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.

Rotor blade design framework for airfoil shape optimization with performance considerations

A framework for optimizing rotor blade airfoil shape is presented. The framework uses two digital workflows created within the Galaxy Simulation Builder (GSB) software package. The first is a workflow enabling the automated creation of a surrogate model for predicting airfoil performance coefficients. An accurate surrogate model for the rapid generation of airfoil coefficient tables has been developed using linear interpolation techniques that is based on C81Gen and ARC2D CFD codes. The second workflow defines the rotor blade optimization problem using GSB and the Dakota numerical optimization library. The presented example uses a quasi-Newton optimization algorithm to optimize the tip region of the UH-60A main rotor blade with respect to vehicle performance. This is accomplished by morphing the blade tip airfoil shape for optimum power, subject to a constraint on the maximum pitch link load.

АНАЛИЗ ХАРАКТЕРИСТИК НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ КОМЛЕВОЙ ЧАСТИ ЛОПАСТИ НЕСУЩЕГО ВИНТА ВЕРТОЛЕТА

The butt part of the main rotor blade (RB) of the helicopter is presented. A geometric model of the calculated connection was developed using the CATIA V5 system. With the help of the ANSYS system, a finite element model of the butt part of the main rotor blade was developed, and the calculation and analysis of the characteristics of the results obtained were 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 case of loading a bolted joint by a centrifugal force arising during the rotation of a blade is considered. To model the contact interaction, a generalized surface-to-surface contact interaction model was adopted. 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 the stress concentration zones. In the course of the calculation, reactions were determined at the points of attachment of the tip along the holes in the lugs. The nature of the deformation of the bolted joint as a whole and of its individual elements is analyzed. The assessment of total displacements and displacement components is carried out. To assess the static and fatigue strength of the elements of the bolted connection of the tip with the blade spar, the stresses in the load-bearing elements were analyzed for typical concentrators. When assessing the static strength, the distribution of equivalent stresses according to Mises was analyzed. The distribution of stresses in the zone of holes along the rows is analyzed, starting from the root section in the direction of increasing the Y coordinate. The maximum von Mises stresses for typical stress concentration zones were compared with the ultimate strength of the structural element material. To assess the fatigue strength, we analyzed the distribution of the main tensile stresses in the load-bearing elements by typical stress concentrators. The maximum values of these stresses were compared with the fatigue limit of the structural element material.

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.

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.