Helicopter slung load control using lagged cable angle feedback

A control design method to address stability and handling qualities issues associated with helicopter slung load operations in hover and low speed is presented. A low-order model is developed using first principle physics, with application of basic control techniques. Subsequently, a nonlinear slung load model is developed and integrated with the GENHEL-PSU simulation of the UH-60. Linear model frequency responses are verified against Aeroflightdynamics Directorate (AFDD) OVERCAST models and flight data, showing good correlation in the relevant frequency ranges. A control architecture based on dynamic inversion is developed, combining fuselage and load state feedback. Slung load states are added in feedback linearization, and lagged cable angle feedback is introduced. The controller is shown to reduce load oscillations with trade-offs in pilot response. A controller that uses only lagged cable angle feedback (and no cable state feedback) is also investigated and found to provide good load stabilization without the use of noisy cable angle and rate sensor signals. Sensitivity to parameter variations and optimization methodologies are considered in aiding the design process. Nonlinear batch and real-time simulations are conducted to evaluate performance of the controller.