Browse Topic: Research and development
This organizational process survey provides insight into the technical aspects of approved airworthy aircraft modifications applied in government organization vertical lift flight test. The publication reviews processes applied by the National Research Council of Canada's Flight Research Laboratory (NRC-FRL) and its Airworthiness Control System to enable research flight testing. Dominated by the need for integrating experimental payloads, the NRC-FRL embeds a Design and Fabrication Service organization for modification of internal and external client projects and flight test aircraft. In context of experimental flight testing, this work reviews technical information on process, facilities, and methodology for airworthy integration of flight test payloads. Information is used to synthesize recommendations in experimental vertical lift flight testing that satisfy both formal (regulated compliance) and informal (compliance intent) airworthiness requirements.
This paper considers the opportunities and challenges of supporting Disaster Relief and Emergency Response (DRER) missions employing new aerial vehicle and systems concepts. This paper is a broad survey of the possible aerial-vehicle-assisted approaches to aid in DRER missions. The intent of this paper is to elevate this DRER mission application domain as a critical area of investigation for rotorcraft, robotics, intelligent systems, and other research. Current work is primarily focused on assessing air space integration challenges for Commercial Off-The-Shelf (COTS) aerial platforms (typically small multirotor drones and/or small fixed-wing uncrewed aerial vehicles (UAVs)) in disasters such as earthquakes and wildfires. Though this is an important area of investigation, truly efficient and effective DRER systems and response efforts will not be possible without the development of novel aircraft, technologies, and system architectures of COTS DRER drones/UAVs. This paper seeks to address that knowledge gap and encourage government, academia, and industry to pursue DRER mission research.
Achieving noise reduction in rotorcraft requires an analysis of various design parameters and flight conditions. However, high-fidelity methods are computationally expensive. To overcome this limitation, reduced order model (ROM)-based surrogate models have been applied to aerodynamics and aeroacoustics prediction. This study proposes a ROM-based surrogate model employing a variational autoencoder (VAE) to predict rotor aerodynamic loads and associated noise. Train and test datasets were generated using reformulated vortex particle method across a wide range of flight conditions. The proposed framework was applied to a single rotor, and its performance was evaluated qualitatively and quantitively in comparison with proper orthogonal decomposition (POD)-based surrogate model. The results show that VAE-based model consistently outperformed the POD model in noise prediction. These results demonstrate that the proposed framework enables accurate rotor noise prediction under various flight conditions and provides a promising approach for low-noise rotorcraft design and operational planning.
This study provides a comprehensive framework for establishing land use compatibility guidelines specific to vertiports serving electric Vertical Takeoff and Landing (eVTOL) aircraft within urban settings. Recognizing critical gaps in current regulatory standards, the research systematically integrates analyses of accident risk, noise propagation, and aerodynamic impacts—including downwash and outwash—to delineate compatibility zones around vertiports. Employing an artificial intelligence (AI) augmented system, the study conducted safety and hazard assessments, various quantitative analyses, and simulations to identify spatial constructs of operational risks and environmental impacts. Results indicated significant discrepancies between existing aviation infrastructure guidelines and the unique operational characteristics of eVTOLs, necessitating revised zoning parameters. The proposed multi-tiered safety zoning framework provides precise, evidencebased recommendations for urban planners, enhancing safety, minimizing noise impacts, and ensuring environmental sustainability. Ultimately, this research offers policymakers and stakeholders practical tools for integrating advanced air mobility infrastructure safely into complex urban landscapes.
Future military missions for Agile Combat Employment (ACE) and next generation Special Operations Forces need an aircraft with effective hover and the ability to operate in transonic cruise. Hover requires significant power that can only be mitigated by larger diameter rotors, but large diameter rotors become a detriment to achieving transonic flight. The stop-fold rotor configuration can “make the rotor disappear” in cruise and stands out as the most viable option for meeting these next-generation air vehicle requirements. This paper discusses the progress Bell has made in developing enabling technologies for a practical and scalable high-speed VTOL (HSVTOL) based on the stop-fold configuration. To this end, a unique Track-Guided Test Vehicle (TGTV) was developed at Bell and tested at the 10-mile High Speed Test Track at Holloman Air Force Base. The test vehicle integrates all subsystems required to demonstrate the key technologies in a representative environment, including multi-mode propulsion, folding proprotors, and fly-by-wire transition controls to automatically manage each step of the prop-to-jet (and reverse) process. The TGTV demonstration validated the stop-fold technical approach and generated critical data to substantiate engineering models. Test results provide confidence that each step in the stop-fold transition process is thoroughly understood and that engineering tools can be used confidently for future aircraft design efforts. This paper documents the first known powered prop-to-jet and jet-to-prop transition and represents a significant milestone in vertical flight technology development.
This study examines the ability of a large (1200 lb gross weight) hexacopter with collective pitch controlled rotors to tolerate single motor failure. The hexacopter is considered in various orientations, and the vehicle is trimmed with one motor inoperative (OMI). Unlike RPM-controlled hexacopters, which were trimmable but uncontrollable in hover, and were untrimmable in cruise with an aft-rotor failure; with pitch-control the hexacopter is controllable in hover as well as trimmable for failure of any rotor in cruise (including an aft rotor failure). The study examines how pitch controls, and thrust are redistributed amongst the operational rotors, post-failure, for the different hexacopter orientations. For each case, the maximum thrust and torque increases on any individual rotor, and the total power increase, post-failure is examined. It is found that the hardest to trim cases are those where the hub torque and the hub drag induced yaw moment of the failed rotor add, and fault compensation for these cases usually comes at a high cost in terms of torque penalty and power requirement (necessitating use of more powerful motors and batteries). The results from the study indicated that operating the pitch-controlled hexacopter in an edge-first configuration with a clockwise spinning rotor 1 is the best choice from a fault tolerance perspective.
