Double the size of an Airbus A380? No problem, aerodynamicists say.
- By Michael Milstein
- Air & Space magazine, July 2006
(Page 4 of 5)
“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.
To an airplane moseying behind, a vortex may seem like no more than a little speed bump, but the whorl could also act like an unseen hand, suddenly flipping an airplane upside down. Aviation authorities manage the problem by imposing buffer zones between aircraft, especially on takeoff and landing, when vortices are most dangerous. A light aircraft, like a Cessna 172, must stay at least six miles behind a 747.
Through wind tunnel tests and computer modeling, Airbus adjusted the A380’s wing design to keep vortices in the same range as those of a 747, but the International Civil Aviation Organization said early simulations and preliminary flight test data found much more powerful vortices, and ordered aircraft to stay at least 10 miles behind the Airbus. Congested airports like Heathrow would have to space flights out so widely they’d lose the advantage of packing more people onto the bigger airplane. An anxious Airbus has now committed to measuring vortices as the A380 continues its early flights at various locations around the world. It’s doubtful the 10-mile buffer will stick; a similar buffer imposed on the 747 when it first entered service turned out to be stricter than necessary.