The Effect of Dimpling on the Drag Force of an Automobile in Motion

Josh Denzler – Lake Shore High School

Mike Oliver – Lake Shore High School

Terminology

• Drag Force – A force that opposes a projectile’s motion

• Wake – Area of turbulent air behind a projectile

• Dimple – A slight depression

Background

• Gas Prices:– Have risen in recent years– New Standards:

• “that will increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by Model Year 2025”

Background

• Car companies:– Making more fuel efficient cars– Hybrid technology– Lightweight materials– Aerodynamics

• More aerodynamic = less energy to move car• Less energy to move car = less fuel consumed

Scientific Concepts • Dimpling:

– Improves aerodynamics of a golf ball– Can it improve the aerodynamics of a car?

Previous Research

• Mythbusters:– Ran an identical course with dimpled and

smooth cars– Saw a fuel efficiency increase of three mpg

• Zipp:– Bicycle manufacturer– Dimples surface of their disk wheels– Better gripping ability on the roads– Takes less effort to spin the tire

Previous Research

• Fastskinz:– Dimpled vinyl skin to go over cars– Tested by Popular Mechanics:

• Did not improve fuel efficiency

Problem

• Do different dimple sizes on a car reduce the drag force acting on that car?

Hypothesis

• The smooth car, six millimeter dimple, eight millimeter dimple, and ten millimeter dimple will not all have equal drag forces

• The ten millimeter diameter dimple will result in the largest reduction of drag.

MaterialsWind Tunnel

Vernier Lab Quest

Asus TabletLab Car Model

Procedure

• We are going to insert a video of our procedures here. We will narrate the video appropriately while it is playing.

Sample Data

Value

Drag Force (N)

Smooth Car

6 mm Dimple Car

8 mm Dimple Car

10 mm Dimple Car

High 0.178 0.230 0.200 0.268

Low .071 0.090 0.012 0.052

Average 0.123 0.140 0.074 0.151

Smooth Car ObservationsTrial Observation

2 String fell off of pulley, trial redone.

3 Car went back before Lab Quest could get data, trial redone

4 Trials 1-4 were abnormal values and were redone.

6 Abnormally small value, trial redone

11 Abnormal graph of data, data kept

12 Abnormally small value, trial redone

13 String fell off of pulley, trial redone.

15 Car did not move, trial redone

16 Car did not move, trial redone

23, 24 Car went back before Lab Quest could get data, trial redone

27 Car did not move, trial redone

6 mm Dimple Car Observations

Trial Observation

8 Car did not move, trial redone

12 Car did not move, trial redone

19 Car did not move, trial redone

8 mm Dimple Car ObservationsTrial Observation

8 Second fan not started on time, trial redone

14 Car did not move, trial redone

15 Car did not move, trial redone

21 Car did not move, trial redone

22 String fell off of pulley, trial redone.

23 String fell off of pulley, trial redone.

10 mm Dimple Car ObservationsTrial Observation

2Car went back before Lab Quest could get data, trial redone

7 String fell off of pulley, trial redone.

8, 10, 12, 15 Car did not move, trial redone

21 Abnormally small value, trial redone

29 Car did not move, trial redone

30 Abnormally small value, trial redone

Data Analysis and Interpretation

Data Analysis and Interpretation

Data Analysis and Interpretation

Data Analysis and Interpretation

Data Analysis and Interpretation

Data Analysis and Interpretation

Conclusion

• Purpose:– To find out if dimples had an effect on the drag

force acting on a car– To find which dimple size has the greatest

effect on that drag force

Conclusion

• The Experiment:– Used a force sensor– Compared drag force acting on different car

types– Used ANOVA and Two-Sample t Tests– Found 8 mm dimple car to have lowest drag

force of all car types

Conclusion

• Initial Hypothesis:– The smooth car, six millimeter dimple, eight

millimeter dimple, and ten millimeter dimple will not all have equal drag forces

– The ten millimeter diameter dimple will result in the largest reduction of drag

Conclusion

• Hypothesis Rejected:– All cars did not have same drag force– BUT 8 mm car had the lowest drag force

• Why?– A car is not a golf ball– Air is not flowing around the car uniformly– Design Flaws

Design Flaws

• Bad Dimpling:– Dimples not uniform distance apart– Dimples went too far into clay– Machine would be more accurate

• Data Not Randomized:– Lurking variables would affect data unevenly– Monetary resources– Machine could also correct this

Further Research

• Different Patterns:– Different dimples

(hexagon, square, etc)

– Troughs/Ridges• Different Car Style:

– Less sports car like– More ball-shaped

• Other forms of transportation:– Planes– Trains – Ships

Real Life Application

• Automotive Design:– More fuel efficient cars– Decrease oil dependency– Help conform to Obama’s standards

• Projectile Design:– Bullets, missiles, balls, etc.– Reduces energy needed to fly– Can fly further/longer

Any Questions?