Browse Topic: Wind tunnel tests
Large-Eddy Simulations of a boundary layer over a rotor blade are performed with and without inclusion of the rotational sources in the code. The numerical setup matches the one of a wind tunnel test available in the literature, and the numerical results are compared to each other and to the experiment. The mean boundary layers obtained from the simulations are studied by means of the linear stability analysis techniques with the aim of reproducing the transition location. It is shown that the non-rotating scenario, even when performed for the matching Mach and Reynolds numbers, predicts the transition location that is much farther downstream than the one seen in the experiment. However, inclusion of the rotational sources in the code moves the transition forward to the location that better agrees with the experiment. This shows that non-inertial forces associated with rotation play a crucial role in the transition in the considered setup. The character of the transition is different
The paper discusses the design and high-fidelity flight dynamics modeling of a 13-lb lift-plus-cruise unmanned aerial vehicle (UAV) using Rotorcraft Comprehensive Analysis System (RCAS) in order to (1) better understand its physics of flight during a wide range of maneuvers, and (2) provide insight into the fidelity needed to achieve quantitative accuracy when compared to flight test data. Wind tunnel tests of the full aircraft were performed at a 65% scale to provide lookup tables for the flight dynamics model. Flight test data was collected while providing high control inputs to excite a variety of dynamic states in hovering and cruising modes to systematically validate the physics model. Near quantitative agreement was observed between the model predictions and test data during hover; however, the predictions began to disagree at higher forward cruising speeds. To address the discrepancy between the prediction and experiment, the flight dynamics model was improved by learning a
A 4.75-ft diameter hingeless hub proprotor model was wind tunnel tested up to the very high speeds of 205 knots, loosely corresponding to 480 knots full-scale, with parametric variations in blades, wing spar, and pylon center of gravity. Testing revealed that a gimballed-hub configuration that reached whirl flutter at 160 knots was completely stabilized when converted to a hingeless hub – using identical blades, span, and pylon. While the gimballed-hub model encountered whirl flutter at 160 knots, the hingeless-hub configuration remained stable throughout the entire test envelope up to 205 knots. The key conclusions are that a hingeless hub can eliminate whirl flutter, and that the most stable configuration is a swept-tip blade hingeless-hub rotor with the pylon center of gravity aft of the wing spar.
The current effort presents novel investigations of rotor-wake–surface interactions for the Dragonfly lander, NASA's rotorcraft lander to explore Titan. The numerical framework couples unsteady RANS with blade-element and virtual disk rotor models and a coupled Lagrangian particle tracking method to examine rotor–ground interactions and brownout. Simulations span a range of complexity, from isolated rotor benchmarks and rotor pairs to full eight-rotor configurations without a fuselage and the eight-rotor configuration with a simplified Dragonfly fuselage. To quantify model fidelity and near-ground shear, blade-resolved simulations of the isolated rotor are performed using Spalart–Allmaras and Reynolds Stress turbulence models with vorticity confinement, demonstrating that virtual blade models under-predict tip-vortex strength and local inflow distortion but reproduce wall shear reasonably well, whereas blade-resolved RSM solutions yield higher peak shear levels relevant to brownout
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
Turbulence conditions at hospital heliports in the built environment are routinely assessed at the design stage through experimental, physical testing in boundary layer wind tunnels. Wind tunnel testing is the gold standard to evaluate wind conditions on and around buildings where human safety is of the upmost concern. Numerical techniques, such as computation fluid dynamics (CFD) are continuously improving and may offer a viable alternative to wind tunnel testing in some cases. Within the CFD toolbox, there are several techniques to simulate a flow field in an urban or suburban context. These techniques have advantages and disadvantages in terms of ease of use, efficiency, costs, level of fidelity, and reliability. This paper compares high-fidelity CFD tools to wind tunnel testing for two vertiport case studies in different urban settings with different wind climates. The results of this research inform the selection of the right tool to support vertiport design and operations and to
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 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
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
This paper presents the results of an ongoing correlation study performed using three different comprehensive rotorcraft codes and data obtained from the Advanced Testbed for TILtrotor Aeroelastics (ATTILA) tiltrotor whirl flutter wind tunnel test campaign. The ATTILA testbed consists of a 1:5 scale semi-span wing with a powered, tip-mounted proprotor reflecting the proprietary design of the Next Generation Civil TiltRotor (NGCTR). Experimental dynamic characterization of the testbed has revealed non-negligible structural nonlinearities. Post-test efforts have focused on refining the damping trends extracted from the test data, and correlating the experimental results with numerical predictions. The objective of this paper is to assess the modelling fidelity required and afforded by modern comprehensive aeromechanics codes to predict tiltrotor whirl flutter instability given an industry-representative design that exhibits structural nonlinearities. Baseline numerical flutter models
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
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 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.
