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Nonwovens / Technical Textiles

Expanding Industrial Fabric Uses

No longer just for lighter-than-air ships, industrial fabrics today are used in many different inflatable applications.

Richard G. Mansfield, Technical Editor

From their beginnings in commercial passenger air travel, blimps today are used extensively for advertising purposes. Photograh courtesy of ILC Dover Inc.Expanding Industrial Fabric Uses No longer just for "lighter-than-air" ships, industrial fabrics today are used in many different inflatable applications.When industrial fabrics for inflatable applications are discussed, one end-use that most people are familiar with is lighter-than-air craft such as hot-air balloons, blimps and zeppelins. However, the field of inflatables encompasses a wider range of fabric-related applications than lighter-than-air end-uses.Types Of AirshipsAirships are essentially big, controllable balloons, sometimes called dirigibles. They come in three classes: rigid, semi-rigid, and non-rigid. Zeppelins (rigid airships) use a framework to retain their shape. Semi-rigid airships have a shape that depends on a combination of framework and gas pressure. Blimps (non-rigid airships) depend on the enclosed gas pressure to retain their shape.All types of airships are propelled by engines, use rudders and elevator flaps for steering, and have a gondola for the pilot, crew and passengers.Progress In AirshipsOne of the earliest flyable airships was developed by a French engineer and inventor, Henri Griffard. In 1852, he constructed a cigar-shaped nonrigid gas bag 143 feet long, driven by a screw propeller, which in turn was driven by a 3-horsepower (hp) steam engine. The airship flew over Paris at a speed of more than 6 miles per hour. Over the next 50 years, airships were developed throughout the world, but a major limitation was that the best available engines were too heavy in proportion to the power they provided.German inventor Count Ferdinand Graf von Zeppelin, for whom the zepplin is named, completed his first airship in 1900. The ship had a rigid frame covered with cotton fabric, and a row of 17 gas cells covered in rubberized fabric. The airship was about 420 feet long and 38 feet in diameter, and the hydrogen gas capacity was 399,000 cubic feet (ft3). Steering was done with forward and aft rudders, and the ship was powered by two 15-hp Daimler internal combustion engines, each with two rotating propellers.Commercial passenger air travel was initiated in 1910. At the beginning of World War I, Germany had 10 zeppelins in service, and by 1918, it had constructed 67. Toward the end of the war, Britain began the intensive development of rigid airships, stimulated by the availability of helium as a replacement for hydrogen. In 1920, the US government purchased a large semi-rigid airship, the Roma. Additional airships were obtained by the US Navy during the 1920s. One of the last big US airships was the Los Angeles, which was built in Germany. The Los Angeles could carry 30 passengers and made about 250 flights. It was decommissioned in 1932.In 1928, the Graf Zeppelin was built in Germany and flew more than 1 million miles over a period of nine years, including a trip around the world. The tragic accident of the Germany-built Hindenburg zeppelin in 1937 spelled the end of the rigid airship era. Subsequent airship development involved non-rigid blimps. These were used for anti-submarine warfare and search missions during World War II. Today, blimps carrying corporate logos are now used extensively for advertising purposes.Logging Balloons, Aerostats and Cargo AirshipsStricter environmental requirements in some logging areas have made it more difficult to develop logging roads, particularly in the mountainous areas of the northwestern United States and western Canada. Logging balloons have been used for retrieving lumber after it has been cut in these regions. In the early 1990s, ILC Dover Inc., Frederica, Del., was involved in the detailed designing and manufacturing of some of these logging balloons. One has a 15-ton lifting capability, is 119 feet in diameter and has a gas volume of 629,000 ft3.Helium-filled aerostats typically are used to carry surveillance radars to altitudes of up to 16,000 feet while tethered to the ground, or up to 3,000 feet tethered to a ship. Aerostats now are used for sea-based border patrols and drug enforcement.Lighter-than-air ship engineers have for many years advocated the use of these airships for picking up and carrying cargo as heavy as 160 tons and as long as 150 feet. One of these advocates was Baron Carl-Heinrich Freiherr von Gablenz. In 1996, von Gablenz started promoting the development of the CL160. He succeeded in convincing German officials and German bankers that the development of this massive airship was possible. In May of 2000, von Gablenzs company, CargoLifter AG, went public on the Frankfurt Stock Exchange with a value of $180 million. Its initial plan was to build a fleet of 50 CL160s at an estimated cost of $50 million each. CargoLifters staff of 240 people, based in Germany and the United States, claimed to have two-thirds of the worlds lighter-than-air experts.CargoLifters first product, the CL75 Air Crane balloon-based system, is