Search Results (194)

This study presents an extended Blade Element Momentum Theory (BEMT) framework for predicting the hover performance of an EC135-class light-twin helicopter rotor while quantifying the impact of sectional aerodynamic uncertainty on global rotor metrics. Because the proprietary EC135 airfoils are not publicly available, a reproducible surrogate blade based on the ONERA OA213 and OA209 airfoils is adopted. The airfoil substitution is explicitly treated as an epistemic modelling assumption, and its effect on rotor-level hover predictions is assessed through a dedicated geometric comparison and bounded sensitivity analysis. The classical BEMT formulation is enhanced with Prandtl tip-loss corrections, Mach-dependent sectional aerodynamics, and an iterative non-uniform inflow model. Aerodynamic coefficients are obtained from Gaussian Process (GP) surrogate models trained on XFOIL-generated databases and calibrated using cross-validation techniques. The calibrated GP models are coupled with the rotor solver and their predictive uncertainty is propagated through Monte Carlo simulations. For the nominal hover trim condition, the rotor was trimmed to $C_T=0.00607$, while the model predicted a power coefficient of 0.00041 and a figure of merit of 0.819. The propagated GP/XFOIL-conditioned uncertainty yields a 95% confidence interval of 0.8074–0.8285 for the figure of merit, indicating limited sensitivity of rotor performance to sectional aerodynamic uncertainty. The influence of compressibility and tip-loss effects is also quantified. In a separate Caradonna–Tung solver-verification case, the thrust-coefficient error is reduced from 32.57% to 7.78% when finite-aspect-ratio corrections are included. The proposed framework provides a fast, reproducible, and uncertainty-aware approach for helicopter rotor hover analysis suitable for preliminary design and performance assessment. Full article

Advances in electric flight technologies have enabled distributed electric propulsion, opening a large design space for electric vertical take-off and landing (eVTOL) aircraft with diverse configurations and mission profiles. To support rapid exploration of these trade-offs, a computationally efficient sizing and performance evaluation tool has been developed. This study focuses on the verification of the key methods within the framework. The propeller sizing and performance model is verified against conventional helicopter rotors and representative eVTOL designs, while the battery discharge model is assessed using experimental data. In addition, the overall aircraft sizing is evaluated for two configurations of NASA’s Urban Air Mobility reference vehicles and compared with results obtained using NASA’s state-of-the-art rotorcraft design tool NDARC. The results show good agreement across all levels of verification. Average deviations are within 8% for propeller performance, below 5% for battery discharge, and within 4% for maximum take-off and empty mass. Mission performance and energy consumption are predicted within approximately 10%, demonstrating the suitability of the methodology for early-stage eVTOL design. Full article

A numerical study was conducted to investigate the effect of embedded piezoelectric actuators integrated into the skin of a model-scale BO105 rotor blade on its torsional behaviour. The analysis was performed for blades with different combinations of spar and skin materials, including UD GFRP and UD CFRP composites. Four finite element models of the helicopter blade were developed in ANSYS 16.0. The piezoelectric response of the MFC (Smart Material Corp., Sarasota, FL, USA) actuators was simulated using a thermal analogy approach. The effects of actuator placement, as well as the selection of spar and airfoil skin materials, on the torsion angle and structural characteristics of the blade were analysed. The largest torsional angle was obtained for rotor blade configurations equipped with MFC actuators and manufactured entirely from UD GFRP composites. The spar material did not affect the torsional angle. Full article

To investigate the contact mechanical performance of helicopter main gearbox rotor shaft bearings under a complex load spectrum, this study focuses on the contact stress and load-carrying characteristics of bearings operating under high-speed and heavy-load conditions. Based on the rotor shaft system of a helicopter main gearbox and Hertzian contact theory, quasi-static analyses were performed on four tapered roller bearings and one cylindrical roller bearing mounted on the shaft system conducted in Romax. The results indicate that the maximum contact stresses of the bearings do not exhibit sustained high-stress states under most operating conditions. The peak-stress conditions account for only extremely small time proportions in limited cases, namely 0.003429% and 0.025%. The contact stresses on both the inner and outer raceways exhibit a non-uniform distribution along the roller length, with local peak values appearing near the highly loaded roller-raceway contact regions. This suggests that during the design process of the helicopter main gearbox rotor shaft, special attention should be given to this region. The present results provide a theoretical basis for subsequent life-index verification and offer an effective analytical method for the design and validation of such critical components. 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

