This is the first of a three part series on the shape of cars.
Automobiles are shaped all wrong; if the laws of aerodynamics were taken into consideration, all cars would be turn upside down. Of course this would present a packaging challenge to the engineers, but the shape of the automobile should be reversed from its current configuration.
An automobile moves across the road and through the air. The road and the air both have an effect on the car as it moves across one and through the other. As speed increases, the air resistance and the dynamics of the air flow over and under the car increase. At highway speeds, the flow of air around the typical car is trying to lift the car off of the road The air acts to lift a car off the road because the typical car is roughly shaped like an airplane's wing, curved on top and flat on the bottom. the curve on top of the wing/car acts to create a longer path for the air flowing over the car than the shorter distance travels for the air going straight under the flat bottom of the car. The air traveling the shortest distance is more densely packed and thus a zone of high pressure exists under the car compared to the lower density air flowing over the top, which creates a zone of low pressure. High pressure below and low pressure above creates lift. To prevent lift and to create down force, which helps stick the car to the road, a car should be flat on top with a curved underside.
Of course this is not a practical shape for packaging purposes and we will continue to see cars with the same general shape. We are seeing more slab sided and box shaped vehicles whose sole purpose is to maximize interior shape while minimizing the exterior "foot print" of the vehicle. These cars are particularly popular in the old cities of Europe and Asia where road are narrow, parking is scarce and all space is at a premium. In Japan, road and parking space is so limited that the government bases some of the tax burden on each car based upon the width of the car. This why Japanese cars meant for their domestic market tend to be tall and narrow.
The principles of aerodynamics have been applied to automobiles since the 1930's as the result of trickle down technology from the emergent aircraft industry. As airplanes shed their two wings in favor of one, automobiles began to become more sleek and in tune with the airflow over them. The 1934 Chrysler Airflow and the Bugatti Type 57S were smoothly shaped to encourage easy passage of air over the body. After World War Two, racecars borrowed engine and aerodynamic technologies from the military to increase speed. At speeds of 150mph and more, their was so much lift and such little contact with the road that car would begin to yaw (twist side to side), compromising traction and safety. The first reaction to yaw was to equip racecars with vertical stabilizers that sprouted like dorsal fins from the rear. But this did not address the problem of lift and loss of contact with the road.
By the late 1950's sophisticated research was being applied to racecar aerodynamics and the more voluptuous shape emerged as the style of choice. Front panels bent farther down to skim above the road and a short abbreviated tail was the fashion. This chopped off tail was the design of Dr. Kamm who believed that the short tail would induce a swirl of air behind the car and push it through the air. Called the Kamm Back and seen on the Cobra Daytona coupe amongst other cars of the early 1960's era, subsequent research demonstrated that the swirl did occur, but that it acted as a drag rather than as help. This led to the long and elegant tails that we see on high-speed cars such as the type that race at the 24 Hours of Le Mans.
More on the shape of cars tomorrow.