DAYTONA BEACH, Fla. -- The new "shark fins" on the back of the Sprint Cup cars at Daytona International Speedway this season have nothing to do with the nearby Atlantic Ocean, or as a tribute to the cars that ran here in NASCAR's early years.
Instead, they're a deceptively simple solution to an increasingly complex problem: how to keep the current chassis from getting airborne in a crash, like Ryan Newman's wild flight at Talladega last fall.
NASCAR's new managing director of competition, John Darby, said finding a solution to that problem was the primary focus of off-season wind tunnel testing, starting with the 2 1/2-inch tall rear window strip, already mandated at restrictor-plate tracks.
As the car starts to spin and the strip now sees the air pressure, it does two things. It slows the rotation of the car down, and as the air comes across it, it packs air on top of the trunk lid.
JOHN DARBY "It came from a couple of days in the wind tunnel, looking at different options, different ideas that we had had, ... trying to do a better job of keeping the cars on the ground," Darby said. "Part of that was going back and looking through all of our old notes and things that we had tested. The strip that has been on the rear window for quite some time, and going back through the history of things we've added to the cars, it was pretty attractive. So it was a matter of 'if that worked pretty good, then maybe, is a little bigger better?' "
According to the initial tests, it was. But NASCAR's engineering staff began to think about taking it one additional step.
"The first step we made was to add an extra inch to the rear window strip," Darby said. "And we saw some gains. It wasn't huge. It wasn't enough to make us stop testing or anything like it.
"But through that process, we started understanding what that strip does, and that's to slow the rotation of the cars as well as pack some more air on that rear window. Our engineers said, 'What would happen if we continued this strip down the trunk lid?' It not only had the same effects but the two enhanced each other and we made some pretty substantial gains by adding that strip."
So how exactly does the new trunk fin work?
"If you ride down the highway and you put your hand out the window and you hold your hand in the direction the car is traveling, there's not a lot of resistance," Darby said. "But turn your hand sidewise and it'll come back and slap you in the forehead. It's a very similar effect."
"If you picture the strip on the car, and you're going down the straightaway, it really doesn't have that much effect. But as the car starts to spin and the strip now sees the air pressure, it does two things. It slows the rotation of the car down, and as the air comes across it, it packs air on top of the trunk lid to help push the car back to the ground before it lifts."
And the reason why the trunk fin is on the left side of the window is also inherently logical.
"It's actually lined up with the left edge of the left roof flap," Darby said. "Because as the air hits that fin, part of what happens is that the airflow travels up to the flap. There's a misconception about the flap. A lot of people think that air pressure blows them open. It's quite the contrary.
"The flaps are contoured on the top and it works much like an airplane wing to where the airspeed that travels over the flap actually pulls it open. If we can put more air to the flap and accelerate where it goes across it, then it's going to open faster and stay up stronger. So part of the air helps deploy the flap and the rest of the air -- because the trunk lid is wide and you have more surface area to come across -- helps hold the car back down on the ground."
Even though the trunk fin seems to be the best solution for Daytona and Talladega at this point, Darby said the process is always evolving -- and more improvements may come from additional wind tunnel testing.
"We spent a lot of time in the wind tunnel over the offseason," Darby said. "In preparation for going to the wind tunnel, we had two pages of things that we wanted to try and look at. That was one of the selections that we had. Some of the things we tried didn't do anything. Some made gains. We still have a few more pieces that show potential with refinement, so we'll be going back to the tunnel again to even do more testing."
Darby said even though there hasn't been an accident that tests the capability of the trunk fin, that doesn't mean it hasn't already been successful. He said one benefit of the trunk fin -- and curved end plates on the wings, mandated for the first time at Daytona this winter -- is increased side force, which can assist drivers in correcting spins.
"Arguably, or subjectively, you can point out many instances where that's happened, both in practice and even in race conditions where they got labeled as 'miraculous saves,' " Darby said. "Could there have been some extra effect from the deck fin? Absolutely. Would I ever try to take some of the drivers' talents away or not give them the credit? Heck, no! Because they were the ones who were saving the car."
All in all, Darby's very pleased with how the refinements to the aerodynamic package have performed to this point.
"So far this week, the entire package -- the bigger plate, the shorter wicker, the new shocks, the deck fins, the curved end plates -- everything we've put on these things, is paying great dividends," Darby said. "I'm still a race fan, and I know I've liked what I've been watching."
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