New chassis design bolsters drag racing safety

  • 22-May-2009 02:55 EDT
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­While engine output grew from 3000 hp (2240 kW) to as much as 10,000 hp (7460 kW) in NHRA Funny Cars, chassis design was virtually static, creating the potential for catastrophic failures.

­­“We pulled a 20-year-old chassis out of our museum for comparison, and it turned out that nothing had changed in 20 years,” exclaimed NHRA (National Hot Rod Association) Funny Car 15-time champion drag racer and team owner John Force.

­The comparison was not just idle curiosity but was unfortunately part of the John Force Racing team’s response to the March 2007 fatal crash of one of its drivers, Eric Medlin, during which the car’s steel tube frame had broken apart.

The problem was that, while the chassis stayed­ the same over the years, engine power did not, said Patrick DiMarco, Vehicle Dynamics and Electronics Supervisor for Ford Racing Technology. “That chassis was designed 20 years ago for a car with a couple thousand horsepower, and they were running 8000 to 10,000 horsepower with the same chassis,” he remarked.

NHRA’s response to the crash was to shorten races for its cars capable of more than 300 mph (480 km/h) from a quarter mile to 1000 ft in a move to limit maximum speed. But Medlin’s fatal crash occurred in an 8-mi (13-km) test run, so preventing such fatalities depends on changing the cars rather than reducing their speed.

Medlin, who was not just a driver for Force’s team but was also the son of Force’s crew chief John Medlin, died when his car suffered a tire failure. The extreme vibration that resulted rattled the driver against the inside of the car’s protective roll cage, immediately inflicting a closed head injury, according to Force. After a short time, the chassis itself shattered from the vibration, which occurred at the resonance frequency of the steel frame.

“It was the first time we had seen the severe vibration that literally shattered 4130 chrome-moly tubing,” recalled Graham Light, Senior Vice President of Racing Operations for the NHRA. “We’d never seen it shatter like a piece of glass. There were dynamics in Eric’s crash no one had experienced before.”

Also shattered was Force’s long-standing belief that NHRA Funny Cars were safe—a belief that led him to not only encourage his crew chief’s son to join him as a driver but also Force’s own daughters, Ashley, Brittany, and Courtney, who have become professional drag racers, too. “I never thought these cars could hurt you,” Force said. “I saw drivers killed in other categories, but it didn’t relate to our cars. In Eric’s crash, what we saw were harmonics and vibration that we had never seen before.”

But he expected he would see it again, so Force withdrew his team from competition until it could devise a chassis it believed was sufficiently safe. “I had millions of dollars in contracts with sponsors, and I said, ‘We are not going racing until the cars are safe,’” he recalled.  To research safety improvements, Force established the Eric Medlin Project, overseen by John Medlin.

Force immediately contacted Ford, which is one of the sponsors of his Mustang Funny Cars, and NASCAR, which he knew had been researching ways to improve the safety of steel-tube-frame race cars.

“Our immediate response was, ‘What can we do right now?’” recalled DiMarco. “We’ve got some pretty good guys with all our five-star crash test scores so why not use them?” he said he thought. “The solution was making the cage wider, with more padding between the driver’s helmet and the cage.” Widening the roll cage area was one of the changes NASCAR made to its Car of Tomorrow racecar design, which was created with safety in mind.

Ford also resurrected the crash-data-acquisition program it had conducted in the defunct Champ Car racing series. “We can’t do anything without knowing anything,” DiMarco said.  “So we worked with Delphi to adapt the current [data recording] box being used in the Indy Racing League for top fuel dragster and Force’s Funny Car.” Shortly afterward, the NHRA mandated the recorders for all of its nitro-methane-fueled racers in both Top Fuel dragster and Funny Car categories, and they were subsequently mandated for Pro Stock, too.

The primary change made for drag racing was to record the entire race, because it only lasts a few seconds. In Indy car racing, the boxes were set to record only a brief time before, after, and during a crash event, but drag races are so brief they were set to record the entire run. The device records data from three accelerometers: one under the driver’s seat, one mounted above the driver’s head, and a third one incorporated into the driver’s radio earphone and inserted in the ear.

If Force pursued these changes as if his life depended on it, so it turned out to be. In September 2007, after the team’s return to competition with its upgraded and instrumented cars, Force suffered a similar crash in which his chassis shattered. In the resulting crash, with the broken car, Force suffered severe injuries to his arms and legs, but his head was not bounced against the new, wider roll cage.

“I had no head injuries, and I should have been dead,” Force observed. “I credit the padding and roll cage with saving my life.”

This time, there was data to study afterward. “John’s accident [was] very similar to Eric’s,” DiMarco said. “The fractures in the chassis looked almost identical.”

The response was to reinforce the chassis at the newly identified weak points. “It became a complete chassis change,” said Force.

That change has produced two optional new designs, according to Light. While the old cars had a pair of horizontal frame tubes running the length of the chassis on each side of the car, the new ones use either two larger-diameter tubes or three tubes of the original diameter, he said. Tube wall thickness is increased for both types.

There are also two cross-braces in the area of the steering rack mount, added DiMarco.  “The changes make it significantly stiffer,” he said.

As part of its all-encompassing push to improve safety, NHRA has also added an automatic engine shutoff device, which stops the engine and deploys the car’s drag parachutes in the event of a supercharger explosion.

The automatic shutoff could potentially be used in the event of a rear wing failure, with the addition of sensors in that area, said Light, or it could even be set to stop the car automatically after the finish line if the driver becomes incapacitated for some reason.
The only concern is ensuring that the device could not be somehow repurposed by teams to provide a performance advantage, Light explained.  “We are looking at that very closely,” he said.

The NHRA raised the minimum weight of its dragsters and Funny Cars to accommodate the stronger chassis, with the goal of maintaining parity among its competitors. Still, there has been some resistance to the changes, but Light pointed to other sports as examples.

“Look at hockey, where there was a lot of resistance to helmets,” he pointed out. Force, meanwhile, was presented the SAE Motorsports Engineering C­onference Motorsports Achievement Award for his role in creating the Eric Medlin Project as an advocate for drag racing safety. “As long as I race, I will be involved in safety,” Force pledged.

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