Browse Topic: Rotary-wing aircraft
Regarding the external sling load system of heavy-lift helicopters, the influence of the law of lifting point position on flight control stability characteristics has not been distinctly explained. To address this challenge, this paper constructs a sling load flight simulation model based on multi-body dynamics. Overall, the proposed model consists of four parts, including the rotor aeroelastic coupling model, the fuselage rigid body dynamics model, the flexible sling model, and the slung object rigid body model. Furthermore, through the hub six-degree-of-freedom rigid model and the flexible sling model, this paper realizes the dynamic coupling between the components. On this basis, taking the CH-53E heavy-lift helicopter as the research object, this paper utilizes real flight test data to validate the multi-body dynamic model. Subsequently, this paper systematically analyzes the influence of different lifting points’ lateral position, sling load mode, load-mass ratio, and forward flying speed on helicopter control stability characteristics. Simulation results indicate that the lifting point location exerts a significant impact on the helicopter’s trim attitude angles and dynamic stability. Of them, the lifting point location of the front center of gravity is the optimal in terms of trim characteristics and eigenvalue distribution. Furthermore, within a certain flight speed range, the lifting point of the front center of gravity demonstrates superior speed adaptability and system robustness. Apart from providing a solid theoretical basis for the lifting point layout design of the external sling load system of heavy-lift helicopters, the research results have important engineering application value for improving the safety of sling load flight of heavy-lift helicopters.
This SAE Aerospace Recommended Practice (ARP) recommends a methodology to be used for the design, analysis and test evaluation of modern helicopter gas turbine propulsion system stability and transient response characteristics. This methodology utilizes the computational power of modern digital computers to more thoroughly analyze, simulate and bench-test the helicopter engine/rotor system speed control loop over the flight envelope. This up-front work results in significantly less effort expended during flight test and delivers a more effective system into service. The methodology presented herein is recommended for modern digital electronic propulsion control systems and also for traditional analog and hydromechanical systems.
This SAE Aerospace Information Report (AIR) outlines a recommended procedure for evaluation of the vibration environment to which the gas turbine engine powerplant is subjected in the helicopter installation. This analysis of engine vibration is normally demonstrated on a one-time basis upon initial certification, or after a major modification, of an engine/helicopter configuration. This AIR deals with linear vibration as measured on the basic case structure of the engine and not, for example, torsional vibration in drive shafting or vibration of a component within the engine such as a compressor or turbine airfoil. In summary, this AIR discusses the engine manufacturer’s "Installation Test Code" aspects of engine vibration and proposes an appropriate measurement method.
The FAA VR-HeliSTART (Virtual Reality-Helicopter Simulator Training for Airplane to Rotorcraft Transition) is a 15-week study conducted at Marshall University (WV) to determine the effectiveness of an H125 VR reduced-motion platform simulator in training fixed-wing pilots to fly helicopters. Eleven students received three four-week blocks of instruction in the flight simulator, each followed by a simulator evaluation and a helicopter evaluation. This paper presents results for eleven hovering maneuvers trained and evaluated in the study. The evaluation of the students relied on both an objective and a subjective evaluation: a flight parameter analysis against Airman Certification Standards criteria, and an assessment by certified flight instructors. A key finding is that simulator training enabled all pilots to perform most hover maneuvers on their first helicopter flight without intervention, although sometimes below standards. Overall, results also suggest that while the simulator provides a useful learning environment for basic hover control, the further refinement of the core hovering skills acquired in the simulator did not appear to transfer effectively to the actual helicopter within the time frame of the study. Therefore, this indicates that initial hover training in the simulator is beneficial, but additional improvements still seem to require practice in the actual helicopter.
Traditional safe-life methodologies for rotorcraft structural components rely on deterministic safety factors to account for uncertainty in loads, material properties, and operational usage. While effective for ensuring safety, these approaches lead to early retirement lives and reduced aircraft availability. This paper presents an updated digital twin-based probabilistic framework for rotorcraft component fatigue life assessment that integrates a probabilistic stress–life (S-N) material model, machine learning-based load estimation from flight data, and Monte Carlo uncertainty propagation. The approach is demonstrated for a critical location on the CH-146 Griffon main rotor yoke. Compared with earlier work, the present study advances the framework through independent validation of the load-estimation model and application to available in-service flight data from multiple mission categories. A probabilistic sensitivity analysis is used to examine the separate and combined effects of material variability and load-estimation uncertainty on fatigue life, cumulative probability of failure, and hazard rate. For the CH-146 demonstration case, the results indicate that the material fatigue strength uncertainty has a major impact on the lower tail of the life distribution and the corresponding reliability-based life, whereas load-estimation accuracy uncertainty has a secondary influence on risk metrics. The application of the digital twin framework to operational, search and rescue, and training mission data further shows that mission-specific usage variability plays an important role in the evolution of fatigue damage accumulation and structural risk. Overall, the proposed framework provides a more informative basis for risk-based rotorcraft life assessment by explicitly quantifying uncertainty and incorporating aircraft-specific operational data. The study is intended as a step toward validation of the framework rather than a completed operational deployment.
