Helicopter Flight Research Articles

Are Pelvic Binders an Effective Prehospital Intervention?

Objective Widespread adoption of prehospital pelvic circumferential compression devices (PCCDs) by emergency medical services (EMS) systems has been slow and variable across the United States. We sought to determine the frequency of prehospital PCCD use by EMS providers. Secondarily, we hypothesized that prehospital PCCD use would improve early hemorrhagic shock outcomes. Methods We conducted a single-center retrospective cohort study of 162 unstable pelvic ring injuries transported directly to our center by EMS from 2011 to 2020. Included patients received a PCCD during their resuscitation (prehospital or emergency department). Prehospital treatment details were obtained from the EMS medical record. The primary outcome was the proportion of patients who received a PCCD by EMS before hospital arrival. Secondarily, we explored factors associated with receiving a prehospital PCCD, and its association with changes in vital signs, blood transfusion, and mortality. Results EMS providers documented suspicion of a pelvic ring fracture in 85 (52.8%) patients and 52 patients in the cohort (32.2%) received a prehospital PCCD. Wide variation in prehospital PCCD use was observed based on patient characteristics, geographic location, and EMS provider level. Helicopter flight paramedics applied a prehospital PCCD in 46% of the patients they transported (38/83); in contrast, the EMS organizations geographically closest to our hospital applied a PCCD in ≤5% of cases (2/47). Other predictors associated with receiving a prehospital PCCD included lower body mass index (p = 0.005), longer prehospital duration (p = 0.001) and lower Injury Severity Score (p < 0.05). We were unable to identify any improvements in clinical outcomes associated with prehospital PCCD, including early vital signs, number of blood transfusions within 24 hours, or mortality during admission (p > 0.05). Conclusion Our results demonstrate wide practice variation in the application of prehospital PCCDs. Although disparate PCCD application across the state is likely explained by differences across EMS organizations and provider levels, our study was unable to identify any clinical benefits to the prehospital use of PCCDs. It is possible that the benefits of a prehospital PCCD can only be observed in the most displaced fracture patterns with the greatest early hemodynamic instability.

Vibration of natural rock arches and towers excited by helicopter-sourced infrasound

Abstract. Helicopters emit high-power infrasound in a frequency range that can coincide with the natural frequencies of rock landforms. While a single previous study demonstrated that close-proximity helicopter flight was able to excite potentially damaging vibration of rock pinnacles, the effects on a broader range of landforms remain unknown. We performed a series of controlled flights at seven sandstone arches and towers in Utah, USA, recording their vibration response to helicopter-sourced infrasound. We found that landform vibration velocities increased by a factor of up to 1000 during close-proximity helicopter flight as compared to ambient conditions immediately prior and that precise spectral alignment between infrasound and landform natural frequencies is required to excite resonance. We define admittance as the ratio of vibration velocity to infrasound pressure and recorded values of up to 0.11 mm s−1 Pa−1. While our results demonstrate a strong vibration response, the measured velocities are lower than likely instantaneously damaging values. Our results serve as a basis for predicting unfavorable degradation of culturally significant rock landforms due to regular helicopter overflights.

Classification of helicopter’s typical flight state based on threshold

Dividing the 37 flying state of a certain line number helicopter. Firstly, dividing the helicopter rotation and single-engine flight. Secondly, performing preliminary state division for the remaining samlpes, the specific division of yaw angle, helicopter flight altitude and indicated air speed are different states, the least squares polynomial method is used for smoothing respectively. Calculating the extreme value of each parameter data, with the difference value of the extreme value of the parameter data being less than 10 as the limiting condition, dividing the original data segment into non-turning, level flight and steady speed state. The remaining sampling points are in the state of unsteady turning and non-level flight. Taking the difference value 0 as the limiting condition, further divide the non-steady speed and non-level flight state. Dividing the state of turning and non-turning, level flight, ascent and descent, steady speed, increase speed and deceleration state, which is the preliminary division state. Finally, dividing the near-ground and non-near-ground, classifying the helicopter status according to the height threshold, and analyze the accuracy of the classification results. The results show that this method is versatile, can quickly divide helicopters with different flight complexity, and has high accuracy.

