bluuebunny/crossref_metadata_2025 huggingface dataset:
A Proposed Approach to Studying Urban Air Mobility Missions Including an Initial Exploration of Mission Requirements
Authors:   NASA Langley Research Center, Patterson Michael , Antcliff Kevin , Kohlman Lee
Published: September 2024

Urban air mobility (UAM) is an emerging aviation market that seeks to revolutionize mobility around metropolitan areas via a safe, efficient, and accessible on-demand air transportation system for passengers and cargo. In this paper we describe our three-pronged approach to studying passenger-carrying UAM missions, and we detail the first phase of this approach, which consists of defining an initial set of requirements for multiple exemplar UAM missions. The development of these mission requirements provides justifiable assumptions that feed the second phase of the approach, which is performing aircraft conceptual design studies. Vehicle design is not included in this paper, but the work described here will define sizing missions for follow-on design and sizing studies. The aircraft that emerge from the design studies can then feed the third phase of our UAM analysis approach, which involves simulating an entire UAM network over a metropolitan area to study transportation-system level characteristics. Iteration between each of the three phases of the UAM analysis approach will be necessary to propagate lessons learned as our research progresses and as the UAM community coalesces on a more unified vision for UAM. Therefore, we anticipate that the mission requirements set forth in this paper will be modified over time as the urban air mobility concept matures.
Tiltwing Multi-Rotor Aerodynamic Modeling in Hover, Transition and Cruise Flight Conditions
Authors:   A3 by Airbus, Droandi Giovanni , Syal Monica , Bower Geoffrey
Published: September 2024

The paper discusses the aerodynamic modeling of a multi-rotor, tandem tiltwing aircraft called Vahana. Vahana is an all-electric, fully-autonomous aircraft being built by A3 by Airbus LLC. Vahana can take off and land vertically using eight fans, and can transition into cruise using fans and tilting wings. Vahana is designed to be able to trim at any speed during transition, even with the failure of any one of its eight motors. Aerodynamic modeling of Vahana is a challenging problem because of the interactions between multiple fans and wings during transition. In the present work, a medium-fidelity aerodynamic modeling tool is used for solving the flow around Vahana in any arbitrary flight condition. The trim involves finding the optimum settings of Vahana's multiple actuators, which include variable speed electric motors, variable pitch fans, tilting wings, and control surfaces. An optimization procedure is developed to find trim solutions through the transition maneuver while minimizing the vehicle total power. To speed up the analyses, surrogate aerodynamic models of the vehicle are created using Gaussian processes, which are then used in the optimization to compute the aerodynamic loads given a set of vehicle states and actuator settings as inputs. The results present a transition trimline for Vahana. A cross-check on the trim solutions is performed using a high-fidelity CFD solver. A comparison of the loads and flow fields predicted by the medium-fidelity tool and the CFD solver is presented.
Chezoia 24-Hour Hovering Machine Conceptual Design - 2017 Student Design Competition Undergraduate Proposal
Authors:   University of Maryland, Desrochers Andrew , Dallas Andrew , Jeremy Foust , Jordan Scott
Published: September 2024

34th Annual AHS International Student Design Competition 2017 - 24 Hour Hovering Machine Conceptual Design, Undergraduate Entry
Researching the Cruise Potential of the Arc Wing VTOL Concept
Authors:   Bertelsen Design LLC, Bertelsen William
Published: September 2024

The Bertelsen arc wing VTOL is an attractive concept for general aviation due to its mechanical simplicity and relatively low cost. Work to realize the performance potential is ongoing. The hover efficiency of the multi-element arc wing in VTOL mode has been demonstrated in tethered tests of a large powered model. It remains to characterize the arc wing in the cruise configuration. While the unique arc wing geometry effectively captures the flow from a large propeller, the radically anhedral wing challenges the intuition as to what behavior to expect in forward flight. An electric-powered radio-controlled model has been built to explore the cruise performance of the rigid arc wing. The preliminary results of that effort are the subject of this paper.
The Semi-Coaxial Multirotor
Authors:   Georgia Institute of Technology, Bershadsky Dmitry ,   Pennsylvania State University, Johnson Eric , Haviland Stephen
Published: September 2024

The "semi-coaxial" multirotor configuration is presented including its advantages over the conventional coaxial rotor configuration. The semi-coaxial configuration retains the benefits of the coaxial configuration, and additionally alleviates the loss of efficiency encountered when rotors are stacked coaxially. In addition to being more power-efficient than the standard coaxial configuration, the described configuration allows for nearly- or fully-actuated control of a multirotor when used in configurations such as the three-armed Y6 hexarotor. Using this configuration, a new Direct Force Control (DFC) multirotor is presented: the Y6sC, a specific example of the semi-coaxial multirotor. The configuration orients six rotors in a way which allows the vehicle to hover in non-zero attitudes and translate without rotating with higher efficiency than the corresponding coaxial design.
Multi-objective Horizontal Stabilizer Optimization Using Genetic Algorithm
Authors:   Turkish Aerospace Industries Inc., Sansal Kaan , Koçak Göktug , Kargin Volkan
Published: September 2024

