In the town of Fellbach, on a street named Stuttgarter Strasse, 10 kilometres from the glittering Mercedes-Benz Museum, there is a a nondescript warehouse with 30-foot ceilings and a ring of small, dusty windows at the upper edges.
These are the Holy Halls, an archive so secretive that Mercedes-Benz bans photos, even posts written on smartphones, because GPS tracking would reveal the exact co-ordinates of the building. Last year, the company unveiled the 1938 540K Streamliner, an early example of aerodynamic car design. Based on the more pedestrian 540K Coupe, the Streamliner featured touches designed to direct the wind, including underbody panels , and a Mercedes-Benz logo painted on the hood in place of the traditional stand-up emblem. The car, a one-off, was built for a race that ran from Berlin to Rome and its advanced aerodynamics (the drag coefficient was 0.36) allowed it to reach 185 km/h in testing.
The early momentum for the aerodynamic movement was mainly skin deep – more visual style than actual substance – but as soon as the practical benefits of aerodynamics were assured, more cars in the mould of the 540K Streamliner appeared.
Fast-forward to the recent Frankfurt Motor Show, where a stunning combination of simple and complex aerodynamic thinking was presented in the form of the Mercedes-Benz Concept IAA (Intelligent Aerodynamic Automobile).
This concept incorporates such 'mundane' aerodynamic devices as an active grille shutter, but it also takes movable aerodynamics to new levels. The carbon-fibre front splitter retracts as speeds rise, and gills at the sides of the front bumper adjust to improve airflow. But the trickery at the back end of the Concept IAA is even more impressive.
The carbon-fibre rear bodywork extends by 390 mm, courtesy of an electro-mechanical device, to reduce the rear surface area of the car. When this takes place, the drag coefficient of this plug-in hybrid concept is slashed from an already sleek 0.25 to an eye-watering 0.19.
"Of course, a concept car such as the Concept IAA features some ideas that are not yet production-ready," says Martin Konermann, manager of passenger car aerodynamics, Mercedes-Benz. "Though, there is a good chance that the extending rear and innovative wheel design could appear on road cars in the future helping to reach the drag coefficient barrier below 0.2."
There are a number of reasons for creating an aerodynamic design; sometimes these reasons flow in direct opposition to each other.
For example, the idea of using a properly sculpted and massive rear wing on a race car is great when the goal is to have the back end of the car produce more negative lift, or downforce, in the corners. The challenge: This rear wing also produces drag, which reduces fuel efficiency and top speed.
In many ways, applying aerodynamics to road cars is even more challenging because the vehicles we use in everyday driving have a wider range of purposes. A road-going vehicle must be comfortable, quiet, stable, quick, fuel-efficient and safe – often, all at the same time, regardless of whether you happen to be behind the wheel of a panel van or a supercar.
There are two schools of thought with respect to aerodynamics on cars – the first promotes creating one shape that serves all possible purposes; the second incorporates movable devices to sculpt airflow for specific driving circumstances.
At the unveiling of the Lamborghini Huracan LP 610-4 last year, design director Filippo Perini noted that his creation required no movable devices to secure what is a decidedly beautiful shape. This supersports car, is exceedingly stable at speed, but has a drag coefficient of 0.33 – not all that spectacular in this day and age.
A surprisingly successful example of "simple" aerodynamics is seen in the 2017 Audi A4, a sedan with a remarkably slippery shape. "The 0.23 drag coefficient is the second-best value for a production car in the world," says Josef Schlossmacher, of Audi AG. "The excellent aerodynamics help reduce fuel consumption and emissions, while improving aero acoustics at the same time."
The other school, represented by exotics such as McLaren and Pagani, uses complex wings, flaps and vents to achieve superior performance.
Under hard braking, the Pagani Huayra automatically deploys flaps that help scrub off speed and adjust the attitude of the car with respect to the ground. This is just the tip of the iceberg with respect to high-tech management of airflow around the car, which has a drag coefficient of between 0.31 and 0.37, depending on the situation. (The name "Huayra" is, not coincidentally, adapted from an Incan term referring to the "God of the winds.")
McLaren adopts a similar approach to aerodynamics, using rear wings that automatically deploy under braking to create increased stability; on the 650S, the rear wing has a profound impact, slowing the car and keeping it glued to the ground when cresting a rise. The wing also uses sensors to detect when the driver is entering a corner, triggering a Formula One-inspired brake-steer effect to help carve that corner more effectively.
For more pedestrian forms of transportation, active aerodynamic devices can still have a profound effect. A number of hybrid and non-hybrid vehicles feature an active front grille shutter. This device can open the grille to create more airflow to the engine in hot operating conditions; in colder conditions, the grille can shut to help warm the engine and to reduce vehicle drag.
"Active aerodynamic measures have been in production for some years now," says Konermann. "[Examples include] extendable spoilers, continuously variable radiator shutters or air-spring suspension systems that automatically lower at a certain speed."
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