On the role of the alula in the steady flight of birds

Full article

Published:

Volume 48(2), December 2001. Pages 161-173.

Language:

English

Keywords:

Alula, high lift devices, steady flight, wing load

Abstract:

The alula is a high lift device located at the leading edge of the birds wings that allows these animals to fly at larger angles of attack and lower speeds without wing stalling. The influence of the alula in the wing aerodynamics is similar, to some extent, to that of leading edge slats in aircraft wings, which are only operative during take-off and landing operations. In this paper, representative parameters of the wing geometry including alula position and size of forty species of birds, are reported. The analysis of the reported data reveals that both alula size and position depend on the aerodynamic characteristics (wing load and aspect ratio) of the wing. In addition, aiming to clarify if the alula is deflected voluntarily by birds or if the deflection is caused by pressure forces, basic experimental results on the influence of the wing aerodynamics on the mechanism of alula deflection at low velocities are presented. Experimental results seem to indicate that the alula is deflected by pressure forces and not voluntarily.