The Path Of Least Resistance
In 1905 Francis and Freelan Stanley, the twins who built the famous steamer automobiles, constructed an aerodynamically advanced steam-powered racing car, the Rocket, shaped like an inverted boat hull. It had a flat full-length underpan and enclosed front and rear suspensions; the driver sat low on the floor, ahead of the engine. In January 1906, with Fred Marriott at the wheel, the Rocket reached a record 121.57 mph, at Ormond-Daytona Beach, Florida. A year later, with its horsepower upped from 120 to 156 bhp (brake horsepower—a precise measure of horsepower), the Rocket had reached 132 mph when it hit a gully. The car became airborne and flew a hundred feet at a height of fifteen feet before it crashed. The driver escaped with few injuries, and an aerodynamic principle was demonstrated: Automobile aerodynamics not only is complicated but is very different from airplane aerodynamics. To reduce drag without preventing lift can be disastrous.
Aerodynamics deals with the atmosphere’s interactions with objects and the efficiency of the shapes of those objects, and the modern study of aerodynamics began with aviation research, late in the nineteenth century. Only slowly and fitfully was the discipline applied to automobiles. From 1900 to 1945 cars were almost always designed without any wind-tunnel data or conscious incorporation of aerodynamic engineering principles, so even designs that looked streamlined embodied serious airflow problems that wasted fuel and prevented optimal handling.
The familiar resistive force that works against a car driving in a straight line is aerodynamic drag (there is another, less known resistive force called rolling resistance, the result of mechanical losses in the drive train and wheels and friction between the tires and the road). The overall efficiency of a vehicle’s shape in terms of aerodynamic drag is indicated by its drag coefficient (Cd), a number calculated so that the same shape will have the same Cd regardless of size. The drag coefficients of simple shapes range from .05 for an airfoil and .10 for a sphere to 1.17 for a flat, square plate and 1.35 for a parachute. The Cd’s of today’s American-made production cars range from a little under .30 to about .50.
But “aero is much more than drag,” as Kent Kelly, manager of aerodynamics on the General Motors design staff, points out, “and we run into too many people who equate aero with drag coefficient.” As the unintended flight of the Rocket showed, while airplanes must have strong positive lift to get off the ground, automobiles must hug the ground. Also, cars must resist lateral winds to steer well and drive in a straight line. Furthermore, the best designs for reducing drag are often poor in terms of vehicle stability. And practical road vehicles must carry several passengers in comfort, meet legal requirements like having headlights and mirrors, and be reasonably priced. So truly viable aerodynamic designs are always complex compromises that reconcile achievable Cd with other aims. And as Kelly notes, a car that does not sell because it doesn’t appeal stylistically to consumers will never save a single gallon of gasoline. “It’s easy for an experienced aerodynamicist to do a low-drag car,” he says. “The challenge is to make them all more efficient, all lower drag, and still have good appearance, variety of product, and producibility.”
The first wind tunnel was built for the Royal Aeronautical Society in London in 1871. From September through December 1901 the Wright brothers, in Dayton, Ohio, tested more than 150 model wing profiles in a six-foot-long wind tunnel that they had devised. But systematic research in aeronautics and aerodynamics in this country began only in 1926, when the philanthropist Daniel Guggenheim established a $2,500,000 trust fund to promote the building of a series of small wind tunnels at universities. As soon as they were built, they began to be used for automobiles as well as planes.
Tests on car shapes conducted at the University of Michigan’s tunnel in 1933 were extremely influential. They showed that simply rounding off the corners of a rectangular box reduced its Cd from .86 to .46, a far lower drag coefficient than that of the production sedans of the time. In 1934 two graduate students at Stanford University’s Guggenheim Aeronautical Laboratory wind tunnel tried to establish an “ideal” automobile body design. They developed four rearengine models that required 19 to 55 percent less power between 20 and 60 mph than did 1934 production cars. Meanwhile, tests conducted at Ohio State University’s wind tunnel demonstrated the importance of front-end shape in reducing a car’s drag.
But Germany was already a decade ahead of America—and the rest of the world—in developing the aerodynamic automobile, and that is where the story of aerodynamic car design really begins. World War I left Germany with substantial facilities for aeronautic research, but the country was forbidden by the Treaty of Versailles to develop and build airplanes. So the nation’s airplane engineers and facilities turned to the study of automobile shapes.
The aircraft designer and builder Edmund Rumpler introduced his closed-bodied Tropfenwagen (teardrop car) at the 1921 Berlin Motor Show. The car was essentially a vertical airfoil, the most aerodynamically efficient simple shape, on wheels. It was tested in 1983 and found to have a drag coefficient of only .28, matching the best of today’s production cars. However, only a few Rumplers were ever built. Benz took out a license to use the design and adapted it for several teardrop-shaped racers. Two of them came in fourth and fifth at the 1923 European Grand Prix race.
