Browse Topic: Wings
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.
Developed in the frame of the European Clean Sky 2 program, the RACER High Speed Helicopter Demonstrator of Airbus performed its maiden flight on April 25th, 2024. In the continuity of the previous high-speed demonstrator X3 (1st flight in 2010) the RACER is a 7/8t (15000 / 18000 lb) class compound helicopter powered by two SHE Aneto-1X engines, including a wing and two propellers. The tail rotor is removed as the two propellers control the yaw axis by differential thrust. At flight 07, with its initial default settings, it reached a true airspeed of 227 kts in level flight, exceeding its objective of 220 kts.
A method for the parameterization of an arbitrary airfoil using a transformation and Chebyshev polynomial interpolation is investigated. The airfoil was transformed into a continuous function using the Class Shape Transformation. A square root spacing was used to smooth out the slope discontinuity found at the origin. This mapping reduces oscillations in the polynomial interpolation caused by the slope discontinuity at the origin. Interpolating a range of NACA 4-digit series airfoils showed that these airfoils could be accurately represented with as little as 10 polynomial terms. However, problems arise with the Class Shape Transformation when trying to parameterize non-analytically defined airfoils. The transformation expects the behavior of the leading edge to be perfectly elliptic, and any deviation from this requirement leads to the divergence of the Class Shape Transformation. As a result, parameterizing with polynomials becomes infeasible for some airfoils. To address this, a
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.
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
This paper investigates the influence of wing-propeller aerodynamic interactions on the aeroelastic damping of a wing-propeller system. The system is modeled in the Rotorcraft Comprehensive Analysis System using the viscous vortex particle method for the propeller aerodynamics and the uniform inflow model for the wing. The aeroelastic damping characteristics are identified from simulated time-history data using a recently developed method that captures amplitude effects due to system nonlinearity. The damping characteristics identified using conventional methods based on linear assumptions are also presented for comparison. The results show that, at lower airspeeds, the local damping decreases with increasing propeller hub displacements, both with and without aerodynamic interactions. This amplitude-dependent behavior cannot be captured by conventional damping identification methods that average amplitude effects. Amplitude-dependent trends are exacerbated by wing flexibility. However
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 an experimental and analytical investigation of whirl-flutter stability in tiltrotor aircraft, focusing on the influence of pitch-flap coupling on stability boundaries. Wind-tunnel tests were conducted using the TiltRotor Aeroelastic Stability Testbed (TRAST), a semi-span model designed for test-analysis correlation. This study examines variations in pitch-flap coupling and compares measured frequency and damping trends with predictions from RCAS and CAMRAD II. Results indicate that less pitch-flap coupling increases stability, with both analytical models capturing general trends. The analysis accurately predicts the wing inplane mode stability, but larger deviations are observed in the vertical bending mode, suggesting missing physical effects in the modeling approach. Differences in damping trends at higher speeds indicate that improvements in modeling may be necessary to refine stability predictions. These results provide valuable insights into the capabilities
An OVERFLOW simulation of a four-bladed rotor in hover is performed, and the resulting steady-state solution for the boundary layer over a rotating blade is analyzed by means of linear stability methods. The techniques employed are the Linear Stability Theory, the Parabolized Stability Equation, and the spanwise BiGlobal analysis. The unstable modes in the boundary layer of the rotating blade are analyzed in comparison with those typically observed in swept wings. The effect of the Coriolis force and the spanwise gradient of the free stream velocity are taken into account, and their influence on the instabilities is evaluated. It is shown that periodic boundary conditions in the spanwise BiGlobal analysis work adequately for a sufficiently small fraction of the length of the blade (~ 1:2%), while increasing the domain would require an alternative approach to the boundary conditions.
