Helicopter Main Rotor Blade Research Articles

Stochastic Dynamic Response of Delaminated Flexbeam Like Structures

In this work, the free vibration characteristics of flexbeam like structures, typically used in helicopter main or tail rotor blades, are investigated. The tapering effect in these laminated composite structures is introduced by terminating plies, which act as potential delamination sites. Delamination and uncertainties in material properties at various scales influence their dynamic behavior. The variational asymptotic method (VAM) is used as a mathematical framework to develop a model of a tapered composite beam with delamination. Subsequently, the modal characteristics are obtained by coupling the VAM model with the reduced 1D finite element beam model. Stochastic natural frequencies are investigated by combining the source uncertainties in the delaminated structure. Following a detailed validation study, the model capability is demonstrated on flexbeams typically used in helicopter rotor blades.

Wind Tunnel Experiments on Parallel Blade–Vortex Interaction with Static and Oscillating Airfoil

This study aims to experimentally investigate the effects of parallel blade–vortex interaction (BVI) on the aerodynamic performances of an airfoil, in particular as a possible cause of blade stall, since similar effects have been observed in literature in the case of perpendicular BVI. A wind tunnel test campaign was conducted reproducing parallel BVI on a NACA 23012 blade model at a Reynolds number of 300,000. The vortex was generated by impulsively pitching a second airfoil model, placed upstream. Measurements of the aerodynamic loads acting on the blade were performed by means of unsteady Kulite pressure transducers, while particle image velocimetry (PIV) techniques were employed to study the flow field over the blade model. After a first phase of vortex characterisation, different test cases were investigated with the blade model both kept fixed at different incidences and oscillating sinusoidally in pitch, with the latter case, a novelty in available research on parallel BVI, representing the pitching motion of a helicopter main rotor blade. The results show that parallel BVI produces a thickening of the boundary layer and can induce local flow separation at incidences close to the stall condition of the airfoil. The aerodynamic loads, both lift and drag, suffer important impulsive variations, in agreement with literature on BVI, the effects of which are extended in time. In the case of the oscillating airfoil, BVI introduces hysteresis cycles in the loads, which are generally reduced. In conclusion, parallel BVI can have a detrimental impact on the aerodynamic performances of the blade and even cause flow separation, which, while not being as catastrophic as in the case of dynamic stall, has relatively long-lasting effects.

Numerical investigation on the use of various blade tips for the helicopter's main rotor blade in forward flight regarding aerodynamic performance and HSI noise considerations

The goal of this research is to investigate aerodynamic performance and high-speed impulsive (HSI) noise of various blade tips for the helicopter's main rotor in forward flight. For this purpose, three-dimensional compressible flow field around the rotor blades is numerically simulated by the solution of the unsteady Reynolds averaged Navier-Stokes (URANS) equations with the "SST k-ω" turbulence model. Solution is quantified by the calculation of torque, drag, and thrust coefficients of CQ, CD, CT, and L/D ratio. HSI noise on the rotor plane is assessed by the calculation of sound pressure level at certain points of the flow field using the Ffowcs Williams-Hawking (FW-H) equation. Blade tips are eleven and include anhedral, dihedral, Eagle and combinations of them, and also Blue Edge and rectangular. The combinations are inspired by the tip configurations of the fixed wings. In this regard effects of the tip geometry parameters including curvature and height of its parts have been considered as well. All of the tips are examined for two flight conditions of Caradonna and Tung two-blade rotor with fixed pitch angle and time-varying pitch angles. Based on the present results, it is found that blade tips of dihedral family do not improve the aerodynamic performance of the helicopter blade. Also, addition of anhedral part to the blade tip improves the L/D ratio. According to the present acoustic analysis, it was seen that after the Blue Edge, the Eagle tip stands in order of priority. For the condition of Caradonna and Tung two-blade rotor with tip Mach number of 0.8 and advance ratio of 0.2, HSI noise of the Eagle-tip blade decreases by 2.39 % compared to that of the two-blade rotor with rectangular tip. However, the aerodynamics performance of the Eagle tip is much better than that of the Blue Edge.

DYNAMIC ANALYSIS OF A HELICOPTER BLADE WITH DAHL FRICTION IN A VERTICAL HINGE

A one-dimensional model of a helicopter main rotor blade in the plane of rotation with a vertical hinge (VSH) is considered. The friction in the VH corresponds to the Dahl model. The resonant frequency, free oscillations and phase trajectories of the model are analyzed depending on the value of the contact stiffness of Dahl friction.

