Dirigibles on the Rise

You won't believe what the engineers at Zeppelin are building these days

By Robert Kunzig|Wednesday, November 01, 2000

The Union Pacific Railroad recently placed an order for 58 new steam locomotives to meet the growing demand for freight shipments across the American continent. Western Union is opening scores of new telegraph offices; it seems that people drowning in cheap e-mail and faxes long for the drama and succinctness of the telegram. And even dirigibles are making a comeback: They may soon see service as airborne tour buses, flying cranes, and stratospheric cell phone antennas.

All those statements are surprising, but unlike the first two, the last one is actually true. Dirigibles, also known as airships, never deserved to go the way of the telegram or the steam locomotive; never deserved to be reduced to flying billboards like the Goodyear blimp. Public relations, ironically, had been part of their downfall: After 36 people died when the Hindenburg burned at Lakehurst, New Jersey, in 1937, it became hard to convince anyone that airships had a future. And in transoceanic passenger service— the business pioneered by the Hindenburg and its predecessor, the Graf Zeppelin— they surely didn't, once airplanes cut the crossing time from days to hours.

But the modern economy is creating many new niches, and in some of them being slow isn't much of a drawback— and being lighter than air is a decided plus. "Nostalgic as they are, airships could play a very interesting role in as innovative a sector as communications," says Reimund Küke, the engineer in charge of the stratospheric airship project at Astrium, a European aerospace company. "That's a charming business. And it may also be a very lucrative one, which is why so many people are giving it a try."

A century after they first took off, half a century after they became quaint, airships are coming back.

From the Archives of the Count

Friedrichshafen, on Lake Constance in southern Germany, is a modern town, because like many German towns it had to be rebuilt after the war. Traces of its old resort atmosphere survive, though. Sometimes on summer evenings a brass band assembles by the lake, in knickers and felt hats, and the genteel blat of their horns winds through the streets and floats into open windows and drifts out over the water to die gently, oompah-pah paaaah, in the feather-bed air. It's easy then to imagine a zeppelin floating offshore— above and in silent harmony with the sailboats that are fanning in from all directions, now that it's dusk and the band is playing and the beer gardens are open on the shore.

On just such an evening a century ago, July 2, 1900, the first zeppelin took off here from a floating hangar. Count Ferdinand von Zeppelin built his hangar on the lake because he figured, wisely, that his airship might need plenty of room and a soft landing place. People lined the shore and circled the hangar in small boats to watch that first flight. It lasted just 17 minutes; the journalist on board barely had time to scribble a few weighty comments— "Everyone saw in it the supreme expression of the human will"— before Zeppelin made a forced landing on the lake, impaling his zeppelin on a buoy. But within a decade he had stayed aloft for 24 hours and had become a national hero. Airplanes then were still fluky gnats. At his funeral in 1917, Zeppelin was compared to figures like Galileo and Columbus, not the Wright brothers.

His great idea had been to make his airships rigid. Earlier dirigibles were kept in shape by the internal pressure of the lifting gas, like balloons— and like blimps, the only airships in active service today. When a blimp develops a large enough leak, even before it falls to the ground it becomes almost unsteerable; it starts to sag, changing from an aerodynamic cigar into a flopping banana. Zeppelins didn't have that problem. Their external envelope, of waterproofed cotton or jute, was held taut by a framework of aluminum rings and longitudinal girders, and the hydrogen itself was contained in a series of internal bags lodged between the rings. A zeppelin could lose one or two of those hydrogen cells and still be kept afloat by the others, and still keep its shape thanks to its rigid skeleton. It had to be big to lift all that aluminum— the very first zeppelin was 420 feet long, the Hindenburg 804 feet— but the skeleton allowed it to be big. A nonrigid dirigible of the size and speed of the Hindenburg would have been so deformed by the air it was plowing through that it would, again, have become un-dirigible.

It wasn't a technical shortcoming that killed zeppelins in the end. The Graf Zeppelin began transatlantic passenger service in 1928, flew around the world in 21 days in 1929, and was retired, after 590 disaster-free flights, in 1937, the year the Hindenburg burned— and two years before airplanes first carried paying passengers across the Atlantic. Even before the Hindenburg, the count's successors knew they should be filling their airships with helium rather than flammable hydrogen; had they been able to do so, airship history might have been very different. But the only source of helium was (and, for the most part, still is) natural-gas fields in Texas and Kansas, and the American government hesitated to supply helium to Hitler's Germany— especially after it annexed Austria in 1938, not to mention the military history of zeppelins, which had bombed London and Paris in World War I. In 1944, Allied planes bombed Friedrichshafen, flattening the Zeppelin hangars.

