Airship
Airship
A technologically advanced cousin of the balloon, airships are streamlined vessels buoyed by gases and controlled by means of propellers, rudders, and pressurized air. Often referred to as blimps and dirigibles, airships come in non-rigid, semi-rigid, and rigid types that rely on the buoyancy of lighter-than-air gases such as helium and hydrogen for lift. For several decades after the turn of the twentieth century, they were engaged commercially in the transport of passengers and cargo. For the last half-century they have been mostly relegated to advertising, but aerospace industry observers report that new, serious applications for the airship, both military and civilian, are nearing deployment in the early twenty-first century.
Airships derive their lift from the buoyancy of gas bags rather than from forward motion forcing air over airfoil, as an airplane does. Airships use the internal combustion engines, like those type used in automobiles, prop planes, and turboprop planes, to propel themselves through the air. The passenger and freight compartments are hung below the bag. Traditional pressure airships house the engine, propeller, and gear box on an outrigger that extends from the side of the car, while the modern British Skyship’s 500 and 600 use inboard engines that turn long prop shafts which allow the propellers to be vectored outboard. The introduction of pivoted, or vectored, engines gave airships the ability to change the direction of thrust and afforded such amenities as near-vertical lift-off, thus reducing the need for long runways. Capable of airborne refueling, airships can remain aloft for weeks at a time, and can reach an average airspeed of 60 mph (96.5 km/h).
Non-rigid airships
Mastery of the skies was a preoccupation of French inventors in the latter half of the eighteenth century. In 1783, Jacques and Joseph Montgolfier designed the first balloon used for manned flight, while concurrently, Jean-Baptiste-Marie Meusnier had thought to streamline the balloon and maneuver it by some mechanized means. While several airships of similar design met with limited success from 1852, Meusnier’s idea did not officially get off the ground until 1898. That year, the Brazilian aeronaut Alberto Santos-Dumont became the first pilot to accurately navigate a hydrogen-filled envelope and basket by means of a propeller mounted to a motorcycle engine.
Because of their non-rigid structure, the first blimps, like the balloon, were prone to collapsing as the gas contracted during descent. To counter this, Santos-Dumont introduced the ballonet, an internal airbag that helps maintain the envelope’s structure and regulates pitch as well as lift, or buoyancy. Modern blimps continue to use ballonets positioned at the front and rear of the envelope, permitting the engineer to pump air into one or the other to change the pitch angle. For example, by increasing the amount of air in the aft ballonet, the airship becomes tail heavy, thus raising the nose skyward. Steering is further achieved by controlling rudders affixed to one of several types of tail fin configurations, allowing for basic left, right, up, and down directions. The long standard cross-shaped fin is slowly being replaced by an X-shaped configuration. While the X is more complicated, requiring a combination of rudders to complete a maneuver, it provides better ground clearance.
The car or gondola serves as the control center, passenger quarters, and cargo hold of the airship. The envelope and car are connected by a series of suspended cables attached to the envelope by different types of load-sharing surfaces. Many modern airships use a curtain structure glued or bonded along the length of the envelope which evenly distributes the weight of the car and engines.
Rigid airships
The German inventor, Count Ferdinand von Zeppelin took the guesswork out of airship aerodynamics by building a rigid structure of lightweight aluminum girders and rings that would hold the
vessel’s streamlined shape under varying atmospheric conditions. Unlike Dumont’s single-unit envelope, Zeppelin incorporated a number of drum-shaped gasbags within compartments of the structure to maintain stabilization should one of the bags become punctured or deflate. The dirigible was then encapsulated by a fabric skin pulled tightly across its framework. Buoyancy was controlled by releasing water ballast to ascend or by slowly releasing the hydrogen gas through a venting system as the ship descended.
Zeppelin was among the first airship designers to realize, in practice, the functionality of greater size in lighter-than-air vessels. As he increased the surface area of the envelope, the volume increased by a greater proportion. Thus, a larger volume afforded better lift to raise the aluminum hull and maximized the dirigible’s cargo carrying capacity. Airships like the Graf Zeppelin, the Hindenburg, and their American counterparts, the Macon and the Akron, reached lengths of up to 800 ft (244 m) with volume capacities nearing seven million cubic feet. Hydrogen was, in part, responsible for such engineering feats because it is the lightest gas known to man and it is inexpensive. Its major drawback, one that would virtually close the chapter on non-rigid airship aviation, was its flammability. While passenger quarters, cargo, and fuel could be secured to or stored within the dirigible’s metal structure, its engines were housed independently and suspended to reduce the possibility of friction-caused ignition of the gas.
Little did English writer Horace Walpole know how closely he had prophesied the future of airships when, upon the launch of the Montgolfier balloon, he wrote, “I hope these new mechanic meteors will prove only playthings for the learned or the idle, and not be converted into engines of destruction.” While zeppelins, as they had become known, were initially put into commercial service, successfully completing nearly 1, 600 flights in a four-year period, they were engaged in the service of Germany during World War I as giant bombers, raiding London itself in May of 1915. After the war, the rigid dirigible was employed as both a trans-Atlantic luxury liner and airborne aircraft carrier, but eventually fell out of favor after the Hindenburg disaster in Lakehurst, New Jersey, on May 6, 1937.