Paul Jaray, chief of design and development at the Zeppelin airship works, began wind-tunnel tests on one-tenth-scale wooden models of automobile shapes in 1921. According to the British automotive engineer and writer Geoffrey Howard, Jaray recognized “that any changes made to one part of the body created an interrelated effect on the others. In this appreciation of the fundamentals of air flow management he was probably almost alone at that time.”
His tests resulted in a new design that basically stuck a vertical airfoil for the passenger compartment atop a horizontal one to enclose the engine and chassis, with a long, tapering, pointed tail. The car established a Cd of .245. Jaray also became the first aerodynamicist to find effective ways to ventilate closed cars and to clear raindrops from the windshield by airflow management. But the only important production car he designed was the 1934 Tatra, a Czech car.
By the late 1930s, as aerodynamic research began to grow more sophisticated, Jaray’s principles came under attack from Wunibald Kamm, director of the Motor Vehicle Research Institute at the Stuttgart Technical School. Founded in 1930, the institute by 1939 employed three hundred people and had the best automotive-research equipment in the world, including a full-size wind tunnel capable of airspeeds up to 180 mph. Using smoke to make wind-tunnel air patterns visible, Kamm revealed that the best low-drag vehicle shape was one that carried the airflow smoothly rearward only as far as the end of the passenger compartment and then dropped off abruptly. He illustrated this with windtunnel tests of an automobile that had interchangeable tail sections. With a rounded tail, the car tested at Cd .29; with the tail dropped off entirely, the Cd was only .23. The resulting flat-back shape came to be called, after Kamm, the K-form. Interest in the K-form was rekindled in the 1960s, and since then it has been used increasingly in aerodynamic automobiles with large, blunt rears and has become known as the wedge.
In 1936 Mercedes-Benz developed a new form of aerodynamic racer body that featured a fully enclosed underpan, enclosed front wheels, and ducted engine cooling. Its Cd was only .232. The car reached 228 mph in a test on the autobahn (which says almost as much about the autobahns’ design as about the car’s) and, further modified, went on to set a new record average speed in 1938 of 268.9 mph over a measured mile in two directions. The building of such specialized German racing cars for high-speed runs over the newly constructed autobahns was probably the most important source of automotive aerodynamic knowledge in the late 1930s.
Despite Germany’s significant head start in research, it was inevitable that the first aerodynamic production cars would be built in the United States. American companies were the past masters of volume production; modern mass-production techniques in fact reached the German auto industry only when General Motors bought the German firm of Opel in 1929. Also, the United States pioneered the all-steel closed body, which made possible the mass production of aerodynamically and structurally streamlined automobiles. (Altogether three very different kinds of streamlining can be defined: aerodynamic, which is based on measurements and manipulation of airflow; visual, which is purely intuitive and aesthetic and often doesn’t make a car any more efficient; and structural, in which efficiency is gained by reducing weight and increasing rigidity, especially through the use of unitary construction, in which a welded chassis and body become a single lightweight unit.) Dodge introduced the first closed sheet-steel body in 1923, with wood and waterproof fabric used only on its roof; Ford incorporated it into the Model T in 1925, and Cadillac, Chrysler, and Packard followed three years later. Steel roofs came in in 1935, on GM cars and Studebakers.
The enthusiasm for visual streamlining seems to have been everywhere in the 1930s. Not only were airplanes, automobiles, and locomotives “streamlined,” but so were household appliances and buildings. The long list of one-of-a-kind or few-of-a-kind streamlined automobiles from the 1930s is a catalogue of curiosities that contributed nothing to the development of truly aerodynamic cars. Examples include André Dubonnet’s fish-back streamliner, Buckminster Fuller’s Dymaxion, Wellington Miller’s Arrowhead Tear Drop, and William Stout’s Scarab—all radical futuristic design concepts powered by Ford V-8 engines.
But the first true mass-produced aerodynamic automobiles were both American—the Chrysler Airflow and the Lincoln Zephyr. Both cars integrated visual, aerodynamic, and structural streamlining and introduced them to the mass market.
Chrysler advertised the 1934 Airflow as “the first real motor car since the invention of the automobile” and “a new and revolutionary type of vehicle which starts … a new period in the automobile industry.” Richard Burns Carson, a historian of luxury cars, adds that it was both “Art Moderne’s furthest extension of influence in American auto building” and “the first American production car whose shape was fashioned according to scientific rather than aesthetic standards.”
