Helicopter Rotor Blades Research Articles

Sensor placement optimization for composite aircraft structures: A multi-objective Kriging-based approach

Efficient sensor placement is critical for optimizing structural health monitoring (SHM) systems, particularly for composite aircraft structures. The challenge lies in determining the optimal number and positions of sensors to balance monitoring accuracy with resource efficiency. This study proposes a novel multi-objective optimization methodology that integrates Kriging interpolation for mode shape reconstruction with the Lichtenberg algorithm for sensor placement optimization. The approach minimizes the number of sensors while maximizing signal quality and minimizing interpolation error. The methodology is validated on both composite plates and the main rotor blade of an AS-350 helicopter using finite element modal analysis data. The results demonstrate significant reductions in the number of sensors required while maintaining high accuracy in capturing the structure’s dynamic response, showing the effectiveness of the proposed method for SHM applications in complex composite structures.

Numerical study on lightning strike protection method for composite rotor blade based on air breakdown and insulating adhesive layer

The protection effectiveness of traditional Lightning Strike Protection (LSP) for composite rotor blade of helicopter can be diminished due to the explosion risk in overlapping attachment under lightning strike, so a new protection method based on Air Breakdown and insulating adhesive layer (AB-LSP method) was designed to avoid it. In this study, a numerical method was developed to simulate the electrical breakdown, and verified by experiment results. Based on this method, a Finite Element Model (FEM) was established to investigate the effect of two factors (breakdown strength and initial ablation temperature of adhesive layer) on the LSP effectiveness. The results show that the breakdown strength impacts more to the ablation damage in composite than that of high-temperature resistance. Then, another FEM was established to predict the ablation damage by lightning strike in the AB-LSP method protected composite rotor blade. The mechanisms and potential key parameters (magnitude of lightning current, discharge channel location, adhesive layer thickness, and air gap width) that could affect the protection effectiveness were analyzed. The introduction of air breakdown changes the current conduction path and reduces explosion risk. After rational design, this method can offer effective lightning protection for composite helicopter rotor blade and other composite structures.

Three-Dimensional Numerical Investigation on the Dynamic Stall Behavior of the Helicopter Rotor Blade at Forward Flight Speeds

Three-Dimensional Numerical Investigation on the Dynamic Stall Behavior of the Helicopter Rotor Blade at Forward Flight Speeds

Transport helicopter blade root cuff attachment modernization concepts

The article discusses the issue of modernizing the blade root cuff attachment of the main rotor blade of a Mi-8 type transport helicopter. Several geometry options were designed and the stress-strain state of various options in a nonlinear formulation under the influence of operational loads was calculated using numerical methods. Conclusions are provided regarding the strength and mass of the blade root cuff attachment options under consideration. The influence of the tightening value of fasteners and the use of adhesive on the stress distribution along the connection is analyzed. Analytical methods were used to determine the optimal dimensions of fastening elements.

Non-Contact Eddy Current Conductivity Measurements as an Effective Tool for Evaluating Aluminum Alloys in Aircraft

ABSTRACT Aluminum alloys (AAs) are pivotal materials in modern aircraft due to their superior mechanical properties and low weight. The structural integrity of these alloys, crucial for aircraft safety, heavily depends on heat treatment processes that alter their mechanical characteristics. Nondestructive evaluation (NDE) techniques, such as eddy current (EC) conductivity measurements, play a vital role in assessing these alloys throughout their lifecycle. EC methods enable the measurement of electrical conductivity, a structure-sensitive parameter that correlates with mechanical properties affected by heat treatments and operational stresses. This paper reviews the application of EC conductivity measurements in the aerospace industry, focusing on their role in assessing AA structural integrity. It discusses how EC methods can penetrate non-conductive coatings, crucial for in-service measurements without surface removal. Recent developments include a novel small-size EC probe and signal processing algorithms aimed at enhancing sensitivity to conductivity changes through dielectric coatings, up to 0.5 mm thick, commonly found in aircraft structures. Key findings include analyses of specific electrical conductivity (SEC) changes in AAs due to heat treatment deviations and long-term operational stresses, crucial for predicting residual life and maintaining safety standards. Case studies on aircraft wing skins and helicopter rotor blades demonstrate the practical application of EC conductivity meters in identifying critical damage zones. The methodology proves effective in evaluating localized degradation based on SEC distributions, thereby enhancing maintenance efficiency and aircraft safety. Overall, this research underscores the significance of EC conductivity measurements in advancing NDE practices for AAs in aircraft applications. The methodologies and findings presented aim to improve safety, durability assessment, and maintenance efficiency in the aerospace industry.

