It’s a hard struggle – even if it’s only thousandths we aim for. For 100 years Mercedes-Benz has been working to produce perfectly aerodynamic bodies for its cars. The CLA now crowns this effort with success: with a record Cd value of 0.23 and a drag area Cd x A of 0.51 m² it is aerodynamics champion within the Mercedes-Benz model range and among all production vehicles. This top figure is bettered only by the CLA 180 BlueEFFICIENCY Edition with a Cd figure of 0.22. With its drag area of only 0.49 m² it crosses a magical line and goes into the record books: as the most streamlined production car in the world.
Though the figures differ only minimally, the effects are tremendous: the smaller a vehicle's wind resistance, the lower its fuel consumption will be. So every thousandth of the Cd figure influences the vehicle’s efficiency.
Intelligent airflow channelling.
With aerodynamics the vehicle can be made not only more efficient, but quieter as well. How big the effect is, Dr. Teddy Woll knows, the head of the Aerodynamics, Aeroacoustics and Wind Tunnel Centre department. “It’s a simple equation: A 10-point improvement in wind resistance means savings of around 0.1 litres of fuel. Travelling on motorways, about a quarter of a litre of fuel per 100 kilometres can be saved this way. If you want to achieve the same effect with lightweight design measures, the vehicle would have to be made about 35 kilograms lighter. But wind noises, too, are a domain of aerodynamics. Less air turbulence means less noise inside the vehicle. And with the CLA we not only have the most aerodynamically efficient vehicle, but the one with the quietest interior in its class.”
The CLA glides through the air with the greatest of ease: owing to numerous technological innovations the engineers have managed to minimise wind resistance. For example with a radiator featuring a shutter which only opens when the engine requires cooling. “We were able to improve the flow of air under the vehicle with extensive underbody panelling plus additional panelling in the middle area of the rear axle with an aerodynamically optimised rear silencer followed by a diffuser,” Dr. Woll explains. “Moreover, with special aerodynamic wheels and serrated wheel spoilers we managed to reduce the flow of air around the wheels appreciably.
In addition, the dynamic rear end with spoiler lips on the boot lid and tail lights concentrates the flow behind the vehicle even better.” The challenge consists in combining optimum flow characteristics with a perfectly designed shape.
“It’s often a matter of millimetres.”
Aerodynamics and design go hand in hand. Dr. Woll works together with the designers in the very early stages of development. “We jointly determine the proportions of the 1:4 models and hone the aerodynamics in the wind tunnel. Good cooperation is important here because it’s often a question of millimetres. As one can see very well from the CLA, there is no contradiction between good aerodynamics and great design. The overall concept is important, and this is the reason why the record Cd figures of the CLA cannot be attained in all model series,” the aerodynamics expert elucidates. “Nonetheless, the other models of our compact car family also will achieve top Cd figures.” Striving to build still more aerodynamic models, the engineers continue their quest for optimisable details: with the goal of besting the record yet again.