High-tech thriller

Drivers passing junction 12 on the M25 might be intrigued by the twisted spike of metal that now towers above the treeline like a giant, curving piece of modern art. This tower is Stealth, Europe’s fastest and tallest rollercoaster — so high that the Civil Aviation Authority had to be consulted on its construction.

Since the £12m ride opened in March at Thorpe Park in Surrey, it has proved so popular that the park has had to close its gates to the thrill-seeking masses on a number of occasions.

The rollercoaster’s interesting design, known as the ‘top hat’, is just part of what makes Stealth so unique in Europe. Riders on Stealth are in for a breathtaking few moments of either white-knuckle thrill or panic, depending on your view of frighteningly fast rollercoasters.

After up to three hours of queuing, riders climb into the 20-seater car and wait in nervous anticipation as the red lights overhead turn to green. Almost silently the car accelerates forward faster than a Formula One car, reaching 80mph in around two seconds. Before a breath can be taken, the car hurtles upwards at a 90 degree angle and catapults up to the top hat, 63m above the ground.

There is little time to enjoy the view over the Surrey countryside. After a split-second’s pause the car plummets back to earth, haring back to base and a sudden, hysterical halt, a mere 15 seconds after it was launched.

Stealth is one of a growing number of ‘hydraulic launch’ rollercoasters, also nicknamed rocket-coasters, a term that sheds some light on their popularity. The technology was developed by world-leading rollercoaster engineer Intamin from Switzerland and was first used in a series of giant rides built in US theme parks.

The biggest of these is Kingda Ka, a 140m-high monster of a ride upon which Stealth’s design is based. According to Andreas Wild, an engineer at rollercoaster expert Ingenieur Buro Stengel, Stealth is really ‘the son of Kingda Ka’.

Ingenieur Buro Stengel is the design company set up by rollercoaster designer and innovator Werner Stengel. Over the past 40 years Stengel has been the driving force behind many of the innovations in the rollercoaster industry and his work with fighter pilots helped set many of the standards on maximum acceleration forces for passengers used in the industry.

His company designed the entire Stealth ride, including its layout, geometry, dynamics and acceleration, and Wild was the ride’s project manager. He explained how many different calculations and designs go into the construction of a new ride.

‘We did static calculations, such as fatigue and stress analysis, as well as detailed drawings for the tracks and columns,’ said Wild. ‘To do this we use our own computer programs; more than 250 programs have been developed for rollercoasters. This is an entirely niche market.’

The key to the new ride’s success — and its unique acceleration — is the hydraulic launch system, which works in a completely different way to conventional rollercoaster launch mechanisms.

The most widely used launch mechanism uses linear induction motors (LIM), which provide linear force instead of rotational torque, and are similar to the systems that power Maglev trains. Hydraulic launch, on the other hand, is quite different.

The launch mechanism for Stealth begins with a two-metre high tank filled with 14,000 litres of hydraulic oil. Three massive hydraulic pumps force the oil through a valve into two banks of six nitrogen accumulator tanks, which pressurises the nitrogen inside to around 50,000psi.

When the gas is fully pressurised, the valve opens, releasing the fluid, which is flung by the gas into 24 powerful motors. These motors power a huge winch drum, which pulls the rope attached to a catch car — the shuttle-like device that pulls the ride along. The winch pulls the catch-car along the 18m of launch track up to the ride station, where it hooks onto the bottom of the ride train and propels it forward.

At the end of the launch track the catch-car lets go and acts like a sling, hurling the ride train — and its 20 screaming passengers — along the track. Once the car has been released, the hydraulic fluid is pumped back into the tank and is then sent straight to the motors, which wind the winch back to its starting point ready for the next launch.

For the ride car, from the point after launch, physics takes over. The design relies entirely on the speed generated from the launch phase to get the ride car straight up and over the top hat. This doesn’t always happen, resulting in occasional ‘rollbacks’, when the ride loses momentum before it reaches the peak and is sent back down, in reverse, to the starting point.

Wild said that one of the main benefits of hydraulic launch over LIM launch is that the hydraulic launch uses far less power. ‘In the US, power for rides isn’t a problem, but here in Europe we have to be more aware of the maximum power available,’ he said.

David Jones is head of engineering and maintenance at Thorpe Park and was the project manager when Stealth was put into place. Before Stealth he had worked on Rita: Queen of Speed at Alton Towers, the only other hydraulic launch ride in the UK.

Stealth has a power correction facility as part of its specially built substation, so that on days when fewer visitors are expected engineers can switch the power down so the train can run more efficiently. But on busy days, when the ride is running two trains and there are 15,000 people in the park, the power can be turned up to full.

Jones explained how Stealth’s special magnetic brakes can bring the ride to a safe and comfortable halt. Permanent magnets are fitted beneath each train with an attractive force between them, he said. To stop the train, copper fins in the track are moved into position into the magnetic field of the ridecar, which creates a resistive force and slows the train down.

‘The brakes are not powered — they work as pure magnets,’ he explained. ‘It’s a fabulously efficient system.’

Stealth might feel like an exercise in reckless endangerment but it is actually packed with the latest safety features, including the restraint design.

However, one of the most important considerations in the design of Stealth was the track itself. According to Wild, a great deal of careful consideration is given to controlling the forces that people on a ride must cope with, particularly in terms of the maximum acceleration that they must endure. Riders on Stealth are said to experience anything up to around 4G, but only for a split second.

The market certainly exists for bigger and better high-acceleration rides. Jeff Bertus, vice-president of the International Association of Amusement Parks (IAAPA), said the market for high-profile new rides is growing rapidly.

‘In an industry such as ours you need repeat customers and so it’s great for park owners to be able to say that they have the fastest ride available — that will guarantee people visiting,’ said Bertus.

However, he added that whether Stealth will eventually produce a good return on what is a massive investment will depend on more than its position as the fastest and tallest rollercoaster in Europe.

‘You can guarantee that within a few months another rollercoaster will be built that that will be slightly quicker or a couple of metres higher, especially as the technology improves,’ he said. ‘All rides stand or fall on how good they are as rides — not on the records they break.’