Abstract:Both drone swarm intensive flight and drone aerial recovery involve the stability problem of drone/carrier-aircraft flight in close range interference flow field. This paper proposes an aerodynamic derivative model for drone/carrier-aircraft interference based on the above application background, simplifies the longitudinal dynamic equations, and derives the simplified stability criteria for the drone. Numerical simulation and analysis indicate that this simplified criterion reflects the relationship between the drone’s motion stability, aerodynamic characteristics, and interference flow field characteristics, and can be used for preliminary analysis and design of flight stability in interference flow fields. Numerical simulation also indicate that the downwash flow can cause the drone to have short-period motion with slower convergence of amplitude, which increases the difficulty of achieving stable and controllable flight in the interference flow field.

Abstract:Full scale aircraft fatigue test is a large, complex and long-lasting ground verification test required by the specification to sustain Aircraft Structural Integrity Program and meet airworthiness requirements. Several important issues of full scale aircraft fatigue test, such as test objective, load spectrum, duration and scatter factor, are the key concern and widely discussed by aircraft designer/engineer. The scatter factor is also a problem studied by scholars. In recent years, our team has completed full scale fatigue tests of several aircraft programs. This paper introduces the study and understanding of the above-mentioned issues, compares the fatigue design and full scale fatigue tests of several fighter jets in China and Europe/America, and puts forward some practical engineering suggestions for full scale aircraft fatigue test. The research in this paper can provide important reference for other full scale aircraft fatigue tests.

Abstract:The supersonic variable Mach number wind tunnel can operate at multiple Mach numbers during a single operation, which has unique advantages for studying supersonic maneuvering process and scramjet Ramjet starting. The supersonic variable Mach number nozzle is the core component for adjusting Mach number during wind tunnel operation, and its design quality directly determines the flow field quality of the experimental section. This article reviews the research progress of nozzle design in supersonic variable Mach number wind tunnels both domestically and internationally in recent years, and introduces four typical variable Mach number wind tunnel nozzle schemes (flexible wall, semi-flexible wall, profile rotation, asymmetric), as well as their numerical simulation and experimental calibration results; Summarized the key considerations in the design of different variable Mach number nozzle schemes, and provided prospects for the next research direction.

Abstract:In recent years, scholars have conducted extensive research on air precoolers, which are used for pre-cooled combined cycle engines for hypersonic aircraft. These precoolers are generally composed of multiple sets of micro-tube bundles, but they have problems such as large flow-induced vibration and high processing requirements. Therefore, it is necessary to redesign the heat exchange core of the precooler and carry out further research on flow heat exchange. This article analyzes the demand for modification based on biomimetic fractals, sorts out the application of honeycomb-like fractals, tree-like fractals, and mixed structures on biological surfaces, which enhance heat exchange in new pre-cooling cores. Additionally, biomimetic concave-convex surface structures and hydrophobic structures are applied to reduce surface flow resistance and suppress frosting. At the same time, three design examples of “cylindrical” biomimetic pre-cooling heat exchange cores are given, which can be applied to the aerospace field. Finally, the article looks forward to the development prospects of combining biomimetic microchannel heat exchange structures with precooler heat exchange core design.

Abstract:The methods of waypoint setting and point curve fitting which are not complex was usually adopted in the path planning of UAV, and the expected heading angle is given in segments. The expected heading does not automatically modified with changes in the route. The ability to automatically and quickly generate the expected heading and position is lacking. In order to solve the ability, a vector field algorithm suitable for complex flight mission path planning is studied, and a simulation verification system to verify the effectiveness of its algorithm is developed in this paper. The concept of vector field is introduced in order to design a heading angle guidance law. An aircraft at any position can smoothly fly to the desired target path along the desired heading angle, and then complete the flight task along the desired target path. The implicit function equation is used to establish the desired path vector field, and the principle and method of path planning based on vector field are geometrically analyzed. According to the Lyapunov stability theory, the boundedness of the planned path error is proved. The distance error and the heading angle error can be stably converged to 0 with the help of the heading guidance law. Taking the path planning of the altitude hold mission for a quad tiltrotor UAV as an example, the desired path of smooth flight is planned using the vector field method and the piecewise transition strategy. The verification is conducted and some simulation results are given, which show that the vector field path planning algorithm is feasible and effective for the mission flight planning of an aircraft.