A common-open data exchange standard for rotorcraft health and usage monitoring systems (CODEX-HUMS), SAE Aerospace Standard AS7140, was issued in September 2025. This standard provides a definition for the CODEX-HUMS open data format produced or used by an on-board or off-board system. The centerpiece of the standard is the data model. This paper describes how the two main data types, stream and batch data, are defined and modeled distinctly by AS7140. The batch data model, targeted at high-frequency, short-duration recorded data, features and delineates a "source", an "indicator", and a "status" element. The streaming data model, intended for lower-frequency, longer-duration HUMS data, covers events and parametric data. The data model is structured by defined data collections to describe the data collected or supporting metadata specifying details about the system or underlying data. In particular, there are definition-type entities and recorded data-type entities. This data model is designed to be flexible and efficient in order to accommodate existing HUMS as well as future HUMS development that support legacy and new rotorcraft platforms.
This paper develops an engineering concept and research framework showing how Cherokee MC2 (Mobile Command Center) and MVP (Mobile Vertipad Platform) can individually, and then as a combined system, resolve key operational and infrastructure challenges facing rotorcraft, eVTOL, VTOL, and UAS missions across civil, commercial, and military contexts. The investigation synthesizes current vertiport / vertipad design guidance, UAM and UTM operational architectures, and recent research on rotor downwash and degraded visual environment hazards to derive a deployable "vertiport node" architecture for austere and time-critical operations. MC2 is treated as the digital and procedural core enabling command, control, communications, data fusion, and manned–unmanned teaming, while MVP is treated as the physical landing interface enabling rapid, load-bearing, illuminated vertical-lift operations without fixed infrastructure. The primary contribution is a traceable topic-to-capability mapping supported by standards and research, plus a modeling, simulation, and optimization workflow to validate safety zones, capacity, scheduling, and resilience. Conclusions identify practical deployment pathways and research gaps for certification-aligned operations.
Rolling-element bearings in rotorcraft dynamic systems are critical components susceptible to rolling contact fatigue (RCF), a dominant degradation mechanism manifesting through subsurface-initiated spalling, surface micropitting, and fatigue fractures. Robust inspection strategies compliant with EASA and FAA requirements are therefore essential. Traditional methods are often invasive, requiring disassembly, and are susceptible to human-factor errors. Smart Duplex introduces a design-for-monitoring architecture integrating in-situ videoscopic and coherence scanning interferometry (CSI) for high-resolution 3D surface mapping, including under partial grease coverage. This paper details a repeatability and reproducibility (R&R) framework ensuring metric consistency; a maintainability assessment projecting significant man-hour reductions and high availability; certification rationale emphasizing airworthiness improvements via enhanced detectability, workload reduction, and digitized inspection records; and an airworthiness mapping supporting threat assessments, Airworthiness Limitations Section (ALS) entries, and usage-based maintenance credits. By embedding sensing capability and digitizing inspection records, Smart Duplex minimizes downtime, mitigates human-factor errors, and facilitates predictive maintenance, optimizing cost, enhancing performance, and ultimately improving safety.
The United Kingdom's convertible rotorcraft studies of the 1960s and early 1970s represent a systematic effort to combine vertical take-off and landing capability of helicopters with the speed and efficiency of fixed-wing transport aircraft. Conducted primarily by Westland Helicopters under the Short Range Transport (SRT) programme, these investigations explored both tiltrotor and tiltwing configurations for civil and military applications. Early work focused on the WE-01 tiltrotor, conceived as a research and demonstrator aircraft to investigate transition aerodynamics, control integration, and rotor–wing interactions, and subsequently scaled to the larger WE-02, intended for intercity and tactical transport missions. In parallel, Westland pursued the more ambitious WG.22 tiltwing, a 100-seat intercity VTOL transport incorporating high-incidence stall wing technology, large prop-rotors, and mechanically scheduled flight controls to ensure benign handling through transition. Although none of these aircraft were built, the studies addressed aerodynamics, structures, propulsion, flight controls, noise, and socio-economic viability with exceptional depth. Shaping the future through the past, this paper revisits Westland's early involvement in tiltrotor and tiltwing research, with the aim of assessing the technical maturity of these configurations and evaluating their lasting relevance to contemporary vertical lift aircraft design.
This paper examines the documented evolution of Kaman Aircraft Corporation's early helicopter development, specifically the progression from the K-225 evaluation aircraft to the groundbreaking HTK-1K drone helicopter. Through analysis of primary and secondary sources, this study establishes the technical and operational foundations that enabled the world's first remotely controlled helicopter. Additionally, this paper critically examines a hypothesis suggesting that 1st Lt. Donald M. Thompson may have been involved in preliminary remote-control helicopter experiments prior to the officially recognized HTK-1K program. While initially appearing speculative, this hypothesis gains substantial support from the discovery of a 1944 Army Air Forces memorandum documenting Thompson's position as Chief of Special Weapons Unit at Wright Field, with explicit responsibility for developing radio-controlled aircraft systems. This primary source evidence establishes Thompson as a documented historical figure with relevant expertise, though direct evidence of helicopter-specific work remains to be discovered. The paper outlines a methodological framework for continued archival investigation and examines the legacy of these early programs on modern unmanned aerial vehicle development.
