Otto Lilienthal
(1848–1896)
You know the story: at about 10:35 on the morning of December 17, 1903, at Kill Devil Hills in Kitty Hawk, North Carolina, Orville Wright made the first sustained powered flight in an aircraft heavier than air. The flight was in part the product of two events, one that took place in 1878 and the other in 1896. The first was the day Milton Wright, father of Wilbur and Orville, gave the boys a gift he believed was educational. It was a toy helicopter designed by an early French aeronautical experimenter named Alphonse Pénaud. In 1912, during testimony in one of many patent suits he and his brother initiated, Orville described the toy as “actuated by a rubber spring which would [drive a four-bladed rotor and] lift itself into the air.” Orville went on to say that “Our interest [in flight] began when we were children,” when “Father brought home to us [this] small toy.” In fact, the brothers were inspired to build “a number of copies of this toy, which flew successfully,” but when they “undertook to build the toy on a much larger scale, . . . it failed to work so well.”
They wanted to make a helicopter sufficiently large and powerful to enable them to fly. They could not do this, and yet they never forgot their dream of flight. Beginning in 1890, the pair avidly followed reports in the fledgling aviation press about the work of Otto Lilienthal, a German experimenter with gliders. Then, in 1896, they read that Lilienthal had been killed on August 10 as a result of injuries sustained when one of his gliders crashed.
“The brief notice of his death,” Wilbur later recalled in an essay titled “Some Aeronautical Experiments,” reawakened “a passive interest which had existed from my childhood.” Otto Lilienthal—and, in particular, the failure that caused his death—disrupted the lives of two bicycle shop owners in Dayton, Ohio: from 1896 on, Wilbur and Orville Wright could hardly think of anything other than manned flight.
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Otto Lilienthal was born on May 23, 1848, in Anklam, Prussia. His father, Carl Gustav, was a merchant, but neither Otto nor his brother Gustav had much interest in pursuing a mercantile life. They attended a grammar school associated with their parents’ church, St. Nikolai, where a schoolmaster’s lessons included material covering the flight of birds. The boys were fascinated. If birds could fly, why couldn’t they?
Together, the brothers fashioned a pair of strap-on wings. When these, naturally, failed, Gustav lost interest in the project of manned flight, but Otto did not. After completing grammar school, he enrolled in a Prussian regional technical school at Potsdam. After completing the two-year course of study, he was hired by an industrial firm, which gave him on-the-job training as a design engineer. The experience left him wanting even more, and he soon enrolled at the Royal Technical Academy in Berlin.
In 1867, Lilienthal began systematically conducting experiments dealing with what he called “the force of air.” These were interrupted when he was commissioned as an engineer in the Prussian Army during the Franco-Prussian War (1870–1871). After his release from the army, he found employment with a succession of engineering companies. He designed and patented a mining machine in 1871, and in 1876 started his own company, making boilers and steam engines. He quickly grew prosperous, and in 1878 he married Agnes Fischer, a young woman with whom he shared a passion for music. She was a gifted amateur pianist and singer, he a French-hornist with a pleasant tenor voice. They married and made their home in Berlin, where they raised a family of four children.
While he continued to develop his engineering company, Lilienthal made a systematic study of bird flight, which he embodied in an 1889 book titled Der Vogelflug als Grundlage der Fliegekunst (Bird Flight as the Basis of Aviation). He studied most closely the flight of storks, creating polar diagrams, which plotted the sink rate of the bird against its horizontal speed. Using these diagrams, he analyzed the aerodynamics of the bird’s wings, and then, beginning in 1891, he started emulating the structure of these wings in manned gliders. His first glider version was called the Derwitzer (after the nearby village of Derwitz), which he flew from an artificial hill he built near Berlin. Later glider iterations were flown from artificial as well as various natural hills—most of the latter in the Rhinow region.
Lilienthal was obsessive in his work, making more than 2,000 manned flights and meticulously recording and evaluating the results. He tirelessly experimented, struggling to achieve better, more sustained, and, above all, more controlled flights. At first, he managed to make jumps and flights as long as eighty-two feet. He typically worked with a photographer to capture each flight for later study. He discovered that he could take advantage of the updraft of a 10 meter-per-second wind against a hill, which was sufficient to hold the glider stationary, so that he could shout to his photographer to find the best position for the photograph.
