The Truth About Cars » aerodynamics http://www.thetruthaboutcars.com The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. Fri, 12 Sep 2014 10:00:45 +0000 en-US hourly 1 http://wordpress.org/?v=3.9.2 The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars no The Truth About Cars editors@ttac.com editors@ttac.com (The Truth About Cars) 2006-2009 The Truth About Cars The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars » aerodynamics http://www.thetruthaboutcars.com/wp-content/themes/ttac-theme/images/logo.gif http://www.thetruthaboutcars.com A Visit To Ford’s Wind Tunnel To Look At The New Mustang’s Slick Aero Tricks http://www.thetruthaboutcars.com/2014/03/a-visit-to-fords-wind-tunnel-to-look-at-the-new-mustangs-slick-aero-tricks/ http://www.thetruthaboutcars.com/2014/03/a-visit-to-fords-wind-tunnel-to-look-at-the-new-mustangs-slick-aero-tricks/#comments Sat, 01 Mar 2014 18:00:55 +0000 http://www.thetruthaboutcars.com/?p=756721 Click on the settings icon in the menu bar of the video above to watch it in 2D or your choice of 3D formats. The second best part about the job of writing about cars is not getting to drive expensive cars for free or being flown to resorts with Jacuzzi tubs. No, the second […]

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Click here to view the embedded video.


Click on the settings icon in the menu bar of the video above to watch it in 2D or your choice of 3D formats.

The second best part about the job of writing about cars is not getting to drive expensive cars for free or being flown to resorts with Jacuzzi tubs. No, the second best part about the gig is that I get to see and do some very cool car guy things. How many of you have watched film or video of a car being tested in a wind tunnel and thought to yourself, “that’s neat!”? Well, this week I got to observe the new 2015 Ford Mustang’s aerodynamic features demonstrated in one of those neat wind tunnels.

As part of the publicity campaign leading up to the April introduction of the all-new 2015 Ford Mustang, Ford is going to have a series of presentations to Detroit area automotive media types and they kicked it off with a visit to FoMoCo’s Driveability Testing  Facility in Allen Park. The DTF contains a number of test cells that allow Ford engineers to duplicate just about any temperature, altitude or meteorological condition (including snow and hail) a driver might experience. Three of the test cells are wind tunnels large enough to test full size cars and Ford’s marketing and engineering folks had a preproduction black 2015 Mustang GT coupe sitting in one of them.

After Kemal Curić, who was in charge of exterior design on the new Mustang, did a walkaround, pointing out the various aerodynamic features of the car, they fired up the fans to 30 mph and a technician used a smoke wand so we could actually see just how effective those features are.

Click here to view the embedded video.

When the 2015 Mustang finally hits the showrooms later this year, you may not notice the differences, but each of the models has been fine tuned for aerodynamic balance. Ford says that they spent twice as much time on the new Mustang’s aerodynamic performance as on the outgoing model. Much of that work was done in the digital domain, which can work at a very fine granular resolution that can’t be replicated with real-world pressure sensors or physical tufts, but still everything is subjected to real-world testing with real airflow in a wind tunnel.

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Some of the changes are almost imperceptible, for example, raising or shaving the surface of the rear deck lid by as little as 1 millimeter will have an observable and significant effect. Each model, Ecoboost 4, V6 or GT, has slightly different aero features and if you order the performance package on the GT, that gets its own special wind-cheating tricks. For example, EcoBoost powered Mustangs will feature active grille shutters that close to reduce drag at higher speeds. Different front splitters and functional rear underbody air extractors were developed for each model. The front fascia on all models incorporates ducts that create aero wheel curtains that isolate the spinning wheels and tires from turbulence, a first for Ford.

Wheel aero curtains on the 2015 Mustang

Wheel aero curtains on the 2015 Mustang

Most of the work is aimed at reducing turbulence and hence drag by keeping the airflow closely attached to the car body’s surface as it passes the car. With the smoke wand set right at the leading edge of the hood, the trail smoothly runs from the nose of the car up over the roof and then down the fastback roofline and over the integrated spoiler on the deck lid. It’s only when the smoke is finally trailing the car that you see any turbulence, though as it transitions past the functional cold air intake for the engine at the base of the windshield you can see the eddies curling air down into the induction system.

