Abstract: This paper presents a resilient, multi-layer architecture designed to ensure reliable autonomous operation of single and multiple quadcopters. The architecture leverages the resilient spacecraft executive to hierarchically organize trajectory-planning and flight-control functions, and integrates Simplex architectures at each level to provide safety assurance. A compound subsystem expands robustness by employing multiple candidate algorithms for planning and control, while a supervisory program adapts Simplex behavior based on system states and environmental conditions to enable high-level mission management. The architecture is evaluated in simulations involving environmental uncertainties, including varying wind and obstacles, within a bridge-inspection mission using both single- and multi-quadcopter configurations. Results show that the system maintains safe and effective operation across a wide range of conditions, demonstrating scalability for cooperative multi-agent tasks.

Abstract: Ti-6Al-4V(Ti64), widely used in aerospace structures for its high specific strength and corrosion resistance, is increasingly produced by additive manufacturing (AM) to enhance material efficiency and design flexibility. However, its fatigue performance remains highly variable due to process-induced microstructural heterogeneities and inherent defects. Since aerospace components are designed under damage-tolerant principles, understanding fatigue crack growth (FCG) behavior in AM Ti64 is essential for reliable life prediction. This short review critically examines FCG in Ti64, focusing on the influence of build orientation, processing routes, heat treatment, mean stress, defects, and environmental conditions. These factors, through their effect on the microstructure, govern crack propagation. Achieving consistent and predictable FCG behavior requires standardized test reporting, high-resolution microstructural and defect characterization, and data-driven approaches, that link processing, microstructure, and mechanical response. To complement this mechanistic perspective, a meta-analysis of 67 studies was conducted to assess how FCG research in AM Ti64 is reported. The results showed that only 66 percent of studies included details on manufacturing processes and specimen preparation, and just 68 percent documented feedstock characteristics and material properties, whereas 99 percent reported testing conditions. These gaps highlight the need for more consistent and harmonized reporting. To address this, a reporting benchmark grounded in established testing standards and domain expertise is proposed. Such standardization will enhance reproducibility, enable meaningful data comparisons, and advance data-driven FCG research in AM.

Abstract: The Wind Wall is an innovative mechanical system system comprising multiple Vertical Axis Wind Turbines (VAWTs) designed to efficiently harness wind energy and convert it into electrical power. This study investigates two critical aspects of optimizing the Wind Wall’s performance which uses symmetrical blade profiles: the ideal spacing between the turbines and the optimal helix angle of the turbine blades. The VAWTs in this design utilize the Savonius-type drag-based mechanism, with symmetrical Ugrinsky-profile blades that incorporate a helical twist. The helical twist improves torque uniformity and reduces pulsation in torque, enhancing overall efficiency, but excessive angles can lead to turbulence and reduce the performance. Using CFD simulations, this paper explores the relationship between helix angles, torque generation, and the Coefficient of Moment (Cm) at a constant wind speed. Additionally, the effect of spacing between turbines on effective velocity (Ve) and torque is analyzed. A simplified correlation between Ve, turbine diameter, and spacing is proposed, providing a practical method for designing a Wind Wall with ease. This research identifies the optimal helix angle (20–30°) and spacing parameters, balancing performance, ease of manufacturing for a sustainable energy solution.

Abstract: Due to emerging strategic demands, this article presents a comprehensive conceptual design investigation into enhancing the MQ-9A Reaper Uncrewed Aerial Vehicle (UAV). Motivated by the need for persistent long-range strike and surveillance capabilities, the research study proposes three primary modifications to create an aircraft titled the MQ-9X Raven. First, we replace the existing turboprop engine with the widely used Williams FJ44-4A turbofan for fuel consumption and excess power at 50,000 feet, with a range of approximately 8000 nm. Second, we update the wing design with a 79 ft wing for a greater aspect ratio and a new LRN1015 airfoil to enable high-altitude, long-endurance standoff of around 24 hours. Third and finally, we integrate Joint Strike Missiles (JSM) for enhanced lethality. The project follows a rigorous methodology beginning with a redefinition of mission requirements, aerodynamic, thrust, and stability analysis, and then verification with flight simulation, computational fluid dynamics, and wind tunnel experiments. Our analysis shows the MQ-9X Raven is highly suitable for the task of pervasive high-altitude standoff maritime strike.