Semi-rigid airships
An intermediate version of the rigid and non-rigid types, the envelope of the semi-rigid airship was fitted with a keel similar to that of a boat. The keel acted as a sort of metal spine which helped maintain the envelope’s shape and supported the gondola and engines. Interest in the semi-rigid airship was short-lived, though it met with some success. In 1926, the Italian pilot Umberto Nobile navigated the airship Norge across the North Pole, accompanied by the Norwegian explorer Roald Amundsen.
The modern age of airships
Helium succeeded hydrogen as the gas of choice for the following generation of airships and continues as such in the early twenty-first century. Though its lifting capacity is less than that of hydrogen, helium is considered a safe resource because it is inflammable. During the 1920s, the United States discovered an abundant source of the gas in its own backyard and reinstated the blimp as a surveillance mechanism during World War II, maintaining a fleet of some of the largest non-rigid airships ever built. “It was the American monopoly of helium that made possible this Indian Summer of the small airship—long after every other country had abandoned the whole concept,” wrote Patrick Abbott in his book Airship.
By the 1950s, the Goodyear Tire and Rubber Co. had become involved in the production of airships as part of the Navy’s intended early warning defense system, and remained one of the largest manufacturers of blimps until the late 1980s. The Goodyear blimp is probably most noted as a high-flying billboard and mobile camera that has offered millions of television viewers a bird’s-eye view of sporting events for several decades.
The early 1990s marked a resurgence in airships with the design of such models as the 222-ft (67.6-m) long Sentinel 1000. Built by Westinghouse Airships, Inc., its envelope is made of a lightweight, heavy-duty Dacron/Mylar/Tedlar composite that may eventually replace the traditional rubberized fabrics used by the Sentinel ’s predecessors. According to Aviation Week and Space Technology, the craft “has a 345, 000-cu-ft. envelope and is powered by two modified Porsche automotive engines fitted with propellers that can be
KEY TERMS
Ballonet— Air compartments capable of maintaining constant internal pressure within an airship’s envelope in response to outside air pressure and temperatures. Manual controls effect pitch, ascent, and descent.
Blimp— Airship in which the structure is supported entirely by internal gas and air pressure.
Dirigible— A lighter-than-airship capable of being piloted and controlled by mechanical means. Lift—An aerodynamic force acting upon an object’s upward motion in air.
Vector— A quantity or term that can be expressed in terms of both magnitude (a number) and a direction.
tilted through a range of plus 120 to minus 90 degrees.” Its potential for transporting heavy pay-loads, its quietness, and relative stability, have brought the airship back to design rooms around the world. Based partly on its fuel efficiency and the fact that its shape and skin make it virtually invisible to other radar, the United States has plans to reintroduce the blimp as a radar platform for its Air Defense Initiative. French scientists have used the airship to navigate and study rainforests by treetop, while environmentalists have considered its usefulness as a means of monitoring coastal pollution. The future may see airships combined with helicopter rotor systems and solar power, as well as the return of the rigid airship. Airships are also being carefully studied by NASA for use in exploring planets and moons in the solar system that have significant atmospheres.
Resources
BOOKS
Abbott, Patrick. Airship. New York: Charles Scribner’s Sons, 1973.
Meyer, Henry Cord. Airshipmen, Businessmen and Politics 1890-1940. Washington, DC: Smithsonian Institution Press, 1991.
PERIODICALS
Bell, Adrian. “On the Roof of the Rainforest.” New Scientist 129 (1991): 48-51.
Garvey, William. “Rebirth of the Blimp.” Popular Mechanics 168 (1991): 30-33.
Hamer, Mick. “Airships Face a Military Future.” New Scientist 115 (1987): 38-40.
Hollister, Anne. “Blimps.” Life Magazine 4 (1988): 65-69.
Hughes, David. “New Westinghouse Airship Designed for Early Warning Surveillance.” Aviation Week and Space Technology 135 (1991): 24-25.
Wilson, J. R. “A New Era for Airships.” Aerospace America. May (2004): 27-31.
OTHER
National Aeronautics and Space Administration (NASA). “Airships for Planetary Exploration (NASA/CR-2004-213345).” 2004. <http://gltrs.grc.nasa.gov/reports/2004/CR-2004-213345.pdf> (accessed October 15, 2006).
John Spizzirri
Dirigibles
DIRIGIBLES
DIRIGIBLES, or motor-driven lighter-than-air craft that can be flown against the wind and steered, were first constructed in America by Caesar Spiegler. His first dirigible made its maiden flight 3 July 1878, with the great American balloonist John Wise as its pilot. Thomas Scott Baldwin built the first dirigible for the government; it was 96 feet long and had a 20-horsepower engine built by Glenn H. Curtiss. Called the SC-1, it made its first flight at Fort Myer, Virginia, in August 1908.
