Browse Topic: Helicopters
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 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.
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.
This paper presents enhancements to the supervisory controller developed for the National Research Council Canada's Bell 412 autonomous helicopter. Building on a Discrete Event System Specification (DEVS)-based framework, the updated Supervisor introduces two new operational modes-Knobs Mode and Sticks Mode-and a structured approach for managing transitions between them and the existing modes. Drawing inspiration from NASA's Flight Guidance System philosophy, the proposed design emphasizes consistency, scalability, and flexibility in handling multiple autonomy modes. Implementation results demonstrate the effectiveness of the updated architecture in supporting future expansion of autonomous mission operations in complex and dynamic environments.
The Enhanced Tiltrotor blade, also known as the RGF3 blade, represents a major milestone in Leonardo Helicopters Division's pursuit of advanced rotorcraft technology. Developed at the Yeovil facility in the United Kingdom as part of a dedicated program and in collaboration with the European Clean Sky 2 initiative, it is a key enabler for the Next Generation Civil Tiltrotor Technology Demonstrator. Leveraging the AW609 airframe, the NGCTR integrates a new lateral rotor control system and a V-tail with ruddervators to expand maneuverability and control authority. The RGF3 blade combines aerodynamic efficiency with manufacturability, cost effectiveness, and certification readiness. Innovations include advanced airfoil families, highly swept anhedral tips, dual-redundant anti-ice systems, and full compatibility with legacy components. A comprehensive test campaign—covering structural loads, lightning and bird strikes, icing, and wind tunnel validation—confirmed its robustness and performance. The RGF3 blade embodies Leonardo's vision for high-speed, sustainable, and reliable next-generation rotorcraft.
This paper evaluates the feasibility of Restricted Icing operations for light to medium helicopters, which typically lack Full Ice Protection Systems (FIPS). Current regulations normally prohibit these aircraft from flying in known icing conditions, leading to frequent mission cancellations for HEMS and SAR operators. To address this, Airbus conducted flight test campaigns in Norway (2023, 2025) to characterize a safe icing envelope for "cold blade" operations. Results demonstrate that the H145 was able to sustain continuous flight in icing conditions between 0°C and -3°C and perform time-limited operations (5–10 minutes) down to -6°C without compromising safety, handling, or structural integrity. Safe Restricted Icing operations require an operational framework that ensures proper planning, safe routing, briefing, in-flight decision making, and specialized crew training. The study concludes that a Restricted Icing Clearance could significantly enhance winter flight safety. By providing an IFR alternative to VFR flights in marginal weather within a clear operational framework, the introduction of a Restricted Icing Clearance could ensure the availability of critical life-saving missions in typical winter weather.
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 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.
The Vertical Flight Society (VFS) was founded as the American Helicopter Society, Incorporated (AHS) in 1943. During the first decade, several means were used to communicate Society news and industry news to its members. Until 1952, the management of the Society was primarily through elected volunteers, and executives from the leading helicopter companies typically served as the AHS president. Letters to the Society's members were typed and mailed by the companies to the few hundred early members. In 1950, AHS also partnered with the broader aviation professional society, the Institute of Aeronautical Sciences (IAS), to typeset and publish a column on Society news in its membership magazine and which was then mailed to AHS members. It wasn't until 1953 that the first regular publication, the monthly "NEWS LETTER" was sent to members. This newsletter continued to increase in its length and depth of industry news -- it was renamed Vertiflite in 1963. Although some of this was covered in previous histories of VFS, this paper publishes the details of this period for the first time.
This paper presents the flight-test evaluation of a velocity-aided navigation solution that integrates inertial measurements with line-of-sight (LOS) Doppler velocity observations from the Psionic Navigation Doppler Lidar (PNDL) prototype to support navigation in GPS-denied environments. LOS velocity measurements collected during a helicopter flight-test campaign were first compared with velocities derived from an Applanix reference navigation system to assess measurement accuracy. The navigation solution was then developed and evaluated under simulated GPS-denied conditions by removing GPS aiding and continuing operation using LOS velocity measurements alone for extended periods. Results show that Doppler lidar velocity aiding effectively constrains inertial navigation error growth and maintains a stable navigation solution during prolonged GPS outages. These flight-test results demonstrate the utility of FMCW Doppler lidar velocity measurements as an enabling technology for Assured Positioning and Navigation (APN) and underscore its applicability to Contested Logistics operations, where resilient, GPS-independent navigation is essential for mission continuity.
