建造飞机的时候，没人认为它们会飞行这么久。 但是装有新式引擎和航空电子设备的飞机能持续飞行很长一段时间。 全世界飞机的平均机龄超过10年，有些客机的机龄超过了25年。

　　Science and Technolgy

　　Metal fatigue in old aircraft

　　Flying rivets

　　A new technique that listens for cracks in ageing aircraft

　　WHEN they were built, no one thought they would fly for so long. But fitted with new engines and avionics, aircraft can be kept going for a very long time. The average age of the world&aposs airliners is more than ten years, with some passenger jets 25 years old or more. Military planes are more geriatric: the Sikorsky Black Hawk helicopter entered service 31 years ago and the Lockheed C-5 Galaxy 40 years back. Both are still going strong. Some Boeing KC-135 aerial-ruelling planes, which are based on the venerable 707, have been flying for over 50 years. Engineers reckon they could still be in the air when they are 80.

　　One thing that does ground old aircraft is the impending failure of their aluminium structure from metal fatigue. This begins in parts that are subjected to repeated strains, such as where the wings join the fuselage. Constant flexing of the structure concentrates stress, which leads to microscopic cracks. These cracks become more numerous and eventually large enough for the structure to fail. Aircraft engineers know a lot about how these cracks progress and keep an eye on them in routine overhauls. Nevertheless, they can be difficult and costly to find. Apart from carul visual inspection, techniques like X-rays and ultrasonic probes are also used.

　　Now a British company has come up with a low-cost way of monitoring cracks in aircraft, even while they are airborne. The trick that Ultra Electronics uses is to listen for them with a system called Asis. It does this by fitting small piezoelectric acoustic sensors to parts of the structure to detect the particular frequency of noise caused by a crack in aircraft-grade aluminium. When first set up, Asis is calibrated to the acoustic signature of the aircraft.

　　The system can point engineers to where cracks are occurring because the sensors also record the precise moment it is "heard". As the sound ripples through the structure it arrives at different sensors at different times, which can be used to work out the location and severity of the crack. Once on the ground, a touch-screen device a bit like an iPad is plugged into the system and shows where any cracks are on a three-dimensional image of the aircraft.

　　Asis will be tried out later this year by America&aposs Dence Advanced Research Projects Agency. A basic set-up to monitor the boom on a small helicopter (a particularly stress-prone part) starts at around $65,000, says Rob McDonald, Ultra Electronics&apos marketing director. As to the future, he expects the company will explore how Asis might also monitor carbon-composite materials, which are being used increasingly in new aircraft. Less is known about the long-term structural integrity of carbon fibre, but it is not prone to corrosion and is extremely tough, so with a bit of care and attention it might allow aircraft to fly even longer.

　　【中文对照翻译】

　　科技

　　老旧飞机的金属疲劳

　　飞行侦查兵

　　一项侦听老化飞机断裂的新技术

　　建造飞机的时候，没人认为它们会飞行这么久。 但是装有新式引擎和航空电子设备的飞机能持续飞行很长一段时间。 全世界飞机的平均机龄超过10年，有些客机的机龄超过了25年。 军用飞机更是超龄：西科斯基公司的黑鹰直升机31年前开始服役，洛克希德公司的C-5银河(运输机)早用到40年了。 这两款飞机还都强劲地飞行着。 波音707原型机上发展起来的波音KC-135空中加油机有些已经飞行50多年了。 工程师们测算80机龄时它们仍然能飞上蓝天。

　　让老旧飞机搁浅的一件事就是飞机铝构造因为金属疲劳产生的故障隐患。 这种故障始于承受反复拉紧的部位，象机翼与机身的连接处。 这些构造部位的频繁伸缩使应力集中，导致微裂纹的产生。 这些微裂纹越来越多，最后多到足以使这些部位的构造断裂。 飞机工程师们对这些裂纹如何发展以及在例行检修中如何注意这些裂纹所知甚详。 不过发现这些裂纹可能很难且费用高昂。 除了仔细地目视检查外，也使用象X射线和超声探头这样的技术。

