The S-Class as an example for aerodynamics development

May 23, 2013
  • Aerodynamics gains momentum for production vehicles after the Second World War
  • Aerodynamics have had a strong influence on vehicle design and styling since the 1970s
Stuttgart – Mercedes-Benz engineers have known since the 1930s what a pivotal role aerodynamically optimised car bodies play in modern car manufacturing: their streamlined, panelled racing and record-setting cars dominated the Grand Prix races and the international speed record runs in the years leading up to the Second World War.
Following the Second World War, aerodynamics began to take on greater significance for Mercedes-Benz production vehicles. The main reason prompting this development was the call for lower fuel consumption and improved energy efficiency. Mercedes-Benz took up this issue early on and began developing vehicles which also met the criteria for optimised aerodynamics. Introduced in 1953 and 1954, the so-called “pontoon” models of the mid-size and full-size categories had a self-supporting chassis-body structure and ushered in a new era at Mercedes-Benz with their modern, smooth body which was roomier and significantly more aerodynamically efficient than the classic bodies of their predecessors.
Beginning in the 1970s, during the time of the first big oil crises, the idea of aerodynamic efficiency gained enormous ground. And thus the S-Class W 126 model series was the first Mercedes-Benz production vehicle to be systematically developed and designed with aerodynamic considerations in mind. The result: with a drag coefficient of 0.359, this S-Class far outranked the international competition in its segment even in the late 1970s.
But rather than focusing on optimising aerodynamics for its own sake in order to achieve new records, the engineers and designers at Mercedes-Benz attached great importance to never losing sight of their vehicles’ suitability for everyday use. Thus for instance they intentionally opted against a stronger windscreen slope in the S-Class W 126 model series, as this would have resulted in increased heat generation and would also have made it more difficult to get into the vehicle.
Two important measured variables characterise a vehicle’s aerodynamics: its frontal area A (in square metres) and the drag coefficient cd (c = constant, d = drag, non-dimensional), which describe the airflow pattern of an object irrespective of its size. Because the overall aerodynamics depends on both values, the most meaningful result of a vehicle measurement is obtained by multiplying cd by A (cd × A).
And because of this principle, there is a surprise when we consider the different S-Class generations: the W 140 model series, which was often criticised due to its size, provides better aerodynamic resistance (cd × A) than the predecessor model series W 126 – even though it has a larger front surface area, it also has a significantly lower cd value of 0.30, which set the standard for saloons in the luxury class when it appeared in 1991.
When considering the numerical values over the years, we can see that although the size of the frontal area does increase slightly from one vehicle generation to the next, the cd value drops continually, and therefore the cd × A value likewise follows a downward trend.
The wind tunnel as an engineering tool
When the first newly developed passenger cars from Mercedes-Benz came onto the market in 1949, after the Second World War, aerodynamic drag and energy efficiency were not of primary importance. And that didn’t change in 1951, when the new models 220 (W 187) and 300 (W 186) took the International Motor Show (IAA) in Frankfurt by storm. At that time, there was no official aerodynamic data for these two cars.
But in the case of the model 220 at least, existing figures for pre-war vehicles with free-standing headlamps, running boards and fenders indicate that the cd value of the W 187 was likely to have been around 0.55.
Here are the cd values of selected Mercedes-Benz models from the period prior to the Second World War:
Model
cd
A (m²)
cd × A
260 (W 02)
0.662
2.53
1.675
130 (W 23) rear-engine vehicle
0.516
1.953
1.008
170 V (W 136)
0.600
n/a
n/a
170 V (W 136) with aerodynamic body as developed by Prof. Dr.-Ing. W. Kamm (prototype vehicle)
0.361
2.0937
0.7558
Measured with cooling-air flow.
 
