Search Results (711)

Cycloidal propellers are known for their omnidirectional vectored thrust, enabling smooth transitions between hovering and forward flight, making them ideal for unmanned aerial vehicles (UAVs) and electric vertical take-off and landing (eVTOL) aircraft. However, cycloidal propellers tend to have lower hovering efficiency than screw propellers at the unmanned aerial vehicle (UAV) scale. Adding end plates to the blade tips can improve hovering efficiency by suppressing blade tip vortices. But the impact of these end plates have not been thoroughly studied. This paper aims to seek the designs with enhanced hovering efficiency and develop design guidelines for cycloidal propellers with end plates. Comprehensive force measurement experiments are performed on designs with and without end plates, and designs with rotating and static end plates. Complementary high-fidelity numerical analysis is performed to gain deeper insights into the complex 3D flow structures and the role of end plates in suppressing induced power losses. Our study reveals that end plates can effectively suppress the efficiency degradation typically associated with low aspect ratio blades. We demonstrate that even with a blade aspect ratio of 1.5, a cycloidal propeller equipped with end plates can achieve high hovering efficiency, thereby establishing a new design guideline for lightweight, high-performance propulsion systems. The designs with stationary end plates are superior to those with rotating end plates because rotation introduces additional torque caused by the friction force. Designs featuring thick end plates (${\overline{t}}_e=0.056$) outperform those with thin end plates (${\overline{t}}_e=0.004$), as the rounded edges can eliminate end plate vortices. A comprehensive parametric study is conducted, evaluating blade chord-to-radius ratios from 0.26 to 0.65, aspect ratios from 0.5 to 3.0, pitching amplitudes from 10° to 50°, as well as end plate configurations (stationary vs. rotating, and thin vs. thick). From this parameter space, the best design was identified as featuring stationary thick end plates (${\overline{t}}_e=0.056$), a chord-to-radius ratio of 0.65, and a large pitching amplitude of 40 degrees. It achieves a hovering efficiency of 0.72 with a blade aspect ratio of 3, which is comparable to that of sub-scale rotors with similar Reynolds number. In contrast, for the cases without end plates, the highest hovering efficiency is lower than 0.6. Full article

The surging need for public security risk mitigation has placed stricter demands on the modernization of emergency response capacities. Unmanned aircraft systems (UASs) offer a promising solution for liquid anti-riot agent dispersion, yet the complex interaction between rotor-induced downwash and droplet trajectories makes nozzle layout optimization a significant challenge. To address the prohibitive computational costs of traditional Computational Fluid Dynamics (CFD) and the limitations of single-objective optimization, this study proposes an integrated “simulation–modeling–optimization–decision” framework. First, a linear nozzle layout was identified as superior to the traditional circular arrangement, achieving a 44.8% increase in deposition rate. Subsequently, Optimal Latin Hypercube Sampling (OLHS) and CFD simulations were combined to construct high-precision Kriging surrogate models for three key indicators: deposition rate, uniformity, and coverage rate. The NSGA-II algorithm was then employed to solve the multi-objective trade-off, followed by the entropy-weighted TOPSIS method to identify the optimal engineering solution. Results indicate that nozzle count is the dominant system-level variable under the constant per-nozzle flow-rate condition, showing strong positive correlations with all performance indicators. The identified optimal configuration (6 nozzles with a 1.88 m boom length) achieved a 66.1% increase in deposition rate and an 18.7% increase in coverage rate compared to the original circular layout. Furthermore, the surrogate-based framework improved optimization efficiency to 296% compared to full factorial methods. This study provides a scientific theoretical basis and a highly efficient technical pathway for the structural design of high-performance UAV spray systems. Full article

The rapid expansion of Unmanned Aircraft Systems (UAS) operations has created an urgent need for scalable strategic conflict resolution methods within the U-space framework. When requested 4D flight plans overlap with previously authorised ones, the Flight Authorisation Service denies the request and can provide the UAS operator with an alternative, conflict-free route. While traditional pathfinding algorithms ensure optimal routes, their computational cost creates a critical bottleneck during the flight activation phase or emergency missions, which demand near-instantaneous responses. To address this, we propose a three-stage framework. First, an Octree spatial partitioning discretises the airspace to identify occupied cells. Second, both A* and JPS algorithms are implemented to establish an optimal reference route. Finally, a standard Deep Reinforcement Learning (DRL) model, trained on realistic PX4 Simulator trajectories and using a well-adjusted reward function, generates alternative paths that optimise distance and energy. Results demonstrate that this DRL architecture achieves near-optimal routing behaviour. Crucially, it reduces computation time by several orders of magnitude compared to traditional algorithms, solving complex conflicts in milliseconds rather than seconds. We conclude that simple, well-tuned DRL architectures overcome latency limitations of classical pathfinding while achieving optimal results, ensuring rapid, safe, and efficient conflict resolution for high-density U-space. Full article

