下面新東方網託福頻道為大家整理了託福聽力背景知識之第一次世界大戰中的AIRSHIP，供考生們參考，以下是詳細內容。
第一次世界大戰中AIRSHIP的背景知識
By the start of the Great War the airship had been developed into two main types - rigid and non-rigid (technically, the latter is more accurately described as pressure-rigid). Cylindrical in cross-section, both were given buoyancy by gas and motion by engine-driven propellers and were controlled by vertical rudders and horizontal elevators.
In the rigid type, a solid framework, which might be likened to a skeleton, supports an external covering of fabric called the envelope (a very few experimental types had a metallic covering). Within the framework are contained bags of gas called balloonets. In the non-rigid, the envelope''s shape is maintained by the pressure of the gas that fills it; there is no framework. The rigid''s control car and engines are suspended from the framework; in the non-rigid they are attached directly to or suspended directly from the envelope. (In some later rigids the engines were mounted internally, driving the propellers by transmission belts.)
There was an intermediate type, now long vanished, called the semi-rigid. It had a pressure-rigid envelope but a solid keel.
The rigid airship, employed so extensively by Germany during the Great War, was perfected soon after the turn of the century by a former Wurttenberg army cavalry officer, Ferdinand Adolf August Heinrich Graf von Zeppelin, who had been inspired by a balloon ascent he had made in the United States on 19-Aug-1863. 2 His craft were, naturally , known as Zeppelins. "Zeppelin" is a proprietary, or trade, name (such as Kodak, Ferris Wheel and Autogiro), and is applied properly only to craft constructed by Luftshiffbau Zeppelin G.m.b.H. or firms licensed to use its patents. It should thus be spelled with a capital Z; modern writers who spell it in lower case are mistaken in their apparent belief that it is generic. 3
It has become customary to refer to all German rigid airships of the Great War as Zeppelins, but in fact not all were. Some were constructed by a rival firm, Luftschiffbau Schutte-Lanz G.m.b.H., which employed a framework of laminated plywood instead of the aluminum alloy used in Zeppelins. 4
The vast amount of literature devoted to German airships can easily, and has, led to the belief that these were the dominant LTA craft of the Great War. Actually, the British navy was the greatest exponent of the airship, receiving more than 200 non-rigids during 1915-1918 for anti-submarine patrolling. This type was also used, although in far fewer numbers, by the U.S. Navy and the French and Italian armies and navies. The German army and navy also had a handful.
The rigid airship no longer exists; none has been built since the 1930s. 5 The demise is usually blamed on the Hindenburg disaster 6 although that had been preceded by the loss of a number of American, British, French and Italian rigids. All airships flying today are non-rigid types, popularly known as blimps.
飛艇按其結構可分為軟式、半硬式、硬式。
(1)軟式飛艇艇體由主氣囊和前後副氣囊組成。氣囊不僅要求密封，還要有相當強度能承受一定的壓強。氣囊上裝有安全活門，壓強超過規定值時能自動放氣保證氣囊不被脹破。主氣囊內充浮升氣體，副氣囊內充空氣。副氣囊的作用是在不排放主氣囊內氣體的條件下，保持主氣囊內外壓強差為定值。當飛艇爬高，外界大氣壓強降低時，副氣囊放氣使主氣囊增大容積，從而保持主氣囊原來的內外壓強差。當外界大氣壓強增大時，向副氣囊內充氣使它膨脹，從而壓縮主氣囊的容積，使主氣囊的壓強仍能保持略高於外界大氣壓強。設置前後副氣囊還可調節浮力中心的位置。僅向後副氣囊充氣時，重心後移，飛艇產生抬頭力矩;反之，產生低頭力矩。
(2)半硬式飛艇氣囊構造與軟式飛艇相似，但在氣囊下部增加剛性的龍骨架，組成半硬式飛艇的艇體。
(3)硬式飛艇艇體由剛性骨架外罩蒙布或薄鋁皮構成整個艇體不密封，主要起維持流線型和連接各部分的作用。艇體內部由隔框分割成許多小氣室，每個小氣室內放有密封的小氣囊，內充比空氣輕的氣體。在地面時，小氣囊沒有完全脹滿氣室。隨著飛行高度增加，外界大氣壓強降低，囊內氣體隨之膨脹，在達到規定高度時，氣囊恰好脹滿氣室。眾多小氣囊可提高飛艇的抗損性和安全性。部分小氣囊受損，整個飛艇的浮力不會完全喪失。
第一艘飛艇是法國的H·吉法爾於1852年製成的。1900年德國的齊柏林公司開始製造大型硬式飛艇，在第一次世界大戰期間，曾多次用飛艇進行遠程轟炸。
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