Germany’s most successful triathlete, Ironman Jan Frodeno, is best described as a perfectionist who is always looking for the tiniest technical advantage that could save him time.  In the complex world of triathlon the cycling leg is by far the most dependent on optimum technique – in particular on the aerodynamics of both the cyclist and their bicycle. Dr Teddy Woll has also made this one of his main missions. However the Head of Aerodynamics at Mercedes-Benz is predominantly concerned about mobility that is as efficient as possible rather than world records or victories. A meeting in the state-of-the-art wind tunnel at Mercedes-Benz in Sindelfingen.

What is the significance of aerodynamics as far as you are concerned?

• Jan Frodeno: Aerodynamics plays a really fundamental role in the central part of a long-distance triathlon, the 112 mile cycle ride. In particular at the World Championships in Hawaii we have to fight against strong gusts of wind as well as the wind resistance. This makes the issue especially complex. And you need to know that it’s not just the aerodynamics of the wheel that makes the difference, it’s the decisive interplay between the bike and its rider. Because the body causes around 80 percent of the contact surface for the wind. It’s definitely worth a few hours in the wind tunnel to find the ideal seat position.
• Teddy Woll: Aerodynamics are an intelligent way of cutting fleet consumption and also help to close the gap between certified and actual consumption. As the wind resistance grows with the square of the speed, a c_d value reduction brings advantages above all at a higher speed. An aerodynamic design is also so important because the vehicles’ frontal area is tending to increase: people are getting taller, the battery in electric vehicles needs space and lots of customers prefer an SUV. We are all the prouder that in the new compact cars we have managed for the first time to cut the c_d figure yet again and also made the frontal area smaller, in spite of wider wheels and more space in the vehicle.

When it comes to the aerodynamics of the bicycle or car, what kind of ballpark figures are we talking about?

• Frodeno: Anyone out for a leisurely ride on a touring bike has a Cd value of around 0.7 m². A mountain biker has about 0.6 m², a racing biker 0.5 m². With me – in combination with a helmet, the pre-determined seat position and an aerodynamically optimised bike – a Cd figure of 0.21 m² was measured. So anyone riding a Dutch bike has to overcome three times the resistance, and at as much as nine times the resistance at twice the speed!
• Woll: Our best is currently the A-Class Saloon. With a c_d value of 0.22 it achieves the current world record amongst series vehicles and has a frontal area of around 2.19 m². This adds up to a drag coefficient of 0.49 m². Two people in an A-Class are therefore much more aerodynamic then two racing bike riders – despite triple the frontal area.

Is it possible to put the benefit of better aerodynamics in figures?

• Frodeno: As the external circumstances are permanently changing, it is so difficult to quantify it in absolute terms. But one thing is clear: the less energy I need the faster I can cycle – or I can save energy for the marathon to come. So we cyclists measure aerodynamics in watts – the power we have to generate in order to overcome the wind resistance – or how many watts we can save at a target speed of, say, 45 km/h.
• Woll: If it is possible to cut the c_d figure by one hundredth, so for example 0.24 to 0.23, the fuel consumption in the customer average falls by one tenth of a litre, at a motorway speed of 140 km/h by approx. 0.2 litres per 100 kilometres or 5 grams of CO₂ per kilometre. Today there is no measure that cuts this much consumption at such low costs. To achieve the same saving with lightweight-construction measures in real traffic we would have to reduce the weight of our cars by at least 50 kilograms, and at a motorway speed of 140 by as much as 200 kg.

What improvement have you achieved in the course of your career?

• Frodeno: In the last few years we have concentrated on working on the bike itself with my bike partner Canyon and we have improved the handlebars and the cockpit. We also tinkered with my seat position and developed a new helmet too. This all resulted in successes. But you also always have to keep an eye on the biomechanics. Because you also have to put power on the pedal too and above all in an Ironman you have to be able to stay in the seat position for 4 hours. It doesn’t help one bit if you save 10 W of air resistance in the wind tunnel but the position is then so “uncomfortable” that your performance decreases by 20 W or you can’t run properly afterwards. Finding this balance and the perfect point between aerodynamics and biomechanics is our biggest challenge.
• Woll: We also have a conflict of interests with different demands when it comes to a vehicle – that’s why not every model is always more aerodynamic than its predecessor. But generally speaking we have made huge progress in the last few years. One spectacular example is the leap the SUVs have made, from the first M-Class with c_d 0.40 to the new GLE, which achieves a new best c_d figure in the segment, 0.29. In this period the saloons have clocked up an improvement of some 20 percent. In recent years we have made great progress thanks to the digitisation of the development process, as calculations are very much faster and much more refined. Digital vehicle models nowadays have over 100 million cells, and can produce results overnight with a precision of over 99 percent. Not that long ago, this same simulation would have taken 6 months and would have been very imprecise. Then there is the fact that today we collaborate very well with our colleagues from Design and we have developed a huge mutual understanding. And it certainly makes us proud that we are setting the trend for the entire car industry in this field.

