Practical practice
There are many products available in the aftermarket to supplant extra forces on the performance of a car's original airflow, partly known now as ground effects. One way is by using a spoiler. Essentially, it is an aerodynamic device normally on the rear of the vehicle (a front spoiler is called an airdam) that changes the direction of airflow in order to reduce lift or aerodynamic drag. A spoiler can reduce drag and lift or create a downward force on the car. It is called a spoiler because it "spoils" the normal airflow over the car. However, it should be noted that most of these attempts to reduce drag, such as adding spoilers, underbody panels, and airdams, are not entirely practical to road-going cars. The results, if any, are very minor, if they don't result in actually impairing the vehicle's daily capabilities, including reduced ground clearance and so on. Simply put, most aerodynamic aftermarket equipment serves more to improve the car's appearance than its performance-not that there's anything wrong with that.

On the track, however, there is nothing more hotly debated than the effects of aerodynamics on a racecar, as the same principles that apply to aircraft are applied here but with a twist. The shape of a racecar chassis is similar to an inverted wing or airfoil that creates downforce rather than lift. This keeps the car on the ground at high speeds and increases traction around curves because the air under the car is moving faster than the air above it. Slower moving air creates greater pressure, forcing the car down against the track. The reverse-wing shape of the underbody creates another area of low pressure that sucks the car to the pavement.

Downforce must be carefully balanced against drag, which slows the car. Designs are refined through research using wind tunnels equipped with moving tracks to simulate racing conditions, and an efficient compromise in the downforce/drag relationship is the goal to obtain the best handling at the highest possible speeds. This concept is mostly lost on production cars.

Throughout the '50s, a typical prototype sports racing car was small and lightweight, had a front engine, and had a body with a nicely designed aerodynamic shell. Due to relatively inefficient engines, racecar designers were relegated to building a car as aerodynamic as possible by making the body round and streamlined so that it cut through the wind to make up for any horsepower deficits. Sometimes they did this too well. Racecars of the era were prone to too much positive lift, causing them to unpredictably launch into the air even if slightly provoked at high speeds.

In 1956, michael may, an engineer, had an idea to construct an airfoil, but flip it over so that it produced a negative force toward the ground, and mount it onto his porsche type 550 to use the downforce to improve the traction, grip, and handling on his car. May's innovation was too successful; race organizers kept him from the track because the wing "restricted the view of the drivers behind him." Nothing more was said of the innovation or anything like it for the rest of the decade.

Ten years later, jim hall mounted a wing onto his 2e can-am chaparral and proved the value of the concept by running competitively in the can-am championship that year, and he introduced it to the europeans the following year. By 1968, wings started to show up on formula one cars, and a new era of aerodynamic development began, specifically in the area of downforce.

In the early '60s, ferrari's engineers discovered that by adding an airfoil to the rear end of the ferrari 246sp endurance racer for the 1962 season they were able to direct the majority of the airflow away from the rear of the car, thereby reducing drag and lift. This technology trickled down the following year to the 250 gto road car, which incorporated a small duck-tail rear wing.

In 1969, porsche introduced the 917 to international sports car racing, a car with a reliable but low-horsepower engine paired with sleek, low-drag bodywork. The combination worked well, but it couldn't get the championships the factory was after. Porsche switched to a higher-horsepower engine, but the car was then plagued with aerodynamic instability problems (drivers soon named it "the ulcer"). Through wind tunnel testing, the front and rear bodywork was restyled and the car soon dominated the sports car world championship in 1970 and 1971.

However, the wing did not get popular until porsche launched its 911 rs 2.7 in 1972, whose big duck tail reduced lift by 75 percent at high speed. Now a trademark of the 911, the "whale tail" appeared the following year on the rs 3.0, and it completely eliminated lift at the rear tires.

Almost 750 years ago, scientist roger bacon was onto something when he uttered the words with which we began this compendium: "when you get it right, mighty beasts float up into the sky. When you get it wrong, people die."

Sometimes, they get it right
Recently, with the increased cost in gas, there has been a sharp increase in the limits of aerodynamics, sometimes as a design study, other times as a practice in public relations to create a buzz. Many years ago, volkswagen introduced its vw arvw test vehicle that looked more like a race boat than a car. It tested a very low drag coefficient of 0.15, about the same as an f-15 jet, but it wasn't the company's only foray into aerodynamics. Several years ago, vw built a three-wheeled, bullet-like car with bobsled-style seating that was made more for lower consumption of fuel (thanks to its anemic engine) than for aerodynamics, but here it was realized that to increase fuel consumption, perfecting aerodynamics was a must.