When the United States entered World War I, the U.S. Navy ordered sixteen dirigibles of the nonrigid type. Developed from a British model the Royal Navy used for antisubmarine patrols, U.S. Navy personnel who had been positioned in England used the English nickname for the nonrigid airship—"blimp"—and the term subsequently came into common usage in the United States. By the end of the war the navy had twenty "B-type" blimps (77,000–84,000 cubic feet; single engine) and ten "C-type" blimps (182,000 cubic feet; twin engine). In 1919 the navy airship C-5 failed in its attempt to fly across the Atlantic, but nevertheless set a 1,177-mile nonstop distance record between Montauk, New York, and Saint John's, Newfoundland, where it was destroyed in an accident.
In 1917 an army-navy joint board delegated to the navy the development of the much larger and more complex rigid airship, and in July 1919 Congress authorized the procurement of two rigid airships, one to be built in the United States and the other to be purchased abroad. The army transferred the site of Camp Kendrick, a military facility near Lakehurst, New Jersey, to the navy, which erected a huge hangar, mooring mast, and other facilities there. The Lakehurst Naval Air Station came into commission in 1921, and for the next forty-one years it was the center of American lighter-than-air aeronautics.
As the navy began the development of rigid airships, the army also began to operate dirigibles, concentrating on the semirigid type and blimps. In 1921 the army purchased the Italian semirigid T-34 airship named Roma, 412 feet long, having a gas volume of 1.2 million cubic feet, and powered by six 400-horsepower Anasaldo engines. As it had been shipped to the United States disassembled, army engineers erected it at Langley Field, Virginia, where it made its first American flight on 21 November 1921. During a trial flight with new Liberty engines on 21 February 1922 the Roma went out of control and flew into a high voltage electrical transmission line. Being inflated with hydrogen, the Roma went up in flames and crashed, killing thirty-four of the forty-five men aboard. In 1922 the army airship C-2 made the first coast-to-coast flight achieved by a lighter-than-air craft. And on 15 December 1924, a Sperry Messenger airplane equipped with a skyhook hooked onto a trapeze hung from the blimp TC-3, demonstrated the possibility of the airship's becoming an aircraft carrier. In 1925 the army procured the semirigid RS-1, fabricated by the Goodyear-Zeppelin Corporation and erected by the army's center of lighter-than-air aeronautics at Scott Field, Illinois. The RS-1 made its first flight on 9 January 1926, and although its project engineers hoped to develop it into an airplane carrier, they never conducted appropriate experiments. Shortly after its last flight on 16 October 1928, during which it sustained serious damage, the army dismantled the RS-1.
In the meantime the navy had progressed in the development of rigid airships. To begin with, the navy purchased the British airship R-38, which became the ZR-2. On 24 August 1921, the ZR-2 suffered a catastrophic structural failure during its flight trials, broke up in the air, and crashed near Hull, England, killing forty-four of the forty-nine men on board. The navy's own first rigid dirigible, the ZR-1, was 677 feet long, had a gas volume of 2.235 million cubic feet, and was powered by six 300-horsepower Packard engines. It made its first flight on 4 September 1923, and became the first rigid airship in the world to be inflated with nonflammable helium gas, following the example of the navy blimp C-7, which became the first airship of any type to use helium rather than hydrogen on 1 December 1921. (The following year, despite the greater cost of helium and its inferior lift, the navy adopted a policy of using only helium in its dirigibles, rather than highly flammable hydrogen.) On 10 October 1923, the navy formally christened the ZR-1 the U.S.S. Shenandoah. The Shenandoah made fifty-seven flights totaling 740 hours, including two coast-to-coast flights in 1924, maneuvers with the Atlantic fleet, and moorings to a floating mooring mast on the stern of the tanker U.S.S. Patoka. On 3 September 1925, the Shenandoah broke up in a violent thunder storm and crashed near Ava, Ohio, killing fourteen of the forty-three men on board.
At the end of World War I the navy was to have received two rigid dirigibles, German zeppelins, as spoils of war, but their German crews destroyed them before they could be delivered. In compensation Germany was obliged to build a new zeppelin for the navy. Germany thus constructed the LZ-126, the navy's ZR-3, best known as the U.S.S. Los Angeles. The Los Angeles was 658 feet long, had a gas volume of 2.762 million cubic feet, and relied on five 530-horsepower Maybach engines for power. It made its first flight at the Zeppelin factory in Friedrichshafen, Germany, on 27 August 1924; it made its delivery flight to the United States from 12–15 October, a transatlantic passage of eighty-one hours with thirty persons on board, the sixth transatlantic flight made by any type of aircraft. (Charles A. Lindbergh's celebrated transatlantic crossing by airplane was the seventh.) During the next eight years the Los Angeles served as a training and experimental airship for the navy, making 331 flights totaling 4,398 hours, which included two flights to Bermuda and two to Panama. The navy decommissioned it on 30 June 1932, but retained it at Lakehurst for various structural tests until scrapping it in 1940.
In 1928 the Goodyear-Zeppelin Corporation started work on two rigid airships for the navy, the ZRS-4 and ZRS-5. They were sister ships, 785 feet long, having a gas volume of 6.850 million cubic feet, and powered by eight 560-horsepower Maybach engines. At that time they were the largest airships in the world, not exceeded in size until 1936, when Germany constructed the airship Hindenburg. These airships were unique in that each could carry five Curtiss F-9C fighter planes housed in a hangar within their hulls; the airplanes were equipped with sky-hooks, and the airships could launch and retrieve planes in flight by means of a trapeze lowered from a T-shaped door in their undersides.
