By on February 17, 2010

[Note: A significantly expanded and updated version of this article is here]

For most of the fifties, sixties and into the early seventies, automotive aerodynamicists were mostly non-existent, or hiding in their 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 bricks. But the energy crisis of 1974 suddenly put the lost science in the spotlight again. And although historic 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 place in the forefront of automotive design.

During the ornate and boxy fifties and sixties, with the exception of Citroen, Saab and a few other minor adherents, aerodynamic progress was relegated mostly to the racing world. The value of reducing forward aerodynamic drag on race cars was understood from the earliest LSR 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 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 improve down force and cross-wind stability.

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.

In Europe, Citroen was mostly the keeper of the aero flame for production cars. But one outstanding example in Germany was the rotary engine-powered NSU Ro 80 from 1967.

It’s Cd of .355 set a low-air mark for sedans that would stand for some years. Other than its rotary engine, the NSU was a remarkably influential car, defining the modern idiom almost perfectly. Citroen’s SM Coupe of 1970 (below) lowered the bar for coupes, with its .26 Cd, thanks in part to its adjustable suspension height setting.

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 influential design 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.

In the USA, the energy crisis of 1974 suddenly thrust aerodynamics into the mainstream, and 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 its 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.

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. The 1983 Thunderbird was the first volley, but the really bold gamble was the 1986 Taurus, and its Sable sibling.

The Taurus and Sable were among the first US cars to use composite headlights, allowing for a smoother front end. 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 .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 .026 is the same value that the 2011 Chevy Volt finally attained after its extensive date with the wind tunnel.

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 .195, the EV1 had a semi-respectable range of 60-100 miles, despite its old-tech lead acid batteries.

The Cd .25 barrier for mass production cars was broken by the 1999 gen 1 Honda Insight, a remarkable accomplishment considering what small 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.

With a Cd of .25, the 2010 Toyota Prius brings our survey of production cars to an end. It 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 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. But if the available energy resources for a rapidly expanding base of of global energy consumers and auto buyers happens to runs into a collision course, cars like the Aptera may well represent a possible solution to maintain personal mobility.

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35 Comments on “An Illustrated History Of Automotive Aerodynamics – Part 3: Finale...”


  • avatar
    Ernie

    Paul,

    Where you get these numbers from? Just curious since it seems like a fairly pertinent spec even though it’s kind of obscure.

    Thanks!

  • avatar
    Russycle

    I like the looks of that Audi A2. Put different wheels on it and give it another chance.

  • avatar
    tokencyclist

    Interesting that the Aptera does not go with the ‘Kammback’ design that the Audi A2 has. I thought it was established that you did not have to go teardrop-shaped at the back and that only the shape had to be suggested, as per the Audi and ‘notchback’ cars, e.g. as started with the likes of the Ford Sierra.
    I also think that fashion for alloy wheels does not help. Citroen know how to make wheels aero – put covers over the back ones. This is not so important with the front ones as the air there is less turbulent, with the back wheels it is all messed up. Another feature that would be good to see with the wheels is the Formula 1 style wing extras to steer the air around the wheel more smoothly.
    Every bit of aero-ness helps, not that you would believe it given the design of most cars. With wheels as smooth a surface as possible needs to be presented, but, today’s crop of cars don’t make the effort, garish alloys are what sells cars. This is as stupid as lead in petrol – alloy wheels typically weigh more than steel, the look is paint (they are painted to look like alloy as aluminium alloy corrodes) and if you hit a kerb with them they don’t come off to well, costing $$$ to replace.
    I don’t know why windscreen wipers are not hidden Calibra style. Apart from anything else it keeps the noise down. Same with the back wiper, time to have a camera on that center console if you really cannot see out the back.
    The Audi 100 from the eighties had massively flush windows compared to everything else at the time, this kept the Cd down. Have windows got less flush over the years? Are we unlearning that trick too?
    What is the deal with the fixed radiator grille on cars? Particularly with clumsy manufacturer badge set in to it. If you had to carry those badges around with you on a bike or on foot they would slow you down. None of them are what you might call aero. Anyway, the classic car grille is something that should be ‘active’, only opening when absolutely necessary to cool the radiator behind. As it is, cars with these grilles are more aero back to front.

  • avatar
    Uncle Mellow

    The main reason the Audi A2 didn’t sell well was that it was very expensive. Since they probably lost money on each one , Audi probably didn’t mind too much. They built it to show how clever they were.

  • avatar
    James2

    @tokencyclist

    One reason for a big snout, which is partly disguised by today’s huge grilles, are the pedestrian safety regulations that Europe has started to impose. That is, when you plow into a jaywalker, the Nanny State wants it to not hurt as much :)

  • avatar
    Ingvar

    I find it interesting how the NSU Ro80 design language was taken over so wholesale by Audi. It really is an extension of that mindset, especially the low front/high butt on the cars of today.

