Why birds and miniscale airplanes need no vertical tail

The vertical tail is a typical component of the aerodynamic configuration of airplanes, existing with any kind of vehicle. In contrast, there is no bird which possesses a vertical tail. This is a striking difference between birds and airplanes with regard to the ability of flight. The functions of the vertical tail are considered in this paper, including issues of flight dynamics as well as control and trim. It is shown that there are unique relationships for the flight mechanics of small flying objects, like birds and miniscale airplanes, and for their aerodynamic configuration so that they need no vertical tail. It turns out that small flying objects can have an adequate level of dynamic yaw response capability (Dutch roll frequency) 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 modeling the fluid flow around complex geometries and for computing the forces and moments with high precision. Other dynamics issues dealt with concern the damping characteristics in the yaw axis. It is shown that there is a reduction in the required aerodynamic damping capability with a decrease in the size. As a result, the wing alone can generate the required level of yaw damping. Furthermore, the effects on the spiral mode are treated. It is shown that the abandoning of the vertical tail is only of partial influence. The control and trim issues dealt with concern asymmetrical flight for which a yawing moment capability is usually required. It is shown how it is possible to cope with such flight conditions without needing a vertical tail. 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 used for airplanes. This is of particular significance for miniscale airplanes the size of which is considered to range from configurations comparable with large birds to micro air vehicles with a length of some centimeters.