Abstract: An eighteen-degrees-of-freedom model of powered parafoil system was developed using hybrid Lagrange's equations of motion in terms of general quasi-coordinates, which is used to simulate the relative motion and connection of a payload with respect to a parafoil. Considering the feature of stable flight phase, the parafoil system is taken as three major parts， including canopy, payload and cord, and the aerodynamic forces on the canopy controlled by brake deflection are expressed in the form of polynomial equations, while the apparent mass and inertia effects are also regarded as external forces. In deriving the equations of motion by the Lagrange approach, the angular and translational velocities of each body are taken as general quasi-coordinates. An illustrative example is used to analyze the gliding and turning flight of the parafoil system, the relative motion simulations of single and multibody dynamic models are investigated for the different cases of design rigging length，change in deflection，and wind gust compared to the 6 DOF system. Results show that the proposed model can reflect the relative motion of parafoil system，and the oscillatory response is preferred to be reduced by use of payload connection. Key

Key words: parafoilsystem, multibodysystemdynamics, quasi-coordinate, flightsimulation, 18degreesoffreedom