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Aim: This initial Norwegian study aimed to quantify the vibrations and sounds experienced by neonates when they were transported by helicopter in an incubator. Methods: Two neonatal manikins weighing 500 and 2000 g were placed in a transport incubator and transported in an Airbus H145 D3 helicopter during standard flight profiles. The vibrations were measured on the mattress inside the incubator and the sound levels were measured inside and outside the incubator. Results: The highest vibration levels were recorded during standard flight profiles when the lighter manikin was used. These ranged 0.27–0.94 m/s2, compared to 0.27–0.76 m/s2 for the heavier manikin. The measurements exceeded the action levels set by the European Union Vibration Directive for adult work environments. The sound levels inside the incubator ranged 84.6–86.3 A‐weighted decibels, with a C‐weighted peak level of 122 decibels. The sound levels inside the incubator were approximately 10 decibels lower than outside, but amplification was observed in the incubator at frequencies below 160 Hz. Conclusion: Vibrations were highest for the lighter manikin. The sound levels during helicopter transport were higher than recommended for neonatal environments and sounds were amplified within the incubator at lower frequencies. [ABSTRACT FROM AUTHOR]

This work presents a construction of a novel system for autonomous inspection of power transmission lines using a quadrotor helicopter. The aircraft follows the power lines at a constant distance and acquires high‐resolution images of the conductors, dampers, and towers. Monitoring of the vegetation under the power lines is also performed. The traditional inspection is carried out by helicopters equipped with high‐resolution cameras or by direct visual examination by personnel climbing over de‐energized power lines. However, visual inspection is time‐consuming, labor‐intensive, and dangerous, and often, helicopter cameras cannot capture the acute details needed for accurate and comprehensive examinations. This work successfully evaluates a mathematical model for the quadrotor helicopter used in autonomous inspection through simulations and flight experiments. Two control strategies for power line tracking are compared: a classical PID and a fuzzy PD control. Several simulations and experimental results confirm the efficiency of both control laws, but the fuzzy controller performs better under strong wind disturbances. The results of this work will be implemented by an electric power company to inspect electrical transmission facilities regularly. © 2024 The Author(s). IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineers of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The research explores transition strategies of a coaxial compound helicopter transitioning to pure coaxial-rotor mode following a complete aft propeller failure. For that, a flight dynamics model is developed to predict the transition path, which is formulated as a multiphase trajectory optimization problem. Additionally, a revised aggressiveness indicator is proposed to quantify the transition difficulty. Next, the flight dynamics with and without the propeller and the accelerations at the propeller loss instant are discussed from a trim perspective. Finally, dynamic transitions are meticulously analyzed and compared using a multidimensional radar map to identify an effective strategy. Contrary to the static trim analysis, dynamic simulation results highlight the critical importance of pitch attitude control, longitudinal speed stability, and incidence instability. The potential threats include blade tip collision, significant height increase up to 300 m, and reverse longitudinal stick control regarding pitch attitude. To mitigate these risks and reduce pilot workload, we recommend gradually pitching up to enter the quasi-autorotation state. Additionally, slightly lowering the position of the propeller and maintaining a positive pitch attitude during normal flight can help improve aircraft transition stability. [ABSTRACT FROM AUTHOR]

This research work emphasizes on the development aspects of a cartridge cable cutter for helicopter application. This cartridge is used to rescue hoist system during emergency for helicopter application under adverse conditions. It is an electrically initiated cartridge in which two electrical squibs are used with specified current and voltage. As the cartridge is initiated, the squib gets incandescent and initiates an explosive train. A cartridge cable cutter is a propellant actuated device (PAD) that generates hot combustion gases having high temperature and pressure on burning of gun powder and propellant inside the cartridge case. The cable cutter cartridge under study is filled with energetic materials (EM) such as propellants and gun powder. It releases the energy very quickly which acts on the projectile i.e. the cutter in actual system. A projectile velocity measurement was carried out using Doppler RADAR (radio detection and ranging). To assess the projectile velocity is the unique design feature in armament field. It is responsible for the measurement of the projectile velocity at the muzzle end of velocity test rig (VTR). The minimum and maximum projectile velocities were experimentally measured in between 70 ms−1 and 150 ms−1. The projectile velocity measurement is an evaluation methodology as performance parameter of this cartridge. The cartridge under study has been developed meeting structural, functional and mechanical requirements. The cartridge has undergone various exhaustive qualification tests during development phase. The cartridge was thus designed, qualified and validated through rigorous development trials. The main objective of this article is to address development aspects of the cartridge cable cutter for helicopter application. In conclusion, after successful design, development and qualification trials, the cartridge was found to meet all the functional and operational requirements considering the end use. [ABSTRACT FROM AUTHOR]