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.
The bird strike performance of the flight critical components of a rotorcraft is to be proved. The study investigates the bird strike performance of the cowling structure through experiments and simulations by considering a Building Block Approach. Based on this approach, bird impact tests on a rigid plate and composite panels are performed to validate Smoothed Particle Hydrodynamics method (SPH) bird model and composite material model in LS-DYNA. The composite material properties are obtained from the coupon level test results. After the composite material model is calibrated and validated, the bird strike performance of the cowling structure at critical locations is assessed. A good correlation between the experimental and numerical results was obtained at coupon, sub-component and component levels. The developed composite material modeling technique and validated bird models may be used in showing bird resistances of other airframe components of similar structure of the rotorcraft.
In this work the authors present a method for estimating the modal properties (natural frequencies, damping and mode shapes) of a helicopter fuselage using available flight data. The identification process is based on Operational Modal Analysis (OMA). The modal parameters obtained from OMA are subsequently used in conjunction with Ground Vibration Testing (GVT) results and the Finite Element Model (FEM) of the helicopter structure to extract scaled mode shapes. Since in-flight vibration testing typically employs a limited number of measuring points, significantly less than the number of points represented in the FEM, the authors propose a method of expanding the OMA identified mode shapes onto the FE model geometry, enabling engineers to regulate the influence of local displacement and achieve improved representation of the structural dynamics.
Full state feedback offers theoretically guaranteed multi-axis stability, making it superior to conventional PID controllers. There is however one drawback, a full state controller has a mathematical difficulty if the B matrix is not square and thus not invertible. This is the case for helicopters with 6 degrees of freedom and 4 inceptors. Variations of linear quadratic regulators are a work around, however complexity dramatically increases. Best would be a direct solution to the original problem. This is the breakthrough result of this paper. This paper documents an approach which removes the analysis roadblock by partitioning the 6 x 6 system "A" matrix into two groups of 4 x 4 matrices. The 4x4 matrices are individually stabilized with full state gain matrices. One matrix is designated “Driver Matrix” which provides actuator commands. The other matrix is designated "Reference Matrix" which provides references. The two matrices are coupled together by requiring that the driver matrix follow references generated by the reference matrix. With each matrix individually stabilized, the coupled combination is also stabilized. Computation of flight dynamics states (u, v, w, p, q, r) is shared between the matrices. Initial results are very encouraging, showing an originally sluggish, heavy lift helicopter having now concise decoupled responses to pitch and roll commands. Stability derivatives are recomputed during flight allowing coverage over the whole flight envelope. A handling qualities task has been defined to relocate a 40 ft standard seaborne container directed by a pilot in a ground control station. Cooper Harper ratings of this task have demonstrated favorable Level 1 handling qualities if use is made of an automated lateral repositioning command.
The present study aims to investigate the dynamic behavior of composite drive shafts operating in the supercritical rotational speed regime, with a particular focus on the mode crossing and the potential emergence of vibratory instabilities. Composite shafts offer significant advantages in terms of mass reduction and mechanical properties, making them attractive for high-performance transmission systems such as helicopter drive lines. However, their operation beyond the first critical speed raises specific challenges related to stability, damping, and sensitivity to mechanical and operational parameters. To address these issues, an experimental and analytical framework was developed to explore a wide design space involving parameters that are known or suspected to influence supercritical behavior. These parameters include unbalance levels, support characteristics, flexible coupling properties, tightening conditions of the damper, and rotational speed. Particular attention was given to the analysis of the mode crossing phenomenon in composite supercritical shafts, as well as to the identification of the most influential contributors to the vibratory response within the defined experimental perimeter. Harmonic- and subharmonic-based analyses were conducted to assess the relevance of each parameter across different frequency regimes. Overall, the results indicate that, despite the wide parametric exploration, no dynamic instability was observed in the supercritical regime, thereby demonstrating the robust vibratory behavior of composite shafts and supporting their suitability for advanced helicopter transmission applications.