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Another of the aero features of the front end are functional air extractors in the hood. Not only do they prevent air pressure from building up under the hood, Curić said that they actually create downforce. Moving back along the car, the side mirrors have been moved from the window frame down to a stalk on the door. That aerodynamically isolates the mirror from the body, allowing laminar flow along the window. The mirror itself has been shaped so that air flows smoothly around and past it. A side skirt below the rocker panel works with the front splitter to keep underbody airflow separate from the upper air. One aero device you might not notice is a small flap spoiler mounted under the car just in front of each rear wheel, intended to smooth the flow of air around the rear tires.

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The rear decklid of the new Mustang GT is the collaborative product of the designers, aerodynamicists and the manufacturing engineers. You may not realize this when you see the complex shapes on modern cars, but there’s a constant struggle between the designers and the body engineers over what is possible, or more importantly, what is possible at a price point. The decklid on the 2015 Mustang is a relatively complicated shape, particularly because they decided on an integrated spoiler, not a bolt on part. It’s one thing to get a clay model to perform well in the wind tunnel, it’s another thing to be able to reproduce that shape in metal or plastic production parts.

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One reason why they don’t just rely on testing aero with fluid dynamics in the digital domain is that the wind tunnel isn’t just used for aerodynamics. Microphone arrays mounted above and to the side of the car are used to measure noise and are part of the process of reducing NVH. Interior sound measurements are taken with the audio equivalent of crash test dummies, but I was told that exterior measurements correlate well with how much noise there is inside the car, which makes sense.

IMG_0027At the event I learned a little bit about how they do wind tunnel testing at Ford and how that affects the way the new Mustang looks and drives. I also learned a bit about just how serious the Ford engineers and designers are about wringing out a small percentage improvement here and another one there. When it comes to aero, all those little things add up. Though they wouldn’t cite a specific drag coefficient, we were told that the new Mustang is 3% better in terms of aerodynamics than the 2014 model, yielding a 1% improvement in highway fuel economy. As you can see from the acoustic testing, though, it’s not only about miles per gallon.

Almost one in five Mustangs that are sold currently are convertibles. Before the wind tunnel presentation we heard about the Webasto supplied folding roof on the new Mustang convertible and how it’s quieter, goes up and down faster (an electromechanical drive replaces hydraulics), folds flatter, looks better both up and down, and, yes, has better aerodynamics than the ragtop on the outgoing model. The old roof had three supporting bows, a vinyl outer skin and an inexpensive inner skin. The new roof has an additional bow to give the roof better shape, the outside is fabric, the inside is real headlining material and between them, for the first time on a Mustang, is a layer of sound and heat insulating foam. One of the reporters asked them if the improvements were made in response to consumer feedback. The Ford engineer replied that yes, they had gotten feedback indicating that Mustang owners wanted a quieter car, and then, almost as an aside, he said, they wanted to give the new Mustang a better roof in general.

It’s quite difficult to convey to people just how massive an undertaking it is to develop a new car. I’m sure that what I saw at Ford is duplicated at every major car company. Because of this job I get a peak behind the curtain now and then and I get to pay attention to the men and women working behind that curtain. However, instead of charlatans pulling levers projecting the image of greatness, there are lots of very hardworking people making great efforts at incremental improvements that, taken cumulatively, positively impact our experiences as drivers and car owners.

Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can get a parallax view at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks for reading – RJS

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The Return of the Running Board http://www.thetruthaboutcars.com/2013/12/the-return-of-the-running-board/ http://www.thetruthaboutcars.com/2013/12/the-return-of-the-running-board/#comments Thu, 12 Dec 2013 12:00:10 +0000 http://www.thetruthaboutcars.com/?p=675250 Gordon Buehrig’s design of the Cord 810/812 was revolutionary for its day. One innovation was that it lacked running boards, something automobiles had featured almost since the dawn of the motoring age. I’m guessing that the origin of running boards has to do with the fact that in the early days car bodies were typically […]

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Gordon Buehrig’s design of the Cord 810/812 was revolutionary for its day. One innovation was that it lacked running boards, something automobiles had featured almost since the dawn of the motoring age. I’m guessing that the origin of running boards has to do with the fact that in the early days car bodies were typically mounted right on top exposed frame rails, putting the body up high, and the running boards were used as step to get up into the interior. From a design standpoint, they also visually connected the front and rear fenders, creating one flowing line. What was stylish in 1913, though, wasn’t necessarily au courant in the mid 1930s. Also automotive design started getting more formally established in the 1930s, with GM and Ford both having in-house design staffs by the end of that decade. Based on the then young science of aerodynamics and the related streamlined aesthetic, new shapes started appearing on cars.

