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How would you design an aircraft if your main aim were to keep its roar from waking up the entire neighbor hood during takeoffs

admin2009-04-23  76
问题     How would you design an aircraft if your main aim were to keep its roar from waking up the entire neighbor hood during takeoffs and landings? A group of 40 engineers from the Massachusetts Institute of Technology and England’s University of Cambridge took on that challenge and, three years later, has unveiled designs for the SAX 40. Thanks to a host of noise-silencing innovations, the 215-seat airplane should be virtually inaudible outside the airport. Designers estimate that the aircraft will emit just 63 decibels(分贝) at takeoff, about as loud as an average conversation, while Today’s airliners hit up to 150 decibels. However, when landing, it still is noisier than at take off, about 100 decibels.
    To achieve such relative silence, researchers needed to rethink’ nearly every aspect of the typical airliner. "There’s no one thing you can do," says Will Graham, who headed up the Cambridge airframe-design team. "You have to treat all the noise sources."
    What aspects should be considered? First, the long exhaust tubes have acoustic liners to get rid of noise, and the size of the exhaust nozzles can be made smaller during takeoff to reduce noise or larger while cruising for fuel efficiency. Second, instead of noisy flaps, a sloped wing and steep landing angle do the braking. Engines embedded in the frame, with air intakes an top, reduce drag and noise. Last, three radial-blade(径向叶片) fans per turbine move large volumes of air at low,quiet speeds. Precisely tuned turbine blades don’t vibrate nonmoving parts.
    Moreover, chief among the aspects is the airframe. The faster a plane flies, the louder it mars. So Graham and his group designed the SAX-40 with a blended-wing body, a concept that discard the tube-and-wing approach for a tailless, triangular structure. That shape provides extra lift, enabling the plane to fly more slowly during takeoffs and landings. It also saves a significant amount of fuel, getting some 35 percent more passenger-miles per gallon than a Boeing 777.
    A number of other researchers are working on similar concepts. But challenges remain. An aircraft without a stabilizing tail would be far more difficult to fly. And then there is the question of how to make its flattened fuselage(机身) as structurally strong as a cylinder. But perhaps the biggest difficulty is the airline industry’s financial in vestment in conservative design. Betting on such a radical plane, Graham says," would be a huge step for manufacturers."
选项 A、The noise SAX-40 made cannot be heard at take off.
B、The noise SAX-40 made cannot be heard during landings.
C、The noise SAX-40 made during landings will decrease sharply.
D、The noise SAX-40 made at takeoff will decrease sharply.
答案D
解析 根据题干achieved by the design of SAX-40可以定位到第一段第四句。根据这句可知设计者估计SAX-40这架飞机在起飞时会产生63分贝的噪音，像谈话时的平均声音那么大，而今天的飞机产生150分贝的噪音。但是，在降落的时候它的噪音要比起飞时大一些，约100分贝。也就是说，SAX-40的成功之处是在起飞时的噪音有显著的下降。文中未提及SAX-40在起飞时听不到，也末提及SAX-40在降落时听不到，可排除A、B；SAX-40在降落时的噪音没有显著的下降，故排除C。
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