This study investigates the dynamics and associated vibratory loads of an underactuated swashplate-less rotor and its impact on the flight dynamics of a small-scale helicopter powered by this rotor via a combined experimental and computational approach. Unlike prescribing cyclic pitch using a swashplate, here the pitch is a response to the 1/rev cyclic rotor speed input. This is enabled on the current two-bladed rotor using a skewed lag hinge that utilizes the cyclic speed variation to produce lagging motion and subsequently pitching the blades in a cyclic fashion (ƍ4 coupling) for generating the pitch and roll control moments. One of the key dynamic characteristics that distinguishes this rotor from a conventional swashplate-controlled rotor is that the two blades have dissimilar pitch and flap responses leading to high fixed-frame vibratory loads. Results show that a large 1/rev vertical shear force is transferred to the fuselage resulting in half-peak-to-peak loads of +/−0.67g. The flap responses of the two blades being out of phase caused a net inertial force, which was the dominant contributor to the vibratory vertical shear force. Upon removal of the flap hinge, the vertical shear force was reduced by almost 85% while increasing the control moment authority by 50%. The inertial moment about the rotor axis generated by cyclic lagging nearly balances the moment due to the angular acceleration (Ω ) of the rotor, which significantly reduced the dynamic torque requirement from the motor.
Flight simulations are critical for aerial firefighting training, but realistic modelling of aircraft-atmosphere interactions within fire scenarios is particularly challenging. To this end, a two-way-coupled flight simulation system, the Daedalus I framework, has been developed at the University of Glasgow for helicopter firefighting research applications. This paper presents the initial results from flight experiments conducted with different coupling schemes between the rotorcraft model and the GPU-accelerated Lattice Boltzmann atmosphere model within the system. The two-way coupling scheme was first validated using an isolated, transient rotor case. To quantify differences in pilot control and strategy between the two-way, fully-coupled rotor-atmosphere method and two (2) one-way, superposition-based coupling methods, a series of flight experiments were conducted using the bimodal modification of the McRuer pilot model representing human pilot controls, in conjunction with objective performance metrics. The results highlighted noticeable changes in helicopter behaviours and pilot responses across the three tested coupling methods, with the two-way coupling method showing the most resistance to the generated fire disturbance.
An internal layout design framework for a medium-class rotorcraft fuselage is attempted to build based on the idea of the energy-based load-transfer index. Load-transfer index will quantify the way in which the flight loads are distributed among the fuselage internal structural members. The static load-transfer analysis will identify an inefficient transfer region in the baseline fuselage configuration, and the resulting layout refinement will lead to a more unified load-transfer pattern and allow an additional weight reduction in the subsequent thickness-optimization stage. For a UH-60A aircraft, the existing literature provides well-established information for an airframe layout, finite-element modeling guideline, and ground vibration test correlation.
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 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 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.
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.
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.
Accurate monitoring of helicopter operational usage relies heavily on robust regime recognition algorithms. How-ever, evaluating these approaches is challenging when they operate as opaque, "black boxes", as in the case of machine learning-based models. This paper introduces a comprehensive evaluation framework designed to assess regime recog-nition models from a number of perspectives and investigate anomalies in the predicted regimes. Centered around a high-fidelity data set derived from scripted flight tests covering a complete usage spectrum, the developed method-ology provides a comparative baseline. The analytical suite includes 3D spatial visualization tools for flight path mapping, sequential anomaly detection, and confusion matrix metrics. While applying the labeled data set to other platforms presents inherent limitations in terms of mapping features and regimes appropriately, the integrated toolset successfully exposes weaknesses in the model and highlights gaps in training data. Ultimately, this evaluation frame-work enhances the interpretability of model outputs and builds confidence in the use of regime recognition algorithms.
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.
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.
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.
Rooftop based hospital heliports represent critical infrastructure, providing rapid access to emergency medical care while reducing the impact of helicopter downwash and outwash on pedestrians and nearby urban spaces. Effective heliport design requires a comprehensive understanding of the reciprocal interactions between helicopter operations and the surrounding built environment. Addressing these interactions during the early design phases enables designers to anticipate, evaluate, and mitigate potential adverse effects.
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.
