Pulling ahead of aerodynamic drag.

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As diesel prices spiral out of sight, truck fleets and truckers are looking for ways to cut fuel costs. While a 1 or 2% improvement might seem tiny, it can save $700 to $1600 when you drive 100,000 miles annually at only 5 to 6 mpg. A 5% improvement can mean "real" money.

At highway speeds, between 50 and 70% of a Class 8 tractor's output goes into overcoming aerodynamic drag. NASA studies have shown streamlining the front, rear and undercarriage of a rectangular vehicle can reduce fuel-wasting drag by more than 30%. While aerodynamic cabs are already widely used, trailers, still inefficient boxes, offer great opportunity for drag-reducing improvements.

A recent study by the Truck Manufacturers Association and the U.S. Department of Energy found if several new aerodynamic technologies were all incorporated on tractor-trailer trucks, aerodynamic drag could be reduced by as much as 23%. Every 2% reduction in aerodynamic drag means about a 1% improvement in fuel economy. These technologies include closing the gap between the tractor and trailer and installing side skirts on trailers, boat tails and more aerodynamic side mirrors.

The Georgia Institute of Technology has installed aerodynamic devices, originally developed for jet wings, on a full-size tractor-trailer truck and tested it at the Transportation Research Center in Ohio where they demonstrated as much as an 11 to 12% fuel savings. They also enhanced braking and directional control to improve safety. The techniques included rounding aft trailer corners, installing fairings and making other changes that smooth airflow over the boxy trailers. Pneumatic devices that blow air from slots at the rear of the trailer are added to prevent drag-producing airflow separation.

All this is great in an ideal world, but trucks operate in the real world with rough roads, snow and ice, and drivers who back into things. Plus, every pound added for aerodynamic devices means one less pound of cargo that can be carried. And devices that impair loading and unloading or require any significant maintenance are to be avoided.

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The Dutch public-private research partnership PART (Platform for Aerodynamic Road Transport) demonstrated several devices both in wind tunnel and extensive road testing. They found aerodynamic side skirts on a trailer cut fuel consumption by 10% in long-term operational tests and boat tails on the rear of a trailer cut air resistance by 30%, with a fuel reduction of 10 to 15%. However, the Dutch researchers say boat tails are limited in practical use, particularly when loading and unloading. They also noted safety issues, and said they can exceed maximum vehicle lengths--preventing their use on many types of trucks.