bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytic Tool Correlation Status for the Joint Multi-Role Technology Demonstrator Program
Authors:   Sikorsky a Lockheed Martin Company, Tuozzo Nick ,   The Boeing Company, Fox Eric , Eller Erez , Mayrides Bryan , Lorber Peter , Zientek Thomas , Narducci Robert , Sproul Taylor
Published: September 2024

The fundamental objectives of the Joint Multi-Role Technology Demonstrator (JMR TD) Air Vehicle Development program are to mature critical technologies as well as analysis tools for Future Vertical Lift (FVL). This paper summarizes the current status of analytic tool correlation performed by the Sikorsky and Boeing JMR Team. The toolset spans the disciplines of aerodynamic performance and external acoustics, dynamics and stability, handling qualities, and loads. The validation database currently includes XH-59A flight test, X2 TECHNOLOGY™ Demonstrator flight test, S-97 RAIDER® wind tunnel tests, and SB>1 DEFIANT™ Aircraft wind tunnel tests. Future planned work is discussed including additional correlation against Powered System Test Bed (PSTB), SB>1 DEFIANT™ Aircraft flight test, and S-97 RAIDER® flight test. The maturity of the toolset at the completion of the program will be sufficient for accurate predictions of X2® architecture aircraft capabilities that meet or exceed the requirements of the FVL Capability Set 3 (CS3) class.
Coupled CFD/CSD Study of a Flexible MAV-Scale Flapping Wing in the Hover Flight Condition
Authors:   University of Maryland, Lankford James , Chopra Inderjit
Published: September 2024

Instantaneous lift force and structural deformation experiments were performed on a flexible, structurally characterized, low-aspect ratio wing modeled after the wing of a hovering flapping micro air vehicle (FMAV). A six-component force balance was used to measure the variation in lift produced by the wing over the course of a flap cycle. A VICON motion capture setup tracked the passive wing deformations at select locations of the wing during experimentation. Measured lift force and wing deflections were compared against the results of a coupled computational fluid dynamics/computational structural dynamics (CFD/CSD) aeroelastic analysis. The CFD analysis was developed based on an unsteady Reynolds-averaged Navier–Stokes (URANS) solver while the CSD analysis consisted of a general purpose multibody dynamics solver capable of modeling geometrically nonlinear beam and shell elements. The CFD/CSD results were able to capture the overall trend in lift force variation and wing deformation, but the magnitude of variations were under-predicted by the coupled aeroelastic solver. The coupled CFD/CSD solver was used to evaluate the influence of increased wing flexibility on the aerodynamic forces, vortical flowfield and wing deformation. Results showed that decreasing wing stiffness increased the time-averaged aerodynamic lift with minimal effect on aerodynamic drag and prolonged the sustainment of the leading edge vortex.
Gear Repair for Helicopters and Wind Turbines via Isotropic Superfinishing
Authors:   REM Research Group, Cline Vincent ,   REM Surface Engineering, Michaud Justin , Winkelmann Lane
Published: September 2024

The wind turbine, aerospace, and helicopter gear industries recognize the importance of surface finish and surface texture for maximizing component and system performance. Optimizing surface finish and surface texture has been shown to reduce failure rates and increase operating safety margins. Isotropic superfinishing in the form of chemically accelerated vibratory finishing has been utilized to increase the performance of new wind turbine, aerospace, and helicopter gears for many years. The wind turbine gearbox industry has also used isotropic superfinishing as a method of repairing damaged gears for over a decade. The aerospace and helicopter gear industries have only minimally employed this technology as a repair technique. As the aerospace and helicopter industries scrap many gears due to only minor surface damage, further consideration of isotropic superfinishing as a repair tool is warranted. This paper will summarize the technical capabilities, recent advancements, and economic benefits of using isotropic superfinishing to repair wind turbine, aerospace, and helicopter gears. With this information, the aerospace and helicopter gear industries will be better positioned to evaluate isotropic superfinishing's potential to recover otherwise scrap gears and thereby reduce sustainment costs.
Hybrid Gear Performance Under Loss-of-Lubrication Conditions
Authors:   US Army Research Laboratory, LaBerge Kelsen ,   NASA Glenn Research Center, Handschuh Robert , Berkebile Stephen , Roberts Gary
Published: September 2024

Hybrid composite gear technology is being investigated to increase power density in rotorcraft drive systems. These gears differ from conventional steel gears in that the structural web material is replaced with a lightweight carbon fiber composite. Past studies have focused on performance of this technology under normal operating conditions, however, for this technology to be viable it must also withstand adverse conditions. The study presented here evaluates the performance of hybrid gears under loss-of-lubrication conditions in NASA Glenn Research Center’s Contact Fatigue Test Facility. Two experiments are presented using small-scale 3.5 inch (8.9 cm) pitch diameter hybrid gears and compared to a baseline steel gear pair. Results of these tests show that there are limitations to the use of a hexagonal interlock pattern between the steel and composite. There is also evidence that the presence of polymer in the gear during an oil out event has a potential to increase time to failure. Further studies are planned to expand on these initial findings.
Computational Investigation and Design Study of Adaptive Axial-Flow Turbomachinery Rotor Blade
Authors:   US Army Research Laboratory - Vehicle Technology Directorate, Murugan Muthuvel ,   Iowa State University, Xu Fei ,   University of California San Diego, Bazilevs Yuri ,   US Army ADD AMRDEC, Kerner Kevin , Ghoshal Anindya , Bravo Luis , Hsu Ming-Chen
Published: September 2024