Helicopter maintenance troubleshooting faces significant challenges due to fragmented documentation, outdated procedural manuals, and reliance on human expertise, all of which threaten flight safety and operational efficiency. While Knowledge Graphs (KGs) effectively model hierarchical system relationships and causal dependencies, they struggle with dynamic unstructured data. Conversely, Retrieval-Augmented Generation (RAG) systems access technical manuals but risk hallucinating unsafe procedures without structural grounding. This paper introduces KG-RAG, a novel hybrid troubleshooting framework specifically engineered for helicopter systems, addressing a critical gap as existing work focuses predominantly on fixed-wing aircraft. The framework merges knowledge graphs modeling fault causality and maintenance history with multi-dimensional retrieval combining graph-based reasoning, vector embeddings, and keyword-based search. This integration enables contextual interpretation of ambiguous fault descriptions, generation of precise diagnostics aligned with operational constraints, and dynamic adaptation to new fault patterns without retraining. By transforming fragmented maintenance knowledge into a verifiable, context-aware troubleshooting guide, the framework directly addresses aviation's persistent obstacles: data incompleteness, knowledge erosion, and slow safety-critical decisions. This work positions KG-RAG not merely as a tool but as a foundational shift toward cognitively augmented maintenance, elevating human expertise through AI that reasons like an engineer and contextualizes like a veteran technician for enhanced safety-critical decision-making in complex helicopter operations.
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 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.
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.
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.
It is recommended that all helicopter engine development programs include an evaluation of engine starting requirements. The evaluation should include starting requirement effects on helicopter weight, cost, and mission effectiveness. The evaluation should be appropriate to the engine stage of development.
In the stringent market of BEV, the development of integrated Drive Modules (iDM) fitting environmental and customer needs is mandatory. It is important to extract the best from the less. To achieve those goals, a deep insight into complex multiphysics phenomena occurring in an iDM has been achieved by accurate and validated models. This engineering methodology is applied through the development of BorgWarner products, comprising non-exhaustively iDM 180-HF, Externally Excited Synchronous Machine and Multi-Level Inverter. The paper will review the methodology development for deeper understanding involving in-house technical excellence and complemented by strategic partnerships with academic institutions and start-ups. It will present the approach of integrating advanced multiphysics models with high-quality experimental validations, specifically on loss evaluation on electrical machines and inverters. Complex models involving multiphysics such as thermal/fluid coupling or electric-magnetic-mechanical behaviors are usually difficult to optimize separately since their objectives are often contradictory. Thus, BorgWarner PDS Engineering uses tools involving close coupling to optimize iDM products. The lecture will focus on innovation and optimization which are supported by several key pillars in the scope of a Next Generation iDM development. These are based on the following strategic levers such as process and design development, material development and control strategy among others. This ensures tailoring all components at the best of their capabilities to reduce their weight and maximize their use. Finally, the results achieved by the high-fidelity model-based optimization on the selected example will be presented (e.g., impact of the cooling improvement on overall iDM performances), demonstrating the benefit of capturing the system from granular view to a helicopter view in the design phase of next generation eDrives.
Previous researchers developed equations to model the induced flow on a 2D airfoil in the finite-state as opposed to the closed-form. Those models, however, were limited in that they could not handle an oscillating free stream that became negative. Recently, a new model was developed to include a single factor to carry the effects of the free stream changing signs. In developing this model, a Floquet instability was discovered at the instant when the flow changes direction. The effect of the instability grows with increasing number of oscillations of the sign of the free stream. The effects can be limited depending on the parameters of the flow. In this paper, the previous 2D model is amended to include a term that considers the effects of the induced flow from all previous vorticity segments that have been generated from each oscillation of the flow. This paper details the beginnings of the testing on the stability limits of the theory, based on changing the parameters of the free stream, airfoil, and timing. It is the intention of this research to further investigate the limits of this model in reversing flow in hopes of using the lessons learned to extend 3D finite-state models that are currently incapable of handling cases where the sign of the free-stream velocity changes as a result of the rotor reentering its own wake such as when a helicopter or quadcopter quickly descends after ascending to avoid an obstacle.
A comprehensive numerical study was conducted to reduce helicopter rotor hub vibratory loads and fuselage vibrations using the Higher Harmonic Control (HHC) technique. A CAMRAD II model of a medium utility helicopter was developed for aeromechanical simulation, and a linear system model representing both hub vibratory load and fuselage vibration characteristics was identified offline. Optimal control inputs were then computed to minimize vibration responses under different weightings on hub vibratory load and fuselage vibration in the objective function. The predicted performance was verified through CAMRAD II simulations. Additionally, a closed-loop HHC system incorporating actuator amplitude limitations was investigated. A control algorithm regulated actuator amplitudes while maintaining phase consistency, dynamically adjusting control inputs after each iteration. The results demonstrate that the amplitude-limited closed-loop control limits excessive pitch link loads while maintaining effective vibration suppression, thereby maintaining structural safety and ensuring practical feasibility for real-world helicopter applications.
