bluuebunny/crossref_metadata_2025 huggingface dataset:
Vision based Collaborative Localization for Swarms of Aerial Vehicles
Authors:   Texas A&M University, Vemprala Sai , Saripalli Srikanth
Published: September 2024

We present a framework for localizing a swarm of multirotor micro aerial vehicles (MAV) through collaboration using vision based sensing. For MAVs equipped with monocular cameras, this technique, built upon a relative pose estimation strategy between two or more cameras, enables the MAVs to share information of a common map and thus estimate accurate metric poses between each other even through fast motion and changing environments. Synchronized feature detection, matching and robust tracking enable the use of multiple view geometry concepts for performing the estimation. Furthermore, we present the implementation details of this technique followed by a set of results which involves evaluation of the accuracy of the pose estimates through test cases in both simulated and real experiments. Our test cases involve a group of quadrotors in simulation, as well as real world flight tests with two MAVs.
Tip Vortex Measurements on a Cycloidal Rotor Blade at Ultralow Reynolds Numbers - Lichten Award Runner-Up Paper
Authors:   Texas A&M University, McElreath James , Benedict Moble , Tichenor Nathan
Published: September 2024

This study provides the first in-depth analysis of the formation, strength, and convection of cycloidal rotor tip vortices. The blade force and PIV-based tip-vortex measurements were conducted for different blade aspect ratios and pitch kinematics in water at a chord Reynolds number of 18,000. Two phase-locked PIV configurations were utilized to investigate the flow field induced by the cyclorotor blade: (1) a laboratory-fixed field of view to enable investigation of vortex development at increasing vortex ages, and (2) a blade-fixed field of view to investigate the early development of the wingtip vortex at fixed 2° vortex age for varying azimuthal locations. The instantaneous blade force measurements on the cycloidal rotor showed a decrease in lift coefficient with decreasing blade aspect ratio. This is due to the higher peak swirl velocity of the tip vortex produced by the low AR blade, thereby resulting in higher induced downwash along the blade span. The aspect ratio of the blade did not affect the shape of the vortex convection trajectory, however, the rate of downward convection increased with increasing aspect ratio due to the higher thrust produced. The tip vortices showed self-similarity in both the velocity and the circulation profiles. The measurements indicate that the core-radius of the vortex experiences a logarithmic growth and the swirl velocity experiences a logarithmic decay, with vortex age due to viscous diffusion. When compared to previous helicopter rotor studies, the observed vortex dynamics from the present study exhibit increased viscous diffusion, likely due to the significantly lower Reynolds number. The tip vortex strength varied cyclically with blade azimuthal location due to the cyclic variation of blade pitch angle and the dynamic virtual camber effects. The periodic variation in tip vortex strength leads to a periodic variation in the induced flow velocity on the blade.
Aerodynamic Installation Effects of Lateral Rotors on a Novel Compound Helicopter Configuration
Authors:   Delft University of Technology, Stokkermans Tom ,   Netherlands Aerospace Centre NLR, Soemarwoto Bambang ,   Airbus Helicopters, Fukari Raphaél , Voskuijl Mark , Veldhuis Leo , Eglin Paul
Published: September 2024

Installation effects of the lateral rotors for a compound helicopter were investigated by means of unsteady CFD simulations. The helicopter featured a box-wing design for additional lift in cruise and wingtip-mounted lateral rotors in pusher configuration for additional thrust in cruise and counter-torque in hover. It was found that propeller performance installation effects for a compound helicopter are highly beneficial in cruise, while some penalties exist in extreme and specific cases in hover and autorotation. In cruise the main interaction was between the wing and lateral rotors, resulting in a propulsive efficiency increase up to 10.6% due to wingtip vortex energy recovery. In hover the main rotor slipstream resulted in a near perpendicular inflow to the lateral rotors, with a disturbance from the wings due to the deflection of the main rotor slipstream. For higher than nominal lateral rotor thrust settings, this resulted in a performance penalty. In autorotation a small power installation penalty was present due to inflow disturbances.
Aerodynamic Geometry Optimization of Coaxial Rigid Rotors in Forward Flight
Authors:   Nanjing University of Aeronautics and Astronautics, Zhao Qijun , Zhu Zheng , Yuan Xin , Wang Bo
Published: September 2024

Coaxial rigid rotor configuration provides helicopter higher forward flight speed than single-rotor configuration. Aiming at obtaining a coaxial-rotor blade shape with better aerodynamics in forward flight, a compressible RANS solver for aerodynamics simulations and an optimization method for blade design are established. The optimization method combining a surrogate-based approach and genetic algorithms is suitable for solving the complicated multiobjective blade geometry optimization problem. On the basis of previous research, the blade geometry is optimized towards a shape with nonlinear chord distribution and a tapered swept-back tip. The optimized rotor blade reaches a higher value of lift-drag ratio over a large advance ratio range compared with rectangular blade of the same size. And the new shape suppresses the flow separation and weakens the shock over the blade surface to a certain degree in high-speed forward flight. Meanwhile, the optimized blade also contributes to reducing high-speed impulsive noise generated in forward flight.
System Level Benefits of a Variable Diameter Rotor System for a Conceptual Tiltrotor Design
Authors:   US Army, D. Robert
Published: September 2024