1937 Cord 812 Roadster

1937 Cord 812 Roadster

One of the clearest points of departure was the lack of running boards. By the end of the 1930s they were seen as old-fashioned, an impression that was helped along by the Cord and other futuristic designs of the day. The Pierce Arrow Silver Arrow show cars from 1933 had bodies with mostly slab sides (except for the rear fenders) and no running boards. The five ’33 Silver Arrows that were built were so revolutionary that the production Silver Arrow of 1935, which borrowed styling from the show car, still had footboards.

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Another show car, perhaps the most important prewar show car because it was General Motors’ first “concept” car, Harley Earl’s Buick Y Job of 1937, also lacked running boards.

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By the end of the decade, with the introduction of the smooth sided production 1939 Lincoln Continental, running boards were on their way out.

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It would take until after World War II for the transformation to be complete, but as far as I know, no all-new postwar car designs had running boards.

The growth of the SUV market brought running boards back to make it easier to climb in and out of utility vehicles’ high seating positions, but those are trucks and we haven’t seen anything like that on cars, until recently. Ironically, what is bringing door sills on cars back is what got rid of them in the first place, aerodynamics. Back in the 1930s, designers were going more by common sense than by using wind tunnels, and a smooth, streamlined look seemed logical and was indeed consistent with what early aerodynamicists like Paul Jaray were espousing. Today, however, automotive designers know that smooth isn’t always aerodynamic. Just look at all of the odd appurtenances hung on modern Formula One racers, and high performance road cars have sprouted spoilers and splitters as well. Now side sills, which cosmetically look pretty much like running boards, are starting to appear as well.

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The Ferrari LaFerrari has what some call undertray sill extensions. Those are narrow  compared to carbon fiber sills on the McLaren P1, essentially continuations of the splitter up front.

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The McLaren P1 and Ferrari LaFerrari hybrid supercars both have aero effective side sills, and if you look at the photos from last week’s reveal of the all-new 2015 Mustang, it has sills as well. I’ll have to wait to find out from Ford engineers if those side sills are actually aerodynamic or just for looks, but whichever they are, they look aero and no car designer ever minded his or her design being associated with the look of a much more expensive car (Tesla designer Franz Von Holzenhaus told me that his Model S “looks completely different” from the front end of current Maseratis, but he smiled broadly when doing so). Since car designers (and their bosses) are some of the most faddish people on the planet, I think we can expect more running boards, er, aerodynamic side sills to proliferate on performance cars and those with sporting aspirations. We’ll be seeing the Z06 version of the new C7 Corvette next month at the NAIAS in Detroit.  The ZR1 version of the C6 ‘Vette had sills and from the teaser photo that GM has released it looks like the next Z06 will have aero “running boards” as well.

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Ronnie Schreiber edits Cars In Depth, a realistic perspective on cars & car culture and the original 3D car site. If you found this post worthwhile, you can get a parallax view at Cars In Depth. If the 3D thing freaks you out, don’t worry, all the photo and video players in use at the site have mono options. Thanks for reading – RJS

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Vellum Venom: Uwe Bahnsen, Car Designer, RIP http://www.thetruthaboutcars.com/2013/08/vellum-venom-uwe-bahnsen-car-designer-rip/ http://www.thetruthaboutcars.com/2013/08/vellum-venom-uwe-bahnsen-car-designer-rip/#comments Thu, 08 Aug 2013 03:51:41 +0000 http://www.thetruthaboutcars.com/?p=498589 Never forget: people make all the difference.  This often overlooked fact in the glamorous world of automotive styling rings true for the life of Mr. Uwe Bahnsen. I froze in my tracks when I heard of his passing on Car Design News. His work at Ford and with the Industrial Design community influenced me, and […]

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Never forget: people make all the difference.  This often overlooked fact in the glamorous world of automotive styling rings true for the life of Mr. Uwe Bahnsen. I froze in my tracks when I heard of his passing on Car Design News. His work at Ford and with the Industrial Design community influenced me, and every American who loved cars in the 1980s.