The rapid expansion of Unmanned Aircraft System (UAS) operations has created an urgent need for scalable strategic conflict resolution methods within the U-space framework. When requested 4D flight plans overlap with previously authorised ones, the Flight Authorisation Service (FAS) denies the request, and can provide the UAS operator with an alternative route, free of conflict. This work introduces a Machine Learning-based tool designed to support this process, which consists of three sequential phases. First, an Octree spatial partitioning technique is proposed, discretising the airspace, further identifying the previously occupied cells and visualising the occupied airspace, so that the UAS operator can manually find an alternative route. Then, the widely known A* pathfinding algorithm is implemented in this discretized airspace, allowing the shortest or most optimal conflict-free alternative route. Finally, the methodology integrates a Machine Learning (Reinforcement Learning) model, created from scratch and trained with realistic flight trajectories from a PX4 Simulator, to further optimise flight paths, explicitly accounting for operational constraints such as distance and battery consumption. In this work, both methods are compared, addressing traditional algorithms limitations with Machine Learning (ML) techniques, showing that a near-optimal behaviour can be achieved with the ML approach, at a fraction of the computation time needed. Full article

The performance of the meteorological measurements of an Unmanned Aircraft System (UAS) is studied in this paper by comparison with the simultaneous data collected by a wind mast, a radiosonde sensing package and ground-based, remote-sensing meteorological instruments at the radiosonde station of King’s Park, Hong Kong. They are found to meet the “breakthrough” level requirement of the World Meteorological Organization. The UAS is then used to collect meteorological data for the first time at a sandbox project location in Hong Kong for low altitude economy (LAE), namely, an area of complex terrain at an isolated island called Peng Chau. Some interesting features are identified in the vertical profiling flight of wind speed and turbulent kinetic energy (TKE), which forms the basis for developing meteorological support for LAE at this site in the future. High-resolution numerical weather prediction (NWP) simulation is then performed and evaluated statistically by comparison with UAS measurements at these two locations. The simulation of wind direction and TKE appears to be rather challenging as demonstrated in this comparison exercise. The root-mean-square-error of the simulated TKE is found to be of a similar order of magnitude as the absolute value itself, and the wind direction from the outer domain is found to have limited “correction” with the use of high-resolution terrain data in the NWP simulation with the mesoscale model. Further research directions for the simulation are discussed, with the objective of providing weather forecasting services for supporting LAE developments in Hong Kong. Full article

Unmanned Aircraft Systems (UAS) have seen a significant growth in civilian space over the past decade. The number one ranked challenge in UAS operations in Europe is regulatory obstacles such as the Specific Operations Risk Assessment (SORA) for 2023–2025. Existing approaches have focused on individual technical solutions (radio technologies, redundancy schemes, or cryptographic protections) or on high-level safety analysis, but have not integrated regulatory compliance, risk assessment, and repeatable systems models that directly support SORA artifact generation and rapid adaptation across BVLOS operational contexts. Thus, the current state-of-the-art apparatus lacks a systematic Model-Based Systems Engineering (MBSE) approach that can cater to Command and Control (C2) data-link design for Beyond Visual Line-of-Sight (BVLOS) missions. In this work, we propose an MBSE methodology designed to assist engineers in designing a C2 data link for BVLOS drone operations that complies with SORA regulations in the Netherlands and Europe. To validate the use of MBSE in a wide range of complex drone operations, we demonstrate how subtle modifications in the proposed engineering models can be made without any major overhaul of new SORA applications, and this is validate these changes through laboratory software tests and simulations. Full article

Efficient communication infrastructure is essential for Unmanned Aircraft Systems (UASs) operating beyond visual line of sight (BVLOS). Both terrestrial and non-terrestrial networks struggle with coverage gaps and are susceptible to disruptions. This paper analyzes integrated terrestrial–non-terrestrial network (TN-NTN) architectures for UAS communications in 6G, focusing on three connectivity methods: terrestrial connectivity, indirect satellite connectivity, and direct UAS–satellite links. We provide the assessment of different connectivity options. Major challenges are discussed, including antenna limitations, reliability, channel modeling, and regulatory alignment. Full article