More currently, in june 2005, DaimlerChrysler put its philosophy of "leaving familiar paths and giving chance to new ideas" to practice when the company unveiled what it considered to be the shape of the future of the automobile. The project was the mercedes-benz bionic car, a concept vehicle based on examples in nature. For the first time, in the case of the mercedes-benz bionic car, the engineers at the mercedes-benz technology center (mtc) and daimlerchrysler research looked for a specific example in nature whose shape and structure approximated their ideas for an aerodynamic, safe, spacious, and environmentally compatible car. They found what they were looking for in the boxfish, an angular but nonetheless very streamlined little fish covered with numerous hexagonal, bony plates that provide it with lightweight armor. While hardly the quickest fish in the sea, the boxfish is highly maneuverable with minimal effort.

When the boxfish shape is applied to a car design, the results are impressive. The drag coefficient value for the car's final design ended up being 0.19, one of the most aerodynamic designs ever penned. This unique vehicle project was a compact car with two doors, four comfortable single seats, a panoramic windscreen, a glass roof, and a large tailgate. In addition to the boxfish-like basic shape, the low drag coefficient was made possible by a number of other aerodynamic features: rear wheels almost completely shrouded with sheets of plastic, flush door handles, and the use of cameras instead of exterior mirrors. Fuel consumption of the 140-hp direct-injection diesel engine was 84 mpg with a maximum speed of 190 km/h (118 mph).

Sometimes, they get it wrong
Bernd rosemeyer was seen as the motor racing idol of his day. In just a few short years, the former motorcycle rider shot to stardom in the era of the silver arrows, winning all possible titles in the auto union 16-cylinder type c, from the european championship to the german road racing and german hill-climbing championships. He took the chances of a superstar and nothing could possibly distract him from the fruits of competition: fame, fortune, and immortality. He considered 13 his lucky number. He was married on july 13, 1936, and 13 days later, he won the german grand prix at nrburgring, which he again won the following year on june 13, 1937. His last victory came on his thirteenth start of the 1937 season at the donnington grand prix.

Three weeks after the last 1937 grand prix, in late october, rosemeyer bested rudi caracciola's speed in a german record week held on a stretch of autobahn between frankfurt and darmstadt (now the a5) by pushing his auto union to a speed of 252 mph. Afterward, rosemeyer commented on his record-setting experience: "at about 240 mph, the joints in the concrete road surface are felt like blows, setting up a corresponding resonance through the car, but this disappears at a greater speed. Passing under bridges, the driver receives a terrific blow to the chest, because the car is pushing the air aside which is trapped by the bridge. When you go under a bridge, for a split second the engine noise completely disappears and then returns like a thunderclap when you are through."

Caracciola and the mercedes team, determined to earn back bragging rights, had a few strings pulled to allow for a new attempt the following january. On january 28, mercedes team manager alfred neubauer verified that weather would be clear of gusty winds, but only until 9 a.m. just past eight, caracciola regained the record for mercedes with a speed of 268 mph, noting that "the road seemed like a narrow white band, the bridges like tiny black holes ahead. It was a matter of threading the car through them..." The first person to push himself through the crowd to congratulate caracciola was rosemeyer, who smiled and said, "my turn now."

The modified 6.5-liter, 545-hp auto union streamliner was rolled out onto the autobahn around noon, and caracciola, concerned about the increasingly poor weather conditions at the far end of the road, suggested to his rival and friend that he wait and try again the next day. Rosemeyer said not to worry, that he was one of the "lucky ones." Later, rudolf caracciola said of his young rival, "bernd literally did not know fear and sometimes that is not good. We actually feared for him in every race. Somehow, i never thought a long life was in the cards for him." After two preliminary runs, rosemeyer was on his third and final attempt at 11:47 a.m. when the car was caught by a gust of wind, skidded to the left and then to the right and off the road, somersaulting several times through the air. The 28-year-old rosemeyer was thrown from the car and died by the side of the road. Today, on the frankfurt to darmstadt autobahn, just beyond the langen-morfelden crossing and set back among the trees, stands a small monument to the once great rosemeyer.