The critical role of specifying micro‐Doppler mode performance in the modelling and development of modern radar systems is investigated. The authors focus on the detection of micro‐Doppler modulation from light aircraft, analysing data from eight helicopters and nine propeller aircraft. With the growing need for accurate target classification in radar technology, incorporating micro‐Doppler detection metrics into radar performance specifications has become increasingly important. This research offers a novel approach to measuring the detectability of micro‐Doppler modulation relative to returns from the main fuselage. The investigation covers the impacts of various preprocessing techniques, polarisation, and aspect angle on detection capabilities. Findings reveal that, on average, micro‐Doppler modulation from propellers is detectable at distances between 50% and 100% of the range at which the fuselage is detected. For helicopters, this range decreases to between 30% and 80%. Additionally, the study introduces empirically derived statistical models designed to predict micro‐Doppler detection ranges in relation to fuselage returns, enhancing the predictability and specificity of radar system performance. This novel contribution presents a basis for improving radar system specifications, leading ultimately to more predictable and reliable light aircraft classification. [ABSTRACT FROM AUTHOR]

Research on helicopter dispatching has received considerable attention, particularly in relation to post-disaster rescue operations. The survival chances of individuals trapped in emergency situations decrease as time passes, making timely helicopter dispatch crucial for successful rescue missions. Therefore, this study investigates a collaborative helicopter rescue routing problem with time window and limited survival time constraints, solving it using an improved iterative greedy (IIG) algorithm. In the proposed algorithm, a heuristic initialization strategy is designed to generate an efficient and feasible initial solution. Then, a feasible-first destruction-construction strategy is applied to enhance the algorithm's exploration ability. Next, a problem-specific local search strategy is developed to improve the algorithm's local search effectiveness. In addition, the simulated annealing (SA) method is integrated as an acceptance criterion to avoid the algorithm from getting trapped in local optima. Finally, to evaluate the efficacy of the proposed IIG, 56 instances were generated based on Solomon instances and used for simulation tests. A comparative analysis was conducted against six efficient algorithms from the existing studies. The experimental results demonstrate that the proposed algorithm performs well in solving the post-disaster rescue helicopter routing problem. [ABSTRACT FROM AUTHOR]

This study investigates a novel tracking control with prescribed performance for an uncertain nonlinear 2‐DOF helicopter subject to actuator failure. The control design aims to address partial actuator faults, and to mitigate their effects, an adaptive auxiliary variable is introduced. Additionally, a neural network is employed to accurately approximate the system uncertainties. The prescribed performance is formulated as time‐varying constraints, and the barrier Lyapunov function (BLF) technique is applied to achieve the constrained control. Finally, the stability analysis of the closed‐loop system is provided, and the validity of the proposed control scheme is illustrated through a simulation study on the 2‐DOF helicopter system. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to describe a numerical simulation method of ice accretion on BO105 helicopter blades for predicting the effects of trailing edge flap deflection on ice accretion. Design/methodology/approach: A numerical simulation method of ice accretion is established based on Myers model. Next, the shape and location of ice accretion of NACA0012 airfoil are calculated, and a comparison between calculated results and experimental data is made to validate the method. This method is used to investigate the effect of trailing edge flap deflection on ice accretion of a rotor blade. Findings: The numerical method is feasible and effective to study the ice accretion on helicopter rotor blades. The downward deflection of the trailing edge flap affects the shape of the ice. Practical implications: This method can be further used to predict the ice accretion in actual flights of the helicopters with multielement airfoils. Originality/value: The numerical simulation method here can lay a foundation of the research about helicopter flight performance in icing condition through predicting the shape and location of ice accretion on rotor blades. [ABSTRACT FROM AUTHOR]

This study investigates the potential of an optimized combination of active nose droop and active Gurney flap (CADAG) in a new flow control strategy to manage dynamic stall over a pitching blade section under variable Mach number flow. The optimization method employs the genetic algorithm coupled with a computational fluid dynamic (CFD) solver and artificial neural network. The base blade section belongs to a section positioned at r/R=0.865 of the rotor blade of the UH-60A helicopter in forward flight condition. A high relative angle of attack on the retreating side makes the flow susceptible to dynamic stall. A nose droop is employed to control the dynamic stall of the blade section, and a Gurney flap is used to maintain the balance of the generated lift of the blade during 360° of rotation. A comprehensive investigation is performed to determine the most significant parameters affecting the performance of the present combined active flow control. The ratio of the total generated lift to the drag is chosen as the objective function of the optimization. Results show that this ratio and the total generated lift in one rotation cycle increase by 193% and 13%, respectively, at the optimum condition of the present combined active flow control, while the ratio of the generated lift over the advancing side to the retreating side is equal to that of the base blade section. In addition, the dynamic stall hysteresis loop reduces significantly, and the maximum value of the drag coefficient and the negative aerodynamic damping decrease up to 87% and 83% compared to the base blade section, respectively. In general, the proposed innovative combined active flow control is an adjustable method to alleviate dynamic stall and improve the aerodynamic performance of rotary wings in different operation conditions. Practical Applications: The rotary blades are extensively used in rotorcraft, turbo engines, and wind turbines. Despite their massive use, they suffer from some essential issues, of which the most important one is the so-called dynamic stall. Dynamic stall is a complex phenomenon that limits the performance of the rotary blades. Due to the physics governing a rotary wing, such as a helicopter rotor blade, dynamic stall and flow separation are very common. Understanding dynamic stall physics and providing solutions to prevent it is still one of the main challenges of aerodynamic scientists. The present study introduces a novel adjustable method for practically alleviating the dynamic stall on helicopter blade section in forward flight conditions to improve its aerodynamic performance in different operational conditions. A comprehensive investigation is carried out to determine the key parameters affecting the proposed method. These findings can serve as a valuable tool for other researchers to develop various active flow control strategies. This article applies an optimization process using artificial neural networks, genetic algorithms, and CFD tools, which forms a comprehensive framework that can be easily extended to other applications. [ABSTRACT FROM AUTHOR]

