bluuebunny/crossref_metadata_2025 huggingface dataset:
Active Flow Control Strategy on Improving Aerodynamic Characteristics of Rotor
Authors:   Nanjing University of Aeronautics and Astronautics, Yi-Yang Ma , Qi-Jun Zhao , Bo Wang
Published: September 2024

A new active flow control strategy by placing a synthetic jet actuator (SJA) and a trailing-edge flap (TEF) has been proposed, and its control effects on mitigation of large negative pitching moments and drag caused by rotor dynamic stall are numerically investigated by CFD method. A moving-embedded grid method and an unsteady Reynolds averaged Navier–Stokes (URANS) solver are established for predicting the complex flowfields of rotor and airfoil. Calculated results of VR-12 and SC1095 airfoils indicate that TEF and SJ can suppress the formation of dynamic stall vortex and postpone flow separation over rotor airfoil, resulting in much lower Cdmax and Cmmax comparing to the baseline state, and aerodynamic characteristics of airfoil could be further improved by the new control method comparing to individual control method. Furthermore, parametric analyses on dynamic stall control of airfoil by the combinational method are conducted, and it indicates that aerodynamic characteristics of an oscillatory rotor airfoil could be significantly improved when non-dimensional frequency (k*) of TEF is about 1.0, and larger angular amplitude help to increase the lift coefficient. At last, simulations are conducted for the flow control of rotor airfoil by the combinational method, and the numerical results indicate that the TEF can better improve the lift characteristics of rotor airfoil, and synthetic jet further increases the aerodynamic characteristics of rotor airfoil.
Structured, Overset Simulations for the 1st Rotor Hub Flow Workshop
Authors:   University of Tennessee, Coder James ,   Pennsylvania State Applied Research Lab, Foster Norman
Published: September 2024

Structured, overset computational fluid dynamics methods are used to simulate a water-tunnel experiment of flow over a rotating, 4-bladed rotor hub at Reynolds numbers near that of full scale. A hybrid RANS/LES method is employed with fifth-order discretization of convective flux terms and second-order time integration to resolve largescale turbulent flow features in the wake. Preliminary simulations on a baseline grid system revealed inadequate grid resolution in the wake region along with contamination from inflow and outflow boundaries being too close to the region of interest. An improved grid system was made based on the lessons learned, and results obtained for this grid are described in detail. Comparison of time-averaged velocities in the wake show an underprediction of the velocity deficit in the mid and far wakes. Frequency spectra of the hub drag loads and downstream wake velocities are presented and compared with experiment.
First Rotor Hub Flow Prediction Workshop Experimental Data Campaigns and Computational Analyses
Authors:   Pennsylvania State University, Schmitz Sven ,   Georgia Institute of Technology, Smith Marilyn ,   US Army, Centolanza Louis , Reich David
Published: September 2024

The rotor hub can account for up to thirty percent of rotorcraft parasite drag. Therefore, reducing hub drag is mandatory to advance the scientific knowledge necessary for future high-speed conventional and compound rotorcraft. The importance of high-Reynolds number testing of rotor hub flows is paramount as turbulent coherent structures persist up to the long-age wake where they interact with the empennage and tail, an observation impossible to make in experiments at lower Reynolds scale due to viscous dissipation. Basic Vertical Lift Center of Excellence (VLRCOE) research at Penn State in water tunnel facilities has provided unique high Reynolds-scale data of rotor hub wakes, providing new data for physical understanding and validation of computational fluid dynamics (CFD) methods. A first rotor hub flow prediction workshop is the result of a collaboration between Penn State and Georgia Tech VLRCOEs with support from the National Rotorcraft Technology Center (NRTC), including participation from academia, industry, and government. This paper describes the experimental data campaigns on hub flows conducted in the Penn State water tunnels and used for CFD comparisons/validations at the workshop. The 'First Rotor Hub Flow Prediction Workshop' is a compelling example of productive exchange between experimental and computational efforts, resulting in suggestions for post-workshop experiments and CFD analyses, some of which are highlighted in this paper.
A Computational Fluid Dynamics Based Viscous Vortex Particle Method for Coaxial Rotor Interaction Calculations
Authors:   University of Michigan, Singh Puneet , Friedmann Peretz
Published: September 2024

The coaxial rotor in hover and forward flight experiences complex unsteady aerodynamic interaction effects. Standard methods used for isolated rotor analysis are not adequate for obtaining the unsteady loads and wake. More accurate and computationally efficient approaches are required. The viscous vortex particle approach based on the Lagrangian formulation of the incompressible Navier-Stokes equations is a grid free method suitable for capturing the vortex wake interaction over long distances. The rational function approximation of unsteady airfoil loads from a CFD database is used to reduce computational effort and improve accuracy of load calculations. The vortex particle method and the rational function approximation are combined and applied to evaluate performance, wake evolution and loads for a coaxial rotor system in hover. The isolated and coaxial rotor thrust and torque performance were accurately predicted. The unsteady hub loads in hover were calculated using this technique. The blade passage frequency was a dominant source of oscillations in aerodynamic loading. The effect of the rotor wake system was determined and a comparison of the aerodynamic loading models was conducted.
Comparison of Advanced RANS Modeling with Dual-Plane PIV Measurements for a Hovering Rotor
Authors:   Embry-Riddle Aeronautical University, Lietzau Zachary ,   US Army Aviation Development Directorate (ADD), Ramasamy Manikandan , Leishman J. , Ekaterinaris John , Jain Rohit
Published: September 2024

Numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equations were conducted to study the development and turbulent decay of the tip vortices in the wake produced by a hovering rotor blade. An extensive series of calculations was performed with the OVERFLOW 2.2l code, the results being compared to detailed dual-plane Particle Image Velocimetry (PIV) measurements of a turbulent tip vortex trailed from a single-bladed rotor. The work investigated both the required mesh resolution and most suitable turbulence closure models with corrections for rotation and streamline curvature by assessing their predictions of the tip vortex properties and the overall physical nature of the rotor wake. It was found that even when using a higher-order spatial discretization scheme, a minimum off-body grid spacing equal to 0.625% of the chord length was required to accurately predict the core size, peak swirl velocity and strength of the tip vortex. The rotational/curvature corrections applied to the Spalart-Allmaras turbulence model better preserved the vortex characteristics to later wake ages than the same corrections applied to the k-w SST model. In both cases, the correction proposed by Spalart and Shur outperformed the simplified correction proposed by Dacles-Mariani et al., with the latter providing little impact on the k-w SST model.
Navier-Stokes Simulation of UH-60A Rotor/Wake Interaction Using Adaptive Mesh Refinement
Authors:   NASA Ames Research Center, Chaderjian Neal
Published: September 2024

Time-dependent Navier-Stokes simulations have been carried out for a flexible UH-60A rotor in forward flight, where the rotor wake interacts with the rotor blades. These flow conditions involved blade vortex interaction and dynamic stall, two common conditions that occur as modern helicopter designs strive to achieve greater flight speeds and payload capacity. These numerical simulations utilized high-order spatial accuracy and delayed detached eddy simulation. Emphasis was placed on understanding how improved rotor wake resolution affects the prediction of the normal force, pitching moment, and chord force of the rotor. Adaptive mesh refinement was used to highly resolve the turbulent rotor wake in a computationally efficient manner. Moreover, blade vortex interaction was found to trigger dynamic stall. Time-dependent flow visualization was utilized to provide an improved understanding of the numerical and physical mechanisms involved with three-dimensional dynamic stall.
Three-Dimensional Effects on Dynamic Stall of Rotor Airfoil
Authors:   Nanjing University of Aeronautics and Astronautics, Wang Qing , Zhao Qijun , Yin Jiangli , Wang Bo
Published: September 2024

In order to research the three-dimensional effects on the dynamic stall of rotor blade, the unsteady flowfields of finite-wing and rotor are simulated under dynamic stall conditions respectively. The unsteady RANS equations coupling with third -order Roe-MUSCL spatial discretizat ion scheme are chosen as the governing equations to predict the three dimensional flowfields of finite-wing and rotor, and the Spalart -Allmaras turbulence model is employed to calculate the viscidity of unsteady flowfields. From the simulat ion results of finite-wing, it is illustrated that the aerodynamic loads of wing would be reduced due to the effect of wing-tip vortex. As a result, the dynamic stall vortex of wing would be weakened near the wing-tip. Therefore, the peaks of lift coefficient, drag coefficient, and pitching moment coefficient are decreased near wing-tip. The spanwise flow on finite-wing would cause accumulat ion of dynamic stall vortex. As a result, the dynamic stall is restricted near the wing-root, and aggravated near wing-tip. By simulating the flowfield of a rotor in forward flight, it is illustrated that the centrifugal force would lead to generate spanwise flow. As a result, the dynamic stall characteristics of rotor would be restricted due to the Coriolis force. What is more, the decrease of angle of attack of rotor blade induced by downwash flow would inhibit the dynamic stall characteristics further.
Implementation of High-Order Methods in the HMB CFD Solver
Authors:   University of Glasgow, Jimenez-Garcia Antonio , Barakos George
Published: September 2024

This work presents the development and implementation of an efficient, compact high-order finite-volume scheme in the HMB CFD solver. This formulation is based on the variable extrapolation MUSCL-scheme, where high-order spatial accuracy (up to 4th-order) is achieved using high-order correction terms through a successive differentiation. The scheme has also been modified to cope with physical and multiblock mesh interfaces, so stability, conservativeness, and high-order accuracy are guaranteed. A wide variety of results for the underlying method are presented, including two-and three-dimensional test cases. The convection of an isentropic vortex, and the aerodynamic interaction between a vortex and a NACA-0012 aerofoil (blade vortex interaction problem BVI) are first studied, demonstrating the high level of accuracy of the new formulation. Theoretical and numerical analyses of the truncation error are also included. The three-dimensional steady flows around the 7AD, S-76, and XV-15 blades are also computed. Results with the proposed scheme, showed better wake and higher resolution of the vortical structures compared with the standard MUSCL solution, even though a coarse mesh was employed. The method was also demonstrated to three-dimensional unsteady flows using overset and moving grid computations for the UH-60A rotor in forward flight. The effect that the present method adds a CPU overhead of 40% in performing multi-dimensional problems encourages its use for routine computations.
PIV Flow Field Measurements of Hovering Rotors with Leading-Edge Protuberances
Authors:   United States Naval Academy, Cully Brian , Milluzzo Joseph , Drayton Scott
Published: September 2024

