Browse Topic: Wings
This paper utilizes a combined experimental and modeling approach to investigate techniques for improving the forward-flight roll-control authority of a Quadrotor Biplane Tailsitter (QBiT). QBiT is a mechanically simple, efficient hover/cruise aircraft whose roll authority in forward flight is traditionally limited by differential propeller-torque-based control. The two roll-control enhancement techniques investigated are propeller canting and the use of ailerons. A 2-kg instrumented QBiT platform was developed and flight tested to collect high-fidelity flight data across multiple flight regimes including hover, transition, cruise, and coordinated turns. A flight dynamics model was developed and validated using wind tunnel measurements and flight-test data. Flight tests showed that the cant-only configuration exhibited limited roll authority during coordinated turns due to motor control saturation, whereas the cant-plus-aileron configuration provided improved roll performance. Using
A method for evaluation of control derivatives is introduced for the purpose of rapid design evaluation of an electric, fixed-pitch multirotor aircraft during the conceptual pre-design phase. This explicit linearization methodology allows rapid co-design of the vehicle configuration and control allocation using the pseudo-inverse method. A multi-objective design analysis is conducted for a 12 rotor lift + cruise eVTOL configuration subject to hover power requirements, controllability, and tolerance to failure conditions. Generalizable design guidelines are found and presented for the cant and rotor spin direction of the lift + cruise aircraft. The benefits shown include the addition of direct lateral force control derivative, a major increase in yaw control derivative, and reconfiguration to accommodate any Two Engine Inoperative failure conditions. These are achieved through mixing anhedral and dihedral rotor cant within each quadrant of the wing, setting the spin direction so the
A novel airfoil was designed at a Reynolds number (Re) of 50,000 using a multi-objective, multi-fidelity framework based on unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and a gradient-free optimization approach, and compared with the DEA-11 airfoil. Aerodynamic performance and flow physics were investigated through water tunnel experiments, two-dimensional and three-dimensional URANS simulations, and microscopic particle image velocimetry (Micro-PIV), with numerical results validated against experimental data. At Re = 50,000, the optimized airfoil achieves approximately 60% drag reduction at matched lift coefficient, a reduced extent of flow separation, lower pitching moment, with comparable maximum lift coefficient relative to the DAE-11 baseline. In the three-dimensional setting, a classical aspect ratio correction recovers the finite-wing lift closely, while three-dimensional URANS consistently under-predicts drag at positive angles of attack. Measurements and
This paper presents an analytical prediction of rotor blade–wake interaction (BWI) noise using a newly developed turbulence intensity model. The new model is developed using high-fidelity computational fluid dynamics (CFD) results and is validated against experimental data for a BO105 rotor, showing good agreement. Compared to the Glegg model, the proposed approach predicts sound pressure levels approximately 3 dB higher at 600 Hz and about 2 dB higher below 800 Hz, highlighting the contribution of turbulence outside the vortex core. Furthermore, high-fidelity CFD simulations of tip vortex impingement on a downstream wing are performed using Large Eddy Simulation (LES), fully turbulent Improved Delayed Detached Eddy Simulation (SST-IDDES), and Gamma Transitional IDDES (GT-IDDES). Both LES and GT-IDDES capture detailed unsteady and boundary layer transitional flow features, whereas SST-IDDES fails to capture transition and produces a RANS-dominated, time-averaged flow field. The swirl
Efforts to increase lift and range capabilities of Mars rotorcraft have determined through comprehensive analysis of chord-scaled rotors that a 6-bladed rotor with a thrust-weighted solidity of 0.3 (high solidity) offers significantly improved thrust and efficiency in a Martian environment. However, while the optimal blade number and thrust-weighted solidity configuration is important, optimization of chord and twist distributions as well as airfoil shape is necessary to fully optimize a rotor. This study utilized the Evolutionary aLgorithm for Iterative Studies of Aeromechanics (ELISA) genetic algorithm to optimize chord and twist distributions in conjunction with Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRADII) analysis and optimized airfoil shape in conjunction with OVERFLOW analysis. This work was conducted under the Mars Exploration Program's High Solidity Testing task and supports both scientific and exploration concepts, such as the Chopper
The University of Maryland undergraduate team presents Draco in response to the 42nd Student design Competition RFP "Pioneering Hydrogen-Electric VTOL". Draco uses a simple, effective configuration: a single main rotor helicopter with compounded wings. Through calculations and trade studies, the team was able to design a rotorcraft capable of performing the prescribed mission with maximized loiter endurance, while meeting all design constraints and requirements.