Abstract: Unmanned airships are highly sensitive to parametric uncertainty, persistent wind disturbances, and sensor noise, all of which compromise reliable path following. Classical control schemes often suffer from chattering and fail to handle index discontinuities on closed-loop paths due to the lack of mechanisms, and cannot simultaneously provide formal guarantees on state constraint satisfaction. We address these challenges by developing a unified, constraint-aware guidance and control framework for path following in uncertain environments. The architecture integrates an extended state observer (ESO) to estimate and compensate lumped disturbances, a barrier Lyapunov function (BLF) to enforce state constraints on tracking errors, and a Super-Twisting Terminal Sliding Mode (ST-TSMC) control law to achieve finite-time convergence with continuous, low-chatter control inputs. A constructive Lyapunov-based synthesis is presented to derive the control law and to prove that all tracking errors remain within prescribed error bounds. At the guidance level, a nonlinear curvature-aware line-of-sight (CALOS) strategy with an index-increment mechanism mitigates jump phenomena at loop-closure and segment-transition points on closed yet discontinuous paths. The overall framework is evaluated against representative baseline methods under combined wind and parametric perturbations. Numerical results indicate improved path-following accuracy, smoother control signals, and strict enforcement of state constraints, yielding a disturbance-resilient path-following solution for the cruise of an unmanned airship.

Abstract:

Flow quality at the engine face, especially total pressure recovery and swirl, is central to the performance and stability of external compression supersonic inlets. The steady-state RANS based numerical computations are performed to quantify bleed/swirl trade-offs in a single-ramp intake. The CFD simulations are done first without a bleed system over M_∞ = 1.4-1.9 to locate the practical onset of a bleed requirement. The deterioration in pressure recovery and swirl beyond M_∞ ≈ 1.6, consistent with a pre-shock strength near the turbulent separation threshold, motivates the use of a bleed system. The comparisons with and without the bleed system are done next at M_∞ = 1.6, 1.8, and 1.9 across the operation map parameterized by the flow ratio. The CFD simulations are performed by using ANSYS Fluent, with pressure-based coupled solver with realizable k-ε turbulence model and enhanced wall treatment. The results provide engine-face distortion metrics using standardized ring to sector swirl ratio alongside pressure recovery. The results show that bleed removes low-momentum near-wall fluid and stabilizes the terminal-shock interaction, raising pressure recovery and lowering peak swirl and swirl intensity across the map, while extending the stable operating range to lower flow ratio at fixed M_∞. The analysis delivers a design-oriented linkage between shock/boundary-layer interaction control and swirl: when bleed is applied at and above M_∞ = 1.6, the separation footprints shrink and the organized swirl sectors weaken, yielding improved operability with modest bleed fractions.

Abstract: Urban Air Mobility (UAM) promises to reduce ground-traffic and journey times by using electric vertical take-off and landing (eVTOL) aircraft for short, low-altitude flights, especially in urban environments. However, low-flying aircraft are at particularly high risk of collisions with wildlife, such as bird strikes. This study builds on previous research into UAM collision avoidance systems (UAM-CAS) by implementing one such system into the BlueSky open-source air traffic simulator and evaluating its efficacy in reducing bird strikes. Several modifications were made to the original UAM-CAS framework to improve performance. Realistic UAM flight plans were developed and combined with real-world bird movement datasets from all seasons, recorded by an avian radar at Leeuwarden Air Base. Fast-time simulations were conducted in the BlueSky Open Air Traffic Simulator using the UAM flight plan, the bird datasets, and the UAM-CAS algorithm. Results demonstrated that the UAM-CAS reduced bird strikes by 62%, with an average delay per flight of 15s. However, a small number of flights faced substantially longer delays, indicating some operational impacts. Based on the findings, specific avenues for future research to improve UAM-CAS performance are suggested.