How ironic that Mr. Bahnsen’s passing was the week TTAC’s own Ford Sierra passed its citizenship test in Texas: so here’s a great Germanic-Texas Beer for you, Mr. Bahnsen.

Every car is designed by a team–not a person—but the kind words spoken about Uwe’s life say he was no ordinary designer.  And he was a good man: so instead of paraphrasing Wikipedia and the great work by Car Design News, let’s see what he did for us.

Bahnsen’s work with the “bathtub” Ford Taunus P3 and second generation Escort/Capri are impressive alone.  Especially the P3, a progressive–if not radical–design for the early 1960s.  But what’s the Super Bowl of a car designer’s career?  Being the VP of Design, making a paradigm-shifting sedan that sells well around the world. A vehicle that lives long enough to go from radical to mainstream over the course of a decade.

That work is the 1982 Ford Sierra. Unlike more exotic brands (Audi 100 and beyond) that went “Aero” thanks to pricey Italian design and/or expensive engineering for limited production, the Sierra was wholly affordable and completely common. A people’s car like the Model T and VW Beetle…just not to that famous of an extent.

Sierra meets the big fan…

But you catch my drift. Us Yanks only know the Sierra in Cosworth/Merkur drag, so perhaps the firsthand experience of Bahnsen’s hard work as told by Mr. John Topley says it best:

“It’s difficult for me to convey just how radical the Sierra was when it was launched. This was the car that replaced twenty years of the Ford Cortina, a favourite with both fleet and family buyers in Britain. By 1982 the Cortina was looking pretty tired. It was still a best seller but by all accounts it wasn’t a great drive and the technology was pretty agricultural. In spite of which, Britain was still buying masses of them.

By contrast, the new Sierra looked like nothing else around, aside from the even more radical Audi 100 which came out at the same time. I think the Sierra was more important though because it was a mass market rather than executive car.”

Moments in time like these are rare, how often does a design change the way a person moves?  On multiple continents, for over a decade?  This moment elevated the car design game thanks in part to Ford’s Aerospace division, the beginnings of finite element analysis, and usage of new technologies that made the Sierra’s wraparound bumpers and ergonomic dashboards so cutting-edge. It’s a most fertile ground for a designer.

While we (probably) live in the Golden Age of technology, Uwe Bahnsen’s world experienced a far more dramatic change from far less technology. Aside from the aforementioned Audi, most carmakers embraced this technology/design philosophy years later. Boo to them: Uwe and his team were on the cusp of something special…the future!

Uwe Bahnsen made the most of this opportunity, take it from the guy that owns one of his creations.  To this day, the original Ford Sierra looks more futuristic than a Toyota Prius, providing an ownership experience that satisfies the senses like a far more expensive BMW. This doesn’t happen often, especially in America.

More to the point, the Sierra is an ergonomic and aesthetic treat. I’d love to ask Mr. Bahnsen hundreds of questions about his life, but the fact remains: his contribution to the Automobile shall never be forgotten.

Thank you all for reading, I hope you have a lovely week.

 

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Piston Slap: Raising the Bar by Lowering It? http://www.thetruthaboutcars.com/2012/02/piston-slap-raising-the-bar-by-lowering-it/ http://www.thetruthaboutcars.com/2012/02/piston-slap-raising-the-bar-by-lowering-it/#comments Wed, 08 Feb 2012 11:56:46 +0000 http://www.thetruthaboutcars.com/?p=429642       TTAC commentator educatordan writes: I know this is an exercise in mental masturbation but I find myself thinking about it and perhaps the B&B with their extensive experience could shed some light on the subject. OK here goes; Will lowering a vehicle improve the vehicle’s fuel economy?  Several manufacturers of lowering systems […]

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Click here to view the embedded video.

 

TTAC commentator educatordan writes:

I know this is an exercise in mental masturbation but I find myself thinking about it and perhaps the B&B with their extensive experience could shed some light on the subject.

