With the design and construction of his first working glider, Otto Lilienthal (1848-1896) bestowed a sense of viability and respectability on the young science of aviation. Lilienthal flew thousands of flights on gliders he designed based on careful observations of birds. His work directly inspired Orville and Wilbur Wright.

During the early days of the Industrial Revolution, notions of human flight were ridiculed. Yet Prussian design engineer Otto Lilienthal disregarded the social stigma associated with flying machine inventors and applied himself in earnest to the study of aerodynamic forces and design concepts. His hope was to further the quest to achieve manned flight. During his lifetime he accumulated 20 patents for his machine designs, including four for aviation devices.

His first crude aviation design was a simple pair of wings with which he attempted to gain altitude by jumping from a board. Eventually, Lilienthal achieved flight distances as high as 1,150 feet (350.75 meters) with his more sophisticated gliders. His efforts won international attention, and experts worldwide consulted him for assistance.

Lilienthal died tragically from injuries sustained in one of his flight experiments. Among his notes, lectures, and other writings he left information that proved invaluable to subsequent aircraft designers, including Wilbur and Orville Wright.

A Tireless Engineer

Otto Lilienthal was born in Anklam, Prussia, on May 23, 1848. Together with his brother Gustav, Lilienthal developed an interest in flying. At any early age, the two boys began to observe the movements of birds to try to understand the mechanisms of flight. In elementary school, Lilienthal's curriculum included bird studies. From 1864 to 1866, Lilienthal studied mechanics at the Regional Technical School in Potsdam.

Lilienthal became a professional design engineer, but aerospace studies remained a hobby and a passion. He spent a year in an on-the-job training program at the Berlin Trade School, then three years at the Royal Technical Academy in Berlin. While still an engineering student in 1867, Lilienthal began to experiment with aerodynamics and human flight. The results of his early experiments, which he later published, proved helpful to others who yearned to fly, even after Lilienthal's death.

As the Franco-Prussian War raged, Lilienthal interrupted his studies and his career in 1870 and enlisted to serve for one year in the Prussian military. He took part in the siege of Paris and got his discharge from the military in 1871. After his military service he was employed as a mechanical engineer at the Weber Company in Berlin. In 1872 he also joined the C. Hoppe machine factory in Berlin as a construction engineer. Lilienthal remained with both companies until 1880. Seemingly indefatigable, he founded a boiler factory the following year, based on machines of his own design. There he manufactured pulleys, sirens, and other apparatuses in addition to boilers. He pioneered a profit-sharing program for his factory workers in 1890.

Lilienthal married Agnes Fischer in 1878, and they had four children. The eldest, Otto Jr., was born in 1879. Even in fatherhood, Lilienthal's creative bent for invention surfaced, when he invented a set of stone building blocks, called Anker-Steinbaukasten, for his children.

Early Flight Experiments

Lilienthal subscribed to glider-based theories of flight, so he focused his attention on the shape of the wings in developing his designs for flying machines. His early experiments in 1874 with the forces of air involved kites and other apparatuses of his own design.

In their zeal for flying, Lilienthal and his brother joined the Aeronautical Society of Great Britain in 1873, while bemoaning the lack of such an organization in their native Germany. Lilienthal first lectured at the Aeronautical Society on his observations and theories about bird flight as the basis of aviation. He went on to lecture frequently to that group and many other audiences. After waiting for more than a decade for a German aviation society to form, he was gratified in 1886 to join a Berlin-based navigation group, Deutscher Verein zur Forderung der Luftschiffahrt (German Club for Promotion of Airship Navigation). In 1888 and 1889, Lilienthal gave a series of three lectures entitled "The Energy Involved in Bird Flight." On June 2, 1890, he lectured on "The Flight of Birds and Humans through the Warmth of the Sun" to a Prussian business society.

After eight years of maneuvering his aircraft designs through thin air, in 1889 he published a volume containing the data that he had accumulated. Lilienthal called his book The Carrying Capacity of Arched Surfaces in Sailing Flight. In it he reported and charted his preliminary findings. That same year he published a manual, Bird Flight as a Basis of Aviation, with details of the physics of flight. The book on bird flight was translated into English in 1911. Among his observations he included his own illustrations of birds.

Strides on Flight Mountain

In 1890, for the first time Lilienthal began to experiment with human passengers in his flying machines. In 1891, with the help of his brother, Lilienthal built his first working glider and tested it at Derwitz/Krilow. After some preliminary hops and jumps, Lilienthal made some design adjustments and shortened the wing span. The aircraft, which was essentially a hang glider, sustained a flight of approximately 80 feet (24.4 meters).