The Sikorsky S-92® helicopter fleet, representing more than 300 aircraft and 2.6 million flight hours, is relied upon to support a large range of important missions across the globe. In previous efforts, a high-fidelity CFD-CSD based full-aircraft simulation methodology, co-simulated with production FCS, was developed and applied to model both coaxial aircraft and single main/tail rotor configurations (Refs. 1-5). The CFD solver is based on the CREATE™-AV HELIOS toolset (Ref. 6) and the CSD solver is based on Rotorcraft Comprehensive Analysis System (RCAS) (Ref. 7). The current paper further correlated the CoSim methodology (Ref. 1) with the S-92® helicopter flight-test database at both hover, cruise and edge-of-envelope maneuver flight conditions. The consistent correlations for flight dynamics, static and fatigue component loads at conditions across the flight envelope demonstrate the reliable predictive capability of the high-fidelity CoSim methodology to be-used as a virtual digital flight test and to support advanced design at early stage.
This paper presents several methods for measuring large flow fields in the wake of a helicopter, including wind vanes ("flags"), tufts, BOS (Background Oriented Schlieren), and BOS-velocimetry. The motivation is to develop methods that can map the outwash distribution of VTOL aircraft with strongly asymmetric wakes and identify jets that can be particularly dangerous for bystanders. Each measurement technique is shown to have specific advantages, and the resulting flow fields are demonstrated for the BO105 helicopter in hovering flight in ground effect above a tarmac.
This study evaluates the capability of Simcenter™ Flightstream™, a viscous surface-vorticity compressible-flow panel method, for predicting aerodynamic performance of rotorcraft configurations. Simulations are performed on the ROBIN-mod7 fuselage, PSP rotor, and combined rotor-fuselage system under conditions consistent with available experimental data. Results are compared against experiments and high-fidelity CFD methods, including DES, URANS, and IBM-ASM. For the isolated fuselage, Simcenter Flightstream accurately captures surface pressure distributions, particularly in attached flow regions. For the isolated rotor, thrust, torque, and figure of merit trends show strong agreement with reference data. In the rotor-fuselage configuration, the solver successfully captures interaction effects and predicts performance within experimental uncertainty. Notably, Simcenter Flightstream achieves these results with one to two orders of magnitude lower computational cost compared to high-fidelity approaches. The findings demonstrate its effectiveness as a rapid, cost-efficient tool for early-stage rotorcraft aerodynamic design and analysis.
This paper presents the contributions of the Royal Netherlands Aerospace Centre (NLR) to a Leonardo-led consortium participating in NATO Next-Generation Rotorcraft Capability (NGRC) Study #5, which is aimed at the development of Integrated Platform Concepts (IPC) to fulfill the NATO NGRC 2035+ Capability Development needs. NLR contributed to this industry effort by providing an independent evaluation of the high-speed tiltrotor concept proposed by the consortium led by Leonardo, considering aspects such as handling qualities, rotorcraft-ship compatibility, as well as a broader operational Battle Lab assessment. The handling qualities assessment and related control law development considered predictive metrics from ADS-33E and MIL-1797A, and yielded Level 1 handling for the baseline tiltrotor concept along with an evaluation of design sensitivities. The ship compatibility assessment, based on in-airwake trim and simulated lateral approach procedures, offered early insight into tentative limits for tiltrotor shipboard operations on Frigate-class navy vessels. The Battle Lab simulations provided an early holistic evaluation of operational effectiveness of the proposed IPC in the Air Assault mission scenario that is part of the NGRC Concept of Operations (CONOPS).
This paper introduces a robust supervised machine learning framework for estimating helicopter gross weight during the takeoff phase. The methodology leverages high-fidelity datasets from Airbus's global in-service fleet to ensure a reliable training foundation. At the core of the approach is a long short-term memory recurrent neural network, supported by a patented data-curation pipeline designed to maintain high data integrity. To align with rigorous aviation safety standards, the study outlines a learning assurance process compliant with EASA guidelines, specifically addressing safety assessment objectives for machine learning. A central innovation is the characterization and monitoring of the model's operational design domain through multidimensional functional principal component analysis. By projecting high-dimensional, non-linear sensor data into a manageable tabular subspace, this approach enables the definition of safety envelopes using explainable and efficient classical methods. Validated against diverse real-world flight profiles, the framework demonstrates high predictive accuracy, marking a significant milestone toward deploying the model on airborne targets for safety-critical functions such as condition-based maintenance.
The current work presents a methodology to estimate the mission and performance capabilities of a generic rotorcraft configuration, to satisfy the need of evaluating the integration of a full electric powertrain in the aircraft design. To include all the design steps, two different approaches are proposed. For the preliminary phase, the "Analytic Method" is considered, which exploits a purely resistive model. Conversely, a method based on look-up tables called "Table Method" is intended to be used in more advanced phase, when the battery pack is defined. Both approaches are tested by evaluating a reference mission and a hover chart. Finally, a verification of the presented methodology is carried out by comparing the mission results with a commercial software, specialized in the evaluation of the cell discharge when a given power spectrum is provided.
