Active fault tolerant control for vertical tail damaged aircraft with dissimilar redundant actuation system

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.

In-process adaptive milling for large-scale assembly interfaces of a vertical tail driven by real-time vibration data

Assembly interfaces,the joint surfaces between the vertical tail and rear fuselage of a large aircraft,are thin-wall components.Their machining quality are seriously restricted by the machining vibration.To address this problem,an in-process adaptive milling method is proposed for the large-scale assembly interface driven by real-time machining vibration data.Within this context,the milling operation is first divided into several process steps,and the machining vibration data in each process step is separated into some data segments.Second,based on the real-time machining vibration data in each data segment,a finite-element-unit-force approach and an optimized space–time domain method are adopted to estimate the time-varying in-operation frequency response functions of the assembly interface.These FRFs are in turn employed to calculate stability lobe diagrams.Thus,the three-dimensional stability lobe diagram considering material removal is acquired via interpolation of all stability lobe diagrams.Third,to restrain milling chatter and resonance,the cutting parameters for next process step,e.g.,spindle speed and axial cutting depth,are optimized by genetic algorithm.Finally,the proposed method is validated by a milling test of the assembly interface on a vertical tail,and the experimental results demonstrate that the proposed method can improve the machining quality and efficiency of the assembly interface,i.e.,the surface roughness reduced from 3.2μm to 1.6μm and the machining efficiency improved by 33%.

Design of aircraft structures against threat of bird strikes

In this paper, a method to design bird-strike-resistant aircraft structures is presented and illustrated through examples. The focus is on bird strike experiments and simulations. The explicit finite element software PAM-CRASH is employed to conduct bird strike simulations, and a coupled Smooth Particles Hydrodynamic（SPH） and Finite Element（FE） method is used to simulate the interaction between a bird and a target structure. The SPH method is explained, and an SPH bird model is established. Constitutive models for various structural materials, such as aluminum alloys, composite materials, honeycomb, and foam materials that are used in aircraft structures,are presented, and model parameters are identified by conducting various material tests. Good agreements between simulation results and experimental data suggest that the numerical model is capable of predicting the dynamic responses of various aircraft structures under a bird strike,and numerical simulation can be used as a tool to design bird-strike-resistant aircraft structures.