Stretch broken carbon fiber (SBCF) offers enhanced formability as compared to continuous carbon fiber (CCF). However, robust, quantitative evaluation of forming defects remains a challenge. This study introduces a unified formability index (UFI) that integrates multiple defect types, including texture anomalies, bridging, wrinkling, thickness variation, spring-back, and resin distribution variation (RDV), into a single weighted score. Each defect is ranked on a scale of 0-5 using normalized metrics with a tunable parameter, α, allowing users to balance defect magnitude and frequency as desired. The full scoring pipeline is demonstrated for texture defects using measured data, while normalized legacy scores from previous work are used for non-texture defects to enable complete formability index computation. Case studies on three laminates illustrate how variations in α affect both texture scoring and the overall formability index and demonstrate the geometry-agnostic nature of the updated ranking and UFI systems. This framework maintains compatibility with existing evaluations while offering improved resolution, consistency, and scalability for assessing laminate quality across complex geometries.
A study of mental workload and the resultant cognitive-motor behavior is essential to understanding the intrinsic limitations of the human information processing system, the results of which have impact on the design of safety-critical systems. While the effects of increased task demand on mental workload and the quality of cognitive-motor performance has been previously investigated, it remains unclear how system controllability (i.e., expected handling qualities) impacts perceptual workload and performance. Furthermore, traditional EEG spectral metrics lack the temporal specificity to capture dynamic workload. Consequently, the purpose of this experiment was to examine objective brain dynamics, task performance, and subjective ratings during piloting tracking tasks of varying complexity while also challenging participants with different expected levels of handling qualities. Our results revealed a trend suggestive of increasing mental workload related to increased task complexity and varying levels of expected handling qualities. To examine dynamic operator workload with increased temporal fidelity, we introduce a time-resolved cross-correlation based approach to assess synchronous dynamics between cortical activity and behavioral performance. The findings herein highlight the practical significance of including analyses of the time domain in workload assessment, in addition to the functional utility of a combination of metrics in the study of the temporally linked cognitive-motor output associated with increased mental workload.
This paper investigates the relationship between broadband noise behavior and helical wake structure in coaxial corotating rotors. Experimental measurements were conducted across variations in collective pitch (9.4°, 12.5°, and 15.0°) and rotor speeds (1500–4500 RPM). The inflow ratio (λ) was shown to govern the slope of broadband noise trends mapped in phase offset versus separation distance space, with experimental and theoretical λ values agreeing within 1%. Tip vortex core growth was estimated using the Ramasamy-Leishman model and normalized by the blade tip chord, reflecting the location of tip vortex formation. Across collective pitch variations, initial vortex core radii ranged between 7.5% and 9.1% and across rotor speeds, it ranged between 7.5% to 8.5% of the blade tip chord. When broadband noise trends became less coherent across phase offset angles, the corresponding vortex core radii were observed to approach or exceed 10% of the tip chord. At 4500 and 3500 RPM, vortex cores radii remained near or slightly above 10% at diffusion and depletion of broadband noise coherence. At 1500 RPM, initial vortex core radius is significantly beyond 10% of blade tip chord, leading to early diffusion, loss of organized wake structures, and broadband noise saturation across all phase offsets. If an inboard chord length were used instead for normalization, the specific normalized values would differ, but the overall trends in vortex diffusion and broadband noise coherence would remain similar. These results define a practical RPM threshold below which coherent wake structures and slope-based inflow prediction are no longer valid. Overall, the findings offer a framework for anticipating wake breakdown and broadband noise saturation, providing guidance for rotor design and operation to preserve low-noise performance.
The vertical flight industry is on its way to a transformative era, with autonomous technologies set to alter aerial vehicle operations. While it seems certain that fully autonomous helicopters will eventually be deployed for a variety of missions, some high-stakes situations—like medical evacuations (MEDEVAC)—will for the foreseeable future demand human participation in the form of Emergency Medical Care-giving Crew. This study describes the testbed built to run and investigate hypothetical future situations in which a helicopter is autonomously piloted while a human medic with no aviation training, subjected to aviation and medical emergencies, manages patient care onboard. A total of 22 participants, with emergency medical technician certification, nursing or a medical board certification, were invited to run and evaluate the use of AI pilot (AP) in different scenarios of medical evacuation under the following emergencies: medical, empty fuel tank, pressure sensor miscalibration, and engine failure. A comprehensive evaluation of both objective and subjective performance metrics revealed that novice medical professionals could effectively execute medical evacuation operations in conjunction with an AI pilot, even during unforeseen circumstances. The analysis of response times unveiled distinct perspectives on how medics perceive and manage various emergency situations when an AP functions as a collaborative and effective team member.
The NASA Revolutionary Vertical Lift Technology project aims to support and guide the development of vertical flight vehicles for the benefit of the U.S. rotorcraft community and to increase the quality of life of the public. As part of this effort, the Multirotor Test Bed (MTB) – designed and built by NASA – has been tested twice at the U.S. Army 7- by 10-Foot Wind Tunnel at NASA Ames Research Center in 2019 (MTB1) and 2022 (MTB2). This study utilizes MTB2 experimental data for sensitivity studies on rotor aerodynamic performance of a quadrotor configuration using two mid-fidelity tools, the Comprehensive Hierarchical Aeromechanics Rotorcraft Model (CHARM) as well as Blade Element Theory based disk modeling in the OVERFLOW CFD solver. Additionally, this study leverages analyzing computational rotor performance predictions with experimental data to help identify future test configurations for the upcoming MTB3 test in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel.