The ZRS-4, christened Akron, made its first flight on 25 September 1931. It made seventy-three flights totaling 1,695 hours, including two coast-to-coast flights and one to Panama. On the night of 4 April 1933, a violent electrical storm over the Atlantic caught and destroyed the Akron, which crashed at sea; of the seventy-six men on board, only three survived. The ZRS-5, christened Macon, made its first flight on 21 April 1933. It made fifty-four flights totaling 1,798 hours, including three coast-to-coast flights, and participated in several war games with the U.S. fleet. While returning from maneuvers on 12 February 1935, it suffered a minor structural failure that became uncontrollable, and the Macon crashed in the Pacific. Miraculously, only two of the eighty-three persons were killed in the accident.
The loss of the Macon ended the navy's development of the rigid airship, but the blimp remained. On the eve of World War II the navy had only a half-dozen blimps, but during the war the navy expanded its blimp forces to more than 160 airships for antisubmarine patrols. By the end of the war the United States had constructed a network of blimp bases that reached from South Weymouth, Massachusetts, to Key West, Florida, extending across the Caribbean and down the coast of South America to Rio de Janiero. In 1944 the navy flew five airships to French Morocco, where, based at Port Lyautey, they flew a low-altitude antisubmarine barrier over the Strait of Gibraltar.
The basic training airship of the war years was the L-type blimp (146 feet long, 123,000 cubic feet gas volume, two 146-horsepower Warner engines). The backbone of the antisubmarine patrol forces was the K-type blimp (251 feet, 425,000 cubic feet gas volume, two 425-horsepower Pratt & Whitney engines). During the war the United States lost only one airship to enemy action, the K-74, on 18 July 1943, after its bombs failed to release in an attack on the German submarine U-134 in the Caribbean.
After the war the navy continued its blimp development, increasing the size, lift, endurance, and versatility of its airships. In 1954 the ZPG-1-type blimp appeared (324 feet, 875,000 cubic feet, two 800-horsepower engines). The ZPG-1 was unusual in the new configuration of its tail surfaces; formerly all airship tail surfaces had been affixed to the hull at right angles to the vertical, but the ZPG-1, and all navy airships thereafter, had their tail surfaces disposed in an X configuration, 45 degrees to the vertical, which contributed to increased maneuverability.
Dirigibles have never been fast aircraft; what has recommended their use is their great lift relative to the small engine power required, and their great endurance. An airplane can be airborne for only a few hours; an airship can cruise the air for days. In 1954, for example, an American ZPG-2 stayed in the air for 200 hours. And in 1957 a ZPG-2 made a leisurely nonstop circumnavigation of the North Atlantic, 8,216 nautical miles, from South Wey-mouth, Massachusetts, to Portugal, Morocco, and the Antilles, finally landing at Key West, Florida, after being in the air for 264 hours.
The ZPG-2 that flew this nonstop double crossing of the Atlantic was 342 feet long and had a gas volume of 975,000 cubic feet. Like all other navy blimps, it was an antisubmarine aircraft. In addition, the navy modified five other ZPG-2's into ZPG-2W's that could carry an extraordinarily large air-search radar for airborne early warning duty. In 1956 the navy procured four more ZPG-3W's to carry an even larger radar. With a gas volume of 1.5 million cubic feet, the ZPG-3W was the largest non-rigid airship ever built.
By 1960 high-speed, deep-cruising nuclear submarines were rendering the blimp's antisubmarine capabilities obsolete; in addition, experts had begun to fear an attack by missiles rather than by bombers, which degraded the airship's early-warning mission. In June 1961 the navy decommissioned its blimp squadrons, and on 21 August 1962, terminated all flight operations by airships.
Since the 1920s the Goodyear Tire & Rubber Company has maintained a small fleet of advertising blimps, beginning with the Pilgrim of 1925. The Goodyear fleet reached its maximum strength in the 1930s, when it operated six airships, the Defender, Resolute, Enterprise, Reliance, Rainbow, and Ranger, all of which had been turned over to the navy as training ships by 1942. Goodyear revived its fleet after the war, but fear of the competition of television advertising caused the company to cut back its investment in the enterprise. Goodyear had only one blimp remaining when a study revealed what the American public had long known: the blimp was a unique advertising vehicle, and "blimp" had become synonymous with "Goodyear." Since 1969 three Goodyear blimps have been cruising the skies of the United States, the Columbia, Mayflower, and America, while a fourth, the Europa, operates in Western Europe. Goodyear's was the only organized airship operation in the world in the 1970s. Since then a number of other companies have built smaller blimps, including MetLife insurance company, which operates the blimps Snoopy One and Snoopy Two (decorated with images of the dog Snoopy, from the Peanuts comic strip). These flying billboards have become common sights at American sporting events, where they often provide aerial shots to television networks in exchange for free advertising.
BIBLIOGRAPHY
Kirschner, Edwin J. The Zeppelin in the Atomic Age: The Past, Present, and Future of the Rigid Lighter-Than-Air Aircraft. Urbana: University of Illinois Press, 1957.