The Zeppelin company survived— but as a manufacturer of construction machinery and industrial equipment. By 1990, the company hadn't built an airship in half a century. And yet Klaus Hagenlocher, its research director, found himself always fielding questions about airships. Marketing surveys convinced him and his colleagues that the interest was more than just nostalgia; there was money to be made using zeppelins as floating tour buses or island ferries— if a safe version could be built. Hagenlocher began looking through the company archives and found that half of all the accidents had been caused by a lack of maneuverability.

A conventional airship is steered the way an airplane is, by adjusting the flow of air over control surfaces; on wingless airships, all the control surfaces are on the tail. By adjusting the angle of the horizontal elevators, the pilot can move the ship's nose up or down (pitch); moving the vertical rudders turns the nose from side to side (yaw). The hard part is landing. When an airplane touches down, it is still moving fast enough to control its pitch and yaw. But an airship is moving at next to no speed, meaning there is next to no airflow over the control surfaces as the pilot tries to maneuver it toward the mooring mast. At that moment, says Scott Danneker, a veteran American airship pilot who is now the chief test pilot at Zeppelin, the poor sap at the controls "is sweating bullets. If the winds are calm he has absolutely no aerodynamic control. None. The only thing he can do is rely on the ground crew."

The Hindenburg required at least 200 men on the ground to stop it; a filmstrip at the Zeppelin Museum in Friedrichshafen shows the captain bawling commands through a megaphone at men who are scurrying to catch ropes dangling from the airship. Even the far smaller Goodyear blimp needs a ground crew of 15 or 20. Using humans as brakes makes airships uneconomical; worse, the brakes are often ineffective. In the archetypal accident, says Hagenlocher, an airship comes in for a landing, gets hit by a sudden crosswind, and is blown into trees or buildings before it can lift off again. In the past few years, it has happened a couple of times in the United States.

It is never supposed to happen to the airship that Hagenlocher and his colleagues built and have been flying around Friedrichshafen for the past three years. The Zeppelin-NT— the NT stands for "new technology"— is designed to carry just 12 passengers and measures only 246 feet long and 46 feet in diameter. But it is a zeppelin: It has a rigid internal frame, unlike any other airship today.

The frame is mostly made of carbon fiber, which is stronger, stiffer, and lighter than aluminum. To save even more weight, it consists of a series of triangles— connected at the corners by longitudinal aluminum girders— rather than rings. The whole frame weighs just a ton, but it is enough to guarantee the basic cigar shape of the airship. Pressure from the helium inside does the rest, stretching the envelope taut; unlike the original zeppelins, the NT doesn't have internal gas cells. But it can lose up to a third of its helium, says Hagenlocher, and still fly for six or seven hours in search of a safe landing.

During normal operation, the ship is actually heavier than air, by about a thousand pounds, so to take off it can't simply jettison ballast, the way the old zeppelins did. Instead it pushes itself off the ground by pointing a propeller on each side up and a propeller on the tail down. Once the ship is under way, air flowing over the hull and the tail generates lift. Helium does the rest. When it comes time to land, being slightly heavier than air is an advantage: The zeppelin is drawn to the ground. By pointing the three propellers upward, it comes in hovering, like a helicopter. Meanwhile, a fourth propeller thrusts the tail from side to side, like the tail rotor of a helicopter, to keep the nose pointed into the wind and toward the mooring mast. The control is so fine Danneker can fly a line dangling from the nose into the hand of a worker who then attaches it to the mooring mast.

Watching this zeppelin rise off the airfield at Friedrichshafen, it seems obvious that many people would pay to ride the thing; it looks like a blast, a peaceful blast, and not from the past at all. "You don't even notice when you lift off," says Hagenlocher. "It's nice and quiet— not like an airplane, where you get this murderous noise."

The next Zeppelin-NT is already taking shape: white, bulbous, already swollen with 8,000 cubic meters of helium— a gentle whale floating inside the hangar. A Swiss entrepreneur has agreed to buy the 12-passenger ship for sight-seeing tours once the German government has certified the prototype. The company is waiting eagerly, though, for someone to order a bigger airship. The Hindenburg had a volume of 200,000 cubic meters, but a ship just a quarter that size, says Hagenlocher, could carry 200 passengers and prove much more economical to operate and build. Airship economy increases rapidly with size: each cubic meter of helium adds about a kilogram of lifting capacity, while the weight of the airship itself— which is proportional to its surface area, not its volume— increases by much less. That's why for some airship builders these days, even the Hindenburg is not the limit.

