The wingtip-hinged multi-body combined Unmanned Aerial Vehicle （UAV） represents a novel conceptual aircraft， comprising multiple individual unmanned aircraft interconnected through wingtip hinges and allowing for relative roll motion. It exhibits significant distinctions in layout parameters and flight dynamics characteristics compared to conventional aircraft， with the presence of aerodynamic coupling between individual unmanned aircraft. First， the state-space vortex lattice method is employed to derive the aerodynamic derivatives specific to this aircraft type. Then， utilizing the Newton-Euler equations， a flight dynamics model is established for trim calculation and stability analysis， elucidating its unstable compound motion flight modes dominated by relative roll motion. Lastly， an investigation is conducted on the influence of layout parameters on flight dynamics stability. The analysis shows that reducing the trim roll angle of individual unmanned aircraft and increasing the sweep angle can enhance flight stability， while an optimal distance between the wing and tail is found to improve flight stability. The research findings can provide guidance and reference for the design of wingtip-hinged multi-body combined UAVs.