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The Dragonfly mission has the scope of studying the surface of Titan, Saturn's largest moon, using a rotorcraft lander. A mission-critical event in the timeline involves Dragonfly's initial flight as it descends into Titan's atmosphere. The preparation for this initial flight involves releasing the heat shield and utilizing the lander's rotors to damp motion while still attached to the parachute-supported aeroshell to ensure a smooth release. The aerodynamics of this event are studied in Titan conditions using high-fidelity computational fluid dynamics (CFD). The CFD model is benchmarked using available experimental measurements relevant to subcomponents of the event and include: (1) an open backshell, (2) bluff bodies similar to the Dragonfly fuselage, and (3) a rotor-body interaction from a helicopter rotor. The CFD results correlate well with measurements to provide confidence in the present studies focused on Titan. The novel studies presented in this work focus on the rotor-based control of the lander–backshell combination and its ability to mitigate spinning about the main parachute support line. This effort finds that the relatively large fuselage combined with near-fuselage rotors (driven by aeroshell space limitations) drives an unexpected aerodynamic interaction between the rotor and fuselage. Specifically, we observe low-pressure zones on the fuselage adjacent to the rotor that create a "suction" force. This first-order force creates an unexpected aerodynamic interaction that demands careful attention. In this paper, this force is documented and solutions are proposed to mitigate undesirable control character. • Aerodynamics of the Dragonfly lander interacting with a parachute-supported backshell. • Efforts supported using high-fidelity numerical models backed with a series of experimental benchmarks. • Elucidation of rotors inducing a strong force on the lander that need special consideration. • Proposed solutions highlighted by careful consideration of rotor orientation. [ABSTRACT FROM AUTHOR]

The main purpose of this work is to investigate the performance of a hybrid fuel cell/battery powertrain concept for a lightweight helicopter in an urban air mobility scenario. Three different hybrid configurations are compared with a battery-electric design and a performance study is carried out over three specific missions, to identify the most appropriate design in each considered operative condition. Results show that a hybrid configuration may outperform the battery-electric one if a suitable balance between power sources is found. The hybrid design with a 70 kW fuel cell triplicates the number of regional transports completed by the battery-electric configuration, but it is less performing on urban routes. On the other hand, a 90 kW fuel cell, turned out to provide enhanced performance for high-power duty cycles, as for an urban mission. In general, the optimal hybrid configuration, in terms of achievable range, strictly depends on the specific duty cycle. • Mission-oriented design of fuel cell electric powertrain for lightweight helicopter. • Improvement of electric rotorcraft performance in urban air mobility scenario. • Hybrid helicopter performance analysis carried out over urban and regional missions. • The optimal layout for a hybrid powertrain depends on the specific helicopter mission. [ABSTRACT FROM AUTHOR]

Conventional turboshaft engines are high power density movers suffering from low efficiency at part power operation and producing significant emissions. This paper presents a design exploration and feasibility assessment of a hybrid hydrogen-fueled powerplant for Urban Air Mobility (UAM) rotorcraft. A multi-disciplinary approach is devised comprising models for rotorcraft performance, tank and subsystems sizing and engine performance. The respective trade-offs between payload-range and mission level performance are quantified for kerosene-fueled and hybrid hydrogen tilt-rotor variants. The effects of gas turbine scaling and fuel cell pressurization are evaluated for different hybridization degrees. Gas turbine scaling with hybridization (towards the fuel cell) results in up to 21% benefit in energy consumption relative to the non-scaled case with the benefits being more pronounced at high hybridization degrees. Pressurizing the fuel cell has shown significant potential as cell efficiency can increase up to 10% when pressurized to 6 bar which translates to a 6% increase in overall efficiency. The results indicate that current fuel cells (1 kW/kg) combined with current hydrogen tank technology severely limit the payload-range capability of the tilt-rotor. However, for advanced fuel cell technology (2.5 kW/kg) and low ranges, hybrid powerplant show the potential to reduce energy consumption and reduce emissions footprint. • Design space exploration of hybrid hydrogen-fueled powerplant for UAM rotorcraft. • Hybrid-electric rotorcraft compared against the hydrogen-fueled counterpart at different hybridization degrees. • Performance and environmental assessment conducted at payload-range and mission level. • Effects of gas turbine scaling with hybridization and fuel cell pressurization are quantified. • Fuel cell technology level sensitivity analysis is conducted. [ABSTRACT FROM AUTHOR]

The Mars rotorcraft can help the Mars rover to optimize the driving route and explore more efficiently. However, the thin and cold Martian atmosphere can heavily increase the consumed power of the rotorcraft blades and reduce the generated thrust, leading to the reduction in power loading. The aerodynamic force generated by the Mars rotorcraft blade can be significantly influenced by the blade structure, which has several main structural characteristics and needs to be well designed. A multivariable optimization design method of blade structure is proposed based on neural network, genetic algorithm, and computational fluid dynamics simulations. Experiments conducted in the Martian atmosphere simulator indicate that the Mars rotorcraft blades with the hyperbolic chord length distribution and twist have higher power loading in the constant collective pitch angle. • A model was built to predict rotor hover performance at low-Reynolds-number. • Established an optimization model of the planform of the Mars rotorcraft blade. • The optimized blade consumes 29% less power than the conventional blade. • The optimization result were verified experimentally in Mars simulated environment. [ABSTRACT FROM AUTHOR]

In recent years, the compound helicopter configuration, featuring the addition of lateral propellers to a helicopter main rotor, has gained renewed interest for its ability to achieve higher flight speed. The aerodynamic behaviour of compound rotorcraft is dominated by mutual interactions between the rotors and the wakes they generate, which can affect their performance and the handling qualities of the aircraft. In order to study the effects of the rotor-wake and wake-wake interactions, a test rig was developed and an extensive wind-tunnel test campaign was carried out measuring the performance of rotor and propellers under different flight conditions. Hovering flight and forward flight at different advance ratios were considered, as well as crosswind flight under various wind directions. In general, an increase in thrust for both main rotor and propellers is found due to the interaction. In particular, the significant increase in the propeller thrust is attributed to the influence of the main rotor downwash, which impacts edgewise on the propellers. In some specific conditions, a decrease in the propeller's thrust is observed, which might be related to blade-vortex interaction (BVI) effects. To aid in the interpretation of the experimental results, numerical simulations with a mid-fidelity aerodynamic code were also performed. • A wind-tunnel campaign studied rotor-rotor interactions on a compound helicopter in various flight conditions. • Load measurements showed little influence of the propellers on the main rotor. • Conversely, important increases in the thrust of the propellers were recorded in general. • Singular performance losses in specific conditions could hint to vortex interactions. [ABSTRACT FROM AUTHOR]