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
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
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
This paper addresses the aerodynamic interaction effects between a wing and a propeller on the whirl flutter boundary. A wing-pylon model with a propeller is defined and modeled in the Rotorcraft Comprehensive Analysis System, considering both a flexible and rigid wing. The aerodynamic interaction effects on the whirl flutter boundary between the wing and the propeller are examined for various inflow models, including the viscous vortex particle method (VVPM), uniform inflow, and dynamic inflow on the propeller, and uniform inflow and vortex wake on the wing. Results show that the whirl flutter boundary is overestimated when the propeller is modeled with the VVPM and aerodynamic interaction effects are neglected. The impact is more prominent for a flexible wing-pylon model. Other propeller aerodynamic inflow models and their associated interaction effects alter the damping trend and increase the flutter speed on a flexible wing-pylon model only, highlighting the need to model propeller
High-speed configurations are among the new emerging concepts that are currently expanding the scope of rotorcraft design. Especially in the field of defense technology research, the capability of a substantial increase in maximum velocity becomes more interesting. For instance, NATO project NGRC is considering this capability for a new medium utility rotorcraft. DLR supports these activities by its continuing defense technology research. In this study the benefits and drawbacks of a high-speed capability for a given mission scenario are analyzed. For that purpose, a contemporary configuration has been modeled, featuring a maximum velocity of 82 m/s (160 KTAS). The high-speed configuration meets with the same mission requirements, but with an increase of about 50% of maximum speed to 125 m/s (242 KTAS). All tasks in this study are conducted with DLRs integrated design environment IRIS. The high-speed configuration features an off-loaded main rotor, a wing, a propeller and a reduction
High-fidelity simulations are used to enhance the understanding of the sensitivity of propeller-wing interactions across a spectrum of conditions, focusing on both aerodynamics and aeroacoustics. The aerodynamics is analyzed using high-fidelity computational fluid dynamics, while the acoustics is assessed through the application of impermeable Ffowcs Williams and Hawkings surfaces. Initial assessments concentrate on the influence of simulation parameters on both convergence and accuracy of numerical results. It is determined that reducing the wake grid spacing from 10% of the reference chord length to 7.5% offers no notable improvement to acoustic predictions. Moreover, comparisons between acoustic predictions employing the SST turbulence model and the SA model, with and without transition modeling, reveals differences that are minor in comparison to the prediction errors observed against experimental data. Then, the sensitivities of both aerodynamic and aeroacoustic responses are
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.
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
This paper introduces a Multidisciplinary Design and Optimization (MDO) approach for the design of a tiltrotor wing, utilizing as test case a semi-wing with integrated nacelle and rotor. Structural integrity is assessed via stress analysis on a GFEM, which also forms the basis for a coupled wing-rotor aeroelastic model to ensure whirlflutter stability. Aerodynamic performance is assessed through CFD analysis of two-dimensional wing's airfoil shape. The MDO workflow leverages three levels of design space control that can influence the structural response of the wing: other than controlling the structural properties of composite materials, the internal wing-box architecture and external airfoil shape are modified acting directly on the FEM by means of a mesh morphing technique. This methodology allows for the use of mid-fidelity finite element models, bypassing CAD reshaping and remeshing. Validation tests confirm the approach's effectiveness in producing optimized designs. Additionally
This paper introduces ABC2, an advanced framework for rotor blade design optimization that can effectively consider the airfoil shape variations during optimization process. A major component of this framework is an reduced-order model (ROM) that leverages deep-neural-network techniques both for airfoil parameterization and performance prediction. Utilizing the UIUC airfoil database and a two-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) solver, the ROM can effectively control the airfoil shapes and predict the resulting aerodynamic performance across the wide range of flow conditions. A comprehensive aerodynamic solver is incorporated for blade design optimization. Enhancement of the fidelity of the comprehensive solver is achieved through the integration of a three-dimensional URANS solver, which also plays a crucial role in analyzing the aerodynamics of the optimized blade and uncovering its underlying physics. The competence of the present framework is demonstrated