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

Over the last decades, progress in modal analysis has enabled the increasingly routine use of modal parameters for applications such as structural health monitoring and finite element model updating. For output-only identification, or operational modal analysis (OMA), widely adopted approaches include stochastic subspace identification (SSI) methods and the Natural Excitation Technique, combined with the Eigensystem Realization Algorithm (NExT-ERA). Nevertheless, SSI-based techniques may become cumbersome on large systems, while NExT-ERA fitting can struggle when measurements are contaminated by noise. To alleviate these, this work investigates an OMA frequency-domain formulation for aeronautical structures by coupling the Loewner Framework (LF) with NExT, yielding the proposed NExT-LF method. The method exploits the computational efficiency of LF, due to the effectiveness of tangential interpolation, together with the impulse response function retrieval enabled by NExT. NExT-LF is assessed on two experimental benchmarks: the eXperimental BeaRDS 2 high-aspect-ratio wing main spar and an Airbus Helicopters H135 bearingless main rotor blade. The identified modal parameters are compared against available experimental references and results obtained via SSI with a Canonical Variate Analysis and NExT-ERA. The results show that the modes identified by NExT-LF correlate well with benchmark data, particularly for high-amplitude tests and in the low-frequency range. 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

The load characteristics of the helicopter tail rotor system are critical to flight safety and handling performance, and flight testing remains the most direct and reliable means to obtain authentic load data. In this paper, the well-established Wheatstone bridge strain measurement method is adopted to carry out accurate load testing on the helicopter tail rotor system. The tail rotor assembly mainly consists of the tail rotor shaft, pitch link, and tail rotor blades, which undertake different load transfer tasks during flight. Under actual operating conditions, the tail rotor shaft bears significant axial tension as well as combined lateral and vertical bending moments; the pitch link is primarily subjected to alternating axial tension and compression; and the tail rotor blades withstand complex loads including flapping bending, lagwise bending, and torsional moments. According to the distinct stress characteristics and force transmission paths of each component, targeted flight test maneuvers are reasonably designed. These maneuvers include steady-level flight at low, medium, and high speeds, zigzag climbing flight, near-ground side-rear flight, as well as deceleration-to-sprint and obstacle slope maneuvers specified in ADS-33E. Key flight parameters are selected for in-depth analysis to reveal the load distribution and dynamic variation patterns of the tail rotor under typical operating conditions. On this basis, a helicopter load risk test point matrix is established to identify high-risk working conditions and key monitoring positions. This study provides a solid theoretical and data foundation for subsequent flight test monitoring and structural strength verification. It effectively reduces flight test risks, improves monitoring efficiency and accuracy, and helps cut down the human, material, and financial costs associated with flight test monitoring. The research results can also provide important references for the design optimization and safety evaluation of helicopter tail rotor systems. Full article

Active rotors with trailing-edge flaps (TEFs) are a promising method applied to the main-rotor blades of the helicopter for vibration suppression. For active rotors, both the TEF actuator and the corresponding deflection control law determine their overall performance and effectiveness for vibration reduction. In this study, a double-acting piezoelectric actuator is designed to actuate the TEFs, where bidirectional push/pull output is achieved by two groups of piezoelectric stacks operating in opposite directions. Benchtop tests indicate that the TEF deflection angle of the active rotor equipped with this actuator can reach ±4.3°. Subsequently, based on the controlled autoregressive moving average (CARMA) model, an adaptive controller is developed to reduce vibrations in the active rotor by using a minimum variance direct self-tuning regulator (MVSTDR). Finally, an unmanned helicopter is retrofitted with the active rotor, and vibration control experiments are performed under tethered hover conditions with vertical cabin vibration as the control target. Experimental results demonstrate the effectiveness of the designed actuator and the MVSTDR for vibration reduction on the helicopter equipped with an active rotor, which also validates the feasibility of active rotors for practical engineering applications in helicopter vibration control. Full article

For high-speed compound helicopters, such as the S-97 Raider, the reflection and diffraction effects of vertical/horizontal tails on pusher propeller noise are inevitable. To investigate the noise distortion effect of the rear-mounted pusher propeller, this study first relies on the Chinese Laboratory of Rotorcraft Navier-Stokes (CLORNS) solver, adopting the high-resolution Perturbed polynomial reconstructed Targeted Essentially Non-Oscillatory scheme (TENO-P) combined with the Delayed Detached Eddy Simulation based on the Spalart–Allmaras (SA-DDES) turbulence model to resolve the multi-scale rotor flowfield. Additionally, a continuous and conserved acoustic source extraction method is proposed to eliminate non-physical waves at the one-way Computational Fluid Dynamics and Computational AeroAcoustics (CFD–CAA) coupling interface, addressing the temporal inconsistency between flowfield evolution and acoustic propagation. Finally, numerical investigations are conducted on the instantaneous acoustic wave propagation and acoustic directivity of the pusher propeller under the influence of vertical/horizontal tails. The results show that significant acoustic distortion occurs when pusher propeller-generated noise interacts with vertical/horizontal tails. This interaction not only produces reflected and diffracted acoustic waves but also leads to wavefront discontinuities, the formation of short acoustic waves, and changes in acoustic directivity. The maximum variation in the sound pressure level reaches 10 dB at local azimuths. The distortion effect of tails on pusher propeller noise is closely correlated with the number of propeller blades. The interaction process between the propeller and tails becomes more complex with the increase in blade count, resulting in the generation of shorter acoustic waves. For the six-blade rotor, the originally continuous acoustic wave branch can be split into up to four short waves. This study confirms that the proposed Hybrid Computational AeroAcoustics (HCAA) method holds significant application prospects in the aeroacoustic research of compound helicopters. Full article