The Airflow’s body style grew out of wind-tunnel tests of models to achieve reduced drag and noise and improved stability. The car’s welded, integral trussed-box structure was designed by Dr. Alexander Klemin, chief engineer at the Guggenheim Foundation for Aeronautics. Consequently the Airflow could be called a “totally engineered car designed from the inside out.” An Airflow sedan was displayed at the 1934 Chicago Century of Progress fair, next to a new Union Pacific M-10000 Streamliner locomotive.
The Airflow was the brainchild of Carl Breer, head of research and advanced engineering at Chrysler until his retirement in 1949. Breer and Owen Skelton and Fred Zeder, his partners in an engineering consulting firm, had been brought to Detroit by Walter P. Chrysler to create the first car to bear his name—the legendary 1924 Chrysler Model 70, the first moderately priced car equipped with a six-cylinder high-compression engine and four-wheel hydraulic brakes. The low-slung lines of the 1924 Chrysler improved the car’s stability at its 70-mph cruising speed, and the look so impressed GM’s president, Alfred P. Sloan, Jr., that he purchased small wire wheels to get his own Cadillac nearer to the ground.
Breer first conceived of the Airflow one evening in 1927 while driving from Detroit to his summer home in Port Huron. He became intrigued by the maneuvers of a formation of Army Air Corps planes that he at first mistook for a flight of geese. He put his arm out the window with his forearm pointing forward. Feathering his hand up and down, he came to “realize the sheer sustaining force of air and its relative effect on both automobile and plane,” and he began to ponder the possible effects of lift and downforce on vehicle safety at high speeds.
“Upon returning to Detroit the next day,” he wrote in 1933, “I assigned a research engineer to the task of investigating what effect wind pressure had on overloading [tires at high speeds] … also to accumulate all information possible about head-on wind resistance. The first work was accomplished by driving a car at high speeds, measuring air pressure at various points with instruments called Pitot tubes, also measuring car spring deflection, etc. After weeks of investigation, the engineer came back with the conclusion that upward lift or downward force that might be caused by the wind pressure was practically negligible. But the analyses indicated worthwhile investigations on head-on wind resistance. We made a search as to what had been done in the past and found practically little available data aside from what was indicated by wind tunnel studies of aeroplane practice.”
Ignorant of Jaray’s groundbreaking work in Germany, Breer began his own experiments to discover basic aerodynamic rules. Tests on simple wood-block shapes in a scalemodel tunnel in Dayton, Ohio, revealed that—as both Jaray and Rumpler had found before—”a car mounted on wheels, running over a road, with other more desirable comfort requirements, calls for many compromises with respect to the ideal of streamlining.” His findings spurred Chrysler to build a larger, more complete tunnel at its Detroit Engineering Division, and testing activities were transferred there in September 1928. Study there of one-tenth-scale models revealed that “with a standard 1928 model sedan, the wind resistance with the car running backwards was far less than when running forward as designed.” Breer grasped the surprising implication: “A funny feeling overcame us when we looked out of the upper story window and visualized that as far as efficiency was concerned all cars on the streets were running backwards.”
By 1932 Chrysler was testing a running prototype for a design based on its wind-tunnel findings. The car was rushed into production by early 1934 because Walter Chrysler had seen a Cadillac show car on display and feared it meant GM would come out with a streamlined car first.
The full aerodynamic shape of the Airflow combined a deco grille, headlights mounted flush in the front fenders, a split, slanted windshield, seating entirely within the wheelbase, and an integral trunk. In motion, the car developed 40 percent less drag than competing models. Chrysler achieved what it called a floating ride by positioning the vehicle’s weight masses over the axles and placing the passengers in the middle, at the point of minimum perpendicular movement (that is, at the natural pivot of any seesawing). Breer claimed that “the streamlined appearance of this new functional design was almost incidental to the new body structure and other fundamental features. … In the conventional car, the body performed no useful function from a stress standpoint; the frame carried all stresses.… In the new Airflow, this relation was reversed.”
Airflow Imperial Coupes broke more than seventy production-car records at Utah’s Bonneville Salt Flats in the summer of 1934. One did 86.2 in a mile at full speed. And in a publicity stunt to prove the strength of its integral welded all-steel body, an Airflow was pushed over the edge of a 110-foot cliff in Pennsylvania, landed on its wheels, and was driven away under its own power. Moreover, the five-passenger sedan sold for a moderate $1,345. But the car was far too revolutionary in its styling for consumers, who especially disliked its relatively short, rounded hood. Only 53,346 Airflows were sold before it was withdrawn from production in 1937. The experience so distressed Chrysler’s executives that the firm became the most conservative of Detroit’s Big Three in styling policy for decades. The Airflow was remembered as the “Airflop,” the automobile industry’s most famous loser until the Edsel.