Multi-objective optimization of horizontal tail of a conventional rotor helicopter is achieved using a genetic algorithm, which is coupled with comprehensive analysis tools, Flightlab® and in-house rotorcraft simulation tool TAI Originated Rotorcraft Simulation (TOROS). Genetic algorithm is used to design a tail that improves static longitudinal stability characteristics of the helicopter during autorotation as well as its longitudinal dynamic stability characteristics at high speeds. Another optimization target is to minimize pitch attitude change in transition to forward flight while keeping pitch attitude close to zero at 140 knots in cruise. This study shows a framework of horizontal stabilizer optimization over its aerodynamic lift characteristics, which can be altered either by introducing gurney flaps and/or slats to change lift characteristics, vortex generators (turbulators) to postpone flow separation or simply by changing incidence angle. By solving a multi-objective optimization problem, the aim of this study is to find an optimum lift curve slope, incidence angle and size of the horizontal stabilizer that satisfies performance and handling qualities requirements of the helicopter. It was witnessed that there are always some trade-offs between optimal design alternatives in Pareto Front and therefore selection of optimum horizontal tail configuration depends highly on these requirements. This study shows that multi-objective optimization can be used as a design tool to replace human effort prior to or during the flight tests by tuning aerodynamic configuration and size of the horizontal tail.
Automated Layout with a Python Integrated NDARC Environment
Authors:   US Army Aviation and Missile Research, Perry Travis , Gallaher Andrew
Published: September 2024

Geometric layout of an aircraft concept is a fundamental aspect of the design process and can often be a primary driver for design choices, and trade space decisions. Most commonly, geometry is either estimated analytically by performance and sizing tools, from in-production aircraft data, or modeled using Computer Aided Design (CAD). Analytic geometry estimates are often not precise, requiring CAD to refine these estimates. Modeling an aircraft design to the fidelity needed to refine these geometric estimates can be a time consuming process. Furthermore, the initial layout design iterations are primarily used to refine prior estimates rather than address layout design choices. There is a need to accomplish these high level layout tasks in a timely manner; allowing for broad trade space analysis, and relying on CAD later in the design process for more detailed geometric layout. This paper will cover the development of the Automated Layout with a Python Integrated NDARC Environment (ALPINE), a Python Application Programming Interface (API) based geometry tool which leverages outputs from NASA Design and Analysis of Rotorcraft (NDARC) and the geometry software OpenVSP to expedite high level layout processes. ALPINE is an object oriented API tool that streamlines the initial conceptual layout process. This is accomplished through mapping NDARC geometry parameters to custom components generated in OpenVSP, and using algorithms native to OpenVSP. Through the use of this tool, the time needed for initial geometric layout is reduced significantly, potential design challenges can be highlighted without a detailed CAD model, geometry can be integrated within closed loop design optimization problems, and analytic geometry estimates from performance sizing codes can be refined and correlated to 3D model-based analyses.
Further Development and Piloted Simulation Evaluation of the Break Turn ADS-33 Mission Task Element
Authors:   Sikorsky a Lockheed Martin Company, Xin Hong ,   The Pennsylvania State University, Horn Joseph ,   Bell Helicopter, Ruckel Paul ,   The Boeing Company, Brewer Roy ,   Systems Technology Inc., Klyde David ,   US Army RDECOM, Ott Carl , Fegely Cody , Fell William , Rigsby James , Conway Frank , Mulato Ray , Pitoniak Sean , Schulze P. , Blanken Christopher
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" is a U.S. Government and Industry co-funded three year research project. A Sikorsky-led 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. Following the mission-oriented approach upon which ADS-33E-PRF is based, the MTEs were designed to meet different levels of precision and aggressiveness. Break Turn MTE was defined for non precision, aggressive applications in order to provide a suitable coverage of aggressive air combat maneuvers in future ADS-33. The MTE objectives, descriptions, and performance criteria were systemically developed via a series of piloted simulation sessions at each team's simulation facility. Formal evaluations were then conducted by US Army test pilots at four simulator facilities, each featuring a unique high-speed platform including an X2 Technology™ compound helicopter, two tiltrotor configurations, 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 Break Turn MTE provided an effective means to discern non-precision, aggressive handling qualities in high speed flight.
Piloted Simulation Evaluation of Attitude Capture and Hold MTEs for the Assessment of High-Speed Handling Qualities
Authors:   Systems Technology Inc., Klyde David ,   Bell Helicopter, Ruckel Paul ,   Sikorsky a Lockheed Martin Company, Xin Hong ,   The Boeing Company, Brewer Roy ,   The Pennsylvania State University, Horn Joe ,   US Army RDECOM, Ott Carl , Pitoniak Sean , Schulze P. , Rigsby James , Fegely Cody , 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 have been 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. The attitude capture and hold MTEs that are the subject of this paper were defined to be precision, non-aggressive tasks that build upon fixed wing analogs. 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 attitude capture and hold MTEs provided an effective means to discern precision, non-aggressive handling qualities in high speed flight.
Model Predictive Path Integral Approach for Trajectory Guidance of Rotorcraft Shipboard Landing
Authors:   Georgia Institute of Technology, Prasad J.V.R. , Comandur Vinodhini , Walters Robert , Guerrero David
Published: September 2024

