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Avian flight wing and feather asymmetries (free pdf)

From: Ben Creisler

A new online paper. The pdf is free.

Hans Försching and Holger Hennings (2012)
Aeroelastic mysteries in avian flight.
CEAS Aeronautical Journal (advance online publication)
DOI: 10.1007/s13272-012-0048-6

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.