Experimental Investigation of Flow About Wing of Robot Bird

Abstract

Bird-like flapping wing robots can be used for different applications, including chasing off birds at airports or surveillance of crowds. A first step towards the understanding of flapping wing flight of birds is the wind tunnel testing of a model bird with fixed, rigid wings. Inspired by an existing, flying, flapping wing robot falcon, designed and manu- factured by Robert Musters, a half span model bird has been designed and manufactured. Lift force and drag force have been obtained in a wind tunnel, using a three-component balance, as function of angle of attack and Reynolds numbers from Re = 0.53×10 5 to Re = 1.57×10 5 . The flow at the surface of the wing is visualized with tufts to investigate stall characteristics as function of the Reynolds number. Results from the flow visualization and the force measurements match very well. A remarkable result is a high slope of the lift curve of the model. Using results of XFOIL, the high lift slope can be explained by the occurrence of a laminar separation bubble on the lower surface of the wing. Furthermore, the maximum lift coefficient, stall angle of attack, minimum drag coefficient and maximum lift-to-drag ratio are reported and discussed. The analysis of the results of the (wind tunnel) model provides insights into the aerodynamics of a fixed, rigid wing robot falcon. I. Introduction In the past decade different robotic flying machines have been developed for a wide variety of purposes. Many designs are based on natural birds or insects, this includes robotic birds with flapping wings (11). These robot birds can be used for different applications, e.g. surveillance of crowds or chasing of birds at airports. Bird flight can be divided in two stages: flapping wing flight and soaring. The latter can divided in three subcate- gories: gliding flight, static soaring and dynamic soaring (17). Gliding flight is a flight, in which the glide path is at an angle with the horizon. Static soaring is accomplished by utilizing air masses with an upward vertical velocity component. Finally, dynamic soaring, is performed by using a gradient in the horizontal velocity of the surrounding air.