Browse Topic: Propellers and rotors
In the electrical machines, detrimental effects resulted often due to the overheating, such as insulation material degradation, demagnetization of the magnet and increased Joule losses which result in decreased lifetime, and reduced efficiency of the motor. Hence, by effective cooling methods, it is vital to optimize the reliability and performance of the electric motors and to reduce the maintenance and operating costs. This study brings the analysis capability of CFD for the air-cooling of an Electric-Motor (E-Motor) powering on Deere Equipment's. With the aggressive focus on electrification in agriculture domain and based on industry needs of tackling rising global warming, there is an increasing need of CFD modeling to perform virtual simulations of the E-Motors to determine the viability of the designs and their performance capabilities. The thermal predictions are extremely vital as they have tremendous impact on the design, spacing and sizes of these motors.
This paper presents the development of an alternative to the traditional multichannel Fiber Optic Rotary Joint (FORJ) using spatial division multiplexing. The proposed solution utilizes phase plates assembly in a compact housing made by a French optical communications company called Cailabs. It is distinguished from conventional multichannel technologies that rely on Dove prisms or wavelength multiplexing by using the housing of a single channel Fiber Optic Rotary Joint (FORJ) without needing strong constraint on the choice of optical transceivers. Our research focused on characterizing the specific mechanical parameters required to transfer optical modes from the rotor to the stator without deformation or misalignment of those. Three test campaigns were conducted, each with iterative improvements. The latest results demonstrate commercially viable performance for transmission of 3G-SDI video stream on up to 6 channels.
Swimming robots play a crucial role in mapping pollution, studying aquatic ecosystems, and monitoring water quality in sensitive areas such as coral reefs or lake shores. However, many devices rely on noisy propellers, which can disturb or harm wildlife. The natural clutter in these environments — including plants, animals, and debris — also poses a challenge to robotic swimmers.
Inspecting the interiors of tanks and ships for defects involves accessing confined and elevated spaces. This can be difficult and hazardous for a person. Ducted aerial vehicles that can hover close to the object of interest can achieve this in a safer and more efficient manner. Such a vehicle is desired to be compact, to have a high hover endurance and to be protected from impact. This paper describes a design concept comprising ducted coaxial counter-rotating rotors with a compact swashplate mechanism for cyclic pitch input to the lower rotor. An experimental setup was used to investigate the effect of the duct. A numerical Blade Element Momentum Theory model was developed and validated to inform rotor selection. A prototype was designed and built with a hover thrust of 9.17 N, outer diameter of 350 mm, and height 173 mm. The duct provided a thrust benefit of 32% for this configuration for a given power. The prototype achieved stable controlled flight in hover and in passing near
An OVERFLOW simulation of a four-bladed rotor in hover is performed, and the resulting steady-state solution for the boundary layer over a rotating blade is analyzed by means of linear stability methods. The techniques employed are the Linear Stability Theory, the Parabolized Stability Equation, and the spanwise BiGlobal analysis. The unstable modes in the boundary layer of the rotating blade are analyzed in comparison with those typically observed in swept wings. The effect of the Coriolis force and the spanwise gradient of the free stream velocity are taken into account, and their influence on the instabilities is evaluated. It is shown that periodic boundary conditions in the spanwise BiGlobal analysis work adequately for a sufficiently small fraction of the length of the blade (~ 1:2%), while increasing the domain would require an alternative approach to the boundary conditions.
Huma, a reconfigurable lift compounded single main rotor (SMR) helicopter, developed by the UMD Graduate Design Team, is capable of exceptional flight time, able to loiter 185-km away from its takeoff point for over 13 hours before needing to return.
