Earlier in the week we began taking a look at the achievements Mercedes-Benz has made in vehicle aerodynamics, in the even that you missed it, click here to read the previous article or read on for Part 2 of our Mercedes-Benz Aerodynamics series.

For almost three decades, the aerodynamic specialists at Mercedes-Benz have been breaking one record after another. At present the brand’s models occupy the top position for aerodynamics in practically every vehicle segment. In its BlueEFFICIENCY Edition, the new CLA-Class has even established a new world record with a Cd figure of 0.22 and wind resistance x A of 0.49 sq. m. Highly sophisticated improvements to both the overall vehicle and detailed features contribute to this good performance. The coming new S-Class will likewise be at the top of its segment for aerodynamic efficiency. Mercedes-Benz models also take the lead in almost all vehicle classes where aeroacoustics are concerned.

1984 saw the debut of cable TV in Germany, the West runway at Frankfurt airport was taken into operation and the Olympic Games were held in Los Angeles. In the same year the W124-series E-Class scored an aerodynamic triumph with a Cd figure of 0.29. It was the first series production saloon to achieve a Cd figure below 0.30, setting a standard by which all saloon cars are judged to this day – and which by no means all can equal.

Since then Mercedes-Benz has established one aerodynamic world record after another – across all vehicle classes and body configurations. The following factors are the secret behind this continued leadership:

• Good basic dimensional concept and optimised external shape
• Aerodynamically optimised underbody with extensive engine compartment and underbody panelling
• Large area of cladding on the rear axle
• Aerodynamically optimised rear silencer followed by a diffuser
• Wheel arches with optimised spoilers and other features such as slits
• Large front wheel overhangs with optimised airflow onto and over the front wheel arches
• Aerodynamically efficient design of the front and rear aprons and the rear roof edge
• Hub covers or specially developed aero light-alloy wheels with low air resistance
• Aerodynamically optimised exterior mirror housings
• Low A-pillar shoulder with adapted A-pillar geometry
• Spoiler lip on each tail light
• Improved sealing of the radiator section and airflow guidance to make efficient use of the available cooling air
• Use of a cooling air metering system (adjustable louvre)

Sealed headlamp surrounds

One very recent underbody feature is the patented wheel spoiler already mentioned, which was developed with the help of airflow analysis. This seemingly innocuous component reduces undesirable air turbulence in the wheel arches in no less than three ways, by lowering linear turbulence, deflecting the airflow from the wheels and stabilising shear waves with its serrated edge. The wheel spoiler remains effective whatever the suspension level and wheel dimensions.

It was first employed for the B-Class (2011), which with its help achieved a new top Cd figure of 0.26 for series production cars with an enclosed rear. Tail-end turbulence is also considerably reduced. With a basic shape defined according to aerodynamic aspects, the large roof spoiler acts as an airflow breakaway, as do the tail lights. A total of 278,000 CPU-hours of computer time and 1100 hours in the wind tunnel went into the aerodynamic optimisation of the B-Class.

The patented wheel spoiler is also used in the CLA-Class (2013), which has the lowest of all Cd figures at 0.23 – both within the Mercedes-Benz model portfolio and amongst all series production cars. The CLA 180 BlueEFFICIENCY Edition, which is due to be launched in June, will even better this benchmark with a Cd figure of 0.22.

When it comes to compact cars like the new A-Class (2012, Cd = 0.26), coupés such as the E-Class Coupé (2010, Cd = 0.24), saloons such as the E-Class (2009, Cd = 0.25), sports cars like the SL (2012, Cd = 0.27) and SUVs like the M-Class (2011, Cd = 0.32), vehicles in these segments have never before achieved such low Cd figures. The new S-Class is set to continue this trend.

An overview of the key aerodynamic figures for the entire Mercedes-Benz passenger car range:

BEE = BlueEFFICIENCY Edition model, 1 Saloon/Coupé/Estate, 2 Saloon/ Coupé/Estate/Cabriolet, 3 Coupé/Shooting Brake, 4 Coupé/Roadster

More driving comfort thanks to less wind noise: aeroacoustics

Models from Mercedes-Benz also take the lead in almost all segments when it comes to aeroacoustics. The new CLA will have the lowest level of wind noise in its segment. Numerous measures contribute to this peak position:

• Frameless doors with a multi-stage sealing concept
• The high insulating effect of the side windows
• Stemmed exterior mirrors with an optimised shapefamiliar from the C, E and S-Class

Exterior noise is also minimised by the reduced height of the A-pillar shoulder.

Thanks to its acoustic soft top fitted as standard, when closed the E-Class Cabriolet has one of the quietest interiors in the segment for four-seater premium convertibles with a fabric roof. The soft top’s exceptionally high-quality insulation brings about a clearly noticeable reduction in the interior noise level compared to conventional fabric soft tops. Exterior noise from other vehicles, as well as wind noise, is more efficiently absorbed.

Contribution to active safety: anti-soiling measures

Anti-soiling measures are another aerodynamic discipline – and another area in which aerodynamic specialists at Mercedes-Benz have led the field for many years. Soiling can arise from rain, vehicles travelling ahead and spray thrown up by the vehicle’s own wheels. Keeping windows and exterior mirror lenses as clean as possible, and therefore having the best possible visibility under all conditions, makes a contribution to active safety.

In the wind tunnel the aerodynamic specialists optimise components with the help of a fluorescent liquid which makes the soiling clearly visible. The aim is to direct water away so that the side windows and exterior mirror lenses remain clean. This is influenced by the geometry of the A-pillar with its integral components and the geometry of the exterior mirrors and window frames, or trim strips in the case of frameless doors.