МЕТОД ПІДТВЕРДЖЕННЯ РЕСУРСНИХ ХАРАКТЕРИСТИК МЕТАЛЕВОЇ ЛОПАТІ НЕСУЧОГО ГВИНТА ВЕРТОЛЬОТА ЗА РЕЗУЛЬТАТАМИ ВИПРОБУВАНЬ

The helicopter main rotor blade is the basic product that determines the reliability and service life of the helicopter as a whole. The problem of predicting and ensuring the specified blade life is an urgent problem considered at the stage of its design. The analysis of the design, structural materials and design and technological solutions of the main rotor blade (RB) of the Mi-8 helicopter has been carried out. A brief description of the main rotor blade of the Mi-8 helicopter is presented. The analysis was carried out and a standard flight cycle (SFC) of the helicopter was developed. The type of bench equipment for carrying out bench fatigue tests of the blade has been selected and justified. The loads on the main rotor blade for the SFC are determined. To determine the fatigue life of a blade, it is necessary to know the characteristics of the stress-strain state. The calculation of the stress-strain state (SSS) of a blade by the finite element method (FEM) using the ANSYS system is presented. The characteristics of the stress-strain state of the spar of the regular and irregular parts of the rotor blade of a helicopter are determined using the ANSYS system. The use of numerical methods for calculating the characteristics of the stress-strain state can significantly reduce the time and cost of designing a blade. The paper presents the results of calculating the regular part of the main rotor blade of the Mi-8 helicopter in the hover mode in the case of its loading with aerodynamic and inertial load from rotation, as well as the force from its own weight. With the help of the ANSYS system, a finite element model of the regular part of the blade was developed, consisting of a set of beam elements of variable section, a calculation was carried out taking into account the geometric nonlinearity of the structure's behavior, and an analysis of the results obtained was carried out. To describe the response of materials to an external action, a model of an elastically deformable isotropic body was used with the assignment of the corresponding elastic constants of the material. The analysis of the calculation results includes the determination of reactions at the attachment points, the values of the maximum displacements of structural elements and stresses in dangerous sections. Dangerous sections are determined and the values of the longitudinal force and bending moment in these sections are calculated. The assessment of the static strength of the blade by the safety factor was carried out. When evaluating the static strength, the equivalent stresses according to Mises were considered as the maximum design stresses. To assess the fatigue strength, we analyzed the distribution of the main tensile stresses in the power elements over typical stress concentrators. The maximum level of the main tensile stresses in the dangerous section indicates that the blade material operates in the zone of high-cycle fatigue. A technique for calibrating strain gauge channels has been developed. The calculation of the characteristics of the rotor blade of a helicopter is based on the requirements set forth in the technical literature, regulatory documents. When performing work, the requirements of the Aviation Rules, Part 29 (AP - 29) were taken into account. These studies were the basis for the development of a method for confirming the resource characteristics of a helicopter main rotor blade based on the results of flight and bench tests.

ANN-Based Estimation of the Defect Severity in the Drilling of GFRP/Ti Multilayered Composite Structure

The main purpose of this study was to develop a model for predicting the quality of holes drilled in the root part of the spar of helicopter main rotor blades made of glass fiber-reinforced plastic (GFRP)-Ti multilayer polymer composite. As the main quality criterion, delaminations at the entry and exit of the drill from the hole were taken. In the experimental study, a conventional drill and two modified geometry drills, a double-point angle drill and a dagger drill, were used. Preliminary experiments showed the best hole quality when using modified drills, which allowed further detailed study only with both modified drills at different drilling speeds and feed rates. Its results in the form of training sets were used to build artificial neural networks (ANNs) to predict delamination at the entry and exit of the drilled holes. An analysis of the fitted response functions presented as 3D surface plots and contour plots led to the selection of the best tool, a double-point angle drill, which demonstrated the lowest achievable delamination both at the entry and at the exit of the holes approximately 1.5 times less (0.45/0.48 mm) compared to dagger drills (0.68/0.7 mm) and determined the ~5 times larger optimal area for the drilling speed and feed rate. The results obtained confirm the possibility of effective prediction of the quality and productivity of mechanically processed composites of complex reinforcement using ANN to quantify the quality criteria and search for the optimal modes of such technologies.