A 4.75-ft (1.45-m) diameter, dynamically-scaled proprotor with swept-tip blades was tested up to very high speeds of 205-kt (380-km/h) including the onset of whirl-flutter. Three important parameters that are difficult to vary at full-scale: hingeless hub, pylon placement, and wing spar, were examined consistent with both straight and swept-tip blades. The stability of all three wing-pylon modes: beam, chord, and torsion were measured. The in-house comprehensive analysis UMARC-II was used judiciously to shed light on the fundamental mechanisms at play and for validation. The key conclusions were: (1) on a gimballed hub, the swept-tip blade has no adverse effect on whirl-flutter, nor does it impede the mechanisms that might eliminate it, such as an aft pylon center of gravity placement or stiffer wing spar, and (2) on a hingeless hub, the swept-tip blade left the beam mode unaffected, but increased the chord>and torsion damping significantly through their interaction with the low
This paper investigates amplitude effects in the aeroelastic damping and frequency characteristics of the Maryland Tiltrotor Rig across four configurations: gimballed or hingeless hubs, each paired with straight or swept-tip blades. The recovery rate method is used to identify the aeroelastic parameters of the primary modes dominated by out-of-plane and in-plane wing bending from experimental free-decay strain time histories, capturing variations in dynamic behavior with the response amplitude. Results from conventional methods that assume linear (amplitude-independent) behavior are also presented for comparison. The local damping ratio of the examined modes generally decreases with increasing strain amplitude across all configurations, a trend missed by conventional linear estimation methods. The strength of amplitude effects varies as the system approaches instability: for gimballed configurations, they weaken near instability; for hingeless configurations, they become more
This paper investigates the impact of aerodynamic interactions on the whirl flutter boundary of wing-twin-propeller configurations. A coupled wing-pylon-propeller model is developed in the Rotorcraft Comprehensive Analysis System (RCAS), where the wing is modeled using uniform inflow and the propeller wake is modeled using the viscous vortex particle method (VVPM). The study examines the effects of spanwise propeller placement and rotation direction by first analyzing a single-propeller configuration and subsequently extending the analysis to twin-propeller configurations. The analyses are performed for both rigid and flexible wings, with the latter designed such that whirl flutter governs the instability boundary. Results show that spanwise propeller placement strongly influences whirl flutter stability, with outboard locations exhibiting higher flutter speeds. Aerodynamic interactions between the wing and the propeller are found to be generally destabilizing, reducing the whirl
The U.S. ARMY Primary Helicopter Center/School, USAPHC/S, was activated at Fort Wolters on September 26, 1956. Located in north-central Texas, the school would train over 40,000 helicopter pilots during 17 years of operation, through the end of the Vietnam War in 1973. Approximately 95 percent of all helicopter pilots who flew in Vietnam would pass through Wolters. Students included active-duty Army Officers, Warrant Officer Candidates, and Officers representing 33 allied countries. They trained for 16 weeks at Wolters and then another 16 weeks of advanced training at Fort Rucker, Alabama before earning army aviator wings. At the peak of activity in 1968, Wolters was sending 608 pilots per month to Fort Rucker. Students flew a total of 1,285 piston-powered OH-13, OH-23D, and TH-55A training helicopters departing out of three different heliports. It is a mystical place that still lives in the history of Army Aviation through the helicopter pilots who trained there. This is their story.
