Given a certain power of engine, and consequently a certain fuel consumption, there is a practical limit to the total weight of an aircraft that can be made to fly. Out of that weight as much as possible is wanted for fuel, radio navigational instruments, passenger seats, or freight 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 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.
When a plane has passed all the tests it can get a government certificate of airworthiness, without which it is illegal to fly, except for test flying.
Making the working parts reliable is as difficult as making the structure strong enough. The flying controls, the electrical equipment, the fire precautions, etc. must not only be light in weight, but must work both at high altitudes where the temperature may be below freezing point and in the hot air of an airfield in the tropics.
To solve all these problems the aircraft industry has a large number of research workers, with elaborate laboratories and test houses, and new materials to give the best strength in relation to weight are constantly being tested.
The two main requirements of aircraft design are______.
A.speed and cost
B.reliability and passenger comfort
C.lightness and dependability
D.ability to stay up in the air and reliability
第2题
A . 端面
B . 外圆
C . 套筒
D . 锥孔
第5题
A.必然影响台钻底座工作面与工作台面的平行度
B.不会影响台钻主轴回转轴线对工作台面的垂直度
C.必然影响台钻主轴回转轴线对工作台面的垂直度
D.该钻床比需报废
第6题
A.分度头主轴与铣床主轴
B.分度头主轴与侧轴
C.分度头主轴与铣床纵向工作台丝杠
D.分度头侧轴与工作台纵向丝杠
E.分度头主轴与工作台横向丝杠
第8题
在数控车床主轴上安装光电编码器是为了()。
A、检验主轴回转精度
B、检验刀具运动精度
C、使主轴和刀具构成内联系传动链
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