Browse Topic: Rotary-wing aircraft
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
This SAE Aerospace Recommended Practice (ARP) discusses design philosophy, system and equipment requirements, environmental conditions, and design considerations for rotorcraft environmental control systems (ECS). The rotorcraft ECS comprises that arrangement of equipment, controls, and indicators which supply and distribute dehumidified conditioned air for ventilation, cooling and heating of the occupied compartments, and cooling of the avionics. The principal features of the system are: a A controlled fresh air supply b A means for cooling (air or vapor cycle units and heat exchangers) c A means for removing excess moisture from the air supply d A means for heating e A temperature control system f A conditioned air distribution system The ARP is applicable to both civil and military rotorcraft where an ECS is specified; however, certain requirements peculiar to military applications—such as nuclear, biological, and chemical (NBC) protection—are not covered. The integration of NBC
In a groundbreaking achievement, the 101st Combat Aviation Brigade, 101st Airborne Division (Air Assault) earlier this year became the first unit to successfully use the Mobile User Objective System (MUOS) function of the Army/Navy Portable Radio Communications (AN/PRC) 158 and 162 radios for conventional rotary wing operations. The trailblazing accomplishment occurred as the brigade continued its mission of providing support to ground forces, April 9, 2025.
This report lists documents that aid and govern the design of aircraft and missile fuel systems. The report lists the military and industry specifications and standards and the most notable design handbooks that are commonly used in fuel system design. Note that only the principle fuel specifications for the U.S. and Europe (Military Specifications, ASTM, and Def Stan) have been included within this report. The specifications and standards section has been divided into two parts: a master list arranged numerically of all industry and military specifications and standards, and a component list that provides a functional breakdown and a cross-reference of these documents. It is intended that this report be a supplement to specifications ARP8615, MIL-F-17874, and JSSG 2009. Revisions and amendments which are correct for the specifications and standards are not listed. The fuel system design handbooks are listed for fuels and for system and component design.
In April of 2024, Sikorsky flight tested an open loop Higher Harmonic Control system on an S-97® helicopter. The S-97® helicopter is a prototype aircraft, based on Sikorsky's X2 Technology™, that first flew in May 2015. It has contra-rotating, stiff in-plane main rotors with fly-by-wire controls, and a pusher propeller. This paper describes the HHC design, how it was implemented on the aircraft, how it was tested, and what the test results were.
A typical helicopter drive system consists of a multi-stage gearbox with highly loaded dynamic components such as gears, shafts, and bearings, crucial for safe flight and landing. Planetary reduction stages are commonly used in the final reduction stage of rotorcraft main gearboxes due to their ability to handle high torques at high gear ratios within a compact envelope. The planet gear, a critical component in this arrangement, is subjected to significant loads on both flanks of its teeth and must meet stringent weight and assembly requirements, leading to a thin rim design with integrated bearing races. This design makes the planet gear susceptible to relevant reduction of its fatigue life. This paper explores analysis methods to evaluate the damage resistance of the planetary stage assembly, focusing on the planet gear. The study aims to assess the "growth" or "no growth" condition of the planet gear against defined flaw defects. An iterative calculation loop determines the critical
We present our ongoing efforts towards the development of crash-tolerant rotorcraft airframe structures through topology optimization, with the goal of enhancing energy absorption and occupant survival during vertical impact events. A high strain rate explicit dynamics solver has been developed, fully accelerated on GPUs, to enable rapid and accurate simulation of impact events critical to crashworthiness evaluation. In parallel, we have built a scalable three-dimensional topology optimization framework that enforces stiffness, weight, and frequency constraints simultaneously, driving structurally efficient and vibration-resistant designs. Benchmarking results demonstrate significant GPU-enabled speedups, facilitating high-fidelity crash simulations and large-scale optimization at practical turnaround times. This work establishes a computational foundation for future integration of crash-centric objectives and constraints into the optimization framework.
