bluuebunny/crossref_metadata_2025 huggingface dataset:
Revisiting Legacy Weight Relationships Using Machine Learning Techniques
Authors:   U.S. Army CCDC Av.&MC, Vegh J. , Milligan Andrew
Published: September 2022

This paper investigates the application of K-Means Clustering algorithms to traditional aircraft conceptual-level weight estimation techniques. As a proof of concept demonstration, application was narrowed to fuselage basic weight estimation with expansion to additional component weights as a planned follow on activity. A variety of weight sources were parsed and curated to produce a large, diverse dataset consisting of 82 separate aircraft with a corresponding new universal baseline regression to compare against. A K-Means Clustering algorithm was then employed that sorted aircraft into groupings based on configuration as well as topology and created an associated regression for each grouping. Configuration-based groupings utilized information such as a high-level abstraction of the structural layout as well as whether the aircraft is a fixed-wing or rotary-wing vehicle. Topology-cased groupings utilized information such as landing gear location and possession of a cargo ramp or wing. The configuration-based groupings showed modest improvement compared to the baseline regression while the topology-based groupings consistently outperformed both the baseline regression as well as the configuration-based regressions. Under all conditions, a subset of the data associated with fixed-wing aircraft was shown to be an outlier in regards to error as a result of a large range of weight and speed scales, as well as possible secondary pressurization impacts. Special treatment of the winged dataset led to further reduction in error based on unique design features, presenting an overall fuselage weight estimation methodology that leverages machine learning algorithms that can improve and inform existing best practices.
Observers for Robust Rotor State Estimation
Authors:   Technical University of Munich, Halbe Omkar , Hajek Manfred , Holzapfel Florian
Published: September 2022

The paper discusses the synthesis of linear and nonlinear observers to estimate rotor states from fuselage state measurements alone. First, the paper reviews two forms of the classical Luenberger linear observer applied to the rotor state estimation problem and identifies some limitations thereof. Thereafter, the paper proposes a new robust nonlinear discontinuous observer based on the sliding mode theory to simultaneously estimate rotor flapping and lead-lagging states from fuselage state measurements. For this new nonlinear observer, the paper presents stability analyses to determine conditions that guarantee rotor state estimation accuracy despite unknown but bounded turbulence input. The nonlinear observer also lends itself to the online estimation of the unknown turbulence input. Simulation results in calm and turbulent air conditions highlight the efficacy and performance of the nonlinear discontinuous observer. Such rotor state observers could provide an independent source of online rotor states estimates to complement or supplement in situ rotor state measurement apparatus for various flight control and health monitoring applications.
Evaluation of Flight Control System Architectures for the AH-64
Authors:   The Boeing Company, Chu Bryan , Klein Gary , Enns Russell
Published: September 2022

The AH-64 would significantly benefit from an improved flight control system, particularly as the aircraft's requirements have evolved and continue to do so. To address this, multiple Vehicle Management System architectures are developed and presented for the AH-64 attack helicopter, each addressing several demanding and possibly conflicting future requirements, including Level 1 handling qualities, operating in degraded visual environments, autonomy, high-speed flight operation, and multiple vehicle coordinated operations. Architecture tradeoffs are performed with the understanding that the current AH-64 flight control system is mechanical with electrical partial authority augmentation, but also possesses a non-redundant full authority fly-by-wire emergency backup system. The various architectures are assessed as to how they satisfy the requirements. They are also assessed with respect to their relative costs, both for typical costs such as design, recurring, operating and sustainment, and training as well as other indirect costs such as size and weight. A methodology is developed to compare and contrast the architectures using informal qualitative-based scores assessed by subject matter experts from both industry and customer organizations, as well as scoring from Boeing program management with various operational experiences. The methodology assigns weightings to each requirement and cost criteria through the use of the Analytical Hierarchy Process. The results suggest that there are several likely cost-effective options, possibly with a higher potential return on investment than a conventional fly-by-wire (FBW) architecture. Some of these solutions are also incremental in nature, thereby providing more flexibility than the conventional FBW system.
An Evaluation of Human Performance with a Large Area Touchscreen in a Simulated Rotary Wing Environment
Authors:   Sikorsky Aircraft a Lockheed Martin Company, Browning Jason , Guy Kathryn , Lampazzi Margaret , Daly Catherine
Published: September 2022

This paper presents results of a human machine interface (HMI) evaluation that examined representative flight deck tasks with a large area touchscreen installed in a ride quality simulator that replicated rotary wing vibration profiles. Touchscreens have made their way onto the flight deck of many fixed-wing aircraft and recently into rotary-wing cockpits as well. As such, there is a need to better understand how task performance is impacted by the unique vibratory environment encountered in helicopters. A large area touchscreen (LAD) was evaluated by 14 pilots conducting various touch tasks (target selection, data entry, swiping, long press and zoom), under three varying levels of vibration with and without flight gloves. Performance was assessed objectively (time to completion, touch accuracy, error rates) and subjectively (usability, musculoskeletal discomfort, and video footage). Design recommendations are made for display interface design, including target size, data entry and use of gestures. This study was reviewed and approved by an independent Institutional Review Board for the protection of human subjects.
Fatal Rotorcraft Accidents for a Ten-Year Period
Authors:   Federal Aviation Administration (FAA), Taylor Amanda , Pellettiere Joseph
Published: September 2022

