Aeroelastic mysteries in avian flight
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ORIGINAL PAPER
Aeroelastic mysteries in avian flight Hans Fo¨rsching • Holger Hennings
Received: 19 March 2012 / Revised: 17 October 2012 / Accepted: 17 October 2012 / Published online: 2 November 2012 Ó Deutsches Zentrum fu¨r Luft- und Raumfahrt e.V. 2012
Abstract Avian flight is one of the remarkable achievements of vertebrate evolution. Thereby, the birds encountered, in principle, the same flight-technical problems and challenges as the human aircraft designers. From an aeronautical point of view, and with the knowledge and experience of modern aircraft design, the present study demonstrates that concealed aeroelastic effects and phenomena are also of basic importance in avian flight. Structural wing asymmetries play a fundamental role. First, as basis for the aeroelastic investigations, significant flight relevant anatomical and structural characteristics of the complex biotechnical architecture of avian wings are exposed. The further considerations are then focussed on two conspicuous asymmetric structural particularities of the wing, which contribute essentially to active flight ability of birds—an asymmetric positioning of the shaft in the vane of the primary flight feathers, and just so the eccentric location of the bony skeleton in the wing profile close to the leading edge. Ornithologists consider the asymmetry of the flight feathers as a diagnostic tool for aerial capability. However, this thesis still remains a topic of controversial debates. The study shows evidently that the magic structural wing asymmetries are imperative aeroelastic requirements for efficient flight, in particular to ensure structural strength and stability of the wing, as well as aerodynamic integrity. But these asymmetries are also fundamental to active aerodynamic generation of lift and thrust in wing flapping. H. Fo¨rsching (&) H. Hennings DLR Institute of Aeroelasticity, Bunsenstr. 10, 37073 Go¨ttingen, Germany e-mail: [email protected] H. Hennings e-mail: [email protected]
Keywords Avian flight Structural wing asymmetries Aeroelastic phenomena
1 Introduction The enigmatical flight of birds with their inimitable flight capabilities has at all times attracted our attention. Flying animals have populated the sky already since more than hundred million years. Here, the birds evolved in their long evolution, from dinosaurs to bipedal feathered flying reptiles, to perfect flight machines of nature [1]. They dominate in exemplary manner the fundamental requirements for an efficient flight—propulsion, aerodynamic lift, flight stability and control, and extreme lightweight construction. Thus, in the early pioneering time of aircraft design, birds were the pilot instructors of the Homo sapiens in his efforts to realise the ancient human dream to fly, finally with the aid of technical resources. Since centuries flight visionaries and scientists have tried to puzzle out the legendary mysteries of avian flight, in particular, after the discovery of a fossil flight feather of the urvogel Archaeopteryx (1860) [2]. Althoug
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