Abstract:Health monitoring technology is the key technology to improve the safety, combat readiness and quick response ability of equipment, which has become the necessary technology of modern high-tech equipment. In order to characterize the aircraft health status clearly and effectively, the parameters "health degree was put forward to characterize the health level of aircraft and its sub-systems, which refers to the extent that the aircraft and its sub-systems keep sound and their functions are not weakened when the aircraft and its sub-systems are completing the specified tasks under the specified conditions. Here the health degree has two expressions, which are the basic health degree and the mission health degree. Based on it, the calculation and determination methods of the basic health degree and the mission health degree of aircraft and its sub-systems were given out. Then, the health status evaluation methods of aircraft and its sub-systems were established based on the "health degree as well as the “healthy”, “sub-healthy” and “unhealthy” employed to express the typical three healthy statuses of them. Finally, the condition-based maintenance (CBM) strategies for aircraft and its sub-systems based on the health statuses were described by means of an example: the aircraft and its sub-systems don’t need maintenance when they are healthy, the aircraft and its sub-systems need to make maintenance plan when they are sub-healthy, the aircraft and its sub-systems need maintenance at once when they are unhealthy, and the final implementation maintenance strategy should be carried out considering the economic requirements. The results of this paper lay a foundation for the effective applications of health monitoring technology in aircraft and its sub-systems, and they can also be extended to the health monitoring of other equipment and systems.

Abstract:Drawing inspiration from the morphological characteristics of the creatures in nature, imitating and learning from the excellent aerodynamic shape to obtain better flight performance is the basic idea of the design of morphological bionic aircraft. This paper introduces the development background of morphological bionic aircraft, and analyzes two research process of morphological bionic aircraft "top-down" and "bottom-up"; According to the categories of bird-like aircraft, fish-like aircraft and other bionic aircraft, the current development status is introduced respectively. The key technologies such as the extraction method of shape features, the method of solving problems in aircraft design process referring to the excellent biological characteristics, identification of aerodynamic parameters of bionic aircraft and other key technologies, and the inspection method of morphological bionic result are explored, and the future development trend of the morphological bionic aircraft is summarized. The content of this article has certain reference significance for the design of morphological bionic aircraft. The content of this article has certain reference significance for the design of morphological bionic aircraft.

Abstract:The advanced fly-by-wire flight control system can greatly improve the maneuverability and stability of civil helicopters, but this novel design also brings huge challenges to safety assessment. Traditional airworthiness standards may not fully cover the design features of fly-by-wire flight control helicopters, and corresponding special conditions need to be formulated to determine whether the helicopter design meets the airworthiness requirements. This article focuses on the four special conditions of civil helicopter fly-by-wire system: interaction of systems and structure, control authority perception, crew alerting system, integrity of command signal and flight envelope protection. First, the technical content of the conditions is given, and then the background and significance of the formulation of the terms are explained. The existing compliance methods and compliance design are given, and the results can provide a certain reference for the airworthiness design and certification of civil helicopters.

Abstract:In order to obtain accurate aerodynamic data from unsteady wind tunnel test, it is necessary to correct the wall interference, so the study on wind tunnel wall interference correction of airfoil low-speed dynamic pressure measurement was carried out in NF-3 wind tunnel of Northwestern Polytechnical University. Using a group of NACA0012 airfoil models with same geometric similarities and different sizes, dynamic pressure measurement were carried out under the conditions of Reynolds number of 1.5x10^6 , mean attack angle of 10°,amplitude of 10° and reduced frequency K=2πf/V=0.03、0.05、0.07.Different scale model test results are interpolated to 0 scale under the same dimensionless dynamic parameters to calculate the wall interference. The wind tunnel test results are used to evaluate and correct the wall interference of dynamic test, which verifies the feasibility of the correction method. This method can provide references and ideas for wall interference correction.

Abstract:Inspired by birds raising their feathers to control the separation flow, vortex flap has become one appoach to control the separation flow over airfoils at high angles of attack. In this paper, the aerodynamic characteristics and physical mechanism of vortex flap controlling separation flow over airfoils under different Reynolds number is numerically studied. The results show that vortex flap is able to greatly improve lift of the airfoil at low Reynolds number under high angle of attack. Its physical mechanism is that the vortex flap makes core position of main separation vortex closer to airfoil camparing to original airfoil, and then the low-pressure characteristics caused by th e vortex core will affect the flow field on the upper airfoil surface. In addition, the pressure filed on the upper surface of the airfoil is divided by vortex flap into two parts: the low pressure aera in the front and the high pressure aera at the back. However, under high Reynolds number (corresponding to conventional aircraft Reynolds number), the effect of vortex flap on improving the aerodynamic characteristics of airfoil at high angle of attack is far less effective compared to the case of low Reynolds number. This explains why birds can improve lift characteristics through feather lifting, while vortex flap can only be used as drag plates in conventional aircraft.

