The Actros consumes up to five per cent less fuel than its predecessor. This is in part due to its improved aerodynamics. This was achieved through testing on the computer, on the road and, indeed, in the wind tunnel.

The enormous blower could easily be the backdrop for a new Hollywood production, serving as the engine of a gigantic spaceship, for example. The axial blower has a diameter of 8.5 metres, while the nine red-painted wings are each 2.5 metres long. Pictures are actually being taken at the facility on the day we are there. There was no movement involved though, rather they were portrait photos of Michael Hilgers, Head of CAE Vehicle Functions in the Commercial Vehicle Development at Mercedes-Benz. 

Here, in the Daimler AG wind tunnel in Untertürkheim near Stuttgart, Hilgers and his colleagues have been instrumental in ensuring that the Actros is more aerodynamic and thus more fuel-efficient than all of its predecessors.

The following figure shows the importance of aerodynamics. In a current truck in long-haul operation in Europe, around one third of the available mechanical energy is used to overcome air resistance. The lower this resistance, and thus the more aerodynamic the truck, the lower its consumption. The Actros enables fuel savings of up to five per cent compared to its predecessor. As much as 1.3 per cent can be attributed to the aerodynamically optimised MirrorCam alone, which replaces the conventional external mirrors.

But how do the engineers actually carry out the testing? The wind tunnel blower can produce storms with speeds of up to 250 kilometres if required. The vehicle is positioned on a hub with an integrated scales for the tests. This enables a wide range of flow conditions to be simulated.

The goal of these simulations is to optimise the cd-value, or the drag coefficient, of a truck. “We carry out random testing here to verify the aerodynamic improvement of concept components,” says Michael Hilgers, explaining the basic approach. “The computational flow calculation always runs in parallel. This digital simulation is based on computational fluid dynamics, or CFD.” The aerodynamic measures are also validated in road use.

With the Actros, the wind tunnel work provided valuable insight into the design of the MirrorCam, as well as for the positioning of its camera arms to the right and left of the driver's cab. “The top and bottom parts of the A-pillar and the top part of the B-pillar were discussed,” Michael Hilgers explains. 

A real Actros was used for the tests, where the wing mirrors were replaced by prototypes of the camera arms – installed one after another in the three positioned being tested. The truck was positioned on the scales and the blower started up. The scales enabled the engineers to measure the aerodynamic force acting on the vehicle as the air flows around it. Result: the optimal position for the camera arms is in the A-pillar in the edge of the roof.

A solution was also sought to prevent scattered light coming in from above from impacting the performance of the cameras. During these tests, the small roof with which the MirrorCam arms are now equipped proved successful. The engineers also played a major role in the development of the new, concave-shaped end flaps of the driver’s cab. The optimised end flaps also ensure that the Actros requires less fuel than any of its predecessors.

In addition to reducing fuel consumption, the engineers also look at dirt retention during the tests in the wind tunnel and the CFD analyses. “This mainly involves safety-related areas such as the front and side windows and the camera arms lenses,” Hilgers explains. “Aerodynamics influences the amount of dirt from your own vehicle and from the vehicles ahead that will stick.”

It is not only the aerodynamics specialists’ own work that is so important, but also coordination with colleagues from other key disciplines, particularly with the designers and constructors. After all, not everything that is useful for aerodynamics is necessarily desirable from a design perspective or feasible for constructors. 

Conversely, the aerodynamics specialists need to veto some of the ideas from their colleagues. “Ultimately, everybody involved is aware of one thing,” Michael Hilgers adds. “The goal is always to develop the best-possible solution together.”