But not all projects are as fanciful as Mr. Massaud’s. For example, a French technology start-up, Aerospace Adour Technologies, is working with the French post office to study the feasibility of transporting parcels by dirigible. Also in France, Theolia, a company specializing in renewable energy, is financing a dirigible, and plans a test flight across the Atlantic.  In Germany, Deutsche Zeppelin-Reederei, the successor to the operator of the Hindenburg, has had success with a new generation of airship it uses to transport sightseers and scientific payloads.  The trend is not entirely new. Zeppelin-Reederei carried 12,000 passengers on sightseeing tours over southern Germany last year. Aerophile, a French company that revived tethered balloons, which compete with dirigibles as carriers of passengers, advertising and scientific instruments, was founded by two young French engineers in 1993.  The aircraft industry is not exactly bracing for a dogfight. Mr. Massaud says that Emirates and Air France have expressed interest in Manned Cloud. But with top speeds of around 100 miles an hour and a maximum capacity of several dozen passengers, dirigibles are expected by most aviation experts to remain niche vessels for ferrying tourists, advertising and occasional scientific payloads.  “A dirigible is something magical,” said Jérôme Giacomoni, who was 25 when he founded Aerophile with a friend. “But most of the ideas are crazy.”  Dirigibles, he said, “are very sensitive to storms. Their size requires large landing spaces; economically they’re not feasible.”  Not yet, say dreamers like Mr. Massaud. But gasoline prices are pushing airlines to reduce the number of flights and retire older, less fuel-efficient aircraft. Aircraft manufacturers like Boeing and Airbus have responded by promising planes that use less fuel and produce less carbon dioxide.  Such concerns pushed Mr. Massaud to start thinking about dirigibles. Five years ago he worked on a design for a resort community in Palm Desert, Calif., but the result was so radical, involving tents rather than fixed buildings, that its developers balked. “They said to me, ‘You French, you’re all Communists!’ ” he said.  So Mr. Massaud conceived of Manned Cloud, a helium-filled dirigible shaped like a whale, with a cruising speed of 80 miles an hour and a cabin to accommodate 50 overnight guests and a crew of 25. “The large whales made a choice in evolution to live in harmony with their environment,” he said. “They are symbols of life in harmony with nature.”  Mr. Massaud submitted his design to the French aerospace agency, whose experts suggested he reduce the number of passengers to 15 and made other recommendations, but withheld judgment on his design’s feasibility.  “There are niches where dirigibles might still serve,” said Philippe Guicheteau, special adviser for military aeronautical systems at the agency, which goes by the French acronym Onera.  In the United States, research into dirigibles continues, but mainly for military purposes. In 2005, the Defense Advanced Research Projects Agency, or Darpa, briefly explored using airships to transport freight over long distances. Two other projects involving high-altitude airships, mainly for communications, continue.  France’s postal service, La Poste, has civilian uses in mind. Postal officials have long searched for alternatives to trucks and planes, aiming to reduce emissions by 15 percent by 2012. At a strategy meeting last year, officials decided to explore the use of dirigibles on routes between France and Corsica or French territories in the Antilles.  “Dirigibles of the new generation are part of our strategy and represent an area of study for us,” said Patrick Widloecher, director of sustainable development at La Poste. The postal service is working with Aerospace Adour, he said, to study the use of dirigibles.  “Over the medium term, the post office would like to test some pilot routes by dirigible, once a prototype has been developed and produced,” Mr. Widloecher said. He said Aerospace Adour was studying a model 420 feet long with a cruising speed of 96 miles an hour.  A dirigible, or rigid airship, has a metal frame, these days usually part aluminum, part carbon fiber, covered with a synthetic canvas. A blimp, in contrast, is a big, inflatable balloonlike sack filled with a lifting gas. Blimps are far less maneuverable than dirigibles and can lift less.  Today’s airships fly with helium, as the Hindenburg would have if not for an American embargo on what was then a fairly valuable commodity. Hence, the Hindenburg had to use inflammable hydrogen on its flights. By the time of the explosion, zeppelins had carried about 405,000 passengers across the Atlantic.  Airships still have their skeptics today. In Britain, an effort to revive the airship industry suffered a setback in 2005 when the Advanced Technologies Group, which planned to build airships called SkyCats, with a 22-ton payload, went bankrupt. An investor group has recently sought to revive it. The Cyclocrane, a large semirigid airship, was to be built in the United States by the start-up Cargolifter, but the company ran out of money in 2002 after a huge hangar was built.  Thomas Brandt, the chief executive of Zeppelin-Reederei and its parent, ZLT Zeppelin Luftschifftechnik, in Friedrichshafen, Germany, jeers at the notion of airships as hotels or freighters. “Illusions,” he said. “Airships are unstable, they depend on the weather, so we fly today from March to November.”  Mr. Brandt’s company succeeded by scaling back its ambitions, ferrying thousands of sightseers and, occasionally, scientific payloads. The company manufactures a zeppelin that costs about $15 million; it just delivered its fourth model, to Airship Ventures, at Moffett Field, near Stanford, Calif. Tickets will cost about $500 for sightseeing trips over the Monterey Bay area.  French political leaders are among those who believe the ships can do more than ferry tourists. For two years, Jean-Marc Brûlé, a Green Party leader and mayor of Cesson, near Paris, has shepherded through budget amendments to finance dirigible research.  “With global warming and the oil crisis,” he said, “It’s good sense to realize this dream.”  An article on July 5 about the entrepreneurs who envision the comeback of the dirigible misidentified the country of origin of the CycloCrane, a semirigid airship that was envisioned as a cargo hauler. It was the United States, not Germany. The article also referred incorrectly to the gas used in the Hindenburg zeppelin, which burned and crashed in Lakehurst, N.J., in 1937. While it was designed to use helium, the Hindenburg flew with hydrogen from the beginning because of an American embargo on helium. It did not switch from helium to hydrogen.
As the cost of fuel soars and the pressure mounts to reduce carbon dioxide emissions, several schemes for a new generation of airship are being considered.