Dynamic modeling of helicopter-slung load system under the flexible sling hypothesis

A physics based and comprehensive model for helicopter with external load is established via Kane's Method in this paper. The weight and flexibility of the cable are taken into account using spring-mass-damper model. The dynamic stability and flight quality of the helicopter-flexible sling-external load system are analyzed and verified through available reference data. Finally, the influences of the flexibility of the sling are discussed through the comparison of the flexible sling model and rigid sling model. The result shows that the rigid sling model is imprecise as the flexible sling will worsen the system's performance in dynamic stability and flight quality.