Aircraft, such as hot-air balloons and dirigibles, or airships, that fly because they are filled with lighter-than-air gases.

The first buoyant aircraft was the hot-air balloon, invented in 1782 by the French brothers Joseph-Michel and Jacques-Étienne Montgolfier, who found that closed bags of hot air rose and stayed aloft until the air inside them cooled. The basis for hot-air balloon flotation is that hot air is less dense, or weighs less, than the volume of air it displaces, so a hot-air balloon is a lighter-than-air aircraft. It soon became clear that hot-air balloons could be kept aloft by hanging under them baskets holding firepots. In this way, gondolas that also carry passengers were created.

Modern hot-air balloons differ from early prototypes only in the fabrics and heaters used. Flammable hydrogen and safer helium are other fill gases, with helium replacing hydrogen in all modern balloons that do not use hot air. Hot-air balloons cannot be steered. Hot-air balloonists rise into the sky by throwing out ballast and descend by letting gas out. Destinations and arrivals depend on the winds. Helium-filled balloons can remain aloft for longer periods and can travel farther than can hot-air balloons. However, their flight methodology and limitations do not change. Recreational balloonists prefer hot air, and commercial balloons use helium.

In 1852, France’s Henri Giffard ended the problems of uncertain destination and arrival times by adding a 3-horsepower steam engine and propeller to a cigar-shaped, hydrogen-filled balloon, allowing for a maximum speed of 6 miles per hour. This nonrigid aircraft and all that followed it were named dirigibles, from the Latin word dirigere, which means “to steer.” Although Giffard’s invention was impractical for prolonged flight, it was innovative in its cigar shape that reduced wind resistance and increased maneuverability. All following dirigibles have been constructed with a similar shape.

Throughout the late nineteenth century, increasingly better-designed buoyant aircraft were invented and used. In 1883, French aeronaut Gaston Tissandier built the first workable airship with an electric motor. From 1898 to 1905, Alberto Santos-Dumont, a Brazilian living in Paris, set airship records in nonrigid, powered airships. All these airships, however, had engines that made them too heavy for commercial flight.

There are three main airship types: nonrigid, semirigid, and rigid. Nonrigids are essentially large, streamlined cylindrical balloons, nicknamed “blimps,” supposedly for the sound made by a finger thumping into the side of the envelope, or gas bag. Nonrigids, such as the Goodyear blimps, get their shape from the gas within a single gas bag or envelope. The engines and a car or a gondola hang below the gas bag.

The design of nonrigid dirigibles simplifies cost and minimizes structural weight, which in turn reduces the net lifting capability. However, nonrigids are limited in size, because an unsupported gas bag may bend unpredictably under heavy loads or strong winds. In a worst-case scenario, a partially deflated gas bag may flop over the gondola or propellers. Conversely, the gas bag cannot be filled too tightly, lest it burst. The one gas bag is a single point of failure that could cause a crash, although the large size of dirigibles means that operations could continue for some hours, even with significant leaks. Another method to compensate for pressure loss in the gas bag is the use of an inner ballonet, which can be inflated with outside air.

Semirigid dirigibles have a keel on the bottom to support a larger gas bag, and the keel can hold the gondola and engines, at the cost of additional weight. The risks associated with a single gas bag also apply to semirigid dirigibles. The most famous semirigid was the Italian semirigid airship Norge, which in 1926 was used by explorer Roald Amundsen to make the first transpolar flight, from Spitsbergen Island to Alaska.

Rigid dirigibles have a framework to support an outer skin and individual gas bags. In rigid dirigibles, an individual gas bag can fail without damaging the aerodynamic integrity of the craft, and there are usually sufficient reserves among the other cells to maintain buoyancy. Those advantages cost additional weight. However, greater weight can be compensated for by greater size. There is theoretically no limit to a rigid’s size. The German passenger airship Hindenburg had an LTA gas capacity of 7,000,000 cubic feet, and designs of twice that size have been proposed.

During World War I, the French army used semirigids for reconnaissance, coast patrol, and to find submarines. Near the end of the war, the British armed forces began developing rigid airships, in response to the expected large-scale availability of nonflammable helium gas. The 643-foot-long R-34, with a gas capacity of 2,000,000 cubic feet, was put into service in 1919 and made the first transatlantic airship flight, from Scotland to Mineola, New York, and back in eight days. Both the R-34 and its sister ship, R-38, were destroyed in 1921.