Dynamic stall continues to be a limiting factor for rotorcraft performance in forward flight. The complex flow physics, resulting from blade kinematics, aeroelastic deformations, and blade-vortex interactions, makes this problem challenging. The availability of results from recent high-fidelity coupled computational aerodynamics-structural dynamics simulations provides an opportunity to gain new insights into the physics of dynamic stall on rotor blades in realistic operating conditions. Recent research efforts have also resulted in the identification of a leading-edge suction parameter (LESP), whose critical value has been shown to correlate with the flow events leading to dynamic stall. Critical LESP is largely independent of motion parameters, and is dependent mostly on the airfoil shape, Reynolds number, and Mach number. In this work, LESP variation along the blades of a UH-60A rotor in forward flight is extracted from high-fidelity computational results. The objective is to
A joint experimental-computational research campaign is underway to develop physical understanding and a validation-quality database for a model-scale tractor propeller-wing system. Separate load measurements on the wing and propeller accompany wing surface pressure distributions and flow field measurements via stereoscopic particle image velocimetry (SPIV) at discrete wing spanwise locations for a range of static propeller tilt angles. The physical wind tunnel test is modeled using a high-fidelity computational approach (Helios). Computational simulations aid in assessing the influence of the wind tunnel facility effects and test support structure wake interference, as well as in reducing uncertainties in the physical experiments for use in computational validation. The behavior of the induced thrust and lift at a zero-degree wing angle of attack in the axial flow regime (cruise configuration) is correlated with flow field measurements, showing distinct differences between upwash and
This paper investigates optimal wing arrangements for electric Vertical Take-Off and Landing (eVTOL) aircraft, leveraging on their design flexibility with electric propulsion system. The study employs a multidisciplinary approach with the objective of integrating aerodynamic analysis, static and dynamic stability assessments, and pilot feedback to evaluate various wing configurations. Analytical techniques were adopted to evaluate aerodynamic performance and static stability, while experimental flight testing on scale models was conducted to validate these findings. Additionally, the Cooper-Harper rating system was introduced to capture pilot perceptions of aircraft handling qualities. Results inform eVTOL designers on wing arrangements that offer enhanced aerodynamic efficiency, stability, and handling qualities, ultimately expanding the operational scope and applications of eVTOL aircraft. The study concludes the versatility of the high aspect ratio conventional wing on eVTOL
Design modifications to a 3lb variant of DEVCOM Army Research Laboratory's Common Research Configuration (CRC-3) are assessed using simulation tools. To identify areas for improvement, the baseline CRC-3 is analyzed in hover and forward flight, and contributors to overall power consumption are identified, with the rotor drag consuming the greatest amount of power, due to the high rotational speeds required to maintain thrust in the face of the freestream velocity. Potential areas for improvement are identified as: wing airfoil, rotor blade pitch, and rotor orientation. Changing the airfoil has little to no measurable effect on the overall power consumption. Increasing the blade pitch improves cruise performance considerably, but at the cost of hover efficiency, for an overall range improvement of up to 28%. Changing the rotor orientation improves rotor efficiency as well, without substantial cost to hover power consumption, increasing the range by 37% but will require a redesign of the
Transition from hover to forward flight and vice versa represents the most critical flight phase of tiltwing aircraft. Despite its importance to ensure a safe operation, the aerodynamics of this maneuver are not sufficiently understood. This paper focuses on the study of transition flight for NASA's six-passenger tiltwing air taxi by means of high-fidelity computational fluid dynamics simulations. On the basis of a static trim solution, four points within the transition corridor are analyzed: transition mode at wing tilt angles of 60! and 44!, and airplane mode at airspeeds of 110 kt and 155 kt. We investigate the balance of forces and moments for rotor-borne and wing-borne regimes, and how rotor-on-rotor and rotor-on-wing interactions affect performance. The simulations indicate that during the early stages of transition, the vortices remain in close proximity to the proprotors, inducing large fluctuations on the order of the mean blade loading. Additionally, the blowing and swirling
