Rear Wing Assembly

The rear wing is made of carbon fiber and is attached to the transmission housing. CART regulations restrict the size to 43 inches in width and 32 inches in heigth, (35 inches for road courses). The rear wing configuration is determined by the type of curcuit being raced on. Low downforce, standard, and high downforce wings are the choices under current CART regulations. The objective is to achieve the best downforce/drag compromise possible. The three piece cascade wing is a high downforce wing used on the street and road courses. It provides maximum downforce (capable of producing 3000 lbs. of downforce) but also a maximum amount of drag. The standard wing used on short ovals is a two piece assembly which creates less drag and downforce than the cascade wing. The speedway design or low downforce wing is the smallest of the three and produces minimum drag.

As the airflow moves toward the rear of the car it becomes more turbulent. The wake from the front wings, mirrors, the driver's helmet, the front wheels and the side pods all influence airflow. All of these obstructions create a turbulent airflow toward the rear of the car. The rear wing is not as aerodynamically efficient as the front wing, yet it must generate more than twice as much downforce to balance the car, thus the rear wing assembly is designed to produce high downforce. To achieve this, large triple element wings are used. Because of the configuration of the wings, unwanted drag is also created, particularly at high speeds. The most efficient aerodynamic setup of the race car is based on a downforce/drag compromise. Downforce is necessary for cornering speed (entry and exit), while efforts are made to minimize accompanying drag in the straights. The efficiency of the wing is based on:

1. Aspect Ratio:
   The amount of downforce produced by a wing is determined by its size. The larger the wing the greater the downforce. The length/width ratio is called the aspect ratio. The higher the aspect ratio, the more efficient the wing. The aspect ratio is the span of the airfoil (the long dimension perpendicular to the airflow) divided by its chord (the dimension parallel to the airflow).
2. Angle of Attack:
   The efficiency of a wing is its downforce/drag ratio. The amount of downforce generated is dependent upon the angle or the tilt of the wing. The angle of attack is greater on a road course rear wing setup than on a speedway setup. The greater the angle of attack, the more downforce and drag. The angle of attack and the size of the rear wing will vary from road, short oval and speedway setup.
3. Drag:
   While increasing downforce a wing also increases unwanted drag. Drag increases with the angle of attack. The downforce generated by the wing works in a vertical, downward direction, while drag acts in the opposite direction.

Author:Bryan Yager, Ralston Middle School, Belmont, CA (12/94)