The first priority when constructing a SolarCar is of course the energy efficiency. Key features are the aerodynamic characteristics of the car’s body: the more streamlined the body is the less energy must be spent to drive the SolarCar.
Experts at Work
But how can the aerodynamic properties be measured? How can these properties be adjusted afterwards?
These measurements and adjustments can only be managed with expert’s help: for the second time the project’s partner Daimler invited the team to test the SolarCar in their wind tunnel in Stuttgart. This institution has a long history and in the 1940s the wind tunnel was launched as first research institution worldwide to measure the aerodynamic qualities of life-sized cars and even large utility vehicles.
With a maximum motor capacity of 5,000 kW the gigantic fan generates wind velocities of up to 250 km/h – making all kinds of wind related measurements possible.
The blue.cruiser does not have to stand such strong velocities – gentle 70 km/h simulate the average travel speed during the BWSC. The car is placed on a rotating platform to simulate various influences including cross-winds.
The team is mainly interested in the number which is in the centre of all attention these days: the cd value. This figure was calculated beforehand by the constructionists – and now they will find out whether their theoretical calculations are also valid in practice.
But why is this figure that important?
To put it in a nutshell: the figure describes the overall aerodynamic drag of the SolarCar. The smaller the figure the better, so that the blue.cruiser will not be out braked by the wind to strongly and to be as energy efficient as possible. “We can positively influence the cd value by adding attachment parts such as rear spoiler or a so-called shark fin, which can also be found on airplane wings.” Leonie Drüppel, chief of Aerodynamics, explains. All parts are self-constructed, of course.
Preparations for the BWSC
And what is all the fuss about? “The better we know about the actual air drag generated by the blue.cruiser, the better the strategists can calculate how much energy is consumed during the challenge and what distance can be travelled with the given battery charge.” Leonie adds. This knowledge contributes crucially to victory or loss and planning the battery consumption is probably the biggest challenge of the BWSC.