• An underwater rotorcraft vehicle based on a U- joint was proposed. • ABSSMC can realize fixed-depth trajectory motion control in proximity to the seabed. • The proposed vehicle can reduce system energy consumption and enhance maneuverability. This paper proposes a novel underwater rotorcraft vehicle with a passively adjustable configuration based on a universal joint (URV-PAU), which addresses the issue of increased propeller load and control stability caused by the rigid structure of existing vehicles when tilted. Compared with designs that do not incorporate a U-joint structure, this vehicle can reduce energy consumption and enhance system manoeuvrability. First, a kinematic and dynamic model of the URV-PAU is established based on its configuration. Considering the nonlinearity of the system, the modelling errors of the dynamic model, and external disturbances, an adaptive backstepping sliding mode controller(ABSSMC) is designed to achieve motion control in proximity to the seabed. A prototype of the underwater rotorcraft vehicle was constructed according to the principles of modular design. Subsequently, underwater trajectory experiments were carried out within a water tank. The experiments demonstrated that the URV-PAU results in a reduction of approximately 10 % in system energy consumption and an improvement in system manoeuvrability compared with designs without a U-joint structure during motion at a constant depth. [ABSTRACT FROM AUTHOR]

During closed-range rotorcraft missions, strong aerodynamic disturbances occur between multiple aircraft, thus affecting the stability and safety of cooperative flight processes. However, owing to the numerous control variables in rotor models, the cost and complexity of experiments and body-fitted grid simulation methods are high, thereby resulting in low analysis efficiency and difficulty in establishing a highly applicable aerodynamic-interference model. In this study, the effectiveness of a two-dimensional quasi-steady momentum source method for calculating the aerodynamic interference of heterogeneous rotors is validated using the sliding-mesh method. Using Latin sampling and momentum source methods to obtain aerodynamic-interference data points, a multiparameter-coupled heterogeneous-rotor aerodynamic-interference model is proposed and validated. The results indicate that the proposed aerodynamic-interference model provides clear physical significance and demonstrates high accuracy under different rotor configurations. In validation samples, the correlation coefficient between the predicted aerodynamic loss on the lower rotor and the computational fluid dynamics (CFD) calculation results is approximately 0.99, with the maximum errors in predicting thrust and moment losses are less than 7 % and 2 %. Meanwhile, the correlation coefficient between the predicted values on the upper rotor and the CFD calculation results is 0.82, with the maximum errors in predicting the dimensionless thrust and moment losses are less than 5.5 % and 1 %. The rapid aerodynamic-interference analysis model proposed herein can serve as a reference for the safe-flight strategy of rotorcraft during close-range cooperative missions. [ABSTRACT FROM AUTHOR]

This paper presents the application of a multidisciplinary approach for the preliminary design and evaluation of the potential improvements in performance and environmental impact through the utilization of compressed (CGH2) and liquefied (LH2) hydrogen fuel for a civil tilt-rotor modelled after the NASA XV-15. The methodology deployed comprises models for rotorcraft flight dynamics, engine performance, flight path analysis, hydrogen tank and thermal management system sizing. Trade-offs between gravimetric efficiency, energy consumption, fuel burn, CO 2 emissions, and cost are quantified and compared to the kerosene-fuelled rotorcraft. The analysis carried out suggests that for these vehicle scales, gravimetric efficiencies of the order of 13% and 30% can be attained for compressed and liquid hydrogen storage, respectively leading to reduced range capability relative to the baseline tilt-rotor by at least 40%. At mission level, it is shown that the hydrogen-fuelled configurations result in increased energy consumption by at least 12% (LH2) and 5% (CGH2) but at the same time, significantly reduced life-cycle carbon emissions compared to the kerosene counterpart. Although LH2 storage at cryogenic conditions has a higher gravimetric efficiency than CGH2 (at 700 bar), it is shown that for this class of rotorcraft, the latter is more energy efficient when the thermal management system for fuel pressurization and heating prior to combustion is accounted for. [Display omitted] • A civil tilt-rotor is retrofitted for liquid and gaseous hydrogen fuel. • The hydrogen-fuelled rotorcraft are compared against the kerosene-fuelled counterpart. • Performance and environmental assessment is conducted at payload-range and mission level. • Liquid hydrogen offers higher gravimetric densities but its requirement for heating penalizes performance. [ABSTRACT FROM AUTHOR]

Dual system Vertical Take-Off and Landing (VTOL) fixed-wing Unmanned Aerial Vehicles (UAVs) combine the advantages of both the rotorcraft and fixed-wing UAV, characterizing horizontal and vertical flight capabilities. However, they face challenges such as aerodynamic coupling between propulsion systems, model uncertainty, and external disturbances, significantly deteriorating the tracking accuracy and robustness. This paper proposes an Extended State Observer based Continuous Finite-Time Control (ESO-CFTC) scheme to solve the attitude and trajectory tracking problem of such a VTOL fixed-wing UAV. Initially, the Nonsingular Fast Terminal Sliding Mode (NFTSM) controller guarantees the tracking errors reach a prescribed manifold in finite time with a continuous reaching law, then converge to the origin in finite time while avoiding singularities. To suppress the inherent chattering problem of the sliding mode control, an ESO technique is incorporated into the ESO-CFTC scheme, which is completely decoupled with the basic NFTSM controller. The supremum of the estimation residual set is derivated theoretically. The scheme forces the tracking errors to converge into the neighborhood of the origin in finite time without requiring prior knowledge of lumped disturbance supremum values. Finally, the numerical simulation results in a Matlab/Simulink environment demonstrate that the presented method outperforms existing benchmark in terms of disturbance estimation, tracking accuracy, convergence rate, and robustness. [ABSTRACT FROM AUTHOR]

This paper develops a neural-network-based model reference adaptive control (MRAC) scheme for a rotorcraft in the presence of input saturation. Such a control scheme provides acceptable tracking performance for the rotorcraft in a wide range of flight conditions. Combined with hyperbolic tangent functions, the MRAC scheme is capable of tracking the reference signals without violating input constraints. A modified projection operator is utilized to prevent system from parameter drift due to the strong nonlinearity and uncertainty of the rotorcraft mathematical model. Stability of the proposed MRAC scheme is proved based on Lyapunov stability theory. The performance of the resulting controller is tested by conducting numerical simulations for an autonomous rotorcraft in various flight missions. • A robust modification of adaptive control is proposed to prevent nonlinear system from parameter drift. • A neural network based MRAC scheme is conducted in the presence of input saturation using hyperbolic tangent function. • The proposed MRAC scheme is applied to a nonlinear rotorcraft model. [ABSTRACT FROM AUTHOR]

During rotorcraft ship-deck landing operations, complex interactional aerodynamic phenomena occur between the rotor and ship airwakes which are not fully understood. To aid in ship–rotorcraft interactional investigations, efficient mid-fidelity ship airwake solutions are needed. Additionally, the effects of ship motion have not been explored much. In this study, the NATO Generic Destroyer, a shared, representative ship geometry created for collaborative studies, was investigated numerically using a GPU-accelerated Lattice-Boltzmann Method solver, and the ship airwake results compared with wind tunnel measurements using discrete velocity probes on the landing deck. The ship surface was modeled using a robust Grad immersed boundary approach, and ship motion was thereby included in the simulations. Ship airwake results showed good agreement with the experiment and excellent computational performance. Simulations took under four hours to run on a single GPU node. This is several orders of magnitude improvement over traditional Delayed Detached-Eddy Simulations typically used to solve this problem, which may take days or weeks on CPU-based HPC clusters. [Display omitted] • Calculated NATO Generic Destroyer ship airwake using Lattice-Boltzmann method in static and motion states. • Achieved excellent simulation performance using GPU-accelerated computing. • Incorporated ship motion through robust immersed boundary approach. [ABSTRACT FROM AUTHOR]

