Search Results (80)

Contactless transmission of mechanical power, which is characteristic of coaxial magnetic gears (CMGs), offers significant advantages over conventional mechanical gears, in particular, reduced maintenance frequency and inherent overload protection. At the same time, there is a lack of design methodologies for this type of gear based on the analysis and systematization of experience gained from already implemented designs. This paper presents a method for determining the maximum magnetic torques of CMGs on the basis of an equivalent magnetic-circuit model. The error associated with the proposed methodology does not exceed ±15%, which enables the influence of geometric parameters and the magnetic properties of materials on the key performance indicators of the gear to be assessed already at the preliminary design stage. A mathematical model of CMG dynamics was also developed, based on a quasi-stationary two-dimensional approximation of the magnetic field, accounting for the geometry of the magnetic circuit, the spatial distribution of the magnetic vector potential, and magnetic-circuit saturation. The proposed mathematical model was verified using the results of physical experiments. The discrepancy between the calculated and experimental values of the torque on the low-speed shaft in the steady state does not exceed 5.5%. Based on the optimization procedure, the dependence of the maximum linear torque density on the outer diameter of the CMG, the number of poles of the high-speed rotor, and the transmission ratio was determined. It was shown that, as the number of poles increases, the linear torque density also increases and, for example, for diameters of approximately 800 mm, it may exceed 100 N·m/m. Full article

In coaxial twin-rotor helicopters, the minimum blade tip distance may approach danger thresholds during rotor intersection under high-speed rotation and complex aerodynamic conditions, posing collision risks. This study proposes a multi-sensor fusion approach for measuring the blade collision warning parameter $d$, which maps the collision risk into a single evaluation metric and provides stable real-time outputs of phase, spatial position, and inter-blade distance under high-speed operational conditions. A collaborative measurement scheme integrating encoder-based phase detection, tip-tracking camera positioning, and millimeter-wave radar distance measurement was developed. A dynamic rotor motion simulation experimental platform with single-side rotation and rigid blades was constructed to validate the measurement performance under varying rotor speeds and blade tip distances. Experimental results indicate that measurement errors remain within ±1.87 mm, repeatability errors are below 0.67 mm, and the coefficient of variation is under 0.2%, confirming the accuracy and stability of the proposed method under dynamic conditions. Additional multi-speed experiments show that, over the tested rotational-speed range, the error of $d$ remains within (−5.86 mm, 6.57 mm), although the fluctuation of the results increases moderately at higher speeds as the blade intersection duration becomes shorter. The proposed approach provides a laboratory-validated technical basis for blade collision risk assessment and future warning implementation in coaxial twin-rotor helicopters. Full article

High-speed capability is a defining feature of next-generation helicopters, enabling time-sensitive missions. This paper compares three high-speed configurations: tiltrotor, coaxial rigid rotor, and compound conventional rotor. Based on existing technology and operational needs, the study focuses on the aerodynamic layout of a compound conventional rotor high-speed unmanned helicopter. With key parameters, including a 300 kg takeoff weight and a maximum speed of 240 km/h, iterative optimization was conducted using theoretical analysis, numerical simulation, and flight dynamics evaluation. A feasible aerodynamic layout based on a “dual-side propulsion concept” was developed, followed by flight performance assessment and full-scale prototype flight tests. The results show: (1) the final layout comprises a two-blade hingeless rotor, three-blade pusher propellers, wings, skid landing gear, an H-tail, and a horizontal stabilizer; (2) flight performance meets all design targets, achieving maximum and cruise speeds of 260.48 km/h and 180 km/h at 1500 m altitude; and (3) full-scale prototype tests confirm the rationality of the aerodynamic layout and the reliability of the design process, achieving a high-speed flight of 242.6 km/h at an altitude of 1280 m. This work provides a valuable configuration reference for high-speed unmanned helicopter development. Full article