Robinson, Douglas H. Giants in the Sky: A History of the Rigid Airship. Seattle: University of Washington Press, 1973.
Smith, Richard K. The Airships Akron & Macon: Flying Aircraft Carriers of the United States Navy. Annapolis, Md.: U.S. Naval Institute, 1965.
Toland, John. Ships in the Sky: The Story of the Great Dirigibles. New York: Holt, 1957.
Richard K.Smith/c. w.
See alsoAir Defense ; Air Force, United States ; Army, United States ; Navy, United States .
Airship
Airship
Background
An airship is a large lighter-than-air gas balloon that can be navigated by using engine-driven propellers. There are three types of airships: rigid (has an internal metal frame to maintain the envelope's shape); semi-rigid (rigid keels run the length of the envelope to maintain its shape); and non-rigid (internal pressure of the lifting gas, usually helium, maintains the envelope's shape). This essay focuses on non-rigid airships (commonly called blimps) because they are the primary type of airship in general use today.
History
The history of airships begins, like the history of hot air balloons, in France. After the invention of the hot air balloon in 1783, a French officer named Meusnier envisioned an airship that utilized the design of the hot air balloon, but was able to be navigated. In 1784, he designed an airship that had an elongated envelope, propellers, and a rudder, not unlike today's blimp. Although he documented his idea with extensive drawings, Meusnier's airship was never built.
In 1852, another Frenchman, an engineer named Henri Giffard, built the first practical airship. Filled with hydrogen gas, it was driven by a 3 hp steam engine weighing 350 lb (160 kg), and it flew at 6 mi/hr (9 km/hr). Even though Giffard's airship did achieve liftoff, it could not be completely controlled.
The first successfully navigated airship, La France, was built in 1884 by two more Frenchman, Renard and Krebs. Propelled by a 9 hp electrically-driven airscrew, La France was under its pilots' complete control. It flew at 15 mi/hr (24 km/hr).
Military airships
In 1895, the first distinctly rigid airship was built by German David Schwarz. His design led to the successful development of the zeppelin, a rigid airship built by Count zeppelin. The zeppelin utilized two 15 hp engines and flew at a speed of 25 mi/hr (42 km/hr). Their development and the subsequent manufacture of 20 such vessels gave Germany an initial military advantage at the start of World War I.
It was Germany's successful use of the zeppelin for military reconnaissance missions that spurred the British Royal Navy to create its own airships. Rather than duplicating the design of the German rigid airship, the British manufactured several small non-rigid balloons. These airships were used to successfully detect German submarines and were classified as "British Class B" airships. It is quite possible this is where the term blimp originates—"Class B" plus limp or non-rigid.
Passenger-carrying airships
During the 1920s and 1930s, Britain, Germany, and the United States focused on developing large, rigid, passenger-carrying airships. Unlike Britain and Germany, the United States primarily used helium to give their airships lift. Found in small quantities in natural gas deposits in the United States, helium is quite expensive to make; however, it is not flammable like hydrogen. Because of the cost involved in its manufacture, the United States banned the exportation of helium to other countries, forcing Germany and Britain to rely on the more volatile hydrogen gas. Many of the large passenger-carrying airships using hydrogen instead of helium met with disaster, and because of such large losses of life, the heyday of the large passenger-carrying airship came to an abrupt end.
The first passenger-carrying non-rigid airship was invented in 1898 by Alberto Santos Dumount, a citizen of Brazil living in Paris. Under a sausage-shaped balloon with a ballonet or collapsible air bag inside, Dumount attached a propeller to his motorcycle's engine. He used both air and hydrogen, not helium, to lift the blimp.
The non-rigid airship of the 1940s and 1950s
After the rigid airship disasters of the 1920s and '30s, the United States as well as other countries refocused their attention on the non-rigid airship as a scientific/military tool. Aerial surveillance became the most common and successful use of the blimp. In the 1940s and '50s, blimps were used as early warning radar stations for merchant fleets along the eastern seaboard of the United States. They were also used and are still used in scientific monitoring and experiments.
Although as a company it no longer makes airships, Goodyear is a name sononymous with the manufacture of blimps. During the first half of the twentieth century, Goodyear manufactured over 300 blimps, more than any other airship manufacturer. Goodyear blimps were primarily used by the U.S. Army and Navy for aerial surveillance.
Modern resurgence of the non-rigid airship
Today, non-rigid airships are known more for their marketing power than for their surveillance capabilities. Blimps have been used commercially in the United States since about 1965. Advertising blimps measure about 150,000 cu ft (4,200 cu m). Since blimps can hover over one space and can be viewed over a large expanse with very little noise disturbance, they are excellent mediums for advertising at large outdoor events.
The use of the night billboard on blimps has been quite an advertising fad. The sign is a matte of multicolor incandescent lamps permanently fixed to the sides of the airship envelope, and it can be programmed to spell out different messages. Originally, the signs were developed by electromechanical relay. Now they are stored on magnetic tape, developed by composing equipment on the ground, which are fed into an airborne reader. The taped information is played back through a computer to the lamp driver circuits. The displayed messages can be seen over long distances. In the late 1980s, the use of blimps in advertising exploded. Its popularity does not seem to have let up.