Micro air vehicles with propellers have been widely used in military and civilian applications due to their high maneuverability and low cost. As the mission scenarios and requirements of rotorcrafts become more complex, proximity effects caused by confined environments, such as the ceiling effect cause significant interference to the performance and stability of rotors. Most researchers have analyzed this phenomenon by considering the ceiling effect in hover conditions. However, few scholars considered the tilt angle between the rotor and the ceiling, which is more likely to occur in real missions, such as the close inspection of bridges or large equipment, flight in narrow indoor environments, and flight near the ceiling for fully actuated multirotors. In this study, a CFD-based study is conducted to evaluate the ceiling effect for small-scale tilted propellers. The aerodynamic analysis was experimentally evaluated through a series of ground tests in a test bench designed for this research. The CFD results were validated by a mesh-independent study and experimental data comparison. The results show that in contrast to the phenomenon of reduced thrust when tilt angles exist between the rotors and ground, the existence of tilt angles between the propeller and the ceiling reduces the thrust-increasing effect of the ceiling when the dimensionless distance is greater than 0.6. When the distance gets smaller, the thrust-increasing effect increases when the tilt angle is greater than 10 ∘. In particular, when the distance is less than 0.3, the existence of tilt angles will increase the thrust-increasing effect of the ceiling. Additionally, a data-driven model has been proposed to predict the thrust with the distance to the ceiling and the angle inclination between the rotor and the ceiling. This model enables future rotorcrafts that require accurate models to operate in narrow environments. [ABSTRACT FROM AUTHOR]

• Hybrid Electric Power Systems offer eco-friendliness, but complexity increases fault risk. • Digital Twin for rotorcraft engine health monitoring using sensor data and machine learning. • Implementation of Engine Health Monitoring in a parallel HEPS with a turboshaft engine. • Multi-net architecture improves predictions in multi-component degradation scenarios. Hybrid Electric Power Systems (HEPS) have gained popularity as a more efficient and eco-friendly alternative. However, with increasing system complexity, fault potential rises. The work aims on implementing a diagnostic system for rotorcraft engine health within a hybrid-electric system. Health monitoring tools are still understudied for HEPS, so this work can represent a valid contribution in the literature. The main goal is assessing degradation and monitoring multi-component simultaneous degradation. Various machine learning techniques for Engine Health Monitoring (EHM) have been compared, varying in network architecture and data reduction. A dynamic model of the entire HEPS generated a dataset including fault information. This dataset trained FFNNs to predict performance parameters (PPs) of degraded components from sensor data. The proposed EHM system's efficacy was evaluated by comparing neural network predictions to dynamic model data. Results show that the Multi-net architecture, with distinct networks for each PP, works more effectively reducing training time. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive numerical environment, obtained by the coupling of a mid-fidelity aerodynamic solver based on a vortex particle method with a multibody dynamics tool, for aeroelastic simulations suitable for the analysis and design of next-generation rotary-wing aircraft. Indeed, the presence of multiple propellers and rotors, together with interactional aerodynamics, have a strong impact on dynamic loads and performance indexes on rotorcraft. A mid-fidelity approach provides an ideal trade-off between the accuracy of the solution and the speed of execution required in the preliminary design phases of these vehicles. A tiltrotor model representative of the Bell XV-15 with different levels of complexity is proposed as a test benchmark, whose characteristics can be similar to an eVTOL. The coupled solver shows the capability to determine the trim conditions in airplane mode and predicts steady and periodic trim loads. Transient analyses are presented as well, considering a roll maneuver and highlighting the importance of the accurate representation of rotary wing aerodynamics provided by the vortex particle method for load evaluation and vibrational assessment. [ABSTRACT FROM AUTHOR]

• High-fidelity aerodynamic and aero-acoustic modelling of a full-size heavy-lift, multi-rotor eVTOL design. • Analysis of the aerodynamics and acoustics of redundant parked propellers on eVTOL. • Wake interactions between lifting surfaces and propellers. • Effect of blade pitch and azimuth on the aerodynamics of parked propellers. As multi-rotor and convertible configurations gain compelling popularity in Advanced Air Mobility designs, the handling of redundant propellers during cruise flight regimes becomes a new challenge. This paper presents a systematic study of the aerodynamic performance of feathered and windmilling redundant propellers on a simplified multi-rotor, multi-wing configuration. High-fidelity CFD simulations were performed with a systematic test matrix including the blade feathering angle, azimuth shift, coning angle, and windmilling pitch angle and RPM. For the feathered blades, the feathering angle had a strong impact on the aerodynamic performance. The feathered blades could substantially reduce the overall lift and increase the overall drag at high feathering angles (up to 25% lift reduction and 70% drag increase). This is correlated with changes in the sectional wing inflow angles induced by the upstream feathered blades. Windmilling propellers, in ideal cases, were found capable of considerable wind energy extraction (50% of required cruise power) and could create slowed inflows for downstream thrusting propellers, at the cost of excessive drag (up to 90% more). Comparisons of vehicle performance with feathered and windmilling blades, showed similar aerodynamic forces and energy consumption. This shows that windmilling could be a feasible option for redundant propellers, given careful balancing of the drag and energy conversions. The presented results provide valuable guidance for the handling of redundant blades, for future multi-rotor aircraft designs for sustainable aviation. [ABSTRACT FROM AUTHOR]

To address the problem of control surface redundancy for compound high-speed rotorcraft in multi-mode conversion process, a hybrid multi-objective control allocation strategy based on adaptive particle swarm optimization (PSO) algorithm is proposed. First, the control allocation problem is converted to a hybrid multi-objective optimization problem to solve the control redundancy, and a hybrid multi-objective optimization performance function is designed to satisfy the multiple requirements of flight mission. Second, a preference matrix is designed to determine the weight coefficients of the optimization performance function. The preference matrix can simplify the complexity of hybrid multi-objective optimization problem. Finally, an adaptive PSO algorithm is designed to solve the hybrid multi-objective control allocation dynamically. The simulation verifies the feasibility and effectiveness of the control allocation strategy, which eliminates the need of extra controllers in the mode conversion, reduces the difficulty of flight control system design and improves the system security. • A control allocation strategy is designed to solve control redundancy problem. • An adaptive PSO is designed to improve optimization. responding speed and accuracy. • A construction method of AMS is proposed to evaluate control allocation efficiency. • A multi-objective optimization function evaluates the multi-flight requirements. [ABSTRACT FROM AUTHOR]

Over the last few decades, multirotor UAVs have become significantly popular because of their various applications. However, multirotors suffer from poor endurance performance as compared to other aircraft configurations with lifting surfaces. This limitation can be addressed by improving the technology of components or by developing design optimization approaches at the vehicle level. This paper presents a co-design approach for the multirotor structure and propulsive system to improve the vehicle's energetic efficiency while respecting dynamic performance requirements. For this purpose, the approach uses a bi-level formulation to optimize the design and control concurrently. The methodology offers the possibility to activate or not a passive fault tolerant strategy in the controller synthesis to be tolerant to single rotor failure. In contrast to conventional design approaches that sequentially design each part, the co-design approach leads to a better optimal solution by considering the interactions and couplings between design and control. With the proposed co-design approach, the results show the soundness of the proposed design methodology and a significant reduction in the consumed energy compared to a reference non-optimal design while maintaining the same requirements in terms of dynamic performance. [ABSTRACT FROM AUTHOR]

