Algorithm for calculating damage accumulation as illustrated by a helicopter blade attachment

In this research we develop an algorithm for calculating damage accumulation for metal-composite joints using the example of a helicopter blade attachment. The degradation of the composite material properties is investigated, since operation of composites leads to decline in their main mechanical properties, namely, stiffness and toughness as a result of possible binder failure. Damage growth in fibre-reinforced composites is a very complex process due to their heterogeneity and anisotropy. Joints are one of the most vulnerable spots in an aircraft, so joint design should be a priority. Joints can fail for various reasons, for example, assembly stresses, stress concentrations, and technological deviations, which affect the strength of bolted joints. The paper uses computational methods described in the interdisciplinary theory of elasticity, structural mechanics, structural strength, materials science, and mechanics of structural failure of composite materials. This study is aimed at determining the optimal joint assembly to ensure the safe operation of the structure during a specified service life.

Noise Cancellation of Helicopter Blade Deformations Measurement by Fiber Bragg Gratings

The work presents data treatment methods aimed at eliminating the noise in the strain sensor data induced by vibrations of the helicopter blade in flight conditions. The methods can be applied in order to enhance the metrological performance of the helicopter weight estimation system based on the deformation measurement of the main rotor blades. The experimental setup included a composite plate fixed to the vibrating stand on the one end, with six fiber-optic strain sensors attached to its surface. In this work, the procedure of the optimal linear smoothing (POLS) and 3D-invariant methods were used to obtain monotone calibration curves for each detector, thereby making it possible to distinguish the increase of load applied to the free end of the plate with an increment of 10 g. The second method associated with 3D invariants took into account 13 quantitative parameters defined as the combination of different moments and their intercorrelations up to the fourth-order inclusive. These 13 parameters allowed the calculation of the 3D surface that can serve as a specific fingerprint, differentiating one set of initial data from another one. The combination of the two data treatment methods used in this work can be applied successfully in a wide variety of applications.

Development of the Wind Tunnel CFD Model for Clarifying Rotor Blade Airfoil Unsteady Aerodynamic Researches

A computational model of a wind tunnel (WT) with a special experimental rig has been developed directly for studying unsteady aerodynamic characteristics of a wing section with a helicopter blade profile. The model was constructed using CFD (Computational Fluid Dynamics) methods based on the URANS approach (Unsteady Reynolds Averaged Navier Strokes Equations). Therefore, the aerodynamic characteristics of the airfoil can be determined, taking into account influence of the WT walls such as walls perforation and various configurations of the experimental rig. Simulation of the flow around the wing section with the SC1095 airfoil in steady and unsteady settings is performed. The flow features in the working section of the WT and the experimental rig are analyzed. For a particular case, the calculation method was validated in a 2D formulation on the basis of available experimental data. The developed model can be used to refine the methods of processing experimental data, taking into account the individual characteristics of the WT and the experimental rig configuration.

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.

Load distribution method in helicopter blade multibody dynamics system

The paper focuses on the loads applied to the helicopter blade cross-sections in the multibody dynamics system. The main objective is to simplify the blade aerodynamics calculation and avoid time-consuming CFD methods. For this reason, the way of computing blade aerodynamics is proposed by using multibody dynamics methods with a linear-elastic blade model. As the primary tool for further research, the MCS Adams software package is selected. Splitting the main rotor blade into a finite number of sections, each having its own average value of installation and coning angles, simplifies the calculation. Afterward, expressions for the total flow velocity around the blade section and its angle of attack are obtained through vector operations. This provides a measure of aerodynamic forces acting on each section in its cross-sectional coordinate system. In conclusion, the article provides the formalized method of aerodynamic force distribution between blade sections in the multibody model as well as the correlation between the flow coordinate system and the blade chord coordinate system.