Corresponding author: Mochammad Agoes Moelyadi E-mail: moelyadi1968@hotmail.com Journal of Bionic Engineering 7 (2010) 95–101 CFD Based Determination of Aerodynamic Effects on Birds with Extremely Large Dihedral Gottfried Sachs 1 , Mochammad Agoes Moelyadi 2 1. Institute of Flight Mechanics and Flight Control, Technische Universität München, 85748 Garching, Germany 2. Aeronautics and Astronautics Department, Bandung Institute of Technology, 40132 Bandung, Indonesia Abstract Using a sophisticated aerodynamic method, the effects of extremely large dihedral on the aerodynamic characteristics of birds are determined. With this method, it is possible to generate solutions for the addressed aerodynamic problem, which shows a high complexity due to interference effects caused by dihedral and pronounced 3-dimensional flow properties as well as due to complex wing geometries. From the obtained results it follows that extremely large dihedral has substantial effects on the aerodynamic force characteristics. There are significant changes in the lift, the drag and the side force, thus affecting the flight performance. Furthermore, the obtained results show that the aerodynamic rolling and yawing moment characteristics are influenced by extremely large dihedral to a high degree. This is a significant outcome for lateral-directional stability because the aerodynamic rolling and yawing moment characteristics have a determinative influence here. Keywords: dihedral, bird, aerodynamics, CFD Copyright © 2010, Jilin University. Published by Elsevier Limited and Science Press. All rights reserved. doi: 10.1016/S1672-6529(09)60191-8 1 Introduction The wing of birds in gliding flight shows often a dihedral configuration in terms of a V-attitude, yielding an upward deflection of the left and right wing halves around the longitudinal axis, Fig. 1. Birds can control and change the dihedral of the wing to a large extent. With dihedral, it is possible to exert an influence on the flight behavior, yielding effects on the flight perform- ance as well as on lateral-directional stability [1–3] . There is a great variation in the magnitude of di- hedral in bird wings. In many cases, comparatively small V-attitude angles are applied by birds, or dihedral may be used only in a part of the wing (outer wing section). Furthermore, birds can also show V-attitude angles in the downward direction which is termed anhedral. However, there can also be extremely large dihe- dral in bird wings. An example is presented in Fig. 1. Birds which show very large V-attitude angles are pi- geons, harriers, auks, mallards, herons, etc. [4–6] . There are several reasons for such a behavior. It is considered that they relate to display maneuvers or to the im- provement of flight stability. Furthermore, extremely large dihedral may be seen in gliding flight conditions at low speed. It may be applied by birds in approaches before alighting on water [6] . Another feature which is observed in the flight of birds with a very large dihedral angle is that there are rotary oscillations in the roll axis [4] . Fig. 1 V-attitude angle ν and bird with very large dihedral (Harrier, from Ref. [4]).