Comparative Analysis of the Vibrational Response of a Homemade Helicopter Main Rotor Blade Profiles

This paper investigates the dynamics of homemade helicopter wooden and aluminum sheet rotor blades. The rotors are articulated and their blades are rigid. The main rotor implementation takes into account flap, lag, and feather degrees of freedom for each of the equispaced blades as well as their dynamic couplings. Transmitted vibrations due to the rotating rotor blades on the body structure (fuselage) are studied. This work presents an aerodynamic model of main rotor blades that allows us to analyse vibrational transmissions on the fuselage (body) of the craft. Vibrations in helicopters is a common problem which involves complex interactions between the inertial, structural and aerodynamic loads, especially in homemade helicopters. The major source of vibrations in helicopters is the main rotor. The efficiency and stability of the main rotor blades is determined by the magnitudes of the predominant frequencies they produce. These vibrations affect the functionality, durability of the engine component parts, increase maintenance frequency (cost), and cause structural failures. The aerodynamic model has been built up using blade element theory. The aerodynamic load creates vibrations on the homemade helicopter and these are analyzed on the fuselage by using a short time Fourier transform that brings out the vibrational spectrum. The results of the analysis serve as a reference to characterize the stability and efficiency of homemade main rotor blade profiles.

Selection of the Optimal Airfoil for the Small-Sized Unmanned Helicopter Main Rotor Blade

Selection of the Optimal Airfoil for the Small-Sized Unmanned Helicopter Main Rotor Blade

Helicopter Main Rotor Blade Parametric Design for a Preliminary Aerodynamic Analysis Supported by CFD or Panel Method.

This work is the preliminary part of a research program which is aimed at finding some new methods and design solutions for helicopter main rotor multidisciplinary optimization. The task was to develop a parametric geometric model of a single-blade main rotor applicable for varied methods of numerical aerodynamic modeling. The general analytical assumptions for the parametric main rotor design were described. The description of the main rotor blade parametric design method based on Open GRIP graphical programming was presented. Then, the parametric model of a blade was used for aerodynamic models independently developed for panel method and advanced CFD solver. The results obtained from the CFD simulations and panel analysis for main rotor aerodynamics were compared and assessed using analytical calculations. The calculations and simulations for a single-blade and completed rotor were performed for different helicopter weights and rotor pitch angles. The results of different computer aerodynamic analysis environments were compared for the possibility of their application in an optimization loop. This is preliminary work that describes only a partial problem that could be used in the future as part of a comprehensive methodology for aerodynamic and structural optimization of a helicopter rotor. As an output of the research, new options for main rotor optimization are developed. The combined parametric modeling with aerodynamic analysis, as described in this paper, provide the preliminary design for a main rotor spiral, as an element of the optimization loop.

Technological Aspects of a Reparation of the Leading Edge of Helicopter Main Rotor Blades in Field Conditions

The Polish Air Force operates more than one hundred helicopters of the Mi family (manufactured by Mil Helicopters), equipped with metal main rotor blades. The main rotor blades are among the most stressed components of these structures. For this reason, they are subject to more frequent inspections during operation than other components. One type of damage detected during inspections is the local disbonding of fragments of the anti-erosion layer from the leading edge. This harmless-looking damage is very dangerous, since it quickly leads to the complete detachment of the layer. The leading edge, unprotected by the metal cover, erodes rapidly. The detached layer, when thrown away at high speed, endangers other parts of the helicopter, such as the tail rotor, and may cause damage to other helicopters if flying in formation. The technology supplied by the manufacturer to date has not encompassed the field repair of this type of damage. Therefore, efforts were made to develop repair technology for rapid repairs of blades in field conditions during missions of the Task Force White Eagle in Afghanistan. This article presents the concept of repair technology feasible in field conditions and presents the results of post-repair edge tests. Test results to identify the materials used in the construction of the trailing edge are also presented. The results of materials testing facilitated the development of technological processes, and, in the future, will aid the selection of a substitute bonding paste system with similar parameters that are essential for repairs.

A Review on Vibration Analysis of Helicopter Rotor Blade

Abstract: Vibration has always been a major disturbance for helicopter. Vibrations, thus, a threat to components of helicopter. The vibration created by a helicopter draws a great contribution to the reduction in life of the components. Reducing the vibration that creates from helicopter rotor blades, tail rotors is a one step closer to this crisis. Helicopter Vibration control is a topic of research into designing helicopter rotor blade which can be operated more efficiently. The major source of the vibration come from the rotor blade rotation. By trying to upgrade new design in the helicopter main rotor blades and tail rotors reduce the vibration and make the operation more efficient. This paper addresses simulation and analysis of vibration level of rotor blades. Keywords: drag, rotor, vibration, air foil, blade profile.