Raw Materials
The envelope is usually made of a combination of man-made materials: Dacron, polyester, Mylar, and/or Tedlar bonded with Hytrel. The high-tech, weather-resistant plastic film is laminated to a rip-stop polyester fabric. The envelope's fabric also protects against ultraviolet light. Usually the envelope is smaller than the bladder to ensure that the envelope takes the load when the blimp is fully inflated. The bladder is made of a thin leak-resistant polyurethane plastic film.
Ballonets are usually made of a fabric lighter than the envelope's because they only retain gas tightness and do not have to withstand normal main envelope pressures. Air scoops channel air to the ballonets.
Blimps obtain much of their lift from lighter-than-air gases, most commonly helium, inside the envelope.
Most of the metal used on the blimp is riveted aircraft aluminum.
Earlier cars were fabric-covered tubing framework. Today's gondolas are made of metal monocoque design.
The nose cone is made of metal, wood, or plastic battens, laced to the envelope.
Design
The main body of the blimp is made up of an inner layer, the bladder, and an outer layer, the envelope. The bladder holds the helium. Because the bladder is not resistant to punctures, it is protected by the envelope.
Inside the envelope are catenery curtains, which support the weight of the car by distributing the loads imposed by the airship into the fabric of the main envelope. Catenery curtains all consist of cable systems attached to the car, which terminate in the fabric curtains.
The envelope's shape is maintained by regulating internal pressure of helium gas inside. Within the bladder are one or more air cells/balloons called ballonets. These are filled with air (as opposed to the rest of the bladder which is filled with helium) and are attached to the sides or bottom of the blimp. The ballonets expand and contract to compensate for changes in helium volume due to varying temperature and altitude. The pilot has direct control of the ballonets via air valves.
The nose cone serves two purposes. It provides the point of attachment for mast mooring and adds rigidity to the nose (which encounters the greatest dynamic pressure loads in flight). On the ground, the inflated blimp is secured to a stationary pole called the mooring mast. The rigid nose dish is attached to the mooring mast. The secured blimp can move freely around the mast with wind changes. There are nose lines attached to the nose dish used by the ground crew to maneuver blimp during takeoffs and landings.
Airship tail surfaces come in three configurations: the cruciform (+), the X, and the inverted Y. These tails are made up of a fixed main surface and a controllable smaller surface on the aft end. These surfaces weigh only 0.9 lb per sq ft (4.4 kg per sq m). Tail fins control flight direction. They are anchored at the rear of the ship and are supported by guide wires. The elevators and rudders also help to guide the blimp's movement and are mounted to the fin's edges with hinges.
The airship car, or gondola, is similar to conventional aircraft construction. The gondola contains a number of lead shot bags which are constantly adjusted based on the crew's analysis. The gondola is attached to the blimp by either an internal load curtain or externally, by being attached to envelope sides.
Inside the gondola, there a series of controls: the overhead control panel containing controls for communications, fuel, and electrical systems; throttles to regulate engine speed and propeller pitch controls to regulate angles at which propeller blades "bite" the air; fuel mixture and heat controls to regulate the degree to which fuel is mixed with air in engine; temperature controls to prevent icing; envelope pressure controls to regulate helium and ballonet air pressure; communication equipment; main instrument panel; rudder pedals to control right/left direction of blimp; elevator wheels to control up/down direction of blimp; navigational instruments; and color weather radar.
The Manufacturing
Process
Envelope
- 1 The envelope is made of patterns of fabric panels. Two or three plies of cloth are impregnated with an elastomer. One of these plies is placed in a bias direction with respect to others. The pieces of the envelope can be put together in a number of ways. They can be cemented and sewn together, or heat-welded (heat-sealed).
- 2 The outside of the envelope is coated with aluminized paint for protection against sunlight. The envelope will have the required shape when filled with gas.
- 3 The catenery curtains are attached on to the main envelope proper in a similar manner.
- 4 The bladder is formed from strips that are welded together.
- 5 The tail construction consists mostly of lightweight metal structural beams covered with doped fabric. They are held to the envelope by cables which distribute the load into fabric patches cemented or heat-welded to the envelope proper. They are not directly attached to the envelope in the manufacturing process, but put on when the blimp is inflated.
Gondola
- 6 The frame of the gondola is made of material similar to the tail construction, covered with doped fabric.
Inflation
The erection of the blimp takes only a short amount of time. (The following is only one method of inflation. There are variations on this method.)
- 7 The envelope is spread out on the floor of the airship hangar, with a net placed over it. This net is held down by sandbags. Gas is fed into the enveloped from tank cars each containing 200,000 cu ft (5,700 cu m) of 99.9% pure helium compressed to 2100 psi (14.5 megapascals). The net is allowed to slowly rise, with the envelope underneath it.
- 8 Fins, nose cone, battens, air valves, and helium valves are attached while the envelope is still near the ground. After these parts are attached, the envelope is allowed to rise high enough to permit rolling the gondola underneath it. After the gondola is attached, the net is removed and the airship is rigged for flight.
