Search Results (125)

The loads of a model tilt-proprotor with a gimbaled hub were measured in the wind tunnel of CHRDI, operating at 90°, 80°, 70°, 60°, and 45° inclination angles to represent the rotor loads of helicopter and transient flight modes. The flap, lead-lag moments, and pitch rod forces were measured. A comprehensive model was established with both linear inflow and free-wake non-linear inflow models. It is shown that there is a better correlation of alternating flap bending moments between test data and linear inflow model predicted values for the helicopter mode and a good correlation between measured data and free-wake predicted values for transition modes. The static moments are well captured by all inflow models at high thrust coefficients, while they fail to reflect the flap bending direction of the blade root at low thrust coefficients. Neither of the inflow models captured higher harmonics of the blade flap bending moments. The measured 2/rev harmonics of the lag bending moments lie between the linear inflow model and the free wake model predicted values. The current model with no dynamic stall model failed to capture the oscillating loads of the pitch rod. Full article

Servo-free tilt-rotor UAVs decouple position and attitude control without using servos, which cuts structural weight and removes the travel limits of traditional designs. In many applications—such as aerial platform operations and airborne photogrammetry—large attitude changes are required during hover. Conventional control-allocation schemes tend to distribute thrust unevenly, making actuators prone to saturation. To overcome these challenges, we propose a thrust-balancing control-allocation strategy specifically for passive-hinge tilt-rotor octocopters. The presented method integrates min–max optimization with the force decomposition (FD) algorithm, effectively handling actuator saturation while maintaining low computational complexity. Additionally, an offline-trained neural network is employed to replace the online optimization process, enabling the complete controller to operate on the flight control board without relying on an onboard computer. Simulation and experiment results confirm the effectiveness of the proposed strategy, demonstrating enhanced control performance and its practical feasibility for real-world UAV applications. Full article

The distributed electric tilt-rotor Unmanned Aerial Vehicle (UAV) combines the vertical take-off and landing (VTOL) capability of helicopters with the high-speed cruise performance of fixed-wing aircraft, offering a transformative solution for Urban Air Mobility (UAM). However, aerodynamic interference between rotors is a new challenge to improving their flight efficiency, especially the dynamic interactions during the transition phase of non-parallel tandem dual-rotor systems, which require in-depth investigation. This study focuses on the aerodynamic performance evolution of the tilt-rotor system during asynchronous transition processes, with an emphasis on quantifying the influence of rotor tilt angles. A customized experimental platform was developed to investigate a counter-rotating dual-rotor model with fixed axial separation. Key performance metrics, including thrust, torque, and power, were systematically measured at various tilt angles (0–90°) and rotational speeds (1500–3500 RPM). The aerodynamic coupling mechanisms between the front and rear rotor disks were analyzed. The experimental results indicate that the relative tilt angle of the dual rotors significantly affects aerodynamic interference between the rotors. In the forward tilt mode, the thrust of the aft rotor recovers when the tilt angle reaches 45°, while in the aft tilt mode, it requires a tilt angle of 75°. By optimizing the tilt configuration, the aerodynamic performance loss of the aft rotor due to rotor-to-rotor aerodynamic interference can be effectively mitigated. This study provides important insights for the aerodynamic performance optimization and transition control strategies of the distributed electric tilt-rotor UAV. Full article

Traditional multirotor UAVs (unmanned aerial vehicles) are inherently underactuated, with coupled position and attitude control, which limits their maneuverability in specific applications. This paper presents a fully actuated quadrotor design based on a swashplateless rotor mechanism. Unlike existing fully actuated UAV designs that rely on servo-driven tilt mechanisms, this approach minimizes additional weight and simplifies the structure, resulting in a more maintainable system. The design, modeling, and control strategies for the quadrotor are presented. Furthermore, we propose a decoupled control method to address the need for both fully actuated and underactuated modes. The control architecture employs parallel attitude and position control structures and decouples the two subsystems using a nonlinear dynamic inversion (NDI) method. A compensation module is introduced to address the constraints imposed by the maximum rotor deflection angle and the corresponding feasible force set. This compensation module actively adjusts the attitude to mitigate the saturation of the required thrust, effectively overcoming the impact of rotor deflection angle limitations on trajectory tracking performance. The approach facilitates seamless switching between fully actuated and underactuated modes, enhancing the system’s flexibility and robustness. Simulation and flight experiments demonstrate the effectiveness and performance of the proposed design. Full article