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
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
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
To validate simulation work towards the design of the Dragonfly rotorcraft lander, a process of extracting a modal model from impact test data is described in this paper. Through a curve-fitting process using Siemens Testlab software, modal frequencies, damping, and mode shapes are extracted and mass-normalized to be imported as a modal model into the Rotorcraft Comprehensive Analysis System (RCAS) to represent the dynamics of the underlying structure more accurately. Wind tunnel conditions were simulated to compare to hub loads measured during wind tunnel testing. An initial comparison of RCAS with VVPM inflow and RCAS coupled with HELIOS show similar hub loads but also show the importance of modeling the rotational degrees of freedom of the structure properly. Additional modeling comparisons between modeling the hubs and the load cell locations further illustrate that by capturing rotational mode shapes based on test data, in-plane hub loads are predicted more accurately.
This paper investigates the amplitude-dependent characteristics of the TiltRotor Aeroelastic Stability Testbed. The recovery rate, MultiProny, and Stockwell transform methods are employed to measure nonlinear effects in the system, overcoming the limitations of conventional methods like logarithmic decrement, moving-block analysis, and Prony series that assume linear (amplitude-independent) behavior. The proposed methods reveal amplitude-dependent trends that conventional methods obfuscate, providing deeper insights into tiltrotor dynamics. A comprehensive study of ground vibration and wind tunnel test data highlights reduced local damping and frequency at larger response amplitudes for various blade materials, rotor speeds, and pitch-flap coupling parameters. This study offers novel analysis capabilities to support design and advances the understanding of tiltrotor nonlinear dynamics.
Large eddy simulations (LES) of the Joby Aviation S4 propeller at the NFAC tunnel are performed with a GPUaccelerated low-Mach (Helmholtz) solver, and compared with experimental data provided by Joby at two flow conditions of hover and pure edgewise flow of 10 m/s. Accurate prediction of the laminar-turbulent transition was seen to be critical to the prediction of the noise sources for hover condition, with additional prominent noise sources found to be near the trailing edge and tip of the propeller. The dominant edgewise noise sources were seen to be from the dynamic outboard flow separation and reattachment from advancing to retreating side of the blade azimuth as well as the convective amplification of the acoustic waves from the 10 m/s flow. The far-field noise at the target set of microphone locations are predicted using the frequency-domain Ffowcs Williams-Hawking (FW-H) formulation. The A-weighted 1/3rd octave band results showed a good prediction of the noise compared with the
This paper discusses the development of a quantitatively-accurate non-linear hybrid flight dynamics model of a hover-capable Air-Launched Tailsitter Unmanned Aerial System (ALUAS) in order to 1) understand its dynamics during complicated maneuvers, and 2) provide a high-fidelity framework to develop novel control laws. Wind tunnel tests were conducted on a 1:1 scale model of the full aircraft to measure the airloads, which were used in the simulation as a lookup table. Flight tests of the ALUAS were performed in hover, transition, and cruise to collect a large amount of unique state measurements by providing large excitations to induce highly transient motion. The flight dynamics predictions using Rotorcraft Comprehensive Analysis System (RCAS) software were then compared with experimental flight test data. To correct any discrepancies in the RCAS physics-based predictions, a correction was learned from the experimental measurements, making use of the large amount of collected flight
With recent advancements in the field of Advanced Air Mobility (AAM), including Electric Vertical Takeoff and Landing (eVTOL), Remotely Piloted Aircraft Systems (RPAS), and Unmanned Aerial System (UAS), it is beneficial to understand the impact of complex flow features on operations in urban and shipboard environments. Testing methods for studying these impacts, including simulated environments such as wind-tunnel flows and engineered equivalence tests, will need to be adapted to prepare for when the vehicles of interest are too large for the available testing facilities, and to permit low-cost alternatives for industry and government. This work demonstrates a development process that can be used to ensure the complex-flow-environment phenomena can be studied. First, this work illustrates the development of downdraft and turbulence flow types in a wind tunnel setting, and assesses the response of an M600 RPAS to these flows. Then, the same parameters are compared for a Mission Task
