Dynamic modeling and characteristics study of airdrop folding multi-body aircraft

In the processes of launch, development and fall at high altitude without initial velocity, the dynamics model of a folding multi-body aircraft shows the characteristics of a multi-rigid body and multi-degree of freedom. The relative motion of each rigid body of the multi-body aircraft has mutual flow field interference, resulting in unsteady flow phenomenon. Therefore, the multi-body dynamic model of a two-body aircraft is established based on the absolute coordinate method. The unsteady vortex lattice method is derived under absolute coordinates. The multi-body dynamics coupling model that considers unsteady effects is obtained under the absolute coordinate system. Based on the multi-body dynamics coupling model and the unsteady vortex lattice method, the influence of three factors on the dynamic behavior of the drop and development processes is analyzed. The factors include initial folding angle, joint stiffness coefficient and joint damping coefficient. According to the convergence condition of the folding angle, the normal launch and development of the multi-body aircraft can be judged. Finally, the safe launch envelopes of the three factors are drawn. The simulation results are compared with the experimental data, verifying that the coupling model established in this paper can accurately describe the dynamic characteristics of the multi-body aircraft in its launch process. The paper provides technical basis for subsequent high-altitude launch research.