Lilienthal – The "Flying Man"

The German engineer Otto Lilienthal was the first man to launch himself into the air, fly, and land safely. He also was an important source of inspiration and information for the Wright brothers in the next decade.

Otto Lilienthal.

Lilienthal was born in Pomerania, Germany in 1848. Even as a teenager, he was interested in flight, and with his brother Gustav, in 1867 built a frail contraption of thin birch veneer. They intended to strap themselves to the pair of 6-1/2-foot (two-meter) wings, run down a hill while flapping their arms, and take off into the air. Their experiment was unsuccessful, but they persevered and built two more winged vehicles. These failed too, but Otto remained committed to the idea of human flight. He studied at Potsdam and Berlin and received a degree in mechanical engineering from Berlin University in 1870. After an interruption to serve in the Franco-Prussian War of 1870-71, he continued with his aeronautical pursuits.

After the war, Gustav became an architect and left Otto to open his own factory in Berlin to manufacture boilers and steam engines. Otto resisted the urge to plunge ahead with building flying machines, even though the pull was strong. He first devoted himself to studying the principles of aerodynamics and analyzed how birds flew before he attempted to apply those principles to a structure.

After experimenting with ornithopters, in 1889 he published a book on the flight of birds that outlined his theories and which became one of the classics of aviation. In Der Vogelflug als Grundlage der Fliegekunst (Bird Flight as the Basis of Aviation), he examined in detail the types and structure of bird wings, the method and aerodynamics of bird flight, and the application of the data he gatheredùespecially that dealing with wing area and liftùto the problem of human flight. He described how birds propelled themselves by the twisting, or airscrew, action of their outer primary feathers. Lilienthal tabulated the amount of air resistance offered to a bird's wing with various degrees of camber and determined that the curve was necessary to flight because it offered more resistance than a flat surface.

He built his first glider in 1891. Before his death in 1896, he had built eighteen models—fifteen monoplanes and three biplanes. á He had also taken more than 2,000 glider flights.

Lilienthal's "Normal" Glider, 1895.

Lilienthal biplane glider in flight, 1895. Shows structure of the glider with the double sailing surface.

Lilienthal's first glider, the 1891 Derwitzer Glider, was constructed of rods of peeled willow covered by highly stretched strong cotton fabric. He used a springboard in his gardenùat first at a height of a little over three feet (one meter), then gradually increasing to 8.2 feet (2.5 meters)ùto launch himself into the air. His first flights took him only a few feet but gradually the distance lengthened until he could glide almost 80 feet (24 meters). The glider originally had a wingspan of 25 feet (7.6 meters).á During the course of the experiments, he reduced its span to 18 feet (5.5 feet). As in all his gliders, he controlled the glider's direction by shifting his weightùa task that required considerable strength.

In 1892, he constructed a more sophisticated glider with fabric that covered both sides of the wings. This glider had a wingspan of 31 feet (9.4 meters). He could fly it up to a distance of 270 feet (82.3 meters).á

 

Lilienthal's Sturmfugel, 1894.

Lilienthal's "Jumping Off" place from the front.

Lilienthal realized he needed more flying space. In 1894, he built an artificial hill topped with an earth-covered shed for storing his machines. He would run down his hill and leap into the face of the wind, reportedly gliding more than 150 feet (45.7 meters). He could also launch himself from the top of the 13-foot (4-meter) shed.á

Lilienthal's gliding experiments, 1892.

From there, he progressed to his Maih÷he-Rhinow-Glider. He called this a ôconvertible flight apparatus,ö and Lilienthal received a patent for its design. It had a bat-like construction and when collapsed, measured 6.6 x 10.5 x 1.6 feet (2 x 3.2 x 0.5 meters). He could change the wing profile by inserting different ribs.

Lilienthal needed still more space for his experiments as well as a location with height and strong, steady winds. He began flying in the Rhinower Hills, about six miles northwest of Berlin. Launching himself from the hillside, he glided up to 1,150 feet (350 meters).á

Lilienthal glides from the top of his hill.