Flying Hospitals to Mozambique

Inside Hangar Number 2 at Cardington, England, stand the shells of two six-story apartment buildings. One of them appears flame-blackened. The buildings belong to the main tenant of the hangar, an outfit that tests building safety standards. Roger Munk's company, Advanced Technologies, occupies a low flank of the hangar. To build the first SkyCat, a new kind of airship he has designed, Munk will need to get rid of those apartment buildings and take over the main hall. To build the full-scale SkyCat, which Munk envisions as capable of hauling 1,000 tons of freight, maybe an armored battalion or two— well, it's not clear yet where that will be built; it may have to be outdoors. A SkyCat 1000, more than 1,000 feet long, more than 40 stories tall, and with 10 times the volume of the Hindenburg, would be far too large for assembly in the Cardington hangar.

Munk has spent the past three decades, ever since he gave up a career as a motor-yacht architect, trying to rescue airships from their history. He has built a series of 20 increasingly modern blimps, including the Fuji blimp and several that were certified for passenger flights. None, however, can compare with the SkyCats for technological derring-do.

The SkyCats, if and when they fly, will be dramatically new in two ways. The first innovation is their shape. From the back a SkyCat will look like two Siamese blimps, with separate tails that fuse in the middle; from the front it will have the cambered profile of an airplane wing, more or less flat on the bottom and curved on top. In flight, a SkyCat will get 40 percent of its lift the way an airplane does, by diverting air downward and thereby pushing itself up. While landing, its wide, flat bottom will make it less vulnerable to the crosswinds that can roll a conventional airship.

At that point a SkyCat will reveal that it is also part hovercraft. As the airship nears the ground, giant fans inside the twin hulls will blow air down into fabric skirts, allowing the ship to set down gently on twin cushions of air. Next the fans will switch into reverse, creating a suction that anchors the SkyCat firmly to the ground. "We've finally got a vehicle that can land anywhere without anyone on the ground," says Munk. "The whole thing just sits down like a limpet."

Then, as Munk sees it, the ramp is lowered at the back of the 10,000-square-foot payload bay, and the tanks, trucks, and jeeps drive off; Munk says the American military is considering a SkyCat 1000 as a transport vehicle for a rapid deployment force. Or, maybe the trucks would be carrying food and medical supplies, or even a whole hospital, to victims of flood or famine. When Britain recently tried to help evacuate flood victims in Mozambique, Munk points out, it had first to dismantle four helicopters, ship them by cargo airplane to Mozambique, and reassemble them there. "It was pretty ridiculous," he says. "By the time they'd done that, half the floodwaters had gone." A SkyCat could have flown right in and sat right down where it was needed— on the water itself, if necessary.

So far Munk only has a contract to build a relatively small SkyCat— 270 feet long, with a payload of 15 tons— for a British company that plans to use it just for sight-seeing flights. But that will give him a chance to demonstrate the technology required for the behemoth. The biggest challenge is the hull, which will have three separate layers: Tedlar on the outside to keep the weather out, Mylar in the middle to keep the helium in, and a Kevlar-like fabric on the inside for strength. That strength will be tested severely at the points where the heavily burdened payload module attaches to the hull, and also by the need to keep the hull so tautly inflated that it can withstand the pressure of going more than 100 miles per hour, faster than any other airship. No rigid frame is required, says Munk; rigid frames are passé.

Instead the airship's unusual shape will be achieved by assembling flat pieces, fused at the joints by a gluey elastomer. Each piece will be cut precisely so that the whole confection inflates to the desired shape. "It's exactly like making a dress for a very curvy lady," says Munk. "What a good tailor does, we have to do on this high-tech, large scale."

Munk is not the only airship builder trying to work on a very large scale these days. Twenty miles south of Berlin, a start-up company called CargoLifter is completing a new hangar, 350 feet high and nearly 400 yards long, in which it plans to build an 850-foot-long and enormously fat airship— so fat it will have nearly three times the volume of the Hindenburg. The company has raised $260 million from private investors and by going public this year on the German stock exchange. "We're not building an airship because it's pretty," says manufacturing director Christoph von Kessel, "but because it's the solution to a particular transport problem."

