M.Ing. (Electrical and Electronic Engineering) / This treatise presents an investigation into the application of multivariable frequency domain techniques in the modelling and control of a helicopter aircraft in forward flight. The presentation is structured in the following sectioned format: I Hypotheses are stated which deal with the use of linear, multivariable, frequency domain theory in the modelling and control of helicopter aircraft. II The stated hypotheses are investigated by the application of relevant theories and techniques to a reference case plant - a single rotor helicopter in forward flight. III Conclusions drawn from the results are used to assess the validity of the hypotheses. The subject matter of the presentation may be summarized as follows: The hypotheses are initially placed in perspective by a discussion of the incentives for their formulation. In essence, the hypotheses state that helicopter dynamics, in a multivariable systems characterization, can be modelled and an appropriate flight control system designed by the use of linear frequency domain theory. The plant in reference to which the hypotheses are investigated is a single rotor utility helicopter - the Aerospatiale Alouette III. A single flight condition - a typical cruising condition - is considered. A comprehensive, nonlinear digital computer simulation of the aircraft is used as a substitute for the actual plant in the execution of the modelling and control design processes. The plant is modelled in terms of a linear model structure, in the form of the frequency response function, by linearization of its highly nonlinear dynamics about an operating point (datum flight condition). The frequency response function model parameters are identified by power spectral density analysis procedures. This method, based on random signal excitation of the plant, provides a valuable quantitative measure of the accuracy of the linearization performed in the identification. The measure, the coherence function, is used as a criterion for the robustness required of a control system of which the design is based on a linear model of a nonlinear plant.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:11409 |
| Date | 04 June 2014 |
| Creators | Muller, Rocco Martin |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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