Investigation on effects of time-frequency characteristics of ship airwake on helicopter flight characteristics

A conventional helicopter flight dynamics model, which can be coupled with ship airwake date, is developed in this study. In the method, the ship airwake data is obtained by the high-accuracy DES model, and a strategy which can transmit CFD data to the flight dynamics model is established based on the "one-way" coupling idea. Then, the SFS2 ship model and UH-60A helicopter are chosen as a combination to investigate the influences of the spatial and temporal characteristics of ship airwake from the aspects of control margins and unsteady level. The time-averaged simulation results show that for the counterclockwise-rotor helicopter, although pilot could have more collective pitch margin under crosswind condition compared to the headwind condition, he might possess much less pedal margin due to the sidewash in the airflow. The unsteady results indicate that the unsteady loading level of the helicopter would increase significantly under the crosswind condition compared to the headwind condition due to the increase of turbulent density in the airwake. Furthermore, for the conventional helicopter, the disturbances on the forces and moments which along the rotor hub (i.e., thrust and yaw moment) are the critical factors that increasing the pilot workload during the landing procedure.

Nonlinear Helicopter Rigid-Elastic Coupled Modeling with Its Applications on Aeroservoelasticity Analysis

This paper represents a new mathematical model for helicopters with flexible fuselages. The theory connects the two commonly separated research areas of flight, dynamics and structural dynamics, by considering all necessary effects of a flexible fuselage on helicopter flight dynamic characteristics. They are rigid-elastic couplings of the flexible fuselage between six rigid-body degrees of freedom and elastic deformations, along with inertial and kinematic couplings between subcomponents and the fuselage. This is achieved by using the floating frame theory and deriving the acceleration coupling matrices of subcomponents analytically. In addition, the obtained formulation is explicitly decoupled such that all unknown absolute accelerations could be obtained in a single step without iterations, which could improve computational efficiency greatly. This model is suited for aeroservoelastic analysis, and is particularly suited for heavy lift helicopters (HLH) because they usually have slower turning rotors and more flexible fuselages due to their larger scale, leading to closer frequency ranges between rigid body motions and high-frequency rotor and structural modes. The model is validated before being applied to a numerical example of a sample HLH with a feedback loop for stability augmentation. The results show that the feedback loop connects actuators, fuselage deformation, and rigid body motion and induces divergent oscillation, which is the aeroservoelastic instability that cannot be predicted without the additional sensor measurements feedback caused by dynamic deformation. Since the 10-second step response could be calculated in three seconds, the presented helicopter mathematical model is expected to be used in real-time simulations or even further in pilot-in-the-loop simulations, ultimately helping with the design of modern helicopters with nonnegligible fuselage flexibility.

Development of Fly Neighborly helicopter model specific operational noise abatement guidance from acoustic flight test data

Improved helicopter noise abatement guidance has been developed based on acoustic test data acquired by NASA, FAA and Volpe in support of the Helicopter Association International (HAI)'s Fly Neighborly Program. This higher fidelity material was developed to supplement previous training programs based on pilot and operator feedback. The manner of presentation allows pilots to readily interpret the directional noise emission of their vehicle at different operating conditions. Flight path, airspeed, approach descent rate, and deceleration rate can be assessed to optimize flight patterns both during the pre-flight planning stage and in real time during flight operations in response to local conditions and events. The resultant sound directivity would be displayed as colored noise exposure contours overlaid onto a map of the area in the vicinity of the helicopter. New Fly Neighborly training modules have been developed utilizing directional operational noise plots based on Volpe's Advanced Acoustic Model (AAM) modeling with empirical sound sphere data from dedicated US Government helicopter flight tests. This paper will describe the acoustic analyses and will present the updated noise guidance for the AS350, AS365, AW139, Bell 205, Bell 206, Bell 407, R-44, R-66 and S-76D helicopters.

Estimation of helicopter emission and greenest helicopters for London

PurposeThis study aims to estimate the greenest helicopters and the emission amount based on the helicopter movement within the London Heathrow and London city control zone.Design/methodology/approachThe helicopter flight data recorded by the UK’s specialist aviation regulator Civil Aviation Authority and the helicopter type with engine emission data from the Federal Office of Civil Aviation (FOCA) were used for calculation. Based on the approach adopted, the greenest and the most environmentally friendly helicopters were identified for a light-duty helicopter with single-engine, a light-duty helicopter with twin-engine and a heavy-duty helicopter with twin-engine.FindingsComparing a flight consisting of landing and take-off cycle, and 1-h phase based on helicopters emissions in the FOCA database, B06 with DDA250-C20R single-engine in the light utility, A109 with PT6B-37 twin-engine in the light utility, and the A139 helicopter with the PT6C-67C twin-engine in the high utility has been identified as the most environmentally friendly helicopter.Practical implicationsThis study provides the opportunity to compare between the best and the worst helicopter with engine type according to the emission values released to the environment.Originality/valueThis study raises awareness of the emission levels caused by helicopter in urban air transport in developed countries in terms of environmental and human health. It also provides justification for the authorities to encourage the development and use of green engines and technologies.