Gas turbine blades of conventional rotorcraft engines are generally optimized to operate at nearly a fixed speed with fixed blade geometries for the design operating condition. When the operating condition of the engine changes, then the flow in the compressor or turbine may need to be guided to more optimum direction. Articulating the pitch angle of turbine blades in coordination with adjustable nozzle vanes can improve performance by maintaining flow incidence angles within the optimum range at all operating conditions of a gas turbine engine. Maintaining flow incidence angles within the optimum range can prevent the likelihood of flow separation in the blade passage and also reduce the thermal stresses developed due to aerothermal loads for variable speed gas turbine engine applications. U.S. Army Research Laboratory has partnered with University of California San Diego and Iowa State University Collaborators to conduct high fidelity stator-rotor interaction analysis for evaluating the aerodynamic efficiency benefits of articulating axial flow turbine blade concept. In addition, a design study for articulating turbine or compressor rotor blade using smart material based actuators using Shape Memory Alloy (SMA) has been carried out. In this paper, the computational flow patterns are compared between the baseline fixed geometry blades and articulating conceptual blades. The computational fluid dynamics studies were performed using a stabilized finite element method developed by the Iowa State University and University of California San Diego researchers, and using a commercial software, CONVERGE for comparison. The results from the simulations together with a design study using SMA actuator for articulating both stator and rotor blades synchronously for axial flow turbomachinery are presented in this paper.
Hybrid Ceramic Bearing Fatigue Testing for the Future Advanced Rotorcraft Drive System Program
Authors:   Bell Helicopter Textron, Anderson Cody ,   CEROBEAR GmbH, Ponten Lars ,   US Army ADD, Fetty Jason , Kiamanesh Roozbeh , Baker Treven
Published: September 2024

Today's rotorcraft transmissions predominately utilize fully metallic bearings where both the raceways and rolling elements are metal. Ceramic bearing materials offer the potential for meeting the demand for weight reduction and increased power-to-weight ratios. Hybrid ceramic bearings incorporate both ceramic and metallic components forming an assembly that lends itself to improvements in weight, corrosion resistance, reduced friction, and improved surface characteristics. Typically, hybrid ceramic bearings consist of ceramic rolling elements and metallic raceways. Hybrid ceramic bearings have demonstrated feasibility for both remotely and non-remotely monitored applications in rotorcraft drive systems. Characterization of potential material combinations of hybrid ceramic bearings is needed to guide the design of hybrid ceramic bearings for use in future and modified rotorcraft transmissions. This research, conducted under the Future Advanced Rotorcraft Drive System (FARDS) program, examined multiple bearing material combinations and characterized them in fatigue testing. Hybrid ceramic bearing material combinations showed increased performance when compared to fully metallic bearing material combinations. Favorable results indicate that hybrid ceramic bearings can have immediate impact on rotorcraft transmission designs.
Epidemiology of Helicopter Accidents: Inspection Blind Spots, Geographic Disparities, and Pilot Demographics
Authors:   Georgia Institute of Technology, Zhang Katherine , Churchwell Jared , Saleh Joseph
Published: September 2024

The objective of this work and its companion article is to provide a better understanding of helicopter accidents and to identify areas that deserve careful attention for improving safety and accident prevention. Three broad questions were here investigated: (1) whether there are safety blind spots in helicopter inspections and any association between inspection time and accidents? (2) whether there are geographic disparities in helicopter accident rates in the U.S. at the regional and state level? And (3) whether there is any association between pilot age and flight experience, and helicopter accident rates? Record Linkage of two Federal data sources, the FAA civil helicopter registration data and the NTSB accident data, enabled the investigation of these and other questions. The main results included the following. First, it was found that there is a clear and significant association between the time of inspection and the accident occurrence, with 10% of all accidents occurring within 4 flight hours of an inspection (all types of inspections). Second, it was found that there are clear and statistically significant geographic disparities in helicopter accident rates in the U. S., both at the regional and state level. Some of the worst-in-class states (e.g., Arkansas, Utah, West Virginia) have helicopter accident rates that are an order of magnitude higher than the best-in-class (e.g., Vermont, Connecticut). Third, it was found that the likelihood of a helicopter pilot to be in an accident is independent of his or her age. Possible confounders were discussed, and hypotheses were proposed as well as recommendations for the FAA and other stakeholders. The end-objective of these recommendations is to improve the safety track record of helicopters, to advance accident prevention, and to reduce their burden of injury, death, and financial losses.
Analysis and Test of Composite Rotorcraft Structure Subject to Ballistic Events
Authors:   The Boeing Company, Andrews Clark ,   US Army ADD, Robeson Mark , Chiu Lisa
Published: September 2024

