1986-03-01

Drag and Driving-Stability-Related Aerodynamic Forces and Their Interdependence-Results of Measurements on 3/8-Scale Basic Car Shapes 860211

The aerodynamics of real cars is strongly influenced by both individual design details and many functional aspects like underbody treatment, engine cooling airflow, mirrors, body gaps, etc. Still, the basic shape has a considerable influence on the final aerodynamic characteristics.
To evaluate the effect of various shape parameters on aerodynamic drag and driving-stability-related coefficients a simplified 3/8-scale model with interchangeable body parts was built and tested in the new wind tunnel of Ford-Werke AG, Köln. The main dimensions of the model reflect a modern European compact size car.
The aim of this paper, is to give a concise overview of the results of the first test sessions in an extended investigation.
The main aspects of aerodynamic optimisation: Aerodynamic drag, lift, rolling moment, sideforce distribution and yaw moment, are discussed individually. Typical interactions of the different aerodynamic forces at straight-ahead and yawed conditions are also pointed out.
A general conclusion is that aerodynamic optimisation towards lower drag coefficients need not result in a deterioration of driving-stability-related coefficients. Drag-, lift-, and rolling moment reductions go hand in hand in many cases.
Conflicts with increased yaw moment are more likely to occur with rear end treatment than with front end optimization. However, as long as the main overall vehicle dimensions remain within realistic limits and extreme low drag shapes are not considered undesirable yaw moment levels can be avoided.

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