bluuebunny/crossref_metadata_2025 huggingface dataset:
Preliminary Assessment of Bird Strike on Low Noise Rotor Blade Sections
Authors:   NASA Langley Research Center, Annett Martin ,   NASA Glenn Research Center, Pereira J.
Published: August 2024

One of the primary research themes for NASA's Revolutionary Vertical Lift Technology Project (RVLT) is evaluation of low-noise vertical lift concepts and configurations. A multidisciplinary design analysis and optimization (MDAO) process, which incorporates acoustics, structures, icing, and impact dynamics design constraints, is in development for the conceptual low-noise rotor blade design. Modifications to conventional rotor blade shape, cross section, and material selection to reduce noise may be limited by the capability of the structure to withstand a bird strike. The bird strike requirement for transport category rotorcraft is specified in 14 CFR §29.631, and requires safe flight and landing following impact of a 2.2 lb bird. An artificial bird simulant has been developed for repeatable laboratory testing, and consists of ballistic gelatin infused with phenolic microspheres. Ballistic testing of a bird simulant on various flat and wedge shaped objects was conducted at NASA Glenn Research Center's Gas Gun Facility. Force and strain data were compared to impact simulations of an LS-DYNA® finite element model (FEM). The bird simulant was modeled using Smooth Particle Hydrodynamics (SPH), and validated based on the data. The bird simulant model was incorporated with a low noise blade design that was verified for aeroelastic stability and contained dimensions typical of a medium lift category rotorcraft. FEM pre-processing capabilities were utilized to morph the cross section to different dimensions, and LS-DYNA analyses were conducted. A parametric assessment of damage will be discussed, with varying factors such as spar thickness, blade thickness, and nonlinear material strength parameters. The geometric constraints on this low noise blade that will be used for follow-on MDAO analyses are a combination of maximum blade twist of 15 degrees and a minimum spar thickness of 50% of the nominal spar thickness.
Evaluation of Lumbar-Load Criterion Based on Test Data and Field Performance Results of the UH-60 Black Hawk Crew Seat
Authors:   BAE Systems, Richards Marvin
Published: August 2024

The BAE Systems legacy UH-60A/L Black Hawk Crew Seat has been in serial production for almost 40 years, and has garnered a reputation for providing a high degree of crash safety to its occupants. The seat has been dynamically tested over 150 times, providing a wealth of test data that are summarized in this paper. This paper also presents a review of data from actual UH-60A/L crashes that verifies the seat's excellent performance with regards to minimizing occupant compressive spinal injuries. In addition, this paper presents a compilation of test data containing ATD lumbar-load readings. The dynamic test results are then compared to the lumbar-load limits specified in JSSG-2010-7 and the more recent Full Spectrum Crashworthiness (FSC) Criteria for Rotorcraft. This comparison shows that the seat most likely would not have passed the FSC criteria, which indicates that either the FSC lumbar-load limits are set too low, or that the dynamic test pulses do not replicate the actual crash environment. The JSSG criteria were found to be a better predictor of the seat's actual crash performance.
SPAACE - 3D Audio Support for Confined Area Operations
Authors:   German Aerospace Center - DLR, Niermann Christian
Published: August 2024

A major challenge in aviation and cockpit design is data overload. Especially in the visual channel and associated breakdowns in monitoring systems. These problems are expected to worsen with new and advancing complex missions, which will require pilots to manage increased amounts of data and adopt new responsibilities. Multimodal approaches and especially new developed 3D audio systems have the potential to become a major part. Current cockpits convey audio only as warning- or information-sound. This paper documents a helicopter simulator study to test a new developed 3D audio system to support pilots in future cockpits, accurate enough for real-time applications. The system named SPAACE - Spatial Pilot Audio Assistance. Sixteen professional helicopter pilots (law enforcement, search and rescue service and VIP transportation) flew an approach, hover and vertical landing close to obstacles in challenging areas and weather conditions. Results show that pilots' can maintain a hover close to an obstacle with the support of spatial audio. The distance to the desired landing position improves noticeable. Results of questionnaires and interviews with the pilots point out, that the system is easy to use and need only minimal training. Pilots reported longer head-up time and better situation awareness during the mission with 3D audio assistance.
Active SARIB: a New Generation of Suspension for Helicopters
Authors:   Airbus Helicopters, Cranga Paul , Jouve Jérémy , Skladanek Yan
Published: August 2024

The main objective of this paper is to present a new generation of active vibration system for helicopters developed by Airbus Helicopters. The design of this system is the result of an analysis performed through numerical simulations to select the most promising strategy of vibrations mitigation. Different solutions have been compared: classic active vibration control with force generators on the cabin floor, passive suspension based on DAVI system and an innovative active version of a suspension called SARIB®. The reduction of vibratory loads in the vicinity of the rotor pylon with active means appears as the most efficient solution. A development of the active suspension has so been undertaken. The principle of the system is presented firstly in an academic way. Then higher fidelity models are set up to design in details the system and to size it. The active suspension has been manufactured and it has been evaluated through lab test on a full scale mock-up. The test results indicate excellent level of attenuation and they validate the interest and feasibility of the concept.
Coupled Vibration Prediction of Rotor-Airframe-Drivetrain-Engine Dynamics
Authors:   University of Maryland, Sidle Stacy , Sridharan Ananth , Chopra Inderjit
Published: August 2024

