The Phenomenon of Side Drafting

In a previous GimmeInfo post, we talked about drag and draft and how the affect of one car drafting up to another can propel both cars forward ar a greater rate of speed. In fact, as Brian Vickers pointed out in an interview for the National Science Foundation’s Science of Speed series, “In a two-car draft, it’s like one car with two engines.” It’s about taking the air off the first car’s rear spoiler by creating a vacuum that sends the air up and over the second car. It’s also about the drag effect when one of the cars in a multi-car draft pack gets separated and winds up without a drafting partner behind it. You’ve probably seen it in a race at one of the superspeedways…where one or two drafting cars move out from behind the lead car, causing it to drop like a rock, like it had an anchor on it.

Drafting has been around for decades, most noticeably at the high speed tracks like Talladega, Daytona, Michigan, and California. These tracks are two or miles in length and high-banked, allowing for the rates of speed that make drafting a major factor. Some drivers became masters at the art of drafting (yes, it’s a science, but it’s also been made an art form for some), like Dale Earnhardt Sr. with his 10 wins at Talladega and 10 consecutive wins at Daytona. And who can forget his final win, the fall race at Talladega when he muscled and drafted his way from 18th place to first in the final five laps.

Besides conventional drafting, though, Earnhardt Sr. also pioneered a technique now known as “side drafting.” With this form of aerodynamic management, one driver can use a technique that actually slows down a faster car simply by moving alongside at high speed. The effect of the move is to cause air flowing from the nose of the car to be transferred to the other car and, if timed precisely enough, to direct this transferred air to the wheel well or to the rear spoiler of the other car to cause drag. For the car being overtaken in a side drafting maneuver, there’s little that can be done other than hold on and keep the car heading straight.

Side drafting has become an element of competition in high-speed stock car racing, and some drivers have worked hard to perfect it. It can be dangerous, since it works to make the car being side-drafted momentarily unstable and, because of the high speeds, the cars are sort of light on their tires, so to speak. Any unplanned or unexpected change in air current can quickly destabilize the car. From an aeronautical design point of view, it’s probable that NASCAR will move at some point to build governing features into the body of the race cars to mitigate the effects of side drafting but, for the time being, it does make things exciting!

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