Aeroelastic mysteries in avian flight

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.