Comprehensive vibration analysis of a rotor-airframe-engine-drivetrain system using a time-domain modal coupling approach was conducted. Pair-wise couplings of components (airframe and drivetrain/engine) were performed to isolate the contribution of each component to the complete coupled system, and the effect of each component on blade loads and hub loads was studied. The drivetrain model is a 6-dof model consisting of inertia and torsional spring elements, while the airframe model is a NASTRAN superelement of a detailed finite element airframe model for a medium-lift utility helicopter. Drivetrain coupling resulted in elastic twist of the rotor shaft by less than 0.02 degrees, but there were noticeable reductions in the chordwise blade bending moments as well the 8/rev hub torque. The airframe coupling produced very small hub translation amplitudes, less than 5×10⁻⁴ inches, however it had a significant impact on the higher harmonic flap bending, increasing the 9/rev flap moment by up to 60% near the root.
Rotorcraft Comprehensive Analysis Calculations of a Coaxial Rotor with Lift Offset
Authors:   NASA Ames Research Center, Ho Jimmy ,   U.S. Army Aviation Development Directorate, Yeo Hyeonsoo
Published: August 2024

This paper presents comparisons of rotor performance, blade pitch, rotor hub loads, and blade clearance between two sets of rotorcraft comprehensive analysis calculations and experimentally measured test data for a coaxial rotor system in forward flight conditions. The calculations are from the U. S. Army’s Rotorcraft Comprehensive Analysis System (RCAS) with one set calculated by using a prescribed vortex wake model and another set calculated by coupling RCAS to a viscous vortex particle method. For rotor performance and blade pitch, the calculations and test data are presented as functions of lift offset for four different advance ratios and for two different test upper rotor collective pitch settings. Rotor hub loads and blade clearance are compared on a time-varying basis for test points that form a lift offset sweep, an advance ratio sweep, and a rotor-to-rotor phase sweep. The main conclusion is that both sets of calculations generally reflect the same trends as the test data, which provides confidence in the ability of RCAS at calculating the aeromechanics behaviors of lift offset coaxial rotors.
A Real Time Scheme for Rotating System Component Load Estimation Using Fixed System Measurements
Authors:   Georgia Institute of Technology, Mballo Chams , Prasad J.V.R
Published: August 2024

Accurate and real-time load monitoring of vital components located in the rotor system is important for not only inferring usage and estimating fatigue in those components, but also for developing load alleviation /limiting control schemes. An approach previously developed for online estimation of rotor component loads is evaluated in this paper in which a linear time invariant (LTI) model of helicopter coupled body/rotor dynamics is combined with a Linear Quadratic Estimator (LQE), that is designed to correct LTI model state response using fixed system measurements. The estimation fidelity of the LTI/LQE scheme is evaluated in simulations using a nonlinear model of a generic helicopter for online prediction of rotor blade pitch link loads arising from vehicle maneuvers.
Rotor Blade Displacement and Load Estimation with Fiber-Optical Sensors for a Future Health and Usage Monitoring System
Authors:   Technical University of Munich, Suesse Soeren , Hajek Manfred
Published: August 2024

Fiber-optical sensors have great potential in rotorcraft applications since they are small and robust in corrosive and electromagnetic environments. In addition, redundant configurations are easily realizable. Recent advances in the size and maturity of measurement equipment enables fiber-optical sensors and the interrogator to be placed even in the rotating system itself. For future Health and Usage Monitoring Systems, they can collect important data in locations where other types of sensors would not be feasible. In this paper, a method is presented for using fiber-optical sensors to identify elastic blade movements based on surface-strain measurements. With this method, it is possible to calculate the displacement and bending moment of the structure with great accuracy. Furthermore, blade properties like the neutral axis and bending stiffness can be determined at cross sections where fiber-optical sensors are located. Test campaigns were conducted on a non-rotating rotor blade test bench and Monte-Carlo simulations were performed to assess the model's sensitivity to its inputs. One of the advantages of the method is that only the location and orientation of the sensors need to be provided and no further input, such as an FE model, is needed.
Learning Operating Conditions for Gearbox Health Monitoring
Authors:   Rochester Institute of Technology, Nenadic Nenad ,   US Army Research Laboratory, Hood Adrian , Thurston Michael
Published: August 2024

