Measurement of flexural and torsional stiffnesses in penguin wings

Abstract

Penguins are propelled through the water by flapping their wings. During swimming, wing flapping causes bending deformation of the wings. The cross section of the wing forms a thick wing shape, and the wing skeleton consists of a humerus, a forearm, a manus, and digits. Previous anatomical studies have shown that penguin wings are mobile in the wing plane at each joint. However, the range of motion and stiffness of bending outside the wing plane have not been investigated. Furthermore, the range of motion and stiffness with respect to torsion is unknown. In this study, we measured the static flexural and torsional stiffness of wings collected from a gentoo penguin (Pygoscelis papua) cadaver. As a result, we found asymmetries in flexural stiffness with respect to the bending direction and torsional stiffness with respect to the torsional direction. Furthermore, assuming that each joint of the penguin wing is a torsional spring and the other parts are rigid, the spring stiffness of each joint during bending and torsional deformation was measured. The results showed that the asymmetry of wing flexural stiffness was strongly influenced by the wrist joint and the asymmetry of wing torsional stiffness was strongly influenced by the elbow joint.