Main landing gear shimmy is jointly affected by tire forces, structural elasticity, damping, and geometric coupling. To investigate the influence of side stay angular coupling on shimmy stability, this article establishes a shimmy dynamic model of a dual-wheel main landing gear considering side stay angular coupling. Numerical continuation bifurcation analysis, Hopf bifurcation frequency mapping, and local sensitivity analysis are then employed to study its influence mechanism on stability boundaries, dominant modes, and multistable behavior. The results show that the horizontal inclination angle of the side stay introduces additional structural coupling between strut torsion and longitudinal bending, causing the longitudinal motion to evolve from a passive response into an important mode participating in shimmy instability. A small horizontal inclination angle can induce the coexistence of multiple stable periodic responses, whereas a larger inclination angle changes the connectivity of Hopf bifurcation curves and forms a new instability branch involving longitudinal motion. Further analysis indicates that adjusting the orientation angle to make the local horizontal inclination angle approach zero can weaken the direct structural coupling between torsion and longitudinal motion and reduce the sensitivity of the longitudinal response to variations in the horizontal inclination angle. These results indicate that the angular design of the side stay should comprehensively consider the coupling effect between the horizontal inclination angle and the orientation angle, so as to avoid multistability and mode transition induced by the side stay angular arrangement.
Investigating high-speed aerodynamics and aerothermodynamics presents a significant challenge for manned re-entry missions. The thermal effects on the surface of the re-entry vehicle and atmospheric stresses are primarily influenced by re-entry type and flight trajectory. This study investigates the monostability characteristics and aerothermodynamics of the Orion re-entry vehicle by incorporating static fins onto the aft fuselage of the vehicle, ensuring the lift-to-drag ratio remains unaffected throughout the numerical simulations. The study evaluated two different Mach numbers of 7 and 9 at various altitudes. The models were analyzed at different angles of attack from 0° to 90° in increments of 15°. The model with static fins exhibits a displacement in the monostable trim point, a reduction in the heat-shield pressure coefficient, and enhanced heat transfer throughout the re-entry vehicle.
The landing gear, as a crucial component of an aircraft, is pivotal for maintaining the safety and reliability of air travel. This study introduces a data-driven structural optimization method aimed at mitigating the peak strain on the landing gear’s rocker arm. The initial phase involves selecting nine design variables for parametric modeling to generate an initial dataset. Subsequently, the Maximum Information Coefficient (MIC) technique is used to conduct a parameter sensitivity analysis, enabling the identification and elimination of variables with minimal influence. A comparative analysis between the Genetic Algorithm–Backpropagation Neural Network (GA-BPNN) and BPNN reveals that GA-BPNN has a superior fitting capability on the enhanced dataset. By applying Particle Swarm Optimization (PSO), the optimal solution for GA-BPNN is identified. The implementation of this optimized method results in a 38.16% reduction in peak strain, validating its feasibility and reliability in enhancing aircraft safety.
Ground effect plays a critical role in enhancing the aerodynamic performance of race cars by increasing downforce without a proportional rise in drag. Despite its importance, the influence of airfoil geometry on inverted airfoils operating in ground proximity remains underexplored in open literature. This study addresses this gap through a detailed numerical investigation of chord-dominated ground effect using two-dimensional Reynolds-Averaged Navier–Stokes (RANS) simulations. A range of NACA four-digit airfoils is systematically analyzed to isolate the effects of camber, thickness, and camber location on aerodynamic performance in ground proximity. Results show that increased camber enhances downforce and efficiency both in and out of ground effect; thinner airfoils yield higher downforce and efficiency in ground effect; and forward camber locations outperform rearward ones in maximizing downforce contrary to out-of-ground-effect trends. Detailed pressure distribution and flow separation analyses explain the underlying mechanisms, offering actionable guidelines for optimizing ground effect airfoil design in motorsport.
