How the London Eye Works

When the architects at Marks Barfield sat down to consider what structure would best commemorate the turning of the century, they noted that London didn't have any observation points for people view the skyline and surrounding landscape. A tall, rotating wheel would not only allow a unique vantage point of the city, but would allow large numbers of people to see that view at the same time.

The London Eye is a modern take on a traditional Ferris wheel with a few distinct differences. For one, the passengers sit in fully enclosed capsules rather than dangling gondolas. Two, the entire structure of the London Eye is supported on one side only, allowing the wheel to hang over the River Thames.

The London Eye is an excellent example of a frame structure. Its steel design forms an "A" shape, with two large tapered legs at the base -- 65 feet (20 meters) apart and each over 190 feet (58 meters) in length. The legs lean toward the river at a 65-degree angle. Cable backstays keep the frame from tilting into the river -- they're anchored to the top of the frame and then buried in a concrete foundation 108 feet (33 meters) deep.

The wheel part of the London Eye resembles a lightning, the strike would be conducted to the ground with no harm to passengers.

The London Eye rotates around the hub much like a bicycle wheel, but motorized. Hydraulic motors, driven by electric pumps, provide energy to turn the wheel. The drive systems are located in two towers, one at each end of the wheel's boarding platform. Here's how the wheel turns: Standard truck tires along the rim of the wheel act as friction rollers. Hydraulic motors turn the tires, and the rotation of the tires turns the wheel. A computer controls the hydraulic motor speed for each tire.

The main components of the London Eye were built offsite. Once they were completed, barges transported them piece by piece up the River Thames to the construction site on the South Bank. Workers assembled the London Eye horizontally on a temporary support platform over the river, which made construction faster, easier and safer than if it had been built vertically. Once it was assembled, hydraulic lifts and cables slowly raised the 1,322 ton (1,200 tonnes) structure over the course of one day, until it reached its 65-degree angle. Once it was in final position, the 32 capsules were attached to the rim, which took eight days.

Instead of being suspended and swinging, the passenger capsules turn within circular mounting rings fixed to the outside of the main rim. As the wheel rotates, the capsules also rotate within their mounting rings to remain horizontal. If the capsules didn't rotate, by the time your capsule went around the wheel, you and your friends would be upside down. Each capsule has its own heating and cooling system, bench seating and is fitted with special glass that can handle weather fluctuations. Capsules also have a built-in stability system, meaning the capsule will stay level even if all the passengers suddenly move to one side. There are 32 capsules, one to represent each borough of London.

Instead of "rides," the London Eye has "flights." The attraction is open daily except for Christmas Day, and is regularly closed for a week in January for maintenance.

At the top of the London Eye, on a clear day, you can see 25 miles (40 km) -- as far as Windsor Castle. Each rotation takes about 30 minutes, and the wheel moves at about 0.6 miles an hour (0.96 kph). Its speed is quite slow, and passengers can easily step on and off without the wheel ever having to stop -- though for elderly or disabled passengers, the wheel can come to a complete stop for safety.

The London Eye carries 3.5 million customers each year. Each of the 32 capsules holds up to 25 people, allowing the London Eye to transport 800 people at a time. A standard ticket is about $28, or 15.50 pounds, and entitles passengers to one rotation, about 30 minutes. The Eye also offers special packages, including private capsule flights, flights with champagne or cocktails, flights with wine tastings, flights with breakfast and the list goes on. Many couples get engaged or married on the London Eye. Just don't forget your wallet -- obviously the more amenities you want, the more you'll pay. For example, a private capsule "champagne flight" costs almost $800, or 430 pounds, and that doesn't even include the champagne. The Eye advises booking flights in advance for any special packages.

Originally, fluorescent tubes lit the London Eye by night. This system proved costly to maintain. In order to bathe the London Eye in different colors for special occasions, workers had to manually cover each fluorescent tube with a colored gel "slip." In 2006, a company named Color Kinetics took over lighting duties and installed computer-controlled LED lighting. The LED Chromacore® lighting technology adds a microprocessor to each cluster of LED lights, allowing networked control of color, intensity or effects. Today, the London Eye can be coated in all sorts of colors and even perform light shows.

We've all read enough horror stories about amusement park rides to wonder if anything has ever gone awry with the London Eye. The answer to that question is, "Yes." In March of 2008, the wheel malfunctioned and stranded 400 passengers for about an hour. Engineers noticed an error in one of the tires that rotates the Eye, and they stopped the wheel to make emergency repairs. Nobody was hurt, but many passengers were quite frightened and angry once they safely returned to ground [source: McCathie]. Back in 2002, engineers closed the London Eye for a few hours after they noticed it was rotating a little too fast. No passengers were on board at the time, however.

During its construction, the London Eye underwent extensive safety monitoring, testing and evaluation. This monitoring continues on a constant basis. Each morning, computers and humans perform a safety check on all aspects of the London Eye. During operation, safety sensors in each capsule send ongoing reports back to a control room on the ground. Every safety system has a back-up system as well. In the event of a problem, the ride operator can return a capsule -- no matter where it is -- back to the boarding platform in eight minutes, by either changing direction or speeding up rotation.