Wind tunnel tests and comprehensive rotorcraft analysis were carried out on a slowed main rotor full-wing lift and thrust-compounded helicopter with a trailing propeller to investigate the effects of rotor and wing configuration on performance, blade structural loads, and hub vibratory loads. Experiments were conducted at advance ratios up to 0.7, incorporating three full-wing configurations with symmetric and asymmetric incidence angles and three different rotor shaft tilt angles. Propulsive thrust was measured by a trailing pusher propeller with its own balance system. The wind tunnel test data was used to validate the University of Maryland Advanced Rotorcraft Code (UMARC). Results showed that the maximum lift-to-drag ratio is achieved using either of the symmetric or asymmetric full-wing lift-compound configurations with high lift offloading and aft shaft tilt. Both blade structural loads and hub vibratory loads are significantly reduced when rotor lift is offloaded to the wings
This paper details the development of a tailsitter unmanned aerial system (UAS) that has the potential to be airlaunched in the near future. By simultaneously integrating air-launch capability with both rotary-wing vertical flight and fixed-wing horizontal flight, the vehicle can be rapidly deployed, perform hovering flight, and achieve high-speed and efficient cruising flight. The aircraft prototype has a mass of 1 kg (2.2 lbs) with wings that can fold to allow the aircraft to fit inside a 6-inch launch tube. A coaxial propeller with vectored thrust is used for control in vertical flight, and a unique avian-inspired wing-folding mechanism is used for stowing and deploying the wings. The aerodynamic design was characterized through a series of wind tunnel experiments, propeller tests, and flight dynamics simulations. High-fidelity simulations of vehicle dynamics validated its air-launch capability and flight tests performed with the prototype demonstrated the ability of the aircraft to
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
This study characterizes the dynamics of a novel lag-pitch-coupled underactuated rotor design that can be incorporated into rotary-wing unmanned aerial vehicles (UAVs) to provide pitch and roll control with effectiveness comparable to that of a conventional swashplate albeit with significantly lower mechanical complexity and weight. The concept integrates a single lag hinge tilted at a 45-degree angle located at the center of the rotor hub with independent flap hinges for each of the two blades. This idea relies on the ability to cyclically vary the angular velocity of the rotor in a 1/rev fashion via motor torque modulation, which induces a cyclic lag resulting in a cyclic pitch variation due to the tilted lag hinge (lag-pitch coupling) and causes the tip path plane (TPP) to tilt in a desired direction for pitch and roll control. To understand this concept, simulations using the Rotorcraft Comprehensive Analysis System (RCAS) were performed to capture the 1/rev response in lag, pitch
The NASA Revolutionary Vertical Lift Technology project aims to support and guide the development of vertical flight vehicles for the benefit of the U.S. rotorcraft community and to increase the quality of life of the public. As part of this effort, the Multirotor Test Bed (MTB) – designed and built by NASA – has been tested twice at the U.S. Army 7- by 10-Foot Wind Tunnel at NASA Ames Research Center in 2019 (MTB1) and 2022 (MTB2). This study utilizes MTB2 experimental data for sensitivity studies on rotor aerodynamic performance of a quadrotor configuration using two mid-fidelity tools, the Comprehensive Hierarchical Aeromechanics Rotorcraft Model (CHARM) as well as Blade Element Theory based disk modeling in the OVERFLOW CFD solver. Additionally, this study leverages analyzing computational rotor performance predictions with experimental data to help identify future test configurations for the upcoming MTB3 test in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind
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.