Performance and phase-resolved particle image velocimetry (PIV) measurements were taken on a rotor hovering out of ground effect to examine the wake structure generated by blades with leading-edge protuberances. The effects of protuberance amplitude and wavelength were examined using four sets of blades with various sinusoidal leading edges, as well as a baseline rectangular blade. At lower thrust conditions, the baseline and modified blades had similar power requirements. However, as thrust increased, the modified blades required additional power compared to the baseline. Specifically, the additional power requirements were found to be directly related to protuberance amplitude, whereas wavelength had a minimal effect. PIV measurements were taken with the rotor operating at a blade loading coefficient of 0.12. The baseline and low amplitude blades produced similar flow fields, containing a concentrated tip vortex that persisted to late wake ages and a less intense wake sheet. Conversely, the higher amplitude blades produced significantly more intense wake sheets and less coherent tip vortices, which persisted for less than one rotor revolution. Furthermore, the higher amplitude blades also generated a more uniform spanwise inflow distribution.
The 505 Low Vibration Solution
Authors:   Bell Helicopter, Romano Peter , Seifert Michael , Smith Michael
Published: September 2024

The original 505 Jet Ranger X prototype used a simple hard-mounted focal pylon to attach the transmission to the airframe. In developmental flight tests, the design resulted in 2/rev vibration levels that exceeded program objectives for ride quality in high speed forward flight. To address the vibration levels, a LIVE pylon mount was designed over a 4-month period to serve as a drop-in replacement with minimal impact to existing systems. An overview of the rapid design process is presented with supporting analysis and test data that led to its incorporation on the aircraft. The LIVE pylon design cut the vertical 2/rev vibrations in half, without negatively impacting existing structures, drive systems, flight controls, or handling qualities. The LIVE pylon mount is part of the Bell 505 Type Design that was certified in December 2016.
Lightweight Exoskeleton Fuel Bladder Transition
Authors:   METSS Corporation, Heater Kenneth ,   US Army AATD, Pilati Bryan ,   Robertson Fuel Systems, Whipple Matt
Published: September 2024

Previous efforts demonstrated the ability to achieve a 30% weight reduction for a MIL-DTL-27422D Phase I test cube construction with Protection Level A gunfire performance, using a lightweight 2-ply exoskeleton design to replace the 4-ply construction otherwise required to meet crash impact test requirements. An additional 20% reduction in weight was projected by replacing the natural gum rubber (NGR) used in conventional fuel bladder constructions with a lightweight formulation. This paper reviews the technical efforts executed to support the transition of the lightweight exoskeleton construction to the Apache AH-64 helicopter. The fuel bladders made with the lightweight sealant were 15.5% lighter for the AH-64 FWD fuel bladder and 13.2% lighter for the AFT. Additional weight savings based on the 2-ply exoskeleton construction was not realized as the existing AH-64 fuel bladders are already relatively lightweight constructions. The final AH-64 fuel bladders demonstrated the ability to be qualified to all MIL-DTL-27422E performance requirements; however, the program concluded without demonstrating Protection Level A gunfire performance. Importantly, there did not appear to be any discernable difference in the self-sealing performance of the fuel bladders made with the lightweight sealant and the constructions based on conventional NGR sealant. While additional work may be required to address this performance deficiency, there were several issues that were noted during the Phase II gunfire testing that should be reviewed and resolved prior to additional testing.
Demonstration of Aviation Mishap Reconstruction with On-Board Crash Recording Technologies
Authors:   NAWCAD, Hall Brandon , Willis Robert , Bark Lindley
Published: September 2024

Current approaches to specifying requirements for crash safety-related products rely on impact characteristics determined from studies conducted during the 1960s and 1970s. In addition, crash investigation techniques rely on methods in which mishap conditions are estimated based upon limited post-crash evidence. In order to address a current knowledge gap, crash recorders were examined for their ability to provide improved aircraft mishap data and to aid in mishap reconstruction. Dynamic testing on the Horizontal Accelerator at NAWCAD, Patuxent River, MD was conducted in order to investigate and ultimately demonstrate the ability of commercialized crash recorder technology to provide data that would greatly aid in aviation mishap investigation and reconstruction. Data collected by the crash recorders was used to create time-history sequences for tri-axial acceleration, estimated velocity, estimated recorder displacement, and estimated rotation. Ultimately, fielding such a system will improve the clarity and fidelity of crash investigations, as well as lead to better understanding of the often unpredictable modern aviation mishap environment.
Experimental Validation of Multi-Mode Tailboom Passive Vibration Control Using Fluidic Flexible Matrix Composite Tubes
Authors:   The Pennsylvania State University, Krott Matthew , Smith Edward , Rahn Christopher
Published: September 2024

