An Illustrated History Of Automotive Aerodynamics: Part 3 (1960 – Present)

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– Posted on January 30, 2012

Mercedes Bionic (2005) Cd: 0.19

For most of the fifties, sixties and into the early seventies, automotive aerodynamicists were mostly non-existent, or hiding in their dust-collecting wind tunnels. The original promise and enthusiasm of aerodynamics was discarded as just another style fad, and gave way to less functional styling gimmicks tacked unto ever larger and squarer bricks. But the energy crisis of 1974 suddenly put the lost science in the spotlight again. And although a trough of historically low oil prices temporarily put them on the back burner, as boxy SUVs crashed through the air, it appears safe to say that the slippery science has finally found its permanent place in the forefront of automotive design.

1958 Lincoln Premier  image source: Plan59 Cd: never tested

During the fifties and sixties, with the exception of Citroen, Saab and a few other minor adherents, aerodynamics was largely left in the wake of increasingly ornate and boxy cars. The buying public was perceived or conditioned to need change, and the rounded pontoon gave way to ever-more dramatic and flamboyant but aerodynamically blunt designs.

Even in Europe, the influence from America as well as the pursuit of design for its own end also largely pushed aerodynamics into the periphery. Although the 1959 Mercedes W111 had a Cd of 0.40, Daimler-Benz never fully stopped using aerodynamics, and utilized it to fine tune certain aspects, such as ventilation and even in keeping its rear taillight lenses clean from road splash. And they certainly didn’t make any spurious claims about the fins adding stability at high speed.

Unless I’ve overlooked something, there’s just no evidence of  passenger cars manufacturers placing any significant priority on aerodynamics during the early sixties, except those already committed to it, like Citroen and Panhard, with their new 24 of 1964 (above). But by then, Panhard was essentially controlled by Citroen.

Aerodynamic progress was mostly relegated to the racing world. The value of reducing forward aerodynamic drag on race cars was understood from the earliest days. But what was not at all so well understood was the role of vertical aerodynamic forces, the tendency of most streamlined shapes to start acting like a wing, and want to take flight with increasing speed. This not only makes high-speed racers unstable, but also contributes to reduced cornering ability.

In 1957, British researcher G.E. Lind-Walker published the results of studies that opened the door to understanding the importance of generating downforce, particularly in racing cars. His work began a revolution in racing car design as down force played such a critical role in improving acceleration, cornering and braking, the three essential components of racing.

By the early sixties, front air dams and rear spoilers were appearing on racing cars, and no one exploited the possibilities more than Jim Hall with his highly successful Chaparral racers. The 2B above shows the first fully functional use of front and rear spoilers and fender vents, all specifically to generate down force. They made the Chaparral essentially unbeatable in 1964 and 1965.

Two years later, Hall introduced the startling Chaparral 2E, which was the paradigm-shaping race car in terms of aerodynamics. In the the 2B, the aero aids were tacked on to a relatively typical sports racer of the time; the 2E was organically designed to maximize down force, including the adjustable rear wing. The 2E profoundly influenced the whole racing world, including NASCAR.

The Plymouth Superbird (and Charger Daytona) shows the extreme lengths taken by Chrysler to incorporate these on a production car for their aerodynamic benefits, although the actual racers did better when they had a much larger lip spoiler added like this one.

We’re not going to pursue the evolution of racing aerodynamics further in this limited survey, but it has become utterly paramount to the design and function of modern racing cars.  But the Chaparrals’ influence would also quickly spill over into passenger cars. GM hired an aerodynamicist back in 1953 to assist with wind tunnel tests on its turbine concept cars, although he was grossly underutilized for years.

But GM’s technical assistance to the Chaparral team was a well-known fact. How much of that was aerodynamics is not clear, but the first mass production car to sport a chin spoiler like the  2B above was the 1966 Corvair. It was added in the second year of the Corvair’s 1965 re-style to reduce drag and to improve down force and cross-wind stability, particularly important in the relatively less-stable rear-engined Corvair.

In Europe, Porsche also put its racing experience to good use, and its 1972 911 Carrera RS sported a full complement of spoilers to dramatically increase high speed stability and handling. And needless to say, Porsche wasn’t the only one.

Spoilers became another huge fad, as manufacturers,

and the aftermarket quickly seized on them for their ability to convey speed and performance, no matter what the vehicle it was mounted on.