capable of carrying a 75-ton payload either in a crane configuration or as a towed vehicle. The unit started its prototype testing in October 2001. In July 2002, Boeing and CargoLifter announced they had signed a contract to jointly explore stratospheric airship concepts. The contract provided for a detailed study of lighter-than-air stratospheric platforms that would enable the companies to coordinate efforts as airship system suppliers for current and future programs.Unfortunately, the program to build the CL160 consumed funds at a greater rate than anticipated, and the company entered insolvency proceedings in August 2002. CargoLifter AG was liquidated, and the assets of the company were acquired by a Malaysia-based firm, Tanjong Plc, in July 2003.Fabrics For AirshipsIf the CargoLifter program had been a success, it would have boosted demand for specialized fabrics used for the envelopes of the CL160 airship. Each airship would have required about 65,000 square yards of fabric. One potential fabric supplier would have been ILC Dover, the worlds largest producer of envelopes for surveillance aerostats, advertising airships and blimps, passenger airships and blimps, high-altitude airships, and hybrid heavy-lift vehicles.The company has an extensive materials development program, which includes solution, transfer and calender coating; foam extrusion; and laminating. The fabrics it works with include nylon, polyester, aramids and liquid crystal polymers.The following information is abstracted from a paper entitled Airship Envelopes: Requirements and Test Methods, by Tim Miller, ILC Dover, and Mathias Mandel, Zeppelin Luftschifftechnik GmbH, presented at the American Institute of Aeronautics and Astronautics (AIAA) Conference held in Denver in April 2002:For non-rigid and semi-rigid airships, the envelope is one of the major structural elements, and the materials, design and workmanship must be of the highest standard possible. The current airworthiness of the airships requires a safety factor of four on envelope materials. The envelope materials must provide a delicate balance between often competing demands such as:highest tensile strength versus lowest possible mass;maximum tear strength versus maximum adhesion;maximum material life versus ease of field repair; andmaximum price versus everything.One critical parameter for airship envelope fabric is its ability to resist tearing after damage. Table 1 shows the delicate balance in materials design for airship envelope fabrics. For example, to minimize mass, a lower-denier, higher-count, plain weave fabric would be chosen. To maximize tear strength, exactly the opposite might be selected a higher-denier, lower-count ripstop fabric.
The Future Of AirshipsAlthough the liquidation of CargoLifter has been a severe setback for cargo transportation by airship, other uses for airships such as advertising, drug enforcement, surveillance, logging and communications continue to grow. The growth of the cellular phone market has renewed interest in the use of high-altitude airships as a means of providing an economical alternative to satellites. ILC Dover has been involved in the Ultra-Long Duration Balloon program to fly a large, pressurized balloon at altitudes approaching 100,000 feet for a period of 100 days to provide data developed by the flight to scientists via the Internet. Also, England-based Lindstrand Balloons Ltd. and Daimler-Chrysler, Germany, have finished a design study for a high-altitude long-endurance airship for telecommunications. Zeppelin Luftschifftechnik has built several semi-rigid airships and has even conducted passenger-carrying sightseeing flights with one of them.Specialty high-performance fibers in combination with polyurethane, polyamide and fluorocarbon films and coatings will continue to play an important role in developing covers for airships. Such high-performance fibers include the para-aramids Kevlar®, Technora and Twaron®; and liquid crystal fibers such as Vectran® and Toyobos Zylon® PBO. Polyamide and polyester yarns also will continue to play a major role in some of these applications.Inflatable DamsInflatable rubber dams are long, tubular-shaped fabrics that can be placed across channels, streams and weir crests to raise the upstream water level when inflated. One unique feature of inflatable dams is their ability to deflate quickly and easily to prevent upstream flooding. Neoprene-coated filament fabrics were introduced for inflatable dams in the 1950s. Both nylon filament and polyester filament coated fabrics are now used for this application. Neoprene is used for coating because it has good resistance to weathering, flexing and abrasion. It also has good resistance to oils, greases, gasoline, and acids and alkalis. Some inflatable dams are designed to fill with either air or water, or both. In colder climates, they generally are filled with air, since freezing would be a problem with water. In open channels, inflatable dams are used to divert water for irrigation and for flood control. Dams also can be used to control chemical spills in streams.In Tempe, Ariz., the Tempe Town Lake on the Rio Salado is contained by an inflatable dam system consisting of eight bladders four in a row at the east end and four in a row at the west end. The