# Building the world's biggest wheel: engineers use tricks of the trade to construct an over-the-top ride.

Engineers at the Great Wheel Corporation are on a roll. They're busy constructing the biggest wheel the world has ever seen--a giant observation wheel in Beijing, China. When it's completed in 2009, the Great Beijing Wheel will lift passengers 208 meters (681 feet) off the ground--three-fourths the height of the Empire State Building.

The first giant observation wheel, the London Eye, which opened in 2000, put a new spin on the traditional Ferris wheel (see Nuts & Bolts, p. 18). Since then, increasingly larger wheels have been constructed in other countries. But as the wheels get bigger, so do the challenges involved in designing them. How do you build the world's biggest wheel? Read on to learn about some of the major challenges engineers face when constructing giant observation wheels.

CHALLENGE #1

Engineers need to know up front whether the wheel will be able to hold up under its load, or weight. This is no small feat considering the total weight of the Great Beijing Wheel and cabins itself is expected to be 2,800 metric tons. That's as much as 515 African bull elephants! And that's not all: The load also includes the additional weight of the passengers and the force of the wind pushing against the wheel.

Before a single piece of the wheel is made, engineers use math to determine which materials are up to the task. "For every part of the wheel, a calculation is made," says Henk Stam, a design engineer at the Great wheel Corporation. Only then will the project move ahead.

CHALLENGE #2

Just because a material is sturdy enough to work doesn't mean it is the right one for the job. Some materials would be too heavy when used on a project as large as an observation wheel. Other materials would have to be used in too large a quantity. Part of the challenge in designing a giant observation wheel is to keep the wheel's weight and its wind resistance down. "Adding more material increases the [wheel's] weight and also the surface exposed to the wind," Stam explains. So designers must find ways to create a strong structure using less material.

One strategy: constructing the wheel's rim of hollow tubes. Engineers of the London Eye connected steel tubes to a frame of triangular shapes. This made for a strong but light rim that offered less wind resistance than a solid rim would have. Engineers of many observation wheels that followed used this same lightweight design.

CHALLENGE #3 Hefty observation wheels could sink into the ground under their own weight, or fall over if not properly supported. So engineers use two opposite forces: compression and tension. Giant A-frames under the axis, or hub, support the wheel's weight. The A-frame legs rest on a compression base. Compression is a force that pushes against a material and threatens to buckle it. In this case, the wheel's weight pushes down to put the base under compression.

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If forces acted in only one direction, a giant wheel could become a giant flop. Engineers offset compression by attaching Stay cables from the wheel's hub to another base on the ground. These cables create tension-a force that pulls and stretches--that tugs up from the ground. The opposite forces of compression and tension balance each other out, so the wheel stays in place.

CHALLENGE #4

Much as spokes connect a bicycle wheel's rim to its axis, steel cables connect a giant observation wheel's rim to its hub. But the wheel's weight pushes down to put the cables under compression. Stare explains, "The cables in the upper half of the wheel will slacken and the cables in the lower part will get very heavily loaded." To prevent this, the cables are prestressed, or stretched tight during construction. This makes the cables pull out from the hub with tension that holds the rim in shape.

CHALLENGE #5

The Great Beijing Wheel will spin nonstop at three revolutions per hour. That means passengers will have to enter and exit one of 48 designated glass-enclosed cabins as the wheel spins. Each capsule holds up to 40 passengers. But if 40 people were to try to step from a stationary platform into a moving capsule, the capsule would pass by before everyone had time to board.

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Solution: Passengers will board special vehicles that will take off to move along a track in the same direction and speed as the cabins. While the vehicle and cabin are in sync, passengers will step from one to another. "Passengers can enter the capsules in a safe manner while the wheel keeps turning," says Ronald Wittenberg, a project manager at Bosch Rexroth Corporation which is working on the Beijing Great Wheel.

Engineers are working hard to create an uplifting experience for the wheel's future passengers. "It is an important and challenging project, working on the biggest wheel in the world," says Wittenberg.

nuts & bolts

A NEW SPIN ON AN OLD IDEA

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When civil engineer George Ferris proposed building a 264-foot-high rotating wheel for the 1893 Chicago World's Fair, people thought he was out of his mind. But Ferris showed them: He built the steel structure, which was powered by steam engines and took 1.5 million passengers for a spin during the Fair. Afterward, Ferris wheels popped up all over the globe.

A recent resurgence in "observation wheels," the modern version of the Ferris wheel, has led to a competition for the title of the world's tallest. Here are some wheels of the past, present, and future.

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```Name: Year Built Ferris Wheel: 1893 Wonder Wheel: 1920

Total Beight 80 meters (264 feet) 46 meters (150 feet)

Max. Riders 2,160 144

Ride Time 20 min. about 6 min.

Fun Fact George Ferris built This Coney Island
the first great wheel landmark, built by the
for the Chicago World's Eccentric Ferris Wheel
Fair to rival Gustave Company, still runs in
Eiffel's tower in Paris. Brooklyn, New York.

Name: Year Built London Eye: 2000 Singapore Flyer: 2008

Total Beight 135 meters (443 feet) 165 meters (541 feet)

Max. Riders 800 784

Ride Time 30 min. 37 min.

Fun Fact Built for the Located in Marina
millennium, this Bay, Singapore's prime
observation wheel waterfront central
10,000 riders a day and

Beijing Great Wheel:
Name: Year Built 2009

Total Beight 208 meters (682 feet)

Max. Riders 1,920

Ride Time 20 min.