Abstract:In order to evaluate the propulsive efficiency of turbofan, turboprop and prop-fan engines, a mathematical model for propulsive efficiency analysis was established by using energy-momentum method based on the model of separate exhaust turbofan engines, and a unified propulsive efficiency analysis method was formed for turbofan, turbofan and propeller fan engines. Different external fan pressure ratio, equivalent bypass ratios and different flight Mach number are selected for calculation. The calculation results show that the propulsion efficiency of turboprop engine is higher at medium to low flight Mach number, the propulsion efficiency of prop-fan engine is higher at medium to high flight Mach number, and the propulsion efficiency of turbofan engine is higher at high subsonic flight Mach number. The results confirm the existing flight Mach number interval distribution law of the superior propulsion efficiency of turboprop, prop-fan and turbofan engines, and provide a method for the research and analysis of the propulsion efficiency of turbofan, turboprop and prop-fan engines.

Abstract:Fuel cell UAVs have become a research hotspot in green aviation because of their high efficiency, pollution-free emissions and high energy density. Parameter matching of fuel cell hybrid system has an important impact on the economy, environmental protection and efficiency of UAVs. In this study, a vertical take-off and landing fixed-wing UAV was used as a hybrid system of fuel cell + lithium-ion battery. According to the technical indicators, the components of the UAV power system are selected. Firstly, the topology of fuel cell hybrid system is designed, and the parameters of fuel cell (PEMFC), lithium battery, brushless DC motor, propeller and unidirectional DC/DC converter in the hybrid system are matched. Then, the load power is created according to the task profile, and finally the MATLAB/Simulink simulation analysis of the hybrid system is carried out using the finite state machine energy management control strategy. The results show that the designed fuel cell hybrid system can meet the flight load requirements, meet the changes of working conditions during flight, and achieve zero-emission flight.

Abstract:This paper uses the theory of failure physics and reliability simulation analysis method to analyze the reliability of electronic controller. By establishing a digital prototype model of electronic controller, the corresponding stress analysis and fault prediction are conducted to evaluate the average time to first failure (MTTFF) reliability index of the electronic controller, and optimize the design based on the weak links found in simulation results. It is indicated that the difference between the reliability results and the theoretical calculation results are not significant, and can be used as a basis for evaluating the reliability indicators of models, reducing the cycle and cost of using physical prototypes for reliability testing; At the same time, the optimization and improvement have significantly improved the reliability design of the electronic controller, laying a theoretical foundation for subsequent model reliability evaluation and design.

Abstract:To clarify the effect of breakaway groove on the breakaway load of emergency fuse-pin for civil main landing gear, a series of FEM simulations were conducted to study the influence of structural changes of breakaway groove on the breakaway load for outer-groove, long outer-groove, inner-groove and short inner-groove emergency fuse-pin. The breakaway load and failure mode were comparison?analyzed between inner-groove and inner-groove emergency fuse-pin by experimental tests. The results reveal that the breakaway failure of fuse-pin is extended from inside to outside. The breakaway loads increase with increasing the sectional area and exhibit a linear relationship. The breakaway load variation with the sectional area(shear strength coefficient) of through-hole pin is the maximum, followed by outer-groove pin, and the inner-groove pin is the minimum. Compared with other pins, the breakaway load of inner-groove pin is easy to control and less affected by sectional area and overall size. The fracture morphology is changed from ductile fracture of outer-groove pin to brittle fracture of inner -groove pin. Accordingly, the design of inner-groove pin meets the aviation regulations requirement for civil main landing gear.

Abstract:The compatibility of aircraft landing gear and pavement is of great significance to the ground motion ability of aircraft. This paper calculates the landing gear load and tire load distribution under different working conditions for a large aircraft. The Portland Cement Association method based on Westgard laminate theory and the United States Army Corps of Engineers method based on California bearing ratio are used to calculate. The influence of the landing conditions, ground mobility, tire number, tire deflation and track widths on the aircraft classification number(ACN) is analyzed. The aircraft floatability under rigid and flexible pavement is analyzed. The increased tire load and uneven load distribution caused by vertical overload and tire deflation can weaken the floatability of aircraft to varying degrees, especially during turning and landing conditions with tail sinking. Therefore, they need to be limited. Increasing the number of tires and the distance between them can improve the floatability, but the structural design, strength margin and other factors should also be taken into consideration to optimize the design of trolley type landing gear.

Abstract:A UAV flight control system based on STM32F4 and FreeRTOS operating system is designed. Aiming at the problem of large size and high cost of processor ,a set of flight control hardware system consisting of dual micro controllers, various sensors and actuators is designed based on STM32F4 ,achieving the control of attitude and rudder position, serial communication capability for data acquisition and ground communication., and aiming at the problem that the operating system is expensive and the source code is not accessible, the flight control software system is designed based on FreeRTOS, reducing the burden of RAM while ensuring real-time performance. For improving the reliability of the system, dual residual design of the controller and the watchdog module are introduced. The system has been validated by flight trail, which confirms that the system has high stability, high control accuracy and fast response.