In the context of emerging technology developed for advanced air mobility concept, its maintenance protocols are not yet mature and existing aviation maintenance systems may not support electric-vertical take-off and landing (e-VTOL) needs. Thus, the operation of e-VTOL aircraft during its deployment stage necessitates the need for qualitative maintenance support. The main purpose of this study is to develop the basic structural principles of the projected new maintenance, repair, and overhaul (MRO) organization for e-VTOL air vehicles, which will support airworthiness through comprehensive maintenance approaches. Thus, the operation of e-VTOL aircraft during its deployment stage necessitates the need for qualitative maintenance support. The importance of the study is to offer standard procedures based on management and maintenance strategies, application of predictive and prescriptive maintenance tools, which pose a significant contribution to ensuring safety, reliability, and cost-effectiveness in e-VTOL operations. The methodology based on leveraging modern management theory in combination with maintenance strategy ensures reaching a goal, creating an effective MRO organization. The findings of the analysis, conducted on the current study, reveal the suitability of the traditional aircraft maintenance approach for e-VTOL air vehicle maintenance processes that can support multi-model aircraft with different design configurations and architectures. To facilitate comprehensive engagement among all relevant stakeholders, the result of the analysis assumes the establishment of an effective aircraft maintenance ecosystem. Effective agreement between e-VTOL operators and MRO providers will contribute to ensuring appropriateness with evolving aircraft architectures in compliance with regulatory standards. This study fills a research gap in the literature relating to aircraft maintenance by proposing a digitally integrated approach and, regulation-compliant framework tailored for e-VTOL aircraft. The suggested multi-strategy maintenance model incorporates predictive analytics, modular diagnostics, and contingency planning tailored for e-VTOL operations, synergizing with AI implementation distinguishes it with its novelty implemented in the modern aviation sector.
The fuel management system for a fixed-wing aircraft has been developed and explored with the model-based systems engineering (MBSE) methodology for maintaining the center of gravity (CoG) and analyzing flight safety. The system incorporates high-level modeling abstractions that exploit a mix of behaviors and physical detail resembling real-world components. This approach enables analysis for a multitude of system requirements, verification, and failure scenarios at high simulation speed, which is necessary during system definition. Initially, the CoG is maintained by directly accessing the flight deck valves and pumps in both wings and controlling them through the bang-bang control law. In the refinement phase of the fuel system controller, the manual and individual controls of the valves and pumps are replaced with an autonomous fuel transfer scheme. The autonomous scheme achieves no more than a 20 kg difference in fuel between the wings during normal conditions. In the event of failures, the controller achieves no more than a 100 kg difference in fuel between the wings. The difference returns to 20 kg within a settling time of 5 sec and a maximum allowable overshoot safety margin of 10% of the 20 kg difference in normal conditions (+/- 2 kg). The specification 20 kg/5 sec band varies with pump and valve parameters. Although this specification is sufficient for a system-level model, it can be refined with pump and valve parameters and nonlinear effects in the network. The system identification method is also trialed to control an individual engine by estimating a proportional integrator derivative (PID) controller of the engine plant. The safety tests are initiated in a user interface enabling error detection and injection. The fuel system model is used for analyzing refueling, defueling, and jettison scenarios with appropriate flow rates. Besides the CoG maintenance, several aspects of configurations of the system's functional and logical architecture, considering increasing component redundancy and activities for MBSE framework, have been conducted. The logical and temporal verification of system requirements is performed in simulation. To ensure traceability and coverage, the requirements and the associated verification artifacts are digitally linked to the implementing blocks. Test scenarios are implemented for investigating resultant and emergent behaviors at various levels of system hierarchy by isolating either the subsystem or the components that have been performed. To further check out the MBSE workflow, the fuel system controller code has been directly emitted from the controller model for DO-178C objectives. At the mission-level validation, a jettison scenario is developed for a mission and flight plan in the digital mission engineering and systems analysis environment of Systems Tool Kit (STK) Aviator. The aircraft fuel system configuration is set using the fuel system model. The power of MBSE methodology supported by a modeling and simulation framework provides plenty of opportunities for through-life analysis in the early design lifecycle phase.
A passive control device to mitigate shock-induced separation in a generic supersonic inlet model is computationally studied. The simulations were based on the Favre-averaged Navier–Stokes equations with the Spalart–Allmaras (SA) turbulence model. The shockwave was generated by an 8° turn supersonic inlet. The Mach number in the inlet was varied between 2.1 and 2.46. The baseline shockwave/boundary layer interaction (SBLI) simulation results compare favorably with experimental data. The passive device, in the form of a splitter plate, eliminates both the separation and flow unsteadiness. The splitter plate causes reduction in the total pressure of the boundary layer at the exit of the inlet due to increased skin friction on the floor and due to wake of the plate.