Novice and experienced hoist operators in a helicopter hoist virtual reality simulator

ABSTRACT Virtual reality (VR) simulation training for helicopter search and rescues (SAR) hoist operators is very uncommon in comparison to the availability of pilot simulation training. SAR hoist operators control winch systems for hoisting objects or people during helicopter flight. Using a rear crew helicopter VR training simulator we sought to quantify hoist operator performance and validate this system by showing that experienced SAR hoist operators and novices hoist differently. We recruited 12 military SARs and 11 persons without hoisting experience and examined their performance in moderate wind conditions over two landscapes, ocean and land. Experienced operators were not affected by environment, completed missions faster than novices, made fewer velocity adjustments, and demonstrated better cable management. These variables can now be used as sources of feedback to train novice hoist operators. Since there were differences between performances of experienced and novice hoist operators we have established construct validity of the simulator.

Improving a real-time helicopter simulator model with linear input filters

For a broad range of applications, flight mechanics simulator models have to accurately predict the aircraft dynamics. However, the development and improvement of such models is a difficult and time consuming process. This is especially true for helicopters. In this paper, two rapidly applicable and implementable methods to derive linear input filters that improve the simulator model are presented. The first method is based on model inversion, the second on feedback control. Both methods are evaluated in the time domain, compared to recorded helicopter flight test data, and assessed based on root mean square errors and the Qualification Test Guide bounds. The best results were achieved when using the first method.

Predicting Cervical Spine Compression and Shear in Helicopter Helmeted Conditions Using Artificial Neural Networks

OCCUPATIONAL APPLICATIONS Military helicopter pilots around the globe are at high risk of neck pain related to their use of helmet-mounted night vision goggles. Unfortunately, it is difficult to design alternative helmet configurations that reduce the biomechanical exposures on the cervical spine during flight because the time and resource costs associated with assessing these exposures in vivo are prohibitive. Instead, we developed artificial neural networks (ANNs) to predict cervical spine compression and shear given head-trunk kinematics and joint moments in the lower neck, data readily available from digital human models. The ANNs detected differences in cervical spine compression and anteroposterior shear between helmet configuration conditions during flight-relevant head movement, consistent with results from a detailed model based on in vivo electromyographic data. These ANNs may be useful in helping to prevent neck pain related to military helicopter flight by facilitating virtual biomechanical assessment of helmet configurations upstream in the design process.

Exploring the Interaction Between Head-Supported Mass, Posture, and Visual Stress on Neck Muscle Activation.

Assess neck muscle activity for varying interactions between helmet, posture, and visual stress in a simulated "helo-hunch" posture. Military aviators frequently report neck pain (NP). Risk factors for NP include head-supported mass, awkward postures, and mental workload. Interactions between these factors could induce constant low-level muscle activation during helicopter flight and better explain instances of NP. Interactions between physical loading (helmet doffed/donned), posture (symmetric/asymmetric), and visual stress (low/high contrast) were studied through neck muscle electromyography (EMG), head kinematics, subjective discomfort, perceived workload, and task performance. Subjects (n = 16) performed eight 30-min test conditions (varied physical loading, posture, and visual stress) while performing a simple task in a simulated "helo-hunch" seating environment. Conditions with a helmet donned had fewer EMG median frequency cycles (which infer motor unit rotation for rest/recovery, where more cycles are better) in the left cervical extensor and left sternocleidomastoid. Asymmetric posture (to the right) resulted in higher normalized EMG activity in the right cervical extensor and left sternocleidomastoid and resulted in less lateral bending compared with neutral across all conditions. Conditions with high visual stress also resulted in fewer EMG cycles in the right cervical extensor. A complex interaction exists between the physical load of the helmet, postural stress from awkward postures, and visual stress within a simulated "helo-hunch" seating environment. These results provide insight into how visual factors influence biomechanical loading. Such insights may assist future studies in designing short-term administrative controls and long-term engineering controls.

Predictors of Emotional Distress in Combat Military Flight Engineers.

