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ing a Hot wheels model of your real car and holding it in the opening of a vacuum cleaner. if you hold it just right (too tight you don’t feel anything, too loose and you’re cutting the bag open) you can feel the aero drag on the car. the third approach is to take a real car, put it on a huge treadmill and blow air

over it at 150 mph, simultaneously running the treadmill at the same speed (also spinning the wheels and tires) while holding the real car with a light touch so as to accurately measure the induced forces (too loose and you’re cutting more than a vacuum bag open!). everybody should get to see this last deal once in their life, it truly looks like a massive wreck just waiting to occur. it always makes me wonder why we don’t just go and drive the car somewhere and measure it (re- member, i’m the guy that pays for it, not the aerodynamicist). actually, the reason that you don’t just go and drive it is because wind, ground undulations, air density and humidity, or just about anything you can think of, screws up the results. How about if you ran a real car inside an environmentally controlled facility with

a totally flat floor? chip Ganassi does just that in an old abandoned pennsylvania turnpike tunnel known as Laurel Hill, so i guess that is actually four ways. to clarify the scale model testing approach, it is actually a lot more sophisti-

cated than hot wheels and vacuum cleaners, but you probably already knew that. the models are big (40 percent scale being the norm) and the vacuum cleaner is now a huge fan and nozzle that assures straight and constant air flow (wind tunnel). nearly all of these wind tunnels now have moving ground surfaces (mGs “belts”). aerodynamic loads are accurately measured and then mathematically scaled so that Zoolanda can understand that it is still valid despite being so small. the natural progression from these “scale model tunnels” is to “full scale tunnels” as previously described. i was going to explain cFd in depth, but when i got to trying to explicate the navier-stokes equations (named after a French engineer and english mathematician) i figured that it wasn’t going to happen in the number of words that the editors give me. think very big computer (or many smaller ones), expensive software and clever

people feeding the beast(s) which produce predictions of downforce and drag, as well as amazing visualizations that you can’t get from a wind tunnel. Ferri cars finished fourth and fifth in a very competitive race and i just finished

writing this article in bed at the dorint hotel at the nurburgring. How did i get here? •

r. Ferri racing (above &#38; opposite page) is off to a great start in the 2014 pirelli world challenge with the help of multimatic.

inside track motorsport news • 11

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