This paper proposes an active fault-tolerant control strategy for an aircraft with dissimilar redundant actuation system(DRAS) that has suffered from vertical tail damage. A damage degree coefficient based on the effective vertical tail area is introduced to parameterize the damaged flight dynamic model. The nonlinear relationship between the damage degree coefficient and the corresponding stability derivatives is considered. Furthermore, the performance degradation of new input channel with electro-hydrostatic actuator(EHA) is also taken into account in the damaged flight dynamic model. Based on the accurate damaged flight dynamic model, a composite method of linear quadratic regulator(LQR) integrating model reference adaptive control(MRAC)is proposed to reconfigure the fault-tolerant control law. The numerical simulation results validate the effectiveness of the proposed fault-tolerant control strategy with accurate flight dynamic model.The results also indicate that aircraft with DRAS has better fault-tolerant control ability than the traditional ones when the vertical tail suffers from serious damage.
Wang JunWang ShaopingWang XingjianShi CunMileta M.Tomovic
Aircraft longitudinal control is the most important actuation system and its failures would lead to catastrophic accident of aircraft. This paper proposes an active fault-tolerant control(AFTC) strategy for civil aircraft with different numbers of faulty elevators. In order to improve the fault-tolerant flight control system performance and effective utilization of the control surface, trimmable horizontal stabilizer(THS) is considered to generate the extra pitch moment. A suitable switching mechanism with performance improvement coefficient is proposed to determine when it is worthwhile to utilize THS. Furthermore, AFTC strategy is detailed by using model following technique and the proposed THS switching mechanism. The basic fault-tolerant controller is designed to guarantee longitudinal control system stability and acceptable performance degradation under partial elevators failure. The proposed AFTC is applied to Boeing 747-200 numerical model and simulation results validate the effectiveness of the proposed AFTC approach.
Planetary gear train plays a significant role in a helicopter operation and its health is of great importance for the flight safety of the helicopter.This paper investigates the effects of a planet carrier plate crack on the dynamic characteristics of a planetary gear train,and thus finds an effective method to diagnose crack fault.A dynamic model is developed to analyze the torsional vibration of a planetary gear train with a cracked planet carrier plate.The model takes into consideration nonlinear factors such as the time-varying meshing stiffness,gear backlash and viscous damping.Investigation of the deformation of the cracked carrier plate under static stress is performed in order to simulate the dynamic effects of the planet carrier crack on the angular displacement of carrier posts.Validation shows good accuracy of the developed dynamic model in predicting dynamic characteristics of a planetary gear train.Fault features extracted from predictions of the model reveal the correspondence between vibration characteristic and the conditions(length and position)of a planet carrier crack clearly.
Fan LeiWang ShaopingWang XingjianHan FengLyu Huawei
Harmonic drives have various distinctive advantages and are widely used in space drive mechanisms. Accelerated life test(ALT) is commonly conducted to shorten test time and reduce associated costs. An appropriate ALT model is needed to predict the lifetime of harmonic drives with ALT data. However, harmonic drives which are used in space usually work under a segmental stress history, and traditional ALT models can hardly be used in this situation. This paper proposes a dedicated ALT model for harmonic drives applied in space systems. A comprehensive ALT model is established and genetic algorithm(GA) is adopted to obtain optimal parameters in the model using the Manson fatigue damage rule to describe the fatigue failure process and a cumulative damage method to calculate and accumulate the damage caused by each segment in the stress history.An ALT of harmonic drives was carried out and experimental results show that this model is acceptable and effective.
