• Dec 26, 2008
Click above to view high-res gallery of the Ford Flex

The classic idea of aerodynamics gives rise to mental pictures of vehicles shaped like a smooth suppository. Reality turns out to be different, thankfully. Cars like the Ford Flex may appear weighty and as slippery to the wind as a barn while actually sliding through the atmosphere far more gracefully than one might guess. Aerodynamics studies by all automakers have led to the startling discovery that vehicles like the squared-off Flex actually manage their airflow quite well, thank you, and sanding off the corners hinders, rather than helps.

It's the same over at Toyota where they're calling strategically-placed folds "aerocorners." While it's long been held that a teardrop shape is the most aerodynamic, that's not necessarily the case and a droplet-shaped vehicle isn't terribly practical; just try to put that armoire in your first-gen Honda Insight. The worry that all cars will look the same when aerodynamicists start to take over is unfounded, as discoveries in the wind tunnel show that things aren't always as they appear, and there's plenty of room for uncommon design to still cheat the wind.


[Source: NYT]


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  • 25 Comments
      • 6 Years Ago
      Just because Rosie O'Donnel "can" also be as aerodynamic as Charlize, it doesn't mean all women "should" look like the former.

      What the Flex wins in function it loses in style.
      • 6 Years Ago
      (I am not a physicist, but let me muse...)

      I've always wondered why the "teardrop" shape has attained the defacto-status of most aerodynamic when raindrops achieve a terminal velocity of only 5-20mph?

      I mean, I understand the reasoning: since water is malleable, it will self-define the most optimum form for it's environment. But since it only falls at 5-20mph, one would have to presume there are ore optimum shapes at other rates of speed (ie the rates at which we judge most modern vehicles -, 30mph+ for medium-long range). And let's not forget the fact that we're conveniently ignoring density and mass (among other things).

      To me, the teardrop is a beautiful natural - and probably optimum - result of a specific set of parameters, which may provide insight into other situations, but would hardly provide the blueprint for everything or anything else.

      Isn't that obvious, or am I missing something?
        • 6 Years Ago
        They're quite limited in speed, because of their weight.

        The force, in Newtons, that air-resistance applies on a falling object will be the same for a specific shape and velocity no matter what.

        The force, however, that the earth's gravitation applies grows linearly in relation to the object's weight, resulting in equal acceleration for every object, in an optimal no-drag situation - for proof, NASA filmed an astronaut dropping a feather and a hammer on the atmosphere-less moon, and they arrived at the ground together.

        When force A (air resistance) is equal regardless of weight and force B isn't, and works in the opposite direction, then the terminal velocity for a falling object will be determined by that weight, as well.
        • 6 Years Ago
        Not really, just that teardrops/drops of water don't have bumper regulations and other stuff that sets a basic shape. One other aspect of the optimal shape that should be taken into consideration is the optimal shape in traffic or open road. We've all tuned into at least a few minutes of NASCAR and Indycar, enough to know about designing a car to draft very well, versus designing a car to drive by itself very cleanly.

        Sure, a giant point on the front of a car would probably make it slice through the air a little better, but then we'd be driving around impaling pedestrians on crosswalks Ming-style all the time Flash. ;)
        • 6 Years Ago
        Teardrops aren't "teardrop shaped" any more than hearts are "heart shaped", and they're not very aerodynamic.

        Fish-shaped on the other hand...
        • 6 Years Ago
        One of the primary reasons for the teardrop shape of raindrops is the 'surface tension' of the liquid. Good luck writing that equation into the shape of a car!
      • 6 Years Ago
      1. If I wanted a Suburban, I'd buy an Escalade.
      2. Flex is still fugly.
        • 6 Years Ago
        the flex is like the clubman, wierd in studio shots, awesome in person
        • 6 Years Ago
        If you want a suburban, why don't you just buy a suburban. Chevy still makes 'em.
        • 6 Years Ago
        I wonder how many people who think the Flex is ugly just love the xB, which is truly, hideously ugly.

