Browse Topic: Aerodynamics
In this study, a multifidelity aeroelastic framework is presented for predicting trim conditions in rotary-wing aircraft, with the main focus placed on the DUST implementation and its application to helicopters and quadrotors. The methodology combines aerodynamic and structural solvers of different fidelity, specifically DUST and the multibody dynamics solver MBDyn, through the preCICE coupling interface to enable direct comparison with rigid and coupled aeroelastic solutions. The trim problem is formulated from the six degree of freedom rigid body equilibrium equations in a helical turn reference frame, naturally covering both steady and maneuvering flight. Although the same formulation can be extended to fixed-wing configurations, the present paper is focused on rotorcraft applications. The framework is first applied to the SA330 Puma helicopter, chosen for the availability of validated flight test data. The methodology is then extended to a multirotor derived from a NASA quadrotor
Helicopter tail shake constitutes a significant limitation to both passenger comfort and aircraft stability. Under powered descent conditions, elevated Angle of Attack (AoA) cause flow separation around the rotor hub and engine cowling, leading to the development of an unsteady wake dominated by large-scale turbulent structures. To support the helicopter tail shake phenomenon investigation, a dedicated Particle Image Velocimetry (PIV) experimental setup was designed in this work, together with four aerodynamic devices aimed at mitigating tail shake. These components were then tested through a wind tunnel campaign with the PIV setup. The proposed aerodynamic components were conceived to either deflect the hub wake away from the tail empennages or to decrease the Turbulent Kinetic Energy (TKE) within the wake. To achieve these objectives, a dorsal fin, a horse-collar, and two spoiler configurations inspired by automotive applications were designed and experimentally evaluated. The
An experimental investigation was conducted to characterize the effects of partial-ground on the aerodynamics of a hovering rotor. A model-scale rotor was tested at a range of heights above ground and under partial-ground coverage, and rotor hub forces and moments were measured using a six-axis force/torque transducer during constant-power operation. The measurements were used to develop a semi-empirical thrust ratio model that accurately captures trends from out-of-ground effect to full-ground effect conditions. This model predicts realistic thrust behavior at low ground-coverage conditions, exhibiting high adjusted R2 and minimal root mean square error. Time-resolved particle image velocimetry was conducted for selected cases to examine induced flow features and to qualitatively assess changes in the downwash and edge-driven crossflow associated with partial-ground interactions. A geometric rotor-ground interaction area based on a circular-segment formulation was correlated to the
RPM-controlled hexacopters offer mechanical simplicity and inherent redundancy, but are unable to re-trim under all failure cases in forward flight. This paper investigates the use of reverse-enabled rotors as a means of expanding the attainable trim envelope and improving fault tolerance in RPM-controlled hexacopters. Isolated rotor experiments are conducted to characterize thrust and torque behavior under forward and reverse rotation, providing validation data for aerodynamic modeling. A blade-element-based model implemented in the Rensselaer Multicopter Analysis Code (RMAC) is then used to perform comprehensive trim analyses for a 1200-lb-class hexacopter in hover and in cruise at the best-range speed of 65 kts. Post-failure trim solutions are evaluated for four configurations, including edge-first and vertex-first orientations with different rotor spin directions. Results show that enabling reverse rotation allows trim recovery for all single-rotor failure cases in cruise
Recent flight tests and simulations have suggested that the outwash from eVTOL air-taxis could be larger than conventional helicopters of equal weight and thus pose greater safety issues for their operation than previously anticipated. This has prompted interest in the analytical and experimental study of the aerodynamics related to multi-rotor aircraft outwash. This paper will describe work investigating some of the related issues, specifically (1) how wake models and wake model parameters impact outwash predictions in comprehensive rotorcraft analyses and (2) considerations when scaling results from model scale to full scale. This work will also compare outwash predictions for conventional and multi-rotor VTOL aircraft obtained with a Lagrangian free-vortex wake model and with an Eulerian velocity-vorticity grid based wake model.