His brother Gustav rejoined him for many of his experiments, as Otto refined the design of the glider’s wings and patented various features of his aircraft, which were, in fact, early forms of hang gliders. Lilienthal built twelve distinct monoplane glider designs in addition to some wing-flapping aircraft and two biplane gliders. Control of flight was achieved by changing the center of gravity simply by the pilot shifting his body, as in today’s hang gliders. Control and stability, however, remained problematic. The gliders were airworthy, but difficult to maneuver. Lilienthal introduced various design features aimed at increasing stability and control, but his success was always limited. He envisioned creating an engine-powered aircraft—in which the engine would flap the wings in the manner of a bird.
By 1892, Lilienthal was flying from a hilly area called Maihöhe, in Steglitz, near Berlin. On this hilly ridge, he built a shed thirteen feet high, the top of which served as a jumping-off platform. The following year, he made use of a higher set of hills, called the Rhinower Berge, and, in 1896, the Gollenberg, which was close to the village of Stölln. He also built an artificial hill near his house in Lichterfelde, which he called Fliegeberg (“Flight Hill”). Perfectly conical, 49 feet high, with a flat top, Fliegeberg allowed him to launch his gliders into the wind, whatever its direction.
Lilienthal’s experiments always drew a fascinated crowd of spectators, and reports of his work spread far beyond Germany—certainly reaching the Wright brothers. Visitors included many luminaries of the early days of manned flight, among them Samuel Pierpont Langley from the United States, Nikolai Zhukovsky from Russia, Percy Pilcher from England, and the Austrian Wilhelm Kress. Zhukovsky called Lilienthal’s gliders the most important inventions in aviation.
On August 9, 1896, Lilienthal flew, as he often did, from the Rhinow Hills. One of his first three flights was a new record for him—or for any other attempt at heavier-than-air flight—820 feet. It was during the fourth flight, however, that Lilienthal’s craft suddenly pitched forward. This was an aerodynamic weakness of his gliders, and one that was difficult to correct using the body-shifting technique. Lilienthal worked to shift his weight, but could not correct the dive. He and his machine plummeted some fifty feet to the ground.
At first, he did not seem badly injured, but his mechanic, Paul Beylich, laid him down in a horse-drawn carriage and drove him to Stölln, where a physician examined him. He diagnosed a fracture of the third cervical vertebra. Shortly after this determination, Lilienthal lost consciousness and was transported by train to Lehrter station in Berlin. The next morning, he was carried to the clinic of Dr. Ernst von Bergmann, an eminent surgeon. It was, however, too late. Some thirty-six hours after the crash, Lilienthal, who drifted in and out of consciousness, uttered to his brother Gustav his last words, “Opfer müssen gebracht werden!—Sacrifices must be made!”
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The death of Otto Lilienthal made a powerful impression on the Wrights of Dayton, Ohio. Wilbur understood that, flying as he did in this hang glider, with his only means of control the shifting weight of his body, Lilienthal had been, sooner or later, doomed. He pronounced the aviator’s “apparatus” for achieving equilibrium in flight “inadequate.”
Importantly, Wilbur Wright did not base his conclusion solely on “the fact that [the glider eventually] failed,” but on his own firsthand observations of bird flight. These had convinced him “that birds use more positive and energetic methods of regaining equilibrium than that of shifting the center of gravity.” They achieved control and maintained equilibrium not by merely shifting their body weight, Wilbur reasoned, but by turning the leading edge of one wingtip up and the other down.
This was the disruptive revelation of Lilienthal’s death: control was everything. Lilienthal died because he failed to achieve sufficient control. Wilbur believed he had a way to achieve it. Control would make all the difference—if, if he and his brother could devise a way to imitate in an artificial wing the opposed twisting of the leading edges of birds’ wings.
Wilbur was working in the Wright Cycle Shop one July afternoon in 1899 when the rectangular cardboard box in which an inner tube had been packed caught his eye. The end tabs of the box had been ripped off. He reached out, picked up the empty box, and twisted it in his hands. It hit him: design a wing that could be twisted in a controlled fashion. The design and method the Wrights came up with would be called “wing warping,” and although it would later be replaced (through the work of other aviation pioneers) with flaplike panels called ailerons, it worked. Lilienthal’s death revealed to the Wrights that the single most important aspect of manned flight was not power or even the shape of the wing: it was control. Now, thanks to Lilienthal’s insights, data, designs, and ultimate failure, the boys from Dayton had it. The German had been correct: sacrifices had to be made.