An extensive test campaign was conducted at the National Full-Scale Aerodynamics Complex 40- by- 80-Foot wind tunnel to acquire performance, loads, and acoustics measurements of the Joby Aviation propeller across a variety of operating conditions. The dataset provided validation of the design methodology as well as verification of computational tools. The Vold-Kalman filter was used to extract the shaft-coherent propeller noise in hover to obtain the residual noise, representing the broadband noise. This data verified broadband noise tip speed scaling laws as well as a low-order empirical model for overall sound pressure level. The OVERFLOW/PSU-WOPWOP method was used to simulate the propeller in pure edgewise flight and shown to accurately predict propeller performance. The low-frequency acoustics were predicted well but the solver underpredicted frequencies above 300 Hz, possibly due to the inability to capture the turbulent component of the blade-wake and blade-vortex interaction
Helicopter rotor blades with several different parts, multiple load paths and/or springs and dampers can be modeled as a multibody system, into which finite element descriptions of flexible bodies can be integrated. When doing so, model order reductions can be necessary for robustness and/or performance reasons. A known drawback of such reductions is that the isolated modes of the particular bodies may not adequately describe their actual deformations in the multibody system. To alleviate this problem, the paper proposes a Craig-Bampton reduction for the flexible bodies. Compared to a standard modal reduction, the additional consideration of static interface modes in the Craig-Bampton approach significantly improves the prediction of eigenfrequencies and mode shapes, as demonstrated for a segmented steel beam with a single load path. Using the same approach, a bearingless rotor blade with multiple load paths is modeled by two beam segments. The model is assessed by code-to-code
Generating multiple high-quality sets of rotor performance data is necessary to validate Vertical Take-Off and Landing (VTOL) aircraft performance prediction codes across a broad range of vehicle configurations. Many aircraft companies are actively pursuing multirotor vehicle configurations, which has created a need for validation data for multirotor systems. The NASA Multirotor Test Bed was designed to accommodate a broad range of reconfigurable multirotor systems and to measure rotor performance and loads in a wind tunnel environment. This paper presents results from the second wind tunnel entry of the test bed, which was completed in August 2022. This wind tunnel test focused on a quadrotor configuration, with variations in rotor placement, blade number, and rotor phasing, across a range of wind tunnel test conditions. This paper describes the test methods and provides and discusses a sample of the quasi-steady and dynamic loads data that were collected during the test program.
A follow-on study to the 2024 paper by Kottapalli, Silva, and Boyd is presented with improved acoustics tools to examine whether the Vertical Aviation International (VAI) Fly Neighborly operational recommendations that are designed for single main rotor/tail rotor configurations will hold for non-conventional UAM rotorcraft with multiple rotors. The 6-occupant quadrotor concept vehicle designed under the NASA Revolutionary Vertical Lift Technology (RVLT) Project is studied. The tip speed is 550 ft/sec, with three blades per rotor. Predictions are made for three steady maneuvers: level turns, descending turns, and climbing turns. The RVLT Toolchain is exercised using CAMRAD II, pyaaron/AARON/ANOPP2 and AMAT (ANOPP2 Mission Analysis Tool). Quadrotor noise trends are analyzed using Sound Exposure Level (SEL) ground maps because it is anticipated that the upcoming updated Fly Neighborly recommendations will involve SEL maps. Importantly, unlike conventional helicopters with a single main
The next generation of Mars rotorcraft may involve an increase in scale and number of rotors. A key focus area that has been identified is to increase the fidelity of rotor wake modeling, including its impact on flight dynamics. To that end, this paper pursues the use of a Viscous Vortex Particle Method (VVPM) for mid-fidelity rotor wake predictions in Mars atmospheric conditions. Simulated aerodynamic hover performance, as well as control efforts in trimmed forward flight, of the Ingenuity Mars Helicopter with a VVPM wake is shown to correlate well with available experimental data. Qualitative and quantitative coaxial wake effects for Ingenuity-type rotors in hover and forward flight as predicted with VVPM are studied. Utilizing VVPM to evaluate rotor-rotor interference effects in a large-scale Mars hexacopter across a wide range of flight conditions showcases the capability to comprehensively model the induced wake of complex multi-rotor configurations within feasible computational
This paper provides an overview on the contributing phenomena to unanticipated yaw described in the FAA Helicopter Flying Handbook. Trimmed aerodynamic - flight-mechanic - coupled simulations with a validated model of the BK117 C-2 capture the relevant interactions for weathervaning, main rotor-to-tail rotor interactions and vortex ring state effects at the tail rotor. An investigation of the impact of the main rotor downwash on the vortex ring state at the tail rotor in sideward flight and yaw turn is provided, concluding that the presence of the main rotor effectively inhibits the occurrence of a fully developed deep vortex ring state at the tail rotor. The consequent limited impact of the incipient tail rotor vortex ring state on the helicopter trim is estimated. Further, maneuver simulations of the BK117 C-2 are provided, describing the typical entry in unanticipated yaw turn and the exit to stop the yaw motion by means of pedal inputs of different magnitude and input speeds.