Abstract:Flight control system is typical safety critical system, and the reliability of flight control system plays an important role in ensuring the safe operation of aircraft. Traditional reliability analysis methods have a heavy reliance on the experience of analysts, which makes it easy for inconsistencies between reliability models and design models. The fault propagation behavior of the system is thoroughly described by the Architecture Analysis Design Language (AADL) and stochastic Petri nets (SPN), and a method for model-based reliability analysis is proposed. The nominal model and error model of a lateral fly-by-wire flight control system were constructed using AADL. A method for extracting error propagation information from the AADL model was proposed, and the SPN model described the fault propagation behavior of the system was automatically generated by extracting the information of AADL model. Based on the SPN model, Monte Carlo simulation was used to evaluate the reliability of the lateral fly-by-wire flight control system, compared with the fault tree analysis method, the error is less than 0.018%, which can be neglected in practice. Through the method of this study, the reliability model is automatically generated by the AADL model, which ensures the consistency between the reliability model and the design model and avoids reliance on the experience of designers.

Abstract:The stability of compressor operation has an inducing and amplifying effect on the stability and performance of the entire engine. Therefore, it is required that the wider the flow margin of the compressor, the better, to adapt to the working stability of the engine under variable operating conditions. This paper attempts to propose a new blade structure with micro pits distributed on the suction surface of the mainstream blade by referring to the "golf ball effect". The flow of a certain type of centrifugal compressor impeller is numerically simulated by using the CFX fluid dynamics software to study the effect of adding micro pits on the performance of flow separation structure and flow margin at different parts of the suction surface of the blade. Study the effect of adding micro pit structures with radii of 0.25-0.3mm at different parts of the blade suction surface on structural performance and flow margin. The research results indicate that adding micro pits at the leading and trailing edges of the mainstream blade suction surface can improve the flow margin. When the radius of the micro pits is 0.3mm, the flow margin effect is the best, increasing by 3.01% and 3.15%, respectively. The use of new structural blades reduces smaller peak efficiency and increases compressor flow margin, providing a reference for the design of centrifugal compressor impellers.

Abstract:The establishment and maintenance of a Design Assurance System (DAS) by the type certificate applicant is part of the requirements of CAAC airworthiness regulations and has legal effect. Due to the late start of China"s civil aviation industry, there is limited experience accumulated in the construction and review of DAS, and the Advisory Circular related to design assurance systems has not yet been formed. The authorities and industry lack effective technical guidance in reviewing and demonstrating compliance. By studying the requirements of domestic and foreign airworthiness authorities on design institutions, this article identify the core contents and relationship of the DAS three major functions, propose the main architecture of DAS manual, propose the 11 modules and 28 elements of DAS review and the corresponding review points, propose a review idea based on modularity and a review mode based on process intervention, in order to help readers better carry out the construction and review of DAS.

Abstract:The theory of aircraft icing and its disaster mechanisms are crucial for preventing icing accidents and enhancing flight performance. This paper systematically summarizes the research progress on the flow field characteristics under different icing conditions and special wing configurations. Actual three-dimensional ice shapes are complex, exhibiting multiple structural features and requiring further investigation into their coupling mechanisms with separated flow and turbulence structures. The aerodynamic performance analysis of special wings under supercooled large droplet conditions is a significant future research direction. Turbulence field analysis focuses on identifying instability characteristics of the iced wing flow field and multi-scale structural interaction mechanisms. Exploring the ice-flow coupling mechanism is vital for developing multi-factor, multi-parameter, and multi-scale icing prediction and computational models.

Abstract:Icing of fuel system is a key problem in air transportation, which is related to the safety and reliability of flight. This paper mainly introduces the relevant standards, regulations and research progress of icing in engine fuel system. On the one hand, combined with domestic and foreign relevant standards and icing test process and other aspects, the similarities and differences of civil aircraft and military aircraft in design criteria are described. On the other hand, the latest progress of icing research on fuel system is described in detail from the aspects of icing mechanism, ice growth and adhesion test. Finally, the paper points out that the green, intelligent and fine icing test standard of engine fuel system will be the key research direction in the future, and the related research of engine fuel system icing is prospected.

