Hot Air Balloons
November 23, 2011 by TMO
In 1783, two French brothers, Jacques Etienne and Joseph Michel Montgolfier, invented the hot-air balloon and sent one to an altitude of 6,000 ft (1,800 m). Later that year, the French physicist Jean Pilatre de Rozier made the first manned balloon flight. While balloons could travel to high elevations, they could not travel on their own propulsion and were at the mercy of the prevailing winds. The shape of the balloon was determined by the pressure of the air or gas (such as hydrogen or helium).
In 1852, Henri Giffard built the first powered airship, which consisted of a 143-ft (44-m) long, cigar-shaped, gas-filled bag with a propeller, powered by a 3-horsepower (2.2-kW) steam engine. Later, in 1900, Count Ferdinand von Zeppelin of Germany invented the first rigid airship.
The rigid airship had a metal framework — 420 ft (123 m) in length, 28 ft (12 m) in diameter — containing hydrogen-gas-filled rubber bags. The first Zeppelin had tail fins and rudders, and was powered by internal combustion engines. It carried five people to an altitude of 1,300 ft (396 m) and flew a distance of 3.75 mi (6 km). Several models of Zeppelins were built in the early 1900s. These vehicles were used for military and civilian purposes, including transatlantic travel. The most famous Zeppelin was the Hindenburg, which was destroyed by a fire in 1937 while landing at Lakehurst, New Jersey. See Fall of the Hindenburg to learn about the ship and the crash.
In 1925, Goodyear Tire & Rubber Company began building airships of the blimp design. These aircraft were used for advertising and military purposes (such as surveillance and anti-submarine warfare) throughout World War II. In 1962, the U.S. military stopped using blimps in their operations. Today, blimps are used mainly for advertising, TV coverage, tourism and some research purposes. However, the airship is coming back.
Airships are called lighter-than-air (LTA) craft because to generatelift, they use gases that are lighter than air. The most common gas in use today is helium, which has a lifting capacity of 0.064 lb/ft3 (1.02 kg/m3). Hydrogen was commonly used in the early days of airships because it was even lighter, with a lifting capacity of 0.070 lb/ft3 (1.1 kg/m3) and was easier and cheaper to acquire than helium. However, the Hindenburg disasterended the use of hydrogen in airships because hydrogen burns so easily. Helium, on the other hand, is not flammable.
While these lifting capacities might not seem like much, airships carry incredibly large volumes of gas — up to hundreds of thousands of cubic feet (thousands of cubic meters). With this much lifting power, airships can carry heavy loads easily.
Because gas provides the lift in an airship or blimp, rather than a wing with an engine as in an airplane, airships can fly and hover without expending fuel or energy. Furthermore, airships can stay aloft anywhere from hours to days — much longer than airplanes orhelicopters. These properties make blimps ideal for such uses as covering sporting events, advertising and some research, like scouting for whales.
Recently, there has been renewed interest in using rigid airships for lifting and/or transporting heavy cargo loads, like ships, tanks and oil rigs, for military and civilian purposes. Modern airships, such as theZeppelin NT and CargoLifter, use lightweight, carbon-composite frames that allow them to be huge, light and structurally sound. In addition to hauling cargo, airships may once again be used for tourism. So, the sight of a large airship moving across the sky may become more common in the near future.