Fun Fact At its opening, the
Beijing Great Wheel
will become the worlds
tallest wheel.
```

1. Which force pulls and stretches?

(A) compression

(B) tension

(C) friction

(D) drag

2. Which wheel could hold the most riders?

(A) Ferris Wheel

(B) Wonder Wheel

(C) London Eye

(D) Singapore Flyer

3. The Beijing Great Wheel looks much like a --.

(A) wind turbine

(B) fan

(C) frisbee

(D) bicycle wheel

1. b 2. a 3. d

web extra

To learn more on the histor of the world's first Ferris wheel, visit: www.scholastic.com/scienceworld and click on "In This Issue."

HANDS-ON SCIENCE

(No lab required)

After reading "Building the World's biggest Wheel" (p. 16), try this activity to design your own turning observation wheel

PREDICT

To build an observation wheel that will hold up under different types of forces and pressures, engineers must come up with a sturdy design and choose the right building materials. What types of materials could you use to create your own turning model wheel?

MATERIALS

pencil * paper * package of dry spaghetti * wooden shish-kebab sticks * large marshmallows * mini marshmallows * modeling clay * scissors * glue*

* Note to Teachers: You may substitute or provide students with other types of building materials, such as tape, pipe cleaners, straws, popsicle sticks, rubber bands, cardboard, or string.

DIRECTIONS

1 Form three-person teams. Each team's challenge: Act as engineers and build a turning model of an observation wheel.

2 Beijing's Great Wheel resembles a giant bicycle wheel. What will yours look like? Sketch a plan for your wheel. What will you do to make sure it can support its weight? Will you glue materials together or add or take away "spokes" for extra support? You will need a central piece that connects the wheel to a base and allows the wheel to rotate.

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3 Decide which of the materials provided by your teacher you will use. If you aren't provided with any curved pieces, how can you alter your materials to form the circle of the wheel? What will you use to connect each piece of your model observation wheel together?

5 Build your wheel. If you are having trouble with your initial design, you may have to revise your plans. (Note: Wheels held together with glue will need to dry overnight.)

6 Present your wheel to the class and explain the materials and design you chose. Which group had the best design?

CONCLUSIONS

1. How well did your design work? How could you alter your wheel to improve it?

2. Which group's design and materials worked best? Why?

3. What must engineers consider when working on a large-scale project like an observation wheel?

TAKE IT FURTHER

Use tea bags to represent passenger cars on your wheel. Tie two bags directly across from each other on the outside of your wheel. Slowly turn the wheel. Can your structure support the added weight?

* The world's biggest observation wheel, called the Great Beijing Wheel, is expected to open in 2009. How high do you think it will lift passengers into the air?

* The Great Beijing Wheel will be three-fourths the height of which of the following structures: Great Pyramid of Giza, the world's tallest roller coaster', or the Empire State Building?

* Can you think of some technical challenges that engineers might need to overcome in order to build the Great Beijing Wheel?

DID YOU KNOW?

* The Great Beijing Wheel is estimated to cost \$99 million to construct.

* From the top of the Singapore Flyer, an observation wheel in Singapore, passengers can view parts of the neighboring countries of Malaysia and Indonesia.

* In Bulgaria during the 1600s, people enjoyed riding in "pleasure wheels." Riders of these wheels sat in wooden packing crates as strong men used hand cranks to power the wheel. A man named Antonio Maguino introduced the pleasure wheel to America in 1848.

CRITICAL THINKING"

* What are the pros and cons of building the Great Beijing Wheel? (Students should consider how the project might affect Beijing's environment, economy, and its citizens' quality of life.)

CROSS-CURRICULAR CONNECTIONS"

ART: A change in perspective alters how you view things. Use the information in the article to hell) you imagine what the Great Beijing Wheel looks like. Then on unlined paper, sketch the wheel as if you were viewing it from afar. Next, create a second sketch as if you were seeing it from standing beside it. Lastly, sketch the wheel as if you were looking down on it from above. Below the sketches, list the similarities or differences of the three drawings.

RESOURCES

* For an eyewitness account of a ride on the Ferris wheel in 1893, read the story at: www.clpgh.org/exhibit/neighborhoods/northside/ nor_nl05b.html

* The worksheet found at this Web site helps students learn what it takes to engineer a big wheel: www.tryengineering.org/lessons/buildabigwheel.pdf

* For a great lesson and worksheet related to the invention of the Ferris wheel, visit this Web site: http://chicagohistory.org/static_media/ pdf/historylab/CHM-historylabFfw01.pdf

DIRECTIONS: Use the information in the story to help you defend or dispute the statements below. (Hint: Defend means to explain why a statement is correct. Dispute means to explain why a statement is incorrect.)

1. The load of the Great Beijing Wheel refers to the structure's weight.

2. To help keep a giant wheel stable, engineers use two opposite forces: compression and tension.

1. Dispute: The load of the Great Belling Wheel includes the structure's weight, as well as the weight of its passengers and the force of the wind pushing against the wheel

2. Defend: Engineers use compression and tension to help keep a giant wheel stable Giant A frames under the axis support the wheel's weight. The A frame legs rest on a compression base. Compression is a force that pushes against a material and threatens to buckle it. In this case, the wheel's weight pushes down to put the base under compression. If forces acted in only one direction, a giant wheel could become a giant flop. So engineers offset compression by attaching stay cables from the wheels hub to another base These cables create tension, a force that pulls and stretches, that tugs up from the ground. The opposite forces of compression and tension balance each other out so the wheel stays in place.