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: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:Compared to conventional powered aircraft, the solar-powered aircraft have characteristics of high-altitude and long-endurance. They can modularly change the task loads and carry out related special tasks. Based on the working principle of long endurance solar-powered aircraft, the coupling relationship between the all-day cruising altitude and wing load of solar-powered aircraft under the energy balance design system was analyzed. The coupling parameters, including aerodynamic parameters, solar panels efficiency and paving rate, propulsion system efficiency and load power factor, flight season and flight latitude, were systematically analyzed for sensitivity, The results indicate that the design or optimization of appropriate lift and drag coefficients should be the first consideration for long endurance solar-powered aircraft to achieve best aerodynamic efficiency; When the efficiency of solar panels reaches 0.35 or above, increasing the installation rate of solar panels has a weaker impact on the all-day cruising altitude, but it helps to increase the upper limit of wing load. The research results can serve as a reference for the overall design and improvement optimization of solar-powered aircraft.

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: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: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:With the large-scale constellation, the importance of a single satellite is reduced. When formulating a replacement strategy for faulty satellites, multiple replacement methods and the retention of faulty satellites should be considered. In response to this demand, a method for formulating constellation orbit satellite replacement strategy based on Markov decision process is proposed. The orbital state is divided according to the number of satellites working in orbit, in-orbit backup and ground backup. On this basis, combined with the different replacement strategies of faulty satellites and the corresponding ordering, storage and penalty costs, a return function model representing the expected maintenance cost is constructed. In order to minimize the expected maintenance cost of each decision cycle, a sequential replacement strategy is developed and applied to a constellation orbit. The results show that when the ground backup is used to replace the fault satellite, it tends to supplement the consumed backup satellite. The longer the mean time between failure, the lower the expected total maintenance cost, but the effect is gradually weakened. The increase of penalty cost will lead to the solidification of replacement strategy, and the upward trend of total maintenance cost is expected to be greatly slowed down. This method can make a sequential decision on the replacement mode of the faulty satellite according to the state of the constellation orbit, which makes the analysis more comprehensive and has certain value for the formulation of the constellation spare strategy.

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: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.