Helicopter Flight Research Articles

An improved dynamic model identification method for small unmanned helicopter

PurposeThe purpose of this paper is to introduce an improved system identification method for small unmanned helicopters combining adaptive ant colony optimization algorithm and Levy’s method and to solve the problem of low model prediction accuracy caused by low-frequency domain curve fitting in the small unmanned helicopter frequency domain parameter identification method.Design/methodology/approachThis method uses the Levy method to obtain the initial parameters of the fitting model, uses the global optimization characteristics of the adaptive ant colony algorithm and the advantages of avoiding the “premature” phenomenon to optimize the initial parameters and finally obtains a small unmanned helicopter through computational optimization Kinetic models under lateral channel and longitudinal channel.FindingsThe algorithm is verified by flight test data. The verification results show that the established dynamic model has high identification accuracy and can accurately reflect the dynamic characteristics of small unmanned helicopter flight.Originality/valueThis paper presents a novel and improved frequency domain identification method for small unmanned helicopters. Compared with the conventional method, this method improves the identification accuracy and reduces the identification error.

Ascending with ultrasound: telementored eFAST in flight—a feasibility study

PurposeTeleultrasound uses telecommunication technologies to transmit ultrasound images from a remote location to an expert who guides the acquisition of images and interprets them in real time. Multiple studies have demonstrated the feasibility of teleultrasound. However, its application during helicopter flight using long-term evolution (LTE) for streaming has not been studied. Therefore, we conducted a study to examine the feasibility of teleultrasound in an Airbus H145 helicopter.MethodsFour anesthesiologists and one military physician were recruited to perform telementored extended Focused Assessment with Sonography in Trauma (eFAST) during nine helicopter flights, each with a unique healthy volunteer. A radiologist was recruited as a remote expert, guiding the physicians in their examinations. The examining physicians reported the user experience of telementored eFAST on a questionnaire, while the remote expert rated the diagnostic quality of the images on a 1–5 Likert scale. In addition, we measured the duration of the examinations and key LTE network parameters including signal strength, quality, and continuity.ResultsThe images were rated to an average of 4.9 by the remote expert, corresponding to good diagnostic quality. The average duration of telementored eFAST was 05:54 min. LTE coverage was negatively affected by proximity to urban areas and ceased above 2000 ft altitude. Occasional audio problems were addressed by using the Voice over LTE network for communication. The examining physicians unanimously reported on the questionnaire that they would use telementored eFAST on patients.ConclusionTelementored eFAST is feasible in ambulance helicopters and can produce images of good diagnostic quality. However, it relies on stable LTE coverage, which is influenced by many factors, including the helicopter’s altitude and flight path. Furthermore, its benefit on patient outcomes remains to be proven.Graphical abstract

Breakdown characteristics and influencing factors of live 500 kV insulators sprayed by extinguishing agents using helicopters

Regarding the problem that helicopters cannot spray live transmission conductors and wildfires directly under an insulator, we built a full-scale 500 kV insulator flashover test platform to simulate high-altitude helicopters spraying fire extinguishing agents. The chemical formulation, spray intensity, and fragmentation method of the fire extinguishing agents were varied. We simulated the breakdown characteristics of insulators when helicopters spray fire extinguishing agents, revealing the mechanism of high-altitude live fire extinguishment for high-spray-intensity and high-conductivity agents. Furthermore, an insulation performance verification test of a helicopter spraying live equipment at different flight speeds and altitudes was carried out, and the behavior of the fire extinguishing agents was divided into a five-zone diffusion law consisting of the (1) water column, (2) continuous water block, (3) semi-continuous water body, (4) large droplet particles, and (5) small droplet particles. We propose a spraying live transmission line method in which the helicopter flight height and speed jointly control the particle size of the fire extinguishing agent. When the particle size of the fire extinguishing agent at the terminal is controlled to 560–4000 μm, the insulation performance of the fire extinguishing agent can be effectively improved. During high-incidence periods of wildfires, such as the Spring Festival and Qingming Festival in 2023, on-site firefighting on the Hunan power grid was performed using helicopters to spray fire extinguishing agents from top to bottom through live transmission conductors to extinguish wildfire disasters directly below the transmission conductors. Neither transmission line flashovers nor power outages occurred when the fires were extinguished.