The Lincoln Zephyr, on the other hand, not only kept the Lincoln Motor Car Company, a subsidiary of Ford, from going under with the collapse of the luxury-car market in the Depression but became the biggest market success Lincoln ever had. Some 130,000 of the cars were built between 1936 and 1942, and another 42,000 were sold after the war was over. The Museum of Modern Art, in New York, singled out the Lincoln Zephyr as the “first successfully designed streamlined car in America,” as its designer, John Tjaarda, boasted in 1954. “As recently as 1951 they referred to the Lincoln as the only car with ‘impeccable, studied elegance.’ Foreign engineers and designers such as Dr. [Ferdinand] Porsche … called it the only car coming out of America to command their interest.”
Ford had become involved with aerodynamics with its development of the Ford trimotor transport plane. A four-foot wind tunnel built in 1929 to test scale models of the trimotor was used to test quarter-scale car models in the early 1930s; then, in 1936, Ford built a full-scale tunnel for auto research. Nonetheless, Ford’s interest in aerodynamics had virtually nothing to do with the birth of the Zephyr, and wind-tunnel testing played no role in its development. The car was intuitively conceived by Tjaarda, a Dutch-born designer who had studied aerodynamics in England and served as a Dutch air force pilot before emigrating to the United States in 1923.
Tjaarda had briefly worked in Hollywood designing custom-bodied cars for movie stars and then designed custom bodies for luxury-car chassis at a firm in upstate New York. He spent two years working for Duesenberg before he was hired by Harley J. Earl in 1930 as a member of GM’s new styling section. Soon he set out on his own again, and in 1932 he became chief of body design for Detroit’s Briggs Manufacturing Company, which built bodies for both Ford and Chrysler. He later recalled: “The new assignment was just what the doctor had prescribed for both Briggs and myself. When W. O. Briggs gave me the go-ahead,on the unit construction and basic ideas of what would later be the Lincoln Zephyr, he kept all of it a secret from much of the Briggs top management. Only Howard Bonbright, Newton Manning and myself knew what plans were under way.”
Howard Bonbright was a close friend of Edsel Ford who had been hired by Briggs in part to improve the firm’s deteriorating relations with the Ford Motor Company. Relations had become strained as Briggs took on more work for Chrysler, which ended up acquiring Briggs in 1953. In the early 1930s Tjaarda worked on the car that would become the Zephyr in a secret studio at Briggs while in another secret studio nearby the Airflow body was being prepared. Briggs hoped that Tjaarda’s revolutionary new design would help Lincoln weather the crisis the Depression had created for luxury-car makers.
According to Tjaarda’s son, Tom, the Zephyr’s design evolved from a series of plans for a rear-engine car that Tjaarda called the Sterkenburg series, after the name of his family’s estate in Holland. He did the first Sterkenburg design in 1926. “Later models showed a definite trend toward aerodynamics and streamlining,” his son explained in 1972, “so when the whole concept was finally put together around 1930 … a very refined automobile resulted. The stage was thus set.”
Only after a structural model was completed was a meeting arranged with the president of Lincoln, Edsel Ford. He gave the project his enthusiastic backing and set up a special design department at Briggs that was kept secret for some time from Henry Ford and Ford’s production chief, Charles E. Sorensen. Tjaarda was given free rein to develop a number of Zephyr prototypes. At first he proposed both rear-engine and front-engine versions otherwise identical in design.
While a prototype of the “pushmobile” version, as Tjaarda called it, was displayed around the country, two of the frontengine version were built to test the unitary body construction at a Ford test track. Tjaarda later wrote: “We hit the weight right on the nose and after testing these two cars on the rough Rouge test track constantly for two weeks they were considered the strongest and lightest cars of their size ever built. Fundamentally those early Zephyrs were the first cars in which a stress analysis, the same as applied to aircraft, definitely proved the advantage of unit body construction. … Stiffness of the structure was accomplished by bracing at the spots where the lightest bracing would be most effective. Therefore, large rounded corners were used in the door openings. The enormous strength of glass was used for bracing the roof by making the windshield and rear window a part of the structure. Today’s hardtops have adopted this practice.”
A poll of public reaction to the pushmobile revealed that while some 80 percent of respondents liked its streamlined looks, only 50 percent approved of its rear engine placement, so it became inevitable that the front-engine car would be the one put into production. It was given a new hundred-horsepower V-12 engine, which unfortunately had many problems that were never to be resolved and became the Zephyr’s Achilles’ heel.