Predictive analysis is performed on configurations representative of small-volume rotorcraft primary structure. Potential failure points are identified and the design is modified to withstand the incoming ballistic event. Live fire testing is then executed on multiple specimens to validate the analysis method developed in the previous study. Predictive strength analysis is then performed to determine potential residual strength. Finally, cyclic and static residual strength testing is performed on two specimens. The results demonstrate that small-volume aircraft structure can be designed with composite sandwich structures to mitigate ballistic events that are often catastrophic for traditional aircraft structures.
The Most Recent Rules on Fatigue and Damage Tolerance - Application and Challenges at Airbus Helicopters
Authors:   Airbus Helicopters, Emmerling Stefan , Ahci-Ezgi Elif , Besson Jean-Marc
Published: September 2024

This paper shows the history and background of the motivation for the recently modified rules concerning the evaluation of fatigue and damage tolerance of metallic and composite structures. The most significant modifications which were made compared to the previous ones are discussed, specifically the split into two paragraphs for metallic and composite structure and the change towards performance based regulations. Examples to demonstrate the application on Airbus Helicopters products are the H145 Fenestron™ hub and blade and the H160 main rotor hub plate.
For the metallic parts of the Fenestron™ hub a substantiation according to the flaw tolerant fatigue evaluation requirements of the FAR 29.571 was chosen. The thermoset carbon composite blade of the H145 Fenestron™ as the second example illustrates the application of the newly introduced composite requirements. Finally the thermoplastic carbon composite main rotor hub plate for the H160 is presented as a new technology in the first case of full applicability of the new rules to complete new helicopter model.
Probabilistic Structural Integrity Framework for Composite Damage Tolerance
Authors:   Sikorsky Aircraft, Weintraub Alexander ,   United Technologies, Gurvich Mark ,   US Army ADD-AATD, Bordick Nathaniel , Furnes Kenneth , Bates Preston , Kiser Jay
Published: September 2024

Airframes in the future will include a significant amount of composite material components that need to be designed for both optimal structural efficiency and damage tolerance. Current composite design methodology relies on the establishment of worst-case scenarios for each of the factors that influence the structural capacity and life of airframe components. The layered application of these factors can result in excessive levels of conservatism and maintenance requirements that reduce aircraft availability. The combat aircraft of the future can be designed and maintained based on specific knowledge derived from data driven methodologies to define risk, threat impact, and measured structural response in order to maximize aircraft availability, while ensuring safety and reliability. This work describes an Advanced Structural Integrity Framework (ASIF) that probabilistically models composite residual strength. Full-scale damage tolerance tests of a UH-60M stabilator provided input data for various threat types and severities. Threat probabilities were derived from prior studies and recent fleet repair data. The model estimated the risk of failure in various structural zones to identify areas for reducing conservatism. Trend studies confirmed that the model appropriately responded to changes in composite material properties and threat exposures, thus showing its potential as a powerful structural risk assessment tool for design and fleet management.
Progressive Fatigue Damage Simulation in Composites based on Explicit Finite Element Formulation
Authors:   University of Texas at Arlington, Nikishkov Yuri , Seon Guillaume , Makeev Andrew , Nguyen Dean
Published: September 2024

Advanced polymeric composites are playing a major role in designing high-performance and lightweight vertical lift structures. However, uncertain residual strength and remaining useful life of the composite rotor and airframe structures due to complexity of failure mechanisms and susceptibility to manufacturing irregularities, which may be precursors to structural damage, impose risks that cannot be mitigated exclusively by time-consuming and costly experimental iterations. Validated analysis techniques accelerating design, certification, and qualification of composite structures are needed. Our team has been taking essential steps towards improving confidence in material qualification for laminated composites. The first step started with our reduced lamina test methods, short-beam shear and small-plate twist based on Digital Image Correlation measuring as a subset the standard material properties; and, in addition, key properties that cannot be currently measured using any standard test methods. The laminate analysis has been the second step increasing confidence in material qualification. A known weakness of the existing progressive damage analysis methods is the lack of effective techniques to predict ultimate failure. The newly developed methodology relies on Explicit finite element modelling and eliminates convergence issues due to severe non-linear discontinuities after propagation of damage beyond detectable size. This work shows preliminary results of applying this methodology to nanosilica-toughened IM7/PMT-F3GHT Open-Hole Tension strength/fatigue, Open-Hole Compression strength/fatigue, and bearing strength multidirectional laminate configurations. The ability to predict ultimate strength and fatigue for advanced material systems including IM7/PMT-F3GHT carbon/epoxy reinforced by nanosilica has been demonstrated for the first time.
Using Wind Tunnel Tests to Investigate Dual Lift Trim, Maneuvers, Stability and Control
Authors:   Technion - Israel Institute of Technology, Raz Reuben ,   US Army ADD, Berrios Marcos ,   San Jose State University Research Foundation, Cicolani Luigi , Fogel Omer , Rosen Aviv
Published: September 2024