This work presents a conceptual variable diameter tiltrotor sized in the NDARC conceptual design code. Both the maximum allowable diameter change and the weight increment due to morphing were varied with the intent of investigating the system level benefits (improved weight, fuel use, etc.) associated with a variable diameter rotor system. Generally, for a 0% increment in rotor weight due to morphing, diameter morphing reduced vehicle gross and component weights, as well as mission fuel weight. As the rotor weight penalty for morphing was increased, the entire system saw a corresponding increase in weight. For these increased rotor weight conditions, diameter morphing was again able to reduce total system weight back to, or lower than, the baseline design. At very high levels of morphing however, (large reductions in rotor radius for cruise) weight was seen to drastically increase. This was traced to the rotor approaching stalled conditions during cruise due to increased blade loading. A conceptual approach for estimating cruise blade loading for a variable diameter or variable speed tiltrotor was then presented. In general, this work shows that even for fairly substantial increases in rotor weight, variable diameter morphing can have a system wide benefit in the form of reduced gross weight and reduced fuel weight for the given design mission.
Piloted Simulation Evaluation of Tracking MTEs for the Assessment of High-Speed Handling Qualities
Authors:   Systems Technology Inc., Klyde David ,   Bell Helicopter, Ruckel Paul ,   Sikorsky a Lockheed Martin Company, Fegely Cody ,   The Boeing Company, Brewer Roy ,   The Pennsylvania State University, Horn Joe ,   US Army RDECOM, Ott Carl , Pitoniak Sean , Schulze P. , Rigsby James , Xin Hong , Fell William , Conway Frank , Mulato Ray , Blanken Chris
Published: September 2024

Updates to the military rotorcraft handling qualities specification are currently being considered that address the high-speed flight regime envisioned for the Future Vertical Lift platform of the US Army. A team that features industry and academia have developed and evaluated a set of Mission Task Elements (MTEs) that are defined to address VTOL high-speed handling qualities. Following the mission-oriented approach upon which ADS-33E-PRF is based, the MTEs were designed to meet different levels of precision and aggressiveness. Tracking MTEs based on a sum-of-sinewaves (SOS) command signal were defined for precision, aggressive and precision, non-aggressive applications. The command signals are derived from fixed wing analogs that have long been used to evaluate aircraft handling qualities. While the precision, aggressive SOS tracking tasks, the primary subject of this paper, are surrogates for air-to-air tracking and nap-of-the-earth tracking, the known forcing function allows for complete open- and closed-loop pilot-vehicle system identification. The MTE objectives, descriptions, and performance criteria were assessed and refined via several checkout piloted simulation sessions. Formal evaluations were then conducted by Army test pilots at four simulator facilities, each featuring a unique high-speed platform including a generic winged compound helicopter, two tiltrotor configurations, and a compound helicopter with coaxial rotors. To aid in the MTE evaluation process, baseline VTOL configurations were varied to achieve different handling qualities levels. Quantitative measures based on task performance and qualitative measures based on pilot ratings, comments and debrief questionnaires were used to assess MTE effectiveness. The piloted simulation results demonstrated that the sum-of-sines tracking MTEs provided an effective means to discern precision, aggressive handling qualities in high speed flight.
Further Development and Evaluation of a New High-Speed Acceleration/ Deceleration ADS-33 Mission Task Element
Authors:   The Boeing Company, Brewer Roy ,   Sikorsky a Lockheed Martin Company, Xin Hong ,   The Pennsylvania State University, Horn Joseph ,   Bell Helicopter, Ruckel Paul ,   Systems Technology Inc., Klyde David ,   US Army RDECOM, Ott Carl , Conway Frank , Mulato Ray , Fegely Cody , Fell William , Rigsby James , Pitoniak Sean , Schulze P. , Blanken Chris
Published: September 2024

Updates to the military rotorcraft handling qualities specification are currently being considered that address the high-speed flight regime envisioned for the Future Vertical Lift (FVL) platform of the US Army. The US Army's National Rotorcraft Technology Center (NRTC) project "Rotorcraft Handling Qualities Requirements for Future Configurations and Missions" was a U.S. Government and Industry co-funded three-year research project. A project team that features industry and academia have developed and evaluated a set of Mission Task Elements (MTEs) that are defined to address rotorcraft high-speed handling qualities. The High Speed Acceleration/Deceleration MTE was designed to provide suitable coverage in ADS-33 for handling qualities in Low/High Speed Transitional flight regimes (e.g. rotor-borne to wing-borne flight). The MTE objectives, descriptions, and performance criteria were developed via a series of piloted simulation sessions at each of the four teams' simulation facility. Formal evaluations were then conducted by US Army and contractor test pilots at the four simulator facilities, each featuring a unique high-speed platform, including two tiltrotor configurations, an X2 Technology compound helicopter, and a generic winged compound helicopter. To enhance the MTE evaluation process, baseline control law (CLAW) configurations were varied to achieve different handling qualities levels. Quantitative measures based on task performance and qualitative measures based on pilot ratings, comments and debrief questionnaires were used to assess MTE effectiveness. The piloted simulation results demonstrated that the High Speed Acceleration/ Deceleration MTE provided a suitable and effective means to evaluate Transitional handling qualities between low and high speed flight, although some refinements may still be warranted.
Analysis of Rotorcraft Pilot Couplings During Active Inceptor Failures
Authors:   German Aerospace Center (DLR), Jones Michael , Barnett Miles
Published: September 2024

