Stealth is a steel roller coaster located in the Amity Cove area of Thorpe Park in Surrey, England, UK. Built and designed by Intamin of Switzerland for £12 million, the Accelerator Coaster model opened in 2006. Riders reach a maximum height of 62.5 metres (205 ft) and accelerate from 0-80 mph in 1.9 seconds. It has the fastest acceleration of any coaster in the UK, and is the tallest among launch coasters in the country. At the base of the top hat element on either side, riders may experience up to 4.5 G.
Stealth's restraint system consists of a thick, rigid lap bar and two thin, flexible over-the-shoulder restraints. Because the over-the-shoulder portions of the restraint are not rigid, the hand grips are mounted to the lap bar. These restraints use a locking system (rather than a ratchet) which allows them to be pulled down to any position; when locked, they can move down to any position but not up. In contrast, a ratchet-based restraint only locks at each notch, and will often be too loose or uncomfortably tight. Stealth's restraints are also held down by a belt in case the main locking system fails. In order to speed up loading, riders are asked to secure their own restraints if they are able to. This restraint system is identical to many Intamin Launch coasters, including Kingda Ka and Rita at Alton Towers.
Once the train has been locked, checked and the catch car has attached, an American accented voice announces "Place your heads back, face forwards, hold on tight and brace yourself." The announcer repeats his message as five red lights turn on one by one, before shouting "Three, two, one, GO, GO, GO!" The lights turn green and the train then accelerates to 80 mph in 1.9 seconds, climbs the top hat, turning 90 degrees to the left, then descends the top hat element, through another 90 degree turn, before climbing the second hill (Bunny Hop) producing a moment of apparent weightlessness then smoothly brought to a stop by the magnetic brakes. The train then returns to the station via a U-turn.
As with many Intamin Launch Coasters, Stealth experiences 'roll backs' if it is unable to complete the course because of energy loss. Although very infrequent, roll backs can be caused by friction between the track and wheels, or in the wheel bearings. Weather can also cause a coaster to roll back. Roller coaster trains run slower in cold weather, so much so that many parks actually heat the trains prior to opening on cool days. Roll backs do not happen very often. Computer sensors are placed under the track along the ride to check the acceleration of the train each ride. A computer takes the average of these readings (for the previous five rides) to calculate whether the train is going too fast/slow and adjust the force to launch the train dependent on this. Newton's second law is used for this calculation, so one cause of roll back can be due to uneven balances of weight each ride. If the mass of the train is large on one ride and then less on a second ride, there is a higher chance of a roll back.