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Chassis The Indy car chassis is designed to produce maximum downforce, while at the same time minimizing drag. Downforce produced by the front and rear wings and the underbody, allow maximum speeds through the corners. To accomplish this the top of the car is designed to slice through the air, while the underbody is shaped to create an area of low pressure between the underbody and the track. The shape of the tunnels under the car resemble an inverted wing. Located under the side pods these venturis have been restricted for safety considerations but still provide downforce for high speeds through the turns. The shape of the underbody and the use of front and rear airfoils create the "ground effect" Indy car. The development of ground effects began in the 1970's. Team designers began to use wings mounted on the rear of the race car to generate downforce on the rear wheels. Safety regulations restricted the size and height of these wings and soon designers were seeking another source of downforce. This led to the redesign of the underbody of the car. The sidepods of the car housing the radiators were designed to allow airflow under the car through tunnels. The tunnels narrowed in the center and expanded toward the rear of the car. As the air moved through the tunnels an area of low pressure was created between the underbody of the car and the track. This resulted in the car being forced down to the track. As testing continued designers found that minimizing lateral airfow under the car improved ground effects. Formula One designers included skirts on the cars to reduce lateral airflow under the car. Skirts were attached to the sidepods and were vertically adjustable to seal off lateral airflow. This proved to be a major aerodynamic improvement but was soon regulated out of Formula One racing for safety reasons. Currently Formula One regulations ban skirts and require a flat bottom chassis. Eliminating the inverted wing shape of the underbody results in a loss of downforce on the car, which reduces cornering speed. This in turn improves safety. CART also banned skirts from Indy car competition and limited the venturis underneath cars. In addition sidepods are open just before the rear wheels to reduce the Venturi Effect of the underbody. The rake or vertical exit height from the underbody cannot exceed 8", which also limits ground effects. Even with these limitations, the underbody is of major importance in the aerodynamic setup of the car. This is particularly true on the speedway circuits. In order to achieve an efficient setup, the front and rear wings are much smaller than on a road or street setup. The frontal area of the car is reduced in size so it can slice through the air, in an effort to reduce the drag coefficient. The front wings are not used for downforce on the speedway setup, but rather as a trimming device. The major downforce comes from the chassis and underbody design. The rear wings are also much different in appearance on the speedway setup. Instead of the standard wing or high downforce wing used on the road and street setup, the rear wing is almost horizontal with smaller endplates. The speedway rear wing is shaped to create less downforce and reduce drag. The optimum setup on the speedway is to create enough downforce on the cars so when they reach the corners they can run flat out. Drag reduction is more important than downforce on the speedway setup. The best setup would be an adjustable wing to reduce drag on the straights, but supply downforce in the corners. CART regulations, however, prohibit this type of setup for safety reasons.Return to Aerodynamics In Car Racing Next page: The Rear Wing Assembly Author:Bryan Yager, Ralston Middle School, Belmont, CA (12/94) | ||||||
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