AIR SHIPS

PROLOGUE

An airship is a type of lighter-than-air aircraft with propulsion and steering systems,  it is used to carry passengers and cargo.  It obtains its buoyancy from the presence of a lighter-than-air gas such as hydrogen or helium.  The first airship was developed by the French, called a ballon dirigible, it could be steered and could also be flown against the wind.

 TYPES OF AIRSHIP

Two basic types of airship have been developed:  the rigid airship, the shape of which is fixed by its internal structure; and the nonrigid blimp, which depends on the pressure created by a series of air diaphragms inside its gas space to maintain the shape of its fabric hull.  Inventors sought to combine the best features of these models in a semirigid type, but it met with only limited success.  Today only the nonrigid airship is used.

 Rigid Airship

The rigid airship's structure resembled a cage that enclosed a series of balloons called gas cells.  These cells were tailored to fit the cylindrical space and were secured in place by a netting that transmitted the lifting force of their gas to the structure.  Each gas cell had two or more valves, which operated automatically to relieve pressure when the gas expanded with altitude, the valves could also be operated manually so that the pilot could release gas whenever desired.

Also on board was a ballast system that used water as ballast. On the ground this ballast served to make the airship heavier than air.  When part of it was released, the airship ascended to a cruising altitude where the engines supplied propulsion, and further ballast could be released to gain more altitude. As fuel was consumed, the airship became lighter and tended to climb.  This was countered in hydrogen-inflated airships by simply releasing gas into the atmosphere.

The method was uneconomical, however, with helium-inflated airships, and they were therefore equipped with ballast generators, apparatuses that condensed moisture out of the engines' exhaust gases to compensate for fuel that was consumed.  But this ballast-generating equipment was expensive, complex, heavy, and difficult to maintain and was thus one of the most serious disadvantages of airships filled with the safer but more expensive helium.

Nonrigid Airship

In contrast to the rigid airship, the nonrigid blimp has no internal structure to maintain the shape of its hull envelope, which is made of two or three plies of cotton, nylon, or dacron impregnated with rubber for gas tightness.  Inside the gas space of the hull are two or more air diaphragms called ballonets that are kept under slight pressure, either by blowers or by air that is forced through scoops as a result of the forward motion (ram effect).  The ballonets in turn exert pressure upon the gas, which fills the envelope, and this pressure in turn serves to stiffen the shape of the envelope and create a smooth flying surface.  On takeoff the ballonets are almost fully inflated, but as the airship gains altitude and the gas expands, air is bled from the ballonets while a constant pressure is maintained throughout the envelope.  When the gas contracts upon descent, air is pumped back into the ballonets.

 HISTORY OF RIGID AIRSHIPS

The German company Luftschiffbau Zeppelin had the most success in building rigid airships. The first Zeppelin was flown on July 2, 1900;  it was 419 ft long, 38 ft in diameter, contained 338,410 cu ft of hydrogen gas in 16 cells, and was powered by two 16-hp engines.  Its range and payload were negligible.  The last Zeppelin was the Graf Zeppelin II, which was first flown on Sept. 14, 1938;  it was 803 ft long, 135 ft at maximum diameter, contained 7,062,100 cu ft of hydrogen, and was powered by four 1,050-hp Daimler Benz diesel engines.  It could carry loads of 30 tons over transoceanic distances.  It was scrapped in May 1940.

A total of 119 Zeppelins were built, most of them during World War I, when 103 airships were delivered to the military.  The most famous Zeppelin was the original GRAF ZEPPELIN, which during 1928-37 made flights to the United States, the Arctic, the Middle East, and South America;  it also made one flight around the world.  Another famous Zeppelin was the airliner hindenburg, which was destroyed by fire at Lakehurst, N.J., on May 6, 1937.

The British made intermittent efforts to develop the rigid airship;  they built eight during World War I and six shortly thereafter.  The most noteworthy was the R-34, which in July 1919 made the first transatlantic round-trip flight.  An effort to develop two airships of 5,000,000 cu ft for intercontinental air service came to grief in October 1930 when the R-101 crashed and burned in France.  The R-100, which had made a successful flight to Canada earlier in the year, was subsequently scrapped.  In the United States, the development of rigid airships was undertaken by the navy, and only five were operated.  The navy-built ZR-1 SHENANDOAH made its first flight on Sept. 4, 1923, and was torn to pieces by a thunderstorm over southern Ohio on Sept. 3, 1925.  The ZR-2 was procured in England but crashed on Aug. 24, 1921, before it could be delivered to the United States.  The ZR-3 Los Angeles, built in Germany by Luftschiffbau Zeppelin, made its transatlantic delivery flight during Oct. 11-15, 1924;  it was flown successfully until decommissioned in 1931 and was scrapped in early 1940.  The ZRS4 and ZRS5 AKRON AND MACON were built by the Goodyear-Zeppelin Co. of Akron, Ohio.  These 6,500,000-cu ft sister ships were 785 ft long and 133 ft at maximum diameter, and were powered by eight 560-hp Maybach engines.  Their design was unique in that it provided for an internal space for five airplanes that could be launched and retrieved while the airships were in flight.  The Akron first flew on Sept. 23, 1931 and was lost in a storm over the Atlantic on Apr. 4, 1933;  the Macon first flew on Apr. 21, 1933, and crashed in the Pacific on Feb. 12, 1935.