Rotorcraft airfoils often feature a tab which aides in the manufacturing of composite rotor blades, but also has aerodynamic merits. This study performs a comprehensive analysis of the impact of this tab on the 2D airfoil performance, structural adjustments and 3D rotor performance. The aerodynamics are evaluated using CFD, with CFD/CSD coupled results for the rotor performance. The structural data is adjusted using an FEM based in-house process. The HART II model rotor has been taken as a baseline and modified according to the tab variation studies. These included the comparison of a sharp trailing edge versus a tabbed airfoil, various tab thicknesses, lengths, and angles. The studies showed a variation of peak Figure of Merit between 66% to 68% and peak rotor L/D from 4.2 to 4.6 The careful design of the airfoil tab is therefore advised, but similarly the structural design of rotor blades.
This paper investigates the impact of aerodynamic interactions on the dynamic aeroelastic stability of a wing-propeller configuration, with emphasis on whirl flutter. The wing structural dynamics are modeled using linear Euler-Bernoulli beam finite elements, while the propeller is represented using Reed's two-degree-of-freedom model. Baseline stability analyses neglecting aerodynamic interactions employ strip theory for the wing and the Houbolt-Reed formulation for the propeller. Analyses that account for aerodynamic interactions are then performed by coupling the wing and propeller structural models with the unsteady vortex-lattice method. Whirl flutter points are identified from transient simulations under both thrusting and windmilling conditions. Results show that three-dimensional aerodynamic effects increase the whirl flutter speed, whereas wing-propeller aerodynamic interactions play a slightly destabilizing role. Thrusting conditions produce a lower critical speed than the wind
A multi-objective optimization of a rotor blade airfoil is presented using compressible unsteady Reynolds-averaged Navier-Stokes simulations directly within the optimization loop. The baseline SC1095 airfoil is optimized using NSGA-II with two objectives: pre-stall aerodynamic efficiency representing hover performance, and lift hysteresis loop area representing dynamic stall severity. The optimized airfoil exhibits increased maximum thickness with an aft-shifted crest and substantially higher camber. Static polars show improved lift-to-drag ratio at $Ma = 0.5$ and $0.6$. Hover performance is essentially unchanged relative to the baseline. In forward flight, a progressive power penalty is incurred above $\mu = 0.2$, attributed to higher profile drag at advancing blade Mach numbers. Dynamic stall simulations show an 80% reduction in peak drag and a 50% reduction in peak pitching moment excursion relative to the SC1095, demonstrating the effectiveness of the optimization for retreating
The aeromechanics of a full-wing lift-compounded slowed-rotor rotorcraft were investigated experimentally at the Glenn L. Martin Wind Tunnel, characterizing the effects of rotor shaft tilt, wing configuration, and advance ratio on performance, blade structural loads, and hub vibratory loads. Measurements were obtained across advance ratios up to μ=0.7, three shaft tilt angles (-4°, 0°, and 4°), and three wing configurations, including an asymmetric wing arrangement. The results were used to validate the University of Maryland Advanced Rotorcraft Code (UMARC) coupled rotor-wing analysis. Rearward shaft tilt and increased wing lift sharing improved lift-to-drag ratio, reduced blade structural loads, and decreased hub vibratory loads due to the rotor being placed in a descent state and being partially unloaded. Rearward shaft tilt alone yielded a 5% improvement in lift-to-drag ratio and a 32% reduction in steady rotor flap bending moment relative to the forward tilt configuration at an
The aerodynamics of propeller--wing interactions during a dynamic tiltrotor conversion maneuver were experimentally studied. This investigation builds upon previous work studying the conversion maneuver as a series of discrete tilt angles. This study varied the freestream velocity, rotational frequency, number of proprotors, proprotor spacing, and conversion time period. Wing loads, surface pressures, and particle image velocimetry were used to investigate tiltrotor aerodynamics. For the multi-proprotor configuration, as the conversion period decreased, wing performance increasingly deviated from quasi-static measurements. Dynamic effects decreased as the freestream velocity increased. Minimal dynamic effects were observed when only one proprotor was used. The greatest dynamic wing performance effects resulted from proprotor-proprotor interactions in proximity to the wing. Several nondimensional parameters including the Transition Number and reduced frequency were evaluated to assess