МЕТОД ВИЗНАЧЕННЯ ХАРАКТЕРИСТИК НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ ЛОНЖЕРОНА РЕГУЛЯРНОЇ ЧАСТИНИ ЛОПАТІ НЕСУЧОГО ГВИНТА ВЕРТОЛЬОТА ЗА ДОПОМОГОЮ СИСТЕМИ ANSYS

The helicopter main rotor blade is the basic product that determines the reliability and service life of the helicopter as a whole. The problem of predicting and ensuring the specified blade life is an urgent problem considered at the stage of its design. To determine the fatigue life of the blade it is necessary to know the characteristics of the stress-strain state. A method has been developed for determining the characteristics of the stress-strain state of the spar of the regular part of the rotor blade of a helicopter using the ANSYS system. Application of numerical methods of stress-strain state characteristics calculation allows to reduce considerably time and cost of blade design. The calculation results of regular part of the Mi-8 main rotor blade at the hover mode when it is loaded by aerodynamic and inertial load from the rotation, as well as the force of its own weight are presented in the work. Using the ANSYS system, a finite-element model of the regular part of the blade, consisting of a set of beam elements of variable cross-section, was developed, the calculation was carried out taking into account the geometric nonlinearity of the structure behavior and the analysis of the obtained results. To describe the response of materials to external influences, an elastically deformable isotropic body model is used with assignment of the appropriate elastic constants of the material. Analysis of calculation results includes determination of reactions at attachment points, values of maximum displacements of structural elements and stresses in weak sections. Diagrams of internal force factors (axial and shear forces and bending moment) along the blade span are plotted. With the help of these diagrams weak sections are determined and values of axial force and bending moment in these sections are calculated. Axial force reaches its maximum value Nx = 333689 N in the section along the axis of rib № 1. In this section, the bending moment reaches a maximum value of Mymax = 3078.3 N×m. At cross section r = 0.73 between axes of ribs No. 13 and No. 14, where shear force equals to zero, value of bending moment My = -1147,5 N×m. Thus, regular part of the blade is in combined stressed state - bending with tension. Static strength of the blade has been estimated using safety factor. To estimate a static strength equivalent von Mises stresses were considered as the maximum stresses. Safety factor of static strength of regular part of the blade in the weak section was 1,7. To estimate fatigue strength, distribution of the first principal stresses in the load-carrying elements was analyzed in terms of typical stress concentrators. The maximum level of the principal stresses in the considered sections was s1 = 138 MPa, which indicates that the blade material operates in the range of high cycle fatigue.

Main rotor blade modeling approaches comparison. Finite element and Craig-Bampton methods

The paper focuses on the helicopter main rotor blade FE model. And the main goal is to prove the feasibility of the helicopter main rotor MBD model in calculations of blade deformation as a result of applied aerodynamic forces. FE model is used as a basis for two different computational methods. A mathematical approach in the MBD based on the Craig-Bampton method on the one hand. And finite element model on the other hand. The results of high-frequency blade rotations are obtained. Calculations of these models are compared in order to determine the best method for modeling a linear-elastic blade. By the results, it is necessary to consider the preloaded state of the blade when using the Craig-Bampton method approach. The comparison of blade nodes displacements at various external conditions for both models are given. The influence of rotor MBS model damping parameters on the amplitude of blade oscillations under sinusoidal action is considered.