This paper explores unconventional configurations of rotary-wing unmanned aerial vehicles (UAVs), focusing on designs that transcend the limitations of traditional ones. Through innovative rotor arrangements, refined airframe structures, and novel flight mechanisms, these advanced designs aim to significantly enhance performance, versatility, and functionality. Rotary-wing UAVs that deviate markedly from conventional models in terms of mechanical topology, aerodynamic principles, and movement modalities are rigorously examined. These unique UAVs are categorized into four distinct groups based on their mechanical configurations and dynamic characteristics: (1) UAVs with tilted or tiltable propellers, (2) UAVs featuring expanded mechanical structures, (3) UAVs with morphing multirotor capabilities, and (4) UAVs incorporating groundbreaking aerodynamic concepts. This classification establishes a structured framework for analyzing the advancements in these innovative designs. Finally, key challenges identified in the review are summarized, and corresponding research outlooks are derived to guide future development in rotary-wing drone technology. Full article

The present work is aimed at investigating the arrangement design of an inner tilted-rotor hexacopter to optimize aerodynamic performance with different rotor spacing ratios (s/D) and dihedral angles (β). Both experiments and numerical simulations were applied for different rotor arrangements, and the better rotor agreement was related to both higher thrust and lower power consumption. The results show that hovering efficiency is mainly affected by rotor spacing ratios and dihedral angles. Appropriate rotor spacing with moderate rotor interference from the blade tip vortices, as well as downwash flow, reduce vortex distortion and fragmentation. The results show that a hexacopter with inner tilted-rotors obtains a larger thrust and smaller power with a high factor of merit (FM) at s/D = 1.6 and β = 40°, and this is considered to be the optimal arrangement for a hexacopter with excellent aerodynamic characteristics. Full article

Electric vertical take-off and landing vehicles introduce challenges in powertrain design with short but high peak loads and low-load phases over longer periods of time during wing-borne flight. In this paper, three powertrain topologies are analyzed for a tilt-rotor urban air mobility vehicle with an expected entry into service after 2030. The powertrains are studied on the level of preliminary sizing for the design mission of the vehicle. The three powertrain topologies studied and compared are battery-only, fuel cell-only and a hybrid of the two energy sources. Parameter studies on the gearbox transmission ratio, the design point of the fuel cell system as well as the degree of hybridization were carried out. The combination of fuel cell and battery was found to be most beneficial in terms of mass when the fuel cell is sized for slightly more than cruise power. In flight phases with higher power requirements, the batteries would provide the additional boost. Full article

The elastic-supported tilting pad journal bearing brings new momentum and opportunities for improving the lubrication performance and dynamic stability of high-speed bearing–rotor systems. The objective of this study is to investigate the dynamic and lubrication characteristics of a dual parallel spring-supported tilting pad journal bearing (DPSTPJB) system under unbalanced journal excitation. Considering the tilting angle and radial displacement of the pads, a 10-DOF dynamic model of the four-pad DPSTPJB system is established, accounting for the effects of unbalanced load, nonlinear fluid film force, and parallel spring force/moment. Numerical solutions are obtained for the dynamic responses of the journal and pads as well as the minimum film thickness and maximum film pressure. The effects of spring stiffness, stiffness ratio, and included angle on journal vibration, minimum film thickness, and maximum film pressure are revealed. The results show that the parallel spring parameters have a positive effect on the optimization of bearing performance with an optimal stiffness ratio that minimizes journal vibration and optimizes fluid film thickness and pressure. This research provides a theoretical basis for the optimization design and application of the DPSTPJB. Full article