Helicopter tailboom vibrations are easily excited and decay slowly due to the tailboom's low inherent structural damping. The resulting vibration causes poor ride quality for passengers, fatigues structural elements, and increases maintenance requirements for the helicopter. Fluidic Flexible Matrix Composite (F²MC) tubes are an emerging technology which can provide lightweight, compact vibration control when attached to a vibrating structure and coupled with a fluidic circuit. This paper presents experimental results to validate a method for combining a finite element structural model of a laboratory-scale tailboom with a model of the F²MC tubes and fluidic circuit dynamics. Reductions of over 70% in both bending and torsional vibration are demonstrated in a coupled 26.7 Hz lateral bending/torsion tailboom mode, indicating that F²MC vibration control is viable at higher frequencies and for more complex vibration modes than previous research had explored. A second group of experiments is performed to demonstrate the effectiveness of a novel fluidic circuit configuration which targets two tailboom vibration modes, in contrast to the previous F²MC treatment which can target only one mode. On the lab-scale tailboom testbed, vibration reductions of over 60% are demonstrated in two modes simultaneously when targeting both a 12.2 Hz vertical mode and a 26.7 Hz lateral bending/torsion mode. The circuit designed to reduce vibrations in two modes has a nearly identical weight to a comparable single-mode treatment but is much more effective in reducing vibrations at the second mode.
Comparison of Calculated and Measured Blade Loads of the Tilt Rotor Aeroacoustic Model (TRAM)
Authors:   Science and Technology Corporation - ARC, Ho Jimmy ,   US Army ADD - AvMC, Yeo Hyeonsoo
Published: September 2024

In an effort to assess the suitability of the U. S. Army's Rotorcraft Comprehensive Analysis System (RCAS) for calculating tiltrotor aeromechanics characteristics, comparisons of rotor performance and blade loads between calculations and test data are presented for the TRAM rotor in helicopter mode at an advance ratio of 0.15. For rotor performance, the comparisons are with test points that form shaft angle sweeps for two different thrust levels. These calculations include those from a free vortex wake model and those from coupling the comprehensive analysis to a viscous vortex particle method. The emphasis of this work is on the comparisons of blade loads, which are analyzed in detail for two test points with 3° forward shaft tilt and different thrust levels. Blade airloads calculations include the two aforementioned sets of calculations while blade structural loads calculations also include those from prescribing experimentally measured airloads. The level of agreement between calculations with the free vortex wake model and test data are generally comparable with those of helicopter rotors at similar conditions. The level of agreement improves with the viscous vortex particle method. Meanwhile, some deficiencies in structural loads calculations with prescribing measured airloads are noted and lead to further investigations.
Tiltrotor Whirl Flutter Stability Augmentation Using Active Wing Tips
Authors:   US Army Research Laboratory, Floros Matthew , Kang Hao
Published: September 2024

Tiltrotor whirl flutter stability augmentation using an active wing tip is investigated. The wing tip is a small active wing segment which is attached to the outboard side of the pylon through a controllable bearing. Using a feedback control system, the tip cancels wing motion to augment whirl flutter stability. Multiple individual and combined feedback schemes and control system parameters are investigated on a scaled XV-15 model using the comprehensive analysis RCAS. The simulated small tip was shown to increase system damping and extend the whirl flutter boundary by 25–33% from 160 kts to over 200 kts by selecting the optimum control parameters for beamwise and chordwise feedback independently and then combining them. The damping resulting from individually feeding back beamwise and chordwise motion was additive when feeding both back together. The required actuation amplitude was on the order of 1 degree.
Investigation and Evaluation of Control Design Requirements for future Personal Aerial Vehicles
Authors:   Max Planck Institute for Biological Cybernetics Tubingen and University of Stuttgart, Gerboni Carlo ,   Max Planck Institute for Biological Cybernetics Tubingen, Geluardi Stefano ,   University of Stuttgart, Fichter Walter , Bulthoff Heinrich
Published: September 2024

The study presented in this paper investigates bandwidth and disturbance rejection requirements for a new kind of vehicle, namely the Personal Aerial Vehicle (PAV). PAVs are here meant as augmented rotorcraft that can be safely flown by pilots after a training comparable in length to that necessary to learn how to drive a car. Therefore, the control augmentation system should ensure both stability and disturbance rejection properties while meeting handling qualities suitable for minimal-trained pilots. The investigation is conducted by designing a family of controllers to achieve different trade-offs between stability, handling qualities and robustness requirements. The goal is to evaluate which control design provides the best characteristics to help minimal-trained pilots when operating in turbulent conditions. The evaluation is conducted by means of a pilot in-the-loop experiment in the Max Planck Institute CyberMotion Simulator. The experiment is conducted with 21 participants with no prior flight experience divided into three groups. Each group has to perform the same control task maneuver but with a different augmented helicopter dynamics. The performance analysis is carried out by considering both objective metrics and subjective evaluations. Results show that the design with improved disturbance rejection properties helped the participants achieve better performance and workload levels in turbulent conditions. However, a relaxation of the stability margins is necessary to achieve these properties and must be taken into account for an actual implementation in a helicopter.
Regime Recognition Accuracy
Authors:   Spire Innovations LLC, Hull Jason ,   Sikorsky Aircraft Corporation, Davis Mark ,   Naval Air Systems Command, Semidey Roberto , Monaco Jeffrey , Beale Raymond , Glucksman-Glaser Mark
Published: September 2024