To accommodate the engine, Eugene (“Bob”) Gregorie, the twenty-six-year-old head of design at Ford, redesigned the Zephyr’s front end. “Gregorie made the most of it,” relates the automotive writer Tim Howley. “He drew up a new ‘ironing board’ hood, hinged at the rear to open ‘alligator’ fashion and running straight forward from the base of the windshield. … Wheelbase was extended to 122 inches, and the prototype’s overall body lines were sharpened up somewhat. In final form, the styling suggested graceful motion even with the car at rest.” Gregorie also designed the car’s interior, and thus the production Zephyr came to be a composite design: Tjaarda’s in its unitary construction and from the windshield back; Gregorie’s from the windshield forward and inside.
Gregorie’s classic long, straight hood undoubtedly helped the Zephyr avoid the Airflow’s main styling pitfall—its stubby front end, which Breer had erroneously thought aerodynamically essential. The Zephyr tested at around Cd .45, compared with the Airflow’s estimated .50 to .53, but Lincoln feared to advertise this finding; aerodynamic design had a bad image now thanks to the Airflow’s failure in the market. Also, the Zephyr weighed 940 pounds less than the Airflow; Klemin had made an error in his stress analysis calculation that caused Chrysler to build its car twice as strong as necessary, the main reason why the car could drop off a 110-foot cliff and be driven away.
Ever since Tjaarda had been Klemin’s student, the two had feuded over the value of precise mathematical calculations in design, with the non-mathematically minded Tjaarda insisting on the superiority of what he called “guessamatics.” This was neither the first nor the last time in automotive history that “eyeball aero” produced a more efficient design than elaborate wind-tunnel work.
The saddest event in the history of the aerodynamic automobile is probably the failure of the flamboyant promoter Preston Tucker to get his Tucker Torpedo into production. Only fifty-one Tucker cars were ever built, all for the 1948 model year, and no two were exactly the same. The Torpedo was designed by Alex Tremulis, who had designed aircraft during the war and designed cars under Tjaarda. His fourdoor fastback Tucker was an advanced aerodynamic design, from its center-mounted third headlight to its rear-mounted modified helicopter engine. The car had a Cd of .39. After harassment by the Securities and Exchange Commission, Tucker and seven associates were indicted for fraud (they were later found not guilty), and he lost his manufacturing facility because of discriminatory treatment by the War Assets Administration. This collapsed the price of Tucker stock and ended all hope of his getting the Tucker automobile into production. What impact the Tucker might have had on trends in automotive design had it succeeded can of course never be known.
The fifties and sixties were “the age of schlock and gorp” in American car design, in the words of Gene Bordinat, a former head of design for Ford. Since larger cars generate far greater unit profits than smaller ones, Detroit was happy to feed the nation’s appetite for bigger-than-ever cars. By 1968 so-called intermediate-size cars such as the Ford Fairlane and Oldsmobile F-85 were larger than the full-size 1949 Ford B-A, and in contrast with that car’s hundred-horsepower engine, the new full-size cars were offering standard V-8s in the two-hundred-horsepower range with optional engines up to four hundred horsepower.
Borrowings from aircraft design evident in the automobiles of the time were by and large phony aero that contributed little, if anything, to performance. In general, engineering was subordinated to very unaerodynamic aesthetic values. Excessive front and rear overhang to make cars look longer, for example, made them corner worse and harder to park.
Yet real progress was made in the 1950s in the development of the modern aerodynamic automobile. A solid foundation was laid from advances in wind-tunnel testing and in race-car innovations; but also several advanced aerodynamic designs were successful in the market, and one of them— not American—became the most phenomenal success in automotive history.
The only American manufacturer to integrate visual, aerodynamic, and structural streamlining in its postwar models was Nash. Charles W. Nash had become interested in small cars as early as 1926 and had wrongly predicted that the nation would come to prefer them for their superior handling. The Nash Airflyte series, introduced in the 1949 model year, looked like inverted bathtubs and featured fully enclosed front wheels. Some 436,000 of them were sold in three years, making the car by far the best-selling aerodynamic automobile up to that time. In 1950 Nash introduced its hundred-inch-wheelbase, 2,576-pound Rambler, the first modern so-called compact. The 1954 full-size Nash had as much interior room as a Big Three car even though it was a foot and a half shorter.
The world leaders in postwar aerodynamic design were Saab, of Sweden, and Citroen, of France. The Swedish aircraft firm began testing aerodynamic car designs during World War II and entered automobile manufacturing in 1949 with its Model 92, an aerodynamic coupe with an incredibly low Cd of .35. Saab designs remained unconventionally aerodynamic until a new look was introduced in 1968. Citroen introduced its Model DS in 1955, and it picked up the nickname La Bombe. It featured air suspension, power front disc brakes, power steering, front-wheel drive, and distinctive aerodynamic styling. That truly classic design remained in production until 1974.