Dimensional reduction of data can be accomplished through various methods and has applications critical to machine learning and surrogate modeling. Within the rotorcraft community, leveraging these techniques allows for improved rotor parameterization and performance prediction. Machine learning models generally perform faster and better with lower input dimensions, so long as all necessary information is retained, making appropriate dimension reduction paramount. Data can also be arranged in a one-dimensional (concatenated/stacked) or two-dimensional arrays to take advantage of function correlations, and this arrangement may allow for greater reduction at lower reconstruction costs. Principal Component Analysis with a stacked input shape proves to be the most effective reduction method considered, with reconstruction accuracy being validated though a suite of mid-fidelity aerodynamic simulations. A blade geometry defined using 204 original parameters can be fully described using just
A high-fidelity computational study is conducted to investigate the aerodynamic behavior and flight response of an electric Vertical Take-Off and Landing (eVTOL) multirotor configuration using unsteady computational fluid dynamics (CFD) framework. Four simulation cases are considered to examine the vehicle aerodynamics under both prescribed and fully coupled conditions. Prescribed hover and forward-flight cases isolate rotor aerodynamics and rotor-airframe interactions under constrained kinematics. Six-degree-of-freedom (6-DoF) free-flight maneuvering simulations capture the coupled evolution of aerodynamic loads, vehicle attitude, and translational motion. The results demonstrate that the high-fidelity unsteady CFD framework, coupled with rigid-body dynamics, effectively resolves the tightly coupled aerodynamic–dynamic interactions inherent to eVTOL configurations. This work provides a foundation for future investigations into trim strategies, control modeling, and expanded flight
This paper presents the design and validation of the Rotor Optimization for the Advancement of Mars eXploration (ROAMX) Hover Test Stand, a vacuum compatible stand developed to measure rotor performance under Mars aerodynamic conditions. The stand integrates a high-speed water-cooled motor, a variable pitch hub, and a structural safety system capable of withstanding the high loads resulting from rotor blade loss while enabling continued experimental operations. The stand also maintains the measurement fidelity required for thrust and torque characterization at low Reynolds number. Aerodynamic blockage was limited to less than 20% through geometric constraints on the stand architecture. Calibration and sensor procedures ensured correct load transfer through the intended structural load path and also verified sensor accuracy. Test Entry 1 demonstrated successful test stand performance and testing of experimental blades. The stand spun blades to 4,000 Revolutions per Minute (RPM) for Test
This paper discusses the design of a 2000-lb manned eVTOL aircraft propelled by a novel cycloidal rotor propulsion system. To systematically evaluate the performance of the proposed configuration, a coupled trim model was developed to quantitatively evaluate the performance of the configuration across a range of forward flight speeds. The trim framework integrates an efficient physics-guided neural-network-based aerodynamic model for cycloidal rotor performance with a vehicle-level dynamic response model. This framework is used to conduct a systematic parametric study to identify key cycloidal rotor and airframe design parameters. The selected configuration is verified using high-fidelity CFD simulations, and a detailed structural design, powertrain design, and CAD model of the aircraft is developed. In addition to CFD validation, the proposed cycloidal rotor underwent structural optimization to confirm the validity of such a concept at this scale. The results demonstrate that the
NASA's successful demonstration of powered flight on Mars through the Ingenuity Helicopter, as part of the Mars 2020 Perseverance rover mission, has led to the development of next generation Martian rotorcraft. The future of Martian rotorcraft has evolved to include high payload-carrying vehicles to possibly contribute to planetary science missions, which will require improved flight dynamics and rotor aerodynamic performance to fly at nominally high forward flight speeds and at higher flight altitudes. To ensure the feasibility and viability of successful mission performance, it is also critical to mature the structural design for advanced Martian rotorcraft to bridge the gap between the best practices of the spacecraft and aircraft communities. This paper focuses on the structural analysis of a Mars Science Helicopter (MSH) blade using finite element methods. Multiple loading conditions including launch and operational flight were applied to investigate the blade’s structural