The coaxial compound helicopter has been offered as an idea for a high-performance rotorcraft that possesses high-speed qualities that conventional helicopters do not. This work seeks to create a flight dynamics model of a coaxial compound helicopter and investigate its trim, stability, and controllability. Regarding this, this study builds aerodynamic models for each component of a coaxial compound helicopter (coaxial rotor, fuselage, horizontal stabilizer, vertical stabilizer, and propeller). For coaxial rotor configuration, an equivalent flapping model, a reflected model, an inflow model taking the upper and lower rotor's impact into account, and a phased cyclic pitch model are done. A nonlinear coaxial compound helicopter mathematical model is constructed, and the trim across the entire flight envelope is carried out. The nonlinear model is linearized in order to evaluate stability and control derivatives. The trim results exhibit a high degree of concordance with the reference, thereby validating the flight dynamics model. [ABSTRACT FROM AUTHOR]

This paper presents a novel incremental sliding mode control scheme to address the attitude-tracking issue in both the helicopter and airplane modes of an electric vertical takeoff and landing vehicle, guaranteeing the stabilization of the attitude-tracking error within a predefined time. Firstly, an incremental model of the vehicle's attitude control system with external disturbances is established. The high-order terms of the incremental model and instantaneous perturbations are retained as lumped terms rather than directly discarding them to ensure the accuracy of the incremental model. Then, a novel nonsingular sliding surface is developed. Once the ideal sliding motion is established, the states on the sliding surface will converge to the equilibrium point within a predefined time. Furthermore, a predefined-time incremental sliding mode controller is developed by using sliding mode control and incremental control techniques. It effectively reduces the reliance on the model information and attenuates the effects of external disturbances. The predefined-time stability of the entire controlled system is rigorously proven using Lyapunov theory. Finally, numerical simulation examples verify the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

HeliCAT-DARTS is a high-fidelity rotorcraft dynamics simulator developed for the design and development of rotorcraft for planetary exploration. While initially developed for the life cycle use of the Ingenuity Mars Helicopter mission, the simulator now supports a broad range of rotorcraft configurations and applications. HeliCAT provides a GNC testbed and aerial mobility analysis platform for rotorcraft design, closed-loop flight software development, verification and validation (V&V), and mission operations. This article discusses the design and use of the HeliCAT simulator and results from technology demonstrations and missions. [ABSTRACT FROM AUTHOR]

Sling configurations significantly influence the coupled dynamics of the helicopter with slung load system (HSLS), resulting in alterations to handling qualities (HQs) that remain inadequately understood. This study introduces a computer-oriented, generalized method for constructing the HSLS model with various sling configurations. To evaluate the HQs of 1-point, 2-point, and 4-point sling configurations, both the stability and response criteria outlined in ADS-33E and a newly proposed criterion for slung loads towards the updated ADS-33F were employed. Modal analysis was conducted to elucidate the coupled mechanisms of the HSLS under different sling configurations. The findings reveal that the dynamics of the main rotor can attenuate the lateral swing motions of the load in the 4-point sling configuration. While multiple-point sling configurations can enhance the helicopter's bandwidth, they also amplify the magnitude notch in the helicopter's response. Nevertheless, when a larger hook distance is employed, the notch frequency is sufficiently distant from the load swing bandwidth, leading to a reduced degradation in HQs. A 4-point configuration with lateral and longitudinal hook distances equal to twice the width and length of the slung load is recommended in practice to achieve sufficient swing stability and mitigate HQ degradation. [ABSTRACT FROM AUTHOR]

