The Aerodynamic Drag of Several Basic Vehicle Shapes

photo of Brennan at Mid-Columbia Science Fair

Researched by Brennan D.
2005-06





PURPOSE

The purpose of this experiment was to determine the aerodynamic drag of several basic vehicle shapes.

I became interested in this idea when I was riding in our convertible and I felt the air hit me in the back of the head instead of the front of my head. I wondered why the air was coming from behind me.

The information gained from this experiment could show designers which shape would be the most aerodynamic. Society would want to build more aerodynamic cars and planes because they are more efficient and would save gas and money.


HYPOTHESIS

My first hypothesis was that the hemispherical nose would be the most aerodynamic, having the least amount of drag.

My second hypothesis was that the conical tail would be the most aerodynamic, having the least amount of drag.

I based my hypothesis on a science project done in 2003 by Landin Arnett, ”The Effect of Different Fuselage Shapes on Drag.” He said, “The hemispherical nose and the conical tail did the best.”


EXPERIMENT DESIGN

The constants in this study were:
•    The speed of wind
•    The size of wind tunnel
•    The type of wind tunnel
•    The spring scale
•    The type of wheels
•    The size of wheels
•    The main body of the car
•    The source of wind
•    The mass of the car

The manipulated variables were the shape of the nose and tail.

The responding variable was the force of drag. 

To measure the responding variable, I used a spring scale to see how much drag force there was in newtons.  


MATERIALS


QUANTITY ITEM DESCRIPTION
2
Hemispherical shapes of Styrofoam

Conical shapes of Styrofoam
2
Square shapes of Styrofoam
1 Air tunnel
1 Spring scale
1
Roller
1 Car body
2
Leaf blowers
3cm string
4”
Wide tube



PROCEDURES

1.    Get all of the supplies listed in “materials”
2.    Construct the car and the interchangeable nose and tail pieces
1.    Use nose and tail pieces that are two conical shapes, two hemispherical shapes, and two flat shapes that are cut out of Styrofoam
2.    Each of the shapes must be four inches wide which is the width of the tube
3.  Make sure that the car rolls easily
4.  Build the car low to the ground so that you only see the tires
5.  Don’t let the pipe touch the tires on the roller
3.    Setup the wind tunnel for use
1.    Attach the spring scale to the wind so it wont slide around during the experiment
2.    Tape the spring scale inside the wind tunnel
3.    Put the two leaf blowers together so they can be used
4.    Install the hemispherical shape of Styrofoam for the nose. Then install a conical shape for the tail of the car (the nose and tail do NOT have to be the same but eventually will have to)
5.    Attach the shapes chosen to the car’s nose and tail and place the shapes inside the tunnel
6. Tie the car to the spring scale with the 3cm string
7. Turn the two leaf blowers on while they are in the wind tunnel
8.  Watch the spring scale closely for force changes
1. This will give you the amount of drag the car produces
9.  Record your observations of the spring scale
10. Watch the car closely for its reaction to the wind
11.  Record your observations of the car’s behavior
12. Do each experiment for each set of shapes 5 times
13. Choose another set of Styrofoam shapes for the car’s nose and tail
14. Repeat steps 4-14 until you run out of shape combinations to use for the nose and tail of the car you made
15. Record your results of each of the experiments
1.    Average out how well each nose did with each of the three tails
2.    Average out how well each tail did with each nose
3.    That will tell you which pair of shapes did the best
4.    It will also tell you which pair of shapes did the worst


RESULTS

The original purpose of this experiment was to determine the aerodynamic drag of several basic vehicle shapes.

The results of the experiment were that the conical nose and the conical tail section, the conical nose and the hemispherical tail, and the conical nose and flat tail section all averaged 0.00 newtons of drag. Thus, the average amount of drag of the conical tail was 0.00 newtons.

The hemispherical nose along with the conical tail section averaged 0.01 newtons of drag, while the hemispherical nose along with the hemispherical tail section averaged 0.05 newtons of drag, and the hemispherical nose and the flat tail section averaged 0.00 newtons of drag. Thus the average amount of drag in newtons for the hemispherical nose was 0.02.

The flat nose along with the conical tail section averaged 0.33newtons of drag, and the flat nose and the hemispherical tail section averaged 0.16 newtons of drag. The flat nose along with the flat tail section averaged 0.29 newtons of drag. Thus, the average amount of drag in newtons of the flat nose was 0.26.   

See the table and graph below.


CONCLUSION

My original hypothesis was that the hemispherical nose would be the most aerodynamic.