This study investigates the application of neural network architectures to predict control inputs required to replicate rotorcraft responses under vertical gust disturbances. Two modeling approaches are developed: the Control Equivalent Gust Input (CEGI) model, using body-axis inputs and the Rotor Control Equivalent Gust Input (RCEGI) model using rotor-specific inputs. Initial models employed single-input single-output (SISO) LSTM networks, which demonstrated limitations in capturing transient behavior and exhibited delay in predicted control inputs. By incorporating multiple vehicle response features and increasing the number of hidden neurons, multiple-input single-output (MISO) architectures significantly improved accuracy and reduced Root Mean Square Error (RMSE). Further enhancement was achieved by implementing bidirectional LSTM (BiLSTM) layers, which reduced both delay and transient error. Comparisons with inverted linear time-invariant (LTI) approximations showed that neural
The vertical flight industry is on its way to a transformative era, with autonomous technologies set to alter aerial vehicle operations. While it seems certain that fully autonomous helicopters will eventually be deployed for a variety of missions, some high-stakes situations—like medical evacuations (MEDEVAC)—will for the foreseeable future demand human participation in the form of Emergency Medical Care-giving Crew. This study describes the testbed built to run and investigate hypothetical future situations in which a helicopter is autonomously piloted while a human medic with no aviation training, subjected to aviation and medical emergencies, manages patient care onboard. A total of 22 participants, with emergency medical technician certification, nursing or a medical board certification, were invited to run and evaluate the use of AI pilot (AP) in different scenarios of medical evacuation under the following emergencies: medical, empty fuel tank, pressure sensor miscalibration
This paper explores the dynamics of rotating Tuned Vibration Absorbers (TVAs), focusing on the phenomena arising from gyroscopic effects. Some products from Leonardo Helicopters (LH) can have a TVA fitted in the rotor mast, counteracting the in-plane vibratory loads of the rotor directly at their source, implying that the absorber rotates with the rotor itself. Although gyroscopic effects are negligible for most of the LH TVAs, specific design choices may have notable impacts on tuning and performance. An analytical model is implemented, demonstrating that the gyroscopic terms influence the dynamics causing a frequency displacement of the anti-resonance evaluated without considering this effect. Additionally, a regression analysis investigates the interplay between this phenomenon and the physics of the system, revealing how to optimize the design to mitigate gyroscopic effects. Finally, the performance of the TVA is analyzed as a coupled problem, showing that the anti-resonance
eVTOL aircraft are a stable part of nowadays rotorcraft industry, gathering attention and investments throughout all geographies. The challenge of designing such a vehicle is the necessity to combine transformative flight and distributed lifting systems. This paper presents a methodology developed within Leonardo Helicopters Division (LHD) to perform the preliminary design of eVTOLs, following an approach that starts from hovering flight, investigating the design permutations able to satisfy certain criteria of performance, maneuverability, and safety.
A robust velocity stability augmentation system was developed for the CoAX 600/2D coaxial-rotor helicopter to enable safe testing of a fly-by-wire system on an optionally piloted variant of the aircraft, developed by Piasecki Aircraft Corporation. The control law design and subsequent stability analysis were based on a validated nonlinear model of the CoAX 600 rotorcraft. A subset of helicopter handling qualities were evaluated through both analytical methods and piloted simulations, conducted with and without the stability augmentation system. Additionally, flight test data contributed to the analysis, albeit to a limited extent.
The use of sub-scale vehicles as a means of predicting full-scale vehicle behavior has historically been applied to flight dynamics testing and evaluation for aircraft operating in Earth atmospheric conditions. However, the use of sub-scale testing on Earth has not been as thoroughly explored for Martian rotorcraft. In this paper, sub-scale vehicles of varying sizes were developed in simulation using Froude scaling laws to evaluate their ability to estimate fullscale linear dynamics for the Mars hexacopter, Chopper. Blade loading, Lock number, and flap frequencies were held fixed when scaling and corresponding relationships for vehicle length, mass, inertia, and rotor speed derived. Full-scale frequency response, gain margin, and instability characteristics are explored for hover and forward flight cases in a variety of Mars-to-Mars and Earth-to-Mars conditions. Mach effects are also analyzed as a consequence of Froude-scaling by comparing sub-scale vehicles that are Mach-matched to
Additive manufacturing presents a promising approach to aerospace component design, thanks to its ability to create intricate geometries that contribute to weight reduction. While numerous efforts have been made to 3D print aerospace parts, their application in helicopter gearboxes remains limited due to the critical nature of these components. This paper explores the design process behind manufacturing a fatigue-critical housing for a helicopter tail gearbox. Specifically, it highlights the design constraints that prompted the adoption of an innovative manufacturing technique in the aerospace sector. Additionally, it examines the methodology used to meet these constraints and details the optimized final geometries achieved through the design process. Finally, results from manufacturing trials and fatigue testing are reported.
