Flying Qualities of Otto Lilienthal's Large Biplane

Abstract

More than 125 years ago, the aviation pioneer Otto Lilienthal was the first person to invent, build, and publicly fly several aircraft. He received a United States patent for his monoplane glider [1] in 1895. Several copies of this Normal Soaring Apparatus were sold to customers in America and Europe. In the same year, he developed his designs further into two different biplane aircrafts, of which the Large Biplane (Großer Doppeldecker) showed the most promise. Lilienthal’s idea behind the transition from his monoplane design to the biplane depicted in Fig. 1 was to increase the wing surface without enlarging the wing span, as this would have made controlling the aircraft in roll more difficult. Countless flights with both biplanes have been photographically documented, making them the first successful, man-carrying biplanes in history. Lilienthal’s flight demonstrations and his theory of cambered wings, developed and published in his book [2], contributed to the epochal shift in the rapid development of aeronautics. Culick [3] also notes that he was the first aeronautical engineer to combine the accepted concepts of equilibrium and stability with his ideas of control in order to maintain equilibrium in the face of disturbances. Among other experts and flight enthusiasts, the American railroad engineer Octave Chanute corresponded with Lilienthal. According to Crouch [4], Chanute served as the focal point of the international community of aviation pioneers at the time by corresponding with leaders of the field such as Lilienthal and Langley. He supported the cause of aviation by spreading news, holding lectures, and establishing a baseline of shared knowledge through publications such as his classic book on flying machines [5]. In the period between 1894 and 1904, Chanute decided to begin his own experiments. By following Lilienthal’s approach of carefully performing increasingly advanced flight tests, he guided several young men, among them Augustus Herring, toward successful flight performances. He introduced bridge building techniques to the truss structures of his bi- and multiplanes to improve their structural integrity as shown in Fig. 1. In his experiments in 1896, this biplane flew as stable as Lilienthal’s biplane [6] with a larger wing span and improved structural rigidity. Chanute focused on maintaining equilibrium in flight by incorporating automatic stability in his designs, which led him to make first steps toward active controls.