Achieving noise reduction in rotorcraft requires an analysis of various design parameters and flight conditions. However, high-fidelity methods are computationally expensive. To overcome this limitation, reduced order model (ROM)-based surrogate models have been applied to aerodynamics and aeroacoustics prediction. This study proposes a ROM-based surrogate model employing a variational autoencoder (VAE) to predict rotor aerodynamic loads and associated noise. Train and test datasets were generated using reformulated vortex particle method across a wide range of flight conditions. The proposed framework was applied to a single rotor, and its performance was evaluated qualitatively and quantitively in comparison with proper orthogonal decomposition (POD)-based surrogate model. The results show that VAE-based model consistently outperformed the POD model in noise prediction. These results demonstrate that the proposed framework enables accurate rotor noise prediction under various flight
A technique for rapidly designing roughness tolerant low drag airfoils has been developed. Airfoils of varying thickness to chord ratio, ranging from 10% to 22% have been designed. A target pressure distribution is specified by the designer for a notional lift coefficient, Reynolds number, and Mach number. The specified pressure distribution is first analyzed using classical integral boundary layer analyses and empirical transition criteria for smooth and rough airfoils to ensure laminar flow over much of the airfoil under design conditions. The resulting airfoil is subsequently analyzed under natural transition, and forced transition caused by the tripping of the boundary layer due to roughness near the leading edge. It is found that the present approach performs well for a broad range of lift coefficients. An in-house propeller design and analysis tool has been used to examine the impact of the low drag airfoil on the pusher propeller performance designed for a fixed wing UAV drone
An experimental investigation was conducted to explore the loads, acoustics, and tip vortex trajectories of coaxial counter-rotating (CCR) rotor with unequal upper and lower radii. The upper and lower rotor radii were tested both at the nominal radius of 1.108 m, and also with a lower rotor radius of 90% nominal radius, for a constant rotor speed of 1180 RPM and a constant inter-rotor spacing of z/R = 0.108. Rotors were torque balanced and tested for a range of upper rotor collective pitch from -2◦ to 10◦ . The power required for both CCR systems was within 0.9% for most trim conditions, and equal thrust was produced at upper rotor collectives of 6◦ and 8◦ (within 1.0%). At low loading conditions the unequal radii configuration produced more thrust for the same power due to a reduction in profile drag. The overall sound pressure level (OASPL) was lower for the CCR rotor with shortened lower rotor blades at all angles of elevation. Larger reductions in A-weighted OASPL(A) were observed
This SAE Information Report has been prepared at the request of the SAE Road Vehicle Aerodynamics Forum Committee (RVAC), incorporating material from earlier revisions of the document first prepared by the Standards Committee on Cooling Flow Measurement (CFM).Although a great deal is already known about engine cooling, recent concern with fuel conservation has resulted in generally smaller air intakes whose shape and location are dictated primarily by low vehicle drag/high forward speed requirements. The new vehicle intake configurations make it more difficult to achieve adequate cooling under all conditions. They cause cooling flow velocity profiles to become distorted and underhood temperatures to be excessively high. Such problems make it necessary to achieve much better accuracy in measuring cooling flows.As the following descriptions show, each company or institution concerned with this problem has invested a lot of time and as a result gained considerable experience in developing
Generalized Predictive Control (GPC) is an advanced form of an adaptive control algorithm that uses experimentally acquired data to determine the input-output relationship of complex systems through a process called system identification. GPC has historically been employed for stability augmentation and vibration reduction of dynamically-scaled tiltrotor aircraft wind-tunnel models since the complex nature of these dynamic systems does not lend itself well to traditional control approaches. The present research expands upon previous analytical and experimental work with wind-tunnel experiments that utilize improved GPC techniques. These techniques improved controller robustness such that a working controller was stable across a multitude of model configurations and wind-tunnel conditions and successfully suppressed vibration and vehicle flutter. Advanced GPC (AGPC) enables self-adaptation of a traditional GPC control law. AGPC was also investigated during the present research but was
This study presents computational analyses of coaxial rotor hub flows and validation against experimental data obtained from the fifth Rotor Hub Flow Prediction Workshop. Experiments were conducted in a 12-inch diameter water tunnel at Pennsylvania State Applied Research Laboratory, employing tomographic particle-image velocimetry (Tomo-PIV) and precise hub drag measurements. Three CFD codes (UMD Mercury, CREATETM-AV Helios, and OVERFLOW) utilizing hybrid Reynolds-Averaged Navier-Stokes (RANS) / Large Eddy Simulation (LES) modeling based on Spalart–Allmaras turbulence model, were applied to replicate and analyze hub flows. Counter-rotating coaxial rotor hubs under free-air condition was simulated as the simplest case and the hub drags are compared between the three CFD codes. The full water tunnel configuration, consisting of two hubs, a fairing, and shafts, was also simulated and compared to experimental results, with a focus on hub drag, wake velocity fields, and turbulence