Abstract: High-speed low-pressure turbines in geared turbofans operate at transonic exit Mach numbers and low Reynolds numbers. Engine-relevant data remain scarce. The SPLEEN C1 linear cascade is investigated at Mout=0.70--0.95 and Reout=65,000--120,000 under steady inlet flow. Experiments are combined with 2D RANS and MISES, including transition modelling and inlet-turbulence decay calibrated to measurements. Results are consistent with conventional LPT behaviour: losses decrease with increasing Mach and Reynolds numbers, except when shocks interact with the blade boundary layer (M≈0.95). Profile loss drops by 23% from M=0.70 to 0.95 at Re=70,000, and by 19% at M=0.80 when open separation is suppressed. Secondary loss decreases by up to 25% at Re=70,000 and shows weak sensitivity to Reynolds number. A coupled loss model predicts profile loss with RMSE=4.7%. Secondary-loss modelling reproduces global trends: separating endwall dissipation from mixing keeps errors within ±10% for most cases, but accuracy degrades near the shock–boundary layer interaction case and at the highest Reynolds number. Mixing dominates endwall loss (∼75%), with the passage vortex contributing ∼50% (±10%) of the mixing component. This article is a revised and expanded version of “An Experimental Test Case for Transonic Low-Pressure Turbines—Part 2: Cascade Aerodynamics at On- and Off-Design Reynolds and Mach Numbers” presented at ASME Turbo Expo 2022, Rotterdam, June 13–17, 2022. All data and documentation are openly available at https://doi.org/10.5281/zenodo.7264761.

Abstract: This theoretical research paper explores a hypothetical advanced drone swarm system comprising 50 AI-automated, self-driven drones, each equipped with face detection, self-target locking, and a destructive payload designed to release energy comparable to a high energy weapon, deployed from a larger aerial platform. Framed strictly for academic inquiry to avoid any harm, the study delves into the scientific and engineering feasibility of such a system. It examines the intricate mechanisms of swarm intelligence and collective autonomy, including advanced coordination algorithms and resilient communication protocols. The report further investigates AI-driven autonomous navigation, focusing on multi-sensor fusion, real-time obstacle avoidance, and precision targeting with integrated face detection. A significant portion addresses the theoretical basis and immense challenges of a high energy payload, contrasting it with more feasible directed energy weapon concepts and their power and thermal management requirements. The logistical aspects of mothership deployment and aerial integration are also explored. Finally, the paper critically analyzes the profound ethical, legal, and societal implications of such Lethal Autonomous Weapon Systems (LAWS), particularly concerning international humanitarian law, the accountability gap, the AI arms race, and the imperative of meaningful human control, highlighting that while many components are subjects of active research, the high-energy payload remains largely speculative and faces fundamental barriers.

Abstract: The European Union Aviation Safety Agency (EASA) is developing guidelines to certify AI-based systems in aviation with learning assurance as a key framework. Central to the learning assurance are the definitions of a Concept of Operations, an Operational Domain, and an AI/ML constituent Operational Design Domain (ODD). However, since no further guidance for these concepts is provided to developers, this work introduces a methodology for their definition. Concerning the concepts of the Operational Domain of the overall system and the AI/ML constituent ODD, a tabular definition language for both is introduced. Furthermore, processes are introduced to define the different necessary artifacts. For the specification process of the AI/ML constituent ODD, different preexisting steps were identified and combined, such as the identification of domain-specific concepts for the AI/ML constituent. To validate the methodology, it was applied to the pyCASX system that utilizes neural network-based compression. For the use case, the methodology proved it was able to produce an AI/ML constituent ODD of finer detail compared to other ODDs defined for the same airborne collision avoidance use case. Thus, the proposed novel framework is an important step toward a holistic framework following EASA’s guidelines.