The concept of active blade twisting as a method for reducing helicopter noise and vibration during flight is presented. Active twisting is achieved through piezoelectric actuators embedded in the blade skin, which generate dynamic twist when subjected to an electric field. Such dynamic deformation can lower fuel consumption while also reducing noise and vibration levels. A methodology for determining the optimal geometric dimensions of the cross-section of a helicopter blade, taking into account design constraints, is proposed to achieve the maximum twist angle of the blade under the action of piezoelectric actuators. First, a three-dimensional numerical model of the BO 105 model-scale rotor blade is developed in the finite element software ANSYS 16.0. The effect of the rotor blade’s cross-sectional dimensions on the cross-sectional properties and twist angle is investigated. It is found that skin thickness, spar flange thickness, and spar flange length affect the twist angle, with skin thickness showing a significant effect. Based on these results, an optimisation strategy is formulated to identify the optimal blade cross-section configuration to achieve the maximum twist angle. It was established that with the optimised geometric parameters of the cross-section the maximum active twist reaches 5.2°, while the positions of the elastic axis and the centre of gravity exhibit only minor deviations from those of the reference model. The placement of the piezoelectric actuators has a significant influence on both the flapwise bending stiffness and the torsional stiffness of the blade. Full article

Helicopter detection plays a vital role in obtaining critical aerial information promptly and ensuring the safety of lives and property. Since a helicopter’s aerodynamic noise primarily consists of main rotor noise, the cyclostationarity of this noise becomes our detection target. This paper proposes a filter based on the Frequency-Shift (FRESH) principle, which is updated using the Adam optimization algorithm. A smoothed global detector is presented to detect the cyclic frequency of rotor noise. The effectiveness of the proposed helicopter detection approach, comprising both the filter and the detector, has been validated through simulations and confirmed by far-field experiments with a ROBINSON R22 helicopter. In these tests, the proposed method was compared against a cyclostationarity adaptive filter based on the Normalized Least Mean Squares (NLMS) algorithm, as well as the traditional Detection of Envelope Modulation on Noise (DEMON) and Cyclic Modulation Coherence (CMC) algorithms. Experimental results demonstrate the superior robustness of the proposed method over these benchmarks. Even at extended ranges between 11 and 13 km, the system retains a consistent detection rate of 77.8%. Full article

Decarbonisation of the aviation sector is essential for achieving global-climate targets, with hydrogen propulsion emerging as a viable alternative to battery–electric systems for vertical flight. Unlike previous studies focusing on clean-sheet eVTOL concepts or fixed-wing platforms, this work provides a comprehensive retrofit evaluation of a two-seat light helicopter (Cabri G2/Robinson R22 class) to a hydrogen–electric hybrid powertrain built around a Toyota TFCM2-B PEM fuel cell (85 kW net), a 30 kg lithium-ion buffer battery, and 700 bar Type-IV hydrogen storage totalling 5 kg, aligned with the Vertical Flight Society (VFS) mission profile. The mass breakdown, mission energy equations, and segment-wise hydrogen use for a 100 km sortie are documented using a single main rotor with a radius of R = 3.39 m, with power-by-segment calculations taken from the team’s final proposal. Screening-level simulations are used solely for architectural assessment; no experimental validation is performed. Mission analysis indicates a 100 km operational range with only 3.06 kg of hydrogen consumption (39% fuel reserve). The main contribution is a quantified demonstration of a practical retrofit pathway for light rotorcraft, showing approximately 1.8–2.2 times greater range (100 km vs. 45–55 km battery-only baseline, including respective safety reserves). The Hawk demonstrates a 28% reduction in total propulsion system mass (199 kg including PEMFC stack and balance-of-plant 109 kg, H₂ storage 20 kg, battery 30 kg, and motor with gearbox 40 kg) compared to a battery-only configuration (254.5 kg battery pack, plus equivalent 40 kg motor and gearbox), representing approximately 32% system-level mass savings when thermal-management subsystems (15 kg) are included for both configurations. Full article

This article represents a numerical approach for estimating the helicopter rotor’s blade longitudinal dynamic characteristics considering several operational parameters. A characterization regarding the blade’s longitudinal, flapping, and vertical responses is derived by solving a system of differential equations that fully describe the rotor’s longitudinal dynamics. Dependencies between the lagging (longitudinal) velocity, the flapping velocity, and the vertical velocity over time are illustrated, taking into consideration the varying flapping frequency in a hovering regime. Additionally, the blade’s longitudinal parameters were evaluated in ground effect conditions when hovering at ${\displaystyle \frac{H}{R}}=1$ and ${\displaystyle \frac{H}{R}}=0.5$. The studied time domain variables represent the rotor’s natural reaction capabilities when a disbalancing condition occurs. Eventually, an increase in the blade’s flapping frequency leads to a rise in the required period for reaching a stable condition with regard to the longitudinal and vertical responses. The ground effect zone reduces the blade’s lagging and flapping reactions as well. Full article