Accurate defect quantification is crucial for ensuring the serviceability of aircraft engine parts. Traditional inspection methods, such as profile projectors and replicating compounds, suffer from inconsistencies, operator dependency, and ergonomic challenges. To address these limitations, the 4D InSpec® handheld 3D scanner was introduced as an advanced solution for defect measurement and analysis. This article evaluates the effectiveness of the 4D InSpec scanner through multiple statistical methods, including Gage Repeatability and Reproducibility (Gage R&R), Isoplot®, Youden plots, and Bland–Altman plots. A new concept of Probability of accurate Measurement (PoaM)© was introduced to capture the accuracy of the defect quantification based on their size. The results demonstrate a significant reduction in measurement variability, with Gage R&R improving from 39.9% (profile projector) to 8.5% (3D scanner), thus meeting the AS13100 Aerospace Quality Standard. Additionally, the 4D InSpec scanner improved detection accuracy, provided automated defect quantification, and eliminated the need for time-consuming replication processes. Beyond performance improvements, the adoption of the 4D InSpec scanner led to a 75% reduction in direct labor time, significant cost savings, and the elimination of ergonomic risks and human error associated with traditional inspection methods, and enhanced defect reporting and data collection. The article closes with implementation requirements and areas for future improvement.
Amid escalating global warming challenges, the aviation industry must adopt low-carbon and green practices. China, aiming to meet its dual carbon goals, urgently requires enhanced research and development in sustainable aviation fuels (SAF), including their sustainability certification. However, China’s regulatory framework and limited research foundation in biofuels exacerbate this endeavor. This article summarizes the development status of SAF sustainability certification internationally and within China, encompassing the indicator framework, full life cycle greenhouse gas (GHG) calculation methodologies, and emission reduction thresholds. It also highlights issues encountered in the application of current international sustainability certification systems in China, such as high certification costs and inadequate data security. Advancement in domestic sustainability certification in China faces obstacles related to the incomplete foundational database, despite possessing life cycle assessment (LCA) calculation capabilities. To address these challenges, it is imperative to expedite the development of SAF certification systems, research in big data tracking systems, and establish targeted international mutual recognition data tracking platforms. Furthermore, enhancing GHG reduction thresholds in SAF sustainability certification is crucial. These steps will expedite SAF adoption in China, significantly contributing to global decarbonization efforts.
In this article the transition of a laminar boundary layer (BL) over a flat plate is characterized using an acoustic technique with a pitot probe linked to a microphone unit. The probe was traversed along a BL plate at a fixed wind tunnel flow velocity of 5.5 m/s. A spectral analysis of the acoustic fluctuations showed that this setup can estimate the streamwise location and length of the BL transition region, as well as the BL thickness, by using the intermittency similitude approach. Further work is required to quantify the uncertainty caused by signal attenuation within the data acquisition system.
In recent years, there has been a significant rise in research focused on estimating the base pressure (Pb) characteristics of convergent–divergent nozzles with sudden expansion regions. This study explores the use of geometrical parameters as a control strategy for nozzles experiencing abrupt expansion at supersonic Mach numbers within an axisymmetric duct. It focuses on four distinct novel expansion duct configurations: square nozzle (SN), step square nozzle (SSN), curved nozzle (CN), and double curved nozzle (DCN). In this work, the high-speed compressible flow investigation is carried out numerically using control volume method on the nozzle with a fixed area ratio (AR) and L/D nozzle. Standard k-ε turbulence model is used in the analysis to access the recirculation region formed near the nozzle walls. The recirculation zone directly influences the Pb and shock cell. For NPR range from 2 to 10, SSN and CN shows an increase in Pb, which further increases the thrust and decreases the base drag provided by the nozzle. The thrust performance analysis shows that at NPR 2, the SN configuration delivers up to 61.8% higher thrust than other nozzles, while at high NPRs (6 to 10), SSN and CN configurations exhibit superior performance with thrust improvements of up to 59.2%. It is also evident that the L/D of the nozzle is also an important parameter that impacts the Pb as well as expansion in the nozzle.