        At least the Flex has style.
        • 6 Years Ago
        To each his own. I personally like the Flex, and in most tests, it's beating it EPA numbers while carrying its passengers more comfortably. Although, it doesn't look very good in some of the colors you can get it in. All white doesn't look good at all IMO. Sterling gray with the white roof looks great though.
      • 6 Years Ago
      As with all designs, the balance between form and function must be met. Is giving up .04 cd worth greater passenger / cargo volume? What's the difference in real world MPG .35 cd vs .31 cd and does that difference outweigh any increase in functionality a larger vehicle with a higher cd may offer? Just because a vehicle has a low cd doesn't equate great MPG alone, as other mechanical factors are involved as well. A 1995 Mazda Millenia had a cd of .29, but could only muster about 27 MPG hwy for example.
        • 6 Years Ago
        > A 1995 Mazda Millenia had a cd of .29, but could only muster about 27 MPG hwy for example.

        It is not correct to compare vehicles with VERY different engines. That is engine technology have gone a long way from 1995 to 2008. I'm sure if we drop a modern fuel efficient engine with modern transmission that 0.29 mazda will do much better.

        Concerning high SUV's, remember, that the drag force is proportional to Cd * frontal area. That is even if we have a large SUV with an amazing Cd = 0.25 it would still consume 50% more fuel than Prius just because of the larger frontal area.

        To conclude, Flex with 0.355 with relatively tall roof is not a very good example of low drag vehicle.
      • 6 Years Ago
      When I read the full story of this a few days ago (NYT maybe?), it implied that a big part of the improvement has to do with pushing air around areas of the car that can't be fixed easily with shaping, such as wheel wells and the undercarriage. So instead of trying to put goofy slats over the rear wheel-wells, or ugly flat wheel covers, you use the front corners of the car to push air out and around the wheels, bypassing the issue all together.
        • 6 Years Ago
        Pushing the air out and around the wheels helps, but is still not as efficient as just smoothing the flow over the wheels. The OEM's use these other tricks because fender skirts aren't popular currently. Take a look at cars purpose-built for good aerodynamics. Many Lake Bonneville racers, as well as the Prius, Insight, EV1 and Aptera all have covered wheels, to name a few. The later Ford Probe concept cars even had flexible skirts over the front wheels to lower drag.
      • 6 Years Ago
      Not really big news for those following aerodynamics...

      Watch the designs Formula 1 comes up, and you'll notice that indeed, smooth shapes aren't always the best. Notice teams that implemented "viking horns" and a plethora of winglets all over the cars, and the results? Drag levels sunk. These devices sometimes act in ways that we don't really understand: Mainly by creating a vortex, sometimes purposely.

      There's an interesting study published by Mitsubishi on their Vortex Generators on the Evo cars, including some CFD data: The vortex created over the roof moved in a way that not only improved the spoiler's efficiency, but also reduced drag compared to a version without the generators. And one would think a car without small protrusions on the roof would've faired better if drag was the object...
      • 6 Years Ago
      I'm actually kinda surprised, but I suppose nothing is really ever quite as it seems. First time I saw the Flex I wondered how un-aerodynamic it would be.

      I'm, for once, happy to be proven wrong. 0.355Cd is damn impressive, lower than, just to name a few, the Mustang, Countach, Escape, and Tiguan.
        • 6 Years Ago
        Derek, the difference between the flex and the benz is that one is a concept and one is production
        • 6 Years Ago
        The people I know that Have a Flex are pretty happy with their vehicle. most of them traded their old minivan. Most of them were impress for the attention this car gets on the street. They also seem to be happy with everything this crossover offers. So kids if your mom is trying to buy a minivan, convince them that this flex is one.
        • 6 Years Ago
        Derek, I don't really think it's that simple. I mean, do you want to be seen in that Merc?

        On the other hand, the inspiration is worth taking, ie from fish, since they have to be fluid-dynamic, and air is essentially a fluid.
        • 6 Years Ago
        .355? It is only good "for a box". While I do like the styling on the Flex, that is far from aerodynamic. The very large frontal area will only increase the drag on the vehicle as well.

        Now, something like the Mercedes Bionic is impressive. A box shape with a 0.19 Cd. That is similar to the EV1 and beats the Prius by 26%.
        http://en.wikipedia.org/wiki/Mercedes-Benz_Bionic
      • 6 Years Ago
      In fact, one of the most sharply creased cars in the last 20 years was also one of the most aerodynamic...

      "In February 1985 the Subaru XT, considered to be the ‘most aerodynamic car in the world' was introduced. "

      http://www.conceptcarz.com/vehicle/z2036/Subaru-XT.aspx
      • 6 Years Ago
      Remember the Trans Am? Or the Buick Park Avenue? They both had a 0.31 cd..
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