The use of active inceptor systems allows for control of the aircraft even during mechanical failures within the control inceptor. For the specific case of isometric failure, whereby the inceptor 'freezes' in position, a virtual force displacement model is used to continue to provide control input. Testing on DLR's experimental helicopter (ACT/FHS) has shown the potential to encounter pilot-induced oscillation (PIO) tendencies when flying using this mode. This paper presents results from a simulation campaign undertaken to determine whether PIOs could be exposed through this use of control and/or the resultant severity. The results show that control limiters cause severe PIOs during the isometric failure. Unacceptable failure characteristics were found for six different vehicle configurations and PIOs were exposed by all four pilots. PIO incipience was predicted through the use of offline tools. In future, it is recommended that specific PIO investigations are undertaken during the evaluation of active inceptor failure modes.
Helicopter Drive Train Load Alleviation In Hover By Nonlinear Control
Authors:   Delft University of Technology, Voskuijl Mark , Bruchem Barend-Jan , Liempt Marcel
Published: September 2024

A new simulation model to predict tail rotor drivetrain maneuver loads at hover is developed. The model consists of a high fidelity dynamic engine simulation coupled to a multibody dynamics simulation of the main rotor system, tail rotor and drivetrain, including torsional flexibility of drivetrain shafts. Simulations of yaw doublets at hover demonstrate that tail rotor drivetrain loads can be reduced without compromising handling qualities for moderate amplitude heading changes. A full autonomous heave/yaw hover control law is developed with a nonlinear element in the heading feedback loop. The nonlinear element specifies the aggressiveness level (gain) as a function of heading angle change. It allows the flight control system engineer to simultaneously minimize tail rotor drivetrain maneuver loads whilst maintaining level 1 handling qualities. The nonlinear flight control system is evaluated for the ADS-33 hover turn mission task element and compared to a conventional linear control system. Level 1 performance is achieved with both control systems and dynamic tail rotor drivetrain loads are reduced up to 58% by the nonlinear element.
Time-to-Contact-Based Control Laws for Flare Trajectory Generation and Landing Point Tracking in Autorotation
Authors:   Georgia Institute of Technology, Rogers Jonathan ,   University of Liverpool, Jump Michael , Eberle Brian , Cameron Neil
Published: September 2024

For many rotorcraft platforms, incorrect timing of the autorotation flare and deceleration maneuvers may result in significant aircraft damage and injury to the crew, or worse. There is a clear need for new pilot cueing and control augmentation technologies that lead to a higher probability of a successful autorotation landing. This paper describes a recent effort to develop two different Tau (time-to-contact)-based autorotation controllers that can be used to drive visual aids to help guide a pilot to apply the required control inputs to complete a safe autorotative landing. Such controllers may also be useful for fully autonomous autorotation landing for unmanned vehicles.
Control Margin Awareness of the AW609 TiltRotor under Asymmetric Aerodynamic Flight Conditions
Authors:   AWPC, Xiao Sid , Belt David , D'Ettorre Pietro , Edwards Paul
Published: September 2024

The ability to model and evaluate aircraft performance prior to flight has generated a significant increase in safety margin in the flight testing of experimental aircraft. Prior to the artificial icing campaign for the AW609 aircraft, a flight model of predicted aerodynamic behavior was used to rapidly generate a control margin monitoring and warning system, which was implemented on-board the aircraft during testing to provide awareness of predicted aircraft behavior under icing conditions.
Extraction of a Dynamic Inflow Model from Wake Measurements on a Hovering Rotor
Authors:   The University of Texas at Austin, Yu Daniel ,   Piasecki Aircraft Corporation, Mortimer Patrick , Sirohi Jayant
Published: September 2024

The parameters of a Pitt-Peters dynamic inflow model for a rotor undergoing collective inputs were extracted from experimental measurements on a hovering rotor. The four-bladed rotor of 2 m diameter featured straight, untwisted blades and a solidity of σ = 0.010. The nominal trim condition was CT /σ = 0.07 at a speed of 840 RPM. The rotor wake was measured using phase-resolved, 2D, 3-component particle image velocimetry (PIV) over a large region of interest (0.84 m x 0.77 m), and the integrated rotor aerodynamic forces were obtained from simultaneous hub loads measurements. The frequency response of rotor inflow to rotor thrust was found by measuring the system response to a stepped-sine collective input, which included frequencies of 0.2, 0.3, 0.4, 0.6, and 0.7/rev. The thrust amplitude increased with input frequency, reaching 27.4% of the steady thrust at the highest input frequency. The inflow amplitude was 4.3% of the steady inflow at 0.2/rev and decreased to 2.0% at 0.7/rev. A first-order transfer function was fit to the discrete frequency response to compute the parameters of the Pitt-Peters dynamic inflow model. The apparent mass term for a rotor undergoing collective inputs was found to be M11 = 0.0288±4.4% and the gain term was found to be ¯L11 = 0.118±6.3%. The results agreed well with examples in literature extracted from high-fidelity numerical models. However, there were differences in the steady-state gain and the frequency at which the inflow magnitude is attenuated. The methodology for extending the present approach to cyclic inflow components is presented.
Usage Spectrum Contribution to Rotorcraft Dynamic Component Reliability
Authors:   US Army CCDC AvMC, Craven Allen
Published: September 2024

