Detroit's new game plan -- cut wind drag

Aerodynamics is firmly entrenched in the driver's seat in Detroit.

Car designers think of aerodynamics -- the effect of the wind on the surface of a car -- as the second stage, following the downsizing of automobiles and the simultaneous reduction in weight, in giving better fuel economy in the future.

''It's just too costly to work with weight reduction any more,'' explains executive engineer Charles Torner of the General Motors design staff.

''That's because exotic and expensive materials would be required to eliminate much more weight,'' he goes on. ''Now it's the wind we're working with.''

GM not long ago completed a multimillion-dollar aerodynamics laboratory -- a wind tunnel -- in Warren, Mich., where wind speeds of up to 150 miles an hour can be achieved.

Mr. Torner says that the 150-mph wind is needed when reduced-size-scale model cars are being tested. In other words, the wind speed can be stepped up to maintain the same relative conditions which a full-size vehicle would experience on the road. As an example, he says that if a one-third scale model of a car were being tested at 50 miles an hour on the road, the air speed in the tunnel would have to be set at about 150 mph.

''We know,'' he goes on, ''that if we can improve the aerodynamic design of a vehicle 10 percent, we can achieve a fuel saving of 3 to 4 percent.'' Simply, creating a more effective shape for a car can help the car to travel more efficiently through the air.

As early as the early 1950s, car designers were testing scale models in aircraft company wind tunnels. ''We did that until the '70s,'' Mr. Torner explains, ''when Lockheed converted one of its tunnels in Marietta, Ga., so we could test full-size clay models of cars.''

Before that the auto industry used wind tunnels only for climate-control tests so as to assure that cars would start in below-zero temperatures as well as in extremely high readings. Also, the manufacturers wanted to make sure that paint would withstand the wide variations in temperature.

Today engineers are looking at the resistance a car creates against the wind in an effort to minimize that resistance, thus improving the use of fuel.

The designers look at the coefficient of drag, a measure of that resistance.

According to Ford Motor Company executives, in a typical 1982-model automobile operating at 24 miles an hour, about half the horsepower is used to overcome air resistance. Thus, a 10 percent decrease in drag, or air resistance, gives a half-gallon-per-mile improvement in fuel economy. On the highway, it's 2 miles per gallon better.

Designers also are looking at ways to make a car as small as possible in cross section, especially from a head-on point of view as the car faces the wind.

''Taking 3 inches out of the roof and dropping straight down requires less force, and thus less fuel,'' adds Torner. Cars such as the Chevrolet Celebrity, Pontiac 6000, Buick Century, and Oldsmobile Ciera -- GM's new A-body (midsize) cars -- are of the new aerodynamic generation.

''A lot of the wind-tunnel work on them isn't as obvious as it may be on other cars,'' he declares.

In an automobile-show display, Volkswagen uses a miniature wind tunnel to point out that better aerodynamic shapes can save fuel. The West German carmaker shows two objects -- a truck and a stylish car -- in the tunnel, pointing out that 67 percent of a vehicle's available energy is used in overcoming air resistance.

The VW Scirocco, for example, offers far lower aerodynamic drag, weight, and roll resistance with its tires than a truck shape.

GM has done some aerodynamic experimentation and come up with its concept car , the Aero X. Ford has its Probe III. GM points out that efficient cars can be designed without sacrificing aesthetics or comfort. The company's fiberglass prototype has been carefully tested in its wind tunnel. The hood slopes in a gentle curve and cooling air is admitted to the engine through an ''under the nose'' inlet.

A smooth transition from hood to windshield improves the flow of air over the upper body. Flush glass is used all around the car, a trend all across the board , with pillars behind the glass. Windshield wipers are recessed and there are no exterior moldings in the Aero X.

Wheel covers are flush with the wheels while the wheels are mounted in line with the body sides to give the car a total ''slippery'' configuration. The rear body form is shaped so that air flows smoothly over it.

Aerodynamic tests show that the wheel-house space usually required for wheel movements in bumps and turns contributes to overall drag. In the Aero X, each wheel opening incorporates a flexible spacer which smoothes the airflow along the entire body side and permits all necessary wheel motions.

Mr. Torner emphasizes that aerodynamic concerns aren't going to result in just one shape of cars. There are a variety of shapes which can meet the standards of less resistance to the wind.

Cars of the future will definitely have softer, sloping shapes.