The paper presents results of wind tunnel tests of a pendant dual lift system. A rig has been designed and built to represent the helicopter hooks and the suspension and load below the hooks. Four of the six degrees of freedom of movement of the hooks are modeled and the hooks are operated by open or closed loop control systems. At first quasi-steady maneuvering is studied. A special analytic model is derived and then used to study a typical maneuver and system sensitivities to servo inputs and drag estimation errors. A good agreement is shown between analytic and test results. Then a nonlinear simulation model is validated via comparisons of its results and test results for various frequency sweeps. The validated model is used to design an equal load distribution control system that is implemented in the wind tunnel test system. Wind tunnel tests show the capability of this control system to reduce significantly load differences during maneuvers.
Experimental Investigation of Dynamic Stall on the SC1094R8 Airfoil and Comparison with Computational Predictions
Authors:   University of Wyoming, Nikoueeyan Pourya ,   Combustion Research and Flow Technology Inc., Ahuja Vineet ,   US Army ADD - AMRDEC, Potsdam Mark , Harms Tanner , Naughton Jonathan , Fabiano Enrico
Published: September 2024

Rotor blade aerodynamics are significantly influenced by dynamic stall. The objective of this study is to use a combined experimental/ computational approach toward better understanding of the dynamic stall phenomenon on the SC1094R8 airfoil. This study is part of a larger effort to alleviate the adverse effects of dynamic stall on rotor blade aerodynamics through airfoil shape optimization. In order to accomplish this goal, time-accurate surface pressure measurements along with lift and moment coefficients are gathered experimentally. Boundary layer tripping is performed to ensure behavior similar to that of the airfoil at larger Reynolds numbers. Sensitivity of dynamic stall under different flow conditions is also studied. Numerical simulations have been performed for similar flow conditions and compared with the experimental results. The result have aided in clarifying the sensitivity of dynamic stall as well as providing encouraging indications of the ability of the simulations to capture the important features associated with dynamic stall.
Quantification of Swirl Recovery in a Coaxial Rotor System
Authors:   The University of Texas at Austin, Uehara Daiju , Sirohi Jayant
Published: September 2024

Experiments were performed in hover on a 2 m diameter, isolated single rotor system, a coaxial counter-rotating rotor (CCR) system, and coaxial co-rotating (stacked) rotor system to quantitatively extract the swirl recovery of a CCR system. The performance comparison was based on induced power factors obtained from curve fits to momentum theory. The three systems were tested up to a CT =σ of 0.1 and tip Mach number was maintained around 0.4 for all experiments. The azimuth spacing between the upper and lower blades, defined as the index angle, was varied in the stacked rotor system. Measurements revealed that the stacked rotor performance was highly dependent on the index angle. When the lower rotor trails the upper rotor by index angle of 10°, there was a 4% performance gain on the stacked rotor, compared to the CCR rotor. Examining and isolating the effect of index angle on the performance of the stacked rotor, the swirl recovery in the CCR rotor was measured to be nearly 4%. Vibratory loads induced by the aerodynamic interaction between two rotors were also investigated.
Development of a Helicopter Sling Load Unmanned Hookup Device
Authors:   US Army Natick Soldier Research Development Engineering Center, Connolly Kevin , Tardiff Marc , Matook George
Published: September 2024

Helicopter Sling Load (HSL) missions pose significant safety risks to the ground personnel involved with hooking up payloads to the helicopter. The goal of this project is to develop a materiel solution to increase the safety of an HSL hookup team by eliminating the personnel subjected to the hazards of the HSL mission. The research reviewed in this paper discusses two concepts that were evaluated for HSL auto hookup capabilities: a grapple hook design with three spring articulating arms and a system that used a cone on cone design. For this project, flight evaluations were conducted on prototypes of the two concepts with the following Army helicopters: LUH-72 Lakota, UH-60 Blackhawk, and CH-47 Chinook. There are two modes of HSL that were looked at for this project: single point sling load and dual point sling loads.
Assessment of Processes and Risks Associated with Extension of Inspection Intervals
Authors:   Starmark Corporation, Green David ,   ACR Inc., Chin Harrison ,   HeliHealth LLC, Barnett Richard
Published: September 2024

This paper addresses processes and findings developed as the result of a program conducted by a Gulf of Mexico (GOM) helicopter Operator involving 14 S-76C+/++ (S-76C) helicopters in a three-year demonstration of operations supporting Oil and Gas Producers. These processes and findings are in many ways applicable to both civil and military helicopters since all civil and military OEMs use a Composite Worst Case (CWC) Usage as a key element of the algorithm for power train design and the establishment of initial power train inspection intervals. The current ability to record and process usage data during flight can allow the industry to develop inspection intervals based upon the actual usage data recorded on each helicopter in an operator's fleet. This allows the Operator to reduce the cost of operations without any degradation in flight safety or operational availability.
Integrated Discrete-Event Simulation Environment for Analysis of Rotorcraft Reliability, Availability, and Maintainability
Authors:   Georgia Institute of Technology, Price Joshua , Ashok Sylvester , Armstrong Ryan , Collins Kyle , Mavris Dimitri , Schrage Daniel
Published: September 2024