Rotorcraft dynamic component fatigue lives and corresponding reliability have long been derived from three major contributors: material strength, loads, and usage. This paper provides a historical perspective of the contribution of aircraft usage to overall U.S. Army rotorcraft dynamic component reliability. A quick background of how we got to a six-nines reliability requirement is first provided. Different types of usage spectra and the nuances and trade-offs of two specific usage gathering methods, pilot surveys and usage monitoring, are discussed. Finally, I describe where usage spectrum fits into fatigue life calculations and the existing reliability policy and requirements. Each OEM (e.g., Bell Helicopter, Boeing, Sikorsky) has been free to develop their own fatigue methods over the years. These differences in method can lead to vastly different results, even with the same input parameters as evidenced by a now well-known round robin problem. There is notable variability between OEM methodologies, each with viable solutions to this trivariate problem. In the interest of normalizing independent U.S. Government (USG) assessments across multiple OEM paradigms, the Army is investigating a USG method to assess the reliability contribution from usage. No new methods are presented herein, only findings of previous work. Uncited opinions herein are those of the author based on literature review, peer discussions, and experience with U.S. Army and U.S. Air Force (USAF) airworthiness processes. Reliability values in this paper are approximate, as there are elements of statistical distribution and non-statistical estimation that contribute.
U.S. Army Helicopter Structural Reliability and Fleet Failure Rate Requirement
Authors:   US Army CCDC AvMC, Janny Stephen
Published: September 2024

This paper presents a framework with associated concepts to define a method of compliance for the failure rate requirements of the Army Military Airworthiness Certification Criteria (AMACC), Chapter 5, for fleet qualification and first flight. The fleet failure rate requirement is paraphrased as less than one structural failure in 20 million flight hours at 95% confidence and applies specifically to fatigue failure of primary structural elements (PSEs). This method of compliance assumes a reliability model sufficient to support an analytical failure rate that bounds the uncertainty arising from practical constraints of an aircraft qualification program and aims to optimize the competing objectives of safety of flight and operational capability. The requirements as defined verify that the aircraft system will perform as intended for a specified fleet life and flight test program duration and serve as the analytical basis for the assessment of emergent issues identified throughout the product life cycle.
Estimating the Length of a Bearing Spall Using Tach from Vibration
Authors:   GPMS International Inc, Bechhoefer Eric ,   Ben-Gurion Unv. of the Negev, Matania Omri , Bortman Jacob
Published: September 2024

Rolling element bearing failures form one of rotating equipment's most critical failure modes. Vibration analysis has been successfully used for bearing fault detection and diagnostics but does not estimate the spall length of the bearing. An estimate of the spall length would provide insight into the degrading reliability of a drivetrain as the fault propagates. This would improve the timeliness of scheduling a maintenance action. In this paper, a synthetic tachometer signal is generated from the bearing fault itself. It is synchronous to the rolling element, allowing for a time-domain representation of waveform using the time-synchronous average. From this, an estimate of the length of the bearing fault can be determined.
Whirl Flutter Testing of ATTILA Tiltrotor Testbed - Initial Results
Authors:   Royal Netherlands Aerospace Centre, Hoff Stefan ,   Leonardo Helicopters, Fonte Federico ,   German Aerospace Centre, Soal Keith ,   German-Dutch Wind Tunnels, Kapteijn Kees , Schneider Oliver
Published: September 2024

This paper presents the preliminary results of the recent whirl flutter wind tunnel test campaign performed within the Advanced Testbed for TILtrotor Aeroelastics (ATTILA) project. The Froude-scale ATTILA testbed consists of a semi-span wing with powered tip-mounted proprotor reflecting the proprietary design of the Next Generation Civil TiltRotor (NGCTR). An overview of the ATTILA testbed, wind tunnel test procedures, team organisation and preliminary flutter results are presented. In line with pre-entry dynamic characterization tests, the wind-on test activities in the DNW Large Low-speed Facility (LLF) revealed notable force-dependent nonlinearity in the modal characteristics of, particularly, the wing torsion mode. Further dimensionality was added by early observations that damping in the rotor gimbal degree of freedom, attributed to stiction in the blade pitch mechanism, had the potential to substantially contribute to the damping of the fundamental wing-pylon modes. Nevertheless, the parallel exploitation of multiple monitoring and online modal estimation methodologies enabled a robust identification and safe test progression. The critical flutter mode was found to be configuration dependent, with the wing chord bending mode generally being marginally stable throughout most of the wind speed range, and the wing torsion mode displaying a sharp trend towards negative damping at higher speeds. Despite technical challenges, valuable test data was gathered to advance the experimental methods and support validation of the numerical tools used to obtained clearance for high-speed flight testing of the full-scale NGCTR Technology Demonstrator.
Adoption Of Virtual Twin Technologies For eVTOL Manufacturers, Infrastructure Providers, And Operators
Authors:   Dassault Systems, Licata Roberto , Benzaquen Isaac
Published: September 2024