In the last years, new rotorcraft configurations have increased the attention among industries, through which the tiltrotor one due to its capability of combining both rotorcraft and aircraft advantages. However, there are situations where the vertical take-off mode could be enhanced in hard environmental and flight conditions. Therefore, to address this challenge, this work aims to develop a methodology to characterize a roll take-off model for a general tiltrotor configuration in such situations. By combining the integration of the equation of motion and geometrical assumptions, the runway distance is determined for an acceptable range of nacelle tilting angles. The process is developed by meeting the requirements defined by the regulations, combining the aircraft certification standards (CS23 and CS25) with the available tiltrotor certification basis from the FAA project #TC3419RC-R. Following the Nominal application, a sensitivity analysis is carried out, which studies the main
Rotorcraft continue to experience higher fatal accident rates compared to fixed-wing aircraft, primarily due to low altitude flight operations and reduced situational awareness in complex environments. A critical factor is the limited availability of accurate, up-to-date information on helipads and surrounding obstacles - such as trees, poles, and buildings - that pose significant risks during takeoff and landing. Existing resources, including the Federal Aviation Administration's heliport registry, are often outdated and incomplete, particularly for private or state-operated sites, and fail to report nearby obstacles. This lack of up-to-date data is largely due to privacy restrictions at certain locations and the high cost associated with comprehensive obstacle surveys. To address this challenge, we develop a deep learning (DL) framework that automatically detects helipads and nearby obstacles from high-resolution satellite imagery. Our approach combines Mask R-CNN for precise pixel
The paper describes a method for optimal design of a helicopter tail shaft that considers rotordynamic effects from long shaft assembly. The tail shaft transmits power from the main gearbox (MGB) to the tail rotor of the helicopter and operates at high speeds that may exceed 6000 rpm. While higher speeds allow for weight reduction, they also pose risks associated with supercritical operation, necessitating careful design optimization. The objective of the optimization is to maximize the first three transverse natural frequencies with the constraint of the safety parameter (avoidance of the resonance/critical zone) while minimizing the weight of the system. A Non-Dominated Sorting Genetic Algorithm (NSGA-II) is used to obtain the solution to this multiobjective optimization problem, which involves shaft design variables such as length, outer diameter, and wall thickness. In addition, the optimization framework also incorporates system related design variables, including the stiffness of
The Main Gearbox of a helicopter is a crucial component that delivers the desired performance and ensures the highest possible level of safety of the aircraft; it includes several gears and bearings, which require to be continuously lubricated by a pressurized oil flow. Undesired circumstances may cause the oil to leak from the main circuit, hence reducing its pressure and consequently the oil flow rate targeted towards the rotating components; this modifies their friction coefficient, and subsequently leads to an overheating of the parts with the risk of degenerating in a catastrophic failure. During the design of a helicopter drive system, engineers need to take proper precautions and make sure that the MGB is fully equipped with the proper features to cope with a loss of lubrication event; specifically, the drive system is supposed to be able to run at least 30 minutes after the oil pressure drops to zero. A lot of effort has been put over the years at Leonardo Helicopters to find
This study numerically investigates the relationship between airspeed, drop height, and ground water coverage during helicopter-based aerial firefighting. With the effect of global warming and human activities the threat of forest fires has increased and finding optimal water dumping strategies for effective suppression is a crucial part of the firefighting operations. How varying airspeed and water drop height influence water dispersion and ground coverage has been analyzed utilizing numerical simulations with the VOF model in STAR-CCM+. Findings show that to maximize firefighting efficiency, balancing two contradicting phenomena is essential. These are, minimizing ineffective mist formation due to high drop height/high airspeed and fueling of the fire from rotor downwash due to low height/low airspeed passing by over the fire zone.
