The structure and modeling of a novel unmanned coaxial rotor ducted fan helicopter(RDFH)are introduced,and then,based on the helicopter air dynamics and kinematics principles,a nonlinear model of the coaxial rotor ducted fan helicopter is developed and implemented on the basis of the wind tunnel experiment.After that,the helicopter′s stability and coupling characteristics of manipulation are analyzed through time-domain.Finally,a sliding mode controller(SMC)with boundary layers is developed on a hardware in the loop platform using digital signal processor(DSP)as the flight control computer.The results show that the RDFH′s tracking ability performs well under the use of proposed controller. The structure and modeling of a novel unmanned coaxial rotor ducted fan helicopter (RDFH) are presented, and then, based on the helicopter air dynamics and kinematics principles, a nonlinear model of the coaxial rotor ducted fan helicopter is developed and implemented on the basis of the wind tunnel experiment. After that, the helicopter’s stability and coupling characteristics of manipulation are analyzed through time-domain. Finally, a sliding mode controller (SMC) with boundary layers is developed on a hardware in the loop platform using digital signal processor (DSP) as the flight control computer. The results show that the RDFH’s tracking ability performs well under the use of proposed controller.