Developing and operating an advanced air mobility service is challenging in many ways. The technical complexity of the task, the lack of available supporting infrastructure, the regulatory environment, and the necessity of collaboration among all stakeholders are barriers to a wide-spread implementation. Digital tools are now available to the whole industry to tackle those challenges, one of them being the virtual twin experience technology. The virtual twin experience is generated by the digital twin technology applied to a certain domain of application. It is a system of systems designed to provide users with a unique and immersive experience of reality, without physically being present in the real-world environment. It offers capabilities that go beyond traditional means, enabling organizations and users to achieve tasks and insights that were previously not possible. This paper describes how the virtual twin experience is adopted within the advanced air mobility ecosystem, that is comprised of the aircraft manufacturer, the vertiport provider and the operator. It reviews the different business processes on electric vertical take-off and landing (eVTOL) vehicle design and manufacturing, vertiport design, and operations, and highlights the associated benefits of such approach. Through these processes, we will see how the virtual twin experiences shape the future of product design, manufacturing, and operations. It changes the way in which stakeholders collaborate in a complex system of systems context. The paper concludes on the ways that the virtual twin experience provides organizations enhanced visualization and understanding, expanded trade-space exploration, and improved decision-making, and how it enables innovators and enterprises alike with greater visibility, efficiency, flexibility, and compliance.
High-Fidelity Digital Twin Autoclave Tool for Quality Informed Composite Fabrication
Authors:   Global Engineering and Materials Inc., Lua Jim ,   University of Illinois, Yan Jinhui ,   Naval Air Warfare Center (PAX), Guay Ian , Shrestha Kalyan , Karuppiah Anand , Phan Nam
Published: September 2024

The Autoclave processing is commonly used in manufacturing high-performance fibre-reinforced thermoset composite components in the aerospace industry. Variations in the cure cycle, sometimes even apparently minor deviations from the prescribed cure cycle, can harm the laminate properties. Given the costly and time-consuming autoclave manufacturing process, there is a strong need to cure the maximum number of parts in the shortest possible time without compromising quality. In order to achieve high-rate automated manufacturing with the optimized autoclave process, it is important to construct a digital twin modelling approach to mirror the physical composite curing process in the virtual domain based on the integration of high-fidelity multi-physics models. The resulting digital twin includes a thermal CFD model, a thermo-chemo-mechanical module, and an efficient and accurate block coupling between these two modules. The customized Abaqus driven by local and spatial variation of the turbulence-induced heat transfer coefficient (HTC) imposed through one-way coupling determines the thermo-mechanical response in composite parts. Using the developed digital twin tool (SMARTCLAVE), HTC's spatial and temporal variation can be generated digitally without invoking an expensive and time-consuming experimental approach. The predicted local boundary conditions are used in SMARTCLAVE to determine the cure kinetics, temperature distribution, and thermal-mechanical response that drives the residual stress and distortion of composite parts after curing. The accuracy of the digital twin for autoclaving is demonstrated first using a benchmark problem followed by the capability demonstration with a single-part L-beam assembly. The benefits of using the digital twin tool are illustrated via the optimal placement of multiple parts in an autoclave to balance the throughput and quality.
Correlation of Rotor Loads during Ground Operations in a Turbulent Wind Environment
Authors:   Leonardo Helicopters, Capizzi Cristiano , Bucciaglia Giuseppe , Frassoldati Gregorio , Prederi Davide
Published: September 2024

Rotorcrafts frequently operate in environments with severe atmospheric turbulence, for instance transferring people offshore to and from oil rigs as well as operating from and around ships. The presence of high turbulence can deteriorate performance, stability, and controllability of the rotorcraft. Additionally, such challenging conditions also generate loads that both airframe and rotor components must withstand. Following this, it is crucial to consider the impact of these operational atmospheric conditions during rotorcrafts design and development. In this context, numerical models are a fundamental tool to provide an easier and quicker way to explore the operative envelopes of the helicopter compared to performing experimental activities. This paper presents a rotor loads correlation activity between an experimental test designed and carried out by Leonardo Helicopters in which an AW189 helicopter was placed in the wake of a C-27J Spartan aircraft and a multibody structural model built using MSC Adams®. Furthermore, an atmospheric turbulence model is proposed and compared with the wind experimental records with the purpose of defining an analytical tool for the estimation of the wind time histories. The main purpose of the work is to detail the extensive correlation activity and highlight the modeling key ingredients to consider for an accurate load prediction in a turbulent wind environment. The correlation focuses on the effect of the wind during ground operations, considering the rotor at rest or running up/shutting down.
Multifidelity Uncertainty Quantification in Battery Performance for eVTOL Flights Under Material and Loading Uncertainties
Authors:   UC San Diego, Guibert Alexandre , Díaz-Flores Álvaro , Chaudhuri Anirban , Kim H. Alicia
Published: September 2024