As a novel aerial vehicle, flapping-wing rotorcrafts (FWRs) leverage both aerodynamic advantages of flapping and rotary wings, which can enhance the lift by using the passive rotational effect generated by the flexible deformation of their center symmetrical flapping wings. Due to FWRs' unique wing kinematics, considering the aeroelastic deformation of wings is essential for the aerodynamic optimization of FWRs. In this paper, we propose a computational method of fluid-structure interaction for FWRs based on a simplified structural model. Such a method guarantees accurate results and works with high computational efficiency. To experimentally validate the proposed computational method, motion capture testing is constructed to simultaneously measure FWR wing deformation and aerodynamic forces during flapping. By comparing the experimental and computational results, the proposed method is capable of predicting the flapping lift effectively. Moreover, it can interpret the wing rotation and twist of the tested FWR. The computational efficiency in this paper is extremely close to that of the CFD calculation without considering the fluid-structure interaction. Based on this proposed computational method, the lift force of the test FWR platform is increased by 36.2 % by changing wing stiffness. [ABSTRACT FROM AUTHOR]

Drones and UAVs are gaining worldwide popularity and are now considered a popular choice for both military and commercial applications. Icing poses tremendous safety and performance concerns for the operation of all types of drones. This paper is part of a project that studies icing effects on the hovering 0.66 m diameter Bell APT70 drone rotor and the development of potential ice protection systems. The objective of this paper is to investigate the use of electrothermal heaters with severe icing conditions and to characterize the energy efficiency of anti-icing or de-icing regimes. Rotor speeds of 3880, 4440 and 4950 RPM were used while two air temperatures, −5 and −12 °C, were also tested. The heat transfer profile on the blade was studied using dry run tests where the rotor operated with heating but without water spray. Anti-icing tests with variable heating power were tested to determine the location of the initial ice accumulation as well as the minimum heating power requirement to protect the leading edge. Moreover, anti-icing tests with constant heating rates were done and compared to previous tests of unprotected blades, under similar condition. On the other hand, de-icing tests with various heating cycles were also carried out. Results indicate that although de-icing requires significantly less heating energy compared to anti-icing, there is clear trade-off on rotor stable aerodynamic output, electrical power consumption and vibration levels, depending on the adopted de-icing mode. Future work is about investigating the rise of secondary effects, such as shed ice impact due to de-icing. Work is also planned for a hybrid ice protection system that combines electro-thermal heaters with icophobic or superhydrophobic coatings. [ABSTRACT FROM AUTHOR]

Autonomous landing is a challenging phase of flight for an aerial vehicle, especially when attempting to land on a moving target. This paper presents vision-based tracking and landing of a fully-actuated tilt-augmented quadrotor on a moving target. A fully-actuated vehicle allows higher freedom in terms of control design and a larger flight envelope since the position and attitude states are decoupled. An adaptive control law is designed to track a moving target with only relative position information from a camera. Low-cost hardware is used, and experiments are carried out to validate the proposed methodology for targets moving at realistic speeds. [ABSTRACT FROM AUTHOR]

In this paper, a computational investigation of a rotorcraft avionics-bay cooling system is carried out. The introduced avionics cooling system utilizes a forced-convection method in which the ambient air is supplied to the avionics bay by a fan and then exhausted back into the ambient after cooling the equipment inside. The aim of this system is to keep the air temperature in the vicinity of the avionics equipment below the operational temperature limits. Depending on the locations of the fan and exhaust, local hot zones may form near some of the equipment. In order to overcome this issue, the fan capacity must be designed to provide a sufficiently high mass flow rate so that the temperature limits are not exceeded, while an excessive amount of cooling should be avoided to reduce power consumption. In this study, the effects of the fan and the exhaust locations on the amount of required mass flow rate are investigated. A prediction function is built by using Gaussian Process Regression method to predict the avionics surface temperatures. The Gaussian Process Regression method is trained by the results obtained from a large number of computational fluid dynamics (CFD) analyses. The prediction function is later used to determine the required mass flow rate depending on the fan and the exhaust locations. It is found out that the required mass flow rate changes significantly as the fan location changes. On the other hand, the exhaust location has a relatively lessened effect on the required mass flow rate. It is observed that depending on the locations of the fan and the exhaust, the required mass flow rate could be reduced to around half of its value. The amount of decrease in the electrical power consumption is even more significant. [ABSTRACT FROM AUTHOR]

This paper presents an integrated approach for the aeroacoustic assessment of four-dimensional rotorcraft operations. A comprehensive rotorcraft code is utilized to model aircraft flight dynamics across complete missions. A free-wake aero-elastic rotor model is employed to predict high-resolution unsteady airloads, including blade-vortex interactions, at each mission element. A rotor aeroacoustics code is developed to calculate source noise and far-field ground acoustic impact. Time-domain acoustic formulations are used to evaluate near-field noise generation across designated acoustic spherical surfaces surrounding the helicopter main rotor. A numerical procedure is developed for the derivation of acoustic spheres on-the-fly, coupled with trajectory-adaptive ground observer grids. The individual analytical models are incorporated into a mission analysis numerical procedure. The applicability of the integrated method on "real-world" rotorcraft operations is demonstrated for two generic, four-dimensional missions, without the need of pre-stored noise data. The proposed approach provides insight into helicopter noise prediction at mission level, elaborating on the coupling of aeroelastic rotor response with rotorcraft flight dynamics and aeroacoustics. [ABSTRACT FROM AUTHOR]

In ground effect conditions, the wake of Quad-copter rotors interacting with the ground causes significant perturbation to the flow near the rotor blades, as well as to the body. These interactions have serious effects on the handling qualities and cause instability in flight. Most studies in the ground effect are focused on hover and landing capabilities of rotorcraft. In this paper, a comprehensive non-linear model of quadrotor is provided in the state-space, which is suitable for all flight types near the ground. First of all, it is tried to add a ground surface quality coefficient in modified ground effect relation by experimental investigations. The experiments have been done in outdoor during calm days with no wind. In the next step, a robust non-linear control strategy is designed based on the modified model. The effects of ground effect and the increase of the advance ratio are then investigated on controller performance. The simulation results show that this model is closer to the actual flight conditions and the stability and the trajectory tracking are significantly improved by implementation of this control strategy. So, this strategy provides an appropriate platform to run other methods without the need for iterative learning techniques and high battery energy consumption. [ABSTRACT FROM AUTHOR]

Abstract This paper reviews lessons learned from the compound helicopter studies performed by NASA and the US Army Aviation Development Directorate to support the NASA Heavy Lift Rotorcraft Systems Investigation and the US Army's Joint Heavy Lift (JHL), Joint Multi-Role Technology Demonstrator (JMR-TD), and Future Vertical Lift (FVL) programs. These studies explored performance potential of advanced rotorcraft and investigated the impact of key modern-technologies in performance, weight, and aerodynamics on rotorcraft. The compound helicopter configurations considered in this paper represent a wide range of sizes, gross weight, rotor systems, and operating conditions. A brief description of design and aeromechanics analysis tools and methodologies is provided. Rotor performance correlation results at high advance ratio, which are critical for the accurate design and analysis of high-speed rotorcraft, are shown. Detailed aeromechanics analysis results, such as the effects of various compounding methods, lift share between rotor and wing, rotor rotational speed, blade twist, aircraft drag, and rotor/wing interference on aircraft performance, are presented. [ABSTRACT FROM AUTHOR]

