The design of micro air vehicles (MAVs) has increasingly drawn inspiration from natural fliers in pursuit of greater flight performance and efficiency. Among these, winged seeds known as samaras have gained significant interest for generating exceptionally high lift. These natural rotors achieve this by sustaining a stable leading-edge vortex (LEV) atop of the wing during autorotation, making them promising models for small-scale autorotating rotors and MAVs. Despite continued interest, a validated and computationally efficient model that can reliably predict their autorotational performance is still lacking. In response, this paper presents an experimentally informed low-order numerical model applicable to both natural samaras and artificial microrotors. The main aerodynamic framework of the model is based on Blade Element Momentum Theory, but the adopted load formulation extends to account for LEV effects, which were experimentally informed by wind-tunnel tests. Extensive measurements of autorotating maple seeds were conducted, and the results were integrated into the numerical model. The model demonstrates good agreement across a wide range of flow velocities and pitch settings. The developed model provides an experimentally validated low-order framework for predicting autorotational performance at low Reynolds numbers and offers practical utility for the aerodynamic design of biologically inspired rotors and samara-inspired MAVs.
Proton exchange membrane fuel cell (PEMFC) powertrains have the potential to contribute significantly to the decarbonization of regional aircraft. Realizing the potential of these powertrains will require payload and cost parity with Jet A-1-fueled counterparts. In this paper, the OpenConcept toolkit for conceptual design of aircraft was employed with PEMFC technology benchmarks operating at low temperature (LT) 80°C and high temperature (HT) 160°C to optimize liquid-cooled PEMFC powertrains in regional aircraft for minimal fuel burn and to compute their payload capacity and associated fuel cost per revenue passenger kilometer (RPK) for comparison with Jet A-1. The outputs from OpenConcept were used to expediently assess the performance of PEMFC powertrains for different aircraft weights and mission ranges with a new metric that was derived from Breguet range theory. This paper provides important findings: first, the optimized powertrains were insensitive to mission range; second, HT-PEMFCs reduced fuel cost per RPK by 37% relative to LT-PEMFCs by 2035 and performed competitively with sustainable aviation fuel (SAF); and third, HT-PEMFCs increased payload by 51% compared with LT-PEMFCs. The Breguet range metric indicated that HT-PEMFCs will be the option most competitive with Jet A-1 by 2035, but to meet payload and cost parity, significant technological advances and policy initiatives are required.
A flexible large-deformation morphing wing based on variable-height composite elastic periodic structures and silicone rubber flexible skins was designed using the NACA0014 airfoil. A pre-morphing mechanism was introduced to address the stiffness issue of flexible silicone rubber skins. Under the premise of satisfying structural strength and stiffness, nonmechanical chord extension and camber variation were achieved. Finite element models and aerodynamic analysis models of the morphing wing were established to evaluate its morphing capability, aerodynamic performance, static strength, and dynamic response. The results show that the pre-morphing design effectively improves the normal stiffness of the silicone rubber flexible skin. The wing can achieve chordwise morphing up to 23.3% and [Formula: see text] deflection angle, and lift and lift-drag ratio increase by 181.24% and 24.10% compared to the original wing. The strength, stiffness and stability requirements of the wing are met under severe and economic cruise load cases. Initial damage of the elastic periodic structure occurs under the critical load which is 2.44 times the static strength load, and the damage mode is fiber compression failure. The wing displacement converges to cruise level within 1.5 s under gust load. The morphing wing with variable-height composite elastic periodic structures incorporating pre-morphing mechanism improves the stiffness of flexible skins, simplifies the morphing method, and significantly enhances the aerodynamic performance of the wing.
Accurate characterization of the frictional behavior at the bead–rim interface of aircraft tires is essential for predicting tire service performance. Aircraft tires are subjected to high torque loads during landing impact and braking, which can readily induce relative slip between the tire and the rim. The interference fit between the tire and the rim generates extremely high contact pressure, while the interfacial friction coefficient exhibits significant pressure-dependent variation, which substantially affects the slip resistance of the interface. However, research on interfacial friction behavior under high-contact-pressure conditions remains relatively limited, and the underlying mechanisms are still not well understood. In this paper, an experimental setup is developed to evaluate the slip resistance of aircraft tires under static radial loads. Combined with numerical simulation methods, the friction coefficient at the bead–rim interface under high-contact-pressure conditions is calculated. The results indicate that as the contact pressure increases, the friction force between the bead and the rim decreases significantly, exhibiting a pronounced pressure-dependent characteristic. Through finite element analysis, the effects of bead wire type, bead heel profile, wire width, and bead interference on the contact pressure distribution are investigated. This study reveals the intrinsic mechanisms governing tire–rim frictional behavior and provides an important basis for optimizing tire–rim slip resistance design.
Aircraft nose landing gear shimmy is a self-excited instability that threatens ground handling safety and structural reliability. To address the limitations of conventional hydraulic and magnetorheological dampers, this paper presents a passive electromagnetic damper integrated into a nose wheel steering actuator platform. An analytical damping torque model is established based on electromagnetic induction and the skin effect, clarifying the inherent dependence of damping behavior on air-gap length and stator disk material properties. The proposed damper inherently delivers high damping at low shimmy velocities while exhibiting natural attenuation at higher speeds, which is beneficial for balancing shimmy suppression and steering performance. An electromagnetic–thermal coupled finite element model is developed to evaluate damping characteristics and temperature rise, and the simulation results are validated through prototype experiments. The measured equivalent damping coefficients meet shimmy suppression requirements, demonstrating the engineering feasibility of the proposed solution.
