This study investigated the axial tensile performance of adhesively bonded T700/C204 carbon fiber composite and TC4 titanium alloy tubular single-lap joints under three distinct temperature conditions: room temperature, low temperature (−65 °C), and room–low–room-temperature cycling. Two configurations of adhesively bonded joints—composite–composite and composite–titanium—were tested. Specimens were designed to evaluate the influence of spew-fillet and perfect lap configurations on uniaxial tensile bonding strength across varying temperature environments. Analysis of the final failure morphology, stress concentration locations, ultimate failure loads, and load-displacement curves revealed that stress concentration and peeling stress were most pronounced at the ends of the bonded region, which served as the initiation points for failure. The adhesively bonded joints exhibited two distinct failure modes, strongly correlated with material properties and environmental temperature. The titanium alloy tubular joints predominantly experienced adhesive layer failure, while the carbon fiber three-way tubular joints were primarily characterized by fiber-tear failure. Environmental temperature significantly influenced the strength of the adhesively bonded joints. Specifically, the tensile failure limit of the bonded specimens subjected to low-temperature cycling (25~−65~25 °C) was approximately 61% higher than that observed under the room or low-temperature conditions. Furthermore, the experimental results demonstrated that a maximum failure load of 27.522 kN and a shear strength of 10.956 MPa were achieved. Notably, the presence of adhesive spew-fillet had a negligible impact on the bonding strength of the joints.

To study the influence of tip clearance on the working characteristics of high-altitude fans, this paper takes the MIX-140 high-altitude fan as the research object. Five different tip clearance (TC) models are selected. The CFD method is used to analyze the changes in the working characteristics of the fan under different flow rates and TCs in ground and high-altitude environments. The reliability of the numerical method is verified through a fan test bench. The results show that the tip leakage flow caused by the TC will continuously deteriorate the working characteristics of the fan. Under the rated flow rate in the ground environment, for every doubling of the blade’s TC, the static pressure difference will decrease by 5%, the efficiency will decrease by 2%, and the power will decrease by 3%. In a high-altitude environment, the flow rate corresponding to the maximum shaft power point of the fan will continuously increase with an increase in the tip clearance, which will bring about additional energy consumption. For high-altitude fans, the deformation caused by the high-speed rotation of the impeller needs to be taken into account. Undoubtedly, it is advantageous to choose the smallest possible tip clearance value. The results of the analysis and test methods in this paper will provide a basis for designing the tip clearance of high-altitude fans.

Low-Speed near-space aerostats (e.g., stratospheric airships and high-altitude balloons) are low-speed unmanned aerial vehicles (UAVs) extensively utilized in communication coverage, remote sensing applications, environmental monitoring, aviation support, and other fields. A paramount challenge constraining their precise and stable operation is the leakage of buoyant gas, such as helium (He), in the harsh and unpredictable near-space environment. One of the primary causes of gas leakage is the degradation of their dedicated sealing rings. This study aims to clarify the aging mechanisms of high-performance rubber seals in near-space environments and establish a reliable service life prediction model to address the gas leakage risk of unmanned platforms. Two widely used high-performance rubber materials—ethylene propylene diene monomer (EPDM) and chloroprene rubber (CR)—were subjected to accelerated aging experiments under simulated near-space environment conditions. Their degradation was then quantified through performance degradation characterization, covering mass loss, hardness, elastic deformation, and tensile strength. A predictive model was established to estimate the mass loss rates and service life of the seals. The model revealed that EPDM exhibits superior performance to CR under near-space conditions: the aging behavior is strongly dependent on material composition, thickness, and preload, while being independent of outer diameter. Results show EPDM seals have a near-space service life of 300 days (50% longer than CR’s 200 days), with aging dependent on material composition, thickness (2 mm seals degrade 110% slower than 0.5 mm ones), and preload, but independent of outer diameter. These results provide actionable design guidelines for optimizing seal materials and geometries in aerostat pressure systems, thereby advancing the development of innovative low-speed UAV technologies and the successful application of these technologies in the emerging near-space field. These findings and the proposed methodology are directly applicable to sealing system optimization for various near-space unmanned platforms (e.g., stratospheric UAVs, high-altitude autonomous balloons), enhancing their long-duration operational reliability and mission success rate in extreme environments.