Operations and support cost constitutes nearly 70% of rotorcraft lifecycle cost. When considering new rotorcraft concepts and technology infusion for current concepts, quantitative performance evaluation is undertaken during conceptual design. However, the effect of design decisions on operations and support metrics are typically evaluated qualitatively. Since operation and support costs constitute an overwhelming majority of rotorcraft lifecycle cost, quantitative evaluation of these metrics is required to fully capture the design trade space. To this end, an integrated discrete-event simulation environment is developed to quantify the impact of architectural decisions and subsystem technology infusion on key metrics including the operational availability, system mean time between failures, Maintenance Free Operating Period, repair cost, and maintenance man-hours needed for a given period of operation. Since data needs are immense, it is appropriate to use data from existing platforms to populate unknown fields. An example is presented in this paper for a notional helicopter to demonstrate the use of the discrete-event simulation environment as a tradeoff environment for operations and supportability metrics.
A Conceptual Framework Leading to Different Dynamic Systems Architectures
Authors:   Airbus Helicopters, Hartmann Chris ,   Ecole Centrale de Nantes, Chenouard Raphael , Mermoz Emmanuel , Bernard Alain
Published: September 2024

The main objective of the work presented is to help architects to develop solutions based on unconventional approaches and to do so, a conceptual framework is presented. The whole framework starts from the requirements and the use cases capture and the Architectural Object database construction. Then it continues with an architectural automated synthesis. The framework uses concepts taken from the System Engineering field and the graph theory and can be applied to several system to design of different domains. The helicopter dynamic systems are multi-domain and totally encounter the scope of the framework.
Advances and Applications in Comprehensive Gearbox Aero-Thermodynamics and Tribology Simulation
Authors:   The Pennsylvania State University, McIntyre Sean , Kunz Robert
Published: September 2024

The current status of an ongoing effort to develop a comprehensive gearbox aero-thermodynamics and tribology simulation tool, named PSULOL, applicable to both well-lubricated and loss-of-lubrication operation is presented. PSULOL employs a multi-scale approach, wherein various physical effects including: meshing tribology, convection heat transfer within the system and to the environment, high-frequency thermodynamic effects induced by the gear meshing frequency, and the long-time response of the overall gearbox temperature to a net imbalance of heat generation and transfer to the environment are simulated separately and coupled with one another iteratively through appropriate boundary and initial conditions. As established in 2014, the first-generation version of PSULOL was the first computational fluid dynamics-based (CFD-based) tool coupled with an all-lubrication regime tribology model capable of simulating transient loss-of-lubrication failure of high-speed gearboxes. This first version was built on an in-house research CFD code, NPHASE-PSU, and relied on a number of physical simplifications, particularly with regard to the geometric configuration of the housing, and to the effects of the coupling between multiphase flow within the system (retained lubricant dynamics) and meshing tribology. Here, present efforts underway to increase the physical fidelity and ease-of-use of PSULOL are outlined, and progress toward simulating physically-realistic gearbox configurations is shown. This includes modeling the disperse multiphase flow of lubricant droplets and film within the system, and transitioning from NPHASE-PSU, an in-house research CFD code, to StarCCM+, a commercial code that is more user-friendly and features additional geometry-handling capabilities.
Evaluation of Aircrew Noise Exposure and Hearing Protection Solutions in CH-147F Chinook Helicopter Cabin
Authors:   National Research Council Canada, Chen Yong , Ghinet Sebastian , Price Andrew , Wickramasinghe Viresh , Grewal Anant
Published: September 2024

High noise levels in the helicopter cabin affect aircrew communication and reduce aircrew comfort, and may lead to hearing loss in the long-term if flight helmets cannot provide sufficient protection to the aircrew, or are improperly fitted. A cabin noise exposure survey has been performed on a Royal Canadian Air Force (RCAF) CH-147F Chinook heavy lift helicopter to evaluate the noise environment. The insertion loss performance of the flight helmet was characterized in a reverberant acoustic chamber facility. Investigation results showed that the low frequency noise attenuation provided by the RCAF flight helmet was marginal at high speed flight conditions in which significant cabin noise levels existed in the helicopter cabin. To enhance the low frequency hearing protection performance and clarity in voice communication, in-canal Communication Ear Plugs (CEPs) integrated with active noise cancellation (ANC) capability was investigated. Simulation and proof-of-concept test results demonstrated that the ANC in-canal CEPs can serve as a feasible technical solution to provide enhanced noise attenuation to mitigate the low frequency N/rev tonal noise generated by the aerodynamic pressure from the helicopter rotor blades.
Mechanism Analyses on Aeroacoustic Characteristics of Iced Rotor for Ice Detection
Authors:   Nanjing University of Aeronautics and Astronautics, Xi Chen , Qi-Jun Zhao , Yi-Yang Ma , Bo Wang
Published: September 2024

