No matter whether it is the Mercedes IAA intelligent aerodynamic concept car, known as “the flying fairy from the sky”, or the Roewe i6, which recently created a Guinness World Record for ultra-low fuel consumption, there is always a term that is intricately linked to these achievements, and that term is – drag coefficient!
Although this advanced vocabulary, which seems to have a professional level of eight, may not be unfamiliar to us, people often only have a concept of it in terms of a numerical value. However, to reduce that value even a little, engineers have put in a lot of effort and imagination!
So, in today’s “Understanding”, let’s talk about what this drag coefficient really is!
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First, let’s talk about what drag coefficient is.
According to Baidu, “The drag coefficient is a mathematical parameter determined through wind tunnel tests and descent tests, which can calculate the air resistance of a car while driving. The greater the drag coefficient, the greater the drag, and vice versa.”
Of course, as we all know, the effects are mutual. Besides air resistance, when a car passes through the air, the air also has a sticking effect on the car. If you want to be extreme, the scene is similar to a car passing through glue!
So, how is this small drag coefficient derived? We must mention the wind tunnel laboratory, this mysterious entity! Simply put, a wind tunnel is a tunnel with a giant fan, where vehicles are placed inside. By using the giant fan located at the front of the tunnel to blow air towards the vehicle, it simulates the real state of air flowing over the car!
Compared to other “high-end, atmospheric, and upscale” laboratories, the wind tunnel laboratory, which consists of a section of tunnel and a fan, may seem a bit shabby. But don’t underestimate it; the usage fees are not low at all. Pushing a car in for a few hours can cost you tens of thousands of yuan!
Although engineers often conduct a lot of fluid simulation analysis on computers to reduce costs for wind tunnel testing, taking the Mercedes CLA-CLASS as an example, the entire vehicle went through nearly 2000 hours of wind tunnel testing to adjust to the current record of 0.22Cd for the lowest drag coefficient of a production vehicle, not counting the labor costs of those engineers!
At this time, Mercedes might feel what it means that “Although money does not come from the wind, it can be blown away by the wind!”
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Since it is so time-consuming and labor-intensive, why do manufacturers still go to great lengths on drag coefficient?
Let me explain the formula for calculating drag coefficient, and perhaps you will understand better! The formula is: Drag Coefficient = Front Drag Force × 2 ÷ (Air Density × Speed² × Frontal Area) This means that the resistance of the vehicle while driving is proportional to the square of the speed. When the speed doubles, the resistance increases fourfold, and the consumption increases eightfold!
From a consumption perspective, the greater the drag coefficient, the greater the fuel consumption.
In today’s era of “I’d rather have low fuel consumption than high horsepower”, reducing fuel consumption has become a top priority for major automakers in developing new models. Therefore, in addition to reducing the weight of the vehicle and enhancing the fuel utilization rate of the engine, lowering the drag coefficient is also an indispensable part!
At this point, you might ask me, “If that’s the case, is a smaller drag coefficient always better?” The answer is definitely no! In conventional streamlined shapes, the lower the drag coefficient, the more significant the lift according to Bernoulli’s principle. This explains why supercars often install large rear wings to increase downforce!
So here comes the question:
Why don’t our ordinary civilian cars have such cool wings?
First, because ordinary civilian cars are not that fast, that little lift wouldn’t even lift you, let alone your car! Secondly, if a wing is installed, due to the increase in downforce, fuel consumption will inevitably increase. Considering the cost of ownership for ordinary people, installing a wing is obviously not the best choice. Therefore, designers usually design the rear of the car to be slightly raised, known as the “ducktail shape”.
This design can provide the vehicle with a certain amount of downforce without increasing fuel consumption, achieving a win-win situation!
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With the continuous advancement of science and technology, the drag coefficients of modern cars are getting lower and lower. The Mercedes CLA-CLASS has a drag coefficient of 0.22Cd, while the Mercedes IAA intelligent aerodynamic concept car has a drag coefficient of 0.19Cd, surpassing everyone! Who knows how low the drag coefficient of vehicles will be in the future? Let’s boldly speculate: will the drag coefficient of vehicles drop to the currently known lowest drag coefficient of 0.04 (teardrop)?
After discussing so much about drag coefficient, do you all understand? If not, feel free to leave a message to interact with me, and I will give you more insights!
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