Abstract The aim of this paper is to assess the accuracy, capabilities and computational performances of the Lattice-Boltzmann/Very Large Eddy Simulation Method to predict the unsteady aerodynamic loads, the rotor wake development and the noise radiation of helicopter rotors in strong Blade-Vortex Interaction conditions. The numerical flow solution is obtained by solving the explicit, transient and compressible Lattice-Boltzmann equation implemented in the high-fidelity CFD/CAA solver Simulia PowerFLOW®. The acoustic far-field is computed by using the Ffwocs-Williams & Hawkings integral solution applied to a permeable surface encompassing the whole helicopter geometry. The employed benchmark configuration is the 40% geometrically and aeroelastically scaled model of a BO-105 4-bladed main rotor tested in the open-jet anechoic test section of the German-Dutch wind tunnel in the framework of the HART-II project. In the present study, only the baseline operating condition of the experimental campaign, without Higher-Harmonic Control enabled, is considered. All simulations are performed by assuming a rigid blade motion, but a computational strategy based on a combination of a rigid blade pitching motion and a transpiration velocity boundary condition applied on the blade surface is employed to take into account the blade elastic deformation motion measured during the experiments. As expected, modeling the blade elastic deformation leads to more accurate predictions of control settings, unsteady air-loads and noise footprint. The effects of the computational grid on the aerodynamic and aeroacoustic prediction is documented as well. [ABSTRACT FROM AUTHOR]

Abstract Incorporating recuperators into gas turbines shows considerable potential for lower emissions and fuel consumption. Nowadays the technology readiness of advanced compact heat exchanger has provided a solid foundation for the availability of lightweight, higher efficient recuperators which would find good acceptance on the rotorcraft without penalizing the operational capabilities. To understand the impact of recuperator on the whole system for further development of future recuperated helicopter, it is proposed to evaluate the potential of recuperated helicopter turboshaft engines with emphasis placed on highly effective primary surface recuperator. This paper presents a comprehensive multidisciplinary simulation framework, and the aircraft configuration selected is a generic helicopter, which is similar to the helicopter Bo105, equipped with two Allison 250-C20B turboshaft engine variants. The improved part-load performance against the reference non-recuperated cycle is discussed first, followed by the analysis and evaluation of two representative flight missions. The study is finally extended to quantify the flight time required to compensate for the additional recuperator weight under the flight condition of 0-250 km/h and 0-3000 m for different recuperator design effectiveness values. It is suggested that the selection of recuperator effectiveness should be dependent on the most commonly involved mission profile and flight duration, in order to offset the added parasitic weight of the recuperator. The established rotorcraft multidisciplinary framework proves to be an effective tool to conduct a comprehensive assessment for the recuperated helicopter under a wide range of flight conditions as well as at mission level. [ABSTRACT FROM AUTHOR]

Abstract The concepts of variable rotor speed and active blade twist constitute promising technologies in terms of improving the operational performance and environmental impact of rotorcraft. Modern civil helicopters typically operate using nearly constant main and tail rotor speeds throughout their operational envelope. However, previous research has shown that decreasing the main rotor speed within salient points of the operational envelope can result in a notable reduction of rotor power requirement, resulting in more efficient aircraft. This work aims to develop an integrated approach able to evaluate the potential improvements in fuel economy and environmental impact through optimum implementation and scheduling of variable rotor speed combined with active blade twist. A comprehensive rotorcraft analysis method is utilized, comprising models applicable to flight dynamics, rotor blade aeroelasticity, engine performance, gaseous emission prediction, and flight path analysis. A holistic optimization strategy comprising methods for Design of Experiment (DOE), Gaussian Process-based (GP) surrogate-modeling, and genetic optimization is developed. The combined framework is used to predict globally optimum variable rotor speed and active blade twist schedules resulting in minimum fuel consumption. The overall method is employed to assess the impact of the investigated concepts for a representative Twin-Engine Light (TEL) helicopter operating within realistic mission scenarios. The optimizations carried out suggest that variable rotor speed combined with active blade twist may result in mission fuel consumption and nitrogen oxides emission (N O x) reductions of the order of 5% and 8%, relative to the fixed rotor speed case. The developed method constitutes an enabling technology for the investigation of novel technologies at multiple levels of assessment including aircraft-engine and mission levels. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an original approach to structural health monitoring of helicopter rotors based on strain measurement on the blades. Three algorithms are presented, one in the time domain and two in the frequency domain. They are based on the analysis of the discrepancies between the strains on damaged and undamaged blades. Two damage types are considered: a mass unbalance at the tip, and a localized stiffness reduction. The performance of the proposed methods is assessed by numerical simulation using a multibody dynamic solver for comprehensive aeroelastic analysis of rotorcraft. The numerical investigation has highlighted the capability of all the presented techniques to detect damages in the blades, even of small entity, in both steady-flight and soft maneuvers. The reduced prediction accuracy in aggressive maneuvered flight suggests the use of these methods only in steady or quasi-steady flight conditions. [ABSTRACT FROM AUTHOR]

Abstract Mars rotorcraft, as an aerial auxiliary platform can assist Mars rover to complete exploration missions, is of great significance in the field of planetary exploration. The complex terrain on Mars limits the working range of the Mars rover, whereas a rotorcraft can acquire high detection speed and efficiency, even fixed-point sample using the ability of vertical takeoff and landing. Very little work has been done to analyze the Mars rotorcraft hovering process and there is also limited experimental data exist on the unique Mars flight conditions. A proper understanding of the hovering process is necessary to design a Mars rotorcraft and verify whether it is appropriate or not. In this work, a modified BEMT-CFD model is developed to analyze inflow distribution in the wingspan direction and to predict the aerodynamic performance of the rotor system. Based on the developed model, a suitable airfoil is selected and the operational parameters are investigated to design a suitable rotor configuration for the Mars rotorcraft. Hover experiments demonstrate that the modified model can effectively predict the rotor hover performance. Using the suitable blade pitch angle and rotational speed, the rotor can generate enough thrust to support a 500 g rotorcraft to fly in the simulated Mars environment. Highlights • A models was built to predict rotor hover performance at low-Reynolds-number. • Airfoil NACA6904 is selected for the rotor by CFD method. • The model can predict the rotor hover performance with error less than 10%. • The rotor can generate thrust for a 500 g rotary-wing aircraft on Mars. • The rotor has maximum FM of 0.58 and PL of 0.47 N/W. [ABSTRACT FROM AUTHOR]