Association of Geographic Distance and Hospital Characteristics With Use of Interhospital Transfer by Air: A Multicenter Retrospective Study

ObjectiveInterhospital transfer by air (IHTA) represents the majority of helicopter air ambulance transports in the United States, but the evaluation of what factors are associated with utilization has been limited. We aimed to assess the association of geographic distance and hospital characteristics (including patient volume) with the use of IHTA. MethodsThis was a multicenter, retrospective study of helicopter flight request data from 2018 provided by a convenience sample of 4 critical care transport medicine programs in 3 US census regions. Nonfederal referring hospitals located in the home state of the associated critical care transport medicine program and within 100 miles of the primary receiving facility in the region were included if complete data were available. We fit a Poisson principal component regression model incorporating geographic distance, the number of emergency department visits, the number of hospital discharges, case mix index, the number of intensive care unit beds, and the number of general beds and tested the association of the variables with helicopter emergency medical services utilization. ResultsA total of 106 referring hospitals were analyzed, 21 of which were hospitals identified as having a consistent request pattern. Using the hospitals with a consistent referral pattern, geographic distance had a significant positive association with flight request volume. Other variables, including emergency department visit volume, were not associated. Overall, the included variables offered poor explanatory power for the observed variation between referring facilities in the use of IHTA (r2 = 0.09). Predicted flights based on the principal component regression model for all referring hospitals suggested the majority of referring hospitals used multiple flight programs. ConclusionGeographic distance is associated with the use of IHTA. Unexpectedly, most basic hospital characteristics are not associated with the use of IHTA, and the degree of variation between referring facilities that is explained by patient volume is limited. The evaluation of nonhospital factors, such as the density and availability of critical care or advanced life support ground emergency medical services resources, is needed.

Analysis of Pilot Distance Estimation in Different Lighting and Visibility Conditions

Several studies on distance and size estimation have focused on normal and night vision goggles (NVGs), but none of them have been performed during the twilight period. Hence, in this study, distance was estimated for the first time during nautical twilight. According to the findings, the accuracy of distance estimation reduces as visibility decreases and is restricted. When compared with Day Limited Helmet Mounted Display Vision (M = 5.27, SD = .59), Twilight Normal Vision (M = 5.33, SD = .69) and Twilight Helmet Mounted Display Vision (M = 5.20, SD = .61), NVG (M = 4.79, SD = .57) appears to have a lower error rate. In this study, distance was estimated considering objects determined during the helicopter flight by the pilots in different visibility conditions, which are significant in the field of aviation. This work is unique owing to its coverage of helicopter pilots and the estimation during the twilight period. In view of our findings, it may be reasonable to postpone the planned helicopter flights during poor visibility conditions.

Deep Learning Based Obstacle Awareness from Airborne Optical Sensors

Aviation statistics identify collision with terrain and obstacles as a leading cause of helicopter accidents. Assisting helicopter pilots in detecting the presence of obstacles can greatly mitigate the risk of collisions. However, only a limited number of helicopters in operation have an installed helicopter terrain awareness and warning system (HTAWS), while the cost of active obstacle warning systems remains prohibitive for many civil operators. In this work, we apply machine learning to automate obstacle detection and classification in combination with commercially available airborne optical sensors. While numerous techniques for learning-based object detection have been published in the literature, many of them are data and computation intensive. Our approach seeks to balance the detection and classification accuracy of the method with the size of the training data required and the runtime. Specifically, our approach combines the invariant feature extraction ability of pretrained deep convolutional neural networks (CNNs) and the high-speed training and classification ability of a novel, proprietary frequency-domain support vector machine (SVM) method. We describe our experimental setup comprising the CNN + SVM model and datasets of predefined classes of obstacles—pylons, chimneys, antennas, TV towers, wind turbines, helicopters—synthesized from prerecorded airborne video sequences of low-altitude helicopter flight. We analyze the detection performance using average precision, average recall, and runtime performance metrics on representative test data. Finally, we present a simple architecture for real-time, onboard implementation and discuss the obstacle detection performance of recently concluded flight tests.

