Airship

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.