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
The oil cooling fan of a Main Gearbox (MGB) is a mechanically-driven component whose purpose is to force an air flow through an air cooled oil cooler; its performance is crucial in ensuring that the MGB oil temperature does not exceed a predefined threshold, set to alert the crew in case of an abnormal situation. The design and the certification of a cooling fan is a process involving several steps and multiple disciplines; mechanical design, aerodynamic analysis, dedicated tests carried out both on rigs and at aircraft level need to be exploited as complementary tools to assess the correct aero-mechanical behavior of the system. The aerodynamic assessment is associated to performance, measured in terms of MGB oil temperature: considering a comparison between two cooling fans, one outperforms the other if the resultant MGB oil temperature is lower, keeping the same boundary conditions (engine torque, wind speed, ambient temperature, etc.). The correct mechanical behavior is instead
This paper expands on a previous exploratory investigation into the safety implications of helicopter operations at hospital landing sites. The paper analyses the interaction between rotor downwash, the turbulent wake shed from nearby buildings and the effect of varying windspeed and aircraft position. A RANS CFD method has been used to compute the mean airflow in the vicinity of a hospital helipad with a helicopter, representative of a Bell 412, hovering at three different positions around the site. The main rotor of the aircraft was modelled using a Virtual Blade Model, enabling a coupled solution between the airflow around nearby structures and the helicopter. The study examines the resulting airflow patterns and velocity magnitudes around the site for two incoming windspeeds and three varying aircraft positions. Results presented are focussed on areas where the rotor downwash is present and likely to impact pedestrians. The findings show that windspeed can affect how the downwash
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 study presents an integrated optimization framework for rotor blade design that combines aerodynamic shape optimization and internal structural design within a unified multidisciplinary process. A variable fidelity modeling (VFM) approach is employed to efficiently optimize the blade outer geometry for improved figure of merit (FM) in hover and lift-to-drag ratio (L/Dq) in forward flight. Based on the optimized aerodynamic shapes, internal structural optimization is subsequently performed using a surrogate model for predicting cross-sectional properties, ensuring dynamic feasibility while minimizing blade vibration and weight. Final aeroelastic performance is evaluated through high-fidelity CFD/CSD loose coupling simulations. Optimization results show that individual designs achieve up to 6.5% improvement in FM or up to 6.6% improvement in L/Dq compared to the baseline HART II rotor. Furthermore, cross-validation comparing blades independently optimized by Seoul National
A wind tunnel investigation to characterise the aerodynamic performance and aeroelastic response of a tiltrotor blade set operating in propeller mode is presented. A custom blade set was instrumented with fully bridged axial strain gauges to monitor the flap bending and torsional strain at several radial locations. Propeller thrust and torque measurements were acquired using a custom six component Rotating Shaft Balance. Measurements of blade tip deflection were obtained via stereoscopic Digital Image Correlation. Testing was performed at a range of rotational frequencies, blade pitch angles and advance ratios to assess the blade aerodynamic performance and aeroelastic response in both attached and stalled operating conditions. Strain measurements were shown to identify stall and blade eigenmode frequencies, where flap bending bridges show a more reliable capture of stalled flow than torsional bridges. Furthermore, blade tip deflection measurements were shown to reduce with increased
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
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 presents an overview of the results from the second wind-tunnel test of the TiltRotor Aeroelastic Stability Testbed (TRAST). The objective of this test was to obtain experimental data for understanding the effects of tiltrotor parameters on whirl flutter and analysis-validation data for the prediction of whirl flutter across a range of system configurations. Frequency and damping were measured at multiple rotor speeds for pitch-flap-coupling angles ranging from -0°to -30°. In addition, measurements were made for changes in blade stiffness, air density and wing-pylon connection stiffness. The paper also presents the results from supporting measurements that may aid analysis validation, such as wing-only damping, rotor frequencies and non-spinning modal frequencies.