This study investigated the feasibility of using Deep Reinforcement Learning (DRL) for aeroelastic stability control of a Tiltrotor Aeroelastic Stability Testbed (TRAST) model. The DRL controllers use rotor swashplate inputs to minimize oscillatory wing root bending moments of the tilt rotor model. First, three DRL-based agents including Deep Deterministic Policy Gradient (DDPG), Twin Delayed Deep Deterministic Policy Gradient (TD3), and Soft Actor-Critic (SAC) were investigated to control the aeroelastic stability of the TRAST model throughout a wide range of airspeed including where the whirl flutter occurs. All three agents demonstrated the capability of stability augmentation while the SAC agent demon-strated the most robust performance. Next, the effectiveness of the SAC agent was studied further by training the SAC agent at a certain airspeed and applying the trained agent through the TRAST whirl flutter conditions. Finally, additional tuning of the SAC agent was performed to
This paper presents a wind tunnel investigation on the interactional aerodynamics of a slowed-rotor lift- and thrust-compounded helicopter model in high-speed forward flight. A systematic configuration study was conducted to isolate the aerodynamic contributions of the main rotor, wings, fuselage, and pusher propeller to the aft flowfield, measured using phase-resolved 2D-3C particle image velocimetry. Measurements were acquired at an advance ratio of 0.5 across multiple rotor thrust levels, lift offset trim states, and propeller rotational speeds. The fuselage induces a streamwise velocity deficit of nearly 50% of the freestream near the tail boom due to oncoming flow blockage. This deficit is modulated by the main rotor and wing configurations. The rotor slipstream partially alleviates the deficit by convecting high-speed freestream flow downwards. Lift offset in the asymmetric half-wing configuration suppresses the rotor wake influence, deepening the velocity deficit relative to a
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
This paper introduces an eigenvalue-based whirl flutter prediction method accounting for aerodynamic interactions between a wing and propeller. The linearized unsteady vortex lattice method was utilized to model fixed-wing aerodynamics while the linearized viscous vortex particle method was utilized to model rotary-wing aerodynamics. The complete aerodynamics model was then coupled with computational structural models to demonstrate the capabilities of the model to predict whirl flutter using an eigenvalue-based method. Two computational structural models were used: the first being an analytical propeller model affixed to a rigid wing via root springs and dampers, and the second being the University of Michigan's Nonlinear Aeroelastic Simulation Toolbox. These models demonstrate the capabilities of the linearized aerodynamics model in predicting instability with structural models of different fidelities, both considering and not considering aerodynamic interactions. The linearized
A new approach that enables the synthesis of fully coupled system dynamics is described in this paper. The approach facilitates collaboration between solver developers by explicitly avoiding inter-code coupling and instead uses a generic interface that enables inputs to be set and flags outputs available to other solvers. The assembly of a fully coupled linearized system matrix is obtained entirely from the existence of coupling maps, and does not rely on user intervention. Tiltrotor whirl flutter in cruise conditions is systematically investigated by careful examination of results obtained through various combinations of domain synthesis and obtained from the Hermes coupling framework. Investigated solver domains include nonlinear rotor dynamics, nonlinear aerodynamics, and linear structural dynamics. Utilized software modules include RCAS; Project Chrono, a purpose-built lifting line aerodynamics solver; and FuselageSolver for linear structural dynamics. Aeroelastic predictions are
