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Optimal Excitation for Aircraft Flutter Testing

The choice of excitation signal for flutter testing of a full-scale aircraft or wind tunnel model is crucial if the flutter test clearance is to be performed quickly and with confidence. The use of chirps (that is, sinusoidal signals with varying frequency) is commonplace but has limitations. In this paper the idea of a simple chirp is extended to the development of a multi-sectional variable amplitude/variable power chirp in which the relative signal amplitude and power between sections may be specified over the frequency range of interest. An optimal chirp for a particular application may thus be designed. Sample results from a wind tunnel model flutter test are presented. In addition, the practice of sweeping up and then down in frequency is shown to be inadvisable under certain circumstances.