Abstract:Aerocraft Operational Integrity (AOI) can be used to show the comprehensive quality attribute of aerocraft in the operational processes. In this study, first of all, the concept of Equipment Operational Integrity (EOI) is shown, while the development process of Aerocraft Operational Integrity (AOI) is introduced. On the other hand, the connotation of AOI is discussed, while the basic characteristics of AOI is introduced, namely objectivity, relativity, randomness and controllability. It also stated that AOI is the basis for Aerocraft Operational Suitability (AOS) and Aerocraft Operational Effectiveness (AOE) in aerocraft operational processes. Meanwhile, three characterizing parameters of AOI is introduced, namely Aerocraft Inherent Readiness Rate, , Aerocraft Inherent Healthy Degree, , and Aircraft Operational Integrity Degree, , while the primary optimum design method of AOI is discussed. Furthermore, the fundamental theory of AOI control is presented, which consists of the concept of AOI control, the connotation of AOI control, the strategy of AOI control and the modes of AOI control. Finally, the foundation of AOI development is analyzed, as well as the research methods of AOI and necessary directions of AOI development in aeronautical and astronautical engineering.

Abstract:As composite materials are playing a more and more important role in advanced aircraft structures, the change of mechanical properties of composites during service is very important to the overall safety of the aircraft. In order to achieve the goal of fatigue evaluation and life prediction of composite components of aircraft based on guided wave in-situ detection. This paper carries out research on three aspects: the degradation law of structural mechanical properties, the influence mechanism of fatigue accumulation on guided wave propagation, and methods on fatigue characterization and life prediction. First of all, the fatigue evolution law of composite materials is studied from the perspectives of macroscopic phenomenology and microscopic physics. Then, the potential of guided wave phase velocity and mode conversion phenomenon for fatigue characterization is discussed through analyzing the guided wave field. At the same time, a deep learning framework is constructed to extract fatigue evolution features from the guided wave field in a data-driven manner. Finally, a fatigue evolution model based on the Bayesian model averaging method is proposed to predict the residual fatigue life of the composite specimen. Results show that: by extracting and analyzing the guided wave propagating features, the fatigue state of composite materials can be accurately characterized. Combining the Bayesian model averaging method and the confidence interval criterion, the goal of residual life prediction before specimen fatigue failure can be achieved.

Abstract:Some thin-walled structures in aircraft structures inevitably bear out-of-plane bending, affecting the safety of aircraft significantly. The FRACN3D-ABAQUS simulation was carried out in this paper to understand this issue. Effects of boundary restraint and initial crack shape on this kind of fatigue crack propagation were studied. The applicability of the simulation method was evaluated. Following results were obtained: applying the crack surface contact and weaker boundary constrains in simulations will increase the calculated Stress Intensity Factor (SIF); the initial hole corner crack has a higher crack propagation rate than the initial surface crack around the hole; the FRACN3D-ABAQUS simulation method cannot simulate the crack propagation in the compressed surface, where the crack is unable to propagate.

Abstract:Broken hold of the skin is one of the most typical forms of aircraft battle damage. At present, the repair methods mainly include rivet repair and adhesive repair, which are insufficient in repair effect or repair time. In this paper, a method of adhesive-rivet hybrid repair was proposed to the skin broken hole. The fatigue test and finite element analysis were used to compare the fatigue properties of four kinds of specimens with prefabricated circular broken hole damage：without repair, riveting repair, adhesive repair and adhesive-rivet hybrid repair. The results showed that compared with the other two repair methods, the adhesive-rivet hybrid repair method has the best repair effect, and the fatigue life is 2.396 times that of the specimen with broken hole; The rivet function in the hybrid connection could effectively improve the bearing capacity of the adhesive layer and inhibit the peeling of the adhesive layer. Compared with the adhesive repair, the peak shear stress of the adhesive layer was increased by 6.3%, and the peak peeling stress was reduced by 23.1%. The adhesive-rivet hybrid repair method has better fatigue performance than riveting repair, and the repair time is shorter than that of gluing repair. It has a good application prospect in the battle damage repair of metal skin perforated structures.

