Flight Dynamics of Unmanned Helicopter without Stabilizer-bar at Low-Speed Flight

Abstract

Increasing total thrust of unmanned helicopter is highly demanded. Stabilizer-bar system is widely applied to improve stability and handling quality of unmanned helicopter. It, however, is a serious obstacle to increase the total thrust. Handling quality of stabi-less unmanned helicopter, which does not have stabilizer-bar system, is usually inferior to conventional unmanned helicopter because of large and very fast cross-coupled responses. For safe operation of stabi-less unmanned helicopter, development of flight control system is required. The purpose of this paper is to develop an accurate model of stabi-less unmanned helicopter. We focused on low-speed flight and induced velocity's change due to angular rate and forward speed. Following results were obtained based on analysis of the derived model; Uniform change of the induced velocity causes trim change due to flight speed and does not cause cross-coupled responses. Non-uniform distribution of the induced velocity causes large and fast cross-coupled responses. Numerical simulation data agree with flight experimental data using a specially developed stabi-less unmanned helicopter. Consequently, a dynamical model proposed in this paper is enough accurate to describe properties of stabi-less unmanned helicopter at low-speed flight.