Rotorcraft shipboard landing continues to be challenging due to increased pilot workload in dealing with effects of ship air wake turbulence on vehicle motion and random ship motion. Some of the recent work has proposed a pilot assist function for reduced pilot workload using model predictive control methods. This paper explores the use of a recently developed Model Predictive Path Integral (MPPI) method based on a stochastic optimal control framework for trajectory guidance solution to the shipboard landing problem. First, a proof-of-concept study is presented by applying the MPPI method to a simple point mass approximation of helicopter dynamics represented in the form of a first-order command acceleration model, representative of helicopter trajectory motion in the vertical plane. Next, the MPPI method is used in conjunction with a six degrees-of-freedom linear model of a helicopter in order to gain further insight into the applicability of the MPPI framework to the rotorcraft shipboard landing problem. The paper concludes with key observations and inferences gained in this study.
Model-Following Control and Actuators Limits Analysis to transform Helicopters into 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 , Bülthoff Heinrich
Published: September 2024

The paper shows the design of a control augmentation system to transform helicopters into Personal Aerial Vehicles, accounting for handling qualities and actuator constraints. In this paper, PAVs are conceived as augmented rotorcraft that can be safely flown by minimal-trained pilots with a training comparable in length to that necessary to learn how to drive a car. The goal of the paper is to evaluate if existing actuators allow current helicopters to achieve PAV's characteristics without incurring into prolonged rate or position saturation due to abrupt or large control inputs given by minimal-expert pilots. The goal is achieved in two steps: in the first step, a model-following control approach is implemented to follow PAV's reference dynamics used as command models. The controller is designed and tested by considering the state-space model of a Sikorsky UH-60 and by including actuator dynamics. An optimization routine is created to achieve a trade-off between handling qualities, disturbance rejection properties and stability margins. In the second step, pilot in-the-loop simulations are conducted with one expert and one non-expert pilot to evaluate the feasibility of the controller implemented in the first step. Results show that PAV requirements can be achieved with the available technology but the current helicopter handling qualities requirements should be relaxed in order to reduce the risk for actuators saturation, especially in presence of disturbances.
Increasing the Fatigue Life of a Structural Web with a Large Rectangular Cutout Under Complex Loading
Authors:   Columbia Helicopters, Truitt Joseph
Published: September 2024

This paper details an analysis methodology for a primary structure component on a tandem rotor helicopter that has been shown to experience fatigue damage in operation. The primary structure component is a web in the aft pylon of the helicopter. The web carries a complex set of loads in flight with various forces and moments applied along its boundaries and rotor torque reacted around a large rectangular cutout in the web. Due to the complex loading applied to the web, there is no clear location that can be considered to carry a "gross" stress, rendering traditional hand calculation methods (such as the use of stress concentration factors applied to a gross stress) impractical. The analysis detailed in this paper considers the application of flight loads to Finite Element Models to determine stresses in the web, which are used to evaluate fatigue life based on various flight conditions.
A Structural Load Comparison of Dynamically Balanced and Imbalanced Main Rotor Blades
Authors:   US Army CCDC AvMC, Viall Wesley ,   University of Alabama in Huntsville, Meyer Emily , Fry Kit , Smith Graham
Published: September 2024

A limited flight load survey was performed on a fleet representative UH-60L aircraft flown with various degrees and combinations of dynamically imbalanced blades. Blades selected for this test ranged in both positive and negative severity of pitching moment slope values to substantiate rotor smoothing efficacy and the effect on dynamic component oscillatory loads for dynamically imbalanced blades compared to a baseline of nominally balanced blades. For every component analyzed, greater than 70% of the maneuvers presented showed an increase in structural loads in the unbalanced configuration compared to the baseline balanced blades. Most components and maneuvers that did experience an increase in loads remained non-damaging. However, the damper experienced several maneuvers where an increase in loads may have indicated a change in fatigue lives. Based on a colloquial rule of thumb.
Deployment Methodologies of Fleet Air Vehicles on New Small Air Capable Ships
Authors:   Fincantieri Marine Group, Ferrier Bernard , Olivari Roberto , Greco Francesco , Librandi Gabriele
Published: September 2024