Abstract The critical role of specifying micro‐Doppler mode performance in the modelling and development of modern radar systems is investigated. The authors focus on the detection of micro‐Doppler modulation from light aircraft, analysing data from eight helicopters and nine propeller aircraft. With the growing need for accurate target classification in radar technology, incorporating micro‐Doppler detection metrics into radar performance specifications has become increasingly important. This research offers a novel approach to measuring the detectability of micro‐Doppler modulation relative to returns from the main fuselage. The investigation covers the impacts of various preprocessing techniques, polarisation, and aspect angle on detection capabilities. Findings reveal that, on average, micro‐Doppler modulation from propellers is detectable at distances between 50% and 100% of the range at which the fuselage is detected. For helicopters, this range decreases to between 30% and 80%. Additionally, the study introduces empirically derived statistical models designed to predict micro‐Doppler detection ranges in relation to fuselage returns, enhancing the predictability and specificity of radar system performance. This novel contribution presents a basis for improving radar system specifications, leading ultimately to more predictable and reliable light aircraft classification.

Abstract This study investigates a novel tracking control with prescribed performance for an uncertain nonlinear 2‐DOF helicopter subject to actuator failure. The control design aims to address partial actuator faults, and to mitigate their effects, an adaptive auxiliary variable is introduced. Additionally, a neural network is employed to accurately approximate the system uncertainties. The prescribed performance is formulated as time‐varying constraints, and the barrier Lyapunov function (BLF) technique is applied to achieve the constrained control. Finally, the stability analysis of the closed‐loop system is provided, and the validity of the proposed control scheme is illustrated through a simulation study on the 2‐DOF helicopter system.

Abstract A signal time‐frequency results inversion method is proposed for extracting micro‐motion features of rotor targets under low signal‐to‐noise ratios (SNRs). In the case of low SNRs, the echo's energy of rotor targets is mainly concentrated in the flash's echo component. Conventional micro‐motion feature extraction of rotor targets primarily utilises the sinusoidal modulation feature in time‐frequency results, whose energy is much lower than the flash. Under low SNRs, the sinusoidal modulation in the echo's time‐frequency results will be submerged in the noise, making feature extraction challenging. A deep learning network is used to inverse the time‐frequency results containing sinusoidal modulation based on the flash's features in the time‐frequency results. Based on the inversion time‐frequency results, the GS‐IRadon algorithm is used to extract micro‐motion features, which can significantly reduce the times of IRadon transformations and improve feature extraction speed and accuracy. Through simulation and analysis, a novel method using a deep learning network like UNet can effectively inverse time‐frequency results under low SNRs, providing a new technical approach for micro‐motion feature extraction. Time‐frequency results inversion is a novelty method used to achieve micro‐motion feature extraction of rotor targets.

Background: At the time of the COVID-19 pandemic, devastating incidents increased due to frequent oxygen administration to patients. The dangers associated with the use of oxygen, especially through local enrichments and formation of "oxygen clouds", have been well understood for years. Nevertheless, dramatic incidents continue to occur, since fire hazard increases exponentially with oxygen concentrations above 23%. Rescue helicopters are at a particular high risk, because of technical reasons such as oxygen use in a very small space, surrounded by kerosene lines, electronic relays and extremely hot surfaces. Methods: In this study three different sized rescue helicopter models (Airbus H135, H145 and MD902) were examined. Oxygen enrichment in the cabin was measured with an oxymeter during a delivery rate of 15 l/min constant flow for 60 min. Furthermore, the clearance of the enriched atmosphere was tested in different situations and with different ventilation methods. To make the airflow visible, a fog machine was used to fill the helicopter cabin. Results: Oxygen accumulation above 21% was detected in every helicopter. After 10–15 min, the critical 23% threshold was exceeded in all three aircrafts. The highest concentration was detected in the smallest machine (MD902) after 60 min with 27.4%. Moreover, oxygen clouds persisted in the rear and the bottom of the aircrafts, even when the front doors were opened. This was most pronounced in the largest aircraft, the H145 from Airbus Helicopters. Complete and rapid removal of elevated oxygen concentrations was achieved only by cross-ventilation within 1 min. Conclusions: Oxygen should be handled with particular care in rescue helicopters. Adapted checklists and precautions can help to prevent oxygen accumulation, and thus, fatal incidents. To our knowledge, this is the first study, which analyzed oxygen concentrations in different settings in rescue helicopters. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to find the characteristics of supercritical airfoil in helicopter rotor blades for hovering phase using numerical analysis and the validation using experimental results. Design/methodology/approach: Using numerical analysis in the forward phase of the helicopter, supercritical airfoil is compared with the conventional airfoil for the aerodynamic performance. The multiple reference frame method is used to produce the results for rotational analysis. A grid independence test was carried out, and validation was obtained using benchmark values from NASA data. Findings: From the analysis results, a supercritical airfoil in hovering flight analysis proved that the NASA SC rotor produces 25% at 5°, 26% at 12° and 32% better thrust at 8° of collective pitch than the HH02 rotor. Helicopter performance parameters are also calculated based on momentum theory. Theoretical calculations prove that the NASA SC rotor is better than the HH02 rotor. The results of helicopter performance prove that the NASA SC rotor provides better aerodynamic efficiency than the HH02 rotor. Originality/value: The novelty of the paper is it proved the aerodynamic performance of supercritical airfoil is performing better than the HH02 airfoil. The results are validated with the experimental values and theoretical calculations from the momentum theory. [ABSTRACT FROM AUTHOR]

