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Otto Lilienthals large biplane glider („Großer Doppeldecker“) was designed and built in 1895 as an advanced stage of the ‚Normalsegelapparat’- a monoplane glider invented by Otto Lilienthal. The „Normalsegelapparat, patented in 1893 (US patent from 1895), was the first production aircraft in history. Like its preceding model, the large biplane is a hang glider, which is controlled through weight shifts by the pilot as hang gliders are to this day.

Development

The objective of the biplane was to increase the wing surface of the the monoplane „Normalsegelapparat“ without increasing the wingspan. This would have made controlling the aircraft more difficult as the pilot only had limited range to shift his or her weight in the cockpit. Lilienthal had already upgraded one of his smaller monoplane models - the ‚Sturmflügelmodell‘ - to a smaller biplane that same year. While building the large biplane he made use of this experience. It was one of the many aircraft designs only flown by Lilienthal himself. Countless flights with both biplanes have been photographically documented. Lilienthal flew both gliders from his personal flying hill in Lichterfelde (Berlin). In 1896 he flew the large biplane at the ‚Gollenberg‘ near Stölln in Havelland. These two gliders are the first successful man carrying biplanes in history.

Construction Details

The lower deck is the exact same size as the one used in Lilienthal’s patented monoplane glider. The upper deck is not, like the lower one, completely foldable, but folds in the middle. Thus the glider is easily reduced to a transportable width of a little more than two meters. Besides the intent to increase lift, the upper deck also changes the flight mechanical properties in comparison to the monoplane. The aerodynamic center is higher and therefore increases flight stability, but reduces lateral control authority. Lilienthal’s goal was to eventually use stronger winds to achieve long-lasting (gliding) flights.

Technical Data

wing span: 6,7 m

weight: 25 kg

maximal flight distance (reached by Lilienthal): 250 m

gliding ratio: 1:4

Reconstruction

The original large biplane glider did not survive. However, there are several exemplars of the original monoplane that the biplane was based on. Reconstructions exist in several museums. The reconstruction of a large biplane used for flight testing was possible by means of the patent drawings of the monoplane glider and many detailed photographs of both, the monoplane and the biplane.

Studies concerning flight stability and operability, as well as test flights have been conducted by Prof. Markus Raffel from the German Aerospace Center (DLR) in 2019. The studies were a continuation of the aerodynamic and flight mechanical examinations conducted by the DLR-Institute of Aerodynamics and Flow Technology in 2016.

Literature

• Octave Chanute: Progress in Flying Machines, 1894, reprint 1997
• Stephan Nitsch: Vom Sprung zum Flug, Berlin 1991

Weblinks

• The Aeroplane Models of Lilienthal Otto Lilienthal Museum, 2016
• Lilienthal's last flight Otto Lilienthal Museum, 2016
• Remembering the Wright Brothers and Otto Lilienthal The Outer Banks Voice, 2019
• Otto Lilienthal’s Glider to Fly in North Carolina’s Outer Banks State Aviation Journal, 2019
• DLR tests confirm Otto Lilienthal as the first ancestor of all aviators German Aerospace Center, 2016
• The biplanes constructed by Lilienthal and the Wright brothers fly together for the first time German Aerospace Center, 2019
• How to Safely Fly the Otto Lilienthal Glider The United States Hang Gliding and Paragliding Association, 2018 (USHPA Pilot Volume 48/Issue 8)