But the aerodynamic car that outsold them all was the Volkswagen “Beetle,” which Ferdinand Porsche had designed at the behest of Adolf Hitler. Hitler, a great admirer of Henry Ford, promised to “do my best to put [Ford’s] theories into practice in Germany. … I have come to the conclusion that the motorcar, instead of being a class dividing element, can be the instrument for uniting the different classes.” He gave Porsche, a Czech, German citizenship and invited him to design the German people’s car. Porsche’s prototype was able to get 35 miles to the gallon at 60 mph on its 25 bhp engine because of its innovative central-tube frame, which saved weight, its undercarriage fully enclosed by a sheet of steel, and its aerodynamic shape. The car had a Cd of .49, which was excellent for the time. On February 17, 1972, when Beetle number 15,007,034 rolled off the assembly line, the car surpassed the Model T to become the best-selling auto of all time. It is still being manufactured in Mexico, where the twenty millionth Volkswagen Beetle rolled off the assembly line in 1981.
Europe remained the aerodynamics leader throughout the fifties and sixties. BMW, Porsche, and Mercedes-Benz all did extensive research at a full-scale tunnel completed in Stuttgart in 1944; Volkswagen had its own full-scale tunnel in Wolfsburg. In France an experimental teardrop-shaped car, the Dynavia, was exhibited in 1948, and shrewd aerodynamic design gave France a long string of winners at the famed Le Mans twenty-four-hour automobile race. In Italy Fiat used a scale-model tunnel to design some of its cars; Pininfarina and Ferrari began testing in a tunnel at the Polytechnic University of Turin in the late 1950s; and Pininfarina completed the country’s first full-scale tunnel in 1973.
British advances lay mainly in specialized cars built to break land speed records; they bore little resemblance to Grand Prix racers, let alone to production cars. But the British researcher G. E. Lind-Walker made an important contribution to aerodynamic knowledge in 1957. He published a report on a program of tests of one-eighth-scale models that demonstrated the importance of aerodynamic stability in improving cornering at high speeds. This led to a new emphasis on increasing downforce in racing-car design. As the writer Geoffrey Howard observes, “In the initial stages of motor sport evolution, the objective was primarily to increase speed by reducing drag forces, while in more recent times the emphasis has shifted to the generation of exceedingly large aerodynamic downforces to improve traction, braking, and cornering power.”
The two most important devices to reduce lift—front underbody air dams and rear deck spoilers—were introduced on racing cars in the early 1960s, about two decades before they became common on production cars. As Howard points out, “One of the first production cars to promote the application of these aids as highly visible body features was the 1972 Porsche Carrera RS coupe. … The effectiveness of these devices was dramatic. At a speed of 90 mph front lift was reduced by some 90 percent from about 45 Ib to less than 5 Ib.”
Europe’s lead in those decades was ensured by the low price of gasoline in America, by the dominance of the family car—such as the nine-passenger station wagon—in this country, by the relative lack of interest here in racing, and by the ascendance of cost-cutting accountants and stylists over engineers in the American automobile industry at the time. It took two successive energy crises in the 1970s to make vehicle aerodynamics truly important in Detroit; however, the first production car to incorporate a front valence dam to reduce lift and drag was the 1966 Corvair.
Ford built a “wind and weather” tunnel at its Dearborn, Michigan, engineering facility in 1958 and used it sporadically to test both production and racing cars. Also, the company made extensive use of the University of Maryland’s scale-model tunnel between 1957 and 1967. But little came of the Ford testing programs insofar as production-car design was concerned. Alex Tremulis, who had designed the Tucker Torpedo, became head of an advanced design studio at Ford in the early 1950s. “The styling chiefs didn’t understand aerodynamics,” he recalled in 1984. “Whenever I was on the verge of selling a wind-tunnel program or an aerodynamic program, I was always shot down.” Kent Kelly recalls likewise that at GM in the late 1950s, there was great interest in applying aerodynamics to race cars but much less interest in applying it to the actual product.
General Motors’ involvement in aerodynamics began when Dr. Peter Kyropoulos conducted wind-tunnel studies of a gas-turbine-powered concept car in 1953. GM hired Kyropoulos away from his faculty position at Caltech to become technical director of the GM styling staff. Kent Kelly joined GM in 1957, and the two began a program of testing at Caltech on selected production cars and trucks.