Shipping
- 9 When transported, the uninflated fabric envelopes can be folded, shipped, and stored in a space that takes up less than 1% of its inflated volume. This feature makes the non-rigid airship more practical than a rigid one.
Quality Control
A blimp requires a big crew, especially on the ground. Pilots must be certified in planes or helicopters and undergo special lighter-than-air pilot training. The FAA requires a separate license to command a blimp. As of 1995, there were only about 30 active blimp pilots in the world. Many blimps require 24-hour monitoring. The envelope and ballast are checked every hour to make sure the proper equilibrium is maintained.
The Future
Propulsive efficiency will be improved by using lightweight, two-stroke aviation diesel engines, gas turbines, or solar energy. New bow and stem thrusters will be developed to improve maneuverability. New lightweight plastics might change the hull design. More lightweight, high strength materials will probably be developed and inevitably improve the overall design and function of the airship. The Pentagon and the U.S. Navy have renewed interested in developing blimps for various defense, missile surveillance, radar-surveillance platforms, and reconnaissance purposes.
Where to Learn More
Books
Botting, Douglas, et al. The Giant Airships. Time-Life Books, 1980.
Ventry, Lord and Eugene M. Kolesnik. Airship Saga: The history of airships seen through the eyes of the men who designed, built and flew them. Blandford Press, 1982.
—AnnettePetrusso
Airship
Airship
A technologically advanced cousin of the balloon , airships are streamlined vessels buoyed by gases and controlled by means of propellers, rudders, and pressurized air systems. More commonly referred to as blimps and dirigibles, the airship is comprised of non-rigid, semi-rigid, and rigid types that rely on lighter-than-air gases such as helium and hydrogen for lift. Since the turn of the twentieth century, they have been engaged commercially in the transport of passengers and cargo and have proven a successful means of advertising.
Airships derive their lift from forward motion , just as an airplane does, and all three types have long used the internal combustion engine , like the type used in automobiles, to propel their massive bodies through the air. These have included the earliest motorcycle engines, the diesel engines of the mammoth American ships Akron and Macon, and the beefed-up Porsche engines used to power a new generation of airships. Traditional pressure airships house the engine, propeller, and gear box on an outrigger that extends from the side of the car, while the modern British Skyship's 500 and 600 use inboard engines that turn long prop shafts which allow the propellers to be vectored outboard. The introduction of pivoted, or vectored, engines gave airships the ability to change the direction of thrust and afforded it such amenities as near-vertical lift-off, thus reducing the need for long runways. Capable of airborne refueling, airships can remain aloft for weeks at a time, reaching an average airspeed of 60 MPH (96.5 km/h).
Non-rigid airships
Mastery of the skies proved a dominant preoccupation with French inventors in the latter half of the eighteenth century. In 1783, Jacques and Joseph Montgolfier designed the first balloon used for manned flight, while concurrently, Jean-Baptiste-Marie Meusnier had thought to streamline the balloon and maneuver it by some mechanized means. While several airships of similar design met with limited success from 1852, Meusnier's idea did not officially get off the ground until 1898. That year, the Brazilian aeronaut Alberto Santos-Dumont became the first pilot to accurately navigate a hydrogen-filled envelope and basket by means of a propeller mounted to a motorcycle engine.
Because of their non-rigid structure, the first blimps, like the balloon, were prone to collapsing as the gas contracted during descent. To counter this, Santos-Dumont introduced the ballonet, an internal airbag that helps maintain the envelope's structure and regulates pitch as well as lift, or buoyancy. Modern blimps continue to use ballonets positioned at the front and rear of the envelope, permitting the engineer to pump air into one or the other to change the pitch angle . For example, by increasing the amount of air in the aft ballonet, the airship becomes tail heavy, thus raising the nose skyward. Steering is further achieved by controlling rudders affixed to one of several types of tail fin configurations, allowing for basic left, right, up, and down directions. The long standard cross-shaped fin is slowly being replaced by an X-shaped configuration. While the X is more complicated, requiring a combination of rudders to complete a maneuver, it provides better ground clearance.
The car or gondola serves as the control center, passenger quarters and cargo hold of the airship. The envelope and car are connected by a series of suspended cables attached to the envelope by different types of load-sharing surfaces. Many modern airships use a curtain structure glued or bonded along the length of the envelope which evenly distributes the weight of the car and engines.
Rigid airships
The German inventor, Count Ferdinand von Zeppelin took the guesswork out of airship aerodynamics by building a rigid structure of lightweight aluminum girders and rings that would hold the vessel's streamlined shape under varying atmospheric conditions. Unlike Du mont's single-unit envelope, Zeppelin incorporated a number of drum-shaped gasbags within compartments of the structure to maintain stabilization should one of the bags become punctured or deflate. The dirigible was then encapsulated by a fabric skin pulled tightly across its framework. Buoyancy was controlled by releasing water ballast to ascend or by slowly releasing the hydrogen gas through a venting system as the ship descended.
