Doing the Math for Fuel Efficiency with Aerodynamics
The science of aerodynamics as it pertains to the trucking industry isn't new, but fleets are beginning to really take heed and look at the fuel efficiency provided. There are still some who aren't ready to move to aerodynamic devices because they don't look traditional when on a trailer, but many are seeing the positives and diving in head first.
Avantechs' VorBlade Wing side fairings can be purchased as individual units to be used on a tractor or trailer or as side fairings for a trailer.
"It's a totally different world than we saw back in 2006 and 2007," said Jeff Grossman, vice president of engineering with ATDynamics. "It is understood in our industry today that the most competitive and profitable fleets are the ones that are adopting aerodynamic technologies ahead of their competitors."
When the results of the U.S. Department of Energy's SuperTruck Program are released next year, Grossman believes understanding by fleets about the powers of aerodynamics will only deepen. Then the program was established in 2010, the goal was to boost commercial vehicle fuel economy to twice the baseline number at the time. Fleets adding aerodynamic devices to their trucks have helped.
"We're already seeing releases stating that number is going to be met," said Grossman. "Aerodynamic devices have played a huge role in hitting that number."
One thing that's important for fleets to remember is to have realistic expectations of what aerodynamic devices can do to their fuel economy numbers. Fuel efficiency percentage boosts based on device combinations aren't cumulative, and to understand the actual increases, a fleet needs to look at the tractor and the trailer as a complete system.
"Each piece that is added will have an effect on the total system," said James Scarcelli, VP and GM for Wabash Composites. "If a gap reducer is added to a system that already has a skirt, the aerodynamic change also will affect the aerodynamics around the skirt. In most cases, you are dealing with the law of diminishing returns - the more you add, the less each part can contribute to the total system."
Wind, weather, temperature, terrain, road conditions and countless other factors can make calculating fuel savings accurately a maddening exercise. For many fleets, it could be more accurate to measure aerodynamic efficiency gains in miles per gallon instead of drag percentages.
"Air drag is a force that drains an amount of certain power from the vehicle's engine," said Natalie Melomed, senior business analyst for VorBlades. Melomed says air drag depends on the vehicle's shape and size, speed and weather conditions. It does not, however, depend on load weight, tire style or type of engine or transmission.
She gives an example of an empty truck with no aerodynamic devices attached. That truck could be getting 8.5 miles per gallon and 8.8 miles per gallon with an aerodynamic device attached. But add a payload of 45,000 pounds and the number drops to 7.5 miles per gallon without the device and 7.8 miles per gallon with the device. Even though the vehicle's overall drag was reduced, the powertrain would have to work harder to move the weight. The 0.3 mpg increase remains the same, but the percentage of fuel savings is changed, so it's important to look at all angles.
Grossman agrees that using the mpg is an excellent way to talk to drivers about the benefits of aerodynamic devices. ATDynamics uses another formula - gallons saved per 1,000 miles driven. It's a pretty simple calculation that also allows for a large enough sample to view results.
To calculate that, simply take the number of miles a tractor-trailer drives per year and divide that by 1,000. Then multiply by a selected device's fuel savings number per 1,000 miles, which at 65 mph is 8 gallons. That means a vehicle running 60,000 miles annually will save 480 gallons of fuel over the course of a year, which at the current average cost of diesel of $3.892 means that driver would save $1,868.16.
One big thing to keep in mind is that aerodynamics can help short-haul trucks as well. The impact won't be quite as big, but aerodynamic drag contributes to about 25 percent of the fuel consumption for a short-haul trucker.
Whatever the route driven, aerodynamics can play a big role in boosting fuel efficiency which adds to that always important bottom line.
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