I heard that a car travelling at 200 kilometres per hour would generate enough downforce (or suction) to allow it to stick to the ceiling. Is this correct? And if it is, how is the force generated?
This is an interesting thought-experiment and gave us some great answers. Clearly the long-running debate over how aircraft wings achieve lift is still alive and kicking 鈥� Ed
鈥� The short answer is 鈥測es鈥�, and downforce is the way to do it. Downforce acts towards the road, whatever the road鈥檚 orientation, and it increases roughly with the square of the vehicle鈥檚 speed. Driven fast enough, the downforce exceeds the weight of the car, which could then run along the ceiling of a tunnel. Depending on the set-up, the downforce and the weight of an F1 car typically become equal when the car is running at 130 kilometres per hour.
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鈥淒rive fast enough and downforce exceeds the car鈥檚 weight, enabling it to run along a tunnel roof鈥�
Filling a wardrobe with clothes boosts its weight. This increases the friction between it and the floor, making it harder to slide. An F1 car designer wants to increase the friction between the tyres of a car and the track so that it can carry more speed into corners without sliding off. But the designer wants to achieve this without increasing its weight.
So downforce is the answer and it can be achieved in two ways. First, upside-down wings are angled to deflect air upwards, away from the track, resulting in a reactive force on the car in the opposite direction. Second, designers exploit the . Pass air through a narrowing gap and it speeds up. This is what happens beneath an F1 car because the space between the ground and chassis represents a constriction to the airflow. According to Bernoulli鈥檚 principle, this leads to reduced pressure under the car. The ambient pressure above the car is higher than that beneath it, leading to a net force in the direction of the road.
Tunnels would need to be adapted to allow racing cars to run along the ceilings, which would make for some interesting overtaking manoeuvres on circuits like Monaco. It would also lead to spectacular crashes: any car that braked heavily while running along the ceiling would lose its downforce 鈥� or 鈥渦pforce鈥� in that scenario 鈥� and fall, upside down, onto the track below.
Mike Follows, Willenhall, West Midlands, UK
鈥� In theory, yes, an F1 car could drive upside down 鈥� but only in theory. Racing cars generate a substantial part of their downforce by creating a low-pressure area under the car. This was most apparent in the late 1970s, when the cars started using skirts that went all the way to the ground in order to contain the low-pressure area. The even built a 鈥渇an car鈥�, that sucked the air from under the car 鈥� ostensibly to cool the engine 鈥� creating a low pressure area underneath.
Three factors are key. Is the ceiling strong enough to withstand the force of the car pushing against it? Is it flat enough to allow the car to run close enough to the ground to generate the required downforce? And finally, you would have to get the car up there in the first place. No doubt if someone built a tunnel long enough, a car could drive up using a curved ramp built into the walls.
Then there鈥檚 the problem of grip. Because the car is being held up by airflow, this is the only thing pushing the tyres against the ceiling, so the driver would have very little control over the car. It would be difficult to generate braking without the wheels locking up and, if the driver tried to turn the car too quickly, it would skid. Then, if it were no longer facing forwards, it would lose its 鈥渦pforce鈥� and fall. Because the car relies on the tyres for directional stability, and has no control surfaces like an aeroplane, the driver would be unable to 鈥渓and鈥� the car back on the ceiling again.
Marco van Beek, London, UK
鈥� F1 cars are capable of generating up to three times their weight in downforce. An F1 car has wings, but these are mounted upside down, generating negative lift which pushes it against the ground.
Ground effect is also used; the underside of an F1 car is completely flat and the closer it is to the ground (its ride height), the smaller the gap becomes. Air travelling under the car is forced to travel faster than air above it, generating further negative lift. Ride height is regulated in Formula 1 because if the car bottoms out or hits a bump the downforce and traction are lost. Such an incident was claimed to have been a contributing factor in the crash that caused the death of former F1 world champion Ayrton Senna in 1994.
Nevertheless, the aerodynamic design and relatively low weight of an F1 car would, in theory, allow it to race upside down.
Michael Macpherson, Automotive engineering student, Glasgow, UK