The Unmanned Aircraft System Traffic Management (UTM) system is designed to autonomously coordinate dense Unmanned Aerial Vehicles (UAVs) within shared airspace, ensuring both the efficiency and safety of aerial traffic. With the rapid proliferation of UAV applications, autonomous UTM systems have become increasingly essential, motivating various stakeholders to develop their distinct UTM solutions. However, due to the lack of common guidelines, these emerging solutions exhibit substantial incompatibilities, which hinder the transferability of existing techniques and the overall standardization of UTM. To address the fragmentation, this paper provides a systematic survey of existing UTM research and identifies commonalities across various UTM systems. Specifically, this paper summarizes core UTM service modules and groups them with similar objectives, thereby proposing a unified UTM framework with four layers: Fundamental Infrastructure, Pre-flight UTM, In-flight UTM, and UTM Application. Based on the framework, existing solutions for each module are reviewed in detail. Furthermore, this paper draws analogies between UTM systems and more mature transportation systems, like railways, to identify transferable solutions and derive UTM future trends. This survey aims to clarify the current state of UTM research and provide guidance for future studies in this field. Full article

Conventional direct communication in Manned–Unmanned Teaming (MUM-T) suffers from fundamental scalability and security limitations. As the number of Unmanned Aerial Vehicles (UAVs) increases, the communication burden on the manned aircraft (MA) grows significantly, while security threats originating from UAVs may directly propagate to the MA. To address these challenges, this paper proposes a hierarchical communication architecture that introduces dedicated Network Drones (NDs) as intermediate communication mediators and trust boundaries between the MA and multiple UAV swarms. In the proposed design, the MA interacts exclusively with NDs, while UAV swarms communicate through ND-mediated links, effectively bounding the number of MA-facing connections and enabling scalable communication. Building on this structured communication model, a message-level Zero-Trust framework is enforced at the MA–ND interface. Each message is evaluated using a multi-dimensional risk model that incorporates authentication consistency, behavioral consistency, content validity, and contextual information, enabling early detection and containment of compromised UAV behavior. Furthermore, the architecture incorporates backup planning mechanisms, including dynamic reassociation and hot-standby operation, to ensure robust communication under ND failure conditions. Experimental results demonstrate that the proposed approach reduces MA-facing communication overhead, stabilizes end-to-end latency, and improves detection performance in terms of false positives and false negatives, while maintaining system robustness under failure scenarios. Full article

This study presents the aerodynamic design of the wing system for a fixed-wing vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV), developed to enhance energy efficiency and operational performance in agricultural applications. The design responds to the limitations of conventional multirotor drones, which are limited by low endurance and high energy consumption, and crop-dusting aircraft, which are unsuitable for irregular terrain such as that found in Chihuahua, Mexico. A comprehensive methodology was adopted, integrating the selection of airfoils optimized for low-Reynolds-number conditions, computational fluid dynamics (CFD) simulations, winglet incorporation, and experimental validation through wind tunnel testing. The SELIG 1223 airfoil was selected for its superior aerodynamic efficiency, demonstrating a potential reduction of up to 55% in power requirements compared to multirotor configurations. Despite some variability in experimental results, the proposed design demonstrated consistent feasibility and reliability. Future work will focus on field validation and geometric adaptation to diverse operational scenarios, reinforcing its applicability across heterogeneous agricultural landscapes. Full article

Distributed electric propulsion (DEP) systems offer a wide range of options for arranging the propulsion units on an aircraft. In most cases, the position of the propulsion systems is optimized for one specific flight phase, e.g., takeoff or cruise. Taking advantage of the high lift potential of the DEP also during descent and approach phases represents a challenge due to increased thrust. Energy harvesting propellers (EHPs) can be used to adapt the resulting thrust, by generation an additional drag force while regenerating a certain amount of energy back into the system. Therefore, the scaled flight demonstrator (SFD) e-Genius-Mod was modified to implement an energy harvesting powertrain in a DEP system. The energy harvesting wingtip propellers are integrated in a pusher configuration. It is possible to investigate different operation modes for recuperation, such as Windmilling and Opposite Pitch, by adjusting different propeller pitch angles. The electronics used for the wingtip propellers (WTPs) enable the control and measurement of the recuperation performance and furthermore to charge recuperated energy back into the battery. The energy harvesting system was tested in a wind tunnel to verify its functionality. In Windmilling mode, the maximum mean electrical power output is −25.7 W. In Opposite Pitch mode, the values were significantly higher, with a maximum mean electrical power of −184 W. This corresponds to up to seven times as much regenerated power in Opposite Pitch mode. Full article