Application of Artificial Neural Networks to a Model of a Helicopter Rotor Blade for Damage Identification in Realistic Load Conditions.

Monitoring the integrity of aeronautical structures is fundamental for safety. Structural Health Monitoring Systems (SHMSs) perform real-time monitoring functions, but their performance must be carefully assessed. This is typically done by introducing artificial damages to the components; however, such a procedure requires the production and testing of a large number of structural elements. In this work, the damage detection performance of a strain-based SHMS was evaluated on a composite helicopter rotor blade root, exploiting a Finite Element (FE) model of the component. The SHMS monitored the bonding between the central core and the surrounding antitorsional layer. A damage detection algorithm was trained through FE analyses. The effects of the load's variability and of the damage were decoupled by including a load recognition step in the algorithm, which was accomplished either with an Artificial Neural Network (ANN) or a calibration matrix. Anomaly detection, damage assessment, and localization were performed by using an ANN. The results showed a higher load identification and anomaly detection accuracy using an ANN for the load recognition, and the load set was recognized with a satisfactory accuracy, even in damaged blades. This case study was focused on a real-world subcomponent with complex geometrical features and realistic load conditions, which was not investigated in the literature and provided a promising approach to estimate the performance of a strain-based SHMS.

Numerical simulation of ice accretion on helicopter rotor blades with trailing edge flap

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

Experimental and numerical investigation on low-velocity impact damage and parametric study of composite rotor blades

Modern helicopter rotor blades are made of composite materials. Due to the harsh service environment, the blades may be impacted by hail and other falling objects at low velocity. The damage behavior of composite rotor blades subjected to low-velocity impact is studied here. Low-velocity impact experiment is conducted on a composite helicopter rotor blade, and the impact force and the damage are measured. Based on the experiment, a finite element model is developed and validated to predict the impact damage of the blade. With the model, a parametric study is performed to investigate the effects of impact energy, impact locations, and foam core on impact responses of the composite blades. The results show that the rib is the most vulnerable part to damage, associated with severe deformation, and delamination rapid expanding under low-velocity impact. The foam crush region is close to the blade top surface below the impact point. The interface between the skin and internal part is especially sensitive to increase in impact energy. Impacts near the leading edge produce higher impact force, while impacts near the trailing edge cause large deformation and small impact force. Better impact performance will be achieved when modulus and density of the foam are increased.

Economic Impact Assessment of Structural Health Monitoring Systems on the Lifecycle of a Helicopter Blade

Structural Health Monitoring Systems (SHMS) are currently widely investigated in the literature, however, their application to the aerospace industry is still limited. One of the reasons lies in the lack of methods aimed at evaluating their economic impact on the lifecycle of the structural element to be monitored [1]. In this work the economic impact of FBG-based SHMS was evaluated on a composite helicopter rotor blade, considering two perspectives: Beginning Of Life (BOL), concerning the blade production, and Middle Of Life (MOL), concerning its usage. The processes were modeled using the IDEF0 methodology, which allowed deriving the cost models for two scenarios: the current one, and the one including the SHMS. In BOL, the SHMS was supposed providing support to the development of new composite rotor blades, including the curing cycle definition and certification tests. In MOL the SHMS was supposed performing automatic scheduled inspections coupled with the traditional ones. The cost model was implemented in the Probabilistic Damage Tolerance Analysis [2] to compare the scenarios having the same blade Probability Of Failure and considering the performances of the SHMS in terms of Probability Of Detection and Probability of False Alarm. Results show that an economic benefit may be achieved using the SHMS in the development of new blades, potentially reducing the number of blades tested and number of autoclave cycles. Moreover, it was found that the traditional scheduled detailed inspection intervals could be extended if automatic SHMS inspections are performed in addition, maintaining the same Probability Of Failure. [1] Büchter, K. D. et al. (2022). Modeling of an aircraft structural health monitoring sensor network for operational impact assessment. Structural Health Monitoring, 21(1), 208-224. [2] Lin, K. Y., & Styuart, A. V. (2007). Probabilistic approach to damage tolerance design of aircraft composite structures. Journal of Aircraft, 44(4), 1309-1317.

