Input-Shaping and Model-Following Control of a Helicopter Carrying a Suspended Load

When a heavy load is suspended from a helicopter, excessive load swing degrades helicopter control and can result in obstacle collisions. This work examines the benefits of combining input-shaping and model-following control to improve performance when carrying a suspended load. Model-following control architectures are used in modern helicopter flight control systems to make the helicopter respond like a prescribed model. On its own, model-following control is ineffective when carrying a suspended load because excessive load swing degrades tracking of the prescribed model dynamics and thus control of the helicopter. Therefore, reducing load swing improves tracking of the prescribed model and increases safety and productivity. Input shaping is a control technique that has been used to control vibration of flexible machines, such as robots, satellites, and cranes. By combining input shaping with model-following control, helicopter payload swing is reduced and tracking of the prescribed model is improved. The design of an attitude-command flight control system that combines input-shaping and model-following control is illustrated using dynamic models of a Sikorsky S-61 helicopter. Simulation results are shown for lateral and longitudinal repositioning movements. These results show that applying input shaping to simulated pilot commands greatly improves helicopter performance when carrying a suspended load.