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How to Drive a Car Upside Down: The Physics of Formula One Racing

By: Hannah Pell

The Starting Line
As I write this, twenty cars are sitting at the starting line of the Formula One (F1) 70th Anniversary Grand Prix at Silverstone based in the UK. The drivers have just finished their formation lap, and the $10 million engines are idling at roughly 5000 rpm (for comparison, the average car idles between 600 to 1000 rpm).

“And it's lights out and away we go!”

The cars accelerate from 0 to 200 kph (125 mph) in about 4 seconds. Drivers downshift through their 8 forward-gear transmissions to 110 kph (70 mph) as they approach their first turn, accelerating back up to maximum speeds of around 315kph (195 mph) on the straightaways within the next few seconds. As they round sharp corners, the drivers experience g-forces similar to astronauts during Earth re-entry. Engines are now revving at more than 10,000 rpm, reaching temperatures greater than 2,500 degrees Celsius. After 52 laps spanning a total distance of 300 km (190 miles), Max Verstappen wins it for the Red Bull Racing Honda team.

Image credit: skysports.com.
2020 is the 70th season of F1 racing. For a sport in which each team’s car is essentially stripped down and remade every year, designing these cars is an optimization challenge over and over again. The goal is to maximize speed. In order to do so, every aspect of the car needs to perform efficiently as one cohesive system. There are limits to the physical power of the car as a direct consequence of its engine, tires, and other material parts. There are limits to whatever a team is able or willing to spend on the vehicle (within the official rules for the sport, of course). There are limits imposed by the drivers, the weather, and the Federation Internationale de L’Automobile (FIA) regulations. Successfully navigating these limits demands creativity, ingenuity, and an understanding of some really astounding physics.

Aerodynamics and CFD
F1 cars are designed to utilize basic principles of aerodynamics to their advantage. Controlling how air flows around the car is crucial for maximizing speed and minimizing drag - a force acting in the opposite direction relative to the acceleration of the car. These cars are designed to guide air so that it flows as closely along with the chassis, or base frame of the vehicle, as possible. The complex-looking wings in front of the tires are specifically designed to guide the “dirty” (or turbulent) air around the tires and create vortices, spirals of air which smooth out the disturbances between the boundary and separated air flows. Vortices help keep the airflow attached to the body of the car, which reduces turbulent air in the car's wake and consequently reduces drag. F1 cars can experience air effects from the car in front of them even several seconds behind (which is about an eternity in these races), so the front wings are also crucial for smoothing out the oncoming turbulence.

Image Credit: autosport.com.

Aerodynamic effects are also manipulated during races to gain advantages. Drivers are allowed to activate their Drag Reduction System (DRS) if they are within 1 second of the car ahead of them and are in a designated DRS zone. With the push of a button, part of the back wing opens, causing drag to decrease and the car to speed up significantly -- about 15 kph more on straightaways. This extra boost allows drivers to strategically overtake one another.

Aerodynamics research is such an important part of F1 that the FIA updated their 2021 regulations with restrictions on aerodynamic testing (using a wind tunnel, for example) and computational fluid dynamics simulations. Teams are only permitted a certain number of hours of simulation time depending on what places they finish in. Computational power is also limited to no more than 25 Teraflops (floating-point operations per second). For reference, average computers operate on orders of gigaflops.

Although simulation time and computational power are limited, other aspects of the computing architecture can be adjusted, such as the computing clusters. For example, the Renault Sport team uses a computing cluster with 18,000 cores (about 2,000 PC laptops) with parallel storage to optimize flops used when reading and writing simulation data.

CFD Results on Formula One Vehicle
Image Credit: SAUBER PETRONAS Engineering AG.

Ground Effect and Downforce
In 1977, the Lotus racing team made an interesting change to their design by incorporating two long hollowed-out channels on the underside of the chassis giving it an upside-down airplane wing shape. The Venturi effect -- which is a consequence of Bernoulli’s principle -- states that fluid pressure decreases when flowing through a smaller area (think air speeding out of an aerosol can). The air flowing underneath the car is increasing in velocity and therefore at a lower pressure relative to atmospheric pressure, so this imbalance manifests as a net force pushing down on the car. The physical consequence is that the car is essentially sucked down to the track. This phenomenon came to be known as “ground effect” aerodynamics. Mario Andretti, who drove the Lotus 78 car, said the ground effects made the car “feel like it’s painted on the road.”


Image Credit: formula1-dictionary.net

Ground effect is one type of a broader aerodynamic phenomenon: downforce. The downforce revolution began in the 1960s with the introduction of inverted wings at the rear of the car. Normal wings help a plane fly, but when inverted they make a car not fly, so downforce is essentially a “negative lift.” Increasing aerodynamic downforce to the car improves its adhesion and grip on the road, which is especially useful for faster accelerations around corners.

Another reason why the DRS is so useful is because opening the rear wing allows drivers to decrease the downforce on the car so they can go so much faster on straight paths. At maximum speeds, F1 cars can experience up to 2500 kg (5500 pounds) of downforce — the equivalent of a small elephant sitting on top of it. Because the minimum weight of the car plus the driver is only 740kg (1600 pounds), the amount of downforce generated is significant enough that they could theoretically drive upside down.

The Finish Line
An incredible amount of work must be done before the race even begins -- hundreds of hours spent running calculations and simulations, designing parts of the car based on the test results, and actually assembling it. Although the physics principles are relatively simple, F1 teams spend hundreds of millions of dollars every year with the same goal -- to design the fastest car possible. Navigating the unique aerodynamics and physical forces experienced by F1 cars is crucial to achieving it.

But does doing so require the bravery and fearlessness of an F1 driver? Fortunately for the rest of us, it does not.

Max Verstappen after his win at Silverstone. 
Image Credit: formula1.com.



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