ARB Research Seminar

This page updated June 19, 2013

Advanced Devices for Rear Drag Reduction on Tractor-Trailers

Chuck Horrell, P.E., Vice President of Engineering, Advanced Transit Dynamics Inc., South San Francisco, California

August 11, 2010
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


The purpose of this project was to explore the commercial feasibility of two separate Active Flow Control (AFC) technologies and compare them to the current best-in-class passive drag-reducing technologies available to improve the fuel efficiency of tractor trailers through aerodynamic improvement. At highway speeds aerodynamic drag accounts for more than half of the fuel consumed by a modern tractor trailer, and any device that can reduce this drag has significant market potential. AFC has been proven to reduce aerodynamic drag in the lab and in some aeronautical applications, but has never been developed on a wide scale in the freight industry. Advanced Transit Dynamics Inc. (ATDynamics) collaborated with two different research institutions to develop full-scale prototypes for tractor trailers based upon their respective AFC configurations and then conducted SAE standardized testing of these devices alongside the leading passive drag-reducing devices.

The first concept was developed at the Georgia Tech Research Institute (GTRI) and produced a constant steady flow of air that curved around a fairing shaped to direct this airflow into the low-pressure region at the rear of a trailer. The second concept was based upon technology developed at the Tel Aviv University (TAU) in Israel and incorporated a row of suction holes to pull off the base layer and then a series of ejection ports that were synchronized to oscillate at a prescribed frequency in ejecting a flow of air. The passive devices tested included skirt fairings to block flow below the trailer and the ATDynamics TrailerTail to reduce the size and turbulence of the wake behind a trailer.

Testing was conducted at the Goodyear Proving Grounds and was done in accordance with the SAE J1321 standard procedure. The GTRI device showed very little drag reduction potential. The TAU device showed some measurable drag reduction, but the energy input required largely negated this. The passive devices showed significant drag reduction, consistently improving fuel economy by 9% or more. For next steps, the researchers at TAU have identified some potentially significant improvements in the design that should increase drag reduction while decreasing required energy input. These changes will be pursued as part of a secondary grant and partnership. The passive devices tested are being aggressively pushed into production and marketed to North American trucking fleets to significantly increase fuel economy of the freight industry.

Speaker Biography

Chuck Horrell, P.E., is Vice President of Engineering, Advanced Transit Dynamics Inc. (ATDynamics), South San Francisco, California . Mr. Horrell has been leading the product development efforts of ATDynamics since 2006. Before coming to ATDynamics Mr. Horrell worked as a design engineer for the Ford Motor Company doing suspension design on their truck lines and development of advanced chassis control systems. Mr. Horrell received a Bachelors of Science in Mechanical Engineering from Dartmouth College and a Masters of Engineering Management from the Thayer School of Engineering.odngine platforms.

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