Abstract Icing represents a major problem in the aviation industry. While icing of aerodynamic surfaces such as airfoils due to the impingement of supercooled liquid water droplets is widely studied, even if not yet fully understood, icing of supporting structures like protection grids of engine air intakes has been investigated to a lesser extent. An optimization of the design of the grids will help to reduce icing severity and delaying or avoiding loss of efficiency that could lead to hazardous situations. The present study investigates the icing behaviour of stainless steel protection grids in use on rotorcraft and turboprop engines. New experimental and analytical tools were developed to enable a quantitative study of grid icing under representative icing conditions in a lab-scale icing wind tunnel. The variation of the most relevant parameters like liquid water content of the cloud, airspeed, ambient temperature and mesh size of the grid allowed the identification of their influence on the icing behaviour. Further analysis of the experimental data led to the development and validation of a general physical model for ice accretion on grid structures. Highlights • A physical model was validated for icing of air intake protection grids of engines. • The model describes grid blockage in several icing conditions and configurations. • The model allows to quantitatively evaluate the icing behaviour. • The model predicts grid icing in different operating environmental conditions. • Several in-flight icing scenarios can be implemented in CFD and flight simulations. [ABSTRACT FROM AUTHOR]

Topographic slopes on Titan are reviewed. Cassini radar topographic profiles describe the large scale (10s–1000s of km) while Arecibo and Cassini radar scattering properties inform the wavelength scale (12.6 and 2.2 cm respectively): terrestrial and Martian analog landforms serve as a guide at intermediate scales. Large scale slopes are considerably shallower on Titan than the terrestrial planets or the Moon. Overall slope statistics seem consistent with a fractal Hurst exponent of ∼0.5, although deviations at the ∼1 km dune and ∼2 cm gravel scale may be present. Exponential probability distributions describe the Arecibo slopes and the slope distributions of terrestrial analog terrains. The slope tolerance of previous planetary lander missions, and their actual landed tilts, are summarized and compared with the specifications of terrestrial rotorcraft. These considerations contextualize the design requirements of the Dragonfly lander and other missions. • Reviews slope information on Titan from radar scattering functions and topographic data. • Reviews slope tolerance requirements for helicopters and landing spacecraft. • Discusses slope distributions for various analog terrains, in particular dunes and interdunes. • Considers implications of above for the Dragonfly mission. [ABSTRACT FROM AUTHOR]

In an attempt to reduce acoustic pollution due to terminal flight phases (lift-offs and landings) in the surroundings of heliport, project MANOEUVRES developed a device capable of estimating the acoustic footprint of helicopters on the ground. This device requires knowledge of certain quantities that cannot be directly measured through physical sensors: the tip-path plane angle of attack and the main rotor thrust coefficient. Previous research has demonstrated that these quantities can be accurately estimated using observers that are properly fed with directly measurable flight mechanics and rotor state variables. However, these observers, which are based on linear mathematical models identified offline and employed through interpolation with respect to nominal airspeed, have shown poor robustness when the number of identification input cases is reduced, as required for a realistic design of observers in the field. This issue has particularly emerged when non-trimmed manoeuvres were considered during observation testing. To address this issue, this paper introduces a new baseline for the observation model, which includes dynamic pressure as an additional input. Moreover, a different model structure is considered depending on the observed variable. Specifically, for the tip-path plane angle of attack, a single model covers the entire airspeed range, while observation models for the rotor thrust coefficient are interpolated based on flight altitude. This new approach demonstrates results of comparable or superior quality to previous observation models. Furthermore, it exhibits increased robustness when the pool of identification cases used for observer synthesis is significantly reduced. Such improved performance and ease of synthesis pave the way for the setup and adoption of the proposed observers in the field. [ABSTRACT FROM AUTHOR]

This work introduces a directly coil-actuated cyclic pitch control method for the swashplate-less aircraft. This method drives the rotor to rotate periodically around the pitch axis through a magnetic field. The sensitive parameters that affect pitch motion are analyzed and optimized by simulation. Next, the aerodynamic model of the rotor is established by idealizing the blade as a centrally hinged rigid body with a spring restraint, and then the kinematic model of the rotor system is obtained. A state feedback attitude control method is proposed based on the kinematic model. The feasibility of the directly coil-actuated cyclic pitch control method is verified by comparing the results of mechanical experiments and numerical calculations. Moreover, the attitude response of the rotor system is evaluated through attitude experiments. [ABSTRACT FROM AUTHOR]

Abstract The scope of this paper is the presentation of the computational methodologies applied in the comprehensive code for rotorcraft developed in the last years at Roma Tre University, along with the assessment of its prediction capabilities focused on flight conditions characterized by strong blade–vortex interactions. Boundary element method approaches are applied for both potential aerodynamics and aeroacoustics solutions, whereas a harmonic-balance/modal approach is used to integrate the rotor aeroelastic equations. The validation campaign of the comprehensive code has been carried out against the well-known HART II database, which is the outcome of a joint multi-national effort aimed at performing wind tunnel measurements of loads, blade deflection, wake shape and noise concerning a four-bladed model rotor in low-speed descent flight. Comparisons with numerical simulations available in the literature for the same test cases are also presented. It is shown that, with limited computational cost, the results provided by the Roma Tre aero-acousto-elastic solver are in good agreement with the experimental data, with a level of accuracy that is in line with the state-of-the-art predictions. The influence of the vortex core modeling on aerodynamic predictions and the influence of the inclusion of the fuselage shielding effect on aeroacoustic predictions are discussed. [ABSTRACT FROM AUTHOR]

Velocity estimation is essential for multicopters to guarantee flight stability and maneuverability. For such a purpose, this paper proposes a new method for multicopter velocity estimation based on visual and inertial information in GPS-denied or confined environments. In this method, no map, artificial landmark of the environment is required, and only the off-the-shelf onboard sensors in a multicopter including a low-cost Inertial Measurement Unit (IMU), a downward-looking monocular camera and an ultrasonic range finder facing downwards are exploited to constitute the vision motion constraint. This constraint connects metric velocity with the point correspondences between successive images in which an efficient approach based on Mean Shift (MS) algorithm is developed to detect outliers and select optimal matching points. Then, it is theoretically verified that the estimation system is observable based on observability analysis. Furthermore, combined with the vision motion constraint and a multicopter dynamic model, the metric velocity is estimated using a standard Linear Kalman Filter (LKF). Finally, the proposed method is tested with a collection of synthetic data from simulation as well as flight experiments using real data from DJI Matrice 100 and Guidance. The simulation and experimental results indicate that the proposed method can accurately estimate the velocity of the multicopter in GPS-denied or confined environments. [ABSTRACT FROM AUTHOR]

Abstract A novel kinematic formation controller based on null-space theory is proposed to transport a cable-suspended payload with two rotorcraft UAVs considering collision avoidance, wind perturbations, and properly distribution of the load weight. An accurate 6-DoF nonlinear dynamic model of a helicopter and models for flexible cables and payload are included to test the proposal in a realistic scenario. System stability is demonstrated using Lyapunov theory and several simulation results show the good performance of the approach. Highlights • It is proposed a multi-objective control for cooperative payload transport with rotorcraft UAVs based on null-space theory. • The proposal allows to set on-line the load weight that each vehicle must transport. • Strategies to avoid conflicts of interest between objectives are proposed. • Accurate dynamic models for helicopters, flexible cables and payload are used to test the proposal in a realistic scenario. • System stability is proven using Lyapunov theory and several simulation results show the good performance of the approach. [ABSTRACT FROM AUTHOR]