This article describes an approach to learning gearbox operating conditions, defined by torque, rotational speed, and power, from acceleration data. Learning operating conditions paves the way to learning gearbox state-of-health because health indicators have to be normalized with respect to operating conditions to avoid false alarms. Moreover, because operational data is vastly larger than data associated with faults, representation learning is easier (and often only possible) from the operational data. The article compares two different solutions, one based on a multi-layer perceptron and the other on a recurrent network using the first four statistical moments as input features. The decision process, including heuristics and domain knowledge, used for selection of the network topology is described in detail. Models were found most effective in estimating the mechanical power transmitted through the gearbox and provided improvements over the second moment (RMS) alone.
Implementing Advanced Technologies in the Sand Casting Supply Chain
Authors:   Sikorsky a Lockheed Martin Company, Woodworth Heather , Jr. William
Published: August 2024

How many castings should be poured before getting a useable part? The ideal answer may be one, but the reality is that the ideal is infrequently realized. What alloy is the part? What is its size? What is the complexity? How is the part complex: many interior cores, many thick to thin section transitions, very thin walls, or something else entirely? No two part geometries will be exactly the same, so the challenges and expectations for each part will be different. At Sikorsky, our sand cast components only seem to be getting more complex, with more demanding dimensional and metallurgical requirements. All of these factors makes the casting of these parts more challenging. This also coincides with a time where lead times and costs to develop a new casting are being scrutinized.
New High-Performance Materials Tailored Specifically For Additive Manufacturing Processes
Authors:   QuesTek Innovations LLC, Grabowski Jeff , Kozmel Tom
Published: August 2024

Integrated Computational Materials Engineering (ICME) technologies have served an integral role in understanding, evaluating and designing material microstructures and heat treatments specifically tailored for the unique processing conditions of Additive Manufacturing (AM). Applying their Materials by Design® methodologies, QuesTek Innovations has expanded their ICME framework under US Army Small Business Innovation Research (SBIR) funding to adapt their high performance Ferrium® C64® gear steel to AM processes, demonstrating printability across multiple systems, achievement of AMS minimum tensile properties, and positive response to heat treatment. Under Office of Naval Research and US Navy SBIR funding, QuesTek has designed and is developing high performance, aluminum alloys that are both printable and demonstrate properties of wrought 6000 and 7000 series alloys. AM builds and testing to date have demonstrated crack-free printability, high strength and good corrosion resistance. QuesTek is also demonstrating its high strength titanium alloys in wire and powder AM processing and showing a 20% increase in strength at a given ductility versus Ti-6Al-4V. These technologies, among several other AM alloy development programs at QuesTek, are advancing into TRL 4 and beyond. QuesTek's work in stainless steel in AM is also covered.
Comparison of Mechanical Properties of Additively Manufactured Ti-6Al-4V Alloy Made Using Different Manufacturing Processes
Authors:   Bell Helicopter Textron Canada, Lapalme Maxime , Thibault Éric , Rousseau Gilles
Published: August 2024

This paper presents a comparison in terms of microstructure and mechanical properties of Ti-6Al-4Vcoupons build by five different Additive Manufacturing (AM) suppliers. Three different manufacturing processes and different equipment are compared. Specimens were built to address any possible impact of fabrication direction and position within a build for the different suppliers. All builds were stress relieved and received Hot Isostatic Pressing (HIP) to ensure optimal mechanical properties. Microstructure was evaluated using both X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Standard test methods were used to measure mechanical properties such as tensile strength, fatigue crack growth rates, fracture toughness and axial fatigue. Results are compared with conventionally machined samples from raw material forms (bar, plates, sheets).
Achieving High Performance Aircraft Modeling in Operational Analysis Software using a Minimum Complexity Model
Authors:   The Boeing Company, Keller James , Colosi Christopher , Nichols Gregory
Published: August 2024

Operational analysis programs are a common tool used by operators to simulate the mission outcomes as a means to estimate mission requirements for both rotary wing and fixed wing aircraft. Operational analysis programs are more commonly referred to as "war games". Mission simulations take into account battlefield topography, atmospheric conditions, aircraft capabilities, and potential threats. The outcomes of these simulations aid operators in decisions such as the number of aircraft to be deployed on a particular mission, what type of aircraft to utilize, as well as the overall risk of the mission. Additionally, operational analysis programs have been used to evaluate developmental platforms against each other in a battlefield environment. A key component of the operational analysis program is the flight dynamics models for each of the aircraft involved in the simulation. Aircraft modeling for this type of simulation presents a unique challenge due to the fact that the models must be computationally compact because many aircraft are being simulated. While much research has gone into the creation of high fidelity rotary-wing and fixed-wing models, there are no established standards for computationally compact models to be used in war games simulations. Past attempts to achieve satisfactory model performance used interpolation of aircraft performance data table collected from flight test or a high fidelity simulation. Boeing has implemented a more rigorous method using 6 degree-of-freedom linear aerodynamic models of body-referenced vehicle response. Proportional navigation and control laws are used to drive the models to allow execution of flight plans. The model uses an explicit set of equations for the speed control, turning flight, and climbing/descending flight. The parameters required to populate this model are based on typical control response requirements derivable directly from handling qualities specifications. Different vehicle configurations can be parameterized by using either published data for specific aircraft or by referring to the appropriate handling qualities performance specification which provides guidelines for desired and adequate response. MIL-F-8785C is used to parameterize fixed wing configurations and ADS-33E-PRF is used for rotary wing. In addition to describing our approach to this type of simulation we seek to propose that a uniform set of standards for aircraft modeling be developed for these "war games" simulations.
Development of Finite State Inflow Models for Multi-Rotor Configurations using Analytical Approach
Authors:   Georgia Institute of Technology, Guner Feyyaz ,   Washington University, Peters David ,   Advanced Rotorcraft Technology Inc, He Chengjian , Kong Yong-Boon , Prasad J.V.R.
Published: August 2024

