Another pair of aviators that made substantial contributions to the field were Otto and Gustav Lilienthal. Probably the greatest contribution that the Lilienthals made was that they attempted to record scientific data about their gliders and how they worked. Otto published this information in his 1889 book entitled "Der Vogelflug als Grundlage der Fliegekunst" (Bird Flight as the Basis of Aviation). The Lilienthals worked with gliders and made more than 2000 glides from 1891 to 1896. The Lilianthals are considered to be the first aviators in history to achieve safe, repeatable glides. Nevertheless, Otto was killed in a crash that broke his back in 1896.
Photo shows the Lilienthal glider in flight.
Library of Congress. Prints and Photographs Division. Washington, D.C.