This paper demonstrates extraction of linear models from a state-space free wake model by applying analytical linearization, extending the research presented in (Ref. 1). Two distinct Linear Time Invariant (LTI) models are developed: the first is a high-order LTI model derived from the direct conversion of the analytical Linear Time Periodic (LTP) model, and the second is a reduced-order LTI model generated by first applying the Proper Orthogonal Decomposition (POD) model order reduction technique to the LTP model, followed by conversion. In both cases, the LTP-to-LTI conversion is achieved using harmonic decomposition. A substantial reduction in the number of wake states, from 15552 to 4050, is accomplished while maintaining a similar degree of accuracy. The time domain responses of step and doublet inputs for rotor collective and cyclic pitch are analyzed by comparing the GENHEL rotor model coupled with the LTI wake against the non-linear free wake model. Good agreement is observed in the rotor forces and hub moments. The paper investigates the feasibility of converting the linearized wake model into a linear parameter-varying inflow model with radial and azimuthal basis functions representative of a Peters-He inflow model. A least squares mapping technique is used to derive equivalent Peters-He inflow coefficients which are shown to accurately model the inflow distribution over the rotor disk and the time variation in induced velocities when compared to the non-linear free wake model.
Research into the feasibility of a scaled rim-drive propulsion product to enable ultra-heavy vertical lift (UHVL) is ongoing at the University of South Carolina in partnership with KRyanCreative, LLC, a start-up aerospace small business. The research team is advancing a superconductive design concept for a rotor system that delivers significant performance gains and flight envelope expansion disruptive to the vertical lift transportation sector. The team has conceived a novel electric tip-driven ducted propulsor to guide architectural and engineering investigations that improve hover and acoustic performance over current practice without penalty to weight and cost. This paper summarizes the data and assumptions that emerge from the systems engineering process of requirements decomposition for product realization. Requirements are categorized as to whether they are explicit (programs of record) or implied (comparable business case or as an alternative to a program of record). Risk reduction enroute to technical feasibility is addressed with a methodology that applies predictive analytics aided by artificial intelligence that will accelerate prototype fabrication by 2030 and fast track market incentives for multiple aviation technologies.
This paper introduces a comprehensive model, specifically developed to inherently capture interactional effects. Due to the high computational cost associated with the large analysis matrix including variations in angle of attack, angle of sideslip, velocity, and weight, a surrogate model is used in creating aerodynamic databases. This database, which reflects interactional effects under a wide range of flight speed, angle of attack, angle of sideslip, and weight configuration, is integrated into a rotorcraft analysis tool. Simulations are performed, and results are compared against flight test data for the T625 Gökbey, covering low-speed, high-speed, rightward and climb conditions. The results highlight the impact of interactional aerodynamics on flight characteristics and load predictions. Overall, the study emphasizes the importance of including interactional effects to ensure accurate and reliable rotorcraft design in the early design stages without requiring flight test data.
This paper deals with the uncertainty estimation of identified frequency and damping trends of whirl flutter modes, obtained by applying system identification methods on experimental data. In particular, two different identification approaches are considered, namely the free-decay analysis by using Matrix Pencil algorithm and the Data-Driven Stochastic Subspace Identification method (SSI), applied to system response to stochastic input. The two approaches lead to as many uncertainty estimation methodologies, both leveraging the bootstrapping statistical process. A full validation procedure is then set up to assess the accuracy of such methods in correctly quantifying the uncertainty of the estimated statistics. To do so, a wing-rotor state-space linear numerical model is used to simulate system response to both dwell and stochastic inputs. The state space numerical system aims to replicate the ATTILA wing-rotor wind-tunnel model, which falls in the framework of Clean Sky 2 European program to investigate the possible occurrence of whirl-flutter instability in tiltrotor configurations. Hence, one of the proposed methodologies is applied to ATTILA experimental data for both modal identification and uncertainty estimation, and the processed flutter trends are reported in a few conditions of particular interest due to the progressive approaching of whirl-flutter condition.
This study presents the design, modeling, and simulation of an Adaptive Speed Gearbox (ASG) with integrated electric variator for the UH-60A Black Hawk helicopter. The proposed drivetrain architecture enables main rotor speed variation independently of turbine speed, addressing operational demands for enhanced efficiency, noise reduction, and performance flexibility. A comprehensive aero-thermal model of the turboshaft engine, a dynamic drivetrain model, and a variable-speed control strategy were developed and validated. The control approach employs a two-degree-of-freedom structure combining nullspace-based feedforward torque allocation and modal-weighted LQR feedback for vibration suppression. A similarity theory-based scaling method was employed to design a demonstrator gearbox, facilitating experimental validation under representative conditions. The results demonstrate the feasibility of the ASG concept and establish a foundation for future experimental investigations and subsequent technology maturation towards higher TRLs.
As part of a human factors research project aimed at optimizing technical documentation used in helicopter maintenance with multimedia elements, we compared different instruction formats to observe their effects on the performance of an assembly task. This task offers us the opportunity to test procedures that call for similar actions as a maintenance task (e.g., localization, action sequencing, assembly). Static (i.e., image and image with text) and dynamic instruction formats (i.e., video, video with text and video with audio) were compared to determine if dynamic formats allowed a better motor performance of the task for assembly reaction time (time needed to complete the assembly) and accuracy. We were also interested in how the use of the text instructions interacted with both visual dynamic and static instructions. Reaction times were recorded and measured with eye tracking data. Subjective data was collected in questionnaires during and after the experiment. Results showed significant differences in the time spent on the instructions and the time spent on the assembly, depending on the format of instructions. Overall, assembly time is shorter with video instruction formats, but videos took longer to be consulted than static formats. Results also showed a difference in the number of actions required to do the assembly. Videos facilitated the right path of action sequence in comparison with static formats. With the analysis of both subjective and objective data, the results give us a better idea of the advantages and drawbacks of using dynamic formats in technical documentation.