Background: Haiti is experiencing a multifaceted crisis marked by severe gang violence and significant economic and social challenges for its people. Despite international interventions, such as the Multinational Security Support mission headed by Kenya, the strategy has been hindered by unclear goals, lack of accountability, and inadequate backing for Haitian institutions. Additional issues include a shortage of armored vehicles, helicopters for medical evacuations, prepared barracks, and proper communications equipment. This mission, which received UN Security Council approval last October, has faced considerable opposition in both Haiti and Kenya. [ABSTRACT FROM AUTHOR]

A coaxial helicopter with a maximum take-off weight of 600 kg was converted to an unmanned aerial vehicle. A minimally invasive robotic actuator system was developed, which can be retrofitted onto the copilot seat of the rotorcraft in a short period of time to enable automatic flight. The automatic flight control robot includes electromechanical actuators, which are connected to the cockpit inceptors and control the helicopter. Most of the sensors and avionic components were integrated into the modular robotic system for faster integration into the rotorcraft. The mechanical design of the control system, the development of the robot control software, and the control system architecture are described in this paper. Furthermore, the multi-body simulation of the robotic system and the estimation of the linear low-order actuator models from hover-frame flight test data are discussed. The developed technologies in this study are not specific to a coaxial helicopter and can be applied to the conversion of any crewed flight vehicle with mechanical controls to unmanned or fly-by-wire. This agile development of a full-size flying test-bed can accelerate the testing of advanced flight control laws, as well as advanced air mobility-related functions. [ABSTRACT FROM AUTHOR]

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In this paper, a composite finite-time prescribed performance tracking control scheme is presented for an unmanned helicopter (UH) system subject to performance constraints, model uncertainties and external perturbations. A new finite-time neural network disturbance observer (FTNNDO) with adaptive laws is designed to deal with the external disturbances and model uncertainties, which not only accelerate the convergence rate in finite time but also eliminate the complicated differential calculation in the traditional backstepping scheme. Using the continuous adaptive law, the neural network (NN) approximate errors can be effectively estimated and compensated online without the chattering and gain overestimation caused by traditional methods, thus further enhancing the robustness of the system. To constrain the tracking performance of the transient process and steady-state accuracy, a novel prescribed performance function is designed to preset the tracking errors within prescribed boundaries. Based on the FTNNDO and barrier Lyapunov function (BLF), an improved finite-time tracking controller is designed to achieve fast convergence with prescribed performance. By using Lyapunov synthesis, it is strictly proven that the finite-time convergence of the closed-loop control system can be achieved and tracking errors are always within the prescribed performance bounds. In the end, simulation results for the UH tracking control system are given to demonstrate the effectiveness of developed control scheme. [ABSTRACT FROM AUTHOR]

In order to realize the most economical operation of helicopter power system, the optimal rotor speed control method is proposed and designed. Firstly, the simplified performance calculation model of helicopter required power and turboshaft engine are established, which constitute the performance calculation model of helicopter power system together. Then, according to the above model, through applying blade loading constraint and selecting the minimum engine fuel flow as the optimization objective, an integrated optimization method of optimal rotor speed based on golden section method is proposed, which reveals the variation law of optimal rotor speed under different operation conditions. Finally, the numerical simulation and hardware-in-loop (HIL) simulation are conducted separately to validate the optimal rotor speed control method. The results indicate that compared with constant rotor speed operation, optimal rotor speed control method can decrease engine fuel flow by more than 21 %, which proves the significant effectiveness and satisfactory feasibility. The optimal rotor speed control method ensures that the helicopter power system operates at the optimal rotor speed, and is beneficial to reach the most economical cruise target. [ABSTRACT FROM AUTHOR]

Determining the guaranteed operational time of helicopter blades is one of the important tasks necessary for successful vehicle use. Flight tests on different modes and special fatigue benches are used to solve such problems. The loads recorded during the flight are applied to ground tests on a bench. The ground fatigue tests of the ultralight helicopter blades have features associated with the influence of the scale factor comparison with the big helicopters. These features are presented in this article as the example of a ground test for a VA115 helicopter blade and a method of recalculating data. The purpose of these tests was to confirm the guaranteed service life of blades and define a reliable method for it. [ABSTRACT FROM AUTHOR]

