Southfield, Mich., February 9, 2009 – Exceptional aerodynamics have long been credited with significantly increasing a vehicle’s fuel economy in addition to providing a quieter, more comfortable ride with less driver fatigue. Accordingly, Cd, or drag coefficient – the measurement of vehicle aerodynamic efficiency – has become a hotly contested performance statistic among automakers in the race for best-in-class fuel economy.
However, comparing drag coefficient among manufacturers is often an ‘apples to oranges’ affair. This is primarily due to differences in wind tunnel facilities where drag coefficients are measured, and to a lesser degree, from variations in testing methodologies.
From a product development perspective, accurate comparisons between products are critical to creating competitive aerodynamic designs. Also, establishing a method to calculate disparities between the various test environments has been a desire among automotive manufacturers for years – not to mention, finding ways to share testing costs.
Today, both are realities, thanks to the efforts of the United States Council for Automotive Research LLC (USCAR) Aerodynamics Working Group, which was formed in 2005 to create a collaborative environment where Chrysler LLC, Ford Motor Company and General Motors Corporation could share aerodynamic benchmark test data and strengthen the U.S. manufacturers’ aerodynamic technology base through sharing non-competitive ideas and technologies.
Before the group could expand its state-of-the art aerodynamics research, it needed to figure out how to compare measurements between the large wind tunnels of each manufacturer. The group began by performing correlation tests on the wind tunnels of Chrysler, Ford and GM, each of which has a substantially different design.
“We designed a meticulous test program to examine the differences in the aerodynamic data generated on example vehicles under similar configurations and conditions,” said Nina Tortosa, chair of the USCAR Aerodynamics Working Group and GM aerodynamics engineer and. “To our delight, the differences between the three turned out to be less than expected.”
Still, the group had to crunch the numbers to develop a formula that would calculate the differences among the facilities to provide a “curve fit” adjustment so that vehicles tested in one wind tunnel could be compared to tests in other tunnels.
Having completed that task in early 2006, the group began work on the Aero Data Exchange where aerodynamic data tests could be “rationalized” through the curve fit calculations and stored in a database. With the data exchange, engineers can access aerodynamic data on products already on the market and improve the aerodynamic efficiency of products under development faster than ever before.
“We started exchanging data at the beginning of 2007 and now have more than 130 vehicles in our database,” Tortosa said. “On more than one occasion we’ve been able to avoid duplicate vehicle rentals because they were already tested by one of our members and added to the database. Our European counterparts have also expressed interest in sharing our tunnel correlation and potentially extending it internationally.”
Tortosa received a USCAR Special Recognition Award last May for her work on the project, having created the reporting template and the shared database. She also co-authored the report on the group’s efforts and presented its findings at the 2008 SAE World Congress in Detroit, Mich.
Founded in 1992, USCAR is the umbrella organization for collaborative research among Chrysler, Ford and General Motors. The goal of USCAR is to further strengthen the technology base of the domestic auto industry through cooperative research and development.
For more information, visit USCAR’s Web site at www.uscar.org