This paper presents the investigation of experimental data belonging to main rotor loads during Never-Exceed-Speed demonstration of T625 Gökbey helicopter. Load data from the critical flight conditions in the VVNNNN envelope including cold-weather testing are collected. Maximum advancing tip Mach number demonstration, power-on and power-off flight conditions are investigated in terms of pitch link loads and blade loads. Blade loads including flapwise and chordwise bending moments, torsional moments and pitch link loads are examined to assess any divergence due to compressibility effects and the onset of stall. Load trends that are correlated with the tip Mach number are isolated from the effect of increasing dynamic pressure. Compressibility effects are observed to be the most dominant factor on the blade torsional moment and pitch link loads in advancing blade. The retreating blade stall phenomenon is apparent cases with a high advance ratio and mainly leads to dynamic stall cycles on the retreating blade, resulting in torsional moments and pitch link loads. Experimental results are compared with blade-resolved Unsteady Reynolds-Averaged Navier-Stokes simulations.
With the flights of the Ingenuity Mars helicopter completed and the development work on the Titan Dragonfly rotorcraft/lander proceeding, it is now time to consider aerial flight on Venus. Challenges of developing aerial explorers for Venus are discussed along with past and present conceptual design vehicles. A summary of the scientific impact and necessary instrumentation to understand Venus’s climate and geographical makeup is provided. This paper presents possible aerial-vehicle-assisted approaches to exploring Venus, with an emphasis on rotary-wing vehicles/systems. Aerial conceptual design vehicles are presented in three categories that include flying: above the clouds (altitudes greater than 60 km), below the clouds (altitudes less than 50 km), and near the surface.
The Rotor Optimization for the Advancement of Mars eXploration (ROAMX) project has demonstrated that rotor designs optimized for the Mars aerodynamic regime can provide substantial improvements in aerodynamic efficiency relative to heritage designs. This paper evaluates the vehicle-level performance implications of these improvements using the NASA Design and Analysis of Rotorcraft (NDARC) tool. Performance predictions for Ingenuity-class and Mars Science Helicopter (MSH)-class rotorcraft are generated using ROAMX rotor aerodynamic inputs and are compared against a configurations using the Ingenuity rotor. Parametric studies are conducted to investigate the trade between increasing payload mass and resulting changes in vehicle range and hover time, including the effects of rotor solidity and rotor type. The results show that ROAMX rotor designs enable significant increases in payload capability and operational range across both vehicle classes. These findings demonstrate how ROAMX rotor performance gains translate directly into enhanced mission capability at the vehicle level and provide a quantitative foundation for future Mars rotorcraft designs.
NASA's successful demonstration of powered flight on Mars through the Ingenuity Helicopter, as part of the Mars 2020 Perseverance rover mission, has led to the development of next generation Martian rotorcraft. The future of Martian rotorcraft has evolved to include high payload-carrying vehicles to possibly contribute to planetary science missions, which will require improved flight dynamics and rotor aerodynamic performance to fly at nominally high forward flight speeds and at higher flight altitudes. To ensure the feasibility and viability of successful mission performance, it is also critical to mature the structural design for advanced Martian rotorcraft to bridge the gap between the best practices of the spacecraft and aircraft communities. This paper focuses on the structural analysis of a Mars Science Helicopter (MSH) blade using finite element methods. Multiple loading conditions including launch and operational flight were applied to investigate the blade’s structural integrity. The blade’s modal natural frequencies were also analyzed to investigate the blade's dynamic behavior.
Recent flight tests and simulations have suggested that the outwash from eVTOL air-taxis could be larger than conventional helicopters of equal weight and thus pose greater safety issues for their operation than previously anticipated. This has prompted interest in the analytical and experimental study of the aerodynamics related to multi-rotor aircraft outwash. This paper will describe work investigating some of the related issues, specifically (1) how wake models and wake model parameters impact outwash predictions in comprehensive rotorcraft analyses and (2) considerations when scaling results from model scale to full scale. This work will also compare outwash predictions for conventional and multi-rotor VTOL aircraft obtained with a Lagrangian free-vortex wake model and with an Eulerian velocity-vorticity grid based wake model.
Bay Area Helicopter Airlines
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