Airship dynamics in a tethered docking maneuver

In the context of the currently growing interest of industry and research towards the field of controlled airships, in particular in association to unmanned flight, the availability of methods and tools for the analysis of specific maneuvers faced by airships over their typical mission profile constitutes a relevant asset. The inherent dynamics of this class of flying vehicles, dominated by buoyancy and by the aerodynamics of their envelope, produces a peculiar response especially in terminal maneuvers and in the docking phase. The latter is often carried out with the help of tethering cables, which further influence the dynamic behavior of the airship, in a way depending on the number and physical characteristics of the cables, the tethering points on board, the rewind velocity, etc. For a better understanding of the airship response in this type of maneuver, mid-fidelity dynamic models of both the airship and tethering cables are employed in this research. They are applied in a first stage to understand the effect of tethering cables on the dynamics of the airship, through a detailed linear analysis. The latter is performed in a parameterized fashion, studying the effect of different parameters on dynamic stability. Then the analysis of the outcome of fully non-linear simulations of an airship anchored to the ground via a rewinding tethering cable is proposed, showing the effect of different simple control logics on the behavior of the airship during an idealized docking manevuer. The proposed modeling and analysis methods allow to efficiently study the behavior of steerable lighter-than-air vehicles in terminal maneuvers, with a detail sufficient for airship design and characterization phases, also making for an interesting asset in the compliance-checking phase with respect to regulatory requirements.