Resistance is futile.
During development of a new car, designers and aerodynamics experts have until now followed competing aims: not every aerodynamic optimisation is necessarily conducive to looks – and the same applies vice versa: “beautiful” is unfortunately not automatically “beautifully aerodynamic”. The smaller the cd values become, the harder aerodynamic optimisation is: “We are slowly approaching an asymptotic limit if we do not dramatically change the look of the cars, i.e. make them significantly longer and sleeker with thin tail ends and thin wheels”, explains Dr Teddy Woll, who has been head of the Aerodynamics/Wind Tunnels department at Daimler AG since April 1999.
TWO CARS IN ONE
The Concept Car IAA, which is being premiered at the International Motor Show in Frankfurt, overcomes this conflict of aims by uniting two cars in one. From a speed of 80 km/h it switches automatically from the design mode to the aerodynamics mode. Through numerous active aerodynamics measures the concept car changes its shape – the four-door coupé becomes an aerodynamic world record-breaker.
In the transformation process the cd value drops from 0.25 to 0.19 – a new world record for a four-door model. “With intelligent innovations, the ‘Concept Car IAA’ solves the conflict of aims relating to function and aesthetics”, says Prof. Dr Thomas Weber, Daimler Board Member responsible for Group Research and Head of Mercedes-Benz Cars Development.
Like many aerodynamically optimised racing and record-holding cars in the long tradition of Mercedes-Benz before it, the study provides indications of how and where aerodynamic optimisations would be possible in series production. As Woll added: “Of course, in a concept car such as the ‘Concept Car IAA’, we also implement ideas which have not yet reached production maturity. The purpose of the ‘Concept IAA’ is to communicate the vision that transforming the external shape of future Mercedes vehicles could offer a way of lowering our already very good cd values even further
TRANSFORMATION BEATS LIGHTWEIGHT CONSTRUCTION
Because, thanks to the aerodynamics experts fighting for thousandths in the wind tunnel, Mercedes drivers benefit as part of the ‘Real Life Efficiency’ strategy. As Woll states: “It’s a very simple calculation: if the Cd figure can be reduced by ten thousandths, fuel consumption across the customer average falls by one tenth of a litre, and at very fast motorway speeds by up to 0.4 litres per 100 kilometres. To achieve the same savings effect with lightweight-construction measures, the weight of our cars would have to be reduced by at least 35 kilograms.”
And here are the active aerodynamic measures at a glance:
· The retractable tail-end extension in a “boat-tail” design is the most spectacular. At the same time, this modification has the biggest influence on the improvement to the cd value. Together with the diffuser, the extension, which is extendable by up to 390 millimetres, ensures that the air flow hugs the vehicle more closely and that the after-flow zone behind the vehicle’s tail end is substantially smaller. This results in a considerable reduction in drag. The rear extension consists of eight segments produced in CFRP in a sandwich structure which extend to form a closed ring.
· From the sporty 5-spoke wheel to the aerodynamically exemplary rim – this visual transformation is achieved by the Active Rims. With the help of centrifugal force they reduce their classification from 55 to 0 millimetres.
· In the front bumper, what are known as the front flaps sit on the sides in front of the wheel arches. In the aerodynamic mode they move 25 millimetres to the outside and 20 to the rear up to the rear edge of the wheel crescent. This substantially improves the inflow of air to the wheels and the flow of air over the front wheel arches.
· On the front side of the bumper there is a slat at the bottom. It moves 60 millimetres backwards and improves the flow into the underbody.
In addition to this there are numerous further aerodynamic optimisations such as discs flush with the outer edge of the body, no door openers, lowering, extensive underbody panelling plus an adjustable radiator grille shutter.
So there’s much spin about the wind, but the result is impressive: with its dynamic form (“drop shape”), the puristically elegant overall design plus the numerous technical innovations the four-door coupé saloon is “a symbiosis of desirable forms which intelligently showcase aerodynamics”, stated Gorden Wagener, Head of Design.
The aeroacoustic wind tunnel
Mercedes-Benz has one of the most modern aeroacustics wind tunnels in the automotive industry. Becoming operational in September 2013, alongside the computer simulation programs it is the most important tool the aerodynamics experts have against wind resistance and wind noise. The wind tunnel has a 5-belt system to simulate the road: beneath each wheel there is a small belt conveyor and between the wheels a central belt conveyor. All five belts are synchronised with the wind, so that they exactly simulate the road conditions. A turntable platform makes it possible for air flow to be directed at the vehicles being measured at an angle too.
Here are the key technical data of the wind tunnel at a glance:
· Diameter of the blower: 18 metres
· Nozzle area: 28 m2
· Number of rotor blades: 18
· Max. torque of the electric drive motor: 202,150 Nm
· Max. wind speed: 265 km/h
· Length of the test section: 19 metres
· Weight of the belt conveyor/weighing machine with turntable platform: 90 tonnes