Two drivers missed the race this year due to severe rear-end collisions. Kurt Busch has been sidelined since a qualifying accident at Pocono in July. Alex Bowman hits the wall in Texas and misses Sunday’s race at his Roval in Charlotte (2pm ET, NBC).
Other drivers said the hits they took in a Next Generation car were among the hardest they’ve felt in a Cup car.
“When I crashed (actually at Auto Club Speedway), I thought the car was broken, but the bumper barely receded. It felt like someone had hit me with a hammer,” Kevin Harvick told NBC Sports. rice field.
The three most important parameters in determining crash severity are:
- the amount of kinetic energy a car carries
- collision time
- car hit angle
Trigonometry is required to properly account for the last of these factors. However, it’s probably intuitive that shallow hits are preferable to hits from the front or back.
If the angle between the car and the wall is small, most of the driver’s momentum will start and stay in the direction parallel to the wall. The speed of the car changes slightly.
The larger the angle, the greater the change in vertical velocity and the greater the force generated. NASCAR notes that many of this season’s crashes are more angled than in the past.
Bush and Bowman both hit at fairly large angles, so they skip the trigger.
Energy — pounds of TNT
A car’s kinetic energy depends on its weight and speed. However, the relationship between kinetic energy and velocity is not linear, but quadratic.you mean go Twice as soon as four times more kinetic energy.
The graph shows the kinetic energy of different types of race cars at different speeds. To help you understand the amount of energy we’re talking about, we’ve expressed kinetic energy in equivalent pounds of TNT.
- At 180 miles per hour, the kinetic energy of a next-generation car is about the same as stored in 3 pounds of TNT.
- IndyCars are about half the weight of NASCAR’s Next Gen cars, so if they both move at the same speed, IndyCars have about half the kinetic energy of Next Gen cars.
- At 330 mph, the Top Fuel drag racer carries kinetic energy equivalent to 6 pounds of TNT.
When a car slows down or stops, all the kinetic energy of the car has to be converted into other kinds of energy. NASCAR says more collisions are occurring at higher speeds. This means more kinetic energy.
long collision > short collision
That seems counterintuitive, doesn’t it? Who wants to crash longer than necessary?
But the longer the collision takes, the longer it takes to convert the kinetic energy.
Cars pitting start slowing well below reaching the pit box. A car’s kinetic energy is converted into thermal energy (brakes and rotors warm up), light energy (rotors glow), and even sound energy (tyres screeching).
A collision requires the same amount of kinetic energy to be converted, but much faster. In addition to heat, light and sound, energy is transduced by the rotation of the car and deformation or breakage of parts. (This video on Michael McDowell’s crash at his 2008 Texas Qualifier goes into more detail.)
The force produced by a crash depends on how long it takes the car to come to a stop. Compare the force of your seatbelt when slowing down at a stop sign to the force you feel when you have to slam on the brakes.
To give you an idea of how fast the crash is, the first wall hit in the crash that killed Dale Earnhardt Sr. lasted only 1/800th (0.08) of a second.
The SAFER Barrier uses the vehicle’s kinetic energy to move heavy steel walls, shattering energy-absorbing foam debris. This extracts energy from the car and the barrier prolongs the collision time.
The disadvantage is that cars with low kinetic energy do not move the barrier. It’s like hitting a wall.
This is the same problem that next-generation vehicles seem to have.
Chassis Stiffness: The Goldilocks Problem
The Next Gen Chassis is a five piece bolted together car skeleton as shown below.
Another important safety feature is missing from this graphic. It’s the energy absorbing foam that covers the outside of the bumper. It’s purple in the picture below.
All cars are designed so that the strongest part of the car surrounds the occupants. Racing cars are no exception.
The Next Gen chassis center section is made of heavy-duty steel tubing and sheet metal. Components become progressively weaker as they move away from the cockpit. For example, bumpers are made of aluminum alloy instead of steel. The goal is to convert all kinetic energy before it reaches the driver.
Since the next-gen car issue is about the rear impact, I’ve expanded and highlighted the last two parts of the chassis.
Bumper and rear clips are not easily broken. The rear end of the Gen-6 car suffered much more damage than the Next Gen car after a similar impact.
If your first thought is “just weaken the struts”, you have good instincts.
I’ve highlighted the first one in red: the fuel cell. Hard collision is the only thing worse than hard collision. When fire.
Another challenge is that the chassis is a holistic structure. He does not do one thing for each part independently of all other parts. Changing one element to soften backward collisions can make other types of collisions more difficult.
Chassis are so complex that engineers must use finite element analysis computer programs to predict chassis behavior. These programs are similar (and just as complex) to the computational fluid dynamics programs used by aerodynamics.
progress takes time
John Patalak, NASCAR’s managing director of safety engineering, pointed out a complex issue that hadn’t been discussed before. He told NBC Sports’ Dustin Long in July that he was surprised by the crash stiffness of the rear end.
Crash data for next-generation vehicles was similar to crash data for Gen-6 vehicles, but the data did not match driver experience. Before dealing with cars, his team needed to understand the discrepancies between his two datasets.
They ran a real crash test on the new configuration on Wednesday. These tests are complex and expensive. Don’t test until you’re confident your changes will make a big difference.
But even if the tests go as expected, that’s not the end of the story.
Safety is a moving target.
And always so.