Water Rocket Project
Introduction
In this project,our main goal was to learn the properties of aerodynamics and energy transfer concerned in building and launching a rocket powered by water and pressurized carbon dioxide. To achieve this learning goal, my partner and I constructed 2 rockets; both were 2 chambered in order to attain the challenge option and hold more pressure and fuel, but mine was our main test subject while my partner's rocket was a backup. We originally planned to test how the rocket's bodyshape affected its flight by having one of us construct a rocket of two 2 liter plastic soda bottles and the other of SmartWater bottles, we never tested this variable even though we had this rocket, which made it on the testing platform only once due to the good performance of the other rocket and its own rather unimpressive display. The design of our primary test subject included a purely plastic body and the two bottles were connected with plastic epoxy to ensure a tight, light, and aerodynamic seal. The nose cone was already partially constructed by the pointed bottle neck of the soda bottle, and we felt that we didn't need to construct a new nose cone as it would be difficult to construct a perfectly even one which would actually increase our rocket's flight altitude.
We decided to test the shape of our fins as our independent variable in our testlaunches. These fins were placed at equal intervals around the rocket's base and they extended halfway up the rocket's body, with all the sets of fins constructed of the same material to ensure consistency and aerodynamics in our tests. We chose this variable because when we looked at the projects which years past had posted online, we encountered a lot of rockets which were unstable and we also realized that the fins of the rocket could aid this problem by altering stability and providing balance. Our fins, we decided, for our test designs to incorporate fins with a thin rim at its top in order to minimize air resistance but a large vertical area to hopefully stabilize the rocket by possessing strong vertical support. We went about these tests by using the 2 liter rocket for each test and new set of fins.
Our question concerning this test was "What shape of fin will stabilize our rocket most effectively?". This question then led us to hypothesize: "If fin shape affects a rocket's balance, then the ideal fin shape will be a hollow cylinder because this fin shape will most effectively provide the most stable support for the rocket's ideally straight path upward by providing vertical support through long vertical sides and little area for air resistance."
We decided to test the shape of our fins as our independent variable in our testlaunches. These fins were placed at equal intervals around the rocket's base and they extended halfway up the rocket's body, with all the sets of fins constructed of the same material to ensure consistency and aerodynamics in our tests. We chose this variable because when we looked at the projects which years past had posted online, we encountered a lot of rockets which were unstable and we also realized that the fins of the rocket could aid this problem by altering stability and providing balance. Our fins, we decided, for our test designs to incorporate fins with a thin rim at its top in order to minimize air resistance but a large vertical area to hopefully stabilize the rocket by possessing strong vertical support. We went about these tests by using the 2 liter rocket for each test and new set of fins.
Our question concerning this test was "What shape of fin will stabilize our rocket most effectively?". This question then led us to hypothesize: "If fin shape affects a rocket's balance, then the ideal fin shape will be a hollow cylinder because this fin shape will most effectively provide the most stable support for the rocket's ideally straight path upward by providing vertical support through long vertical sides and little area for air resistance."
(Above) The body of our rocket without fins
Procedure
We went about testing our variable by creating 3 sets of 4 test fins; each in the form of a different shape whose effectiveness on our rocket's balance we wanted to test. The 3 shapes were conical, 2 dimensional triangles, and a hollow cylindrical shape. These shapes each had differing properties of thickness and size of area which would attract air resistance. We taped each set of fins tightly on the rocket before each test flight, and on each flight we recorded the results of each set of fins. We flew each test set only once; we were rather pressed for time. Other than the shapes of our sets of fins, we kept all of our variables constant with each trial (these variables are listed below) but the variable which we were unfortunately not able to keep constant was the amount of pressure we pumped into the rocket for each test flight. On our first test flight, there were several leaks in the rocket and the P.S.I. was only able to reach 30. After some work on the rocket, we returned it to the launchpad only to find that there were more leaks and we therefore had to pump the pressure to about 20 P.S.I., while the next time we wanted to again return to 30 P.S.I. in order to correspond with our first test flight air pressure.
(Above) Our first set of 2D triangle fins
(Above) Our rocket on the launchpad outfitted with conical fins

(Above) Our rocket on the launchpad outfitted with hollow cylindrical fins

Data
We collected our data by diligently recording the angle of elevation and hang time of each test launch. The angle was always taken 10 m away from the launchpad using an astrolabe. When the rocket reached its highest point, the angle was recorded. The hang time was recorded using a cellphone timer from the time the rocket left the launchpad to the time it no longer ascended. During each launch, however, data may have been skewed by weather or human error. The results we collected were used in this trigonometric equation: tan(angle of elevation) x distance = height. I chose to graph our data in the bar graph which is featured below because our independent variable (x axis) was not a numerical value. A scatter plot would be used if this value was a number, but bar graphs are ideal when it is not but the dependent variable (y axis) is a numerical value.
Conclusion
Our results in relation to our hypothesis were that our original hypothesis (If fin shape affects a rocket's balance, then the ideal fin shape will be a hollow cylinder because this fin shape will most effectively provide the most stable support for the rocket's ideally straight path upward by providing vertical support through long vertical sides and little area for air resistance) was correct in estimating that a hollow cylindrical shape would best aid the rocket's stability and therefore elevation as opposed to a conical or 2 dimensional triangle shape. The cylindrical fins proved to go .57 meters higher than its closest competitor, the conical fins, and 1.63 meters higher then the 2 dimensional triangles. Some difficulties which we found in this experiment included leaks which our rocket often suffered from. These leaks, as stated before on this page, prohibited us from launching our rocket at a pressure higher than 30 P.S.I. in the tests and therefore increased the liability of errors in our tests which would skew data for our final launch. Our testing helped improve our final rocket design by enhancing our ideas of what fins helped to most balance a rocket's flight path. These tests advised us on how vertical stability and cross sectional area (area liable to cause drag) were immensely important in rocket flight and how the balance of a rocket was one of the main factors in the success of this pressurized system. Recommendations which I would have for future students include featuring tests which consist exactly of the planned P.S.I., water volume, and body and fin materials used in the proposed final launch. I find that because our group didn't correspond with our plans concerning these factors in our final launch for this negligence in our tests we suffered complications later in our exhibition. I would also advise any future students who undertake this project to ensure that there is a tight seal between their bottles which make up their rocket if they choose to make a 2+ chambered rocket. To do this, it is first necessary to pour boiling water over the section of one bottle which will go into the other bottle in order to shrink this bottle and decrease chances of bends or bubbles between the two bottles. The next step in order to achieve maximum assurance of the seal's security is to sand the sections on each bottle where the seal will be to increase friction between the two bodies and therefore a tighter hold.