Stability and stability augmentation of dynamic soaring orbits

Dynamic soaring is a technique by which wind gradients are utilized to extend flight times. This was originally observed amongst birds like albatrosses, eagles and is exploited in the flight of UAVs. Earlier works have focussed on generating dynamic soaring trajectories including periodic orbits through various methods like Gauss-Pseudo spectral method, IPOPT, numerical integration methods etc. Such orbits find applications for surveillance UAVs. The study on the stability of a 3 degree of freedom dynamic soaring model is a more recent work. Stability of dynamic soaring orbits is important since the trajectories can get disturbed by a strong gust or crosswinds causing the UAV to veer off-course. Although control system can be designed, a stable orbit can reduce the control effort and power. In this paper, the problem of augmenting the stability a 6 DOF and 3 DOF dynamic soaring model is treated from the context of a periodic coefficient system. The Eigenvalues and Eigenvectors are compared to a 3 degree of freedom system and the mode shapes to level flight and banked turn. A stability augmentation system has been proposed for both 3 DOF and 6 DOF models.