In March 1960 Kelly, Kyropoulos, and William Tanner presented a paper at the annual meeting of the Society of Automotive Engineers, laying out the importance of aerodynamics and the validity of studies on scale models and establishing parameters for future testing. In the early 1960s the company began testing models of more and more of its cars at university and aircraftcompany tunnels; in 1969 full-scale testing began at a large tunnel in Marietta, Georgia, owned by Lockheed.
Following the fuel shortage brought on by the 1973 OPEC oil embargo, GM’s aerodynamicists began to be flooded with calls from elsewhere within the corporation asking whether they were aware that aerodynamics affected fuel economy. Kent Kelly had been waiting for those calls. “When the crunch came, we happened to be ready, and our business went straight up from that point,” he says. “Luckily, there had been support for us to learn the discipline, the tunnel testing, and the model making, so when the time came that aero was needed in the United States, we were in very good shape and able to move into it aggressively.”
In general, a 10 percent reduction in a car’s aerodynamic drag will yield a 3.5 percent increase in fuel economy. By contrast, a 10 percent cut in weight will yield a 2.5 percent increase; a 10 percent cut in horsepower, 4 percent; and a 10 percent decrease in the specific fuel consumption of the engine, 10 percent. After the oil embargo, Japanese and European manufacturers concentrated on vehicle weight and horsepower improvements rather than aerodynamic design. In America General Motors led the industry in significantly downsizing its cars, beginning in the 1975 model year. In 1975 Congress passed the Corporate Average Fuel Economy regulation, mandating that automobile manufacturers have an average annual fuel economy of 27.5 miles per gallon for their full line of cars by 1985.
While simply making the engine more efficient is potentially the most effective way of increasing fuel economy, it is incredibly expensive. In the early 1970s Elliott (“Pete”) Estes, then president of GM, estimated that it would cost between one and five million dollars to decrease an engine’s specific fuel consumption just one-half mile per gallon. (The most important recent breakthrough in this area is GM’s revolutionary Quad-4 engine, introduced in 1987, which combines eight-cylinder performance with four-cylinder fuel economy.) Compared with expensive and difficult programs to improve engines and power trains and trim weight, aerodynamic design comes cheap. As Jack Telnack, Ford’s design chief, says, “It’s all free. It doesn’t require major technical development programs. You have to shape the metal anyway, so why not shape it right?”
Aerodynamic wind-tunnel testing suddenly became very big in the seventies; GM did less than 350 hours of testing in 1972 and almost 2,600 hours of it in 1978. The main site for Big Three full-scale testing became the Lockheed facility in Georgia, with a lot of work also done at a Canadian national tunnel in Ottawa. Ford and Chrysler still rely on these facilities; GM has transferred most of its testing to its gigantic aerodynamics Laboratory in Warren, Michigan, the first fullscale automotive aerodynamic wind tunnel in the United States and the largest in the world. It was completed in 1980 and does only GM work, yet is booked two months in advance, operating two shifts five days a week.
The first significant integration of aero into new designs began at GM in 1974, with the design of the 1977 Chevrolet Caprice. Ford claims the 1979 Mustang as its first fully aerodynamic design. But such developments were totally overshadowed by what followed. In the words of Geoffrey Howard, “Two cars stood out from the crowd by the end of 1982, the Audi [5000 series] and the [European-designed] Ford SierraMerkur. One became the first production five-seater to reach a Cd of .30, and the other showed how .34 was perfectly feasible in high-volume, low-cost family cars. Both achieved drag reductions between 24 and 28 percent that alone accounted for 15 and 17 percent fuel savings at 70 mph.” Also outstanding was the 1983 Pontiac Firebird Trans Am, which GM advertised as having “the lowest Cd number of any production automobile in the world,” after obtaining a Cd measurement of .309.
In the mid-1980s aerodynamic design in American-made cars came to be associated in the public mind with Ford, which broke sharply with conventional design concepts with its 1983 Thunderbird/Cougar, 1984 Tempo/Topaz, and 1986 Taurus/Sable models. At first these cars were derided by some critics as “jelly beans”; Lee Iacocca, the chairman of Chrysler, mocked them as “flying potatoes,” but the boldly designed cars restored Ford’s profitability to its highest levels since the mid-1920s and established Ford as the styling pacesetter of the American automobile industry. Ford’s chairman, Donald Petersen, took an enormous risk in bringing out these new cars at a development cost of some ten billion dollars over two years, and it paid off handsomely. Understandably, Ford has advertised itself heavily as the aerodynamics company, and a series of Ford commercials in 1987 poked fun at the outward similarity of General Motors models.
