Why birds and mini-aircraft need no vertical tail

The vertical tail is a typical component of the aerodynamic configuration of aircraft, existing with any type of vehicle. By contrast, there is no bird which possesses a vertical tail. This is a most striking difference between birds and aircraft with regard to the ability of flight. The functions of the vertical tail are addressed in this paper, including dynamics as well as trim and control issues. It is shown that there are unique relationships for the flight mechanics of small flying objects (like birds and mini-aircraft) and their aerodynamic configuration so that they need no vertical tail. It turns out that small flying objects can have a high dynamic response capability in the yaw axis even if their static aerodynamic stability is very small. Furthermore, it is shown that the wing alone can provide the required aerodynamic yawing moment if it has appropriate features. For identifying these features, results from flow simulation using a sophisticated aerodynamic method are presented. For this purpose, a modern and efficient aerodynamic method was used for modelling the fluid flow around complex geometries and for computing the forces and moments with high precision. Aerodynamic configurations needing no vertical tail are an issue which is of relevance for technical applications. From the characteristics of birds, it can be learned how such configurations and the related benefits may be utilized for aircraft. This is of particular significance for mini-aircraft the size of which is considered to range from large birds to micro air vehicles with a length of some cm.