Launch, recovery, and deck handling operations are among the most challenging tasks in the deployment of fleet piloted and unpiloted air vehicles on board of air capable ships. In today's long-lead acquisition process, some existing devices are installed on new ship platforms for which the air vehicle was not initially designed. As part of the Navy deployment process, a ship suitability assessment is conducted in the form of Dynamic Interface (DI) testing. DI testing evaluates all aspects of shipboard helicopter including suitability, compatibility, adequacy, effectiveness, safety of air vehicle shipboard Flying Qualities and Performance (FQ&P), aviation support facilities and procedures for all ship-based aircraft types. With monohulled rudder/screws steered legacy vessels, certain seakeeping and turbulent boundary properties have open-ocean performance similarities. When faced with a deployment target ship producing different ship properties, a systematic approach to adapt to the new environmental condition is devised. A significant example involves the deployment of air vehicles (both piloted and unpiloted) on-board LCS class vessels where large, unexpected roll oscillations, coupling with rapid motions of the stern, are recorded. These unusual deck responses have been traced to shipboard operational characteristics which do not relate to the seaway alone. The implications for air vehicle operations encountering seemingly random large motions further underscores the need for an accurate definition of the ship's dynamics and, possibly, refined models able to predict steep motions anticipating the onset of excessive movements.
In this paper we describe a new instrumentation with the goal to predict ship motions conditions with sufficient forecasted time (over a minute) to launch, recover and complete other motion sensitive tasks regardless of the seaway. The fundamental concept is to measure remote sea surface profiles to predict the future wave forces acting upon a vessel as a function of the approaching air vehicle. The final objective is to expand ship operating deck limits to approximately Sea State 6+. This will allow the air's vehicle operator to have a more complete deck information and ship behavior. This article describes the common test procedures being developed at Fincantieri to define the deck behavior with the least air vehicle modifications. Enhanced dynamic interface testing is designed to better understand how the new ship classes affect the deck environment. The enhanced trial methodology test results clearly characterize essential aspects of the ship responses to the maritime climate and its impacts on air vehicle launch and recovery.
Inflow Model Effects on Propeller Whirl Flutter
Authors:   Georgia Institute of Technology, Gali Sai ,   University of Michigan, Chang Jasmine , Riso Cristina , E. Carlos
Published: September 2024

This paper investigates an output-based approach for tiltrotor whirl flutter bifurcation analysis. The approach uses free decay output data for a quantity of interest at various forward speeds to estimate the system's recovery rate to equilibrium while capturing its variation with amplitude. The recovery rate is then extrapolated to predict the bifurcation diagram, which gives the limit-cycle oscillation amplitude for the quantity of interest as a function of the forward speed. The approach is demonstrated using output data from transient simulations of a notional tiltrotor model with polynomial structural nonlinearities. The approach accurately predicts the tiltrotor whirl flutter speed and limitcycle oscillation amplitudes while only requiring two free decays. This approach can facilitate whirl flutter bifurcation analyses of tiltrotor systems exhibiting nonlinear dynamics.
Piloted Simulation Handling Qualities Evaluation of a UAM-Scale Quadcopter with Hybrid RPM and Collective Pitch Control
Authors:   Rensselaer Polytechnic Institute, Walter Ariel ,   North Carolina State University, Gandhi Farhan ,   US Army CCDC AvMC, Berger Tom , Niemiec Robert
Published: September 2024

A real-time capable simulation model is developed for a 1200 lb quadcopter with hybrid variable-RPM and collective pitch control. Linear models and trim points are calculated using the Rensselaer Multicopter Analysis Code (RMAC), and controllers are designed to meet flying qualities specifications in hover and forward flight. Four control modes are flown by test pilots in a flight simulator. Three hybrid control configurations (Eco, Standard, and Sport modes) are evaluated, along with a baseline variable-RPM case. Five mission task elements (MTEs) are flown to test the handling qualities of each axis: Depart/Abort, Slalom, Hover Turn, Vertical Maneuver, and Precision Hover Task. Pilot feedback is collected in the form of handling qualities ratings (HQRs), as well as general comments. The baseline RPM control case is shown to be undesirable to pilots due to its increased delays, with the average HQR in the Level 2 region. Sport mode performs the best overall, with the average HQR being near the Level 1/2 boundary, though some pilot comments suggest that it may be over designed. The average HQR for Standard mode also falls on near the level 1/2 boundary, and pilots are generally satisfied with its performance. Eco mode is limited by its low pitch actuator margin, and has the lowest HQR due to its slow response and reduced magnitude of commands. Overall, it is shown that the hybrid control quadcopter is able to significantly outperform its variable-RPM counterpart in piloted simulation of MTEs.
PIO and Handling Qualities Prediction Using the USAFTPS Bjorkman PIO Data Set
Authors:   San Jose State University, Bachelder Ed ,   Air Force Test Center, Bjorkman Eileen ,   Federal Aviation Administration, Aponso Bimal
Published: September 2024

