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Abstract

Results of calculation of the helicopter main rotor loads and deformations of rotor blades are presented. The simulations concern level flight states and cases of boundary flight envelope such as wind gust, dive recovery and pull-up manoeuvre. The calculations were performed for data of the three-bladed articulated rotor of light helicopter. The method of analysis assumes modelling the rotor blades as elastic axes with sets of lumped masses of blade segments distributed along radius of blade. The model of deformable blade allows flap, lead-lag and pitch motion of blade including effects of out-of-plane bending, in-plane bending and torsion due to aerodynamic and inertial forces and moments acting on the blade. Equations of motion of rotor blades are solved applying Runge-Kutta method. Parameters of blade motion, according to Galerkin method, are considered as a combination of assumed torsion and bending eigen modes of the rotor blade. The rotor loads, in all considered cases of flight states, are calculated for quasi-steady conditions assuming the constant value of the following parameters: rotor rotational speed, position of the main rotor axis in air and position of swashplate due to rotor axis which defines the collective and cyclic control pitch angle of blades. The results of calculations of rotor loads and blade deflections are presented in form of time-runs and as distributions on rotor disk due to blade elements radial and azimuthal positions. The simulation investigation may help to collect data for prediction the fatigue strength of blade applying results for steady flight states and for definition the extreme loads for boundaries of helicopter flight envelope.

Abstract

Noise generated by helicopters is one of the main problems associated with the operation of rotorcrafts. Requirements for reduction of helicopter noise were reflected in the regulations introducing lower limits of acceptable rotorcraft noise. A significant source of noise generated by helicopters are the main rotor and tail rotor blades. Radical noise reduction can be obtained by slowing down the blade tips speed of main and tail rotors. Reducing the rotational speed of the blades may decrease rotor thrust and diminish helicopter performance. The problem can be solved by attaching more blades to main rotor. The paper presents results of calculation regarding improvement of the helicopter performance which can be achieved for reduced rotor speed but with increased number of rotor blades. The calculations were performed for data of hypothetical light helicopter. Results of simulation include rotor loads and blade deformations in chosen flight conditions. Equations of motion of flexible rotor blades were solved using the Galerkin method which takes into account selected eigen modes of the blades. The simulation analyzes can help to determine the performance and loads of a quiet helicopter with reduced rotor speed within the operational envelope of helicopter flight states.

Abstract

Results of simulation of main rotor blade loads and deformations, which can be generated during boundary states of helicopter flight, are presented. Concerned cases of flight envelope include hover at maximum height, level flight at high velocity, pull-up manoeuvres applying cyclic pitch and mixed collective and cyclic control. The simulation calculations were executed for data of light helicopter with three-bladed articulated rotor. For analysis, the real blades are treated as elastic axes with distributed masses of blade segments. The model of deformable blade allows for out-of-plane bending, in plane bending, and torsion. For assumed flight state of helicopter, the equations of rotor blades motion are solved applying Runge-Kutta method. According to Galerkin method, for each concerned azimuthal position of blade the parameters of its motions are assumed as a combination of considered bending and torsion eigen modes of the blade. The loads of rotor blades generated during flight depend due to velocity of flight, helicopter mass, position of rotor axis in air and deflections of swashplate that correspond to collective and cyclic pitch angle applied to rotor blades. The results of simulations presenting rotor loads and blade deformations are shown in form of time-runs and as plots of rotor-disk distributions. The simulations of helicopter flight states may be useful for prediction the conditions of flight-tests without exceeding safety boundaries or may help to define limitations for manoeuvre and control of helicopter.

Abstract

The article presents results of simulations concerning possibilities of rotorcraft performance enhancements for compound helicopters with introduced additional wings and propellers. The simple model of helicopter including a point mass of fuselage and a rotor treated as a disk was used for calculations of helicopter flight equilibrium conditions. For the defined flight states, the more detailed model of elastic blade was applied to compute magnitude of rotor loads and level of blade deformations. The model of elastic blade includes out-of-plane bending, in plane bending, and torsion effects due to variable aerodynamic and inertial loads of rotor blades. Equations of motion of rotor blades are solved applying Runge-Kutta method. Taking into account Galerkin method, parameters of blade motion are computed as a combination of assumed torsion and bending Eigen modes of the rotor blade. The six-bladed rotor with stiff connections of blades and hub was applied for comparison of flight envelope for conventional helicopter and versions of compound rotorcraft with additional propellers and with wings and propellers. Simulations indicate that, in the case of compound helicopter configuration, achieving the operational flight conditions at high speed of 400 km/h is possible without generating excessive loads and blade deformations. The results of calculations of rotor loads and generated blade deflections are presented in form of time-run plots and as rotor disk distributions, which depend on radial and azimuthal positions of blade elements. The simulation investigation may help to define demands for rotor of high-speed helicopter.

Bearingless Rotor”, American Helicopter Society 50 th Annual Forum , Washington D.C., May 11-13. [10] Gula P., Gorecki T., 2013,”Design, Experiments and Development of a Polish Unmanned Helicopter ILX-27”, 39 th European Rotorcraft Forum , Moscow, Russia, 3-6 September. [11] Stanisławski J., 2015, “Pattern of Helicopter Rotor Loads and Blade Deformations in Some States of Flight Envelope”, Transactions of the Institute of Aviation, No.1(238), pp. 70-90. [12] Stanisławski J., 2016, “Simulation Investigation of Aerodynamic Effectiveness Reduction of Helicopter Tail Rotor

Abstract

The article discusses the main features of the applied simulation model of helicopter flight indicating references, where it was elaborated in detail. It focuses on presenting the simulation results of pull-up manoeuvre during which the helicopter does not respond correctly. The reasons for the behaviour as mentioned above were explained based on the results of calculations. The capabilities of the simulation model were used to determine the current loads of particular blades of the helicopter’s main rotor. The results were illustrated by maps of the angles of attack and aerodynamic lift on the surface of the main rotor and the distributions of these parameters along blades on characteristic azimuth for individual manoeuvre phases.

Abstract

Simulation results concerning performance of helicopter suitable for high-mountain rescue operations are presented. Including operations in regions of the highest Himalaya Mountains, the possibility of hover ceiling out of ground effect (OGE) at 10,000 m above sea level is assumed. Demand of high ratio of developed lift to power required for hover leads to choice the coaxial rotor configuration as the best for rescue helicopter, which can operate in extremely high mountain environment, and gives good stability features in wind gust conditions in comparison with single main rotor helicopter. For performance calculations the simple model of helicopter is applied, which consists of fuselage point mass and rotor disk. The cases of partial and total power loss are considered to define range of H-V zones and possibilities of flight continuation due to height of landing surface over level of sea. The rotor blades and rotor loads are calculated applying detail model of elastic blade, which includes effects of its deflections due to out-of-plane bending, in plane bending, and torsion. The Runge-Kutta method is applied to solve equations of motion of rotor blades with taken into account effects of blade pitch control and variable deflections of blades. According to Galerkin method, the blade parameters of motion are treated as a combination of torsion and bending eigen modes of the rotor blades. Elastic blade model allows defining behaviour rotor blades in selected states of flight: hover, level flight, wind gust conditions, and pull-up manoeuvre. The results of simulation for upper and lower rotor for blade deflections and loads are shown in form of time-run plots and rotor disk distributions. The simulation investigation may be applied to define features of helicopter configuration suitable for operation in extremely high mountain conditions.