Time Varying Rotor Aerodynamics for Quadrotor Vehicles

This paper has illustrated the potential accuracy of often-used Blade Element Momentum Theory (BEMT) model in hovering thrust predictions and a limiting feature of the Blade Element Theory (BET) model during forward flight. When employed in hover, BEMT with the linear lift curve slope assumption and small angle approximation is shown to accurately predict the hover thrust. However, during forward flight an underprediction of the thrust and torque is likely to occur because the lift boost from dynamic stall and the extra torque due to post stall drag are missing. Additionally, without a dynamic stall model the rotor flapping angles for a quadrotor aircraft can contain higher frequencies that are likely fictitious. A state space dynamic stall model has been integrated into BET and it has been shown that reasonable predictions of lift and rotor flapping angle are produced. Finally, a reduced order model amenable to inclusion in 6DOF flight simulations is presented. The reduced order model seeks to make inclusion of the often-neglected time varying thrust due to blade flapping. It also includes the effects of dynamic stall on the thrust generated by the rotor.