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The aero counterintuitive flex.

You might think that the Ford Flex is approximately as aerodynamic as a porcelain brick (the ceramic representing the overall smoothness of the sheet metal as compared with the straight-up rough-surfaced clay that we're familiar with). However, according to Wayne Koester, Ford aerodynamic development engineer, the coefficient of drag of the Flex is 0.355, while that of its competitors in the full-size crossover segment (e.g., GMC Acadia; Toyota Highlander) have significantly more drag: 0.375. While it might seem that a slight difference wouldn't make a whole lot of difference, Koester says that the better aero of the Flex helps provide a gain of about one mile-per-gallon at highway speeds.

Standing within the Drivability Test Facility in Allen Park, Michigan, which is managed by Jacobs Technology (, Koester points out that the Flex posed a particular challenge to the aerodynamicists, as the concept vehicle, the Ford Fairlane, which had been shown at auto shows and elsewhere, had built up a fan following: "Everyone liked the style and the shape, so we couldn't change it." He says, ''We had to keep the boxiness," adding, "The doors and the roof shape--we couldn't touch that." Rich Gressens, chief designer of the Flex, stands nodding nearby. Gressens says that he is a big believer in the importance of collaboration in product development, so working with Koester and his colleagues was essential.

A Flex is in Wind Tunnel No. 8, which is capable of producing wind speed of up to 150 mph, mounted on a six-component balancer that has three load cells for measuring vertical forces, two for side forces, and one for the X-direction. This setup, Koester explains, helps provide precise results. "The balancer doesn't lie," he says, pointing out that sometimes what would seem to make something more aerodynamic doesn't: "It's counterintuitive."

While they do perform digital assessments of vehicles under development, he says that when they get to the point of having full-size clay models, it is into the wind tunnel. For one reason: They can make a change to a clay model in about 15 minutes and run the test. "An analytical run can take a couple of days," Koester says.

On the Flex they found that making slight changes to things like the sweep of the front fascia and pulling out the area by the rocker helped improve the aero--actually by making them more square, rather than less.

Which is seemingly counterintuitive.--GSV


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Title Annotation:NOTABLE
Publication:Automotive Design & Production
Date:Oct 1, 2008
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