bluuebunny/crossref_metadata_2025 huggingface dataset:
Utilizing 3D Point Clouds and Deep Learning Technology in Multimedia Instruction for Sports Mechanics
Authors: Yuan Bentan
Published: September 2024

In this paper, an optimization model based on 3D point cloud and deep learning theory is constructed, which improves the fluency and accuracy of multimedia sports operation. The model has performed well in sports mechanics teaching and proved its outstanding performance. It is found that the changes of the three kinds of point clouds have different laws, and the spherical neighborhood gradually decreases, while the adjacent neighborhood shows an upward fluctuation trend. The neighborhood of cylinder shows linear and nonlinear characteristics. The parameter curve of point cloud model fluctuates greatly, and the curve corresponding to function output value fluctuates widely, while the curve corresponding to feature extraction method fluctuates relatively little. The ability training index plays a significant role in improving the model output, the multimedia input index fluctuates well, and the teaching method index shows an approximate linear change law. The accuracy of the model is verified by data calculation method, which provides theoretical guidance for multimedia sports mechanics teaching.
Language Learning Through Zoom
Authors: White Jonathan R.
Published: September 2024

Attributable to the COVID pandemic, Zoom has become one of most widely used digital tools for online interaction. Schools and universities had to transition to wholly online teaching, and Zoom was one of the platforms used for real-time sessions. Therefore, it is necessary to investigate students' experiences of using tools like Zoom to see the positive and negative sides of videoconferencing for language learning. Students' and teachers' digital competence is an important factor that impacts online learning, and therefore students' experiences are analyzed in relation to the TPACK framework, which looks at teachers' digital competences and the intersections between their technological, pedagogical, and content knowledge (TPACK). It is found that especially the intersection between technological and pedagogical competences is sometimes lacking among teachers and is identified as the cause of a lot of negative experiences. Thus, the conclusion of this study is that such competences need to be developed by teachers.
Numerical Evaluation of the Influence of Different Parameters on the Thermoenergetic Performance of the Earth-Air Heat Exchanger in a Social Housing
Authors: Moura Paula Wrague , Leite Leonardo Rodrigues , Moura Márcio Wrague , Rocha Luiz Alberto Oliveira , dos Santos Elizaldo Domingues , Brum Ruth da Silva , Isoldi Liércio André
Published: September 2024

Earth-Air Heat Exchanger (EAHE) is a device that cools or heats air as it flows through underground ducts, helping to lower energy usage while ensuring comfortable thermal conditions. This investigation is designed to assess the thermoenergetic performance of an EAHE in Social Housing (SH) when submitted to different operating and constructive parameters and suggest strategies to improve energy efficiency in buildings. The study involves thermal and energy evaluations of a device integrated into SH, exploring varying air velocity, duct length, and duct diameter. Dynamic simulations using EnergyPlus software were employed for these evaluations. The findings show that incorporating the EAHE to the SH enhances the thermoenergetic efficiency of built environments. The system's best performance was achieved by a duct measuring 34 m long and 110 mm in diameter with a 3.3 m/s airflow, striking a balance between thermal and energy considerations. This contributes to providing validated references and parameters for future projects in the pursuit of enhanced efficiency.
Close Coupled Channels Method: For Hydrogen Atom in Strong Laser Fields
Authors: Chuluunbaatar Aldarmaa , Lochin Khenmedekh , Gombosuren Zorigt , Ochirbat Altangoo
Published: September 2024

The interaction of short laser pulses with hydrogen atoms will be discussed in this paper. We chose laser pulses with photon energies lower than the ionization threshold energy of hydrogen atoms. Here, the close coupled channel method is used to solve the time-dependent Schrödinger equation. Our goal is to demonstrate how this approach can be used to calculate the phenomenon of multiphoton absorption-induced excitation to the 2S and 2P states. It was also shown how the probability of excitation depends on the duration and strength of the laser pulse. This approach exhibits good agreement when compared to the findings of other studies.
First Principles Study on the Point Defects of Compound FeMnP0.67Si0.33
Authors: Jiang Yong Jing , Wu Xiao Xia , Ou Zhi Qiang , Narsu Bai
Published: September 2024

This study is based on the density functional theory and employs the projected augmented wave method within the VASP program package. It investigates the variation of lattice constants in Fe2P-type compound FeMnP0.67Si0.33 in the ferromagnetic (FM) and antiferromagnetic (AFM) states, with the presence of Mn and Fe vacancy defects and Mn and Fe anti-site defects. the defect formation enthalpy of compounds containing vacancy and substitution defects were calculated using the Wagner-Schottky point defect thermodynamic model. It also investigates the relationship between the equilibrium concentration of point defects and the Mn content in the compound, as well as the variation of defect equilibrium concentration with temperature T. The calculation results show that the presence of point defects in the compound affects the lattice constants. In the FM and AFM states, the formation enthalpies of Fe anti-site and Mn anti-site defects is lower than that of Fe vacancy and Mn vacancy defects. The concentration of point defects increases with increasing temperature. The calculated results provide valuable theoretical references for the experimental preparation, defect analysis, and mechanical properties improvement of the Fe2P-type iron-manganese-based FeMnP0.67Si0.33 compound.
Expressions for Elements of Dynamical Matrix for HCP Crystals
Authors: Myagmarsuren Genden , Amartaivan Tsenddavaa , Enkhtor Lkhamsuren
Published: September 2024