This paper analyses the possibility of using photovoltaics as additional energy provider for small to medium-sized eVTOL UAVs. A simplified model for eVTOL UAVs, which covers all relevant areas of aircraft design, including aerodynamics, structural mechanics, propulsion and systems modelling, is presented. Sensitivity studies covering various design parameters, such as airfoil, wing geometry and propulsion system selection are performed to show their influence on the configurations' performance. The first result of this paper is, that a photovoltaic powered configuration can outperform a battery electric and it can be worth the effort to implement the solar cells. To achieve this, the aircraft needs to be as aerodynamic efficient as possible. Also higher efficiency solar cells increase the possible performance. Additionally there is a big influence of the time of year and the latitude onto the performance. Secondly a multi mission study is performed. This uses a more detailed model, as
Airfoil optimization for rotor blades is a critical endeavor aimed at enhancing aerodynamic performance and reducing noise. This paper employs a Kriging surrogate model combined with a multi-objective genetic algorithm to optimize thrust, power, and broadband noise. Three airfoil parameterization methods including ParFoil, PARSEC, and CST are compared when used to generate various airfoil shapes for the surrogate model and optimization process. We utilize low-fidelity aerodynamic tools such as XFOIL and blade element momentum theory for aerodynamics. In addition, acoustic modeling is conducted using Lee's wall pressure spectrum model alongside Amiet's trailing-edge noise model. The paper focuses on small-scale rotor configurations, specifically an ideally twisted rotor using the NACA 0012 airfoil and a modified XV-15 blade. Both blades are used as baseline models for hover optimization. The optimization of the ideally twisted rotor across various parameterization methods demonstrates a
Rotor hub parasite drag remains one of the challenges in further improving the forward-flight capabilities of coaxial rotorcraft. Comprehensive datasets on notional coaxial hub configurations are rare, and more so at Reynolds numbers sufficiently high to preserve dominating flow structures downstream into the wake where they interact with the rotorcraft empennage and tail. The present investigation was designed specifically to improve the understanding of interactional aerodynamics effects and wake flow physics of counter-rotating coaxial rotor hubs. A unique dataset is presented on a rotor hub design equipped with the DBLN 526 airfoil at a diameter-based Reynolds number of 1.13x106, corresponding to approximately quarter-scale Reynolds conditions of a coaxial compound helicopter at 200 knots. The experiments measured the time-averaged and time-varying drag on the hub configuration, with focus on a cruise advance ratio of 0.25 and a high-speed condition at 0.60. In addition to
ABSTRACT A proof of concept test to measure the unsteady boundary layer transition locations on the lower surface of a Machscaled rotor in forward flight was performed during the Summer of 2017 in the NASA Langley 14- by 22-Foot Subsonic Tunnel. The transition locations were measured using high-speed infrared thermography with a rotating mirror assembly that could be remotely actuated to acquire data at several rotor azimuths. Data were acquired for eight unique rotor flight conditions for a range of advance ratios (μ=0:10 : 0:38), thrust coefficients (CT/α =0:04 : 0:12) and rotor shaft angles (αs = -6 deg : 0 deg). This paper presents the transition locations as a function of azimuth and radius for an advance ratio of, μ, of 0.30, and thrust coefficent, CT/α, of 0.08. At this condition, the lower surface is fully laminar on the retreating side and mostly turbulent on the advancing side except near the tip. The tip airfoils were greater than 60 percent laminar on the lower surface
ABSTRACT The present study considers two notional rotorcraft models: a conventional utility helicopter, representative of an H-60, and a wing-only compound utility rotorcraft, representative of an H-60 with with a wing similar to the X-49A wing. An Explicit Model Following (EMF) control scheme is designed to achieve stability and desired Rate Command / Attitude Hold (RCAH) response around the roll, pitch and yaw axes, while alleviating vibratory loads through both feed-forward and feedback compensation. The harmonic decomposition methodology is extended to enable optimization of primary flight control laws that mitigate vibratory loads. Specifically, Linear Time Periodic (LTP) systems representative of the periodic rotorcraft dynamics are approximated by Linear Time Invariant (LTI) models, which are then reduced and used in LQR design to constrain the harmonics of the vibratory loads. The LQR gains are incorporated in the EMF scheme for feedback compensation. One innovative approach is