Based on mechanism analyses on aeroacoustic characteristics of iced rotors, a new icing detection method is proposed, and a corresponding numerical method for calculating aeroacoustic characteristics of iced rotors is developed. Firstly, the CFD simulation method for 3-D flowfield around the blade is established by solving the unsteady RANS equations. Using the Eulerian approach, the conservation equations of mass and momentum are solved to obtain the droplet flowfield properties. Then, combined with the characters of rotor blade motion, a 3-D icing model considering influences of centrifugal force, the movement of water film and azimuthal angle variations is put forward. On this basis, the acoustic characteristics of iced rotor are calculated by the Ffowcs Williams-Hawkings equations with penetrable data surface in time domain, and the sensitivity of the acoustic characteristics to the ice accretion on rotor is analyzed. The calculated results are validated through the ice amount comparisons with experimental results of SRB rotor model and the sound pressure comparisons with experimental results of AH-1G/OLS model rotor in forward flight. Additionally, the influences of ice parameters on aeroacoustic characteristics of rotor are calculated, such as the ice accretion time and the icing position on blade. At last, some monitor locations compromising between sensitivity and enablement are found, and some new conclusions are obtained. The tiny ice amount on rotor can make the aeroacoustic characteristics change a lot, for instance, the ice with only 1.2% of blade volume makes the sound pressure decrease by 15% at the 255° azimuthal angle. The icing position can be identified through the variations of sound pressure at different monitor points.
A Permeable Self-adaptive Integration Surface for HSI Noise Prediction of Helicopter Rotor in Forward Flight
Authors:   Nanjing University of Aeronautics and Astronautics, Si-Yu Chen , Qi-Jun Zhao , Zheng Zhu , Yi-Yang Ma
Published: September 2024

In this paper, a new permeable self-adaptive integration surface is developed for the prediction of rotor HSI noise by KFWH method in forward flight. Firstly, the nonlinear near flowfield solution is computed by a N-S solver and as input for acoustic calculations by KFWH formula. Then, the acoustic pressure predictions of the AH-1 model rotor with cylinder-shaped integration surfaces at different locations are shown, which reveals that the results calculated by KFWH method show a large sensitivity to the location of integration surface. In order to avoid the calculation error caused by the uncertainties in determining the cylinder-shaped integration surface, a new permeable self-adaptive integration surface is determined by density adaptively according to some principles. These principles have been validated in hover flight in previous paper. Then, the acoustic pressure of AH-1 model rotor at different tip Mach numbers and different observer locations are simulated. In comparison with cylinder-shaped integration surface, the self-adaptive integration surface, which is determined by density, can reach higher accuracy in the prediction of rotor HSI noise.
Cheeseman Award Paper: Bluecopter Demonstrator: The State-of-the-Art in Low Noise Design
Authors:   Airbus Helicopters, Schneider Sascha , Heger Rainer , Konstanzer Peter
Published: September 2024

The present paper intents to present the state-of-the-art in current rotorcraft noise reduction technologies using the example of the innovative BLUECOPTER™ demonstrator (Figure 1). All described noise reduction features, notably the active rudder and the Fenestron® noise measures such as the advanced rotor blades, the evolved stator design and the innovative Fenestron® lining concept, contribute to the challenging and ambitious objective of reducing the noise emission of the rotorcraft directly at the source in a wide range of operationally relevant flight states. The paper incorporates results from the latest BLUECOPTER™ acoustic flight test campaign in final configuration and demonstrates the exceptional low noise signature of the BLUECOPTER™ demonstrator in various flight conditions.
Advancement of the SNUF Blade Design through Flap Configuration Parametric Study and Optimization Framework
Authors:   Seoul National University, Eun WonJong ,   Korea Aerospace Industries, Sim JiSoo , Lee SangWoo , Shin SangJoon
Published: September 2024

This paper focused on improving a small-scaled prototype of a helicopter rotor blade with a flap-driving mechanism termed as the Seoul National University Flap (SNUF). The design of SNUF included realizing vibratory load reduction. First, a multibody structural dynamics analysis was performed to determine the influence of the flap dimension and location within the rotor blade with respect to hub vibratory load reduction. This process selected a specific blade configuration that maximized vibration reduction capability. Then, a numerical optimization technique was applied to improve the cross-sectional design of the SNUF blade. The design optimization procedure established improved blade sectional design with desired first torsional frequency and reduced blade weight while satisfying sufficient structural integrity. Three-dimensional nonlinear static structural analysis was also performed for the optimized SNUF design. Von Mises stress distribution on the blade and components were predicted by considering external aerodynamic loads, centrifugal loads due to rotation, and contact among the internal components. Future studies will include fabricating the prototype blade based on the optimized design and performing a whirl tower test.
Experimental Evaluation of a Quadrotor Biplane with Variable Pitch Rotors
Authors:   University of Maryland, Phillips Brandyn , Hrishikeshavan Vikram , Yeo Derrick , Chopra Inderjit
Published: September 2024