Dynamic Strain Measurement of Rotor Blades in Helicopter Flight Using Fiber Bragg Grating Sensor.

Fiber Bragg grating (FBG) sensor has a lot of advantages over the resistance strain gauge and has been used in many applications. However, there are few applications of rotor blade dynamic measurement in helicopter flight. In this paper, a method for blade dynamic strain measurement using an FBG sensor in a helicopter's real flight is presented. The corresponding measurement system is established and can eliminate the effects of the helicopter's electromagnetic environment on the electrical sensing components in the measurement system with the orthogonal frequency-division multiplexing modulation. The measured dynamic strains on the rotor blades of the helicopter in real flight contain six harmonic frequencies with the vibration characteristics of rotor blades, indicating that the established FBG measurement method and system have practical engineering applications.

Unwanted Supplementary Vibrations of Helicopter Radio Communication Systems

A helicopter in flight can be considered an unstable dynamic system with many unwanted vibrations originating from multiple sources, such as the operation of the engines and individual components. These vibrations cause the degradation of the structural and functional components of a helicopter, thereby generally reducing the utility and technical efficiency of the aircraft. During the analysis of frequently recurring errors of medium-heavy helicopters, partial damage to antenna elements with vertical polarisation was detected. These damages provided the basis for the presented research, based on which supplementary vibrations caused by unwanted electromagnetic oscillations were revealed. These oscillations were detected in the process of communication between the helicopter crew and the ground ATC (air traffic control) station. This phenomenon’s existence and negative influence were confirmed via measurements and modal analysis, based on which an exact synergy between harmonic frequencies of the helicopter’s normal vibrations was discovered. The obtained results serve as a theoretical and practical basis for the future monitoring of this phenomenon, especially in the process of determining the “health status” of medium-heavy helicopters.

A multi-model and multi-objective approach to the design of helicopter flight control laws

A multi-model and multi-objective approach to the design of helicopter flight control laws

Evaluation of sequential algorithms for solving the problem of measuring the angular coordinates of low-flying radar targets

The problem of measuring the angular coordinates of low-flying radar targets has been known for a long time [1, 2] and is still relevant and unresolved, which is confirmed by a large number of articles that propose methods and algorithms to improve the accuracy of measuring angular coordinates, demonstrate the development of aerial objects capable of flying at low and ultra-low altitude [3, 4]. Confirmation of relevance can be seen from the recent situation [5, 6], the reason for which is the flight of helicopters at low altitude. The paper proposes a method for accounting for shading for a mathematical model of a signal reflected from a low-flying radar target and a method for forming a two-dimensional sea surface, which reduces the amount of calculations. The result of the analysis of sequential algorithms showed the lack of direction resolution, which is eliminated by the long signal accumulation time, which can be critical at high object speed. The change in frequency from pulse to pulse shortened the accumulation time, since the change in the nature of reflection affected the rate of change in the phase difference. The results of the study can be applied in the development of algorithms for measuring the angular coordinates of low-flying radar targets and their semi-natural testing.

Research on General Structure of Double Returns Vertical Wind Tunnel

Vertical wind tunnels play very important role in parachute training, helicopter rotor test, flight experience and other aspects, among which the double returns vertical wind tunnel has spread widely due to its low lose and low running cost. By using innovative structure design and finite element method, the general layout, research on design of supports and important sections are completed. The design part mainly describes glass flight section, integrated fan section, wind speed adjust device, ventilation door and the whole raft foundation structure. The dynamic debugging results show that the double return vertical wind tunnel has rational design, little vibration and high efficiency.

Satellite-Linked Remote Physiologic Monitoring During Simulated Rural Ground Ambulance and Rotor Wing Transports