The Federal Aviation Administration implemented regulations and guidance material to protect occupants in the event of a rotorcraft crash. These rules apply to all newly developed rotorcraft. There has been a recent push to develop similar standards for the existing fleet and for the newly constructed rotorcraft. Two major areas of concern are injuries and fatalities resulting from either blunt force trauma or post-crash fire. To understand the effects of these two factors on survivability outcomes, the National Transportation Safety Board accident database was queried for rotorcraft accidents from January 1, 2009 to December 31, 2018. During this period, a total of 1489 accidents occurred, and after refinement, 187 listed fatal. Of the fatalities, blunt force trauma was by far the greatest cause. Though thermal injuries resulted in fewer fatalities, post-crash fires were still a frequent occurrence and protective measures should be put in place for both.
Further Simulated Flight Trial Assessment of Novel Autorotation Cueing Methods
Authors:   Cranfield University, Alam Mushfiqul ,   University of Liverpool, Jump Michael ,   Georgia Institute of Technology, Rogers Jonathan
Published: September 2022

Autorotation maneuvers in helicopters are generally performed in an emergency following some form of catastrophic mechanical or system failure. It is a complex maneuver to perform because the pilot is required to perform several tasks simultaneously and the timing of each of them needs to be precise. Workload can be high and the consequences of getting things wrong can be fatal. Following on from a series of studies that investigated the use of symbology presented on a Head-Up Display to try to assist a helicopter pilot to fly the autorotation maneuver more safely and accurately, this paper presents a pilot-in-the-loop flight simulation study to explore the use of haptic cueing to help the pilot maintain indicated air- and main rotor speeds. Various entry conditions to autorotation maneuver are assess via simulated flight trial at Liverpool's HELIFLIGHT-R full motion flight simulator. Subjective evaluation of the results show that the haptic cues are useful to pilots in terms of reducing the workload to perform a successful autorotation landing.
3D Conformal Pilot Cueing for Rotorcraft Shipboard Landings: On-Demand Trajectory Generation used with a Flight Path Marker Cue
Authors:   Georgia Institute of Technology, Walters Robert , Hayajnh Mahmoud , Feigh Karen , Prasad J.V.R.
Published: September 2022

Shipboard landings are one of the most challenging piloted maneuvers. Trajectory guidance can aid the pilot and reduce workload. Bezier curves provide a mathematical framework that is stable, can be easily constrained, and executes quickly on a computer. These properties allow for dynamic trajectory generation for use in pilot cueing. A pilot-in-the-loop study was used to test the impact on pilot workload and performance of these trajectories as part of an advanced cueing system. The results show that perceived pilot workload decreased while maintaining or improving performance across the measured metrics.
Higher Harmonic Control Simulation with Actuators Designed by the Physics-Based Approach
Authors:   Seoul National University, Kong Kunhyuk , Im Byeonguk , Shin SangJoon
Published: September 2022

A higher harmonic control simulation along with actuators designed by the physics-based approach is attempted in this paper. The object rotorcraft used in the simulation is UH-60A Black Hawk and a multibody dynamics analysis program DYMORE is used for the simulation. The three actuators are located upon the non-rotating swashplate, and represented by the prismatic joints. Pitch angles of the rotor blades are adjusted by the combination of linear motion of the actuators. The rotor system is verified by the comparison against the references via the modal and trim analysis. The response of the fuselage is reflected regarding its entire hardware by the order reduction according to Herting's method. The fuselage is finally modeled as the beam element. A higher harmonic control with the transformation from the harmonic coefficients to the displacements of the servo actuators is to be simulated. By LQG based algorithm that is proposed by the authors, the vibration reduction capability of the present control algorithm will be verified.
Evolution in Buffet Loads Determination for Tilt Rotor
Authors:   Leonardo Helicopters, Dall'Aglio Maria , Donini Nicola , Cassinelli Carlo , Trezzini Alberto
Published: September 2022

This work presents the state-of-the-art of the validated buffet loads determination methodology developed by Leonardo Helicopters, with particular attention to the aerodynamic modelling and the related structural loads calculation. The modern CFD, validated by WT data, is the first major topic addressed in the paper: simulations are performed with ANSYS Fluent to characterize the oscillatory pressure distributions generated by the wing stall. The structural loads calculation is the next part of this process, with a focus on the interface with the aerodynamic input and on the necessary statistical analyses to predict safe loads. Buffet is considered a random phenomenon, which is robust and repeatable only in terms of statistic quantities, and, to estimate the maximum likely values, a probabilistic approach is used to calculate a reasonable safety factor. The last topic is the analysis of actual flight data in compatible high angle of attack conditions in order to substantiate both the load analysis deterministic results and the statistical approach to predict peak values for aircraft design.
Relative Rotor Phasing for Vibratory Load Minimization for a Coaxial Multicopter
Authors:   Rensselaer Polytechnic Institute, Makkar Gaurav , Niemiec Robert , Gandhi Farhan
Published: September 2022

