The shear pin structure is widely used in aeronautics and astronautics structures to deal with emergency structure separation problems. The shear pin design has a strict restriction on the precise failure load and definite failure mode. Previous research has conducted shear fracture tests and simulations of solid shear pins while there is a lack of detailed research on the shear fracture of hollow shear pins with large diameters. In this research, a 3-dimensional finite element model was built based on the actual shear pin installed on the aircraft engine pylon and the model was validated by the experiment. The influences of the inner diameter of hollow shear pins on the shear fracture process were investigated by conducting finite element simulations. The structural deformation, energy dissipation in the fracture process, and failure load of shear pins were evaluated. It is found that as the inner diameter increases, the failure mode of shear pins changed and would result in difficulties on the structure separation. To solve this problem, a new configuration of hollow shear pin was proposed for the purpose of obtaining both desired failure load and failure mode. The new configuration was verified by the fracture simulation and it is found that the new configuration is effective and can be used to improve the shear fracture performance.

Purpose This paper aims to investigate the rebound process and the secondary-impact process of the fuselage section that occurs in the actual crash events. Design/methodology/approach A full-scale three-dimensional finite element model of the fuselage section was developed to carry out the dynamic simulations. The rebound process was simulated by removing the impact surface at a certain point, while the secondary-impact process was simulated by striking the impact surface against the fuselage bottom after the first impact. Findings For the rebound process, the fuselage structure restores deformation due to the springback of the fuselage bottom, and it results in structural vibration of the fuselage section. For the secondary-impact process, the fuselage deformation is similar with that of the single impact process, indicating that the intermittent impact loading has little influence on the overall deformation of the fuselage section. The strut failure is the determining factor to the acceleration responses for both the rebound process and the secondary-impact process. Practical implications The rebound process and the secondary-impact process, which is difficult to study by experiments, was investigated by finite element simulations. The structure deformations and acceleration responses were obtained, and they can provide guidance for the crashworthy design of fuselage structures. Originality/value This research first investigated the rebound process and the secondary-impact process of the fuselage section. The absence of the ground load and the secondary-impact was simulated by controlling the impact surface, which is a new simulating method and has not been used in the previous research.

Low-altitude flight in mountainous terrains is a difficult flight task applied in both military and civilian fields. The helicopter has to maintain low altitude to realize search and rescue, reconnaissance, penetration, and strike operations. It contains complex environment perception, multilevel decision making, and multi-objective flight control; thus, flight is currently mainly conducted by human pilots. In this work, a control framework is implemented to realize autonomous flight for unmanned helicopter operations in an unknown mountainous environment. The identification of targets and threats is introduced using a deep neural network. A 3D vector field histogram method is adopted for local terrain avoidance based on airborne Lidar sensors. In particular, we propose an intuitive direct-viewing method to judge and change the visibilities of the helicopter. On this basis, a finite state machine is built for decision making of the autonomous flight. A highly realistic simulation environment is established to verify the proposed control framework. The simulation results demonstrate that the helicopter can autonomously complete flight missions including a fast approach, threat avoidance, cover concealment, and circuitous flight operations similar to human pilots. The proposed control framework provides an effective solution for complex flight tasks and expands the flight control technologies for high-level unmanned helicopter operations.

The requirements for the quantity and quality of pilots are getting more and more demanding. The helicopter robot pilot was put forward as a new autonomous driving scheme which can achieve fast switch between pilot driving and autonomous driving without modifying helicopters. The overall design of the robot was determined and the actuators of the robot was demonstrated in detail according to the handling characteristics of helicopter manipulation mechanism. Based on the detailed design scheme, the robot pilot was processed and assembled. In order to test the control performance of the robot pilot, the robot was installed in the flight simulator to carry out helicopter flight simulations. The test results illustrated that the robot pilot is able to accomplish basic flight control of helicopter.

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