Telemedicine and remote monitoring are rapidly gaining momentum in health care, including in-home and postdischarge monitoring. However, remote monitoring for telemedicine teams and receiving medical centers is yet to reach emergency medical services. When transporting a critically ill patient, continuous vital sign monitoring may be helpful to enhance receiving center collaboration and change care delivery before arrival when necessary. Our primary objective was to demonstrate successful transmission and reception of real-time physiologic summary data to a hospital base station during ambulance transport using a low-energy Bluetooth wireless wearable device linked to iridium satellite communications. We completed our proof-of-concept study on 2 simulated ground ambulance transports and 1 helicopter flight in rural areas surrounding Rochester, Minnesota. Each simulated transport used Mayo Clinic–developed wearable devices paired one-to-one with a physiologic communication kit. Electrocardiographic and photoplethysmographic waveforms were processed on the wearables every 5 minutes, with vital sign data generated and transmitted to an iridium satellite and relayed to a base station network–protected computer and mobile application with real-time display of summary and location. Data and geolocation were tracked in real time with a mobile application during the simulated transport, and summary data packets were saved on Mayo Clinic servers. During the 3 simulated rural transports, all (n=7; 100%) wearables successfully captured, recorded, and transmitted raw waveform physiologic signals. All devices transmitted successfully via the iridium satellite to the base station network–protected computer and mobile application. In all, 106 (69%) of 154 transmissions were successfully processed. Our project demonstrated successful remote monitoring of physiologic vital signs during transport in rural, low–cellular signal areas. The use of live remote monitoring should be explored to understand its utility in practice and outcomes.

The development of the helicopter non-technical skills (HeliNOTS) behavioural marker systems

Behavioural marker systems (observational frameworks geared towards the assessment of non-technical skills by way of behavioural markers) exist across a variety of high-risk occupations, however, no identifiable system currently exists developed from rotary operative data. In this study, discussion groups (n = 9) were undertaken with subject matter experts (n = 20)—including pilots and technical crew operating across search and rescue and offshore transport environments—with the objective of identifying role-specific behavioural markers. Systems were reviewed on an iterative basis by the academic team and received final reviews by additional subject matter experts (n = 6). Two behavioural marker systems were constructed: HeliNOTS (O) for offshore transport pilots and HeliNOTS (SAR) for search and rescue crews; each with domain-specific behavioural markers. Both represent a significant step towards a nuanced approach to training and assessment of helicopter flight crews’ non-technical skills and are the first publicly available systems tailored to these distinct mission types. Practitioner summary: There is no publicly available behavioural marker system based on data from rotary operatives. Across this study, two prototype systems were developed: HeliNOTS (SAR) for helicopter search and rescue, and HeliNOTS (O) for helicopter offshore transport. Both HeliNOTS systems represent a nuanced approach towards rotary CRM training and assessment.

Flight data-driven intelligent prediction for fuselage vibration of helicopter

PurposeHelicopter fuselage vibration prediction is important to keep a safety and comfortable flight process. The helicopter vibration mechanism model is difficult to meet of demand for accurate vibration prediction. Thus, the purpose of this paper is to develop an intelligent algorithm for accurate helicopter fuselage vibration analysis.Design/methodology/approachIn this research, a novel weighted variational mode decomposition (VMD)- extreme gradient boosting (xgboost) helicopter fuselage vibration prediction model is proposed. The vibration data is decomposed and reconstructed by the signal clustering results. The vibration response is predicted by xgboost algorithm based on the reconstructed data. The information transfer order between the controllable flight data and flight attitude are analyzed.FindingsThe mean absolute percentage error (MAPE), root mean square error (RMSE) and mean absolute error (MAE) of the proposed weighted VMD-xgboost model are decreased by 6.8%, 31.5% and 32.8% compared with xgboost model. The established weighted VMD-xgboost model has the highest prediction accuracy with the lowest mean MAPE, RMSE and MAE of 4.54%, 0.0162, and 0.0131, respectively. The attitude of horizontal tail and cycle pitch are the key factors to vibration.Originality/valueA novel weighted VMD-xgboost intelligent prediction methods is proposed. The prediction effect of xgboost model is highly improved by using the signal-weighted reconstruction technique. In addition, the data set used is collected from actual helicopter flight process.