A key objective of this work was to develop a quantitative rationale to explains some aspects of pilot rating variability, as this would point to the fundamental principles driving pilot response that may not be observable if averaged ratings are used as a handling qualities metric. This paper hypothesizes that the factors affecting a pilot's ability to stabilize and control an aircraft following abrupt control motion is neither the damping nor the frequency of the ensuing oscillation, but rather the length of time that the oscillation remains large enough to interfere with the task (i.e., the product of damping and frequency). A handling qualities metric is introduced called the decay rate parameter that reflects the decay rate of the closed loop dominant mode. Closed loop pilot-vehicle oscillation decay rates were generated by a pilot model employing pitch (visual channel) and pitch rate (vestibular channel) tracking strategies. These decay rates were used to predict minimum and maximum handling qualities ratings and pilot induced oscillation (PIO) ratings which closely matched actual pilot ratings from an inflight PIO study using a variable stability NT-33A aircraft. PIO frequency prediction results were excellent. Predicted handling qualities and PIO ratings from a piloted NASA Vertical Motion Simulator study also closely matched the actual ratings. The results indicate that even with the highest fidelity motion simulation, pilot control relies primarily on the visual channel and is constrained by its inherent limitations. Conversely, the dominant control strategy appears to be the vestibular channel when pilots conduct a visual task that is anchored in the physical, out-the-window environment. The vestibular channel is shown to incur effectively no time delay.
Redundancy Concepts, Considerations and Experiences on Electric Propulsion Systems
Authors:   Compact Dynamics GmbH, Kloetzl Johannes , Oswald Johann , Denk Fabian , Blamberger Oliver
Published: September 2024

Within this paper redundancy concepts on electric propulsion systems - consisting of electrical sources, inverters, electrical machines, gearboxes and drag generation units - are discussed. In a first steps different possible concepts are explained. In a general section considerations on the possible concepts are made, with a special focus on the design of the inverters, electrical machines and gearboxes. Advantages and disadvantages are shown and therefore some general assumptions on possible applications discussed. Later, two engineering examples for the concepts of shared drag generation unit and shared electrical machines with inverters are shown. The functionality is shown on measurement examples and experiences made during the design and testing phases are given. Finally, a new concept to reduce the risk of failure propagation in multi-wound motors is shown and discussed.
Aeroelastic Computations of an Isolated Rotor in Forward Flight with a Dual-Solver Hybrid CFD/CSD Methodology in HPCMP CREATE-AV Helios
Authors:   Naval Air Warfare Center, Moushegian Alex
Published: September 2024

Advancements in coupling techniques between computational fluid dynamics (CFD) and computational structural dynamics (CSD) codes have permitted highly-accurate computations of rotor aeromechanics. The computational fluid dynamics portion of these methods can be extraordinarily expensive, however, so the application of dual-solver hybrid codes is of interest. This work investigates best practices for the application of the dual-solver hybrid code OVERCHARM within the Helios framework in a CFD/CSD coupled simulation, and compares the accuracy and computational cost to conventional Helios CFD/CSD simulations in two different flight conditions. It was found that large time steps and a contiguous OVERFLOW domain are most appropriate for this application, and that Helios OVERCHARM simulations can provide aerodynamic and structural loads with the same level of accuracy as conventional Helios simulations at a 2-10X speedup.
Sikorsky Crack Initiation versus Propagation Certification Methodology
Authors:   Sikorsky a Lockheed Martin Company, Toni Darryl
Published: September 2024

Sikorsky has successfully planned and executed several significant aircraft structural certification programs for military aircraft in the past few decades. These certifications included the CH-53K® with NAVAIR, the HH-60W with the Air Force and the Raider X® Competitive Prototype Aircraft with the Army. The methodologies for these certifications addressed the different requirements of each of these branches of the military as well as satisfying emerging techniques for structural life management ("Sikorsky Airframe Full Spectrum Customer/Supplier Collaboration", Reference 1). Safe Life Crack Initiation, Flaw Tolerant (Enhanced) Safe Life Crack Initiation and Fail Safe Life Limit Crack Propagation analysis had been rigorously pursued and demonstrated in these programs. This paper takes a retrospective look at what turns out to be many similarities in these methodologies that previously have been the subject of significant debate in the industry. The combined knowledge of these techniques can lead to reduced cost and schedule based on reuse of similar data from these prior certifications.
System Installation Disparity Between Theory and Practice
Authors:   Airbus Helicopters, Gatti Jean-Loup , Anthonioz Hugo , Dayan David , Fruitet Pierre
Published: September 2024