In 1892 an improved and redesigned Lilienthal glider achieved still greater distance. He next built a hill that he called Fliegeberg (flight mountain) at Lichterfelde in 1893. Lilienthal used the extended mound as a launch pad for his test flights. At times his glides from Fliegeberg surpassed 150 feet (45.75 meters). That same year he devised his first motor-driven apparatus with flapping wings.

Lilienthal modeled his flying craft after birds and butterflies and constructed the prototypes from wax, cloth, wire, and willow rods. A typical Lilienthal glider design was comprised of 140 square feet (13 square meters) of mono-wing surface. Through his studies of birds, he became intent on replicating the flight motions of the seagull, because of its extremely broad wing strokes and its ability to sail on the sea breeze. Also intriguing to Lilienthal was the stork. He said that it "seems to have been created for the purpose of serving as a model for human flight."

Lilienthal's popular "no. 11" model, the most often reproduced of his designs, went into serial production in 1894. As many as eight of these so-called "normal soaring apparatuses" were built. He gave some of his planes as gifts to clients and sold others. Lilienthal recorded with meticulous precision his activities and experiments with manned flight, including many photographs in his documentation.

Lilienthal's goal in his experiments was to comprehend the forces and motions involved in flight. He not only could fly but also could recreate his flights repeatedly with the same apparatus. This display of control was a clear indication that he was not just falling from the air but actually guiding the movement of the aircraft. Lilienthal flew more than 2,500 flights and achieved a maximum flight distance of approximately 1,150 feet (350.75 meters). He designed 18 different gliders, including 15 monoplanes and three biplanes. All were controlled by weight distribution of the passenger. By 1896, the Lilienthal brothers had built a motorized biplane with adjustable wing tips, powered by carbonic acid.

From 1890 through 1895, Lilienthal contributed a number of articles to the journal Prometheus, including book reviews and reports. His magazine articles included his practical experiences in soaring and discussed known impediments to successful flying. In 1895, foreign dignitaries intrigued by his aviation projects visited him. Among them were J. Shukowski, a Muscovite aviation expert, and S. P. Langley, a representative of the Smithsonian Institute in Washington, D.C.

In 1896, Lilienthal lectured at the Trade Exhibition in Berlin on June 16; it was his last known lecture. On August 10, 1896, he died in a Berlin hospital from injuries following a crash from an altitude of 50 feet (15.2 meters) on the previous day. The accident occurred when a heat eddy blew him off balance. His glider stalled when he attempted a recovery effort, and the resulting impact from the fall caused a fracture to his spine.

From Jump to Flight

At the time of his death, Lilienthal had begun to explore the issues of wing stroke. His belief that learning to glide was the natural forerunner to learning to fly was embodied in the opening paragraph of his article "Our Teachers in Sailing Flight," published in Prometheus. He wrote: "All perplexities concerning light motors, and speculations on the amount of power required for flying, are relegated to the background by the fact that the power of the wind alone is sufficient to effect any kind of independent flight [as seen by] those magnificent models in flying, those large and heavy birds."

Lilienthal's notion "from jump to flight" is widely regarded as the inspiration for aviation pioneers Orville and Wilbur Wright. In an article in Century in September 1908, the Wright Brothers wrote: "It was not until the news of the sad death of Lilienthal reached America in the summer of 1896 that we gave more than passing attention to the subject of flying. We then studied several pamphlets published by the Smithsonian Institute, especially articles by Lilienthal " The Wrights said that the wing surface shape of their 1901 machine was modeled after a Lilienthal design.

Throughout his experiments and his writings, Lilienthal upheld that flight was not to be realized suddenly by the invention of one single machine. He fostered the notion that a long process of study, and a thorough examination of the axioms of aerodynamics, was imperative to the successful invention of a progressive series of viable flying machines, with each machine proving more capable than its predecessor.

Two of Lilienthal's original flying machines survived into the twenty-first century. One of his "no. 11" gliders is on exhibit at the National Space and Air Museum at the Smithsonian Institute. Another of his planes, a "little biplane," also survived. Lilienthal's first flying apparatus, however, was lost; only replicas remain. In the 1980s, the Otto Lilienthal Museum in his hometown of Anklam opened in honor of the 100th anniversary of his first flights.

Further Reading

• Lilienthal, Otto, Bird Flight as a Basis of Aviation, New York, 1911.
• Century, September 1908.
• "Otto Lilienthal's Aeronautical Bibliography," Archives Otto-Lilienthal-Museum Anklam, http://home.t-online.de/home/LilienthalMuseum/e4.htm (February 22, 2001).