The paper proposes a simulation approach to evaluate the power required by a rotorcraft in standard flight missions and in emergency landing maneuvers, and the corresponding fuel consumption, in order to compare the feasibility and potential fuel savings for different hybrid power systems. More in detail, three options are analyzed, namely electrification of the tail rotor, fully hybrid electric propulsion and electric emergency landing. Weight penalty and potential fuel saving for the proposed hybridization schemes are evaluated for an Agusta-Westland A109 twin engine helicopter model. Nonetheless the discussed methods of analysis have general validity for single main rotor helicopter configurations. Two different scenarios are considered in this investigation: current technologies for batteries and motors and improved electrical components, with performance projections as of 2040. According to this analysis, electrification of the tail rotor and parallel hybridization are feasible with available technology, whereas a fully electrical power system for emergency landing could be developed only in the future. Finally, a parallel hybrid electric power system is sized according to the analysis of power request over four different missions. Fuel savings are evaluated for different energy management strategies. According to the results of this investigation, the parallel hybrid electric power system with present-day and future technologies can save fuel up to 5% and 12%, respectively, with an appropriate energy management strategy. [ABSTRACT FROM AUTHOR]

This work presents a helicopter dynamic model that captures the fuselage vibrations for an accelerated main rotor. Some rotor parameters are modified with the purpose of study their impact on the rotorcraft. Being this, a tool that allows to predict vibrations on the helicopter. The rotorcraft model has been built up by using VehicleSim, software specialized in modelling mechanical systems composed by rigid bodies. The rotors are articulated, the main rotor takes into account flap, lag and feather degrees of freedom for each of the equispaced blades and their dynamic couplings. The dynamic performance and the control action are embedded in a single code, thereby VehicleSim does not require external connection to other software package. This generates some advantages such as to reduce the compilation time. The control methodology makes use of PID controllers (Proportional, Integral, Derivative), which allows to use VehicleSim commands exclusively. The state space matrices have been obtained in order to analysis the uncoupled main rotor flap and lag modes. The detection of vibrations from the offset flap hinge as well as the lag hinge are not straightforward tasks and this helicopter model provides an accurate tool to study these. A short time Fourier transform processing is used to analysis the vibrations and these have shown to agree with the expected behaviour. [ABSTRACT FROM AUTHOR]

This paper presents the development and an application of a multidisciplinary methodology for the preliminary design assessment of compound coaxial rotorcraft with a counter-rotating rotor system and a rear-mounted propeller. A comprehensive optimisation strategy is deployed to evaluate the environmental and operational benefits of the aforementioned rotorcraft architecture. The code is validated against experimental data prior to the application of the methodology to the evaluation of a conceptual vehicle for intercity taxi applications. Response Surface Models (RSMs) are generated to mimic the rotorcraft performance in order to accelerate the optimisation process. The effects of the defined mission input parameters such as cruise speed, altitude, climb rate or mission length are evaluated. Pareto fronts for fuel burn, N O x emissions and mission duration are obtained. The method was applied to a hypothetical scenario of mission length ranging from 50 to 300 km. Best estimate mission scenario are selected from the Pareto fronts, providing on average 23%, 20%, and 13% simultaneous reductions in mission duration, fuel burn, and N O x emissions when compared to a conventional flight procedure. The picked scenarios coincide with the fuel optimised mission scenarios for each mission length, thus the multi-disciplinary environment was not required. Besides, an “improved” mission procedure is outlined, defining the mission characteristics independently of the mission's length. This procedure yields on average 22%, 14%, and 8% reductions in mission duration, fuel burn, and N O x emissions, respectively. [ABSTRACT FROM AUTHOR]

In this paper, an efficient aerodynamic analysis framework is developed for the conceptual design of lift-fan type aircraft. The lift-fan type aircraft includes and uses a rotor in the body or wing for vertical takeoff and landing, and flies differently from a rotorcraft in cruise/forward flight. Since the lift-fan type aircraft can fly like a fixed wing vehicle during cruise past the transition flight phase, it is possible to overcome the range and velocity limits of conventional rotorcraft. To investigate a wide range of design options during the conceptual design, rapid analyses of various design candidates are significant as high-fidelity analysis may be too expensive. A cost-efficient, lift-fan aircraft aerodynamic analysis (LFAAA) method is developed which consists of a linear potential flow solver with viscous correction, the Blade Element Momentum Theory (BEMT), a Power Induced Effects (PIE) module and momentum drag correction. The greatest advantage of the LFAAA method is low computational cost with considerable solution accuracy as long as the flow conditions are in relatively linear regions, by which the individual component analysis method is derived. Wind-tunnel data of various geometries including an isolated propeller of a UAV, Lockheed Martin innovative control effector (ICE), and YAV-8B Harrier II aircraft are used to validate each component of the LFAAA method, respectively. For the validation of the LFAAA method for comprehensive analysis, a complete geometry of NASA's 1/8 scale model of fan-in-wing (FIW) aircraft is solved and the computation results are validated with the existing wind-tunnel data and unsteady RANS computations. Results predicted by the LFAAA method show good agreements with high-fidelity URANS and wind-tunnel data over the linear flow regimes where no flow separation is observed. [ABSTRACT FROM AUTHOR]

The Mars rotorcraft is an auxiliary aerial exploration platform to expand the rovers' patrol range. Attitude control is a fundamental aspect of autonomous flight control. So far, there has been no detailed investigation of the orientation dynamics of the rotor in the Martian atmosphere. A swashplate mechanism for manipulating isolated rotors is proposed to control the blade pitch angle, whose kinematics equation is established based on the closed condition of space vectors. Considering the blade as a rigid beam flapping around a central hinge, the flapping equation of the hingeless rotor is established to analyze the aerodynamic load for orientation adjusting. The Mars rotorcraft orientation dynamics model is constructed to develop an attitude control algorithm by combining the swashplate kinematics equation and the rotor flapping equation. The orientation experiment is conducted to verify the theoretical model and investigate the response law of the body's heading angle to the cyclic pitch input. The experimental results indicate that the attitude response is more sensitive to the blade pitch angle input under a smaller collective pitch angle or a higher rotor speed. The rigid rotor hypothesis may be unsuitable for the case where the collective pitch angle is smaller than 22°. The hovering flight tests prove that the orientation dynamics model proposed in this paper can effectively support the development of the Mars rotorcraft attitude control system. [ABSTRACT FROM AUTHOR]

