| AerodynamicsA key consideration when designing a vehicle body are the aerodynamics, which have an impact on fuel consumption, top speed and acoustic levels. The drag coefficient (Cd value) as measured in the wind tunnel is the figure generally quoted in publications in relation to a vehicle's aerodynamic qualities. A number of variables influence the Cd value, including the vehicle shape (saloon, estate or fastback). Narrow gaps and joints reduce the buffeting effect, thereby helping to keep drag low. The design of the underbody also has an effect. Special plastic underbody panelling produces favourable flow characteristics. In addition to its aerodynamic qualities, the plastic panelling also protects the underbody from flying stones, it is lighter than the conventional underseal and it can be easily recycled. Aerodynamic drag is caused by the displacement of the air surrounding the vehicle and the friction between the air and the surfaces of the vehicle as it passes over them. The drag acts against the vehicle's direction of travel and varies depending on the vehicle's road speed, the size of its frontal area, the drag coefficient (Cd) and the air density. Aerodynamic drag is calculated using the following formula: Drag = vehicle speed squared x frontal area x Cd value x ½ air density. The typical streamlined Volkswagen body design is combined with narrow gaps and joints to reduce buffeting and keep drag low, which in turn translates into favourable fuel consumption and lower fuel costs. The most critical variable is the vehicle speed, however, as doubling the speed quadruples the aerodynamic drag. |
