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July 17, 2005The shape of cars part 2 of 3We continue to examine the shape of cars in the second of three parts. In the 1960's innovative Texas racer car builder and racers Jim Hall introduced the concept of the wing to motor racing. Standing on stanchions well above the car and flying in the clean air traveling above the car's body, Hall's wing was a revolution in extra down force for racecars. But a wing also has a cost in drag, the down force acts like an anchor when you are trying to travel at the greatest speed in straight line. Hall designed his wing to flatten out for the straight and to dip down for extra down force when the brakes were applied for a turn. It was not long before other racers complained and the moveable wing was soon banned. But the floodgates of wings were let loose on nearly every form of auto racing and wings appeared in a bizarre variety. Racecar driver and builder Dan Gurney made the major improvement to the wing in the early 1970's. He discovered that putting a small "lip" at the trailing edge of a wing works to increase the effective area of the wing. The Gurney Flap as it became known seems counter intuitive, this little tab sticking up at a 90-degree angle to the wing, would be a drag inducer and ruin the flow of air over the wing. Which is exactly what it does, it creates a small eddy of swirling air juts behind the rear edge of the wing. But his swirling air acts to create a boundary that lengthens the effective length of the wing and gives it the effect of a wing with a much larger area. This principle is used by NASCAR racers who have a blunt spoiler at the rear of the car sticking up almost straight into the air. Again, the swirling air of the NASCAR spoiler creates a swirl effect that lengthens the flow of air over the race cars and reduces the kind of drag that the Kamm Back did. Another round of aerodynamic research was unleashed upon auto racing and the effect of air passing under the car was harnessed with the concept of ground effects in the 1970's. By limiting the flow of air under a car and then controlling what air that did pass under the car, it was possible to create a low pressure zone under the and in effect "suck" the car down onto the pavement. Side skirts to limit air travel under the car were used by some racers. Innovator Jim hall combined side skirts with a second engine in the car to drive a large fan that would operate like a vacuum sucking the car to the ground. The greatest drawback to ground effects is that disastrous things happened to the car if the low pressure zone under thc car was disrupted and nasty crashes were the result. Side skirts, sucking fans and creative shapes to the car's bottom were all outlawed by most sanctioning bodies as present too many risks against the danger of some part of the ground effects failing. Today, most sanctioning bodies today have struck a relatively safe compromise of designs to create down force without radial appendages. The notable exception to the radical appendage rule is Formula 1. Today's F1 racer is a dazzling array of wings, winglets, bargeboards and various types of air shapers that create awesome down force. But the high strung racing cars of Formula 1 are designed to create down force at speeds approaching 200mph, the common consumer car spends its life at much lower speeds, the advantages wings and other dooh-dads plastered over every surface like a F1 cars are lost at those speeds. A clean, uncluttered shape is the best for the street. And those wings you see hunched over the rear deck of daily drivers are there for no reason other than style. More on the shape of cars tomorrow.
Posted by Scott at July 17, 2005 9:13 PM CommentsPost a comment |
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