This article presents the development and implementation of active noise abatement flight control laws utilizing redundant control allocation in rotorcraft. The study starts by finding a periodic equilibrium of coupled rotorcraft flight dynamics and acoustics using a modified harmonic balance trim solution method. Next, the rotorcraft nonlinear time-periodic dynamics are linearized about its periodic equilibrium and transformed into an equivalent higher-order linear time-invariant system in harmonic decomposition form. Composite aeroacoustic measures are formulated as outputs of this system. To enable faster runtime and tractable control design, a reduced 8-state model representative of the coupled rigid-body dynamics and acoustics is obtained through residualization. An explicit model following control law with pseudoinverse allocation to redundant control surfaces--an active horizontal stabilizer in this study--is synthesized using the 8-state model. The article further assesses the impact of noise alleviation control on handling qualities of conventional and compound rotorcraft in forward flight. The results demonstrate that redundant control allocation is an effective method for active reduction of unsteady rotor noise, with increasing effectiveness during aggressive maneuvers. Future-generation rotorcraft, particularly future vertical lift configurations featuring high control redundancy and aggressive maneuvering capabilities, can significantly benefit from noise abatement through redundant control allocation. Furthermore, the article highlights that while implementing noise abatement control in conventional helicopters can degrade handling qualities, the use of redundant control allocation in compound configurations offers noise reduction without compromising handling qualities. [ABSTRACT FROM AUTHOR]

This paper explores the synthesis of a novel load alleviation scheme based on active rotor control for critical helicopter component life extension. The proposed load alleviation scheme is innovative as it demonstrates how individual blade control (IBC) and model prediction can be combined using higher-order linear time-invariant models to develop a life-extending control scheme. Using a reduced-order coupled body-rotor-inflow dynamic model onboard the vehicle and a cost function, cost-minimizing higher harmonic IBC inputs are computed over a selected time horizon and used to reduce selected harmonics of component loads during flight. The proposed component load alleviation using the IBC scheme is implemented in a comprehensive nonlinear model of a generic helicopter to evaluate its performance. Nonlinear model simulations show that significant individual harmonic load reduction can be obtained with very little impact on the maneuver performance, vibratory hub loads, and uncontrolled harmonics of component loads. Furthermore, using the handling qualities requirement on small-amplitude pitch changes in forward flight, alongside the pitch attitude and agility quickness metrics, it is demonstrated that the proposed scheme does not cause handling qualities degradation. [ABSTRACT FROM AUTHOR]

The article's main provisions are the development and application of a neural network method for helicopter turboshaft engine thermogas-dynamic parameter integrating signals. This allows you to effectively correct sensor data in real time, ensuring high accuracy and reliability of readings. A neural network has been developed that integrates closed loops for the helicopter turboshaft engine parameters, which are regulated based on the filtering method. This made achieving almost 100% (0.995 or 99.5%) accuracy possible and reduced the loss function to 0.005 (0.5%) after 280 training epochs. An algorithm has been developed for neural network training based on the errors in backpropagation for closed loops, integrating the helicopter turboshaft engine parameters regulated based on the filtering method. It combines increasing the validation set accuracy and controlling overfitting, considering error dynamics, which preserves the model generalization ability. The adaptive training rate improves adaptation to the data changes and training conditions, improving performance. It has been mathematically proven that the helicopter turboshaft engine parameters regulating neural network closed-loop integration using the filtering method, in comparison with traditional filters (median-recursive, recursive and median), significantly improve efficiency. Moreover, that enables reduction of the errors of the 1st and 2nd types: 2.11 times compared to the median-recursive filter, 2.89 times compared to the recursive filter, and 4.18 times compared to the median filter. The achieved results significantly increase the helicopter turboshaft engine sensor readings accuracy (up to 99.5%) and reliability, ensuring aircraft efficient and safe operations thanks to improved filtering methods and neural network data integration. These advances open up new prospects for the aviation industry, improving operational efficiency and overall helicopter flight safety through advanced data processing technologies. [ABSTRACT FROM AUTHOR]

Double-propeller compound high-speed unmanned helicopter, which is currently one of the hottest research topics in high-speed aircraft, has the advantages of both helicopter and fixed wing aircraft. In this paper, the flight-dynamics related analysis and manipulation strategy research of the double-propeller compound high-speed unmanned helicopter are carried out. The aerodynamic interference model of rotor to wing is constructed by using the interference factor, and the fuselage model is based on the wind tunnel test data. Then, the nonlinear flight dynamics model of double-propeller compound high-speed unmanned helicopter is presented. In view of the problem of control redundancy, a manipulation strategy is proposed, which allocates the control channel with the weight coefficient, and controls the forward flight speed by the longitudinal channel of the mean propeller pitch. On this basis, the smooth transition of each rod between the three modes is realized, which verifies the rationality of the control strategy. [ABSTRACT FROM AUTHOR]