This paper carries out experimental investigation of propeller and wing interactions under various geometric variations such as the horizontal and vertical distance between the propeller axis and the leading edge of the wing under different angle of attack conditions for a half wing setup for a wing made of symmetric airfoil. Rotor and wing performance is measured using independent six-component load cells. Through this study it is identified that for a wing made of symmetric airfoil optimal aerodynamic performance is significantly influenced by the position of the propeller. Positioning the propeller near the leading edge (x/c = 0.25) and on the negative side of the y-axis (y/c = −0.75) yields the best lift-to-drag ratios and enhanced lift, particularly in the moderate α range (4°–6°). Forward movement of the propeller along the x-axis (towards x/c = 0.75 or 1.00) increases drag and adversely affects performance.
This paper explores a significant step forward, regarding the further detailed understanding of the Fenestron®. Since its patent in 1968 – for the Gazelle helicopter –, the shrouded tail rotor has been resized, inclined, modulated, etc. and has thus been continuously enhanced on different rotorcraft. Half a century after its invention, Airbus is once again exploring in more detail the magic of the Fenestron®, with the objective of optimizing it even further, for future helicopter applications. To grasp and observe properly some specific phenomena, a model (scaled to one third) capable of both unprecedented functions and modularities, was developed. The present paper will describe in detail the novel model and the related challenges and solutions. This model is capable of high rotor speed and dynamic pitch inputs, delivering power levels high enough to reach stall effects, while allowing the measurement of propulsive efficiency and to differentiate rotor vs fairing thrust. Furthermore
This study investigates the interactional aerodynamics of multi-rotor systems with longitudinally canted rotors, focusing on force, moment, and wake behavior. Experiments using two 24-inch, two-bladed rotors in hover varied cant angle (0–20°) and hub spacing (1.1–1.5D). Increasing longtitudinal cant angle had the greatest effect on maximum longitudinal force, (| Fx |), yielding a reduction of up to -6.18% per 1°. Hub spacing had greater influence, especially on longitudinal force, | Fx |, and pitching moment, (| Mx |), which decreased by up to -16.00% and -31.07% per 0.1D increase, respectively. Time averaged flow results from Particle Image Velocimetry (PIV), showed that larger hub spacings and cant angles improved wake separation and flow symmetry. These results provide foundational data for minimizing parasitic loads and maximizing aerodynamic performance in advanced multi-rotor designs.
This paper investigates the relationship between broadband noise behavior and helical wake structure in coaxial corotating rotors. Experimental measurements were conducted across variations in collective pitch (9.4°, 12.5°, and 15.0°) and rotor speeds (1500–4500 RPM). The inflow ratio (λ) was shown to govern the slope of broadband noise trends mapped in phase offset versus separation distance space, with experimental and theoretical λ values agreeing within 1%. Tip vortex core growth was estimated using the Ramasamy-Leishman model and normalized by the blade tip chord, reflecting the location of tip vortex formation. Across collective pitch variations, initial vortex core radii ranged between 7.5% and 9.1% and across rotor speeds, it ranged between 7.5% to 8.5% of the blade tip chord. When broadband noise trends became less coherent across phase offset angles, the corresponding vortex core radii were observed to approach or exceed 10% of the tip chord. At 4500 and 3500 RPM, vortex
The emergence of three-dimensional Computational Structural Dynamics for helicopter rotors warrants the development of a higher fidelity fluid-structure interface that can replace the one-dimensional sectional airload interface commonly used for coupled analysis with Computational Fluid Dynamics. Three methods of progressively higher fidelity are examined for imposing airloads onto the structure. These are defined as level-III, II, and I, based on fluid stresses, patch forces, and sectional airloads (baseline), respectively. A model problem investigating a 3-D cylindrical shell with large deformations near the boundaries is used to verify the methods. The patch force interface (level-II) approaches the stress interface (level-III) when the mesh is highly refined. Level-I (baseline) produces no solution at all (or zero solution). Level-II is then applied to a UH-60A-like rotor and compared with level-I. Only a forced response was carried out, not a full-fledged trim solution. For this