The FAA VR-HeliSTART (Virtual Reality-Helicopter Simulator Training for Airplane to Rotorcraft Transition) is a 15-week study conducted at Marshall University (WV) to determine the effectiveness of an H125 VR reduced-motion platform simulator in training fixed-wing pilots to fly helicopters. 11 students received three four-week blocks of instruction from certified flight instructors in the flight simulator, each followed by evaluations in both the simulator and an actual H125 helicopter, covering 36 maneuvers drawn from the commercial helicopter Airman Certification Standards. A mixed-methods approach combined objective flight parameter analysis with subjective assessments from evaluators, instructors, and students. Results indicate broadly positive transfer of training, with students demonstrating at least private pilot level performance on 70% or more of maneuvers on their first helicopter flight, and consistent improvement across subsequent evaluations. However, specific areas of negative or limited transfer were identified, most notably Vortex Ring State recovery, approaches, and hover work, driven by limitations of the head-mounted display and motion platform. This paper presents the methodology and overall results, with future papers addressing individual maneuver groups in greater detail.
Ground resonance, a self-excited instability typical of helicopters, that can lead to catastrophic failure. Its analysis becomes particularly complex in non-symmetric rotor configurations, such as those with an inoperative damper, which give rise to Linear Time-Periodic (LTP) systems. The stability investigation of the equations of motion can be handled through the Floquet method of characteristic exponents, or with the more recent linear time-invariant (LTI) harmonic decomposition (HD) method. The two methods are presented and their relationship is explored through Hill's infinite matrix and its modal solutions. Numerical results are given for rotors with different blade counts and two damper arrangements—blade-to-hub (BH) and interblade (IB)—under single and multiple damper failure conditions. A minimum-harmonics rule is derived that links the required number of harmonic terms directly to the multi-blade coordinate (MBC) structure of the rotor. Finally, the LTI state-space system produced by the HD is coupled with a describing-function framework to extend the stability analysis to rotors equipped with nonlinear dampers, enabling efficient limit-cycle prediction without recourse to time integration.
This paper presents the design, development, and successful demonstration of the first-ever ballistically tube-launched tailsitter unmanned aerial system. The vehicle expands upon the capabilities of existing tube-launched systems by simultaneously integrating the hovering capability of a rotary-wing aircraft with the efficiency and speed of a fixed-wing aircraft. To achieve this, the platform's design incorporates a novel coaxial thrust-vectoring propeller system for control in vertical flight and a unique foldable wing design for ultra-compact storage in the launch tube. The aeromechanics of the foldable wings during deployment are studied through a combination of wind tunnel experiments and flight dynamics model simulations, and the results are used to formulate a methodology for executing the ballistic launch. Simulations are also performed to characterize the robustness of the system against asynchronous deployment of the left and right wings. Experimental data, collected from flying a prototype in vertical, horizontal, and transitioning flight, demonstrate the aircraft’s flying performance. The study ultimately culminates with a demonstration of the prototype being rapidly launched from a tube at 25 m/s (56 mph) and autonomously unfolding, stabilizing, and transitioning into self-powered cruising flight.
This paper explores the potential of three different hybridization solutions for a medium-sized rotorcraft: an electric tail rotor, an "eco-mode", and a "boost-mode". The solutions were evaluated as a retrofit to a generalized medium lift rotorcraft and the impact on performance across five mission types, representative of the typical use cases for a military rotorcraft, was assessed. Two separate rotorcraft performance modelling tools were used to carry out the assessment, allowing for the results to be cross-examined. The models predicted performance gains for the eco-mode configuration when utilizing the single engine cruise capability for low-speed applications. Likewise, the models predicted improved performance for the boost-mode configuration when operating at hot and high (6,000 ft, 95°F) conditions due to the increased power provided by the battery system. However, all three solutions suffered from increased platform empty weight which negatively impacted performance at certain flight states.
This paper investigates the impact of aerodynamic interactions on the whirl flutter boundary of wing-twin-propeller configurations. A coupled wing-pylon-propeller model is developed in the Rotorcraft Comprehensive Analysis System (RCAS), where the wing is modeled using uniform inflow and the propeller wake is modeled using the viscous vortex particle method (VVPM). The study examines the effects of spanwise propeller placement and rotation direction by first analyzing a single-propeller configuration and subsequently extending the analysis to twin-propeller configurations. The analyses are performed for both rigid and flexible wings, with the latter designed such that whirl flutter governs the instability boundary. Results show that spanwise propeller placement strongly influences whirl flutter stability, with outboard locations exhibiting higher flutter speeds. Aerodynamic interactions between the wing and the propeller are found to be generally destabilizing, reducing the whirl flutter speed across all spanwise locations, with the largest reduction observed at outboard positions. In twin-propeller configurations, amplitude modulation is observed due to coupling between closely spaced modes enabled by wing flexibility and aerodynamic interactions. The inboard propeller is found to govern the instability boundary across all spanwise arrangements. Inter-propeller aerodynamic interactions are generally destabilizing, particularly for closely spaced configurations, while contra-rotating propeller configurations exhibit slightly higher flutter speeds due to the reduced impact of interaction effects. These results provide insight into the directional nature of aerodynamic interaction effects on whirl flutter in wing-twin-propeller configurations, highlighting their configuration-dependent behavior and generally modest influence on the whirl flutter boundary.
