You want to overcome the speed of sound

1997/11/01 Azkune Mendia, Iñaki - Elhuyar Fundazioa Iturria: Elhuyar aldizkaria

• Patenteak/Asmakizunak
• Fisika

Four-wheeled vehicles began breaking speed records long ago. Nine years after the presentation of the first car in Paris (1898), the Count of Chasseloup got the mark of 63 km/h. Jeantaud brand vehicle and powered by electric motor.

The car “Serpollet”, with steam engine in 1902, ran 120 kilometers per hour. In 1925, the British Campbell climbed the brand to 240 km/h and ten years later to 480 km/h. Within four years (1939), John Cobb left the border at 593.5 km/h and from there it was difficult to set better records. In 1947 John Cobb himself reached a speed of 637 km/h, but the vehicle was as flat as the dish and as demanding as the flight fin. In addition, it had two 1,000 kW aircraft engines to power it. The main problem at this speed was the vehicle's air resistance.

In 1939 Daimler-Benz engineers had designed an aerodynamic 2.600 kW power vehicle with expectations of reaching a speed of 700 km/h. The project was suspended by World War II.

In 1964, Donald Campbell supplied his fireball with a turbine of 3,700 kW of power until reaching a speed of 648.7 km/h. The following year, however, Bob Summers marks in the United States with a lighter vehicle 655.7 km/h. Chrysler's four engines affected it with a total power of 1,800 kW.

Speeds 500-1000 km/h

Meanwhile, American Graig Breedlove followed another path. Because the planes go faster than the car and the jet aircraft is faster than the propeller aircraft, he prepared a vehicle with turboreactor on three-wheeled chassis. Utah's Great Salt Lake reached 657 km/h, but the International Automobile Federation did not accept this mark.

In fact, the Breedlove vehicle was a trailer pulled by the reactor, not a car with drive wheels. However, the International Federation of Motorcyclists was immediately organized and the new category was premiered, that of sid propelled by reaction.

However, the conditions for homologating the record were the same: in two ways the distance of a mile (1,609 meters) must be traversed in an hour. Outside this mile, the vehicle is located at a sufficient distance to accelerate and then to brake. The approved mark is the average of the two passes, so it is lower than the maximum instantaneous speed of the vehicle. In addition, new brands must have at least 1% more than the previous ones.

There are few places in the world to perform the above tests. These are normally dry salt lakes: Nevada's Black Roc in the United States, Utah's Great Salt Lake or Eyre Lake in Australia.

In 1963 the fastest man on the ground was 26-year-old Craig Breedlove, with a speed of 657 km/h. The following year Art Arfons climbed the brand to 863.8 km/h in a similar vehicle called Green Monster, but in 1965 Breedlove advanced and reached a speed of 893.2 km/h. Four days later Arfons raised the mark to 927.9 km/h and a week later Breedlove to 966.6 km/h.

Near the speed of sound

In 1970 Gary Gabelich began to compete. He prepared a vehicle called Blue Flame with rocket engine. This drive reached a speed of 1,001.6 km/h, a mark that lasted thirteen years. In fact, in 1983 the British Richard Noble rolled 1,019.47 kilometers per hour in a vehicle driven by the reactor.

Since then, more than one team has worked to break that brand and above all to get the speed of sound. But problems are not all kinds. It is difficult to maintain balance when the vehicle circulates above the wheel at a speed greater than 600 km/h and keep the travel straight when it is stopped. In addition, when approaching the speed of sound serious aerodynamic problems occur. There is experience in aircraft about these problems, but in addition to tests and laboratory simulations on the ground, no real testing has yet been done.

Serious shock wave problems

First of all it is necessary to clarify that the speed of sound in the air does not vary depending on the pressure, but depends on the temperature. The speed at 0 (C) is 1.195 km/h, from 15 (C) to 1.225 km/h, from 20 (C) to 1.235 km/h and from 30 (C) to 1.250 km/h. In salt lakes, air speed is usually around 1,235 km/h.

The difficulties are more in the subsonic to supersonic range than at supersonic speed, that is, between 1.100-1.300 km/h. This critical area is well known by aircraft pilots. The air slides irregularly and at different speeds in the different sections of the body. Therefore, aerodynamic pressure varies greatly from point to point. This generates shock waves and high-pressure hazardous areas. Richard Noble, when he established his brand in 1983, saw these shock waves at the end of the vehicle.

Today they know how to avoid the impact of shock waves on planes, but what to do in the four-wheel machine that circulates on the ground is the cider of the other cuba. On the one hand, there is no experience and on the other, the sea level air is denser than at large altitudes. In addition, the extreme shock waves of the plane can be spread in the air in all directions, but in the ground vehicle, even though the high and the sides are free, below there is land.

Pressure differences caused by shock waves can result in vehicle take-off, ground nailing, or side rotation.

Current competitors

The main current competitors to break the brand are Breedlove (with his “New Spirit of America”) and Noble (with his “Thrust SSC”). Both are trying to solve the risks we just mentioned. Breedlove wants to prepare the material based on the data it gets when testing faster. Noble, on the other hand, is based on computer simulations and tests carried out with skating models at a speed of 1,300 km/h.

Each of these vehicles has its own stability and travel control system. At these speeds the vehicle is not driven with a steering wheel but with computer control. The Breedlove device has three guide wheels aligned at the end of the vehicle. In the noble, the two rear wheels determine the travel and the hydraulic suspension modifies the balance.

In addition to these two competitors, there are others. Art Arfons prepares its new “Green Monster”. Australian Ross McGlashan has reached a speed of 900 km/h with its “Aussie Invader III” machine on a dry lake next to Adelaide. McL’s house, dedicated to the manufacture of fireballs for Formula 1, prepares a vehicle called “Maverick”. These last two machines have turboreactors, but from there we know little.