A Methodology of Resonance Avoidance for Helicopter Rotor Blade Considering the Stiffness Characteristics of a Torsion-Type Elastic Hub

A Methodology of Resonance Avoidance for Helicopter Rotor Blade Considering the Stiffness Characteristics of a Torsion-Type Elastic Hub

Beam modeling in a floating frame of reference for torsion dynamics of helicopter rotor blades

AbstractIn the ongoing development of DLR’s Versatile Aeromechanics Simulation Tool, an elastic-beam model is integrated into the multibody system based on the floating frame-of-reference formulation. Although the application of this formulation for one-dimensional beam models has already been addressed in the literature, the challenge remains to properly model the torsion dynamics of rotor blades – especially under high centrifugal loads. To this aim, this work suggests the consideration of rotational shape functions in the inertia shape integrals and in the application of gravitational, inertial, and external loads. This modified approach is validated based on the structural analysis of a rotor blade with complex geometrical properties.

Geometrically Exact Aeroelastic Stability Analysis of Composite Helicopter Rotor Blades in Hover by Updated VABS

Geometrically Exact Aeroelastic Stability Analysis of Composite Helicopter Rotor Blades in Hover by Updated VABS

Material Selection Using Hybrid Grey Relation Analysis Approach Based on Weighted Entropy for Ranking: The Case of Helicopter Rotor Blade

Engineering design relies highly on the selection of suitable materials. Because there are many engineering materials, selecting a suitable material for a product requires a systematic selection approach. This paper provides a hybrid strategy for choosing the best material for an engineering design to give the best performance at the lowest cost based on Ashby's performance indices. Then, it ranks the result by the grey relational approach integrated with the Weighted Entropy Method to choose the optimum material for the main rotor blade of a helicopter. Different materials used for manufacturing rotor blades, such as Aluminium alloys, titanium alloys, steel, composites, and wood, have been discussed. The performance indices chosen are stiffness, strength, and fracture toughness. The performance indices proved that the composite material has excellent structural strength, stiffness, and toughness. The result shows that CFRP is the best material for manufacturing helicopter rotors, while wood and steel were the best and cheapest when the design had to be economical.

Hovering performance analysis of helicopter rotor blades using supercritical airfoil

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

Modeling and vibration control of a rotating flexible plate actuated by MFC

The macro fiber composite (MFC) is a novel piezoelectric intelligent material, which is widely used in the field of vibration control due to its flexibility and larger actuation forces than PZT. In this paper, a laminated plate model considering the anisotropy of MFC is developed and applied to the vibration control of a rotating plate. The laminated plate is defined as a layerwise model, which deformation is described by the Absolute Nodal Coordinate Formulation (ANCF). The MFC laminated plate element contains 48 degrees of freedom (DOFs) where the effect of MFC element can be internally incorporated without increasing the DOFs of system. Simultaneously, a neural network PD control is adopted to control the vibration of the rotating plate. Eventually, static, dynamic, and modal analyses are performed to investigate the effects of different parameters. Several vibration simulations are carried out to illustrate the ability of MFC patches on vibration control. The findings in this article would be applied to mechanical prediction and control for rotor blades of helicopters, solar panels, etc.

Modal Parameter Identification and Damage Localization of Composite Helicopter Rotor Blades Based on AR/PR Identification

The structural characteristics and application background of helicopters determine that the primary dynamic components work in environments with high cyclic amplitude and low‐stress vibration fatigue load. As the most critical structural system of helicopters, structural health monitoring of the rotor blades is necessary to avoid fatigue damage under working conditions. Modal parameters, as functions of the physical properties of structural systems, change when there is damage or internal defects (the mass, stiffness, and damping of the structure will change). This article completes the identification of modal parameters of composite rotor blades under working conditions based on operational modal analysis (OMA). Specifically, using the AR/PR (autoregressive/polyreference) time‐domain identification method, experiments are designed to identify the modal parameters (natural frequency, modal damping ratio, and mode shape) of composite rotor blades based on acceleration and strain signals. The results of the identification of modal parameters are verified through finite element simulation and modal measurement experiments. In addition, the application of OMA for the location of composite rotor blade damage is also studied.

Retracted: Wind Tunnel Testing and Validation of Helicopter Rotor Blades Using Additive Manufacturing

Retracted: Wind Tunnel Testing and Validation of Helicopter Rotor Blades Using Additive Manufacturing

Sand Erosion Resistance and Failure Mechanism of Polyurethane Film on Helicopter Rotor Blades.