This study addresses safety concerns within the rapidly evolving Electric Vertical Takeoff and Landing (eVTOL) aircraft domain, focusing on efficient tools to quantify uncertainties in lithium-ion battery behavior - a critical aspect of eVTOL. One major issue with quantifying uncertainty is the prohibitive computational cost associated with many queries of an expensive-to-evaluate computational model. This work employs three physics-based battery models models of varying fidelity and cost to estimate the mean and the variance of the selected quantities of interest through a multifidelity method to reduce the computation cost. By combining information from multiple cheaper, lower-fidelity models through the Multifidelity Monte Carlo method, we significantly reduce the number of high-fidelity samples required for a prescribed mean-squared error, consequently reducing computational costs down to a tractable level. The proposed methodology is applied to estimate the mean and the variance of the battery temperature and voltage, accounting for uncertainties in flight conditions and materials. The first example focuses on a 580-second flight and is benchmarked against a standard Monte Carlo sampling technique. Results indicate a notable fourfold speed-up using the Multifidelity Monte Carlo method compared to the standard Monte Carlo method for the same mean-squared error for the voltage estimate. To showcase the method's generality, the multifidelity method is then applied to a longer flight of 3580 seconds for estimating the mean and the variance and utilizing these statistics to approximately estimate the probability of the flight completion. This demonstrates the adaptability of the methodology to various power profiles and considered uncertainties, with potential extensions to any battery chemistry. In conclusion, the presented multifidelity method offers a robust approach to enhance eVTOL safety by efficiently estimating uncertainties in battery behavior.
Shot Peen Surface Repair: The Impact of Residual Stress
Authors:   Lockheed Martin, Conklin Craig , Barrett Arild , Flores Ric
Published: September 2024

Shot peened components present a challenge for the structural analyst when nicks, scratches and gouges are discovered. A common repair scheme calls for blending away of the defect with an appropriate grit abrasive. Though the blending operation removes the defect, it also takes away a portion the beneficial compressive layer as well as the cold-worked material. Large repair facilities may have touch-up shot peen capability but technicians in a field repair setting typically do not. If the shot peen cannot be restored, the structural analyst must have a method to quantify the effect on fatigue life of the repaired part. The purpose of this technical paper is to substantiate analytical techniques for evaluating the fatigue life of a shot peened part after a blend operation. In addition to practical methods to estimate the magnitude of the residual stresses, a numerical method is introduced using finite element modeling of shot peen impacts with non-linear finite element code and validation by a simulated Almen strip.
Advancing Cockpit Safety: Cost-Effective Flight Data Monitoring with Deep Learning
Authors:   Rowan University, Khelifi Amine ,   ESPRIT, Trabelsi Mohamed ,   Federal Aviation Administration - FAA, Thompson Lacey , Carannante Giuseppina , Bouaynaya Nidhal , Johnson Charles
Published: September 2024

The rotorcraft community faces significantly higher accident rates compared to fixed-wing commercial aircraft, underscoring the critical need for enhanced safety measures. While Helicopter Flight Data Monitoring programs hold promise in improving safety, their widespread adoption remains limited, partly due to challenges associated with the acquisition and analysis of flight data. This paper proposes a Deep Learning (DL) solution to address safety concerns within the rotorcraft community by efficiently acquiring and analyzing flight data for a more automated and comprehensive safety assessment. Specifically, we leverage data obtained with cost-effective off-the-shelf cameras, and process it through Convolutional Neural Networks for automated detection and classification of gauges from several helicopters' cockpits. Our DL pipeline integrates a classifier for helicopter identification, an object detector for cockpit gauges detection and classification, and a network to infer the reading of each detected gauge. The contribution of this work is two-fold: (1) enhance rotorcraft safety by developing a DL framework capable of detecting, classifying, and inferring gauge readings for different helicopter types, and (2) boost research in the field by constructing a curated dataset valuable for aviation and machine learning communities.
Characterization and Modelling of Composite Fastened Joint for Impact Analysis
Authors:   Politecnico di Milano, Novembre Edoardo ,   Leonardo SpA, Cacchione Benedetta , Airoldi Alessandro , Brunori Filippo , Janszen Gerardus
Published: September 2024

