Modeling and Hover Control of a Novel Unmanned Coaxial Rotor/Ducted-Fan Helicopter

In this paper, we consider the problem of controlling a novel rotor/ducted-fan helicopter. After some qualitative introduction on the new arrangement helicopter and its flight behavior, we establish the nonlinear model of the helicopter using a top-down principle based on Newton-Euler equations. Then the linearized model for the helicopter in hover is derived in order to perform analysis and controller design. By observing the helicopter response to control inputs, we found that the coaxial ducted-fan has very different crossed-coupling characteristics in comparison with conventional helicopter, that is, the strong couplings between pitch and roll as well as vertical to yaw. This is mainly caused by the special coaxial and axial symmetric arrangement. Finally, a hover controller is designed for the helicopter by means of robust H-infinity control methodology. The selection of the weighting matrices in the process of H-infinity design is also discussed. Simulation results demonstrate the validity of the analysis and control design.