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Science and technology
科學技術
Metal fatigue in old aircraft
老舊飛機的金屬疲勞
Flying rivets
飛行偵查兵
A new technique that listens for cracks in ageing aircraft
一項偵聽老化飛機斷裂的新技術
WHEN they were built, no one thought they would fly for so long.
建造飛機的時候，沒人認為它們會飛行這么久。
But fitted with new engines and avionics, aircraft can be kept going for a very long time.
但是裝有新式引擎和航空電子設備的飛機能持續飛行很長一段時間。
The average age of the world's airliners is more than ten years, with some passenger jets 25 years old or more.
全世界飛機的平均機齡超過10年，有些客機的機齡超過了25年。
Military planes are more geriatric:
軍用飛機更是超齡：
the Sikorsky Black Hawk helicopter entered service 31 years ago and the Lockheed C-5 Galaxy 40 years back.
西科斯基公司的黑鷹直升機31年前開始服役，洛克希德公司的C-5銀河早用到40年了。
Both are still going strong.
這兩款飛機還都強勁地飛行著。
Some Boeing KC-135 aerial-refuelling planes, which are based on the venerable 707, have been flying for over 50 years.
波音707原型機上發展起來的波音KC－135空中加油機有些已經飛行50多年了。
Engineers reckon they could still be in the air when they are 80.
工程師們測算80機齡時它們仍然能飛上藍天。
One thing that does ground old aircraft is the impending failure of their aluminium structure from metal fatigue.
讓老舊飛機擱淺的一件事就是飛機鋁構造因為金屬疲勞產生的故障隱患。
This begins in parts that are subjected to repeated strains, such as where the wings join the fuselage.
這種故障始于承受反復拉緊的部位，象機翼與機身的連接處。
Constant flexing of the structure concentrates stress, which leads to microscopic cracks.
這些構造部位的頻繁伸縮使應力集中，導致微裂紋的產生。
These cracks become more numerous and eventually large enough for the structure to fail.
這些微裂紋越來越多，最后多到足以使這些部位的構造斷裂。
Aircraft engineers know a lot about how these cracks progress and keep an eye on them in routine overhauls.
飛機工程師們對這些裂紋如何發展以及在例行檢修中如何注意這些裂紋所知甚詳。
Nevertheless, they can be difficult and costly to find.
不過發現這些裂紋可能很難且費用高昂。
Apart from careful visual inspection, techniques like X-rays and ultrasonic probes are also used.
除了仔細地目視檢查外，也使用象X射線和超聲探頭這樣的技術。
Now a British company has come up with a low-cost way of monitoring cracks in aircraft, even while they are airborne.
目前一家英國公司提出了一種成本低廉的監測飛機裂紋方法，即使飛機在飛行中。
The trick that Ultra Electronics uses is to listen for them with a system called Asis.
超級電子公司采用的訣竅是偵聽帶有自動語音識別系統的飛機。
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.
把小型壓電聲傳感器安裝到這種構造部位上，檢測由航空級鋁材裂紋所致的特定頻率的噪音，靠這樣就能監測飛機裂紋。
When first set up, Asis is calibrated to the acoustic signature of the aircraft.
安裝之初，Asis就按飛機的聲波標記圖進行了校準。
The system can point engineers to where cracks are occurring because the sensors also record the precise moment it is “heard”.
這個系統能向工程師指明哪里正在出現裂紋，因為傳感器也記錄裂紋噪音被“聽到”的精確時刻。
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.
因為聲音呈波形在飛機構造中傳播，它在不同的時間到達不同的傳感器，這點能用來算出裂紋的位置和嚴重程度。
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.
一經在地面上把有點象iPad的觸摸屏設備用插頭插入系統中，它就會在飛機的三維圖像上顯示所有裂紋。
Asis will be tried out later this year by America's Defence Advanced Research Projects Agency.
Asis將由美國國防高級研究計劃局在今年晚些時候進行試驗。
A basic set-up to monitor the boom on a small helicopter starts at around $65,000, says Rob McDonald, Ultra Electronics' marketing director.
超級電子公司的營銷總監羅伯?麥克唐納說，監測小型直升機嗡嗡聲的基本設備起價大約6.5萬美元。
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.
至于未來，他期待公司會探究怎么讓Asis也能監測碳復合材料，碳復合材料在新式飛機中的應用漸增。
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.
雖然對碳纖維的長期結構完整性所知甚少，但是它不易腐蝕且極為堅硬，因此稍加關注它就可能讓飛機飛行得更久。