This work proposes an experimental and numerical activity aimed at developing methods to evaluate the strength and toughness of Kevlar/Epoxy composite fastened joints used in aeronautical structures and exposed to high energy impacts. Experiments were conducted using an Arcan rig that allowed applying various loading conditions, ranging from pull-through to bearing. A non-linear model of the material based on a bi-phasic decomposition and hybrid meshing technique was built and calibrated. The material model was used to develop a high-fidelity model of the junction to simulate the pull-through test with the Abaqus/Explicit finite element solver. The results of the analysis point out that the implemented progressive damage laws are capable of achieving an appreciable experimental-numerical correlation, both from the qualitative and the quantitative standpoint. Therefore, the combined experimental-numerical approach is promising for developing a validated numerical tool capable of predicting the overall response of different junctions with minimal experimental effort, so to provide data for simulating impact scenarios at the rotorcraft structural scale and designing critical joints.
Corrosion Prediction for Helicopter Application for Maintenance
Authors:   Airbus Helicopters, Snopoli David , Devilliers Georges , Dias Patricia
Published: September 2024

Corrosion occurs in diverse environments mainly on metallic parts. Helicopters are made of a huge percentage of metallic parts and need to have several maintenance steps to guarantee its functioning and its durability. The military helicopters are flying in different kinds of environment, which cover large spectrum of severity of the atmospheric corrosion [1]. In maritime conditions, the most influencing factor is the Time of Wetness, which is a direct result Relative Humidity and Salt loading. The main material used for aircraft and that is suffering from corrosion is aluminium. There are plenty of data to follow the corrosion as a function of the environmental conditions, mainly on the sensitivity with sodium chloride, Relative Humidity, film thickness, etc... [2][3]. The maintenance efficiency on helicopters is dependent on the environmental severity. The U.S. armed forces estimate $10.2 billion in corrosion costs for their aviation and missile fleets during 2016 [4] [5] [6]. The aim of the present analysis consists of defining the Condition Based Maintenance related to corrosion risk to better apply a maintenance program when it is really needed.
Multicyclic Control for Vibration Reduction of Lift-Offset Coaxial Rotorcraft
Authors:   Konkuk University, Hong Seong ,   Korea Aerospace Research Institute, Kim Do-Hyung , Kim Dong , Jung Sung
Published: September 2024

This study explores the best vibration reduction using a multicyclic controller through an individual blade control (IBC) actuation scheme for a lift-offset coaxial helicopter in high-speed flight. The rotorcraft dynamics model consists of coaxial, three-bladed counter-rotating rotors and a finite element fuselage stick model constructed based on the measured data of the XH-59A helicopter. The two-way coupled rotor-body vibration analysis results exhibit excellent correlations with the test data for rotor hub loads and airframe vibrations. The best actuation scenarios are sought for the minimum vibration of the vehicle using either open- or closed-loop control scheme. It is shown that the IBC actuation effectively reduces the vibrations at both locations of the rotorcraft. The co-reduction of 3P (per rotor revolution) and 6P vibration of the rotorcraft is achieved using the multicyclic control with offline system identification. A multicyclic harmonic IBC actuation enables to suppress the rotorcraft vibration by 81.4% and 3P pilot seat vibration by 92%, respectively, as compared to the uncontrolled case, leading to a significantly reduced vibration level (below 0.05g) of the rotorcraft. The closed-loop multicyclic control using the identified system and the aircraft model shows a good correlation ensuring the suitability of the present optimal control simulations.
Lightning Strike Experiments and Their Direct Effects on Flax Fiber-Reinforced Polymer Panels for Rotorcraft Components
Authors:   Technical University of Munich, Gaugelhofer Lucas , John Jonas , Hajek Manfred , Yavrucuk Likay
Published: September 2024

This paper experimentally investigates direct effects of lightning strikes on flax fiber-reinforced polymers. Highcurrent artificial lightning strikes are conducted on coupon level to evaluate thermo-mechanical damage and to quantify the sufficiency of copper wire mesh as lightning strike protection (LSP). The dataset shall also serve for verification of prospected numerical simulation. The natural fiber flax, as a sustainable source of composite reinforcement, has been demonstrated to be suitable for semi-structural parts of rotorcraft. However, its low electrical and thermal conductivity requires a functional LSP layer for aviation applications. The test panels are investigated regarding their material combination, stacking sequence and level of LSP. Results show that two as well as three layers of 72 g/m2 copper mesh are not sufficient to withstand the standardized lightning current component A waveform of 200 kA. The high induced currents and low capability of energy dissipation leads to electro-explosion of metal and transient mechanical forces from shock waves causing mechanical damage on the test panels. Back surface-velocities increase with higher peak currents and higher level of protection results in lower damage. It is shown that a stacking of copper wire mesh results in less arc root dispersion.
Modeling Activities of Propulsion System Engine Installation Survey
Authors:   Turkish Aerospace, Sancar Emre , Daldal Abdurrahman , Çakiroğlu Taylan , Bayat Akay , Ezertaş Ahmet
Published: September 2024

The multi-role utility helicopter T625 GÖKBEY is designed by Turkish Aerospace and it is equipped with a pair of two-spool CTS800-4AT turboshaft engine developed by Light Helicopter Turbine Engine Company (LHTEC). Components of the cowlings, intakes and exhausts were designed with supplementing CFD analyses and performance of various alternatives were evaluated. Final designs were achieved based on the helicopter performance and engine limits. In order to verify the estimated engine installed performance in design phase, performance of the instrumented engine with its integrated equipment on the platform is examined using flight test data. This paper focuses on the CFD simulations based performance predictions of the air induction system, exhaust system, and IPS blower exhaust. A comprehensive study is assessed to create more realistic models by using flight test data.
Development of Turbulence Based Design Criteria for Vertiports
Authors:   RWDI, Larose Guy , Schajnoha Sharon , Labbad Maryam
Published: September 2024

