Aerodynamic design: providing the shape of cars to come

Take a look at the 1985-model cars and see how the designers have tried to reduce the power-stealing effect of air flowing over, under, and around the body.

What they've done is make the new cars more aerodynamic, but with a difference.

''The last thing we want to happen is to arrive at 1990 or 2000 and have all of our cars look like Spartan little boxes,'' says Donald F. Kopka, vice-president of design for Ford. ''An important aspect of a car's appearance is that they have to look like automobiles, not motorized market baskets.''

That clearly is not going to happen if the designs now hitting the road are any indication of what lies ahead.

Aerodynamics, in fact, could be the single most influential force in the exterior shape of cars for years to come. The stability of a car, windows, radiator flow, dirt deposit - all that is aero, designers assert.

''People too often say that 'aero' means drag, period,'' says Bernard N. Smith, assistant executive designer on the General Motors styling staff, ''but that's just not true. What makes for good stability is not necessarily always low drag. We have to compromise on how to do it properly, how to stabilize a car without losing drag reduction or without increasing drag. Also, you have to have a car that will sell.

''The low-drag car sitting in the showroom, not in the hands of the public, doesn't help us or anybody else.''

Still, the reduction of drag is indeed an issue as the cars of tomorrow move toward the assembly line.

''We've experienced a reduction in drag by simply removing a small trim strip , or a very slight change in the shape of the car,'' says Irvin W. Rybicki, vice-president of design for GM. ''Aerodynamics is in its early adolescence,'' he adds. ''There is a lot we don't know about it.''

One thing the engineers and designers do know very well is the need for a new car to conform to the law as defined by the federal government's automotive safety and emissions standards.

A few years ago the government asked Lockheed to design a new car. The result was a low drag figure of perhaps 0.38, a superlow number at the time.

''That's great,'' carmakers said, but then asked: ''But did you notice that you've violated the headlight and bumper regulations, the cooling flow is inadequate, and you haven't even attended to half the things that we have to do for an average car in meeting the federal law as well as the public's willingness to buy?''

The point is, the car could not be built, despite the low aerodynamic drag.

Automotive designers and engineers are working hard to lower all the components under the hood. The new Chevrolet Corvette has a composite front leaf spring which gives the customer a lower hood and a more aerodynamic, better-looking car. But if GM could have gotten coil springs at the same hood height, it very likely would have done it.

Beyond the smooth lines themselves, which have a major impact on the visual impression a car makes, aerodynamics in recent years has had far more impact on fuel economy than the designers suspected only a decade or two ago.

Above 20 miles an hour, the slippery shape of a car begins to show up. If the speed is doubled, aerodynamic drag rises fourfold, and it takes an eightfold rise in horsepower to handle it.

Stylists also are trying to lessen the drag of the cooling system in a car. By supplying only the air that a car requires under its load cycle, the air opening can be reduced in size to lessen drag.

''I think you'll see more local attention paid to component alignment,'' predicts GM stylist Smith. ''With all the other requirements of cost and feasibility, you'll see more segmented smooth underbodies on cars in the future.

''When you reach the extremely low drag levels,'' he adds, ''even the drag of the tire is important. What we'd like to do is streamline the wheels and tires.''

Nagging the designer at every turn, of course, are the cost accountants.

Jack Telnack, chief design executive for Ford, explains: ''I could paint a Mona Lisa every hour on the hour, but if it doesn't stay within our cost parameters, I haven't done my job. We're very aware of our cost restraints and have to be a lot sharper so as to keep our costs in line.''

Looking a few years ahead, the back shape of cars is due for major work. Smith describes what he calls ''a half fastback'' in a vehicle that's only 140 inches in length. ''We want the air to cling to the roof profile as long as we can, so that tends to describe a more squared-off, almost station-wagon-type vehicle. You really can't describe it as a fastback or notchback because the profile is different.

''It's really a challenge because it's a very stubby box,'' he says.

The GM designer expects more drivable space frames in the future, such as that used for the Pontiac Fiero, to which the exterior plastic panels are attached. In a space-frame car, all of the outer body surfaces can be removed and the car can still be driven.

It all depends on the car, the volume, and the marketplace. ''I don't think it will be used for all cars,'' observes Mr. Smith.

With hang-on panels, the design can be changed more cheaply and with far less work. Yet it's a compromise because, as some designers say, if the panels aren't working, then they're redundant and add to the weight of the car.

''It isn't all a free ride,'' Mr. Smith concludes.

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