Exposure to distressing sights (DSs) during combat missions may cause emotional distress. The present study aimed to investigate the association between exposure to DSs involving severe injuries and fatalities during rescue missions and emotional distress, in Israeli Air Force (IAF) helicopter flight engineers (FEs). Cross-sectional design using self-report questionnaires. The independent variables included demographics, personal, and military variables-exposure to DSs throughout a whole career service. The dependent variables included Depression (Beck Depression Inventory); State-Trait Anxiety Inventory; Post-traumatic stress disorder (PTSD Checklist-PCL-5); Somatization (Patient Health Questionnaire); Maslach Burnout Inventory; and Coping Strategies (The Brief COPE). The variables PTSD, depression, and anxiety were examined twice: once as dichotomous variables according to the pathology cutoff point and again as a continuous variable to reveal the intensity of symptoms. Participants were 106 IAF helicopter FEs (mean age = 39.32, SD = 8.75). Linear regression revealed that initial exposure to distressing battlefield sights (i.e., exposure to severe injuries and fatalities) was a predictor of depression symptoms. Career service FEs aged 31-40 were found to be at the highest risk of emotional distress, with a predictive factor for anxiety symptoms. Use of nonadaptive coping strategies was found to predict depressive symptoms, anxiety symptoms, and post-traumatic stress symptoms. A significant association was found between exposure to DSs involving severe injuries and fatalities during rescue missions and anxiety, depression, somatization, and burnout. This population is generally perceived as tough and resilient, and this study has a unique contribution in identifying its vulnerabilities. Psychological intervention is crucial after participating in such missions.

Performances of airborne vapor cycle system under a typical helicopter flight profile

Performances of airborne vapor cycle system under a typical helicopter flight profile

GUI FOR VIBRATION PREDICTIONS DURING RTB OF A SERVICED HELICOPTER

Vibrations on helicopter induced in Main Rotor System and Tail Rotor System due to in plane unbalanced masses and out of plane rotation of rotor blades. Rotor Track and Balance (RTB) of helicopter is performed to reduce vibrations of helicopter. Number of vibration flights will increase if RTB is not optimised. Main Rotor and Tail Rotor vibrations can be reduced by predicting the vibrations prior to flight using Multiple Linear Regression and Analysis of Variance (MLR &amp; ANOVA). The Inputs for the Multiple Linear Regression would be in terms of mass changes, track changes and tab changes based on established sensitivities of these Inputs and cross sensitivities between them. The outputs are vibration changes of Main Rotor / Tail Rotor. Change in vibrations is the difference between the vibration values of two successive flights / ground runs. For Main Rotor, there are 12 inputs to adjust 2 outputs (MR Lateral and MR Vertical), for Tail Rotor, there are 8 inputs to adjust 2 outputs (TR Radial and TR Axial) for satisfactory vibrations during ground run, HOGE and two steady speed forward flight regimes. In this Research work, three types of Regression Models for Main Rotor System and Two types of Regression Models for Tail Rotor System were made to predict the vibrations of helicopter prior to ground run or flight. The Regression Coefficients were evaluated using MatLab and models were generated. ANOVA is performed for regression models and found satisfactory. The Coefficient of Regression (Multiple-R / R 2 ) values obtained are more than 0.9. The results of the regression indicated that the model was a significant predictor of vibration changes. Graphical User Interface (GUI) using Regression Models is made for vibration predictions of Main Rotor and Tail Rotor Vibrations of Serviced helicopter. This research work recommends for the implementation of Multiple Linear Regression and its applications for vibration predictions of Serviced helicopters to reduce vibration fl

Розрахункове дослідження аеродинамічних характеристик рульового гвинта вертольота типу Мі-8 з урахуванням інтерференції з несучим гвинтом на режимі висіння при боковому вітрі