The development of turbulence criteria to provide early guidance for the design of vertiports is presented in this paper. For any aircraft, winds, in particular crosswinds and gusty winds, are top of mind for all pilots engaging in take-off and landing maneuvers. It is anticipated that the same will be true for VTOL and eVTOLs landing on vertiports, in particular as new vertiports are built closer and closer to urban centres. First, a review of the current design criteria for vertiports around the world related to wind is presented, highlighting the commonality between the guidance and the gaps in their content. Second, the controllability criteria that VTOL and eVTOLs will likely need to meet in the pursuit of an airworthiness certification are reviewed and their pertinence with regards to vertiport design are discussed. Third, the characters of the wind and their impact on eVTOL flights at or near take-off and landing infrastructure is explored. Finally, a set of turbulence criteria for vertiports and a turbulence index are proposed. The index includes a scale for conditions ranging from favorable for take-off and landing; to more and more demanding conditions; up to turbulence conditions to be firmly avoided.
Dynamic Behaviour of a Rotorcraft Main Rotor System with Variable Speed
Authors:   TU Wien, Scheu Thomas , Poks Agnes , Weigand Michael , Koch Jonas
Published: September 2024

Current Rotorcraft Developments like under the Future Vertical Lift Program in the USA (e.g. Bell V-280, see figure 1) respectively RACER (Airbus Helicopters, see figure 2) and NextGENCivil Tiltrotor (Leonardo, see figure 3) in Europe deal with High-Speed Rotorcraft or Tiltrotor-/Tiltwing Aircraft. They can expand and optimize their performance by using a variable rotor speed either to adopt the rotor speed to high forward speed or to meet the different requirements of a rotor in Hover and Aircraft Mode of a Tiltrotor-/Tiltwing Aircraft. As the required speed range can not be covered by the turbine, TU Munich (Germany), TU Wien (Vienna, Austria), ADT - Advanced Drivetrain Technologies (Austria) and Zoerkler Gears (Austria) work in the transnational project "VARI-SPEED II" on a rotor system that can change the rotor speed via change of the ratio of the transmission (variable rotor speed with constant turbine speed). The project is based on the results of "VARI-SPEED" and the direct follow-up project. VARI-SPEED showed that a rotor speed variation performed by a transmission system is possible. The efficiency and the flight envelope of the rotorcraft can be improved by this technology. Furthermore, a method for rotor blade design in a RPM range was invented. VARI-SPEED II now has built up a model of the complete dynamic system from engine to rotor of a helicopter with a variable speed rotor. This model is used for dynamic simulations of the components and the whole system. A scaled model of the module that changes the speed will be developed and pilot studies in a simulator are planned to find out the characteristics of such a system. Aim of the project is to reach TRL 3 as basis for further development of the technology with interested OEM's. This paper deals with the dynamic behaviour of the components and the whole drive train. The Bell V-280 is in the flight testing phase, RACER has recently conducted its maiden sortie and for the NextGENCtr the first flight is announced for the first half of 2024. All mentioned aircraft use transmission systems with a fixed gearbox ratio; this is feasible as a new technology like Vari-Speed normally is not added to completely new rotorcraft. However as the OEM's rate Vari-Speed positive, variable rotor speed can be integrated in a later development stage of the rotorcraft and thus development timelines of the rotorcrafts and Vari-Speed match quite well.
Fatigue Simulation Method based on the Calculation of the J-Integral in the Cohesive Zone Delamination Model
Authors:   University of Texas at Arlington, Nikishkov Gennadiy ,   US Army DEVCOM AvMC, Matthews Peter , Nikishkov Yuri , Seon Guillaume , Makeev Andrew
Published: September 2024

A state-of-the-art emerging progressive damage failure analysis tool CDMat has been successfully applied to multiple material systems on open-hole tension and compression, and double shear bearing laminate coupons under static and fatigue loading including simulation to ultimate failure. CDMat also successfully demonstrated component-level strength/fatigue analysis under the Air Force Composite Airframe Life Extension (CALE) and the Fail-Safe Technologies for Bonded and Unitized Composite Structures (FASTBUCs) Programs. Building on the success of CDMat an integrated software solution for certification and sustainment of rotorcraft primary composite structures is being developed. A method and an algorithm for fatigue crack growth simulation in laminated structures are proposed to improve the accuracy of CDMat fatigue predictions. The method is based on using cohesive material model, tracking material points at the crack front, and calculating the pointwise energy release rate employing the J-integral. The algorithm was implemented as a set of user material subroutines developed within the framework of explicit finite element formulation for ABAQUS. The effectiveness of the method is demonstrated on several examples of Mode I and II fatigue crack growth.