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Superduperjumbo

Double the size of an Airbus A380? No problem, aerodynamicists say.

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In Singapore, where Singapore Airlines has ordered 10 A380s, with options for 15 more, costing a total of $8.6 billion, and where the first commercial A380 flight will likely take off early next year, Changi Airport is expanding 19 gates with extra seating, restrooms, and three jetways to handle A380s. Crews at Changi, which promises to be a hub for the megaliners on crowded Asian routes, have widened runways, expanded runway-taxiway intersections, and added shields to block the intense blast from the A380’s engines.

Airbus designed the A380 so airports wouldn’t have to strengthen existing runways. Though it weighs far more than a 747, its tires put no more pressure on runways because its weight is spread out over more wheels: 22. The immense weight of the new airliners does require some airports to reinforce bridges they will use. Its span and engine placement require them to widen runways from 150 feet, the standard for a 747, to 200 feet. Some airports, such San Francisco International, will work around that requirement by closing adjoining taxiways when an A380 arrives.

Airbus has strained to coax every bit of per-passenger performance possible from its superjumbo, and that’s the reason the airplane has two decks. Airplanes that pack people onto two levels—like the A380—or even three levels—like Kroo’s superduperjumbo—make more efficient use of their space. Kroo figured that by stacking 1,500 passengers in an airliner’s triple-deck fuselage, for example, he would reduce the ratio of nonlifting fuselage area to lifting wing area, which would reduce the power needed to carry each person. (Pity the poor pilot who’d have to stand there and say goodbye as all those people file off.)

But the payoff multiplies not only because per-person thrust is optimized but because the basic costs of flying any airliner—the salary of our friendly pilot, for instance—are spread across the ticket price of more passengers, so the cost of moving each person is smaller.

“You get some help from the aerodynamics [in a larger airplane], but you get even more help by putting another 50 to 80 people on it,” says William Crossley, a professor at Purdue University’s School of Aeronautics and Astronautics in Indiana. “That’s why the airlines really like it. They’re in the business of moving people, and the more people they can move, the better.”

Moving more people through the air, however, sometimes seems easier than moving them on and off an airliner. The A380, says Airbus, is focused on efficient loading and unloading. The exits were located so that once the airplane pulls up to the terminal, passengers can gather their belongings and get off quickly, and the next load can get on and fasten their seatbelts—all in 90 minutes, keeping time on the ground to a minimum.The ultimate test of exit efficiency, however, would come in an emergency, and the FAA and the European Aviation and Safety Agency required Airbus to load the A380 to maximum capacity and then get every last one of its 853 passengers off within 90 seconds. The test had to mimic real emergency conditions: At least 35 percent of the “passengers” were over 50 years old, at least 40 percent were women, carry-on baggage and pillows were strewn about the cabin, and only half the airplane’s doors were workable. And the evacuation had to be performed in total darkness.

Last March in Hamburg, Germany, 853 volunteers and 20 crew members left an A380 in 78 seconds. One man broke his leg and there were several other minor injuries, but the airplane passed the test.

Risk analysts wonder if a test can truly simulate all real world conditions. Emergency exit slides are rated to inflate within 10 seconds even in a 25-knot wind, but a critical question for the A380 is whether passengers will balk at sliding almost 30 feet from the uppermost deck. Passengers must leap onto the slide faster than one per second, so more than a blink of hesitation will clog the flow.

Exit slides, made by North Carolina-based Goodrich, are designed so the slope doesn’t look as steep as it really is, Champion says. But exit slides were a problem for at least one passenger very familiar with airliners. Juan Trippe wanted the Boeing 747 to be a double decker for the economic advantage, but it ended up with only a partial upper level in its hump after Trippe was invited to try out an exit slide—and chose the stairs instead.

One of the more contentious issues in the A380’s test program was the danger of the vortices the airliner will trail. Air swirling around the wings not only cuts into performance, it also trails the wings  in the form of invisible whirlwinds. Every airplane creates them, but the heavier the airplane and the shorter its wingspan, the more powerful they can be.

About Michael Milstein

Michael Milstein is a freelance writer who specializes in science. He lives in Portland, Oregon.

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