Multi-rotor configurations require accurate inflow models for performance, aeromechanics and handling qualities analyses. Single rotor finite state inflow models have been used for performance, aeromechanics and handling qualities analyses and shown to have good correlation with experimental data. Recently, finite state inflow models based on pressure and velocity potential superposition approaches have been developed for coaxial rotor configurations. Furthermore, Pressure Potential Superposition Inflow Model (PPSIM) has been extended to arbitrary number of rotors and arrangements. In this paper, a finite state multi-rotor inflow model based on Velocity Potential Superposition Inflow Model (VPSIM) approach is developed. In addition, the developed finite state multi-rotor inflow models are compared with a high fidelity numerical model known as viscous Vortex Particle Method (VVPM) for three different configurations; a coaxial and two tandem rotor configurations with different longitudinal separation distances. Rotors induced inflow distributions in these configurations are investigated in hover and at a low speed flight condition of advance ratio equal to 0.04. Differences in the uniform, fore-to-aft and side-to-side inflow variations among the three models are found in both steady-state and transient responses to rotor load perturbations.
CFD Analysis for Flexible Flapping Wing in Hover Flight
Authors:   Texas A&M University, Yang Xuan ,   University of Maryland, Badrya Camli , Benedict Moble , Lankford James
Published: August 2024

Complexities in hummingbird scale flapping wing aerodynamics pose significant challenges to the design of flapping wing micro air vehicles (MAVs). These challenges arise from the unsteady nature of the aerodynamic loads and flow field, which consists of highly viscous flow coupled with complicated wing kinematics. The current study introduces a CFD simulation to understand the force generation and flow structure of flexible flapping wing. The CFD analysis used a compressible Reynolds-averaged Navier-Stokes solver to resolve the complex, highly vortical, three-dimensional flow. The objectives of the effort were to understand the unsteady aerodynamic mechanisms and their relation to force production on a rigid wing undergoing an avian-type flapping motion. The results comparison between simulation and experiment suggest a number of potential causes for discrepancies in force predictions, including the effect of complex deformation and the development of a vortex pair that becomes attached to the wing at stroke reversal which appears to be dependant on minor details of the wing geometry.
Nonlinear Aeroelastic Coupled Trim Analysis of a Twin-Cyclocopter in Forward Flight
Authors:   Texas A&M University, Halder Atanu , Benedict Moble
Published: August 2024

In this paper, detailed development of a nonlinear aeroelastic coupled trim model of a twin-cyclocopter in forward flight is presented. Twin-cyclocopter consists of two cycloidal rotors as main thrusters and a conventional nose rotor for pitch-torque balance. It is shown that five control inputs (mean and differential rpm, mean and differential phase offset of cyclorotors, rpm of nose rotor) are needed to balance three moments and two forces on cyclocopter in forward flight while forces along lateral direction remain balanced at all stages. In this coupled trim procedure, blade aeroelastic response equations and vehicle trim equations are solved together by simultaneously updating control inputs and blade response. To obtain the blade response and forces for a given set of control inputs, an aeroelastic model of cyclorotor and an aerodynamic model of the conventional nose rotor in forward flight is developed. The nonlinear aeroelastic model of the cyclorotor is developed by coupling unsteady aerodynamic model of cyclorotor in forward flight with a geometrically exact beam based structural framework capable of predicting large bending and torsional deflections of rotor blade. Towards this, complex aerodynamics of the cyclorotor is thoroughly investigated and various underlying phenomena, such as dynamic virtual camber, effects of near and shed wake and leading-edge vortices are rigorously modeled. A modified Double Multiple Streamtube (D-MS) model is implemented to capture the complex dynamic inflow characteristics of cyclorotor in forward flight. The present model is validated with previously published in-house experimental data on the performance of a trimmed cyclorotor at different forward speeds.
Structural Dynamics of a Dual Clutch Offset Compound Gear Transmission with Electro-Magnetically Actuated Engagement
Authors:   University of Tennessee, DeSmidt Hans ,   Pennsylvania State University, Smith Edward , Bill Robert
Published: August 2024

