At first glance, NASCAR’s Car of Tomorrow seems more like a vehicle from the past. The venerable racing organization has, after all, changed the shape, height, and width of its competing cars with the intent of boosting drag forces and ultimately slowing them down.
First impressions, however, can be deceiving. Within the close-knit stock car racing community, engineers understand the design of NASCAR’s Car of Tomorrow and they acknowledge its changes are needed as a step into the future. Yes, it looks boxier; drag is greater; speed is down. But it’s safer.
“There’s a constant across all racing,” notes Pat Suhy, NASCAR group manager for General Motors Racing. “Rules makers are always trying to reduce speed, cost, and horsepower. But NASCAR realized that unless they started to increase drag and drop the speeds back down, they’d be in an uncomfortable situation.”
Indeed, some say that the death of Dale Earnhardt in the 2001 Daytona 500 served as the launching pad for CoT. It brought a stronger focus on safety innovations, they say, and NASCAR has been working with automotive engineers since on ways to help drivers.
As a result, the Car of Tomorrow is about two inches taller and four inches wider than its predecessors. It sports a so-called “splitter;” its front bumper is more box-like; the windshield is more upright; and a wing has been added to the rear. As such, drag is higher; speeds are lower.
NASCAR, however, wasn’t satisfied with simply slowing the car down. Engineers have been working for more than five years on the addition of a rigid seat that supports the driver more efficiently against high-G forces. What’s more, they’ve moved the transmission shifter to the right, allowing the driver to slide four inches inward from the driver’s side door. They’ve also shifted the roll cage three inches to the rear and added more “crush-ability” on both sides of the driver, providing even greater protection.
“All of it is important for the safety of the drivers,” says David Holden, research and development engineer at Joe Gibbs Racing. “We’ve moved the roll cage away from the drivers, given them more head room, provided more side impact protection, and created a more secure cocoon. It’s all bonus, bonus, bonus.”
All of the changes, however, have left engineers scrambling for new ways to build winners.
“It’s the job of the manufacturers and the racing teams to work through the restrictions and gain back what we’ve lost,” says Suhy of GM.
That’s exactly what GM did, in parallel with competing NASCAR teams representing the Dodge Avenger, Ford Fusion, and Toyota Camry. To do it, manufacturers used supercomputers to run computational fluid dynamics (CFD) and finite element analysis programs to tweak the parts of the vehicles that weren’t specifically configured by NASCAR.
GM, for example, started with NASCAR’s so-called “gold surface,” then worked on areas above the front bumper, such as the upper grille, headlights, and majority of the hood, back to the front axle. They also applied CFD analysis to the rear bumper area, rear windows and rear quarter-panels. Their goal in all cases was to boost the performance aspects of the car that weren’t covered by the multitude of rules surrounding the Car of Tomorrow program.
“We’re always trying to decrease drag and increase downforce,” notes Kevin Bayless, an aerodynamics program manager for GM. “You can’t get both. You just have to strike the best possible compromise.”
GM engineers worked with Pratt & Miller Engineering & Fabrication, applying a supercomputer that uses approximately 300 microprocessors to break up the problems and do its computations in parallel. Engineers programmed the processors to do air flow calculations in approximately 10 million nodes around the car, then ran the program on the supercomputer for between 72 and 96 hours for each set of computations.
“It allowed us to identify high and low pressure areas on the vehicle, especially those areas that might be more sensitive to pressure than others,” Bayless recalls.
In particular, he says, CFD enabled them to fine tune areas around the headlights and atop the hood that might have otherwise been prone to lift. By doing so, they were able to transform those potential lift surfaces to downforce surfaces, thus improving vehicle performance.
Designers from General Motors’ Design Studio then worked with the engineering team by creating clay scale models that incorporated the changes that would combine better performance with vehicle styling for the Chevrolet Impala SS Car of Tomorrow.
“The CFD gave us guidance on how to change the scale models,” Bayless says. “We can’t run every iteration in CFD. We just do a few rough cuts in CFD and then try a number of options on the scale model.”
Engineers estimate that such efforts enabled the vehicle to pick up “a couple” of miles per hour, and possibly less than that on such speedways as Talladega and Daytona, where corner entry speeds are lower.
“We’re looking for a few percent gain at best,” Bayless says. “As the rules become more restrictive, we’re scrapping for any gain we can get. Even the smallest of differences are important on the race track.”
Looking for ‘Crush-ability’
While groups of engineers worked to squeeze a few extra miles per hour from the Car of Tomorrow, separate teams used finite element analysis, sled tests, and data recorders to make the vehicle safer. Their goals: To add “crush-ability” to the vehicles and support for drivers.
Starting in 2001, manufacturer teams began working with NASCAR to slide the driver’s seat away from the left side of the car, thus providing a little more “crumple room” on the driver’s side. To do that, they studied the position of the transmission tunnel and shifting linkage, ultimately deciding that drivers would be best served by moving the shifter to the opposite side of the transmission. This, in turn, resulted in about four inches of precious extra room between the driver and the left side window.
Engineers then began work on driver support systems. They studied so-called crash recorders from NASCAR accidents, and re-created those crash pulses on sleds in their labs.
“It’s one of the best ways to test seats,” says Tom Gideon, racing safety manager for GM. “We can take the pulses from very bad accidents, put them on the sled test, and essentially recreate the effects of the accident on the driver.”
As a result of those tests, NASCAR and the vehicle manufacturers collaborated on a rigid seat design that would provide greater shoulder, neck and head support for drivers. Teams reportedly are using a mixture of materials – including reinforced aluminum and/or carbon fibers – for the new breed of rigid seats. In contrast to earlier models that used a strip of aluminum to provide about 2G of head support, the new seat offers about 40Gs of head support. Engineers then combined the rigid seat with a six-point harness that more effectively confines drivers in a safer space.
“By looking at crash data, we learned that if you don’t allow the driver to move very much, you probably have a better chance of having him come out without broken bones or a broken neck,” Gideon says.
Although the six-point harness and rigid seats won’t be used in consumer cars, engineers involved in the Car of Tomorrow project say much of their work will affect production vehicles. The urgency of the racing business, they say, is teaching engineers how to take CFD data and quickly incorporate it into production car testing.
“In the production world, going from a CFD run to the track might take 18 months,” says Suhy of GM. “But in racing, we can take a CFD run put the parts in a wind tunnel for testing within weeks or even days. When our engineers leave racing and go back into the production world, they usually take a greater sense of urgency with them.”
Moreover, engineers say that the changes wrought by the Car of Tomorrow are important for the safety of race car drivers, who will always drive as fast as possible. It’s the job of the engineers, they say, to help them achieve that within the rules.
“If you told us we had to race dump trucks, we’d make the coolest, best-engineered dump trucks out there,” says Holden of Joe Gibbs Racing. “At the end of the day, it’s our job to do what the rule book says and make our cars go as fast as they can.”
|Changes for the Car of TomorrowBy increasing drag forces, NASCAR wants to slow down its racers and promote safety.
For 16 NASCAR Car of Tomorrow races in 2007, the following design changes are in effect for all vehicles:
Windshield is more upright
Wing added to rear
Car is two inches taller, four inches wider
Splitter added to front
Roll cage moved three inches to rear
Driver moved four inches inward
Driver’s seat is more rigid