The paper presents a general framework for building an aeromechanic model in FLIGHTLAB, suitable for high fidelity, pilot-in-the-loop simulator. The focus is on aerodynamic modeling of AW609 tiltrotor in Airplane Mode flight regime. The framework can be extended to helicopter and conversion modes with additional considerations for rotors-airframe aerodynamic interference. It can also be adapted to different tiltrotor geometries, with some adjustments depending on their peculiarities. The model uses Blade Element Theory loads evaluation of lifting surfaces, corrected with tabulated distributed loads to tune FLIGHTLAB predictions against high-fidelity aerodynamic references. Bluff bodies are modeled using force and moment tabulated data. Verification was conducted against reference data in wind tunnel mode and against flight data in trim analysis. The proposed method allowed to match lift distribution on slender bodies, as well as lift and drag integral loads, with aerodynamic references
Acoustic flight testing of rotorcraft often involves generating noise source hemispheres to gain an understanding about the aircraft's acoustic emissions. However, aerodynamically complex Urban Air Mobility and Future Vertical Lift vehicles may not maintain a steady aerodynamic state during flight, making source hemispheres measured using traditional linear arrays unreliable or difficult to interpret. To address this challenge, all emission angles need to be measured simultaneously. This has lead to the concept of the two dimensional 'snapshot' array layout. A mathematically defined microphone distribution was utilized to achieve uniform coverage on the source hemisphere. Within the chosen distribution, two lower microphone count distributions are embedded, allowing for a comparison of the effects of number of microphones. The array was deployed as part of a joint Army/NASA acoustic research flight test in July of 2024. Data were collected using an MD530F helicopter as the test vehicle
The NASA Revolutionary Vertical Lift Technology project supports advanced air mobility missions through various vertical take-off and landing related projects. These efforts expand rotorcraft technology to improve the quality of life and perform "public good" missions through numerous mission concepts. The work presented herein introduces Multi Modular-Rotorcraft (MMR) technology, which explores the multifunctionality of sub-vehicles to expand the number of simultaneous missions for a rotorcraft. MMR technology can advance aeronautics through inspired transformational innovations. In this paper, the MMR concept is described, and examples of applications, 1) Disaster Relief, 2) Package Delivery, 3) Applied Science, and even 4) Planetary Exploration, are presented as potential reference missions for the MMR. With reference to an applied science mission, results from a rotor sizing demonstration and aerodynamic performance analyses of a MMR sub-vehicle, the Orb, are presented.
While known and largely studied, the Vortex-Ring-State (VRS) phenomenon remains the cause of numerous accidents every year and many questions are still open. In order to better understand the VRS phenomenon on different kinds of helicopters and to evaluate the effectiveness of recovery manoeuvres such as the one proposed by Capt. Vuichard, the European Union Aviation Safety Agency (EASA) launched the Helicopter Vortex-Ring-State Experimental Research project (EASA.2022.C11). Both objectives required to set-up flight test campaigns on two helicopter types, with a total of eight flights performed during the project. In addition to the description of the procedures that such flights required, the paper presents the Flight Test Instrumentation used and the analyses of the flight test data, including vibration measurements. Thus, flight conditions at which the VRS starts to develop, main parameters that influence and contribute to VRS symptoms and effects, or the effectiveness of the
The oil cooling fan of a Main Gearbox (MGB) is a mechanically-driven component whose purpose is to force an air flow through an air cooled oil cooler; its performance is crucial in ensuring that the MGB oil temperature does not exceed a predefined threshold, set to alert the crew in case of an abnormal situation. The design and the certification of a cooling fan is a process involving several steps and multiple disciplines; mechanical design, aerodynamic analysis, dedicated tests carried out both on rigs and at aircraft level need to be exploited as complementary tools to assess the correct aero-mechanical behavior of the system. The aerodynamic assessment is associated to performance, measured in terms of MGB oil temperature: considering a comparison between two cooling fans, one outperforms the other if the resultant MGB oil temperature is lower, keeping the same boundary conditions (engine torque, wind speed, ambient temperature, etc.). The correct mechanical behavior is instead
Leveraging lessons learned from NASA's Ingenuity Mars helicopter and concepts such as the Mars Sample Recovery Helicopter, and Mars Science Helicopter has enabled partners at NASA's Jet Propulsion Laboratory (JPL), NASA Ames, and AeroVironment, Inc. to mature a hexacopter vehicle concept (Chopper) with the ability to support a wide range of mission scenarios. This work focuses on the critical aeronautics-related challenges encountered transitioning from an Ingenuity-size vehicle to a much larger vehicle (˜15 times the mass) and discusses engineering efforts to address these challenges. Critical upgrades include optimized airfoils, higher solidity blades, and higher fidelity computational models. Because multiple rotors are required to lift the heavier vehicle, increased understanding of the impact of rotor-to-rotor interactions is also necessary. Rotors have been designed that are tailored to more demanding missions and will be validated in a joint test campaign between the partners
