What Shape Produces the Least Amount of Drag in a Wind Tunnel?

Researched by Sam J.
2000-01


 
 

PURPOSE




The purpose of this experiment was to determine what shape produces the least amount of aerodynamic drag.
 

I became interested in this idea when I was reading a book on blimps and I wondered what shape produces the least amount of drag.
 

The information gained from this experiment will help anyone who needs aerodynamic information such as people working in Boeing who are designing jet liners and hobbiests who need some basic aerodynamic information.
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HYPOTHESIS




My hypothesis was that the "teardrop" design would produce the least aerodynamic drag. 
 

I base my hypothesis on information from World Book Encyclopedia that says that a teardrop shape will produce the least drag.


EXPERIMENT DESIGN



The constants in this study were: 

  • the wind tunnel used 
  • setting of vacuum cleaner 
  • vacuum cleaner
  • material shapes are made of
  • surface area of shapes
  • source of dry ice
  • room wind tunnel is in
  • type of spring scale used
  • size of spring scale used
  • fullness of bag in vacuum cleaner
  • type of glass used on all sides
  • type of wood used on all sides of wind tunnel
  • method of making shapes
  • tools that helped me make the shapes
  • device use to hold the shapes
  • type of attachment used to fasten shapes to spring scale.


The manipulated variable was the shape used.
 

The responding variable was the amount of drag produced.
 

To measure the responding variable I used a spring scale connected to the shapes.
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MATERIALS

QUANTITY  ITEM DESCRIPTION
1 small vacuum cleaner
1 30x60 cm plywood panel
1 20x30 cm plywood panel
1 30x40 cm plywood panel
2 12.5x30 cm plywood panels
1 12.5x30 cm strip of styrofoam
11 drinking straws
1 hand drill with .62 cm bit
1 heavy duty black trash bag
1 roll of black cloth tape or duct tape
1 bottle of epoxy glue
1 device for poking small straw-sized holes
1 can of flat black paint
1 each double sided cone, teardrop, cube, and sphere, all with same frontal surface area
1 string
1 can of yellow paint
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PROCEDURES



1. Stand the two strips of plywood edgewise on a flat surface, separated by 30 cm.
2. Lay the largest panel across the strips so that the edges match up.
3. Nail them together.
4. Punch holes in the styrofoam 1.25 cm apart.
5. Punch a hole between the two center holes.
6. Put the straws into the holes in the styrofoam.
7. Cut off the straws where they protrude.
8. Lay the 20x30 cm panel across the left side of the structure so it fits neatly over the vent to create a box.
9. Nail the panel into place.
10. Paint the panels black.
11. Lay the piece of plexiglass on the top of the tunnel so that it fills up the remaining space.
12. Paint the styrofoam shapes yellow so that no small holes are to be seen.
13. Allow the paint to dry.
14. Hang the spring scale above the wind tunnel.
15. Take out the styrofoam vent piece.
16. Attach the shape you are going to use to the spring scale using the string.
17. Make sure the wind tunnel is air tight.
18. Do necessary adjustments.
19. Hook up vacuum cleaner to the bottom of the wind tunnel, making sure no air can get out.
20. Measure the weight of the shape you are going to use.
21. Turn the vacuum cleaner on.
22. Measure the spring scale.
23. Subtract the first measurement from the second.
24. Repeat steps 14-23 twice, with different shapes.
25. Record data.
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RESULTS



The original purpose of this experiment was to determine which of these shapes produced the least drag: double-sided cone, teardrop, cube, and sphere
 

The results of the experiment were that the teardrop produced the least drag, 1 gram, the double-sided cone was second, with 1.5 grams, the sphere was third, with 3 grams, and the cube was fourth with 6.5 grams.
 

See the table and graph below.


CONCLUSION

My hypothesis was supported.
 

The results indicate that this hypothesis should be accepted.
 

Because of the results of this experiment, I wonder if the surface texture made a difference
 

If I were to conduct this project again I would vary surface texture.

See table and graph

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RESEARCH REPORT
 

INTRODUCTION

Aerodynamics is an interesting subject.  It is the study of how air and water affect objects moving through them.  The four basic principles of aerodynamics are lift, drag, thrust, and weight.
 
 

Lift

Lift is the force that keeps aircraft in the air.  It is dependant on thrust to give it enough energy.  The standard aircraft wing is rounded at the front and on the top, flat on the bottom and with a leading edge at the back.  Air flowing over the top goes faster than the air flowing under the wing and so creates a zone of lower pressure.  The low pressure zone creates more lift the more rounded the wing is and the faster the wing is traveling, but creates more drag.
 
 

Thrust

Thrust is the force acting to propel the airplane forward.  Thrust is usually created using a gasoline engine driving a propeller or a jet engine.  The more thrust there is, the more lift there is.
 
 

Drag

Drag is the force that slows the aircraft down.  Drag is created when molecules of air collide with the molecules of the hull.  This is a type of friction.  The denser the atmosphere and the faster the aircraft is going, the more drag there is. 
 
 

Weight

Gravity pulls an airplane toward the earth.  Weight is the total pull of the earth on each of the molecules of the aircraft.  The lower the altitude and the more massive the plane, the more weight there is.  For an airplane to fly, its weight must be counteracted by an equal amount of lift.
 
 

Aerodynamic Efficiency

Aerodynamic efficiency has to do with how much drag is created by speed.  By rounding corners and polishing surfaces, aircraft can become much more efficient.  Also, there are different tricks to make aircraft much more efficient, but they are mostly known only by the professionals.  One trick is to have a rounded shape in the front, tapering to a point in the back.  This leads the air smoothly into the airstream.  Without this technique, swirling air pockets form in the air behind the shape, slowing the shape down.
 
 

SUMMARY

Aerodynamics is, therefore, a complicated and interesting subject.  It not only covers aircraft but also cars and any other method of transportation, especially boats, the only difference being lift does not apply to ground and sea-based methods.
 

BIBLIOGRAPHY




"Aerodynamics",  World Book Encyclopedia,  2000.
"Beginners Guide to Aerodynamics", avalible on http:\\www.nasa.gov downloaded on November 2, 2000
"Aerodynamics", Encarta 2001
Jim Mc Cabe, "An Introduction to Aerodynamics", availible at http://www.nas.nasa.gov/services/education/resources/tutorials/jmccabe/aerodynamics-introduction.html
"Aerodynamic Drag Force", Robert Vigars, availible at http://www.instruct.uwo.ca/kinesology/241a/ppoints/ss20/
"Aerodynamics: Drag", Encarta 2001
 

Acknowledgements
The people I would like to thank for help on my project are: Mr. Ken Newkirk, Mrs. Rita Pasckvale, my father, Mr. Jeffrey J., and my mother, Mrs. Holly J.
Mr. Newkirk is the best science teacher (in my opinion) in the state of Washington.  He gave me huge amounts of help and encouragement regarding my science project.  Also, I hope he will give me a better science grade for writing this paragraph, even though he said, smiling, that he would not.  Mrs. Pasckvale is Mr. Newkirk’s aide in the classroom.  She was of great aid in helping me get the materials in my project and helping me to remake my board and journal after it got trashed at the Regional Science Fair.
My father and mother also gave great support.  My father helped me construct the wind tunnel and do the experiment, and he gave me invaluable help on doing my procedures and the rest of my journal.  My mother helped me with the aesthetics of my project.  She helped me to revise my display board, among other things.
 
 


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