Within the conceptual framework of the De Launay model, this study delineates the formulations for elements constituting the dynamical matrix of hexagonal close-packed (HCP) crystals, incorporating the effect of interatomic forces exerted by the first eight nearest neighboring atoms. To validate these derived formulations, the phonon dispersion of magnesium was computed and juxtaposed against the empirical phonon dispersion results reported by other researchers. Subsequently, leveraging the fit of experimental phonon dispersion data of yttrium, as reported by secondary sources, this research delineates the radial and tangential force constants pertaining to the first three neighboring atoms. These constants were then employed to approximate the elastic constants of yttrium. The calculated phonon dispersion branches along the Γ-M and Γ-A directions, as well as the derived values of yttrium's elastic constants, exhibit congruence with the corresponding empirical observations reported in literature.
Rapamycin Prevents Expansion of Costimulation Blockade-resistant CD8+ Alloreactive Memory Cells following Depletional Induction in Renal Transplant Recipients
Authors: Li Shu , Gao Qimeng , Xu He , Kirk Allan D
Published: September 2024

Alemtuzumab induction with belatacept/rapamycin-based maintenance immunotherapy (ABR) prevents kidney allograft rejection and specifically limits early costimulation blockade–resistant rejection (CoBRR). To evaluate the mechanisms by which this regimen alters CoBRR, we characterized the phenotype and functional response of preexisting memory cells to allogeneic endothelial cells using intracellular cytokine staining and flow cytometry. IL-7–induced lymphocyte proliferation in the presence or absence of rapamycin was assessed to characterize the phenotype of proliferating cells. Lymphocytes from 40 recipients who underwent transplant using the ABR regimen were studied longitudinally. The rapid immunoresponses of preexisting alloreactive cells to allogeneic endothelial cells were predominantly CD8+TNF-α+/IFN-γ+ cells. These cells were effector memory (TEM) and terminally differentiated effector memory cells lacking CD28 expression, and most were CD57+PD1−. Neither rapamycin nor belatacept directly inhibited these cells. IL-7, a cytokine induced during lymphopenia postdepletion, provoked dramatic CD8+ TEM cell proliferation and a low level of CD8+CD57+PD1− cell expansion in vitro. The IL-7 stimulation induced CD8+ cell mTOR phosphorylation, and rapamycin treatment markedly inhibited IL-7–induced TEM and CD57+PD1− cell expansion. This effect was evident in patients receiving the ABR in that the repopulation of CD8+CD57+PD1− TEM cells was substantially suppressed for at least 36 mo after transplant. These findings help define one mechanism by which a costimulation blockade/rapamycin-based therapy following alemtuzumab induction minimizes CoBRR, namely that in the presence of rapamycin, costimulation-resistant alloreactive cells are disproportionately ineffective at repopulating following post-transplant T cell depletion.
IL-1β Induces Human Endothelial Surface Expression of IL-15 by Relieving let-7c-3p Suppression of Protein Translation
Authors: Mullan Clancy W , Summer Luanna , Lopez-Giraldez Francesc , Tobiasova Zuzana , Manes Thomas D , Yasothan Shruthi , Song Guiyu , Jane-Wit Daniel , Saltzman W Mark , Pober Jordan S
Published: September 2024

Expression of IL-15 on the surface of human graft endothelial cells (ECs) bound to the IL-15Rα subunit can increase the activation of CTLs, potentiating allograft rejection. Our previous work showed that surface expression of this protein complex could be induced by alloantibody-mediated complement activation through increased IL-1β synthesis, secretion, and autocrine/paracrine IL-1–mediated activation of NF-κB. In this article, we report that cultured human ECs express eight differently spliced IL-15 transcripts. Remarkably, IL-1β does not alter the expression level of any IL-15 transcript but induces surface expression independently of RNA polymerase II–mediated transcription while requiring new protein translation. Mechanistically, IL-1β causes an NF-κB–mediated reduction in the level of microRNA Let-7c-3p, thereby relieving a block of translation of IL-15 surface protein. Let7c-3p anti-miR can induce EC surface expression of IL-15/IL-15Rα in the absence of complement activation or of IL-1, enabling IL-15 transpresentation to boost CD8 T cell activation. Because of the complexity we have uncovered in IL-15 regulation, we recommend caution in interpreting increased total IL-15 mRNA or protein levels as a surrogate for transpresentation.
An Overview of the U.S. Army Aviation Development Directorate Quadrotor Guidance, Navigation, and Control Project
Authors:   US Army ADD - AMRDEC NASA Ames Research Lab, Cheung Kenny ,   US Army ADD - AMRDEC, Tischler Mark ,   Saint Jose State University - US Army ADD - AMRDEC, Juhasz Ondrej ,   Defence Science and Technology Group Melbourne, Lehmann Rhys , A. Joseph , Ivler Christina , Berrios Marcos , Berger Tom , Tobias Eric , Goerzen Chad , Barone Patrick , Sanders Frank , J. Mark
Published: September 2024

