We are all familiar with wiper blades, but there is a wiper on the rear window for some cars. But have you noticed that these cars are SUV and MPV? Why? Is the car being reduced?
Let me talk about the common sense of physics first. We all know that current cars are all streamlined in design, trying to reduce wind resistance as much as possible, and the air has some turbulence to the car.
Look at the airflow diagram below, maybe you can see the general idea.
According to the body shape, cars can be divided into two types. One is a car with a "butt" trunk; the other is a car without a trunk, which actually includes SUV, MPV, hatchback, and even many crossovers that are difficult to classify.
When the vehicle is running, the front of the car will push away the airflow, and the split airflow will go back along the car body. When driving at high speed, the space that cannot be filled in time will form a vacuum area at the rear of the car. It can also be seen from the above figure that because the C-pillar of the car is flatter, the air can continue to go down, and the vacuum area basically appears at the height of the trunk.
However, because the rear of SUV and MPV etc is relatively straight, the air begins to disperse after passing the tail pillar, and the height of the vacuum area is higher, even covering the rear window glass.
What problems can a vacuum zone cause?
The larger the vacuum area, the first result is greater air resistance. This is one of the reasons why a sedan is always more fuel-efficient than a hatchback or an SUV with the same platform and the same engine. The airflow of the sedan is better.
And the most important thing is that because of the vacuum, it has a certain attraction, and it will absorb air from all directions to fill the void. If you're walking in a clean urban area, it doesn't feel like much. If you run on dusty, bad roads and muddy roads, the effect will be obvious. The vacuum area at the rear of the car will get very dirty.
The vacuum area of a car is relatively low, so it will basically not affect the rear window glass; while the rear window glass of an SUV cannot be spared. The blurred glass will make the central rearview mirror in the car unable to see the situation behind, which also reduces the safety of driving, so it is still necessary to install a rear wiper.
In addition, some rear wipers also have a water spray function, which will have a better cleaning effect when there is a lot of mud.
Automobile manufacturers always control the cost very strictly. If you can save, you can save. The rear wiper is not as important for a car as it is for an SUV, so it will not increase. Moreover, the design of the car is smoother, and naturally, a conspicuous rear wiper will not be added at the back, which will affect the aesthetics of the design.