A new installation at the Anti-Icing Materials International Laboratory was developed to study the effects of icing on the degradation of a hovering drone rotor aerodynamic performance and to test different potential ice protection solutions. Following a study on icing parameters effects on aerodynamic performance, this paper studies a methodology developed to assess the performances of coatings as a potential ice protection system under severe icing conditions and rotor speeds up to 4950 RPM. Four different coatings, commercial or under development, were applied to the rotor blades and their effect on the resulting ice accumulation and aerodynamic degradation were measured and compared to those previously obtained on similar, uncoated blades. Results show that passive icephobic coatings in general are a promising solution to limit the negative effect of icing conditions for drone applications, without any additional energy consumption from the system. Moreover, the repeatability assessment of tests under similar conditions and for the same coating showed agreement within ±5% between repetitions, showing no signs of ice protection efficiency degradation for any of the tested coatings. • The work of this article marks the continuity of a series of studies done with a new spinning rotor drone test setup in hover flight mode performed at the 9-m high cold chamber of the Anti-Icing Materials International Laboratory (AMIL). Four different surface protection coatings are applied on their own set of blades for testing in the cold room. The resulting ice accumulation and performance degradation of the spinning rotor are then monitored, recorded and compared to the results obtained of bare uncoated blades. The effects and performances of the coatings tested are then assessed. • This report presents a new test methodology and setup to assess the performances of protective surfaces as a passive ice protection system for small and medium drone rotors, which differs than for the rotorcraft application actually found in the literature. It also presented unique results on the possibility of using those surfaces for drones, which cannot be simply deduced from rotorcraft studies found in the literature. This demonstrates the importance of this work and of this new methodology and test setup for the industry since the literature greatly lacks reported data of similar icing tests using ice protection coatings on a UAV. • This first test campaign has proven the ability of icephobic surface coatings to efficiently perform as ice protection systems. Moreover, coatings have a positive potential of being combined with an active ice protection system (such as electrothermal) as a way to reduce the power consumption of those systems. Further research will be done with additional products and also combined with active ice protection systems to help lower their power consumption. [ABSTRACT FROM AUTHOR]

In recent years, the important advances that have been made in unmanned aerial vehicles (UAVs) are being widely applied for civil purposes. However, several difficulties continue to exist in the implementation of missions, such as delivery and surveillance, in the private sector. Autonomous safe landing-area determination for small rotorcraft UAVs (RUAVs) is one of these unresolved issues, for the successful implementation of which adequate terrain information on the potential landing area is necessary. Previously, vision and light detection and ranging (LIDAR)-based methods were investigated for solving this problem. However, these light-based sensors have the disadvantage of being affected by weather or light conditions. The impulse radio ultra-wide band (IR-UWB) radar is a radar sensor with a wide frequency band that generates short-wavelength pulses. It has advantages such as light weight, small size, low power consumption, robustness to external environmental changes, and high range and distance resolutions. In this paper, we propose a novel safe landing-area determination system based on multiple IR-UWB radars, suitable for small RUAVs. Methods for detecting the ground and obstacles and estimating the ground slope and roughness values, based on the signals acquired by multiple IR-UWB radars are proposed. Through experiments, we demonstrate the feasibility and performance of the proposed method. [ABSTRACT FROM AUTHOR]

The problem of attitude tracking control for a miniature rotorcraft with partial loss of actuator effectiveness is investigated in this paper. By using adaptation mechanism and by combining with Nussbaum gain technique, an adaptive tolerant control strategy capable of attenuating immeasurable disturbances, compensating system parameters uncertainties, and accommodating actuation faults is developed. Then, the rotorcraft attitude system subjected to control constraints is further considered, and a novel fault tolerant controller equipped with auxiliary systems is designed to achieve both attitude tracking and saturation alleviation of control signal. Moreover, fault detection and diagnosis unit are not needed in using and implementing the proposed method. It is proven that attitude errors can asymptotically converge to a small neighborhood of equilibrium point in the face of faulty actuator, model uncertainties, external disturbances and even actuator saturation. Finally, the simulation results demonstrate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

The rotorcraft industry has recently shown a new interest in compound rotorcraft as a feasible alternative to tackle the rapid growth of civil aviation activities and associated environmental impact. Indeed, aircraft contribution to the global emissions of CO 2 , NO x , and noise are driving the development of innovative technologies and vehicles. At present, compound rotorcraft architectures are regarded by the industry as promising platforms that can potentially increase productivity at a reduced environmental cost. In order to quantify the benefits of compound rotorcraft, this paper details the performance analysis of a coaxial counter-rotating rotor configuration with a pusher propeller. A comprehensive approach targeting the assessment of the aforementioned rotorcraft design for civil applications is presented herein. The methodology developed encompasses a rotorcraft flight dynamics simulation module and an engine performance module, coupled with a gaseous emissions prediction tool for environmental impact studies. They have been integrated together to constitute a standalone performance simulation framework and verified with the performance calculations of Harrington's “rotor 1” and the Sikorsky X2TD. The method is then applied to evaluate the performance of a conceptual coaxial rotorcraft, during a notional inter-city air taxi mission, in terms of cruise altitude, speed, and range, overall mission time and environmental impact. The several trade-offs between these parameters highlight the need for an integrated optimisation process. Besides, the concept demonstrates the benefits of the compound rotorcraft architecture with a best range speed reaching 90 m/s leading to reduced response times and increase of round trips in a given time. As a consequence, operators will need fewer vehicles and heliports to cover the same areas. This outcome is highly attractive in the current growing market. [ABSTRACT FROM AUTHOR]

Cargo-bearing unmanned aerial vehicles (UAVs) have tremendous potential to assist humans by delivering food, medicine, and other supplies. For time-critical cargo delivery tasks, UAVs need to be able to quickly navigate their environments and deliver suspended payloads with bounded load displacement. As a constraint balancing task for joint UAV-suspended load system dynamics, this task poses a challenge. This article presents a reinforcement learning approach for aerial cargo delivery tasks in environments with static obstacles. We first learn a minimal residual oscillations task policy in obstacle-free environments using a specifically designed feature vector for value function approximation that allows generalization beyond the training domain. The method works in continuous state and discrete action spaces. Since planning for aerial cargo requires very large action space (over 10 6 actions) that is impractical for learning, we define formal conditions for a class of robotics problems where learning can occur in a simplified problem space and successfully transfer to a broader problem space. Exploiting these guarantees and relying on the discrete action space, we learn the swing-free policy in a subspace several orders of magnitude smaller, and later develop a method for swing-free trajectory planning along a path. As an extension to tasks in environments with static obstacles where the load displacement needs to be bounded throughout the trajectory, sampling-based motion planning generates collision-free paths. Next, a reinforcement learning agent transforms these paths into trajectories that maintain the bound on the load displacement while following the collision-free path in a timely manner. We verify the approach both in simulation and in experiments on a quadrotor with suspended load and verify the method's safety and feasibility through a demonstration where a quadrotor delivers an open container of liquid to a human subject. The contributions of this work are two-fold. First, this article presents a solution to a challenging, and vital problem of planning a constraint-balancing task for an inherently unstable non-linear system in the presence of obstacles. Second, AI and robotics researchers can both benefit from the provided theoretical guarantees of system stability on a class of constraint-balancing tasks that occur in very large action spaces. [ABSTRACT FROM AUTHOR]

A helicopter flying through an atmosphere containing particulates may accumulate high electrostatic charges which can challenge its operational safety. In this paper we elaborate and validate a triboelectric charging model to predict the electrification experienced by a helicopter while hovering in dusty air. We employed Large Eddy simulations to describe the turbulent structures inherent in the flow around the rotorcraft. The dust particles were tracked individually in a Lagrangian framework. A model accounting for the triboelectric charge transfer when a particle hits the helicopter was introduced. The results demonstrate the accuracy of the proposed approach and allow a detailed analysis of the location of the charge accumulation. [ABSTRACT FROM AUTHOR]