle rockets, we had to keep in mind a variety of topics and apply our knowledge of physics in order to be successful in doing so. The competition requires the boundaries of 76 cm for a height value and a 16.5 cm for a radius. Before beginning the complex process of designing an efficient rocket, we looked at previous models for guidance and ideas. We also received instructions from our SECME coordinator. After learning and witnessing what design performs best, we began our construction.

To start with, we used a basic design of two 2-liter bottles. We found that some of the most simplistic designs easily had a longer lasting trajectory, ranging from seven to twelve seconds in air, from some of the more complex designs that only had a maximum of six seconds. To begin with, we cut off ¼ of the total height of one of the 2-liter bottles, or 14 centimeters. We then filled the cut bottle with newspaper. This added weight will serve the purposing of balancing the rocket once in midair and keeping it steady to prevent too much torque, or spin, from occurring. The goal of rocket designing is to balance the weight of the bottle, so that the bottle can reach its maximum hang time. If the bottle endures too much spin, it will not be aerodynamic and will not fly efficiently. Once adding the extra mass of the newspaper, we proceeded to tape the remaining ¾ of the bottle to the whole one. The whole piece serves as the water chamber, where the water will be stored and then exit once the rocket engages flight. The ¾ piece serves, as stated before, as more mass to balance the rocket and provide a steady flight. The whole bottle’s opening is faced downward when gluing on, as the ¾ piece is faced upward, producing two openings in the structure. After developing the basics of the rocket, we continued to make the rocket more aerodynamic to enhance our rocket’s performance.

Our next task would be in designing the nose cone of the rocket. To do so, we used a template designed by our SECME coordinator. The nose cone should be designed out of a thick type of paper; we used manila folders to construct this part. We used an entire sheet of a folder, making the dimensions of the cone to be 20.3 centimeters by 30.5 centimeters, minus the area cut out to make the cone’s shape. After cutting out the cone, we rolled it up and placed it on the top of the ¾-cut part of the bottle, our front. After fitting it, we then taped it on. To finish our design of the rocket’s nose, we added on a paper towel roll with a golf ball placed at the top of it. This is used to serve the same purpose as the newspaper did; it isn’t necessary, but it does enhance the performance because it adds more mass to the structure of the bottle, which balances it. We used a paper towel roll with a length of 22.6 centimeters.

Once finishing the upper parts of the bottle, the only part that remained was to design the fins. The fin design is very significant in the rocket’s flight. When the rocket is descending after reaching its maximum height, it begins to accelerate as it falls back towards Earth due to gravitational force. During the rockets descent, its center of mass begins to move backward due to its loss of water, which presented most of the mass on the journey up. In order to balance the rocket, the fins are placed near the bottom of the rocket. Also, if the fins are designed properly and the conditions are right, gliding may occur rather than a simple vertical, up and down motion of the rocket. Gliding increases the hang time significantly. We found that like the design of our rocket, simplicity works best. We used a triangle-like design for the fins. It measured 5cm on one of its sides, 10.5 cm on the other, and 23cm for its hypotenuse. We then spaced a total of four fins equally over a circumference of 30.48 centimeters. We glued them on and made sure that it was secured to ensure that it wouldn’t fall off the rocket when it’s traveling at a maximum velocity of after designing the fins, nose cone, and structure, our rocket was complete.