Accurate characterization of fleet and vehicle usage spectrums would allow component retirement times to be based on actual aircraft usage rather than on an assumed worst case usage spectrum used in a traditional time-based maintenance approach. A key enabling technology for such a Usage or Condition Based Maintenance (UBM/CBM) program is Regime Recognition (RR). In general, production RR algorithms with the required accuracy have not been fielded, in part because of the challenges associated with Verification and Validation (V&V). The multi-class classifier analysis methods and associated visualizations presented herein address the need to maximize the utility of available data and rigorously perform V&V of RR algorithms and software. The resultant methods clearly show the performance range that can be expected when an RR code is deployed to the fleet, and provide a single accuracy metric that highlights error characteristics that are most important to a UBM/CBM program.
Condition (Usage) Based Maintenance and SLL Computation using Flight Regime Recognition Algorithm
Authors:   Airbus Helicopters, Laillet Emmanuel , Maisonneuve Pierre-Loic , Reveillon Damien
Published: September 2024

Condition (Usage) Based Maintenance (CBM) function is becoming a standard and classical investigation topic for Original Equipment Manufacturers (OEM) for many reasons. Significant benefits can be earned by developing and using such functions: Better knowledge of the customer's usage of the helicopters, improvements in the building of the Design Usage Spectrums (DUS) for both high cycle fatigue mode (time ratio spent and occurrences of flight regimes) and low cycle fatigue mode (start/stop cycles, landing/take-off cycles, torque cycles, -), better understanding of the customer's own fleet's management, and of course maintenance optimization.
In order to achieve this target and in particular the maintenance burden reduction, AH has developed a complete end-to-end CBM function proven to be efficient for customers. This paper intends to describe briefly the general concept already published, recall the expected benefits previously evaluated on H225, and focus deeper on the validation of the Flight Regime Recognition (FRR) Algorithm, allowing to confirm and reinforce the robustness of the function proposed. It details the means proposed by AH to validate the regime recognition and the potential credit, as well as the cautions to be taken when implementing such a function. General continued airworthiness and certification issues are also included in this paper, as required and proposed by AMC 29.1465 and AC29-2C MG15.
Study on the Impact of Post-Flight CBM Reporting on Readiness and Maintenance Metrics
Authors:   Naval Surface Warfare Center, Scates Erica ,   In-Service Support Center, Bullock John , Fuller Brian
Published: September 2024

The Department of the Navy has been developing and deploying Health and Usage Monitoring Systems (HUMS) for more than 20 years. One of the many uses of HUMS is as an enabling technology for implementing Condition Based Maintenance (CBM), the goal of which is to improve aircraft safety, affordability, and availability through an as-needed (rather than scheduled) approach to maintenance. To drive the fleet toward a more realized implementation of CBM, a CBM event detection and reporting system was developed for the Navy's fleet of H-60 aircraft, accompanied by updated policy requiring the fleet to adhere to the guidance within these CBM reports. For this investigation, five years of maintenance and readiness data from two naval H-60 aircraft types were studied to identify trends related to this platform's implementation of CBM. This five year period includes two years of data from before the CBM reports and policy were introduced, one year of data during which the technology and policy were being implemented, and two years of data from after the reports and policy were in effect. The metrics chosen to evaluate changes in fleet behavior were Mission Capable Rate (MC Rate), Non-Mission Capable Rate due to Unscheduled Maintenance (NMCMU Rate), Unscheduled Maintenance Man-Hours per Flight Hour (UMMF), Scheduled Maintenance Man-Hours per Flight Hour (SMMF), and Functional Check Flight Hours per Flight Hour (FCF Rate). Overall, the fleet mean MC Rate decreased, NMCMU Rate, UMMF, and SMMF increased, and FCF Rate was unchanged in the period after the reports and policy were introduced. However, for most of these metrics, a squadron-level analysis showed that the individual squadrons did not trend uniformly in the direction of these fleet averages. In a continued effort to characterize the fleet response to the implementation of CBM, it is recommended that further investigation into additional metrics and analysis techniques be pursued.
Enhanced Safety Management and Risk Mitigation through Robust HFDM
Authors:   GPMS Inc., Bechhoefer Eric ,   IVHM Inc., Augustin Michael
Published: September 2024

