The new Mercedes-Benz SL – the most aerodynamically efficient sports vehicle – is now on sale. It has a cd of 0.27 for the 350. Not since the 1959 Porsche 356A has there been a sports vehicle as aerodynamic as this. Dr Teddy Woll, a Mercedes-Benz aerodynamicist, disclosed that the Porsche had a drag coefficient of 0.29.
He added that over the last 50 years, this trend has been for higher drag as engine and wheels became larger. With the new SL, the trend has been reversed. The B-class with an eco package has an even lower coefficient, being at 0.24. However, reducing a drag is a constant struggle.
The industry, at best, has only paid lip service to aerodynamic efficiency, if not largely ignored, for many years. However, the need for even lower carbon dioxide emissions is giving new thrust for the works of the aerodynamicist.
The impressive figure of the SL has been accomplished without resorting to tricks such as having a spoiler or lip on the back of the boot lid. Woll related that achieving a low drag is a gradual, meticulous approach. One of the obvious methods is smoothing the airflow on the underside and above the vehicle.
The SL's shape assists with long front and back overhangs. Then, there are also the not-so-obvious ones. For one, achieving the ideal shape to lower drag and noise for the A pillars was a challenge.
They need to prevent water from dripping off the front screen and the side screens, while still enabling smooth airflow. The solution to this dilemma is a small channel that catches the water and brings it up and over the top. In the same way, a groove in the top of the door mirrors traps water coming off the front of the mirror and brings it down to run off the bottom edge rather than the side windows.