When the target value of functional geometrical specification is too tight, its cascade of tolerances is at the feasibility limit of production. In this case, the geometrical Tolerancing method loses its benefits and generates an excessive level of non-Conformity which induces additional costs that are not acceptable. The aim of this paper is first to introduce the background concerning chain of dimension method and tolerances capabilities based on test specimen results. Secondly, demonstrate ability to apply statistical calculation. Thirdly extend conventional chain of dimension in one dimension to multi-holes system installation. And, then analyze potential effect by stress evaluation. And confirm the demonstration of improvement on Tolerancing installation calculations, by onboarding all stakeholder (design, manufacturing, stress) early in design phase (interfaces maturation) and by analyzing more in detail installations constraints. This method should be applied first on "non-critical" junction, because it needs to be further matured and so it is not yet mature enough for primary structure and associated quality checks. In conclusion, as a result, it is possible to increase tolerance specification of parts and manage risks of non-assembly. In conclusion, tolerances for holes localization could be approximatively multiplied by two compared to basic calculation method.
Proposed Yaw-Axis Target Acquisition and Tracking Handling Qualities Requirement Updates
Authors:   US Army CCDC AvMC, Berger Tom ,   US Army Redstone Test Center, Brown Daniel ,   US Army, Borden Christopher , Gong Anthony , Lusardi Jeffery , Mansur M. , Boehringer Ryan , Ogden Wesley , Ott Carl , Daniels David
Published: September 2024

A piloted simulation experiment was conducted in the NASA Ames Vertical Motion Simulator to investigate the effects of bandwidth, phase delay, attitude quickness, and maximum achievable rate on yaw-axis handling qualities in hover and forward flight. Two different aircraft were tested, representative of advanced scout-class rotorcraft. Five target acquisition and tracking Mission Task Elements were used in the study. Two of the tasks were modified versions of tasks used to determine the ADS-33E target acquisition and tracking yaw attitude quickness boundaries. Two of the tasks were modified versions of attitude capture and hold and sum-of-sines tracking previously used to evaluate pitch and roll axis handling qualities. The final task was a forward flight target acquisition task developed for this study based on a ground attack or strafing maneuver. Eight Army pilots participated in the study and evaluated 60 yaw-axis configurations. The results of the study suggest that the current yaw-axis hover/low-speed and forward flight bandwidth and hover/low-speed attitude quickness requirements for target acquisition and tracking are too low. Updated boundaries for these requirements are recommended.
Field Measurements of the Airflow in the Urban Environment: An RPAS Use-Case in Montreal, Canada
Authors:   National Research Council, McTavish Sean , Barber Hali , Wall Alanna
Published: September 2024

A use-case was conducted in Montréal in the summer and fall of 2023 to measure urban airflow characteristics using a small Remotely-Piloted Air System (sRPAS). The goal of the study was to acquire urban airflow data in a real environment in order to validate urban airflow characteristics from laboratory-scale testing conducted previously. The use-case took place in the downtown core of Montréal and involved flights from two hospitals to a variety of other buildings. The sRPAS was instrumented with an airflow measurement system. Fixed rooftop anemometer stations were also installed on top of buildings along the flight paths to measure urban airflow at altitudes within close proximity to rooftops. The study generated a valuable data set for characterizing sRPAS operations in urban environments. A number of operational challenges were experienced including the difficulty associated with visual line of sight operations with an urban backdrop, avoiding conditions that could lead to loss of command and control link, and the need to monitor electromagnetic interference during flight operations. The use-case produced evidence of the impact of urban airflows on the stability and response of sRPAS. High wind speeds and turbulence intensities were found in the urban flow field of Montréal. The sRPAS use-case results were used to validate wind-speed and turbulence characteristics from laboratory-scale testing on Canadian cities.
A Fundamental Investigation of Ship Airwake Influence on Rotorcraft
Authors:   Continuum Dynamics Inc., Sharma Abhinav , Keller Jeffrey , Whitehouse Glen
Published: September 2024