Mercedes-Benz 220 “Ponton”/“pontoon” (model series W 180)
After the war, the previous technical management team was replaced by a new generation of engineers. These included Fritz Nallinger, Rudolf Uhlenhaut, Josef Müller, Wolf-Dieter Bensinger and Hans Scherenberg, for example. In 1952, Scherenberg succeeded Max Wagner, who had held the position of Head Design Engineer since 1926.
The presentation of the model 220 (W 180) in Geneva in March 1954 marked the paradigm shift which, for the first time, was to play a role in the design of an S-Class predecessor vehicle: the significance of aerodynamic drag. Developed in parallel and presented seven months prior, the mid-sized model 180 (W 120), which corresponded largely to the model 220 (W 180) in terms of its body, was described by Chief Engineer Nallinger as embodying the “link between the traditional Mercedes-Benz design and a new-age, aerodynamically efficient overall design”.
With a cd value significantly below 0.50, the model 220 (W 180) meets optimal conditions for better performance with lower fuel consumption thanks to more favourable aerodynamics, despite its larger body when compared with its predecessor.
Model
cd
A (m²)
cd × A
220 (W 180)
0.473
2.07
0.9791
Measured with cooling-air flow.
 
Mercedes-Benz “Heckflosse”/“tailfin” (model series W 111)
Yet another advancement became clear with the introduction of the W 111 model series in 1959. Compared with the “Ponton” (“pontoon”) W 180 model series, the drag coefficient had improved by 13 per cent. Despite a 3.86 per cent larger front surface area, the total aerodynamic resistance obtained by multiplying A by cd dropped by 9.7 per cent. In the “tailfin”, the arched design of the roof and the high rear end of the boot lid had a favourable effect which reduced flow losses.
The following analysis was published in issue 10/1960 of the trade journal Auto Motor und Sport: “We were unable to work out just how 120 horsepower was enough to propel this full-sized car to a timed speed of 174 km/h until we were handed the precisely measured data on the frontal surface and drag coefficient.”
Model
cd
A (m²)
cd × A
220, 220 S, 220 SE (W 111)
0.411
2.15
0.8837
Measured with cooling-air flow.
 
Mercedes-Benz model series W 108/109
With the appearance of the W 108/109 model series in 1965, a style icon was born. Aerodynamic issues were not a priority in the technical endeavours of the time, however. In fact, the flatter roof and lower rear end of the W 108 model series even resulted in a less favourable drag coefficient compared with the W 111 model series. Nevertheless the level achieved with the W 111 model series was essentially maintained: a 2.2 per cent higher cd value was accompanied by an 1.9 per cent decrease in front surface area, resulting in a nearly identical total resistance value from the combined front surface area and cd value.
Model series
cd
A (m²)
cd × A
W 108/109
0.420
2.108
0.8854
Measured with cooling-air flow.
 
Mercedes-Benz S-Class (model series W 116)
The W 116 model series, the first to be called Mercedes-Benz S-Class in official communications, achieved nearly the same values as the W 111 model series due to its high rear end and it scored a somewhat better in total resistance owing to its reduced front surface area.
Model
cd
A (m²)
cd × A
280 SE (W 116)
0.412
2.14
0.8817
Measured with cooling-air flow.
 
Mercedes-Benz S-Class (model series W 126)
When planning the W 126 model series, Werner Breitschwerdt, then Chief Developer in Sindelfingen and later Chief Engineer, focused his attention on the consumption-influencing factors of weight and aerodynamic drag. As with the transition from the “pontoon” W 180 model series to the “tailfin” W 111 model series, the changeover from the W 116 model series to the W 126 model series marked not only a leap within the Mercedes-Benz model series; this S-Class also far outranked the international competition in its segment. The major optimising factors for a favourable drag coefficient were the sharper falling slope of the roofline, the high rear end with its rearward structure slightly tucked in at the sides, the steeper inclination of the windscreen (54 degrees), the recessed windscreen wipers, drip moulding integrated into the body, a stepless transition of the front wall pillars and a seamless transition from the bumpers to the body.
The success of all these measures was impressive: the cd value improved compared with the predecessor W 116 model series by 12.9 per cent – tops in the industry at that time. The front surface area decreased by roughly 1 per cent, and the total resistance by 13.3 per cent.
Model
cd
A (m²)
cd × A
280 SE (W 126)
0.359
2.1283
0.7641
Measured with cooling-air flow.
 
