09 June 2009

Dirigible

The invention: Arigid lighter-than-air aircraft that played a major role in World War I and in international air traffic until a disastrous accident destroyed the industry. The people behind the invention: Ferdinand von Zeppelin (1838-1917), a retired German general Theodor Kober (1865-1930), Zeppelin’s private engineer Early Competition When the Montgolfier brothers launched the first hot-air balloon in 1783, engineers—especially those in France—began working on ways to use machines to control the speed and direction of balloons. They thought of everything: rowing through the air with silk-covered oars; building movable wings; using a rotating fan, an airscrew, or a propeller powered by a steam engine (1852) or an electric motor (1882). At the end of the nineteenth century, the internal combustion engine was invented. It promised higher speeds and more power. Up to this point, however, the balloons were not rigid. Arigid airship could be much larger than a balloon and could fly farther. In 1890, a rigid airship designed by David Schwarz of Dalmatia was tested in St. Petersburg, Russia. The test failed because there were problems with inflating the dirigible. A second test, in Berlin in 1897, was only slightly more successful, since the hull leaked and the flight ended in a crash. Schwarz’s airship was made of an entirely rigid aluminum cylinder. Ferdinand von Zeppelin had a different idea: His design was based on a rigid frame. Zeppelin knew about balloons from having fought in two wars in which they were used: the American Civil War of 1861-1865 and the Franco-Prussian War of 1870-1871. He wrote down his first “thoughts about an airship” in his diary on March 25, 1874, inspired by an article about flying and international mail. Zeppelin soon lost interest in this idea of civilian uses for an airship and concentrated instead on the idea that dirigible balloons might become an important part of modern warfare. He asked the German government to fund his research, pointing out that France had a better military air force than Germany did. Zeppelin’s patriotism was what kept him trying, in spite of money problems and technical difficulties. In 1893, in order to get more money, Zeppelin tried to persuade the German military and engineering experts that his invention was practical. Even though a government committee decided that his work was worth a small amount of funding, the army was not sure that Zeppelin’s dirigible was worth the cost. Finally, the committee chose Schwarz’s design. In 1896, however, Zeppelin won the support of the powerful Union of German Engineers, which in May, 1898, gave him 800,000 marks to form a stock company called the Association for the Promotion of Airship Flights. In 1899, Zeppelin began building his dirigible in Manzell at Lake Constance. In July, 1900, the airship was finished and ready for its first test flight. Several Attempts Zeppelin, together with his engineer, Theodor Kober, had worked on the design since May, 1892, shortly after Zeppelin’s retirement from the army. They had finished the rough draft by 1894, and though they made some changes later, this was the basic design of the Zeppelin. An improved version was patented in December, 1897. In the final prototype, called the LZ 1, the engineers tried to make the airship as light as possible. They used a light internal combustion engine and designed a frame made of the light metal aluminum. The airship was 128 meters long and had a diameter of 11.7 meters when inflated. Twenty-four zinc-aluminum girders ran the length of the ship, being drawn together at each end. Sixteen rings held the body together. The engineers stretched an envelope of smooth cotton over the framework to reduce wind resistance and to protect the gas bags fromthe sun’s rays. Seventeen gas bags made of rubberized cloth were placed inside the framework. Together they held more than 120,000 cubic meters of hydrogen gas, which would lift 11,090 kilograms. Two motor gondolas were attached to the sides, each with a 16-horsepower gasoline engine, spinning four propellers.The test flight did not go well. The two main questions—whether the craft was strong enough and fast enough—could not be answered because little things kept going wrong; for example, a crankshaft broke and a rudder jammed. The first flight lasted no more than eighteen minutes, with a maximum speed of 13.7 kilometers per hour. During all three test flights, the airship was in the air for a total of only two hours, going no faster than 28.2 kilometers per hour. Zeppelin had to drop the project for some years because he ran out of money, and his company was dissolved. The LZ 1 was wrecked in the spring of 1901. A second airship was tested in November, 1905, and January, 1906. Both tests were unsuccessful, and in the end the ship was destroyed during a storm. By 1906, however, the German government was convinced of the military usefulness of the airship, though it would not give money to Zeppelin unless he agreed to design one that could stay in the air for at least twenty-four hours. The third Zeppelin failed this test in the autumn of 1907. Finally, in the summer of 1908, the LZ 4 not only proved itself to the military but also attracted great publicity. It flew for more than twenty-four hours and reached a speed of more than 60 kilometers per hour. Caught in a storm at the end of this flight, the airship was forced to land and exploded, but money came from all over Germany to build another. Impact Most rigid airships were designed and flown in Germany. Of the 161 that were built between 1900 and 1938, 139 were made in Germany, and 119 were based on the Zeppelin design. More than 80 percent of the airships were built for the military. The Germans used more than one hundred for gathering information and for bombing during World War I (1914-1918). Starting in May, 1915, airships bombed Warsaw, Poland; Bucharest, Romania; Salonika, Greece; and London, England. This was mostly a fear tactic, since the attacks did not cause great damage, and the English antiaircraft defense improved quickly. By 1916, the German army had lost so many airships that it stopped using them, though the navy continued. Airships were first used for passenger flights in 1910. By 1914, the Delag (German Aeronautic Stock Company) used seven passenger airships for sightseeing trips around German cities. There were still problems with engine power and weather forecasting, and it was difficult to move the airships on the ground. AfterWorldWar I, the Zeppelins that were left were given to the Allies as payment, and the Germans were not allowed to build airships for their own use until 1925. In the 1920’s and 1930’s, it became cheaper to use airplanes for short flights, so airships were useful mostly for long-distance flight. ABritish airship made the first transatlantic flight in 1919. The British hoped to connect their empire by means of airships starting in 1924, but the 1930 crash of the R-101, in which most of the leading English aeronauts were killed, brought that hope to an end. The United States Navy built the Akron (1931) and the Macon (1933) for long-range naval reconnaissance, but both airships crashed. Only the Germans continued to use airships on a regular basis. In 1929, the world tour of the Graf Zeppelin was a success. Regular flights between Germany and South America started in 1932, and in 1936, German airships bearing Nazi swastikas flew to Lakehurst, New Jersey. The tragic explosion of the hydrogen-filled Hindenburg in 1937, however, brought the era of the rigid airship to a close. The U.S. secretary of the interior vetoed the sale of nonflammable helium, fearing that the Nazis would use it for military purposes, and the German government had to stop transatlantic flights for safety reasons. In 1940, the last two remaining rigid airships were destroyed.

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