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Selasa, 7 September 2010

The Effect of Fin Area and Amount vs. Altitude of Water Rocket

Special thanks to the author for this experiment.....


The purpose of this experiment was to determine if the area of the fins and the number of fins would affect a rocket’s performance or altitude, which the rocket reached. I became interested in this idea while pondering if number of fins would affect the altitude of rockets that I launch, I also enjoy rocketry and thought it would be fun to put my question to the test. The information gained from this experiment can lead scientists and rocketers alike to make aerodynamic fins and to increase the performance of rockets without adding more fuel or using a larger engine.


My first hypothesis was that the rocket that contains 3 fins with a small surface area would reach the highest altitude. I based my hypothesis on information and data gathered from the Handbook of Model Rocketry and World Book Encyclopedia that summarizes that drag should be reduced by surface area.

My second hypothesis was that the rocket situated with 5 large fins would have the lowest altitude. I based my hypothesis on information and data gathered from the Handbook of Model Rocketry and World Book Encyclopedia that summarizes that drag should be reduced by surface area.


The constants in this study were:

* The type of rocket used

* The size of the pop bottle

* The shape of the pop bottle

* The volume of the pop bottle

* The amount of water in the pop bottle

* The pressure inside the pop bottle

* The shape of the rocket

* The recovery device

* The shape of the rocket’s nose cone

* The height of the rocket

* The width of the rocket

* The weight of the rocket (may change a little due to number and size of fins)

* The same launcher

* The same launch pad

* The same launch device

* The same weather conditions

* The shape of the fins so the fins are proportional

* The airfoil of the fins (Square shaped airfoil)

The manipulated variable was the number of fins (3, 4, and 5) and the area of the fins.

The responding variable was the altitude of which the rocket reached at apogee. To measure the responding variable, Estes, Alti-trak was used to measure the altitude of the rocket at apogee in meters.

Below is a table of the different treatments.

3, small fins 4, small fins 5, small fins

3, medium fins 4, medium fins 5, medium fins

3, large fins 4, large fins 5, large fins



1 Pitsco pop bottle Water Rocket

N/A Water

1 Pitsco launcher

1 Sheet of 1/16" by 3" by 36" Balsa wood

1 Sheet of 1/16" by 6" by 36" Balsa wood

1 Estes Altitrak (a rocket altitude measuring device)

1 X-Acto Knife

1 Cool Melt Glue Gun

1 Bottle of White or yellow Glue

1 Tube of plastic cement

N/A Sand paper

1 Pitsco Pressure pump


1. The first step is to construct the rocket you are using, but don’t add any fins yet. Mark on the rocket where the 3, 4, and 5 different fins will be (use one mark for a central point for the other marks). Then I labeled them as follows:

The 3 fins marks are A, B, and C these fins are spaced 120 degrees apart

The 4 fins marks are C1, C2, C3, and C4 these fins are spaced 90 degrees apart

The 5 fins marks are 1, 2, 3, 4, and 5 and these fins are spaced 72 degrees apart.

Construction Tip: for porous materials like paper, cardboard, and balsa wood put glue on the material then let it sit for a while to let the glue sink into the pours. Then put on more glue and fit the pieces together.

2. The next step is to make a template of the different fins you are using. You can make the templates by cutting out cardboard that is the same sizes as the fins.

3. The next step is to trace an outline of the fins on the sheet balsa wood with the templates. The fins can be any shape you want, but make sure all fins are the same size and proportional. I used a trapezoid shaped fin.

4. Then cut out the fins with an X-Acto Knife.

5. Next take the fins of the same size and hold them even in your hand. Sand all edges (not the sides) so the rough edge is removed and all of the fins are the same precise size. Caution: Don’t sand the fins too much because you will change their size the more you sand them.

6. Next step is to glue on 5, large fins to the rocket with the cool melt glue gun. Construction Tip: Use the glue sparingly because you want to easily remove the fins from the rocket to put on new fins.

7. Now launch the rocket 3 times and record the data. Note: Follow instructions provided with the kit on how to launch the rocket. Note: Use the exact same amount of water for each launch.

8. Cut off the fins of the rocket with the X-Acto Knife and sand the root where the fin was glued so that the body tube was like nothing was ever glued to it.

9. Repeat steps 7-9 for all of the fins and make sure the weather conditions are approximately the same for all launches.


The original purpose of this experiment was to determine if the difference in the area and number of fins would change the altitude of the rocket. The results of the experiment were the rocket with 4 medium fins had the highest average altitude and the rocket with 5 large fins had the lowest average altitude.


My first hypothesis was that the rocket that contains 3 fins with a small surface area would reach the highest altitude. The results indicate that this hypothesis should be rejected. My second hypothesis was that the rocket situated with 5 large fins would have the lowest altitude. The results indicate that this hypothesis should be accepted. Because of the results of this experiment, I wonder if the reason the rockets that had 3 fins and the rocket that had 4 small fins didn’t go higher than the rocket with 4 medium fins is because the area didn’t matter from that point on and the stability of them wasn’t as good as the rocket with 4 medium fins.

If I were to conduct this project again I would have more trials for more accurate data, I would try to find a better and more accurate way to measure the altitude, and then if I find a better way to find the altitude I could use solid fuel rockets.