In recent years, there has been growing commercial and military interest in small-scale multi-rotor unmanned aerial systems (UAS), from commercial package delivery, to performing search and rescue missions, to providing surveillance and reconnaissance support. The Vehicle Management and Control (VMC) Technical Area under the U.S. Army Aviation Development Directorate (ADD) at Moffett Field, California has strong experience and expertise in applying advanced flight control and obstacle field navigation (OFN) technologies to full-size manned and unmanned rotorcraft. The Quadrotor Guidance, Navigation, and Control project was established to develop and apply these advanced technologies to a small-scale commercial-off-the-shelf (COTS) multi-rotor UAS to support emerging Department of Defense and industry needs. This paper provides an overview of the project, from the organizational aspect, to the development of the hardware and software infrastructure, to the application of the aforementioned advanced technologies to a 3D Robotics IRIS+ quadrotor research vehicle. Example results for each core technology component (system identification, flight control design and optimization, hardware-in-the-loop simulation, flight testing and validation) are presented to demonstrate its successful application to the IRIS+. Current work in developing scoring metrics and scaled ADS-33 Mission Task Elements (MTEs) for evaluating the performance of control designs based on aggressiveness, tracking, and robustness are discussed. Recent development of a quadrotor-specific Control Equivalent Turbulence Input (CETI) turbulence model and its application in the design of a performance-based disturbance rejection flight control system are also summarized.
Hover Flight Control Design for UAS Using Performance-based Disturbance Rejection Requirements
Authors:   US Army ADD, Berrios Marcos ,   San Jose State University Research Foundation, Juhasz Ondrej , Berger Tom , Tischler Mark , Sanders Frank
Published: September 2024

A key class of UAS are VTOL vehicles, which afford the ability to hover and maneuver in tight spaces; often in windy and turbulent conditions. This paper presents the development and flight testing of optimized control laws for the 3DR IRIS+ quadrotor designed to aggressively hold its position in a hover while subjected to wind gusts and turbulence. Performance-based disturbance rejection requirements, such as attitude/position tracking error in turbulence and maximum position displacement for a 1-cosine gust, are directly incorporated into the flight control design and optimization process. A Control Equivalent Turbulence Input (CETI) was then used to simulate turbulence in flight and the optimized control laws allowed for the quadrotor to hold its position to within 3.5 inches, a factor of 13.5 improvement over the stock position hold controller.
Assessing the Impact of Hybrid Distributed Electric Propulsion On VTOL Aircraft Design and System Effectiveness
Authors:   VLRCOE - Georgia Institute of Technology, Schrage Daniel ,   Praxis Technologies Inc., Stanzione Kaydon ,   Georgia Institute of Technology - PRICE Systems, Sirirojvisuth Apinut
Published: September 2024

Current VTOL aircraft design processes require significant changes in computational methodologies resulting from innovations in distributed hybrid and electric propulsion technology. Electric VTOL (eVTOL) aircraft design offers radically different configurations by eliminating limitations in weight, size and location of Internal Combustion Engines (ICE) and associated fuel systems. Hybrid Distributed Electric Propulsion (HDEP) solutions, to include eVTOL, allow designers to incorporate a greater number of smaller, lightweight propulsors throughout the airframe structure as necessary to meet complex mission requirements. Additional benefits of HDEP versus fossil fuel counterparts, include reduced acoustic and thermal signatures and lighter and smaller structures. Because of the many advantages of DEP, it is quickly becoming the preferred choice for autonomous aircraft design. This paper addresses the necessary changes to VTOL Synthesis to include DEP and Autonomy for HDEP aircraft. Two of the authors, Dr. Daniel P. Schrage and Mr. Kaydon Stanzione have substantial expertise and experience in VTOL aircraft design and the methodologies for vehicle synthesis. They will use this expertise and experience to identify and present the necessary changes in the VTOLTradeoff Environment (VTE) for HDEP VTOL aircraft design and assessment. The VTE will also be focused on using an Overall Evaluation Criterions (OEC) for the VTE that address value as a ratio of System Effectiveness to Life Cycle Cost (LCC). The third author, Dr. Apinut "Nate" Sirirovisuth, a research fellow in the Georgia Tech's Integrated Product Lifecycle Engineering (IPLE) Laboratory, and a Cost Research Analyst at PRICE Systems has significant experience in VTE modeling efforts and is an expert in affordability analysis for advanced aerospace systems.
A Preliminary Systems Engineering Study on a Concept for Mars Exploration with an Unmanned Autonomous Vehicle and Ground Rover
Authors:   Georgia Institute of Technology, Lacerda Michel , Park Dongjin , Patel Srujal , Schrage Daniel
Published: September 2024

