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This paper will deal with an emerging technology in the world of design known as Knowledge-Based Design, or KBE. KBE, also known as Rule-Based Design, provides the design engineer with the ability to develop a true virtual prototype of a product prior to committing to manufacturing. A virtual prototype is a combination of the design rules, or product model, and the vehicle geometry. A virtual prototype has all of the geometric characteristics, or attributes, of the product as well as all of the non-geometric attributes such as materials, mass properties, stress and deflection characteristics, etc. KBE allows the development of computer-based tools for the design engineer that extends beyond the capability of current CAD and parametric tools. The early stages of automobile design differs from the traditional method used in aircraft or marine design where there is a well-defined conceptual, or early stage, design phase.

The objective of the development of the aerodynamic drag predictive tool CDaero was for use as a module for the Automobile Design Support System (AutoDSS). CDaero is an empirically based drag coefficient predictive tool based initially on the MIRA (Motor Industry Research Association) algorithm. The development philosophy was to be able to predict the aerodynamic drag coefficient of an automobile with knowledge of the features of the surface geometry control curves. These are the curves that control the 3-dimensional geometry as seen in the profile, plan and front and rear views. CDaero has been developed in a computing environment using the equation solver TKSolver™. Fifty-one input feature values are first determined from the automobile geometry and then entered into the program. CDaero models the drag coefficient with thirteen different components covering the basic body, as well as additional components such as the wheels, mud flaps, etc.