This paper describes a structural dynamic analysis of a dual clutch Offset Compound Gear (OCG) transmission for application in a two-speed rotorcraft transmission with Electro-Magnetically Actuated (EMA) clutch engagement. This model includes the nonlinear axial contact dynamics between clutch plates. The applied electro-magnetic engagement force is proportional to the magnetic flux traveling axially through the clutch pack. Since the magnetic reluctance is inversely related to the dynamic air gaps between clutch plates, the engagement force rapidly increases as the plates come into contact. Due to the momentum and inertia of the clutch plates, the impacting plates generate an impulsive axial spike in clutch pressures. Since the friction torque transmitted by the clutch is proportional to the instantaneous clutch pressure, the axial plate contact dynamics can be a significant source of shock torque loads delivered to the driveline during shifting. The simulation results capture this phenomena and demonstrate the magnitude of the effect. To the authors’ knowledge, axial clutch plate contact dynamics have not been previously considered or accounted for in the literature on clutch dynamics.
Two-Speed Rotorcraft Research Transmission Power-Loss Associated with the Lubrication and Hydraulic Rotating Feed-Through Design Feature
Authors:   NASA Glenn Research Center, Stevens Mark ,   US Army Research Laboratory, Valco Mark , LaBerge Kelsen
Published: August 2024

An investigation was completed into the power loss associated with a rotating feed-through (RFT) design feature used to transfer lubrication and a hydraulic control signal from the static reference frame to a rotating reference frame in the NASA GRC two-speed transmission tests conducted in the Variable-Speed Drive Test Rig. The RFT feature, not commercially available, was created specifically for this research project and is integral to all two-speed transmission configurations tested, as well as a variant concept design for a geared variable-speed transmission presented at AHS Forum 71 in 2015. The experimental set-up and results from measurements in the isolated rotating-feed-through (RFT) experiments are presented. Results were used in an overall power loss assessment for a scaled conceptual 1,000 horsepower inline concentric two-speed transmission to support a NASA Revolutionary Vertical Lift Technologies (RVLT) Technical Challenge, demonstrating 50% speed change with less than 2% power loss while maintaining current power-to-weight ratios.
Mass and Kinematic Analysis of Compound Split with Simulation of the Shifting Process for Variable Rotor Speed
Authors:   Vienna University of Technology, Amri Hanns , Hartenthaler Katharina , Weigand Michael
Published: August 2024

The investigation presented in this paper is part of the project VARI-SPEED which aims to invent a speed variable drivetrain for different rotorcraft configurations. A kinematic and a mass analysis of compound split transmissions (CS) variations and a rotorcraft drivetrain simulation model to analyze the dynamic behavior during rotor speed change were performed. All solutions have the same power flow in the variator path but different fixed carrier transmission ratios of the planetary gears, which lead to a difference in mass. CS can be used as two speed transmissions and as continuous variable transmissions (CVT). As a two speed transmission less torque and friction energy is induced in the clutches than in a double clutch transmission, but CVT enable a smooth transition with no friction losses. CS offer the opportunity to vary rotor speed which decreases the overall power demand and lead to a more ecologically efficient rotorcraft aviation.
NITROS: An Innovative Training Program to Enhance Rotorcraft Safety
Authors:   Politecnico di Milano, Quaranta Giuseppe ,   University of Glasgow, Barakos George ,   University of Liverpool, White Mark ,   TU Delft, Pavel Marilena , Mulder Max
Published: August 2024

Helicopters are currently used in important applications providing a valuable contribution to society and economic growth. Thanks to their operational flexibility it is possible to accomplish increasingly complex missions. If the expansion of the usage of rotorcraft is to follow the pace of growth achieved by the fixed-wing public transport in the last years, several issues need to be urgently addressed to increase the use and the public acceptance of rotorcraft. Aspects related to complexity of the operations and safety are of primary importance, since in the last 20 years helicopter accident rates, worldwide, remained unacceptably high, when compared to fixed-wing aircraft. The complexity of the phenomena involved in rotorcraft flight calls for the training of engineers with a genuine multidisciplinary background. This paper presents the doctoral research and training program NITROS, which is set up under the Marie Skłodowska-Curie Action of the European Union to address complex solutions to rotorcraft safety.
Functional Safety Management Approach for Certification of Evolving eVTOL Air Taxi Concepts
Authors:   Georgia Institute of Technology, Schrage Daniel ,   Georgia Institute of Technology and PRICE Systems, Sirirojvisuth Apinut , Walters Robert
Published: August 2024