    • 0 avatar
      Paul Niedermeyer

      How true. The Ro 80 was a brilliant and profoundly influential design, flawed by its rotary engine. If it had had a modern lightweight piston engine, it could have really amounted to something. No wonder VW bought NSU, and Audi copied its basic design.

  • avatar
    mikeolan

    I think you’re overlooking the major contributions of Chrysler during the 90′s. The Dodge Intrepid, Stratus and Minivans were the most influential designs of the 90′s.

  • avatar
    IanZedcode

    Great Articles, just one minor correction… the Lincoln Mark VII was the first car in the US with composite headlights. (Model Year 1984)

  • avatar

    I am fairly sure that the 1984 Lincoln Continental Mark VII was the 1st U.S. Auto with Flush Headlights.

  • avatar
    KitaIkki

    The 1984 Lincoln Mark VII was the first US production car to use composite headlights. It predates the 1986 Taurus/Sable by 2 years.

  • avatar
    JMII

    Wasn’t the 1989 Opel Calibra known as the Chevrolet Beretta here in the US? Sure looks like the same car. A friend in high school had one and it was a very slick car that featured door handles hidden in the window pillars.

    I’ve said it before: under-body trays are were its at! I swear half the reason my ’00 VW Passat gets 30 mpg is because the underside of the car is as almost as smooth as the top. The oil change guy hates it but clearly it works! A few bits of plastic could easily generate that extra 3-4 mpg everyone is seeking. So why aren’t all new cars (and SUVs) fitted bumper to bumper with underbody trays? It can’t be the cost or the extra assembly time/parts can it?

    Also on a list of odd aero-add-ons was the Lancer Evolution VIII: it featured these little triangles where the roof and rear window met, they created some kind of vortex to increase downforce without adding the drag of a huge wing from what I’ve read.

    • 0 avatar
      Paul Niedermeyer

      No; the Beretta had nothing in common with the Calibra. Here’s s recent Beretta CC :
      http://www.thetruthaboutcars.com/curbside-classic-outtake-packing-a-hot-beretta-edition/

  • avatar
    gslippy

    It is interesting that Volt development has worked so hard to bring its Cd down to 0.26, given the premise that its main utility will be creeping around town, where Cd plays almost no role. And its highway economy will mostly be affected by the drivetrain efficiency and road friction, not the Cd.

    My favorite benefit of low Cd is decreased wind noise at high speeds. And in the case of the new Mercedes E-Coupe, it can help produce beautiful cars.

  • avatar
    fincar1

    I wonder what the Cd is on first-generation RX7′s.

  • avatar
    MarcKyle64

    I had a Subaru XT Turbo, I didn’t know the Cd was so low! It sure was fun to drive.

  • avatar
    djn

    I wonder what the Cd (CX) were of the Alfa Giulietta Sprint Zagato and the Guilia Tubolare Zagato. They sure looked ahead of their time, as well as beautiful.

    http://automodelli.eu/images/1965_AlfaRomeo_GiuliaTZ2b.jpg

    http://italianclassicmotors.co.uk/img/photos/giulietta-sz.jpg

  • avatar
    Martin Schwoerer

    Back from Norway and late to this excellent party. Man Paul, this series is good stuff!

    Some tidbits from me:

    The Audi A2 has become an extremely popular used car, with class-leading resale. No wonder: when I drove it a few years ago, it felt like a narrow, taller A6 — very solid and serene. The best economical car ever.

    I’d note that the Citroen GS / GSA had class-leading aerodynamics for an inexpensive car. It’s easy to make a large car aerodynamic and its not overly hard to make an oddjob like the Insight slippery. But they sold millions of GS’s.

    One thing I might have mentioned is that there tends to be a basic conflict between slipperiness and rigidity. Alec Issigonis knew how to fold the metal of the Mini to make it lightweight yet sturdy. He wasn’t that interested in making an urban car like the Mini aerodynamic. A jelly bean is not rigid.

    Indeed, it is profoundly difficult to make a car lightweight and rigid and aerodynamic. Which cars are in the intersection of these three desirable characteristics — what I’d call the holy grail of automotive design? I’d vote for the Mercedes 124, but also for the unmentioned Citroen BX, the Honda NSX, the 1-series BMW, the Prius, the current Benz C-class, and once more, above all, for the Audi A2.

    • 0 avatar
      Uncle Mellow

      The 1960 Lotus Elite fits the bill. Very light (GRP monocoque with very little steel added) very rigid, giving handling and roadholding of race-car standards , and very slippery. Cost as much as an E-Type Jag though , and the latter had three times as much engine.

  • avatar
    NickR

    the 1989 Opel Calibra coupe set a new record for its class, with a superb Cd of .26.

    So GM had a car that slippery back then huh? Pretty good looking to me. Don’t want to bash GM but this seems like one of GMs designs they should have transplanted, and spared as the execrable Beretta.

    Honestly, the Aptera appeals to me visually. Maybe because if I was driving it I could pretend I was a WWII fighter pilot.