The advent of electric propulsion technology has led to a paradigm shift in aircraft design over the past few decades. This shift has expanded the possibilities for design and optimization processes more than at any previous time. To support these advancements, efficient flight dynamics simulation models that can be employed in iterative optimization and design processes are essential. Among the modules of a typical flight dynamics framework—namely, control, flight dynamics, and aerodynamics—the aerodynamics module, which includes the rotor performance model, generally demands the most computational effort, thereby limiting simulation efficiency. In this study, a novel machine learning (ML)-assisted flight dynamics framework is developed, incorporating a Neural Network Blade Element Theory (NN-BET) model as the rotor performance module. The results show a 7- to 8-fold reduction in computational time compared to fast, physics-based frameworks utilizing efficient Blade Element Momentum
Dynamic stall is an undesirable flow phenomenon that could occur on rotor blades of helicopters in forward flight due to azimuthal changes in local angle of attack resulting from blade motion, blade deformation and blade-vortex interactions. It is characterized by leading-edge vortex (LEV), or dynamic-stall vortex (DSV) shedding and significantly affects rotor performance and longevity. Therefore, the capability to predict dynamic stall, especially using rapid low-order approaches, is beneficial for vehicle design and flight-dynamics simulation. Recent work has resulted in the development of a theoretical parameter called leading-edge section parameter (LESP), which provides a measure of the suction force acting on the leading edge. It has been shown that the occurrence of dynamic stall on airfoils and finite wings corresponds to the time in an unsteady motion when the instantaneous LESP crosses a predetermined critical value. The current work shows that the critical LESP value
This study investigates Reynolds number effects on rotor wake vortex development using a hyperbaric rotor facility capable of pressurizing air up to 100 bar. Background-oriented schlieren (BOS) and hot-wire anemometry (HWA) were applied to characterize vortex trajectories, core growth, and circumferential velocity distribution. BOS measurements revealed consistent blade-to-blade trajectory deviations and vortex pairing across all operating conditions, despite that the investigated three-bladed rotor was milled from a single piece of aluminum, ensuring precise manufacturing and a highly symmetric geometry. A statistical scheme was developed to analyze the radial structure of fluctuating tip vortices, which traverse the pointwise fiber-film sensor in a fixed position. With increasing vortex Reynolds number, the tip vortices are more compact with a reduction in core growth. The circulation in the vortices grows with the vortex radial coordinate, and converges at a radial position
This paper investigates an output-based approach for predicting limit-cycle oscillations caused by freeplay, which can affect actuated structures of vertical lift vehicles. The proposed approach uses pre-critical time-history data to estimate the recovery rate to equilibrium following perturbations as a function of amplitude and a varying parameter. Recovery rate data points in the parameter-amplitude plane are fitted and extrapolated to predict limit-cycle oscillation solutions, corresponding to a recovery rate of zero. While previous work demonstrated this approach for systems with geometrical or polynomial stiffness nonlinearities, this study investigates its applicability to freeplay for the first time. The study uses time-history data from simulations of an analytical model of an idealized, elastically mounted tilting propeller in airplane mode, with freeplay in the tilting mechanism. The results highlight the promise of the proposed approach, paving the way for addressing more
In April of 2024, Sikorsky flight tested an open loop Higher Harmonic Control system on an S-97® helicopter. The S-97® helicopter is a prototype aircraft, based on Sikorsky's X2 Technology™, that first flew in May 2015. It has contra-rotating, stiff in-plane main rotors with fly-by-wire controls, and a pusher propeller. This paper describes the HHC design, how it was implemented on the aircraft, how it was tested, and what the test results were.
