Development Of An Unsteady Aerodynamics Model To Improve Correlation Of Computed Blade Stresses With Test Data

A reliable rotor aeroelastic analysis operational at Hughes Helicopters, Inc. that correctly predicts the vibration levels for a helicopter is utilized for the present study to test various unsteady aerodynamics models with the objective of improving the correlation between test and theory. This analysis called Rotor Aeroelastic Vibration (RAVIB) computer program is based on a frequency domain forced response analysis which utilizes the transfer matrix techniques to model helicopter/rotor dynamic systems of varying degrees of complexity. The analysis is a nonmodal analysis and it includes effects of periodic coefficients for the forward flight conditions. The first new aerodynamics model incorporated in the analysis was based on the current state-of-art of unsteady aerodynamics. The results based on this aerodynamics model for the AH-1G helicopter rotor were compared with the flight test data during high speed operation and they indicated a reasonably good correlation for the beamwise and chordwise blade bending moments, but for torsional moments the correlation was poor. As a result, a new aerodynamics model based on unstalled synthesized data derived from the large amplitude oscillating airfoil experiments was developed and tested with RAVIB analysis. The results indicate a significant improvement in the correlation for the torsional moments.