dams, purchased from Bridgestone Corp. in Japan, took a year to produce. The dams are made of three main elements:a strong, flexible, rubber-coated tube that is fixed securely to a concrete base slab by clamping bars and anchor bolts;an operating system that controls inflation and deflation of the tube; andan automatic safety device that ensures tube deflation in flood situations.Each bladder is about 240 feet long, weighs 40 tons and is more than 1-inch thick. At times, a small amount of water can be seen flowing over the top of the west dams, creating a 19-foot waterfall. This water is recaptured by a recycling system and pumped back into the lake. The east dams are 3 feet high and sit on a 3-foot cement base. The west dams are 16 feet high and sit on a 3-foot base. Each section of rubber is embedded with fabric mesh and ceramic chips, and is designed to resist tearing. The rubber also contains a self-sealing material to re-close small holes. The dams are computer-controlled and maintain an air pressure of 6 pounds per square inch. The dams can be deflated and inflated within 30 minutes.
In Mountain Pass, Calif., three lacquer-coated nylon-reinforced polyvinyl chloride VanDuzen dams from Superior Dam provide ballast security.There are estimated to be at least 2,200 inflatable dams in use throughout the world. Manufacturers of inflatable dams include: Superior Dam LLC, Carlotta, Calif.; Queensland Rubber Co., Australia; Satujo, France; Bridgestone Corp., Japan; Rubena, the Czech Republic; and Hydroconstruct Co. Ltd., Austria.Liquid Container SystemsElastomeric-coated fabrics of nylon and polyester are used extensively to transport a wide range of liquids including water, oil and chemicals. An important device for transporting liquids is the dracone barge, a flexible tube designed to carry petroleum and other liquids. The skin of the dracone is made of nylon cord and woven nylon fabric coated with a weather-and abrasion-resistant elastomer. Dracones range up to 300 feet in length and 15 feet in height when fully inflated. They were developed in 1956 by Dunlop GRG Holdings Ltd., England, in cooperation with their inventor, Sir William Hawthorne. Dracone barges are designed to operate at 85 percent of their nominal capacity in open sea conditions, and they often are used for oil-spill clean-up work. When not under tow, they can be used on land for fuel storage.Dracones also are used to supply fresh water to some island communities that do not have adequate sources of water. There have been several studies made to explore the feasibility of transporting water by dracones from Canada or Alaska to the West Coast areas of the United States. Some of these concepts look technically feasible, but the economic and political aspects of enacting them are important obstacles.Collapsible storage containers using the same type of materials as the dracones provide logistical support in military operations in which the storage and quick movement of fuel is essential. Dunlop GRG is the only approved supplier of these units to the Ministry of Defence in the United Kingdom. Dunlop fabricates units that can hold up to 60,000 gallons of liquid. A US supplier of towable and collapsible drums for military and other uses is Amfuel Co., Magnolia, Ark. Amfuel is a fully integrated manufacturer of these fuel and water storage units. It coats the nylon and polyester substrates with elastomeric coatings including neoprene and EPDM. The collapsible storage drums are made in 55-, 250- and 500-gallon sizes in accordance with US military specifications.Towable drums are lighter-weight than metal drums, non-contaminating, puncture-resistant and easily repaired. In addition, they collapse to 15 percent of their filled volume, can be dropped by parachute or lifted by helicopter, have Low Altitude Parachute Extraction System (LAPES) capability, and can be rolled or towed.Amfuel sells a truck-mounted elastomeric-coated fabric tank called Fabritank®. The tanks are used to carry materials such as latex paint, roofing slurry, lubricating oils, styrene polymer and liquid fertilizer. The Food and Drug Administration-approved liners are available for carrying food-grade materials. Capacities of these units range from 1,500 gallons to 5,600 gallons. Using Fabritank, a flat-deck trailer or vans productivity can be increased by allowing it to haul its normal dry cargo and return home with a liquid haul.Dunnage BagsInflatable dunnage bags have replaced rigid wooden shoring frames for protecting freight when shipping by rail, truck or ship. After loading has been completed, the dunnage bags are inflated to secure freight and provide cushioning. The bags are deflated for further use after the cargo reaches its destination. Rubber-coated filament nylon fabrics and coated film or coated heavy paper are used for the bags. Suppliers of reusable dunnage bags include Amfuel and Universal Rope Fabrication Ltd., Canada.Pneumatic Fenders For ShipsLow-pressure pneumatic fenders are used for ship/shore berthing of vessels. They are designed to spread berthing forces over a large area. The units are made from elastomeric-coated nylon fabrics. Pneumatic fenders are particularly suitable for naval ships whose thin hulls and sensitive electronic systems require careful berthing.

September 2003