And where are the improvements taking place?

• Frodeno: Take a look at my current racing bike. My partners at Canyon really took care of every last detail. For instance, my Speedmax CF SLX has a tailor-made cockpit: in order to keep the frontal area as small as possible Canyon milled a special attachment that sits in the centre of the stem. And Continental made me a special tyre with the low rolling resistance of the GrandPrix TT and the reduce wind resistance of the GrandPrix 4000 S2: through the profile in the tread the wind dissipates faster, which saves one to two W compared with the smooth tread of the TT.
• Woll: This encompasses three areas – the air flow through the engine compartment, the air flow around and within the front wheels, and the underbody. These measures include, for example, the latest generation of active radiator shutters, a complex interplay between 3D wheel spoilers, slotted wheel arch liners and aero wheels, fully trimmed underbodies and also the active level control system on some vehicles. But we take a close look at every nook and cranny of the vehicle, from the front apron with all its edges and apertures to the small spoiler lips in the lenses of the tail lights, to perfect the breakaway of the air flow at the rear.

Will the development then continue or has the end of the road been reached?

• Frodeno: Development is always ongoing as long as weirdos like me are so obsessed with every detail. If you want to win you have to be better than the rest. And this means that if you stand still you fall behind. We constantly have to learn, measure, buy, develop – and start all over again.
• Woll: And that is precisely our attitude too. Our company motto “The best or nothing” amounts to the same thing. Of course we are gradually approaching an asymptotic limit if we do not dramatically change the appearance of our cars, e.g. by making them much longer and sleeker, and equipping them with slim rear ends and narrow wheels. Fortunately, however, we can always still find details where improvements are possible — both in the wind tunnel and, increasingly often, on the computer. After all, aerodynamics is the most efficient way to even more efficiency.

In conversation

Jan Frodeno (37) was the first triathlete to win both Olympic gold (Peking 2008) and the Ironman World Championship title in Hawaii (2015, 2016). He is Germany’s most successful triathlete and also a legend worldwide. Since July 2016 he has held the record for the best time in the world, 7:35:39 hours for a long-distance triathlon, which he set at Challenge Roth.

Dr-Ing Teddy Woll (56) studied business engineering sciences, specialising in electrical engineering at the TU Darmstadt. His doctorate was on the topic of “Measurement of intraocular pressure with a closed eyelid” and in parallel, with the Akasol he developed solar-powered and light electric vehicles, which achieved successes such as winning the Tour de Sol three times. After two years at smart Woll moved to Advance Development at Daimler AG in 1996 and since 1999 he has headed the Aerodynamics and Wind tunnels department.

The aeroacoustic wind tunnel: measurements up to 265 km/h

With its “large wind tunnel” in Stuttgart-Untertürkheim – the first measurement was recorded 75 years ago, on 5 February 1943 – Mercedes-Benz was the first automotive manufacturer to have its own wind tunnel. The new aeroacoustic wind tunnel at the development centre in Sindelfingen, which commenced operation in September 2013, once again put the company at the forefront of aerodynamic testing. The wind tunnel follows the so-called Göttingen design, whereby the air is redirected to the blower after the measuring section and then re-accelerated to 265 km/h. Before the air accelerated by the blower reaches the measuring section, via a nozzle system that encompasses 28 sq m, it must be straightened and smoothed to eliminate unwanted turbulence and eddies. This is 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 section is therefore as quiet as a whisper.

The centrepiece of the 19-metre-long measuring section in the wind tunnel is the roughly 90-ton conveyor belt/balance system with a turntable. Five separate belt conveyors simulate the road, whose movement relative to the vehicle influences the air flow in particular on the underbody. The conveyor belt/balance system is integrated into a turntable with a diameter of twelve metres, which means that the test vehicles can also be subjected to an angled flow of air in order to simulate cross-winds.

The aerodynamics world champion from Mercedes-Benz: A-Class Saloon

Fresh wind for saving fuel: for three decades now, the aerodynamics engineers at Mercedes-Benz have been setting one record after another. The world record for series production vehicles is currently held by the new A-Class Saloon with a c_d value of 0.22 and a drag of less than 0.49 m². It thus defends the original world record set by the CLA Coupé, the new model of which achieves 0.23 c_d, still an outstandingly good figure.

The good aerodynamic properties make a key contribution to low fuel consumption under everyday conditions. The A-Class Saloon was improved down to the smallest detail by a multiplicity of computation loops, CAE simulations (computer-aided engineering) and measurements in the wind tunnel in Sindelfingen. In addition to the outstanding exterior shape, there are many small measures that led to the new record: a sophisticated reduction of the frontal area despite significantly improved interior comfort dimensions, an extensive sealing concept (such as the sealing of the headlamp surroundings) as well as almost complete panelling of the underbody, which includes the engine bay, main floorpan, parts of the rear axle and the diffuser.