Exploration of Mars has been one of the focus of the aerospace community for its similarity with the Earth. The characteristics of Mars make possible an aerial flight even with the low pressure in its atmosphere. In an age where the ground rover exploration is dominant, the addition of a rotary-wing unmanned autonomous vehicle (UAV) would expand the exploration possibilities, increasing the range and the amount of scientific data collected. In this work, it is shown a conceptual systems design that combines a rotary-wing UAV and a ground rover in collaboration, for the exploration of the terrain. The work was developed in the Systems Engineering level of conceptualization and Design phase. Subsequent Computer-Aided-Design (CAD), Finite Element Analysis (FEA) and Rapid Prototyping were performed as well in this study.
Load Alleviation Control Design Using Harmonic Decomposition Models, Rotor State Feedback, and Redundant Control Effectors
Authors:   The Pennsylvania State University, Saetti Umberto , Horn Joseph
Published: September 2024

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 the addition of rotor state feedback to standard rigid body state feedback. A Pseudo Inverse (PI) strategy is incorporated into the EMF scheme for redundant control allocation. Finally, simulation results with and without load alleviation are compared and the impact of PI feed-forward and rotor state feedback compensation on handling qualities is assessed in terms of ADS-33E specifications.
Using the Task-Pilot-Vehicle (TPV) Approach to Investigate Envelope Protection Design for eVTOL Aircraft
Authors:   Systems Technology Inc - STI, Musso Dakota , Berg Austin , Jones Michael
Published: September 2024

Pilot models have been successfully utilized for design and analysis of rotorcraft for decades. These models are commonly used as analysis tools, usually coupled to flight dynamics models. A method that has been developed is the Task-Pilot-Vehicle (TPV) approach, which utilizes the pilot model in a specific task. This paper presents results from the application of the TPV approach to investigate envelope protection (EP) methods. Four EP methods were chosen for these studies, i) Control Limiting, ii) Command Limiting, iii) MPC Based, iv) Virtual Control Limiting. These methods are exercised with pilot models inside a specifically designed toolbox across several different vehicles, including representative Tiltwing and Quadrotor vehicles, and Handling Qualities Task Elements (HQTEs). Results show that each envelope protection method has advantages and disadvantages, ranging from ease of implementation to potential adverse interactions with the pilot-vehicle system. Overall, the TPV approach shows promise as a method to investigate EP methods for eVTOL/VTOL aircraft.
Predicting Whirl Flutter Bifurcations Using Machine Learning
Authors:   Georgia Institute of Technology, Gatlin Maia , Riso Cristina
Published: September 2024

This paper investigates the feasibility of using machine learning to predict whirl flutter bifurcation diagrams. The machine learning techniques selected for the study are XGBoost and the long short-term memory neural network. These techniques are selected for their suitability for sequential and nonlinear data. The techniques are investigated for a propeller-nacelle test case with polynomial structural nonlinearities resulting in supercritical or subcritical whirl limit-cycle oscillations. The techniques are trained to learn the bifurcation diagram for the amplitude variation of pitch angle limit-cycle oscillations of the propeller-nacelle system as a function of the forward speed for various levels of cubic structural nonlinearity. Bifurcation diagram learning and testing data are generated using the bifurcation forecasting method. XGBoost is computationally faster to train but less accurate for low amounts of learning data, especially for the most weakly and strongly nonlinear cases. The long short-term memory neural network is more computationally expensive to train but shows a less scattered error pattern for sparse learning data. However, it is sensitive to the amplitude resolution of the bifurcation diagrams. The approach to sample the cubic nonlinearity range does not significantly impact the results once the techniques have a sufficient amount of data to learn from. The data requirements observed in the study suggest that, for these techniques, direct learning of bifurcation diagrams may not scale beyond a handful of input parameters.
Piloted Simulation Evaluation of MTEs for the Assessment of Low-Level Handling Qualities
Authors:   German Aerospace Center - DLR, Jusko Tim ,   US Army CCDC AvMC, Berger Tom
Published: September 2024