Helicopter air tours operate in one of the most challenging and least-controlled environments of commercial aviation, yet the safety outcomes of these operations remain inconsistent across regulatory frameworks. This study examined 55 helicopter air tour accidents in the United States from 2014 to 2024 using data from the NTSB Case Analysis and Reporting Online database. Defining event narratives, contributing factors narratives, and probable cause were coded to identify causal relationships between accidents and identify safety trends between 14 CFR Part 91 operations and Part 135 operations. CFR Part 91 operations exhibited accident rates approximately three times higher than Part CFR 135, averaging 3.94 per 100,000 flight hours compared to 1.23. Maintenance/mechanical was the most common initiating cause for accidents under CFR Part 91, accounting for 52% of cases compared to 37% under Part 135. Pilot/related cases were more prevalent under CFR Part 135, accounting for 53% of accidents. The two regulatory frameworks operated substantially different fleets, with CFR Part 91 relying on reciprocating-engine helicopters (76%) and Part 135 on turbine-powered aircraft (81%). Engine and powerplant/related events accounted for 27% of all defining events, and nearly half of all events involved a technical or mechanical initiator.
The bird strike performance of rotorcraft components must be demonstrated to the airworthiness authority in accordance with the certification requirements of CS 29.631. This necessitates continuous efforts to design and validate birdstrike-resistant structures through a combination of experiments and simulations. In this study, an integrated experimental and numerical investigation is conducted to evaluate the structural response and failure characteristics of the main rotor pitch link subjected to bird impact. In the experimental program, high-speed imaging and strain measurements were used to capture the transient deformation and impact force history. In parallel, a highly nonlinear finite element model was developed using the LS-DYNA solver. The numerical model was validated against experimental results. Results demonstrate that localized plastic deformation and stress concentrations occur near the impact region, consistent with damage patterns observed in real-world incidents. This research provides a validated methodology supporting CS 29.631 bird strike certification for rotorcraft flight-control components.
An advanced coupling framework was leveraged to assemble analytic sensitivities of lifting line theory aerodynamic loads with respect to externally-defined blade geometry parameters for optimization of main rotor performance of conventional helicopter configurations. Three vehicle weights and two flat-plate-equivalent drag configurations were examined across the flight envelope from hover to an advance ratio of 0.3. Two types of twist controls were investigated: quasi-static and fully active. Power savings were strongly correlated to the forward flight to hover power, ranging between 1.5 and 3.5% for quasi-static geometries and 2.0 and 4.5% for fully active controls when the installed power is twice of that required in hover. Blade twists optimized at higher power ratios were observed to favor high shaft tilt angles. Optimal twist deformation relative to hover-optimized designs is nonlinear across the blade span. Minimal penalties to aerodynamic vibrations were incurred through the use of either quasi-static or fully active twist controls as measured with a vibration intrusion index.
This paper presents the integration and use of state-space free-vortex wake models within closed-loop rotorcraft flight dynamics simulations. The free-vortex wake models are formulated in state-variable form, such that they constitute a system of nonlinear, time-varying ordinary differential equations in first-order form that augment the baseline rigid-body and rotor dynamics. The wake models considered include a tip-vortex-only formulation, as well as a formulation combining a vortex-lattice near wake with a tip-vortex representation of the far wake. Following trimming, linearization, and model-order reduction of the flight dynamics at discrete increments in flight speed, Dynamic Inversion (DI) flight control laws are synthesized to enable automatic transition from hover to cruise flight. Two-way-coupled losed-loop simulations are then performed for a generic utility helicopter representative of an H-60 in transition from hover to forward flight using three inflow models: (i) Pitt-Peters, (ii) tip-vortex-only wake, and (iii) vortex-lattice near wake with tip-vortex far wake. These simulations are compared both for validation purposes and to assess whether the different wake representations lead to significant differences in the predicted closed-loop response.
Rotorcraft pilots operating in degraded visual environments encounter significant challenges during hover flight, where the absence of critical visual cues increases the risk of spatial disorientation. At low altitudes and in obstacle-rich environments, even minor losses in situational awareness can have severe consequences. Understanding the visual cues that support stable hover in good visual environments, and how their absence impacts performance and cognitive workload, is essential for mitigating these risks. This study examined key human factors in hover flight, focusing on the role of peripheral vision and microtextures in supporting pilot performance. It evaluated whether naturally relied-upon visual cues in good visual environment conditions can be artificially replicated to restore visual dominance in simulated degraded visual environments. Analysis included flight performance metrics, control inputs, physiological workload indicators, subjective assessments, and pilot feedback. The findings contribute to improved understanding of visual cueing and pilot adaptation in degraded conditions.
Within the next years, it is expected that the capabilities that are demanded to the rotorcraft fleet would be enhanced with respect to the current ones. Very long range, speed above typical rotorcraft performance, hot and high HOGE capability and high payload capacity are foreseen, together with limitation on aircraft take-off weight (TOW): among these sizing cardinal requirements, speed characteristics and long-range operations drive the sizing towards innovative solution, to overcome the physical limitation of a conventional rotorcraft. The work starts with a performance-based comparison of different fast rotorcraft architectures, comparing it with respect to the conventional helicopter, used as benchmark. Once first investigation loop is completed with a preliminary sizing analysis, a detailed one is focused on tiltrotor architecture, showing the impact of hover and high-speed capability on lifting and powerplant systems, as well as the impact of sizing criteria on the overall performance. In such second step, a matrix scenario is proposed, where both requirements and sizing criteria are evaluated to show the peculiarity on tiltrotor solution. In conclusion, considerations on balanced criteria for tiltrotor sizing are reported, with focus on sizing trade-off.