Helicopter Flight Data Monitoring (HFDM) can be a central and effective component of an operator's safety management strategy. By capturing and processing operational information from aircraft flight data, the operator/owner can identify safety hazards, facilitate monitoring and assessment of the interaction between the pilot and the aircraft, initiate remedial actions, and support continuous improvement of the safety management system. The Robust HFDM system described in this paper also provides improved results via automation of data download and reporting. Automation is achieved by formalizing the concept of a flight operation, adding exceedance reporting, and improving the HFDM architectural design to allow for the transfer of data to secure ground based storage. In the extreme, robust HFDM also provides protection of data in the event of a mishap event that would usually only be available via post incident analysis of a crash survivable memory. This paper discusses the formalized concept of a flight operation, how regime recognition has been tailored to support the more robust application, and finally the addition of exceedance monitoring. The changes in architecture, processing and data transfer, result in a new and more robust HFDM system.
Integrated Hybrid Structural Management System (IHSMS) - Usage and Loads Monitoring
Authors:   Sikorsky a Lockheed Martin Company, LeFevre Brian ,   Lord Corporation, Marr Conor ,   US Naval Air Systems Command, Rusk David , Davis Mark , Johnson Courtney
Published: September 2024

The overarching objective of the Integrated Hybrid Structural Management System (IHSMS) program is to mature key capabilities, which support eventual implementation of a holistic on-condition or reliability-based maintenance paradigm for rotorcraft. As one of the constituent elements of the IHSMS program, development of Usage and Loads Monitoring (ULM) technologies is achieved through refinement and testing/evaluation of a suite of physical sensors and model-based technologies. This paper describes the IHSMS ULM architecture, and explores the efforts to develop and test two prototype physical sensor systems for the Sikorsky CH-53K aircraft: a smart main rotor elastomeric bearing and a landing gear load monitoring system. Validation test results for each of these technologies are discussed, with successes and remaining challenges highlighted for each system. ULM technology validation efforts, including those for the two physical sensor systems discussed herein, were largely successful with most features of each technology meeting or exceeding the corresponding technical performance goals. As such, the path for transition of these technologies remains positive, with the ground work already being laid for follow-on maturation efforts.
Additive Manufacturing of Simulator Parts
Authors:   Sikorsky Aircraft Corporation, Shields Paul
Published: September 2024

The DARPA Aircrew Labor In-Cockpit Automation System (ALIAS) program aims to develop custom, tailorable kits that can be implemented into existing aircraft to provide autonomous and optionally piloted vehicle capabilities. In support of this program, Sikorsky Aircraft has developed kits for both fixed wing and rotary wing aircraft. During the development of ALIAS kits, Sikorsky used Additive Manufacturing for prototyping and to meet critical program milestones. Additive Manufacturing was shown to be a viable solution for producing simulator and demonstrator parts required for various aspects of the program. Additively manufactured parts were used for integration demonstrations, cockpit controls evaluations, system simulation, and flight demonstrations. This paper summarizes how Sikorsky used Additive Manufacturing to support the completion of DARPA ALIAS Program milestones.
SB>1 Defiant Joint Multi-Role Technology Demonstrator: The Way Forward for Rotorcraft Manufacturing
Authors:   Sikorsky a Lockheed Martin Company, Newman Jessica , Forster William , Gatley Christopher , Pinney Thomas , Kinlan Jeff , Saha Anshuman
Published: September 2024

Modern manufacturing processes have been streamlined over time to ensure build accuracy and minimize waste related to cost and schedule. For future aircraft development, rapid prototyping has afforded the ability to hone these processes further. The Joint Multi-Role Technology Demonstrator (JMR TD) Program is focused on building the next generation of rotorcraft, known as Future Vertical Lift (FVL), to replace the current military fleet. The Sikorsky-Boeing SB>1 DEFIANT™ Technology Demonstrator Team has created several innovative approaches for this purpose. Legacy methodologies from both companies were tailored for the rapid prototyping environment. Advancement in manufacturing technologies from research and development projects being executed by the JMR team, in partnership with the government and academia, has helped to provide additional insight on the best approach to FVL.
Parametric Study of Dynamic Inflow for Coaxial Rotor System
Authors:   Technion - Israel Institute of Technology, Rand Omri , Khromov Vladimir
Published: September 2024

The paper presents a comprehensive study of the sensitivity of aerodynamic response predictions of coaxial rotor systems to a wide range of variations in the embedded dynamic inflow model at various flight regimes. The dynamic inflow model is founded on the classical first order system hypothesis and is extracted from a generic high fidelity aerodynamic scheme using the single frequency analysis methodology.
The methodology is carrying out by a systematic series of wake excitations and is primarily based on time simulation via a time marching free wake analysis. A free wake model is activated by a sequential periodic rotor loads that excite various periodic responses of the wake. The corresponding time histories of the induced velocity enable the determination of the mass and gain matrices associated with the dynamic inflow model. Unlike existing estimations, the present methodology enables a detailed determination of all elements of the above matrices and shows regions where the first order system behavior, which is a fundamental assumption of the dynamic inflow formulation, is valid.
The parametric study presented in this paper deals with both single and coaxial rotor systems operated in hover and forward flight. The paper provides analysis by free wake model and comprehensive aeromechanics numerical solutions in addition to various analytic insights into the associated phenomena and interactions. In particular, the issue of the liftoffset effect on the dynamic inflow characteristics is analytically reviewed along with analytic modelling of the crosscoupling between the rotors in coaxial rotor system that is induced by the dynamic inflow. In addition, the paper addresses the importance of the rotors flapping stiffness and rotors clearance. Wherever meaningful, comparisons with similar prediction of single rotor systems are also presented.
Accurate Real-Time Extensible Simulations of Dynamic Bodies
Authors:   Georgia Institute of Technology, Koukpaizan Nicholson , Movva Jagadeesh , Butori Marin , Smith Marilyn
Published: September 2024

