Giving a Lift to Cargo

Modern airships use helium to provide lift. The Hindenburg used hydrogen gas, which provides about twice the lift of helium but is no longer used because it is extremely flammable. The hehum is contained in bags made of a space-age, leakproof fabric called Tedlar, a type of plastic. The bags are loosely inflated so that the helium pressure is about the same as atmospheric pressure. The quantity of helium determines the lifting ability of the ship. 

As the airship rises, atmospheric pressure decreases and the helium expands, as Boyle s law predicts. As the ship reaches the desired altitude, air is pumped into another bag called a ballonet. The pressure of the ballonet prevents the helium bags from expanding further, thus keeping the ship at that altitude. To descend, more air is pumped into the ballonet. This added pressure squeezes the helium bags, causing the volume to decrease and the density of the helium to increase. Also, the compressed air adds weight to the ship. The tiffing power of the helium is reduced and the airship moves downward. 

The old airships of 1900 to 1940 were used mostly for luxury passenger service. Among modem airships, the German Zeppelin-NT and a ship being 

Thinking Critically No plastics, fabrics, or metals that are lighter-than-air exist.Yet these materials are used to make airships. Why is it possible to describe an airship as a lighter-than-air craft  

Visit the Chemistry Web site at chennistrymc.confi to find links to more information about airships. 

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