A velocity potential-based finite state model (VPBFSM) has been developed to analyze an isolated rotor in ground effect. The model uses mass source distributions to represent the ground and enforces the non-penetration of flow boundary condition. In previous VPBFSM approaches to impose this boundary condition, the r = j terms were excluded to avoid singularities. This exclusion required adjustments to the source strengths and ground rotor size in order to impose the boundary condition properly, which reduced the model’s robustness. In the present study, the r = j terms are incorporated using a solution for the gradient of the velocity potential from the literature, which avoids singularities. This inclusion allows for effectively enforcing the boundary condition without requiring adjustments. The model is applied to an isolated rotor in full, inclined, and partial ground effect cases, including analysis of the R−50 rotor using geometric and aerodynamic data from the literature. Results
To document noise characteristics and provide validation data for acoustic modeling of rotor systems appropriate for eVTOL/UAM aircraft, the authors performed an outdoor static test of a subscale 5-blade proprotor. The testing was carried out as part of a program to demonstrate feasibility and overall performance of a quiet proprotor system in support of the eVTOL industry. The authors designed a low-tip speed proprotor to approximate performance required by a 4-5 passenger UAM vehicle. A driving design feature was low-tip speed operation (Mtip ˜0.27) at system disk loadings of 7 to 8 psf (˜3.7 N/m2). The test article was designed as a ground adjustable pitch 5-blade proprotor, with aerodynamic and acoustic data collected in outdoor static hover testing. The test article diameter of 3 feet (0.91 m) represented a scale factor of approximately 30% to 40% compared to vehicles currently in operation or development. The aerodynamic performance in hover was consistent with other rotor
Dragonfly is a rotary-wing lander, and its mission is to explore Titan. It will make multiple flights over several years to explore different sites on Titan. There is limited information on the chemical processes that led to life on earth. Among the other places in the solar system, Titan is the most like the early earth and therefore exploring its organic surface chemistry will help to better understand our own prebiotic history. During Titan flight the rotor induced unsteady aerodynamic loads, as well as the interactional aerodynamic loads due to the rotor to rotor and rotor to lander interferences drive the structural vibrations. Therefore, robust and accurate predictions of Dragonfly structural loads and vibrations are essential for designing a vehicle that can successfully perform its mission. This paper presents the structural loads and vibration predictions of the Dragonfly lander using Rotorcraft Comprehensive Analysis System (RCAS) coupled with the Viscous Vortex Particle
The subject of this paper is the conceptual development of two new configurations for HEMS Operations as a new fleet concept for the European theater. Previous studies showed an increase of the required flight range for an emergency patient transport. But in conjunction with an average share of less than 30% of the flights actually with the patient. In the most rescue missions an emergency physician is transported to the scene, the patients further transport is conducted on-road by an ambulance. Considering an improved flight performance, the first DLR design study revealed a growth of the maximum take-off mass of the primary rescue helicopter of 32%. That makes the rescue helicopter inefficient for the transport of only the emergency physician. Consequently, if an ambulance is already at the scene, an emergency doctor shuttle is the sensible approach. The requirements for such a configuration are developed from a feasibility study lead by the ADAC Air Rescue (ADAC Luftrettung
Enhancing rotor efficiency has been a persistent challenge in the development of micro aerial vehicles (MAV) especially for surveillance and covert operations. This study introduces a new Hybrid Flapping Wing Rotor (Hybrid FWR) configuration inspired by insect's wing flapping mechanics to address the efficiency limitation of traditional rotor designs. Unlike traditional rotary systems that rely solely on rotational motion, the Hybrid FWR combines rotational and flapping motions to significantly enhance lift generation. A comprehensive mathematical model was developed to analyze and predict the optimal aerodynamic performance, demonstrating that the Hybrid FWR configuration achieves a substantial improvement, with a power efficiency increase of up to 2.148-fold compared to conventional micro rotorcraft. Experimental validation was conducted to confirm the theoretical predictions, identifying an optimal hybrid ratio of approximately 0.7, which effectively minimizes aerodynamic resistance
This study explores the aerodynamics of aerial screws, drawing inspiration from Leonardo da Vinci's visionary 16th-century designs. Using high-fidelity Computational Fluid Dynamics (CFD) analysis, the research identifies a vortex-based thrust generation mechanism, centered on the formation of a "da Vinci vortex"—a coherent helical structure critical to performance. Systematic investigations into the effects of pitch and taper variations reveal nuanced strategies for optimizing thrust efficiency. Bilinear modifications to these parameters achieve up to a 13% improvement in figure of merit over linear designs. Detailed wake analyses further elucidate the importance of early vortex anchoring, swirl minimization, and coherent wake contraction for maximizing aerodynamic efficiency. This work not only deepens the understanding of aerial screw physics but also lays the groundwork for their application in next-generation Vertical Take-Off and Landing (VTOL) vehicles.
