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Airship (Wallpaper 1)

Sunday, October 9, 2011

Airship Wallpaper 1
image dimensions : 1092 x 682
Airship (Wallpaper 1)
1. Photo wallpaper gallery of Airship. 1. Airship pictures and images collection.
An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms. Unlike aerodynamic aircraft such as fixed-wing aircraft and helicopters, which produce lift by moving a wing through the air, aerostatic aircraft stay aloft by having a large "envelope" filled with a gas which is less dense than the surrounding atmosphere. The first lifting gas used was hydrogen, although this had well-known concerns over its flammability. Where helium was available, which was only in the USA, this non-flammable gas was used instead. All modern airships, since the 1960s, use helium. The main types of airship are non-rigid (or blimps), semi-rigid and rigid. Blimps are "pressure" airships where internal pressure, maintained by forcing air into internal ballonet, is used to both maintain the shape of the airship and its structural integrity. Semi-rigid airships maintain the envelope shape by internal pressure, but have some form of internal support such as a fixed keel to which control and engine gondolas and stabilizers and steering surfaces are mounted. Rigid airships have structural skeletons which maintain the shape and carry all loads from gondolas, engines, control surfaces and stabilizers. The skeleton contains numerous balloons, known as "gas cells" which supply the static lift without having to bear any structural loading. The name Zeppelin as the type was invented by Count Zeppelin and the vast majority of rigid airships built were manufactured by the firm he founded. Airships were the first aircraft to enable controlled, powered flight, and were widely used before the 1940s, but their use decreased over time as their capabilities were surpassed by those of airplanes. Their decline continued with a series of high-profile accidents, including the 1937 burning of the hydrogen-filled Hindenburg near Lakehurst, New Jersey, and the destruction of the USS Akron. Airships are still used today in certain niche applications, such as advertising, freight transportation, tourism, camera platforms for sporting events, and aerial observation and interdiction platforms, where the ability to hover in one place for an extended period outweighs the need for speed and maneuverability. There is some confusion around the term aerostat with regard to airships. This confusion arises because aerostat has two different meanings. One meaning of aerostat refers to all craft that remain aloft using buoyancy (static not dynamic lift): in this sense airships are a type of aerostat. The narrower and more technical meaning of aerostat refers only to tethered or moored balloons: in this sense airships are not aerostats. In some countries, airships are also known as dirigibles from the French (diriger to direct plus -ible), meaning "directable" or steerable. The first airships were called dirigible balloons. Over time, the word balloon was dropped from the phrase. In modern usage, balloon refers to any buoyant aircraft that generally relies on wind currents for horizontal movement, and usually has a mechanism to control vertical movement. The term "gondola" is used to describe the passenger/instrument and/or engine area of an airship. There may be one or more. The term zeppelin is a genericised trademark that originally referred to airships manufactured by the German Zeppelin Company, which pioneered dirigible design in the early years of the twentieth century. The word Luftschiff, German for "airship", usually prefixed their crafts' names. In modern common usage, the terms Zeppelin, dirigible and airship are used interchangeably for any type of rigid airship, with the term blimp alone used to describe non-rigid airships. Although the blimp also qualifies as a "dirigible", the term is seldom used with blimps. In modern technical usage, airship is the term used for all aircraft of this type, with Zeppelin referring only to aircraft of that manufacture, and blimp referring only to non-rigid airships. Non-rigid airships (blimps) use a pressure level in excess of the surrounding air pressure to retain their shape during flight. Unlike the rigid design, the non-rigid airship's gas envelope has no compartmentation. At sea level, the ballonets (internal flexible cells) are filled with air. As altitude is increased, the lifting gas expands and air from the ballonets is expelled through air valves to maintain the same hull shape. To return to sea level, the process is reversed. Air is forced back into the ballonets by both scooping air from the engine exhaust and using auxiliary blowers. Semi-rigid airships, like blimps, require internal pressure to maintain their shape, but have extended, usually articulated keel frames running along the bottom of the envelope to distribute suspension loads into the envelope and allow lower envelope pressures.


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