Unsteady Rotor Airload Prediction Using a Comprehensive Aeroelastic Analysis

An accurate prediction for helicopter rotor loadings requires detail analyses with both sophisticated structural and aerodynamic capabilities. This paper presents a comprehensive analysis for a coupled rotor system incorporated consistent blade structural, aerodynamic and inertial couplings. Using the rigid rotations of the blade about the flap, lag and pitch hinges as general coordinates, it accounts for the dynamic coupling effect between the rigid motion of the blade and moderately large elastic deflections discretized by a finite element formulation. A nonlinear aerodynamic analysis for attached flow, separated flow and dynamic stall based on the work of Leishman and Beddoes is incorporated and used to investigate rotor blade section airloads. The inflow is evaluated with the free wake analysis. The equations of motion for the nonlinear periodic time variant system are derived based on the dynamics of flexible multibody systems. A modified implicit Newmark scheme is used to calculate blade response as one coupled solution. Results are corrected with SA349/2 Aerospatiale Gazelle flight test data. The blade airloads and the flap angles predicted by the analysis show that the flight test data are efficient.