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 principles and analyzed using basic control techniques. Subsequently, a non-linear slung load model is developed and integrated with the GENHEL-PSU simulation of the UH-60. High-order linear models are generated and frequency responses are verified against AFDD OVERCAST models and flight data, showing good correlation in the relevant frequency ranges. A control architecture based on model following/dynamic inversion is developed. The control law combines fuselage and load state feedback in order to augment load damping and improve response to pilot inputs. Slung load states are added in feedback linearization and lagged cable angle feedback is introduced. The controller is shown to considerably reduce load oscillations with tradeoffs in satisfying handling qualities specifications. A controller that uses only lagged cable angle feedback (and no cable state feedback) is also investigated and found to provide good load stabilization while not relying on noisy cable angle and rate sensor signals. Sensitivity to parameter variations and automated optimization methodologies are considered in aiding the design process. Non-linear batch and realtime simulations are conducted to evaluate performance of the controller in stabilizing the slung load and tracking pilot inputs.