2. 外语
  3. There are two main things that make aircraft engineering difficult: the need to make every component as reliable as possible and

There are two main things that make aircraft engineering difficult: the need to make every component as reliable as possible and

admin2015-12-31  59
问题     There are two main things that make aircraft engineering difficult: the need to make every component as reliable as possible and the need to build everything as light as possible. The fact that an aeroplane is up in the air and cannot stop if anything goes wrong makes it perhaps a matter of life or death that its performance is absolutely dependable.
    Given a certain power of engine, and consequently a certain fuel consumption, there is a practical limit to the total weight of aircraft that can be made to fly. Out of that weight as much as possible is wanted for fuel, radio navigational (航行的，航运的) instruments, passenger seats, or freight (货物) room, and, of course, the passengers or freight themselves. So the structure of the aircraft has to be as small and light as safety and efficiency will allow. The designer must calculate the normal load that each part will bear. This specialist is called the "stress man". He takes account of any unusual stress that may be put on the part as a precaution (预防, 预防措施) against errors in manufacture, accidental damage, etc.
    The stress man’s calculations go to the designer of the part, and he must make it as strong as the stress man says is necessary. One or two samples are always tested to prove that they are as strong as the designer intended. Each separate part is tested, then a whole assembly—for example, a complete wing, and finally the whole aeroplane. When a new type of aeroplane is being made, normally only one of the first three made will be flown. Two will be destroyed on the ground in structural tests. The third one will be tested in the air.
The maximum possible weight of an aircraft is determined by______.
选项 A、international regulations
B、the number of passengers
C、the amount of freight room
D、the engine power
答案D
解析 本题问飞机的最大的可能的重量是由什么决定的。文章第二段指出，在发动机指定的功率之下，油耗为某一定量，致使飞机能起飞，于是便有一个实际的临界重量，其中要尽可能多地计入燃料的重量、无线电导航仪、乘客座位或货舱的重量，当然，还要计入乘客及货物本身的重量。由此我们可以推断出本题的正确答案应是D“由发动机的功率决定的”。
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