Mercedes-Benz S-Class (model series W 140)
When designing the W 140 model series, which was finished in 1991, engineers likewise devoted their attention to the aerodynamics. Compared with the W 126 model series, they directed much effort towards once again significantly reducing the drag coefficient. The measures included, for instance, a rearward sloping front section, a larger radius in the transition from the radiator grille to the engine bonnet surface, a somewhat flatter slope to the windscreen, flush-fitted side windows, exterior mirrors with an integrated catch groove for dirty water, generously sized wheel trims and light-alloy wheels, less front-axle lift to minimise crosswind sensitivity and smooth-surfaced design of the underbody.
By introducing these measures, the engineers were able to decrease the drag coefficient by a further 16.4 per cent, thereby achieving a new record in this vehicle class. Although the frontal area increased by 12.2 per cent compared with the predecessor, (thus also earning it a new record in the comparison segment), this S-Class also had the most favourable total resistance value of all S-Class cars since the “pontoon” W 180 model series. This was made possible thanks to its drastically lower cd value. The W 140 beats the W 180 in this regard by 26.8 per cent and outperforms the legendary predecessor W 126 model series by 16.4 per cent. This fact is particularly astonishing given the car’s imposing overall appearance.
Model
cd
A (m²)
cd × A
300 SE 2.8 (W 140)
0.30
2.39
0.717
Measured with cooling-air flow.
 
Mercedes-Benz S-Class (model series W 220)
When the W 220 model series of the S-Class was presented in 1998, it again attained the top ranking in the luxury car class with a drag coefficient of 0.27. This value was achieved by a number of measures, in particular a slightly sharper slope of the front and rear windscreens, a boot lid with an integrated spoiler edge, a more tucked-in side body, a wheel spoiler in front of the front and rear wheels, a covered engine bay underbody, a sophisticated enclosure concept for the remaining underbody, and a speed-dependent vehicle lowering mechanism.
In connection with a 4.2 per cent smaller front surface area and 10 per cent lower cd value, the W 220 model series achieved a 13.8 per cent earning it a world record in this area at the time of its press launch.
Model
cd
A (m²)
cd × A
S 280 (W 220)
0.27
2.29
0.618
Measured with cooling-air flow.
 
