The Aero Spec

| November 16, 2008

Normandin Transit of Quebec focuses on aerodynamics and fuel-saving techniques for its fleet of 250 trucks and 500 trailers that covers the United States and Canada. To boost fuel economy, the company uses trailer skirts and APUs to reduce idling and outfits trucks with wide-single tires, such as those on this Kenworth T660, one of three the company recently spec’d for its aerodynamic features.

Next time you’re rolling down the road at 65 mph, stick your arm out the window. Hold your arm straight up and feel the wind pushing against it, then lower your arm and feel the resistance disappear. That gives you an idea of the dynamic at work between your truck and the air.

At 55 mph, half the energy generated by your truck is devoted to moving air around your vehicle. Speed up to 65 and two-thirds of the energy at your disposal is required to slice through air. The bottom line is the more you make aerodynamics work for you, the less you have to fight the wind and the less fuel you have to burn.

Aerodynamics is an industry buzzword these days. Truck manufacturers are incorporating aero-consciousness into the styling of their newest models and beefing up education for their customers. For example, Volvo Trucks North America recently launched Fuelwatch as a means to help owner-operators and fleet managers achieve maximum fuel economy through proper specs, maintenance, monitoring and driver development.

Everyone’s paying attention, of course, as fuel costs soar. For instance, the last three trucks bought by Normandin Transit of Napierville, Quebec, were new Kenworth T660s, a more aerodynamic update to the manufacturer’s classically aero T600. A 2006 study by the Truck Manufacturers Association and the U.S. Department of Energy concluded that performing a wide range of aerodynamic improvements on a single vehicle could achieve a 23-percent reduction in aero drag, or more than 11 percent in increased fuel economy. In the unlikely event that every tractor/van semi-trailer combination adopted these technologies and boosted fuel economy by 10 percent, the industry could achieve fuel savings of about one billion gallons per year.

“With an aerodynamic truck, when you start adding all those features up, you could be looking at 30- to 40-percent difference in aerodynamic drag,” says Ron Schoon, chief engineer for aerodynamics at Navistar.

The rule of thumb is that a 2-percent reduction in aerodynamic drag will reward you with a 1-percent improvement in fuel economy. While many trucking operators prefer a traditionally styled, boxy-looking truck, an aerodynamic model could save you four cents per mile or more in fuel, according to Peterbilt. A full cab fairing by itself could save 8 to 12 percent in fuel economy.

“The whole idea of aerodynamics is to get airflow up over and around the trailer,” says Ben Smith, manager of product strategy for Freightliner on-highway vehicles. If your roof fairing is just a few inches shy of the top of your trailer, he says, “you’re wasting a few percentage points of fuel economy.”

Spec’ing an axle-back model is a common aerodynamic choice, Smith says, as it allows air to flow more easily around the bumper and past the front tire. Another is attaching fairings around fuel tanks and battery boxes, which can result in up to 3 percent increased fuel efficiency depending on the model. “If averaging 6 mpg and driving 120,000 miles per year and paying $4 per gallon, you’re potentially going to save $2,700 per year,” Schoon says.

Smith also recommends moving wind-catchers like exhaust stacks and antennas to behind the cab and choosing streamlined mirrors over West Coast mirrors. “Mirrors can have a huge aerodynamic penalty,” Smith says. “You want to reduce the number of attachment points and to make the mirror more aerodynamic in shape.

“You pay a penalty if you don’t pay attention to aerodynamics. About 30 to 35 percent of fuel economy is aerodynamics. Tires and rolling resistance is one segment, engine and drivetrain is another, and aerodynamics is the third area of a payback that is money in your pocket.”

Financing to Save Fuel
Economic conditions are discouraging owner-operators and small fleets from investing in technologies to improve fuel economy, says Sharon Banks, founder and CEO of Cascade Sierra Solutions, a non-profit group with two locations in Oregon (including at Jubitz Travel Center) and one in California (Sacramento), dedicated to saving fuel and reducing emissions from heavy-duty diesel equipment. “Fleets are finding it hard to get financing, and many companies are strapped to the gills,” she says. Financing help is available.

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