This study focuses on vibration reduction for a coaxial multicopter with 2-bladed, synchronized RPM, variable-pitch rotors through the use of rotor phasing. The study also examines the effect of aerodynamic interference between the rotors of a coaxial pair on the vibration predictions. A set of seven multi-rotor phase parameters are defined—a crossover azimuth for each the four coaxial pairs along with three aircraft level modes—pitch phasing, roll phasing, and differential phasing. The phase modes are examined in both a cross- and plus-configuration multicopter. Irrespective of whether interference was included or not, crossover azimuth of 0◦ tends to minimize the 2/rev lateral loads, while moderate values of crossover azimuth reduces the 2/rev longitudinal loads, for a coaxial rotor pair. For minimizing overall vibratory moments at the C.G., crossover azimuth corresponding to minimum 2/rev thrust is chosen for all the coaxial rotor pairs. It was observed that when interference is not included in the model, vibrations at the aircraft level are almost zero for pitch phasing and very low for the roll phase mode. However, when interference is included pitch phase is no longer a free parameter. With interference modeled, the 2/rev forces for the cross-configuration are ∼ 65% lower than the plus-configuration, while the 2/rev moments are ∼ 70% lower.
An Integrated Three-Dimensional Aeromechanical Analysis of Lift-Offset Coaxial Rotors
Authors:   University of Maryland, Patil Mrinalgouda , Arias Paulo , Baeder James , Datta Anubhav
Published: September 2022

This paper presents the first use of integrated three-dimensional (3D) aeromechanics modeling, defined as the coupling of 3D solid finite elements based comprehensive analysis (CA) with 3D Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD), to study modern lift offset coaxial rotors. The goal is to demonstrate the development of this methodology and assess its capabilities. The X3D structural dynamics solver is coupled with the UMD Mercury CFD framework for this analysis. Metaltail- a notional hingeless coaxial rotorcraft, developed as an open-access model for the U.S. Army / DoD's High Performance Computing Framework Helios is used as the test case here. The analysis is performed at a low speed transition flight and preliminary predictions of airloads and three-dimensional stresses are discussed. Modern coaxial rotors are compromised by heavy rotor hubs reducing their performance. This paper aims to demonstrate a high-fidelity capability that can help overcome this barrier through accurate predictions of 3D dynamic stresses of blade and hub.
High-Fidelity Modelling of Actuation Systems for Nonlinear Aeroservoelastic Analysis of Tiltrotor
Authors:   Leonardo Helicopters, Pellegrino Federico ,   Politecnico di Milano, Quaranta Giuseppe , Trezzini Alberto
Published: September 2022

Recent evolutions in regulatory practices place an increasing emphasis on nonlinear aeroservoelastic analysis to prevent adverse phenomena like Limit Cycle Oscillations (LCO). Thanks to enhanced computational capabilities, this field is set to take an even more important role in the certification process of new aircraft, and in particular of tiltrotor, together exploiting the increasing ability to build multidisciplinary and high-fidelity modelling of complex aeronautical systems.
In this paper, a comprehensive model of a tiltrotor control surface actuation system is introduced, capable of accurately representing the main nonlinear features and helping to better comprehend their origin. The model includes the entire control chain, starting from the Flight Control System (FCS) logic and getting to the control surface structure, passing through the hydraulic servo-actuator and the related mechanical linkages. The behavior of the servo-actuator model as a subsystem and the one of the entire control chain are compared to experimental data. Finally, a simplified nonlinear aeroservoelastic simulation shows the potential effects of the nonlinearities present in the system.
Damper Model Identification Using Hybrid Physical and Machine Learning Based Approach
Authors:   Leonardo Helicopters, Zilletti Michele , Fosco Ermanno
Published: September 2022

In this paper the identification of a time domain model of a helicopter main rotor lead-lag damper is discussed. Previous studies have shown that lead-lag dampers have a significant contribution to the overall aircraft dynamics, therefore an accurate damper model is essential to predict complex phenomena such as, instabilities, limit cycles, etc. Due to the inherently nonlinear dynamics and the complex internal architecture of these components, the model identification can be a challenging task. In this paper, a hybrid physical/machine learning based approach, has been used to identify a damper model based on experimental test data. The model, called grey box, consists of a combination of a white box, i.e. a physical model described by differential equations and a black box, i.e. regression numerical model. The white box approximates the core physical behaviour of the damper while the black box improves the overall accuracy by capturing the complex dynamic not included in the white box. The paper shows that, at room temperature, the grey box is able to predict the damper force when either a multi-frequency harmonic or a random input displacement is imposed. The model is validated up to 20 Hz and for the entire damper dynamic stroke.
Time-Frequency Analysis of Experimental and Analytical Hub Loads of a Rotor Undergoing a Rotor Speed Change
Authors:   NASA Langley Research Center, Sekula Martin ,   NASA Ames Research Center, Russell Carl
Published: September 2022

