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Using a Wind Tunnel to Measure the Drag Coefficient with Students Designed Dragster Cars


SUBJECT: Aeronautics
TOPIC: Drag
DESCRIPTION: A set of activities using a student wind tunnel.
CONTRIBUTED BY: Carol Hodanbosi
EDITED BY: Jonathan G. Fairman - August 1996

A Ninth Grade Science Project

Abstract:

Barberton High School has a subsonic open circuit wind tunnel. The wind tunnel was deigned by NASA wind tunnel experts and built by high school students. A project was planned that involved three ninth grade sciences to design and manufacture small dragster cars to be tested in the wind tunnel

 

Rationale:

The Ohio model science course of study has emphasized the need for improved science resources and an increase in student projects. By emphasizing the discovery approach through experimentation and allowing the students to visualize their products in a wind tunnel, the students will be able to appreciate the role of research and testing in the technical world.

Building upon the resources that the high school has developed through its partnership with NASA Glenn Research Center, the project will have an aeronautics theme.

 

Project Description:

  1. Design stage
    1. Fifty student dragster car kits were ordered from Pitsco Company. The kits include:
      • a workbook with clear directions
      • styrofoam
      • balsa wood
      • wheels
      • axles
      • sandpaper
      • grid paper

      Also ordered were knives and coping saws. Paint, varnish and decals could also be ordered from the company, if desired.
      **Included with the kits were carbon dioxide cartridges which were removed and not given to the students.

    2. Students worked in groups of 2 or 3.
    3. The workbook gave clearly outlined steps for the students to follow to complete their car. No weight or size restriction was given, however, this is something that one might consider. The car had to fit inside the test bed which was 12 inches by 12 inches by 24 inches.
    4. Both the styrofoam pieces and the balsa wood were tapered from back to front, and were 4 inches by 4 inches by 10 inches in dimension.
    5. Each team of students was encouraged to design a car that had the least amount of drag, which was to be determined by placing in the high school wind tunnel.
    6. They were allowed to paint, decorate and name their cars to their own liking.
  2. Testing
    Twenty three cars were tested in the wind tunnel.
    1. Each car was numbered and an eyelet was placed in the nose of each car.
    2. The test bed floor was wooden plywood. A long slot was made in the floor to allow for one degree of freedom of motion ( forward and backward, only).
    3. Two large L-shaped metal strews were placed in the bottom of each car, along the midline .
    4. Each car was placed one at a time into the test bed, on top of the lengthwise slot.
    5. The L-shaped screw was turned so that it could pass through the slot to the outside.
    6. A string was tied to the eyelet on the front of the car and over a pulley attached to the plywood floor.
    7. A round hole was placed in front of the pulley, allowing the string to pass out of the tunnel beneath the car.
    8. A one-hundred gram mass was tied to the other end of the string. The mass was given enough slack so that it could rest on an electronic scale, located just below the hole from which the string passed.
    9. The electronic scale was 'zeroed ' with no weight resting on the scale, then the one hundred gram mass was placed on it.
    10. Care was taken to insure that the cars could slide forward and backward above the slots before actual testing was begun.

Evaluation:

Drag was determined by the amount that the air pushed against the car's surface. The greater the push the air made on the car, the more the car moved backward. The backward motion of the car caused the string to pull on the one hundred gram mass. The more the mass was pulled upward, the lower the scale went from the one hundred gram reference amount. That is, the car with no drag would read 100, while one with 20 grams of drag would have a reading of 80.

Each car was rated on two values. The first value was the lowest scale reading obtained by that car at a particular wind speed. The second value was the middle reading. All of the the tests involved some vibrating, which caused the readings to rise and fall. Human judgement was used to determine the mean of those high and low values.

These two values were added for each car. Then the cars were ranked from low to high. The cars having the low values had less drag then the cars with the high numbers.


Related Pages:
Aeronautics Activities
Aerospace Activities Page
Aerodynamics Index
Wind Tunnel Index
The Drag Equation
Drag Coefficient
Shape Efects on Drag

 

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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Jun 12 2014

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