Each day at Universal Studios Hollywood, thousands of people climb onto a  bicycle ride with Steven Spielberg's beloved character, E.T., from the movie with the same name. In a thrilling recreation of scenes from the movie,  wide-eyed spectators fly through a moonlit evening, dodge obstacles and menacing pursuers, and brave fog and chill of night, all in a last-ditch effort to help E.T. rendezvous with his spacecraft so he can return home.

Important components in the complex series of carefully timed events in Universal's E.T. Adventure are air springs that produce a series of bounces that add to the excitement of car chases and near-crashes every 18 sec. This translates to 200 times every hour, 12 hours a day.

Setting the scene
The original E.T. Adventure at Universal Studios Florida has been a big hit. So when Universal Studios Hollywood set out to duplicate the attraction for their facility, they invited selected vendors to look over the Florida installation and suggest improvements.

In both attractions, riders climb aboard a ride vehicle that simulates a bicycle made airborne in the movie by E.T. The vehicles are actually suspended from and driven through a ceiling-mounted track. As the ride vehicle rounds a corner, riders are jolted by the sudden appearance of a jeep headed straight toward them. The jeep seems to bounce and rock over rough terrain as it stays in hot pursuit of the ride vehicle. The jeep stops just short of the ride vehicle, which veers into a tunnel to avoid capture.

Emerging from the tunnel, riders immediately encounter a second pursuit jeep, which approaches from between trees, again convincingly rocking back and forth over apparent bumps and gullies. In both cases, air springs generate the natural-looking, bouncy motion of the jeeps. Air springs were cast into this unusual role by Brian Whittier of Cinnebar, a group of Hollywood special-effects wizards that has put the whiz, bang, smoke, and mirrors into films, amusement parks, and other exciting attractions.

"I worked as a truck mechanic before getting into this business," says Whittier, "and I saw the application of air springs on the rear axles of trucks. I knew they'd be perfect for the special rigors of what we needed to accomplish for the E.T. ride — the ability to stand up to lots of action in a dirty environment. They also have a snubbing effect that helps to keep the impact of the vehicle from being transmitted down to hydraulic mechanisms that drive it."

Unlike conventional cylinders, air springs have flexible walls that allow the actuator to expand axially like an accordian when air is pumped into it. Because no seals, piston, or rod are needed, contamination poses nowhere near the potential maintenance problems of conventional cylinders.

Improving the ride
A metal cam system mounted under each jeep was used to create vehicle bounce In the Florida attraction. Not only was the metal system rigid and susceptible to the elements, any adjustments in bouncing action required modifying the cam profile.

Convinced that air springs were the answer, Cinnebar developed a prototype vehicle for the Universal Studios Hollywood ride. Golden State Hydraulics provided the vehicles' hydraulic systems, and the project got the go-ahead for production from Universal's Ed Huntington.

Action behind the scenes
The first pursuit jeep (appropriately dubbed a "collision jeep" because one appears imminent) must hurl toward the ride vehicle, decelerate abruptly, bounce and rock in front of the awe-struck public, then quickly return to prepare for the next cycle. The collision jeep assembly is mounted to a sled, which is propelled forward by a single hydraulic cylinder controlled through a proportional valve that maintains acceleration, maximum velocity, deceleration, and return parameters.

Two four-ply, double-convoluted air springs are mounted to a steel plate which, in turn, is attached to the sled. When pressurized at 65 psi, the air springs lift the vehicle up and help propel it forward. A tank supplied by the building's air system is attached to the jeep and temporarily stores air to provide plenty of capacity on demand. Solenoid valves are switched on and off during the cycle forward, varying the air spring displacement to give the appearance of bouncing over  irregular surfaces. "The action appears random and realistic," says Whittier, "but each movement is timed and planned."

A third air spring is mounted below the sled and attached to the jeep via a post that runs between the first two air springs. As the first two air springs are deflated, the third, maintained at lower pressure, is allowed to expand and move the post, pulling the jeep back down. Because it never loses pressure, this third air spring also acts as a snubber, preventing the jeep from hitting the outer parameters of its envelope too hard. Not only does the cushioning provide added realism to the bounce, it helps protect vital components from excessive jarring.

The collision jeep is followed by the appearance of a "headlight jeep," so named because it is actually only the front half of the jeep, partially visible through the trees. This jeep is mounted to its hydraulic sled with bearings, front and back, that allow it to rock from side to side. A bar runs from driver to passenger side, with air springs mounted at each end. As the air spring under the passenger side is pressurized, the jeep tilts toward the driver side. When the other air spring is inflated, the jeep tilts toward the passenger side. By alternately filling and exhausting the two air springs, the headlight jeep is rocked back and forth.

With more than 20 different scene triggers in the pursuit vehicle episodes, literally hundreds of operations are occurring at once. The air springs require no servo loop and were programmed "simply by feel," says Whittier. "Air springs create more animation, and when the vehicle comes out and stops, they also act as shocks," he adds. "If we had used cylinders, the effect wouldn't have worked as well."

Braving the elements
One of Cinnabar's main considerations in choosing air springs was their performance under adverse conditions. Although efforts are made to keep the E.T. building's air supply dry and filtered, conditions are far from ideal. Temperature variations throughout the building, coupled with the intense fog needed to create the ride's fairy-tale atmosphere, make component maintenance a potential nightmare.

"I was concerned about the moisture, cold, temperature variations, dust and dirt," says Whittier. It was then that the idea of using air springs occurred to him. "I realized," says Whittier, "that compared to the water, salt, and dirt these air springs face everyday underneath trucks, this would be an easy environment for them. Even if there is moisture in in the air supply, the air springs are not affected."

A flawless performance
Indeed, the E.T. ride is operating like a well-scripted movie, providing continuous thrills for as many as 18,000 riders per day. And every 18 seconds, air springs jump into action, unbeknownst to the thousands of guests.