Abstract
M.Ing.
In this study the design of a multivariable inner loop controller for a helicopter, which is
based upon pilot-in-the-Ioop considerations, is proposed. A study of previous research regarding pilot-in-the-Ioop behaviour was made. Consequently another study was conducted on previous research regarding the interaction between the pilot, helicopter and the environment. With typical pilot behaviour known, the .emphasis of the study shifted to the helicopter. The effect of speed and controller configuration changes on the dynamic behaviour of the helicopter was analysed. Design assumptions were made which are based upon the crossover model of the pilot. Standard frequency domain and time domain techniques for example a-plane analysis, root loci, pole zero contours, Bode diagrams, state space formulations and step responses were used for analysis and synthesis. Helicopter models and controller models were defined and linked in the state space to form a combined state space model. Inner loop control is the control of rotational movements of the airframe. Inner loop control is sub-divided into damping and stability augmentation control which is achieved by means of rotational rate feedback, attitude hold control which is achieved by means of attitude and rate feedback, control augmentation which is achieved by means of feedforward and additional rate feedback, de-coupling which is achieved by means of cross-feedforward and turn coordination which is achieved by means of cross-feedback. The effect of loop closure in one axis on the dynamic behaviourof the other axes was analysed by means of sequential loop closure techniques. Both the damping and stability augmentation controller and the attitude hold controller were flight tested. Conclusions made from the flight test results led to updates to the initial design assumptions. From these flight tests definite pilot preferances became clear regarding the controller configuration to be used for different flight regimes. The techniques used in this study was compared with some of the most rescent techniques used internationally. Problem areas were identified and proposals made regarding possible future research. Although many new theories exist, it was found that the s-plane is still used by many helicopter control experts. For this reason this study can be regarded as a good foundation for future research on controllers for helicopters.