A 1/5th scale powered coaxial rotor and propeller system has been developed and tested in the National Full Scale Aerodynamic Complex (NFAC) 40x80 ft Wind Tunnel. Test conditions include airspeeds in excess of 250 kts, the highest recorded for a rotor in edgewise flight at the NFAC. The system was studied in four configurations: a powered coaxial rotor, a powered coaxial rotor with a propeller wake rake, a powered coaxial rotor with a powered propeller, and a bare hub rotor with a propeller wake rake. The high-quality data from the test included propeller, fuselage and main-rotor performance; aerodynamic-interactions between the rotors, fuselage, empennage, and propeller; acoustics and handling-qualities attributes. These results have been used to validate physics-based rotorcraft modeling tools and enhance the quality of full-scale X2 Technology® aircraft designs. Innovative solutions to test measurement challenges included rotor shaft strain gages, balance thermal control systems
Aeroelastic stability prediction is critical to the successful design, development and flight testing of rotorcraft. As configurations reach higher speeds, new challenges in high Mach number unsteady aerodynamic modeling need to be addressed, especially for higher frequency aeroelastic modes with significant coupling. In this paper, Linear Unsteady aerodynamics and Leishman-Beddoes attached flow models are applied and compared to 2D CFD (airfoil) and 3D CFD/CSD (rotor) analysis for operating conditions of interest. The Leishman-Beddoes model demonstrates improved agreement with CFD data. In the 2D assessment, RCAS is used to model a representative airfoil undergoing prescribed pitch and heave oscillations. CFD results are presented to compare each model (Linear Unsteady and Leishman-Beddoes). In the 3D assessment, a full rotor CFD/CSD test case is evaluated for aeroelastic stability and compared to RCAS standalone analysis. The RCAS rotor structural model is coupled with the HELIOS CFD
The performance and acoustics of a scaled propeller designed for an eVTOL vehicle were investigated in axial and edgewise flight. The measured performance compared well with BEMT predictions in axial flight conditions. The noise produced by the propeller is dominated by broadband noise sources, where there is evidence of contributions from blade wake interaction noise, turbulent boundary layer trailing edge noise, and laminar boundary layer vortex shedding noise. The directivity of the noise was found to be dependent on the advance ratio. Beamform maps also identified changes in the dominant noise source at different observer locations as a function of advance ratio.
This paper investigates the influence of wing-propeller aerodynamic interactions on the aeroelastic damping of a wing-propeller system. The system is modeled in the Rotorcraft Comprehensive Analysis System using the viscous vortex particle method for the propeller aerodynamics and the uniform inflow model for the wing. The aeroelastic damping characteristics are identified from simulated time-history data using a recently developed method that captures amplitude effects due to system nonlinearity. The damping characteristics identified using conventional methods based on linear assumptions are also presented for comparison. The results show that, at lower airspeeds, the local damping decreases with increasing propeller hub displacements, both with and without aerodynamic interactions. This amplitude-dependent behavior cannot be captured by conventional damping identification methods that average amplitude effects. Amplitude-dependent trends are exacerbated by wing flexibility. However
Developed in the frame of the European Clean Sky 2 program, the RACER High Speed Helicopter Demonstrator of Airbus performed its maiden flight on April 25th, 2024. In the continuity of the previous high-speed demonstrator X3 (1st flight in 2010) the RACER is a 7/8t (15000 / 18000 lb) class compound helicopter powered by two SHE Aneto-1X engines, including a wing and two propellers. The tail rotor is removed as the two propellers control the yaw axis by differential thrust. At flight 07, with its initial default settings, it reached a true airspeed of 227 kts in level flight, exceeding its objective of 220 kts.