The TiltRotor Aeroelastic Stability Testbed (TRAST) was developed to experimentally investigate whirl-flutter stability of tiltrotor aircraft. Previous wind-tunnel testing focused on configurations representative of current generation tiltrotors utilizing gimballed rotor hubs. The TRAST platform was also designed to support a hingeless rotor system to investigate whirl-flutter mechanisms representative of stiff proprotor configurations. This paper presents analytical whirl-flutter predictions for a hingeless rotor configuration of the TRAST model. Structural mode shapes derived from a NASTRAN finite-element model are combined with comprehensive aeroelastic analyses in CAMRAD II and RCAS. The results show that the dominant whirl-flutter mechanism differs from the gimballed configuration, with instability occurring through the wing in-plane mode rather than the wing vertical bending mode. Parametric studies examining rotor speed, pitch-spring stiffness, rotor flexibility, and diaphragm
The paper presents the successful drag reduction of the Racer demonstrator's rotor head through its innovative full fairing, based on a robust de-risking methodology leveraging 2D Robust Design Optimization (RDO) for airfoils, 3D CFD analysis with multiple fidelity levels, and experiments. We provide a unique end-to-end comparison across the full development cycle, correlating simulation predictions with both experimental and flight-test data. The fully faired architecture achieves a significant 42% reduction in rotor-hub form drag. At the full-vehicle level, flight tests confirm a 10% net drag reduction, including complex interactions with the airframe. This real-world measurement correlates highly with dynamic URANS predictions (11-12%), while effectively contextualizing the more optimistic 16% gains observed during static wind-tunnel and steady RANS evaluations. These findings provide a comprehensive validation of the low-drag fairing concept, offering valuable insights for the
This study presents the development and evaluation of two multi-fidelity surrogate models for predicting the first blade-passage frequency acoustic directivity of a propeller-wing configuration across a parametric sweep of wing leading-edge positions. The configuration follows the experimental setup at NASA Langley Research Center, comprising a three-bladed Mejzlik propeller operating upstream of a NACA 632-215 MOD B wing at 40 discrete leading-edge positions spanning the horizontal and vertical parameter space. Medium-fidelity predictions from the Rotorcraft Comprehensive Analysis System (RCAS), using the Viscous Vortex Particle Method, serve as the low-fidelity input, while high-fidelity predictions from NASA's OVERFLOW solver coupled with PSU-WOPWOP, both serve as the training datasets. QR decomposition is employed in both frameworks to identify the most informative subset of wing positions for high-fidelity simulation. The first surrogate model, a linear regression model, requires
The front wing of a Formula 1 car is one of the most important aerodynamic components in design development. Particularly, as it is the first to interact with the upcoming airflow, the aerodynamic flow structures generated will have a strong interaction with the remainder of the car’s components. In 2026, the Fédération Internationale de l’Automobile will introduce new regulations that incorporate new aerodynamic philosophies for the front wing, including active aerodynamics. This paper presents a design methodology study for the development of a Formula 1 2026 front wing, compliant with Issue 9 of the technical regulations. A computational-based, structured optimisation series was conducted to enhance the aerodynamic performance of a front wing concept with a focus on improving downforce, maximising efficiency, and enhancing trailing flow for the remainder of the car. The final front wing concept at 40%, running at 30 m/s, generated 189 N of downforce and 19 N of drag. Active
A research team developed a smart strake system that dynamically adapts to flight conditions, showing a promising drag reduction in the wind tunnel with respect to passive strakes. This approach has the potential to save airlines hundreds of kilograms of fuel per flight. University of Washington Department of Aeronautics & Astronautics (A&A), Seattle, WA For decades, aircraft have carried a fundamental compromise between their engines and wing flow interactions by using strakes. These are small fins attached at the sides of engine nacelles that generate helpful vortices during takeoff and landing that boost lift and avoid stall, but create unwanted drag during cruise flight. Now, seven William E. Boeing Department of Aeronautics & Astronautics (A&A) undergraduates have advanced a solution that improves this trade-off, achieving up to 33 percent drag reduction, on the limited tested conditions, during cruise while maintaining critical safety benefits at high angles of attack. The team