The Dragonfly relocatable lander was selected as NASA's New Frontiers mission in 2019 to explore the organic-rich surface of Titan, Saturn's largest moon. The coaxial quadrotor vehicle will fly to multiple geologic sites covering a distance of over 50 miles near the Titan equator. At each site, Dragonfly will sample materials, determine the surface composition, and investigate how far prebiotic chemistry has progressed on Titan. Upon arrival, the lander will enter the Titan atmosphere protected inside an aeroshell, which will descend and decelerate with parachutes. At an altitude of approximately 1 km above the ground, the lander will separate from the backshell and perform a controlled transition to powered flight. Prior to separation from the backshell and after the heatshield has been ejected, the Preparation for Powered Flight (PPF) sequence will be initiated, which ensures the lander is in a safe and stable state for autonomous descent. A critical element of PPF is the de-spin
Precision flight in windy conditions is a common challenge for multirotor UAS. It is especially challenging for in contact tasks that require high-precision positioning and good disturbance rejection capabilities. Such tasks include landing on high-voltage powerlines for in-contact inspections. This paper presents the implementation of small lateral thrusters to improve the lateral position hold ability of a large power line inspection UAS in windy conditions. Arranged in antagonistic pairs on each side, the lateral thrusters handle the high-frequency but smaller-amplitude wind turbulence components with a frequency split control. Using an identified model of the UAS flight dynamics alongside flight data in high-wind conditions, a control architecture with a frequency split in the lateral axis was optimized to increase the disturbance rejection. Experimental tests showed a 67% reduction in lateral position error with the proposed approach in high-wind conditions.
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.
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
Current paper summarizes a correlation study of two flow solvers (CREATETE-AV Helios and Simcenter STAR-CCM+), routinely used at Sikorsky, with multiple model-scale wind-tunnel tests. The Helios modeling approach was aiming for a high-fidelity accurate simulation, whereas the STAR-CCM+ modeling approach was aiming for a fast turn-around time with reasonable solution accuracy with a relatively coarse mesh and simplifications. The two solvers generally agreed well with the test data within reasonable accuracy and captured the airloads and flowfield trends. The calculations presented herein show the impact of the turbulence model on component loads, the aerodynamic interactions among components, and the effect of transition modeling on rotor performance. The Reynolds-Averaged Navier-Stokes CFD model generally delayed separation and resulted in lower drag. By modeling the airframe supporting structure in CFD simulations, an improvement on correlation for inflow on the propeller plane was
The UH-60A slowed rotor test campaign carried out at the 40- by 80-Foot Wind Tunnel at the U.S. Air Force's National Full-Scale Aerodynamics Complex (NFAC) provided valuable information of a classical helicopter rotor blades operating at very high advance ratios. This paper aims to show the correlation of the RCAS and HOST comprehensive analysis (CA) tools with respect to several experimental campaign cases. Particularly the influence of the rotor aerodynamic performance as a function of the advance ratio and the collective angle is studied. The influence of the shank drag modeling is observed and its importance to obtain accurate results is highlighted. The RCAS and HOST simulations are capable of reproducing the rotor performance trends observed in the test campaign. Furthermore, the correlation of RCAS and HOST with respect to the measured rotor loads data is studied for the advance rations of 0.4, 0.5 and 0.7 at iso-thrust coefficient conditions. The aerodynamic loads and the
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
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.
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