This study introduces three new proposed Mission Task Elements (MTEs) - "Big Air", "Giant Slalom", and "Super Combined" - aimed at evaluating handling qualities during low-level and high-speed flight profiles. These MTEs are designed to reflect operational task elements critical in military engagements, particularly where rotorcraft capabilities in evading radar detection and maneuvering at high speeds are paramount. Utilizing piloted simulations with four generic rotorcraft configurations under various flight control laws, the MTEs' effectiveness in exposing aircraft characteristics and handling deficiencies is systematically assessed. The evaluation, conducted with a diverse group of pilots, underscores the MTEs' relevance to real-world scenarios and their robustness in handling qualities assessment across different rotorcraft designs. The study reveals that while some configurations exhibit consistent Level 1 Handling Qualities Ratings (HQRs), others show varied performance, particularly when integrating additional means of velocity control, such as pusher propellers or velocity hold modes. Findings suggest modifications to current evaluation frameworks to better accommodate the dynamic operational requirements of future vertical lift platforms.
Impact of Engine Failure on the Wiring Harness Design of Electric VTOL Aircraft
Authors:   Technical University of Munich, Oberschwendtner Sebastian , Hornung Mirko
Published: September 2024

This paper deals with the influence of engine failure during hover on the wiring harness mass of electrical Vertical Take-Off and Landing (eVTOL) aircraft. It starts by presenting possible strategies which can be used to distribute the additional thrust needed during an engine failure among the remaining engines. The most efficient strategy is selected and the impact of different single engine failures on the overall thrust share, while using this strategy, is discussed. The paper proceeds by applying the selected thrust compensation strategy to the mission simulation of three common reference models, which are representative of current eVTOL aircraft configurations. This simulation is used to determine the worst flight phase for the One Engine Inoperative (OEI) condition to occur. The main purpose of the simulation is to optimize the wire sizes of the wiring harness of each configuration while satisfying different design objectives. The results of these optimizations are used to discuss the criticality of each engine failure and its influence on the wiring harness design, especially its mass. It concludes with design recommendations for the wiring harness of eVTOL aircraft.
Systems Engineering - Requirements Development
Authors:   Columbia Helicopters, Pelletier Brad
Published: September 2024

Today's world of engineering is moving faster with a goal of producing more, in less time. This leads to the question that every engineer faces, "do I take the time to develop requirements or jump straight into the design effort?" This question is easily answered when the engineer understands the role of requirements and how they fit into the product life cycle. Once the role of requirements is understood the next step is to understand what requirements are and how they work. The goal is to produce efficient, precise, and professional requirements that describe one system or a system of multiple systems for the project that is in work. When requirements are done right, the project will be completed on time, on budget, with a happy customer that is receiving the product they paid for.
This paper is intended to train engineers to understand what requirements are and how to develop them. The paper will cover the basic reasoning for requirements, where requirements fit into the product design lifecycle, and rules for writing good requirements.
Rotorcraft Cost Too Much - Revisited
Authors:   US Army DEVCOM AvMC, Scott Robert , Nunez Gerardo
Published: September 2024

The findings of the parametric Harris-Scully cost model, also known as the "Cost Too Much" model, are reviewed and re-examined using an updated database of rotorcraft surveyed from government and commercial sources. The sensitivity of flyaway cost as assessed by the updated model is compared to trends in helicopter design and economic inflation to review the recommendations made by original set of helicopter affordability analysis published between 1995 and 1998.
Motor and Drive Design for eVTOL Aircraft
Authors:   LaunchPoint EPS, Rahn Ryan , McDonald Robert , Myers Jack , Paden Brad , Ricci Michael
Published: September 2024

The design of a powertrain for an eVTOL is a complex, multidisciplinary challenge whose solution is best approached as a constrained optimization problem. We use a motor and drive optimization tool based on both first principles and empirical models to examine the design space for a medium-sized eVTOL aicraft. The tool is used to perform optimizations based on continuous power requirements in conjunction with time-dependent mission profiles to achieve an optimal powertrain system weight given efficiency and diameter constraints. Additionally, efficiency and diameter sweeps are performed to illuminate the trades surrounding the "optimal" design point. Access to both detailed system-level optimizations and multi-dimensional sensitivity studies gives eVTOL aircraft designers unique and pivotal insights into the interaction between the propulsion system and the rest of the aircraft. A bespoke, integrated, approach also provides significant weight savings over a commercial off-the-shelf (COTS) solution.
Aeroelastic Stability of a Hingeless Hub Tiltrotor at High Speeds
Authors:   University of Maryland, O'Brien Nathan , Datta Anubhav
Published: September 2024

A 4.75-ft diameter dynamically scaled advanced hingeless hub swept-tip tiltrotor was tested up to unprecedented speeds of 200 knots. This paper describes its design, wind tunnel test, data, and comprehensive analysis predictions. The data consists of beam, chord, and torsion mode damping of the wing-pylon at a loosely Froude scaled RPM of 1050 extracted via the moving-block method. Three systematic parametric variations are studied; hingeless versus gimballed, hingeless versus gimbal-locked, and straight versus swept tip blades. In house comprehensive analysis, UMARC-II, was used to predict the data. The key conclusions were that the hingeless hub increases stability in the chord mode to more than twice that of a gimballed hub. The stability of the torsion mode increased when the hingeless hub was equipped with swept tip blades. The chord damping is slightly higher than the gimbal-locked hub. The beam mode remains unaffected. Comprehensive analysis is able to predict the beam mode but not quite the chord and torsion modes. Thus, the test provides data for validation as well as insights into the aeroelastic stability of hingeless hub tiltrotors.
About the Stabilizing Effect of the Torque on Propeller Whirl Flutter
Authors:   RMIT University, Kantzidis Paul ,   FH Aachen, Böhnisch Nils ,   Politecnico di Milano, Masarati Pierangelo , Muscarello Vincenzo
Published: September 2024