A model-based simulation technique has recently been developed and is being transitioned for use in two-body aerodynamic-dynamic problems of interest (slung loads, airdrops) to the vertical lift community. This model, the Georgia Tech Aerodynamics for Bluff Bodies (GTABB), has been shown to accurately predict the behavior of rectangular loads, validated with both computational fluid dynamics and flight test. This paper presents additional validation of the GTABB solver and its six degree of freedom dynamic modeling tool (6DOF) with flight test on new slung load configurations that are connected via either a hook or a gimbal. A new tether algorithm capable of modeling wind-up is demonstrated. In addition, the introduction of a long tether model in 6DOF and a graphical user interface to rapidly build and analyze, visually and quantitatively, tethered load simulations are described. In this paper, a new pre-processor that develops the quasi-steady data tables for arbitrary configurations, COMPlex Aerodynamic Shape Simulator (COMPASS), is introduced with initial verification and validation, demonstrating a concept first introduced in 2011-2012. COMPASS demonstrates the ability to reconstruct the dynamic mechanisms responsible for driving the motion of two-body aerodynamic-dynamic problems.
A Free Wake Linear Inflow Model Extraction Procedure for Rotorcraft Analysis
Authors:   Continuum Dynamics Inc., D. Jeffrey ,   US Army ADD - AMRDEC, Tischler Mark , McKillip Robert , Wachspress Daniel , Juhasz Ondrej
Published: September 2024

Linearized inflow models have been used to represent dynamic wake effects for control law development and flight dynamics simulation of conventional main rotor/tail rotor helicopters. For advanced rotorcraft configurations based on compound-coaxial and multi-rotor distributed propulsion, rotor-on-rotor and rotor-on-wing interactions lead to a breakdown of classical dynamic inflow theory. An approach for extracting low-order inflow models from comprehensive aerodynamic analyses has been investigated as part of continuing research and development toward an automated procedure for inflow/wake model identification. This paper describes the initial results for inflow model extraction from a full-span free wake analysis in hover, forward flight, and maneuvering flight conditions. Emphasis has been placed on the model structure formulation to yield identified inflow models that capture the critical dynamics associated with the rotor wake and induced velocity without being over-parameterized. Model structures previously reported in the literature do not capture all wake dynamics observed in a free wake model, some of which impact the coupled rotor-body response characteristics. Wake distortion effects due to tip path plane angular rate, off-rotor interference, and coaxial rotor interactions are examined herein.
Design of a Haptic Helicopter Trainer for Inexperienced Pilots
Authors:   Max Planck Institute for Biological Cybernetics Tubingen and University of Pisa, Fabbroni Davide ,   Max Planck Institute for Biological Cybernetics Tubingen, Geluardi Stefano ,   University of Pisa, Pollini Lorenzo , D'Intino Giulia , Gerboni Carlo , Olivari Mario , Bülthoff Heinrich
Published: September 2024

This paper investigates the effectiveness of a novel method of training for helicopter pilots, with flight simulators. A software trainer based on haptic force-feedback was implemented, namely the Haptic Helicopter Trainer (HHT). The HHT is an extension of an existing automated trainer based on a Optimal Control pilot Model. With the addition of a force-feedback, the HHT is able to mimic the action of an instructor pilot on dual controls. To test the effectiveness of the HHT with respect to other types of training, an experiment was performed in a fixed-based helicopter simulator with three groups of participants: one group trained with the HHT, one group trained with the automated trainer and a control group. The training was carried out as a realistic flight lesson, divided in phases to bring the student pilots to satisfying skill levels. Results showed that the designed training phases are effective for learning how to stabilize the helicopter model. Moreover, the group trained with the HHT achieved better performances than the other groups, proving the effectiveness of the haptic force-feedback in the training of inexperienced helicopter pilots.
CFD Analysis of the Effect of Atmospheric Boundary Layer on Wind Turbine Wake
Authors:   The University of Tokyo, Kimura Keita ,   JAXA, Tanabe Yasutada , Arakawa Chuichi , Iida Makoto , Aoyama Takashi , Matsuo Yuichi
Published: September 2024

The wake behind a wind turbine in an atmospheric boundary layer (ABL) is investigated using a numerical simulation method. From the viewpoint of cost effectiveness, collective installations (wind farms) are desired because they can reduce the total length of the power-transmission lines and labor costs for maintenance. However, a wake from an upwind turbine may significantly reduce power production downstream and cause large load variations on the blades. Numerical methods based on computational fluid dynamics (CFD) are efficient for investigating the structures and characteristics of wind-turbine wakes. This study mainly discusses the effect of wind shear of ABL on a wind turbine wake by focusing on the behavior of tip vortices and recovery process of velocity deficits. It is found that the wind shear mainly influence on near-wake structure and the effect on far-wake is relatively weak.
Experimental Based Numerical Studies of Bird Impact Response on Helicopter Horizontal Stabilizer
Authors:   Hindustan Aeronautics Limited, Vijayakumar R. , Lavakumar M. , Ravindranath R. , Chalwade D.
Published: September 2024

