Helicopter Unsteady Maneuver Analysis Using Inverse Flight Dynamics Simulation and Comprehensive Analysis

Abstract

This paper describes the development of an inverse flight dynamics simulation for helicopters and its application for blade loads prediction using comprehensive analysis for a helicopter undergoing unsteady maneuvers. The inverse simulation is carried out for an unsteady pull-up maneuver and the estimated control angles are used as input to University of Maryland Advanced Rotorcraft Code comprehensive analysis for prediction of blade loads. Inverse simulation is carried out using an integration-based approach using a simplified helicopter dynamics model with rigid blades having only flap degree of freedom, quasi-steady aerodynamics, and Drees inflow model. The predicted control angles and blade loads are compared against the flight-test data for a UH-60A Black Hawk helicopter. The inverse flight dynamics with simple rotor dynamics is able to predict the correct trend of variation of control angle time history for this severe maneuver. The control angle time history estimated using the linear aerodynamics-model-based inverse simulation predicts all three stalls. Advancing blade transonic stall is predicted for the first time using a coupled lifting-line-based analysis. The magnitude of negative peak of stall loads and corresponding structural loads prediction is less satisfactory.