A two-part analytical study was conducted examining a small-scale, two-bladed rotor undergoing a change in rotor speed. First, a parametric study was conducted to understand how rotor transient response, determined using a time-marching solution, is affected by the choice of rotor wake model, blade elasticity, and inclusion of an elastic support structure model. The second part of the study compared results from an analytical model of the NASA Multirotor Test Bed (MTB) undergoing a rotor speed change to wind tunnel data. Since the analytical and experimental time histories were nonstationary signals, a Stockwell transform was employed to analyze the data in lieu of traditional Fourier transform-based methods. The analysis included extraction of time-varying frequency content of the rotor thrust and hub motion, damping ratios, instantaneous rotor speed, and instantaneous phase difference between thrust and hub motion. Use of a free wake model was found to be necessary to predict higher-harmonic thrust, however, it underpredicted the amplitude of the unsteady loads. Modeling the elasticity of the stiff rotor blades installed on the MTB resulted in minimal impact on the computed vibratory loads compared to a rigid blade model. The current analytical model of the MTB, including an elastic support structure, properly predicted the measured trends in the frequency content of the thrust.
Pre-test Analysis on Slowed Mach-scaled Thrust Compounding Rotorcraft
Authors:   University of Maryland, Maurya Shashank , Chopra Inderjit , Datta Anubhav
Published: September 2022

This paper details the propeller analysis in forward flight to finalize the wind tunnel test matrix of the thrust compounding rotorcraft model. First, the University of Maryland Advanced Rotorcraft Code (UMARC) is validated with main rotor hover test data at the tip Mach number of 0.2 and 0.5. It is further validated with slowed rotor (tip Mach number 0.2) wind tunnel test data up to a high advance ratio of 0.7. Next, the lifting-line-based propeller analysis is integrated into UMARC and validated with the propeller hover test data at various RPMs and propeller pitch settings. This analysis examines the isolated propeller performance in forward flight followed by a combined main rotor and propeller analysis using Maryland Freewake in the time domain. The wind tunnel test will be carried out at the propeller pitch of 30◦, and 35◦ and RPM will be varied between 1400 to 3500 up to a wind speed of 100 knots. A rotorcraft system-level comparison study is conducted using previous Mach-scaled wind tunnel test data at different shaft tilts and the propeller analysis at the corresponding speeds. Based on this coupled main rotor-propeller analysis, it is found that the thrust compound does not have much impact on rotorcraft efficiency, L/D. However, it helps extend the speed by using the propeller for propulsive force and the main rotor shaft tilted backward for efficient lift.
Comprehensive Simulation for eVTOL Aircraft-Diagnosing Coupled Airframe-Propulsion Dynamic Instabilities
Authors:   Gamma Technologies LLC, Brenner Felix ,   Advanced Rotorcraft Technology, Goericke Jan , O'Heron Pat , Gomez Llorenc , Hasbun Matt
Published: September 2022

The design, development, and testing of an eVTOL aircraft requires multiple physics-based simulation applications to address technical challenges and optimize the configuration for stringent mission requirements. While existing rotorcraft simulation and analysis tools are utilized for the analysis of eVTOL configurations, the adoption of an electrified propulsion system introduces new challenges. These tools are tailored for analysis of coupled system dynamics including elastic structures, airloads, and wake interactions, but are lacking capability for detailed electrified drive system dynamics. As a result, the dynamics of the electric drive system are often analyzed separate from the flight and structure dynamics. This can cause important coupled interactions to be overlooked and require costly latestage design changes. This paper describes and demonstrates the coupling of GT-SUITE, a detailed electric propulsion modeling and analysis tool, with the comprehensive rotorcraft analysis tool, FLIGHTLAB. The objective of coupling these applications was to provide eVTOL analysis capabilities that enable improved designs in terms of mission range, operation capabilities, and flight safety. The successful coupling of these applications was demonstrated with lift and cruise propellers based on the Uber Elevate configuration.
Flight Characteristics of AAM/UAM-Scale Quadcopters Under Atmospheric Turbulence
Authors:   Rensselaer Polytechnic Institute, Bahr Matthew , Ferede Etana , Gandhi Farhan
Published: September 2022

The flight responses of quadcopters of various scales (50-1200 lb) are evaluated in the presence of a 20 kt turbulent headwind. Nominal flight controllers are tuned for each aircraft to meet HQ specifications, where the controllers will reject disturbances to the aircraft groundspeed, attempting to maintain zero groundspeed. Froude-scaling is performed to scale the handling qualities specifications of the smaller aircraft, utilizing the additional agility. The nominal and scaled controllers are then compared in rejecting disturbance due to the turbulent headwind. Non-linear dynamic simulations are performed to evaluate the rigid body response of each aircraft, finding that scaling the flight controllers (on aircraft less than 1200 lb) reduces the pitch and roll attitude response so that all aicraft have similar peak-to-peak values. Following scaling, the peak-to-peak roll and pitch attitudes for all four aircraft are within 0.5° and 0.4° of each other, respectively. The improvement in disturbance rejection capabilities from scaling comes at the cost of 24% increase in the RMS current, and 2% additional current margin for the 50 lb aircraft (which is the largest increase). Overall, the increase in actuator activity due to scaling the controllers is less than the current margin required for maneuvering, resulting in the motors not needing to increase in size.
Hover Dynamics and Flight Control of a UAM-Scale Quadcopter with Hybrid RPM and Collective Pitch Control
Authors:   Rensselaer Polytechnic Institute, Walter Ariel ,   US Army Combat Capabilities Development Command AvMC, Berger Tom , McKay Michael , Niemiec Robert , Gandhi Farhan
Published: September 2022