The front and rear wheel spoilers were optimised specifically to route the air around the wheels as efficiently as possible. The rims and tyres also underwent aerodynamic fine-tuning. Depending on the market, an optional two-part shutter system behind the radiator grille is available, which minimises the airflow through the engine bay.

The A-Class Saloon was launch at the end of 2018. The four-door notchback has the wheelbase of the hatchback (2729 millimetres) as well as the proportions of a dynamic and yet compact saloon with short overhangs at front and rear. It is at the top of its segment with regard to rear headroom. In addition, the saloon model has the familiar A-Class virtues. These include modern, efficient engines, a high level of safety thanks to state-of-the-art driving assistance systems with S-Class functions, and the intuitively operated and learning MBUX – Mercedes-Benz User Experience infotainment system.

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:

Model series	Cd figure	Frontal area (A) sq. m.	Wind resistance (Cd x A) sq. m.
A-Class	0.27 BEE: 0.26	2.20 BEE: 2.20	0.59 BEE: 0.57
B-Class	0.26 BEE: 0.24	2.42 BEE: 2.42	0.63 0.58
CLA-Class	0.23 BEE: 0.22	2.21 BEE: 2.21	0.51 BEE: 0.49
C-Class1	0.26/0.26/0.29	2.16/2.11/2.18	0.56/0.56/0.64
GLK-Class	0.34	2.55	0.87
E-Class2	0.25/0.24/0.29/0.28	2.31/2.12/2.30/2.14	0.59/0.51/0.66/0.60
CLS-Class3	0.26/0.29	2.28/2.30	0.59/0.66
S-Class	0.26	2.40	0.62
SLK-Class	0.30	1.98	0.59
SL-Class	0.27	2.12	0.58
M-Class	0.32	2.87	0.93
GL-Class	0.35	2.96	1.04
R-Class	0.31	2.80	0.87
G-Class	0.54	2.97	1.60
SLS AMG4	0.36/0.36	2.14/2.11	0.77/0.76

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.

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.

“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.

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.

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.

In everyday driving, the aerodynamics of a vehicle plays a major role on fuel consumption, leaving you to wonder how the 2012 Mercedes-Benz B-Class is able to achieve good gas mileage. Designers at Mercedes worked hard to give the new B-Class an outstanding drag coefficient of cd = 0.26, placing the new Mercedes B-Class at the forefront of its market segment. In the near future, with the optional ECO Technology package, the five-door B-Class will achieve the world-class aerodynamic credentials of the E-Class Coupé, attaining a drag coefficient of cd = 0.24 which is nothing short of sensational for a vehicle with a station wagon rear end.

If you are unfamiliar with cd values, a change of cd .01 adds up to .11 gallons per 62 miles at a speed of 80 mph. It may not sound like much but you are saving over a gallon of gas between every fill up.

“A whole range of measures were necessary in order to attain the excellent drag coefficient of cd = 0.26,” explains Dr. Teddy Woll, Head of Aerodynamics at Daimler AG. “Apart from an aerodynamically efficient basic design, these include numerous optimisation measures on points of detail, such as the air flow around the front wheels, the underbody design and the flow of cooling air.”

Designers and aerodynamicists worked closely together. Aerodynamically efficient lines are demonstrated by the exterior mirrors with braces, for example. The low height of the shoulder on the A-pillar accompanied by optimised A-pillar geometry also contributes to the good aerodynamics. The entire front apron is sealed, including special seals fitted on the headlamps, for example. The large roof spoiler at the rear provides for defined flow separation.

Flow losses at the front wheel arches have been reduced substantially with the aid of innovative serrated wheel spoilers at front and rear – patent pending -, slots in the wheel arches and optimised hub caps. These measures result in improved wind flow around the wheel arches.

Equally comprehensive measures have been undertaken to design the underbody along aerodynamic lines. The main floor panel features extensive cladding up to the rear wheel arch, followed by additional cladding of the rear axle. The rear silencer has also undergone aerodynamic optimisation.

The improved cooling air flow by means of an adjustable radiator shutter which is familiar from other Mercedes models now features on the basic petrol-engine model in the B-Class. This feature enables infinite adjustment of the air flow through the engine’s cooling module and the engine compartment by means of a circular louvred shutter installed in parallel with the fan. When there is no special need for cooling air, the shutter is closed. This improves the aerodynamics and reduces fuel consumption.

The ECO Technology package, which will be optionally available for all versions of the B-Class, incorporates additional optimisation measures designed to further reduce drag. These include lowering of the body, the sealing of joints at the rear window and the cladding of chassis components at the rear axle.

The aerodynamics of the new B-Class were optimised at an early stage in the development process by means of complex computer calculations and flow simulations. Over 275,000 CPU hours were required for the purposes of digital flow simulation. Models and prototypes spent around 1100 hours in the wind tunnel for measurement purposes.