GREAT DANE TRAILERS, International Truck and Engine Corp, and Wal-Mart don't know exactly what the future holds, but they like the view from here.
The three companies announced in November that they had collaborated on an experimental aerodynamic trailer that could ultimately be integrated into Wal-Mart's fleet, providing fuel savings while allowing drivers and warehouse workers to continue to use dry vans the way they have been.
Charlie Fetz, Great Dane's VP of research and development, credits Wal-Mart — which has the nation's second-largest fleet of trucks and a billion-miles-a-year travel log — for innovatively pushing the envelope and incorporating research Great Dane has done over the years.
“We've worked on aerodynamics for a long time, but you don't often have a customer that steps up and is committed to moving forward with it as Wal-Mart has,” he says. “I think aerodynamics for trailers definitely works. I'd hesitate to say aerodynamics is in its infancy, because it's been around for a long time. Things like skirts and other types of devices have been around, but they really haven't taken off.
“It's like anything else — until they get out there and get used a lot and refined and they work well in people's operations and people are comfortable that the cost benefit is sufficient for their purposes, there's reluctance. To me, the significant thing about this project is that Wal-Mart is committed and is taking what would appear to be a step in the right direction.”
The experimental trailer has external geometric features designed to improve trailer aerodynamics and reduce fuel consumption by the tractor, which is important because according to the US Department of Energy, Class 8 trucks account for 11%-12% of total US petroleum consumption, and 50% of their energy expenditure is in overcoming aerodynamic drag at highway speeds.
The trailer utilizes improvements in three key areas to reduce drag and at the same time meet necessary design and functional criteria. Reductions in frontal, underbody and base (rear) drag are designed to accompany efficient tractor aerodynamic design, leveraging the benefits of both and leading to significant improvements as compared to conventional equipment.
Reduced overall height (by one foot) contributes to an 8% reduction in frontal area. Cargo volume is maintained by utilization of a drop-deck configuration, while a “maxi lift” suspension allows the trailer to adjust to a normal dock height for loading and unloading — making the trailer look more like a low-floor moving van than a typical freight box.
Deployable underbody skirts improve aerodynamics, particularly in the presence of crosswinds. Below 35 mph, the skirts are raised to improve ground clearance. Above 35 mph, they automatically deploy to improve aerodynamics and reduce drag.
The aft section of the trailer is tapered to help keep airflow attached to the trailer body better than conventional square construction. A “cavity back” increases pressure behind the trailer. Both design details effectively reduce the trailer's “wake”, contributing to reduced drag and improved economy.
The trailer also makes use of single-wide tires to reduce weight, reduce rolling friction, and reduce fuel consumption. It's also equipped with smooth wheel covers to reduce drag associated with the wheels and tires.
Wal-Mart believes the trailer's drag has been reduced by 7% to 8%, resulting in a fuel-economy improvement of 3% to 4% — meaning that a fleet the size of Wal-Mart's could potentially save the equivalent of 7.6 million gallons of diesel fuel a year.
International says its Department of Energy-funded project has produced systems and devices that reduce the aerodynamic drag of Class 8 tractor-trailer applications by 14%, substantially increasing fuel efficiency and potentially saving millions of gallons of diesel fuel.
“The Energy Department estimates that Class 8 trucks consume as much as 12% of the US petroleum supply and half of that is spent overcoming aerodynamic drag at highway speeds,” says Patrick Charbonneau, International's VP/government relations. “The industry must continue to squeeze as much performance as possible from these heavy trucks while also limiting the drain on natural resources and, ultimately, the cost to customers. That's what this initiative is all about.”
During the two-phase program managed by the Truck Manufacturers Association on behalf of the Department of Energy, International employed wind-tunnel and on-road testing and partnered with Great Dane to develop the experimental trailer for Wal-Mart.
International focused on the three major sources of aerodynamic drag in the typical Class 8 tractor-trailer application - the tractor-trailer gap, trailer side, and trailer wake. The tractor-trailer gap was addressed with two alternative solutions involving partial gap closure and total gap closure. Various trailer-skirting options were developed and evaluated to improve the aerodynamic performance of the trailer side. For the trailer wake, International considered the impact of varying taper lengths, angles, and shapes.
International also has completed early testing of a trailer forebody device and automatically deployable tractor side extenders. Both technologies impact air flow traversing the gap between the tractor and trailer. Initial on-road tests reveal an additional 2% fuel-economy improvement.
Wal-Mart has been testing the trailer at the Goodyear Proving Grounds in San Angelo, Texas, and at International's facility in Fort Wayne, Indiana. Wal-Mart wants to discover the full benefits and to try to understand operationally what the impact would be to real business in the company's application.
“We've been trying to add some pieces to the trailer as far as aerodynamics at the tail end to clean up some of the air that's coming off the back of it,” says Mark Helms, Wal-Mart's fleet maintenance manager. “We haven't been able to put it into a real-world application at all yet to see if operationally the crew could load it the way it needs to and unload it at the store the way it should be.
“The trailer is one foot shorter in height, so we have to modify the truck air fairing, too. So we are working with International to develop something where we get the full benefit of the package being one foot shorter.
“The side skirts are an area of concern. They deploy when you slow down and they retract back up. Hopefully, that will clear all the pits where we back down to unload. We've done the measuring, and if everything works the way it should, we'll be able to work with that.”
The project was born out of Wal-Mart's company-wide initiative to save energy, not just fuel in transportation. Its eco-initiative calls for the efficiency of its vehicle fleet to increase by 25% over the next three years and double in 10 years; a 30% reduction in energy used in stores; and a 25% reduction in solid waste from its US stores in three years.
Fetz says Wal-Mart came to Great Dane and asked, “What could you do to potentially offer some improvement in anything related to the products you sell us?”
Fetz and Adam Hill, Great Dane's engineering liaison manager, met with Wal-Mart officials in September 2005 to talk about trailer aerodynamics. When Great Dane officials went back a month later, they showed Wal-Mart officials two straight-frame trailers and two drop trailers. After Wal-Mart made its selection, Great Dane officials worked on the design in the first two months of 2006, then built it in its Brazil, Indiana, manufacturing plant. The trailer was delivered to Wal-Mart in June.
Helms says Wal-Mart is excited about the possibilities.
“From where we began three years ago, it seems like it's really moving faster than we expected when we first started working on this project,” Helms says. “There's a lot more interest out there today than there was.
“It's exciting to be able to look at new things and try to be innovative and be out there leading. But I think this is just the first step of where we're headed. We're actually looking farther down the road past this trailer. We're excited about going farther forward with technology, trailers, and tracks as far as hybrid vehicles and alternative fuels.”