Hover trim and dynamic analyses were performed on a UAM-scale quadcopter with both variable rotor speed and variable collective blade pitch. The bare-airframe dynamics were first considered at three different hover trim points, where power consumption is increased to improve authority. The control and stability derivatives were examined at each trim point and an increase in base RPM caused increased authority for pitch inputs (and decreased authority for RPM inputs) in thrust-dominated axes. Explicit model following control laws wre then optimized using CONDUIT® to meet ADS-33E-PRF handling qualities specifications. Design margin optimization was then performed on each axis. Heave and yaw responses of the linearized system were examined for the three trim points with either RPM or pitch control. It was found that pitch-control outperformed RPM-control in heave, while the opposite was true for yaw. Hybrid control mixing was considered using a complementary filter, so that it uses pitch actuators for short-term responses, and RPM for trim. Effects of changes in motor time constant and complementary filter cutoff frequency were examined. The benefits of hybrid control were demonstrated through simulations that involved transition between trim points. Hybrid control required lower maximum power during thrust-driven maneuvers by allowing the aircraft to accelerate using pitch actuators, and recovers the original stall margin by using the rotor speed to re-trim. For a drop-off of 176 lbs of payload, hybrid control provided 5.0% lower trim power than pitch control with the reduced weight. Hybrid control also allowed a 3.9% reduction in power compared to pitch control at a flight speed of 30 kts.
Flight Test of scaled MTEs for VTOL Certification using an Ultralight Coaxial Helicopter
Authors:   German Aerospace Center (DLR), Jusko Tim ,   Systems Technology Inc., Jones Michael ,   edm aerotec GmbH, Grebing Benedikt
Published: September 2022

New methods are currently being investigated to perform certification of future electric Vertical Take-Off and Landing (VTOL) aircraft. Due to the expected mission requirements, classical certification methods do not lend themselves to this type of vehicle. One aspect being investigated is a new approach to evaluate Handling Qualities (HQs) as means of compliance demonstration. The EUROCAE Working Group 112 has proposed new Flight Test Manoeuvres (FTM) that could be used for this purpose. These FTMs are scaled based on vehicle geometry. This paper presents first results obtained from a flight campaign to test a set of the proposed FTMs. The flight tests were performed with a coaxial ultralight helicopter and conducted at airport Obermehler (EDCO) in Germany. One pilot flew seven proposed FTMs. Pilot feedback and analysis of results are used to propose modifications to the FTMs.
Analysis of Handling Qualities and Power Consumption for Urban Air Mobility (UAM) eVTOL Quadrotor with Degraded Heave Disturbance Rejection and Control Response
Authors:   NASA Ames Research Center, Aires Jeremy , Withrow-Maser Shannah , Ruan Allen , Malpica Carlos , Schuet Stefan
Published: September 2022

A piloted handling qualities study of urban air mobility (UAM) electric vertical take-off and landing (eVTOL) quadrotors was performed utilizing the Vertical Motion Simulator (VMS) facility at NASA Ames Research Center. Rotor speed and variable pitch-controlled variants of a six-passenger conceptual design vehicle were assessed with different levels of degradation to control response and disturbance rejection bandwidth (DRB) in the heave axis. In previous work, preliminary trends across several handling quality rating categories reflected the effects of these degradations. Additionally, the impact of using different test standards and turbulence on the ratings were discussed. This paper elaborates on those results, but also provides insight into unexpected trends observed during the study including: a disharmony in attitude response, subpar ratings for the baseline Level 1 performance vehicle, and excessive drift and yaw couplings observed in a lateral reposition maneuver. Moreover, shortcomings of the handling quality scales and comparisons of power consumption among the vehicles in the various test conditions are presented.
Evaluation of Pilot Assistance Systems for Helicopter Ship Deck Landing
Authors:   German Aerospace Center (DLR), Štrbac Alexander , Maibach Malte-Jörn , Greiwe Daniel , Kalra Arti , Gardner Anthony
Published: September 2022

The operation of helicopters on ships is one to most challenging tasks due to adverse weather conditions, the lack of visible cues, turbulent airwakes behind the ship and a moving confined landing spot on the ship. Currently, only a very limited number of pilot assistance systems are available to ease helicopter ship deck landings. The focus of this paper is the evaluation of a Head-DownDisplay(HDD),aHead-MountedDisplay(HMD)andtwodifferentAttitudeCommand Attitude Hold (ACAH) flight control architectures for ship deck landings based on piloted simulation. A ship deck landing scenario at the research flight simulation facility Air Vehicle Simulator (AVES) has been extended to include turbulent ship airwakes from high-fidelity Computational Fluid Dynamics (CFD). The pilot assistance systems have been implemented at the simulator and evaluated by four helicopter pilots. In particular, the results show a favorable potential of the Head-Mounted Display and the flight control architectures.
Evaluation of Helicopter Ship Deck Landing Control Laws in Piloted Simulations
Authors:   German Aerospace Center (DLR), Kalra Arti , Štrbac Alexander , Maibach Malte-Jörn
Published: September 2022