This study evaluates the operational impact of multiple concurrent spatialized auditory cues during high-workload rotorcraft missions. A controlled, within-subject flight simulation experiment was conducted in which military-qualified rotorcraft pilots completed continuous multi-objective missions including formation flying, visual asset detection, collision avoidance, and emergency landing tasks. Each mission was flown under spatialized (3D) and non-spatialized (2D) audio rendering conditions while cue composition remained constant. Preliminary results indicate that under complex, formation-dominant workload conditions, pilots consistently prioritized visually anchored tasks and largely deprioritized auditory cue information regardless of spatial rendering. Collision avoidance cues did not produce observable evasive responses, and reported cue trust remained low without prior training. Although limited performance improvements were observed in isolated conditions, participants reported consciously suppressing audio cues. These findings suggest that effective integration of spatial audio requires structured training, procedural embedding, and deliberate workload redistribution rather than perceptual enhancement alone.
This paper presents results of flight tests conducted on a coaxial ultralight helicopter. An automated flight test evaluation method is presented and exemplified through its application to steady horizontal flight. The results shown include pilot controls, helicopter attitude angles, power, thrust and torque distribution between the rotors, rotor harmonic thrust components, and teeter angles, along with their rotor harmonic components across varying flight speeds. This study focuses on the dependencies of these parameters on center of gravity position and sideslip angle.
This work extends an integrated VABS (iVABS) framework for rotor blade structural optimization by incorporating enhanced cross-sectional parameterization and manufacturing-aware design considerations. The refined model includes features such as curved spar corners, continuous wrap-around skins, conformal non-structural mass, and ply-level discretization, enabling a more realistic representation of composite blade structures within a scalable optimization framework. Multi-objective blade-level optimization studies are conducted on a UH-60A-based blade using three representative cross-sections, considering both unconstrained and strength-constrained design cases. For the unconstrained problem, the optimal design achieves close agreement with target stiffness properties while also providing improved matching of mass center and shear center locations compared to prior design. When a minimum strength ratio is enforced, the feasible design space is significantly reduced, resulting in increased deviation from the target stiffness properties. However, strength-constrained designs exhibit improved agreement in mass per unit length, indicating a positive correlation between strength requirements and mass matching. The resulting structural trends are physically consistent, with thicker spars near the blade root and thinner, more elongated spars toward the tip. To connect computational design with physical realization, a manufacture–test campaign is conducted using a representative spar section. A composite spar based on an iVABS-derived layup is fabricated using aerospace-grade prepreg materials and standard tooling procedures. Experimental measurements show good agreement with iVABS predictions, including approximately 5.3\% error in mass per unit length and 1 2\% error in center-of-gravity location. These results provide preliminary validation of the framework and demonstrate its capability to generate manufacturable designs with consistent structural predictions.
Autorotation is an emergency flight maneuver in which a helicopter descends safely without engine power by using rotor energy. This paper investigates the use of reinforcement learning (RL) for autorotation trajectory generation and systematically evaluates it against optimal control problem (OCP) solutions. A one-degree-of-freedom powered descent problem is first solved as a surrogate to identify robust hyperparameter settings. The surrogate case results demonstrate that the RL policy closely matches the OCP solution in terms of landing time, confirming its effectiveness. The autorotation problem is then solved under both frameworks, and the resulting Height-Velocity diagrams are compared, with crash behavior in the deadman zone analyzed for each. The RL framework is shown to produce autorotation trajectories comparable to OCP, establishing it as a viable real-time alternative. Warm-starting the OCP with RL-derived solutions improves convergence compared to conventional initialization. Finally, the RL policy's versatility is discussed with an example of varying initial helicopter weight, capturing different fuel states at engine failure.
This paper presents the implementation of a fully automated Health and Usage Monitoring System (HUMS) data chain designed to accelerate installed engine performance diagnostics during the pre-delivery phase of new-generation helicopters. Ensuring that engine performance remains consistent with original engine manufacturer (OEM) baseline data is a critical step in the final assembly process, yet traditionally time-consuming. The developed system automates data offloading and integrates three distinct streams: OEM engine performance characteristics, in-flight Engine Power Checks (EPC), and high-frequency continuous recordings. The core innovation lies in a multi-source data fusion methodology combined with a physics-based model to differentiate between genuine installation discrepancies and sensor anomalies through temperature deviation analysis. Results from the production environment demonstrate that this automated approach significantly reduces troubleshooting lead times and ensures on-time aircraft delivery. By shifting advanced monitoring from in-service operations to manufacturing, this system establishes a new digital benchmark for quality control in helicopter production.
A Rotor Control Equivalent Turbulence Input (RCETI) model for characterizing vehicle response in urban environments turbulent airwakes is investigated. By extracting transfer functions from the nonlinear, high fidelity UH-60 rotorcraft model implemented within the FLIGHTLAB®framework, vehicle response to vertical turbulence is evaluated and inverse mapping between the rotor hub thrust coefficient and the control input spectrum is determined. Furthermore, the RCETI methodology develops filters that produce time history samples of collective input that produce hub loads that are stochastically similar to those induced by atmospheric air wakes.
