PORTER DISMISSED THE fantastic reports as mere rumor, but, sadly, they were all too true. Henri Giffard, a twenty-seven-year-old engineer and balloon hobbyist, had built a light steam engine—“light” meaning that the power plant and its empty boiler weighed 330 pounds—that could produce 3 horsepower and drive a large rear-facing propeller. This he placed on a small platform suspended beneath a spindle-shaped 144-foot-long balloon that held some 88,300 cubic feet of coal gas. Giffard dubbed it a dirigeable (French for “steerable,” soon Anglicized to “dirigible”).
On September 24, 1852, at 5:15 P.M., Giffard took off from the Hippodrome in Paris and chugged his way to Élancourt, seventeen miles away, on a three-hour, one-way voyage averaging nearly 6 mph. Once he reached his destination, Giffard, dressed for the occasion in a frock coat and top hat, demonstrated his ability to control his craft by making several turning circles in calm air before landing safely at his destination.
Giffard was never able to repeat his success. He had made a great leap forward, certainly, but had collided with a wall. His engine was simply not sufficiently powerful to drive his dirigible in anything but still air. At the merest hint of a breeze, he found himself at its mercy.
In terms of hard numbers, his steam engine had a dry weight-to-power ratio of 110 to 1 (the 330 pounds of the boiler/engine combination divided by the 3 horsepower it indicated). In other words, it required 110 pounds of weight to produce 1 horsepower. (A rule of thumb at the time was that an actual horse weighed a thousand pounds and produced 1 horsepower—itself.) Giffard’s ratio beat anyone else’s at the time, but it was nowhere near enough to sustain powered flight or to allow controlled aerial navigation in anything but the most favorable conditions.
There were two possible solutions to the problem. Realistically, you could increase the power output or reduce the weight of the engine to boost the ratio. Ideally, you would do both, as the Wright brothers would a half-century later, when their first engine (180 pounds) produced 12 hp, yielding a weight-to-power ratio of 15—just enough to allow true flight. Unfortunately, Giffard could do neither. Coaxing more horsepower out of the already taxed engine was out of the question, and paring its weight to the barest possible minimum made little difference because the iron engine remained so heavy that it still ate up a large proportion of his dirigible’s “useful lift.”
Useful lift was one of two related metrics that were becoming of greater importance. Every airship is defined by its gross lifting power and its useful lift. The former is derived from its gas volume. The more gas there is, the more weight the airship can bear as it floats. But from that figure you need to subtract the total fixed weight the airship is expected to carry, which includes the airship itself, the aeronaut(s), the balloon material, the gas, the engine, propellers, payload, ballast, and fuel. The net result is the useful lift.
Because he had used cheap and dirty household coal gas rather than expensive purified hydrogen, Giffard’s gross lifting power was modest to begin with. But after taking away the various fixed weights, Giffard had so little useful lift left that he had been pushing his luck in merely getting off the ground.1
Alas, no one could improve on Giffard, and by the Civil War interest had petered out. Instead, Thaddeus Lowe, an impossibly glamorous, imposingly mustached New Hampshireman, successfully built balloons like the 725,000-cubic-foot City of New York and the smaller Enterprise, but they lacked engines. Not until “a propelling power can be discovered the weight of which shall be but one third of that we now employ,” he sadly judged, could “aerial navigation…become a practical science.”2
Lowe would soon found the Union’s Balloon Corps, which would perform only occasional reconnaissance duties in small, tethered balloons at an altitude of between 500 and 1,000 feet until its official dissolution in August 1863—the same month that Zeppelin met Steiner in Saint Paul. While the Civil War would bring to the fore many modern innovations—railroads, land mines, ironclads, rapid-firing guns, submarines—in terms of lighter-than-air flight it was as if time had stopped sometime in the Montgolfier era.
In the absence of a lightweight engine, the quest for aerial navigation was a fool’s errand.
THOSE TAKING AN evening stroll down Paris’s Champs-Élysées in the late summer or fall of 1881 could not help but notice the yellowish aura eerily emanating from the Palais de l’Industrie, a huge Gothic building on the bank of the Seine. Attracted to the light and intrigued by the growl and whirl of machinery, they entered a spectacular cathedral of science where congregants prostrated themselves not before God but before the high priests of Electricity, a far more mysterious power now finally revealed to mankind.
To demonstrate the new technology’s marvels, a model of a lighthouse greeted visitors as they entered. Powered by an electrical generator, its beam revolved and even changed color. Surrounding it was a small lake in which toy electric boats whirred contentedly around. Illuminating the central pavilion were statues bearing scores of electric lamps; the chandeliers were adorned with still more.