Abstract:As the most vulnerable part of the aircraft, the fuel tank is damaged by hydrodynamics ram effect when attacked by high-speed projectiles, which will directly threaten the safety of the aircraft. The numerical research on the hydrodynamics ram effect is of great significance. In this paper, CEL method is used to simulate the hydrodynamics ram effect. Firstly, the accuracy of the numerical model is verified by comparing with the existing experimental results; Then, the effects of impact velocity and liquid filling rate on the hydrodynamics ram effect are analyzed. In order to reduce the damage power of hydrodynamics ram effect, the design of protective structure is numerically analyzed. The results show that the damage power of hydrodynamics ram effect comes from shock wave. The greater the kinetic energy of projectile and the higher the liquid filling rate, the greater the damage of oil tank. The protective baffle can reduce the damage caused by shock wave to the oil tank structure to a certain extent, and the air-interlayer protective structure is the best for the protective effect.

Abstract:The aircraft structures combat survivability is one of the critical factors, which affect the integration combat efficiency of aircraft. The efficient design of aircraft structures survivability is of great significance to improve the combat ability, decrease the expenses in service, and ensure the well combat readiness of aircraft. The paper first organized the design factors of aircraft structures combat survivability, based on the connotation of Survivability and the design requirement of structures survivability for aircraft. The design guidelines of aircraft structures combat survivability are discussed. Also, it gives the design and analysis methods of aircraft structures survivability, under the effects of explosions—overpressure field and gust field，which are the two different aspects of blast wave，and the analysis example is presented, finally. The results show that the design factors of aircraft structures combat survivability are similar to the damage tolerance design, and the design process of damage tolerance could be used in structures combat survivability design. The fuselage panel ,Leading Edge, moveable surface and cover, which are sensitive to overpressure of blast wave, could be designed to high structures survivability by configuration optimization.

Abstract:The whole life cycle support work of American military equipment is systematically combed and, distinguishes four stages of demonstration, development, service and decommissioning. The work contents and characteristics of each stage is analyzed, and corresponding countermeasures and suggestions is put forward from the whole life cycle point of view.

Abstract:Aiming at the problems of lack of design standards, high complexity and low accuracy in the design and engineering application of prognostic and health management (PHM) system for military aircraft, the design requirements of data, structure and function dimensions of PHM system are analyzed. Based on the study of the relations and characteristics of the three dimensions, the three-dimensional multiphase iterative design criteria is proposed. A three-in-one design architecture of real-time health management based on embedded system, knowledge logic visualization based on knowledge graph, and PHM system modeling based on MBSE is proposed. The PHM system design process is constructed by analyzing the PHM system design strategy, which provides a method for the engineering application of military aircraft PHM system.

Abstract:WVR air combat is still inevitable in future. Accurate and agile nose-pointing capability at high-angle-of-attack is still essential and significant for fighter to survive and gain air superiority . This paper in terms of military fighter configura-tion reviews the technology and design considerations of high angle of attack problems of which wind tunnel experi-ments, aerodynamic modeling, nonlinear flight dynamics analysis, control law design and flight test are discussed. The research direction of high-angle-of-attack flight in the future is prospected.

Abstract:As one of the main factors affecting the shimmy stability of aircraft in high speed gliding, the structural clearance of landing gear determines the safety and comfort of aircraft gliding. In this paper, the existing forms of landing gear structural clearance are summarized, and the formation reasons of landing gear structural clearance on shimmy are analyzed. The existing landing gear shimmy clearance analysis models are described in detail, and the limitations of the models and the future modeling direction are pointed out. Furthermore, the solving methods of the shimmy model with clearance are summarized, and the applicability of different methods is illustrated. Finally, the future research direction is prospected.

