On the necessity of flexible modelling in fault detection for a flexible aircraft

High aspect ratio aircraft built from lighter and therefore more flexible materials are increasingly used in aviation. One of the challenges in designing a Fault Detection and Isolation (FDI) system for a flexible aircraft is to obtain an appropriate flexible model of it as opposed to rigid aircraft where modelling (or identification) is more traditional. Such a model is in general more complex and its construction requires special expertise. This paper demonstrates that fast and accurate FDI indeed necessitates the use of a flexible model but if the performance criteria can be relaxed and the sensor configuration can be changed, a rigid aircraft model can also be sufficient. Our case study revolves around an unmanned flexible aircraft built for flutter experimentation. H-infinity synthesis is used to design filters that detect the fault of the elevator actuator and the angle of attack sensor. Various sensor configurations and bandwidth specifications are used to compare the performance of the rigid and the flexible model-based designs. Copyright (C) 2021 The Authors.