Stealth performance evaluation of helicopter against airborne early warning radar considering trimming control

Airborne pulse Doppler radar is a key threat to the military helicopter, and assessing the stealth performance of helicopter against airborne early warning radar is helpful to the helicopter’s stealth design and operational planning. In this paper, the Shooting and Bouncing Ray (SBR) and Uniform Theory of Diffraction (UTD) based high-frequency algorithms are used to calculate the Radar Cross Section (RCS) of helicopter, and the radar range equations are used to evaluate the stealth performance. In order to account for the effects of rotor flapping motions during actual flight, the aerodynamics model of whole helicopter is established and the attitudes and controls of helicopter at different flight states are trimmed and input into the RCS calculation module. The effects of helicopter flight speed, flying direction and operational environment on radar stealth performance are studied in focus. It is demonstrated by the results that the trimming control does have a great influence of more than 5 dB on the RCS of helicopter, and the introduction of the trim calculation brings the helicopter’s returns calculation closer to the reality. Variations in flight speed lead to the changes in the stealth performance of helicopter against Early Warning Aircraft (EWA), and the helicopter flight speed can be planned according to the operational requirements to minimize exposure distance or exposure time. Variations in flying direction mainly affect the detection properties of helicopter returns, and flying in the same direction with EWA usually gives the helicopter better low-observability than flying head-on. Variations in operational environment mainly affect the radar detection performance and the sensitivity of the detection performance to external factors; the same amount of change in some external factor causes a different amount of change in the helicopter’s detectability in different environments.

Erosion-damage-induced vibration response of aero-gas generator rotor system

When a turboshaft engine operates in harsh environments such as deserts, plateaus, and coastal areas, the erosion damage to compressor blades leads to uneven mass distribution of the blade disk of the gas generator and further induces unbalance fault vibration of the rotor system, which seriously endangers helicopter flight safety and mission execution. The vibration characteristics of the rotor system of the gas generator of an aero-turboshaft engine under blade erosion damage are studied innovatively in this paper. The theoretical formula for the blade erosion damage depth is derived. The key parameters for the calculation of the erosion damage to the blades are obtained by combining the particle impact velocity test, Ti-6Al-4 V alloy erosion wear test, and finite element analysis. A new data extraction method for erosion damage based on distribution characteristics and the sparseness–denseness path (DC-SP) is proposed. The unbalance fault mechanism of the rotor system caused by erosion damage is revealed. Using a turboshaft engine as an example, a dynamic model of the rotor system of a gas generator is developed. Unbalance load samples caused by erosion damage are applied, and the whirl trajectory and vibration spectrum characteristics of the rotor system analyzed. The results show that the unbalance magnitude of 1-stage and 3-stage rotor blades caused by erosion damage is 2.33 times and 1.22 times that of 2-stage rotor blades, respectively. The vibration response of the supporting position of the rotor changes with the unbalance phase difference of the rotor blade disk. The vibration amplitude of the supporting position is the lowest when the unbalance phase difference is 0°-180°-180° and is the highest when the unbalance phase difference is 0°-0°-0°. At design speed, the vibration amplitude fluctuation range of the left side of the supporting position is concentrated, whereas that of the right side is large. When the unbalance magnitude increases from 20 to 120 g·mm, the vibration amplitudes of the left and right sides of the supporting position increases by 97% and 263%, respectively.

An Investigation on the Aerodynamics of Flight of a Hand Helicopter

A simple hand helicopter can be made by attaching rotor blades to one end of a vertical stick. The helicopter moves upwards when the stick is spun above a threshold angular velocity and released — a mechanism of common toys found in toy shops. This study uses computational fluid dynamics to predict the airflow around a hand helicopter from which the lift and drag acting on the hand helicopter’s blades can be obtained. Newton’s Second Law is then applied to find the hand helicopter’s equations of motion. These are solved to predict the helicopter’s trajectory and maximum height. The angle of attack, length of blades and thickness of blades are varied and their effects on the lift coefficient, drag coefficient, lift-off and maximum height are investigated. The findings offer insight into the parameters which will allow a hand helicopter to achieve its optimal maximum height. The conditions required for the hand helicopter to fly stably are also investigated and explained using the Tennis Racket Theorem.