Research Report


A rocket is an engine that is used to propel a vehicle at an extremely fast speed. A rocket engine the same size as a medium sized automobile engine will produce almost three thousand times the power. Rockets can range from just a couple feet tall (61 centimeters) to almost 380 feet (115 meters). Rockets are called chemical rockets if they burn fuel to produce their power. There are some experiments with rockets that use heat to make their fuel expand causing thrust. Although chemical rockets do burn fuel rapidly they produce an extremely large amount of thrust. The Saturn 5 rocket engine used 1,018,181.8 gallons (3,853,100 liters) of fuel to power itself for just five minutes. The temperature in some rockets can reach 6,000 degrees Fahrenheit (3316 degrees Celsius) or more!

The main purposes for which people use rockets today are research, space travel, and military strikes with warheads. Ancient civilizations used rockets with explosives attached to blow up enemy encampments. Rockets lately have been used for researching space as well as to transport warheads on military missiles. The use of rockets for exploration and research has been during only the past 50 years and has opened a new window for exploring space. The satellites that rockets carry into space can take pictures, record data of the universe, and track weather.

Rockets work on one of Newton’s laws, "For every action there is an equal and opposite reaction". In this case rockets burn a special fuel in a combustion chamber and create pressure that has only one direction to go. This direction of the pressure is out of the nozzle on the bottom of the rocket, the great pressure of the rapidly expanding gas causes an action of pressure on the ground. The opposite action is the rocket moving in the opposite direction. Some experiments have been tried with other rockets powered by nuclear power, but researchers have found that this doesn’t provide as much energy. Some small rockets used for recreation also use-pressurized air and water in a sealed compartment.

Model Rocket

Model rockets are the counterparts of full size rockets. These small rockets are mainly used for research and recreation. They are a lot cheaper than the rockets at Cape Canaveral and they only weigh 31/2 pounds (1.5 kilograms) or less. These rockets are only about 8-24inches (20-40 centimeters). All model rocket engines use solid fuel (or water and air pressure on water rockets.) Model rockets can reach 2000 feet (610 meters) in altitude in a few seconds because the rockets can travel at speeds of 300 mph (480 kph).


Aerodynamics is the study of how forces act on an object as it moves trough a fluid. Aerodynamic forces act on airplanes, sailboats, motorboats, submarines, cars, rockets, busses, and anything that moves through a liquid or gas. Scientists and engineers study these aerodynamic forces for a way to prevent them from hindering the performance (affecting the best operation) of the machine (like oil lubricates gears so there is less friction). These aerodynamic forces affect the movement of the object in many ways and how fast it can travel. The Wright Brothers had to understand aerodynamics before they could succeed in building the first aircraft. Today aircraft manufacturers use the same principles to make their aircraft fly the fastest with the cheapest engine. These principles also affect engineers and architects and the structures that they design with the way the air flows around a building or bridge.

Drag is the main force that affects moving objects. This force resists movement of objects in motion. The shape of the object influences the amount of drag. Although drag cannot be eliminated it can be reduced. Objects shaped to produce the littlest amount of drag possible are called a streamlined or aerodynamically clean object. Aircraft designers design planes that produce the least amount of drag possible because planes with low drag need less engine power to fly at the same speed. Automobiles, trucks, planes, trains, rockets, boats and all other vehicles in motion encounter or are affected by drag. There are two types of drag that exist that affect all moving objects, friction drag and form drag. There is a third type of drag called induced drag, but it only affects objects that create lift. There is still another drag that affects aircraft and other objects going faster than the speed of sound.

Friction drag occurs next to the surface of an object and is produced in a thin layer of air called the boundary layer. The friction results when one layer of fluid slides over another layer of fluid. Molecules of air in the boundary layer either have an ordinary path parallel to the surface or an irregular path. Engineers call an ordinary path laminar flow and an irregular path turbulent flow. A turbulent flow increases friction drag. The boundary layer usually has a laminar flow, but the airflow can become turbulent at some point as the air moves along the abject. Aircraft designers try to delay the change of laminar flow to turbulent flow for as long as possible to reduce the friction drag.

Form drag occurs when the airflow past an object breaks away from the object. This type of drag produces swirling eddies that takes energy from an object that slows it down. Form drag occurs with non-streamlined objects like a large semi truck at a high speed. The driver may experience a rough ride due to the eddies from the non-streamlined truck. To stop this occurring to aircraft, which need to fly fast, airline companies put vortex generators on an airplane’s wing, which keep the boundary layer from breaking away from the wing. They are small devices that are shaped like airfoils that stick up along the top of the main wing in rows. The vortex generators produce small disturbances in the boundary layer that keeps the air from breaking away.


Cliff, Eugene M. "Rocket," World Book Encyclopedia. 1999. Volume R, #16. Pg. 384-391

Estes Industries "Beginners Guide to Model Rocketry"

Heimber, Charles H. and Price, Jack. Focus on Physical Science. Merrill Publishing Company 1987. Pg. 12-27

Miller, Patrick J. "Rocket, Model," World Book Encyclopedia. 1999. Volume R, #16. Pg. 391-393

Platkin, Allen. "Aerodynamics," World Book Encyclopedia. 1999. Volume A, #1. Pg. 85-88

Stine, G. Harry. Handbook of Model Rocketry. John Wiley & Sons Inc. 1994. Pg. 2-9



This science project couldn’t have been possible without the help and assistance of several people. I would like to thank and acknowledge each of them for their help.

My father for devoting lots of time and effort even though I procrastinated he still helped me to the finish.

My mother for helping me to right my journal and give me support.

Mr. Kenneth Newkirk for not only helping me, but the rest of the class in completing their science projects, even when he had more important things to do.


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