Abstract:This article is based on the objective requirements and main technical difficulties of natural icing flight test for developing of civil aircraft. It deeply studies the background and limitations of the formation of icing meteorological standards in Ap-pendix C of CCAR25, and proposes a flight method for ice detection using icing test research aircraft. This method includes the selection, modification, detection target area determination, flight operation strategy, flight safety management, data pro-cessing, etc. of experimental research aircraft. Based on statistical analysis of detection data, the selection criteria for meteor-ological conditions for natural icing flight test of civil aircraft have been determined. The compliance processing methods and criteria for a series of meteorological data, such as cloud gaps, liquid water content, total water collection rate, icing rate, icing thickness, and degree of ice shedding, have been standardized. The domestic icing meteorological prediction algorithms have been calibrated and verified, and the safety control strategies and risk degradation measures for natural icing flight test have been explored, providing strong support for the qualified certification of civil aircraft flight test.

Abstract:In order to evaluate the quality of the aerodynamic flowfieldand the thermodynamic flowfield of 0.75m ×0.5m icing wind tunnel, the compliance calibration test of the aerodynamic flowfield and thermal flowfield of the 0.75m×0.5m icing wind tunnel was carried out according to the SAE 5905 icing wind tunnel standard, the quality of the aerodynamic flowfield, air flow angularity and thermodynamic flowfield of the center section of the test section were investigated, and the airflow velocity correction relationship and airflow temperature correction relationship of the test section were obtained. The results show that the maximum deviation of aerodynamic flowfield is less than ±2%, and the uniformity of aerodynamic flowfield is improved with the increase of airspeeds. The maximum deviation of air flow angu-larity is less than 0.8°. While the airflow total temperature is within -20℃, the spatial uniformity can reach ±1℃, and when the airflow total temperature is -30℃, the spatial uniformity can reach ±2℃. The quality of aero-thermal flowfield of the 0.75m×0.5m icing wind tunnel meets the requirement of SAE ARP 5905-2003 under the main test conditions.

Abstract:Superhydrophobic coatings are ideal anti-icing materials, superhydrophobic materials can delay the formation of ice crystals or reduce the strength of ice adhesion, but the existing coatings have problems such as poor mechanical properties and fast natural aging of performance parameters. In this paper, a new type of coating is produced by partially embedding modified graphene into elastomers. This new type of coating not only has the advantages of traditional anti-icing coatings, but also shows excellent performance in mechanical properties, anti-aging, etc. Due to the addition of graphene, the coating also shows a certain degree of electro-thermal properties, which gives the coating both active and passive dual attributes, and lays a certain foundation for the wide application of anti-icing coatings in the industry.

Abstract:At present, the civilian aircraft cargo hold is mainly used photoelectric smoke detector as a fire smoke identification, due to the aircraft cargo hold will be suspended in other interference particles (dust, or water vapor, etc.) will trigger the fire detector alarm, there is a high false alarm rate problem. Based on the dual-wavelength photoelectric smoke detector can effectively reduce the problem of high false alarm rate, the collection of aircraft cargo hold typical combustibles as well as interference sources of infrared light scattering power, blue light scattering power as a fire parameter, through the particulate matter of infrared light scattering power and blue light scattering power analysis, as well as a collection of the Sauter average particle size analysis for the subsequent development of composite smoke detector optimization of the fire parameter, the results show that: the infrared and blue light have a good effect on the fire smoke particles, the results of which are: infrared and blue light have a good effect on the fire smoke particles. blue light have a better response to fire smoke particles, combined with the average particle size of Sauter can effectively distinguish between fire smoke particles and non-fire smoke particles, reduce the false alarm rate, the false alarm rate of the interference source does not exceed 6.7%.

Abstract:The cargo compartments of most current aircraft types are equipped with ventilation function. It is of great significance for flight safety to explore the influence of ventilation effect on smoke diffusion in the cargo compartment and determine the layout of smoke detectors in the cargo compartment under ventilation conditions. A numerical model of fire smoke in DC-10 aircraft cargo compartment is established by using computational fluid dynamics method, and the flow field characteristics of fire smoke are analyzed by simulation. POD flow field orthogonal decomposition theory was used to reveal the influence mechanism of ventilation on fire smoke flow field, the layout of smoke detector in smoke cargo compartment under ventilation condition is studied by simulation and experiment. The results show that ventilation can inhibit the upward diffusion of fire smoke and delay the time for smoke to reach the cargo compartment ceiling. With the increase of ventilation volume, the energy proportion of small and medium-sized disordered flow modes in flow field increased, while the energy proportion of large-scale flow modes of smoke moving close to the cargo ceiling decreased, which resulted in a longer time for smoke to reach the ceiling. By comparing the response performance of the three different detector layouts experimentally, it is concluded that the optimal detector layout is to install the detector near the corner of the cargo hold and away from the vent.