A compact millimeter-wave radar system operating at 33 GHz is presented for integration on small unmanned aerial systems (UAS) and for ground-based counter-UAS reconnaissance. The design is specifically motivated by civil-sector agricultural applications, where large-payload crop-dusting and precision-spraying drones operating under FAA 14 CFR Part 137 require lightweight sense-and-avoid radar that conforms aerodynamically to existing aircraft or ground vehicles. The system is based on a 36-element hemispherical conformal phased array of crossed half-wave dipole radiators that generate right-hand circular polarization (RHCP) on transmit and selectively receives left-hand circular polarization (LHCP) echoes from targets, providing passive first-stage suppression of co-polarized rain and ground clutter. A Linearly Constrained Minimum Variance (LCMV) digital beamformer, applied to per-element analog-to-digital converter (ADC) outputs, delivers closed-form beam weights that enforce a distortionless response at each scan direction while globally minimizing sidelobe power. The formulation resolves the main-beam drift caused by the ill-conditioned re-scaling step in iterative Chebyshev tapering, achieving sidelobe levels below $-20$ dB with main-beam peaks within $0.1$° of their commanded angles across all evaluated positions. Mutual coupling between array elements is modeled analytically using the induced-EMF method, yielding a $36\times 36$ impedance matrix whose off-diagonal entries are at most 8.2% of the element self-impedance at the minimum inter-element separation of 2.70 $\lambda$. A closed-form decoupling matrix is applied to the receive manifold prior to LCMV weight computation. Seven simultaneous independent receive beams covering $0$°–$60$° elevation are formed from a single data snapshot. A Scaled Conjugate Gradient neural network classifier, trained on radar-equation-scaled micro-Doppler features following Swerling I–IV radar cross-section (RCS) fluctuation statistics, achieves overall classification accuracy above 85% across five target classes. The five classes comprise two bird-signature classes (SW-I and SW-II), two UAV-signature classes (SW-III and SW-IV), and a clutter class. The design is entirely simulation-based; experimental validation using a sub-array prototype is identified as the primary direction for future work. Full article

This study presents a flight-envelope-based methodology for aerodynamic load assessment and composite material selection applied to a hybrid fixed-wing tri-rotor VTOL (Vertical Take-Off and Landing) unmanned aerial vehicle (UAV). A certification-oriented maneuver and gust envelope was established to define the critical load cases. Reynolds-averaged Navier–Stokes (RANS) simulations of the full aircraft at nominal cruise were performed to determine global aerodynamic coefficients and distributed pressure fields, including interference effects from the fuselage and externally mounted VTOL system. A complementary wing-only angle-of-attack study was used to characterize lift, drag, and chordwise pressure distributions over the relevant incidence range. Critical envelope points were mapped to equivalent aerodynamic states in terms of lift coefficient and angle of attack, enabling a quasi-steady correlation between certification loads and CFD (Computational Fluid Dynamics) results. In parallel, carbon fiber-reinforced polymer (CFRP) laminates were experimentally evaluated under tensile, open-hole tensile, and flexural loading. The results indicate that, within the two investigated laminate configurations, the [0°/90°] CFRP laminate provides the more suitable strength and stiffness for primary wing structures, while off-axis laminates are better suited for secondary regions. The proposed workflow links flight-envelope definition, aerodynamic analysis, and material selection, providing a basis for preliminary structural design. Full article

Maneuverability and performance of UAVs are strongly influenced by the adopted propulsion layout. Electrification has enabled modern UAVs to achieve unprecedented maneuverability, including hovering and VTOL (Vertical Take Off and Landing) capabilities, allowing the adoption of complex propulsion layouts otherwise impossible to manage with conventional fossil powered machines. Despite significant advancements in lithium-based cell technologies, the energy densities achieved by current storage systems remain insufficient to ensure extended operational autonomy. Hybrid systems represent an effective compromise, combining the high energy density of conventional fuels with agile power management of electric storage systems. In this work, the authors investigate the design, modelling, and control of an innovative autonomous compound helicopter equipped with a hybrid propulsion system. For this purpose, a comprehensive digital twin has been developed, capable of simulating the interactions among the vehicle, propulsion system, and energy management systems under a predefined mission profile. Full article