In the realm of transitioning eVTOL aircraft, hindrance may be placed on performance in each of the two flight modes due to the existence of apparatuses or devices intended wholly for the other mode. For example, the presence of wings will normally reduce hover endurance due to their weight, and the use of a plurality of exposed lift-propellers - for hover stability and control - can lower flight speed and range in airplane mode because of the excess drag. It would seem, then, that transitioning eVTOL aircraft are generally poor performers in any mode when compared to their dedicated, single-mode cousins. This paper explores another possibility, of substantial performance improvement when the devices or their use become elements augmenting performance in the other mode - or cross-modally. Through an example dual-propeller aircraft, several cross-modal elements - including phenomena like the fan-in-wing effect and the inverse of Custer's channel-wing effect - are identified and their
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
Winged Quadcopters are an increasingly popular UAS configuration due to their mechanical simplicity and high degree of aerodynamic efficiency, but this efficiency is highly sensitive to the chosen blade pitch and rotor orientation. In this study, a rotor-wing system representative of a winged quadcopter is simulated and a parametric sweep of blade pitch, rotor tilt, cruise speed, and weight is conducted. At the baseline 30 kts cruise speed and 3 lb vehicle weight, the optimal configuration (blade pitch: 10° – 20°, rotor tilt: 30° – 40°) is 4.4 times more efficient than the baseline Quadrotor Biplane Tailsitter (blade pitch: 0°, rotor tilt: 0°). Even if flight speed and weight is increased (up to 50 kts and 9 lb), combinations of blade pitch and rotor tilt can offer improved efficiency; and at the optimal condition, 12.5° blade pitch and 35° rotor tilt is 5.3 times more efficient than the baseline QBiT. The rotor-wing system is also simulated using CFD with the rotor at 58 different
The AW609 tiltrotor features a unique high-mounted wing with rotatable nacelles positioned at the wing tips, it is capable of operating both in airplane and vertical flight mode. To achieve suited protection of the occupants during emergency landing, the wing - which is particularly stiff in order to sustain the heavy weights at the tips, where rotors, engines and transmissions are positioned - implements a controlled failure mechanism at root, so that during emergency landings it breaks and unloads the fuselage of the weight of wingbox and nacelles, thus avoiding catastrophic collapse. As the effectiveness of such mechanism was never demonstrated under impact conditions, certification agencies requested an empirical validation through experimental testing. The test was carried out July 2022 at Polytechnic of Milan, Italy; the present work details the Test activity, from its preliminary phases to the Test Day, to the analyses of its outcomes.
The succession of the BK117 D-2 main rotor concept from the semi-rigid rotor to the BK117 D-3 bearingless main rotor (BMR) system, derived from the H135, held many new and innovative additional benefits in its wake. Although the H135 system is the best on the market regarding maintenance effort and maintenace cost (DMC), it was the purpose to push this benchmark even further. To achive additional benefits, three major improvements needed to be successfully implemented and none of them was a given. First to mention is the concept of the blade being separated in three parts. In case of foreign object damage (FOD), most of the time only the outer part needs to be repaired. In parallel a new possibility to fold the system with a full folding capacity was introduced with the challenge to realize the extremely low DMCs of the H135, in a decisively bigger helicopter and to benefit from the experience of millions of flight hours and thousands of helicopters operated throughout the world
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.
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
Revealed in 1941, the Dirigible Helicopter or 'Koun's Craft,' was an ambitious but ill-fated fusion of convertiplane and lighter-than-air technology. This S/VTOL (Short/Vertical Take Off and Landing) concept (a veritable puzzle of diverse airplane parts) was powered by a single, tilting propeller engine and was affixed with wing mounted, helium filled enclosures for additional buoyancy. Dismissed historically as being an eccentric folly of its layman inventor, Korean-American Young Ha Koun, the development of the Dirigible Helicopter has never been thoroughly studied. This paper will examine the origins of this unique design, its creator's possible motivations for building such an aircraft, and successor convertiplane concepts that attempt to achieve the same purpose to this day.