AbstractThe unique mission of the helicopter compared to the fixed-wing aircraft introduces challenges to the aerodynamic stability of the turboshaft engine. Thus, the assessment of the availability of stability margin for special operating conditions in the envelope of this equipment is required to guarantee flight safety. In this paper, a rapid nonlinear complete engine method is developed to investigate the effect of helicopter ground-effect operation and high-altitude hovering on aerodynamic stability by considering factors including inlet distortion and component matching. Research indicated that the most dangerous point of stability margin in a unique section of the flight envelope is high altitude hovering, with about a 16.7% reduction in available stability margin compared to standard ground test conditions. This paper also investigates the effects of typical helicopter ground effects on a turboshaft engine and shows that the stability margin will be reduced by a maximum of 1.43% in hovering if the influence of ground effects in the flight envelope is not considered in the design. [ABSTRACT FROM AUTHOR]

Featured Application: The research in this paper can provide a feasible technical means for the assembly sequence optimization of aviation reducers with complex structures, effectively promote the progress of the complex assembly sequence optimization technology of aviation reducers, and realize the comprehensive evaluation of the overall assembly quality and performance index of aviation reducer products. It can be applied to the assembly control of tanks, armored vehicles, ships, and other complex equipment to improve their assembly quality. An assembly sequence evaluation is one of the most important research directions of assembly sequence planning (ASP) for complex mechanical transmission products. Currently, aviation reducers lack a multi-perspective and multi-level evaluation of their assembly sequence. The existing evaluation indicators vary. The evaluation methods have low effectiveness and poor practicability. Therefore, a comprehensive multidimensional evaluation method for complex assembly sequences is proposed in this paper. A multidimensional comprehensive evaluation of the overall assembly quality and performance indices of aviation reducer products is realized. Firstly, the main factors affecting assembly sequence planning are considered: the attributes of the basic unit parts and the cost control of the assembly process. An evaluation index system of assembly sequence planning based on the two dimensions of assembly cost and ontology is constructed. Then, according to the multidimensional evaluation index, fuzzy evaluation theory is used to establish a fuzzy set and a matrix for each dimensional evaluation index. The index weight is divided. A comprehensive evaluation model and the function of each dimension are established. After a comprehensive evaluation, the multidimensional assembly sequence evaluation method for aviation reducers is formed. Finally, the method is applied to the assembly process of the primary reducer of a helicopter's main reducer, and a comprehensive evaluation of its assembly sequence scheme is completed to verify the feasibility of the proposed method. This article constructs a complex assembly sequence evaluation method that includes 12 evaluation indicators, improves the assembly sequence planning evaluation index system of aviation reducers, and can effectively promote the progress of optimization technology for complex assembly sequences of aviation reducers. [ABSTRACT FROM AUTHOR]

This paper presents an overview on the state of the art in copter drones and their components. It starts by providing an introduction to unmanned aerial vehicles in general, describing their main types, and then shifts its focus mostly to multirotor drones as the most attractive for individual and research use. This paper analyzes various multirotor drone types, their construction, typical areas of implementation, and technology used underneath their construction. Finally, it looks at current challenges and future directions in drone system development, emerging technologies, and future research topics in the area. This paper concludes by highlighting some key challenges that need to be addressed before widespread adoption of drone technologies in everyday life can occur. By summarizing an up-to-date survey on the state of the art in copter drone technology, this paper will provide valuable insights into where this field is heading in terms of progress and innovation. [ABSTRACT FROM AUTHOR]

A signal time‐frequency results inversion method is proposed for extracting micro‐motion features of rotor targets under low signal‐to‐noise ratios (SNRs). In the case of low SNRs, the echo's energy of rotor targets is mainly concentrated in the flash's echo component. Conventional micro‐motion feature extraction of rotor targets primarily utilises the sinusoidal modulation feature in time‐frequency results, whose energy is much lower than the flash. Under low SNRs, the sinusoidal modulation in the echo's time‐frequency results will be submerged in the noise, making feature extraction challenging. A deep learning network is used to inverse the time‐frequency results containing sinusoidal modulation based on the flash's features in the time‐frequency results. Based on the inversion time‐frequency results, the GS‐IRadon algorithm is used to extract micro‐motion features, which can significantly reduce the times of IRadon transformations and improve feature extraction speed and accuracy. Through simulation and analysis, a novel method using a deep learning network like UNet can effectively inverse time‐frequency results under low SNRs, providing a new technical approach for micro‐motion feature extraction. Time‐frequency results inversion is a novelty method used to achieve micro‐motion feature extraction of rotor targets. [ABSTRACT FROM AUTHOR]