OK here goes; Will lowering a vehicle improve the vehicle’s fuel economy?  Several manufacturers of lowering systems claim that it will, but would it be measureable?  In my mind even 1 mpg would be significant on certain vehicles.  This question sprung to mind as I was looking at low resale values on fairly clean early to mid 2000s American SUVs.  Those TrailBlazers, Envoys, Raineers, Explorers, Mountaineers, and Aviators are likely as close as were gonna get to a modern version of the all American family wagon and you can buy lowering kits for even the 4wd/AWD versions.  I know lowering a vehicle improves handling a rollover resistance but what about fuel economy?

Sajeev answers:

I hope this isn’t an exercise in mental masturbation, as I sometimes consider this quandary while exiting the freeway in my 1995 Lincoln Mark VIII LSC. That’s because the Mark’s air compressor refills the air springs to raise the ride height 20mm when the car goes below 45 MPH. And, compared to the low-speed ride height, they drive better (variable-assist steering too) and looked pretty cool lowered on the highway…back when they were a common sight on the highway. You may not see a new “Quadra-Lift” Jeep Grand Cherokee perform the same trick, but they do.

Alrighty then! According to this thread, there can be a fuel economy benefit to a lowered vehicle. In theory. Always in theory.

I like the theory of lowering a car to reduce the “frontal footprint” of your tires.  Whether or not lowering the vehicle will mess up downforce to the point of fuel economy detriment is anyone’s guess, unless you have a fluid dynamics lab in your garage. For the purposes of a street car that can be lowered enough to not ruin wheel alignment/suspension travel/load carrying abilities, I suspect lowering a vehicle will improve fuel economy.

 

 

Enough to matter? Maybe not with the massive frontal area of a modern passenger car with zero overhang and nerdy ride heights, but maybe with the long, bullet nose of a Lincoln Mark VIII hugging the ground. Your guess is as good as mine.

Send your queries to sajeev@thetruthaboutcars.com . Spare no details and ask for a speedy resolution if you’re in a hurry.

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It’s A Drag: Does Wind-Tunnel-Vision Kill Car Design? http://www.thetruthaboutcars.com/2011/06/it%e2%80%99s-a-drag-does-wind-tunnel-vision-kill-car-design/ http://www.thetruthaboutcars.com/2011/06/it%e2%80%99s-a-drag-does-wind-tunnel-vision-kill-car-design/#comments Mon, 20 Jun 2011 18:31:04 +0000 http://www.thetruthaboutcars.com/?p=399560 Do you think that cars have lost their soul? Nina Tortosa, General Motors aerodynamicist for the Voltec/E-Flex programs, says that cars look more and more alike because “we all have to abide by the same laws of physics. It doesn’t matter if we don’t like them,” Nina Tortosa told WardsAuto. Mere mortals have to contend […]

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Do you think that cars have lost their soul? Nina Tortosa, General Motors aerodynamicist for the Voltec/E-Flex programs, says that cars look more and more alike because “we all have to abide by the same laws of physics. It doesn’t matter if we don’t like them,” Nina Tortosa told WardsAuto.

Mere mortals have to contend with two certainties – death and taxes. Car designers are faced with a third one: Cd, or the drag coefficient.

When I was in advertising, countless engineers tried to explain the drag coefficient (a.k.a. “Cw-Beiwert” – we were in Germany) to me, until one found an ingenious solution: “You want a low one.”

They also told me the secret why the final car never looks like that flashy design study. The wind tunnel, or now rather the drag simulator is the big equalizer.  “It’s a drag,” complained one designer to me, “those damned aerodynamics kill all my ideas.”

Joe Dehner, chief of Dodge and Ram Design at Chrysler, had the same experience: “We, as designers in the late ’80s and early ’90s, were in an organic phase, but aerodynamicists didn’t want organic lines,” he told WardsAuto. “We would take it to the wind tunnel and they would put corners on (it), and (we) would say, ‘You’re ruining my design.’”

Larry Erickson, chairman of the Detroit-based College for Creative Studies Transportation Design Dept. and a former Ford designer, says design doesn’t need to become a victim of aerodynamics. He cites the Opel Calibra, built from 1989-1997: “That car had a killer drag number and looked great.” His advice to students: “Good teams work together to come up with a solution that looks good and is aerodynamic.”