In January 1984, the Georgia Tech School of Aerospace Engineering (AE) hired Dr. Daniel P. Schrage as the Rotorcraft Design Professor and the Associate Director of the Georgia Tech Center of Excellence in Rotary Wing Aircraft Technology (CERWAT), one of the Army-sponsored Rotorcraft Centers of Excellence (RCOE). Dr. Schrage left St. Louis, MO at the end of 1983 as the Director for Advanced Systems (DAS) and the Associate Director of Army Aviation Science and Technology in the Aviation Research and Development Command (AVRADCOM). His departure was a tough decision for Dr. Schrage as he was designated to become the Technical Director of the new Aviation Systems Command (AVSCOM). However, the new AVSCOM motto was "Readiness Immediate and Development Eventual," which, as it turned out, meant that new Army Aviation Systems would not be developed for the next 35 years. Dr. Schrage was also recruited by Bob Lynn, Bell Helicopters VP Engineering, as the Bell Helicopters Director of Technology, with a promotion to VP Engineering upon Lynn's retirement in the next few years. This was one of the most challenging decisions of his life for Dr. Schrage and his family, as they had to move from their home in O'Fallon, IL - a great town and home for his growing family.. In addition, his wife Nancy's parents and his mother and sisters, all lived within a half hour from his home. His father, Albin, had passed away while we were moving to the St. Louis Area following his MSAE graduation from Georgia Tech in May 1974. When he arrived at Georgia Tech in January 1974, he started teaching the Rotorcraft Design Courses, which were similar in content to what he had developed in AVRADCOM and to what Dr. Dick Carlson taught at Stanford U. He also developed and taught design courses in his two weeks each year in the Department of Mechanics at USMA West Point during his reserve duty from 1978-1983. He continued in the U.S. Army Reserves and taught two weeks at USMA until 1996. He then retired as Colonel in the USAR in 2004. He used a computer-integrated environment and the top-down design decision support process taught at West Point. This provided a Framework for using Systems Engineering Methods for Product Design Driven and Quality Engineering Methods for Process Design Driven, as illustrated in Figure 1. Value-based Acquisition decision-making is a lost art in Digital Engineering and other attempts to produce effective and affordable systems. The Army FARA Contract termination in 2022 was primarily due to lack of Development Assurance Value Based Acquisition (DAVBA) (Ref. 1).
This research analyzes flight safety occurrences such as incidents and accidents in the vertical lift community over the last two decades. A study of civil vertical lift occurrence data was performed for flight occurrences from 2000 to 2024. Focusing on North America (Canada, United States), research data was acquired from the respective government Transportation Safety Board agency of either country. The study data set consisted of 4623 occurrences (occ.) or observations (i.e.; 861 for Canada and 3762 for the United States). The research methodology involved a 6-step process to analyze data quantitatively (descriptive statistics) and qualitatively (trends, mitigation projections). For the study period, quantitative findings indicated occurrence rates (4.53 occ. per 100k flight hours (Canada); 3.39 occ. per 100k flight hours (United States)), occurrence rates of change (declining Canadian and United States rates (-2.3%/yr. & -2.2%/yr.) respectively), and occurrence event types (in Canada, Engine Failures (121 occ.) while in United States Loss of Control (589 occ.) events indicated the most occurrences). For this investigation, qualitative findings highlighted a series of general groupings or conditions in areas of System Failures, Flight Control, Vehicle Collisions, Flight Operations, and Pilotage. It was projected that technologically, open-loop and closed-loop control systems may provide the best potential for occurrence mitigation. Key pilot assistance domain systems include envelope/limit protection, detect/avoid, perception, and flight control (stability, trajectory following, navigation).
The development of a coupled computational structural dynamics (CSD) and electrodynamic suspension (EDS) system was critical in modeling and predicting the aeromechanics of MagLev Aero's (MLA) propulsion system, ensuring safe testing and proving viability of levitated rotors for vertical lift systems. This advancement validates the feasibility of this enabling technology in applications of uncrewed aerial systems (UAS) with high hover lift efficiencies. This paper explores the implementation of an electromagnetic motor hub on a large-root-cutout, slowed rotor system with a specific focus on the impacts on aeromechanics: loads, performance, vibrations, and aeroelastic stability. The performance benefits of a large-root-cutout system, with an external or internal rotor, are well known; however, the mechanisms to implement such a design have been impractical. The development of an EDS motor bearing enables previously unattainable configurations like large-root-cutout and tip-driven ducted systems that have advantageous loading, acoustic, and vibration performance; such benefits thus require characterization in dynamics and aeroelastic stability to prove the feasibility of these complex concepts. Furthermore, the ability to investigate a multidisciplinary, multiphysics-based system is nontrivial; customization and advancement of existing comprehensive analysis systems is required to solve these complex problems. The investigation of performance, dynamics, and aeroelastic stability for the EDS rotor on a subscale thrust test system, EXO600, is being substantiated through MagLev Aero's test programs. The results presented herein are a subset of the validations in aeromechanics and electrodynamics.
The unconventional configuration of a 2 × two-bladed stacked rotor with a diameter of 0.82 m is studied experimentally throughout this paper. With the rotational speed kept constant at 2453 RPM and the dimensionless axial spacing fixed at 0.06, the main objective is to assess the effect of azimuthal spacing across multiple configurations in forward flight, varying the shaft angle and freestream velocity. First, an analysis of the baseline rotor in forward flight is presented, featuring four blades evenly spaced in a single plane. This is followed by results for the stacked rotor in hover flight, revealing a consistent trend with the literature: a low-performance region offering lower blade loading values for smaller azimuthal spacings, when both rotors closely overlap, and a region of increased performance for larger azimuthal spacings in both positive and negative directions. Most azimuthal spacings exhibit higher performance relative to the baseline rotor, with a maximum positive change of 7.82%. Finally, a performance comparison between the baseline rotor and the stacked rotor in forward flight reveals a similar trend to hover flight regarding the low-performance region for small azimuthal spacings, but with a less significant region where the stacked rotor outperforms the baseline rotor. Moreover, the vibratory loads of the stacked rotor depend on the azimuthal spacing, varying from a two-per-revolution harmonic at an azimuthal spacing of 0° to a four-per-revolution harmonic at 90°, resulting in higher vibratory loads transmitted to the rotor hub when the blades of both rotors are unevenly spaced.