This work addresses the problem of planning and tracking collision-free trajectories with a laboratory helicopter restrained to three degrees of freedom (DOF) using model predictive control (MPC) with mixed-integer programming (MIP) encoding. We propose a multirate structure that divides the system dynamics into slower and faster modes. The MPC-MIP is then employed to directly control only the slower portion, allowing it to operate in a closed loop in spite of its relatively time-demanding optimizations. Experimental results show that the proposed control structure allows the computation of globally optimal trajectories and controls with the required frequency, resulting in the successful maneuvering of the helicopter toward a target in an obstacle-filled environment. [ABSTRACT FROM AUTHOR]

The shape and structure of helicopter fuselage are complex, and it is difficult for a finite element method (FEM) to investigate helicopter fuselage projectile damage in a multi-projectile environment. An efficient analysis method for helicopter fuselage projectile damage is then proposed by coupling the projectile breakdown theory, which is derived from the existing empirical formula for penetrating ductile metals, and the model of projectile impact. Then, the characteristics of the helicopter fuselage impact coordinate, residual velocity, and fuselage damage area under a multi-projectile attack are investigated. The results show that the predicted residual velocities agree with the experiments. The maximum errors of the residual velocity and the fuselage damage area are 4.7% and 9.56%, respectively. Compared with the FEM, the computational time of the proposed method is reduced by 92.1%, and its efficiency is obviously improved. As the incidence angle increases, the residual velocity decreases, and the damage area increases. When the incidence angle of the projectile body is large, the projectile body cannot penetrate the surface of the fuselage, resulting in flume skid damage and a large area of damage. [ABSTRACT FROM AUTHOR]

This paper proposes an advanced model predictive control (MPC) scheme for the attitude tracking of coaxial drones under wind disturbances. Unlike most existing MPC setups, this scheme embeds steady-input, steady-output, and steady-state conditions into the optimization problem as decision variables. Consequently, the coaxial drone's attitude can slide along the state manifold composed of a series of steady states. This allows it to move toward the optimal reachable equilibrium. To address disturbances that are difficult to accurately measure, an extended state observer is employed to estimate the disturbances in the prediction model. This design ensures that the algorithm maintains recursive stability even in the presence of disturbances. Finally, numerical simulations and flight tests are provided to confirm the effectiveness of the proposed method through comparison with other control algorithms. [ABSTRACT FROM AUTHOR]

In this study, the influence laws of different parameters on the exclusion characteristics of hailstone and ice flake, and on the aerodynamic performance of the inlet are studied by numerical method. The motion of the hailstone and ice flake is simulated using the 6-DOF method. Results show that the inhalation of hailstone in the inlet decreases total pressure distortion by about 20%, and the total pressure recovery coefficient is essentially unchanged. Icing of the upper lip decreases the total pressure distortion of the inlet by about 22%, and the total pressure recovery coefficient decreases by 0.6%. The ice flakes on the inner and outer lip, when shed and brake by collision with the center body, will cause damage to the engine duct. The shedding and breaking of ice flake at an angle of 150° to the lip can result in a large amount of ice flake debris entering the engine duct, threatening the performance and structure of the engine in the rear. The motion characteristics of hailstone and ice flake under helicopter fuselage/rotor/inlet integration conditions are revealed. It also provides a reference on the numerical methods for the numerical study of hailstone/ice flake exclusion characteristics of helicopter fuselage/rotor/inlet integration conditions. [ABSTRACT FROM AUTHOR]

Most accidents and serious incidents of commercial air transport helicopters occur during standard flight phases, whereby a main cause is pilots' situational awareness. Enabling pilots to better assess their situational awareness can make an important contribution in reducing the risk of fatal accidents. One approach is to examine a pilot's gaze behavior with the help of eye tracking. This paper reports the results of a case study with eye tracking measurements during real flight and simulator studies of a standard mission profile. The general gaze behavior is characterized by a dominant, external view, and the airspeed and altitude indicator as the most important flight instruments. A real-world applicability of gaze data obtained in the simulator could be shown. [ABSTRACT FROM AUTHOR]

Due to their complex aerodynamics, helicopters may enter different dangerous aerodynamic conditions under certain adverse circumstances. In this paper, we examine one such phenomenon—the Vortex Ring State (VRS). We present a simulation of the formation and evolution of a vortex ring around a helicopter's main rotor. The calculations were carried out by solving Navier–Stokes equations using the Ansys CFX code. The simulations modeled a real helicopter using the rotor wing concept, assuming that only the main rotor blade's geometry was modeled. A sensitivity study assessed the impact of the calculation domain and mesh size on main rotor thrust and required moment parameters. Simulations were conducted to determine the VRS region by observing the transition of the helicopter from a level flight, with the main rotor blades held at a fixed pitch position, to a gradual increase in vertical descent. The VRS region was compared with experimental results obtained from other authors, revealing sufficient coincidences. The main characteristics of the identified region were then described. [ABSTRACT FROM AUTHOR]