Using the side window as an example, minor geometrical modifications to the mirror housing and detailed refinements using seals and a special water-retaining strip enable soiling to be considerably reduced. The standard at Mercedes-Benz is that in the so-called core visibility area, no spray, no trickles and only individual water drops must appear on the mirror lens.

For the last few years, Mercedes-Benz has lead the way in vehicle aerodynamics, whether it be minimizing wind resistance, reducing noise levels, increasing open-top driving comfort and anti-soiling measures, the models from Mercedes-Benz are without question aerodynamically superior to their competition. Mercedes previously relied on the University of Stuttgart and its original wind tunnerl, but now with the new aeroacoustics wind tunnel at the development center in Sindelfingen, the company is also taking the lead in aerodynamic testing.

Before reading on, in order to enjoy this series of articles, here’s a quick overview of what a Cd figure is and how Mercedes-Benz stacks up against others.

The Cd figure is the measure of the aerodynamic efficiency of a solid body, in this case, a car. When a car’s speed increases, wind resistance becomes an increasing factor, adding to the total resistance against the car.  In direct terms, if the Cd figure can be reduced by ten thousandths, fuel consumption falls on average by one tenth of a litre.  The Mercedes-Benz CLA has the lowest of all Cd figures of all at 0.23 – both within the Mercedes-Benz model portfolio and amongst all series production cars. The CLA 180 BlueEFFICIENCY Edition even betters this benchmark with a Cd figure of 0.22.  Compare this to the the Toyota Prius which is rated at 0.25 Cd and the BMW 320d at 0.26 Cd and you see why the CLA’s numbers are so impressive.

Mercedes-Benz CLA

For almost three decades, aerodynamic specialists at Mercedes-Benz have been breaking one record after another. “At present the brand’s models occupy the top position for aerodynamics in practically every vehicle segment”, says Prof. Dr. Thomas Weber, who is responsible for Group Research and Mercedes-Benz Cars Development. In its BlueEFFICIENCY Edition, the new CLA-Class has even established a new world record with a Cd figure of 0.22 and wind resistance x A of 0.49 sq. m. Weber: “This means that the CLA-Class is more streamlined than any other vehicle. Maintaining aerodynamic leadership is a major component of our MBC 2020 product strategy, which we are following systematically for all new vehicle models.”

When it comes to compact cars like the new A-Class (2012, Cd = 0.26), coupés such as the E-Class Coupé (2010, Cd = 0.24), saloons such as the E-Class (2009, Cd = 0.25), sports cars like the SL (2012, Cd = 0.27) and SUVs like the M-Class (2011, Cd = 0.32), vehicles in these segments have never before achieved such low Cd figures. The new S-Class is set to continue this trend.

The SL achieves a Cd figure of 0.27

“Highly sophisticated improvements to both the overall vehicle and detailed features contribute to this good performance,” says Dr. Teddy Woll, Head of aerodynamics/wind tunnels. Emotion meets efficiency: the more aerodynamically efficient a vehicle is, the lower its fuel consumption. Woll: “In the New European Driving Cycle (NEDC), improving the Cd figure by 0.01 already lowers CO2 emissions per km by one gram, by two grams as a function of mean on-the-road consumption, and at 150 km/h by no less than five grams of CO2 per kilometre.” Moreover, safety, comfort and the environment also benefit from the elimination of air turbulence. Because low levels of lift ensure good roadholding, while low wind noise is welcome to both passengers and pedestrians.

Models from Mercedes-Benz also take the lead in almost all segments when it comes to aeroacoustics. The new CLA will have the lowest level of wind noise in its segment.

The blower of the new aeroacoustics wind tunnel has a diameter of nine metres and has 18 vanes that set the air in motion. The maximum wind speed is 265 km/h.

New aeroacoustics wind tunnel: measurements up to 265 km/h

With the “large wind tunnel” in Stuttgart-Untertürkheim, Mercedes-Benz was the first automobile manufacturer to possess a wind tunnel – the first documented measurement was carried out there exactly 70 years ago, on 5 February 1943. With the new aeroacoustic wind tunnel at the development centre in Sindelfingen, the company has once again placed itself at the forefront of aerodynamic testing. The new wind tunnel, which will be taken into operation in mid-2013, follows the Göttingen design. This means that after the measuring stretch the air is directed back to the blower and again accelerated to up to 265 km/h. Before the air accelerated by the blower reaches the measuring stretch via a nozzle system covering 28 sq. m., it must be directed and smoothed to eliminate unwanted turbulence and eddies. This done using rectifiers and sieves. Extensive noise insulation measures are integrated to allow use as an acoustic tunnel where interior and exterior wind noise can be measured for the relevant test vehicle. Even at 140 km/h the air flowing through the measuring stretch is therefore as quiet as a whisper.

Aerodynamic optimisation, taking the Mercedes-Benz CLA 180 BlueEFFICIENCY Edition as an example

The centrepiece of the 19-metre long measuring stretch in the wind tunnel is the roughly 90-tonne conveyor belt/balance system with a turntable. The new wind tunnel has a 5-belt system to simulate the road. The conveyor belt/balance system is integrated into a turntable with a diameter of twelve metres. This means that the vehicles to be measured can also be subjected to an angled airstream to simulate cross-winds. The traversing system enables the engineers to position various aerodynamic sensors and microphones around the test vehicle with very high precision.