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## Wind Tunnel 1

#### Assignment

Although the battle against excess weight was won by the body work manufacturers, it was lost again through more safety and comfort, the search for a streamlined shape counts to the successes. Although, there are tendencies to once again, gamble away the saved energy through larger cross-sectional areas, indeed, the drag coefficient, which is a pure value of the aerodynamic shape, could be lowered in the next 40 - 50 years by 0,4 - 0,5 to under 0,3. This is also very important, because with modern vehicles, even at much less than 50 km/h, the air resistance exceeds the rolling resistance and then increases to the square of the speed.

#### Function

In the model in the above picture, it is shown how the value is determined. The vehicle is placed on a movable base-plate, in a turbulence-free air flow, whose speed can be exactly adjusted. Not only the type of flow is important, also the width and height of the tunnel must be sufficient. If one now determines, how much force is to be applied to the base-plate or to the vehicle, one can, with a given cross sectional area, calculate the drag coefficient.

The reduced size model does not always allow conclusions regarding the behaviour of a full-size vehicle. Normally one reduces to a maximum of 1/5 of the original size. Modern mass-produced motor cars achieve a max. value of 0,25, whereby the large saloons do have an advantage. All the others still lie at above 0,3, some of them, clearly higher.
The drag coefficient of motorcycles is particularly unfavourable. In this case, the fairing, the add-ons and not least, the riders position also play a role. With the rider folded in behind the fairing, the value can lie anywhere between almost 0,5 and much higher than 0,6. Nevertheless, the single- track vehicle can, because of the low cross sectional area, reach speeds in excess of 200 km/h with only 50 kW (69 Hp) of power. 10/10

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