This paper investigates the role of the aerodynamic torque on propeller whirl flutter stability. The generalized force due to the torque is first computed and subsequently included in the equations of motion of a rigid propeller-pylon system. Preliminary evaluations indicate that the torque modifies the real part of the backward and forward modes, providing a stabilizing effect on powered propellers. Analyses are conducted on a 3-bladed propeller driven by an electric motor. Stability predictions are obtained with a simple analytical model and validated by multibody simulations coupled with a mid-fidelity aerodynamic solver, based on a vortex particle method. Furthermore, a simple control law acting on the propeller's collective pitch and rotational speed is presented. The control variables are modified to increase the whirl flutter stability margins, without altering the trim conditions of the aircraft. Results demonstrate the effectiveness of the proposed control strategy, although propeller efficiency is reduced. In a failure scenario, the control law can be exploited to compensate for a weak mounting stiffness, allowing the aircraft to land safely.
Development of a Common, Open Data Exchange (CODEX) for Rotorcraft HUMS Data
Authors:   Bell, Tucker Brian ,   National Research Council, Cheung Catherine ,   Textron, Royar Kenneth ,   Collins Aerospace, Carney Eric ,   The Boeing Company, Fok Derek
Published: September 2024

A Common Open Data Exchange format for rotorcraft Health and Usage Monitoring Systems (CODEX-HUMS) would offer a more affordable, capable and effective Integrated Vehicle Health Management System. The Society of Automotive Engineers (SAE) HM-1R committee is developing a standard definition for the CODEX-HUMS open data format produced or used by an on-board or off-board system, SAE Aerospace Standard AS7140. The standard format benefits end users (e.g., operators, developers, suppliers, integrators, and maintainers) with the capability to more rapidly operationalize HUMS data. This HUMS open data format meets the intent of a Modular Open System Approach (MOSA) and provides a foundation for rapid realization of operational benefits from the point of maintenance and from the exchange of HUMS data with external enterprise systems.
Direct Load Recognition Application to Main Rotor Pitch-Link Load on the H175 Fleet: A New Wavelet Approach
Authors:   Sorbonne University, Del Caroline ,   Airbus Helicopters S.A.S, Nikolajevic Konstanca , Denoulet Julien , Granado Bertrand , Marsala Christophe , Beroul Frederic
Published: September 2024

This paper presents a new approach, variant of the Direct Load Recognition (DLR) methodology, to estimate the main rotor (MR) pitch-link load on customer flights. The original DLR methodology is based on the combination of a harmonic decomposition and the use of Machine Learning algorithms. The DLR variant replaces the harmonic decomposition by a wavelet decomposition. The application of this paper consists in two parts. First, the comparison between the original DLR and DLR variant on prototype flight test data. Two results are highlighted in this part. The capacity of representation of the pitch-link load is better for the wavelet decomposition. The modelling of its coefficients enables to slightly improve the pitch-link load estimation, especially on the high load values having more impact on the fatigue computation. This first part allows to study the feasibility of the DLR variant to estimate the pitch-link load. The second part of this paper focuses on the application of the pitch-link load estimator built with DLR variant on the H175 fleet. From the estimated MR pitch-link load, the MR pitch horn damage is derived and compared to the Design Usage Spectrum (DUS), used today for the certification. The damage of all the studied customer aircraft is well below the DUS, showing a potential gain in component life time. The results of this paper manifest the advantage of the DLR methodology, and more precisely DLR variant methodology, for predictive maintenance on the MR pitch horn, that is to adapt the maintenance to the aircraft usage.
Surface Mount On-Blade Optical Telemetry System
Authors:   Continuum Dynamics Inc., Jr. Robert
Published: September 2024

AAM concepts use multiple distributed electric motors driving propellers and rotors to augment or directly generate lift and propulsive forces. Several current concepts incorporate separate drive systems for providing vertical lift, for takeoff and landing, and propulsive thrust for wing-borne cruising flight. Measurement of loads and performance on these rotating systems is very important in both the design and development stage, as well as for certification use and ultimately supporting HUMS monitoring. However, providing instrumentation in the rotating frame and extracting their associated measurements is often problematical, as it requires some means for both power and signals to bridge the rotating interface between the blade of the rotor/propeller and the fixed frame (fuselage) system. This paper describes work conducted to leverage prior CDI development of a novel optical telemetry/ instrumentation system to create a prototype unit that can support ground and flight tests, allowing for multiple installations on the many rotors that constitute current AAM configurations. The resulting hardware was designed to expand the capabilities developed previously in types and rates of data collected, on-board processing, and user configuration options, supporting NASA and commercial organizations in their testing activities.
Aeromechanics Investigation of a Dual-Wing Lift Compounded Slowed Mach Scale Rotor
Authors:   University of Maryland, Uppoor Vivek , Patil Mrinalgouda , Chopra Inderjit
Published: September 2024