Abstract: Unmanned aerial vehicles have been around for decades in the aerospace community, looking into the numerous technological and sophisticated solutions for transport alternatives, opening up new frontiers for aerial supremacy, accounting for the exponentially increasing population density. Now, UAVs accountable for their broad variation in their sizes from being minuscule up to a humungous weaponized system, primarily operate on electric systems to achieve better performance and effective payload allowances. With electricity dominating the technological race, improvising the same for sustainability requirements is also a budding area of scrutiny and research. That being well noted, solar power is another dimension of exploiting the concept of renewability and sustainability, owing to its adaptability. Hence, this work is a comprehensive, detailed review of the research that had been undertaken so far, in integrating solar power sources to unmanned aerial vehicles.

Abstract: This study presents numerical simulations of turbulent flow over a thick airfoil, modeled here as a semicircular cylinder, incorporating aerodynamic flow control (AFC) based on trapped vortex cells. Building upon previous work that focused on viscous effects, we now examine the influence of compressibility at various Mach numbers (M = 0.1, 0.2, and 0.3), corresponding to a diameterbased Reynolds number of 130, 000. The simulations employ a conventional RANS methodology, coupled with the Spalart-Allmaras and realizable k-ϵ turbulence models. To reinforce the validity of the results, cross-platform validation is performed using multiple numerical solvers, including pressure-based, density-based, and hybrid approaches (combining PISO/SIMPLE algorithms with the Kurganov-Noelle-Petrova scheme). Under the investigated conditions, the flow over the AFCintegrated configuration remains fully unseparated and exhibits outstanding lift performance. At Mach 0.2 (cruise conditions), the concept achieves a lift coefficient of approximately 6, about 95% of the theoretical maximum for a half-circular airfoil (2π), with a corresponding lift-to-drag ratio of around 24. As the Mach number increases to 0.3, the accelerated flow over the upper surface of the airfoil becomes locally transonic. Further analysis across a range of angles of attack (±150) at Mach 0.2 confirms the concept’s ability to maintain high lift and unseparated flow behavior, underscoring the effectiveness of the AFC system in enhancing aerodynamic performance.

Abstract: In the continuous quest to enhance the efficiency and sustainability of flight, the natural world offers a plethora of strategies and adaptations that can be harnessed in aviation technology. This review paper explores the multifaceted approaches of energy harvesting and drag reduction observed in nature, emphasizing their potential applications in modern aircraft and drone design. It delves into the study of micro and macro structures in various species, such as the drag-reducing micro-structures of riblets on bird feathers. The paper further investigates the broader morphological adaptations in birds and insects, including topics such as beak shape, coloration, flight configurations, materials, molting, and airfoil design for their contributions to aerodynamic proficiency. In addition, this review highlights various energy harvesting techniques observed in nature, such as soaring and ground effect exploitation, and their potential integration into aircraft design for improved endurance. Through a comprehensive review of these natural phenomena, this work aims to provide valuable insights for the development of innovative, eco-friendly aviation technologies, contributing to the global effort to reduce the environmental impact of air travel while improving the viability of drones in the nano to micro range.

Abstract: Aviation permanent magnet synchronous motors (PMSMs) are particularly susceptible to demagnetization faults due to the thermal sensitivity of permanent magnet materials, compounded by high-altitude conditions where reduced air density significantly limits cooling. In addition, the pursuit of high power density and compact structure in aviation design intensifies local thermal stress, while stringent reliability requirements mean even minor degradation can threaten operational safety. This paper investigates the operating characteristics of aviation PMSMs under demagnetization faults and proposes an effective diagnostic approach. A coupled electromagnetic–thermal finite element model is established to evaluate rated and no-load performance and calculate losses under rated conditions, and its validity for the motor body is confirmed using the RT-LAB semi-physical simulation platform. Subsequently, altitude-dependent ambient air parameters are incorporated to analyze the thermal–magnetic field distribution, highlighting the influence of high-altitude operation. Based on the thermal results, a fault dataset is constructed by selecting typical local demagnetization cases and classifying global faults into levels according to temperature criteria, with features extracted in both time and frequency domains. Finally, an intelligent diagnostic method integrating a deep belief network (DBN) and an extreme learning machine (ELM) is developed. Comparative results demonstrate superior accuracy and robustness over conventional methods, advancing demagnetization fault diagnosis for aviation PMSMs.