The paper presents a general framework for building an aeromechanic model in FLIGHTLAB, suitable for high fidelity, pilot-in-the-loop simulator. The focus is on aerodynamic modeling of AW609 tiltrotor in Airplane Mode flight regime. The framework can be extended to helicopter and conversion modes with additional considerations for rotors-airframe aerodynamic interference. It can also be adapted to different tiltrotor geometries, with some adjustments depending on their peculiarities. The model uses Blade Element Theory loads evaluation of lifting surfaces, corrected with tabulated distributed loads to tune FLIGHTLAB predictions against high-fidelity aerodynamic references. Bluff bodies are modeled using force and moment tabulated data. Verification was conducted against reference data in wind tunnel mode and against flight data in trim analysis. The proposed method allowed to match lift distribution on slender bodies, as well as lift and drag integral loads, with aerodynamic references
The Rotor Blown Wing (RBW) is a tailsitter Vertical Takeoff and Landing (VTOL) Unmanned Aerial System (UAS) configuration that leverages cutting-edge autonomous flight controls through Sikorsky's MATRIX™ technology to create a highly capable, efficient, and scalable technology platform. By combining the benefits of fixed- and rotary-wing aircraft, the RBW configuration eliminates the need for traditional UAS launch and recovery infrastructure. This paper describes the RBW-5 prototype, a 100-pound, dual 5-foot diameter proprotor demonstrator, and discusses the comprehensive evaluation of its design and operability through a combination of flight tests, wind tunnel experiments, and computational fluid dynamics (CFD) simulations. The results demonstrate the maturity of the UAS and highlights key accomplishments of the RBW-5 program, including successful autonomous takeoff and landing and transitions between hover and forward flight, the extraction of critical "blown-physics" underlying
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
This study examines the acoustics of a wing operating in the wake of a propeller. The propeller wing system is simulated at 24 knots cruise and 8° wing angle of attack. The propeller is simulated using an actuator line model, while the wing is simulated using two different turbulence models: a DDES turbulence model and a higher fidelity LES model. Chordwise compact loads, on-wing pressure surfaces, and pressure surfaces at distances of 2.34% and 10% thickness around the wing surface are used as inputs to PSU-WOPWOP to predict noise at an observer below the wing. Using on-wing surface pressures, the LES broadband noise predictions are 13.5 dB higher than DDES. Chordwise compact loads result in lower noise predictions than on-wing surface pressures, by 11.3 dB for LES and 2.3 dB for DDES. Using off-body pressure surfaces, DDES results remain similar to noise predictions from on-wing pressure surfaces, but with LES the broadband noise predictions are about 2.5 dB lower.
This paper discusses the development of a fully-nonlinear flight dynamics model of a hover-capable Air-Launched Uncrewed Aerial System (ALUAS) in order to (1) understand the dynamics, controllability, and air loads of these type of aircraft while performing complicated maneuvers, (2) formulate design principles to feed back into the development of the realized physical aircraft, and (3) provide a high-fidelity dynamic framework to develop novel control laws. The flight dynamics model is developed using a software called Rotorcraft Comprehensive Analysis System (RCAS), where each component of the vehicle was modeled with varying fidelity. Wind tunnel tests were conducted on fullscale models to measure the forces and moments on the propeller, the isolated fuselage, and the full aircraft. Wind tunnel tests were also conducted to measure the forces and moments on the full aircraft for different wing folding angles. The thrust and torque of the propeller as well as the lift predictions for
Rotorcrafts frequently operate in environments with severe atmospheric turbulence, for instance transferring people offshore to and from oil rigs as well as operating from and around ships. The presence of high turbulence can deteriorate performance, stability, and controllability of the rotorcraft. Additionally, such challenging conditions also generate loads that both airframe and rotor components must withstand. Following this, it is crucial to consider the impact of these operational atmospheric conditions during rotorcrafts design and development. In this context, numerical models are a fundamental tool to provide an easier and quicker way to explore the operative envelopes of the helicopter compared to performing experimental activities. This paper presents a rotor loads correlation activity between an experimental test designed and carried out by Leonardo Helicopters in which an AW189 helicopter was placed in the wake of a C-27J Spartan aircraft and a multibody structural model