Vertical Takeoff and Landing (VTOL) capable air vehicles such as quadcopters are being chosen for missions requiring higher payload capacities, longer endurance in hover, longer range, and most importantly faster travel time. To meet this need, hybrid air vehicles that incorporate the design features of fixed wing vehicles and rotorcraft have come to the forefront. One such hybrid vehicle, the quadrotor biplane, is being explored especially for package delivery capability. This vehicle configuration has four proprotors beneath which two wings are placed in a biplane configuration parallel to the rotor shafts. For control of the vehicle in both hover and forward flight mode a conventional quadrotor control methodology is utilized. The quadrotor biplane takes flight in tail-sitter configuration and uses differential thrust vectors to pitch forward into forward flight configuration. This control method takes the place of conventional control surfaces, therefor the system is more mechanically simple. The vehicle design and package delivery functionality have been validated experimentally, in both hover and forward flight. An experimental investigation of a variable pitch proprotor in a wind tunnel revealed large gains in efficiency at higher airspeeds. Furthermore, a relationship between free stream velocity and pitch angle required for lowest power consumption was determined. As such, a test vehicle incorporating a variable pitch mechanism on each rotor was devised. The vehicle has a gross takeoff weight (GTOW) of 2.86 kg (6.31 lbs). Each variable pitch mechanism’s independent actuation was verified using VICON motion capture cameras. To control the vehicle, three different flight control modes were devised. The first mode holds the servo position and varies the motor RPM, and is the typical control used for quadrotors. The second mode is the opposite of the first, holding RPM constant and varying each proprotor's blade pitch. This mode was tested on a commercial quadcopter with fixed RPM and independent blade pitch control. Finally, the third mode is a novel combination of differential RPM and variable pitch. The response of each mode was validated in hover testing.
Botulinum toxin-A in acute acquired comitant esotropia during COVID pandemic in children and young adolescents
Authors: Pawar Neelam , Shyam Praveena , Ravindran Meenakshi , Allapitchai Fathima
Published: September 2024

Purpose:

To study the effectiveness of botulinum toxin A (BTX-A) in the treatment of patients with acute acquired comitant esotropia (AACE) due to excessive use of mobile and laptops in the COVID era in the pediatric population and adolescents.

Methods:

This was a retrospective, interventional study of pediatric patients and young adults who presented with AACE and received unilateral or bilateral BTX-A. All the patients complained of binocular diplopia and sudden onset of esotropia with a history of mobile or laptop usage during the COVID era (2020–2023). Twenty-seven patients with acute-onset esotropia in 3 years (2020–2023) were included. All patients were administered 2.5–7.5 units of BTX-A (Botox, Allergan, India) into the unilateral or bilateral medial rectus muscle of the deviating eye under short general anesthesia or local anesthesia. The main outcome measures were pre- and post-injection angle of deviation, pre- and post-injection stereopsis, final level of stereopsis achieved, recurrence, and whether strabismus surgery was later required.

Results:

The mean age of patients was 12.85 ± 7.15 years (range: 4–25 years). The mean dosage of Botox was 6 U (2.5–7.5 U). The mean follow-up was 6 months (6 months–2 years). The mean preoperative angle of deviation (AOD) was 41.11 ± 10.9 prism diopters (PD) for distance and 41.67 ± 10.9 PD for near. The maximum effect of BTX-A was seen at 1 month; post-injection AOD was 13.65 ± 14.7 PD for distance and 14.87 ± 15.8 PD for near (P < 0.001). Over half of the patients achieved optimal outcomes, with improvements in stereopsis and sensory fusion. Early intervention (within 3 months of symptom onset) significantly correlated with treatment success.

Conclusion:

While BTX-A therapy for acute-onset esotropia demonstrates efficacy, patient-specific considerations are essential. This study highlights the evolving nature in the digital age and early administration of BTX-A along with close follow-up to monitor residual and recurrence of esotropia. The surgical intervention can increase the final success rate.
Incidence, etiology, and risk factors for tube explantation in patients undergoing patch-free glaucoma drainage device
Authors: Senthilkumar Vijayalakshmi A , Akbar Umme Salma , Rajendrababu Sharmila
Published: September 2024

Purpose:

To report the incidence, etiology, and risk factors for tube explantation in patients undergoing patch-free glaucoma drainage device (GDD).

Methods:

Of the total 1303 patients who underwent patch-free GDD (703 non-valved GDD and 600 valved GDD) for refractory glaucoma during January 2020–October 2023, we identified five cases of postoperative complications following GDD that required tube or shunt removal.