My second hypothesis was that the conical tail would be the most aerodynamic.


The results indicate that this hypothesis should be rejected, because the conical nose and the hemisperical  tail did the  best, instead of the hemisperical nose and the conical tail.


After thinking about the results of this experiment, I wonder if I used the same shapes in hydrodynamics if the results would be the same. I also wonder if  I used the same shapes only as sails if I would get the same results.


If I were to conduct this project again I would use a lighter pipe, different shapes and smoother shapes, a different material for the shapes, and I would do more trials.



Research Report

Introduction
Humans use aerodynamics in many every day things. For example, aerodynamics are used to get better gas mileage in our cars. Aerodynamics are used to make planes fly fast through the air. Aerodynamics are what gets us from one place to another so quickly.

Lift
Lift is what makes an airplane come off of the ground and fly. The lift amount must be greater than gravity so the airplane lifts off the ground and remains in the air. Lift is undesirable in cars. It can lift the car off the ground causing the car to get in a crash. That is why engineers design cars to stay on the ground. Cars today are much safer than previous ones were. Designers understand aerodynamics better and try to make cars more efficient for safety.

Speed
Speed has a lot to do with how much lift there is. The faster you go, the more lift there is. The slower you go, the less lift there is. There is such a thing as too much lift. If you go to fast and get to much lift in an airplane, you can go straight up and stall, which will cause you to fall back to the earth. Speed also increases drag.

Air Density
The amount of lift depends on how dense the air is. The more dense the air, the more lift you will get. The less dense the air, the less lift you will get. In other words, the lift amount increases with density.

Angle of Attack
The angle of attack is the angle at which air goes around an object such as an airplane wing. The pilot can increase the angle of attack by pulling back on the wheel, which will increase the lift amount on the airplane. The pilot can also decrease the angle of attack by pushing in on the wheel, which will decrease the amount of lift on the airplane. If the angle of attack increases too much the airplane will stall and return to the earth.
 
Drag
Drag is caused by air friction and is undesirable. No matter what you are driving you most likely want to minimize the effect of drag on your vehicle. Drag will slow you down so you cannot go so fast. Racecars have very little drag affecting them so they can go faster.

Supersonic
To go supersonic speeds, you have to go faster than the speed of sound. The speed of sound is a variable. Being a variable it is written as mach 1. At sea level the speed of sound is 760 mph. If an airplane is not made out of the right material it can be ripped to shreds when going at supersonic speeds.

History
Cars are just modern versions of horse drawn carriages. The first car race was at the speed of 7 mph. Cars were not very safe in the early days. Now, although cars are not 100% crash free, they are still safer than ever before.  Cars today are also much faster. So cars have gotten better and better as time has moved on.

How aerodynamics work
Aerodynamics work by wind flowing around an object and creating a force that creates a suction that keeps the car down. With this force the car will not come off the ground and get in a crash. You could just imagine what would happen if we did not have this force in cars. Aerodynamics are definitely something that we need to know about.

How humans use aerodynamics
Humans use aerodynamics for a number of different things. We use it to design efficient cars. It is used to model efficient buildings as well. It is even used in airplanes to make sure that they will fly well and the lift amount is greater than the amount of gravity pulling the airplane down to the earth again.

Summary
Aerodynamics are used in many every day things. Aerodynamics have effect on your car’s gas mileage as well as on airplanes gas mileage. Aerodynamics make airplanes fly faster and get you to your destination in a quicker amount of time. Drag is undesirable and designers try to make vehicles more efficient and safer.
 

Bibliography

“Aerodynamics and cars,” Encarta researcher, 2004

"Aerodynamics,” World Book Encyclopedia, 2004

“Aerodynamics and trucks” Encarta researcher, 2001

“Aerodynamics in cars” World Book Online 11-23-05

Arnett, Landin “The Effect of Different Fuselage Shapes on Drag” 2005 
http://www.selah.k12.wa.us/SOAR/SciProj2003/LandinA.html

Steve Parker Flight New York: Dorling Kindersley, 1990 1-14
 


ACKNOWLEDGEMENTS

I would like to thank the following people for helping make my project possible:
•    My parents for always being there for me, never giving up on me, and always encouraging me. They also printed my pictures and I appreciate that.
•    Mr. Newkirk for always trying to help my project to be better and more interesting.
•    Mrs. Viernes for helping me to keep all my work together and to work harder on my project so that I could get my project done.
•    My sister for helping me to do my experiment and helping set up the wind tunnel. Also for helping decorate my Styrofoam shapes.


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