The Sikorsky BLACK HAWK® is the primary medium lift helicopter for the U.S. Army performing a wide range of missions that encompass Air Assault, MEDEVAC, CSAR, Command and Control, and VIP transport. The Multimission UH-60M is one of the latest in the BLACK HAWK helicopter product family, more capable, more survivable, more maintainable, more powerful, and more effective than its predecessors. In previous efforts, a high-fidelity CFDCSD based full-aircraft trim and maneuvering simulation methodology was developed and applied to model both coaxial aircraft and single main/tail rotor configurations (Refs. 1-4). The CFD solver is based on the CREATE™-AV HELIOS toolset (Ref. 5) and the CSD solver is based on Rotorcraft Comprehensive Analysis System (RCAS) (Ref. 6). The current paper further enhances the previously developed 6-DOF CFD-CSD full-aircraft trim methodology to robustly handle the trim solution for the single main/tail rotor configurations. The enhanced methodology was applied to
Helicopters' Vertical Take-Off and Landing (VTOL) capabilities are essential for maritime operations, especially for small-deck naval vessels. Unmanned Aerial Vehicles (UAVs) offer a cheaper, expendable, and efficient alternative for certain tasks, such as reducing pilot risk and lowering fuel consumption. While the procedures to approach and land on (moving) ships are standardized and bound to established operational limits in the case of crewed helicopters, UAVs lack such guidelines. This study investigates optimal rotary-wing UAV approach trajectories to a moving ship, for varying wind conditions and relative initial positions, and for different objectives. The goal is to provide preliminary guidelines for maritime UAV recovery operations, and a preliminary estimation of performance-based operational limits. The optimal trajectories are obtained using a global path-performance optimization framework based on Optimal Control Theory. The trajectories are compared to each other and to
Wind tunnel tests and comprehensive rotorcraft analysis were carried out on a slowed main rotor full-wing lift and thrust-compounded helicopter with a trailing propeller to investigate the effects of rotor and wing configuration on performance, blade structural loads, and hub vibratory loads. Experiments were conducted at advance ratios up to 0.7, incorporating three full-wing configurations with symmetric and asymmetric incidence angles and three different rotor shaft tilt angles. Propulsive thrust was measured by a trailing pusher propeller with its own balance system. The wind tunnel test data was used to validate the University of Maryland Advanced Rotorcraft Code (UMARC). Results showed that the maximum lift-to-drag ratio is achieved using either of the symmetric or asymmetric full-wing lift-compound configurations with high lift offloading and aft shaft tilt. Both blade structural loads and hub vibratory loads are significantly reduced when rotor lift is offloaded to the wings
The empennage of a helicopter is largely responsible for its stability in forward flight. Its performance is mainly determined by its aerodynamics. In this paper, the empennage of a CoAX 2D ultralight research helicopter is analyzed in detail. For this purpose, the helicopter was equipped with flow measurement devices and flight tests were performed, covering different flight conditions. Measurements from a nose boom as well as the pilot’s control inputs and helicopter's position are available for evaluation. For the empennage in particular, seven-hole flow probes were mounted on it and various cameras were used to record the movement of the surface tufts.
Survivability in the future operating environment is becoming more challenging as threat systems evolve and become more sophisticated. The ability to tailor and manage signatures will be one of the key methods to improve survivability, allowing operators to minimise detection and maximise the effectiveness of countermeasures. This paper presents the findings of an investigation into the application of classical Signal Detection Theory (SDT) to the aural detectability of helicopter noise signatures, considering human auditory capabilities. The paper has thus developed a novel methodology, applied it to both the experimental and numerical helicopter acoustics signatures of an LH platform, and used these results to infer the detectability characteristics of the aircraft, as well as how they are affected by the presence of background noise in different environments.
Heavy wind and high sea states pose challenges to operating unmanned rotorcraft on-board a naval ship, in particular the recovery phase. A novel autonomous landing strategy for unmanned rotorcraft is proposed and investigated. The new landing strategy makes use of a prediction of the future deck motion based on a sensor on the ship deck. The study is based on a nonlinear simulation environment which includes the dynamics of a 100 kg unmanned helicopter and the dynamics of an ocean-going patrol vessel of the Royal Netherlands Navy. The performance of the autonomous landing strategy is evaluated for a wide variety of environmental conditions (sea state) and operational conditions (ship speed and heading). The results clearly indicate that the environmental conditions have a strong influence on the landing performance in terms of touchdown velocity and landing accuracy. Furthermore, the autonomous landing strategy is effective in reducing the mean and peak value of the touchdown velocity
This paper presents a meshless large eddy simulation approach for rotorcraft wake prediction, using a vortex particle method accelerated on GPUs. The solver couples a rotor model with a vortex particle wake model, employing the Fast Multipole Method for computational efficiency and implementing viscous diffusion through Particle Strength Exchange and Core Spreading Methods. GPU acceleration achieves speed-ups of up to 10x compared to CPU execution. The solver’s predictions are validated against experimental data, showing excellent agreement. Effects of time step size, numerical integration schemes, viscous models, and particle overlap factors on simulation accuracy and computational cost are systematically analyzed. This GPU-based vortex particle framework provides a fast, accurate, and scalable tool for rotorcraft wake simulations.
