Otto Lilienthal (1848-1896)

Otto Lilienthal is credited with having established experimental the foundations of flight and aerodynamics. He attempted at least 2000 flights that kept him airborne for a total of several km. The longest flight was about 250 m down a launch base on top of a purpose-built hill. His best machines had an aerodynamic efficiency L/D estimated at about 8.

Lilienthal took off for the first time in the summer of 1891 with an “aircraft” (more properly a glider) having a wing span of 7.5 metres and a wing area of just 15 square metres.

Over the next five years he attempted to fly nearly every day. He took off from his hilltop at Stolln, south of Berlin, before crashing to death in 1896. Wilbur Wright wrote in 1912 that “no one else grasped the basics of human flight as clearly and throughly as he did”. The Frenchman Ferdinand Ferber wrote that his studies were “from step to jump, from jump to flight”.

Lilienthal was the first to understand the virtues of the curved wing. He realized that a plate appropriately bent was able to produce more lifting force. During his meticolous investigations he understood that taking off was not as difficult as controlling his flight. Soon he realized that he also needed lateral stabilization, which could be achieved by adding a vertical rudder.

Besides the rudder, he is the inventor of the airfield, having built a 15 metre high Flying Hill (Fliegeberg) at Berlin-Lichtenfelde (1894), after trials at several different locations convinced him that he needed to work more systematically. In summary, his work resulted in

• Definition of the drag polar
• Means for stabilization of flight (rudder)
• Invention of the cambered airfoil

Lilienthal’s theoretical work was summarized in his book “The Flight of Birds as a Model for the Art of Aviation” (Der Vogelflug als Grundlage der Fliegekunst, 1890). This book was the most important scientific publication on flight to appear at the end of the 19th century. In the meantime the media turned him into a hero. Newspapers around the world called him “The Flying Man” or “The Winged Prussian”.

A much credited view of manned flight was:

To design one is nothing,
To build one is easy,
To fly one is everything.

• Lilienthal O. Bird Flight as the Basis of Aviation, Longmans and Green, London, 1911 (translation of the original Der Fogelflug als Fliegelage der Fliegekunst, Gaertners, Berlin, 1899.)

• Anderson JD. A Hystory of Aerodynamics,
  Cambridge Aerospace Series No. 8, Cambridge University Press, 1997

• Gibbs-Smith CH. The Rebirth of European Aviation, 1902-1908: A Study of the Wright Brothers’ Influence, Her Majesty’s Stationary Office, London 1974.