Fault-Tolerant Flight Control System Design Based on Classification of Faults 2020-01-6003
The major emphasis in Fault-Tolerant Flight Control (FTFC) System is towards Fault Detection and Diagnosis (FDD). FDD is used to isolate the aircraft’s fault and provides information for reconfiguration mechanisms to recover the system from a faulty state. In this paper, based on the classification of faults in actuators and sensors, FTFC system design methods are proposed while retaining the existing flight control system (FCS) architecture. Fault scenarios broadly can be classified as one that can be identified and addressed using a sensor or actuator redundancy management (RM) algorithm and the other that need to be identified using real-time system identification techniques. The reconfiguration carried out for the former is termed as passive FTFC, whereas the latter as active FTFC. In this paper, various methods are proposed for reconfiguration of flight control laws for the known failures such as rate sensor, actuator, air data sensor, and faults/failures detected by the FDD scheme. In the active FTFC, if fault identification is not carried out correctly or if incorrectly interpreted by the reconfiguration mechanism, then it can lead to a complete loss of system stability. Therefore, there is a need to research for reliable fault identification in near real time, especially for the unanticipated fault scenarios. Towards this, a single control surface damage fault scenario arising due to either bird strike or battle damage is considered. Fault detection and identification (FDI) are done with extended Kalman filter (EKF), considering state and observation equations of a lateral and directional axis. The control allocation algorithm is also proposed for faults where a reduction in control surface effectiveness occurs.