Mathematical Modelling of Helicopter Slung-Load Systems

Abstract : The primary goal of this work is to use mathematical modelling to assist in defining the operational limits of the Australian Army CH-47D Chinook when carrying mixed density slung loads. This report presents the first phase in the program: the development of a simple helicopter slung-load model for simulation and analysis of the system dynamics. General system equations of motion are obtained from the Newton-Euler equations in terms of generalized coordinates and velocities. The system is partitioned into coordinates such that the motion due to cable stretching is separated from that due to rigid-body, coupled dynamics. In the formulation used, the constraint forces appear explicitly and a solution to the resultant generalized accelerations can be determined by modelling the cable as a simple spring. An inelastic solution is also possible by nulling the stretching coordinates to obtain a relation for the suspension forces. The system equations are also extended for the multiple load case. The model is verified by imposing certain constraints in order to approximate a simple pendulum system and then comparing its behaviour with analytical results. Various configurations of the complete helicopter slung-load system, based on the CH-47B Chinook carrying standard military containers, are then examined in an investigation of the open-loop characteristics. In the investigation, several parameters such as the helicopter-load mass ratio, suspension configuration, and number of loads are varied and the resulting system modes examined. A number of simulations are also presented which demonstrate the characteristic behaviour of such systems.

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