Count Ferdinand von Zeppelin, a German military officer, had spent time as a military observer for the Union Army during the American Civil War. While in the United States, he took some balloon flights and became fascinated with balloons before returning to Germany to continue his military service in the Seven Weeks and Franco-Prussian Wars. After his retirement from the military in 1890, Zeppelin devoted all his efforts to the construction of rigid airships.

Zeppelin worked to allay one of the main problems in airship design, that of maintaining a cigar-shaped gas bag and avoiding partly deflated bags that cannot be steered. He made steerable, unchanging shapes by designing rigid, strong, light frames that were mated to gas bags. In 1900, Zeppelin’s first airship, LZ-1, flew for seventeen minutes. In 1908, the 446-foot-long LZ-4, with a gas capacity of 500,000 cubic feet, flew for one half-day at 40 miles per hour.

Soon, Zeppelin’s airships, widely known as zeppelins, made practical air transport available. In 1910, the first commercial airline and dirigible manufacturer, Deutsche Luftschiffahrts Aktien-Gesellschaft (Delag), was established. Delag’s luxurious dirigibles interconnected many German cities, carrying 15,000 travelers per year. By 1914, when World War I began, Delag had in service twenty-seven dirigibles, including the Sachsen and the Deutschland, that had achieved airspeeds of over 50 miles per hour. In the next five years, 1,600 dirigible flights carried more than 35,000 passengers over 200,000 miles. Although Zeppelin died in 1917, before transatlantic airship flight was achieved, Delag carried on.

The first military buoyant aircraft were French hot-air/hydrogen tethered reconnaissance balloons, crewed by aerostiers. From 1794 to 1799, reports from these balloons aided French armies in battle. Similar reconnaissance balloons were used in the American Civil War, but true military aviation began only with the perfection of navigable airships in the late nineteenth century. Airships were the most formidable aircraft before World War I. They were made of fabric-covered metal frames and gas bags full of hydrogen. Airships were used by the Allies for antisubmarine patrols during World War I. The German zeppelins were the most functional airships, used during World War I to carry five 110-pound bombs and twenty 7-pound incendiaries at a time when military airplanes carried no weapons. More than one hundred zeppelin bombers were used by the Germans to bomb Paris and London. The German dirigibles were so effective that, after Germany lost the war, they were all confiscated. Further German production of zeppelins was prohibited until the late 1920’s.

Airship construction continued in Europe and the United States throughout the 1920’s and 1930’s. The British dirigible R-34 made a round-trip transatlantic crossing in July, 1919. In 1926, Amundsen flew the Italian semirigid airship Norge in his expedition to the North Pole. In the late 1920’s after Germany was again allowed to produce airships, Delag built the Graf Zeppelin, an outstanding zeppelin of the time. The Graf Zeppelin had an approximate length of 800 feet and a gas capacity of almost 4,000,000 cubic feet. The luxurious airship began its nine-year service in 1928, ultimately making 600 flights, including 144 ocean crossings, covering 1,000,000 miles. It crossed the Atlantic to North and South America 139 times and made a complete trip around the world in three weeks at a cruising speed of 71 miles per hour, faster than comparable train or boat transportation.

In 1936, Germany began regular transatlantic passenger service with a new Delag zeppelin, the Hindenburg, also known as LZ-129. The Hindenburg cruised at a speed of 78 miles per hour, held 7,000,000 cubic feet of hydrogen, and carried fifty passengers in luxurious style. The airship had been rushed into production by German chancellor Adolf Hitler to show off the greatness of his Reich and was successful in a number of transatlantic flights. However, on May 6, 1937, while docking at Lakehurst, New Jersey, the Hindenburg caught fire and exploded, killing thirty-six people in one of the greatest air disasters of all time. After this event, the reputation of dirigibles as air carriers was irretrievably damaged.

Although the wreck of the Hindenburg was the most notorious airship disaster, it was not the only one. Others had preceded it. For example, a U.S. purchase, the semirigid Roma, 400 feet long, with a gas capacity of more than 1,000,000 cubic feet, was lost in 1922. The USS Shenandoah, a Navy airship, became the first zeppelin built in the United States in 1923. Filled with helium, the airship was 700 feet long, with a gas capacity of more than 2,000,000 cubic feet. After making a few long trips, the Shenandoah broke apart in a thunderstorm and was wrecked in 1925.

