On-Line Prediction of Loss of Control Using Wavelets

Loss of control in aircraft can result from changes in the controlled element, the control system, the environment, or adverse pilot-vehicle interaction. Each of these paths can be characterized by a loss of phase margin. It is not possible to predict or compensate for all possible sources of additional phase lag in the design process, and so there is a need for on-line health monitoring of the flight control system. The challenge then is to detect the erosion of phase margin in a timely manner and either warn the pilot or automatically take corrective action. In the Phase I effort we intend to use an innovative Time Varying Transfer Function technique to track the phase margin of a time-varying system. These special transfer functions are based on Wavelet Transforms. In contrast to windowed Fourier transforms, these transforms have the ability to analyze a signal at multiple scales, thus allowing for quick response to high frequency changes in the system, without sacrificing low frequency resolution. In Phase I we will develop the methodology and an associated on-line health monitoring toolbox to implement our approach. Example scenarios and available flight test data will be used to demonstrate feasibility.