Simulation investigation of rotor loads and blade deformations in steady states and at boundaries of helicopter flight envelope

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 timeruns 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