Abstract:(小5号黑正)：Discrete Vortex Method (DVM) is a grid-free vortex motion algorithm, which is suitable for solving unsteady problems that are easy to produce separate flow. Applying it to the flow solution in the ice accretion process can effectively simulate the separate flow, while avoiding the influence of the sharp ice-shaped corner on the grid quality. However, the discrete vortex method is based on the incompressible N-S equation, it cannot be applied to predict the ice accretion process in a compressible flow. In this paper, Prandtl-Glauert compressibility correction is added on the basis of the discrete vortex method. And the numerical simulation of compressible flow based on the discrete vortex method is realized and applied to the prediction of airfoil ice accretion. The calculation results show that the discrete vortex method with compressibility correction can simulate the compressible flow better. Compared with the experimental value, the icing numerical simulation results obtained based on this method are in good agreement. It provides a certain reference for the application of icing numerical simulation in engineering.

Abstract:The aerodynamic configuration of the tiltrotor aircraft was constantly changed during the tilting transition process, and the aerodynamic characteristics had been strongly nonlinear characteristics. Aiming at the complex states of continuous tilting transition for the tiltrotor aircraft, the grid system suitable for the simulation of the continuous tilting transition for the tiltrotor aircraft had been established through the moving embedded grid and local coordinate system theory in this paper，and based on the RANS equation, a CFD method suitable for unsteady flow field analysis with strongly nonlinear aerodynamic characteristics was established. The method was used to simulating the aerodynamic characteristics of the continuous tilt transition for a certain type tiltrotor aircraft from helicopter mode to fixed wing mode. The results showed that the aerodynamic characteristics of the rotors and the airframe had the same trend with the increase of the rotor tilt angle for different tilt transition time（t=1s and t=2s）; As the rotor tilt angle increase, the lift coefficient of airframe was first increases and then decreases, and achieved the maximum value near 40°, which was about 30% increase compared to the initial state and level flight; As the rotor tilt angle, collective pitch angle and forward flight speed linearly increase, the rotor tension coefficient and its vertical component gradually decreased.; With the linear increase of the rotor tilt angle and forward flight speed, the total lift of the tiltrotor aircraft could be kept near the target value by using a suitable nonlinear variation curve of the collective pitch angle.

Abstract:With the rapid development of artificial intelligence and the proposal of “Smart Airport”, it is of great importance to actively explore the application of AI in airports to assist airport controllers and pilots to command aircrafts to taxiing on the aircraft ground effectively. Firstly, a reinforcement learning mobile model of aircraft airport is constructed, and then Meilan Airport of Haikou is taken as an example to achieve the scene simulation by using the Python built-in toolkit Tkinter. Considering the aircraft taxiing rules of the airport, the Q -Learning algorithm in Off-policy is used to solve the Bellman equation, which achieves the requirement of AI static path planning of aircraft in the model-based environment. Finally, the simulation results show the effectiveness of the proposed method.。

Abstract:In order to study the hovering flow field and sand dust movement law of a rotorcraft in ground effect (IGE) hovering due to sand dust inhalation, Fluent software was used to calculate the flow field continuously based on Reynolds averaged N-S equation and K-ω(SST) turbulence model, combined with the parallel algorithm of CFD (Computational Fluid Dynamics) and DEM(Discrete Element Method). Through API(Application Programming Interface), the hovering flow field of helicopter rotor is calculated and compared with the PIV（Particle Image Velocimetry） measurement results. After that, the momentum data of flow field is transmitted to discrete phase to calculate the complete trajectory and particle distribution of dust. The results show that: when the convection field is accurately simulated, the force movement and spatial distribution of sand dust particles are well simulated by using the discrete element method, which can understand the ground effect flow field and the force movement law of fine dust particles with multi parameters, and directly present the development process of sand blindness.

Abstract:As the future development direction of green aviation, electric aircraft has attracted wide attention from various countries. Most electric airplanes adopt a large aspect ratio aerodynamic layout, and the wings deform elastically during flight. The focus of the wind tunnel test results cannot reflect the actual flight requirements well. The focus of the wind tunnel test results cannot reflect the actual flight requirements well. This article is to determine the center of gravity range of light electric aircraft and get the accurate focus position in flight. Taking a certain type of carbon fiber composite material electric aircraft as an example, a mathematical model of steady straight and level flight and steady circling maneuvering flight was established. Based on the test data obtained from the circling maneuver flight test, the object understanding algorithm is used to identify the actual flight focus and compare it with the focus position measured by the wind tunnel experiment. The results show that the focal position of the aircraft identified by the circling maneuver flight test is higher than the result of the wind tunnel test.