　　目前一家英国公司提出了一种成本低廉的监测飞机裂纹方法，即使飞机在飞行中(也可进行监测)。 超级电子公司采用的诀窍是侦听带有自动语音识别系统(Asis)的飞机。 把小型压电声传感器安装到这种构造部位上，检测由航空级铝材裂纹所致的特定频率的噪音，靠这样就能监测飞机裂纹。 安装之初，Asis就按飞机的声波标记图进行了校准。

　　这个系统能向工程师指明哪里正在出现裂纹，因为传感器也记录裂纹噪音被"听到"的精确时刻。 因为声音呈波形在飞机构造中传播，它在不同的时间到达不同的传感器，这点能用来算出裂纹的位置和严重程度。 一经在地面上把有点象iPad的触摸屏设备用插头插入系统中，它就会在飞机的三维图像上显示所有裂纹。

　　Asis将由美国国防高级研究计划局在今年晚些时候进行试验。 超级电子公司的营销总监罗伯?麦克唐纳说，监测小型直升机(特别是易受压力的部位)嗡嗡声的基本设备起价大约6.5万美元。 至于未来，他期待公司会探究怎么让Asis也能监测碳复合材料，碳复合材料在新式飞机中的应用渐增。 虽然对碳纤维的长期结构完整性所知甚少， 但是它不易腐蚀且极为坚硬，因此稍加关注它就可能让飞机飞行得更久。

【双语阅读】飞行侦查兵 中文翻译部分

　　建造飞机的时候，没人认为它们会飞行这么久。 但是装有新式引擎和航空电子设备的飞机能持续飞行很长一段时间。 全世界飞机的平均机龄超过10年，有些客机的机龄超过了25年。

　　Science and Technolgy

　　Metal fatigue in old aircraft

　　Flying rivets

　　A new technique that listens for cracks in ageing aircraft

　　WHEN they were built, no one thought they would fly for so long. But fitted with new engines and avionics, aircraft can be kept going for a very long time. The average age of the world&aposs airliners is more than ten years, with some passenger jets 25 years old or more. Military planes are more geriatric: the Sikorsky Black Hawk helicopter entered service 31 years ago and the Lockheed C-5 Galaxy 40 years back. Both are still going strong. Some Boeing KC-135 aerial-ruelling planes, which are based on the venerable 707, have been flying for over 50 years. Engineers reckon they could still be in the air when they are 80.

　　One thing that does ground old aircraft is the impending failure of their aluminium structure from metal fatigue. This begins in parts that are subjected to repeated strains, such as where the wings join the fuselage. Constant flexing of the structure concentrates stress, which leads to microscopic cracks. These cracks become more numerous and eventually large enough for the structure to fail. Aircraft engineers know a lot about how these cracks progress and keep an eye on them in routine overhauls. Nevertheless, they can be difficult and costly to find. Apart from carul visual inspection, techniques like X-rays and ultrasonic probes are also used.

　　Now a British company has come up with a low-cost way of monitoring cracks in aircraft, even while they are airborne. The trick that Ultra Electronics uses is to listen for them with a system called Asis. It does this by fitting small piezoelectric acoustic sensors to parts of the structure to detect the particular frequency of noise caused by a crack in aircraft-grade aluminium. When first set up, Asis is calibrated to the acoustic signature of the aircraft.

　　The system can point engineers to where cracks are occurring because the sensors also record the precise moment it is "heard". As the sound ripples through the structure it arrives at different sensors at different times, which can be used to work out the location and severity of the crack. Once on the ground, a touch-screen device a bit like an iPad is plugged into the system and shows where any cracks are on a three-dimensional image of the aircraft.

　　Asis will be tried out later this year by America&aposs Dence Advanced Research Projects Agency. A basic set-up to monitor the boom on a small helicopter (a particularly stress-prone part) starts at around $65,000, says Rob McDonald, Ultra Electronics&apos marketing director. As to the future, he expects the company will explore how Asis might also monitor carbon-composite materials, which are being used increasingly in new aircraft. Less is known about the long-term structural integrity of carbon fibre, but it is not prone to corrosion and is extremely tough, so with a bit of care and attention it might allow aircraft to fly even longer.

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