Minimaler Windbedarf für den dynamischen Segelflug der Albatrosse

The problem of minimum wind strength required for dynamic soaring of albatrosses is considered and it is shown with a flight mechanics investigation which is the flight profile for maximum energy gain for the bird. As a starting point, basic considerations for the energy transfer between moving air and a bird are presented. A mathematical model is then developed for describing the bird motion taking horizontally moving air into account. This includes a model for the wind boundary layer within which dynamic soaring is performed. Computations of flight trajectories yield the mimimum wind strength with the use of which dynamic soaring in the boundary layer is possible for albatrosses. Furthermore, the flight profiles as well as the history of speed and altitude are shown. Other quantities presented are the lift coefficient and bank angle with the use of which the bird controls the flight path. A more detailed investigation of the energy transfer between moving air and bird in the course of the flight path shows that there is a certain phase which is of primary significance. This phase is the upper turn where the bird changes its flight direction from a course against the wind into a course with the wind. The upper turn may be understood as a characteristic element of dynamic soaring of albatrosses to achieve an energy gain. Besides a double-S shaped trajectory which represents from an energy transfer standpoint the best flight path, albatrosses also perform a spiral type of flight path. This case is also considered and a trajectory is presented which requires the minimum shear wind strength for this type of flight path.