In 2023, Joby Aviation conducted a test of a prototype propeller for an electric vertical takeoff and landing (eVTOL) tilt-propeller aircraft in the 40- by 80-Foot Wind Tunnel at the National Full-Scale Aerodynamics Complex (NFAC). There were three objectives of the test: measuring 1) propeller performance, 2) dynamic blade loads, particularly in resonance, and 3) aeroacoustics. This paper is part of a trio and is focused on performance and blade loads measurements and validation; two companion papers cited in the text present an overview of the test and provide details on aeroacoustics analysis, respectively. Test measurements are compared to predictions generated by a CFD-trained model called AeroRef, the comprehensive analysis code RCAS with a finite state dynamic wake model, the Helios ROAM mid-fidelity blade loads solver coupled to RCAS, and OVERFLOW CFD coupled to RCAS. For performance, the AeroRef model and CFD were able to accurately predict thrust and rolling and pitching
This paper describes the design, development, and testing of a full-scale eVTOL propulsor optimized for quiet and efficient operation. To design the propulsor, a design tool was developed for predicting the aerodynamic and acoustic performance of eVTOL propellers and rotors. The design tool consists of an aerodynamic prediction code, AMP (Aerodynamic Modeling of Propulsor), and an acoustics prediction code, OpenCOPTER, coupled with an acoustics propogator, PSU-WOPWOP, which can receive inputs from either an acoustic solver or high-fidelity CFD. The tool was used to design a coaxial eVTOL propulsor, and both subscale and full-scale blades were manufactured. The aerodynamic and acoustic performance of the subscale propulsor was tested in hover and edgewise flight in an anechoic wind tunnel. A custom test stand was developed and used to measure the aerodynamic and acoustic performance of the 8-ft diameter full-scale propeller in hover. The experimental results were used to validate the
The use of sub-scale vehicles as a means of predicting full-scale vehicle behavior has historically been applied to flight dynamics testing and evaluation for aircraft operating in Earth atmospheric conditions. However, the use of sub-scale testing on Earth has not been as thoroughly explored for Martian rotorcraft. In this paper, sub-scale vehicles of varying sizes were developed in simulation using Froude scaling laws to evaluate their ability to estimate fullscale linear dynamics for the Mars hexacopter, Chopper. Blade loading, Lock number, and flap frequencies were held fixed when scaling and corresponding relationships for vehicle length, mass, inertia, and rotor speed derived. Full-scale frequency response, gain margin, and instability characteristics are explored for hover and forward flight cases in a variety of Mars-to-Mars and Earth-to-Mars conditions. Mach effects are also analyzed as a consequence of Froude-scaling by comparing sub-scale vehicles that are Mach-matched to
Preparation for Powered Flight (PPF) is a critical phase for Dragonfly, the National Aeronautics and Space Administration (NASA) mission to Saturn’s moon Titan. During PPF the descending Lander is lowered below the Backshell and uses its rotors to remove or “despin” any residual yaw motion of the vehicle. A 1/2-scale model of the Dragonfly PPF configuration was tested in the National Full-Scale Aerodynamics Complex (NFAC) 80 by 120-foot wind tunnel to measure aerodynamic loads and surface pressures on the Lander and Backshell. The results were used to improve understanding of the complex aerodynamic interactions and provide validation data for the Computational Fluid Dynamics (CFD) simulations used to develop the aerodynamic databases for full-scale, Titan conditions. Configurations tested in the wind tunnel included Lander-alone-no-rotors (L), Lander-alone-with-rotors (LR), and Lander-with-Rotors-and-Backshell (LRB). Both LR and LRB configurations were tested at multiple descent
We extend the previously developed integrated VABS (iVABS) framework for rotor blade structural optimization with an enhanced cross-section template for practical manufacture considerations; these include the introduction of curved spar corners, a continuous wrap-around skin, trailing-edge tabs and a conformal non-structural mass. The added fidelity is exercised on a UH-60A-based outer mold line through three multi-objective optimization case studies, including a case where the cross-sections are optimized independent of each other, and two cases where all the cross-sections are optimized simultaneously with manufacture considerations. It was found that the latter cases produce straight spars that are relatively more practical to manufacture when compared to the first case, while achieving significant reduction of up to 80% in the mismatch of stiffness values, inertia properties, and shear center locations, when compared to the prior work. A subsequent sensitivity analysis of the
Active vibration damping by rotor torque modulation has been demonstrated for vibratory modes in the rotor disk plane. In this study, we introduce a simple, first-principles model, which includes kinematic coupling between lag movement and blade pitch, in order to extend damping authority to strut vibratory modes normal to the rotor disk plane. Using a medium-sized (12kg) quadcopter drone model, we demonstrate the capability to excite strut vibrations normal to the rotor disk plane, indicating control authority for vibration damping. For this vehicle model, a steady state strut deflection of over 12% is obtained using a 15% voltage perturbation, with under 2% rotor speed change. Redesign of the vehicle to have lower and/or co-located lag and structural frequencies increases the control authority of rotor torque actuation with pitch-lag coupling.
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