Results:

Median (IQR) age of our study cohorts was 54.5 (8–66) years. The incidence of tube exposure and tube explantation was 0.003% and 0.004%, respectively. The median time interval for tube or plate explantation from the time of GDD surgery was 11.5 (2–16) months. The diagnoses of refractory glaucoma for which GDD was performed were secondary glaucoma following multiple vitreoretinal (VR) surgery (60%), primary open-angle glaucoma (20%), and aphakic glaucoma (20%). Of these, two patients (40%) presented with recurrent tube exposures, two patients (40%) with tube exposure and early endophthalmitis, and one patient (20%) with persistent hypotony. Four patients (80%) had undergone non-valved Aurolab aqueous drainage implant and one underwent (20%) Ahmed glaucoma implant. Three patients (60%) had diabetes mellitus with a history of multiple VR surgical intervention. GDD explantation was done in three patients (60%), and the remaining two patients (40%) required only tube amputation. One patient presented with orbital cellulitis, and there was no culture growth seen in any of our study cohorts.

Conclusion:

Tube and plate exposures pose a significant risk for potential infections and warrant prompt explantation of GDD to avoid endophthalmitis. Previous history of multiple VR surgeries, diabetes mellitus, and non-valved implants were the common risk associations noted for tube exposures in our retrospective study.
Towards an Analytical Method for a Combined Energy Management and Shift Strategy in Hybrid Electric Vehicles, and Its Rule-Based Implementation
Authors: Ehrenberg Bastian , Engbroks Lukas , Schmiedler Stefan , Hofmann Peter
Published: September 2024

In conventional vehicles the shift strategy has a well-known impact on the system’s efficiency. An appropriate gear choice allows the internal combustion engine (ICE) to operate in efficient operating points (OPs) and thus contributes significantly to a reduced fuel consumption. Further efficiency improvements can be achieved by the hybridization of the powertrain. Due to the two propulsion systems, an additional degree of freedom arises, that requires an energy management strategy (EMS). The EMS controls the split of the requested power between the electric machine (EM) and the ICE. Accordingly, the system’s overall efficiency in hybrid electric vehicles (HEVs) is highly influenced by the quality of the EMS. This paper proposes to adapt an existing method for deriving fuel-optimal rule-based EMS by including the shift strategy for parallel HEVs. It is shown that fuel-optimal control can be achieved. The analytically derived look-up tables can be used to automatically calibrate in-vehicle EMS and the shift strategy for HEVs. The fuel-optimal shift strategy is characterized by high shift frequency, which hinders a straightforward in-vehicle integration. To further pave the way towards in-vehicle implementation, hysteresis based on energetic characteristics are proposed and a method for implementation in rule-based EMS is deduced. Finally, the benefits of coupling the shift strategy and EMS are depicted by an analysis of charging the battery (BAT) during vehicle operation. This exemplary study proves that the presented strategy allows operation at higher efficiency while improving the electric driving (ED) share. This positive effect is made possible by operating the ICE at higher speeds, which enables a more efficient charging of the BAT and additionally less energetic expenditure for boosting and lowering the ICEs OPs.
Optimization with Dynamic Programming of the Energy Management Strategy for a Fuel Cell Hybrid Heavy-Duty Truck Minimizing Hydrogen Consumption and Degradation
Authors: Moratti Giancarlo , Villani Manfredi , Beltrami Daniele , Uberti Stefano , Iora Paolo , Tribioli Laura
Published: September 2024

Achieving sustainable mobility requires the implementation of alternative and carbon-free technologies, especially in the sector of heavy-duty vehicles where powertrain electrification is challenging due to the high loads and long distances involved. In this context, hydrogen proton exchange membrane (PEM) fuel cell technology is considered a promising power source for heavy-duty hybrid electric vehicles. At the fuel cell level, the membrane electrode assembly (MEA) degradation and the system thermal management remain two major areas of research, that can be addressed not only with the development of new materials but also with the implementation of optimal control strategies. Working under operating points that lead to MEA aging and performance degradation can reduce the lifetime of the fuel cell with repercussions on the vehicle’s total cost of ownership. Typical fuel cell powertrains are hybridized in a parallel configuration with a battery, which requires solving an energy management control problem to define the optimal power split among the two power sources. For a given powertrain design and sizing of the components, different control strategies can greatly impact the performance of the system and its durability. In this work, a fuel-cell hybrid electric heavy-duty truck is modeled, and Dynamic Programming is used to find the optimal control strategy for the fuel cell operation that minimizes hydrogen consumption. At the same time, by limiting the current ramp rate and fuel cell shutdowns, the aim is to reduce fuel cell aging, enabling operation under minimal degradation conditions and higher efficiencies. Dynamic Programming off-line simulations provide an optimal benchmark control strategy for the fuel cell, that can be leveraged for the development of real-time implementable controllers. The simulation results show that introducing limitations on the current ramp rate and fuel cell shutdowns slightly affects energy consumption while greatly reducing the aging and degradation of the fuel cell.