Great Dane Trailers is building a handful of aerodynamic trailers to help Wal-Mart’s private fleet determine how it might boost fuel savings without compromising ease of use of dry vans by drivers, warehouse workers and others.

“What’s central to understanding this prototype is that the customer drives the trailer specs,” John Jones, Great Dane research engineer, told FleetOwner. “They [Wal-Mart] are giving us the freedom to put our theoretical knowledge into practice to come up with a design that reduces aerodynamic drag to improve fuel economy yet is still functional and practical to use in everyday freight operations.”

At first glance, the Great Dane prototype, which recently appeared at a Department of Energy news conference, looks more like a low-floor moving van than a typical freight box-- and for good reason. Great Dane is using a special air suspension that lowers the freight floor to reduce airflow resistance but raises it back to dock level for loading and unloading freight.

To cut weight, the trailer’s all-aluminum wheels are equipped with wide-base tires. These also make it easier for drivers to check tire pressure, as they need only check four tires as opposed to eight. Retractable side skirts – lowered automatically when the trailer goes over 35 mph for a sustained period of time then automatically retracted when under 35 mph – reduce crosswind resistance and smooth out the profile, said Jones.

An 8% smaller frontal area reduces the trailer’s forward drag, while a unique inset rear door that creates a “cavity” at the rear of the trailer reduces turbulence and drag.

“All of these design enhancements use ‘off-the-shelf’ components,” said Jones. “It’s certainly more expensive to build a drop-deck trailer like this and incorporate extra solenoid valves to deploy and retract the side skirts. Also, cubic volume is reduced due to the inset door and smaller nose area but weight capacity isn’t. These are the trade-offs to get better fuel mileage over the life of the trailer.”

While the verdict is still out on the structural integrity, durability, and practicality of this new design, Jones said Wal-Mart is indicating the trailer’s drag has been chopped by 7% to 8% – resulting in a fuel economy improvement of 3% to 4%.

“Our goal is to design practical aerodynamic solutions that lead to immediate fuel savings,” added Charlie Fetz, vp-research and development for Great Dane. “Incorporating important aerodynamic concepts into a very functional trailer is our goal… and Wal-Mart’s request for an experimental trailer as a way to save fuel is both the motivation and momentum behind this project.”