The soft body high energy impact response on rotorcraft composite layered structures is investigated by analysis based on tests carried out. The experimentally and numerically assessed deformation and energy absorption capabilities of Horizontal stabilizer is attributed under high energy bird impact, which is an important aspect in the computer simulations for correlation studies followed by any design modifications. The ability to withstand bird impact of forward facing components is one of the major requirements of rotorcraft to comply bird strike certification test requirement. The main difficulties encountered in achieving accurate finite element analysis are related to modeling of the bird which undergoes severe deformations and the state-of-the art of composite layered modeling. The current study further investigates the impact behavior of soft body projectiles on Horizontal stabilizer through full scale testing.
Rotorcraft Fastener Electrical Contact Analysis for Optimal Carbon Fiber Composite Lightning Strike Protection
Authors:   Arconic, Liebscher Andreas , Rizza Gregory , Prachumsri Wudhidham
Published: September 2024

In this paper we investigate the importance of electrical contact efficiency between fasteners and skin-level expanded metal mesh and how it influences lightning current energy transport. Since carbon fiber reinforced polymer composites (CFRPs) are electrically anisotropic and typically exhibit relatively low conductivities which are directionally distinct, aerospace manufacturers frequently use metallic foil layers or an expanded metal mesh on outer surfaces of composite structures for lightning strike protection. Due to irregular topology and associated micro-texture of machined holes in composites it is shown non-uniform interface surfaces between the fastener and composite layers reduces electrical continuity, thereby impeding current flow as a result of increased contact resistance levels. Furthermore, lightning strike experiments have indicated that metal mesh intimacy around the perimeter of the fastener head directly affects overall electromagnetic response of the rotorcrafts outer surface when subjected to lightning currents due to impedance modification of the electrical network. The effect of electrical continuity between the fastener head and mesh strand contact points is calculated using a Multiphysics model to demonstrate the effects on current load distribution and fusing lifetime of the individual strands. Additionally, total number of fastener-mesh strand contact points and cross sectional area of each strand are shown as being important parameters which ultimately determine the amount of lightning current efficiently transferred across the rotorcraft skin surface.
Risk Assessment: Quantitative Versus Qualitative
Authors:   Sikorsky Aircraft, Hewitt John , Pham Loan
Published: September 2024

This paper provides a detailed examination of Quantitative Risk Assessment and qualitative risk assessment, and it compares the advantages, disadvantages, and usefulness of each process. It describes why Quantitative Risk Assessment is becoming more commonly used in rotorcraft safety risk management; it concludes with an approach that would employ the best of both methods, and it provides resources for further study.
A Modified Method of Deriving Fatigue Load Spectra from Historical Flight Test Data
Authors:   US Army Aviation Engineering Dir., E. Robert ,   Vencore, Chandler Michael , Appleton Chad
Published: September 2024

Normalized design load spectra permit a recently proposed framework for fair, early, and meaningful assessments of rotorcraft dynamic-component fatigue durability. In prior work, a mission-rainflow method defines fatigue load spectra from historical flight test data. This paper proposes maximum-oscillatory and regime-rainflow alternatives with a goal of decreasing the effort required to generate each load spectrum. A maneuver-to-maneuver technique ensures representation of ground-air-ground cycles in the maximum-oscillatory and regime-rainflow alternatives. Discussion includes comparison to prior methods and an explanation of challenges and benefits associated with each method. To enable comparison to prior methods, tables provide the newly derived mission spectrum load occurrences for main rotor pitch link load and tail rotor flap-wise bending, as well as characterizing parameters using piecewise exponential distributions. Figures demonstrate the similarity of piecewise exponential distribution results between regime-rainflow and mission-rainflow methods, while also suggesting conservatism for the maximum-oscillatory method. Fatigue analysis supports similar conclusions.
Method to Assess the Effects of a Flaw with Residual Stress for Rotorcraft Metallic Structures
Authors:   Bell Helicopter Textron, Rajagopal Balaji , Green W. , Reddy Manjunatha , Li Xiaoming
Published: September 2024

Accounting for effects of damage on the fatigue strength of metallic principal structural elements (PSE) is a requirement for fatigue tolerance evaluation of transport category rotorcraft. Parallel to the current structural test approach for showing regulatory compliance, an analysis method is sought. However, developing and executing an analytical compliance methodology has many challenges. One example is the stress state at the root of a flaw, and how that stress state interferes with the residual stress induced by specific processes such as shot peening. This paper presents an analysis method to determine the stress state at the root of a flaw with the presence of residual stresses. The method can quantify the effect of the residual stress on various flaw shapes and sizes, to avoid overly conservative assumptions in certification analysis.