1938 Kamm-back BMW prototype Cd: 0.25

Perhaps we did an injustice to the groundbreaking work of the German aerodynamicists Baron Reinhard von Koenig-Fachsenfeld and  Wunibald Kamm by not including it in Part 2 of this series. But since their work mostly came to fruition in the sixties and later, let’s acknowledge their highly significant contribution here. They proved that a long tapered tail, once considered a key component of any aerodynamic body, was not actually necessary for a low-drag body, especially if it wasn’t a truly long and gently tapered shape. They demonstrated that an abruptly ending squared-off tail was almost as beneficial, as the air flow tended to act as if the tail was actually still there.

Their 1938 BMW prototype (above) proved their experiments convincingly, with a stellar Cd of 0.25 as well as facilitating practical advantages such as a roomy passenger cabin.

Probably because of stylistic reasons, the Kamm-back was not adopted to any significant extent in its most pure form, except in racing cars, such as this 1961 Ferrari 250 GT SWB “Breadvan”.

The “K” word entered the popular American lexicon when it was adopted for mainstream American cars such as the Vega Kammback wagon (above) and the AMC Spirit Kammback hatch. Given that the front of these cars showed no effort at reducing their drag, they exploited the name more than its potential benefit.

Pininfarina 1967 BMC-1800 Berlina-Aerodinamica_01_-600x325

Although the 1955 Citroen DS was highly aerodynamic for its time, its influence was undeniably but rather limited, especially stylistically. It was so unique and uncompromising, that it didn’t lend itself well to “imitation”. But in 1967, Pininfarina showed the BMC 1800 Berlina Aerodinamica, designed by Leonardo Fioravanti. It was based on the ungainly BMC ADO17 “Landcrab“, whose body emphasized practical qualities over aerodynamics. Fioravanti was a student of Kamm’s design principles, and became the first to really put it to proper use in a practical passenger car. The influence of his Berlina Aerodynamica is vast; both in other cars that soon picked up its lines and design language, as well as still today. This car rightly is the mother of almost all modern automotive aerodynamic design.

Citroen GS 1970  Cd: 0.31 (is that verified?)

In Europe, Citroen was the most diligent keeper of the aero flame for production cars. The compact GS arrived in 1970, with many of the design elements that now look so familiar now, thanks to cars such as the Prius. A sloping front end, fastback rear window, and an abbreviated Kamm-tail. It sported the lowest Cd in the world at the time, for a production car. Its debt to the Berlina Aerodynamica is substantial.

As is its bigger sibling. Curiously, despite its name being the nomenclature for Coefficient of drag (Cx), the large Citroen Cx arrived in 1974 with a Cd of 0.36. That’s counter-intuitive, because longer bodies tend to intrinsically have a lower relative drag. Still, it was a commendable number for a car that had a difficult birth, but went on to lead a long life. It certainly played an important role in acculturating the European public to highly aerodynamic design.

A truly pioneering car was the rotary engine-powered NSU Ro 80 from 1967. Its Cd of 0.355 set a low-air mark for sedans that would stand for some years. Other than its rotary engine, the NSU was a highly influential car, defining the modern idiom almost perfectly.

After NSU was bought by VW, Audi took up the work that had begun with the Ro 80. This resulted in an aerodynamic breakthrough and one of the most (if not the most) influential designs of the modern era, the Audi 100/5000 of 1982. With flush mounted windows and a modified wedge shape that paid tribute to the NSU, the Audi became the first mass-production sedan to achieve a Cd of .30. More than any other car, it launched the “aero era”, when manufacturers suddenly found themselves in a race for ever-lower numbers, or at least with cars that created that impression.

1977 Chevrolet Caprice Estimated Cd: 0.55 ? (Seems a bit high)

Backing up just a few years, in the USA, the energy crisis of 1974 suddenly thrust aerodynamics back into the mainstream, if not in the foreground. The long-neglected aerodynamicists were now finally embraced and integrated into the design process. GM’s downsized sedans of 1977 were the first to benefit from their knowledge, although it’s quite obvious that these cars like the Caprice below were relatively slow learners of the art. Although well behind Europe’s state of the art, even fine detailing for aerodynamic efficiency made an effective difference.

Ghia Ford Probe I 1979  Cd: 0.22

While GM was dipping their toes, Ford suddenly plunged wholly into the aerodynamic ether. Determined to jettison their boxy image after their near-death experience in 1979, Ford’s new management made a bold commitment to a complete embrace, and was determined to be the leader in the field. A series of ever-more aerodynamic Probe Concepts started with the Probe I,

and ended with the Probe V of 1985, which held the world record Cd of 0.137 for some years.