Tailsitter configurations that operate in both fixed and rotary wing flight modes are typically capable of generating large control forces and moments, making them inherently capable of rapid transitions and aggressive maneuvers. However, harnessing these capabilities requires feedback control strategies that can effectively estimate the non-linear aerodynamics loads involved to successfully exploit them. This paper describes initial steps in combining an onboard flow sensing strategy with a data-driven approach to estimating inflight air loads. A neural network is trained to use measurements from a multi-hole probe to predict the output from a set of pressure sensors embedded in a wing section undergoing a series of pitch motions in a wind tunnel. We hypothesize that this limited context of emulating a sensor network represents a focused and compartmentalized approach to applying emerging data-driven techniques to challenging aeronautical problems. We compare estimation results from a
The aeroelastic stability of rotor blades in the flap, lag, and torsion degrees of freedom is analyzed in preparation for high-advance ratio wind tunnel testing of Mach-scaled rotors. A wide range of advance ratios (0 ≤ μ ≤ 3) are evaluated for articulated and hingeless rotor configurations. Linearized equations of motion in the rotating frame are derived, which consider periodic coefficients, reverse flow, pitch-flap and pitch-lag coupling, and control inputs. The steady state trim is compared with wind tunnel data. Floquet theory is used to evaluate the stability of the equations of motion in response to perturbations from trim. Results are compared to past analyses and expanded to higher advance ratios. Damping and frequency response behavior are evaluated, and rotor stability boundaries are presented.
Full-scale rotorcraft aerodynamics are challenging to study in the field due to the lack of control over ambient conditions as well as the complexity and cost of operating a full-scale vehicle. Small-scale testing can provide significant insight into rotorcraft operation and aerodynamics but is limited by the scale factor between model and prototype. An alternative method for testing rotor performance is presented that utilizes compressed air as the working fluid. By compressing the air, flight-scale aerodynamic conditions can be achieved in hover (Reynolds number, Mach number, and advance ratio matched on small models). In this way, new and unconventional rotor configurations can be tested easily and at low cost before implementing larger prototype tests. An experimental facility at Penn State known as the Compressed Air Wind Tunnel (CAWT) is utilized to examine the scaling of thrust and power coefficient for the NASA Dragonfly rotor geometry in the single rotor configuration. Trends
This paper describes wind tunnel testing of small remotely piloted aircraft systems (RPAS) to understand better the maximum wind speeds in which they can be safely operated. Urban flow fields can contain complex flow structures such as speed changes, direction changes, shear layers, turbulence and vorticity; all of these can impact the safety of urban RPAS operations. The work described in this paper is part of an ongoing effort to provide Canadian regulators with knowledge to guide safe RPAS operations in urban environments. In the wind tunnel, flow fields representative of urban flows were created using simple flow manipulators like bluff bodies and vanes. The flow manipulators and the resulting flow fields, in relation to representative urban flows, are described in this paper. Wind tunnel testing of a number of RPAS in these representative airflows was conducted to evaluate the sustained wind speed limit at which the vehicle could maintain a stable hover. These tests enabled a step
An aeromechanics analysis of a Mach-scaled rotor with lift compounding was conducted to understand the impact of various wing configurations on performance and loads. An assessment of the single retreating side wing and dual wing configurations was conducted for advance ratios up to μ = 0.7, two wing incidence angles (4° and 8°), and three rotor shaft angles (-4°, 0°, and 4°). Aircraft performance, control angles, blade structural loads, hub vibratory loads, and aerodynamic interactions between the rotor and wing were evaluated using the University of Maryland Advanced Rotorcraft Code (UMARC). Additionally, UMARC coupled rotor-wing analysis was validated with wind tunnel data of a lift and thrust compounded rotor. The study shows that the single wing configuration is beneficial for peak vehicle performance (L/D), though the dual wing configuration minimizes blade loads. The single wing configuration observed a 7% greater wing L/D than the dual wing configuration for the same 8° wing
