poita
20th September 2010, 03:24 PM
Part One
I have never really understood drag cars - until recently, when I actually got a chance to have a decent look at them. To the uninitiated outsider, they look like a poorly-assembled pile of crap. The reality is very different.
It all began on my Triple J Show radio show when, in answer to some question about acceleration, I made some comment about how the "Funny Cars" could accelerate really fast, and get up to a few hundred kilometres within 10 seconds. Very quickly, while I was still on air, I got a few emails telling me how I was underestimating the cars. Later, I got an email inviting me to come out to see the drags at the Western Sydney International Dragway.
There are many categories of drag cars, but the most impressive are the so-called "Top Fuellers". They're the ones with the supercharged 500 cubic inch Hemi engines, huge 36"Goodyear slicks at the back, and skinny bike wheels at the front. When they take off, they become the fastest-accelerating piloted vehicles known to the human race. They generate 5G on take-off - and 7G in slowing down, if both parachutes are deployed at the same time. In a decent start, by the time the back wheels get to where the front wheels were, they're already doing 100 kph. In less than 5 seconds, they are travelling at half the speed of sound - about 500 kph. My lame estimate of "within 10 seconds" was very weak.
There is so much acceleration, and so little weight on the front wheels that they don't steer the Fueller by touching the ground - they steer it by behaving like a rudder in the wind! In fact, the front wheels are a few centimetres off the ground for the first 60 metres. This helps transfer the weight to the back for better traction - but it does make steering at lower speeds (when the wind velocity is still low) a lot more difficult.
The back tyres cannot stick properly to the ground until they have been warmed up. So the very impressive crowd-pleasing burnout before each car does a run is not just to look good - it's essential. The marshalls lay down some water in front of the starting area. The cars blip the accelerator as they pass through the water, pop the driving wheels loose, and continue spinning as they slowly trundle up the launch pad, with huge billowing clouds of light blue smoke coming off the tyres. Then they stop, and with the aid of a guide in front of them, reverse as closely as possible along the track of the rubber that they laid down on the launch pad. The huge back tyres run at about 4 psi - and it's the 9.5 mm of tread that have to be heated, cleaned, and softened to the consistency of chewing gum by the burnout. This heat/clean/soften treatment gives them huge grip. The tyres will survive only 4 - 6 runs - a little over 3 km. That's a lot worse than the mileage you would expect from the tyres on your car.
As the tyres scrabble for grip at take-off, the massive centrifugal force makes them simultaneously taller and skinnier - the tread width shrinks from 18" to about half of that. In fact, during the take-off, the inside of the tyres gets ahead of the outside - so the sidewalls wrinkle. The inner diameter of the tyres is held fast to the rim of the wheel by a "beadlock", which holds it tightly to stop it from spinning on the rim. Occasionally, the colossal 6,000 HP doesn't get fed smoothly down the drive train through the tyres onto the track - and then the tyres can shake with up to 21G of violent lateral harmonic vibration. In this case, the Fueller can be wrecked, and the driver forced unconscious.
Normally, the take-off pad (roughly the size of a tennis court) is made from bitumen laid on concrete, while the rest of the track is made from concrete. So there is a join between the bitumen and the concrete. In the early days, somebody noticed that a dip was developing at the front of the track, at the same rate that a little hill of bitumen was growing at the back. The forces generated on take-off by the increasingly-powerful Fuellers was enough to force the heavy bitumen/concrete launch pad backwards!
The marshals at the take-off line are very obsessive about the condition of the track. It has to have the right amount of rubber on it - and definitely no oil. If an engine blows up and spills oil on the track, everything has to stop until the oil is cleaned up.
Nothing happens without the engine, and I'll talk about that next time...
http://www.drkarl.com/the-karl-collection/karl-in-the-car/drag-cars-part-1
I have never really understood drag cars - until recently, when I actually got a chance to have a decent look at them. To the uninitiated outsider, they look like a poorly-assembled pile of crap. The reality is very different.
It all began on my Triple J Show radio show when, in answer to some question about acceleration, I made some comment about how the "Funny Cars" could accelerate really fast, and get up to a few hundred kilometres within 10 seconds. Very quickly, while I was still on air, I got a few emails telling me how I was underestimating the cars. Later, I got an email inviting me to come out to see the drags at the Western Sydney International Dragway.
There are many categories of drag cars, but the most impressive are the so-called "Top Fuellers". They're the ones with the supercharged 500 cubic inch Hemi engines, huge 36"Goodyear slicks at the back, and skinny bike wheels at the front. When they take off, they become the fastest-accelerating piloted vehicles known to the human race. They generate 5G on take-off - and 7G in slowing down, if both parachutes are deployed at the same time. In a decent start, by the time the back wheels get to where the front wheels were, they're already doing 100 kph. In less than 5 seconds, they are travelling at half the speed of sound - about 500 kph. My lame estimate of "within 10 seconds" was very weak.
There is so much acceleration, and so little weight on the front wheels that they don't steer the Fueller by touching the ground - they steer it by behaving like a rudder in the wind! In fact, the front wheels are a few centimetres off the ground for the first 60 metres. This helps transfer the weight to the back for better traction - but it does make steering at lower speeds (when the wind velocity is still low) a lot more difficult.
The back tyres cannot stick properly to the ground until they have been warmed up. So the very impressive crowd-pleasing burnout before each car does a run is not just to look good - it's essential. The marshalls lay down some water in front of the starting area. The cars blip the accelerator as they pass through the water, pop the driving wheels loose, and continue spinning as they slowly trundle up the launch pad, with huge billowing clouds of light blue smoke coming off the tyres. Then they stop, and with the aid of a guide in front of them, reverse as closely as possible along the track of the rubber that they laid down on the launch pad. The huge back tyres run at about 4 psi - and it's the 9.5 mm of tread that have to be heated, cleaned, and softened to the consistency of chewing gum by the burnout. This heat/clean/soften treatment gives them huge grip. The tyres will survive only 4 - 6 runs - a little over 3 km. That's a lot worse than the mileage you would expect from the tyres on your car.
As the tyres scrabble for grip at take-off, the massive centrifugal force makes them simultaneously taller and skinnier - the tread width shrinks from 18" to about half of that. In fact, during the take-off, the inside of the tyres gets ahead of the outside - so the sidewalls wrinkle. The inner diameter of the tyres is held fast to the rim of the wheel by a "beadlock", which holds it tightly to stop it from spinning on the rim. Occasionally, the colossal 6,000 HP doesn't get fed smoothly down the drive train through the tyres onto the track - and then the tyres can shake with up to 21G of violent lateral harmonic vibration. In this case, the Fueller can be wrecked, and the driver forced unconscious.
Normally, the take-off pad (roughly the size of a tennis court) is made from bitumen laid on concrete, while the rest of the track is made from concrete. So there is a join between the bitumen and the concrete. In the early days, somebody noticed that a dip was developing at the front of the track, at the same rate that a little hill of bitumen was growing at the back. The forces generated on take-off by the increasingly-powerful Fuellers was enough to force the heavy bitumen/concrete launch pad backwards!
The marshals at the take-off line are very obsessive about the condition of the track. It has to have the right amount of rubber on it - and definitely no oil. If an engine blows up and spills oil on the track, everything has to stop until the oil is cleaned up.
Nothing happens without the engine, and I'll talk about that next time...
http://www.drkarl.com/the-karl-collection/karl-in-the-car/drag-cars-part-1