Passing through the various halls they saw displays of batteries, telephones, telegraphs, and electro-locomotives. Hall 20 contained a collection of “electro-pneumatic clocks,” while Halls 3 and 4 resembled a World of Tomorrow exhibit: A mock-up of a fashionable apartment featured a “tastefully furnished” dining room, kitchen, and bathroom illuminated by battery-powered lamps. Dominating the American pavilion were Thomas Edison’s new incandescent bulbs, which promised long-lasting light suitable for homes, all controllable with the simple flick of a switch.3
But one visitor, Captain Charles Renard, ignored the domestic novelties and paid close attention instead to an unheralded piece of equipment that served to power many of the smaller displays. Invented by Zénobe Gramme, a Belgian engineer, the “Gramme dynamo” was an adaptable, lightweight generator that could be employed as a general-purpose workhorse for any number of applications.4
It was just what he was looking for.
AFTER ITS CALAMITOUS performance during the Franco-Prussian War, the humiliated French army had undergone a number of reforms, not least of which was the creation of a Military Balloon Establishment. Captains Charles Renard and Arthur Krebs had been recruited to conduct research into powered, lighter-than-air flight, and by 1883 they had adapted a small Gramme dynamo and a bank of batteries (for power storage) to fit into an airship they patriotically christened La France.
Steam, they argued, was obsolete in this new modern age of electricity, and La France was going to be a radical step forward. Their craft was 160 feet long with a 23-foot-diameter propeller placed at the front of a silk-and-bamboo control car that was suspended underneath the balloon. Within the car, Renard and Krebs operated the dynamo and battery array, which produced around 8.5 horsepower and weighed 1,232 pounds, owing to the weight of the batteries.
On August 9, 1884, as officials from the War Ministry watched, they took off from Meudon, a suburb in southwestern Paris. Unfortunately, they didn’t have enough hydrogen on hand, so Renard had had to remove half the batteries to lift off, but that helpfully improved the weight-to-power ratio. Ultimately, La France would triumph in an extraordinary feat that marked the very first time in history an aircraft made a sustained, controlled, powered round trip.
Against a light breeze of 3.3 mph, the airship embarked on a twenty-three-minute voyage of 4.25 miles and returned safely to its origin. Though speed dropped drastically during the turning maneuver at the halfway point, its average speed was 12 mph. A triumph!
The only problem was that meteorologists had lately decided that 15 mph was the “average of the rate of air currents in which even in a calm day a balloon floats.” They had recently found that wind speeds at ground level differ significantly from those at higher altitudes. Records taken for a 101-day period between June and October 1889 at the top of the Eiffel Tower (984 feet) found that the average daily velocity was 15.75 mph, whereas on the ground in the same location, it averaged a mere 4.9 mph. Until this discovery, any number of aeronauts had unwittingly made the error of building their craft to cope with ground-level winds.
Had the wind blown harder on that atypically calm August day, in other words, La France would have been pushed backward. Even on subsequent flights, with the full complement of batteries, La France never traveled faster than 14.5 mph—lower than the wind-speed benchmark—and merely holding the dirigible steady taxed the electric motor so heavily that the batteries drained in less than an hour.
The result was that, as one journal summarized, a genuine “solution of the problem of aerial navigation” would only be within sight when a balloon could “be propelled for some time at a rate of at least fifteen miles per hour.” The bar had been raised against an already faltering contender.
Renard pointed out that electric power was in its infancy and would surely mature over coming years, just as steam technology had. “We are now masters of the air balloon,” he declared, and “the entire matter [aerial navigation] is now only a question of time and money.” Sadly, he was granted neither by the army, and the airship program was killed, cited as a waste of both.5
BEFORE HIS FORCED retirement, Zeppelin had read of La France with great interest—and mounting alarm at the resurrection of France’s military ambitions—and it was during that period that he was prompted to write his 1887 memorandum “The Necessity of Dirigible Balloons.”
In 1890, back in his study in forced retirement, Zeppelin reread that memorandum and turned over in his mind what he had learned of the previous century’s attempts at aerial navigation. First, based on Meusnier’s experiments, it was clear that any successful airship would have to be cigar-shaped and filled with gas cells. Second, as Brunel had proven, it would have to be massive to benefit from the “cubed carrying capacity” principle and the associated economies of scale. Third, Giffard had shown that hydrogen, owing to its impressive lifting ability, must be the gas, and that structural lightness was critical. And fourth, as Renard and Krebs—and everyone else—had unpleasantly discovered, steam engines and electric motors alike were both underpowered and overweight for their assigned task of propelling an air vehicle into the wind.
He had the clues, he had the evidence, and now it was up to him and him alone to solve the mystery of aerial navigation.