Abstract:The evasive maneuver strategy for a fighter against a medium-range air-to-air missile is crucial to improving aircraft survivability. This paper studies that the deep deterministic policy gradient algorithm trains the agent to learn the evasive maneuver strategy. The missile-aircraft engagement model parameters are the input states. The aircraft control commands are taken as the output actions. The missile-aircraft pursuit-evasion model is the environment. The shaping reward, including engagement model parameters and flight parameters, and the sparse reward of the engagement results are designed. Finally, the agent realizes the end-to-end evasive maneuver strategy from the state parameters to the aircraft control variables. Compared to the attack zones of four classic evasive maneuvers based on prior knowledge by simulating, this paper proves that the evasion strategy developed by the agent is second only to the tail dive maneuver. However, this strategy has the lowest dependence on the specialized domain knowledge of missile evasion.

Abstract:In order to prevent the aircraft from rollover due to excessive deflection of the nosewheel during takeoff and landing, the nosewheel deflection should be reasonably limited according to the taxiing speed. Based on the principle of the rollover phenomenon, we analyzed resultant moments of the aircraft relative to the rollover axis while the nosewheel deflecting, determined nosewheel rolling direction limitation, studied on the relationship between the rolling direction of the nosewheel and the deflection, calculated the deflection angle of the nosewheel at different speeds and the neutral position of the nosewheel while considering the asymmetric slip flow of the propeller, then got the deflection range of the nosewheel during takeoff and landing phase. The limited range of the nosewheel deflection obtained by the calculation results show that the limited range accords with the general characteristics of deflection limitation, which can prevent rollover while retaining the correcting capability of the nosewheel.

Abstract:In order to analysis the dynamic characteristic and optimize the rectification control scheme of UAV ground taxiing, based on the assumption of tire lateral force model, elastic tire and rigid body, a whole nonlinear mathematical model and rectification control scheme of was established in the Matlab environment. The engine torque and crosswind conditions are analyzed, and two different rectification control schemes are compared in addition. The simulation results show that the model can reflect the dynamic characteristic of ground taxiing, also the optimized control scheme can shorten the takeoff distance and achieve better rectification performance.

Abstract:Reasonable and lightweight design of aviation driving mechanism can greatly improve the accuracy of travel angle control, durability, torque / mass ratio and electromagnetic compatibility of aviation driving mechanism, and reduce the output shaft sloshing clearance. Based on the current domestic existing aircraft landing lights by air driving mechanism, put forward a king of lightweight aircraft design drive mechanism, the scheme adopts brushless dc motor drive, through the planetary gear, parallel shaft spur gear and worm pair combinations such as slow, using high precision non-contact displacement sensor position feedback signal, and construct a three dimensional mathematical model of mathematical mode of mathematical simulation calculation. The planetary gear and other transmission parts is simulated by KISSsoft. UG10.0 3D mathematical model was established for structure such as shell and gear cover, and advanced simulation ANALYSIS was carried out by using the "FEM and simulation" function module of UG10.0.Through dynamic calculation simulation and advanced simulation analysis, the results show that the design scheme of lightweight aviation drive mechanism can meet the requirements of lightweight, high torque/mass ratio and other relevant technical indicators. The design parameters and strength of the key transmission parts and structural parts of the driving mechanism meet the requirements, and the design scheme is reasonable and feasible.

Abstract:The direct operating cost of aircraft is directly related to the design scheme and parameters of the aircraft，which is the main factor to be considered in aircraft economic design. Reliability and safety are the inherent attributes of aircraft and the prerequisite for ensuring safety in use. The parameterized design is regarded as an important factor which is restricting the efficiency-cost ratio of an aircraft. In order to improve the competitiveness of civil aircraft in the aviation market，a optimization model is constructed to consider reliability and safety simultaneously during the initial design stage from the view of system engineering. An integrated design idea of reliability and safety based on cost is proposed. The model is on the basis of connection of reliability，safety and cost，where the reliability and safety indexes being as the objective，and the plane cost and performance parameters being as constraints. Finally，an integrated design method of reliability and safety and its validation procedures are established based on the cost constraint，which provides technical support for the development of new generation large civil aircraft in China.

