Why is the Sneed4Speed wing 3D
What is a 3D wing –
A 3D wing is an airfoil that has multiple angles of attack across its span. Most modern aircraft and the Sneed4Speed wings are 3D. When used on a sedan or coupe production-based race car, the outer sections will typically have much more AOA built-in than the center section.
Why to use a 3D wing -
Word around the paddock will lead you to believe that in order for an airfoil to function on a race car, the airfoil needs to be in clean, free-air above the rear roofline of the car. This is only a partially-true statement. On cars with solid roofs and angled rear windows, the air that flows from the rear edge of the roof will travel downward at an angle toward the trunk lid. The problem with a 2D wing is that only it’s center section will see this downward "push" of air, while the outer section of the 2D wing will see much less of this, because it is seeing straighter freer flowing air. Decreasing the 2D wing’s angle-of-attack to accommodate for the downward airflow causes the outer sections to produce less downforce. Increasing the 2D wing’s angle-of-attack causes the center section to produce more downforce. The 2D wing ends up functioning inefficiently in this unbalanced state. To get the 2D wing into a balanced state it must be mounted above the roof line but this will cause an increase in total frontal area of the car and increase drag.
The advantage of the 3D wing is that it operates in a balanced, efficient state below the roof line where drag is reduced and downforce levels can still equal the 2D design. The 3D wing’s built-in angle-of-attack variations are what allow it to function more efficiently mounted below the roofline. When the center section is mounted at 0 degrees angle-of-attack, it acts as though it has a positive angle-of-attack relative to the airflow coming over the rear center of the roof. The outer sections, with the higher angle-of-attack built-in, are better-suited to take advantage of the cleaner, free flowing air traveling down the sides of the car. Therefore, the 3D wing, when used on a sedan-type car and mounted below the roofline, is able to function more efficiently and balanced than a 2D wing.
Which wing is best for my car –
In order to find the answer, we must know our intended for the wing and car.
1. Type of car (sedan, coupe, hatchback, open-wheel, etc.).
2. Horse Power limited race class?
3. Is it legal in my race series? Special rules like mounting-heights?
When racing in a horse power limited race class and/or with a mounting-height restriction requiring the wing below the roofline, a 3D wing will work better than a 2D because the 3D wing will work in a balanced state under the roof line. If there is not height restriction using a 3D wing and moving it under the roof line will also reduce drag, meaning it will take less horse power to get the car to top speed than with a 2D wing.
source - APR Performance