The 1983 Thunderbird was the first volley, but the really bold gamble was the 1986 Taurus (above), and its Sable sibling. The Taurus and Sable were among the first US cars to use composite headlights, allowing for a smoother front end. And they came to define the American aero or jelly-bean era.

The Sable was slightly more aerodynamically optimized, and beat the Audi with a .29 Cd. The race was on, and within a few years, GM would also be fielding dramatically more aerodynamic cars.

Mercedes had been utilizing aerodynamics to fine tune their cars for decades but the W126 began a more aggressive push to stay on the leading edge. The highly influential W124 (above) achieved a Cd of .28 in its most slippery variant. From this point forward, there were continual improvements from the major global manufacturers, although total aero drag often rose because cars were generally getting wider and taller too.

Needless to say, the SUV phase set aerodynamic influence in that segment back to the horse and buggy era. The ultimate wind-offender was the Hummer H2, which not only sported a .57 Cd, but its total aero drag of 26.5 sq. ft. is the highest on record for any modern vehicle listed. Wikipedia has nice charts of both Cd and total drag here.

To give GM credit, the 1989 Opel Calibra coupe set a new record for its class, with a superb Cd of 0.26. Fine detailing, now including the vehicle under-belly, paid off without having to resort to extreme or stylistically unpalatable measures. It led the way into the mainstreaming of super-low Cd vehicles.

Incidentally, that 0.26 is less than the 0.28 attributed to the Chevy Volt. It should be noted that different labs achieve different results, so none of these numbers should be taken as an absolute.

GM’s experience with the Calibra and long hours in the wind tunnel paid off dramatically with the EV1. Electric vehicles’ limited energy storage density necessitates optimized aerodynamics if the vehicle is to run at highway speeds. Thanks to its phenomenal Cd of 0.195, the EV1 had a semi-respectable range of 60-100 miles, despite its old-tech lead acid batteries.

The Cd 0.25 barrier for mass production cars was broken by the 1999 gen 1 Honda Insight, a serious accomplishment considering what a short car it is. Given that the Coefficient of Drag (Cd) is relative, its generally easier to attain a high number in a larger vehicle without having to resort to more drastic measures. The Insight shows plenty of those, including its rear wheel spats.

A more practical solution that also achieved a .25 Cd (in the specially optimized 3L version)was the advanced Audi A2 from 2001 (above). A lightweight four seater with aluminum construction, the TDI three-cylinder diesel powered A2 was the first four/five door car sold in Europe to be rated at less than 3 liters per 100 kilometers (78.4 US mpg). Surprisingly fun to drive too, it was not a sales success, likely due to its rather odd styling. It may well have suffered from Airflow syndrome, being just a tad too far ahead of mainstream styling acceptance. Note how similar its highly effective Kamm-influenced shape is to the 1938 Kamm prototype we looked at a bit earlier.

With a Cd of .25, the 2010 Toyota Prius has made highly aerodynamic cars an every-day reality, and on a very mass scale.

The current record holder for mass-production cars is the Mercedes E 220 CDI Blue Efficiency Coupe, with a Cd of 0.24. Undoubtedly, that will be broken before long. The Prius and Mercedes represents the current state-of-the-art for a production sedan without any compromises or additional tweaks. Undoubtedly, we’ve arrived in the full flowering of the aerodynamic age, even without the teardrop pointed tails and dorsal fins. That the aerodynamic frontier will continue to be cleft with ever less resistant vehicles is now an absolute given. We’re well beyond the point of no return, although the same sentiments were also widely held in the late thirties.

While continued refinement of the traditional automotive package will undoubtedly yield further reductions in the aerodynamic coefficient, to make a more dramatic jump requires extreme measures, like the still-born Aptera. Its Cd of .15 is stellar, but substantial compromises are involved. It’s highly unlikely that this represents the shape of mass-production cars in the foreseeable future.

More likely, the Mercedes Bionic of 2005 shows the way forward. With a Cd of 0.19, it offers a more practical package than the uncompromising Aptera.  But then the Aptera’s frontal area is also significantly lower, and its total aerodynamic drag is undoubtedly not easily beat.

Even if energy prices hold steady or moderate, it seems safe to say that the aero-era has returned, and is here to stay. Government mandates, environmental and social pressures assure that optimizing fuel consumption, or maximizing EV range, will be priorities in every category of vehicle. And aerodynamics plays one of the most crucial elements in facilitating that.

Postscript: This Three Part Survey in no way pretends to be comprehensive. My apologies if your favorite aero-hero has been left out. But if there’s been a serious omission, I’d love to hear about it, as this is a work in progress.

Part 1 here Part 2 here Related article on Total Aero Drag here