Abstract:In order to explore the matching mechanism between nozzle throat area and afterburner fuel supply in turbofan engine afterburner process, and to find the technical way to improve the engine afterburner characteristics, the number of engine afterburner on and off process considering the dynamic volume effect of afterburner and external duct was established based on the afterburner fuel supply sequence, fuel filling sequence and tailpipe area regulation law of a turbofan engine The influence of nozzle throat area adjustment delay on the afterburner transition process is studied. The calculation example and result analysis show that: in the process of afterburner connection, the influence of nozzle delay adjustment on the fan stability margin and speed is not more than 4%, and the impact on the main engine stability margin and speed is not more than 1%; when the nozzle area adjustment is delayed or stuck, in order to ensure the main engine to work stably, the afterburner fuel supply can be appropriately reduced to improve the nozzle flow capacity and improve the safety and stability Under special circumstances, fuel supply of main combustion chamber should be increased to ensure afterburner thrust. The research results can provide reference for similar engine afterburner control law research, design and troubleshooting.

Abstract:In this paper, based on the principle of multi-beam interference, a new type of extrinsic fiber Fabry-Perot (F-P) sensor is fabricated to explore its deformation measurement performance during static tensile testing of aero-engine component materials at room temperature/high temperature. Two types of specimens, flat plate and round bar, were used to perform static tensile tests at room temperature and high temperature under different surface roughness and two loading rates, respectively, compared with Advanced Video Extensometer (AVE). The test results show that the extrinsic optical fiber F-P sensor with a new structure has the advantages of large measurement range, high measurement accuracy, and the measurement results are not affected by external factors, and can achieve over-range full-strain measurement of aero-engine component materials. In addition, it is significantly better than AVE in terms of measurement accuracy and equipment volume. This paper verifies the accuracy and practicability of the extrinsic optical fiber FP sensor with the new structure in the room temperature/high temperature environment static tensile test process, and lays the foundation for its application in the high temperature creep test of micro specimens of aeroengine component materials.

Abstract:In order to analyze the geometric rotation accuracy of the rotor system, a set of rotor system tolerance model was established. Based on the small displacement spin volume, the key tolerances on the component assembly path are modeled, and the error transmission on the closed-loop link is analyzed by the homogeneous coordinate transformation method to obtain the geometric rotation accuracy model of the rotor system. On this basis, combined with Monte Carlo simulation, the example model of the rotor system is analyzed. The results show that the variation range of the root of the rotor blade in space is approximately an ellipsoid, which has complex fluctuations during the rotation. Among them, the radial fluctuation error percentage of the blade root in the plane of the blade is about 0.58%. The fluctuation in the direction perpendicular to the plane of the paddle is relatively large, about 0.89%.

Abstract:In order to further clarify the influence of buoyancy on the regeneration cooling effect of aviation kerosene, and to provide theoretical support for improving the regeneration cooling effect, this paper established an RNG k-ε turbulence three-dimensional model, which was verified by comparing the wall temperature obtained by other experiments and simulations under the same conditions. Aiming at the variation of temperature distribution, secondary flow velocity, convective heat transfer coefficient and turbulent kinetic energy induced by the buoyancy of the aviation kerosene RP-3 in the horizontal pipe under different gravity conditions, the effect of jet fuel buoyancy on the heat transfer flow is discussed. The research results show that the increase of gravity will significantly increase the influence of buoyancy on convection, and the turbulent kinetic energy will increase nonlinearly, and the convective heat transfer coefficient will be significantly improved. When the gravitational conditions change, the secondary flow induced by buoyancy in the direction of gravity undergoes a complicated evolution. The convective heat transfer coefficient first decreases, then increases, and finally decreases. When the temperature of aviation kerosene exceeds the supercritical temperature, the convective heat transfer coefficient changes abruptly, causing significant differences in the wall temperature.

Abstract:The process of folding and inflating the cylindrical airbag is complicated, and there are many inconveniences in using experimental methods to study its expansion process. Two different folding methods are proposed for the cylindrical airbag and the corresponding numerical analysis models are established respectively. The nonlinear dynamics software is used to study the dynamic application characteristics of the cylindrical airbag after being folded, which will affect the skin stress during the airbag expansion process. The factors of volume and internal pressure curve change are analyzed, and the influence of different folding methods and external environmental parameters on the dynamic characteristics of the cylindrical airbag is discussed. The results show that the two folding methods have their own advantages in storage space and material strength. In addition, in the environmental parameters, the external pressure has a greater impact on the stable state of the airbag after expansion, while the temperature has no obvious effect.