This paper describes the development and implementation of newly designed helicopter ship deck landing control modes and their evaluation in a piloted simulation study. The ship deck landing modes are embedded in a model following controller architecture. The employed control design is a complete model-following control system which imposes the desired command model dynamics on the controlled helicopter. Different command types combined with various hold functions are implemented to make the task easier for the pilots. Three basic command types and three advanced command types, one without ship communication and two with ship communication, are implemented. A piloted simulation study was performed in a simulator to evaluate and compare the implemented control modes within a complete maritime scenario design. The evaluation of control modes is based on the success of helicopter ship deck landings which is assessed by a quantitative as well as a qualitative assessment. Simulation results demonstrate that the advanced command types improved the task performance as well as reduced the pilot workload extensively in comparison to the basic command types.
An Explanation of Unanticipated Yaw Phenomenom on Helicopters
Authors:   Airbus Helicopters, Ferullo David
Published: September 2022

The helicopter community has been plagued during the latest forty years by accidents due to unanticipated yaw, also called Loss of Tail rotor Effectiveness (LTE). Thanks to official reports, the first part of this paper will be devoted to the genesis of this problem and recommendations provided at that time. An analysis of accident databases, available in different countries, is astonishing with 18 accidents occurring on average each year. Surprisingly, three out of four accidents took place close to the ground where the recovery actions recommended in AC 90-95 are not applicable. A part of the mystery remains and especially no clear explanation of the phenomenon was provided at that time. The benefit of this paper is to provide an explanation of the phenomenon using the pedal curve approach. During hovering flight with wind, the pedal curve is useful to understand how and under what conditions unanticipated yaw can develop. The lack of effectiveness of the tail rotor perceived sometimes by the pilot is a consequence of a too limited action on the pedal during the recovery maneuver. Finally, flight tests carried out on AH130 confirm the explanation given thanks to the pedal curve and provide a clear recommendation to recover from such situation. A quick and large action on the pedal (up to the stop if necessary) in the opposite direction of the yaw is the only possible response to unanticipated yaw, regardless of the yaw rate reached during the phenomena. Authorities, Manufacturers and Schools must convey the same message towards the pilot community in order to reduce the number of accidents and to restore confidence in the effectiveness of the tail rotor.
NGCTR-TD Tiltrotor Autorotation Numerical Investigation
Authors:   Line Up Aviation s.r.l, Riccardi Fabio ,   Leonardo Helicopters, DelGrande Federico , Prando Giuliano , Giuliani Valentina , Pecoraro Matteo , Ragazzi Andrea
Published: September 2022

Within the Clean Sky 2 Fast Rotorcraft platform, a Next Generation Civil Tilt-Rotor Technology Demonstrator (NGCTR-TD) is under development. The design phase has been successfully completed and first flight phase is planned within 2023. As part of design verification, the capability to perform a safe landing procedure after losing all engines power is investigated, with dedicated analysis planned in order to improve the transport category performance requirements, as verified for Legacy tilt-rotor platform. Such procedure consists in 4 different steps when starting from AP mode, and the analysis are focused on VTOL steady autorotation phase, being the one where tilt-rotor configuration shows higher peculiarity with respect to helicopter configuration, due to the presence of lifting surfaces. As first, preliminary considerations from helicopter theory are cited, and tilt-rotor peculiarities listed. Then, adopting the developed FlightLab numerical model, different solutions are investigated, starting from characterization in airspeed for a baseline configuration. Different sensitivity analyses are conducted to map the major effect for the specific topic, and best trade-off autorotation configuration/control strategy is obtained for NGCTR-TD. Such solution is investigated in the complete Weight/CG envelope to ensure control strategy robustness.
Ensemble Integration Methods for Load Estimation
Authors:   National Research Council Canada, Cheung Catherine , Hamaimou Zouhair
Published: September 2022

Helicopter component load estimation can be achieved through a variety of machine learning techniques and algorithms. To increase confidence in the load estimation process, ensemble methods are employed combining multiple individual load estimators that increase predictive stability across flights and add robustness to noisy data. In this work, several load estimation methods are applied to a variety of machine learning algorithms to build a large library of individual load estimation models for main rotor yoke loads from 28 flight state and control system parameters. This paper explores several ensemble integration methods including simple averaging, weighted averaging using rank sum, and forward selection. From the 426 individual models, 25 top models were selected based on four ranking metrics, root mean squared error (RMSE), correlation coefficient, and interquartile ranges of these two metrics. All ensembles achieved improved performance for these four metrics compared to the best individual model, with the forward selection ensemble obtaining the lowest RMSE, highest correlation, and closest load signal prediction visually of all models.
Validation of Probabilistic Regime Recognition and Damage Estimation with Large Fleet Datasets
Authors:   Georgia Institute of Technology, Musso Dakota ,   Technical Data Analysis Inc., Sarkar Subhasis , Rogers Jonathan
Published: September 2022

