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This content is taken from the UNSW Sydney's online course, Through Engineers' Eyes: Engineering Mechanics by Experiment, Analysis and Design. Join the course to learn more.
6.1

## UNSW Sydney

Skip to 0 minutes and 9 seconds [INDISTINCT CONVERSATIONS]

Skip to 0 minutes and 15 seconds So this is eVe? Yes this is our two-seater solar car. She looks a lot more practical than most other solar cars I’ve seen. That’s the intention. She was designed for the Cruiser Class competition of the World Solar Challenge, which is a race from Darwin down to Adelaide. And its main focus is towards practicality as opposed to just speed. But the challenges faced by the car in construction are still the same. Well, what are they?

Skip to 0 minutes and 36 seconds The main one is just very limited power, so in order to combat that we have to sort of work with reducing the weight as much as possible, reducing the frontal area as much as possible to create a streamlined shape, and then just getting as low rolling resistance as we can. Now is she solar or battery? A bit of both actually. So she’s got a battery there which can store up to 16 kilowatt hours of charge and then 800 watts of solar panels to charge the battery. So what’s the range? The range on the battery alone is 500 kilometres. If you’re then driving while charging, so with the solar panels going, 800 kilometres. And how fast?

Skip to 1 minute and 11 seconds We’ve got it up to a top speed of 132. Well she’s definitely a car for the future then. That’s right. UNSW SUNSWIFT. For you design task this time, you’ll investigate the sources of drag in an electric car and what power you’ll need to overcome them. You’ll need to know how engineers predict drag, gravity on hills, rolling resistance, and air resistance. And you’ll need to know about work and power. Both of these terms have precise meanings in engineering mechanics, which you will learn about in the analysis section. Gravity resistance you can calculate by using your free-body diagram approach and equilibrium. Rolling resistance is related to dry friction and, for many cases, the same model is good enough.

Skip to 2 minutes and 2 seconds That’s what we are going to use. Air resistance is new. In the analysis section, you’ll learn how engineers describe it. There is a neat experiment that will demonstrate the principle. We will start with rolling resistance.

# Wind loads

Civil Engineers need to know wind loading on buildings. Aerospace Engineers and Naval Architects need to know lift and drag on wings and sails. Automotive Engineers need to know wind resistance of vehicles.

Engineers use the same basic equation for all of these.

You will see it demonstrated, and use it as you find the power requirements of a car, such as eVe the UNSW Sunswift solar car.

We are expanding from statics towards dynamics. But we won’t encounter acceleration, so our equations for static equilibrium will still apply. And of course FBDs do too.

But we will need to understand power and velocity. We’ll quote the definitions and let the concepts seep into you as you absorb the experiments, follow the analysis and do the exercises.

### Talking points

• Are we at the beginning of the age of the electric car? If so, how can Engineers contribute?