Recently, technology advances have made it practical to build a new class of electrical VTOL (eVTOL) aircraft. Over a dozen companies, with as many different design approaches, are passionately working to make eVTOLs a reality1. The establishment of Uber Elevate has helped spur this development by providing the launch customer and a proposing the necessary operational infrastructure for its implementation. However, to understand the path to improving safety and certification for urban air transportation, we need to understand the root causes of historical crashes. Thus, a Functional Safety Management (FSM) approach much be implemented. Also, before eVTOL air taxis can operate in any country, they will need to comply with regulations from aviation authorities—namely the US Federal Aviation Administration (FAA) and European Aviation Safety Agency (EASA) who regulate 50% and 30% of the world's aviation activity, respectively - charged with assuring aviation safety. eVTOL aircraft are new from a certification standpoint, and progress with certification of new aircraft concepts has historically been very slow, though the process is changing in a way that could accelerate things significantly. The planned approach is to start with FAR - Part 23 standards along with new ASTM F44 consensus standards. This approach offers the potential to radically accelerate the development of new standards (which is required for the certification of new eVTOLs) because the community takes responsibility for developing the certification basis and then presents it for adoption by the regulator. To help initiate this planned approach, Georgia Tech, in collaboration with Coventry University, is conducting a Safety Assessment and Certification (SAC) Study as part of the Georgia Tech Course, AE6362: Safety By Design and Flight Certification. This paper will review the overall proposed FSM approach and provide some emerging results from the SAC Study.
Multiphysics Simulation of Pylon Fluid-Elastomeric Isolators
Authors:   Bell, Knoll Jonathan ,   ITT Enidine Inc., Ott Mark ,   TechSource Engineering Inc., Cooney Kevin , Seifert Michael
Published: August 2024

A coupled fluid-structure interaction (FSI) simulation was developed to evaluate a new design feature in the LIVE® vibration isolation system of the 505 Jet Ranger X. Efficient modeling of fluid and elastomeric characteristics is enabled by simplifying the internal fluid boundaries and adjusting fluid compressibility. The approach provides an accurate analysis of the internal loading within the LIVE structure. Computed results substantiate the LIVE design in terms of strength, durability, and component deflection. The FSI simulation also supports dynamic tuning of the LIVE to achieve the target operating frequency. Validation is demonstrated by comparison to laboratory test measurements. Correlation to test results, in terms of fluid pressure, is within 3.5% and correlation to natural frequency is within 5%.
High Cycle Fatigue Assessment of a Diesel Engine Turbocharger
Authors:   US Army, Dang Khanh ,   SAIC, Meininger Rik ,   US Army, Gibson Joseph , Wiersma Henry , Kim Kenneth , Szedlmayer Michael
Published: August 2024

Many technical papers describe turbocharger turbine/compressor failures caused by foreign object damage, contaminated lube oil, lack of lubrication, high exhaust temperatures, low cycle fatigue, or overspeed. However, High Cycle Fatigue (HCF) is a potential failure mode that has not been widely assessed. This paper describes steps to investigate an HCF fatigue failure of a turbine blade. Metallurgical analysis determined that the failure surfaces are indicative of fatigue and that the initiation location coincided with the location of maximum stress as identified by finite element modal analysis. High Cycle Fatigue was identified as the root cause of the failures. Finite element based modal analysis indicates that the turbine blade could quickly fail if the turbocharger is operated at one of several resonant speeds since turbine blade resonances occur at very frequencies. HCF analysis with combined modal and stress analyses coupled with a high altitude engine test using the candidate turbocharger is recommended for the new turbocharger to ensure high reliability of the compressor and turbine from an HCF perspective.
Experimental Evaluation of Multi-rotor UAV Operation under Icing Conditions
Authors:   The Pennsylvania State University, Yan Sihong ,   Transport Canada, Germain Louis-David , Opazo Tomas , Palacios Jose , Langelaan Jack
Published: August 2024

Unmanned aerial vehicles (UAV) with multi-rotor configurations have become a popular platform for aerial surveillance and and are forecast for use in delivery of packages. During these missions, UAVs can be exposed to icing conditions. In this paper, two icing experiments on representative UAV configurations are discussed. The object of this paper is to investigate the effects of ice accretion on the operation of a UAV. The first experiment is to measure degradation in thrust and increase in power requirements of a co-axial rotor configuration in an icing wind tunnel. The second experimental set-up tested a commercial UAV (DJI Mavic Pro) in a forward flight regime in an artificial icing environment. These co-axial UAV rotors are controlled by two algorithms. The first algorithm keeps a constant rpm during 60 seconds in an icing cloud. The second algorithm maintains thrust until ice shed from rotors. In addition, a DJI Mavic Pro icing flight test was conducted inside an icing chamber. Both experiments demonstrate that ice accretion on UAV rotors can lead to an intimidating deficit in thrust and abrupt increase in power consumption that could result in catastrophic failure. When rpm is fixed, increase in power and decrease in thrust are linearly correlated with icing time. When thrust is constant, rpm and power could be modeled as a linear function of time before ice sheds. Power change rates under varying icing conditions were compared and discussed. In addition, ice shedding events were observed in the wind tunnel test. A shedding event could result in abrupt change in thrust and power affecting the capability of the motor control algorithm to operate. In the DJI icing flight test, motor current exceeded the current safety limit of the motor within 30 seconds of ice exposure. The motor coils heated during the ice accretion process melting the insulation on wires. The test confirmed the almost immediate damage to small UAV (under 50 Kg.) motors and batteries during icing process.
A Trajectory Generation Method for Time-Optimal Helicopter Shipboard Landing
Authors:   Rensselaer Polytechnic Institute, Zhao Di , Krishnamurthi Jayanth , Mishra Sandipan , Gandhi Farhan
Published: August 2024