Helicopter pilots are exposed to a wide range of vibration frequencies, primarily generated by engine and rotor dynamics. These vibrations, particularly within the 0.5–80 Hz range, pose significant risks to pilot health, including musculoskeletal injuries and fatigue. To mitigate these effects, vibration isolators are employed, with passive and active isolation systems offering different advantages. This study investigates the initial design and performance of a novel metal additive manufactured vibration isolator, optimized for placement under the pilot's seat in a rotorcraft simulator. The isolator was designed with key structural parameters including stiffness, coil dimensions, and material properties while maintaining a lightweight and durable form, with a primary goal of validating the additive manufacturing of a metallic isolator. Experimental corroboration was conducted by incorporating modifications to the Gannon Biomechanics Flight Simulator test stand (GBFS), comparing the novel isolator to an elastomeric isolator. Results demonstrate the successful fabrication of the initial additive isolator design. The additive isolator displayed a similar performance to the rubber isolator after being installed in the GBFS, though limitations on the current test rig and sensing configuration did not allow accurate characterization of the transmissibility. This research sets the groundwork for further development of a novel additive isolator and test facility.
The National Research Council of Canada is conducting a multi-year autonomous flight systems research and technology development project entitled Advanced Autonomy Systems for Challenging ENvironments Development & Demonstration (AASCEND). As part of AASCEND a no-hover landing capability has been developed and demonstrated in a variety of environmental conditions, including in limited degraded visual environment (DVE) operations. This paper discusses the requirements for no-hover landings, their value within an Autonomous Flight System (AFS), and the implementation of this capability in the NRC's AASCEND autonomous flight system. It presents a methodology for identifying a no-hover landing envelope, taking into account the complex maneuvering required. Within that methodology a proposed set of assessment criteria for no-hover landing performance and behaviour is introduced. The paper reports on the results of applying this methodology to the AASCEND no-hover landing algorithm in a simulation study, along with associated Landing Zone Evaluation (LZE) system performance requirements.
This paper presents an experimental and analytical investigation of whirl-flutter stability in tiltrotor aircraft, focusing on the influence of pitch-flap coupling on stability boundaries. Wind-tunnel tests were conducted using the TiltRotor Aeroelastic Stability Testbed (TRAST), a semi-span model designed for test-analysis correlation. This study examines variations in pitch-flap coupling and compares measured frequency and damping trends with predictions from RCAS and CAMRAD II. Results indicate that less pitch-flap coupling increases stability, with both analytical models capturing general trends. The analysis accurately predicts the wing inplane mode stability, but larger deviations are observed in the vertical bending mode, suggesting missing physical effects in the modeling approach. Differences in damping trends at higher speeds indicate that improvements in modeling may be necessary to refine stability predictions. These results provide valuable insights into the capabilities and limitations of current whirl-flutter analysis methods and inform future refinements in tiltrotor aeroelastic modeling.
The performance and acoustics of a scaled propeller designed for an eVTOL vehicle were investigated in axial and edgewise flight. The measured performance compared well with BEMT predictions in axial flight conditions. The noise produced by the propeller is dominated by broadband noise sources, where there is evidence of contributions from blade wake interaction noise, turbulent boundary layer trailing edge noise, and laminar boundary layer vortex shedding noise. The directivity of the noise was found to be dependent on the advance ratio. Beamform maps also identified changes in the dominant noise source at different observer locations as a function of advance ratio.
Survivability in the future operating environment is becoming more challenging as threat systems evolve and become more sophisticated. The ability to tailor and manage signatures will be one of the key methods to improve survivability, allowing operators to minimise detection and maximise the effectiveness of countermeasures. This paper presents the findings of an investigation into the application of classical Signal Detection Theory (SDT) to the aural detectability of helicopter noise signatures, considering human auditory capabilities. The paper has thus developed a novel methodology, applied it to both the experimental and numerical helicopter acoustics signatures of an LH platform, and used these results to infer the detectability characteristics of the aircraft, as well as how they are affected by the presence of background noise in different environments.
This paper presents handling qualities (HQs) research findings for electrical Vertical Take-off and Landing vehicles. Testing in the Vertical Motion Simulator (VMS) investigated handling qualities of vehicle configurations having a degraded powertrain. Powertrain components, including batteries and electric motors, can degrade as the vehicle is flown. This paper investigates the impact of low battery charge and high motor temperature degradations on the pilot's ability to execute precise maneuvers. Pilot comments and ratings that were collected from four rotorcraft test pilots in VMS testing are used to quantify the effects that powertrain degradations had on the HQs of the vehicle.
This paper presents an overview of the results from the second wind-tunnel test of the TiltRotor Aeroelastic Stability Testbed (TRAST). The objective of this test was to obtain experimental data for understanding the effects of tiltrotor parameters on whirl flutter and analysis-validation data for the prediction of whirl flutter across a range of system configurations. Frequency and damping were measured at multiple rotor speeds for pitch-flap-coupling angles ranging from -0°to -30°. In addition, measurements were made for changes in blade stiffness, air density and wing-pylon connection stiffness. The paper also presents the results from supporting measurements that may aid analysis validation, such as wing-only damping, rotor frequencies and non-spinning modal frequencies.