 HISTORY OF NONRIGID AIRSHIPS

The first successful nonrigid airships were built by the French.  In 1852 Henri Giffard built an airship of 113,000 cu ft powered by a steam engine.  The brothers Albert and Gaston Tissandier constructed a 37,500-cu ft airship propelled by a battery-powered electric motor in 1883, and the following year Charles Renard and Arthur C. Krebs built the 66,000-cu ft La France, which also used electric power.  At the turn of the century the Brazilian aeronaut Alberto Dumont built and flew a series of small airships in France, all of which used gasoline engines.  Blimps were effectively used by the British and French in World War I in maritime reconnaissance against German submarines.  The term blimp, a British slang expression of unknown origin, came into use about this time.

In World War II, the United States was the only power to use airships.  The navy used them for minesweeping and antisubmarine patrols.  Its more than 150 blimps were operated from bases on the east and west coasts, the Gulf of Mexico, the Caribbean, and as far south as Brazil.  The workhorse of these forces was the K-type blimp, 253 ft long, 60 ft in diameter, containing 456,000 cu ft of gas, and powered by two 425-hp engines that gave a top speed of 50 mph.  Blimps are not fast, but whereas an airplane can remain airborne for only a few hours, a K-ship could stay aloft for 60 hours.  In 1944, six K-ships flew across the Atlantic to Morocco, where they established a low-altitude antisubmarine barrier across the Strait of Gibraltar;  later they operated from bases at Cuers, France, and Pisa, Italy.

 AIRSHIPS TODAY

The most long-lasting use of airships has been by the Goodyear Tire and Rubber Company.  The Pony was built in 1919 and the Pilgrim in 1923.  After 1928 the fleet was expanded with the Puritan, Volunteer, Mayflower, Vigilant, Defender, Reliance, Resolute, Enterprise, Ranger, and Columbia.  During the 1930s these airships were used for advertising, and they barnstormed all over the United States.  During World War II, the fleet was used for reconnaissance by the U. S. Navy.  Three Goodyear blimps still operate,  the newest, the Spirit of Akron, which was launched in 1989, was for a short time the world's largest operating airship 205.5 ft, with a volume of 248,000 cu ft.

Goodyear no longer builds blimps, but other companies continue to produce and operate the craft.  Among new types are the smaller blimps, some remote-controlled, that are tethered inside stadiums and used to provide television audiences with bird's-eye views of sports events.

In 1991, Westinghouse Airships launched the 220-ft long Sentinel 1000, the first in a projected series of blimps to be used by the U. S. Defense Department for a range of surveillance, communications, and patrol duties.  The envelope of the Sentinel 1000 is made of a mix of synthetic fibers that is impervious to weather and almost invisible to radar.

Data collected in flight tests will aid in the development of the much-larger Sentinal 5000.  Twice the length of the Sentinal 1000, its envelope will be seven times larger, with a 2.5 million-cu ft helium-gas capacity.  It will carry an 25,000-lb payload, including a 3-story, pressurized gondola, a crew of 15, and extensive radar arrays and optical flight control systems.  The craft will be refuelable while it is under way, with refueling lines carried to it by the ship-based helicopters.  It will be launched in 1997.

HINDENBURG

The Hindenburg, originally designated the L.  Z.  129, was a rigid airship built by the firm of Luftschiffbau Zeppelin in Friedrichshafen, Germany.  Completed and tested in 1936, it was the world's first transatlantic commercial airliner.  The airship was 804 ft long, had a maximum diameter of 135 ft, and was kept aloft by 7,000,000 cu ft of hydrogen in 16 cells.  Four 1,050-hp Daimler-Benz diesel engines provided a top speed of 82 mph.  In May 1936 the Hindenburg inaugurated the first scheduled air service across the North Atlantic, between Frankfurt am Main, Germany, and Lakehurst, N.J.  It accommodated more than 70 passengers and had a dining room, a library and lounge with a grand piano, a cocktail lounge, and promenades with large windows.  The flight to the United States took 60 hours, and the return trip to Europe, 50 hours.  In 1936 the Hindenburg carried more than 1,300 passengers and several thousand pounds of mail and cargo on transatlantic flights.

While maneuvering to land at Lakehurst on May 6, 1937, the airship's hydrogen was ignited and the Hindenburg was destroyed by the resulting fire.  Thirty-five of the passengers and crew died, along with one member of the ground crew.  Claims and speculation that the Hindenburg was a victim of sabotage have never been supported by evidence.  The destruction of the Hindenburg marked the end of the use of airships in world air commerce.