The U.S. Navy’s Los Angeles, a German war reparation, was a bright spot in the airships’ dark safety record. The 650-foot-long airship, with a gas capacity of 2,500,000 cubic feet, carried thirty passengers on each of 250 long flights between 1924 and 1932. However, the success of the Los Angeles did not outweigh the failures of other airships, which continued to prove problematic around the world.

In 1926, Italy’s semirigid Norge flew Amundsen’s expedition to Alaska but had to be dismantled. A polar flight two years later in the closely related Italia was disastrous. Only German zeppelins seemed to survive for long time periods.

Elsewhere, though, airship catastrophes continued to occur. In England, the dirigibles R-100 and R-101, with lengths of approximately 700 feet and gas capacities of 5,000,000 cubic feet and accommodating one hundred passengers, had short terms of service. The R-100, christened in 1929, crashed in 1930 and burned to cinders, killing forty-six people. After this incident, the R-101 was immediately scrapped, and Britain gave up dirigible construction.

The U.S. Navy built two dirigibles, the USS Akron and the USS Macon, each of which was 785 feet long, with a gas capacity of 6,500,000 cubic feet. Both ships could carry five scout planes and release or take them aboard in flight. Each ship survived for only about two years before crashing into the sea during storms. After the destruction of these two ships, the United States discontinued the building of rigid airships. Despite their varied uses, airships were virtually abandoned in the late 1930’s, due to their high production cost, low speed, vulnerability to storms, a series of airship disasters, and advances in heavier-than-air craft. In 1938, American military blimps were put under Navy control for World War II scout, convoy, and antisubmarine work. In peacetime, small blimps have provided aerial television views of sports events and advertising.

After World War II, the U.S. Navy continued for approximately twenty years to develop blimps for antisubmarine, research, and early warning use. The largest, ZPG-2 type, 324 feet long, with a gas capacity of 0.9 million cubic feet, could remain aloft for a week without refueling. The Navy stopped almost all airship use in 1961. During the late 1980’s, there was renewed Coast Guard and Navy interest in airship use for early warning and electronic antisubmarine warfare, although not much came of it.

However, enthusiasts attest that blimps can be used for many tasks unsuited to planes. For example, because airships can move very heavy, large objects over short distances much better than planes can, blimplike airships are sometimes used for short-haul and heavy-lift operations in remote areas. This use may continue to increase.

Another proposed use of airships is for intraurban passenger service and other short-distance transportation. Here, low airship speed is not a problem and ability for vertical and short takeoff and landing (V/STOL) is a major advantage over planes. Another advantage of airships over airplanes is their low noise production and fuel consumption.

One final modern use of airships could involve making rigid airships from modern materials and adding contemporary flight instruments and computers. Such airships, it is thought, would be useful for military surveillance of the oceans and coastal areas or for the scientific study of the environment. Thus, it seems probable that in the future many blimps and dirigibles will again take to the air.

• Capelotti, Peter Joseph. By Airship to the North Pole: An Archeology of Human Exploration. New Brunswick, N.J.: Rutgers University Press, 1999. An account of the transportation of Amundsen’s party by dirigible and their exploration of the North Pole.
• Collier, Basil. The Airship: A History. New York: G. P. Putnam’s Sons, 1984. A history of airships, their proponents, and the events fostering their development and leading to the near-cessation of their modern manufacture.
• Hall, George, Baron Wolman, George Larson, and Neil Shakery. Blimp. New York: Van Nostrand Reinhold, 1981. A brief, well-designed book with useful information on the history of buoyant aircraft, blimp construction, airship operation and uses, and ideas for future uses, as well as plentiful, interesting illustrations.
• Hayward, Keith. The Military Utility of Airships. London, England: Royal United Services Institute for Defence Studies, 1998. A brief publication covering many aspects of military airship use.
• Toland, John. Ships in the Sky: The Story of the Great Dirigibles. New York: Henry Holt, 1957. A classic book describing the great events in the history of balloon and airship development and use.
• Ventry, Lord, and Eugene M. Kolinski. Airship Saga. Poole, England: Blandford Press, 1982. A book covering aspects of airship history and development in airship-producing nations, with much detail on prospects for future airships. Included are good illustrations and a useful bibliography.

Balloons

Dirigibles

Goodyear blimp

Hindenburg

Lighter-than-air craft

Military flight

Montgolfier brothers

Reconnaissance

Alberto Santos-Dumont

Transatlantic flight

Vertical takeoff and landing

World War I

World War II

Ferdinand von Zeppelin