Several efforts have been made to develop Flight Test Maneuvers for Handling Qualities evaluations, aimed at quantifying the effects of vehicle characteristics and assistance systems on a Helicopter Air-to-Air Refueling mission profile. However, these Flight Test Maneuvers have not achieved widespread adoption, likely due to the substantial logistical challenges associated with tanker deployment. Depending on a tanker aircraft not only incurs significant costs but also requires extensive organizational effort and prior testing, before Handling Qualities can be evaluated for the aerial refueling capabilities of a new rotorcraft design. Additionally, these available Flight Test Maneuver setups are not standardized or widely applied to the same degree as Mission Task Elements of the Aeronautical Design Standard, which limits repeatability and comparability. A new approach is proposed to address these limitations by introducing a repeatable, standardized method to reveal Handling Qualities
Electric aviation is advancing rapidly, with aircraft from manufacturers like Joby and Archer well on their way to certification, aircraft electrification will continue and begin to apply to larger aircraft. To support larger electrified rotorcraft, rotors will need to grow if disc-loading and hover efficiency are to be maintained. A consequence of this is the need to reduce rotor speed to maintain an acceptable acoustic signature, especially for operation in urban environments. Most current applications utilize radial flux motors, sometimes with a reduction gearbox. Gearboxes can improve overall propulsion system power density by enabling higher motor speeds but are generally not preferred as they introduce additional potential failure modes and maintenance schedules. In this paper a holistic approach is used to understand the trade-offs between rotor and motor and their consequences on propulsion system power density.
The next generation of Mars rotorcraft may involve an increase in scale and number of rotors. A key focus area that has been identified is to increase the fidelity of rotor wake modeling, including its impact on flight dynamics. To that end, this paper pursues the use of a Viscous Vortex Particle Method (VVPM) for mid-fidelity rotor wake predictions in Mars atmospheric conditions. Simulated aerodynamic hover performance, as well as control efforts in trimmed forward flight, of the Ingenuity Mars Helicopter with a VVPM wake is shown to correlate well with available experimental data. Qualitative and quantitative coaxial wake effects for Ingenuity-type rotors in hover and forward flight as predicted with VVPM are studied. Utilizing VVPM to evaluate rotor-rotor interference effects in a large-scale Mars hexacopter across a wide range of flight conditions showcases the capability to comprehensively model the induced wake of complex multi-rotor configurations within feasible computational
This paper proposes a first iteration towards a framework for enhancing the trustworthiness of machine learning in the health and usage monitoring of in-service helicopters. This bottom-up approach is based on our experience operating machine learning models for monitoring Airbus Helicopters' customer fleets. Key factors for improving trustworthy machine learning have been identified for both the development and execution phases, with specific methods defined for each enabler. These methods have been implemented in two use-cases involving machine learning models for regression tasks: monitoring the helicopter's main gearbox lubrication system, deployed in the FlyScan predictive maintenance service, and tracking the usage of the main rotor lead-lag damper loads. The results from both use cases show that confidence in machine learning model predictions can be effectively improved.
Gearbox casing cracks in helicopters would be critical impacting the aircraft's reliability and operation safety directly. The Defense Science and Technology Group (DSTG) HUMS2025 gearbox casing failure data set was the unexpected result of a test stand operation. The gearbox undergoes high cycle (> 400 acquisitions) under high torque (100% and 125% nominal torque) conditions. We hypothesized that the any cracking would be due to the planet/ring gear interaction. A condition indicator (CI) would be sensitive to a crack feature and this would be sensitive to change in gearbox torque. This paper explores the development of both a cyclo-stationary based CI (frequency-domain) and a time synchronous average CI (time-domain). The trend shows that proposed methods can help to detect localized defects in gearbox casing at an early stage and trend as the crack propagates before catastrophic failure occurs.