АНАЛІЗ КОНСТРУКТИВНО-ТЕХНОЛОГІЧНИХ ОСОБЛИВОСТЕЙ ЛОПАТЕЙ НЕСУЧИХ ГВИНТІВ ВАЖКИХ ТРАНСПОРТНИХ ВЕРТОЛЬОТІВ

The analysis of the design and technological features of the rotor blades of heavy transport helicopters is carried out. The main performance characteristics of heavy helicopters are presented. General requirements to helicopter main rotor blades design and specifications for their production are formulated. The design and force diagram of heavy helicopter main rotor blades is considered. The features of structural materials for the main rotor blades of heavy transport helicopters are marked. The main rotor blades differ in their design due to different approaches to materials, manufacturing and layout of blade elements. The main rotor blades of an all-metal design, for design and technological reasons, are divided into two groups: a frame structure with a tubular steel spar and an aluminum extruded spar. As a result of a number of design and technological measures the service life of the main rotor blade of helicopter Mi-6 was brought from 50 hours to 1500 hours. The principal peculiarity of the steel tubular spar of the main rotor blade of the Mi-26 helicopter is the absence of the shaft lug. The features of mixed design main rotor blades are presented. The method of parametric modeling of helicopter main rotor blades is presented. The application of the three-dimensional parametric models of structural elements in practice of designing and construction enables to perform numerical calculations of aerodynamic and strength characteristics both of separate aggregates, units and details and of the helicopter as a whole by means of the finite element method. The method of parametric modeling of the main rotor blade of the transport helicopter with the computer system CATIA V5 is a modification of the method of integrated designing of the elements of aviation constructions. Parametric master geometry of the main rotor blade is a linear surface, created by basic profiles of the blade. On the basis of parametric master geometry a space distribution model is created that determines the position of axial planes of the power set of the blade for further creation of the blade detail models. Technological flowchart of main rotor blade manufacturing is presented, manufacturing and surface hardening technology of steel tubular spar is considered. The technology of manufacturing and molding the nose part of the blade of the main rotor mixed design. The technological features of slipway assembly-gluing of the main rotor blade are considered, the content of off-slipway work is given.These materials can be useful in theoretical and experimental studies to extend the service life of the rotor blades of Mi-26 helicopters, which are currently in operation in Ukraine.

RELIABILITY ANALYSIS OF HELICOPTER BLADE ROTOR PLAY BELL 412 USING NORMAL DISTRIBUTION METHOD

At the beginning of operation, a main rotor blade on helicopter is certainly in the best condition. When it gets older, the main rotor blade condition will decrease because of the presence of bent, material fatigue and human error during operation. Based on the background, it is necessary to identify the level of reliability of main rotor blade on the Bell 412 helicopter using the normal distribution method. The research data were the age of components of main rotor blade on Bell 412 helicopter during 27 years.Based on the analysis of calculation of the reliability level, employing the normal distribution method and using Microsoft Excel, the reliability value (R) of all serial numbers of Bell 412 helicopter main rotor blade was 99%, which indicates the reliability of the Bell 412 helicopter main rotor blade is very good.

An inverse damage location problem applied to AS-350 rotor blades using bat optimization algorithm and multiaxial vibration data

In this study, a damage identification method is proposed using both the finite element method and the bat optimization algorithm applied to the AS-350 helicopter main rotor blade. First, the structure is numerically modeled and evaluated with and without the presence of induced damages. In a second approach, an inverse problem of optimization is constructed in order to identify certain damages in terms of its position and severity level. Three different objective functions are evaluated according to the modal parameters of the rotor blade (vibrations in x, y and z directions). Numerical results, through analysis of variance, showed that local damage significantly modifies the modal response into a non-linear aspect. The modal response used was able to identify, with great efficiency, the actual (noise simulated) damages induced in terms of location and severity. Accordingly, a damage identification method is developed in order to better handle any measurement data (to find/regarding) structural changes (or damages) in complex aerospace structures. The obtained results from these numerical examples indicate that the proposed approach can detect true damage locations and estimate damage magnitudes with satisfactory accuracy, even under high measurement noise.

헬리콥터 주로터 블레이드의 동적밸런싱 시험에 대한 데이터베이스 설계 및 적용

헬리콥터 주로터 블레이드의 동적 밸런싱 시험은 헬리콥터의 비행시험 전 각 블레이드의 트랙과 피치로드 하중을 동일한 수준으로 조절하기 위해 수행되는 지상회전시험이다. 이러한 동적밸런싱 시험의 목적은 블레이드 간 특성차이로 인해 나타나는 주로터 시스템 진동을 감소시키기 위함이다. 고흥 항공센터의 훨타워 시험설비에서는 오랜 기간에 걸쳐 수리온 주로터 블레이드에 대한 동적밸런싱 시험을 수행하고 데이터를 축적해 왔다. 이에 데이터양이 점차 방대해짐에 따라 시험결과를 효율적으로 관리하기 위한 데이터베이스 프로그램의 개발의 필요성이 제기되어 왔다. 본 연구에서는 훨타워 시험설비에서 수행한 동적밸런싱 시험결과를 바탕으로 구축한 데이터베이스 시스템에 대해 기술하였다. 본 연구에서 구현된 데이터베이스 시스템은 동적밸런싱 시험 결과를 각 정보별로 논리적으로 모델링하고 각각의 데이터가 상호 관계를 이룰 수 있도록 연결하여 관계형 구조를 이루도록 설계되었다. 아울러 본 논문을 통해 기 설계된 데이터베이스 시스템이 동적밸런싱 시험 결과의 축적과 시험 결과 분석에 효과적으로 활용될 수 있음을 보였다.