NASA's 4th New Frontiers Mission is the Titan Dragonfly relocatable lander. This coaxial quadrotor vehicle will be launched on a rocket to Titan in 2028. Following a gravity assisted Earth flyby and an approximate 6-year transit, Dragonfly will enter the Titan atmosphere around 2034 with the goal of exploring Titan's pre-biotic chemistry and habitability. The multirotor design for this unique application has continually evolved since 2016 with constraints such as Titan's cryogenic atmosphere at 95 Kelvin (-288 F), gravity 14% that of Earth's, atmospheric density 440% of standard sea-level air, and the inability to test the entire system together under all these conditions until the first flight on Titan. This paper focuses on rotor design aspects of the Dragonfly lander and introduces a novel framework for multirotor design optimization considering multiple flight conditions. The methodology leverages machine learning methods and is demonstrated in the context of Dragonfly. A new
ABSTRACT A full-scale Reynolds number water tunnel experiment was performed to generate a data set used to analyze the effects of helicopter rotor hub wake impingement on a canonical horizontal stabilizer. The experiment was designed and performed in the Pennsylvania State University Applied Research Laboratory Garfield Thomas Water Tunnel, where a 10.5 inch constant chord stabilizer was placed in the 48-inch diameter test section downstream of a 1/4 scale helicopter hub. Two rotor hubs were tested, a baseline configuration and a low-drag model. The stabilizer was mounted in the long-age wake. Lift, pitching moments, and unsteady pressures were measured on the horizontal stabilizer at a Reynolds number of 0:9x10⁶, 1:8x10⁶ and 2:7x10⁶, corresponding to hub diameter-based Reynolds numbers of 2:2x10⁶, 4:3x10⁶, 6:5x10⁶ and rotor advance ratios of 0.1, 0.2, and 0.3. The hub-wake interaction results were compared to a baseline airfoil test, which was performed without a hub upstream
ABSTRACT Accurate prediction of aeroelastic coupling between rotor wake and structure remains a key challenge to the development of advanced rotorcraft. Limitations of existing analysis tools to predict such aeroelastic interactions, notably empennage buffeting effects, have resulted in costly late-cycle design changes in multiple rotorcraft development programs, including the UH-60A and AH-64A. Aeromechanical phenomena involving interactions of the fuselage and rotor wake are complex, interdisciplinary, and three-dimensional in nature. For this reason, full vehicle CFD/CSD coupled analysis is essential to accurately capture the mutually dependent interactions between the aerodynamic loads and the aeroelastic response associated with these phenomena. The current state-of-the-art in rotorcraft analysis involves CFD/CSD coupled analysis of aeroelastic rotors and wings, but rigid representations of the fuselage and empennage structures (Ref. 1). To address this limitation, an elastic
ABSTRACT An investigation was performed into the effect of positive and negative sweep angle on the boundary layer transition and dynamic stall behaviour of a finite wing. The finite wing had a 6:1 aspect ratio, modern (SPP8) tip shape and positive twist, moving the maximum load on the wing away from the wind tunnel wall. Experiments were performed with sweep A=±30° and A=0° for static polars and sinusoidal pitching. The positively twisted wing shows a similar S-shaped boundary layer transition on the pressure side to that previously seen for helicopter rotor blades in hover. The transition positions on the suction side of the wing are comparable for the same local angle of attack at all values of the sweep L at each of the three pressure sections, and for dynamic pitching motions a hysteresis around the static transition positions is seen. Sweeping the wing led to later stall and higher maximum lift for both static polars and dynamic stall, except for a single case. The negative
ABSTRACT In this work, a genetic algorithm was implemented to perform an airfoil shape optimization with constraints applied to the airfoil cross-sectional area and pitching-moment coefficient. Constraints are enforced through the use of an augmented Lagrange penalty function. The design variables are formed through a class shape transformation approach with orthogonal, polynomial basis modes. The use of an orthogonal basis provides decreased levels of multicollinearity in higher-order design spaces, while still maintaining the completeness of lower-order spaces. The optimization methodology is demonstrated on the tip airfoil of a UH-60A baseline rotor. The design trade-offs of a new tip airfoil are investigated where the optimized tip section shows improvements in forward-flight performance in exchange for a small reduction in the rotor's stall margin.
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