SAE International promoting recommended practice for measuring aerodynamic performance for light duty vehicles
01 September 2011
SAE International is promoting “J2881: Measurement of Aerodynamic Performance for Mass-Produced Cars and Light-Duty Trucks”, a recommend practice detailing procedures to measure the aerodynamic performance of passenger vehicles, such as mass-produced cars and light-duty trucks intended primarily for individual consumers.
J2881, published in June 2010, provides a comprehensive overview of successful, aerodynamic testing and measurement practices in a full-scale wind tunnel.
Aerodynamic performance—primarily the aerodynamic drag coefficient (CD)—relies significantly on vehicle content and loading, as well as the type, scale and simulation qualities of the wind tunnel used to make the measurement. The recommended practice is critical to the automotive industry because publication of non-standard test results generates an incorrect perception of a vehicle’s anticipated aerodynamic performance by government, academia, and the general public.
J2881 is used by manufacturers for measurement and documentation for a particular vehicle. The intent is to promote uniform test protocols and traceable results of published aerodynamic performance.
As fuel economy standards become more stringent and fuel prices continue to increase, aerodynamic performance naturally becomes a more prominent part of the product development process. We are combining the best practices of automotive wind tunnels around the world so that J2881 will provide a meaningful metric for both consumers and manufacturers. We anticipate seeing published or advertised aerodynamic performance as “measured according to SAE J2881” just as we already do with J1349 for engine horsepower. Doing so will provide a better picture for the consumer and also enhance the reputation and credibility of the aerodynamics discipline.—Dr. Joel Walter, sponsor of J2881 and Chairman of the Road Vehicle Aerodynamics Committee
Testing a vehicle in a lab environment has its limitations. Do they for example measure aerodynamic performance in crosswinds and turbulence? Every day life is not like a wind tunnel which is designed to generate a perfect airflow.
There is a noticeable rise in the fuel consumption of my Prius even in moderate winds. The Prius may have a very good Cw, but I suspect a lot of the advantage is lost in windy circumstances. Which is nearly always where I live.
Posted by: Arne | 01 September 2011 at 11:27 PM
The Prius is high and offer big lateral surfaces with vertical sidewalls like shape so clearly in side winds it is a disadvantage. Some car makers test their cars under lateral wind loads.
Posted by: Treehugger | 02 September 2011 at 09:49 AM
With all of the computing power available for tless than a dollar and also the cheap modern sensors, every automobile could give a real time indication of the kilowatts delivered to the wheels. People with big expensive engines would be the most surprised to see the actually delivered value. A 1981 automobile gave an estimate of the fuel consumption which is very similar. A value of about 200 watt-hours per mile was determined by electric automobile makers. At thirty miles per hour, this is only six kilowatts. ..HG..
Posted by: Henry Gibson | 02 September 2011 at 09:48 PM