Regime recognition (RR) and damage estimation is a critical step in the creation of usage and damage spectra and in development of component replacement timelines. While a variety of methodologies exist for regime recognition based on deterministic classification, recent work has demonstrated the benefit of approaching the problem of regime classification and damage estimation from a probabilistic standpoint. However, while studies have shown the successful deployment of probabilistic algorithms on simulated data, little work has been done to validate their use on large f leet datasets that contain actual flight data. This paper seeks to address two main points. First, the damage estimation scheme proposed in prior work is extended to incorporate uncertainty in the component damage rates, allowing for a complete treatment of the damage estimation problem that fully captures all major sources of uncertainty. Second, this paper exercises the probabilistic regime recognition and damage estimation algorithms published in previous work on 500 hours of actual fleet data, validating the efficacy of the approach. Detailed analysis of the results show that the probabilistic algorithms are effective in estimating flown regimes and component damage fractions and offer unique insights that are not available from comparable deterministic algorithms.
Digital Transformation of a 6000-Year-Old Process
Authors:   Sikorsky a Lockheed Martin Company, Woodworth Heather
Published: September 2022

Integration of advanced technologies in the casting commodity through digital transformation efforts is essential to future success of rotorcraft transmission castings. This paper reviews the advanced technologies that have been integrated into the casting process for transmission housings. The transformation in casting designs, solidification modeling, mold fabrication, casting techniques, thermal and mechanical post processing, inspection, and quality management are all impacted by new technologies and driven by the continued digital thread in the manufacturing process. The casting manufacturing process is 6000 years old, but the complexity of aircraft requirements and part designs has outpaced capability of standardized casting processes. Digital transformation driven technologies create repeatable processes that reduce production scrap and development lead times.
Global Model Identification for a Coaxial Helicopter
Authors:   Technical University Munich, Hosseini Barzin ,   edm aerotec GmbH, Grebing Benedikt , Sax Franz , Rhein Julian , Holzapfel Florian , Maier Lukas , Barth Aaron , Hajek Manfred
Published: September 2022

In this paper, the Blade Element Momentum Theory (BEMT) hast been applied to setup a nonlinear model structure for a coaxial helicopter with a maximum take-off weight (MTOW) of 600kg. The model includes unknown aerodynamic parameters, which are estimated using flight test data. An extensive flight test campaign, with a fully instrumented CoAx 600 helicopter has been carried out to generate the required flight test data for parameter estimation. In this study, we use the maneuvers performed in the vicinity of the hover flight condition for system identification. The nonlinear model can be trimmed and linearized for the analysis of the system dynamics and control design. This has been done for one trim point in the study and the corresponding pole plan has been provided.
Implementation and Linearization of a State-Space Free-Vortex Wake Model for Flapping-Wing Flight
Authors:   Auburn University, Saetti Umberto ,   Pennsylvania State University, Horn Joseph
Published: September 2022

This paper describes the extension of a free-vortex wake method in state-variable form originally developed for rotary-wing applications to flapping-wing flight. Following a detailed mathematical description, the wake model is implemented for a hovering insect representative of a hawk moth. A periodic solution to the wake model is found at hover using a modified harmonic balance algorithm. Next, linearized harmonic decomposition models are obtained and validated against the nonlinear dynamics using simulations. Order reduction methods are explored to guide the development of linearized wake models that provide increased runtime performance compared to the nonlinear and linearized harmonic decomposition wake models while guaranteeing satisfactory prediction of the periodic response of the wake.
Design, Modeling, and Flight Dynamics Analysis of Generic Lift-Offset Coaxial Rotor Configurations
Authors:   San Jose State University, Padthe Ashwani ,   U.S. Army CCDC AvMC, Lopez Mark ,   U.S. Naval Academy, Juhasz Ondrej , Glover Emily , Berger Tom , Tobias Eric
Published: September 2022

Lift-offset coaxial compound rotorcraft designs have been proposed for the U. S. Army Future Vertical Lift (FVL) programs. Without a need for the tail rotor and equipped with a pusher-propeller, the coaxial compound configuration is capable of achieving high airspeeds and perform maneuvers not feasible for the conventional rotorcraft. To facilitate an independent assessment of the lift-offset coaxial configurations by the U. S. Army, two designs are presented in this paper. Physics-based flight dynamic models are developed using open source data and implemented into the HeliUM-A comprehensive analysis code. On-axis frequency responses from the models are validated against available flightdata showing good agreement. The models are trimmed for a range of vehicle airspeeds, pitch angles, and rotor speeds. Trends in trim controls, hub loads, and power consumption are studied. Linearized time-invariant (LTI) models are extracted from the nonlinear HeliUM-A models. The LTI models are used to study trends in system eigenvalues, stability and control derivatives. Vehicle flight dynamics are examined through frequency response plots at various flight conditions.
Verification, Validation and Calibration Under Uncertainty for a Scaled Experimental Rotor Model
Authors:   Politecnico di Milano, Abate Giuseppe , Daniele Matteo , Taymourtash Neda , Quaranta Giuseppe
Published: September 2022