To comply with the Paris Agreement targets set in 2015, significant reductions in aircraft emissions are required. This demands a fundamental shift in aircraft design. Therefore, it is essential to study how future aircraft designs will affect the integration and design of landing systems. This research project examines the landing gear issues that arise from adopting specific future aircraft configurations. The study focuses on two primary configurations: the high-aspect-ratio wing and the ultra-high-aspect-ratio wing, with selected aircraft concepts from Cranfield University as baselines. It investigates the design and integration of conventional landing systems into these new aircraft concepts, highlighting the limitations posed by the modified airframes. The selected concepts include either telescopic or trailing arm arrangements, with attachment points on the wings or fuselage. A methodology for preliminary sizing of landing systems is presented, emphasizing automation and determining key performance indicators to assess the suitability of each solution for different aircraft architectures. The challenges of these novel airframes highlight opportunities to move away from conventional solutions and explore unconventional methods of interfacing between the aircraft and the ground.
This study presents a novel reinforcement learning (RL)-based control framework aimed at enhancing the safety and robustness of the quadcopter, with a specific focus on resilience to in-flight one propeller failure. This study addresses the critical need of a robust control strategy for maintaining a desired altitude for the quadcopter to save the hardware and the payload in physical applications. The proposed framework investigates two RL methodologies, dynamic programming (DP) and deep deterministic policy gradient (DDPG), to overcome the challenges posed by the rotor failure mechanism of the quadcopter. DP, a model-based approach, is leveraged for its convergence guarantees, despite high computational demands, whereas DDPG, a model-free technique, facilitates rapid computation but with constraints on solution duration. The research challenge arises from training RL algorithms on large dimension and action domains. With modifications to the existing DP and DDPG algorithms, the controllers were trained to not only cater for large continuous state and action domain but also achieve a desired state after an in-flight propeller failure. To verify the robustness of the proposed control framework, extensive simulations were conducted in a MATLAB environment across various initial conditions and underscoring their viability for mission-critical quadcopter applications. A comparative analysis was performed between both RL algorithms and their potential for applications in faulty aerial systems.
Sustainable aviation fuels (SAFs) derived from renewable sources are promising solutions for achieving carbon neutrality and further controlling aircraft engine emissions, operating costs, and energy security. These SAFs, primarily consist of branched and normal paraffins and exhibit significantly reduced sooting tendencies compared to conventional petroleum-based jet fuels, due to their lack of aromatics content. Our previous study investigated soot formation in non-premixed combustion for three ASTM-approved alternative jet fuels, namely Fischer–Tropsch synthetic paraffinic kerosene (FT-SPK), hydroprocessed esters and fatty acids from camelina (HEFA-Camelina), and alcohol-to-jet (ATJ), and demonstrated that the varying paraffinic composition within SAFs results in diverse sooting propensities, in the order of ATJ > FT-SPK > HEFA-Camelina. To evaluate the impact of iso-paraffins on sooting tendency and validate the suitability of utilizing binary blends of iso-dodecane (iC12) and normal dodecane (nC12) as surrogates for emulating sooting characteristics of SAFs, an experimental study was conducted to measure the soot volume fraction profiles of iC12/nC12 blends with varying blending ratios in the counterflow non-premixed flame configuration using laser-induced incandescence technique. It is shown that ATJ and HEFA-Camelina can be well-represented by pure iC12 and the blend of 25% iC12 and 75% nC12 (in liquid volume), respectively. At high (low) reactant concentrations, the blend of 75% iC12/25% nC12 (90% iC12/10% nC12) exhibits similar sooting characteristics of FT-SPK. The present experimental results indicate that binary blends of iC12 and nC12 have the potential to serve as effective surrogates for SAFs, as they are predominantly composed of these two types of paraffinic components. Furthermore, it is found that when the iC12 blending ratio exceeds 90%, the maximum soot volume fraction exhibits a stronger nonlinear increase. This experimentally observed nonlinearity in maximum soot volume fraction with increasing alkane branching in the binary fuel blend signifies the importance of fuel molecular structure effects on soot formation pathways in counterflow non-premixed flames.