Inspecting the interiors of tanks and ships for defects involves accessing confined and elevated spaces. This can be difficult and hazardous for a person. Ducted aerial vehicles that can hover close to the object of interest can achieve this in a safer and more efficient manner. Such a vehicle is desired to be compact, to have a high hover endurance and to be protected from impact. This paper describes a design concept comprising ducted coaxial counter-rotating rotors with a compact swashplate mechanism for cyclic pitch input to the lower rotor. An experimental setup was used to investigate the effect of the duct. A numerical Blade Element Momentum Theory model was developed and validated to inform rotor selection. A prototype was designed and built with a hover thrust of 9.17 N, outer diameter of 350 mm, and height 173 mm. The duct provided a thrust benefit of 32% for this configuration for a given power. The prototype achieved stable controlled flight in hover and in passing near walls and surrounding obstacles. Some oscillations in attitude were seen in flight. Future work includes improving the control algorithm of the vehicle.
A method for the parameterization of an arbitrary airfoil using a transformation and Chebyshev polynomial interpolation is investigated. The airfoil was transformed into a continuous function using the Class Shape Transformation. A square root spacing was used to smooth out the slope discontinuity found at the origin. This mapping reduces oscillations in the polynomial interpolation caused by the slope discontinuity at the origin. Interpolating a range of NACA 4-digit series airfoils showed that these airfoils could be accurately represented with as little as 10 polynomial terms. However, problems arise with the Class Shape Transformation when trying to parameterize non-analytically defined airfoils. The transformation expects the behavior of the leading edge to be perfectly elliptic, and any deviation from this requirement leads to the divergence of the Class Shape Transformation. As a result, parameterizing with polynomials becomes infeasible for some airfoils. To address this, a conformal mapping-based unwrapping method is suggested.
This paper describes a combined visual and haptic localization experiment that addresses the area of multi-modal cueing. The aim of the present investigation is to characterize accuracy and precision of tactile cue-ing in the peri-personal space (PPS), the space around the body in which sensory information is perceived as meaningful (Ref. 1). Outcomes of the unimodal (visual and haptic) and multi-modal (combined visual-haptic) localizations are used to make predictions about the multimodal integrative phenomenon. In the localization experiment, participants are presented with visual, haptic, or multimodal target cues using the body-centered reference frame and are instructed to indicate the corresponding hypothetical target location in space using a mouse pointer in an open-loop feedback condition.
This investigation reveals many DoD contractors do not treat integration as a stand-alone activity. Instead, integration is an inherent part of the development process. The contractors did not have a specific documented process for integration beyond calling out integration as an activity in the development process. Integration is an integrator unique step within the development process to meet functional and performance requirements. Identification of the interfaces and engineering to match the interfaces requires substantial individual expertise and heuristics for each integration effort resulting in inconsistent non-repeatable integrations. This increases risk, and limits third party integration effectiveness and utility. This paper identifies steps that can be taken to increase the speed and effectiveness of integration while decreasing the effort and dependency on individual expertise.
On July 19, 1990, Senator Danial Inouye chaired a subcommittee to address the fate of the USMC V-22 Osprey program. Prior to this meeting, Secretary of Defense Dick Cheney, at a time of increasing fiscal constraints on defense spending, in a controversial decision, terminated the V-22tilt rotor aircraft program. However, it was resurrected by Congress. Proponents of the V-22claimed the aircraft costs were justified since it represented revolutionary technology with long-term benefits to military and civil aviation. Therefore, a study was authorized through the office of the Honorable David Chu, then Assistant Secretary of Defense for Program Analysis and Evaluation. The Institute for Defense Analyses (IDA), a Federally Funded Research and Development Center (FFRDC), was tasked to conduct the analyses. IDA conducts studies and analyses for the Office of the Secretary of Defense, the Joint Staff, the unified commands, and the Defense agencies. IDA was specifically tasked to conduct an "Assessment of Alternatives for theV-22 Assault Aircraft Program." The study was led by Dr. L. Dean Simmons and supported by Professor Alfred Gessow and Kaydon A. Stanzione who served as Air Vehicle Technical Expert. The focus was on two key considerations that related to the cost of the aircraft: 1) the overall cost effectiveness of the alternative fleets measured over a 20-year period that was used as the principal basis for conclusions, and 2) the difference in the near-term costs for the alternative fleets.
This paper investigates the amplitude-dependent characteristics of the TiltRotor Aeroelastic Stability Testbed. The recovery rate, MultiProny, and Stockwell transform methods are employed to measure nonlinear effects in the system, overcoming the limitations of conventional methods like logarithmic decrement, moving-block analysis, and Prony series that assume linear (amplitude-independent) behavior. The proposed methods reveal amplitude-dependent trends that conventional methods obfuscate, providing deeper insights into tiltrotor dynamics. A comprehensive study of ground vibration and wind tunnel test data highlights reduced local damping and frequency at larger response amplitudes for various blade materials, rotor speeds, and pitch-flap coupling parameters. This study offers novel analysis capabilities to support design and advances the understanding of tiltrotor nonlinear dynamics.
This study presents an integrated optimization framework for rotor blade design that combines aerodynamic shape optimization and internal structural design within a unified multidisciplinary process. A variable fidelity modeling (VFM) approach is employed to efficiently optimize the blade outer geometry for improved figure of merit (FM) in hover and lift-to-drag ratio (L/Dq) in forward flight. Based on the optimized aerodynamic shapes, internal structural optimization is subsequently performed using a surrogate model for predicting cross-sectional properties, ensuring dynamic feasibility while minimizing blade vibration and weight. Final aeroelastic performance is evaluated through high-fidelity CFD/CSD loose coupling simulations. Optimization results show that individual designs achieve up to 6.5% improvement in FM or up to 6.6% improvement in L/Dq compared to the baseline HART II rotor. Furthermore, cross-validation comparing blades independently optimized by Seoul National University (SNU) and DLR reveals similar aerodynamic trends and performance, demonstrating the robustness and general applicability of the proposed framework across different simulation setups.