“From a design standpoint, having them do that was great because everyone here woke up and realized we had to do something,” GM’s vice-president for design, Chuck Jordan, told the Wall Street Journal in December 1987. “People talk like Ford invented aerodynamics. They didn’t. They went from carved granite to round cars. I told Jack Telnack he’d better enjoy this lead while he’s got it.”
What irked Jordan was that his staff had long had aerodynamic models ready but their production had been postponed because of corporate priorities. “The GM 10 sedans have been sitting around this building for years,” he complained. “The best designer in the world can’t live with that situation. You have to design a car and get it out there.” The aerodynamically designed Chevrolet Corsica and Beretta were introduced in March 1987; the aerodynamic Oldsmobile Cutlass Supreme, Buick Regal, and Pontiac Grand Prix came out several months later.
By 1987 it was hard for any company to claim leadership in aerodynamic design. Automotive News , the leading industry journal, illustrated this with a list it published in April of that year revealing the cars with the lowest and highest Cds. Imported cars ranged from .29 claimed for a Subaru XT coupe to .43 for a Mercedes 560 SL. The Big Three manufacturers spread from .32 for a (Ford) Mercury Sable, .33 for a (GM) Chevrolet Camaro, and .35 for a Chrysler Le Baron to .46 for a (GM) Cadillac Brougham, .48 for a Chrysler Fifth Avenue, and .50 for a Ford Crown Victoria. In other words, every car today has a Cd comparable to or better than the Chrysler Airflow’s. As Telnack told The New York Times in May 1987, “Aero is now the price of admission. You must have great aerodynamics to be competitive.” Growing Japanese interest in wind-tunnel testing and in introducing aerodynamic designs is perhaps the best indication that Telnack is right.
With aero finally so institutionalized, what does the future hold? Several concept cars developed since the mid-1970s have tried to establish the practical limits of aerodynamic car design. One of them, a 1981 Renault with a Cd of only .25, can get ninety-four miles per gallon in mixed city and highway driving carrying four passengers and luggage. Two 1985 prototypes, built by Ford and Chevrolet, reached a Cd of .14, a drag coefficient previously attained only in land-speed-record cars and jet aircraft.
Meanwhile, the pressure for lower Cd’s has eased considerably since the OPEC cartel has weakened and world oil prices have stabilized (however, that may change, since a move began in the summer of 1989 to impose higher industry fueleconomy standards). Geoffrey Howard predicted in 1986 that “unless there are further disruptions of oil supplies, the aerodynamic design of production cars has reached a viable limit at a Cd value of around .30. Although the technology exists to lower this to .25, progress in fuel economy … is much more likely to swing toward power units where environmental pressure for clean air is forcing massive investments in new designs and new manufacturing facilities.”
Within aerodynamics the emphasis has been shifting from the styling of the car’s body to under-the-hood airflow management. And in part because air under the hood is hard to see in a wind tunnel, there has been increasing reliance on computational fluid dynamics. The wind tunnel may never fall out of use, but the computer now can bring aerodynamics into the design process much earlier and more cheaply. GM is doing this with a supercomputer that has a memory of two million sixty-four-bit words.
Computational aerodynamics is only one area in which the computer is revolutionizing automobile design, engineering, and manufacturing. Traditional engineering know-how, cut-and-try methods, and intuition are rapidly being abandoned in favor of computer-aided engineering (CAE), computer-aided design (CAD), and computer-aided manufacturing (CAM). CAE and CAD greatly reduce both the cost and lead time for developing new models. Electronic scanners trace,the form of a clay model to gather precise data that are stored in the computer. The computer then produces engineering drawings for die making. The computer can also be programmed to show the effects of the stresses to which parts will be subjected.
Chrysler claims that its 1984 Chrysler Le Baron and Dodge Lancer GTS were the world’s first completely computerdesigned cars. In a 1984 article in Science , the technical staff of Ford predicted that “the product design, development, and manufacturing process of the future will rely on the integration of a wide range of computer-based application programs. Properly implemented, the boundaries between CAE, CAD, and CAM will disappear.”
Tremulis recalls the traditional relationship between the engineer and the stylist as “like the relationship between a cobra and a mongoose.” But the marriage of the computer and the wind tunnel has helped make the engineer and the stylist close partners in the design process. Not only has the stylist’s hegemony ended, but the word styling itself has gone out of fashion, in favor of design . Aerodynamicists are now members of the design teams in the design studios, where appeal to engineering principles and objectively gathered data has largely replaced intuition.
The time has ended when designs could be accepted or rejected on the basis of the whims of powerful styling chiefs or corporate brass. Thus the arrival of the aerodynamic automobile not only has institutionalized, rational design but also has been part of a revolution in the corporate culture of the world’s major industry.
