Mack, Volvo studies show aerodynamic modifications can improve fuel economy

Truck News

WASHINGTON, D.C. — Simple modifications to heavy truck aerodynamics could provide a decrease in fuel costs, according to studies by Mack and Volvo. The OEMs findings were displayed during an event outside the US Department of Energys headquarters in Washington, D.C.

According to a two-year study by Mack, truck operators could improve their fuel economy by as much as 8% by facilitating smooth air flow around their tractor-trailer units during highway travel.

Mack officials said that results of the study demonstrated that significant fuel savings can be achieved by enclosing the gap between the tractor and trailer, and equipping the trailer with what are referred to as side skirts and a boat tail to improve its aerodynamic profile while on the road. The side skirts which attach to the bottom edges of the trailer on both sides and run nearly its entire length are designed to help minimize overall drag by preventing air flow from interacting with the underside of the trailer, as well as the axles and wheels. The boat tail is another two-piece drag-reducing system that is affixed to the rear of the trailer.

Mack engineers are already looking to generate an actual production gap enclosure based on the rough prototype used in the study. The company is also sharing the results of the project with trailer manufacturers who might consider incorporating side skirts and boat tails.

Volvos research showed a 2.3% improvement in fuel economy through the use of four modifications to a typical highway tractor and trailer. Three of the modifications are prototype designs, while the fourth is already available on Volvo trucks.

Volvo addressed improving airflow under the vehicle and reducing the interaction between the underside and the gap between the back of the tractor and the trailer. Controlling airflow on the underside of tractor-trailer combinations can reduce the amount of turbulence and aerodynamic drag produced by a moving vehicle when air rushes by axles, wheels and other objects, the company said.

Three devices were used for underside airflow management, said Michael Sorrells, Volvos lead design engineer for aerodynamic development.

The first was a smooth underside area on the front of its test truck, essentially an extension of the bumper made from composite material.

The second modification was a plate between the chassis rails on the space between the back of the cab and
the fifth wheel, called a deck closure.

The most noticeable modification was on the trailer, where Volvo installed an air deflector that wrapped around the front and sides of the trailer bogie. Sorrells said this reduces drag by smoothly moving air around trailer wheels and axles, which otherwise act as a dam to the airflow. Though the company said the air deflector is not as effective as a full aerodynamic skirt on a trailer, it is designed to be smaller, lighter and less susceptible to damage.

The final modification involved the use of roof and side fairing extenders already available to customers from Volvo. These extenders reduce the gap between the rear of the tractor and the front of the trailer. The roof extender can be adjusted to not only reduce the trailer gap, but to optimize aerodynamics when using trailers of different heights or with different kingpin settings.

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