Why Nascar uses roof flaps

Every time there is a spin, minor crash or even in a big one, they are always there, rarely being noticed. However, they are avoiding much worse crashes, such as this one on the 1993 Winston 500 at Talladega, suffered by Rusty Wallace. The images will make you cringe:

Now, why were these flaps installed? Let’s begin with the story of how these smart devices were conceived and the reason why they had to be created in the first place.
In 1993, Rusty Wallace got spun by Dale Earnhardt and turned backwards. At that momentd, things got absurdly wrong absurdly quickly. Rusty’s car wasn’t generating downforce anymore. It was generating lift and acting like a huge airfoil. As air flowed around the car, it had greater speed above the car than underneath it. This creates a pressure difference which is the same found on wings. As this happened, the lift force pushed the rear of the car upwards, where this effect is the strongest. This sent the car to a thundering roll, creating a scary scene to watch. Fortunately, Rusty walked away from the crash, but another similar crash with Johnny Benson at Michigan in August of 1993 prompted an action by Nascar, which made restrictor plates mandatory in September that year for the Charlotte race, but drivers pressured the association to come up with another solution, as they didn’t want the cars to be slower because of these crashes. They already had to use restrictor plates in superspeedways since 1988 and didn’t wanted the cars to have them in another race tracks. Thus,after development by Roush Racing, the roof flaps were born.
Roof flaps are two plates located on the roof, which measure 12x8 inches (30x20 cm) and are depolyed as the car is either sideways or going backwards at high speeds. It will spoil the airflow around the car, making the car penetrate the air like a stalled wing. A wing stalls when the airflow hasn’t enough energy to remain attached to the wings’ surface, with a much lower speed relative to the wings’ surface due to excessive attack angle or too low speed. This makes the pressure difference between the sides of the airfoil drop dramatically. Consequently, lift drops abruptly. The same applys to the cars, making sticking them to the ground.

These flaps are creating turbulence and creating a huge volume of slow, high pressure air on the side of the car on the opposite direction of the movement. This makes the car generate much less lift. This reduction is enough to prevent the car from flying over the security fences into the expectators. However, they do not stop the cars from taking off. Carl Edwards’ crash at ‘Dega 2009 proves that. It came dangerously close to flying into the crowd. So Nascar changed regulations in order to make the roof flaps larger in the name of safety. Watch Edwards’ crash and notice it is frighteningly similar to Wallace’s. Notice that Carl hits Ryan Newman’s car before getting wild airtime. Had the flaps not been installed, a much worse scene would have happened. Hero roof flaps saved the day, as they do in all Nascar races.

Do you approve roof flaps? Do you think they take some of the action away from Nascar Races? Leave your comments below!

EDIT: Restrictor plates were only used in Charlotte 1993 and were already used in superspeedways since 1988. Thanks to AeroBoost for helping.