Pimp your ride

Focus questions

How does closing a grill affect drag of a car?

How do spoilers at different angles affect drag of a car?

How does the presence of side skirts affect drag of a car?

How do the removal of side mirrors affect drag of a car?

Background theory

There are quite a few factors that effect aerodynamic coefficient. Namely, velocity, density and area exposed to the flow of a fluid. Other factors like surface roughness, attitude to oncoming flow, viscosity, elasticity(compressibility) of the fluid. Aerodynamic resistance depends on the shape, size and attitude of the body towards oncoming air. The properties of the fluid like density and pressure and the relative velocity between the object and the air. Side skirts are used to reduce the amount of air that rushes in from the high pressure area on the side of the car entering the low pressure area under the car. They have to be quite close to the ground or they become useless. A spoiler can keep air from tumbling and creating a swirling vortex behind a car which increases drag and creates lift. They block the air creating a high pressure area on the car (down force). Side mirrors and any other objects projecting from the side of the car create a lot of drag because they create a swirling vortex that slow oncoming air. A rear diffuser sucks air from under the car to the low pressure area behind the car. It increases the speed of the air under the car thereby reducing its pressure, creating down force. The vertical fences ensure that the airflow remains attached to the top of the diffuser. A wing is generally an upside down air plane wing that creates negative lift. It is usually mounted quite high up. Its angle of attack etc can be adjusted. A splitter is designed to separate the oncoming air at the lower-leading edge of the car. The air is channelled above the car to radiator or below car to brake ducts or air channels. Canards are little winglets on the front of a car to create down force buy directing airflow over the car but mainly by creating a spinning vortex that acts as a barrier to stop air from entering the low pressure area underneath the car. They create a lot of drag. Decreasing ride height reduces the amount of air that flows under the car reducing drag.

Hypothesis

Adding a closed grill will decrease drag.

Adding side skirts will decrease drag.

Adding a spoiler will increase drag.

Removing mirrors will decrease drag

Apparatus

Wind tunnel, model car, scale, protractor, cardboard.

Testing Procedure

We designed, built and tested a wind tunnel. We modified a model car and tested what force the wind was applying on the car. We measured this force using a scale.

Controlled Variables

Speed of air, constant car, cars position, no external environmental factors.

Measurement

Force that wind applies to the car.

Precautions

Same environmental temperature, same motor temperature, cars position, air pressure, used a variety of mesh to limit turbulence.

Results

Raw data tables

Graphs

Conclusion

Adding side skirts and removing side mirrors decreases drag. Adding a spoiler decreases drag, but a spoiler at a high angle increases drag. Closing the grill does not seem to have a effect on drag.

Significance

Crude oil is a non renewable energy source and it is quickly being used up. If the average cars efficiency increases by 1 %, millions of litres of crude oil can be saved everyday. It would be cheaper to run the cars due to their lower fuel consumption. People then can afford more expensive cars because they would be cheaper to run. This would increase consumer consumption of cars, causing firms to increase production of cars, which would increase our GDP, meaning economic growth. A more aerodynamic car is also safer to drive in because it holds the road better. It would also be quieter due to less wind noise. Companies will invest more into improving the aerodynamic properties of a car.

Limitations

The heating of the motor might gave slowed it down, causing less air flow.

There might have been a little turbulence in the air.

The fans pitch might have changed due to fatigue and continuous use, causing less air flow.

We have limited amount of data due to time and resources constraints.

Suggestions for further investigation

We will test what affect a diffuser has on drag.

Close rear wheel arches and have a smooth wheel cover.

We will test what affect splitters have on drag.

We will test what affect the ride height has on drag.

We will test what affect wheel width has on drag.

We will test which factors affect down force.

Bibliography

www.Dummies.com

www.f1technical.net

www.sportcompactcarweb.com

people.bath.ac.uk/atj20/Drag

www.grc.nasa.gov

Acknowledgements

Coligny Marloth provided some ideas and let us use his facilities.

Our parents support.

Angela Stott as our science teacher.

Herman Meyer for ideas and physical help.

Tinus Marloth provided computer/internet facilities

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