Sound success

fifty years after Chuck Yeager, the American test pilot, became the first man to fly faster than the speed of sound, Squadron leader Andy Green of the Royal Air Force (raf) has achieved the same feat on land.

Green, 35, drove the jet-powered British car, Thrust ssc to set the world land speed record on October 15, averaging a speed of 1,227.95 km per hour on the Nevada desert track, usa. Thrust ssc made two successful runs within an hour as required to officially break the record. The official time is calculated by the average of two runs. Thrust ssc hit a speed of 1,229.77 km per hour on the first run and 1,223.28 km per hour in the second.

On October 12, Thrust ssc broke the sound barrier twice, but missed the record by being 60 seconds slow in getting back on course. The jet-powered Thrust ssc streaked across the desert track at a speed of 1,229.8 km per hour, then made return trip at a speed of 1,223.2 km per hour. It took 61 minutes to turn the car around and position it for the second sprint. The rules require two runs in opposite directions within one hour. The actual speed of sound is in the 1,207-1,231 km per hour range depending on weather conditions. The runs were clocked by the United States Auto Club and authenticated by the International Federation of Automobile Sport, which also sanctions Formula 1 races.

"We have achieved the greatest land speed record in history," said Richard Noble, the leader of the Thrust team. Noble himself had set a record on October 4, 1983, when he achieved a speed of about 1,019.4 km per hour. For the present mission team had worked for six weeks to prepare for the record. The team arrived in Nevada in early September and were under pressure to finish the job because they were short of finances. Many volunteers of the team had to get back to their full-time jobs. The team was also aware that the rainy season in Nevada, which was not far away, could play spoilsport.

When Noble and designer Ron Ayers began working on the Thrust ssc project in 1993 -- as an independent sporting venture with various corporate sponsors -- they started by studying the aerodynamic factors. When a vehicle travels at subsonic speeds, the air ahead is "warned" of its approach by an advance pressure wave that travels outward at the speed of sound. This eases its passage through the air. At supersonic speeds, the vehicle is moving faster than its own pressure wave. This displaces the air abruptly, generating a cone-shaped shock wave in its wake.

When the vehicle is moving at about the speed of sound, its behaviour shows a complex mixture of subsonic and supersonic characteristics that is particularly hard to model. Noble enlisted the help of the ministry of Defence's Proof and Experimental Establishment at Pendine in Wales in the uk to test a rocket-powered scale model for the initial design for Thrust ssc.

The 10-tonne car, equipped with two Rolls-Royce engines from a Phantom fighter jet, has the power of 1,000 Ford escorts or 141 Formula One cars. Noble said that a huge transport aircraft would take the car back to the uk. Ayers said that the record-breaking car most likely would not run again and was probably destined for a museum.

Both Yeager and Green broke the sound barrier. But there is a difference. Yeager's achievement led to the commercialisation of supersonic flights. But supersonic cars stand no chance of becoming anything more than a one-off. There are very few desert tracks in the world long enough for cars to travel at a speed of about 1,200 km per hour.

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