ATLANTA - The cloud of mist trailing big trucks on drizzly days is the most common evidence of the problem researcher Bob Englar aims to overcome.
Mr. Englar, principal research engineer at Georgia Institute of Technology Research Institute's Aerospace, Transportation and Advanced Systems Lab, is taking what he learned about air flow as a Navy plane and helicopter designer and applying it to the largest trucks on the road.
Mr. Englar also advises racers. For 11 years, he's consulted with the Miss Budweiser hydroplane team and tested his ideas on cars run by the Georgia Tech Motorsports Club.
He estimates he could reduce by half the drag from tractor-trailers - that turbulent air following the big rigs - which would save a projected 1.7 billion gallons of diesel fuel a year, if his innovations were adapted to every 18-wheeler in the country.
"They are extremely draggy vehicles," he said.
THE TURBULENCE LEFT in a truck's wake creates a vacuum that pulls on the vehicle, wasting fuel. For typical semis, doubling the speed from 35 mph to 70 requires eight times the horsepower and energy consumption because added speed increases drag even faster. A more orderly airflow would allow the truck to slip with less disturbance and reduce the buffeting that light cars experience when trying to pass the big rigs.
Scientists have known the benefits of smooth trailing airflow for years, but until Mr. Englar's wind-tunnel experiments panned out, their only solution was to mount 15-to-25-foot cones on the rear similar to exaggerated fins on a 1950s-era roadster.
Mr. Englar's solution is twofold: install patented curves running corner-to-corner along the top, bottom and both sides; and then blow compressed air along the curves. Pressure coming off the engine's turbocharger at 1 pound per square inch would be all would take.
"It then trains what was a separated airflow" so it glides gently around the back of the truck, he said.
The compressed air is delivered by slots running in front of the special curved edges and controlled by a series of valves.
"You have the ability to increase drag at the same time just by changing which of the slots you blow," Mr. Englar said. "The guy who is worried about his brakes coming down a mountain can increase the drag just by changing a valve."
CONTROLLING THE AIRFLOW under differing driving conditions has other benefits.
"There is one more really neat gain," Mr. Englar said. "We have found that you can change the drag to increase the safety of the truck."
Airstreams over curved surfaces create what engineers call lift, similar to that caused by an airplane's wing. Increased airflow on the bottom edge creates a downward to press the tires more firmly against the pavement. That could be helpful in reducing jackknife accidents, which tend to occur when a truck returns lighter after unloading its cargo.
In addition, quick bursts of air on one side of a truck could counteract a gust of wind on the opposite side that often makes handling difficult.
The Department of Energy funds Mr. Englar's research and is eager to move from scale models to a full-size prototype truck. Others, such as the American Trucking Associations and makers of sport utility vehicles, are also eager to see it reach application stage.
"Reducing the drag on the trailer could make it easier to keep it in lane," said Guy Young, a representative of the Georgia Motor Trucking Association. "Obviously, anything you can do to reduce drag would also reduce costs."
TRUCKING COMPANIES already have taken steps to improve the aerodynamics of the front of tractors and many of their trailers. Adding skirting and airfoils called fairings cuts fuel costs 17 percent, according to Alfred Gordon, safety director of Cocke Brothers Transportation in Savannah.
Many trailers have plastic cones added to their front to slice through the air above the truck cab. The rear end, though, has remained pretty uniform, mostly to fit the standard dimensions of loading docks.
"I can tell you, yes, with absolute certainty, that if there was a trailer that is round instead of square on the top and the bottom, it would save fuel, and it would make it travel straight," Mr. Gordon said.
Some practical considerations do remain, such as how to open the cargo doors with the curves Mr. Englar is proposing. Hinges run along the edges he wants to put curves on. And the material the curves are made of will have to be durable enough to withstand striking loading docks and yet be compact enough to fit in the restricted truck bays at some buildings.
Mr. Englar admits he has to solve all those problems, which is one reason his innovations aren't already on trailers today.
Reach Walter C. Jones at (404) 589-8424.