  • avatar
    nutbags

    Loved the aerodynamics lessons. It has always intrigued me since a kid. Thanks.
    I always thought the original Isuzu Impulse (Piazza outside the US) had a smooth, clean and slippery design. Loved it so much that I bought one back in 1985. Curious what the Cd was on that car. It too had flush mounted windows around the same time as the Audi 100/5000.

  • avatar
    kps

    I’d rather have a car that looks like a Tatra T77 (Cd = .21) or Alfa Bat 7 (Cd = .19) than a car that looks like a Toyota Prius (Cd = .25).

    • 0 avatar
      Joel

      So would I, in a New York minute, but they’re totally different kinds of cars. Though, the Prius would have modern accouterments that would make it probably a better long distance driver than the older cars…..buuuut, I’d still take one of the older cars.

  • avatar
    Joel

    The Mercedes Bionic (http://en.wikipedia.org/wiki/Mercedes-Benz_Bionic) is one car that I think makes a great footnote to this great series. They used a frikin fish as the basis for their design, their car looks like a van, and has a .cd somewhere in the range of the EV1. But, since it never made it past research play toy levels and into real world production, it’s not really suitable in the article proper. That said, I woulda probably bought one if they made it.

    • 0 avatar
      fred schumacher

      The Mercedes Bionic Boxfish car is the most interesting design exercise of the last 10 years. By copying the fluid dynamics of the boxfish (Ostraciidae family),they were able to produce a rectangular box with a Cd of 0.19. They were also able to lower the weight of the car by adopting the boxfish’s lattice shell construction. Mercedes made a mistake by not continuing this line of research.

      The boxfish has a square section body with four chines which have the same curve in plan and profile. The late Phil Bolger, master designer of sharpie sailboats, independently discovered that he could reduce turbulance in these flat-bottomed, slab-sided boats by making the chine curve the same in plan and profile, resulting in a boat with more rocker, or belly, than has been normally used. His simple boats are known for their speed even while using traditional, non high-tech sail plans.

      The Audi A2 was hampered by its all-aluminum body for two reasons: cost and vibration. Aluminum transfers vibration much more effectively than steel. Just compare riding a steel bike to an aluminum one. Jim Hall’s Chaparral co-driver Hap Sharp used to call their all aluminum monocoque race car the EBJ for eye ball jiggler.

  • avatar

    The author misses the most aerodynamic 4 wheeled passenger car ever, the 1938 Schlörwagen “Pillbug”:
    [URL]http://img.photobucket.com/albums/v724/NeilBlanchard/Schlr-SideProfile.jpg[/URL]
    [URL]http://img.photobucket.com/albums/v724/NeilBlanchard/Schlor-FrontView.jpg[/URL]
    Cd of this near production car was 0.186.

  • avatar
    CRConrad

    You write, about the Honda Insight: “…a remarkable accomplishment considering what small 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.” I think you meant to say it’s [sic, BTW] “generally easier to attain a low number”, nicht wahr?

    Also, in part two (comments closed there), you wrote: “Frazier, Hudson and Nash…” Frazier? I thought it was Fraser? Ah, no: Frazer. As in Frazer Nash as well as Kaiser-Frazer (so it doesn’t even matter which one you meant).

    HTH!

  • avatar
    Bob Trent

    “Citroen’s SM Coupe of 1970 (below) lowered the bar for coupes, with its .26 Cd, thanks in part to its adjustable suspension height setting.”
    Amazing that the Cd would be that low. The SM’s aerodynamic defects range from the rain gutters, deeply recessed rear side windows, sharp edges on the roof edges and pillars. The slot between the front edge of the hood (bonnet) and the headlight glasses doesn’t help, either. The USA-butchered headlight buckets, disposing of the glasses over the headlights, had to make it worse on USA models.
    The suspension isn’t really adjustable for highway travel. There is a higher setting that raises the car about 1″ above normal. The car is not drivable in the low setting, and the high setting is usable only for low speed negotiation of abrupt humps like in some driveways. The low and high positions are for tire changing.
    The real advantage of the Citroen suspension is that it keeps the car at the same height above the road surface despite loading and high speed lift. A fully loaded trunk (boot) and two people in the back seat do not make the rear of the car squat.
    The SM has a small interior for the size of the exterior. The spare tire takes up most of the otherwise decent trunk.
    There is no front spoiler or air dam as the shape of the rather flat bottom, lowest between the front wheels and gradually rising toward the rear, forms a venturi that creates downforce at speed. The rear edge of the rear hatch has a central spoiler to counter the lift of the sloping rear glass. The rear is a real Kammback complete with recessed rear panel to make a clean break of the airflow, minimizing drag.

  • avatar
    65corvair

    Having owned a 65 Corvair without a spoiler in front, I decided to add one because I thoughtit look nice. To my surprise, it made a huge difference at highway speeds. The front didn’t seem as light. More stability.


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