The quest for speed has always been a captivating pursuit for engineers and enthusiasts alike. From the groundbreaking achievement of the Thrust SSC in 1997 to the upcoming Bloodhound SSC, these vehicles have pushed the boundaries of land speed records. But achieving such astonishing speeds comes with its own set of challenges, particularly when it comes to designing wheels that can withstand the extreme forces involved.
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Understanding the Physics of High-Speed Cars
When designing a high-speed car, engineers face two major physics problems that become more pronounced as the speed increases. First, the drag force experienced by the vehicle grows exponentially with the speed. This means that the returns in top speed decrease for every unit of horsepower added. But in this article, we will focus on the second problem: the massive inertial forces that the tires experience at high speeds.
To understand the impact of these forces, let’s consider a spinning mass. As demonstrated by The Slow Mo Guys, spinning a CD at high speeds can lead to it shattering under the weight of its own inertia. This effect also limits the speed of cars like the Bugatti Chiron and the Koenigsegg Agera from reaching the coveted milestone of 300 mph. At higher speeds, no tire on Earth can withstand the inertial forces, causing the rubber to peel away from the hub.
But what about the Thrust SSC, the land speed record holder since 1997? The Thrust SSC had a distinct advantage when it came to wheels. Unlike traditional high-speed cars, it did not rely on the wheels to transmit rotational motion from the engine to linear motion. Instead, it used jet engines and rockets for propulsion. This meant that the wheels only needed to bear the weight of the vehicle and provide enough lateral traction for steering.
The Wheel Design Process
Now, let’s delve into the design process for creating wheels capable of reaching speeds over 1,000 mph. The first step is material selection. Given the specific requirements of strength, lightness, and damage absorption, a solid metal wheel is chosen over a rubber tire. Forged aerospace-grade aluminum, known for its strength and lightness, is the ideal material for this purpose.
Once the material is selected, the team begins forging blanks. Huge billets of aluminum alloy 7037 are heated and compressed with a 3,600-ton forging press to create the blank, which is then passed to a milling machine to shape the wheel. This forging process significantly strengthens the material by increasing its density and work hardening it.
With the blank material in hand, the team starts the prototyping process. They determine the general thickness needed for stability and stress resistance, and computational analysis using tools like simscale helps refine the design. To minimize costs, initial prototypes are created using cheaper materials like cast aluminum. These prototypes undergo extensive testing to ensure they can handle the intense forces imposed by the vehicle.
The design and prototyping process continues until a suitable design is found. Once finalized, the forged aluminum is passed to a CNC milling machine, which cuts the wheel to its final shape. To counteract any potential cracks on the surface caused by machining, a surface treatment called shot peening is applied. This creates a thin layer of higher compression, reinforcing the material and preventing crack growth.
The Future of Land Speed Records
The Bloodhound SSC, powered by a jet engine and a hybrid rocket engine, aims to reach speeds of 1,000 mph. The rotating wheels of the Bloodhound will spin at a staggering 10,000 times per minute, creating immense inertial forces that could crush a 1-kilogram bag of sugar to the weight of a fully laden articulated truck. However, with their advanced wheel design, the team behind the Bloodhound is confident in their pursuit of breaking their own record.
Conclusion
Designing wheels for the fastest land vehicles in history requires a meticulous and iterative process. Material selection, forging, prototyping, and surface treatment are crucial steps in creating wheels that can withstand the extreme forces involved. The Thrust SSC and the upcoming Bloodhound SSC have both demonstrated the remarkable engineering feats required to push the boundaries of speed. By overcoming the challenges associated with high-speed wheels, these vehicles inspire a sense of excitement and curiosity about the possibilities of engineering.
FAQs
Q: Can rubber tires withstand the inertial forces at high speeds?
A: No, at higher speeds, the rubber would simply peel away from the hub due to the intense inertial forces involved.
Q: What is the advantage of using forged aerospace-grade aluminum for the wheels?
A: Forged aluminum combines strength, lightness, and damage absorption, making it the ideal material for withstanding the centrifugal forces caused by the spinning wheels.
Q: How do engineers ensure the wheels can handle the extreme forces before finalizing the design?
A: Engineers use computational analysis tools and create prototypes with cheaper materials like cast aluminum for extensive testing.
Q: What is the purpose of shot peening in the wheel manufacturing process?
A: Shot peening introduces a thin layer of higher compression on the surface of the machined product, reinforcing the material and preventing crack growth.
Q: What is the goal of the Bloodhound SSC project?
A: The goal of the Bloodhound SSC project goes beyond breaking the land speed record. It aims to inspire people to get excited about engineering and share the passion and skill of the engineering team.
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