A hybrid RANS/LES simulation of the Ideally Twisted Rotor (ITR) in hover was interrogated to identify bluntness vortex shedding (BVS) and determine the contribution to the predicted rotor broadband self-noise. Three rotor blade stations were extracted to study spanwise variations in the BVS shedding frequency and amplitude. Corresponding 2-D airfoil simulations were performed to evaluate a simplified modeling approach that effectively isolates BVS. The BVS shedding frequencies predicted by the 2-D airfoil simulations differed by less than 2% from the corresponding rotor stations in the 3-D simulation. The increased computational cost incurred by performing 3-D airfoil simulations did not lead to a worthwhile increase in simulation fidelity. Farfield noise was predicted for the three rotor stations and the 2-D airfoil simulations, and trends in frequency agreed well. The 2-D approach overpredicted the 3-D peak amplitudes by 5 - 10 dB. This work demonstrates that 2-D hybrid RANS/LES airfoil simulations can be used to investigate BVS noise trends on the ITR.
We present the flight testing and integration of the Microsoft HoloLens 2 as a head-worn display (HWD) in DLR's research helicopter. Building on its successful use in a helicopter simulator, initial flight tests confirmed its feasibility in a real helicopter. Current tests focused on system optimization, with head tracking identified as the critical component for hologram stability. Since the HoloLens' inside-out tracking fails in moving vehicles, it was fused with an external infrared tracker, automatically calibrated via an optimization approach adaptable to various trackers and mounting positions. A test pilot with HWD experience rated the system as fully functional, enabling the first successful experiments with holographic Mission Task Elements. Beyond the helicopter, the HoloLens was tested in a car and on a high-speed boat, where holograms remained spatially stable despite high-frequency movements, with a maximum low-frequency error of 0.6° in heading. Static errors depended solely on the external tracker's quality. These results demonstrate the HoloLens 2's potential for operational use in dynamic vehicle environments, enhancing immersion. Its mixed-reality features and adaptability proved particularly valuable for rapid research and development across platforms.
Electric Vertical Takeoff and Landing (eVTOL) aircraft present a series of challenges to traditional aviation infrastructure that was designed for conventional rotorcraft. Questions have arisen within the vertical flight community as to the validity and applicability of applying current heliport markings and symbology to vertiports. Several of these questions were addressed in a previous paper from VFS Forum 80: "A Comparison of Proposed Concepts for Vertiport Markings and Symbology" (Ref. 6). In contrast, this paper extends that work and presents the results of additional research to enhance the visibility of the Federal Aviation Administration’s (FAA) “Broken Wheel” symbology. These notional enhancements to the "Broken Wheel" symbology were evaluated over the course of an experimental study using helicopter-rated pilots in the FAA William J. Hughes Technical Center’s S76-D and Loft Dynamics H125 and R22 rotorcraft flight simulators.
The emerging Advanced Air Mobility (AAM) market is an increasingly important area of research and development within vertical lift. AAM operations will be characterized by short- to mid-range flight that will include urban and suburban corridors and high utilization business models such as on-demand ride-share and package delivery operations. AAM operations also have an enhanced need for durability of vehicle components with respect to impact and fatigue within unsteady environments such as urban canyons. Further business model constraints include the minimization of scheduled maintenance, while maintaining safety levels. A university leadership initiative (ULI), Innovative Manufacturing, Operation, and Certification of Advanced Structures for Civil Vertical Lift Vehicles (IMOCAS), combined research and software development to address these operational aspects. Another major focus of the ULI was the development of processes to integrate new advanced composite materials into AAM designs. These new composites, such as thermosets and thermoplastics, offer equal or enhanced performance at lower weights than traditional aviation materials. This paper provides an overview of the outcomes of the ULI, introducing new software, processes, and data available to the community for the AAM market, crosscutting large passenger operations and smaller medical or commercial cargo operations.
In this work, a vision-based solution is developed to address the challenge of landing on a ship deck with precision and accuracy. For an autonomous landing, it is important to have a fast and accurate pose estimation system along with a reliable control strategy. This research uses fractal ArUCo markers instead of multiple separate markers to allow smooth pose estimation at different heights. Pose estimates are further improved using an Extended Kalman Filter, and a tracking algorithm then uses these estimates to guide the landing. A four degree-of-freedom (roll, pitch, heave and sway) simulator platform was built and used to validate the algorithm. The accuracy of the vision system is compared against that of a motion capture system. Real-world experiments were performed on different quadrotors to demonstrate tracking and landing on the platform with sway, roll, and pitch motions. The results show that the system is efficient and reliable in achieving safe and successful landings. The proposed landing system is concluded to be applicable for landings on the deck of the ship under sea-state 4.
We extend the previously developed integrated VABS (iVABS) framework for rotor blade structural optimization with an enhanced cross-section template for practical manufacture considerations; these include the introduction of curved spar corners, a continuous wrap-around skin, trailing-edge tabs and a conformal non-structural mass. The added fidelity is exercised on a UH-60A-based outer mold line through three multi-objective optimization case studies, including a case where the cross-sections are optimized independent of each other, and two cases where all the cross-sections are optimized simultaneously with manufacture considerations. It was found that the latter cases produce straight spars that are relatively more practical to manufacture when compared to the first case, while achieving significant reduction of up to 80% in the mismatch of stiffness values, inertia properties, and shear center locations, when compared to the prior work. A subsequent sensitivity analysis of the Pareto set isolates five critical combinations of design variables, out of the original nearly 100 variables, such as root/mid-span skin-ply count and spar-web placement, that can be adjusted to refine the Pareto solution. The study demonstrates that manufacturability-aware parameterization and data-driven variable reduction can deliver practical composite-blade designs within a scalable optimization loop.