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 incidence angle at μ = 0.5 and αs = 0°, however, the dual wing configuration yielded a 20% lower steady flap bending moment. The study showed that the wing wake has a negative effect on the rotor performance especially at rearward rotor shaft angles; this is overcome with the efficiency gains from lift offset present in a single wing configuration but absent in the dual wing configuration. Hence, the single wing configuration attains the highest performance while the dual wing configuration minimizes structural loads. A lift compounded rotor is limited at high advance ratios since it is almost entirely offloaded, resulting in increased total lift to drag ratio at the cost of large blade structural loads.
Analytical Linearization of a State-Space Free Vortex Wake Model
Authors:   The Pennsylvania State University, Manjhi Ashish ,   University of Maryland, Saetti Umberto , Horn Joseph
Published: September 2024

This paper presents the development and application of analytical linearization of a State-Space Free Vortex Wake Model. Previous work developed a state-space free wake model that could be numerically linearized via finite differences into a Linear Time Periodic (LTP) system, but the numerical linearization process was computationally expensive. An improved method is developed that uses exact analytical linearization of the Biot-Savart Law. The analytical method is found to speed up linearization computations by O(N), where N is the number of free wake nodes. A simple decoupled wake model is used to develop and test the method, where the wake system's inputs are prescribed blade bound circulations. The state space matrices computed by the analytical linearization method are verified to match those of the numerical linearization method exactly as perturbation sizes approach zero. The analytically linearized LTP model was converted into a Linear Time Invariant (LTI) model using Harmonic Decomposition. The on-blade induced velocities predicted by the LTI wake model are found to match the non-linear wake model in both frequency response and for small amplitude step inputs to the blade circulation. The linearized wake model is then coupled with a non-linear blade element simulation of a utility helicopter rotor (using the GenHel rotor model). Step responses to rotor collective and cyclic pitch inputs are compared between the rotor model coupled with the linearized wake and with the non-linear wake model. The rotor forces, hub moments, and induced velocities of the two models are found to have good agreement.
Vertical Flight Infrastructure Data Quality Shortcomings
Authors:   Five-Alpha LLC, Alexander Rex ,   FAA William J. Hughes Technical Center, Johnson Cliff
Published: September 2024

This paper represents an assessment of how vertical flight infrastructure data is accounted for, the criteria and standards used to accomplish this, what shortcomings may exist in both the data as well as the process, and what changes need to be implemented in preparing for the next generation of vertical flight transportation. The primary focus of this paper will be to review the regulations, criteria, standards, and processes that apply to aviation infrastructure data Collection, Accuracy, Resolution, Integrity, Traceability, Timeliness, Completeness, and Format and to what extent it is successfully being accomplished in the vertical flight industry. Based on these findings, this paper will strive to identify the current gaps in data accountability for vertical flight infrastructure and provide recommendations for remediating these issues. While this assessment will be specific to current and traditional helicopter infrastructure, it is intended to provide insights into identifying best practices as it applies to the Advanced Air Mobility (AAM) industry and its supporting infrastructure as well.
Parametric Rotor Control Equivalent Turbulence Input (RCETI) Models for Different Rotor Configurations
Authors:   Georgia Institute of Technology, Hayajnh Mahmoud , Prasad J.V.R.
Published: September 2024

This paper presents results from an ongoing research that aims to create Parametric Rotor Control Equivalent Turbulence Inputs (RCETI) models for different rotor configurations. In RCETI modeling, the rotor swash-plate deflections are utilized as inputs to match the turbulence-related spectra of rotor hub-loads in order to achieve the parametrization and generalization of these models. The development of the RCETI model, which aims to produce rotor loads spectra similar to those generated by two-dimensional spectra of turbulence, is conducted using a representative rotor model in FLIGHTLAB®. The effect of rotational sampling of turbulence on the rotor response is analyzed. The hub-fixed sampling, rotational sampling at 0.75R as well as the blade-element sampling of turbulence are considered and compared. Furthermore, parametric analysis is carried out to study the effect of altering rotor parameters on the developed RCETI model and presented in the paper.
Full Flight Regime Controller Design for a Lift-plus-Cruise eVTOL Aircraft
Authors:   Rensselaer Polytechnic Institute, Keller Alexander ,   North Carolina State University, Gandhi Farhan , Walter Ariel , Niemiec Robert
Published: September 2024

