When you’re going to buy an electric car, what’s the first thing that comes to your mind? People rarely mention “aerodynamics.” While it’s true that aerodynamics is not the absolute most important factor, it determines several important factors about the car in a very subtle way.
To demonstrate the importance of aerodynamics in an electric car, we’re going to take a look at one of the finest electric vehicles ever made: the Tesla Model S.
Understanding Automobile Aerodynamics
Aerodynamics is essentially a set of interactions between air and moving objects. A car with good aerodynamics shapes how the air pushes the car in some ways that benefit the vehicle in terms of explosive power and fuel efficiency.
Two factors govern the aerodynamics of a car: Pressure and Drag.
A pressure difference between the air flowing on the bottom part of a car and the upper part of the car (the roof) creates force. If the pressure on the upper side is less than the lower side, it will create an upward force called lift. If the pressure is the other way around, it will create a downward force, called downforce.
You can create a downforce or lift by adding a spoiler on the back of your car. Downforce makes the tire grip the road better. By creating a better grip, you improve handling and cornering speed.
As a car moves through the air, the car displaces air around it, resulting in a force exerted back to the car. That force exerted by the air is called drag. The drag function is:
Drag force = 1/2 p v2 x Cd x A
p = Mass density of air (1.269 kg/m or 0.12 sq/ft)
v = Velocity (Km/H or M/H)
Cd = Drag coefficient
A = Frontal area of the car
Based on that function, we see that to get a low drag force, we need to reduce the drag coefficient and frontal area of the car. The lower the drag, the faster the car can run. Since the drag force is negated, efficiency also improves because the car will consume less fuel for the same distance.
Tesla Model S
The brainchild of Elon Musk’s Tesla Inc, the Tesla Model S is a five-door luxury sedan. Tesla Model S first arrived in 2012. It’s an $80.000 all-electric sedan.
Rocking a 100KWh battery, Tesla Model S has a 335-mile range on its base version and 375-mile on the long-range version. Model S has an insanely powerful explosive power.
It’s able to go 0-100 km/h (or 0-60m/h) in just 3.7 seconds on the base model, and an insanely quick 2.4 seconds on the performance model + ludicrous mode.
For comparison, the $4.700.000 Lamborghini Aventador can only do 0-100 km/h in 2.5 seconds. A critical key to achieving that impressive number is excellent aerodynamics.
Tesla Model S’ Drag Coefficient
The drag coefficient number of Tesla Model S is 0.24. At the same time, its frontal area is 25.2 square feet (2012 Model S). This results in a mere 77 pounds of drag force exerted on Tesla Model S. So, how do Tesla engineers manage to create a 0.24 drag coefficient?
How Car Features Affect Drag
From the front, the grill is very minimalized. The front face redirects most of the air to the top of the car to increase downforce, making the car handle better. The rest of the air will flow sideways, and a tiny bit will flow to the bottom. The front bumper shape allows the wind to hit squarely on the front wheel. If done otherwise, the air would come to the sides of the wheel, where the rims will pick it up and create a massive drag.
Moving slightly to the center, we have the wiper hidden underneath the slightly slanted hood, so the wind will not hit the wiper arm and create drag. The rear-view mirror has a teardrop shape to decrease the aerodynamic drag further. The door handle is cleverly tucked in within the body sides, allowing air to slide smoothly along the sides.
The rearmost side of the car is slightly pointed upwards, like a mini-spoiler. The air will flow from the grille, the roof, to the back of the car, where it will create a negative pressure, which increases the drag and create lift. The mini-spoiler helps to disturb that flow, mitigating most of the negative pressure.
The bottom of the car is completely covered. So it’s smooth and flat, allowing the low-pressure air to flow smoothly along the bottom. Since it’s an electric car, the lack of exhaust helps very much. Finally, the rear bumper also includes a diffuser in the bottom. The rear diffuser accelerates the air exited from underneath the car, so when it meets the air coming from the top of the car, it doesn’t create much turbulence.
Aerodynamics is an often-overlooked factor of a car. It determines how the car handles, its fuel efficiency, and maximum speed. In electric vehicles, the effect becomes more pronounced because power management is vital to its overall performance.
The Tesla Model S uses a streamlined body, a minimalist grille, aerodynamic mirrors, a hidden door handle, and rear diffusers to give it’s tear-drop shape such a low drag coefficient.