Abstract: Amphibious light sport aircraft (LSA) combine the versatility of land and water operations but suffer aerodynamic penalties from their inherent design requirements, limiting cruise performance. This study investigates two drag reduction features for a proposed high-performance amphibious LSA developed by Altavia Aerospace. The concept targets a 140-knot cruise speed, using retractable wingtip pontoons and a novel retractable hull step fairing. A 1/5-scale flying model was built and flight tested to assess the aerodynamic benefits of these features and evaluate sub-scale flight testing as a tool for drag measurement. Estimated propulsive power and GPS-based speed data corrected for wind were used to compute an estimated 17% reduction in drag coefficient by retracting the pontoons. The hull step fairing showed no measurable gains, likely due to inconsistent battery voltage, despite literature indicating potential 5% drag savings. Drag measurement precision of 7–9% was achieved using the power-based method, with potential precision better than 3% achievable if the designed thrust data system were fully validated and an autopilot integrated. A performance estimation for Altavia Aerospace’s concept predicts a cruise speed of 134 knots at 10000 ft. Achieving the 140-knot target may require further aerodynamic refinement, with investigation of a tandem seating configuration to reduce frontal area recommended. The study provides an initial drag assessment of retractable wingtip pontoons and demonstrates the potential of sub-scale flight testing for comparative drag analysis – two novel contributions to the field.

Abstract: Stable attitude control of unmanned or autonomous operations of vehicles moving in three spatial dimensions is essential for safe and reliable operations. Rigid body attitude control is inherently a nonlinear control problem, as the Lie group of rigid body rotations is a compact manifold and not a linear (vector) space. Prior research has shown that the largest possible domain of convergence provided by continuous attitude feedback control laws are obtained using a Morse function on as a measure of the attitude stabilization or tracking error. A polar Morse function on has four critical points, which precludes the possibility of global convergence of the attitude state. When used as part of a Lyapunov function on the state space (the tangent bundle ) of attitude and angular velocity, it gives a globally continuous state-dependent feedback control scheme with the minimum of the Morse function as the almost globally asymptotically stable (AGAS) attitude state. In this work, we explore the use of explicitly time-varying gains for Morse functions for rigid body attitude control. This strategy leads to discrete switching of the indices of the three critical points that correspond to the unstable equilibria of the feedback system. The resulting time-varying feedback controller is proved to be AGAS, with the additional desirable property that the time-varying gains destabilize the (locally) stable manifolds of the unstable equilibria. Numerical simulations of the feedback system with appropriate time-varying gains show that a trajectory starting from an initial state close to the stable manifold of an unstable equilibrium, converges to the desired stable equilibrium faster than a corresponding feedback system with constant gains.