Thermal-Fluid-Solid Coupling Simulation and Oil Groove Structure Optimization of Wet Friction Clutch for High-Speed Helicopter

Wet friction clutch is the key functional component of the high-speed helicopter variable-speed transmission system, which is used to change the power transmission path. In the engagement process of wet friction clutch, the driving/driven disc will produce drag torque under the shearing of lubricating oil, which reduces the transmission efficiency. This unnecessary drag torque reduces efficiency and increases clutch temperature. The temperature increase promotes the wear of gears and bearings and the aging deformation of friction plates, which leads to local wear and reduces the service life of the clutch. From the principle of wet friction clutch, the oil groove structure is directly related to the drag torque and the temperature rise of friction disc. It is very important for the long-distance flight and service life of high-speed helicopters to obtain the groove structure with low drag torque and low temperature rise. In order to solve this problem, taking the wet friction clutch of a high-speed helicopter as the research object, based on the radial and annular compound groove, the thermal-fluid-solid coupling simulation model of the wet friction clutch is established to obtained the flow characteristics and temperature field distribution of the lubricating oil in the friction disc oil groove, and to analyze the influence law of the oil groove structure parameters on the drag torque and temperature field. In order to improve the transmission efficiency and the service life of friction disc, Taguchi experiment and non-dominated neighborhood immune algorithm were used to optimize the structural parameters of the oil grooves. The comparison results show that the optimized structural can effectively reduce the drag torque and the temperature rise. This work can provide a theoretical reference for the structure design of a wet friction clutch.

Speech enhancement for helicopter headsets with an integrated ANC-system for FPGA-platforms

During flights, helicopter pilots are exposed to high noise levels caused by rotor, engine and wind. To protect the health of passengers and crew, noise-dampening headsets are used. Modern active noise control (ANC) headset can further reduce the noise exposure for humans in helicopters. Internal or external voice transmission in the helicopter must be adapted to the noisy environment and speech signals are therefore heavily amplified. To improve the quality of communication in helicopters speech and background noise in the transmitted audio signals should be separated. Subsequently the noise components of the signal are eliminated. One established method for this type of speech enhancement is spectral subtraction. In this study, audio files recorded with an artificial head during a helicopter flight are used to evaluate a speech enhancement system with additional ANC capabilities on a rapid prototyping platform. Since both spectral subtraction and the ANC algorithm are computationally intensive, an FPGA is used. The results show a significant enhancement in the quality of the speech signals, which thus lead to improved communication. Furthermore, the enhanced audio signals can be used for voice recognition algorithms.

Tilt perception is different in the pitch and roll planes in human.

Neurophysiological tests probing the vestibulo-ocular, colic and spinal pathways are the gold standard to evaluate the vestibular system in clinics. In contrast, vestibular perception is rarely tested despite its potential usefulness in professional training and for the longitudinal follow-up of professionals dealing with complex man-machine interfaces, such as aircraft pilots. This is explored here using a helicopter flight simulator to probe the vestibular perception of pilots. The vestibular perception of nine professional helicopter pilots was tested using a full flight helicopter simulator. The cabin was tilted six times in roll and six times in pitch (-15°, -10°, -5°, 5°, 10° and 15°) while the pilots had no visual cue. The velocities of the outbound displacement of the cabin were kept below the threshold of the semicircular canal perception. After the completion of each movement, the pilots were asked to put the cabin back in the horizontal plane (still without visual cues). The order of the 12 trials was randomized with two additional control trials where the cabin stayed in the horizontal plane but rotated in yaw (-10° and +10°). Pilots were significantly more precise in roll (average error in roll: 1.15 ± 0.67°) than in pitch (average error in pitch: 2.89 ± 1.06°) (Wilcoxon signed-rank test: p< 0.01). However, we did not find a significant difference either between left and right roll tilts (p= 0.51) or between forward and backward pitch tilts (p= 0.59). Furthermore, we found that the accuracies were significantly biased with respect to the initial tilt. The greater the initial tilt was, the less precise the pilots were, although maintaining the direction of the tilt, meaning that the error can be expressed as a vestibular error gain in the ability to perceive the modification in the orientation. This significant result was found in both roll (Friedman test: p< 0.01) and pitch (p< 0.001). However, the pitch trend error was more prominent (gain=0.77 vs gain=0.93) than roll. This study is a first step in the determination of the perceptive-motor profile of pilots, which could be of major use for their training and their longitudinal follow-up. A similar protocol may also be useful in clinics to monitor the aging process of the otolith system with a simplified testing device.