Between the 1920s and 1930s, aluminum started replacing wood as the primary material in aircraft construction and soon became the backbone of modern aviation. Its popularity stemmed from a combination of properties, high strength-to-weight ratio, corrosion resistance, and ease of forming that made it ideal for demanding aerospace applications. Throughout much of the 20th century, high-strength aluminum alloys dominated aircraft design, accounting for 70-80 percent of commercial airframes and more than half of many military aircraft. Even after the introduction of fiber-polymer composites in the early 2000s, aluminum has remained a critical material because it continues to offer the strength, lightness, and versatility needed for modern aviation. Industry forecasts predict that commercial air travel will double in the next 25 years, which means more pollution will be released into the atmosphere. One way to help reduce these emissions is by building airplane fuselages and wings with
This study examines the capability of medium-fidelity comprehensive analysis models to predict the acoustics for manned and unmanned rotorcraft configurations. Using the automated tool NDARC2RCAS developed at DEVCOM Army Research Laboratory, multiple configurations including a single main rotor, tilt rotor, coaxial and pusher, quadcopter, and hexacopter are evaluated at various mission segments including hover, advancing climb, and forward flight. Each configuration and condition is evaluated using a range of aerodynamic models from lower to higher fidelity, including uniform inflow, dynamic inflow, prescribed wake, free wake, and viscous vortex particle method (VVPM). These evaluations are then used with another automated tool, RCAS Acoustics, to predict noise on a Voronoi observer sphere. A comparison of the results for the single main showed good agreement between all of the aerodynamic models except VVPM. For the tilt rotor in forward flight, the higher-fidelity models produced
Previous researchers developed equations to model the induced flow on a 2D airfoil in the finite-state as opposed to the closed-form. Those models, however, were limited in that they could not handle an oscillating free stream that became negative. Recently, a new model was developed to include a single factor to carry the effects of the free stream changing signs. In developing this model, a Floquet instability was discovered at the instant when the flow changes direction. The effect of the instability grows with increasing number of oscillations of the sign of the free stream. The effects can be limited depending on the parameters of the flow. In this paper, the previous 2D model is amended to include a term that considers the effects of the induced flow from all previous vorticity segments that have been generated from each oscillation of the flow. This paper details the beginnings of the testing on the stability limits of the theory, based on changing the parameters of the free
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
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.
Mathematician hopes to harness principles of dynamic soaring for long-distance flights. University of Cincinnati, Cincinnati, OH How does one of the biggest birds in the world spend so much time in the air? Albatrosses have 11-foot wingspans that carry them across oceans. But it's how they use these wings that makes them world-class flyers, according to a University of Cincinnati aerospace engineering professor.
In a groundbreaking achievement, the 101st Combat Aviation Brigade, 101st Airborne Division (Air Assault) earlier this year became the first unit to successfully use the Mobile User Objective System (MUOS) function of the Army/Navy Portable Radio Communications (AN/PRC) 158 and 162 radios for conventional rotary wing operations. The trailblazing accomplishment occurred as the brigade continued its mission of providing support to ground forces, April 9, 2025.
In a groundbreaking achievement, the 101st Combat Aviation Brigade, 101st Airborne Division (Air Assault) earlier this year became the first unit to successfully use the Mobile User Objective System (MUOS) function of the Army/Navy Portable Radio Communications (AN/PRC) 158 and 162 radios for conventional rotary wing operations. The trailblazing accomplishment occurred as the brigade continued its mission of providing support to ground forces, April 9, 2025. The MUOS function, of the AN/PRC-158 and 162 radios, operates by transmitting ultra-high frequency radio waves through a constellation of satellites to create a steady communications network. MUOS is a component of a bigger Integrated Tactical Network (ITN).