Under certain conditions of a helicopter flight, the main rotor can exert a rather strong effect on the tail rotor, changing its traction and power characteristics. The calculated and experimental characteristics of an isolated tail rotor under such operating conditions can differ significantly from those under conditions of interaction with the main rotor. The study of this phenomenon is an urgent task, since a change in the characteristics of the tail rotor and the conditions of its operation in the presence of the main rotor can cause a decrease in controllability margins and, as a consequence, the cause of an aircraft accident, for example, the so-called. "left rotation" of the helicopter. Since 1985, on helicopters from M. L. Mile, 42 aviation accidents occurred in units and subdivisions of the state and civil aviation of the USSR (and now Russia) due to helicopters falling into spontaneous left rotation. Over the past 10 years, 29 accidents (8 accidents and 21 accidents) have occurred for this reason. 29 helicopters were lost: 20 Mi-8, 5 Mi-24, 4 Mi-2. Experience shows that getting into an uncontrolled left rotation in almost 100% of cases ends with a collision of the helicopter with the ground and overturning it on the starboard side. The interaction of the main and tail rotor is most significantly manifested in the modes of horizontal flight with sliding at low speeds and hovering in crosswind conditions. This is due to the peculiarities of the formation of the main rotor vortex wake. In this article, the case of aerodynamic interference of the main rotor and several helicopter configurations in horizontal flight mode with the low speed with sliding (hovering in a crosswind) is considered. Using the methods of computational fluid dynamics, the degree of influence of the main rotor on the tail rotor was investigated in the described modes. The most severe operating modes of the tail rotor of each configuration have been determined. Based on the results of calculations, the most rational configuration of the tail rotor has been chosen, which has the greatest reserves of controllability under unfavorable operating conditions. The results obtained have been used in the design of a new perspective helicopter, modernization of the existing fleet, as well as improving the flight safety level.

Heat Strain with Two Different Ventilation Vests During a Simulated 3-Hour Helicopter Desert Mission.

BACKGROUND: The study investigated the heat strain of personnel operating in the rear cabin of a helicopter during desert-climate missions, and to what extent the strain can be mitigated by use of battery-driven ventilation vests.METHODS: Eight men undertook 3-h simulated flight missions in desert conditions (45C, 10% humidity, solar radiation). Each subject participated in three conditions wearing helicopter flight equipment, including body armor, and either: a ventilation vest with a 3-dimensional mesh (Vent-1), a ventilation vest with a foam sheet incorporating channels to direct the air flow (Vent-2), or a T-shirt (NoVent); each mission comprised a 10-min walk, followed by sitting for 30 min, kneeling on a vibration platform for 2 h, and finally 30 min of sitting. Core temperature, heart rate, skin temperatures and heat flux, oxygen uptake, sweating rate, and subjective ratings were recorded. Evaporative capacity and thermal resistance of the garments were determined using a thermal manikin.RESULTS: All subjects completed the NoVent and Vent-1 conditions, whereas in the Vent-2 condition, one subject finished prematurely due to heat exhaustion. The increase in core temperature was significantly (P 0.01) greater in Novent (0.93C) and Vent-2 (0.88C) than in Vent-1 (0.61C). Evaporative capacity was significantly higher for Vent-1 (7.8 g min1) than for NoVent (4.1 g min1) and Vent-2 (4.4 g min1).DISCUSSION: Helicopter personnel may be at risk of heat exhaustion during desert missions. The risk can be reduced by use of a ventilation vest. However, the cooling efficacy of ventilation vests differs substantially depending on their design and ventilation concept.Grönkvist M, Mekjavic I, Ciuha U, Eiken O. Heat strain with two different ventilation vests during a simulated 3-hour helicopter desert mission. Aerosp Med Hum Perform. 2021; 92(4):248256.

High-Fidelity Aeromechanical Analysis of Coaxial Mars Helicopter

A high-fidelity coupled computational fluid dynamics and comprehensive analysis solver is developed for helicopter flight on Mars. The objectives are accurate prediction of flight loads and fundamental understanding of Martian aeromechanics. Performance, structural loads, pitch link loads, rotor wake, and interrotor blade separation are studied for hingeless and flap articulated coaxial rotors. In the absence of any validation data, pressure chamber tests are carried out at Mars-like conditions on a single rotor in hover. The data provided an elementary assessment of rotor behavior and a baseline for model validation. Predictions of the high-fidelity solver are also compared with a lower-fidelity lifting-line comprehensive analysis. It is generally concluded that lower-fidelity tools are not adequate for capturing the complex flow phenomena encountered on Mars. A motion and loads comparison of two fundamental hub types revealed that 1) an articulated hub has similar interrotor blade separation as hingeless on Mars, 2) a hingeless hub experiences only marginally higher (6–7%) flap bending moments, and 3) an articulated hub can lower steady pitch link loads (by an order of magnitude) at a marginal expense of oscillatory loads, 15% higher.

