The Identification of Aircraft Powerplant Dynamic Response from Flight Tests Using Power Spectral Techniques.
ROYAL AIRCRAFT ESTABLISHMENT FARNBOROUGH (ENGLAND)
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Power spectral techniques have been used successfully to identify the transfer function of the Rolls Royce Avon engines in a Comet aircraft from flight results. Although primarily an investigation of the method, the results are interesting. The transfer function is found to depend on the magnitude of the input to the autothrottle servo but not on the mean level of thrust at typical approach settings. The output of a second-order model determined from spectral analysis is compared with the flight recorded acceleration output using identical input and a good match is found. As an application, the new model is incorporated in the investigation of a Comet glide path autopilot and autothrottle system and this analysis indicates that the conventional model underestimates throttle activity. The application of pseudo random binary sequences to the identification of engine response is shown to have advantages which include using fairly small perturbations in the normal operating region and obtaining the total frequency response from one run during which the flight conditions remain constant. Author
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