ASSESSMENT OF AN EMPIRICAL TECHNIQUE FOR ESTIMATING VEHICLE AERODYNAMIC DRAG FROM VEHICLE SHAPE PARAMETERS

This report presents the results of a determination of aerodynamic drag coefficient, CD, based on an empirical prediction technique developed by The Aerospace Corporation in a previous EPA-sponsored study. This method utilizes an aircraft type drag build-up approach wherein the total drag is calculated as the sum of CD contributions from components of the vehicle. Component contributions are determined from various body/chassis shape parameters. The present study was directed toward the acquisition and application of vehicle measurements data as required to evaluate aerodynamic road load by this prediction method for comparison with measured values. Twenty 1977/1978 model year passenger cars were examined for which aerodynamic drag coefficients were derived. Comparison of these results with wind tunnel test data on twelve of the vehicles showed good agreement on an average basis; the maximum disparity in an individual result was 18 percent.