Abstract:The internally blown flap is of efficient lift enhancement ability, but stall angle of attack drops significantly at a higher jet momentum. In order to improve the stall characteristics, this paper studies the stall characteristics of the internally blown flap with the droop nose. The flow fields of a subsonic airfoil with droop noses combined with seamless flaps under the effect of circulation control are obtained based on numerical simulation. The influence of the blowing momentum coefficient on the stall characteristics is studied. The effects of leading edge rigid deflection, camber and thickness changes on the improvement of stall characteristics are studied. The effects of doop nose with different flap angle are also studied. It reveals that as the blowing momentum coefficient increases, the stall angle of attack first drops rapidly and then slightly increases. The leading edge droop devices reduce the pressure gradient on the upper surface of the airfoil, delay the trend of the momentum thickness of the foil boundary layer increasing with the angle of attack and delay the stall angle of attack effectively. By gradually changing the curvature of the leading edge surface, the leading edge droop design has the best effect on the improvement of stall characteristics.

Abstract:Producing structured mesh at the immediate vicinity of the crack front for three-dimensional (3D) crack modelling is a very time consuming and difficult task. A geometry feature based method for 3D crack modelling based on virtual crack closure-integral method (VCCM) for the tetrahedral finite element is proposed, and the implementation details of employing tetrahedral finite elements for 3D crack modelling on the basis of ABAQUS are described. On this basis, a 3D crack analysis package is developed by applying the Python programming language combined with NumPy and SciPy to automate the whole process of crack problem analysis. The stability and robustness of the 3D crack automated modelling is improved by employing tetrahedral finite element. The numerical examples are in good agreement with the results in the literature, proving the accuracy and reliability of the modelling method.

Abstract:In order to reduce direct maintenance costs of civil aircraft, which is an important way to improve aircraft economics and enhance market competitiveness. Based on the background that the maintenance cost is largely determined in the development stage of civil aircraft, by constructing a hierarchical diagram of the design parameter structure that reflects the cost characteristics of civil aircraft, the TOPSIS-Grey correlation method model is established to calculate the relative similarity of similar aircraft and to carry out the direct maintenance cost allocation of civil aircraft. The direct maintenance cost data of typical systems of similar aircraft types is input into the allocation model for verification. The results show that the model in the article can predict the system-level direct maintenance cost of civil aircraft well, and the calculation result can meet the engineering requirements, which can provide a reference for predicting the direct maintenance cost of the newly developed aircraft.

Abstract:Based on Wickens" information processing and cognitive model, the relationship between attention resources and control workload is constructed. Based on the SIR model, the dynamic equations of attention resources and control workload are established. The stability of the equation at the equilibrium point is proved by Lyapunov stability theorem. Based on this algorithm, the opening and closing valve for sector operation is designed. Sector opening and closing valve can provide decision support for team resource management and sector opening and closing decision. Through numerical simulation, the evolution rules of attention resources and residual workload of controllers are verified. The sector opening and closing valve can provide sector opening warning for large flow and capacity environment and predict the future workload of controllers.

Abstract:The wake flow field of tanker aircraft can produce the complex flow interference on receiver aircraft during aerial refueling. The computational fluid dynamics（CFD）method based on Navier-Stokes（N-S）equations isused to analyze the wake flow field of the tanker，and simulate the aerodynamic interference between tanker aircraft and receiver aircraft. The longitudinal and lateral-direct aerodynamic characteristics of the receiver aircraft are systematically studied under certain conditions，such as different tanker’s angles of attack，different height differences between two aircrafts，different lateral distances and different front and rear positions. The results show that，under typical conditions，the aerodynamic interference to the receiver is increased with the increase of the tanker’s angle of attack. The higher of the height difference between the receiver and the tanker is，the smaller of the aerodynamic interference to the receiver is. With the increase of the lateral distance is，the aerodynamic interference to the receiver is increased firstly，then decreased. The influence of fore-and-aft distance on the receiver is small.

Abstract:Structural modeling takes lots of time and energy of engineers, rapid structural modeling is one of the keys to raise the efficiency of structure design in the process of civil aircraft design. A method of rapid structure modeling for civil aircraft is proposed in this paper which is based on the secondary development technology of CATIA. Decompose frequently used part models into the combination of typical machining features based on analyzing and summarizing of the common civil aircraft structure model. Create a CATIA knowledge template for each feature, then, establish a structural feature template library to integrate all templates. In addition, CAA secondary development technology is used to design a visual interface which can call feature templates from the library. On this foundation, by simulating the material reduction process and calling the machining feature template one by one to create structure models. This method has been verified and applied in existing projects, which improves the efficiency and quality of structure modeling.

