Institut für Fahrzeugtechnik / Automotive Engineering
Institutsleiter: Dr. Kurt Steiner

FH JOANNEUM Gesellschaft mbH
Alte Poststraße 149
A-8020 Graz
Tel.: +43 (0)316 5453-8400
Fax.: +43 (0)316 5453-8401
FH-JOANNEUM - Institut für Fahrzeugtechnik / Automotive Engineering

Aerodynamic Drag Analysis

The programs "Cw Aerodynamic Drag" and "aero-drag calculator" were developed to facilitate data reduction and data analysis of on-road aerodynamic drag investigations using the coastdown method. This method usually demands the measurement of vehicle velocity, airspeed, yaw angle and some additional environment characteristics like temperature and air pressure. However, if one is only interested in aerodynamic drag differences due to modifications of the vehicle's outer skin, it is, in principle, only necessary to measure the vehicle's speed-time history during the test, from which the road load results can be derived by mathematics of inversion.

The velocity data of different aerodynamic vehicle configurations is then reduced simultaneously by constrained linear inversion of the equation of motion. The differences in rolling resistance are kept minimal during the inversion, which is reasonable for the relative comparisons of the aerodynamic configuration changes.

Both programs were written at Joanneum University of Applied Sciences, Department of Automotive Engineering. They were student research projects undertaken by teams of three students in their third semester ("Cw Aerodynamic Drag" by Bernhard Lang, Christian Papst and Khai Vidmar, and "aero-drag calculator" by Susanne Baschnegger, Lukas Gohm and Christian Nußbaumer). Both programs serve the same purpose and differ only in style and handling (for instance "Cw Aerodynamic Drag" makes use of MS Excel for data plots, while "aero-drag calculator" uses a different plot style). They are available free of charge and can be downloaded from
as zip-file, which includes the programs with the setup routines and six coastdown velocity data files that can be used for program testing (ConfigA1.txt, ConfigA2.txt, ConfigB1.txt, ConfigB2.txt, ConfigC1.txt and ConfigC2.txt - A,B,C represent the different configurations, 1 and 2 form one pair of consecutive coastdowns). The programs are written in ANSI C with Visual Basic GUIs and can be operated on MS Windows operating systems. Both programs include a manual, which is available by pressing the "help" button. You can find additional information concerning the method and the mathematical algorithm in use in: On-Road Aerodynamic Drag Analysis by Simultaneous Linear Inversion of the Equation of Motion, G. Bischof, E. Bratschitsch and M. Mandl, SAE Technical Paper 2005-01-1456 (2005).

Although the programs were tested carefully, we cannot guarantee that the program is free of errors or that it will meet your requirements. Unfortunately we cannot provide technical support for either program, nevertheless feel free to contact us if you have any comments or if you need further information.

Günter Bischof, Graz, 2005-03-18