Coaxial contra-rotor unmanned aerial vehicles (UAVs) are attractive for their compact structure and aerodynamic efficiency, making them suitable for long-endurance and heavy-payload operations. However, the coaxial configuration introduces strong rotor coupling, phase lag, and additional disturbances, which pose significant challenges for stable control. To overcome these issues, we propose a cascaded Active Disturbance Rejection Control (ADRC-C) framework, in which a two-level control structure is adopted. The outer loop employs a classical ADRC controller to estimate and compensate for the lumped external forces, providing the compensated attitude command to the inner loop. The inner loop, in turn, adopts an $SO\left(3\right)$-based Extended State Observer (ESO) to handle high-frequency torque disturbances through real-time estimation and compensation. The proposed approach is validated through numerical simulations. Results confirm that the cascaded ADRC consistently outperforms conventional PID control in tracking accuracy, transient response, and disturbance rejection, demonstrating strong robustness for demanding coaxial UAV missions. Full article

This work presents a nonlinear aerodynamic model that describes the dynamics of a coaxial-rotor MAV. We have designed seven control laws based on linear and nonlinear controllers for path-following with a coaxial-rotor MAV in the presence of unknown disturbances, such as wind gusts. The linear controllers include Proportional–Derivative (PD) and Proportional–Integral–Derivative (PID). The nonlinear techniques encompass nested saturation, sliding mode control, second-order sliding mode, high-order sliding mode, and adaptive backstepping. The results are shown after multiple computer simulations. Full article

This work presents an analytical 2D model for estimating eddy current losses in the permanent magnets (PMs) of a coaxial magnetic gear (CMG), with a focus on loss minimization through magnet segmentation. The model is applied under various operating conditions, including different rotational speeds, load levels, and segmentation configurations, to derive empirical expressions for eddy current losses in both the inner and outer rotors. A 1D lumped-parameter thermal model is then used to predict the steady-state temperature of the PMs, incorporating empirical correlations for the thermal convection coefficient. Both models are validated against finite element analysis (FEA) simulations. The analytical eddy current loss model exhibits excellent agreement, with a maximum error of 2%, while the thermal model shows good consistency, with a maximum temperature deviation of 5%. The results confirm that eddy current losses increase with rotational speed but can be significantly reduced through magnet segmentation. However, achieving an acceptable thermal performance at high speeds may require a large number of segments, particularly in the outer rotor, which could influence the manufacturing cost and complexity. The proposed models offer a fast and accurate tool for the design and thermal analysis of CMGs, enabling early-stage optimization with minimal computational effort. Full article

This study presents the configuration design and attitude control of a moving-mass coaxial dual-rotor UAV (MMCDRUAV) for indoor applications. Compared with existing configurations, the proposed configuration avoids additional actuation mass and improves the control authority. Based on these improvements, a promising micro UAV platform with a high payload ability for agile indoor flight could be developed. Ground validation tests demonstrated its maneuverability, as provided by a moving-mass control (MMC) module requiring only the repositioning of existing components (e.g., battery packs) as movable masses. For trajectory tracking, an adaptive backstepping active disturbance rejection controller (ADRC) is proposed. The architecture integrates extended-state observers (ESOs) for disturbance estimation, parameter-adaptation laws for uncertainty compensation, and auxiliary systems to address control saturation. Lyapunov stability analysis proved the existence of uniformly ultimately bounded (UUB) closed-loop tracking errors. The results of the ground verification experiment confirmed enhanced tracking performance under real-world disturbances. Full article

This study investigates an aerodynamic optimization framework inspired by marine biological morphology, utilizing the sailfish profile as a basis for airfoil configuration. Through Latin hypercube experimental design combined with optimization algorithms, four key geometric variables governing the airfoil’s hydrodynamic characteristics were systematically analyzed. Parametric studies revealed that pivotal factors including installation angle significantly influenced the fluid dynamic performance metrics of lift generation and pressure drag. Response surface methodology was employed to establish predictive models for these critical performance indicators, effectively reducing computational resource consumption and experimental validation costs. The refined bio-inspired configuration demonstrated multi-objective performance improvements compared to the baseline configuration, validating the computational framework’s effectiveness for hydrodynamic profile optimization studies. Furthermore, a coaxial dual-rotor vertical axis turbine configuration was developed, integrating centrifugal and axial-flow energy conversion mechanisms through a shared drivetrain system. The centrifugal rotor component harnessed tidal current kinetic energy while the axial-flow rotor module captured wave-induced potential energy. Transient numerical simulations employing dynamic mesh techniques and user-defined functions within the Fluent environment were conducted to analyze rotor interactions. Results indicated the centrifugal subsystem demonstrated peak hydrodynamic efficiency at a 25° installation angle, whereas the axial-flow module achieves optimal performance at 35° blade orientation. Parametric optimization revealed maximum energy extraction efficiency for the centrifugal rotor occurs at λ = 1.25 tip-speed ratio under Re = 1.3 × 10⁵ flow conditions, while the axial-flow counterpart attained optimal performance at λ = 1.5 with Re = 5.5 × 10⁴. This synergistic configuration demonstrated complementary operational characteristics under marine energy conversion scenarios. Full article