In this work, the large-angle rotational movement and vibration suppression of a flexible spacecraft are carried out based on an adjustable system. First the spacecraft model is transformed into a canonical affine control form, then two fuzzy systems are used: The first (of Takagi-Sugeno type) estimates the feedback linearization control law as a whole, while the second (of Mamdani type) adjusts and stabilizes the control parameters using the gradient descent technique and based on the minimization of the control error rather than the tracking error. Stability results are presented in terms of Lyapunov's theory, and simulation tests illustrate the significant transient robustness of the closed-loop system against perturbations, the accurate trajectory control, and vibration suppression of the flexible spacecraft. Consequently, as will be shown later, the error will stay confined and converges quickly to zero, confirming the smoothing property of the proposed method using fuzzy logic systems.
This article explores the utilization of simple-cubic, diamond, octet-truss, and X-type lattice structures for low-pressure turbine blades in engine turbines to enhance natural frequency and decrease overall engine weight while maintaining structural integrity. The research method involves analyzing polylactic acid (PLA) hollow T106C blades with fully infilled and 50–80 location-based lattice arrangements. The study modifies the strut thickness of lattice structures using both constant and variable-based approaches and applies a generalized formula based on relative density to evaluate how changes in lattice thickness and arrangements influence natural frequencies. Furthermore, the investigation extends to multi-lattice configurations, introducing a parameter 𝑘 to signify the transition between different lattices. The modified blades were 3D printed using PLA and tested for natural frequencies through modal testing. The results demonstrate that location-based 50–80 exponential-based lattice structures combining octet-truss and X-type lattices yield the best performance, achieving a 15% increase in the first mode and 14.6% in the second mode when compared to hollow blade. In comparison, fully infilled 50–80 exponential-based lattice structures with a combination of octet-truss and X-type lattices achieve a 9.4% increase in the first mode and 12.7% in the second mode. These findings highlight that lattice structures can effectively improve natural frequencies across all modes.
Establishing critical useful life plays a central role to determine aeroengine health status including aeroengine parameter changes from adverse material conditions or metal fatigue. The useful life assessment serves to support maintenance teams by enabling predictive maintenance followed by part replacement or conditions improvement. The proposed research works to improve the ability of turbofan aeroengine useful life estimation while targeting practical deployment during maintenance operations at field locations. A field maintenance–oriented ensemble bagged regression model for aeroengines represents the proposed method within this research. The present study reaches an error index of 7.06 with 98.95% model fitness when applying it to critical useful life training data. The projected model received its validation through experiments on test and field datasets. Field tests revealed that among 25 machine learning models the proposed model delivered optimal results since its error index was determined at 10.5337 with 97.60% accuracy compared to prior research findings. This study delivers an optimal solution, which enables aviation maintenance crew and techno managers to achieve effective critical useful life evaluation and decision-making for maintenance needs. This research provides essential guidance to industries under maintenance and repair operations for the reassessment of field-based critical parameters identification.
Modern aircraft, ships, and offshore structures are increasingly constructed using fiber-reinforced composite materials. However, when subjected to lightning strikes, these materials can suffer significant structural and functional damage due to their electrical and thermal properties. This study aims to develop a novel finite element (FE) model to minimize the error in estimating the thermal damage caused during lightning strikes. This will aid in design and optimization of lightning protection systems. The developed model introduces a simplified numerical approach to model the lightning arc interaction with CFRP laminate. The existing FE model includes idealized loading conditions, leading to high error in estimation of severe damage area and in-depth damage. The proposed methodology incorporates a more realistic lightning-induced loading pattern to improve accuracy. Several cases are analyzed using available FE methods and compared to the proposed model (case 6) to evaluate the extent of damage. The thermal damage results are validated against baseline experimental data, demonstrating that the proposed FE model reduces the error from over 40% (observed in rest of the cases representing existing FE approaches) to within 10%.
A pathway to in-flight application of filtered Rayleigh scattering (FRS) is herein presented, including a viable concept, based on recently published related work. The proposed pathway considers the key technical, operational, and regulatory challenges to enable in-flight measurements using FRS for inlet flow distortion characterization ahead of the aeroengine. Solutions to these challenges are proposed, in particular methods for light delivery, flow imaging and integration of the measurement system in the in-flight environment. This complements the experimental lab-scale demonstration of an FRS concept for flow distortion measurements and provides a route for further exploitation as a diagnostic tool for next-gen aircraft.