In this paper, a time-optimal trajectory generation algorithm is proposed for helicopter shipboard landing. The algorithm utilizes a simplified model of the helicopter's dynamics and exploits the differential flatness of the model to formulate a nonlinear programming problem, whose solution provides time-optimal reference approach/landing trajectories. The trajectories are then tracked by an inner-loop linear dynamic inversion (LDI) controller to generate the actual inputs that steer the full-state nonlinear helicopter model. The proposed algorithm reduces approach/landing flight time and enables a higher degree of maneuverability in comparison to typical state of the art methods of trajectory generation. Because of its computational efficiency, the path planner can also be used in real-time, i.e., through iterative recalculation of the remaining trajectory to account for deviations from the planned flight path. High fidelity simulations have been conducted on a verified UH-60A Black Hawk model, which show the effectiveness of the proposed method.
A System for Autonomous Rotorcraft Dual-Lift Flight Research
Authors:   US Army Aviation Development Directorate AvMC, Takahashi Marc ,   NASA Ames Research Center, Schulein Gregory , Whalley Matthew , Berrios Marcos
Published: August 2024

A system for dual-lift research was developed and flight tested using two Yamaha RMAX helicopters equipped with customized avionics and sling-load hardware. Important features of the system were tested including precision dual-lift maneuvering, load tension equalization, and load motion damping. Result are presented from flight testing that include autonomous takeoff and landing, and oval racetrack pattern flying at 5 m/s carrying 171% of the rated maximum load for one aircraft. Results of formation changes while flying oval patterns are also presented as well as results on active control to equalize the sling tensions between the two aircraft. In addition, sling-load feedback results to increase the sling damping in hover are presented. Finally, the feasibility of migrating the concept to full-scale is shown in simulation using two UH-60 models in a dual-lift configuration carrying 6000 lbs at 80 kts.
LQR Gain Tuning for On-Demand Performance Using Reinforcement Learning
Authors:   U.S. Army Research Laboratory, Reddinger Jean-Paul
Published: August 2024

A reinforcement learning agent is trained to optimally scale the weighting matrices of a linear quadratic regulator for full state feedback control. Training is done using the model-free Deep Deterministic Policy Gradient on a dynamic simulation of the linearized model of an AeroQuad Cyclone ARF quadrotor. In the first task, the reinforcement learning agent is designed to produce an optimal control response for a step input of between 0 and 20 meters. The optimality target is randomly varied between incentivizing low power and incentivizing rapid settling times, and the agent is able to learn an optimal control policy from simulated experience. The second task applied the learning algorithm to an energy budgeting task. The mission consisted of a randomly selected number of repetitive tasks and a randomly initialized amount of available on-board energy. The agent learned to budget energy consumption to maximize the likelihood that the entire mission would be successful. Conversely, when sufficient energy was available it allows greater control effort from the controller.
System Identification of a Meso-Scale Twin-Cyclocopter in Hover
Authors:   Texas A&M University, Runco Carl , Benedict Moble
Published: August 2024

The paper discusses experimental system identification of a 29 gram twin cyclocopter, which is currently the world's smallest cycloidal rotor based aircraft. The twin cyclocopter uses two cycloidal rotors rotating in the same direction and a conventional tail rotor to overcome the reaction pitch torque. Miniaturizing the vehicle to the present size required overcoming significant technical barriers pertaining to vehicle deign, control and flight testing. This vehicle, being inherently unstable, utilized an on-board PD controller and demonstrated stable, hovering flight. A VICON motion capture system was used to collect attitude and position data for several maneuvers in hovering flight intended to excite the dynamic modes of the system. This data was used to extract a bare airframe linear time invariant flight dynamics model of the vehicle around the trim state, hover, using time-domain system identification techniques. From analyzing the structure of the model, it was inferred that the present micro-cyclocopter exhibits dynamic behaviors, which was not previously obsered on significantly larger twin-cyclocopters. Eigen-analysis of the model reveals that the states are highly coupled to one another. This is due to the lower inertia of the vehicle and the increased relative magnitude of the tail rotor angular momentum. It was also observed that the system is non-linear in several modes and that because of this and the coupled control inputs, the twin-cyclocopter has the potential to be very agile.
Load Distribution Control and Swing Angle Feedback for an Autonomous Dual Lift System with Flight Test Results
Authors:   U.S. Army Aviation Development Directorate, Berrios Marcos ,   San Jose State University, Cicolani Luigi ,   Stanford University, Powell J. , Takahashi Marc , Whalley Matthew , Schulein Gregory
Published: August 2024