Virtual Engineering (VE) in rotorcraft design is a well-established approach to support decision-making throughout the rotorcraft's life-cycle (Ref. 1). The effectiveness of structural design, analysis and CAD software, CFD solvers and rotor aeromechanics codes is crucial throughout rotorcraft life-cycle, from preliminary design phase development to certification process (Ref. 2). The required fidelity level and reducing the number of physical tests during development can be achieved by building a reliable and repeatable protocol for Verification, Validation and Uncertainty Quantification (VVUQ) of numerical models (Refs. 3-5). UQ can be exploited to both determine how much the variability of numerical and physical parameters affect the simulation outcome and perform a calibration of numerical models. This paper aims to perform the three steps of VVUQ for a digital twin of a scaled helicopter designed for wind tunnel tests. In this study, the experimental setup and numerical model will be introduced. Then, the statistical methods implemented for each step will be explained in more detail.
Towards Certification by Simulation with Model-based continuous Engineering Processes showcased on eVTOL Application
Authors:   ESI Group, Gottschall Marcel , Binder Bastian , Castel Alexis
Published: September 2022

Aerospace industry OEMs and suppliers are progressing their engineering processes and performance to the next maturity level gearing to digital thread solutions. Current challenges like continuous engineering, virtual certification, distributed development, consolidated virtual proving grounds, homologation, digital twin and operational applications, require well informed decision making in a comprehensive, reliable, traceable and customizable environment. In particular, in aerospace domain, with widespread tight collaborative ecosystems between integrators and suppliers, the capability of tracing each decision and its underlying artifacts becomes a key value of an engineering platform. This paper will outline a middleware approach to reuse generated artifacts and their relationships in a federated engineering environment supporting a "best tool for the job" approach by introducing a layer providing unification and consistency throughout all managed artifacts. Based on an exemplary eVTOL setup, the benefits of integrated data and workflows from specification to virtual design verification are highlighted to motivate their value towards realisation of MBSE methodologies.
XV-15 Rotor Simulation in Flow360 using the Blade Element Theory
Authors:   FlexCompute Inc., Moore John ,   Massachusetts Institute of Technology, Wang Qiqi , Jia Feilin
Published: September 2022

This paper presents results of the numerical study of the Bell XV-15 rotor with the flow solver Flow360 using a coupled Navier-Stokes/Blade Element Theory model. Results are presented for both steady-state and transient simulations. The resulting thrust, torque, and blade loadings show good agreement with high-fidelity DDES results computed with Flow360 and experiments.
Application of MSG-3 Maintenance to the Bell 525
Authors:   Bell Textron Inc., Mooney Corey , Ciazinski Jim
Published: September 2022

In the early days of aviation, maintenance requirements were determined by a few experienced mechanics with assistance from the Original Equipment Manufacturer (OEM). As aircraft became more complex, a more sophisticated method of developing an aircraft maintenance program was needed. The approach aimed for a data driven maintenance philosophy. Just as sequential aircraft designs introduced new enhancements, each revision to the maintenance logic improved the maintenance approach in terms of effectiveness. The latest approach to this maintenance philosophy is known by the acronym MSG-3, for Maintenance Steering Group 3. As scheduled maintenance requirements for aircraft continue to change, the procedures need to be effective, reliable, and economically reasonable. The approach and benefits of an MSG-3 program are discussed in reference to the Bell 525, a new fly-by-wire, 16-passenger commercial helicopter under development at Bell Textron Inc. The development of the 525's MSG-3 maintenance program and its benefits to operators are discussed. The MSG-3 process schedules aircraft maintenance tasks necessary to maintain the stated levels of reliability and safety, reducing direct maintenance costs by 30% while maximizing aircraft availability (Ref 1).
Integrating a Torque Measurement System for the GE T408 Engine into a CH-47D Chinook
Authors:   Parker LORD, Kakaley Daniel ,   GE Aviation, Kyff Robert ,   DVCOM AvMC, Lane Gregory ,   The Boeing Company, Ignatuk Kevin , Kennedy Scott , Kopay Caryn , Martin Gary , Durbin Kenneth
Published: September 2022

This paper presents an overview of the efforts associated with integrating a new torque measurement system for T408 engines into an NCH-47D airframe and performance of the torque measurement system during operation on the aircraft. The effort described was performed collaboratively between GE Aviation, The Boeing Co, Parker LORD, and DEVCOM AvMC. The Torque Measurement System was utilized in the T408 Engine Control System during its demonstration on an NCH-47D airframe at Ft. Eustis, VA. In addition, based on DEVCOM AvMC program requirements, health monitoring capability was successfully implemented and demonstrated during the NCH-47D T408 Engine Demonstration. Lessons learned from the torque measurement system's health monitoring features are included.