Merging an Analytical Aerodynamic Model for Helicopter Applications with a State-Space Formulation for Unsteady Airfoil Behavior

Abstract

A new comprehensive simulation tool for computation of the whole helicopter is currently being developed at the Institute of Flight Systems of DLR. A main requirement of such a tool is the calculation of the aerodynamic forces acting at the blades, including all effects that are typical for helicopter rotor operational conditions, while maintaining small calculation times. Therefore, for the calculation of the rotor blade element aerodynamics, a semi-empirical analytical model is used. A formulation in state-space description was chosen to represent the unsteady circulation lag and the modeling of the noncirculatory force response was also added. The analytical models' formulation of the unsteady viscous effects, i.e. stall delay, was transferred to state-space form as well. The resulting combined model is used for the calculation of steady airfoil data as well as unsteady hysteresis curves for a harmonically oscillating airfoil. The results are compared to CFD data.