A new flow

by John G. Smith

NASHVILLE, Tenn. – While engineers continue to sculpt trucks to make them more aerodynamic, several researchers and entrepreneurs are paying more attention to uncharted territory – the gaps between tractors and trailers, and the shapes of trailers themselves.

A tractor’s front end accounts for 40 per cent of a rig’s aerodynamic drag, but the gap between a tractor and trailer can account for another 20 per cent, explained Vic Suski of the American Trucking Association’s engineering department, during a session at this spring’s meeting of The Maintenance Council. The trailer itself, and particularly the area behind the barn doors, accounts for yet another 20 per cent.

The U.S. federal government is already funding a look at the aerodynamics of tractor-trailers since improvements here are seen as the most promising ways to improve fuel efficiency, said Frank Tokarz of Lawrence Livermore National Laboratory. Looking 20 years into the future, a 25 per cent drop in drag could in itself improve fuel efficiency by 10 to 15 per cent, he says. “At 70 mph, 65 per cent of (a truck’s) total energy expended is in overcoming aerodynamic drag.”

“You do not have to have a physical boat tail at the end of a trailer to have a significant difference,” added Suski, referring to ways to improve aerodynamics behind trailers. “There’s a way to fool the air to make it think the boat tail is there.”

“The front is in pretty good shape, but the rest needs work,” agreed pilot Shawn Coyle of Aeroserve Technologies, referring to potential improvements in tractor-trailer designs.

Any trailer gap that’s more than 18 inches wide creates aerodynamic drag, he says of one area of concern. So too are there problems with areas under a trailer. Side skirts closing gaps between a trailer deck and the road could make a difference in managing air flow, although current designs could be clogged by snow, make it difficult to inspect tires, and could be damaged on steep docks, he notes.

There are more than 60 patents filed on devices meant to reduce drag at the back of trailers, but none of them have been successful, Coyle added. His company is marketing plastic, triangular-shaped “vortex generators” that are attached around trailer edges to manage the flow of air as it rushes off equipment.

But another solution may be found in air itself. Bob Englar of Georgia Tech Research Institute said aerodynamics could be improved by forcing jets of air around rounded corners, in an approach used to improve the aerodynamics of some military fighters. The air could come from a form of a dedicated turbocharger, by bleeding air from a traditional engine turbocharger, or even from the exhaust system, he suggests. And the back edge of trailers would only need to be rounded to a radius of two to eight inches to make a difference.

The lift that’s created could even reduce or increase rolling resistance on command, he added, noting that shooting air from the sides of trailers could help improve overall stability and handling.

It’s simply a matter of charting a new course for the air. n

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