The rotor shaft is a critical component responsible for transmitting engine power to the helicopter’s rotor. Deformation of the rotor shaft can affect the meshing performance of the output stage gears in the main gearbox, thereby affecting load transfer efficiency. By adjusting the support parameters of the rotor shaft, deformation at critical positions can be minimized, and the meshing performance of the output stage gears can be improved. Therefore, it is imperative to investigate the influence of rotor shaft support parameters on the deformation of the rotor shaft. This paper takes coaxial reversing dual rotor shaft (CRDRS) support configuration with intermediate bearing support as object. Utilizing Timoshenko beam theory, a rotor shaft model is developed, and static equations are derived based on the Lagrange equations. The relaxation iteration method is employed for a two-level iterative solution, and the effects of bearing support positions and support stiffness on the radial and angular deformations of rotor shaft gears under two support configurations, simply supported outer rotor shaft–cantilever-supported inner rotor shaft, and simply supported outer rotor shaft–simply supported inner rotor shaft, are analyzed. The findings indicate that the radial and angular deformations of gear s₁ are consistently smaller than those of gear s₂ in the CRDRS system. This difference is particularly pronounced in the selection of support configuration. The bearing support position plays a dominant role in gear deformation, exhibiting a monotonic linear relationship. In contrast, although adjustments in bearing support stiffness also follow a linear pattern in influencing deformation, their impact is relatively limited. Overall, optimal design should prioritize the adjustment of bearing positions, particularly the layout of b₃ relative to s₂, while complementing it with coordinated modifications to the stiffness of bearings b₂, b₃, and b₄ to effectively enhance the static characteristics of the dual-rotor shaft gears. 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

This research introduces the first design concept for a ducted coaxial-rotor amphibious spherical robot (BYQ-A1), utilizing the principle of variable mass control. It investigates whether the BYQ-A1’s variable-mass slider has a certain regularity in its impact on the aerodynamic properties of the BYQ-A1. Utilizing the Blade Element Momentum Theory (BEM) and Wall Jet Theory, an aerodynamic calculation model for the BYQ-A1 is established. An orthogonal experimental method is used to conduct tests on the impact of the variable-mass slider on the aerodynamic properties of the ducted coaxial-rotor system and validate the effectiveness of the aerodynamic calculation model. The results show that the slider generates an internal ground effect and ceiling effect within the BYQ-A1 that enhance the lift of the upper and lower rotors when the robot is equipped with it. The increased total lift compensates for the additional aerodynamic drag caused by the presence of the slider. This novel finding provides guidance for the subsequent optimization design and control method research of the BYQ-A1 and also offers valuable references for configuration schemes that incorporate necessary devices between coaxial dual rotors. Full article