Hover-capable unmanned aerial vehicles (UAVs), including rotary-wing UAVs such as unmanned helicopters, multi-rotor drones, and tilt-rotor UAVs, are widely employed due to their hovering capabilities. In recent years, tilt-rotor aircraft, which offer both vertical takeoff and landing as well as rapid maneuverability, have increasingly become a research focus. This paper first proposes a design concept for a flying-wing configuration tilt-rotor tri-rotor UAV, detailing the selection of airfoils and the calculation of aerodynamic parameters. To address the specific operational requirements and flight characteristics of this UAV, a specialized tilting mechanism was developed, and a flight control system was designed and implemented using classical PID control methods. Finally, a prototype of the tilt-rotor tri-rotor UAV was fabricated and subjected to flight tests. The results from both simulations and flight tests confirmed that the UAV met the design performance criteria and that the control method was effective. Full article

Flying cars are envisioned as key components of the Future Comprehensive Transport Network System. Current flying car designs struggle to balance ground maneuverability with aerial agility, which means they cannot operate on standard roads (3.5 m width). Additionally, the low energy density of existing aviation batteries limits their operational range. Therefore, a high lift-to-drag ratio (L/D) improves efficiency by reducing drag and extending the operational range. This leads to more economical and efficient flight performance, making it particularly beneficial for flying cars. This paper addresses the challenges of the land–air amphibious design and high-L/D configuration design of flying cars, and Computational Fluid Dynamics (CFD) simulations were conducted to optimize the overall configuration of a flying car, followed by creating a 1:4-scale model and validating its aerial posture. The results confirmed the structural integrity of the tilting and folding wing design for amphibious flying cars, achieving a fixed-wing mode L/D of 11. This design effectively addresses the traditional flying car issue of neglecting ground travel requirements by focusing solely on the flight capabilities of simulated aircraft or drones. Full article

The spacecraft microgravity simulation air-bearing platform is a crucial component of the spacecraft ground testing system. Special disturbances, such as the flatness and roughness of the contact surface between the air bearings and the granite platform, increasingly affect the control accuracy of the simulation experiment as the number of air bearings increases. To address this issue, this paper develops a novel compensation control system based on Active Disturbance Rejection Control (ADRC), which estimates and compensates for the disturbing forces and moments caused by the roughness and levelness of the contact surface, thereby improving the control precision of the spacecraft ground simulation system. A dynamic model of the multi-air-bearing platform under disturbance is established. A cascade ADRC algorithm based on the Linear Extended State Observer (LESO) is designed. The Gauss–Newton iteration method is used to identify the parameters of the sliding friction coefficient and the tilt angle of the air-bearing platform. A full-physics simulation experimental platform for spacecraft with rotor-based propulsion is constructed, and the proposed algorithm is validated. The experimental results show that on a marble surface with a flatness of grade 00, an overall tilt angle of 0–1 degrees, and a surface friction coefficient of 0–0.01, the position control accuracy for the simulated spacecraft can reach 1.5 cm, and the attitude control accuracy can reach 1°. Under ideal conditions, the identification accuracy for the contact surface friction coefficient is 2 × 10⁻⁴, and the recognition accuracy for the overall levelness of the marble surface can reach 1 × 10⁻³, laying the foundation for high-precision ground simulation experiments of spacecraft in multi-air-bearing scenarios. Full article