Stereoscopic particle image velocimtery (PIV) was used to characterize a hovering rotor wake at four collective pitch settings in the world's largest wind tunnel test section. The PIV measurements are a subset of a comprehensive dataset acquired during the hover test of the HVAB rotor. Substantial effort was made to cross-validate PIV results with other test measurements and fluid mechanic theories to ensure accuracy in the reported HVAB dataset. Blade coning and flap bending were validated against early tip vortex locations. Tip vortex trajectory was compared against shadowgraphy results and free-jet boundaries. Tip vortex circulation was evaluated using a line-integral approach and least-squares curve-fit to a vortex model. Downwash velocity was compared against momentum theory values. Best practices were followed to correct inherent tip vortex aperiodicity. PIV-specific challenges were exacerbated by testing in a large facility, such as identifying and removing noisy vector fields
The Joint Tactical Aerial Resupply Vehicle (JTARV) project is supporting the expansion of the Army's unmanned aerial reconnaissance capability by working to obtain high-quality test data that is scarce for group 2 and group 3 UAVs to validate physics-based models. This paper will evaluate the system identification results from transient testing at a wind tunnel speed of 29.2 kts (15 m/s) of the commercial off the shelf T-motor '28x9.2' rotor which is used on the TRV-80 platform, a group 3 UAV. Rotor angles of attack of -90° to 0°, which represent climb to edgewise flight respectively, were tested in the wind tunnel. Chirp Pulse-Width Modulation (PWM) sweep inputs that varied the ΔPWM amplitude by 50, 100, and 150 (approximately 3%, 6%, and 10% of the steady state PWM) were analyzed to derive an electric motor model that can be used in a physics-based simultion. Additionally, it was found that the identified coefficients of thrust and torque were higher in transient condtions versus
This paper presents the preliminary results of the recent whirl flutter wind tunnel test campaign performed within the Advanced Testbed for TILtrotor Aeroelastics (ATTILA) project. The Froude-scale ATTILA testbed consists of a semi-span wing with powered tip-mounted proprotor reflecting the proprietary design of the Next Generation Civil TiltRotor (NGCTR). An overview of the ATTILA testbed, wind tunnel test procedures, team organisation and preliminary flutter results are presented. In line with pre-entry dynamic characterization tests, the wind-on test activities in the DNW Large Low-speed Facility (LLF) revealed notable force-dependent nonlinearity in the modal characteristics of, particularly, the wing torsion mode. Further dimensionality was added by early observations that damping in the rotor gimbal degree of freedom, attributed to stiction in the blade pitch mechanism, had the potential to substantially contribute to the damping of the fundamental wing-pylon modes. Nevertheless
A two-phase wind tunnel test was conducted to evaluate aerodynamic performance on a 1/5th scale model of the Sikorsky/Boeing X2™ technology representative aircraft for Future Vertical Lift (FVL). The test program provided valuable aerodynamic data for two important elements of the design: the faired coaxial hub system and the main inlet flow leading to the engine interface. Studies from previous X2™ technology aircraft have shown that hubs, pylons and sail fairings have strong interactions, and if well integrated can lead to low drag aircraft designs. Rotorcraft main inlets generally have aggressive turns; therefore, this inlet design was investigated for distortion and total pressure loss. Accuracy of modeling these aerodynamic interactions using Computational Fluid Dynamics (CFD) and other forms of computational aerodynamic assessment requires supporting empirical testing for validation. The two wind tunnel facilities used in Phase 1 and 2 offered different and unique advantages
The tiltrotor whirl flutter stability of a gimballed hub and a hingeless hub are investigated using multibody dynamics simulations. A semi-span wind tunnel tiltrotor model are developed using the multibody dynamics code: Dymore. CAMRAD II predictions are used to correlate the Dymore predictions of the baseline tiltrotor characteristics. The rotor structural frequencies of the gimballed tiltrotor and the hingeless tiltrotor are compared between Dymore and CAMRAD II predictions with good agreements. CAMRAD II model of the baseline TRAST gimballed tiltrotor is used for correlating the whirl flutter stability with that of the Dymore model. Overall good agreements are shown for both the frequencies and damping ratios of all three wing modes. The effects of key design variables, such as blade stiffness, rotor RPM, and ƍ3 on tiltrotor whirl flutter stability of both hubs are studied.
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