MATHEMATICAL MODELS OF THE RADAR SIGNAL REFLECTED FROM A HELICOPTER MAIN ROTOR IN APPLICATION TO INVERSE SYNTHESIS OF ANTENNA APERTURE

Introduction. The basis for solving the problem of aircraft recognition is the formation of radar portraits, reflecting the constructive features of aerial vehicles. Portraits, which are radar images of the propellers of aerial vehicles, have high informativeness. These images allow us to distinguish the number and relative position of the propeller blades, as well as the direction of its rotation. The basis for obtaining such images are mathematical models of reflected signals. Objective. The aim of this paper is to develop mathematical models of the radar signal reflected from the helicopter main rotor applied to inverse synthetic aperture radar (ISAR). Methods and materials. ISAR processing is used to produce a radar image of a propeller in a radar with a monochromatic probing signal. The propeller blades in the models are approximated by different geometric shapes. The models used to describe the reflection from the propellers of helicopters and fixed-wing aircraft have significant differences. In the process of moving each blade of the helicopter main rotor makes characteristic movements (flapping, dragging, feathering), as well as bends in a vertical plane. Such movements and bendings of the blades are influence the phase of the signal reflected from the main rotor. It is necessary to take the phase change of the reflected signal into account as accurately as possible when developing an ISAR algorithm for imaging the main rotor. Results. We found that in the centimeter wavelength range the mathematical model of the signal reflected from the helicopter main rotor as a system of blades is most accurately described by representing each blade with a set of isotropic reflectors located on the main rotor’s blade leading and trailing edges. Taking into account the flapping movements and curved shapes of the blades in the model allows you to get as close as possible to the features of the real signal. Conclusion. The developed model which takes into account the flapping movements and bends of the helicopter main rotor blades can be used to improve the ISAR algorithms providing the radar imaging of aerial vehicles.

Recent Experiences of Helicopter Main Rotor Blade Damage

Results of a survey investigating commonly occurring minor rotor blade damage incidents are presented in this paper. Over 100 participants worldwide ranging from test pilots to commercial pilots and licensed engineers answered the survey. The focus of this work was to provide a user-oriented context that can inform the decision-making process for integrating state-of-the-art instrumentation systems for rotor blade health monitoring onboard operational helicopters. This paper highlights the dichotomy faced by designers who have a choice to follow either a reactive strategy based on operational experience or a preventative approach based on technological trends.

A Vision-Based Technique for in-Flight Measurement of Helicopter Blade Motion

The measurement of helicopter main rotor blade angles during flight is a key capability to implement advanced applications, such as strategies for the reduction of emitted noise and to develop innovative flight control laws. The approach proposed in this work for the real-time estimation of blade angles is based on a stereoscopic system mounted on the top of the main rotor and pointing to an optical target placed on the blade root. An advanced image-processing algorithm was developed to match the target features in the left and right camera images, which was required for the 3D reconstruction of the target based on a triangulation method. This algorithm was customized for the target used in this specific application, in order to implement a procedure that is both reliable in blob matching and characterized by a very low computation effort. This allowed the system to speed up the triangulation procedure aimed at obtaining the 3-D coordinates of the features, in view of real-time applications, even with very compact processing units that can be accommodated on the main rotor head. An inverse problem for the 3-D rotation of the target was solved using the Singular Value Decomposition technique, thus improving the robustness of the measurement. The stereoscopic system was developed in order to be integrated on board an AW139 helicopter main rotor hub, equipped with a synchronous lighting device and a pre-processing unit. The latter enabled the system to automatically extract the minimum set of information to be transferred, by means of a slipring, to the processing unit hosted in the fuselage. For the full assessment of the reliability and accuracy of the integrated system, harsh dynamic and accuracy trials were conducted on laboratory test benches. The harsh dynamic tests demonstrated that the system can work continuously in realistic conditions without any structural or data acquisition problems. The accuracy tests, based on a robot test rig simulating the motion of the blade, demonstrated the capability of the system and the accuracy of the measurement technique developed. The discrepancy between the reference blade angles and the estimated ones was found to be less than 0.360 for all the realistic blade angle combinations tested.