Using two helicopters to carry a single load, termed dual lift, provides heavy lift on demand and avoids the very costly design and development of a special purpose heavy lift helicopter. The benefits of dual lift include increased lifting capability, increased range, and and the ability to fly at higher density altitudes, but are contingent on proper load distribution between the helicopters. This paper discusses the development and flight validation of a load distribution control concept to equalize the cable tension between the two helicopters in flight and a swing angle feedback controller that increases the damping of the load's swinging motion while in a hover. The load distribution controller allowed the dual lift system to maintain the RMS of the cable tension error to be less than 1.5% of the external payload weight when flying a racetrack pattern at 10 knots as compared to a RMS of 4.3% when no distribution control was active. In addition, the swing angle feedback controller increased the damping ratio of the external payload's swinging motion by more than 50% when compared to a dual lift system without augmentation.
Febrile Seizures: a narrative review of the current evidence
Authors: Abdullahi Abba Musa , Onimisi Abdulrahim Abdulrashid
Published: August 2024

Febrile Seizures (FS) are the most common childhood seizures that cause intense anxiety and fear in parents. However, it is a benign condition that does not generally cause brain damage. It mainly affects children aged three months to five years, with peak incidence at 18 months of age. To provide a clinical update on the epidemiology, clinical manifestations, diagnosis, evaluation, and management of children with febrile seizures, major databases comprising of PubMed, ScienceDirect, and Google Scholar were searched. The search contents were 'fever' AND 'convulsion', 'febrile seizure' AND 'clinical features', 'febrile seizure' AND 'management'. Both MeSH and regular keyword search strategies were used. Any form of study on FS was included and any study that was not in English or translated into English was excluded. The overall incidence of FS was estimated to be 460/100,000 in the age group of 0-4 years, the majority of which are simple, but approximately 30% will have some complex features. Although associated with a relatively moderate rate of recurrence, only a small minority of patients with FS will subsequently develop epilepsy. Many risk factors have been attributed to either the initial development or recurrence of FS, with some factors identified as risk for developing epilepsy, and these include positive family history, premature birth, developmental delay, brain disorders, and genetic mutations. Conventionally, FS are classified into simple and complex types, and they typically present with fever, body jerking, or twitching. The management basically involves abortion of the seizure event, control of the fever, airway management, and respiratory and circulatory support.
Leadership discourses in early childhood education during the COVID-19 pandemic in South Africa and Finland
Authors: Fonsen Elina , Ruohola Vivian , Modise Matshediso R. , Mampane Sharon T. , Phatudi Nkidi C. , Kupila Päivi , Liinamaa Tarja , Mohamed Elhassan Hana Awad
Published: August 2024

Background: This study explores the experiences of early childhood education (ECE) leaders during the coronavirus disease 2019 (COVID-19) pandemic, drawing insights from case studies in Finland and South Africa. Theoretical frameworks of contextual and pedagogical leadership inform the understanding of ECE leadership.Aim: The aim is to analyse and compare the experiences of ECE leaders in two diverse contexts, Finland and South Africa, during the pandemic.Setting: The study involves two case studies conducted in Finland and South Africa, focussing on the experiences of ECE leaders amid the COVID-19 pandemic.Methods: Discursive analysis of interviews was conducted to uncover the experiences of ECE leaders. The study compared the discourses from Finland and South Africa.Results: In Finland, the discourses revealed the persistence of pedagogical leadership’s importance, challenges to distributed pedagogical leadership and deepening difficulties in maintaining leadership quality. In South Africa, discourses included reconfigured pedagogical leadership, acceptance of new experiences driven by fear of uncertainty and changes in leadership practices and teachers’ roles. Despite national diversity, both cases emphasised the resilience of pedagogical aims.Conclusion: The study underscores the significance of pedagogical leadership in ECE, even in times of crisis. The contextual leadership model offers valuable insights into ECE leadership across diverse contexts, highlighting the need for adaptive leadership strategies.Contribution: This research contributes to understanding ECE leadership dynamics during the pandemic, providing insights into the challenges faced by leaders and the resilience of pedagogical goals across different national contexts. It also emphasises the importance of contextual leadership models in developing effective leadership practices in ECE.
Dynamics of glutamine synthetase expression in hepatic ischemia-reperfusion injury: Implications for therapeutic interventions
Authors: Huang Zhi-Hao , Dong Meng-Qi , Liu Feng-Yong , Zhou Wei-Jie
Published: August 2024

BACKGROUND

Hepatic ischemia-reperfusion injury (IRI) poses a great challenge in liver surgery and transplantation because of oxidative stress and inflammatory responses. The changes in glutamine synthetase (GS) expression during hepatic IRI remain unclear.

AIM

To investigate the dynamic expression of GS during hepatic IRI.

METHODS

Following hepatic ischemia for 1 h and reperfusion, liver tissue samples were collected at 0.5, 6, and 24 hours postreperfusion for fixation, embedding, sectioning. Hematoxylin and eosin staining and GS staining were performed.

RESULTS

GS expression rapidly decreases in hepatocytes around the central vein after IRI, reaching its lowest point at 6 hours postreperfusion, and then gradually recovers.

CONCLUSION

GS is highly sensitive to IRI, highlighting its potential role as an indicator of liver injury states and a target for therapeutic intervention.