This paper focuses on the modeling, control, and simulation of an over-actuated hexacopter tilt-rotor (HTR). This configuration implies that two of the six actuators are independently tilted using servomotors, which provide high maneuverability and reliability. This approach is predicted to maintain zero pitch throughout the trajectory and is expected to improve the aircraft’s steering accuracy. This arrangement is particularly beneficial for precision agriculture (PA) applications where accurate monitoring and management of crops are critical. The enhanced maneuverability allows for precise navigation in complex vineyard environments, enabling the unmanned aerial vehicle (UAV) to perform tasks such as aerial imaging and crop health monitoring. The employed control architecture consists of cascaded proportional (P)-proportional, integral and derivative (PID) controllers using the successive loop closure (SLC) method on the five controlled degrees of freedom (DoFs). Simulated results using Gazebo demonstrate that the HTR achieves stability and maneuverability throughout the flight path, significantly improving precision agriculture practices. Furthermore, a comparison of the HTR with a traditional hexacopter validates the proposed approach. Full article

Tilting pad bearings are core components of rotating machinery. Due to factors such as manufacturing, installation and operation, there may be a mismatch between the bearing pad surface and the shaft diameter, leading to issues like high bearing temperature and rotor system vibration. In engineering practice, surface grinding is often used to resolve these problems. This paper analyzed the mechanism of surface grinding, systematically studies the impact of individual or combined surface grinding on the static and dynamic characteristics of tilting pad bearings and summarizes reasonable pre-load adjustment schemes. The results show that the principle of pad surface grinding is to change the pre-load coefficient of the bearings. The grinding of the oil inlet and outlet sides of the pad surface changes the clearance of the pad, increases the pre-load coefficient, reduces the working temperature of the bearing, increases the thickness of the oil film, and increases power consumption; the grinding of the middle parting surface of the pad changes the clearance of the bearing, increases the pre-load coefficient, and increases the main stiffness and damping coefficient of the bearing. Using these results, a fault diagnosis was performed on a turbine unit with excessive vibration during an on-site operation, leading to effective control. The research provides technical references for the condition monitoring of turbine tilting pad bearing vibrations and the safe operation of units, offering significant engineering implications. Full article

Work on trajectory optimization is evolving rapidly due to the introduction of Artificial-Intelligence (AI)-based algorithms. Small UAVs are expected to execute versatile maneuvers in unknown environments. Prior studies on these UAVs have focused on conventional controller design, modeling, and performance, which have posed various challenges. However, a less explored area is the usage of reinforcement-learning algorithms for performing agile maneuvers like transition from hover to cruise. This paper introduces a unified framework for the development and optimization of a tilt-rotor tricopter UAV capable of performing Vertical Takeoff and Landing (VTOL) and efficient hover-to-cruise transitions. The UAV is equipped with a reinforcement-learning-based control system, specifically utilizing algorithms such as Deep Deterministic Policy Gradient (DDPG), Trust Region Policy Optimization (TRPO), and Proximal Policy Optimization (PPO). Through extensive simulations, the study identifies PPO as the most robust algorithm, achieving superior performance in terms of stability and convergence compared with DDPG and TRPO. The findings demonstrate the efficacy of DRL in leveraging the unique dynamics of tilt-rotor UAVs and show a significant improvement in maneuvering precision and control adaptability. This study demonstrates the potential of reinforcement-learning algorithms in advancing autonomous UAV operations by bridging the gap between dynamic modeling and intelligent control strategies, underscoring the practical benefits of DRL in aerial robotics. Full article

This paper considers a hybrid vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV). By tilting its propellers, the aircraft can transition from rotary-wing (RW) multirotor mode to fixed-wing (FW) mode and vice versa. A novel architecture of a neural network-based controller (NNC) is presented. An “imitative learning” approach is employed to train the NNC to mimic the response of an expert but computationally expensive model predictive controller (MPC). The resulting NNC approximates the MPC’s solution while significantly decreasing the computational cost. The NNC is trained on the longitudinal axis. Successful simulations and real flight tests prove that the NNC is suitable for the longitudinal axis control of a complex nonlinear system such as the tilt-rotor VTOL UAV through a sequence of transitions between the RW mode to the FW mode, and vice versa, in a forward flight. Full article