Vehicle Modeling Additions for Off-Axis Improvements in a Real-Time Helicopter Model

Abstract

An ongoing concern with helicopter simulations is that they often have an incorrect off-axis response to cyclic control inputs when compared with the corresponding flight-test data. The more commonly suggested contributing factors for this discrepancy include the influence of dynamic wake distortion, rotor blade elasticity, and unsteady blade airfoil aerodynamics. A rotor model was developed using a Ritz expansion approach with constrained elastic modes to account for the blade elasticity, as it is computationally compact and efficient and therefore suitable for use in a real-time simulation. The effect of including this blade flexibility on the dynamic response, and in particular the on-axis and off-axis response, of the University of Toronto Institute for Aerospace Studies helicopter models is examined. In addition, the combined effects of dynamic wake distortion, unsteady blade section aerodynamics, and blade flexibility on the dynamic response are examined. The various features were successful in altering the off-axis response, with improvements in some areas, while not disrupting the on-axis response. In some conditions, the magnitude of the resulting change due to flexibility was greater than the differences noted due to the addition of dynamic wake distortion or unsteady aerodynamics.