Maat cruiser/feeder airship design: Intrinsic stability and energetic flight model

Airships are expected to have in future an increasing diffusion in the aeronautic scenario. The use of airships is not necessary expected to be the same proposed in the past. Several new uses will assume a relevant importance in the next 20 years. The resurgence of airships has created a need for dynamics models and simulation capabilities of these lighter-than-air vehicles. A theoretical framework for designing flexible airships has developed deriving the equations for determining the flight behavior of an airship directly form the data of wind tests and CFD simulations. This model has been a fundamental part of the final design activities of the MAAT (Multibody Advanced Airship for Transport) EU FP7 project, which has studied an innovative cruiser feeder airship based transport system. Main results relates to the definition of a specific mathematical model, which allow approximating the behavior of a flexible or low structured semi rigid airship in presence of external oscillations, in pitch or yawing. Different shapes of airships with different shapes, also not conventional, are assumed and aerodynamic behavior has been evaluated when slightly disturbed from steady forward motion or from hovering conditions in presence of an impacting wind. New uses and the exigency of adopting photovoltaic energy for long endurance missions, is producing airship shapes, which are slightly different from traditional Parsifal. The model presents defines effective criteria based on constructal law, which allow designing an airship with an intrinsic stability in pitch and yaw. An approximate condition for a dynamically stable motion, such as unamplifying pitch, has been expressed in familiar aerodynamic quantities. These results allow stating the following theorem, which has been demonstrated: "Stable pitch flight conditions can be ensured if damping moment is in rotational equilibrium with the disturbing moment and if the disturbing force, the damping force, and the inertia force, are in translational balance". If pitch angle and angular speed are small it can be obtained a relation that must be necessarily satisfied for ensuring a stability condition. An effective flight model based on energetic model of flight is also produced and results have been compared with traditional models giving a good accordance in terms of results.