Abstract: The transition to electric aircraft for zero-emission transport requires integrating thermal management systems for high-performance batteries without incurring significant weight, balance, or aerodynamic penalties. This study focuses on the aerodynamic penalties associated with air-cooling systems that can compound the presently unavoidable reduction in endurance imposed by current battery energy density limitations. Building on previous research into battery installation layouts and internal cooling flows, this study is the first to investigate the lift-to-drag (L/D) optimisation for the multiple wing-mounted inlets and outlets necessary for air-cooling batteries in the wing of an electrified aircraft. Wing-leading-edge inlets and NACA (National Advisory Committee for Aeronautics) ducts were analysed by systematically varying their layout, number, and dimensions. The analysis evaluated their effects on the wing’s lift, drag, and moment to maximise the L/D. Multiple highly efficient experimental test designs were developed to screen for the main factors to identify the best inlet and outlet configuration, resulting in 66 different Computational Fluid Dynamics (CFD) simulations in ANSYS Fluent. Following this, three CFD verifications cases of the best configuration were conducted to verify the cooling effect by combining both internal and external flow simulations with heat generation. Compared to the baseline wing of the carbon combustion aircraft, the best configuration caused a 1.75% reduction in L/D, range, and endurance. While the aerodynamic penalty is now minimised, the internal battery pack layout requires further optimisation to re-establish uniform cooling across the battery pack. Designers may still be able to separate the CFD analysis of the internal and external flow regimes with idealised inlets and outlets; however, more whole-field CFD iterations are needed to guide such subdivision to a viable and safe design for wing-mounted batteries. Further, the margins are such that wing-mounted electrification warrants careful instrumented validation in an aircraft. These findings provide crucial design guidance for sustainable aviation, particularly to enable after-market electrification projects.

Abstract: The rapid accumulation of space debris presents a serious threat to operational spacecraft, with the capture and removal of rapidly tumbling non-cooperative targets being a primary challenge. Non-contact electromagnetic de-tumbling technology is a promising solution due to its enhanced safety. This paper addresses the issue of torque modeling and validation in the electromagnetic de-tumbling process for a specific configuration involving a magnetic dipole and a spherical shell under a symmetrically distributed magnetic field. Based on the principles of electromagnetic induction, an approximate analytical expression for the electromagnetic eddy current torque on a rotating spherical shell within a dipole magnetic field is first derived. A high-fidelity finite element model is then established, which reveals a systematic discrepancy between the initial theoretical model and numerical simulation results. A distance-dependent power-law correction factor is introduced to calibrate the theoretical model, significantly improving its accuracy and reducing the average error to 1.5 percent. Finally, a ground-based experimental platform is designed and implemented. Experimental results demonstrate that the corrected approximate analytical model agrees well with the empirical data, verifying its validity and accuracy under the given conditions and providing a reliable theoretical basis for the design of future space debris de-tumbling controllers.

Abstract: Close formation flight is a practical strategy for fixed-wing unmanned aerial vehicle (UAV) swarms. Maintaining UAVs at aerodynamically optimal positions is essential for efficient formation flight. However, aerodynamic optimization methods based on computational fluid dynamics (CFD) are computationally intensive and difficult to apply in real time for large-scale formations. Inspired by bio-formation flight, this study proposes an on-board sensing-based method for wake flow field estimation, with potential for extension to complex formations. The method is based on a parameter identification-induced velocity model (PI-Model), which uses only onboard sensors, including two lateral air data systems (ADS), to sample the wake field. By minimizing the residual of the induced velocity, the model identifies key parameters of the wake and provides a dynamic estimation of the wake velocity field. Comparisons between the PI-Model and CFD simulations show that it achieves higher accuracy than the widely used single horseshoe vortex model in both wake velocity and aerodynamic effects. Applied to a two-UAV formation scenario, CFD validation confirms that the trailing UAV achieves a 15%–25% drag reduction. These results verify the effectiveness of the proposed method for formation flight and demonstrate its potential for application in complex, dynamic multi-UAV formations.

Abstract: Composite materials are extensively employed in aircraft due to their high specific strength and stiffness, superior impact resistance, and fatigue performance. Bird strikes can inflict severe damage to critical aircraft components such as the fuselage, engines, and wings, compromising flight safety. Certification regulations mandate that all components must demonstrate a specified level of bird strike resistance prior to aircraft installation. Consequently, this study focuses on carbon fiber composite laminates. By varying impact velocity, impact angle, and ply orientation, it investigates the resulting patterns of bird strike impact behaviors in these composites. The derived patterns provide theoretical reference for further research into the impact mechanics of composite materials subjected to bird strikes.