Rotor performance in a Martian environment was analyzed with an objective of increasing thrust with minimal impact on efficiency. The Sample Recovery Helicopter (SRH) and Rotorcraft Optimization for the Advancement of Mars Exploration (ROAMX) rotors were studied by varying solidity, blade count, and chord distribution to determine which configuration delivered the most desirable performance. For all configurations, the ROAMX rotor displayed better performance than the SRH rotor. It was observed that increasing solidity reduced the blade loading required to achieve the peak figure of merit, and beyond a solidity ratio of 0.3 the figure of merit was negatively impacted. For both rotors a 6-bladed configuration with a solidity ratio of 0.3 delivered the optimal figure of merit.
A velocity potential-based finite state model (VPBFSM) has been developed to analyze an isolated rotor in ground effect. The model uses mass source distributions to represent the ground and enforces the non-penetration of flow boundary condition. In previous VPBFSM approaches to impose this boundary condition, the r = j terms were excluded to avoid singularities. This exclusion required adjustments to the source strengths and ground rotor size in order to impose the boundary condition properly, which reduced the model’s robustness. In the present study, the r = j terms are incorporated using a solution for the gradient of the velocity potential from the literature, which avoids singularities. This inclusion allows for effectively enforcing the boundary condition without requiring adjustments. The model is applied to an isolated rotor in full, inclined, and partial ground effect cases, including analysis of the R−50 rotor using geometric and aerodynamic data from the literature. Results for full ground effect show excellent correlation with the Hayden model. The normalized induced torque also exhibits good agreement with experimental data for full, inclined, and partial ground effect cases.
This paper explores novel airfoils for rotorcraft applications using a gradient-free, multi-objective genetic algorithm with 2D URANS simulations. The study considers dynamic kinematics at a Reynolds number of 5×105 and a mean Mach number of 0.35. Two optimization scenarios are analyzed: 1) pre-stall kinematics (0° ≤α ≤10°) and 2) dynamic stall kinematics (0° ≤ α ≤ 20°). The paper compares two objective functions: f1, based on the cycle averaged lift, and ˜ f1, which modifies f1 by penalizing hysteresis in the lift coefficient. The effects of uniform vs. fluctuating freestream velocity and reduced frequency on optimal airfoils are also discussed. The proposed optimization approach has resulted in novel airfoil shapes that are characterized by a drooped nose, with a convex surface on the aft upper surface similar to a reflex camber in pre-stall kinematics and less unsteadiness in the air loads for the optimized airfoils under the dynamic stall kinematics.
This paper explores the dynamics of rotating Tuned Vibration Absorbers (TVAs), focusing on the phenomena arising from gyroscopic effects. Some products from Leonardo Helicopters (LH) can have a TVA fitted in the rotor mast, counteracting the in-plane vibratory loads of the rotor directly at their source, implying that the absorber rotates with the rotor itself. Although gyroscopic effects are negligible for most of the LH TVAs, specific design choices may have notable impacts on tuning and performance. An analytical model is implemented, demonstrating that the gyroscopic terms influence the dynamics causing a frequency displacement of the anti-resonance evaluated without considering this effect. Additionally, a regression analysis investigates the interplay between this phenomenon and the physics of the system, revealing how to optimize the design to mitigate gyroscopic effects. Finally, the performance of the TVA is analyzed as a coupled problem, showing that the anti-resonance effectiveness is reduced by the orthogonal contribution introduced by the gyroscopic matrix.
This paper investigates an output-based approach for predicting limit-cycle oscillations caused by freeplay, which can affect actuated structures of vertical lift vehicles. The proposed approach uses pre-critical time-history data to estimate the recovery rate to equilibrium following perturbations as a function of amplitude and a varying parameter. Recovery rate data points in the parameter-amplitude plane are fitted and extrapolated to predict limit-cycle oscillation solutions, corresponding to a recovery rate of zero. While previous work demonstrated this approach for systems with geometrical or polynomial stiffness nonlinearities, this study investigates its applicability to freeplay for the first time. The study uses time-history data from simulations of an analytical model of an idealized, elastically mounted tilting propeller in airplane mode, with freeplay in the tilting mechanism. The results highlight the promise of the proposed approach, paving the way for addressing more complex configurations.
Generalized Predictive Control (GPC) is an advanced form of an adaptive control algorithm that uses experimentally acquired data to determine the input-output relationship of complex systems through a process called system identification. GPC has historically been employed for stability augmentation and vibration reduction of dynamically-scaled tiltrotor aircraft wind-tunnel models since the complex nature of these dynamic systems does not lend itself well to traditional control approaches. The present research expands upon previous analytical and experimental work with wind-tunnel experiments that utilize improved GPC techniques. These techniques improved controller robustness such that a working controller was stable across a multitude of model configurations and wind-tunnel conditions and successfully suppressed vibration and vehicle flutter. Advanced GPC (AGPC) enables self-adaptation of a traditional GPC control law. AGPC was also investigated during the present research but was not needed as anticipated because of the robustness resulting from improvements made to traditional GPC.
ABSTRACT In this paper, we propose a new approach to developing advanced simulation environments for use in performing human-subject experiments. We call this approach the mission-based scenario. The mission-based scenario aims to: 1) Situate experiments within a realistic mission context; 2) Incorporate tasks, task loadings, and environmental interactions that are consistent with the mission’s operational context; and 3) Permit multiple sequences of actions/tasks to complete mission objectives. This approach will move us beyond more traditional, tightly-scripted experimental scenarios, and will employ concepts from interactive narrative as well as nonlinear game play approaches to video game design to enhance the richness and realism of Soldier-task-environment interactions. In this paper, we will detail the rationale for adopting such an approach and present a discussion of significant concepts that have guided a proof-of-concept test program of the mission-based scenario, which we intend to integrate into ongoing S&T research efforts.
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