That problem is the transport of huge indivisible, or hard-to-divide, loads— tunnel drivers, power-plant turbines and the like. Nowadays those things are loaded by crane onto trucks, delivered to a port— sometimes bridges have to be dismantled en route— loaded onto a ship, and off-loaded at another port onto another truck. A CargoLifter airship, the company says, would hoist such a load at the manufacturing plant and deliver it directly to its final destination, even thousands of miles away, more rapidly and at lower cost.

The CargoLifter airship, called the CL 160, will have a payload capacity of 160 tons. Its structure is semirigid: a soft body with a rigid aluminum keel at the bottom. The major loads— payload platform, gondola, and 16 engines— will be attached to the keel. The engines are necessary for maneuvering the airship, especially during takeoff and landing, operations that promise even more ticklishness than usual for an airship.

Once at its destination, a CL 160 will hover at an altitude of 300 feet. The payload platform, bearing the 160-ton cargo, will be lowered on steel cables to an altitude of 120 feet. There it will hang while it is anchored to the ground by other cables and while ballast water is taken on to compensate for the enormous load the airship is about to shed. (Otherwise the ship would become far too lighter-than-air and would soar into the sky.) Cargo would then be lowered by cable from the payload platform; the off-loading operation would last around two hours. It seems a bit precarious, and it elicits polite skepticism from others in the industry.

CargoLifter sees no insurmountable obstacles, though. Over the next decade or so, it plans to build and operate 200 airships from its own bases all over the world. "History is being written here," says von Kessel, who left a senior position at Airbus to work for CargoLifter. "Something absolutely new is being made here. And that is very exciting."

Into the Stratosphere by the Hundreds

CargoLifter hopes to launch a fleet of 200 giant airships that will crisscross the planet at an altitude of no more than 600 feet. The 250 giant airships that an American company called Sky Station International hopes to launch will fly much, much higher, around 65,000 feet, and without pilots. Technical details of the Sky Station plan are difficult to come by because the company, fearing competitors, refuses to discuss them. In fact, several groups right now are interested in putting a fleet of unmanned airships into the stratosphere. "I believe it's going to happen," says Reimund Küke of Astrium, which carried out a feasibility study for the European Space Agency (ESA). "It's just a matter of time."

The idea is this. Cell phones are becoming ubiquitous, yet spotty reception makes them maddeningly unreliable. As more people start using their cell phones to connect to the Internet, and eventually to transmit large data files, the problems of inadequate capacity and intermittent coverage will become acute— even as the landscape becomes increasingly littered with ugly relay towers. But talking by satellite requires expensive high-power phones that few people really want, while the costs of launching a global network are huge, as Iridium, the newly defunct satellite-phone company, discovered.

An unmanned airship floating in the stratosphere, 12 miles up, would not face the same problems. Ordinary cell phones would have enough power to send signals to it. Hovering above a city, it would add capacity and coverage— you probably wouldn't see it, but it would almost always be in your telephone's line of sight. In industrialized countries, airships could complement existing telephone networks. In underdeveloped countries they could be even more important: With a single airship and a lot of cell phones, you could provide phone service to a whole city that had none. "We had a delegation from China come here, and they said, 'Where can we buy one?'" says Peter Groepper of ESA.

The biggest technical challenge is designing a stratospheric airship that can keep on-station. The rough design Küke and his team came up with calls for a 720-foot airship whose top surface would be covered with thin-film solar cells made of amorphous silicon. Solar energy collected during the day would be stored in fuel cells for use at night and would power a single propeller, 100 feet in diameter, at the stern; its huge size and slow rate of rotation would make it more efficient in the thin air of the stratosphere. The propeller would swivel like a rudder to help point the airship into the wind— which would be its nemesis. Roger Munk, who has the contract to build the airship for Sky Station, says his airship would draw on other sources of power besides solar cells to achieve the speed it needs to stay on-station even in winter, when winds in the stratosphere can reach 110 mph.

The biggest challenge of all, however, — as with all airship projects— is finding the money. "The problem is to convince people that an old technology can be used for new purposes," says Groepper. Stratospheric airship proponents face a more conventional competitor: An American firm called Angel Technologies plans to use piloted airplanes instead of unmanned airships as high-altitude communications antennae. The pilots would fly tight circles in the stratosphere above their service area for six hours, until the next plane arrived to take over. "I don't think there are many pilots who would find that job fulfilling," says Küke— and there is something curiously retro about the scheme. It seems a bit like proposing a return to human switchboard operators. Sometimes the most modern and forward-looking technology is not the one that fits our preconceptions; sometimes the elegant solution is a big, fat, slow-moving blimp.

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