Like several others before him, Lilienthal never quite abandoned the idea that flapping wings was the key to motion. In 1893 and again in 1896, he built gliders with flapping wings in the ornithopter fashion. Each machine had a lightweight carbonic acid engine that produced about two horsepower (1.5 kilowatts). The engine was supposed to make the wing tips flap up and down and move the aircraft forward. Neither model was successful.á

Otto Lilienthal's 1893 glider.

From 1894 until his death in 1896, Lilienthal constructed his ôstandardö glider. These monoplanes were highly successful, and he sold or gave several of them to clients. They had cambered wings with radiating ribs that could be folded for transport and a fixed rear fin and tailplane that freely hinged upward. With these machines, Lilienthal could glide from 300 feet (91.4 meters) to more than 750 feet (228.6 meters). His design incorporated a prellbugel, or rebound bow. This was a flexible willow hoop fitted in front of the pilot that would reduce the impact in case of a crash. The apparatus saved Lilienthal's life during one flight when the glider stalled and nose-dived toward the earth from more than 60 feet (18.3 meters) above ground.

Lilienthal's "jumping off" place.

Lilienthal continued testing and enhancing his standard glider. In 1895, he tested unsuccessfully a leading-edge flap device that was intended to counteract air pressure on the cambered upper surfaces of the wings as well as steering air-brakes and a form of wing-warping. At the time of his death, he was developing a body-harness elevator control to supplement his body movements. He became a skilled pilot and could ride the wind and handle his craft skillfully. During this time, he also was visited by several aerodynamic experts, including Samuel Langley, secretary of the Smithsonian Institution in Washington, D.C., and N.J. Shukowsky, an aerodynamics expert from Moscow.

However, Lilienthal's gliders had one major fault. They had no means of control other than the motions of the pilot who had to contort himself and exercise considerable strength to affect the direction and stability of the glider. To fly the glider, Lilienthal had to crawl under the craft, position his arms in a set of cuffs, grasp a bar near the front edge of the wings, and run down a slope. Once aloft, his legs dangled below him. His only way to balance the craft was to shift his weight. He moved the lower half of his body in the direction he wished to go, which changed the center of gravity. By shifting his weight, he reacted to the movement of the glider rather than directing it.

Lilienthal shifts his body to move the glider to the right.

Shows how Lilienthal changed the center of gravity and particularly the position of his legs to the left in order to press down the left wing. From "Practical Experiments for the Development of Human Flight."

 

On August 9, 1896, the glider he was piloting stalled and went into a nosedive.á It had no prellbugel to protect him, and he died the next day of a broken spine. His last words were ôSacrifices must be made.ö

Lilienthal piloting his 1896 glider.

Lilienthal soars through the air.

 

Although his designs had flaws, Lilienthal had an immense influence on aviation. His writings were translated and distributed worldwide, and the photographs that documented his flights visually proved that a human could launch himself into the air and stay aloft.á He demonstrated the importance of identifying the principles that governed an experiment before proceeding, and his meticulous documentation of his research provided guidance for those that came after him.

References:

Crouch, Tom P. Dream of Wings:á Americans and the Airplane, 1875-1905. New York: W.W. Norton, 1981; reprint ed., Washington, D.C.: Smithsonian Institution Press, 1988.

Moolman, Valerie and the editors of Time-Life Books. The Road to Kitty Hawk. Alexandria, Virginia: Time-Life, 1980.

Scott, Phil. The Shoulders of Giants: A History of Human Flight to 1919. Reading, Mass.: Addison-Wesley Publishing Company, 1995.

On-Line References:

Lilienthal, Otto. Der Vogelflug als Grundlage der Fliegekunst (Bird Flight as the Basis of Aviation. English edition (translated from the 2nd edition). New York, 1911. The second edition was published in 1910 with an additional chapter by Gustav Lilienthal http://home.t-online.de/home/LilienthalMuseum/e6.htm

Lilienthal, Otto. Practical Experiments for the Development of Human Flight. In James Means' The Aeronautical Annual, 1896. http://hawaii.psychology.msstate.edu/LilienthalMuseum/library/Lilienthal_Practical_Exp.html

Lilienthal, Otto. The Carrying Capacity of Arched Surfaces in Sailing Flight. http://hawaii.psychology.msstate.edu/LilienthalMuseum/library/Lilienthal_Flying.html