Polyurethane is widely used on the surface of composite materials for rotor blades as sand erosion protection materials. The failure mechanism investigation of polyurethane film under service conditions is useful for developing the optimal polyurethane film for rotor blades. In this article, the sand erosion test parameters were ascertained according to the service environment of the polyurethane film. The sand erosion resistance and failure mechanism of polyurethane film at different impact angles were analyzed by an infrared thermometer, a Fourier transform infrared spectrometer (FTIR), a differential scanning calorimeter (DSC), a field emission scanning electron microscope (FESEM), and a laser confocal microscope (CLSM). The results show that the direct measurement method of volume loss can better characterize the sand erosion resistance of the polyurethane film compared to traditional mass loss methods, which avoids the influence of sand particles embedded in the polyurethane film. The sand erosion resistance of polyurethane film at low-angle impact is much lower than that at high-angle impact. At an impact rate of 220 m/s, the volume loss after sand erosion for 15 min at the impact angle of 30° is 57.8 mm3, while that at the impact angle of 90° is only 2.6 mm3. The volume loss prediction equation was established according to the experimental data. During low-angle erosion, the polyurethane film damage is mainly caused by sand cutting, which leads to wrinkling and accumulation of surface materials, a rapid increase in roughness, and the generation of long cracks. The linking of developing cracks would lead to large-scale shedding of polyurethane film. During high-angle erosion, the polyurethane film damage is mainly caused by impact. The connection of small cracks caused by impact leads to the shedding of small pieces of polyurethane, while the change in the roughness of the film is not as significant as that during low-angle erosion. The disordered arrangement of the soft and hard blocks becomes locally ordered under the action of impact and cutting loads. Then, the disordered state is restored after the erosion test finishes. The erosion of sand particles leads to an increase in the temperature of the erosion zone of the polyurethane film, and the maximum temperature rise is 6 °C, which does not result in a significant change in the molecular structure of the polyurethane film. The erosion failure mechanism is cracking caused by sand cutting and impact.

Nonlinear free vibration analysis of internal thickness-tapered multi-layered composite rectangular plates undergoing moderately large deflections

Thickness-tapering in multi-layered composites is achieved by terminating the plies at discrete locations. This allows for effective material utilization and significant weight savings and is adopted in applications involving multi-layered composites that demand variation in thickness such as helicopter yokes, flexbeams and rotor blades, aircraft wing-skin structures and turbine blades. In the present work, the nonlinear free vibration of such tapered composites undergoing moderately large deflections is investigated for the first time. A general nonlinear finite element formulation for tapered multi-layered composite plates based on Reddy's higher-order shear deformation theory and considering Von Karman nonlinearity is developed. Newton–Raphson scheme in conjunction with Newmark time-integration technique is employed to obtain the time response. The developed model is validated against available results in the literature and through experimentally obtained linear natural frequencies of a honeycomb sandwich plate with tapered face sheets. Parametric studies are conducted to deeply understand the nonlinear dynamic behaviour of tapered composite structures. The investigation reveals that tapered multi-layered composite plates exhibit higher nonlinearity compared to uniform plates thus necessitating the consideration of nonlinear effects in the analysis of such structures.

Multi-objective sensor placement optimization in SHM systems with Kriging-based mode shape interpolation

Sensor location optimization plays a key role in the application and development of structural integrity monitoring methodologies, especially in large mechanical structures. Given the existence of an effective damage detection and identification procedure, the question of how many and where to place the acquisition points (sensors) so that the monitoring system operates at peak efficiency arises. In this study, an innovative methodology is proposed in order to maximize the quality of modal information and minimize the number of sensors in the SHM system. To maximize the quality of modal information, it considered the reconstruction of mode shapes using Kriging interpolation. The study was carried out on plate-type composite material structures for initial validation and later applied and validated on a main rotor blade of the AS-350 helicopter. The initial modal information (modal deformation) was obtained through the finite element method, and the multi-objective Lichtenberg algorithm was used in the complex optimization process. The proposed method presented in this work allows for the best possible distribution of a minimum and sufficient number of acquisition points in a structure in order to obtain more modal information for a better modal reconstruction from kriging interpolation of these minimum points. Numerical examples and test results show that the proposed method is robust and effective for distributing a reduced number of sensors in a structure and at the same time guaranteeing the quality of the information obtained, even in noisy situations. Numerical results considering both the simple and complex geometric cases show that the proposed combined FS-kriging method is effective in distributing a finite number of sensors on the structures and at the same time guaranteeing the quality of the modal information obtained. The results also indicate that the layout of sensors obtained by multi-objective optimization does not become trivial and symmetrical when a set of modes is considered in the objective function formulation. The proposed strategy is an advantage in modal testing as it is only necessary to acquire signals at a limited number of points, saving time and operating costs in vibration-based processes.