Modeling, Estimation, and Control of Helicopter Slung Load System

This thesis treats the subject of autonomous helicopter slung load flight and presents the reader with a methodology describing the development path from modeling and system analysis over sensor fusion and state estimation to controller synthesis. The focus is directed along two different application branches: Generic cargo transport using a helicopter slung load system and landmine clearing using helicopter slung load deployed mine detector. This is reflected in the methodology and contributions of this thesis where some are shared by the two branches and some are specific for each branch.

This first major contribution of this thesis is the development of a complete helicopter and slung load system model that is shared between the two branches. The generic slung load model can be used to model all body to body slung load suspension types and gives an intuitive and easy-to-use way of modeling and simulating different slung load suspension types. It further includes detection and response to wire slacking and tightening, it models
the aerodynamic coupling between the helicopter and the load, and can be used for multilift systems with any combination of multiple helicopters and multiple loads.

To enable slung load flight capabilities for general cargo transport, an integrated estimation and control system is developed for use on already autonomous helicopters. The estimator uses vision based updates only and needs little prior knowledge of the slung load system as it estimates the length of the suspension system together with the system states. The controller uses a combined feedforward and feedback approach to simultaneously prevent exciting swing and to actively dampen swing in the slung load.

For the mine detection application an estimator is developed that provides full system state information, including slung load heading. A linear trajectory tracking controller for the generic helicopter slung load system is devised using an optimal approach and it can be tuned to any given suspension system. To generate a full system reference for the
controller, a trajectory mapping algorithm is developed. It is capable of mapping a desired slung load trajectory to a feasible full state reference based on the dynamic and kinematic system behavior.

The methods and algorithms developed in this thesis are validated by systematic simulation and flight testing, and the results presented throughout the thesis show very good agreement between theory and practice.