Feature Article: The Dynamics of Aero
Silver Eagle Manufacturing takes a parallel-wall approach to its trailer skirting. Since it positions its skirt 18 inches off the ground to avoid banging into curbs, docks and other structures, it installs a second skirt 14 inches in from the outer skirt. “That wall catches air that gets inside the first wall and creates a vortex between the two walls, keeping air from getting beneath the trailer,” says Mark Jurman, sales and marketing vice president. “Wind blows across the tires and out the back of the trailer.”
ATDynamics offers a package of Transtex skirts and a TrailerTail at the back door that achieves fuel savings of 9.5 to 11.5 percent, says Andrew Smith, president and CEO. The package costs $5,000. Smith says the tail helps calm the turbulent airflow at the trailer’s back end and also reduces spray.
Mind the gap
The trailer’s back end and the tractor-trailer gap are aerodynamic hotspots for Airtab LLC. The company designs and makes wishbone-shaped “vortex generators” aimed at minimizing aerodynamic drag when attached vertically at the back of the trailer next to the doors or the sides of the tractor cab. “Each Airtab creates two counter-rotating vortices – like when you pull the plug on your bathtub and the swirl that’s created by water rushing down the drain,” says Jack Latimer, managing member. “We’re basically changing the vertical eddy that rolls down the truck into a horizontal airflow.”
Latimer says the stick-on devices – $2.75 apiece – are popular with owner-operators because they help stabilize the vehicle against crosswinds and provide better side mirror visibility. “Fuel savings is icing on the cake,” he says. “We advertise 2 to 4 percent. One driver we know is right around 4 to 5 percent.”
The trailer front has attracted less competition among manufacturers, in part because aerodynamic tractors and reduced gaps tend to minimize savings that can be achieved. Nonetheless, with a trailer nose cone, an owner-operator can achieve fuel savings of 3.5 percent for a tractor with a full-height roof fairing to more than 7 percent with a mid-roof tractor, says Kathy Rose, vice president sales and marketing for Nose Cone Manufacturing. The cost of $1,100 for an installed cone or $1,500 for a cone and side panels can be recouped within months.
Greg Decker thinks operator attitudes about aerodynamics are changing. “At first a lot of other drivers thought I was nuts when I put on the fairings,” he says. “With the price of fuel going up, I’m now getting calls about what I’m doing.” n
California’s aero mandates for trailers
Impending California regulations could affect how and when trailer owners enhance their equipment aerodynamically. Here’s a summary of the aero-related requirements planned by the California Air Resources Board:
• All 2011 and newer dry van trailers must be U.S. EPA SmartWay certified trailers or equipped with SmartWay-approved aero technologies and low-rolling resistance tires that achieve at least 5 percent fuel savings
• All 2011 and newer reefers must be SmartWay certified trailers or use SmartWay-approved aero technologies and low resistance tires that combine for a minimum 4 percent fuel savings.
• All older dry vans and reefers must meet the same tire and aero technology requirements applied to new models by Jan. 1, 2013, or a phased-in schedule for fleets that ranges between the end of 2010 and 2019.
‘Texas fly swatter’ replaces mudflaps
Aerodynamic benefits can come in the most mundane places. Barry Andersen found fuel savings by replacing mud flaps on tractors and trailers with his Eco-flaps.
The product produces an average annual savings of $1,500 per truck, based on a 3.5 percent mpg improvement and a fuel cost of $2.20 a gallon, Anderson says.