Evaluating rotor component clearances is a multidisciplinary process aimed at ensuring that no contact occurs between rotor parts during a rotorcraft's operational life. It begins with calculating relative distances between components across all possible displacements and deformations combinations using a rotor kinematic model, and ends with clearance verification through flight data analysis and simulation. This task requires coupling detailed rotor aeroelasticity with flight mechanics to predict deformation under load, which is computationally expensive and unsuitable for real-time use. This work proposes a machine learning–based alternative: a neural network to estimate rotor clearances from flight mechanics inputs, with a specific application demonstrated in a simulated tiltrotor emergency maneuver with a pilot in the loop. The trained model successfully captures nonlinear relationships between maneuver parameters and rotor structural response, providing accurate predictions with reduced computational cost. The proposed framework can support both preliminary and detailed rotorcraft design and offers potential for real-time load prediction in applications where conventional aeroelastic tools are computationally expensive.
In this study, a multifidelity aeroelastic framework is presented for predicting trim conditions in rotary-wing aircraft, with the main focus placed on the DUST implementation and its application to helicopters and quadrotors. The methodology combines aerodynamic and structural solvers of different fidelity, specifically DUST and the multibody dynamics solver MBDyn, through the preCICE coupling interface to enable direct comparison with rigid and coupled aeroelastic solutions. The trim problem is formulated from the six degree of freedom rigid body equilibrium equations in a helical turn reference frame, naturally covering both steady and maneuvering flight. Although the same formulation can be extended to fixed-wing configurations, the present paper is focused on rotorcraft applications. The framework is first applied to the SA330 Puma helicopter, chosen for the availability of validated flight test data. The methodology is then extended to a multirotor derived from a NASA quadrotor, demonstrating that the same trim strategy can be transferred to distributed-lift rotorcraft. Results highlight the potential of the proposed approach to provide physically consistent and computationally affordable predictions of helicopter and multirotor equilibrium states.
This paper presents two distinct Lagrangian models developed for efficient rotorcraft inflow prediction: an Extended Vortex Ring Wake (EVRW) model and a Viscous Vortex Particle Method Actuator Disk (VVPM-AD). The EVRW model represents wake vorticity as circular rings with a harmonic distribution of bound circulation, thereby avoiding explicit coordinate-by-coordinate calculations. In contrast, the VVPM-AD discretizes shed vorticity into an independent Lagrangian particle cloud. This formulation naturally captures wake roll-up and viscous effects via a meshless Large Eddy Simulation solver, eliminating the need for empirical core-radius formulations. Validated against experimental data, these separate modeling tracks provide a scalable toolkit that balances computational speed with simulation fidelity.
The University of Maryland undergraduate team presents Draco in response to the 42nd Student design Competition RFP "Pioneering Hydrogen-Electric VTOL". Draco uses a simple, effective configuration: a single main rotor helicopter with compounded wings. Through calculations and trade studies, the team was able to design a rotorcraft capable of performing the prescribed mission with maximized loiter endurance, while meeting all design constraints and requirements.
The impact of ship airwake on helicopter operations to rear flight decks has been a topic of much research over the past three decades. While generic ships have been developed over the years to enable analysis tool and knowledge development, actual ships can vary significantly, resulting in different airwake features. The study of variations in ship geometry is important both to understand how differences may impact operations, but also to understand the level of geometrical fidelity that is required on ship models undergoing analysis. In Canada, the newly launched (2018) Harry DeWolf-class Arctic Offshore Patrol Ships (AOPS) have unique features that have been studied for their impact on airwake characteristics. This paper explores different geometrical characteristics from the perspective of their operational impacts and also considering their importance for inclusion in simulation. The paper shows that turbulence level is the parameter most affected by the minor variations that were examined, and helps guide the inclusion or exclusion of details in future ship models.
This paper tests and validates an electric rotor-propeller phase-locking system to emulate a mechanical gearbox for lift- and thrust-compound helicopter configurations. A comprehensive control scheme is designed and integrated into the UMD compound rig to rotate the main rotor and pusher propeller at desired gear ratios with known azimuthal positions. Wind tunnel testing is completed with the system to validate the mechanically decoupled, phase-locked rotor and propeller using time-accurate camera imaging. Flowfield measurements are collected to examine longitudinal velocity variation at multiple rotor phases and gear ratios. The objective of this study is to demonstrate the feasibility of an electric gearbox-less coupled rotor-propeller system for high-speed compound helicopter wind tunnel testing.
In September 2025 a test was conducted at the NASA Ames Research Center's Outdoor Aerodynamics Research Facility to characterize the outwash flow from a hovering rotor. The studied configurations included variations in rotor height above the ground plane as well as variations in rotor speed, thrust, and trim state. Outwash flow was measured using a rake of hot-film anemometers mounted to a semi-autonomous instrumentation cart. Flow measurements were conducted for a single rotor azimuth at distances between 0.6 and 4.0 diameters from the rotor center. In addition to hot-film anemometry, additional flow data was captured using a Background Oriented Schlieren Velocimetry technique that provides a detailed measurement over time of flow velocity in an image plane upstream of the hot-film sensors. The downwash and outwash produced by a lifting rotor in the presence of a ground plane can pose significant risks to life and property in the area of operations. Rotor wake interactions exhibited by modern, multi-rotor aircraft designs can amplify these flows and increase the risk. The rotorcraft community is therefore motivated to better understand rotor downwash and outwash to establish safe operating limits in the vertiport environment.
