Simulation Analysis of the Controllability of a Tandem Ducted Fan Aircraft

A generic simulation model was developed for stability / control analysis and real-time simulation of ducted fan aircraft. The generic simulation model features a modified inflow model for ducted rotors, a basic model of control vane forces and moments, and empirical correction factors to account for duct thrust augmentation, duct pitching moment, and flow turning effects. Two empirical flow turning efficiency factors, one applied before the plane of the rotor and the other from freestream to far-wake flow, were investigated. A model of duct pitching moment was developed in which the duct thrust offset normalized by the rotor radius is given as a function of airspeed. Wind tunnel data and literature from several sources have been analyzed and compared in order to refine the pitching moment model and tune the empirical factors. Validation of the simulation model is provided through correlation studies with experimental data of a 29-inch ducted fan UAV. Steady-state and trim results obtained using the generic simulation model are presented and discussed.