BLOODHOUND SSC Competition - Secondary
How does a car move fast?
Dstl is involved in a project to design and build the world's fastest land vehicle. This project is known as the BLOODHOUND Project and the vehicle will be known as BLOODHOUND SSC (Super Sonic Car). To claim the world record for speed, the car must travel at over one thousand miles per hour, much faster than a normal car. The BLOODHOUND project team must carefully design the supersonic car to help it achieve such high speeds. But what does a vehicle need to make it go fast? Although normal family cars can't go one thousand miles per hour, they can be pretty speedy, especially on a motorway! Looking at the ways a normal car reaches high speed can help us understand how to make things go fast.
Going Forward
One very important thing a car must do to reach high speeds is move easily through the air. The better a car is at moving through the air, the faster it will go. It is the engine of a car that pushes it forward through the air and allows it to speed up. This pushing is known as thrust. The engine's thrust provides the power to move the car forward. The higher the thrust from the engine, the faster a car will go. Cars with more powerful engines will go faster than other cars because they are pushed through the air with more force. Lighter cars will also be speedier because the engines' thrusts have to push less weight.
Don't go back!
When a car pushes itself through the air, the air around it will push back. Just like walking through strong winds can slow us down, the pushing of the air can slow the car. The air pushing back is known as air resistance. You can feel air resistance when you are inside a car travelling along the motorway and you open the window. Air comes rushing back through the window, you can feel it blowing your hair about and pressing on your skin. The faster the car travels, the harder the air pushes back. When a driver's foot is taken off a car's accelerator pedal, air pushing against the car will cause it to slow and help it to stop, even without the brakes. The cars that go the fastest are those that make sure as little air as possible can push back on them. Cars can do this by directing air away from their bodies. Some cars, for example racing cars, have narrow fronts that help them pierce the air and push through it more effectively. We will look at how they do this later on.
Sticking to the earth
As well as high thrust and ways to reduce air resistance, fast cars need other things to help them reach high speeds. To move quickly along a road, a car must also be kept firmly on the ground. This is to allow its wheels to grip the road. Gravity is the force that keeps things on the surface of the Earth, it's what stops us floating off into space! Gravity pulls down on the car, keeping it on the ground and making sure its tyres stay pressed onto the road.
Don't fly away!
However, when a car is travelling really fast, air rushes underneath the body work and gets trapped there. When this happens, the trapped air pushes the car upwards. This is called lift.
When a car is going really fast a lot of air gets trapped, and this air can push up from beneath the car hard enough to lift its tyres away from the road. Lift causes a car to lose its grip on the road and so can slow it down and cause it to skid on bends. If we want to keep a car going as quickly as possible, we must stop air from getting underneath the car. Racing cars have specially shaped bodies to ensure the air is forced over the upper surface of the car, to push it down onto the road (like an upside down wing) and to prevent it from getting trapped underneath.
So, to go faster a car must:
- Have higher thrust
- Reduce air resistance
- Reduce or prevent lift
If a car does these things, we would say it has good aerodynamics. This basically means it can move easily through the air.
Racing cars have excellent aerodynamics, because they have low air resistance and very little lift. With powerful engines (high thrust), this allows them to whizz around tracks at high speeds. The Bloodhound Super Sonic Car must do these things very well indeed if it is to reach a speed of one thousand miles per hour.
Follow this link to read our competition question.