Rotorcraft responses to idealized disturbances are examined to gain insights into model fidelity requirements for flight simulations of the ship-rotorcraft dynamic interface. Two disturbance fields are considered: an isolated straight vortex that represents the canonical vortex that results from the corners of flat top ships in oblique wind-over-deck conditions and a horseshoe vortex derived from a nondimensional characterization of the time-averaged flow observed aft of a simplified ship superstructure. Rotorcraft models considered include: an analytical blade element theory-based rotor model, where the disturbance velocities are integrated over the rotor, and a coupled blade element / free wake flight dynamic model of the full UH-60 aircraft, which is used to perform time-marching simulations with the disturbances modeled as a frozen field that is fixed in space and not interacting with the aircraft (one-way coupling), and as a distorting field (two-way coupling). Analytical thrust responses of four idealized rotors to the disturbance associated with the horseshoe vortex suggest the existence of a scaling relationship between nondimensional blade loading and the product of nondimensional vortex width and strength. Time-averaged rotor thrust responses to the disturbance induced by the isolated straight vortex indicate significant distortion of the rotor wake and disturbance field at low forward speeds, with the frozen field assumption indicating greater disk tilt responses. Modeling the horseshoe vortex disturbance as a frozen field generates a greater rotor response than in the distorting case. Inclusion of full aircraft dynamics attenuates rotor responses to the disturbances when compared to isolated rotor responses.
System Identification of a Free-Flying Quadrotor in a Wind Tunnel using Motion Capture Feedback
Authors:   Naval Surface Warfare Center, Brown Robert
Published: September 2024

A system identification study was conducted on a quadrotor unmanned aerial system (UAS) that was free-flying inside the test section of the Naval Surface Warfare Center Carderock Division's Subsonic Wind Tunnel. Motion capture cameras installed in the wind tunnel provided position feedback information to the aircraft in real time, enabling autonomous flights. Longitudinal, lateral, heave, and yaw axis frequency sweeps were conducted at airspeeds up to 20 knots, in 5 knot increments. The extracted flight dynamics model showed excellent agreement in both the time and frequency domains across all airspeeds. Variation in the aircraft's stability derivatives, power usage, and trim information with airspeed was determined. This paper documents the test procedures, challenges with flying aircraft inside the wind tunnel, the controller model, and the system identification results. This free-flight wind tunnel testing methodology has wide applicability to assist with UAS flight control development, and represents a new opportunity in the way traditional wind tunnels can be utilized for UAS research, development, and testing.
eVTOL Modeling Frameworks: A Comparative Study
Authors:   National Research Council, Hui Kenneth ,   CAE, Myrand-Lapierre Vincent , Hodonou Claudia
Published: September 2024

For the last few decades, Canada's National Research Council (NRC) has been at the forefront in analyzing dynamic systems and developing tools to construct aircraft models based on flight test data. With a fixed and rotary-wing aircraft fleet available, NRC has the capability to perform leading edge R&D System Identification (SI); this world-leading SI technology has been developed and has assisted industry partners, Department of National Defense (DND), and various universities in aircraft simulation and development. As a result, NRC has gained extensive experience in modeling aircraft using SI techniques. In collaboration with CAE, this paper demonstrates the acceleration of the NRC's current flight modeling techniques, highlighting recent advances in Artificial Intelligence (AI) and Machine Learning (ML). A new Bayesian ML software is being developed to identify a 6 degrees of freedom (6-DoF) quasisteady model using simulated flight test data. To achieve this, data from the CAE Sample electric Vertical Take-Off and Landing (eVTOL) simulation platform vehicle during hover maneuvers is utilized. Additionally, this paper presents results on extending the model to include rotor dynamics using the classical SI approach for comparison purposes. In summary, all methods provide a high-fidelity model; with the higher model structure, the vertical acceleration match was noticeably better.
Adding Digital Twin Concepts to Helicopter Component Structural Life Assessment
Authors:   National Research Council Canada, Renaud Guillaume , Asaee Zohreh , Cheung Catherine , Wooldridge Jack
Published: September 2024

The airframe digital twin analysis framework developed at the National Research of Canada is being transposed to safe life applications for rotorcraft components. A probabilistic safe life prediction approach, consisting of uncertain material property data and uncertain load spectra is used to calculate risk assessment metrics, such as the cumulative probability of failure, the hazard rate, and the average hazard rate as a function of time. A demonstration of this approach is presented for a CH-146 Griffon component, for which the uncertain loads are estimated from a model developed through machine learning. This preliminary assessment shows the feasibility of using digital twin concepts as a viable alternative to traditional deterministic life predictions, with the potential to reduce maintenance costs and increase aircraft availability.
Finite State Modeling of Ground Effect Using Mass Source Distribution at the Ground Plane
Authors:   Georgia Institute of Technology, Metry Aandro ,   Washington University, Peters David , Prasad J.V.R.
Published: September 2024