Abstract:The oil characteristics and inflation pressure inside the oil-air shock absorber will change with the ambient temperature, which will affect the cushioning performance of landing gear. In order to explore the effect of temperature on the cushioning performance of oil-air landing gear, this paper proposes a buffer environment temperature simulation method based on the landing gear drop shock test, and studies the cushioning performance of oil-gas landing gear buffer at ambient temperature from 20 ℃ to 80 ℃. The results show that within the studied temperature range, the initial inflation pressure of the buffer is sensitive to the change of temperature. With the increase of temperature, the stiffness of the air spring in the buffer increases and the oil damping force decreases, the ground vertical load of the landing gear system increases and the efficiency coefficient of the buffer system decreases. The temperature has a significant impact on the performance of the oil-gas landing gear buffer.

Abstract:Abstract：Aiming at the problem of inaccurate life prediction caused by multiple degradation information during the operation of complex aviation equipment, a multi-information fusion life prediction model based on kernel principal component analysis (Kernel Principal Component Analysis,KPCA) and bidirectional long short-term memory (Bi-directional Long Short-Term Memory ,BLSTM) neural network is proposed. First, the kernel principal component method is used to perform dimensionality reduction and information fusion on the multi-dimensional degraded data set to obtain a low-dimensional feature data set that can characterize equipment degradation. Then use the BLSTM neural network model to predict the remaining life of aviation equipment (Remaining Useful Life,RUL) with multi-dimensional degradation information, and obtain the mapping relationship between the monitoring data and the remaining life. Finally, the C-MAPSS aero-engine degradation data set is used to simulate and verify the proposed multi-information fusion life prediction model. The results show that KPCA can perform dimensionality reduction and fusion of multi-state nonlinear monitoring data. The proposed KPCA-BLSTM can predict RUL under multi-dimensional degradation information very well, and by building support vector machines (Support Vector Regression ,SVR), Convolutional neural network (Convolutional Neural Networks ,CNN) and BLSTM neural network models are compared with the prediction results of the proposed model. The proposed model error and score are better than the other three models, indicating that the proposed model has higher prediction accuracy.

Abstract:ETOPS is an operational requirement put forward by the International Civil Aviation Organization (ICAO) in order to ensure the safe flight of civil aviation aircraft, which is widely used in intercontinental routes, especially cross ocean flight. The core of ETOPS type design approval is the airworthiness certification of ETOPS significant systems. ETOPS significant systems airworthiness certification is studied. The airworthiness requirement that refers to ETOPS significant systems is analyzed. The Methods of determining and verifying ETOPS significant systems are proposed. The approval requirement for time-limited ETOPS significant systems are analyzed. The determination method and verification method of ETOPS significant systems proposed in this paper have been applied in engineering practice, and substantive progress has been made. It has proved that the research of this paper can provide guidance for civil aircraft ETOPS type design and airworthiness certification.

Abstract:Aiming to effectively evaluate the risk level of the exceeding tire speed rating during take-off of the transport aircraft, and an evaluation model based on cloud model and Bayesian network is proposed. This research selects eight risk indexes, including rotation speed, total weight, low pressure rotor speed, rotation rate, rotation time, elevator control amount, wind component and total air temperature to build the risk index system for exceeding tire speed rating. Then, the cloud model based on heuristic Gaussian cloud transformation algorithm and forward Gaussian cloud algorithm is used to realize the soft classification of exceeding tire speed rating risk level and the discretization of the indexes, and the prior probability of the indexes is calculated. Moreover, the Bayesian network for exceeding tire speed rating risk is constructed, and based on the established network and nodes information, the posterior probability of the said nodes is calculated and the main inducement of exceeding tire speed rating is obtained through network reverse diagnosis. Finally, the simulation experiment has been completed by using the actual operation data from the airlines, and the results show that the evaluation results are consistent with the actual situation, which verify the effectiveness of the model. Therefore, the research can provide theoretical basis for the exceeding tire speed rating analysis and civil aviation takeoff safety risk management.