Electric Vertical Take-Off and Landing (eVTOL) aircraft, conceptualized to be used as air taxis for transporting cargo or passengers, are generally lighter in weight than jet-fueled aircraft, and fly at lower altitudes than commercial aircraft. These differences render them more susceptible to turbulence, leading to the possibility of instabilities such as Dutch-roll oscillations. In traditional fixed-wing aircraft, active mechanisms used to suppress oscillations include control surfaces such as flaps, ailerons, tabs, and rudders, but eVTOL aircraft do not have the control surfaces necessary for suppressing Dutch-roll oscillations.
This paper explores novel airfoils for rotorcraft applications using a gradient-free, multi-objective genetic algorithm with 2D URANS simulations. The study considers dynamic kinematics at a Reynolds number of 5×105 and a mean Mach number of 0.35. Two optimization scenarios are analyzed: 1) pre-stall kinematics (0° ≤α ≤10°) and 2) dynamic stall kinematics (0° ≤ α ≤ 20°). The paper compares two objective functions: f1, based on the cycle averaged lift, and ˜ f1, which modifies f1 by penalizing hysteresis in the lift coefficient. The effects of uniform vs. fluctuating freestream velocity and reduced frequency on optimal airfoils are also discussed. The proposed optimization approach has resulted in novel airfoil shapes that are characterized by a drooped nose, with a convex surface on the aft upper surface similar to a reflex camber in pre-stall kinematics and less unsteadiness in the air loads for the optimized airfoils under the dynamic stall kinematics.
By its seventh flight after the first take-off, the RACER (Rapid And Cost-Effective Rotorcraft) demonstrator smoothly reached the targeted 220kts speed in stabilized forward flight, validating the high-speed compound architecture developed by Airbus Helicopters in the frame of Clean Sky 2 programme. During the flight envelope exploration, the dynamic behavior of the main rotor was carefully assessed, by monitoring the vibratory loads and validating its aeroelastic stability. Particular care was taken to validate the predicted stability domain of the Dual Rotor phenomenon, a particular case of flap-lag coupling associated with high-speed flight conditions. This paper presents the most significant results shaping the success of RACER flight test campaign. After having introduced the theoretical background and the associated analytical equations, the simulation framework based on the comprehensive analysis tool STORM is presented to discuss the numerical resolution of the stability
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
This paper presents findings from a joint computational-experimental venture that seeks to advance the physical understanding and validation-quality database for a model-scale generic tractor proprotor–wing system during the tiltrotor conversion maneuver. This study evaluates the interactions in a quasi-static manner for various proprotor tilt angles (θ) across the tiltrotor conversion maneuver. Independent experimental measurements of the wing and proprotor loads accompany synchronous wing surface pressure measurements along with stereoscopic particle image velocimetry flow field measurements at discrete spanwise locations. High-fidelity computational fluid dynamics simulations leverage the multi-disciplinary rotorcraft simulation tool CREATE™-AV Helios to assess the interactional aerodynamics of the proprotor–wing configuration across the tiltrotor conversion maneuver. Computational simulations use a newly implemented Helios module to trim to the experimental proprotor thrust
A hybrid RANS/LES simulation of the Ideally Twisted Rotor (ITR) in hover was interrogated to identify bluntness vortex shedding (BVS) and determine the contribution to the predicted rotor broadband self-noise. Three rotor blade stations were extracted to study spanwise variations in the BVS shedding frequency and amplitude. Corresponding 2-D airfoil simulations were performed to evaluate a simplified modeling approach that effectively isolates BVS. The BVS shedding frequencies predicted by the 2-D airfoil simulations differed by less than 2% from the corresponding rotor stations in the 3-D simulation. The increased computational cost incurred by performing 3-D airfoil simulations did not lead to a worthwhile increase in simulation fidelity. Farfield noise was predicted for the three rotor stations and the 2-D airfoil simulations, and trends in frequency agreed well. The 2-D approach overpredicted the 3-D peak amplitudes by 5 - 10 dB. This work demonstrates that 2-D hybrid RANS/LES
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.
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