Ground effect analytical models in the literature, such as the Pressure Potential Based Finite State Model (PPBFSM) or Velocity Potential Based Finite State Model (VPBFSM) have been developed to study an isolated rotor in full ground effect. These models use the mass source distributions to account for the ground plane. Also, these models consider that the exit pressure of those distributions is equal to the pressure exerted from the rotor at the ground plane. However, PPBFSM and VPBFSM do not satisfy the non-penetration of flow boundary condition at the ground plane. This paper develops a new ground effect model using the VPBFSM that considers the non-penetration of flow boundary condition at the ground plane by varying ground rotor size and using optimization to find the strength of the mass source distributions. Additionally, it captures the flow at any point below the disk which is missing in the previous study of ground effect using VPBFSM. The developed model is applied to the R-50 unmanned helicopter rotor using its geometric and aerodynamic data from the literature. The results show a good correlation compared to the Hayden model. Additionally, the present model exhibits a similar trend of rotor inflow in ground effect at different rotor heights above ground compared to the PPBFSM.
Haptic Device Embedded in Rotorcraft Seats to Provide Motion Onset Cues in Flight Simulator
Authors:   Politecnico di Milano, Lukasiewicz Marek , Zanoni Andrea , Quaranta Giuseppe
Published: September 2024

This paper describes development and testing of a low-cost device mounted on in the pilot seat of a rotorcraft simulator with the aim of improving the perceived realism of the flight. The device acting vertically from the bottom of the seat is used to communicate changes of acceleration in the vertical direction corresponding to heave movement of the simulated aircraft. A bespoke flight simulator system was developed, featuring modular design and virtual reality (VR) visualisation to enable comparative testing with a full motion system. Objective analyses have shown similarities between the two motion cueing configurations when contrasted with only using visual cues.
High-Fidelity Finite Element Modeling of Rotorcraft Shafting System for Critical Speed Prediction
Authors:   Sikorsky a Lockheed Martin Company, Liu Lin , Wright Zachary , Vermillion Therese-Ann
Published: September 2024

An accurate critical speed prediction of shafting systems in rotorcraft is required during preliminary design, so that dynamic loads do not lead to premature component failure within the full operational speed range, i.e. from stationary to maximum operational speed. If all modes are above the operational speed range, the shafting systems is considered subcritical and when design constraints do not allow for this type of design and so one or more critical speeds must be passed through before the shaft reaches its maximum speed the shafting system is considered supercritical and deflection limiters are required. Analytical simulations of the critical speeds of a shafting system can not only assist designers in making decisions in the earlier phase of design, but also helps mitigate risk during the qualification testing, ground run and flight test of the aircraft. Moreover, there are three factors important for an accurate critical speed prediction, i.e. gyroscopic effect, centrifugal force (CF) stiffening effect, or stress stiffening effect, and boundary conditions. The current paper focuses on the first two factors, especially the stress stiffening effect, but the discussion of the boundary conditions will be in a follow up paper. Ultimately, with the advancements of finite element analysis software, and the parallel processing provided by High Performance Computing, high fidelity finite element modeling of rotorcraft shafting system to assess critical speed is possible and practical.
Quadrotor Aerodynamic Interaction Model Identification using Free-Flight Data
Authors:   The Ohio State University, Herz Sage , Valcarcel Michael , McCrink Matthew
Published: September 2024

Aerodynamic interactions impact multirotor vehicle performance throughout its entire flight envelope and change with vehicle orientation, attitude, and forward flight speed. This paper presents efforts in incorporating these interaction effects into a reduced-order numerical quadrotor model informed by experimental flight test data. The interaction model employed system identification tools to compensate for discrepancies between actual rotor performance data and a Blade Element Theory (BET) based baseline model. Incorporation of the interaction model derived from system identification techniques improved the accuracy of model predicted rotor performance. The interaction model also provided insight into interaction effects predominantly influencing rotor performance for multiple flight conditions. The results demonstrate the utility of system identification techniques for accurate multirotor modeling capabilities.
An Uncertainty Propagation Approach to Collective Bounce Rotorcraft-Pilot Couplings Analysis
Authors:   Politecnico di Milano, Zanoni Andrea ,   Leonardo Helicopters, Zilletti Michele , Cassoni Gianni , Talamo Carmen , Marchesoli Davide , Masarati Pierangelo , Colombo Francesca
Published: September 2024

In the context of Rotorcraft Pilot Couplings, the biomechanics of the pilot body play a fundamental role in determining the stability of the pilot-vehicle closed loop system. The response of the pilot body is, in turn, inherently stochastic, being a function of pilot biometrics and muscular activation. Coupling the statistical distribution of pilot biomechanical behavior determined in specialized experimental campaign with linear models of the helicopter heave dynamics, an uncertainty propagation procedure is developed, with the aim of estimating the statistical distribution of the stability margins of the closed loop pilot-vehicle system. Results obtained varying the collective lever characteristics, as well as the helicopter model parameters, align well with results obtained previously in deterministic settings. However, the new scheme allows to define quantitative robustness indices.