Full flight regime trim strategies are examined for a Lift+Cruise eVTOL aircraft. Control laws are designed for hover, transition, and cruise conditions to satisfy standard flying-qualities requirements based on the characteristic behavior of the vehicle (rotorcraft versus fixed wing) while ensuring realistic motor limits (peak and continuous) are satisfied. CONDUIT® is used to optimize control laws to minimize actuator activity while meeting flying-qualities constraints. Variable-RPM control is shown to be sufficient to satisfy Level 1 flying-qualities requirements in hover and low-speed flight where control surfaces have inadequate control authority. Time domain simulations are presented to verify controller performance and ensure actuator limits are not violated while following step commands. The aircraft is able to follow commands well in all axes and flight regimes. Transition through the full flight regime (hover to cruise) is simulated using a stitched model.
Design Investigation and Hover Testing of an On-blade Active Trailing-edge Flap for Higher Harmonic Control
Authors:   Seoul National University, Im Byeonguk ,   Chungnam National University, Ryi Joeha ,   Supernal, Eun Wonjong ,   Korean Air, Lee Hyunjae , Kong Kunhyuk , Lim Taekyung , Lee Changbae , Shin SangJoon
Published: September 2024

This paper presents an open-loop hover experiment and analysis for a 4-blade Mach-scaled Seoul National University Flap (SNUF) rotor. A detailed finite element analysis is attempted to predict allowable experiment range that provides sufficient structural integrity. Multi-body dynamic analysis DYMORE and cross-sectional design program VABS are used to analyze the present trailing-edge flap rotor blade, and the flap hinge stiffness is calibrated on the static bench test. Ground testing on the present rotor shows a linear strain-displacement response, and the relevant result shows better than 80% correlation against DYMORE prediction. Appropriate test matrices are constructed and two of those are attempted herein. The first one is the baseline no-actuation collective sweep test at two different rotating speeds at tip Mach of 0.22 and 0.3, respectively. The results are utilized to correlate between the momentum theory and free wake empirical parameters. Next, a single active flap blade test is attempted to assess the trailing-edge flap driving component. It is found that the dynamic trailing-edge flap deflection result needs to be both electrically and mechanically isolated from the test stand. In the future, trailing-edge flap deflection will be recorded for 1 - 5/rev activation at tip Mach 0.5, while four-blade actuation engaged. The frequency response of the trailing-edge flap mechanism will be identified, and 1/rev tracking control will be attempted.
Preliminary Results from Dynamic Testing of a Pericyclic Drive System
Authors:   The Pennsylvania State University, McGovern Jeremy ,   University of Tennessee, DeSmidt Hans ,   IIT Kanpur, Mathur Tanmay ,   DEVCOM ARL, Mistingas Constandinos , Smith Edward , Bill Robert , Stevens Mark , Schroen Erik
Published: September 2024

Over 4 decades of research works on the nutating, now pericyclic, mechanical transmission have studied its capability to achieve high power density, low noise, and amplified single-stage reduction ratios of up to 100:1. These analytical efforts have culminated into the fabrication of a 50 HP and 32:1 reduction ratio pericyclic transmission prototype. This work introduces the prototype with highlights of the assembly and alignment procedures validated by static testing evaluation. Then, discussion of the dynamic test stand integration, instrumentation, and lubrication components lay out the framework of the high-speed testing plan. Power transmission data validated the pericyclic reduction ratio model. Accelerometer data demonstrated the transmission's capability to operate at low vibration, with peak amplitudes of 1.2 and 2.5 inches per second on the pericyclic gear train and output shaft respectively. Acoustic emission data captured the first 5 harmonics of the shaft speed as well as gear mesh frequencies. The thermal profile showed the shaft bearings remained below 180°F throughout testing, implying safe operating conditions. Finally, strain and vibration data showed the pericyclic gear train maintained load sharing throughout the entire operating envelope, further validating static testing and assembly procedures. The results of the experiments demonstrate the technological readiness of pericyclic mechanical transmission.
Wing and Propeller Aerodynamic Interaction Effects on Whirl Flutter Instability
Authors:   University of Michigan, Chang Jasmine , Sanghi Divya , E. Carlos
Published: September 2024

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 wake at a higher fidelity. Using the VVPM model on the propeller and vortex wake on the wing, it was found that the wing-to-propeller aerodynamics interactions have the most significant impact on a rigid wing and flexible pylon model, while both wingto-propeller and propeller-to-wing interactions had a significant impact on a flexible wing-pylon model. The impact of aerodynamic interaction effects are also characterized with respect to the pylon-length-to-propeller-radius ratio by varying the pylon length. Results show that aerodynamic interactions have a more significant impact on damping at lower airspeeds, regardless of the pylon length. Aerodynamic interactions were also found to be destabilizing at both operational and windmilling conditions. Overall, aerodynamic interactions should be considered if induced inflow over the lifting surface is expected to be a significant portion of the total propeller disk inflow.