An analysis of commercially recommended profiles for normobaric preacclimatization

Introduction: Normobaric hypoxic training (NHT) for preacclimatization at home has found its way into commercial expedition mountaineering. Portable NH-generators produce a normobaric hypoxic gas mixture that can be inhaled using breathing masks at rest or during exercise or it can be pumped into lightweight tents for sleeping. These devices can be rented from commercial companies. Materials and methods: Prior to an expedition to Manaslu (8163 m) NHT was used for preacclimatization over a period of 10 days. Our regimen involved a greater increase in sleeping altitude (10 nights to reach 5400 m) than recommended by the rental company (30 nights to reach 3900 m). Results: No incidents occurred during NHT. Our regimen induced sufficient acclimatization to Manaslu Base Camp (4900 m), as evidenced by the fact that none of the expedition members suffered from AMS although they reached base camp within 2 days from Kathmandu – by helicopter flight to 3500 m and a one day walk the next day. Eight days after leaving Kathmandu, camp III was reached at 6850 m. Conclusions: At natural altitudes above 2500 m an increase of sleeping altitude should not exceed 300-500 m per day. Below 2500 m, there are no restrictions. It is therefore unclear why the company recommends such a slow increase in sleeping altitude. In our opinion, it is not necessary for healthy persons to start with a sleeping altitude below 2500 m. In contrast to natural altitudes, NH exposure can be instantly stopped if symptoms occur. Therefore, it seems safe to expose healthy persons to more liberal normobarichypoxic conditions.

A Method for Assessing the State of the Snow and Ice Cover by the Brewster Angle

Introduction. Landing is the most challenging and dangerous part of the helicopter flight. The development of systems facilitating safe landing is a priority task for both Russian and foreign engineering companies. Landing on unprepared sites covered with snow and ice may be determined by the need to deliver cargo and ammunition in combat conditions, during search and rescue operations, evacuations of victims, etc.Aim. Development of a method for remote assessment of the snow and ice cover based on the results of oblique sensing of the underlying surface with a radio signal with vertical polarization.Materials and methods. In the MatLab environment, the authors conducted numerical simulations of Fresnel reflection coefficients of echo signals with vertical polarization in the 40–90 degree sensing range in the operating frequency range when solving the direct and inverse problem of reconstruction of the parameters of snow and ice layers.Results. Intervals of the Brewster angle values were obtained at which the value of the Fresnel reflection coefficient from the boundaries of the snow and ice cover takes minimal. Thus, was found to be – 47...55°, – 55...58° and – 58...61° for dry snow, dry firn and dry ice, respectively. The depth resolution when using an ultra-wideband LFM signal with a frequency from 2 to 8 GHz is about 4 cm. The methodological error in determining the dielectric permittivity of layers by the Brewster angle comprises not more than 3 %.Conclusion. The error in determining the relative permittivity and the depth of k layers under an increase in the RMS values of the noise level from 3.8 to 4.8 with a step of 0.1 for 100 implementations of each with a probability of 0.95 does not exceed 10 %, which confirms the validity of this method. The implementation of which allows you to automate the process of evaluating the possibility of a safe landing, thereby reducing the decision-making time and increasing the level of safety.

Temporal signals to images: Monitoring the condition of industrial assets with deep learning image processing algorithms

The ability to detect anomalies in time series is considered highly valuable in numerous application domains. The sequential nature of time series objects is responsible for an additional feature complexity, ultimately requiring specialized approaches in order to solve the task. Essential characteristics of time series, situated outside the time domain, are often difficult to capture with state-of-the-art anomaly detection methods when no transformations have been applied to the time series. Inspired by the success of deep learning methods in computer vision, several studies have proposed transforming time series into image-like representations, used as inputs for deep learning models, and have led to very promising results in classification tasks. In this paper, we first review the signal to image encoding approaches found in the literature. Second, we propose modifications to some of their original formulations to make them more robust to the variability in large datasets. Third, we compare them on the basis of a common unsupervised task to demonstrate how the choice of the encoding can impact the results when used in the same deep learning architecture. We thus provide a comparison between six encoding algorithms with and without the proposed modifications. The selected encoding methods are Gramian Angular Field, Markov Transition Field, recurrence plot, grey scale encoding, spectrogram, and scalogram. We also compare the results achieved with the raw signal used as input for another deep learning model. We demonstrate that some encodings have a competitive advantage and might be worth considering within a deep learning framework. The comparison is performed on a dataset collected and released by Airbus SAS, containing highly complex vibration measurements from real helicopter flight tests. The different encodings provide competitive results for anomaly detection.