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An Illustrated History Of Automotive Aerodynamics – Part 3: Finale http://www.thetruthaboutcars.com/2010/02/an-illustrated-history-of-automotive-aerodynamics-part-3-finale/ http://www.thetruthaboutcars.com/2010/02/an-illustrated-history-of-automotive-aerodynamics-part-3-finale/#comments Wed, 17 Feb 2010 21:25:50 +0000 http://www.thetruthaboutcars.com/?p=345762 [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 […]

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[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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Curbside Classic Outtake: Aerodynamics Then And Now http://www.thetruthaboutcars.com/2010/02/curbside-classic-outtake-aerodynamics-then-and-now/ http://www.thetruthaboutcars.com/2010/02/curbside-classic-outtake-aerodynamics-then-and-now/#comments Sun, 14 Feb 2010 20:58:05 +0000 http://www.thetruthaboutcars.com/?p=345328 This 1965 Falcon Futura first caught my eye, not the Prius. But seeing them jowl-to-cheek gave me a dramatic lesson in how far car aerodynamics have come. Well, at least in common everyday cars. The Tatra T77 of 1934 still has this Prius’ Cd of .25 handily beat. The Falcon? Who knows; probably around .50 […]

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This 1965 Falcon Futura first caught my eye, not the Prius. But seeing them jowl-to-cheek gave me a dramatic lesson in how far car aerodynamics have come. Well, at least in common everyday cars. The Tatra T77 of 1934 still has this Prius’ Cd of .25 handily beat. The Falcon? Who knows; probably around .50 or so. But this semi-fastback roof on the Falcon was the hot new thing when it came out on the 1963.5 Fords, specifically to help the big Galaxie on the high speed NASCAR tracks.

The Prius’ slippery shape has become pretty ubiquitous now, and its not such a strange sight. But when you see it next to the boxy Falcon, it’s apparent that we’re finally getting the hang of what the early pioneers of aerodynamics were getting at.

This particular Falcon evokes lots of memories, and they’re not so good. I had an Assistant Scout Master who drove one exactly like this, despite being rich. He was a royal PIA, dragging our asses out of our sleeping bags on camping trips at 6 AM for calisthenics. After our late night rumbles and Lord Of The Flies-type devolutionary activities, it did not engender warm feelings to him. And having to ride three across in that cramped back seat, stinking to high heaven, while he found the nearest Catholic Church on Sunday morning for Mass, gave us time to hatch various assassination plans, while listening to the nasal whine of the little 170 cubic inch six as it struggled with its load of hung-over scouts. At least he was a good driver and drove pretty damn fast on the winding Maryland back roads; I’ll give him that. It’s the only thing that kept us from executing our evil plans.

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An Illustrated History Of Automotive Aerodynamics – In Three Parts http://www.thetruthaboutcars.com/2010/02/an-illustrated-history-of-automotive-aerodynamics-in-three-parts/ http://www.thetruthaboutcars.com/2010/02/an-illustrated-history-of-automotive-aerodynamics-in-three-parts/#comments Sun, 14 Feb 2010 20:29:41 +0000 http://www.thetruthaboutcars.com/?p=345269 [Note: A significantly expanded and updated version of this article can be found here] That air presented the greatest obstacle to automotive speed and economy was understood intuitively, if not scientifically since the dawn of the automobile. Putting it into practice was quite another story. Engineers, racers and entrepreneurs were lured by the potential for […]

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[Note: A significantly expanded and updated version of this article can be found here]

That air presented the greatest obstacle to automotive speed and economy was understood intuitively, if not scientifically since the dawn of the automobile. Putting it into practice was quite another story. Engineers, racers and entrepreneurs were lured by the potential for the profound gains aerodynamics offered. The efforts to do so yielded some of the more remarkable cars ever made, even if they challenged the aesthetic assumptions of their times. We’ve finally arrived at the place where a highly aerodynamic car like the Prius is mainstream. But getting there was not without turbulence.

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Racers, particularly those chasing the coveted Land Speed Record (LSR), were generally the first to employ aerodynamic aids. The La Jamais Contente (The Never Satisfied) was the first automobile to break the 100kmh (62 mph) record, in 1899. Like all the first batch of LSR holders, it was an EV. The driver’s position seems to negate the aerodynamic aids, or maybe he was just posing, and more likely crouched down for the actual run.

