On Stabilization of Rectilinear Flight of a Quadrotor with a Slung Load Partially Filled with Liquid

The spatial motion of a quadrotor with slung load is considered in the presence of a steady horizontal wind. It is assumed that the load contains a spherical cavity partially filled with an ideal liquid. The drag force acting on the load is described using the quasi-steady approach. In order to simulate oscillations of the liquid in the cavity, a pendulum model is used. The equations of motion of the quadrotor–load–liquid system are composed. Controllability and observability in the vicinity of the uniform rectilinear flight are studied. A controllable subsystem is found. A control is proposed that stabilizes the target mode. Numerical simulation of the system dynamics is performed for different flight directions and different wind speeds. The results of the simulation show the feasibility of the constructed control.