Zeppelin was among the first airship designers to realize, in practice, the functionality of greater size in
lighter-than-air vessels. As he increased the surface area of the envelope, the volume increased by a greater proportion. Thus, a larger volume afforded better lift to raise the aluminum hull and maximized the dirigible's cargo carrying capacity. Airships like the Graf Zeppelin, the Hindenburg, and their American counterparts, the Macon and the Akron, reached lengths of up to 800 ft (244 m) with volume capacities nearing seven million cubic feet. Hydrogen was, in part, responsible for such engineering feats because it is the lightest gas known to man and it is inexpensive. Its major drawback, one that would virtually close the chapter on non-rigid airship aviation, was its flammability. While passenger quarters, cargo, and fuel could be secured to or stored within the dirigible's metal structure, its engines were housed independently and suspended to reduce the possibility of friction-caused ignition of the gas.
Little did English writer Horace Walpole know how closely he had prophesied the future of airships when, upon the launch of the Montgolfier balloon, he wrote, "I hope these new mechanic meteors will prove only playthings for the learned or the idle, and not be converted into engines of destruction..." While zeppelins, as they had become known, were initially put into commercial service, successfully completing nearly 1,600 flights in a four-year period, they were engaged in the service of Germany during World War I as giant bombers, raiding London itself in May of 1915. After the war, the rigid dirigible was employed as both a trans-Atlantic luxury liner and airborne aircraft carrier, but eventually fell out of favor after the Hindenburg disaster in Lakehurst, New Jersey, on May 6, 1937.
Semi-rigid airships
An intermediate version of the rigid and non-rigid types, the envelope of the semi-rigid airship was fitted with a keel similar to that of a boat. The keel acted as a sort of metal spine which helped maintain the envelope's shape and supported the gondola and engines. Interest in the semi-rigid airship was short-lived, though it met with some success. In 1926, the Italian pilot Umberto Nobile navigated the airship Norge across the North Pole, accompanied by the Norwegian explorer Roald Amundsen.
The modern age of airships
Helium succeeded hydrogen as the gas of choice for the following generation of airships and continues as such in the early twenty-first century. Though its lifting capacity is less than that of hydrogen, helium is considered a safe resource because it is inflammable. During the 1920s, the United States discovered an abundant source of the gas in its own backyard and reinstated the blimp as a surveillance mechanism during World War II, maintaining a fleet of some of the largest non-rigid airships ever built. "It was the American monopoly of helium that made possible this Indian Summer of the small airship—long after every other country had abandoned the whole concept," wrote Patrick Abbott in his book Airship.
By the 1950s, the Goodyear Tire and Rubber Co. had become involved in the production of airships as part of the Navy's intended early warning defense system, and remained one of the largest manufacturers of blimps until the late 1980s. The Goodyear blimp is probably most noted as a high-flying billboard and mobile camera that has offered millions of television viewers a bird'seye view of sporting events for several decades.
The early 1990s marked a resurgence in airships with the design of such models as the 222-ft (67.6-m) long Sentinel 1000. Built by Westinghouse Airships, Inc., its envelope is made of a lightweight, heavy-duty Dacron/Mylar/Tedlar composite that may eventually replace the traditional rubberized fabrics used by the Sentinel's predecessors. According to Aviation Week and Space Technology, the craft "has a 345,000-cu.-ft. envelope and is powered by two modified Porsche automotive engines fitted with propellers that can be tilted through a range of plus 120 to minus 90 degrees." Its potential for transporting heavy payloads, its quietness, and relative stability, have brought the airship back to design rooms around the world. Based partly on its fuel efficiency and the fact that its shape and skin make it virtually invisible to other radar , the United States has plans to reintroduce the blimp as a radar platform for its Air Defense Initiative. French scientists have used the airship to navigate and study rainforests by treetop, while environmentalists have considered its usefulness as a means of monitoring coastal pollution . The future may see airships powered by helicopter rotor systems and solar power, as well as the return of the rigid airship.
Resources
books
Abbott, Patrick. Airship. New York: Charles Scribner's Sons, 1973.
Meyer, Henry Cord. Airshipmen, Businessmen and Politics1890-1940. Washington, DC: Smithsonian Institution Press, 1991.
periodicals
Bell, Adrian. "On the Roof of the Rainforest." New Scientist 129 (1991): 48-51.
Garvey, William. "Rebirth of the Blimp." Popular Mechanics 168 (1991): 30-33+.
Hamer, Mick. "Airships Face a Military Future." New Scientist 115 (1987): 38-40.
Hollister, Anne. "Blimps." Life Magazine 4 (1988): 65-69.
Hughes, David. "New Westinghouse Airship Designed for Early Warning Surveillance." Aviation Week and Space Technology 135 (1991): 24-25.
John Spizzirri
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Ballonet
—Air compartments capable of maintaining constant internal pressure within an airship's envelope in response to outside air pressure and temperatures. Manual controls effect pitch, ascent, and descent.
- Blimp
—Airship in which the structure is supported entirely by internal gas and air pressure.
- Dirigible
—A lighter-than-airship capable of being piloted and controlled by mechanical means.
- Lift
—An aerodynamic force acting upon an object's upward motion in air.
- Vector
—A quantity or term that can be expressed in terms of both magnitude (a number) and a direction.
airship
airship
air·ship / ˈe(ə)rˌship/ • n. a power-driven aircraft that is kept buoyant by gas (typically helium, formerly hydrogen) that is lighter than air.