Rotorcraft airfoils often feature a tab which aides in the manufacturing of composite rotor blades, but also has aerodynamic merits. This study performs a comprehensive analysis of the impact of this tab on the 2D airfoil performance, structural adjustments and 3D rotor performance. The aerodynamics are evaluated using CFD, with CFD/CSD coupled results for the rotor performance. The structural data is adjusted using an FEM based in-house process. The HART II model rotor has been taken as a baseline and modified according to the tab variation studies. These included the comparison of a sharp trailing edge versus a tabbed airfoil, various tab thicknesses, lengths, and angles. The studies showed a variation of peak Figure of Merit between 66% to 68% and peak rotor L/D from 4.2 to 4.6 The careful design of the airfoil tab is therefore advised, but similarly the structural design of rotor blades.
This study presents the development and evaluation of two multi-fidelity surrogate models for predicting the first blade-passage frequency acoustic directivity of a propeller-wing configuration across a parametric sweep of wing leading-edge positions. The configuration follows the experimental setup at NASA Langley Research Center, comprising a three-bladed Mejzlik propeller operating upstream of a NACA 632-215 MOD B wing at 40 discrete leading-edge positions spanning the horizontal and vertical parameter space. Medium-fidelity predictions from the Rotorcraft Comprehensive Analysis System (RCAS), using the Viscous Vortex Particle Method, serve as the low-fidelity input, while high-fidelity predictions from NASA's OVERFLOW solver coupled with PSU-WOPWOP, both serve as the training datasets. QR decomposition is employed in both frameworks to identify the most informative subset of wing positions for high-fidelity simulation. The first surrogate model, a linear regression model, requires 15 high-fidelity snapshots to outperform the RCAS predictions, achieving l∞ norm, l2 norm, and RMSEs below the RCAS baselines of 32.98%, 8.56%, and 5.67 dB, respectively, over the entire parameter space. The second surrogate model, a Co-Kriging surrogate model implemented via the Surrogate Modeling Toolbox 2.0, requires only seven high-fidelity snapshots and achieves an RMSE of 4.45 dB and an R² value of 0.67. Both surrogate models accurately reproduce the high-fidelity directivity at wing positions where the CFD and RCAS trends are in reasonable agreement, but struggle at positions where the two solvers predict substantially different trends, highlighting the sensitivity of multi-fidelity methods to solver discrepancies and the potential need for denser parameter space sampling in regions of high acoustic variability.
The U.S. ARMY Primary Helicopter Center/School, USAPHC/S, was activated at Fort Wolters on September 26, 1956. Located in north-central Texas, the school would train over 40,000 helicopter pilots during 17 years of operation, through the end of the Vietnam War in 1973. Approximately 95 percent of all helicopter pilots who flew in Vietnam would pass through Wolters. Students included active-duty Army Officers, Warrant Officer Candidates, and Officers representing 33 allied countries. They trained for 16 weeks at Wolters and then another 16 weeks of advanced training at Fort Rucker, Alabama before earning army aviator wings. At the peak of activity in 1968, Wolters was sending 608 pilots per month to Fort Rucker. Students flew a total of 1,285 piston-powered OH-13, OH-23D, and TH-55A training helicopters departing out of three different heliports. It is a mystical place that still lives in the history of Army Aviation through the helicopter pilots who trained there. This is their story.
This paper extends a previously developed adaptive pilot model framework for inner-loop roll-attitude tracking [1] to outer-loop position tracking tasks. Pilot Model identification is performed for two command signal types - a discrete step-like signal and a continuous Sum-of-Sines (SOS) signal - yielding distinct parameter signatures that reflect the different anticipatory and tracking demands of each signal type. An adaptive pilot model for the outer-loop position tracking task is formulated using a model-reference neural network (MRNN) architecture with a linearly parameterized neural network updated by a Lyapunov-stable adaptive law. Simulation results for both discrete and continuous tasks demonstrate that the adaptive pilot model remains stable and maintains position tracking performance under both a doubling and a halving of the nominal control sensitivity. Preliminary results are also presented for a multi-axis maritime task, extending the framework to simultaneous lateral and vertical position tracking.
A generalized turbulence model for rotorcraft, analogous to the Dryden or von Kármán models commonly used for fixed-wing aircraft, does not yet exist. The closest available formulations are Control-Equivalent Turbulence Input (CETI) models, which reproduce the portion of the vehicle response attributable to atmospheric disturbances through equivalent control inputs applied at the inceptor or effector level. While the underlying concept is broadly applicable, these models are highly configuration dependent, making their broader generalizability uncertain. This paper adopts a recently developed methodology to extract CETI models directly from simulation and extends it to the identification of State-Equivalent Turbulence Input (STETI) models, which are Dryden-like in form and inject turbulence-equivalent excitations directly into the state dynamics. The approach is applied to six conventional main-tail rotor helicopters spanning trainer, light, intermediate, medium, heavy, and ultra-heavy classes, from the Robinson R-22 to the Mil Mi-26, and to four tiltrotors spanning the current range of tiltrotor weight classes, from the Bell XV-15 to the Bell Boeing V-22. The resulting CETI and STETI models are used to examine cross-vehicle trends, assess the extent to which they generalize across configurations, and evaluate whether they can be parameterized in terms of fundamental rotorcraft properties, including gross weight and rotor radius, as well as derived parameters such as disk loading.
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