This study investigates the evolution of axial and radial velocities in the downwash-outwash region of a counter-rotating coaxial rotor hovering in-ground effect (IGE). The presence of the ground deflects the axial flow of the rotor wake radially outward, with mean radial velocities reaching approximately 2Vh along the ground. Based on the observed velocity profiles, the wake was classified into three distinct regions: the downwash region characterized by maximum wake contraction, the transition region where flow turns from axial to radial, and the outwash region exhibiting wall jet behavior. Results show that increasing inter-rotor spacing d/R and rotor height above ground (z/R)l extends the downwash and transition regions, delaying the onset of radial outwash. Aerodynamic loads on personnel were estimated, showing maximum mean forces and moments of 120N and 120Nm, remaining within safety thresholds for untrained personnel. However, the loads exceeded these limits for heavy-category
Civil and military rotorcraft operators desire enhanced capabilities from their vehicles in terms of mission efficiency, effectiveness, productivity, and availability. A critical element of this challenge is associated with providing cold weather availability. Currently, cold weather operations are enabled by regulatory actions leading to Limited Approvals, Qualifications, Clearances, and Restrictions. Cold weather certification (clearance of a new aircraft) and continuing airworthiness (maintaining effectiveness of fielded aircraft) are data driven processes. This work provides guidance on an Icing Encounters Survey (IES) based data gathering method supporting continuing airworthiness organizations in improving fleet safety and capabilities during cold weather operations.
We extend the previously developed integrated VABS (iVABS) framework for rotor blade structural optimization with an enhanced cross-section template for practical manufacture considerations; these include the introduction of curved spar corners, a continuous wrap-around skin, trailing-edge tabs and a conformal non-structural mass. The added fidelity is exercised on a UH-60A-based outer mold line through three multi-objective optimization case studies, including a case where the cross-sections are optimized independent of each other, and two cases where all the cross-sections are optimized simultaneously with manufacture considerations. It was found that the latter cases produce straight spars that are relatively more practical to manufacture when compared to the first case, while achieving significant reduction of up to 80% in the mismatch of stiffness values, inertia properties, and shear center locations, when compared to the prior work. A subsequent sensitivity analysis of the
Maintaining the operational readiness of military helicopters demands repair solutions that are fast, reliable, and adaptable. This paper presents the integration of Gamma Alloys' advanced metal matrix composites (MMCs) into additive manufacturing (AM) techniques - specifically Cold Spray and Friction Stir Additive Manufacturing (FSAM) - as a transformative approach to helicopter repair and replace for the US Army.
A follow-on study to the 2024 paper by Kottapalli, Silva, and Boyd is presented with improved acoustics tools to examine whether the Vertical Aviation International (VAI) Fly Neighborly operational recommendations that are designed for single main rotor/tail rotor configurations will hold for non-conventional UAM rotorcraft with multiple rotors. The 6-occupant quadrotor concept vehicle designed under the NASA Revolutionary Vertical Lift Technology (RVLT) Project is studied. The tip speed is 550 ft/sec, with three blades per rotor. Predictions are made for three steady maneuvers: level turns, descending turns, and climbing turns. The RVLT Toolchain is exercised using CAMRAD II, pyaaron/AARON/ANOPP2 and AMAT (ANOPP2 Mission Analysis Tool). Quadrotor noise trends are analyzed using Sound Exposure Level (SEL) ground maps because it is anticipated that the upcoming updated Fly Neighborly recommendations will involve SEL maps. Importantly, unlike conventional helicopters with a single main
This paper discusses the development of a quantitatively-accurate non-linear hybrid flight dynamics model of a hover-capable Air-Launched Tailsitter Unmanned Aerial System (ALUAS) in order to 1) understand its dynamics during complicated maneuvers, and 2) provide a high-fidelity framework to develop novel control laws. Wind tunnel tests were conducted on a 1:1 scale model of the full aircraft to measure the airloads, which were used in the simulation as a lookup table. Flight tests of the ALUAS were performed in hover, transition, and cruise to collect a large amount of unique state measurements by providing large excitations to induce highly transient motion. The flight dynamics predictions using Rotorcraft Comprehensive Analysis System (RCAS) software were then compared with experimental flight test data. To correct any discrepancies in the RCAS physics-based predictions, a correction was learned from the experimental measurements, making use of the large amount of collected flight