The evolution of aerodynamics for LSR cars was remarkably rapid, as this Stanley Steamer Rocket of 1906 evidently shows. And the increase in speed was even more dramatic: the Rocket broke the 200km barrier, with a run of 205.44 kmh (127.66  mph). That would not be bettered until 1924, and not until 2009 for steam powered vehicles.

The first known attempt at streamlining a passenger car is this Alfa Romeo from 1914, built by the coach builder Castagna for the Italian Count Ricotti. Due to the very heavy bodywork, it turned out to not improve on the top speed of the open Alfa it was based on.

Undoubtedly, the real breakthrough aerodynamic passenger car was the German Rumpler “Tropfenwagen” (teardrop car) of 1921. Unlike the impractical and heavy Castagna Alfa, the Rumpler was as dramatically different (and influential) for its completely integrated and original design and engineering. It had a mid-engined W6 engine, and four wheel independent suspension using swing axles which Rumpler patented. The Tropfenwagen was tested in VW’s wind tunnel in 1979, and achieved a remarkable Coefficient of drag (Cd) of .28; a degree of slipperiness that VW’s Passat wouldn’t equal until 1988.

It’s important to remember that the Cd is a coefficient, and denotes the relative aerodynamic slipperiness of a body, regardless of its overall size. A brick of any size has a Cd of 1.0; a bullet about .295.  To arrive at the critical total aerodynamic drag that determines power required and efficiency, the frontal area (cross section of the vehicle looking straight on) is multiplied by the Cd. The Rumpler was relatively very aerodynamic, but it was also quite tall and boxy, which resulted in the one hundred or so production cars being used primarily as taxis. An ironic ending for Rumpler, but his ideas spawned imitations and extensions world-wide, and opened the whole field.

To put the nascent field of automotive aerodynamics in perspective, the typical two-box car of the twenties was more aerodynamic going backwards than forwards, as this ass-backwards car showed. That brings back memories of Bob Lutz stating that the Volt concept would have had better aerodynamics if they put it in the wind tunnel backwards.

Hungarian-born Paul Jaray used his experience working int the aeronautical field, and especially designing Zeppelins, to develop a specific formula for automotive aerodynamic design principles that lead to a patent, applied for in 1922 and issued in 1927.  His approach was influential, and numerous companies used Jaray licensed bodies during the streamliner craze that unfolded in the early thirties. His early designs tended to be very tall, and with questionable proportions and space utilization (below).

His designs eventually became more mainstream, and Mercedes, Opel, Maybach, and numerous other makes, primarily German, built special streamliner versions using Jaray bodies, like this Mercedes below:

The limitation of these cars is like the Castagna Alfa, they were re-bodied conventional cars with frames, front engines and RWD. Jaray only addressed the aerodynamics, not the complete vehicle like Rumpler had. It was a start, but others were taking up where Rumpler left off, like the English Burney, below:

Obviously more Rumpler influenced and less by Jaray, the 1930 English Burney featured a then-radical rear engine and also four wheel independent suspension.

One of the most influential and lasting designers of the whole era was Austrian Hans Ledwinka. After he took over as chief design engineer at the Czech firm Tatra in 1921, he developed the basis of a series of remarkable Tatra cars and eventually streamliners with platform frames, independent suspensions and rear air-cooled engines that Ferdinand Porsche cribbed from heavily in his design of the Volkswagen (VW made a substantial payment to Tatra in the 1960s to compensate them for this theft of IP).

The compact Tatra v570 of 1933 (above) is the forerunner of both the larger Tatras soon to come, and obviously of the Volkswagen. We’ll come back to Tatra later.

This Volkswagen prototype from 1934 (above) shows a very strong resemblance to the cribbed Tatra v570, with the benefit of some further refinement. Although the visual cues are not really as significant as they might appear to us now, because these were the leading-edge design elements of the time, and widely imitated or shared, on both side of the Atlantic.

As this 1934 prototype for an American rear-engined sedan by John Tjaarda shows, the Europeans weren’t working alone. This fairly radical design became tamed-down for the production 1936 front-engined Lincoln Zephyr, of which the less common but handsome coupe version is shown below:

Of course, Americans’ introduction to streamlining had come two years earlier  in 1934, with the stunning Chrysler Airflow (below). An essentially pragmatic approach, the Airflow also kept the traditional Body On Frame (BOF) front-engine RWD standard, but made some significant advances in terms vehicle design by pushing the engine further forward over the front wheels. This, combined with a wider body, dramatically improved interior space and accommodations. The Airflow had the same basic configuration as American cars from the late forties and early fifties. Progress is not always linear.