This study investigates the aerodynamic and aeroacoustic performance of a novel two-stage two-bladed coaxial propeller that is axially and angularly spaced. Aerodynamic propulsive thrust and efficiency are validated and evaluated using a Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) model for the two-bladed APC27x13 propeller. Aeroacoustic assessment is conducted using a Ffowcs Williams–Hawkings integral model. A four-bladed coplanar APC27x13 propeller is simulated and considered as the baseline propeller. The CFD results suggest that changes in the rotor thrust for the coaxial blades are within $3\%$ for propellers with $0.25D$ axial spacing (where D is the propeller diameter) and ${30}^{\circ }$ angular spacing for the advance ratio of $J=0.3$–$0.5$. The aeroacoustic assessment for $J=0.3$ reveals that blades with ${30}^{\circ }$ and ${60}^{\circ }$ azimuthal spacing and $0.25D$ axial spacing significantly reduce noise compared to the baseline propeller. The reduction is attributed to the redistribution of tonal noise blade passing frequencies, resulting in a reduction in the A-weighted noise levels by up to 2 dBA. Additionally, the study accounts for the effect of the blade tip Mach number, concluding that a tip Mach number ranging between $0.7$ and $0.9$ is optimal for noise reduction in the ${30}^{\circ }$ configuration. The results highlight the potential noise reduction benefits of uneven axial and angular blade spacing while maintaining similar aerodynamic performance. Full article

Coaxial rotor helicopters have a wide range of civilian and military applications; however, the collision risk of the upper and lower blades that comes with the coaxial rotor system remains. This paper introduces a blade-tip distance measurement method based on coded ultrasonic ranging to tackle this challenge. Coded ultrasonic ranging with phase modulation was adopted to improve the measurement rate. In this paper, seven-bit M-sequences and Gold codes are chosen with four periods of 200 kHz sine wave carriers as the excitation signals, and the received signals are filtered by a bandpass filter and decoded by a matching filter. The coding performance is evaluated by the distinguishability and energy level of the received signals. The experimental results show that the measurement rate can reach 3060 Hz for a distance of one meter. They also give the potential solution for other high-speed measurement problems. Full article

Coaxial rotor helicopters have many advantages and have a wide range of civilian and military applications; however, there is a risk of blade collision between the upper and lower rotor blades, and the challenge still exists in balancing rotor parameters and flight control. In this paper, a blade tip distance measurement method based on coded ultrasonic ranging and phase triggering is proposed to tackle this measurement environment and expand the application of ultrasonic ranging in high-speed dynamic measurement. The time of flight (Tof) of coded ultrasonic ranging is calculated by the amplitude threshold improvement method and cross-correlation method, and the sound velocity is compensated by a proposed multi-factor compensation method. The static distance error of coded ranging with different codes are all within ±0.5 mm in the range of 10–1000 mm. The measurement error characteristics under different trigger phases and different rotational speeds are studied, and the error model is fitted by the back-propagation neural network method. After compensation, the vertical distance measurement errors are within ±2 mm in the range of 100–1000 mm under the condition that the rotational speed of the blade is up to 1020 RPM. It also provides a potential solution for other high-speed measurement problems. Full article

Rotor-to-rotor interactions have been found to significantly contribute to acoustic characteristics. The present research presents a novel idea to conduct comparative studies on the aeroacoustics characteristics of conventional, coaxial, and hybrid octocopter configurations in hover and steady forward flight to identify the configuration that has minimal noise levels. Moreover, the influence of vertical spacing in the coaxial octocopter is explored, and an aeroacoustics comparison of coaxial and hybrid configurations with larger-diameter rotors in the same confined vehicle space for missions that require a high thrust is presented at the end. The virtual blade method (VBM) is employed herein for aerodynamic analysis due to its high computational efficiency, and a numerical analysis code based on FWH equations is developed for the acoustics analysis. The hover results show that coaxial configurations produce a peak SPL value of 93 dB, which is 5 dB louder than the conventional configuration and 3 dB louder than the hybrid configuration. The coaxial configuration with 0.125 R vertical spacing produced a peak SPL of 92 dB, which is 5 dB louder than the 0.5 R and 10 dB louder than the 1.5 R. In steady forward flight with normal-sized rotors, the hybrid configuration outperformed the others with a peak SPL value of 85 dB, which is 7 dB lower than that of the conventional configuration; meanwhile, the other configurations had similar noise values. The noise attributed to larger rotors in a confined vehicle space during hover flight in the coaxial configuration is 5 dB less than that of the hybrid configuration at almost all elevation angles in the farfield; meanwhile, a 5 dB difference was observed in the front half of the vehicle in forward flight and minute differences were found in the rear half. Full article