Aerodynamics remains an important benchmark
Still today, aerodynamics is a major development objective at Mercedes-Benz and will remain so in the future. A pertinent example is the Mercedes-Benz CLA which was unveiled in January 2013. Its drag coefficient cd = 0.23 sets new standards in production vehicle aerodynamics and manifests itself positively in lower fuel consumption.
At speeds as low as 60 km/h, aerodynamic drag becomes a factor which significantly influences consumption. Just as important is the perfect harmonisation of lift coefficients at the front and rear suspension (cLF and cLR value). They allow for agile handling, strong directional stability at higher speed ranges and a safe driving feel in crosswinds. The effects of the superb aerodynamics can be felt even in the interior, where the wind-noise comfort is unparalleled in this class. This proves once again that good aerodynamics is never an end in itself, but rather has lasting effects in many directions.
126 model series Mercedes-Benz S-Class (1979 to 1992) in the wind tunnel in Untertürkheim. Photo from 1980.
80F135
Wind tunnel at the Untertürkheim plant. The origins of the wind tunnel and of the turbine date back to 1939, and it was one of the first installations used to measure full-sized vehicles.
13C487_042
Mercedes-Benz S-Class, model series 126 (1979 to 1991), in the wind tunnel at the Untertürkheim plant. Photo from 1980. This S-Class was the first Mercedes-Benz production vehicle to be systematically developed and designed with aerodynamic considerations in mind. The result: with a drag coefficient of 0.359, it far outranked the international competition in its segment.
80F134
Mercedes-Benz S-Class saloon from model series 126 (1979 to 1992). This series was the first Mercedes-Benz production vehicle to be consistently developed and designed with aerodynamics in mind. The result was that, with a cd rating of 0.36 at the end of the 1970s, it already occupied a leading position in its segment by international standards.
80F137
Mercedes-Benz S-Class, model series 126 (1979 to 1991), in the wind tunnel at the Untertürkheim plant. Photo from 1980. This S-Class was the first Mercedes-Benz production vehicle to be systematically developed and designed with aerodynamic considerations in mind. The result: with a drag coefficient of 0.359, it far outranked the international competition in its segment.
80F139
Mercedes-Benz S-Class, model series 126 (1979 to 1991), in the wind tunnel at the Untertürkheim plant. Photo from 1980. Woollen threads affixed to the body indicated where unfavourable eddy currents were occurring. This S-Class was the first Mercedes-Benz production vehicle to be systematically developed and designed with aerodynamic considerations in mind. The result: with a drag coefficient of 0.359, it far outranked the international competition in its segment.
80F138
Wind tunnel at the Mercedes-Benz Untertürkheim plant with traversing system, schematic drawing. The origin of the wind tunnel dates back to 1939, and it was one of the first installations used to measure full-sized vehicles.
87F318
Mercedes-Benz S-Class, model series 126 (1979 to 1991), in the wind tunnel at the Untertürkheim plant, together with the diesel-powered economobile, the world-record holder at the time. Photo from 1980. Woollen threads affixed to the body indicated where unfavourable eddy currents were occurring. This S-Class was the first Mercedes-Benz production vehicle to be systematically developed and designed with aerodynamic considerations in mind. The result: with a drag coefficient of 0.359, it far outranked the international competition in its segment.
80F263
Wind tunnel at the Untertürkheim plant with Mercedes-Benz 300 SL Coupé (W 198, 1954 to 1957). The origin of the wind tunnel dates back to 1939, and it was one of the first installations used to measure full-sized vehicles.
1998M326
Wind tunnel at the Untertürkheim plant with Mercedes-Benz 300 SL Coupé (W 198, 1954 to 1957). Photo from 1955. The origin of the wind tunnel dates back to 1939, and it was one of the first installations used to measure full-sized vehicles.
2007DIG896
Mercedes-Benz S-Class, model series 126 (1979 to 1991), type 280 SE, in the wind tunnel at the Untertürkheim plant. This S-Class was the first Mercedes-Benz production vehicle to be systematically developed and designed with aerodynamic considerations in mind. The result: with a drag coefficient of 0.359, it far outranked the international competition in its segment.
2007M922
Wind tunnel building at the Untertürkheim plant, historical photo. Photo from 1972. The origin of the wind tunnel dates back to 1939, and it was one of the first installations used to measure full-sized vehicles.
72204-9A
Wind tunnel building at the Untertürkheim plant, historical photo. Photo from 1972. The origin of the wind tunnel dates back to 1939, and it was one of the first installations used to measure full-sized vehicles.
72204-2A
Design model of the Mercedes-Benz S-Class, model series 140 (1991 to 1998), in the wind tunnel at the Untertürkheim plant. Photo from 1990. With a drag coefficient of 0.30, this S-Class achieved a new world record over the international competition – and also showed that a vehicle´s size and excellent aerodynamics are not a contradiction in terms.
A90F1654
Design model of the Mercedes-Benz S-Class, model series 140 (1991 to 1998), in the wind tunnel at the Untertürkheim plant. Photo from 1990. With a drag coefficient of 0.30, this S-Class achieved a new world record over the international competition – and also showed that a vehicle´s size and excellent aerodynamics are not a contradiction in terms.
A90F1653
Underbody of Mercedes-Benz S-Class, model series 140 (1991 to 1998). The covered underbody plays a key role in this car´s excellent drag coefficient of 0.30, which earned it a new world record over the international competition – and also showed that a vehicle´s size and exemplary aerodynamics are not a contradiction in terms. Photo from 1990.
D90F2062
Mercedes-Benz 220 S (W 111, 1959 to 1965) in the wind tunnel at the Untertürkheim plant. The origin of the wind tunnel dates back to 1939, and it was one of the first installations used to measure full-sized vehicles.
U5569
Loading