As aerodynamic as his car was, equally that of his rivals at mercedes-they could slice through the air, appearing to slip between the molecules-he crashed because of a simple gust of wind no stronger than that which rustles the leaves in a tree. The aerodynamics that helped rosemeyer and auto union achieve the speed that day were the same that led to his demise.

Aerodynamics Buyers Guide
The wind beneath our wings
More aftermarket aerodynamics from the world's best design houses
Conversations and theories about aerodynamics abound in the automotive industry, and if you wanted to throw puns around, you could say it is a lot of hot air passing over stiff resistance. Does a car go fast enough to warrant a full body kit? Is a spoiler or airdam necessary on american highways? Will i affect my car's performance enough to offset the cost of the variety of packages on the market today? These questions can be argued until your car becomes an antique, but the only solid answer with any kernel of truth that everyone can agree on is that most aerodynamic-themed accessories make your car look cool. Whether they improve handling, fuel economy, or 60-foot times are issues best left to physicists, engineers, and bench racers (unless, of course, you have the time slips to prove it).

Glossary of terms
Aerodynamics: the study of the motion of gas on objects and the Forces created.

Airflow: the movement of air around the chassis of the car.

Bernoulli effect: states that the pressure of a fluid (liquid or gas) decreases as the fluid (liquid or gas) flows faster.

Carbon fiber: carbon-based composite material that is strong in tension but reasonably flexible. It can be bound in a matrix of plastic resin by heat, vacuum, or pressure. It is strong, light, and expensive.

Cd: drag coefficient, or coefficient of drag. It is determined by the shape and smoothness of the object, in this case, the car.

Chassis: refers to all mechanical parts of the car attached to the Structural frame.

Computational fluid dynamics (cfd): equations that are known are programmed into computers. The computers provide solutions to the problem of external airflow over vehicle shapes. The body of the configuration and the space surrounding it are represented by clusters of points, lines, and surfaces; equations are solved at these points. Cfd is divided into three steps: grid generation, numerical simulation, and post-process analysis.

Downforce: a vertical force directed downward, produced by airflow around an object. Downforce is generated from the front and rear wings and the venturi tunnels on a ground effect car.

Drag: force acting on an object in motion through a fluid (in this case, air) in a direction opposite to the object's or chassis' motion, produced by friction.

Ground effects: downforce created by an a low pressure area between the underbody and the ground, and downforce created by the front And rear wings.

Laminar: laminar flow means the fluid is moving in smooth layers around the object. Airflow becomes turbulent moving from the front to the rear of the car, forced around obstructions such as mirrors, helmets, and roll bars.

Lift: the upward reaction of an object to the flow of air forced over the shape of the wing (airfoil). The front and rear wings of ground effect cars are shaped like inverted wings to create downforce or negative lift.

Monocoque: a body structure that derives its strength and rigidity from unitized construction, rather than a framework of thick members.

Telemetry: an electronic device that transmits specific data (measurements) to a remote site. It electronically records performance of engine and actuation of controls by the driver. The data is then used as a foundation for determining car setup.

Turbulent: turbulent airflow is when the fluid streamlines break into eddies and complex changing patterns. This can cause unstable forces on an object. As the airflow moves from the front of the car to the rear it becomes turbulent.

Turning vane: deflectors located between the front wheels and side pods to direct turbulent flow away from the tunnels. This eliminates a source of turbulent air to the tunnels. Cleaner air to the tunnels creates more downforce-currently seen on most f1 racecars, and on some indy cars.

Venturi: a narrow tunnel under the side pod, shaped like an inverted wing. As air enters and is forced through the narrow center, its speed increases, creating a low pressure area between the bottom of the car and the track. This creates a suction effect which holds the car to the track.

Venturi effect: fluid speed increases when the fluid is forced through a narrow or restricted area. The increased speed results in a reduction in pressure. The underbody venturi is shaped to create a low pressure area between the road and chassis, which creates downforce.

Vortex: when a fluid rotates around its own center, it is called a vortex. Turbulent flow is made up of many little vortices.

Wind tunnel: a tube-like structure where wind is produced, usually by a large fan, to flow over the test object. The object is connected to instruments that measure and record aerodynamic forces that act upon it.

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