On the aerodynamics of leading-edge high-lift devices of avian wings

Abstract

The alula is a high-lift device located at the leading edge of bird wings that allows these animals to fly at large angles of attack and low speeds without wing stalling. The influence of the alula in the wing aerodynamics seems to be similar to that of leading-edge slats in aircraft wings. Aiming to clarify the role of the alula in the aerodynamics of the bird wings, the aerodynamic forces generated by a model simulating the wing of a pigeon equipped with different alulae were measured in a wind tunnel. Experimental results show that alula deflection causes the boundary layer to remain attached at large values of the angle of attack (at least in the wing area protected by this device: from the alula position to the wing root), so that lift forces can be up to 22 per cent higher than those measured at the same angle of attack without alula deflection.