The failure of the practical Airflow can probably comes down to one thing: that overly flat waterfall grille. That was too much of  a break for the symbolism still engendered in the remnants of the classic car prow. The Zephyr had one, and it was a success, despite not being nearly as a good a car as the Airflow.

An even less pragmatic but remarkably practical and effective American vehicle was the Stout Scarab (above). Aviation engineer William B. Stout designed this extremely roomy mini-van precursor using  a unitized body structure and a rear Ford V8 engine. The first was built in 1932, and several more variations, a total of nine, were built in the mid thirties, but series production never got off the ground, due to an asking price almost four times higher than a Chrysler Imperial Airflow of the times, and even those weren’t selling so well just then.

A much more radical approaches to streamlining was Buckminster Fuller’s Dymaxion. The first of several prototypes also saw the light of day in 1933, in the midst of this fertile period on both side of the Atlantic. The Dymaxion also had a rear Ford V8, but with a tricycle carriage and rear wheel steering, which allowed it to turn on the length of its body.

Another lesser-know variation of the popular Ford V8 engined aerodynamic vehicles was this Dubonnet Ford of 1936, whose very slippery body allowed it to reach 108 mph. I appears to have  Isetta-type front doors for the front seat passengers. About as much crumple zone too.

Let’s jump back to Czechoslovakia and the fertile Tatra design studios. Here are some clays from about 1933 or so, showing the development of both the smaller VW-like v570 on the right, and the larger streamliners in the rear. The first of these, the T77, arrived in 1934 (below):

The T77 was measured to have a Cd of .212, a number that was not broken by a production car until GM’s EV-1 of 1995, which measured at .195.  A remarkable achievement, the long-tailed T77 was powered by a rear air-cooled V8, and began a long series of Tatras until the 1980′s along similar lines. My retrospective of Tatra is here.

Tatra became synonymous with the advanced streamliner of the pre-war era, enabling remarkably fast travel (100 mph) on the fledgling Autobahns of the Third Reich. Favored especially by Luftwaffe brass, they had a nasty habit of killing them, due to its wickedly-abrupt oversteer, thanks to the combination of rear V8 and swing axles. That earned it the nick name of “the Czech secret weapon”.  So many died at its hands, that supposedly Hitler forbade his best men to drive them. In many (other) ways, the Tatra 87 was the Porsche Panamera of its time.


To demonstrate just how far the aerodynamic envelope was pushed in this golden decade of streamlining, this 1939 Schlörwagen prototype was tested originally at Cd .186, and a model of it was retested by VW in the seventies with a Cd of .15. Either of these values put the “pillbug” at or near the top of the list of the most aerodynamic concept cars ever built, like the Ford Probe V of 1985, with a Cd of .137. Built on the chassis of the rear-engine Mercedes 170H, it was substantially faster as well as 20% to 40% more fuel efficient than its donor car. The Russians took the Schlörwagen as war booty and conducted tests as a propeller driven vehicle. It represents a state of aerodynamic efficiency in league with the most aerodynamic cars being considered today, such as the Aptera.

Its important to note that the rise of interest in aerodynamics in the 1930s arose out of the desire to reinvent the automobile from its horse and wagon origins and the assumptions that average driving speeds would be on the rise with modern roads. This made it a forward looking undertaking, as most drivers were plodding along at 35-45 mph outside of cities. But the first freeways were being built in Germany, and improvements in US roads, including the first parkways and freeways were taking place. It also explains the particularly strong interest and adoption of streamlining in Germany.

Note that I have not attempted to survey the influence of aerodynamics on the styling of cars in the latter thirties and up to WW II. Needless to say the influence was utterly profound, and gave us some of the most remarkable cars of the late classic era. But this had relatively more to do with style (and even affectation) than a genuine effort to push the envelope in terms of leading edge aerodynamics. Nevertheless, the benefits and beauty that resulted, like in this Bugatti Atlantique coupe are undeniable, but beyond our scope here.

Part 2: 1939 to 1955

Part 3: 1955 to the Present

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