Neonatal patients in need of specialized care may require transport by rotary-wing air ambulances. These patients are subjected to environmental stressors during transport, including elevated levels of mechanical vibration. Aircraft vibration is transmitted through the transport system and incubator to the patient. The unique vibration profile is dependent on vehicle model and phase of flight. To improve safety for these patients, we aim to evaluate the vibration exposure across this complex system. The purpose of this paper is to present and evaluate the methods used for aircraft data collection and replication of aircraft vibration profiles in a laboratory setting. Our current focus is on neonatal transportation in Ontario, Canada, where Leonardo AW139 helicopters are used for patient transport. AW139 field data were collected and processed to generate excitation profiles for discrete phases of flight. The vehicle data were used to drive a series of laboratory shaker-table
Electric Vertical Takeoff and Landing (eVTOL) aircraft present a series of challenges to traditional aviation infrastructure that was designed for conventional rotorcraft. Questions have arisen within the vertical flight community as to the validity and applicability of applying current heliport markings and symbology to vertiports. Several of these questions were addressed in a previous paper from VFS Forum 80: "A Comparison of Proposed Concepts for Vertiport Markings and Symbology" (Ref. 6). In contrast, this paper extends that work and presents the results of additional research to enhance the visibility of the Federal Aviation Administration’s (FAA) “Broken Wheel” symbology. These notional enhancements to the "Broken Wheel" symbology were evaluated over the course of an experimental study using helicopter-rated pilots in the FAA William J. Hughes Technical Center’s S76-D and Loft Dynamics H125 and R22 rotorcraft flight simulators.
We present the flight testing and integration of the Microsoft HoloLens 2 as a head-worn display (HWD) in DLR's research helicopter. Building on its successful use in a helicopter simulator, initial flight tests confirmed its feasibility in a real helicopter. Current tests focused on system optimization, with head tracking identified as the critical component for hologram stability. Since the HoloLens' inside-out tracking fails in moving vehicles, it was fused with an external infrared tracker, automatically calibrated via an optimization approach adaptable to various trackers and mounting positions. A test pilot with HWD experience rated the system as fully functional, enabling the first successful experiments with holographic Mission Task Elements. Beyond the helicopter, the HoloLens was tested in a car and on a high-speed boat, where holograms remained spatially stable despite high-frequency movements, with a maximum low-frequency error of 0.6° in heading. Static errors depended
Structural testing of full-scale blade geometries with flap-bending/twist composite coupling was performed to evaluate the impact of coupling. Full-scale spar geometries were first fabricated with three different coupling distributions, including two with a uniform positive flap-bending/twist coupling, in which a flap up deformation induces a nose down elastic twist. The third spar geometry incorporated a mixed coupling, with a uniform positive coupling at the inboard end and a uniform negative coupling at the outboard end, where the negative flap-bending twist coupling produces a nose up elastic twist when experiencing flap up deformation. A full-scale blade was then fabricated with a positive flap-bending/twist coupling. Measurements of the structural twist distribution of the cured spars were taken to ensure the coupling did not result in any hygrothermal instabilities. Tip twist and strains were then measured under various combinations of flatwise bending and torsional bending
Big Data technologies have become quite ubiquitous in the last years, allowing for the storage of substantial amounts of data, typically flight test data as recorded by the flight test installation. On recent helicopter prototypes, we generate in excess of 50 GB of raw data per flight hour, usually in a format not adequate for efficient large-scale processing. With some specific optimizations and the setup of a specialized infrastructure, there are now practicable means to store timeseries in ways that allow for requests spanning hundreds or thousands of flights to complete within minutes, opening the way to some substantial savings and new insights. However, to make the most of these data and make informed decisions it is often quite important to store contextual data that go beyond the pure timeseries data, typically on helicopters where optional installations can have a significant impact on aircraft performance or behavior. This paper explores the various kinds of data and metadata
To strengthen the transition from conceptual to preliminary rotorcraft design, this work develops an integrated methodology combining early mass and load predictions with structural optimization. Embedded within the DLR frameworks IRIS and PANDORA, the approach orchestrates mass estimation, flight load prediction, and structural assessment in a semi-automated process. Topology optimization techniques are employed to design internal reinforcements between the aerodynamic fuselage and the cabin, enhancing structural fidelity ahead of preliminary design. A primary rescue helicopter serves as a case study, using representative ground and flight load cases as a basis for optimization. Although a full certification load spectrum is not covered, the selected cases capture the main design-driving conditions, demonstrating the benefits of early structural optimization. The presented method enables more informed structural decisions immediately after conceptual design, laying a solid foundation
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