Control of a helicopter with a deployed dipping sound navigation and ranging (SONAR) is no trivial task due to the complex dynamics of the suspension cable. The cable can change shape, which influences the effect of water, wind and the motion of the helicopter itself. To control such a system, a control method is needed that can cope with these complex dynamics.
In this paper, an investigation is performed on how to model and control a helicopter and a dipping SONAR through the suspension cable using incremental nonlinear dynamic inversion (INDI) as well as a comparison between the use of INDI and linear proportional integral derivative (PID) control. The controller uses only the cable states at the attachment point of the cable to the helicopter in order to determine the control inputs to the helicopter. This means that only these measurements are needed and no complex model of the cable is required for control. This reduces model dependency of the controller.
The control system is simulated in different wind conditions in order to analyse its performance in turbulent conditions, where the cable changes shape constantly. It was found that, although INDI performs better than PID control at low wind speeds, an INDI position hold controller appeared to perform better than an INDI cable controller at high wind speeds.